Complexes of flexible ditopic catechol phosphines: synthesis, metal assisted self- assembly and catalytic application Von der Fakultät Chemie der Universität Stuttgart Zur Erlangung der Würde eines Doktors der Naturwissenschaften (Dr. rer. Nat.) genehmigte Abhandlung vorgelegt von Samir H. Chikkali aus Solapur (Indien) Hauptberichter: Prof. Dr. D. Gudat Mitberichter: Prof. Dr. W. Kaim Tag der mündlichen Prüfung: 12.09.2007 Institut für Anorganische Chemie der Universität Stuttgart 2007 2 To My Grandmother 3 “The most beautiful experience we can have is the mysterious….the fundamental emotion which stands at the cradle of true art and true science”- ---Albert Einstein “ I do not agree with the view that the universe is a mystery”- ---Stephen Hawking 4 Acknowledgements My deepest appreciation goes to my Ph. D. mentor Prof. Dr. Dietrich Gudat for the brainstorming discussions on basic as well as applied scientific issues related to the present work. He taught me very basic to very complicated inorganic chemistry, showed different ways to approach a research problem and the need to be persistent to accomplish any goal. I would like to thank Prof. Dr. W. Kaim for his efforts to correct the present work. I also thank Prof. Dr. H. Bertagnolli for being the chairperson of this dissertation. Further I am thankful to Prof. Dr. G. Becker and Prof. Dr. T. Schleid for providing the institute facilities, without which this work would not have completed. I am obliged to Priv.-Doz. Dr. M. Niemeyer, Dr. M. Nieger, Dr. F. Lissner, Dr. I. Hartenbach for measuring the single crystals, sometime really small crystals. Let me also say “thank you” to the following people at University of Stuttgart: Herr P. Bergk, Frau K. Toroek for the NMR measurements and Frau. B. Foertsch for her accurate CHN analysis as well as NMR measurements. I am thankful to Herr Naegelein, Herr Wesch and Herr Lenz for their anytime help, Herr Zahl, Herr Heim who helped me to build the Schlenk line and gave a good start, Herr Achstetter, Herr Jergler for blowing special glass apparatus required. I am thankful to Herr Dr. J. Opitz, Herr J. Trinkner and Frau K. Wohlbold for the Mass Spectrometric measurements, which changed the course of my research during the final days. A special thanks goes to my lab mates Sebastian, Zoltan, Andrea, Laura, Imre, Samith, Dirk, Gernot, Nicholas, Anke and Daniela for the lively lab atmosphere and endless discussions. Thanks to Paula, Tushar and Christian, for their help in the preparation of this manuscript. 5 I am grateful to my research students for their contribution to this dissertation, specially for their outstanding research work. Also many thanks to my Indian friends Amar, Venkat, Mahendra and the Busnau group who made my life at Stuttgart easy. I am also greatly indebted to many teachers in the past: Dr. Sivaram, Dr. Wadgaonkar, Dr. Saxena, Dr. Mohandas, Dr. Guruswamy, Dr. Lele and Dr. Premnath at National Chemical Laboratory, Pune, India, for the motivation and for getting me interested in research and coming to Germany. Prof. Maldar and Prof. Lonikar who taught me basics of polymer Chemistry with its importance in day to day life. Dr. Manikshetti and Mr. Battin for introducing me to chemistry. My school teacher Handge sir who gave me the vision to see things differently. Thanks to working group Sivaram, Wadgaonkar and CFPE for making my stay comfortable at NCL. I feel myself very lucky to have a company of genuine, jolly and spiritful friends. Mohan, Wasif, Amit, Suleman, Chandrashekhar, Ankush and Jabeen deserve special mention for their out of the way help during my dissertation. I am thankful to my competitive exam group “Mahatma Gandhi Mitramandal”. I should mention Kiran and my graduate friends who were always there to hear my complaints and frustration and made me comfortable during those difficult times. Last, but not least, I thank my family: my Abba and Ammi, for educating me with aspects from both social and personal life, for unconditional support to pursue my interests and for believing in me. My brothers, Amin, Sharif and sisters, Mohaseena, Madeena, for sharing their happy moments in life. My Dada, Bade-abba, Shabeer-chacha and Papa-chacha, for the care and love during my childhood days. My fiancée Nasreen, for believing in me, for her support and love. 6 Symbols and Abbreviations B3LYP = Becke-3-Lee-Yang-Parr br = Broad CN = Coordination number COD = 1,5 cyclooctadiene CP/MAS = Cross polarization/ Magic angle spinning conc. = Concentrated d = Doublet δ = Chemical Shift D = Donor D = Diffusion coefficient DABCO = 1,4-Diazabicyclo [2.2.2] octane DCM = Dichloromethane DFT = Density functional theory DMAP = Dimethyl aminopyridine DME = 1,2-dimethoxyethane DMF = Dimethylformamide DOSY = Diffusion ordered spectroscopy E = Element Erel = relative energy EI-MS = Electron Ionization-Mass Spectroscopy Et = Ethyl EXSY = Exchange spectroscopy F = Functional group FAB = fast atom bombardment 7 Fig. = Figure HSAB = Hard/ Soft/ Acid/ Base HMQC = Heteronuclear multiple-quantum coherence HOMO = Highest Occupied Molecular Orbital I = isotop KJ/mol. = Kilo joule/mol LUMO = Lowest Unoccupied Molecular Orbital M = Metal m = multiplets m/e = Mass to charge ratio MAS = Magic angle spinning Me = Methyl Mes = Mesityl, 2,4,6-Trimethyl phenyl NLO = Non linear-optical NMR = Nuclear Magnetic Resonance NOESY = Nuclear overhauser enhancement and exchange spectroscopy OTf = Triflate PGSE = Pulsed Graadient Spin Echo Ph = Phenyl ppm = parts per million PTSA = p-toluenesulfonic acid rH = Hydrodynamic radii s = singlet Sec. = Secondary sect. = section THF = tetrahydrofuran Tol = Toluene 8 9 Table of Contents 1. Introduction..............................................................................................................15 1.1. Self-assembly, ligand designing and catalysis:..................................................15 1.2. Setting the Goals: .............................................................................................19 2. Syntheses of diphenyl-phosphinomethyl substituted phenols and catechols and mechanistic details on their formation ..............................................................................23 2.1. Introduction:.....................................................................................................23 2.2. Results and discussion: .....................................................................................25 2.2.1. Syntheses and mechanistic insights on the formation of methyl phosphinoyl phenols and catechols:..............................................................................................25 2.2.2. Synthesis and characterization of chiral mesityl phenyl phosphinoyl methyl catechols: .................................................................................................................30 2.3. Reduction of the phosphine oxides to ditopic phosphines:.................................31 2.4. Syntheses and characterization of transition metal complexes of diphenyl- phosphanyl methyl phenols and catechols: ...................................................................34 2.5. Synthesis and characterization of a palladium complex of 3-[(Mesitylphenyl phosphanyl)-methyl]-benzene-1,2-diol: ........................................................................41 2.6. Conclusions:.....................................................................................................41 3. Phosphine functionalized catechol borates and their Lewis-acid/base behavior.........43 3.1. Introduction......................................................................................................43 3.2. Results and discussion: .....................................................................................46 3.2.1. Detailed investigations on the synthesis and Lewis acid/base behavior of Diphenyl-(2-phenyl-benzo[1,3,2]-dioxaborol-4-ylmethyl) phosphine: ......................46 3.2.2. Syntheses and characterization of Silver (I) bis {diphenyl- (benzo- [1,3]- dioxo-4-ylmethyl)-phosphane} 2-borate: ..................................................................52 10 3.2.3. Synthesis and characterization of a Silver (I) bis {diphenyl- (benzo-[1,3]- dioxo-5-ylmethyl)-phosphane} 2-borate macrocycle:............................................... 58 3.3. Attempted synthesis of Triethyl ammonium [Dichloro palladium bis {diphenyl- (benzo- [1,3]-dioxo-4-ylmethyl)-phosphane}] 2-borate:............................................... 63 3.4. Conclusions: .................................................................................................... 64 4. Transition metal complexes of templated symmetric bisphosphane ligands and potential application in catalysis ...................................................................................... 65 4.1. Introduction: .................................................................................................... 65 4.2. Results and discussion:..................................................................................... 67 4.2.1. Synthesis and characterization of self-assembled palladium-bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4-ylmethyl) phosphane)}-gallium chloride (25): ........... 67 4.2.2. Syntheses and characterization of self-assembled palladium–bis {diphenyl- (benzo-[1, 3]-µ-oxo-k-oxo-4-ylmethyl) phosphane)}-tin complexes:........................ 72 4.2.3. Synthesis and characterization of a platinum -bis{diphenyl-(benzo-[1, 3]-µ- oxo-k-oxo-4-ylmethyl) phosphane)}-tin complex (28): ............................................ 81 4.2.4. Synthesis and characterization of a palladium- bis{diphenyl-(benzo-[1, 3]- µ-oxo-k-oxo-4-ylmethyl) phosphane)}-bismuth complex (29a):............................... 84 4.2.5. Zirconium assisted synthesis of a trinuclear di-palladium zirconium complex of 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (30): ..................... 87 4.2.6. Stoichiometry controlled syntheses of tri- and octanuclear palladium- yttrium complexes of 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (31):...... 91 4.3. Investigations on the catalytic behavior of selected metal complexes: .............. 99 4.4. Conclusions: .................................................................................................. 101 5. Some considerations on stereochemical aspects in octahedral tin templated bisphosphine complexes ................................................................................................ 104 5.1. Introduction: .................................................................................................. 104 5.1.1. Stereochemistry in bis-chelating octahedral complexes: ......................... 105 5.2. Results and discussion:................................................................................... 108 5.2.1. Chiral tin templated assemblies of 3-[(Diphenylphosphanyl)-methyl]- benzene-1, 2-diol (33):........................................................................................... 108 5.2.2. Tin templated chiral assemblies of 3-{[Phenyl- (2,4,6-trimethyl-phenyl)- phosphanyl]-methyl}-benzene-1, 2-diol (34):......................................................... 112 5.3. Conclusions: .................................................................................................. 117 11 6. Experimental details...............................................................................................119 6.1. General remarks: ............................................................................................119 6.2. General procedure for the syntheses of phenol functionalized phosphane oxides (5a-e and 9f):..............................................................................................................121 6.2.1. 2-[(Diphenyl phosphinoyl) methyl] phenol (5a): .....................................121 6.2.2. 3-[(Diphenyl phosphinoyl) methyl] benzene-1, 2-diol (5b):.....................122 6.2.3. 4-[(Diphenyl phosphinoyl) methyl] phenol (5c): .....................................122 6.2.4. 4-[(Diphenyl phosphinoyl) methyl] benzene-1, 2-diol (5d):.....................123 6.2.5. 3-[(Diphenyl phosphinoyl) methyl] phenol (5e): .....................................124 6.2.6. 3-[(Mesitylphenylphosphinoyl) methyl] benzene-1, 2-diol (10):..............124 6.2.7. 2-[(Diphenylphosphanyl)hydroxymethyl]phenol Hydrochloride (6a): .....125 6.2.8. 4-[(Diphenylphosphanyl) hydroxymethyl] phenol (4c):...........................125 6.2.9. Bis [hydroxy (3-hydroxyphenyl) methyl] diphenyl phosphonium Toluenesulfonate (7e/7e_): .....................................................................................126 6.3. General procedure for the synthesis of phenol-functionalized phosphanes 9a-d and 101: .....................................................................................................................127 6.3.1. 2-[(Diphenylphosphanyl) methyl] phenol (9a): .......................................127 6.3.2. 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (9b):.......................127 6.3.3. 4-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (9d):.......................128 6.3.4. 3-[(Mesitylphenyl phosphanyl)-methyl]-benzene-1, 2-diol (9g): .............129 6.4. General procedure for the syntheses of transition metal complexes of 9b-d:....129 6.4.1. Bis {3-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol} Palladium dichloride, 13b: ......................................................................................................130 6.4.2. Bis {4-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol} Palladium dichloride, 13d: ......................................................................................................130 6.4.3. Silver- bis {3-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol}, 14b: .131 6.4.4. Silver- bis {4-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol}, 14d: .131 6.4.5. Bis {4-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol} platinum dichloride, 15: ........................................................................................................132 6.4.6. Bis{3-[(Mesitylphenyl phosphanyl)-methyl]-benzene-1, 2-diol} palladium(II), 101: .................................................................................................133 6.5. General procedure for the syntheses of boranes: .............................................134 12 6.5.1. (a) Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol-4-ylmethyl)-phosphane 16a:……................................................................................................................ 134 6.5.1 (b) Diphenyl- (2-pentaflurophenyl-benzo [1,3,2]-dioxaborol-4-ylmethyl)- phosphane 16b:...................................................................................................... 134 6.5.2. (a) Synthesis of Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol-4-ylmethyl)- phosphane-3- (Dimethyl amino pyridine) 17a: ....................................................... 135 6.5.2 (b) Synthesis of Diphenyl- (2-pentaflurophenyl-benzo [1,3,2]-dioxaborol-4- ylmethyl)-phosphane-3- (Dimethyl amino pyridine) 17b:....................................... 136 6.5.3. Synthesis of Dichloro bis {Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol-4- ylmethyl)-phosphane}-palladium, 18: .................................................................... 136 6.5.4. Synthesis of Dichloro palladium bis {Diphenyl- (2-phenyl-benzo [1,3,2]- dioxaborol-4-ylmethyl)-phosphane-3- (Dimethyl amino pyridine)}, 19:................. 137 6.5.5. General procedure for the syntheses of borates 20 and 22: ...................... 137 6.5.6. Synthesis of the silver complex [Ag (20)], 21: ........................................ 139 6.5.7. Synthesis of the Ag-B macrocycle Ag2 (22)2, 23:.................................... 140 6.6. Transition metal complexes of templated symmetric bisphosphane ligands and their potential application in catalysis ........................................................................ 142 6.6.1. Synthesis of palladium-bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4- ylmethyl) phosphane)}- gallium chloride (25):....................................................... 142 6.6.2. Synthesis of palladium-bis {diphenyl- (benzo- [1, 3]-µ-oxo- k-oxo-4- ylmethyl)-phosphane)}-tin dichloride (26a): .......................................................... 143 6.6.3. Synthesis of palladium-bis {diphenyl- (benzo- [1, 3]-µ-oxo- k-oxo-4- ylmethyl)-phosphane)}-dimethyl tin (26b): ............................................................ 144 6.6.4. Synthesis of platinum -bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4- ylmethyl) phosphane)}-dimethyl tin (28): .............................................................. 145 6.6.5. Syntheses of palladium- bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4- ylmethyl) phosphane)}-bismuth chloride (29): ....................................................... 146 6.6.6. (a) Synthesis of bis {palladium- bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo- 4-ylmethyl) phosphane)}- zirconium (30): ............................................................. 147 6.6.6 (b) Synthesis of dicyclopentadienyl {palladium- bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4-ylmethyl) phosphane)}- zirconium (30A): ................................. 148 6.6.7. Synthesis of tetrakis {palladium- bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo- 4-ylmethyl) phosphane)- yttrium} µ4-hydroxy tri-chloride (31):............................. 148 13 6.6.8. Synthesis of bis {palladium- 3-[(Diphenyl phosphanyl)-methyl]-2-{4- [(diphenyl phosphanyl)-methyl]-benzo[1,3,3’] µ-oxo- µ’-oxo k-oxo -2-yloxy}- phenol]}- yttrium chloride (32): .............................................................................149 6.6.9. Investigations on the catalytic behavior of selected metal complexes: Sonogashira C-C coupling reaction: .......................................................................150 6.7. Transition metal complexes of templated bisphosphane ligands with diastereotopic donor sites: ..........................................................................................151 6.7.1. Synthesis of palladium -bis {phenyl, 2,4,6-trimethyl-phenyl (benzo- [1, 3]- µ-oxo-k-oxo-4-ylmethyl) phosphane)}-dimethyl tin (33a/b): ..................................151 6.7.2. Synthesis of palladium -bis {biphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4- ylmethyl) phosphane)}-methyl tin chloride (34): ....................................................152 6.8. Results of computational studies on complex 26a/27a:....................................153 7. Summary and outlook ............................................................................................155 7.1. Summary: .......................................................................................................155 7.2. Outlook: .........................................................................................................159 7.2.1. Prospective ligands: ................................................................................159 7.2.2. Extending the self-assemblies: ................................................................161 7.2.3. Applications: ..........................................................................................161 7.3 Zusammenfassung:.....................................................................………………163 8. Crystallographic Appendix.....................................................................................168 9. References: ............................................................................................................190 10. Curriculum vitae……………………………………………………………………...200 15 1. Introduction 1.1. Self-assembly, ligand designing and catalysis: Among many theories put forward in the creation of earth, physics played an important role. In the later stage came the chemistry followed by biology. After the big bang, particles united to form atoms,1 atoms to molecules, molecules to supermolecules and supermolecules to supramolecules. This higher ordering some time later resulted in to the creation of first living being “Ameba”. Chemistry is the science of atoms and molecules, which are the simplest building blocks of variety of materials and are unavoidable ingredients of many processes. Chemistry helps us in understanding the properties of matter and there by resulting in the creation of new materials. It is a bridge between basic and applied, simple and complex, between living and non-living. Chemistry is a toolbox, which has the power to produce new molecules and materials that never existed before they were created by chemists. Self-assembling based on the range of noncovalent inter or intra molecular interactions2 is another tool in the kit of chemistry and nature provides range of examples of this kind, such as, a few amino acids in human body assemble in different ways to carry out thousands of processes. An important factor in the process of assembling are the complementary binding motifs on the components and these components could be simple organic molecules to metals to complex amino acids. A precautious engineering of the process components can provide the desired architecture. Shortening the width of the broad spectrum of self-assemblies to the relatively smaller [1] P. J. E. Peebles, D. N. Schramm, E. L. Turner, R. G. Kron, Nature, 1991, 352, 769-776; S. W. Hawking, G. F. R. Ellis, 1968, The Astrophysical Journal, 1968, 152, 25; G. L. Schroeder, “Genesis and the big bang” Bantam Books, New York, 1990. [2] H.J. Schneider, A. K. Yatsimirsky, Principles and Methods in Supramolecular Chemistry, Wiley-VCH, New York, 2000. 16 class of inorganic self-assemblies will probably provide better insight into these architectures. Inorganic self-assembly involves spontaneous organization of organic ligands around the metal center. The metal center acts both as cement to hold the ligands and as center to orient the ligands in a particular direction. The importance lies in designing ligands and the choice of the metal to obtain a desired architecture from the mixture of subunits. Metal ions have their own stake in this process, a) they prefer particular geometries of ligands, b) they have varying strength in terms of acidity or basicity, c) in addition to this they can be redox or photochemically active providing further interesting properties. A range of architectures can be obtained by fine-tuning the ligand or metal or both ligand and metal. These assemblies show a range of excellent properties. For example a triangle3 or square assembly4 can be utilized as a host for trapping a guest molecule. Star5 or rectangular box6 like assemblies bound to the substrate molecules7 may enable to perform chemical transformations on the substrate molecule. Supramolecular capsules8 can act as catalysts in unimolecular rearrangements.9 A triple helix obtained by self-assembly provides insights into the double helix interactions.10 Supramolecular self-recognition may provide details of amino acid sequencing in proteins.11 A great diversity of polynuclear metal clusters have been obtained by self-assembly where in the number of metals atoms range from few to over hundred which shows a metallic behavior12 or catalytic activity.13 One of the important components of an assembling process is the ligand. A crucial ligand design may circumvent laborious syntheses. The properties of an assembly or complex can be very easily fine-tuned by varying the ligand, though it’s teamwork. In order to assist the ligand design on rational basis there is a need of a general concept. In an effort, Tolman introduced the concept of “cone angle (Θ)”.14 According to Tolman’s definition, cone [3] G. Suess-Fink, J. L. Wolfender, F. Neumann, H. Stoeckli-Evans, Angew. Chem. Int. Ed. 1990, 29, 429. [4] G. Newton, I. Haiduc, R. B. King, C. Silvestru, J. Am. Chem. Soc. 1993, 115, 1229. [5] S. Gambarotta, C. Floriani, A. Chiesi-Villa, C. Guastini, J. Am. Chem. Soc. 1983, 105, 1156. [6] S. K. Mandal, L. K. Thompson, M. J. Newlands, E. J. Gabe, F. L. Lee, J. Chem. Soc. Chem. Commun. 1989, 744. [7] A. W. Maverick, M. L. Ivie, J. H. Waggenspack, F. R. Fronczek, Inorg. Chem. 1990, 29, 2403. [8] A. W. Kleij, J. N. H. Reek, Chem. Eur. J. 2006, 12, 4218. [9] D. Fiedler, H. van Halbeek, R. G. Bergman, K. N. Raymond, J. Am. Chem. Soc. 2006, 128, 10240. [10] J. M. Lehn, Supramolecular Chemistry: Concepts and Perspectives, VCH, Weinheim 1995. [11] D. L. Caulder, K. N. Raymond, Angew. Chem. Int. Ed. 1997, 36, 1440. [12] F. M. Mulder, T. A. Stegink, R. C. Thiel, L. J. de Jongh, G. Schmid, Nature, 1994, 367, 716. [13] M. N. Vargaftik, I. I. Moiseev, D. I. Kochubey, K. I. Zamaraev, Faraday Discuss. 1991, 92, 13. [14] C. A. Tolman, Chem. Rev. 1977, 77, 313. 17 angle is a mean of describing the steric properties of a monodentate ligand. He was the first to quantify the electronic properties of some of the ligands and went on to introduce a term X to describe them.15 Much later the importance of the geometry of the bidentate ligand was recognized and was termed as “Natural bite angle” by Leeuwen and coworkers.16 The natural bite angle can be defined as the angle at which the two donor atoms of a chelating ligand bite at the metal center. A very close term to the bite angle is the “flexibility range” which is defined as the accessible range of bite angles within less than 12.6 kJ/mol excess strain energy from the calculated bite angle.17 Though the above factors are quantified, there are other factors, which equally influence the ligand design. The nature of donating atoms in a ligand is very important in order to achieve coordination with a particular metal center. The availability of range of soft to very hard donors allows chemists to select donors of their choice. Substituents, more precisely steric bulk on the donors, as well influence the coordination. Bulky substituents may shield the donor subsequently, decreasing the donating ability, and vice versa. Electronic factors are of equal importance; hence while designing ligands, electronic factors should also be considered. Electron withdrawing substitutents may decrease the donating ability and electron accepting substituents may increase the donating ability. Tolman’s method provides a rough quantification of steric and electronic factors, but a precise determination of these factors is still missing, although good sophisticated guesses can be made with the help of modern computational methods. Depending on the number of donor sites, ligands can be classified as mono-, bi-, tri- or polydentate. Monodentate ligands can be easily synthesized but have limited applications. On the other hand bidentate ligands can induce rigidity in a complex and thus increase the regio or stereo selectivity. But syntheses of bidentate ligands are generally multistep, time consuming and laborious. In order to circumvent the tedious syntheses there is a need of a new synthetic strategy.18 Having designed the ligand and selected a metal, a step forward could be utilizing them to demonstrate the true power of chemistry in catalysis. Catalysis can be defined as an action between two or more substrates, initiated by an agent called catalyst that itself remains [15] C. A. Tolman. J. Am. Chem. Soc. 1970, 92, 2953. [16] P. W. N. M. van Leeuwen, P. C. J. Kamer, J. N. H. Reek, P. Dierkes, Chem. Rev. 2000, 100, 2741; P. W. N. M. van Leeuwen, P. C. J. Kamer, J. N. H. Reek, Pure Appl. Chem. 1999, 71, 1443. [17] A. J. Sandee, J. N. H. Reek, J. Chem. Soc. Dalton. Trans. 2006, 3385. [18] J. M. Tackas, D. S. Reddy, S. A. Moteki, D. Wu, H. Palencia, J. Am. Chem. Soc. 2004, 126, 14, 4494. 18 unaffected by the action and accelerates the rate of action. Assembling ligands around a metal to obtain a catalyst of interest is a challenge in chemistry. Traditional synthetic pathways to develop a catalyst are multi-step and time consuming; this is specially inconvenient where a large ligand library has to be screened in order to find out the most suitable candidate for a suitable application. New synthetic strategies are therefore necessary. Major break throughs have been achieved in recent years and a few interesting strategies have been emerged. Breit and coworkers (see Fig. 1) came up with the idea of utilizing hydrogen bonding between two monodentate ligands and assembling them on a metal center, which then mimics a bidentate ligand.19 The key role is played by the ligand-ligand interactions. Depending on the ligand-ligand interaction a continuum can be drawn beginning with the weakest and ending in the strongest ligand-ligand interaction. Thus with a small number of monodentate ligands a large library of metal complexes can be easily synthesized.20 M D D M D D M D D M D D Increasing attractive ligand-ligand interaction Fig. 1: Monodentate ligands that mimic bidentate ligand. Another strategy is to assemble the ligands on a preformed template. Takacs et. al. used Zinc bis-oxazoline complexes (see Fig. 2) as template and attached a long organic tether with a functional group at the end of the tether, which offer donating sites for further coordination and assembly.18 In a similar fashion Reek and coworkers used [19] B. Breit. Angew. Chem. Int. Ed. 2005, 44, 6816. [20] B. Breit, W. Seiche, Angew. Chem. Int. Ed. 2005, 44, 1640. 19 L L L L M L LM Fig. 2: Template controlled complex designing zinc porphyrin as template and assembled ligands on this template which are capable of coordinating further metals.21 They demonstrated that the assembly of heteroleptic complexes was preferred over homoleptic ones. Complexes generated using self- assembling approaches were shown to be highly active and selective in hydration of terminal alkynes,22 asymmetric hydroformylation23 and in many other catalytic reactions.24 Recently Love25 and Reek26 independently introduced a similar concept called “anion sequestering” in that one end of the ligand is anchored on an anion and the other end is coordinated to a metal. The development of these and related strategies has already been summarized in a number of recent reviews.19, 27 1.2. Setting the Goals: Recent years have witnessed a few break-throughs in the field of catalyst designing via self-assembly, but there is immense need of new approaches. The chemistry of self- assembly relies on non-covalent interactions such as hydrogen bonding, van der Waals interactions, cation-π interactions, electrostatic interactions, charge transfer interactions, π stacking interactions and coordinative interactions.2 The present study is aimed at utilizing the coordinating behavior of a phosphine at one end of a bifunctional molecule, whereas the other end is templated on an element (E) (refer to Fig. 4). The template E is expected to assemble two or more catechol phosphines to generate bi- or multifunctional ligands. The template E is anticipated to play a crucial role in controlling the bite angle and coordination behavior of the phosphine donors and can be any hard acid from in the sense [21] V. F. Slagt, M. Roeder, P. C. J. Kamer, P. W. N. M. van Leeuwen, J. N. H. Reek, J. Am. Chem. Soc. 2004, 126, 4056. [22] F. Chevallier, B. Breit, Angew. Chem. Int. Ed. 2006, 45, 1599. [23] M. Kuil, P. E. Goudriaan, P. W. N. M. van Leeuwen, J. N. H. Reek, J. Chem. Soc. Chem. Commun. 2006, 4679. [24] B. Breit, W. Seiche, J. Am. Chem. Soc. 2003, 125, 6608. [25] P. A. Duckmanton, A. J. Blake, J. B. Love, Inorg. Chem. 2005, 44, 7708. [26] L. K. Knight, Z. Freixa, P. W. N. M. van Leeuwen, J. N. H. Reek, Organometallics, 2006, 25, 954. [27] M. J. Wilkinson, P. W. N. M. van Leeuwen, J. N. H. Reek, Org. Bio. Chem. 2005, 3, 2371. 20 of the hard/soft/acid/base concept28 main group elements to transition metals, providing an array of diversity. Phosphines are well known in catalysis due to their easily accessible lone pair (Fig. 3). Phosphines are known to be soft donors and according to hard/soft acid/ base theory28 these may selectively coordinate to soft acceptors. Thus, coordination of a metal with bi- or multidentate E produces the final “Assembly” i. e. E, M-chelate complex (see Fig. 4). Changing the substituents on phosphorus may allow to fine-tune the steric and electronic properties of the ligand. Thus the first aim of this work is to rationally design phosphine functionalized monodentate ligands and to develop a short synthetic methodology for the syntheses of these ligands, which may suite to a self-assembling approach to generate bidentate donors. F F P Functional groups Lone pair Fig. 3: Functional phosphine with lone pair An attempt will be made to demonstrate the feasibility of the template formation by exploring a stepwise “Aufbau” of a supramolecular bidentate ligand, followed by introduction of a transition metal across the soft phosphine donors. Thus the template with the ligand now mimics a bidentate ligand that can be self-assembled on a metal. Another area of interest is to explore the Lewis acid base chemistry of the functional phosphine ligands. The coordination of hard acids at the hard donor sites generating acidic center will be utilized to synthesize multimetallic complexes, which have attracted great interest in recent years. The main goal of this study is to employ the new classes of functionalized phosphines in the process of supramolecular self-assembly, which may produce the templated metal complexes in a single step (Fig. 4 demonstrating the goals). Such an assembling methodology may offer greater opportunities over the traditional synthetic protocols [28] R. G. Pearson, J. Chem. Ed. 1987, 64, 561-567. 21 established in the syntheses of metal complexes. In that, varying the size and coordination geometry of the template center (E) shall control the preorganization of the phosphines. F F P F F F F P P E F F F F P P E Template Assembly Functional phosphine Self-assembly E M M E, M Fig. 4: Schematic representation of Aufbau and self-assembling approaches. Variation in the template center may allow to study the bite angle properties of the final assembly. A closer look at the complexes obtained by the self-assembling approach revealed that the composition of these complexes resembles to those used in C-C coupling reactions. The catalytic potential of selected complexes in the Sonogashira coupling of phenyl acetylene with p-iodo-nitrobenzene will be explored. Nature provides an immense number of examples of chiral entities, but rational syntheses of such chiral entities presents an active challenge to synthetic chemists around the world. In this view, a further point of interest in this work is to synthesize chiral complexes by a self-assembling approach. This goal can be achieved either by introducing chirality at the template center or at the phosphine moiety. In short, the goal of the present study is a) to synthesize bidentate phosphine functionalized ligands in possibly the least number of synthetic steps, which may suite for a self- assembling approach, b) to generate a template which mimics a bidentate ligand and can self-assemble to produce a metal complex, c) to develop a new strategy based on supramolecular self-assembly wherein hard donors reacts with hard acids and soft donors to soft acid in a single step to produce the desired architectures, d) to study changes in bite 22 angle and cone angle of a complex by varying the geometry of the template center, e) to demonstrate the catalytic potential of the self-assembled complexes and f) to synthesize chiral complexes by the self-assembling approach. 23 2. Syntheses of diphenyl-phosphinomethyl substituted phenols and catechols and mechanistic details on their formation 2.1. Introduction: Phosphines are one of the most commonly used class of ligands in modern day catalysis. They are routinely employed in C-C coupling reactions,29 in hydrogenation,22 allylic alkylation,21 etc. As the complexity of their applications increases, synthesis of the phosphine also becomes complex. The last few decades have been dominated by an increasing use of bidentate phosphines (bis-phosphines) rather than their monodentate counterparts.30 The bidentate ligands offer diverse characteristics like variable coordination sites, controlled (regio and stereo) selectivity, and structural rigidity. But many times the synthesis of such bidentate ligands is multistep and time consuming. Multistep synthesis is practically inconvenient where a large ligand library is needed in order to find out the most suitable ligand for a particular application. To avoid this, there is an immense need of new strategies that will provide easy synthetic pathways towards the syntheses of bidentate ligands. In this chapter the focus will be on providing an easy synthetic pathway to functional phosphines that can be used to build bidentate ligands. Phosphines functionalized with hard donor groups appear to be interesting candidates in applications such as self- assembly. As rigidity is one of the most important criteria in self-assembly, it was envisioned that phosphines with functional groups on a rigid framework would further [29] J. Tsuji, Palladium Reagents and Catalysts, Wiley, 2000. [30] I. V. Komarov, A. Borner, Angew. Chem. Int. Ed. 2001, 40, 1197; T. Hayashi, Acc. Chem. Res. 2000, 33, 354. 24 benefit the purpose. In this view, functionalzing the phosphines with catechol or phenol substituents was thought to be a good starting point. The addition of a P–H bond to a carbonyl group is a synthetically useful and fundamental reaction mode of phosphorus-hydrogen substituted phosphines. In particular, the reaction between an aldehyde/ketone and secondary phosphine is an important pathway to prepare organophosphorus compounds and was reported as early as in 1962 by Buckler et al.31 These transformations proceed normally strictly regioselective via P–C bond formation to give α-phosphanyl-carbinols (Scheme 1, a) and have found application in the synthesis of functional tertiary phosphines.32 Recently it has been found that N-heterocyclic phosphines 1 deviate from the common behavior as they react with aldehydes and ketones via reduction rather than alkylation of the carbonyl moiety (Scheme 1, b).33 The unusual reversed regioselectivity ("Umpolung") has been related to the unique hydride-like polarization of the P–H bond in 1 which owes to the special bonding situation in the heterocyclic ring .33 P H + O P OH N R P R N H + O N R P R N O H (a) (b) 1 Scheme 1: Possible reaction modes of phosphanes with carbonyl groups During a literature survey on hydrophosphanation of carbonyl compounds it was found that the reaction of diphenyl phosphine with salicylic aldehyde proceeds directly to give a benzyl phosphine oxide (Scheme 2).34 Similar reactions had been observed earlier and were explained by a two-step sequence involving a "normal" hydrophosphanation followed by isomerization of the transient α-phosphanyl-carbinol (pathway (i), Scheme 2).35 In the context of present studies on controlling the regioselectivity of hydrophosphanations33 it was of interest to elucidate the mechanistic aspects of this reaction in more detail. Of [31] M. Epstein and S. A. Buckler, Tetrahedron, 1962, 18, 11, 1231. [32] K.V. Katti, H. Gali, C. J. Smith, D.E. Berning, Acc. Chem. Res. 1999, 32, 9. [33] D. Gudat, A. Haghverdi, M. Nieger, Angew. Chem. 2000, 112, 3211-3214; S. Burck, D. Gudat, M. Nieger, W.W. Du Mont, J. Am. Chem. Soc. 2006, 128, 12, 3946. [34] V. I. Evreinov, V. E. Baulin, Z. N. Vostroknutova, N. A. Bondarenko, T. Kh. Syundyukova, E. N. Tsvetkov, Izv. Akad. Nauk SSSR, Ser. Khim. 1989, 1990. [35] S. Trippett, J. Chem. Soc. 1961, 1813. 25 particular interest was to exclude the possibility that the product was formed via "inverse" addition of the P–H bond of the phosphine and subsequent Michaelis-Arbuzov rearrangement of a transient phosphinite (pathway (ii) in Scheme 2) which might, in view of the reactivity of 1 and earlier observations of Michaelis-Arbuzov rearrangements under conditions similar to the ones applied here,36 provide a conceivable alternative to the standard mechanism. Ph2P H + OH (i) (ii) CHO OH PPh2HO OH PPh2 O OH O PPh2 [H+] [H+] [H+] [H+] Scheme 2: addition of P-H bond to an aldehyde and rearrangement modes Herewith the results of studies of the transformations of diphenyl phosphine and phenolic aldehydes into phenol-functionalized phosphine oxides are presented, and it is demonstrated that these species can be easily converted into phosphines. The products thus accessible belong to a class of multifunctional ligands and may find interesting applications in host-guest chemistry37 or catalysis.38 2.2. Results and discussion: 2.2.1. Syntheses and mechanistic insights on the formation of methyl phosphinoyl phenols and catechols: The reaction of equimolar amounts of diphenyl phosphine 2 and salicylic aldehyde 3a in methanol or ethers (Et2O, DME) in the presence of catalytic amounts of hydrochloric or p- toluenesulfonic acid affords directly the phosphine oxide 5a,34 which has been isolated in [36] P. Y. Renard, P. Vayron, C. Mioskowski, Organic Lett. 2003, 5, 1661; A. N. Bovin, A. N. Yarkevich, A. N. Kharitonov, E. N. Tsvetkov, Chem. Commun. 1994, 973. [37] X. Sun, D. W. Johnson, D. L. Caulder, K. N. Raymond, E. H. Wong, J. Am. Chem. Soc. 2001, 123, 2752. [38] N. T. Lucas, J. M. Hook, A. M. McDonagh, S. B. Colbran, Eur. J. Inorg. Chem. 2005, 496; N. T. Lucas, A. M. McDonagh, I. G. Dance, S. B. Colbran, D. C. Craig, Dalton Trans. 2006, 680. 26 good yield after work-up (Scheme 3). Monitoring the progress of the reaction by 31P NMR spectroscopy revealed that 5a remained the only spectroscopically detectable species beside unreacted 2 (which disappeared when the reaction took progress) and minor side products. Even though the latter were not further characterized, the observed chemical shifts precluded a structural assignment as an α-phosphanyl-carbinol. In order to elucidate mechanistic details it was attempted to find reaction conditions that facilitated the detection of a precursor to 5a. In these studies it was established that treatment of an ethereal solution of 2 and 3a with excess conc. hydrochloric acid led to immediate precipitation of a colorless solid, which was isolated by filtration. A solid-state 31P CP/MAS NMR spectrum disclosed an isotropic shift δ31Piso = -0.8 which differs clearly from that of 5a Ph2P H + R1 CHO R1 PPh2HO R1 PPh2 O R2 R3 R2 R3 R2 R3 2 3a-e 4a-e 5a-d [H+] [H+] 7b,b'PPh2 OH HO R2 OH PPh2HO H Cl 6a R1 R2 R3 3a-9a OH H H+ 3b-5b OH OH H+ 3c-5c H H OH+ 3d-5d H OH OH+ 3e-7e H OH H+ R1R2 R3 R1 R3 Scheme 3: Designing and syntheses of catechol phosphine oxides (δ 31Piso = 39.3) but resembles that of the α-phosphanyl-carbinol obtained from the reaction of 2 and benzaldehyde. As a spectrum recorded under conditions that allow to detect scalar couplings to protons revealed a doublet splitting attributable to a one-bond J-coupling (Fig. 1, JPH = 501 Hz), the product was assigned as the α-phosphanyl-carbinol hydrochloride 6a which is deemed to represent the initial product formed by attack of the nucleophilic phosphine on the protonated aldehyde. The structural assignment was further corroborated by satisfactory analytical data. 6a was isolated as white solid melting at 27 104ºC in 90% yield. Attempts to characterize 6a by solution NMR spectroscopy revealed that the product decayed upon dissolution in methanol to give a mixture of the starting materials and the phosphine oxide 5a, and emphasized thus its nature as a reaction intermediate. The results presented above allow to conclude that the reaction of 2 with salicylic aldehyde involves a "normal" hydrophosphanation as the key step. Reaction of 3b was carried out under similar conditions as that of the 3a. The same regioselectivity was observed in the acid-catalyzed reaction of 2 with 2,3- dihydroxybenzaldehyde 3b as that of 3a. NMR studies allowed in this case the direct detection of a small amount of the α-phosphanyl- carbinol 4b and two further intermediates. The constitution of the latter was assigned as diastereomeric phosphonium 10 0 - 10 δ31P Figure 1: Isotropic line of the solid state CP/MAS 31P NMR spectrum of 6a at a spinning speed of 13.2 kHz recorded with high power proton decoupling (top trace) and frequency- shifted Lee-Goldburg decoupling (bottom trace) for the suppression of homonuclear dipolar coupling between protons. As the decoupling sequence scales heteronuclear couplings by a factor of 0.577, the observed splitting of 289 Hz corresponds to a value of 1JPH = 501 Hz. salts 7b, 7'b by two-dimensional NMR studies, and dynamic exchange between all four species was established by a 2D 31P EXSY NMR spectrum. Similar species as 7b, 7'b have previously been obtained by reaction of diphenyl phosphine with formaldehyde and strong acids.32,39 All products were eventually converted into the phosphine oxides 5a-d. The [39] J. Fawcett, John; P. A. T. Hoye, R. D.W. Kemmitt, D. J. Law, D. R. Russell, J. Chem. Soc. Dalton Trans. 1993, 2563. 28 Bond lengths [Å] Bond lengths[Å] Bond angles [°] Bond angles [°] P2-O2 1.500(1) P1-O1 1.510(3) C41-P2-C51 106.06(1) O1-P1-C11 110.75(1) P1-C21 1.797(2) P1-C1 1.817(1) O2-P2-C51 110.98(1) O1-P1-C21 111.3(1) P2-C2 1.812(1) H32-O1 1.786(1) O2-P2-C41 110.3(1) C1-P1-C21 108.1(1) P2-C41 1.806(1) H62-O2 4.606(2) O2-P2-C2 114.1(1) C1-P1-C11 107.2(1) Fig. 2.2: Molecular structure of 5b; H-atoms except H32 and H62 are omitted for clarity (50% probability thermal ellipsoids), important bond lengths and bond angles are given in the table. phosphine oxide 5b was isolated after work-up as white solid in 85% yield and melts at 194°C. The 31P NMR spectrum of the white solid displayed a single resonance at 40.4 ppm. EI-Mass spectroscopy showed a molecular ion peak at m/e = 324, which corresponds to the expected molar mass of 5b. As a representative of all phosphine oxides, the molecular structure of 5b was determined by a single crystal X-ray diffraction study. Suitable single crystals were obtained by crystallization from a concentrated DME solution at room temperature. The phosphine oxide 5b crystallizes in a triclinic unit cell in the space group P1(bar) (Fig. 2.2). The asymmetric unit contains two crystallographically independent molecules of 5b, which are disposed in head to tail fashion (see fig. 2.2) and a solvent molecule (THF). The P2 centered molecule shows a weak hydrogen bonding (H62- O71: 1.99 Å) interaction with the solvent (THF) molecule, whereas the P1 centered 29 molecule does not show any intermolecular interaction. On the other hand the P1 centered ligand display intramolecular hydrogen bonding, where H32 is weakly bonded to O1 (1.78 Å). As a consequence, the O1-O32 (2.60 Å) distance is shorter than the O2-O62 (3.89 Å) distance. Further noticeable is the P-O distance (1.51 Å), which confirms the P-O double bond as is expected.40 The phosphorus atoms display tetrahedral geometry with minor deviation of all the angles from the standard tetrahedral angle of 109.4º (see Table 1). The remaining bond distances and angles show no peculiarities. The reaction of 2 with 4-hydroxybenzaldehyde 3c afforded as primary product the α- phosphanyl-carbinol 4c, which was isolated in 90% yield as colorless powder with melting point of 168ºC by precipitation from methanol and characterized by 31P CP/MAS NMR. Key to the structural assignment was the observation of a single resonance [δ(31P) = -7.2] which appeared at somewhat higher field than that of 6a and showed no splitting due to 1JPH coupling. In contrast to the elusive 2-hydroxy-substituted carbinol 4a, the signal of 4c was also observable in solution 31P NMR spectra [δ(31P) = -2.3] although in these solutions, even in the absence of additional acid, partial decomposition into 2 and 3c occurred (obviously the acidity of the phenolic OH-moiety is sufficient to promote an auto- catalytic reaction). Acid catalysts promoted complete conversion of the mixture into the phosphine oxide 5c. The 31P NMR spectrum showed a single resonance at 32 ppm confirming the complete conversion. The phosphine oxide 5c was isolated as white solid, melting at 223ºC in 60%. The same behavior was observed as well in the reaction of 2 with 3,4-dihydroxybenzaldehyde 3d which afforded the phosphine oxide 5d as final product. A single 31P resonance at 40.4 ppm supports the complete conversion to the phosphine oxide 5d which was isolated as white powder in 90% yield with a melting point of 192°C. Finally, acid-catalyzed reaction of 2 with 3-hydroxybenzaldehyde 3e gave a mixture of products which were assigned as the phosphanyl-carbinol 4e and phosphonium ions 7e/7e' on the basis of a comparison of the observed 31P chemical shifts with those of the products of the previously described reactions. Although after some hours a weak signal of a new [40] P. Perez-Lourido, J. A. Gracia-Vazquez, J. Romero, A. Sousa, Inorg. Chem. 1999, 38, 538. 30 PPh2HO 8 + H+ R PPh2 H2O R PPh2 HO R + H+ PPh2 HO R Scheme 4: Presumed mechanism of the phosphanyl-carbinol – phosphine oxide isomerization product with a chemical shift compatible with a phosphine oxide structure was observable, the conversion remained incomplete even after prolonged reaction time. As isolation and identification of individual products proved unfeasible, the reaction was not pursued further. In summary, it can be stated that all reactions of the phosphine 2 with hydroxyl- benzaldehydes 3a-e proceed via hydrophosphanation to yield α-phosphanyl-carbinols 4a-e as initial products. The reactions of aldehydes 3a-d featuring at least one OH-substituent in 2- or 4-position are distinguished by the fact that the equilibrium between the starting materials and the addition product is shifted to side of the former, and that the α- phosphanyl-carbinols rearrange easily to the isomeric phosphine oxides. The reduced stability of these adducts with respect to the starting materials can be understood as a consequence of the electron releasing nature of the additional hydroxyl-substituents which should render the aldehydes weaker electrophiles and the attack by the nucleophilic phosphine energetically less favorable. Aldehydes with 2-hydroxy-substituents such as 3a,b may further benefit from additional stabilization by strong intramolecular hydrogen bonding. As a consequence of these effects, the concentration of α-phosphanyl-carbinols in these reactions may be very low (4b) or not detectable at all (4a). Considering that the conversion of 4a-d to the phosphine oxides 5a-d proceeds presumably via an electrophilic methylenephosphonium type intermediate 8 (Scheme 4), the same substituent effects can be considered to facilitate the isomerization into the phosphine oxides. 2.2.2. Synthesis and characterization of chiral mesityl phenyl phosphinoyl methyl catechols: The successful syntheses of the above mentioned mono/di-hydroxy ligands enhanced the confidence level and it was decided to design more challenging ligands. As chirality is one 31 of the important aspects in catalysis, attention was turned towards the syntheses of chiral catechol phosphines. Mesityl phenyl phosphine was synthesized according to the reported literature.41 Addition of a racemate of the chiral phosphine to 2,3 dihydroxy benzaldehyde along with a catalytic amount of p-toluene sulfonic acid, followed by stirring for 24 hours at room temperature gave a white powder. The 31P NMR spectrum of the white powder displayed a single resonance at 46.4 ppm indicating the formation of the expected phosphine oxide 4f. Filtration followed by washing (thrice) with DME and drying gave a clean product. The white powder with the melting point of 220°C was isolated in 85% yield. The Mass spectrum showed a molecular ion peak at m/e = 366[M], further confirming the formation of a phosphine oxide. OH CHO OH P O OH OH OH P OH Ph Mes Mes Ph 9f + MeI LiAlH4[H] + PPhMesH 4f Scheme 5: Synthesis of 3-[(Mesitylphenylphosphinoyl) methyl] benzene-1, 2-diol 2.3. Reduction of the phosphine oxides to ditopic phosphines: Deoxygenation of the phosphine oxides 5a-d was readily achieved by adaptation of an established procedure involving quaternization of the phosphine oxide moiety with methyl R1 PPh2 O R2 R3 5a-d R1 R2 R3 5, 9a OH H H+ 5, 9b OH OH H+ 5, 9c H H OH+ 5, 9d H OH OH+ R1 PPh2 R2 R3 9a-d 1. MeI 2. LiAlH4 Scheme 6: Reduction of phosphane oxides to phosphanes. iodide and subsequent reduction with LiAlH4 (Scheme 6).42 No special protection of the phenol groups was necessary, however, the use of a sufficient excess of the hydride to achieve complete deprotonation of the acidic OH-groups was mandatory to obtain reasonable yields of products. The reaction was monitored by TLC and complete [41] I. Kovacik, D. K. Wicht, N. S. Grewal, D. S. Glueck, C. D. Incarvito, I. A. Guzei, A. L. Rheingold, Organometallics, 2000, 19,6, 950. [42] T. Imamoto, S.-I. Kikuchi, T. Miura, Y. Wada, Org. Lett. 2001, 3, 1, 87. 32 conversion was achieved in 4-6 hours. Aqueous work-up of the reaction mixture and purification of the crude products by column chromatography afforded the phosphines 9a- d as moderately oxygen sensitive materials. Compounds 9a-d were isolated as colorless oils (9a) or white solids (9b-d) in yields of 60-70%. As a representative of all other phosphines (9a-d), 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (9b) is discussed in detail herein. The white solid of 9b melts at 82°C and was isolated in 60% yield. A single 31P resonance was detected at –13.1 ppm as can be expected for such a phosphine.43 The proton NMR displayed a multiplet between 7.5-7.3 ppm, accounting for 10 protons which is assigned to the phenyl groups. A doublet (AX spin system) at 6.78 ppm was observed which can be assigned to a catechol proton next to the hydroxy group. A triplet at 6.64 ppm is assigned to a central proton on the catechol ring and another doublet at 6.43 ppm is assigned to the catechol proton Bond lengths [Å] Bond angles [º] P1-C14 1.840(1) C8-P1-C14 101.66(1) P1-C7 1.867(1) C7-P1-C14 100.37(1) P1-C8 1.839(0) C7-P1-C8 101.78(1) O2-H1 2.170(2) Fig. 2.3: Molecular structure of 9b; (H-atoms omitted for clarity, thermal ellipsoids with 50% probability) important bond angles and bond lengths are given in the table. [43] K. Kellner, S. Rothe, E. M. Steyer, A. Tzschach, Phosphorus, Sulfur, Relat. Elem. 1980, 9, 269. 33 next to the CH2PPh2 substituent. The methylene protons appear as a doublet at 3.52 ppm with a small two bond phosphorus proton coupling of 1.7 Hz. The Mass spectrum showed an ion peak at m/e = 308.1[M+] and further fragments at 186.1 [Ph2PH+], 185.1 [Ph2P+], 183.0 [Ph2P+–H2], 123.1[M+–PPh2], confirming the formation of 9b. The phosphine 9b was crystallized from Ethyl acetate: hexane (3:7) at room temperature. The compound crystallizes in a monoclinic unit cell in the space group P21/c (see fig. 2.3). The crystals contain discrete molecules of 9b with specific intramolecular hydrogen bonding (H1-O2 2.17Å) interactions. The coordination sphere around phosphorus is a regular trigonal pyramid. The sum of the three bond angles (303º) is much less than 360º and is comparable with triphenyl phosphine (308º)44 or tri-o-tolyl phosphine (308º).45 The P-C7 (1.87 Å) bond distance was found to be longer than the other two P-C14/8 (1.83 Å) bonds and the P-C distances in triphenyl phosphine.44 The hydroxy groups on the catechol ring are on the same side of the phosphorus lone pair. This particular arrangement of hydroxy groups and lone pair indicate that compound 9b may prefer concave coordination. The chiral phosphine oxide 4f was reduced to the phosphine 9f under similar reaction conditions as mentioned for 9b. The white solid of 9f obtained after column chromatography melts at 93°C and was isolated in good yields (70%). A single 31P NMR resonance at –27.6 ppm was detected, the observed up field shift compared to the achiral phosphine (9b/d) is attributed to increased shielding of the phosphorus atom by the sterically bulky mesityl group. This observation is in accordance with the literature reported46 fact that trimesityl phosphine (-35.8 ppm) is much more upfield shifted compared to the less bulky triphenyl phosphine (-5.6 ppm). The proton NMR of 9f displayed a multiplet at 7.35-7.20 ppm accounting for five protons that are assigned to the phenyl group. A doublet at 6.9 ppm with a four-bond phosphorus proton coupling of 1.9 Hz was attributed to the two m-mesityl protons. The aliphatic protons show at the AB part an ABX spin pattern due to coupling with each other and the phosphorus atom(X) and appear at 3.7 and 3.5 ppm. The three methyl groups appeared as multiplet at 2.30-2.28 ppm, accounting for nine protons. The remaining NMR signals were similar to that of 9b. ESI-MS positive mode spectrum of this phosphine showed pseudo-molecular ion peaks at m/e = 351.15 [M+H]+ and m/e = 373.13 [M+Na]+. [44] J. J. Daly, J. Chem. Soc. 1964, 3799. [45] T. S. Cameron, B. Dahlen, J. Chem. Soc. Perkin Trans. 2, 1975, 1737. [46] E. C. Alyea, J. Malto, Phosphorus, Sulfur and silicon, 1989, 46, 175. 34 2.4. Syntheses and characterization of transition metal complexes of diphenyl-phosphanyl methyl phenols and catechols: There is a long standing interest in metal complexes with catechol phosphines, where the P-only, O-only or P-O coordination mode can be observed. The latter is particularly interesting with respect to the well studied coordination chemistry of phosphino phenols such as 11, which may give complexes (see Scheme 7) of type 1243 with different metals like Pd,47 W,48 Ni, Co, Pt49 and Rh50 with variable substituents on the metal. These complexes have been studied because of their potential use as catalysts for olefin polymerization or hydrogenation. OH PPh2 11 O P 12 MX MPh Ph X Scheme 7: Transition metal complexes of rigid catechol phosphine. Having synthesized the above mentioned catechol phosphines 9b-d, it was decided to study their coordination behavior, with particular emphasis on the generation of complexes with a P-only coordination mode. Selection of the metal center is another important issue in metal complex chemistry. According to the HSAB theory28, soft metals like palladium and silver prefer soft phosphine donors and have low affinity towards hard donors like oxygen. Inspection of mechanical molecular models suggested that it might be difficult to form a chelating complex with a similar coordination mode as 12 with soft metals and hence Pd and Ag were selected in order to achieve the P-only coordination complexes. To perform the reaction, two equivalents of 9b were dissolved in dry THF and one equivalent of (COD)PdCl2 was added to it under constant stirring. The reaction progress was monitored by 31P NMR and showed completion of the reaction in 2 hours. THF was [47] J. Heinicke, M. Koehler, N. Peulecke, M. K. Kindermann, W. Keim, M. Kockerling, Organometallics, 2005, 24, 344. [48] L. Dahlenburg, K. Herbst, G. Liehr, Zeitschrift fuer Kristallographie - New Crystal Structures 1998, 213 (1), 209. [49] H. D. Impsall, B. L. Shaw and B. L. Turtle, J. C. S. Dalton. Trans. 1976, 1500. [50] S. Priya, M. S. Balakrishna and J. T. Mague, J. Organomet. Chem. 2004, 689, 3335. 35 evaporated to half the total volume and the Schlenk tube was kept at +4ºC overnight. Decanting the supernatant solution, followed by 3 hours drying of the precipitated solid in vacuum gave the neutral complex 13b as shining yellow crystalline compound (See scheme 8). The yellow powder of 13b melts at 176ºC and was isolated in 95% yield. The 31P NMR spectrum of 13b at ambient temperature in CDCl3 displayed a sharp singlet at 19.1 ppm that can be attributed to a P-only coordinated trans complex of 9b. The observed 1H and 13C NMR resonance data are similar to those of the free ligand. R R1 b d OH H H OH R OH Ph2P 2 9b,d P P R HO Ag Ph Ph Ph Ph AgOTf 14b,d R1 R1 R1 OTf R OH (COD)PdCl2 P P R HO Pd Ph PhPh Ph R1 R1 R OH Cl Cl 13b,d P P R HO Pt Ph Ph Ph Ph R OH Cl Cl (PhCN)2PtCl2 15 Scheme 8: Syntheses of transition metal complexes of 9b,d. The yellow powder of 13b was dissolved in a minimum amount of THF and suitable crystals for a single crystal X-ray diffraction study were grown at +4°C. The compound 13b crystallizes in a monoclinic unit cell in the space group P21. The crystal contains discrete molecules that lie on a crystallographic C2 axis. The unit cell contains further four molecules of THF per molecule of 13b. Two of the THF molecules show strong hydrogen bonding interactions with the hydroxy protons [O5-H2 1.91 Å and O7-H4 2.05 Å], whereas the third THF molecule interacts only weakly (O6-H29A 2.54 Å) with a hydroxy group and the fourth THF does not show any kind of interaction with the complex. Apart from these intermolecular interactions, there were no further particular inter- or intramolecular interactions observed. The palladium atom displays a square planar geometry with two chlorides and two phosphines completing the coordination sphere. The P-Pd-P array is nearly linear with an angle of 178.1º. The Pd-P distances (2.33 Å) are normal and the observation of rather long distances to the oxygen atom (more than 5 Å) in 36 2-position of the catechol ring ruled out the presence of any Pd-O interaction and thus demonstrated the P-only coordination mode. The phosphorus atom features a distorted tetrahedral geometry with the largest angle of 118.3º (C14-P1-Pd1). Thus, the crystal structure and solution NMR studies of 13b unambiguously support the formation of a P- only coordinating palladium complex. Bond lengths [Å] Bond angle [º] Pd-Cl2 2.307(1) P1-Pd-P2 178.05(1) Pd-Cl1 2.301(0) C14-P1-Pd1 118.31(2) Pd-P1 2.338(0) Cl1-O2 6.161(1) Fig. 2.4: Molecular structure of 13b (H-atoms omitted, 50% probability thermal ellipsoids), important bond angles and bond lengths are given in the table. Complex 13d was synthesized according to the procedure mentioned for 13b and was isolated in 95% yield. The light yellow powder of 13d melts at 223ºC. The 31P NMR spectrum displayed a single resonance at 20 ppm indicating P-only coordination and a trans configuration. The 1H NMR spectrum at ambient temperature in CD3CN displayed a multiplet at 7.3-6.96 ppm accounting for 20 protons, which is attributed to the phenyl groups. Three catechol protons appear as distinct multiplets with three bond proton-proton 37 couplings of about 7 Hz at 6.38, 6.31 and 6.14 ppm. The two aliphatic protons displayed a doublet at 3.65 ppm with a 2JPH coupling of 12 Hz. Suitable crystals for a single-crystal X-ray diffraction study were obtained from a concentrated THF solution of 13d at +4ºC. The yellow monoclinic (space group C2/c) crystals contain molecules of 13d that lie on a crystallographic C2 axis. The crystal contains further one disordered molecule of THF per molecule of 13d, which does not show any kind of intermolecular interactions with the complex. The palladium atom displays a square planar geometry with 180.0º P1-Pd-P1i and Cl-Pd-Cl angles. The P-Pd (2.30 Å) distance is a bit shorter compared to that found in 13b. The catechol oxygen atom in 3-position is far away (approximately 6 Å) from having any kind of interaction with the palladium atom. The phosphorus atom displays a distorted tetrahedral geometry. The two catechol rings are trans to each other. The silver complex 14b was readily obtained by mixing two equivalents of ligand 9b with one equivalent of silver triflate in THF (with a few drops of DMF). The reaction mixture was stirred at room temperature for one hour and the solvent was then evaporated in vacuum. The residue was dissolved in dichloromethane, a few drops of diethyl ether were added and the Schlenk tube was kept for crystallization at –28ºC overnight. White needle like crystals were isolated by filtration and dried in vacuum, which gave a white powder of 14b in 73% yield with a melting point of 109ºC. The positive mode ESI-MS experiment showed a pseudo-molecular ion peak at m/e = 781.09, corresponding to the cation of 14b [M+NaCl-OTf]+. A peak attributable to [M-OTf]+ was observed at m/e = 723, where M = 14b. The 31P NMR resonance of the complex 14b at ambient temperature appeared as broad doublet centered at 6.2 ppm with a mean 107/109Ag-31P coupling of 445 Hz. The line broadening is attributable to slow intermolecular ligand exchange which is a common feature for many silver complexes.51 The downfield shift of the 31P signal of 14b compared to the free ligand is typical for the coordination of phosphorus to a silver center. The 1H and 13C chemical shifts appeared similar to those of the ligand 9b. Suitable crystals for single-crystal X-ray diffraction were obtained by recrystallizing 14b from a CH2Cl2/Et2O/DMF mixture at –28ºC. The colorless monoclinic crystals (space group P21/n) of 14b contain two half crystallographically independent cations [Ag(9b)2] [51] R. Terroba, M. B. Hursthouse, M. Laguna, A. Mendia, Polyhedron, 1999, 18, 807; E. L. Muetterties, C. W. Alegranti, J. Am. Chem. Soc. 1972, 94, 18, 6386. 38 along with a triflate anion and one molecule of each CH2Cl2 and DMF in the asymmetric unit. The bonding parameters in the two cations do not deviate significantly. The hydroxy Bond lengths [Å] Bond angles [º] Bond angles [º] Ag1-P1/P1i 2.402(2) P1-Ag1-P1i 180.0 Ag1-P1-C7 111.2(1) Ag1-O1/2 3.16-3.25 C8-P1-C14 102.5(2) Ag1-P1-C8 114.0(2) C7-P1-C14 106.9(3) Fig. 2.5: Molecular structure of 14b (H-atoms omitted, thermal ellipsoids with 50% probability), important bond angles and bond lengths are given in the table. groups in 2-position of the catechol units show hydrogen bonding interactions to the chlorine atom of a molecule of CH2Cl2, and those in 3-positions to an oxygen atom of a triflate anion. Taking these interactions into account, the crystal packing can be described in terms of chains of alternating, weakly interacting cations and anions. The silver ions in the complex cations lie on a crystallographic center of symmetry (Ci-symmetry) and feature a linear coordination by the two phosphorus atoms. The Ag-P distances (2.40 Å) are normal. Rather short contacts to the oxygen atoms in 2-position of the catechol ring (Ag1-O1 3.16Å) compared to 13b-d are interpreted in terms of additional weak secondary Ag…O interactions. The phosphorus atom displays a distorted tetrahedral geometry with larger Ag-P-C7/8 (111.2°/114.0°) angles compared to C14-P-C7/8 (106.9°/102.5°). 39 Bond lengths [Å] Bond angles [°] P2-Ag1 2.399(1) P1-Ag1-P2 159.23(3) P1-Ag1 2.401(1) Ag1-P1-C1 112.57(1) Ag1-O1 2.576(2) P1-C1-C2 113.63(2) P1-C1 1.841(2) P2-C20-C21 110.99(2) Fig. 2.6: Molecular structure of 14d (H-atoms omitted, thermal ellipsoids with 50% probability), important bond lengths and bond angles are given in the table. Complex 14d was synthesized according to the procedure mentioned for 14b. The product was isolated in 95% yield as a white solid melting at 112ºC. Positive mode ESI-MS produced a molecular ion peak m/e [M]+ = 725 corresponding to the cationic silver complex. The 31P NMR spectrum of 14d at ambient temperature in CDCl3 displayed a broad doublet ranging from 13 to 18 ppm, which may arise from a medium fast ligand exchange process. Cooling down the sample to –50°C split the broad doublet into two doublets of almost equal intensity centered at δ 16.41 due to 31P coupling with the two naturally occurring silver isotopes ( 107Ag, I = ½, 51.82%; 109Ag, I = ½, 48.18%). The magnitude of these coupling constants of 501 Hz (1J107Ag-P) and 579 Hz (1J109Ag-P) is consistent with the linear P-Ag-P array and very weak coordination of one or two oxygen atoms.52 [52] R. G. Goel, P. Pilon, Inorg. Chem. 1978, 17, 2876; R. Terroba, M. B. Hursthouse, M. laguna, A. Mendia, Polyhedron, 1999, 18, 807; X. Sun, D. W. Hohnson, K. N. Raymond, E. H. Wong, Inorg. Chem. 2001, 40, 4504. 40 Suitable crystals for single-crystal X-ray diffraction measurements were grown at room temperature from a THF solution. The unit cell contains two molecules of solvent (THF) per molecule of 14d. The colorless monoclinic crystals (space group P21/n) of 14d contain a silver center which is bonded to one of the oxygens of the triflate [Ag-O1 2.58 Å], thus producing [Ag(9d)2OTf] as a neutral complex. The P-Ag-P array is slightly bent (P1-Ag- P2 159.2°) so as to accommodate the triflate, and the overall geometry around silver can be best described as intermediate between T-shaped and trigonal planar. No secondary Ag…O interactions like in 14b were observed as all the Ag-O distances exceeded 5 Å. Complex 15 was synthesized according to the procedure mentioned for 13b except that a platinum complex [(PhCN)2PtCl2)] was employed instead of a palladium complex (see Scheme 8). The light yellow compound was isolated by crystallization from THF solution in quantitative yield and melts at 235°C. The 31P NMR spectrum of the isolated product displayed two resonances at 18.8 and 11,0 ppm in 1:2 ratio along with two sets of platinum satellites. The resonance at 18.8 ppm with a 1JPt-P coupling of 1296 Hz is attributed to a trans complex of 9b, whereas signal at 11,0 ppm with a larger coupling of 1861 Hz is assigned to a cis complex. The proton NMR spectrum displayed two sets of multiplets for the aromatic as well as for the aliphatic protons due to the cis-trans isomerism. The positive mode ESI-MS spectrum revealed that the complex 15 spontaneously eliminates one molecule of HCl to give a P-O chelate. The pseudo-molecular ion peak at m/e = 810.14 [(C38H32O4P2Pt = M)+H]+ corresponds to cation of 15 generated by eliminating one HCl and a chloride. Further pseudo-molecular ion peaks were observed at m/e = 832.13 (M+Na)+, 873.06 (M-H+NaCl+Li)+, 895.05 (M-2H+2Na+Cl+Li)+. Storing the sample for two months lead to a spontaneous conversion into a new product. The 31P NMR spectrum of this complex displayed two doublets (AB spin system), which appeared at 49.7 and –0.6 ppm with a 2JP-P coupling of 21 Hz (1JPt-P = 2141, 1727 Hz respectively) and a singlet at 28.6 ppm (1JPt-P = 1942 Hz). The AB spin system observed can be best interpreted assuming that one of the ligand forms a P-O chelate while the other displays P-only coordination so that the two phosphorus atoms coordinating to platinum become inequivalent and display an AB spin system. The remaining singlet can be attributed to a fully chelated (P-O chelate only) complex. 41 2.5. Synthesis and characterization of a palladium complex of 3- [(Mesitylphenyl phosphanyl)-methyl]-benzene-1,2-diol: Two equivalents of 9f were dissolved in dry THF and one equivalent of (COD)PdCl2 was added under constant stirring. After one hour, half of the THF was evaporated in vacuum and the Schlenk tube was kept at +4ºC overnight. Filtering the supernant solution, followed by 3 hours drying in vacuum, gave a yellow powdered compound, which was isolated quantitatively. OH OH MesPhP 2 9f (COD)PdCl2 P PPd 101 O OH O HO P PPd OH OH HO HO Mes PhPh Mes Ph Mes PhMes 102 + Scheme 9: Synthesis of P-O chelating and P-only complex 102 and 102. The 31P NMR spectrum of the reaction mixture displayed two major signals at 5.4 and 4.3 ppm which are attributable to diastereomers (meso and rac pair) of the P-only coordinated complex 102(see Scheme 9). The other two minor signals at 55.7 and 19.2 ppm (together about 1%) were hard to interpret. The 31P NMR spectrum of the isolated product showed a major peak (about 95%) at 53.5 ppm, which is attributable to the P-O chelate complex 101. The other two resonances at 1.3 and –0.9 ppm (together about 2%) can be assigned to diastereomeric (meso and rac) complexes 102. The ESI-MS positive mode spectrum displayed a molecular ion peak at m/e = 805.2[101+H]+, corresponding to the cation of chelated palladium complex 101. A pseudo-molecular ion with sodium was observed at m/e 827.2. The above observations allow to state that increased steric bulk at phosphines presumably forces the diastereoisomeric complexes to eliminate HCl and to produce a P-O chelated complex 101 as the major product. 2.6. Conclusions: It has been confirmed that the reaction of diphenyl phosphine with phenolic aldehydes proceeds via initial formation of α-phosphanyl-carbinols. The presence of OH-groups in p- or o-position destabilizes the adducts relative to the starting materials and facilitates their subsequent rearrangement into isomeric phosphine oxides. The latter may further be reduced to phenol-functionalized phosphines. The overall reaction permits to access 42 phosphines with pendant phenolic functionalities from readily available starting materials, without the necessity of additional efforts for the introduction and removal of protecting groups at the phenol functionalities. This procedure constitutes a substantial improvement over previously known synthetic protocols which required often more complicated approaches.32,43 The application of this procedure should prove useful for the preparation of functional phosphines in applications as chelating ligands in catalysis or as supramolecular building blocks. With the procedures outlined for the syntheses of transition metal complexes it was possible to selectively generate P-only coordinating transition metal complexes rather than P-O chelates. The neutral palladium complexes 13b,d, and cationic silver complexes 14b,d of the corresponding catechol phosphines (9b,d respectively) were easily prepared and isolated in good yields and thus demonstrated the P-only coordination mode of 9b,d. The platinum complex 15 displayed a different behavior and can be very easily converted from a P-only to P-O coordination mode. Increasing the steric bulk at phosphorus lead to the preferential formation of a P-O chelated complex 101. 43 3. Phosphine functionalized catechol borates and their Lewis-acid/base behavior 3.1. Introduction It was envisioned that borate might be a useful template for the catechol-phosphine ligands and a good starting material to explore the template centered ligand-designing strategy. The most easily accessible tricoordinate boron compound to name is boric acid. The reaction between boric acid and alcohols is well established, in fact it is routine laboratory practice to use methyl borate as a qualitative test for boron, which colors the flame green confirming the presence of boron. Boric acid derivatives, e.g. phenyl boronic acid, are known to undergo likewise condensation with a variety of substrates such as penyldiamines53, anthranilic acids54 1,2-diols55 and with catechols56 to yield the corresponding condensation products. These tricoordinated boron compounds can further act as Lewis acid centers. This Lewis acidity is attributable to the existence of an empty 2p orbital on boron. This orbital can be utilized to build Lewis acid-base adducts, where the B N Fig. 3.1: Boron acid-base adducts [53] W. R. Purdum, E. M. Kaiser, Inorg. Chim. Acta 1975, 12, 45. [54] M. Pailer, W. Fenzl, Monatsh. Chem. 1961, 92, 1294. [55] H. G. Kuivila, A. H. Keough, E. J. Soboczenski, J. Org. Chem. 1954, 19, 780; R. A. Bowie, O. C. Musgrave, J. Chem. Soc. 1963, 3945. [56] M. Wieber, W. Kuenzel, Z. Anorg. Allg. Chem. 1974, 403, 107. 44 base donates its electron pair to the vacant 2p orbital (Fig. 3.1) on boron 4,57. Generally these tetra-coordinated adducts are in equilibrium with the tricoordinated species in solution (Scheme 1). The equilibrium can be shifted towards the product side by i) adding an excess of base, ii) using strong bases, iii) using sterically less bulky bases or iv) increasing the acidity of the boron center by electron withdrawing substituents such as pentaflurophenyl groups.58, 70 B O O B O O N N Scheme 1: Lewis acid-base equilibrium. In recent years, boron acid base adducts have been rigorously studied owing to their ability to produce catalytically active centers for olefin polymerization.59 The simple acid/base chemistry has been further extended to high-end applications such as photo switching.60 Recently a new concept called “borate centered ligands” in which the boron bound hydrogen has been replaced by an alternative group such as tris(pyrazolyl) has emerged but it has not been intensively studied.61 Apparently the newly synthesized catechol phosphine 9b suffices all the criteria required to synthesize boron centered ligands. In order to contribute to this challenging and developing field a detailed investigation of the synthesis of esters of the catechol phosphines with boric and boronic esters, and the behavior of the latter as Lewis-acids in reactions with pyridine derivatives was carried out. The products B O O N PPh2 D61 [57] F. Norberto, C. Rosalinda, J .Chem. Soc. Perkin Tran. 2, 1987, 6, 771. [58] H. Sakurai, N. Iwasawa, K. Narasaka, Bull. Chem. Soc. Jpn. 1996, 69, 2585. [59] F. Focante, P. Mercandelli, A. Sironi, L. Resconi, Coord. Chem. Rev. 2006, 250-(1-2), 170. [60] N. Kano, J. Yoshino, T. Kawashima, Org. Lett. 2005, 7, 18, 3909. [61] P. J. Bailey, D. Lorono-Gonzale, C. McCormack, F. Millican, S. Parsons, R. Pfeifer, P. P. Pinho, F. Rudolphi, A. S. Perucha, Chem. Eur. J. 2006, 12, 5293. 45 formed can be used as borate centered bidentate ligands such as 61. These boron centered ligands like 61 are promising candidates for building chelate complexes if the spatial arrangement of the donor sites can be made to fit accordingly. In the following, a detailed report on the synthesis, characterization and possible complex formation reactions will be given. The second part of this chapter is focused on tetra-coordinate borate compounds. The above boron acid/base chemistry was explored to synthesize stable borate anions rather than just equilibrium reaction mixtures. The intramolecular interaction between tricoordinated boron and an oxygen donor produced a reasonably stable borate.62 It was in 1925 when Meulenhoff first reported on the synthesis of catechol borates.63 The ongoing controversy about tri or tetra coordinated boron64 was recently resolved by White et al. who reported the first crystal structure of a catechol borate.10,65 Since then tetra coordinated boron complexes have attracted much attention,66 but reports on second donor substituted catechol-borates are very scarce.67 Incidentally, the ligands 9b-d carry a catechol function along with a phosphine donor. Section 2.3 demonstrated that coordinating complexes of 9b-d with palladium and silver can be very easily accessed and that these catechol phosphines (9b-d) form P-coordinating complexes rather than chelating complexes. In the following it will be demonstrated that, a tetrahedral BO4 unit can be used as template to assemble two ligands 9b-d to give an aggregate that behaves as/mimics a bidentate phosphine. Further the selection of the boron building blocks allows to control the molecular structure of the complexes formed, producing either a monometallic silver complex or a macrocycle. [62] W. P. Griffith, A. J. P. White, D. J. Williams, Polyhedron, 1995, 15, 17, 2835. [63] J. Meulenhoff, Rec. traav. Chim., 1925, 44, 150. [64] D. F. Kuemmel, M. G. Mellon, J. Am. Chem. Soc. 1956, 78, 4572. [65] A. Mitra, L. J. DuPue, J. E. Struss, B. P. Patel, S. Parkin, D. A. Atwood, Inorg. Chem. 2006, 45, 9213. [66] E. Graf, M. W. Hosseini, Angew. Chem. Int. Ed. 1995, 34, 1115. [67] S. Mohr, G. Heller, U. Timper, K. H. Woller, Z. Naturforsch. 1990, 45, 308. 46 3.2. Results and discussion: 3.2.1. Detailed investigations on the synthesis and Lewis acid/base behavior of Diphenyl-(2-phenyl-benzo[1,3,2]-dioxaborol-4-ylmethyl) phosphine: The catechol functionalized phosphine 9b was synthesized in two simple steps as reported earlier in chapter 2, section 2.2.1-2.2.3. The condensation reaction between phenyl boronic acid and 9b with excess of triethyl amine as acid scavenger at room temperature produced Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol-4-ylmethyl) phosphine 16a. Evaporation of solvents followed by an hour vacuum drying gave a quantitative yield of a white solid. A single 11B NMR resonance at 31.7 ppm in dichloromethane was observed, which is typical of tricoordinated borates.68 The 31P NMR resonance appeared as singlet at –11 ppm indicating the presence of a free phosphine and ruled thus out the formation of phosphine- borane adducts which might be expected. Detailed NMR studies of similar tetra/tri- coordinate boron compounds with nitrogen bases have been reported by Goetz et al.69 PPh2 OH OH RB(OH)2 PPh2 O O B R PPh2 O O B N N(Me)2 R O O B N N(Me)2 P O O B Pd Cl Cl Ph Ph DMAP DMAP 2DMAP R Ph + 16a-b DMAP = 2PhB(OH)213b 18 19 a b C6F5 17a 0.5 (COD)PdCl2 0.5 (COD)PdCl2 9b DMAP P O O B P O O B Pd Cl Cl Ph Ph P P HO HO Pd Cl Cl P OH OH PhPhPh PhPh Ph Ph Ph PhPh Ph Ph [68] F. Zettler, H. D. Hausen, H. Hess, Acta Crystallog. Sect.B: Struct. Crystallogr.Cryst.Chem. 1974, 30, 1876. [69] R. Goetz, H. Noeth, H. Pommerening, D. Sedlak, B. Wrackmeyer, Chem. Ber. 1981, 114, 1884. 47 Scheme 2: Syntheses of boron-centered ligand and their complexes. Having confirmed the formation of borane 16a, it was of further interest to investigate its Lewis acid behavior towards various bases. The simple base pyridine was selected for the ease of availability of comparable 11B NMR data.70 One equivalent of borate 16a was treated with one equivalent of pyridine, the 11B NMR of this reaction mixture showed a peak similar to that of the starting material indicating that the equilibrium shown in Scheme 1 is still shifted to the left side. A series of reactions with increasing equivalents of pyridine was found to produce an easy upfield shift of the 11B resonance. A considerable change to δ = 11.9 in the 11B NMR shift was observed when 16a was mixed together with six equivalents of pyridine. Further addition of pyridine did not change the 11B NMR shift, indicating saturation. These observations made it clear that the borane 16a is too weak Lewis-acid to allow generation of a stable adduct with a stoichiometric quantity of pyridine. In this case two strategies could be followed to obtain more stable adducts; i) introduction of an electron withdrawing substitutent on boron, making it more acidic, or ii) use of a stronger base. To perceive on the first strategy pentaflurophenyl boronic acid was chosen. Similar boron compounds of 2,3 dihydroxynaphthalene with pentaflurophenyl substituents were reported recently.71 Reaction of the catechol phosphine 9b and pentaflurophenyl boronic acid produced a white powder after stripping off the solvent. The 11B NMR displayed four resonances at 21.6, 14.3, 9.9 and 5.3 ppm indicating formation of more than one product. The 31P NMR spectrum displayed a single broad resonance ranging from – 10.6 to -8.5 ppm. The proton NMR displayed a multiplet at 7.7-7.2 ppm, which is attributed to the phenyl groups, and a second multiplet at 7.1-6.6 ppm which is assigned to the catechol protons. The aliphatic protons appear at 3.62 ppm as broad singlet. These spectral observations indicated formation of a dynamic equilibrium mixture of the expected boronic ester 16b together with one (or more) B-P adducts. Hoping that addition of a strong Lewis base may break the B-P adduct it was decided to go ahead without further characterizing the product. In a combined (i and ii) strategy, an equimolar amount of DMAP in dichloromethane was added to the isolated product (16b). Evaporating the solvent under vacuum followed by vacuum drying produced a clean [70] N. Farfan, R. Contreras, J. Chem. Soc. Perkin Trans 2, 1987, 771. [71] D. Vagedes, R. Froehlich, G. Erker, Angew. Chem. Int. Ed. 1999, 38, 22, 3362. 48 product. The 11B NMR spectrum displayed two major resonances, a singlet at 14.3 ppm and a doublet at 8.47 ppm in 1:1 ratio. The 31P NMR spectrum showed two singlets at – 12.6 and –13.9 ppm. On comparing with 11B literature data72 it appears that the former signal arising from a borane-DMAP adduct and the latter doublet could not be clearly assigned. The above observations indicated that the pentaflurophenyl substituent makes the boron much more acidic so that it may then coordinate to the phosphine. Considering that the formation of unwanted reaction products could not be suppressed, the focus was shifted to the second strategy, i.e. the use of a stronger base as donor. To realize this approach, dimethyl amino pyridine was chosen, which is also of interest owing to the presence of a potential secondary donor site in the Me2N-group. The reaction of a stoichiometric amount of the borate 16a and DMAP produced a mixture whose 11B NMR spectrum showed a single resonance at 11 ppm. This can be interpreted as a stable adduct arising from strong coordination of the base to the boron center. The product was isolated quantitatively by evaporating the solvent and drying the white powder under vacuum. The 31P NMR spectrum showed a singlet at –17.1 ppm confirming the presence of a free phosphine. The proton NMR of a solution of the white powder in CDCl3 showed a multiplet (broad doublet of triplets) at 8.25 ppm with 3JH-H of 7.4 Hz corresponding to the ortho protons of DMAP. Signals at 7.55 to 7.40 ppm and at 7.30 can be assigned to the phenyl substituents on boron and phosphorus. A multiplet at 6.55 to 6.35 ppm can be assigned to one catechol proton and two m-DMAP protons. Two doublets of triplets (6.62 and 6.39 with 3JH-H of 7.34 and 8 Hz respectively) were observed for the remaining catechol proton. In the aliphatic region, two singlets at 3.5 and 3 ppm were observed which can be assigned to the CH2 protons of catechol phosphine and the CH3 protons of DMAP, respectively. Unambiguous support for the structure of the DMAP Lewis acid base adduct 17a came from a single-crystal X-ray diffraction study. Shining white crystals were obtained after dissolving a small amount of the isolated white powder in a minimum amount of dichloromethane, addition of a few drops of THF, and crystallization at room temperature. The molecular structure of 17a is shown in Fig. 3.2. The crystal structure determination showed that the compound crystallizes in the space group P21/c along with one THF molecule in the periphery, without any hydrogen bonding interactions. No pi-stacking [72] W. Clegg, A. J. Scott, F. E. S. Souza, T. B. Marder, Acta Crystallogr. Sect. C: 1999, C55, 11, 885. 49 interaction between any of the aromatic rings was observed, as none of the rings are parallel to each other. The phosphorus atom displays a distorted pyramidal geometry (sum of the angles is 302°) with two phenyl rings and a catechol substituent. The angle between C6-C7-P1 (116.0°) is by few degrees larger than in the free ligand (9b, 111.9°). The boron atom displays a distorted tetrahedral arrangement with the catechol Bond lengths [Å] Bond angles [°] B1-O2 1.491 (1) C20-B1-N1 111.6 (1) B1-O1 1.475 (1) O1-B1-O2 105.3 (1) B1-N1 1.608 (1) C6-C7-P1 116.0(4) B1-C20 1.613(1) O-B1-C20 111.86-114.70 Fig. 3.2: Crystal structure of 17a (50% probability thermal ellipsoids). Important bond lengths and angle are given in the table. chelate, phenyl substituents, and the nitrogen donor atom completing the coordination sphere (Fig. 3.2). The catecholate unit gives an O1-B1-O2 angle of 105.2°, which is considerably sharper than the ideal tetrahedral angle of 109.5°. The remaining three angles (C20-B1-N1 111.5 and O1/2-B1-C20 111.9-114.7) are wider than the ideal one. The 50 phenyl substituent on boron is directing outwards with an angle of 111.5° (C20-B1-N1). Raising the boron coordination number from three to four in 17a considerably lengthens the B1-O and B1-C20 bonds (1.47 to 1.49 Å, respectively) which are in accordance with the literature reported distances (1.48 and 1.58 Å, respectively).68 The NMe2 group and the aromatic ring in DMAP lie in the same plane with both nitrogen atoms. Having shown that P-only complexation and B-complexation (16a/b) of 9b in two independent reactions is feasible it was envisioned to combine both reactions to generate extended oligomers or coordination polymers. Such species are of great interest for preparing multimetallic complexes, molecular devices,73 novel electronic, magnetic74 or polymeric materials.75 The first step to put this concept into reality was to synthesize a metal complex of 9b, which has been demonstrated in section 2.3. The logical next step was to utilize the hydroxyl functionalities in order to incorporate an acidic boron center alongside. This was achieved simply by stirring 13b with phenyl boronic acid. Subsequent solvent removal produced a yellow colored powder of 18 (Scheme 2) in quantitative yield. The yellow powder decomposes at 240ºC. A single 11B NMR signal at 29.1 ppm was observed which indicated the presence of a trigonally planar coordinated boronic ester.76 The 31P NMR resonance appeared at 21.2 ppm, indicating that the phosphorus coordination to palladium remains unchanged from that of 13b. The proton NMR of 18 displayed a slight downfield shift of all signals compared to the free ligand 9b. A multiplet at 7.8 to 7.5 ppm is attributed to the phenyl and another multiplet at 7.1 to 6.7 ppm to the catechol protons. A broad doublet of triplets (ABX spin system) at 4.3 ppm with a 2JPH coupling of P PdCl2L Ph Ph Hacat Hb Scheme 3: Newman projection along the Ph2P-CH2 bond showing inequivalency of Ha and Hb. [73] H. Sleiman, P. Baxter, J. M. Lehn, J. Chem. Soc. Chem. Comm. 1995, 7, 715. [74] T. Goslinski, C. Zhong, M. J. Fuchter, C. L. Stern, A. J. P. White, A. G. M. Barrett, B. M. Hoffman, Inorg. Chem. 2006, 45, 9, 3686. [75] Hoffman, M. Brian, Barrett, G. M. Anthony, U.S. (1999), 37 pp., Cont.-in-part of U.S. 5,675,001. CODEN: USXXAM US 5912341 A 19990615 Application: US 97-928415 19970912. Priority: US 95- 403302 19950314. CAN 131:27113 AN 1999:384025 [76] P. Diehl, E. Fluck, R. Kosfeld, Nuclear Magnetic spectroscopy of boron compounds, Springer-Verlag, Berlin, Heidelberg, New York, 1978, p. 144 51 11.3 Hz and a triplet at 4.2 ppm with 2JPH coupling of 3.8 Hz was observed and can be assigned to the CH2 protons. The two signals are attributed as being due to diastereotopic protons, the presence of which can be explained by assuming that 18 exists in a preferred conformation as shown in a Newman projection model (Scheme 3). The species Ha and Hb are in a different chemical environment and hence appear as two distinct signals. The yellow powder was dissolved in THF and crystals of X-ray quality were grown at 4ºC. The complex 18 crystallizes with two molecules of THF in a monoclinic unit cell in the space group P21/c (Fig. 3.3). The palladium atom lies on a crystallographic C2 axis and shows a typical square-planar coordination with the two catechol rings trans to each other and a normal P-Pd distance of 2.33Å. The boron atom is trigonal planar but the exocyclic angle O1-B1-O2 is reduced to 110.9° from the ideal angle of 120°. On the other hand, the two O1-B1-C20 angles (125.2°) are considerably larger than the standard angle. The Bond angles [Å] Bond lengths [°] B1-O2 1.403(2) O1-B1-C20 125.3(1) B1-O1 1.394(2) O1-B1-O2 110.91(1) B1-C20 1.544(2) Cl1’-Pd-P1 86.267(3) P1-Pd 2.332(1) Cl1-Pd-P1 93.72(2) Fig. 3.3: Molecular structure of 18 in the crystal. (H-atoms omitted, 50% probability thermal ellipsoids); important distances and angles are given in the table. 52 torsional angle around the P-CH2 unit is 118.3°. The B1-O bonds (1.39-1.40 Å) and the B1-C20 bond (1.53 Å) are in close agreement with previous reports on 2-phenyl-1,3,2- benzodioxaborol.68 After confirming the constitution of complex 18, it was decided to explore the coordination of a base to the boron center as demonstrated for 17a. Two simple methodologies can be designed to realize such complexes: i) Reaction of two equivalents of 17a with one equivalent of (COD)PdCl2, and ii) treating the complex 18 with two equivalents of DMAP. During the efforts to synthesize the adduct 19, it was established that route i) gave better results (Scheme 2). Thus, reaction of two equivalents of 17a with (COD)PdCl2, in a THF/dichloromethane mixture gave within 5 minutes a yellow precipitate, which was filtered and dried in vacuum. The yellow powder was soluble in a mixture of acetonitrile and dimethyl formamide and in DMSO. The 11B NMR spectrum of the isolated powder in DMSO displayed a single resonance at 11 ppm confirming that the coordinated DMAP donors remain in place. However, 31P NMR spectra showed two products; one giving a singlet signal at δ = 19.4 and the second one appears as AB spectrum with resonances of two chemically inequivalent phosphorus atoms at 82 and 29 ppm with a coupling of 31 Hz. It appears that the first signal could be the possible product although there is no further clear evidence. The AB spectrum is not yet assigned and hence the second product remains unknown. However, the 31P NMR findings indicate in both cases that the phosphorus atoms are coordinated to palladium. At this stage deeper investigations are required in order to state the constitution of the product unambiguously. 3.2.2. Syntheses and characterization of Silver (I) bis {diphenyl- (benzo- [1,3]- dioxo-4-ylmethyl)-phosphane} 2-borate: Motivated by the importance of borate esters in naturally occurring antibiotics such as boromycin,77 aplasmomycin78 and having understood that the smallest feasible templates are tetrahedrally coordinated second row elements, it was decided to explore the borate ester chemistry of 9b-d. The idea behind this work is to synthesize borate esters of 9b-d, which can mimic a bidentate ligand and the geometry of which can control the bite angle. [77] R. Huetter, W. Keller-Schierlein, F. Knuesel, V. Prelog, G. C. Rodgers, P. Sutter, G. Vogel, W. Voser, H. Zaehner, Helv. Chim. Acta. 1967, 50, 9, 1533. [78] T. Okazaki, T. Kitahara, Y. Okami, J. Antibiot. 1975, 28, 176; T. J. Stout, J. Clardy, I. C. Pathirana, W. Fenical, Tetrahedron, 1991, 47, 22, 3511. 53 The three-components 9b, B(OH)3, and NEt3 were reacted in THF to give the borate 20 (Scheme 4). The reaction mixture was evacuated to dryness and a white powder of m. p. 92ºC was isolated in good yield (83%). The 11B NMR displayed a resonance at 14.3 ppm which is typical for a tetra-coordinated borate.79 The 31P resonance at –13.2 ppm corresponds to the free phosphine. The proton NMR displayed signals between 7.60 and 7.26 ppm which can be easily assigned to the phenyl protons on phosphorus, and a multiplet between 6.44 and 6.34 ppm, which is assigned to the catechol ring protons. A doublet of doublets centered at 3.51 and a doublet at 3.44 ppm are attributed to the diastereotopic aliphatic CH2 protons, as the group is prochiral. Excessive line broadening was observed for the NH proton of the triethyl amine counter ion, which appeared as a very broad singlet at 6.8 ppm. O O Ph2P O O B- B(OH)3 Et3N P O O P O O B- Ph Ph Ph Ph AgCF3SO3 OH OH Ph2P PPh2 Ag 2 21209b Et3NH+ Scheme 4: Syntheses of catechol borate template 20 and its silver complex 21. A quartet at 3.13 and a triplet at 1.23 ppm were assigned to the CH2 and CH3 protons of the triethyl ammonium ion, respectively. Coordination of the catechol units of 9b to boron was further supported by the significant 13C NMR downfield shift (5-10 ppm) of the C-O carbon atoms as compared to the free ligand 9b. A Positive ion FAB-MS showed a triethyl ammonium cation at m/e = 102 (Et3NH)+, a protonated cation [B(catphos)2H2]+, at m/e = 625 and the protonated complex 20 at m/e = 726 [B(catphos)2(H)(Et3NH)]+. The negative FAB-MS ion spectrum displayed a peak at m/e = 623 arising from the borate anion [B(catphos)2]¯. White needle like crystals of 20 suitable for X-ray diffraction measurement were obtained from a THF solution at –28°C. The single crystal X-ray diffraction study revealed that the product crystallizes in a triclinic unit cell in the space group P1(bar). The crystal structure determination disclosed the presence of two crystallographically independent ion pairs whose constituents show minor differences in their bonding parameters. Both are [79] R. A. Baber, J. P. H. Charmant, J. D. Moore, N. C. Norman, and A. G. Orpen, Acta. Cryst. Sect. E, Stru. Rept. 2004, E60, o1140. 54 composed of a spirocyclic anion which is assembled around a central BO4-tetrahedron, and a triethyl ammonium cation that interacts with the anion via a NH…O hydrogen bridge (Fig. 3.4). As a consequence of this interaction, the B–O2 bond (1.51 Å) is slightly longer than the other B–O bonds (1.46 – 1.48 Å); similar observations have been reported by Bong lengths [Å] Bond angles [°] B1-O4 1.460 (4) O4-B1-O3 105.7(2) B1-O1 1.478 (4) O1-B1-O2 103.4(2) B1-O2 1.511(4) O1-B1-O4 112.9(3) H1-O2 1.83 O2-B1-O3 110.6 (2) Fig. 3.4: Molecular structure of 20 (H-atoms omitted except the NH atom; 50% probability thermal ellipsoids); selected bond lengths and bond angles are given in the table. Moore et al.79 The catecholate chelating O1-B1-O2 array has a very acute angle of 103° which is considerably sharper than the ideal tetrahedral angle of 109.5°. On the other hand, the O1-B1-O4 angle is 112.8°, i. e. considerably larger than the tetrahedral angle. The distorted tetrahedral coordination at boron enforces further a mutually orthogonal arrangement of the catechol ring planes in the phosphine fragments, and the spatial 55 separation between the methylene carbon atoms was found to be 7.6 Å and the phosphorus donor atoms are separated by 10.6 Å. The successful isolation of the borate 20 (Scheme 4) proved that formation of a template is in principle feasible. The isolated product was then treated with AgSO3CF3 in DMF and the solution was stirred at room temperature for an hour. Diethyl ether was added to produce a precipitate which was filtered and finally dried in vacuum to obtain a product that was characterized as the silver borate 21. The soluble side product (triethyl ammonium triflate) was eliminated by filtration. NMR studies of 21 showed a single 11B NMR resonance at 13.9 ppm corresponding to a tetra-coordinated boron atom. The 31P resonance displayed two doublets centered at 2.9 ppm with silver couplings to 107Ag (I = ½, 51.82 %) and 109Ag (I = ½, 48.18 %) of 506 and 584 Hz, indicating that the two phosphorus atoms are equivalent F2 [ppm] 4.4 4.3 4.2 4.1 4.0 F1 [p pm ] 74 0 72 0 70 0 68 0 66 0 64 0 F1 [p pm ] 74 0 72 0 70 0 68 0 66 0 64 0 O O P Ph Ph Ag HcHt Fig. 3.5: 1H-109Ag 2D NMR displaying proton- silver cross peaks. Fig. 3.6: Newman projection along the Ph2P-CH2 bond showing schematically the conformation of the chelate ring in the crystal. The benzylic protons are labeled as Hc and Ht respectively. 56 and are coordinating to the silver atom.80 The proton NMR displayed only one set of signals for the aromatic catechol protons indicating equivalence of the catechol rings, whereas two sets of signals were observed for the phenyl groups and for the aliphatic CH2 protons, which prove the geminal protons and arene rings in each Ph2PCH2-unit to be diastereotopic. It was possible to explain the splitting of the signal of one of the CH2 protons (at δ = 3.95 in Fig. 3.5) by assuming coupling to the geminal proton (2JPH = 13.3 Hz) and the phosphorus atoms, whereas the multiplet structure of the second signal (at δ = 4.01) suggested that coupling to an additional nucleus is present. The assignment of the extra interaction to scalar coupling with silver was established by a 1H-109Ag HMQC experiment (Fig. 3.5), and analysis of the cross peak profile permitted to determine 3JAg,H = -7 Hz. The absence of a similar correlation for the second methylene proton indicated that 3JAg,H is in this case close to zero. The diastereotopic nature of the methylene protons in 21 owes to the embedding of the CH2-moiety into a non-planar chelate ring. The strict absence of dynamic exchange processes between both signals suggests that no ring inversion and concomitant racemization of the configuration at boron occur on the NMR time scale and led to conclude that the rigid conformation established for solid 21 (see below) persists at ambient temperature in solution. The imbalance of 3JAg,H for the CH2 protons is under these conditions attributable to a difference in Ag-P-C-H dihedral angles (Fig. 3.6; Ht is assigned to the proton with the larger absolute value of 3JAg,H). The 13C NMR resonances remained similar to those of the boron template 20. The formation of the silver complex 21 was further confirmed by ESI Mass spectra. A positive mode ESI experiment showed a pseudo molecular ion peak at m/e = 733.08 (21+H)+ formed by capture of a proton and one at m/e = 755.07 (21+Na)+ formed by capture of a sodium cation. Crystals of compound 21 suitable for X-ray measurement were obtained by dissolving the white powder in DMF: diethyl ether (1:1) at room temperature. The monoclinic crystals (space group Cc) contain discrete mononuclear complexes consisting of one silver ion and one chelating bisphosphine moiety (see Fig. 3.7), along with one molecule of DMF per formula unit. An interesting feature to note is the deviation of the silver coordination from linearity, as the silver and phosphorus atoms in each complex form a distinctly non-linear array (P1-Ag-P2 154.4°). The Ag-P bonds (Ag-P ~2.45 Å) are longer than those in 14b,d [80] P. S. Pregosin, R. W. Kunz, In 31P and 13C of Transition Metal Phosphine Complexes, Springer-verlag, New York, 1979, p. 89. 57 (2.39 – 2.40 Å). The silver atom displays two additional short contacts to oxygen atoms in the borate unit at distances (Ag-O2/O3 2.81 – 2.85 Å) that exceed the secondary Ag-O interaction in 14b but are still much shorter than the sum of van-der-Waals radii (3.55 Å). The phosphorus atom displays a distorted tetrahedral arrangement with the two phenyl groups, the catechol moiety and the silver atom completing the coordination sphere. The distorted tetrahedral coordination at the boron atom is characterized by a slight lengthening of the B-O bonds to the bridging oxygen atoms (1.49 – 1.50 Å for B-O2/3 vs. 1.47 – 1.48 Å for B-O1/4), and a contraction of the O2-B-O3 (107.0°) and a widening of the O1-B-O4 Bond lengths in [Å] Bond angles [°] B-O4/1 1.470-1.473 P1-Ag-P2 154.43(6) B-O2/3 1.493-1.502 O1-B-O2 104.8 (4) Ag-O2/3 2.802-2.849 O2-B-O3 107.0(5) Ag-P1/2 2.446-2.450 O1-B-O4 112.4(5) Fig. 3.7: Molecular structure of 21 (H-atoms omitted for simplicity; 50% probability thermal ellipsoids); selected bond lengths and angles are given in the table. angle (112.4°), which deviate considerably from the ideal tetrahedral angle of 109.5°. All structural features together suggest that 21 represents, in a similar manner as 14b and d, a bis-phosphine complex with a linear two-coordinate silver ion that exhibits additional, presumably electrostatic, interactions with oxygen atoms of the borate unit. It remains currently undecided if the Ag-P bond lengthening in 21 is a direct electronic consequence 58 of these secondary interactions, or is rather attributable to the presence of conformational strain in the chelate ring. 3.2.3. Synthesis and characterization of a Silver (I) bis {diphenyl- (benzo-[1,3]- dioxo-5-ylmethyl)-phosphane} 2-borate macrocycle: In this section, another catechol phosphine 9d will be utilized which differs from 9b only in the relative position of the hydroxy groups to the phosphorus atom. The three components B(OH)3, 9d and Et3N were reacted in THF to give the borate 22. The reaction mixture was evacuated to dryness and a white powder of m. p. 197ºC was isolated in good yield (90%). The 11B NMR displayed a resonance at 14.33 ppm, which is typical of a tetra- coordinated borate.79 The 31P resonance at –10.2 ppm corresponds to a free phosphine. The proton NMR spectrum displayed signals between 7.5 and 7.3 ppm which can be easily assigned to the protons of the phenyls at phosphorus. A broad singlet at 3.37 ppm is attributed to the aliphatic CH2 protons. An excessive line broadening was observed for the NH proton, which appeared as a very broad singlet at 6.8 ppm. A quartet at 3.08 and triplet at 1.18 ppm were assigned to the CH2 and CH3 protons of triethyl ammonium, respectively. Coordination of the catechol units of 9d to boron was further supported by the significant 13C NMR downfield shift (5-10 ppm) of the C-OH carbon atoms as compared to the free ligand 9d. Bond lengths [Å] Bond angles in [°] O4-B1 1.496(4) O1-B1-O3 105.88(2) O3-B1 1.494(4) O2-B1-O4 104.91(2) O1-B1 1.476(1) O3-B1-O4 109.45(2) O4-H45 1.957(1) O1-B1-O2 113.0(2) Fig. 3.8: Molecular structure of 22. (H-atoms omitted except the NH atom; 50% probability thermal ellipsoids); selected bond lengths as given in the table. 59 Suitable single crystals for X-ray diffraction measurements were obtained from tetrahydrofuran solution at –28ºC. The molecular structure of 22 (monoclinic, space group Cc) disclosed as in the case of 20 the presence of two crystallographically independent ion pairs. Both are composed of a spirocyclic anion which is assembled around a central BO4- tetrahedron, and a triethyl ammonium cation that interacts with the anion via a NH…O hydrogen bridge. As a consequence, the B-O4 (1.49 Å) bond is slightly elongated as compared to the other three B-O bonds (1.47-1.48 Å) although not significantly (Fig. 3.8). The spirocyclic ring structure induces also a contraction of the O-B-O angles in the five- membered rings (104 – 105°) and a concomitant widening of the remaining bond angles (109 – 112°C) with respect to the tetrahedral angle of 109.4°. Other bonding parameters in the spirocyclic catechol borate unit are similar to those observed in 20 but the distance between the two methylene carbon atoms (C9…C12 12.0 Å) and the phosphorus donor atoms (P1…P2 13.3 Å) shows, as a direct consequence of the different substituent pattern, a further substantial increase. A stoichiometric reaction between template 22 and AgO3SCF3 in DMF at room temperature produced a colorless solution. The product was precipitated by adding excess PPh2 OO OO B- B(OH)3 Et3N AgCF3SO3 OH Ph2P OH PPh2 PPh2 O O O O B- Ph2P Ph2P O O O O B- PPh2 Ag Ag2 229d 23 Et3NH+ Scheme 5: Syntheses of boron template 22 and boron-silver macrocycle 23. diethyl ether. The white solid was filtered off, dried in vacuum, and characterized by NMR and Mass Spectroscopy. The material obtained melts at 272ºC and is sparingly soluble in highly polar solvents. The presence of a 11B resonance at δ =14.8 confirms that the boron template 22 remained intact and a broad 31P signal at 12.8 ppm with a splitting of 314 Hz due to P-Ag coupling indicates that the phosphorus is coordinated to the silver and is undergoing fast intermolecular ligand exchange. Cooling down the sample did not cause 60 simple sharpening of the signals but resulted in decoalescence to give a complicated pattern of several multiplets (due to coupling with 107/109Ag nuclei) that could not be fully analyzed. The 1H NMR signals were likewise broad, but the appearance of a single signal for the benzylic protons indicated that a similar resolution of different environments of diastereotopic CH2 protons as in 21 was unfeasible. Starting with the assumption that formation of a mononuclear complex with similar constitution as 21 is incompatible with the arrangement of the donor sites in the template ligand 22, it was concluded that the available analytical and spectroscopic data are best interpreted by assuming the presence of oligomeric complexes of composition [(22)Ag]n (n> 1) which are formed by µ-bridging coordination of n bis-phosphine units to n silver Fig. 3.9: Positive mode ESI-MS spectra displaying m/e = 1485.14 (23+Na)+ and 754.05 (23+Na)2+ with 13 C isotopic splitting of 1.0 Da and 0.5 Da respectively. ions. Since each fragment 22 represents an axially chiral building block, the oligomeric assembly may exist in several diastereomeric forms, and mutual interconversion between 61 individual isomers via intermolecular ligand exchange and/or racemization of individual borate units can provide a satisfactory explanation for both the observed line broadening effects in the 1H and 31P NMR spectra and the observation of multiple 31P NMR resonances at low temperature. Direct experimental evidence for the presence of the postulated oligomers was also obtained from a positive mode ESI mass spectrum of a DMF solution of the isolated product which displayed a peak at m/e = 1485.13 assigned to a pseudo-molecular ion (23+Na)+ (fig. 3.9 top trace). The small peaks at the bottom suggest that a small amount of a tetrameric complex is presumably also present. The ESI-MS spectra further displayed a doubly charged ion peak at 754.1 assigned as [23+2Na]2+(fig. 3.9 bottom trace).81 These pseudo-molecular ions were unequivocally identified by comparison of observed and simulated isotope patterns. As at the same time no ions indicating the presence of mononuclear complexes were found we deduce that the predominant species present in solution is the dinuclear complex 23. The conclusions derived from the mass spectral studies of complexes 21 and 23 were further validated by diffusion coefficient measurements using Pulsed Gradient Spin Echo NMR experiments.82 -2 -1.8 -1.6 -1.4 -1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0 500 1000 1500 2000 2500 3000 lo g(I /I 0 ) G2 [(G/cm)2] Fig. 3.10: Plots of log I/I0 for the signal of the benzylic protons vs. the square of gradient amplitude. Data refer to solutions of 21 in CDCl3 (□) and DMF-d7 (+), and to a solution of 23 in DMF-d7 (◊). Diffusion coefficients were calculated from the slope of the straight lines, and values are given in text. [81] A. P. Gies, D. M. Hercules, A. E. Gerdon, D. E. Cliffel, J. Am. Chem. Soc. 2007, 129, 1095. [82] P. S. Pregosin, P. G. Anil Kumar, I. Fernandez, Chem. Rev. 2005, 105, 8, 2977. 62 The diffusion coefficient D allows one to compute hydrodynamic radii rH via the Stokes- Einstein equation, rH = kT/6piηD, and rH may in turn be used to estimate molecular volumes. A common application of PGSE techniques in chemistry concerns the comparison of relative molecular sizes of species in solution and is based on the perception that the ratio of the diffusion coefficients of two molecules determined in the same solvent and at the same temperature is inversely proportional to the ratio of rH, and thus the molecular volumes, of these species.82 Measurement of the diffusion coefficients of solutions of 21 and 23 in DMF-d7 at 30°C (Fig. 3.10) gave values of D = 4.3(1) · 10-10 m2/s for 21 and D = 2.2(1) · 10-10 m2/s for 23, respectively. These data suggest that the hydrodynamic radius of 23 is nearly twice as large as that of 21, which is well in accord with the proposed nature of 23 as a dimer. Carrying out the experiment on a solution of 21 in CDCl3 at the same temperature gave D = 9.2(1) · 10-10 m2/s which indicated a higher mobility of the complex in CDCl3 than in DMF. Although this is in principle to be expected as a consequence of the lower solvent viscosity,83 the noticeable deviation of the measured ratio of diffusion coefficients of 4.3/9.2 = 0.47 from the inverse ratio of viscosities of 0.68 suggests that this effect is not attributable to the viscosity influence alone. A likely explanation for the deviation can be given by postulating that the silver ion in 21 is in DMF solution involved in additional donor-acceptor interactions with solvent molecules which should increase the hydrodynamic radius and thus lead to an overproportional decrease of the diffusion coefficient. Further support for this hypothesis is gained from the observation of a noticeable solvent dependence of the values of δ(109Ag) and 1JAgP as well as the relative chemical shifts of the benzylic protons Ht and Hc (see Expt. section for details) in 21 which is interpreted to reflect directly the interaction between the metal ion and the additional solvent molecules. [83] Dynamic viscosities at 30ºC from Landolt Boernstein, Springer, 2002, 18B; η = 0.506 (CDCl3), 0.743 (DMF-d7) m Pa.s. The value for DMF-d7 was interpolated from the available data in the temperature region between 15 and 45ºC. 63 3.3. Attempted synthesis of Triethyl ammonium [Dichloro palladium bis {diphenyl- (benzo- [1,3]-dioxo-4-ylmethyl)- phosphane}] 2-borate: O O Ph2P O O B- P O O P O O B- Ph Ph Ph Ph (COD)PdCl2PPh2 Pd 103 20 Et3NH+ P O OH P O HO Ph Ph Ph Ph Pd (COD)PdCl2 Et3NH + Cl Cl 104 P O O B- Ph Ph OH Cl + 105 Scheme 6: Attempted synthesis of the palladium borate complex 103. The isolated product 20 was treated with (COD)PdCl2 in DMF and the solution was stirred at room temperature for 24 hours. Diethyl ether was added to produce a precipitate which was filtered and finally dried in vacuum to obtain an orange yellow powder of melting point 142ºC. NMR studies of 103 showed a single 11B NMR resonance at 14.6 ppm corresponding to a tetra-coordinated boron atom. The 31P NMR spectrum displayed three broad singlets at 40.7, 31.2, and 19.5 ppm indicating that a mixture of several products had formed. The ESI-MS positive mode experiment displayed quite surprising spectra. A pseudo-molecular ion peak was observed at m/e = 743.07 corresponding to [(catphos)2Pd+2H+Na]+, where (catphos) = C19H15O2P. A further ion was observed at m/e = 1465.15 {[(catphos)2Pd+2H]2+Na}+. The ESI-MS negative mode spectra displayed a pseudo-molecular ion peak at m/e 719.07 corresponding to [(catphos)2+HPd]¯ , another peak at 404.96 corresponding to [(catphos)BOHCl]¯ could also be assigned. The above observations suggest that complex 103 was not at all formed, whereas fragments containing separate palladium complex (104) and borate anion (105) were found in ESI- MS spectra. A likely explanation for the failure to observe 103 could be that the palladium atom likes to be square planar which induces more strain on the borate anion and forces it to open up, giving two separate fragments. Thus efforts to synthesize 103 were 64 unsuccessful. 3.4 Conclusions: In Summary, the catechol phosphine 9b reacts with phenyl boronic acid to give the corresponding borane 16a. The moderately strong boron acidic center of 16a required six equivalents of pyridine for complete conversion into the acid/base adduct, whereas only one equivalent of dimethyl amino pyridine was sufficient to obtain the corresponding adduct 17a. Two equivalents of 17a on treatment with one equivalent of palladium complex produced a mixture of products, one of them is likely to be 19, though further evidence is required. The presented experimental findings allow to state that, by varying the substituent on boron, either a strongly acidic or a weakly acidic center can be generated, which can be further utilized to coordinate a bidentate base that can act as a building block for organometallic polymers. It was demonstrated that the tetrahedral borate unit can be used to assemble the catechol phosphines 9b,d to yield the supramolecular bis phosphines 20 and 22 respectively. These borates can act as bidentate ligands towards soft metals like Ag+ forming either a mononuclear complex 21 or a dinuclear complex 23. The nature of the product is determined by the control of the bite angle of the bis-phosphine, which is in turn commanded by the relative arrangement of the catechol and phosphorus donor sites in the molecular backbone of the catechol phosphine. The observed product selectivity during the complexation step suggest that the template-based approach allows one not only to link two simple monodentate ligand fragments to form a bidentate donor, but that the resulting assemblies are sufficiently rigid to permit tuning of the geometric parameters of the ligand assembly. The procedures reported here should thus encourage further efforts to combine catechol phosphines 9b,d with different main group or transition metal templates to generate ligand libraries whose geometric properties can be fine-tuned. 65 4. Transition metal complexes of templated symmetric bisphosphane ligands and potential application in catalysis 4.1. Introduction: In Chapter 2 facile and rational syntheses of a series of functional catechol phosphine ligands was demonstrated (see Fig. 4.1). A peculiarity of these ligands is that they are composed of hard donors (oxygen atoms) at one end and soft donors (phosphine) at the other end. Important to note is the relative disposition of these donors, which are in close proximity to each other. The ligand can form a six-membered ring with a metal atom utilizing both a hard and soft donor available. Alternatively, hard acids may selectively react with the oxygen donors and soft acids with the soft phosphine. OH OH PPh2 9b Fig.4.1: Ligand 9b. Another feature is that these ligands are equipped with a CH2 unit which acts as a spacer to provide limited but sufficient flexibility. Chapter 3 demonstrated that a main group element such as boron may act as template to assemble two bifunctional ligands 9b to give a bifunctional phosphine which may then react with a transition metal ion to form a complex. Recently Raymond and coworkers demonstrated that the relative placement of hard and soft donors could be exploited for designed syntheses of heterometallic clusters, 66 allowing to construct complex metal-ligand aggregates in a single step by “self- assembly”.84 Taking into account these features, it is highly likely that in the presence of a hard and soft acid, ligand 9b may likewise undergo template directed self assembly to generate a di- or multinuclear complex. It is envisioned that alteration of the template center may allow the study of a series of complexes featuring ligands with different geometric properties. In particular, the size of the template may control the ligand bite angle, and varying the template size may provide better insights into the complexation properties of ligands with different bite angles. In order to study the effect of alteration of the template, various ions of group 3, 4, 13, 14 and 15 with three or four positive charges will be used. Though there is in principle a similar variability in the metal used for complexation, the studies in this chapter will focus on Pd(II) and Pt(II) because of the frequent use of these elements in catalysis. The final goal of this study is to employ the self-assembled complexes as catalysts for C-C coupling reactions. Investigations on boron compounds, as detailed in chapter 2, indicated that the use of boron as a template is limited in view of its small size. Due to its large ion radius and high reactivity, gallium, the higher analogue of boron, was selected for further investigations. The close similarity of gallium (III) with iron (III) makes it further interesting, as iron is an important component in many biological processes.85 It is assumed that gallium complexes may be useful as mimics for analogous iron complexes which may have useful properties owing to the redox activity of iron.86 Shifting the focus from group 13 to 14, tin was selected owing to its larger size and higher chlorophilicity than gallium. Furthermore, tin is known to form penta- coordinated complexes with mixed O,S-donors and hexa- coordinated complexes with oxygen donors.87 At the application end, tin compounds are known to show non-linear optical (NLO) properties,88 and organo-tin halides are important alkyl transfer reagents in Stille type C-C coupling reactions.89 Recently, Ishii and coworkers reported the oxidative carbonylation of phenols to diphenyl carbonate.90 In this [84] X. Sun, D. W. Johnson, K. N. Raymond, E. H. Wong. Inorg. Chem. 2001, 40, 4504. [85] a) B. Kersting, J. R. Relford, M. Meyer, K. N. Raymond, J. Am. Chem. Soc. 1996, 118, 5712. b) M. Meyer, B. Kersting, R. E. Powers, K. N. Raymond, Inorg. Chem. 1997, 36, 5179. [86] T. B. Karpishin, T. M. Dewey, K. N. Raymond, J. Am. Chem. Soc. 1993, 115, 1842. [87] R. R. Holmes, S. Shafieezad, V. Chandrasekhar, A. C. Sau. J. M. Holmes, R. O. Day, J. Am. Chem. Soc. 1988, 110, 1168. [88] C. Lamberth, J. C. Machell, D. M. P. Mingos, T. L. Stolberg, J. Mater. Chem. 1991, 1(5), 775. [89] a) J. K. Stille, Angew. Chem. Int. ed. 1986, 25, 508. b) T. N. Mitchell, Synthesis 1992, 803. c) L. S. Hegedus, Coord. Chem. Rev. 1996, 147, 443. [90] H. Ishii, M. Ueda, K. Takuechi, M. Asai, J. Mol. Catal. A: Chem. 1999, 138, 311. 67 reaction, a mixture of palladium and tin compounds was employed to generate complexes in situ and no further explanation on the composition of the complex was provided. Bismuth was picked up as a representative of group 15, applying to similar size criteria as gallium and tin. Whereas trivalent arsenic and antimony catecholates are well studied,91 less is known about bismuth compounds. Rosenheim in1931 reported coordination of three catechols to bismuth,92 and Smith et al93 reported a dimeric penta-valent bismuth catecholate complex {(NH4)2[Bi2(C6H4O2)4].2C6H4O2.2H2O}. Lately, organo-bismuth compounds have attracted much interest,94 due to the potential biological activity and their use as catalysts in organic synthesis.95 Bismuth is the heaviest stable element in the periodic table, and bismuth compounds often show special behavior, both electronically and sterically.96 Moving from the main group elements to transition metals and considering the commercial importance of zirconium complexes in polymer industry,97 zirconium was chosen as a possible template. To check out the reactivity of the lanthanides, which are known to be very oxophilic, the near neighbor yttrium was chosen. Detailed report on the reactivity of all above elements with the catechol phosphine 9b will be provided in the following section. 4.2. Results and discussion: 4.2.1. Synthesis and characterization of self-assembled palladium-bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4-ylmethyl) phosphane)}-gallium chloride (25): A reaction aiming at preparing a chelate complex by self-assembly was carried out by placing a mixture of 9b (2 equivs.), (COD)PdCl2, GaCl3 and excess Et3N (2.5 equivs.) into a Schlenk tube and dissolving this mixture in a suitable solvent. In view of the lower solubility of some of the reaction components and previous reports on similar reactions98 dimethyl formamide was chosen as the most suitable solvent. The progress of the reaction [91] A. Rosenheim, I. Baruttschisky, Ber. Dtsch. Chem. Ges. 1925, 58, 891. [92] A. Rosenheim, Z. Anorg. Allg. Chem. 1931, 200, 173. [93] G. Smith, A. N. Reddy, K. A. Byriel, C. H. L. Kennard, Aust. J. Chem. 1994, 47, 1413. [94] H. Suzuki, Y. Matano, Eds. Organobismuth Chemistry; Elsevier Science B. V.: Amstredam, 2001. [95] C. Silvestru, H. J. Breunig, H. Althaus, Chem. Rev. 1999, 99, 3277. [96] N. Guilhaume, M. Postel, Heteroatom. Chem. 1990, 1(3), 233. [97] M. J. Ferreira, A. M. Martins, Coord. Chem. Rev. 2006, 250(1-2), 118. [98] D. L. Caulder, R. E. Powers, T. N. Parac, K. N. Raymond, Angew. Chem. Int. Ed. 1998, 37, 1840. 68 was monitored by 31P NMR and showed complete conversion in 5 hours. A red solution with a white precipitate was obtained which was first filtered through a celite bed, followed by evaporation of the filtrate to dryness. The dried red powder was dissolved in 10 ml of dimethyl formamide and precipitated out by adding 60 ml of diethyl ether; this was repeated one more time. At the end of this procedure an orange red powder of m. p. 358ºC was isolated in 70% yield. The product was submitted to further characterization by analytical and spectroscopic methods. A sharp singlet at 65 ppm in the 31P NMR spectrum in CDCl3 indicated the exclusive formation of a single product. The relatively large down field shift in phosphorus NMR as compared to complexes like 24 raised speculations about the formulation of the product. The observed deshielding is compatible with the formation of chelate complexes, as similar deshielding was reported for the palladium chelates of related phosphinoalcohols.99 OH OH PPh2 9b 2 (COD)PdCl2 GaCl3 (COD)PdCl2 GaCl3, Et3N O O Ph2 P O O Ph2 P Ga Cl Pd O O Ph2 P O O Ph2 P Ga- Pd Cl Cl 24 25 Et3NH + Et3N Scheme 4.1: Synthesis of palladium-gallium dinuclear complex 25. The 1H NMR spectrum was similar to that of the free ligand and no signals indicating an ammonium cation were visible, thus ruling out the expected constitution as 24. Presumably, the triethyl ammonium cation present in 24 can abstract chloride from the palladium atom, spontaneously eliminating triethyl ammonium chloride and resulting in weak intramolecular palladium oxygen interactions to give complex 25 (see Scheme 4.1). The positive mode ESI-MS spectrum showed a pseudo-molecular ion peak at m/e = 825 [99] D. J. Brauer, P. M. Machnitzki, T. Nickel, O. Stelzer, Eur. J. Inorg. Chem. 2000, 65. 69 (M+H)+ where M = C38H30O4P2GaPdCl (See 25, Scheme 4.1). Another pseudo-molecular ion peak was observed at m/e = 847 (M+Na)+. An oxidation product was also observed at m/e = 857 (M+O2+H)+. The negative mode ESI-MS displayed two peaks corresponding to the pseudo-molecular ion at m/e = 823(M-H)¯ and 858.9 (M+Cl) ¯ . Bond lengths [Å] Bond angles [º] Bond angles [º] Ga-O1 1.974(1) O1-Ga-O2 83.56(1) P2-Pd-O3 92.34(1) Ga-O2 1.918(1) O1-Ga-O3 76.26(1) O1-Pd-O3 74.31(2) Ga-O3 2.085(1) O3-Ga-O4 83.86(1) O2-Ga-Cl 104.64(1) Ga-O4 1.885(1) O2-Ga-O4 96.23(1) O1-Ga-Cl 116.61(1) Pd-O1 2.064(1) P1-Pd-O1 92.18(1) O3-Ga-Cl 110.42(1) Pd-P1 2.250(1) P1-Pd-P2 101.8(1) O4-Ga-Cl 111.42(1) Fig. 4.2: Molecular structure of complex 25, (H-atoms omitted, 50% probability thermal ellipsoids); selected bond lengths in and bond angles are given in table. Unambiguous confirmation of the constitution of the product as complex 25 came from the crystal structure determination. Suitable crystals for single crystal X-ray diffraction were obtained from a highly concentrated solution of the isolated product in dichloromethane, tetrahydrofuran, and an equivalent amount of diethyl ether at room temperature. A single 70 crystal X-ray diffraction study disclosed the presence of complex 25 together with three molecules of solvent (CDCl3 from the NMR) per formula unit in a monoclinic unit cell in the space group P21/n. One of the solvent molecules is weakly hydrogen bonded to the chloride on gallium, and the second one is weakly hydrogen bonded to the benzylic hydrogen via a chloride, whereas the third molecule does not show such interactions. The palladium atom displays a square planar geometry with the two phosphorus and two µ2- bridging oxygen atoms completing the coordination sphere. The phosphine donors exhibit a cis-arrangement with a normal P-Pd bond length of 2.24 Å, but the bond angles deviate from the standard angle of 90º with a very acute O1-Pd-O3 angle of 74.3º and a larger P1- Pd-P2 angle of 101.8º. The most striking feature of the assembly are the oxygen atoms O1/O3 which act as µ2-bridging ligands towards palladium and gallium. The PdO2Ga four membered ring is planar. A space filling model displays nicely the cavity built by the two catechol rings and the phenyl substituents on phosphorus. This cavity allows easy access to palladium which would be of further interest in catalysis.100 Fig. 4.2a: Space filling model of complex 25 displaying the cavity at palladium(center) made by the catechol and phenyl groups on phosphorus. The phosphorus atom displays a distorted tetrahedral geometry. The phosphine donors bite into palladium with a bite angle of 101.7º. In order to have less steric hindrance, the phenyl [100] E. Negishi, R. A. John, J. Org. Chem. 1983, 48, 4098. 71 rings on phosphorus atom are oriented in a way to have minimum steric repulsive interactions and thus one phenyl ring from each phosphorus atom is oriented trans to the other while the other ring points out of the P-Pd-P plane. Of particular interest is the distorted square pyramidal geometry at the gallium atom, in which the four oxygen atoms occupy the basal square and the chloride the top of the pyramid. The Holmes model101 allows to estimate the deviation of the arrangement of ligands around a pentacoordinate central atom from ideal trigonal bipyramidal (TBP) and sqiare pyramidal (SP) geometries. By the dihedral angle method102 to assess displacements, complex 25 is displaced 11% from an ideal SP toward a TBP coordination. Noteworthy is the displacement of the gallium above the oxygen plane by 0.8Å (O1/2/3-Ga), which reduces the sum of O-Ga-O angles to 340º, compared to a value of 360º for ideally square planar coordination. The observed distortion can be rationalized by the development of certain ring strain in the molecule forming the GaO2Pd ring. Thus the four oxygen atoms are being pressed down out of the gallium plane. A similar observation was reported earlier103 in case of the aliphatic 2,2-dimethylpropane-1, 3-diol (neol) gallium complex [Ga3(tBu)5(neol)2]. The oxygen bridging in 25 results in elongation of the O1/O3-Ga bonds (1.97-2.08 Å) compared to the non-bridging O2/O4-Ga bonds (1.88-1.91 Å). The Ga-O (terminal) bonds in 25 are also shorter than in similar cationic gallium catechol complexes104 reported earlier [Ga-O:1.94 Å]. All four O-Ga-O angles are smaller than the standard square pyramidal angle of 90º, the smallest is O1-Ga-O3 with 76.3º. The inter- atomic distance between the two metals is Pd-Ga 3.21 Å, which is considerably larger than the sum of the covalent radii (2.53 Å) and thus rules out existence of any metal-metal interaction. Hexa- and tetracoordinate gallium complexes are well known in the literature,105 but there are very few reports on square pyramidal, penta-coordinate gallium compounds.103, 106 [101] R. R. Holmes, ACS Monogr. 1980, 175, Chapter 2; R. R. Holmes, J. A. Deiters, J. Am. Chem. Soc. 1977, 99, 3318; R. R. Holmes, R. O. Day, A. C. Sau, J. M. Holmes, Phosphorus, Sulfur, and Silicon and Related Elements, 1995, 98, 423. [102] E. L. Muetterties, L. J. Guggenberger, J. Am. Chem. Soc. 1974, 96, 1748. [103] C. N. McMahon, S. J. Obrey, A. Keys, S. G. Bott, A. R. Barron, J. Chem. Soc. Dalton Tans. 2000, 2151. [104] T. B. Karpishin, T. D. P. Stack, K. N. Raymond, J. Am. Chem. Soc. 1993, 115, 182. [105] B. A. Borgias, S. J. Barclay, K. N. Raymond, J. Coord. Chem. 1986, 15, 109; M. A. Brown, A. A. El- Hadad, B. R. McGarvey, R. C. W. Sunf, A. K. Trikha, D. G. Tuck, Inorg. Chim. Acta. 2000, 300, 613. [106] N. R. Bunn, S. Aldridge, C. Jones, Appl. Organometal. Chem. 2004, 18, 425; W. Ziemkowska, P. Stella, R. Anulewicz-Ostrowska, J. Organomet. Chem. 2005, 690, 722. 72 In summary, simple mixing of the four complementary reactants at room temperature produces selectively a single, neutral, palladium-gallium complex 25 by self-assembly. The complex 25 was fully characterized by 31P, 1H NMR, elemental analysis, electron spray ionization mass spectrometry, and a single crystal X-ray diffraction study. A very unique feature of the complex is the presence of µ2-bridging oxygen atoms. It has been found that the complex 25 is the first palladium-gallium hetero-dinuclear complex with penta-coordinate square-pyramidal gallium, and it is believed that the ligand design is crucial for this special assembly. 4.2.2. Syntheses and characterization of self-assembled palladium–bis {diphenyl- (benzo-[1, 3]-µ-oxo-k-oxo-4-ylmethyl) phosphane)}-tin complexes: In section 4.2.1, it was illustrated that ligand 9b allows to produce a dinuclear palladium- gallium complex 25 in one straightforward step by self-assembly. It was envisioned that expanding a similar strategy to group 14 elements may provide more insight and may allow to study the effect of variation in the coordination geometry of the template center on the P-M-P bite angle in the product. Tin, principally larger than gallium and an important component of many catalytic reactions, was explored. Stille coupling is an effective cross- coupling reaction where an alkenyl tin compound undergoes coupling with a wide variety of organic halides in presence of a palladium catalyst.107 Mixing of 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (9b), tin tetrachloride, cyclooctadiene palladium dichloride and triethyl amine in a 2:1:1:2.5 ratio in 20 ml of dry dimethyl formamide and stirring the solution for 24 hours at room temperature produced a red suspension which was filtered through celite. The filtrate was evaporated in vacuum and the residue washed with dichloromethane and dissolved in little DMF. The same volume of dichloromethane and finally small portions of diethyl ether were added until a precipitate began to form. The mixture was stored over night at 4ºC to yield a microcrystalline solid which was collected by filtration and dried in vacuum for four hours at 70ºC to yield 40% of a red powder, melting at 214ºC (dec.). The powder was characterized as complex 26a by means of spectroscopic data, analytical data, and a single [107] a) S. Casson, P. Kocienski, J. Chem. Soc. , Perkin Trans. 1 1994,1187, b) T. Takeda, Y. Kbasawa, T. Fujiwara, Tetrahedron, 1995, 51, 2515. 73 OH OH PPh2 9b 2 (COD)PdCl2 R2SnCl2, Et3N O O Ph2 P O O Ph2 P SnR2 Pd 26a/b 26a:R = Cl, 26b:R = Me O O Ph2 P O O Ph2 P SnR2 Pd 27 DMF27a:R = Cl, 27b:R = Me DMF DMF Scheme 4.2: Syntheses of palladium-tin complexes (26a/b) of ditopic catechol phosphine 9b. crystal X-ray diffraction study. In an attempt to improve the yield, above reaction was repeated at 60ºC, and complex 26a was isolated in 60% yield. It is interesting to note that complex 26a was obtained even in the presence of an excess of ligand 9b, suggesting that displacement of the chlorine atoms on tin by a third catechol phosphine ligand was unfeasible. The 31P NMR spectrum of the isolated compound at 30ºC in DMF-d7 displayed a single broad resonance at 76.4 ppm. The considerable down field shift is similar as in 25. The 1H NMR spectra at 30ºC displayed broad signals with similar chemical shifts as the free ligand. The 119Sn NMR signal was unobservable owing to the low solubility of the complex. Cooling down the sample to –30ºC eventually sharpened the 31P NMR signal, and at the same time 1H NMR resonances decoalesced into two sets of signals, indicating that the methylene groups and phenyl protons of Ph2PCH2 moieties become chemically equivalent. 74 Fig. 4.3: 31P{1H} NMR spectra of 26/27 recorded between +30ºC and –60ºC. Fig. 4.4: 1H, 31P-HMQC (in DMF-d7) spectra of 26a/27a at –50ºC showing correlation between two sets of signals. Surprisingly, cooling the sample below –30ºC resulted in the appearance of a new 31P resonance at 55.5 ppm, which grew in intensity upon cooling to –55ºC (see fig. 4.3). All the changes were reversible upon warming up to ambient temperature. The above observations revealed that there should be two products 26a and 27a, which are in equilibrium at room temperature and give rise to separate signals at lower temperatures 75 which are according to 2D 31P EXSY spectra still in dynamic exchange. Assignments of the 1H NMR signals of the second product from 2D NMR spectra (see Fig. 4.4) reveals the methylene protons and phenyl groups in the CH2PPh2 fragment to remain chemically equivalent. The exchange can be described as pseudo-unimolecular reaction between 26a and a second compound 27a, and evaluation of the temperature dependence of the equilibrium constant K = [27a]/[26a] yielded values of ∆H = -5.4 kcal/mol and ∆S = -26 kcal/mol. The observed dynamic phenomena can be interpreted by assuming that 27a arises from coordination of extra solvent molecules to 26a in a process which is favored by enthalpy and disfavored by entropy. The isolated compound was sparingly soluble in CDCl3. The 31P NMR spectrum at room temperature in CDCl3 displayed two doublets (AB spin system) at 71.3 and 64.5 ppm with a 2JP-P coupling constant of 27 Hz each. Presumably, the observed compound is a C1 symmetric isomer of 26a where the phosphorus atoms are inequivalent (an inherent property of C1 symmetry) and thus display an AB spin system. Details on the stereochemistry of complex 26a will be discussed in chapter 5. Crystals of the product suitable for single crystal X-ray measurements were grown in DMF: CH2Cl2 (8:2) at +4ºC. The crystals contain a discrete complex 26a that lies on the crystallographic C2 axis in a monoclinic unit cell (space group P2/c) (Scheme 4.2 and Fig. 4.5). Further three solvent (CH2Cl2) molecules per molecule of complex were found in the asymmetric unit of the unit cell. The 26a molecules are linked together via a weak hydrogen bond between a chloride on tin and the CH2 hydrogen of a neighboring complex forming a chain. The tin atom features a distorted octahedral geometry being coordinated by the four oxygens of two chelating catechols and two chloride atoms. Three catechol oxygens (O1/2/2’) and one chloride lie in the same plane as the tin atom forming a rectangle, and the remaining oxygen and chloride are positioned axially. The oxygen atoms O1/O1’act as µ2-briding ligands towards tin and palladium, with the bridging Sn-O1 bonds being distinctly longer (2.17 Å) than the terminal Sn-O2 bonds (2.03 Å) (see fig. 4.5). Further, the terminal Sn-O bond distances are in fair accordance with literature reported values (2.05 Å).87 The formation of two five membered rings and a four membered ring around tin is presumably responsible for the substantial bond angle distortion at tin (smallest O1’-Sn-O1 = 73.5º). 76 Bond lenghts Å Bond angles [º] Bond angles [º] O1-Sn 2.171(2) O1-Sn-O2 79.08(1) P-Pd-P’98.79(1) O2-Sn 2.033(3) O1-Sn-O1’73.52(1) Cl-Sn 2.391(1) O1-Pd-O1’76.96(1) O1-Pd 2.088(2) Cl-Sn-O2 91.46(1) P1-Pd 2.251(3) Cl-Sn-Cl’104.28(5) Fig. 4.5: Molecular structure of complex 26a (H-atoms omitted for clarity, 50% thermal ellipsoids), bond lengths in Å and angles in [º] are given in the table. The palladium atom displays a square planar geometry with the two bridging oxygens and two phosphines completing the coordination sphere. The phosphine donors exhibit a cis- arrangement with a normal P-Pd bond length of 2.25 Å, whereas the bond angles deviate from the ideal angle of 90º with a very acute O1-Pd-O1’ angle of 76.9º and a larger P1-Pd- P2 angle of 98.8º, probably due to the SnO2Pd ring constraints. Of particular interest is the Pd- O1/O1’ distance of 2.08 Å which is considerably larger than observed in the P- µ1-O distances in chelate complexes (Pd-O 1.92 Å)108 and falls into the known range for Pd-µ2-O [108] G. S. Ferguson, P. T. Wolczanskl, Organometallics, 1985, 4, 1601. 77 bonds (2.02-2.17 Å).109 The constraints of the polycyclic structure inflict a strictly pyramidal coordination at the µ2-briding oxygen atoms (sum of the angles 323º) with a trans-arrangement of the exocyclic O-C bonds at the SnO2Pd-ring, in contrast to the planar µ2- bridging O-atoms in phenoxide or alkoxides. The above facts allow to conclude that the assembling of the complex goes along with the build-up of a certain ring strain. As expected, the increase in the size of the template center as compared to the gallium template in complex 25 results in a decrease of the bite angle: the gallium centered assembly 25 gave a bite angle of 101.7º, whereas in the tin centered assembly the bite angle decreases to 98.8º. In order to obtain further details, solid state NMR experiments were carried out. The 31P{1H} CP-MAS spectrum displays two resonances at δiso = 79.5 and 74.1 with a 2JPP coupling of 41 Hz (from J-resolved 2D spctra), clearly indicating the presence of a AB spin system with two inequivalent phosphorus atoms. A likely explanation for this observation is that 26a x DMF forms a pseudo-polymorph to the dichloromethane solvate that was characterized by X-ray diffraction, and that the crystallographic equivalence between the phosphorus atoms in the former is lost. The 119Sn CP-MAS NMR spectrum of the solid sample shows a isotropic line at δiso = -455, indicating the presence of only one type of tin center. Thus, the above CP-MAS measurements allow to state that the second species observed in solution (27a) is not present in the solid state. After knowing that 27a exists only in solution, it was of further interest to decide if the new donors in 27a bind preferably to tin or to palladium. In order to model the interaction of 26a with formamide in gas phase, DFT calculations were performed with the B3LYP functional. Energy optimization of 26a and of two different adducts with two molecules of formamide were carried out using a 3-21g* basic set. The relative energies Erel of both adducts were obtained by computing the energy optimized molecular structure of formamide at the same level of theory and evaluating the difference, Erel = E (adduct) – E (26a) – 2E (Formamide). [109] J. S. Kim, A. Sen, I. A. Guzei, L. M. Liable-sands, A. L. Rheingold, J. Chem. Soc. Dalton Trans. 2002, 4726. 78 Fig. 4.14: Wire model of the energy optimized molecular structure of a solvent adduct of 26a X 2H2NCHO (at the b3lyp/3-21g* level of theory). Table 1: Relative energies in kcal/mol. Erel (in kcal mol-1): Complex 26a + 2 Formamide: 0.0 Complex 26a × 2 Formamide (coordination at Pd, trans-isomer) -15.0 Complex 26a × 2 Formamide (Coordination at Sn) -18.6 The outcome of these studies suggested that formation of a macrocyclic complex with trans-configuration at palladium (see fig.4.14) is favored by 3.6 kcal/mol over coordination of formamide to tin. Attempts to locate a structure with trans-coordination of the chloride ligands at tin did not lead to a minimum. Attempts to locate a complex with cis- coordination of the formamide ligands at palladium produced a strongly distorted structure with very low energy gradient at high relative energy. As all attempts to locate further stationary points representing complexes with cis-configuration at palladium or cis/trans- 79 configuration at tin on the energy hypersurface failed, it was concluded that the molecular structure displayed in fig. 4.14 is most likely to represent that of the transient complex 27a. Whereas all attempts to improve the yield of 26a were unsuccessful, other tin (IV) compounds were explored in order to obtain improved yields and to reduce the reaction time. Dry DMF (20 ml) was thus added to a mixture of 9b (2 eq.), Me2SnCl2 (1 eq.), (COD)PdCl2 (1 eq.), and finally Et3N (5 eq.) was injected. The reaction mixture was stirred at room temperature to give a red suspension. Monitoring the reaction by 31P NMR revealed that the reaction took 3 hours for complete conversion. Dark red crystals were obtained after workup (refer to experimental details), which were dried in vacuum at 120ºC for four hours to give compound 26b in 95% yield. The red powder melts at 310ºC and positive mode electron spray ionization mass spectrometry displayed pseudo-molecular ion peaks at m/e = 869.02 (M+H)+, and 891.02 (M+Na)+. The 31P NMR spectrum of 26b at ambient temperature showed a single broad resonance at 74.6 ppm. Cooling the sample to 233K produced a very weak and broad singlet at δ = 51.6. Careful evaluation of low temperature NMR studies of solutions of 26b suggested that similar dynamic equlibria as in the case of 26a/27a are likewise present, even if the unambiguous identification of a transient species was in this case precluded due to its much lower concentration. The observation of tin satellites in the 31P{1H} NMR spectrum and a triplet in the 119Sn{1H} NMR spectrum (δ = -199.4, JSn-P = 15 Hz) disclosed that the bimetallic complex remains kinetically stable on the NMR time-scale and does not undergo ligand exchange.111 The 1H NMR spectrum at ambient temperature appeared very much similar to that of 26a with an additional singlet at 0.53 ppm with 117/119Sn satellites (JSn-H = 71 Hz) arising from the methyl protons at tin. The diastereotopic CH2 protons were not detectable even at low temperature indicating rapid dynamic racemization of the chiral coordination environment at tin which is facilitated by the easy dissociation of the oxygen donors from palladium. A considerable down field shift (7-9 ppm) of the 13C signals of the C-O carbon atoms in 26b as compared to the free ligand 9b indicate the coordination of the oxygen atoms to metals and thus further support the formation of complex 26b. The methyl carbon (SnCH3) on tin appeared as singlet at 25.6 ppm. Dark red crystals suitable for a single crystal X-ray diffraction study were grown in a DMF diethyl ether mixture (1:4) at +4ºC. The discrete molecules of 26b crystalizes in a monoclinic unit cell (space group P21/n) (see fig. 4.6) which contains further one molecule 80 of solvent (DMF). The crystal structure exposed similar features as that of 26a with few differences. The Sn-C bonds are shorter than the Sn-Cl bonds, which can be attributed to the smaller covalent radius of a C as compared to Cl. Bond lengths [Å] Bond angles [º] Bond angles [º] Sn-O1 2.238(3) O1-Sn-O2 75.59(1) O4-Sn-C3 97.1(2) Sn-O2 2.105(4) O3-Sn-O4 74.93(1) O1-Pd-O3 79.0(1) Sn-O3 2.286(3) O1-Sn-O3 70.83(1) P1-Pd-O1 91.31(1) Pd-O1 2.056(3) O2-Sn-C4 94.73(2) P1-Pd-P2 99.4(1) Sn-C3 2.137(1) C3-Sn-C4 114.2(2) Pd-P1 2.255(1) Pd-P2 2.244(1) Sn-C4 2.167(5) Sn-O4 2.103(5) Fig.4.6: Molecular stru.of 26b; (H-atoms omitted for simplicity, thermal ellipsoids at 50% probability) important bond distances and bond angles are given in the table. Although the methyl groups are cis to each other, the C-Sn-C (114º) bond angle is considerably larger than the Cl-Sn-Cl (104º) angle. This observation is in accordance with Bent’s rule (small bond angle are formed between electronegative ligands since the central atom to which the ligands are attached tends to direct bonding hybrid orbitals of greater p- 81 character towards its more electronegative substituents).110 The presence of less electronegative substituents at tin (chlorides formally replaced by methyl groups) increases the Sn-O1/3 bond length by 0.10Å. A minor increase in bite angle (P-Pd-P) was also observed (26a: 98.8, 26b: 99.4). The two catechol rings are inequivalent in the sense that one ring plane is bent towards tin by 15.5º (C11-C12-C13-C14) and the other by 12.1º (C64-C65-C66-C61). A similar deviation was also reported in Me2Sn(chelate)2 ( where chelate can be picolinate or tropolonate) type complexes.111 In summary, it was established in this section that the flexible catechol phosphine 9b effectively and selectively discriminates between hard and soft acids, and reacts to produce dinuclear tin-palladium complexes in good yields. Though the two complexes 26a, 26b appear very similar they also display a few differences which are attributable to the electronegativity difference between the methyl and chloride substituents. 4.2.3. Synthesis and characterization of a platinum -bis{diphenyl-(benzo-[1, 3]- µ-oxo-k-oxo-4-ylmethyl) phosphane)}-tin complex (28): The two previous sections (4.2.1 and 4.2.2) demonstrated that variation in the template can have consequences on the bite angle of the ligand. Considering that alteration in the catalytic metal might shade light on further interesting aspects of the dinuclear complexes and in view of the catalytic importance of platinum,112 a detailed investigation of platinum- tin complexes was undertaken. Reaction of 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (9b), tin tetrachloride, LPtX2 (L = cyclooctadiene, bis-benzonitrile X = bromide, chloride) and triethyl amine in a 2:1:1:2.5 ratio in 20 ml of dry dimethyl formamide at room temperature produced a yellow suspension. Monitoring the reaction by 31P NMR indicated completion of the reaction within 3 hours. A yellow solution was obtained after work-up which was evacuated to dryness to yield a yellow powder in almost quantitative yield. A concentrated DMF solution of the yellow residue at room temperature produced shining yellow needles, which were dried at 70ºC in vacuum for 4 hours. [110] H. A. Bent, Chem. Rev. 1961, 61, 275. [111] C. Camacho-Camacho, R. Contreras, H. Noth, M. Bechmann, A. Sebald, W. Milius, B. Wrackmeyer, Mag. Reson. Chem. 2002, 40, 31. [112] M. Colladon, A. Scarso, G. Strukul, Synlett. 2006, 20, 3515; M. V. Baker, D. H. Brown, P. V. Simpson, B. W. Skelton, A. H. White, C. C. Williams, J. Organomet. Chem. 2006, 691, 26, 5845. 82 OH OH PPh2 9b 2 (COD)PtBr2 Me2SnCl2, Et3N O O Ph2 P O O Ph2 P Sn Me Pt 28 Me Scheme 4.3: self-assembly of 9b to dinuclear platinum-tin complex 28. The product which was identified as compound 28 by spectral and X-ray diffraction studies melts at 354ºC and has one of the highest melting points among the series of complexes reported in this work. The ESI-MS positive mode experiment displayed two pseudo-molecular ions peaks at m/e = 957.08 (M+H)+ and 979.07 (M+Na)+. The 31P NMR 1H,119Sn HMQC, 303K F2 [ppm] 0.8 0.6 0.4 F1 [pp m] - 16 0 - 18 0 - 20 0 - 22 0 1H,119Sn HMQC, 303K m] 0 0 0 0 Fig.4.7: 1H 119Sn HMQC spectrum of 28 displaying cross peaks. specturm of complex 28 in CDCl3 at room temperature produced a singlet at 39.5 ppm with platinum satellites (JPt-P 4120 Hz), confirming the formation of only one product. The upfield shift with respect to 26a/b is attributable to the lower coordination of shift of platinum as compared to palladium complexes. Both the 1H, 119Sn, HMQC (see fig. 4.7) and 119Sn NMR spectra show a single 119Sn resonance at –183.8 ppm indicating the formation of a single product. The proton NMR at room temperature in CDCl3 displayed a similar signal pattern as that of 26b, except that the methyl (CH3) protons appeared at 0.62 ppm. Low temperature 1H and 13C NMR of 28 showed signal broadening, presumably due to the formation of solvent adducts. 83 Bond lengths [Å] Bond angles [º] P-Pt 2.242(1) O1-Sn-O2 74.17(4) O1-Pt 2.064(3) O2-Sn-C2 96.4(2) O1-Sn 2.303(3) C2-Sn-C2 120.0(4) O2-Sn 2.110(4) O1-Pt-O1 76.7(2) C2-Sn 2.14(1) P-Pt-P’ 100.78(1) Fig.4.8: Molecular structure of the platinum-tin complex 28. (H-atoms omitted for clarity, thermal ellipsoids at 50% probability), important bond lengths and bond angles are given in the table. Shining yellow crystals were grown from a DMF: dichloromethane mixture at +4ºC. A single crystal X-ray diffraction study showed that the complex 28 crystalises in a monoclinic unit cell in space group C2/c. The molecule lies on a crystallographic C2 axis (see Fig. 4.8). The tin atom displays octahedral geometry and the platinum atom is square planar. The observed bond lengths and bond angles closely match those found in complex 26b, with few exceptions. Compared to 26b, the bite angle (P-Pt-P) increases to 100.7º. The C2-Sn-C2 angle in 28 is 120.0º compared to the smaller angle of (114.2º) observed in complex 26b. The two catecholate planes intersect at the tin center with an angle of 83.7º, 84 whereas in complex 26b they intersect with a larger angle of 88.6º. These observations are attributed to the bigger size of the platinum compared to the palladium atom, which probably reduces the steric-repulsive interactions between the catechol phosphines. In summary, the platinum-tin based heterodinuclear complex 28 was successfully synthesized in one simple step and in almost quantitative yield. Changing the transition metal center from palladium to platinum has a rather small effect on the structural properties of the complex. 4.2.4. Synthesis and characterization of a palladium- bis{diphenyl-(benzo-[1, 3]-µ-oxo-k-oxo-4-ylmethyl) phosphane)}-bismuth complex (29a): The heavier elements of group 15 are particularly interesting as designing element in supramolecular chemistry due to the rare preference for a trigonal pyramidal coordination geometry, which is very difficult to obtain using transition metals.113 Another aspect is their Lewis acidity, which increases markedly as one moves down the group. For example, bismuth predominantly behaves as a lewis-acid whereas the lighter nitrogen behave as base. Smith et. al. reported a penta-coordinated bismuth compounds and demonstrated the presence of a dimeric bismuth complex, which was reported as four coordinated bismuth earlier.93 In the view of larger size, increased acidity, predefined geometry, a detailed investigation of the reaction of BiCl3 with 9b was undertaken. The solid mixture of (COD) PdCl2, BiCl3 and 9b (1:1:2, respectively) was dissolved in 8 ml of DMF, followed by addition of triethyl amine (5 eq.). Monitoring the reaction by 31P NMR evidenced complete conversion of the starting material 9b to a product 29a (see Scheme 4.4) in 3 hours. The dark red product, which melted at 273ºC with decomposition, was isolated in good yield (70%) by following the standard procedure established for the previously discussed products. The 31P NMR spectrum at ambient temperature in DMF-d7 displayed two broad resonances at 70.8 and 52.1 ppm. The signal at 70.8 ppm is assigned to the complex 29a and the resonance at 52.6 ppm is to a solvent adduct 29b (see scheme 4.4) with an analogous constitution as 27a. The 1H NMR spectrum of 29b at ambient temperature displayed similar chemical shifts as that of complex 26a. Cooling down the sample eventually sharpened the 31P and 1H NMR signals of 29a and 29b, which were readily assigned by 31P, 1H HMQC and 1H-COSY experiments, but the nuclei in Ph2PCH2 [113] W. J. Vickaryous, R. Herges, D. W. Jonson, Angew. Chem. Int. Ed. 2004, 43, 5831. 85 moieties remained chemically equivalent, an effect that was observed in 27a as well. The above observation revealed that there should be two products, which are in equilibrium at ambient temperature. The observed dynamic phenomena can be interpreted as pseudo- unimolecular reaction by assuming that 29b arises from coordination of extra solvent molecules to 29a. Electron spray ionization mass spectra in positive mode disclosed two pseudo-molecular ion peaks at m/e = 927.04 (M-Cl)+, and the other at m/e = 969.03 (M+Li)+ confirming the presence of a monomeric complex 29a.93 O O Ph2 P O O Ph2 P Bi Cl Pd 29b DMF DMF DMF OH OH PPh2 9b 2 (COD)PdCl2 BiCl3 Et3N O O Ph2 P O O Ph2 P Bi Cl Pd 29a Scheme 4.4: assembling of palladium-bismuth dinuclear complex 29a. Suitable single crystals for X-ray diffraction measurement were grown at room temperature from a concentrated dichloromethane solution. Complex 29a crystallizes in the monoclinic crstal system in the space group P21/c (see Fig. 4.9) with one molecule of solvent CH2Cl2). The solvent molecules form weak hydrogen bonds with the chloride on bismuth, and a chlorine atom in the CH2Cl2 molecule builds another weak hydrogen bridge to a CH2- unit of the neighboring complex. Thus, the overall structure can be described as three-dimensional network of 29a and solvent molecules that are held together by weak hydrogen bonds. (Surprisingly, the single-crystal X-ray diffraction study revealed that complex 29a appears as a dimer with hexa-coordinated, strongly distorted octahedral bismuth atom. The dimer is a neutral, centrosymmetric entity with the chlorides bridging the two bismuth centers. The bridging Bi-Cl bond measures 3.30Å, indicating weak intermolecular bismuth-chloride interactions. 86 Bond lengths [Å] Bond angles [º] Bond angles [º] O3-Bi 2.439(5) O1-Bi-Cl 149.99(1) O1-Bi-O3 66.03(2) P1-Pd 2.256(2) O4-Bi-Cl 83.29(2) Bi-Cl-Bi1 102.444(2) O2-Bi 2.175(1) O2-Bi-Cl 89.48(1) Cl-Bi-Cl1 77.56(2) O3-Pd 2.089(5) O2-Bi-O4 85.7(2) Cl-Bi 2.765(3) P1-Pd-P2 97.14(5) µ - Cl-Bi 3.301(2) O3-Bi-Cl 144.11(1) Fig. 4.9: Molecular structure of the dimeric palladium-bismuth dinuclear complex 29a. H- atoms are omitted for the clarity, thermal ellipsoids with 50% probability, important bond lengths and bond angles are given in the table. However, in other respects, the coordination is unusual for bismuth (III), displaying a large coordination void of almost 149º, presumably occupied by the inert lone pair of electrons. Similar observation were reported by Smith et. al for a complex {(NH4)2[Bi2(C6H4O2)4].2C6H4O2.2H2O}, where a third catechol ligand was found to bridge the two bismuth centers and a coordination void of 147º was observed.93 The lone pair effect results for 29a in a huge deviation of the O3-Bi-Cl angle (144.1º) from the ideal octahedral angle. The O2-Bi-O4 angle is 85.7º, whereas the O1-Bi-O3 angle is much smaller (66.0º). The effect of an increase in the size of the template center as compared to complex 26b reflects on the µ2-O-M bond lengthening so that the µ2-O1/3-Bi bonds in 29a are 0.26Å longer than the µ2-O-Sn distances in 26b. Thus, the combined effect of O1/3-Bi 87 bond lengthening (increases the P-Pd-P bite angle), the O1-Bi-O3 angle shortening (decreases the bite angle) and the presence of a lone pair (decreases the bite angle) is likely to be responsible for the observed overall reduction of the P1-Pd-P2 bite angle to 97.0º compared to 101.8º in the square pyramidal gallium-palladium assembly 25. The palladium atom in 29a displays a square planar geometry with a cisoid arrangement of the catechol phosphine moieties in the resulting planar BiO2Pd four-membered ring, but the two BiO2Pd units in the dimer display a trans-arrangement along the Bi-Bi axis. No metal- metal inter/intra molecular interactions were found as all distances exceeded the sum of their respective covalent radii (Bi-Bi: 4.74 Å, Pd-Bi: 3.64 Å). The dimeric structure makes the coordination at the template center very different from that of other complexes discussed so far. In summary, a surprisingly dimeric, hexa-coordinated, palladium-bismuth complex was obtained in solid state, though the NMR and ESI-MS analysis showed a monomeric complex as the dimer presumably dissociates in solution. A large coordination void present on bismuth is assumed to be occupied by the inert lone pair. 4.2.5. Zirconium assisted synthesis of a trinuclear di-palladium zirconium complex of 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (30): Detailed investigation was set to study the role of oxophilic transition metals as template centers. With respect to increasing interest in zirconium oxide materials114 and zirconia supported palladium cross-coupling catalysts,115 syntheses of heteromultinuclear transition metal complexes were targeted. As the group 4 metals are known to react with two or four units of a catechol to give di- or tetra-catecholato-complexes116 it was of further interest to study the behavior of 9b. 2 equivalents of 9b, 1 equivalent of (COD)PdCl2, 1 equivalent of ZrCl4, and excess of the base Cs2CO3 (1.3 equiv) were dissolved in 15 ml of DMF and stirred for 6 days at room temperature. A dark red reaction mixture was formed which was filtered and taken to dryness. 5 ml each of DMF and dichloromethane was added and the solution diluted with 50 ml of diethyl ether to produce a reddish gray precipitate. The precipitate was filtered and dried in vacuum for 4 hours. The isolated powder that melts at [114] K. G. Caulton, L. G. Hubert-Pfalzgraf. Chem. Rev. 1990, 90, 969 ; C. N. R. Rao, B. Raveau, Transition Metal Oxides, VCH Publishers, New York, 1995. [115] D. Villemin, P. A. Jaffres, B. Nechab, F. Courivaud, Tetra. Lett. 1997, 38(37), 6581; M. Xuebing, F. Xiangkai, J. Mol. Cat. A: Chem. 2004, 208(1-2), 129; G. Potenzo, N. Cosimo-Francesco, M. Giovanni, L. G. Aldo, F. Carla, M. M. Antonietta, P. Pasquale, J. Mol. Cat., 1989, 53, 349. [116] T. J. Boyle, L. J. Tribby, T. M. Alam, S. D. Bunge, G. P. Holland, Polyhedron, 2005, 24, 1143. 88 390ºC with decomposition was identified as 30 (see Scheme 4.5) by analytical and spectroscopic studies. The complex is insoluble even in polar solvents but was soluble in DMSO. The 31P NMR spectrum recorded at ambient temperature in DMSO displayed a single resonance at 52.4 ppm, indicating phosphorus coordination to palladium. Interesting to note was the reasonably sharp 31P signal at room temperature, in contrast to all previous complexes discussed so far. Likewise, the 1H NMR spectrum displayed well separated phenyl proton signals at 7.5, 7.3 and 7.1 ppm, corresponding to ortho, para and meta groups respectively, The catechol ring protons could also be identified as a multiplet (6.0-6.2, m) and a doublet (5.9, 3JHH = 7.11 Hz). (COD)PdCl2 OH PPh2 OH ZrCl4/ Cs2CO3 2 Zr O O O O O O O O Ph2P Ph2P PPh2 PPh2 Pd Pd 9b 30 Scheme 4.5: Syntheses of trinuclear palladium-zirconium complex 30. These spectral observations strongly suggested that the complex must be less prone to undergo addition of solvents than the previously reported complexes, where solvent adducts were easily observable. It is assumed that the extra stability of the complex may arise from the di-palladium-zirconium trinuclear complex, but further evidence was required in order to support this assumption. The positive mode ESI-MS displayed pseudo- molecular ions peaks at m/e = 1716.9 (L4Pd2Zr+NaCl+Cs)+, 1662.17(L4Pd2Zr+Cs)+, 1530.27 (L4Pd2Zr+H)+, 1552.25 (L4Pd2Zr+Na)+, 842.93 (L2PdZrCl)+, 788.01 (L4Pd2Zr+2Na)2+ 777.02 (L4Pd2Zr+H+Na)2+, 765.5 (L4Pd2Zr+2H)2+, where is L = C19H15O2P. The pseudo-molecular ion peak at 842.93 corresponds to a dinuclear 89 . Bond lengths [Å] Bond angles [º] P1-Pd 2.223(1) P1-Pd-P2 99.78(1) O4-Pd 2.061(5) O3-Zr-O4 70.7(1) O2-Zr 2.296(1) C2-O3-Zr 121.94(1) O1-Zr 2.162(2) C9-O2-Zr 116.92(2) Zr-Pd 3.408(1) O3-Zr-O4 70.80(1) P2-Pd 2.230(1) O1-Zr-O2 71.20(1) Fig. 4.10A: Molecular structure of trinuclear palladium-zirconium complex 30 ( H-atoms are ommited for clarity, thermal ellipsoids at 50% probability), important bond lengths and bond angles are given in the table. palladium-zirconium complex. All other peaks are attributable to the tri-nuclear complex 30. The pseudo-molecular ion peak at 1662.17 showed additional weak 13C isotopic peak with a separation of 0.5 Da, which suggested the presence of a small amount of hexa- nuclear complex. Slow evaporation of diethyl ether into the DMSO solution of 30 produced red colored needle like crystals suitable for X-ray studies. The X-ray crystal structure revealed indeed that the discrete molecules of 30 (see Fig. 4.10A) are formed by assembly of four catechol phosphine units around one zirconium center with two phosphines ending each on a palladium atom. The formation of this highly unexpected compound can be rationalized in 90 view of the size of the template, which can accommodate eight oxygen ligands and thus promotes the formation of a neutral, trinuclear complex 30. The monoclinic unit cell (space group C2/n) contains two molecules of solvent (DMF) per molecule of the complex. Fig. 4.10B illustrates that the central zirconium is octacoordinated by the catecholate oxygens and adopts a distorted square antiprismatic geometry as was observed in [Zr(ETAM)4]4¯ (ETAM = N, N’ diethyl-2,3-dihydroxyterepthalamide) by Raymond et al.117 A closer look at the zirconium coordination sphere revealed that the four oxygen atoms (O1/2/3/4) form a square below the plane of this paper shown by dashed line in fig. 4.10B and the remaining four oxygen atoms (O1/2/3/4) forms a square above the plane of the paper shown with a continuous line in fig.4.10B. The catechol chelating ligands make Fig. 4.10B: Closer view of zirconium coordination sphere in complex 30. angles of 70.5-71.2º (O-Zr-O) with the central zirconium. The approach of the ligand to the zirconium center makes an angle of 116-121º between the catecholate plane(C8/9- O1/2-Zr) and zirconium with the central zirconium lying out of plane of the catechol rings by 0.17-0.26Å (e.g.O1-C8-C9-O2 x O1-Zr-O2). The bridging O-Zr bonds are approximately 0.12 Å longer than the non-bridging O-Zr bonds. The catecholic phenyl ring planes are tilted towards the central ZrO2 planes of each chelate ring by 4.4-5.5º. The two palladium atoms display a distorted square planar geometry and cap the zirconium centred ZrO8 polyhedraon. The P-Pd-P bite angle is ~99.7º, which does not differ by a significant extent from the other assemblies discussed in the present work. The bridging oxygen- [117] C. J. Gramer, K. N. Raymond, Inorg. Chem. 2004, 43, 6397. 91 palladium distances are between 2.05-2.06 Å. The two four membered Pd'O'2Zr vs. PdO2Zr rings intersecting at zirconium are almost perpendicular to each other with an angle of 85.8º. The Pd-Zr distance is 3.4 Å, considerably larger than the sum of covalent radii of the two atoms (2.73 Å), thus ruling out any metal-metal interaction. In an attempt to synthesize Cp2Zr(catphos)2, 2 equivalents of 9b (=catphos H2), 1 equivalent of (COD)PdCl2, 1 equivalent of Cp2ZrCl2 and excess of Et3N (5 equiv.) were dissolved in 15 ml of DME:THF (1:1) and stirred for 2 hours at room temperature. A dark red reaction mixture was filtered and the precipitate was dissolved in THF. This was diluted by adding excess of diethyl ether, and the precipitate formed was filtered and dried in vacuum for two hours. Microcrystals of the product were obtained from THF: Et2O solution at room temperature, which were dried in vacuum and characterized by NMR. The 31P NMR spectrum displayed a very broad singlet around 50 ppm. The 1H NMR in CDCl3 displayed signals corresponding to catechol phosphine moiety only, no Cp proton signals were detectable. These observations ruled out formation of Cp2Zr(cat.phos)2 type complex and indicated that the product formed is presumably of similar composition as 30. Detailed investigations are necessary in order to unambiguously assign the product. In summary, a trimetallic dipalladium-zirconium complex was synthesized with an octa- coordinated zirconium. Interesting to note is the formation of L4M2M' type of assembly even when 2:1 ligand to metal (Zr) ratio was employed (i.e. less than stoichiometric amount of the ligand L). This observation underlines the basic principle of supramolecular self-assembly, which prefers the formation of a thermodynamically more stable product over stoichiometric control. 4.2.6. Stoichiometry controlled syntheses of tri- and octanuclear palladium- yttrium complexes of 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (31 and 32): As lanthanides are a) oxophilic in nature and b) have found many applications in catalysis,118 they make interesting candidates as template for catechol phosphine complexes. Yttrium was chosen for the further studies as 1) it has comparable size to Gadolinium (Gd) and 2) complexes are diamagnetic which facilitates NMR spectroscopic [118] C. Benelli, D. Gatteschi, Chem. Rev. 1998, 27, 2369; M. Shibasaki, N. Yoshikawa, Chem. Rev. 2002, 102, 2187. 92 characterization.119 In this respect it was worth exploring possibilities of synthesizing yttrium complexes of the catechol phosphine 9b. O P Ph2 O Y Y Y Y O P Ph2 O O Ph2P O O Ph2P O O PPh2 O O PPh2 O O Ph2 P O O Ph2 P O OPd Pd Pd Pd DMF DMF DMF DMF OH PPh2 OH (COD)PdCl2 Et3N YCl3 (COD)PdCl2 0.5YCl3 Et3N Y+ OH O O O O OH O O Ph2P Ph2P PPh2 PPh2 Pd Pd Cl- 2 9b 31 32 3+ 3Cl Scheme 4.6: Syntheses of octanuclear palladium-yttrium cluster 31 and trinuclear palladium yttrium complex 32. Stoichiometric amounts of 9b, (COD)PdCl2, and YCl3 (2:1:1 respectively) were dissolved in DMF and excess of triethyl amine was added. A dark red suspension was obtained after 3 hours of stirring at room temperature. The suspension was filtered and kept at –28ºC overnight. A white precipitate of triethyl ammonium chloride was separated by decantation and the filtrate was evaporated to dryness in vacuum. Finally, the residue was dried at 120ºC for 4 hours to obtain a red powder in good yield (60%). The red powder decomposes at 345ºC. [119] P. W. Roesky, G. Canseco-Melchor, A. Zulys, Chem. Commun. 2004, 738. 93 The 31P NMR spectrum of the isolated product at ambient temperature in CDCl3 displayed a single resonance at 69.7 ppm. A proton NMR spectrum similarly displayed a single set of aromatic protons but the aliphatic diastereotopic CH2 protons are split into two groups and appear as broad doublets at 4.2-4.0 and 2.3-2.9 ppm. Solvent (DMF) signals were also observed. The NMR data are thus compatible with the presence of a bimetallic complex showing coordination of the phosphorus atoms of the catechol phosphine to the palladium metal and the oxygen atoms to the yttrium. The electron spray ionization spectra revealed the presence of a huge cluster molecule of composition [C152H120O16P8Pd4Y4]3+, a tetranuclear cation with one excess oxygen atom, presumably an oxygen centered cluster. Three chlorides can be added to obtain a neutral species, which is compatible with the analytical data. Fig. 4.11: 13C isotopic splitting of a triply charged species of 31. The positive mode spectrum displayed a triply charged pseudo-molecular ion peak at m/e = 1082.7 (L8Pd4Y4+OH)3+ (where L = C19H15O2P) (see Fig. 4.11). Another peak at m/e = 1646.8 (L8Pd4Y4+OH+LiF2)2+, with a 13C isotopic splitting of 0.5 Da certainly indicating a doubly charged ion, was observed. Though the source of LiF cannot be stated, it might come from the impurities in the solvent used, or the glass tube, or as an impurity in the spectrometer itself. Nevertheless, ESI-MS observation can be very well correlated with the crystal structure data discussed below, allowing to assign the product as 31. 94 Bond lengths [Å] Bond angles [º] Bond angles [º] O(1-8)-Y(1-4) 2.28-2.35 P1/3-Pd-P2/4 97.33-97.69 Y-O10-Y ~89.8-90.1 O10-Y(1-4) 2.46-2.47 Y1/1’-O10-Y2/2’ 90 O2-Y2-O4 69.66(1) O1/8/4/5-Pd1/2 2.07-2.09 O1-Y1-O6 68.7 (1) O1-Y1-O6 68.68(2) P(1-4)-Pd(1/2) 2.23-2.24 Y1-O3-Y2 97.0 Fig. 4.12: Molecular structure of the octanuclear palladium-yttrium cluster 31 ( H-atoms are omitted for clarity, thermal ellipsoids at 50% probability), important bond lengths and bond angles are given in the table. The formation of a complex [31]Cl3 was unambiguously ascertained by single crystal X- ray diffraction study. Suitable triclinic crystals (space group P1 bar) were grown from a concentrated DMF solution at room temperature. The data revealed that, complex [31]Cl3 crystallizes together with four uncoordinated solvent (DMF) molecules that were found to be trapped in the periphery. The whole cluster 31 comprises four dinuclear subunits, each formed by two catechol phosphine units, an yttrium atom and a palladium atom. The four subunits are arranged around a central µ4- bridging hydroxide anion. The central oxygen, 95 the yttrium atoms, and the peripheral palladium atoms are coplanar with the catechol phosphines in each subunit being stapled on each other. All together the molecule 31 is cationic, and three chlorides balance the charges to produce a neutral cluster [31]Cl3. Though the source of hydroxide cannot be firmly named, the product can be considered as arising from partial hydrolysis, with the water originating from DMF or an impurity in YCl3, and its presence seems to be necessary in order for the structure to be stable. The central µ4- bridging oxygen atom displays a perfect square planar geometry with Y- µ4O-Y angles of 89.8-90.1º and Y-O distances of ~2.4 Å. The unusual geometry of the central oxygen and the bond distance found are very commonly observed in oxygen bridged yttrium compounds.120 Each yttrium atom in 31 displays a square antiprismatic arrangement and coordinates to four catechol oxygens, two oxygens from neighboring units, one solvent molecule, and the central oxygen atom. The catechol chelates form (O- Y-O) angles of 68.6-69.5º, which are the smallest catechol-chelating angles observed so for in this chapter. The increased steric crowding around yttrium is likely to be responsible for the reduced angles observed. The Y-Y distances are found to be ~ 3.48 Å, and the Y- µ2O distances are 2.28-2.34 Å, which falls in the literature reported range (2.27-2.57 Å).121 All four palladium atoms display square planar geometry with two sites occupied by bridging oxygens and two phosphorus atoms completing the coordination sphere with a normal Pd- P distance of 2.23-2.24 Å. The Pd- µ2O distances are 2.07-2.09 Å and the P-Pd-P bite angle is found to be 97.3-97.6º, which is lower than that in zirconium complex (99.7º) but is nearly equivalent to that found in the dimeric bismuth complex 29 (97.0º). Rational evaluation of the above facts suggested that one yttrium atom should also be able to accommodate four catechol phosphine ligands and might then form similar assemblies as complex 30. The prerequisite for such a complex could be use of the starting materials in appropriate stoichiometry and strict exclusion of water. In an attempt to prove this hypothesis, four equivalents of the catechol phosphine were treated with one equivalent of yttrium trichloride and two equivalents of cyclooctadiene palladium dichloride. The reaction was carried in a similar manner as the synthesis of 31. The isolated crude product was dissolved in little DMF, and diethyl ether was added dropwise until a precipitate [120] P. Miele, J. D. Foulon, N. Hovnanian, L. Cot, J. Chem. Soc. Chem. Commun. 1993, 29; B. A. Vaartstra, J. C. Huffman, W. E. Streib, K. G. Caulton, J. Chem. Soc. Chem. Commun.1990, 1750; O. Poncelet, W. J. Sartain, L. G. Hubert-Pfalzgarf, K. Folting, K. G. Caulton, Inorg. Chem. 1989, 28, 263. [121] W. J. Evans, M. S. Sollberger, J. Am. Chem. Soc. 1986, 108, 6095; M. R. Buergstein, P. W. Roeky, Angew .Chem. Int. Ed. 2000, 39, 549. 96 started to form. An extra drop of DMF was added and the Schlenk tube kept for crystallization at room temperature. This procedure afforded a dark red powder which was dried at 70ºC for 4 hours and which melts at 197ºC. The 31P NMR spectrum in CDCl3 at room temperature produced two broad resonances at 70.8 and 60 ppm. The 1H NMR spectrum displayed two sets of well-separated catechol protons at 6.25, 6.17, 6.0, 5.93, 5.85, 5.7 and 5.6 ppm. Hydroxy protons were also detectable and appeared as broad singlet at 7.65 ppm, and the phenyl groups appeared as multiplet at 7.5-6.6 ppm. The aliphatic protons produced two broad doublets at 3.8-3.6 and 3.2-3.0 ppm. The 31P and 1H NMR signals of 32 were readily assigned by 31P, 1H HMQC Fig. 4.13: Positive mod e ESI-MS 13C isotopic splitting of a doubly charged species of 32. and 1H-COSY experiments. The above NMR observations indicated the presence of two different coordination modes of the catechol phosphines. The presence of free hydroxy groups indicated that the coordination of catecholate moieties to yttrium remained incomplete, thus displaying separate set of 31P and 1H NMR signals. Positive mode ESI-MS spectra displayed two pseudo-molecular ion peaks at m/e = 1529.06, 765.1, which corresponds to ions of composition [L4Pd2YCl+2H]+ and [L4Pd2YCl+3H]2+ respectively. Further pseudo-molecular ion peaks were observed at m/e 776.05, 786.01, 743.07 and 510.35, corresponding ions of composition [L4Pd2YCl+2H+Na]2+, [L4Pd2YCl+H+2Na]2+, (L2Pd+2H+Na)+ and [L4Pd2YCl+4H]3+ 97 respectively, where L = C19H15O2P. A pseudo-molecular ion peak at 1529.06 can be well assigned to (M-Cl)+, where M = 32. The second peak is a doubly charged pseudo- molecular ion peak at 765.1 (M-Cl+H)2+ with an 13C isotopic splitting of 0.5 Da. (see fig. 4.13). Other species observed at 776.05, 786.01 can be assigned to (M-Cl+Na)2+, (M- HCl+2Na)2+ respectively and a triply charged species at m/e 510.35 to (M-Cl+2H)3+. The ESI-MS negative mode experiment displayed two pseudo-molecular ion peaks at m/e 1527 with the composition [C76H62ClO8P4Pd2Y-2H]¯ that can be assigned for (M-Cl-2H)¯ and another at 719 (C38H32O4P2Pd1-H)¯ . The formation of a complex 32 was unambiguously ascertained by a single crystal X-ray diffraction study. Suitable crystals were grown from a DMF diethyl ether (1:1) mixture at room temperature. The monoclinic unit cell (space group P21/n) contains three molecules of solvent (DMF) per molecule of the complex. One of the solvent molecules is coordinating to the central yttrium via oxygen donor, the other forms a hydrogen bridge with the chloride anion, and the third is trapped in the periphery of the complex. The X-ray crystal structure revealed indeed that the discrete molecule of 32 (see Fig. 4.15) is formed by assembly of two inequivalent (independent) catechol phosphine-palladium blocks around one yttrium center. The complex is a zwitterionic species with the chloride balancing the charge to produce neutral 32. The chloride forms a hydrogen bridge with one of the catecholic hydroxides (H40-Cl 2.17 Å). The central yttrium atom displays a distorted antiprismatic geometry and is coordinated to eight oxygen ligands. In contrast to the zirconium complex 30, only seven of the catechol oxygens are coordinated to the yttrium and the coordination sphere is completed by one molecule of DMF. The catechol chelating angles (O-Y-O: 68.2-69.0º) are similar to those in 31. The non-bridging Y-O bonds are shorter (2.28-2.30 Å) than the bridging yttrium oxygen (2.35-2.37 Å) bonds. The oxygen atom O40 that carries a proton is very weakly coordinating to the yttrium and displays the longest Y-O distance of 2.44 Å observed in 32. The palladium atoms display a distorted square planar geometry with very different P-Pd-P bite 98 Bond lengths [Å] Bond angles [º] Y-O1D 2.346(4) P1-Pd1-P2 102.6(1) Y-O40 2.435(5) P3-Pd2-P4 98.55(1) Y-O21 2.281(4) O20-Y-O21 68.4(1) Y-O20 2.358(4) O1-Y-O2 69.19(1) Y-O2 2.307(4) Y-O39 2.371(4) H40-Cl 2.176(3) Fig. 4.15: Molecular structure of palladium-yttrium complex 32 (H-atoms except H59 & H40 are omitted for clarity, thermal ellipsoids at 50% probability), important bond lengths and bond angles are given in the table. angles. The first block displays a considerably small P3-Pd2-P4 angle of 98.5º which can be attributed to the fact that the free and weakly coordinating hydroxy groups enable the phosphorus donors to come closer and thus reduce the bite angle. The other block displays a P1-Pd1-P2 angle of 102.6º. The two four membered YO2Pd rings with a common yttrium are almost perpendicular to each other (interplanar angle of 83.8º). The formation of 32 can be attributed to the oxophilicity and the size of the template, which can 99 accommodate eight oxygen ligands and thus promotes the formation of a trinuclear complex. In summary, an octanuclear palladium-yttrium cluster 31 stabilized on a central µ4-oxygen atom was produced when 9b:LPdX2:YX3 [L = (COD), X = Cl] were employed in 2:1:1 ratio. The cluster 31 displayed a P-Pd-P bite angle of 97º, which is smallest among all complexes discussed in this chapter. Except the central one, all oxygen atoms are µ2- bridged and are equidistant from the metals and could not be differentiated as terminal and bridging ones, as in other complexes. Changing the ratio of 9b:LPdX2:YX3 to 4:2:1 gave a trinuclear dipalladium-yttrium complex 32. Interestingly, complex 32 is zwitterionic in contrast to the all other reported complexes in this chapter being neutral. 4.3. Investigations on the catalytic behavior of selected metal complexes: In section 4.2.2 the occurrence of equilibrium reactions illustrated in Scheme 4.7 was confirmed. The DFT calculation performed at the B3LYP/3-21g* level of theory suggested that formation of a macrocyclic complex with trans-configuration at palladium (see fig.4.14) is favored by 3.6 kcal/mol over coordination of formamide to tin. The outcome of these studies lead to conclude that the found molecular structure is most likely to represent that of the transient complex 27a. O O Ph2 P O O Ph2 P SnR2 Pd 26a/b 26a:R = Cl, 26b:R = Me O O Ph2 P O O Ph2 P SnR2 Pd 27 DMF 27a:R = Cl, 27b:R = Me DMF DMF Scheme 4.7: Equilibrium reactions demonstrating hemilabile behavior of complexes 26a/b. In view of the easy displacement of catechol oxygens from palladium, the complexes 26a/b can be seen as palladium complexes with a hemilabile ligand that can switch between tetradentate O2P2- and bidentate P2- coordination. Easy replacement of the solvent molecules by other donors is very much expected, and hence a similar catalytic activity as 100 for other palladium-phosphines complexes is anticipated.122 Palladium complexes are effective catalysts in the coupling reaction between terminal alkynes and aryl halides (Sonogashira coupling).123 A palladium bis-catechol phosphine complex similar to that of 26a was recently employed in Sonogashira coupling reaction.124 In order to demonstrate the potential of 26a in catalysis, the Sonogashira125 C-C coupling reaction was selected as a model reaction for further catalytic investigations. Phenyl acetylene (0.44 mmol), copper iodide (0.056 mmol) and 3 mol% of 26a (0.033 mmol) were added to a solution of 4-iodonitro-benzene (0.44 mmol) in 15 ml of triethyl amine/DMF (2:1). The mixture was stirred for 20 hours at room temperature. n-Hexane (20 ml) was then added and the precipitate filtered off. The filtrate was evaporated to dryness and the dark solid was purified by column chromatography using neutral silica as stationary phase and dichloromethane/hexane as eluent to give 94% of the coupled product 4-nitrophenyl-phenylacetylene (See Scheme 4.8). The isolated product was characterized by 1H NMR. + I NO2 3 mol.% Pd-Sn complex CuI/Et3N DMF NO2 Scheme 4.8: Coupling of phenylacetylene to 4-iodonitro benzene with 26a/b as pre-catalyst The corresponding reaction using 26b as pre-catalyst was performed under identical conditions. In order to monitor the status of the reaction, 31P NMR spectra were recorded after 1, 5 and 20 hours. All spectra displayed a single resonance at 76 ppm, confirming that 26b remained intact during the reaction. After 24 hours, all volatiles were evaporated in vacuum. The residue was extracted with 10 ml of toluene. The suspension formed was allowed to settle for 15 minutes and the supernant toluene layer was decanted. The filtrate was evaporated to dryness and the dark solid was purified by column chromatography using neutral silica as stationary phase and dichloromethane/hexane as eluent to give 90% of the coupled product 4-nitrophenyl-phenylacetylene. The residue was dried in vacuum [122] S. Braese, A. de Meijere, Metal-catalyzed Cross-coupling Reactions (Hrsg. F. Diederich, P. J. Stang), Wiley-VCH, Weinheim, 1998, p. 99. [123] C. C Tzschucke, C. Markert, H. Glatz, W. Bannwarth, Angew. Chem. Int. Ed. 2002, 41, 4500. [124] N. T. Lucas, A. M. McDonagh, I. G. Dance, S. B. Colbran, D. C. Craig, Dalton Trans. 2006, 680. [125] K. Sonogashira, Compreh. Org. Synth. 1991, 3, 551. 101 and dissolved in 5 ml of DMF. The 31P NMR spectrum of this solution still showed the broad signal of 26b at 76 ppm as the only visible resonance. The residue of 26b obtained after solvent evaporation was recovered and reused for further catalytic transformations. After the same reaction time and under same condition as the first batch the coupling product was produced in 75% yield, which was worked up according to the procedure mentioned for the first cycle. The 31P NMR of the residue still showed the resonance of 26b as the only visible product. The same cycle as above was repeated for the third time and the catalyst was reused for further transformations. Although the coupling product was observed in the proton NMR, the yield of this cycle was not determined. The above experiments clearly demonstrated the potential of 26a/b as a C-C coupling catalyst. 4.4. Conclusions: The syntheses of discrete di or polynuclear complexes containing hard and soft transition metal by self-assembly of simple metal precursors and bifunctional phosphine-catecholate ligands have been demonstrated. The most striking feature of the synthesized complexes is the presence of µ2-bridging oxygen atoms which bridge the two metal centers. The coordination of the soft palladium center by µ2-briding catecholate oxygen atoms that are easily displaced by donor solvents can be viewed in terms of hemilabile coordination. In this respect complexes 26a/b mimic the behavior of complexes containing a supramolecular bis-phosphine ligand which is formed by the assembly of two phosphine- catecholate fragments on a main-group metal template and can switch between tetra dentate -O2P2 and bidentate -P2 coordination. The experimental findings allow to state that the coordination geometry of the template center and its size has great impact on the assembly process. A small template like gallium Table 4.1: Template vs. properties Template(E) Cov.radii Å No. Ligands O-E termi.Å O-E bridg.Å Ga 1.25 5 1.898 2.027 Sn 1.4 6 2.033 2.171 Zr 1.45 8 2.145 2.273 Bi 1.52 6 2.173 2.448 Y 1.62 8 2.294 2.356 102 can accommodate only five donor atoms (see table 4.1), whereas larger templates like zirconium and yttrium can accommodate as many as eight donor atoms. In all complexes, the µ2-briding oxygen-E bonds were found to be longer than the terminal oxygen-E bonds. The oxygen-E bond lengths (bridging and terminal) vary according to the size of the E, understandably, as the size increase the bond length increases (see Table 4.1). On the other hand, changing the transition metal from palladium to platinum had negligible effects on the properties of the complexes. A stoichiometry controlled synthesis of an octanuclear palladium-yttrium cluster and a tri-nuclear palladium-yttrium complex was also demonstrated. Bite angle is an important factor in catalysis and can control regio- or stereo selectivity. Using the self-assembly tool, it was demonstrated that variable bite angles could be achieved using a single step synthetic protocol. Diagram 4.1 shows the relation between covalent radii of group III, IV and V elements versus the P-Pd-P bite angle in the complexes 25, 26a and 29a which all carry chloride substituents and hence can be rationally compared. Covalent radii vs. Bite angle 96 97 98 99 100 101 102 1.2 1.25 1.3 1.35 1.4 1.45 1.5 1.55 Covalent radii [Å] B ite an gl e [º] Ga Sn Bi Diagram 4.1: covalent radii of main group elements vs. P-Pd-P bite angle in complexes 25, 26a, and 29 103 As can be seen, the bite angle decreases with increasing size of the main group element. It is postulated that the above trend can be utilized to predict the bite angles obtained by using other main group elements as templates. The transition metals zirconium (30) and yttrium (31) have different coordination numbers and hence displayed a different behaviour, giving P-Pd-P bite angles of 99.7 and 97-99º, respectively. The rational ligand design allowed to synthesize a great variety of complexes wherein hard acids react with the hard oxygen donors and the soft phosphine donors coordinate to the soft acids. The products are distinguished from known heterometallic complexes of phosphinoalcohols in requiring neither the dedicated syntheses of a polydentate chelate ligand,126 nor the need for introducing the metal atoms in separate reaction steps.127 Finally, the hemilabile nature of the synthesized complexes promoted to study the catalytic behavior of these complexes and the first experimental proof of their catalytic potential was demonstrated by the application of 26a/b in the Sonogashira C-C coupling reaction (section 4.3). [126] A. Kless, C. Lefeber, A. Spangenberg, R. Kempe, W. Baumann, J. Holz, A. Boerner, Tetrahedron, 1996, 52, 14599. [127] G. S. Ferguson, P. T. Wolczanski, J. Am. Chem. Soc. 1986, 108, 8293. 104 5. Some considerations on stereochemical aspects in bisphosphine complexes with octahedral tin templates 5.1. Introduction: Objects or molecules that exist as pairs of enantiomers which are non-superimposable mirror images of each other are regarded as chiral. The existence of chirality in nature is of utmost importance. Let us take a simple example of limonene, which exists in two different isomeric forms, namely, the R-(+) or S-(–) isomers, with the same molecular formula but with different spatial arrangements (see Fig. 5.1).128 Certainly the two forms have different characteristics: R-limonene has orange odor whereas S-limonene has lemon odor. In medicinal and pharmaceutical sciences, chiral discrimination is an important subject, because many drugs consist of chiral molecules, and often only one of them carries a certain desired chemical activity while the other often causes unwanted side effects. An example is the anti-emetic activity of one of the enantiomers of thalidomide while the other can cause death.129 R-(+) limonene S-(-) limonene Fig. 5.1: Orange and lemon odor of R-(+) and S-(-) limonene, respectively. [128] L. Friedman, J. G. Miller, Science, 1971, 172, 1044. [129] T. Nakanishi, N. Yamakawa, T. Asahi, N. Shibata, B. Ohtani, T. Osaka, Chirality, 2004, 16, S36. 105 Although nature simply generates chiral molecules and assemblies in enantiopure form, designing and enantioselective synthesis of chiral entities presents an active challenge to synthetic chemists. As a rule of thumb, chirality can be induced in a molecule via chiral precursors, or via achiral precursors which assemble to give a chiral product. Importantly, highly symmetric architectures, such as the quartz minerals present in nature, are generated from the self-assembly of identical achiral subunits. Inspired by this fact, chemists have created chiral assemblies that can act as reaction vessels130 for storage and recognition of ions 131 or molecules,132 and for various chemical transformations.133 A selective synthesis of desired architectures is another area of high interest. At this application end of chirality, chemists around the world have developed methodologies which enable them to synthesize the desired architectures.134 5.1.1. Stereochemistry in octahedral complexes with two chelating ligands: Chirality in inorganic chemistry often deals with coordination compounds.135 The metal- ligand interactions are generally kinetically more labile and dynamically more flexible than covalent interactions. The two enantiomers of an enantiomeric pair are usually separated by a very low energy barrier, which results in a spontaneous interconversion process called racemization. Isomerization of the racemates to give different diastereomers is another important process. The energy barriers between the individual enantiomers and diastereomers determine if the separation of individual isomers is in principle possible or not. The above mentioned stereoisomers can racemize mainly by two pathways, 1) intermolecular or dissociative racemization, 2) intramolecular racemization. Now, in octahedral tris-chelate complexes the latter can occur via two mechanisms, namely a) Bailar twist, b) Ray-Dutt twist. 136 Both mechanisms proceed via trigonal prismatic transition states. Though it is difficult to predict which mechanism will be followed, [130] N. Takeda, K. Umemoto, K. Yamaguchi, M. Fujita, Nature, 1999, 398, 794. [131] A. Caneschi, A. Cornia, A. C. Fabretti, S. Foner, D. Gatteschi, R. Grandi, L. Schenetti, Chem. Eur. J. 1996, 2, 1379; B. Hasenknopf, J-M. Lehn, B. O. Kneisel, G. Baum, D. Fenske, Angew. Chem. Int. Ed. 1996, 35, 1838; J. S. Fleming, K. L. V. Mann, C. A. Carraz, E. Psillakis, J. C. Jeffery, J. A. McCleverty, M. D. Ward, Angew. Chem. Int. Ed. 1998, 37, 1279. [132] D. Fiedler, D. H. Leung, R. G. Bergman, K. N. Raymond, J. Am. Chem. Soc. 2004, 126, 3674. [133] D. Fiedler, D. H. Leung, R. G. Bergman, K. N. Raymond, Acc. Chem. Res. 2005, 38, 349; T. Kusukawa, M. Fujita, J. Am. Chem. Soc. 1999, 121, 1397. [134] A. von Zelewsky, Stereochemistry of Coordination Compounds, 1996, Wiley, New York. [135] G. Seeber, B. E. F. Tiedemann, K. N. Raymond, Top. Curr. Chem. 2006, 265, 147. [136] D. L. Kepert, Prog. Inorg. Chem. 1977, 23, 1. 106 theoretical studies have indicated that delicate ligands with small bite angles will prefer Bailar twist, whereas those with large bite angles favor the Ray-Dutt mechanism. 137 B A A B a a A B A B a a C2v C2h a A A a B B a B B a A A C2 C2 a B A a A B a A B a A B a A A a B B a B B a A A C2 C2C1C1 71 72 73 74 75767778 Diagram 5.1: Stereoisomers in M(A=B)2a2 type octahedral complexes. As the present work mainly deals with bis-chelating catechol phosphine ligands with an octahedral metal center, it is of atmost importance to know their stereochemistry. Consider a coordination of two catechol phosphine units with an SnCl2 unit. Diagram 5.1 displays all theoretically possible stereoisomers in complex 26a, where “A=B” represents the stereochemically inequivalent oxygen atoms of a catechol phosphine unit and “a” represents the chloride ligands. In total eight isomers (71-78) of which six form three chiral pairs 73/74, 75/76, 77/78 with C2, C2 and C1 symmetry, respectively, are possible. In complex 26a, the presence of the stereoisomers 72, 73 and 75 can be ruled out as the oxygen atoms (A) coordinating to palladium are trans to each other. The remaining 5 stereoisomers with 2 chiral pairs (73/76-C2 and 77/78-C1) might be observed. As mentioned in sect. 4.2.2, the CDCl3 soluble material may possibly contain a mixture of stereoisomers 77 and 78. Clear differentiation of each isomer was impossible as medium- fast exchange between all isomers resulted into line broadening. Having understood the importance of chirality and considering (chapter 3 and 4) that the tin centered complexes can be created in a single step via self-assembly, it is envisioned to [137] A. Rodger, B. F. G. Johnson, Inorg. Chem. 1988, 27, 3061. 107 explore mainly two aspects in this chapter, namely 1) variation in the stereochemistry at tin center by employing (A=B)2ab type ligand coordination, where A=B is the chelating catechol ligand and “a” is a methyl group and “b” a chloride substituent, 2) employing catechol phosphines with chiral phosphorus centers. The catechol phosphine 9f is presumed to be a good candidate for such a modification. Now, the (A=B)2ab type coordination at tin can possibly produce 11 isomers with 5 chiral pairs134 i. e. in a complex 33a (see following section). But assuming that the cis-disposition of the catechol oxygens “A” is a necessary and sufficient condition, four isomers can be ruled out and only the remaining seven (80-86) should be theoretically observable (see Diagram 5.2). B A A B a b a A A b B B a A A b B B a A B b A B C1 C1 a B A b B A a B A b A B a A B b B A C1 C1C1 80 81 82 83 848586 Cs C1 Diagram 5.2: Theoretically observable Stereoisomers of complex 33. The chiral ligand 9f on complex formation with (COD)PdCl2/Cl2SnMe2 can produce the diastereoisomers with the backbones 87-91 which are further differentiated by the possibility to accommodate phosphine ligands with R and S configuration. The diastereoisomer 87 can thus exist as RR/SS-C2 or RS/SR-Cs isomers. Assuming that 88 has a clockwise rotational axis ∆, and 89 has an anticlockwise rotational axis Λ, they can produce altogether 20 stereoisomers of which 16 form 8 pairs (refer to Diag. 5.3). Although the complex 34b can produce all these diastereoisomers, only a very few were detectable (refer to sect. 5.2.2). In a likewise manner a complex 34a featuring two distinguishable monodentate ligands a + b can produce 28 diastereoisomers (12 chiral pairs) based on the seven stereoisomers presented in diagram 5.2. 108 B A A B a a a A A a B B a A A a B B a A B a A B C2 C1 a B A a A B C1 87 88 89 90 91 C2v C2 Diagram 5.3: Representation of diastereoisomers of complex 34. 5.2. Results and discussion: 5.2.1. Chiral tin templated assemblies of 3-[(Diphenylphosphanyl)-methyl]- benzene-1, 2-diol (33): Mixing of 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (9b), MeSnCl3, (COD)PdCl2 and triethyl amine in a 2:1:1:2.5 ratio in 20 ml of dry dimethyl formamide OH OH PPh2 9b 2 (COD)PdCl2 MeSnCl3, Et3N O O Ph2 P O O Ph2 P Sn Me Pd 33a Cl Scheme 5.1: Synthesis of tin centered chiral palladium-tin complex 33a. Diastereoisomers of 87 Diastereoisomers of 88/89 Pairs in 88/89 Diastereoisomers in 90/91 Pairs in 90/91 RR ∆RR ∆RR RS/SR ∆RS ∆RS ∆SR ∆RR/ ΛSS-C2 ∆SR ∆RR/ ΛSS-C1 ∆SS ∆SS/ ΛRR-C2 ∆SS ∆SS/ ΛRR-C1 ΛRR ∆RS/ ΛSR-C1 ΛRR ∆RS/ ΛSR-C1 ΛRS ΛSR/ ∆RS-C1 ΛRS ΛSR/ ∆RS-C1 ΛSR ΛSR ΛSS ΛSS 109 and stirring the solution for 3 hours at room temperature produced a dark red suspension which was filtered through celite (Scheme 5.1). The filtrate was dried in vacuum and the residue redissolved in DMF. Upon dilution with excess diethyl ether, the precipitate formed again and was filtered and dried in vacuum at 70ºC for 4 hours. The complex 33a was thus isolated in good yield, melting at 255ºC with decomposition. Suitable crystals for single crystal X-ray diffraction were grown from a concentrated DMF: diethyl ether (2:1) mixture at room temperature. The complex 33a crystallizes in a monoclinic unit cell in space group P21/n with one molecule of solvent (DMF) per molecule of complex. The units of 33a are linked together by weak hydrogen bonds between the chloride on tin and phenyl hydrogens of neighboring complexes in a 1D chain- like motif. The tin atom displays a distorted octahedral coordination by a chloride, a methyl and four oxygen ligands (see Fig. 5.6). The non chelating substituents make a C- Sn-Cl angle of 106.6º that is considerably smaller than the 114º C-Sn-C angle observed in 26b, and slightly larger than the Cl-Sn-Cl angle of 104º in 26a. No disorder of the chloride and methyl substituents was observed. The Sn-C bond distance in 33a is 0.10 Å longer than in 26b. The electronegativity difference between the methyl and chloride group are likely to be responsible for the observed bond angle and bond distance variation in 33a compared to that in 26a, 26b (Bent’s rule). The two catechol planes intersect at tin with an angle of 88.6º. The palladium atom displays a distorted square planar geometry with a P- Pd-P bite angle of 98.8º which is comparable to that observed in 26a (98.8º) and 26b (99.4º). The SnO2Pd ring is planar with an O1-Pd-O3 angle of 78.7º. 110 Bond lengths [Å] Bond angles [º] O3-Sn 2.207(5) P1-Pd-P2 98.87(7) O4-Sn 2.083(5) O1-Sn-O2 77.41(2) O3-Pd 2.081(5) O1-Sn-O3 73.57(2) P1-Pd 2.255(2) Cl-Sn-C3 106.6(2) Cl-Sn 2.358(3) O1-Pd-O3 78.78(2) C3-Sn 2.227(6) Cl-Sn-O2 92.27(2) O1-Sn 2.192(1) O3-Sn-O4 77.32(1) O2-Sn 2.075(1) O2-Sn-O4 170.53(1) O1-Pd 2.070(1) P2-Pd 2.243(1) Fig. 5.6: Molecular structure of the chiral complex 33a; (H-atoms omitted for clarity, thermal ellipsoids with 50% probability), important bond lengths and bond angles are given in the table. The positive mode electron spray ionization mass spectra displayed two distinct pseudo- molecular ion peaks at m/e = 852.9 corresponding to a cation (33a-Cl)+, and at 894.9, corresponding to a cation (33a+Li)+. 111 [ppm] 80 75 70 65 60 55 [ *1e 6] 0 10 20 30 40 50 chikkali070201-SH329.108 2 1 C:\Bruker\TOPSPIN chikkali Fig. 5.5: 31P NMR of complex 33a/33b at 303 (bottom) and 203K (top). The 31P NMR spectrum of 33a in DMF-d7 at ambient temperature displayed a single broad resonance at 69.6 ppm (bottom trace in Fig. 5.5). At the same time, the 119Sn 1H HMQC NMR spectrum displayed a broad 119Sn singlet at –327 ppm with tin satellites to the CH3 protons. The 31P NMR signal sharpens eventually upon cooling to 203ºK and the single broad signal split into four resonances which make up two AB spin systems with chemical shifts at 78.2, 76.4 ppm and 2JP-P of 45 Hz, and at 72.8, 53.8 ppm with 2JP-P 22 Hz, respectively (top trace in Fig. 5.5). A 31P NOESY experiment revealed the presence of intermolecular and intramolecular exchange between the four phosphorus sites as shown in Fig. 5.7. As can be seen in the NOESY spectrum with the longer mixing time, all four phosphorus sites displayed mutual correlation peaks indicating intermolecular and intramolecular exchange processes taking place (Fig. 5.7, right). When the mixing time was shortened the exchange was restricted to the intramolecular interconversion of the signals at 72.8, 53.8 ppm. In this spectrum, the absence of any exchange correlations between the nuclei of the second AB spin system suggests that this isomer is configurationally more stable and the interconversion of the two phosphorus sites requires first isomerization to the other diastereomer. In a likewise manner, the 1H NMR spectrum at 203ºK displayed two singlets at 0.9 and 0.7 ppm (2JSn-H 105, 99 Hz respectively) corresponding to the Sn-CH3 protons of two different products. Integrating the 31P and 1H peaks disclosed that the proton signal at 0.7 ppm corresponds to the AB spin system at 78.2 112 and 76.4 ppm and the proton signal at 0.9 ppm to the 72.8/53.8 AB spin system. All the proton phosphorus correlations were established from a 1H 31P HMQC experiment. 31P NOESY in DMF, 213K Me(Cl)Sn(2.3-catCH2PPh2)Pd F2 [ppm] 80 75 70 65 60 55 F1 [p pm ] 80 75 70 65 60 55 31P NOESY in DMF, 213K 31P NOESY in DMF, 213K Me(Cl)Sn(2.3-catCH2PPh2)Pd F2 [ppm] 80 75 70 65 60 55 F1 [p pm ] 80 75 70 65 60 55 31P NOESY in DMF, 213K Fig.5.7: 31P{1H} NOESY Spectra of 33a recorded with different mixing times (right: 40ms. left: 12,5ms.) for chemical exchange. Careful evaluation of the low temperature NMR data showed the presence of two of the three possible enantiomeric pairs. There was no clear evidence for the presence of the Cs symmetric isomer. Further, no clear evidence for the Pd-O bond breaking was obtained although the isomer with upfield resonance could possibly be 33b. O O Ph2 P O O Ph2 P Sn Me Pd 33b Cl DMF Piecing together the NMR, ESI-MS and crystal structure results allow to state that, a chiral palladium-tin complex 33a was synthesized in good yields. Low temperature NMR experiments proved very useful in order to evaluate that the product formation occurred stereoselective in the sense that not all possible stereoisomers were observed although the nature of all isomers present could not be unambiguously established. 113 5.2.2. Tin templated chiral assemblies of 3-{[Phenyl- (2,4,6-trimethyl-phenyl)- phosphanyl]-methyl}-benzene-1, 2-diol (34): The chiral catechol phosphine 3-[(Mesitylphenyl phosphanyl)-methyl]-benzene-1, 2-diol (9f) was synthesized in two simple steps as reported in chapter 2. Appropriate amounts (2:1:1) of 9f, (COD)PdCl2, and dimethyl tin-dichloride were dissolved together with an excess of triethyl amine in DMF, and the mixture stirred at room temperature. The reaction progress was monitored by 31P NMR and showed complete conversion in 3 hours. The reaction mixture was filtered and the Schlenk tube was kept at –28ºC overnight. White needles of triethyl ammonium chloride formed were separated by filtration. The filtrate was diluted by adding excess diethyl ether and the precipitate formed filtered off and dried at 70ºC in vacuum for 6 hours. The dark red powder was isolated in moderate yields (70%) and melts at 230ºC with decomposition. OH OH PPhMes 9f 2 (COD)PdCl2 Me2SnCl2, Et3N O O PhMes P O O PhMes P Sn Me Pd 34 R 34a: R = Cl, 34b: R = Me Scheme 5.2: Synthesis of chiral palladium-tin complex 34. Fig. 5.3 displays a solid-state 2D 31P CP/MAS J-resolved spectrum of the product at a spinning speed of 15.000 kHz. The spectrum shows signals attributable to an AB spin system with chemical shifts at δ = 57.4 and 55.4, and a 2JPP coupling of 40 Hz. As the chiral phosphorus atoms can have RR, SS or RS/SR configuration, chemical inequivalence and the observance of an AB spin system is possible. A 119Sn CP/MAS spectrum displayed two signals at –207 and –308 ppm. The 119Sn CP/MAS NMR data indicate that the sample must consist of a mixture of two components: the signal at –207 is attributable to a tin center carrying two methyl substituents, i.e. complex 34b (see scheme 5.2 and the tin NMR data in sec. 4.2.2.2), and the peak at –308 ppm can be assigned to a tin center carrying a methyl and a chloride substituent in (34a). This interpretation was further confirmed by the results of elemental analysis. 114 (Mes-Ph-2,3-catphos)2PdSnMeCl 31P 2D CP-MAS J-resolved rot. 15.000 kHz F2 [ppm] 100 80 60 40 20 0 F1 [p pm ] 0.2 0.1 0.0 Fig. 5.3: Solid state 31P CP/MAS 2D NMR spectra of 34. Positive mode ESI-MS spectra displayed two peaks at m/e = 937.08 and 994.14. The peak at 937 corresponds to a cation of composition (L2PdSnMe)+ generated by taking off either a methyl group or a chloride resp., from 34a,b. The peak at m/e = 994 is attributed to a cationic species (L2PdSnMeCl+Na)+ generated by attachment of a sodium ion to 34a. No definite proof for the presence of 34b was thus obtained from the ESI-MS experiment. Suitable crystals for single crystal X-ray diffraction were grown from DMF, diethyl ether 1:1 mixture at room temperature. The X-ray diffraction study of one of the monoclinic crystals (space group P21/n) revealed the presence of complex 34a (Fig. 5.4). The discrete molecules are linked together via weak Cl-H intramolecular hydrogen bridges between two units, forming zigzag, head to tail linked chains. The crystal structure disclosed that the tin atom carries one chloride and one methyl substitutent instead of two methyl groups, along with two catechol phosphine units, and displays a distorted octahedral geometry. The Sn- Cl distance of 2.34Å is close to that found in 26a (2.39 Å), 34a (2.35 Å) and is also in accordance with the literature reported Sn-Cl distance (2.30 Å) in phenoxy- cholorostannates.138 The two-catechol planes intersect at tin with an angle of 84.7º. [138] H. Jolibois, F. Theobald, R. Mercier, C. Devin, Inorg. Chim. Acta. 1985, 97, 119. 115 Bond lengths [Å] Bond angles [º] Bond angles [º] O1-Sn 2.248(4) P1-Pd-P2 104.64(5) C27-P1-Pd 118.43(2) O2-Sn 2.083(5) O1-Pd-O3 80.23(2) Cl-Sn-O4 90.86(1) Cl-Sn 2.344(2) Cl-Sn-C3 105.91(1) Cl-Sn-O3 159.48(1) P1-Pd 2.290(2) O3-Sn-O4 76.63(2) P1-Pd-O1 88.29(1) O1-Pd 2.081(4) C13-O2-Sn 114.2(4) C3-Sn-O2 91.3(2) C3-Sn 2.214(5) C12-O1-Sn 108.8(3) C3-Sn-O1 159.39(2) O3-Sn 2.277(1) O1-Sn-O2 75.57(2) O4-Sn 2.066(1) O1-Sn-O3 72.65(1) O3-Pd 2.081(1) O2-Sn-O4 162.95(0) P2-Pd 2.285(1) O1-Sn-C3 159.38(2) Fig. 5.4: Molecular structure of 34a; (50% thermal ellipsoids, H-atoms omitted for clarity), important bond lengths and bond angles are given in the table. The palladium atom displays a distorted square planar geometry with the two bridging oxygens and the two phosphorus atoms completing the coordination sphere. The Pd-P bond distance of 2.28-2.29 Å are slightly elongated with respect to 34a (2.25 Å). The P- Pd-P bite angle of 104.6º in complex 34a is the largest bite angle of all complexes discussed in chapter 4 and 5. The increased steric bulk of the mesityl groups at the phosphorus atoms is presumably responsible for these features. The two tetrahedrally coordinated phosphorus atoms dispose a trans-arrangement of the phenyl and mesityl substituents in order to have minimum steric hindrance. Thus, only one stereoisomer (34a) 116 out of 28 as indicated in sect. 5.2.1 was found in the measured crystal. It could be that other stereoisomers might have crystallized as well but the crystal picked up for measurement was accidentally one of 34a. The 31P NMR spectrum of the isolated product in DMF-d7 at room temperature displayed a broad singlet at 63.8 ppm, suggesting the presence of a dynamic equilibrium between different diastereoisomers. Cooling the sample to 243ºK split the 31P line into two lines that appeared at 62.1 and 65 ppm. The 1H, 119Sn HMQC experiment showed two correlation signals at –202 and –206 ppm that correspond to tin bound methyl groups (see Fig. 5.2, right trace). [ppm] 75 70 65 60 55 50 Nutzer chikkali SH-359 in dmf-d7, nach FK-NMR 213K chikkali070509-SH359.122 32 1 C:\Bruker\TOPSPIN chikkali Nutzer chikkali SH-359 in dmf-d7, nach FK-NMR 243K F2 [ppm] 0.6 0.4 0.2 F1 [p pm ] - 19 5 - 20 0 - 20 5 - 21 0 F1 [p pm ] - 19 5 - 20 0 - 20 5 - 21 0 Fig. 5.2: 31P NMR of 34 at 213K (left) and 1H, 119Sn HMQC (right) plot of complex 34 at 243K. Further cooling down to 213ºK led to the appearance of additional 31P NMR signals at 72, 64, 60, 59 and 50 ppm. Two singlets at 64.8 and 61.3 ppm were observed, whereas the signals at 64.2 and 59.2 were found to be an AB spin system with a JPP coupling of 32 Hz. Another pair of broadened lines was tentatively assigned to a second AB spin system with the chemical shifts at 72.4, 59.8 ppm and an unresolved coupling (see fig. 5.2). A very weak singlet at 50 ppm which was not unequivocally assigned was also observable. The two broad singlets can be attributed to the C2 symmetric enantiomeric pair of the dimethyl tin complex 34b. The two AB spin systems can be tentatively assigned to 34a although the presence of C1 isomers of 34b could not be completely ruled out. 117 Warming up to 333ºK led to irreversible decomposition of the complex, producing several new species which were not further characterized. Thus, the NMR experiments showed the presence equilibrium mixture of diastereoisomers of 34a and 34b in solution even at lower temperatures indicating a very low energy difference between the diastereoisomers. In summary, complex 34a can have theoretically 28 diastereoisomers (12 chiral pairs + 4 meso isomers) and 34b 19 diastereoisomers (8 chiral pairs + 3 mesoisomers). The solid state NMR spectrum of an isolated sample suggested the presence of a mixture of 34a and 34b. A diastereoselective reaction was achieved. The major isomers of 34b are found to be homochiral ones (either RR or SS). Though the crystal structure displayed 34a as one of the stable diastereoisomers, its formation is mechanistically unclear. Hence it is necessary to repeat the experiment to avoid formation of 34a, and to get unequivocal results on the diastereoselectivity. 5.3. Conclusions: The complex 33a was synthesized in good yield and was characterized by NMR, ESI-MS and a single crystal X-ray diffraction study. The crystal displayed the presence of one of the stereoisomers 81 or 82 (depending on the sense of the rotational axis through chiral center) (see Diag. 5.2) with planar arrangement of O1/3, C3 and Cl and axially situated O2/4 atoms. Low temperature NMR experiments proved very useful in order to observe the existence of at least two possible stereoisomers of 33a. A mixture of chiral complexes 34a/b with three chiral elements was synthesized and obtained in good yield utilizing the established one pot synthetic methodology. The solid state NMR of the crystals of 34 showed the presence of mixture of 34a and 34b, suggesting that accidental replacement of one methyl group had occurred during the synthesis. The solution NMR showed the presence of diastereoisomers of 34b with broad singlets at 64.8 and 61.3 ppm. At least two diastereoisomers of 34a could also be observed at 64.2, 59.2 and 72.4, 59.8 ppm as AB spin systems indicating inequivalent phosphorus atoms. Crystal structure measurements revealed presence of one of the diastereoisomer of 34a (either 81or 82) with ∆RR or ∆SS configuration (see Diag. 5.2) and planar arrangement of O1/3, C3 and Cl and axially situated O2/4. Thus, easy syntheses of chiral assemblies was achieved although it is necessary to repeat the reaction to obtain pure 34b. 118 Such chiral complexes are known to perform selective transformations such as asymmetric syntheses.139 The catalytic potential of complexes 34 and 33a has to be explored. [139] J. Okuda, S. Verch, R. Stuermer, T. P. Spaniol, J. Organomet. Chem. 2000, 605, 55; J. P. Genet, N. Kopola, S. Juge, J. Ruez-Montes, O. A. C. Antunes, S. Tanier, Tetra. Lett. 1990, 31, 22, 3133. 119 6. Experimental details 6.1. General remarks: As primary and secondary phosphines are known to undergo oxidation in air and metal alkoxides or phenolates may easily hydrolyze, most of the intermediates, and compounds studied are air and moisture sensitive. In order to avoid the oxidation or hydrolysis, all manipulations were therefore carried out under dry argon atmosphere, and solvents were dried by standard procedures if required.140 The compounds are fully characterized by NMR, the prefixes i, o, m, p denote phenyl ring positions of P-C6H5 substituents. Chemicals: The following chemicals were synthesized according to experimental procedures reported in the literature: Diphenyl phosphine,141 Mesityl phenylphosphine,41 Pentafluro-phenyl boronic acid,142 Dichloro-[1,5-cyclooctadien] palladium,143 Dibromo-[1,5-cyclooctadien] platinum,144 and Bis-{benzonitrile}-palladium dichloride.145 All other chemicals were commercially available and purchased from Acros, Merck, Fluka, Strem, Chempure, Aldrich and Riedel-deHaehn. Nuclear Magnetic Resonance Spectroscopy: [140] D. D. Perrin, W. L. Armarego, L. F. Willfred, Purification of Laboratory Chemicals, Oxford: Pergamon Pr. 1988. [141] D. Wittenberg, H. Gilman, J. Org. Chem. 1958, 23, 1063; Diphenyl phosphine was synthesized as reported in the above literature with little modification. Triethyl amine hydrochloride was employed as proton source instead of water. [142] H. J. Frohn, N. Y. Adonin, V. V. Bardin, V. F. Starichenko, Z. Anorg. Allg. Chem. 2002, 628, 2827. [143] P. M. Maitlis, The Organic Chemistry of Palladium Metal Complexes, V.1, 1971, Academic Press, New York; and references there in. [144] J. Chatt, L. M. Vallarino, L. M. Venanzi, J. Chem. Soc. 1957, 2496. [145] M. Schlosser, Organometallics in Synthesis: A Manual; Wiley, 2002. 120 The Solution NMR spectra were recorded on Bruker Avance 400 (1H, 13C, 31P, 11B, 119Sn, 195Pt) or AC 250 spectrometers (1H, 13C, 31P, 19F) with Tetramethylsilane as external standard. 1H-NMR: 250,0/300,0/400,0 MHz, sec. Standard: Tetramethylsilane (TMS); δ = 0,0 (Ξ = 100,000000 MHz) 11B-NMR: 128,4 MHz, sec. Standard: Et2O.BF3; δ = 0,0 (Ξ = 32,083974 MHz) 13C-NMR: 62,9/75,5/100,6 MHz, sec. Standard: TMS; δ = 0,0 (Ξ = 25,1454004 MHz) 31P-NMR: 101,2/121,5/161,9 MHz, sec. Standard: 85% H3PO4; δ = 0,0 (Ξ = 40,480737 MHz) 195Pt-NMR: 86,7 MHz, sec. Standard: H2PtCl6 in D2O; δ = 0,0 (Ξ = 21,497426MHz) 119Sn-NMR: 148.7 MHz, sec. Standard: Tetramethyltin (SnMe4); δ = 0,0 (Ξ = 37.290632 MHz) 109Ag-NMR: 14.0 MHz, sec. Standard AgNO3 in D2O/sat. (Ξ = 4.653533 MHz) In ambiguous cases assignments were derived from 2D experiments such as gs1H31P HMQC, gs1H13C HSQC, gs1H-COSY, 31P gsNOESY and gs1H119Sn HMQC. Solid state MAS NMR spectra were recorded on a Bruker Avance 400 instrument equipped with a 4 mm MAS probe and using spinning rates between 3 and 14 kHz. Cross polarization with a ramp-shaped contact pulse and mixing times between 3 and 5 ms was used for signal enhancement. MAS NMR spectra aiming at the determination of 1JP,H couplings were recorded under frequency-shifted Lee–Goldburg decoupling of homonuclear proton– proton interactions146 which scales the visible splitting by a factor of 0.577. All coupling constants are given as absolute values. The resonances of OH protons were not always detectable, presumably as a consequence of chemical exchange, and data are not listed when unequivocal assignment was unfeasible. Elemental Analysis: The C, H, N analyses were recorded on a Perkin-Elmer 240 CHSN/O Analyzer, and Cl was determined by argentometric titration. [146] A. Bielecki, A. C. Kolbert, M. H. Levitt, Chem. Phys. Lett. 1989, 155, 341; M. H. Levitt, A. C. Kolbert, A. Bielecki, S. J. Ruben, Solid State NMR, 1993, 2, 151. 121 IR: IR spectra were measured between 4400 and 400 cm-1 on a Perkin Elmer FTIR Paragon 1100 spectrometer either as nujol paste or as KBr pallet. EI-Mass-spectroscopy: Varian MAT 711, EI, 70 eV. ESI-Mass-spectroscopy: Bruker Daltonics-micrOTOF-Q. Melting point: Melting points were determined in sealed capillaries on a Büchi B-545 melting point apparatus. Single Crystal X-ray Measurements: The Diffractometer Nonius Kappa CCD and Siemens P4 were used and the structure solutions and refinements were carried out using SHELXS, SHELXL and SHELXTL programs. 6.2. General procedure for the syntheses of phenol functionali- zed phosphane oxides (5a-e and 10a): Diphenyl phosphine 2 (12 mmol) was added to a solution of the appropriate aldehyde 3a–e (12 mmol) in DME (10 ml). The solution was stirred for five minutes at room temperature. A catalytic amount of p-toluenesulfonic acid (approx. 3–6 mmol) was added and the stirring continued for 48 h. The colorless precipitate formed was isolated by filtration, washed twice with 5 ml of DME, and dried in vacuo for 4 hours. 6.2.1. 2-[(Diphenyl phosphinoyl) methyl] phenol (5a): Yield: 2.59 g (70 %); Melting point: 177°C. Elemental analysis: C19H17O2P (308.32): calcd. C 74.02 H 5.56 found: C 73.90 H 5.37. Spectroscopic data are identical with the values reported in the literature.147 [147] N. A. Bondarenko, E. N. Tsvetkov, E. I. Matrosov, M. I. Kabachnik, Izv. Akad. Nauk. SSSR, Ser. Khim. 1979, 432; V. I. Evreenov, V. E. Baulin, Z. N. Vostroknutova, N. A. Bondarenko, T. Kh. Syundyukova, E. N. Tsvetkov, Izv. Akad. Nauk. SSSR, Ser. Khim. 1989, 1990. 122 6.2.2. 3-[(Diphenyl phosphinoyl) methyl] benzene-1, 2-diol (5b): OH PPh2 O OH Yield: 3.31 g (85 %); Melting point: 194°C Elemental analysis: C19H17O3P (324.32): calcd. C 70.37 H 5.28 found: C 70.44 H 5.35. 31P NMR (101 MHz, CDCl3): δ = 40.4 (s). 1H NMR (400 MHz, CDCl3): δ = 8.2 (br., 2 H, OH), 7.74 (m, 4 H, o-Ph), 7.58 (m, 2 H, p- Ph), 7.50 (m, 4 H, m-Ph), 6.81 (ddd, 3JHH = 8.0 Hz, 4JHH = 1.7 Hz, 6JPH = 1.7 Hz, 1 H, C6H3), 6.63 (dt, 3JHH = 8.0 Hz, 5JPH = 0.9 Hz, 1 H, C6H3), 6.34 (dddm, 3JHH = 7.7 Hz, 4JHH = 1.7 Hz, 4JPH = 1.7 Hz, 1 H, C6H3), 3.73 (d, 2JPH = 12.8 Hz, 2 H, CH2). 13C{1H} NMR (100 MHz, CDCl3): δ = 148.2 (d, JPC = 2.7 Hz), 143.9 (d, JPC = 4.2 Hz), 133.2 (d, JPC = 2.7 Hz, p-C), 131.6 (d, JPC= 9.6 Hz, o-C), 130.9 (d, JPC = 100.4 Hz, i-C), 129.4 (d, JPC = 12.1 Hz, m-C), 122.9 (d, JPC = 6.3 Hz), 121.7 (d, JPC = 1.9 Hz), 119.9 (d, JPC = 8.4 Hz), 114.6 (d, JPC = 2.5 Hz), 35.6 (d, JPC = 67.1 Hz, CH2). MS (EI = 70 eV): m/e (%) = 324.1 (100) [M]+; 202.1 (38) [Ph2POH]+; 201 (54) [Ph2PO]+. 6.2.3. 4-[(Diphenyl phosphinoyl) methyl] phenol (5c): PPh2 O OH Yield: 2.22 g (60 %); Melting point: 223°C. Elemental analysis: C19H17O2P (308.32): calcd. C 74.02 H 5.56 found: 74.19 H 5.82. 31P NMR (162 MHz, CDCl3): δ = 32.2 (s). 123 1H NMR (400 MHz, CDCl3): δ = 8.2 (br., 1 H, OH), 7.76 (m, 4 H, o-Ph), 7.57 (m, 2 H, p- H), 7.49 (m, 4 H, m-Ph), 6.82 (m, 2 H, C6H4), 6.56 (m, 2 H, C6H4), 3.62 (d, 2JPH = 12.2 Hz, 2 H, CH2). 13C{1H} NMR (100 MHz, CDCl3): δ = 156.9 (d, JPC = 1.7 Hz), 132.7 (s), 131.8 (d, 2JPC = 9.2 Hz, o-C), 131.6 (d, JPC = 4.8 Hz), 129.3 (d, 3JPC = 11.7 Hz, m-C), 128.6 (d, JPC = 99.6 Hz), 120.7 (d, JPC = 7.5 Hz), 117.0 (d, JPC = 2.1 Hz), 37.4 (d, JPC = 72.1 Hz, CH2). 6.2.4. 4-[(Diphenyl phosphinoyl) methyl] benzene-1, 2-diol (5d): PPh2 O OH OH Yield: 3.50 g (90 %); Melting point: 192°C Elemental analysis: C19H17O3P (324.32): calcd. C 70.37 H 5.28 found: C 69.98 H 5.17. 31P NMR (101 MHz, CDCl3): δ = 40.4 (s). 1H NMR (250 MHz, CDCl3): δ = 7.47 to 7.23 (m, 10 H, C6H5), 6.53 (s, 1 H, C6H3), 6.31 (d, 3JHH = 8.1 Hz, 1 H, C6H3), 6.12 (d, 3JHH = 8.1, 1 H, C6H3), 3.42 (d, 2JPH = 12.9 Hz, 2 H, CH2). 13C{1H} NMR (62 MHz, CD3CN/CDCl3): δ = 143.8 (d, JPC = 2.3 Hz), 143.2 (d, JPC = 3.1 Hz), 131.7 (d, JPC = 1.8 Hz, p-C), 130.3 (d, JPC = 9.4 Hz, o-C), 128.1 (d, JPC = 11.7 Hz, m- C), 126.9 (d, JPC = 101.8 Hz, i-C), 121.2 (d, JPC = 6.1 Hz), 120.9 (d, JPC = 8.4 Hz), 116.6 (d, JPC = 4.8 Hz), 114.4 (d, JPC = 2.3 Hz), 35.1 (d, JPC = 68.2 Hz). 124 6.2.5. 3-[(Diphenyl phosphinoyl) methyl] phenol (5e): PPh2 O OH Yield: 2.22 g (60 %); Melting point: 198°C. Elemental analysis: C19H17O2P (308.32): calcd. C 74.02 H 5.56 found: C 74.10 H 5.60. 31P{1H} NMR (101 MHz, CDCl3): δ = 31.4. 1H NMR (250 MHz, CD3CN/ CDCl3): δ = 7.55 (m, 4 H, o-Ph), 7.40 to 7.25 (m, 6 H, m/p- Ph), 6.80 (t, 3JHH = 8.0 Hz, 1 H, C6H4), 6.59 (s, 1 H, C6H4), 6.44 (d, 3JHH = 8.0 Hz, 1 H, C6H4), 6.41 (d, 3JHH = 8.0 Hz, 1 H, C6H4), 3.50 (d, 2JPH = 13.4 Hz, 2 H, CH2). 13C{1H} NMR (62 MHz, CD3CN/CDCl3): δ = 157.1 (d, JPC = 2.6 Hz), 132.4 (d, JPC = 2.9 Hz, p-C), 131.2 (d, JPC = 9.5 Hz, o-C), 131.0 (s), 130.9 (d, JPC = 102.3 Hz, i-C), 129.5 (d, JPC = 2.1 Hz), 128.9 (d, JPC = 11.8 Hz, m-C), 121.8 (d, JPC = 5.8 Hz), 117.5 (d, JPC = 5.0 Hz), 114.2 (d, JPC = 2.9 Hz), 37.1 (d, JPC = 67.1 Hz). 6.2.6. 3-[(Mesitylphenylphosphinoyl) methyl] benzene-1, 2-diol (4f): PPhMes O OH OH Yield: 3.73 g (85 %); Melting point: 220°C. Elemental analysis: C22H23O3P (366.40): calcd. C 72.12 H 6.33 found: C 72.21 H 6.41. 31P NMR (250 MHz, CDCl3): δ = 46.38 (s). 1H NMR (400 MHz, CDCl3): δ = 7.65-7.38 (m, 5 H, Ph), 6.86 (d, 4JHH = 3.65 Hz, 2 H, mes-H), 6.78 (dt, 3JHH = 8.0 Hz, 1 H, Ph), 6.56 (t, 3JHH = 7.9 Hz, 1 H, Ph), 6.18 (dt, 3JHH = 125 7.7 Hz, 1 H, Ph), 3.83 (p, 2JHH = 12.6 Hz, 2 H, CH2), 2.31 (d, 2JHH = 16.9 Hz, 9 H, Mes- CH3). 13C{1H} NMR (250 MHz, CDCl3): δ = 147.5 (d, JPC = 3 Hz. C6H3), 143.4 (d, JPC = 4 Hz C6H3), 143.0 (d, JPC = 10.5 Hz C6H3), 142.4 (d, JPC = 2.8 Hz C6H3), 134.9 (s, p-Mes), 133.4 (s, p-Ph), 132 (d, JPC= 2.8 Hz, C6H3), 131.3 (d, JPC = 11.5 Hz, m-Ph), 129.9 (d, JPC = 9.8 Hz, i-Ph/Mes), 128.8 (d, JPC = 12 Hz, m-Mes), 122.2 (d, JPC = 6 Hz, o-Mes), 120.9 (d, JPC = 2.3 Hz, o-Ph), 119.9(s, o-Ph), 113.7 (d, JPC = 2.8 Hz, o-Mes), 36.2 (d, JPC = 65.3 Hz, CH2), 23.5 (d, JPC = 3.8 Hz, o-CH3-Mes), 20.9 (d, JPC = 1.3 Hz, p-CH3-Mes). MS (EI = 70 eV): m/e (%) = 366.1 (100%) [M]. 6.2.7. 2-[(Diphenylphosphanyl)hydroxymethyl]phenol Hydrochloride (6a): 2-Hydroxybenzaldehyde (0.64 ml, 6 mmol) was added to a solution of diphenyl phosphine (1.05 ml, 6 mmol) in diethyl ether (10 ml). This mixture was stirred for five minutes at room temperature and an excess of conc. hydrochloric acid (2 ml, 24 mmol) was added. A colorless precipitate formed immediately. The reaction mixture was then stirred for further 60 minutes, the precipitate filtered off, washed twice with diethyl ether (5 ml), and dried for 1 h in vacuo. PPh2 OH HO H Cl- + Yield: 1.86 g (90 %); Melting point: 104°C. Elemental analysis: C19H18ClO2P (344.78): calcd. C 66.19 H 5.26 Cl 10.28 found: C 66.76 H 5.38 Cl 8.54. 31P{1H} NMR (solid, 162 MHz, CP/ MAS): δiso = –0.8. 6.2.8. 4-[(Diphenylphosphanyl) hydroxymethyl] phenol (4c): A solution of diphenyl phosphine (2) (1.43 ml, 8.2 mmol) and 4-hydroxybenzaldehyde (3c) (1.00 g, 8.2 mmol) in methanol (10 ml) was stirred for 5 minutes at room temperature and conc. hydrochloric acid (0.25 ml, 3 mmol) was added. A colorless precipitate formed 126 immediately. The reaction mixture was stirred for further 60 minutes, the precipitate filtered off and dried for 1 h in vacuo. PPh2HO OH Yield: 2.27 g (90 %); Melting point: 168°C. Elemental analysis: C19H17O2P (308.32): calcd. C 74.02 H 5.92 found: 74.29 H 5.92. 31P NMR (101 MHz, THF): δ = –2.3 (s). 31P{1H}NMR (solid, 162 MHz, CP/MAS): δiso = –7.2. 6.2.9. Bis [hydroxy (3-hydroxyphenyl) methyl] diphenyl phosphonium Toluenesulfonate (7e/7e_): A solution of diphenylphosphane (1.43 ml, 8.2 mmol) and 3-hydroxy benzaldehyde (1.00 g, 8.2 mmol) in DME (5 ml) was stirred for 5 minutes at room temperature and p- toluenesulfonic acid (0.60 g, 3.2 mmol) was added. A colorless precipitate began to form after 10 minutes. The reaction mixture was stirred for 12 h, the precipitate filtered off, washed twice with DME, and dried for 4 h in vacuo. PPh2HO OH OH HO + SO3_ Yield: 1.73 g (90 %); Melting point: 121°C. Elemental analysis: C33H31O7PS (602.64): calcd. C 65.77 H 5.19 found: 65.39 H 5.30. 31P{1H}NMR (solid, 162 MHz, CP/MAS): δiso = 30.5, 29.9. 127 6.3. General procedure for the synthesis of phenol-function- alized phosphanes 9a-d and 101: The appropriate phosphine oxide 5a–d or 9f (10 mmol) was dissolved in dry THF (100 ml). Methyl iodide (0.69 ml, 11 mmol) was added via a syringe and the solution stirred for 2 h at room temperature. The mixture was then cooled to 0°C and solid LiAlH4 (1.7 g, 45 mmol) added in several small portions. The reaction mixture was warmed to ambient temperature, and stirring was continued for another 5–6 h. The progress of the reaction was monitored by TLC. The reaction flask was again cooled to 0°C, and 50 ml of 1M. hydrochloric acid was added in several portions (the first few drops had to be added very carefully until the exothermic reaction became less violent). The organic layer was separated and the aqueous layer washed with ethyl acetate (3×50 ml). The combined organic phases were dried overnight with Na2SO4 and all volatiles evaporated in vacuo. The crude products were purified by column chromatography (silica, petroleum ether: ethyl acetate = 7:3). 6.3.1. 2-[(Diphenylphosphanyl) methyl] phenol (9a): PPh2 OH Yield: 1.81 g (62 %); colorless oil. Elemental analysis: C19H17OP (292.32): calcd. C 78.07 H 5.86 found: C 74.33 H 5.91. 1H NMR (250 MHz, [D8] toluene): δ = 6.8 to 7.5 (m, 10 H, C6H5), 6.80 (t, 1 H, 3JHH = 7.7 Hz), 6.74 (d, 1 H, 3JHH = 7.7 Hz), 6.61 (d, 1 H, 3JHH = 7.8 Hz), 6.50 (t, 1 H, 3JHH = 7.5 Hz), 3.32 (s, 2 H, CH2). The 1H NMR spectroscopic data match those published earlier.126 31P{1H} NMR (101 MHz, [D8] toluene): δ = –15.0. 6.3.2. 3-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (9b): PPh2 OH OH 128 Yield: 1.85 g (60 %); Melting point: 82°C. Elemental analysis: C19H17O2P (308.32): calcd. C 74.02 H 5.56 found: C 73.91 H 5.73. 31P NMR (101 MHz, CDCl3): δ = –13.1 (s). 1H NMR (400 MHz, CDCl3): δ = 7.52 to 7.30 (m, 10 H, C6H5), 6.78 (dm, 3JHH = 7.9 Hz, 1 H, C6H3), 6.64 (tm, 3JHH = 7.9Hz, 1 H, C6H3), 6.43 (dm, 3JHH = 7.9 Hz, 1 H, C6H3), 6.02 (br., 1 H, OH), 5.86 (br., 1 H, OH), 3.52 (d, 2JPH = 1.7 Hz, 2 H, CH2). 13C{1H} NMR (100 MHz, CDCl3): δ = 145.0 (d, JPC = 1.6 Hz), 141.7 (d, JPC = 3.7 Hz), 132.8 (d, 3JPC = 17.4 Hz, m-C), 130.9 (d, 2JPC = 9.5 Hz), 129.3 (s, p-C), 128.9 (d, 3JPC = 12.1), 128.6 (d, JPC = 7.4 Hz, o-C), 122.4 (d, JPC = 6.3 Hz), 121.0 (d, JPC = 1.6 Hz), 113.6 (d, JPC = 2.6 Hz), 30.7 (d, 1JPC = 10.5 Hz, CH2). MS (EI = 70 eV): m/e (%) = 308.1 (100) [M+], 186.1(45) [Ph2PH+], 185.1 (44) [Ph2P+], 183.0 (54) [Ph2P+–H2], 123.1 (45) [M+–PPh2], 108.1 (54). 6.3.3. 4-[(Diphenylphosphanyl) methyl] benzene-1, 2-diol (9d): PPh2 OH OH Yield 2.16 g (70 %); Melting point: 144°C. Elemental analysis: C19H17O2P (308.32): calcd. C 74.02 H 5.56 found: C 74.06 H 5.59. 1H NMR (400 MHz, [D8]- THF): δ = 7.68 (s, 1 H, OH), 7.53 (s, 1 H, OH), 7.41 (m, 4 H, o-H), 7.33 to 7.25 (m, 6 H, m/p-H), 6.58 (dd, 4JHH = 1.7 Hz, 4JPH = 1.7 Hz, 1 H, C6H3), 6.52 (d, 3JHH = 8.1 Hz, 1 H, C6H3), 6.38 (dm, 3JHH = 8.0 Hz, 1 H, C6H3), 3.31 (s, 2 H, CH2). 13C{1H} NMR (100 MHz, [D8] THF): δ = 145.6 (d, JPC = 1.5 Hz), 144.2 (d, JPC = 2.9 Hz), 139.9 (d, JPC = 16.8 Hz, i-C), 133.3 (d, JPC = 18.7 Hz, m- C), 129.1 (d, JPC = 8.8 Hz), 128.7 (s, p-C), 128.6 (d, JPC = 6.3 Hz, o-C), 120.9 (d, JPC = 7.1 Hz), 116.7 (d, JPC = 7.6 Hz), 115.3 (d, JPC = 1.5 Hz), 35.6 (d, JPC = 15.1 Hz). 129 31P{1H} NMR (162 MHz, CDCl3): δ = –10.4. MS (EI = 70 eV): m/e (%) = 308.1 (48) [M+], 186.1 (38) [Ph2PH+], 183.0 (27) [Ph2P+–H2], 123.1 (100) [M+ _PPh2], 108.1 (27). 6.3.4. 3-[(Mesitylphenyl phosphanyl)-methyl]-benzene-1, 2-diol (9f): PPhMes OH OH Yield: 2.45 gms (70%), Melting point: 93ºC. Elemental analysis: C22H23O2P, Calcd. C 75.41 H 6.62 Found: C 74.73 H 6.83 31P NMR (250 MHz, CDCl3): δ = -27.64 (s). 1H-NMR (CDCl3) δ = 7.35 to7.20 (m, 5 H Ph), 6.9 (d 4JHH = 1.9 Hz, 2 H, Mes), 6.73 (d, 2JHH = 7.5 Hz, 1 H C6H3), 6.66 (t, 2JHH = 7.8 Hz 1 H C6H3), 6.59 (d, 2JHH = 7.5 Hz, 1 H C6H3), 6.5 (broad s, 2 H, OH), 3.76 (broad, s, 1 H, CH2), 3.52 (dd, 2JPH = 13.5 Hz 1 H, CH2), 2.30-2.28 (m, 9 H, Mes-CH3). 13C-NMR (CDCl3) δ = 145.3 (s, C6H3), 145.1 (s, C6H3), 144.8 (d, 4JPC = 1.5 Hz, C6H3), 142.1 (d, 3JPC = 3.8 Hz, C6H3), 140.5 (s, C6H3), 140.3 (s, C6H3), 139.9 (d, 4JPC = 1.5 Hz, p- Mes.), 129.8 (d, 3JPC = 4.5 Hz, m-Ph.), 129.5 (s, o-Ph), 128.4 (d, 3JPC = 4.3 Hz, m-Mes), 126.8 (d, 4JPC = 1 Hz, p-Ph), 125.3 (d, 1JPC = 8.5 Hz, i-Ph), 122.0 (d, 1JPC = 7.3 Hz, i-Mes), 120.7 (d, JPC = 2 Hz, o-Mes), 113.3 (d, 3JPC = 4.5 Hz, m-Mes.), 28.3 (d, 1JPC = 14.56 Hz CH2), 21.1 (s, Mes-CH3). 6.4. General procedure for the syntheses of transition metal complexes of 9b-d: To the THF (20 ml) solution of 200 mg (0.64 mmol) of 3/4-[(Diphenylphosphanyl)- methyl]-benzene-1,2-diol was added 0.32 mmol of the corresponding transition metal complex. The reaction mixture was stirred for two hours at room temperature and then concentrated in vacuum to approximately half of the total volume. Storage of the 130 remaining solution at +4°C gave shining needle like crystals that were isolated nearly quantitatively by filtration. 6.4.1. Bis {3-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol} Palladium dichloride, 13b: Ph2 P OH OH Ph2 P HO HO Pd Cl Cl Elemental analysis: Calcd. for PdCl2(9b)2 × THF: C 58.25 H 4.89 Found: C 58.06 H 5.27. Yield: 240 mg (95%); Melting point: 176ºC. 31P{1H}-NMR (CD3CN): δ = 19.1 (s). 1H NMR (CD3CN): δ = 7.8 to 7.1 (m, 20 H, Ph), 7.0 to 6.5 (m, 6 H, C6H3), 4.23 (d, 2J PH = 11.6 Hz, 4 H, CH2). 13C{1H} NMR (CD3CN): δ = 145.28 (2C, C6H3), 144.6 (2C, C6H3), 134.88-134.48 (m, 8 C, o-Ph), 131.8 (d, 1Jpc = 11.05 Hz, 4 C, i-Ph), 129-130.71 (m, 2 C, C6H3), 128.9(t, 3Jpc = 7.4 Hz, m-Ph), 123.9 (d, 2JPC = 15.8 Hz, C6H3), 120-121 (m, p-Ph), 115.2 (s, 2C C6H3), 114.7 (s, 2 C, C6H3), 26.24 (s, 4C, CH2). 6.4.2. Bis {4-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol} Palladium dichloride, 13d: Ph2 P OH Ph2 P HO Pd Cl Cl OH OH Yield: 240 mg (95%); Melting Point: 223ºC 31P{1H}-NMR (CD3CN): δ = 20.0 (s). 131 1H (CD3CN): δ = 7.30-6.96 (m, 20 H, Ph), 6.38 (d, 3JHH = 7.93 Hz, 2 H, C6H3), 6.31 (d, 3JHH = 7.47 Hz, 2 H, C6H3), 6.14 (d, 3JHH = 8.24 Hz, 2 H, C6H3), 3.65 (d, 2JPH = 11.59 Hz, 4 H, CH2). 6.4.3. Silver- bis {3-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol}, 14b: Crystals were grown from a dichloromethane: diethyl either mixture (10:1). Ph2 P OH Ph2 P HO Ag CF3SO3_ + OH HO Elemental analysis: Calcd. for [C39H34 AgO7P2S Х DMF Х CH2Cl2] : C 50.07 H 4.20 N 1.36 Found: C 51.51 H 4.39 N 1.76. ESI-MS (positive mode): m/e = 781.09 (M-OTf+NaCl)+, 723.09 (M-OTf)+, 725 (M- OTf)+. Yield: 261 mg (95%); Melting Point: 109ºC. 31P{1H}-NMR (CDCl3, 303K): δ = 6.16 (d, broad, 1JAg-P, 444.5 Hz). 1H NMR (CDCl3): δ = 7.55 to 7.3 (m, 20 H, Ph), 6.70 (dd, 3JHH = 7.8 Hz, 2 H, C6H3.), 6.4 (t, 3JHH = 7.9 Hz, 2 H, C6H3), 6.1 (dd, 3JHH = 7.5 Hz, 2 H, C6H3), 5.29 (s), CH2Cl2, 3.7 (broad, s, 4 H, CH2). 13C{1H} NMR (CDCl3): δ = 144.2 (s, C6H3), 142.8 (s, C6H3), 133.1(broad, 8 C, Ph), 130.8 (broad, 4 C, Ph), 128.9 (broad, 4 C, Ph), 122.2(s, 2 C, C6H3), 120.8 (s, 2 C, C6H3.), 119.9 (s, 2 C, C6H3), 116.9 (s, 8 C Ph), 114.2 (s, 2 C, C6H3), 28.9 (broad, 4 C, CH2). 6.4.4. Silver- bis {4-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol}, 14d: Crystals were grown from THF solution at room temperature. 132 Ph2 P OH Ph2 P HO Ag OH OH CF3SO3_ + Elemental analysis: Calcd. for [C39H34AgF3O7P2S Х 1.5 THF]: C 55.47 H 4.95 Found: C 55.48 H 4.95. Yield: 261 mg (95%); Melting Point: 112ºC ESI-MS (positive mode): m/e = 723.09 (M-OTf)+, 725 (M-OTf)+ 31P{1H}-NMR (CDCl3, 300K): δ = 16.5 (broad d, 1JAg-P = 465 Hz). 31P{1H}-NMR (CDCl3, 223K): δ = 16.4 (dd, 1JP-Ag = 580 Hz). 1H NMR (CDCl3): δ = 7.5 to 7.2 (m, 20 H, Ph), 7.02 (s, 2 H, C6H3.), 6.58 (d, 3JHH = 8.24 Hz, 2 H, C6H3), 6.08 (dd, 3JHH = 6.4 Hz, 2 H, C6H3), 3.53 (broad, s, 4 H, CH2). 13C{1H} NMR (CDCl3): δ = 144.9 (s, C6H3), 144.3 (s, C6H3), 133.6 (broad, Ph), 131.6 (broad, Ph), 130.9 (broad, Ph), 129.7 (s, Ph), 126.5 (s, C6H3), 121.8 (s, C6H3), 116.3 (s, Ph), 115.8 (s, C6H3), 34.5 (broad, CH2). 6.4.5. Bis {4-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol} platinum dichloride, 15: Ph2 P OH OH Ph2 P HO HO Pt Cl Cl Elemental analysis: Calcd. for (C38H34Cl2O4Pt + PhCN): C 54.87 H 3.99 N 1.42 Found: C 54.17 H 4.43 N 1.03. Yield: 268 mg (95%); Melting point: 235ºC. 31P{1H}-NMR (CDCl3) δ = 18.8 (s, 1JPt-P 1296 Hz, 33%), 11.0 (s, 1JPt-P 1861 Hz, 66%). 133 1H NMR (CDCl3): δ = 7.8 to 6.9 (m, 25 H, Ph + PhCN), 6.81 (t, 3JH-H = 8.24 Hz, 2 H, C6H3.), 6.6-6.4 (m, 2 H, C6H3.), 6.0-5.7 (m, 2 H, C6H3.), 4.14 (d, 2JP-H, 11 Hz, 3 H, CH2), 3.5 to3.4 (br, s, 1 H, CH2). The same sample (solid) was stored for two months in inert atmosphere, 31P NMR of this displayed following chemical shifts. 31P{1H}-NMR (CDCl3) δ = 28.6 (s, 1JPt-P = 1942 Hz), 24.5 (dd, 1JPt-P = 2141, 1727 Hz). 6.4.6. Bis{3-[(Mesitylphenyl phosphanyl)-methyl]-benzene-1, 2-diol} palladium(II), 101: To the THF (20 ml) solution of 100 mg (0.28 mmol) of 33-[(Mesitylphenyl phosphanyl)- methyl]-benzene-1, 2-diol was added 0.14 mmol of (COD)PdCl2. The reaction mixture was stirred for one hour at room temperature and then concentrated in vacuum to approximately half of the total volume. Storage of the remaining solution at +4°C gave yellow powder that was isolated nearly quantitatively by filtration and drying in vacuum. PhMes P OH O PhMes P HO O Pd Yield: 107 mg (95%). ESI-MS (positive mode): m/e = 805.2[M+H]+, 827.2[M+Na]+. 31P{1H}-NMR (CDCl3) δ = 55.7 (s), 19.2 (br, s), 5.4 (s), 4.3 (s). 31P{1H}-NMR (CDCl3) δ = 53.5 (br, s), 1.3 (s), -0.9 (s). of isolated product. 1H NMR (CDCl3): δ = 7.7-7.3 (m, 8 H, Ph/Mes), 6.9-6.6 (m, 6 H, Ph/Mes), 6.56-5.9 (m, 4 H, C6H3), 5.7-5.5 (m, 2 H, C6H3), 4.3-4.0 (br, d, 2 H, CH2), 3.65-3.5 (br, d, 2 H, CH2), 2.26 (br, s, 9 H, Mes-CH3). Though the proton signals of the cis-trans complexes where observable, it was hard to assign them. 134 6.5. General procedure for the syntheses of boranes: 620 mg (2 mmol) of solid 3-[(Diphenylphosphanyl)-methyl]-benzene-1, 2-diol was dissolved in 20 ml of dry dichloromethane. 245 mg (2 mmol) of aryl boronic acid was dissolved in 10 ml of dichloromethane in another schlenk tube and was transferred to the diol solution. The reaction mixture was stirred for 30 minutes, the solvent was evaporated to dryness and the white, powdered product was obtained in quantitative yield. 6.5.1. (a) Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol-4-ylmethyl)-phosphane 16a: PPh2 O O BPh Elemental analysis: Calcd. for (C25H20BO2P): C 76.12 H 511 Found: C 75.50 H 5.11. Yield: 773 mg (98%.). 31P{1H}-NMR (CH2Cl2) δ = -11.1(s). 11B-NMR (CH2Cl2) δ = 31.7 (br, s). 1H NMR (CDCl3): δ = 8.05-7.9(m, 2 H, BC6H5), 7.57 (t, 3JHH = 1.5 Hz, 1 H, BC6H5), 7.54 (t, 3JHH = 2.7 Hz, 1 H, BC6H5), 7.51 (t, 3JHH = 1.5 Hz, 1 H, BC6H5), 7.5-7.4 (m, 5 H, Ph), 7.35-7.25 (m, 5 H, Ph), 7.07 (dt, 3JHH = 7.8 Hz, 1 H, C6H3), 6.93 (t, 3JHH = 7.9 Hz, 1 H, C6H3), 6.82 (t, 3JHH = 7.9 Hz, 1 H, C6H3), 3.62 (br., s, 2 H CH2). 6.5.1 (b) Diphenyl- (2-pentaflurophenyl-benzo [1,3,2]-dioxaborol-4-ylmethyl)- phosphane 16b: PPh2 O O BC6F5 Yield: 891 mg (92%). Elemental analysis: Calcd. for (C25H15BF5O2P): C 66.26 H 3.34 found: C 64.53 H 3.99. 135 31P{1H}-NMR (CDCl3) δ = -9.3 (broad, s). 11B-NMR (CH2Cl2) δ = 21.6 (broad, s) 14.3 (broad, s), 9.9 (broad, s), 5.3 (broad, s). 1H NMR (CDCl3): δ = 7.7 -7.2 (m, 10 H, Ph), 7.1-6.6 (broad, m, 3 H, cat.), 3.62 (s, CH2). 6.5.2. (a) Synthesis of Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol-4- ylmethyl)-phosphane-3- (Dimethyl amino pyridine) 17a: To 560 mg (1.42 mmol.) of Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol-4-ylmethyl)- phosphane was added 15 ml of dichloromethane. Stirring for 5 minutes was followed by addition of 172 mg (1.42 mmol.) of 4-dimethyl amino pyridine. The reaction mixture was stirred for another 30 minutes, dichloromethane was stripped off, and the white powder was dried for another 30 minutes. The residue was obtained quantitatively and was characterized by spectroscopic techniques (see below). The white powder was again dissolved in a minimum amount of dichloromethane, and few drops of THF were added. Storing the solution at room temperature gave crystals suitable for single crystal X-ray diffraction study. PPh2 O O B N N(Me)2 Ph Yield: 697 mg (95%); Melting point: 167ºC. Elemental analysis: Calcd. for (C32H30BN2O2P): C 74.43 H 5.86 N 5.43 Found: C 74.20 H 5.93 N 5.41. 31P{1H}-NMR (CDCl3) δ = -17.14 (s). 11B-NMR (CDCl3) δ = 11.07 (s). 1H NMR (CDCl3): δ = 8.25 (d, 3JHH = 7.34 Hz, 2 H, DMAP), 7.55-7.40 (m, 6 H), 7.30- 7.20 (m, 9 H), 6.62 (dt, 3JHH = 7.34 Hz, 1 H, C6H3), 6.55-6.45 (m, 3 H), 6.39 (dt, 3JHH = 8.03 Hz, 1 H, C6H3), 3.5 (br, s, 2 H, CH2), 3.01 (br, s, 6 H, DMAP). 136 6.5.2 (b) Synthesis of Diphenyl- (2-pentaflurophenyl-benzo [1,3,2]-dioxaborol- 4-ylmethyl)-phosphane-3- (Dimethyl amino pyridine) 17b: To 428 mg (0.9 mmol.) of Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol-4-ylmethyl)- phosphane was added 10 ml of dichloromethane. Stirring for 5 minutes was followed by addition of 110 mg (0.9 mmol.) of 4-dimethyl amino pyridine. The reaction mixture was stirred for another 30 minutes, dichloromethane was stripped off, and the white powder was dried for another 30 minutes. The residue was obtained in quantitative yields. PPh2 O O B N N(Me)2 C6F5 31P{1H}-NMR (CDCl3) δ = -12.6 (s), -13.9 (s). 11B-NMR (CDCl3) δ = 18.0 (br, s), 14.25 (s, major), 8.47 (d). 6.5.3. Synthesis of Dichloro bis {Diphenyl- (2-phenyl-benzo [1,3,2]-dioxaborol- 4-ylmethyl)-phosphane}-palladium, 18: To the THF solution of 397 mg (0.5 mmol) of bis-diphenyl-{2-phenyl-benzo (1,3,2) dioxaborol-4-ylmethyl}-phosphane palladium dichloride was added 122mg (1mmol) of Phenyl boronic acid. This reaction mixture was stirred for two hrs at room temperature. Finally the solvent was evaporated in vacuum to give a yellow powder. The powder was then dissolved in THF and the saturated solution kept at +4ºC. Microcrystals of orange yellow color were obtained, dried in vacuum, and characterized by analytical techniques. P O O B P O O B Pd PhPh Ph PhCl Cl PhPh Yield: 333 mg (69%); Melting point: 240°C (dec). Elemental Analysis: Calcd. for (C50H40B2Cl2O4P2Pd): C 62.19 H 4.18 Found: C 61.2 H 4.68. 31P{1H}-NMR (CDCl3) δ = 21.2. 137 11B-NMR (CDCl3) δ = 29.06. 1H NMR (CDCl3): δ = 7.8-7.25 (m, 30 H, Ph), 7.1-6.7 (m, 6 H, C6H3), 4.3 (br, d, 2JpH, = 11.24 Hz, 2 H, CH2), 4.2 (t, 2JPH = 3.8 Hz, 2 H, CH2). 6.5.4. Synthesis of Dichloro palladium bis {Diphenyl- (2-phenyl-benzo [1,3,2]- dioxaborol-4-ylmethyl)-phosphane-3- (Dimethyl amino pyridine)}, 19: In a dry schlenk was taken 300 mg (0.6 mmol) of Diphenyl-(2-phenyl-benzo[1,3,2]- dioxaborol-4-ylmethyl)-phosphane-3-(Dimethyl amino pyridine), 10 ml P O O B P O O B Pd PhPh Ph PhCl Cl PhPh DMAP DMAP of dry THF was added to it. In another flask (COD)PdCl2 [85 mg (0.3 mmol)] was dissolved in 5 ml of dichloromethane and added to the above schlenk. Within few minutes yellow precipitate starts falling out, which was filtered, dried and characterized by NMR. Yield: 272 mg (75%). 31P{1H}-NMR (DMSO) δ = 82.1 (d, 2JPP = 32 Hz), 29.3 (d, 2JPP = 30 Hz), 19.4 (s). 11B-NMR (DMF) δ = 10.4 (s). 6.5.5. General procedure for the syntheses of borates 20 and 22: Catechol phosphines 9b-d (355 mg, 1.15 mmol) dissolved in 10 ml of dry DMF were stirred for 5 minutes. To these solutions was added 35.6 mg (0.57 mmol) of boric acid and the reaction mixture was then heated to 40°C under slight (12 torr) vacuum. After 30 minutes DMF was taken off, the obtained white residue was washed thrice with diethyl ether and finally dried in vacuum. The remaining solid was then dissolved in 5 ml acetonitrile and 0.35 ml (2.5 mmol) of triethylamine was added. The resulting solution was again stirred at room temperature under slight vacuum (12 torr) for 15 minutes. Finally the reaction mixture was taken to dryness. 138 Crystals of 20 and 22 were grown from a concentrated THF solution at –28°C. Triethyl Ammonium [Bis- diphenyl phosphane {benzo (1, 3) dioxa-4-methyl}] 2- borate (20): O O Ph2P O O B- PPh2 Et3NH+ Elemental analysis: Calcd. for: [C44H46 BNO4P2): C 72.83 H 6.39 N 1.93 Found: C 70.83 H 6.78 N 1.70. Yield: 343 mg (83%). Melting point: 92ºC. 31P{1H}-NMR (CD3CN) δ = -13.1 (s). 11B-NMR (CD3CN) δ = 14.33 (s). 1H NMR (CD3CN): δ = 7.6 to 7.26 (m, 20 H, Ph), 6.8 (broad, 1 H, NH), 6.44 to 6.34 (m, 6 H, C6H3), 3.51 (dd, 2 H, 2JHH = 13.9 Hz, 2JPH = 0.9 Hz, CH2), 3.44 (d, 2 H, 2JPH = 13.9 Hz, CH2), 3.13 (q, 6 H, 3JHH = 7.3 Hz, NCH2), 1.23 (t, 9 H, 3JHH = 7.4 Hz, CH3). 13C{1H} NMR (CD3CN): δ = 151.3 (d, JPC = 1.2 Hz, C6H3), 149.9 (d, JPC = 4.2 Hz, C6H3), 139.5 (d, 1JPC = 16.5 Hz, i-C), 139.2 (d, 1JPC = 16.3 Hz, i-C), 132.78 (d, 2JPC = 18.9 Hz, m- C), 132.76 (d, 2JPC = 18.9 Hz, m-C), 128.53 (s, p-C), 128.48 (s, p-C), 128.40 (d, 2JPC = 6.5 Hz, o-C), 128.38 (d, 2JPC = 6.7 Hz, o-C), 118.9 (d, JPC = 8.4 Hz, C6H3), 117.1 (d, JPC = 1.5 Hz, C6H3), 105.9 (br, C6H3), 47.0 (s, NCH2), 27.5 (d, 1JPC = 13.4 Hz, PCH2), 8.2 (s, NCCH3). Triethyl Ammonium [Bis- diphenyl phosphane {benzo (1, 3) dioxa-5-methyl}] 2- borate (22): Ph2P O O O O B- PPh2 Et3NH+ 139 Elemental analysis: Calcd. for (C44H46BNO4P2): C 72.83 H 6.39 N 1.93. Found: C 72.90 H 6.39 N 1.90. Yield: 372 mg (90%); Melting point: 197ºC. 31P{1H}-NMR (CD3CN) δ = -10.2 (s). 11B-NMR (CD3CN) δ = 14.3 (s). 1H NMR (CD3CN): δ = 7.50 to 7.40 (m, 8 H, C6H5), 7.40 to 7.30 (m, 12 H, C6H5), 6.8 (broad, 1 H, NH), 6.37 to 6.30 (broad m, 6 H, C6H3), 3.37 (s, 4 H, CH2), 3.08 (q, 6 H, 3JHH = 7.3 Hz, NCH2), 1.18 (t, 9 H, 3JHH = 7.3 Hz, NCCH3). 13C{1H} NMR (CD3CN): δ = 152.5 (d, JPC = 1.3 Hz, C6H3), 151.0 (d, JPC = 2.7 Hz, C6H3), 140.2 (d, 1JPC = 17.3 Hz, i-C), 133.8 (d, 3JPC = 18.6 Hz, m-C), 129.6 (s, p-C), 129.3 (d, 2JPC = 6.5 Hz, o-C), 127.4 (d, JPC = 8.3 Hz, C6H3), 119.3 (d, JPC = 7.5 Hz, C6H3), 110.3 (d, JPC = 6.7 Hz, C6H3), 108.3 (s, C6H3), 47.9 (s, NCH2), 35.6 (d, 1JPC = 13.6 Hz, PCH2), 9.12 (s, NCCH3). 6.5.6. Synthesis of the silver complex [Ag (20)], 21: To a solution of 130 mg (0.179 mmol) of solid 20 was added 5 ml of DMF, and the mixture was stirred for 5 minutes. 46 mg (0.179 mmol) of silvertriflate was then added with constant stirring. After an hour, the reaction mixture was diluted with 60 ml of diethyl ether. A white precipitate was produced immediately which was filtered off and dried at 40°C/0.001 mbar for 3 hours. White crystals were obtained from DMF: Ether (1:1) mixture at room temperature. P O O P O O B- Ph Ph Ph Ph Ag + Elemental Analysis: Calcd. for [C38H30AgBO4P2 (731.28)]: C 62.41 H 4.14 Found: C 60.81 H 4.12. ESI-MS (positive): m/e = 733.06 (M+ H)+, 755.07 (M+Na)+. 140 Yield: 91.6 mg (70%); Melting point: 253ºC. 31P{1H}-NMR (CDCl3): δ = 2.9 (1JP-107/109Ag = 585/507 Hz). 11B{1H}-NMR (CDCl3) δ = 14.3. 109Ag NMR (CDCl3): δ = 645. 1H NMR (CDCl3): δ = 7.6 to 7.22 (m, 20 H, Ph), 6.80 (broad d, 3JHH = 7.7 Hz, 2 H, C6H3), 6.53 (dd, 3JHH = 7.7 Hz, 2 H, C6H3), 6.21 (broad d, 3JHH = 7.8 Hz, 2 H, C6H3), 3.95 (d of pseudo-t, 2JHH = 13.3 Hz, ΣJPH = 4.6 Hz, 2 H, CH2), 3.51 (dd pseudo-t, 2JHH = 13.3 Hz, 3JAgH = 7.5 Hz, ΣJPH = 12.3 Hz, 2 H, CH2). 13C{1H} NMR (CDCl3): δ = 151.4 (m, C6H3), 149.0 (m, C6H3), 133.1 (m, ΣJPC = 16.2 Hz, 4JAgC = 2.4 Hz, m-C), 132.5 (m, ΣJPC = 15.3 Hz, 4JAgC = 2.4 Hz, m-C), 132.2 (i-C), 131.9 (i-C), 131.0 (s, p-C), 129.8 (s, p-C), 129.1 (pseudo-t, ΣJPC = 9.6 Hz, o-C), 128.9 (pseudo-t, ΣJPC = 10.2 Hz, o-C), 119.5 (m, C6H3), 118.9 (m, C6H3), 113.2 (s, C6H3), 109.6 (m, C6H3), 30.8 (d, 1JPC = 0.8 Hz, CH2). 31P{1H} NMR (DMF-d7): δ = 3.0 (1JP-107/109Ag = 571/494 Hz). 109Ag NMR (DMF-d7): δ = 702. 1H NMR (DMF-d7): δ = 8.00 to 7.86 (m, 12 H, Ph), 7.68 (m, 4 H, Ph), 7.58 (m, 4 H, Ph), 6.72 (broad d, 3JHH = 7.7 Hz, 2 H, C6H3), 6.57 (dd, 3JHH = 7.7/7.7 Hz, 2 H, C6H3), 6.48 (broad d, 3JHH = 7.8 Hz, 2 H, C6H3), 4.09 (m, 2JHH = 13.3 Hz, 3JHAg = 7 Hz, ΣJPH = 14 Hz, 2 H, CH2), 3.95 (d pseudo-t, 2JHH = 13.3 Hz, ΣJPH = 4 Hz, 2 H, CH2). 6.5.7. Synthesis of the Ag-B macrocycle Ag2 (22)2, 23: To 330 mg (0.455 mmol) of 22 was dissolved under stirring (15 min) in13 ml of DMF. To this solution was added 117 mg (0.455 mmol) of silver triflate and stirring was continued for an hour at room temperature. 40 ml of diethyl ether was added and white precipitate was produced immediately. The precipitate was filtered off and dried at 50°C/0.001 mbar for 3 hours. Yield: 470.9 mg (70%); Melting Point: 180ºC. 141 Elemental analysis: Calcd. for [C76H60Ag2B2O8P4 X 2DMF (1460.15)]: C 61.22 H 4.64 N 1.74 Found: C 60.03 H 4.83 N 2.27. ESI-MS (positive mode) : m/e = 1485.13 (M + Na)+, 754.06 (M + Na)2+. PPh2 O O O O B- Ph2P Ph2P O O O O B- PPh2 Ag Ag+ + 31P{1H}-NMR (DMF-d7) δ = 12.8 (d-broad,1JAg-P = 313.7 Hz). 11B{1H}-NMR (DMF-d7) δ = 14.6. 1H NMR (DMF-d7): δ = 7.8 to 7.3 (m, 40 H, Ph), 6.42 ( s, 4 H, C6H3.), 6.34 (d, 3JHH = 8.1 Hz, 4 H, C6H3), 6.24 (dd, 3JHH = 7.7 Hz, 4 H, C6H3), 3.76 (broad, s, 8 H, CH2). 6.5.8. Triethyl ammonium [Dichloro palladium bis {diphenyl- (benzo- [1,3]- dioxo-4-ylmethyl)-phosphane}] 2-borate(104): To the 130 mg(0.179mmol) of solid, Bis[{benzo(1, 3, 2) dioxaborol-3-methyl}-diphenyl phosphane] was added 5ml of DMF and was stirred for 5 mins. To this solution was added 51mg (0.179mmol) of (COD)PdCl2 with constant stirring. The reaction mixture was stirred at room temp. for another 24 hours. To the DMF solution was added 60ml of diethyl ether. Immediately a orange precipitate falls out. This was filtered out and dried at 400C at 0.001 mbar for 3 hours. The dried orange-red powder was than characterized using different analytical techniques. M.P 142ºC 31P{1H}-NMR (DMF-d7) δ = 40.7 (s), 31.2 (s), 19.5(s). 11B{1H}-NMR (DMF-d7) δ =14.6. 142 ESI-MS(positive): m/e = 743.07 [(catphos)2Pd+2H+Na]+, where (catphos) = C19H15O2P, 1465.15 {[(catphos)2Pd+2H]2+Na}+. ESI-MS (negative mode): m/e = 719.07 [(catphos)2+HPd]¯ , 404.96 [(catphos)BOHCl]¯ . 6.6. Transition metal complexes of templated symmetric bisphosphine ligands and their potential application in catalysis 6.6.1. Synthesis of palladium-bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4- ylmethyl) phosphane)}- gallium chloride (25): 400 mg (1.29 mmol) of 3-(Diphenyl-phosphinoylmethyl)-benzene-1, 2-diol, 114 mg (0.64 mmol) of gallium trichloride, 185 mg (0.64 mmol) cyclooctadienyl palladium dichloride and 0.5 ml (3.25 mmol) of triethyl amine were placed in a dried 100ml Schlenk tube, 10 ml of dried DMF was added and the reaction mixture was stirred at room temperature for 3 hours. The precipitate was filtered through a P4 glass filter frit with a celite bed. The filtrate was dried in vacuum. The red powder was dissolved in 10 ml DMF, diluted by adding 80 ml of diethyl ether and filtered; this was repeated one more time. The remaining residue was dried in vacuum at 70ºC. Crystals were grown from a 1:1 mixture of dichloromethane: diethyl ether or THF: diethyl ether. O O Ph2 P O O Ph2 P Ga Cl Pd Yield: 369mg (70%); Melting Point: 358ºC. Elemental analysis: Calcd. for [C38H30ClGaO4P2Pd (824.17 g/mol)]: C 55.38 H 3.67 Found: C 53.02 H 3.50. ESI-MS (positive mode): m/e = 825.0 (M+H)+, 847.0 (M+Na)+, 857.0 (M+2O+H)+. ESI-MS (negative mode): m/e = 823.0 (M-H)¯, 856.9 (M+Cl)¯. 31P{1H}-NMR (CDCl3) δ = 64.7 (s). 143 1H NMR (CDCl3): δ = 7.5-6.80 (m, 20 H, Ph), 6.80 (broad, C6H3), 6.51 (t, 3JHH = 7.8 Hz, C6H3), 6.1 (d, 3JHH = 7.4, C6H3), 3.55 (d, 2JPH = 12.4 Hz, 2 H, CH2), 3.2-3.1 (br, s, CH2). 6.6.2. Synthesis of palladium-bis {diphenyl- (benzo- [1, 3]-µ-oxo- k-oxo-4- ylmethyl)-phosphane)}-tin dichloride (26a): A mixture of 3-(Diphenyl-phosphinoylmethyl)-benzene-1, 2-diol (600 mg, 1.95 mmol), SnCl4 (1.1 ml, 0.97 mmol), (COD)PdCl2 (280 mg, 0.97 mmol), and NEt3 (0.8 ml, 5.7 mmol) in dry DMF (20 ml) was stirred for 6 days at room temperature. The red suspension was filtered through celite. Solvents were evaporated in vacuum. The residue was washed with CH2Cl2 (10 ml) and dissolved in little DMF. The same volume of CH2Cl2 and, finally, small portions of diethyl ether were added until a precipitate began to form. The mixture was stored overnight at +4°C to yield a microcrystalline solid which was collected by filtration and dried in vacuum for 4 hours at 70°C to yield 40% of 26a. Increasing the reaction temperature to 60ºC improved the yield and 26a was isolated 60%. O O Ph2 P O O Ph2 P Sn Pd ClCl Yield: 528 mg (60%); Melting point: 214°C. Elemental analysis: Calcd. for (26a × DMF): C 50.16 H 3.80 N 1.43 found: C 49.92 H 3.77 N 1.58. 119Sn{1H} CP-MAS NMR: δ iso = -455. 31P{1H} CP-MAS NMR: δ iso = 79.5, 74.1; JPP = 41 Hz (from 2D-J-resolved). 31P{1H}-NMR (DMF-d7) δ = 77,00 (br, s). 1H NMR (DMF-d7) δ = 7.7 to 7.25(m, broad, 20 H, C6H5), 6.9 (d, 3JHH = 8.0 Hz, 2 H ), 6.58 (broad, s, 2 H ), 6.1 to 6.03 (broad, s, 2 H ), 4.0 to 3.7 (broad, 4 H, CH2). Cooling down the 26a to –30ºC results into appearance of a new 31P resonance at 55.5 ppm, which grew in intensity upon cooling to –55ºC. This observation revealed that there should be two products that are in fast equilibrium at room temperature and can be access 144 at reduced temperatures. The theoretical calculations (DFT) and 2D NMR measurements revealed the formation of solvent (DMF) adduct of 26a at lower temperatures, which is designated as 27a. 1H NMR (DMF-d7, 223K): assignments were derived from 1H-TOCSY, 1H-NOESY, 1H, 31P-HMQC NMR spectra): 26a: 31P{1H}-NMR (DMF-d7, 223K) δ = 77,0 (br, s). 1H NMR (DMF-d7, 223K) δ = 7.87, 7.73, 7.62 (all br, 10 H, C6H5), 7.57, 7.43, 7.28 (all br, 10 H, C6H5), 6.93 (br d, 2 H, C6H3), 6.55 (br t, 2 H, C6H3), 5.98 (br d, 2 H, C6H3), 4.64 (br m, 2 H, PCH2), 3.86 (br m, 2 H, PCH2). 27a: 31P{1H}-NMR (DMF-d7, 223K) δ = 55,5 (br, s). 1H NMR (DMF-d7, 223K) δ = 7.74, 7.68, 7.43 (all br, 10 H, C6H5), 7.6 – 6.5 (br, 6 H, C6H3), 4.16 (br, 4 H, PCH2). 6.6.3. Synthesis of palladium-bis {diphenyl- (benzo- [1, 3]-µ-oxo- k-oxo-4- ylmethyl)-phosphane)}-dimethyl tin (26b): Dry DMF (20 ml) was added to a mixture of 9b (550 mg, 1.79 mmol), Me2SnCl2 (196 mg, 0.89 mmol), (COD)PdCl2 (250 mg, 0.89 mmol) and Et3N (0.93 ml, 5.34 mmol). The reaction mixture was stirred for 3 hours at room temperature to give a red suspension, which was filtered through a celite bed in a P4 glass filter frit. The red filtrate was stored overnight at –28ºC. The colorless crystalline precipitate formed was separated by decantation, the solution diluted by addition of 50 ml of diethyl ether, and stored at +4ºC. Dark red crystals formed which were collected by decantation and dried in vacuum at 120ºC for 4 hours. O O Ph2 P O O Ph2 P Sn Me Pd Me 145 Elemental analysis: Calcd. for (C40H36O4P2PdSn + DMF): C 54.78 H 4.81 N 1.49 Found: C 54.68 H 4.78 N 1.41. Yield: 733 mg (95%); Melting point: 310ºC. ESI-MS (positive mode): m/e = 869.02 (100%) (M+H)+. 31P{1H} NMR (CDCl3, 303 K): δ = 74.6 (broad, s). 1H NMR (CDCl3, 303 K): δ = 7.96 (broad, s, 1 H, DMF), 7.4-6.8 (m, 20 H, Ph), 6.74 (d, 3JHH = 8.0 Hz, 2 H, C6H3), 6.34 (t, 3JHH = 7.91 Hz, 2 H, C6H3), 5.61 (d, 3JHH = 7.8 Hz, 2 H, C6H3), 3.6-3.2 (broad, 4 H, CH2), 2.89 (s, 3 H, DMF), 2.82 (s, 3 H, DMF), 0.53 (s, 6 H, SnMe). 13C{1H} NMR (CDCl3, 303 K): δ = 162.6 (s, DMF), 154.5 (br., s), 148.9 (s), 132.4 (br., s), 131.7 (s), 128.5 (t, JPC = 4.6 Hz), 120.7 (s), 119.4 (s), 115.8 (s) 115.6 (s), 36.4 (s, DMF), 33.4 (br., CH2), 31.4 (s, DMF), 25.6 (s, SnCH3). 6.6.4. Synthesis of platinum -bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4- ylmethyl) phosphane)}-dimethyl tin (28): Complex 28 was synthesized under identical condition as described in section 6.6.3 for 26b. Crystals were grown from a concentrated DMF solution of the light yellow colored product at room temperature. O O Ph2 P O O Ph2 P Sn Pt RR R = Me Yield: 809 mg (95%); Melting point: 354°C (dec). Elemental analysis: Calcd. for (C40H36O4P2PtSn + DMF): C 50.17 H 4.21 N 1.36 Found: C 50.09 H 4.21 N 1.41. ESI-MS (positive): m/e = 957.08 (M+H)+, 979.07 (M+Na)+. 31P{1H}-NMR (CDCl3) δ = 39.5 (s, 1JPt-P = 2041 Hz). 146 31P{1H}-NMR (CDCl3, 213K) δ = 41.7 (s, 1JPt-P = 2042 Hz). 119Sn{1H}-NMR (CDCl3) δ = -183.8 (s). 1H NMR (CDCl3) δ = 7.99 (br, s, 1 H, DMF), 7.4 - 6.9(m, 20 H, Ph), 6.77 (d, 3JHH = 7.7 Hz, 2 H, C6H3), 6.39 (t, 3JHH = 7.78 Hz, 2 H, C6H3), 5.64 (d, 3JHH = 7.24 Hz, 2 H, C6H3), 3.6 - 3.2 (br., s, 4 H, CH2), 2.92 (s, 3 H, DMF), 2.85 (s, 3 H, DMF), 0.62 (broad, s, 6 H, Sn-Me). 6.6.5. Syntheses of palladium- bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4- ylmethyl) phosphane)}-bismuth chloride (29): O O Ph2 P O O Ph2 P Bi Cl Pd The mixture of 280 mg (0.90 mmol) of 3-(Diphenyl-phosphinoylmethyl)-benzene-1, 2- diol, 143 mg (0.45 mmol) of BiCl3, 130 mg (0.45 mmol) of (COD)PdCl2 and 0.32 ml (2.27 mmol.) of Et3N was dissolved in 8 ml of dry DMF. Though the 31P NMR indicated completion of the reaction in 3 hours, stirring was continued overnight. The dark-red suspension was filtered through a P4 glass filter frit; the filtrate was kept at –28ºC overnight. White needle like crystals of triethyl ammonium chloride were decanted off. The filtrate was diluted with excess of ether and the precipitate obtained was dissolved in dichloromethane. Dark red crystals of good quality were grown from a concentrated dichloromethane solution at room temperature. The crystals were filtered off and dried in vacuo. Yield: 303 mg (70%); Melting point: 273ºC (dec). Elemental analysis: Calcd. for (C38H30BiO4P2Pd + CH2Cl2): C 44.68 H 3.08 Found: C 44.51 H 3.03. ESI-MS (positive mode): m/e: 927.04 (M-Cl)+, 969.03 (M+Li)+. 31P{1H}-NMR (DMF-d7) δ = 70.8 (br, s), 52.1 (br, s). 147 1H NMR (DMF-d7) δ = 8.3 (br, s, 1 H, DMF) 7.9 - 7.2 (m, 20 H, Ph), 6.8 - 6.1 (br., s, 6 H, C6H3), 6.0 (s, 2 H, CH2Cl2), 3.9 - 3.70 (br., d, 4 H, CH2), 3.1 - 2.8 (br., 6 H, DMF). 31P{1H}-NMR (DMF-d7, 223K) δ = 69.8 (s), 50.0 (s). 1H NMR (DMF-d7, 223K) δ = 8.0 (s, 1H, DMF), 8.0-7.9 (br, s, o-Ph), 7.7 (t, 3JHH = 6.9 Hz, Ph), 7.6 (t, 3JHH = 7 Hz, Ph), 7.5 (t, 3JHH = 7.1 Hz, Ph), 7.3 (t, 3JHH = 7.2 Hz, Ph), 7.2- 7.1 (br, s, Ph), 6.6 (t, 3JHH = 7.3 Hz, C6H3), 6.5 (t, 3JHH = 7.1 Hz, C6H3), 6.3 (t, 3JHH = 7.2 Hz, C6H3), 6.2 (s, CH2Cl2), 3.9 (br, s, CH2), 3.8 (d, 2JPH = 11.1 Hz, CH2). 6.6.6. (a) Synthesis of bis {palladium- bis {diphenyl- (benzo- [1, 3]-µ-oxo-k- oxo-4-ylmethyl) phosphane)}- zirconium (30): 200 mg (0.64 mmol) of 3-(Diphenyl-phosphinoylmethyl)-benzene-1, 2-diol, 75.6 mg (0.32 mmol) of zirconium-tetrachloride, 124 mg (0.32 mmol) Bis (benzonitrile) palladium dichloride and 423 mg (1.3 mmol) of Cesium carbonate were placed in a Schlenk tube. The solid mixture was dissolved in 15 ml of DMF and stirred for 6 days at room temperature. Zr O O O O O O O O Ph2P Ph2P PPh2 PPh2 Pd Pd The red colored suspension was filtered, and the filtrate evacuated to dryness. The red residue was dissolved in DMF: dichloromethane (1:1), and diluted with 50 ml of ether. The formed precipitate was filtered off and dried in vacuum. Crystals suitable for X-ray measurements were grown by slow diffusion of diethyl ether into a concentrated DMF solution of 30. As similar reactions with gallium (25) and tin (26b), with triethyl amine as base have shown that the reaction time can be reduced to 3 hours, similar behavior is expected with zirconium as well. Yield: 293 mg (60%); Melting point: 390°C (dec). Elemental analysis: Calcd. for (C76H60O8P4Pd2Zr + 3DMSO): C 55.85 H 4.46 Found: C 55.38 H 4.40. 31P{1H}-NMR (DMSO-d6) δ = 52.4 (s). 148 1H NMR (DMSO-d6): δ = 7.53 (t, 3JPH = 8.72 Hz, 16 H, Ph), 7,36 (t, 3JHH = 7.34 Hz, 8 H, Ph), 7.15 (t, 3JHH = 6.8 Hz, 16 H, Ph), 6.0 - 6.2 (m, 8 H, C6H3), 5.97 (d, 3JHH = 7.11 Hz, 4 H, C6H3), 3.64 (br, d, 8 H, CH2). 6.6.6 (b) Synthesis of dicyclopentadienyl {palladium- bis {diphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4-ylmethyl) phosphane)}- zirconium (30A): In a Schlenk was added 190mg (0.62 mmol.) of 3-(Diphenyl-phosphinoylmethyl)-benzene- 1,2-diol, 90 mg (0.31 mmol.) of Cp2ZrCl2, 118 mg (0.31 mmol.) Bis(benzonitrile) palladium dichloride and 0.21ml (1.5 mmol.) of Et3N. This was dissolved in 15 ml of dried DME:THF and stirred for 2 hours at room temperature. A dark red reaction mixture was filtered and the precipitate was dissolved in THF. This was diluted by adding excess of diethyl ether, the residue formed was filtered and dried in vacuum for two hours. Microcrystals of the product were obtained from THF: Et2O solution at room temperature, dried in vacuum and characterized by NMR. 31P{1H}-NMR (DMSO-d6) δ = 49.8(s). 1H NMR (DMSO-d6): δ = 8.0-6.9 (m, Ph), 6.7-5.6(br., m, C6H3), 3.7-3.5 (br, d, CH2). 6.6.7. Synthesis of tetrakis {palladium- bis {diphenyl- (benzo- [1, 3]-µ-oxo-k- oxo-4-ylmethyl) phosphane)- yttrium} µ4-hydroxy tri-chloride (31): To a mixture of 320 mg (1.04 mmol) of 3-(Diphenyl-phosphinoylmethyl)-benzene-1,2- diol, 101 mg (0.52 mmol) of YCl3, 148 mg (0.52 mmol) of (COD)PdCl2 and 0.36 ml (2.59 mmol) of Et3N was added 10 ml of dry DMF. This reaction mixture was stirred for 3 hours at room temperature to give a dark red suspension, which was filtered through celite bed in a P4 glass filter frit. The red filtrate was kept at –28ºC overnight, to give needle like white crystals. The solution was decanted to another Schlenk tube and kept at room temperature for crystallization. The dark red colored square crystals separated within 24 hours. The product was dried at 120ºC for 4 hours. Yield: 275 mg (60%); Melting point: 345ºC (dec). Elemental analysis: Calcd. for (C164H148Cl3N4O21P8Pd4Y4): C 54.02 H 4.09 N 1.54 Found: C 53.14 H 4.04 N 1.20. 149 O P Ph2 O Y Y Y Y O P Ph2 O O Ph2P O O Ph2P O O PPh2 O O PPh2 O O Ph2 P O O Ph2 P O OPd Pd Pd Pd DMF DMF DMF DMF Cl- Cl- Cl- ESI-MS (positive mode): m/e = 1644.95 (M-Cl+LiF2)2+, 1082.7 (M-3Cl)3+. 31P{1H}-NMR (CDCl3): δ = 69.8 (s). 1H NMR (CDCl3) δ = 7.95 (s, broad, DMF) 7.7 - 6.7(m, 80 H, Ph), 6.25 (t, 3JHH = 7.2 Hz, 8 H, C6H3), 6.13 (q, 3JHH = 8.70 Hz, 8 H, C6H3), 5.79 (t, 3JHH = 6.65 Hz, 8 H, C6H3), 4.2 - 4.0 (br., d, 8 H, CH2), 3.1 - 2.90 (br., d, 8 H, CH2), 2.85 to 2.9 (br, DMF). 6.6.8. Synthesis of bis {palladium- 3-[(Diphenyl phosphanyl)-methyl]-2-{4- [(diphenyl phosphanyl)-methyl]-benzo[1,3,3’] µ-oxo- µ’-oxo k-oxo -2- yloxy}-phenol]}- yttrium chloride (32): Y+ OH O O O O OH O O Ph2P Ph2P PPh2 PPh2 Pd Pd Cl- To a mixture of 450 mgs (1.4 mmol) of 3-(Diphenyl-phosphinoylmethyl)-benzene-1,2-diol, 71 mg (0.36 mmol) of YCl3, 208 mg (0.7 mmol) of (COD)PdCl2 and 0.51 ml (3.65 mmol) of Et3N was added 12 ml of dry DMF. This mixture was stirred for 3 hours at room temperature, giving a dark red suspension. The suspension was filtered through a celite bed and the filtrate was kept at –28ºC overnight, to give needle like white crystals. The solution was decanted to another Schlenk tube, an equal amount of diethyl ether was added 150 and the solution kept at room temperature for crystallization. Dark red colored prismatic crystals of X-ray quality were obtained. The residue was dried at 100ºC for 4 hours. Yield: 741mg (65%); Melting point: 197ºC (dec). ESI-MS (positive mode): m/e = 1529.06 (M-Cl)+, 765 (M-Cl+H)2+, 776.05 (M-Cl+Na)2+, 786.01 (M-HCl+2Na)2+, 510.35 (M-Cl+2H)3+, 743.07 (C38H32O4P2Pd1+Na)+ ESI-MS (negative mode) m/e : 1527 (M-2H)¯ , 719.1 (C38H31O4P2Pd)¯ . 31P{1H}-NMR (CDCl3) δ = 70.8 (br, s), 66.0 (br, s). 1H NMR (CDCl3) δ = 8.2 (s, broad, 1 H, DMF) 7.5-6.6 (m, 40 H, C6H5), 6.25 (t, 3JHH = 8.1 Hz, 2 H, C6H3), 6.17 (d, 3JHH = 7.7 Hz, 2 H, C6H3), 6.0 (d, 3JHH = 7.0 Hz, 2 H, C6H3), 5.93 (d, 3JHH = 7.3 Hz, 2 H, C6H3), 5.85 (br, s, 1 H, C6H3), 5.7 (d, 3JHH = 7.6 Hz, 1 H, C6H3), 5.6 (d, 3JHH = 7.6 Hz, 2 H, C6H3), 3.3 (d, 2JPH = 13.5 Hz, 4 H, CH2), 3.0 (d, 2JPH = 14.4 Hz, 4 H, CH2), 2.85 to 2.9 (broad, 6 H, DMF). 6.6.9. Investigations on the catalytic behavior of selected metal complexes: Sonogashira C-C coupling reaction: The palladium-tin complexes 26a and 26b synthesized according to the procedures reported in section 6.6.2, 6.6.3 respectively were employed as catalysts for the Sonogashira coupling of phenyl acetylene and 4-iodo nitrobenzene. The reaction was carried out under standard condition as follows: Phenyl acetylene (44 mg, 0.44 mmol), copper iodide (33 mg, 0.16 mmol), and 26a (30 mg, 3 mmol %) were added to a solution of 4-iodo-nitrobenzene (98 mg, 0.44 mmol.) in 15 ml of triethyl amine/DMF (2:1). The mixture was stirred for 20 hours at room temperature. N- Hexane (20 ml) was then added and the precipitate filtered off. The filtrate was evaporated to dryness and the dark residue purified by column chromatography using neutral silica as stationary phase and dichloromethane/hexane (3:7) as eluent to give 92 mg (94%) of 4- nitrophenyl-phenylacetylene. The coupling product was characterized by 1H NMR. The corresponding reaction using 26b as (pre)catalyst was performed under identical conditions except that the ratio of 26b: CuI was changed to 2:1. 31P NMR spectra which were recorded after 1, 5 and 20 hours in order to monitor the status of the catalyst showed a single resonance at 76 ppm confirming that 26b remained intact during the reaction. 151 After 24 hours, all volatiles were evaporated in vacuum. The residue was extracted with 10 ml of toluene. The suspension formed was allowed to settle for 15 minutes and the supernant toluene layer decanted, which on purification (by column chromatography as in 26a) gave the coupling product in (88 mg) 90% yield. The residue was dried in vacuum and dissolved in 5 ml of DMF. The 31P NMR spectrum of this solution still showed the resonance of 26b at 76 ppm. The residue obtained after evaporation of the solvent was recovered and reused for the second catalytic cycle that produced (73 mg) 75% of the coupling product. The same cycle as above was repeated for the third time and the catalyst was reused for further transformations. + I NO2 3 mol.% Pd-Sn complex CuI/Et3N DMF NO2 1H NMR (CDCl3): δ = 8.22 (m, 2 H, C6H4NO2), 7.67 (m, 2 H, C6H4NO2), 7.55 (m, 2 H, Ph.), 7.35 - 7.45 (m, 3 H, Ph). 6.7. Transition metal complexes of templated bisphosphine ligands with diastereotopic donor sites: 6.7.1. Synthesis of palladium -bis {phenyl, 2,4,6-trimethyl-phenyl (benzo- [1, 3]-µ-oxo-k-oxo-4-ylmethyl) phosphane)}-dimethyl tin (34a/b): 3-[(Mesitylphenyl phosphanyl)-methyl]-benzene-1, 2-diol (0.69 mmol) was dissolved in 8 ml of dimethyl formamide. Addition of 98 mgs (0.34 mmol) of 1,5-cyclooctadiene- palladium dichloride, 75 mg (0.34 mmol) of dimethyl tin dichloride followed by 0.24 ml (1.7 mmol) of triethyl amine gave a dark deep red suspension. Monitoring the reaction by 31P NMR indicated completion of the reaction after 3 hours. The suspension was then filtered and the filtrate diluted with an excess of diethyl ether. The dark red colored powder formed was filtered off, and dried in vacuum at 80°C. According to the spectroscopic and analytical data (see below) a mixture of two products was obtained. The X-ray crystal structure determination showed a product with methyl and chloride substituents at tin center. 152 O O PhMes P O O PhMes P Sn Me Pd R R =Me/Cl Yield: 231mg (70%); Melting point: 230°C (dec). Elemental analysis: Calcd. for (C46H48O4P2PdSn + C45H45ClO4P2PdSn) C 56.80 H 4.87 Found: C 57.08 H 5.22. ESI-MS (positive mode): m/e = 937.08 (M-Cl)+, 973.04 (M+H)+, 994.14 (M+Na)+. 31P{1H}-NMR (DMF-d7) δ = 63.6 (s). 31P{1H}-NMR (DMF-d7, 273K) δ = 65.0 (s), 62.3 (s). 31P{1H}-NMR (DMF-d7, 243K) δ = 64.3 (s), 61.1 (s), 50.5 (s). 31P{1H}-NMR (DMF-d7, 213K) δ = 72.6 (s), 64.83 (s), 61.8 (dd, JPP = 32 Hz) 61.3 (s), 59.9 (s), 50.5 (s). 1H NMR (DMF-d7, 243K) (the assignments were made from 1H, 31P and 1H, 119Sn 2D experiments) δ = 8.0-6.7 (br, m, Ph), 6.65 (d, 3JHH = 7.7 Hz, C6H3), 6.53 (t, 3JHH = 7.6 Hz, C6H3), 6.05 (d, 3JHH = 7.6 Hz, C6H3), 3.8-3.4 (br. m, CH2), 0.82 (br, s, SnCH3), 0.77(br, s, SnCH3), 0.43 (br, s, SnCH3), 0.34 (br, s, SnCH3). 31P{1H} CP-MAS NMR: δ iso = 55. 119Sn{1H} CP-MAS NMR: δ iso = -207, -308. 6.7.2. Synthesis of palladium -bis {biphenyl- (benzo- [1, 3]-µ-oxo-k-oxo-4- ylmethyl) phosphane)}-methyl tin chloride (33a): To a DMF solution of 200 mg (0.65 mmol) of 3-(Diphenyl-phosphinoylmethyl)-benzene-1, 2-diol was added 78 mg (0.32 mmol) of methyl tin trichloride and 93 mg (0.32 mmol) of 1,5 cyclooctadiene palladium dichloride. Short stirring followed by addition of 2.5 equivalents (1.6 mmol) of triethyl amine resulted in formation of a red suspension. The reaction mixture was filtered and volatiles were evaporated in vacuum. The red colored 153 residue was dissolved in a minimum amount of DMF, few drops of diethyl ether were added and the solution was kept for crystallization at room temperature. Shining red crystals formed which were collected by filtration. O O Ph2 P O O Ph2 P Sn Me Pd Cl Elemental analysis: Calcd. for (C39H33ClO4P2PdSn + 2DMF): C 52.25 H 4.58 N 2.71 Found: C 52.19 H 4.56 N 2.37. Yield: 199 mg (70%); Melting point: 255°C (dec). ESI-MS (positive mode): m/e = 852.99(100%) (M-Cl)+, 894.98 (M+Li)+. 31P{1H}-NMR (DMF-d7) δ = 69.6 (br, s). 119Sn{1H}-NMR (DMF-d7, 213K) δ = -327 (br, s). 1H NMR (DMF-d7) δ = 7.9-7.2 (m, 20 H, Ph), 6.8 (d, 3JHH = 7.7 Hz, 2 H, C6H3), 6.6 (t, 3JHH = 7.8 Hz, 2 H, C6H3), 6.3 (d, 3JHH = 7.6 Hz, 2 H, C6H3), 4.1 to 3.8 (broad, d, 4 H, CH2), 0.9 (broad, t, 2JSnH, 106 Hz, 3 H, SnCH3). 31P{1H}-NMR (DMF-d7, 213K) δ = 77.5 (dd, 2JPP = 297 Hz), 72.64 (broad, s), 54.24 (broad, s). 1H NMR (DMF-d7, 213K) δ = 8.0-6.3 (br, m), 6-5.8 (br, m), 4.8-4.5 (br, s, CH2), 4.3-4.0 (br, s, CH2), 0.92 (t, 2JSnH = 105.1 Hz, SnCH3), 0.72 (t, 2JSnH = 99.4 Hz, SnCH3). 6.8. Results of computational studies on complex 26a/27a: All DFT-computations were performed with the program package Gaussian 03148 using the B3LYP functional and a normal grid for numeric integration. Energy optimizations of 26a [148] Computations were performed at the B3LYP/3-21g* level of theory with the Gaussian program suite: Gaussian 98 (Rev. A.7), M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, V.G. Zakrzewski, J. A. Montgomery, R. E. Stratmann, J. C. Burant, S. Dapprich, J. M. Millam, A. D. Daniels, K. N. Kudin, M.C. Strain, O. Farkas, J. Tomasi, V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clifford, J.Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K. 154 and of two different adducts with two molecules of formamide were carried using a 3-21g* basis set. The relative energies Erel of both adducts were obtained by computing the energy-optimized molecular structure of formamide at the same level of theory and evaluating the difference Erel = E(adduct) – E(3) – 2 E(formamide). Attempts to locate a structure with trans-coordination of the Chloride ligands at Sn did not lead to a minimum. Attempts to locate a complex with a cis-coordination of formamide ligands at Pd lead to the location of a strongly distorted structure at high energy (Erel = 28.7 kcal mol-1), which is not reported here. A short summary of the computational study is listed below. An electronic version of the computed structures and energies of 26a and its formamide adducts is saved in a CD which is attached at the end of the thesis. Complex 26a (point group C2): E = -14270.3118843 HartreeComplex 26a × 2 Formamide (Coordination at Sn) (point group C2): E = -14608.2311568 Hartree Complex 26a × 2 Formamide (coordination at Pd, trans-isomer) (point group C2) E = -14608.2368014 Hartree Formamide (point group Cs): E = -168.9476573 Hartree Relative Energies Erel (in kcal mol-1): Erel (in kcal mol-1): Complex 26a+ 2 Formamide: 0.0 Complex 26a × 2 Formamide (coordination at Pd, trans-isomer) -15.0 Complex 26a× 2 Formamide (Coordination at Sn) -18.6 Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.Foresman, J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L.Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C. Gonzalez, M. Challacombe, P. M. W. Gill, B.G. Johnson, W. Chen, M. W. Wong, J. L. Andres, M. Head-Gordon, E. S. Replogle and J. A. Pople, Gaussian, Inc., Pittsburgh PA, 1998. 155 7. Summary and outlook 7.1. Summary: The present work deals with the syntheses of functionalized phosphine ligands and their self-assembly to produce di- or multinuclear complexes. A bifunctional ligand with a phosphine functionality at one end and a catechol unit at the other end was designed. The rationale behind the design was to have a ligand which can differentiate between hard and soft metals, and react with a combination of both selectively to produce hetero di-nuclear assembly in single a step. In an effort to synthesize the desired ligands, it was found that the reaction of diphenyl phosphine with phenolic aldehydes proceeds via initial formation of α-phosphanyl- carbinols. The presence of OH-groups in p- or o-position destabilizes the adducts relative to the starting materials and facilitates their subsequent rearrangement into isomeric phosphine oxides. LiAlH4 treatment followed by hydrolysis further allowed to reduce the latter to phenol-functionalized phosphines (see Scheme 7.1). The overall reaction sequence permits to access phosphines with pendant phenolic functionalities from readily available starting materials, without the necessity of additional efforts for the introduction and removal of protecting groups at the phenol functionalities. This procedure constitutes a substantial improvement over previously known synthetic protocols which required often more complicated multi-step approaches.43 The catechol-phosphines 9b and 9d were shown to coordinate to soft acids such as palladium(II) and silver(I) selectively via the phosphorus atom. Though the major goal of this work is to self-assemble the catechol-phosphines to generate multinuclear complexes, it was also planned to explore the Lewis base behavior of these catechol-phosphines itself. A boric acid ester 16a/b was generated by reaction of 156 Ph2P H + R1 CHO R1 PPh2HO R1 PPh2 O R2 R3 R2 R3 R2 R3 2 3a-e 4a-e 5a-d [H+] [H+] R1 R2 R3 3a-9a OH H H+ 3b-9b OH OH H+ 3c-9c H H OH+ 3d-9d H OH OH+ R1 PPh2 R2 R3 9a-d 1. MeI 2. LiAlH4 OH PPhMes OH 9f Scheme 7.1: Syntheses of catechol functionalized phosphine ligands. 9b with aryl boronic acid and its reactivity with hard and soft donors was reported. The catechol-phosphine reacts readily, giving the corresponding alkyl borate. It is envisioned that the phosphine can coordinate to a soft acid and the boron to a hard base, this enable the species to act as a building block for inorganometallic coordination polymers. Thus, six equivalents of pyridine were required to convert 16a quantitatively into the amine adduct 17c, whereas only one equivalent of dimethyl amino pyridine was sufficient to obtain a similar acid-base adduct 17a (see Scheme 7.2). These experimental findings allow to state that the alkyl borate unit behaves as a moderately strong Lewis acid. A strongly electron withdrawing substituent on boron (R = C6F5) makes 17b a stronger acid, leading to intramolecular acid base interactions. A palladium complex of 9b on treatment with phenyl boronic acid produced the corresponding palladium borate complex in good yields, which on treatment with a strong base like dimethyl amino pyridine likewise produced a mixture of products. One of them is likely to be 19, though further evidence is required (Scheme 7.2). An adduct like 19 with appropriately modified donor functions might be of interest as an building block for supramolecular complexes with unsymmetric bidentate “pseudo” ligand. Taking advantage of the selective reactivity of 9b towards hard and soft donors, boron templated metal complexes were synthesized in a stepwise manner. Reacting two equivalents of the catechol-phosphine with one equivalent of boric acid in the presence of a base generated the borate templates 20/22, which were characterized by NMR, ESI-MS and crystal structure. A crystal structure study of 20/22 revealed that changing the relative position of the hard hydroxy donors with respect to the phosphine fragment lead to borate templates with distinctly different P-P distances. The corresponding borate template of 9b 157 PPh2 OH OH 1. RB(OH)2 PPh2 O O B N D P O O B P O O B Pd PhPh Ph PhCl Cl PhPh DMAP DMAP 2. DMAP or Py 2. 1 DMAP R Ph 2. 1 PhB(OH)2 19 a b C6F5 17a,b,c 1. 0.5 (COD)PdCl2 9b R = Ph, D = NMe2 C D --- Ph H R NMe2 Scheme 7.2: Lewis acid-base behavior of catechol-phosphine. showed a relatively small P-P distance (10.6 Å), whereas 9d produced a borate template with P-P distance of 13.3Å. The difference in P-P distance is reflected in differences in B(OH)3, Et3N P O O P O O B- Ph Ph Ph Ph AgCF3SO3 R1 R2 Ph2P Ag 2 219b/dPPh2 O O O O B- Ph2P Ph2P O O O O B- PPh2 Ag Ag 23 B(OH)3, Et3N AgCF3SO3 R3 9b 9d OH OH H H OH OH R1 R2 R3 PPh2 O O PPh2 O O B- PPh2 O O O O B- Ph2P 2022 Scheme 7.3: Synthesis of borate templates 20, 22, monometallic silver complex 21 and a dimmer 23. their activity. 20 reacts with silver triflate to produce the complex 21 whereas 22 reacted in 2:2 ratio and gave 23 (see Scheme 7.3). The monometallic silver complex 21 showed unusual secondary oxygen-silver interactions, which led to a visible deviation of P-Ag-P moiety from linearity. The macrocyclic complex 23 was difficult to crystallize and its constitution was hence established by ESI-MS and DOSY NMR measurements. The main focus of the present work was on performing the assembly of catechol phosphine fragments on a hard acid center and the coordination to a catalytic metal in one step. This working concept was successfully demonstrated by using various hard acid centers and catalytically relevant metals (Scheme 7.4). 158 OH OH PPh2 (COD)PdCl2 GaCl3 DABCO O O Ph2 P O O Ph2 P Ga Cl Pd (COD)PdCl2 BiCl3 Et3N O O Ph2 P O O Ph2 P Bi Cl Pd (COD)PdCl2 Et3N O O Ph2 P O O Ph2 P SnR2 Pd 9b 2 25 29a26a/b26a:R = Cl, 26b:R = Me R2SnCl2 0.5 (COD)PdCl2 ZrCl4/ Et3N Zr O O O O O O O O Ph2P Ph2P PPh2 PPh2 Pd Pd 30 O P Ph2 O Y Y Y Y O P Ph2 O O Ph2P O O Ph2P O O PPh2 O O PPh2 O O Ph2 P O O Ph2 P O OPd Pd Pd Pd DMF DMF DMF DMF Cl- Cl- Cl- (COD)PdCl2 Et3N YCl3 31 (COD)PdCl2 0.5YCl3/ Et3N Y+ OH O O O O OH O O Ph2P Ph2P PPh2 PPh2 Pd Pd 32 (COD)PtBr2 Et3N O O Ph2 P O O Ph2 P Sn Me2 Pt 28 (COD)PdCl2 MeSnCl3, Et3N O O Ph2 P O O Ph2 P Sn Me Pd 33 Cl Me2SnCl2 Cl-- Scheme 7.4: Schematic of self-assembly of 9b to produce various metal complexes. A four-component reaction between gallium (III) chloride, cyclooctadienyl palladium dichloride, catechol phosphine (9b) and excess base produced a heterobimetallic assembly 25 in good yields. Interesting to note is the presence of µ2-bridging oxygen atoms which connect the two metal centers. Complexes 26a/b, 28, 29, 30, 31and 32 were synthesized under identical conditions. The products are distinguished from known heterometallic complexes of phosphinoalcohols in requiring neither the dedicated syntheses of a polydentate chelate ligand,126 nor the need for introducing the metal atoms in separate reaction steps.149,152 [149] G. S. Ferguson, P. T. Wolczanski, Organometallics, 1985, 4, 1601; G. S. Ferguson, P. T. Wolczanski, J. Am. Chem. Soc. 1986, 108, 8293; G. S. Ferguson, P. T. Wolczanski, L. Parkanyi, M. C. Zonnevylle, Organometallics, 1988, 7, 1967. 159 The experimental findings allow to state that the coordination geometry of the template center and its size have considerable impact on the assembly process. For example, a small template like gallium can accommodate only five donor atoms whereas a larger template like zirconium can accommodate as many as eight donor atoms. In the case of bismuth, increasing the size of the template center leads to formation of a dimer in the solid state. In the reaction of 9b with yttrium trichloride it was possible to direct the assembly of multinuclear complexes by controlling the stoichiometric ratio of the starting materials. On the other hand, changing the transition metal from palladium to platinum had negligible effects on the complex formation. The chiral catechol phosphine 9f produced a mixture of diastereoisomeric bimetallic palladium-tin complexes which were characterized by NMR and crystal structure determination. All synthesized complexes displayed µ2-briding oxygen donors and the µ2-briding oxygen- template center bonds were found to be longer than the terminal oxygen-template center bonds. The oxygen-template center bond lengths (bridging and non-bridging) vary according to the size of the template center. The complexes studied here allowed to vary the P-Pd-P bite angles between 97º to 102º depending on the size and nature of the substituents on the template. The solution behavior of 26a/b was fully explored by NMR studies which allow to conclude that complexes 26a/b mimic the behavior of complexes containing a supramolecular bis-phosphine ligand which is formed by the assembly of two catecholate phosphine fragments on a hard acidic metal template and can switch between tetra-dentate O2P2- and bidentate P2- coordination. This hemilabile behavior stimulated a study of the application of these complexes in catalysis and the first experimental proof for the catalytic potential was demonstrated by the application of 26a/b in the Sonogashira C-C coupling reaction (section 4.3). 7.2. Outlook: 7.2.1. Prospective ligands: Throughout the present work it was assumed that the ligand design and the selection of the right template center are crucial for controlling the self-assembly. It is believed that fine- tuning of the ligands may offer further opportunities to study the steric, electronic and 160 stereochemical properties of the assemblies. In this view, the synthesis of further types of ligands is proposed (see Scheme 7.5) as outlined below. CHO OH OH CHO HPPh2/ H+ OH OH PPh2 PPh2 CH3/LiAlH4 41 42 43 OH CHO OH OH OH PPh2 HPPh2/ H+ CH3/LiAlH4 44 Scheme 7.5: Proposed synthesis of a bis phosphine-catechol 42 and biphenyl ligand 44. Ligand 42 can be considered as multifunctional ligand with two phosphine donors and two hydroxy donors and can be employed in various organometallic transformations. Ligand 44 with hydroxy functionality on two aryl rings can be chiral when the aryl rings are not in one plane and may behave very differently. Further, it is envisioned that employing these ligands in complexation may produce either M1L2M'2 type trinuclear complexes or M2L6M'3 (M = Main group elements, M' = transition metals) type multinuclear complexes. Rigid ligands with suitable metals can produce a desired architecture and hence rigidity is another area of great interest in self-assembly process. Increasing the spacer length between the phosphine and the catechol moieties may enable to produce complexes with hard-hard and soft-soft combinations of donors and metal centers. In 51 the donor atoms are directly bound to the aromatic rings, providing rigidity and the biphenyl moiety ensures the separation between the hard and the soft donors. Due to its enhanced rigidity and increased spacer length, ligand 51 will be a promising candidate to study the bite angle, steric and electronic properties of the resulting assemblies. OH OH PPh2 51 Scheme 7.6: 51. 161 7.2.2. Extending the self-assemblies: Inspection of the present work pointed out a few loopholes. Whereas the described work dealt mostly with varying the template center, changing the transition metal (including metals like Rh, Ir, Ru, Cu, Au and Ni ) may shade further light on the redox and catalytic properties of these complexes. As indicated in compound 23, ligand 9d can be a suitable candidate to synthesize macrocyclic assemblies that can be used as host capsule to encapsulate a guest molecule. Section 3.2.1 dealing with the Lewis-acid/base behavior of 9b demonstrated that a palladium complex of 9b with two boron acidic centers 18, can be synthesized and isolated. The complex 18 can be coordinated to a bidentate base, thus can act as a building block (as a bifunctional monomer) for organometallic polymers. In chapter 5 syntheses of diastereomeric bimetallic complexes 33 and 34 was discussed, but the isolation of these complexes proved very difficult. It is highly anticipated that similar complexes with other template centers such as Ga, Ge, Bi, Y and Zr can be synthesized and may enable better isolation of the diastereoisomers. These chiral assemblies can be employed as catalysts in asymmetric syntheses. 7.2.3. Applications: The catalytic potential of 26a/b was demonstrated in section 4.3. Complexes 26a/b were found to be catalytically active in a C-C coupling reaction. Detailed mechanistic investigations and theoretical calculations may help to outline the energy profile of the catalytic cycle and thus provide further insights into the behavior of 26a/b during the catalytic process. All the complexes presented in this work are dinuclear, which can be seen as an asset of these assemblies. The transition metal moiety may activate nucleophiles and at the same time the Lewis acid center (Ga, Sn, Y, Zr) may activate electrophiles. Thus, the heterodinuclear complexes discussed in the present work may provide double activation.150 As an example, synthesis of diphenyl carbonate is catalyzed by palladium-tin complexes, though the mechanism is not clearly established.90 In this regards, it can be postulated that complexes 26a may catalyze the phenol coupling reaction to give diphenyl carbonate. The postulated catalytic cycle is represented in Scheme 7.7. A electron rich CO can break the [150] M. Shibasaki, N. Yoshikawa, Chem. Rev. 2002, 102, 2187. 162 bridging oxygen palladium bonds and addition of CO on palladium can take place. In the next step a phenolate ion adds to the tin center giving out Base.H+ and repeatdely generating an intermediate like 52 (when R = Cl), and finally add itself to the CO the same sequence would continue to produce the diphenyl carbonate (DPC). Thus, there is a lot of scope to explore the phenol coupling reaction and to prove the feasibility of the above hypothesis. O O Ph2 P O O Ph2 P Sn R2 Pd CO, Base HO O O Ph2 P O O Ph2 P Sn Pd C O O R2 C O O O 26a 26a DPC 52 Scheme 7.7: Postulated reaction mechanism of phenol coupling reaction. In view of recent reports on chiral ligands in bifunctional asymmetric catalysis,151 similar transformations are expected from complex 33 and 34. A direct aldol reaction of hydroxyketones can be considers as a good starting point to explore the potential of 33 and 34. In short, using catechol-phosphines as ligands, various catalytic reactions can be realized by modifying transition metals, template centers, organic spacers and peripheral substituents on the phosphorus donor. [151] M. Shibasaki, S. Matsunaga, Chem. Soc. Rev. 2006, 35, 269. 163 7.3. Zusammenfassung: Die vorliegende Arbeit behandelt die Synthese funktionalisierter Phosphane und ihrer Aggregation zu zwei- oder mehrkernigen Komplexen. Es wurde ein bifunktioneller Ligand mit einer Phosphanfunktionalität an einem und einer Katecholeinheit am anderen Ende entworfen. Dieser Ligand sollte die Fähigkeit besitzen, sowohl zwischen harten und weichen Metallen zu unterscheiden als auch in einem einzelnem Schritt selektiv mit diesen Metallen zu Heterozweikern-Komplexen reagieren zu können. Im Verlauf von Bemühungen zur Synthese der gewünschten Liganden stellte sich heraus, dass die Reaktion von Diphenylphosphan mit phenolischen Aldehyden über die Bildung von α-Phosphanylcarbinolen verläuft. Die Anwesenheit der OH-Gruppen in p- oder o- Position destabilisiert die Addukte im Vergleich zu den Ausgangsmaterialien, erleichtert aber im Folgenden die Umlagerung zu isomeren Phosphanoxiden. Durch Umsetzung mit LiAlH4 und nachfolgende Hydrolyse können diese zu entsprechenden phenolfunktionalisierten Phosphanen reduziert werden (Scheme 7.1). Die Gesamtreaktion ermöglicht es, Phosphane mit freien (flexiblen) phenolischen Funktionalitäten aus leicht verfügbaren Ausgangsmaterialien zugänglich zu machen, und zwar ohne die Einführung von Schutzgruppen an den Phenolgruppen. Dieses Verfahren stellt gegenüber der bekannten Literatur, in der häufig komplizierte Mehrstufensynthesen beschrieben wurden, eine erhebliche Verbesserung dar.43 Es wurde auch gezeigt, dass die Katecholphosphane 9b und 9d selektiv über das Phosphoratom an weiche Säuren wie Palladium (II) und Silber(I) koordinieren können. Obwohl das Hauptziel dieser Arbeit die Selbstassoziation von Katecholphosphanen zu mehrkernigen Komplexen war, wurde auch das Lewis Säure/Base Verhalten der Katecholphosphane untersucht. Boronsäureester 16a/b wurden durch Reaktion von 9b mit Arylboronsäuren erzeugt und ihre Reaktivität gegenüber harten und weichen Donormolekülen untersucht. Dabei wurde davon ausgegangen, dass das Phosphoratom an eine weiche Säure und das Bor an eine harte Base koordinieren kann und das Katecholphosphan so als Baustein für metallanorganische Koordinationspolymere dienen kann. So wurden sechs Äquivalente Pyridin benötigt, um 16a quantitativ in das Aminaddukt 17c umzuwandeln, während zur Bildung des analogen Säure-Base Addukts 17a (Scheme 7.2) ein Äquivalent Dimethylaminopyridin ausreicht. 164 Ph2P H + R1 CHO R1 PPh2HO R1 PPh2 O R2 R3 R2 R3 R2 R3 2 3a-e 4a-e 5a-d [H+] [H+] R1 R2 R3 3a-9a OH H H+ 3b-9b OH OH H+ 3c-9c H H OH+ 3d-9d H OH OH+ R1 PPh2 R2 R3 9a-d 1. MeI 2. LiAlH4 OH PPhMes OH 9f Scheme 7.1: Synthese katecholfunktionalisierten phosphanLiganden. Diese experimentellen Ergebnisse zeigen, dass sich die Alkylboronateinheit als mäßig starke Lewis-Säure verhält. Ein stark elektronenziehender Substituent (R = C6F5) am Bor macht 17b zu einer starken Lewis-Säure und induziert intermolekulare Säure-Base- Wechselwirkungen. PPh2 OH OH 1. RB(OH)2 PPh2 O O B N D P O O B P O O B Pd PhPh Ph PhCl Cl PhPh DMAP DMAP 2. DMAP or Py 2. 1 DMAP R Ph 2. 1 PhB(OH)2 19 a b C6F5 17a,b,c 1. 0.5 (COD)PdCl2 9b R = Ph, D = NMe2 C D --- Ph H R NMe2 Scheme 7.2: Lewis Säure-Base Reaktionen von Katecholphosphinen. Der Palladiumkomplex von 9b lieferte mit Phenylboronsäure in guter Ausbeute den entsprechenden Borsäureester. Die Reaktion mit einer starken Base wie Dimethylaminopyridin ergab eine Mischung verschiedener Produkte. Eines dieser Produkte könnte der Komplex 19 sein, obwohl zu dessen eindeutigem Nachweis noch weiter Beweise notwendig sind. (Scheme 7.2). Ein Addukt wie 19 mit entsprechend modifizierten Donorfunktionen könnte als Baustein für supramolekulare Komplexe mit unsymmetrischen, zweizähnigen „Pseudo-“Liganden interessant sein. Unter Ausnutzung der selektiven Reaktivität von 9b gegenüber harten und weichen Donormolekülen wurden Metallkomplexe schrittweise an Bortemplaten synthetisiert. Die Reaktion von zwei Äquivalenten Katecholphosphan mit einem Äquivalent Borsäure in Anwesenheit einer Base erzeugte die Borattemplate 20/22, die durch NMR, ESI-MS und Kristallstrukturanalysen charakterisiert wurden. Die Kristallstrukturen von 20/22 zeigen, dass die Änderung der Position der harten Hydroxyldonatoren relativ zu dem 165 Phosphanfragment zu deutlich unterschiedlichen P-P Abständen führt. Das Borat 20 zeigt einen deutlich kleineren P-P-Abstand (10.6Å) als 22 (13.3 Å). Der Unterschied im P-P Abstand wird in den unterschiedlichen Reaktivitäten von 20/22 reflektiert. Der Ligand 20 reagiert mit Silbertriflat zum Komplex 21, während 22 im Verhältnis 2:2 reagiert und den Makrozylus 23 liefert. Der einkernige Silberkomplex 21 zeigt ungewöhnliche sekundäre- Sauerstoff-Silber-Wechselwirkungen, die zu einer sichtbaren Abweichung der P-Ag-P Einheit von der Linearität führen. Der makrozyklische Komplex 23 war schwierig zu kristallisieren, und sein chemischer Aufbau wurde durch ESI-MS und DOSY NMR Messungen etabliert. PPh2 OH OH 1. RB(OH)2 PPh2 O O B N D P O O B P O O B Pd PhPh Ph PhCl Cl PhPh DMAP DMAP 2. DMAP or Py 2. 1 DMAP R Ph 2. 1 PhB(OH)2 19 a b C6F5 17a,b,c 1. 0.5 (COD)PdCl2 9b R = Ph, D = NMe2 C D --- Ph H R NMe2 Scheme 7.2: Lewis Säure-Base Reaktionen von Katecholphosphinen. B(OH)3, Et3N P O O P O O B- Ph Ph Ph Ph AgCF3SO3 R1 R2 Ph2P Ag 2 219b/dPPh2 O O O O B- Ph2P Ph2P O O O O B- PPh2 Ag Ag 23 B(OH)3, Et3N AgCF3SO3 R3 9b 9d OH OH H H OH OH R1 R2 R3 PPh2 O O PPh2 O O B- PPh2 O O O O B- Ph2P 2022 Scheme 7.3: Synthese der Bormatrix 20/22, des einkernigen Silberkomplexes 21 und des Dimeren 23. Das Hauptziel der vorliegenden Arbeit war es, in einem Schritt die Bildung von Katecholphosphanfragmenten an einem harten Säurezentrum und die Koordination des P- atoms an ein katalytisch aktives Metall zu erreichen. Dieses Arbeitskonzept wurde unter Nutzung verschiedener harter Lewis-Säuren und katalytisch aktiver Metalle erfolgreich durchgeführt (Scheme 7.4). Eine Reaktion zwischen Gallium(III)chlorid, Cyclooctadienpalladiumdichlorid, Katecholphosphan 9b und überschüssiger Base lieferte 166 den Heterozweikernkomplex 25 in guten Ausbeuten. Besonders erwähnenswert ist die Anwesenheit der µ2-verbrückenden Sauerstoffatome, die die beiden Metallzentren verbinden. Die Komplexe 26a/b, 28, 29, 30, 31 und 32 wurden unter identischen Bedingungen hergestellt. Die Produkte sind gegenüber bekannten Heterometall-komplexen von Phophanylalkoholen bemerkenswert, da ihre Darstellung weder die aufwendige Synthese eines vielzähnigen Chelatliganden126 noch die Notwendigkeit zur Einführung von Metallatomen in unterschiedlichen Reaktionsschritten erfordert.152 OH OH PPh2 (COD)PdCl2 GaCl3 DABCO O O Ph2 P O O Ph2 P Ga Cl Pd (COD)PdCl2 BiCl3 Et3N O O Ph2 P O O Ph2 P Bi Cl Pd (COD)PdCl2 Et3N O O Ph2 P O O Ph2 P SnR2 Pd 9b 2 25 29a26a/b26a:R = Cl, 26b:R = Me R2SnCl2 0.5 (COD)PdCl2 ZrCl4/ Et3N Zr O O O O O O O O Ph2P Ph2P PPh2 PPh2 Pd Pd 30 O P Ph2 O Y Y Y Y O P Ph2 O O Ph2P O O Ph2P O O PPh2 O O PPh2 O O Ph2 P O O Ph2 P O OPd Pd Pd Pd DMF DMF DMF DMF Cl- Cl- Cl- (COD)PdCl2 Et3N YCl3 31 (COD)PdCl2 0.5YCl3/ Et3N Y+ OH O O O O OH O O Ph2P Ph2P PPh2 PPh2 Pd Pd 32 (COD)PtBr2 Et3N O O Ph2 P O O Ph2 P Sn Me2 Pt 28 (COD)PdCl2 MeSnCl3, Et3N O O Ph2 P O O Ph2 P Sn Me Pd 33 Cl Me2SnCl2 Cl-- Scheme 7.4: Zusammenlagerung von 9b zu verschieden Metallkomplexen Die experimentellen Befunde zeigen, dass die Koordinationsgeometrie und die Größe des Templatzentrums beträchtliche Auswirkungen auf den Aufbauprozess haben. [152] O. Kühl, S. Blaurock, J. Sieler, E. Hey-Hawkins, Polyhedron, 2001, 20, 2171. 167 Beispielsweise kann ein kleines Templat wie Gallium nur fünf Liganden binden, während ein größeres Templat wie Zirkonium bis zu acht Liganden aufnehmen kann. Im Falle von Wismut führt die Vergrößerung des Templatzentrums zur Bildung von Dimeren im Festkörper. In der Reaktion von 9b mit Yttriumtrichlorid gelanes, den Aufbau multinuklearer Komplexe durch die Variation des stöchiometrischen Verhältnis der Ausgangsmaterialien zu bestimmen. Die Variation des Übergangsmetalls von Palladium zu Platin hatte keinen wesentlichen Einfuss auf die Komplexstruktur. Das chirale Katecholphosphin 9g lieferte eine Mischung diastereoisomerer, zweikerniger Palladium- Zinn-Komplexe, die durch NMR- Daten und eine Kristallstrukturanalyse charakterisiert wurden. Alle dargestellten Komplexe zeigen µ2-verbrückende Sauerstoffatome, deren Bindungen zum Zentralatom länger sind als die entsprechenden Bindungen zu terminalen O-Atomen. Die Bindungslängen (sowohl zu verbrückenden als auch nicht-verbrückenden O-Atomen) schwanken außerdem entsprechend der Größe des Zentralatoms. Die untersuchten Komplexe gestatten es, den Winkel P-Pd-P je nach Größe und Typ des Substituenten zwischen 97º und 102º zu verändern. Das Verhalten von 26a/b in Lösung wurde umfassend durch NMR- Experimente untersucht. Es ist festzustellen, dass sich die Komplexe 26a/b ähnlich verhalten wie Komplexe mit einem supramolekularen Bisphosphan-Liganden, der aus der Anlagerung zweier Katecholatphosphan-Fragmente an ein hartes Lewis-acides Metalltenplat resultiert, und der zwischen vierzähniger O2P2- und zweizähniger P2-Koordination wechseln kann. Dieses hemilabile Verhalten regte eine Studie der Anwendung dieser Komplexe in der Katalyse an, und der erste experimentelle Beweis ihres katalytischen Potentials wurde durch die Anwendung von 26a/b in der Sonogashira C-C Kupplungsreaktion erhalten (Kap. 4.3). 168 8. Crystallographic Appendix Crystal data including atom coordinates, bond distances, bond angles, torsion angles is saved as electron data files. The CD is attached at the end of chapter 9 in this dissertation. Primary information on the crystals reported in this work is provided in the following tables. Crystal data and structural refinement for 5b with 0.5 THF: Identification code Chi01 Empirical formula C21 H21 O3.5 P1 Formula weight 360.35 Temperature 173(2) K Wavelength 0.71073 A Crystal system, space group Triclinic, P1(2)/c (no.14) Unit cell dimensions a = 12.551(3) A alpha = 83.17(3) deg. b = 12.623(3) A beta = 73.50(3) deg. c = 12.767(3) A gamma = 74.13(3) deg. Volume 1863.6(6) A^3 Z, Calculated density 4, 1.284 Mg/m^3 Absorption coefficient 0.167 mm^-1 F(000) 760 Crystal size 0.30 x 0.30 x 0.20 mm Theta range for data collection 1.67 to 27.00 deg. 169 Limiting indices 0 =< h =< 16, -15 =< k =< 16, -15 =< l =< 16 Reflections collected / unique 82031 / 4396 [R(int) = 0.0280] Completeness to theta = 27.00 99.9 % Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 8127 / 0 / 506 Goodness-of-fit on F^2 1.312 Final R indices [I>2sigma(I)] R1 = 0.0647, wR2 = 0.1296 R indices (all data) R1 = 0.0479, wR2 = 0.1214 Largest diff. peak and hole 0.448 and -0.334 e.A^-3 Crystal data and structure refinement for 9b. Identification code dg007_hy Empirical formula C19 H17 O2 P Formula weight 308.30 Temperature 123(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, P2(1)/c (no.14) Unit cell dimensions a = 12.369(2) A alpha = 90 deg. b = 8.320(1) A beta = 101.61(1) deg. c = 15.596(3) A gamma = 90 deg. Volume 1572.1(4) A^3 Z, Calculated density 4, 1.303 Mg/m^3 Absorption coefficient 0.179 mm^-1 F(000) 648 Crystal size 0.45 x 0.30 x 0.25 mm Theta range for data collection 2.97 to 27.48 deg. 170 Limiting indices -15<=h<=16, -10<=k<=10, -20<=l<=20 Reflections collected / unique 15742 / 3524 [R(int) = 0.0230] Completeness to theta = 25.00 98.4 % Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 3524 / 3 / 207 Goodness-of-fit on F^2 1.058 Final R indices [I>2sigma(I)] R1 = 0.0318, wR2 = 0.0756 R indices (all data) R1 = 0.0453, wR2 = 0.0832 Largest diff. peak and hole 0.385 and -0.256 e.A^-3 Crystal data and structure refinement for 13b. Identification code scsep04_cif Empirical formula C38 H34 O4 P2Cl2Pd Formula weight 793.89 Temperature 293(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, P2(1)/c (no.4) Unit cell dimensions a = 10.2633(2)A alpha = 90 deg. b = 22.7369(4)A beta = 112.5860(10) deg. c = 11.6400(2) A gamma = 90 deg. Volume 2507.93(8)A^3 Z, Calculated density 2, 1.34515 Mg/m^3 Absorption coefficient 0.568 mm^-1 F(000) 808 Theta range for data collection 2.10 to 28.27deg. Limiting indices -12<=h<=13, -30<=k<=30, -15<=l<=15 171 Reflections collected / unique 42973 / 10252 Completeness to theta = 28.27 98.9% Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 12092 / 1 / 749 Goodness-of-fit on F^2 1.032 Final R indices [I>2sigma(I)] R1 = 0.0699, wR2 = 0.1263 R indices (all data) R1 = 0.0534, wR2 = 0.1179 Crystal data and structure refinement for 13d. Identification code scdez05a Empirical formula C44 H42 P2PdCl2 O5 THF (C4H8O) Formula weight 866.07 Temperature 100(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, C2(1)/n (no.15) Unit cell dimensions a = 18.54740(110)A alpha = 90 deg. b = 10.39230(70) A beta = 110.2944(39)deg. c = 26.20550(150)A gamma = 90 deg. Volume 4737.555(518)A^3 Z, Calculated density 4, 1.23323 Mg/m^3 Absorption coefficient 0.60 mm^-1 F(000) 1684 Crystal size 0.70 x 0.20 x 0.40 mm Theta range for data collection 1.018 to 28.283 deg. Limiting indices -22<=h<=24, -13<=k<=13, -34<=l<=34 172 Reflections collected / unique 28824 / 5642 [R(int) = 0.1731] Max theta = 56.65 Absorption correction Mulit-scan Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 5642 / 0 / 261 Goodness-of-fit on F^2 1.029 R indices (all data) R1 = 0.1122, wR2 = 0.3573 Largest diff. peak and hole 2.42 and -1.18 e.A^-3 Crystal data and structure refinement for 14b. Identification code dg004_hy Empirical formula C43 H43 Ag Cl2 F3 N O8 P2 S [C38 H34 Ag O4 P2]+ [CF3SO3]-, CH2Cl2, DMF (C3H7NO) Formula weight 1031.55 Temperature 123(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, P2(1)/n (no.14) Unit cell dimensions a = 13.818(1) A alpha = 90 deg. b = 22.343(2) A beta = 104.46(1) deg. c = 15.085(1) A gamma = 90 deg. Volume 4509.7(6) A^3 Z, Calculated density 4, 1.519 Mg/m^3 Absorption coefficient 0.747 mm^-1 F(000) 2104 Crystal size 0.40 x 0.24 x 0.12 mm Theta range for data collection 2.93 to 25.03 deg. 173 Limiting indices -16<=h<=16, -26<=k<=26, -17<=l<=17 Reflections collected / unique 37390 / 7908 [R(int) = 0.0473] Completeness to theta = 25.03 99.3 % Absorption correction Mulit-scan Max. and min. transmission 0.9157 and 0.6172 Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 7908 / 27 / 561 Goodness-of-fit on F^2 1.045 Final R indices [I>2sigma(I)] R1 = 0.0592, wR2 = 0.1375 R indices (all data) R1 = 0.1064, wR2 = 0.1603 Largest diff. peak and hole 1.391 and -2.510 e.A^-3 Crystal data and structure refinement for 14d: Identification code gudat141 Empirical formula C47 H50 Ag F3 O9 P2 S [C38 H34 Ag O4 P2]+ [CF3SO3]- 2 thf Formula weight 1017.74 Temperature 123(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, P2(1)/c (No.14) Unit cell dimensions a = 14.3659(3) A alpha = 90 deg. b = 16.1257(4) A beta = 92.338(1) deg. c = 19.8458(6) A gamma = 90 deg. Volume 4593.7(2) A^3 Z, Calculated density 4, 1.472 Mg/m^3 174 Absorption coefficient 0.621 mm^-1 F(000) 2096 Crystal size 0.15 x 0.10 x 0.05 mm Diffractometer Nonius KappaCCD Theta range for data collection 3.06 to 25.02 deg. Limiting indices -16<=h<=17, -19<=k<=18, -15<=l<=23 Reflections collected / unique 25126 / 8092 [R(int) = 0.0462] Completeness to theta = 25.02 99.7 % Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 8092 / 110 / 580 Goodness-of-fit on F^2 0.910 Final R indices [I>2sigma(I)] R1 = 0.0324, wR2 = 0.0555 R indices (all data) R1 = 0.0705, wR2 = 0.0612 Largest diff. peak and hole 0.499 and -0.349 e.A^-3 Crystal data and structure refinement for 17a: Identification code gudat139 Empirical formula C36 H38 B N2 O3 P Formula weight 588.46 Temperature 173(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, P2(1)/c (No.14) Unit cell dimensions a = 14.7942(4) A alpha = 90 deg. b = 9.5746(4) A beta = 93.558(2) deg. c = 22.8934(7) A gamma = 90 deg. Volume 3236.57(19) A^3 175 Z, Calculated density 4, 1.208 Mg/m^3 Absorption coefficient 0.122 mm^-1 F(000) 1248 Crystal size 0.12 x 0.06 x 0.03 mm Diffractometer Bruker KappaAPEXII Theta range for data collection 3.05 to 25.03 deg. Limiting indices -17<=h<=17, -10<=k<=11, -27<=l<=27 Reflections collected / unique 10492 / 5703 [R(int) = 0.1450] Completeness to theta = 25.03 99.8 % Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 5703 / 96 / 390 Goodness-of-fit on F^2 1.103 Final R indices [I>2sigma(I)] R1 = 0.1199, wR2 = 0.1846 R indices (all data) R1 = 0.2273, wR2 = 0.2272 Largest diff. peak and hole 0.385 and -0.335 e.A^-3 Crystal data and structure refinement for 18: Identification code gudat143 Empirical formula C58 H56 B2 Cl2 O6 P2 Pd (C25 H20 B O2 P)2 Pd Cl2 - 2 thf Formula weight 1109.89 Temperature 123(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, P2(1)/c (no.14) Unit cell dimensions a = 11.7333(7) A alpha = 90 deg. b = 22.9485(17) A beta = 111.424(4) deg. 176 c = 10.3897(5) A gamma = 90 deg. Volume 2604.2(3) A^3 Z, Calculated density 2, 1.415 Mg/m^3 Absorption coefficient 0.572 mm^-1 F(000) 1144 Crystal size 0.20 x 0.10 x 0.05 mm Theta range for data collection 3.25 to 25.03 deg. Limiting indices -12<=h<=13, -27<=k<=24, -12<=l<=12 Reflections collected / unique 22106 / 4480 [R(int) = 0.1020] Completeness to theta = 25.03 97.5 % Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 4480 / 66 / 322 Goodness-of-fit on F^2 0.862 Final R indices [I>2sigma(I)] R1 = 0.0475, wR2 = 0.0753 R indices (all data) R1 = 0.1307, wR2 = 0.0884 Largest diff. peak and hole 0.672 and -0.429 e.A^-3 Crystal data and structure refinement for 20: Identification code gudat117 Empirical formula C48 H56 B N O6 P2 Formula weight 815.69 Temperature 123(2) K Wavelength 0.71073 A Crystal system, space group Triclinic, P-1 (No.2) Unit cell dimensions a = 16.3386(2) A alpha = 84.929(1) deg. b = 16.3500(2) A beta = 88.028(1) deg. 177 c = 16.7372(2) A gamma = 89.833(1) deg. Volume 4450.97(9) A^3 Z, Calculated density 4, 1.217 Mg/m^3 Absorption coefficient 0.146 mm^-1 F(000) 1736 Crystal size 0.40 x 0.30 x 0.20 mm Diffractometer Nonius kappaCCD Theta range for data collection 2.94 to 27.48 deg. Limiting indices -21<=h<=20, -21<=k<=21, -21<=l<=21 Reflections collected / unique 46944 / 19875 [R(int) = 0.0334] Completeness to theta = 27.48 97.4 % Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 19875 / 353 / 1045 Goodness-of-fit on F^2 1.102 Final R indices [I>2sigma(I)] R1 = 0.0733, wR2 = 0.2187 R indices (all data) R1 = 0.1036, wR2 = 0.2398 Largest diff. peak and hole 1.813 and -1.281 e.A^-3 Crystal data and structure refinement for 22: Identification code scnov05 Formula C38 H30 B O4 P2, C6 H16 N Formula Weight 725.57 Crystal System Monoclinic Space group Cc (No. 9) a, b, c [Angstrom] 8.1733(2) 43.277(1) 11.0401(3) alpha, beta, gamma [deg] 90 94.894(2) 90 178 V [Ang**3] 3890.82(17) Z 4 D(calc) [g/cm**3] 1.239 Mu(MoKa) [ /mm ] 0.155 F(000) 1536 Crystal Size [mm] 0.20 x 0.10 x 0.20 Temperature (K) 100 Radiation [Angstrom] MoKa 0.71073 Theta Min-Max [Deg] 4.0, 28.3 Dataset -10: 10 ; -57: 57 ; -14: 14 Tot., Uniq. Data, R(int) 32901, 9084, 0.090 Observed data [I > 2.0 sigma(I)]7638 Nref, Npar 9084, 476 R, wR2, S 0.0561, 0.1140, 1.05 w = 1/[\s^2^(Fo^2^)+(0.0256P)^2^+7.4395P] where P=(Fo^2^+2Fc^2^)/3 Max. and Av. Shift/Error 0.00, 0.00 Flack x -0.02(8) Min. and Max. Resd. Dens. [e/Ang^3] -0.26, 0.29 Crystal data and structure refinement for 21: Identification code scjan07 Empirical formula C38H30Ag1B1O4 P2 + C3H7N1O1 (DMF) Formula weight 804.34.69 Temperature 100(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, Cc Unit cell dimensions a = 18.8664(8) Å alpha = 90.00 deg. b = 15.1936(5) Å beta = 124.062(2) deg. 179 c = 15.0136(5) Å gamma = 90.00 deg. Volume 3565.3(2) A^3 Z, Calculated density 4, 1.498 Mg/m^3 Absorption coefficient 0.703 mm^-1 F(000) 16486 Crystal size 0.80 x 0.50 x 0.50 mm Diffractometer Nonius kappaCCD Theta range for data collection 1.018 to 28.283 deg. Limiting indices -24<=h<=24, -20<=k<=19, -20<=l<=19 Reflections collected / unique 8102 / 4325 [R(int) = 0.0989] Completeness to theta = 28.29 97.6 % Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 8102 / 2 / 458 Goodness-of-fit on F^2 1.032 Final R indices [I>2sigma(I)] R1 = 0.0715, wR2 = 0.1292 R indices (all data) R1 = 0.0562, wR2 = 0.1217 Largest diff. peak and hole 0.77 and -1.06 e.A^-3 Rms deviation from mean = 0.10 e/A^3 Crystal data and structure refinement for 25: Identification code chi06 Empirical formula C38H30Pd1Ga1O4 P2 + 3CDCl3 Formula weight 1182.23 Temperature 173(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, P2 180 Unit cell dimensions a = 16.125(4) Å alpha = 90.00 deg. b = 14.211(4) Å beta = 106.642(19) deg. c = 21.533(5) Å gamma = 90.00 deg. Volume 4728(2) A^3 Z, Calculated density 4, 1.61429 Mg/m^3 Absorption coefficient 1.623 mm^-1 F(000) 2352.0 Crystal size 0.35 x 0.30 x 0.15 mm Diffractometer Nonius kappaCCD Theta range for data collection 1.74 to 28.00 deg. Limiting indices 0<=h<=20, 0<=k<=18, -27<=l<=26 Reflections collected / unique 7304 / 10308 [R(int) = 0.0497] Completeness to theta = 28.00 99.8 % Absorption correction None Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 10308 / 0 / 535 Goodness-of-fit on F^2 1.032 Final R indices [I>2sigma(I)] R1 = 0.0883, wR2 = 0.1017 R indices (all data) R1 = 0.0514, wR2 = 0.1148 Largest diff. peak and hole 0.79 and -0.89 e.A^-3 Rms deviation from mean = 0.12 e/A^3 Crystal data and structure refinement for 26a: Identification code chi06 Formula C38 H30 Cl2 O4 P2 Pd Sn Formula Weight 908.59 Crystal System Monoclinic 181 Space group P2/c (No. 13) a, b, c [Angstrom] 12.227(2) 11.707(2) 16.475(3) alpha, beta, gamma [deg] 90 102.516(12) 90 V [Ang**3] 2302.2(7) Z 2 D(calc) [g/cm**3] 1.311 Mu(MoKa) [ /mm ] 1.149 F(000) 900 Crystal Size [mm] 0.00 x 0.00 x 0.00 Temperature (K) 173 Radiation [Angstrom] MoKa 0.71073 Theta Min-Max [Deg] 2.2, 28.0 Dataset -16: 15 ; -5: 15 ; -21: 21 Tot., Uniq. Data, R(int) 6056, 5523, 0.024 Observed data [I > 2.0 sigma(I)] 4516 Nref, Npar 5523, 220 R, wR2, S 0.0445, 0.1248, 1.04 w = 1/[\S^2^(FO^2^)+(0.0844P)^2^] WHERE P=(FO^2^+2FC^2^)/3' Max. and Av. Shift/Error 0.00, 0.00 Min. and Max. Resd. Dens. [e/Ang^3] -1.08, 1.94 Crystal data and structure refinement for 26b: Identification code scnov06 Formula C40 H36 O4 P2 Pd Sn, C3 H7 N O Formula Weight 940.85 Crystal System Monoclinic 182 Space group P21/n (No. 14) a, b, c [Angstrom] 10.8862(2) 19.1979(3) 20.0183(3) alpha, beta, gamma [deg] 90 102.811(1) 90 V [Ang**3] 4079.52(12) Z 4 D(calc) [g/cm**3] 1.532 Mu(MoKa) [ /mm ] 1.176 F(000) 1896 Crystal Size [mm] 0.00 x 0.00 x 0.00 Temperature (K) 100 Radiation [Angstrom] MoKa 0.71073 Theta Min-Max [Deg] 3.3, 28.3 Dataset -14: 12 ; -25: 25 ; -26: 26 Tot., Uniq. Data, R(int) 56490, 10028, 0.142 Observed data [I > 2.0 sigma(I)] 8455 Nref, Npar 10028, 483 R, wR2, S 0.0633, 0.1568, 1.10 w = 1/[\s^2^(Fo^2^)+(0.0589P)^2^+22.3688P] where P=(Fo^2^+2Fc^2^)/ Max. and Av. Shift/Error 0.00, 0.00 Min. and Max. Resd. Dens. [e/Ang^3] -2.17, 2.20 Crystal data and structure refinement for 28: Identification code chi10 Formula C40 H36 O4 P2 Pt Sn Formula Weight 956.42 Crystal System Monoclinic Space group C2/c (No. 15) 183 a, b, c [Angstrom] 11.4113(14) 22.727(3) 16.324(2) alpha, beta, gamma [deg] 90 107.695(10) 90 V [Ang**3] 4033.2(9) Z 4 D(calc) [g/cm**3] 1.575 Mu(MoKa) [ /mm ] 4.199 F(000) 1864 Crystal Size [mm] 0.20 x 0.25 x 0.25 Temperature (K) 173 Radiation [Angstrom] MoKa 0.71073 Theta Min-Max [Deg] 2.1, 28.0 Dataset -15: 14 ; 0: 30 ; 0: 21 Tot., Uniq. Data, R(int) 5227, 4865, 0.064 Observed data [I > 2.0 sigma(I)] 3479 Nref, Npar 4865, 222 R, wR2, S 0.0358, 0.0906, 0.91 w = 1/[\S^2^(FO^2^)+(0.0448P)^2^] WHERE P=(FO^2^+2FC^2^)/3' Max. and Av. Shift/Error 0.00, 0.00 Min. and Max. Resd. Dens. [e/Ang^3] -1.05, 1.80 Crystal data and structure refinement for 29: Identification code dg002_hy Empirical formula C39 H32 Bi Cl3 O4 P2 Pd C38 H30 Bi Cl O4 P2 Pd - CH2Cl2 Formula weight 1048.32 Temperature 123(2) K Wavelength 0.71073 A 184 Crystal system, space group Monoclinic, P2(1)/c (no.14) Unit cell dimensions a = 11.264(1) A alpha = 90 deg. b = 17.247(1) A beta = 98.52(1) deg. c = 19.346(1) A gamma = 90 deg. Volume 3716.9(4) A^3 Z, Calculated density 4, 1.873 Mg/m^3 Absorption coefficient 5.554 mm^-1 F(000) 2032 Crystal size 0.15 x 0.06 x 0.04 mm Theta range for data collection 2.99 to 25.03 deg. Limiting indices -13<=h<=13, -20<=k<=19, -23<=l<=23 Reflections collected / unique 21315 / 6485 [R(int) = 0.0695] Completeness to theta = 25.03 98.7 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8084 and 0.4579 Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 6485 / 0 / 451 Goodness-of-fit on F^2 1.033 Final R indices [I>2sigma(I)] R1 = 0.0472, wR2 = 0.0837 R indices (all data) R1 = 0.0979, wR2 = 0.0978 Largest diff. peak and hole 2.226 and -0.989 e.A^-3 Crystal data and structure refinement for 30: Identification code scfeb06 Formula C76 H60 O8 P4 Pd2 Zr, 4(C3 H7 N O), C2 O Formula Weight 1861.58 Crystal System Monoclinic 185 Space group C2/c (No. 15) a, b, c [Angstrom] 25.0208(7) 15.3922(5) 25.6866(5) alpha, beta, gamma [deg] 90 107.045(2) 90 V [Ang**3] 9458.0(5) Z 4 D(calc) [g/cm**3] 1.307 Mu(MoKa) [ /mm ] 0.610 F(000) 3808 Crystal Size [mm] 0.00 x 0.00 x 0.00 Temperature (K) 293 Radiation [Angstrom] MoKa 0.71073 Theta Min-Max [Deg] 3.2, 28.3 Dataset -33: 33 ; -19: 20 ; -34: 33 Tot., Uniq. Data, R(int) 45844, 11301, 0.107 Observed data [I > 2.0 sigma(I)] 6855 Nref, Npar 11301, 510 R, wR2, S 0.1020, 0.3134, 1.08 Crystal data and structure refinement for 31: Identification code scokt06 Formula 4 O21 P8 Pd4 Y4, 10(C3 H N O), 2(C4 N), 3(C3), 3(Cl), 4(C) Formula Weight 4572.82 Crystal System Triclinic Space group P-1 (No. 2) a, b, c [Angstrom] 16.3740(2) 18.8825(2) 20.6120(3) alpha, beta, gamma [deg] 67.152(1) 70.115(1) 74.181(1) 186 V [Ang**3] 5449.58(13) Z 1 D(calc) [g/cm**3] 1.393 Mu(MoKa) [ /mm ] 1.538 F(000) 2295 Crystal Size [mm] 0.00 x 0.00 x 0.00 Temperature (K) 293 Radiation [Angstrom] MoKa 0.71073 Theta Min-Max [Deg] 3.8, 28.3 Dataset -21: 21 ; -25: 25 ; -27: 27 Tot., Uniq. Data, R(int) 121778, 26741, 0.119 Observed data [I > 2.0 sigma(I)] 19288 Nref, Npar 26741, 1180 R, wR2, S 0.0730, 0.2075, 1.03 Crystal data and structure refinement for 32: Identification code dg018_hy Empirical formula C88 H86 Cl N4 O12 P4 Pd2 Y [C76 H62 O8 P4 Pd2 Y]+ Cl- dmf, 3 free dmf Formula weight 1852.65 Temperature 123(2) K Wavelength 0.71073 A Crystal system, space group Monoclinic, P21/n Unit cell dimensions a = 19.804(4) A alpha = 90 deg. b = 20.246(4) A beta = 98.08(2) deg. c = 21.280(4) A gamma = 90 deg. 187 Volume 8448(3) A^3 Z, Calculated density 4, 1.457 Mg/m^3 Absorption coefficient 1.272 mm^-1 F(000) 3784 Crystal size 0.25 x 0.15 x 0.10 mm Theta range for data collection 2.94 to 25.03 deg. Limiting indices -23<=h<=23, -24<=k<=21, -25<=l<=24 Reflections collected / unique 56587 / 14752 [R(int) = 0.0849] Completeness to theta = 25.03 98.9 % Absorption correction Semi-empirical from equivalents Max. and min. transmission 0.8833 and 0.6347 Refinement method Full-matrix least-squares on F^2 Data / restraints / parameters 14752 / 171 / 1015 Goodness-of-fit on F^2 1.112 Final R indices [I>2sigma(I)] R1 = 0.0631, wR2 = 0.1012 R indices (all data) R1 = 0.1344, wR2 = 0.1210 Largest diff. peak and hole 0.734 and -0.822 e.A^-3 Crystal data and structure refinement for 33a: Formula C39 H33 Cl O4 P2 Pd Sn, C3 H7 N O Formula Weight 961.27 Crystal System Monoclinic Space group P21/n (No. 14) a, b, c [Angstrom] 10.8914(3) 19.0086(5) 20.1077(6) alpha, beta, gamma [deg] 90 103.320(2) 90 V [Ang**3] 4050.9(2) Z 4 188 D(calc) [g/cm**3] 1.576 Mu(MoKa) [ /mm ] 1.250 F(000) 1928 Crystal Size [mm] 0.00 x 0.00 x 0.00 Temperature (K) 100 Radiation [Angstrom] MoKa 0.71073 Theta Min-Max [Deg] 3.8, 28.3 Dataset -14: 14 ; -25: 25 ; -26: 26 Tot., Uniq. Data, R(int) 55811, 10000, 0.153 Observed data [I > 2.0 sigma(I)] 7137 Nref, Npar 10000, 481 R, wR2, S 0.0769, 0.1622, 1.06 w = 1/[\s^2^(Fo^2^)+(0.0430P)^2^+43.0179P] where P=(Fo^2^+2Fc^2^)/ Max. and Av. Shift/Error 3.78, 0.01 Min. and Max. Resd. Dens. [e/Ang^3] -3.21, 5.31 Crystal data and structure refinement for 34a: Crystal System Monoclinic Space group P21/n (No. 14) a, b, c [Angstrom] 12.2118(3) 22.0395(5) 14.6819(4) alpha, beta, gamma [deg] 90 94.379(2) 90 V [Ang**3] 3939.98(17) Z 4 D(calc) [g/cm**3] 1.628 Mu(MoKa) [ /mm ] 1.265 F(000) 1948 Crystal Size [mm] 0.00 x 0.00 x 0.00 189 Temperature (K) 100 Radiation [Angstrom] MoKa 0.71073 Theta Min-Max [Deg] 3.6, 28.3 Dataset -16: 16 ; -29: 29 ; -19: 19 Tot., Uniq. Data, R(int) 51594, 9673, 0.147 Observed data [I > 2.0 sigma(I)] 7659 Nref, Npar 9673, 490 R, wR2, S 0.0731, 0.1520, 1.14 w = 1/[\s^2^(Fo^2^)+(0.0350P)^2^+28.7466P] where P=(Fo^2^+2Fc^2^)/ Max. and Av. Shift/Error 0.03, 0.00 Min. and Max. Resd. Dens. 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Curriculum Vitae: Mr. Samir H. Chikkali M.Sc. Institute of Inorganic Chemistry University of Stuttgart Pfaffenwaldring 55 D-70569 Stuttgart Germany Phone : +49 711 9719461 Email : chikkali@iac.uni-stuttgart.de Present status Working with Prof. Dr. D. Gudat at the University of Stuttgart, Germany. I will be completing my doctoral work by Sep. 2007. Educational details University of Stuttgart, Stuttgart, Germany • Ph.D. (Organometallic Chemistry) – Nov. 2003 onwards • Research work titled: Complexes of flexible ditopic catechol phosphines: Synthesis, metal assisted self-assembly and catalytic application. • Supervisor: Prof. Dr. D. Gudat National Chemical Laboratory, Pune, India • Summer Fellow of Indian Academy of Science, Banglore: May 2001 to July 2001. Work titled: Syntheses of new bisphenol monomers for the preparation of high performance polymers. • Supervisor: Dr. S. Sivaram, Director, National Chemical Laboratory. • Project Assistant under the supervision of Dr. P. K. Saxena: Aug. 2001 to March 2003. Work titled: Synthesis of super high molecular weight polyolefins using Supported Ziegler-Natta catalyst. • Project Assistant under the supervision of Dr. K. Guruswamy: March 2003 to Oct. 2003. Work titled: Modification of Natural clays and synthesis of polymer nanocomposites Shivaji University Kolhapur, Maharashtra, India 200 • M.Sc. (Polymer Chemistry) – June 1999 to Apr 2001 – First class with distinction. • B. Sc. (General Chemistry)- June 1996 to May 1999 – First class with distinction. Technical skills • Spectroscopy – 1D-2D NMR, MS, ESI/MS, FT-IR, UV-vis. • Polymer characterization – GPC, VPO, DTA, TGA, DSC and Digital viscometry. Teaching experience • Teaching assistant for Inorganic chemistry practical courses at University of Stuttgart, Germany: Nov. 2003 onwards. Publications : (1) S. Chikkali, D. Gudat Hydrophosphanation of Phenolic Aldehydes as Facile Synthetic Approach to Catechol-Functionalized Phosphane Oxides and Phosphanes Euro. J. Inorg. Chem. 2006, 15, 3005-3009. (2) S. Chikkali, D. Gudat, M. Niemeyer Template controlled self-assembly of bidentate phosphine complexes with hemilabile coordination behaviour. Chem. Comm. 2007, 9, 981-983. (3) S. Chikkali, D. Gudat, M. Nieger, F. Lissner, T. Schleid Boron templated catechol phosphines as bidentate ligands in silver complexes. J. Chem. Soc. Dalton Trans. 2007, in press. (4) S. Chikkali, P. K. Saxena. Titanium phthalocyanine complex, novel catalyst for ethylene polymerization. J. Polym. Res.. Communicated. Oral presentations (1) S. Chikkali, D. Gudat, F. Lissner, M. Niemeyer, M. Nieger, T. Schleid. “Template complexes with Novel ditopic phosphines: Stepwise Aufbau, self- assembly and catalysis” Presented at: 233rd ACS National meeting, Chicago, USA ( March 25 to 27 2007) (2) S. Chikkali, D. Gudat, F. Lissner, M. Niemeyer, M. Nieger, T. Schleid. 201 “Novel self-assembly of transition metal-bidentate phosphine complexes on main group templates and potential applications in catalysis” Presented at: 4th Ph.D. workshop on phosphorus chemistry, Center parcs, Zandvoort, Vrije University, Amstredam, Netherland (March 20 & 21 2007) (3) S. Chikkali, D. Gudat, M. Niemeyer. “Supramolecular phosphines: stepwise aufbau, self-assembly and catalysis” Presented at: German-Austrian Scientific-coworkers workshop on main-group element chemistry, Techinical University of Graz, Austria (April 20 to 22 2006). (4) S. Chikkali, D. Gudat, M. Nieger, “Supramolecular Phosphines: New synthetic methodology and Lewis acid-base behaviour” Presented at: IX th Regional seminar of Ph. D. Students on organometallic and organophosphorus chemistry, Szklarska Poreba, Poland (April 10 to14, 2005). Poster presentations (1) “Supramolecular phosphines: New synthetic methodology, acid-base behaviour and potential catalysis” P 023, P-57. Presented at 13th Woehler-Vereinigung fur Anorganische Chemie, GDCh, (German Chemists society) 18-19 Sep. 2006, RWTH Aachen, Germany. (2) “Studies on the stereospecific polymerization of styrene using new titanium catalyst” P 2.17. Presented at Frontiers of polymer science and engineering, MACRO-2002, Indian Institute of Techonology, Khargpur, India. (Dec. 2002). Invited oral presentations (1) “Supramolecular phosphines: New synthetic methodology, acid-base behaviour and petential catalysis” Presented at National Chemical Laboratroy, Pune, Inida (Dec. 2004) (2) “Supramolecular phosphines: stepwise aufbau, self-assembly and catalysis” Presented at National Chemical Laboratory, Pune, India ( May 2006) Academic references (1) Prof. Dr. D. Gudat Institute of Inorganic Chemistry University of Stuttgart Pfaffenwaldring 55 D-70569 Stuttgart Germany E-mail : gudat@iac.uni-stuttgart.de 202 (2) Dr. K. Guruswamy Scientist Department of polymer science and engineering National Chemical Laboratory Pune – 411008 Maharashtra India E-mail : g.kumaraswamy@ncl.res.in