Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
13 results
Search Results
Item Open Access Annellated 1,3,4,2-triazaphospholenes-simple modular synthesis and a first exploration of ligand properties(2022) Richter, Ferdinand; Birchall, Nicholas; Feil, Christoph M.; Nieger, Martin; Gudat, DietrichThe successful use of 1,3,4,2-triazaphospholenes (TAPs) as organo-catalysts stresses the need for efficient synthetic routes to these molecules. In this study, we establish the [1 + 4]-cycloaddition of PBr3 to azo-pyridines as a new approach to preparing pyrido-annellated TAPs in a single step from easily available precursors. The modular assembly of the azo-component via condensation of primary amines and nitroso compounds along with the feasibility of post-functionalization at the P-Br bond under conservation of the heterocyclic structure allows, in principle, to address a wide range of target molecules, which is illustrated by prototypical examples. The successful synthesis of a transition metal complex confirms for the first time the ability of a TAP to act as a P-donor ligand. Crystallographic studies suggest that hyperconjugation effects and intermolecular interactions induce a qualitatively similar ionic polarization of the P-Br bonds in TAPs as in better known isoelectronic diazaphospholenes.Item Open Access Synthesis and thermally and light driven cleavage of an N‐heterocyclic diphosphine with inorganic backbone(2020) Blum, Markus; Feil, Christoph M.; Nieger, Martin; Gudat, DietrichA diphosphine with an unsupported PP bond connecting two carbon‐free “inorganic” 1,3,2,4,5‐diazaphosphadisilolidine rings was prepared by reductive coupling of a P‐chloro‐substituted monocyclic precursor molecule. VT‐EPR studies revealed that the diphosphine exists in solution, like other compounds of this kind, in dynamic equilibrium with the corresponding phosphinyl radicals. Determination of the radical concentration from the EPR spectra permitted to calculate thermochemical parameters for the homolytic PP bond fission. The results disclose that both the enthalpy and entropy of dissociation are higher than in topologically related bi(diazaphospholidines). The impact of the entropy term allows explaining that, regardless of the presence of an energetically rather stable PP bond, the onset of dissociation is observable even at ambient temperature. Irradiation experiments showed that radical formation cannot only be induced thermally, but also by photolysis.Item Open Access Silyl‐ and germyl‐substituted diorganophosphonites(2023) Hettich, Thomas D.; Rudolf, Richard; Birchall, Nicholas; Nieger, Martin; Gudat, DietrichReactions of metalated diorganophosphonite boranes with triorganosilyl and ‐germyl halides provided borane adducts of diorgano(tetryl)phosphonites. Further treatment with excess Et3N or DABCO yielded the borane‐free species (RO)2P‐ER′>3 (E=Si, Ge; R, R′=alkyl, aryl). The products of all reactions were characterized by elemental analyses and NMR data, and in selected cases by MS and single‐crystal XRD studies. Reactions of selected ligands with Ni(CO)4 and selenium were shown to produce Ni(CO)‐complexes or diorgano(tetryl) phosphonoselenoates (RO)(R′3E)P=Se, respectively, which were identified spectroscopically but could not be isolated. Evaluation of the TEP and 1JPSe coupling constants were used for a first assessment of the electron donor properties of the new molecules.Item Open Access Chromium complexes with benzanellated N‐heterocyclic phosphenium ligands : synthesis, reactivity and application in catalytic CO2 reduction(2024) Birchall, Nicholas; Hennhöfer, Fridolin; Nieger, Martin; Gudat, DietrichA chromium complex carrying two benzanellated N‐heterocyclic phosphenium (bzNHP) ligands was prepared by a salt metathesis approach. Spectroscopic studies suggest that the anellation enhances the π‐acceptor ability of the NHP‐units, which is confirmed by the facile electrochemical reduction of the complex to a spectroscopically characterized radical anion. Co‐photolysis with H2 allowed extensive conversion into a σ‐H2‐complex, which shows a diverse reactivity towards donors and isomerizes under H-H bond fission and shift of a hydride to a P‐ligand. The product carrying phosphenium, phosphine and hydride ligands was also synthesized independently and reacts reversibly with CO and MeCN to yield bis‐phosphine complexes under concomitant Cr‐to‐P‐shift of a hydride. In contrast, CO2 was not only bound but reduced to give an isolable formato complex, which reacted with ammonia borane under partial recovery of the metal hydride and production of formate. Further elaboration of the reactions of the chromium complexes with CO2 and NH3BH3 allowed to demonstrate the feasibility of a Cr‐catalyzed transfer hydrogenation of CO2 to methanol. The various complexes described were characterized spectroscopically and in several cases by XRD studies. Further insights in reactivity patterns were provided through (spectro)electrochemical studies and DFT calculations.Item Open Access A P‐functionalized [3]ferrocenophane with a dynamic SPS‐bridge(2021) Weller, Stefan; Klenk, Robert; Kelemen, Zsolt; Nyulászi, László; Nieger, Martin; Gudat, DietrichFerrocene‐1,1′‐dithiol reacts with PCl3 and P(NMe2)3 to give [3]ferrocenophanes with SPS‐ansa‐bridges comprising potentially reactive P-Cl and P-N bonds at the central bridge atom. The products were characterized by NMR data and single‐crystal XRD studies. The P‐chloro‐derivative exists both in the solid state and in solution as a mixture of two energetically nearly degenerate conformers with different stereochemical disposition of the ansa‐bridge. Activation parameters for the dynamic equilibration between both isomers in solution were determined by dynamic NMR spectroscopy. Computational studies suggest that the isomerization proceeds via a torsional motion of the bridging SPS‐unit rather than via configuration inversion at the phosphorus atom.Item Open Access Approaching dissolved species in ammonoacidic GaN crystal growth: a combined solution NMR and computational study(2020) Becker, Peter; Wonglakhon, Tanakorn; Zahn, Dirk; Gudat, Dietrich; Niewa, RainerItem Open Access Adducts of diaminophosphines with organoboranes(2022) Dunaj, Tobias; Feil, Christoph M.; Nieger, Martin; Gudat, DietrichReactions of chlorodiaminophosphines (R2N)2PCl (R=Et, iPr) with organoborohydrides M[BR′nH4‐n] (M=Na, Li; n=1-3; R′=alkyl, Ph, CN) proceed via H/Cl metathesis to furnish secondary phosphines and boranes which may either combine to afford isolable donor‐acceptor adducts (R2N)2P(H)-BR′nH3‐n, coexist without any sign of mutual interaction, or give rise to mixtures comprising both a labile phosphine borane and its constituents in a temperature dependent equilibrium. Stable phosphine complexes of BH2CN and BH2Ph react with KN(SiMe3)2 under PH‐bond metalation to afford spectroscopically detectable diaminophosphide boranes whose usability as nucleophilic building blocks is illustrated by trapping one specimen in a PC‐bond formation reaction with an alkyl halide. The selectivity of the individual H/Cl‐metathesis and electrophilic substitution steps as well as the thermal stability of the various reaction products depend subtly on the Lewis acidity of the borane fragment and on steric factors. Several complexes of (iPr2N)‐substituted phosphines with cyano‐ and phenylborane were characterized by single‐crystal XRD.Item Open Access A ditopic phosphane‐decorated benzenedithiol as scaffold for di‐ and trinuclear complexes of Group‐10 metals and gold(2020) Schlindwein, Simon H.; Sibold, Carlo; Schenk, Mareike; Ringenberg, Mark R.; Feil, Christoph M.; Nieger, Martin; Gudat, DietrichThe ability of 3‐(diphenylphosphinomethyl)‐benzene‐1,2‐dithiol (pbdtH2) to act as ditopic ligand was probed in reactions with selected group‐10‐metal complexes. Reactions with [(cod)PdCl2] afforded a mixture of products identified as [Pd(pbdtH)2], [Pd2(μ2‐pbdt)2] and [Pd3(μ2‐pbdt)2Cl2]. The polynuclear complexes could be isolated after suitably adjusting the reaction conditions, and heating of a mixture in a microwave reactor effected partial conversion into a further complex [Pd3(μ2‐pbdt)3]. Reaction of pbdtH2 with [Ni(H2O)6Cl2] gave rise to a complex [Ni2(μ2‐pbdt)2], which was shown to undergo two reversible 1e-‐reduction steps. Reaction of [Pd(pbdtH)2] with [Au(PPh3)Cl] afforded heterotrinuclear [PdAu2(μ2‐pbdt)2(PPh3)]. All complexes were characterized by analytical, spectroscopic and single‐crystal X‐ray diffraction studies. Their molecular structures confirm the ability of the pbdt2- unit to support simultaneous P,S‐ and S,S‐chelating coordination to two metal centers.Item Open Access Reversible binding of hydrogen and styrene coordination on a manganese phosphenium complex(2023) Papendick, Marius; Gudat, DietrichThe reactions of two complexes [(RNHP)Mn(CO)4] (RNHP=N-arylated N-heterocyclic phosphenium) with H2 at elevated pressure (≈4 bar) were studied by NMR spectroscopy. Irradiation with UV light initialized in one case (5 a, R=Dipp) the unselective formation of (RNHP-H)MnH(CO)4] (6 a) via cooperative addition of H2 across the Mn=P double bond. In the other case (5 b, R=Mes), addition of H2 was unobservable and the reaction proceeded via decarbonylation to a dimeric species [(RNHP)2Mn2(CO)7] (7 b) that was isolated and identified spectroscopically. Taking into account the outcome of further reaction studies under various conditions in the absence and presence of H2, both transformations can be explained in the context of a common mechanism involving decarbonylation to 7 a,b as the first step, and the different outcome is attributable to the fact that 7 b is unreactive towards both H2 and CO while 7 a is not. DFT studies relate this divergence to deviations in the molecular constitution and stability arising from a different level of steric congestion. Preliminary studies suggest further that 5 a/H2 as well as 6 a enable the photo-induced hydrogenation of styrene to ethyl benzene, even if the mechanism and possibly catalytic nature of this process remain yet unknown.Item Open Access Isolable diaminophosphide boranes(2020) Blum, Markus; Dunaj, Tobias; Knöller, Julius A.; Feil, Christoph M.; Nieger, Martin; Gudat, DietrichMetalation of secondary diaminophosphine boranes by alkali metal amides provides a robust and selective access route to a range of metal diaminophosphide boranes M[(R2N)2P(BH3)] (M=Li, Na, K; R=alkyl, aryl) with acyclic or heterocyclic molecular backbones, whereas reduction of a chlorodiaminophosphine borane gave less satisfactory results. The metalated species were characterized in situ by NMR spectroscopy and in two cases isolated as crystalline solids. Single‐crystal XRD studies revealed the presence of salt‐like structures with strongly interacting ions. Synthetic applications of K[(R2N)2P(BH3)] were studied in reactions with a 1,2‐dichlorodisilane and CS2, which afforded either mono‐ or difunctional phosphine boranes with a rare combination of electronegative amino and electropositive functional disilanyl groups on phosphorus, or a phosphinodithioformate. Spectroscopic studies gave a first hint that removal of the borane fragment may be feasible.