Browsing by Author "Gudat, Dietrich"

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Open Access
31P NMR spectroscopic investigations of low-coordinated multiple bonded PN systems
(1994) Niecke, Edgar; Gudat, Dietrich
In this chapter, we attempt to give a systematic analysis of the influence on the 31P chemical shift and coupling 1JPN in terms of substituent effects, double-bond stereochemistry, and molecular dynamics for iminaphosphines and related compounds containing partial phosphorus-nitrogen triple-bond character. Although the main focus is on properties in the isotropic phase, reflecting that the majority of measurements were made in solution, the tensorial properties of the chemical shift as obtained from solid-state NMR measurements are also mentioned.
Open Access
Adducts of diaminophosphines with organoboranes
(2022) Dunaj, Tobias; Feil, Christoph M.; Nieger, Martin; Gudat, Dietrich
Reactions 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.
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, Dietrich
The 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.
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, Rainer
Open Access
Azasilatrane methanolysis pathways: stereoelectronic influences
(1990) Gudat, Dietrich; Verkade, John G.
Trigonal-bipyramidal azasilatranes of the type ZSi(NHCH2CH2)3N (Z = H, Me, OEt) solvolyze in MeOH to give N(CH2CH2NH2)3 (tren) and ZSi(OMe)3. Whereas intermediates in this reaction are not detected, ZSi[N-(SiR3)CH2CH2]3N species afford detectable intermediates of the type ZSi[N(SiR3)CH2CH2]n(NHCH2CH2)3-nN (n = 1, 2) before complete conversion to tren and ZSi(OMe)3 occurs. In cases where steric encumbrances weaken the Si-Nax bond in these molecules, monocyclic intermediates are detected. In contrast, methanolysis of HSi[N(BMe2)CH2CH2]3N gives N(CH2CH2NHBMe2)3 (and HSi-(OMe)3), which in the presence of CD3OD gives (CD3O)nSi(OMe)4-n and the novel adduct N-[CH2CH2NHD·B(OCD3)Me2]3. The possible steric and electronic influences of the equatorial substituents on the solvolysis pathways are discussed.
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, Dietrich
A 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.
Open Access
Coordination isomerism in pentamethylcyclopentadienyl-substituted iminophosphanes: from classical structures to a π-complexed iminophosphenium ion
(1992) Gudat, Dietrich; Schiffner, Hans M.; Nieger, Martin; Stalke, Dietmar; Blake, Alexander J.; Grondey, Hiltrud; Niecke, Edgar
Novel iminophosphanes of the type (Me5C5)P=NR [R = C6H2tBu3 (5a), Si-i-Pr3 (5b), SiMe3 (5c)] are prepared via either thermolytic or base-promoted elimination reactions and characterized by analytical and spectroscopic methods. The x-ray crystal structures of 5a,b establish the presence of coordination isomerism of the cyclopentadienyl ring, which at the same time strongly alters the characteristics of the P-N multiple bond. For 5a, η1-attachment of the Me5C5 moiety to the phosphorus and a localized phosphorus-carbon σ-bond are found, and the P-N double bond compares to that of alkylated iminophosphanes (rPN = 155.1 (8) pm). 5b exhibits η2-coordination of the cyclopentadienyl ring leading to increased P-N triple-bond character, as evidenced by shortening of the P-N distance (153.3 (3) pm) and the remarkable opening of the nitrogen valence angle (153.3 (2)°). The structure is discussed as an intramolecular π-complex between a formal cyclopentadienyl anion and an iminophosphenium cation. The 1H and 13C NMR spectra show that rapid elementotropic rearrangements around the five-membered ring take place both in solution and in the solid state. The unique temperature dependence of δ31P in solution together with the considerable differences in δ 31P between the solution and solid states are interpreted in a model assuming a "haptotropic" mechanism for the fluxionality involving dynamic η1/η2-coordination isomerizations in solution. As expected, nucleophilic displacement of the Me5C5 moiety takes place in the reaction of 5b,c with LiC6H2tBu3, yielding the iminophosphanes tBu3H2C6P=NR (R = Si-i-Pr3 (8b), SiMe3 (c)) as products.
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, Dietrich
The 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.
Open Access
Diverse reactivity of a cationic N-heterocyclic phosphenium complex towards anionic substrates : substitution vs. reduction
(2024) Feil, Christoph M.; Goerigk, Florian; Stöckl, Yannick; Nieger, Martin; Gudat, Dietrich
A cationic N-heterocyclic phosphenium (NHP) iron tetracarbonyl complex was synthesised from the free cation and its behaviour towards various anionic reactants studied. Reactions with fluoride, chloride, and hydride sources proceeded under attachment of the anion at phosphorus to yield Fe(CO)4-complexes of neutral diazaphospholenes, while bromide and iodide reacted under addition of the anion at the metal and decarbonylation to yield NHP iron halides. Reactions with amides and organometallics were unselective. At room temperature, predominantly reduction of the cationic complex to yield a spectroscopically detectable Fe-centred radical and its deactivation products was observable. At -78 °C, CH-metalation at the heterocycle was preferred, as evidenced by the structural characterisation of a neutral borane-adduct of the metalation product of a modified NHP complex. The dimer of the Fe-centred radical formed also in reactions of chloro- and bromo-diazaphospholenes with Fe2(CO)9, which proceed not only by complexation of the P-donors as expected, but involve also oxidative addition steps and single electron transfer processes in which excess iron complex acts as the reductant. The title complex and the products isolated in the reaction studies were characterised by spectroscopic data and in many cases by XRD studies. Computational studies were employed to analyse the differing reactivity of the cationic NHP complex towards light and heavy halide ions, and to help in the assignment of the radical intermediate observed. The more diverse reactivity of the cationic NHP complexes compared to their neutral analogues is attributed to their higher electrophilicity.
Open Access
First examples of η1-ligated halogenophosphaalkenes - crystal structures of trans-[RhCl(PPh3)2{η1-PX=C(SiMe3)2}] (X = F or Cl)
(1989) Hitchcock, Peter B.; Meidine, Mohamed F.; Nixon, John F.; Wang, Hongrui; Gudat, Dietrich; Niecke, Edgar
Syntheses and single crystal X-ray diffraction studies of the η1-halogenophosphaalkene complexes trans-[RhCl(PPh3)2{η1-PX=C(SiMe3)2}] (X = F, Cl) are reported.
Open Access
Iminophosphane - unkonventionelle Hauptgruppenelement-Verbindungen
(1991) Niecke, Edgar; Gudat, Dietrich
Niederkoordinierte Phosphorverbindungen zählen angesichts der großen Zahl stabiler Verbindungen längst nicht mehr zu den „Exoten” unter den Hauptgruppenelement-Verbindungen. Neben P-C-Mehrfachbindungssystemen, deren Chemie durch die enge Verwandtschaft mit organischen Verbindungen geprägt wird, gilt das Interesse vor allem P-N-Mehrfachbindungssystemen (Iminophosphanen). Diese Verbindungsklasse zeichnet sich durch eine ungewöhnliche Strukturvielfalt und ein variationsreiches chemisches Verhalten aus, so daß Iminophosphane zu wertvollen Synthesebausteinen in der Organoelementchemie wurden.
Open Access
Iminophosphanes: unconventional compounds of main group elements
(1991) Niecke, Edgar; Gudat, Dietrich
The large number of known stable compounds in which phosphorus has a low coordination number makes it clear that such compounds can no longer be regarded as "exotic" in main group chemistry. While the rich chemistry of P-C multiply bonded systems makes clear their affinity to their organic congeners, iminophosphanes in particular are also of increasing importance. The linkage of a phosphinidine fragment with an imine fragment via a multiple bond gives rise to a class of compounds with an unusually wide range of structural types. This in turn leads to a broad spectrum of chemical behavior which makes iminophosphanes extremely useful synthetic building blocks in organoelement chemistry.
Open Access
Isolable diaminophosphide boranes
(2020) Blum, Markus; Dunaj, Tobias; Knöller, Julius A.; Feil, Christoph M.; Nieger, Martin; Gudat, Dietrich
Metalation 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.
Open Access
Metallophospha-alkenes: a simple access and some reactivities involving the phosphorus atom
(1985) Gudat, Dietrich; Niecke, Edgar; Malisch, Wolfgang; Hofmockel, Ullrich; Quashie, Sapé; Cowley, Alan H.; Arif, Atta M.; Krebs, Bernt; Dartmann, Mechtild
The synthesis and studies on the reactive behaviour of metallophospha-alkenes are reported.
Open Access
Methylenphosphanyl-Komplexe von Chrom, Molybdän, Wolfram, Eisen und Nickel: Synthese und Reaktionen
(1993) Niecke, Edgar; Metternich, Hans-Jürgen; Nieger, Martin; Gudat, Dietrich; Wenderoth, Peter; Malisch, Wolfgang; Hahner, Christoph; Reich, Wolfgang
The reaction of the functionalized P/C double bond systems X-P=C(R)SiMe3 [R = SiMe3 and X = Cl (1a), Cp* (5a) or R = Ph and X = Br (1b), Cp* (5b)] with alkali carbonylmetallates or carbonyl complexes of group 6, 8, and 10 metals leads to the formation of the transition metal-substituted phosphaalkenes [{M}-P=C(R)SiMe3 3a-j and 4a-i], in which the P-C fragment acts as a one-electron donor. Depending on the nucleophilicity of the transition metal anion used, but also on the methylene carbon substituents [1a: (SiMe3)2; 1b: (Ph)-SiMe3], a different stability of the (methylenephosphanyl)1-metal complexes is observed, which results in a broad spectrum of reactivities. As demonstrated by the reactions of the (methylenephosphanyl)metal complexes with sulfonic acid derivatives (10a-c), diverse transition metal complexes (11a-c), as well as chalcogenes (14a-c, 15), a change in the reactivity is observed, indicating a transition from an olefinic to a carbenic character of the methylenephosphane. In comparison to the phenyl-substituted derivatives 4a-i the bis(trimethyl)1-substituted species 3a-j exhibit an increased reactivity. This is reflected in the easy decarbonylation of 3a-d to the phosphavinylidene complexes 12a-d.
Open Access
Multinuclear magnetic resonance study of sterically crowded stannylphosphines and stannylamines : stereochemical influences on chemical shielding and spin-spin couplings
(1994) Dörr, Armin; Gudat, Dietrich; Hänssgen, Dieter; Hens, Heribert; Stahlhut, Edith
Multinuclear (1H, 15N, 29Si, 31P, 119Sn) NMR data of sterically crowded acyclic stannylphosphines tBu3SnPHY (Y = H, SnMe3, SntBu3, SiMe3; 1-3, 10), (tBu2RSn)2PH (R = Me, Cl; 4, 5), tBu3SnPY2 (Y = SnMe3, SiMe3; 6, 11), PH(SntBu2PHSntBu3)2 (7), SntBu2(PY2)2 (Y = H, SiMe3, PHSntBu3; 8, 9, 12), cyclic stannylphosphines (tBu2SnPY)n (n = 2, Y = H, C3H6Cl, tBu, SnMe3; 13-16; n = 3, Y = H; 18), (Me2SnPSntBu3)2 (17), and stannylamines tBu3SnNHY (Y = H, SnMe3, SntBu3; 19-21) were obtained by various 1D- and 2D-techniques. 31P- and 15N-shieldings may be explained qualitatively in terms of two counteracting influences, viz electronegativity differences and steric requirements of the substituents. In a similar manner, the trends in one-bond coupling 1KSnP and 1KSnM may be rationalized using a simple model based on the deformation of bond angles by sterically demanding substituents. The signs of long-range couplings 2KSnPH and 1KPSnCCH could be determined, which may be useful for future structural studies. Temperature-dependent effects in the spectra of 13, 18 allow conclusions about the conformational dynamics of the molecules.
Open Access
New azasilatranes: bidentate and tridentate coordination modes of the novel ligand EtOSi(Ph2PNCH2CH2)2(HNCH2CH2)N
(1990) Gudat, Dietrich; Daniels, Lee M.; Verkade, John G.
The synthesis and characterization of EtOSi(Ph2PNCH2CH)2(HNCH2CH2)N (ethoxy-N,N'·bis(di-phenylphosphino)azasilatrane, the title compound 3b) is reported. Its reactions with sulfur and MeI proceed easily via quaternization at the phosphorus sites to give the bis(phosphonium) salt and the bis(phosphine) sulfide, respectively. Synthesis and characterization of the coordination compounds (3b) Ni(CO)2, (3b) PtCl2, (3b) M(CO)4 (M = Mo, W), and (3b) M(CO)3 (M = Mo, W) give evidence for the existence of two possible coordination modes; one wherein 3b behaves as a bidentate (P,P') ligand and the other as a tridentate (P,P',O) ligand. The latter coordination mode provides a rare example of coordination of a silyl ether to a transition metal. NMR spectroscopic studies in solution and the solid state establish the presence of transannular Si-N bonding and hypercoordination at silicon. Solid-state 31P NMR spectra give direct evidence for the presence of a twisted, helically chiral conformation of the silatranyl cage, which in solution is lost as a consequence of rapid conformational mobility on the NMR time scale. These findings are further corroborated by the results of crystal structure determinations of the bis(phosphine) sulfide and (3b) PtCl2.
Open Access
New azasilatranes: sterically induced transannular bond weakening and cleavage
(1989) Gudat, Dietrich; Daniels, Lee M.; Verkade, John G.
Silylation of azasilatrane I (R = R1 = R2 = H) with ClSiMe3/NEt3 gives disilylated I (R = R1 = Me3Si, R2 = H) (II), via the spectroscopically detected monosilylated intermediate. Treatment of II with BuLi gives the stable lithiated deriv. I (R = R1 = Me3Si, R2 = Li) which can be converted to I [R = R1 = Me3Si, R2 = Me, Me3Si (III)], via reaction with MeI or ClSiMe3, resp. The novel structure of III, inferred from NMR data and confirmed by x-ray means, features an Nax nitrogen in a nearly trigonal pyramidal stereochem. with an exceptionally long NaxSi bond [ 2.775(7)?]. Reaction of III with MeOSO2CF3 gives IV, the Nax methylated product.
Open Access
New azasilatranes: synthesis and substitution reactions
(1989) Gudat, Dietrich; Verkade, John G.
The syntheses of new azasilatranes XSi(NRCH2CH2)3N (R = H, X = OEt (2f), OPh (2g); R = Me, X = H (8a), OEt (8b); R = SiMe3, X = H (9a)) via condensation reactions of tetraamines N(CH2CH2NHR)3 and substituted tris(dimethylamino)silanes, XSi(NMe2)3, are described. In the case of 2g, the required silane PhOSi(NMe2)3 was generated in situ from the reaction of PhOH and Si(NMe2)4. The chloroazasilatrane, 2h (R = H, X = Cl), whose synthesis was not feasible by the above method, was obtained by reaction of hydroazasilatrane, 2a (R = H, X = H) (V) with CCl4 in the presence of a platinum or palladium catalyst. Reaction of azasilatranes 2a and 2f with ClSiMe2R' (R' = H, Me, Ph) in the presence of triethylamine affords the silyl-substituted azasilatranes XSi(N(SiMe2R')CH2CH2)3N (X = H, R' = H (9b), Me (9a), Ph (9c); X = OEt, R' = H (14a)) and XSi(N(SiMe2R')CH2CH2)2NHCH2CH2N (X = OEt; R' = Me (14b), Ph (14d)), respectively, while no reaction was observed between either 2a or 2f and ClSiMe2-t-Bu. The new azasilatranes are characterized by 1H, 13C, and 29Si NMR spectroscopy, by high-resolution mass spectroscopy, and by an x-ray crystal structure determination in the case of 8b.
Open Access
Novel properties of new phosphatranes and silatranes
(1989) Gudat, Dietrich; Lensink, Cornelis; Schmidt, Harry; Xi, S.-K.; Verkade, John G.
The synthesis of the new pro-phosphatranes YP(MeNCH2CH2)3N (Y = lone pair, 0, S, Se, BH3 and CH3+) containing four-coordinate phosphorus, and the tbp phosphatranes YP(MeNCH2CH2)3N (Y = H+, BrCH2 and Cl+) are reported. New azasilatranes of the type YSiRNCH2CH2)3N (R = H, Me, SiMe3; Y = H, OMe, OEt) are also reported and the results of nucleophilic substitution studies of the labile hydrogen on the equatorial nitrogens are given.