Platinum Bis(tricyclohexylphosphine) Silyl Hydride Complexes Danny Chan, † Simon B. Duckett,* ,† Sarah L. Heath, † Iman G. Khazal, † Robin N. Perutz,* ,† Sylviane Sabo-Etienne, ‡ and Philippa L. Timmins † Department of Chemistry, University of York, York YO10 5DD, U.K., and Laboratoire de Chimie de Coordination du CNRS, 205 Route de Narbonne, 31077 Toulouse Cedex 04, France Received June 20, 2004 A series of platinum metal silyl hydride complexes, cis-Pt(PCy 3 ) 2 (H)(SiR 2 R′) (SiR 2 R′ ) SiPh 2 H, SiEt 2 H, SiPh 3 , SiEt 3 , SiMe 2 (OSiHMe 2 ), Si(OSiMe 3 ) 2 Me, SiMe 2 (CH 2 CHdCH 2 ), SiMe 2 - Et, SiMe 2 [OCH 2 C(Me)dCH 2 ], Si(OMe) 2 (CH 2 CHdCH 2 ), SiPh 2 (OSiPh 2 H)), have been prepared in solution by reaction of Pt(PCy 3 ) 2 with the appropriate silane, HSiR 2 R′. The complex cis- Pt(PCy 3 ) 2 (H)(HSiPh 2 )(1-cis) has been characterized by X-ray crystallography at -100 °C. The platinum center exhibits a distorted-square-planar geometry with angles P(1)-Pt- P(2) ) 113.55(3)°, P(1)-Pt-Si ) 146.83(3)°, and P(2)-Pt-Si ) 99.37(3)°. The reaction of Pt(PCy 3 ) 2 with chlorinated hydrosilanes at -78 °C yields the analogous complexes cis-Pt- (PCy 3 ) 2 (H)(SiR 2 R′) (SiR 2 R′ ) SiMe 2 Cl, SiMeCl 2 , SiCl 3 ), which isomerize to their trans isomers on warming to room temperature. The complex 1-cis and several analogues convert to the trans isomers photochemically at room temperature. Ready silane exchange is demonstrated by the reaction of HSiPh 3 with cis-Pt(PCy 3 ) 2 (D)(SiPh 3 ) and by the reaction of H 2 SiPh 2 with cis-Pt(PCy 3 ) 2 (H)(SiPh 3 ). These experiments also revealed the relative thermodynamic stability of some of the platinum silyl complexes, of which the most stable was cis-Pt(PCy 3 ) 2 (H)- (SiPh 2 H). NMR spectroscopy demonstrates that the inequivalent phosphine ligands of the cis isomers undergo intramolecular mutual exchange on the NMR time scale. In competition with this process, the complexes undergo reversible reductive elimination of silane. Analysis of the NMR spectra yields the thermodynamic data for dissociation of silanes for SiR 2 R′ ) SiPh 3 , SiMe 2 Et. Rate constants for phosphine exchange were calculated via line-shape analysis of 1 H NMR spectra. Rate constants for reductive elimination of silane in cis-Pt- (PCy 3 ) 2 (H)(SiR 2 R′) (SiR 2 R′ ) SiPh 2 H, SiMe 2 Et, SiPh 3 ) were calculated via 1 H EXSY measurements. The three distinct reaction pathways, photochemical cis-trans isomerization, intramolecular thermal phosphine site exchange, and reductive elimination, are shown to involve three distinct transition states. The transition states for the independent processes of phosphine site exchange and for reductive elimination must retain substantial Pt-H and Pt-Si interactions, while there is also significant Si-H bond formation. This situation can therefore be described as involving Pt(η 2 -H-SiR 3 ) interactions. Introduction Silylmetal complexes are known for nearly all of the transition metals 1,2 and have been shown to play a key role in many metal-catalyzed silylation reactions. 3 The oxidative addition of a Si-H bond to a coordinatively unsaturated metal complex has proved to be a very versatile method for their synthesis. Indeed, the activa- tion of Si-H bonds is featured in the industrial pro- cesses hydrosilylation, dehydrogenative silylation, and polysilane production. 4 The silyl ligand exerts a high trans influence, which is manifested in NMR spectra as well as in metal-ligand bond lengths. Silyl hydrides may also bind in the η 2 -Si-H mode, and complexes containing this grouping are becoming increasingly important. Metal η 2 -Si-H complexes are also thought to be involved in the oxidative addition and reductive elimination of Si-H bonds. 2,5 Recent investigations of the dynamics of metal η 2 -silane hydride complexes have shown the importance of metal silyl dihydrogen isomers in fluxional behavior. 6 In this paper, we are concerned with the oxidative addition of Si-H bonds at platinum and the dynamics of the resulting complexes. * To whom correspondence should be addressed. E-mail: rnp1@ york.ac.uk (R.N.P.). † University of York. ‡ Laboratoire de Chimie de Coordination du CNRS. (1) Corey, J. Y.; Braddock-Wilking, J. Chem. Rev. 1999, 99, 175. (2) Schubert, U. Adv. Organomet. Chem. 1990, 30, 151. (3) Speier, J. L. Adv. Organomet. Chem. 1979, 17, 407. (4) (a) Reichl, J. A.; Berry, D. H. Adv. Organomet. Chem. 1999, 43, 197. (b) Gauvin, F.; Harrod, J. F.; Woo, H. G. Adv. 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