Reactions of secondary silanes with [{Pr(i)(2)PCH2CH2PPr(i)(2)}Rh](2)(mu-H)(2). A series of dinuclear silyl-hydride complexes and their possible involvement in the catalytic hydrosilylation of olefins

Addition of a 1 equiv of a secondary silane (RR'SiH2) to [(dippe)Rh](2)(mu-H)(2) (1) gives the complexes [(dippe)Rh](2)(mu-H)(mu-eta(2)-HSiRR') (2a, R = R' = Ph; 2b, R = R' = Me; 2c, R = Ph, R' = Me; dippe = 1,2-bis(diisopropylphosphino)ethane). X-ray diffraction studies of 2a,b confirm the presence of a three-center, two-electron, Rh-H-Si bond. The observed fluxionality of 2a-c in solution is due to exchange of the silicon and rhodium hydrides. Complexes 2a-c lose hydrogen in the presence of 1 equiv of carbon monoxide to give complexes 3a-c, [(dippe)Rh](2)(mu-SiRR')(mu-CO). A catalytic cycle is proposed for the hydrosilylation of olefins by diphenylsilane to give Ph(2)SiR(2) (R = Et) or Ph(2)SiHR (R = Bu), which occurs in the presence of 1, One of the active species is thought to be [(dippe)Rh](2)(mu-H)(mu-eta(2)-HSiPh(2)) (2a).