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)-HSiR R') (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. Th e observed fluxionality of 2a-c in solution is due to exchange of the silicon and rhodium hydrides. Complexes 2a-c lose hydrogen in the pres ence 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 hydrosilyl ation 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) .