HYDROSILATION OF ALKYNES BY AN OSMIUM CLUSTER COMPLEX - ISOLATION AND STRUCTURAL CHARACTERIZATION OF AN INTERMEDIATE

Reactions of the complex Os3(CO)10(NCMe)-[Si(OMe)3](mu-H) (1a) with the alkynes HC2R (R = Bu(t), p-tolyl) yield complexes that upon treatment with CO at 68-degrees-C produce the silylolefins trans-R(H)C = C(H)Si(OMe)3 (R = Bu(t), p-tolyl). One of the complexes, Os3(CO)10-[Si(OR)3][mu-C(H)C(H)Bu(t)] (2a; R = Me) was characterized crystallographically and found to contain a bridging eta(2)-tert-butylvinyl ligand and a terminally coordinated trimethoxysilyl group positioned cis to the bridging carbon atom of the tert-butylvinyl group. The characterization of this intermediate demonstrates that the mechanism of hydrosilation by this cluster complex is initiated by a hydride insertion mechanism.