Metathesis between E-C(sp ) and H-C(sp ) σ-Bonds (E=Si, Ge; n=2, 3) on an Osmium-Polyhydride.

The silylation of a phosphine of OsH (P Pr ) is performed via net-metathesis between Si-C(sp ) and H-C(sp ) σ-bonds (n=2, 3). Complex OsH (P Pr ) activates the Si-H bond of Et SiH and Ph SiH to give OsH (SiR )(P Pr ) , which yield OsH {κ -P,η -SiH-[ Pr PCH(Me)CH SiR H]}(P Pr ) and R-H (R=Et, Ph), by displacement of a silyl substituent with a methyl group of a phosphine. Such displacement is a first-order process, with activation entropy consistent with a rate determining step occurring via a highly ordered transition state. It displays selectivity, releasing the hydrocarbon resulting from the rupture of the weakest Si-substituent bond, when the silyl ligand bears different substituents. Accordingly, reactions of OsH (P Pr ) with dimethylphenylsilane, and 1,1,1,3,5,5,5-heptamethyltrisiloxane afford OsH (SiR R')(P Pr ) , which evolve into OsH {κ -P,η -GeH-[ Pr PCH(Me)CH SiR H]}(P Pr ) (R=Me, OSiMe ) and R'-H (R'=Ph, Me). Exchange reaction is extended to Et GeH. The latter reacts with OsH (P Pr ) to give OsH (GeEt )(P Pr ) , which loses ethane to form OsH {κ -P,η -GeH-[ Pr PCH(Me)CH GeEt H]}(P Pr ).