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

The silylation of a phosphine of OsH 6 (P i Pr 3 ) 2 is performed via net-metathesis between Si-C(sp n ) and H-C(sp 3 ) σ-bonds (n=2, 3). Complex OsH 6 (P i Pr 3 ) 2 activates the Si-H bond of Et 3 SiH and Ph 3 SiH to give OsH 5 (SiR 3 )(P i Pr 3 ) 2 , which yield OsH 4 {κ 1 -P,η 2 -SiH-[ i Pr 2 PCH(Me)CH 2 SiR 2 H]}(P i Pr 3 ) 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 6 (P i Pr 3 ) 2 with dimethylphenylsilane, and 1,1,1,3,5,5,5-heptamethyltrisiloxane afford OsH 5 (SiR 2 R')(P i Pr 3 ) 2 , which evolve into OsH 4 {κ 1 -P,η 2 -GeH-[ i Pr 2 PCH(Me)CH 2 SiR 2 H]}(P i Pr 3 ) (R=Me, OSiMe 3 ) and R'-H (R'=Ph, Me). Exchange reaction is extended to Et 3 GeH. The latter reacts with OsH 6 (P i Pr 3 ) 2 to give OsH 5 (GeEt 3 )(P i Pr 3 ) 2 , which loses ethane to form OsH 4 {κ 1 -P,η 2 -GeH-[ i Pr 2 PCH(Me)CH 2 GeEt 2 H]}(P i Pr 3 ).