Si-C(sp3) bond activation through oxidative addition at a Rh(i) centre

Metathesis between E-C(spn ) and H-C(sp3 ) σ-Bonds (E=Si, Ge; n=2, 3) on an Osmium-Polyhydride

The silylation of a phosphine of OsH₆(PⁱPr₃)₂ is performed via net‐metathesis between Si−C(spⁿ) and H−C(sp³) σ‐bonds (n=2, 3). Complex OsH₆(PⁱPr₃)₂ activates the Si−H bond of Et₃SiH and Ph₃SiH to give OsH₅(SiR₃)(PⁱPr₃)₂, which yield OsH₄{κ¹‐P,η²‐SiH‐[ⁱPr₂PCH(Me)CH₂SiR₂H]}(PⁱPr₃) 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 OsH₆(PⁱPr₃)₂ with dimethylphenylsilane, and 1,1,1,3,5,5,5‐heptamethyltrisiloxane afford OsH₅(SiR₂R′)(PⁱPr₃)₂, which evolve into OsH₄{κ¹‐P,η²‐GeH‐[ⁱPr₂PCH(Me)CH₂SiR₂H]}(PⁱPr₃) (R=Me, OSiMe₃) and R′−H (R′=Ph, Me). Exchange reaction is extended to Et₃GeH. The latter reacts with OsH₆(PⁱPr₃)₂ to give OsH₅(GeEt₃)(PⁱPr₃)₂, which loses ethane to form OsH₄{κ¹‐P,η²‐GeH‐[ⁱPr₂PCH(Me)CH₂GeEt₂H]}(PⁱPr₃).