Direct hydrosilylation by a zirconacycle with β-hydrogen

Abstract

Azasilazirconacycle Cp₂Zr{κ²-N(SiHMe₂)SiHMeCH₂} (1) and formaldehyde react through an uncatalyzed addition reaction (hydrosilylation) to form an exocyclic methoxysilyl-substituted zirconacycle. Although 1 contains 2-center-2-electron SiH groups, this transformation parallels the reactions of non-classical [Cp₂ZrN(SiHMe₂)₂]⁺ ([2]⁺) with carbonyls. Reactions of 1 with a series of nucleophilic and electrophilic agents were explored, as well as reactions of related β-SiH-containing silazidozirconium compounds, to develop a rationale for the unexpected hydrosilylation. For example, carbon monoxide and 1 react at the Zr–C bond to form Cp₂Zr{κ²-OC(CH₂)SiHMeN(SiHMe₂)} (7). The Lewis acid B(C₆F₅)₃ also reacts at the Zr–C bond to give Cp₂Zr{N(SiHMe₂)SiHMeCH₂B(C₆F₅)₃} (8). OPEt₃ and N,N-dimethylaminopyridine (DMAP) do not appear to interact with 1. In contrast, OPEt₃ and DMAP react with non-classical compounds [2]⁺ and zwitterionic 8.