Direct hydrosilylation by a zirconacycle with β-hydrogen.

Azasilazirconacycle Cp2Zr{κ(2)-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{κ(2)-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.