Synthesis and Reactivity of 16-Electron Hafnocene Silyl Hydride Complexes

The synthesis and reactivity of monomeric, 16-electron hafnocene silyl hydride complexes are described. The complex CpCp*Hf[Si(SiMe3)3]H (1; Cp* = η5-C5Me5), prepared by the reaction of CpCp*Hf(H)Cl with (THF)3LiSi(SiMe3)3, reacts rapidly with both ethylene and diphenylacetylene with elimination of HSi(SiMe3)3 to afford the corresponding hafnacyclopentane and tetraphenylhafnacyclopentadiene complexes. Complex 1 reacts with acetone to give the insertion product CpCp*Hf(OCHMe2)[Si(SiMe3)3] (4). Reaction of 1 with the secondary silane H2Si(SiMe3)2 proceeds smoothly to the new silyl hydride complex CpCp*Hf[SiH(SiMe3)2]H (5), which was characterized by X-ray crystallography. Deuterium labeling experiments indicate that the latter reaction occurs with significant scrambling of label between the SiH and HfH positions. The tertiary silane Ph3SiH does not react under comparable conditions. The silane H2Si(SiMe3)2 undergoes a similar σ-bond metathesis reaction with CpCp*Hf[Si(SiMe3)3]Cl, to give CpCp*Hf[SiH(SiMe3)2]Cl (7). For the latter reaction, there is a photochemical dependence on the rate and course of the reaction pathway. Exposure of the reaction mixture to room light is critical for complete conversion to 7.