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(SiMe 3 ) 3 ]H ( 1; Cp* = η 5 -C 5 Me 5 ), prepared by the reaction of CpCp*Hf(H)Cl with (THF) 3 LiSi(SiMe 3 ) 3, reacts rapidly with both ethylene and diphenylacetylene with elimination of HSi(SiMe 3 ) 3 to afford the corresponding hafnacyclopentane and tetraphenylhafnacyclopentadiene complexes. Complex 1 reacts with acetone to give the insertion product CpCp*Hf(OCHMe 2 )[Si(SiMe 3 ) 3 ] ( 4 ). Reaction of 1 with the secondary silane H 2 Si(SiMe 3 ) 2 proceeds smoothly to the new silyl hydride complex CpCp*Hf[SiH(SiMe 3 ) 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 Ph 3 SiH does not react under comparable conditions. The silane H 2 Si(SiMe 3 ) 2 undergoes a similar σ-bond metathesis reaction with CpCp*Hf[Si(SiMe 3 ) 3 ]Cl, to give CpCp*Hf[SiH(SiMe 3 ) 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 .