Condensation of primary silanes in the presence of Cp 2MCl 2/ nBuLi (M  Ti, Zr, Hf)

Abstract

The condensation of RSiH 3 (R  Ph, nBu, nHex) to silicon oligomers in the presence of the catalyst precursor combination Cp 2MCl 2/2 nBuLi (M  Ti, Zr, Hf) has been monitored by gas chromatography and the intermediate oligomers characterized by GC-MS. The average molecular weights of the isolated products from PhSiH 3 depend on the catalyst and increase through the sequence, Hf < Ti < Zr, to a maximum of about 1800 for reactions conducted at room temperature. In the condensation of alkylsilanes linear oligomers are produced in the initial stages of the reaction and as the reaction continues cyclic polysilanes are formed with increasing numbers of isomers as the number of silicon atoms increases. A large rate difference is observed in the formation of the diastereomers of the tetrasilane produced from PhSiH 3 for all three catalysts. For reactions conducted at 50°C both diastereomers of H( nBuSiH) 4H are produced in equal amounts throughout the reaction period for M  Ti but at different rates for M  Zr and only one diastereomer is observed for M  Hf. The observations are discussed in terms of chain growth through sigma-bond metathesis processes.