The condensation of RSiH3 (R Ph, nBu, nHex) to silicon oligomers in the presence of the catalyst precursor combination Cp2MCl2/2nBuLi (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 PhSiH3 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 PhSiH3 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.
Bibliographical noteFunding Information:
The donors of the Petroleum Research Fund, administeredb y the American Chemical Society,p rovided partial support for this work. Additional support was providedb y an Improved ResearchQ uality Grant from the Universityo f Missouri-St. Louis. The Hewlett-Packard 5988A GC/MS systemw as purchasedw ith the supporto f the National ScienceF oundation( Grant No. CHE-8813154).