Coupling of Deuteriosilanes in the Presence of Cp₂MCl₂/nBuLi

The condensation reactions of secondary deuteriosilanes to give oligomer products in the presence of the catalyst precursor Cp₂MCl₂/nBuLi have been investigated. The products from PhMeSiD₂ with M = Zr are not the expected deuterium-terminated chains D(PhMeSi)_xD but a mixture of isotopomers with an average deuterium content near two per oligomer, as determined by mass spectroscopy and with deuterium located at silicon as well as the methyl groups, as shown by ²H NMR of isolated oligomers. Deuterium scrambling in the oligomers was not observed in the condensation of PhEtSiD₂ with all three catalyst systems and only marginally in the products produced from the condensation of PhCH₂(Me)SiD₂ (M = Zr). The cocondensation of PhMeSiD₂ and TolMeSiH₂ provides a near-statistical distribution of combinations of disilanes through tetrasilanes with deuterium scattered almost equally within each combination including those that contain only TolMeSi units. The monosilane product PhMeBuSiD which is believed to form from hydrosilylation of coordinated butene in [Cp₂Zr-(butene)] contains from three to eight deuteriums with an average between four and five. Mechanisms for enhanced deuterium incorporation in PhMeBuSiD and deuterium scrambling in the oligomers produced from PhMeSiD₂ are proposed that have features in common.