Catalytic Dehydrogenative Coupling of Secondary Silanes with Cp₂MCI₂/nBuLi

The catalytic dehydrogenative coupling of secondary silanes has been achieved with the combination of Cp₂ZrCl₂ and 2 equiv of nBuLi in toluene at 90 °C. The products produced from PhMeSiH₂ contain disilane through pentasilanes after 2 days, and longer time periods produce oligomeric mixtures up to the octamer. Disilane through tetrasilane have been isolated as distillable, air-stable liquids and are produced as mixtures of stereoisomers. The distribution of oligomers has been determined under various conditions of temperature, time, solvent, and Si/Zr and Zr/Li ratios as well as with a combination of Cp₂ZrCl₂ with Grignard reagents. Disilane is formed from Ph₂SiH₂ even at 110 °C, although silafluorene condenses rapidly even at room temperature to a mixture of oligomers. The combination of Cp₂TiCl₂/nBuLi with PhMeSiH₂ provides oligomers from disilane through hexasilane, whereas Cp₂HfCl₂ produces disilane and trisilane. A possible mechanism for the coupling reaction is presented.