CATALYTIC DEHYDROGENATIVE COUPLING OF SECONDARY SILANES WITH CP2MCL2/NORMAL-BULI

The catalytic dehydrogenative coupling of secondary silanes has been achieved with the combination of Cp2ZrCl2 and 2 equiv of nBuLi in toluene at 90-degrees-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-degrees-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.