Metal Catalyzed Oligomerization Reactions of Organosiloxanes

摘要

Transition metal complexes, e.g. L2Pt(C2H4), L3RhCl, and L2Ir(CO)Cl (L=Ph3P), react with tetraalkyldisiloxanes, (HRR'Si)2O, to produce metallacycles featuring the transition metal, two silicons, and the oxygen in a four-membered ring, MSiOSi. When R=Me and R'=Ph, stereoselectivity in the formation of the metallacycle from a mixture of stereoisomers of the starting disiloxane is observed. The catalytic activity of these complexes for the oligomerization of the disiloxanes has been investigated in the hope of obtaining stereoregular silicones. It has been found that extensive rearrangements occur which redistribute the groups on the silicon atoms. Increased selectivity for the desired exchange type (SiO-groups for Si-H) was found when the catalysts were adsorbed on oxide supports. Although the goal of synthesizing stereoregular silicones has not yet been achieved, the results warrant further investigation.