PT-0 COMPOUNDS BOUND IN A SILSESQUIOXANE LAYER - ACTIVE HYDROSILATIONCATALYSTS PROTECTED BY THE GEL

Colloidal silica particles modified with a hydrosilane (Si-H), trietho xysilane (TES), reacted with Karstedt's catalyst, t-x(1,1,3,3-tetramet hyl-1,3-divinyldisiloxane)(y), to give a supported platinum catalyst. The silica-supported platinum nanoparticles were catalytically active in the hydrosilation reaction; the catalytic activity was maintained a fter recovering and recycling the catalyst through at least three furt her hydrosilation experiments. Differences between the supported catal yst and Karstedt's catalyst are noted. Upon drying, catalytically inac tive surface-bound platinum nanoparticles with an average diameter of 2 nm were produced. Larger platinum aggregates, which typically form i n solution from platinum compounds without a stabilizer or in the pres ence of silica particles surface modified with monofunctional Si-H gro ups (Me2SiHOEt), were not observed with the silica particles modified with TES. A hydridosilsesquioxane (HSiO3/2) layer grafted to the silic a surface was believed to be critical in controlling the ultimate size of the supported platinum nanoparticles. (C) 1997 Elsevier Science S. A.