Pt-0 compounds bound in a silsesquioxane layer: active hydrosilation catalysts protected by the gel

Colloidal silica particles modified with a hydrosilane (Si-H), triethoxysilane (TES), reacted with Karstedt's catalyst, Pt-x(1,1,3,3-tetramethyl-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 after recovering and recycling the catalyst through at least three further hydrosilation experiments. Differences between the supported catalyst and Karstedt's catalyst are noted. Upon drying, catalytically inactive surface-bound platinum nanoparticles with an average diameter of 2 nm were produced. Larger platinum aggregates, which typically form in solution from platinum compounds without a stabilizer or in the presence of silica particles surface modified with monofunctional Si-H groups (Me2SiHOEt), were not observed with the silica particles modified with TES. A hydridosilsesquioxane (HSiO3/2) layer grafted to the silica surface was believed to be critical in controlling the ultimate size of the supported platinum nanoparticles. (C) 1997 Elsevier Science S.A.