Heck coupling by Pd deposited onto organic-inorganic hybrid supports

Organic-inorganic hybrid silica materials were prepared by modification through reaction with various chloroorganohydrosilanes. The resulting precursors bearing surface methyl or phenyl groups were further reacted with PdCl2 solution to deposit Pd through reduction with surface Si-H functions. The Pd-on-silica catalysts thus prepared were characterized by physical methods (BET, H-2 chemisorption, TEM, MAS NMR). The catalysts are active and highly selective in the Heck coupling with aromatic iodo and activated bromo compounds. Surface functional groups were found to affect catalyst activity. Leaching of Pd was detected, however, Pd species in solution do not appear to promote the reaction under the conditions applied. The performance of these new catalysts in recycling studies are found to be comparable to that of commercial Pd-on-carbon, which is considered to be one of the best heterogeneous catalyst. (C) 2004 Elsevier B.V. All rights reserved.