Pentamethylcyclopentadienylrhodium(I) complexes incorporated into porous polysiloxanes prepared by a sol-gel process: Catalysts for hydrogenation of crotonic acid in water

Pentamethylcyclopentadiene-functionalized polysiloxanes were prepared by a sol-gel process from tetraethoxysilane and (pentamethyl-cyclo pentadienylme thyl)methyldiethoxysilane without a catalyst. The polysiloxanes are micropo rous-mesoporous solids, of which the BET surface areas and micropore volume s are inversely proportional to the concentration of the functionalizing ag ent (5-21 mol%) in the starting mixture of alkosysilanes, The polysiloxanes were also characterized by CP MAS C-13 NMR spectroscopy, revealing essenti ally the same structure of organofunctional ligand as that in particulate m aterials with low surface areas prepared earlier in a sol-gel process catal yzed by dibutyltin diacetate, Novel alkoxysilyl-substituted pentamethylcycl opentadienyl (1,5-cyclo-octadiene)rhodium(T) complexes were synthesized fro m the corresponding cyclopentadienes by deprotonation followed by reaction with [(cod)RhCl](2) (cod = cyclo-octadiene). Polysiloxane-bound rhodium com plexes were prepared by a sol-gel reaction analogous to the one mentioned a bove and mere found to catalyze the hydrogenation of crotonic acid in water ; to the best of our know-ledge, this constitutes the first example of cata lysis by a well-defined polysiloxane-bound transition metal complex in an a queous system, Copyright (C) 2000 John Wiley & Sons, Ltd.