Aqueous enantioselective hydrogenations involving silica-heterogenised catalysts

A mesoporous silica (HMS) has been prepared with an average pore size of 26 Å. The pores have been shown to include typical chiral catalysts for enantioselective hydrogenation viz Rh–BPPM and Ru–BINAP. The heterogenised catalysts have been shown to be effective for hydrogenations of water-soluble alkenes, e.g. itaconic acid 3 and the sodium salt of N-acetamidocinnamic acid (1a). Modest enantioselectivity was achieved for hydrogenation of the cinnamic acid derivative (40–60% ee) but only poor values for the itaconic acid (0≤16% ee). In some cases, the catalysts could be recovered and reused without significant loss of activity or selectivity.