Studies of Immobilized Homogeneous Metal Catalysts on Silica Supports

摘要

The tethered, chiral, chelating diphosphine rhodium complex, which catalyzes the enantioselective hydrogenation of methyl-(alpha)-acetamidocinnamate (MAC), has the illustrated structure as established by (sup 31)P NMR and IR studies. Spectral and catalytic investigations also suggest that the mechanism of action of the tethered complex is the same as that of the untethered complex in solution. The rhodium complexes, (Rh(COD)H)(sub 4), (Rh(COD)(sub 2))(sup+)BF(sub 4)(sup -), (Rh(COD)Cl)(sub 2), and RhCl(sub 3)(center-dot) 3H(sub 2)O, adsorbed on SiO(sub 2) are optimally activated for toluene hydrogenation by pretreatment with H(sub 2) at 200 degrees C.