Effects of Polymer Support on the Substrate Selectivity of Covalently Immobilized Ultrafine Rhodium Particles as a Catalyst for Olefin Hydrogenation

Ultrafine rhodium particles prepared by alcohol reduction in the presence of a protective polymer were covalently immobilized onto a cross-linked polymer support by forming the amide bond between the primary amino group contained in the support and the methyl acrylate residue in the protective polymer of the particles. Catalytic activity of the immobilized particles was investigated in catalytic hydrogenation of olefins. The activity strongly depended on the substrates used in the reactions. The immobilized ultrafine rhodium particles preferentially hydrogenated hydrophilic substrates. In particular, the substrates containing a carboxyl group were hydrogenated by the immobilized catalyst more easily than by the dispersed catalyst of the ultrafine rhodium particles before the immobilization. The difference in the hydrogenation rates can be correlated with the solubility parameter of the substrates. Electrostatic interaction between the substrates and the polymer support leads to increased reaction rates.