USE OF POLYSTYRENE BOUND ORTHOMETALATED SCHIFF-BASE COMPLEXES OF PALLADIUM(II) AS CATALYSTS FOR THE DIHYDROGEN REDUCTION OF NITROALKANES, NITRILES AND KETONES

Dihydrogen reduction of nitroalkanes, aliphatic and aromatic nitriles and ketones to their corresponding saturated products was successively achieved in DMF medium using polystyrene based acetato-bridged orthom etalated Schiff base complexes of palladium (II) as catalysts, at 80-1 30 degrees C and 6.0-14.0 x 10(3) (kN m(-2)) of P-H2. The acetato-brid ged Schiff base complexes are the catalyst precursors and the actual c atalysts are the corresponding hydrogen activated orthometalated compl exes with the acetate bridge replaced by H and DMF. The immobilization of the palladium (II) complexes in the polymer matrix slightly decrea sed their catalytic activities on the basis of metal content but impro ved the chemical and thermal stabilities and product selectivities rel ative to those of the corresponding homogeneous ones. The same specime n of the catalyst can be used repeatedly for the reduction of differen t substrates and stored for a long time without suffering any apprecia ble loss of activity. XPS data suggest the presence of palladium (II) in the fresh and used catalyst and kinetic studies indicate Ist order rate dependence on palladium (II) content, second order on P-H2 and in dependent of substrate concentration. A plausible mechanistic route ha s been suggested on the basis of kinetic data and experimental observa tions. (C) 1997 Elsevier Science B.V.