Liquid phase hydrogenation of nitrobenzene and cyclohexene over inorganic polymer bearing phosphine group-supported palladium complexes

Palladium acetate was supported on polyorganosiloxane bearing phosphine group, as a catalyst for hydrogenation. The catalytic hydrogenation of cyclohexene and nitrobenzene over the inorganic polymer-supported Pd complexes in the presence of hydrogen, pressure 1 arm, at 25 degrees C, was investigated. Polyorganosiloxane (POS)-supported Pd catalyst with 7.36 of P/Pd, which indicates mole ratio of the phosphine group on POS to palladium, revealed maximum catalytic activity fur both substrates, when the ratio of P/Pd in the catalyst was changed from 3.84 to 27.94. The activity of POS-supported catalyst with a variety of P/Pd ratios for both substrates increased, in the following order: P/Pd = 7.36 > 14.50 > 3.84 > 27.94. These results suggested that catalytically active species on POS-supported Pd complexes for both substrates are the same. It seems that reactivities of supported Pd complexes reflect the amount of coodinatively unsaturated land catalytically active) species, following the above order. Effect of solvent on hydrogenation reaction of cyclohexene and nitrobenzene with the catalysts was also evaluated. As the relative permittivity (epsilon(r)) of solvent increased, the activity usually increased for both substrates. For DMF and DMSO, the activity, however, decreased as epsilon(r) increased. Effects of solvent on catalytic hydrogenation system was expressed by relative permittivity (epsilon(r)), E-T(30)-parameter, and cation-solvating tendencys (B) of solvents and substrates.