Selective hydrogenation of acetylenes to olefins catalyzed by polymer-bound palladium(II) complexes

Abstract

Semihydrogenations of 15 acetylenes to olefins catalyzed by polymer-bound palladium(II) complexes have been studied synthetically and mechanistically, and the hydrogenation of phenylacetylene has been studied kinetically. In the hydrogenation of isolated acetylenes, the catalyst generated corresponding olefins in high selectivities (above 92%). In the case of conjugated acetylenes, the catalyst generated corresponding conjugated olefins in relatively low selectivities (71–85%), whereas phenylacetylene was hydrogenated to styrene in a high selectivity (93%). A high activity of the catalyst was observed in oxygen-containing solvents such as dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, and ethanol. The catalytic activity is affected more strongly by the π-acidity of acetylenes than their steric factor. The hydrogenation rate of phenylacetylene is expressed by the form: R = k 2[H 2][ A], where [H 2] and [ A] are hydrogen and the catalyst concentrations, respectively. A mechanism for the hydrogenation is proposed on the basis of kinetic studies. Finally, it is summarily discussed what factors control the activity and the selectivity of the polymer catalyst for the hydrogenation of carbon-carbon double and triple bonds. This polymer-bound palladium complex was shown to be comparable in selectivity to cationic rhodium and the Lindlar catalysts.