Mechanisms of catalytic hydrogenation of olefins using rhodium chloride complexes in non-aqueous solvents

Abstract

Solutions of rhodium chloride complexes in dimethylacetamide are efficient catalysts for the hydrogenation of a variety of substituted ethylenes and ethylene itself. Detailed kinetic studies on the maleic acid system indicate that Rh^III is initially reduced to Rh^I which is stabilized in solution by complexing with the olefin. The reduction of the olefin proceeds under mild conditions at about 1·0 M chloride concentration through reaction of H₂ with a monomeric Rh^I olefin complex; at low chloride, dimeric complexes may be involved. Isotope effects, solvent effects, effects of acid and temperature have been studied, and mechanisms consistent with the data are presented.