Homogeneous Hydrogenation of Unsaturated Carboxylic Acids Using Chlororhodate(I) Complexes and Rhodium(I) Diethylsulfide Complexes

Abstract

N,N-Dimethylacetamide solutions of the cyclooctene complex [Rh(C8H14)2Cl]2, in the presence of excess chloride or diethylsulfide, are effective for the homogeneous hydrogénation of unsaturated carboxylic acids at ca. 80 °C and 1 atm H2. Kinetic studies on the hydrogenation of maleic acid are consistent with a rate determining step involving oxidative addition of H2 to square planar rhodium(I) olefin species. Rate constants and activation parameters agree with those determined previously from similar studies using corresponding rhodium(III) complexes and give confirmation that rhodium(I) catalysts are involved in the rhodium(III) systems. Discussion of the systems is limited by the somewhat uncertain nature of the catalysts; however, chlororhodate(I) species are involved in the chloride solutions, and bis(diethylsulfide) complexes appear likely in the sulfide systems.