Catalytic Hydrogenation of Unsaturated Carboxylic Adds Using N,N-Dimethylacetamide Solutions of Ruthenium(I) Chlorides

N,N-Dimethylacetamide solutions of dimeric ruthenium(I) chlorides catalyze homogeneously the hydrogenation of ethylene and unsaturated carboxylic acids under mild conditions. Kinetic and mechanistic studies show that the catalysis involves a monomeric Ru(I) complex which forms reversibly a steady state concentration of a Ru(III)H 2 species; this reacts with olefinic substrate to yield saturated product by two successive single hydrogen atom transfers with regeneration of the Ru(I) catalyst. The overall hydrogen addition to fumaric acid is cis. Hydrogenation of maleic acid is accompanied by an efficient isomerization to fumaric acid.