Phosphine complexes of rhodium as homogeneous catalysts

A general survey is given of the developments leading to enantioselective hydrogenation catalysts based on phosphinerhodium complexes. The rates and optical yields obtained in ketone hydrogenation strongly depend on the structure of the phosphine ligand and on the phosphorous: rhodium ratio. The results can be interpreted by assuming several parallel catalytic mechanisms. The addi tion of amines often greatly enhances the activity of the catalyst systems which may be used in this form also for hydrodehalogenation and the hydrogenation of nitro compounds. New types of catalysmwhich are based on rhodium carboxylate complexes have been developed. Using chiral carboxylates asymmetric hydrogenation of olefins has been achieved with nonchiral phosphines as ligands.