Complex-catalyzed hydrogenation reactions in aqueous media

The review summarizes recent work in the field of hydrogenation reactions catalyzed by transition metal complexes in aqueous media. This development was stimulated by the availability of water-soluble ligands and facilitated the recycling of the catalyst from multiphase systems. Another possibility is the immobilization of the catalytic system on insoluble or water-soluble polymers. The asymmetric hydrogenation of prochiral substrates was realized in several examples with remarkable success. An enhancement of enantioselectivity and activity was achieved in the hydrogenation of amino acid precursors in micro-heterogeneous (aqueous micellar) systems. Beside the reduction of the C=C bond, also reported are the reduction of C=O and C=N bonds including methods which involve transfer hydrogenation.