Catalytic Enantioselective Hydrogenation of Ketones and Imines Using Platinum Metal Complexes
A brief overview is presented on systems that effect catalytic enantioselective hydrogenation of ketones and imines using H2, or transfer from 2-propanol, and platinum metal complexes. Recent developments from my own group are then presented, and these describe Ir and Rh systems with inexpensive chiral ligands based on naturally occurring carboxylic acids (mandelic acid, methionine); up to 80% ee has been achieved for certain alkylarylketone substrates using N-acetyl-S-methionine (R,S)-sulfoxide as ligand. Nonfunctionalized chiral sulfoxides at Rh and Ir centers provide ineffective catalyst systems. Recently reported Ru-chiral phosphine catalysts realize enantioselectivities up to 100% for certain ketones (M. Kitamura et al., J. Am. Chem. Soc., 110, 629 (1988)); our work on closely related systems shows that trimeric hydrides are present, and these effect catalytic H2 hydrogenation of acetophenone, imines, and acetonitrile.