Iridium-Catalyzed Asymmetric Hydrogenation of Olefins with Chiral N,P and C,N Ligands

Asymmetric hydrogenation is one of the most important catalytic methods for the preparation of optically active compounds. For a long time, chiral rhodium- and ruthenium–diphosphine complexes were the catalysts of choice in this field. However, their application range in the asymmetric hydrogenation of olefins is limited to substrates bearing a coordinating group adjacent to the C=C bond. These limitations were surmounted with the advent of iridium complexes with chiral N,P-ligands. For a wide range of unfunctionalized olefins, excellent enantioselectivities can now be achieved with low catalyst loadings. Moreover, these catalysts also allow highly enantioselective hydrogenation of various functionalized olefins, heterocycles such as furans or indoles, and imines. Research in this field is productive with new catalysts giving high enantioselectivities for difficult substrates appearing at an ever more frequent rate. These methods greatly expand the repertoire of reactions available to synthetic chemists for the preparation of optically active compounds in a reliable and an atom-economical fashion.