Résumé
We recently developed that halogen-bridged dinuclear iridium complexes bearing chiral diphosphine ligand [{Ir(H)[(S)-diphosphine]}2(mu-Cl)3]Cl which showed high catalytic activities and high enantioselectivities in catalytic asymmetric hydrogenation of 2-substituted quinolinium salts. Herein we report that a highly enantioselective asymmetric hydrogenation of 2-substituted quinoxalines catalyzed by iridium dinuclear complexes. Reactivity and enantioselectivity strongly depended on a combination of the halide ligand and diphosphine ligand bound to various iridium complexes, and DIFLUORPHOS and chloride ligands successfully catalyzed asymmetric hydrogenation of various 2-alkyl- and 2-aryl-substituted quinoxalines to afford the corresponding 1,2,3,4-tetrahydroquioxalines in quantitative yields and up to 95% ee. Study on mechanism concerning to catalytic active species will be disclosed.