Unprecedented Halide Dependence on Catalytic Asymmetric Hydrogenation of 2‐Aryl‐ and 2‐Alkyl‐Substituted Quinolinium Salts by Using Ir Complexes with Difluorphos and Halide Ligands

A better way: Halide ligands bound to an iridium atom are the key to achieving high catalytic activity and enantioselectivity on asymmetric hydrogenation of 2-aryl- and 2-alkyl-substituted quinolinium salts. The reaction was catalyzed by a cationic dinuclear iridium(III) complex with difluorphos and chloride or bromide ligands and gave the corresponding 2-substituted 1,2,3,4-tetrahydroquinolines in high enantioselectivities (up to 95 % ee; see scheme, difluorphos=[(4,4′-bi-2,2-difluoro-1,3-benzodioxole)-5,5′-diyl]bis(diphenylphosphine)).