Chiral CNN pincer Ir(III)-H complexes. Transient ligand and counterion influences in the asymmetric hydrogenation of imines and quinolines

Abstract

Building upon the success of Ir-IMMAX catalysts, we designed a novel cationic Ir(III)–H catalyst featuring a meridional CNN pincer ligand with a perpendicular monodentate phosphine, where chirality arises from both the chiral oxazoline moiety and the metal center itself. The catalyst is readily synthesized from commercially available precursors, obtained as a single diastereomer, and exhibits high activity in the asymmetric hydrogenation of imines and quinolines under mild conditions. One of the synthesized Ir(III)–H complexes efficiently reduced N-methylimines and 2-methylquinoline at room temperature under 3 bar of H2 pressure, positioning itself among the most active catalysts described to date. The incorporation of a weakly coordinating transient ligand, such as acetonitrile, significantly enhanced catalytic performance. Additionally, the counterion displayed an important influence on both enantioselectivity and activity, with the BArF complex providing higher selectivity and the triflate complex exhibiting superior reactivity.