Lutidine-Based Chiral Pincer Manganese Catalysts for Enantioselective Hydrogenation of Ketones

Abstract

A series of Mn^I complexes containing lutidine-based chiral pincer ligands with modular and tunable structures has been developed. The complex shows unprecedentedly high activities (up to 9800 TON; TON=turnover number), broad substrate scope (81 examples), good functional-group tolerance, and excellent enantioselectivities (85-98 % ee) in the hydrogenation of various ketones. These aspects are rare in earth-abundant metal catalyzed hydrogenations. The utility of the protocol have been demonstrated in the asymmetric synthesis of a variety of key intermediates for chiral drugs. Preliminary mechanistic investigations indicate that an outer-sphere mode of substrate-catalyst interactions probably dominates the catalysis.

Keywords: PNN ligands; asymmetric catalysis; hydrogenation; ketones; manganese.