Cobalt-Catalyzed Highly Enantioselective Hydrogenation of Quinolines under Mild Conditions

A cobalt pincer complex has been designed, synthesized, and successfully applied to catalytic asymmetric hydrogenation of quinolines under mild conditions. Containing a PNN ligand that features both a P and a C-stereogenic center, the cobalt catalyst allows for the hydrogenation of a variety of quinolines to afford chiral 1,2,3,4-tetrahydroquinolines with high yields and excellent enantioselectivities in general (51 examples, up to 99.9% ee). Probe reactions and DFT calculations suggest that the hydrogenation proceeds via a stepwise 1,2-1,2-hydride transfer pathway. The results obtained could provide a valuable hint for the development of more efficient 3<i>d</i> transition metal catalysts for asymmetric catalysis.