Self-Assembly of a Chiral Bis-phosphine Ligand Bearing Pyridyl Crown Ethers and Chiral Primary Ammoniums: Application to Catalytic Asymmetric Hydrogenation Reactions

A chiral bis-hosphine ligand bearing two pyridyl crown ethers was complexed with primary ammonium salts of different absolute configuration to form supramolecular chiral catalysts, which were successfully applied in the Rh-catalyzed asymmetric hydrogenation of alpha-dehydroamino acid esters and Ir-catalyzed asymmetric hydrogenation of quinoxalines. By comparison with the non-assembled catalysts, the complexation between the chiral catalysts and primary ammoniums obviously improved enantioselectivities. Up to 11% enhancement in ee values in asymmetric hydrogenation of alpha-dehyciroamino acid esters and 304 enhancement in ee values in asymmetric hydrogenation of quinoxalines were achieved.