Exploring New Ligand Designs for Asymmetric Catalysis

Abstract

Chiral cooperative catalysis enabling simultaneous activation of both an electrophile and a nucleophile has emerged as a powerful strategy in catalytic asymmetric synthesis. In our laboratory, a series of novel hydrogen-bond functionalized salen-transition metal catalysts have been developed to facilitate bimetallic or bifunctional activation of both reaction partners. For example, a self-assembling dinuclear Co(II)-salen catalyst featuring the pyridone/aminopyridine H-bonding pair results in significant rate acceleration as well as excellent enantioselectivity in nitro-aldol reaction. Bis-urea functionalized salen-Co(III) complexes exhibited significant rate acceleration in hydrolytic kinetic resolution of epoxides even at low catalyst loading (0.05 mol%). The bis-urea salen-Co(III) complexes are also excellent catalysts for antiselective asymmetric Henry reaction where broad substrate scope, good yield, excellent enantio- and diastereoselectivity were observed. During this presentation, synthesis of ligands/catalysts, applications in asymmetric transformations, and plausible mechanisms will be discussed in detail.