Naphthyridine-2NO, a new C2-symmetric rigid tetradentate bimetallic ligand and its application in asymmetric Friedel-Crafts alkylation

The development of dinuclear metal complexes as catalysts in asymmetric catalysis is in great demand but remains a particularly challenging goal. Herein, we rationally designed and developed a series of novel and easily accessed tertiary amine-derived C2-symmetric rigid tetradentate bimetallic naphthyridine-N,N '-dioxide ligands, namely Nar-2NO ligands, which incorporate the advantages of both the naphthyridine skeleton and the pyrroloimidazolone-based N-oxide moiety. The chiral dinuclear Nar-2NO-2Ni(ii) complex is generated in situ avoiding isolation and handling of sensitive species, and it performed successfully in enantioselective Michael-type Friedel-Crafts alkylation reactions of indoles and beta-nitrostyrenes, affording the chiral functionalized indole derivatives with up to 92% yield and 99% ee under mild conditions. These results demonstrated the promising utility of the tetradentate bimetallic naphthyridine-2NO ligands, which can coordinate two metals in close proximity to each other, in asymmetric catalysis.