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

Abstract

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 β-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.