Highly Efficient N, O Donor Ligand-Assisted Copper Complex-Catalyzed N-Arylation of Nitrogen-Containing Heterocycles...

Herein, we have successfully implemented two dinuclear copper complexes based on N, O donor ligands as efficient and selective catalysts for the arylation of N-heterocycles using aryl iodides, aryl bromides, and even less reactive aryl chlorides under relatively mild conditions. This is a dinuclear approach where metal-metal cooperation through a bridging ligand can enhance the catalytic process more efficiently than traditional mononuclear complexes. The structural characterization of a dinuclear copper complex of the form Cu₂L¹ ₄, 1 based on N, O donor 8-hydroxyquinoline (HL¹), reveals the formation of interesting isomeric structures. The complex 1 shows better catalytic activity toward N-arylation compared to the bis-chelating Schiff base N, O donor 2,2^'-[naphthalene-1,5-diylbis(nitrilo-methanylyl-idene)]diphenol (H₂L²)-coordinated dinuclear copper complex ClCu(μ-L²)CuCl, 2. The current protocol is effective for the arylation of imidazole, pyrazole, benzimidazole, 1,2,4-triazole, pyrrole, and indole, with tolerance of common functional groups. The N-arylation reaction catalyzed by 1 has been successfully scaled up to Gram scale without significantly reducing the product yield. A mechanistic route for this N-arylation reaction has been proposed by considering various control experimental and spectroscopic results.