Dual-Functional Reductant/Copper Catalytic System for Aerobic Oxidation of Alcohols and N -Heterocycles without an External Base

Abstract

This work developed a practical and highly efficient Cu(II) catalytic system for the aerobic oxidation of alcohols and the dehydrogenative aromatization of N-heterocycles. This approach overcomes the reliance of traditional Cu(II) catalysts on strong bases. We designed a new N,N,O-tridentate Cu(II) complex (Cat 2), based on the concept of simplifying the catalytic system, and synthesized a dual-functional reductant CoBr2(NMI)2, which combines both reducing and coordination ability. Under mild conditions, this system employs air or O2 as the oxidant and efficiently catalyzes the transformation of various benzyl alcohols, aliphatic alcohols, and N-heterocyclic compounds into aldehydes and N-heterocyclic aromatic compounds in excellent yields. The cooperative catalytic system, resulting from Cat 2 and CoBr2(NMI)2, exhibits outstanding activity and high stability in air. Mechanistic studies reveal that the imine unit on the ligand acts as a “noninnocent ligand” participating in hydrogen-atom transfer, which is critical for the high efficiency of the system. This work provides a new strategy for developing stable, efficient, and Cu-based oxidation catalysts without an external base.