Effective coupling of aliphatic primary amines to imines on Cu-doped WO3 photocatalyst under aerobic and anaerobic conditions

Abstract

Imide, a key intermediate in organic synthesis, has extensive applications. The oxidative coupling of aliphatic primary amines to imines is challenging due to low reactivity. In this study, under visible light irradiation, Cu-doped WO₃ photocatalysts significantly enhanced the oxidative performance of aliphatic primary amines in both aerobic and anaerobic conditions, achieving imine yields of 94 % and 80 %, respectively. This performance is substantially superior to that of undoped WO₃ and is broadly applicable to both aliphatic and aromatic amines. This improvement is attributed to the Cu doping, which not only enhances the light absorption capabilities of WO₃ but also introduces oxygen vacancies that increase the adsorption and activation capacity for reactant molecules, altering the material’s band structure, enhancing light responsiveness, and promoting effective carrier separation. Additionally, radical quenching experiments confirmed the roles of holes and singlet oxygen in the aerobic reactions, while under anaerobic conditions, holes (h⁺) and electrons (e⁻) dominate, leading to high conversion rates and selectivity, as well as the detection of hydrogen. These findings provide important insights for designing efficient, non-precious metal-doped photocatalysts and advance the understanding of amine oxidative coupling.