Cu(II)/TEMPO-Catalyzed Aerobic Oxidation of Primary Alcohols and Oxidative Dehydrogenation of N-Heterocycles

Four Cu(II)-N3 complexes were synthesized and evaluated for their catalytic performance in the aerobic oxidation of primary alcohols to aldehydes. The reactions were carried out under base-free conditions by using TEMPO as an additive and O2 as the oxidant. The system exhibited high activity and excellent selectivity, with no overoxidation products detected. Moreover, various N-heterocycles were converted to their corresponding products in moderate to excellent yields via oxidative dehydrogenation using the Cu/TEMPO/O2 system. The catalyst displayed high activity and good stability and could be recycled up to five times without significant loss of activity. A series of control experiments were carried out using UV-vis spectroscopy, confirming that no H2O2 was generated during the reaction. A plausible reaction mechanism is also discussed on the basis of HRMS and XPS experiments, together with DFT calculations. It is demonstrated that O2 plays a crucial role in oxidizing CuIClL to CuIIClL within the catalytic cycle.