Imine Synthesis by Benzylamine Self-Coupling Catalyzed by Cerium-Doped MnO2 under Mild Conditions

Primary amine self-coupling is of significant importance in imine synthesis, yet the thermal catalysis of amine self-coupling normally requires a high temperature or the addition of expensive oxidants. Herein, Ce-doped MnOx catalysts were prepared by three different methods, and their surface properties were thoroughly characterized. The Ce-doped MnOx catalyst obtained by redox-precipitation (CeMn-RO) showed efficient catalytic performance toward imine synthesis from benzylamine oxidation under mild conditions (80 °C, 8 h, air balloon), achieving high benzylamine conversion (92%). The exceptional oxidative ability of this catalyst could be attributed to its high concentration of surface Ce3+, Mn3+, and oxygen vacancies, facilitating the formation of surface oxygen species that play a vital role in the reaction. Furthermore, DRIFTS studies were carried out under the reaction conditions, offering powerful evidence of the benzylamine oxidation mechanism over CeMn-RO.