Steering the Au−FexCo1Oy interface for efficient imine synthesis at low temperature via oxidative coupling reaction

Low-temperature imine formation through oxidative coupling of alcohols with amines under base-free conditions is very important for fine-chemical synthesis. Supported-Au catalysts show superior performances toward selective oxidation reactions but are scarcely reported for the above application. In this work, the finely-dispersed Au nanoparticles (ca. 2.4 nm) loaded on magnetic Fe x Co 1 O y oxides were developed as novel, efficient and reusable heterogeneous catalyst. Varying the Fe/Co molar ratio allowed tuning the Au−Fe x Co 1 O y interface and further boosting the selective oxidation performance of Au. The optimum Au/Fe 0.25 Co 1 O y catalyst showed >99% yield of benzylideneaniline and 20.1 mol imine mol Au −1 h −1 productivity using the model reaction at 30 °C under air atmosphere without alkaline additives. This was the best result compared to benchmark Au-based catalysts in the literature. In addition, this catalyst exhibited superior performances towards gram-scaled synthesis and diverse substrates. XRD, N 2 -physisorption, TEM, H 2 -TPR, O 2 -TPD, EPR, pyridine-adsorbed FT-IR, and kinetic investigations were used to study this Au catalytic system. It was found that the synergy between Fe 2 O 3 and Co 3 O 4 can induce formation of abundantly mobile and reactive oxygen species (i.e., O 2 − and O − related to oxygen vacancies) and electron-rich metallic Au species on the surface of mesoporous Fe x Co 1 O y oxides. These interfacial features were disclosed to be vital to activating molecular O 2 and O H bond in an alcohol. Besides, it was demonstrated that the surface Lewis acidic sites associated with coordinatively unsaturated Co 3+ ions can help facilitate the tandem oxidation-condensation reactions.