Oxygen-free water-promoted selective photocatalytic oxidative coupling of amines†
A novel photocatalytic selective oxidative transformation of amines to imines using water as a primary oxidant is achieved under oxygen-free conditions. In the presence a single 1%Pt@TiO2-500 catalyst, the photocatalytic oxidative coupling of benzylamine to N-benzylidenebenzylamine has been efficiently performed using water as an oxidant, in which a 99.8% conversion and a 92.5% selectivity were obtained at room temperature; meanwhile, a certain amount of hydrogen was detected that confirms the simultaneous occurrence of water splitting reaction. Further investigations revealed that the introduction of the Pt element facilitates the formation of O-holes on the surface of TiO2, which efficiently promotes the generation of active oxygen species from water and the following oxidative coupling of benzylamine. Then, the photocatalytic oxidative coupling of various aromatic and aliphatic amines with water as the primary oxidant were also studied, and excellent conversion and high selectivities to corresponding products were attained. Based on the control experiment and the catalytic principle, a possible reaction mechanism is proposed for the oxidative coupling of benzylamine with water as the primary oxidant.