Copper Phenylacetylide and TiO 2 Modification for an Efficient Visible-Light-Driven Oxidative Coupling of Amines.

The selective oxidation of amines to imines under mild conditions has attracted much attention. Our study reveals that copper phenylacetylide (PhC ₂ Cu) could serve as an efficient photocatalyst for imine synthesis under visible-light irradiation (>400 nm). Utilizing benzylamine as a model reactant, PhC ₂ Cu achieves an imine yield of 50.4%, which is 5 times higher than that of P25 under the same conditions and comparable to the yield obtained by the 3 wt % Au/P25 photocatalyst (55.4%). Further loading 3.9 nm TiO ₂ onto PhC ₂ Cu through tetrabutyl titanate hydrolysis increases the imine yield to 84.7%, with a Ti:Cu atomic ratio of 3.65%. Control experiments, photoluminescence (PL) spectra, optical pump terahertz probe (OPTP) spectra, and electron spin resonance (ESR) tests confirm that the optimized TiO ₂ modification promotes the separation of excited carriers and electron transfer in PhC ₂ Cu and facilitates the activation of surface oxygen, thereby enhancing the formation of superoxide radicals, a key active oxygen species in the reaction system. This work presents a promising strategy for efficient imine synthesis via amine coupling and expands the application field of PhC ₂ Cu-based photocatalysts.