Visible light-driven selective oxidation of amines by cooperative photocatalysis of niobium oxide nanorods with an electron–proton transfer mediator

Cooperative photocatalysis has gained increasing interest to better an existing redox reaction with a mediator. Herein, an ingenious system is constructed for the visible light-driven selective oxidation of a variety of amines by merging niobium oxide (Nb2O5) photocatalysis with an electron–proton transfer mediator, 2,2,6,6-tetramethylpiperidine-1-oxoammonium hexafluorophosphate (TEMPO+PF6−). The visible light-driven dissociative adsorption of amine over Nb2O5 nanorods gives rise to an amine–Nb2O5 complex with a weak response to visible light (λ < 460 nm). With adding 4 mol% of TEMPO+PF6−, the conversion of benzylamine over Nb2O5 is approximately 2.5 times that without TEMPO+PF6−. The proton and electron transfer between the amine–Nb2O5 complex and TEMPO+PF6− is the key to assuring cooperative photocatalysis. Besides, the oxidant dioxygen is predominantly reduced to superoxide anion in affording the imine products. This work highlights it is feasible to ameliorate selective organic conversions over metal oxide photocatalysts with a suited mediator.