Water-involving transfer hydrogenation and dehydrogenation of N-heterocycles over a bifunctional MoNi4 electrode

A room-temperature electrochemical strategy for hydrogenation (deuteration) and reverse dehydrogenation of N-heterocycles over a bifunctional MoNi4 electrode is developed, which includes the hydrogenation of quinoxaline using H2O as the hydrogen source with 80% Faradaic efficiency and the reverse dehydrogenation of hydrogen-rich 1,2,3,4-tetrahydroquinoxaline with up to 99% yield and selectivity. The in situ generated active hydrogen atom (H*) is plausibly involved in the hydrogenation of quinoxaline, where a consecutive hydrogen radical coupled electron transfer pathway is proposed. Notably, the MoNi4 alloy exhibits efficient quinoxaline hydrogenation at an overpotential of only 50 mV, owing to its superior water dissociation ability to provide H* in alkaline media. In situ Raman tests indicate that the NiII/NiIII redox couple can promote the dehydrogenation process, representing a promising anodic alternative to low-value oxygen evolution. Impressively, electrocatalytic deuteration is easily achieved with up to 99% deuteration ratios using D2O. This method is capable of producing a series of functionalized hydrogenated and deuterated quinoxalines.