Oxygen Vacancy Engineering in Metal–Organic Frameworks Regulates the Generation of Reactive Oxygen Species (ROS) for Photocatalytic C═N and C–N Coupling

The synthesis of nitrogen-containing structural motifs with high efficiency under mild conditions is challenging. Herein, controllable regulation of reactive oxygen species (ROS) in NH2-MIL-125(Ti) via oxygen vacancies engineering is achieved to effectively promote the photocatalytic C═N and C–N coupling to synthesize imines and benzimidazole compounds under mild conditions. The oxygen vacancies and structural integrity in NH2-MIL-125(Ti) can be well-controlled by facilely changing the temperature during mild heat treatment. Compared with pristine NH2-MIL-125(Ti), the NH2-MIL-125(Ti)-derived NM-Vo-T show stronger capacities to photoreduce oxygen to form ROS including superoxide anion radicals (O2•–) and hydroxyl radicals (•OH), leading to obviously improved photocatalytic activity for both amine oxidation to imines and C–N coupling between diamines and ethanol to form benzimidazole. This work not only offers an effective way toward efficient C═N and C–N coupling but, more importantly, provides significant guidance for the design of novel photocatalysts for the synthesis of fine chemicals in a green way.