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-V_o-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.