Design of a Photoactive Metal–Organic Framework with Bimetallic Sites for Light-Driven C–X (X = S, N, O) Coupling-Cyclization

Donor–acceptor-type heterogeneous photocatalysts offer an effective and green approach for the synthesis of benzoheterocyclic compounds through photoinduced C–X (X = S, N, O) coupling cyclization. This study describes the synthesis of a photoactive metal–organic framework with dual Cu/Mo open metal sites, known as CuMo–TIPA, from the semiflexible electron-rich ligand tri-(4-(1H-imidazol-1-yl)-phenyl)amine (TIPA) and ammonium molybdate using a hydrothermal method. The introduction of Mo(VI) results in the long-range delocalization of photogenerated carriers, which allows photogenerated electrons in the excited state to activate molecular oxygen, breaking its spin-prohibitive barrier. Photoinduced electron transfer via a Type I pathway generates superoxide anion radicals (O2•–), which promote C–X coupling cyclization in air under room temperature and visible-light irradiation, achieving excellent yields. The apparent quantum yield at 400 nm is 7.54%. Notably, CuMo–TIPA enables scalable synthesis of the pharmaceuticals tiabendazole and CJM 126 (8 mmol). The ligand-to-metal charge transfer process from TIPA to Cu(II) in the photocatalytic system is elucidated via in situ X-ray photoelectron and electron paramagnetic resonance spectroscopies.