Designing a polyoxometalate-pillared metal-organic framework with long-range delocalization for photocatalytic oxidative cross-coupling

The development of a simple, mild and efficient strategy for synthesizing benzimidazole core structures and their 2-substituted derivatives remains challenging, particularly under ambient conditions using visible light irradiation without external cocatalysts. In this study, we synthesized a new polyoxometalate-based metal–organic framework (POMOF) [Ni(TPT)(H₂O)₅]{[Ni(TPT)(H₂O)₃][Ni_0.5(H₂O)] (H₂W₁₂O₄₀)}·TPT·H₂O (NiW–TPT) by incorporating [H₂W₁₂O₄₀]^6- clusters into a photoactive MOF matrix through hydrothermal synthesis. The designed architecture features strategically arranged electron donors and acceptors, coupled with strong interligand interactions, which synergistically promote efficient electron-hole pair separation. Notably, the integration of polyoxometalate (POM) clusters as “electron sponges” within the catalyst framework significantly suppresses charge recombination. This unique configuration enables selective generation of superoxide radicals (O₂^•–) via type I photogenerated electron transfer pathways under aerobic conditions. The optimized photocatalyst demonstrated exceptional performance, achieving high-yield synthesis a range of valuable benzimidazole derivatives under mild conditions, including pharmaceutically relevant compounds such as pipemidic acid and thiabendazole. Remarkably, this method proved particularly effective for condensing reactive heterocyclic aldehydes. Furthermore, the NiW–TPT catalyst maintained over 93 % of its initial activity through five consecutive recycling cycles, demonstrating excellent operational stability.