A new polyoxometalate-based Mo/V coordinated crystalline hybrid and its catalytic activity in aerobic hydroxylation of benzene

A novel self-assembled polyoxometalate-based Mo/V coordinated crystalline organic-inorganic hybrid compound [Mo₂V₂O₈(2,2′-bpy)₆][HPMo₁₀V₂O₄₀]·2H₂O (bpy = bipyridyl) was hydrothermally synthesized by introducing polyoxometalate into a metal-organic unit containing metal nodes and 2,2′-bipyridyl ligands. The unit of the crystal consists of one Keggin-structure heteropolyoxoanion [HPMo₁₀V₂O₄₀]^4-, one tetranuclear organic-metal coordination cation [Mo₂V₂O₈(2,2′-bpy)₆]⁴⁺ and two water molecules. The crystalline hybrid presents heterogeneous catalytic performance and superior activity towards benzene hydroxylation with molecular oxygen as the oxidant and ascorbic acid as the sacrificial reducing agent, giving a phenol yield of 12.5% and a high TON (turnover number) of 41. The result indicates that the polyoxometalate-based crystalline organic-inorganic hybrid compound provides an efficient heterogeneous catalyst for the liquid-phase aerobic hydroxylation of benzene to phenol.