Solventless Heterogeneous Catalysis with [P₂Mo₅O₂₃]^6--Based Complexes: Achieving High-Efficiency and Rapid Oxidation...

The oxidation of C-H bonds holds paramount importance in the realms of organic synthesis and industrial chemistry. However, conventional methods are fraught with environmental concerns and economic drawbacks. Consequently, heterogeneous catalysis and solvent-free reactions have emerged as the focal points of research. This work reports two polyoxometalates-based complexes incorporating the [P₂Mo₅O₂₃]^6- ({P₂Mo₅}) unit as catalysts for solvent-free C-H bond oxidation: (Cu^IL₂)₄[H₂(P₂Mo₅O₂₃)]·H₂O (1) and (HL)₆(P₂Mo₅O₂₃)·H₂O (2) (L = benzimidazole), which exhibit similar stacking modes but obvious structural differences: ligands L coordinated with Cu ions to form {Cu^IL₂} subunits in complex 1, while complex 2 has fully protonated ligands L. Notably, complex 1 demonstrated exceptional heterogeneous catalytic activity compared to complex 2, efficiently oxidizing diphenylmethane (DPM) in the absence of the solvent and achieving conversion rates as high as 99.5% and selectivity for benzophenone (BP) of 100% within 6 h. The reasons for their different catalytic performances were unveiled. More importantly, even when the catalytic reaction was scaled up by 10-fold (with the amount of substrate DMP reaching 10 mmol), complex 1 still maintained high catalytic activity, highlighting its substantial potential for industrial applications.