Solventless Heterogeneous Catalysis with [P₂Mo₅O₂₃]^6–-Based Complexes:Achieving High-Efficiency and Rapid Oxidation of C–H Bonds

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^I<b>L</b>₂)₄[H₂(P₂Mo₅O₂₃)]·H₂O (<b>1</b>) and (H<b>L</b>)₆(P₂Mo₅O₂₃)·H₂O (<b>2</b>) (<b>L</b> = benzimidazole), which exhibit similar stacking modes but obvious structural differences: ligands <b>L</b> coordinated with Cu ions to form {Cu^I<b>L</b>₂} subunits in complex <b>1</b>, while complex <b>2</b> has fully protonated ligands <b>L</b>. Notably, complex <b>1</b> demonstrated exceptional heterogeneous catalytic activity compared to complex <b>2</b>, 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 <b>1</b> still maintained high catalytic activity, highlighting its substantial potential for industrial applications.