Hydrogen peroxide activation by a C-scorpionate vanadium(III) catalyst for the peroxidative oxidation reaction of cyclohexane in mild conditions: A DFT and experimental study

We report the first combined DFT and spectroscopic mechanistic investigation of a V(III)-chloride scorpionate complex, [VCl3{HC(pz)3}] (1), as a catalyst for the peroxidative oxidation of cyclohexane under mild conditions. DFT calculations reveal that 1 activates H2O2 through a multi-step oxidative mechanism following a V(III)→V (IV)→V(V) sequence, generating HOO⋅ radicals as the primary oxidizing species. The catalytic activity emerges from a competition between productive radical generation and self-trapping processes whose balance is governed by the H2O2/1 ratio, providing a molecular-level explanation for the experimentally observed trends in TON and alcohol/ketone selectivity. Unlike previously studied V(IV)/V(V) systems, the productive catalytic cycle follows a V(IV)→V(III)→V(IV) redox sequence, representing a novel mechanistic feature of vanadium-catalysed peroxidative oxidations. The proposed mechanism is validated experimentally by CW-EPR, pulsed ESEEM, and UV–Vis spectroscopy. These findings establish a clear optimization principle for V(III)-scorpionate catalysts in selective alkane oxidation under environmentally benign conditions.