Elucidating the catalytic mechanisms of O generation by [Mn(μ-O)(terpy)(OH)] using DFT calculations: a focus on ClO as oxidant.

The experimentally reported Mn(IV)Mn(III) complex [Mn(μ-O)(terpy)(OH)] has been observed catalyzing O generation with oxidants like ClO and HSO. Previous mechanistic studies primarily focused on O generation with HSO, concluding that Mn(IV)Mn(III) acts as a catalyst, generating a Mn(IV)Mn(IV)-oxyl species as a key intermediate responsible for O-O bond formation. This computational study employs DFT calculations to investigate whether the catalytic generation of O using ClO follows the same mechanism previously identified with HSO as the oxidant, or if it proceeds through an alternate pathway. To this end, we explored multiple pathways using ClO as the oxidant. Interestingly, our findings confirm that in the case of ClO as the oxidant, similar to what was observed with HSO, the Mn(IV)Mn(IV)-oxyl species indeed plays a crucial role in driving the catalytic evolution of O with the potential formation of the binuclear complexes Mn(IV)Mn(IV)-oxy and Mn(IV)Mn(IV)-OH during the reaction. These complexes are reactive in producing O, with activation free energies of 15.9 and 14.3 kcal mol, respectively. However, our calculations revealed that the Mn(IV)Mn(IV)-oxyl complex is significantly more reactive in producing O than Mn(IV)Mn(IV)-oxy and Mn(IV)Mn(IV)-OH, with a lower free energy barrier of 8.1 kcal mol. Consequently, even though Mn(IV)Mn(IV)-oxyl is predicted to be present in much lower concentrations than Mn(IV)Mn(IV)-oxy and Mn(IV)Mn(IV)-OH, it emerges as the species acting as the active catalyst for catalytic O generation. This study enhances our knowledge of high oxidation state (+3 and +4) manganese chemistry, highlighting its key role in catalysis and paving the way for more efficient Mn-based catalysts with broad applications.