Elucidating the catalytic mechanisms of O 2 generation by [Mn 2 (μ-O) 2 (terpy) 2 (OH 2 ) 2 ] 3+ using DFT calculations: a focus on ClO - as oxidant.

The experimentally reported Mn(IV)Mn(III) complex [Mn 2 (μ-O) 2 (terpy) 2 (OH 2 ) 2 ] 3+ has been observed catalyzing O 2 generation with oxidants like ClO - and HSO 5 - . Previous mechanistic studies primarily focused on O 2 generation with HSO 5 - , 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 2 using ClO - follows the same mechanism previously identified with HSO 5 - 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 5 - , the Mn(IV)Mn(IV)-oxyl species indeed plays a crucial role in driving the catalytic evolution of O 2 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 2 , with activation free energies of 15.9 and 14.3 kcal mol -1 , respectively. However, our calculations revealed that the Mn(IV)Mn(IV)-oxyl complex is significantly more reactive in producing O 2 than Mn(IV)Mn(IV)-oxy and Mn(IV)Mn(IV)-OH, with a lower free energy barrier of 8.1 kcal mol -1 . 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 2 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.