Elucidating the catalytic mechanisms of O2 generation by [Mn2(μ-O)2(terpy)2(OH2)2]3+ using DFT calculations: a focus on ClO− as oxidant
Publication Name
Dalton Transactions
Abstract
The experimentally reported Mn(iv)Mn(iii) complex [Mn2(μ-O)2(terpy)2(OH2)2]3+ has been observed catalyzing O2 generation with oxidants like ClO− and HSO5−. Previous mechanistic studies primarily focused on O2 generation with HSO5−, 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 O2 using ClO− follows the same mechanism previously identified with HSO5− 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 HSO5−, the Mn(iv)Mn(iv)-oxyl species indeed plays a crucial role in driving the catalytic evolution of O2 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 O2, 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 O2 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 O2 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.
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