Electrochemical formation and reactivity of a manganese peroxo complex: acid driven H2O2 generation vs. O-O bond cleavage
Résumé
The formation of a side-on peroxo [(MnL)-L-III(O-2)] complex (L = phenolato-containing pentadentate ligand), resulting from the reaction of electrochemically reduced O-2 and [(MnL)-L-II](+), is monitored in DMF using cyclic voltammetry, low temperature electronic absorption spectroscopy and electron paramagnetic resonance spectroscopy. Mechanistic studies based on cyclic voltammetry reveal that upon addition of a strong acid the Mn-O bond is broken, resulting in the release of H2O2, whereas in the presence of a weak acid the O-O bond is cleaved via a concerted dissociative electron transfer. This dichotomy of MO versus O-O bond cleavage is unprecedented for peroxomanganese(III) complexes and the latter offers a route for electrochemical O-2 activation by a manganese(II) complex.