Electrochemical formation and reactivity of a manganese peroxo complex: acid driven H2O2 generation vs. O–O bond cleavage

The formation of a side-on peroxo [MnIIIL(O2)] complex (L = phenolato-containing pentadentate ligand), resulting from the reaction of electrochemically reduced O2 and [MnIIL]+, 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 M–O versus O–O bond cleavage is unprecedented for peroxomanganese(III) complexes and the latter offers a route for electrochemical O2 activation by a manganese(II) complex.