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

Abstract

The formation of a side-on peroxo [Mn^IIIL(O₂)] complex (L = phenolato-containing pentadentate ligand), resulting from the reaction of electrochemically reduced O₂ and [Mn^IIL]⁺, 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.