Transition metal peroxo (M-OO) and hydro-peroxo (M-OOH) adducts are postulated as key intermediates in various catalytic oxygenation reactions like for instance transition metal catalyzed oxidation of organic compounds as well as in fundamental enzymatic reactions such as respiration and photosynthesis.In the four-electron water oxidation and the four-electron O2 reduction, these intermediates are involved in a key step of the mechanism, i.e. the formation or the cleavage of the O−O bond respectively. The proper control of the proton delivery to the peroxo intermediate is an important parameter that governs the dichotomy between M−O or O−O cleavage. In the case of manganese, a number of biomimetic, mononuclear peroxomanganese(III) complexes resulting from reaction with dioxygen, superoxide or hydrogen peroxide have been reported. Although these complexes have been nicely characterized, a detailed understanding of the structure- reactivity relationship is still limited. In the present work we (i) report on the preparation and spectroscopic properties of a novel mononuclear peroxomanganese(III) adducts resulting from the reaction of electrochemically reduced O2 and a Mn(II) complex; (ii) discuss the reactivity of a peroxomanganese(III) complex in various protic media by means of cyclic voltammetry (CV) and UV-vis absorption spectroscopy. The unprecedented electrochemical approach described herein allows for a mechanistic comparison of Mn-O and O-O bond cleavage reactions for a peroxomanganese(III) intermediate. Importantly, the peroxo ligand in this system is derived from molecular oxygen. We also report on a similar study with Fe complexes. Thus, this work not only describes a new method for electrochemical O2 activation by a metal centre, but also provides insights into factors affecting the gating of M-O versus O-O bond cleavage by peroxometal species.

Electrochemistry to probe the reactivity of metal-(hydro)peroxo species derived from reductive activation of O2

251st National Meeting (2016)

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