Electrochemical study of a nonheme Fe(ii) complex in the presence of dioxygen. Insights into the reductive activation of O at Fe(ii) centers.

Recent efforts to model the reactivity of iron oxygenases have led to the generation of nonheme Fe(OOH) and Fe(O) intermediates from Fe complexes and O but using different cofactors. This diversity emphasizes the rich chemistry of nonheme Fe(ii) complexes with dioxygen. We report an original mechanistic study of the reaction of [(TPEN)Fe] with O carried out by cyclic voltammetry. From this Fe precursor, reaction intermediates such as [(TPEN)Fe(O)], [(TPEN)Fe(OOH)] and [(TPEN)Fe(OO)] have been chemically generated in high yield, and characterized electrochemically. These electrochemical data have been used to analyse and perform simulation of the cyclic voltammograms of [(TPEN)Fe] in the presence of O. Thus, several important mechanistic informations on this reaction have been obtained. An unfavourable chemical equilibrium between O and the Fe complex occurs that leads to the Fe-peroxo complex upon reduction, similarly to heme enzymes such as P450. However, unlike in heme systems, further reduction of this latter intermediate does not result in O-O bond cleavage.