Selective Formation of an FeIVO or an FeIIIOOH Intermediate From Iron(II) and H2O2: Controlled Heterolytic versus Homolytic Oxygen–Oxygen Bond Cleavage by the Second Coordination Sphere

Don't cleave me this way: A novel synthetic iron(II) complex bearing a second sphere intra‐molecular base efficiently forms an iron(IV)‐oxido species in the presence of H₂O₂ rather than the usual formation of an Fe^III species. Mechanistic studies demonstrate an overall heterolytic cleavage of the O−O bond proceeding by a homolytic cleavage with a concerted proton coupled electron transfer (PCET).

Abstract

We demonstrate that the devised incorporation of an alkylamine group into the second coordination sphere of an Fe^II complex allows to switch its reactivity with H₂O₂ from the usual formation of Fe^III species towards the selective generation of an Fe^IV‐oxo intermediate. The Fe^IV‐oxo species was characterized by UV/Vis absorption and Mössbauer spectroscopy. Variable‐temperature kinetic analyses point towards a mechanism in which the heterolytic cleavage of the O−O bond is triggered by a proton transfer from the proximal to the distal oxygen atom in the Fe^II‐H₂O₂ complex with the assistance of the pendant amine. DFT studies reveal that this heterolytic cleavage is actually initiated by an homolytic O−O cleavage immediately followed by a proton‐coupled electron transfer (PCET) that leads to the formation of the Fe^IV‐oxo and release of water through a concerted mechanism.

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