Selective Formation of an Fe IV O or an Fe III OOH Intermediate From Iron(II) and H 2 O 2 : Controlled Heterolytic versus Homolytic Oxygen–Oxygen Bond Cleavage by the Second Coordination Sphere

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 H 2 O 2 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 ‐H 2 O 2 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.