Selective Formation of an FeIVO or an FeIIIOOH Intermediate From FeII-H2O2 : Controlled Heterolytic vs Homolytic O-O Bond Cleavage by the Second Coordination Sphere

We demonstrate that the devised incorporation of an alkylamine group into the second coordination sphere of an FeII complex allows to switch its reactivity with H2O2 from the usual formation of FeIII species towards the selective generation of an FeIV‐oxo intermediate. The FeIV‐oxo was characterized by UV‐visible absorption and Mössbauer spectroscopy. Variable temperature kinetic analyses point towards a mechanism where the heterolytic cleavage of the O‐O bond is triggered by a proton transfer from the proximal to the distal oxygen atom in the FeII‐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 that leads to the formation of the FeIV‐oxo and release of water through a concerted mechanism.