Phenol-Induced O–O Bond Cleavage in a Low-Spin Heme–Peroxo–Copper Complex: Implications for O2 Reduction in Heme–Copper Oxidases

This study evaluates the reaction of a biomimetic heme–peroxo–copper complex, {[(DCHIm)(F8)FeIII]–(O22–)–[CuII(AN)]}+ (1), with a phenolic substrate, involving a net H-atom abstraction to cleave the bridging peroxo O–O bond that produces FeIV═O, CuII—OH, and phenoxyl radical moieties, analogous to the chemistry carried out in heme–copper oxidases (HCOs). A 3D potential energy surface generated for this reaction reveals two possible reaction pathways: one involves nearly complete proton transfer (PT) from the phenol to the peroxo ligand before the barrier; the other involves O–O homolysis, where the phenol remains H-bonding to the peroxo OCu in the transition state (TS) and transfers the H+ after the barrier. In both mechanisms, electron transfer (ET) from phenol occurs after the PT (and after the barrier); therefore, only the interaction with the H+ is involved in lowering the O–O cleavage barrier. The relative barriers depend on covalency (which governs ET from Fe), and therefore vary with DFT functional...