The O<sub>2</sub>-coupled hydroxylation of unactivated C-H bonds is a metabolically important and characteristic reaction catalyzed by the monooxygenase enzymes. In the key steps of this reaction, in cytochrome P450s in particular, an Fe(IV)-oxo porphyrin π-radical cation (Cpd-I) abstracts an H-atom from an aliphatic substrate to form an Fe(IV)-hydroxo complex (protonated Cpd-II) which then “rebounds” the hydroxyl unit to the organic radical. Understanding the factors that control the selectivity and reaction outcome of enzyme hydroxylation depends on the C-OH bond formation step. However, this step is not rate-determining and is usually too fast to be observed spectroscopically. In this presentation, we report the synthesis and spectroscopic characterization of an isolable iron-hydroxide complex at the same oxidation level as protonated Cpd-II, the key precursor for examining the rebound step. The reactivity of this complex with stable carbon-centered radicals is demonstrated, and kinetic analyses provide mechanistic insights into the radical rebound process.

Direct observation of oxygen rebound in an iron-hydroxide complex

254th National Meeting (2017)

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