Determination of Spin Inversion Probability, H‑Tunneling Correction, and Regioselectivity in the Two-State Reactivity of Nonheme Iron(IV)-Oxo Complexes

We show by experiments that nonheme FeIVO species react with cyclohexene to yield selective hydrogen atom transfer (HAT) reactions with virtually no CC epoxidation. Straightforward DFT calculations reveal, however, that CC epoxidation on the S = 2 state possesses a low-energy barrier and should contribute substantially to the oxidation of cyclohexene by the nonheme FeIVO species. By modeling the selectivity of this two-site reactivity, we show that an interplay of tunneling and spin inversion probability (SIP) reverses the apparent barriers and prefers exclusive S = 1 HAT over mixed HAT and CC epoxidation on S = 2. The model enables us to derive a SIP value by combining experimental and theoretical results.