Trapping of a Highly Reactive Oxoiron(IV) Complex

Oxoiron(IV) species are the active oxidants in catalytic oxidation reactions by nonheme iron enzymes, but have been rarely captured and/or identified as the actual oxidizing species in catalytic epoxidation or hydroxylation reactions involving synthetic nonheme iron complexes. We now report the generation of a nonheme oxoiron(IV) intermediate, [(cyclam)FeIV(O)(CH3CN)]2+ (2; cyclam = 1,4,8,11-tetraazacyclotetradecane), in the reactions of [(cyclam)FeII]2+ with aqueous hydrogen peroxide (H2O2) or a soluble iodosylbenzene (sPhIO) as a rare example of an oxoiron(IV) species that shows a preference for epoxidation over allylic oxidation in the oxidation of cyclohexene. Complex 2 is kinetically and catalytically competent to perform the epoxidation of olefins with high stereo- and regioselectivity. More importantly, 2 is likely to be the reactive intermediate involved in the catalytic epoxidation of olefins by [(cyclam)FeII]2+ and H2O2. In spite of the predominance of the oxoiron(IV) cores in biology, the present study represents a rare example of high-yield isolation and spectroscopic characterization of a catalytically relevant oxoiron(IV) intermediate in chemical oxidation reactions. It was published today in Angewandte Chemie-International Edition:

X. Engelmann, D.D. Malik, T. Corona, K. Warm, E.R. Farquhar, M. Swart, W. Nam, and K. Ray
“Trapping of a Highly Reactive Oxoiron(IV) Complex in the Catalytic Epoxidation of Olefins by Hydrogen Peroxide”
Angew. Chem. Int. Ed. 2019, ASAP- [abstract]
DOI: 10.1002/anie.201812758