Trapping of a Highly Reactive Oxoiron(IV) Complex in the Catalytic Epoxidation of Olefins by Hydrogen Peroxide

Abstract

The generation of a nonheme oxoiron(IV) intermediate, [(cyclam)Fe-IV(O) (CH3CN)](2+) (2; cyclam=1,4,8,11-tetraazacyclotetradecane), is reported in the reactions of [(cyclam)Fe-II](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)-Fe-II](2+) and H2O2. In spite of the predominance of the oxoiron(IV) cores in biology, the present study is a rare example of high-yield isolation and spectroscopic characterization of a catalytically relevant oxoiron(IV) intermediate in chemical oxidation reactions.