Stoichiometric Formation of an Oxoiron(IV) Complex by a Soluble Methane Monooxygenase Type Activation of O<sub>2</sub> at an Iron(II)-Cyclam Center
Dustin Kass, Teresa Corona, Katrin Warm, Beatrice Cula, Uwe Kuhlmann, Eckhard Bill, Stefan Mebs, Marcel Swart, Holger Dau, Michael Haumann, Peter Hildebrandt, Kallol Ray
Abstract
In soluble methane monooxygenase enzymes (sMMO), dioxygen (O2) is activated at a diiron(II) center to form an oxodiiron(IV) intermediate Q that performs the challenging oxidation of methane to methanol. An analogous mechanism of O2 activation at mono- or dinuclear iron centers is rare in the synthetic chemistry. Herein, we report a mononuclear non-heme iron(II)-cyclam complex, 1-trans, that activates O2 to form the corresponding iron(IV)-oxo complex, 2-trans, via a mechanism reminiscent of the O2 activation process in sMMO. The conversion of 1-trans to 2-trans proceeds via the intermediate formation of an iron(III)-superoxide species 3, which could be trapped and spectroscopically characterized at −50 °C. Surprisingly, 3 is a stronger oxygen atom transfer (OAT) agent than 2-trans; 3 performs OAT to 1-trans or PPh3 to yield 2-trans quantitatively. Furthermore, 2-trans oxidizes the aromatic C–H bonds of 2,6-di-tert-butylphenol, which, together with the strong OAT ability of 3, represents new domains of oxoiron(IV) and superoxoiron(III) reactivities.