Stoichiometric
Formation of an Oxoiron(IV) Complex
by a Soluble Methane Monooxygenase Type Activation of O2 at an Iron(II)-Cyclam Center

Kass, Dustin; Corona, Teresa; Warm, Katrin; Braun-Cula, Beatrice; Kuhlmann, Uwe; Bill, Eckhard; Mebs, Stefan; Swart, Marcel; Dau, Holger; Haumann, Michael; Hildebrandt, Peter; Ray, Kallol

doi:10.1021/jacs.9b13756.s001

ja9b13756_si_001.pdf (3.75 MB)

Stoichiometric Formation of an Oxoiron(IV) Complex by a Soluble Methane Monooxygenase Type Activation of O₂ at an Iron(II)-Cyclam Center

journal contribution

posted on 2020-03-18, 19:35 authored by Dustin Kass, Teresa Corona, Katrin Warm, Beatrice Braun-Cula, Uwe Kuhlmann, Eckhard Bill, Stefan Mebs, Marcel Swart, Holger Dau, Michael Haumann, Peter Hildebrandt, Kallol Ray

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.