Stoichiometric formation of an oxoiron(IV) complex by a soluble methane monooxygenase type activation of O2 at an iron(II)-cyclam centre

Abstract

In soluble methane monooxygenase enzymes (sMMO) dioxy-gen (O2) is activated at a diiron(II) center to form an ox-odiiron(IV) intermediate Q that performs the challenging oxidation of methane to methanol. An analogous mechanism of O2 activation at mono- or di-nuclear iron centres 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 inter-mediate 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 aro-matic C-H bonds of 2,6-di-tert-butylphenol, which, together with the strong OAT ability of 3 represent new domains of oxoiron(IV) and superoxoiron(III) reactivities