Formation of cobalt-oxygen intermediates by dioxygen activation at a mononuclear nonheme cobalt(ii) center

A mononuclear nonheme cobalt(ii) complex, [(TMG₃tren)Co^II(OTf)](OTf) (1), activates dioxygen in the presence of hydrogen atom donor substrates, such as tetrahydrofuran and cyclohexene, resulting in the generation of a cobalt(ii)-alkylperoxide intermediate (2), which then converts to the previously reported cobalt(iv)-oxo complex, [(TMG₃tren)Co^IV(O)]²⁺-(Sc(OTf)₃)_n(3), in >90% yield upon addition of a redox-inactive metal ion, Sc(OTf)₃. Intermediates2and3represent the cobalt analogues of the proposed iron(ii)-alkylperoxide precursor that converts to an iron(iv)-oxo intermediateviaO-O bond heterolysis in pterin-dependent nonheme iron oxygenases. In reactivity studies,2shows an amphoteric reactivity in electrophilic and nucleophilic reactions, whereas3is an electrophilic oxidant. To the best of our knowledge, the present study reports the first example showing the generation of cobalt-oxygen intermediates by activating dioxygen at a cobalt(ii) center and the reactivities of the cobalt-oxygen intermediates in oxidation reaction.