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

Abstract

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. Intermediates 2 and 3 represent the cobalt analogues of the proposed iron(II)-alkylperoxide precursor that converts to an iron(IV)-oxo intermediate via O–O bond heterolysis in pterin-dependent nonheme iron oxygenases. In reactivity studies, 2 shows an amphoteric reactivity in electrophilic and nucleophilic reactions, whereas 3 is 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.