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

A mononuclear nonheme cobalt( ii ) complex, [(TMG 3 tren)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, [(TMG 3 tren)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. The present study represents the first example showing the generation of Co( ii )-alkylperoxide and Co( iv )-oxo intermediates by employing dioxygen as an oxidant.