Synthesis and reactivity of a mononuclear non- haem cobalt(IV)-oxo complex

Abstract

Terminal cobalt(IV)-oxo (Co-IV-O) species have been implicated as key intermediates in various cobalt- mediated oxidation reactions. Herein we report the photocatalytic generation of a mononuclear non- haem [(13-TMC) Co-IV(O)] (2+) (2) by irradiating [ Co-II(13-TMC)(CF3SO3)] (+) (1) in the presence of [Ru-II( bpy)(3)] (2+), Na2S2O8, and water as an oxygen source. The intermediate 2 was also obtained by reacting 1 with an artificial oxidant (that is, iodosylbenzene) and characterized by various spectroscopic techniques. In particular, the resonance Raman spectrum of 2 reveals a diatomic Co-O vibration band at 770 cm (-1), which provides the conclusive evidence for the presence of a terminal Co-O bond. In reactivity studies, 2 was shown to be a competent oxidant in an intermetal oxygen atom transfer, C-H bond activation and olefin epoxidation reactions. The present results lend strong credence to the intermediacy of CoIV-O species in cobalt-catalysed oxidation of organic substrates as well as in the catalytic oxidation of water that evolves molecular oxygen.