Generation, Characterization and Reactivity of a High‐Valent Mononuclear Cobalt(IV)−Diazide Complex

Abstract

AbstractHigh‐valent Fe(IV)=O intermediates of metalloenzymes have inspired numerous efforts to generate synthetic analogs to mimic and understand their substrate oxidation reactivities. However, high‐valent M(IV) complexes of late transition metals are rare. We have recently reported a novel Co(IV)−dinitrate complex (1‐NO3) that activates sp3 C−H bonds up to 87 kcal/mol. In this work, we have shown that the nitrate ligands in 1‐NO3 can be replaced by azide, a more basic coordinating base, resulting in the formation of a more potent Co(IV)−diazide species (1‐N3) that reacts with substrates (hydrocarbons and phenols) at faster rate constants and activates stronger C−H bonds than the parent complex 1‐NO3. We have characterized 1‐N3 employing a combination of spectroscopic and computational approaches. Our results clearly show that the coordination of azide leads to the modulation of the Co(IV) electronic structure and the Co(IV/III) redox potential. Together with the higher basicity of azide, these thermodynamic parameters contribute to the higher driving forces of 1‐N3 than 1‐NO3 for C−H bond activation. Our discoveries are thus insightful for designing more reactive bio‐inspired high‐valent late transition metal complexes for activating inert aliphatic hydrocarbons.