Implicating the Role of Enhanced Oxyl Attribute in Facilitating Exceptional C-H Activation by a [Co₂^III,IV(μ-O)₂]...

The soluble methane monooxygenase (sMMO), a metalloenzyme consisting of a bimetallic Fe diamond core, serves as the quintessential example of a biological system capable of activating strong C-H bonds. Over decades, inspired by sMMO's unique ability, chemists have devised elegant strategies for developing biomimetic bimetallic first-row transition-metal complexes for C-H bond activation. In line with this advancement, Li and coworkers synthesized a Co diamond-core complex, $[{\mathrm{Co}}_2^{\mathrm{III},\mathrm{IV}}(\mu -O{)}_2]$ (J. Am. Chem. Soc., 2019, 141, 20127) that exhibits enhanced C-H activation ability compared to its iron diamond-core counterparts. This study employs a host of theoretical techniques ranging from broken-symmetry density functional theory (DFT) to multiconfigurational methods (CASSCF/NEVPT2) to investigate the cobalt complex's electronic structure and exceptional reactivity relative to its iron congeners. The electronic structure of the Co complex reveals that C-H activation proceeds exclusively through a hydrogen-atom-transfer (HAT) pathway, triggered by the localization of enhanced radical character on one of the bridging oxygen atoms of the diamond-core motif. In contrast to its iron congener, the radical character of the bridging oxygen is not confined to the oxygen alone but is delocalized onto the iron center, which accounts for its higher activation barrier compared with the cobalt analogue.