Implicating the Role of Enhanced Oxyl Attribute in Facilitating Exceptional C–H Activation by a [CoIII, IV2(μ-O)2] Diamond-Core Complex: A Theoretical Perspective.

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. Recently, Li and co-workers synthesized a Co diamond-core complex, [CoIII,IV 2 (μ−O)2] 1(J. Am. Chem. Soc. 2019, 141, 20127-20136) that exhibits enhanced C-H activation ability compared to its iron diamond core counterparts. In this study, we employed a host of theoretical techniques ranging from broken-symmetry density functional theory (DFT) to multi-configurational methods (CASSCF/NEVPT2) to understand the exceptional reactivity of the cobalt complex from an electronic-structure perspective and to compare it with 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 localization of enhanced radical character on one of the bridging oxygen atoms of the diamond-core motif. To compare and contrast to that of its iron congener, we found that the radical character of the bridging oxygen is not confined to the oxygen atom alone but is also delocalized onto the iron center, which accounts for its higher activation barrier compared with the cobalt analogue.