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Abstract:
High-valent metal–oxo species serve as key intermediates in the activation of inert C–H bonds. Here, we present a comprehensive DFT analysis of the parameters that have been proposed as influencing factors in modeled high-valent metal–oxo mediated C–H activation reactions. Our approach involves utilizing DFT calculations to explore the electronic structures of modeled FeIV=O (species 1) and CoIV=O ↔ CoIII–O˙ (species 2), scrutinizing their capacity to predict improved catalytic activity. DFT and DLPNO-CCSD(T) calculations predict that the iron–oxo species possesses a triplet as the ground state, while the cobalt–oxo has a doublet as the ground state. Furthermore, we have investigated the mechanistic pathways for the first C–H bond activation, as well as the desaturation of the alkanes. The mechanism was determined to be a two-step process, wherein the first hydrogen atom abstraction (HAA) represents the rate-limiting step, involving the proton-coupled electron transfer (PCET) process. However, we found that the second HAA step is highly exothermic for both species. Our calculations suggest that the iron–oxo species (Fe–O = 1.672 Å) exhibit relatively sluggish behavior compared to the cobalt–oxo species (Co–O = 1.854 Å) in C–H bond activation, attributed to a weak metal–oxygen bond. MO, NBO, and deformation energy analysis reveal the importance of weakening the M–O bond in the cobalt species, thereby reducing the overall barrier to the reaction. This catalyst was found to have a C–H activation barrier relatively smaller than that previously reported in the literature.
