This journal is © the Owner Societies 2024 Phys. Chem. Chem. Phys., 2024, 26, 4349–4362 | 4349 Cite this: Phys. Chem. Chem. Phys., 2024, 26, 4349 C–H bond activation by high-valent iron/cobalt–oxo complexes: a quantum chemical modeling approach† Manjeet Kumar, a Manoj Kumar Gupta, a Mursaleem Ansari* b and Azaj Ansari * a 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 Fe IV Q O (species 1) and Co IV QO 2 Co III –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. Introduction The activation of C–H bonds using transition metal based catalysts is becoming an increasingly attractive technique for synthesizing organic compounds, natural products, and essen- tial components of organic materials. 1 C–H bond catalysis based on non-precious metals is an alternative to the particu- larly abundant, precious metals (such as Rh, Pd, Ru, and Ir) that are frequently used in this field. 2 However, the scarcity of precious metals enforced scientists to look to more abundant metal-incorporating catalyst systems for C–H bond cleavage reactions. Recently, the development of transition metal–oxo complexes as intermediates in a number of catalytic processes has been significantly determined, mostly with groups 3–10 which have received a great deal of attention. 3 In biology, owing to the widespread abundance of iron in nature, metalloenzymes containing mononuclear or binuclear iron centers are relatively common. 4 In the literature, both heme and non-heme iron enzymes are found in high-valent iron–oxo intermediates, which have been well characterized and play an essential role in the mechanisms of C–H bond activation reactions. 5 Moreover, it is well established that both heme enzymes (such as those in the cytochrome P450 family) and non-heme iron enzymes 6 (including methane mono- oxygenase 7 and Rieske dioxygenases 5a,8 ) exhibit outstanding selectivity in catalyzing aliphatic C–H bonds under mild reac- tion conditions. 9 In 2010, the key intermediate in P450 com- pound I (P450-I) was characterized for the first time, both spectroscopically and kinetically. 10 Furthermore, the electronic structure of P450-I was best described as having an S = 1 for Fe(IV)oxo coupled with an S = 1/2 radical of the ligand. 11 Certainly, the reactivity and efficiency of high-valent transition metal–oxo species have been controlled by various factors. More precisely, two factors commonly control the catalytic ability and efficiency of any catalytic species: first the spin state of the central metal ion of the species and second the surrounding environment (ligand) around the metal ion of the complex. 12 a Department of Chemistry, Central University of Haryana, Mahendergarh-123031, Haryana, India. E-mail: ajaz.alam2@gmail.com b Max-Planck-Institut fu ¨r Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mu ¨lheim an der Ruhr, Germany. E-mail: mansaribhu@gmail.com † Electronic supplementary information (ESI) available. See DOI: https://doi.org/ 10.1039/d3cp05866b Received 1st December 2023, Accepted 19th December 2023 DOI: 10.1039/d3cp05866b rsc.li/pccp PCCP PAPER Published on 22 December 2023. Downloaded by INDIAN INSTITUTE OF TECHNOLOGY BOMBAY on 4/30/2024 12:25:09 PM. View Article Online View Journal | View Issue