Deciphering the mechanistic insights and reactivity trend of high-valent Mn/Fe/Co–oxo species toward C–H bond activation and oxygen atom transfer

Abstract

Understanding the structure and reaction pathways of high-valent metal–oxo species in C–H bond activation and oxygen atom transfer reactions is of great importance for improving their reactivity. Herein, we examine the reactivity of heme-based Mn/Fe/Co–oxo porphyrin complexes supported by an axial 1,3-dimethylimidazole ligand with substrates such as methane, 1,4-cyclohexadiene and dimethyl sulfide using density functional theory. Our calculations predicted quartet, triplet and doublet as the ground state for Mn, Fe and Co species, respectively. This study also reveals a reactivity trend of species Co > Fe > Mn during C–H bond activation and oxygen atom transfer reactions. Computed reaction profiles consistently identify the Co–oxo species as the most reactive, establishing the reactivity order. Furthermore, the formation of Co(III)-oxyl rather than a Co(IV)O species in species 3 is supported by the pronounced spin density localized on the oxygen atom, orbital analysis, M–O bond length and stretching frequency trends. Non-covalent interactions and quantum theory of atoms in molecules analyses show stronger dispersive stabilization and greater Co–O bond polarization relative to the Mn and Fe analogues. Energy decomposition analysis further confirms more favorable interaction energies for the Co–O transition states. Our analysis demonstrates that the higher reactivity of species 3 arises from its uniquely polarized electronic structure, enhanced oxyl radical character, enhanced non-covalent transition state stabilization and stronger polarization in the Co–O bond. Overall, this work provides a new mechanistic understanding that moves beyond the traditional focus on the spin state and oxyl radical character and offers definitive design principles for developing bioinspired catalysts capable of selective C–H bond and oxygen atom transfer functionalization.