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 the 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, which establishing the reactivity order. Further, 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 spin state and oxyl radical character and offering definitive design principles for developing bioinspired catalysts capable of selective C-H bond and oxygen atom transfer functionalization.