Theoretical studies on the reaction mechanism of alcohol oxidation by high-valent iron-oxo complex of non-heme ligand

Abstract

The catalytic mechanism for the oxidation of methanol to formaldehyde and water catalyzed by the biomimetic non-heme iron complex, [(tpa)Fe^IVO]²⁺ (tpa = tris(2-pyridylmethyl)amine), is presented by the density functional method B3LYP. Experimentally, acetate and CH₃CN could be coordinated to the Fe center as the sixth ligand to form the catalyst [(tpa)Fe^IVO]²⁺. To investigate the detailed reaction mechanisms for the two possible ligands, two models (acetate-bound ferryl model A and CH₃CN-bound ferryl model B) are chosen. In total, six routes have been presented for two models. Our calculations show that both acetate and CH₃CN could provide reasonable pathways. The calculated energy barriers for these routes are between 19.0 and 23.7 kcal mol⁻¹ in solution, within the error limits of B3LYP. It is also found that the CH₃CN molecule acts only as a ligand throughout the reaction cycle. By contrast, the acetate ligand acts as a proton sink to assist the product formation. In addition, the less polarized solvent is more suitable for the alcohol oxidation catalyzed by non-heme model complexes.