Mechanistic Insights and Catalytic Efficiency of a 2,2′‐Bipyridine–Coordinated Peroxidovanadium Complex as a Haloperoxidase Biomimetic

A peroxidovanadium(V) complex mimics vanadium haloperoxidases for eco-friendly halogenation of organic substrates. Density functional theory studies reveal two major reaction pathways for iodide/bromide oxidation. The catalyst offers high-yield bromination/iodination of 8-hydroxyquinoline (73/86%) under mild conditions (30 °C, pH 5.8), and it also oxidizes phenol red (990 ± 90 mol⁻² L² min⁻¹) efficiently to bromophenol blue.

The peroxidovanadium(V) complex [V^VO(O₂)(HO₂)(bpy)]·3H₂O·0.5bpy (1), where bpy = 2,2′-bypiridine, featuring η ²-coordinated peroxide and hydroperoxide ligands, is reported as an efficient functional model of vanadium haloperoxidases (VHPOs). Structural and spectroscopic analyses indicate similarities between 1 and VHPO active sites, including peroxide ligand protonation. Mechanistic studies employing ab initio computational methods are based on the presence of [V^VO(O₂)(HO₂)(bpy)] and its aqueous equilibrium species [V^VO(O₂)(HO₂)(H₂O)], in solutions of 1 (pH = 5.8). For each compound, two reaction pathways are explored for the oxidation of iodide and bromide: 1) direct HOX, where X = Br or I, formation through nucleophilic attack on the protonated η ²-peroxide, affording ΔG ^‡= 20.0–26.5 kcal mol⁻¹ and 2) V–OX intermediate formation after the nucleophilic attack on the η ²-peroxide resulting in ΔG ^‡= 15.6–17.6 kcal mol⁻¹. Catalyst regeneration via end-on H₂O₂ coordination is exergonic (ΔG = −15.2 and −21.6 kcal mol⁻¹), indicating sustainable turnover. Complex 1 catalyzes the oxidative bromination of phenol red with a rate constant of 990 ± 90 mol⁻²L²min⁻¹ and achieves high-yield halogenation of 8-hydroxyquinoline (73 and 86% for 5,7-dibromoquinolin-8-ol and 5,7-diiodoquinolin-8-ol) in mild conditions (30 °C, pH 5.8). The results highlight 1 as an efficient catalyst, with potential applications in the pharmaceutical and agrochemical industries.

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