Second-Coordination Sphere Effect on the Reactivity of Vanadium-Peroxo Complexes: A Computational Study.

Area of Science:

• Bioinorganic Chemistry
• Computational Chemistry
• Catalysis

Background:

• Vanadium-oxo and vanadium-peroxo complexes are key biological intermediates, notably in vanadium haloperoxidases.
• Biomimetic chemistry utilizes synthetic models to replicate the coordination environment of these vanadium species.
• Novel bowl- and dome-shaped vanadium-oxo complexes with trigonal bipyramidal ligand designs have been recently synthesized.

Purpose of the Study:

• To investigate the reaction mechanisms of novel bowl- and dome-shaped vanadium-oxo complexes with tert-butylhydroperoxide and thioanisole using Density Functional Theory (DFT) calculations.
• To understand the influence of the second-coordination sphere and ligand architecture on the reactivity of vanadium-oxo and vanadium-peroxo species.
• To compare the oxidative efficiency of vanadium-peroxo species with analogous iron(IV)-oxo oxidants.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model the reaction pathways.
• Analysis of reaction barrier heights for the formation of vanadium-peroxo species and their subsequent reactions with thioanisole.
• Investigation of structural differences between bowl-shaped (solvent-exposed vanadium) and dome-shaped (caged vanadium) complexes.
• Utilized thermochemical cycles and valence bond patterns to analyze reactivity differences.

Main Results:

• DFT calculations revealed that ligand architecture, specifically the second-coordination sphere, strongly influences reaction barrier heights despite minimal structural differences in transition states.
• Both bowl- and dome-shaped vanadium-peroxo species were found to be efficient oxidants for sulfoxidation reactions.
• Vanadium-peroxo species exhibited higher reaction barriers compared to analogous iron(IV)-oxo heme and nonheme oxidants.

Conclusions:

• The ligand's second-coordination sphere plays a crucial role in modulating the reactivity of vanadium-oxo and vanadium-peroxo complexes.
• Vanadium-peroxo complexes are effective sulfoxidation agents, though less reactive than comparable iron complexes.
• Computational analysis provides insights into how ligand design can be tuned to control chemical reactivity in vanadium-based catalysis.