Reactivity patterns of vanadium(/)-oxo complexes with olefins in the presence of peroxides: a computational study

• Published in: Dalton transactions : an international journal of inorganic chemistry 2019-11, Vol.48 (45), p.16899-1691
• Main Authors: Mubarak, M. Qadri E, de Visser, Sam P
• Format: Article
• Language: English
• Subjects: Aliphatic compounds; Alkenes; Cartesian coordinates; Chemical industry; Crude oil; Cyclohexene; Density functional theory; Epoxidation; Hydrogen peroxide; Hydroxylation; Ligands; Oxidation; Oxidizing agents; Peroxides; Reactivity; Substrates; Vanadium
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt03048d

Vanadium porphyrin complexes are naturally occurring substances found in crude oil and have been shown to have medicinal properties as well. Little is known on their activities with substrates; therefore, we decided to perform a detailed density functional theory study on the properties and reactivities of vanadium( iv )- and vanadium( v )-oxo complexes with a TPPCl 8 or 2,3,7,8,12,13,17,18-octachloro- meso -tetraphenylporphyrinato ligand system. In particular, we investigated the reactivity of [V V (O)(TPPCl 8 )] + and [V IV (O)(TPPCl 8 )] with cyclohexene in the presence of H 2 O 2 or HCO 4 − . The work shows that vanadium( iv )-oxo and vanadium( v )-oxo are sluggish oxidants by themselves and react with olefins slowly. However, in the presence of hydrogen peroxide, these metal-oxo species can be transformed into a side-on vanadium-peroxo complex, which reacts with substrates more efficiently. Particularly with anionic axial ligands, the side-on vanadium-peroxo and vanadium-oxo complexes produced epoxides from cyclohexene via small barrier heights. In addition to olefin epoxidation, we investigated aliphatic hydroxylation mechanisms by the same oxidants and some oxidants show efficient and viable cyclohexene hydroxylation mechanisms. The work implies that vanadium-oxo and vanadium-peroxo complexes can react with double bonds through epoxidation, and under certain conditions also undergo hydroxylation, but the overall reactivity is highly dependent on the equatorial ligand, the local environment and the presence or absence of anionic axial ligands. Density functional theory calculations on vanadium-oxo and -peroxo porphyrins are reported and show these systems to be versatile oxidants.