Robust and electron deficient oxidovanadium(iv) porphyrin catalysts for selective epoxidation and oxidative bromination reactions in aqueous media

Abstract

meso-Tetrakis(3,5-dimethoxyphenyl)porphyrinatooxidovanadium (1) and β-octabromo-meso-tetrakis(2,6-dibromo-3,5-dimethoxyphenyl)porphyrinatooxidovanadium (2) were synthesized in excellent yields. The synthesized oxidovanadium(IV) porphyrin complexes were characterized by various spectroscopic methods such as UV-Vis, FT-IR, EPR and MALDI-TOF mass spectrometry, as well as by single crystal X-ray crystallography. The acetonitrile coordinated porphyrin 1 is relatively planar whereas 2 is highly nonplanar as shown by their crystal structures and also by electrochemical studies. Selective epoxidation studies of alkenes were successfully carried out in CH₃CN/H₂O as the solvent mixture at ambient temperature resulting in very high TOF numbers (12 227–14 347 h⁻¹ for 2) even with low catalyst loadings. Remarkably, 2 biomimics the vanadium bromoperoxidase (VBrPO) enzyme with extremely high TOF values (83 333–87 719 h⁻¹) for the oxidative bromination of thymol and some other phenols. Both the catalysts were successfully recovered at the end of the reactions, indicating their viability and industrial applicability.