Selective bromination of β-positions of porphyrin by self-catalytic behaviour of VOTPP: Facile synthesis, electrochemical redox properties and catalytic application

Abstract:
Oxidative bromination of thymol and other phenolic derivatives has industrial importance. Iron and manganese porphyrins have been widely utilized as effective homogeneous catalysts for such oxygenation reactions in the last few decades. The major drawbacks of homogeneous MTPP-based catalysts are the macrocyclic ring which is liable to oxidative self-destruction, aggregation of metalloporphyrins through π–π interactions, lower turnover frequency (TOF) and poor product selectivity. Notably, vanadyl porphyrins have gained significant interest as useful molecules with applications in the fields of therapeutics, catalysis and 3D supramolecular assemblies. Herein, we synthesized vanadyl complex of β-octabromo-meso-tetraphenylporphyrin (VOTPPBr₈) by self-catalytic reaction of VOTPP in excellent yield at room temperature under mild bromination conditions using KBr/H₂O₂ in presence of HClO₄. Further, VOTPPBr₈ was utilized as an efficient catalyst for the oxidative bromination of various phenols. In this presentation, we will present facile synthesis, spectral and electrochemical properties and catalytic efficiencies of VOTPP and VOTPPBr₈ in detail.