Facile synthesis of β-brominated manganese porphyrins via self-catalytic reaction and their catalytic potentials for the oxidative-bromination via haloperoxidases-like activity have been explored.

Abstract

A novel and sustainable approach has been developed for the synthesis of β-brominated Mn porphyrins, [Mn^III(Br)(TPPBr₄)] (2), [Mn^III(Br)(TPPBr₆)] (3) and [Mn^IV(Br)₂(TPPBr₈)] (4) by self catalytic haloperoxidase mimicking activity of [Mn^III(Br)(TPP)] [bromo(meso-tetraphenylporphyrinato)manganese(III)] (1) in aqueous medium under different mild and controlled reaction conditions. By precisely tweaking important parameters (e. g. H₂O_2, HClO₄ and KBr), these polybrominated porphyrin complexes have been synthesized. This method is safer and applicable under milder reaction conditions than the conventional procedures for β-bromination of porphyrins. These complexes were characterized by various spectroscopic techniques, including UV–Vis spectroscopy, elemental analysis, MALDI-TOF mass spectrometry, cyclic voltammetry, DFT calculations and single crystal X-ray diffraction analysis. Bromination of various phenol derivatives via haloperoxidase-catalyzed reaction using these manganese complexes has been explored. Carrying out the catalytic reaction at room temperature in the presence of H₂O₂ as an oxidant and KBr as a brominating agent in a mild aqueous acidic condition results in good to excellent yield of the brominated product(s). Extra stability of 4 compared to other catalysts due to trans-[Br−Mn^IV−Br] structure possibly prevents the interaction of Mn with oxidant which makes it less potential catalyst compared to 1, 2 and 3. Suitable catalytic reaction mechanism has been proposed for the bromination of substrates after identifying the reaction intermediates using mass spectrometry.