Selective Bromination of <i>β</i>‐Positions of Porphyrin by Self‐Catalytic Behaviour of VOTPP: Facile Synthesis, Electrochemical Redox Properties and Catalytic Application
Mannar R. Maurya, Ved Prakash, Fernando Avecilla, Muniappan Sankar
Abstract
Abstract Oxidovanadium(IV) complex of β ‐octabromo‐ meso ‐tetraphenylporphyrin, {[V IV O(TPPBr 8 )], 2 } was synthesized by self‐catalytic oxidative bromination of meso ‐tetraphenylporphyrinatooxidovanadium(IV) {[V IV O(TPP), 1 } in excellent yield under mild conditions at 25 °C and its structure was confirmed by single crystal X‐ray study. UV‐Vis and 1 H NMR spectra further confirmed that the meso ‐phenyl rings are not brominated and thus emphasizes on the selectivity as well as synthetic importance of this catalytic method. In the presence of substrates e. g. phenol derivatives, 1 biomimics the vanadium bromoperoxidase (VBPO) enzyme and catalyses the oxidative bromination of substrates in water at 25 °C. Remarkably, 2 also catalyses the oxidative bromination of phenol derivatives under similar reaction conditions with very high turnover frequency (TOF) values (ca. 29 s −1 ) along with its recyclability. It was found that 2 showed superior catalytic performance as compared to 1 because of its electron deficient nature due to electron withdrawing bromo substituents and robust saddle shaped nonplanar structure (further supported by DFT studies).