Oxidovanadium(IV) complex of β‐octabromo‐meso‐tetraphenylporphyrin, {[VIVO(TPPBr8)], 2} was synthesized by self‐catalytic oxidative bromination of meso‐tetraphenylporphyrinatooxidovanadium(IV) {[VIVO(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 1H 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).
0tetraphenylporphyrinatooxidovanadium(IV) {[V IV OTPP(CN) 4 ], 2} has been prepared by nucleophilic substitution of β-bromo groups of the corresponding 2,3,12,13tetrabromo-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[V IV OTPP(Br) 4 ], 1} using CuCN in quinoline. Both complexes show biomimetic catalytic activity similar to enzyme haloperoxidases and efficiently brominate various phenol derivatives in the presence of KBr, H 2 O 2 , and HClO 4 in the aqueous medium. Between these two complexes, 2 exhibits excellent catalytic activity with high turnover frequency (35.5− 43.3 s −1 ) due to the strong electron-withdrawing nature of the cyano groups attached at β-positions and its moderate nonplanar structure as compared to 1 (TOF = 22.1−27.4 s −1 ). Notably, this is the highest turnover frequency value observed for any porphyrin system. The selective epoxidation of various terminal alkenes using complex 2 has also been carried out, and the results are good, specifying the importance of electronwithdrawing cyano groups. Catalysts 1 and 2 are recyclable, and the catalytic activity proceeds through the corresponding [V V O(OH)TPP(Br) 4 ] and [V V O(OH)TPP(CN) 4 ] intermediates, respectively.
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