Facile Synthesis of β-Tetracyano Vanadyl Porphyrin from Its Tetrabromo Analogue and Its Excellent Catalytic Activity for Bromination and Epoxidation Reactions.

Complex 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[V IV OTPP(CN) 4 ], 2 } has been prepared by nucleophilic substitution of β-bromo groups of the corresponding 2,3,12,13-tetrabromo-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 electron-withdrawing 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.