The synthesis of highly nonplanar oxidovanadium(IV) porphyrins as robust catalysts for oxidative bromination of phenols in aqueous medium

Two new complexes, oxidovanadium(IV) 2,3,5,10,12,13,15,20-octaphenyl-7,8,17,18-tetrabromoporphyrin V(IV)O(OPP)Br 4 (2), and oxidovanadium(IV) 2,3,5,10,12,13,15,20-octaphenyl-7,8,17,18-tetrachloroporphyrin V(IV)O(OPP)Cl 4 (3) starting from oxidovanadium(IV) 2,3,5,10,12,13,15,20-octaphenylporphyrin V(IV)O(OPP) (1) have been prepared in good yields and characterized by various spectroscopic techniques. The single-crystal and DFT-optimized structures of these porphyrins showed a highly nonplanar saddle-shape conformation of the porphyrin macrocycle. In the cyclic voltammograms, the first ring oxidation potential and the first ring reduction potential of V(IV)O(OPP)Br 4 (2) and V(IV)O(OPP)Cl 4 (3) showed anodic shift as compared to V(IV)O(OPP) (1), indicating the electron-deficient nature of both the porphyrins. The oxidation state of vanadium in the synthesized complexes as +4 was confirmed by EPR spectroscopy, and these porphyrins exhibited axially compressed [Formula: see text] configuration. These porphyrins were utilized as catalysts for the oxidative bromination of thymol and other phenol derivatives with excellent conversion ([Formula: see text] 99.9%), good selectivity, and high TOF value (86869 h[Formula: see text].