β-CYANOPORPHYRINS: SYNTHESIS, SPECTRAL, ELECTROCHEMICAL REDOX PROPERTIES AND ITS CATALYTIC APPLICATIONS

Abstract

2-Cyano-5,10,15,20-tetraphenylporphyrin (H2TPPCN) has been synthesized from nucleophilic substitution of 2-nitro-5,10,15,20-tetraphenylporphyrin using TBACN as the cyanide source in good yield. H2TPPCN is characterized by various spectroscopic techniques and electrochemical methods. Further, H2TPPCN is metalated with VOSO45H2O in order to get the corresponding vanadyl porphyrin complex, [VOTPPCN], and characterized using UV-Vis, IR, NMR and EPR spectroscopic techniques and cyclic voltammetry studies. Due to steric hinderance between β-cyano and the meso-phenyl groups in [VOTPPCN], the DFT studies showed slightly nonplanar saddle shape conformation for both H2TPPCN and [VOTPPCN]. H2TPPCN and [VOTPPCN] exhibited a dipole moment of 2.11 D and 2.16 D, greater than H2TPP (0.052 D) due to due to electron withdrawing effect of –CN at β-position. [VOTPPCN] had two reversible oxidation potentials at 1.25 and 1.54 V and two reduction potentials at -0.93 and -1.31 V due to macrocyclic ring. H2TPPCN had two reversible oxidation potentials at 1.14 and 1.40 V and two reduction potentials at -1.00 and -1.30 V. Catalytic investigations employing [VOTPPCN] as the catalyst were carried out under optimal conditions for two reactions: bromination of phenols and epoxidation of olefins. In the case of oxidative bromination, the reaction was carried out in water under mild conditions in the presence of KBr/H2O2/HClO4 as the brominating agent. Bromination of phenol resulted in a 100 percent conversion in 30 minutes, with a TOF value as high as 70469 h-1. Epoxidation was carried out in the presence of H2O2/NaHCO3 in a CH3CN/H2O solvent mixture at 60 °C, with cyclohexene achieving the maximum conversion with a turnover frequency of 7047 h-1.