Synthesis, Structural and Redox Properties of Vanadyl β‐Cyanoporphyrin and its Utilization as Efficient Catalyst for Epoxidation of Olefins and Oxidative Bromination of Phenols

Abstract

2‐Cyano‐5,10,15,20‐tetraphenylporphyrin [H2TPPCN] (1) having cyano group at one of β‐pyrrolic positions using nucleophilic substitution reaction of tetrabutylammonium cyanide (TBACN) on free‐base 2‐nitro‐5,10,15,20‐tetraphenylporphyrin, and its oxidovanadium(IV) complex [VIVOTPPCN] (2) were synthesized and characterised by various spectroscopic techniques. Single crystal X‐ray crystallography revealed quasi‐planar geometry for 1. Compounds 1 and 2 exhibited a red shift (λmax = 7–9 nm) in the Soret band relative to [MTPP] owing to the electron‐withdrawing effect of the cyano group at the β‐position. The first oxidation (∆E1/2 = 110–140 mV) and reduction potentials (∆E1/2 = 220–260 mV) of [MTPPCN] are anodically shifted relative to [MTPP]. 2 has been utilized as a catalyst for two reactions: epoxidation of olefins and bromination of phenols. The bromination of phenol using KBr/H2O2/HClO4 in water resulted in 100% conversion with a TOF value as high as 19.6 s–1 in 0.5 h. Using H2O2/NaHCO3 in a CH3CN/H2O solvent mixture at 60 °C, epoxidation was carried out, and the highest conversion rate with a turnover frequency of 1.9 s–1 was achieved in the case of cyclohexene. Catalyst 2 was recovered successfully at the end of the reaction up to 5 cycles and had good thermal stability, indicating its industrial viability and applicability.