Highly Efficient β‐Functionalized Oxidomolybdenum(V) Corroles for Catalytic Oxidative Bromination of Phenols at Room Temperature

Abstract

Two new β‐functionalized oxidomolybdenum(V) corroles, oxido[3‐formyl‐5,10,15‐triphenylcorrolato]molybdenum(V) (Mo‐1) and oxido[3‐dicyanovinyl‐5,10,15‐triphenylcorrolato]molybdenum(V) (Mo‐2) were synthesized and characterized by various spectroscopic techniques and electrochemical studies. Mo‐2 manifests splitted B bands due to x and y polarizations and highly red shifted longest B and Q bands due to the electron‐deficient nature of the dicyanovinyl group. EPR data showed that these complexes exhibit an axial compression with dxy1 configuration. DFT studies revealed that HOMO and LUMO orbitals are stabilized in Mo‐2 relative to Mo‐1. Mo‐1 exhibits two successive reversible reductions and two oxidation potentials in cyclic voltammetry. Surprisingly, Mo‐2 exhibits three successive reversible reductions and two oxidations; the one extra reduction could possibly be due to the reduction of the dicyanovinyl moiety. The catalytic activities of Mo‐1 and Mo‐2 for the oxidative bromination of various phenols using H2O2– KBr– HClO4 mixture in water have been explored and exhibited excellent activity at a very low catalyst loading of 0.0030 and 0.0028 mol%, respectively. Both synthesized β‐functionalized Mo(V) corroles manifest much higher conversion and TOF (59801–71174 h–1) for oxidative bromination of phenols relative to earlier reported meso‐functionalized Mo(V) corroles (20781–61646 h–1). Hence, Mo‐1 and Mo‐2 mimic vanadium bromoperoxidase (VBPO) and act as functional models for these catalytic applications.

Facile Synthesis of β‐Brominated Manganese Porphyrins and their Catalytic Potentials for Haloperoxidases‐Like Activity

“…Recently, [V IV O(TPP)] (TPP=free base meso‐tetraphenylporphyrinato anion) and other related complexes have been used as functional models of haloperoxidases where these complexes not only catalyzed the bromination of a whole range of organic substrates, they also acted as self‐catalyst and brominated β ‐positions of the pyrrole ring of complex as well in excellent yield [39,40] . Some molybdenum corroles were also reported as catalyst for the oxidative brominations of phenols [41,42] . Such haloperoxidase mimicking activity by Mn‐porphyrin complexes has rarely been explored ( vide infra ).…”

Panchromatic and Perturbed Absorption Spectral Features and Multiredox Properties of Dicyanovinyl- and Dicyanobutadienyl-Appended Cobalt Corroles

“…Corroles are less explored in the areas of photonics and photocatalysis and have shown promising properties. − Kar and co-workers developed NIR-emissive β-tetrathiocyano functionalized corrole-based dyes via a photocatalytic pathway in good yields. − Our strategy is to synthesize a novel β-functionalized corrole with strong π-acceptor groups such as dicyanovinyl (DCV) and dicyanobutadienyl (DCBD), resulting in perturbation of the Soret and Q bands in the absorption spectrum. The recent literature on corroles revealed that π-extended corroles exhibit tunable photophysical and electrochemical redox properties. − For example, copper corroles demonstrate hypercorrole spectra, and the Soret band contains more than one electronic transition with significant phenyl-Cu­(d x 2 –y 2 ) charge-transfer characteristics. , Gros et al have shown ligand-to-ligand charge transfer interactions in biscyano cobalt corroles to meso -NO 2 Ph groups . Kadish and co-workers described the ground state of (DPP •2– )­Co II as noninnocent and analogues to CorCo­(PPh 3 ) and some other metallocorroles of Pt, FeNO, FeCl, MnCl, Cu, and Fe 2 (μ-O) …”