SYNTHESIS, CHARACTERIZATION AND STUDIES OF COBALT CORROLES

Abstract

Corroles are synthetic and tetrapyrrolic systems that are frequently referred to as contracted porphyrins. In the past two decades, corroles have attracted a great deal of interest. These organic compounds have distinctive characteristics for undergoing metalation and, hence, co-ordinating to different metals. As a consequence, in the corrole cavity, several different metal ions across the periodic table covering the s, p, d, and f block elements have been introduced. Metallocorroles, because of their ease of synthesis as well as their fascinating spectral, electrochemical, and co-ordination properties, have gained significant attention since the very beginning. Their structure can be tuned by functionalization on β-pyrrole, meso- and axial positions, which affect their activity and, therefore, their characteristics towards different reaction processes, resulting in their suitability for a variety of applications. Cobalt corrole has been one of the earliest synthesized and extensively studied forms of metallocorrole. Apart from applications in the field of electrocatalysis such as HER, OER, ORR and CO2 reduction reactions, the complexes of this family also perform well as sensors. The present thesis also encircles one such series of A2B-cobalt corroles and has been divided into six chapters. Chapter 1 provides a comprehensive overview of the history and significance of corroles and metallocorroles. This overview assisted us in identifying the research gaps that required further investigation. In Chapter 3, the synthesis of a series of A2B type bispyridine-ligated cobalt corroles has been explained. Various techniques, such as 1H NMR and 19F NMR spectroscopy, mass spectrometry, and Single Crystal XRD, have been used for characterization of those complexes. The complexes are characterized via UV–Visible spectroscopy also when present in their 10−4 M DCM, xvii 10−6 M DCM and 10−5 M pyridine solutions. In Chapter 4, the potential of the synthesized cobalt corroles to sense anions has been investigated using colorimetric and spectroscopic approaches with 14 different tetrabutyl ammonium salts of F - , CN- , CH3COO- , NO3 - , AsO3 3- , AsO4 3- , Cl- , Br- , I- , ClO4 - , H2PO4 - , S2- , HS and PF6 - . The three complexes are exclusively found to be binding F - , CN and CH3COO anions at their axial positions. Also, the limits of detection for the different anions have been calculated. In Chapter 5, the electrochemical properties of cobalt corroles in CH3CN and DCM solvent using 0.1M TBAP as a supporting electrolyte are shown. The impact of substituting electron withdrawing or electron donating substituents on the overall oxidation/reduction potential is also examined by cyclic voltammetry. The catalytic efficiency of cobalt corroles has also been assessed.