SYNTHESIS, SPECTRAL AND ELECTROCHEMICAL REDOX PROPERTIES OF MESO/β-FUNCTIONALIZED CORROLES FOR SENSING, NLO AND CATALYTIC APPLICATIONS

Abstract

π-Extended corroles exhibit interesting physiochemical and electrochemical properties. Limited reports on regioselective bromination of corrole is very difficult due to the electronic richness of macrocyclic ring. Ag(III) corroles give the regioselective bromination at 3,17- positions in the presence of NBS which is further utilized for functionalization with Ph, Me, PE and MA groups. Furthermore, [2+2] cycloaddition–retroelectrocyclization (CA–RE) click reaction between β-diphenylethynyl-substituted Ag(III)/Cu(III) corroles and TCNE/TCNQ has been explored to create nonplanar D–A “pull–push” chromophores. There is no reports of CA-RE click reaction on corroles in the literature. β-Formylcorroles could be versatile starting material for synthesis of various new class of compounds on reaction Wittig reagents, amines, active methylene compounds like malononitrile (MN), cyanoacetic acid and other nitrogen based derivatives. Limited reports are available on β-formylcorroles. 3-Formyl-meso-triphenylcorrole has been utilized for synthesis of 3-dicyanovinyl-meso-triphenylcorrole possessing interesting and distinct spectral and electrochemical properties. The Knoevenagel condensation reaction on formyl and acroleyl groups with MN, we have used to generate “push–pull” type of Co(III) corroles. The formation of dicyanovinyl/dicyanobutadienyl-substituted with distinct spectral features were obtained. Regioselective bromination of β-formylcorroles is very difficult and not explored in corrole chemistry. Herein, we have heptabrominated 3-formyltriphenylcorrole copper using liquid bromine. Molybdenum based complexes are efficient catalyst in epoxidation of olefins, bromination of phenols, Hantzsch reaction and variety of other organic conversions. We have utilized oxido-Mo(V) based corroles for the selective epoxidation of olefins and oxidative bromination of phenol derivatives. Thesis contains eight chapters provided below: Chapter 1 deals with the chemical literature on porphyrin and its analogues mainly corroles. This chapter also included recent synthetic developments in corrole chemistry and the utilization of corroles in different arena such as sensitizers in solar cells and photodynamic therapy, as anion sensors, as catalysts for various organic transformations and in nonlinear optics. Chapter 2 involves the facial synthesis, photophysical and electrochemical redox properties of symmerically β-disubstituted Ag(III) corroles (R2[TTC]Ag) from Br2[TTC]Ag (1) to elucidate the effect of the various β-substitution like Me, Ph, MA and PE on the macrocyclic ring via Pd-catalyzed reaction. Optical absorption spectra exhibit broadening of the Soret band and redshifts in both Soret and Q bands in MA2[TTC]Ag (4) and MA2[TTC]Ag (5) due to delocalization of π electrons via the double or triple bond and ICT. In cyclic voltammetric studies, the HOMO and LUMO energy gap decrease in the range of 0.2–0.8 V compared to unsubstituted [TTC]Ag.Chapter 3 includes the synthesis of β-dicyanovinyl (DCV) appended corroles represented as MTPC(MN) (where M = 3H, CuIII, AgIII and CoIII(PPh3) and MN = malononitrile) from their respective free-base mono β-formyl corroles, H3TPC(CHO), whose metal complexes where also investigated. It is significant to note the quite large substituent effect of the formyl or DCV groups on the electrooxidations and reductions of the investigated triphenylcorrole. The DCV- appended corroles are substantially easy to reduce and difficult to oxidize than formyl or unsubstituted corroles. CuTPC(MN) (2a) and AgTPC(MN) (2b) act as chemodosimeters for cyanide ions detection via nucleophilic attack at the vinylic carbon of the DCV substituent while CoTPC(MN)PPh3 (2c) acts as chemosensor for cyanide ions via axial coordination to the metal center. Cyanide adducts were monitored by UV–Vis and 1H NMR spectroscopic techniques and mass spectrometry exhibited 1:1 stoichiometry.Chapter 4 describes the synthesis of mixed β-octasubstituted CuTPC(CHO)R7 (where R = H, Br, Ph, Me or Th) corroles with their photophysical, electrochemical and nonlinear studies. The bromination and Suzuki-coupling reactions had a subsequent effect on absorption properties and redox potentials. CuTPC(CHO)Br7 (Cu-2) exhibited the first reversible reduction at 130 mV, the highest anodic shift of any other meso-triphenylcorrole. DFT studies revealed that all the octasubstituted copper corroles exhibited highly nonplanar saddled shape conformation of the corrole ring indicates the noninnocence and Cu(II)-Corrole•2– character of the complexes. First-time copper corroles have been investigated for NLO studies. CuTPC(CHO) (Cu-1) exhibits a maximum σ2PA value (69800 GM) compared to remaining corrole complexes. These copper corroles exhibited strong 2PA coefficients (β) and high χ(3) values, proving to be excellent NLO materials in photonic devices.Chapter 5 deals with the synthesis, spectral and electrochemical studies of π-extended ‘push–pull’ CoIII corroles with one and two dicyanovinyl (DCV) or dicyanobutadienyl (DCBD) entities. Regioselective 3,17-diformylation of CoIII corrole was done in very good yield via Vilsmeier formylation. The introduction of DCV/DCBD entities leads to perturbation in the absorption and redox properties. (MN)2-Co and A2MN2-Co exhibited eight to nine times enhancement in the molar absorptivity in the Q band compared to [TTC]CoPPh3. The 220 mV positive shift per DCV group and 160 mV positive shift per DCBD group was revealed in the first oxidation potentials compared to [TTC]CoPPh3 in the desired direction for the utility of these CoIII complexes in electrocatalysts.Chapter 6 deals with the synthesis of symmetrically donor-acceptor corrole conjugates of copper and silver tritolylcorrole (TTC) as donor and tetracyanobutadienyl (TCBD) as acceptor via [2+2] cycloaddition–retroeletrocyclization (CA–RE) reaction using strong electron acceptor tetracyanoethylene (TCNE) in excellent yield. The addition of TCBD moieties leads to a considerable hypsochromic shift in the Soret band and the formation of a broad band in the NIR region (700–900 nm). (TCBD)2[TTC]Ag (Ag-2) exhibited four reversible one-electron reductions to give [(TCBD)2[TTC]Ag]4− while (TCBD)2[TTC]Cu (Cu-2) exhibited five reversible one-electron reductions to give [(TCBD)2[TTC]Cu]5−. DFT studies revealed strong ICT from corrole ring to electron-deficient TCBD groups. The main feature of this work is the synthesis of D–A corrole conjugate via [2+2] CA–RE reaction with TCNE, resulting in tuning the optical absorption and electrochemical redox properties. We have also demonstrated the first evidence of electro-generated tetraanionic silver and pentaanionic copper corrole in the CV timescale.Chapter 7 includes the synthesis of two new meso-substituted oxido-molybdenum corroles were synthesized and characterized by various spectroscopic techniques. In the thermogram, MoO[TTC] (1) exhibited very high thermal stability upto 491 °C, while MoO[TNPC] (2) exhibited good stability upto 318 °C. The oxidation states of the molybdenum(V) were confirmed by EPR spectroscopy and exhibited an axially compression with dxy1 configuration. Oxido-molybdenum(V) complexes were utilized for the selective epoxidation of different olefins with good TOF values (2066–3287 h−1) in good yields in a CH3CN/H2O mixture in the presence of hydrogen peroxide as an oxidant and NaHCO3 as a promoter. The oxidative bromination catalytic activity of oxido-molybdenum(V) complexes have been reported for the first time. Surprisingly, 2 biomimics the vanadium bromoperoxidase (VBPO) enzyme with extremely high TOF values (42536–61446 h−1) for the oxidative bromination of industrially important thymol and other phenolic derivatives. Catalyst 2 exhibited higher TOF values and better catalytic activity than catalyst 1.Chapter 8 summarizes the current work with future perspectives.