Publication Date

2024

Document Type

Dissertation

Committee Members

Kuppuswamy Arumugam, Ph.D. (Committee Chair); Steven R. Higgins, Ph.D. (Committee Member); Jitendra Kumar, Ph.D. (Committee Member); Amit Sharma, Ph.D. (Committee Member); Ioana E. Pavel, Ph.D. (Committee Member)

Degree Name

Doctor of Philosophy (PhD)

Abstract

N-heterocyclic carbenes (NHCs), a characteristic 5-membered ring structure, contain a carbene carbon and at least one nitrogen atom. The presence of nitrogen atoms in the cyclic structure has two effects on its electronic structure: it withdraws σ-electrons and donates π-electrons to the carbene carbon, significantly enhancing the electronic richness and stability of the carbene center. Incorporating heteroatoms like sulfur, oxygen, or phosphorus into the NHC framework has paved the way for advanced developments in their structural properties. The incorporation of additional aromatic ring/heteroatom into NHC offers novel pathways for functionalization, ultimately broadening its scope of potential applications. The primary goal of this research project is to investigate the synthesis of metal-free tetrathiafulvalene annulated benzimidazolium (TTF-BzIm) salts and their possible application in redox-flow batteries (RFB) to be more eco-friendly. Additionally, the project aims to explore the properties and applications of a novel trithiocarbonate (TTC) annulated benzimidazolium (BzIm) carbene and its metal complexation studies. The beginning stages of the project focus on finding an efficient synthesis route to prepare trithiocarbonate-annulated benzimidazole NHC precursors, and their structural confirmation will be carried out by various characterization techniques such as Nuclear Magnetic Resonance (NMR), High-resolution mass spectrometry (HR-Mass), Fourier-transform infrared spectroscopy (FT-IR). Further, this new class of NHC precursors is complexed with transition metals to study their electrochemical behavior using Cyclic voltammetry (CV) and donor property in the presence of trithiocarbonate NHC backbone. NHCs are valued in material fabrication due to their stable metal-carbene bonds and ability to facilitate electron transfer. These beneficial properties stem from their ease of synthesis, the availability of synthetically modified ligands for various catalytic reactions, and their widespread use in organometallic chemistry, owing to their strong σ-donating property. The versatility of N-heterocyclic carbenes (NHCs) as ligands is well-established, with their metal complexes frequently employed as effective homogeneous catalysts for diverse organic transformations. Modifying NHCs can precisely manipulate the corresponding metal complexes' reactivity, selectivity, and stability. These developments have proven to be highly beneficial in enhancing the performance of redox-active systems and other advanced applications. The presence of sulfur functionality in trithiocarbonate moiety, with its unique electronic and structural properties, could serve as a precursor in synthesizing TTF complexes with NHC characteristics. Redox flow batteries (RFBs) can be employed as electrochemical storage of intermittent renewable energy for large-scale. Recent developments in the energy sector have shown promising results using various organic-based active materials. Even though there has been remarkable progress, the practical use of RFBs is significantly hindered by their limited energy density, primarily caused by the restricted solubility of the redox species. In order to develop non-aqueous redox flow batteries, it is crucial to focus on exploiting high-performance redox-active substances. Tetrathiafulvalene (TTF) is a stable sulfur-containing heterocyclic organic compound capable of undergoing multiple one-electron reversible redox transformations. TTF annulated N-Heterocyclic compound possesses two important properties: they act as redox-active mediators and enhance the solubility profile of the overall TTF complex. A promising approach to enhance the performance of non-aqueous redox flow batteries involves simultaneously increasing the redox potential and solubility of redox-active materials. This novel TTF compound can be tested for enhancing the solubility profile and redox-active behavior in redox flow batteries. These characteristics will help improve the battery's efficiency by playing a vital role in overcoming limitations such as reaction kinetics and energy density, which eventually help to achieve better efficiencies in RFBs. Overall, Chapter one will be focused on synthesizing the trithiocarbonate-annulated benzimidazole NHC precursors and studying their structural characteristics. Chapter two will be designing this new class of NHC-metal complexes; TTC-NHCs are complexed with transition metals to study their electrochemical behavior using Cyclic voltammetry (CV) and donor property in the presence of trithiocarbonate NHC backbone. Further, chapter three will be focused on utilizing the TTC-NHC precursors to proceed with the coupling reaction to synthesize Tetrathiafulvalene annulated benzimidazole compounds for the redox flow battery applications.

Page Count

236

Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded

2024

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