Design, synthesis, and evaluation of new organometallic and polymeric materials for electrochemical applications
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ChemistryThe efforts described in this thesis were bifurcated along two distinct projects, but generally were directed toward the development of new materials to solve outstanding issues in contemporary electrochemical applications. The first project involved the synthesis and application of redox-switchable olefin metathesis catalysts. N-heterocyclic carbenes (NHCs) bearing ferrocene and other redox-active groups were designed, synthesized, and incorporated into model iridium complexes to evaluate their intrinsic electrochemical and steric parameters. Using these complexes, the ability to switch the electron donating ability of the ligands via redox processes was quantified using a variety of electrochemical and spectroscopic techniques. The donicity was either enhanced or attenutated upon reduction or oxidation of the redox-active group, respectively. The magnitude of the change in donicity upon reduction or oxidation did not vary significantly as a function of the proximity of the redox-active group from the metal center. Thus, other factors, including synthetic considerations, sterics, and redox potential requirements, were determined to guide ligand design. Regardless, redox-active NHCs were adapted into ruthenium-based olefin metathesis catalysts and used to gain control control over various ring-opening metathesis polymerizations and ring-closing metathesis reactions. The second project was focused on the development of new basic polymers for acid/base crosslinked proton exchange membranes intended for applications in direct methanol fuel cells. Polymers containing pendant pyridinyl and pyrimidinyl groups were obtained via the post polymerization functionalization of UDEL® poly(sulfone) and then blended with sulfonated poly(ether ether ketone) (SPEEK). Fuel cells containing these blends were found to exhibit reduced methanol crossover, higher open circuit voltages, and higher maximum power densities compared to plain SPEEK. The differences in fuel cell performance were attributed to the basicity and sterics of the pendant N-heterocycles.