Nitrogen and oxygen containing heteroaromatic systems: synthesis and characterization by 1d and 2d NMR techniques

Strong, Zack H (2022) Nitrogen and oxygen containing heteroaromatic systems: synthesis and characterization by 1d and 2d NMR techniques. Masters thesis, Northern Arizona University.

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Abstract

Polyaromatic systems containing fused benzene rings such as; fluoranthene, coronene and triphenylene and heteroaromatic systems such as; pyrylium, pyridine and pyridinium are important structures and motifs in materials, analytical, environmental, and synthetic chemistry. This research demonstrates how modular systems can be created to give a range of pyridine and pyridinium based systems as well as their potential use in material and synthetic applications. Previous work from Watson and co-workers found that if primary alkylamines were reacted with 2,4,6-triphenylpyrylium tetrafluoroborate an N-alkyl pyridinium salt would be created. In the presence of an aryl boronic acid and nickel catalyst the N-alkyl system would undergo radical fragmentation, resulting in the formation of a new C(sp2)-C(sp3), aryl-alkyl bond. This work expands on that idea by utilizing primary arylamines to synthesize a library of N-(aryl)-2,4,6-triphenylpyridinium tetrafluoroborate salts. Two different methods were developed for the synthesis of these salts. The first involving more electron-rich or electron neutral species in which both the pyrylium salt and arylamine starting materials are put into a round bottom flask with ethanol and refluxed and 7 hours. The second method was employed for more electron-deficient systems and included the addition of an acid (acetic acid) and base (triethylamine) to the previous methods. It was eventually discovered that the N-aryl salts of interest could not undergo radical fragmentation due to unfavorable thermodynamic conditions; however, a new N-aryl tetrahydroacridinium based system has recently been identified that shows the ability to fragment. This new system is currently being explored as a way to form aryl-aryl bond via nickel catalysis. Work by Surendranath and co-workers as well as the work of Gokhale et al. have shown that hetero-polyaromatic systems are capable of binding to different metal centers. These new scaffolds are known as graphene-conjugated catalysts and have been shown to be able to perform oxygen and carbon dioxide reduction reactions. This work sets out a synthesis a library of nitrogen-containing graphene scaffolds based on the benzene, fluoranthene and triphenylene structures. Two approaches were taken to incorporate the pyridine motifs needed for transition metal binding. The first was by a 1,2-bis(pyridine)ethyne synthesized over three steps involving two Sonogashira reactions and a deprotection. This method proved difficult as many issue were discovered to occur over the course of the multi-step synthesis of the 1,2-bis(pyridine)ethyne component. The second method proved much more viable as the pyridine motifs could be incorporated into the scaffold from the aldol condensation reaction resulting in a cyclopentadienone derivative. Continuing work will investigate the ability of different transition metals to bind to these scaffolds as well as examining their photochemical and electrochemical properties.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Chemistry; NMR; Organic; Pyridinium; Pyrylium; Synthesis
Subjects:	Q Science > QD Chemistry
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > Chemistry and Biochemistry
Date Deposited:	01 Jun 2023 16:24
Last Modified:	01 Jun 2023 16:24
URI:	https://openknowledge.nau.edu/id/eprint/5934

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