Design and synthesis of new organomain group radicals
Date
2018-11-01
Authors
Patenaude, Greg William
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Abstract
The goals of this thesis were to design and synthesize new stable radicals and to study their properties. The attempted synthesis of new stable thioaminyl, verdazyl, and dioxadiazinyl radicals is described. Successfully prepared radicals were characterized by spectroscopic methods.
The synthesis of new thioaminyl radicals and diradicals was attempted. Preparation of thioaminyl precursors, the sulfenamides, was accomplished with sulfenyl chlorides and amines. Oxidation with DDQ yielded radicals which decomposed back to the sulfenamides within 1–2 minutes. A bis(sulfenamide) was synthesized using a sulfenyl chloride and an appropriate bis(amine). The structure of the bis(sulfenamide) was confirmed by NMR spectroscopy and x-ray crystallography. Oxidation of the bis(sulfenamide) to the thioaminyl diradical was unsuccessful.
New phosphaverdazyl radicals were prepared and studied using EPR spectroscopy. The phosphaverdazyl precursors, the tetrazines, were prepared from the corresponding bis(hydrazides). The tetrazines were oxidized with benzoquinone to yield phosphaverdazyls. The phosphaverdazyls prepared do not share the same level of stability as the parent carbon-based verdazyls; they slowly decompose back to tetrazines. Incorporation of phosphorus into the verdazyl core has several effects on the properties of the radical relative to the parent verdazyl system. Through a combination of EPR and computational studies, it was concluded that the geometry of the verdazyl ring and the electronic nature at phosphorus appear to be sensitive to the nature of the substituents attached to phosphorus. Exocyclic “spin-leakage” was observed for one phosphaverdazyl, which can be rationalized using a spiroconjugative mechanism. The phenomena of spiroconjugation was further explored through the synthesis of a phosphaverdazyl derivative attached to phosphazene in a spirocyclic manner.
Synthetic routes to the hitherto unknown dioxadiazinyl system were explored. An intermediate hydroxyamidoxime was synthesized and fully characterized. Cyclization reactions of the hydroxyamidoxime to putative dioxadiazines were carried out using aldehydes and a ketone. The cyclization products could not be unambiguously assigned. The cyclization products can be rationalized as the desired dioxadiazine or the 5-membered oxadiazolidine. One derivative was oxidized to a persistent radical, the EPR of which is consistent with a nitroxide structure.
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Keywords
Radicals (Chemistry), Verdazyl, Thioaminyl, Pure sciences