Rocher, Mathias
(2010).
Towards interlocked structures based on H-bonded barbiturate complexes.
University of Birmingham.
Ph.D.
Abstract
Despite the privileged position of Hamilton’s barbiturate binding system in supramolecular chemistry, this motif has never been used in generating interlocked structures, such as rotaxanes or catenanes. This thesis demonstrates the feasibility of such structures. A series of Hamilton-like receptors has been synthesised. Their conversion from “open” to “closed” forms by metathesis and their binding with barbital was studied, demonstrating the importance of the macrocycle size. Barbiturates disubstituted with flexible chains terminated either by reacting groups (anthracenes, olefins) or stoppers (trityl) were also synthesised. The fluorescence properties of anthracene-tagged barbiturates and their kinetics of intramolecular anthracene photodimerisation and thermal return were studied, demonstrating remarkable differences depending on the chain length. Binding studies of these barbiturates with the receptors were then undertaken, revealing smaller binding constants compared with barbital. A series of ring-closing experiments involving the barbiturate complexes was then undertaken, either by anthracene photodimerisation or olefin metathesis. In one metathesis experiment, indirect evidence for the formation of a low amount of catenane was obtained by mass spectrometry, where the smallest ring is formed by a chain of only 19 carbon atoms, which is unprecedented. Finally, different synthetic pathways for the synthesis of barbiturates substituted with large rigid substituents were investigated. Models of their complexes with the receptors and IR studies are presented that suggest that their structure would facilitate the formation of interlocked complexes.
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