Topologically Complex Molecules: Synthesis and Properties

Abstract

The first chapter outlines some of the latest advancements in the field of dynamic combinatorial chemistry (DCC) and highlights different interlocked molecules synthesised using this approach.
The second chapter describes the design and synthesis of a new p-donor building block for DCC (BDT – benzo[1,2-b:4,5-b’]dithiophene derivative) and its behaviour in the presence of an acceptor molecule (NDI – naphthalenediimide) in aqueous system. The most peculiar feature of this building block is the difference in its reactivity towards the enantiomers of NDI. This means different dynamic combinatorial library (DCL) distributions are obtained depending on the NDI enantiomer used. In each case, a different type of [2]catenane is formed, giving rise to the first ever structural divergent synthesis using DCC. This is studied and discussed in detail as well as the outcome of the 1:1 enantiomeric mixture NDI mixture in the presence of BDT. This is compared with the libraries containing the 1:1 enantiomeric mixture of BDT and either enantiomer of NDI. Lastly, a racemic mixture of the another p-donor building block (DN – dialkoxynaphthalene – also extensively studied in Sanders’ / Pantoș’ groups) in the presence of NDI is discussed.
The third chapter reports the discovery of an aromatic all-donor [2]catenane, and the synthesis of the structural isomer of BDT (iso-BDT – benzo[1,2-b:5,4-b’]dithiophene). BDT on its own in the presence of salt (which increases the hydrophobic effect) leads to the first ever aromatic all-donor catenane formed through DCC. Its isomer, iso-BDT, does not form any catenane either on its own, or in mixed libraries with NDI (only macrocycles are obtained).
The fourth chapter introduces the design of a new homochiral acceptor-donor-acceptor trimer. The library of this trimer on its own in the presence of salt contains just one major species. The analysis of this shows a very complex 1H NMR spectrum; NMR, MS and computational studies suggest that this is a Figure-of- Eight knot. When the library concentration is decreased ten times, a [2]catenane is formed instead of the knot. Very interesting is the chirality mismatch: the homochiral trimer forms a knot, while the heterochiral one leads to a [2]catenane.
In the next chapter (Chapter 5), the design and behaviour in DCLs of another p-donor molecule (BDF – benzo[1,2-b:4,5-b’]difuran derivative) is reported. In
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comparison to BDT, this one does not form an all-donor catenane, but the structural divergence is present again and it is more clean than for BDT.
Chapter 6 gives a brief conclusion of all work reported in this thesis and suggests directions for future work.
Chapter 7 is the Experimental Section, including all synthetic routes used in this work, characterisation of all reported molecules, all analytical methods and details about computational studies.

Date of Award	13 May 2020
Original language	English
Awarding Institution	University of Bath
Sponsors	ESF and EPSRC
Supervisor	Tony James (Supervisor) & Dan Pantos (Supervisor)