Abstract
Cavitands (or container molecules) possess an enforced cavity suitable for binding small guests in solution and the solid state. The aryl units of arene-rich cavitands act as both structural elements and binding sites to generate molecular hosts with well-defined geometries that are complementary to electron-poor guests. For these reasons, resorcin[4]arene octols have been extensively investigated as a framework for the synthesis of deep and rigid cavitands. However, until now, these macrocycles have been primarily extended by O-alkylene and O-arylene bridges using methods first disclosed by Cram nearly 40 years ago. This thesis describes the synthesis, characterisation and supramolecular self-assembly of resorcin[4]arene derived container molecules in which the cavitand walls are extended by four non-ether arylene units.
Chapter 1 introduces host-guest chemistry, resorcin[4]arenes and cavitands, with a particular focus on the synthesis and application of aryl-rich container molecules.
Chapter 2 describes the use of C2v- and C4-symmetric resorcin[4]arene-derivatives as a scaffold for the synthesis of a new class of arylene-extended cavitand with an octaarylene core (Aryl-8). Several aryl-substituted macrocycles are prepared and investigated for intramolecular aromatic coupling with a range of reagents. Exemplifying the importance of precursor geometry and substitution, only one substrate undergoes the desired fourfold cyclisation over two steps. The Aryl-8 cavitand and intermediates are extensively characterised including NMR and UV-visible spectroscopies, and X-ray crystallography, the latter demonstrating the capacity for hosting of solvent guest molecules.
The self-assembly behaviour of the new Aryl-8 cavitands in solution are investigated in Chapter 3. 1H and DOSY NMR spectroscopic experiments show that an octol-functionalised cavitand forms a well-defined, stable dimeric capsule in solution that encapsulates complementary cationic guests with high affinity.
Chapter 4 explores the synthesis of cavitands extended by four more aryl units (Aryl-12). Octaaryl substituted resorcin[4]arene macrocycles are prepared via multiple strategies that require regioselective modification of the reduced-symmetry precursors. Although the target Aryl-12 was not obtained in this study, a number of related π-extended cavitands were prepared and characterised in solution and the solid state.
A new class of macrocyclic belt, [8]collarene, is synthesised in Chapter 5 utilising a reduced-symmetry resorcin[4]arene derivative prepared in earlier chapters. Preliminary investigations into host-guest applications of the macrocycle are presented