Colossal Aromatic Molecules
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis describes the preparation of a series of compounds containing π-excessive, five-membered, heterocyclic rings with peripheral aryl substituents, designed to investigate their oxidative cyclodehydrogenation and/or photocyclisation to form curved, fused aromatic systems with a heterocyclic atom at the core of the compound. The ability of these compounds to undergo oxidative cyclodehydrogenation was investigated using a range of conditions, including the use of Lewis acidic transition metals, organic reagents and light as catalysts to carry out the desired carbon-carbon bond forming reactions. Two backbone linked 2,2’-biimidazole ligands were prepared to investigate their coordination chemistry with a range of different metal ions and counter ions.
Two families of model compounds, including ten previously unreported compounds, were prepared and subjected to various conditions for oxidative cyclodehydrogenation and photocyclisation resulting in the isolation of compounds with one carbon-carbon bond formed between the peripheral aryl rings in the same position on the heterocyclic ring, nineteen previously unreported compounds were isolated. Additionally, in one case oxidative cyclodehydrogenation resulted in the formation of two carbon-carbon bonds, producing a highly strained aromatic compound containing a heterocyclic ring. Photocyclisation of one family of compounds resulted in the formation of a different heterocyclic core dependent upon the substituent on the nitrogen atom. Five pentaarylpyrrole compounds, three of which were previously unreported, were also prepared after the exploration of various synthetic routes towards the pentaarylpyrrole motif. Photocyclisation also resulted in the formation of one carbon-carbon bond. The compounds resulting from oxidative cyclodehydrogenation and photocyclisation were characterised by NMR spectroscopy, UV/vis spectroscopy and fluorometry, where possible X-ray crystallography was also used.
The coordination chemistry of backbone linked 2,2’-biimidazole ligands to various metal ions could be controlled by the length of the backbone linker. The ethyl linked 2,2’-biimidazole ligand formed bridging and monodentate coordination compounds with various metal ions, the metallosupramolecular assemblies produced with silver ions could be controlled by the anion present. Discrete coordination complexes were usually formed, but in two cases metallopolymers were produced. The propyl linked 2,2’-biimidazole ligand formed exclusively discrete, chelating complexes with copper (II) metal ions. Eighteen coordination complexes were prepared during the course of this study characterized by X-ray crystallography, and NMR spectroscopy where appropriate.