New highly functionalised porphyrazines and their precursors : structure, synthesis and spectral data

M.Sc.Porphyrazines, having similar structures to porphyrins, exhibit interesting characteristics as well as applications. These mainly stem from the highly conjugated nature of these compounds, making them useful in fields ranging from functional dyes to molecular devices to biomedical applications. Of these a highlight must be the photodynamic treatment of cancer. The usefulness of porphyrazines in these fields is very closely linked to the structure of the macrocycles. Therefore it is necessary to find methods to customise these compounds in the hopes of improving the current applications as well as broaden the horizons. There exists a gap in porphyrazine synthesis in the sense that it has not been possible before to ensure the formation of cis-porphyrazines. Therefore, the main effort in this project was directed towards addressing this void. A focus of the research was to investigate introduction of a linker between two monomer dinitrile units, used during the macrocyclisation step, to force the cis geometry into the porphyrazine. Attention was also given to finding a way to functionalise the macrocycles in such a way that the functionality could be removed at a later stage to be able to differently functionalise the porphyrazines to yield other potentially interesting structures. By manipulating existing methods to prepare porphyrazines, we were able to synthesise, with a great deal of selectivity, a cis-porphyrazine from monomers that were generally viewed as trans-directors. This represented a breakthrough in porphyrazine research. It was also possible to prepare a macrocycle with removable functionality (ally! groups) on the peripheral oxygens, thereby opening up the way towards further functionalisation. Building on this success, in which two new porphyrazines (one of which was cis functionalised) had been synthesised, it was attempted to introduce the linker unit as previously described, such that cis geometry only was possible in the macrocycle. Various reaction conditions and reaction types, ranging from Mitsunobu reactions to imine formation and reduction, were utilised in various synthetic approaches to these moieties. This effort allowed the successful synthesis of a variety of linked dinitrile dimers, which were set up to undergo Linstead macrocyclisation. However due to time constraints, these compounds have not yet been subjected to macrocyclisation but represents a challenge for the future