Phthalocyanine hybrids; old chemistry revisited and new syntheses

Abstract

The work described in this thesis is concerned with the investigation of synthetic pathways toward tetrabenzoporphyrin/phthalocyanine hybrid macrocycles, specifically tetrabenzomonoazaporphyrins (TBMAPs) or other less-nitrogenous hybrids. The initial investigation was conceived to modify the latest synthetic procedure developed in the Cammidge group whereby utilisation of a less nitrogenous precursor (alkynylbenzonitrile, 1 x N) replaced phthalonitrile (2 x N) as co-macrocyclisation partner with an aminoisoindoline. Unfortunately, no hybrids were formed and instead the formation of a six- membered ring isoquinoline from the acetylene was observed under these conditions. Linstead’s method to synthesise TBMAPs was then revisited, and different malonyl aminoisoindolines were synthesised and isolated. These precursors proved to be unstable under many conditions which resulted in the formation of their keto-esters and dimers during their purification process. Fusion of these precursors with zinc dust at 220oC proved to give a mixture of hybrids but no evidence for the expected TBMAPs’ formation, according to MALDI-MS analysis. Isolation of the hybrids was challenging and complicated by slow decomposition during chromatography. We switched to investigate Linstead’s conditions of fusion in the presence of zinc metal at high temperature on our proposed reactants (alkynylbenzonitrile with aminoisoindoline) and, interestingly, formation of ZnTBTAP, cisTBDAP, transTBDAP and traces of ZnTBMAP were observed. However, the formation of these hybrids proved to be a result of macrocyclisation of one reactant only – the aminoisoindoline. Full analysis of all hybrids was obtained, except ZnTBMAP due to its low quantity. In the final part of the thesis, we further explored the latest Cammidge procedure to synthesise TBTAPs by employing substituted phthalonitriles (“B”) with aminoisoindolines (“A”), in this case using different metals to track the origin of each unit in the final TBTAPs. ABBB TBTAPs were selectively obtained in high yield when zinc chloride was utilised while a mixture of ABBB and ABBA TBTAPs were obtained when different metals were employed. Full characterisation of the obtained hybrids and intermediates was achieved. The formation of these hybrids is somewhat surprising and no obvious mechanisms for their formation are apparent.