The synthesis and characterization of metal-free, unsymmetrical azaphthalocyanines with hydroxy groups and their complex formation with pyridine

Three, unsymmetrical metal-free azaphthalocyanines (AzaPc) were prepared using the statistical condensation of 5,6-bis(diethylamino)-pyrazine-2,3-dicarbonitrile (A) and the pyrazinedicarbonitrile (B) substituted with alkylamine chains bearing one or two hydroxy groups. The desired AAAB type, metal-free compounds were isolated, purified and characterized; the compounds contain one or two hydroxy groups that can be modified with suitable ligands. The mechanism leading to the unusual formation of a new morpholine ring during the preparation of some pyrazinedicarbonitriles is explained. Metal-free AzaPcs form a proton-transfer complex with two molecules of pyridine, this complex formation being accompanied by a change of solution color from purple to blue. The complex is formed directly with two molecules of pyridine, one on either side of the macrocycle. The rate constants of this process were found to be of the order ∼10−4 s−1; the rate of complex formation was not the same for all compounds and may depend on the AzaPc structure. The influence of hydroxy groups on the rate constant was not confirmed.