Porphyrazines with annulated diazepine rings 4: Synthesis and properties of MgII tetradiazepinoporphyrazine carrying exocyclic styryl fragments

A novel tetradiazepinoporphyrazine MgII complex bearing eight peripheral styryl substituents, [St8TDzPAMg(H2O)] (St = -CH=CHAr, where Ar = 4-methoxyphenyl) was prepared by template cyclotetramerization of the corresponding precursor — 5,7-distyryl substituted diazepino-2,3-dicarbonitrile — in the presence of MgII butoxide in n-butanol. UV-visible and 1H NMR spectral data indicate that the complex is strongly aggregated in non-coordinating solvents (dichloromethane, chloroform, benzene), it is dimeric in pyridine, whereas it is predominantly monomeric in dimethylsulfoxide and dimethylformamide. The fluorescence response is high for solutions in which the monomeric form is prevalent, but it is strongly quenched as the content of the dimer is increased. Evidence was obtained that dimerization occurs due to intermolecular hydrogen bonding between acidic CH2 groups in the diazepine ring (6H form) of one molecule with meso- and/or diazepine N atoms of another molecule, dimerization being also contributed by the presence of chlatrated water. In the presence of fluoride anions the dimer is destroyed with formation of the monomeric species, which is changed to the 1H form upon heating, as indicated by 1H NMR spectra.