Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 3. A New Highly Electron-Deficient Octacationic Macrocycle: Tetrakis-2,3-[5,6-di(2-(N-methyl)pyridiniumyl)pyrazino]porphyrazine, [(2-Mepy)8TPyzPzH2]8+

A new octacationic macrocycle, tetrakis-2,3-[5,6-di{2-(N-methyl)pyridiniumyl}pyrazino]porphyrazine, was obtained in its hydrated form as the water-soluble iodide salt. This compound, abbreviated as [(2-Mepy)8TPyzPzH2](I8).8H2O (2-Mepy ) 2(N-methyl)pyridiniumyl moiety), was obtained by demetalation of the corresponding Mg(II) complex, [(2-Mepy)8TPyzPzMg(H2O)](I8).5H2O, which in turn was prepared from its corresponding neutral hydrated species tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazinato(monoaquo)magnesium(II), [Py8TPyzPzMg(H2O)].4H2O, by reaction with CH3I in N,N-dimethylformamide. The quaternization reactions by using CH3I or methyl p-toluenesulfonate were also conducted on the monomeric precursor 2,3-dicyano-5,6-di(2-pyridyl)-1,4-pyrazine, [(CN)2Py2Pyz], with formation of the monoquaternized ion [(CN)2Py(2-Mepy)Pyz]+ neutralized by iodide and p-toluenesulfonate anions. Single-crystal X-ray work allowed elucidation of the structure of the two salt-like species. The diquaternized ion [(CN)2(2-Mepy)2Pyz]2+ could also be obtained as a p-toluenesulfonate salt, but attempts at direct macrocyclization of this dicationic species were unsuccessful. The iodide salt [(2-Mepy)8TPyzPzH2](I8).8H2O is water-soluble, with different solubilities depending on the range of pH explored. It was established that the macrocycle [(2- Mepy)8TPyzPzH2]8+ undergoes facile deprotonation and behaves as a strong acid. Aggregation phenomena are observed for both the octacation [(2-Mepy)8TPyzPzH2]8+ and its corresponding centrally deprotonated species [(2- Mepy)8TPyzPz]6+. Nevertheless, both cationic moieties exist in their monomeric form under specific experimental conditions. UV-visible monitored titrations with NaOH provide information about the type of protonation/deprotonation equilibria which are complicated by the occurrence of aggregation phenomena.