Porphyrazines with annulated diazepine rings. 6. Synthesis and properties of the alkyl substituted derivative - Mg^II complex of tetrakis-2,3-(5,7-di-tert-butyl-6H-1,4-diazepino)porphyrazine

Novel Mg^II porphyrazine 3 bearing four appended seven-membered tert-butyl substituted 1,4-diazepine rings was prepared via Linstead macrocyclization of 5,7-di-tert-butyl-6[Formula: see text]-1,4-diazepine-2,3-dicarbonitrile 2, obtained by condensation of diaminomaleonitrile and 2,2,6,6-tetramethylheptanedione-3,5 (1) in anhydrous ethanol in the presence of P₂O₅. The structure of the dinitrile precursor 2 was established by single crystal X-ray work. ¹H NMR study revealed that the 1,4-diazepine ring is present in the 6[Formula: see text] tautomeric form both in the dinitrile precursor 2 and the Mg^II complex 3. The inversion of the tert-butyl substituted diazepine ring occurs more easily than in the case of aryl and alkenyl substituted species. Although porphyrazine 3exhibit some tendency to aggregation in low-polar solvents the presence of bulky tert-butyl substituents stabilizes the monomeric form and hinders formation of H-bonded dimers characteristic for aryl and styryl substituted analogues.