Substituted tetra-2,3-pyrazinoporphyrazines. Part I. Angular annelation of tetra-2,3-quinoxalinoporphyrazine

Several derivatives of 2,3-dicyanopyrazine were prepared via the condensation of o-quinones with diaminomaleodinitrile. Benzo[f]quinoxaline-2,3-dinitrile was obtained from 1,2-naphthoquinone, and a series of isomeric, di-tert-butyl substituted 5,6-(9,10-phenanthro)-2,3-dicyanopyrazines were prepared from the corresponding di-tert-butyl-9,10-phenanthrenequinones. Complexation of benzo[f]quinoxaline-2,3-dinitrile, and unsubstituted 5,6-(9,10-phenanthro)-2,3-dicyanopyrazine, with an appropriate metal salt yielded metal complexes of tetra-2,3-(benzo[f]quinoxalino)porphyrazine and tetra-2,3-[5,6-(9,10-phenanthro)]porphyrazine, respectively. Metal-free tetra-2,3-[5,6-(9,10-phenanthro)porphyrazine was obtained from the dilithium derivative by demetallation in HCl. These compounds have limited solubility in organic solvents, such as quinoline, and are aggregated in solutions. To eliminate the aggregation phenomenon and to determine the spectral properties of angularly annelated naphthalocyanine aza analogs, we prepared several isomeric tetra-2,3-[5,6-(di-tert-butyl-9,10-phenanthro)pyrazino]porphyrazines. These octa(tert-butyl) substituted complexes were synthesized via complexation of di-tert-butyl substituted 5,6-(9,10-phenanthro)-2,3-dicyanopyrazines with metal salts in the presence of urea, quinoline, and tri(n-butyl)amine, and purified by silica gel chromatography. They are soluble in chloroform and substantially monomerized in solutions. A hypsochromic shift of the Q-band of octaaza naphthalocyanines versus their carbocyclic analogs was observed for all aza analogs, with the extent of the shift depending on the composition of the aromatic macrocycle. Thus, the first angularly annelated benzo ring addition causes a hypsochromic shift (∼25 nm) of the Q-band of tetra-2,3-quinoxalinoporphyrazine, whereas addition of a second condensed benzo ring has little effect. Key words: phthalocyanine, aza analog, tetra-2,3-quinoxalinoporphyrazine, angular annelation.