Porphyrazines

Functional supramolecular materials, formation by self-assembly of phthalocyanins and porphyrazines 96CC2385. 

Star porphyrazines and related multimetal macrocycles 98JHC1013. 

Meso substitution of porphyrines to give tetraazaporphyrines, so-called porphyrazines, modulates the electronic character of the macrocycle. While porphyrazines have received considerably less attention than porphyrines over many years, this has changed due to the development of efficient syntheses of soluble derivatives.1 6-1809 Also, various porphyrazines (and phtalocyanines) with peripheral groups for metal ion coordination have been prepared and used for the construction of multimetallic complexes.1806 Ni porphyrazines (695) typically show absorptions spectra with a strong Q band at around 615nm. 

The Ni complex of ra-dihydroxylated porphyrazine (696) gives (697) upon reaction with air.1810 The decaptation reaction is assumed to result from Ni-mediated air oxidation of the ds-diol unit and subsequent loss of C02. 

The effect of peripheral substituents on absorption spectrum and in vitro PDT activity has been studied for the zinc(II) porphyrazine (5,10,15,20-tetraazaporphyrin) system.276 277 Water-soluble zinc(II) polyazaphthalocyanines have been synthesized for PDT applications.278,279 A zinc(II) bis(dimethylamino)porphyrazine is photooxidised to give the zinc(II)-,seco-porphyrazine, the reaction being autocatalytic.280 The zinc(II)-complex of a hexaalkyltexaphyrin chloride has Amax (MeOH) 732 nm and A 0.61,281 but the system does not appear to have been developed for PDT. 

C. Metal-Metal Bonded Dimers from Porphyrazines... 

Porphyrazines (pz), or tetraazaporphyrins, are compounds that can be viewed as porphyrin variants in which the meso carbon atoms are replaced with nitrogen atoms, as Fig. 1 shows (1). This difference intrinsically gives porphyrazines discrete physiochemical properties from the porphyrins. In addition, despite their similar molecular architecture, porphyrazines are prepared by an entirely different synthetic route than porphyrins—by template cyclization of maleonitrile derivatives, as in Fig. 2, where the open circle with the A in it represents the peripheral substituent of the pz—rather than by the condensation of pyrrole and aldehyde derivatives (1). The pz synthetic route allows for the preparation of macrocycles with chemical and physical properties not readily accessible to porphyrins. In particular, procedures have been developed for the synthesis of porphyrazines with S, N, or O heteroatom peripheral functionalization of the macrocycle core (2-11). It is difficult to impossible to attach the equivalent heteroatoms to the periphery of porphyrins (12). In addition, the preparation and purification of porphyrazines that bear two different kinds of substituents is readily achievable through the directed cocyclization of two different dinitriles, Fig. 3 (4, 5, 13). 

In this chapter, the porphyrazines are named in one of two ways. For simple substitution patterns, substituents will be denoted directly for example, Cu(II) oc-taethylporphyrazine can be written Cu[pz(Et)g], When the pattern is more complex, or general concepts are discussed, the porphyrazines are systematically named based on the nature of their substituents, using the general formula, M[pz (AmB4 ), where M represents the metal ion and its axial ligands (or two hydro-... 

Figure 1. Structural distinctions between porphyrins and porphyrazines.

Figure 3. Synthesis of unsymmetrical porphyrazines via cocyclization of two dinitriles.

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