Tetraazaporphyrines

Tetraaza macrocycles nickel complexes, 5, 5 synthesis, 2, 903 Tetraazaporphyrin, octaphenyl-metallation, 2, 858 Tetraazaporphyrins synthesis, 2, 857... 

Organometallic complexes are known which contain a wide variety of macrocycles closely related to porphyrins corroles, porphycenes, tetraazaporphyrins. phthalocyanines, tetraazaannulenes, and porphyrinogens are the best known examples. Examples containing the first four of these macrocycles are included where there is a useful comparison or contrast with the relevant porphyrin chemistry, but the discussion will not be comprehensive. The four macrocycles are shown in Fig. 2. 

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 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. 

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). 

Cationic porphyrinic macrocycles, in particular the archetypical tetracationic, meso-telra-W-melhylpyridyl (porphyrin, have applications in biology, medicine, catalysis, and materials (95-103). Cationic tetraazaporphyrins, or porphyrazines, which represent a novel alternative and class of cationic porphyrinic compounds, were recently reported (37). 

Let us conclude shortly with tetraazaporphyrins, the most popular members of which are constituted by phthalocyanines and porphyrazines, Scheme 12. 

L. Lee, N. H. Sabelli, and P. R. LeBreton, Theoretical characterization of phthalocyanine, tetraazaporphyrin, tetrabenzoporphyrin, and porphyrin electronic spectra, J. Phys. Chem, 86, 3926-3931 (1982). 

The photochemistry of true organomagnesium compounds remains almost completely unexplored. A literature search in preparation of this work found only a few scattered examples of photochemical studies, mostly in relation to Grignard reactions and 1,3-diketonate chelates Similar to the situation with organozinc compounds magnesium tetrapyrrole chelates, i.e. magnesium porphyrins 1, 5,10,15,20-tetraazaporphyrins (por-phyrazines) 2 and phthalocyanines 3 have found more interest. This is primarily related... 

For practical purposes we have concentrated on the literature of the last decade, focusing on publications that address photochemical transformations involving zinc(II) chelates of porphyrins and 5,10,15,20-tetraazaporphyrins. Nevertheless, even with such a limited approach the body of available literature is significant and we can only use selected examples to highlight the state of the art of this field. A description of syntheses, methodology or electron transfer reactions is outside the purview of this work and the present work can only give a rather selective and personal view on ongoing studies in this area. 

Tetraazaporphyrins are easily prepared by cyclotetramerization of maleonitrile or its analogues, in the presence of metal salts (Scheme 53).178,183... 

Tetraazaporphyrin, octaphenyl-metallation, 858 Tetraazaporphyrins synthesis, 857 Tetraethylenepentamine metal complexes, 56 Tetraglycine metal complexes, 764 Tetraketones metal complexes, 399 1,3,5,7-Tetraketones metal complexes, 400 Tetramines cyclic... 

Schnurpfeil G, Sobbi AK, Spiller W, Kliesch H, Wohrle D. Photooxidative stability and its correlation with semi-empirical MO calculations of various tetraazaporphyrin derivatives in solution. J Porphyrins Phthalocyanines 1997 1 159-167. 

---