Porphyrins tetrapyridyl

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

In 2005, Rowan, Nolte, and coworkers described an efficient and templated synthesis of porphyrin boxes using DCC and reversible metathesis reaction [54]. Cyclic tetramers were successfully prepared in good yields (62%) from an olefin-functionalized zinc porphyrin in the presence of first generation Grubb s catalyst and upon addition of a tetrapyridyl porphyrin (TPyP) serving as a template. While a mixture of linear and cyclic oligomers was obtained in the absence of template, addition of TPyP resulted in a reorganization of the DCL to favor the formation of the desired tetrameric box (Fig. 7a). 

The use of metal ion templates to achieve selective cyclisation reactions is one of the most successful applications of templating [18] and the concept has been extended to other cyclisations. In this context Sanders et al. [19] have described a negative template, a tetrapyridyl porphyrin. They have used this template to suppress formation of the otherwise favoured cyclic dimer por-... 

Very available and promising square panels are tetrapyridyl porphyrins 15 and 16. In fact, 4-pyridyl-substituted porphyrin 15 has been frequently employed for infinite assemblies. In contrast, there seems to be difficulty in constructing discrete 3D assemblies from tetrapyridyl porphyrins, though there are some examples of 2D assemblies such as porphyrin squares 17 [27] and 18 [28] from dipyridyl porphyrins. 

Fig. 2 Scheme showing the stmcture of a supramolecular species obtained by coordination of peripheral transition metal complexes, clusters or nanoparticles to the At-pyridyl atoms of meso-(tetrapyridyl)porphyrins, M-TPyPs, and exerting electron-withdrawing or donor effects that can be tuned by their oxidation state... 

Synthesis and chararterization of poly(catechol) catalyzed by tetrapyridyl porphyrin and HRP were examined. The... 

Figure 32. Structural foritiulae of mono- to tetrapyridyl meso-substituted porphyrins 45 and 58-64.

Clear-cut examples of this type of cooperativity are the bisporphyrin tetrapyridyl receptor reported by Wilson and Anderson (Fig. 19), and the double-wheel octapyridyl receptor reported by Shinkai and coworkers (Fig. 20). Anderson s receptor consists of two porphyrins connected... 

Figure 19 Anderson s c-B4-(AA)2 type complex formed by a bisporphyrin tetrapyridyl receptor (64) and two bisfzinc porphyrin) (AA) ligands.

Interesting self-assembled multi-layer thin films 65 of covalently bonded porphyrins were utilized starting from chloromethylphenylsilylated oxide surfaces in the reaction with tetrapyridyl-substituted porphyrins and dichloro-/7-xylene [269]. The growth of the film was studied by monitoring the absorption intensity of the Soret-band. It is said that a highly ordered and closely packed film was obtained. 

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