Cyclic porphyrin tetramer

Scheme 1-11 Tetrapyridylporphyrin 42 templated formation of cyclic porphyrin tetramer 43.

Synthesis of cyclic porphyrin tetramer 4 from linear tetramer 6 using y4Porph and Bipy as positive cyclisation templates. 

Wylie, R.S. and Sanders, J.K.M. (1994) Catalytic acyl tr ansfer by a cyclic porphyrin trimer - efficient turnover without product inhibition. J. Am. Chem. Soc., 116, 3141-3142 Okumura, A., Eunatsu, K., Sasaki. Y. and Imamura, T. (1999) A novel porphyrin octamer with a cyclic tetramer core. Chem. Lett., 779-780. 

Fig. 4 A dynamic combinatorial library of cyclic and linear arrays of mixed metallopoi-phyrins which, upon addition of a 4.4 -dipyridine guest, transforms quantitatively into a macrocyclic porphyrin tetramer. (Adapted from Ref. [1 1].) View this art in color at WWW. dekker. com.)...

Funatsu, K., T. Imamura, A. Ichimura, and Y. Sasaki (1998). Synthesis and properties of cyclic ruthenium(II) porphyrin tetramers. Inorg. Chem. 37, 1798-1804. 

A polymeric structure can be generated by intermolecular coordination of a metalloporphyrin equipped with a suitable ligand. Fleischer (18,90) solved the crystal structure of a zinc porphyrin with one 4-pyridyl group attached at the meso position. In the solid state, a coordination polymer is formed (75, Fig. 30). The authors reported that the open polymer persists in solution, but the association constant of 3 x 104 M 1 is rather high, and it seems more likely, in the light of later work on closed macrocycles (see above), that this system forms a cyclic tetramer at 10-3 M concentrations in solution (71,73). 

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). 

For the first time we report the synthesis of macrocycles like calixpyrrole, cyclotriveratrylene (CTV), cyclotetraveratrylene (CTTV), porphyrine ete over molecular sieve as a catalyst. Calixpyrroles are synthesized from pyrrole and a ketone like acetone over MCM-41 under reflux conditions using suitable solvent. In case of MCM-41 cyclic calixpyrroles were obtained. On the other hand due to shape selectivity in case of Y zeolite linear di-, tri- and tetra- polypyrroles were obtained and cyclic tetramers were not observed. The mechanism of the synthesis of calixpyrrole is either by the dimerization of dimer with simultaneous cyclization to cyclic tetramer or cyclization of linear tetramer via recoil phenomenon. 

Fig. 17 Formation of cyclic trimer 37 and tetramer 38 from imidazolyl Co(ll) porphyrin...

It is remarkable that no polymeric systems were observed for 33. In discussing this point. Hunter and coworkers suggested that in the case of the 4-pyridyl-OT. ro-substituted porphyrin 29 of Fleischer et there was an equilibrium between a cyclic tetramer and a polymeric species, the latter being predominant at room temperature or higher. A definitive answer to this is.sue will be provided below. 

As described in Section III.A.2, Sanders and McCallien assembled four Zn(II) dioxoporphyrins bearing acetylenic groups on the tetrakis(4-pyridyl) porphyrin template 61. They subsequently submitted the complex to the Glaser-Hay coupling reaction which produced the cyclic tetramer in 70% yield. Without a template, the same reaction was not so selective it afforded the tetramer and trimer species in 40%... 

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