Tetra-meso-phenylporphyrin

The phenomenon of atropisomerism (formation of rotational isomers) in porphyrins with meso aryl substituents has been first described in 1969 by Gottwald and Ullman [78] with tetra-me o-o-hydroxyphenylporphyrins. This concept has been exploited with me o-tetra amino-phenylporphyrins to design porphyrin scaffolds with different symmetry [79-81]. The atropisomerism phenomenon in porphyrin is caused by the steric hindrance induced by the presence of a substituent in ortho position of meso aryl substituents. In contrast, wieta-substitution of the meso aryl substituents very rarely shows restricted aryl rotation in tetra- and di-arylporphyrins. Few examples of atropisomerism in meta position are nevertheless found in literature (such as porphyrin carborane [82], fuUerene porphyrins [83, 84] and multimetallic porphyrin monomers [85, 86]. In these examples, the large size of the meso aryl substituents (carborane, fiiUerene...) despite substituted in meta position, hinders rotation around the Cme -Caryi bond leading to rotational isomers. 

Various nmr techniques have been used to investigate the intramolecular double proton transfer which occurs in the tautomerisation of meso-tetra-phenylporphyrin (40) (Limbach et al., 1982). The reaction has been studied (Storm and Teklu, 1972) by observation of the nmr signals due to the protons... 

Zinc tetramethylpyridilporphyrin tetraiodide was prepared by refluxing in water the free base meso-tetra (4-N-methylpyridine) porphyrin tetraiodide (Strem Chemicals) with finely divided zinc oxide (Hermann et al., 1978). An identical procedure was used to obtain zinc tetrasulphonate phenylporphyrin from the free base tetrasodium-meso-tetra (4-sulphonate-phenyl) porphyrin (12 hydrate) (Strem Chemicals). The purity of these porphyrins was checked by comparing the absorption spectra of the metallated porphyrin with those of the free base. 

Another class of synthetic porphyrins comprises the meso-tetra-phenylporphyrins, which can be easily prepared in large amounts, and which have some unusual properties, not found in natural porphyrins. Only the parent compound tetraphenylporphyrin (IIR = H, TPP) with unsubstituted benzene rings is discussed here. 

Several other research groups are actively contributing in this field of CcO model chemistry. Naruta et al. have reported tris(2-pyridylmethyl)amine Cu complex-linked iron meso-tetra-phenylporphyrin derivatives and well-characterized Fe—(O2)—Cu species that are similar to [( L)Fe -(0 )-Cu ]+ (Structure (7)). A CcO model developed by Casella and co-workers is a natural porphyrin derivative, in which a polybenziimidazole residue for the Cu coordination site is attached to the propionic acid side chain of the deuteroporphyrin. A new class of picket porphyrin, bearing covalently linked, axially placed tris(heterocycle) chelates for a copper ion, has been synthesized and characterized by Wilson and co-workers. ... 

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