Artificial porphyrins

Porphyrinogen-porphyrin relationship the discovery of artificial porphyrins 96CC1257. 

C. Floriani, Chem. Commun. 1996,1257 (artificial porphyrins 21 references) D. Dolphin, ed., The Porphyrins, Academic Press, New York (reference work in 7 volumes) B. Frank and A. Nonn, Angew. Chem. Int Ed. Engl. 1995,34, 1795 (biomimetic syntheses of porphy-rinoids) R. Sheldon and Y. Naruta, Metalloporphyrins in Catalytic Oxidations, Dekker, New York, 1994 F. Montanari and L. Casella, eds., Metalloporphyrin Catalysed Oxidations, Kluwer, Dordrecht, 1994. 

To date, few porphyrin derivatives has been revealed to exist in natural plant and animals despite that a large number of porphyrin derivatives having been artificially synthesized. Usually, artificial porphyrin derivatives are prepared by substituting the hydrogen atoms at the 5,10,15, and 20 positions of porphin ring, but the natural porphyrin derivatives are the product substituted at the 2, 3, 7, 8, 12, 13, 17, and 18 positions [38]. Some of the most representive porphyrin derivatives are shown in Figure 4.23. 

Because of its immense scope, a detailed description of corrins (and vitamin B12) will not be presented here. The reader is instead referred to reviews of B12 chemistry and its biosynthesis that have appeared recently. Further, because they are more directly related to the corrins than are the corroles, the chemistry of the dehydrocorrins will not be discussed here. Also not included in this review are the so-called artificial porphyrins of Floriani, et al. (e.g., 2.5), since it is deemed by these authors in their review that these macrocycles are more dehydrocorrin-like than corrole-like in their nature. Other systems omitted here include the spiro porphyrins of Battersby and coworkers, the tetraphosphole macrocycles of Mathey and coworkers and the tetrapyrrolic systems of Bartczak and Smith and co-workers. Thus, the emphasis will be on those contracted porphyrins that are most removed, in structural and chemical terms, from the macrocyclic unit found in coenzyme B12 and its analogs. 

While the natural porphyrin derivatives are exclusively hydrophobic, some artificial porphyrins having ionic substituents made it possible to prepare water-soluble metaUoporphyrins of both regular and SAT type. Kinetically labile complexes are mostly examined in the excess of the ligand. 

Redox Chemistry of the Porphyrinogen Skeleton Pathways to Artificial Porphyrins and Porphodimethenes Carlo Floriani... 

ARTIFICIAL PORPHYRINS CONTAINING CYCLOPROPANE UNITS FUNCTIONING AS ELECTRON SHUTTLES... 

The present report deals with an overview on the very recent metal-assisted redox chemistry of /w o-octaalkylporphyrinogen. This investigation has led to the discovery of oxidized forms of porphyrinogen other than porphyrins, the so-called artificial porphyrins . 

Artificial porphyrins oxidized forms of porphyrinogen other than porphyrins... 

The successful synthetic elucidation of the stepwise formation of artificial porphyrins using different transition metals is summarized in Scheme 9. 

In 1986, Emanuel Vogel, professor of organic chemistry at the Institute of Organic Chemistry in Cologne, synthesized porphycene, the first artificial porphyrin isomer.Until then nobody had succeeded in synthesizing a stable macrocyclic compound of four pyrroles and four sp -hybridized carbon atoms, other than porphyrin. For some time it was thought that if people could not do it, probably even nature could not do it either. In the meantime, the synthesis of porphycene was successfully completed, see Figure 8.7.1 ... 

Porphyrin-based diboronic acids as artificial receptors for saccharides 98YGK831. 

Covalent and noncovalent combination of porphyrins as well as calix[4]arenes, resorcin[4]arenes including macroheterocyclic fragments, and cyclodextrins by construction of supramolecular artificial receptors 98EJ02689. 

Fig. 5.17 Comparison of the experimental PVDOS determined from NIS measurements on Fe (TPP)(NO) (upper panel) with the PVDOS predicted on the basis of DFT calculations using the B3LYP (center panel) and BP86 (lower panel) functionals. Blue traces represent the PPVDOS Dp (v)for oriented crystals (see Appendix 2, Part III, 3 of CD-ROM), scaled by a factor of 3 for comparison with the total PVDOS Dpe(v)of unoriented polycrystalline powder (red traces). Since the X-ray beam direction k lies 6° from the porphyrin plane, modes involving Fe motion in the plane of the porphyrin are enhanced, and modes with Fe motion primarily normal to the plane are suppressed, in the scaled oriented crystal PVDOS relative to the powder PVDOS. In-plane Fe modes dominate the 200-500 cm range of the data, while Fe motion in modes observed at 74, 128, and 539 cm is predominantly out-of-plane. Crosshatching in the upper panel indicates the area attributable to acoustic modes. In the lower two panels, the Fe-NO bend/stretch modes predicted at 386 and 623 cm , have been artificially shifted to the observed 539 cm frequency to facilitate comparison with the experimental results. Predicted PVDOS are convolved with a 10 cm Gaussian (taken from [101])...

In artificial photosynthetic models, porphyrin building blocks are used as sensitisers and as electron donors while fullerenes are used as electron acceptors. Triads, tetrads, pentads and hexads containing porphyrins and Qo have been reported in the literature (see the Further Reading section). 

The intramolecular electron transfer kg, subsequent to the rapid reduction, must occur because the Ru(III)-Fe(II) pairing is the stable one. It is easily monitored using absorbance changes which occur with reduction at the Fe(III) heme center. Both laser-produced Ru(bpy)3 and radicals such as CO (from pulse radiolysis (Prob. 15)) are very effective one-electron reductants for this task (Sec. 3.5).In another approach," the Fe in a heme protein is replaced by Zn. The resultant Zn porphyrin (ZnP) can be electronically excited to a triplet state, ZnP which is relatively long-lived (x = 15 ms) and is a good reducing agent E° = —0.62 V). Its decay via the usual pathways (compare (1.32)) is accelerated by electron transfer to another metal (natural or artificial) site in the protein e. g.. 

Reaction of 217 with Cjq leads to the amino-protected porphyrin-fulleropyrroli-dine, which can easily be deprotected to the corresponding amine [229, 277]. By further functionalization via amide coupling an easy access to extended donor-acceptor systems is possible. A carotene-porphyrin-fullerene triad was prepared by reaction of the amine with the appropriate carotene acid chloride. The motivation for the synthesis of all these donor-acceptor systems is the attempt to understand and imitate the photosynthetic process. On that score, a model for an artificial photosynthetic antenna-reaction center complex has been achieved by attaching five porphyrin cores in a dendrimer-like fashion to the fullerene [242]. 

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