Porphyrin function

The ligand group can be introduced either on the meso or on the /5-pyrrole position of the porphyrin ring, but the synthesis of the meso-functionalized derivatives is easier and has been more widely exploited. Balch (50-53) reported that the insertion of trivalent ions such as Fe(III) (32) and Mn(III) (33) into octaethyl porphyrins functionalized at one meso position with a hydroxy group (oxophlorins) leads to the formation of a dimeric head-to-tail complex in solution (Fig. 11a) (50,51). An X-ray crystal structure was obtained for the analogous In(III) complex (34), and this confirmed the head-to-tail geometry that the authors inferred for the other dimers in solution (53) (Fig. lib). The dimers are stable in chloroform but open on addition of protic acids or pyridine (52). The Fe(III) octaethyloxophlorin dimer (52) is easily oxidized by silver salts. The one-electron oxidation is more favorable than for the corresponding monomer or p-oxo dimer, presumably because of the close interaction of the 7r-systems in the self-assembled dimer. 

The aniline-zinc porphyrin interaction has also been exploited to form dimers. Hunter (60) reported the dimerization of porphyrins functionalized at one meso position with ortho or meta aniline groups (47, 48, Fig. 15). Both compounds showed concentration-dependent H NMR spectra with large upfield shifts for the aniline protons. The dimerization constants are 160 and 1080 M-1 respectively for 47 and 48, and these values are an order of magnitude higher than the association constants of simple reference complexes (K — 10 and 130 M 1 respectively), which is indicative of cooperative self-assembly. The complexa-tion-induced changes in chemical shift were used to obtain three-dimensional structures of the dimers. 

Fig. 16. Cooperative closed dimers assembled from porphyrins functionalized with pyridine at the /3-pyrrole position.

Scheme 8.9 Formation of a phosphite-phosphine bidentate ligand by simply mixing the porphyrin-functionalized phosphite and the 3-pyridyldiphenylphosphine ligand in the presence of a metal precursor.

The derivatization of adequately substituted porphyrins has been appUed to the synthesis of polymeric glycoconjugates [101,102]. Daub et aL have reported the synthesis of a porphyrin functionalized cellulose [101]. The idea was to prepare multichromophore assemblies, organized along regular chains, for studying their optical, electronic, and photophysical properties [101,103]. Also spectroscopic and electrochemical studies were performed in order to obtain information concerning porphyrin-porphyrin n-7z stacking interactions. 

Here we report on the exocyclic coordination of porphyrins, functionalized with appropriate ligands appended at the /3-pyrrolic and/or meso... 

Similar slipped cofacial dimers, 17 and 18 meso substituents omitted), were reported for zinc and magnesium porphyrins functionalized with 2-pyridyl groups at the meso position [74,75]. The stepwise formation con-... 

Murakami H, Nomura T, Nakashima N (2003) Noncovalent porphyrin-functionalized single-walled carbon nanotubes in solution and the formation of porphyrin-nanotube nanoctunpo-sites. Chem Phys Lett 378 481-485... 

Chavan S A, Maes W, Gevers LEM, Wahlen J, Vankelecom IFJ, Jacobs PA, Dehaen W, De Vos DE. Porphyrin-functionalized dendrimers Synthesis and application as recyclable photocatalysts in a nanofiltration membrane reactor. Chem A Eur J 2005 11(22) 6754-6762. 

Note that the dodeca-substituted porphyrins functionalized in the eight j3 positions by ester chains, and in the four meso positions by alkoxyphenyl groups ((21) M = 2H, Zn, Cu, n = m =, 12) were not mesomorphic despite the presence of twelve chains. The absence of mesophase was connected to a strong distortion from planarity of the porphyrin core. 

SchaferUng, M., and P. Bauerle. 2004. Porphyrin-functionalized oligo- and polythiohenes. / Mater Chem 14 1132-1141. 

ECPs including coordination complexes are also able to show electrocatalytic properties e.g., toward the oxidation of nitric oxide in the case of porphyrin functionalized polypyrroles containing various metallic centres [275], for the oxygen or hydrogen peroxide reduction in the case of cobalt-salen PEDOT [276] or iron-containing polysalen [245], or for oxidation of ascorbic acid in the case of osmium bipyridyl functionalized PPy [277]. 

Ricard, D., B. Andrioletti, B. Boitrel, and M. L Her (1999). Electrocatalytic reduction of dioxygen to water by tren-capped porphyrins, functional models of cytochrome c oxidase. Chem. Commun. 1523-1524. 

Carvalho de Medeiros, M.A., S. Cosnier, A. Deronzier, and J.-C. Moutet (1996). Synthesis and characterisation of a new series of nickel(II) m w-tetrakis-(polyfluorophenyl)porphyrins functionalized by pyrrole groups and their electropolymerized films. Inorg. Chem. 35, 2659-2664. 

Schaferling, M. and P. Bauerle (2001). Electrochemical properties of porphyrin-functionalized poly thiophenes. Syn. Met. 119, 289-290. 

Platinutn(II) ions inside the aqueous compartment of the vesicle were reduced to colloidal platinum by bubbling molecular H2 through the dispersions, and a manganese porphyrin functionalized with long alkyl chains was anchored in the bilayer. Methylene blue acted as an electron carrier which shuttles back and forth through the bilayer. The proposed mechanism for the epoxidation reaction in this system is depicted in Figure 8 ... 

M. Schaferling and P. Bauerle, Synthesis and properties of porphyrin-functionalized poly(bithiophenes), Synth. Met., 101, 38-39 (1999). 

M. Schaferling and P. Bduerle, Porphyrin-functionalized oligo- and polythiophenes, J. Mater. Chem., 14, 1132-1141 (2004). 

Efforts towards the preparation of porphyrin-functionalized polythiophenes have centered on complexes 38-41, in which thiophenes are tethered to porphyrin cores (Chart 5.9) [50], The syntheses employed either porphyrin formation using MacDonald-type conditions (38-40) or Wittig coupling to produce 41. No electronic properties of these materials have yet been reported. 

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