Metallo-chlorins

Metallo-chlorins and bacteriochlorins have lower oxidation potentials than the corresponding metalloporphyrins. The replacement of a pyrrole by a hydrogenated pyrroline ring lowers the potentials by about 100 mV. Furthermore, the oxidation potentials are generally somewhat lower in polar solvents or in micelle and vesicle membranes than in apolar solutions because the charged oxidation and reduction products become more solvated in polar media. 

RR spectra of Cu(OEC) were first reported by Ozaki et al.. Figure 15 compares the polarized RR spectra of Cu(OEC) with those of Cu(OEP). The RR bands of Cu(OEC) in the 900-1700 cm region were assigned on the basis of frequency shifts upon 15,20-deuteration of meso-carbons and N substitution of pyrrolic nitrogens . Anderson et and Hanson et al. also reported the RR spectra of metallo-chlorin derivatives. Ozaki et al. extended the comparative study of Fe(OEP) and Fe(OEC) to the Fe-L stretching and ligand internal modes. Here the vibrational spectra of M(OEC) are explained on the basis of M(OEP) and then the difference in the Fe-L interaction between Fe(OEC) and Fe(OEP) will be discussed. 

Platinum Platinum-coated titanium is the most important anode material for impressed-current cathodic protection in seawater. In electrolysis cells, platinum is attacked if the current waveform varies, if oxygen and chlorine are evolved simultaneously, or if some organic substances are present Nevertheless, platinised titanium is employed in tinplate production in Japan s. Although ruthenium dioxide is the most usual coating for dimensionally stable anodes, platinum/iridium, also deposited by thermal decomposition of a metallo-organic paint, is used in sodium chlorate manufacture. Platinum/ruthenium, applied by an immersion process, is recommended for the cathodes of membrane electrolysis cells. ... 

Halogen Compounds.—Practically all of the elements unite with chlorine, bromine, and iodine to form the corresponding halogen compounds. With the metals, well-defined solid salts are formed, save in cases in which the metal has a high valence and is a metallo-acid... 

Cytochrome P-450 can perform both intramolecular and intermolecular nitrene insertions with 106 in water solution [181]. However, the intermediate metallo-nitrene (108) also hydrolyzed to some extent so the enzyme performed a hydroxylation as well as an amidation. Although we have also performed an intermolecular amidation of a steroid, using such a metalloporphyrin reaction with 106 to form 112 [182], we have not yet extended it to the kinds of directed functionalizations described above with either benzophenones or chlorinations. 

Keywords Metallo-Disilanes / Regiospecific Oxofiinctionalization / Regiospecific Chlorination... 

The reactivity of fluorine toward synthetic vanadyl porphyrins, Boscan crude, and fractions derived therefrom was surprisingly benign. The halogen was actually less reactive than chlorine toward metallo-porphyrins. Though the crude and its fractions did react with the formation of hydrogen fluoride, the processes did not exhibit explosive violence at ambient and even higher temperatures. 

In the synthesis of 173, the relative stereochemistry is set in the addition of a 4-(l-metallo-ethyl)-5-fluoropyrimidine derivative to l-(2,4-difluorophenyl)-2-(17/-l,2,4-triazol-l-yl)-l-ethanone 174 (Scheme 12.27). The diastereocontrol of this can be controlled by pyrimidine substitution pattern and reaction conditions of the metalation step. Good diastereoselectivity (12 1) is obtained using an zinc derivative of 175. After removal of the chlorine from the pyrimidine ring, of the desired stereoisomer of 173 is isolated via a diastereomeric resolution using salt (l/ )-10-camphorsulfonic acid (10-CSA). Synthetic routes to the pyrimidine partner have also been evaluated. Shown in Scheme 12.28, the initial six-step route from 5-fluorouracil 177 can be replaced by a four-step process, involving fluorination of methyl 3-oxopentanoate and cyclization with formami-dine acetate. ... 

Thus it is positioned, that at interaction MoClj with acetylene in not polar mediums there is allocation FICl, downturn of a degree of oxidation of molybdenum and formation metallo-oiganic nanoclusters. Two distances Mo-Mo are found out in these nanoclusters by method EXAFS spectroscopy. In coordination sphere. Mo there are two nonequivalent atom of chlorine and atom of carbon. On the basis of results MALDI-TOF mass spectrometry, the conclusion is made that cluster of molybdenum has 12- or the 13-nuclear metal skeleton and its structure can be expressed by formulas[MOj,Cl,(q j)] or [MOj3CyCj3H,)]. ... 

Porphyrins and chlorin derivatives bearing a thiobarbaturic acid functionality at the meso- and -pyrrole positions have been synthesized by Morgan et and Pandey et from a series of chlorins 411-416. All these free-base metallo derivatives show highly perturbed electronic spectra, with major absorptions observed in the range of 700-870 nm (Scheme 84). 

Recent reconstitution experiments open the possibility of selectively introducing other metallo bacteriochlorins (or chlorins) at the acceptor BChl or BPheo sites. Zinc substitutions are obvious choices since the optical and coordination properties of Zn complexes resemble those of Mg derivatives but the former are easier to reduce (and harder to oxidize) than the latter. Perhaps a less obvious candidate for metal replacement is nickel which offers several advantages Ni complexes are also easier to reduce and harder to oxidize than Mg compounds but, in addition, redox potentials of Ni porphyrins and chlorins are close to those of the metal-free derivatives the optical properties of Ni chlorins are similar to those of Mg ones they possess shortlived excited states as a result of which they have proved to be valuable for resonance Raman studies. A more practical advantage of Ni complexes is their enhanced stability towards demetallation, compared to Mg or Zn complexes, a property of merit if the chromophores are to be used in reconstitution reactions. (Ni protoporphyrins IX have been successfully exchanged for the histidine-bound hemes in hemoglobin.) ... 

The most intense band in the FT Raman spectrum of oxidized RCs is at 1600 cm l (not including the carotenoid band). It most likely corresponds to the 1608 cm" band observed for neutral P. This C Cj mode thus seems to downshift by 7 cm" upon oxidation of P. A similar downshift has been observed in the one-electron oxidation of BChl a [9,10] and is consistent with the one-electron oxidation of metallo-porphyrins and chlorins with aj -like redox orbitals [11,12]. Thus the downshift of the C Cj mode upon RC oxidation is interpreted in terms of BChl a oxidation. Since the frequency of this mode is also senstive to the BChl core size and macrocycle conformation, its observed frequency may not accurately reflect the localization of the unpaired electron in P + - [6]. 

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