Iron complex, with macrocyclic

Figure 11. Approximate electrode potentials of iron complexes with macrocyclic ligands—comparison to the natural dioxygen earners.

Among many different complexes that have been synthesized in attempt to mimic the structure and/or functionality of SODs (16-22), the most active SOD mimetics known to date are seven-coordinate Mn(II) complexes with macrocyclic ligands derived from C-substituted pentaazacyclopentadecane [15]aneNs and its pyridine derivative (Scheme 4) (12d,16a,23-25). Some of them possess SOD activity that exceeds the one of native mitochondrial MnSOD, and are the first SOD mimetics which entered clinical trials (12d,16a,23,26-28). A few Fe(III) complexes with the same type of ligands have also been studied and they are one of the best iron-based SOD catalysts (18). It should be stressed that the decomposition of superoxide catalyzed by these complexes has been quantified by direct stopped-fiow method, in the presence of a substantial superoxide excess over catalyst, as a reliable method for determining true SOD activity (29). 

Chanda, A. Popescu, D. L. Tiago de Oliveira, F. Bominaar, E. L. Ryabov, A. D. Miinck, E. Collins, T. J. High-valent iron complexes with tetraamido macrocyclic ligands ... 

Though some diflBculties persist, it has been possible to synthesize a large number of iron complexes with synthetic macrocycles. Brief attention will be given first to the derivatives of TAAB (40). As summarized in Figure 19, o-aminobenzaldehyde condenses in the presence of ferrous chloride to form a TAAB complex. Because of the ease of oxida-... 

A variety of other macrocycles have been used in the synthesis of iron and other transition element compounds. The structures of some of these are presented in Figure 20. The abbreviations presented herein are used in the following discussion. Although iron complexes with several of these ligands have been prepared and characterized, only those of the cyclic diene 1,7-CT will be considered here (41). The several... 

Horwitz et al. developed nonheme iron complexes with tetraamido macrocyclic ligands (TAML) that are efficient for the dye bleaching reactions with HjOj in water from neutral to basic Pinacyanol chloride as a reference,... 

To mimic the square-pyramidal coordination of iron bleomycin, a series of iron (Il)complexes with pyridine-containing macrocycles 4 was synthesized and used for the epoxidation of alkenes with H2O2 (Scheme 4) [35]. These macrocycles bear an aminopropyl pendant arm and in presence of poorly coordinating acids like triflic acid a reversible dissociation of the arm is possible and the catalytic active species is formed. These complexes perform well in alkene epoxidations (66-89% yield with 90-98% selectivity in 5 min at room temperature). Furthermore, recyclable terpyridines 5 lead to highly active Fe -complexes, which show good to excellent results (up to 96% yield) for the epoxidation with oxone at room temperature (Scheme 4) [36]. 

It is essential to characterize the reactant species in solution. One of the problems, for example, in interpreting the rate law for oxidation by Ce(IV) or Co(III) arises from the difficulties in characterizing these species in aqueous solution, particularly the extent of formation of hydroxy or polymeric species. We used the catalyzed decomposition of HjOj by an Fe(III) macrocycle as an example of the initial rate approach (Sec. 1.2.1). With certain conditions, the iron complex dimerizes and this would have to be allowed for, since it transpires that the dimer is catalytically inactive. In a different approach, the problems of limited solubility, dimerization and aging of iron(III) and (Il)-hemin in aqueous solution can be avoided by intercalating the porphyrin in a micelle. Kinetic study is then eased. 

Several macrocyclic polycatechols, with up to six catechol units incorporated into the ring, have been designed for possible treatment for iron overload and were prepared using high dilution techniques. They form stable iron(III) complexes the complex with the three-catechol ring as ligand has log K= ii.l... 

CO2 molecule, or Mg + and CO2 play the role of oxide acceptor to form water, carbonate, and MgC03, respectively [38]. The reactions of the iron carboxylate with these Lewis acids are thought to be fast and not rate determining. For the cobalt and nickel macrocyclic catalysts, CO2 is the ultimate oxide acceptor with formation of bicarbonate salts in addition to CO, but it is not clear what the precise pathway is for decomposition of the carboxylate to CO [33]. The influence of alkali metal ions on CO2 binding for these complexes was discussed earlier [15]. It appears the interactions between bound CO2 and these ions are fast and reversible, and one would presume that reactions between protons and bound CO2 are rapid as well. 

The original Jager-type complexes can be deacylated by treatment with acid demetallation follows and the free macrocycles can be isolated (Scheme 20).134 These can be converted into iron(II) complexes with acetonitrile coordinated in the axial positions. However, these are unstable in the example with 15- and 16-membered rings and undergo cyclization as a result of carbanion attack on the coordinated acetonitrile (Scheme 21).134 136 A similar reaction occurs with the cobalt... 

In the case of the iron complex Fe(OMC) the intensity of the absorption has been related to the existence of stacking phenomena among the macrocyclic units, which are eliminated by interactions with chloride ions or axial ligands [28],... 

History. Braun and Tschemak [23] obtained phthalocyanine for the first time in 1907 as a byproduct of the preparation of o-cyanobenzamide from phthalimide and acetic anhydride. However, this discovery was of no special interest at the time. In 1927, de Diesbach and von der Weid prepared CuPc in 23 % yield by treating o-dibromobenzene with copper cyanide in pyridine [24], Instead of the colorless dinitriles, they obtained deep blue CuPc and observed the exceptional stability of their product to sulfuric acid, alkalis, and heat. The third observation of a phthalocyanine was made at Scottish Dyes, in 1929 [25], During the preparation of phthalimide from phthalic anhydride and ammonia in an enamel vessel, a greenish blue impurity appeared. Dunsworth and Drescher carried out a preliminary examination of the compound, which was analyzed as an iron complex. It was formed in a chipped region of the enamel with iron from the vessel. Further experiments yielded FePc, CuPc, and NiPc. It was soon realized that these products could be used as pigments or textile colorants. Linstead et al. at the University of London discovered the structure of phthalocyanines and developed improved synthetic methods for several metal phthalocyanines from 1929 to 1934 [1-11]. The important CuPc could not be protected by a patent, because it had been described earlier in the literature [23], Based on Linstead s work the structure of phthalocyanines was confirmed by several physicochemical measurements [26-32], Methods such as X-ray diffraction or electron microscopy verified the planarity of this macrocyclic system. Properties such as polymorphism, absorption spectra, magnetic and catalytic characteristics, oxidation and reduc-... 

These compounds are the first examples for the stabilization of the LS state of iron(II) with saturated nitrogen as the most abundant donors this has been ascribed by the authors to the enhanced ligand field strength due to the constrictive effect of the mechanically confining in-plane macrocyclic ligand . Six-coordinate iron(II) complexes are formed with relatively weak axial ligands such as X = CH3C002 >... 

Macrocycle LXXXVIII was prepared (13) in an 8% yield from the reaction of the disodium salt of ethane-1,2-dithiol with di(2-bromo-ethyl)amine in ethanol at high dilution, and it was found to complex with Ni(II) and Co(II) ions when these were added as salts. A macrocycle containing the same donor atoms (LXXXIX) has been obtained in the form of complexes (87) by the template reactions of l,2-bis(2-aminophenylthio)ethane and 1,4-bis (2-formylphenyl)-1,4-dithiabutane with Ni(II) and Co(II) perchlorates. Iron, cobalt, nickel, and zinc as their M(II) perchlorates have been used as templates in the formation of XC (55, 133). 

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