Iron complexes redox chemistry

Reaction of the manganese tropocoronand complex [Mn(tc-5,5)(NO)] with [Fe(tc-5,5)] results in complete transfer of the NO to the [Fe(tc-5,5)]. Other nitric oxide complexes appear in the sections on nitroprusside (Section S.4.2.2.6 above), on phthalocyanines (Section 5.4.3.7.4 above), and on polynuclear iron-sulfide complexes (Roussin s salts Section 5.4.5.9.2 below) Fe-por-phyrin-NO redox chemistry has been mentioned in Section 5.4.3.7.2 above. 

Figure 1 The mitochondrial respiratory chain. Electron transfer (brown arrows) between the three major membrane-bound complexes (I, III, and IV) is mediated by ubiquinone (Q/QH2) and the peripheral protein c)dochrome c (c). Transfer of protons hnked to the redox chemistry is shown by blue arrows red arrows denote proton translocation. NAD+ nicotinamide adenine dinucleotide, FMN flavin mononucleotide, Fe/S iron-sulfur center bH,bi, and c are the heme centers in the cytochrome bc complex (Complex III). Note the bifurcation of the electron transfer path on oxidation of QH2 by the heme bL - Fe/S center. Complex IV is the subject of this review. N and P denote the negatively and positively charged sides of the membrane, respectively...

The insertion into porphyrins of central metals capable of easy oxidation or reduction can shift the site of redox chemistry from the macrocycle n-electron system to the metal. While this substitution allows large changes in the redox properties of a porphyrin, it may introduce changes in the photophysics if a transition metal is employed. For example, iron (III) porphyrins are particularly good electron acceptor moieties, and have been used as components of porphyrin dyad and more complex systems that show photoinduced electron transfer behavior [11, 18, 19, 26, 31, 32, 34, 43, 44]. McLendon and coworkers used this strategy with dyad 3, in... 

This triad of elements have played a crucial role in the development of the chemistry of 2,2 -bipyridine. The characteristic red color of [Fe(bpy)3l + was first observed by Blau in his pioneering studies on 2,2 -bipyridine (73-75), and iron complexes of bpy have continued to be of interest in the past century. The complexes of iron, ruthenium, and osmium probably account for about a third of all literature references to 2,2 -bipyridine complexes. This in part represents the facile synthesis of the complexes, their high stability, and extensive redox chemistry. The recent interest in the use of these compounds as photocatalysts has led to an explosive interest in the literature. Recent reviews have concerned themselves generally or partially with the chemistry of iron (342, 552, 688, 814) and ruthenium (800, 803-806, 814) complexes of 2,2 -bipyridine, so these complexes are not discussed further here. In particular, the reader is referred to excellent recent reviews of the photochemical applications of these compounds (41, 43, 44, 176, 194, 443, 624, 625, 877, 954). 

Only with iron has the redox chemistry in the porphyrin series been worked out in more detail than with manganese. It is mainly the groups of M. Calvin and L. J. Boucher who have investigated these metalloporphyrins, and extensive reviews are available from both [Boucher [11), Calvin [22)]. The interest of these complexes lies in the fact that manganese is always found in photosynthetically active plant material and seems to be active in the oxidation of water [Park [138)]. Because of... 

Equilibrium and rate constants for the hydrolysis and chloride complexation of Fe(III) and Fe(II) ions are necessary in a detailed study of iron redox chemistry. Table I lists an internally consistent set of values for the relevant equilibrium constants. Their accuracy is discussed later in the context of a brief sensitivity analysis of the data. The rates of iron hydrolysis and chloride complexation reactions are also mentioned. 

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