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Dioxygen outer-sphere electron transfer

Contrast in Outer-Sphere Electron-Transfer Reactivity of Dioxygen Complexes-... [Pg.423]

While the hemochromes are substitutionally labile, their autoxidation ultimately producing p-oxo complexes of the type [Fe2(P)2]0 accompanied with the loss of the nitrogen donor axial ligands, the ruthenochromes and osmo-chromes are stable. Autoxidation occurs in an outer-sphere electron transfer, e.g. from Os(II) to a dioxygen molecule, see Sect. 3.22. [Pg.26]

Aromatic and aliphatic thioles RSH (R = 2-, 3-, or 4-tolyl, 2-hydroxyethyl, 2-ethoxyethyl, 4-chlorphenyl, etc.) in the presence of a base yield anionic dithiolatorhodium(III) porphyrins (path j) which show the so-called hyperporphyrin spectra and are susceptible to autoxidation yielding hyperoxide ions. Although the formation of the latter ones is formulated via a nucleophilic exchange of coordinated OJ with thiolate, it could well be that an outer-sphere electron transfer between he anionic bis(thiolato) complex and molecular dioxygen initiates the observed formation of disulfides RSSR. [Pg.37]

One-electron dioxygen reduction may also occur via an outer-sphere electron transfer, affording a noncoordinated superoxide and a one-electron oxidized metal complex. Essentially, all low-valent 3d transition metal ions and numerous 4d and 5d metal ions can react as one-electron reducing agents. [Pg.114]

Coordinatively saturated metal complexes that are kinetically inert with respect to ligand substitution may undergo outer-sphere electron transfer reactions with dioxygen. Typical examples include oxidations of six-coordinate chromium(II) complexes29 (Equation 4.6) and oxidations of polyoxometallate anions.30... [Pg.121]

The nonheme diiron centers in proteins and model complexes with 0,N-donors can reach a number of oxidation states spanning from FenFen to FeIVFeIV The diiron(II) state is reactive with dioxygen yielding different products depending on the nature of ligands and reaction conditions (Figure 4.21). Outer-sphere electron transfer may occur for coordinatively saturated and sterically impeded complexes with sufficiently low redox potential.17... [Pg.147]

Fig. 55. Reaction scheme of superoxide dismutation following the bovine enzyme numbering. The first O2 molecule binds to Cu(II) and is stabilized by the H bond to Arg-141. A second superoxide molecule then approaches the active site and, by an outer-sphere electron transfer via the Cu-bound first O2 molecule, reduces the copper to Cud) 44) (step III). Alternatively, O2" directly reduces superoxide to peroxide 336) (step IV), leaving as dioxygen. Note that the Cu(I)-superoxide and Cu(II)-peroxide complexes are resonant forms of the same molecular arrangement. The newly formed peroxide is protonated by Arg-141 and leaves as HO2. Arg-141 receives a proton from the solvent, restoring the active enz5Tne (I). These reaction proposals do not require the breaking and reforming of the Cu-His-61 bridge. Fig. 55. Reaction scheme of superoxide dismutation following the bovine enzyme numbering. The first O2 molecule binds to Cu(II) and is stabilized by the H bond to Arg-141. A second superoxide molecule then approaches the active site and, by an outer-sphere electron transfer via the Cu-bound first O2 molecule, reduces the copper to Cud) 44) (step III). Alternatively, O2" directly reduces superoxide to peroxide 336) (step IV), leaving as dioxygen. Note that the Cu(I)-superoxide and Cu(II)-peroxide complexes are resonant forms of the same molecular arrangement. The newly formed peroxide is protonated by Arg-141 and leaves as HO2. Arg-141 receives a proton from the solvent, restoring the active enz5Tne (I). These reaction proposals do not require the breaking and reforming of the Cu-His-61 bridge.
Ruthenium porphyrins represent an additional possibility, viz. outer-sphere electron transfer to dioxygen, followed by phosphine oxidation by the produced ... [Pg.368]

Electron Transfer Reactions. The reactions in which the oxidation state of the metal dioxygen system is changed may be discussed either in terms of outer or inner sphere electron transfer or as abstraction reactions. [Pg.35]

Reaction (2) is an outer-sphere exothermic process (AE° is about —0.4 V) and therefore, the equilibrium of this reaction is completely shifted to the right, i.e., the reoxidation of reduced cytochrome c by dioxygen is impossible. However, the rate constant for Reaction (2) (2.6 + O.lxlO5 1 moR1 s 1) is unexpectedly low for the exothermic one-electron transfer... [Pg.961]

However, benzil [PhC(O)C(O)Ph] cannot enolize and is dioxygenated by Oz - to give two benzoate ions. Scheme 7-11 outlines a proposed mechanism that is initiated by nucleophilic attack. An alternative pathway has been proposed i in which the initial step is electron transfer from 02 - to the carbonyl, followed by coupling of the benzil radical with dioxygen to give the cyclic dioxetanelike intermediate. However, the outer-sphere reduction potential for electron transfer from O2 to a carbonyl carbon is insufficient (-0.60 V versus NHE, Chapter 2). [Pg.173]

The electron self-exchange rate constants for several Fe(II)/Fe(III) porphyrin couples have been measured by H NMR line-broadening techniques in 5 1 acetone/water at -20 The relative rate constants for the [Fe(P)(l-MeIm)2] couples, P = octaethylporphyrin chlorin < isobacteriochlorin, have been attributed to differences in outer-sphere reorganization, related to the steric bulk. The rate-determining step in the metallopophyrin-catalyzed reductions of dioxygen by substituted ferrocenes is the electron transfer between the ferrocene and the metalloporphyrin (M = Fe, Co, and The Marcus relationship provides a... [Pg.19]


See other pages where Dioxygen outer-sphere electron transfer is mentioned: [Pg.422]    [Pg.19]    [Pg.683]    [Pg.223]    [Pg.35]    [Pg.48]    [Pg.2135]    [Pg.952]    [Pg.364]    [Pg.434]    [Pg.291]    [Pg.4154]    [Pg.77]    [Pg.21]    [Pg.634]    [Pg.330]    [Pg.104]    [Pg.35]    [Pg.216]    [Pg.111]    [Pg.240]    [Pg.329]    [Pg.337]    [Pg.105]    [Pg.197]    [Pg.207]    [Pg.225]    [Pg.75]   


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