Electron transfer reactions involving

Electron-Transfer Reactions Involving Transition-Metal Ions... 

SECTION 12.8. ELECTRON-TRANSFER REACTIONS INVOLVING TRANSITION-METAL IONS... 

Electron transfer reactions involving alkali metals are heterogeneous, and for many purposes it is desirable to deal with a homogeneous electron transfer system. It was noticed by Scott39 that sodium and other alkali metals react rapidly with aromatic hydrocarbons like diphenyl, naphthalene, anthracene, etc., giving intensely colored complexes of a 1 to 1 ratio of sodium to hydro-... 

Scheme 36). Interestingly, the higher order cuprate 206 underwent conjugate addition with only moderate selectivity. This is likely due to the intervention of an electron transfer pathway. Competing electron transfer reactions involving a-alkoxymetal reagents of this type have also been reported by Cohen [81]. 

Several of these features remain unexplained but it is clear that here we have an example of a relatively well-behaved reversible electron transfer reaction involving radical intermediates. 

Lafferty, J., Truscott, T.C., and Land, E.J., Electron transfer reactions involving chlorophylls a and b and carotenoids, J. Chem. Soc. Farad. Trans., lA, 2760, 1978. Burri, B.J., Clifford, A.J., and Dixon, Z.R., Beta-carotene depletion and oxidative damage in women, in Natural Antioxidants and Anticarcinogens in Nutrition, Health and Disease, Kumulainen, J.T. and Salonen, J.T., Eds., Royal Society of Chemistry, Stockholm, 1999, 231. 

Schmickler W. 1996. Interfacial Electrochemistry. New York Oxford University Press. Schmickler W, Koper MTM. 1999. Adiabahc electrochemical electron-transfer reactions involving frequency changes of iimer-sphete modes. Electrochem Comm 1 402-405. Schmickler W, Mohr J. 2002. The rate of electrochemical electron-transfer reachons. J Chem Phys 117 2867-2872. 

Outer-sphere electron transfer reactions involving the [Co(NH3)6]3+/2+ couple have been thoroughly studied. A corrected [Co(NH3)6]3+/2+ self-exchange electron transfer rate (8 x 10-6M-1s-1 for the triflate salt) has also been reported,588 which is considerably faster than an earlier report. A variety of [Co(NH3)g]3+/2+ electron transfer cross reactions with simple coordination compounds,589 organic radicals,590,591 metalloproteins,592 and positronium particles (electron/ positron pairs)593 as redox partners have been reported. 

McVie, J., Sinclair, R.S., Tait, D., Truscott, T.G., and Land E.J. 1979. Electron transfer reactions involving porphyrins and carotenoids. J. Chem. Soc. Faraday Trans. 775 2869-2872. 

In aqueous solutions, Cr2+ is a strong reducing agent, and it reduces Co3+ to Co2+. A number of electron transfer reactions involving complexes of these metals have been studied. High-spin complexes of... 

Many of the features of electron transfer reactions involving excited states can be understood based on electron transfer theory. 

Titanium catalysts have long been used in electron transfer reactions involving epoxides, mostly as stoichiometric reagents. Gansauer et al. have developed a catalytic version of these reactions using titanocenes along with zinc metal to generate the active catalyst (Scheme 60). In situ reduction of Ti(IV) with zinc metal provides Ti(III) species 231, which coordinates... 

In this equation g(r) is the equilibrium radial distribution function for a pair of reactants (14), g(r)4irr2dr is the probability that the centers of the pair of reactants are separated by a distance between r and r + dr, and (r) is the (first-order) rate constant for electron transfer at the separation distance r. Intramolecular electron transfer reactions involving "floppy" bridging groups can, of course, also occur over a range of separation distances in this case a different normalizing factor is used. 

In the early 1990s a few classical semimoleculai and molecular models of electron transfer reactions involving bond breaking appeared in the literature. A quantum mechanical treatment of a unified mr el of electrochemical electron and ion transfer reactions involving bond breaking was put forward by Schmickler using Anderson-Newns Hamiltonian formalism (see Section V.2). 

Vanadium(iv) Complexes.—Aqueous electron-transfer reactions involving V as a reductant have been reviewed. 

A values have been obtained for oxidation of benzenediols by [Fe(bipy)(CN)4], including the effect of pH, i.e., of protonation of the iron(III) complex, and the kinetics of [Fe(phen)(CN)4] oxidation of catechol and of 4-butylcatechol reported. Redox potentials of [Fe(bipy)2(CFQ7] and of [Fe(bipy)(CN)4] are available. The self-exchange rate constant for [Fe(phen)2(CN)2] has been estimated from kinetic data for electron transfer reactions involving, inter alios, catechol and hydroquinone as 2.8 2.5 x 10 dm moF s (in dimethyl sulfoxide). 

REDOX HALF-REACTIONS. Electron transfer reactions involve oxidation (or loss of electrons) of one component and reduction (or gain of electrons) by a second component. Therefore, a complete redox reaction can be treated as the sum of two half-reactions such that the stoichiometry and electric charge is balanced across a chemical equilibrium. For each such half-reaction, there is an associated standard potential E°. The hydrogen ion-hydrogen gas couple is ... 

In contrast to metal electrodes, for a semiconductor-electrolyte interface most of the potential drop is located in the semiconductor making it difficult to study interfacial processes using potential perturbation techniques [11,20,55,58,60-65,75-78]. H. Gerischer [76] proposed a model in which electrons and holes are considered as individual interfacial reactants. Distinct and preferential electron transfer reactions involve either the conduction band or valence band as dependent on the nature of the redox reactants of the electrolyte, with specific properties dependent upon the energy state location. 

The d-electron configurations most commonly observed for Mn (IV) through Mn (II) electron-transfer reactions involve Mn (III) in the high-spin state (t2g eg ) ... 

In the course of an extensive study of the mode of action of anionic catalysts, A. G. Evans used exclusively h.v.t. His investigation of the electron-transfer reactions involving 1,1,3,3-tetraphenylbutene-l, tetraphenylethylene and sodium naphthalide is of particular interest here because all the reaction mixtures were prepared by h.v.t. and both UV and ESR spectra were measured (J. E. Bennett et al, 1963). The paper contains full experimental details. 

From this brief description it is quite apparent that the qualitative elements of the Marcus treatment for an electron transfer process are identical to the CM model. In CM terms the reaction involves the avoided crossing of reactant (Fe2+ + Fe3+) with product (Fe3+ + Fe2+) configurations, with the reaction co-ordinate just being the distortion-relaxation motion of the solvation sphere. Thus in CM terms any electron transfer reaction involves the avoided crossing of the DA (donor-acceptor) and D+A" configurations, and for such reactions at least, based on the equivalence with Marcus theory, the CM model has a solid foundation. 

The principal question addressed, is there any kind of chiral recognition in electron transfer reactions involving GO or HRP and enantiomerically pure metal complexes. The chirality of optically active metal complexes may be different. Examples include central carbon chirality, when a complex has a side chain with an asymmetric sp3 carbon (Chart 2A), planar chirality as in the case of asymmetrically 1,2-substituted ferrocenes (Chart 2B,C), and central metal chirality when an octahedral central metal itself generates and enantiomers (Chart 2D) (202). These three types are discussed in this section. 

Light generation in ECL processes is realized in electron transfer reactions involving strong oxidant and reductant. Principally, both reactants can be prepared in the common chemical way if reactive intermediates are stable enough,49-51 but usage of the chemically produced oxidants and/or reductants seems to be quite cumbersome, especially in quantitative works. The electrochemical way appears to be much more practical (in the cases of relatively unstable intermediates) and advantageous (due to... 

Jovanovic SV, Steenken S, Simic MG (1991) Kinetics and energetics of one-electron-transfer reactions involving tryptophan neutral and cation radicals. J Phys Chem 95 684-687 Kagiya T, Kimura R, Komuro C, Sakano K, Nishimoto S (1983) Promotion effect of 2,2,6,6-tetrameth-ylpiperidine-1-oxyls on the radiolytic hydroxylation of thymine in deaerated aqueous solution. Chem Lett 1471-1474... 

Similarly, the back electron transfer reactions involving alkylated pyridinium acceptors are very rapid and no net photochemistry is observed. 

This article is intended to review the published work on the photochemistry and photophysics of osmium complexes that has appeared in the literature over the past several years. We have attempted to cover, albeit somewhat selectively, literature dating back to the year 2000. A variety of reviews pertaining to particular aspects of osmium photophysics and photochemistry were published prior to 2000. A few reviews discuss the photophysical behavior of primarily monometallic Os complexes in solution [1,2]. Several earlier reviews discuss light induced energy and electron transfer reactions involving osmium complexes in much of this work the Os complex is not the chro-mophore [3-6]. Finally, one review exists discussing the photochemistry of Os carbonyl complexes [7]. 

An interesting subset of the inner-sphere electron transfer reactions involves the irreversible formation of a stable metal-02 adduct as the product. A series of such reactions (Figure 9.4) has been investigated by reacting d8 and d10 organometallic complexes with O2.45 These reactions result in the formation of structurally defined side-on peroxide complexes. 

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