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Redox induced reactions

The application of techniques of pulse radiolysis offers the potential to determine rates of primary radiolysis induced reaction processes. This knowledge can be of great value in the determination of redox processes of Pu ions occurring in a wide variety of aqueous solutions. As a matter of fact, such information is essential to a prediction of the Pu oxidation states to be expected in breached repository scenarios. For an... [Pg.245]

Although the redox reactions in Sch. 12 have not been achieved electrochemically, they illustrate another type of redox-induced structural change in a dimolybdenum compound with a sulfur-rich coordination sphere. In this case, Mo2(/r-S)2 ring opening in 18 (cleavage of Mo—Mo and Mo—S bonds) is associated with the exposure of vacant coordination sites, and the uptake of two carbonyl ligands in 17 [7, 53]. [Pg.576]

The specific phenomenon in this copper-induced reaction is the configuration of the reduced complex which facilitates the oxidation of Cu(I) to Cu(III). The effect of configuration on the redox behavior of a ligand may be important in interpreting metal-induced enzymatic redox reactions. [Pg.139]

There is a wider general interest in understanding the oxidation of cysteine thiolates in proteins since they are involved in redox-sensing reactions [99], Therefore, such oxidation reactions of thiols induced by Ru coordination may also play a more general role in the pharmacological activity of Ru-arene complexes by coupling Ru coordinative binding to redox processes both outside and inside cells. [Pg.35]

Initiation by electrochemical induction may have the disadvantage of low yields of substitution due to the reduction of the radicals formed near the electrode, mainly in those cases in which the radical anion of the halide compound fragments at a considerably high rate. Redox catalysis, that is activation involving a suitable ET mediator, is an important means to avoid termination steps in electrochemically induced reactions. This approach has been extensively studied by the Saveant group15. A general equation has been proposed in order to predict the yield of ET-initiated S l chain reactions and related mechanisms under preparative electrochemical conditions in the presence of a redox mediator35. [Pg.1399]

The electrochemically induced reaction of /j-chlorobenzonitrile with malononitrile anion in liquid ammonia, using 4,4 -bipyridine as a redox mediator, gave the substitution product 172 in 85% yield (equation 1 1 1)204. [Pg.1438]

In view of the demonstrated ease in which the tetrameric cluster cleaves (equation 1) and the redox-induced decomposition of dimeric 5, the integrity of the complexes at the end of the catalytic reaction and the nature of the iron species under a reducing environment are ambiguous. The possibility that mononuclear species are involved in the... [Pg.100]

As with oxidation, the reduction of HNCC can be complicated by redox condensation reactions and by cluster degradation induced by free carbon monoxide. The latter is most commonly observed when reduction is effected... [Pg.174]

Reactions occurring in pristine or polluted waters typically include acid-base (protolysis), electron transfer (redox), electron-sharing, complexa-tion, ligand exchange, and light-induced reactions. The master variables here are normally pH and pE, as defined in Chapter 2. Such reactions are normally responsible for the incorporation, removal, or transformation of ions and compounds in aqueous media these reactions are considered next. Hereafter, we will proceed to a brief discussion of other chemical and physical phenomena mentioned above. [Pg.116]

There are many examples of redox-induced structural rearrangements in organometallic complexes the reader is referred to a review by Connelly. The simplest rearrangement is cis/trans or fac/mer isomerization, usually induced by oxidation. Thus, cw-[Mn(CO)2(dppe)2] slowly converts to the trans isomer with a rate constant of 10 s at room temperature. Upon oxidation, the cis — trans isomerization increases in rate by 7 powers of 10. The process is not catalytic, so that stoichiometric oxidation followed by reduction is required to synthetically utilize the increased reactivity of the radicals in the conversion of 18-electron cis-[Mn(CO)2(dppe)2l to frani-[Mn(CO)2(dppe)2]. An example of oxidatively induced fac mer isomerization is given in Scheme 10. The fac mer reaction for the neutral 18-electron isomer is slow, with 2 = 2 X 10 s , K2 = 4. The reaction fac mer is much faster and... [Pg.205]

Kochi s book from 1978 [la] helped to establish electron-transfer and radical reactions as a crucial part of mainstream organometallic chemistry. The importance of such reactions is evident from Astruc s book [lb], still the most comprehensive and authoritative book in the area, and from several reviews and review collections [2] on aspects of organometallic electron-transfer reactivity. This chapter will be fully devoted to the use of electrochemical techniques to obtain bond-energy data for organometallic complexes, a topic that has not been previously reviewed. Aspects of the energetics of redox-induced structural changes and isomerizations, a thoroughly pursued topic, has been reviewed [2o] and will not be included here. [Pg.1340]

From the previously described electrochemical behavior of the catenane-type complexes [95-97], and assuming some analogous values for the redox couples Cu (4)/ Cu (4) and Cu (5)/Cu (5j, the same type of electron transfer-induced reaction is expected [111]. [Pg.2303]

In summary, coupled reactions can be used in some cases to bring about induced reactions that, taken alone, would be thermodynamically impossible. In many cases, determination of the coupling index affords important clues to the mechanisms of complex redox reactions. [Pg.303]

Metal alkylidyne complexes undergo a variety of oxidation and reduction reactions as well as redox-induced transformations of the alkylidyne ligands. A method for the direct transformation of Fischer-type carbyne complexes into Schrock-type alkylidyne complexes was developed in our laboratory. Bromine oxidation of the /ra/7, -carbyne bromo tetracarbonyl complexes 49 of molybdenum and tungsten in the presence of dimethox-yethane affords the dme-stabilized alkylidyne tribromo metal complexes 50 [Eq. (42)] (81). For alkyl-substituted complexes (R = Me, CH2CMe3)... [Pg.259]

An area which has been little touched on is the influence of cations in promoting redox reactions between anions. There is of course the obvious effect of inducing reactions by generating intermediates in a redox process, and such effects have been the subject of considerable study. But there should also be effects which arise from including both reactants in a complex with the metal ions. In such a case the intermediates would not necessarily be formed as discrete entities. The question at issue is this Do cations act as electron mediators for reactions of anions in the same way that anions serve for cations There is no reason why this should not be the case and, in fact, the work of Ward and Weissman (I3S) on cation influence on the rate of electron transfer between naphthalene and naph-thalenide salts is a beginning in this field. [Pg.49]

Tp NbI(CO)(PhC=CMe)(RC=N) (Scheme 47).621 The assigned formal electron counts on the alkyne and nitrile ligands are compatible with detailed 13C NMR data. Electrochemical studies indicated that an equilibrium existed in solution between the f72(3e)-alkyne/ 72(3e)-nitrile and 72(4e)-alkyne/771(2e)-nitrile complexes.50 PhCN is displaced by PMe2Ph or PhC=CMe to provide Tp Nb(CO)(PhC=CMe)(PMe2Ph) and Tp Nb(CO)(PhC=CMe)2, respectively. Protonation of these species can induce intramolecular redox coupling reactions to produce Nbv metallocycles (e.g., Scheme 47). [Pg.294]

Mam heterogeneous processes such as dissolution of minerals, formation of he solid phase (precipitation, nucleation, crystal growth, and biomineraliza-r.on. redox processes at the solid-water interface (including light-induced reactions), and reductive and oxidative dissolutions are rate-controlled at the surface (and not by transport) (10). Because surfaces can adsorb oxidants and reductants and modify redox intensity, the solid-solution interface can catalyze rumv redox reactions. Surfaces can accelerate many organic reactions such as ester hvdrolysis (11). [Pg.8]


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See also in sourсe #XX -- [ Pg.263 ]




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