Irreversible reduction/oxidation

Using higher frequencies (of the 10 Hz-order) it is possible to supress the irreversible reduction/oxidation waves (e.g., the reduction wave of ions and thus allowing other ions, as Ca to be determined). In the same way the reduction wave of dissolved oxygen may be supressed... 

The 1,4,7-trithiacyclononane ligand, [9]aneS3, zinc complex was synthesized to compare with the electrochemistry of related complexes and showed an irreversible oxidation and an irreversible reduction at +1.30 V and —1.77 V vs. ferrocene/ferrocenium, and the X-ray crystal structure of the bis macrocycle zinc complex was reported.5 0,720... 

At 2 V the eel was very weak. Upon addition of equimolar amounts of THPO the eel intensity increased by a factor of 3. The hydroperoxide which is known to undergo an irreversible reduction at E1/2 = °-73 v vs SCE (52) is apparently reduced during the cathodic cycle while the complex is oxidized during the anodic... 

Herrmann and coworkers183 reported a series of Cp-manganese carbonyl complexes which bind Ge, Sn and Pb as central atoms linearly coordinated in clusters, to two Mn atoms in one series and trigonal-planar coordinated to three Mn atoms in another series 8 and 9. The group 14 atoms are double-bonded to two Mn atoms in these compounds, or carry one double bond and two single bonds to three Mn atoms. Potentiometric measurements of these compounds show irreversible reductions and oxidation by CV. No products could be isolated from either reduction or oxidation. The exceptionally high oxidation potential of (/i-Pb) r/ -CsHs )Mn(CO)2]2 as compared to the apparently similar Sn compound is noteworthy (Table 15). 

As illustrated in Figure 65, such a complex undergoes a chemically reversible Fen/Fem oxidation (in the long times of macro electrolysis the original blue solution turns red) and an irreversible reduction. As we will discuss in Chapter 6, Section 5, this latter process is probably ligand-centred. 

In fact, the latter displays a first (one-electron) reversible reduction followed by a second irreversible reduction that in turn shows, on the reverse scan, the oxidation peak of the Rh(I)-dimethylfumarate complex, Figure 21b. The complete interconversion process is illustrated in Scheme 10. 

The results actually showed a deracemization of the racemic hydroxyester 10 as opposed to enantioselective hydrolysis with formation of optically pure (R)-hydroxyester 10 and only 20 % loss in mass balance. Small quantities of ethyl 3-oxobutanoate 9 (<5%) were also detected throughout the reaction, leading the authors to suggest a multiple oxidation-reduction system with one dehydrogenase enzyme (DH-2) catalysing the irreversible reduction to the (R)-hydroxy-ester (Scheme 5). 

The diyne complexes Co2(/u.-fj -RC2C=CR)(CO)6 (R = Ph, Fc) give irreversible reduction waves even at 213 K which indicates that fast chemical reactions follow the electrochemical production of the corresponding radical anions [Co2(jU-)j -RC2C=CR)(C0)6]. The ESR spectra of the anion radical generated in situ were not consistent with the presence of two different Co centers. In the case of the ferrocenyl-substituted complex, two distinct oxidation waves separated by 70 mV are observed, which indicates a modest degree of interaction between the Fc cores through the cluster. 

Cyclic voltammetry of [Os(N)(Tp)(X)(Y)] (X, Y = Ph, Cl) shows a quasi-reversible or irreversible oxidation wave and an irreversible reduction wave. The potentials of the couples... 

Other electrochemically characterized organometallic V(IV) complexes are rare. The thiolate bridged [Cp(CO)2V(/o,-SR)2V(CO)2Cp] (R = Me, Ft, Ph) have reversible reduction processes that range from —1.89 to —2.01 V versus Cp2Fe/THF in addition to two other irreversible reduction processes at more negative potentials. For R = Me, an oxidation at —0.20 V versus Cp2Fe/THF is reported. Reductive bulk electrolysis results in the decomposition of [Cp CO)2V(fi-SMe)2V(CO)2Cp] by loss of SMe [62]. 

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