Monoelectronic reduction

The base catalysis and the monoelectronic reductive activation processes have been described by a computational investigation at the R(U)B3LYP/6-31 + G(d,p) level of theory for the model imide NI (Scheme 2.14) 47 both in the gas phase and in aqueous solution, using PCM solvation model.40... 

Dendrimers Terminated with Cobaltocenium and Ferrocene-Cobaltocenium Units Like ferrocene, cobaltocenium is an excellent organometallic moiety to incorporate in or functionalize dendritic systems. As already discussed, it is indeed isoelectronic with ferrocene, highly stable, positively charged complex, which undergoes a reversible monoelectronic reduction to yield the neutral cobaltocene. 

Other Monometallofullerenes Eu C74 and Tm C78 Dunsch et al. performed the electrochemistry of Eu C7455 and Tm C7856 in a glove box under inert conditions. Based on Raman measurements and the absence of an ESR signal, it was concluded that the formal oxidation number of the metal is +2 in Eu C74. Interestingly, in addition to four reversible and monoelectronic reduction steps, two anodic events were also observed, contrary to all the other metallofullerenes with divalent metals described previously (Fig. 8.5). Therefore, Eu C74 has a significantly... 

Figure 13.27 Dual-pathway square scheme mechanism that accounts for the rearrangements induced by the monoelectronic reduction of deprotonated rotaxane 92+. The species A and C represent the stable structure of the deprotonated rotaxane and its monoreduced form, respectively, whereas and D are metastable intermediates. Note that the exact position of the macrocycle along the axle in the reduced forms and C is not known. From a simple digital simulation of the cyclic voltammetric patterns, the following values have been obtained = - 0.59V, E°dc = - 0.34V, /cAD 0.15S- da<2.5s kBC > 100 s and kCB 1 s V...

Lateral macrobicycles are dissymmetric by design thus, monoelectronic reduction of the Cu(ll) ion bound to the [12]-N2S2 macrocyclic subunit in the bis-Cu(ll) cryptate 45, gives a mixed valence Cu(i)-Cu(ll) complex [4.6]. Macrotricycle 46 forms a dinuclear Cu(ll) cryptate that acts as a dielectronic receptor and exchanges two electrons in a single electrochemical wave [4.7]. Complexes of type 47 combine a redox centre and a Lewis acid centre for the potential activation of a bound substrate [4.8]. 

The voltammograms of ETRPyP exhibit reversible waves at Ey2 = 1.00 and —0.65 V in DMF solution, which were assigned to the Ru(III/II) redox pair and to the monoelectronic reduction of the porphyrin ring to the 7t-radical anion, respectively, and a shoulder at = — 1.04 V attributed to the formation of the respective porphyrin dianion (Fig. 38). The monoelectronic reduction of a 5-Clphen ligand on each peripheral ruthenium complex occurs at E = — 1.11 V. Its anodic wave is broad, more intense, and shifted to positive potentials because of the overlap with the anodic wave corresponding to the reoxidation of the porphyrin dianion. 

The quaternary salts of A -heterocycles are readily reduced and often give reversible one-electron reduction waves, as, for example, with pyridium salts [122]. Dimers have been obtained by this pathway e.g. from acridizinium and benzothiazolium salts [116]. Such processes are particularly important both with biological substrates (e.g. NAD is reported to give essentially 4,4 -dimers on reduction) [123] and in the monoelectronic reduction of di-cations such as dipyridinium and a variety of diaza polycyclic aromatic di-cations [124]. 

In the case of the phen complex, reduction of the monovalent state leads to copper metal, the initial electron transfer occurring either in the Cu 4s orbital or via a phen n orbital. Fast dissociation follows this monoelectronic reduction step. The redox orbitals involved during the reduction process of the copper catenate are likely to be ligand-localized. This is also supported by the small difference between the redox potentials of the Cu+ / and Cu°/ couples (A i/2 200 mV). Electrolysis of Cu.5+ in the cavity of an EPR spectrometer confirms the radical anion nature of the formally copper(O) complex obtained by one-electron reduction of the catenate g = 2.000 + 0.002, Ai/ = 39 G. 

In the H. anomala enzyme the monoelectronic reduction potentials for the FMN (F) group are altered in the presence of pyruvate (58, 59, 71) to such an extent that the value for Fox/Fsq lies above that of the heme (Table I). This effectively means that flavosemiquinone heme... 

As it is well known, nucleophilic substitution of a C-X bond, one of the key synthetic reactions with aliphatic compounds is severely limited with aromatic derivatives, where it occurs thermally only with electron-withdrawing substituted compounds and/or under severe conditions. Alternatives include time honored reactions involving the phenyl radical generated by decomposition of diazonium salts after a reductive step, such as the Meerwein and the Gomberg-Bachmann reactions, as well as the (often photoinitiated) SrnI reaction, where a (usually weak, e.g. carbon-iodine) bond is cleaved after monoelectronic reduction to give an aryl radical as the active inter-mediate that adds to an enolate, cyanide or other nucleophiles (and thus again with an aryl radical as the key intermediate. Scheme S). ... 

The monoelectronic reduction of the poly anion, also observed by P NMR in the case of the dodecaphosphomolybdate, suggests the intermediate formation of a radical cation [R3P=C(R,)R2] + which further evolves to the phosphonium cation by hydrogen... 

Reduction processes of the bis-phosphinine 49 was thoroughly investigated by a combination of EPR spectroscopy and DFT calculations. It was shown that the monoelectronic reduction of 49 with sodium naphthalenide at low temperature affords the corresponding radical anion 54 in which the odd electron is localized in a one-electron P-P bond 2.763 vs 3.256 A in the neutral molecule) [37], DFT calculations suggest that formation of this bond results from the in-phase combinations of the LUMOs of phosphinine which exhibit a large coefficient at phosphorus (7T orbital) (Scheme 11). Unfortunately, anion radical 54 could not be crystallized but the X-ray crystal structure of the corresponding dianionic species was recorded. 

Scheme 19 a Electrochemical monoelectronic reduction, b Electrochemical monoelectronic oxidation... 

The presence of this ligand most likely occurs through monoelectronic reduction of pyridine by Tm" followed by coupling of the resulting radical anion at the 4,4 -position (Fedushkin et al., 2003). 

The reduction of platinum(IV) complexes can be carried out with outer-sphere as well as inner-sphere monoelectronic reductants. A possible first example of this outer-sphere pathway is in the reduction of platinum(IV) complexes by Cr(bipy)3 Other examples are the reduction of fro/ts-PtX4(amine)2 (X = Cl, Br) by ferrocyanide, ° ° of trans-PiX l (X = Cl, Br L = neutral ligands) by ferroceneof PtCl by of PtCl2(pn)2 by of... 

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