Electroreductive coupling of organic

The complex [Ni(bpy)2]2+ catalyzes the electroreductive coupling of organic halides and carbon monoxide into ketones under a CO atmosphere,226 or in the presence of a metal carbonyl,227 especially iron pentacarbonyl. Unsymmetrical ketones have been obtained from mixtures of two different organic halides.228 CO is very reactive towards reduced Ni° species to form the stable [Ni°(bpy)(CO)2]° complex, which probably evolves to a transient arylnickel [Nin(bpy)(R)(CO)X]° complex in the presence of both ArX and [Ni°(bpy)]° species.229,230... 

Tab. 15 Electroreductive coupling of organic halides by using Ni complexes as mediators [268]... 

The electroreductive coupling of organic dihalides is an interesting approach to synthesize polymers. 

In some cases, a small amount of cosolvent such as DM F was added to attain good conductivity. For example, the Ni-catalyzed electroreductive coupling of organic halides with activated olefins was carried out in [omin][BF4] (omin-l-octyl-3-methy-limidazolium) using DMF as a cosolvent (Equation 12.5) [12]. 

Electroreductive coupling of ketones with silyl-substituted olefins promotes interesting reactions that are useful for organic synthesis. For example, coupKng of ketones with trimethylvinylsilanes affords /I-trimethylsilyl alcohols, which are easily transformed to the corresponding olefins (Scheme 40). This reaction is interesting from the synthetic point of view since vinylsilane behaves as the equivalent to a /I-trimethylsilyl group-substituted anion [77, 83]. 

It is about 20 years since the combination of transition-metal catalysis and electroreduction was shown to be applicable to the coupling of organic molecules. This was followed by a number of fundamental investigations and basic syntheses using various nickel, cobalt, or pdladium compounds which can easily be reduced in situ electrochemically to low-valent reactive intermediates. The last decade has been less characterized by reports on new catalytic systems than by the development of new synthetic applications. The aim of this review is to show that the electrochemical processes described here offer valuable advantages in organic synthesis. 

Barhdadi, R., Courtinard, C., Nedelec, J.-Y. and Troupel, M. (2003) Room-temperature ionic liquids as new solvents for organic electrosynthesis. The first examples of direct or nickel-catalyzed electroreductive coupling involving organic halides. Chem. Commun. (Cambridge) 12, 1434-1435. 

The reduction of organic halides is of practical importance for the treatment of effluents containing toxic organic halides and also for valuable synthetic applications. Direct electroreduction of alkyl and aryl halides is a kinetically slow process that requires high overpotentials. Their electrochemical activation is best achieved by use of electrochemically generated low-valent transition metal catalysts. Electrocatalytic coupling reactions of organic halides were reviewed in 1997.202... 

Organic Electroreductive Coupling Reactions using Transition Metal Complexes as Catalysts Table 2. Reductive electropolymerisation of aryl dihalides using nickel catalysts... 

Apart from the electrocarbonylation reactions of organic halides described in Sect. 6, other Ni-catalyzed reactions leading to ketones have been reported. Thus the electroreductive coupling between acylchlorides and alkyl halides, catalyzed by NiBr2bpy leads to unsymmetrical ketones [129]. Recently acylchlorides have been converted to symmetrical ketones in an undivided cell fitted with a nickel or stainless steel anode. In this reaction the active metallic species... 

N d lec J-Y,P richon J,Troupel M (1997) Organic Electroreductive Coupling Reactions Using Transition Metal Complexes as Catalysts. 185 141-174 Nicotra F (1997) Synthesis of C-Glycosides of Biological Interest. 187 55-83 Nishimura J,see Inokuma S (1994) 172 87-118 Nolte RJM,see Sijbesma RP (1995) 175 25-56 Nordahl A,see Carlson R (1993) 166 1-64... 

Baizer and Chruma reported electrolytic reductive coupling, in a broad study in which reduction of organic halides was conducted in the presence of electrophiles as seen in equation 1034. Controlled potential electroreduction of reactive halides at a mercury cathode in the presence of olefinic substrates with electron-withdrawing groups (Michael receptors) gave moderate yields (50-75% in many cases) of carbanion addition products35. Current yields in excess of 100% in the case where chloroform was used as a cosolvent with carbon tetrachloride indicated the intervention of electrocatalytic reactions (equations 10 and 11). 

We have now succeeded in the development of two new methods for the preparation of organofunctional silanes, both involving electroreductive coupling. The first synthesis concept comprises the anionic cleavage of electrochemically formed disilanes and subsequent reaction with organic halides, whereas the second even more general route involves the direct electrochemical Si-C bond formation. 

Nickel-catalyzed electroreductive homocoupling reaction of organic hahdes and coupling reaction between organic halide and activated olefins could be carried out with iron anode in ionic liquid. With addition of small amount of DMF, coupling compounds were obtained at room temperature in good to high... 

Shono et al. [7] and Yoshida et al. [8] showed in the early 1980s that electroreductive cross coupling is possible in a divided cell with Pt anodes, but no defined anodic oxidation products w reported. In contrast to this, Bordeau et al. electrolyzed different organic substrates with Me2SiCl2 in an undivided cell with sacrificial anodes, thus yielding MgCh as by-product [9]. However, to maintain one of the chloro substituents on the silicon a lai e excess of chlorosilane and the use of an Ni catalyst is unavoidable. Furthermore, HMPA was used as co-solvent. 

Again the dimerization or coupling reactions will involve free radicals or radical ions, but the intermediates are generated cathodically. Suitable substrates are electrophiles such as activated olefins and carbonyl compounds. In this section, it is intended to focus only upon the electroreduction of activated olefins, partly because the electrode reactions of aldehydes and ketones has been discussed earlier. However, it is the electrohydrodimerization of an activated olefin that has become a successful, commercial electro-organic process, i.e., the electroreduction of acrylonitrile developed by Monsanto ... 

The combination of EK and electrooxidation (EK-EO) was developed by Wang et al. [42]. In this coupled process, electrooxidation on the anode surface and the EK process of anionic impurities under the electric field occur and, as a consequence, an enhancement of the organic pollutant is removed in the electrolysis process. The authors suggested that both electrooxidation-electroreduction and electromigration pathways coexisted in EK-EO process. 

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