Carbon-halogen bonds reductive cleavage

The dynamics of carbon-halogen bond reductive cleavage in alkyl halides was studied by MP3 ab initio calculations, using pseudopotentials for the halogens and semidiffuse functions for the heavy atoms [104], The effect of solvent was treated by means of the ellipsoidal cavity dielectric continuum model. Both a concerted (i.e., a one-step) and a stepwise mechanism (in which an anion radical is formed at first) were... 

Bertran, J., Gallardo, I., Moreno, M. and Saveant, J. M. Dissociative electron transfer. Ab initio study of the carbon-halogen bond reductive cleavage in methyl and perfluoromethyl halides. Role of the solvent, JAm.Chem.Soc., 114 (1992), 9576-9583... 

Isse AA, Gennaro A, Lin CY, Hodgson JL, Coote ML, Guhashvili T. Mechanism of carbon-halogen bond reductive cleavage in activated alkyl halide initiators relevant to living radical polymerization theoretical and experimental study. J Am Chem Soc 2011 133 6254-6264. 

An irreversible reaction of the intermediate of a redox reaction will greatly facilitate redox catalysis by thermodynamic control. A good example is the reduction of the carbon halogen bond where the irreversible reaction is the cleavage of the carbon halogen bond associated, or concerted, with the first electron transfer -pEe... 

Mann and Barnes [45] have discussed the mechanism of reduction of substituted and optically active 1-bromo-and 1-iodocyclopropanes, and Hazard and coworkers [46] have investigated the reduction of l-bromo-l-carboxy-2,2-diphenyl-cyclopropane. At mercury cathodes, electrolyses of 1-bromo- and 1-iodonorbornane proceed via two-electron cleavage of the carbon-halogen bond to give mainly nor-bomane, plus a small amount of bis(l-norbomyl)mercury [47]. 

Apart from the carbon-halogen bond, the carbon-oxygen one is rather active toward the reductive cleavage due to its polarity, so different types of compounds bearing a carbon-oxygen bond are able to undergo this reaction. 

Several research groups ha ve been involved in the study of ET reactions from an electrochemically generated aromatic radical anion to alkyl halides in order to describe the dichotomy between ET and polar substitution (SN2). The mechanism for indirect reduction of alkyl halides by aromatic mediators has been described in several papers. For all aliphatic alkyl halides and most benzylic halides the cleavage of the carbon-halogen bond takes place concertedly with the... 

The reductions of halogenated organic compounds (RX) involve the cleavage of carbon-halogen bonds [62]. Depending on the solvent, supporting electrolyte, electrode material and potential, it is possible to electrogenerate either alkyl radicals (R ) or carbanions (R ), which then can lead to the fonnation of dimers (R-R), alkanes (RH) and olefins [R(-H)] ... 

Because only one stable electroactive product arises from the reduction of /7-chlorobenzonitrile, the interpretation of the cyclic voltammetric behavior is relatively straightforward. The fact that electron attachment to halogen-containing compounds frequently results in the cleavage of the carbon-halogen bond immediately suggests benzonitrile as a possible product. The similarity between the cyclic voltammetric behavior of benzonitrile and that of the p-chlorobenzo-nitrile reduction product supports this prediction (see Fig. 21.1). 

The silver ion assisted carbon-halogen bond cleavage and the unraveling of the cyclopropane ring by the cyclopropyl-allyl rearrangement was first noted in the formation of 2-bromocyclohexen-l-ol from dibromobicyclo[3.l.0]hexane under solvolytic conditions (equation 86).220 The silver ion assisted solvolysis of the dihalocyclopropane adduct (43), derived from a Birch reduction product, smoothly rearranges to the tropone (equation 87).221 A number of other synthetic applications222-226 have beien reported... 

Trichloroethylene (TCE) and perchloroethylene (PCE) require cleavage of the carbon-halogen bonds. Two methods of cleavage are P-elimination by dehy-drohalogenation, as shown in Equation (13.14), and nucleophilic substitution by either water or hydrogenolysis in Equation (13.15). The proposed pathways for reduction of chloroethylenes by zero-valent iron are as follows ... 

Reductive cyclization of a/p/M-bromoacetamides and 3-bromopropanamide to beta-lactams has been performed by electroreduction in the presence or absence of a probase 41). The cyclization seems to involve the reductive cleavage of carbon-halogen bonds generating carbanions which would act as nucleophiles or bases in the electrolysis media. 

Electroreduction of l-(4-fluorophenyl)-5-(2-halogenophenyl)tetrazoles (89), when the halogen substituent is Cl, Br or I, leads to cleavage of the carbon-halogen bond to give a phenyl radical (equation 52). Competition then follows between intramolecular radical substitution giving 7-fluorotetrazolo[l,5-f]phenanthridine (90). Further reduction of the... 

Fedurco, M., Sartoretti, C.J. and Augustynski, J. (2001) Reductive cleavage of the carbon-halogen bond in simple methyl and methylene halides. Reactions of the methyl radical and carbene at the polarized electrode/aqueous solution interface. Langmuir 17, 2380-2387. 

Peters and Sweeny carried out cyclic voltammetry of nickel(ll) salen at a glassy carbon electrode in [BMlMJiBFJ. They found that nickel(ll) salen exhibits one-electron, quasi-reversible reduction to nickel(l) salen, and that the latter species serves as a catalyst for cleavage of carbon-halogen bonds in iodoethane and... 

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