Reactions of Carbon-Halogen Bonds

Klabunde has reported limited reactivity toward oxidative addition reactions of carbon halogen bonds with nickel slurries prepared by the metal vaporization technique(65). 

Reactions at a Group Vill Metai Center The Ni, Pd, Pt Triad 10.3.8.5. Reactions of Carbon-Halogen Bonds... 

The cleavage reaction of carbon-halogen bond is one of the most well studied reactions from the early stage of development of organometallic chemistry. For... 

The last example represents a fairly rare elimination of hydrogen fluoride in preference to hydrogen chloride, a reaction that deserves a more detailed discussion A comparison of bond dissociation energies of carbon-halogen bonds shows that the carbon-fluorine bond is much stronger than the carbon-chlorine, carbon-bromine, and carbon-iodme bonds 108-116, 83 5, 70, and 56 kcal/mol, respec-... 

Significantly, the pre-exponential factors decrease with increasing reactivity, and this suggests that the Wheland intermediate is more nearly formed in the transition state, the more reactive the compound. Or, considered another way, the position along the reaction co-ordinate at which a given amount of carbon-halogen bond formation occurs is nearer to the ground state the more reactive the compound. 

The iron slurries show exceptional reactivity toward oxidative addition reactions with carbon halogen bonds. In fact, the reaction with C.FcI is so exothermic that the slurry has to be cooled to 0 °C before the addition of C F L The reaction of iron with C F Br is also quite exothermic, hence, even for this addition, the iron slurry is cooled to about 0 ° C. The organoiron compound formed in the above reactions, solvated Fe(C.F )2, reacts with CO at room temperature and ambient pressure to yiela Fe(C,F3)2(CO)2(DMEL. 

The polarity of carbon-halogen bond of alkyl halides is responsible for their nucleophilic substitution, elimination and their reaction with metal atoms to form organometallic compounds. Nucleophilic substitution reactions are categorised into and on the basis of their kinetic properties. Chirality has a profound role in understanding the reaction mechanisms of Sj l and Sj 2 reactions. Sj 2 reactions of chiral all l halides are characterised by the inversion of configuration while Sj l reactions are characterised by racemisation. 

Cook, M. A. Eabom, C. Walton, D. R. M. Organosilicon compounds XLVIII. Effects of a-trimethylsilyl groups on rates of reaction at carbon-halogen bonds./. Organomet. Chem. 1971, 29, 389-396. 

S. Torii, T. Inokuchi, Addition Reactions with Formation of Carbon-Halogen Bonds, in Comprehensive Organic Synthesis (B. M. Trost, I. Fleming, Eds.), Vol. 7, 527, Pergamon Press, Oxford, 1991. 

The reactivities of several azanaphthalene anion-radicals, alter polaro-graphic generation, are discussed by van der Meer.122,123 This includes the radicals of quinazoline and cinnoline whose ESR spectra do not appear to have been reported. The stability of carbon-halogen bonds in various azine anion-radicals, including quinoxaline and quinoline, has been discussed, as has the reactivity of quinoline anions toward alkyl halides.92,182 In the latter reaction alkylation occurs at the 1,2- and 2,4-positions. Heteroarylation of a range of electron-rich substrates by azine anion-radicals has been reported.183 No mechanism is implied in the available abstract, but the apparent electrophilicity on the part of the azine anions is surprising. 

Addition Reactions with Formation of Carbon-Halogen Bonds... 

Reduction of carbon-halogen bond by metal yields carbanion. Reaction of alkyl halide with Mg in the presence of anhydrous ether as solvent generates Grignard reagent. The Grignard reagent behaves like a carbanion. Alkyllithiums are also obtained from alkyl halides and behave as carbanions. 

The overall reaction results in the reduction of carbon-halogen bonds to carbon- hydrogen bonds. 

Another important homolytic reaction of tin hydrides is the reduction of carbon-halogen bonds the reaction is promoted by initiators and retarded by radical traps (Scheme 13). Reactivity decreases in the sequence X = I > Br > Cl and BusSnH > Bu2SnH2 Ph3SiiH > BuSnH3. Other groups X in RX that can be reduced by tin hydrides include -OC(S)R, SR, SePh, TePh, NC, and NO2. The intermediate radical, R in Scheme 13, can be trapped by additional substances, e.g. alkenes, or may undergo... 

Addition Reactions with Formation of Carbon-Halogen Bonds Table 1 Halogenation of Enol Ethers and Esters with Metallic Reagents... 

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