Organic halides, hydrogenolysis

Hydrogenolysis of organic halides is another general reaction performed by nickel complexes (examples 11 and 12, Table VIII). 

The air-sensitive Cp-substituted hydridovanadium complex is obtained by hydrogenolysis of the corresponding methyl derivative. The corresponding anionic compound is obtained by reduction of CpV(CO)4 with sodium and protonation with water (Scheme 64). Thus obtained [CpVH(CO)3] (106) is a useful one-electron reductant to reduce bromo- and iodoalkanes, bromoalkenes, and arylbromides in THF. Furthermore, acid chlorides are reduced to the aldehydes. A similar reduction with (106) is performed by using phase-transfer conditions in the presence of tetrabutylammonium hydrogen sulfate. Nitro compounds and organic halides are reduced under these conditions. 

In 1980, Finder presented an excellent review dealing with the hydrogenolysis of organic halides. Many other reviews are also available, although they are not devoted to reductive dehalogenation but deal with it as part of the broader topic of reduction. 

Organic halides are known to be subject to hydrogenolysis in the presence of a catalyst, such as Pd/C or Raney nickel. This catalytic hydrogenolysis is one of the more convenient ways of removing halogens under mild conditions and numerous examples have been reported. Several reviews dealing with this subject have been published. 

Hydrodechlorination. With binary Co(OAc)2-PdClj supported on poly(A-vinyl-2-pyrroIidinone) as catalyst, hydrogenolysis of organic halides proceeds quantitatively. 

Hydrogenolysis of the C-halogen bond is an important reaction both from preparative and from environmental points of view. [ HCo(CN)5]3 was studied in detail as a catalyst for reductive dehalogenations of organic halides, which proceed according to Eqs. (38) and (39). The results of the early experiments are summarized in [12]. 

Hydrogenolysis of the carbon-halogen bond is an important reaction, both from synthetic and from environmental points of view. The results of the early experiments with [HCo(CN)5] as catalyst are summarized in Ref [4], A variety of organic halides could be effectively dehalogenated with aqueous sodium formate with [PdCl2L2] (L= various sulfonated phosphines) [57], [RuCl2(TPPMS)2]2 and [Ru(H20)3(PTA)3] + [63], and [Ir(bipy)(Cp )(H20)] [64] catalysts. 

Hydrogenolysis can be a useful method to destroy organic halide wastes (128). This reaction is not very efficient with homogeneous catalysts and H2. However, carbon tetrachloride, chloroform, benzyl chloride, and several 1-he l halo-genides were effectively dehalogenated (129) by hydrogen transfer from aqueous Na-formate catalyzed by [RuCl2(TPPMS)2]2 at 80°C (Scheme 12). Initial turnover frequencies up to 1000 h were observed, but the catalyst stability still has to be improved. 

Hydrogenolysis. In the removal of halogen from an organic molecule by hydro-genolysis, the hydrogen halide formed poisons the catalyst unless neutralized. Reinecke25 found that triethylamine can be used and is sometimes superior to sodium... 

Halides are common components of organic molecules, and in many cases they must be removed. One way to do this is reduction to the corresponding hydrocarbon by hydrogenolysis. A nickel catalyst (usually... 

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