Hydrodehalogenation, transition metal

Hydrodehalogenation - that is, hydrogenolysis of the carbon-halogen bond -involves the displacement of a halogen bound to carbon by a hydrogen atom. This chapter is devoted to dehalogenations mediated by transition-metal complexes (Eq. (1)) ... 

Rocek and coworkers [10] attempted to compare the activity of various transition-metal complexes in the hydrodehalogenation of 5-iodouracil with atmospheric H2 at 70-80 °C. The majority of the examined complexes decomposed to metal, but [(PPh3)2CoCl2], and [(PPh3)3RuCl2] in DMA (N, N-d i me lb yl -act I a-mide) remained homogeneous. The more active Ru complex catalyzed also the preparation of [5-2H]uracil using D2 instead of H2. 

Transition metal complexes such as Fe(CO)5, in the presence of alcohols, cause a trichloromethyl compound to be selectively reduced to the corresponding dichloromethyl compound. This reaction has been reviewed elsewhere and is a very useful means of generating a dihalomethyl group130. Also chromium(II) complexes have been used to reduce aryl bromides131,132. Aromatic compounds such as benzene, aniline and pyridine have been used as hydrogen donors for the hydrodehalogenation of a-haloketones in the presence of tin(II) and iron(II) salts133. 

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