SELECTIVITY TOWARDS HYDRODEHALOGENATION AND DEHALO-COUPLING IN THE REDUCTION OF TRICHLOROMETHYL DERIVATIVES WITH IRON(II) CHLORIDE

The reductive electron transfer (ET) induced on a series of RCCl(3) de rivatives by iron(II) chloride has been studied. The main reaction pro ducts are the homocoupling dimer, RCCl(2)-CCl(2)R, and the H/Cl substi tution derivative, RCHCl(2), and the majority of the compounds examine d exhibit a highly selective tendency to form just one of these produc ts. As a general rule, the RCHCl(2) compound is the main product when the R group contains substituents which,make further reduction of the radical to the carbanion easier and behave as ligands towards the iron (II) ion. In the other cases, the dimer RCCl(2)-CCl(2)R is the main pr oduct. A few exceptions are found, and these are discussed in view of the possible effects of the R moiety on the different possible routes for the reaction products. The presence of unsaturated derivatives, RC Cl=CClR (E/Z mixture), was observed in the case of the reactions where the homocoupling product was also obtained and is ascribed, on the ba sis of experimental evidence, to a dehalogenation mechanism of the dim er RCCl(2)-CCl(2)R assisted by the iron(II) ion.