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) derivatives by iron(II) chloride has been studied. The main reaction products are the homocoupling dimer, RCCl(2)-CCl(2)R, and the H/Cl substitution derivative, RCHCl(2), and the majority of the compounds examined exhibit a highly selective tendency to form just one of these products. 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 product. 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, RCCl=CClR (E/Z mixture), was observed in the case of the reactions where the homocoupling product was also obtained and is ascribed, on the basis of experimental evidence, to a dehalogenation mechanism of the dimer RCCl(2)-CCl(2)R assisted by the iron(II) ion.