Selectivity towards hydrodehalogenation and dehalo-coupling in the reduction of trichloromethyl derivatives with iron(II) chloride
Abstract
The reductive electron transfer (ET) induced on a series of RCCl3 derivatives by iron(II) chloride has been studied. The main reaction products are the homocoupling dimer, RCCl2–CCl2R, and the H/Cl substitution derivative, RCHCl2, and the majority of the compounds examined exhibit a highly selective tendency to form just one of these products. As a general rule, the RCHCl2 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 RCCl2–CCl2R 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, RCClCClR (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 RCCl2–CCl2R assisted by the iron(II) ion.