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.