Dechlorination of chlorinated ethylenes by a photochemically generated iron(0) complex.

The reactivity of Fe(0) toward chlorinated ethylenes was examined utilizing a photochemically generated, highly reactive Fe(0) complex. Irradiation of (dmpe)2FeH2 (dmpe = Me2PCH2CH2PMe2) with 360 nm light generated a 16-e(-), Fe(0) intermediate that reacted to dechlorinate chlorinated ethylenes in a stepwise fashion, consistent with a hydrogenolysis dechlorination pathway. The source of the hydrogen atoms in the hydrogenolysis were the hydride ligands of an additional equivalent of (dmpe)2FeH2, as evidenced by deuterium labeling experiments. The reaction was observed to be first-order in (dmpe)2FeH2, chlorinated ethylene substrate, and the intensity of 360 nm radiation. The rate of chlorinated ethylene substrate decay increased with increasing substrate chlorination in the order CH2=CHCl < cis-CHCl=CHCl < trans-CHCl=CHCl < CCl2=CHCl. A mechanism of reaction was proposed that accounts for the reaction kinetics, the observed intermediates, and the origin of hydrogen atoms incorporated into reaction products.