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

The reactivity of Fe⁰ toward chlorinated ethylenes was examined utilizing a photochemically generated, highly reactive Fe⁰ complex. Irradiation of (dmpe)₂FeH₂ (dmpe = Me₂PCH ₂CH₂PMe₂) with 360 nm light generated a 16-e^-, Fe⁰ 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 CH₂CHCl < cis-CHClCHCl < trans-CHClCHCl < CCl₂CHCl. 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.