Catalytic Dehalogenation of Aryl Chlorides Mediated by Ruthenium(II) Phosphine Complexes

The catalytic dechlorination of aryl chlorides performed by RuHCl(H2)2(PCy3)2 and RuH2(H2)2(PCy3)2 in alcohols is rapid and complete within 1 h. The mechanism involves a transfer hydrogenation step with participation of the alcohol. The system exhibits significant functional group tolerance. The catalyst can be generated in situ from [RuCl2(COD)]x (COD = cyclooctadiene) and 2 equiv of phosphine (PCy3 or PiPr3). Catalytic conversions are similar to those observed when an isolated precatalyst is used. Mechanistic considerations and the scope of the process are discussed.