Catalytic dehalogenation of aryl chlorides mediated by ruthenium(II) phosphine complexes

The catalytic dechlorination of aryl chlorides performed by RuHCl(H-2)(2)(PCy3)(2) and RuH2(H-2)(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 (PPr3)-Pr-i). Catalytic conversions are similar to those observed when an isolated precatalyst is used. Mechanistic considerations and the scope of the process are discussed.