Palladium-catalyzed vinylation of aryl chlorides. Chelate effect in catalysis

By use of the dippb ligand (dippb = 1,4-bis-(diisopropylphosphino)butane) it is possible to effect the synthetically useful Pd-catalyzed direct vinylation of aryl chlorides; the reaction tolerates various substituents and generally results in high yields. The reaction is very sensitive to the nature of the chelating ligand, probably as a result of the need for chelate opening to allow olefin coordination and chelate closure to promote insertion. Monophosphines are ineffective. A mechanistic scheme is presented.