First application of secondary phosphines, as supporting ligands for the palladium-catalyzed Heck reaction: Efficient activation of aryl chlorides

Secondary dialkylphosphines were successfully used for the first time as efficient supporting ligands for the palladium-catalyzed Heck reaction of electron-rich and electron-poor aryl chlorides with olefins such as acrylate, ethylene, styrene, and n-butyl vinyl ether. The yields with HP(t-butyl)(2) and HP(adamantyl)(2) were comparable or better than those obtained with known systems of tertiary phosphines such as P(cyclohexyl)(3) and P(t-butyl)(3), especially at a catalyst loading of <1 mol %. In comparison with tertiary phosphines, the secondary phosphines have the advantage of being readily available at low cost on a technical scale, and are comparable with respect to handling and oxygen sensitivity.