Palladium/Phosphinated Polystyrene as a Catalyst in the Heck Arylation. A Comparative Study

Article abstract of DOI:10.1021/jo00220a041

Palladium anchored to phosphinated polystyrene with a Pd/P ratio of 1/1 gives very high activity in the arylation of methyl acrylate and styrene with iodobenzene.A comparative study shows that this catalyst is considerably more efficient than Pd/C, Pd(OAc)2, PdCl2, Pd(OAc)2/2PPh3, or Pd(PPh3)4.ESCA and X-ray studies have been used to determine that the active state of the catalyst is metallic palladium.This is further supported by a study of the product distribution of two reactions that are very sensitive to the type of catalyst employed, namely, the arylation of butyl vinyl ether and trimethylallylsilane, as well as by the fact that iodo- but not bromobenzene reacts with this catalyst.The polymer-bound catalyst with a Pd/P ratio of 1/5 was unable to bring about any arylation starting from iodobenzene, after 3 h.During the same time the catalyst with a ratio Pd/P of 1/1 gave full conversion.Nevertheless the former catalyst resulted in the highest activity when bromobenzene was used as the reagent.This suggests that a comparatively stable palladium (0) phosphine complex is the reacting species in this special case.Addition of triphenylphosphine to Pd/C gives, in contrast to plain Pd/C, a similar product pattern as Pd(OAc)2/2PPh3 on arylation of butyl vinyl ether and trimethylallylsilane, respectively.