Metal π-allyl chemistry III. The preparation of π-allylpalladium complexes from palladium(II) salts

A number of routes for the preparation of π-allylpalladium complexes from palladium(II) salts were investigated with a view to obtaining a quantitative yield. Quantitative yields were obtained rapidly when a stream of ethylene was passed through an aqueous solution of Na₂PdCl₄ and the allylic chloride, and more slowly on vigorously shaking an aqueous solution of Na₂PdCl₄ with a 3-fold excess of allyl chloride.Spectroscopic evidence is presented to confirm that the first stage of the reaction of allylic compounds with palladium(II) salts involves the formation of an olefinic complex. It is found that such palladium(II)olefin complexes of CH₂CHCH₂X are very much less susceptible to nucleophilic attack when X = Cl than when X = C₅H₁₁, OH or OAc, which are all attacked rapidly by nucleophilic solvents, such as methanol, with deposition of palladium metal.