Synthesis and Properties of Cationic Organopalladium Complexes. Remarkable Rate Enhancement in Olefin Insertion into the Palladium–Aryl Bond by the Generation of a Cationic Palladium Complex from trans-[PdBr(Ph)(PMe3)2]

By removing the bromide ligand in trans-[PdBr(Ph)(PMe3)2] (1) by AgBF4 in the presence and absence of pyridine, pyridine-coordinated and solvent-coordinated cationic complexes, trans-[PdPh(py)(PMe3)2]BF4 (2) and trans-[PdPh(solvent)(PMe3)2]BF4 (3), have been obtained. These cationic phenylpalladium complexes show much greater reactivities than do the parent neutral complex 1 toward olefins to give phenylated olefins by insertion followed by β-hydrogen elimination processes. Kinetic studies concerning the insertion of methyl acrylate into the phenyl-palladium bond have indicated that the reactions are first order in the phenylpalladium complexes and that addition of pyridine to a system containing 2 and methyl acrylate inhibits the insertion reaction of the olefin. The results suggest that the generation of a cationic arylpalladium complex with a vacant site is important for the olefins to be inserted.