Synthesis and characterization of some cationic eta(3)-propargylpalladium complexes

Some cationic eta(3)-propargylpalladium complexes were prepared upon treatm ent of the corresponding eta(1)-propargyl- or eta(1)-allenylbis(triphenylph osphine)palladium(II) chloride with Ag[BF4] or Na[BPh4]. The effectiveness of the latter reagent suggests that a eta(1)-propargyl- or eta(1)-allenyl(c hloro)palladium complex equilibrates with a cationic eta(3)propargylpalladi um complex with the liberation of a C1(-) ligand. A qualitative comparison of trends in a series of analogous equilibrium systems suggests that the et a(3)-coordination models favored to a greater extent when (i) propargyl lig ands have an alkyl substituent at the propargylic position, (ii) phosphine ligands are bidentate, such as dppe, (iii) polar solvents are used, and (iv ) the liberating ligand is a Cl- one. A possible implication of eta(3)-coor dination of propargyl ligands in a catalytic cycle of Pd-catalyzed transfor mations of propargylic or allenylic substrates is presented.