Reactions involving palladium(II) acetate and phosphine ligands proceed by a third mechanism, the anionic pathway. Base mediates the oxidation of a phosphine ligand by palladium(II) to a phosphine oxide. Oxidative addition then generates the anionic palladium complex IX. Loss of halide leads to neutral complex X, which undergoes steps analogous to the neutral pathway to regenerate anionic complex IX. A similar anionic pathway is also likely operative in reactions of bulky palladium tri(tert-butyl)phosphine complexes.