EVIDENCE FOR AN EQUILIBRIUM BETWEEN NEUTRAL AND CATIONIC ARYLPALLADIUM(II) COMPLEXES IN DMF - MECHANISM OF THE REDUCTION OF CATIONIC ARYLPALLADIUM(II) COMPLEXES

In DMF, neutral arylpalladium(II) complexes ArPdX(PPh3)(2) (Ar = Ph; X = Cl, Br, I, OAc) are involved in an equilibrium with the cationic co mplex ArPd(PPh3)(2)(DMF)(+) and the anion X-. The values of the equili brium constants K-X have been determined and the affinity of X- for Ar Pd(PPh3)(2)(DMF)(+) is found to be in the order: Cl- > Br- > I- > AcO- . Therefore, albeit the usual reactions with nucleophiles are performe d from the neutral complex, the real reactive intermediate might well be the cationic complex. The electrochemical reduction of cationic com plexes ArPd(PPh3)(2)(+) affords biaryl, and the mechanism of this reac tion has been investigated, It proceeds via transient arylpalladium (I ) complexes.