Oxidative addition of aryl halides and sulfonates to palladium(0), and reductive elimination of aryl halides and diaryl ethers from palladium(II): Mechanistic investigations and synthetic applications

Mechanistic studies on the oxidative addition and reductive elimination of aryl halides and sulfonates, along with catalytic applications of these reactions, are reported. The oxidative addition of aryl tosylates to Pd(RPF- t-Bu)[P(o-tolyl)3] (R=Ph, Cy) occurred at room temperature, with the rate of oxidative addition accelerated by anions. However, the role played by added anions varied for palladium complexes of bidentate ligands and monodentate ligands. The mild conditions discovered for the oxidative addition of aryl tosylates led to studies on the palladium-catalyzed Kumada and amination reactions of aryl tosylates at room temperature. The reductive elimination of aryl halides from palladium(II) complexes was also studied. Reductive elimination of aryl halide from {lcub}Pd[P(o-tolyl) 3](Ar)(X){rcub}2 complexes (X = halide) occurred upon addition of bulky P(t-Bu)3. Equilibrium between addition and elimination was established, and equilibrium constants were measured for X = Cl, Br, and I. Studies on the mechanism of the reductive elimination of aryl halide from arylpalladium halide dimers revealed the presence of P( t-Bu)3Pd(Ar)(X) intermediates. Similar P(t-Bu) 3-ligated three-coordinate arylpalladium halide complexes were synthesized, and reductive elimination of aryl halide was observed directly from these three-coordinate complexes. Mechanistic studies were performed on the reductive elimination of aryl halide from Pd[P(t-Bu)3](Ar)(X), and revealed a surprising mechanism involving reversible reductive elimination of aryl halide followed by rate-limiting association of P(t-Bu)3 to palladium to form Pd[P(t-Bu)3]2. The reductive elimination of aryl halides from palladium led to studies on metal-catalyzed aromatic Finkelstein reactions.