Reactivity of palladium(0) complexes in the oxidative addition of allylic acetates

The oxidative addition of the allyl acetate CH2=CH-CH2-OAc to the Pd-0 comp lex generated from [Pd-0(dba)(2)] and 2 equiv. PPh3 (monodentate ligand) or 1 equiv. dppb (bidentate ligand) gives a cationic (eta (3)-allyl)palladium (II) complex with AcO- as the counter-anion. This reaction is reversible an d proceeds from SPd0(PPh3)(2) or from SPd0(dppb) through at least two succe ssive equilibria. The overall equilibrium constants have been determined. T he overall equilibrium lies more in favor of the cationic (eta (3)-allyl)pa lladium(II) complex when dppp is considered, compared to PPh3. The reaction proceeds via a neutral intermediate complex Pd-0(eta (2)-CH2=CH-CH2-OAc)(d ppb)] whose formation has been kinetically established. The rate constants of the successive steps have been determined in DMF by UV spectroscopy and conductivity measurements, for the dppb ligand. The overall complexation st ep of the Pd-0 by the allyl acetate C=C bond is faster than the oxidative a ddition/ionization step which gives the cationic (eta (3)-allyl)palladium(I I) complex. (C) 2001 Elsevier Science Ltd. All rights reserved.