Rate and mechanism of the reaction of (E)-PhCH=CH-CH(Ph)-OAc with palladium(0) complexes in allylic substitutions

The reaction of (E)-1,3-diphenyl-3-acetoxyprop-1-ene, PhCH=CH-CH(Ph)-OAc, with palladium(0) complexes (PdL2)-L-0, generated from Pd-0(PPh3)(4) or Pd-0(dba)(2) + 2L (L = PPh3 or L-2 = dppb), gives cationic [(eta(3)-PhCH-CH-CHPh)PdL2](+) complexes with AcO- as the counteranion in DMF. It is established that this reaction proceeds through two successive equilibria via neutral intermediate complexes (eta(2)-PhCH=CH-CH(Ph)-OAc)(PdL2)-L-0, characterized from the kinetics and by UV and P-31 NMR spectroscopy. The rate constants and equilibrium constants of the successive steps have been determined in DMF. They depend on the ligand and the Pd-0 precursor. In all cases, for the concentration range investigated here, the complexation is considerably faster than the ionization, which is the rate-determining step of the overall process. Under similar experimental conditions, the formation of the cationic complex [(eta(3)-PhCH-CH-CHPh)Pd(dppb)](+) is considerably slower than the formation of the complex 1(eta(3)-CH2-CH-CH2)Pd(dppb)(+) in DMF.