Rate and Mechanism of the Reaction of (<i>E</i>)-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 Pd0L2, generated from Pd0(PPh3)4 or Pd0(dba)2 + 2L (L = PPh3 or L2 = dppb), gives cationic [(η3-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 (η2-PhCHCH-CH(Ph)-OAc)Pd0L2, characterized from the kinetics and by UV and 31P NMR spectroscopy. The rate constants and equilibrium constants of the successive steps have been determined in DMF. They depend on the ligand and the Pd0 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 [(η3-PhCH-CH-CHPh)Pd(dppb)]+ is considerably slower than the formation of the complex [(η3-CH2-CH-CH2)Pd(dppb)]+ in DMF.