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The reactivity of Pd(0) complexes generated by addition of PPh₃ (PPh₃/Pd = 2, 4) to either Pd⁰₂(dba-n,n‘-Z)₃ (n,n‘-Z = 4,4‘-F, 4,4‘-H, 4,4‘-MeO, 3,3‘,4,4‘,5,5‘-OMe) or Pd⁰(dba-n,n‘-Z)₂ (n,n‘-Z = 4,4‘-Br, 4,4‘-Cl, 4,4‘-H, 4,4‘-CH₃, 3,3‘,5,5‘-OMe) in DMF is affected by the electron-donating or -accepting properties of the groups Z substituted on the aromatic rings of dba. Whatever the nature of Z, the unreactive major complexes Pd⁰(η²-dba-n,n‘-Z)(PPh₃)₂ are formed, which are in equilibrium with the common reactive complex Pd⁰(PPh₃)₂ and dba-n,n‘-Z. The latter controls the concentration of the reactive Pd⁰(PPh₃)₂ and, consequently, also controls the rate of the overall oxidative addition with phenyl iodide. The more electron donating the Z group, the lower the affinity of dba-4,4‘-Z for Pd⁰(PPh₃)₂. As a result, the overall rate of the oxidative addition with PhI is faster when Z is an electron-donating group. For a given Z, the …