Formation of anionic palladium(0) complexes ligated by the trifluoroacetate ion and their reactivity in oxidative addition

As established previously for Pd(OAc)2, Pd0 complexes are formed in situ from Pd(OCOCF3)2 and n equiv. triarylphosphines (4-Z-C6H4)3P (Z = CF3, F, Cl, H, CH3; n ⩾ 3). The phosphines are the intramolecular reducing agents and are oxidized to triarylphosphine oxides. The generated Pd0 complexes are anionic species ligated by the trifluoroacetate anion: Pd0(PAr3)n(OCOCF3)− (n = 2 or 3). Pd0(PAr3)2(OCOCF3)− is the reactive species involved in the oxidative addition to PhI. This leads to trans-PhPd(OCOCF3)(PPh3)2, involved in equilibrium with the cationic complex trans-[PhPd(PPh3)2(DMF)]+, instead of the expected trans-PhPdI(PPh3)2 complex. The existence of anionic Pd0 complexes ligated by the acetate or trifluoroacetate ions delivered by the precursors Pd(OAc)2 or Pd(OCOCF3)2, respectively, as well as their comparative reactivity in oxidative additions are consistent with theoretical DFT calculations.