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

As established previously for Pd(OAc)(2), Pd-0 complexes are formed in situ from Pd(OCOCF3)(2) and n equiv. triarylphosphines (4-Z-C6H4)(3)P (Z = CF3, F, Cl, H, CH3; n greater than or equal to 3). The phosphines are the intramolecular reducing agents and are oxidized to triarylphosphine oxides. The generated NO complexes are anionic species ligated by the trifluoroacetate anion: Pd-0(PAr3)(n)(OCOCF3)(-) (n = 2 or 3). Pd-0(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 Pd-0 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. (C) 2004 Elsevier B.V. All rights reserved.