- As established previously for Pd(OAc) 2 , Pd 0 complexes are formed in situ from Pd(OCOCF 3 ) 2 and n equiv. triarylphosphines (4-Z-C 6 H 4 ) 3 P (Z = CF 3 , F, Cl, H, CH 3 ; n ⩾ 3). The phosphines are the intramolecular reducing agents and are oxidized to triarylphosphine oxides. The generated Pd 0 complexes are anionic species ligated by the trifluoroacetate anion: Pd 0 (PAr 3 ) n (OCOCF 3 ) − ( n = 2 or 3). Pd 0 (PAr 3 ) 2 (OCOCF 3 ) − is the reactive species involved in the oxidative addition to PhI. This leads to trans -PhPd(OCOCF 3 )(PPh 3 ) 2 , involved in equilibrium with the cationic complex trans -[PhPd(PPh 3 ) 2 (DMF)] + , instead of the expected trans -PhPdI(PPh 3 ) 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(OCOCF 3 ) 2 , respectively, as well as their comparative reactivity in oxidative additions are consistent with theoretical DFT calculations.