The role of trinuclear species in a palladium acetate/trifluoroacetic acid catalytic system.

Reactions catalyzed by palladium(ii) acetate and trifluoroacetic acid (TFA) have a clear preactivation phase. However, the structure of real catalytic species remains unclear. We show that the key species are cyclic trinuclear complexes of composition [Pd ₃ (OAc) _6-x (OTFA) _x ] (x = 1-6) formed by a sequential ligand exchange from [Pd ₃ (OAc) ₆ ]. Furthermore, we prove that the trinuclear palladium backbone of the precatalyst remains preserved during the first phase of the C-H activation reaction of acetanilides. In other words, the reaction pathway including the trinuclear species should be taken into account in discussion about mechanisms of the reactions catalyzed by palladium acetates.