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

Abstract

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.

Mechanism of Mechanochemical C−H Bond Activation in an Azobenzene Substrate by PdII Catalysts

“…These intermediates remained elusive as they could not be isolated or even detected by any employed spectroscopic method. This is similar to behavior of the unstable trinuclear complexes reported for the C−H activation of acetanilides . Hereafter, the trinuclear species enters the liquid‐assisted C−H bond activation accompanied by cleavage of the acetate bridges that ultimately leads to the dimeric palladated product.…”

Functionalized 1,3‐Diaminotruxillic Acids by Pd‐Mediated C–H Activation and [2+2]‐Photocycloaddition of 5(4H)‐Oxazolones

“…Trinuclear complexes of stoichiometry [(C ^ N)Pd(µ‐OAc) 2 Pd(µ‐OAc) 2 Pd(C ^ N)], such as those shown in Scheme , are sometimes found in orthopalladation processes involving C–H bond activation, but these are quite rare. Such complexes have a symmetry that is compatible with the number of signals found in both the 1 H and 19 F NMR spectra of 2h and we therefore propose a trinuclear complex such as that shown in Scheme for the third compound in the mixture 2h .…”

Bi and trinuclear complexes in palladium carboxylate-assisted C–H activation reactions

“…10 On the other hand, sequential ligand exchange leading to the formation of cyclic trinuclear Pd 3 (OTFA) 6 in dichloromethane was recently described in detail. 11 Next, coordinating solvents like DMSO or acetone cause the opening of the cyclic trinuclear species giving the linear ones 4 (Fig. 1) or cause fragmentation to mono and dipalladium species.…”

“…Over time, several complexes containing linear trinuclear palladium carboxylate motifs together with C-H activated ligands have been observed and characterized. 11,18 These C(sp 2 )H and C(sp 3 )H activated complexes are summarized in Fig. 2.…”