Palladium mono- N -protected amino acid complexes: experimental validation of the ligand cooperation model in C-H activation.

Mechanistic proposals for the C-H activation reaction enabled by mono- N -protected amino acid ligands (MPAAs) have been supported by DFT calculations. The direct experimental observation of the ligand-assisted C-H activation has not yet been reported due to the lack of well-defined isolated palladium complexes with MPAAs that can serve as models. In this work, palladium complexes bearing chelating MPAAs (NBu 4 )[Pd(κ 2 - N , O -AcN-CHR-COO)(C 6 F 5 )py] (Ac = MeC(O); R = H, Me) and [Pd(κ 2 - N , O -MeNH-CH 2 -COO)(C 6 F 5 )py] have been isolated and characterized. Their evolution in a solution containing toluene leads to the C-H activation of the arene and the formation of the C 6 F 5 -C 6 H 4 Me coupling products. This process takes place only for the ligands with an acyl protecting group, showing the cooperating role of this group in a complex with a chelating MPAA, therefore experimentally validating this working model. The carboxylate group is inefficient in this C-H activation.