Theoretical study on the mechanism of palladium-catalyzed sp2 C[sbnd]H bond activation using cyano as a directing group

Abstract

A systematic theoretical study has been carried out on the mechanism for the Pd-catalyzed aromatic CH activation reaction of aryl nitrile and aryl halide using cyano as the directing group. The entire catalytic cycle divides into four main processes involving CH activation, CF3COOH dissociation, oxidative addition, and reductive elimination and catalyst regeneration. The calculations indicate that the ortho carbon of the directing group cyano in aryl nitrile is activated by Pd(II) resulting in the activation of CH bond. In CF3COOH dissociation, it is found that the 5b is an essential intermediate, which facilitates the dissociation of CF3COOH ligand leading to the intermediate (η2-CF3COO−)(η2-aryl nitrile)Pd(II) (6). The Pd(II) intermediate further undergoes oxidative addition with PhI to form Pd(IV) intermediate, which proceeds by reductive elimination and catalyst regeneration to give the final product. And the reductive elimination and catalyst regeneration process can determine the reaction rate. Furthermore, the roles of additive Ag2O, directing group cyano, and solvent Trifluoroacetic acid have also been examined.