Insertion of imine into palladium-methyl and palladium-acyl bonds. A density functional study

The insertion mechanism of imine into the Pd-methyl and Pd-acyl bonds with a phosphane or a nitrogen-based ligand coordinated to the Pd atom has been studied with density functional theory. In agreement with the experimental findings, σ coordination of the imine is preferred. Imine insertion into the Pd-methyl bond present high energy barriers (>40 kcal mol^-1) independently of the Pd-ligand used. On the contrary insertion into the Pd-acyl bond is more facile, with energy barriers close to 20 kcal mol^{- 1}. A geometrical and energetic analysis of the transition states suggests that the formation of the very strong amide linkage constitutes the added driving force for the imine insertion into the Pd-acyl bond.