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 presents 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.