Ligand effects on migratory insertion by the Heck reaction

Abstract

Ligand effects on ethene insertion into a series of cationic phenylpalladium complexes with diverse bidentate phosphine ligands were studied by using the density functional methods. For the complexes with n-membered ring ligands (n = 4–6), a correlation was found between the ring size and the insertion barrier. This behavior was explained by considering the P—Pd—P bond angle. In the case of complexes with ligands of different rigidity, almost no difference was found for the insertion barriers. Furthermore, the bidentate phosphine ligand was systematically substituted by Me, t-Bu, F and Ph groups. It was found that the electron-donating substituents increased the insertion barrier, whereas the electron-withdrawing groups decreased it. The substantial increase of insertion barrier by the t-Bu group indicated that steric effect also had great effect on the migratory insertion.