Kinetic Study of the Insertion of Norbornadiene into Palladium−Carbon Bonds of Complexes Containing the Rigid Bidentate Nitrogen Ligand Bis(arylimino)acenaphthene

Abstract

The ionic [Pd(C7H8C(O)R)(Ar-BIAN)]X (R = Me, Et, iPr, Ph; X = Cl, Br, I; Ar = p-An, p-FC6H4, p-BrC6H4, p-Tol, Ph, o,o‘-Me2C6H3, o,o‘-iPr2C6H3) complexes (1b−12b), bearing the bidentate nitrogen ligand bis(arylimino)acenaphthene (Ar-BIAN), have been synthesized via reaction of the corresponding neutral acylpalladium complexes Pd(C(O)R)X(Ar-BIAN) (1a−12a) with norbornadiene (nbd). For the first time, an extensive kinetic study of this migratory alkene insertion into acyl−palladium bonds of neutral complexes containing α-diimine ligands has been carried out. It has been found that under pseudo-first-order circumstances these reactions follow the rate law kobsd = k1 + k2[nbd], which shows that these reactions proceed via a pathway independent of alkene concentration (k1 pathway) and a pathway dependent on alkene concentration (k2 pathway). The dramatic decrease of the rate constants k1 and k2 upon increasing the steric bulk of the BIAN ligand and the large negative entropy of activation and low enthalpy of ac...