Effects of beta-substituents and ancillary ligands on the structure and stability of (eta(3)-allyl)palladium complexes. Implications for the regioselectivity in nucleophilic addition reactions

(eta(3)-Allyl)palladium complexes possessing various allylic beta-substituents (X = Cl, OCH3, H) and ancillary ligands on palladium (L = Cl-, F-, PH3) have been studied at the second-order Moller-Plesset (MP2) and fourth-order Moller-Plesset (MP4) perturbation theory level including single, double, and quadruple excitations (MP4SDQ), Interactions between the beta-substituents and palladium have been analyzed as a function of the conformation and configuration of the complexes. Asymmetric polarization of the electron density by beta-substituents leads to significant structural changes of the complexes. The beta-substituent effects considerably increase the thermodynamic stability of the complexes and facilitate the heterolytic fission of the C-X bond. The intensity of these effects depends on the nature of the beta-substituent, on the conformation and configuration of the complex, as well as on the sigma-donor/pi-acceptor character of the ancillary ligands on palladium, Since (eta(3)-allyl)palladium complexes are key intermediates of some important palladium catalyzed transformations, the beta-substituent effects on the regiochemistry of the nucleophilic attack are also discussed. It was concluded that the regioselection is considerably enhanced in the presence of strong beta-substituent effects.