Effects of polar γ-substituents on the structure and stability of palladacyclobutane complexes

Abstract

Palladacyclobutane complexes possessing various γ-substituents (X=H, Cl, OH) and ancillary ligands on palladium (L=NH 3, Cl −, PH 3) have been studied by second order Møller–Plesset (MP2) perturbation theory. Interactions between the γ-substituents and palladium have been analysed as a function of the conformation of the complexes. The γ-substituent effects lead to substantial structural changes in the four membered ring. The conjugative interactions increase the thermodynamic stability of the complexes, and facilitate the heterolytic fission of the C–X bond. The intensity of these interactions depends on the nature of the γ-substituent, on the conformation of the complex, as well as on the σ-donor/π-acceptor character of the ancillary ligands on palladium. Since palladacyclobutanes are key intermediates of some important catalytic transformations, the implications for the palladium chemistry are also discussed.