Effects of the ancillary ligands on palladium-carbon bonding in (eta(3)-allyl)palladium complexes. Implications for nucleophilic attack at the allylic carbons

[(eta(3)-allyl)Pd](+) (1) and (eta(3)-allyl)PdL(2) (L = F-, Cl-, NH3, CH2 = CH2 and PH3) species (2-6) have been studied at the second-order Moller-Plesset (MP2) and fourth order Moller-Plesset (MP4) perturbation theory levels, the latter including single, double, and quadruple excitations (MP4SDQ). The nature of palladium-carbon interactions has been investigated on the basis of calculated electron density and energy density distributions. Complexation of 1 with sigma-donors (F-, Cl-, NH3) strengthens the palladium-carbon bonds and weakens the carbon-carbon bonds of the allyl moiety. This effect is more pronounced for F- than Cl- or NH3 ligands. In contrast to sigma-donors, pi-acceptors significantly weaken the interactions between the palladium and eta(3)-allyl groups. On the basis of the computational results, expected ligand effects on the reactivity and regioselectivity in nucleophilic additions are also discussed.