Mechanisms of Reactions Involving Allyl Palladium Complexes According to Quantum Chemical Calculations (A Review)

The chemistry of allyl complexes of palladium, and of transition metals more broadly, dates back to 1959, when η3-allylpalladium chloride was first synthesized and characterized at the Department of Physical Chemistry of Moscow Institute of Fine Chemical Technology named after M.V. Lomonosov by Yakov Syrkin and Ilya Moiseev. This discovery established allyl complexes as fundamental tools in both catalysis and synthetic chemistry. These coordination compounds are now central to a wide range of experimental and theoretical studies. This review addresses the structural and reactivity features of palladium allyl complexes within the framework of quantum chemical approaches. Density functional theory methods have been used to determine the structural characteristics of isomeric η1- and η3-allyl palladium complexes and to evaluate the energetic parameters of η3–η1–η3 isomerization. A plausible mechanism has been proposed for the formation of η3-allyl palladium complexes via oxidative addition of allyl carboxylates to the metal center. Theoretical analyses of reactions involving allyl–palladium intermediates are presented, with particular attention to nucleophilic allylic substitution, including the Tsuji–Trost reaction. The performance of computational methods in describing regioselectivity and enantioselectivity in nucleophilic attack within this class of reactions is evaluated. From a synthetic standpoint, the allylation of norbornadiene and norbornene derivatives provides an effective route to structurally complex polycyclic systems. Extensive experimental data in this area have enabled detailed theoretical studies. Density functional theory calculations have identified and analyzed the most probable pathways leading to the major products of norbornadiene allylation. The enantioselectivity of these reactions in the presence of chiral phosphine ligands has also been modeled using modern density functional theory methods.