Electronic Differentiations in Palladium Alkene Complexes: trans-Phosphine Preference of Allylic Leaving Groups

B3LYP-computations of (Cl−)(PH3)Pd–alkene complexes reveal a distinct preference for arrangements with trans-phosphine situated allylic chlorine atoms (e.g. for E-2-chloro-pent-3-ene 1.6 kcal/mol in the gas phase and 1.5 kcal/mol in THF solution). Geometrical analyses show that Pd–alkene complexes with trans-phosphine positioned allylic chlorine atoms exhibit more strongly evolved allylic character than the analog cis-phosphine complexes. These differentiations, caused by the Pd-ligands (i.e. Cl−, PH3), represent electronic origins for memory effects in Pd-catalyzed allylic substitutions.