Aryl Fluoride Reductive Elimination from Pd^II Complexes: a Descriptor to Guide Ligand Selection

Abstract

Abstract The effect of ligand selection on the reductive elimination barrier of Pd II aryl fluoride complexes was analyzed by using density functional theory (DFT) calculations. A separate Evans–Polanyi relationship between the activation barriers and the reaction energies is found for CF reductive elimination from monodentate and bis(monodentate) Pd II complexes. For comparable reaction energies, the reductive elimination barriers for monodentate complexes [LPd(Ar)F] (L=PR 3 , Ar=aryl) were calculated to be 80 kJ mol −1 lower than for bis(monodentate) complexes [L 2 Pd(Ar)F]. Natural population analysis demonstrated that the partial charges on the Pd center and on the aryl α‐carbon can be used as a descriptor for the reductive elimination barriers. The presence of a trans phosphine ligand in bis(monodentate) complexes increases the PdC charge density and hence increases the CF reductive elimination barrier. The importance of the PdC charge density can be understood by performing a natural bond orbital analysis. Indeed, CF reductive elimination is best described as the nucleophilic attack of one of the fluorine lone pairs on the antibonding PdC orbital, and the energy difference between this fluorine lone pair and the antibonding PdC orbital determines the rate of this nucleophilic attack.