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

作者：Cui Luchao; Saeys Mark^*

来源：ChemCatChem, 2011, 3(6): 1060-1064.

DOI：10.1002/cctc.201000461

• fluorine
• homogeneous catalysis
• ligand effects
• palladium
• reductive elimination

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- 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=PR3, Ar=aryl) were calculated to be 80 kJ mol(-1) lower than for bis(monodentate) complexes [L2Pd(Ar) F]. Natural population analysis demonstrated that the partial charges on the Pd center and on the aryl alpha-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.

• 出版日期2011-6