A DFT Study of the Effect of the Ligands in the Reductive Elimination from Palladium Bis(allyl) Complexes

Abstract

The effect of some selected ligands (L = empty, PMe3, ethylene, maleic anhydride) in the reductive elimination of the palladium complexes cis-[Pd(η1-allyl)(η1-allyl)(PMe3)L] and Pd(η1-allyl)(η3-allyl)L to form hexa-1,5-diene was computationally studied using DFT methods. Among the various possible coupling processes (C1sp3−C1′sp3, C3sp2−C3′sp2, and C1sp3−C3′sp2), C3−C3′ bond formation is the most favored in all cases, as reported before for cis-[Pd(η1-allyl)(η1-allyl)(PH3)2]. Interestingly, the activation energy for this coupling changes with the L ligand: empty (4.6 kcal/mol) < MA (5.8 kcal/mol) < CH2CH2 (12.5 kcal/mol) < PMe3 (17.3 kcal/mol). Therefore, tricoordinated Pd(η1-allyl)(η1-allyl)L complexes undergo reductive elimination at higher rates than the tetracoordinated counterparts. The order L = empty < L = MA is inverse to that found for carbon ligands (alkyl, aryl, alkenyl) that couple via direct C1−C1′ reductive elimination; the order L = empty < L = MA is also followed by the allyl groups when t...