A DFT study on the Pd-mediated decarboxylation process of aryl carboxylic acids

Abstract

Decarboxylation process in a series of PdL(2)X(η(2)-OOCAr(R)) complexes 2OS(R) (L = DMSO; X = OOCCF(3)(-); R = H, OMe, NO(2), Me and CN) with substituent R at an ortho, meta or para position were investigated with the aid of density functional theory calculations. Through our study, we found that the OOCCF(3)(-) ligand is not just a spectator ligand but assists the decarboxylation process. The results indicated that electron-donating substituents have greater promotion effect than electron-withdrawing substituents on the decarboxylation process. An ortho substituent in the substrate ligands OOCAr(R)(-) is normally necessary for a successful decarboxylation. The reason behind this has been explained.

Mild Aromatic Palladium-Catalyzed Protodecarboxylation: Kinetic Assessment of the Decarboxylative Palladation and the Protodepalladation Steps

“…Thus, the activation entropy value for TS-1 is in better agreement with our experimentally determined activation entropy value (−6.7 cal/K•mol). Comparison of Figure 5 with work done by Liu 67 and Su 68 on monosubstituted benzoic acids undergoing decarboxylative palladation shows that bis- ortho -substituted arenes decarboxylate with lower ΔG ‡ and that the ipso-carbon palladium bond is much shorter promoting intramolecular electrophillic palladation of 13 before decarboxylation. Overall, it appears that pathway C is operative in the decarboxylative palladation.…”

Carboxylic Acids as Traceless Directing Groups for Formal meta‐Selective Direct Arylation

“…Based on computational studies, Su, Lin, and Xue have previously hypothesized that Pd-mediated decarboxylation may be influenced by steric factors. [17] Notably Pd II salts have only been reported to mediate the protodecarboxylation of highly electron-rich benzoic acids, [18] whereas our system seems to be independent of the electronic nature of the initial ortho substituent. To further explore this new hypothesis, we attempted the metaarylation protocol on ortho-toluic acid (1 t) which, lacking a strong electron-withdrawing or electron-donating ortho substituent, does not decarboxylate with either Ag or Pd catalysts.…”

Carboxylic Acids as Traceless Directing Groups for Formal meta‐Selective Direct Arylation

“…This remarkable selectivity suggests that electronics are not the only factor controlling the Pd‐mediated decarboxylation of benzoic acids. Based on computational studies, Su, Lin, and Xue have previously hypothesized that Pd‐mediated decarboxylation may be influenced by steric factors 17. Notably Pd II salts have only been reported to mediate the protodecarboxylation of highly electron‐rich benzoic acids,18 whereas our system seems to be independent of the electronic nature of the initial ortho substituent.…”