Computational Study on Homolytic Bond Energies of the Ag-X (X = C, O, and H) Complexes and Hammett-Type Analysis of Reactivity.

Abstract

Thirty-seven calculation methods were benchmarked against the available experimental bond lengths and energies data regarding the Ag–X bonds. The theoretical protocol PBE0/VDZ//ωB97x-D/mVTZ was found to be capable of accurately predicting the homolytic bond dissociation energies (BDEs) of Ag–X complexes with a precision of 1.9 kcal/mol. With the available method in hand, a wide range of different Ag–X BDEs were estimated. BDE(Ag–CH2X), BDE(Ag–PhX), BDE(Ag–OPhX), and BDE(Ag–OCOPhX) (X = NH2, OMe, Me, H, Cl, and NO2) were found to be in the ranges of 27–47, 51–54, 19–39, and 64–70 kcal/mol, respectively. Subsequently, Hammett-type analysis was carried out with reactivity parameters. Good positive linear relationships were found for BDE of Ag−O bands and decarboxylation barriers of Ag–OCOPhX with the Hammett constant σ. It suggested that electron-donating substituents could promote either the homolytic cleavage of the Ag–OPhX bond to undergo a radical process or Ag–OCOPhX decarboxylation. Moreover, ligand effects on Ag–H bonds were investigated using BDE(Ag–H) and related NPA charges on Ag. In the case of P-ligands, carbene ligands, and other small molecule ligands (i.e., CO, CO2, and H2O), a good negative linear relationship was found. In contrast, N-ligands could have a reverse effect. Understanding the intrinsic relationships of BDE(Ag–X) with related reactivity parameters might help gain insights into the structure–reactivity relationships in Ag–X-assisted C–H activation/decarboxylation.