Evaluation of Alkali Metal Cation Affinities and Basicities Using Extrapolation to the Complete Basis Set Limit

The complete basis set (CBS) extrapolation is used at Hartree–Fock and second-order Møller–Plesset perturbation theory levels and with the def2-<i>x</i>ZVP <i>x</i>-ζ basis set (<i>x</i> = 2–4). This approach leads to general, robust, and well-calibrated methods, especially when Hartree–Fock energy (<i>E</i>_HF) and correlation energies (<i>E</i>_CE) are extrapolated separately. Indeed, the absolute deviations between theoretical and experimental data are usually smaller than the reported experimental errors. We also point out the need to change usual parameters utilized in CBS methods when calculations involve atoms from third and subsequent rows. The best CBS scheme studied in the current work for obtaining energies for the estimation of alkali metal cation affinities and basicities is <i>E</i>_CBS[∞] = 1.10529·<i>E</i>_HF[4] – 0.10529·<i>E</i>_HF[2] + 0.92703·<i>E</i>_CE[4] – 0.07297·<i>E</i>_CE[2], where <i>E</i>_HF[2], <i>E</i>_HF[4], <i>E</i>_CE[2], and <i>E</i>_CE[4] are the Hartree–Fock energy (<i>E</i>_HF) and MP2 correlation energies (<i>E</i>_CE) obtained with def2-QZVP (<i>x</i> = 4) and def2-SV­(p) (<i>x</i> = 2) basis sets

Critical Test of Some Computational Chemistry Methods for Prediction of Gas-Phase Acidities and Basicities

Gas-phase acidities and basicities were calculated for 64 neutral bases (covering the scale from 139.9 kcal/mol to 251.9 kcal/mol) and 53 neutral acids (covering the scale from 299.5 kcal/mol to 411.7 kcal/mol). The following methods were used: AM1, PM3, PM6, PDDG, G2, G2MP2, G3, G3MP2, G4, G4MP2, CBS-QB3, B1B95, B2PLYP, B2PLYPD, B3LYP, B3PW91, B97D, B98, BLYP, BMK, BP86, CAM-B3LYP, HSEh1PBE, M06, M062X, M06HF, M06L, mPW2PLYP, mPW2PLYPD, O3LYP, OLYP, PBE1PBE, PBEPBE, tHCTHhyb, TPSSh, VSXC, X3LYP. The addition of the Grimmes empirical dispersion correction (D) to B2PLYP and mPW2PLYP was evaluated, and it was found that adding this correction gave more-accurate results when considering acidities. Calculations with B3LYP, B97D, BLYP, B2PLYPD, and PBE1PBE methods were carried out with five basis sets (6-311G**, 6-311+G**, TZVP, cc-pVTZ, and aug-cc-pVTZ) to evaluate the effect of basis sets on the accuracy of calculations. It was found that the best basis sets when considering accuracy of results and needed time were 6-311+G** and TZVP. Among semiempirical methods AM1 had the best ability to reproduce experimental acidities and basicities (the mean absolute error (mae) was 7.3 kcal/mol). Among DFT methods the best method considering accuracy, robustness, and computation time was PBE1PBE/6-311+G** (mae = 2.7 kcal/mol). Four Gaussian-type methods (G2, G2MP2, G4, and G4MP2) gave similar results to each other (mae = 2.3 kcal/mol). Gaussian-type methods are quite accurate, but their downside is the relatively long computational time

Computational Study of Copper-Free Sonogashira Cross-Coupling Reaction

The copper-free Sonogashira cross-coupling reaction consisting of oxidative addition, <i>cis–trans</i> isomerization, deprotonation, and reductive elimination was computationally modeled using the DFT B97D/cc-pVDZ method for reaction between phenyl bromide and phenylacetylene. Tetrakis(triphenylphosphano)palladium was used as a catalyst and <i>sec</i>-butylamine as a base. The reaction mechanism was studied in dichloromethane solution. Oxidative addition proceeds through the biligated pathway, and the catalytically active palladium species is Pd(PPh₃)₃. Amines, present in the reaction mixture, can inhibit oxidative addition by coordinating to Pd(PPh₃)₃