Monosubstituted Phenylboronic Acids, R–B(OH)2 (R = C6H5, C6H4CH3, C6H4NH2, C6H4OH, and C6H4F): A Computational Investigation

Abstract

Phenylboronic acids (PBAs) are an important class of compounds with diverse applications in synthetic, biological, medicinal, and materials chemistry. In this investigation we report structural and thermochemical parameters for several monosubstituted ortho, meta, and para PBAs, R–B(OH)2 (R = C6H5, C6H4CH3, C6H4NH2, C6H4OH, and C6H4F). Equilibrium geometries of all the PBAs discussed in this article were obtained using second-order Møller-Plesset perturbation theory (MP2) with the Dunning-Woon aug-cc-pVDZ basis set; heats of formation (HOF) were calculated at the Gaussian-3 (G3) level of theory. The endo-exo conformers of all the positional isomers of these PBAs were lowest in energy. Using HOF for the monosubstituted PBAs calculated at the G3 level of theory, in conjunction with the experimental HOF for benzene, toluene, aniline, phenol, and fluorobenzene, the values of normalΔH2980 for the transfer processes C6H6 + C6H4X–B(OH)2 → C6H5X + C6H5–B(OH)2 (X = CH3, NH2, OH, and F) are found to be in good agreement with values of normalΔH2980 calculated at the MP2(FC)/aug-cc-pVTZ//MP2(FC)/aug-cc-pVTZ computational level; the bonding in the reactants and products for these transfer reactions are well-matched and thermochemical calculations at this level are expected to be very accurate, providing checks on the G3 HOF calculations.

Computational thermochemistry: extension of Benson group additivity approach to organoboron compounds and reliable predictions of their thermochemical properties

“…108 Furthermore, substituted boronic acids are one of the few groups of organoboron compounds whose thermochemical properties have been investigated by computational means using Gaussian-n composite methods, the other being boroxines. [109][110][111] Specifically, Rao et al have calculated the standard enthalpies of formation of selected monosubstituted phenylboronic acids and their different isomers at the G3 level of theory (Table 7). 109 As the parent compound is included amongst those in Table 1, we have now estimated the enthalpies of all systems investigated by Rao et al with the help of group contributions derived herein.…”

“…[109][110][111] Specifically, Rao et al have calculated the standard enthalpies of formation of selected monosubstituted phenylboronic acids and their different isomers at the G3 level of theory (Table 7). 109 As the parent compound is included amongst those in Table 1, we have now estimated the enthalpies of all systems investigated by Rao et al with the help of group contributions derived herein. The expected uncertainties of the two different approaches are similar, making a comparison between them particularly illustrative.…”