A comparison of the structure and bonding in the donor-acceptor complexes H3N BR(OH)2 and H3N BRH(OH) (R = H; NH2, OH, and F): a computational investigation

Boronic acids, R-B(OH)(2), play an important role in synthetic, biological, medicinal, and materials chemistry. Borinic acids, R-BH(OH), find relevance in similar fields, although their properties, e.g., binding affinity to diols, can vary significantly. Dative boron-nitrogen bonds, NB, are critical for protecting the boron atom in these acids from nucleophilic attack. In this article, we study the structure, bonding, and formation thermodynamics of the model donor-acceptor complexes H3NBR(OH)(2) and H3NBRH(OH) (R=H; NH2, OH, and F). Geometry optimizations were performed using second-order MOller-Plesset perturbation theory (MP2) with the Dunning-Woon aug-cc-pVTZ basis set; single-point CCSD(FC)/aug-cc-pVTZ//MP2(FC)/aug-cc-pVTZ level calculations were used to generate a QCI density for analyses of the bonding. Extensive comparisons are made with results from density functional theory (DFT) optimizations with/without empirical dispersion corrections. The addition of an ammonia molecule dative bonded to the boron atom for these boronic and borinic acids results in the elongation of bonds to the boron atom, e.g., the boron-oxygen bond lengths increase in the range from similar to 4.5 to similar to 6.5%. The calculated values of H2980 for the ammoniation reactions, R-B(OH)(2)+NH3H3NBR(OH)(2) are -0.6, +4.6, +0.1, and -6.0kcal/mol for R=H, NH2, OH, and F, respectively, at the CCSD(FC)/aug-cc-pVTZ//MP2(FC)/aug-cc-pVTZ level; the corresponding values of H2980 for the borinic acid reactions are -8.9, +2.1, -1.5, and -7.9kcal/mol.