A comparison of the structure and bonding in the aliphatic boronic R–B(OH)2 and borinic R–BH(OH) acids (R=H; NH2, OH, and F): a computational investigation

• Published in: Structural chemistry Vol. 27; no. 4; pp. 1081 - 1091
• Main Authors: Rao, Niny Z., Larkin, Joseph D., Bock, Charles W.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-08-2016
• Subjects: Chemistry; Chemistry and Materials Science; Computer Applications in Chemistry; Original Research; Physical Chemistry; Theoretical and Computational Chemistry; Borinic acids; Structure; Bonding; Boronic acids; Boronic Acids; Borinic Acids
• ISSN: 1040-0400; 1572-9001
• DOI: 10.1007/s11224-015-0730-5

Boronic acids, R–B(OH)
2
, play an important role in synthetic, biological, medicinal, and materials chemistry. This investigation compares the structure and bonding surrounding the boron atoms in the simple aliphatic boronic acids, R–B(OH)
2
(R=H; NH
2
, OH, and F), and the analogous borinic acids, R–BH(OH). Geometry optimizations were performed using second-order Møller–Plesset perturbation theory (MP2) with the Dunning–Woon aug-cc-pVTZ, aug-cc-pVQZ, and aug-cc-pV5Z basis sets; single-point CCSD(FC)/aug-cc-pVTZ//MP2(FC)/aug-cc-pVTZ level calculations were used to generate a QCI density for natural bond orbital analyses of the bonding. The optimized boron–oxygen bond lengths for the X–B–O
t
–H
trans
-branch of the
endo
-
exo
form of the boronic acids and for the X–B–O–H
cis
-branch of the boronic and borinic acids (X=N, O, and F, respectively)
decrease
as the electronegativity of X
increases
. The boron–oxygen bond lengths are generally longer in the
endo
-
exo
or
anti
forms of the boronic acids than in the corresponding borinic acids. NBO analyses suggest the boron–oxygen bond in H
2
BOH is a double bond; the boron–oxygen bonding in the remaining boronic and borinic acids in this study has a significant contribution from dative pπ–pπ bonding. Values for Δ
H
298
0
for the highly balanced reaction, R–B(OH)
2
 + R–BH
2
 → 2 R–BH(OH), suggest that the bonding surrounding the boron atom is stronger in the borinic acid than in the corresponding boronic acid.