Thermodynamics of Boroxine Formation from the Aliphatic Boronic Acid Monomers R鈥揃(OH)2 (R = H, H3C, H2N, HO, and F): A Computational Investigation

详细信息    查看全文

• 作者：Krishna L. Bhat ; George D. Markham ; Joseph D. Larkin ; Charles W. Bock
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：July 7, 2011
• 年：2011
• 卷：115
• 期：26
• 页码：7785-7793
• 全文大小：864K
• 年卷期：v.115,no.26(July 7, 2011)
• ISSN：1520-5215

文摘

Boroxines are the six-membered cyclotrimeric dehydration products of organoboronic acids, 3R鈥揃(OH)₂ 鈫?R₃B₃O₃ + 3H₂O, and in recent years have emerged as a useful class of organoboron molecules with applications in organic synthesis both as reagents and catalysts, as structural components in boronic-acid-derived pharmaceutical agents, and as anion acceptors and electrolyte additives for battery materials [Korich, A. L.; Iovine, P. M. Dalton Trans. 2010, 39, 1423鈭?431]. Second-order M酶ller鈥揚lesset perturbation theory, in conjunction with the Dunning鈥揥oon correlation-consistent cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis sets, was used to investigate the structures and relative energies of the endo鈥揺xo, anti, and syn conformers of the aliphatic boronic acids R鈥揃(OH)₂ (R = H, H₃C, H₂N, HO, and F), as well as the thermodynamics of their boroxine formation; single-point calculations at the MP2/aug-cc-pVQZ, MP2/aug-cc-pV5Z, and CCSD(T)/aug-cc-pVTZ levels using the MP2/aug-cc-pVTZ optimized geometries were also performed in selected cases. The endo鈥揺xo conformer was generally lowest in energy in vacuo, as well as in PCM and CPCM models of aqueous and carbon tetrachloride media. The values of 螖H₂₉₈⁰ for boroxine formation via dehydration from the endo鈥揺xo conformers of these aliphatic boronic acids ranged from 鈭?.9 for (H₂N)₃B₃O₃ to +12.2 kcal/mol for H₃B₃O₃ at the MP2/aug-cc-pVTZ level in vacuo; for H₃B₃O₃, the corresponding values in PCM/UFF implicit carbon tetrachloride and aqueous media were +11.2 and +9.8 kcal/mol, respectively. On the basis of our calculations, we recommend that 螖H_f(298鈥塊) for boroxine listed in the JANAF compilation needs to be revised from 鈭?90.0 to approximately 鈭?77.0 kcal/mol.