Challenges in Predicting 螖rxnG in Solution: The Mechanism of Ether-Catalyzed Hydroboration of Alkenes

详细信息    查看全文

• 作者：Daniel J. S. Sandbeck ; Colin M. Kuntz ; Christine Luu ; Rachelle A. Mondor ; John G. Ottaviano ; Aravind V. Rayer ; Kazi Z. Sumon ; Allan L. L. East
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：December 18, 2014
• 年：2014
• 卷：118
• 期：50
• 页码：11768-11779
• 全文大小：497K
• ISSN：1520-5215

文摘

Ab initio (coupled-cluster and density-functional) calculations of Gibbs reaction energies in solution, with new entropy-of-solvation damping terms, were performed for the ether-catalyzed hydroboration of alkenes. The goal was to test the accuracy of continuum-solvation models for reactions of neutral species in nonaqueous solvents, and the hope was to achieve an accuracy sufficient to address the mechanism in the 鈥淧asto case鈥? B₂H₆ + alkene in THF solvent. Brown鈥檚 S_N2/S_N1 鈥渄issociative鈥?mechanism, of S_N2 formation of borane鈥揺ther adducts followed by S_N1 alkene attack, was at odds with Pasto鈥檚 original S_N2/S_N2 hypothesis, and while Brown could prove his mechanism for a variety of cases, he could not perform the experimental test with THF adducts in THF solvent, where the higher THF concentrations might favor an S_N2 second step. Two diboranes were tested: B₂H₆, used by Pasto, and (9BBN)₂ (9BBN = 9-borabicyclo[3.3.1]nonane, C₈H₁₅B), used by Brown. The new entropy terms resulted in improved accuracy vs traditional techniques (鈭? kcal mol^鈥?), but this accuracy was not sufficient to resolve the mechanism in the Pasto case.