Dynamics and the Failure of Transition State Theory in Alkene Hydroboration,Journal of the American Chemical Society

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Dynamics and the Failure of Transition State Theory in Alkene Hydroboration
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2009-03-11 , DOI: 10.1021/ja807666d
Yatsandra Oyola ₁ , Daniel A Singleton

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Transition state theory fails to accurately predict the selectivity in an example where it is ubiquitously invoked, hydroboration. The hydroboration of terminal alkenes with BH(3) is moderately regioselective, affording an 88:12-90:10 ratio of anti-Markovnikov/Markovnikov adducts. High-level ab initio calculations predict too large of an energy difference between anti-Markovnikov and Markovnikov transition structures to account for the observed product ratio, and consideration of calculational error, solvent, tunneling, and entropy effects does not resolve the discrepancy. Trajectory studies, however, predict well the experimental selectivity. The decreased selectivity versus transition state theory arises from the excess energy generated as the BH(3) interacts with the alkene, and the observed selectivity is proposed to result from a combination of low selectivity in direct trajectories, moderate RRKM selectivity, and high selectivity after thermal equilibration.

中文翻译：

烯烃硼氢化中过渡态理论的动力学和失效

过渡态理论无法准确预测选择性，在它无处不在的例子中，硼氢化。带有 BH(3) 的终端烯烃的硼氢化反应具有适度的区域选择性，提供了 88:12-90:10 的反马尔科夫尼科夫/马尔科夫尼科夫加合物的比率。高级从头计算预测反马尔科夫尼科夫和马尔科夫尼科夫跃迁结构之间的能量差异太大，无法解释观察到的产物比，并且考虑计算误差、溶剂、隧道效应和熵效应并不能解决差异。然而，轨迹研究很好地预测了实验选择性。与过渡态理论相比，选择性降低的原因是 BH(3) 与烯烃相互作用时产生的过剩能量，

更新日期：2009-03-11

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