Alkene Hydroboration: Hot Intermediates That React While They Are Cooling
Alkene Hydroboration: Hot Intermediates That React While They Are Cooling
复制标题
DOI：
10.1021/ja105100f
复制
发表时间：
2010-10-06
影响因子：
15
通讯作者：
Pilling, Michael J.
中科院分区：
文献类型：
--
作者：
Glowacki, David R.;Liang, C. H.;Pilling, Michael J.
非TST行为最近引起了极大的关注。如果这种行为是普遍的，那么合成化学家合理化和预测反应性和选择性的标准方法至少部分无效。这篇文章中的工作受到最近结果的启发，这些结果强调了TST对硼氢化反应机制的区域化学结果合理化的预测的偏离，表明异构体产物比的出现是因为非统计动力学效应（J. Am. 2009，131，3130-3131）。我们建议，新的计算使用弱碰撞RRKM主方程（ME）模型的基础上，另一种解释的实验结果，保留了统计反应模型。虽然这是一个共同的假设，所有中间体和过渡态沿着反应路径是在与溶剂的热平衡，我们的ME结果表明，热的中间体可能会发生反应，而他们正在经历逐步松弛通过弱碰撞，即使在解决方案。据我们所知，这项工作代表了主方程方法的第一个应用程序，在有机化学的溶液相热反应，不能用传统的TST解释。显式建模的溶剂和溶质动力学往往是昂贵的，然而，主方程提供了一个计算上易于处理的模型，具有相当大的预测能力，可用于调查是否逐步碰撞弛豫是普遍存在于其他多原子系统。
Non-TST behavior has recently attracted a great deal of attention. If such behavior is general, then the standard way in which synthetic chemists rationalize and predict reactivity and selectivity would be at least partially invalid. The work in this article was inspired by recent results which highlighted a departure from the predictions of TST for rationalization of the regiochemical outcome of the hydroboration reaction mechanism, suggesting that the isomeric product ratios arise because of nonstatistical dynamical effects (J. Am. Chem. Soc. 2009, 131, 3130-3131). We suggest, based on new calculations using a weak collision RRKM-Master Equation (ME) model, an alternative interpretation of the experimental results which preserves a statistical reaction model. While it is a common assumption that all intermediates and transition states along the reaction path are in thermal equilibrium with solvent, our ME results show that hot intermediates may react while they are undergoing stepwise relaxation through weak collisions, even in solution. To our knowledge, this work represents the first application of master equation methodology to a solution phase thermal reaction in organic chemistry that cannot be otherwise explained using conventional TST. Explicit modeling of solvent and solute dynamics is often prohibitively expensive; however, the master equation offers a computationally tractable model with considerable predictive power that may be utilized to investigate whether stepwise collisional relaxation is prevalent in other polyatomic systems.