Mechanistic molecular motion of transition-metal mediated β-hydrogen transfer: quasiclassical trajectories reveal dynamically ballistic, dynamically unrelaxed, two step, and concerted mechanisms
Mechanistic molecular motion of transition-metal mediated β-hydrogen transfer: quasiclassical trajectories reveal dynamically ballistic, dynamically unrelaxed, two step, and concerted mechanisms
复制标题
过渡金属介导的β-氢转移的机械分子运动：准经典轨迹揭示动态弹道、动态非松弛、两步和协同机制
DOI：
10.1039/d0dt01687j
复制
发表时间：
2020
影响因子：
4
通讯作者：
Ess, Daniel H.
中科院分区：
文献类型：
--
作者：
Wheeler, Josh I.;Carlsen, Ryan;Ess, Daniel H.
β-氢从金属烷基向乙烯的转移是一种基本的有机金属转化。先前提出的这种转化机制包括两步β-氢消除和金属氢化物中间的迁移插入序列或一步协同途径。在这里，我们报告了密度泛函理论（DFT）准经典直接动力学轨迹，揭示了[Cp*RhIII(Et)（乙烯）]+ β-氢转移的新动力学机制。尽管DFT能量格局显示了Rh-H中间体的两步机制，但从β-氢消除过渡态开始的准经典轨迹显示了该中间体的完全动力学跳过。通过动态弹道机制，跳变速度极快（通常<100飞秒），或者通过动态非放松机制，跳变速度较慢。与从过渡态开始的轨迹一致，所有从Rh-H中间体开始的轨迹都沿反应坐标延续。所有这些轨迹结果都与Rh-H中间体<1 kcal mol−1稳定相对于β-氢消除和迁移插入过渡态相一致。Co在能量景观上是一步协调机制，其轨迹在过渡状态区表现出极快的穿越速度（<50 fs），这种协调机制与Rh的弹道机制在动力学上是不同的。与Rh相反，对于Ir，除了动态弹道和非松弛机制外，轨迹也停止在Ir - h中间。这与Ir-H中间体相对于β-氢消除和迁移插入过渡态稳定了~ 3 kcal mol−1是一致的。总的来说，Rh与Co和Ir的比较提供了对能量表面形状与有机金属转化的动力学机制之间关系的理解。
The transfer of a β-hydrogen from a metal-alkyl group to ethylene is a fundamental organometallic transformation. Previously proposed mechanisms for this transformation involve either a two-step β-hydrogen elimination and migratory insertion sequence with a metal hydride intermediate or a one-step concerted pathway. Here, we report density functional theory (DFT) quasiclassical direct dynamics trajectories that reveal new dynamical mechanisms for the β-hydrogen transfer of [Cp*RhIII(Et)(ethylene)]+. Despite the DFT energy landscape showing a two-step mechanism with a Rh–H intermediate, quasiclassical trajectories commencing from the β-hydrogen elimination transition state revealed complete dynamical skipping of this intermediate. The skipping occurred either extremely fast (typically <100 femtoseconds (fs)) through a dynamically ballistic mechanism or slower through a dynamically unrelaxed mechanism. Consistent with trajectories begun at the transition state, all trajectories initiated at the Rh–H intermediate show continuation along the reaction coordinate. All of these trajectory outcomes are consistent with the Rh–H intermediate <1 kcal mol−1 stabilized relative to the β-hydrogen elimination and migratory insertion transition states. For Co, which on the energy landscape is a one-step concerted mechanism, trajectories showed extremely fast traversing of the transition-state zone (<50 fs), and this concerted mechanism is dynamically different than the Rh ballistic mechanism. In contrast to Rh, for Ir, in addition to dynamically ballistic and unrelaxed mechanisms, trajectories also stopped at the Ir–H intermediate. This is consistent with an Ir–H intermediate that is stabilized by ∼3 kcal mol−1 relative to the β-hydrogen elimination and migratory insertion transition states. Overall, comparison of Rh to Co and Ir provides understanding of the relationship between the energy surface shape and resulting dynamical mechanisms of an organometallic transformation.