Correlating Thermodynamic and Kinetic Hydricities of Rhenium Hydrides
Correlating Thermodynamic and Kinetic Hydricities of Rhenium Hydrides
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DOI：
10.1021/jacs.2c07192
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发表时间：
2022-09-21
影响因子：
15
通讯作者：
Smith, Nicholas E.
中科院分区：
文献类型：
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作者：
Ertem, Mehmed Z.;Hazari, Nilay;Smith, Nicholas E.
测定了从 Re((R)bpy)(CO)(3)H（bpy = 4,4'-R-2,2'-联吡啶；R = OMe、Bu-t、Me、H、Br、COOMe、CF3）到 CO2 和七种不同的阳离子 N-杂环的氢化物转移动力学。此外，主要使用计算方法确定了 Re((R)bpy)(CO)(3)H 类型配合物的热力学水度。通过关联热力学和动力学水度得出的线性自由能关系（LFER）表明，一般来说，氢化物转移速率随着反应热力学驱动力的增加而增加。动力学同位素效应的范围从驱动力小的氢化物转移反应的逆向到驱动力大的反应的正向。哈米特分析表明，具有较大热力学驱动力的氢化物转移反应对金属氢化物电子性质的变化不太敏感，大概是因为在越来越早的过渡态中电荷的积累较少。获得了一系列氢化物转移反应的布朗斯台德 α 值，并且 DFT 计算表明这些反应是一致的，这使得能够使用马库斯理论来分析涉及过渡金属氢化物的氢化物转移反应。然而，值得注意的是，即使Re氢化物或氢化物受体的空间性质发生轻微扰动，也会导致基于热力学驱动力的预测氢化物转移速率出现较大偏差。这表明仅热力学考虑因素不能用于预测氢化物转移速率，这对催化剂设计具有影响。
The kinetics of hydride transfer from Re((R)bpy)(CO)(3)H (bpy = 4,4'-R-2,2'-bipyridine; R = OMe, Bu-t, Me, H, Br, COOMe, CF3) to CO2 and seven different cationic N-heterocycles were determined. Additionally, the thermodynamic hydricities of complexes of the type Re((R)bpy)(CO)(3)H were established primarily using computational methods. Linear free-energy relationships (LFERs) derived by correlating thermodynamic and kinetic hydricities indicate that, in general, the rate of hydride transfer increases as the thermodynamic driving force for the reaction increases. Kinetic isotope effects range from inverse for hydride transfer reactions with a small driving force to normal for reactions with a large driving force. Hammett analysis indicates that hydride transfer reactions with greater thermodynamic driving force are less sensitive to changes in the electronic properties of the metal hydride, presumably because there is less buildup of charge in the increasingly early transition state. Bronsted alpha values were obtained for a range of hydride transfer reactions and along with DFT calculations suggest the reactions are concerted, which enables the use of Marcus theory to analyze hydride transfer reactions involving transition metal hydrides. It is notable, however, that even slight perturbations in the steric properties of the Re hydride or the hydride acceptor result in large deviations in the predicted rate of hydride transfer based on thermodynamic driving forces. This indicates that thermodynamic considerations alone cannot be used to predict the rate of hydride transfer, which has implications for catalyst design.