How to Predict Activation Barriers – Conformational Transformations of Compounds CH3C(CH2PPh2)3–n[CH2P(oTol)2]nMo(CO)3 (n = 1–3): Force Field Calculations versus NMR Data
How to Predict Activation Barriers – Conformational Transformations of Compounds CH3C(CH2PPh2)3–n[CH2P(oTol)2]nMo(CO)3 (n = 1–3): Force Field Calculations versus NMR Data
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如何预测激活势垒 - 化合物 CH3C(CH2PPh2)3–n[CH2P(oTol)2]nMo(CO)3 (n = 1–3) 的构象转变：力场计算与 NMR 数据
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
Rainer Soltek
中科院分区：
文献类型：
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作者：
Stefan Beyreuther;A. Frick;J. Hunger;G. Huttner;Björn Antelmann;P. Schober;Rainer Soltek
三脚架金属实体tripodM是空间拥挤的系统。因此，化合物CH 3C（CH 2 PPh 2）3-n[CH 2 P（oTol）2]nMo（CO）3（n = 1：1，n = 2：2，n = 3：3）所采用的构象将在很大程度上取决于作用在这些分子中的排斥力。邻甲苯基基团的空间需求阻碍了它们的自由旋转，并且涉及化合物作为整体的对映异构化过程足够慢以允许通过NMR技术对其进行分析。通过线形分析、EXSY方法和聚结实验相结合的方法，确定了化合物1、2和3的构象对映异构化过程的ΔG_（max）值分别为ΔG_（max）298 K = 54.3、57.9和65.5 kJ·mol ~（-1）。通过对力场生成超曲面的穷举搜索，计算出反应的活化能分别为53、57和69 kJ·mol-1.因此，力场的方法正确地再现了邻甲苯基取代的程度上的活化能的依赖性。此外，力场模拟还提供了对映体化途径的各个微步骤的洞察。
Tripod metal entities tripodM are sterically congested systems. The conformations adopted by compounds CH3C(CH2PPh2)3–n[CH2P(oTol)2]nMo(CO)3 (n = 1: 1, n = 2: 2, n = 3: 3) will thus be largely determined by the repulsive forces acting in these molecules. The steric demand of the o-tolyl groups impedes their free rotation and enantiomerization processes referring to the compounds as a whole are sufficiently slow to permit their analysis by NMR techniques. Through a combination of line-shape analysis, EXSY methods, and coalescence experiments, the ΔG‡ values for these conformational enantiomerization processes have been determined as ΔG‡298K = 54.3, 57.9, 65.5 kJ·mol–1 for compounds 1, 2, and 3, respectively. By an exhaustive search on a force field generated hypersurface, activation energies of 53, 57 and 69 kJ·mol–1 have been calculated. Thus, the force field approach correctly reproduces the dependence of the activation energy on the degree of o-tolyl substitution. Moreover, the force field simulation also gives an insight into the individual microsteps of the enantiomerization pathways.