Do special noncovalent π-π stacking interactions really exist?
Do special noncovalent π-π stacking interactions really exist?
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DOI：
10.1002/anie.200705157
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Grimme, Stefan
中科院分区：
文献类型：
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作者：
Grimme, Stefan
非共价相互作用在现代化学研究中发挥着越来越重要的作用，现在被认为是超分子化学，材料科学甚至生物化学的基石。[1]当不饱和有机基团参与非共价相互作用时，通常使用术语“π-π堆积”或更一般地“π-π相互作用”。正如最近所指出的，[2]这种分类有一种相当神秘的味道。对于更大的结构，π-π堆叠是一种理论上没有很好理解的现象，尽管已经取得了一些进展。[3，4]从苯二聚体[5-7]和其他涉及苯环的络合物[2，8]的许多研究中可以得出结论，π轨道不像传统的π驱动共价键那样起作用，尽管这不是常识。[9]原型苯二聚体现在被认为是一种典型的货车范德华络合物，其中长程色散相互作用（相互作用能对碎片间距离的主要Rd 6依赖性[10]）起主要作用。因此，二聚体在不相关的Hartree-Fock和许多密度泛函理论（DFT）水平下是未结合的。[11]这种更复杂的观点越来越多地取代亨特的π-π相互作用模型[12]，该模型（过度）强调苯型系统中相互作用的主要四极-四极静电分量（见参考文献14）。[13]因为货车德瓦耳斯络合物由几乎所有的中性、封闭壳层分子形成，这在本文中被排他地考虑，所以与例如大约相同大小的饱和（氢化）环相比，堆叠的芳族单元之间的相互作用应该如此特别。这种主要的能量差异在本文中被称为π-π堆叠效应（PSE）。例如，苯和环己烷在室温下都以流体形式存在，这表明类似的分子间相互作用。根据精确的CCSD（T）计算，堆叠的（平行位移，PD）苯二聚体具有比戊烷二聚体更小的结合能（102.八对十三。9 kcal molecular 1），[2，14]其中有
Noncovalent interactions play an increasingly important role in modern chemical research, and are nowadays considered as cornerstones in supramolecular chemistry, materials science, and even biochemistry.[1] When unsaturated organic groups are involved in noncovalent interactions, the terms “π–π stacking”, or more generally “π–π interactions” are often used. As noted recently,[2] this classification has a quite mysterious flavor. For larger structures, π–π stacking is a phenomenon that is theoretically not well understood, although some progress has been made.[3, 4] From many studies of the benzene dimer [5–7] and other complexes involving phenyl rings,[2, 8] it can be concluded that the π orbitals do not function as in conventional overlapdriven covalent bonding, although this is not common knowledge.[9] The prototypical benzene dimer is nowadays considered a typical van der Waals complex in which the long-range dispersion interactions (dominant RÀ6 dependence of the interaction energy on interfragment distance [10]) play the major role. As a consequence, the dimer is unbound at uncorrelated Hartree–Fock and many density functional theory (DFT) levels.[11] This more sophisticated view is increasingly replacing Hunter s model [12] of π–π interactions, which (over) emphasises the mainly quadrupole–quadrupole electrostatic component of the interaction in benzene-type systems (see Ref.[13] for recent theoretical work on polar πsystems).Because van der Waals complexes are formed by almost all neutral, closed-shell molecules, which are considered exclusively herein, what should be so special about the interaction between stacked aromatic units compared to, for example, saturated (hydrogenated) rings of about the same size. This mainly energetic difference is termed herein the π–π stacking effect (PSE). For example, benzene and cyclohexane both exist as fluids at room temperature, which indicates similar intermolecular interactions. According to accurate CCSD (T) computations, the stacked (parallel-displaced, PD) benzene dimer has an even smaller binding energy than the pentane dimer (À2. 8 vs. À3. 9 kcal molÀ1),[2, 14] which has the