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首页> 外文期刊>Chemistry: A European journal >Valence-Shell Charge Concentrations and Electron Delocalization in Alkyllithium Complexes: Negative Hyperconjugation and Agostic Bonding
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Valence-Shell Charge Concentrations and Electron Delocalization in Alkyllithium Complexes: Negative Hyperconjugation and Agostic Bonding

机译：烷基锂络合物中的价-壳电荷浓度和电子离域：负超共轭和Agostic键合。

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摘要

In this paper we present the results of density functional theory (DFT) calculations on the ethyl ligand and some related organic moieties; we then proceed to consider a range of alkyllithium complexes studied by DFT calculations and high-resolution X-ray and neutron diffraction. Topological analysis of the charge density is used to follow changes in the electronic structure of the organic fragment. The charge concentrations (CCs) in the valence shell at the #alpha# and #beta# atoms reveal faithfully the delocalization of the lone pair at the C_#alpha# atom or of the Li-C bonding electrons. Negative hypercon-jugation is thus shown to arise from delocalization of the lone pair or the Li-C bonding electrons over the alkyl fragment, with depletion of the metal-directed charge concentration at C_#alpha#, and characteristic ellipticity profiles for the bonds involved in hyperconjugative delocalization. In the case of so-called lithium agostic complexes, we show that close Li…H contacts are a consequence of this delocalization and further secondary interactions, with Li…H-C agostic interactions, playing only a minor role. The ellipticity profiles and the magnitude of the CCs at C_#alpha# provide a quantitative measure of the extent of delocalization, and show excellent agreement between experiment and theory.
机译：本文介绍了乙基配体和一些相关有机部分的密度泛函理论（DFT）计算结果;然后，我们继续考虑通过DFT计算以及高分辨率X射线和中子衍射研究的一系列烷基锂络合物。电荷密度的拓扑分析用于跟踪有机片段电子结构的变化。价壳中＃alpha＃和＃beta＃原子处的电荷浓度（CCs）忠实地揭示了孤对在C_＃alpha＃原子处或Li-C键合电子的离域。因此显示负超共轭是由于孤对或Li-C键电子在烷基片段上的离域，C_＃alpha＃处金属定向电荷浓度的耗尽以及所涉及键的特征椭圆度分布而引起的在超共轭离域。在所谓的锂原子复杂体中，我们表明紧密的Li ... H接触是这种离域和进一步次级相互作用的结果，其中Li ... H-C原子间相互作用仅起次要作用。椭圆度轮廓和C_＃alpha＃处CC的大小提供了离域程度的定量度量，并且显示了实验和理论之间的极好的一致性。

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