Valence-shell charge concentrations and electron delocalization in alkyllithium complexes: negative hyperconjugation and agostic bonding.
Valence-shell charge concentrations and electron delocalization in alkyllithium complexes: negative hyperconjugation and agostic bonding.
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DOI：
10.1002/1521-3765(20020517)8:10
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发表时间：
2002-05
期刊：
影响因子：
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通讯作者：
W. Scherer;Peter Sirsch;D. Shorokhov;G. Mcgrady;Sax A. Mason;Michael G. Gardiner
中科院分区：
文献类型：
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作者：
W. Scherer;Peter Sirsch;D. Shorokhov;G. Mcgrady;Sax A. Mason;Michael G. Gardiner
在本文中，我们提出的乙基配体和一些相关的有机部分的密度泛函理论（DFT）计算的结果，然后，我们着手考虑一系列的烷基锂配合物的DFT计算和高分辨率的X-射线和中子衍射研究。电荷密度的拓扑分析用于跟踪有机片段的电子结构的变化。在α和β原子处的价层中的电荷浓度（CC）忠实地揭示了在Calpha原子处的孤对电子或Li-C键合电子的离域。因此，负超共轭所示，从离域的孤对或锂-C键合电子的烷基片段，与消耗的金属定向电荷浓度在Calpha，和特征椭圆曲线的超共轭离域中所涉及的债券。在所谓的锂agostic配合物的情况下，我们表明，密切的Li. H接触是这种离域和进一步的二次相互作用的结果，与Li.H-C agostic相互作用，只发挥次要作用。的椭圆率配置文件和在Calpha的CC的大小提供了一个定量的测量的程度的离域，并表现出良好的实验和理论之间的协议。
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 Calpha atom or of the Li-C bonding electrons. Negative hyperconjugation 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 Calpha, 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 Calpha provide a quantitative measure of the extent of delocalization, and show excellent agreement between experiment and theory.