Insight into the Bonding and Aggregation of Alkyllithiums by Experimental Charge Density Studies and Energy Decomposition Analyses

In
this Article, the organolithiums [((−)-sparteine)­LitBu] (1), [(ABCO)­LitBu]2 (2), and [(ABCO)2(LiiPr)4] (3) are investigated by means of experimental and theoretical charge
density determination to elucidate the nature of the Li–C and
Li–N bonds. Furthermore, the valence shell charge concentrations
(VSCCs) in the nonbonding region of the deprotonated Cα-atom will provide some insight on the localization of the carbanionic
lone pair. Analysis of the electron density (ρ­(rBCP)), Laplacian (∇2ρ­(rBCP)), and the energy decomposition (EDA) confirmed
that the Li–C/N bond exhibits astonishingly similar characteristics,
to reveal an increasingly polar contact with decreasing aggregate
size. This explains former observations on the incorporation of halide
salts in organolithium reagents. Furthermore, it could be shown that
the bonding properties of the iPr group
are similar to those of the tBu substituent.
The accuracy of fit to all previously determined properties in organolithiums
is remarkable.

本文对有机锂化合物[(-)-sparteine)LitBu]（1）、[(ABCO)LitBu]2（2）以及[[(ABCO)2(LiiPr)4]（3）]进行了研究，通过实验和理论电荷密度测定方法探究了Li-C和Li-N键的本质。此外，非键合区域去质子化Cα原子的价壳层电荷浓度（VSCCs）将有助于揭示碳阴离子孤对电子的局域化。对电子密度（ρ(rBCP)）、拉普拉斯算子（∇²ρ(rBCP)）和能量分解（EDA）的分析证实，Li-C/N键展现出令人惊讶的相似特性，揭示了随着聚合体尺寸的减小，其极性接触逐渐增强。这解释了先前关于卤化物盐在有机锂试剂中嵌入的观察。此外，还表明异丙基（iPr）基团的成键性质与叔丁基（tBu）取代基相似。与之前确定的有机锂化合物所有性质的良好拟合度令人瞩目。