Direct insight into the ion pair equilibria of lithium organocuprates by 1H,6Li HOESY experiments
Direct insight into the ion pair equilibria of lithium organocuprates by 1H,6Li HOESY experiments
复制标题
DOI：
10.1021/om000068n
复制
发表时间：
2000-07-24
期刊：
影响因子：
2.8
通讯作者：
Boche, G
中科院分区：
文献类型：
--
作者：
Gschwind, RM;Rajamohanan, PR;Boche, G
研究了具有代表性的双有机酸锂me2cui的单体溶剂分离离子对（SSIP）和接触离子对（CIP）之间的平衡。在THF中，使用H-1，Li-6 HOESY技术。有趣的是，相关体系的晶体结构也属于SSIP型和CIP型，后者以二聚体为基本结构元素，其结构类型取决于溶剂的Li+溶剂化能力。在cip的晶体结构中，锂-碳的最短距离约为220 pm，这将导致强烈的偶极相互作用。事实上，对于Et2O中的无盐Me2CuLi，在H-1，Li-6 HOESY光谱中可以看到铜酸盐的锂和CH3基团之间的强交叉峰，表明溶液中的主要物质是CIP。相反，sips的晶体结构表明，锂与铜的有机部分之间的距离太长，无法导致任何偶极相互作用（最短的锂-碳距离超过530 pm）。MeCu(CN)Li和t-Bu2CuLi的H-1、Li-6 HOESY光谱证实了这一点。THF中的lcn。然而，与纯SSIP结构不同，Me2CuLi中锂与CH3基团之间存在弱的偶极相互作用。在THF中，LiCN和Me2CuLi是直接偶极相互作用的结果。这种偶极相互作用的大小被用来确定Me2CuLi的SSIP和CIP之间的平衡。THF中的lcn。在213 K时，THF的优势种是SSIP， CIP有一定贡献。正如预期的那样，这种平衡可以在较低的温度下向SSIP转移。结果表明，H-1，Li-6 HOESY技术可以直接了解溶液中重有机酸锂的结构特征。这对它们的反应性有重要意义。
An equilibrium between a monomeric solvent-separated ion pair (SSIP) and a contact ion pair (CIP) is observed directly for a representative Lithium diorganocuprate, Me2CuLi . LiCN, in THF, using the H-1,Li-6 HOESY technique. Interestingly, crystal structures of related systems are also of the SSIP and the CIP type, whereby the latter shows a dimer as the fundamental structural element and the structure type depends on the Li+ solvating capability of the solvent. In crystal structures of CIPs the shortest lithium-alpha-carbon distances are around 220 pm, which should lead to a strong dipolar interaction. Indeed, for the salt-free Me2CuLi in Et2O a strong cross-peak between lithium and the CH3 groups of the cuprate is seen in the H-1,Li-6 HOESY spectrum, indicating that the main species in solution is a CIP. In contrast, the crystal structures of SSIPs show that the distance between lithium and the organic moiety of the cuprate is too long to lead to any dipolar interaction (shortest lithium-alpha-carbon distances longer than 530 pm). This is confirmed by the H-1,Li-6 HOESY spectra of MeCu(CN)Li and t-Bu2CuLi . LiCN in THF. However, deviating from the pure SSIP structures, a weak dipolar interaction between lithium and the CH3 groups could be observed for Me2CuLi . LiCN and Me2CuLi in THF, which was attributed to a direct dipolar interaction. The magnitude of this dipolar interaction was used to identify an equilibrium between the SSIP and the CIP of Me2CuLi . LiCN in THF. At 213 K the dominant species in THF is the SSIP with some contributions of the CIP. As expected, this equilibrium could be shifted at lower temperatures toward the SSIP. It is demonstrated that the H-1,Li-6 HOESY technique can be used to get direct insight into the structural features of Lithium diorganocuprates in solution. which is of great significance for their reactivity.