“Unexpected” 29Si NMR Chemical Shifts in Heteroatom-Substituted Silyllithium Compounds: A Quantum-Chemical Analysis
“Unexpected” 29Si NMR Chemical Shifts in Heteroatom-Substituted Silyllithium Compounds: A Quantum-Chemical Analysis
复制标题
杂原子取代的硅基锂化合物中“意外”的 29Si NMR 化学位移：量子化学分析
DOI：
10.1021/om049812k
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发表时间：
2004
期刊：
影响因子：
2.8
通讯作者：
C. Strohmann
中科院分区：
文献类型：
--
作者：
D. Auer;M. Kaupp;C. Strohmann
先前对各种杂原子取代的甲硅烷基锂化合物的29 Si NMR光谱研究揭示了“出乎意料的”高硅化学位移。为了找到这些观察结果的解释，29 Si化学位移张量的各种甲氧基，二甲氨基，和甲硫基取代的氯和lithiosilanes已被评估的量子化学计算。通过IGLO-DFT计算分析了取代基对屏蔽的影响。关于原子电荷和取代基电负性对中心原子位移的影响的流行概念不适用。在杂原子取代的硅基锂化合物中，极负电性和正电性取代基的组合导致大的去屏蔽贡献。如所示的局域化分子轨道（LMO）的屏蔽贡献的分析，这是由于键合和反键轨道与大硅字符和小的能量差的耦合。在比较IGLO-LMO结果和基于GIAO的自然...
Previous 29Si NMR spectroscopic investigations of various heteroatom-substituted silyllithium compounds revealed “unexpectedly” high silicon chemical shifts. To find explanations for these observations, the 29Si chemical shift tensors of various methoxy-, dimethylamino-, and methylthio-substituted chloro and lithiosilanes have been evaluated by quantum-chemical calculations. Substituent effects on shielding have been analyzed by IGLO-DFT calculations. Popular notions on the influence of atomic charge and substituent electronegativity on the central-atom shifts are not applicable. The combination of very electronegative and electropositive substituents leads to large deshielding contributions in heteroatom-substituted silyllithium compounds. As shown by analyses of localized molecular orbital (LMO) contributions to shielding, this is due to a coupling of bonding and antibonding orbitals with large silicon character and small energy differences. After a comparison of IGLO-LMO results and GIAO-based natural ...