Schulich Faculty of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum Chemistry, Technion-Israel Institute of Technology, Haifa, 32000, Israel.
Angew Chem Int Ed Engl. 2016 Aug 22;55(35):10258-62. doi: 10.1002/anie.201603640. Epub 2016 Jul 28.
Reaction of bromoacylsilane 1 (pink solution) with tBu2 MeSiLi (3.5 equiv) in a 4:1 hexane:THF solvent mixture at -78 °C to room temperature yields the solvent separated ion pair (SSIP) of silenyl lithium E-(tBuMe2 Si)(tBu2 MeSi)C=Si(SiMetBu2 ) Li⋅4THF 2 a (green-blue solution). Removal of the solvent and addition of benzene converts 2 a into the corresponding contact ion pair (CIP) 2 b (violet-red solution) with two THF molecules bonded to the lithium atom. The 2 a⇌2 b interconversion is reversible upon THF⇌ benzene solvent change. Both 2 a and 2 b were characterized by X-ray crystallography, NMR and UV/Vis spectroscopy, and theoretical calculations. The degree of dissociation of the Si-Li bond has a large effect on the visible spectrum (and thus color) and on the silenylic (29) Si NMR chemical shift, but a small effect on the molecular structure. This is the first report of the X-ray molecular structure of both the SSIP and the CIP of any R2 E=E'RM species (E=C, Si; E'=C, Si; M=metal).
溴代酰基硅烷 1（粉红色溶液）与叔丁基二甲基硅基锂（3.5 当量）在 4:1 的正己烷：THF 溶剂混合物中，在-78°C 至室温下反应，生成硅烯基锂的溶剂分离离子对（SSIP）E-(叔丁基二甲基硅基)(叔丁基二甲基甲硅基)C=Si(SiMetBu2 ) Li⋅4THF 2a（绿色-蓝色溶液）。除去溶剂并加入苯，将 2a 转化为相应的接触离子对（CIP）2b（紫红色溶液），其中两个 THF 分子与锂原子键合。2a ⇌ 2b 的互变异构在 THF ⇌ 苯溶剂变化时是可逆的。2a 和 2b 均通过 X 射线晶体学、NMR 和 UV/Vis 光谱以及理论计算进行了表征。Si-Li 键的离解程度对可见光谱（因此对颜色）和硅烯基（29）Si NMR 化学位移有很大影响，但对分子结构影响较小。这是首次报道任何 R2 E=E'RM 物种（E=C、Si；E'=C、Si；M=金属）的 SSIP 和 CIP 的 X 射线分子结构。
