A Planar Rhombic Charge-Separated Tetrasilacyclobutadiene
A Planar Rhombic Charge-Separated Tetrasilacyclobutadiene
复制标题
DOI：
10.1126/science.1199906
复制
发表时间：
2011-03
期刊：
影响因子：
56.9
通讯作者：
Katsunori Suzuki;Tsukasa Matsuo;D. Hashizume;H. Fueno;Kazuyoshi Tanaka;K. Tamao
中科院分区：
文献类型：
--
作者：
Katsunori Suzuki;Tsukasa Matsuo;D. Hashizume;H. Fueno;Kazuyoshi Tanaka;K. Tamao
一种稳定的硅类似物的反应性，反芳烃已被合成和表征。环丁二烯（CBD）分子C4 H4偏离高对称性正方形几何结构，以补偿其反芳族电子结构。在这里，我们报道了CBD硅类似物Si 4（EMind）4（1），其通过大体积的1，1，7，7-四乙基-3，3，5，5-四甲基-s-氢化茚满-4-基（EMind）基团稳定，通过用三当量的萘锂还原（EMind）SiBr 3获得为空气和水分敏感的橙子晶体。X射线晶体学揭示了Si 4四元环的平面和菱形结构，在硅原子处具有交替的金字塔和平面构型。在固态核磁共振谱中，29 Si的化学位移差异很大（Δδ > 350 ppm），这表明交替电荷分离结构的贡献。因此，化合物1的菱形电荷分离单重态以与键长交替形成鲜明对比的方式稳定其环状4π电子反芳香性，其特征在于碳基CBD的矩形畸变。
A stable silicon analog of a reactive, antiaromatic hydrocarbon has been synthesized and characterized. The cyclobutadiene (CBD) molecule C4H4 deviates from a high-symmetry square geometry to compensate for its antiaromatic electronic structure. Here, we report a CBD silicon analog, Si4(EMind)4 (1), stabilized by the bulky 1,1,7,7-tetraethyl-3,3,5,5-tetramethyl-s-hydrindacen-4-yl (EMind) groups, obtained as air- and moisture-sensitive orange crystals by the reduction of (EMind)SiBr3 with three equivalents of lithium naphthalenide. X-ray crystallography reveals a planar and rhombic structure of the Si4 four-membered ring, with alternating pyramidal and planar configurations at the silicon atoms. The large 29Si chemical shift differences (Δδ > 350 parts per million) in the solid-state nuclear magnetic resonance spectra suggest a contribution of an alternately charge-separated structure. The rhombic-shaped charge-separated singlet state of compound 1 thus stabilizes its cyclic 4π-electron antiaromaticity in a manner that contrasts sharply with the bond-length alternation, characterizing the rectangular distortion of carbon-based CBD.