Nazish Mohd, Patten Tim, Huang Yuqing, Kushvaha Saroj Kumar, Zhao Lili, Krawczuk Anna, Frenking Gernot, Roesky Herbert W
Anorganische Chemie, Universität Göttingen, Göttingen, Germany.
State Key Laboratory of Materials-Oriented Chemical Engineering, School of Chemistry and Molecular Engineering, Nanjing Tech University, Nanjing, China.
Commun Chem. 2024 Dec 28;7(1):307. doi: 10.1038/s42004-024-01396-9.
The search for stable compounds containing an antiaromatic cyclic 4π system is a challenge for inventive chemists that can look back on a long history. Here we report the isolation and characterization of the novel 4π-electron tetrasilacyclobutadiene, an analogue of a 4π neutral cyclobutadiene that exhibits surprising features of a Möbius-type aromatic ring. Reduction of RSiCl (R = (Pr)PCH) with KC in the presence of cycloalkyl amino-carbene (cAAC) led to the formation of corresponding silylene 1. Compound 1 shows further reactivity when treated with RSiCl under reducing conditions resulting in the formation of unsymmetrical bis-silylene 2, which was isolated as a dark red crystalline solid. Compound 3 was obtained when chlorosilylene was reduced with potassium graphite in the presence of 2. Although 3 is, according to Hückel's rule an antiaromatic system it possesses significant aromatic character due to the unusual delocalization of the HOMO-1 and the loss of degeneracy of the higher-lying π MOs. The aromatic character of 3 is indicated by the structural stability of the compound by the very similar Si-Si bond lengths and by the NICS values. There is an unusual π conjugation between the 4 π electrons in the nearly square-planar Si ring where the delocalization of the HOMO-1 occurs at two opposite sides of the ring. The reversal of the π conjugation resembles the twisting of the π conjugation in Möbius aromatic systems and it contributes to the stability of the compound.
寻找含有反芳香性环状4π体系的稳定化合物，对于有着悠久历史的富有创造力的化学家来说是一项挑战。在此，我们报告了新型4π电子四硅环丁二烯的分离与表征，它是4π中性环丁二烯的类似物，展现出莫比乌斯型芳香环的惊人特征。在环烷基氨基卡宾（cAAC）存在下用KC还原RSiCl（R = (Pr)PCH）导致形成相应的硅烯1。化合物1在还原条件下用RSiCl处理时显示出进一步的反应活性，生成不对称双硅烯2，其作为暗红色结晶固体被分离出来。当在2存在下用钾石墨还原氯硅烯时得到化合物3。尽管根据休克尔规则3是一个反芳香体系，但由于HOMO - 1的异常离域以及较高能级π分子轨道简并性的丧失，它具有显著的芳香特征。化合物3的芳香特征通过其结构稳定性、非常相似的Si - Si键长以及核独立化学位移（NICS）值得以体现。在近乎平面正方形的Si环中的4个π电子之间存在异常的π共轭，其中HOMO - 1的离域发生在环的两个相对侧。π共轭的反转类似于莫比乌斯芳香体系中π共轭的扭曲，这有助于化合物的稳定性。
