Studies on Properties of Long Ladder Polysilanes with Double Helix Structures

本课题合成了长阶梯型聚硅烷，并对其结构和性能进行了研究。同时，对三环阶梯型聚硅烷中的离子进行了分离，并对其结构和反应进行了研究。采用1,1,4,4-四氯六异丙基四硅烷和1,1,2,2-四氯二异丙基二硅烷与锂的偶联方法合成了六环-八环阶梯型聚硅烷。x射线分析表明，这些化合物的硅骨架为双螺旋结构，硅硅端阶之间的扭角分别为96.2°和101.1°（六环）、119.6°（七环）和128.5°（八环）。随着梯状聚硅烷环数的增加，紫外可见光谱中最低能量吸收最大值呈色移，氧化电位降低。分子轨道计算表明，这些电子性质可以用最高已占据分子轨道（HOMO）能级的不稳定和最低未占据分子轨道（LUMO）能级的稳定来解释。在18-冠-6存在的情况下，用钾还原三环梯状聚硅烷，三环梯状聚硅烷1,2位上的硅-硅键断裂得到二（2-钾六异丙基环四硅烷基）。x射线分析表明，在还原过程中，硅原子在1,2位附近发生了反转，两个钾离子被纳入18-crown-6中。该离子与二甲基二氯硅烷或三甲基氯硅烷反应得到具有三环[5.2.0.0^<2,5>]非硅烷和双（环四硅烷）骨架的新型聚硅烷。

In this research project, long ladder polysilanes were synthesized, and their structures and properties were studied. Also, the dianion of the tricyclic ladder polysilane was isolated, and its structure and reactions were studied.The hexa- to octacyclic ladder polysilanes were synthesized by the coupling of 1,1,4,4-tetrachlorohexaisopropyl-tetrasilane and 1,1,2,2-tetrachlorodiisopropyldisilane with lithium. The X-ray analysis showed that the silicon skeletons of these compounds have double helix structures, and the twist angles between the terminal silicon-silicon rungs are 96.2 and 101.1°(hexacyclic), 119.6°(heptacyclic), and 128.5°(octacyclic). As the number of cyclotetrasilane rings of the ladder polysilanes increases, the lowest energy absorption maximum in the UV-visible spectra shifts bathochromically, and the oxidation potential decreases. Molecular orbital calculations showed that these electronic properties are explained by the destabilization of the energy level of the highest occupied molecular orbital (HOMO) and the stabilization of the energy level of the lowest unoccupied molecular orbital (LUMO).By the reduction of the tricyclic ladder polysilane with potassium in the presence of 18-crown-6, the silicon-silicon bond at the 1,2-positions of the tricyclic ladder polysilane was cleaved to give bis(2-potassiohexaisopropylcyclotetrasilanyl). The X-ray analysis showed that the inversion around the silicon atoms at the 1,2-positions took place during the reduction, and two potassium ions were incorporated into 18-crown-6. The reactions of this dianion with dimethyldichlorosilane or trimethylchlorosilane gave novel polysilanes with tricyclo[5.2.0.0^<2,5>]nonasilane and bis(cyclotetrasilanyl) skeletons.