Syntheses and Properties of Cyclopolysilanes with Well-defined Structures as Models for σ-Conjugation

1. 在一系列梯形聚硅烷的反异构体中，随着环四硅烷环数的逐渐增加，最长波长的吸收最大值向较长波区移动。这种变化可以用Si-Si - σ-共轭扩展对最低未占据分子轨道（LUMO）的稳定化来解释。梯状聚硅烷容易被Na和K还原生成自由基阴离子。由此产生的自由基阴离子的显著特征是它们不同寻常的稳定性。例如，在没有二氧的情况下，五环十二烷基硅烷的半衰期太长而无法测量。x射线晶体学表明，反阶梯型聚硅烷可以看作是硅双螺旋结构，其中两个线性聚硅烷链单向螺旋并由Si-Si键桥接。反三环己烷可以实现手性对称性破缺。对映体M或p各有一个大的结晶。缺乏间氯过苯甲酸（MCPBA）的双环己硅烷氧化生成7-氧化合物，该化合物具有较强的紫外吸收和荧光。多米诺氧化分别在三环十二硅烷、四环十硅烷和五环十二硅烷与MCPBA的三、四和五氧化中占主导地位。从顺式、顺式和顺式环三硅烷[Ph (Thex) Si]_3 （Thex= 1,1,2 -三甲基丙基）与卤素开环的立体化学结果来看，Si-Si键的断裂是伴随着Si原子构型的保留反转发生的。为了比较烷基取代的八苯甲醚与相应的八苯甲醚的化学性质和物理性质，合成了八苯甲醚。在紫外-可见光下，八角霉素非常稳定，这表明多面体锗骨架具有不同寻常的电子和光化学性质。少

1. In a series of the anti isomers of the ladder polysilanes, the absorption maxima of the longest wavelength shift to the longer wavelength region as the number of cyclotetrasilane rings progressively increases. The shift is explained in terms of the stabilization of the lowest unoccupied molecular orbitals (LUMO) by the extension of the Si-Si σ-conjugation. The ladder polysilanes can be readily reduced by Na and K to generate the radical anions. The remarkable feature of the resulting radical anions is their unusual stability. For example, in the absence of dioxygen, the half-life of the pentacyclododecasilane is too long to be measured. The X-ray crystallography disclosed that the anti ladder polysilanes can be seen as silicon double helices, in which two linear polysilane chains screw in one way and are bridged by Si-Si bonds. Chiral symmetry breaking could be realized for anti-tricyclooctasilane. The crystallization gave one large crystal of each enantiomer M or P.The oxidation of … More the bicyclohexasilane with a deficient amount of m-chloroperbenzoic acid (MCPBA) resulted in the formation of 7-oxa compound, which shows stronger UV absorption and fluorescence. The domino oxidation predominates in the tri-, tetra-, and penta-oxidations of the tricyclooctasilane, tetracyclodecasilane, and pentacyclododecasilane with MCPBA, respectively.2. From the stereochemical results observed in the ring-opening of the cis, cis- and cis, transcyclotrisilane [Ph (Thex) Si]_3 (Thex=1, 1, 2-trimethylpropyl) with halogens, it is concluded that the cleavage of the Si-Si bonds occurs with retention -inversion of the configuration of the Si atoms.3. Octathexyloctagermacubane was synthesized to allow a comparison of chemical and physical properties of the alkyl-substituted octasilacubane with those of the corresponding octagermacubane. The octagermacubane is very stable to UV-Visible light, suggesting the unusual electronic and photochemical properties of the polyhedral germanium framework. Less