Creation, Structure, and Reactivity of Novel Hypercoordinate Organosilicon Compounds

四配位硅烷与相应的五配位氟硅酸盐之间的氟离子交换反应是一类在主族原子中心的原子转移自交换反应，其机理研究很少。该交换被认为是通过具有[Si-F-Si]线性排列的过渡态进行的。理论研究表明，SiH_nF_<4-n>（n=1-3）在气相中与[SiH_nF_ ]^-形成稳定的线性Si-F-Si桥<5-n>。我们已经开发了新型分子内氟离子供体-受体系统和相关的双硅酸盐的合成和结构。动态13 <13>C NMR研究表明，在单分子和双分子过程中，氟离子供体-受体体系中氟离子的交换。双分子交换的大的负活化熵表明该反应通过一个相当不寻常的氟桥环芳类过渡态进行。用X射线晶体学分析了分子内氟离子给体-受体体系的晶体结构。这些体系有望为离子导电材料的设计提供新的思路。X-射线晶体学分析表明，这些硅酸盐具有八面体结构，在顺式位置有两个烷基和苯基。基本上没有键交替的C-C键的tropolonate环表明，tropolonate作为分子内抗衡阳离子的硅酸盐。对这些硅酸盐的动态~ 13 <13>C NMR谱分析表明，它们的异构化过程是通过键断裂-重组机制而不是协同机制进行的。

Fluoride-ion exchange reactions between a tetracoordinate silane and the corresponding pentaccordinate fluorosilicate constitute a class of atom-transfer selfexchange reactions at a main-group atom center, the mechanism has been studied very scarcely. The exchange has been supposed to proceed via a transition state having linear arrangement of [Si-F-Si]. A theoretical study have shown that SiH_nF_<4-n> (n=1-3) forms a stable linear Si-F-Si bridge with [SiH_nF_<5-n>]^- in the gas phase. We have developed the synthesis and structure of novel intramolecular fluoride-ion donor-acceptor systems and related bissilicates. A dynamic ^<13>C NMR study has shown exchange of the fluoride-ions in the fluoride-ion donor-acceptor systems in both unimolecular and bimolecular processes. The large negative activation entropies for the bimolecular exchange suggest that the reaction proceeds via a rather unusual fluorine-bridged cyclophane-like transition states.Crystal structures of the intramolecular fluoride-ion donor-acceptor systems have been analyzed by X-ray crystallography. These systems are expected to give a novel concept to design the ion conducting materials.Novel neutral hexacoordinate silicates having tropolonate ligands were synthesized. X-ray crystallographic analysis for diphenyl- and dimethylbis (tropolonato)- silicates showed that these silicates have octahedral structure with the two alkyl and phenyl groups at the cis positions. Essentially no bond alternation in the C-C bonds of tropolonate rings suggests that the tropolonates serve as intramolecular countercations in the silicates. Analysis of the dynamic ^<13>C NMR spectra of these silicates revealed that there exists an isomerization process through a bond-rupture-recombination mechanism rather than a concerted mechanism.