Generation of Silyl Cations by Hydroalumination Reactions

在该项目的第一阶段，我们合成了高度官能化的硅和锗化合物，其在一个分子中具有与第14族元素结合的刘易斯碱性给体原子（X）和在β-位置的刘易斯酸性受体原子（Al，Ga）。相反的功能之间的分子内相互作用产生的E-X键的伴随激活的加合物。基团X完全转移到铝和镓原子上以及E-X键的断裂可能导致形成具有甲硅烷基或甲锗烷基阳离子的化合物，由于它们的两性离子性质，它们应该可溶于非极性有机溶剂中。这种基于独立离子的阳离子的独特结构和反应性引发了当前激烈的研究活动。在我们的化合物中，X代表氮或氯原子和炔的α-碳原子。活化的炔发生有趣的重排，生成具有显著荧光行为的硅杂环丁烯或锗杂环丁烯。第一甲硅烷基阳离子可以作为不对称双晶重排中的中间体形成。这些具有活化的Si-X或Ge-X键的化合物代表了合成我们的目标分子的第一个成功步骤，并且我们已经学会了合成大量具有E-X键活化的化合物。这些结果显然有助于为我们未来的工作和阳离子物种的产生制定合理的策略。E-X键的完全断裂可通过与硅或锗原子键合的给电子取代基的存在、离去基团在其硬或软方面的改性以及铝或镓原子的增加的受体强度（其可通过吸电子基团实现）来促进。迄今为止获得的活化化合物显示出独特的反应性，类似于著名的和深入研究的阻挫刘易斯对之一，并可能对有机和无机底物的无过渡金属活化作出重要贡献。促进了到活化的Si-X和Ge-X键中的插入反应或取代基交换反应。

In the first period of this project we synthesized highly functionalized silicon and germanium compounds which had in one molecule Lewis basic donor atoms (X) bound to the group 14 element and Lewis acidic acceptor atoms (Al, Ga) in beta-position. Intramolecular interactions between the opposite functionalities yielded adducts with the concomitant activation of the E-X bonds. Complete transfer of the groups X to the aluminum and gallium atoms and cleavage of the E-X bonds may result in the formation of compounds with silyl or germyl cations which due to their zwitterionic nature should be soluble in non-polar organic solvents. The unique structures and reactivity of cations of this type based on separate ions initiated intense current research activities. In our compounds X represents nitrogen or chlorine atoms and the alpha-carbon atoms of alkynes. The activated alkynes gave an interesting rearrangement to yield sila- or germacyclobutenes which showed a remarkable fluorescent behavior. A first silyl cation may be formed as an intermediate in an unsymmetric dyotropic rearrangement. These compounds with activated Si-X or Ge-X bonds represent the first successful step for the synthesis of our target molecules, and we have learned to synthesize a large variety of compounds with E-X bond activation. These results clearly help to develop a reasonable strategy for our future work and the generation of cationic species. Complete cleavage of the E-X bond may be favored by the presence of electron donating substituents bound to silicon or germanium atoms, the modification of the leaving groups with respect to their hard- or softness and an increased acceptor strength of the aluminum or gallium atoms which may be achieved by electron withdrawing groups. The activated compounds obtained so far show a unique reactivity which resembles that one of the famous and intensely investigated Frustrated Lewis Pairs and may make an important contribution to the transition-metal-free activation of organic and inorganic substrates. Insertion reactions into the activated Si-X and Ge-X bonds or substituent exchange reactions are facilitated.