Modern Approaches to Silylium Cations in Condensed Phase
Modern Approaches to Silylium Cations in Condensed Phase
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凝聚相硅阳离子的现代方法
DOI：
10.1002/chin.199545304
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发表时间：
1995
期刊：
影响因子：
--
通讯作者：
Shizhong Zhang
中科院分区：
文献类型：
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作者：
J. B. Lambert;L. Kania;Shizhong Zhang
直到最近，许多碳基功能的硅类似物被认为是不太可能的结构实体。然而，现在已经制备了许多键合硅的例子，并获得了x射线结构，包括Si= C, Si= N和Si= Si。这些进展的一个突出的例外是三坐标，带正电的硅，R3-Si+，碳离子的类似物。碳离子在有机化学中的核心重要性似乎要求它的硅类似物发挥类似的作用，这是自然界所拒绝的。为了克服自然界的这种沉默，化学家们一直在寻求制造这样的材料，既可以作为活性中间体，也可以作为稳定的物质。随着其他硅中间体堡垒的倒塌，三坐标阳离子成为人们关注的焦点，可能超过了它的内在价值。在本综述中，游离的硅离子（以前称为硅或硅离子）是带正电的平面三坐标物质。此外，当硅为四配位，与第四配位位部分共价键并具有正电荷优势时，阳离子可能具有不同程度的硅离子特征。相反，硅离子是带正电的物质，其中硅的配位高于4。有些作者倾向于把“硅离子”一词限定为全三坐标形式。然而，在碳离子化学中，带电结构的连续体是很好的先例，其中碳-金属键可以具有不同程度的共价键。术语硅基阳离子或硅位在上下文中可适用于硅离子或硅离子。
Many silicon analogues to carbon-based function-alities were considered to be unlikely structural entities until recently. Numerousexamples of^-bond-ed silicon, however, now have been prepared and X-ray structures obtained, including Si= C, Si= N, and Si= Si. 1 A prominent exception to these advances has been tricoordinate, positively charged silicon, R3-Si+, the analogue of the carbenium ion. The central importance of the carbenium ion in organic chemistry seemed to demand a similar role for its silicon analogue that nature resisted. To overcome this reticence on the part of nature, chemists have sought to produce such materials, both as reactive intermediates and as stable species. As other bastions of silicon intermediates fell, the tricoordinate cation became a focus of attention that probably exceeded its inherent value.For the purposes of this review, free silylium ions (formerly silylenium or silicenium ions) are positively charged, planar, three-coordinate species. In addi-tion, cations may have varying degrees of silylium ion character when the silicon is four coordinate with partial covalent bonding to the fourth coordination site and possesses the preponderance of the positive charge. In contrast, siliconium ions are positively charged species inwhich silicon has higher than four coordination. Some authors prefer to restrict the term silylium ion to the fully tricoordinate form. A continuum of charged structures, however, is well precedented in carbanion chemistry, in which carbon-metal bonds can have varied degrees of covalent character. 2 The term silyl cation or silicocation may apply to either silylium or siliconium ion, within context.