Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
J Am Chem Soc. 2011 Aug 17;133(32):12442-4. doi: 10.1021/ja205538t. Epub 2011 Jul 22.
Trivalent silicon cations are exceptionally strong electron pair acceptors that react, either desired or undesired, with almost any σ and π basic molecule. One way of intramolecular attenuation of the Lewis acidity of these superelectrophiles is by installation of a ferrocene unit at the electron-deficient silicon atom. While well-understood for isoelectronic α-ferrocenyl-substituted carbenium ions and also boranes, the stabilizing interactions between the ferrocene backbone and a positively charged silicon atom are not clear due to the challenge of crystallizing such cations. The structural characterization of our ferrocene-stabilized silicon cation now reveals an unprecedented bonding motif different from its analogues. An extreme dip angle of the silicon atom toward the iron atom is explained by two three-center-two-electron (3c2e) bonds through participation of both the upper and the lower aromatic rings of the ferrocene sandwich structure. The positive charge is still localized at the silicon atom that also retains a quasi-planar configuration.
三价硅阳离子是异常强的电子对受体，几乎可以与任何 σ 和 π 碱性分子发生所需或不需要的反应。这些超亲电试剂路易斯酸度的分子内衰减的一种方法是在缺电子硅原子上安装二茂铁单元。尽管对于等电子的 α-二茂铁取代的碳阳离子和硼烷，二茂铁骨架与带正电荷的硅原子之间的稳定相互作用由于难以结晶这些阳离子而不明确，但我们现在对二茂铁稳定的硅阳离子的结构特征的研究揭示了一种与其类似物不同的前所未有的成键模式。硅原子朝向铁原子的极端倾斜角度可以通过两个三中心两电子（3c2e）键来解释，其中两个茂铁夹心结构的上芳香环和下芳香环都参与了键的形成。正电荷仍然定域在硅原子上，该原子仍然保持准平面构型。
