Studies on Crystal Structures and Properties of Stable Silyl Radicals

本课题以晶体形式分离了一个硅基自由基和一个硅基双自由基，并对其结构和性质进行了研究。用钠在庚烷中还原三（三异丙基硅基）氯硅烷，得到三（三异丙基硅基）硅基自由基为黄色晶体，产率67%。x射线晶体学分析表明，硅基自由基中心呈平面结构；围绕硅基自由基中心的三个Si-Si-Si键角之和为359.99°。在庚烷中，这种硅基自由基在室温下的半衰期为4天，而在含有芴、萘等芳烃的庚烷溶液中，其半衰期为1.5-3个月。这些事实表明，这种硅基通过与芳烃的相互作用而稳定下来。苯中钾还原反式-1,3-二溴-1,2,2,3,4,4-六叔丁基环四硅烷通过三种顺磁中间体得到（反式-1,2,2,3,4,4-六叔丁基-1,3-环四硅二基）二钾。第三种顺磁物质在ESR光谱中与卫星呈双偶态，并被分离为红色晶体。x射线晶体分析表明，该物质为1,2,2,3,4,4-六-叔丁基-1,3-环四硅二基双自由基。硅基自由基中心具有平面结构。两个硅基自由基中心之间的距离为2.796(3)Å，两者之间没有形成共价键。这是第一个用ESR观察到硅基双基并分离出硅基双基晶体的例子。还原的最终产物（反式-1,2,2,3,4,4-六-叔丁基-1,3-环四烷二基）二钾被分离为紫色晶体。x射线晶体分析表明，硅基离子与苯相互作用，形成了一种新的一维超分子结构。

In this project, a silyl radical and a silyl biradical were isolated as crystals, and their structures and properties were studied.The reduction of tris(triisopropylsilyl)chlorosilane with sodium in heptane gave tris(triisopropylsilyl)silyl radical as yellow crystals in 67% yield. The X-ray crystallographic analysis showed that the silyl radical center has a planar structure ; the sum of three Si-Si-Si bond angles around the silyl radical center is 359.99°. In heptane, this silyl radical has the half-life of 4 days at room temperature, while in a heptane solution containing aromatic hydrocarbons such as fluorene, naphthalene, etc., its half-life is 1.5-3 months. These facts indicate that this silyl radical is stabilized by the interaction with aromatic hydrocarbons.The reduction of trans-1,3-dibromo-1,2,2,3,4,4-hexa-tert-butylcyclotetrasilane with potassium in benzene gave (trans-1,2,2,3,4,4-hexa-tert-butyl-1,3-cyclotetrasilanediyl)dipotassium via three kinds of paramagnetic intermediates. The third paramagnetic species showed a doublet with satellites in the ESR spectrum and was isolated as red crystals. The X-ray crystallographic analysis showed that this species is 1,2,2,3,4,4-hexa-tert-butyl-1,3-cyclotetrasilanediyl biradical. The silyl radical centers have a planar structure. The distance between two silyl radical center is 2.796(3)Å, and a covalent bond is not formed between them. This is the first example of the observation of a silyl biradical by ESR and the isolation of a silyl biradical as crystals.The final product of this reduction, (trans-1,2,2,3,4,4-hexa-tert-butyl-1,3-cyclotetrasilanediyl)dipotassium, was isolated as purple crystals. The X-ray crystallographic analysis showed that the silyl dianion forms a novel 1-D supramolecular structure, in which the silyl dianion interacts with benzene.