Studies on Crystal Structures and Properties of Stable Silyl Radicals

本课题分离出了一种硅基自由基和一种硅基双自由基的晶体，并对其结构和性质进行了研究，三（三异丙基硅基）氯硅烷在庚烷中用钠还原得到了黄色晶体三（三异丙基硅基）硅基，产率为67%。X射线晶体学分析表明，硅自由基中心为平面结构，硅自由基中心周围的三个Si-Si-Si键角之和为359.99°。在庚烷中，这种甲硅烷基自由基在室温下的半衰期为4天，而在含有芳烃如芴、萘等的庚烷溶液中，其半衰期为1.5-3个月。反式-1，3-二溴-1，2，2，3，4，4-六叔丁基环四硅烷在苯中被钾还原，通过三种顺磁性中间体得到（反式-1，2，2，3，4，4-六叔丁基-1，3-环四硅烷）二钾。第三顺磁性物质在ESR谱中显示出具有卫星的双峰，并被分离为红色晶体。X-射线晶体学分析表明该化合物为1，2，2，3，4，4-六叔丁基-1，3-环四硅烷基双自由基。甲硅烷基中心具有平面结构。两个硅基中心之间的距离为2.796（3）nm，并且它们之间不形成共价键。这是第一个用ESR观察到甲硅烷基双自由基并分离出结晶的甲硅烷基双自由基的例子，该还原反应的最终产物（反式-1，2，2，3，4，4-六叔丁基-1，3-环四硅烷基）二钾分离出紫色晶体。X-射线衍射分析表明，硅基二价阴离子与苯相互作用形成了一维超分子结构。

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.