Takeda Nobuhiro, Kajiwara Takashi, Suzuki Hiroyuki, Okazaki Renji, Tokitoh Norihiro
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
Chemistry. 2003 Aug 4;9(15):3530-43. doi: 10.1002/chem.200204643.
The first stable silylene-isocyanide complexes, [Tbt(Mes)SiCNAr] (5 c: Ar=Tip, 5 d: Ar=Tbt, 5 e: Ar=Mes*; Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Mes=mesityl, Tip=2,4,6-triisopropylphenyl, Mes*=2,4,6-tri-tert-butylphenyl) were successfully synthesized by the reaction of a kinetically stabilized disilene, [Tbt(Mes)Si=Si(Mes)Tbt] (1), with bulky isocyanides, ArNC (3c-e). The spectroscopic data of 5 c-e and theoretical calculations for a model molecule indicated that 5 c-e are not classical cumulative compounds but the first stable silylene-Lewis base complexes. The reactions of 5 c-e with triethylsilane and 1,3-dienes gave the corresponding silylene adducts, and they underwent isocyanide-exchange reactions in the presence of another isocyanide at room temperature. These results indicate dissociation of complexes 5 c-e to the corresponding silylene 2 and isocyanides 3 c-e under very mild conditions. The reaction of 5 c with methanol gave the MeOH adduct 16, [Tbt(Mes)SiHC(OMe)NTip], which has a hydrogen atom on the silicon atom. This regioselectivity can be explained in terms of the contribution of zwitterionic resonance structures D and E, which have an anion on the silicon atom. This result indicates that 5 c is not a classical cumulene having Si=C double bonds that should react with methanol to give adducts bearing a methoxyl group on the silicon atom. Although the reactions of 5 c-e with electrophilic reagents such as methanol, hydrogen chloride, and methyl iodide gave the formal silylene adducts, the studies on the reaction mechanism by trapping experiments and the observation of the intermediate suggested that the reaction mainly or partially proceeds by initial nucleophilic attack of the silicon atom, as is the case in the formation of 16 in the reaction of 5 c with methanol. It was revealed that 5 c-e show the nucleophilicity of the silicon atom, most likely resulting from the contribution of the zwitterionic resonance structures D and E.
首个稳定的硅烯 - 异腈配合物，[Tbt(Mes)SiCNAr]（5c：Ar = Tip，5d：Ar = Tbt，5e：Ar = Mes*；Tbt = 2,4,6 - 三[双（三甲基硅基）甲基]苯基，Mes = 均三甲苯基，Tip = 2,4,6 - 三异丙基苯基，Mes* = 2,4,6 - 三叔丁基苯基）通过动力学稳定的乙硅烯[Tbt(Mes)Si = Si(Mes)Tbt]（1）与位阻异腈ArNC（3c - e）反应成功合成。5c - e的光谱数据以及对模型分子的理论计算表明，5c - e并非传统的累积化合物，而是首个稳定的硅烯 - 路易斯碱配合物。5c - e与三乙基硅烷和1,3 - 二烯反应生成相应的硅烯加合物，并且它们在室温下于另一种异腈存在时会发生异腈交换反应。这些结果表明配合物5c - e在非常温和的条件下会解离为相应的硅烯2和异腈3c - e。5c与甲醇反应生成MeOH加合物16，[Tbt(Mes)SiHC(OMe)NTip]，其硅原子上有一个氢原子。这种区域选择性可以用两性离子共振结构D和E的贡献来解释，这两个结构在硅原子上有一个阴离子。该结果表明5c并非具有Si = C双键的传统累积烯烃，这种累积烯烃与甲醇反应会生成硅原子上带有甲氧基的加合物。尽管5c - e与亲电试剂如甲醇、氯化氢和碘甲烷反应生成形式上的硅烯加合物，但通过捕获实验对反应机理的研究以及对中间体的观察表明，反应主要或部分通过硅原子的初始亲核进攻进行，就像5c与甲醇反应生成16的情况一样。结果表明5c - e表现出硅原子的亲核性，这很可能是由于两性离子共振结构D和E的贡献。
