Nonhydrolytic synthesis of branched alkoxysiloxane oligomers Si[OSiH(OR)2]4 (R=Me, Et).
Nonhydrolytic synthesis of branched alkoxysiloxane oligomers Si[OSiH(OR)2]4 (R=Me, Et).
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DOI：
10.1002/anie.201001640
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发表时间：
2010-07
影响因子：
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通讯作者：
Ryutaro Wakabayashi;Kazufumi Kawahara;K. Kuroda
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文献类型：
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作者：
Ryutaro Wakabayashi;Kazufumi Kawahara;K. Kuroda
硅醇盐是制备硅基材料的理想原料。开发具有精细控制的结构和反应性的各种烷氧基硅氧烷低聚物的合成方法对于合成具有定义的组成、结构、形态和功能的材料是重要的。3]然而，烷氧基硅氧烷低聚物的合理合成的实例是有限的。硅氧硅键的可控形成是合成烷氧基硅氧烷低聚物的关键步骤。常规合成涉及硅醇盐或氯硅烷的水解以形成硅烷醇基团和随后的缩合反应。尽管已经报道了氯代烷氧基硅烷与有机硅烷醇的反应，4]通过使用该反应合成的分子的数量是相当有限的，因为该反应限于其中所得有机硅烷醇稳定的情况。在反应期间硅烷醇基团的形成引起不希望的副反应，例如硅烷醇的自缩合和随后的末端烷氧基的水解。因此，合成含有具有限定结构的烷氧基的硅氧烷低聚物在避免副反应的问题方面是一个挑战。在不使用硅烷醇的情况下形成硅氧烷键引起了很大的兴趣。烷氧基硅氧烷可以通过氯硅烷和烷氧基硅烷醇钠之间的反应来合成。另一方面，使用烷氧基硅烷作为前体与刘易斯酸催化剂是最有前途的途径。硅氧烷键的形成随着RX（X = Cl、Br、I、AcO或H）的产生而进行。在整个过程中不涉及竞争试剂，例如含有硅烷醇基团、H2O或HCl的化合物。具有含有一个以上烷氧基的限定结构的低聚硅氧烷难以合成，15]因为副反应，例如配体交换，与硅氧烷键的形成竞争。9，13，14]在此，我们报道了具有反应性SiOR和SiH基团的支链烷氧基硅氧烷Si[OSiH（OR）2]4（R = Me（1），Et（2））的非水解合成，副反应得到抑制。反应通过在BiCl 3存在下用ClSiH（OR）2直接烷氧基硅烷化四烷氧基硅烷来进行（方案1）。BiCl 3，一种弱刘易斯酸，
Silicon alkoxides are ideal starting materials for the preparation of silica-based materials. The development of synthetic methods toward various alkoxysiloxane oligomers with finely controlled structures and reactivities is important for the synthesis of materials with defined compositions, structures, morphologies, and functionalities. 3] However, examples of the rational synthesis of alkoxysiloxane oligomers are limited. The controlled formation of Si O Si bonds is a key step in the synthesis of alkoxysiloxane oligomers. A conventional synthesis involves hydrolysis of silicon alkoxides or chlorosilanes to form silanol groups and a subsequent condensation reaction. Although the reaction of chloroalkoxysilanes with organosilanols have been reported, 4] the number of molecules synthesized by using this reaction are quite limited because the reaction is restricted to the cases where the resulting organosilanols are stable. The formation of silanol groups during the reaction causes unwanted side reactions, such as self-condensation of silanols and subsequent hydrolysis of terminal alkoxy groups. Therefore, the synthesis of siloxane oligomers that contain alkoxy groups with defined structures is a challenge in circumventing the problem of side reactions. The formation of siloxane bonds without using silanols has attracted much interest. Alkoxysiloxanes can be synthesized by the reaction between chlorosilane and sodium alkoxysilanolates. On the other hand, the use of alkoxysilanes as a precursor with a Lewis acid catalyst is the most promising pathway. The formation of siloxane bonds proceeds with the generation of RX (X = Cl, Br, I, AcO, or H). No competing reagents, such as compounds containing silanol groups, H2O, or HCl, are involved in the overall process. Oligosiloxanes with defined structures that contain more than one alkoxy group are difficult to synthesize, 15] as side reactions, such as ligand exchange, compete with the formation of siloxane bonds. 9, 13,14] Herein we report the nonhydrolytic synthesis, with suppressed side reactions, of branched alkoxysiloxanes Si[OSiH(OR)2]4 (R = Me (1), Et (2)), which possess both reactive SiOR and SiH groups. The reaction proceeds by direct alkoxysilylation of tetraalkoxysilanes with ClSiH(OR)2 in the presence of BiCl3 (Scheme 1). BiCl3, a weak Lewis acid,