B(C_6F_5)_3催化Si—H/Si—OR缩聚反应机理及产物结构

Mechanism and polymer structure of B(C_6F_5)_3 catalyzed polycondensation of Si—H/Si—OR

根据DFT理论,用量子化学的方法对B(C6F5)3催化Si—H/Si—OR缩聚反应的机理进行了研究,用29SiNMR对1,4-双(二甲基硅基)苯(BDSB)与二甲基二甲氧基硅烷、甲基乙烯基二甲氧基硅烷、二苯基二甲氧基硅烷缩聚产物的微观结构进行了表征,结合反应机理,对单体的结构与缩聚产物的微观结构的关系进行了讨论。B(C6F5)3先与Si—H形成弱加合物,然后Si—OR进攻Si—H/B(C6F5)3加合物使Si—H断裂,形成氧钅翁离子中间体,最后H-向正电中心迁移形成产物。H-迁移方向的不同将导致3种反应:缩合、交换、逆反应。烷氧基硅烷中的乙烯基、苯基可以增加烷氧基C的正电性,并使C—O键伸长,减少Si—H/Si—OR交换反应的发生,使得缩聚产物具有更为交替的结构。

The mechanism of B（C6F5）3 catalyzed Si-H/Si-OR polycondensation reaction was studied through the quantum chemistry methods. Poly （ silphenylene-siloxane ） s were prepared by polycondensation of 1,4-bis（ dimethylsilyl ） benzene （ BDSB ） and dimethyldimethoxylsilane, vinylmethyldimethoxylsilane and diphenyldimethoxylsilane respectively. The microstructure of the polymer was characterized by ^29Si NMR and the influence of vinyl and phenyl groups of alkoxylsilane on the microstructure of the polymer was also discussed. B（C6F5）3 first activated Si--H to form weak adduct, then Si--OR attacked Si H/B （C6F5）3 adduct to break Si H and form oxonium ion complex. The decomposition of the complex occurred by the H transfer to one of the three electrophilic centers, which explained the competition between condensation and Si--H/Si--OR exchange. Vinyl or phenyl group of alkoxysilane decreased the positive charge of Si atom and increased the positive charge of C which bonded to O, and it also reduced the strength of C-O, resulting in more alternated polymers.