Cover Picture: Nonhydrolytic Synthesis of Branched Alkoxysiloxane Oligomers Si[OSiH(OR)₂]₄ (R=Me, Et) (Angew. Chem. Int. Ed. 31/2010)

Abstract

Discrete alkoxysiloxane oligomers were synthesized by nonhydrolytic heterocondensation reactions between alkoxysilanes and chlorosilanes. In their Communication on ff., K. Kuroda and co‐workers show that the combination of the Lewis acid catalyst bismuth trichloride and alkoxysilanes that can form stable carbocations play an important role in the formation of siloxane bonds prior to the occurrence of other competing side reactions. The photograph of bismuth metal was provided by Dr. Ryoji Tanaka.

Direct alkoxysilylation of alkoxysilanes for the synthesis of explicit alkoxysiloxane oligomers

“…Similar shifts of signals in 29 Si NMR measurements were also observed for transesterification between Si(OMe) 4 and other silicon alkoxides [18,31].…”

“…Although the formation of Si[OSiR 1 (OMe) 2 ] 4 with R 1 ¼ Ph (3) is suggested by the same analyses above, its isolation was unsuccessful because of its high boiling point for vacuum distillation and its potential reactivity toward silica in flash chromatography. On the other hand, branched oligomer Si[OSiR 1 (OMe) 2 ] 4 was not obtained at all when R 1 ¼ OMe (Scheme 2 bottom), and a mixture of linear alkoxysiloxane oligomers was formed as mentioned in our previous report [18].…”

“…These signals can be assigned to Si(Ot-Bu)(OMe) 3 and Si(Ot-Bu) 2 (OMe) 2 respectively. These assignments are based on the fact that the signal of Si(OMe) 4 and Si(Ot-Bu) 4 appears at around d ¼ À78.0 and À98.0 ppm [14,18].…”

“…Previously, we demonstrated the synthesis of Si[OSiH(OMe) 2 ] 4 and Si[OSiH(OEt) 2 ] 4 [18]. Therefore, our interests are focused whether functional groups can be successfully introduced to oligomers by the reaction.…”

“…It is difficult to develop synthetic approaches to silicates for the purposes explored here because the reactions are quite complicated, involving the competitive formation and dissociation of siloxane bonds in water. To solve this problem, we have developed a nonhydrolytic reaction to synthesize discrete alkoxysiloxane oligomers [18]. It is accomplished by optimizing nonhydrolytic solegel process generally for preparing amorphous silica and other inorganic oxides [19e24].…”