Rapid Assembly of Complex 3D Siloxane Architectures

Abstract

Few routes to well-defined 3D silicone structures exist because of their susceptibility to depolymerization/metathesis in the presence of acids or bases. The Lewis acid B(C6F5)3 can be employed to condense hydrosilanes with alkoxysilanes, producing siloxanes and alkanes (R3SiH+R'OSiR' '3 --> R3SiOSiR' '3 + R'H). We demonstrate that balancing the steric demands at both the hydrosilane and alkoxysilanes, and the careful control of reaction conditions, permits clean condensation reactions to occur in the absence of competing metathesis processes. The resulting linear or highly branched siloxane compounds can be rapidly and easily assembled into explicit, complex 3D silicone structures in high yield.

The Power of Non-Hydrolytic Sol-Gel Chemistry: A Review

“…It is catalyzed by tris(pentafluorophenyl)borane and utilized mainly in the synthesis of siloxane polymers, but its application to the preparation of hybrid mixed oxide (Si-O-B) systems was shown recently [25,26,[52][53][54].…”

“…Finally all three members of the siloxane family (molecular compounds [26,127], linear [128] and 3D cross-linked [53,129,130] polysiloxanes) were successfully prepared by the Piers-Rubinsztajn reaction (or dehydrocarbon condensation) as reviewed elsewhere [25,111]. Although research into this reaction type is strongly focused on the polymer science, the first examples of the preparation of porous silica-based hybrid materials [131] and mixed Si-O-B oxides [54] have been reported.…”

“…Similar to the other NHSG syntheses, this reaction suffers from ligand exchange and homocondensation, which led to lower homogeneity in the final products. However, it can be strongly suppressed by a careful selection of starting compounds [26,128]. Thus it was shown by 29 Si NMR that diphenyldimethoxysilane condenses with 1,4-bis(dimethylsilyl)benzene to produce almost perfectly alternating polymer, while a mixture of dimethyldimethoxysilane and 1,4-bis(dimethylsilyl)benzene is prone to ligand scrambling and only random homogeneity was achieved [128].…”

“…Significant differences in reactivity and tendency to ligand exchange were also observed when comparing tetramethoxysilane, tetraethoxysilane and tetra(isopropoxy)silane. This was explained by different steric hindrance at the Si atoms by the organic groups (Scheme 7) [26].…”

Photo Lewis acid generators: photorelease of B(C6F5)3 and applications to catalysis

“…16,17 The ability of B(C 6 F 5 ) 3 to activate Si-H bonds has lead not only to the development of a number of hydrosilation applications, but a method for preparing complex, monodisperse silicone structures that would be difficult if not impossible to prepare using conventional methods. 18,19 These applications rely on the "Piers-Rubinsztajn reaction", 20 a dealkylative siloxane synthesis generally depicted in eqn (1). This versatile reaction can also be used to form polymeric structures, 21,22 or as a vector for crosslinking macromolecules and changing the physical properties of polysiloxane materials.…”