John B. Grande

New Synthetic Strategies for Structured Silicones Using B(C6F5)3

The dehydrocarbonative condensation of alkoxysilanes + hydrosilanes in the presence of the Lewis acid catalyst B(C6F5)3 (R3SiOR′ + HSiR3 ′′ → R3SiOSiR3 ′′ + R ′ H) – described throughout this review as the Piers-Rubinsztajn reaction – provides a new, mild strategy for the controlled synthesis of silicones. In this review we examine the mechanistic parameters that control the reaction, and outline the types of accessible small molecules, linear, branched, and cross-linked materials (resins and elastomers) that can be prepared using this and related reactions.

Siloxane−Triarylamine Hybrids: Discrete Room Temperature Liquid Triarylamines via the Piers−Rubinsztajn Reaction

A series of room temperature liquid siloxane-triarylamine hybrids were synthesized using the Piers-Rubinsztajn reaction. These materials displayed well behaved electrochemical oxidation and low T(g)s and were free-flowing liquids. The interaction between the Lewis acidic tris(pentafluorophenyl)borane catalyst and the Lewis basic starting triarylamine substrate was also investigated by steady state UV-vis spectroscopy and (19)F NMR.

Morphology-controlled synthesis of poly(oxyethylene)silicone or alkylsilicone surfactants with explicit, atomically defined, branched, hydrophobic tails.

Silicone surfactants are widely used in commerce because of the unusual surface activity when compared with fluorocarbon or hydrocarbon surfactants. However, most silicone surfactants are comprised of ill-defined mixtures, which preclude the development of an understanding of structure-surface activity relationships. Herein, we report a synthetic strategy that permits exquisite control over silicone structure by using the B(C(6)F(5))(3)-catalyzed condensation of hydro- and alkoxysilanes. Six different, precise hydrophobes were then mated to hydrophilic poly(oxyethylene)s of three different molecular weights by a metal-free click cyclization to generate a library of explicit silicone surfactants. These compounds were calculated to have a relatively linear value range of the hydrophilic-lipophilic balance, ranging from about 8 to about 15. The solubility of some of the compounds was too low to measure a critical micelle concentration (CMC). The others exhibited a broad range of surface tension values at the CMC that depend both on the length of the hydrophilic tail and, more importantly, the nature of the hydrophobic head group. Subtle distinctions in surfactant-related properties, which can be attributed to the three-dimensional structures, can be seen for compounds with comparable numbers of hydrocarbons and silicon groups.

Amphiphilic silicone architectures via anaerobic thiol-ene chemistry.

Despite broad application, few silicone-based surfactants of known structure or, therefore, surfactancy have been prepared because of an absence of selective routes and instability of silicones to acid and base. Herein the synthesis of a library of explicit silicone-poly(ethylene glycol) (PEG) materials is reported. Pure silicone fragments were generated by the B(C(6)F(5))(3)-catalyzed condensation of alkoxysilanes and vinyl-functionalized hydrosilanes. The resulting pure products were coupled to thiol-terminated PEG materials using photogenerated radicals under anaerobic conditions.

Silicone dendrons and dendrimers from orthogonal SiH coupling reactions

There are many potential applications for precise, large molecular weight silicone structures. The available elegant routes to silicone dendrimers are compromised by the use of reactions that involve acid/base formation: either type of catalyst can initiate silicone equilibration, which can lead to the loss of structural integrity of the dendrimers. Platinum-catalyzed hydrosilylation and B(C6F5)3-catalyzed Piers Rubinsztajn reactions were shown to be orthogonal. Sequential utilization of the two reactions can be applied both convergently and divergently to prepare both silicone dendrons and dendrimers. Precise silicone compounds of molecular weights in excess of 13 500 g mol−1 were prepared in good to excellent yield without the problems of degradative metathesis.