Fluoride Rearrangement Reactions of Polyphenyl- and Polyvinylsilsesquioxanes as a Facile Route to Mixed Functional Phenyl, Vinyl T-10 and T-12 Silsesquioxanes

Richard Laine

M. Z Asuncion and R. M Laine (2010)

Journal Of The American Chemical Society, 132(11):3723-3736.

Polyphenylsilsesquioxane [PhSiO1.5]n (PPS) and polyvinylsilsesquioxane [vinylSiO1.5]n (PVS) are polymeric byproducts of the syntheses of the related T8 octamers [PhSiO1.5]8 and [vinylSiO1.5]8. Here we demonstrate that random-structured PPS and PVS rearrange in the presence of catalytic amounts of Bu4N+F in THF to form mixed-functionality polyhedral T10 and T12 silsesquioxane (SQ) cages in 80−90% yields. Through control of the initial ratio of starting materials, we can statistically tailor the average values for x for the vinylxPh10−xT10 and vinylxPh12−xT12 products. Metathetical coupling of x ≈ 2 vinyl cages with 4-bromostyrene produces SQs with an average of two 4-bromostyrenyl substituents. These products can be reacted via Heck coupling with vinylSi(OEt)3 to produce SQs with vinylSi(OEt)3 end-caps. Alternately, Heck coupling with the originally produced x ≈ 2 vinyl SQs leads to “beads on a chain” SQ oligomers joined by conjugated organic tethers. The functionalized T10 and T12 cages, metathesis, and Heck compounds were characterized by standard analytical methods (MALDI-TOF MS, 1H and 13C NMR spectroscopy, TGA, and GPC). MALDI confirms the elaboration of the cages after each synthetic step, and GPC verifies the presence of higher molecular weight SQ oligomers. TGA shows that all of these compounds are thermally stable in air (>300 °C). The UV−vis absorption and emission behavior of the Heck oligomers reveals exceptional red-shifts (≥60 nm) compared to the vinylSi(OEt)3 end-capped model compounds, suggesting electronic interactions through the SQ silica cores. Such phenomena may imply 3-D conjugation through the cores themselves.