Fluoride rearrangement reactions of polyphenyl- and polyvinylsilsesquioxanes as a facile route to mixed functional phenyl, vinyl T10 and T12 silsesquioxanes.
Polyphenylsilsesquioxane [PhSiO(1.5)](n) (PPS) and polyvinylsilsesquioxane [vinylSiO(1.5)](n) (PVS) are polymeric byproducts of the syntheses of the related T(8) octamers [PhSiO(1.5)](8) and [vinylSiO(1.5)](8). Here we demonstrate that random-structured PPS and PVS rearrange in the presence of catalytic amounts of Bu(4)N(+)F(-) in THF to form mixed-functionality polyhedral T(10) and T(12) 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 vinyl(x)Ph(10-x)T(10) and vinyl(x)Ph(12-x)T(12) products. Metathetical coupling of x approximately = 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 approximately = 2 vinyl SQs leads to "beads on a chain" SQ oligomers joined by conjugated organic tethers. The functionalized T(10) and T(12) cages, metathesis, and Heck compounds were characterized by standard analytical methods (MALDI-TOF MS, (1)H and (13)C 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 degrees C). The UV-vis absorption and emission behavior of the Heck oligomers reveals exceptional red-shifts (> or = 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.
Asuncion
M Z
MZ
Department of Macromolecular Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136, USA.
Laine
R M
RM