Abstract
We have recently reported the synthesis of octopus molecules of defined shape and size with molecular weights well into the thousands. These octopus molecules were made by placing eight pendant groups symmetrically about a central silsesquioxane core via the H2PtCl6 catalyzed hydrosilylation of 1-alkenes as well as vinyl- and allyl-siloxanes by T8 hydrogen silsesquioxane, (HSiO32)8. The chemistry of addition was studied and it was found that while the addition of the 1-alkenes to T8 was regioprecise with only α-addition being observed, both α- and β-addition occurred with vinyl-siloxane. In addition, H-vinyl exchange on silicon was observed to occur with addition of vinyl-siloxane to T8. In the current studies, the effect of the hydrosilylation catalyst. homogeneous and heterogeneous, on the regioselectivity of addition and on the extent of exchange on silicon was evaluated. It was found that the heterogeneous catalysts Pt−C, sulfided Pt−C, and Rh−C required higher temperature and longer times to get complete reaction than the homogeneous catalysts. H2PtCl6 and the tetramethyldivinyldisiloxane complex of Pt. Pd supported catalysts were not effective catalysts for this hydrosilylation. The extent of exchange on silicon and the degree of the second mode of addition occurring were higher with the heterogenous catalysts and may be a result of the higher reaction temperatures.
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Gentle, T.E., Bassindale, A.R. Effect of catalyst on regioselectivity and vinyl/H exchange on silicon in the hydrosilylation of vinyl-siloxanes by T8 hydrogen silsesquioxane. J Inorg Organomet Polym 5, 281–294 (1995). https://doi.org/10.1007/BF01057898
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DOI: https://doi.org/10.1007/BF01057898