Te. Gentle et Ar. Bassindale, EFFECT OF CATALYST ON REGIOSELECTIVITY AND VINYL H EXCHANGE ON SILICON IN THE HYDROSILYLATION OF VINYL-SILOXANES BY T-8 HYDROGEN SILSESQUIOXANE/, Journal of inorganic and organometallic polymers, 5(3), 1995, pp. 281-294
We have recently reported the synthesis of octopus molecules of define
d shape and size with molecular weights well into the thousands. These
octopus molecules were made by placing eight pendant groups symmetric
ally about a central silsesquioxane core via the H2PtCl6 catalyzed hyd
rosilylation of 1-alkenes as well as vinyl- and allyl-siloxanes by T-8
hydrogen silsesquioxane, (HSiO3/2)(8). The chemistry of addition was
studied and it was found that while the addition of the 1-alkenes to T
-8 was regioprecise with only alpha-addition being observed, both alph
a- and beta-addition occurred with vinyl-siloxane. In addition, H/viny
l exchange on silicon was observed to occur with addition of vinylsilo
xane to T-8. In the current studies, the effect of the hydrosilylation
catalyst, homogeneous and heterogeneous, on the regioselectivity of a
ddition 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 tetramethyldivinyldisi
loxane complex of Pt. Pd supported catalysts were not effective cataly
sts for this hydrosilylation. The extent of exchange on silicon and th
e degree of the second mode of addition occurring were higher with the
heterogenous catalysts and may be a result of the higher reaction tem
peratures.