Monophasic and biphasic hydrosilylations of enones and ketones using a fluorous rhodium catalyst that is easily recycled under fluorous–organic liquid–liquid biphasic conditions
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Additions of PhMe2SiH to 2-cyclohexen-1-one, 2-cyclopenten-1-one, 4,4-dimethyl-2-cyclohexen-1-one, and cyclohexanone (11) are catalyzed by the rhodium complexes ClRh[P(CH2CH2(CF 2)n-1CF3)3]3 (1; n = 6, 8), which have very high affinities for fluorous liquid phases. Reactions of the enones are conducted with 0.80 mol% 1 at 60 °C under biphasic conditions in CF3C6F11-toluene or monophasic conditions in CF3C6F11-hexanes. The reactions are faster under the latter conditions and the catalyst and products are efficiently separated at lower temperatures under biphasic conditions. Distillations of the non-fluorous phases give mixtures of 1,4- and 1,2-hydrosilylation products (>99-92: <1-8) in 93-88% yields. The catalyst-containing CF 3C6F11 phases are recycled two times with similar results. Reactions of 11 are studied under analogous conditions (0.2 mol% 1) at 28 and 40 °C and give cyclohexyl dimethylphenylsilyl ether. Rate profiles show induction periods for the first cycle, indicating an irreversible transformation of 1, but not for subsequent cycles. Only minor decreases in activity are observed over four cycles, consistent with little catalyst leaching or decomposition. When catalyst loadings are decreased to 0.02 mol%, TON of 4400 can be obtained.
author list (cited authors)
Dinh, L. V., & Gladysz, J. A.