R. Abu-Reziq, D. Avnir, J. Blum
SHORT COMMUNICATION
phatic terminal olefins (1-hexene, 1-octene; Entries 5 and 6) started immediately and was completed within 30 min. The gel was
dried at 98°C and 0.5 Torr for 24 h. The dry material was refluxed
yield preferentially the linear products (l/b = 1.38–1.58), so
with dichloromethane (20 mL) for 1 h and then redried to give 3.5–
do the two allylarenes (Entries 7 and 8; l/b = 2.03 and 2.33)
2 3 3 2 3
3.6 g of {Rh(cod)[S(CH ) Si(O) ϵ]} /5PPh @hydrophobicized sol-
despite the fact that the latter substrates undergo catalytic
double bond isomerization along the hydroformylation pro-
cess. This phenomenon can be rationalized by the fact that
gel. Upon replacement of the triethoxy(octyl)silane by trimeth-
oxy(phenyl)silane (1.5 g), 3.4–3.5 g of {Rh(cod)[S(CH
Si(O) ϵ]} /5PPh @phenylated silica was obtained.
Preparation of the Microemulsions: Typically, to a solution of N-
2 3
) -
3
2
3
at 80 °C, in the presence of the added PPh , under 13.8–
3
2
7.6 bar H , a reverse double bond migration to the ter-
2
[7]
dodecyl-N-(2-hydroxyethyl)-N,N-dimethylammonium
bromide
minal olefins prevails.
(
1.2 g) in water (10 mL) the substrate (13.1 mmol) was added drop-
wise under vigorous stirring. The emulsion so formed was titrated
with n-butanol until a clear transparent mixture was obtained (1–
Conclusions
3
mL). The w/w composition of the various microemulsions studied
here are summarized in Table 1.
Hydroformylation of hydrophobic alkenes can be per-
formed in an aqueous medium under micro-EST conditions Catalytic Hydroformylations:
A Teflon-lined microautoclave,
using a suitably selected surfactant and a cyclooctadiener- equipped with a mechanical stirrer and a sampling device, was
charged with the sol-gel entrapped catalyst and the substrate-con-
taining microemulsion (typically 15–20 mL). The autoclave was se-
aled and purged three times with hydrogen and then pressurized
2
with H (6.9–13.8 bar) and with the same pressure of CO. The reac-
tion mixture was then heated with stirring at the desired tempera-
ture for the required time. After cooling to room temperature, the
gases were released and the remaining mixture was filtered. Upon
addition of sodium chloride (200 mg) to the filtrate, the reaction
hodium catalyst, chemically entrapped within a hydro-
phobicized silica sol-gel matrix. The successful hydrofor-
mylation in a highly selective manner requires the addition
of triphenylphosphane to the catalyst. Recycling of the im-
mobilized catalyst is possible. Since we have already demon-
strated the utility of the EST system for the catalytic hydro-
genation of hydrophobic substrates in water,[1,2] we believe
that this technology is of general applicability to a wide mixture separated into two phases. The organic layer was diluted
range of reactions of hydrophobic substrates in aqueous with dichloromethane (20 mL), dried with MgSO , concentrated
and analyzed by GC, MS and NMR and compared with authentic
4
media.
samples. The filtered ceramic catalyst was suspended in refluxing
methanol (20 mL) for 30 min, dried at room temperature and
0.5 Torr for 3 h, sonicated with dichloromethane (20 mL) for
Experimental Section
30 min and dried again at room temperature and 0.5 Torr for 2 h
Chemicals:
Di-µ-chlorobis[(1,2,5,6-η)-1,5-cyclooctadiene]dirho-
before reapplication in a second catalytic run.
[
8]
dium
and N-dodecyl-N-(2-hydroxyethyl)-N,N-dimethylammo-
[
7]
nium bromide were synthesized according to published pro-
cedures. All other chemicals except for the catalyst were obtained
from commercial sources.
Acknowledgments
This work was supported by the Israel Science Foundation through
Grant Nos. 143/00-12 and 177/03-12 and by the Ministry of Sci-
ence, Art and Sport through the Tashtiot project.
Preparation
methoxysilyl)propanethiolato-(S,SЈ)]}dirhodium {Rh(cod)[S(CH
Si(OMe) ]} : To a solution of (CH O) Si(CH SH (0.38 mL) in
of
Bis[1,2,5,6-η-(1,5-cyclooctadiene)]bis{µ-[3-(tri-
2 3
) -
3
2
3
3
2 3
)
dry THF (100 mL) was added under exclusion of air oil-free so-
dium hydride (0.06 g). The mixture was stirred at room temperature
for 60 min. A solution of [Rh(cod)Cl] (500 mg) in THF (50 mL)
2
was added dropwise and the stirring was continued for another 2 h.
The NaCl was removed by filtration through Celite and the THF
was removed by distillation under reduced pressure at room tem-
perature. The resulting yellow oil was chromatographed on silica
gel using ether/pentane mixtures as eluent. Drying at 0.01 Torr for
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[
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962.
[
3] a) R. Atkin, V. S. T. Craig, E. J. Wanless, S. Biggs, Adv. Colloid
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and references cited therein.
2
(
4 h afforded the rhodium complex in 74% yield. 1H NMR
300 MHz, CDCl ): δ = 0.72 (t, J = 8 Hz, 4 H), 1.57–1.68 (m, 4
H), 1.95–2.07 (m, 8 H), 2.02 (t, J = 9 Hz, 4 H), 2.39–2.41 (m, 8
3
H), 3.53 (s, 18 H), 4.16 (m, 8 H). 1 C NMR (75 MHz, CDCl
8.78, 25.53, 27.35, 31.37, 50.45, 78.92. C28 Rh
812.849): calcd. C 41.37, H 6.70; found C 41.17, H 6.74. The rho-
3
3
): δ
Si
=
(
H
54
O
6
2
S
2
2
[
dium complex was redissolved in THF (20 mL) and kept under Ar
in the refrigerator as a stock solution.
Preparation of {Rh(cod)[S(CH
ized Sol-Gel: To the stock solution (2 mL) of {Rh(cod)[S(CH
OMe) ]} in THF was added triphenylphosphane (133 mg), under
2
)
3
Si(O)
3
ϵ]}
2
/5PPh
3
@Hydrophobic-
2 3
)
Si-
[
[
[
(
3
2
exclusion of air. The resulting red solution was stirred for 2 h and
then treated with tetramethoxysilane (TMOS) (5 mL), prehy-
drolyzed triethoxy(octyl)silane (2.1 mL) and triply distilled water
7] J. Schulz, A. Roucous, H. Patin, Chem. Eur. J. 2000, 6, 618–
624.
8] G. Giordano, R. H. Crabtree, Inorg. Synth. 1990, 28, 88–90.
(4 mL). After agitation for 3 h, a 0.1 solution (0.2 mL) of tetrabu-
Received April 6, 2005
tylammonium fluoride (TBAF) in THF was added. Gelation
Published Online: July 14, 2005
3642
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 3640–3642