Hydrosilylation of alkynes with a cationic rhodium species formed in an anionic micellar system

Article abstract of DOI:10.1021/ol049308b

Rhodium-catalyzed hydrosilylation of alkynes in an aqueous micellar system has been developed. A combination of [RhCl(nbd)]₂ and bis-(diphenylphosphino)propane (dppp) effects (E)-selective hydrosilylation in the presence of sodium dodecyl sulfa

Full text of DOI:10.1021/ol049308b

ORGANIC
LETTERS
2004
Vol. 6, No. 13
2217-2220
Hydrosilylation of Alkynes with a
Cationic Rhodium Species Formed in an
Anionic Micellar System
,†
Akinori Sato,† Hidenori Kinoshita,† Hiroshi Shinokubo,*,‡,§ and Koichiro Oshima*
Department of Chemistry, Graduate School of Science, Kyoto UniVersity, Kyoto
606-8502, and Department of Material Chemistry, Graduate School of Engineering,
Kyoto UniVersity, Kyoto 615-8510, Japan
hshino@kuchem.kyoto-u.ac.jp; oshima@fm1.kuic.kyoto-u.ac.jp
Received April 15, 2004
ABSTRACT
Rhodium-catalyzed hydrosilylation of alkynes in an aqueous micellar system has been developed. A combination of [RhCl(nbd)]2 and bis-
(diphenylphosphino)propane (dppp) effects (E)-selective hydrosilylation in the presence of sodium dodecyl sulfate (SDS) in water. The (E)-
selectivity strongly indicates the formation of a cationic rhodium species via dissociation of the Rh−Cl bond by the action of anionic micelles.
The addition of sodium iodide provided (Z)-alkenylsilanes predominantly.
Water is a strongly coordinating solvent for ionic solutes.
Due to its large dielectric constant (ꢀ), it weakens coulombic
Scheme 1
interaction between anions and cations. In water, conse-
quently, ionic compounds usually dissociate to their com-
ponent ions in hydrated forms.
We have recently found that mixing [RhCl(nbd)]2 and an
anionic surfactant, sodium dodecyl sulfate (SDS), in water
afforded a clear yellow homogeneous solution, although the
rhodium chloride dimer itself is insoluble in water.1 The
combination of [RhCl(nbd)]2-SDS in water provides a
highly reactive catalyst for intramolecular [4 + 2] annulation
the utility of the [RhCl(nbd)]2-SDS combination in aqueous
reactions.3-5
of 2,4-dienyl propargyl ethers without the use of any
phosphine ligands (Scheme 1). We have proposed formation
of a cationic rhodium species in this aqueous reaction system
[RhCl(nbd)]2 + H2O SDS8
[Rh(nbd)(H2O)n]+ + [Cl(H2O)m]- (1)
on the basis of the detection of chloride ion by the electrode
analysis (eq 1). Because cationic rhodium catalysts are
frequently employed as a homogeneous catalyst in a number
of transformations in organic synthesis,2 we explored further
Transition metal-catalyzed hydrosilylation of alkenes and
alkynes has been extensively investigated and has found
† Graduate School of Engineering.
(3) For the use of surfactants in organic synthesis, see: Kobayashi, S.;
Manabe, K. Acc. Chem. Res. 2002, 35, 209.
‡ Graduate School of Science.
§ PRESTO, Japan Science Technology Agency (JST).
(1) Motoda, D.; Kinoshita, H.; Shinokubo, H.; Oshima, K. Angew. Chem.,
Int. Ed. 2004, 43, 1860.
(2) (a) Suginome, M.; Ito, Y. In Encyclopedia of Reagents for Organic
Synthesis; Paquette, L., Ed.; Wiley: Chichester, 1995; p 426. (b) Schrock,
R. R.; Osborn, J. A. J. Am. Chem. Soc. 1971, 93, 3090.
(4) For transition metal-catalyzed reactions in aqueous media, see: (a)
Sinou, D. In Modern SolVent in Organic Synthesis; Knochel, P., Ed.;
Springer-Verlag: Berlin, 1999; p 41. (b) Cornils, B.; Herrmann, W. A.
Aqueous-Phase Organometallic Chemistry; Wiley-VCH: Weinheim, 1998.
(c) Li, C.-J.; Chan, T.-H. Organic Reactions in Aqueous Media; John
Wiley: New York, 1997.
10.1021/ol049308b CCC: $27.50 © 2004 American Chemical Society
Published on Web 05/28/2004

widespread application from asymmetric synthesis to material
science.6,7 A variety of transition metal complexes catalyze
this process, and platinum and rhodium catalysts are most
frequently employed. Among them, cationic rhodium com-
plexes have achieved high regio- and stereoselectivity in
hydrosilylation of terminal alkynes (Scheme 2).8 This process
Table 1. Rhodium-Catalyzed Hydrosilylation of 1-Octyne in
Watera
yield (%)
Scheme 2
entry
ligand
additive
SDS
SDS
SDS
SDS
SDS
SDS
SDS
Triton-X100
Oct3NMeCl
MeOSO3Na
SDS
(E)-1
(Z)-1
2
1
2b
3
4
5
6
7b
8
9
none
PPh3
dppe
dppp
dppb
dppf
tppts
dppp
dppp
dppp
dppp
dppp
46
59
77
76
56
11
0
0
2
3
3
7
exhibits high (E)-selectivity, whereas neutral rhodium complex-
catalyzed hydrosilylation usually provides (Z)-alkenylsilanes
predominantly.9 We anticipated that a cationic rhodium
species formed from the [RhCl(nbd)]2-SDS combination in
aqueous media would also exhibit (E)-stereoselectivity in
hydrosilylation of alkynes.
The aqueous rhodium catalyst was prepared by just mixing
[RhCl(nbd)]2 (0.005 mmol) and SDS (0.5 mmol) in degassed
water (2.5 mL) at room temperature. After stirring for 10
min, the rhodium complex was cleanly dissolved to afford a
clear light yellow solution. Then, 1-octyne (1.0 mmol) and
triethylsilane (1.1 mmol) were sequentially introduced. The
reaction mixture was stirred for 3 h, and then extracted with
ethyl acetate. The reaction provided only polymeric material,
and none of alkenylsilanes could be isolated (Table 1, entry
1). We then examined the addition of phosphine ligands,
because the desired alkenylsilane 1 was obtained by the use
53
23
10
11c
12c
0.6
39
36
0.3
38
33
1
2
none
a Reaction conditions: [RhCl(nbd)]2 (0.005 mmol), 1-octyne (1.0
mmol), triethylsilane (1.1 mmol), additive (0.5 mmol), diphosphine (0.013
mmol), water (2.5 mL), room temperature, 3 h. b Monodentate phosphine
(0.02 mmol) was employed. c Reaction was carried out in acetone instead
of water.
of triphenylphosphine (entry 2). Bis(diphenylphosphino)-
propane (dppp) worked nicely to provide alkenylsilane 1 with
high stereoselectivity, although a minor amount of the regio-
isomer 2 was obtained (entry 4). A water-soluble phosphine,
the trisodium salt of tris(m-sulfonatophenyl)phosphine (tppts),
which is employed in a number of aqueous rhodium-
catalyzed reactions, was not effective (entry 7). Interestingly,
the use of a neutral surfactant, Triton X-100, resulted in
nonstereoselective hydrosilylation (entry 8). A cationic
surfactant, methyltrioctylammonium chloride, provided none
of the hydrosilylation products (entry 9). Furthermore,
sodium methyl sulfate instead of SDS yielded a trace of the
desired products (entry 10). The use of anionic surfactant is
essential for the high stereoselectivity. It is also noteworthy
that the reaction in acetone did not show any significant
stereoselectivity (entries 11 and 12).
(5) For recent examples of rhodium-catalyzed reactions in aqueous media,
see: (a) Dwars, T.; Oehme, G. AdV. Synth. Catal. 2002, 344, 239. (b) Dwars,
T.; Schmidt, U.; Fischer, C.; Grassert, I.; Kempe, R.; Fro¨hlich, R.; Drauz,
K.; Oehme, G. Angew. Chem., Int. Ed. 1998, 37, 2851. (c) Selke, R.; Holz,
J.; Riepe, A.; Bo¨rner, A. Chem. Eur. J. 1998, 4, 769. (d) Ludwig, M.;
Kadyrov, R.; Fiedler, H.; Haage, K.; Selke, R. Chem. Eur. J. 2001, 7, 3298.
(e) Fuji, K.; Morimoto, T.; Tsutsumi, K.; Kakiuchi, K. Angew. Chem., Int.
Ed. 2003, 42, 2409. (f) Kinoshita, H.; Shinokubo, H.; Oshima, K. J. Am.
Chem. Soc. 2003, 125, 7784. (g) Lautens, M.; Roy, A.; Fukuoka, K.; Fagnou,
K.; Mart´ın-Matute, B. J. Am. Chem. Soc. 2001, 123, 5358. (h) Sakai, M.;
Ueda, M.; Miyaura, N. Angew. Chem., Int. Ed. 1998, 37, 2409. (i) Itooka,
R.; Iguchi, Y.; Miyaura, N. Chem. Lett. 2001, 722. (j) Yonehara, K.; Ohe,
K.; Uemura, S. J. Org. Chem. 1999, 64, 9381. (k) Huang, T.; Meng, Y.;
Venkatraman, S.; Wang, D.; Li, C.-J. J. Am. Chem. Soc. 2001, 123, 7451.
(l) Amengual, R.; Michelet, V.; Geneˆt, J.-P. Tetrahedron Lett. 2002, 43,
5905. (m) Amengual, R.; Michelet, V.; Geneˆt, J.-P. Synlett 2002, 1791. (n)
Pucheault, M.; Darses, S.; Geneˆt, J.-P. Eur. J. Org. Chem. 2002, 3552.
(6) (a) Hiyama, T.; Kusumoto, T. In ComprehensiVe Organic Synthesis;
Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 8,
Chapter 3.12. (b) Ojima, I.; Li, Z.; Zhu, J. In The Chemistry of Organosilicon
Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: Chichester, 1998;
Vol. 2, Part 2, Chapter 29. (c) Corey, J. Y. In AdVances in Silicon Chemistry;
Larson, G. L., Ed.; JAI: Greenwich, 1991; Vol. 1, p 355. (d) Marciniec,
B. ComprehensiVe Handbook on Hydrosilylation; Pergamon Press: Oxford,
1992.
(7) Hydrosilylation in aqueous media has been reported recently. (a) Wu,
W.; Li, C. J. Chem. Commun. 2003, 1668. (b) Motoda, D.; Shinokubo, H.;
Oshima, K. Synlett 2002, 1529.
(8) (a) Takeuchi, R.; Tanouchi, N. J. Chem. Soc., Chem. Commun. 1993,
1319. (b) Takeuchi, R.; Tanouchi, N. J. Chem. Soc., Perkin Trans. 1 1994,
2909. (c) Takeuchi, R.; Nitta, S.; Watanabe, D. J. Org. Chem. 1995, 60,
3045.
(9) (a) Ojima, I.; Clos, N.; Donovan, R. J.; Ingallina, P. Organometallics
1990, 9, 3127. (b) Ojima, I.; Kumagai, M.; Nagai, Y. J. Organomet. Chem.
1974, 66, C14. (c) Doyle, M. P.; High, K. G.; Nesloney, C. L.; Clayton, T.
W., Jr.; Lin, J. Organometallics 1991, 10, 1225.
Table 2 summarizes the results of hydrosilylation with a
variety of alkynes in water under catalysis of the [RhCl-
(ndb)]2-SDS combination. Alkynes with bulky substituents
also yielded the products with high stereoselectivity, although
a prolonged reaction time was required (entries 2 and 3).
The use of aromatic alkynes afforded low yields due to the
concomitant polymerization of the alkynes (entries 4 and 5).
The reaction was compatible with functionalities such as
alcohol, ether, ester, and carboxylic acid. Internal alkynes
also provided the desired products with high stereoselectivity
(entries 14 and 15). The solubility of alkynes in water seems
to be related with the reaction efficiency. The use of very
water-soluble alkynols resulted in lower yields (entries 6-9).
We believe that the reaction proceeds in a micelle formed
from SDS in water (vide infra), and a water-soluble substrate
2218
Org. Lett., Vol. 6, No. 13, 2004

Scheme 3
Table 2. [RhCl(nbd)]2-SDS-Catalyzed Hydrosilylation of
Alkynes in Watera
effect on the selectivity and found that sodium iodide (1.0
equiv) inverted the sense of stereoselectivity to provide (Z)-
isomers predominantly (Table 3). Mori and Hiyama have
Table 3. [RhCl(nbd)]2-SDS-NaI-Catalyzed Hydrosilylation
of Alkynes in Watera
a Reaction conditions: [RhCl(nbd)]2 (0.005 mmol), alkyne (1.0 mmol),
triethylsilane (1.1 mmol), SDS (0.5 mmol), dppp (0.013 mmol), water (2.5
mL), room temperature, 3 h. b Reaction time was 16 h.
is predominantly present in the exterior phase of the micelle
to lower the reaction rate.
From these experimental results, it is obvious that SDS
plays a key role in this hydrosilylation reaction. We then
investigated the effect of the concentration and amount of
SDS on the yield and selectivity (Scheme 3). The yield and
selectivity stay virtually constant with variations in the
amount of SDS from 100 to 2.5 mol %. The efficiency and
the stereoselectivity of the reaction decreased dramatically
at 1.25 mol %. Meanwhile, in the presence of the same
amount of SDS and [RhCl(nbd)]2, a change in the concentra-
tion of SDS also has a significant effect.10 Both the
concentration and amount of SDS is essential. On the basis
of these findings as well as the fact that sodium methyl
sulfate does not work (Table 1, entry 10), we concluded that
the formation of anionic micelle in water is critical for the
generation of a cationic rhodium species that catalyzes (E)-
selective hydrosilylation.
a Reaction conditions: [RhCl(nbd)]2 (0.005 mmol), alkyne (1.0 mmol),
triethylsilane (1.1 mmol), SDS (0.5 mmol), dppp (0.01 mmol), NaI (1.0
mmol), water (2.5 mL), room temperature.
already reported that the addition of sodium iodide to RhCl-
(PPh3)3 resulted in (Z)-selective hydrosilylation.11 Imperfect
selectivity might indicate that a cationic rhodium species that
provides the (E)-isomer is still present in the reaction system
even in the presence of sodium iodide.
In conclusion, we have developed a stereoselective rhodium-
catalyzed hydrosilylation of alkynes in aqueous media. A
combination of [RhCl(nbd)]2 and bis(diphenylphosphino)-
propane (dppp) effects (E)-selective hydrosilylation in the
presence of SDS in water. The observed (E)-selectivity
indicates the formation of cationic rhodium species. Finally,
In the presence of halide ions, dissociation of the rhodium-
chloride bond (eq 1) would be unfavorable, and the observed
selectivity of alkenylsilanes would be affected. In fact, the
addition of excess sodium chloride (2.0 equiv) reduced the
stereoselectivity (E/Z ) 90/10). We then examined the salt
(10) Critical micelle concentration (cmc) of SDS without organic
substrates is 8.1 × 10-3 M.
(11) Mori, A.; Takahashi, E.; Kajiro, H.; Hirabayashi, K.; Nishihara, Y.;
Hiyama, T. Chem. Lett. 1998, 443.
Org. Lett., Vol. 6, No. 13, 2004
2219

the selectivity can be switched from E to Z in the presence
of sodium iodide.
Supporting Information Available: Experimental pro-
cedures and compound data. This material is available free
of charge via the Internet at http://pubs.acs.org.
Acknowledgment. H.K. acknowledges the Research
Fellowships of the Japan Society for the Promotion of
Science for Young Scientists for financial support.
OL049308B
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Org. Lett., Vol. 6, No. 13, 2004