Catalytic asymmetric dihydroxylation of olefins with new catalysts: The first example of heterogenization of OsO42- by ion-exchange technique [4]

Full text of DOI:10.1021/ja016101u

9220
J. Am. Chem. Soc. 2001, 123, 9220-9221
shared metal M(II) and M(III) hydroxide octahedra, with charges
neutralized by An- anions located in the interlayer spacing or at
the edges of the lamellae. LDHs have recently received much
attention in view of their potential usefulness as anion exchan-
gers7a-c and catalysts.9 Small hexagonal LDH crystals with
Mg1-xAlx(OH)2(Cl)x‚zH2O composition are synthesized following
existing procedures (here x ) 0.25).7c OsO42- is exchanged onto
the chloride-saturated LDH to obtain LDH-OsO4. X-ray powder
diffraction patterns of the initial LDH and the LDH-OsO4 hardly
differ in the range 2θ ) 3-65°. The observed d003 basal spacing
of the support that appeared at ∼7.8 Å remained unchanged after
the anion exchange, which indicates that OsO42- is mainly located
in edge positions.
Catalytic Asymmetric Dihydroxylation of Olefins
with New Catalysts: The First Example of
2-
Heterogenization of OsO4 by Ion-Exchange
Technique
Boyapati M. Choudary,* Naidu S. Chowdari,
Mannepalli L. Kantam, and Kondapuram V. Raghavan
Indian Institute of Chemical Technology
Hyderabad 500 007, India
ReceiVed April 30, 2001
ReVised Manuscript ReceiVed August 3, 2001
2-
Similarly, the OsO4 is also exchanged onto quaternary
Osmium-catalyzed asymmetric dihydroxylation of olefins
provides one of the most elegant methods for the preparation of
chiral vicinal diols.1 Although the reactions could be applied to
the synthesis of pharmaceuticals, fine chemicals, and so forth,
the high cost, toxicity, and possible contamination of osmium
catalysts in the products restrict its use in industry. Heterogeni-
zation of the ligands on polymer or silica gel support and eventual
complexation with osmium, a possible solution to address this
issue attempted by several groups, failed to recover and reuse
the osmium, since the coordination of anchored ligands and
osmium tetroxide is in equilibrium.2-4 The microencapsulation
technique adopted by Kobayashi to envelop osmium tetroxide in
the polymer capsule afforded a recoverable and reusable osmium
catalyst for asymmetric dihydroxylation.5 Recently Jacobs et al.
immobilized OsO4 on silica through a tetrasubstituted olefin and
used for achiral dihydroxylations only.6
In this communication, we report the design of an ion-exchange
technique for the development of recoverable and reusable
osmium catalysts immobilized on layered double hydroxides
(LDH), modified silica and resin for asymmetric dihydroxylation
of olefins for the first time. The catalysts thus developed through
ion-exchange technique show higher performance over Kobayashi
catalyst in terms of activity and ee.
ammonium groups of silica and organic resin to obtain SiO2-
OsO4 and resin-OsO4. All of these catalysts are well character-
ized10 by IR and UV-DRS, which indicate that the majority of
the osmate is unaffected during the exchange process except for
experiencing very weak interaction with the support. The osmium
content in the catalysts LDH-OsO4 (0.975 mmol g-1), resin-
OsO4 (0.641 mmol g-1), and SiO2-OsO4 (0.317 mmol g-1) is
determined by SEM-EDX and counterchecked with the quantita-
tive analysis of potassium halide formed in the exchange process.
The exchanger-OsO4 catalysts thus prepared are first screened
for achiral dihydroxylation of trans-stilbene. In a general experi-
mental procedure, a mixture composed of trans-stilbene, N-
methylmorpholine N-oxide (NMO), and 1 mol % of catalyst in
H2O-CH3CN-acetone (1:1:1) was stirred at room temperature.
After completion of the reaction (2-5 h), the catalyst was filtered
and washed with methanol to obtain the corresponding diol.10 An
activity profile of the dihydroxylation of trans-stilbene with
various exchanger-OsO4 catalysts conducted under similar condi-
tions described in Figure 1 reveals that LDH-OsO4 displays the
highest activity and the heterogenized catalysts in general have
distinctly faster reactivity than K2OsO4‚2H2O. The large positive
electric potential and spatial organization of the exchanger-OsO4
may be responsible for the superior performance. This result is
in consonance with LDH-WO4-catalyzed oxidative bromination7a
and ionic polymer-supported osmium tetroxide in achiral
dihydroxylation.4a All of these catalysts are reused for five cycles
with consistent activity.
Encouraged by these promising results, we then performed
asymmetric dihydroxylation of olefins according to the Sharpless
procedure11 using the exchanger-OsO4 catalysts (Scheme 1). We
chose trans-stilbene as a model, and varying conditions are
examined. When trans-stilbene was added to a mixture of LDH-
OsO4, 1,4-bis(9-O-dihydroquinidinyl)phthalazine (DHQD)2PHAL),
a chiral ligand (1 mol % each) and NMO, the desired diol is
obtained in 96% yield with 99% enantiomeric excess (ee).12
Similarly, excellent ees are obtained with resin-OsO4 and SiO2-
OsO4 in the dihydroxylation of trans-stilbene.10 The LDH-OsO4
is further subjected to the dihydroxylation of other olefins, and
To understand the scope and generality of ion-exchange
technique for immobilization of osmate catalyst, various ion
exchangers sourced from inorganic and organic materials7,8 were
prepared and examined in dihydroxylation reactions. Layered
double hydroxides (LDH) consist of alternating cationic M(II)1-x
-
M(III)x (OH)2 and anionic An-‚zH2O layers. The positively
x+
charged layers in layered double hydroxides (LDH) contain edge-
(1) (a) Kolb, H. C.; VanNieuwenhze, M. S.; Sharpless, K. B. Chem. ReV.
1994, 94, 2483. (b) Marko, I. E.; Svendsen, J. S. In ComprehensiVe Asymmetric
Catalysis II; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer, Berlin,
1999; p 723. (c) Dobler, C.; Mehltretter, G.; Sundermeier, U.; Beller, M. J.
Am. Chem. Soc. 2000, 122, 10289. (d) Bergstad, K.; Jonsson, S. Y.; Ba¨ckvall,
J.-E. J. Am. Chem. Soc. 1999, 121, 10424.
(2) Review: (a) Bolm, C.; Gerlach, A. Eur. J. Org. Chem. 1998, 1, 21. (b)
Salvadori, P.; Pini, D.; Petri, A. Synlett 1999, 1181.
(3) For polymer-supported chiral ligands see: (a) Kim, B. M.; Sharpless,
K. B. Tetrahedron Lett. 1990, 31, 3003. (b) Pini, D.; Petri, A.; Nardi, A.;
Rosini, C.; Salvadori, P. Tetrahedron Lett. 1991, 32, 5175. (c) Han, H.; Janda,
K. D. Angew. Chem. Int. Ed. Engl. 1997, 36, 1731.
(4) For achiral ligand-osmium tetroxide, see (a) Cainelli, G.; Contento,
M.; Manescalchi, F.; Plessi, L. Synthesis 1989, 45. (b) Herrmann, W. A.;
Kratzer, R. M.; Blu¨mel, J.; Friedrich, H. B.; Fischer, R. W.; Apperley, D. C.;
Mink, J.; Berkesi, O. J. Mol. Catal. 1997, 120, 197.
(5) For microencapsulated osmium tetroxide, see (a) Nagayama, S.; Endo,
M.; Kobayashi, S. J. Org. Chem. 1998, 63, 6094. (b) Kobayashi, S.; Endo,
M.; Nagayama, S. J. Am. Chem. Soc. 1999, 121, 11229.
(6) Severeyns, A.; De Vos, D. E.; Fiermans, L.; Verpoort, F.; Grobet, P.
J.; Jacobs, P. A. Angew. Chem. Int. Ed. 2001, 40, 586.
(9) Choudary, B. M.; Kantam, M. L.; Rahman, A.; Reddy, C. V.; Rao, K.
K.; Angew. Chem. Int. Ed. 2001, 40, 763.
(10) Details are described in Supporting Information.
(11) Wai, J. S. M.; Marko, I. E.; Svendsen, J. S.; Finn, M. G.; Jacobsen,
E. N.; Sharpless, K. B. J. Am. Chem. Soc. 1989, 111, 1123.
(12) Experimental procedure is as follows: Exchanger-OsO4 (0.01 mmol),
(DHQD)2PHAL (7.8 mg, 0.01 mmol), and N-methylmorpholine N-oxide
t
(NMO, 1.3 mmol) were taken in a round-bottomed flask containing BuOH-
water (1:1, 6 mL) and stirred at room temperature. To this mixture was added
an olefin (1 mmol) slowly for 12 h. After completion of the reaction, the
catalyst was filtered and washed with methanol. Ethyl acetate and 1 N HCl
were added to the combined filtrates. The chiral ligand was recovered from
the aqueous layer. After removing the solvent, the crude material was
chromatographed on silica gel to afford the corresponding cis-diol.
(13) Our preliminary experiments revealed that the use of exchanger-OsO4,
(DHQD)2PHAL and potassium ferricynide also worked well to afford the
desired diols in high yields and ees without resorting to slow addition. Details
will be reported in due course.
(7) (a) Sels, B.; De Vos, D.; Buntinx, M.; Pierard, F.; Kirsch-De
Mesmaeker, A.; Jacobs, P. A. Nature 1999, 400, 855. (b) Trifiro, F.; Vaccari,
A. In ComprehensiVe Supramolecular Chemistry; Pergamon, Elsevier Sci-
ence: Oxford, 1996; Vol. 7, p 251. (c) Miyata, S. Clays Clay Miner. 1975,
23, 369. (d) Bleloch, A.; Johnson, B. F. G.; Ley, S. V.; Price, A. J.; Shephard,
D. S.; Thomas, A. W. Chem. Commun. 1999, 1907.
(8) (a) Hinzen, B.; Ley, S. V. J. Chem. Soc., Perkin Trans. 1 1997, 1907.
(b) Hinzen, B.; Lenz, R.; Ley, S. V. Synthesis 1998, 977.
10.1021/ja016101u CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/22/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 37, 2001 9221
Table 1. Asymmetric Dihydroxylation of Olefins with LDH-OsO4
Figure 1. An activity profile of the dihydroxylation of trans-stilbene
with NMO as oxidant in H2O-CH3CN-acetone (1:1:1) solvent by (a)
LDH-OsO4, (b) resin-OsO4, (c) SiO2-OsO4, (d) K2OsO4‚2H2O.
Scheme 1. Dihydroxylation of trans-Stilbene
the results are summarized in Table 1. Slow addition of olefin to
the reaction mixture is warranted except in case of trans-stilbene
(as indicated above) to keep the availability of the olefin at a
bare minimum level to achieve higher ee.10,14 Various olefins
ranging from mono- to trisubstituted, activated to simple, are
subjected to dihydroxylations. In most cases, the desired diols
are formed in higher yields, albeit with almost similar ees as
reported in the homogeneous system. The trisubstituted olefin is
also dihydroxylated to the corresponding diol with higher ee in
the presence of tetraethylammonium acetate (TEAA) additive
(Table 1, entry 9). This phenomenon substantiates that the
hydrolysis of osmate ester, a pronounced slow process in case of
trisubstituted olefin, is accelerated with the addition of the additive
to afford higher yield and ee.11,12
The present LDH-OsO4 is superior in terms of activity,
enantioselectivity, and scope of the reaction on comparison with
that of Kobayashi catalyst. For example, the present LDH-OsO4
catalyst is 30-fold more active than the Kobayashi catalyst in
achiral dihydroxylation of trans-â-methylstyrene.5b,10 Second, the
scope of the LDH-OsO4 is extended successfully to encompass
stilbene (entry 1), cinnamates (entries 5,6), and aryl allyl ether
(entry 8) in the present studies over the Kobayashi methodology,5b
because these chiral diol derivatives are important intermediates
to several chiral ligands and drugs such as taxol, diltiazem,
propranolol, and so forth. As to the enantioselectivities in
asymmetric dihydroxylation, the present system offers distinctly
higher ees 90 and 91% as against the 78 and 85% with Kobayashi
catalyst for entries 4 and 9, respectively.
The osmate in all the exchangers is localized on the surface.
This assumes significance in particular in LDH, wherein the other
possible option of intercalation of osmate is ruled out. The com-
plexation of the large chiral ligand, (DHQD)2PHAL is only pos-
sible with the OsO42- located at the edge (surface), as accessibility
of the chiral ligand to OsO42- present in very small interlamellar
space, 3 Å of LDH is very remote. These results reconfirm the
presence of OsO42- at the surface of the LDH as is evident from
XRD.
a Determined by HPLC analysis. b The absolute configuration was
determined by comparison of the specific rotation with literature value.
c Determined by comparison of specific rotation with literature value.
d Two equivalents of TEAA is used.
above protocol. It is thus unambiguously demonstrated that os-
mium was bound to the support, while undergoing redox cycle
Os(VI)/Os(VIII) during the reaction. The neutral Os(VIII) com-
plex formed during reaction is physisorbed on the support.10
In summary, the active osmium catalysts are readily prepared
from nonvolatile, K2OsO4‚2H2O by a simple ion-exchange tech-
nique on various supports such as LDH, organic resin, and silica.
These catalysts afford chiral diols with high yields and ee’s having
consistency over a number of cycles, which contributes to the
development of benign chemical processes and products.
The LDH-OsO4 was recovered quantitatively by simple
filtration, and the chiral ligand was also recovered by simple acid/
base extraction (>95% recovery). The recovered catalyst along
with the replenished chiral ligand (to make up 1 mol %) was re-
used, and consistent activity was noticed even after the fifth cy-
cle.10 When the reaction was conducted with the filtrate obtained
by treatment of the catalyst in a solvent system for prolonged
time, no product formation was observed. The absence of osmium
in the filtrate is further reconfirmed using the iodometry test.5b
All the catalysts exhibited similar trend, when subjected to the
Acknowledgment. N.S.C. thanks the Council of Scientific and
Industrial Research, India, for the award of a research fellowship. We
also thank K. Jyothi, Ch. V. Reddy for technical support and Professor
I. E. Marko for helpful comments on this manuscript.
Supporting Information Available: Experimental details, preparation
and characterization of catalysts as well as products of the reaction (PDF).
This material is avilable free of charge via the Internet at http://pubs.acs.org.
JA016101U