Markedly enhanced recyclability of osmium catalyst in asymmetric dihydroxylation reactions by using macroporous resins bearing both residual vinyl groups and quaternary ammonium moieties

Article abstract of DOI:10.1039/b504223b

Markedly enhanced recyclability of osmium catalyst in asymmetric dihydroxylation has been achieved by using osmylated macroporous resins bearing both residual vinyl groups and quaternary ammonium moiety. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b504223b

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COMMUNICATION
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Markedly enhanced recyclability of osmium catalyst in asymmetric
dihydroxylation reactions by using macroporous resins bearing both
residual vinyl groups and quaternary ammonium moieties{
Kwang Jin Kim,a Han Young Choi,a Soon Ho Hwang,a Yil Sung Park,*a Eun Kyung Kwueon,b
Doo Seong Choib and Choong Eui Song*b
Received (in Cambridge, UK) 29th March 2005, Accepted 29th April 2005
First published as an Advance Article on the web 27th May 2005
DOI: 10.1039/b504223b
resins exhibited excellent catalytic activity in the asymmetric
dihydroxylation of olefins, and could be recycled. Even when only
0.2 mol% of osmium was used, the resins could be reused three
times. Unfortunately, leaching of OsO4 into solution has been
found upon reuse. Thus, there is still a demand driven by economic
and environmental considerations, to develop more efficient
immobilization methods for recovery and reuse of osmium
catalyst.
Markedly enhanced recyclability of osmium catalyst in asym-
metric dihydroxylation has been achieved by using osmylated
macroporous resins bearing both residual vinyl groups and
quaternary ammonium moiety.
Os-Catalysed asymmetric dihydroxylation (AD) of olefins is
undoubtedly one of the most efficient synthetic methods for chiral
vicinal diols, which could be key intermediates in the synthesis of
chiral drugs, natural products and fine chemicals, etc.1 However,
the high cost of the catalysts (osmium and the cinchona alkaloid
ligands) as well as the high toxicity and volatility of the osmium
component have made their large-scale industrial applications
difficult. To overcome this drawback, much effort has been
devoted to the development of effective immobilization of the
osmium component. Early attempts to immobilize OsO4 on solid-
supported alkaloid ligands failed due to severe osmium leaching.2
Recently, Kobayashi et al. reported that microencapsulated OsO4
in a polymer matrix can be used as a recyclable osmium catalyst.3
However, high loading (5 mol%) of osmium was required in a
typical dihydroxylation reaction. Very recently, another approach
to immobilise K2OsO4?2H2O has been achieved by using an ion-
exchange technique on solid supports bearing quaternary ammo-
nium moieties (Fig. 1).4 In terms of catalyst recycling, these
immobilization techniques seem successful, however, turn over
number (TON) is much lower compared to that of the
homogeneous AD reactions. In homogeneous cases, 0.2 mol% of
osmium is enough to complete most of the reactions. We recently
reported that OsO4 could be simply immobilised by osmylation
onto resins bearing residual vinyl groups such as Amberlite XAD-
4 or XAD-7 (Fig. 1).5 These air-stable and non-volatile osmylated
In this communication we report that use of macroporous resins
bearing both residual vinyl groups and quaternary ammonium
moieties provides a simple and highly practical approach to the
recycling of osmium catalyst. As depicted in Scheme 1, the resins
possessing both residual vinyl groups and ammonium moiety
might immobilize osmium tetroxide as well as osmate ion dissolved
in solution and, thus, enhance the recyclability of osmium catalyst
in asymmetric dihydroxylation.
The osmium complex of the resin bearing both residual vinyl
groups and quaternary ammonium moieties (abbreviated as
VinylAmm resin) was prepared by the suspension polymerisation
of divinylbenzene and 4-vinylbenzyl chloride at an 80:20 ratio,
followed by a reaction of the resulting the macroporous copolymer
1 (0.91 mmol Cl per g) with triethylamine yielding the VinylAmm
resin (0.50 mmol N per g) and the subsequent osmylation of the
VinylAmm resin with OsO4 according to the procedure5 reported
by us (Scheme 2). The Os complex of VinylAmm resin was then
analysed by elemental analysis, UV, IR, XRF, UV-DRS and XPS
(see supplementary information{). Os content in the resins was
determined by UV and XRF (X-ray Fluorescence Spectrometer)
analysis (0.18 mmol/g of Os). In the XPS (X-ray Photoelectron
Spectroscopy) spectrum of this resin, Os 4f7/2 lines appeared at
y53 eV and y50 eV.6 Based on these values, it is clear that the
osmium tetroxide is reduced to Os(VI) monoglycolate and Os(IV)
bisglycolate in the reaction with vinyl groups of resins.
Fig. 1
{ Electronic supplementary information (ESI) available: experimental
procedure and spectroscopic data. See http://www.rsc.org/suppdata/cc/b5/
b504223b/
*s1673@skku.edu (Choong Eui Song)
Scheme 1
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Scheme 2 Preparation of VinylAmm–OsO4 complex.
To investigate catalytic performance of the osmylated resin,
VinylAmm resin–OsO4 , the AD reaction of styrene was first
carried out under the standard K3Fe(CN)6 conditions in the
presence of VinylAmm–OsO4 (1 mol%) and (DHQ)2PHAL
(1 mol%). The reaction using this solid Os catalyst was completed
within 30 min to give the desired diol in excellent yield (93%) with
95% ee (entry 1 in Table 1). Even using 0.2 mol% catalyst, the
reaction went very smoothly, affording the diol after 2 h in
excellent yield and ee (entry 2 in Table 1). This solid osmium
catalyst, VinylAmm–OsO4, was then applied to the oxidation of
other olefins. As shown in the entries 3–6 in Table 1, in all cases,
the VinylAmm resin–Os catalyst exhibited a similar activity and
enantioselectivity compared with those of homogeneous OsO4.
To investigate the recyclability of the VinylAmm resin–OsO4, the
AD reactions of styrene were next carried out using 1 mol% of
osmium catalyst and the results obtained here were compared with
those obtained with the solid osmium catalyst reported in the
literature (XAD 4–OsO4 and MerrAmm–OsO4, Fig. 1). For these
experiments, VinylAmm resin–OsO4 was loaded onto a commer-
cially available small cylindrical container with mesh wall
(MicroKan2) in order to minimise grinding of resins through
Fig. 2 Reaction time upon reuse.
stirring during the reaction. The black-coloured resins were
recovered by simple filtration after the reaction. The XPS analysis
of the recovered resin showed clearly that these recovered resins
contain osmium species of +VI and +IV oxidation states (see
supplementary information{). The alkaloid ligand was also almost
quantitatively recovered by simple acid/base extraction. The
recovered resins along with the replenished chiral ligand were
subjected to further AD reactions of styrene. As shown in Table 2
and Fig. 2, the VinylAmm resin–OsO4 maintained its catalytic
activity for almost five cycles. On the other hand, the catalytic
activity of the resins having only residual vinyl groups (i.e., XAD
4–OsO4) or having only ammonium moieties (i.e., MerrAmm–
OsO4) decreased upon reuse significantly, causing increased
turnover time. The difference of recyclability of each solid catalysts
was shown to be more significant, when the reduced amounts
(0.2 mol%) of osmium catalyst was used. Whereas Os-complex of
MerrAmm resin and XAD-7 lost their catalytic activity after their
first and third runs, respectively (MerrAmm resin: 2 h, 93%, 94% ee
(1st run), 24 h, ,10%, 82% ee (2nd run); XAD-7: 4 h, 98%, 93% ee
(1st run), 6 h, 94%, 93% ee (2nd run), 15 h, 73%, 91% ee (3rd run),
our solid osmium catalyst, the VinylAmm resin–OsO4, exhibited
much better recyclability than the above-mentioned solid osmium
catalysts (5 h, 98%, 94% ee (1st run), 7 h, 93%, 94% ee (2nd run),
9 h, 98%, 93% ee (3rd run), 24 h, 94%, 92% ee (4th run).
Table 1 Asymmetric dihydroxylation using VinylAmm–OsO4
complexa
Entry
Substrate
Time/h
Yield (%)
Ee (%)
1
2b
3
4
5
6
a
Styrene
Styrene
trans-Stilbene
b-Methylstyrene
Methyl trans-cinnamate
1-Phenyl-1-cyclohexane
0.5
2
8
1.5
3.5
4.5
93
94
94
97
92
93
95
93
.99
95
.99
94
Considering all these results, osmium anchored to the
VinylAmm resin is highly exposed to the oxidant, and once
oxidised, it become free to react more readily with alkenes in
solution. After the oxidant and starting alkenes are consumed, not
only can the residual osmium tetroxide form new bonds with less
accessible resin-bound vinyl groups but the osmate ion dissolved in
Experimental conditions: see supplementary information).
(DHQ)2PHAL (0.5 mol%) and VinylAmm–OsO4 (0.2 mol%).
b
Table 2 Recyclability of solid Os-catalysts (1 mol%) in AD of styrenea
Solid
Os-catalyst
Run 1 (time,
yield, ee)
Run 2 (time,
yield, ee)
Run 3 (time,
yield, ee)
Run 4 (time,
yield, ee
Run 5 (time,
yield, ee)
VinylAmm–OsO
XAD 4–OsO4
MerrAmm–OsO4
a
2h, 94%, 95% ee
2h, 93%, 95% ee
2h, .99%, 96% ee
2h, 91%, 95% ee
2h, 92%, 95% ee
4h, .99%, 96% ee
2h, 93%, 95% ee
2.5h, 90%, 95% ee
6h, .99% 96% ee
c
2h, 90%, 95% ee
6h, 88%, 95% ee
24h, ,10%, 94% ee
3.5h, 90%, 95% ee
24h, 88%, 95% ee
b
b
Recycling experiment conditions: see supplementary information see Ref. 5. This resin was prepared according to the procedure reported
by Choudary et al.4b
3338 | Chem. Commun., 2005, 3337–3339
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bInstitute of Basic Science, Department of Chemistry, Sungkyunkwan
University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do,
440-746, Korea. E-mail: s1673@skku.edu
solution can also form complexes with the quaternary ammonium
salts onto resin. This means that the synergic effect of
both functionalities in the VinylAmm resin can markedly
enhance the recyclability of the osmium catalyst in asymmetric
dihydroxylation.
Notes and references
In conclusion, as we assumed, the synergic effect of both
functionalities in the VinylAmm resin can markedly enhance the
recyclability of osmium catalyst in asymmetric dihydroxylation.
Although osmium leaching with the VinylAmm resin–OsO4 was
still found,7 causing increased turnover time upon reuse, to the best
of our knowledge, our result is the most successful work reported
until now on the solid osmium-mediated asymmetric dihydroxyl-
ation of olefins (total TONs 5 1915!). Optimisation studies on this
type of resin which can minimise osmium leaching, are currently in
progress.
1 H. C. Kolb, M. S. VanNieuwenhze and K. B. Sharpless, Chem. Rev.,
1994, 94, 2483.
2 For reviews: C. E. Song and S.-G. Lee, Chem. Rev., 2002, 102, 3495;
Q.-H. Fan, Y.-M. Li and A. S. C. Chan, Chem. Rev., 2002, 102,
3385.
3 S. Nagayama, M. Endo and S. Kobayashi, J. Org. Chem., 1998, 63, 6094;
S. Kobayashi, M. Endo and S. Nagayama, J. Am. Chem. Soc., 1999, 121,
11229; S. Kobayashi, T. Ishida and R. Akiyama, Org. Lett., 2001, 3,
2649.
4 (a) B. M. Choudary, N. S. Chowdari, M. L. Kantam and
K. V. Raghavan, J. Am. Chem. Soc., 2001, 123, 9220; (b)
B. M. Choudary, N. S. Chowdari, K. Jyothi and M. L. Kantam,
J. Am. Chem. Soc., 2002, 124, 5341.
Financial support from Ministry of Education in Korea (BK-
program) is acknowledged.
5 J. W. Yang, H. Han, E. J. Roh, S.-G. Lee and C. E. Song, Org. Lett.,
2002, 4, 4685.
6 A. Severeyns, D. E. De Vos, L. Fiermans, F. Verpoort, P. J. Groet and
P. A. Jacobs, Angew. Chem. Int. Ed., 2001, 40, 586.
7 Os content in the resins was determined by XRF (X-ray Fluorescence
Spectrometer) analysis: 0.18 mmol per g of Os before use; 0.12 mmol per g
of Os after first run.
Kwang Jin Kim,a Han Young Choi,a Soon Ho Hwang,a Yil Sung Park,*a
Eun Kyung Kwueon,b Doo Seong Choib and Choong Eui Song*b
aDongWoo Fine-Chem Co., Ltd, 1177, Wonjung-ri, Poseung-myun,
Pyungtaek-si, Gyeonggi-do, 451-820, Korea
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 3337–3339 | 3339