Catalytic asymmetric dihydroxylation of olefins using a recoverable and reusable OsO42- in ionic liquid [bmim][PF6]

Article abstract of DOI:10.1039/b208631j

The use of the solvent systems water/ionic liquid or water/ionic liquid/tert-butanol provides a recoverable, reusable, robust and simple system for the asymmetric dihydroxylation of olefins, based on the immobilization of the osmium-ligand catalyst in the ionic liquid phase.

Full text of DOI:10.1039/b208631j

Catalytic asymmetric dihydroxylation of olefins using a recoverable and
2
2
reusable OsO4 in ionic liquid [bmim][PF ]†
6
Luís C. Branco and Carlos A. M. Afonso*
REQUIMTE/CQFB, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de
Lisboa, 2829-516 Caparica, Portugal. E-mail: cma@dq.fct.unl.pt; Fax: +351 21 2948550; Tel: +351 21
2948358
Received (in Cambridge, UK) 4th September 2002, Accepted 30th October 2002
First published as an Advance Article on the web 15th November 2002
The use of the solvent systems water/ionic liquid or water/
ionic liquid/tert-butanol provides a recoverable, reusable,
robust and simple system for the asymmetric dihydroxyla-
tion of olefins, based on the immobilization of the osmium-
ligand catalyst in the ionic liquid phase
experiments performed using the solvent tert-butanol/water
under similar conditions (Table 1).
In general for each of the substrates tested, there was always
one solvent system that gave comparable or even higher
chemical yields and enantiomeric excess to the tert-butanol/
water solvent system.
The Sharpless catalytic asymmetric dihydroxylation (AD) of
olefins has become a very useful and reliable transformation for
the synthesis of a wide range of enantiomerically pure vicinal
diols.1 Nevertheless, the high cost, toxicity and possible
contamination of the product with osmium catalyst in the
product restricts the use of AD reactions in industry.2 To
address this issue, several groups have investigated the
immobilization of chiral ligands onto soluble and insoluble
polymers.3 However, this approach suffers from several
disadvantages as e.g. the need for synthesis of each chiral
ligand–polymer system, reduction of the enantioselectivity and
uncompleted recovery and reuse of the Os-ligand catalytic
system. On the other hand, the alternative immobilization of
Encouraged by these results, the possibility of recycling and
reusing the osmium–ligand catalysts based on their preference
partioning to the ionic phase when being extracted with diethyl
ether and water were studied. This procedure should also allow
the reduction of the osmium contamination in the reaction
product and in the aqueous phase. Therefore, as a model
reaction, we studied the AD of 1-hexene in [bmim][PF
6
]/water
and in [bmim][PF ]/water/tert-butanol (Table 2). After each
6
cycle diethyl ether was added to the reaction mixture and the
aqueous and the etheral layers were removed, followed by the
addition of more 1-hexene and aqueous solution containing the
2 3
co-oxidant and K CO . For each solvent system, the experiment
was performed in duplicate in order to obtain additional
information about the distribution of osmium in each phase.
One experiment was used to determine the enantiomeric excess
and the yield, after purification by flash chromatography. The
other parallel experiment was used for the determination of the
osmium content by Inductively Coupled Plasma spectroscopy
(ICP) analysis (relative to the initial amount) in the aqueous,
etheral and ionic liquid phases. In the case of the ionic liquid
osmium catalyst by microencapsulation of OsO
4
in polystyrene
4
type capsules, or on silica-anchored tetrasubstituted olefins
(
limited to achiral dihydroxylation) or by ion-exchangers6
5
allows a recoverable and reusable system for the osmium
catalyzed AD reaction. Here, we report a simple and efficient
recoverable and reusable method for the osmium-catalyzed
asymmetric dihydroxylation of olefins based on the anchoring
of the osmium–ligand catalyst in a room temperature ionic
liquid.
6
phase 50 mL of the [bmim][PF ] was taken before the addition
of the reagents to next cycle.
7
Room temperature ionic liquids (RTILs), specially those
based on 1,3-dialkylimidazolium cations7 have been recog-
,8
Table 1 Asymmetric dihydroxylation of olefins using the ionic liquid
bmim][PF
nised as a possible environmentally benign alternative to
] as a co-solventa
6
[
chemical volatile solvents, mainly due to their negligible vapor
9
pressure and insolubility in supercritical CO
2
(scCO
2
). Recent
RTIL/
H
2
O/t-BuOHd
t-BuOH/H
2
Ob RTIL/H
Yield ee
2
Oc
applications includes their use as a recyclable media for
7
10
chemical processes, including bio- and chemical catalysis,
biphasic RTIL-aqueous11 and RTIL-scCO
lective transport using supported liquid membranes, perva-
9,12
Yield ee
Yield ee
2
extraction,
se-
Olefin
Ligande (%)
(%)
(%)
(%)
(%)
(%)
13
poration,14 dissolution of cellulose and in CO
recently, the recyclable and reusable OsO -catalysed olefin
dihydroxylation using the co-oxidant NMO in [bmim][PF ]/
water/tert-butanol system and in 1-ethyl-3-methylimidazolium
tetrafluoroborate [emim][BF
] has been reported.17
Initially we observed that the chiral ligand 1,4-bis(9-O-
dihydroquinidinyl)phthalazine ((DHQD) PHAL) is soluble in
RTIL 1-n-butyl-3-methylimidazolium hexafluorophosphate
bmim][PF ] and the occurrence of the AD reaction in a
biphasic system just by replacing tert-butanol by [bmim][PF
15
capture. Very
16
2
f
f
f
PHAL
PYR
88
91
97
93
87
86
62
75
86
90
94
89
4
f
6
PHAL
83
95
92
77
80
77
66
71
85
97
84
80
f
PYR
4
PHAL
92
93
90
94
71
96
90
90
88
96
89
91
f
PYR
2
PHALg
PYRg
91
63
87
90
47
66
92
86
53
57
87
83
[
6
PHALh
PYRh
89
94
96
87
87
81
98
96
92
79
99
77
6
]
18
using OsO
optimization of the experimental conditions to the more
advantageous K OsO (OH) /K Fe(CN) system, for styrene,
allowed us to find two protocols: biphasic [bmim][PF ]/water
and monophasic [bmim][PF ]/water/tert-butanol procedures.
Both procedures were applied to representative substrates using
the ligands (DHQD) PHAL and 1,4-bis(9-O-dihydroquinidi-
nyl) biphenyl-pyrimidine (DHQD) PYR and compared to
4 3 6
and the co-oxidants NMO or K Fe(CN) . Further
PHALh
PYRh
94
79
94
75
69
52
87
63
96
92
92
96
2
2
4
3
6
a
6
All reactions were carried out using olefin (0.5 or 1 mmol), K
PHAL or (DHQD) PYR, 1.0 mol%),
(3.0 mol eq.), solvent, rt, 24 h. t-BuOH/
2 2 4
OsO (OH)
(0.5 mol%), ligand ((DHQD)
K
H
2
2
6
b
3
Fe(CN)
6 2 3
(3.0 mol eq.), K CO
c
d
2
O (1+2, 1.5 mL). [bmim][PF
6
]/H
2
O (1+2, 1.5 mL). [bmim][PF
6 2
]/H O/
2
e
t-BuOH (1+1+2,
2 mL). PHAL and PYR refers respectively to
2
f
(
(
DHQD)
2 2
PHAL and (DHQD) PYR. Absolute configuration of the diol is
R). Absolute configuration of the diol is (1S,2R). h Absolute configuration
g
†
Electronic supplementary information (ESI) available: experimental
of the diol is (R,R).
section. See http://www.rsc.org/suppdata/cc/b2/b208631j/
3
036
CHEM. COMMUN., 2002, 3036–3037
This journal is © The Royal Society of Chemistry 2002

In both solvent systems the [bmim][PF
system is extremely effective for a considerable number of runs
e.g. run 1, 88%, ee 90%; run 9, 83%, ee 89%). Only after 11
and 12 cycles a dramatic drop in the chemical and optical purity
was observed respectively for [bmim][PF ]/water and
bmim][PF ]/water/tert-butanol solvent systems. Additionally,
when more K OsO (OH) and (DHQD) PHAL were added to
6
]–osmium–ligand
In summary, we have developed a recoverable, reusable,
robust and simple system for the asymmetric dihydroxylation of
olefins, based on the immobilization of the osmium–ligand
catalyst in the ionic liquid.
We thank Fundação para a Ciência e Tecnologia (SFRH/BD/
6792/2001) for financial support.
(
6
[
6
2
2
4
2
the remaining ionic liquid the reaction occurred again in high
optical and chemical yield (runs 12 and 13). After 13 runs, the
recovered [bmim][PF
6
] presented identical spectroscopic data
Notes and references
‡ Experimental procedures and details of osmium content in each phase and
spectral data of reused room temperature ionic liquid are provided in the
ESI.†
1
13
31
(
H, C and P NMR) to the initial sample, allowing the
2
conclusion that both imidazolium and PF
6
ions are stable
under these conditions.‡ The only observed limitation on these
recycling and reuse experiments is the overall reduction of the
ionic liquid phase to 65% and 72% of the initial volume,
6 6
respectively, for [bmim][PF ]/water and [bmim][PF ]/water/
1
R. A. Johnson and K. B. Sharpless, in Catalytic Asymmetric Synthesis,
nd, ed. I. Ojima, VCH, Weinheim, 2000, pp. 357; H. C. Kolb, M. S.
2
VanNieuwenhze and K. B. Sharpless, Chem. Rev., 1994, 94, 2483.
tert-butanol solvent systems. This reduction should arise from
some solubility of the RTIL in water and in diethyl ether.
Concerning the important issue of product contamination by
osmium, it is noteworthy that in the case of the organic phase,
the osmium present is in the range of the detection limit of the
method used (@ 3% or @ 7 ppb). On the other hand, by
performing the AD reaction on 1-hexene using the water/t-
butanol solvent, followed by partitioning between the aqueous
and organic phases, the osmium content was 96% and 6%
respectively. This comparison demonstrates the remarkable
reduction of the osmium contamination in the product phase and
in the aqueous phase by using the RTIL. The osmium content in
the aqueous phase is considerable higher in the first run than in
2 X. Lu, Z. Xu and G. Yang, Org. Process Res. Dev., 2000, 4, 575; L.
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6
7
the remained runs for the [bmim][PF
%). On the other hand, the RTIL phase persistently retains
more than 90% of the osmium of the previous cycle. The
comparison between the [bmim][PF ]/water and [bmim][PF ]/
6
]/water system (14% vs
4
6
6
water/tert-butanol solvent systems shows that the longer life of
the latter system should arise from the higher affinity of the
osmium ligand to the RTIL phase. Additionally, because of the
peculiar properties of the RTIL, the osmium leaching from the
RTIL phase can be potentially minimized by using more
environmentally friendly methods such as using supercritical
8 J. D. Holbrey and K. R. Seddon, J. Chem. Soc., Dalton Trans, 1999, 13,
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(scCO ) extraction or pervaporation.
5
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2
002, 200; L. C. Branco, J. N. Rosa, J. J. M. Ramos and C. A. M.
Table 2 Asymmetric dihydroxylation of 1-hexene in the ionic liquid
bmim][PF ] using the K OsO (OH) /K Fe(CN) system as a recyclable
and reusable catalyst
Afonso, Chem. Eur. J., 2002, 8, 3671.
[
6
2
2
4
3
6
9 L. A. Blanchard, D. Hancu, E. J. Beckman and J. F. Brennecke, Nature,
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a
[bmim][PF ]/H
6 2
Oa
[bmim][PF ]/H
6 2
O/t-BuOHb
Os in Os in
Os in Os in
11 A. E. Visser, R. P. Swatloski, W. M. Reichert, S. T. Griffin and R. D.
Rogers, Ind. Eng. Chem. Res., 2000, 39, 3596; A. E. Visser, R. P.
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Yield ee
H
(%)
2
O
RTIL
(%)c
Yield ee
H
(%)
2
O
RTIL
(%)
c
c
c
Run
(%)
(%)
(%)
(%)
1
2
3
4
5
6
7
8
9
78
74
76
72
71
74
75
77
70
59
24
88
85
81
84
87
83
86
85
83
71
61
87
84
14
4
3
3
3
4
3
3
3
3
4
19
5
91
88
88
93
90
69
57
51
46
44
44
87
83
88
90
91
85
84
87
89
86
83
77
63
32
90
85
87
83
88
84
91
92
89
82
75
64
86
6
6
4
4
3
3
3
3
4
4
4
4
8
98
97
93
93
90
84
82
71
61
55
56
47
96
10
11
12
13
a
13 L. C. Branco, J. G. Crespo and C. A. M. Afonso, Angew. Chem., Int. Ed,
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Commun., 2001, 1622.
d
73
75
d
85
All reactions were carried out using 1-hexene (0.5 mmol), K
2
OsO
(3.0 mol eq.), K
2
(OH)
CO
4
1
5 R. P. Swatloski, S. K. Spear, J. D. Holbrey and R. D. Rogers, J. Am.
Chem. Soc., 2002, 124, 4974.
(
(
0.5 mol%), (DHQD)
2
PHAL, 1.0 mol%), K
3
Fe(CN)
6
2
3
3.0 mol eq.), [bmim][PF6]/H O (1+1, 6 mL), rt, 24 h followed by extraction
2
1
6 E. D. Bates, R. D. Mayton, I. Ntai and J. H. Davis Jr, J. Am. Chem. Soc.,
2002, 124, 926.
with diethyl ether, removal of both phases and reloading with 1-hexene,
b
water (3 mL), co-oxidant and K
2 3
CO .
Similar procedure to footnote a
c
17 Q. Yao, Org. Lett., 2002, 4, 2197; R. Yamada and Y. Takemoto,
Tetrahedron Lett., 2002, 43, 6849.
using [bmim][PF ]/H O/t-BuOH (1+1+1, 7.5 mL). Percentage of osmium
relative to initial amount detected by ICP in the aqueous and in the RTIL
6
2
1
8 Using (DHQD)
OsO (OH) the 84% yield and ee of 76% for styrene was observed.
Using NMO instead of K Fe(CN) 86% yield and ee of 81% for
-hexene (slow addition) was observed.
2
PHAL in [bmim][PF
6
]/H
2
O (1+1) and OsO
4
instead of
phases; for the etheral phases no osmium was detected for all cycles, error
d
K
2
2
4
of the ICP method ±3%. New addition of K
2 2
OsO (OH)
4
(0.5 mol%) and
3
6
(
2
DHQD) PHAL, (0.5 mol%).
1
CHEM. COMMUN., 2002, 3036–3037
3037