have found widespread application in organic synthesis, the
high cost of the osmium catalyst as well as the ligand in the
ionic liquid layer by ether. Standard chromatographic
purification gave the pure diol product in 96% yield (Table
1, entry 1, run 1). A second run of the reaction was then
conducted using the recovered ionic liquid with a new batch
of the olefin under otherwise identical conditions. It is
noteworthy that the diol was isolated in 90% yield (Table 1,
entry 1, run 2) even without any replenishment of the
catalyst, indicating that both the ionic liquid and the catalyst
were recyclable and reusable. However, further recycling and
reuse of the catalyst system resulted in a dramatic decrease
in the yield of the product (Table 1, entry 1, runs 3 and 4).
case of asymmetric dihydroxylation (AD), coupled with the
6
hazardous toxicity and volatility of OsO
4
, obstructs their
7
large-sale industrial application. Early attempts to im-
mobilize OsO on polymeric supported tertiary amines
4
8
,9
failed to recover and reuse the catalyst due to osmium
leaching and catalyst decomposition. Kobayashi has previ-
1
0
4
ously reported that OsO could be microencapsulated in a
polymer matrix and used as a recyclable and reusable catalyst
for olefin dihydroxylation. However, high loading of osmium
was required in a typical dihydroxylation reaction. Very
recently, two conceptually new approaches to the im-
mobilization of osmium catalyst have been achieved on the
basis of the formation of a hydrolytically stable osmium
monoglycolate derived from a silica-bound tetrasubstituted
This suggested that the active catalytic species, either OsO
itself or complex 1 (Figure 1), formed in situ during the
4
11
12
olefin and by using an ion-exchange technique on various
solid supports.
In searching for a more practical and efficient approach
to the immobilization of the osmium catalyst, we were
attracted by the unique properties of room-temperature ionic
liquids that have recently emerged as environmentally
benign reaction media as well as new vehicles for the
immobilization of transition metal-based catalysts. Using
Figure 1. Formation of Complexes between OsO
Ligands. 1: NMM‚OsO . 2: DMAP‚OsO
4
and Amine
4
4
.
1
3
course of the reaction, underwent significant leaching after
each recycling and reuse. Since complex formation between
1-octene as a test substrate, we set out to examine the
osmium-catalyzed dihydroxylation under the standard Upjohn
OsO and an amine ligand is expected to be reversible, it is
reasonable to assume that a stronger binding and more polar
4
4
4 2
conditions (OsO /NMO in t-BuOH/H O) in the presence of
the room-temperature ionic liquid 1-butyl-3-methylimida-
zolium hexafluorophosphate ([bmim] PF ) (Table 1). After
6
amine might help in preventing complex dissociation and
enhance its partitioning in the more polar ionic liquid layer.
This reasoning was then tested with 4-(dimethylamino)-
pyridine (DMAP), with the anticipation that complex 215
would be more resistant to osmium leaching. To our delight,
14
4
Table 1. Effect of DMAP on OsO -Catalyzed Dihydroxylation
of 1-Octene in Ionic Liquida
(
8) Cainelli, G.; Contento, M.; Manescalchi, F.; Plessi; L. Synthesis 1989,
5-47.
9) Herrmann, W. A.; Kratzer, R. M.; Bl u¨ mel, J.; Friedrich, H. B.;
Fischer, R. W.; Apperley, D. C.; Mink, J.; Berkesi, O. J. Mol. Catal., A
997, 120, 197-205.
10) (a) Nagayama, S.; Endo, M.; Kobayashi, S. J. Org. Chem. 1998,
4
(
1
(
b
63, 6094-6095. (b) Kobayashi, S.; Endo, M.; Nagayama, S. J. Am. Chem.
Soc. 1999, 121, 11229-11230. (c) Kobayashi, S.; Ishida, T.; Akiyama, A.
Org. Lett. 2001, 3, 2649-2652.
yield (%)
entry
cat. (quantity)
run 1
run 2
run 3
run 4
(11) Severeyns, A.; De Vos, D. E.; Fiermans, L.; Verpoort, F.; Grobert,
1
2
OsO4(2 mol%)
OsO4(2 mol%) +
DMAP (2.4 mol%)
96
99
90
94
62
97
36
93
P. J.; Jacobs, P. A. Angew. Chem., Int. Ed. 2001, 40, 586-589.
(12) (a) Choudary, B. M.; Chowdari, N. S.; Kantam, M. L.; Raghavan,
K. V. J. Am. Chem. Soc. 2001, 123, 9220-9221. (b) Choudary, B. M.;
Chowdari, N. S.; Madhi, S.; Kantam, M. L. Angew. Chem., Int. Ed. 2001,
40, 4620-4623. Choudary, B. M.; Chowdari, N. S.; Jyothi, K.; Kumar, N.
S.; Kantam, M. L. Chem. Commun. 2002, 586-587. (c) (d) Choudary, B.
M.; Chowdari, N. S.; Jyothi, K.; Kantam, M. L.; J. Am. Chem. Soc. 2002,
a
All reactions were performed with 2 mmol of 1-octene, 1.1-1.2 equiv
of NMO in the following solvent system: [bmim]PF6 (1 mL), H2O (1 mL),
and t-BuOH (2 mL) at room temperature for 16 h. Isolated yield.
b
1
24, 5341-5349.
[bmim]PF6 ) 1-butyl-3-methylimidazolium hexafluorophosphate.
(
13) For recent reviews on ionic liquids and their application as innovative
solvents in transition metal-catalyzed reactions, see: (a) Welton, T. Chem.
ReV. 1999, 99, 2071-2083. (b) Wasserscheid, P.; Keim, W. Angew. Chem.,
Int. Ed. 2000, 39, 3772-3789. (c) Sheldon, R. Chem. Commun. 2001,
1
6h at room temperature, all the volatiles were removed
2399-2407.
under reduced pressure and the product extracted from the
(14) Although [bmim]PF6 is essentially immiscible with either solvent,
a completely homogeneous mixture was formed upon addition of NMO
and the olefin under these conditions.
(5) (a) Jacobsen, E. N.; Mark o´ , I.; Mungall, W. S.; Schr o¨ der, G.;
(15) An NMR experiment established that upon mixing equimolar
amounts of OsO and DMAP in CDCl , a deep orange-red complex was
Sharpless, K. B. J. Am. Chem. Soc. 1988, 110, 1968-1970. For selected
reviews on Sharpless asymmetric dihydroxylation, see: (b) Kolb, H. C.;
Van Niewenhze, M. S.; Sharpless, K. B. Chem. ReV. 1994, 94, 2483-
4
3
immediately formed:
2
2
547. (c) Johnson, R. A.; Sharpless, K. B. In Catalytic Asymmetric Synthesis,
nd ed.; Ojima, I., Ed.; VCH: Weinheim, 2001; pp 357-398.
(6) Even when other forms of osmium such as OsCl3 and K2[OsO2(OH)4]
are used, volatile-free OsO4 is present in some stage of the catalytic cycle.
7) For a case study, see: Ahrgren, L.; Sdutin, L. Org. Proc. Res. DeV.
997, 1, 425-427.
(
1
2198
Org. Lett., Vol. 4, No. 13, 2002