Ionic liquid-immobilized catalytic system for biomimetic dihydroxylation of olefins

Article abstract of DOI:10.1039/b403333g

A biomimetic catalytic system for dihydroxylation of olefins consisting of OsO₄, N-methylmorpholine, and a flavin has been immobilized in an ionic liquid. This immobilized catalytic system is highly efficient for dihydroxylation with 30% aqueous H₂O₂ and it can be reused (at least 5 times) without loss of activity.

Full text of DOI:10.1039/b403333g

Ionic liquid-immobilized catalytic system for biomimetic dihydroxylation
of olefins†
Adam Closson, Mikael Johansson and Jan-E. Bäckvall*
Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm,
Sweden. E-mail: jeb@organ.su.se; Fax: +46 8 154908; Tel: +46 8 6747178
Received (in Cambridge, UK) 4th March 2004, Accepted 16th April 2004
First published as an Advance Article on the web 24th May 2004
A biomimetic catalytic system for dihydroxylation of olefins
consisting of OsO4, N-methylmorpholine, and a flavin has been
immobilized in an ionic liquid. This immobilized catalytic
system is highly efficient for dihydroxylation with 30% aqueous
H2O2 and it can be reused (at least 5 times) without loss of
activity.
Various methods for immobilization of OsO4 have been reported
in the literature.11–13 Recent developments have concerned poly-
mer encapsulation of osmium tetroxide,12a–c chemically anchoring
of osmium to a solid support,12d–f and dissolving osmium tetroxide
in ionic liquids.13 Ionic liquids have recently attracted much
attention.14,15 Changing one or both of the counterions can result in
a change in solubility properties, which has given them the name
“designer solvents”.16 For example, [bmim]PF6 is hydrophobic.17
We realized that use of ionic liquids presented an especially
convenient method of immobilizing not only one, but multiple
components. Accordingly, we began investigations using
[bmim]PF6 and the components of our triple catalytic system with
flavin 1 as ETM (Scheme 1). The components of the biomimetic
triple catalytic system were immobilized in the ionic liquid
([bmim]PF6) and TEAA and DMAP were added. Acetone was
added as co-solvent and reaction of styrene with aqueous 30%
H2O2 in this medium for 3h at room temperature afforded the diol
product in 85% isolated yield after workup (Scheme 2, Table 1,
entry 1).
A number of representative olefins were dihydroxylated using
these reaction conditions. In this series of reactions, 1.5 equiv. of
hydrogen peroxide (30% aqueous solution) was added over a 1.5 h
period via syringe pump, followed by a further 1.5 h of stirring.
After this time, the acetone was removed under reduced pressure
and the reaction mixture was extracted with diethyl ether. The crude
product obtained was chromatographed on silica gel to give the diol
in good yield. The results are summarized in Table 1. The isolated
yields of diol from these simple olefins ranged from 75–88%.
After obtaining these promising results, we moved on to testing
the reusability of the system. The remaining ionic liquid residues
from the reaction of a-methyl styrene and allyl phenyl ether were
therefore recharged with 1 equiv. of olefin. Co-solvents and
hydrogen peroxide were added as above with the same reaction
times. Reaction workup was carried out again by removing volatile
solvents under reduced pressure followed by extractions with
diethyl ether and silica gel chromatography of the crude extracts.
The ionic liquid was recovered and again submitted to further
reactions with fresh starting material, co-solvents, and hydrogen
peroxide until five cycles were reached. The yields for each of the
five cycles were good, although with some minor variations. We
were pleased to find that the flavin as well as the osmium and NMM
(NMO) were retained within the ionic liquid for multiple runs,
allowing for continued H2O2-based dihydroxylation to occur
without loss of activity.‡ The results are given in Table 2. Control
reactions run without flavin under otherwise identical conditions
The osmium-catalyzed dihydroxylation of olefins is one of the most
useful and easily performed oxidation reactions in organic
synthesis.1 In this process, osmium(VIII) is reduced to osmium(VI
)
by reaction with an olefin to yield a vicinal diol. A range of oxidants
for recyling Os(VI) to Os(VIII) have been reported.1–4
We have recently developed biomimetic catalytic systems for the
dihydroxylation of olefins with hydrogen peroxide.4–6 A stepwise
low-energy electron transfer7 via electron transfer mediators
(ETMs), in analogy with biological systems, leads to a mild and
selective dihydroxylation by hydrogen peroxide. The latter is an
inexpensive and environmentally friendly oxidant.8,9 In Scheme 1,
N-methyl morpholine (NMM) and an additional ETM was used to
carry electrons from Os(VI) to H2O2. Examples of H2O2-activating
ETMs in Scheme 1 that we have used are 1,4 2,5 and 36 (Fig. 1).
One of the mildest oxidation systems according to Scheme 1 was
obtained with flavin 1 as the H2O2-activating ETM. Flavin 1 is an
efficient ETM but fragile and attempting to isolate it after the
reaction is difficult. Also, the other catalysts of the triple catalytic
system (Scheme 1) are difficult to recover and reuse. One way to
circumvent this problem would be to immobilize one or more
components of the catalytic system. We now report on a successful
and novel10 ionic-liquid immobilization of the whole biomimetic
system of Scheme 1, where the three-component system can be
recovered and reused.
Fig. 1 Electron Transfer Mediators (ETMs) successfully used in a triple
catalytic system.
Scheme 1 Biomimetic system for dihydroxylation of olefins.
† Electronic supplementary information (ESI) available: experimental
details. See http://www.rsc.org/suppdata/cc/b4/b403333g/
Scheme 2 Biomimetic dihydroxylation in ionic liquid.
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C h e m . C o m m u n . , 2 0 0 4 , 1 4 9 4 – 1 4 9 5
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

Table 1 Biomimetic dihydroxylation in ionic liquida
Notes and references
Yieldb
85%
‡ At the end of the reaction the NMM is in the form of polar NMO and the
flavin is in a cationic form. Therefore they are not extracted.
Entry
1
Olefin
Product
1 Review: H. C. Kolb, M. S. Van Nieuwenhze and K. B. Sharpless, Chem.
Rev., 1994, 94, 2483–2547.
2 (a) V. VanRheenen, R. C. Kelly and D. F. Cha, Tetrahedron Lett., 1976,
17, 1973–1976; (b) M. Minato, K. Yamamato and J. Tsuji, J. Org.
Chem., 1990, 55, 766–768.
2
3
4
84%
75%
84%
3 (a) C. Döbler, G. M. Mehltretter and M. Beller, Angew. Chem. Int. Ed.,
1999, 38, 3026–3028; (b) C. Döbler, G. M. Mehltretter, U. Sundermeier
and M. Beller, J. Am. Chem. Soc., 2000, 122, 10289–10297.
4 (a) K. Bergstad, S. Y. Jonsson and J.-E. Bäckvall, J. Am. Chem. Soc.,
1999, 121, 10424–10425; (b) S. Y. Jonsson, K. Färnegårdh and J. E.
Bäckvall, J. Am. Chem. Soc., 2001, 123, 1365–1371; (c) S. Y. Jonsson,
H. Adolfsson and J. E. Bäckvall, Org. Lett., 2001, 3, 3463–3466.
5 A. H. Éll, S. Y. Jonsson, A. Börje, H. Adolfsson and J. E. Bäckvall,
Tetrahedron Lett., 2001, 42, 2569–2571.
5
6
88%
79%
6 (a) S. Y. Jonsson, H. Adolfsson and J. E. Bäckvall, Chem. Eur. J., 2003,
9, 2783–2788; (b) A. H. Éll, A. Closson, H. Adolfsson and J. E.
Bäckvall, Adv. Synth. Catal., 2003, 345, 1012–1016.
7 D. V. Deubel, J. Am. Chem. Soc., 2004, 126, 996–997.
8 G. Strukul, Catalytic Oxidations with Hydrogen Peroxide as Oxidant,
Kluwer, Dordrecht, The Netherlands, 1992.
9 Direct reoxidation of Os(VI) in dihydroxylation reactions without ETMs
lead to nonselective reactions and over-oxidation: (a) N. A. Milas and S.
Sussman, J. Am. Chem. Soc., 1936, 58, 1302–1304; (b) N. A. Milas, J.
H. Trepagnier, J. T. Nolan and M. I. Iliopulos, J. Am. Chem. Soc., 1959,
81, 4730–4733.
a Unless otherwise noted 7.2 mg of K2OsO4 (1 mol%), 16 mg of flavin 1 (3
mol%), 28 mL of N-methyl morpholine (NMM) (12 mol%), 2.6 mg of
DMAP and Et4N+OAc2 (TEAA) (0.5 equiv.) were stirred in 0.5 mL of
[bmim]PF6. 1 mL of acetone and 0.25 mL of H2O were added as co-solvents
together with the olefin (2 mmol). 30% H2O2 (3 mmol) was added over 1.5
h followed by 1.5 h of reaction. b Isolated yields.
10 The only immobilization previously done with a H2O2 driven Os-
catalyzed dihydroxylation was on solid support with layered double-
hydroxides (LDHs).10a Jacobs and DeVos have also reported on a
related immobilized system on solid support, but there the Os-catalyzed
dihydroxylation and the NMM recycling by H2O2 had to be run in
separate compartments.10b (a) B. M. Choudary, N. S. Showdari, S.
Madhi. and M. L. Kantam, Angew. Chem. Int. Ed., 2001, 40,
4619–4623; (b) A. Severeyns, D. E. De Vos and P. A. Jacobs, Green
Chem., 2002, 4, 380–384.
Table 2 Yields of diol in dihydroxylation after catalyst recycling
Yielda
Entry
Olefin
Run 1
Run 2
Run 3
Run 4
Run 5
11 (a) C. Bolm and A. Gerlach, Eur. J. Org. Chem., 1998, 21–27; (b) G.
Cainelli, M. Contento, F. Manescalchi and L. Plessi, Synthesis, 1989,
45–47; (c) W. A. Herrmann, R. M. Kratzer, J. Blümel, H. B. Friedrich,
R. W. Fischer, D. C. Apperley, J. Mink and O. Berkesi, J. Mol. Catal.
A, 1997, 120, 197–205.
1
2
84%
88%
84%
76%
90%
90%
71%
73%
89%
84%
12 (a) S. Nagayama, M. Endo and S. Kobayashi, J. Org. Chem., 1998, 63,
6094–6095; (b) S. Kobayashi, M. Endo and S. Nagayama, J. Am. Chem.
Soc., 1999, 121, 11229–11230; (c) S. Kobayashi, T. Ishida and A.
Akiyama, Org. Lett., 2001, 3, 2649–2652; (d) A. Severyns, D. E. De
Vos, L. Fiermans, F. Verpoort, P. J. Grobert and P. A. Jacobs, Angew.
Chem. Int. Ed., 2001, 40, 586–589; (e) B. M. Choudary, N. S. Chowdari,
K. Jyothi, N. S. Kumar and M. L. Kantam, Chem. Commun., 2002,
586–587; (f) B. M. Choudary, N. S. Chowdari, K. Jyothi and M. L.
Kantam, J. Am. Chem. Soc., 2002, 124, 5341–5349.
13 (a) Q. Yao, Org. Lett., 2002, 4, 2197–2199; (b) L. C. Branco and C. A.
M. Afonso, Chem Commun., 2002, 3036–3037; (c) R. Yanada and Y.
Takemoto, Tetrahedron Lett., 2002, 43, 6849–6851; (d) C. E. Song, D.
Jung, E. J. Roh, S. Lee and D. Y. Chi, Chem. Commun., 2002,
3038–3039.
14 (a) S. T. Handy, Chem. Eur. J., 2003, 9, 2938–2944; (b) J. H. Davis Jr.
and P. A. Fox, Chem. Commun., 2003, 1209–1212; (c) C. E. Song,
Chem. Commun., 2004, 1033–1043; (d) C. Baudequin, J. Baudoux, J.
Levillain, D. Cahard, A. C. Gaumont and J. C. Plaquevent, Tetrahedron:
Asymmetry, 2003, 14, 3081–3093.
15 Review: (a) T. Welton, Chem. Rev., 1999, 99, 2071–2083; (b) P.
Wasserscheid and W. Keim, Angew. Chem. Int. Ed., 2000, 39,
3772–3789.
a Isolated yields.
resulted in 66% yield of diol from a-methyl styrene and 35% yield
of diol from trans-2-octene on the first runs, indicating that direct
H2O2 oxidation is possible, but not as efficient as with the flavin-
based system. We also performed some experiments using
VO(acac)2 (2) as ETM, which gave essentially the same results as
with flavin 1 for the styrenes. However, the results were not as
consistent for the other olefins as with the flavin system.
The yields are consistently good over the five reaction cycles,
demonstrating the effective immobilization of the complete
biomimetic system of Scheme 1, where the ETM is flavin 1. The
successful recycling of the triple catalytic system components
allows for a more economic and environmentally friendly process.
It becomes operationally very simple: after extraction of the
product, new olefin and hydrogen peroxide are added to the
immobilized biomimetic system for an additional dihydroxyla-
tion.
16 Review: J. Dupont, R. F. de Souza and P. A. Z. Suarez, Chem. Rev.,
2002, 102, 3667–3692.
17 J. S. Yadav, B. V. S. Reddy and G. Baishy, J. Org. Chem., 2003, 68,
7098–7100.
Financial support from the Swedish Research Council, and the
Swedish Foundation for Strategic Research is gratefully ac-
knowledged.
C h e m . C o m m u n . , 2 0 0 4 , 1 4 9 4 – 1 4 9 5
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