Magnetically recoverable osmium catalysts with osmium-diolate esters for dihydroxylation of olefins

Article abstract of DOI:10.1055/s-0032-1316910

We prepared magnetically recoverable osmium catalysts with stable osmium-diolate esters and applied them to the dihydroxylation of olefins. By employing 2 mol% of the magnetic osmium catalyst, the dihydroxylation reaction proceeded smoothly to provide the corresponding vicinal diol with a low level of osmium leaching. After completion of the dihydroxylation, the osmium catalyst was readily recovered by use of an external magnet and was recycled up to five times. Georg Thieme Verlag Stuttgart . New York.

Full text of DOI:10.1055/s-0032-1316910

LETTER
▌947
lMettear gnetically Recoverable Osmium Catalysts with Osmium–Diolate Esters for
Dihydroxylation of Olefins
Magnetically Recoverable Osmium Catalysts
Ken-ichi Fujita,* Satoshi Umeki, Hiroyuki Yasuda
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Fax +81(29)8614577; E-mail: k.fujita@aist.go.jp
Received: 26.02.2013; Accepted after revision: 18.03.2013
from the reaction mixture without the removal of organic
Abstract: We prepared magnetically recoverable osmium catalysts
reaction solvent (acetone) after the dihydroxylation, and
with stable osmium–diolate esters and applied them to the dihy-
the leaching of osmium off the magnetic backbone was
um catalyst, the dihydroxylation reaction proceeded smoothly to considerable during dihydroxylation (3.3%). We report
provide the corresponding vicinal diol with a low level of osmium herein a new type of magnetically recoverable osmium
droxylation of olefins. By employing 2 mol% of the magnetic osmi-
leaching. After completion of the dihydroxylation, the osmium cat-
alyst was readily recovered by use of an external magnet and was
recycled up to five times.
catalyst prepared through the formation of stable osmi-
um–diolate esters in the reaction of OsO with magnetite-
4
linked tetrasubstituted olefins. Due to the linkage through
the covalent bond between catalytic osmium and the mag-
netic backbone, the leaching level of osmium off the mag-
Key words: osmium catalysts, magnetically recoverable, dihy-
droxylation reaction
netic backbone was suppressed during dihydroxylation.
Furthermore, this magnetic osmium catalyst was clearly
collected from the reaction mixture without the removal
of organic reaction solvent and could be reused repeated-
ly.
The osmium-catalyzed cis-dihydroxylation of olefins is a
unique process for the preparation of vicinal diols. De-
1
spite the widespread application of this type of reaction in
organic synthesis, several obstacles stand in the way of
their large-scale application to the pharmaceutical and
fine chemical industries, including high cost, hazardous
toxicity, volatility, and the possibility of contamination
O
2
with toxic osmium in the final product. One of the most
promising solutions to these problems is the immobiliza-
tion of catalytic osmium on an insoluble support. Hetero-
genization of catalytic osmium by immobilization on
various organic and inorganic supports has previously
been successful, making it possible for the immobilized
osmium catalyst to be recovered by filtration of the reac-
tion mixture.3
1
/2 [OsO42–
]
O
O
O
O
Fe3O4
N+
Si
O
Me
OMe
Me
O
O
1
Magnetic nanoparticles have emerged as smart and prom-
ising supports for immobilization with great industrial po-
tential, as magnetic nanoparticle-supported catalysts can
be easily separated from the reaction medium by applica-
tion of an external permanent magnet, allowing for simple
Figure 1 Magnetic osmate(VI) catalyst 1
4
separation of the catalysts without filtration. The magnet-
ic separation circumvents time-consuming and laborious
separation steps and allows for practical continuous catal-
ysis. We recently prepared a magnetic nanoparticle-sup-
ported osmium catalyst 1 by use of dendritic quaternary
ammonium salts immobilized on magnetite (Fe O ) and
A magnetic nanoparticle-supported osmium catalyst 6
was synthesized as follows (Scheme 1). The silane cou-
6
pling agent 2 and magnetite were refluxed in ethanol for
20 hours under an argon atmosphere to afford magnetite-
3
4
supported amine 3, which was separated by magnetic de-
potassium osmate(VI) by an ion-exchange technique
Figure 1), and it was found that the osmium catalyst 1 ef-
5
cantation using an external magnet. The organic loading
(
of 3 was 0.42 mmol/g, which was determined by elemen-
tal analysis of carbon. The magnetite-supported tetra-
substituted olefin 5 was prepared by coupling of the
ficiently catalyzed the dihydroxylation reaction of olefins
in acetone–H O and could be recovered by use of an ex-
2
5
ternal magnet after the dihydroxylation. However, the
7
obtained 3 and 4 in dichloromethane at room temperature
magnetic osmium catalyst 1 could not be clearly collected
for 15 hours, followed by magnetic decantation. The or-
ganic loading of 5 was 0.22 mmol/g, which was deter-
mined by elemental analysis of carbon. The magnetite-
supported osmium catalyst with osmium–diolate ester 6
SYNLETT 2013, 24, 0947–0950
Advanced online publication: 11.04.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0032-1316910; Art ID: ST-2013-U0179-L
Georg Thieme Verlag Stuttgart · New York
was prepared from 5 and OsO with vigorous stirring at
4
©

948
K. Fujita et al.
LETTER
Cl
Fe3O4
O
OMe
Si
4
MeO
O
O
DMAP additive
MeO Si
NH2
Fe3O4
NH2
MeO
EtOH
reflux, 20 h
CH Cl2
2
r.t., 15 h
2
3
OMe
Si
OMe
Si
O
O
O
O
O
OsO4
O
H
H
Os OH
OH
Fe3O4
Fe3O4
N
N
t-BuOH–CH2
Cl2–H2O
O
r.t., 7 h
O
O
5
6
Os content
.20 mmol/g
0
Scheme 1 Preparation of 6
room temperature for seven hours in t-BuOH–CH Cl – we currently have no definitive explanation for this de-
2
2
8
Η Ο, followed by magnetic decantation. The osmium crease in the osmium leaching, the suppression of the hy-
2
content of 6 was 0.20 mmol/g, which was determined by drolysis of osmium–diolate esters caused by the reduction
X-ray fluorescence analysis (XRF) in the decanted solu- in water in the reaction media could be responsible.
tion.
Table 1 Dihydroxylation of trans-β-Methylstyrene Catalyzed by 6a
We then examined the catalytic activity of 6 by perform-
ing cis-dihydroxylation of olefins (Table 1). The proce-
6
(2 mol% Os)
NMO, H2O
HO
Ph
OH
dure employed here was the modified Jacobs’s synthetic
sequence. By employing 2 mol% of the catalyst 6, a cis-
dihydroxylation reaction of trans-β-methylstyrene was
Ph
3f
t-BuOH–CH2Cl2
r.t.
carried out through the use of N-methylmorpholine N-ox- Entry H O (equiv) Time (h) Yield (%)b Osmium leaching (%)
2
ide (NMO) as a reoxidant in the presence of water (11
1
11
2.6
9
8
98
94
4.1
2.4
equiv) in t-BuOH–CH Cl (2:1, v/v) at room temperature.
2
2
The dihydroxylation reaction proceeded to completion in
nine hours. The magnetic osmium catalyst 6 was collected
using an external magnet rapidly, and the reaction mixture
2
a
Reaction conditions: 6 (2 mol%), trans-β-methylstyrene (1 equiv),
9
NMO (1.3 equiv), H O, t-BuOH–CH Cl (2:1, v/v, 0.33 M based on
2 2 2
was then transferred out of the reaction vessel. As a re-
olefin), carried out at r.t. for the indicated time.
sult, the corresponding diol was obtained in an excellent
chemical yield (98%), although the leaching level of os-
mium off the catalyst, as determined by XRF, remained
somewhat high during dihydroxylation (4.1%; Table 1,
entry 1). In contrast, by performing the dihydroxylation in
the presence of 2.6 equivalents of water, the leaching level
of osmium decreased (2.4%; Table 1, entry 2). Although
b
1
Determined by integration of H NMR absorptions referring to an
internal standard.
In order to suppress the hydrolysis of osmium–diolate es-
ters by the construction of the hydrophobic catalytic envi-
ronment, we next prepared magnetic osmium catalysts
OMe
O
H
1
2
R Si(OR )3
O
Si
N
OsO4
5
Fe3O4
Si R1
OR2
t-BuOH–CH Cl –H O
2
2
2
8
0 °C, 20 h
O
O
O
r.t., 7 h
1
2
7
7
a (R = C18H37, R = Me)
1
2
b (R = CH2CH2C8F17, R = Et)
O
O
OMe
Si
O
O
H
Os OH
N
O
Fe3O4
OH
Si R1
OR2
O
O
O
Os content
0.14 mmol/g
0.10 mmol/g
1
2
8
8
a (R = C18H37, R = Me)
1
2
b (R = CH2CH2C8F17, R = Et)
Scheme 2 Preparation of 8
Synlett 2013, 24, 947–950
© Georg Thieme Verlag Stuttgart · New York

LETTER
Magnetically Recoverable Osmium Catalysts
949
with hydrophobic groups such as octadecyl or heptadeca-
fluorodecyl groups on the magnetite surfaces 8a and 8b,
respectively (Scheme 2). In response to vigorous stirring
of the mixture of 5 and the hydrophobic silane coupling
agent at 80 °C for 20 hours, followed by magnetic decan-
tation, hydrophobic groups were grafted to afford 7a and
1
0
7
b, respectively. The magnetic osmium catalysts 8a and
8
b were prepared according to procedures similar to those
1
1,12
used for 6.
The osmium contents of 8a and 8b are also
shown in Scheme 2.
We then examined the catalytic activity and leaching level
of osmium by carrying out cis-dihydroxylation reactions Figure 3 Recovery of 8a
of trans-β-methylstyrene (Table 2). By employing a mag-
netic osmium catalyst with an octadecyl group on the
magnetite surface 8a, the dihydroxylation proceeded
smoothly in a good chemical yield and the leaching level
of osmium decreased during dihydroxylation, compared
with the case of using 6 (Table 2, entry 1). Figure 2 shows
the reaction mixture of the dihydroxylation catalyzed by
We subsequently performed the cis-dihydroxylation of
various olefins by employing 2 mol% of the magnetic os-
mium catalyst with an octadecyl group on the magnetite
surface 8a, as shown in Table 3. In all cases, the dihydrox-
ylation reactions proceeded. In particular, in the case in
which some styrene derivatives were used, the dihydrox-
ylations were almost complete in 8–9 hours (Table 3, en-
tries 1–3).
8a. In this case, the magnetic osmium catalyst 8a was also
rapidly collected from the reaction mixture, as shown in
Figure 3. On the other hand, by employing a magnetic os-
mium catalyst with a heptadecafluorodecyl group on the
magnetite surface 8b, the leaching level of osmium was
the same as that in the case of 6, contrary to our expecta-
tion (Table 2, entry 2).
Table 3 Various Dihydroxylations Catalyzed by 8aa
8
a (2 mol% Os)
R3
R1
HO
OH
NMO, H2O (2.6 equiv)
R3
R1
R2
t-BuOH–CH2Cl2
R4
R2
R4
r.t.
Table 2 Dihydroxylation of trans-β-Methylstyrene Catalyzed by 8a
Entry
Olefin
Time (h)
Yield (%)b
8
(2 mol% Os)
HO
Ph
OH
NMO, H2O (2.6 equiv)
Ph
1
2
8
8
95
97
Ph
Ph
t-BuOH–CH2Cl2
r.t.
Entry
1
Osmium
catalyst
Time (h)
Yield (%)b
Osmium
leaching (%)
3
4
9
84
85
Ph
Ph
8a
8b
8
8
95
98
1.8
2.4
68
2
a
The reaction conditions were the same as those indicated in Table 1.
Determined by integration of H NMR absorptions referring to an
5
32
90
b
1
internal standard.
6
7
Ph
48
48
99
97
C8H17
C4H9
8
C H
94
91
4
9
a
The reaction conditions were the same as those indicated in Table 2.
Isolated yield.
b
Finally, the reusability of the catalyst 8a was examined
using trans-β-methylstyrene (Table 4). In this experiment,
it was found that the catalyst 8a could be efficiently recy-
cled up to five times by magnetic separation, and that the
corresponding diol could be consistently obtained in a
good chemical yield. Although the reaction times were
progressively prolonged with each successive reuse of 8a,
Figure 2 Dihydroxylation catalyzed by 8a
©
Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 947–950

950
K. Fujita et al.
LETTER
(
4) (a) Baig, R. B. N.; Varma, R. S. Chem. Commun. 2013, 752.
(b) Polshettiwar, V.; Luque, R.; Fihri, A.; Zhu, H.; Bouhrara,
M.; Basset, J.-M. Chem. Rev. 2011, 111, 3036. (c) Schätz,
A.; Reiser, O.; Stark, W. J. Chem. Eur. J. 2010, 16, 8950.
Table 4 Catalyst Recycling in the Dihydroxylation of trans-β-Meth-
ylstyrene by Use of 8aa
1st
2nd
3rd
4th
5th
Number of recycle
(d) Lu, A.-H.; Salabas, E.-L.; Schüth, F. Angew. Chem. Int.
Ed. 2007, 46, 1222.
5) Fujita, K.; Umeki, S.; Yamazaki, M.; Ainoya, T.;
Time (h)
8
10
96
17
99
19
96
20
97
(
(
(
(
Yield (%)b
95
Tsuchimoto, T.; Yasuda, H. Tetrahedron Lett. 2011, 52,
3
137.
Osmium leaching (%) 1.8
1.7
1.5
1.8
1.5
6) (a) Liu, X.; Ma, Z.; Xing, J.; Liu, H. J. Magn. Magn. Mater.
2004, 270, 1. (b) Massart, R. IEEE Trans. Magn. 1981, 17,
1247.
7) (a) Donohoe, T. J.; Callens, C. K. A.; Thompson, A. L. Org.
Lett. 2009, 11, 2305. (b) Al-Zoubi, R. M.; Marion, O.; Hall,
D. G. Angew. Chem. Int. Ed. 2008, 47, 2876.
a
The reaction conditions were the same as those indicated in Table 2.
Isolated yield.
b
the leaching level of osmium was less than 1.8% in all
rounds.
8) Severeyns, A.; De Vos, D. E.; Jacobs, P. A. Green Chem.
2
002, 4, 380.
In summary, by employing a novel magnetic osmium cat-
alyst with a stable osmium–diolate ester, the dihydroxyl-
ation reaction proceeded smoothly, and the leaching level
of osmium during dihydroxylation was suppressed by the
introduction of an octadecyl group on the magnetite sur-
face. Furthermore, the osmium catalyst was efficiently re-
cycled up to five times by magnetic separation.
(9) General Procedure
To a t-BuOH–CH Cl (2:1, v/v) solution (3 mL) of the olefin
2
2
(1 mmol) was successively added a magnetic osmium
catalyst (0.02 mmol), NMO (1.3 mmol), and H O (2.6 or 11
2
mmol) at r.t. under an argon atmosphere. After stirring of the
resulting mixture, the dihydroxylation reaction was
completed (monitored by TLC). A magnetic osmium
catalyst was separated by magnetic decantation using an
external magnet followed by washing with t-BuOH–CH Cl ,
2
2
and the recovered magnetic osmium catalyst was reused for
subsequent dihydroxylation reactions.
References and Notes
(
10) Compound 7a: olefin moiety 0.19 mmol/g, C H group
1
8
37
(
(
(
1) (a) Kobayashi, S.; Sugiura, M. Adv. Synth. Catal. 2006, 348,
496. (b) Kolb, H. C.; Van Nieuwenhze, M. S.; Sharpless, K.
B. Chem. Rev. 1994, 94, 2483. (c) Schröder, M. Chem. Rev.
980, 80, 187.
2) (a) Hammond, C. R. In CRC Handbook of Chemistry and
Physics; Lide, D. R., Ed.; 81st ed.; CRC Press: Boca Raton,
0.41 mmol/g; compound 7b: olefin moiety 0.16 mmol/g,
1
CH CH C F group 0.44 mmol/g.
2
2
8 17
(
11) Preparation of 8a
1
OsO was prepared in situ by stirring a CH Cl –Η Ο (5:1,
4
2
2
2
v/v) solution (90 mL) of K OsO ·2H O (111 mg, 0.3 mmol)
2
4
2
and NMO (703 mmol, 6 mmol) overnight at r.t. under an
argon atmosphere. To the resulting solution, 7a (1.67 g,
2
1
000, 4. (b) Leadbeater, N. E.; Marco, M. Chem. Rev. 2002,
02, 3217.
0
.316 mmol) and t-BuOH (150 mL) were added, and the
3) (a) Akiyama, R.; Matsuki, N.; Nomura, H.; Yoshida, H.;
Yoshida, T.; Kobayashi, S. RSC Adv. 2012, 2, 7456. (b) Jun,
B.-H.; Kim, J.-H.; Park, J.; Kang, H.; Lee, S.-H.; Lee, Y.-S.
Synlett 2008, 2313. (c) Kim, K. J.; Choi, H. Y.; Hwang, S.
H.; Park, Y. S.; Kwueon, E. K.; Choi, D. S.; Song, C. E.
Chem. Commun. 2005, 3337. (d) Ley, S. V.; Ramarao, C.;
Lee, A.-L.; Østergaard, N.; Smith, S. C.; Shirley, I. M. Org.
Lett. 2003, 5, 185. (e) Choudary, B. M.; Chowdari, N. S.;
Jyothi, K.; Kantam, M. L. J. Am. Chem. Soc. 2002, 124,
mixture was vigorously stirred for 7 h at r.t. under an argon
atmosphere. The obtained magnetic nanoparticles were
separated by magnetic decantation using an external magnet
and washed five times with t-BuOH–CH Cl . After drying
2
2
under reduced pressure, 1.67 g of 8a was obtained as a black
powder.
(
12) Selected Data for Compound 8a
Black powder. IR (KBr) 2922, 2853, 1655, 1638, 1047,
–
1
1
0
015, 993, 571 cm . Anal. Found: C, 11.21; H, 1.89; N,
.45; Os, 2.63.
5341. (f) Severeyns, A.; De Vos, D. E.; Fiermans, L.;
Verpoort, F.; Grobet, P. J.; Jacobs, P. A. Angew. Chem. Int.
Ed. 2001, 40, 586.
Synlett 2013, 24, 947–950
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