Highly efficient Wacker oxidation catalyzed by heterogeneous Pd montmorillonite under acid-free conditions

Article abstract of DOI:10.1016/j.tetlet.2005.12.082

Palladium-montmorillonite was proven to be highly efficient for the Wacker oxidation of terminal olefins to the corresponding methyl ketones. The catalyst was reusable while maintaining high activity and selectivity.

Full text of DOI:10.1016/j.tetlet.2005.12.082

Tetrahedron
Letters
Tetrahedron Letters 47 (2006) 1425–1428
Highly efficient Wacker oxidation catalyzed by heterogeneous
Pd montmorillonite under acid-free conditions
Takato Mitsudome, Takuya Umetani, Kohsuke Mori, Tomoo Mizugaki,
Kohki Ebitani and Kiyotomi Kaneda*
Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama,
Toyonaka, Osaka 560-8531, Japan
Received 17 November 2005; revised 7 December 2005; accepted 15 December 2005
Abstract—Palladium-montmorillonite was proven to be highly efficient for the Wacker oxidation of terminal olefins to the corre-
sponding methyl ketones. The catalyst was reusable while maintaining high activity and selectivity.
ꢀ
2005 Elsevier Ltd. All rights reserved.
Wacker oxidation is one of the most efficient and impor-
tant organic synthetic methods for converting terminal
olefins to the corresponding methyl ketones and is gen-
erally catalyzed by homogeneous palladium salts com-
Montmorillonites (mont) have attracted considerable
interest as highly efficient heterogeneous catalysts.
7
These minerals are hydrophilic clays and can be
structurally defined as layers of negatively charged
two-dimensional silicate sheets separated by interlayer
cationic species. Various metal cations can be success-
fully introduced within the interlayers via a simple ion-
exchange method, providing active metal ion species
having unique structures owing to the sterically
restricted nano-order interlamellar regions. Recently,
we have succeeded in creating within the interlayers of
the mont a chain-like metal species and a monomeric
aqueous metal complex, which act as unique hetero-
geneous catalysts for various C–C bond-forming reactions
1
bined with copper salts under aerobic conditions.
Addition of strong acids, for example, HClO , H SO ,
4
2
4
and MeSO H is often required to achieve a favorable
3
0
reoxidation of Pd , preventing aggregation of transient
0
2
atomic Pd species to inactive Pd metal. However, these
not only corrode the reactor wall but also lead to the low
3
selectivity toward methyl ketone. In the context, some
acid-free Wacker oxidation systems have been
4
reported.
8
Conventional Wacker oxidation using homogeneous Pd
catalysts often leads to difficulties in isolation of the
products, separation of the catalysts from the reaction
mixture, and recyclability of the catalysts. Therefore,
much effort has been devoted to development of highly
and for oxidation of olefins using molecular oxygen.
We report herein that a Pd montmorillonite (Pd-mont),
prepared by cation-exchange in an aqueous
Pd(CF COO) solution, acted as a highly efficient hetero-
3
2
5
,6
efficient Wacker oxidation by heterogeneous catalysts.
geneous catalyst for liquid-phase Wacker oxidation of
a wide range of terminal olefins to the corresponding
methyl ketones under acid-free conditions. The catalytic
activity of the Pd-mont for the above oxidation was
superior to those of other reported Pd catalysts. Fur-
thermore, the spent Pd-mont catalyst could be reused
without an appreciable loss of catalytic activity and
selectivity.
Various Pd complex catalysts immobilized on organic or
inorganic supports have been reported for this purpose,
but these catalyst systems often have drawbacks such as
low catalytic activity, and are limited in application to a
narrow range of terminal olefins.
+
A mixture of 1.0 g of Na -mont Na (OH) Si7.7-
0
.66
4
Keywords: Wacker oxidation; Palladium; Heterogeneous catalyst;
Montmorillonite.
(Al3.34Mg0.66Fe0.19)O20 (Kunipia F, Kunimine Industry
*
Corresponding author. Tel./fax: +81 6 6850 6260; e-mail: kaneda@
cheng.es.osaka-u.ac.jp
Co., Ltd) and aqueous hydrogen chloride (100 mL,
0.027 M) was stirred at 80 ꢁC for 48 h to afford a
0040-4039/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.12.082

1426
T. Mitsudome et al. / Tetrahedron Letters 47 (2006) 1425–1428
+
+
H -mont. The obtained H -mont (1.0 g) was treated
with an aqueous solution of Pd(CF COO) (100 mL,
mely simple and efficient catalyst system for acid-free
Wacker oxidation. The Pd-mont exhibited the highest
9
3
2
1
mM) at 80 ꢁC for 24 h. The obtained slurry was then
catalytic activity in DMA compared with other solvents,
affording 2-decanone in 85% yield with 99% selectivity
without addition of acids (entry 1 vs 4–8).1 Among
Cu compounds tested, CuCl2 was the most effective
and only 4 equiv of CuCl2 to Pd were required to
achieve the high catalytic activity. Other Cu compounds,
such as Cu(OAc) and Cu(NO ) , barely functioned as
filtered, washed with distilled water, and dried under
vacuum to afford Pd-mont as a brown powder (Pd con-
tent: 0.08 mmol g ). The X-ray diffraction pattern
verified the retention of the mont layered structure with
a basal spacing of 6.1 A, and XPS spectra (Pd 3d
0
À1
˚
=
/2
5
3
37.4 eV) revealed the oxidation state of the Pd species
2
3 2
1
1
in the mont was divalent. IR measurement showed a
m(C@O) band at around 1700 cm , and the ratio of
co-catalysts (entries 10 and 11).
À1
Pd/F in the Pd-mont was determined to be 1:3 by
XPS. The above results as well as the curve-fitting anal-
After ca. 50% conversion, the Pd-mont was filtered off at
80 ꢁC; subsequent treatment of the filtrate under similar
reaction conditions did not afford any products, and
ICP analysis of the filtrate confirmed that the Pd content
was below the detection limit (<1 ppb). An obvious
advantage of this catalytic system is the facile separation
3
ysis of the Fourier transform of k -weighted Pd K-edge
II
+
EXAFS revealed the formation of a [Pd (CF COO)]
3
species within the interlayer of the mont.
1
2
Initially, liquid-phase Wacker oxidation of 1-decene was
performed as a model reaction using the Pd-mont under
several sets of conditions, as shown in Table 1. We have
of the oxidized products from the reaction mixture.
Upon completion of oxidation, n-heptane is added to
the reaction mixture and the n-heptane phase containing
the oxidized products is removed from the reaction
mixture. Further oxidation after addition of successive
portions of olefin to the reaction mixture allows recy-
recently disclosed that PdCl in combination with N,N-
2
dimethylacetamide (DMA) solvent could offer an extre-
cling of the Pd-mont and CuCl in the residual DMA
2
Table 1. Wacker oxidation of 1-decene catalyzed by Pd-mont under
various conditions
solution under identical reaction conditions (Scheme
1). For example, the second and third oxidation cycles
of 1-decene proceeded at rates similar to that of the
original reaction, affording 2-decanone in yields of more
than 84% (entries 1–3).
a
O
Pd-mont, Cu
n
-C H
n-C H
7 15
7
15
+
2
H O
o
O , Solvent, 80 C
2
b
Entry
Co-catalyst
Solvent
Conv. (%)
Yield (%)
It is noteworthy that the turnover number (TON) based
on Pd reached 2400; this value is considerably greater
than those reported for other Pd catalyst systems under
acid-free conditions (Table 2).
1
2
3
4
5
6
7
8
9
1
1
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
CuCl
2
2
2
2
2
2
2
2
DMA
DMA
DMA
85
85
84
75
17
13
8
5
63
8
85
84
84
73
17
13
0
0
63
0
c
d
e
NMP
f
DMF
The scope of this Pd-mont catalyst in Wacker oxidation
of various alkenes is demonstrated in Table 3. Wacker
oxidation of a wide range of terminal olefins proceeded
efficiently, and the corresponding ketones were obtained
in high yields in all cases. For example, the oxidation of
long-chain olefins such as 1-hexadecene and 1-eicosene
occurred efficiently to give 85% and 81% yields of the
ketones, respectively (entries 7 and 8). Olefins possessing
functionalized groups were also converted smoothly to
the corresponding ketones selectively, with suppression
EtOH
CH CN
3
g
DMSO
DMA
DMA
DMA
CuBr
Cu(NO
Cu(OAc)
2
0
1
3
)
2
2
5
0
a
1
-Decene (1.0 mmol), Pd-mont (0.05 g; Pd: 0.004 mmol), Cu com-
pound (0.016 mmol), H
1 atm).
Yields were determined by GC analysis.
Reuse 1.
2
O (0.5 mL), solvent (3 mL), 3 h, 80 ꢁC, O
2
(
b
c
d
e
f
1
4
of hydration and alcohol oxidation (entries 9–11). In
scale-up conditions, 1-decene (20 mmol; 2.8 g) was suc-
cessfully converted to 2-decanone (88% isolated yield;
2.7 g) (entry 5). Furthermore, it was revealed that, in
the case of 1-hexene, the TON reached 6000 (entry 2).
Reuse 2.
N-Methylpyrrolidone.
N,N-Dimethylformamide.
Dimethyl sulfoxide.
g
n-heptane Phase
Addition of
substrate
Oxidation
0 oC, 3 h
product
Cooled tt o r.t
DMA/H O Phase
2
substrate
CuCl2
Pd-mont
product
CuCl2
Pd-mont
8
Addition of
n-heptane
CuCl2
Pd-mont
CuCl2
Pd-mont
Separa tt ion oo f n-heptane phase
Recyclable
Scheme 1. Recycling of catalytic composition by phase-separation technique.

T. Mitsudome et al. / Tetrahedron Letters 47 (2006) 1425–1428
1427
Table 2. The catalytic activity of Pd-mont compared with other reported catalysts in Wacker oxidation of 1-decene
a
Entry
Catalyst system
Pd-mont/CuCl
PBI-supported Pd catalyst /CuCl
Pd2060 cluster–TiO /CuCl
Time (h)
TON
Yield (%)
Ref.
b
1
2
48
11
2
72
24
48
2400
93
88
9
7
18
92
100
88
87
73
This work
c
2
3
4
5
6
2
5e
5b
4c
1c
13
2
2
PdCl
PdCl
PdCl
2
2
2
/Cu(OAc)
/CuCl
+ CTAB /CuCl
2
2
d
2
73
a
b
c
Yield were based on alkene.
Substrate (2.0 mmol), Pd-mont (0.01 g; Pd: 0.0008 mmol), CuCl
PBI = polybenzimidazole.
2
(0.0032 mmol), H
2
O (0.5 mL), DMA (3 mL), 48 h, 80 ꢁC, O
2
(1 atm).
d
CTAB = cetyltrimethylammonium bromide.
a
Table 3. Wacker oxidation of various olefins catalyzed by Pd-mont
b
Entry
1
Substrate
Time (h)
3
Conv. (%)
82
Product
Yield (%)
81
n
-C H
O
3
7
n
-C H
3
7
c
2
95
82
95
82
O
3
4
n
-C5H11
-C7H15
3
3
n
-C H
5
11
O
n
85
85
n-C H
7
15
d
5
3
3
89
91
89 (88)
91
O
6
7
n
n
n
-C9H19
n
n
n
-C H
9 19
O
-C13H27
3
3
88
82
85
-C13H27
-C17H35
O
e
8
-C17H35
81 (79)
O
f
9
4
90
75
89 (86)
73 (70)
MeO C
2
7
MeO C
2
7
O
f
1
1
0
NC
HO
15
NC
HO
O
f
1
4
3
92
86
91 (88)
82 (80)
7
7
O
f
1
1
2
3
O
O
f
O
12
90
86 (83)
a
b
c
d
e
f
Substrate (1.0 mmol), Pd-mont (0.05 g, Pd: 0.004 mmol), CuCl
Yields were determined by GC analysis. Values in parenthesis are isolated yields.
Substrate (5.0 mmol), Pd-mont (0.01 g; Pd: 0.0008 mmol), CuCl (0.0032 mmol), 48 h.
, (0.4 mmol), H O (10 mL), DMA (60 mL).
2
(0.016 mmol), H
2
O (0.5 mL), DMA (3 mL), 3 h, 80 ꢁC, O
2
(1 atm).
2
Substrate (20 mmol), Pd-mont (1.0 g; Pd: 0.08 mmol), CuCl
DMA (5 mL).
2
2
Substrate (0.5 mmol).
In conclusion, we have developed a highly active hetero-
geneous Pd catalyst for liquid-phase Wacker oxidation
without the external addition of strong acids. The Pd-
mont catalyst was shown to have high catalytic activity

1428
T. Mitsudome et al. / Tetrahedron Letters 47 (2006) 1425–1428
for conversion of various terminal olefins. Moreover,
this catalyst was reusable while maintaining the high
activity and selectivity.
6. A recyclable catalytic system using ionic liquid, see:
Ansari, I. A.; Joyasawal, S.; Gupta, M. K.; Yadav, J. S.;
Gree, R. Tetrahedron Lett. 2005, 46, 7507.
7
. (a) Izumi, Y.; Onaka, M. Adv. Catal. 1992, 38, 245; (b)
Laszlo, P. Acc. Chem. Res. 1986, 19, 121; (c) Pinnavaia, T.
J. Science 1983, 220, 365.
Acknowledgments
8. (a) Mitsudome, T.; Nosaka, N.; Mori, K.; Ebitani, K.;
Mizugaki, T.; Kaneda, K. Chem. Lett. 2005, 34, 1626; (b)
Kawabata, T.; Kato, M.; Mizugaki, T.; Ebitani, K.;
Kaneda, K. Chem. Eur. J. 2005, 11, 288; (c) Kawabata, T.;
Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc.
This work is supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture,
Sports, Science, and Technology of Japan (16206078).
We thank the center of excellence (21COE) program
Creation of Integrated Ecochemistry’ of Osaka Univer-
sity and we thank Dr. Uruga (Spring-8) for XAFS
measurements.
2
003, 125, 10486; (d) Kawabata, T.; Mizugaki, T.; Ebitani,
K.; Kaneda, K. Tetrahedron Lett. 2003, 44, 9205; (e)
Kawabata, T.; Kato, M.; Mizugaki, T.; Ebitani, K.;
Kaneda, K. Chem. Lett. 2003, 32, 648; (f) Ebitani, K.; Ide,
M.; Mitsudome, T.; Mizugaki, T.; Kaneda, K. Chem.
Commun. 2002, 690; (g) Kawabata, T.; Mizugaki, T.;
Ebitani, K.; Kaneda, K. Tetrahedron Lett. 2001, 42, 8329;
‘
(
h) Ebitani, K.; Kawabata, T.; Nagashima, K.; Mizugaki,
References and notes
T.; Kaneda, K. Green Chem. 2000, 2, 157.
. Mitsudome, T.; Umetani, T.; Nosaka, N.; Mori, K.;
Ebitani, K.; Mizugaki, T.; Kaneda, K. Angew. Chem., Int.
Ed., published online: 2 December 2005, DOI:10.1002/
anie.2005.2886.
10. A typical example for Wacker oxidation using Pd-mont:
Into a reaction vessel equipped with a reflux condenser
and a rubber balloon were placed the Pd-mont (0.05 g, Pd:
0.004 mmol), CuCl2 (0.016 mmol), 1-decene (0.140 g;
9
1
. (a) Tsuji, J. Palladium Reagents and Catalysts; John Wiley
Sons: Chichester, 2004; pp 32–35; (b) Henry, P. M. In
Handbook of Organopalladium Chemistry for Organic
Synthesis; Negishi, E., Ed.; John Wiley & Sons: New
York, 2002; Vol. 2, pp 2119–2140; (c) Tsuji, J. Synthesis
984, 369; (d) Smidt, J.; Hafner, W.; Jira, R.; Sieber, R.;
Sedlmeier, J.; Sabel, A. Angew. Chem., Int. Ed. Engl. 1962,
, 80; (e) Smidt, J.; Hafner, W.; Jira, R.; Sedlmeier, J.;
Sieber, R.; R u¨ ttinger, R.; Kojer, K. Angew. Chem. 1959,
1, 176.
&
1
1
1.0 mmol), DMA (3 mL), and H O (0.5 mL). The mixture
2
was vigorously stirred at 80 ꢁC under an atmospheric O
pressure for 3 h. After the reaction, the catalyst was
separated by filtration, and 15 mL water was added to the
filtrate. The product was extracted using diethylether
(2 · 15 mL). The diethylether layer containing the product
2
7
2
. (a) B a¨ ckvall, J. E.; Hopkins, R. B.; Grennberg, H.; Mader,
M. M.; Awasthi, A. K. J. Am. Chem. Soc. 1990, 112, 5160;
(
2
b) B a¨ ckvall, J. E.; Hopkins, R. B. Tetrahedron Lett. 1988,
9, 2885; (c) B a¨ ckvall, J. E.; Awasthi, A. K.; Renko, Z. D.
was dried over MgSO , then filtered, and concentrated
4
J. Am. Chem. Soc. 1987, 109, 4750.
under reduced pressure. The resultant crude mixture was
3
4
. Kolb, M.; Bratz, E.; Dialer, K. J. Mol. Catal. 1977, 2,
purified by column chromatography (silica gel), using
an 1:4 EtOAc/hexane mixture as eluent, to give pure
2-decanone (0.13 g, 85%).
399.
. Acid-free Wacker oxidation, see: (a) Cornell, C. N.;
Sigman, M. S. J. Am. Chem. Soc. 2005, 127, 2796; (b)
Nishimura, T.; Kakiuchi, N.; Onoue, T.; Ohe, K.; Uemu-
ra, S. J. Chem. Soc., Perkin Trans. 1 2000, 1915; (c) Smith,
A. B., III; Cho, Y. S.; Friestad, G. K. Tetrahedron Lett.
11. The formation of l-Cl between Cu and Pd may play an
important role in Wacker oxidation, see: Hosakawa, T.;
Takano, M.; Murahashi, S.-I. J. Am. Chem. Soc. 1996,
118, 3990.
1
998, 39, 8765; (d) ten Brink, G.-J.; Arends, I. W. C. E.;
Papadogianakis, G.; Sheldon, R. A. Chem. Commun.
998, 2359.
12. Recycling and reuse of the Pd-mont and CuCl : After
2
completion of the reaction, the reaction mixture was cooled
to room temperature, and washed with n-heptane (2 ·
5 mL). The n-heptane phase was decanted, and another
portion of 1-decene (1 mmol) was successively added into
the residual DMA phase containing Pd-mont and CuCl2,
followed by stirring under identical reaction conditions.
13. Januszkiewicz, K.; Alper, H. Tetrahedron Lett. 1983, 24,
5159.
1
5
. Wacker oxidation using heterogeneous catalyst, see: (a)
Zweni, P. P.; Alper, H. Adv. Synth. Catal. 2004, 346, 849;
(
b) Choi, K.-M.; Mizugaki, T.; Ebitani, K.; Kaneda, K.
Chem. Lett. 2003, 32, 180; (c) Yokota, T.; Sakakura, A.;
Tani, M.; Sakaguchi, S.; Ishii, Y. Tetrahedron Lett. 2002,
43, 8887; (d) Yokota, T.; Fujibayashi, S.; Nishiyama, Y.;
Sakaguchi, S.; Ishii, Y. J. Mol. Catal. A. 1996, 114, 113; (e)
Tang, H. G.; Sherrington, D. C. J. Catal. 1993, 142, 540.
14. The oxidation of cyclohexene did not proceed efficiently,
and trace amounts of cyclohexanone were obtained.