Diatomite-supported Pd nanoparticles: An efficient catalyst for Heck and Suzuki reactions

Article abstract of DOI:10.1021/jo061179k

The Pd nanoparticles immobilized on natural diatomite were achieved by a simple procedure. The catalysts are highly active for Heck and Suzuki reactions and can be recovered and reused many times. The catalytic process was also investigated.

Full text of DOI:10.1021/jo061179k

5
6
Diatomite-Supported Pd Nanoparticles: An
Efficient Catalyst for Heck and Suzuki Reactions
zeolites) palladium catalysts have been reported. Diatomite,
which is a type of widespread natural porous material, provides
a suitable support. Herein, we report a new supported catalyst,
in which Pd nanoparticles are immobilized on diatomite, and
its application for Heck and Suzuki coupling reactions.
The synthesis of the diatomite-supported Pd nanoparticles was
carried out using a slight modification of the procedure
previously reported for the synthesis of silver nanoparticles on
Zuhui Zhang and Zhiyong Wang*
Hefei National Laboratory for Physical Science at Microscale
and Department of Chemistry, UniVersity of Science and
Technology of China, Hefei, Anhui 230026,
People’s Republic of China
7
silica spheres (Scheme 1). Specifically, 200 mg of diatomite
was added to 10 mL of water, together with 1 mmol of SnCl2‚
2H2O and 3 mmol of CF3COOH. After the mixture was stirred
for 1 h, 200 mg of PVP (poly(vinylpyrrolidone)) and 100 mL
of H2PdCl4 (2 mM) were added. Then, the supported Pd
nanoparticles were achieved by refluxing the above mixture.
The transmission electron microscope (TEM) image clearly
shows that the Pd nanoparticles were formed with a size in the
zwang3@ustc.edu.cn
ReceiVed June 8, 2006
8
range of 20-100 nm. The X-ray powder diffraction (XRD)
pattern of the diatomite-supported Pd catalyst is consistent with
9
2+
the metallic Pd data in the literature, and no Pd was detected,
which suggests that the H2PdCl4 is completely converted into
the metal. X-ray photoelectron spectroscopy (XPS) analyses
showed that 3.66 wt % of Pd was found in the diatomite-
supported Pd nanoparticles catalyst.
The Pd nanoparticles immobilized on natural diatomite were
achieved by a simple procedure. The catalysts are highly
active for Heck and Suzuki reactions and can be recovered
and reused many times. The catalytic process was also
investigated.
The diatomite-supported Pd prepared above was first used
in Heck coupling reactions, which is a versatile method for
carbon-carbon bond formation in organic synthesis. The
coupling of iodobenzene with methyl acrylate was initially
studied as a model reaction. The reaction conditions were
systematically optimized, and the results are presented in Table
1
. It was found that the best system for the reaction was NMP
Palladium catalysts are often used for versatile transformation
in organic synthesis. Many palladium complexes have been
(1-methylpyrrolidin-2-one) in combination with triethylamine,
which delivered a 96% isolated yield of the product 1 within
25 min when 0.1 mol % of diatomite-supported Pd was used
(Table 1, entry 5). The catalyst loading could be decreased even
further, to 0.01 or 0.001 mol %, when 1.5 or 15 h were required
to complete the reaction, respectively (entries 9 and 10; TON
1
used as homogeneous systems in these reactions, but most of
them are expensive and air-sensitive. These homogeneous
systems always exhibit better activity and selectivity than
heterogeneous ones,2 while heterogeneous catalysts have many
advantages over their homogeneous counterparts in industrial
,3
processes, such as recycling and lower cost. In view of these
(5) For recent reports, see: (a) Choudary, B. M.; Madhi, S.; Chowdari,
N. S.; Kantam, M. L.; Streedhar, B. J. Am. Chem. Soc. 2002, 124, 14127.
b) Kwon, M. S.; Kim, N.; Park, C. M.; Lee, J. S.; Kang, K. Y.; Park, J.
advantages, many polymer-supported4 and inorganic solid-
(
supported (e.g., carbon, metal oxides, sol-gel, clays, and
Org. Lett. 2005, 7, 1077. (c) Mori, K.; Yamaguchi, K.; Hara, T.; Mizugaki,
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B.; Wai, C. M. J. Am. Chem. Soc. 2005, 127, 17174. (e) Hagiwara, H.;
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S.-M.; Alper, H. J. Am. Chem. Soc. 2005, 127, 14776. (g) Djakovitch, L.;
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Dupont, J.; Fonseca, G. S.; Umpierre, A. P.; Fichtner, P. F. P.; Teixeira, S.
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D.; Blum, J. Org. Lett. 2004, 6, 925. (k) Crudden, C. M.; Sateesh, M.;
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M. Chem. ReV. 2002, 102, 3275. (b) De Vos, D. E.; Dams, M.; Sels, B. F.;
Jacobs, P. A. Chem. ReV. 2002, 102, 3615. (c) Leadbeater, N. E.; Marco,
M. Chem. ReV. 2002, 102, 3217. (d) Astruc, D.; Chardac, F. Chem. ReV.
2001, 101, 2991. (e) Benaglia, M.; Puglisi, A.; Cozzi, F. Chem. ReV. 2003,
103, 3401. (f) Fan, Q.-H.; Li, Y.-M.; Chan, A. S. C. Chem. ReV. 2002,
102, 3385. (g) Br a¨ se, S.; Kirchhoff, J. H.; K o¨ bberling, J. Tetrahedron 2003,
59, 885.
(
1) (a) Negishi, E. Handbook of Organopalladium Chemistry for Organic
Synthesis; Wiley: Chichester, UK, 2002. (b) Tsuji, J. Palladium Reagents
and Catalysts; Wiley: Chichester, UK, 2004. (c) Nicolaou, K. C.; Bulger,
P. G.; Sarlah, D. Angew. Chem., Int. Ed. 2005, 44, 4442. (d) Stahl, S. S.
Angew. Chem., Int. Ed. 2004, 43, 3400.
(2) For Heck reaction, see: (a) Littke, A. F.; Fu, G. C. J. Am. Chem.
Soc. 2001, 123, 6989. (b) Shaughnessy, K. H.; Kim, P.; Hartwig, J. F. J.
Am. Chem. Soc. 1999, 121, 2123.
(3) For Suzuki reaction, see: (a) Littke, A. F.; Dai, C.; Fu, G. C. J. Am.
Chem. Soc. 2000, 122, 4020. (b) Barder, T. E.; Walker, S. D.; Martineli, J.
R.; Buchwald, S. L. J. Am. Chem. Soc. 2005, 127, 4685.
(4) For recent publications, see: (a) Okamoto, K.; Akiyama, R.; Yoshida,
H.; Yoshida, T.; Kobayashi, S. J. Am. Chem. Soc. 2005, 127, 2125. (b)
Dahan, A.; Portnoy, M. Org. Lett. 2003, 5, 1197. (c) Yang, Y.-C.; Luh,
T.-Y. J. Org. Chem. 2003, 68, 9870. (d) Ooe, M.; Murata, M.; Mizugaki,
T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc. 2004, 126, 1604. (e) Garcia-
Martinez, J. C.; Lezutekong, R.; Crooks, R. M. J. Am. Chem. Soc. 2005,
1
27, 5097. (f) Cal o` , V.; Nacci, A.; Monopoli, A.; Fornaro, A.; Sabbatini,
L.; Cioffi, N.; Ditaranto, N. Organometallics 2004, 23, 5154. (g) Huang,
J.; Jiang, T.; Gao, H.; Han, B.; Liu, Z.; Wu, W.; Chang, Y.; Zhao, G. Angew.
Chem., Int. Ed. 2004, 43, 1397. (h) Parrish, C. A.; Buchwald, S. L. J. Org.
Chem. 2001, 66, 3820. (i) Yamada, Y. M. A.; Takeda, K.; Takahashi, H.;
Ikegami, S. Org. Lett. 2002, 4, 3371. (j) Desforges, A.; Backov, R.; Deleuze,
H.; Mondain-Monval, O. AdV. Funct. Mater. 2005, 15, 1689.
(7) Kobayashi, Y.; Salgueirino-Maceira, V.; Liz-Marzan, L. M. Chem.
Mater. 2001, 13, 1630.
(8) TEM image and XRD pattern are shown in the Supporting Informa-
tion.
(9) The XRD patterns have three characteristic dihedrals: 40.119, 46.659,
and 68.125, with the relative intensities of 100, 60, and 42%, respectively.
1
0.1021/jo061179k CCC: $33.50 © 2006 American Chemical Society
Published on Web 08/18/2006
J. Org. Chem. 2006, 71, 7485-7487
7485

TABLE 2. Heck Reaction of Aryl Halides with Olefinsa
SCHEME 1. Preparation of Diatomite-Supported Palladium
Nanoparticles
TABLE 1. Optimization of Base and Solvent for Heck Reaction of
a
Iodobenzene with Methyl Acrylate
Pd
(mol %)
yield
(%)b
entry
base
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
solvent
DMF
time
1
2
3
4
5
6
7
8
9
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
40 min
2 h
2 h
95
30
53
trace
96
89
49
38
96
96
toluene
CH3CN
EtOH
2 h
c
NMP
25 min
50 min
5 h
3 h
1.5 h
15 h
NMP/H2O (1/1)
NMP
NMP
NaOAc
K2CO3
Et3N
NMP
0.01
0.001
1
0
Et3N
NMP
a
Reaction conditions: iodobenzene (1 mmol), methyl acrylate (2 mmol),
base (2 mmol), diatomite-supported Pd (0.1 mol %), and 3 mL of solvent
b
c
at 120 °C. Isolated yield. 1-Methylpyrrolidin-2-one.
4
)
9.6 × 10 within 15 h in entry 10). With these results in
hand, several examples of diatomite-supported palladium-
catalyzed Heck coupling of aryl halides with olefins were then
tested, and the results are summarized in Table 2. Iodobenzene
can react with various alkenes, including acrylate, acrylic acid,
styrene, or its derivatives, and gave the corresponding products
1-7 with good yields (Table 2, entries 1-7). Besides, these
conditions allow for the coupling of both electron-rich and
electron-deficient aryl iodides (Table 2, entries 8-16). Notably,
the reaction occurred exclusively to aryl iodides in the presence
of aryl chloride or aryl bromide as for 1-chloro-4-iodobenzene
or 1-bromo-4-iodobenzene (Table 2, entries 9 and 10). Namely,
complete chemoselectivities were achieved for the Heck reac-
tions in these cases. Active aryl bromides can undergo the
coupling reactions catalyzed by either 0.1 or 1 mol % of Pd to
yield similar results with corresponding reaction times (entries
1
7 and 18). When bromobenzene was used as reactant, 3 mol
a Reaction conditions: ArX (1 mmol), alkene (2 mmol), Et N (3 mmol),
3
b
%
of Pd catalysts was required to achieve a similar yield (entry
diatomite-supported Pd (0.1 mol %), and 3 mL of NMP. Diatomite-
c
supported Pd (1 mol %) was used. Diatomite-supported Pd (3 mol %)
1
9).
was used. d Isolated yield.
Furthermore, the diatomite-supported Pd catalyst can also be
applied to the Suzuki reaction, another very important meth-
odology for the generation of carbon-carbon bonds, especially
applied to the synthesis of biaryls. As listed in Table 3, the
conditions tolerated the presence of a wide variety of functional
groups, afforded excellent yields of corresponding products 18-
similar results after the fourth cycle. Even after the sixth round,
the supported Pd had a good catalytic activity for this reaction.
For large-scale processes, however, it is reasonable to believe
that the catalyst can be easily recovered by filtration.
2
4 within 1 h starting from either aryl iodides or aryl bromides
The mechanism of catalytic processes utilizing a heteroge-
neous palladium source has frequently been disputed in the
(Table 3, entry 1-10). Moreover, activated chloride can also
give the coupling product with moderate yield in the presence
of tetrabutylammonium bromide (TBAB) (Table 3, entry 11).
The feasibility of recycling the diatomite-supported Pd was
also examined. In Table 4, we presented the experimental results
on the recycling of the supported Pd on a model reaction of
iodobenzene with methyl acrylate. After each round, the
supported catalyst was recovered by simple centrifugation and
used directly for the next round of the reaction without further
manipulation. The diatomite-supported Pd exhibited only a
marginal loss in activity and required a bit longer time to achieve
1
0
literature recently. It was proposed that dissolution of pal-
ladium species from the surface of the solid support or Pd
clusters led to the formation of the active species in solution,
and the palladium was redeposited onto the support or Pd
5
h,11
clusters after the reaction was finished.
The slight loss of
catalyst activity after cycles in this case may be due to the loss
(10) For recent reviews on this topic, see: (a) Phan, N. T. S.; Van Der
Sluys, M.; Jones, C. W. AdV. Synth. Catal. 2006, 348, 609. (b) Astruc, D.;
Lu, F.; Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 44, 7852.
7
486 J. Org. Chem., Vol. 71, No. 19, 2006

TABLE 3. Suzuki Reaction of Aryl Halides with Boronic Acida
the leaching of palladium was necessary for this sustaining
catalytic activity, and the diatomite-supported palladium pro-
vided the source of palladium in the process. Although the
catalytic process involved a homogeneous catalysis, the diatomite-
supported palladium, like a catalytic reservoir, is in a different
phase from that of reactants and products. This catalytic system
has the advantages of both homogeneous and heterogeneous
catalysis to some extent. Therefore, it is easy for the catalyst to
be reused, and this catalyst has a potential application in
industrial scale.
In summary, we presented a new supported catalyst, in which
the Pd nanoparticles were immobilized on widespread natural
diatomite by a simple procedure which was confirmed by TEM
and XRD analyses. The catalyst shows high activity for Heck
and Suzuki reactions, and excellent TONs were achieved (TONs
4
up to 9.6 × 10 for the reaction of iodobenzene and methyl
acrylate within 15 h) and can be recovered easily and reused
many times. This novel supported catalyst is air-stable, and all
the reactions can be conducted in air. All these virtues indicate
that the diatomite-supported catalyst has a potential application.
The studies also reveal that the palladium leaching into the
solution during the reaction provides the catalytic site. Further
study of the scope of its application is in progress in our
laboratory.
Experimental Section
Typical Procedure for the Preparation of Diatomite-Sup-
ported Pd Nanoparticles: 200 mg of diatomite was added to 10
a
Reaction conditions: halide (1 mmol), boronic acid (1.2 mmol), Na2CO3
(
2 mmol), diatomite-supported Pd (0.1 mol %), and DME/H2O (1/1).
TBAB (0.5 mmol) was used. Isolated yield.
mL of water, together with 10 mmol of SnCl
of CF COOH. After the mixture was stirred for 1 h, 100 mL of
PdCl (2 mM) and 200 mg of PVP (poly(vinylpyrrolidone)) was
2
‚2H
2
O and 30 mmol
b
c
3
H
2
4
added. After the mixture was heated at 110 °C for 2 h, it was cooled
to room temperature and filtrated. The catalyst was then obtained
by drying the solid under vacuum at 50 °C for 12 h.
General Procedure for the Heck Reaction Catalyzed by
Diatomite-Supported Pd: In a 10 mL glass flask were placed
TABLE 4. Recycling of Diatomite-Supported Pd for the Heck
Reaction of Iodobenzene with Methyl Acrylate
time
isolated
entry
catalyst
(min)
yield (%)
1
2
3
4
5
6
first cycle
20
20
20
20
40
70
96
95
97
95
96
95
aryl halide (1 mmol), alkene (2 mmol), Et
diatomite-supported Pd (3 mg, 0.1 mol %) in 3 mL of NMP at 120
C for the appropriate time. The reaction was monitored by TLC,
3
N (2 mmol), and
second cycle
third cycle
fourth cycle
fifth cycle
sixth cycle
°
and after completion of the reaction, the mixture was extracted with
ethyl acetate three times. The combined organic extracts were dried
using anhydrous Na SO and evaporated under reduced pressure,
2 4
and the mixture was then purified by column chromatography over
silica gel to afford product with high purity.
General Procedure for the Suzuki Reaction Catalyzed by
of palladium from the support during the reaction. To confirm
this assumption, several experiments were then performed. On
one hand, with a model reaction of iodobenzene and methyl
acrylate, the solid in the reaction mixtures was separated from
the hot solutions by filtration after the reaction was completed.
The filtrate was then used for the next round, affording
conversion of 95% within 40 min, and the Pd content in the
filtrate was 8.48 ppm based on elemental analysis of ICP-AES.
On the other hand, the supported Pd freshly prepared was placed
in NMP at 120 °C for 30 min, and only 2.67 ppm of Pd was
detected from the filtrate. This suggested that the oxidation
Diatomite-Supported Pd: In a 10 mL glass flask were placed
aryl halide (1 mmol), boronic acid (1.2 mmol), Na
and diatomite-supported Pd (3 mg, 0.1 mol %) in DME-H
2
CO
3
(2 mmol),
O (1.5
2
mL/1.5 mL) at 110 °C for the appropriate time. The reaction was
monitored by TLC, and after completion of the reaction, the mixture
was extracted with ethyl acetate three times. The combined organic
extracts were dried over anhydrous Na SO and evaporated under
2
4
reduced pressure, and the mixture was then purified by column
chromatography over silica gel to afford product with high purity.
0
0
addition of the aryl iodide to the surface Pd converted Pd into
Acknowledgment. The authors are grateful to the Natural
Science Foundation of China (20472078 and 30572234).
2+
Pd , resulting in the leaching of a certain amount of palladium
particles into the solution. The experimental results showed that
Supporting Information Available: TEM image and XRD
pattern of the diatomite-supported Pd; characterization data and
original H and C NMR spectra for products 1-24. This material
is available free of charge via the Internet at http://pubs.acs.org.
(
11) (a) Thathagar, M. B.; ten Elshof, J. E.; Rothenberg, G. Angew.
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A.; Mommers, J. H. M.; Henderickx, H. J. W.; De Vries, J. G. Org. Lett.
003, 5, 3285. (c) Reetz, M. T.; Westermann, E. Angew. Chem., Int. Ed.
000, 39, 165.
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JO061179K
J. Org. Chem, Vol. 71, No. 19, 2006 7487