Polyion complex stabilized palladium nanoparticles for Suzuki and Heck reaction in water

Article abstract of DOI:10.1016/j.tet.2010.05.076

Palladium nanoparticles stabilized by a polyion complex composed of poly{4-chloromethylstyrene-co- (4-vinylbenzyl) tributylammonium chloride} and poly(acrylic acid) were easily recovered by filtration after pH treatment. The polyion complex stabilized pal

Full text of DOI:10.1016/j.tet.2010.05.076

Tetrahedron 66 (2010) 5642e5646
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Polyion complex stabilized palladium nanoparticles for Suzuki and Heck reaction
in water
a
,
a
a
a
a
a,b
*
Atsushi Ohtaka , Yuji Tamaki , Yuta Igawa , Koji Egami , Osamu Shimomura , Ryôki Nomura
a
Department of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi, Osaka 535-8585, Japan
Nanomaterials and Microdevices Research Center, Osaka Institute of Technology, 5-16-1 Ohmiya, Asahi, Osaka 535-8585, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Palladium nanoparticles stabilized by a polyion complex composed of poly{4-chloromethylstyrene-co-
4-vinylbenzyl) tributylammonium chloride} and poly(acrylic acid) were easily recovered by filtration
after pH treatment. The polyion complex stabilized palladium nanoparticles have high catalytic activity
for the Suzuki and Heck reactions in water.
Received 11 March 2010
Received in revised form 19 May 2010
Accepted 19 May 2010
(
Available online 25 May 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Palladium nanoparticles
Polyion complex
Coupling reaction
Water
1. Introduction
observed in the recycling of the catalyst, due to loss of the catalyst
during the collection process.
A polyion complex (PIC) can easily be formed when oppositely
charged polyelectrolytes are mixed in aqueous solution and
1
The palladium catalyzed coupling of aryl halides by Suzuki- and
2
Heck-type reactions is a well-established methodology in modern
1
1
organic synthesis. The coupling products find good applications as
intermediates in the preparation of materials, natural products, and
bioactive compounds.3 The current trend is to conduct organic
reactions in water because it is an eco-friendly, nontoxic, and
economic solvent. Jeffery and Bandone discovered that the use of
quaternary ammonium salts considerably enhances the rates of
interact via electrostatic (Coulombic) interactions. Hirai has
reported that a colloidal palladium supported on PIC composed of
poly(acrylic acid) and poly(ethylene imine) catalyzes the selective
hydrogenation of conjugated diolefins to monoolefins. We report
herein our results demonstrating that both the Suzuki and Heck
reactions proceed in water in the presence of PdNPs stabilized by
PIC composed of poly{4-chloromethylstyrene-co-(4-vinylbenzyl)
tributylammonium chloride} and poly(acrylic acid).
1
2
4
5
6
both the Heck and Suzuki coupling reactions in water. Reetz et al.
demonstrated that Pd(OAc) in combination with tetrabutyl-
2
ammonium bromide (TBAB) gave rise to nanometric Pd-colloids,
which were the actual catalysts under the so-called Jeffery condi-
tions. Recently, it was found that surfactant-stabilized palladium
2
2
. Results and discussion
7
nanoparticles (PdNPs) have high catalytic activity for the Suzuki
.1. Synthesis of polyion complex stabilized palladium
8
and Heck reactions in water. However, it was difficult to reuse the
nanoparticles (PIC-PdNPs)
catalyst because the PdNPs were dispersed in water. Zhang syn-
thesized pH-responsive core-shell microspheres of poly[styrene-
A polystyrene derivative was chosen because the stability of PICs
co-2-(acetoacetoxy)ethyl methacrylate-co-methyl acrylic acid]
11b
is dependent on the hydrophobicity of the polymer.
thesis of poly{4-chloromethylstyrene-co-(4-vinylbenzyl) tributyl-
ammonium chloride} (2) is shown in Scheme 1. A homopolymer of
The syn-
9
(
PS-co-PAEMA-co-PMAA) supported PdNPs and thermoresponsive
10
poly(N-isopropylacrylamide)-grafted PdNPs. These catalysts have
high catalytic activity toward Suzuki and Heck reactions in water,
and were recovered by filtration after pH or thermal treatment.
However, a significant decrease in the catalytic activity was
4
-chloromethylstyrene was prepared by conventional radical
polymerization using AIBN as the initiator. The molecular weight
) of poly(4-chloromethylstyrene) (1) estimated by gel perme-
(M
n
3
ation chromatography (GPC) was low (5.6ꢀ10 ) and the molecular
weight distribution (M
w
/M
n
) was slightly broad (1.8). The reaction
ꢁ
*
Corresponding author. E-mail address: otaka@chem.oit.ac.jp (A. Ohtaka).
of 1 with tributylamine was performed in THF at 70 C for 20 h to
0
040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.05.076

A. Ohtaka et al. / Tetrahedron 66 (2010) 5642e5646
5643
7
n
3n
n
AIBN
NBu
3
NBu
3
DMF, 70 °C,
THF, 70 °C,
20 h
MeOH, 65 °C,
20 h
2
0 h
Cl
3
NBu Cl
Cl
Cl
1
2a
M
= 5.6 x 103
n
M /M = 1.80
w
n
Pd(OAc)2,
Figure 2.
n
9n
PAA (Mn = 6.5 x 105)
PIC-PdNPs (3)
K CO , H O, 90 °C, 5 h
2
3
2
3
< pH < 6
10 < pH
Cl
NBu3 Cl
2b
NBu OH
COOK
3
Scheme 1.
KOH
HCl
+
COOK
NBu OH
3
give a partially quaternarized polymer 2a, which is insoluble in
water. In the 1H NMR spectrum of 2a, new signals at
3.02, 1.67,
.27, and 0.91 are observed, which are assigned to the butyl protons
of the (4-vinylbenzyl)tributylammonium chloride unit (30% of the
-chloromethylstyrenes converted to ammonium units). A water-
d
COO Bu N
3
1
Association
Dissociation
Scheme 2. The stability of polyion complex.
4
soluble polymer 2b (90% of the 4-chloromethylstyrenes converted
to ammonium units) was obtained from the reaction of the partially
quaternarized polymer 2a with tributylamine in MeOH.
2.2. Suzuki coupling reaction in water
For the preparation of PIC stabilized PdNPs (3), the mixture of Pd
(
OAc)
PAA (M
b) was added to a 1.5 mol L
2
, polymer 2b [12 equiv of ammonium unit for Pd(OAc)
2
], and
5
To test the potency of 3 as a catalyst, we examined the Suzuki
n
¼6.5ꢀ10 , 3 equiv of AA unit for each ammonium unit in
ꢂ1
coupling reaction of various aryl halides with arylboronic acids in
2
2 3
K CO aqueous solution and stirred
ꢂ1
ꢁ
7
1.5 mol L aqueous KOH solution as a test reaction (Table 1). The
for 5 h at 90 C. Aggregation of PIC-PdNPs was observed when the
pH of the solution was changed (pH <6). H NMR of the aqueous
phase confirmed the absence of polymer, indicating that all poly-
mers were recovered completely by formation of PIC. Inductively
coupled plasma-atomic emission spectroscopy (ICP-AES) revealed
that 3 contained an average of 0.13 mmol/g of Pd. Figure 1 shows
a TEM image of 3, where a fairly uniform particle size of 2.6ꢃ0.5 nm
is evident. In addition, PIC-PdNPs 3 were easily re-dispersed in
water by changing the pH, due to the stability of the PIC (Fig. 2,
Scheme 2).
1
coupling of bromobenzene with 4-methylphenylboronic acid took
ꢁ
place smoothly in water at 60 C to give 4-methylbiphenyl in 99%
13
yield (entry 1). The Suzuki coupling reaction of 4-bromotoluene
and 4-bromoanisole bearing electron donating groups at their para
positions gave the corresponding coupling products in 99% and 87%
yields, respectively (entries 2 and 3). 4-Bromobenzotrifluoride with
an electron deficient aromatic ring also underwent the Suzuki
coupling reaction with 4-methylphenylboronic acid under similar
0
conditions to afford 4-methyl-4 -trifluoromethylbiphenyl in 93%
yield (entry 4). The coupling of 4-trifluoromethylphenylboronic
acid and 4-methoxyphenylboronic acid took place with bromo-
benzene to give the corresponding product in 99% and 98% yields,
respectively (entries 5 and 6). Sterically hindered substrates were
0
also examined. The formation of 2,4 -dimethylbiphenyl could be
achieved by the coupling of 2-bromotoluene with 4-methyl-
phenylboronic acid or 4-bromotoluene with 2-methylphenylbor-
onic acid in 74% and 77% yields, respectively (entries 7 and 8).
However, 2-bromo-m-xylene and 4-chlorobenzotrifluoride gave
the low yields (entries 9 and 10).
2.3. Heck reaction in water
Heck reactions of aryl halides with styrene using 3 as a catalyst
were also studied. Heck reactions are generally performed at rela-
ꢁ
tively high temperatures, thus we conducted our reactions at 80 C.
Representative results are summarized in Table 2. The coupling of
iodobenzene with styrene took place smoothly in water in the
presence of 3 equiv of KOH and 1 mol % palladium of PIC-PdNPs 3 to
give a quantitative yield of (E)-stilbene (Table 2, entry 1). The Heck
reaction of 4-iodotoluene and 4-iodoanisole bearing electron do-
nating groups at their para positions gave the corresponding cou-
pling products in 99% and 88% yields, respectively (entries 2 and 3).
4-Iodobenzotrifluoride with an electron deficient aromatic ring
Figure 1. TEM images of PIC-PdNPs (3).

5644
A. Ohtaka et al. / Tetrahedron 66 (2010) 5642e5646
Table 1
Table 2
PIC-PdNPs catalyzed Suzuki coupling reaction in water
PIC-PdNPs catalyzed Heck reaction in water
PIC-PdNPs 3
1 mol% of Pd)
PIC-PdNPs 3
(
(1 mol% of Pd)
Ar1
X
Ar2 B(OH)2
0.75 mmol
Ar1 Ar2
Ar1
X
Ar2
Ar1
+
+
Ar2
KOH, H O, 60 °C, 3 h
KOH, H O, 80 °C, 20 h
2
2
0
.50 mmol
0.50 mmol
0.75 mmol
1
2
1
Ar2
Entry
1
Ar eX
Ar eB(OH)
2
Yield (%)
Entry
Ar eX
Yield (%)
99
Br
I
99
99
1
2
(HO)2B
I
Br
Br
Br
99
88
2
3
4
(HO)2B
I
3
87
93
MeO
F3C
(
HO)2B
MeO
I
4
5
90
98
F C
(HO)2B
3
I
I
CF3
Br
5
99
OMe
Cl
(
HO)2B
6
7
75
97
OMe
Br
Br
Br
6
7
98
74
(
HO)2B
I
I
(HO)2B
8
9
29
5
8
9
77
37
(HO)2B
Br
Br
Cl
F3C
(HO)2B
10
2a
(2.4ꢃ0.6 nm), probably due to the stabilization by arylboronic
15,16
F C
(HO)2B
3
acid (Fig. 3).
Indeed, B 1s peak was observed in the recovered
a
The reaction was carried out for 12 h.
catalyst by XPS analysis. On the contrary, the palladium size in-
1
7,18
creased to 6.0ꢃ1.3 nm in the Heck reaction.
The reaction so-
lutions were analyzed by ICP-AES after every run to determine the
amount of palladium leaching during the reaction. The total
amount of palladium leaching after the fourth run was <1.5% in
both reactions.
also underwent the Heck reaction with styrene under similar
conditions to afford 4-trifluoromethylstilbene in 90% yield (entry
). The coupling of 4-methoxystyrene and 4-chlorostyrene took
4
place with 4-iodotoluene to give the corresponding products in 98%
and 75% yields, respectively (entries 5 and 6). 2-Iodotoluene was
easily converted to the corresponding product (entry 7). However,
PIC-PdNPs 3
Br
(
1 mol% of Pd)
2
-iodo-m-xylene and bromobenzene gave the low yields (entries 8
+
KOH, H O, 60 °C, 3 h
and 9).
(HO)2B
0.75 mmol
2
0
.50 mmol
1st run: 98%
2nd run: 99%
2
.4. Recycling of the catalyst
3
rd run: 99%
Lastly, the recycling of the catalyst was evaluated by both the
4th run: 90%
Suzuki coupling reaction of bromobenzene with 4-methyl-
phenylboronic acid and the Heck reaction of 4-iodotoluene with
styrene (Scheme 3). The Suzuki coupling reaction proceeded ef-
ficiently to give 4-methylbiphenyl in 99% yield. When the reaction
PIC-PdNPs 3
I
(
1 mol% of Pd)
+
KOH, H2O, 80 °C, 20 h
was completed, PIC-PdNPs were recovered by filtration after pH
treatment.14 The catalyst 3 was recycled at least two times
1st run: 98%
0
.50 mmol
0.75 mmol
2
nd run: 99%
without any loss of activity. However, a slight decrease in the yield
was observed in the fourth run in the Suzuki and the Heck
reaction. TEM images of the recovered catalyst revealed a similar
size of palladium was observed in the Suzuki reaction
3
4
rd run: 92%
th run: 88%
Scheme 3.

A. Ohtaka et al. / Tetrahedron 66 (2010) 5642e5646
5645
4.3. Preparation of poly{4-chloromethylstyrene-co-
(4-vinylbenzyl) tributylammonium chloride} (2)
Synthesis of polymer (2) was performed in two stages. To a screw-
ꢂ3
capped vial with a stirring bar were added 1 (0.795 g, 5.2ꢀ10 mol
of 4-chloromethylstyrene unit), tributylamine (2.4 mL, 10.3ꢀ
ꢂ3
ꢁ
mol), and THF (8 mL). After stirring at 70 C for 20 h, the solvent
10
was removed in vacuo to give a partially quaternarized polymer (2a,
.996 g). Subsequently, to a screw-capped vial with a stirring bar
0
were added
a
partially quaternarized polymer (0.503 g,
ꢂ3
1
5
.3ꢀ10 mol of 4-chloromethylstyrene unit), tributylamine (1.2 mL,
ꢂ3
ꢁ
.1ꢀ10 mol), and MeOH (4 mL). After stirring at 65 C for 20 h, the
solvent was removed in vacuo to give a crude product. The residual
tributylamine was extracted ten times with hexane. The aqueous
phase was lyophilized with a freeze dryer to give 2b (0.63 g) as
a white powder. The ammonium unit content in 2b (90%) was de-
termined by H NMR spectra. H NMR (D
br, 4H), 4.23 (br, 2H), 2.80e3.15 (br, 6H), 1.53e0.72 (br, 21H). Ni-
trogen content (3.95 wt %) was determined by elemental analysis.
Figure 3. TEM images of recovered PIC-PdNPs. (a) After Suzuki coupling reaction. (b)
After Heck reaction.
1
1
2
O, 300 MHz): d 6.52e7.10
3
. Conclusions
(
In summary, highly efficient polyion complex supported palla-
dium nanoparticles for Suzuki and Heck reactions in water were
prepared. The PIC-supported PdNPs were easily re-dispersed in
water by changing the pH.
4
.4. Preparation of PIC-PdNPs (3)
To a screw-capped vial with a stirring bar were added 2b
(
22 mg, 60
monomer unit), Pd(OAc)
CO
mmol of ammonium unit), PAA (13 mg, 180 mmol of
2
(1.1 mg, 5
m
mol), and 1.5 M aqueous
4
4
. Experimental
ꢁ
K
2
3
solution (1 mL). After stirring at 90 C for 5 h, the reaction
mixture was cooled to room temperature by immediately im-
.1. General remarks
ꢁ
ꢂ1
mersing the vial in water (w20 C), and then 6.0 mol L
HCl
1H NMR spectra in DMSO-d
aqueous solution (0.22 mL) was added to the reaction mixture.
Subsequently, the aqueous phases were removed, and recovered
catalyst was washed with acetone (3ꢀ1.0 mL).
6
3
or CDCl were recorded with
a 300 MHz NMR spectrometer (UNITY 300, Varian, Palo Alto, CA)
using tetramethylsilane (
d
¼0) as an internal standard. Gel per-
meation chromatographic (GPC) analysis in DMF was carried out
with a HPLC-8020 instrument (Tosoh Co., Tokyo, Japan) (column:
4.5. Determination of the amount of palladium
Tosoh TSKgel a-3000 and a-5000). The columns were calibrated
with polystyrene of narrow molecular weight distribution stan-
dards. Lyophilization was carried out with a freeze dryer (FDU-
Compound 3 (36 mg) was placed in a screw-capped vial and
ꢁ
then added aqua regia (5 mL). The mixture was heated at 80 C to
dissolve completely. After cooled to room temperature, the solution
was adjusted to 50 g by nitric acid and then measured the amount
of Pd metal by ICP-AES analysis (9.5 ppm).
After the catalytic reaction, the aqueous phase was adjusted to
0 g by nitric acid and then measured the amount of Pd metal by
8
30, Tokyo Rikakikai Co., Ltd., Tokyo, Japan). CHN elemental mi-
croanalyses were carried out using a CHN-Corder MT-5 (Yanaco,
Japan). Inductively coupled plasma-atomic emission spectros-
copy (ICP-AES) was performed using ICPS-8100 (Shimadzu Co.,
Kyoto, Japan). Pd nanoparticles were investigated by trans-
mission electron microscopy (TEM) on a JEM 2100F transmission
electron microscope (JEOL Ltd., Tokyo, Japan). The samples were
prepared by placing a drop of the solution on carbon coated
copper grids and allowed to dry in air. X-ray photoelectron
spectroscopy (XPS) analysis was carried out using a PHI 5700MC
1
ICP-AES analysis.
4
.6. Typical procedures for Suzuki coupling reaction
To a screw-capped vial with a stirring bar were added bromo-
benzene (78.5 mg, 0.5 mmol), p-methylphenylboronic acid
(
ULVAC-PHI, Inc., Kanagawa, Japan). Polystyrene of narrow mo-
(
102 mg, 0.75 mmol), 3 (36 mg, 0.9 mol % of Pd), and 1.5 M aqueous
lecular weight distribution standards was purchased from Tosoh
ꢁ
KOH solution (1 mL). After stirring at 60 C for 3 h, the reaction
mixture was cooled to room temperature by immediately
Co., Ltd. (Tokyo, Japan). Pd(OAc)
Aldrich Co. (Missouri, USA).
2
was obtained from Sigma/
ꢁ
ꢂ1
immersing the vial in water (w20 C), and then 6.0 mol L HCl
aqueous solution (0.22 mL) was added to the reaction mixture.
Subsequently, the aqueous phases were removed, and recovered
catalyst was washed with 1.5 M aqueous KCl solution (5ꢀ1.5 mL)
and diethyl ether (5ꢀ1.5 mL), which were then added to the
aqueous phase. The aqueous phase was extracted five times with
diethyl ether. The combined organic extracts were dried over
4
.2. Preparation of poly(4-chloromethylstyrene) (1)
Into a two-necked reaction vessel were added 4-chloromethyl-
ꢂ3
-4
styrene (2.07 g, 13.6ꢀ10 mol), AIBN (0.11 g, 6.2ꢀ10 mol), and
ꢁ
DMF (8 mL). After stirring at 70 C for 20 h under N
2
atmosphere,
the solvent was removed in vacuo to give a crude product. Repre-
cipitation was carried out at least three times in a THF/MeOH
system. The last precipitate was dried under reduced pressure and
lyophilized with a freeze dryer to give 1 (1.7 g, 82% yield) as a white
4
MgSO and concentrated under reduced pressure. The resulting
1
product was analyzed by H NMR. The recovered 3 was dried in
vacuo and reused. Furthermore, the amount of Pd metal in the
aqueous phase determined by ICP-AES analysis was 0.1 ppm.
powder. The number-average molecular weight (M
molecular weight distribution (M /M ) determined by GPC analysis
were ca. 5.6ꢀ10 and 1.8, respectively. H NMR (DMSO-d
00 MHz): 7.40 (br, 2H), 6.78 (br, 2H), 4.93 (br, 2H), 2.04e1.62
br, 3H).
n
) and the
w
n
4.7. Typical procedures for Heck reaction
3
1
6
,
3
(
d
To a screw-capped vial with a stirring bar were added 4-iodo-
toluene (109 mg, 0.5 mmol), styrene (79 mg, 0.75 mmol), 3 (36 mg,

5646
A. Ohtaka et al. / Tetrahedron 66 (2010) 5642e5646
1
mol % of Pd), and 1.5 M aqueous KOH solution (1 mL). After
3. For example, see: (a) Bonazzi, S.; Eidam, O.; Guttinger, S.; Wach, J.-Y.; Zemp,
I.; Kutay, U.; Gademann, K. J. Am. Chem. Soc. 2010, 132, 1432e1442; (b) Jeffrey,
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ꢁ
stirring at 60 C for 3 h, the reaction mixture was cooled to room
temperature by immediately immersing the vial in water (w20 C),
and then 6.0 mol L HCl aqueous solution (0.22 mL) was added to
the reaction mixture. Subsequently, the aqueous phases were re-
moved, and recovered catalyst was washed with 1.5 M aqueous KCl
solution (5ꢀ1.5 mL) and diethyl ether (5ꢀ1.5 mL), which were then
added to the aqueous phase. The aqueous phase was extracted five
times with diethyl ether. The combined organic extracts were dried
ꢁ
ꢂ1
2
405e2494.
4. (a) Li, C.-J.; Chen, L. Chem. Soc. Rev. 2006, 35, 68e82; (b) Li, C.-J. Chem. Rev. 2005,
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1
Organic Synthesis in Water; Blackie Academic & Professional: London, 1998.
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over MgSO
4
and concentrated under reduced pressure. The
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62, 7170e7173.
1
resulting product was analyzed by H NMR. The recovered 3 was
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4
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Acknowledgements
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This work was grateful to the Nanomaterials and Microdevices
Research Center (NMRC) of OIT for financial and instrumental
supports. We wish to thank Prof. Y. Uozumi and Dr. G. Hamasaka for
assistance with the TEM measurements. We also thank Dr. T. Shi-
nagawa for assistance with the ICP-AES measurements.
9
1
. Zheng, P.; Zhang, W. J. Catal. 2007, 250, 324e330.
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12. Nakamura, Y.; Hirai, H. Chem. Lett. 1976, 1197e1202.
3. When the preparation of PIC-PdNPs was performed with reduced amount of
Supplementary data
1
PAA (1 equiv of AA unit for each ammonium unit in 2b), the signals of polymer
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.tet.2010.05.076.
b were confirmed by 1H NMR in aqueous phase after pH treatment.
2
1
14. No polymer was confirmed by H NMR in aqueous phase.
1
5. Narayanan, R.; El-Sayed, M. A. J. Am. Chem. Soc. 2003, 125, 8340e8347.
1
6. When the recycling experiment was performed with 1 equiv of p-methyl-
phenylboronic acid, the gradual decrease in yield was observed (first run: 97%,
second run: 76%, third run: 58%).
References and notes
1
. For general reviews on the Suzuki coupling reaction, see: (a) Miyaura, N.; Su-
zuki, A. Chem. Rev. 1995, 95, 2457e2483; (b) Hassan, J.; Sevignon, M.; Gozzi, C.;
Schulz, E.; Lemaire, M. Chem. Rev. 2002, 102, 1359e1469.
17. Similar results have been reported. (a) Sin, E.; Yi, S.-S.; Lee, Y.-S. J. Mol. Catal. A
2010, 315, 99e104; (b) Yi, S.-S.; Lee, D.-H.; Sin, E.; Lee, Y.-S. Tetrahedron Lett.
2007, 48, 6771e6775.
2
. For general reviews on the Heck reaction, see: (a) Heck, R. F. Acc. Chem. Res.
18. It was reported that a biphenyl compound poisoned an active site of PVP-Pd
and decreased the product yield (see Ref. 15). However, no biphenyl by-prod-
ucts were observed in the Heck reaction.
1979, 12, 146e151; (b) Dounay, A. B.; Overman, L. E. Chem. Rev. 2003, 103,
2945e2964.