Palladium nanoparticles on thermoresponsive hydrogels and their application as recyclable Suzuki-Miyaura coupling reaction catalysts in water

Article abstract of DOI:10.1002/adsc.201100965

Palladium nanoparticles were immobilized on PNIPAM:4-VP hydrogels. The resultant puealladium catalysts showed high activities for Suzuki-Miyaura coupling reactions in water. The recyclability of the catalysts was improved by using 4-VP as a co-monomer in the hydrogels due to reduced Pd leaching during the reactions. Copyright

Full text of DOI:10.1002/adsc.201100965

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DOI: 10.1002/adsc.201100965
Palladium Nanoparticles on Thermoresponsive Hydrogels and
their Application as Recyclable Suzuki–Miyaura Coupling
Reaction Catalysts in Water
Myeng Chan Hong,a Myung Chan Choi,b Young Wook Chang,b Yongwoo Lee,a
Jongsik Kim,c,* and Hakjune Rheea,b,*
a
Department of Chemistry and Applied Chemistry, Hanyang University, Ansan, South Korea
Fax : (+82)-31-400-5457; phone: (+82)-31-400-4120; e-mail: hrhee@hanyang.ac.kr
Department of Bio-Nanotechnology, Hanyang University, Ansan, South Korea
Department of Chemistry, Dong-A University, Busan, South Korea
b
c
Fax : (+82)-51-200-7259; phone: (+82)-51-200-7253; e-mail: jskimm@dau.ac.kr
Received: December 12, 2011; Published online: April 19, 2012
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201100965.
Abstract: Palladium nanoparticles were immobi-
lized on PNIPAM:4-VP hydrogels. The resultant
pꢀalladium catalysts showed high activities for
Suzuki–Miyaura coupling reactions in water. The
recyclability of the catalysts was improved by using
4-VP as a co-monomer in the hydrogels due to re-
duced Pd leaching during the reactions.
after reactions are completed. To overcome these
problems, various methods have been investigated for
developing heterogeneous Pd catalysts, including the
immobilization or stabilization of Pd nanoparticles on
ionic liquids,[3] functionalized polymers,[4] graphene
oxide and its derivatives,[5] and inorganic substrates
such as silica, zeolites, etc.[6] However, the catalytic
activity of heterogeneous catalysts is still not as effi-
cient as those of homogeneous Pd catalysts. In addi-
tion to the development of recyclable catalysts, the re-
action conditions for large-scale Suzuki applications
need to be more environmentally benign and eco-
nomically attractive. For example, a lower reaction
temperature could be used, and water could be used
instead of organic solvents.[7]
Keywords: palladium nanoparticles; PNIPAM:4-VP
co-polymers; reusable catalysts; Suzuki–Miyaura re-
actions; water
The Suzuki reaction is one of the most powerful syn-
Poly(N-isopropylacrylamide) (PNIPAM) is a well
thetic pathways for constructing the aryl-aryl bond. It known temperature-responsive polymer that demon-
involves a palladium-catalyzed coupling reaction be- strates phase separation (i.e., the coil-to-globule tran-
tween an aryl halide and an areneboronic acid. The sition) from an aqueous solution at the lower critical
synthesis of biaryl compounds via Suzuki coupling is solution temperature (LCST), which is typically about
very attractive because this reaction can tolerate the 328C.[8] The swelling of PNIPAM hydrogels is mainly
presence of water. In addition, the reaction works due to changes in the hydrogen bonding of the
with a wide range of functional groups, and the non- PNIPAM network with water molecules.[9] At a tem-
toxic by-products are easily separated from the de- perature above LCST, some of the hydrogen bonds
sired compound.[1] The Suzuki reaction is usually car- are dissociated, and the hydrophobic interactions
ried out with a homogeneous Pd catalyst, phosphorus among the hydrophobic groups in the PNIPAM net-
derivatives as ligands, and an inorganic base (i.e., car- work are dominant. This causes the water molecules
bonate, bicarbonate, and hydroxide) in aqueous or- trapped in the network to be released, making the hy-
ganic solvents.[1e,2] However, in order to use the drogel collapse. By changing the solution tempera-
Suzuki reaction in a wide range of industrial applica- ture, PNIPAM can selectively provide hydrophilic or
tions, a heterogeneous Pd catalyst must be developed. hydrophobic nanoenvironments. Hydrophobic mole-
This is necessary because homogeneous Pd catalysts cules can be dissolved into the brushes of PNIPAM in
are not reusable, and they need toxic and expensive water if the temperature of the medium is above its
ligands to stabilize the catalytically active Pd(0) spe- LCST. Therefore, the Suzuki reaction with hydropho-
cies. Moreover, complicated purification steps are bic substrates can likely be carried out in water with-
often required to remove the residual Pd and ligand out any surfactants or organic solvents. The LCST of
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PNIAPM can also be controlled by forming a co-poly- try (DSC) experiments were performed to measure
mer with a co-monomer.[10] For example, the LCST of the LCST of the synthesized PNIPAM-co-4-VP co-
PNIPAM-N-(acryloyloxy)succinimide (NASI) co- polymers (M1–M5) [Figure 2, (a)]. DSC curves
polymer is at about 88C.[10] On the other hand, the showed noticeable endothermic peaks in the tempera-
LCST of PNIAPM-sulfonic acid-containing copolymer ture range of 31 to 488C. M1 showed the coil-to-glob-
is above 1008C.[10] Furthermore, PNIPAM can easily ule transition at about 318C, which is very close to
be recovered from aqueous solution above its LCST the previously reported LCST of PNIPAM.[8] As the
by simple filtration. Because of these versatile proper- ratio of 4-VP in PNIPAM-co-4-VP co-polymers in-
ties, PNIPAM-grafted Pd nanoparticles have been in- creased from 8:2 (PNIPAM:4-VP) to 5:5, the LCST
vestigated as recyclable heterogeneous Pd catalysts in gradually increased from 43 to 488C. The observed
water and aqueous organic solvents.[10–11] However, shifts in LCST with 4-VP can be attributed to the in-
due to Pd leaching during reactions, the recyclability creased number of hydrogen bonds between the
of these catalysts still requires improvement. Milder PNIPAM networks and water molecules trapped in
reaction conditions, including a low reaction tempera- the network. This is due to the increased amount of
ture, are also desirable.
4-VP, which contains electron-rich nitrogen.[10] There-
In this study, temperature-responsive poly(N-iso- fore, higher enthalpy is likely needed to break the hy-
propylacrylamide-co-4-vinylpyridine) (PNIPAM-co-4- drogen bonds. The DSC measurements allowed the
VP) co-polymers[12] were employed as supports for determination of a temperature range for the Suzuki
catalytic Pd nanoparticles (instead of PNIPAM). Pyri- coupling with Pd-grafted co-polymers as catalysts.
dine is a well known ligand that forms complexes
The Pd nanoparticles grafted on the PNIPAM-co-4-
with transition metal ions.[7e,13] It is expected to pro- VP co-polymers (M1–M5) were synthesized by reduc-
vide a stronger binding site for Pd nanoparticles ing aqueous Pd2+ on the copolymers with NaBH4
within the co-polymer and to decrease Pd leaching [Figure 1, (b)]. The formation of Pd nanoparticles was
during the Pd-catalyzed organic reactions. Thus, the visually observed with the mixtureꢂs change in color
recyclability of Pd nanoparticles can be improved to black, and it was confirmed by TEM and energy
with the PNIPAM-co-4-VP copolymer. Due to the dispersive X-ray analysis (EDAX) measurements
PNIPAM moiety, the Suzuki reaction can be per- [Figure 2, (b)–(d) and Supporting Information].
formed in water and with easy work-up after reaction Figure 2, (b) shows a TEM image of the Pd nanopar-
completion. Due to these advantages, Pd nanoparti- ticles on M5 as a representative sample, which has ir-
cles were synthesized and embedded in a series of the regular morphologies with a diameter of about
PNIPAM-co-4-VP co-polymers. The catalytic activity 0.6 mm. The Pd nanoparticles on M1, M2, M3, M4,
and recyclability of the co-polymers were also investi- and M5 were named C1, C2, C3, C4, and C5, respec-
gated for use in the Suzuki reactions of arylboronic tively. TEM images of the other Pd catalysts are not
acids and aryl bromides with a wide range of func- shown here (see Figure S2 in the Supporting Infor-
tional groups in water and under mild reaction condi- mation). C5 shows spherical morphology with diame-
tions (ꢀ608C). In the present study, PNIPAM-co-4- ters of less than 8 nm and narrow particle size distri-
VP co-polymers with various molar ratios of butions of about 2 nm [Figure 2, (b)–(d) and Figure
NIPAM:4-VP (9:1, 8:2, 7:3, 6:4, and 5:5) were synthe- S3 in the Supporting Information]. Multiple lattice
sized and named M1, M2, M3, M4, and M5, respec- fringes were observed in the high-resolution TEM
tively [Figure 1, (a)]. Differential scanning calorime-
Figure 1. (a) Preparation of the PNIPAM-co-4-VP (M1–M5) co-polymers and (b) preparation of Pd nanoparticles on them.
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Palladium Nanoparticles on Thermoresponsive Hydrogels and their Application
Figure 2. (a) Differential scanning calorimetry (DSC) curves for M1–M5 at pH 10 and (b)–(d) transmission electron micro-
scopic (TEM) images of Pd nanoparticles grafted on the PNIPAM-co-4-VP copolymer [PNIPAM:4-VP=5:5 (M5)].
image [Figure 2, (d)], confirming the crystalline struc- 4-bromoacetophenone 1j with benzeneboronic acid 2a
ture of the Pd nanoparticles.
as a function of temperature from room temperature
To estimate the catalytic activities of the Pd cata-
lysts (C1–C5), coupling reactions between bromoben-
zene 1a and 4-methylbenzeneboronic acid 2b were
carried out with 1 mmol% Pd catalysts and K2CO3
(3 equiv.) as a base at 608C in water (Table 1). The
highest catalytic activity was observed with C5, which
allowed quantitative conversion of the substrates
within 30 min. The other catalysts afforded 65–89%
yields of 4-methylbiphenyl 3e. These results indicate
that C5 is the most suitable catalyst for the Suzuki re-
action in water. It is worthy of note that when we
used commercially available 10% Pd/C (1 mmol% Pd,
Aldrich) to compare the catalytic activity with that of
C5, it showed only a 70% yield of 3e under the same
reaction conditions, which represents a lower catalytic
activity than that of C5.
Table 1. Suzuki coupling reactions of bromobenzene 1a and
4-methylbenzeneboronic acid 2b with Pd nanoparticles on
the PNIPAM-co-4-VP co-polymers (C1–C5).[a]
Catalyst
9:1
8:2
7:3
6:4
5:5
(C1)
(C2)
(C3)
(C4)
(C5)
Yield
[%][b]
83
65
65
89
Quant.
[a]
Reaction conditions: bromobenzene (1a, 1 mmol), 4-
methylbenzeneboronic acid (2b, 1.5 mmol, 1.5 equiv.),
K2CO3 (3 mmol, 3 equiv.), H2O (2 mL), 1 mmol% Pd cat-
alyst, and a reaction time of 30 min.
[b]
The optimal reaction temperature using C5 was
also investigated by performing coupling reactions of
Isolated yield (the purity of the isolated product was con-
firmed by 1H NMR).
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Table 2. Suzuki coupling reactions of 4-bromoacetophenone
1j and benzeneboronic acid 2a with C5 as a function of tem-
perature.[a]
complete conversion in 30 min. The coupling reac-
tions of bromobenzene 1a with various areneboronic
acids (entries 13–15 and 17) also showed excellent
yields above 93%. However, the coupling reaction
with 4-nitrobenzeneboronic acid 2f afforded a modest
conversion of about 50%, even in a solvent mixture
of H2O and THF (v/v=1:1) and with a longer reac-
tion time of 10 h (entry 16).
Finally, the recyclability of C5 was estimated by re-
peatedly carrying out Suzuki coupling reactions at
608C in water with two model reactions. The coupling
reaction of 4-bromoacetophenone 1j with benzene-
boronic acid 2a was performed for the first five runs
(Table 4) and then the reaction between bromoben-
zene 1a and 4-methylbenzeneboronic acid 2b was per-
formed for the next five runs (Table 5). As shown in
Table 4, the catalyst showed excellent activity for the
first five runs, resulting in high yields above 90–95%
in 40 min. The high catalytic activity was preserved
for the following five runs of the model reactions, re-
sulting in 93–96% conversion (Table 5). After each
run, the amount of Pd leaching from C5 was estimat-
ed by performing ICP (inductively coupled plasma)
measurements on the supernatant solutions. The solu-
tions were collected by filtering the catalyst from the
reaction mixture after the reactions were complete.
Entry
Time [h]
Temp. [8C]
Yield [%][b]
1
2
3
4
24
r.t.
50
60
80
NR[c]
93.8
97
1.3
0.6
0.6.
94.4
[a]
Reaction conditions: 4-bromoacetophenone (1j, 1 mmol),
benzeneboronic acid (2a, 1.5 mmol, 1.5 equiv.), K2CO3
(3 mmol, 3 equiv.), H2O (2 mL), and 1 mmol% Pd cata-
lyst (C5).
[b]
[c]
Isolated yield (the purity of the isolated product was con-
firmed by 1H NMR).
1
No biaryl was detected by H NMR.
to 808C (Table 2). At room temperature, no conver- No significant Pd leaching (<0.5 ppm) was observed.
sion reaction was observed, even with a reaction time In addition, there was no significant agglomeration of
of 24 h. When the reaction temperature was increased Pd nanoparticles on the TEM images prepared after
to 50, 60, and 808C, much higher yields of 93.8, 97, the recycling experiments (Figure S4 in the Support-
and 94.4% were achieved within a shorter reaction ing Information). This suggests that the excellent re-
time (<1.5 h). These experimental data demonstrate cyclability is attributed to the 4-VP moiety, the co-
that the Suzuki reaction can be efficiently performed monomer introduced to PNIPAM to increase the
at 508C. These results are well matched with our binding strength of the co-polymer with Pd nanoparti-
DSC data, which showed the LCST of C5 at about cles.
488C. As mentioned above, hydrophobic substrates
In conclusion, Pd nanoparticles were successfully
can be solubilized into the brushes of the PNIPAM- immobilized on PNIPAM-co-4-VP co-polymers. The
co-4-VP co-polymer above the LCST in water. The Pd catalysts were applied to Suzuki coupling reactions
excellent yields observed above 508C can be ascribed and demonstrated high catalytic activity. The reac-
to the increased local concentration of hydrophobic tions formed various biaryl compounds at a relatively
substrates around Pd nanoparticles in the hydropho- low reaction temperature of 608C, even in water. The
bic nanoenvironment of the co-polymer in water.[11e] catalysts were successfully reused with constant cata-
From these data, 608C was confirmed as the optimal lytic activity in the repeated recycling studies.
reaction temperature for the Suzuki coupling reaction Through this research, we have developed a highly
with C5 in water.
active heterogeneous Pd catalyst. This Pd catalyst will
The scope of the Suzuki coupling reaction was thor- be industrially and environmentally valuable because
oughly investigated under the established reaction of its mild reaction conditions, which include a low re-
conditions of 1 mmol% C5 and 608C in water action temperature and water as a sole solvent. We
(Table 3). High conversions (above 93%) were ob- believe that these Pd catalysts can be applied to a vari-
served in the coupling reactions of benzeneboronic ety of Pd-catalyzed reactions such as Heck, Stille, So-
acid 2a with a wide range of aryl bromides 1 contain- nogashira, Hiyama, Negish, and oxidation/reduction
ing electron-donating groups (entries 1–5) and elec- reactions.
tron-withdrawing groups (entries 6–12). Due to the
very low solubility of 1-bromo-4-nitrobenzene 1f and
4-bromobenzonitrile 1g in H2O, the reactions were
performed in a solvent mixture of H2O and dioxane
(v/v=1:1) (entries 6 and 7). The reactions showed
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Palladium Nanoparticles on Thermoresponsive Hydrogels and their Application
Table 3. Suzuki coupling reactions of various aryl bromides 1 and benzeneboronic acids 2 with C5 at 608C in water.[a]
Entry
1 (R1)
2 (R2)
Product 3
Time [h]
Yield [%][b]
1
1a (H)
2a (H)
2a
3a
3b
3c
3d
3e
3f
3g
3h
3i
1
95
2
1b (NH2)
1c (OH)
4
95
3
2a
1.5
2
98
4
1d (OCH3)
1e (CH3)
1f (NO2)
1g (CN)
2a
94
5
2a
5
95
6
2a
0.5
0.5
4
quant.[c]
quant.[c]
98
7
2a
8
1h (CO2CH3)
1i (COOH)
1j (COCH3)
1k (CHO)
1l (CF3)
2a
9
2a
5
93
10
11
12
2a
3j
1
95
2a
3k
5
quant.
quant.
2a
3l
3
13
14
1a
1a
2b (CH3)
2c (OCH3)
3e
3d
0.5
2
quant.
96
15
1a
2d (Cl)
3m
4
93
16
17
1a
1a
2f (NO2)
2g (CO2CH3)
3f
3h
10
4
50[d]
quant.
[a]
Reaction conditions: bromobenzene (1, 1 mmol), phenylboronic acid (2, 1.5 mmol, 1.5 equiv.), K2CO3 (3 mmol, 3 equiv.),
H2O (2 mL), and 1 mmol% Pd catalyst (C5).
Isolated yield (the purity of the isolated product was confirmed by H NMR).
Solvent mixture: H2O:dioxane=1:1 by volume.
Solvent mixture: H2O:THF=1:1 by volume.
[b]
[c]
[d]
1
Table 4. Recycling experiments (runs 1–5) of C5 in Suzuki
coupling reactions at 608C in water.[a]
Experimental Section
Poly(N-isopropylacrylamide-co-4-vinylpyridine) Co-
Polymers
Poly(NIPAM-co-4-VP) co-polymer hydrogels were prepared
by free radical solution polymerization according to the
standard procedure.[12d] The molar ratio of NIPAM:4-VP
varied from 9:1, 8:2, 7:3, 6:4, and 5:5, with 6 mol%
MBAAm. In a typical run for the synthesis of a 6 mol%
cross-linked 5:5 poly(NIPAM-co-4-VP) co-polymer hydro-
gel, 1.173 g of NIPAM (10.1 mmol, 47 mol%) dissolved in
2 mL of methanol, 0.2 g of MBAAm (1.28 mmol, 2 mol%)
dissolved in 2 mL of methanol, and 1.06 g 4-VP (10.1 mmol,
47 mol%) dissolved in 16 mL of toluene were placed in
a 100-mL flask. The polymerization was initiated by adding
2 mol% AIBN and then the reaction mixture was heated at
808C for 4 h. The white solid polymer was filtered off,
washed with methanol and diethyl ether, and dried under
vacuum at 508C for 24 h.
Entry
1st
95
2nd
94
3rd
97
4th
94
5th
90
Yield [%][b]
[a]
Reaction conditions: 4-bromoacetophenone (1j, 1 mmol),
benzeneboronic acid (2a, 1.5 mmol, 1.5 equiv.), K2CO3
(3 mmol, 3 equiv.), H2O (2 mL), 1 mmol% Pd catalyst
(C5), and a reaction time of 40 min.
[b]
Isolated yield (the purity of the isolated product was con-
firmed by 1H NMR).
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Table 5. Recycling experiments (runs 6–10) of C5 in Suzuki
coupling reactions at 608C in water.[a]
chromatography with an eluent of EtOAc and hexane. The
resulting product was analyzed by H NMR spectroscopy.
1
Recycling the Pd Catalyst
Two kinds of Suzuki reactions were performed. The first
five runs were with bromoacetophenone 1j and benzenebor-
onic acid 2a, and the second five runs were with bromoben-
zene 1a and 4-methylbenzeneboronic acid 2b. The Suzuki
reactions were carried out as described above. After the
first reaction was complete, C5 was recovered by filtration
and air-dried. The collected catalyst was reused in the next
run of the coupling reaction under the same reaction condi-
tions (e.g., concentration of reactants) as the first run. The
filtrate (H2O) was analyzed with ICP (inductively coupled
plasma) measurements to estimate the amount of Pd leach-
ing after each run.
Entry
6th
96
7th
95
8th
93
9th
95
10th
96
Yield [%][b]
[a]
Reaction conditions: bromobenzene (1a, 1 mmol), 4-
methylbenzeneboronic acid (2b, 1.5 mmol, 1.5 equiv.),
K2CO3 (3 mmol, 3 equiv.), H2O (2 mL), 1 mmol% Pd cat-
alyst (C5), and a reaction time of 30 min.
[b]
Isolated yield (the purity of the isolated product was con-
firmed by 1H NMR).
Acknowledgements
Pd(0) Nanoparticles Grafted on the Co-Polymer
This research is partially supported by the Basic Science Re-
search Program through the National Research Foundation
of Korea (NRF) funded by the Ministry of Education, Sci-
ence and Technology (2011-00000001765). Y. Lee acknowl-
edges financial support by a grant from Eco-Innovation proj-
ect funded by Ministry of Environment, Korea (No. 405-111-
004).
As-synthesized poly-NIPAM-co-4-VP co-polymer (100 mg)
was dispersed in MeOH (20 mL) under mechanical shaking.
Palladium acetate [PdACTHNUTRGNE(NUG OAc)2] (10 mg, 0.0445 mmol) was
then gradually added to the suspension, followed by sonica-
tion for 1 min to thoroughly dissolve the Pd source. The Pd
mixture was shaken for 12 h. As the hydrogel reacted with
PdACHTUNGTRENNUNG(OAc)2, the hydrogel color changed to yellow. The mix-
ture was filtered using a 0.20 mm Millipore nylon membrane
filter and washed three times with 20 mL MeOH. The fil-
tered Pd2+ adsorbed copolymer was then dried in air for
12 h. Black Pd(0) nanoparticles were generated by adding
10 mg (0.264 mmol) NaBH4 as a reducing reagent into a sus-
pension of the dried copolymers in THF (20 mL) under me-
chanical shaking for 12 h. 10 mL MeOH were added to
remove the residual NaBH4 and then the Pd(0)-grafted co-
polymer was separated by filtration. The filtered co-polymer
was thoroughly washed with 20 mL MeOH and 20 mL THF
and then dried in air for 12 h. A series of Pd-grafted co-
polymers (C1–C5) was prepared with M1–M5 by the same
method. ICP measurements estimate the amount of Pd(0)
nanoparticles in C1–C5 as 0.69, 0.95, 1.63, 0.94, and 0.65
mmol Pd/g, respectively.
References
[1] a) P. T. Anastas, M. M. Kirchhoff, Acc. Chem. Res.
2002, 35, 686–694; b) N. Miyaura, T. Yanagigand, A.
Suzuki, Synth. Commun. 1981, 11, 503; c) A. Suzuki, N.
Miyaura, J. Chem. Soc. Chem. Commun. 1979, 866–867;
d) Y. Deng, L. Gong, A. Mi, H. Liu, Y. Jiang, Synthesis
2003, 337–339; e) N. Miyaura, A. Suzuki, Chem. Rev.
1995, 95, 2457- 2483.
[2] E. Negishi, A. de Meijere, (Eds.), Handbook of Orga-
nopalladium Chemistry for Organic Synthesis, Vol. 1,
John Wiley & Sons, Hoboken, NJ, 2002.
[3] a) V. Calo, A. Nacci, A. Monopoli, F. Montignelli, J.
Org. Chem. 2005, 70, 6040–6044; b) R. R. Deshmukh,
R. Rajagopal, K. V. Srinivasan, Chem. Commun. 2001,
1544–1545; c) X. Yang, Z. Fei, D. Zhao, W. H. Ang, Y.
Li, P. J. Dyson, Inorg. Chem. 2008, 47, 3292–3297.
[4] a) Y. Li, X. M. Hong, D. M. Collard, M. A. El-Sayed,
Org. Lett. 2000, 2, 2385–2388; b) R. Narayanan, M. A.
El-Sayed, J. Am. Chem. Soc. 2003, 125, 8340–8347;
c) B. J. Gallon, R. W. Kojima, R. B. Kaner, P. L. Diaco-
nescu, Angew. Chem. 2007, 119, 7389–7392; Angew.
Chem. Int. Ed. 2007, 46, 7251–7254; d) S. M. Sarkar, Y.
Uozumi, Y. M. A. Yamada, Angew. Chem. Int. Ed.
2011, 50, 9437–9441; e) A. Houdayer, R. Schneider, D.
Billaud, J. Ghanbaja, J. Lambert, Appl. Organomet.
Chem. 2005, 19, 1239–1248; f) P. Das, D. Sharma, A. K.
Shil, A. Kumari, Tetrahedron Lett. 2011, 52, 1176–1178;
g) S. M. Islam, P. Mondal, A. S. Roy, S. Mondal, D.
Hossain, Tetrahedron Lett. 2010, 51, 2067–2070; h) B.
Karimi, P. F. Akhavan, Inorg. Chem. 2011, 50, 6063–
General Procedure for the Suzuki Reaction
A 10-mL round-bottom flask was charged with 4-bromoace-
tophenone (1j, 1 mmol, 1 equiv.), benzeneboronic acid (2a,
1.5 mmol, 1.5 equiv.), K2CO3 (414 mg, 3 mmol, 3 equiv.),
H2O (2 mL), and Pd catalyst (1 mmol%). The content of
flask was stirred at 608C in air. The reaction was monitored
by thin layer chromatography (TLC). After the reaction was
complete, the reaction mixture was cooled to room tempera-
ture and then filtered to recover the catalyst. It was then
washed with 10 mL of H2O and ethyl acetate (EtOAc). The
organic phase was separated from the aqueous phase, which
was extracted three times with 30 mL EtOAc. The organic
phases were collected together, dried over MgSO4, and fil-
tered. The solvent was then evaporated under reduced pres-
sure. The pure product was obtained via silica gel column
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Palladium Nanoparticles on Thermoresponsive Hydrogels and their Application
6072; i) S. Schweizer, J.-M. Becht, C. L. Drian, Org.
Lett. 2007, 9, 3777–3780; j) T. Suzuka, K. Kimura, T.
Nagamine, Polymers 2011, 3, 621–639; k) B. Tamami, S.
Ghasemi, J. Mol. Catal. A: Chem. 2010, 322, 98–105;
l) A. Ohtaka, T. Teratani, R. Fujii, K. Ikeshita, O. Shi-
momura, R. Nomura, Chem. Commun. 2009, 7188–
7190.
2002, 4, 2997–3000; k) Q. Yang, S. Ma, J. Li, F. Xiao, H.
Xiong, Chem. Commun. 2006, 2495–2497.
[8] a) Y. Hirokawa, T. Tanaka, E. S. Matsuo, J. Chem.
Phys. 1984, 81, 6379–6380; b) K. Kubota, S. Fujishige, I.
Ando, J. Phys. Chem. 1990, 94, 5154–5158; c) K.
Makino, S. Yamamoto, K. Fujimoto, H. Kawaguchi, H.
Ohsima, J. Colloid Interface Sci. 1994, 168, 251–258;
d) R. H. Pelton, H. M. Pelton, A. Morphesis, R. L.
Rowell, Langmuir 1989, 5, 816–818; e) H. G. Schild,
D. A. Tirrell, J. Phys. Chem. 1990, 94, 4352–4356; f) S.
Fujishige, K. Kubota, I. Ando, J. Phys. Chem. 1989, 93,
3311–3313.
[5] a) G. M. Scheuermann, L. Rumi, P. Steurer, W. Bann-
warth, R. Mulhaupt, J. Am. Chem. Soc. 2009, 131,
8262–8270; b) Y. Li, X. Fan, J. Qi, J. Ji, S. Wang, G.
Zhang, F. Zhang, Nano Res. 2010, 3, 429–437; c) P.-P.
Zhang, X.-X. Zhang, H.-X. Sun, R.-H. Liu, B. Wanga,
Y.-H. Lin, Tetrahedron Lett. 2009, 50, 4455–4458.
[9] M. Shibayama, Y. Suetoh, S. Nomura, Macromolecules
[6] a) H. Buluta, L. Artoka, S. Yilmazub, Tetrahedron Lett.
2003, 44, 289–291; b) B. M. Choudary, S. Madhi, N. S.
Chowdari, M. L. Kantam, B. Sreedhar, J. Am. Chem.
Soc. 2002, 124, 14127–14136; c) G. Budroni, A. Corma,
H. Garcꢃa, A. Primo, J. Catal. 2007, 251, 345–353; d) K.
Dhara, K. Sarkar, D. Srimani, S. K. Saha, P. Chattopad-
hyay, A. Bhaumik, Dalton Trans. 2010, 39, 6395–6402;
e) H. Hagiwara, H. Sasaki, N. Tsubokawa, T. Hoshi, T.
Suzuki, T. Tsuda, S. Kuwabata, Synlett 2010, 1990–
1996; f) H. Qiu, S. M. Sarkar, D.-H. Lee, M.-J. Jin,
Green Chem. 2008, 10, 37–40; g) J. D. Webb, S. Mac-
Quarrie, K. McEleney, C. M. Crudden, J. Catal. 2007,
252, 97–109; h) H. Zhao, J. Peng, R. Xiao, M. Cai, J.
Mol. Catal. A: Chem. 2011, 337, 56–60; i) J. Zhi, D.
Song, Z. Li, X. Lei, A. Hu, Chem. Commun. 2011, 47,
10707–10709.
[7] a) P. Zheng, W. Zhang, J. Catal. 2007, 250, 324–330;
b) A. Arcadi, G. Cerichelli, M. Chiarini, M. Correa, D.
Zorzan, Eur. J. Org. Chem. 2003, 4080–4086; c) R. B.
Bedford, M. E. Blake, C. P. Butts, D. Holder, Chem.
Commun. 2003, 466–467; d) G. A. Molander, B. Biolat-
to, Org. Lett. 2002, 4, 1867–1870; e) X. Jiang, G. Wei,
X. Zhang, W. Zhang, P. Zheng, F. Wen, L. Shi, J. Mol.
Catal. A: Chem. 2007, 277, 102–106; f) M. L. Kantam,
S. Roy, M. Roy, B. Sreedhar, B. M. Choudary, Adv.
Synth. Catal. 2005, 347, 2002–2008; g) M. Lamblin, L.
Nassar-Hardy, J.-C. Hierso, E. Fourquet, F.-X. Felpin,
Adv. Synth. Catal. 2010, 352, 33–79; h) H. Sakurai, T.
Tsukuda, T. Hirao, J. Org. Chem. 2002, 67, 2721–2722;
i) Y. Uozumi, H. Danjo, T. Hayashi, J. Org. Chem.
1999, 64, 3384–3388; j) Y. Uozumi, Y. Nakai, Org. Lett.
1996, 29, 6966–6968.
[10] D. E. Bergbreiter, B. L. Case, Y.-S. Liu, J. W. Caraway,
Macromolecules 1998, 31, 6053–6062.
[11] a) Y. Mei, Y. Lu, F. Polzer, M. Ballauff, M. Drechsler,
Chem. Mater. 2007, 19, 1062–1069; b) D. E. Bergbreiter,
P. L. Osburn, A. Wilson, E. M. Sink, J. Am. Chem. Soc.
2000, 122, 9058–9064; c) T. Tamai, M. Watanabe, T. Ter-
amura, N. Nishioka, K. Matsukawa, Macromol. Symp.
2009, 282, 199–204; d) H. Hamamoto, Y. Suzuki,
Y. M. A. Yamada, H. Tabata, H. Takahashi, S. Ikegami,
Angew. Chem. 2005, 117, 4612–4614; Angew. Chem.
Int. Ed. 2005, 44, 4536–4538; e) G. Wei, W. Zhang, F.
Wen, Y. Wang, M. Zhang, J. Phys. Chem. C 2008, 112,
10827–10832.
[12] a) H. I. Melendez-Ortiz, E. Bucio, G. Burillo, Radiat.
Phys. Chem. 2009, 78, 1–7; b) H. Nur, V. T. Pinkrah,
J. C. Mitchell, L. S. Benꢄe, M. J. Snowden, Adv. Colloid
Interface Sci. 2010, 158, 15–20; c) Y. Wang, G. Wei, F.
Wen, X. Zhang, W. Zhang, L. Shi, J. Mol. Catal. A:
Chem. 2008, 280, 1–6; d) K. S. Kim, B. Vincent, Polym.
J. 2005, 37, 565–570; e) Y. Wang, G. Wei, F. Wen, X.
Zhang, W. Zhang, L. Shi, Eur. Polym. J. 2008 44, 1175–
1182.
[13] a) A. N. Vedernikov, P. Wu, J. C. Huffman, K. G. Caul-
ton, Inorg. Chim. Acta 2002, 330, 103–110; b) U.
Rosenthal, S. Pulst, R. Kempe, K.-R. Pçrschke, R.
Goddard, B. Proft, Tetrahedron 1998, 54, 1277–1287;
c) T. Harada, S. Wada, H. Yuge, T. K. Miyamoto, Acta
Crystallogr. Sect. C: Cryst. Struct. Commun. 2003, C59,
m37–m39.
Adv. Synth. Catal. 2012, 354, 1257 – 1263
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asc.wiley-vch.de
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