A recyclable "Boomerang" linear polystyrene-stabilized pd nanoparticles for the suzuki coupling reaction of aryl chlorides in water

Full text of DOI:10.1002/cctc.201300204

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DOI: 10.1002/cctc.201300204
A Recyclable “Boomerang” Linear Polystyrene-Stabilized
Pd Nanoparticles for the Suzuki Coupling Reaction of Aryl
Chlorides in Water
[
a]
[a]
[a]
[b]
Atsushi Ohtaka,* Erina Sakaguchi, Tomohiro Yamaguchi, Go Hamasaka,
[b]
[a]
[a, c]
Yasuhiro Uozumi, Osamu Shimomura, and Ryꢀki Nomura
A polymer-supported “boomerang” catalyst that operates
through the reversible release of homogeneous catalyst into
the solution phase from the polymer support has the advan-
tages of both homogeneous (high activity) and heterogeneous
Linear polystyrene-stabilized PdO NPs (PS-PdONPs) were pre-
pared through the thermal decomposition of Pd(OAc) in the
2
[6]
presence of polystyrene, as described previously. The compo-
sition (PdO) and size (2.6Æ0.3 nm) of the NPs were observed
by using XRD and TEM, respectively (Figures S1 and S2). The
[
1]
(recovery and recyclability) catalysts. For example, Reiser
À1
et al. developed a method for the reversible immobilization of
pyrene-tagged palladium–N-heterocyclic carbene complexes
on highly magnetic, graphene-coated cobalt nanoparticles
loading value of palladium (2.5 mmolg ) was confirmed by in-
ductively coupled plasma-atomic emission spectrometry (ICP-
AES) analysis. The SEM image showed that PS-PdONPs pos-
sessed a particle aggregate-like structure (Figure S3). According
to the nitrogen adsorption analysis, the BET surface area of PS-
[
1a]
(
NPs) through p–p stacking interactions. In contrast, metal
NPs as catalysts have attracted attention because they possess
[
2]
2
À1
high catalytic activity in water. Metal NPs have been used not
only as a semi-heterogeneous catalyst but also as a semi-heter-
PdONPs was 27.3 m g after vacuum pretreatment at 1008C.
PS-PdONPs had an irregular hollow shape, with a hollow size
distribution centered at 2.7, 8.6, and 10.6 nm (Figures S4 and
S5).
[
3]
ogeneous support. However, the heterogenization of metal
NPs decreased catalytic activity. In addition, the recovery and
reuse of metal NPs has been difficult to achieve because of
a significant loss and/or morphology change of the metal NPs
In the Suzuki coupling reaction of aryl bromides with aryl-
boronic acids in the presence of PS-PdONPs, no leaching of
palladium into the reaction solution occurred after the reac-
[
2c–e]
during the reaction and workup.
Because leaching of solu-
[6]
ble metal species from the support is a major cause of catalyst
deactivation, efforts have been made to develop an effective
tion, as confirmed by ICP-AES analysis. No increase in the
yield of coupling product was observed in the hot filtration
test. In addition, the TEM image of the recovered catalyst
showed that the size of the NPs was maintained even after the
tenth run. With these results in mind, we checked leaching of
palladium after the exposure of PS-PdONPs to different re-
[
2f–i]
support that prevents leaching of metal species.
In contrast,
leaching of palladium species has been observed directly,
[
4]
which showed high catalytic activity in some systems. Palladi-
um NPs generated in situ for the Suzuki coupling reaction and
aerobic alcohol oxidation in water were recovered with linear
À1
agents in 1.5 molL of aqueous KOH solution at 808C for 1 h
[5]
[4a]
polystyrene, even in the presence of organic compounds.
(Table 1). No detectable levels of palladium (<0.1 ppm) were
These reports prompted efforts to find recyclable “boomerang”
NPs that can overcome the aforementioned problems. This
communication describes the development of a catch–release
system for soluble palladium species in water with linear poly-
styrene as an efficient reservoir.
observed in the absence of reagent (entry 1) or in the presence
of 4-methylphenylboronic acid (entry 2). However, 19% of pal-
ladium leached into the aqueous solution when the mixture of
À1
PS-PdONPs and bromobenzene was heated in 1.5 molL of
aqueous KOH solution at 808C for 1 h (entry 3). These results
indicated that a recyclable homogeneous/heterogeneous cata-
lytic system could be constructed with PS-PdONPs and aryl
halide.
[a] Dr. A. Ohtaka, E. Sakaguchi, T. Yamaguchi, Dr. O. Shimomura,
Prof. R. Nomura
Department of Applied Chemistry
Faculty of Engineering
Osaka Institute of Technology
Ohmiya, Asahi-ku, Osaka 535-8585 (Japan)
Fax: (+81)6-6954-4268
Table 1. Leaching test.
E-mail: otaka@chem.oit.ac.jp
Entry
Reagent
Amount of leached
palladium [%]
[
a]
[
b] Dr. G. Hamasaka, Prof. Y. Uozumi
Institute for Molecular Science (IMS)
Higashiyama 5-1, Myodaiji, Okazaki 444-8787 (Japan)
1
2
3
none
<0.3
<0.3
19
4-methylphenylboronic acid
bromobenzene
[
c] Prof. R. Nomura
Department of Nanomaterials and Microdevices Research Center
Osaka Institute of Technology
Ohmiya, Asahi-ku, Osaka 535-8585 (Japan)
[
a] Average weight percentage of palladium atoms detected by using in-
ductively coupled plasma-atomic emission spectrometry in the superna-
tant liquid after the exposure of polystyrene-stabilized PdO NPs to differ-
ent reagents in KOH aqueous solution at 808C for 1 h.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201300204.
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To increase the stability of the leached palladium species,
the Suzuki coupling reaction of chlorobenzene with 4-methyl-
À1
phenylboronic acid in 1.5 molL of aqueous KOH solution was
examined in the presence of
a water-soluble stabilizer
(Table 2). In a control experiment, only 6% of 4-methylbiphenyl
Table 2. Effect of additive for the Suzuki coupling reaction of chloroben-
[
a]
zene with 4-methylphenylboronic acid in water.
[
b]
[c]
Entry
Additive
Yield [%]
[
d]
1
2
3
4
none
TBAB
SDS
CTAB
TBAB
TBAB
TBAB
TBAB
TBAB
6
92
2
20
90
82
76
76
76
[
[
[
[
[
e]
f]
5
6
7
8
9
g]
h]
i]
Figure 1. a) TEM image of the recovered catalyst after the third run (scale
bar=20 nm); b) size distribution of the recovered catalyst after the third
run; c) TEM image of the recovered catalyst after the fifth run (scale
bar=20 nm); d) size distribution of the recovered catalyst after the fifth run.
[a] All reactions were performed with chlorobenzene (0.5 mmol), 4-meth-
ylphenylboronic acid (0.75 mmol), polystyrene-stabilized PdO NPs
À1
(
[
1.5 mol% of palladium), 1.5 molL of KOH aqueous solution (1 mL);
b] CTAB= cetyltrimethylammonium bromide; TBAB=tetrabutylammoni-
covered catalyst. These results suggest that the leached palla-
dium species participate in the catalytic process and redeposit
um bromide; SDS=sodium dodecyl sulfate; [c] NMR yields; [d] Reaction
time was 20 h; [e] Polystyrene-stabilized PdO NPs (0.15 mol% of palladi-
um) was used; [f] Second use; [g] Third use; [h] Fourth use; [i] Fifth use.
[11,12]
onto linear polystyrene after the reaction is complete.
To evaluate the use of a homogeneous/heterogeneous cata-
lytic system, the scope with respect to aryl chloride was inves-
tigated (Table 3). The Suzuki coupling reaction of 4-chloroto-
luene and 4-chloroanisole bearing electron-donating groups at
their para positions with 4-methylphenylboronic acid gave the
corresponding coupling products in 78 and 66% yields, respec-
tively (entries 1 and 2). 4-Chloroacetophenone with an elec-
was obtained after the reaction components were heated at
[
6a]
8
08C without a stabilizer for 20 h (entry 1). In contrast, the
reaction proceeded efficiently at 808C for 1 h in the presence
of tetrabutylammonium bromide (TBAB) to give 4-methylbi-
phenyl in 92% yield (entry 2). When the reaction was interrupt-
ed at 22% conversion and then allowed to continue after the
removal of the catalyst (hot filtration test), the residual activity
of the reaction mixture was significant (64% after 1 h). Neither
sodium dodecyl sulfate nor cetyltrimethylammonium bromide
was an effective stabilizer under these reaction conditions (en-
[
a]
Table 3. Reaction of various aryl chlorides with arylboronic acids.
[
7,8]
tries 3 and 4),
which ruled out a mechanistic scenario in
which TBAB acts as a phase-transfer catalyst. Notably, the turn-
1
2
Entry
R
R
Yield
[%]
À1
[b]
over frequency of 600 h was higher than those of recent re-
[
9]
ports using palladium NPs. After the reaction, the catalyst
was recovered and successively subjected to second through
fifth runs of the coupling reaction under the same conditions
to afford 4-methylbiphenyl in 82, 76, 76, and 76% yields, re-
spectively (entries 6–9). ICP-AES analysis revealed that no palla-
dium species remaining after the reaction and quantitative re-
covery of palladium was achieved. Although the particle size
of the recovered catalyst after the third run (3.6Æ0.5 nm) in-
creased slightly compared with that of the fresh catalyst (2.6Æ
1
2
3
4
5
6
7
8
9
4-CH
4-CH
4-CH
H
4-CH
4-CH
H
4-CH
4-CH
H
4-CH
4-CH
2-CH
3
À
4-CH
4-CH
4-CH
4-CH
4-CH
4-CH
3
À
78
66
95
98
87
91
68
83
86
90
63
99
53
3
3
OÀ
3
À
3
COÀ
À
3
3
3
OÀ
OÀ
OÀ
3
À
3
COÀ
4-CF
4-CF
4-CF
2-CH
2-CH
2-CH
4-CH
3
À
3
À
3
À
3
COÀ
3
À
1
0
3
À
3
1
1
3
À
À
3
0
.3 nm), similar size of NPs was observed by using TEM after
12
3
COÀ
À
13
3
À
3
À
the fifth run (3.6Æ0.6 nm) (Figure 1). The formation of palladi-
um NPs was confirmed by XRD analysis of the recovered cata-
[a] All reactions were performed with chlorobenzene (0.5 mmol), 4-meth-
ylphenylboronic acid (0.75 mmol), polystyrene-stabilized PdO NPs
[
10]
lyst after the reaction (Figure S6). In addition, the 1 s peak of
nitrogen was not observed by using XPS analysis, which indi-
cated the absence of tetrabutylammonium species in the re-
À1
(
1.5 mol% of palladium), 1.5 molL of KOH aqueous solution (1 mL);
[
b] NMR yields.
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tron-deficient aromatic ring also underwent the Suzuki cou-
pling reaction with 4-methylphenylboronic acid under similar
conditions to afford 4-acetyl-4’-methylbiphenyl in 95% yield
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sponding product in good to excellent yields (entries 4–9).
Sterically hindered substrates were also examined. The forma-
tion of 2,4’-dimethylbiphenyl could be achieved by the cou-
pling of 4-chlorotoluene with 2-methylphenylboronic acid or
1009.
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yield, respectively (entries 11 and 13).
In summary, the reversible transfer of palladium species be-
tween water (reaction medium) and polystyrene (polymer sup-
port) was confirmed for the Suzuki coupling reaction of aryl
chloride with arylboronic acid in the presence of TBAB. After
the restabilization of palladium species on linear polystyrene,
no change in particle size was observed clearly by using TEM.
Leached palladium species have greater catalytic activity for
the Suzuki coupling reaction than do PS-PdONPs. The catalyst
was recycled without significant loss of activity.
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1
Typical method for the Suzuki coupling reaction
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Chlorobenzene (56.2 mg, 0.5 mmol), 4-methylphenylboronic acid
3
279–3282; c) A. Gniewek, A. M. Trzeciak, J. J. Ziꢅłkowski, L. K e˛ pi n´ ski, J.
(
110 mg, 0.75 mmol), PS-PdONPs (2.9 mg, 1.5 mol% of palladium),
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TBAB (161 mg, 0.5 mmol), and aqueous KOH solution (1 mL, 1.5
[
À1
molL ) were added to a screw-capped vial with a stirring bar.
After stirring at 808C for 1 h, the reaction mixture was cooled to
RT by immediately immersing the vial in water (ꢀ208C) for ap-
proximately 10 min. After separating the catalyst and the aqueous
phase through centrifugation, the aqueous phase was decanted.
The recovered catalyst was washed with water (5ꢂ3.0 mL) and di-
ethyl ether (5ꢂ3.0 mL), which were then added to the aqueous
phase. The aqueous phase was extracted eight times with diethyl
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2
005, 46, 3557–3560.
À1
[
8] On heating the mixture of PS-PdONPs and chlorobenzene in 1.5 molL
ether. The combined organic extracts were dried over MgSO and
4
of aqueous KOH solution at 808C for 1 h in the presence of TBAB or ce-
tyltrimethylammonium bromide, 1.2 or 0.5%, respectively, of palladium
leaching into the aqueous solution was confirmed by ICP-AES analysis.
In contrast, no leaching of palladium (<0.1 ppm) was observed in the
presence of sodium dodecyl sulfate.
concentrated under reduced pressure. The product was analyzed
1
by using H NMR. The recovered catalyst was dried in vacuo and
reused. Furthermore, the amount of palladium in the aqueous
phase determined from ICP-AES analysis was <0.1 ppm.
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9] a) R. B. Bedford, M. E. Blake, C. P. Butts, D. Holder, Chem. Commun. 2003,
4
66–467; b) M. Lysꢆn, K. Kçhler, Synthesis 2006, 692–698.
0
[
[
10] The formation of Pd was also confirmed by XPS analysis (Figure S7).
11] Similar processes have been observed in organic solvent: a) I. Pryjom-
ska-Ray, A. Gniewek, A. M. Trzeciak, J. J. Ziꢅłkowski, W. Tylus, Top. Catal.
Acknowledgements
This work was grateful to the Nanomaterials and Microdevices
Research Center (NMRC) of the Osaka Institute of Technology
2
006, 40, 173–184; b) F. Zhao, K. Murakami, M. Shirai, M. Arai, J. Catal.
2000, 194, 479–483.
[
12] After the reaction, leached palladium species were restabilized onto
linear polystyrene, probably because of the chelate effect: W. Sun, S.
Zhou, B. You, L. Wu, Chem. Mater. 2012, 24, 3800–3810.
(OIT) for financial and instrumental supports. This work was sup-
ported by the Joint Studies Program (2012) of the Institute of Mo-
lecular Science and the Science Research Promotion Fund. We
thank Dr. T. Shinagawa, Dr. Y. Kashiwagi, and Prof. Y. Nakamura
for assistance with ICP-AES, XRD, XPS, and N2 sorption
measurements.
Keywords: boomerang
palladium · water
·
cross-coupling
·
nanoparticles
·
Received: March 19, 2013
Published online on && &&, 0000
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A. Ohtaka,* E. Sakaguchi, T. Yamaguchi,
G. Hamasaka, Y. Uozumi, O. Shimomura,
R. Nomura
Boomerang! It keeps coming back!
The reversible transfer of Pd species be-
tween water (reaction medium) and
polystyrene (polymer support) was con-
firmed for Suzuki coupling reaction of
aryl chloride with arylboronic acid in the
presence of tetrabutylammonium bro-
mide. No clear change in particle size
was observed by TEM after re-stabiliza-
tion of the Pd species on linear
&& – &&
A Recyclable “Boomerang” Linear
Polystyrene-Stabilized Pd
Nanoparticles for the Suzuki Coupling
Reaction of Aryl Chlorides in Water
polystyrene.
ꢁ
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 0000, 00, 1 – 3
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4
&
ÞÞ
These are not the final page numbers!