Copper-free sonogashira coupling in water with linear polystyrene- stabilized PdO nanoparticles

Article abstract of DOI:10.1055/s-0030-1258018

Linear polystyrene-stabilized PdO nanoparticles generated by thermal decomposition of palladium acetate have high catalytic activity for Sonogashira coupling in water under copper-free conditions. The catalyst was recovered and reused at least four times

Full text of DOI:10.1055/s-0030-1258018

LETTER
2271
Copper-Free Sonogashira Coupling in Water with Linear
Polystyrene-Stabilized PdO Nanoparticles
S
onogashira Co
a
uplinginW
k
ater
w
ithL
i
u
near Polysty
t
t
o
abilizedPdO
NanoT
particles eratani,a Atsushi Ohtaka,* a Takahiro Kawashima,a Osamu Shimomura,a Ryôki Nomura*a,b
a
Department of Applied Chemistry, Faculty of Engineering, Osaka Institute of Technology,
5-16-1 Ohmiya, Asahi, Osaka 535-8585, Japan
Fax +81(6)69572135; E-mail: otaka@chem.oit.ac.jp
Nanomaterials and Microdevices Research Center, Osaka Institute of Technology,
5-16-1 Ohmiya, Asahi, Osaka 535-8585, Japan
b
Fax +81(6)69544604; E-mail: nomura@chem.oit.ac.jp
Received 26 May 2010
However, it is difficult to reuse the catalyst because PdNP
are dispersed in water. Recently, Cacchi et al. have report-
ed that perfluoro-tagged PdNP immobilized on silica gel
was reusable many times for Sonogashira coupling reac-
tion in water under copper-free conditions.15 Here we re-
port that the Sonogashira coupling of various aryl halides
with terminal acetylenes proceeds in water in the presence
of linear polystyrene-stabilized PdNP under copper-free
conditions.
Abstract: Linear polystyrene-stabilized PdO nanoparticles gener-
ated by thermal decomposition of palladium acetate have high cat-
alytic activity for Sonogashira coupling in water under copper-free
conditions. The catalyst was recovered and reused at least four
times without any loss of catalytic activity.
Key words: polystyrene, water, PdO nanoparticles, Sonogashira
coupling
Transition-metal nanoparticles as catalysts have attracted
a great deal of attention in the last 15 years,1 with their ef-
ficacy in water of particular interest because water is a
readily available, safe, and environmentally benign sol-
vent.2 Metal nanoparticles are typically formed in the
presence of a protecting agent because they tend to precip-
itate or aggregate and lose their catalytic activities. Popu-
lar protecting agents include tetraalkylammonium salts,3
functionalized polymers,4 and dendrimers.5 Hydrophilic
polymers such as poly(ethylene glycol) (PEG)6 and
poly(N-isopropylacrylamide) (PNIPAM)7 or hydrophobic
polymers such as hypercrosslinked-polystyrene-stabilized
palladium nanoparticles (PdNP)8 have high catalytic ac-
tivity toward C–C coupling reactions in water. However,
a significant decrease in catalytic activity is observed for
recycling because of a siginificant loss of such PdNP dur-
ing workup and/or morphology change (Ostwald ripen-
ing). In contrast, PdNP stabilized by a hydrogel of poly-
(N-isopropylacrylamide-co-poly[2-methacrylic acid 3-
Linear polystyrene-stabilized palladium nanoparticles 1
were prepared by thermal decomposition of Pd(OAc)2 in
the presence of polystyrene (Mn = 6.0×103, Scheme 1).12,16
An XRD pattern of 1 is presented in Figure 1 (a). Besides
the broad diffraction with 2q ranging from 12° to 28° as-
cribed to the polystyrene, other five diffraction peaks as-
signed to PdO (JCPDS 41-1107) are observed clearly.
Figure 1 (c) shows a TEM image of 1, where a fairly uni-
form particle size of 2.6 0.4 nm is evident. Inductively
coupled plasma-atomic emission spectroscopy (ICP-
AES) revealed that 1 contained an average of 2.5 mmol g–1
of Pd.17
polystyrene-stabilized
PdO nanoparticles (1)
Pd(OAc)2
polystyrene
(Mn = 6,000)
+
K2CO3, H2O,
90 °C, 1 h
Scheme 1 Preparation of polystyrene-stabilized Pd nanoparticles
For preliminary optimization of the reaction conditions,
we studied the reaction of iodobenzene with phenylacety-
lene in the presence of linear polystyrene-stabilized PdO
nanoparticles 1 (1.5 mol% of Pd) in water at 80 °C for 6
hours. Representative results are summarized in Table 1.
The coupling with cesium carbonate, potassium phos-
phate, sodium acetate, potassium carbonate, and potassi-
um hydroxide gave diphenylacetylene in 12%, 21%, 21%,
31%, and 35% yields, respectively (entries 1–5). In con-
trast, organic amines were found to promote the Sono-
gashira coupling efficiently in water. Thus, the reaction
with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gave a
77% yield of the product under similar conditions (entry
6). When triethylamine was used, the chemical yield of
diphenylacetylene increased significantly, resulting in the
quantitative formation of the coupling product (entry 7).18
(bis-carboxymethylamino)-2-hydroxypropyl
ester]
(PNIPAM-co-PMACHE),9 an amphiphilic copolymer of
styrene and MACHE,10 polyaniline nanofibers,11 or linear
polystyrene12 are easily reusable for Suzuki coupling re-
action in water.
On the other hand, the palladium-catalyzed reaction of
aryl halides with terminal alkynes, known as the Sono-
gashira coupling, is recognized as a powerful and reliable
synthetic method for the formation of substituted acety-
lenes.13 The PEG-stabilized PdNP and in situ generated
PdNP have high catalyitc activity for Sonogashira cou-
pling reaction in water under copper-free conditions.6,14
SYNLETT 2010, No. 15, pp 2271–2274
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x
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x
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Advanced online publication: 06.08.2010
DOI: 10.1055/s-0030-1258018; Art ID: U04510ST
© Georg Thieme Verlag Stuttgart · New York

2272
T. Teratani et al.
LETTER
Table 2 Sonogashira Coupling of Aryl Halides with Alkynes in
Watera
1 (1.5 mol% of Pd)
Ar
X
+
R
Ar
R
H2O, Et3N, 80 °C, 6 h
Entry ArX
1
Alkyne
Yield (%)b
99
99
99
99
93
I
O
2
I
I
3
F3C
4
I
5
MeO
I
6
74
I
I
Figure 1 (a) XRD patterns of 1; (b) JCPDS data (41-1107) for PdO;
(c) TEM image of 1
7
8
84
99
On the contrary, PS-stabilized Pd(0) nanoparticles re-
duced by NaBH4 or Pd/C exhibited the low catalytic activ-
ities (entries 8 and 9).19
O
I
The scope of the reaction was studied with various aryl
halides and terminal alkynes (Table 2). The coupling of
9
10
11
12
13
91
97
80
74
49c
I
I
I
I
Table 1 Screening of Bases for Sonogashira Coupling of Iodoben-
zene with Phenylacetylene in Watera
OMe
1
(1.5 mol% of Pd)
I
+
H2O, base,
80 °C, 6 h
(CH2)5Me
SiMe3
Entry
Base
Yield (%)b
1
Cs2CO3
K3PO4
NaOAc
K2CO3
KOH
12
21
21
31
35
77
99
47
67
Br
2
3
a Reaction conditions: aryl halide (0.5 mmol), alkyne (0.55 mmol),
Et3N (1.5 mmol), 1 (1.5 mol% of Pd), H2O (1 mL), 80 °C, 6 h.
b Isolated yield.
4
5
c Reaction was carried out at 90 °C for 24 h.
6
DBU
iodobenzene with phenylacetylene took place smoothly in
water at 80 °C in the presence of 3 equivalents of Et3N and
1.5 mol% palladium of 1 to give diphenylacethylene in
99% yield (entry 1).20 Both the electron-rich and electron-
deficient aryl iodides were applicable, affording the de-
sired coupling products in excellent yields (entries 2–5).
Sterically hindered aryl iodides such as 2-iodotoluene and
1-iodonaphthalene also underwent the Sonogashira cou-
pling with phenylacetylene to give the corresponding
products in 74% and 84% yields, respectively (entries 6
and 7). The coupling of various terminal alkynes bearing
7
Et3N
8c
9d
Et3N
Et3N
a Reaction conditions: iodobenzene (0.5 mmol), phenylacetylene
(0.55 mmol), base (1.5 mmol) in the presence of catalyst 1 (1.5 mol%
Pd) in 1.0 mL of H2O at 80 °C for 6 h.
b NMR yield.
c PS-stabilized Pd(0) nanoparticle reduced by NaBH4 was used as a
catalyst.
d Pd/C was used as a catalyst.
Synlett 2010, No. 15, 2271–2274 © Thieme Stuttgart · New York

LETTER
Sonogashira Coupling in Water with Linear Polystyrene-Stabilized PdO Nanoparticles
2273
Shinagawa and Dr. Y. Kasiwagi for assistance with the ICP-AES
measurements and the XRD measurement.
electron-withdrawing groups and electron-donating
groups took place with iodobenzene to give the corre-
sponding product in 99%, 91% and 97% yields, respec-
tively
(entries
8–10).
1-Octyne
and
References and Notes
trimethylsilylacetylene reacted with iodobenzene to gen-
erate the corresponding products in good yields (entries
11 and 12). However, bromobenzene gave a low yield
(entry 13).
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The recyclability of 1 was also examined for the Sono-
gashira coupling reaction of iodobenzene with phenyl-
acetylene. After the first reaction, which gave a
quantitative yield of the coupling product (Table 2, entry
1), the catalyst 1 was recovered and successively subject-
ed to the second through the fifth run of the coupling
reaction under the same conditions to afford diphenylac-
ethylene in 99%, 99%, 97%, and 98% yields, respectively
(Scheme 2). Importantly, ICP-AES analysis of the aque-
ous phases revealed barely detectable levels of palladium
residue. In addition, TEM image of the recovered catalyst
showed that the size of palladium (2.7 0.6 nm) was
maintained even after the fifth run (Figure 2).
1
(1.5 mol% of Pd)
I
+
H2O, Et3N,
80 °C, 6 h
(8) Lyubimov, S. E.; Vasil’ev, A. A.; Korlyukov, A. A.; Ilyin,
M. M.; Pisarev, S. A.; Matveev, V. V.; Chalykh, A. E.;
Zlotin, S. G.; Davankov, V. A. React. Funct. Polym. 2009,
69, 755.
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P. L. Angew. Chem. Int. Ed. 2007, 46, 7251.
1st use: 99%
2
3
4
5
nd use: 99%
rd use: 99%
th use: 97%
th use: 98%
Scheme 2 Recycling experiments
(12) Ohtaka, A.; Teratani, T.; Fujii, R.; Ikeshita, K.; Shimomura,
O.; Nomura, R. Chem. Commun. 2009, 7188.
(13) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron
Lett. 1975, 16, 4467. (b) Sonogashira, K. J. Organomet.
Chem. 2002, 653, 46.
(14) Liang, B.; Dai, M.; Chen, J.; Yang, Z. J. Org. Chem. 2005,
70, 391.
(15) Bernini, R.; Cacchi, S.; Fabrizi, G.; Forte, G.; Petrucci, F.;
Prastaro, A.; Niembro, S.; Shafir, A.; Vallribera, A. Org.
Biomol. Chem. 2009, 2270.
(16) Preparation of Polystyrene-Stabilized PdO
Nanoparticles (1)
Figure 2 TEM image of the recovered catalyst
Linear polystyrene-stabilized palladium nanoparticles 1 was
prepared according to our previous publication.12 To a
screw-capped vial with a stirring bar were added polystyrene
(9.0 mg, 85 mmol of styrene unit), Pd(OAc)2 (5.5 mg, 25
mmol), and 1.5 M aq K2CO3 solution (3 mL). After stirring
at 90 °C for 1 h, the reaction mixture was cooled to r.t. by
immediately immersing the vial in H2O (ca. 20 °C) for about
10 min. Subsequently, the aqueous phases were removed,
and recovered catalyst was washed with H2O (5 × 1.0 mL)
and MeOH (5 × 1.0 mL).
In summary, we have demonstrated the Sonogashira cou-
pling of aryl iodides with terminal alkynes using linear
polystyrene-stabilized PdO nanoparticles to give various
arylalkynes in water under copper-free conditions. This
catalyst was recovered and reused four times without any
loss of catalytic activity.
(17) Compound 1 (2.9 mg) was placed in a screw-capped vial and
then added 13 M nitric acid (5 mL). The mixture was heated
at 80 °C to dissolve completely. After cooled to r.t., the
solution was adjusted to 50 mL by H2O and then measured
the amount of Pd metal by ICP-AES analysis (15.3 ppm).
(18) The related papers discussing the effect of triethylamine as
strong base in the palladium-catalyzed Sonogashira coupling
reaction: (a) Suzuka, T.; Okada, Y.; Ooshiro, K.; Uozumi, Y.
Acknowledgment
This work was grateful to the Nanomaterials and Microdevices Re-
search Center (NMRC) of OIT for financial and instrumental sup-
ports. We wish to thank Prof. Y. Uozumi and Dr. G. Hamasaka for
assistance with the TEM measurements. We also thank Dr. T.
Synlett 2010, No. 15, 2271–2274 © Thieme Stuttgart · New York

2274
T. Teratani et al.
LETTER
Tetrahedron 2010, 66, 1064. (b) Ljungdahl, T.; Bennur, T.;
Dallas, A.; Emtenäs, H.; Mårtensson, J. Organometallics
2008, 27, 2490. (c) Nakai, Y.; Kimura, T.; Uozumi, Y.
Synlett 2006, 3065.
mg, 0.55 mmol), 1 (2.9 mg, 1.5 mol% of Pd), Et3N (152 mg,
1.5 mmol), and H2O (1.0 mL). After stirring at 80 °C for 6
h, the reaction mixture was cooled to r.t. by immediately
immersing the vial in H2O (ca. 20 °C) for about 10 min.
Subsequently, the aqueous phases were removed, and
recovered catalyst was washed with H2O (5 × 3.0 mL) and
Et2O (5 × 3.0 mL), which were then added to the aqueous
phase. The aqueous phase was extracted eight times with
Et2O. The combined organic extracts were dried over
MgSO4 and concentrated under reduced pressure. The
recovered 1 was dried in vacuo and reused. The resulting
product was analyzed by 1H NMR.
(19) Similar results have been reported: (a) Liu, C.; Yang, W.
Chem. Commun. 2009, 6267. (b) Han, W.; Liu, C.; Jin, L.
Adv. Synth. Catal. 2008, 350, 501. (c) Han, W.; Liu, C.; Jin,
Z.-L. Org. Lett. 2007, 9, 4005.
(20) General Procedure for Sonogashira Coupling (Table 2,
Entry 1)
To a screw-capped vial with a stirring bar were added
iodobenzene (52.0 mg, 0.5 mmol), phenylacetylene (56.2
Synlett 2010, No. 15, 2271–2274 © Thieme Stuttgart · New York

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