A self-supported palladium-bipyridyl catalyst for the Suzuki-Miyaura coupling in water

Article abstract of DOI:10.3987/COM-09-S(S)58

A self-supported palladium catalyst (PdCI₂BPy-Cu) was prepared via construction of a metal-organic framework (MOF) of a bipyridyl-palladium complex bearing carboxylic groups and a copper(II) linker. PdCI₂BPy-Cu efficiently catalyzed the Suzuki-Miyaura coupling of phenyl halides with arylboronic acids in water under atmospheric conditions to afford the corresponding biaryl products in high yield. The catalyst was reused four times without loss of catalytic activity.

Full text of DOI:10.3987/COM-09-S(S)58

HETEROCYCLES, Vol. 80, No. 1, 2010
505
HETEROCYCLES, Vol. 80, No. 1, 2010, pp. 505 - 514. © The Japan Institute of Heterocyclic Chemistry
Received, 17th July, 2009, Accepted, 18th August, 2009, Published online, 20th August, 2009
DOI: 10.3987/COM-09-S(S)58
A SELF–SUPPORTED PALLADIUM–BIPYRIDYL CATALYST FOR THE
SUZUKI–MIYAURA COUPLING IN WATER
Takao Osako and Yasuhiro Uozumi*
Institute for Molecular Science (IMS), 5-1 Higashiyama, Myodaiji, Okazaki,
4
44-8787, Japan. E-mail: uo@ims.ac.jp
Abstract – A self-supported palladium catalyst (PdCl BPy–Cu) was prepared via
2
construction of a metal-organic framework (MOF) of a bipyridyl-palladiumꢀ
complex bearing carboxylic groups and a copper(II) linker. PdCl BPy–Cu
2
efficiently catalyzed the Suzuki-Miyaura coupling of phenyl halides with
arylboronic acids in water under atmospheric conditions to afford the
corresponding biaryl products in high yield. The catalyst was reused four times
without loss of catalytic activity.
INTRODUCTION
The Suzuki-Miyaura coupling is one of the most important and useful reactions for the formation of
2
2
1
sp -sp carbon-carbon bonds. To date, various excellent catalyst systems for the Suzuki-Miyaura
coupling have been developed and widely utilized to synthesize biaryl compounds. From a viewpoint of
green sustainable chemistry, many researchers have recently paid much attention to recycle the catalyst
and reduce the consumption of organic solvents.
In particular, heterogeneous-switching of
homogeneous catalysts, e.g. polymeric immobilization, and aqueous-switching of organic solvents are
2
,3
recognized as the major keys for the achievement of environmentally benign Suzuki-Miyaura coupling.
Self-supported polymeric transition metal complexes have recently emerged as a new type of
4
immobilized catalysts where catalytic metal species are incorporated in the polymeric composites via
5
construction of metal-organic frameworks (MOFs) with organic ligands. Only a few self-supported
6,7
catalysts have been reported for the Suzuki-Miyaura coupling reaction so far.
We have previously
developed a 3D palladium-network complex via assembly of PdCl (CH CN) and a trisphosphine ligand
2
3
2
(
Scheme 1a) to exhibit high catalytic activity and recyclability in the Suzuki-Miyaura coupling in water to
achieve a high level of chemical greenness, where the palladium species concurrently serves as a
7
catalytically active center as well as a hub linker of the network complex. If a catalytically active

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HETEROCYCLES, Vol. 80, No. 1, 2010
transition metal complex is assembled with an external linker unit to form an insoluble polymeric
composite (Scheme 1b), the resulting composite should reflect the catalytic properties of the mother
monomeric complex to make development of a self-supported catalyst more flexible and practical. We
have previously reported that the palladium(II) trifluoroacetate complex of a bipyridyl ligand bearing
carboxylic groups assembled with copper nitrate to afford an insoluble self-supported palladium-bipyridyl
complex, which efficiently catalyzed the aerobic oxidation of benzylic alcohols in water with high
8
recyclability.
In this report, we describe the extended application of the self-supported
palladium-bipyridyl complex to the aqueous Suzuki-Miyaura coupling of phenyl halides with arylboronic
acids.
Scheme 1. Strategy for the Construction of Self-Supported Catalysts
(
a) assembly of catalytic center and organic ligand (ref 7)
+
R
PdCl (CH CN)
2
catalytic center = hub linker
2
3
trisphosphine ligand
=
3D pallladium network complex
R
R
R = O(CH
2
)
6
6 4 2
OC H PPh
(
b) assembly of metal complex and metal species (ref 8 and this study)
+
catalytic complex
external metal linker
self–supported composite
RESULTS AND DISCUSSION
The palladium(II) chloride complex coordinated with a 2,2’-bipyridyl ligand having carboxylic groups at
- and 5’-positions (PdCl BPy) was prepared by mixing PdCl and 2,2’-bipyridine-5,5’-dicarboxylic acid
5
2
2
9
(
BPy) in the presence of an excess amount of NaCl in H O at 100 °C (76% yield) (Scheme 2). The
2
self-supported palladium(II) bipyridyl complex (PdCl BPy–Cu) was obtained by treatment of PdCl BPy
2
2
and Cu(NO ) •3H O in water in the presence of Et N at room temperature for 12 h to give the desired
3
2
2
3
insoluble polymeric composite in 79% yield.
Scanning electron microscopy (SEM) analysis of PdCl BPy–Cu revealed that block-like nanoclusters
2
were assembled to form big cluster units (Figure 1a). Transmission electron microscopy (TEM) analysis
supported that the size of the block-like nanoclusters was about 10–100 nm (Figure 1b). ICP analysis

HETEROCYCLES, Vol. 80, No. 1, 2010
507
Scheme 2. Preparation of PdCl BPy–Cu
2
O
O
O
O
PdCl , NaCl
2
HO
N
N
OH
HO
N
N
OH
H
2
O, 100 °C, 12 h
Pd
Cl
Cl
76%
BPy
PdCl BPy
2
O
O
O
O
Cu(NO ) •3H O
Cu
3
2
2
N
N
Et N
3
n
Pd
H O, rt, 12 h
2
Cl
Cl
PdCl BPy–Cu
7
9%
2
Scheme 3. Representive Linkage Modes of the Copper-Carboxylate Unit
in MOF Structures
O
O
O
O
O
O
O
Cu
Cu
Cu
O
O
O
O
O
O
O
O
Cu
Cu
O
Cu
O
O
O
O
1
) linkage mode A
2) linkage mode B
(sheet MOF)
3) linkage mode C
(linear MOF)
(
porous MOF)
showed that the ratio of Pd:Cu was 1.0:0.98 in the self-supported composite. Combustion elemental
analysis revealed that the self-supported composite PdCl BPy–Cu was comprised of
2
PdCl (OC(O)-C H N-C H N-COO)Cu•4H O. Typically, the assembly of a dicarboxylate derivative and
2
5
3
5
3
2
a copper(II) ion would afford three different linkage modes of the copper-carboxylate unit in MOFs
1
0
(
Scheme 3).
The nitrogen adsorption experiment indicated that the nitrogen BET surface area of
2
–1
PdCl BPy–Cu was very small (1.99 m g ). The porous MOF structure could provide a large BET area.
2
X-ray powder diffraction (XRPD) analysis of PdCl BPy–Cu showed the diffraction pattern derived from
2
a crystalline structure having monoclinic P2/2m (#10) space group (Figure 2), though the detailed
structure of PdCl BPy–Cu was not exactly determined.
2
With the self-supported Pd(II)-bipyridyl polymeric composite in hand, we initiated to investigate the
Suzuki–Miyaura coupling reaction of phenyl halides with arylboronic acids in water. The reaction of
iodobenzene (1.0 mmol) with p-tolylboronic acid (1.5 mmol) was carried out with 0.5 mol% of
PdCl BPy–Cu in the presence of Na CO (3.0 mmol) in refluxing water (2 mL) for 6 h under atmospheric
2
2
3
conditions to afford 4-methylbiphenyl in 90% yield (Scheme 4).

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HETEROCYCLES, Vol. 80, No. 1, 2010
Figure 1. SEM (left) and TEM (right) images of PdCl BPy–Cu
2
Monoclinic P2/m (#10)
a = 16.638 Å, b = 5.522 Å, c = 16.146 Å,
ꢁ
= 115.1°, V = 1343.5 Å3
1
0
20
30
40
50
2
ꢀ / ˚
Figure 2. XRPD pattern of PdCl BPy–Cu
2
The self-supported composite also catalyzed the reaction of bromobenzene with p-tolylboronic acid to
give 4-methylbiphenyl in 90% yield. However, the reaction of chlorobenzene gave only a 2% yield of
the product even for longer reaction time (10 h).
Scheme 4. Suzuki-Miyaura Coupling of Phenyl Halides with p-Tolylboronic Acid
with PdCl BPy–Cu
2
PdCl BPy–Cu (0.5 mol%)
2
X
+
(HO)2B
Me
Me
Na CO (3.0 mmol)
2
3
H O (2 mL), 100 °C
2
(
X = I, Br)
.0 mmol
6
h, air
90% yield (X = I)
1
1.5 mmol
90% yield (X = Br)
2% yield (X = Cl, 10 h)

HETEROCYCLES, Vol. 80, No. 1, 2010
509
The scope of arylboronic acids was examined for the Suzuki–Miyaura coupling with phenyl halides in
water using the self-supported catalyst PdCl BPy–Cu. Representative results are summarized in Table 1.
2
PdCl BPy–Cu efficiently catalyzed the coupling of iodobenzene and bromobenzene with phenylboronic
2
acid to afford biphenyl in 99% and 91% yield, respectively (entries 3 and 4). The coupling reaction of
various arylboronic acids bearing both electron-donating and electron-withdrawing p-substituents also
proceeded to give the corresponding p-substituted biphenyls in 76–97% yield (entries 5–14). Ortho- and
meta-substituted arylboronic acids were tolerated for the reaction (77–93% yield in entries 15–18).
1
1
-Naphthylboronic acid also underwent the Suzuki-Miyaura coupling with phenyl halides to give
-phenylnaphthalene in 75% yield (entries 19 and 20).
The recyclability of the insoluble self-supported catalyst PdCl BPy–Cu was examined for the
2
Suzuki–Miyaura coupling reaction of iodobenzene with p-tolylboronic acid (Scheme 5). Thus, after the
first reaction, which gave 90% of 4-methylbiphenyl, the catalyst was recovered by centrifugation, washed
with H O, dried under vacuum, and successively subjected to a second, third, fourth, and fifth reaction
2
under the same conditions to afford 4-methylbiphenyl in 94%, 98%, 94%, and 93% yield, respectively
(
Scheme 5). TEM analysis of the recovered catalyst after the reaction showed the block nanoclusters (ca.
00 nm) were assembled to form the big clusters and the palladium nanoparticles (ca. 5 nm) were
1
generated in the clusters (Figure 3).
Scheme 5. Catalyst Recycling Experiment
PdCl BPy–Cu (0.5 mol%)
2
I
+
(HO)2B
Me
Me
90% yield (1st run)
Na CO (15.0 mmol)
2
3
H O (10 mL), 100 °C
2
5.0 mmol
7.5 mmol
6
h, air
94% yield (2nd run)
98% yield (3rd run)
94% yield (4th run)
93% yield (5th run)
In conclusion, we have developed a novel self-supported catalyst PdCl BPy–Cu via mixing a
2
palladium-bipyridyl complex bearing carboxylic groups at the 5- and 5’ positions and a copper(II) ion,
which efficiently catalyzed the Suzuki-Miyaura coupling of phenyl halides with arylboronic acids in
water under atmospheric conditions to give the corresponding biaryls with high recyclability. Further
extensive scope for the Suzuki-Miyaura reaction and the application of this catalyst to the other organic
transformations are in progress in our lab.

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HETEROCYCLES, Vol. 80, No. 1, 2010
Figure 3. TEM images of the recovered catalyst after the reaction.
Table 1. Suzuki–Miyaura Coupling of Phenyl Halides with Arylboronic
a
Acids Catalyzed by PdCl BPy–Cu in Water
2
PdCl BPy–Cu (0.5 mol%)
R
2
R
X
+
(HO)2B
Na CO (3.0 mmol)
2
3
H O (2 mL), 100 °C
2
(
X = I, Br)
6
h, air
1.0 mmol
1.5 mmol
b
entry phenyl halide
arylboronic acid
product
yield / %
90
1
2
3
4
5
6
7
8
9
0
1
2
I
(HO)
(HO)
(HO)
(HO)
(HO)
(HO)
(HO)
(HO)
(HO)
(HO)
(HO)
(HO)
B
2
Me
Me
Br
I
B
Me
Me
90
99
91
79
89
91
76
94
95
95
94
2
B
2
Br
I
B
2
B
2
OMe
OMe
Ph
OMe
OMe
Ph
Br
I
B
2
B
2
Br
I
B
2
Ph
Ph
B
B
B
B
t-Bu
t-Bu
t-Bu
t-Bu
2
2
2
2
1
1
1
Br
I
CF
CF
3
3
Br
CF
CF
3
3

HETEROCYCLES, Vol. 80, No. 1, 2010
511
1
3
4
I
(HO)
2
B
CN
CN
95
97
1
Br
I
(HO)
B
2
CN
CN
(HO)2B
(HO)2B
(HO)2B
(HO)2B
(HO)2B
15
16
17
18
93
87
77
93
Me
Me
Br
Me
Me
I
Me
Me
Br
Me
Me
I
1
2
9
0
75
75
Br
(HO)2B
a
All the reactions were carried out with 0.5 mol% of the catalyst and
Na CO (3 equiv) in water (2 mL) at 100 °C for 6 h under atmospheric
2
3
b
conditions. GC yield.
EXPERIMENTAL
General.
All chemicals were commercially available and used without further purification.
9
2
,2’-Bipyridine-5,5’-dicarboxylic acid (BPy) was prepared according to the reported procedure. Water
1
13
1
was deionized with a Millipore system as a Milli-Q grade. H and C{ H} NMR spectra were recorded
on a JEOL JNM-AL500 spectrometer. GC analysis was carried out on a Hewlett Packard 4890 system.
GC-MS was measured with an Agilent 6890 GC/5973 N MS detector. IR spectra were recorded on a
JASCO FT/IR 460 Plus spectrometer. SEM images were obtained by a JEOL JSM-6700F scanning
electron microscope. TEM images were obtained by a JEOL JEM-2100F transmission electron
microscope. ICP analysis was performed on a LEEMAN LABS Profile plus plasma spectrometer.
Elemental analysis was conducted on a Yanaco CHN Corder MT-6 elemental analyzer. XRPD analysis
was carried out on a Rigaku RINT-Ultima III powder X-ray diffractometer. Nitrogen adsorption was
analyzed on a BEL BELSORP-mini II.
Synthesis:

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HETEROCYCLES, Vol. 80, No. 1, 2010
PdCl BPy. A suspension of PdCl (0.35 g, 2.0 mmol), NaCl (1.16 g, 200 mmol), and BPy (0.49 mg, 2.0
2
2
mmol) in H O (40 mL) was heated at 100 ˚C for 12 h. After being cooled, the resulting solid was
2
collected by filtration, washed with H O (10 mL x 3), and dried under vacuum to give a pale yellow
2
1
powder (0.64 g, 75.6%). H NMR (500 MHz, D O, NaOD): ꢀ 8.63 (d, J = 2.0 Hz, 2H, H ), 8.43 (d, J
2
Py-6
–
1
=
8.5 Hz, 2H, H ), 8.21 (d, J = 8.5 Hz, 2H, H ). FT-IR/cm (ATR): 3029, 3015, 2996, 2975, 2958,
Py-3 Py-4
2
6
363, 2340, 2005, 1701, 1611, 1542, 1424, 1413, 1400, 1256, 1139, 1051, 944, 868, 856, 823, 760, 683,
–
1
60, 570 cm . Anal. Calcd for PdCl BPy•2H O (C H Cl N O Pd): C, 31.50%; H, 2.64%; N, 6.12%.
2
2
12 12
2
2
6
Found: C, 31.48%; H, 2.17%; N, 6.16%.
PdCl BPy–Cu. A mixture of PdCl BPy (211 mg, 0.5 mmol), Et N (101 mg, 1.0 mmol),
2
2
3
Cu(NO ) •3H O (362 mg, 1.5 mmol), and H O (20 mL) was stirred for 12 h at room temperature. The
3
2
2
2
resulting solid was collected by filtration, washed by H O (5 mL x 3) and acetone (5 mL x 3) and dried
2
under vacuum to give a green solid (191 mg, 79%). FT-IR (ATR): 3511, 3427, 2360, 2342, 1616, 1563,
–
1
1
415, 1318, 1138, 1047, 857, 768, 739, 710, 600, 592, 584, 572, 562 cm .ꢀꢀICP analysis showed the
ratio of Pd:Cu was 1.0:0.98. Anal. Calcd for PdCl BPy–Cu•4H O (C H N O Cl PdCu): C, 25.96%; H,
2
2
12 14
2
8
2
2
.54%; N, 5.05%. Found: C, 26.22%; H, 2.81%; N, 5.16%.
General Procedure for the Suzuki–Miyaura Coupling of Boronic Acids with Pheny Halides in
Water with PdCl BPy–Cu. A mixture of phenyl halide (1.0 mmol), arylboronic acid (1.5 mmol),
2
PdCl BPy–Cu (2.41 mg, 5.0 μmol), Na CO (249.0 mg, 3.0 mmol), and water (2 mL) was stirred at
2
2
3
1
00 °C for 6 h under air. After being cooled, the resulting mixture was extracted with EtOAc (1 mL x 5).
The extract was analyzed with GC and GC–MS. The yields of the products were determined by GC
with an internal standard (mesitylene). The chemical identification of the product was performed using
the NIST Mass Spectral Search Program Ver. 1.6d for Windows unless otherwise noted.
All products are known compounds whose CAS registry numbers are provided as below:
4
4
4
1
1
-Methylbiphenyl: 644-08-6 (Table 1, entries 1 and 2); biphenyl: 92-52-4 (entries 3 and 4);
-methoxybiphenyl: 613-37-6 (entries 5 and 6); p-terphenyl: 92-94-4 (entries 7 and 8);
-tert-butylbiphenyl: 1625-92-9 (entries 9 and 10); 4-(trifluoromethyl)biphenyl: 398-36-7 (entries 11 and
2); 4-phenylbenzonitrile: 2920-38-9 (entries 13 and 14); 3-methylbiphenyl: 643-93-6 (entries 15 and
6); 2-methylbiphenyl: 643-58-3 (entries 17 and 18); 1-phenylnaphthalene: 605-02-7 (entries 19 and 20).
Catalyst Recycling Experiment. A mixture of phenyl iodide (1.02 g, 5.0 mmol), p-tolylboronic acid
1.02 g, 7.5 mmol), PdCl BPy–Cu (12.1 mg, 25.0 μmol), and Na CO (1.25 g, 15.0 mmol) in water (10
(
2
2
3
mL) was stirred at 100 °C for 6 h under air. After being cooled, ethyl acetate (5 mL) was added to the
reaction mixture, which then stirred vigorously. The ethyl acetate layer was decanted and analyzed by
GC to determine the yield. The aqueous layer was centrifugated at 4000 rpm for 5 min. After
concentration in vacuo, the resulting black powder was subjected to the next reaction.

HETEROCYCLES, Vol. 80, No. 1, 2010
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ACKNOWLEDGEMENTS
This work was financially supported by the MEXT (Science Research on Priority Areas, no. 460) and the
NEDO (GSC Project).
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