A reusable palladium(II)/cationic 2, 2-bipyridyl catalytic system for hydroxycarbonylation of aryl iodides in water

Article abstract of DOI:10.1002/jccs.201200595

A water-soluble palladium(II)/cationic 2, 2′-bipyridyl system was utilized to catalyze hydroxycarbonylation of aryl iodides in the presence of a pressurized CO atmosphere under a basic aqueous solution at 100 °C. The residual aqueous solution could be reused in several times with only a slight decrease in catalytic activity. Thus, it reduced wastage of the precious metal in the reaction. A variety of aromatic carboxylic acids could still be obtained in high yields with the catalytic amount to 0.01 mol%.

Full text of DOI:10.1002/jccs.201200595

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
A Reusable Palladium(II)/Cationic 2,2¢-Bipyridyl Catalytic System for
Hydroxycarbonylation of Aryl Iodides in Water
Sheng-Wen Tsai, Shao-Hsien Huang, Han-Sheng Lee and Fu-Yu Tsai*
Institute of Organic and Polymeric Materials, National Taipei University of Technology, 1, Sec. 3, Chung-Hsiao E. Rd.,
Taipei 106, Taiwan
(Received: Nov. 14, 2012; Accepted: Dec. 28, 2012; Published Online: Feb. 1, 2013; DOI: 10.1002/jccs.201200595)
A water-soluble palladium(II)/cationic 2,2¢-bipyridyl system was utilized to catalyze hydroxycarbonyla-
tion of aryl iodides in the presence of a pressurized CO atmosphere under a basic aqueous solution at 100
°C. The residual aqueous solution could be reused in several times with only a slight decrease in catalytic
activity. Thus, it reduced wastage of the precious metal in the reaction. A variety of aromatic carboxylic
acids could still be obtained in high yields with the catalytic amount to 0.01 mol%.
Keywords: Reusable catalyst; Palladium; Cationic 2,2¢-bipyridyl; Hydroxycarbonylation; Water.
INTRODUCTION
Palladium-catalyzed hydroxycarbonylation of aryl
phase for reuse.
We have recently utilized PdCl2(NH3)2 to associate
halides in the presence of a carbon monoxide atmosphere is
a common method for the preparation of aromatic carbox-
ylic acids.1 Generally, a basic aqueous–organic two–phase
solvent system is used for the reaction, which may lead to
difficult separation and recycling of the catalyst from the
product for the further reuse.2 Therefore, a reusable palla-
dium catalyst for hydroxycarbonylation of aryl halides is
highly valuable with regards to economic and environmen-
tal concerns. Leadbeater’s group reported microwave-pro-
moted hydroxycarbonylation of aryl iodides catalyzed by
palladium salts in water with loading amounts of either
0.01 mol% or 1 mol%; however, the reuse of the catalyst
was not studied.3 An amphiphilic resin-supported phos-
phine-palladium complex4 and a nanoparticle-supported
palladium complex5 can serve as recyclable catalysts for
the hydroxycarbonylation of aryl halides under aqueous al-
kaline conditions, but a high catalyst loading (3 and 2
mol%, respectively) is required for the reactions. Recently,
ionic liquids have also been employed as green solvents for
palladium-catalyzed hydroxycarbonylation of aryl halides
for the purpose of reuse.6 In these reactions, an excess
amount of water is still required. A basic aqueous environ-
ment is necessary for Pd-catalyzed hydroxycarbonylation
of aryl halides. Hence, it would be useful to develop a wa-
ter-soluble, highly efficient and reusable palladium cata-
lytic system to achieve hydroxycarbonylation of aryl
halides using neat water as the reaction medium, in which
there is no need to separate the catalyst from the aqueous
with cationic 2,2¢-bipyridyl ligand (Figure 1, denoted L) to
form a water-soluble catalytic system for C–C bond cou-
pling reactions in water under air.7 As part of our continu-
ing studies on this highly efficient and reusable catalytic
system, we report here that our catalytic system can not
only catalyze hydroxycarbonylation of aryl iodides, giving
high yields of aromatic carboxylic acids at a very low cata-
lyst loading level, but can also be reused several times with
only a slight decrease in activity, rendering this hydroxy-
carbonylation reaction green and economic.
EXPERIMENTAL
General. All chemicals were purchased from commercial
suppliers and were used without further purification. The cationic
2,2¢-bipyridyl ligand was prepared according to our previous pub-
lished procedure.7a,b The catalytic aqueous solution was prepared
by mixing equal molar amounts of L and PdCl2(NH3)2 in water at
1
room temperature and was stored in air. All H and 13C NMR
spectra were recorded in CDCl3 or d6-DMSO at 25 °C on a Bruker
300 or 400 NMR spectrometer.
Typical procedure for the hydroxycarbonylation of aryl
iodides. In a fume hood, to a 25 mL stainless autoclave equipped
Br Me3N
NMe3
Br
N
N
L
Fig. 1. Cationic 2,2¢-bipyridyl ligand (L).
Special Issue Dedicated to Prof. Yu Wang in Honor of Her 70th Birthday
* Corresponding author. Fax: +886-2-2731-7174; E-mail: fuyutsai@ntut.edu.tw
J. Chin. Chem. Soc. 2013, 60, 769-772
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Article
Tsai et al.
with a magnetic stirrer bar was added aryl iodide (1.0 mmol),
Na2CO3 (1.2 mmol), and H2O (3 mL). After the addition of
PdCl2(NH3)2/L aqueous solution (1 mL; 1 ´ 10-3 mmol in 1 mL
H2O for Tables 1 and 2 and 1 ´ 10-4 mmol in 1 mL H2O for Table
3), the reaction mixture was pressurized with CO (10 atm). The
reaction vessel was then placed in an oil bath at 100 °C for 9 h (for
Tables 1 and 2) or 24 h (for Table 3). After cooling of the reaction
mixture to room temperature, CO gas was released in the fume
hood and the aqueous solution was transferred to a test tube. This
aqueous solution was added to 3 N HCl aqueous solution (2 mL)
and then extracted with EtOAc (3 ´ 5 mL), the combined organic
phase was dried over MgSO4, and the solvent was then removed
under vacuum. Column chromatography on silica gel afforded the
desired product. All known hydroxycarbonylation products ob-
tained were pure, and their spectra (1H, and 13C NMR) were in
agreement with authentic samples.
166.2. 2-Toluic acid (2h)8. 1H NMR (CDCl3, 400 MHz) d 2.65 (s,
3H), 7.25–7.29 (m, 2H), 7.42–7.46 (m, 1H), 8.05–8.07 (m, 1H);
13C NMR (CDCl3, 100 MHz) d 22.1, 125.9, 128.4, 131.6, 131.9,
1
132.9, 141.4, 173.1. 2-Methoxybenzoic acid (2i)10. H NMR
(CDCl3, 300 MHz) d 4.05 (s, 3H), 7.03–7.13 (m, 2H), 7.52–7.58
(m, 1H), 8.14 (d, J = 7.8 Hz, 1H); 13C NMR (CDCl3, 75 MHz) d
56.8, 111.8, 117.7, 122.3, 133.6, 135.3, 158.2, 165.8. 3-Toluic
acid (2j)11. 1H NMR (CDCl3, 300 MHz) d 2.41 (s, 3H), 7.32–7.43
(m, 2H), 7.90–7.93 (m, 2H); 13C NMR (CDCl3, 75 MHz) d 21.3,
127.4, 128.4, 129.2, 130.7, 134.6, 138.3, 172.6. 3-Methoxyben-
1
zoic acid (2k)11. H NMR (CDCl3, 300 MHz) d 3.85 (s, 3H),
7.13–7.17 (m, 1H), 7.37 (t, J = 8.1 Hz, 1H), 7.61 (d, J = 1.2 Hz,
1H), 7.70–7.73 (m, 1H); 13C NMR (CDCl3, 75 MHz) d 55.5,
114.4, 120.5, 122.7, 129.6, 130.6, 159.6, 172.3. 3,5-Dimethyl-
benzoic acid (2l)11. 1H NMR (CDCl3, 300 MHz) d 2.37 (s, 6H),
7.23 (s, 1H), 7.72 (s, 2H); 13C NMR (CDCl3, 75 MHz) d 21.2,
127.9, 129.1, 135.5, 138.2, 172.7. 1-Naphthoic acid (2m)11. 1H
NMR (CDCl3, 300 MHz) d 7.52–7.58 (m, 2H), 7.63–7.68 (m,
1H), 7.91 (d, J = 7.8 Hz, 1H), 8.09 (d, J = 8.1 Hz, 1H), 8.41 (d, J =
7.5 Hz, 1H), 9.09 (d, J = 8.7 Hz, 1H); 13C NMR (CDCl3, 75 MHz)
d 124.6, 125.6, 125.9, 126.4, 128.2, 128.8, 131.7, 131.9, 133.9,
134.7, 173.1.
Typical procedure for the reuse of the catalytic aqueous
solution. The reaction was conducted following the procedure
described previously under the reaction conditions shown in Ta-
ble 2. After transferring the resulting aqueous solution to a test
tube, it was extracted with EtOAc (3 ´ 5 mL). The combined or-
ganic phase was washed with 3 N HCl aqueous solution and then
dried over MgSO4. The pure product was isolated by column
chromatography. The residual aqueous solution was then trans-
ferred to the stainless autoclave and charged with 1c, Na2CO3, and
CO for the next reaction.
RESULTS AND DISCUSSION
We initiated our investigation by examining the ef-
fects of bases in the hydroxycarbonylation of aryl iodides,
and the influences of reaction temperature and CO pressure
on the reaction were not investigated. As shown in Table 1,
hydroxycarbonylation of iodobenzene 1a catalyzed by 0.1
mol% of PdCl2(NH3)2/L in the presence of 1.2 equiv Bu3N
and CO (10 atm) in water at 100 °C for 6 h led to no forma-
tion of benzoic acid 2a (Entry 1). Hence, Bu3N was re-
placed by several inorganic bases to improve the reaction.
Among the inorganic bases screened, 2a was delivered in
yields between 21% and 76% (Entries 2–6), and Na2CO3
was found to be the best base (Entry 6). We further pro-
longed the reaction time to 9 h using Na2CO3 as the base,
which furnished 2a in a 93% isolated yield (Entry 7). The
presence of the cationic 2,2¢-bipyridyl ligand is critical in
this Pd-catalyzed hydroxycarbonylation reaction, as only
5% of 2a was obtained in the absence of this ligand (Entry
8). Unfortunately, this catalytic system could not catalyze
hydroxycarbonylation of bromobenzene, even when acti-
vated 4-bromoacetophenone was employed (Entries 9 and
10).
1
Benzoic acid (2a)8. H NMR (CDCl3, 300 MHz) d 7.44-
7.49 (m, 2H), 7.58–7.63 (m, 1H), 8.11 (d, J = 8.1 Hz, 2H); 13C
NMR (CDCl3, 75 MHz) d 128.5, 129.3, 130.2, 133.9, 172.2. 4-
Methylbenzoic acid (2b)8. 1H NMR (CDCl3, 300 MHz) d 2.45 (s,
3H), 7.30 (d, J = 8.0 Hz, 2H), 8.03 (d, J = 8.0 Hz, 2H); 13C NMR
(CDCl3, 75 MHz) d 21.8, 126.6, 129.2, 130.3, 144.7, 172.6. 4-
Methoxybenzoic acid (2c)8. 1H NMR (CDCl3, 400 MHz) d 3.88
(s, 3H), 6.95 (d, J = 9.0 Hz, 2H), 8.07 (d, J = 9.0 Hz, 2H); 13C
NMR (CDCl3, 100 MHz) d 55.5, 113.8, 121.6, 132.4, 164.0,
171.5. 4-Hydroxybenzoic acid (2d)5. 1H NMR (d6-DMSO, 400
MHz) d 6.81 (d, J = 6.4 Hz, 2H), 7.78 (d, J = 6.4 Hz, 2H), 10.17
(br, 1H); 13C NMR (d6-DMSO, 100 MHz) d 115.6, 121.9, 132.0,
162.0, 167.6. 4-Fluobenzoic acid (2e)9. 1H NMR (d6-DMSO, 300
MHz) d 7.11–7.24 (m, 2H), 8.10–8.14 (m, 2H); 13C NMR (d6-
DMSO, 75 MHz) d 116.1 (d, J = 21.8 Hz), 127.8, 132.6 (d, J = 9.8
Hz), 163.7, 166.9 (d, J = 13.5 Hz). 4-Chlorobenzoic acid (2f)8.
1H NMR (d6-DMSO, 400 MHz) d 7.56 (d, J = 8.6 Hz, 2H), 7.94 (d,
J = 8.6 Hz, 2H); 13C NMR (d6-DMSO, 100 MHz) d 134.0, 134.9,
1
136.4, 143.0, 171.7. 4-Nitrobenzoic acid (2g)9. H NMR (d6-
DMSO, 300 MHz) d 8.16 (d, J = 8.7 Hz, 2H), 8.32 (d, J = 8.7 Hz,
2H); 13C NMR (d6-DMSO, 75 MHz) d 124.2, 131.2, 136.8, 150.5,
After the best base for hydroxycarbonylation of aryl
iodides was identified, the reusability of the aqueous cata-
770
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J. Chin. Chem. Soc. 2013, 60, 769-772

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CHEMICAL SOCIETY
Reusable Pd Catalyst for Hydroxycarbonylation
Table 1. Base effects in the hydroxycarbonylation of iodoben-
zene (1a) catalyzed by PdCl2(NH3)2/L in water[a]
Table 3. PdCl2(NH3)2/L-catalyzed hydroxycarbonylation of aryl
iodides in water[a]
I
I
COOH
COOH
PdCl2(NH3)2/L (0.1 mol%)
base, CO, H2O, 100 o
PdCl2(NH3)2/L (0.01 mol%)
R
R
Na2CO3, CO, H2O, 100 oC, 24 h
C
1a
2a
2
1
Entry
Base
Time (h)
Yield (%)[b]
Entry
1
Aryl iodide
Product
Yield (%)[b] TON
1
Bu3N
KOH
6
6
6
6
6
6
9
9
9
9
0
21
41
52
45
76
93
5
I
COOH
2
99
9900
3
K3PO4·H2O
NaHCO3
K2CO3
1a
2a
2b
2c
2d
2e
2f
4
I
COOH
COOH
COOH
COOH
5
2
82
93
83
74
65
76
71
8200
9300
8300
7400
6500
7600
7100
6
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Me
Me
MeO
HO
1b
7
I
8
9[c]
10[d]
0
3
MeO
HO
0
1c
1d
1e
1f
I
[a] Reaction conditions: 1a (1 mmol), PdCl2(NH3)2/L (0.1
mol%), base (1.2 mmol), CO (10 atm), and H2O (4 mL) at
100 °C.
4[c]
[b] Isolated yields.
I
[c] Bromobenzene was used instead of 1a.
[d] 4-Bromoacetophenone was used instead of 1a.
5
F
F
I
COOH
COOH
6
Table 2. Reuse studies of PdCl2(NH3)2/L-catalyzed hydroxycar-
bonylation of 4-iodoanisole (1c) in water[a]
Cl
Cl
I
I
COOH
PdCl2(NH3)2/L (0.1 mol%)
Na2CO3, CO, H2O, 100 o
7
O2N
O2N
C
MeO
MeO
1g
1h
2g
COOH
1c
2c
I
Run Yield (%)[b] TON
Run
Yield (%)[b]
TON
8
Me
Me
2h
COOH
1
2
3
4
5
93
88
85
82
80
930
880
850
820
800
6
79
74
790
740
760
560
7130
I
7
9
82
86
76
8200
8600
7600
8
9
76
OMe
OMe
56
2i
1i
1j
Me
MeO
Me
I
Me
MeO
Me
COOH
COOH
COOH
Overall
713
10
11
[a] Reaction conditions: 1c (1 mmol), PdCl2(NH3)2/L (0.1 mol%),
Na2CO3 (1.2 mmol), CO (10 atm), and H2O (4 mL) at 100 °C
2j
I
for 9 h.
[b] Isolated yields.
1k
2k
I
lytic system was then evaluated. 4-Iodoanisole 1c was used
as the reactant under the reaction conditions shown in Ta-
ble 1, Entry 7. As illustrated in Table 2, after extraction of
the reaction mixture with EtOAc at the end stage of the ini-
tial run (Run 1), the residual aqueous solution was able to
be reused for the same reaction at least 8 times with only a
slight decrease in activity in each reuse run. It gave overall
yields of 713%, corresponding to turnover numbers (TON)
of 7130 and an average yield of 79% for each reuse run. In
comparison with hydroxycarbonylation of iodobenzene in
12
13
85
90
8500
9000
Me
Me
1l
2l
COOH
I
1m
2m
[a] Reaction conditions: 1 (1 mmol), PdCl2(NH3)2/L (0.01
mol%), Na2CO3 (1.2 mmol), CO (10 atm), and H2O (4 mL) at
100 °C for 24 h.
[b] Isolated yields.
[c] Na2CO3 (2.2 mmol) was used.
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Article
Tsai et al.
ionic liquid under an identical catalyst loading,6 our cata-
lytic system showed excellent stability during the reuse ex-
periments. The slow gradual decrease in the product yield
in each reuse run may be mainly due to the loss of catalyst
concentration upon successive extraction with EtOAc and
transfer of the aqueous catalytic solution between auto-
clave and test tube in each reuse run. However, the possibil-
ity of gradual deactivation of the catalyst during each reuse
run may not be excluded.
ACKNOWLEDGEMENTS
The research was financially supported by the Na-
tional Science Council of Taiwan (NSC98-2113-M-027-
001-MY3).
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The results of the reuse studies encouraged us to fur-
ther reduce the catalyst loading to 0.01 mol%. To our de-
light, under the reaction conditions shown in Table 3, 1a
was transformed to 2a completely in 24 h, providing an iso-
lated yield of 99%, corresponding to a TON of 9900 (Entry
1). When various para-substituted aryl iodides were em-
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1i, were employed, 71% and 82% yields were obtained, re-
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tuted aryl iodides and 1-iodonaphthalene, 1j–1m, the hy-
droxycarbonylation reaction took place smoothly, resulting
in the formation of corresponding aromatic carboxylic ac-
ids 2j–2m in yields between 76% and 90% (Entries 10–
13).
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CONCLUSIONS
We have shown here that hydroxycarbonylation of
aryl iodides catalyzed by a water-soluble PdCl2(NH3)2/
cationic 2,2¢-bipyridyl catalytic system gives aromatic car-
boxylic acids in high yields at a very low catalyst loading
level (0.01 mol%). This water-compatible catalytic system
enables easy separation from the organic product by simple
extraction, and the residual aqueous solution can be reused
for further reactions, which reduces wastage of the pre-
cious metal.
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J. Chin. Chem. Soc. 2013, 60, 769-772