Cross-linked polymer supported palladium catalyzed carbonylative Sonogashira coupling reaction in water

Article abstract of DOI:10.1016/j.tetlet.2011.01.095

A cross-linked polymer-supported ionic liquid immobilized palladium catalyst, which is prepared by reaction of the Pd(OAc)₂ with copolymer of 3-butyl-1-vinylimidazolium iodide and divinylbenzene, was well characterized and employed as an effective heterogeneous catalyst for carbonylative Sonogashira coupling reaction of aryl iodides with terminal alkynes in water, affording the corresponding α,β-alkynyl ketones in good to excellent yields. The catalytic system not only solves the basic problem of homogeneous palladium catalyst recovery and reuse but also avoids the use of toxic phosphine ligands. The stability of supported palladium was also discussed.

Full text of DOI:10.1016/j.tetlet.2011.01.095

Tetrahedron Letters 52 (2011) 1587–1591
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Cross-linked polymer supported palladium catalyzed carbonylative
Sonogashira coupling reaction in water
Yan Wang a,b, Jianhua Liu a, , Chungu Xia a,
⇑
⇑
a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, No. 18 Tianshui Middle Road,
Lanzhou 730000, China
b Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, No. 19 Yuquan Road, Beijing 100049, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A cross-linked polymer-supported ionic liquid immobilized palladium catalyst, which is prepared by
reaction of the Pd(OAc)2 with copolymer of 3-butyl-1-vinylimidazolium iodide and divinylbenzene,
was well characterized and employed as an effective heterogeneous catalyst for carbonylative Sonogash-
Received 9 December 2010
Revised 12 January 2011
Accepted 21 January 2011
Available online 27 January 2011
ira coupling reaction of aryl iodides with terminal alkynes in water, affording the corresponding a,b-alky-
nyl ketones in good to excellent yields. The catalytic system not only solves the basic problem of
homogeneous palladium catalyst recovery and reuse but also avoids the use of toxic phosphine ligands.
The stability of supported palladium was also discussed.
Keywords:
Supported catalyst
Palladium
Ó 2011 Elsevier Ltd. All rights reserved.
Carbonylative Sonogashira coupling
Recyclable
Water
From an environmental and economic point of view, the use of
volatile organic compounds as solvents for chemical transforma-
tions is under critical discussion and alternatives, such as scCO2,1
ionic liquids,2 or water3 are actively studied.4 Since the RCH/RP
hydroformylation process was carried out in an aqueous-organic
solvent mixture,5 water has been receiving special attention as a
cheap and non-toxic solvent.
their advantages such as more easily separated from products and
recycled, thus providing an environmentally cleaner process. In re-
cent years, immobilization of catalysts on suitable supports has
been a topic of interest, especially; immobilization of catalyst onto
ionic liquid containing polymers10 sharing some properties of ionic
liquids has been studied. For example, Han and coworkers11 syn-
thesized copolymer PDVB-IL from imidazolium IL with an amine
group with cross-linker divinylbenzene, which was used for the
immobilization of Pd nanoparticles for Heck reaction. However,
to the best of our knowledge, there has been no general study of
carbonylation reactions catalyzed by ionic liquid containing poly-
mers supported palladium catalysts.
In the framework of our continuous efforts for effective and
green processes for the carbonylative Sonogashira coupling reac-
tion,9,12 herein we report the synthesis of a cross-linked copolymer
P(DVB-IL) supported palladium catalyst and illustrate its applica-
tion in the carbonylative Sonogashira coupling reaction of aryl
a,b-Alkynyl ketones are important carbonyl compounds, which
appear in many biologically active molecules and also play crucial
roles as intermediates in the synthesis of natural products.6 An
atom economic route to prepare these compounds is carbonylative
Sonogashira coupling reaction: metal-catalyzed direct coupling of
aryl halides with terminal alkynes in the presence of carbon mon-
oxide.7 In the early reports, considerable efforts have been ad-
dressed to this reaction.8 But the most restricting aspect of these
studies is that they were focused on homogeneous catalytic sys-
tems together with phosphine ligands. Recently, our group had
developed the first heterogeneous catalyst based on palladium on
charcoal (Pd/C) with good catalytic efficiency for the carbonylative
coupling reactions.9 Although the recycle of expensive transition
metal catalyst was achieved, its catalytic performance was still
not so efficient. Consequently, it is necessary to investigate another
efficient, recyclable, and environmentally benign catalyst system
for the reaction. It is well known that heterogeneous catalysts have
iodides with terminal alkynes to form
water.
a,b-alkynyl ketones in
The route to synthesize the ionic liquid composite material
supported palladium catalyst13 is schematically described in
Scheme 1.
P(DVB-IL) and P(DVB-IL)-Pd catalyst were characterized by
thermogravimetric analysis (TGA). The thermograms are shown
in Figure 1. The small weight loss of P(DVB-IL) before 210 °C under
an argon atmosphere was attributed to the loss of the adsorbed
water. It can be seen from the two thermograms that the weight
loss between 210 °C and 410 °C was due to the elimination of the
⇑
Corresponding authors. Fax: +86 931 8277088 (J.L.).
E-mail addresses: jhliu@licp.cas.cn (J. Liu), cgxia@licp.cas.cn (C. Xia).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.01.095

1588
Y. Wang et al. / Tetrahedron Letters 52 (2011) 1587–1591
The catalyst P(DVB-IL)-Pd was also characterized by X-ray pho-
N
N
toelectron spectroscopy (XPS) before reaction and the results are
shown in Figure 3. Obviously, C, O, N, I, and Pd appeared on the
activated surfaces (Fig. 3a). It can be seen that the Pd 3d spectrum
was resolved into two spin–orbit pairs with binding energies of
338.0 eV and 343.3 eV, respectively, which are assigned to electron
transitions of 3d5/2 and 3d3/2 of Pd2+ (Fig. 3b). On the basis of pre-
vious measurements, the Pd 3d5/2 signal for PdI2 was reported at
336.2 eV and the Pd 3d5/2 signal for Pd(OAc)2 was reported at
338.6 eV. And electron transition of the O 3d5/2 in the catalyst is
shown at 533.0 eV, which is consistent with standard spectrum O
of acetate. So we can speculate there may be an electrostatic inter-
action between the Pd atoms with the iodine atoms and the oxygen
atoms of acetate. In other words, the Pd atom may form a bond
with iodine atom, oxygen atom, and the support, Pd particle was
immobilized on the cross-linked polymer through a covalent bond-
ing as the supported palladium N-heterocyclic carbene (NHC). The
content of Pd in the catalyst was 3.13 wt % (0.295 mmol gÀ1), as
determined by the AAS analysis.
DVB
N
N
+
I
AIBN
I
*
*
N
N
Pd(OAc)2
DMSO
I
P(DVB-IL)-Pd
*
*
*
Scheme 1. Synthesis of the cross-linked polymer supported palladium.
The catalytic activity of P(DVB-IL)-Pd was examined for its abil-
ity to catalyze the carbonylative Sonogashira coupling. In order to
optimize the reaction conditions, the carbonylative coupling of
iodobenzene and phenylacetylene was carried out with P(DVB-
IL)-Pd as a model reaction. Different solvent, base, reaction temper-
ature, and time were investigated (Table 1). The solvent plays an
important role in the reaction: when the reaction was performed
in acetonitrile, THF and acetone, the isolated yields reached 62%,
85%, 46% (Table 1, entries 2, 3 and 5). Toluene and H2O both lead
to the yield of
a,b-alkynyl ketones in excellent yield (Table 1, en-
tries 1 and 4). Therefore, water was chosen as a non-toxic solvent
and the best mediate. Noteworthy, Et3N was the most suitable base
for the water system. Increasing the reaction temperature and time
also had a positive effect on the catalytic activity (Table 1, entries
8–11).
Figure 1. The thermogram of P(DVB-IL)-Pd under nitrogen at a heating rate of
10 °C/min.
With water as the solvent, 0.5 mmol % Pd catalyst loading, start-
ing with terminal alkynes and aryl iodides, we carried out the car-
bonylative Sonogashira coupling reaction under 3.0 MPa CO with
Et3N as the base. To explore the generality and scope of the car-
bonylative coupling reaction, we evaluated various aryl iodides
and terminal alkynes as substrates.14,15 The results are given in
Table 2. A wide range of aryl iodides bearing an electron-withdraw-
ing group or an electron-donating group all gave corresponding
carbonyl products in excellent yields when they react with phenyl-
acetylene (entries 1–13). Iodobenzenes containing substituents at
the 2-position gave poorer results because of the steric influence
(entry 3). 2-Iodoanisole, 3-iodoanisole, and 4-iodoanisole were
converted smoothly into the corresponding products in 81%, 88%,
ILs immobilized on the polymers. Further weight loss at a higher
temperature (above 410 °C) was attributed to the decomposition
of PDVB.11
Figure 2 shows the typical transmission electron microscopy
(TEM) images of the catalyst (P(DVB-IL)-Pd). The dark spots in
the TEM image indicate the presence of palladium nanoparticles
that were bound to the copolymers. The diameter of palladium
nanoparticles was about 20 nm and the size distribution was very
narrow (Fig. 2a). Palladium can disperse very well after carbonyl-
ation reaction.
Figure 2. (a) The TEM images of the fresh P(DVB-IL)-Pd; (b) The TEM image of the recovered P(DVB-IL)-Pd after being reused five times in carbonylative Sonogashira coupling
reaction.

Y. Wang et al. / Tetrahedron Letters 52 (2011) 1587–1591
1589
Table 1
Evaluation of the reaction parametersa
O
C
P(DVB-IL)-Pd
Ph-I
Entry
Ph
R
+
+
R
CO
Solvent
Base
T (°C)
t (h)
Yieldb (%)
1
2
3
4
5
6
6
7
8
9
10
11
Toluene
CH3CN
THF
H2O
Acetone
—
H2O
H2O
H2O
H2O
NEt3
NEt3
NEt3
NEt3
NEt3
NEt3
Cs2CO3
Pyridine
NEt3
NEt3
130
130
130
130
130
130
130
130
120
100
130
130
6
6
6
6
6
6
6
6
6
6
2
3
89
62
85
90
46
21
15
47
88
46
80
87
H2O
H2O
NEt3
NEt3
a
Reaction condition: iodobenzene 1.0 mmol, phenylacetylene 1.2 mmol, solvent
5.0 mL, base 2.0 mmol.
b
Isolated yield.
and 95% yields, respectively (Table 2, entries 2–4). The reaction of
4-chloro-iodobenzene, 4-bromo-iodobenzene, and phenylacety-
lene also afforded the corresponding products in satisfactory yields
(Table 2, entries 5–7). When 4-methyl-iodobenzene, 2-methyl-
iodobenzene and 4-ethyl-iodobenzene were employed in the reac-
tion with phenylacetylene, the desired products were isolated in
excellent yields (Table 2, entries 8–10). We also investigated sev-
eral acetylenes containing different groups for the reaction. All
substituted phenylacetylenes were coupling with iodobenzene to
afford a,b-alkynyl ketones in good to excellent yield (Table 2, en-
tries 13–15). While the reaction of 1-hexyne with iodobenzene
only 27% yield of the carbonylative coupling product was obtained
(Table 2, entry 16). The results demonstrated that the catalytic sys-
tem was not suitable for the carbonylative coupling of aliphatic
acetylene with iodobenzene.
To evaluate the recyclability of P(DVB-IL)-Pd in the carbonyla-
tive Sonogashira coupling reaction, the continuous carbonylative
coupling reaction of iodobenzene with phenylacetylene in water
Figure 3. XPS spectra of the catalyst (a) and the Pd atom (b).
Table 2
Carbonylative Sonogashira coupling terminal alkynes with aryl iodides to form
a
,b-alkynyl ketones in watera
O
C
P(DVB-IL)-Pd
Et3N, H2O
Aryl-I
R
Aryl
R
+
CO +
Entry
1
Aryl
Ph
R
Product
Yieldb (%)
O
C
Ph
90
81c
O
C
2
3
4-CH3O-Ph
2-CH3O-Ph
Ph
Ph
95
O
O
C
81
O
O
C
4
3-CH3O-Ph
Ph
88
92
O
O
C
5
6
4-Cl-Ph
4-Br-Ph
Ph
Ph
Cl
O
C
92
Br
(continued on next page)

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Y. Wang et al. / Tetrahedron Letters 52 (2011) 1587–1591
Table 2 (continued)
Entry
Aryl
R
Product
Yieldb (%)
93
O
C
7
8
4-CH3-Ph
Ph
O
C
2-CH3-Ph
Ph
89
O
C
9
4-C2H5-Ph
Ph
Ph
91
82
O
C
10
4-CH3CO-Ph
O
O
11
Naphthalene
2-OH-Ph
Ph
Ph
85
88
O
O
12d
O
O
+
O
C
13
14
15
Ph
Ph
Ph
4-CH3O-Ph
4-tBu-Ph
4-Br-Ph
94
94
87
O
O
C
O
C
Br
O
C
16
Ph
nBu
27
Reaction time was 4h.
a
Reaction condition: aryl iodide (1 mmol), terminal alkyne (1.2 mmol), P(DVB-IL)-Pd (20 mg, 0.005 mmol Pd), Et3N (0.4 mL), distilled water (5.0 mL), temperature: 130 °C,
time: 6 h, CO pressure: 3.0 MPa.
b
Isolated yield.
Reaction time was 4 h.
The total yield of the two products.
c
d
was investigated and the results are presented in Figure 4. The cat-
alyst could be reused five times only with a slight loss of activity
(the fifth recycle yield still can obtain 83.8%). The aggregation of
the Pd particles in the used catalyst was not obvious, which obtains
from TEM in Figure 2b, and the content of Pd in the catalyst was
2.43 wt % (0.229 mmol gÀ1), as determined by the AAS analysis.
In summary, a highly cross-linked polymer matrix was success-
fully prepared and proved to be an effective support for immobiliz-
ing palladium complex. The polymer supported palladium catalyst
exhibited high efficiency for the carbonylative Sonogashira cou-
pling of aryl iodides with terminal alkynes in water. In addition,
the catalyst offered practical advantages such as easy separation
from the products and reuse without activity loss. The heteroge-
neous carbonylation reaction provides a practical and environmen-
tally friendly procedure for the synthesis of a,b-alkynyl ketones.
Acknowledgment
This work was financially supported by the National Natural
Science Foundation of China (Nos. 20625308, 21073209).
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.01.095.
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Figure 4. The reuse of carbonylative Sonogashira coupling with iodobenzene and
phenylacetylene in water.

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