Palladium Nanoparticles Supported on a Porous Organic Polymer: An Efficient Catalyst for Suzuki-Miyaura and Sonogashira Coupling Reactions

Article abstract of DOI:10.1002/cjoc.201500797

A new porous organic polymer (POP) with high thermal stability and large surface area has been synthesized and applied in the preparation of Pd/POP catalyst. Pd/POP was characterized by XRD, TGA, SEM and TEM. The catalyst consists of highly dispersed palladium nanoparticles of 0.9-4 nm size on POP with a large surface area of 650 m²/g. It presents high catalytic activity for Suzuki-Miyaura and Sonogashira reactions. The catalyst was reusable for three to five times without significant loss of activity. A new porous organic polymer (POP) was synthesized and applied in the preparation of Pd/POP catalyst. Pd/POP exhibits high catalytic activity for Suzuki-Miyaura and Sonogashira reactions and is reusable in these heterogeneous catalytic reactions.

Full text of DOI:10.1002/cjoc.201500797

FULL PAPER
DOI: 10.1002/cjoc.201500797
Palladium Nanoparticles Supported on a Porous Organic
Polymer: An Efficient Catalyst for Suzuki-Miyaura and So-
nogashira Coupling Reactions
Xiaomeng Ren, Shengnan Kong, Qiding Shu, and Mouhai Shu*
School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
A new porous organic polymer (POP) with high thermal stability and large surface area has been synthesized
and applied in the preparation of Pd/POP catalyst. Pd/POP was characterized by XRD, TGA, SEM and TEM. The
catalyst consists of highly dispersed palladium nanoparticles of 0.9－4 nm size on POP with a large surface area of
650 m2/g. It presents high catalytic activity for Suzuki-Miyaura and Sonogashira reactions. The catalyst was reus-
able for three to five times without significant loss of activity.
Keywords heterogeneous catalysis, palladium, porous organic polymers, Suzuki-Miyaura reaction, Sonogashira
coupling reaction
Introduction
densation reactions.[36-45] POPs, just like the metal-or-
ganic framework (MOF) counterparts,[46,47] are the
promising solid platforms for heterogeneous catalysis
due to their large surface area, low skeleton densityand
high thermal and chemical stability. Furthermore, POPs
have the advantages of synthetic diversity and tunability
of the pore size and surface area, and can easily be pre-
pared by conventional methods. Therefore, they are at-
tractive materials for heterogeneous catalyst supports.
Great efforts have led to the rapid development of vari-
ous POPs with interesting structures and properties, but
there is still a pressing requirement to improve their ap-
plication in heterogeneous catalysis.
The palladium-catalyzed Suzuki-Miyaura[1] and So-
nogashira[2] coupling reactions are very important and
powerful methods for the construction of carbon-carbon
bonds. Significant progress has been achieved with var-
ious homogeneous palladium catalysts.[3-5] However, it
is difficult to separate and reuse the expensive palla-
dium catalysts and palladium species may also be a tox-
ic contamination in the product in the homogeneous
catalysis system. To overcome these problems, consid-
erable efforts have been made to the development of the
heterogeneous palladium catalysts.[6,7] A successful
example is that palladium nanoparticles (PdNPs) have
been used for the formation of C－C bonds. It is a
well-known fact that PdNPs without stabilization are
prone to aggregate and lose their catalytic activity.
Therefore, looking for suitable support materials is still
an attractive challenge in the field of heterogeneous ca-
talysis. So far various solid materials, such as mesopor-
ous silica,[8-14] ionic liquids,[15-17] polymers,[18-23] metal
oxides,[24-28] inorganic and organic hybrid materials,[29,30]
and metal organic frameworks (MOFs)[31-34] have been
successfully applied as catalyst supports, but less atten-
tion has been paid to the porous organic polymers
(POPs).[35-37]
This work describes the preparation of the PdNPs
which were supported on a porous organic polymer
(Pd/POP) and their application in Suzuki-Miyaura and
Sonogashira coupling reactions.
Experimental
Materials and instruments
The FTIR spectra were taken at Perkin-Elmer Para-
gon 1000 spectrometer with KBr tablet at the ratio of
1∶100, wavelength range from 400－4000 cm1. The
nitrogen adsorption-desorption isotherms were meas-
ured at 77 K with a Quantachrome Nova 4200E Po-
rosimeter. Powder X-ray diffraction patterns were re-
corded using a Rigaku D/MAX-2200/PC equipped with
Cu Kα radiation (40 kV, 20 mA) at the rate of 5.0
(°)/min over the range of 3°－60° (2θ). Thermogravim-
etric analysis (TGA) was performed from 20－800 ℃
Porous organic polymers (POPs), including covalent
organic frameworks (COFs), porous aromatic frame-
works (PAFs), porous polymer networks (PPNs) and
microporous organic networks (MONs) are constructed
from well-designed organic groups by coupling or con-
*
E-mail: mhshu@sjtu.edu.cn; Tel.: 0086-021-54747241; Fax: 0086-021-54741297
Received November 7, 2015; accepted December 3, 2015; published online January 8, 2015.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201500797 or from the author.
Chin. J. Chem. 2016, 34, 373—380
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Ren et al.
FULL PAPER
in nitrogen atmosphere with a Pyris 1 TGA instrument
at a heating rate of 10 ℃/min. The scanning electron
microscopy (SEM) patterns were observed by JSM-
7401F instrument. High-resolution transmission elec-
tron microscopy (HRTEM) was performed by JEOL-
JEM-3010 microscope operating at 200 kV (Cs＝0.6
mm, resolution 1.7 Å). Images were recorded by means
of a CCD camera (MultiScan model 794, Gatan, 1024×
1024 pixels, pixel size 24 m×24 m) at 5－80 k
magnification under low-dose conditions. The concen-
tration of palladium supported on POP was determined
by using inductively coupled plasma-atomic emission
acetylene (818 mg, 8 mmol) in DMF (25 mL) was
stirred at 90 ℃ for 48 h. The precipitate was collected
by filtration, washed with excessive water, followed by
methanol and dichloromethane, dried under vacuum.
The model compound was obtained as a yellow solid.
1H NMR (400 MHz, DMSO) δ: 9.27 (s, 4H), 7.97 (d,
J＝8.8 Hz, 8H), 7.91 (d, J＝7.2 Hz, 8H), 7.60 (d, J＝
8.8 Hz, 8H), 7.6 (d, J＝8.8 Hz, 8H), 7.46 (t, J＝7.7 Hz,
8H), 7.35 (t, J＝7.4 Hz, 4H); 13C NMR (100 MHz,
DMSO) δ: 148.00, 146.71, 135.52, 132.40, 130.87,
129.69, 128.98, 126.03, 120.74, 120.32, 59.98.
spectrometry (ICP-AES, iCAP 6000 Radial). 1H and 13
C
General procedure for the Pd/POP-catalyzed Suzu-
ki-Miyaura coupling reaction
NMR spectra were recorded on a Varian Mercury
plus-400 spectrometer in CDCl3 with TMS as the inter-
nal standard unless otherwise specified. Column chro-
matography was run on silica gel (200－300 mesh). All
chemicals were purchased from Energy Chemical China,
they were AR grade and used as received.
Bromobenzene (0.314 g, 2.0 mmol), phenylboronic
acid (0.366 g 3.0 mmol), a certain base and Pd/POP
(10.0 mg, 0.14 mol%) and solvent (10 mL) were added
to a 50 mL flask, stirred at 70 ℃ for appropriate time.
The mixture was cooled to room temperature, the solid
was isolated by filtration and washed with MeOH (10
mL×2) and CH2Cl2 (10 mL×2), the solution was col-
lected and the solvents were removed under vacuum.
The residue was extracted with CH2Cl2 (20 mL×2),
washed with brine (20 mL), dried over sodium sulfate,
and the solvent was removed under reduced pressure.
The obtained crude product was purified by silica gel
chromatography using hexane as the eluent.
Preparation of the catalyst
Preparation of POP A mixture of tetra(4-azido-
phenyl)methane (484 mg, 1 mmol), 1,4-dialkynyl-ben-
zene (252 mg, 2 mmol), CuSO4•5H2O (100 mg, 0.4
mmol) and sodium ascorbate (80 mg, 0.4 mmol) was
stirred in DMF (100 mL) under nitrogen at 70 ℃ for
12 h, then stirred at 100 ℃ for 72 h.[48] The isolated
solid was suspended in water (100 mL), to which
EDTA-2Na (745 mg, 2 mmol) was added, the mixture
was stirred for 12 h at room temperature. The solid was
isolated by filtration and treated with EDTA-2Na solu-
tion for another 12 h. The solid was isolated by filtration,
washed with water several times, followed by ethanol
and ether. The material was further purified by Soxhlet
extraction in a mixture of THF, chloroform and acetone
for 24 h to eliminate the traces of unreacted starting
materials, and dried under vacuum. POP was obtained
as dark yellow powder (700 mg, yield 95%).
Preparation of Pd/POP The catalyst Pd/POP was
prepared following the reported procedure.[31] PdCl2
(0.14 g, 0.79 mmol) and NaCl (0.16 g, 2.63 mmol) were
stirred in DMF (80 mL), and a clear orange solution was
obtained. The freshly prepared POP (2.8 g) was added
to the solution. After stirring for 10 min, 85% hydrazine
hydrate (1 mL) was added dropwise to the suspension
under vigorous stirring, the mixture changed to dark
gray immediately. The resulted solid was isolated by
filtration, washed with DMF (20 mL×2), followed by
ether (10 mL×2), and dried under vacuum. Pd/POP
was obtained as a black powder and kept under nitrogen
atmosphere. The concentration of palladium supported
on POP was 3 wt%, determined by ICP-AES.
Reuse of the catalyst in Suzuki-Miyaura coupling
reaction
After the first run of the coupling reaction between
bromobenzene and phenylboronic acid, the catalyst was
isolated by centrifuge, and washed with MeOH (10 mL
×2), transferred to a 50 mL Schlenk flask, then KOH
(0.224 g, 4.0 mmol), bromobenzene (0.314 g, 2.0 mmol)
and phenylboronic acid (0.366 g, 3.0 mmol) were added.
The mixture was heated for a certain time while stirring.
The product was isolated following the procedure as the
first run and the catalyst was collected and reused for
the next cycle.
General procedure for the Pd/POP-catalyzed So-
nogashira coupling reaction
A 50 mL Schlenk flask was charged with Pd/POP
(15 mg, 0.14 mol% of Pd) and a certain base, and
purged with nitrogen, solvent (10 mL) and phenylace-
tylene (0.337 g, 3.3 mmol) were added, followed by
iodobenzene (0.612 g, 3.0 mmol). The flask was main-
tained at 80 ℃ in an oil bath and stirred for the appro-
priate reaction time under nitrogen. The isolation and
purification procedures of the product were similar to
those in Suzuki-Miyaura coupling reaction.
Reuse of the catalyst in Sonogashira coupling reac-
tion
Preparation of model compound tetrakis[4-(4-phe-
nyl-1H-1,2,3-triazo-1-yl)phenyl]methane
After the first run of the coupling reaction between
phenylacetylene and iodobenzene, the catalyst was iso-
lated by centrifuge, and washed with methanol (10 mL
×2). The catalyst was transferred to a 50 mL Schlenk
A mixture of tetrakis(4-azidophenyl)methane (200
mg, 0.4 mmol), CuSO4•5H2O (119.8 mg, 0.48 mmol),
sodium ascorbate (221.9 mg, 1.12 mmol) and phenyl-
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Palladium Nanoparticles Supported on a Porous Organic Polymer
flask, then NaOH (0.3 g, 7.5 mmol), phenylacetylene
(0.337 g, 3.3 mmol) and iodobenzene (0.612 g, 3 mmol)
were added, and the mixture was heated while stirring
for a certain time. The product was isolated following
the procedure as the first run and the catalyst was col-
lected and reused for the next cycle.
with the formation of the expected triazole ring. IR
stretches from unreacted azide could not be observed at
2120 cm1, implying that the azide-alkyne coupling is
complete. A strong and broad stretch at 3400 cm1 is
also observed, elucidating the presence of adsorbed wa-
ter. The solid state 13C NMR spectrum of POP (Figure 2)
matches well with that of the model compound, further
confirming the formation of POP.
Results and Discussion
Characterizations of POP and Pd/POP
As shown in Scheme 1, POP was obtained in an ex-
cellent yield by copper catalyzed Huisgen 1,3-dipolar
cycloaddition, the so-called click reaction[49,50] between
1,4-dialkynylbenzene and 4-tetra(azidophenyl)methane
[Caution: tetra(azidophenyl)methane is a potential ex-
plosive)]. The FTIR spectrum of POP (Figure 1)
matches with that of the model compound. A broad N＝
N stretch can be observed at 1610 cm1, together with a
weak C＝CH band at 3030 cm1, which are consistent
Figure 2 The solid 13C NMR of POP and the model compound.
The N2 sorption isotherms (Figure 3) were measured
at 77 K. POP gave a Brunauer-Emmett-Teller (BET)
surface area of 651 m2/g, including micropore area of
596 m2/g and external surface area of 55 m2/g. Pd/POP
exhibited a BET surface area of 573 m2/g, including
micropore area of 494 m2/g and external surface area of
79 m2/g. The obvious abrupt on the desorption curve at
p/p0＝0.4 proves the existence of the microporous and
mesoporous pores. The pore size (Figure 4) distributions
of POP range from 0.4 to 1.2 nm and the maximum
pores are at 0.45 nm calculated by density functional
Figure 1 The FTIR spectra of POP and the model compound.
Scheme 1 Synthesis of POP
N
N
N
N3
N
N
N
N
N
N
N
N
.
CuSO4 5H2O, DMF
N
N3
2
+
Sodium ascorbate
70 oC, 12 h
then 100 oC, 72 h
N3
N
N
N
N3
N
N
N
N
N
N
N
N
N
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Ren et al.
FULL PAPER
theory (DFT). The sizes of Pd nanoparticles range from
0.9 to 4 nm estimated by TEM image (Figure 5).
weight loss between 240 and 350 ℃ is related to the
decomposition of small molecular fragments of low po-
lymerization. The last zone of weight loss from 350 to
800 ℃ corresponds to the decomposition of molecular
fragments of higher molecular weight polymer.
Figure 3 Nitrogen adsorption-desorption isotherms of POP and
Pd/POP.
Figure 6 Powder X-ray diffraction patterns of POP and Pd/
POP.
Figure 4 Pore size distribution curves of POP and Pd/POP.
Figure 7 TGA of POP and Pd/ POP under nitrogen atmosphere.
Application in Suzuki-Miyaura reaction
Bromobenzene and phenylboronic acid were used as
the substrates to investigate the reaction conditions. The
influence of different bases (Table 1) on the reaction
was studied using CH3OH as solvent. No product was
obtained (Entry 1) in the absence of base, lower yields
were observed in case of Na2CO3 (Entry 2), K2CO3
(Entry 5), and Cs2CO3 (Entry 9). The reactions using
Na3PO4•12H2O, K3PO4•3H2O or KOH as the base gave
the yield nearly 60%. The yield is related to the molar
ratio of these bases (Entries 3, 4, 6－8, 11－14). It gave
the highest yield of 68% when 2 equiv. of KOH was
used (Entry 11).
A significant effect of the reaction temperature was
observed (Table 1). Raising the temperature of oil bath
from 20 to 70 ℃ improved the yields (Entries 15—17,
20), 70 ℃ gave the highest yield of 92% (Entry 20),
but the yield was reduced at 80 ℃ (Entry 11).
Figure 5 The TEM image of Pd/POP and the histogram illus-
trating the particle size distribution of Pd(0) nanoparticles.
The powder X-ray diffraction of POP and Pd/POP
(Figure 6) showed that the materials were amorphous,
and the characteristic peak of Pd(111) at 2＝40.1°
confirms the existence of palladium nanoparticles.
Thermogravimetric analysis (TGA) showed that POP
and Pd/POP were stable up to 200 ℃, and decomposed
above 250 ℃ (Figure 7). Weight loss up to 100 ℃
was about 10% for both POP and Pd/POP, resulting
from loss of the absorbed solvent DMF. The second
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Palladium Nanoparticles Supported on a Porous Organic Polymer
Table 1 The optimization of reaction conditions for Suzuki-
Miyaura reactiona
drawing or electron-donating functional groups, the re-
sults are summarized in Table 2.
Table 2 Suzuki-Miyaura reaction with various substituentsa
Entry Base (Dosage/equiv.)
Solvent (V∶V) T/℃Yieldb/%
1c
None
Na2CO3 (2.0)
Na3PO4•12H2O (2.0)
Na3PO4•12H2O (2.5)
K2CO3 (2.0)
K3PO4•3H2O (1.5)
K3PO4•3H2O (2.0)
K3PO4•3H2O (2.5)
Cs2CO3 (2.0)
NaOH (2.0)
KOH (2.0)
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
THF
80
80
80
80
80
80
80
80
80
80
80
80
80
80
20
40
60
70
70
70
0
2
19
57
22
32
60
36
31
18
35
68
57
64
48
38
50
72
13
4
Entry
1
R1
H
R2
H
Product Time/h Yieldb/%
3
3a
3b
3c
3d
3e
3f
3
3
92
97
91
91
77
76
32
18
95
96
90
72
32
18
11
73
69
49
14
14
4
2
H
4-CF3
3,5-CF3
4-Me
2-MeO
2-Me
4-MeO
2-CF3
H
5
3
H
3
6
4
H
3
7
5
H
12
3
8
6
H
9
7
H
3g
3h
3d
3g
3e
3f
12
12
3
10
11
12
13
14
15
16
17
18d
19d
20
21d
22d
23
24
8
H
9
4-Me
4-MeO
2-MeO
2-Me
4-CF3
3,5-CF3
2-CF3
4-Me
4-CF3
2-MeO
4-MeO
2-Me
KOH (1.0)
10
11
12
13
14
15
16
17
18
19
20
H
3
KOH (1.5)
H
3
KOH (2.5)
H
3
KOH (2.0)
H
3b
3c
3h
3i
3
KOH (2.0)
H
3
KOH (2.0)
H
3
KOH (2.0)
4-Me
4-CF3
2-MeO
4-MeO
2-Me
3
KOH (2.0)
Dioxane
MeOH
3j
3
KOH (2.0)
92
66
45
83
69
3k
3l
12
12
12
KOH (2.0)
MeOH/H2O (2∶1) 70
MeOH/H2O (1∶1) 70
KOH (2.0)
3m
KOH (2.0)
EtOH
70
70
a
Reaction conditions: bromobenzene derivatives (2.0 mmol),
KOH (2.0)
i-PrOH
derivatives of phenylboronic acid (3.0 mmol), Pd/POP (10.0 mg,
0.14 mol%), KOH (0.224 g, 4.0 mmol), CH3OH (10 mL), 70 ℃
(oil bath). b Isolated yield.
a Reaction conditions: bromobenzene (0.314 g, 2.0 mmol), phenyl-
bronic acid (0.366 g, 3.0 mmol), Pd/POP (10.0 mg, 0.14 mol%), 10
mL of solvent, oil bath, 3 h. b Isolated yield. c 24 h. d 6 h.
Phenylboronic acid reacts with various bromoben-
zene with electron-rich and electron-deficient groups
(Table 2, Entries 2－6), giving the corresponding prod-
ucts 3b－3h with good yields. Electron-deficient pa-
ra-substituted aryl bromides (Entry 2) showed higher
activity compared to electron-rich aryl bromides (Entry
7), in the process of coupling with phenylboronic acid.
ortho-Bromobenzotrifluoride gave the lowest yield of
18% (Entry 8), another two ortho-substituted aryl bro-
mides gave the yield of no more than 80% (Entries 5, 6),
this implies that their steric effect is lower than that of
ortho-bromobenzotrifluoride. The electron-donating
function group on aryl bromides is unfavorable to the
coupling reaction, this can also be clearly seen from the
reaction between 4-methoxybromobenzene and phenyl-
boronic acid (Entries 7). Electronic-rich para-substi-
tuted arylboronic acids (Entries 9, 10) process better
than electron-deficient ones (Entries 13－15). Cross
couplings of both substituted substrates with various
The solvent is also an important factor, both aprotic
and protic solvents were tested (Table 1). Aprotic sol-
vents such as THF and dioxane (Entries 18, 19) gave
low yields. Protic solvents like pure alcohol and mixed
alcohol aqueous solvents were tested, the mixed alcohol
aqueous solvents gave moderate yield (Entries 21, 22),
which may be due to the reduced solubility of reactants
in mixed solvents. Among alcohol solvents, i-PrOH
gave 69% yield (Entry 24), and 83% yield for EtOH
(Entry 23), however MeOH resulted in full conversion
and 92% yield in 3 h (Entry 20).
It was found that the best system for the reaction was
2.0 mmol of bromobenzene, 3.0 mmol of phenylboronic
acid, 10 mg (3 wt%) Pd/POP, 4.0 mmol of KOH, 70 ℃
(oil bath) and 10 mL of methanol as solvent. These con-
ditions were applied for various aryl bromides and phe-
nylboronic acid to assess the scope towards a wide
range of aryl bromides bearing either electron-with-
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Ren et al.
FULL PAPER
electron-withdrawing or electron-donating functional
groups were also investigated and all gave yields less
than 75% (Entries 16－20).
The catalytic system was applied for the coupling
rection bewteen chlorobenzene and phenylboronic acid,
however poor yield was obtained.
affording excellent yields of corresponding products. As
shown in Table 4, coupling reactions between the
arynes and iodobenzene with electron-withdrawing
groups at para-position enhanced the yields (Entries 6,
8, 12 －14). Phenylacetylene with electron-donating
group gave the lower yield (Entry 9). When iodoben-
zene bearing electron-donating groups or phenylacety-
lene with electron-withdrawing groups were used as
substrates, the yield was low (Entry 15). However, the
catalyst is not active enough for bromobenzene.
Application in Sonogashira coupling reactions
Pd/POP catalyst was also applied to the Sonogashira
reaction. The coupling of iodobenzene (0.612 g, 3.0
mmol) with phenylacetylene (0.337 g, 3.3 mmol) was
initially studied as a model reaction. The reaction condi-
tions were systematically optimized. MeOH, EtOH, and
i-PrOH were used in the presence of K3PO4•3H2O as the
base to optimize the solvent which resulted in 82%, 4%
and 71% yields, respectively (Table 3, Entries 1－3). So
MeOH was chosen as the appropriate solvent.
Table 4 Study of the Sonogashira reaction with various sub-
stituentsa
No product was found without base (Table 3, Entry
4). Low yield was observed in case of Na2CO3 (Entry
14). The reactions using KOH, K2CO3, NaOH,
K3PO4•3H2O as the base gave better yields, the molar
ratio of these bases were changed to further increase the
yields (Entries 5－13). Finally 2.5 equiv. of NaOH gave
the highest yield of 99% (Entry 10).
Entry
1
R3
H
R4
H
Product Time/h Yieldb/%
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
99
93
6a
6b
6c
6d
6e
6f
2
4-Me
2-MeO
4-MeO
2-CF3
4-CF3
3,5-CF3
4-NO2
H
H
3
H
93
4
H
97
Table 3 Optimization of reaction conditions for Sonogashira
reactiona
5
H
49
6
H
＞99
92
7
H
6g
6h
6b
6i
8
H
＞99
57
Yieldb/%
82
9
4-Me
4-F
Entry
1
Base (Dosage/equiv.)
K3PO4•3H2O (1.5)
K3PO4•3H2O (1.5)
K3PO4•3H2O (1.5)
None
Solvent
CH3OH
C2H5OH
i-PrOH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
CH3OH
10
11
12
13
14
15
16
17
18
H
94
2
4
H
4-C5H11
4-MeO
4-MeO
4-Me
4-F
93
6j
3
71
4-NO2
4-CF3
4-CF3
4-Me
4-MeO
4-Me
4-MeO
99
6k
6l
4
0
99
5
KOH (1.5)
77
99
6m
6n
6o
6p
6q
6
KOH (2.0)
94
51
7
K2CO3 (1.5)
91
4-F
92
8
NaOH (1.5)
94
4-Me
4-MeO
83
9
NaOH (2.0)
98
41
10
11
12
13
14
NaOH (2.5)
99
a Reaction conditions: iodobenzene derivatives (3.0 mmol), de-
rivatives of phenylacetylene (3.3 mmol), Pd/POP (15.0 mg, 0.14
mol%), NaOH (0.3 g, 7.5 mmol), CH3OH (10 mL), 80 ℃ (oil
bath). b Isolated yield.
NaOH (1.0)
61
K3PO4•3H2O (1.5)
K3PO4•3H2O (2.0)
Na2CO3 (1.5)
82
75
28
a Reaction conditions: iodobenzene (0.612 g, 3.0 mmol), phenyl-
acetylene (0.337 g, 3.3 mmol), Pd/POP (15.0 mg, 0.14 mol%),
CH3OH (10 mL), 80 ℃ (oil bath), 12 h. b Isolated yield.
Activity of recycled Pd/POP catalyst was also ex-
amined. No significant change was found in the second
run (Table 5, Entry 2), but the activity decreased from
the third run (Entries 3－5) in Suzuki reaction, however,
it did not change significantly up to the fifth run in So-
nogashira reaction (Table 6). The reduction of the cata-
lyst reactivity may result from dissolution of palladium
particles from the surface of the solid support or for-
mation of Pd clusters in solution, and the palladium may
The best system for Sonogashira reaction was 3.0
mmol of aryl iodide, 3.3 mmol of phenylacetylene, 15
mg (0.14 mol%) Pd/POP, 7.5 mmol of NaOH, 80 ℃
(oil bath) and 10 mL of methanol. The conditions toler-
ated the presence of a wide variety of functional groups,
378
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© 2016 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2016, 34, 373—380

Palladium Nanoparticles Supported on a Porous Organic Polymer
redeposite onto the support.[51-55] Leaching of Pd in fil-
trate may lead to lowering its concentration in the
Pd/POP catalyst. In order to find out the reasons for de-
activation of catalyst, the ICP-AES analysis was per-
formed to the cold filtrations after the first, third and
fifth runs, Pd leaching amount was less than 0.3 and 0.5
mg•L1 in Suzuki, and Sonogashira reactions, respec-
tively. Negligible Pd leaching confirmed the heteroge-
neous process similar to the Pd/C system.[56] The cata-
lyst is not active enough for aryl chlorides in Suzuki
coupling reactions compared with the Pd/C[56] and
＋
Poly-NHC-2-Pd2 [43] catalysts, but it is more stable than
Pd/MOF-5, which has the similar reactivity in catalyz-
ing Sonogashira reaction.[31] XPS survey scans of both
fresh and used catalyst showed characteristic peaks of
Pd3d along with C1s peak (Figure 8). High resolution
narrow scans for Pd3d level show peaks at 336.6, 341.8
eV (fresh); 335.3, 340.5 eV (used in Suzuki reaction)
and 335.5, 340.7 eV (used in Sonogashira reaction) for
Pd 3d5/2 and Pd 3d3/2, which clearly indicates that the
palladium is in the zero oxidation state even after five
catalytic cycles. The slight negative XPS shift in the
used catalyst comparing to the fresh one may be caused
Figure 8 The XPS scan of fresh Pd/POP, Pd/POP in Suzuki
reaction and Pd/POP in Sonogashira reaction after the 5th run.
by the size changes of the PdNPs before and after
use.[57]
The TEM images of the Pd/POP after fifth run (Fig-
ure 9) elucidate that the PdNPs aggregated at certain
places. Therefore, the deactivation of the catalyst is
mainly due to the aggregation of PdNPs.
Table 5 Reusability of Pd/POP in Suzuki-Miyaura reactiona
Entry
Run
1
Time/h
Yieldb/%
1
2
3
4
5
3
3
3
5
5
92
90
63
52
47
2
3
4
5
a Reaction conditions: bromobenzene (0.314 g, 2.0 mmol), phe-
nylboronic acid (0.366 g, 3.0 mmol), Pd/POP (10.0 mg, 0.14
mmol%), KOH (0.224 g, 4.0 mmol), CH3OH (10 mL), 70 ℃
(oil bath), 3 h. b Isolated yield.
Table 6 Reusability of Pd/POP in Sonogashira reactiona
Figure 9 The TEM images of Pd/POP and the histograms illus-
trating the particle size distribution of Pd (0) nanoparticles in
Suzuki-Miyaura reaction (a) and Sonogashira reaction (b) after
the 5th run.
Pd/POP, solvent
+
I
Base
6a
5a
4a
Entry
Run
1
Time/h
12
Yieldb/%
Conclusions
1
2
3
4
5
99
94
91
88
72
In summary, a porous organic polymer has been
prepared from tetra(4-azidophenyl)methane and 1,4-di-
alkynylbenzene. Subsequent modification with palla-
dium nanoparticles yielded a Pd/POP catalyst. Gas ad-
sorption showed that Pd/POP had a BET specific sur-
face area of 573 m2•g−1 and a pore volume of 0.23
cm3•g−1. Although Pd nanoparticles are not in the pores,
Pd/POP showed good catalytic activity in the Suzuki-
Miyaura coupling reaction of arylboronic acids and aryl
2
12
3
12
4
12
5
12
a Reaction conditions: iodobenzene (0.612 g, 3.0 mmol), phenyl-
acetylene (0.337 g, 3.3 mmol), Pd/POP (15.0 mg, 0.14 mol%),
CH3OH (10 mL), NaOH (0.3 g, 7.5mmol). 80 ℃ (oil bath).
b Isolated yield.
Chin. J. Chem. 2016, 34, 373—380
© 2016 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
379

Ren et al.
FULL PAPER
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© 2016 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2016, 34, 373—380