Anchoring Pd(OAc)2 on amide-bonded covalent organic frameworks: An efficient heterogeneous Pd@OC-MA catalyst for Suzuki-Miyaura coupling reactions in water

Article abstract of DOI:10.1016/j.tet.2020.131664

Nitrogen-rich of a melamine-based mesoporous covalent organic frameworks (COFs) materials were synthesized and used as a carrier to support a Pd(OAc)₂. The Pd@OC-MA revealed an efficient catalytic activity and selectivity for Suzuki-Miyaura coupling reactions in an environmentally friendly water medium at room temperature. Specifically, it had moderate to excellent conversion for inactive chlorinated aromatic hydrocarbons. The catalyst was synthesized simply, had high stability and good selectivity, and was easy to recycle. Excellent catalytic activity of the Pd@OC-MA was also observed after five consecutive cycles.

Full text of DOI:10.1016/j.tet.2020.131664

Journal Pre-proof
Anchoring Pd(OAc) on amide-bonded covalent organic frameworks: an efficient
2
heterogeneous Pd@OC-MA catalyst for Suzuki-Miyaura coupling reactions in water
Shang Wu, Ying Zhang, Hongyan Jiang, Lan Wu, Ning Ding, Pengwei Jiang, Hong
Zhang, Lianbiao Zhao, Fenping Yin, Quanlu Yang
PII:
S0040-4020(20)30871-1
https://doi.org/10.1016/j.tet.2020.131664
TET 131664
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 8 July 2020
Revised Date: 3 October 2020
Accepted Date: 6 October 2020
Please cite this article as: Wu S, Zhang Y, Jiang H, Wu L, Ding N, Jiang P, Zhang H, Zhao L,
Yin F, Yang Q, Anchoring Pd(OAc) on amide-bonded covalent organic frameworks: an efficient
2
heterogeneous Pd@OC-MA catalyst for Suzuki-Miyaura coupling reactions in water, Tetrahedron,
https://doi.org/10.1016/j.tet.2020.131664.
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Graphical Abstract
.
Anchoring Pd(OAc)2 on amide-bond
Leave this area blank for abstract info.
covalent organic frameworks: an efficient
heterogeneous Pd@OC-MA catalyst for
Suzuki-Miyaura coupling reactions in water
Shang Wua, Ying Zhanga , Hongyan Jianga , Lan Wua, Lianbiao Zhaoa , Fenping Yina , Ning Dinga , Pengwei
Jianga and Quanlu Yangb,
a Key laboratory for Utility of Environmental Friendly Composite Materials and Biomass in University of
Gansu Province, College of Chemical Engineering, Northwest Minzu University, Lanzhou, 730030, China
E-mail: chwush84@163.com (S. Wu), yangquanlu2002@163.com (Q. L. Yang), 945934161@qq.com (L. Wu)
b College of Chemical Engineering, Lanzhou University of Arts and Science, Beimiantan 400, Lanzhou, Gansu
730000, China

1
Tetrahedron
journal homepage: www.elsevier.com
Anchoring Pd(OAc)2 on amide-bond covalent organic frameworks: an efficient
heterogeneous Pd@OC-MA catalyst for Suzuki-Miyaura coupling reactions in
water
Shang Wua, Ying Zhanga , Hongyan Jianga , Lan Wua, Lianbiao Zhaoa , Fenping Yina , Ning Dinga ,
Pengwei Jianga and Quanlu Yangb,
a Key laboratory for Utility of Environmental Friendly Composite Materials and Biomass in University of Gansu Province, College of Chemical Engineering,
Northwest Minzu University, Lanzhou, 730030, China
E-mail: chwush84@163.com (S. Wu), yangquanlu2002@163.com (Q. L. Yang), 945934161@qq.com (L. Wu)
b College of Chemical Engineering, Lanzhou University of Arts and Science, Beimiantan 400, Lanzhou, Gansu 730000, China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A nitrogen-rich of a melamine-based mesoporous COFs material was synthesized and used as a
carrier to support Pd(OAc)2. The catalyst Pd@OC-MA revealed an efficient catalytic activity
and selectivity for Suzuki-Miyaura coupling reactions in an environmental friendly water
medium at room temperature. It has moderate to excellent conversion for inactive chlorinated
aromatic hydrocarbons. The catalyst was synthesized simply, high stability, good selectivity and
easy to recycle. Excellent catalytic activity of the Pd@OC-MA was observed after five
consecutive cycles.
Available online
Keywords:
covalent organic frameworks (COFs)
palladium catalyst
2009 Elsevier Ltd. All rights reserved
.
Suzuki-Miyaura coupling reactions
1. Introduction
with highly stable and the catalyst are more stable due to the
coordination between metal particles and nitrogen atoms.18
Covalent organic frameworks (COFs) are rising classes of 2D
or 3D porous crystalline polymers, they are linked by covalent
bonds.1-3 These materials have stable structure and pre-set
porosity4-5. Various of COF materials have been synthesized after
Yaghi first discovered them in 2005.6 In these COFs materials, a
variety of two-dimensional (2D) and three-dimensional (3D)
COFs have been reported and shown excellent properties in
The establishment of the carbon–carbon bonds is an
extraordinary and significant method in organic synthesis and
medical chemistry.19-23 Transition metal palladium catalyzes
cross-reaction of Suzuki–Miyaura, which was provided a general
method for the formation of various organic compounds.24-26 Due
to its excellent functional group tolerance of the catalytic process,
it was widely used to prepare asymmetric diaryl derivatives.27-28
Palladium catalysts are also diffusely used in the Heck,29
Sonogashira30 and carbonylative31 reactions.
various applications such as gas adsorption and storage,7-8
9-10
optoelectronics,
catalysis, 11-12, etc. The COFs materials are
comprised of some lightweight elements like C, B, N linked by
covalent bonds such as amide linkage,13-15 imine linkage16 into a
predictable structural 2D or 3D porous polymer. They are found
to be admirable carrier of heterogeneous catalyst owing to their
high surface areas, low density, large porosity and excellent
stability. Some carriers are unstable when combined with metal
particles through physical adsorption.17 In order to solve these
difficulties, novel nitrogen-rich triazine COFs were synthesized
In the beginning, homogeneous palladium compounds were
used as catalysts. Nevertheless, they have many disadvantages,
such as high cost of ligands, difficult to separation, low
recyclability and lead to environmental pollution. To resolve
these disadvantages, heterogeneous catalysts were developed. In
recent years, a variety of carriers were emerged in an endless
stream. For example, inorganic carriers (SiO2,32 TiO2,33 CuO,34
Shang Wu. e-mail: chwush84@163.com
Lan Wu. e-mail: 945934161@qq.com
Quanlu Yang. e-mail: yangquanlu2002@163.com

2
Tetrahedron
Scheme 1. Synthesis of Pd@OC-MA
CeO2,35 ZrO236), natural carriers (wool,37 palygorskite,38
The peak at 3077 cm-1 can vest in C-N coupled vibration and
3409 cm-1 to N-H stretching vibration. Therefore, it can be
proved that the COFs was formed. The FT-IR absorption
spectrum of the catalyst Pd@OC-MA is similar to the OC-MA,
but there are several weak characteristic absorption peaks at 3100
cm-1 ~ 2500 cm-1. The peak at 2986 cm-1 is attributed to the
stretching vibration of methyl, asymmetric deformation vibration
of methyl group has shifted to a wave number (1420 cm-1) and
the band at 2859 cm-1 is attributed to the stretching vibration of
methylene. The band at 2669 cm-1 and 2550 cm-1 can be indexed
to the -OH in the carboxyl group. The absorption peak showed a
slight red shift at 1685 cm-1 because a coordination bond is
formed between palladium acetate and C=O. Therefore, it can be
proved that palladium acetate was supported on OC-MA
successfully and obtained the catalyst Pd@OC-MA.
halloysite39) and organic polymer carriers (chitosan,40 SNW1,41
COFs,42 MOF43).
Nowadays, using of water as a solvent has developed rapidly
in organic reactions. It is a non-toxic property, cheap,
environment friendly solvent, therefore, regarded as an excellent
substitute for expensive organic solvent.
Melamine is a chemical material with abundant nitrogen
atoms and widely used in the synthesis of porous COFs. In this
work, we have reported a novel covalent organic frameworks
OC-MA was synthesized by one-step condensation reaction with
melamine (MA) and 4,4' - oxybisbenzoyl chloride (OC) as raw
materials. Further, OC-MA was used as a carrier to obtain
Pd@OC-MA (to see Scheme 1). The catalyst has excellent
catalytic activity and high stability towards the Suzuki - Miyaura
cross-coupling reaction in water, and the catalytic activity did not
decrease significantly after five consecutive cycles.
2. Results and Discussion
2.1. Synthesis and characterization of the catalyst Pd@OC-MA
A 100 mL round-bottomed flask was charged with melamine
(0.2 mmol, 25.2 mg), 10 mL of THF and fully stirred. Then drop-
wise added 4,4' - oxybisbenzoyl chloride (0.3 mmol, 89.1 mg)
dissolved in THF (10 mL) and Na2CO3 (0.3 mmol, 31.8 mg). The
mix was stirred at 40 ℃ for 24 h. After the reaction, the solvent
was removed by high speed centrifugation. Subsequently, the
solid was washed with THF and hot water to get rid of the
unreacted reactant. Finally, the product was dried at 70℃ for 12
h to get white solid OC-MA in 74% yield.
Figure 1. FT-IR spectra of compounds (a) OC-MA and (b) Pd@OC-MA
OC-MA (200 mg) was added to solution of Pd(OAc)2 (20 mg)
in CH3CN (15 mL), followed by agitation at r.t. for 24 hours.
After that, a yellow solid was obtained by high-speed
centrifugation. And then, the solid was washed with secondary
water (3×5mL) and CH3CN (3×5mL), dried overnight at 70 ℃ to
get light yellow powder Pd@OC-MA. The palladium content in
the Pd@OC-MA was 0.816 wt% (0.077 mmolg-1) by ICP-AES.
The crystal structure and properties of the OC-MA and
catalyst Pd@OC-MA were confirmed by the powder X-rays
diffraction analysis and the results were shown in Figure 2. The
peaks at 17.53, 19.52, 21.50, 23.53 and 27.16 2θ could be
assigned to the (010), (011), (102), (012) and (110) Bragg peaks
of P1/1 respectively. The experiment data is basically consistent
with the XRD of the OC-MA using Material Studio simulation. It
was shown that OC-MA was triclinic system and the cell
parameters was a = 7.4179 Å, b = 6.1916 Å, c = 11.9510 Å, and α
= β =90° γ = 120°. The structure of the OC-MA was reserved still
The prepared covalent organic frameworks OC-MA was
confirmed by FT-IR spectrum (Figure 1 (a)). The characteristic
absorption peaks of OC-MA at 1594 cm-1 and 1254 cm-1 were put
down to the absorption Ⅱ and Ⅲ band of amide respectively.

3
well after anchoring Pd(OAc)2. Probably because of the loading
of palladium acetate was so less that it was below the detection
limit of the instrument on the power XRD pattern of the catalyst
Pd@OC-MA. Therefore, it is needed to use X-ray photoelectron
spectroscopy (XPS) to confirmed further the Pd(OAc)2 anchor on
Pd@OC-MA.
was clearly confirmed Pd particles supporting on OC-MA in
Figure 3 (a). It can be seen from Figure 3 (b) that the binding
energy of the N1s in the synthesized OC-MA was changed from
399.67 eV to 399.04 eV after loading Pd(OAc)2, which was
indicated that the coordination bond between Pd (Ⅱ) and N
atoms generated the Pd@OC-MA rather than simple adsorption.
There are two peaks at 338.1 eV and 343.5 eV corresponds to
Pd3d5/2 and Pd3d3/2 for the catalyst, therefore, it can be stated that
the Pd particles were bivalence33(Figure 3 (c)).
The morphologies of the OC-MA and catalyst Pd@OC-MA
were confirmed by SEM and TEM further (Figure 4). In Figure 4
(a), the OC-MA was shown a porous cross-networking structure,
which was confirmed the preparation of the covalent organic
frameworks successfully. However, the morphology of the
Pd@OC-MA was flower-like structure (Figure 4 b). It was
changed from a network structure to a flower-like structure may
be the reason for Pd(OAc)2. It can be seen from Figure 4 (C) that
some of the sheet-like morphology of the reused catalyst was
corroded leading to a reduction in catalytic activity. Figure 4 (d,
e, f) shows the TEM at different magnifications of the Pd@OC-
MA, and the TEM images clearly showed that the Pd (Ⅱ)
particles were symmetrical distribution on OC-MA. And its
partical sizes were mainly distributed in 4-6 nm (Figure 4 g). The
average partical size of Pd ( Ⅱ ) was obtained by statistical
calculation is 5.24 nm. Additionally, the elemental composition
of OC-MA and catalyst Pd@OC-MA were confirmed by EDS,
shown in Fig. S1 and Fig. S2.
Figure 2. Powder XRD pattern and simulated structures of OC-MA and
Pd@OC-MA.
The elemental composition of the catalyst Pd@OC-MA and
the chemical valence of Pd were further analyzed by XPS
spectral analysis (Figure 3). The survey scan for Pd@OC-MA
Figure 3. XPS analysis of (a) survey scan for Pd@OC-MA, (b) N 1s comparison chart of OC-MA and Pd@OC-MA (c) Pd 3d for Pd@OC-MA.
Figure 4. SEM images of OC-MA (a), Pd@OC-MA (b), Pd@OC-MA cycle (c), TEM images of Pd@OC-MA (d, e, f) and particles size distribution in (g).

4
Tetrahedron
The surface area and pore volume of the catalyst Pd@OC-
demonstrated that Pd@OC-MA was playing a considerable role
in Suzuki-Miyaura coupling reaction. The effects of
miscellaneous contributing factors on the reactivity further.
Firstly, the reactivity time was studied in coupling reaction. And
the optimal reaction time was 5 h. (Table 1, entries 4-8).
Secondly, the reaction was investigated with different bases such
as NaHCO3, NaOAc, TEA, Cs2CO3, Na2CO3, NaOH ( Table 1,
entries 3, 8-12). Among them only NaHCO3 and NaOH have the
highest yield and other bases have a middle yield. NaOH has a
strong alkalinity to corrode the catalyst, which is disadvantage to
the recyclability of catalyst Pd@OC-MA. So NaHCO3 was the
optimum base. Finally, the amount of catalyst was optimized in
the reactivity (Table 1, entries 3, 13, 14): by using 1 mg, 2 mg
and 3 mg of Pd@OC-MA (Pd 0.816 wt%), the yield of biphenyl
were 24 %, 82 % and 99 % severally. In summary, optimal of the
reaction conditions were bromobenzene (0.1 mmol), benzene
boricacid (0.15 mmol), NaHCO3 (0.15 mmol), Pd@OC-MA (3
mg), water as solvent in r.t. for 5 h.
MA were characterized by the N2 adsorption desorption
isotherms measurement at 77K. From the Figure 5 (a) we can get
it belongs to Ⅲ model nitrogen adsorption desorption isotherm.
The application of the BET accounted in the porosity and specific
surface area of the material Pd@OC-MA were found to be
0.03975 cm3g-1 and 8.5929 m2g-1 respectively (P/P0=0.994). The
pore-size of Pd@OC-MA was calculated by nonlocal density
functional theory methods applied to the N2 adsorption
desorption isotherms at Figure 5 (b) and the pore-size is 3.3 nm
and it is a mesoporous material.
Table 1.Optimization of Suzuki - Miyaura coupling reaction
conditionsa
Figure 5. (a) N2 adsorption (square symbol) / desorption (circle symbol) and
(b) pore size distribution of Pd@OC-MA.
The thermostability of the synthesized OC-MA and Pd@OC-
MA were performed by TGA under N2 ambience, the
temperature range from room temperature (r.t.) to 800 ℃ and the
heating rate was 10 K/min as shown in Figure 6. Both OC-MA
and Pd@OC-MA exhibits 4.38 % of weight loss from r.t. to 280
℃, it was attributed to the evaporation of water and solvent
molecules entrapped in the synthesized materials. The
decomposition of Pd@OC-MA starts at near 300 ℃, it can be
clearly shown that the catalyst has high thermal stability. And the
difference was appeared between 380 ℃ to the end, which was
authorized the Pd(OAc)2 successful supporting on OC-MA.
Entry
Catalyst
Solvent Base
NaHCO3
Time (h)
Yield %
1
-
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
5
5
5
1
2
3
4
5
5
5
5
5
5
5
5
-
2
OC-MA
NaHCO3
NaHCO3
NaHCO3
NaHCO3
NaHCO3
NaHCO3
NaOAc
TEA
-
3
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd@OC-MA
Pd(OAc)2
99
34
51
76
87
88
78
90
93
100
24
82
100
4
5
6
7
8
9
10
11
12
13b
14c
15
Cs2CO3
Na2CO3
NaOH
NaHCO3
NaHCO3
NaHCO3
aReaction condition: bromobenzene (0.1 mmol), benzene boricacid (0.15
b
mmol), base (0.15 mmol), H2O (3 mL), catalyst (3 mg), catalyst (1 mg),
ccatalyst (2 mg)
Figure 6. TGA of synthesized OC-MA and Pd@OC-MA.
With the optimal coupling reaction conditions, the reactivity
was investigated with different substituted aryl halides (X= Br,
Cl) with different substituted boric acid and the results were
shown in Table 2. It's worth noting that the electron character has
no obvious affect on the conversions of the brominated aromatic
hydrocarbon coupling reaction (Table 2, entries 1-8). These
results were indicated that Pd@OC-MA was a high-efficiency
catalyst for Suzuki cross-coupling reactions. Nevertheless, the
ortho-substituted bromoaryl and phenyl boronicacid were reacted
hardly in the reactivity (Table 2, entry 19). The result shows that
the steric-hindrance effect has a significant effect on the C-C
coupling reaction. Chlorinated aromatic hydrocarbons are less
active than brominated aromatics, because they are not conducive
to the oxidative addition of palladium, which was leaded to a low
2.2. Catalytic studies of Pd@OC-MA in Suzuki-Miyaura
coupling reaction
In succession, we researched the catalytic activity of Pd@OC-
MA complex in Suzuki - Miyaura coupling reaction. Water is the
best solvent in organic reactions due to its green, cheap and non-
toxic properties. Hence, we selected water instead of organic
solvent in the optimization of reaction conditions and the
consequences were shown in Table 1. Furthermore, in the blank
control experiment, no biphenyl product was obtained either
without catalyst Pd@OC-MA or only with OC-MA (Table 1,
entries 1and 2). However, the biphenyl in 99 % yield was
acquired with Pd@OC-MA catalyst in the with Pd@OC-MA
catalyst in the coupling reaction (Table 1, entry 3 ). It is

5
conversion rate of the coupling reaction. Simultaneously, the
electronic-effect also has a significant affect on the coupling
reaction of chlorinated aromatic hydrocarbons. Chlorinated
aromatic hydrocarbons with electron donor (Me-, OMe-) have
more conversion than chlorinated aromatic hydrocarbons with
electron acceptor (NO2-, Cl-) (Table 2, entries 10-14).
Table 2. Suzuki-Miyaura coupling reaction catalyzed by Pd@OC-MA with various substituents
Entry
1
Aryl halides
Arylboronic acid
Product
Product
Yield (%)
TON
428
3a
99
2
3
4
5
6
3b
3c
3d
3e
3f
99
95
96
91
94
428
411
415
394
406
Br
Me
7
8
3g
3h
91
95
394
411
9
3i
95
411

6
Tetrahedron
10
11
12
13
14
3j
3k
3l
84
90
63
65
80
364
390
272
281
347
3m
3n
Cl
Me
15
16
17
3o
3p
3q
87
99
68
377
428
294
18
19
3r
3s
55
238
Trace
2.3. Thermal filtration experiment of catalysts Pd@OC-MA
Generally speaking, thermal filtration experiment can be
judged whether the catalysis was concluded from the Pd@OC-
MA or from the leached palladium. It was carried out using
bromobenzene and phenylboronic acid as reactants in the Suzuki
reaction (Figure 7). The reactivity was conducted under the
optimal conditions for 3 h and it had a conversion of 76 %; the
catalyst Pd@OC-MA was separated from the reaction mixture
and further stirred under the preceding conditions for 2 h. There
is no change in the conversion of the reaction mixture by GC
analysis. It can be seen that Pd@OC-MA catalyst plays a
catalytic role in the reaction rather than the leached Pd in the
solution.
Figure 7. The influence of reaction time on the conversion of bromobenzene
in Suzuki reactions and thermal filtration experiment for Pd@OC-MA.

7
2.4. Recyclability test of catalyst Pd@OC-MA
MA was evaluated by thermogravimetry analysis (SCINCO
thermal gravimeter S-1000, Japan) under nitrogen protection, and
the heating rate from r.t. to 800℃ was 10 K/min. All NMR
spectra were recorded on MERCURY (400 MHz for NMR)
spectrometers; chemical shifts are expressed in ppm (δunits)
relative to TMS signal as internal reference in CDCl3. XPS
measurement of the OC-MA and Pd@OC-MA were conducted
by the ESCALAB 250 Xi Mg X-ray resource (Thermo
Scientific).
The active-life and recyclability of catalysts are obvious
chanracteristics of heterogeneous catalysts. Hence, the
recyclability of the Pd@OC-MA was studied under the optimal
conditions for the reactions and the results were shown in the
Figure 8. (a). After the reaction, the catalyst Pd@OC-MA was
separated by high-speed centrifugation and then washed with
water (3 × 10 mL) and CH3COOC2H5 (3 × 10 mL) and the
reclaimed catalyst was dried at 60℃ for 8 hrs. Under the same
reaction conditions, the catalyst was continuously recycled for
five times and the catalytic activity of the catalyst was not
significantly reduced (in 99%, 99%, 98%, 98%, 98% yield). XPS
analysis was again used to detect the reused catalyst Pd@OC-
MA. In the Figure 8. (b), there are two different valences of Pd,
with the peaks at 335.5 eV (Pd 3d5/2), 341.2 eV (Pd 3d3/2) that can
be confirmed the existence of Pd (0) in the reused Pd@OC-MA
catalyst.31 It was shown that a small amount of Pd (Ⅱ) was
reduced to Pd (0) during the coupling reactions.
4.2. General procedure for Pd@OC-MA catalysted Suzuki-
Miyaura coupling reactions
In a representative experiment, Pd@OC-MA catalyst (3 mg)
was added to mixture of bromobenzene (0.1 mmol), arylboronic
acid (0.15 mmol), NaHCO3 (0.15 mmol) in H2O (3 mL), and the
reaction mixture stirred violently at r.t. for 5 h. After the reaction,
it was extracted with CH3COOC2H5 and monitored by TLC
analysis. The catalyst was detached by high speed centrifugation
and then washed with H2O (3×3 mL) and CH3COOC2H5 (3×3
mL) and dried at 60 ℃ for 8 h for the next run. Furthermore, the
organic components were concentrated on a rotary evaporator to
give the desired biaryl group. The homologous product was
obtained by flash chromatography. The product was analyzed by
NMR.
4.3. Characterization
1
4.3.1 Biphenyl (3a, 3i), H NMR (400 MHz, CDCl3): δ = 7.51-
7.48 (m, 4H), 7.35-7.32 (m, 4H), 7.26-7.22 (m, 2H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 141.32, 128.83, 127.33, 127.25
ppm.
Figure 8. (a) the recyclability of the Pd@OC-MA, (b) XPS of Pd3d in reused
Pd@OC-MA.
4.3.2 3-nitro-1,1'-biphenyl (3b, 3m),1H NMR (400 MHz, CDCl3):
δ = 7.55-7.50 (m, 2H), 7.45-7.32 (m, 6H), 7.15-7.00 (m, 2H) ppm.
13C NMR (100 MHz, CDCl3): δ = 143.6, 140.0, 130.3, 130.2,
128.9, 127.9, 127.1, 122.8, 114.2, 114.0 ppm.
3. Conclusions
In summary, we have obtained a melamine-based mesoporous
COFs material OC-MA for anchoring Pd(OAc)2. The
heterogeneous catalyst Pd@OC-MA has a high-efficiency
recyclable for Suzuki - Miyaura cross-coupling reaction,
NaHCO3 as base and H2O as solvent, to obtain the product in 99
% yield. With a low catalyst loading, Pd@OC-MA also has
moderate to excellent conversion for inactive chlorinated
aromatic hydrocarbons in eco-friendly water. The catalytic
activity of the heterogeneous catalyst Pd@OC-MA did not
decrease significantly after five consecutive cycles. The catalyst
Pd@OC-MA has stable chemical properties, simple synthesis
process, low cost of raw materials, easy separation and recycling
and has potential applications in industrial production.
4.3.3 4-methoxy-1,1'-biphenyl (3c, 3k), 1H NMR (400 MHz,
CDCl3): δ = 7.70-7.63 (m, 4H), 7.55-7.43 (m, 5H), 3.80 (s, 3H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 140.62, 138.07, 137.80,
128.97, 127.60, 127.35, 127.05, 126.95, 15.95 ppm.
4.3.4 4-methylbiphenyl (3d, 3j), 1H NMR (400 MHz, CDCl3): δ =
7.62-7.60 (m, 2H), 7.53-7.44 (m, 4H), 7.36-7.26 (m, 3H), 2.42 (s,
3H) ppm. 13C NMR (100 MHz, CDCl3): δ = 141.17, 138.37,
137.01, 129.48, 128.71, 127.00, 126.97, 126.97, 21.10 ppm.
1
4.3.5 4-chlorobiphenyl (3e), H NMR (400 MHz, CDCl3): δ =
7.57-7.52 (m, 4H), 7.47-7.42 (m, 4H), 7.39-7.36 (m, 1H) ppm.
13C NMR (100 MHz, CDCl3): δ = 139.99, 139.66, 133.37, 128.90,
128.87, 128.38, 127.57, 126.97 ppm.
4. Experimental section
4.3.6 4-nitrobiphenyl (3f, 3l),1H NMR (400 MHz, CDCl3): δ =
8.43 (s, 1H), 8.19-8.18 (m, 1H), 7.91-7.90 (m, 1H), 7.62-7.58 (m,
3H), 7.51-7.48 (m, 2H), 7.45-7.42 (m, 1H) ppm. 13C NMR (100
MHz, CDCl3): δ = 142.81, 138.59, 132.98, 129.70, 129.15,
128.54, 127.11, 121.99 ppm.
4.1. Materials and methods
If not specified, all chemicals and reactants can be used
directly without further processing. The chemical reagents were
analytically pure. The FT-IR spectra analysis was obtained on a
JASCO FT/IR-660 Plus spectrometer. Powder X-ray
diffractometer was obtained on a Rigaku using CuKα (λ=1.5404
Å) source with a scan rate of 0.5° min-1. The micromorphology of
OC-MA and Pd@OC-MA were surveyed by SEM (ULTRA Plus,
Zaiss) and TEM(TECNAI G2F20STWIN D2278, FEI). Elemental
analysis of the catalyst Pd@OC-MA was performed on a
scanning electron microscope using an energy dispersive x-ray
spectrometer (EDX). The N2 adsorption-desorption isotherms
was measured on a BEL sorp-Max (BEL, Japan) at 77 K. The
specific surface area and pore size of the catalyst were calculated
by using the BET method. The thermal stability of the Pd@OC-
4.3.7 4-bromobiphenyl (3g, 3q), 1H NMR (400 MHz, CDCl3): δ =
7.58-7.56 (m, 4H), 7.47-7.44 (m, 4H), 7.39-7.36 (m, 1H) ppm.
13C NMR (100 MHz, CDCl3): δ = 139.94, 139.63, 133.32, 128.78,
128.87, 128.34, 127.51, 126.98 ppm.
1
4.3.8 3-methylbiphenyl (3h, 3n), H NMR (400 MHz, CDCl3): δ
= 7.66-7.65 (m, 2H), 7.51-7.46 (m, 4H), 7.41-7.38 (m, 2H), 7.24-
7.22 (m, 1H), 2.49 (s, 3H) ppm. 13C NMR (100 MHz, CDCl3): δ
= 141.41, 141.29, 138.35, 128.73, 128.71, 128.04, 128.02, 127.22,
127.20, 124.32, 21.59 ppm.

8
Tetrahedron
1
19. Devendar, P.; Qu, R. Y.; Kang, W. M.; He, B.; Yang, G. F. J. Agr.
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7.57-7.55 (m, 2H), 7.45-7.26 (m, 6H), 7.04-7.00 (m, 4H) ppm.
13C NMR (100 MHz, CDCl3): δ = 164.47, 162.03, 143.56, 139.99
(d, J = 2.0 MHz), 128.93, 127.89, 127.15, 122.82, 122.79, 114.17,
113.97 ppm.
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1
4.3.10 4'-methoxy-[1,1'-biphenyl]-4-carbaldehyde (3p), H NMR
(400 MHz, CDCl3): δ = 10.03 (m, 1H), 7.93-7.91 (m, 2H), 7.72-
7.70 (m, 2H), 7.60-7.58 (m, 2H), 7.02-6.99 (m, 2H), 3.86-3.84 (s,
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146.74, 134.66, 132.02, 130.28, 128.47, 127.02, 114.46, 55.37
ppm.
1
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4.3.11 4-chloro-4'-nitro-1,1'-biphenyl (3r), H NMR (400 MHz,
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2H), 7.40-7.39 (m, 2H) ppm. 13C NMR (100 MHz, CDCl3): δ
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Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (No. 21962017, 31760608 and
21968032), the Fundamental Research Funds for the Central
Universities (31920200002, 31920190016, 31920200042,
31920200086,), the project of cultivating higher education
teaching
achievements
in
Gansu
Province
(No.
2019GSJXCGPY-10), Graduate Research Innovation Project
(No. Yxm 2019137) and the Northwest Minzu University’s
Double First-class and Characteristic Development Guide Special
Funds-Chemistry Key Disciplines in Gansu Province (No.
11080316). We also thank Key laboratory for Utility of
Environmental Friendly Composite Materials and Biomass in
University of Gansu Province (Northwest Minzu University), for
financial support.
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A stable heterogeneous palladium catalysts, the porous COFs anchored Pd complex, was
synthesized by a simple technique.
Pd@OC-MA complex has been developed an efficient and stable catalyst for Suzuki -
Miyaura coupling reactions in an environmental friendly water medium at room
temperature.
The catalyst shows outstanding stability and reusability, it can be separated simply,
effectively and reused five times without any activity decrease.

Declaration of interests
√ The authors declare that they have no known competing financial interests or personal relationships
that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be considered
as potential competing interests: