Salen-porphyrin-based conjugated microporous polymer supported Pd nanoparticles: Highly efficient heterogeneous catalysts for aqueous C-C coupling reactions

Article abstract of DOI:10.1039/c8ta11330k

The salen-porphyrin based conjugated microporous polymer (SP-CMP) was first constructed by polycondensation reaction of a salen-dialdehyde derivative and pyrrole. Due to the outstanding chemical and thermal stability, abundant micropores with a reasonable pore size, and ordered salen-porphyrin arrays in the A₄B₄-type polymer framework, the functional CMP was further applied as a Pd nanoparticle support by the coordinate interactions between the polydentate chelating sites with Pd(OAc)₂ and subsequent reduction with NaBH₄. The as-synthesized composite material (Pd@SP-CMP) was fully characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and solid-state ¹³C nuclear magnetic resonance (NMR). The porous property of Pd@SP-CMP was also characterized by N₂ adsorption/desorption isotherms and the obtained material exhibited a Brunauer-Emmett-Teller (BET) surface area of 266 m² g^-1, together with a pore volume of 0.192 cm³ g^-1. The microscopic morphology of Pd@SP-CMP was further evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Pd@SP-CMP material with highly dispersed Pd nanoparticles exhibited excellent catalytic activity towards Suzuki-Miyaura and Heck-Mizoroki coupling reactions in water or in the dioxane/water mixture. In addition, Pd@SP-CMP also displayed outstanding stability and recyclability, and it can be reused without loss of activity in ten successive reactions. More importantly, the salen-porphyrin based CMPs could be the promising candidates for developing high-performance heterogeneous catalysts.

Full text of DOI:10.1039/c8ta11330k

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Salen–porphyrin-based conjugated microporous
polymer supported Pd nanoparticles: highly
efficient heterogeneous catalysts for aqueous C–C
coupling reactions†
Cite this: DOI: 10.1039/c8ta11330k
a
a
a
Pengyao Ju, Shujie Wu, Qing Su, Xiaodong Li,a Ziqian Liu,a Guanghua Lib
*
a
*
and Qiaolin Wu
The salen–porphyrin based conjugated microporous polymer (SP-CMP) was first constructed by
polycondensation reaction of a salen-dialdehyde derivative and pyrrole. Due to the outstanding chemical
and thermal stability, abundant micropores with a reasonable pore size, and ordered salen–porphyrin
arrays in the A4B4-type polymer framework, the functional CMP was further applied as a Pd nanoparticle
support by the coordinate interactions between the polydentate chelating sites with Pd(OAc)2 and
subsequent reduction with NaBH4. The as-synthesized composite material (Pd@SP-CMP) was fully
characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), Fourier transform
infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and solid-state 13C nuclear
magnetic resonance (NMR). The porous property of Pd@SP-CMP was also characterized by N2
adsorption/desorption isotherms and the obtained material exhibited a Brunauer–Emmett–Teller (BET)
surface area of 266 m2 gꢀ1, together with a pore volume of 0.192 cm3 ꢀ1. The microscopic morphology
g
of Pd@SP-CMP was further evaluated by scanning electron microscopy (SEM) and transmission electron
microscopy (TEM). The Pd@SP-CMP material with highly dispersed Pd nanoparticles exhibited excellent
catalytic activity towards Suzuki–Miyaura and Heck–Mizoroki coupling reactions in water or in the
dioxane/water mixture. In addition, Pd@SP-CMP also displayed outstanding stability and recyclability, and
it can be reused without loss of activity in ten successive reactions. More importantly, the salen–
porphyrin based CMPs could be the promising candidates for developing high-performance
heterogeneous catalysts.
Received 25th November 2018
Accepted 4th January 2019
DOI: 10.1039/c8ta11330k
rsc.li/materials-a
palladium contamination in the products, which result in
restricting their practical applications.5 To overcome these
Introduction
disadvantages, considerable efforts have been devoted to
develop heterogeneous palladium catalysts. So far, some porous
materials such as silica-supported salts,6 zeolites,7 carbon-
based materials,8 and porous organic polymers (POP)9 have
been employed as supports in heterogeneous catalysis. Among
these supports, the POP materials have been found to be
attractive supports for heterogeneous catalyst systems, due to
their high surface areas, permanent porosity and easy structure
tunable functionality.
Conjugated microporous polymers (CMPs)10 emerging as
a class of promising POPs have received growing attention in
recent years, due to their excellent performance in gas adsorp-
tion,11 ion sensing,12 catalysis,13 and energy storage and
conversion.14 Signicantly, tremendous efforts have been made
on the development of CMP materials with structure–property
correlations. Although much progress has been made in
improving the inherent porous properties, it is highly desirable
Carbon–carbon cross-coupling reactions have been among the
most useful synthetic transformations, and therefore have
attracted tremendous academic and industrial interest.1,2 In
this regard, homogeneous palladium catalysts containing
a large number of ancillary ligands such as arenes, N-
heterocyclic carbenes (NHC), acyclic diaminocarbenes (ADC),
and bipyridines have been developed in recent decades.3
Generally, homogeneous catalysts with uniform and well-
dened active sites exhibit excellent activity, high turnover
frequency, good selectivity, and high yields.4 However, homo-
geneous catalysis has some drawbacks, such as the use of
expensive ligands, metal leaching, poor recyclability, and
aCollege of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R.
China. E-mail: suqing@jlu.edu.cn; wuql@jlu.edu.cn
bState Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin
University, 2699 Qianjin Street, Changchun 130012, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ta11330k
to develop functionalized CMPs for
a
wider range of
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applications. The immobilization of the CMPs with Pd nano- ESCALAB 250 spectrometer. The palladium contents were
particles was successfully used for the hydrogenation of 4- determined by using a Perkin-Elmer ICP-OES Optima 3300 DV
nitrostyrene and N-benzylideneaniline and oxidation of benzyl spectrometer. Scanning electron microscopy (SEM) images were
alcohol,15 which offered a new opportunity for creating nano- obtained with a Hitachi SU8000. High-resolution transmission
porous hybrid materials. Recently, the porphyrin-based porous electron microscopy (HRTEM) and transmission electron
polymers also exhibited high catalytic activity and superior microscopy (TEM) images were obtained with a JEM-2100F. The
recyclability by loading of Pd nanoparticles on the frame- selected area electron diffraction (SAED) image was obtained
works.16 In such nanoporous catalyst systems, porous structures with a Tecnai G2 F20 S-TWIN.
and the interaction of loading nanoparticles with supports are
responsible for the catalytic performance. Moreover, the inter-
disciplinary research efforts offered new approaches for explo-
Synthetic procedures
ration of high-performance heterogeneous catalysts. Currently,
Synthesis of SP-CMP. A mixture of monomer 3 (554 mg, 1.27
in terms of cost, safety and environmental impact, it is of great mmol) and propionic acid (20 mL) was placed in a 50 mL round-
ꢁ
signicance to explore the catalytic properties of the supported bottom ask, and heated to 150 C. The steamed pyrrole (0.09
metal nanoparticles in environmentally friendly media such as mL, 1.27 mmol) was added to the reaction mixture. Then the
water and/or its co-solvents.17 However, up to now, there are no mixture was treated under reux conditions for 5 h, and cooled
examples involving CMP-supported Pd nanoparticles for appli- to room temperature. The resulting precipitate was obtained by
cation in heterogeneous catalysis in water.18
ltration and washed with hot water and THF. Further puri-
With continuous efforts for development of functional cation of the crude product was carried out by Soxhlet extraction
porous materials,9b,19 a salen–porphyrin-based CMP (SP-CMP) from THF for 24 h. The powder was collected and dried at 65 ꢁC
was facilely prepared by aldehyde–pyrrole polycondensation. under vacuum overnight to produce SP-CMP as a black solid in
The resulting CMP material possessed a high surface area and 92% isolated yield.
thermal stability, hydrophilic microporous nature, and rational
Synthesis of Pd@SP-CMP. The SP-CMP (100 mg) was
tunability of salen and porphyrin units in the A4B4-type polymer dispersed in 10 mL of acetone under ambient conditions, and
framework. The ultrane Pd nanoparticles were further stabi- then palladium acetate (45 mg, 0.2 mmol) was added. The
lized on the microporous network of SP-CMP with uniform mixture was kept stirring for 12 h at room temperature. To this
dispersion via the coordinate interactions between the poly- solution, 4 mL of MeOH was subsequently added to the slurry,
dentate chelating sites with Pd(OAc)2 and subsequent reduction followed by the addition of 3 mL of 2 M NaBH4 solution under
with NaBH4. Moreover, the Pd nanoparticle supported SP-CMP vigorous stirring. Aer 3 h, the resulting solid was isolated by
(Pd@SP-CMP) with high stability and hydrophilic microporous centrifugation, and thoroughly washed with MeOH (3 ꢂ 10 mL)
properties also demonstrated excellent activities and good and acetone (3 ꢂ 10 mL) to remove any impurities. Further
recyclability for catalyzing Suzuki–Miyaura and Heck–Mizoroki purication of the crude product was carried out by Soxhlet
coupling reactions in water or a dioxane/water mixture.
extraction from THF for 24 h. The as-prepared sample was
further dried in a vacuum drying oven at 65 ꢁC for 12 h to yield
Pd@SP-CMP (yield 77%).
General procedure for the Suzuki–Miyaura coupling reac-
tion. In a typical run, a mixture of phenylboronic acid (0.75
Experimental
Materials and methods
All reagents and solvents were purchased from commercial mmol), halobenzenes (0.5 mmol), Pd@SP-CMP (0.3 mol%),
suppliers and used as received, unless otherwise indicated. K2CO3 (0.75 mmol) and solvent (5.0 mL) was stirred at 80 ꢁC for
Column chromatography was performed using silica gel (200– a certain amount of time under a nitrogen atmosphere. The
300 mesh). FT-IR spectra analyses were performed using reaction mixture was then cooled to room temperature, treated
a Bruker IFS66 V spectrometer from 400 to 4000 cmꢀ1 by using with ethyl acetate (10.0 mL), and then ltered over a celite pad,
KBr pellets. 1H and 13C spectra were obtained by using a Bruker which was washed three times with ethyl acetate. The ltrate
AVANCE-400 NMR spectrometer. 13C CP-MAS NMR measure- was washed with distilled water to remove potassium
ments were carried out using a Bruker Avance III 400WB spec- carbonate, and the organic layer was collected and dried over
trometer at a MAS rate of 5 kHz and a CP contact time of 2 ms. anhydrous sodium sulfate. The solvent was evaporated under
Thermogravimetric analysis (TGA) was performed on a TA-Q500 vacuum and the residues were puried by silica gel chroma-
thermogravimetric analyzer by measuring the weight loss under tography to afford a pure product. In recycling tests, the catalyst
nitrogen. Powder X-ray diffraction (PXRD) data were collected was separated by ltration, washed with ethyl acetate and THF,
using a PANalytical B. V. Empyrean by depositing the powder on and activated under vacuum at 65 ꢁC for 12 h, which was reused
a glass substrate. The nitrogen adsorption and desorption in the next run.
isotherms were measured at 77 K with a Micromeritics ASAP
General procedure for the Heck–Mizoroki coupling reaction.
2020M system. Surface areas were calculated using Langmuir In a typical run, a mixture of olens (0.6 mmol), halobenzenes
and Brunauer–Emmett–Teller (BET) methods, respectively. The (0.5 mmol), Pd@SP-CMP (0.6 mol%), K2CO3 (0.75 mmol) and
pore size distribution curves were calculated from nitrogen solvent (5.0 mL) was stirred at 80 ꢁC for a certain amount of time
adsorption isotherms using non-local density functional theory under a nitrogen atmosphere. The reaction mixture was cooled
(NLDFT). XPS measurements were performed using an to room temperature, treated with ethyl acetate (10.0 mL), and
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then ltered over a celite pad, which was washed three times material. The reections with 2q values of 39.5ꢁ and 45.6ꢁ could
with ethyl acetate. The ltrate was washed with distilled water to be assigned to the (111) and (200) planes, similar to the previous
remove potassium carbonate, and the organic layer was observations in the structures of palladium.23
collected and dried over anhydrous sodium sulfate. The solvent XPS was used to gain further insight into the compositions
was evaporated under vacuum and the residues were puried by and conrm the oxidation state of the palladium. The XPS data
silica gel chromatography to afford a pure product.
collected for Pd@SP-CMP material are shown in Fig. 1D, and
the typical peaks for C1s, N1s and O1s are shown in Fig. S6 to S9
in the ESI.† As shown in Fig. 1E, the binding energies at
340.6 eV and 335.2 eV correspond to Pd 3d3/2 and 3d5/2 orbitals,
which also indicate the incorporation of Pd nanoparticles into
the CMP material.24 The palladium content was further deter-
mined by inductively coupled plasma (ICP) analysis with
21.3 wt% Pd loading level.
Results and discussion
The salen–porphyrin based conjugated microporous polymer
(SP-CMP) was rst constructed by polycondensation reaction of
a salen-dialdehyde derivative and pyrrole according to the
literature procedure.20 As shown in Scheme 1, the interactions
of polydentate chelating sites of SP-CMP with Pd(OAc)2 gave rise
to the supported polymer Pd/SP-CMP, and subsequent reduc-
tion with NaBH4 afforded Pd@SP-CMP. The chemical structure
of the Pd@SP-CMP was characterized by FT-IR and 13C CP/MAS
NMR spectroscopies. The FT-IR spectra of Pd@SP-CMP showed
the disappearance of the aldehyde carbonyl stretching band
(1693 cmꢀ1) of monomer 3 (red), indicating the absence of the
starting material. Meanwhile, the characteristic stretching
vibration bands of the imine group appeared at 1620 cmꢀ1 and
1622 cmꢀ1 in the IR spectra of SP-CMP and Pd@SP-CMP,
respectively. The vibrations at 1100 cmꢀ1 and 976 cmꢀ1 were
observed for the presence of porphyrin rings, demonstrating
that the products are fully imidized networks (Fig. 1A).21 The 13C
CP-MAS NMR spectrum of Pd@SP-CMP further indicated that
salen and porphyrin units were well integrated into the skeleton
of the conjugated polymer (Fig. 1B). The characteristic signal at
152.9 ppm was assigned to the carbon atom of imine bonds of
salen units. The peak at 151.2 ppm corresponded to the carbon
atom of phenoxyl attached to the oxygen atom. The broad
signals from 132.5 to 108.5 ppm could be assigned to the carbon
atoms of the porphyrin ring and the phenyl group in the
polymer.22
The porous properties of SP-CMP and Pd@SP-CMP were
evaluated by N2 adsorption and desorption measurements at 77
K. As shown in Fig. 1C, the nitrogen adsorption isotherm of SP-
CMP exhibits a type I sorption prole, while the nitrogen
adsorption isotherm of Pd@SP-CMP exhibits a combination of
the type I and IV sorption prole.25 The irreversible adsorption
occurs in the nitrogen adsorption isotherm of SP-CMP, which is
indicative of small micropores and a kinetic barrier to adsorp-
tion.26 The Brunauer–Emmett–Teller (BET) surface areas were
calculated to be 482 m2 gꢀ1 and 266 m2 gꢀ1 for SP-CMP and
Pd@SP-CMP, respectively. Compared with the original SP-CMP,
the BET surface area of Pd@SP-CMP is signicantly reduced,
indicating that Pd nanoparticles were successfully loaded on
the framework of the host material. And the total pore volume
of the obtained CMP materials was estimated to be 0.198 and
0.192 cm3 gꢀ1 for SP-CMP and Pd@SP-CMP, respectively. The
level of microporosity in the obtained materials was further
assessed by the ratio of micropores to the total pores (0.772 and
0.518, for SP-CMP and Pd@SP-CMP), which also suggested that
SP-CMP and Pd@SP-CMP were essentially microporous mate-
rials.27 The pore size distribution was obtained by the nonlocal
density functional theory (NLDFT) method as shown in Fig. 1F.
Pd@SP-CMP exhibited abundant micropores with the domi-
nant pore width centered at 1.1 and 1.8 nm and a small amount
of mesopores at 2.9 nm.
Thermogravimetric analysis was performed to test the
thermal stabilities of the SP-CMP and Pd@SP-CMP. As shown in
Fig. S1,† SP-CMP exhibited a 20% weight loss around 410 ꢁC and
Pd@SP-CMP was stable up to 520 ꢁC with a weight loss of 20%.
The structure of the resulting polymer was also identied by
PXRD analysis with CuKa radiation as shown in Fig. S2,† which
was indicative of the formation of the amorphous polymer
To understand the morphologies of the surface of Pd@SP-
CMP, its microstructure was investigated by scanning electron
microscopy (SEM) and transmission electron microscopy (TEM)
as shown in Fig. 2. The SEM images of Pd@SP-CMP revealed the
Scheme 1 Schematic representation of the synthesis of SP-CMP and Pd@SP-CMP.
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Fig. 1 (A) FT-IR spectra of monomer 3 (red) and Pd@SP-CMP (black). (B) Solid-state 13C NMR spectrum of Pd@SP-CMP. (C) Nitrogen adsorption
and desorption isotherms of Pd@SP-CMP and SP-CMP at 77 K. (D) XPS survey scan of Pd@SP-CMP. (E) High resolution XPS spectra of palladium
3d for Pd@SP-CMP. (F) The pore size distribution of Pd@SP-CMP.
amorphous morphology composed of large agglomerated (EDS) analysis also displayed a homogeneous distribution of
spheres (Fig. 2A). The high resolution TEM image (HR-TEM) of palladium within the material (Fig. 3).
the Pd@SP-CMP (Fig. 2B) showed that the Pd nanoparticles are
Pd nanoparticles supported on porous organic polymers
in the crystalline phase with a crystal plane spacing of 0.224 nm, have become highly important in synthetically useful organic
which corresponds to the (111) plane of Pd nanoparticles.28 In reactions because of their favourable properties, such as large
addition, the corresponding selected area electron diffraction surface area, high thermal and chemical stability, and easy
(SAED) pattern (insertion in Fig. 2B) also showed the charac- recyclability.29 To evaluate the catalytic performance of Pd@SP-
teristic diffraction planes at (111) and (200), which are consis- CMP as a heterogeneous catalyst, Suzuki–Miyaura coupling
tent with the PXRD pattern of the Pd@SP-CMP. The TEM reactions of halobenzenes with phenylboronic acid derivatives
images show the uniform distribution of Pd NPs with an were studied. Initially, we performed the model reaction
average diameter of 5.8 nm (Fig. 2C and D), which could be between iodobenzene and phenylboronic acid using the
derived from the strong interactions of Pd nanoparticles with Pd@SP-CMP catalyst. The inuence of solvent, reaction time,
polydentate coordination sites in the support material. The base, and temperature on the catalytic properties of Pd@SP-
elemental mapping by energy-dispersive X-ray spectroscopy CMP was systematically explored, and the results are presented
in Table S1.†The coupling product with the best yield (99%) was
obtained aer reacting in H2O for 5 h at 80 ꢁC in the presence of
K2CO3 under a nitrogen atmosphere.
Under the optimal reaction conditions, the scope of
substrates was extensively investigated. As shown in Table 1,
Fig. 2 The morphologies of the surface of Pd@SP-CMP: (A) SEM
image; (B) HRTEM image, the inset shows the selected area electron
diffraction (SAED) pattern; (C) TEM image; (D) the size distribution Fig. 3 Energy-dispersive X-ray elemental mapping images of Pd@SP-
profile of Pd nanoparticles.
CMP.
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Table 1 Catalytic activity test of Pd@SP-CMP in the Suzuki–Miyaura
phenylboronic acid with chlorobenzene (entry 14) and other
chlorobenzenes (entry 15–17).
coupling reactiona
A typical kinetic prole of the coupling reaction of the
iodobenzene and phenylboronic acid catalyzed by Pd@SP-CMP
is shown in Fig. 4A (black line). Each experiment was performed
at least in duplicate and average yields were used for kinetics
calculations. In the model reaction, the yield of the product
increased with the increasing reaction time, and a maximum
yield of 99% was achieved aer 5 hours. To determine whether
Pd@SP-CMP was truly heterogeneous or not, a hot ltration
experiment was carried out using iodobenzene and phenyl-
boronic acid as substrates (Fig. 4A, red line). Aer 1 hour, the
reaction mixture was ltered to remove the catalyst, and the
ltrate was allowed to react for additional 4 hours under the
same conditions. The Suzuki–Miyaura reaction stopped
completely without an increase in the yield aer the removal of
the solid catalyst, which indicated that palladium active species
did not leach from the supports and the observed catalyst
system should be heterogeneous in nature.
The high catalytic activity of Pd@SP-CMP for the Suzuki–
Miyaura reaction prompted us to examine its recyclability,
which is also an important factor in heterogeneous catalytic
systems. Thus, the recyclability of Pd@SP-CMP was examined
by using iodobenzene and phenylboronic acid as substrates. In
each cycle, the Pd@SP-CMP was recovered by ltration, and
then washed, dried and reused in the next run of the reaction.
The results demonstrated that the Pd@SP-CMP was reusable up
to ten cycles without signicant loss of catalytic activity
(Fig. 4B), which indicated that Pd@SP-CMP could be a highly
stable and economical catalyst. To our delight, the comparison
of the FT-IR spectra before and aer ten reaction runs indicated
that the original skeleton connectivity was almost maintained
(Fig. 4C). The SEM images of the reused catalyst revealed that
the surface morphologies were not changed (Fig. S10†). X-ray
photoelectron spectroscopy (XPS) of Pd@SP-CMP before and
aer ten reaction runs indicated that the electronic state of
palladium was almost maintained (Fig. S11†). The palladium
content in the recovered Pd@SP-CMP by ICP analysis was
20.2%, which was very close to that (21.3%) of the newly
prepared catalyst. The above results also demonstrated that Pd
nanoparticles are strongly supported in the CMP network.
Moreover, we have performed more tests to examine the
Entry
R1
X
R2
Time/h
Yieldb/%
1
2
3
4
5
6
7
8
H
I
I
I
I
I
I
I
Br
Br
I
H
H
H
H
H
H
H
H
5
5
5
5
5
5
5
5
5
5
5
12
12
8
12
12
24
99
95
98
94
95
95
92
94
95
98
96
92
93
95
91
86
78
4-OCH3
4-CH3
4-OH
4-NO2
4-CN
4-COOMe
4-CH3
4-CN
H
9
H
10
11
12
13
14c
15c
16c
17c
4-OCH3
4-F
4-Br
4-CN
H
H
H
4-CN
H
4-Br
I
Br
Br
Cl
Cl
Cl
Cl
4-CN
H
4-CH3
4-NO2
4-CN
a
Halobenzenes (0.5 mmol), arylboronic acids (0.75 mmol), K2CO3 (0.75
mmol), H2O (5 mL), Pd@SP-CMP (0.3 mol%), 80 ꢁC, and N2. b Isolated
c
yields based on halobenzenes. Solvent: DMF 5 mL and 120 ꢁC.
Pd@SP-CMP can effectively catalyze a series of coupling reac-
tions with a wide range of substrates, and exhibits high to
excellent catalytic activity. In the case of iodobenzene deriva-
tives with the electron-withdrawing and electron-donating
groups, the corresponding products were obtained in excel-
lent yields (92–98%, entries 2–7). Under the same conditions,
the reaction of the substituted bromobenzene with phenyl-
boronic acid gave biaryl products with excellent yields up to
95% (entries 8, 9). Additionally, for the substituted phenyl-
boronic acids containing electron-withdrawing or electron-
donating groups, the corresponding products could be ob-
tained with a nearly quantitative yield (entries 10–13). Further-
more, we applied the catalytic system for the Suzuki–Miyaura
coupling reaction of chlorobenzenes. It is worth noting that
high yields were achieved in the coupling reaction of
Fig. 4 (A) Kinetic profile of the iodobenzene and phenylboronic acid coupling reaction. Reaction conditions: phenylboronic acid (0.75 mmol),
iodobenzene (0.5 mmol), Pd@SP-CMP (0.3 mol%), K2CO3 (0.75 mmol), H2O (5.0 mL) and 80 ꢁC (blank); Hot filtration test (red). (B) Recycling
catalytic test for the iodobenzene and phenylboronic acid coupling reaction. Reaction conditions: phenylboronic acid (0.75 mmol), iodobenzene
(0.5 mmol), Pd@SP-CMP (0.3 mol%), K2CO3 (0.75 mmol), H2O (5.0 mL), 80 ꢁC and 5 h. (C) FT-IR spectra of Pd@SP-CMP (black) and Pd@SP-CMP
after the ten reaction runs of catalysis (red).
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stability of our catalyst.30 As shown in Fig. S12,† FT-IR spectra of reactions, which are evaluated by comparison with the literature
Pd@SP-CMP upon treatment in aqueous solutions with pH data obtained with other Pd supported catalysts, which are
values of 1 and 13 for 3 days indicated that the original skeleton shown in Table S3 and S4† in the ESI.†
connectivity was almost maintained. Aer the immersion tests,
the recovered Pd@SP-CMP was further evaluated for the
performance towards the Suzuki–Miyaura coupling reaction
Conclusions
using iodobenzene and phenylboronic acid as substrates. The In summary, a salen–porphyrin-based conjugated microporous
obtained result demonstrated that the immersion Pd@SP-CMP polymer with ordered salen–porphyrin arrays in the A4B4-type
material showed similar catalytic activity to that of the fresh polymer framework, and high chemical and thermal stability
catalyst.
has been successfully synthesized, and further employed as
The results obtained from the Suzuki–Miyaura coupling a good support for loading Pd nanoparticles. The resulting
reactions further motivated us to evaluate the catalytic perfor- composite material Pd@SP-CMP has been thoroughly charac-
mance of Pd@SP-CMP for other C–C bond-forming reactions. terized by spectroscopic techniques, sorption and electron
We then examined the potential of the Pd@SP-CMP catalyst in microscopy analyses. The Pd nanoparticles formed by the
the Heck–Mizoroki coupling reaction. The Heck coupling reduction of NaBH4 are uniformly distributed within the
reactions of iodobenzene with styrene were tested under frameworks of SP-CMP with an average diameter of 5.8 nm, and
different conditions, and it was found that a high yield of 99% also possess remarkable features such as high stability and
using K2CO3 as a base in the 1,4-dioxane/H2O mixed solution dispersibility in water. The Pd@SP-CMP exhibited excellent
for 12 h at 80 ꢁC under a nitrogen atmosphere was obtained catalytic activity and wide substrate adaptability in the Suzuki–
(Table S2†). Under optimal reaction conditions, Pd@SP-CMP Miyaura and Heck–Mizoroki cross coupling reactions in water
was used to catalyze the Mizoroki–Heck reaction of various or a dioxane/water mixture, together with outstanding recycla-
halobenzenes with olens in 1,4-dioxane/H2O mixed solvent, bility without loss of activity in ten successive reactions. The
and the results are shown in Table 2. Under the optimized excellent catalytic performance of the material could be attrib-
conditions, various iodobenzenes containing electron- uted to the outstanding chemical and thermal stability, hydro-
withdrawing and electron-donating groups reacted efficiently philic micropores, and the synergistic effect between the salen–
with methylacrylate or acrylic acid to afford excellent isolated porphyrin based CMP and Pd nanoparticles. This work also
yields (entries 1–6). For the coupling of bromobenzene and highlighted the potential of developing salen–porphyrin based
styrene, a good yield was obtained at 100 ꢁC in DMF/H2O mixed CMPs as nanosized metal-based catalyst materials, which
solvent (entry 8). It is worth mentioning that the reaction of should afford new opportunities for transition metal nano-
inactivated-aryl chlorides with styrene by Heck–Mizoroki particle composites with
coupling reactions could also be performed smoothly at 120 ꢁC transformations.
in DMF solvent (entries 9–11). The results demonstrate that
a
broad range of catalytic
Pd@SP-CMP could be used as an excellent heterogeneous
catalyst for Suzuki–Miyaura and Heck–Mizoroki coupling
Conflicts of interest
There are no conicts to declare.
Table 2 Catalytic activity test of Pd@SP-CMP in the Heck–Mizoroki
Acknowledgements
coupling reactiona
This work was supported by the National Natural Science
Foundation of China (No. 51703076) and the Excellent Young
Teachers Program of Jilin University. Q. S. thanks the open
projects in State Key Lab of Inorganic Synthesis and Preparative
Chemistry, Jilin University.
Entry
R1
X
R2
Time/h
Yieldb/%
1
2
3
4
5
6
7
H
I
I
I
I
I
I
I
Br
Cl
Cl
Cl
COOH
COOH
COOH
COOCH3
COOCH3
COOCH3
Ph
Ph
Ph
Ph
Ph
12
12
12
12
12
12
12
24
12
12
24
99
93
95
96
94
95
99
92
95
93
82
Notes and references
4-OH
4-NO2
H
4-OCH3
4-NO2
H
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