Palladium nanoparticles embedded in metal-organic framework derived porous carbon: Synthesis and application for efficient Suzuki-Miyaura coupling reactions

Article abstract of DOI:10.1039/c6ra00378h

A nanoporous carbon (NPC) material was prepared by one-step direct carbonization of a metal-organic framework, MOF-5, without additional carbon precursors. Pd nanoparticles were immobilized on the MOF-5-derived NPC by an impregnation method coupled with subsequent reduction with NaBH₄. The prepared catalyst was in-depth characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and N₂ adsorption. The catalyst was used to catalyze the Suzuki-Miyaura coupling reactions and exhibited high catalytic efficiency with yields ranging from 90% to 99% under mild conditions. The results demonstrated the great application potential of MOF precursor-based metal nanoparticle composites in catalysis.

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ARTICLE
Palladium Nanoparticle Embedded in Metal Organic Framework
Derived Porous Carbon: Synthesis and Application for Efficient
Suzuki-Miyaura Coupling Reaction
Received 00th January 20xx,
Accepted 00th January 20xx
†,1
†,1
2
1*
1
1
DOI: 10.1039/x0xx00000x
Wenhuan Dong , Li Zhang , Chenhuan Wang , Cheng Feng , Ningzhao Shang , Shutao Gao ,
Chun Wang *
1
www.rsc.org/
A nanoporous carbon (NPC) material was prepared by one-step direct carbonization of metal organic framework, MOF-5,
without additional carbon precursors. Pd nanoparticles were immobilized on MOF-5-derived NPC by an impregnation
method coupled with subsequent reduction with NaBH4. The prepared catalyst was in-depth characterized by X-ray
photoelectron spectroscopy, transmission electron microscopy, scanning electron microscope, and N2 adsorption. The
catalyst was used to catalyze the Suzuki-Miyaura coupling reactions and exhibited high catalytic efficiency with the yields
ranging from 90% to 99% under mild conditions. The results demonstrated the great application potential of the MOF
precursor based metal nanoparticles composite in catalysis.
supports for metal nanoparticles also play an important role to
prevent the aggregation of metal nanoparticles, which would
result in loss of their catalytic activity. Therefore, suitable
Introduction
Palladiumꢀcatalyzed
SuzukiꢀMiyaura
crossꢀcoupling
supports for Pd nanoparticle catalysts are highly desirable.
Several solid materials, such as active carbon9, zeolites10,
mesoporous silica11 and polymers12,13, have been used as
heterogeneous catalyst supports for CꢀC coupling reactions.
However, some of the supported catalysts involve
disadvantages such as, uneven distribution of the active sites,
tedious preparation of the catalyst, lower catalytic activity and
so on. Therefore, the development of highly active and
selective heterogeneous catalysts for catalyzing CꢀC coupling
reactions under mild conditions is required for practical use.
Recently, nanoporous carbons (NPCs) materials, have been
touted as ideal catalyst support for heterogeneous catalyst
because of their high specific surface area and porosity14 in
combination with high chemical (acid and base resistant),
reaction plays a key role in the synthesis of pharmaceuticals,
herbicides, polymers and so on1ꢀ3. Palladium organic complexes
containing ligands such as phosphine, dibenzylideneacetone,
and carbenes have been widely used as homogeneous catalysts
for the SuzukiꢀMiyaura crossꢀcoupling reaction4,5. Although
homogeneous catalytic systems are known to exhibit high
activity, problems associated with the separation and recovery
of the expensive catalysts limit their large scale application in
industry6,7. On the contrary, heterogeneous catalysts can be
easily recovered from the reaction system and readily reused.
Recently, as a new generation of heterogeneous catalysts, Pd
nanoparticles supported on solid supports has gained much
attention due to their ease of separation and satisfactory
reusability, superior catalytic performance, good stability in
comparison to the traditional homogeneous catalysts8. The
thermal (>1000K) and excellent mechanical stability15,16
.
Highly porous carbons can be prepared via a variety of methods,
including direct pyrolysis of organic precursors, activation
(physical or chemical) of carbon17, hardꢀtemplate or softꢀ
template route18, and nanocast method19. However, these
methods often encounter one or more shortcomings, such as the
obtained carbon materials often contain disordered structures,
the templates need to be removed after carbonization, the
preparation process is tedious and so on. Therefore, the
development of novel synthesis strategy based on facile,
versatile, and reproducible method is highly desirable.
†
The authors contribute equally to this work.
1College of Sciences, Agricultural University of Hebei, Baoding 071001,
Hebei Province, P. R. China; 2 College of Environmental and Chemical
Engineering, Yanshan University, Qinhuangdao 066004, China.
Fax: (+86)312ꢀ7528292
Eꢀmail: fengchencctv@163.com (C. Feng); chunwang69@126.com (C.
Wang)
Electronic Supplementary Information (ESI) available: The nitrogen
adsorptionꢀdesorption isotherms and element mappings of the catalyst,
TEM and XPS images of the catalyst after 5 cycles, 1H NMR data of the
products. See DOI: 10.1039/b000000x/
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As an emerging class of highly porous material, metalꢀ chloroform, and NꢀN dimethylformamide (DMF) were all
organic frameworks (MOFs) have gained particular attention in obtained from Chengxin Chemical Reagents Company
recent years mainly due to their ease of preparation, designable (Baoding, China). Aryl boronic acids, aryl halides, and
framework structures and multifunctional nature20. MOFs with palladium chloride (PdCl2) were purchased from Aladdin
fascinating diverse structures, topologies, permanent nanoscale Reagent Limited Company and used as received.
porosity, high surface area and uniform structured cavities,
Xꢀray photoelectron spectroscopy (XPS) was performed with
have been demonstrated to be ideal templates for fabricating a PHI 1600 spectroscope using Mg Kα Xꢀray source for
nanoporous carbon. Highly nanoporous carbon can be excitation. Scanning electron microscopy (SEM) studies were
fabricated by direct carbonization of different MOFs without conducted on a Hitachi (Model S4800) instrument. The size and
the need of additional carbon precursors because MOFs was morphology of the nanoparticles were observed by transmission
taken as both a sacrificial template and a secondary carbon electron microscopy (TEM) using a JEOL model JEMꢀ
precursor. Several MOFs, such as UiOꢀ6621, MILꢀ10022, and 2011(HR) at 200 kV. The Brunauer–Emmett–Teller (BET)
AlꢀPCP23, have recently been demonstrated as promising surface areas were determined from the N2 adsorption at 300 K
templates to construct porous carbons. Compared with the using VꢀSorb 2800P (China). The amount of Pd and Zn was
conventional nanocasting technique with several steps, the determined by means of inductively coupled plasma atomic
merit of this approach lies in that it is a facile, controllable, and emission spectroscopy (ICPꢀAES) on Thermo Elemental IRIS
singleꢀstep procedure method. NPCs derived from MOFs have Intrepid II.
found a wide range of applications in different fields, such as
water treatment, contamination removal24, separation, electrode
Synthesis of MOF-5-NPC
materials18, gas storage25 and carriers for drug delivery systems
MOFꢀ5 nanocrystals were prepared according to the reported
26, due to their high specific surface area, large pore volume,
synthesis protocol30. Typically, MOFꢀ5 was prepared by mixing
high thermal stability and excellent electrochemical
performance.
In continuation of our efforts in the development of a
sustainable and active catalyst system27ꢀ29, in this paper, porous
ZnNO3·6H2O (10.4 g) and H2BCD (2 g) in DMF (140 mL)
until complete dissolution of the solids. Then, the mixture was
transferred into a roundꢀbottom flask connected to a condenser
o
and heated at 120 C for 24 h. After cooling, the supernatant
carbon was fabricated by one–step direct carbonization of
was removed and crystals deposited on the bottom of the flask
MOFꢀ5 (Zn4O(HꢀBDC)3, BDC = 1,4ꢀbenzenedicarboxylate)
were collected, washed with DMF, and then immersed in fresh
without using any additional carbon precursors. The obtained
chloroform overnight. The chloroform was changed twice
MOFꢀ5ꢀderived NPC exhibited a high specific surface area and
during two days. Finally, crystals were collected and dried in a
large pore volume. Pd nanoparticles were immobilized on
vacuum at 50 oC for 3 h. For the synthesis of MOFꢀ5ꢀNPC,
MOFꢀ5ꢀderived NPC by an impregnation method coupled with
MOFꢀ5 was directly carbonized at various temperatures (from
subsequent reduction with NaBH4. To evaluate the performance
700 to 1000 oC) under a flow of nitrogen gas. After the
the MOFꢀ5ꢀNPCꢀPd, Suzuki–Miyaura reaction was selected as
carbonization, the obtained black samples were denoted as
the model reaction. The results indicated that the MOFꢀ5ꢀNPCꢀ
MOFꢀ5ꢀNPCꢀ700, MOFꢀ5ꢀNPCꢀ800, MOFꢀ5ꢀNPCꢀ900, and
Pd can catalyzed the Suzuki–Miyaura reaction efficiently under
MOFꢀ5ꢀNPCꢀ1000, respectively.
mild conditions.
Synthesis of MOF-5-NPC-Pd
Pd nanoparticles were supported on the MOFꢀ5ꢀNPC by an
Selfꢀassembly
Carbonization
impregnation method. 50 mg of MOFꢀ5ꢀNPC was dispersed in
5 mL (1 mg/mL) chlorine palladium acid solution. Then the
resulting mixture was magnetically stirred in ambient
tempreture. After 5 hours later, the obtained solution was
filtered off and washed three times with distilled water, then
dried under vacuum at 60 °C. The resultant was dispersed in 5
mL of water, and 5.5 mg NaBH4 (0.027 mmol) was added
slowly to the resulting mixture. Subsequently, the pH of the
mixture was adjusted to 10 with 10% sodium hydroxide
solutions and the reaction was stirred for 2 h at 98 °C. Finally,
the isolated product was washed with distilled water and dried
at 60 °C for 5 hours in vacuum.
ꢀ ꢀNPC
MOFꢀ5ꢀNPC
MOFꢀ5
Br
R1
HCl
H2PdCl4
NaBH4
B(OH)2
H2BCD
R2
(ZnNO3)2—6H2O
R1
R2
Zn-free MOF-5-NPC-900-Pd
Scheme 1 The preparation process of the catalyst and the
Suzuki coupling reaction.
To preparation of the Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd, 50 mg of
MOFꢀ5ꢀNPCꢀ900 powder was dispersed in 20 mL of 10 % HCl
and standed for 6 h. And then the mixture was filtered and
washed with distilled water. Finally, the MOFꢀ5ꢀNPCꢀ900
without Zn or ZnO was obtained by vacuum drying at 60 oC for
2 hours.
Experimental
Materials and methods
Zinc nitrate hexahydrate (Zn(NO3)2⋅6H2O), terephthalic acid
(H2BCD), sodium borohydride, potassium carbonate,
2 | J. Name., 2012, 00, 1-3
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The Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd was prepared according to NPCꢀ900 raised to 2700 m2·gꢀ1 after the removal of Zn or ZnO
the same procedure mentioned above except that 50 mg MOFꢀ impurities through washing with HCl solution. After embedded
5ꢀNPCꢀ900 was replaced by 50 mg Znꢀfree MOFꢀ5ꢀNPCꢀ900.
Pd NPs in the Znꢀfree MOFꢀ5ꢀNPCꢀ900, the BET surface area
of the sample deceased to 2200 m2·gꢀ1, the result indicated that
Pd NPs were embedded in the Znꢀfree MOFꢀ5ꢀNPCꢀ900
successfully. The amount of Zn in ZnꢀfreeMOFꢀ5ꢀNPCꢀ 900
was determined by means of ICPꢀAES and the amount is <
0.001 wt %.
General procedure for Suzuki–Miyaura reactions
Phenylboronic acid (0.6 mmol), aryl halide (0.5 mmol), base
(1.5 mmol), solvents (EtOH/H2O = 1: 1, v/v, 4 mL) and a
certain amount of the catalyst was placed in a 25 mL roundꢀ
bottom flask, then the reaction mixture was shaken in an air
atmosphere for an appropriate time at room temperature. After
completing of the reaction, the reactor was diluted with 10mL
of H2O and the organic products were extracted with ethyl
acetate (3 × 10 mL). Then the combined organic solution dried
over anhydrous MgSO4 and filtered. The pure products were
obtained by flash chromatography using petroleum ether: ethyl
acetate as the eluent. The preparation process of the catalyst
and the Suzuki coupling reaction were illustrated in Scheme 1.
B
A
C
D
Results and discussion
Characterization of the catalyst
Table 1 The nitrogen adsorptionꢀdesorption isotherm and pore
size distributions of the MOFꢀ5ꢀNPC.
Pore
SBET
/m2·gꢀ1
V b
/cm3·gꢀ1
Catalysts
width a
/nm
Fig. 1 TEM (A), HRTEM (B,C) and SEM (D) images of Zn-free
MOFꢀ5ꢀNPCꢀ700
222
9.10
6.60
4.8
0.51
0.56
2.96
2.93
2.88
2.65
MOF-5-NPC-900-Pd.
MOFꢀ5ꢀNPCꢀ800
400
MOFꢀ5ꢀNPCꢀ900
2478
1778
2700
2200
1600
1400
MOFꢀ5ꢀNPCꢀ1000
5.47
4.35
4.83
ZnꢀfreeMOFꢀ5ꢀNPCꢀ900
ZnꢀfreeMOFꢀ5ꢀNPCꢀ900ꢀPd
C
Pd %
&
1200
1000
800
600
400
200
0
a. total adsorption average pore width; b. total pore volume.
In order to explore the pore structure of MOFꢀ5ꢀNPC
samples, the nitrogen adsorption and desorption isotherms were
recorded at 77 K. As we can see from Table 1, the sample
＆
％
o
o
carbonized at 700 C and 800 C, the BET surface area is just
222 and 400 m2·gꢀ1 and the total adsorption average pore width
is 9.1 nm to 5.47 nm, respectively. These results indicate that
the heat treatment at 700 oC and 800 oC is insufficient to
carbonize MOFꢀ5 into porous carbon. When the temperature
10
20
30
40
50
60
70
80
2 Theta (degree)
o
Fig. 2 The XRD image of Zn-free MOF-5-NPC-900-Pd.
increased to 900 C, the BET surface area is 2478 m2·gꢀ1 and
the total adsorption average pore width is 4.8 nm. As displayed
in Fig. S1 (see ESI†), the sample MOFꢀ5ꢀNPCꢀ900 showed
typical Type IV isotherm with sharp uptakes at low relative
pressure (P/P0 < 0.1) and slight uptakes at high relative pressure
(P/P0 > 0.9), indicating that they are totally microporous
materials with some macropores probably forming between
particles. However, when the carbonization temperature was
raise to 1000 oC, the BET surface area decreased to 1778 m2·gꢀ1
and the total adsorption average pore width rise to 5.47 nm. The
reason may be ascribed to that the carbon framework of MOFꢀ5
has already graphitization at high temperature. In addition, it
also worth mentioned that the surface area of Znꢀfree MOFꢀ5ꢀ
The TEM investigations are carried out to observe the size,
and the distribution of Pd nanoparticles embedded in Znꢀfree
MOFꢀ5ꢀNPCꢀ900ꢀPd. The highly existence of Pd nanoparticles,
which embedded in Znꢀfree MOFꢀ5ꢀNPCꢀ900 was clearly
observed in Fig. 1A and 1B. The density of Pd nanoparticles in
Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd nanocatalyst is abundant and
these nanoparticles did not form clusters. Fig. 1B and 1C
showed the highꢀresolution TEM (HRTEM) image of the asꢀ
prepared catalyst, wherein the lattice spacing is 0.22 nm, which
is just the lattice spacing of face centered cubic (fcc) Pd (0.22
nm), further indicating that is Pd nanoparticles. Besides, the
mean diameter of the particles was just 2.7 nm and was almost
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similar to the pore diameter of the nanoporous carbon support.
The Xꢀray diffraction (XRD) pattern in Fig. 2 showed the
It also can be clearly seen from the SEM image (Fig. 1D) that crystalline structure of the Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd
some of the Pd NPs supported on the surface of the Znꢀfree samples. The wide diffraction peak at 2 = 25° can be indexed
θ
MOFꢀ5ꢀNPCꢀ900, and the most of them inserted into the to porous carbon19. Besides, we characterized the XRD of the
cavities of Znꢀfree MOFꢀ5ꢀNPCꢀ900. The element mapping catalyst, the broadly peak appear at 40°, and the peaks at 47°
images (Fig. S2, †) clearly showed the uniform distribution of and 68° were very poor, which suggests the well dispersion of
fine Pd nanoparticles throughout the Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀ Pd nanoparticles31,32. The three peaks appear at 40°, 47° and
Pd composite.
68° can be assigned to (111), (200) and (220) crystal planes of
Pd0, respectively.
Pd03d5/2
13000
12000
11000
10000
9000
Pd03d3/2
Entry Catalysts
Yields / %
68
1
2
3
4
5
MOFꢀ5ꢀNPCꢀ700ꢀPd
MOFꢀ5ꢀNPCꢀ800ꢀPd
73
Pd2+3d5/2
Pd2+3d3/2
MOFꢀ5ꢀNPCꢀ900ꢀPd
92.1
90.3
98.6
MOFꢀ5ꢀNPCꢀ1000ꢀPd
Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd
8000
7000
Table 2 SuzukiꢀMiyaura coupling reactions catalyzed by
different catalysts
6000
346 344 342 340 338 336 334 332
Bingding Energy (eV)
n (K2CO3): n (Aryl iodide): n (Phenylboronic acid) = 4: 1:
1.3; solvent: 2 mL ethanol + 2 mL H2O; the dosage of
catalyst was 0.1 mol %; room temperature.
Fig. 3 The XPS image of Zn-free MOF-5-NPC-900-Pd.
Table 3 Suzuki coupling reactions of aryl halide with phenylboronic acid catalyzed by different catalysts.
Reaction conditions:
solvent/temp./time/Pd loading
Yield/
%
Aryl halide
Catalyst
Ref.
Bromobenzene
Bromobenzene
Bromobenzene
Iodobenzene
MOFꢀ5ꢀNPCꢀ900ꢀPd
Pd/MILꢀ53ꢀNH2
PdꢀMCMꢀ41
Pd/G
EtOH–H2O/25 oC/1h /0.1mol%
EtOH–H2O/40oC /0.5h/0.5mol%
EtOH–H2O/80oC /12h/0.05mol%
EtOH–H2O/60oC /02ꢀ24h/0.3 mol%
EtOH–H2O/60oC /2ꢀ24h/0.3mol%
98.6
94
This work
35
36
37
37
90
74
Iodobenzene
Pd/SBAꢀ15
42
4ꢀBromophenyl
acetaldehyde
Pd@pꢀSiO2
Pd/CMKꢀ3
DMF–H2O/200oC /3h/0.003 mol %
DMFꢀH2O/150oC/10min/0.02 mol %
65
99
38
39
Iodobenzene
phenyl boronic acid and phenyl bromide was chosen as model
The XPS spectra (Fig. 3) demonstrated that the Pd species reaction. As we can see in Table 2, among all the catalysts
embedded in the sample Znꢀfree MOFꢀ5ꢀNPCꢀ900 was present tested, Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd was found to be the
in metallic state rather than in oxidation state with the bond efficient catalyst for it gave the highest yield of product.
energies of 335.4 and 341.0 eV in the Pd 3d5/2 and 3d3/2 levels. Besides, as the data in Table 3, comparing with the other
As displayed in Fig. 3, the Pd 3d binding energy region was reported Pd nanoparticles catalysts in terms of the reaction
deconvoluted into four peaks with binding energies of 335.6, temperature, the dosage of catalyst and the yield of the product,
337.1, 340.9 and 342.0 eV. The two minor peaks in the Pd 3d the catalyst of Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd can efficiently
spectrum centered at 342.0 and 337.1 eV were ssigned to Pd2+ catalyze the Suzuki–Miyaura coupling reaction with
3d3/2 and Pd2+ 3d5/2, and the other two peaks centered at 340.9 comparable or higher yield, especially the coupling reaction
and 335.6 eV are very sharp with a huge intensity. These peaks which catalyzed by the MOFꢀ5ꢀNPCꢀ900ꢀPd can be performed
are assigned to Pd0 3d3/2 and Pd0 3d5/2, respectively33,34
.
efficiently at room temperature. Good dispersion of the Pd NPs
on the Znꢀfree MOFꢀ5ꢀNPCꢀ900 is the key factor for the high
Suzuki–Miyaura reactions catalyzed by the prepared catalytic activity of the catalyst. This is mainly owing to the
catalyst
high surface area of Znꢀfree MOFꢀ5ꢀNPCꢀ900, which leads to
In order to investigate the catalytic activity of the different high dispersion of Pd on the surface of support.
catalysts for Suzuki–Miyaura coupling reaction, the coupling of
4 | J. Name., 2012, 00, 1-3
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To standardize the reaction conditions, a series of reactions acids and aryl halides were carried out using 0.1 mol% Znꢀfree
were performed using several bases, solvents, and different MOFꢀ5ꢀNPCꢀ900ꢀPd as catalyst at room temperature (Table 5).
catalyst dosage to obtain the best possible combination. Initially, It was seen that the catalytic system was applicable to various
the experiment was performed using SuzukiꢀMiyaura crossꢀ aryl bromides and tolerant to a broad range of functional groups
coupling reaction of bromobenzene with phenyl boronic acid. and for most of the substrates, the reaction could be completed
As we can see from Table 2, when the reaction was carried out in 0.75–1.5 h with high yields, with the substrates having either
in MeOH, EtOH, DMF and H2O under the same reaction electronꢀwithdrawing groups (ꢀOH, ꢀCOCH3, ꢀCHO) or
conditions, the products were obtained in poor yields of 38% ꢀ electronꢀdonating groups (ꢀOCH3, ꢀH, ꢀCH3). It was also found
70% (Table 4, entries 1–4). However, when we adopted the that the yield of reaction paraꢀ or metaꢀsubstituted aryl bromide
organic/aqueous coꢀsolvent, high yields of 78–98% were is higher than those of orthoꢀposition aryl bromides. To test the
obtained (Table 4, entries 5–7). The merit of the coꢀsolvent can feasibility of the aforementioned protocol for challenging
be attributed to the good solubility of the organic reactants and substrates, several aryl chlorides with phenylboronic acid were
the inorganic base, which can accelerate the transmetalation employed and the reaction time was extended to 5 h. And the
and contributed to fast overall coupling40. The reaction desired products were obtained in moderate yields (Table 5,
conditions were also optimized with respect to the base. The entries 13, 14, 15), this just owning to the strength of the CꢀCl
reactions were carried out under similar conditions using bond, whose bond dissociation energy was 96 kcal/mol41.
different bases such as Na2CO3, KOH, NaOH and K2CO3
(Table 4, entries 7–12), it clearly indicated that K2CO3 was the Table 5 Suzuki–Miyaura coupling of arylboronic acids and aryl
optimal base for the reaction. No product was obtained without halides catalyzed by Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPda.
base (Table 4, Entry13). We can also found that the amount of
the catalyst has a great influence on the transformation (Table 4
Entries 14–16). When the dosage of the catalyst was above 0.1
mol%, the yield of the product was nearly quantitative (Table 4
Entry 14–15). And yield of the product was decreased to 77%
(Table 3, Entry 16) with 0.05 mol% Pd. No product was
obtained in the absence of Pd NPs (Table 4, Entry 17).
X
(HO) B
2
Y
Z
Y
Z
Entry
X
Y
H
Z
t/
Yieldc/%
min
60
45
45
60
90
90
50
45
60
45
50
50
1
2
3
4
5
6
7
8
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
H
H
H
2ꢀCH3
H
4ꢀNO2
4ꢀNO2
H
3ꢀCH3
H
4ꢀNO2
4ꢀNO2
H
98.6
93.1
95.4
94.6
91.3
93.8
91
96.3
96.2
96.1
93.8
95.3
4ꢀOCH3
4ꢀOH
4ꢀOH
Table 4 Optimization of the reaction conditions for the Suzuki
reaction of bromobenzene with phenylboronic acida.
2ꢀCH3
4ꢀCH3
4ꢀOCH3
4ꢀCOCH3
4ꢀOH
4ꢀCHO
4ꢀCHO
4ꢀCOCH3
H
Entry Solvents
Bases
Pd
/mol%
Yield
/%
Solvents effect
1
2
3
4
5
6
7
MeOH
EtOH
DMF
H2O
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
0.1
0.1
0.1
0.1
0.1
0.1
0.1
53
9
70.2
68.1
38
78.1
98.6
82.3
10
11
12
13b
14b
15b
EtOH/ H2O (1 : 3)
EtOH/ H2O (1: 1)
EtOH/ H2O (3 : 1) K2CO3
300 74.2
300 30.7
330 25.2
4ꢀOCH3
2ꢀCH3
H
H
Bases effect
a. Reaction conditions: bromobenzene (0.5 mmol), phenyl
boronic acid (0.6 mmol), K2CO3 (1.5 mmol), solvent: 2 mL
ethanol + 2 mL H2O, catalyst: Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd
(0.1 mol%), room temperature; b. aryl chlorides (0.5 mmol),
phenyl boronic acid (0.6 mmol), K2CO3 (1.5 mmol), solvent: 2
mL ethanol + 2 mL H2O, catalyst: Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd
(0.5 mol%), 78 oC, c. yield based on column chromatography.
8
EtOH/ H2O (1: 1)
NaOH
KOH
Et3N
Na2CO3 0.1
K2CO3
no base
0.1
0.1
0.1
72.1
78.4
65
89.7
98.6
trace
9
EtOH/ H2O (1: 1)
EtOH/ H2O (1: 1)
EtOH/ H2O (1: 1)
EtOH/ H2O (1: 1)
EtOH/ H2O (1: 1)
10
11
12
13
0.1
0.1
Pd mol%
14
15
16
17
EtOH/ H2O (1: 1)
K2CO3
K2CO3
K2CO3
K2CO3
0.15
0.1
0.05
0
99.5
98.6
77
The recovery and reusability of the catalyst were performed,
using the reaction of bromobenzene with benzeneboronic acid
as the representative reactants, which catalyzed by 0.1 mol % of
Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd. The results demonstrated that
EtOH/ H2O (1: 1)
EtOH/ H2O (1: 1)
EtOH/ H2O (1: 1)
trace
a. Reaction conditions: bromobenzene (0.5 mmol), Znꢀfree MOFꢀ5ꢀNPCꢀ900ꢀPd can be reused 5 times without
phenylboronic acid (0.75 mmol), base (1.5 mmol), solvents (4 significant loss of catalytic activity (Fig. 4). The catalyst after 5
mL), room temperature.
cycles was characterized by TEM (Fig. S3, †) and XPS (Fig. S4,
†), which was similar with that of the fresh prepared catalyst.
To generalize the application of the Znꢀfree MOFꢀ5ꢀNPCꢀ The amount of Pd in the catalyst after five cycles decreased
900ꢀPd catalyst, the reaction with a diverse range of arylboronic
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COMMUNICATION
Journal Name
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In summary, we have demonstrated that the fabrication of
nanoporous carbon drived from a lowꢀcost, facile and readily
reproducible MOF and served as the carrier material for
palladium nanoparticles. The resultant Znꢀfree MOFꢀ5ꢀNPCꢀ
900ꢀPd possessing large pore volumes and high surface area,
the catalyst is highly efficient in the SuzukiꢀMiyaura coupling
reaction between aryl boronic acid and aryl halide even the
reaction was carried out at ambient temperature. Besides, good
yield was obtained after the catalyst reused five cycles. The
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Foundation of Hebei Province (B2015204003) and the Natural
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Graphical abstract
An efficient Pd catalyst supported on novel nanoporous carbon was developed for the Suzuki-Miyaura coupling reaction for the
first time. The prepared catalyst can be readily recovered and reused 5 times without significant loss of catalytic activity.
Self- assembly
Carbonization
MOF-5-NPC
MOF-5
Br
R1
H2PdCl4
NaBH4
B(OH)2
H2BCD
R2
(ZnNO3)2·6H2
R1
R2
Zn-free MOF-5-NPC-Pd