Preparation of recoverable Fe3O4/PPy-PdII catalysts for carbonylative cross-coupling reactions

Article abstract of DOI:10.1016/j.molcata.2014.05.024

The hierarchical porous Fe₃O₄/PPy-Pd^II catalyst has been synthesized using Fe₃O₄ microspheres both as chemical template and oxidant source under sonication. The catalyst characterized by TEM, XRD, FT-IR, XPS and vibrating sample magnetometry (VSM). The catalyst showed high reactivity for the carbonylative cross-coupling reaction of aryl iodides with arylboronic acids. This newly developed catalyst could be easily recovered and revealed high efficiency and high stability under the reaction conditions and during recycling stages.

Full text of DOI:10.1016/j.molcata.2014.05.024

Accepted Manuscript
Title: Preparation of recoverable Fe3O4/PPy-PdII catalysts for
carbonylative cross-coupling reactions
Author: Jianrui Niu Miao Xie Xiaohang Zhu Yu Long Peng
Wang Rong Li Jiantai Ma
PII:
S1381-1169(14)00230-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.molcata.2014.05.024
MOLCAA 9124
To appear in:
Journal of Molecular Catalysis A: Chemical
Received date:
Revised date:
Accepted date:
12-12-2013
15-4-2014
23-5-2014
Please cite this article as: J. Niu, M. Xie, X. Zhu, Y. Long, P. Wang, R.
Li, J. Ma, Preparation of recoverable Fe3O4/PPy-PdII catalysts for carbonylative
cross-coupling reactions, Journal of Molecular Catalysis A: Chemical (2014),
http://dx.doi.org/10.1016/j.molcata.2014.05.024
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Preparation of recoverable Fe3O4/PPy-PdII catalysts for
carbonylative cross-coupling reactions
Jianrui Niu, Miao Xie, Xiaohang Zhu,Yu Long, Peng Wang, Rong Li∗ and Jiantai Ma∗
State Key Laboratory of Applied Organic Chemistry, College of
Chemistry and Chemical Engineering, Lanzhou University, Lanzhou,
Gansu 730000, P. R. China
Highlights
The preparation method meets the ideas of simpleness, fast and efficiency.
The catalyst was easily recovered.
The catalyst revealed high efficiency and high stability during recycling stages.
Abstract
The hierarchical porous Fe3O4/PPy-PdII catalyst has been synthesized using Fe3O4
microspheres both as chemical template and oxidant source under sonication. The
catalyst characterized by TEM, XRD, FT-IR, XPS and vibrating sample
magnetometry (VSM). The catalyst showed high reactivity for the carbonylative
cross-coupling reaction of aryl iodides with arylboronic acids. This newly developed
catalyst could be easily recovered and revealed high efficiency and high stability
under the reaction conditions and during recycling stages.
∗ Corresponding author: Tel: +86-931-891-3597. Fax: +86-0931-891-2582
E-mail address: liyirong@lzu.edu.cn.
∗ Corresponding author: Tel: +86-931-891-2311. Fax: +86-0931-891-2582
E-mail address: majiantai@lzu.edu.cn.
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Keywords: carbonylative cross-coupling, environmental friendly, heterogeneous
catalysis, palladium,
1. Introduction
It is well known that Pd-catalyzed carbonylative cross-coupling is of significant
importance in modern chemical transformations, as these compounds are important
moieties in many biologically active molecules, natural products, and pharmaceuticals
[1]. Many palladium-based homogeneous catalysts, such as Pd(tmhd)2/Pd(OAc)2 [2],
Pd2(dba)3 [3], Pd(PPh3)4 [4] and N-heterocyclic carbene palladium [5], have good
activity in carbonylative cross-coupling reactions. Nevertheless, one key challenge for
the practical use of homogeneous catalysts is the separation of product from the
catalytic media. This process is often complicated and usually accomplished by means
of complex work-up procedures [6]. Thus, more researches focus on heterogeneous
palladium (immobilizing palladium complexes on various supports such as silica [7]
and zeolites [8]) complexes as catalysts for Suzuki carbonylative coupling reactions.
Cai et al. used MCM-41-2P-PdII [9] and MCM-41–2N–PdII [10] as catalysts for
Suzuki carbonylative coupling reactions. Bhanage et al [11]. used Pd/C as a catalyst in
Suzuki carbonylative coupling reactions. In our previous work for improving the
recyclability, we immobilized Pd complexes on silica-coated magnetic nanoparticles
(Fe3O4@SiO2-SH-PdII) to catalyze Suzuki carbonylative coupling reactions, so that
the catalyst (Fe3O4@SiO2-SH-PdII) could be separated from the mother solutions by
applying an external magnetic field [12]. Unfortunately, most of the conventional
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synthetic methods require long reaction time, toxic solvent and tedious synthetic
steps.
Polymers are commonly used as supports for catalyst loading. It can not only
prevent the Fe3O4 NPs from aggregating but also provide a useful platform for further
functionalization.[13] Among these systems, polypyrrole (PPy), with the advantages
of good environmental stability, reversible redox and virtue of easy preparation by
both chemical and electrochemical approaches, was used in many areas such as
secondary batteries, catalysis, and biosensors.[14] Chen et al.[15] reported the
preparation of a Fe3O4–Ppy–Au nanocomposite which exhibited excellent
electrocatalytic activity. Koon Gee Neoh et al.[16] reported the functionalization of
polypyrrole-Fe3O4 nanoparticles for applications in biomedicine to ascorbic acid. Xu
et al.[17] reported Fe3O4/Ppy/Au nanocomposites with Core/shell/shell/structure.
These catalysts exhibited good catalytic activity. However, it is difficult to synthesize
magnetic-based polymer composite materials, since polymer such as polypyrrole is
hydrophobic but the surfaces of magnetic particles are hydrophilic, Although surface
modifiers such as PVP surfactant are commonly adopted, the development of facile
methods to fabricate magnetic-based polymer composite materials is still a challenge.
[18]A simple, fast and efficient method is therefore required for the construction
magnetic nano-catalyst [19].
In order to meet the ideas of simpleness, fast and effectivity, we synthesize the
magnetic polymer-supported catalyst by loading Pd on the surface of the orange-like
Fe3O4/PPy composite microsphere using Fe3O4 microspheres both as chemical
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template and oxidant source under sonication and applied the catalyst in carbonylative
cross-coupling reactions.
2. Experiment
2.1. Characterization
FT-IR spectra were recorded on a Nicolet NEXUS 670 FTIR spectrometer with a
DTGS detector and samples were measured with KBr pellets. XRD measurements
were performed on a Rigaku D/max-2400 diffractometer using Cu-Ka radiation as the
X-ray source in the 2θ range of 5–90◦.The size and morphology of the magnetic
nanoparticles were observed by a Tecnai G2 F30 transmission electron microscopy
and samples were obtained by placing a drop of a colloidal solution onto a copper grid
and evaporating the solvent in air at room temperature. Magnetic measurements of
Fe3O4 and Fe3O4/PPy-PdII were investigated with Quantum Design vibrating sample
magnetometer (VSM) at room temperature in an applied magnetic field sweeping
from -15 kOe to 15 kOe. X-Ray photoelectron spectroscopy (XPS) was recorded on a
PHI-5702 instrument and the C1S line at 292.1 eV was used as the binding energy
reference.
2.2. Catalyst preparation
2.2.1. Synthesis of Fe3O4 microspheres
The magnetic Fe3O4 particles were prepared through a solvothermal reaction.
.
Typically, FeCl3 6H2O (1.35 g) and sodium acetate (3.6 g) were dissolved in ethylene
glycol (40 mL) with magnetic stirring. The obtained homogeneous yellow solution
was transferred to a Teflon-lined stainless-steel autoclave (60 mL) and heated at 200
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℃for 10 h. The obtained black particles were washed with ethanol four times and
then dried in a vacuum at 60 ℃ for 12 h.
2.2.2. Synthesis of Fe3O4/PPy composite microspheres [20]
Fe3O4 particles (0.30 g) were dispersed in 70 mL H2O under sonication, and then
pyrrole (3 mL) in alcohol (15 mL) and HCl solution (15 mL, 6 M) were added into the
above solution in turn under sonication for 1.5 h. Finally, the black product was
collected with the help of a magnet, washed with deionized water repeatedly to
remove the residual pyrrole monomers and HCl acid, and then dried in a vacuum
overnight. The corresponding PPy microspheres were obtained by treating Fe3O4/PPy
composite microspheres in acidic solution.
2.2.3. Loading of Pd on Fe3O4/PPy (Fe3O4/PPy-PdII)
500 mg of Fe3O4/PPy samples were first dispersed in a 50 mL ethanol solution
under ultrasonication for 0.5 h. The formed black suspension was ultrasonically
mixed with 3.0 mmol of a PdCl2 solution for 1 h. The solid product was filtered by
suction, washed three times with ethanol, distilled water and ethanol successively, and
dried at 50 ºC under vacuum for 24 h to give the palladium complex (Fe3O4/PPy-PdII).
2.2.4. Typical procedure for the carbonylative Suzuki coupling reaction
A mixture of aryl iodide (0.5 mmol), arylboronic acid (0.6 mmol), K2CO3 (1.5
mmol), and 2 mol% palladium catalyst in anisole (5 mL) were stirred at 80 ºC under 1
atm pressure of CO. An aliquot was taken with a syringe and subjected to GC analysis
1
and H NMR (See the supplementary material). Yields were calculated against the
consumption of the aryl iodides.
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3. Results and discussion
3.1. Catalyst preparation
Scheme 1 Preparation of Fe3O4/PPy-PdII catalyst.
The process for preparation of the catalyst Fe3O4/PPy-PdII is schematically
described in Scheme 1. Firstly, Fe3O4 particles were prepared by the method given in
previous reports. Secondly, in the strong acidic solution, the Fe3+ released from Fe3O4
microspheres and the polymerization of pyrrole monomers. A layer of polypyrrole
was coated on the surface of Fe3O4 [20]. Thirdly, under magnetic stirrers, PdCl2 was
supported on the surface of polypyrrole.
3.2 Catalyst characterization
Fig. 1 TEM images of (a) Fe3O4 and (b) Fe3O4/PPy-PdII
The typical TEM image of Fe3O4, Fe3O4/PPy-PdII microspheres was showed in Fig.
1. The average diameter of the as-synthesized spherical particles was about 400 nm
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(Figure 1a). A continuous layer of PPy could be observed on the outer shell of the
Fe3O4 microsphere cores and the thickness of the PPy shell was about 25 nm. The
resultant Fe3O4/PPy-PdII composites had good dispersibility and spherical morphology.
In the TEM image of Fe3O4/PPy-PdII (Figure 1b), it could be seen that the
morphology of Fe3O4/PPy-PdII almost kept spherical after coating process under
acidic conditions and fastening PdCl2 on the supporter.
Fig. 2 XRD patterns of (a) Fe3O4 and (b) Fe3O4/PPy-PdII
The crystalline structure of the resulting products was investigated by X-ray
powder diffraction (XRD). In Figure 2, the main peaks of the Fe3O4/PPy-PdII
composite were similar to the Fe3O4. It exhibited that the coating process under acidic
conditions and fastening PdCl2 on the supporter did not affect the structure of Fe3O4.
Both of the two patterns showed strong peaks which confirmed the products were
well-crystallized and detected diffraction peaks in every pattern could be indexed as
cubic Fe3O4 (JCPDS card No. 82-1533). A broad peak was observed at 2θ = 10。- 30。,
which suggested newly generating a layer of PPy [21].
Magnetic measurements were performed using a vibrating sample magnetometer
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(VSM) at room temperature. The magnetization curves for Fe3O4 particles and
Fe3O4/PPy-PdII were compared in Figure S1. There was no hysteresis in the
magnetization for the two types of particles. Additionally, neither coercivity nor
remanence could be observed, which suggested that the two particles were
superparamagnetic[22]. The measured saturation magnetizations were 76.2 emug-1 for
Fe3O4 particles and 22 emug-1 for Fe3O4/PPy-PdII, respectively. The saturation
magnetization significantly decreased after pyrrole monomer was polymerized and
PdCl2 was loaded onto Fe3O4 particles microspheres. However, the prepared
Fe3O4/PPy-PdII microspheres still maintained good magnetic properties and could be
completely and quickly separated from the solvent when an external magnetic force
was applied.
Fig. 3 FT-IR of (a) Fe3O4, (b) Fe3O4/PPy and (c) Fe3O4/PPy-PdII
The compositions of Fe3O4/PPy-PdII composite microsphere were confirmed by
FT-IR (Figure 3). For comparison Fe3O4 and Fe3O4/PPy were also shown in the
picture. From the spectrogram, the peaks at around 1560 cm-1, 1200 cm-1 and 930
cm-1 were attributed to C=C stretching vibrations, C-N stretching vibrations and C-H
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stretching vibrations, respectively. From the Fe3O4/PPy-PdII pattern, we can see the
C=C, C-N, C-H stretching vibrations take place blue shift, which exhibited PdCl2 was
fastened on the supporter.
Fig. 4 XPS spectra for (a) Fe3O4/PPy-PdII and (b) Fe3O4/PPy-PdII showing Pd 3d5/2
and Pd 3d3/2 binding energies
The XPS elemental survey scans of the surface of the Fe3O4/PPy-PdII catalyst were
showed in Figure 4a. Peaks corresponding to iron, oxygen, nitrogen, palladium and
carbon were clearly observed. To ascertain the oxidation state of the Pd, X-ray
photoelectron spectroscopy (XPS) studies were carried out. In Figure 4b, the Pd
binding energy of Fe3O4/PPy-PdII exhibited two strong peaks centered at 343.8 and
338.4 eV, which were assigned to Pd 3d 3/2 and Pd 3d 5/2, respectively. These values
agreed with the PdII binding energy of PdCl2.
3.3 Catalytic Carbonylative Suzuki coupling reaction
To explore the optimal reaction conditions, the coupling of iodobenzene with
phenylboronic acid was determined at the model reaction (Table 1). The preliminary
results indicated that temperature, base and solvent had a significant effect on the
coupling reaction. From Table 1, when the temperature increased from 60 °C to 80 °C
9
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high yield of the desired product (92%) was obtained (Table 1, entry 1-2). But at the
temperature of 100 °C (Table 1, entry 3), the yield of the desired product (90%) was
decreased. Therefore, the best temperature was 80°C. According to the evaluated
results of solvents, anisole was found to be the best (Table 1, entry 2, 4-6). Under the
optimized reaction temperature and solvent, several bases were examined, such as
NaOAc, K3PO4, Cs2CO3 and K2CO3(Table 1, entry 2, 7-9). As a result, the most used
base K2CO3 was the most efficient base to produce carbonylative cross-coupling
product. Therefore, the optimized reaction conditions are: 80 °C, anisole, and K2CO3.
Table 1
Carbonylative Suzuki coupling reaction under diffident conditions. a
Entry
Solvent
Base
Temp./◦C
Time/h
Yield b (%)
1
2
3
4
5
6
7
8
9
Anisole
Anisole
Anisole
Toluene
Dioxane
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
NaOAc
Cs2CO3
K3PO4
60
80
100
80
80
80
80
80
80
8
8
8
8
8
8
8
8
8
41
92
90
69
78
70
0
Anisole
Anisole
Anisole
63
69
10
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a
The reactions were carried out with iodobenzene (0.5 mmol), arylboronic acid (0.6
mmol), CO (1 atm), base (1.5 mmol), solvent (5 mL), and 2 mol% palladium catalyst.
b Determined by GC.
The activity of palladium-complexes immobilized on Fe3O4/PPy was tested in the
Suzuki carbonylative coupling reactions of aryl halides, namely the reactivity of aryl
halides with arylboronic acids using K2CO3 as a base under balloon pressure of CO in
anisole. Firstly, The Suzuki carbonylative reaction of iodobenzene with phenylboronic
acid was chosen as the model reaction to evaluate the reaction time. To our delight,
the catalyst was active for it and with 92% conversion in 8 h and the products of the
diphenyl ketone were highly selective (Table 2, entries 1, 2, 3). Further investigation
of the substrate scope was carried out under the optimized reaction conditions. In
Table 2, various aryl iodides as well as arylboronic acids were examined and good
functional group tolerance of the Fe3O4/PPy-PdII catalytic system was observed. For
example, aryl iodides containing electron-withdrawing groups including 4-CH3CO
and 2-NO2 produced desired ketones in excellent yields (Table 2, entries 15-20), the
reason should be that the existence of electron-withdrawing groups could promote the
oxidative addition of the organic halide to palladium (0) (Scheme S2 step 1) . It was
noteworthy that up to 98 % yield of unsymmetrical biaryl ketone was obtained for
4-chlorobenzeneboronic acid with the 4-iodonitrobenzene (Table 2, Entry 17). In
addition, both 4-methylbenzeneboronic acid and 4-chlorophenylboronic acid reacted
smoothly with aryl iodides to give unsymmetrical biaryl ketones in high yields (Table
2, Entries 4, 5, 7, 8, 10, 11, 13, 14, 16, 17, 19 and 20).
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Table 2
Carbonylative Suzuki coupling reaction of various aryl iodides with arylboronic acids
in the presence of the Fe3O4/PPy-PdII catalyst. a
Yieldb (%)
Entry
R1
R2
t/h
TOF (h-1)
1
2
1
H
H
4
40
63
92
88
84
89
87
90
91
89
92.5
85
80
88
99
100
5
5.00
5.25
5.75
5.50
5.25
5.56
5.43
5.63
5.69
5.56
5.78
3.54
3.33
3.67
8.25
8.33
2
H
H
6
9
3
H
H
8
6
4
H
4-CH3
4-Cl
H
8
9
5
H
8
6
6
4-CH3
4-CH3
4-CH3
4-CH3O
4-CH3O
4-CH3O
2-NH2
2-NH2
2-NH2
2-NO2
2-NO2
8
6
7
4-CH3
4-Cl
H
8
10
5
8
8
9
8
6.7
9
10
11
12
13
14
15
16
4-CH3
4-Cl
H
8
8
2
12
12
12
6
9
4-CH3
4-Cl
H
11
10
0.5
0
4-CH3
6
12
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17
18
19
20
2-NO2
4-Cl
H
6
6
6
6
98
93
89
90
<0.1
6
8.17
7.75
7.42
7.50
4-CH3CO
4-CH3CO
4-CH3CO
4-CH3
4-Cl
10
7
a
The reactions were carried out with iodobenzene (0.5 mmol), arylboronic acid (0.6
mmol), CO (1 atm), K2CO3 (1.5 mmol), solvent (5mL) and 2 mol% palladium
catalyst.
b Determined by GC and 1H NMR.
Furthermore, we investigated the recyclability of the Fe3O4/PPy-PdII. After the first
cycle of the reaction, the catalyst was recovered with the help of a magnet,
successively washed with distilled water (to remove excess of base), ethanol, and
dried at room temperature ready for the next cycle. The carbonylative cross-coupling
reaction of 4-Iodoacetophenone with phenylboronic acid catalyzed by recycled
catalyst were displayed in Table 3. The weight percentage of Pd in the Fe3O4/PPy,
determined by atomic absorption spectroscopic (AAS) analysis, was 4.21 wt% before
and 3.1 % after four cycles.
Table 3
The carbonylative cross-coupling reaction of 4-Iodoacetophenone with phenylboronic
acid catalyzed by recycled catalyst. a
Recycle
Catalyst cycle
Yield (%)
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1
2
6
1
4
1
4
93
80
10
a The reactions were carried out with 4-Iodoacetophenone (0.5 mmol), PhB(OH)2 (0.6
mmol), CO (1 atm), K2CO3 (1.5 mmol) and 2 mol% palladium catalyst in anisole (5
mL) at 80 ºC.
As a comparison, we compared the results achieved in this work with those reported
elsewhere over many supported catalysts. Take phenylboronic acid with 4-iodoanisole
as an example, the results were listed in Table 4. What was worth mentioning, the
Fe3O4/PPy-PdII was outstanding over the other heterogeneous catalysts. In contrast
with the catalysts of Pd/C [11] and Imm Pd-IL [23], our catalyst took less reaction
time and in a mild environment towards the carbonylative cross-coupling(Table 4
entries 2, 4, 5). Although the catalysts of MCM-41-2P-PdII [9] and MCM-41-2N-PdII
[10] give a good yields in a short time and 80℃, the yield is lower than the catalyst of
Fe3O4/PPy-PdII (Table 4 entries 1, 3, 5).
Table 4
The carbonylative cross-coupling of phenylboronic acid with 4-iodoanisole with
different catalysts. a
Entry
1
Catalyst
Catalyst amount
Time/h
5
Temp./◦C
80
Yield (%)
85
(mol%)
2
MCM-41-2P-PdII
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2
3
4
5
Pd/Cb
2
2
2
2
8
6
8
6
100
80
85
86
76
93
MCM-41-2N-PdII
ImmPd-ILc
100
80
Fe3O4/PPy-PdII
aReaction conditions: CO (1 atm), anisole.
b Reaction conditions: CO (200 psi), anisole.
c Reaction conditions: CO (1 MPa), toluene.
4 Conclusions
We have developed a hierarchical porous, practial and economic heterogeneous
catalytic system for the Suzuki carbonylative cross-coupling reaction by using PPy
modified MNPs that were supported on Pd as the catalyst in anisole under an
atmospheric pressure of carbon monoxide. This novel Pd catalyst can be conveniently
prepared by using Fe3O4 microspheres both as chemical template and oxidant source
under sonication; it exhibited high activity and selectivity for the Suzuki
carbonylative coupling reaction. The catalyst revealed high efficiency and high
stability under the reaction conditions and during recycling stages. Our catalyst used
the polymer as ligands, which renders it more environmentally friendly.
5 Acknowledgements
The authors are grateful to the Key Laboratory of Nonferrous Metals Chemistry
and Resources Utilization, Gansu Province for financial supports. Additionally, we are
also very thank you for the Scholarship Award for Excellent Doctoral Student granted
by Lanzhou University
6 Appendix A. Supplementary data
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Supplementary data to this article can be found at the supplementary material.
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