Macroporous magnetic poly(GMA-EGDMA-DVB) microspheres supported palladium complex as an efficient catalyst for Heck reaction

Article abstract of DOI:10.1016/j.cclet.2010.04.025

Macroporous magnetic poly(GMA-EGDMA-DVB) microspheres synthesized by suspension polymerization were used as supports for palladium catalyst. The results showed the novel magnetic catalyst can promote Heck reaction of aryl halides with acrylic acid efficiently without an inert atmosphere. In addition, the novel catalyst can be conveniently recovered by applying an external magnet and reused at least five times without significant loss of its activity.

Full text of DOI:10.1016/j.cclet.2010.04.025

Available online at www.sciencedirect.com
Chinese Chemical Letters 21 (2010) 1062–1066
www.elsevier.com/locate/cclet
Macroporous magnetic poly(GMA-EGDMA-DVB)
microspheres supported palladium complex as an
efficient catalyst for Heck reaction
*
Ding Zhong Yuan, Qiu Yu Zhang , Jin Bo Dou
Department of Applied Chemistry, School of Science, Northwestern Polytechnical University, Xi’an 710129, China
Received 30 December 2009
Abstract
Macroporous magnetic poly(GMA-EGDMA-DVB) microspheres synthesized by suspension polymerization were used as
supports for palladium catalyst. The results showed the novel magnetic catalyst can promote Heck reaction of aryl halides with
acrylic acid efficiently without an inert atmosphere. In addition, the novel catalyst can be conveniently recovered by applying an
external magnet and reused at least five times without significant loss of its activity.
# 2010 Qiu Yu Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Macroporous magnetic microspheres; Heterogeneous catalyst; Heck reaction; Palladium; Suspension polymerization
The palladium catalyzed Heck reaction has been received considerable attention in recent years, as it is an excellent
method for synthesis of various organic molecules under mild conditions [1–5]. Palladium compounds such as PdCl2,
Pd(OAc)2 and Pd(PPh3)4 have been widely used for this reaction as homogeneous catalysts. However, these traditional
homogeneous catalysts have several drawbacks to be resolved, such as an easy contamination of palladium species in
the reaction products, difficulties in recovery and recycling the expensive homogeneous palladium catalyst, which
have so far limited their widespread industrial application to a large extent [6–10].
These problems can be minimized by the immobilization of homogeneous catalysts on various support materials,
such as organic polymers, biopolymer, inorganic silica and other metal oxides [11–16]. This is because heterogeneous
catalysts have fewer of the drawbacks of homogeneous catalysts, such as the difficulties in recovery and regeneration.
In recent years, a large variety of heterogeneous palladium catalysts have been developed for Heck reaction, which
results in a remarkable extension of supporting materials such as mesoporous silicane and zeolites and polymer
materials. It is demonstrated that the supporting material crucially influences the catalytic performance of
immobilized catalysts [17]. Therefore, it is still important to develop more efficient catalysts from new supporting
matrix with a particular purpose to make the reaction more easily separable and recyclable.
Recently, macroporous magnetic poly(GMA) microspheres have received much attention in many fields. This is
mainly ascribed that they have the following three interesting features. Firstly, macroporous magnetic poly(GMA)
* Corresponding author.
E-mail address: qyzhang@nwpu.edu.cn (Q.Y. Zhang).
1001-8417/$ – see front matter # 2010 Qiu Yu Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.04.025

[(Scheme_1)TD$FIG]
D.Z. Yuan et al. / Chinese Chemical Letters 21 (2010) 1062–1066
1063
Scheme 1. Preparation macroporous Fe3O4/P (GMA-EGDMA-DVB) microspheres and macroporous Fe3O4/P (GMA-EGDMA-DVB)-Pd.
microspheres have a regular pore diameter with a wide range, which can allow passage of large molecules such as
organic reactants and metal complexes through the pores to reach to the surface of the channel [18]. Secondly, they
have an advantage of the presence of relative oxirane groups, which can be relatively easily modifiable to a variety of
functional groups suitable for prospective immobilized of enzyme, nuclei acids and other required bimolecules
[19,20]. Thirdly, macroporous magnetic poly(GMA) microspheres are usually superparamagnetic, which can allow
them to be conveniently recovered and separated by using an external magnetic field [21,22]. And so far, macroporous
magnetic poly(GMA) microspheres have been used frequently in many fields such as wastewater treatment,
environmental engineering and enzyme immobilization [23–25]. However, macroporous magnetic poly(GMA)
microspheres, to the best of our knowledge, have not been used as supports for palladium catalyst.
Herein, we would like to report the feasibility of using macroporous magnetic poly(GMA) microspheres for
supporting homogeneous catalyst. As shown in Scheme 1, firstly, micron-sized macroporous magnetic poly(GMA-
EGDMA-DVB) microspheres with epoxy groups on the surface were prepared by suspension polymerization in the
presence of inert diluents and oleic acid coated magnetic Fe3O4 nanoparticles. Secondly, the amino groups were
introduced onto the magnetic microspheres by reacting with diethylene triamine. Finally, the amino-functionalized
microspheres reacted with palladium acetates. The palladium content was determined to be 3.57 wt% by atomic
absorption spectroscopy (AAS).
Fig. 1 shows the image of Fe3O4/P (GMA-EGDMA-DVB)-Pd. As shown in Fig. 1, it can be observed that the
magnetic microspheres still maintained their configuration after coordination with palladium acetates. Furthermore,
the magnetic microspheres were not broken in the coordination process.
XPS is used to study not only the coordination of macromolecular ligands with metal ions but also the chemical
state of palladium presenting in the supported catalysts. The XPS data for samples are listed in Table 1. It can be seen
that the binding energy of N1s of Fe3O4/P (GMA-EGDMA-DVB)-NH2 is 399.6 eV, which is lower than the binding
energy of N1s of Fe3O4/P (GMA-EGDMA-DVB)-Pd. Meanwhile, the binding energy of Pd3d5/2 in the supported
[(Fig._1)TD$FIG]
Fig. 1. SEM micrograph of Fe3O4/P (GMA-EGDMA-DVB)-Pd.

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D.Z. Yuan et al. / Chinese Chemical Letters 21 (2010) 1062–1066
Table 1
XPS data for samples.
Samples
Binding energy/(eVa)
Pd3d5/2
N1s
Pd(OAc)2
338.7
–
–
Fe3O4/P (GMA-EGDMA-DVB)-NH2
Fe3O4/P (GMA-EGDMA-DVB)-Pd
399.6
400.2
336.2
a
All relative to C1s = 284.6 eV.
[(Fig._2)TD$FIG]
Fig. 2. The magnetization curves measured at room temperature for Fe3O4/P (GMA-EGDMA-DVB)-Pd.
catalyst is 336.2 eV, which is almost similar to the binding energy of the Pd3d5/2 of Pd(OAc)2. These results indicate
that coordination between N and Pd is formed in the polymer supported palladium.
Fig. 2 shows the magnetization curve of the novel catalyst at room temperature. It can be observed that the
magnetization curve exhibits typical ferromagnetic behavior. Saturation of the magnetization was found to be
8.64 emu/g at an external filed of 10 kOe. With such high magnetization value, the magnetic supported catalyst can be
easily separated form the solutions by using a relatively low external magnetic field.
In order to confirm whether the macroporous magnetic microspheres still maintained their mesostructure after
coordination with palladium acetates, the macroporous microspheres were subsequently determined by using N2
adsorption at 77 K. And Table 2 listed some typical pore parameters of the samples. As shown in Table 2, it can be seen
that the specific surface area, pore volume and pore size of the Fe3O4/P (GMA-EGDMA-DVB)-Pd slightly decreased
in comparison to the Fe3O4/P (GMA-EGDMA-DVB), which corresponds to relatively low amount of palladium
particles deposited. Nevertheless, the catalyst still had a surface area of 61.7 m2 gÀ1 and a pore size diameter of
13.2 nm. These results indicate that Fe3O4/P (GMA-EGDMA-DVB)-Pd still preserve mesostructure and mesopores
Table 2
Pore properties of samplesa.
Samplesb
SBET (m2 gÀ1
)
Vp (cm3 gÀ1
)
Pore size (nm)
1
2
3
64.5
63.8
61.7
0.22
0.20
0.21
13.7
13.4
13.2
a
Given by N2 sorption at 77 K.
b
1: Fe3O4/P (GMA-EGDMA-DVB); 2: Fe3O4/P (GMA-EGDMA-DVB)-NH2; 3: Fe3O4/P (GMA-EGDMA-DVB)-Pd.

[(Scheme_2)TD$FIG]
D.Z. Yuan et al. / Chinese Chemical Letters 21 (2010) 1062–1066
1065
Scheme 2. Heck reaction of aryl halide with acrylic acid catalyzed by Fe3O4/P (GMA-EGDMA-DVB)-Pd.
well after coordination with palladium acetates, which can allow passage of large molecules through to the pores to
reach to the surface of the channel.
Furthermore, the catalytic properties of the novel magnetic catalyst for the reactions of various aryl halides with
acrylic acid were also examined (Scheme 2). The results are listed in Table 3. It can be seen from the table that the
Heck reactions of aryl iodides with acrylic acid can be efficiently carried out at 90 8C to afford the trans-product in
high yields and no cis-product was observed. Due to the high reactivity of the aryl iodides, neither electron-donating
group (entries 2–3) nor electron-withdrawing group (entries 4–5) has much influence on the yields of product. As for
bromobenzene, no corresponding product (entry 6) was detected under the same reaction condition as iodobenzene.
While the moderate yield (entry 7) was obtained when the reaction time extended to 10 h and the reaction temperature
increased to 140 8C. It can also be seen that the reactivity of aryl bromides with electron-withdrawing substituents
(entry 9) was higher than that of aryl bromides with electron-donating substituents (entry 8).
For the practical application in the Heck reaction, the lifetime of heterogeneous catalysts and their reusability are
also very important factors. Thus, in order to check the recycling efficiency of the novel magnetic supported catalyst,
the Heck reaction of acrylic acid with iodobenzene was investigated. After a reaction, the magnetic catalyst can be
easily recovered and separated by using an external magnet, washed with ethanol and reused directly in next reaction
of acrylic acid with iodobenzene without further purification. As indicated in Table 4, the novel catalyst can be reused
at least five times only with a slight loss of its activity for the Heck reaction. Less than 0.1 wt% Pd leaching into the
products was observed. Meanwhile, from the SEM of the supported magnetic catalyst after fifth run, we did not
observe much change compared to the fresh catalyst (see Supporting information). All these results show that the novel
magnetic catalyst is an excellent potential candidate for reusable and recoverable catalyst.
Table 3
Heck reactions of various aryl halides and acrylic acid catalyzed by the magnetic catalysta.
Entry
R
X
Time (h)
T (8C)
Yield (%)b
1
2
3
4
5
6
7
8
9
H
I
2
2
90
90
97.6
92.2
92.0
93.5
98.5
0.0
OCH3
CH3
Cl
I
I
2
90
I
2
90
NO2
H
I
2
90
Br
Br
Br
Br
2
90
H
10
10
10
140
140
140
52.8
45.6
91.5
CH3
NO2
a
Reaction conditions: aryl halide (5 mmol), AA (7.5 mmol), Bu3N (10 mmol), and DMF (5 mL). Catalyst (0.3 mol% Pd) in the air.
HPLC yield based aryl halide.
b
Table 4
Catalyst recycling experimentsa.
Run
Time (h)
Yield (%)b
1
2
3
4
5
2
2
2
2
3
97.6
98.2
96.5
95.4
92.5
a
Reaction conditions: aryl halide (5 mmol), AA (7.5 mmol), Bu3N (10 mmol), and DMF (5 mL). Catalyst (0.3 mol% Pd) in the air at 90 8C.
HPLC yield based aryl halide.
b

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D.Z. Yuan et al. / Chinese Chemical Letters 21 (2010) 1062–1066
In conclusion, we have developed a novel magnetic catalyst system composed of palladium catalyst immobilized
on the backbone of macroporous magnetic microspheres prepared by suspension polymerization. The novel catalyst
shows high activity in promoting Heck reaction of aryl iodides and acrylic acid. Additionally, the novel catalyst can be
easily recovered and separated by using an external magnet and reused at least five times with a slight loss of its
activity for the Heck reaction of iodobenzene with acrylic acid.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at doi:10.1016/
j.cclet.2010.04.025.
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