Synthesis of polyphenol microsphere-supported palladium complex and evaluation of its catalytic performance for Heck reaction

Article abstract of DOI:10.1002/aoc.2917

Polyphenol microspheres were prepared by template polymerization of phenol in the presence of horseradish peroxidase as bio-enzyme catalyst and aqueous 1,4-dioxane as solvent. The morphology of polyphenol microspheres thus obtained was observed with a scanning electron microscope. Further, polyphenol microspheres as obtained were loaded with palladium to generate polyphenol microsphere-supported Pd complex. Resultant Pd complex catalyst supported by polyphenol microspheres was characterized by means of Fourier transformation infrared spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy, and its thermal stability was examined. Moreover, the catalytic activity of polyphenol microsphere-supported Pd catalyst as synthesized for the Heck reactions of acrylic acid with aryl iodides was evaluated. Results indicate that the polyphenol microsphere as obtained has a diameter of about 500 nm. Polyphenol microsphere-supported Pd catalyst, as synthesized, at a dosage of 0.37 mol% Pd, possesses good catalytic activity for the Heck reactions of acrylic acid with aryl iodides in air at a low temperature of 50°C, and it also exhibits catalytic activity for bromide and activated chlorobenzene. The polyphenol microsphere-supported Pd complex has good thermal stability, and it can be readily separated and reused; the yield of the reaction of iodobenzene with acrylic acid remains at 82% after five recycle runs, showing promising potential as a catalyst for Heck reactions. Copyright

Full text of DOI:10.1002/aoc.2917

Full Paper
Received: 26 June 2012
Revised: 28 July 2012
Accepted: 5 August 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2917
Synthesis of polyphenol microsphere-
supported palladium complex and evaluation
of its catalytic performance for Heck reaction
Guangrui Nie, Lei Zhang and Yuanchen Cui*
Polyphenol microspheres were prepared by template polymerization of phenol in the presence of horseradish peroxidase as
bio-enzyme catalyst and aqueous 1,4-dioxane as solvent. The morphology of polyphenol microspheres thus obtained was
observed with a scanning electron microscope. Further, polyphenol microspheres as obtained were loaded with palladium
to generate polyphenol microsphere-supported Pd complex. Resultant Pd complex catalyst supported by polyphenol micro-
spheres was characterized by means of Fourier transformation infrared spectrometry, X-ray diffraction, X-ray photoelectron
spectroscopy and scanning electron microscopy, and its thermal stability was examined. Moreover, the catalytic activity of
polyphenol microsphere-supported Pd catalyst as synthesized for the Heck reactions of acrylic acid with aryl iodides was
evaluated. Results indicate that the polyphenol microsphere as obtained has a diameter of about 500 nm. Polyphenol
microsphere-supported Pd catalyst, as synthesized, at a dosage of 0.37 mol% Pd, possesses good catalytic activity for the Heck
reactions of acrylic acid with aryl iodides in air at a low temperature of 50ꢀC, and it also exhibits catalytic activity for bromide
and activated chlorobenzene. The polyphenol microsphere-supported Pd complex has good thermal stability, and it can be
readily separated and reused; the yield of the reaction of iodobenzene with acrylic acid remains at 82% after five recycle runs,
showing promising potential as a catalyst for Heck reactions. Copyright © 2012 John Wiley & Sons, Ltd.
Keywords: horseradish peroxidase; polyphenol microsphere; supported Pd catalyst; heck reaction; catalytic activity
templates. We also obtained desired phenolic polymers in high
Introduction
yield by enzymatic polymerization of phenol in an aqueous
micelle system.[26]
As a powerful tool for the construction of C-C bonds in organic
synthesis, the palladium-catalyzed Heck reaction[1] has received
Noting that strict control of the structure and morphology
increasing attention in recent decades.[2–5] For example, the
plays a key role in adjusting the function of polymers, and
palladium-catalyzed Heck reaction can be used to synthesize a
variety of compounds, including cinnamic acid ester derivatives
and pharmaceutical intermediates,[6] in which palladium com-
pounds such as PdCl2 and Pd(OAc)2 (palladium acetate) are widely
used as homogeneous catalysts.[7,8] However, these traditional
homogeneous catalysts are expensive and hard to separate and
recycle, which significantly limits their widespread application in
industry.[9,10] These drawbacks, fortunately, can be overcome by
adopting polymer-supported palladium catalysts that can be easily
separated and recovered in synthetic and industrial chemistry. In
this respect, studies on polymer-supported palladium complexes
for the Heck reaction are of particular significance.[11–14]
polymer-supported noble metal catalysts of homogeneous mi-
crometer size can be readily recycled,[27,28], we pay special atten-
tion to palladium complexes supported by microsphere materials
exhibiting unique high volume-to-surface ratio properties relative
to their larger counterparts.[29–31] Here we report the synthesis
and characterization of a polyphenol microsphere-supported
palladium complex and its application as a catalyst with excellent
yield and high trans-selectivity for Heck reactions.
Experimental
We are particularly interested in enzyme-catalyzed polymeriza-
tion,[15–17] since it can be well adapted to synthesize polymers as
a support for palladium complexes for the Heck reaction. For
example, a new class of useful and high-performance polymeric
materials can be prepared in the presence of peroxidase as cata-
lyst, which is usually infeasible using conventional methods.[18–20]
Specifically, the enzymatic oxidative polymerization of a variety
of phenol derivatives produce phenolic polymers without the
use of toxic formaldehyde,[21,22] providing an alternative route
for preparing phenolic resins. By making use of the enzymatic
polymerization of phenol in water, many researchers have
successfully prepared phenolic polymers in the presence of
cyclodextrin derivatives[23,24] and carbon nanotubes[25] as
Materials and Methods
Horseradish peroxidase (HRP; RZ = 2.5, activity ≥ 200 U mgÀ1) was
purchased from Shanghai Guoyuan Biotechnology Co. and used
*
Correspondence to: Yuanchen Cui, Key Laboratory of Ministry of Education for
Special Functional Materials, Henan University, Kaifeng 475004, People’s
Republic of China. E-mail: yuanchencui@126.com
Key Laboratory of Ministry of Education for Special Functional Materials,
Henan University, Kaifeng 475004, People’s Republic of China
Appl. Organometal. Chem. 2012, 26, 635–640
Copyright © 2012 John Wiley & Sons, Ltd.

G. Nie et al.
without further purification. Acrylic acid, styrene and DMF were
distilled before use. Aryl halides were obtained from Lancaster
Co. and used as received. All other reagents were obtained from
commercial sources and were used as received.
OH
OH
Buffer
O
OH
H
n
O
An Avatar360 FT-IR spectrometer (Nicolet Co., USA) was
performed to record IR spectra. X-ray diffraction (XRD) patterns
were measured with a Philips X’Pert Pro X-ray diffractometer
(Philips Co., Holland; Cu-Ka radiation, 2θ range 10–80ꢀ, scan step
size 0.04ꢀ, time per step 0.5 s, generator voltage 40 kV, tube
current 40 mA). Polymer molecular weight was estimated by gel
permeation chromatography (GPC) using a Waters 515 apparatus
with THF as the eluent at a flow rate of 1.0 mL minÀ1. The calibra-
tion curves for the GPC analysis were obtained using polystyrene
as the standard. X-ray photoelectron spectra were measured with
an AXISULTRA spectrometer (Kratos Co., UK; monochromatized
Al-Ka radiation). The binding energy of contaminant carbon
(C1s, 284.8 eV) was used for binding energy calibration. An
EXSTAR6000 (Seiko Co., Japan) thermal analysis system was
performed at a heating rate of 10ꢀC minÀ1 for thermogravimetric
analysis (TGA) and scanning differential thermal analysis (SDTA).
A JSM-7001F scanning electron microscope (JEOL Co., Japan;
accelerating voltage 30 kV) was performed to observe the
morphology and microstructure of the product as synthesized.
The elemental composition of the product was analyzed with
an Oxford Link ISIS energy dispersive spectrometer attached to
the scanning electron microscope.
OH
H
n
HRP
O
O
Pd
PdCl2
O
O
Pd
n
polyphenol microsphere
the novel catalyst
Scheme 1. Schematic procedure for preparation of the novel catalyst
R2
X
R1
X= I Br Cl
Cat.
Preparation of Catalyst
R2
Phenol (0.47 g, 5 mmol) and polyethylene glycol-400 (PEG-400,
0.24 g) were dissolved in a mixed solution of 5 mL of 0.1 M
phosphate buffer (pH 7) and 15 mL of 1,4-dioxane, followed by
addition of the enzyme solution of HRP (2 mg) in 0.1 M phosphate
buffer (5 mL, pH 7). To the resultant mixed solution was added
hydrogen peroxide (5%, 0.25 mL) every 5 min for 14 times with
mild stirring at room temperature. The mixture was stirred for
an additional 30 min. After that, the black mixture obtained was
vacuum filtered and washed with water thoroughly to remove
HRP, phenol, residual PEG-400 and hydrogen peroxide. The
dark-brown filtered solid was dried at 60ꢀC under vacuum to give
polyphenol microspheres.
R1
Scheme 2. Heck coupling reaction
mixture was cooled to room temperature. To the cooled mixture
were added 25 mL H2O and 0.6 g Na2CO3, followed by stirring at
room temperature for 20 min. The catalyst was then separated
from the reagent by filtration, while the pH of the filtrate was
adjusted to 1–2 with a diluted aqueous solution of HCl. The white
precipitate obtained was filtered, washed with H2O several times
and dried in air to give the desired product, whose yield was
calculated based on the aryl halide.
Ethanol (60 mL) followed by 0.04 g PdCl2 were added to a
100 mL round-bottomed flask and stirred for 20 min. To the
resultant mixed solution was added polyphenol microspheres
(0.2 g), followed by stirring at 60ꢀC for 72 h. The mixture obtained
was filtered, washed with ethanol and water, and dried at 60ꢀC
under vacuum for 12 h to give about 0.2 g palladium complex
supported by polyphenol microspheres. The Pd content of the
polymer-supported complex, determined by inductively coupled
General Procedure for Heck Arylation of Aryl Halides with
Styrene (Scheme 2)
Aryl halide (1 mmol), styrene (1.5 mmol), tri-n-butylamine
(1.5 mmol) and polyphenol microsphere-supported Pd complex
(0.37 mol% Pd, mixed with 1.0 mL DMF) were introduced into a
three-necked flask (50 mL) equipped with a reflux condenser.
The charged flask was heated at a pre-set temperature in an oil
bath and stirred for 7 h. The reactant mixture was then cooled
to room temperature and dissolved in diethyl ether (30 mL),
followed by stirring at room temperature for 20 min and filtration.
The filtrate was treated with 3 N HCl (2 Â 15 mL) and brine
(3 Â 15 mL) and dried over MgSO4. The desired solid product
was obtained by recrystallization from ethyl ether (Et2O).
plasma mass spectrometry, was 0.466 mmol gÀ1
.
The synthesis of polyphenol microspheres and loading of
palladium are outlined in Scheme 1.
General Procedure for Heck Arylation of Aryl Halides with
Acrylic Acid (Scheme 2)
Aryl halide (1 mmol), acrylic acid (1.5 mmol), tri-n-butylamine
(3 mmol) and polyphenol microsphere-supported Pd complex
(0.37 mol% Pd, mixed with 1.0 mL DMF) were introduced into a
three-necked flask (50 mL) equipped with a reflux condenser.
The charged flask was heated at a pre-set temperature in an oil
bath and stirred for 7 h. At the end of the reaction, the reactant
General Procedure for Catalyst Recycling
After the Heck arylation reactions of aryl halide with acrylic
acid and styrene were completed, the polyphenol microsphere-
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 635–640

Synthesis of polyphenol microsphere-supported palladium complex
supported Pd catalyst was recovered from the reaction system by
filtration and washed with distilled H2O (2 Â 15 mL), ethanol
(EtOH, 2 Â 15 mL) and Et2O (2 Â 15 mL). The washed catalyst
was then dried at 60ꢀC under vacuum for 24 h and was ready
for further runs in the Heck reaction.
Results and Discussion
Characterization of the Catalyst
The molecular weight of the THF-soluble part was evaluated by
gel permeation chromatography (GPC) with refractive index
(RI)-light-scattering (LS) detectors. The weight-average molecular
weight of the polyphenol microsphere was 4.3 Â 104. Figure 1
shows the FT-IR spectra of polyphenol microspheres and poly-
phenol microsphere-supported Pd catalyst. As seen in Fig. 1(a),
the broad peak at 3427 cmÀ1 is ascribed to phenolic O-H bond,
which has coordination ability with palladium chloride. The peaks
at 1588, 1489, 833, 753 and 693 cmÀ1 arise from the polyphenol
microspheres and can be assigned to various vibration modes
of the C-H and C-C bonds of aromatic nuclei/rings. The strong
peak at 1207 cmÀ1 is due to the asymmetric stretching vibration
of C-OH and/or C-O-C, while the peak at 1103 cmÀ1 corresponds
to the symmetric vibration of the ether bond. These FT-IR data
are very similar to those of phenol polymers obtained in an
aqueous micelle system.[26] Polyphenol microsphere-supported
Pd catalyst displays all the characteristic absorption bands of
polyphenol microspheres, but the FT-IR bands shift to some
extent as compared with those of the phenolic polymer (Fig. 1b),
which is due to the interaction between polyphenol microspheres
and Pd.
Figure 2. XRD patterns of polyphenol microsphere (a) and polyphenol
microsphere-supported Pd catalyst (b)
Figure 3 shows the X-ray photoelectron survey spectrum as well
as Pd3d and O1s spectra of polyphenol microsphere-supported Pd
catalyst, where the O1s spectrum of the polyphenol microspheres
is also provided for comparison. The polyphenol microsphere-
supported Pd catalyst as synthesized shows a Pd3d peak together
with C1s and O1s peaks derived from the polyphenol microspheres
(Fig. 3a); the two characteristic peaks of Pd3d5/2 appear at 336.0
and 338.3 eV (Fig. 3b), which suggests that Pd in the catalyst
coexists as Pd0 and Pd2+, as reported elsewhere.[30] In the mean-
time, the O1s binding energy of the novel catalyst (533.25 eV) is
higher than that of the polyphenol microspheres (531.85 eV), which
is attributed to the coordination of O with Pd0 or Pd2+
.
Figure 2 shows the XRD patterns of polyphenol microspheres
and polyphenol microsphere-supported Pd catalyst. Polyphenol
Figure 4 shows SEM images of polyphenol microspheres and
polyphenol microsphere-supported Pd catalyst. It is seen that
polyphenol microspheres as prepared are nearly monodispersed
and have an average diameter of about 500 nm (Fig. 4a). This
differs from what is reported by Young-Jin in that the aggregates
of irregular-shaped products are formed by the enzymatic oxida-
tive polymerization of phenol in the presence of PEG template in
water,[33] which is possibly attributed to the adoption of different
reaction systems and different modes to add hydrogen peroxide
as well. Besides, polyphenol microsphere maintains their configu-
ration after coordination with palladium chloride (Fig. 4b), while a
large number of fine Pd particulates are uniformly adsorbed on
polyphenol microspheres (Fig. 4c), as evidenced by relevant
energy-dispersive spectrometric analysis (Fig. 5).
microspheres exhibit
a
broad scattering peak at 19.1ꢀ,
corresponding to their homogeneous amorphous phase (Fig. 2a).
Also, the polyphenol microsphere-supported Pd catalyst shows
major diffraction peaks at 2θ of 40.1ꢀ, 46.7ꢀ and 68.1ꢀ (Fig. 2b),
which can be indexed to the diffraction of (1 1 1), (2 0 0) and
(2 2 0) crystallographic planes of face-centered cubic palladium
(JCPDS file no. 89-4897).[32] Moreover, the additional peak at
19.1ꢀ in Fig. 2(b) is attributed to the polyphenol microspheres,
which indicates that Pd is readily deposited on the polyphenol
microspheres.
Figure 6 presents the TGA and SDTA curves of polyphenol
microsphere-supported Pd catalyst. Polymer-supported Pd
catalyst as synthesized is stable up to 250ꢀC, and it experiences
continuous weight loss within 250–350ꢀC (Fig. 6a). The novel
catalyst shows a strong exothermic peak at 330ꢀC (Fig. 6b),
corresponding to oxidation of the polymer support. These
thermal analysis results indicate that the novel catalyst possesses
good thermal stability.
Catalytic Activity
The ideal substrates for Heck reactions are aryl chlorides, since
they are cheaper and more widely available than their bromide
or iodide counterparts, but so far few polymer-supported Pd
catalysts have been found to convert aryl chlorides effectively
at high temperatures.[34–36] In the present research we adopt
Figure 1. FT-IR spectra of polyphenol microsphere (a) and polyphenol
microsphere-supported Pd catalyst (b)
Appl. Organometal. Chem. 2012, 26, 635–640
Copyright © 2012 John Wiley & Sons, Ltd.
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G. Nie et al.
Figure 3. X-ray photoelectron spectrum (a) and Pd3d spectrum (b) of polyphenol microsphere-supported Pd catalyst as well as O1s spectra of poly-
phenol microsphere (c) and polyphenol microsphere-supported Pd catalyst (d)
Figure 4. Scanning electron microscopy images of polyphenol microsphere (a) and polyphenol microsphere-supported Pd catalyst (b, c)
Figure 5. EDS pattern of the region containing fine Pd particulates on the surface of polyphenol microsphere-supported Pd catalyst as synthesized
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 635–640

Synthesis of polyphenol microsphere-supported palladium complex
entry 8). To our surprise, the novel catalyst remains active at a
low temperature of 50ꢀC, giving an acceptable yield of 61%. It
also gives excellent yields at a fixed reaction time of 7 h (Table 2,
entry 7).
In order to prove the efficiency of the novel catalyst, we
studied the Heck reactions of different types of aryl halides with
acrylic acid and styrene under optimized reaction conditions. As
shown in Table 3, aryl iodide with either electron-withdrawing
or electron-donating substituents reacts with acrylic acid or
styrene at 90ꢀC, generating corresponding coupled products in
excellent yield after 7 h reaction (entries 1–8).
The coupling reactions of aryl bromides with alkenes require
higher temperatures and a nitrogen atmosphere because of the
relatively high bond energy of the C-Br bond. As summarized in
Table 4, bromobenzene and 4-nitrobromobenzene in association
with acrylic acid or styrene also perform effectively when the
reactions are carried out in tetrabutyl ammonium bromide
under nitrogen atmosphere (Table 4, entries 1, 3, 4 and 6). When
p-bromoanisole is allowed to react with acrylic acid or styrene at
135ꢀC for 7 h, the coupled product is produced in low yields
(Table 4, entries 2 and 5).
Figure 6. TGA (a) and SDTA (b) curves of polyphenol microsphere-
supported Pd catalyst
the polyphenol microsphere-supported palladium complex as
synthesized as a catalyst for Heck reactions of various aryl halides
with olefins. The influences of amount of catalyst, reaction
temperature and reaction time on catalytic activity have been
systematically investigated using the coupling of iodobenzene
and acrylic acid as a model reaction. Relevant results are pre-
sented in Tables 1 and 2. It is seen that the optimum amount of
polymer-supported Pd catalyst is 0.37 mol% Pd (Table 1).
However, a decrease in the Heck reaction yield was observed
for concentrations over 0.37 mol%. This result is probably due
to the aggregation of palladium particulates to ‘palladium black’
at higher concentrations.[37,38] Therefore, increase of palladium
catalyst concentration was accompanied by a decrease in the
reaction yield. As the reaction temperature increases from 50
to 90ꢀC, the yield increases (Table 2; entries 3, 4, 5, 6, and 7),
but the yield remains almost unchanged above 90ꢀC (Table 2,
Moreover, more challenging couplings of olefins with aryl
chloride were also investigated, but no coupled product was
obtained from the coupling reaction between chlorobenzene
with acrylic acid or styrene in the presence of the polyphenol
Table 3. Heck reactions of acrylic acid and styrene with different aryl
iodide.a
Entry
R1
R2
X
Time (h)
T(ꢀC)
Yield (%)
1
2
3
4
5
6
7
8
H
CO2H
CO2H
CO2H
CO2H
Ph
I
I
I
I
I
I
I
I
7
7
7
7
7
7
7
7
90
90
90
90
90
90
90
90
91
95
97
97
94
80
90
90
p-Me
p-OCH3
p-NO2
H
Table 1. Influence of amount of catalyst on model reactiona
p-Me
p-OCH3
p-NO2
Ph
Ph
X (Pd) (mol%)
Yield (%)
0.19
58
0.28
80
0.37
91
0.47
87
0.93
86
Ph
aReaction conditions:
1 mmol aryl iodide, 1.5 mmol alkene,
aReaction conditions: 1 mmol iodobenzene; 1.5 mmol acrylic acid;
3 mmol tributylamine; 1.0 mL DMF; 90ꢀC, 7 h.
tributylamine, 1.0 mL DMF, 90 ꢀC, 0.37 mol% Pd.
Table 4. Heck reactions of acrylic acid and styrene with different aryl
halides.a
Table 2. Influence of reaction temperature and reaction time on
model reactiona
Entry
R1
R2
X
Time (h)
T (ꢀC)
Yield (%)
Entry
Time (h)
Temp (ꢀC)
Yield (%)
1
2
H
p-OCH3
p-NO2
H
CO2H
CO2H
CO2H
Ph
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
7
7
120
135
120
120
135
120
120
120
120
120
77
44
94
87
50
95
0
1
2
3
4
5
6
7
8
9
3
5
7
7
7
7
7
7
9
90
90
76
82
61
68
70
78
91
90
87
3
7
50
4
7
60
5
p-OCH3
p-NO2
H
Ph
7
70
6
Ph
7
80
7
CO2H
Ph
10
10
10
10
90
8
H
0
100
90
9
p-NO2
p-NO2
CO2H
Ph
53
86
10
aReaction conditions: 1 mmol iodobenzene; 1.5 mmol acrylic acid;
3 mmol tributylamine; 1.0 mL DMF; 0.37 mol% Pd.
aReaction conditions: 1 mmol aryl halide, 1.5 mmol alkene, 2.5 mmol
tetrabutyl ammonium bromide (TBAB), 0.37 mol% Pd.
Appl. Organometal. Chem. 2012, 26, 635–640
Copyright © 2012 John Wiley & Sons, Ltd.
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G. Nie et al.
for better immobilization of Pd and to gain their enhanced
performance.
Conclusions
Polyphenol microsphere has been prepared via template polymer-
ization of phenol catalyzed by the bio-enzyme catalyst HRP in
aqueous 1,4-dioxane. Polyphenol microspheres as obtained were
effectively employed as a substrate to load Pd particles. The
catalytic activity of the resultant polyphenol microsphere-
supported Pd catalyst for Heck reactions of iodide, bromide and
activated aryl chloride under phosphine-free conditions was evalu-
ated. It was found that the novel catalyst possesses good activity
for the above-mentioned Heck reactions. Besides, as-synthesized
polyphenol microsphere-supported Pd catalyst can be easily sepa-
rated and recycled, showing potential as a promising catalyst for
Heck reactions.
Figure 7. Application of hot filtration to the novel catalyst-catalyzed
Heck reaction
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group (Table 4, entries 9 and 10).
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Furthermore, the reusability of the catalyst was tested by
carrying out repeated runs of the model reaction and the
reaction of bromobenzene with styrene separately. It has been
found that, when the catalyst is repeatedly used for up to five
times, the target product of the model reaction is obtained in a
yield of 91%, 90%, 88%, 83% and 82%, respectively. Meanwhile,
the catalyst was reused for the Heck reaction of bromobenzene
with styrene. Repeatedly using the catalyst for four times, the
yield of the product was 87%, 82%, 74% and 50%, respectively.
The results indicate that polyphenol microsphere-supported Pd
catalyst, as synthesized, possesses practical utility.
A hot filtration technique is preferred to check whether the
leached metal species are responsible for the catalytic activity.[39]
As shown in Fig. 7, when the novel catalyst was hot filtered after
1 h of reaction and the filtrate placed back into the flask, the yield
was highly dependent on whether the solid catalyst was
removed or not. Thus the yield with hot filtration remained at
nearly 52% after reaction for up to 7 h, which is similar to the
yield observed immediately after filtration and is much lower
than that without filtration (91%). This may imply that the
supported Pd is the active site of the reaction.
Further, the performance of the polyphenol microsphere-
supported palladium catalyst was compared with aggregates
of irregular-shaped polyphenol-supported palladium catalyst by
Heck reaction between iodobenzene and acrylic acid. Aggregates
of irregular-shaped polyphenol was obtained in an aqueous micelle
system.[26] Both the control experiment using irregular-shaped
polyphenol-supported palladium catalyst and the typical experi-
ment with polyphenol microsphere-supported palladium catalyst
were conducted under identical conditions. The yield of target
product in the presence of polyphenol microsphere-supported
palladium catalyst was found to be 91%, while the yield of the
same target product using irregular-shaped polyphenol-supported
palladium catalyst was found to be 72%. This results are probably
due to the unique high volume-to-surface ratio properties of the
polyphenol microsphere relative to irregular-shaped polyphenol.
On the whole, the polyphenol microspheres are ideal platforms
[36] J. Zhu, J. H. Zhou, W. K. Yuan, Appl. Catal. A 2009, 352, 243.
[37] J. G. De Vries, Dalton Trans. 2006, 421.
[38] M. T. Reetz, J. G. De Vries, Chem. Commun. 2004, 1559.
[39] M. Lamblin, L. N. Hardy, F. X. Felpin, Adv. Synth. Catal. 2010, 352, 33.
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 635–640