Palladium supported on zinc oxide nanoparticles as efficient heterogeneous catalyst for Suzuki-miyaura and hiyama reactions under normal laboratory conditions

Article abstract of DOI:10.1002/hlca.201400331

Nanoscale Pd supported on ZnO was prepared by a facile coprecipitation method. Pd/ZnO Nanoparticles were characterized by using XRD, TEM, SEM, XPS, BET specific surface area measurement, and thermogravimetric analysis. This catalyst was used as novel and excellent heterogeneous catalyst for ligand-free C-C bond-formation particularly in the synthesis of unsymmetrical biaryls by Suzuki-Miyaura and Hiyama cross-coupling reactions under air atmosphere without use of any Ar or N₂ flow. The catalyst can be recovered and recycled several times without marked loss of activity.

Full text of DOI:10.1002/hlca.201400331

Helvetica Chimica Acta – Vol. 98 (2015)
805
Palladium Supported on Zinc Oxide Nanoparticles as Efficient
Heterogeneous Catalyst for SuzukiÀMiyaura and Hiyama Reactions under
Normal Laboratory Conditions
by Mona Hosseini-Sarvari* and Zahra Razmi
Department of Chemistry, Shiraz University, Shiraz 71454, Iran
(phone: þ 98-711-6137169; fax: þ 98-711-6460788; e-mail: hossaini@shirazu.ac.ir)
Nanoscale Pd supported on ZnO was prepared by a facile coprecipitation method. Pd/ZnO
Nanoparticles were characterized by using XRD, TEM, SEM, XPS, BET specific surface area measure-
ment, and thermogravimetric analysis. This catalyst was used as novel and excellent heterogeneous
catalyst for ligand-free CÀC bond-formation particularly in the synthesis of unsymmetrical biaryls by
SuzukiÀMiyaura and Hiyama cross-coupling reactions under air atmosphere without use of any Ar or N2
flow. The catalyst can be recovered and recycled several times without marked loss of activity.
Introduction. – Pd Catalysts are used in CÀC coupling reactions including
SuzukiÀMiyaura and Hiyama cross coupling [1]. Despite its remarkable usefulness,
homogeneous Pd catalysts suffer from a number of drawbacks such as availability,
stability, costs of the Pd complexes and phosphine ligands, and they are not used in
industrial applications because of difficult separation and recycling procedure [2].
Therefore, heterogeneous Pd catalysts have been developed and seem particularly well
suited since the Pd metal immobilized onto a support (including organic, polymeric, or
inorganic support materials) could be easily removed by filtration leaving products
virtually free of residual Pd [1][3]. Pd Nanoparticles and colloidal Pd species have also
been reported as recyclable catalysts [4][5]. However, these heterogeneous Pd
catalysts often suffer from problems, such as low catalytic efficiency, degradation,
leaching of the metal species, and difficult synthetic procedures.
Among the important II – VI semiconductors, ZnO has been widely studied
because of its fundamental properties and potential uses in devices, such as gas sensors,
solar cells, resonators, field-effect transistors, and catalyst [6]. In recent years, the
modification of ZnO with noble metals, such as Ag, Au, Pt, and Pd, has attracted
significant attention [7]. As a noble metal, Pd, whose ionic radius (0.080 nm) is close to
that of Zn2þ (0.074 nm), has been widely used in industrial catalysis especially for
MeOH synthesis [8]. However, modifying ZnO with Pd has already been applied in the
area of catalytic reaction [8][9]; to the best of our knowledge, there are a few studies on
CÀC coupling reactions with ZnO modified with Pd [10][11]. Kim and Choi [10]
reported a method for preparing Pd/ZnO and PdÀM (M ¼ Cu, Ni, and Ag) nano-
particles (PdÀM/ZnO) by g-irradiation and their catalytic efficiencies were evaluated
in hydrogenation and Suzuki reactions. But, these systems actually suffer from huge
drawbacks, such as using large amounts of ZnO nanopowder, N2 gas to remove O2 from
ꢀ 2015 Verlag Helvetica Chimica Acta AG, Zürich

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the reaction vessel, g-ray irradiation, and organic solvents, such as MeOH, or in the
case of Suzuki CÀC coupling reactions the limitation to only iodohalides and
phenylboronic acid and the use of EtOH as solvent. Also, the molar ratio of iodohalide/
phenylboronic acid/Pd/ZnO catalyst was 1:2 :1.3, and the loaded amount of Pd on
ZnO, which was determined by ICP data, was 19.4 wt%. Up to now, other supported Pd
catalysts have been reported for Suzuki reactions of aryl halides under different
reaction conditions [12]. Though, there are still problems, such as long reaction times,
using organic solvents, or using ligands [12f].
In the present study, we focused on the preparation of Pd/ZnO, which appeared to
be one of the best catalysts for SuzukiÀMiyaura and Hiyama reactions. The aim of our
work described in this article was the synthesis of Pd supported on ZnO by
coprecipitation (CP) method (Pd loading was 9.84 wt%, determined by ICP) for
ligand-free CÀC bond-formation by Suzuki and Hiyama reactions in H2O and
ethyleneglycol, respectively.
Results and Discussion. – As part of our continuing attempts to broaden the scope
of nano metal oxides as catalysts [10][12a][12c], we have recently reported the
efficiency of nano Pd/ZnO in MizorokiÀHeck and Sonogashira reactions, and also for
the formation of CÀO and CÀN bonds [13]. This catalyst was synthesized and fully
characterized by powder X-ray diffraction (XRD), transmission electron microscopy
(TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy
(XPS), thermogravimetric analysis (TGA), BET surface area measurement, FT-IR
spectroscopy, inductively coupled plasma (ICP) analysis, and atomic absorption
spectroscopy (AAS) analysis, some of these results are shown in Table 1, and Figs. 1 – 5
[13]. SEM and TEM images of the synthesized Pd/ZnO nanoparticles are shown in
Fig. 1. The amount of Pd supported on ZnO nanoparticles was determined by ICP
technique. According to this analysis, the amounts of Pd in 0.001 and 0.009 g of the
catalyst were determined as 925 · 10À9 and 8325 · 10À9 mol-%, respectively.
The activity of Pd/ZnO nanoparticle catalyst was first examined in the Suzu-
kiÀMiyaura reaction. This choice was based on the fact that such a reaction provides a
powerful tool for CÀC coupling for the synthesis of many natural and synthetic biaryls.
To determine the optimal reaction conditions, the cross coupling of 1-(4-bromophe-
nyl)ethanone (1 mmol) in the presence of Pd/ZnO nanoparticles was studied under
variation of different parameters, such as solvent, base, temperature, and amount of
catalyst (Scheme and Tables 2 – 5).
Table 1. Physical Characterization of Nano Pd/ZnO
XRD
BET Surface area
Crystallite sizes of ZnO and Pd/ZnO: 21 – 23 nm
40.61 m2 gÀ1
Pore size distribution
1.81 nm
TEM
XPS
TGA
ICP
25 nm
Binding energy of the Pd3d5/2: 335.5 eV
Percentage of accessible Pd in catalyst: 2.72 Æ 0.01%
9.84%
9.80%
AAS

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807
Fig. 1. a) TEM and b) SEM images of nano Pd/ZnO
At first, the base was optimized (Table 2). Various bases were tested and all of them
gave similar results. As can be seen from Entry 8, this reaction can occur even without
any addition of base, but the reaction time increased and the yield of the product
decreased. Compared with Entries 5 – 7, with addition of 0.25 mmol K2CO3 the yield of
the product was much better, therefore, K2CO3 as an inexpensive and readily available
inorganic base was used in this study.
As the results listed in Table 3 revealed that the selection of solvent was also
important for the presented method. Using H2O as solvent gave satisfactory results,
whereas the use of other protic and aprotic polar solvents, such as EtOH, ethane-1,2-
diol, DMSO, and DMF, which are commonly used in Pd-catalyzed coupling reactions,
was not very effective. Thereafter, we examined the effect of temperature. The results
are shown in Table 4. Finally, the amounts of Pd/ZnO nanoparticles were optimized
(Table 5). As it can be seen from Entries 2 – 4, by increasing the amount of catalyst from
0.0005 g to 0.005 g, the yield of the desired product was not changed, but the reaction
time decreased. A catalytic amount of 0.001 g (which contains 925 · 10À9 mol-% Pd;

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Fig. 2. XPS Spectra of a) Pd3d, b) Zn2p, and c) O1s of 9.8 wt% nano Pd/ZnO
Entry 3) was applied because of the lower amount of Pd loading compared with 0.005 g
(Entry 4). Also, nano ZnO was prepared without modification with Pd by the same
procedure as for the preparation of Pd/ZnO. As expected, no reaction occurred with
nano ZnO (Table 5, Entry 5).
On the basis of the optimized reaction conditions, coupling reactions between aryl
halides (X ¼ I, Br, and Cl) and different arylboronic acids were carried out. The results
are shown in Table 6. The reaction of aryl iodides, bromides, and chlorides with a
variety of electron-rich and electron-poor substituents proceeded smoothly, giving the
coupling products in good to excellent yields. In addition, various arylboronic acids
with electron-donating or electron-withdrawing substituents were also used in this
reaction (Table 6). It was found that the yields of the coupling reactions decreased
slightly for arylboronic acids containing electron-withdrawing groups, such as (3,4,5-
trifluorophenyl)boronic acid, while the reactions with arylboronic acids with electron-
rich groups, such as (4-ethylphenyl)boronic acid, proceeded more efficiently than those

Helvetica Chimica Acta – Vol. 98 (2015)
809
Fig. 3. XRD Pattern of a) nano ZnO and b) 9.84 wt% of Pd-modified ZnO calcined at 723 K for 2 h
of phenylboronic acid in agreement with the results reported by Liu and co-workers
[14]. This is due to the effect of the substituents on the nucleophilicity of arylboronic
acids. The stronger the nucleophilicity, the more active is the arylboronic acid.
Furthermore, steric hindrance due to ortho-substituents on the aryl iodides affected the
reaction progress. Thus, the reaction time for 1-iodo-2-methylbenzene was higher than
for 4-substitued iodobenzenes (Table 6, Entries 5 and 6). Because some of the NO2 and
CN substrates were insoluble and solid in H2O at 1008, a mixture of H2O/EtOH 1:1
under reflux, in which the substrates were soluble, was used as solvent (Table 6, Entries
4, 11, and 16).

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Fig. 4. FT-IR Spectrum of nano Pd/ZnO
Fig. 5. a) Trace showing the interaction of CO as molecular probe with ZnO and Pd/ZnO nanoparticles.
b) Thermogram showing the interaction of CO as molecular probe with Pd/ZnO nanoparticles under N2
atmosphere.

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Scheme. Suzuki Reaction of 1-(4-Bromophenyl)ethanone and Phenylboronic Acid Using Pd/ZnO
Nanoparticles as Catalyst
Table 2. Optimization of Basesa)
Entry
Base
Amount of base [mmol]
Time [h]
Yieldb) [%]
1
2
3
4
5
6
7
8
Na2CO3
KF · 2 H2O
K3PO4
KOH
K2CO3
K2CO3
K2CO3
None
1
1
1
1
1
1
96
96
96
96
96
96
96
80
0.5
1
0.25
0.5
0.5
3
1
0.5
0.25
–
a) Reagents and conditions: 1-(4-bromophenyl)ethanone (1 mmol), phenylboronic acid (1 mmol), Pd/
ZnO nanoparticles (0.001 g), H2O (1 ml), and base, 1008. b) Yield of isolated product.
Table 3. Optimization of Solventsa)
Entry
Solvent
Time [h]
Yieldc) [%]
1
2
3
4
5
6b)
7
8
9
H2O
EtOH
H2O/EtOH 1 : 1
Ethane-1,2-diol
Toluene
CH2Cl2
DMSO
DMF
None
0.5
0.75
0.70
6
6
6
6
6
6
96
90
95
15
20
15
60
70
60
a) Reagents and conditions: 1-(4-bromophenyl)ethanone (1 mmol), phenylboronic acid (1 mmol), Pd/
ZnO nanoparticles (0.001 g), H2O (1 ml), K2CO3 (0.25 mmol), and solvent (1 ml), 1008. b) Reaction
conducted at 508. c) Yield of isolated product.
Table 4. Optimization of Temperaturesa)
Temperature [8]
Time [h]
100
0.5
96
80
0.75
96
70
2
96
60
5
90
50
10
80
r.t.
24
70
Yield [%]b)
a) Reagents and conditions: 1-(4-bromophenyl)ethanone (1 mmol), phenylboronic acid (1 mmol), Pd/
ZnO nanoparticles (0.001 g), H2O (1 ml), K2CO3 (0.25 mmol). b) Yield of isolated product.

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Table 5. Optimization of the Amounts of Pd/ZnO Nanoparticlesa)
Entry
Pd/ZnO [g] ([mol-% of Pd]b)c)
0.0001 (925 · 10À10
0.0005 (4625 · 10À10
Time [h]
Yield) [%]
1
2
3
4
5c)
)
4
2
95
96
96
96
)
0.001 (925 · 10À9
)
0.5
0.25
24
0.005 (4625 · 10À9
0.001
)
None
a) Reagents and conditions: 1-(4-bromophenyl)ethanone (1 mmol), phenylboronic acid (1 mmol), H2O
(1 ml), K2CO3 (1 mmol), and Pd/ZnO nanoparticles, 1008. b) Determined by ICP. c) Nano ZnO as
catalyst. d) Yield of isolated product.
Table 6. SuzukiÀMiyaura Reaction of Aryl Halides with Arylboronic Acids Catalyzed by Pd/ZnO
Nanoparticles
Entry
X
R
Ar
Time [min]
Yieldb) [%]
1
2
3
4a)
5
6
7
8
9
10
11a)
12
13
14
15
16a)
17
18
19
20a)
21a)
22
23
24
25
I
I
I
I
I
I
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
I
H
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
50
60
90
45
120
90
240
300
360
25
40
30
300
360
55
60
40
50
40
40
50
96
84
93
96
90
94
90
92
89
90
94
96
89
87
92
96
97
96
96
97
90
95
90
90
95
4-MeO
4-NH2
4-NO2
2-Me
4-Me
H
4-Me
4-MeO
4-OH
4-CN
4-Ac
H
4-Me
4-CN
4-NO2
H
4-Ac
4-Ac
4-CN
4-CN
4-OH
4-OH
4-CN
4-CN
3,4,5-F3ÀC6H2
4-EtÀC6H4
3,4,5-F3ÀC6H2
4-EtÀC6H4
4-EtÀC6H4
3,4,5-F3ÀC6H2
4-EtÀC6H4
3,4,5-F3ÀC6H2
3,4,5-F3ÀC6H2
4-EtÀC6H4
I
Br
Br
Br
Br
Br
Br
Cl
Cl
45
50
70
55
a) Reactions conducted in H2O/EtOH 1 : 1 (1 ml) under reflux. b) Yield of isolated product.

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Table 7. Comparison of Activities of Different Catalysts in the Suzuki Reactiona)
Entry Catalyst
Reaction Conditions
Time Yieldb) Ref.
[%]
1
2
Nano Pd/Al2O3 (0.1 mol-%)
NMP, Na2CO3, H2O, Ar
flow, 658
K3PO4, Bu4NBr (TBAB), 5 min 98
3 h
72
[12a]
[12b]
Nano Pd/chitosan (0.5 mol-%)
H2O, MW, 1508
3
4
5
6
7
Pd/SiO2ÀTiO2 (0.05 mmol)
K2CO3, EtOH, 788
6 h
30 min 96
48 h
10 h
30 min 96
91.3
[12c]
[12d]
[12e]
[12f]
PdÀNHC/hybrid silicac) (0.2 mol-%) K2CO3, DMF/H2O, 1108
PdÀPhosphine/SiO2 (0.025 g)
K2CO3, MeOH/H2O, r.t.
K2CO3, DMF, 1108
K2CO3, H2O, 1008
87
85
SS-Pdd) (2 mol-%)
Nano Pd/ZnO (925 · 10À9 mol-%)
This study
a) See Scheme. b) Yield of isolated product. c) Hybrid silica-based catalyst derived from PdÀNHC (N-
d
heterocyclic carbenes) complexes. ) Solid-supported nano- and microparticles of Pd0 (SS-Pd).
Table 8. Recycling of the Catalyst in the Reaction of 1-(4-Bromophenyl)ethanone with Phenylboronic
Acid in the Presence of Pd/ZnO Nanoparticlesa)
Run
1
30
96
2
35
95
3
35
95
4
37
95
5
40
94
6
40
94
7
45
94
Time [min]
Yieldb) [%]
a) Reagents and conditions: 1-(4-bromophenyl)ethanone (1 mmol), phenylboronic acid (1 mmol), Pd/
ZnO nanoparticles (0.001 g), H2O (1 ml), K2CO3 (0.25 mmol), 1008. b) Yield of isolated product.
To show the merit of this catalytic method, we compared our results with similar
data published by other groups which used other catalysts (Table 7). Having
established the efficacy of Pd/ZnO nanoparticles in Suzuki-coupling reactions, we
then investigated the recyclability of the catalyst in the reaction of 1-(4-bromophe-
nyl)ethanone with phenylboronic acid in H2O (Table 8). Pd/ZnO could be reused
successfully for ten runs without either significant loss of yield or extension of the
reaction time. The first reaction was carried out within 30 min. Similarly, the repeated
runs of the reaction were conducted. After appropriate time, the mixture was
centrifuged to separate the catalyst. Then, it was washed with AcOEt (5 ml) and H2O
(5 ml) and dried in vacuo for the next cycle. The results indicate that only 0.02 wt% Pd
were leached out from the catalyst surface after seven cycles (the initial 9.84 wt% Pd
decreased to 9.82 wt%).
The XRD pattern (Fig. 6,a) and TEM image (Fig. 6,b) of the recovered nano
catalyst after the 7th run showed that no significant aggregation of the particles has
occurred and the morphology and the size of the particles were not disturbed notably in
comparison with the TEM picture of the catalyst before the reaction. This observation
confirmed that Pd/ZnO nanoparticles were stable under the reaction conditions and
were not affected by the reactants.
Also, the heterogeneity of the catalyst was evaluated to study whether the reaction
used solid catalysts or was catalyzed by nano Pd/ZnO species in the liquid phase.
To address this issue, two separate experiments were conducted with 1-(4-bromophen-

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Helvetica Chimica Acta – Vol. 98 (2015)
Fig. 6. a) XRD and b) TEM images of Pd/ZnO nanoparticles used for the reaction of 1-(4-
bromophenyl)ethanone with phenylboronic acid, after the 7th run recycling of the catalyst
yl)ethanone (1 mmol) and phenylboronic acid (1 mmol). In the first experiment, the
reaction was terminated after 15 min; at this point, the catalyst was separated from the
mixture by centrifugation, and the reaction was continued with the filtrate for
additional 5 h. In the second experiment, the reaction was terminated after 15 min. In
both cases, the desired product was obtained in the same yield (48%). Pd was not
detected in the filtrate in either experiment by ICP analysis. This observation confirms
that Pd/ZnO nanoparticles are stable under the reaction conditions and behave indeed
as heterogeneous solid catalyst [13].

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815
Driven by the results of the SuzukiÀMiyaura coupling reaction, we further explored
the application of the nano Pd/ZnO catalyst in another important CÀC bond forming
reaction, namely Hiyama cross coupling of aryl halides with trimethoxy(phenyl)silane.
At first, the Hiyama cross-coupling reaction between 1-(4-bromophenyl)ethanone
(1 mmol), trimethoxy(phenyl)silane (1 mmol), and K2CO3 (1 mmol) as base in the
presence of Pd/ZnO (0.009 g), in H2O as solvent was studied, i.e., the reaction
conditions were the same as those for the SuzukiÀMyaura coupling described above.
The obtained yields under these conditions were low, but the Hiyama cross coupling
could be improved in light of the results of solvent screening as shown in Table 9. Using
ethane-1,2-diol as solvent gave satisfactory results, whereas the use of other protic and
aprotic polar solvents, which are commonly used in Pd-catalyzed coupling reactions,
was not effective (Table 9, Entries 3 – 8). The bases were screened as well. According to
the results shown in Table 9 (Entries 2 and 10 – 12), K2CO3 was chosen as base in terms
of cost (Entry 2), although K3PO4 led to an excellent yield as well (Entry 10). In
addition, the effect of temperatures was also studied, and the results are shown in
Table 9 (Entries 2 and 13 – 16). The results indicate that the best temperature under the
applied reaction conditions was 1008 for 1 h reaction time (Entry 2).
Similar to the Suzuki reaction, we continued our studies and optimized the amount
of Pd/ZnO catalyst for the Hiyama coupling reaction after selection of the best solvent
Table 9. Effects of Solvents, Bases, and Temperature on the Hiyama Coupling Reactiona)
Entry
Solvent
Base
Time [h]
Temp. [8]
Yieldb) [%]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
H2O
Ethane-1,2-diol
EtOH
PEG-300
PEG-2000
1,4-Dioxane
DMSO
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K3PO4
KOH
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
5
1
5
5
5
5
5
5
5
5
5
5
1
4
10
24
100
100
100
100
100
100
100
100
100
100
100
100
80
15
95
60
80
35
None
25
20
None
95
90
90
95
85
75
30
None
Ethane-1,2-diol
Ethane-1,2-diol
Ethane-1,2-diol
Ethane-1,2-diol
Ethane-1,2-diol
Ethane-1,2-diol
Ethane-1,2-diol
50
40
r.t.
a) Reagents and conditions: 1-(4-bromophenyl)ethanone (1 mmol), trimethoxy(phenyl)silane
(1 mmol), base (1 mmol), Pd/ZnO nanoparticles (0.009 g), solvent (1 ml). b) Yield of isolated product.

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and base (Table 10). On the basis of the optimized reaction conditions, the coupling
reactions between aryl halides and trimethoxy(phenyl)silane were carried out
(Table 11). The electronic property of the substituent has a strong influence on the
reactivity of aryl bromides and chlorides. As shown in Table 11, the electron-deficient
aryl bromides and chlorides showed an excellent reactivity and furnished the products
in high yields after short reaction times (Table 11, Entries 6 – 10). Furthermore, in the
presence of aryl iodides as reactants, substrates with electron-withdrawing or electron-
donating groups gave the desired products in good yields (Table 11, Entries 1 – 5).
To conclude, Pd supported on ZnO has been used as heterogeneous and recyclable
catalyst for CÀC cross-coupling reactions in H2O and ethyleneglycol as solvents
without using any ligands and under normal atmosphere, i.e., without the need of Ar or
N2 as protecting gas. These reaction conditions allow the easy extractive recovery of the
final product, and the solid residue showing catalytic activity can be reused several
times. This method will provide a facile, efficient, and environmentally friendly process
for Suzuki and Hiyama reactions because of its wide applicability to various substrates,
Table 10. Optimization of the Amount of Pd/ZnO in the Hiyama Coupling Reactiona)
Entry
Pd/ZnO [g, mol-% of Pdb)]
Time [h]
Yieldc) [%]
1
2
3
4
0.001, 925 · 10À9
0.005, 4625 · 10À9
0.009, 8325 · 10À9
0.04, 37 · 10À6
3
2
1
1
80
90
95
95
a) Reagents and conditions: 1-(4-bromophenyl)ethanone (1 mmol), trimethoxy(phenyl)silane
(1 mmol), ethyleneglycol (1 mmol), K2CO3 (1 mmol), and Pd/ZnO, 1008. b) Determined by ICP.
c) Yield of isolated product.
Table 11. Hiyama Coupling of Aryl Halides with Trimethoxy(phenyl)silane Catalyzed by Nano Pd/ZnO
Entry
X
R
Time [min]
Yielda) [%]
1
2
3
4
5
6
7
8
9
I
I
I
I
H
50
70
45
70
60
70
80
45
40
60
96
85
94
90
90
92
91
93
92
95
4-MeO
4-NO2
2-Me
4-NH2
4-CN
4-NO2
4-OH
4-CN
4-Ac
I
Cl
Cl
Br
Br
Br
10
a) Yield of isolated product.

Helvetica Chimica Acta – Vol. 98 (2015)
817
the use of less toxic reagents, mild reaction conditions, and a small amount of Pd (925 ·
10À9 mol-%). We believe that this type of nanocrystalline metal oxides will find
excellent use as active catalysts not only for laboratory scale research but also for
industrial applications.
The authors are thankful to the Research Council of Shiraz University and the Iran National Science
Foundation (Grant No. 90003779) for financial support.
Experimental Part
General. Reagents and solvents were purchased from Fluka, Aldrich, Alfa Aesar, and Merck.
Nanoparticles of Pd/ZnO and ZnO were synthesized as reported previously [13]. Evaporation of solvents
was performed under reduced pressure with a Büchi rotary evaporator. The progress of the reactions was
monitored by thin-layer chromatography (TLC) using silica gel SILG/UV 254 plates (SiO2). Column
chromatography (CC): short columns of SiO2 60 (70 – 230 mesh) in glass columns (2 – 3 cm i.d.); 15 – 30 g
of SiO2 per 1 g of crude mixture.
General Procedure for the Synthesis of Pd/ZnO Nanoparticles. Pd/ZnO Catalyst was prepared by CP
method. To a mixture of Pd(NO3)2 (0.027 gmlÀ1) and Zn(NO3)2 (0.267 g mlÀ1) solns., an aq. 1m Na2CO3
soln. was added at r.t. until pH 8 was reached. Then, the mixture was kept for 2 h at 70 – 808, and the
precipitate was filtered, washed several times with dist. H2O and anh. EtOH, dried at 808 overnight, and
then calcinated at 723 K for 2 h [13].
General Procedure for the Synthesis of ZnO Nanoparticles. Nano ZnO catalyst was prepared by CP
method. A Zn(NO3)2 soln. (0.267 gmlÀ1) was precipitated with 1m Na2CO3 soln. at r.t. until pH 8 was
reached. After keeping the mixture for 2 h at 70 – 808, the precipitate was filtered, washed several times
with dist. H2O, dried at 808 overnight, and then calcined at 723 K for 2 h.
General Procedure for SuzukiÀMiyaura Reaction. A mixture of aryl halide (1 mmol), phenylboronic
acid (1 mmol), K2CO3 (0.25 mmol), and nano Pd/ZnO (0.001 g) in H2O (1 ml) was added to a round-
bottom flask under atmospheric pressure. The mixture was stirred at 1008. The progress of reaction was
monitored by TLC. After the reaction was finished, the mixture was cooled to r.t. and diluted with
AcOEt (5 ml). The slurry was stirred at r.t. to ensure removal of the product from the surface of the
catalyst. Then, it was centrifuged to separate the catalyst. The centrifugate was washed with H2O (2 Â
5 ml), dried (Na2SO4), further concentrated under reduced pressure, and purified by CC (SiO2) to
give the desired product. All compounds were characterized by comparison of their physical and
spectroscopic data with those reported in the literature.
General Procedure for Hiyama Coupling Reaction. A mixture of aryl halide (1 mmol), trimethoxy-
(phenyl)silane (1 mmol), K2CO3 (1 mmol), and Pd/ZnO (0.009 g) in ethane-1,2-diol (1 ml) was added to
a round-bottom flask under atmospheric pressure. The mixture was stirred at 1008. After appropriate
time, the mixture was centrifuged to separate the catalyst. Then, it was extracted with AcOEt (5 ml). The
combined org. extracts were dried (Na2SO4), concentrated under reduced pressure, and purified by CC
(SiO2) to give the desired product. All compounds were characterized by comparison of their physical
and spectroscopic data with those reported in the literature.
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Received October 15, 2014