Palladium Nanoparticles Supported on Zirconium Metal Organic Framework as an Efficient Heterogeneous Catalyst for the Suzuki-Miyaura Coupling Reaction

Article abstract of DOI:10.1007/s10562-015-1674-5

Nanoparticles of zirconium metal organic framework UiO-66 (about 100 nm) have been used as proper supports for Pd nanoparticles. Highly dispersed Pd nanoparticles (about 3-15 nm) were deposed on activated UiO-66 metal organic framework using simple wet impregnation method at room temperature. UiO-66 and the supported Pd nanoparticles (Pd/UiO-66) were characterized by X-ray diffraction, N₂ sorption, field emission scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and inductively coupled plasma atomic emission spectroscopy. Investigation of the catalytic performance of Pd/UiO-66 showed that the synthetic nanocomposites can effectively catalyze the Suzuki-Miyaura cross-coupling reaction of benzeneboronic acid with different aryl halides under mild reaction conditions using environmentally benign solvents. In addition, the stability and reusability of the catalyst were studied during the catalytic reaction and it is worth noting that the structure of Pd/UiO-66 catalyst remains intact during the catalytic reaction and the catalyst can be recycled four times without significant decrease in its catalytic activity.

Full text of DOI:10.1007/s10562-015-1674-5

Catal Lett
DOI 10.1007/s10562-015-1674-5
Palladium Nanoparticles Supported on Zirconium Metal Organic
Framework as an Efficient Heterogeneous Catalyst
for the Suzuki–Miyaura Coupling Reaction
1
1
1
M. Pourkhosravani
•
S. Dehghanpour
•
F. Farzaneh
Received: 15 August 2015 / Accepted: 3 December 2015
Ó Springer Science+Business Media New York 2015
Abstract Nanoparticles of zirconium metal organic
framework UiO-66 (about 100 nm) have been used as
proper supports for Pd nanoparticles. Highly dispersed Pd
nanoparticles (about 3–15 nm) were deposed on activated
UiO-66 metal organic framework using simple wet
impregnation method at room temperature. UiO-66 and the
supported Pd nanoparticles (Pd/UiO-66) were character-
ized by X-ray diffraction, N2 sorption, field emission
scanning electron microscopy, transmission electron
microscopy, energy dispersive X-ray spectroscopy, X-ray
photoelectron spectroscopy and inductively coupled
plasma atomic emission spectroscopy. Investigation of the
catalytic performance of Pd/UiO-66 showed that the syn-
thetic nanocomposites can effectively catalyze the Suzuki–
Miyaura cross-coupling reaction of benzeneboronic acid
with different aryl halides under mild reaction conditions
using environmentally benign solvents. In addition, the
stability and reusability of the catalyst were studied during
the catalytic reaction and it is worth noting that the struc-
ture of Pd/UiO-66 catalyst remains intact during the cat-
alytic reaction and the catalyst can be recycled four times
without significant decrease in its catalytic activity.
Graphical Abstract
Keywords Pd nanoparticles Á UiO-66 Á Metal organic
frameworks Á Suzuki coupling
1
Introduction
Palladium-catalyzed carbon–carbon bond formation via
cross coupling play an important role in modern organic
chemistry for synthesize of complex organic molecules [1–
&
M. Pourkhosravani
Khosravani.moones@yahoo.com
5
]. In this area, application of palladium nanoparticles (Pd
1
NPs) as green and efficient heterogeneous catalysts has
attracted a considerable attention [6–8]. Since the highest
Department of Chemistry, Alzahra University,
Vanak, Tehran, Iran
123

M. Pourkhosravani et al.
Scheme 1 Schematic representation of Pd/UiO-66 catalyst preparation
Fig. 2 The FTIR spectra of (a) UiO-66 nanoparticles and (b) palla-
dium nanopartticles supported on UiO-66 (Pd/UiO-66)
minimize aggregation of Pd NPs including the introduction
of stabilizing agents during the synthesis of nanoparticles
[
9, 10] and using suitable supports to produce supported Pd
NPs [7, 11]. According to the literature, supported Pd NPs
show promising applications in heterogeneous catalysis
and therefore various organic, inorganic and organic–
inorganic hybrid carriers have been utilized for this pur-
pose [12–24]. Recently, metal–organic frameworks
(MOFs), as a new class of organic inorganic hybrid porous
materials, have attracted considerable attention for stabi-
lization of metal nanoparticles due to their outstanding
textural features such as high specific surface area, tunable
pore sizes and adjustable functional groups [25–28]. For
catalytic applications, Pd NPs have been successfully
deposited at the outer surface of the MOF supports (Pd/
MOFs) [29–34] or loaded inside the cavities of the MOFs
(Pd@MOFs) [35–41] via various methods such as
impregnation [29–40] and chemical vapor deposition [41].
Fig. 1 The XRD patterns of (a) activated UiO-66 nanoparticles,
b) as synthesized palladium nanopartticles supported on UiO-66 (Pd/
(
UiO-66) with characteristic peaks of metallic Pd at 40.1°, 47.22°, 68°,
8
0
3.75° and 86.22°, respectively, corresponding to (1 1 1), (2 0 0), (2 2
), (3 1 1) and (2 2 2) reflections and (c) Pd/UiO-66 after five circles
catalysis. Reaction conditions for each cycle of catalysis; catalyst
20 mg), 4-iodoanisole (0.5 mmol), benzeneboronic acid (0.6 mmol),
Na Co (1 mmol), solvent H O/EtOH (2:1, v/v, 6 ml) temperature,
0 °C, 30 min
(
2
3
2
8
selectivity and reactivity are achievable in the presence of
well-dispersed nanoparticle catalysts, many efforts have
been devoted to develop synthetic routes for preparation of
well-dispersed Pd NPs with narrow particle size distribu-
tions, well-defined shapes and identical properties. Gener-
ally, these synthetic routes employ two strategies to
1
23

Palladium Nanoparticles Supported on Zirconium Metal Organic Framework as an Efficient…
Fig. 3 Nitrogen adsorption–desorption isotherms at 77 K for activated UiO-66 NPs (a) and Pd/UiO-66 nanocomposite (b)
Table 1 Textural properties of
activated UiO-66 and Pd/UiO-
2
-1
)
3
Total pore volume (cm g
-1
)
Material
S
BET (m g
Mean pore diameter (nm)
6
6 materials
Activated UiO-66
Pd/UiO-66
1430
1030
0.88
0.78
0.64
0.46
fragment to produce a cubic closed pack structure [43]. The
exceptional properties of this MOF such as high surface
2
area (1187 m /g), good chemical resistance against sol-
vents like water, acetone, benzene and dimethylformamide,
2
suitable mechanical ([10 tons/cm ) and thermal stability
(up to 773 K) arising from the strong interactions of zir-
conium with oxygen donor BDC ligands, make it a good
candidate for different applications such as separation [44],
gas adsorption [45], removal of toxic metal ions [46],
catalysis [47] modification and functionalization [48, 49].
These attractive properties encouraged us to study the
potential of this MOF as a support for Pd NPs in order to
produce a new heterogeneous catalyst for Suzuki coupling
reaction. Recently, Tangestaninejad and his coworkers
reported immobilizing Pd NPs on amino functionalized
UiO-66 (UiO-66-NH ) [50]. They prepared UiO-66-NH
2
2
from the reaction of ZrCl and 2-amino terephthalic acid
4
Fig. 4 The BJH pore size distribution curve of Pd/UiO-66
nanocomposite
under solvothermal conditions. For preparation of Pd/UiO-
66-NH , UiO-66-NH was added to a methanolic solution
2 2
of Na PdCl and the resultant mixture was stirred at 60 °C
2
4
However, this application of MOFs is still a challenging
issue due to the limited stability of most of MOFs under
reaction conditions [42]. Therefore, in order to generate
recyclable supported nanocatalysts, it is desirable to utilize
MOFs with good chemical and thermal stabilities. UiO-66
is a good example of highly stable MOFs. UiO-66 is a
zirconium based, metal–organic framework consisting of
for 24. Then, the mixture was reacted with sodium acetate
?
to reduce Pd ions to Pd [50]. They have reported that
2
o
the amine groups of UiO-66-NH can stabilize palladium
2
nanoparticles. They also investigated the catalytic activity
of Pd/UiO-66-NH in Suzuki cross-coupling reaction of
2
different aryl halides with benzeneboronic acid and they
reported that the best results were obtained in a mixed
solvent system of DMF/H O in the presence of K CO base
Zr O (OH) (CO ) clusters [(–CO ) originating from the
2 12
6
4
4
2
2
2
3
benzenedicarboxylate linker] connected through benzene
(95 % conversion for 4-iodoanisole substrate in 10 min
123

M. Pourkhosravani et al.
Fig. 5 TEM micrograph of Pd/UiO-66 nanocomposite
?
2
o
reduction method, Pd
cations are converted to Pd
nanoparticles deposed on the surface of activated UiO-66
carriers. The as prepared Pd/UiO-66 nanocomposite show
good catalytic activity and reusability in the Suzuki cou-
pling reaction of different aryl halides with benzeneboronic
acid under mild reaction conditions in an ethanol–water
green solvent mixture.
2
Experimental
2.1 Chemicals and Instruments
All chemicals and solvents were purchased from Merck or
Aldrich Chemical Companies and used without further
purification. X-ray diffraction (XRD) data were recorded
on a Phillips PW 1800 X-ray diffractometer using Cu Ka
radiation. The X-ray photoelectron spectroscopy (XPS)
measurements were performed using a Gamma data-sci-
enta ESCA200 hemispherical analyzer equipped with an Al
Fig. 6 The histogram of the palladium nanopartticles size
distribution
with 3 % Pd leaching to the reaction media). In this study,
UiO-66 has been shown to act as a proper support for
deposition of Pd NPs. Using a simple and fast ethanol
Fig. 7 SEM image (a) and EDS spectrum (b) of Pd/UiO-66 nanocomposite
1
23

Palladium Nanoparticles Supported on Zirconium Metal Organic Framework as an Efficient…
(
Ka = 1486.6 eV) X-ray source. Scanning electron
reaction completion, the catalyst was separated by centrifug-
ing and the obtained products were extracted with diethyl
ether. The extracted phase was subjected to GC and GC mass
for quantitative detection of products using toluene as the
internal standard.
microscope (SEM) micrographs were obtained using a
S4160 field emission SEM (Hitachi, Japan). Energy dis-
persive X-ray spectroscopy (EDS) analysis was also per-
formed during the SEM measurements. Transmission
electron microscopy (TEM) images were taken by a Zeiss-
Em10c TEM with an accelerating voltage of 80 kV.
Inductively coupled plasma atomic emission spectroscopy
3 Results and Discussion
(
ICP-AES) measurements were carried out using an IRIS
Intrepid IIXSP (Thermo Fisher Scientific, USA). Nitrogen
sorption isotherms were recorded on a Belsorp Mini-II
instrument at 77 K. Gas chromatography (GC) were per-
formed on a gas chromatograph (HP, Agilent 6890 N)
equipped with an FID detector, HP-5, 5 % phenylmethyl-
siloxane capillary column. Gas chromatography-mass
spectroscopy (GC-MS) of products were recorded using an
Agilent 5973 Network, mass selective detector, HP-5 MS
3.1 Catalyst Synthesis and Characterization
Scheme 1 represents the overall synthetic procedure for the
Pd/UiO-66 catalyst. UiO-66 support was prepared from the
reaction of zirconium chloride and benzenedicarboxylic
acid under solvothermal condition [45]. After solvent-ex-
change activation, Pd nanoparticles were deposed on the
activated UiO-66 by reduction of palladium (II) acetate in
methanol under anhydrous conditions at room temperature
via a simple wet impregnation method.
6
989 Network GC system.
2
.2 Catalyst Preparation
The crystallinity and phase purity of the synthetic UiO-66
and Pd/UiO-66 samples were identified by XRD technique.
The XRD pattern of activated UiO-66 NPs (Fig. 1a) is
completely similar to that previously reported by Cavka
et al. [43] indicating that no structural collapse has happened
during the activation process [45]. The XRD pattern of Pd/
UiO-66 (Fig. 1b) shows that the crystalline structure of UiO-
66 is maintained after deposition of Pd NPs. However, the
peak intensities of the XRD pattern of UiO-66 are reduced
due to the slight change in the structural regularity of the
framework. Furthermore, the appearance of the character-
istic peaks of metallic Pd at 40.1°, 47.22°, 68°, 83.75° and
86.22°, respectively, corresponding to (1 1 1), (2 0 0), (2 2
0), (3 1 1) and (2 2 2) reflections, in the XRD pattern of Pd/
UiO-66 shows the successful loading of Pd NPs (low peak
intensities is attributed to low Pd content) [51].
UiO-66 was prepared and activated according to a literature
method [45]. Typically, a mixture of ZrCl (2.27 mmol,
4
0
0
.529 g), 1,4-benzenedicarboxylic acid (BDC) (2.27 mmol,
.377 g) and DMF (405.38 mmol, 31.39 mL) was kept in an
autoclave at 393 K for 24 h. After cooling to room temper-
ature, the solid was separated and washed with DMF
(
30 mL). Activation process was performed by immersing
the as-synthesized UiO-66 nanoprticles (0.3 g) in chloro-
form (80 mL) for 5 days followed by separation and vacuum
drying at 463 K for 48 h.
Pd/UiO-66 nanocomposite was prepared using the
alcohol reduction method [51]. Anhydrous Pd (OAc)2
(
20 mg) was dissolved in anhydrous MeOH (50 mL) under
inert atmosphere. As soon as a clear yellow solution was
obtained, the flask was removed to ambient atmosphere and
immediately 500 mg of activated UiO-66 was added to the
solution and the mixture was stirred for 10 min. The flask
was then attached to a rotary evaporator at ambient tem-
perature. After about 1 h, the obtained gray damp powder
was collected, washed with MeOH (2 9 30 mL) and dried
under vacuum. The palladium content of Pd/UiO-66 was
The FTIR spectra of UiO-66 and Pd/UiO-66 samples are
shown in Fig. 2. In the FTIR spectrum of UiO-66 (Fig. 2a),
-1
the peaks centered at 1399, 1507, 1575,550and 746 cm are
assigned to msym(O–C–O), msym(C–C), masym(O–C–O),
masym(Zr–(OC))andinphaseC–Hbendingoftheterephthalate
linker, respectively [45, 52]. All of the frequency bands of the
UiO-66 framework are consistent with the literature values
and remained unchanged after deposition of Pd Nps (Fig. 2b).
N2 adsorption–desorption isotherms and textural
parameters of activated UiO-66 NPs and Pd/UiO-66 are
presented in Fig. 3 and Table 1, respectively. Obvious
decreases in specific surface area, mean pore diameter and
total pore volume of activated UiO-66 support are observed
after deposition of Pd NPs on the UiO-66 support. This is
mainly due to the fact that the cavities of UiO-66 support
could be occupied and/or blocked by the Pd NPs [50]. The
pore size distribution (PSD) curve for Pd/UiO-66 catalyst
1
.57 wt% using ICP-AES.
2
.3 Catalytic Procedure for the Suzuki Coupling
Reaction
Typically, halobenzene (0.5 mmol), benzeneboronic acid
(
0.6 mmol), base (Na CO or K CO ) (1 mmol), catalyst
2 3 2 3
(
20 mg, 0.59 mol% Pd) and 6 mL of solvent [H O, EtOH or
2
H O/EtOH (2:1, v/v)] were introduced into a round bottomed
2
flaskunder stirring. The reaction wasallowed toproceed atthe
desired reaction temperature for appropriate time. After
calculated from the adsorption branch of the N isotherm
2
123

M. Pourkhosravani et al.
dots) (Fig. 5) and histogram of the Pd NPs size distribution
(Fig. 6), the size of Pd NPs ranging from 3 to 15 nm (mean
diameter of 8.56 nm) is too large to allow it to get into the
pores of UiO-66 and thus Pd NPs are attached to the outer
surface of support. Furthermore, successful deposition of
Pd NPs on the surface of UiO-66 NPs is confirmed by SEM
images (Fig. 7a) and EDS spectra (Fig. 7b). XPS technique
has been used to analyze the surface chemistry of the
synthetic Pd/UiO-66 nanocomposites. The XPS elemental
survey of the sample (Fig. 8a) confirms the EDS spectrum
(
Fig. 7b) and shows the presence of Zr, Pd, C and O in the
IV
sample. Figure 8c reveals deconvolution of Zr 3d curves
into two peaks for Zr 3d5/2 and Zr 3d3/2 located at 182.07
and 184.57 eV, respectively. A slight shift to the lower
energy compared to the untreated UiO-66 is observed [51].
Figure 8b shows the peaks related to 3d and 3d3/2 of the
5
/2
0
Pd at 341.15 and 336.15 eV, respectively, which have
occurred at higher energies compared to the literature
0
values of Pd [37]. Moreover, peaks centered at 346.5 and
333.10 eV are assigned to the Zr 3p1/2 and Zr 3p3/2,
respectively [37].
Fig. 8 The XPS elemental survey of Pd/UiO-66 nanocomposite (a),
the XPS spectrum of Pd/UiO-66 in the Zr 3p and Pd 3d regions
4 Catalytic Suzuki Reactions
(
b) and the XPS spectrum of Pd/UiO-66 in the Zr 3d reigion(c)
The synthetic Pd/UiO-66 was employed as a catalyst in the
Suzuki coupling reaction. It is noticeable that the nature of
base and solvent greatly affect the efficiency of the Suzuki
coupling reaction [36]. Results related to the study of the
using Barrett–Joyner–Halenda (BJH) method is depicted in
Fig. 4. The PSD curve shows two peaks centered at 1.2 nm
(
microporous region) and 33 nm (mesoporous region). As
effect of different protic solvent systems including H O,
2
it is evidenced by the TEM image of Pd/UiO-66 (black
EtOH and H O/EtOH (2:1, v/v) and inorganic bases such
2
Table 2 Effect of some protic solvents and bases on Suzuki coupling reaction catalyzed by Pd/UiO-66 catalyst
Catalyst
I +
B(OH)2
Solvent, Base
a
Entry
Solvent
Base
Conversion (%)
Selectivity toward
biaryl product (%)
TON
1
2
3
4
5
6
H
2
O
O
Na
2
CO
3
3
3
83
100
70
100
100
100
100
100
100
143
172
121
171
172
172
H
2
K
2
CO
3
EtOH
Na
2
CO
EtOH
K
2
CO
3
99
EtOH/H
EtOH/H
2
O
O
Na
2
CO
100
100
2
2 3
K CO
Reaction conditions: catalyst (20 mg), iodobenzene (0.5 mmol), benzeneboronic acid (0.6 mmol), base (1 mmol), solvent (6 ml), 80 °C, air
atmosphere, 30 min
a
Calculated as products (mmol)/Pd(mmol)
1
23

Palladium Nanoparticles Supported on Zirconium Metal Organic Framework as an Efficient…
Table 3 Suzuki coupling reaction of different aryl halides with benzeneboronic acid catalyzed by Pd/UiO-66 catalyst
Catalyst
X +
B(OH)2
Solvent, Base
R
R
X= I, Br, Cl; R= CH
3
, OCH
3
, HCO, CN, C
2
H
5
Conversion
%)
Selectivity toward
a
Entry
Aryl halide
Product(s)
Time (h)
TON
(
Related biphenyl Product (%)
1b
0.5
63
100
109
I
2c
3
0.5
0.5
80
100
100
138
172
I
I
100
CH
3
3
H
3
C
2
98
100
167
I
4
5
6
I
O
0.5
2
100
100
98
100
100
100
172
172
167
O
CH
3
CH3
Br
2
H
3
C
Br
CH3
7
2
98
98d
167
O
O
Br
8
9
N
Br
O
N
2
2
100
100
100
100
172
172
O
Br
1
1
0
1
Br
Br
2
2
98
97
100
100
167
167
3
H C
CH
3
O
O
CH
3
CH
3
O
3
H C
1
1
2
3
O
2
96
70
100
80e
165
121
CH
3
Br
20
Cl
2 3 2
Reaction conditions: catalyst (20 mg, 0.59 mol% Pd), aryl halide (0.5 mmol), benzeneboronic acid (0.6 mmol), Na Co (1 mmol), H O/EtOH
(
a
2:1, v/v) (6 ml), reaction temperature; 80 °C
Calculated as products (mmol)/Pd (mmol)
b
c
d
e
At room temperature
At 45 °C
By product: triphenylboroxin
By product: triphenylboroxin
123

M. Pourkhosravani et al.
Table 4 Suzuki coupling reaction of aryl halides with benzeneboronic acid catalyzed by different MOF supported Pd nanoparticles
a
Catalyst
Mol% Mean Pd
NPs size
nm)
Temprature Solvent/base
o
( C)
TOF
Bromobenzen Iodobenzene Chlorobenzene
Refs.
Pd
(
Pd@MIL-101
0.15
3.00
0.50
2.4
25
25
40
EtOH-H
O/Cs
EtOH-H
Na CO
DMF/K
O/K
MeOH/K
EtOH-H O/K
O/K
O/K
O/Na
2
O/K
2
CO
3
323
633
–
Trace
–
[35]
[36]
[29]
b
Pd@MIL-101Cr-NH
2
\2.5
3.12
H
2
2
CO
3
5.5
c
Pd/MIL-53(Al)-NH
2
2
O/
388
396
3
2
3
d
e
Pd@MOF-5
Pd/MCoS-1
4.20
0.37
0.90
0.50
0.25
0.25
0.59
2–5
90
2
CO
3
Trace
52
–
[41]
[30]
[31]
[34]
[50]
[50]
f
5–10
8–13
70
100
40
H
2
2
CO
3
53
–
16
4.3
44
g
Pd@NH
2
-MIL-125
2
CO
3
–
Pd/ScBTC
3.32 ± 0.54
5.28 ± 0.5
5.28 ± 0.5
8.56
2
2
CO
CO
CO
3
396
720
396
2203
h
Pd/UiO-66-NH
Pd/UiO-66-NH
Pd/UiO-66
2
2
60
DMF-H
EtOH-H
EtOH-H
2
2
3
470
i
60
2
2
3
284
j
80
2
2
CO
3
305
339
6
Current
study
Pd(H bpydc)Cl
2
immobilized on UiO-67
2
0.46
2.50
0.024
100
95
DMF-EtOH/KOH
9.8
[53]
[54]
[55]
k
UiO-67-Pdbpydc0.5
bpdc0.5
/
Toluene/K
2
CO
3
2.22
IRMOF-3-PI-Pd
a
Calculated as TON/hour
80
EtOH-H O/K
2
2
CO
3
2041.6
1361
132
b
For 4-bromoanisol substrate
c, h
The reaction was performed at 80 °C
d, f, g
Pd NPs size (nm)
e
Under Ar atmosphere
i
For 4-iodoanisol substrate
j
Under N
2
atmosphere
k
For 4-bromotoluene substrate
as Na CO and K CO on the Suzuki coupling reaction of
2
electron-donating or—withdrawing nature of the sub-
stituents on the reactants [35]. Since the energy of the C–X
bond increases as follows; C–Cl [ C–Br [ C–I, it is
expected that longer reaction time is required for the
activation of aryl chlorides compared with arylbromides or
iodides (Table 3, entries 2, 5 and 9). However, the presence
of electron-withdrawing substituent on the aryl bromide
substrate enhances the efficiency of Suzuki coupling
reaction [35]. Good to excellent yields (96–100 %) with
high selectivity (98–100 %) toward substituted biphenyl
products have been obtained for both electron-deficient and
electron-rich aryl bromides at 80 °C.
3
2
3
iodobenzene with benzeneboronic acid at 80 °C (model
reaction) are shown in Table 2. Carbonates were preferred
because the slow release of hydroxyl anions into the
reaction media is needed to prevent formation of unreactive
-
boronate (ArB(OH) ) species during the reaction [35].
3
Results show that the model catalytic reaction is com-
pletely selective toward production of biphenyl product
and the Pd/UiO-66 can effectively catalyze the model
reaction (Table 2, entries 2, 5 and 6). Furthermore, the
activity of the catalyst in the Suzuki coupling reaction of
different aryl halides with benzeneboronic acid in the H O/
2
EtOH (2:1, v/v) mixed solvent system in the presence of
Na CO base was evaluated and the results are presented in
Results related to the optimized conditions for the
Suzuki coupling reactions of different aryl halides with
benzeneboronic acid catalyzed by MOF supported Pd NPs
(Pd@MOFs or Pd/MOFs) and Pd (II) complexes incorpo-
rated into some MOFs are given in Table 4. It is worth-
while to compare the results related to the catalytic activity
of the synthesized Pd/UiO-66 nanocomposite with some
results reported in the Suzuki coupling reaction catalyzed
by different MOF supported Pd NPs. Of these catalysts, the
catalytic system of Pd@MIL-101 with several advantages,
including low catalyst loading, relatively short reaction
time, non-toxic solvents and room temperature reaction
2
3
Table 3. At first, the effect of temperature on the reaction
of iodobenzene with benzeneboronic acid was investigated
and results showed a remarkable increase in the yiel-
d of biphenyl product (63–100 %) by increasing the reac-
tion temperature from room temperature to 80 °C (entries
1
, 2 and 3, Table 3). In addition, control experiment veri-
fied no substrate conversion in the presence of bare UiO-66
nanoparticles. This underlines the catalytic role of the Pd
NPs. The yield of the Suzuki coupling reaction depends on
the type of the aryl halide halogen and the positions and
1
23

Palladium Nanoparticles Supported on Zirconium Metal Organic Framework as an Efficient…
Table 5 Recyclability test of the Pd/UiO-66 catalyst towards the Suzuki coupling reaction of 4-iodoanisole and benzeneboronic acid
a
Number of catalytic cycles
1
2
3
4
5
Conversion (%)
100
100
98
98
98
Selectivity toward related biphenyl product (%)
b
Pd content of the catalyst(%)
100
100
100
1.567
100
1.567
100
1.567
1.570
1.567
Reaction conditions: catalyst (20 mg), 4-iodoanisole (0.5 mmol), benzeneboronic acid (0.6 mmol), Na
(
2
Co
3
(1 mmol), H O/EtOH (2:1, v/v)
2
6 ml), Reaction temperature, 80 °C
a
After each run, the catalyst was separated by centrifuge, washed with ethanol, and dried for the next cycle
b
Determined by ICP
catalyst was mostly retained after five catalytic cycles.
Also a comparison between XPS spectra of fresh Pd/UiO-
6
6 and Pd/UiO-66 after five catalytic runs confirms the
stability of the catalyst during the catalytic reaction
Fig. 9). In order to investigate Pd leaching into the reac-
(
tion medium after 30 min, the catalyst was separated from
the hot reaction mixture of bromobenzene and ben-
zeneboronic acid and the filtrate was analyzed by ICP-
AES. Negligible Pd leaching (less than 0.1 ppm) was
detected in the first run (Table 5). In addition, the same
filtrate was allowed to remain under the same reaction
conditions for another 2 h. Observation of no significant
increment in substrate conversion clearly indicates that the
reaction is catalyzed in a heterogeneous fashion and com-
pletely stops after catalyst removal. These results showed
the good satiability of the catalyst during the catalytic
reaction.
Fig. 9 The XPS spectra of fresh Pd/UiO-66 and Pd/UiO-66 after five
catalytic runs in the Zr 3p and Pd 3d regions
conditions is superior to the others. This superiority arises
from the good dispersion of Pd NPs in the pores of MIL-
5 Conclusions
1
01 and the confinement effect [35]. In addition, the best
result (80 % conversion after 41 min) for the Suzuki cou-
pling reaction of chlorobenzene with benzeneboronic acid
has been reported for Pd/UiO-66-NH2 catalytic system
In summary, using simple wet impregnation method, we
have succeeded to prepare Pd NPs supported on UiO-66
Metal Organic Framework as an efficient heterogeneous
catalyst for the Suzuki coupling reaction of different aryl
halides especially bromo- and iodo-arenes with ben-
zeneboronic acid in environmentally benign system of
H O/EtOH mixture and in the presence of Na CO base.
[
50]. The data in Table 4 indicates that the as prepared Pd/
UiO-66 nanocomposite can catalyze the coupling reaction
of different aryl halides with benzeneboronic acid more
efficiently than Pd@MOF-5 and Pd@NH -MIL-125 cata-
2
2
2
3
lysts. Due to the different reaction conditions, we cannot
thoroughly compare the catalytic performances.
Moreover, the Pd/UiO-66 catalyst exhibits high stability
during the catalytic reaction and can be reused several
times without significant reduction of catalytic activity.
Beside the catalytic performance, the stability of the
catalyst in the reaction media and its recyclability are two
important issues, which should be investigated for an
efficient heterogeneous catalytic system. Results of the
recyclability test of the Pd/UiO-66 catalyst in the Suzuki
coupling reaction of 4-iodoanisole with benzeneboronic
acid are shown in Table 5. It is observed that the catalyst
remained highly active after each cycle of catalysis and can
be reused four times without a significant decrease in its
catalytic activity. Furthermore, as evidenced by XRD pat-
tern (Fig. 1c), the crystalline structure of the Pd/UiO-66
Acknowledgments This study was financially supported by the
research council of the Alzahra University.
References
´
1
. Moln a´ r A (2013) Palladium-catalyzed coupling reactions, prac-
tical aspects and future developments. Wiley VCH, New York
´
. Moln a´ r A (2011) Chem Rev 111:2251–2320
. Wan Y, Wang H, Zhao Q, Klingstedt M, Terasaki O, Zhao D
(2009) J Am Chem Soc 131:4541–4550
2
3
123

M. Pourkhosravani et al.
4
. Dhara K, Sarkar K, Srimani D, Saha SK, Chattopadhyay P,
Bhaumik A (2010) Dalton Trans 39:6395–6402
. Yin L, Liebscher J (2007) Chem Rev 107:133–173
. Astruc D (2007) Inorg Chem 46:1884–1894
. Astruc D, Lu F, Aranzaes JR (2005) Angew Chem Int Ed
32. Gao S, Zhao N, Shu M, Che S (2010) Appl Catal A 338:196–201
33. Yuan B, Pan Y, Li Y, Yin B, Jiang H (2010) Angew Chem Int Ed
49:4054–4058
34. Zhang L, Su Z, Jiang F, Zhou Y, Xu W, Hong M (2013) Tetra-
hedron 69:9237–9244
5
6
7
4
4:7852–7882
. Balanta A, Godard C, Claver C (2011) Chem Soc Rev
0:4973–4985
. Strimbu L, Liu J, Kaifer AE (2003) Langmuir 19:483–485
35. Shang N, Gao S, Zhou X, Feng C, Wang Z, Wang C (2014) RSC
Adv 4:54487–54493
36. Pascanu V, Yao Q, Bermejo Gomez A, Gustafsson M, Yun Y,
Wan W, Samain L, Zou X, Martin-Matute B (2013) Chem Eur J
19:17483–17493
37. Shen L, Wu W, Liang R, Lin R, Wu L (2013) Nanoscale
5:9374–9382
38. Juan-Alcaniz J, Ferrando-Sori J, Luz I, Serra-Crespo P, Skupien
E, Santos VP, Pardo E, Llabres i Xamena FX, Kapteijn F, Gascon
J (2013) J Catal 307:295–304
8
9
4
1
1
1
1
0. Ohde H, Wai CM, Kim H, Ohde M (2002) J Am Chem Soc
24:4540–4541
1. Taladriz-Blanco P, Herves P, Perez-Juste J (2013) Top Catal
6:1154–1170
2. Ricciardi R, Huskens J, Holtkamp M, Karst U, Verboom W
2015) ChemCatChem 7:936–942
3. Huang W, Liu JHC, Alayoglu P, Li Y, Witham CA, Tsung CK,
Toste FD, Somorjai GA (2010) Am Chem Soc
32:16771–16773
1
5
(
39. Pascanu V, Hansen PR, Bermejo Gomez A, Ayats C, Platero-
Prats AE, Johansson MJ, Pericas MA, Martin-Matute B (2015)
ChemSusChem 8:123–130
J
1
1
4. Hattori T, Tsubone A, Sawama Y, Monguchi Y, Sajiki H (2015)
Catal 5:18–25
40. Huang Y, Liu S, Lin Z, Li W, Li X, Cao R (2012) J Catal
292:111–117
1
1
5. Meric P, Yu KMK, Tsang SC (2004) Langmuir 20:8537–8545
6. Choudary BM, Mahdi S, Chowdari NS, Kantam ML, Sreedhar B
41. Zhang M, Guan J, Zhang B, Su D, Williams CT, Liang C (2012)
Catal Lett 142:313–318
(
2002) J Am Chem Soc 124:14127–14136
7. Lemo J, Heuze K, Astruc (2006) Inorg Chim Acta
59:4909–4911
42. Corma A, Garcia H, Llabres i Xamena FX (2010) Chem Rev
110:4606–4655
1
D
3
43. Cavka JH, Jakobsen S, Olsbye U, Guillou N, Lamberti C, Bordiga
S, Lillerud KP (2008) J Am Chem Soc 130:13850–13851
44. Barcia PS, Guimaraes D, Mendes PAP, Silva JAC, Guillerm V,
Chevreau H, Serre C, Rodrigues AE (2011) Microporous Meso-
porous Mater 139:67–73
1
1
8. Wang J, Song G, Peng Y (2011) Tetrahedron Lett 52:1477–1480
9. Magdesieva TV, Nikitin OM, Levitsky OA, Zinovyeva VA,
Bezverkhy I, Zolotukhina EV, Vorotyntsev MA (2012) J Mol
Catal A 353–354:50–57
2
2
2
2
2
2
2
0. Durap F, Rakap M, Aydemir M, Ozkar S (2010) Appl Catal A
45. Abid HR, Tian H, Ang HM, Tade MO, Buckley CE, Wang S
(2012) Chem Eng J 187:415–420
46. Shahat A, Hassan HMA, Azzazy HME (2013) Anal Chim Acta
793:90–98
47. Silva CG, Luz I, Llabres i Xamena FX, Corma A, Garcia H
(2010) Chem Eur J 16:11133–11138
48. Chavan S, Vitillo JG, Uddin MJ, Bonino F, Lamberti C, Groppo
E, Lillerud KP, Bordiga S (2010) Chem Mat 22:4602–4611
49. Kandiah M, Usseglio S, Svelle S, Olsbye U, Lillerud KP, Tilset
M (2010) J Mater Chem 20:9848–9851
50. Kardanpour R, Tangestaninejad S, Mirkhani V, Moghadam M,
Mohammadpoor-Baltork I, Khosropour AR, Zadehahmadi F
(2014) J Organomet Chem 761:127–133
51. Burton PD, Boyle TJ, Datye AK (2011) J Catal 280:145–149
52. Valenzano L, Civalleri B, Chavan S, Bordiga S, Nilsen MH,
Jakobsen S, Lillerud KP, Lamberti C (2011) Chem Mater
23:1700–1718
53. Chen L, Rangan S, Li J, Jiang H, Li Y (2014) Green Chem
16:3978–3985
54. Fei H, Cohen SM (2014) Chem Commun 50:4810–4812
55. Saha D, Sen R, Maity T, Koner S (2013) Langmuir 29:3140–3151
3
82:339–344
1. Chattopadhyay K, Dey R, Ranu BC (2009) Tetrahedron Lett
0:3164–3167
2. Wang J, Xu B, Sun H, Song G (2013) Tetrahedron Lett
4:238–241
5
5
3. Zhonga L, Chokkalingama A, Chaa WS, Lakhi KS, Su X,
Lawrence G, Vinu A (2015) Catal Today 243:195–198
4. Niembro S, Shafir A, Vallribera A, Alibes A (2008) Org Lett
1
0:3215–3218
5. Dhakshinamoorthy A, Asiri AM, Garcia H (2015) Chem Soc Rev
4:1922–1947
4
6. Kuppler RJ, Timmons DJ, Fang QR, Li JR, Makal TA, Young
MD, Yuan D, Zhao D, Zhuang W, Zhou HC (2009) Coord Chem
Rev 253:3042–3066
2
2
2
3
3
7. Dhakshinamoorthy A, Garcia
1:5262–5284
H (2012) Chem Soc Rev
4
8. Meilikhov M, Yusenko K, Esken D, Turner S, Tendeloo GV,
Fischer RA (2010) Eur J Inorg Chem 2010:3701–3714
9. Huang Y, Zheng Z, Liu T, Lu J, Lin Z, Li H, Cao R (2011) Catal
Commun 14:27–31
0. Roy AS, Mondal J, Banerjee B, Mondala P, Bhaumik A, Islama
SKM (2014) Appl Catal A 469:320–327
1. Puthiaraj P, Ahn WS (2015) Catal Commun 65:91–95
1
23