Pd(0)-Arg-boehmite: As Reusable and Efficient Nanocatalyst in Suzuki and Heck Reactions

Article abstract of DOI:10.1007/s10562-016-1927-y

Abstract: The direct supporting of Pd-arginine complex on boehmite nanoparticles (Pd(0)-Arg-boehmite) was reported as a moisture- and air-stable, heterogeneous, excellent and novel organometallic catalyst, which applied for the Suzuki and Heck cross coupling reactions through coupling of phenylboronic acid, 3,4-difluoro phenylboronic acid, sodium tetraphenyl borate, butyl acrylate, methyl acrylate, acrylonitrile and styrene with a wide range of aryl halide including Cl, Br and I. Pd(0)-Arg-boehmite was prepared for the first time via simple, environmental and inexpensive procedure in water and ethanol without inert atmosphere or high temperature using commercially available materials, and characterized by XRD, TGA, TEM, SEM, EDS and ICP-OES techniques. The leaching of palladium and heterogeneity test of this catalyst was studied by hot filtration and ICP-OES techniques; resulting we found that this catalyst was demonstrated remarkable and excellent recyclability. Graphical Abstract: Boehmite nanoparticles were prepared by inexpensive procedure in water at room temperature and directly immobilized with a new type of Pd-arginine complex. After characterization of this catalyst, its application has been studied for the C–C coupling reactions. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1927-y

Catal Lett
DOI 10.1007/s10562-016-1927-y
Pd(0)-Arg-boehmite: As Reusable and Efficient Nanocatalyst
in Suzuki and Heck Reactions
Bahman Tahmasbi1 · Arash Ghorbani-Choghamarani1
Received: 17 September 2016 / Accepted: 17 November 2016
© Springer Science+Business Media New York 2017
Abstract The direct supporting of Pd-arginine com-
plex on boehmite nanoparticles (Pd(0)-Arg-boehmite)
was reported as a moisture- and air-stable, heterogeneous,
excellent and novel organometallic catalyst, which applied
for the Suzuki and Heck cross coupling reactions through
coupling of phenylboronic acid, 3,4-difluoro phenylboronic
acid, sodium tetraphenyl borate, butyl acrylate, methyl
acrylate, acrylonitrile and styrene with a wide range of
aryl halide including Cl, Br and I. Pd(0)-Arg-boehmite was
prepared for the first time via simple, environmental and
inexpensive procedure in water and ethanol without inert
atmosphere or high temperature using commercially avail-
able materials, and characterized by XRD, TGA, TEM,
SEM, EDS and ICP-OES techniques. The leaching of pal-
ladium and heterogeneity test of this catalyst was studied
by hot filtration and ICP-OES techniques; resulting we
found that this catalyst was demonstrated remarkable and
excellent recyclability.
Graphical Abstract Boehmite nanoparticles were pre-
pared by inexpensive procedure in water at room tem-
perature and directly immobilized with a new type of
Pd-arginine complex. After characterization of this cata-
lyst, its application has been studied for the C–C coupling
reactions.
* Arash Ghorbani-Choghamarani
1
Department of Chemistry, Faculty of Science, Ilam
University, P.O. Box 69315516, Ilam, Iran
Vol.:(0123456789)
1 3

B. Tahmasbi, A. Ghorbani-Choghamarani
boehmite NPs
OH
OH
OH
OH
OH
HO
HO
OH
OH
OH
OH
OH
room temperature
OH
OH
HO
HO
HO
OH
HO
OH
OH
HO
HO
Al(NO3)3.9H2O
HO
H2O
OH
1. Arginine
2. Pd(OAc)2
3. NaBH4
B(OH)2
or NaBPh4
X
+
R1
R2
R2
R1
Pd-Arg-Boehmite
R3
R1
X
R1
R3
+
synthetic organic chemistry for the preparation of natural
products, advanced materials, polymers, pharmaceuticals,
agrochemicals, biologically active compounds, herbi-
cides, UV screens and liquid crystal materials [5–8]. For
this aim, many methods including variety homogeneous
or heterogeneous catalysts have been developed over the
years to find efficient C–C bond formation such as Suzuki
and Heck reactions. However, in order to perform fac-
ile catalyst recovery and excellent reusability of catalysts;
Keywords Boehmite nanoparticles · Arginine · Palla-
dium · Suzuki reaction · Heck reaction · C–C coupling
1 Introduction
Carbon–carbon coupling reactions are commonly have
been catalyzed by homogeneous or heterogeneous Pd-com-
plexes [1–4] and were used as a powerful tools in modern
1 3

Pd(0)-Arg-boehmite: As Reusable and Efficient Nanocatalyst in Suzuki and Heck Reactions
immobilization of homogeneous catalysts on insoluble sup-
ports have been widely employed as useful and efficient
procedure in organic synthesis [9, 10]. In order to combine
the advantages of both homogeneous (high catalytic activ-
ity) and heterogeneous (easily recyclable, moisture and air
stable) catalysts, nanoparticles (NPs) have been recently
emerged as great and useful heterogeneous supports for the
immobilization of homogeneous catalysts [11, 12]. How-
ever, many supports such as MCM-41 [13], SBA-15 [14] or
some nanoparticles such as TiO2 NPs [15] and iron oxide
[16, 17] have been employed for the catalyst supports,
which requires high temperature for calcination or inert
atmosphere and a lot of time and tedious condition to pre-
pare. Also, most of previously heterogeneous supports such
as carbon nanotubes [18], heteropolyacids [19], molecular
sieve [20], ionic liquids [21, 22], graphene oxide [23] or
some polymers [24] are cost effective. While preparation
of boehmite nanoparticles was not air or moisture sensitive,
more important boehmite nanoparticles was prepared in
water at room temperature without inert atmosphere using
commercial materials such as Al(NO3)3·9H2O and NaOH
[25]. Boehmite nanoparticles are an orthorhombic structure
of aluminum oxide hydroxide (γ-AlOOH) [26]. Although
nanoboehmite has large specific surface area (>120 m2/g)
[27] and high thermal, chemical and mechanical stability
[28, 29], but nanoboehmite is rarely used as heterogeneous
support for the immobilization of homogeneous catalysts
[27, 28, 30]. Therefore owing to the context of reuse of
palladium, herein Pd-arginine complex on boehmite nano-
particles as a novel nano heterogeneous catalyst has been
reported for C–C coupling reactions.
DRX-400 spectrometer at 400 MHz. Melting points were
measured with an Electrothermal 9100 apparatus.
2.2 Preparation of Catalyst (Pd(0)-Arg-boehmite)
The solutions of NaOH (6.490 g) in 50 mL of distilled
water was added to solutions of Al(NO3)3·9H2O (20 g) in
30 mL distilled water as drop to drop under vigorous stir-
ring. The resulting milky mixture was subjected to mix in
the ultrasonic bath for 3 h at 25°C. The resulted nano alu-
minum oxihydroxide was filtered and washed by distilled
water and were kept in the oven at 220°C for 4 h. The
obtained boehmite nanoparticles (1.5 g) were dispersed
in 50 mL deionized water, and then 2.5 mmol of l-Argi-
nine was added to the mixture. The reaction mixture was
stirred at 90°C for 24 h. Then, the prepared nanoparticles
(Arg@boehmite) was filtered, washed with ethanol and
dried at room temperature. The obtained Arg@boehmite
(0.5 g) was dispersed in 25 mL ethanol, and then palladium
acetate (0.25 g) was added to the reaction mixture. The
reaction mixture was stirred at 80°C for 20 h. Then, the
NaBH4 (0.3 mmol) was added to the reaction mixture and
was allowed to run for another 2 h. The final product (Pd-
Arg@boehmite) was filtered, washed by ethanol and dried
at room temperature.
2.3 General Procedure for the Suzuki Reaction
A mixture of aryl halide (1 mmol), boronic compound
(0.5–1 mmol), Na2CO3 (3 mmol), and Pd(0)-Arg-boe-
hmite (0.008 g, 1.08 mol%) were added to a reaction ves-
sel. The resulting mixture was stirred in PEG at 80°C and
2 Experimental
2.1 Materials
OH
OH
Chemicals and solvents used in this work were obtained
from Sigma-Aldrich, Fluka or Merck chemical companies
and used without further purification. Boehmite nanoparti-
cles and Pd-SMTU-boehmite were identified using a Hol-
land Philips X’pert X-ray powder diffraction (XRD) dif-
fractometer, at a scanning speed of 2° per minute from 2°
to 80°. Thermogravimetric analyses (TGA) of the samples
were recorded using a Shimadzu PL-STA 1500 device in
the temperature range 30–800°C. The particle size and
morphology were examined by measuring SEM using
FESEM-TESCAN MIRA3, on an accelerating voltage of
30.0 kV and also using Zeiss-EM10C transmission elec-
tron microscope (TEM). The content of Pd was measured
by inductively coupled plasma-optical emission spectrom-
etry (ICP-OES). NMR spectra were recorded with a Bruker
room temperature
NaOH
Al(NO3)3.9H2O(aq)
+
OH
H2O
Boehemite NPs
NH
O
O
L-Arginine
H2O, 90 °C
N
NH2
H
NH2
Arg-boehmite
1. Pd(OAc)2,
EtOH, 80 °C, 20 h
N
Pd
O
O
N
N
H
H
NH2
2. NaBH4, 2 h
Pd-Arg-boehmite
Scheme 1 Synthesis of Pd(0)-Arg-boehmite
1 3

B. Tahmasbi, A. Ghorbani-Choghamarani
Fig. 1 SEM images of boe-
hmite nanoparticles (a) and
Pd(0)-Arg-boehmite (b)
Fig. 3 EDX spectrum of Pd(0)-Arg-boehmite
completion of the reaction, the mixture was cooled to room
temperature and catalyst was separated and washed with
diethyl ether and the reaction mixture was extracted with
H2O and diethyl ether. The organic layer was dried over
Na2SO4 (1.5 g). Then the solvent was evaporated and pure
products were obtained in good yields.
Fig. 2 TEM image of Pd(0)-Arg-boehmite
the progress of the reaction was monitored by TLC. After
completion of the reaction, catalyst was separated and
washed with ethylacetate and the reaction mixture was
extracted with H2O and ethylacetate and dried over anhy-
drous Na2SO4 (1.5 g). Then the solvent was evaporated and
pure biphenyl derivatives were obtained in good to excel-
lent yields.
2.5 Selected Spectral Data
2.5.1 1,1′‑Biphenyl
1H NMR (400 MHz, CDCl3): δH =7.65–7.63 (m, 4H),
7.51–7.41 (m, 4H), 7.41–7.37 (tt, J=7.6, 1.2 Hz, 2H) ppm.
2.4 General Procedure for the Heck Reaction
2.5.2 4‑Chloro‑1,1′‑biphenyl
A mixture of aryl halide (1 mmol), alkene (1.2 mmol),
Na2CO3 (3 mmol), and Pd(0)-Arg-boehmite (0.016–0.02 g,
2.16–2.7 mol%) was stirred in DMF at 120°C and the
progress of the reaction was monitored by TLC. After
1H NMR (400 MHz, CDCl3): δH =7.60–7.58 (m, 2H),
7.57–7.54 (m, 2H), 7.50–7.43 (m, 4H), 7.42–7.38 (tt, J=6,
1.6 Hz, 1H) ppm.
1 3

Pd(0)-Arg-boehmite: As Reusable and Efficient Nanocatalyst in Suzuki and Heck Reactions
500
2H), 3.85 (s, 3H), 1.73–1.67 (quint, J=6.8 Hz, 2H), 1.51–1.42
(sixt, J=8 Hz, 2H), 1.01–0.97 (t, J=7.6 Hz, 3H) ppm.
450
400
350
300
250
200
150
100
50
2.5.6 1,2‑Diphenylethene
1H NMR (400 MHz, CDCl3): δH =7.58–7.56 (d, J=7.6 Hz,
4H), 7.43–7.39 (t, J=7.6 Hz, 4H), 7.33–7.29 (m, 2H), 7.16
(s, 2H) ppm.
a
2.5.7 1‑Methyl‑4‑styrylbenzene
b
1H NMR (400 MHz, CDCl3): δH =7.56–7.54 (d, J=7.6 Hz,
2H), 7.47–7.45 (d, J=8 Hz, 2H), 7.41–7.37 (t, J=7.2 Hz,
2H), 7.30–7.28 (t, J=4 Hz, 1H), 7.22–7.20 (d, J=8 Hz,
2H), 7.12–711 (d, J=2.4 Hz, 2H), 2.40 (s, 3H) ppm.
0
10
20
30
40
50
60
70
80
2θ / degree
Fig. 4 The XRD patterns of boehmite nanoparticles (a) and Pd(0)-
Arg-boehmite (b)
2.5.8 3‑(p‑Tolyl)acrylonitrile
110
100
90
1H NMR (400 MHz, CDCl3): δH= 7.42–7.37 (m, 3 H),
7.29–7.23 (m, 2 H), 5.88–5.84 (d, J = 16.4 Hz, 1 H), 2.42
(s, 3 H) ppm.
80
70
3 Result and Discussion
3.1 Catalyst Preparation
60
50
0
100
200
300
400
500
600
700
800
Temperature(◦C)
The Pd(0)-Arg-boehmite was prepared according to the
concise route outlined in Scheme 1. Initially boehmite
nanoparticles has been synthesized by addition of sodium
hydroxide to the aqueous solution of aluminum nitrate as
aluminum source, at room temperature and subsequently
Pd-arginine complex was supported on surface of pre-
pared particles, directly.
Fig. 5 TGA diagram of boehmite (red line) and Pd(0)-Arg-boehmite
(green line)
2.5.3 3,4‑Difluoro‑1,1′‑biphenyl
1H NMR (400 MHz, CDCl3): δH =7.81–7.75 (m, 1H),
7.71–7.69 (m, 2H), 7.57–7.53 (m, 2H), 7.51–7.46 (m, 2H),
7.43–7.39 (m, 1H) ppm.
3.2 Catalyst Characterizations
2.5.4 Butyl cinnamate
This catalyst has been characterized by scanning electron
microscopy (SEM), transmission electron microscopy
(TEM), energy-dispersive X-ray spectroscopy (EDS),
X-ray diffraction (XRD), thermogravimetric analysis
(TGA) and inductively coupled plasma atomic emission
spectroscopy (ICP-OES).
1H NMR (400 MHz, CDCl3): δH =7.74–7.70 (d, J=16 Hz,
1H), 7.57–7.55 (m, 2H), 7.43–7.40 (m, 3H), 6.50–6.46 (d,
J=16 Hz, 1H), 4.26–4.23 (t, J=6.4 Hz, 2H), 1.76–1.70 (m,
2H), 1.50–1.45 (m, 2H), 1.02–0.98 (t, J=7.6 Hz, 3H) ppm.
The SEM images of boehmite nanoparticles and
Pd(0)-Arg-boehmite are shown in Fig. 1. As shown in
these images, the size and morphology of boehmite and
Pd(0)-Arg-boehmite are quite homogeneous particles in
the range of 20–25 nm. SEM images of boehmite and
catalyst are in good agreement with each other in terms
of size and shape. Also, TEM image of catalyst (Fig. 2)
2.5.5 Butyl 3‑(4‑methoxyphenyl)acrylate
1H NMR (400 MHz, CDCl3): δH=7.68–7.64 (d, J=15.6 Hz,
1H), 7.51–7.49 (d, J=6.8 Hz, 2H), 6.93–6.92 (d, J=7.2 Hz,
2H), 6.36–6.32 (d, J=16 Hz, 1H), 4.24–4.21 (t, J=6.4 Hz,
1 3

B. Tahmasbi, A. Ghorbani-Choghamarani
Fig. 6 FT-IR spectra of, a boehmite, b Arg-boehmite and c Pd(0)-Arg-boehmite
1 3

Pd(0)-Arg-boehmite: As Reusable and Efficient Nanocatalyst in Suzuki and Heck Reactions
Scheme 2 C–C coupling reac-
tion through Suzuki reaction
in the presence of Pd(0)-Arg-
boehmite
B(OH)2
Pd-Arg-boehmite (Cat.)
Na2CO3
R1
X
R2
R1
R2
NaBPh4
+
PEG, 80 oC
or
X= Cl, Br, I
Table 1 Optimization of
reaction conditions for the
C–C coupling reaction of
iodobenzene with PhB(OH)2
Entry
Catalyst (mg)
Solvent
Base
Temperature Time (min)
(ºC)
Yield (%)a
1
2
3
4
5
6
7
8
–
6
8
10
8
8
8
8
8
8
8
8
8
8
PEG
PEG
PEG
PEG
DMF
H2O
DMSO
Dioxane
PEG
PEG
PEG
PEG
PEG
PEG
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
NaOEt
KOH
80
80
80
80
80
80
80
80
80
80
80
60
40
r.t
600
100
45
40
40
85
50
180
50
50
No reaction
97
98
97
93
90
96
31
Trace
42
69
64
Trace
Trace
9
10
11
12
13
14
Et3N
50
Na2CO3
Na2CO3
Na2CO3
100
100
180
aIsolated yields
revealed more accurate information about morphology
and particles size of the palladium nanoparticles. As
shown in Fig. 2, most of the palladium nanoparticles are
in nano size with an average diameter about 5–7 nm.
In order to show the types of elements in catalyst, the
EDS analysis of Pd(0)-Arg-boehmite has been examined
(Fig. 3). As shown in Fig. 3, Al, O, C, N and Pd species
were observed in the catalyst structure.
Qualitative determination of the organic groups grafted
on the boehmite surface was studied by TGA analysis with
a heating rate of 10°C/min in the range 30–800°C. TGA
curves of boehmite nanoparticles and Pd(0)-Arg-boehmite
are shown in Fig. 5. The TGA curve of boehmite nanopar-
ticles showed a 6% weight loss from 25 to 250°C, which
is related to desorption of water and hydroxyl groups. The
TGA curve of the Pd(0)-Arg-boehmite shows the mass
loss of the organic functional group as it decompose upon
heating (Fig. 5). The TGA analysis of catalyst showed
three decreasing peaks. The first one that appeared at low
temperature shows a weight loss of 5% which is probably
related to the physically adsorbed solvents on the surface of
particles [25, 32]. Second peak has appeared at 250–450°C
which corresponded to the loss of the organic spacer group
and palladium complex grafted on boehmite nanoparticles.
Final weight loss about 11% between 500 and 800°C may
be related to the transformation of thermal crystal phase of
boehmite particles.
In order to quantitative analysis and find out the
exact amount of palladium, ICP-OES has been per-
formed. According to the ICP analysis, the exact amount
of palladium supported on Arg-boehmite is estimated
(1.35×10−3 mol/g).
The XRD patterns of boehmite nanoparticles and Pd(0)-
Arg-boehmite are shown in Fig. 4. Which the boehmite
phase was characterized by the 2θ values at 14.40, 28.41,
38.55, 46.45, 49.55, 51.94, 56.02, 59.35, 65.04, 65.56, 68.09,
and 72.38 from the XRD patterns, which these peaks are
related to (0 2 0), (1 2 0), (0 3 1), (1 3 1), (0 5 1), (2 0 0), (1
5 1), (0 8 0), (2 3 1), (0 0 2), (1 7 1), and (2 5 1) reflections,
respectively which is in a good agreement with standard boe-
hmite XRD spectrum and the all peaks can be confirmed the
crystallization of boehmite with an orthorhombic unit cell
[31]. Also, it could be seen that the boehmite phase has not
been destroyed during the modifications.
Figure 6 shows the FT-IR spectrums of boehmite, Arg-
boehmite and Pd(0)-Arg-boehmite. The FT-IR spectrum
of the boehmite nanoparticles (Spectrum a) shows two
strong bands at 3085 and 3306/cm, which are attributed to
the both symmetrical and asymmetrical modes of the O–H
bonds on the surface of boehmite nanoparticles [25]. In
FT-IR spectrums a–c, several peaks that appear at 481, 615
1 3

B. Tahmasbi, A. Ghorbani-Choghamarani
Table 2 Results of Suzuki reaction in the presence of catalytic amounts of Pd(0)-Arg-boehmite under optimized condition
Entry
Aryl halide
I
Phenylating reagent
Product
Time (min) Yield (%)a TOF (h–1)
1
C6H5B(OH)2
45
40
98
97
121
r
B
Cl
2
3
C6H5B(OH)2
C6H5B(OH)2
134.7
Cl
r
B
H
3C
50
95
105.5
H
3C
I
H
3CO
4
5
6
C6H5B(OH)2
C6H5B(OH)2
C6H5B(OH)2
70
170
80
97
94
92
77
H
3CO
r
B
N
C
30.7
63.9
N
C
r
B
H
O
H
O
r
B
N
O2
7
8
9
C6H5B(OH)2
C6H5B(OH)2
C6H5B(OH)2
110
240
400
96
91
93
48.5
21.1
12.9
N
O2
I
H
3C
H
3C
r
B
H
3CO
H
3CO
r
B
10
11
C6H5B(OH)2
C6H5B(OH)2
80
94
90
62.3
35.7
Cl
140
H
3CO
r
H
3CO
B
12
C6H5B(OH)2
60
95
88
r
B
H
O C
13
14
C6H5B(OH)2
C6H5B(OH)2
150
360
90
81
33.3
12.5
H
O C
Cl
N
C
N
C
I
15
C6H5B(OH)2
50
96
106.7
H
OC
H
OC
3
3
1 3

Pd(0)-Arg-boehmite: As Reusable and Efficient Nanocatalyst in Suzuki and Heck Reactions
Table 2 (continued)
Entry
Aryl halide
Phenylating reagent
Product
Time (min) Yield (%)a TOF (h–1)
F
r
B
16
3,4-diF-C6H3B(OH)2
70
60
70
95
93
96
75.4
86.1
76.2
F
N
O2
N
O2
F
F
F
I
17
18
3,4-diF-C6H3B(OH)2
3,4-diF-C6H3B(OH)2
F
F
F
r
B
Cl
I
19
20
21
3,4-diF-C6H3B(OH)2
NaBPh4
110
30
91
96b
95b
46
177.8
105.6
r
B
H
3C
NaBPh4
50
H
3C
I
22
23
NaBPh4
NaBPh4
60
95
97b
93b
89.8
54.4
H
3CO
H
3CO
r
B
N
O2
N
O2
aIsolated yield
bReaction conditions: aryl halide (1 mmol), Pd(0)-Arg-boehmite (8 mg,1.08 mol%), sodium tetraphenyl borate (0.5 mmol) and Na2CO3
(3 mmol) in PEG at 80°C
and 737/cm can be related to the absorption of Al–O bonds
[27]. Also, the nitrate impurity vibration at 1633/cm and
the vibrations of hydrogen bands OH⋯OH by two strong
absorption bands at 1164 and 1069/cm were observed in
FT-IR spectrum [31]. The FT-IR spectra of catalyst was
indicated that the boehmite phase has not been destroyed
during the modifications.
H
N
Ar
X
N
Ar Ph
Pd
HN
Oxidative
Addition
Pd(0)-Arg-boehmite
Reductive
elimination
3.3 Catalytic Activity of Pd(0)-Arg-boehmite
in the C–C Coupling Reactions
H
N
N
II
Ar
X
H
N
HN
Pd
N
HN
Ar
Ph
II
Pd
As a part of our ongoing program directed towards the cata-
lytic activity of modified boehmite nanoparticles in organic
reactions [25, 31], we were interested in finding a simple
and efficient method for the carbon–carbon cross coupling
reaction in the presence of immobilized Pd-Arginine on
boehmite nanoparticles (Pd(0)-Arg-boehmite) as a new and
recoverable nanocatalyst. The Suzuki reaction in the pres-
ence of this catalyst is shown in Scheme 2.
Transmetallation
PhB(OH)3
Base
X + B(OH)3
PhB(OH)2
Scheme 3 Mechanism of the Pd(0)-Arg-boehmite catalyzed Suzuki
reaction
1 3

B. Tahmasbi, A. Ghorbani-Choghamarani
Scheme 4 Pd(0)-Arg-boehmite
Pd-Arg-boehmite (Cat.)
catalyzed the Heck reaction
X
R
Na2CO3
R
R
+
R
DMF, 120 oC
X= Cl, Br, I
R = COOBu, COOMe, Ph, CN
Table 3 Optimization of
reaction conditions for the
coupling of iodobenzene with
butyl acrylate
Entry Catalyst (mg) Solvent Base
Amounts of Temperature (ºC) Time (min) Yield (%)a
base (mmol)
1
2
3
4
5
6
–
8
DMF
DMF
DMF
DMF
PEG
H2O
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
3
3
3
3
3
3
3
3
3
3
3
120
120
120
120
120
100
120
Reflux
120
120
120
120
100
80
600
150
150
50
100
100
60
100
60
60
No reaction
46
64
98
69
46
96
Trace
Trace
31
51
59
14
16
16
16
16
16
16
16
16
16
16
16
7
8
9
10
11
12
13
14
DMSO Na2CO3
EtOH
DMF
DMF
DMF
DMF
DMF
DMF
Na2CO3
NaOEt
KOH
Et3N
Na2CO3 1.5
Na2CO3
Na2CO3
60
60
3
3
60
60
60
36
aIsolated yields
In order to illustrate the catalytic activity of Pd(0)-Arg-
boehmite in the C–C coupling reaction, we first examined
the coupling of iodobenzene with phenylboronic acid
(PhB(OH)2), and the results are summarized in Table 1. In
order to optimize reaction conditions, we examined influ-
vence of different parameters such as solvent, tempera-
ture, base, and different amounts of Pd(0)-Arg-boehmite,
on the outcome of C–C coupling reaction of iodobenzene
and phenylboronic acid. The results show that the reac-
tion cannot proceed in the absence of Pd(0)-Arg-boehmite
even running the reaction for 10 h, (Table 1, entry 1). In
order to choose the reaction media, different solvents such
as PEG, DMF, DMSO, H2O and dioxane were screened
(Table 1, entries 4–8) and the best results were obtained
in PEG using 0.008 g (1.08 mol%) of Pd(0)-Arg-boehmite
(Table 1, entry 3). Also, the effect of base were studied
which in the presence of Na2CO3 at 80°C quantitative con-
version of product was observed (Table 1, entry 3). But,
when the other bases (such as NaOEt, KOH, and Et3N)
were employed, suitable yield was not detected in com-
parison to Na2CO3 (Table 1, entries 9–11). Also, we found
that the coupling reaction yields were susceptible to tem-
perature changes. Therefore, the effect of temperature were
studied (Table 1, entries 12–14). The results shown that at
room temperature the reaction cannot proceed even running
the reaction for 3 h (Table 1, entry 14), and the best results
were obtained at 80°C (98% of yield), while conversion
reduced to 64% at 60°C (Table 1, entry 12).
Aiming to extend the scope of our methodology, we next
used different aryl halides as coupling partner for this cross
coupling reaction. The results are summarized in Table 2.
Thus, various aryl iodides and bromides were coupled
with phenylboronic acid and converted into corresponding
biphenyls. We also examined the cross coupling reaction
of several substituted aryl chlorides with phenylboronic
acid under the optimized reaction conditions. However,
aryl bromides and aryl iodides show lower reaction times
in comparison with those corresponding aryl chlorides. In
order to show the chemoselectivity of the presented proto-
col, 1-chloro-4-bromobenzene was coupled with phenylb-
oronic acid. Interestingly, chloro- group remained intact
during the coupling reaction, while the bromo- group was
coupled successfully. The results revealed that this method-
ology is effective for a wide range of aryl halide including
Cl, Br and I; however, aryl chlorides showed less reactiv-
ity toward the coupling reaction than their aryl iodides and
bromides analogs.
After this pioneering examples, we also applied opti-
mized reaction conditions for the coupling of aryl halides
with 3,4-difluoro phenylboronic acid (Table 2, entries
1 3

Pd(0)-Arg-boehmite: As Reusable and Efficient Nanocatalyst in Suzuki and Heck Reactions
TOF (h–1)
54.4
Table 4 Coupling of aryl
Entry
1
Aryl halide
I
Product
Time (min)
50
Yield (%)a
98
halides with butyl acrylate,
methyl acrylate, styrene or
acrylonitrile in the presence of
catalytic amounts of Pd(0)-Arg-
boehmite
O
u
B
O
O
I
u
B
O
2
3
4
5
6
250
300
230
350
60
94
95
88
94
97
10.4
8.8
H
3CO
H
3CO
O
I
u
B
O
H
OC
I
3
H
OC
3
O
u
B
O
10.6
7.5
H
C
3
H
C
3
O
r
B
u
B
O
NC
NC
O
I
u
B
O
44.9
H
3C
H
3C
O
r
B
u
B
O
7
8
60
89
41.2
N
N
O
r
B
F
3C
F
3C
u
420
91
6
B
O
I
I
N
C
9
80
97
94
33.7
13.1
I
N
C
10
200
H
3C
H
3C
I
N
C
11
12
140
140
96
96
19
19
H
3CO
H
3CO
O
e
M
O
O
I
e
M
O
13
14
150
120
97
98
18
H
3C
H
3C
O
I
e
M
O
22.7
H
3CO
H
3CO
O
I
e
M
O
15
240
98
11.3
H
OC
3
H
OC
3
I
16
17
18hb
18hb
77
72
1.9
1.4
I
H
3C
H
3C
I
18
18hb
73
1.5
H
3CO
H
3CO
aIsolated yield
bReaction conditions: aryl halide (1 mmol), Pd(0)-Arg-boehmite (20 mg, 2.7 mol%), alkene
(1.2 mmol) and K2CO3 (3 mmol) in DMF at 120°C
1 3

B. Tahmasbi, A. Ghorbani-Choghamarani
H
N
such as H2O, DMSO, PEG and DMF (Table 3, entries
4–8). The best result was obtained in the presence of 16 mg
(2.16 mol%) of Pd(0)-Arg-boehmite in DMF. The reac-
tion was also carried out with the little amount of catalyst
(Table 3, entries 2, 3), but in these cases only low yields of
the C–C coupled products were obtained. The reaction was
significantly affected by the nature of base and the additive.
Therefore, the effect and amount of base on the outcome
of the reaction was explored (Table 3, entries 9–12). We
found that Na2CO3 afforded the best results for this reac-
tion and allowed the coupling product obtained in 98%
yield after 50 min (Table 3, entry 4). The other bases such
as NaOEt, KOH, and Et3N were not as effective as Na2CO3,
only afforded moderate to low yields of corresponding
coupling product. Also when the amount of Na2CO3 was
reduced to 1.5 mmol, the yield of the reaction decreased
to 59%. Finally, the effect of temperature was examined,
which undesirable results were observed at 80 and 100°C
(Table 3, entries 13, 14). Therefore, the best results were
obtained in DMF at 120°C for 50 min in the presence of
16 mg (2.16 mol%) of Pd(0)-Arg-boehmite using 3 mmol
of Na2CO3 (Table 3, entry 4).
N
Pd
B
H
Ar
X
HN
Pd-Arg-boehmite
Deprotection
Pd (0)
Oxidative
Pd (0)
Reduction
Oxidative Addition
Pd (II)
B
H
Pd (II)
N
N
H
N
HN
PdII
N
H
Ar
HN
Ar
PdII
X
Beta-
Alkene
elimination
R
Coordination
R
H
N
HN
H
N
Ar
Ar
N
N
X
PdII
PdII
HN
Insertion
R
R
Scheme 5 Pd(0)-Arg-boehmite catalyzed the Heck reaction
16–19) and sodium tetraphenyl borate (NaBPh4) (Table 2,
entries 20–23) and the corresponding biphenyls were
obtained in short reaction times with good to excellent
yields.
Catalytic cycle for Suzuki reaction in the presence of
Pd(0)-Arg-boehmite was outlined in Scheme 3.
This optimized conditions were also applied for the cou-
pling of other aryl halides including electron-donor and
electron-withdrawing functional groups with butyl acrylate
to afford the corresponding products and the all products
were obtained in good yields (Table 4, entries 1–8).
In order to extend the catalytic activity of Pd(0)-Arg-
boehmite, we report the application of Pd(0)-Arg-boehmite
as catalyst for the Heck reaction via coupling of various
aryl halides with butyl acrylate, methyl acrylate, acryloni-
trile and styrene (Scheme 4). In order to optimize the reac-
tion conditions, the coupling of iodobenzene with butyl
acrylate was studied in the presence of different amounts
of catalyst (Table 3, entries 1–4) and in the various solvents
We also applied optimized reaction conditions for the
coupling of aryl halides with acrylonitrile (Table 4, entries
9–11), methyl acrylate (Table 4, entries 12–15) and styrene
(Table 4, entries 16–18). The electron-neutral, electron-rich
Table 5 Recyclability of Pd(0)-
Run no.
1
2
3
4
5
6
Arg-boehmite in the coupling of
iodobenzene with PhB(OH)2
Time (min)
Yield
45
98
45
98
50
95
60
97
70
94
95
93
Table 6 Comparison results of Pd(0)-Arg-boehmite with other catalysts for the coupling of iodobenzene with phenylboronic acid
Entry
Catalyst
Condition
Time (h)
Yield (%)
TOF (/h)
Refs.
1
2
3
4
5
LDH-Pd(0)
Pd NP
Pd(II)-NHC complex
CA/Pd(0)
K2CO3, 1,4-dioxane: H2O (5:1), 80°C
H2O, KOH, 100°C
DMF, Cs2CO3, 100°C
H2O, K2CO3, 100°C
10
12
24
2
96
95
99
94
97
–
[33]
[34]
[35]
[36]
[37]
7.9
4.1
94
32
N,N’-bis(2-pyridinecarboxamide)-
H2O, K2CO3, 100°C
3
1,2-benzene palladium complex
6
7
8
9
NHC-Pd(II) complex
Pd/Au NPs
Pd-MPTAT-1
PANI-Pd
Pd(0)-Arg-boehmite
THF, Cs2CO3, 80°C
12
24
8
4
0.75
88
88
95
91
98
7.3
3.6
–
10.3
120.9
[38]
[39]
[40]
[41]
EtOH/H2O, K2CO3, 80°C
NaOH, DMF: H2O (1:5), 85°C
K2CO3, 1,4-dioxane: H2O (1:1), 95°C
PEG, Na2CO3, 80°C
10
This work
1 3

Pd(0)-Arg-boehmite: As Reusable and Efficient Nanocatalyst in Suzuki and Heck Reactions
and electron-poor aryl halides reacted with acrylonitrile,
methyl acrylate and styrene efficiently to produce the cor-
responding coupled products in good to excellent yields.
Whereas, styrene has been coupled with aryl halides in
the presence of 20 mg (2.7 mol%) of Pd(0)-Arg-boehmite.
Therefore, these results revealed that this methodology is
effective for a wide range of alkenes and aryl halides.
Catalytic cycle for Heck reaction in the presence of
Pd(0)-Arg-boehmite was outlined in Scheme 5.
catalyst showed shorter reaction time and better yield than
other catalysts. Also Pd(0)-Arg-boehmite is comparable in
terms of price, non-toxicity, stability and easy separation
with other reported catalyst. In addition, the recovery and
recycleability of this catalyst is more rapid and easier than
the other catalysts. Also, a comparison of activity based
on turnover frequency (TOF) showed excellent results for
Pd(0)-Arg-boehmite in C–C coupling reactions. As shown
in Table 5, Pd(0)-Arg-boehmite was showed a high TOF
number in comparison with other catalysts, this results
was indicate that Pd(0)-Arg-boehmite is more effective and
more efficient in compared to other catalysts. More impor-
tantly, in comparison with other catalysts, Pd(0)-Arg-boe-
hmite has been easily prepared using cheap and commer-
cially available materials in a short period of time.
3.4 Reusability of the Catalyst
The reusability of the catalysts is an important factor for
industrial applications. Therefore, the recovery and reus-
ability of Pd(0)-Arg-boehmite was investigated using the
reaction of iodobenzene with phenylboronic acid in the
presence of described catalyst (Table 5). After completion
of the reaction, the catalyst was recovered via centrifuga-
tion, washed with ethyl acetate to remove residual product
and the catalyst reused for next reactions for at least 6 times
without any significant loss of its catalytic activity or pal-
ladium leaching. Which clearly demonstrates the practical
recyclability of this catalyst.
4 Conclusions
In conclusion a novel and efficient heterogeneous catalyst
(Pd(0)-Arg-boehmite) was synthesized by direct support-
ting of Pd-arginine complex on boehmite nanoparticles
for the first time. This catalyst was characterized by XRD,
TGA, TEM, SEM, EDS and ICP-OES techniques. The
Pd(0)-Arg-boehmite exhibits an excellent catalytic activity,
high reusability and air- moisture stability for the Suzuki
and Heck reactions. This methodology is effective for a
wide range of aryl halide including Cl, Br and I. Also the
catalyst can be recovered and recycled over 6 times without
any significant loss of its activity or palladium leaching.
3.5 Catalyst Leaching Study
The amounts of palladium leaching in reaction mixture was
studied by checking the Pd loading amount before and after
recycling of the catalyst by ICP-OEIS technique. Based on
ICP-OEIS analysis, the amount of palladium in fresh cata-
lyst and the recycled catalyst after 6 times recycling is 1.35
and 1.28 mmol/g, respectively, which indicated that palla-
dium leaching of this catalyst is very low.
Acknowledgements Authors thank the research facilities of Ilam
University, Ilam, Iran, for financial support of this research project.
In order to perform hot filtration experiment, two reac-
tion of iodobenzene with PhB(OH)2 has been performed
under optimized reaction conditions. In the first reaction,
the biphenyl was obtained after 22 min (in the half time of
the reaction) in 64% yield. Simultaneously in second reac-
tion, the same reaction was repeated, but in the half time
of the reaction (after 22 min), the catalyst was removed
from the reaction mixture by filtration and the reaction
mixture was allowed to run for another 22 min. The yield
of reaction in this stage was 66%. These experiments con-
firmed that Pd(0)-Arg-boehmite are essential for comple-
tion of reaction and the leaching of palladium hasn’t been
occurred.
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