Boehmite@tryptophan-Pd nanoparticles: A new catalyst for C–C bond formation

Article abstract of DOI:10.1002/aoc.4977

A boehmite@tryptophan-Pd nanoparticulate catalyst was prepared by a simple, fast and convenient route. The nanomaterial was characterized using various techniques and employed as a thermally stable catalyst for Heck, Stille and Suzuki cross-coupling reactions. Optimized conditions for these reactions are described. The catalyst could be isolated, post-reaction, by simple filtration and recycled for several consecutive cycles without a notable change in its activity.

Full text of DOI:10.1002/aoc.4977

Received: 7 January 2019
DOI: 10.1002/aoc.4977
Revised: 29 March 2019
Accepted: 9 April 2019
F U L L P A P E R
Boehmite@tryptophan‐Pd nanoparticles: A new catalyst for
C–C bond formation
1
1
2
Arash Ghorbani‐Choghamarani
| Masoud Mohammadi
| Robert H.E. Hudson |
3
Taiebeh Tamoradi
1
Department of Chemistry, Faculty of
A boehmite@tryptophan‐Pd nanoparticulate catalyst was prepared by a simple,
fast and convenient route. The nanomaterial was characterized using various
techniques and employed as a thermally stable catalyst for Heck, Stille and
Suzuki cross‐coupling reactions. Optimized conditions for these reactions are
described. The catalyst could be isolated, post‐reaction, by simple filtration
and recycled for several consecutive cycles without a notable change in its
activity.
Science, Ilam University, PO Box,
69315516 Ilam, Iran
2
Department of Chemistry, University of
Western Ontario, London, Ontario,
Canada, N6A 5B7
3
Department of Chemistry, Faculty of
Science, University of Kurdistan,
Sanandaj, Iran
Correspondence
KEYWORDS
Arash Ghorbani‐Choghamarani,
Department of Chemistry, Faculty of
Science, Ilam University, PO Box
Boehmite, Heck reaction, Stille reaction, Suzuki reaction
69315516, Ilam, Iran.
Email: arashghch58@yahoo.com; a.
ghorbani@ilam.ac.ir
Funding information
Ilam University; The Natural Sciences and
Engineering Research Council of Canada
[
21]
[22]
1
| INTRODUCTION
rheology control,
their carrier,
as medicinal
desiccants and
[
23]
[24]
[25]
as absorbents,
trochemical sensors,
petrochemical industry
lysts and catalyst carriers.
for coatings,
as vaccine adjuvants, in the
and most widely used as cata-
in elec-
[
26]
In recent years, with the aim of combining the
advantages of homogeneous and heterogeneous
catalytic processes, nanoparticles have been employed
due to their high surface area and facile recovery.
Important nano‐heterogeneous supports such as metal
[
27]
[
28]
More importantly, the
[
1–6]
immobilization of transition metal complexes on the
nano‐boehmite surface has been rarely reported in
the literature for the purpose of synthesizing heteroge-
oxides, carbon nanotubes, ionic liquids, molecular sieves
[
29–33]
(SBA‐15, MCM‐41 and MCM‐48), alumina, peptide
neous catalysts.
nanofibers, silica nanoparticles, polymers, graphene oxide
L‐Tryptophan is an amino acid that contains an
α‐amino group, an α‐carboxylic acid group and a side‐
chain indole, making it a nonpolar aromatic amino
and heteropoly acids have been employed for the
[7–19]
heterogenization of homogeneous catalysts.
Among
[
34]
the various supports, boehmite nanoparticles are consid-
ered as outstanding solid supports because of their physical
and chemical properties such as excellent thermal and
chemical stability, large internal surface area and high
concentration of surface OH groups. Boehmite nanoparti-
cles have applications in a wide variety of endeavors
acid.
Generally speaking, the presence of an amino
group beside a carboxylic acid group can accelerate the
immobilization process which may be aided by the
N─H group of tryptophan which is capable of forming a
hydrogen bond with the O─H groups on a boehmite sur-
face. Also, the final complex can be synthesized
using stable interaction between the amine group of
[
20]
suchz as: the preparation of sol–gel ceramics,
for
Appl Organometal Chem. 2019;e4977.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
1 of 11
https://doi.org/10.1002/aoc.4977

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GHORBANI‐CHOGHAMARANI ET AL.
tryptophan and a palladium atom. It should be men-
tioned that tryptophan which has a natural origin was
selected as an inexpensive and green ligand.
apparatus. The content of Pd was measured using
inductively coupled plasma optical emission spectrometry
(ICP‐OES).
Over the past several decades, there has been growing
interest in the improvement of experimental procedures
for the design and synthesis of transition metal catalysts
with nanoscale size. There are many reports of palladium
complexes supported on the surface of various solids
such as magnetic nanoparticles and mesoporous
2
.2 | Preparation of L‐tryptophan complex
of Pd supported on surface of boehmite
nanoparticles (boehmite@tryptophan‐Pd)
[35]
[36]
[37]
Boehmite nanoparticles were prepared by the sol–gel
method as reported in our previous work.
materials (MCM‐41,
MCM‐48
and SBA‐15 ). In
[
15]
For the
particular, special attention has been paid to heteroge-
neous palladium catalysts because of their applications
in carbon–carbon bond forming reactions such as
synthesis of L‐tryptophan supported on boehmite nanopar-
ticles, 1 g of the prepared boehmite nanoparticles was dis-
persed in 50 ml of deionized water by sonication for
15 min, and then L‐tryptophan (2.5 mmol) was added to
the mixture. The reaction mixture was stirred under nitro-
gen atmosphere at reflux conditions for 24 h. Then, the
obtained boehmite@tryptophan product was separated
by simple filtration and washed with hot water and hot eth-
anol to remove the unreacted amino acid and dried in an
oven at 50°C for 4 h. The obtained boehmite@tryptophan
(0.5 g) was dispersed in 25 ml of ethanol by sonication for
30 min and then palladium acetate (0.25 g) was added to
the reaction mixture. The reaction mixture was stirred
under nitrogen atmosphere at 80°C for 24 h. Then, 3 mmol
[
38]
[39]
[40]
[41]
[43]
Suzuki–Miyaura,
Espinet/Echavarren
Hatanaka,
Hiyama,
Stille,
[
42]
and Heck and Sonogashira
reactions. It should be noted that there are only few
reports describing complexes supported on the surface
[44–46]
of boehmite for C–C bond formation.
As reported
in several reviews, the use of Suzuki, Stille and Heck cou-
pling reactions is indispensable for the synthesis of
[
47]
high‐value chemicals such as natural products,
[48]
[49]
[50]
agrochemicals,
pharmaceuticals,
polymers,
bio-
[
50]
logically active compounds and advanced materials.
These reactions benefit from the low toxicity and com-
mercial availability of boronic acid, boronate ester deriva-
[
51–54]
of NaBH was added to the reaction and stirred for a fur-
4
tives or triphenyltin chloride and alkene sources.
ther 2 h. The final product (boehmite@tryptophan‐Pd)
was separated by simple filtration and washed with
ethanol to remove the unattached substrates. The
boehmite@tryptophan‐Pd nanoparticulate product was
dried in an oven at 50°C for 4 h.
In our continuing efforts towards the development of
efficient, inexpensive and green catalysts for carbon–
carbon bond formation reactions, we have designed a
novel heterogeneous catalyst for the reactions mentioned
above. Herein, we present a simple and inexpensive proce-
dure, combining ease of operation, easy separation of the
catalyst, short reaction times and high yield of products.
2.3 | General procedure for Suzuki
reaction
2
2
| EXPERIMENTAL
.1 | Materials
A mixture of aryl halide (1 mmol), phenylboronic acid
(
1 mmol) and Na CO (1.5 mmol) was dissolved in 2 ml
2 3
of ethanol. Boehmite@tryptophan‐Pd (0.075 mol%) was
added to the mixture, and the flask was sealed and stirred
at 70°C. The progress of the reaction was monitored by
TLC. Upon completion of the reaction, the mixture was
cooled to room temperature and the catalyst was
separated by simple filtration and washed with EtOAc.
Finally, the reaction mixture was extracted with water
and EtOAc. The organic layer was dried over Na SO .
All chemicals and solvents used in this work were obtained
from Sigma‐Aldrich and Merck. They were used without
further purification. The particle size and morphology
were examined using scanning electron microscopy
1
(SEM) with an FESEM‐TESCAN MIRA3. H NMR spectra
were recorded with a Bruker NMR (400 MHz) spectrome-
ter. Powder X‐ray diffraction (XRD) measurements were
performed using a Philips X’pert powder X‐ray diffractom-
eter (Cu Kα radiation, λ = 1.54060 Å). Fourier transform
infrared (FT‐IR) spectra of samples were recorded with
KBr pellets using a Bruker VRTEX 70 FT‐IR spectropho-
tometer. Thermogravimetric analysis (TGA) curves were
obtained with a Shimadzu DTG‐60 instrument. Melting
points were obtained using an Electrothermal 9100
2
4
Finally, the solvent was evaporated, and the pure
biphenyl derivative was obtained.
2.4 | General procedure for Stille reaction
A mixture of aryl halide (1 mmol), triphenyltin chloride
(0.5 mmol) and Na CO (1.5 mmol) was dissolved in
2
3

GHORBANI‐CHOGHAMARANI ET AL.
3 of 11
SCHEME 1 Synthesis of boehmite@tryptophan‐Pd nanoparticles
2
ml of ethanol. Boehmite@tryptophan‐Pd (0.075 mol%)
was stirred at 120°C. The progress of the reaction was
monitored by TLC. Upon completion of the reaction,
the mixture was cooled to room temperature, and the
catalyst was separated by simple filtration and washed
was added to the flask and the reaction vessel was sealed
and stirred at 70°C. The progress of the reaction was
monitored by TLC. Upon completion of the reaction,
the mixture was cooled to room temperature, and the
catalyst was separated by simple filtration and washed
with EtOAc. The reaction mixture was then extracted
with water and EtOAc. The organic layer was dried
over Na SO . The solvent was evaporated, and pure
with Et O. The reaction mixture was extracted with
2
water and Et O. The organic layer was dried over Na SO .
2
2
4
The solvent was then evaporated, and the corresponding
pure productwas obtained.
2
4
biphenyl derivative was obtained in good yield.
2.5 | General procedure for Heck reaction
A mixture of aryl halide (1 mmol), butyl acrylate
1.2 mmol) and K CO (3 mmol) was dissolved in 2 ml
(
2
3
of dimethylsulfoxide (DMSO). Boehmite@tryptophan‐Pd
0.105 mol%) was added to the flask, and the mixture
(
FIGURE
1
FT‐IR
spectra
of
(a)
boehmite,
(b)
boehmite@tryptophan and (c) boehmite@tryptophan‐Pd
FIGURE 2 EDX analysis of boehmite@tryptophan‐Pd

4
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GHORBANI‐CHOGHAMARANI ET AL.
1
3
2
.6 | Selected spectral data
4‐Nitro‐1,1′‐biphenyl (Table 2, entry 8). C NMR
101 MHz, CDCl , δ , ppm):147.63, 147.08, 138.76,
129.16, 128.93, 127.80, 127.47, 127.39, 124.11.
(
3
C
1
1
,1′‐Biphenyl (Table 2, entry 1). H NMR (400 MHz,
1
CDCl , δ , ppm): 7.67–7.59 (m, 4H), 7.53–7.42 (m, 4H),
Butyl cinnamate (Table 5, entry 1). H NMR
(400 MHz, CDCl , δ , ppm): 7.73–7.69 (d, J = 16.0 Hz,
3
H
7
.42–7.34 (m, 2H).
‐Methyl‐1,1′‐biphenyl (Table 2, entry 6). H NMR
400 MHz, CDCl , δ , ppm): 7.64–7.60 (m, 2H), 7.54–
3
H
1
4
1H), 7.56–7.53 (m, 2H), 7.42–7.38 (m, 3H), 6.49–6.45
(d, J = 16.0 Hz, 1H), 4.24 (t, J = 6.7 Hz, 2H), 1.74–
1.68 (m, 2H), 1.51–1.42 (m, 2H), 1.01–0.97
(t, J = 7.4 Hz, 3H).
Butyl 3‐(4‐methoxyphenyl)acrylate (Table 5, entry
3). H NMR (400 MHz, CDCl , δ , ppm): 7.68 (d,
(
3
H
7
.52 (m, 2H), 7.50–7.44 (m, 2H), 7.39–7.33 (m, 1H),
7
.30–7.28 (m, 2H), 2.43 (s, 3H).
1
4‐Methoxy‐1,1′‐biphenyl (Table 3, entry 3). H NMR
1
(400 MHz, CDCl , δ , ppm): 7.60–7.54 (m, 4H), 7.48–7.46
3
H
3
H
(m, 2H), 7.36–7.30 (m, 1H), 7.03–6.98 (m, 2H), 3.88 (s, 3H).
J = 16.0 Hz, 1H), 7.45–7.43 (m, 2H), 7.22–7.20 (m, 2H),
.42 (d, J = 16.0 Hz, 1H), 4.23 (t, J = 6.7 Hz, 2H), 1.71
m, 2H), 1.51–1.42 (m, 2H), 0.99 (t, J = 7.4 Hz, 3H).
6
(
3
| RESULTS AND DISCUSSION
.1 | Catalyst preparation
3
Previously, we reported the synthesis of a heterogeneous
nanocatalyst by simple procedures and available materials,
the catalyst being applicable in the Heck, Stille and Suzuki
[
55–57]
coupling reactions.
As illustrated in Scheme 1,
the synthesis of the new heterogeneous nanocatalyst
was realized by attaching tryptophan to the boehmite
nanosubstrate. Ultimately, boehmite@tryptophan‐Pd
nanocatalyst was prepared using the stable interaction
between the nitrogen atom (primary amine) of tryptophan
and palladium (Scheme 1).
FIGURE
nanocatalyst
3
XRD pattern of boehmite@tryptophan‐Pd
FIGURE 4 X‐ray mapping analysis of boehmite@tryptophan‐Pd nanocatalyst

GHORBANI‐CHOGHAMARANI ET AL.
5 of 11
3
.2 | Catalyst characterization
In all the FT‐IR spectra, several peaks at 480, 618
−
1
and 743 cm were observed that are related to the
[
58]
The prepared heterogeneous catalyst was characterized
using FT‐IR spectroscopy, SEM, energy‐dispersive X‐ray
spectroscopy (EDX), XRD, TGA and X‐ray mapping.
The FT‐IR spectra of boehmite, boehmite@tryptophan
and boehmite@tryptophan‐Pd are shown in Figure 1.
In the FT‐IR spectrum of the boehmite nanoparticles,
absorption of Al─O bonds.
In the spectrum of
boehmite@tryptophan (Figure 1b), the peaks at around
−
1
1615 and 2842–2946 cm
are the most important,
characteristic of the stretching vibrations of aromatic
C═N bond and aliphatic C─H stretching vibration,
respectively. More importantly, the bending vibration
−
1
−1
two strong bands at 3086 cm (symmetric mode) and
of NH2 near 1450 cm
in the FT‐IR spectrum of
−
1
3
295 cm
(asymmetric mode) are attributed to the
boehmite@tryptophan is shifted to lower wavenumber
O─H bonds on the surface of boehmite nanoparticles.
in the spectrum of boehmite@tryptophan‐Pd (Figure 1
FIGURE 5 SEM images of boehmite@tryptophan‐Pd nanocatalyst at different magnifications
FIGURE 6 TGA curves of boehmite@tryptophan‐Pd nanocatalyst

6
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GHORBANI‐CHOGHAMARANI ET AL.
c), confirming the coordination of nitrogen atom of
amino groups to palladium.
in order to determine the amounts of carbon and
nitrogen in the catalyst, elemental analysis was per-
formed. According to this analysis, the amount of carbon
and nitrogen immobilized on boehmite nanoparticles was
13.2 and 2.8%, respectively.
The XRD pattern of the boehmite@tryptophan‐Pd
nanocatalyst is shown in Figure 3. The peaks at 2θ
values of 14.01°, 18.54°, 20.13°, 24.95°, 28.95°, 41.45°,
47.25°, 53.24°, 55.22°, 59.12°, 64.24° and 68.26° are
related to (0 2 0), (1 2 0), (0 3 1), (1 3 1), (0 5 1), (2 0
In order determine the elemental composition of the
boehmite@tryptophan‐Pd nanocatalyst, the components
were analyzed using EDX (Figure 2). The elements Al,
O, C, N and Pd were observed in the EDX analysis of
boehmite@tryptophan‐Pd. In order to determine the
exact amount of palladium, the ICP‐OES technique was
applied. According to the ICP‐OES results, the exact
−
3
−1
amount of Pd in this catalyst is 1.52 × 10 mol g . Also,
SCHEME 2 Carbon–carbon coupling
reactions in the presence of
boehmite@tryptophan‐Pd
TABLE 1 Optimization of reaction conditions for C–C cross‐coupling of iodobenzene with phenylboronic acid
a
Entry
Catalyst (mol%)
Solvent
Base
Temperature (°C)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
—
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
DMF
Na
Na
Na
Na
Na
Na
Na
Na
Na
2
2
2
2
2
2
2
2
2
CO
CO
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
3
3
70
70
70
70
70
70
70
70
70
70
70
70
70
70
70
Reflux
65
40
25
600
30
30
30
30
30
30
30
30
30
30
30
30
30
320
30
30
30
360
NR
62
80
98
98
93
92
45
94
85
82
77
95
87
0.015
0.045
0.075
0.105
0.135
0.075
0.075
0.075
0.075
0.075
0.075
0.075
0.075
0.075
0.075
0.075
0.075
0.075
2
H O
PEG
10
11
12
13
14
15
16
17
18
19
EtOH
EtOH
EtOH
EtOH
DMSO
EtOH
EtOH
EtOH
EtOH
EtOH
KOH
CO
NaOH
Et
K
2
3
3
N
Na
—
2
CO
3
b
—
Na
Na
Na
Na
2
2
2
2
CO
CO
CO
CO
3
3
3
3
97
62
46
NR
a
Isolated yield.
b
Reaction conditions: aryl halide (1 mmol), boehmite@tryptophan‐Pd, phenylboronic acid (1 mmol), base (1.5 mmol) and solvent (2 ml).

GHORBANI‐CHOGHAMARANI ET AL.
7 of 11
TABLE 2 Catalytic C–C coupling reaction of aryl halides using
0), (1 5 1), (0 8 0), (2 3 1), (0 0 2), (1 7 1) and (2 5 1)
reflections, respectively, which are in agreement with
PhB(OH)
2
in the presence of catalytic amounts of
[
59]
boehmite@tryptophan‐Pd in EtOH at 70°C
the standard boehmite XRD pattern.
More impor-
tantly, the phase of boehmite is not destroyed during
the modifications.
Time
(min)
Yield
(%)
a
Entry
Aryl halide
Product
The X‐ray mapping of the boehmite@tryptophan‐Pd
nanocatalyst is shown in Figure 4. The good dispersion
of Pd on the surface of the catalyst was confirmed from
the elemental mapping images.
To investigate the size and morphology of the
boehmite@tryptophan‐Pd nanocatalyst, SEM images
were obtained (Figure 5). The images show that most of
1
30
98
2
3
4
55
96
40
70
97
82
TABLE 3 Coupling of aryl halides with Ph
3
SnCl in the presence
of catalytic amounts of boehmite@tryptophan‐Pd in EtOH at 70°C
5
6
45
70
91
92
Time
(min)
Yield
(%)
a
Entry
Aryl halide
Product
1
50
96
7
8
55
96
88
2
3
4
95
93
110
80
94
87
180
9
120
81
5
6
95
91
90
1
0
1
60
30
93
98
150
1
7
8
110
180
93
85
1
2
3
120
100
88
91
1
9
210
77
1
1
1
1
4
5
6
7
230
160
195
220
86
91
87
92
1
1
1
0
1
2
140
135
100
92
94
78
a
Isolated yield.
a
Isolated yield.
b
Reaction conditions: aryl halide (1 mmol), boehmite@tryptophan‐Pd
0.075 mol %), phenylboronic acid (1 mmol) and Na CO (1.5 mmol) in
b
Reaction conditions: aryl halide (1 mmol), boehmite@tryptophan‐Pd
0.075 mol %), triphenyltin chloride (0.5 mmol) and Na CO (1.5 mmol) in
(
2
3
(
2
3
EtOH at 70°C.
EtOH at 70°C.

8
of 11
GHORBANI‐CHOGHAMARANI ET AL.
the boehmite@tryptophan‐Pd nanoparticles are quite
homogeneous with an average size in the region of 62 nm.
The immobilization of tryptophan‐Pd complex on the
surface of boehmite was also confirmed by TGA
A
reaction optimization study was undertaken
wherein the amount of catalyst, type of solvent and
base and also the effect of temperature were investi-
gated via the reaction of iodobenzene (1 mmol)
with phenylboronic acid (1 mmol). The results are sum-
marized in Table 1. According to the observed results,
the optimal conditions for this reaction are:
aryl halide (1 mmol), phenylboronic acid (1 mmol),
boehmite@tryptophan‐Pd (5 mg) and Na CO
(Figure 6). It should be mentioned that the weight
loss below 200°C may be due to the removal of the phys-
ically and chemically adsorbed solvents or surface
hydroxyl groups. The weight loss between 200 and
5
00°C is due to the decomposition of organic groups on
2
3
[58]
the surface of boehmite.
(1.5 mmol) in ethanol at 70 C (Table 1, entry 4).
In order to investigate the scope and generality of
this procedure, various types of aryl halides were reacted
with phenyl donors including phenylboronic acid and
triphenyltin chloride under the optimized conditions.
The results are summarized in Tables 2 and 3.
The experimental results show that various ortho‐, meta‐
and para‐substituted aryl halides including aryl iodides,
aryl bromides and aryl chlorides having both electron‐
3
.3 | Catalytic studies
As a part of the present research, it was decided to
consider the catalytic activity of boehmite@tryptophan‐
Pd in some organic reactions including the synthesis
of biphenyl and butyl cinnamate derivatives (Scheme 2).
SCHEME 3 Boehmite@tryptophan‐Pd‐
catalyzed Heck reaction
TABLE 4 Optimization of reaction conditions for C–C coupling reaction of iodobenzene with butyl acrylate
a
Entry
Catalyst (mg)
Solvent
Base
Temperature (°C)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
—
DMSO
DMSO
DMSO
DMSO
DMSO
PEG
K
K
K
K
K
K
K
K
K
K
2
2
2
2
2
2
2
2
2
2
CO
CO
CO
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
3
3
3
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
r.t
One day
85
NR
45
0.015
0.030
0.075
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
0.105
85
68
85
87
85
95
85
68
DMF
85
87
Toluene
EtOH
85
41
85
86
10
11
12
13
14
15
16
17
18
19
20
H
2
O
85
Trace
83
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
Et
KOH
NaOH
3
N
85
85
37
85
46
Na
2
CO
3
85
85
—
500
85
NR
Trace
55
K
K
K
K
K
2
2
2
2
2
CO
CO
CO
CO
CO
3
3
3
3
3
80
85
100
110
130
85
71
85
84
85
96
a
Isolated yield.
b
Reaction conditions: aryl halide (1 mmol), boehmite@tryptophan‐Pd, butyl acrylate (1.2 mmol), base (3 mmol) and solvent (2 ml).

GHORBANI‐CHOGHAMARANI ET AL.
9 of 11
TABLE 5 Coupling of aryl halides with butyl acrylate in the
presence of catalytic amounts of boehmite@tryptophan‐Pd
withdrawing and electron‐donating groups produced
their corresponding biphenyl derivatives in good to excel-
lent yields. However, it is worth mentioning that the reac-
tion time for aryl halides with electron‐donating groups
on the aromatic ring was longer than that for aryl
halides with electron‐withdrawing groups. In order to
investigate the chemoselectivity of this new catalytic
system, the reaction of 1‐bromo‐4‐chlorobenzene was
also investigated in which the bromide showed more
reactivity (Tables 2 and 3, entry 10). This selectivity
allows an active halide site to remain for further
functionalization.
In the next experiment, the catalytic activity of
boehmite@tryptophan‐Pd for the Heck reaction was
examined (Scheme 3). For this purpose, the C–C cross‐
coupling reaction between iodobenzene and butyl acry-
late, in the presence of boehmite@tryptophan‐Pd, was
considered as a model reaction and performed under con-
ditions of various solvents and amounts of the catalyst to
elucidate the best reaction conditions (Table 4). Initially,
the effect of the amount of catalyst on the reaction was
studied, and this revealed that the highest yield
of product was obtained in the presence of 7 mg of
boehmite@tryptophan‐Pd. Meanwhile, in the absence of
the catalyst, the reaction did not proceed at all even after
Time Yield
a
Entry Aryl halide Product
(min) (%)
1
85
120
85
95
94
92
92
2
3
4
280
5
6
70
90
94
87
7
8
9
70
85
95
90
24 h (Table 4, entry 1). In the next step, the effect of
solvent was investigated, and the best result was obtained
with DMSO. Then, the effect of various bases was
investigated and K CO was selected as the most effective
2
3
80
300
360
450
96
92
92
91
base. Also, the effect of the temperature was studied,
with the highest yield of product being obtained at 120°C
(
Table 4, entries 9 and 10).
1
1
1
0
1
2
With the optimal conditions in hand, a variety of aryl
halides bearing various functional groups were examined.
The results presented in Table 5 show that the
boehmite@tryptophan‐Pd catalytic system worked very
well, and various types of aryl halides exhibited good
reactivities and the corresponding butyl cinnamate
derivatives were obtained in excellent yields.
1
1
1
3
4
5
750
700
660
88
90
95
3
.4 | Recyclability of catalyst
The reusability of a heterogeneous catalyst is an impor-
tant factor from an industrial point of view. Thus, the
recyclability of boehmite@tryptophan‐Pd was examined
via the Heck cross‐coupling reaction. After completion
of the reaction, the mixture was cooled to room temper-
ature, the catalyst was separated by simple filtration from
the reaction mixture and the filtered catalyst was washed
a
Isolated yield.
with CH Cl2 and EtOAc and then with hot doubly
distilled water several times. Afterwards, the recovered
catalyst from the model reaction was dried in an oven
b
2
Reaction conditions: aryl halide (1 mmol), boehmite@tryptophan‐Pd
0.105 mol%), butyl acrylate (1.2 mmol) and K CO (3 mmol) in DMSO at
(
2
3
1
20°C.

10 of 11
GHORBANI‐CHOGHAMARANI ET AL.
at 120°C for 4 h and was reused in the next run. This cat-
alyst was recycled and reused over five times without
significant loss of its catalytic activity (Figure 7).
an efficient support for palladium. The catalytic activity of
this nanostructural material was investigated in the
Suzuki, Stille and Heck C–C cross‐coupling reactions.
Our reported procedure offers the outstanding benefits of
excellent yields and green reaction conditions, easy cata-
lyst preparation, use of inexpensive and available mate-
rials, short reaction times, easy separation, catalyst
recyclability and high catalyst chemical stability.
3.5 | Leaching study
In order to determine the leaching of palladium into reac-
tion media, ICP‐OES analysis was performed. The palla-
dium content in reaction media in the synthesis of 1,1′‐
biphenyl (Suzuki reaction), 4‐methoxy‐1,1′‐biphenyl
ACKNOWLEDGMENTS
(Stille reaction) and butyl cinnamate (Heck reaction)
was found to be 0.72, 0.85 and 1.11%, respectively. The
results show that the leaching of palladium into reaction
media is negligible.
This work was supported by the research facilities of Ilam
University, Ilam, Iran. The Natural Sciences and Engi-
neering Research Council of Canada is gratefully
acknowledged for support (R.H.E.H.).
3.6 | Hot filtration test
ORCID
Also, the heterogeneity of boehmite@tryptophan‐Pd in the
reaction mixture was studied using the hot filtration test.
The hot filtration test was performed in Heck cross‐
coupling reaction as the model reaction under the
optimal reaction conditions. After 43 min (half the reaction
time), the reaction was terminated, and corresponding
product obtained in 55% yield. Then, the reaction was
repeated, and at half the reaction time, the catalyst was
separated by simple filtration from the reaction mixture
and the filtrate was allowed to react further (in the absence
of catalyst). We found that only a trace conversion (<6%)
of the coupling reaction was observed upon heating of
the catalyst‐free solution for another 43 min.
Arash Ghorbani‐Choghamarani
002-7212-1317
Masoud Mohammadi
470
https://orcid.org/0000-
0
https://orcid.org/0000-0002-1043-
3
Taiebeh Tamoradi https://orcid.org/0000-0002-8548-271X
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