Pd–ninhydrin immobilized on magnetic nanoparticles: synthesis, characterization, and application as a highly efficient and recoverable catalyst for Suzuki–Miyaura and Heck–Mizoroki C–C coupling reactions

Article abstract of DOI:10.1007/s13738-019-01833-w

Abstract: In this work by controlling the interaction between the inorganic complexes and the support material, we have designed a high-activity nanostructured combined of magnetic nanoparticles and Pd–ninhydrin-terminated complex as catalyst. The as-prepared catalyst was characterized by FT-IR, XRD, VSM, SEM, EDAX, ICP, and TGA techniques. This magnetic nanostructure can be used as a novel, green, and efficient heterogeneous catalyst for Suzuki–Miyaura and Heck–Mizoroki C–C coupling reactions. This catalyst showed promising catalytic activity and excellent yields toward various aryliodides and arylbromides in mild reaction conditions. In Suzuki–Miyaura reactions, various aryl halides (I, Br) were coupled with phenyl boronic acids in 5?mg of catalyst and 8?mg of catalyst used for Mizoroki–Heck reaction of aryl halides (I, Br) with n-butyl acrylate or acrylonitrile. The catalyst was reusable and recycled six times without a significant loss in activity and leaching of palladium. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s13738-019-01833-w

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01833-w
ORIGINAL PAPER
Pd–ninhydrin immobilized on magnetic nanoparticles: synthesis,
characterization, and application as a highly efcient and recoverable
catalyst for Suzuki–Miyaura and Heck–Mizoroki C–C coupling
reactions
Maryam Hajjami1 · Zeinab Shirvandi1
Received: 24 May 2019 / Accepted: 16 December 2019
© Iranian Chemical Society 2020
Abstract
In this work by controlling the interaction between the inorganic complexes and the support material, we have designed a high-
activity nanostructured combined of magnetic nanoparticles and Pd–ninhydrin-terminated complex as catalyst. The as-prepared
catalyst was characterized by FT-IR, XRD, VSM, SEM, EDAX, ICP, and TGA techniques. This magnetic nanostructure can be
used as a novel, green, and efcient heterogeneous catalyst for Suzuki–Miyaura and Heck–Mizoroki C–C coupling reactions.
This catalyst showed promising catalytic activity and excellent yields toward various aryliodides and arylbromides in mild
reaction conditions. In Suzuki–Miyaura reactions, various aryl halides (I, Br) were coupled with phenyl boronic acids in 5 mg
of catalyst and 8 mg of catalyst used for Mizoroki–Heck reaction of aryl halides (I, Br) with n-butyl acrylate or acrylonitrile.
The catalyst was reusable and recycled six times without a signifcant loss in activity and leaching of palladium.
Graphic abstract
Keywords Pd–ninhydrin complex · Fe3O4 · Suzuki reaction · Heck reaction · C–C coupling
Extended author information available on the last page of the article
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
catalytic application in Kabachnik–Fields multicomponent
reaction. Subsequently in 2017, Heidarizadeh et al. [26] have
reported the immobilization of an enzyme (lipase) to Fe3O4/
GO nanocomposite, and in 2018, Rakhtshah et al. [27] have
reported copper Schif base complex immobilized on silica-
coated magnetic nanoparticles as catalyst for the synthesis
of polysubstituted pyrroles.
Introduction
An interesting goal in green chemistry is the development
and improvement of the catalytic processes and homogene-
ous catalysts, which include removal of toxic and expensive
reagents, minimization of by-products, and simplifcation
of workup procedures [1]. Homogeneous catalyst has the
advantage due to accessibility of all catalytic sites to reac-
tants in solution and, possibility to tune the chemo, regio
and enantio selectivity of the catalyst, high selectivity, better
yield, and higher turnover numbers. Although homogeneous
catalysts are very active and are widely used in a number of
commercial applications, but have two main problems, time
consumed for the catalyst separation from the reaction mix-
ture and tedious recovery process. One efcient way to solve
these problems in homogeneous catalysis is the heterogeni-
zation of active catalytic molecules which would be the use
of a heterogeneous catalyst [2–5]. Despite the advantages of
heterogeneous catalysis, such as easy separation, efcient
recycling, minimization of metal traces in the product, and
waste disposal, they having lower reactivity and selectivity
than corresponding homogeneous catalysts. Therefore, there
is need to a catalyst system that can show high activity and
selectivity on one hand, and also the ease of catalyst separa-
tion and recovery on the other hand [6–8].
Suzuki–Miyaura and Heck–Mizoroki cross-coupling
reactions are versatile and important methods for C–C bond
formation in organic synthesis. These reactions have many
applications in industrial processes such as the synthesis
of natural products, organic building blocks, biologically
active compounds, pharmaceuticals, and agricultural deriva-
tives [28–32]. The Suzuki and Heck C–C cross-coupling
reactions catalyzed by palladium catalyst in the presence
of phosphine auxiliary ligands. However, there are several
problems in usage of palladium–phosphine systems like
separation, recovery, and catalyst instability at high tem-
peratures; moreover, phosphine ligands are toxic, expensive,
and sensitive to air, which also limit their use in large-scale
industrial application [33–36]. Therefore, the development
of new heterogeneous phosphorus-free catalysts for the reac-
tions under mild conditions is of immense interest, and there
are reports of C–C coupling reactions with several hetero-
geneous catalysts [37–40]. In continuation of our research
[41–43], herein, we report the preparation of novel, ef-
cient, and green Fe3O4–Schif base–Pd complex as catalyst
(Scheme 1), and its high catalytic activity in carbon–carbon
bond formation reactions. Moreover, the catalyst separation
is done easily by an external magnet and the nanocatalyst
can be reused for several times without signifcant degrada-
tion in activity.
With the development of nanoscience and nanotechnol-
ogy, chemists achieved the various catalytic reactions due
to a wide variety of nanostructured catalysts or immobi-
lization of homogeneous catalysts on nanostructured sup-
ports such as mesoporous molecular sieve (MCM-41 [9],
MCM-48 [10], and SBA-15 [11]), metal organic framework
materials [12] bohemite [13], polymers [14], and graphene
oxide [15]. Recently, magnetic nanoparticles (MNPs) have
attracted great interest due to their remarkable advantages
such as small size, large specifc surface area, excellent cata-
lytic activity and selectivity, easy synthesis and functionali-
zation, and high dispersion property as well as low toxicity
and price. Moreover, the intrinsic advantage of magnetic
nanoparticles is that it can be efective and easily separated
from the reaction mixture by applying an external mag-
netic without using of tedious fltration. Thus, novel nano-
particles efciently bridge the gap between homogeneous
and heterogeneous catalysis that preserving the desirable
attributes of both systems [16–21]. In recent years, there
are several reports of magnetic nanocatalysts that contain
various metal complexes (Cu, Pd, Mo) which are used for
oxidation of sulfdes and oxidative coupling of thiols [22],
Mannich reaction [23], and Suzuki coupling reactions [24].
Also, in 2015, Rostamnia et al. [25] have reported the suc-
cessful synthesis of water-dispersed magnetic nanoparticles
(H2O-DMNPs) of β-cyclodextrin modifed Fe3O4 and their
Experimental
Preparation of the Fe3O4 magnetic nanoparticles
(MNPs)
The mixture of FeCl3·6H2O (5.838 g, 0.0216 mol) and
FeCl2·4H2O (2.147 g, 0.0108 mol) was dissolved in 100 mL
deionized water at 80 °C under N2 atmosphere and vigorous
mechanical stirring conditions, until the salts dissolved com-
pletely. Then, 10 mL of 25% NH4OH was added quickly into
the reaction mixture and stirring was continued for 30 min.
After 30 min, the reaction mixture was cooled to room tem-
perature, and the black precipitate obtained was magneti-
cally separated and washed several times by distilled water.
Finally, the 2.5 g of the magnetic nanoparticles (MNPs)
recovered.
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Journal of the Iranian Chemical Society
were added, and the mixture was refuxed for 24 h under
N2 atmosphere. Then, the reaction mixture was cooled, the
precipitate was separated by magnetic decantation, washed
several times by dry ethanol to remove the unattached sub-
strates. The 1.2 g of the nanoparticles product (Fe3O4–Schif
base) was dried at room temperature.
Preparation of MNPs coated by 3‑amino propyl
triethoxy silane (Fe3O4–NH2)
The obtained magnetic nanoparticles (MNPs) powder (1.5 g)
was dispersed in 250 mL solution of ethanol and water (vol-
ume ratio, 1:1) by sonication for 30 min. Then, 3 mL of
3-aminopropyltriethoxysilane was added to the reaction
mixture at 33–38 °C under N2 atmosphere and mechanical
stirring conditions for 8 h. The resulting product was sepa-
rated by an external magnet and washed thoroughly with dry
ethanol and dried under vacuum at room temperature that
the 1.65 g of the amino-functionalized MNPs (Fe3O4–NH2)
obtained.
Preparation of Fe3O4–Schif base–Pd catalyst
The Fe3O4–Schif base (1 g) were dispersed in 20 mL dry
ethanol, and solution by ultrasonic bath for 20 min, and then
Pd(OAc)2 (0.5 g) was added reaction mixture. The result-
ing mixture was refuxed for 20 h under nitrogen atmos-
phere. Subsequently, excess of 0.203 g (1.2 mol) NaBH4
were added to the reaction mixture for the reduction of Pd
particles, and the reaction mixture was refuxed for 2 h under
N2 atmosphere. After that, the fnal product was magneti-
cally separated and washed with copious amounts of dry
ethanol and dried at room temperature and the 1.15 g of the
Fe3O4–Schif base–Pd catalyst obtained.
Preparation of Fe3O4 functionalized ninhydrin–
Schif base (Fe3O4–Schif base)
The amino-functionalized MNPs (1 g) were dispersed in
dry ethanol (10 mL) by ultrasonic bath for 20 min. Subse-
quently, ninhydrin (0.534 g, 3 mmol) and 0.5 mL acetic acid
Scheme 1 Synthesis of Fe3O4–
Schif base–Pd
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General procedure for the Suzuki reaction
The Fe3O4–Schif base–Pd (0.91 mol%) was added to mix-
ture of aryl halides (1 mmol), phenylboronic acid (1 mmol)
and K2CO3 (3 mmol) in 2 mL of PEG-400 (polyethylene gly-
col) at 80 °C, and the mixture was stirred for the appropriate
time. Completion of the reaction was indicated using TLC.
After completion of the reaction, the catalyst was separated
with an external magnet, then product was extracted with
10 mL of H2O and ethyl acetate (3×10 mL). The organic
layer was dried over Na2SO4. Then, the solvent was evapo-
rated, and corresponding biphenyl was obtained in good to
high yield.
Fig. 2 XRD pattern of Fe3O4 (a), Fe3O4–Schif base–Pd (b) and
reused catalyst (c)
General procedure for the Heck reaction
A mixture of aryl halides (1 mmol), n-butyl acrylate (or
acrylonitrile) (1.2 mmol), K2CO3 (1.5 mmol) (base for acry-
lonitrile Na2CO3 3 mmol), 2 mL of PEG-400 (polyethylene
glycol) and Fe3O4–Schif base–Pd catalyst (1.46 mol%) was
stirred at 120 °C temperature for an appropriate time. The
progress of the reaction was monitored using TLC. After
completion of the reaction, the reaction mixture was cooled
to room temperature. The catalyst was separated using a
Fig. 3 TGA diagram of Fe3O4 (MNPs) (a), Fe3O4–Schif base–Pd (b)
Fig. 4 VSM curve of Fe3O4 nanoparticles (a), Fe3O4–Schif base–Pd
(b)
magnet, then mixture was diluted with 10 mL of H2O and
extracted with diethyl ether (3×10 mL) and the organic layer
was dried over anhydrous Na2SO4. Then, the solvent was
evaporated, and the desired products was obtained.
Fig. 1 FT-IR spectra of Fe3O4 (MNPs) (a), Fe3O4–NH2 (b), Fe3O4–
Schif base (c), Fe3O4–Schif base–Pd (d), reused Fe3O4–Schif base–
Pd (e)
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Journal of the Iranian Chemical Society
Fig. 5 SEM images of Fe3O4–Schif base–Pd at 500 nm (a) and 200 nm (b)
Fe3O4–Schif base could also be obtained by the reaction of
amine groups of APTES supported on Fe3O4 nanoparticles
and ninhydrin ligand. Finally, the supported magnetic nano-
catalyst Fe3O4–Schif base–Pd was prepared via reaction of
palladium(II) acetate and Fe3O4–Schif base. Eventually, the
supported magnetic nanocatalyst was obtained and charac-
terized by diferent techniques such as FT-IR, XRD, TGA,
ICP, VSM, SEM, and EDX-MAP.
Catalyst characterization
The catalyst has been characterized by Fourier transform
infrared spectroscopy (FT-IR, Bruker, Germany), X-ray dif-
fraction (XRD, GBC-Diftech MMA), thermogravimetric
analysis (TGA, PerkinElmer Pyris Diamond, UK), induc-
tively coupled plasma atomic emission spectrometry (ICP-
OES, Optima 8000, PerkinElemr), vibrating sample mag-
netometer (VSM, MDKFD), scanning electron microscopy
(SEM, FESEM-TESCAN MIRA3), and energy dispersive
X-ray spectroscopy (EDS, FESEM-TESCAN MIRA3).
FT-IR spectrum for the samples of Fe3O4 MNPs (a), Fe3O4
nanoparticle functionalized with APTES (Fe3O4–NH2) (b),
Fe3O4–Schif base (c) and Fe3O4–Schif base–Pd catalyst
(d) is shown in Fig. 1. The FT-IR spectrum for the MNPs
(a) shows a stretching vibration of –OH group at about
3440 cm−1, which are attached to the surface iron atoms.
The strong absorption at 581 cm−1 is the characteristic of the
Fig. 6 EDS spectrum of Fe3O4–Schif base–Pd
Results and discussions
Scheme 1 was shown the detail synthetic procedure for the
preparation of Fe3O4–Schif base–Pd as novel magnetic
nanoparticle catalyst. The procedure for the synthesis of
Fe3O4 nanoparticle is presented in the literature [42]. In
the next step, the 3-amino propyl triethoxy silane (APTES)
supported on Fe3O4 nanoparticle (Fe3O4–NH2) was synthe-
sized according to the reported procedure [44], and then,
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Journal of the Iranian Chemical Society
Table 1 Optimization of diferent parameters for the Suzuki reaction of iodobenzene with phenyl boronic acid in the presence of Fe3O4–Schif
base–Pd
Entry
Solvent
Base
Temp (°C)
Cat. (mol%)
Time (min)
Yielda (%)
1
PEG
H2O
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
–
60
60
60
60
60
60
60
60
60
60
60
40
80
60
60
60
60
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
0.91
–
20
15
20
20
20
300
20
20
20
20
20
20
15
1440
20
20
20
98
95
75
64
52
–
50
63
50
20
64
38
95
–
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
EtOH
DMSO
DMF
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
Et3N
Na2CO3
EtONa
KOH
K2COb3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
0.18
0.54
1.28
55
76
98
Reaction condition: iodobenzene (1 mmol), phenyl boronic acid (1 mmol), base (3 mmol), and solvent (2 mL)
Bold indicates opimized condition
aIsolated yield
bK2CO3 =1.5 mmol
Fe–O stretching vibration, which demonstrates the existence
of Fe3O4 components. In the FT-IR spectrum of Fe3O4–NH2
(b), the existence of the anchored 3-aminopropyl triethoxy
silane (APTES) is confirmed by stretching vibration of
aliphatic C–H group that appear at 2920 cm−1, and also
a broad band appears at 3396–3432 cm−1 and 1004 cm−1,
which is related to the N–H and Si–O stretching vibrations,
respectively. A new band observed in FT-IR spectrum of
Fe3O4–Schif base (c) at 1717 cm−1 can be attributed to the
carbonyl bonds and the band observed at 1626 cm−1 could
be assigned to the C=N stretching vibrations. These bands
are evidence that ninhydrin has been successfully attached
with terminal amine in Fe3O4–NH2 and also confrm to the
formation of Fe3O4–Schif base. In the FT-IR of catalyst (d),
the C=N bond shifted to a lower wave number and appear at
1594 cm−1, which indicate the formation of Pd Schif base
complexes. The spectrum of the recovered Fe3O4–Schif
base–Pd (e) shows that the catalyst is stable during the
reaction.
Fe3O4 at 2θ = 30.3°, 35.7°, 43.3°, 53.7°, 57.3°, and 62.9°
corresponding to the refections of (2 2 0), (3 1 1), (4 0 0), (4
2 2), (5 1 1), and (4 4 0). The XRD pattern of Fe3O4–Schif
base–Pd catalyst matches well with the characteristic peaks
of bare Fe3O4, which indicates retention of the crystalline
spinel ferrite core structure during functionalization of
MNPs. The new peaks appeared at 2θ=39.8, 47.6 and 67.4
which attributed to the Pd species. The XRD diagram of
reused catalysts shows that the structure of catalyst is stable
during the reaction.
The thermogravimetric analysis (TGA) was used to deter-
mine the thermal stability and percentage of chemisorbed
organic functional groups on the surface of the magnetic
nanoparticles. The TGA curve of the bare Fe3O4 nanoparti-
cles (a) and Fe3O4–Schif base–Pd (b) shows the mass loss
of the organic groups as it decomposes upon heating (Fig. 3).
The weight loss about 4% in the TGA curve of Fe3O4, at
temperatures below 200 °C is assigned to the removal of
physically adsorbed organic solvents and surface –OH
groups (Fig. 3a). Moreover, the weight loss occurs about
5% in the temperature range between 250 and 630 °C may be
due to the thermal crystal phase transformation from Fe3O4
Crystal structure of synthesized nanocatalysts was inves-
tigated by X-ray powder difraction analysis (XRD) (Fig. 2).
The XRD pattern shows the characteristic peaks of bare
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Journal of the Iranian Chemical Society
Table 2 Suzuki coupling of
various aryl halides with phenyl
boronic acid catalyzed by
Fe3O4–Schif base–Pd catalyst
Time
(min)
Entry
Aryl halide
Yield (%)a TOF (h-1)
MP (°C) [Ref.]
66–68 [46]
1
2
20
70
98
93
324.5
87.6
44–46 [47]
3
4
90
80
91
97
66.3
79.7
Oil [48]
84–86 [49]
5
8
60
30
96
91
104.9
198.9
Oil [50]
66–68 [46]
9
80
95
93
78
44–46 [47]
84–86 [49]
10
165
36.9
11
75
98
85.6
Oil [51]
12
13
14
35
50
55
99
98
98
186.5
129
156–159 [52]
112–114 [51]
83–86 [52]
116.9
15
16
60
75
90
92
98.3
80.4
56–58 [53]
48–50 [50]
17
30
88
192.3
Viscous liquid [54]
18
19
40
96
158.9
36.61
70–72 [55]
120
67b
112–114 [51]
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Table 2 (continued)
Reaction condition: aryl halides (1 mmol), phenyl boronic acid (1 mmol), K2CO3 (3 mmol), Fe3O4–Schif
base–Pd (0.91 mol%) in 2 mL of PEG and at 60 °C
aIsolated yield
bFe3O4–Schif base–Pd (1.83 mol%) in 2 mL of PEG and at 80 °C
Scheme 2 Mechanism of the Fe3O4–Schif base–Pd catalyzed Suzuki reaction
to γ-Fe2O3 [45]. There are three weight loss steps in the
TGA curve of Fe3O4–Schif base–Pd (Fig. 3b). Firstly, indi-
cates a weight loss at about 5% below 200 °C which is owing
to the removal of water molecules from the catalyst surface.
The steps two and three of weight losses at 200–800 °C
may correspond to the degradation of 3-(aminopropyl)
triethoxysilane groups and organic ligands in the Schif
base–Pd complex.
The magnetic property of Fe3O4 nanoparticles and
Fe3O4–Schiff base–Pd recorded at room temperature
using a vibrating sample magnetometer (VSM) tech-
nique (Fig. 4). The magnetic measurement shows that the
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Table 3 Optimization of diferent parameters for the Heck reaction of iodobenzene with n-butyl acrylate in the presence of Fe3O4–Schif base–
Pd
Entry
Solvent
Base
Temp (°C)
Cat. (mol%)
Time (min)
Yielda (%)
1
PEG
H2O
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
–
120
120
120
120
120
120
120
120
120
120
120
80
100
120
120
120
120
1.46
1.46
1.46
1.46
1.46
1.46
1.46
1.46
1.46
1.46
1.46
1.46
1.46
–
10
10
10
10
10
300
10
10
10
10
10
10
10
1440
10
10
10
98
25
20
78
83
–
87
75
40
20
95
50
90
–
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
EtOH
DMSO
DMF
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
Et3N
Na2CO3
EtONa
NaHSO4
K2COb3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
0.73
1
1.83
88
90
98
Reaction condition: aryl halides (1 mmol), n-butyl acrylate (1.2 mmol), base (1.5 mmol), and solvent (2 mL)
Bold indicates opimized condition
aIsolated yield
bK2CO3 =3 mmol
Fe3O4–Schif base–Pd has a saturated magnetization value of
49.9 emu g−1. The VSM curve of the Fe3O4 nanoparticle is
71 emu g−1 which has higher magnetic value in comparison
with synthesized nanocatalyst. Decrease in magnetic prop-
erty of Fe3O4–Schif base–Pd is due to the coating of silica
and the attached of organic layers on Fe3O4 nanoparticles.
The morphology and nanoparticle size of the catalyst was
characterized by scanning electron microscopy. The SEM
images of the Fe3O4–Schif base–Pd nanocatalyst at difer-
ent magnifcations are shown in Fig. 5. According to Fig. 5,
the surface morphology of the catalyst shows uniform and
spherical particles with size of less than 24 nm.
Catalytic study
After preparation of Fe3O4–Schif base–Pd, its catalytic
activities were evaluated for C–C bond forming reactions
such as the Suzuki–Miyaura and Mizoroki–Heck coupling
reaction. For this purpose, the Suzuki coupling reaction
of iodobenzene with phenyl boronic acid was chosen as a
simple model reaction to optimize the reaction conditions,
including catalyst amount, solvent, base and efect of tem-
perature (Table 1). Initially, diferent solvents such as H2O,
dimethylformamide (DMF), dimethylsulfoxide (DMSO),
polyethylene glycol (PEG-400), and ethanol were examined
(entries 1–5) in the presence of 0.91 mol% of Fe3O4–Schif
base–Pd. In both PEG (98%) and water (95%) (entries 1
and 2), high yields of the product were observed, but trace
amounts of products were obtained in Suzuki reaction of the
various aryl halides with phenyl boronic acid in water; thus,
PEG was as the best solvent for this reaction. To investigate
the efect of bases in the model reaction, various bases such
as K2CO3, Na2CO3, EtONa, Et3N, and KOH were examined
(entries 7–10). In the case of K2CO3, the catalyst was very
The energy dispersive X-ray spectroscopy (EDS) spec-
trum shows the presence of various elements in the catalyst
(Fig. 6).
The amount loading of Pd on the Fe3O4–Schif base,
determined by inductively coupled plasma atomic emis-
sion spectrometry (ICP-AES). The ICP analysis showed
amount of Pd in catalyst was 1.88 × 10−3 mol g−1. Also
analysis of the recovered catalyst by the ICP technique was
1.80 × 10−3 mol g−1 indicates that the leaching of the Pd
metal was negligible and about 0.72%.
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Journal of the Iranian Chemical Society
Table 4 Heck coupling of
various aryl halides with
n-butyl acrylate or acrylonitrile
catalyzed by Fe3O4–Schif
base–Pd catalyst
Time
(min)
Yield
Entry
Aryl halide
Reagent
TOF (h-1) MP (°C) [Ref.]
(%)a
1
a
a
10
15
98
419.5
268.4
Oil [57]
Oil [55]
2
98
99
92
3
4
5
a
a
a
30
30
60
135.6
126
65
Oil [55]
Oil [55]
Oil [55]
95
88
6
a
30
120.5
Oil [57]
7
8
9
a
a
a
60
80
90
90
98
61.6
46.3
29.8
Oil [55]
40–42 [58]
Oil [58]
135
10
11
12
13
14
15
a
a
b
b
b
b
270
285
50
88b
80b
92
13.3
11.5
74.2
20.5
32.4
10.9
Oil [57]
40–42 [58]
Oil [59]
Oil [60]
Oil [59]
Oil [60]
180
105
300
90
83
80
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Journal of the Iranian Chemical Society
Table 4 (continued)
Reaction condition reagent (a): aryl halides (1 mmol), n-butyl acrylate (1.2 mmol), K2CO3 (1.5 mmol),
Fe3O4–Schif base–Pd (1.46 mol%) in 2 mL of PEG and at 120 °C. Reaction condition reagent (b): aryl
halides (1 mmol), acrylonitrile (1.2 mmol), Na2CO3 (3 mmol), Fe3O4–Schif base–Pd (1.46 mol%) in 2 mL
of PEG and at 120 °C
aIsolated yield
bReaction condition: aryl halides (1 mmol), n-butyl acrylate (1.2 mmol), K2CO3 (3 mmol), Fe3O4–Schif
base–Pd (2.1 mol%) in 2 mL of PEG and at 120 °C
Scheme 3 Mechanism of the Fe3O4–Schif base–Pd catalyzed Heck reaction
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Journal of the Iranian Chemical Society
active and best yield of product obtained for the reaction
(entry 1), when the amount of K2CO3 from 3 to 1.5 mmol
was decreased, lower yield is obtained (entry 11). In the next
step, this model reaction by diferent temperatures including
40, 60, and 80 °C was examined, and the best results were
obtained in temperature of 60 °C. Increasing the temperature
to 80 °C, did not efectively increase the yield of product
(entry 13).
yield was obtained at 120 °C (entries 12–13). In addition,
diferent amounts of catalyst were investigated for this
reaction, and 1.46 mol% of catalyst was found to optimal
amount (entries 15–17). The higher amounts of catalyst,
the desired product was obtained in an almost similar
yield. After the optimized reaction conditions, to investi-
gate the scope of the catalytic system in Heck reaction, the
coupling of various aryl halides with n-butyl acrylate was
examined and the results are shown in Table 4.
Finally, to optimize the catalyst amount, diferent quan-
tities of catalyst were evaluated in the model reaction. As
shown in Table 1, for the coupling reaction in the absence
of catalyst, no formation of product occurs after 24 h (entry
14), but experiments showed that 0.91 mol% of catalyst
are the sufcient amount for the completion of the reac-
tion. Using more of catalyst did not efectively increase on
the yield or decrease time of the reaction (entry 17). With
the optimized reaction conditions, the generality and scope
of the catalytic utility of Fe3O4–Schif base–Pd catalyst in
Suzuki reaction was demonstrated with a range of aryl hal-
ides (chlorides, bromides and iodides) and phenyl boronic
acid (Table 2). The biphenyl derivatives were obtained
in satisfactory yields and the results are summarized in
Table 2. However, the results of the Suzuki coupling reac-
tions depend on the type of halide element, the positions of
the substitution groups on aromatic ring and the efect of
various electron donating and electron withdrawing groups.
The catalyst high activity and excellent yield of products
were obtained in reaction of aryl iodides and bromides with
phenyl boronic acid.
The results demonstrated that the Fe3O4–Schif base–Pd
catalyst was efective for the couplings of the aryl hal-
ides with both electron withdrawing and donating groups
with butyl acrylates. To extend the scope of our work, we
next examined the coupling of various aryl halides with
acrylonitrile (1.2 mmol), in the presence of 1.46 mol% of
catalyst, PEG and 3 mmol of Na2CO3 as base at 120 °C.
The results are summarized in Table 4. In the Heck reac-
tion, the reaction time of aryl iodides and aryl bromides
were less than aryl chlorides.
The proposed mechanism for Heck reaction in the pres-
ence of Fe3O4–Schif base–Pd catalyst was outlined in
Scheme 3 [56].
Recyclability of the catalyst
The recycling of the heterogeneous catalysts is an impor-
tant advantage for commercial applications. To investigate
this issue, the recovery and reusability of the catalyst was
examined for a Suzuki reaction of iodobenzene and phe-
nyl boronic acid, and a Heck reaction of iodobenzene and
n-butyl acrylate as model reactions under the optimized con-
ditions. After the completion of reaction, the catalyst was
simply separated from the reaction mixture using an external
magnet and washed with water and ethanol to remove of
organic residuals, dried and reused for next runs. As shown
in Fig. 7, the catalyst can be recovered for six runs without
any signifcant loss in its catalytic activity and performance.
The suggested mechanism for Suzuki reaction in the
presence of Fe3O4–Schif base–Pd catalyst is outlined in
Scheme 2 [56].
In the second part of our organic program, the applica-
tion of Fe3O4–Schif base–Pd catalyst was examined in the
Heck cross-coupling reaction of aryl halides and olefns
in the presence of a base. For fnding the optimal reac-
tion conditions, the Heck reaction of iodobenzene with
n-butyl acrylate was chosen as a model reaction, and vari-
ous parameters such as catalyst amount, kind of solvent,
efects of bases and temperature were investigated for
the model reaction (Table 3). Initially, diferent solvents
including H2O, EtOH, DMF, DMSO and PEG-400 were
examined and the best results for the Heck reaction were
obtained in PEG (entry 1). Also, the efects of diferent
bases were examined. The highest yield in the shortest
reaction time was achieved using 1.5 mmol of K2CO3.
While use of Na2CO3 and Et3N give moderate yields and
in the presence of other bases, EtONa and NaHSO4 low-
to-moderate yields of product are obtained (entries 7–10).
The use of 3 mmol amount of K2CO3 does not efectively
increase on the yield and time of the reaction (entry 11).
Evaluation of the model reaction under diferent tempera-
tures such as 80, 100, and 120 °C has shown that greatest
Fig. 7 Recyclability of Fe3O4–Schif base–Pd in the Suzuki–Miyaura
and Heck–Mizoroki model reaction
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Journal of the Iranian Chemical Society
Table 5 Comparison results of Fe3O4–Schif base–Pd with other catalysts for the coupling of iodobenzene with phenylboronic acid
Entry Catalyst
Condition
Time (min) Yield (%) TOF (h−1
)
References
1
2
Pd(II)–NHC complex (0.01 mmol)
DMA, Cs2CO3, 100 °C
H2O, K2CO3, 100 °C
24 h
180
99
97
4.1
32.3
[57]
[61]
N,N′-bis(2-pyridinecarboxamide)-1,2-
benzene palladium complex (1 mol%)
3
4
5
6
7
8
9
10
Pd/TiO2 (0.7 mol%)
NMP:H2O, Na2CO3, 120 °C, N2
240
120
90
70
900
15
97
99
97
92
83
95
98
98
34.6
495
129
138.3
5.17
292
[62]
[63]
[64]
[41]
[37]
[42]
[56]
This work
PdeSchif base@MWCNTs (0.1 mol%) K2CO3, DMF/H2O (v/v ¼ 1:1), 60 °C
Pd@SBA-15/ILDABCO (0.5 mol%)
Pd-TEDETA-MCM-41 (0.57 mol%)
(ZrO)2Fe2O5
HMS–CPTMS–Cy–Pd (0.008 g)
Pd(0)-Arg-boehmite (8 mg, 1.08 mol%) Na2CO3, PEG, 80 °C
Fe3O4–Schif base–Pd (0.91 mol%) K2CO3, PEG, 60 °C
K2CO3, H2O, 80 °C
H2O, Na2CO3, 60 °C, r.t
KOH, DMSO, 110 °C
K2CO3, PEG, 100 °C
45
20
121
324.5
catalyst ofers several advantages including high catalytic
activity, excellent yields, short reaction time, and mild
reaction conditions. Furthermore, the catalyst could be
simply recovered from the reaction mixture using an exter-
nal magnet and reused up to 6 times without a signifcant
loss in activity.
Hot fltration test
Also hot fltration test was examined to discard the possi-
bility of palladium leaching. In this light, we studied a hot
fltration technique for the Suzuki coupling of 4-boromoben-
zonitrile with phenylboronic acid. This reaction carried out
at 55 min and yield of product was 98%. We repeated the
reaction and yield of product in half time of the reaction was
55%. In another same reaction after 25 min, catalyst was
separated by an external magnet and washed with hot etha-
nol, and then the solution was allowed to go for the remain-
ing half stirring. After purifcation, yield of product was
obtained 52%. This test indicates that the leaching of the Pd
metal was negligible.
Acknowledgements This work was supported by the research facilities
of Ilam University, Ilam, Iran.
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Afliations
Maryam Hajjami1 · Zeinab Shirvandi1
1
* Maryam Hajjami
Department of Chemistry, Faculty of Science, Ilam
mhajjami@yahoo.com; m.hejami@ilam.ac.ir
University, P.O. Box 69315516, Ilam, Iran
1 3