Suzuki, Stille and Heck cross-coupling reactions catalyzed by Fe3O4@PTA-Pd as a recyclable and efficient nanocatalyst in green solvents

Article abstract of DOI:10.1039/c6nj00088f

The use of a supported Pd complex on magnetic nanoparticles as an efficient and green catalyst for the Suzuki, Stille and Heck cross-coupling reactions is presented. The present research is focused on investigating the recycling, reusability and stability of the catalyst in the reaction. The recycled Fe₃O₄@PTA-Pd catalyst was used at least five times with comparable activities to that of the fresh catalyst. The catalytic coupling of 4-bromotoluene as a model reaction suggested that there was no leached palladium in the reaction mixture. The structure of the catalyst was characterized by TGA, EDS, ICP-OES, XRD, VSM, FT-IR and SEM analysis.

Full text of DOI:10.1039/c6nj00088f

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New Journal of Chemistry
ARTICLE
Suzuki, Stille and Heck cross-coupling reactions catalyzed by
Fe O @PTA-Pd as recyclable and efficient nanocatalyst in green
3
4
Received 00th January 20xx,
Accepted 00th January 20xx
solvents
DOI: 10.1039/x0xx00000x
Arash Ghorbani-Choghamarani,* Masoumeh Norouzi
www.rsc.org/
The use of supported Pd complex on magnetic nanoparticles as an efficient and green catalyst for the Suzuki, Stille and
Heck cross-coupling reaction is presented. The present research is focused on investigation of recycling, reusability and
3 4
stability of the catalyst in the phase reaction. The recycled Fe O @PTA-Pd catalyst was used at least five times with
comparable activities to that of fresh catalyst. The catalytic coupling of 4-bromotoluene as a reference reaction suggested
that there were no leached palladium in the reaction mixture. The structure of the catalyst characterized by TGA, EDS,
ICP–OES, XRD, VSM, FT-IR and SEM analysis.
disciplines including physics, biomedicine, biotechnology, material
science and catalysis support applications [9-11]. Additionally, the
MNP-supported catalysts show high dispersion and reactivity with a
Introduction
Mounting interest is recently expressed for surface
functionalization of nanocatalysts in which the nanoscale
architecture of active centre plays a dominant role in determining
their efficiency and selectivity [1-4]. In this regard, the use of
supported magnetic nanoparticles (MNPs) materials has been
efficiently employed as heterogeneous catalysts. The main
advantage of a catalytic system based on magnetic nanoparticles is
that the nanoparticles can be efficiently isolated from the product
high degree of chemical stability. By utilizing these advantages of
magnetic nanoparticles over other supporting materials, various
catalysts and ligands have been immobilized on these particles,
successfully [12]. Reactions leading to the formation of C-C bonds
are important to the synthesis of complex organic molecules.
Among these reactions, the Suzuki–Miyaura [13], Stille reaction [14]
and Heck–Mizoroki [15] reactions have been widely used for
construction of a carbon–carbon bond [16]. These reactions have
been widely used for the assembly of complex organic molecules in
a broad range of applications in the chemical and pharmaceutical
industries [17]. The traditional Suzuki reaction usually precedes
using phosphine-based palladium catalysts, and there has been
considerable recent interest in the development of new catalysts
that are environmentally benign and efficient. Some significant
advances have been made, including the use of water-soluble
phosphines as ligands [18], microwave technology [19], nucleophilic
carbene ligands [20], ionic liquids [21], and so on. In this paper, we
will focus on the investigation of a novel and heterogeneous
solution through
a simple magnetic separation process after
completing the reaction [5]. According to the green chemistry
principles [6], the “green” catalyst is the one that can be simply
removed from the reaction mixture and reused in the next run.
Nanoparticles have emerged as efficient alternative supporting
materials for homogeneous catalyst immobilization [7, 8]. These
nanoparticles, because of their high surface area and unique
magnetic properties, have a broad range of potential uses in
3 4
nanocatalyst (named as Fe O @PTA-Pd) in the C–C cross-coupling
reactions. Catalyst reusability and hot filtration were also studied.
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ARTICLE
New Journal of Chemistry
disintegrates the supported organic compound with a calculated
loss of 29.86%.
Results and discussion
Characterization of the Fe O @PTA-Pd nanocatalyst
3
4
Scheme 1 illustrates the detail synthetic procedure for the
Fe -tridentate-Pd complex. Magnetic nanoparticles were
3
O
4
1
00
prepared through chemical coprecipitation method, and
subsequently were coated with tridentate ligand (TEDETA) to
achieve functionalized magnetic nanoparticles. Ultimately, the
(a)
9
8
7
6
0
0
0
0
3 4 2
Fe O @PTA-Pd complex were prepared by reactions of Pd(OAc)
with the individual ligand MNP-TEDETA in ethanol. TEDETA was
chosen as a ligand for chelating Pd due to the fact that Pd-N
bonding interactions were stable and inert toward cleavage.
0
200
400
600
800
1000
Temperature (°C)
100
(b)
9
8
7
6
0
0
0
0
Mass Change
2
9.86%
0
200
400
Temperature (°C)
600
800
Figure 1. TGA curves of Fe O (a), Fe O @PTA-Pd (b)
3
4
3 4
3 4
The infrared absorption frequency of Fe O nanoparticles and
functionalized Fe
3
O
4
, are shown in Fig. 2. The strong absorption at
-
1
−1
5
73 cm and 3500-3000 cm was characteristic of the Fe–O and O-
3 4
Scheme 1. Synthesis of Fe O @PTA-Pd nanocatalyst
H stretching vibration (Fe O nanoparticles Fig. 2a). The spectrum of
3
4
amino-functionalized-Fe
3
O
4
, display a number of absorption peaks,
Successful modification of the magnetic nanoparticles with PTA-Pd
was evidenced by thermal and FTIR analyses.
indicating the 3-aminopropyl (triethoxy) silane was bonded on the
surface of MNPs. The FT-IR spectroscopic analysis shows broad
Thermogravimetric analysis (TGA) of the magnetic nanoparticles
before and after modification with TEDETA-Pd complex has been
−1
−1
band at 1001 and 1111, 3394 cm and 2922–2854 cm
2
corresponds to Si–O stretching vibration, –NH and aliphatic C–H
3 4
outlined in Fig. 1a-b. Fe O MNPs showed a small amount of weight
groups, respectively.
loosing that is due to the removal of physically adsorbed solvents
and surface hydroxyl groups.
In the spectrum of Fe
3 4
O -acryloxyl (Fig. 2c) a peak is observed at
−
1
wave number of 1710 cm due to stretching vibration of carboxyl
3 4
In the curve of Fe O @PTA-Pd (Fig. 1b), the first step in the curve is
−1
group. An absorption band at 1642 cm correspondence to the C=C
associated with the loss of water molecules and surface hydroxyl
stretching mode, which conjugate with C=O bond (amide 1 band).
°
groups (below 200 C). The second weight loss, starting at 200 °C
2
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The peak observed at 3020 cm corresponds to the secondary
NP lee wa s eJ od uo r nn oa tl aod fj uC s ht em ma ri sg it nr sy
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ARTICLE
−1
FeKα
−
1
amide group. The peak observed at 1245 and 1164 cm could be
assigned to C-N and C–O stretching vibrations, respectively.
Finally, FT-IR spectrum confirms the formation of MNP-TEDET-Pd
PdLα
2000
−
1
1500
(
Fig. 2d). The band observed at 1566 cm is probably due to Pd-N
O Kα
FeLα
vibration.
1000
N Kα
C Kα
PdLβ
500
SiKα
FeKβ
keV
0
0
5
10
Element
W%
A%
C
5.69
0.88
5.32
0.37
71.30
16.45
20.48
2.71
N
O
14.38
0.56
Si
Fe
Pd
55.19
6.68
1
00.00
Figure 3. The EDS analysis of Fe
4
The X-ray diffraction pattern of Fe O @PTA-Pd nanoparticles was
100.00
3 4
O @PTA-Pd
3
brought in Fig. 4. A definite line broadening of the XRD peaks shows
that the synthesized catalysis including particles in nanoscale range.
From this XRD patterns analysis, we determined peak intensity,
position and width, full-width at half-maximum (FWHM) data. The
diffraction peaks located at 31.54°, 35.22°, 41.50°, 50.63°, 63.26°,
6
8.13°, and 74.48° have been keenly indexed as a cubic spinel
structure. The prepared nanoparticle diameter was calculated using
Debye-Scherrer formula: =0.89 cos , (1) where 0.9 is Scherrer’s
constant, is the wavelength of X-rays, is the Bragg diffraction
angle, and is the full width at half-maximum (FWHM) of the
Figure 2. FT-IR spectra of Fe
3
O
4
nanoparticles (a), amino-
@PTA-Pd (d).
3 4
O @PTA-Pd is summarized in Fig. 3; as it can be
3 4 3 4
functionalized-Fe O (b), MNP-acryloxyl (c), Fe O
͘
ꢀ
/ꢁ
ꢂ
The EDS data of Fe
ꢀ
ꢂ
seen from these data Si, C, O, N, Fe and Pd species have been
observed in the catalyst. The exact amount of Pd in the supported
nanocatalyst, found to be 1.64 mmol/g, which determined by ICP-
OES analysis.
ꢁ
diffraction peak corresponding to plane (311). The average particle
size of the sample was found to be 16.65ꢀnm which is derived from
the FWHM of more intense peak corresponding to 311 planes
located at 41.50° using Scherrer’s formula. Other major peaks at
about 45.2, 54.61, 73.61 which represent the Bragg reflections from
the (111), (200), and (311) planes can be clearly observed for Pd(0)
particles. No other crystalline impurities are observed, suggesting
3 4
that the compositions of the above structures are Fe O and Pd.
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3 4
Transmission electron microscope (TEM) images of Fe O @PTA-Pd
catalyst is shown in Figure 6. The magnetic cores of nanoparticles
had an average diameter of about 5-18 nm and were uniform both
in shape and in size.
Figure 4. XRD patterns Fe
3 4
O @PTA-Pd.
20
20 nm
The SEM pictures of Fe O @PTA-Pd nanoparticles at different
3
4
n
m
magnifications were represented in the figure 5. These pictures
confirm the formation of nanoparticles, and most of the particles
having approximately spherical shape. From the pictures, it also can
be seen that the size of the nanoparticle is 14 nm which was in
good agreement with the particle sizes that calculated from the
Debye-Scherrer formula (16.65ꢀnm).
2
0 nm
Figure 6. TEM images of Fe
3 4
O @PTA-Pd
Vibrating sample magnetometer curves of Fe
3
O
4
nanoparticles and
Fe O @PTA-Pd catalyst at room temperature have been illustrated
3
4
in Figure 7. Ms value for Fe
3
O
4
@PTA-Pd nanoparticles was found to
−
1
be 32 emug . The Ms value for the PTA-Pd bound magnetic
−1
nanoparticles was lower than that for the naked ones (78 emug ).
This might result from the binding of Pd-tridentate complex on the
particle surface, which might quench the magnetic moment.
9
7
5
3
1
0
0
0
0
0
(a)
(b)
-
-
-
-
-
10
30
50
70
90
-10000
-5000
0
5000
10000
Figure 5. SEM images of Fe
3
O
4
@PTA-Pd at different magnification
a-b)
Applied Field (Oe)
(
Figure 7. Magnetization curves for Fe (a) Fe
3
O
4
3
O
4
@PTA-Pd (b).
4
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Catalytic studies
ARTICLE
performing of model reaction in water leads to 98 % of biphenyl
During the course of our studies directed towards the development yield, therefore we chose the water as reaction media in all C-C
of practical and eco-friendly procedures for organic synthesis [22– coupling reaction by phenylbronic acid.
25], we developed preparation of a stable, cheap and efficient Effect of bases was also investigated and as it is shown in Table 1
heterogeneous Fe O @PTA-Pd nanocatalyst and used with entry 10-14 the reaction does not occur in the absence of the base
3
4
excellent activity in Suzuki, Stille and Heck cross-coupling reactions and indicated base has significant effect in the Suzuki coupling
with different aryl halides.
The catalytic activity of Fe
reaction. Et
3
N was considerably less effective, the use of N,N-
3 4
O @PTA-Pd was evaluated in the C-C dimethylpyridin-4-amine (DMAP) as base also led to no conversion.
coupling reaction of aryl halides with tetrephenylborate, In the presence of other bases, KOH, Na CO and NaHCO good
2
3
3
phenylboronic acid and chlorotriphenylstannane.
effect on the coupling of 4-bromotoluene and desirable yields of
product were obtained (Table 1, entries 13-15). However, the use of
O
N
Pd
N
O
O
O
2 3
Na CO led to 98% biphenyl, and this base was selected in all
Si
N
N
H
reactions.
Finally, effect of reaction temperature was examined in the
synthesis of 4-methylbiphenyl in the presence of 5 mg of
X
PhB(OH)2
or
NaPh4B
Fe3O4@PTA-Pd
Base, Solvent
+
R
3 4
Fe O @PTA-Pd nanocatalyst (Table 1, entries 16-19). Findings
or
R
Ph SnCl
3
revealed that yield was enhanced by increasing reaction
temperature from 25 to 80 °C. Any further increase in the
3 4
Scheme 2. Fe O @PTA-Pd for cross-coupling reaction.
In order to obtain the optimum conditions, preparation of 4- temperature failed to enhance the reaction rate substantially. Thus,
methylbiphenyl was considered from the reaction of 4- temperature 80 °C was selected as the optimum for all reactions.
bromotoluene (1 mmol) and phenylboronic acid (1 mmol) as a
model reaction in the absence and presence of the Fe @PTA-Pd
Table 1. C-C Coupling of 4-bromotoluene with phenylboronic acid in the
a
3 4
presence of Fe O @PTA-Pd under various conditions.
3
O
4
nanocatalyst in order to establish the effectiveness of the catalyst.
It was found that 4-methylbiphenyl was produced in trace amount
after 24 h in the absence of Fe O @PTA-Pd catalyst; whereas 3 mg
3
4
of catalyst led to 81% yield after 120 min (Table 1, entries 1 and 2).
The best conditions to prepare the 4-methylbiphenyl was achieved
when 5 mg (0.82 mol%) of nanocatalyst was used, and any excess of
Entry
Solvent Base
Temperature Catalyst Time
Yield
b
(mmol)
(°C)
(mg)
(min) (%)
the catalysts did not lead to an increase in the conversion and yield Catalyst effect
(
Table 1, entries 3 and 4) .
1
H
H
H
H
2
2
2
2
O
O
O
O
Na
Na
Na
Na
2
2
2
2
CO
CO
CO
CO
3
3
3
3
80
80
80
80
--
5
5
8
24h
120
14
trace
81
2
Subsequently, we screened various solvents for the model reaction
in the presence of 5 mg (0.82 mol%) of nanocatalyst. The results
showed that the reaction was performed efficiently in water and
PEG-400, giving 98 % yields and 14 min (Table 1, entries 5 and 6).
DMF and DMSO were also used as aprotic polar solvents but the
conversions of 4-methylbiphenyl in these two solvents were 61%
and 70%, respectively, which is lower than that in two above
mentioned solvents. As a proton type polar solvent, EtOH is less
favourable for the coupling reaction of aryl halides and a conversion
3
98
4
14
98
solvent effect
5
6
H
2
O
Na
2
2
CO
CO
3
3
80
80
5
5
14
14
98
98
PEG
Na
7
8
DMF
Na
2
CO
CO
3
3
80
80
5
5
14
14
61
70
DMSO Na
EtOH Na
2
9
2
CO
3
Reflux
5
14
57
of only 57% was obtained. Increasing interest of organic chemists Base effect
for the use of water as a solvent of choice and its unique properties
turned our attention to examine it for the presence study. The
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1
1
1
1
1
1
0
1
2
3
4
5
H
H
H
H
H
H
2
O
O
O
O
O
O
---
Et
80
80
80
80
80
80
5
5
5
4
5
4
5h
14
14
14
14
35
---
19
H
2
O
Na
2
CO
3
100
5
14
98
a
2
2
2
2
2
3
N
32
Reaction conditions: 4-bromotoluene (1 mmol), PhB(OH) (1 mmol), base
2
(1.5 mmol), solvent (2mL).
DMAP
KOH
Trace
70
b
Isolated yield.
On the basis of these obtained results, the coupling reaction
catalyzed by Fe O @PTA-Pd was examined with several different
NaHCO
3
64
3
4
Na
2
CO
3
98
aryl halides, including bromides and iodides with phenylboronic
acid in water. The results are summarized in Table 2. Both
electronrich and electron-deficient aryl iodides and bromides are
suitable substrates for this reaction to provide the corresponding
biphenyl in good to excellent yields. A variety of functional groups
of aryl halides are known to tolerate this reaction condition, which
Temperature
effect
1
1
1
6
7
8
H
2
H
2
H
2
O
O
O
Na
Na
Na
2
CO
2
CO
2
CO
3
3
3
Room temp
5
5
5
3h
3h
14
----
40
98
50
80
include alkoxyl, amino, nitro, carbonyl, and cyano groups.
a
Table 2. Suzuki C-C coupling reaction of aryl halides with phenylboronic acid
b
-1
Entry
Aryl halide
Time
Yield
(%)
Mp (°C)
TON
TOF (h )
(min)
Found
67-68
Reported
68–70[26]
1
2
10
99
95
1204
7224
1873
37
107-109
111-113[33]
1155
3
4
5
6
7
8
9
16
13
14
7
96
98
94
95
97
93
97
94
44-47
84-85
44-47
67-68
82-83
56-58
162-163
70-71
44– 46[26]
88–90[26]
44– 46[26]
68–70[26]
85-86[28]
54–56[27]
163-164[28]
77-79[26]
1167
1192
1143
1155
1180
1131
1180
1143
4376
5501
4899
9906
2832
2715
3540
2744
25
25
20
25
1
0
1
1
1
2
12
10
98
95
113-115
52-54
112–114[26]
50–53[27]
1192
1155
5961
6934
a
b
Reaction conditions: Aryl halide (1 mmol), PhB(OH)
2 3 4 2
(1 mmol), base (1.5 mmol), 5 mg of Fe O @PTA-Pd, H O (3 mL).
Isolated yield
Encouraged by the results obtained from C-C Coupling of aryl optimum conditions the product formed in a trace amount.
halides with phenylboronic acid in the presence of Fe @PTA-Pd, Therefore, the reaction parameters such as catalysts amount, base,
we investigated a number of other organoboronic and organotin kind of solvent and effect of temperature were studied in the
reagents such as sodium tetraphenylborate (NaB(Ph) and reaction. Surprisingly, by replacement of PEG with water solvent a
triphenyltin chloride (Ph SnCl) to probe their behaviour under the significant improvement was observed and the yield of biphenyl
current conditions. When the reaction was carried out under
3
O
4
4
)
3
6
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was dramatically increased. From these studies it was deduced that 3). The reaction of halobenzenes with Ph BNa (0.5 mmol) in the
4
PEG appears to be the most favourable solvent.
presence of 5 mg of the catalyst in PEG-400 (2 mL), as solvent, was
Furthermore, we successfully coupled a variety of aryl iodides and carried out.
bromides with sodium tetraphenylborate in excellent yields (Table
a
Table 3. Suzuki C-C coupling reaction of aryl halides with sodium tetraphenylborate
b
-1
Entry
Aryl halide
Time
Yield
%)
Mp (°C)
TON
TOF (h )
(min)
(
Found
Reported
1
2
30
40
99
91
67-68
68–70[26]
1204
2408
1660
107-109
111-113[33]
1107
3
4
5
6
7
8
9
35
16
20
50
40
43
17
36
42
33
97
90
92
92
96
97
97
94
99
94
44-47
84-85
44– 46[26]
88–90[26]
44– 46[26]
68–70[26]
85-86[28]
1216
1094
1119
1119
1168
1180
1180
1143
1204
1143
2085
4105
3357
1343
1752
1646
4165
1906
1720
2079
44-47
67-68
82-83
56-58
54–56[27]
163-164[28]
77-79[26]
162-163
70-71
1
1
1
0
1
2
113-115
52-54
112–114[26]
50–53[27]
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ARTICLE
a
4 3 4
Reaction conditions: Aryl halide (1 mmol), NaPh B (0.5 mmol), base (1.5 mmol), 5 mg of Fe O @PTA-Pd, PEG-400 (3 mL).
b
Isolated yield
The Stille coupling as a powerful intermolecular carbon-carbon (C-C) coupling reactions was tested next. Using the optimized reaction
bond formation process is an excellent candidate in generation of conditions, an array of aryl halides were investigated in this
3 4
biphenyl. Encouraged by Fe O @PTA-Pd catalyst application to the reaction, resulting in high yields of products (Table 4).
Suzuki reaction, the effectiveness of the catalyst for the Stille
a
Table 4. Stille C-C coupling reaction
b
-1
Entry
Aryl halide
Time
Yield
(%)
Mp (°C)
TON
TOF (h )
(min)
Found
67-68
Reported
68–70[26]
1
2
3
4
5
12
100
45
97
94
78
98
93
1180
5900
44-47
84-85
44-47
67-68
44– 46[26]
88–90[26]
44– 46[26]
68–70[26]
1143
949
686
1265
1788
1939
40
1192
1131
35
6
7
30
95
97
82-83
56-58
85-86[28]
54–56[27]
1156
1180
2311
373
190
8
9
100
45
90
97
79
70-71
162-163
70-71
77-79[26]
163-164[28]
68–70[26]
1094
1180
657
1573
384
1
0
150
961
a
b
Reaction conditions: Aryl halide (1 mmol), Ph
In order to investigate another potential activity of catalyst, herein,
we wish to disclose a simple bench top procedure for the Heck Initial investigation of Fe O @PTA-Pd catalyst was carried out with
3
SnCl (0.5 mmol), base (1.5 mmol), 5 mg of Fe
3
O
4
@PTA-Pd, PEG-400 (3 mL). Isolated yield
3
4
cross-coupling reaction between aryl halides and olefins.
iodobenzene and n-butyl acrylate in DMF at 80 °C for 3 h there by
providing butyl cinnamate in 60% yield. Therefore, in an attempt to
reduce the reaction time and increase the product yield, model
reaction was tested at higher temperatures like 100 °C that
enormous decrease in reaction time was observed along with
increase in the reaction yield to 71%.
O
N
Pd
N
O
O
O
Si
N
H
N
X
R'
Fe O @PTA-Pd
3
4
+
R'
Base, Solvent
To provide suitable reaction media, different solvents such as
water, DMSO and PEG were examined. We have seen that PEG
afforded the best yield of product. Also, the use of 7 mg of catalyst
instead of 5 mg results in a significant increasing of catalytic activity
R
R
2 4 9
R': -CO C H , -CN
3 4
Scheme 3. Fe O @PTA-Pd for Heck cross-coupling reaction
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ARTICLE
(
after 25 min at 100 °C, a conversion of 85% is reached, whereas
7% of trans-butyl cinnamate is obtained in the presence of 7 mg of
catalyst). Finally, no product forms in the absence of the catalyst.
5
6
7
PEG
PEG
PEG
100
100
100
5
7
25
25
25
85
97
--
9
--
a
Reaction conditions: iodobenzene (1 mmol), n-butyl acrylate (1.2
2 3
mmol), Na CO (3 mmol) and solvent (2 mL).
Table 5. Heck–Mizoroki reaction. of iodobenzene with n-butyl
b
Isolated yield.
a
acrylate.
We finally studied the scope of our methodology on the Heck cross-
coupling reaction of aryl halides with two types of vinylic substrates
(
n-butyl acrylate and acrylonitrile) under obtained optimized
conditions (Table 6). Both the aryl iodides and bromide on heck
reaction gave satisfactory to good yields of the corresponding
product. The acrylonitrile was also found to be reactive toward heck
reaction under the same reaction condition and the product was
obtained in excellent yield (Table 6, entry 7-11). Alkenes were
obtained in high yields and selectivity, being the expected trans
isomer as major product. In some case the reaction afforded the
expected trans-alkene with trace amount of the (Z)-isomers alkene.
Entry
Solvent
Temperature
°C)
Catalyst
Time
(min)
60
Yield
b
(
(mg)
(%)
1
2
3
4
DMF
DMF
80
5
5
5
5
60
71
20
55
100
100
100
25
H
2
O
25
DMSO
25
a
Table 6. Heck C-C coupling reaction.
b
-1
Entry
1
Aryl halide
olefins
Time (min)
Yield (%)
TON
TOF (h )
25
97
1180
2832
2311
2
30
95
1155
3
4
5
25
120
50
96
91
89
1168
1107
1083
2803
553
1299
6
7
8
9
110
90
93
95
91
85
50
1131
1155
1107
1034
608
617
770
553
413
202
120
150
180
1
0
a
b
Reaction conditions: Aryl halide (1 mmol), vinylic substrates (1.2 mmol), base (1.5 mmol), 7 mg of Fe
3 4
O @PTA-Pd, PEG-400 (3 mL).
Isolated yield
The Suzuki, Stille and Heck coupling reactions were occurred with and 6. These results demonstrate the high efficient and stability of
low catalyst loadings (0.82 mol% or 1.15 mol% of Pd), therefore, the catalyst in these reactions.
high turnover number (TON) and turnover frequency (TOF) were In order to prove the heterogeneous nature of the catalyst, a hot-
obtained in these reactions. These data are shown in Tables 2, 3, 4 filtration test was performed.
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New Journal of Chemistry
The catalyst was separated from the reaction mixture from the hot under the optimized reaction conditions (Fig. 9). After completion
reaction mixture (in half time of reaction) using an external magnet. of the reaction the Fe @PTA-Pd was easily separated using an
3
O
4
The progress of reaction was monitored after half time of reaction external magnet and the reaction tube was charged with fresh
in the absence of catalyst (Fig. 8). No further coupling occurs even substrates for the next run. The catalyst was recycled efficiently for
at extended times, indicating that no active species (palladium) five cycles that the reaction conversion did not decrease
significantly.
leach from the support during reaction The PEG maybe serves as
.
The Pd leaching experiment was performed to ascertain if the
reaction is truly heterogeneous. ICP-OES analysis of recycled
catalyst showed minor changes of Pd contents (1.64 mmol/g), only
both solvent and phase transfer catalyst (PTC) in the Suzuki C-C
coupling reaction of aryl halides with sodium tetraphenylborate. As
PTC, PEG can enhance the solubility of NaBPh
as promote basicity of Na CO
4 2 3
and Na CO , as well
1
% leaching was observed. These phenomena indicate that the
2
3
coupling reaction indeed goes through a heterogeneous catalytic
reaction process. In addition, the very low metal leached during the
reaction progress.
6
5
4
3
2
1
0
0
0
0
0
0
0
Suzuki reaction
00
Stille Reaction
Heck reaction
1
80
60
0
7
14
30
60
Time (min)
4
0
2
0
0
Fig. 8. Heterogeneity test for Suzuki Coupling of 4-bromotoluene.
To determine the heterogeneous nature of described catalyst, the
poisoning test of catalysts has also been employed, where we have
used CS2 as an efficient scavenger for Pd. In a typical experimental
procedure, iodobenzene (1 mmol), phenylboronic acid (1 mmol),
Na2CO3 (1.5 mmol), water (10 mL) were mixed in a round bottom
flask along with 4 mg Fe3O4@PTA-Pd catalyst and 0.04 g CS2 and
heated at 80 °C. We observed that the reaction rate was decreased
1
2
3
4
5
Cycle
Fig. 9. Recyclability of catalyst for the preparation of 4-
methylbiphenyl
in the presence of CS2, and only 60 % of corresponding coupled Conclusions
product was obtained after 10 min (the time that was needed to
In conclusion, we have successfully developed a highly efficient
complete this reaction in the absence of CS2). Also we have
observed described reaction could be completed in more reaction
time, which if the reaction left for 120 min (12 times of common
reaction rate) the coupled product might be obtained in near to 100
process for the Suzuki, Stille and heck cross-coupling reactions of a
wide range of aryl halides using Fe O @PTA-Pd whit significant
3
4
features such as efficient recyclability, waste-free process, easy
isolation of the product, phosphine-free catalyst, short reaction
time, clean reaction and small quantity of catalyst, high efficiency
under relatively mild conditions and use of water or PEG as green
solvents. Also, this work focuses on a suite of techniques used to
%
of conversion. This result reveals that presence of CS2 in reaction
media leads to decrease the catalytic activity of Fe3O4@PTA-Pd,
which showed the heterogeneous nature of the present
methodology.
determine heterogeneous catalysis Such as: hot filtration, CS
2
poisoning, Pd leaching experiment and analysis of product yield
after recovery and recycle.
One major advantage of catalyst is its recyclability. In a final set of
experiments, we performed the stability and recycling of
3 4
Fe O
@PTA-Pd catalyst for Suzuki, Stille and Heck cross-coupling Experimental Section
1
0 | J. Name., 2012, 00, 1-3
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ARTICLE
decantation, and dried under vacuum at room temperature
overnight.
Materials
The reagents and solvents were used in this work obtained from
Sigma-Aldrich, Fluka or Merck chemical Companies and utilized
without further purification.
Fe
3
O
4
@PTA-Pd catalyst preparation. The amino-functionalized
Cl (3 mL) by ultrasonic bath
MNPs (1 g) were dispersed in dry CH
2
2
for 10 min, and the flask was cooled in an ice-water bath.
Triethylamine (3.2 mL) was added and stirred for 30 min.
Subsequently, acryloyl chloride (0.8 mL, 9.84 mmol) was added drop
wise over a period of 30 min at room temperature. The mixture was
stirred at room temperature for 48 h. Then, functionalized MNPs
were separated by magnetic decantation and washed three times
with acetone and deionized water to remove the unattached
substrates. The resulting materials was dispersed in methanol (10.0
mL), and N,N,N",N"-tetraethyldiethylenetriamine (TEDETA) (1.0 mL,
3.8 mmol) was added to this mixture. The reaction mixture stirred
for 1 week at room temperature. The solids were separated using a
magnet and washed with acetone. The resulting product was dried
The particle morphology was examined by measuring SEM using
FESEM-TESCAN MIRA3. The products component measurement was
carried out by the energy dispersive spectroscopy (EDS) using
FESEM-TESCAN MIRA3 scanning electron microscopes. The
thermogravimetric analysis (TGA) curves are recorded using a
Shimadzu DTG-60 instrument. VSM measurements were performed
using a Vibrating Sample Magnetometer (VSM) MDKFD. The
magnetization measurements were carried out in an external field
up to 15 kOe at several temperatures.
,
Nanostructures were characterized using a Holland Philips X pert X-
ray powder diffraction (XRD) diffractometer (Co Ka, radiation=
0
.154056 nm). IR spectra were recorded as KBr pellets on a VRTEX
0 model BRUKER FTIR spectrophotometer. The Pd amount of
3 4
under vacuum for 12 h. The Fe O @PTA (0.5 g), was added to the
7
round-bottom flask containing a solution of Pd(OAc)2 (0.25 g) in
ethanol (20 mL). The mixture was then stirred vigorously at reflux
conditions for 20 h. The solid was separated by magnetic
decantation. The magnetic catalyst was washed with copious
amounts of ethanol and dried under vacuum at room temperature.
catalyst was measure by Inductively Coupled Plasma Atomic
Emission Spectrometer (ICP-OES). NMR spectra were recorded on a
Bruker Avance III 400MHz. Chemical shifts are given in ppm (δ)
relative to internal TMS and coupling constants J are reported in Hz.
Melting points were measured with an Electrothermal 9100
apparatus.
Synthesis of biphenyl (General procedure for Suzuki reaction
). To
a stirred solution of iodobenzene (1 mmol), Na CO (0.212 g, 1.5
2
3
Syntheses
mmol) and sodium tetraphenylborate (0.5 mmol) or phenylboronic
acid (1 mmol) in PEG or water (3 mL) were added Fe O @PTA-Pd (5
Fe
FeCl
were dissolved in 100 mL of deionized water in a three-necked
bottom (250 mL) at 80 °C under N atmosphere. Thereafter, 10 mL
of aqueous NH solution (32%) was added into mixture within 30
3
O
4
-(3-aminopropyl)-triethoxysilane preparation. The mixture of
3
4
3
.6H O (5.838 g, 0.022 mol) and FeCl .4H O (2.147 g, 0.011 mol)
2
2
2
mg) and the reaction mixture was stirred at 80 °C. Completion of
the reaction was indicated by TLC. After cooling the reaction
mixture, the catalyst was separated by an external magnet and
reused as such for the next experiment. The mixture was diluted
with diethyl ether and water and the extracted organic layer was
2
3
min with vigorous mechanical stirring. The formed black precipitate
was isolated by magnetic decantation, washed with double-distilled
water until neutrality, and further washed twice with ethanol and
dried at 80 °C in vacuum. The obtained magnetic nanoparticles
2 4
dried over Na SO (1.5 g) and the solvent was evaporated to obtaine
pure biphenyl product.
Synthesis of 4-Cyanobipheyl
(
General procedure for Stille
CO
0.212 g, 1.5 mmol) and chlorotriphenylstannane (0.5 mmol) in PEG
3 mL) and Fe @PTA-Pd (5 mg) was stirred at 80 °C. Completion of
(
MNPs) powder (1.5 g) was dispersed in a mixture of ethanol and
reaction
).
A mixture of 4-bromobenzonitrile (1 mmol), Na
2
3
water (250 mL, 1:1 by volume) solution by sonication for 30 min.
Then 3-aminopropyl (triethoxy) silane (99%, 3 mL) was added to the
(
(
3
O
4
2
mixture under mechanical stirring and N atmosphere at room
the reaction was indicated by TLC. After cooling the reaction
mixture, the catalyst was separated by an external magnet and
reused as such for the next experiment. The mixture was diluted
with diethyl ether and water and the extracted organic layer was
temperature for 8 h. The settled product was redispersed in ethanol
by sonication. The final product was washed with copious amounts
of deionized water and ethanol, separated by magnetic
2 4
dried over Na SO (1.5 g) and the solvent was evaporated.
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ARTICLE
New Journal of Chemistry
1
4
7
7
4
7
-Cyanobipheyl, white solid. H NMR (CDCl , 400 MHz): δ = 7.48-
3 H
Acknowledgements
.44(m, 1H), 7.54-7.48 (m, 2H), 7.64-7.61(m, 2H), 7.73-7.70 (m, 2H),
Authors thank the research facilities of Ilam University, Ilam, Iran,
.78-7.75 (m, 2 H).
for financial support of this research project
.
1
-Nitrobiphenyl, yellow solid. H NMR (CDCl
3
H
, 400 MHz): δ = 7.50–
Supplementary data
.46 (1H, m), 7.56–7.51(2H, m), 7.67−7.64 (2H, m), 7.77 (d, J = 8.8
Hz, 2H), 8.33 (d, J = 8.8 Hz, 2H).
Supplementary data associated with this article can be found, in the
online version, at….
1
3 H
4-Methoxybiphenyl, white solid. H NMR (CDCl , 400 MHz): δ =
3.89 (s, 3H), 7.02 (d, J = 8.8 Hz, 2H), 7.34 (t, J = 7.6 Hz, 1H), 7.47-7.43 Notes and references
(
m, 2H), 7.60–7.55 (m, 4H).
Synthesis of (E)-Butyl 3-(4-methoxyphenyl)acrylate
procedure for Heck reaction Fe @PTA-Pd (7 mg) was added to a
mixture of 4-Iodotoluene (1 mmol), Na CO (0.212 g, 1.5 mmol) and
[
1] M. Z. Kassaee, H. Masrouri, F. Movahedi, Appl. Catal. A. Gen, 2011,
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95, 28-33.
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[
[
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3
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mixture was stirred at 100 °C. Completion of the reaction was
indicated by TLC. After cooling the reaction mixture, the catalyst
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7
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(E)-Butyl 3-(4-methoxyphenyl)acrylate (Table 5, entry 3): Light
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1
yellow liquid, H NMR (CDCl , 400 MHz): δ = 0.99 (t, 3H, J = 7.2 Hz),
3
H
1
.45 (sex, 2H, J = 6.8 Hz), 1.69 (quint, 2H, J = 6.8 Hz), 3.85 (s, 3H),
.22 (t, 2H, J = 6.4 Hz), 6.32 (d, 1H, J = 16 Hz), 6.90 (d, 2H, J = 8.8
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1
4811.
(
E)-Butyl 3-(p-tolyl)acrylate (Table 5, entry 2): Light yellow liquid. H
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H
NMR (CDCl3, 400 MHz): δ = 1.00 (t, 3H, J = 7.6 Hz), 1.47 (sex, 2H, J =
7.6 Hz), 1.72 (quint, 2H, J = 6.4 Hz), 2.40 (s, 3H), 4.23 (t, 2H, J = 6.4
Hz), 6.42 (d, 1H, J = 16 Hz), 7.22 (d, 2H, J = 8 Hz), 7.45 (d, 2H, J = 8
Hz), 7.69 (d, 1H, J = 16 Hz)
2
68.
1
Butyl cinnamate(Table 5, entry 1 and 4)
CDCl3, 400 MHz): δ
Hz), 1.73 (quint, 2H, J = 3.2 Hz), 4.24 (t, 2H, J = 6.4 Hz), 6.48 (d, 1H, J
16 Hz), 7.39 (m, 3H), 7.42 (m, 2H), 7.71 (d, 1H, J = 16 Hz).
E)-Butyl 3-(4-chlorophenyl)acrylate(Table 5, entry 5) Light yellow
= 0.99 (t, 3H, J = 7.2 Hz), 1.47 (sex, 2H, J = 5.2 Hz), 1.72
:
Light yellow liquid. H NMR
[
17] H. A. Elazab, A. R. Siamaki, S. Moussa, B. F. Gupton, M. S. El-Shall,
Appl. Catal. A: Gen., 2015, 491, 58-69.
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= 1.00 (t, 3H, J = 7.8 Hz), 1.47 (sex, 2H, J = 2
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998, 557, 93-96.
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2
016, 401, 832-840.
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(
p
-Tolyl)acrylonitrile (Table 5, entry 8)
:
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3
): Light yellow liquid . δ
H
= 7.42-7.37 (m, 3H), 7.29-7.23 (m, 2H),
5.88-5.84 (d, J= 16.4 Hz, 1H), 2.42 (s, 3H) ppm.
1
2 | J. Name., 2012, 00, 1-3
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ARTICLE
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[
[
[
Online,
=
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Graphical Abstract
Suzuki, Stille and Heck cross-coupling reactions catalyzed by Fe O @PTA-Pd as
3
4
recyclable and efficient nanocatalyst in green solvents
*
Arash Ghorbani-Choghamarani, Masoumeh Norouzi
A novel heterogeneous Pd-catalyst was designed and successfully employed in the C–C coupling
reactions under green conditions.