Palladium supported on diaminoglyoxime-functionalized Fe3O4 nanoparticles as a magnetically separable nanocatalyst in Heck coupling reaction

Article abstract of DOI:10.1002/aoc.3375

A hybrid material of palladium supported on diaminoglyoxime-functionalized Fe₃O₄ was used as an effective and recyclable catalyst in Mizoroki-Heck coupling reactions. The catalyst was very effective for the Mizoroki-Heck reaction of aryl halides with styrene and conversion was in most cases excellent. The yields of the products were in the range 75-98%. The catalyst showed good stability and could be recovered and reused for six reaction cycles without significant leaching and loss its catalytic activity.

Full text of DOI:10.1002/aoc.3375

Full paper
Received: 7 July 2015
Revised: 28 July 2015
Accepted: 7 August 2015
Published online in Wiley Online Library: 16 September 2015
(wileyonlinelibrary.com) DOI 10.1002/aoc.3375
Palladium supported on diaminoglyoxime-
functionalized Fe3O4 nanoparticles as a
magnetically separable nanocatalyst in Heck
coupling reaction
Hojat Veisia*, Alireza Sedrpoushanb and Saba Hemmatia
A hybrid material of palladium supported on diaminoglyoxime-functionalized Fe3O4 was used as an effective and recyclable cat-
alyst in Mizoroki–Heck coupling reactions. The catalyst was very effective for the Mizoroki–Heck reaction of aryl halides with sty-
rene and conversion was in most cases excellent. The yields of the products were in the range 75–98%. The catalyst showed good
stability and could be recovered and reused for six reaction cycles without significant leaching and loss its catalytic activity.
Copyright © 2015 John Wiley & Sons, Ltd.
Keywords: Fe3O4/DAG/Pd; magnetic nanocomposite; catalysis; recyclable; Heck reaction
However, conventional separation methods may become inefficient
for support particle sizes below 100 nm. The incorporation of
Introduction
Today, the heterogenization of metal complexes with catalytic ac-
tivity within inorganic matrixes such as SiO2,[1–3] MCM-41,[4,5] SBA-
15,[6–11] clay, zeolites and mesoporous materials is a field that has
progressed due to the combination of high reactivity and chemical
selectivity (like homogeneous catalysts) with facile separation of
the catalyst from the reaction mixture. Due to their properties, par-
ticular attention has been paid to reusable, thermally stable and
low-cost catalysts.
Palladium-catalysed cross-coupling reactions are important for
the generation of C–C bonds.[12–16] Among various methods,
the coupling of aryl halides with olefinic compounds (Heck reac-
tion) is an excellent procedure for the synthesis of useful organic
compounds.[17,18] Many palladium complexes have been used in
these reactions,[19–24] and although some have the potential to
be recycled,[22–24] most suffer from problems such as deactivation
and difficulties in separating them from solution due to the ag-
gregation of the palladium nanoparticles that are formed in situ
during the Heck reaction. Thus, it is necessary to develop sup-
ported catalysts which can easily be recovered from the reaction
system and reused.
magnetic nanoparticles (MNPs) into supports offers a solution to this
problem. The renewed interest in synthesis of MNPs is due to their
technological applications such as in data storage, biological imaging
and biomedicine.[25–29] One of the attractive features of MNPs is the
possibility of fast and cost-efficient separation by applying an
external magnetic field, which makes them ideal candidates for
practical use in catalysis. This new direction in catalysis has
galvanized academic research and led to the development of a great
number of magnetic-based catalysts, especially magnetite (Fe3O4),
that have found application in various reactions.[30–39] Several
accounts of the synthesis, characterization and application of Fe3O4
MNPs utilized in coupling reactions have been reported in the
literature.[40–51]
Recently, we have reported the preparation of palladium nano-
particles incorporated into Fe3O4/diaminoglyoxime nanocomposite
(Fe3O4/DAG/Pd) as a new magnetically recoverable heterogeneous
catalyst in the Suzuki–Miyaura reaction.[45] Herein we describe its
catalytic activity in Mizoroki–Heck reactions.
Immobilization of homogeneous catalysts on various insoluble
supports (especially porous materials with high surface areas) can
lead to simple catalyst recycling via filtration or centrifugation. How-
ever, a substantial decrease in the activity of the immobilized catalyst
is frequently observed due to the loss of the catalyst in the separation
processes and/or diffusion factors. In an attempt to resolve such
problems, nanoparticles have been used as alternative soluble ma-
trixes for supporting homogeneous catalysts. When the size of the
support materials is decreased to the nanometre scale, the surface
area of such nanoparticles will increase dramatically. As a conse-
quence, nanoparticles could have higher catalyst loading capacity
and higher dispersion than many conventional support matrixes,
leading to improved catalytic activity of the supported catalysts.
Experimental
Preparation of magnetic Fe3O4 nanoparticles
Naked Fe3O4 nanoparticles were prepared by chemical
coprecipitation of Fe3+ and Fe2+ ions with a molar ratio of 2:1.
*
Correspondence to: Hojat Veisi, Department of Chemistry, Payame Noor
University, Tehran, Iran. E-mail: hojatveisi@yahoo.com
a Department of Chemistry, Payame Noor University, Tehran, Iran
b Institute of Industrial Chemistry, Iranian Research Organization for Science and
Technology, Tehran, Iran
Appl. Organometal. Chem. 2015, 29, 825–828
Copyright © 2015 John Wiley & Sons, Ltd.

H. Veisi et al.
Typically, FeCl3Á6H2O (5.838 g, 0.0216 mol) and FeCl2Á4H2O (2.147
g, 0.0108 mol) were dissolved in 100 ml of deionized water at
85°C under nitrogen atmosphere and with vigorous mechanical
stirring (500 rpm). Then, 10 ml of 25% NH4OH was quickly
injected into the reaction mixture in one portion. The addition
of the base to the Fe2+/Fe3+ salt solution resulted in the immedi-
ate formation of a black precipitate of MNPs. The reaction contin-
ued for another 25 min and the mixture was cooled to room
temperature. Subsequently, the resultant ultrafine magnetic parti-
cles were subjected to magnetic separation and washed several
times with deionized water.
field emission scanning electron microscopy (FESEM) and transmis-
sion electron microscopy (TEM) images (Fig. 1). The FESEM image
(Fig. 1(b)) of the synthesized Fe3O4/DAG/Pd-loaded MNPs confirms
that the catalyst is made up of uniform nanometre-sized particles.
The TEM image of the Fe3O4/DAG/Pd catalyst (Fig. 1(a)) reveals that
palladium nanoparticles with nearly spherical morphology are
formed on the surface of the modified Fe3O4 nanoparticles. In
TEM images, iron oxide nanoparticles of 10–15 nm in diameter
and palladium nanoparticles of ca 2 nm entrapped in iron oxide
are observed. Also, the TEM image of the Fe3O4/DAG/Pd catalyst
shows that the functionalized MNPs possess almost spherical mor-
phology and are nearly monodisperse.
In order to evaluate the catalytic activity of the prepared Fe3O4/
DAG/Pd hybrid material as a heterogeneous catalyst, the Heck cou-
pling reaction was chosen as a probe reaction (Scheme 1). Initially,
we explored the catalytic ability for this reaction and the optimized
conditions for the coupling reaction between bromobenzene and
styrene as a model reaction with various amounts of catalyst, sol-
vents and bases (Table 1).
The palladium complex (Fe3O4/DAG/Pd)-catalysed Heck reaction
was carried out using styrene and bromobenzene as a model reac-
tion to investigate various parameters, such as effect of solvent, di-
verse bases and concentration of catalyst. Among the bases
evaluated, Et3N is found to be the most effective and other bases
are substantially less effective. We also investigated the effect of
solvents on the Heck coupling reaction and found that DMF is the
best choice.
Preparation of Fe3O4/DAG
The obtained MNP powder (500 mg) was dispersed in 50 ml of
ethanol–water (1:1 v/v) solution using sonication for 20 min, and
then DAG (250 mg) was added to the mixture. After mechanical ag-
itation at 40°C for 5 h, the suspended substance was separated
using centrifugation. The settled product was re-dispersed in etha-
nol with sonication and then was isolated with magnetic decanta-
tion five times. The precipitated product (Fe3O4/DAG) was dried
at room temperature under vacuum.
Preparation of Fe3O4/DAG/Pd(0)
Fe3O4/DAG (500 mg) was dispersed in CH3CN (30 ml) using an ultra-
sonic bath for 30 min. Subsequently, a yellow solution of PdCl2 (30
mg in 30 ml of acetonitrile) was added to the dispersion of Fe3O4/
DAG and the mixture was stirred for 10 h at room temperature.
Then, Fe3O4/DAG/Pd(II) was separated by magnetic decantation
and washed successively with CH3CN, water and acetone to re-
move the unattached substrates.
The reduction of Fe3O4/DAG/Pd(II) using hydrazine hydrate
was performed as follows. An amount of 50 mg of Fe3O4/DAG/
Pd(II) was dispersed in 60 ml of water, and then 100 μl of hydra-
zine hydrate (80%) was added. The pH of the mixture was ad-
justed to 10 with 25% ammonium hydroxide and the reaction
was carried out at 95°C for 2 h. The final product, Fe3O4/DAG/
Pd(0), was washed with water and dried in vacuum at 40°C.
The concentration of palladium in Fe3O4/DAG/Pd(0) was 2.80 wt
% (0.28 mmol gÀ1), as determined using inductively coupled
plasma atomic emission spectroscopy.
General procedure for Heck reaction
A mixture of aryl halide (1 mmol), styrene (1.5 mmol), triethylamine
(2 mmol), dimethylformamide (DMF; 3 ml) and Fe3O4/DAG/Pd(0)
(10 mg= 0.003 mmol Pd) was added into a round-bottomed flask
and stirred at 110°C in atmosphere for 1–12 h. After completion
of the reaction, the reaction mixture was cooled to room tempera-
ture and the catalyst was recovered using an external magnet and
washed with ethanol, and then dried under vacuum for reuse. The
residual mixture was extracted with CH2Cl2 (3× 20 ml), and the
combined organic layer was dried over MgSO4. The solvent was
evaporated and the crude products were purified using column
chromatography (hexane–acetone, 6:1).
Results and discussion
As a part of our ongoing research programme to develop new
synthetic methodologies,[52] after successful fabrication of the
catalyst,[45] we investigated again the surface morphology from
Figure 1. (a) TEM and (b) FESEM images of Fe3O4/DAG/Pd.
wileyonlinelibrary.com/journal/aoc
Copyright © 2015 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2015, 29, 825–828

Fe3O4/DAG/Pd as an effective nanocatalyst in Heck reaction
Table 2. Scope of Heck–Mizoroki reactiona
Entry
R1
R2
X
Time Yield
(h) (%)b
M.p. (°C)
Found
Reported
1
Ph
H
I
1
3
98
98
122–124
122–124
122–124
134–136
134–136
37–39
142–145
118–120
118–120
118–120
—
121–123[53]
121–123[53]
121–123[53]
135–137[53]
135–137[53]
38–40[54]
142–145[24]
117–119[24]
117–119[24]
117–119[24]
—
2
Ph
H
Br
Cl
I
3
Ph
H
12 85
4
Ph
4-OMe
2
6
2
7
2
5
96
96
98
80
96
90
5
Ph
4-OMe Br
4-Cl
4-COCH3 Br
Scheme 1. Fe3O4/DAG/Pd as a heterogeneous catalyst in the Heck
coupling reaction.
6
Ph
I
7
Ph
8
Ph
4-CH3
4-CH3
4-CH3
H
I
9
Ph
Br
Cl
I
Table 1. Optimization of conditions for Heck reaction of
bromobenzene with styrenea
10
11
12
13
14
Ph
10 75
0.5 96
CO2Bu
CO2Bu
H
Br
I
2
1
3
85
90
85
—
—
CO2Me H
CO2Me H
—
—
Br
—
—
aReaction conditions: bromobenzene (1 mmol), styrene (1.5 mmol),
Fe3O4/DAG/Pd (10 mg, 0.3 mol%), Et3N (2 mmol), DMF (3 ml).
bIsolated yield.
Entry
Solvent
Pd (mol%)
Base
Time (h) Yield (%)b
1
EtOH/H2Oc
Toluene
EtOH
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.5
0.2
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Et3N
5
5
60
75
2
3
10
10
10
10
2
35
4
MeOH
CH2Cl2
H2O
35
5
Trace
45
6
7
CH3CN
DMF
60
8
3
85
9
DMF
3
98
10
11
12
13
14
DMF
NaOAc
KOH
3
75
DMF
3
65
DMF
NaOH
Et3N
3
55
DMF
3
98
DMF
Et3N
6
70
aReaction conditions: bromobenzene (1mmol), styrene (1.5 mmol),
Fe3O4/DAG/Pd, solvent (3 ml), reflux.
bIsolated yield.
After optimizing the reaction conditions and with a reliable
set of conditions in hand (Table 1, entry 9), the scope and gen-
erality of the developed protocol with respect to aryl halide
structures and olefins were investigated using 0.3 mol% of
Fe3O4/DAG/Pd in the presence of 2 eq. of Et3N in DMF at
110°C. The results are summarized in Table 2. As is evident, un-
der optimized conditions, phenyl iodide, phenyl bromide and
phenyl chloride react efficiently with styrene (Table 2, entries
1–3). Both electron-withdrawing and electron-releasing groups
with styrene afford the corresponding trans-stilbene in good
yields (Table 2, entries 4–10). Olefins such as methyl acrylate
or butyl acrylate are very well tolerated under these conditions
(Table 2, entries 10–14).
Figure 2. Recycling of Fe3O4/DAG/Pd for the Heck coupling reaction.
50°C and used in the next run. The results show that this cata-
lyst can be reused six times without any significant loss in activ-
ity (Fig. 2). This high catalytic activity is possibly related to the
strong interaction of palladium nanoparticles with active sites
of DAG. This result also demonstrates that the palladium
leaching of the catalyst is low.
Conclusions
In view of industrial purposes and green chemistry, the reus-
ability of the catalyst was tested by carrying out repeated runs
of the model reaction (Table 1) with the same batch of the cat-
alyst. In order to regenerate the catalyst, after each cycle, it was
separated using a magnet, and washed several times with de-
ionized water and ethanol. Then, it was dried in an oven at
Palladium immobilized on Fe3O4/DAG nanocomposite was found
to be an effective nanocatalyst in the Mizoroki–Heck reaction of aryl
halides with styrene, and especially for less reactive aryl chlorides.
This new heterogeneous catalyst shows the following advantages:
(a) simple preparation; (b) easy separation after reaction using an
external magnet; and (c) reusability several times without any
Appl. Organometal. Chem. 2015, 29, 825–828
Copyright © 2015 John Wiley & Sons, Ltd.
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