Supported molybdenum on graphene oxide/Fe3O4: An efficient, magnetically separable catalyst for one-pot construction of spiro-oxindole dihydropyridines in deep eutectic solvent under microwave irradiation

Article abstract of DOI:10.1016/j.catcom.2016.09.028

Magnetically separable graphene oxide supported molybdenum (Fe₃O₄/GO-Mo) nanoparticles were prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and vibrating sample magnetometry (VSM) techniques. The synthesized heterogeneous material was found to exhibit high catalytic activity in one-pot, three-component reaction of isatins, malononitrile and anilinolactones using choline chloride (ChCl)/urea as a green solvent under microwave irradiation. It provided an efficient method for the synthesis of spirooxindole dihydropyridines in high to excellent yields. The catalytic system can be successfully reused eight times with a small decrease of its catalytic performance.

Full text of DOI:10.1016/j.catcom.2016.09.028

Supported molybdenum on graphene oxide/Fe3O4: An efficient, magnetically
separable catalyst for one-pot construction of spiro-oxindole dihydropyridines
in deep eutectic solvent under microwave irradiation
Mo Zhang, Yu-Heng Liu, Ze-Ren Shang, Hai-Chuan Hu, Zhan-Hui Zhang
PII:
DOI:
Reference:
S1566-7367(16)30348-X
doi:10.1016/j.catcom.2016.09.028
CATCOM 4797
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
22 June 2016
28 August 2016
17 September 2016
Please cite this article as: Mo Zhang, Yu-Heng Liu, Ze-Ren Shang, Hai-Chuan Hu,
Zhan-Hui Zhang, Supported molybdenum on graphene oxide/Fe3O4: An efficient, mag-
netically separable catalyst for one-pot construction of spiro-oxindole dihydropyridines
in deep eutectic solvent under microwave irradiation, Catalysis Communications (2016),
doi:10.1016/j.catcom.2016.09.028
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Catalysis Communications
Supported molybdenum on graphene oxide/Fe3O4: an efficient, magnetically
separable catalyst for one-pot construction of spiro-oxindole dihydropyridines
in deep eutectic solvent under microwave irradiation
Mo Zhang,a Yu-Heng Liu,*b Ze-Ren Shang,a Hai-Chuan Hua and Zhan-Hui Zhang*a
a College of Chemistry and Material Science, Hebei Normal University, Shijiazhuang 050024, P. R. China.
b College of Preclinical Medicine, Hebei Medical University, Shijiazhuang 050017, P. R. China.
ABSTRACT
Magnetically separable graphene oxide supported molybdenum (Fe3O4/GO-Mo) nanoparticles were
prepared and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission
electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), and vibrating sample
magnetometry (VSM) techniques. The synthesized heterogeneous material was found to exhibit high
catalytic activity in one-pot, three-component reaction of isatins, malononitrile and anilinolactones using
choline chloride (ChCl)/urea as a green solvent under microwave irradiation. It provided an efficient method
for the synthesis of spiro-oxindole dihydropyridines in high to excellent yields. The catalytic system can be
successfully reused eight times with a small decrease of its catalytic performance.
Keyword: Graphene oxide; Magnetic nanoparticles; Deep eutectic solvents; Multi-component reaction;
Spiro-oxindole dihydropyridines; Microwave irradiation
________________
*Corresponding authors. Fax: +86 31180787431. E-mail address: zhanhui@126.com (Z.-H. Zhang);
liu2795478@163.com (Y.-H. Liu)
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1. Introduction
From the viewpoint of green chemistry, the design of novel, efficient and clean reaction protocols
using supported nanocatalysts in environmentally benign solvents to synthesize fine chemical and
pharmaceutical products via multicomponent reactions (MCRs) has recently gained significant interest
from academia and industry. In this context, carbon materials such as activated carbon [1], carbon
nanofibers [2], carbon nanotubes (CNTs) [3-4] and graphene oxide (GO) [5-7] as promising supports have
attracted significant attention as they are inexpensive and readily obtained. Particularly, GO as a novel
nanocomposite has become one of the most widely used catalyst support due to its intriguing properties
such as large surface area, high mechanical strength, unique layered structure, excellent physicochemical
stability, and high flexibility. Most importantly, GO has abundant surface functional groups such as
hydroxyl, carbonyl, epoxide and carboxylic acid, which makes GO as a fascinating support to provide
covalent attachment of various specific groups. Despite their excellent catalytic performance in some
organic reactions, some traditional separation methods such as filtration or high-speed centrifugation were
usually required for the recycling of catalysts, thus limiting their wide use. In order to solve this problem,
magnetic separation occurred as an intriguing alternative to filtration or centrifugation because it reduces
loss of catalyst and makes the recovery and reusability of catalyst easier by magnetic force after completion
of the reaction [8-10]. Thus, the incorporation of magnetic components into GO is most favoured and will
provide high catalytic activity and improve separation capability [11-12]. Next, since conventional
hazardous organic solvents pollute our environment severely, replacement of these toxic solvents by green
and environmentally benign media is also of key relevance. Recently, deep eutectic solvents (DESs) have
emerged as substitutes of conventional volatile organic solvents thanks to their advantages of low toxicity,
nonvolatility, low flammability, biodegradability, simple and cheap preparation [13-14]. Besides, one pot,
MCRs are becoming important tools for the rapid and efficient construction of structurally diverse complex
molecules with excellent atom and step economy [15]. In addition, microwave irradiation has become
particularly popular in recent years and a large number of organic reactions can be performed in improved
yields, shorter reaction time and milder conditions under microwave irradiation [16]. With these aspects of
green synthesis in mind, the development of microwave-promoted multicomponent reactions in
environmentally benign media by use of a reusable magnetic nano-catalyst might be one exciting and
desirable direction.
Synthesis of multi-heterocyclic compounds has received great attention in recent years because they
show structural complexity and diversity. The importance of this type of molecule in pharmaceutical
industry, material sciences and coordination chemistry has been demonstrated [17]. 1,4-Dihydropyridines
represent an important class of calcium-channel modulating agents and have experienced widespread use in
the treatment of cardiovascular disease [18]. They are useful as anti-Alzheimer's disease agent [19],
calcium antagonists [20], TGF/Smad inhibitors [21] and anticancer drugs [22]. Additionally, the
dihydrofuran skeleton is another important heterocyclic scaffold and it constitutes the structural subunit of
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many natural compounds and exhibits a broad range of biological properties [23]. The synthesis of
spiro-heterocycles presents an interesting synthetic challenge due to their structural rigidity and complexity.
Spirooxindoles, especially those spiroannulated with heterocycles at the 3-position, have been reported to
possess good biological activities [24]. Based on the importance of these structural frameworks, the
development of a simple procedure for the straightforward construction of spiro-heterocyclic compounds
including the 1,4-dihydropyridine moiety and dihydrofuran framework using simple and readily available
starting materials is highly desirable and valuable for medicinal chemistry and drug discovery.
By considering the above-mentioned points and continuing our efforts to develop environmentally
benign synthetic methodologies [254-29], herein, we report for the first time, magnetically separable
molybdenum immobilized to Fe3O4/graphene oxide as catalyst for the synthesis of spiro-oxindole
dihydropyridines via one pot multi-component reaction of isatins, malononitrile and anilinolactones in
ChCl/urea under microwave irradiation.
2. Experimental
2.1 General information
See in supporting information.
2.2 Synthesis of Fe3O4/GO nanocomposite
Magnetite-graphene oxide was prepared according to the modified method reported by Islam and
co-workers [30]. 100 mg of GO was dispersed into 100 mL of deionized water with sonication for 1 h. 2.0
g of FeCl3 and 0.75 g of FeCl2 were added to 125 mL of deionized water with stirring for 30 min at room
temperature. The aforementioned two systems were then mixed together, and stirred at 85 °C for 30 min.
The mixture was adjusted to a pH of 10.0 with 25 % ammonia solution, and stirred for 45 min. The
resultant Fe3O4 decorated GO suspension was cooled to room temperature and separated from the solution
with the aid of an external permanent magnet, washed with distilled water and dried in a vacuum oven at 60
°C for 12 h.
2.3 Amine-functionalized of Fe3O4/GO
The obtained nano Fe3O4/GO (0.5 g) was dispersed in 10 ml water by sonication for 30 min at room
temperature. Dopamine hydrochloride (0.5 g) dissolved in water (5 mL) was added, and the resulting
mixture was again sonicated for 2 h. The prepared amine-functionalized magnetic nanoparticles were
separated by magnetic decantation, and then washed with water and ethanol, and dried under vacuum at 60
°C for 2 h.
2.4 Immobilization of molybdenum on magnetic Fe3O4/GO
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Amine-functionalized nano-Fe3O4/GO (0.5 g) was ultrasonically dispersed in dry MeOH (15 ml),
bis(acetylacetonato)dioxomolybdenum (1.0 mmol) was added to the reaction mixture. The reaction
mixture was then refluxed for 24 h. The catalyst was harvested with the aid of a magnet, washed several
times with water and ethanol, and dried under vacuum at 60 °C for 2 h.
2.5 General procedure for synthesis of spiro-oxindole dihydropyridines
A mixture of isatin (1 mmol), malononitrile (1 mmol), anilinolactones (1 mmol) and Fe3O4/GO-Mo (20
mg, 0.015 mmol of Mo) in ChCl/urea (1 ml), was stirred under microwave irradiation at 90 °C for an
appropriate time. After completion of the reaction as indicated by TLC, the catalyst was separated by
external magnet and washed with acetone followed by water, and dried under vacuum and reused directly
for the next round of reaction. After that, water (5 mL) was added to the reaction mixture to dissolve DES.
The formed solid product was collected by filtration and recrystallized from ethanol (5 mL) to afford the
pure product. The filtrate, consisting of the aqueous phase containing the DES, was evaporated under
reduced pressure and then dried in vacuum at 100 °C to recover the DES for subsequent cycles.
3. Results and discussion
As shown in Scheme 2, the catalyst Fe3O4/GO-Mo was prepared in a four-step process. At first,
graphene oxide (GO) was synthesized by oxidation of graphite powder according to a slightly modified
Hummer’s method [31]. The synthesized graphene oxide was suspended into water and treated with FeCl3
and FeCl2 to obtain black colored Fe3O4/GO nanocomposites. High specific surface area of GO along with
easily accessible oxygen-donating groups on GO sheets provided a better support for anchoring of Fe3O4
NPs. Amine-functionalized Fe3O4/GO NPs were prepared by sonicating Fe3O4/GO with dopamine in water
[32-33]. Furthermore, the addition of bis(acetylacetonato)dioxomolybdenum into the Fe3O4/GO suspension
in MeOH yielded magnetically separable Fe3O4/GO-Mo nanocomposites.
Scheme 1 Preparation of Fe3O4/GO-Mo
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The XRD patterns of graphite, GO, and Fe3O4/GO-Mo are presented in Fig. 1. The original graphite
shows a sharp characteristic diffraction peak at 2θ = 26.5o, corresponding to the (002) crystal plane. After
o
the oxidation treatment, the (002) diffraction peak for graphite shifted to lower angle at 2θ = 12.5 C,
indicating the formation of GO. The main peaks in Fe3O4/GO-Mo at 2θ = 30.1º, 35.5º, 43.5º, 57.0o and
62.6o corresponding to the diffractions of (220), (311), (400), (511) and (440), show the characteristics of
Fe3O4 (JCPDS 19-0629), which implied that the crystal structure of the Fe3O4 core was still
well-maintained after functionalization [34]. But no significant diffraction peak characteristic of Mo was
detected, which was likely due to its low concentrations and poor crystallinity. The elemental composition
of the Fe3O4/GO-Mo sample was determined by energy dispersive spectrum (EDS) analysis. The result
indicates (Fig. S1 in supporting information) that the prepared catalyst contains C, N, O, Fe, and Mo
element. It was revealed that Mo had been successfully immobilized on the surface of GO. The amount of
Mo and Fe in Fe3O4/GO-Mo catalyst was found to be 7.70% and 55.2% respectively based on inductively
coupled plasma mass spectrometry (ICP-MS) analysis.
The surface modification of the Fe3O4/GO-Mo nanoparticles was also investigated by X-ray
photoelectron spectroscopy (XPS) analysis (Fig. S2 in SI), which shows the characteristic peaks for C 1s
(284.8 eV), N 1s (399.5 eV), O 1s (530.0 eV), Fe 2p (711.6 eV), and Mo 3d (235.0 eV). Furthermore, the
high-resolution narrow scan for Mo 3d displays energy peaks of Mo 3d5/2 and Mo 3d3/2 at 232.0 and
235.1 eV, respectively, which corresponded to the characteristic of Mo at a VI oxidation state. It clearly
indicates that Mo complex has been successfully introduced on GO.
The magnetic property of the Fe3O4/GO-Mo was measured by using vibrating sample magnetometry
(VSM) at room temperature. Magnetic measurement indicates the magnetic behaviour of the prepared
Fe3O4/GO-Mo and the saturation magnetization value was found to be 28.6 emug-1 (Fig. S3 in SI). A
suitable magnetic property of the prepared Fe3O4/GO-Mo fulfils our aim to develop a more efficient and
easily separable catalyst for organic reactions.
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(a)
(b)
(c)
10
20
30
40
50
60
70
80
2Theta(degree)
Fig. 1 XRD pattern of graphite (a), GO (b), and Fe3O4/GO-Mo (c)
The TEM images of GO, Fe3O4/GO and Fe3O4/GO-Mo are shown in Fig. S4 (in SI) and Fig. 2,
respectively. The TEM image of Fe3O4/GO shows that Fe3O4 nanoparticles are distributed homogeneously
throughout the graphene oxide surface. This image is the direct proof of the formation of Fe3O4/GO by
chemically deposited Fe3O4 on GO. The TEM image of the Fe3O4/GO-Mo shows that the graphene oxide
sheets are decorated with large quantities of Fe3O4 and molybdenum NPs. The average size of these
particles was estimated to be about 30 nm, which is also in accordance with the result calculated by the
Debye–Scherrer’s equation by XRD data. The SEM image of Fe3O4/GO (Fig. 5 in SI) and Fe3O4/GO-Mo
(Fig. 3) confirms that these nanoparticles are uneven-sized particles and most of the particles have a
quasi-spherical shape.
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Fig. 2 TEM images of Fe3O4/GO-Mo.
Fig. 3 SEM image of Fe3O4/GO-Mo.
The catalytic activity of the prepared catalyst was then evaluated in the model reaction of isatin,
malononitrile and 4-(p-tolylamino)furan-2(5H)-one. As shown in Table 1, the desired product 4c was
o
obtained in 40% yield using 1.5 mol% Fe3O4/GO-Mo at 90 C in glycerol for 1 h under microwave
irradiation (Table 1, entry 1). Ghahremanzadeh and co-workers reported that this reaction was performed in
the presence of a catalytic amount of manganese ferrite nanoparticles in PEG-400 to give product 4c in
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83% yield [35]. To further improve the yield, various reaction parameters were evaluated systematically.
Some solvents were first screened and ChCl/urea was proved to be optimal and gave 4c in 96% yield (entry
10). Control experiments confirmed that, in the absence of any catalyst or the presence of Fe3O4 or GO,
only trace amount of the targeted product was detected (Table 1, entries 11-13). Other metal supported on
graphene oxide/Fe3O4 such as Zn, Sn, Mn, Cu and Co were examined for this reaction, but unfortunately
afforded unsatisfactory results (entries 14-18). In addition, we also investigated the influence of not having
microwave irradiation on the model reaction (entry 19). It was found that the reaction under heating
condition without microwave irradiation needed longer time and the yield of the expected product was
lower than under microwave irradiation. The effect of microwave power on the reaction was also examined.
The results showed that 500 W was the appropriate power for this reaction. The catalyst loading had a
dramatic effect on reaction outcomes. When the amount of catalyst was reduced to 1.0 mol%, the yield of
product 4c dropped to 89%. A further increase of the amount of catalyst to 2 mol% did not affect the yield.
A survey of the temperature was also conducted. The desired product 4c was only formed in 54% yield at
o
70 C. And decreasing the temperature to room temperature did affect the reaction efficiency and only
traces of expected product were obtained (entry 26). However, the yield of the product was not improved as
the reaction temperature increased from 90 oC to 100 oC.
Table 1
The effect of reaction condition on the reaction of isatin, malononitrile, and
4-(p-tolylamino)furan-2(5H)-onea
MW
(W)
500
Time
(min)
60
Yield
(%)b
40
Entry Catalyst
Solvent
Glycerol
EtOH
Temp (oC)
1
Fe3O4/GO-Mo
90
2
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4
500
500
reflux
90
60
60
60
60
60
60
60
60
50
120
120
62
3
H2O
trace
trace
trace
17
4
ChCl/L-(+)-tartaric acid (2:1) 500
90
5
ChCl/glucose (1:2)
ChCl/fructose (1:2)
ChCl/itaconic acid (1:1)
ChCl/citric acid (1:2)
ChCl/glycerol (1:2)
ChCl/urea (1:2)
500
500
500
500
500
500
500
500
90
6
90
7
90
21
8
90
53
9
90
67
10
11
12
90
96
ChCl/urea (1:2)
90
trace
trace
GO
ChCl/urea (1:2)
90
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13
14
15
16
17
18
19
20
21
22
23
24c
25d
26
27
28
No
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
ChCl/urea (1:2)
500
500
500
500
500
500
0
90
90
90
90
90
90
90
90
90
90
90
90
90
25
70
80
100
120
60
trace
35
Fe3O4/GO-Zn
Fe3O4/GO-Sn
Fe3O4/GO-Mn
Fe3O4/GO-Cu
Fe3O4/GO-Co
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
Fe3O4/GO-Mo
60
60
60
83
60
71
60
47
240
120
120
90
93
200
300
400
600
500
500
500
500
500
500
91
93
94
50
96
90
89
50
96
120
90
trace
54
90
81
29
50
94
a
Reaction was performed with isatin (1 mmol), malononitrile (1 mmol), and
4-(p-tolylamino)furan-2(5H)-one (1 mmol), catalyst (20 mg, 0.015 mmol of Mo) in 1 ml solvent otherwise
specified in the Table.
b Isolated yields.
c Catalyst (0.01 mmol of Mo).
d Catalyst (0.02 mmol of Mo).
Having established the optimized reaction conditions, the scope and generality of this protocol were
explored and representative results are displayed in Table 2. Firstly, isatin was fixed as the substrate to test
various substituted anilinolatctones. It was found that anilinolactones bearing electron-neutral, electron-rich
or electron-poor groups on benzene ring reacted with isatin and malononitrile to produce the desired
products 4a-4f in high yields. It was noted that anilinolactones possessing halogenated functional groups
such as Cl and Br were well-tolerated and led to a beneficial effect on the reaction outcome, which allowed
for easy further functionalization. However, the target product was not formed when the reaction was
carried out using 4-(pyridin-2-ylamino)furan-2(5H)-one.
Subsequently, various isatins with electron-rich or electron-poor groups on the benzene ring were also
tested. In most cases, this three-component reaction proceeded smoothly and the expected products were
obtained in high yields. In contrast, no product was observed under above conditions when
4-bromoindoline was used as a substrate.
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Table 2
Scope of substrates for synthesis of spiro-oxindole dihydropyridine derivativesa.
a Reaction conditions: isatins (1 mmol), malononitrile (1 mmol), and anilinolactones (1 mmol) in ChCl/urea
(1 ml), MW 500 W, 90 °C.
Finally, we investigated the recovery and reusability of the catalytic system in the model reaction. After
completion of the reaction, the reaction mixture was cooled to room temperature, the catalyst was separated
magnetically, and washed with acetone followed by water, and dried under vacuum. Then, water was added
to the reaction mixture to dissolve DES. The formed solid product was collected by filtration. The water of
the aqueous phase containing the DES, was evaporated under reduced pressure in order to recover the DES.
The recover DES and catalyst were reused in the model reaction for the next round. It was found that the
catalytic system could be reused up to eight consecutive catalytic runs without a significant change in
catalytic activity (Fig. 4). The amount of Mo and Fe leaching was also determined by ICP-MS analysis and
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found that the Mo and Fe contents after eight cycles were 0.82 and 0.66 ppm in ChCl/urea, respectively.
This result confirmed that only a slight loss of the catalyst occurred during the course of work-up process.
In order to prove the heterogeneous nature of the catalyst, a hot-filtration test was performed. The
catalyst was separated from the reaction mixture (after 30 min associated with approximate 50% conversion)
using an external magnet. The progress of the reaction was monitored after removal of the catalyst. No
further improvement of the yield of product was observed even after an extended time (1.5 h), indicating
that the catalyst was stable under the reaction conditions and no leaching of the active species from the
support.
Fig. 4 Reusability of the Fe3O4/GO-Mo in ChCl/urea catalytic system in the model reaction. Reaction
conditions: isatin (10 mmol), malononitrile (10 mmol), and 4-(p-tolylamino)furan-2(5H)-one (10 mmol),
catalyst (200 mg) in ChCl/urea (10 ml).
4. Conclusion
In summary, we have developed a new type of magnetically separable graphene oxide supported
molybdenum (Fe3O4/GO-Mo) catalyst and demonstrated that it was an efficient heterogeneous catalyst for
synthesis of spiro-oxindole dihydropyridines via one-pot, three-component reaction of isatins, malononitrile
and anilinolactones in ChCl/urea under microwave irradiation. Moreover, catalytic system could be easily
recovered and reused eight times without significant loss of activity, conferring great potential for industrial
application.
Acknowledgments
We are grateful for the financial support from the National Natural Science Foundation of China
(21272053), the Natural Science Foundation of Hebei Province (B2015205182 and H2015206393) and the
Natural Science Foundation of Hebei Education Department (QN2014126).
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• Graphical Abstract:
Supported molybdenum on graphene oxide/Fe3O4: an efficient, magnetically separable catalyst for
one-pot construction of spiro-oxindole dihydropyridines in deep eutectic solvent under microwave
irradiation
Mo Zhang, Yu-Heng Liu,* Ze-Ren Shang, Hai-Chuan Hu and Zhan-Hui Zhang*
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Highlights
 Preparation of a new magnetic graphene oxide supported molybdenum catalyst.
 It showed high catalytic activity for the synthesis of spiro-oxindole dihydropyridines.
 The catalyst could be easily isolated by magnetic decantation.
 The catalyst was reused several times without any significant loss in catalytic activity.
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