Core–shell structured Fe3O4?SiO2-supported IL/[Mo6O19]: A novel and magnetically recoverable nanocatalyst for the preparation of biologically active dihydropyrimidinones

Article abstract of DOI:10.1016/j.jpcs.2020.109601

The synthesis and catalytic application of a novel magnetic silica-nanomaterial-supported ionic liquid/hexamolybdate (Fe₃O₄?SiO₂-IL/[Mo₆O₁₉]) are reported. The Fe₃O₄?SiO₂

Full text of DOI:10.1016/j.jpcs.2020.109601

Journal Pre-proof
Core–shell structured Fe O @SiO -supported IL/[Mo O ]: A novel and
3 4
2
6 19
magnetically recoverable nanocatalyst for the preparation of biologically active
dihydropyrimidinones
Shiva Kargar, Dawood Elhamifar, Ali Zarnegaryan
PII:
S0022-3697(20)30337-1
https://doi.org/10.1016/j.jpcs.2020.109601
PCS 109601
DOI:
Reference:
To appear in: Journal of Physics and Chemistry of Solids
Received Date: 6 February 2020
Revised Date: 31 May 2020
Accepted Date: 1 June 2020
Please cite this article as: S. Kargar, D. Elhamifar, A. Zarnegaryan, Core–shell structured Fe O @SiO -
3 4
2
supported IL/[Mo O ]: A novel and magnetically recoverable nanocatalyst for the preparation of
6 19
biologically active dihydropyrimidinones, Journal of Physics and Chemistry of Solids (2020), doi: https://
doi.org/10.1016/j.jpcs.2020.109601.
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Author statement
Shiva Kargar: Investigation, Writing - Original Draft
Dawood Elhamifar: Conceptualization, Writing - Review & Editing, Supervision, Visualization
Ali Zarnegaryan: Resources, Formal analysis

Graphical abstract
A novel core–shell structured magnetic silica-supported ionic liquid/hexamolybdate complex
(Fe3O4@SiO2-IL/[Mo6O19]) has been prepared and characterized, and its catalytic performance
in the Biginelli reaction has been investigated.

Core–shell structured Fe3O4@SiO2-supported IL/[Mo6O19]: A
novel and magnetically recoverable nanocatalyst for the
preparation of biologically active dihydropyrimidinones
Shiva Kargar, Dawood Elhamifar* and Ali Zarnegaryan
Department of Chemistry, Yasouj University, Yasouj, 75918-74831, Iran
E-mail: d.elhamifar@yu.ac.ir
Abstract: The synthesis and catalytic application of a novel magnetic silica-nanomaterial-
supported ionic liquid/hexamolybdate (Fe3O4@SiO2-IL/[Mo6O19]) are reported. The
Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst was prepared through modification of magnetic
Fe3O4@SiO2 nanoparticles with alkyl-imidazolium ionic liquids followed by treatment
with hexamolybdate anions. The Fe3O4@SiO2-IL/[Mo6O19] was characterized using FTIR,
EDX, TGA, SEM, TEM, PXRD, and VSM techniques. This nanocatalyst exhibited
excellent activity in the one-pot synthesis of biologically active dihydropyrimidinones
through the Biginelli reaction. Furthermore, this magnetically recoverable nanocatalyst
could be reused at least seven times without a significant loss of efficiency.
Keywords: Core–shell structure; Nanocatalyst; Polyoxometalate; Biginelli reaction
1

1. Introduction
Magnetic NPs are a very important group of nanomaterials incorporating Fe, Ni, and/or
Co in their cores. Among them, applications of magnetic Ni and Co NPs are limited by
their toxicity and high susceptibility to oxidation. Meanwhile, magnetite nanoparticles
(MNPs) have attracted much attention from researchers due to their ease of preparation,
nontoxicity, and eco-friendly nature [1-10]. However, the stability of Fe3O4 NPs has
remained a challenge since they are sensitive to acidic and basic conditions and also tend
to aggregate due to their magnetic nature. The aggregation and conversion of small MNPs
into larger clusters limits their use in various processes [11-15]. To overcome these
problems, many methods have been proposed for the protection of MNPs, which has led
to the creation of core–shell nanostructures. These structures are defined as composites of
nanomaterials with an inner core and one or more outer layer(s) as a shell [16-31]. Such
core–shell structured MNPs have found numerous applications in diverse areas, such as
biosensors [32-34], bioimaging [32, 35], drug delivery [36-40], optoelectronics [41-43],
environmental extraction [44, 45], and especially in the field of catalysis [44, 46-49].
Different types of shell materials, such as polymers [50], silica [51, 52], carbon [48], and
noble metals can be used for coating of magnetic NPs [53-55]. Among them, silica is often
most attractive due to its facile modification with different organic or inorganic catalytic
functional groups. In core–shell structures of this type, iron oxide nanoparticles form the
cores and the silica layer acts as a protective shell. Therefore, silica-coated magnetic
nanoparticles provide a clear perspective on the design and synthesis of recyclable and
efficient magnetic nanocatalysts [56, 57]. Some recently reported magnetic catalytic
systems with protective silica shells include Fe3O4/SiO2-PIL [58], Fe3O4@SiO2@mSiO2-
2

Fe [59], Fe3O4@SiO2@Ag@COOH [60], Fe3O4@SiO2@ZnO [61], Fe3O4@SiO2@PPy
[62], Fe3O4@SiO2/Bi2WO6/Bi2S3 [63], Fe3O4@SiO2@C-Ni [64], Fe3O4@SiO2-EDTA
[65], Fe3O4/SiO2/ZnO/ZnSe [66], and ionic-liquid-functionalized magnetic silica
composites [67].
On the other hand, polyoxometalates (POMs) are inorganic complexes with significant
physical and chemical properties that are based on transition metals (TM=V, W, Nb, Mo,
Ta) in their highest oxidation states and oxygen bridges [68-70]. These are diverse in
shape, size, and composition, varying from small species such as [Mo6O19]2- to
nanoparticles such as ([HxMo368O10329(H2O)240(SO4)48])[Mo368]. The properties of
polyoxometalates, such as high thermal stability, solubility in polar solvents, good
electron capture and electron capability, and high stability during oxidation reactions,
endow them with strong potential for applications in different areas of chemical
processing [71-75]. Moreover, variation of the structures of polyoxometalates has
facilitated their applications in pharmaceuticals [76], coatings [77], separation [78],
sensors [79], membranes [80], dyes [81], electrochemistry [82], capacitors [83], and
catalysis [84-90]. However, the high solubility of POMs in polar solvents is a drawback,
hampering separation and recovery of these complexes [91]. Therefore, the
immobilization of POMs on solid supports such as silica and MNPs is a way to overcome
this problem. Some recently developed systems of this type include AILs/HPW/UiO-66-
2COOH [92], Fe3O4@SiO2@NH-NH2–PW [93], Fe3O4@SiO2@ADMPT/H6P2W18O62
[94], and Fe3O4@D-NH2-HPA [95].
Meanwhile, multicomponent reactions (MCRs) have a special place in organic and
pharmaceutical chemistry, playing a key role in the production of different fine chemicals
3

and drug intermediates [96]. The Biginelli reaction [97] is a type of MCR used for the
preparation of dihydropyrimidinones with good biological profiles, such as anti-viral [98],
anti-hypertensive [99], and anti-bacterial properties [100]. To date, many homogeneous
and heterogeneous catalysts have been used for the Biginelli reaction. These include
Fe3O4@CM [101], Fe3O4-MWCNT [102], IL-HSO4@MCM-41@Cu [103], ompg-
C3N4/SO3H [104], ZnO/AlSBA-15 [105], AgNdSiW11 [106], ZnO@SBA-15 [107],
Ca7Mg3Hap [108], BPMO–IL–SO3H [109], Mn@PMO-IL [110], Cu@PMO-IL [111],
Cu/SB-Fe3O4 [112], PEt@Fe/IL [113], and Fe3O4@MCM-41-OB(OH)2 [114]. However,
some of the reported catalytic systems suffer from problems of long reaction times, harsh
conditions, the use of a toxic organic solvent, low efficiency, and safety concerns.
Therefore, the design and preparation of novel heterogeneous catalysts with high
efficiency and recoverability to overcome the aforementioned restrictions is an important
challenge in this context.
In view of the above, and due to the importance of polyoxometalates in catalytic
processes, we report herein the synthesis and characterization of a novel magnetite core–
shell silica-supported ionic liquid/polyoxometalate complex, Fe3O4@SiO2-IL/[Mo6O19].
This system has been employed as an effective, highly stable, and reusable nanocatalyst in
the Biginelli reaction.
2. Experimental
2.1. Materials
4

All chemicals and reagents, namely iron(II) chloride tetrahydrate (99%), iron(III) chloride
hexahydrate (99%), concentrated HCl, tetramethoxysilane (TMOS, 99%), ammonia
(28%), 1-methylimidazole (99%), (3-chloropropyl)trimethoxysilane (97%), toluene,
dimethyl sulfoxide, and the respective aldehyde derivatives, were purchased from Merck,
Fluka, or Sigma-Aldrich.
2.2. Preparation of Fe3O4@SiO2-IL
Firstly, Fe3O4@SiO2 NPs were synthesized by a chemical co-precipitation method [115].
To prepare Fe3O4@SiO2-IL, Fe3O4@SiO2 NPs (0.5 g) were completely dispersed in
toluene (15 mL) under ultrasonication. 1-Methyl-3-(3-trimethoxysilylpropyl)imidazolium
chloride (30 mg) was then added and the resulting mixture was heated under reflux for
24 h. The precipitate produced was collected with the aid of an external magnet, washed
with EtOH, and dried at 70 ºC for 5 h. The product was designated as Fe3O4@SiO2-IL.
2.3. Preparation of Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst
For this, tetrabutylammonium hexamolybdate ((n-Bu4N)2[Mo6O19]) was first prepared
according to a previously reported procedure [113]. In order to immobilize [Mo6O19]2- on
the Fe3O4@SiO2-IL nanomaterial, Fe3O4@SiO2/IL (0.5 g) was completely dispersed in
dimethyl sulfoxide (15 mL) under ultrasonication. (n-Bu4N)2[Mo6O19] (0.2 g) was then
added and the resulting mixture was stirred at 25 °C for 24 h. The obtained product was
separated magnetically, washed with EtOH, and dried at 60 ºC for 5 h. It was designated
as Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst.
2.4. Synthesis of 3,4-dihydropyrimidinones using Fe3O4@SiO2-IL/[Mo6O19]
5

For this, Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst (0.01 g, 0.25 mol%) was added to a
mixture of urea (1.5 mmol), aldehyde (1 mmol), and alkyl-acetoacetate (1 mmol). This
mixture was sonicated at 65 ºC and the progress of the reaction was monitored by TLC.
After completion of the reaction, warm EtOH (10 mL) was added and the mixture was
filtered while hot. The 3,4-dihydropyrimidinone products were obtained after adding some
ice followed by recrystallization from EtOH.
2.5. Characterization
Fourier-transform infrared (FTIR) spectra were recorded on a Bruker Vector 22
spectrometer. Energy-dispersive X-ray spectra (EDX) were obtained on a TESCAN Vega
spectrometer. Scanning electron microscopy (SEM) images were acquired with a Philips
XL30 emission scanning electron microscope. The magnetic properties of the particles
were studied by vibrating sample magnetometry (VSM) on an instrument from Meghnatis
Daghigh Kavir Co. Powder X-ray diffraction (PXRD) patterns were acquired with a
PANalytical X-Pert diffractometer. TGA was performed using a Netzsch STA 409 PC/PG
apparatus. Transmission electron microscopy (TEM) was performed with an FEI TECNAI
12 BioTWIN microscope. Melting points were determined using a Krüss KSB1N
apparatus with samples in open capillary tubes. A KMM1-120WE301 ultrasonicator was
used to disperse the particles and to promote the organic reactions.
3. Results and discussion
The preparation of Fe3O4@SiO2-IL/[Mo6O19] nanocomposite is illustrated in Scheme 1.
As shown, a silica shell was first coated on the Fe3O4 surface through a sol–gel process to
6

give Fe3O4@SiO2 nanoparticles. The Fe3O4@SiO2 NPs were then reacted with an alkyl-
imidazolium IL to give Fe3O4@SiO2-IL. Finally, Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst
was obtained by treatment of Fe3O4@SiO2-IL with (n-Bu4N)2[Mo6O19] (Scheme 1).
Scheme 1. Preparation of Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst.
Figure 1 shows the FTIR spectra of the prepared nanomaterials. In the IR spectrum of
Fe3O4, the peak at 579 cm-1 is due to the vibration mode of Fe–O bonds and the band at
3478 cm-1 can be assigned to O-H bonds on the surface of the Fe3O4 NPs. For the
Fe3O4@SiO2 and Fe3O4@SiO2-IL/[Mo6O19] nanomaterials (Figures 1b, 1c), the peaks at
1091 and 800 cm-1 are related to Si-O-Si bonds [116]. Moreover, the peaks at 3200–
7

3500 cm-1 are assigned to OH bonds on the silica surface. For the latter sample, Fe-O
bands were observed at 550–590 cm-1. In the spectrum of Fe3O4@SiO2-IL/[Mo6O19]
(Figure 1c), weak peaks discernible at 2900–3000 cm-1 are related to aliphatic C-H bonds
of methyl and propyl groups, and a peak at 3030 cm-1 can be attributed to aromatic C-H
bonds of imidazolium rings. Moreover, peaks at 1640 and 1417 cm-1 can be ascribed to
C=N and C=C bonds of IL rings, respectively. In addition, for Fe3O4@SiO2-IL/[Mo6O19],
the peaks at 958 and 796 cm-1, corresponding to stretching vibrations of Mo=O and Mo-
O-Mo bonds, respectively, of the [Mo6O19] complex anion, are overlapped with the Si-O-
Si bands [117]. These results fully confirm the incorporation/immobilization and high
stability of silica, ionic liquid, and polyoxometalate moieties into/onto the material
framework.
8

Figure 1. FTIR spectra of Fe3O4 (a), Fe3O4@SiO2 (b), and Fe3O4@SiO2-IL/[Mo6O19] (c).
The EDX analysis of the Fe3O4@SiO2-IL/[Mo6O19] catalyst is shown in Figure 2. The pattern
demonstrated the presence of C, N, O, Si, Mo, Cl, and Fe in the sample. This result is in good
agreement with the FTIR data, indicating immobilization of the ionic liquid and [Mo6O19]
moieties on Fe3O4@SiO2.
9

Figure 2. EDX analysis of the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst.
The thermal stability of the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst was studied from 25 to
900 ºC by means of thermal gravimetric analysis (Figure 3). The first weight loss observed
below 130 ºC (about 2%) is related to the removal of H2O and residual EtOH/MeOH
solvents from the extraction process. The second weight loss between 220 and 310 ºC
(about 2%) corresponds to the removal of organic moieties located on the catalyst surface.
The main weight loss at 350–650 ºC (about 8%) can be attributed to the decomposition
and removal of ionic liquid groups that make up the material network. The final weight
loss above 650 ºC (about 2%) corresponds to the removal of residual organic groups
appended to the material framework.
10

Figure 3. TG analysis of the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst.
The surface morphology of the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst was investigated
by SEM (Figure 4). This analysis showed the catalyst to be composed of spherical
particles. Particles of this type have potential applications in catalytic and adsorption
processes.
11

Figure 4. SEM image of Fe3O4@SiO2-IL/[Mo6O19].
A TEM image (Figure 5) of the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst clearly showed a
core–shell structure, with black cores (magnetite particles) and gray shells (silica layers).
12

Figure 5. TEM image of Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst.
Figure 6 shows the PXRD pattern of the nanocatalyst. It features seven reflection peaks at
2θ=30.29º, 35.61º, 43.26º, 53.65º, 57.22º, 62.86º, and 74.48º, corresponding to Miller
indices (hkl) of 220, 311, 400, 422, 511, 440, and 533, respectively. These are related to
the crystalline structure of Fe3O4, confirming high stability of magnetite NPs after
modification with different functional groups. A weak reflection peak at 2
corresponds to the amorphous silica shell.
θ=18.14º
13

Figure 6. PXRD pattern of Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst.
VSM was carried out to verify the magnetic properties of the designed catalyst (Figure 7).
The magnetic saturation value of the catalyst was evaluated as 40 emu/g, confirming its
high degree of paramagnetism. This is a very good characteristic, especially in the fields
of catalysis and adsorption.
14

Figure 7. VSM analysis of Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst.
After characterization of the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst, its performance in
the Biginelli reaction was studied (Table 1). The condensation of benzaldehyde with ethyl
acetoacetate and urea was chosen as a test reaction, and was conducted under
ultrasonication.
15

Table 1. Screening different parameters in a Biginelli reaction catalyzed by Fe3O4@SiO2-
IL/[Mo6O19].
O
O
O
O
O
Fe3O4@ SiO2/IL-Mo6O19
EtO
H3C
NH
H2N
NH2
H
H3C
OEt
N
O
H
Yield (%)a
T (⁰C)
Entry
Solvent
Time (min)
Catalyst (mol % of Mo)
ethanol
toluene
1
2
3
0.25
0.25
0.25
65
65
65
40
40
40
84
21
73
H2O
-
4
5
0.25
0.2
65
65
65
75
45
25
65
40
40
40
40
40
40
40
92
81
93
93
54
<7
5
-
6
0.3
-
7
0.25
0.25
0.25
-
8
-
-
9
b
10 b
H2O
Fe3O4@SiO2
11 c
12
65
65
40
40
10
H2O
Fe3O4@SiO2/ILc
-
(n-Bu4N)2[Mo6O19]d
67
a
b
c
d
Isolated yield. 0.01 g of Fe3O4@SiO2 was used. 0.01 g of Fe3O4@SiO2/IL was used. (n-
Bu4N)2[Mo6O19] was used as catalyst.
16

Performing the reaction in different solvents, yields of 73% and 84% were obtained in
H2O and ethanol, respectively. In toluene, however, the yield was only 21%. Pleasingly,
under solvent-free conditions, the best conversion and yield were obtained (Table 1,
entries 1–4). Therefore, in subsequent experiments, the reactions were performed without
a solvent. Next, the effect of catalyst amount was studied (Table 1, entries 4–6). The
results showed that the reaction gave satisfactory conversions using 0.2 to 0.25 mol% of
catalyst. Increasing the catalyst loading to 0.3 mol% did not result in a significant change
in the reaction yield. The study also showed the reaction to be affected by temperature,
and the best result was observed at 65 °C. Accordingly, 0.25 mol% of Fe3O4@SiO2-
IL/[Mo6O19] under solvent-free conditions, 65 °C, and ultrasonic irradiation were
identified as the optimal conditions. In order to demonstrate the effect of the
hexamolybdate centers on the catalytic process, the catalytic activities of Fe3O4@SiO2 and
Fe3O4@SiO2/IL were also investigated, and the results were compared with those for
Fe3O4@SiO2/IL-Mo6O19. These experiments showed that both hexamolybdate-free
nanomaterials gave only low yields of the desired product, verifying that the reaction is
actually catalyzed by the supported hexamolybdate species (Table 1, entry 4 vs entries 10,
11). Interestingly, the unsupported hexamolybdate also showed significantly lower
catalytic activity compared with Fe3O4@SiO2/IL-Mo6O19, which may be attributed to the
tendency of POMs to form agglomerates or inactive dimers in homogeneous solution.
Importantly, ionic liquids as stabilizing agents can reduce these drawbacks through
electrostatic interaction between the imidazolium cation and the hexamolybdate anions
(Scheme 1) [118].
17

We then proceeded to apply various aldehyde derivatives as substrates to deliver the
corresponding dihydropyrimidinones under the optimal conditions (Table 2).
Table 2. Synthesis of 3,4-dihydropyrimidone derivatives in the presence of Fe3O4@SiO2-
IL/[Mo6O19] nanocatalyst.
O
Ar
O
O
O
Fe3O4@SiO2/IL-Mo6O19
Solvent free, 65 oC, )))
ArCHO
R
NH
H2N
NH2
H3C
R
H3C
N
H
O
Time
(min)
Yielda
m. p.
m. p.
Entry
1
R
TONb
368
TOFc
557.5
Aldehyde
(%)
(found) (reported)
201–203
201–203
OEt
OMe
OEt
40
40
50
50
92
[119]
208–211
210–212
2
3
4
90
88
87
360
352
348
545.4
424.0
419.2
[120]
213–
213–215
215[120]
251–253
250–252
OMe
[121]
199–201
198–200
5
OEt
50
86
344
414.4
[119]
18

191–193
[119]
6
7
OMe
OEt
50
30
85
94
340
376
409.6
752
193–195
209–211
210–211
[120]
193–195
[110]
8
9
OEt
OEt
55
60
87
83
348
332
382.4
332
194–196
233–235
231–233
[120]
a
b
Isolated yield. Turnover number [defined as yield (%)/ cat. (mol%)]. c Turnover frequency
[defined as TON/reaction time (h)].
As can be seen, aldehydes bearing both electron-donating and electron-accepting
substituents were employed as substrates, all of which delivered the corresponding
Biginelli products in high to excellent yields. It was also found that Fe3O4@SiO2-
IL/[Mo6O19] offers high turnover number (TON) and turnover frequency (TOF) for all
products, indicating high performance of the designed catalyst in the preparation of
different dihydropyrimidinone derivatives.
The recoverability and reusability of the catalyst were also investigated. These
experiments showed that the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst could be reused at
19

least seven times in the Biginelli process with no significant reduction in efficiency
(Figure 8), indicating high stability and durability of this nanocatalyst under the applied
conditions.
Figure 8. Reusability of the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst.
In the next experiment, a leaching test was performed. For this, after the condensation was about
45% complete, the catalyst was separated magnetically and the reaction of the residue was
allowed to continue under the optimum conditions. Interestingly, after 60 min, no further
progress of the reaction was observed, confirming the heterogeneous nature of the catalyst as
well as the high efficiency of the Fe3O4@SiO2-IL support in the immobilization of active
polyoxometalate species.
A mechanism for the Biginelli reaction using Fe3O4@SiO2-IL/[Mo6O19] catalyst is proposed in
Scheme 2. As shown, the aldehyde (1) is first activated by Lewis acidic Mo sites of the
20

hexamolybdate species. In the next step, nucleophilic attack of urea (2) on the activated carbonyl
group followed by elimination of water produces an N-acyliminium cation (3). Subsequently,
nucleophilic attack of the enolate form of β-ketoester 4 followed by deprotonation by Lewis
basic oxygen groups of the catalyst produces intermediate 5. Finally, the desired Biginelli
product is obtained by ring-closure and the elimination of water.
21

Scheme 2. Proposed mechanism for Biginelli reaction using Fe3O4@SiO2-IL/[Mo6O19]
nanocatalyst.
Finally, the performances of Fe3O4@SiO2-IL/[Mo6O19] and previously reported catalysts in the
Biginelli reaction were compared (Table 3). The results showed that although the previous
catalytic systems have advantages of good recoverability and separation, the present catalyst is
better, especially in terms of the mild conditions applied, reaction rate, and recovery times.
Moreover, the TON and TOF of the present catalytic system exceed those quoted in previous
reports. These findings may be attributed to the magnetic nature of this catalyst, the chemically
immobilized ionic liquid moieties, as well as the bifunctional properties (both Lewis acidic and
Lewis basic sites) of the supported polyoxometalate.
Table 3. Comparative study of the efficiency of the Fe3O4@SiO2-IL/[Mo6O19] nanocatalyst
with previously reported catalytic systems in the Biginelli reaction.
Entry
1
Catalyst
Conditions
Time
(min)
TON
TOF
84.4
Recovery Ref.
times
PEt@Fe/IL
Cat.
90
50
126.7
7
[113]
(0.75 mol%),
solvent-free,
80 °C
2
GO-ZrPPh
Cat.
121.3
146.1
4
[122]
22

(0.28 mol%),
solvent-free,
70 °C
3
4
5
n-ZrSA
Cat. (10 mol%),
solvent-free,
90 °C
30
40
40
9.8
208.8
367
19.6
316.3
557.5
5
4
7
[123]
[124]
SnCl2/nano SiO2 Cat.
(0.45 mol%),
EtOH, reflux
Fe3O4@SiO2-
IL/[Mo6O19]
Cat.
This
(0.25 mol%),
solvent-free,
65 °C
work
Abbreviations: PEt@Fe/IL: polyethylene-supported Fe/ionic liquid complex; GO-ZrPPh:
zirconium(IV) porphyrin graphene oxide; n-ZrSA: nano-ZrO2 sulfuric acid; SnCl2/nano SiO2:
nanosilica-supported tin(II) chloride.
4. Conclusion
A
novel core–shell magnetite silica-supported ionic liquid/hexamolybdate complex
(Fe3O4@SiO2-IL/[Mo6O19]) has been prepared for the first time, and its properties have been
investigated. FTIR, EDX, TGA, SEM, TEM, PXRD, and VSM analyses of the Fe3O4@SiO2-
23

IL/[Mo6O19] proved successful coating and immobilization of silica, ILs, and hexamolybdate
ions on the surface of the Fe3O4 NPs. The Fe3O4@SiO2-IL/[Mo6O19] catalyst has been
heterogeneously and powerfully employed in the Biginelli reaction to give dihydropyrimidinones
in high yields. Other advantages of this catalytic system are easy separation of the products and
catalyst, short reaction times, solvent-free conditions, low catalyst loading, and high efficiency of
the catalyst. Further application of Fe3O4@SiO2-IL/[Mo6O19] is underway in our laboratory.
Acknowledgements
The authors acknowledge Yasouj University and the Iran National Science Foundation (INSF)
for supporting this work.
24

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