Synthesis, Characterization, and Heterogeneous Catalytic Activity of Sulfamic Acid Functionalized Magnetic IRMOF-3

Article abstract of DOI:10.1002/ejic.201801054

In this work, post-synthesis modification of Fe₃O₄/IRMOF-3 nanocomposite with chlorosulfonic acid groups afforded sulfamic acid-functionalized magnetic metal-organic frameworks (Fe₃O₄/IRMOF-3/SO₃H). F

Full text of DOI:10.1002/ejic.201801054

A Journal of
Accepted Article
Title: Synthesis, characterization and heterogeneous catalytic activity
of sulfamic acid functionalized magnetic IRMOF-3
Authors: Mohammad Mahdi Mostafavi and Farnaz Movahedi
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201801054
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
Synthesis, characterization and heterogeneous
catalytic activity of sulfamic acid functionalized
magnetic IRMOF-3
Mohammad Mahdi Mostafavi and Farnaz Movahedi∗
Department of Chemistry and Petrochemical Engineering, Standard Research Institute, P.O.
Box 31745-139, Karaj, Iran
Abstract
Here in, post-synthesis modification of Fe3O4/IRMOF-3 nanocomposite with chlorosulfonic acid groups afforded sulfamic acid-
functionalized magnetic metal-organic frameworks (Fe3O4/IRMOF-3/SO3H). Functionalization was followed through FT-IR, XRD,
TGA, BET, FE-SEM/EDS and elemental analyses. The catalytic efficiency of the as prepared nanocomposite was evaluated
through one-pot pseudo four-component reaction of secondary amines, malononitrile and salicylaldehydes in EtOH under mild
conditions. Magnetic tendency of the functionalized IRMOF-3, made simple decantation by external magnetic field from the
reaction mixture, continued with catalyst reuse for at least five times without significant loss of catalytic efficiency.
Introduction
The use of multicomponent reactions (MCRs) strategy leading to the construction of novel and complex molecular
structures in comparison to conventional multi-step synthesis, is fascinating for the scientific community.[1-3] The virtues
of procedure simplicity, reduction of time, energy and costs, and avoidance of time-consuming expensive purification
processes[4,5] play decisive roles. On the other hand, Bronsted acids are general catalysts in various organic reactions
because of their good reactivity and selectivity in catalysis fields.[6] However, there are some disadvantages in using
homogeneous Bronsted acid catalysts, such as difficulties in their separation, recovery and recycling, environmental
pollution and intense corrosion of equipment.[7] Recently, some kind of heterogeneous Bronsted acid catalysts, in which
can be reached through the chemical cross-linking of acid resources with solid phase supports, such as phenylsulfonic
acid and tungstic acid groups with mesoporous SBA-15,[8,9] and sulfonic acid groups with Fe3O4 magnetic nanoparticles
and MCM-41[10-12] have represented numerous advantages over homogeneous catalysts in the aspect of recovery and
recycling to put forward the MCRs.
In recent years a considerable attention to porous coordination polymers or metal-organic frameworks (MOFs) has been
focused within a relatively short time-frame.[13] The current uses and the possible future applications of MOFs, including
separation,[14] storage[15,16] optical devices[17] drug delivery,[18,19] luminescence,[20] etc. have attracted significant research
attention in this wide scientific field. Because of the porosity in structure, large surface area and highly tailorable properties,
∗ Corresponding author Tel.: +98-912-7031230; Fax: +98-26-32803880; E-mail: Fzmovahedi@yahoo.com, Homepage URL:
en.standard.ac.ir/Farnaz_Movahedi_cv.aspx
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
MOFs have interesting potential to be used as heterogeneous Bronsted acid catalysts in organic synthesis, even though
few successful Bronsted acid-MOFs have been reported in recent years.[21-23] Accordingly, post-synthesis and employing
of MOFs as supporting phase with the other functional groups would be desirable for preparation of specific MOFs with
excessive catalytic potential. The post-synthetic modification (PSM) of MOFs introduces a highly desirable method by
attaching various catalytic centers through stable covalent bonds in order to form a wide range of stronger Brønsted acidic
functionalized MOFs.[24-26] Also anchoring of magnetic compounds such as Fe3O4 magnetic nanoparticles into MOFs
scaffold involves great advantages from the point of separation in comparison with the other methods.[27]
Benzopyranopyrimidines have gained much attention in recent years due to their inherent and various pharmacological
potential such as analgesic, in vivo antitumor, anti-inflammatory and anti-aggregating activities.[28-31] These compounds
are considered as a class of important medicinal scaffolds that are commonly derived from the condensation reaction of
salicylaldehydes, malononitrile and secondary amines in the presence of acid catalysts. Recently, ionic liquids, LiClO4,
ZrOCl2, manganese oxide salen complex immobilized on Fe3O4 magnetic nanoparticles and microwave irradiation have
been utilized for their synthesis.[32-35]
In 2013, we investigated the capability of one-pot multicomponent synthesis of benzopyranopyrimidine derivatives in the
presence of silica nanoparticles immobilized benzoylthiourea ferrous complex as a catalyst in EtOH at room
temperature.[36] Following our previous researches on multicomponent reactions,[37,38] here in, we report a novel approach
for the synthesis of benzopyranopyrimidine derivatives using sulfamic acid functionalized magnetic IRMOF-3. For this
purpose, a facile fabrication of Fe3O4/IRMOF-3 nanocomposite is presented through preparation of IRMOF-3 in the
presence of amino-modified Fe3O4@SiO2 NPs by a solvothermal method. Afterwards sulfamic acid-functionalized
Fe3O4/IRMOF-3 was prepared by
a post-functionalization strategy. The obtained Fe3O4/IRMOF-3/SO3H was
systematically characterized and its catalytic efficiency was evaluated for the one-pot pseudo four-component synthesis
of benzopyranopyrimidines.
Results and discussion
Characterization of Fe3O4/IRMOF-3/SO3H
The X-ray diffraction pattern of the as-prepared Fe3O4@SiO2 is shown in Fig. 1a. The relative intensities and positions of
the peaks confirmed well with a cubic spinel magnetic structure (JCPDS No. 19-0629).[39] On the other hand, the X-ray
diffraction patterns of the IRMOF-3 are shown before and after post synthetic modification with Fe3O4 and chlorosulfonic
acid (Fig. 1b, 1c). The reflections peaks around 2θ = 6.8° and 9.6° indicate that a desirable crystalline material was
produced (Fig. 1b).[40,41] Also the Fe3O4/IRMOF-3/SO3H (Fig. 1c) exhibited the same characteristic peaks as the
unmodified IRMOF-3. The XRD results obtained from the reused catalyst showed that the overall structure of the catalyst
could be retained even after 5th run during the reactions.
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
Fig. 1. XRD patterns of (a) Fe3O4@SiO2, (b) IRMOF-3, (c) Fe3O4/IRMOF-3/SO3H and (d) reused Fe3O4/IRMOF-3/SO3H.
The FT-IR spectra of the Fe3O4@SiO2 MNPs, IRMOF-3 and Fe3O4/IRMOF-3/SO3H nanocomposite are shown in Fig. 2.
The peaks at 575 and 1085 cm-1 are ascribed to Fe-O and O-Si-O stretching vibrations, respectively (Fig. 2a). The spectra
of the IRMOF-3 exhibited a strong peak at 1573 cm-1, indicating the deprotonation of -COOH groups in 2-
aminoterephthalic acid upon the reaction with metal ions (Fig. 2b). In addition, two peaks at 3358 and 3475 cm-1 due to
the N-H stretching vibration of the amine functionalities and the peak at 1256 cm-1 related to the C-N vibrations are
assigned, respectively.[42] In Fe3O4/IRMOF-3/SO3H (Fig. 2c) two new bands are appeared at 1282 and 1151 cm-1, which
would be ascribed to the O=S=O asymmetric and symmetric stretching modes, respectively, and the peak at 1093 cm-1
which would be assigned to S-O stretching vibration. Also the peak near 3500 cm-1 was probably attributed to the NH
groups, which was overlapped by the O-H stretching vibrations. As a result, all of these evidences confirm successful
modification of the amines to sulfamic acid groups.
Fig. 2. FT-IR spectra of (a) Fe3O4@SiO2, (b) IRMOF-3, and (c) Fe3O4/IRMOF-3/SO3H.
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
To evaluate the morphology of IRMOF-3 and Fe3O4/IRMOF-3/SO3H, the prepared samples were investigated by FESEM
(Fig. 3). The Fe3O4 NPs have spherical shape ordered with an average size of 37 nm (Fig. 3a). As it is shown (Fig. 3b
and 3c), the IRMOF-3 and Fe3O4/IRMOF-3/SO3H have an acceptable crystalline structure, and Fe3O4 MNPs are well
dispersed within the network homogeneously, due to the electrostatic interactions between the Fe3O4 NPs owning
negative charges and IRMOF-3 with positive charges.[43] Also, the post modification of Fe3O4/IRMOF-3 with chlorosulfonic
acid groups seems not to interfere in the crystalline structure of IRMOF-3 (Fig. 3c), which is in accordance with the XRD
results. Also the elemental composition of Fe3O4/IRMOF-3/SO3H nanocomposite was determined by SEM-EDS (Fig. 3d).
It shows a generic spectrum with separate peaks from C, N, Si, Zn, S, O and Fe, in which was used to determine the
relative elemental analysis. The quantitative analysis of N and S gives weight ratios of 4.21% and 9.85%, respectively,
with a loading at ca. 2.99 mmol/g for N and 3.07 mmol/g for S. The results show that all of the amine groups in IRMOF-3
structure were modified successfully with chlorosulfonic acid groups. Finally, individual weight percent of each component
in functionalized magnetic IRMOF-3 was estimated 8.12% for Fe3O4, 7.96% for SiO2, 59.03% for MOF and 24.88% for –
SO3H, approximately.
Fig. 3. The FESEM images of (a) Fe3O4 NPs, (b) IRMOF-3, (c) Fe3O4/IRMOF-3/SO3H, and (d) SEM-EDS analysis.
On the other hand, the number of H+ determined by acid-base titration was 2.93 mmol g-1 that this value is close to the
EDS results for the sulfur content (3.07 mmol g-1). It was concluded that most of sulfur species on the surface of the
Fe3O4/IRMOF-3/SO3H nanocomposite are in the form of sulfamic acid groups. It is noteworthy that the total concentration
of H+ for unmodified Fe3O4/IRMOF-3 was not placed on detection range by titration and it was resulted that the acidity of
Fe3O4/IRMOF-3/SO3H is caused by the sulfamic acid groups.
The BET surface area and pore volume were calculated using the N2 adsorption and the pore size distribution pattern
calculated from desorption branch of the N2 isotherm by Barrett-Joyner-Halenda (BJH) model (Fig. 4). The IRMOF-3
nanocomposite exhibit a typical type I isotherm (Fig. 4a, 4b), with a distinct hysteresis loop above 0.8 of P/P0 in desorption
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
branch for Fig. 4a, indicating the presence of mesoporosity. Comparatively, both the pore volume and specific surface
area have large decrease after the incorporating of the -SO3H groups into the Fe3O4/IRMOF-3. In the case of Langmuir
surface area, the N2 adsorption revealed a decrease after post modification of Fe3O4/IRMOF-3 to Fe3O4/IRMOF-3/SO3H
from ca. 400 m2/g to 70 m2/g and the average pore volume decreased from 0.52 cm3/g to 0.08 cm3/g, respectively.
Obviously, the inclusion of the –SO3H groups into the nanocages would be responsible for such a decrease. Similar
results are reported previously for modification of the IRMOF-3.[44] As can be seen from Fig. 4c and 4d, the pore-size
distribution of the as-prepared magnetic IRMOF-3 and Fe3O4/IRMOF-3/SO3H nanocomposites from the desorption branch
of the N2 isotherm by BJH model was calculated 8.0 nm and 5.4 nm, respectively.
Fig. 4. N2 adsorption–desorption isotherms of (a) Fe3O4/IRMOF-3 and (b) Fe3O4/IRMOF-3/SO3H, the BJH pore size distributions of (c)
Fe3O4/IRMOF-3 and (d) Fe3O4/IRMOF-3/SO3H.
Thermogravimetric analysis (TGA) of IRMOF-3 and Fe3O4/IRMOF-3/SO3H was investigated under N2 flow and running
from room temperature to 600 °C (Fig. 5.). IRMOF-3 showed two steps weight loss, first weight loss of about 8 wt % below
170 °C due to the removing of the remaining trapped solvent, and a second weight loss of 42 wt% due to the
decomposition of organic linkers between 350 and 550 °C. The Fe3O4/IRMOF-3/SO3H revealed the same thermal
behavior as IRMOF-3 before 170 °C but it showed sensible differences versus IRMOF-3 with an excess weight loss (~10
[45]
wt %) between 250 and 350 °C, that is likely due to the thermal crystal phase transformation from Fe3O4 to γ-Fe2O3
and breakdown of the sulfamic acid functionalities, indicating that the Fe3O4/IRMOF-3/SO3H is stable only up to 250 °C.
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
Fig. 5. TGA analysis of Fe3O4/IRMOF-3/SO3H vs. IRMOF-3.
Catalytic activity of Fe3O4/IRMOF-3/SO3H nanocomposite
Catalytic activity of Fe3O4/IRMOF-3/SO3H nanocomposite was explored for the one-pot pseudo four-component
condensation reaction of salicylaldehydes, malononitrile and secondary amines for synthesis of the
benzopyranopyrimidines (Scheme 1). For this purpose, various reaction conditions were appraised by salicylaldehyde,
malononitrile, and morpholine as a model test reaction (3j) and the results are summarized in Table 1. Fe3O4/IRMOF-3
and IRMOF-3 catalyzed the reaction with 20% and 10% yields, respectively (Table. 1, entries 8 and 9). In the presence
of Fe3O4 MNPs only trace amounts of the product was accomplished, while under catalyst-free conditions, the reaction
did not proceed anyway (Table, 1, entries 10 and 15). Nevertheless, the modified catalyst, i.e. Fe3O4/IRMOF-3/SO3H
increased the yield up to 95% (Table, 1, entry 7).
In order to select the most suitable media, the model reaction was performed in various solvents in the presence of
Fe3O4/IRMOF-3/SO3H (10 mg per 1mmol of reactants) as the catalyst (Table 1, entries 1-7). Clearly, using polar protic
solvents such as EtOH, MeOH and H2O led to higher yields 80-98% (Table 1, entries 1, 3, 7), while the reaction did not
proceed using nonpolar or polar aprotic solvents such as n-Hexane and THF (Table 1, entries 4, 5). Besides, in the
solvent-free conditions, the reaction did not achieve reasonable yields (Table 1, entry 6).
In order to study the effect of the catalyst concentration, the reaction proceeded using different amounts of the
Fe3O4/IRMOF-3/SO3H under constant reaction conditions. Increasing the quantity of the catalyst from 5 mg to 10 mg led
to an increase in the yield of the model reaction. However, we found only 10 mg catalyst is enough to catalyze the reaction
up to high yields and using more amounts of the catalyst did not raise the yields to an appreciable extent (Table 1, entries
11-14).
NR2
X
X
CHO
-3
3O4/IRMOF /SO3
Fe
H
N
OH
+
+
NC
CN
R2NH
rt
EtOH,
OH
N
O
X
2
3
1
4
Scheme 1. One-pot pseudo four-component synthesis of benzopyranopyrimidines promoted by Fe3O4/IRMOF-3/SO3H.
Table 1. Optimization of the Fe3O4/IRMOF-3/SO3H catalyzed model reaction (3j) for the α-amino nitrile synthesis.a
Entry
Catalyst
Solvent
H2O
CH2Cl2
MeOH
Yield (%) b
1
2
3
Fe3O4/IRMOF-3/SO3H (10 mg)
Fe3O4/IRMOF-3/SO3H (10 mg)
Fe3O4/IRMOF-3/SO3H (10 mg)
80
40
90
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
4
5
6
7
8
Fe3O4/IRMOF-3/SO3H (10 mg)
THF
n-Hexane
Solvent-free
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
-
-
20
95
20
10
5
Fe3O4/IRMOF-3/SO3H (10 mg)
Fe3O4/IRMOF-3/SO3H (10 mg)
Fe3O4/IRMOF-3/SO3H (10 mg)
Fe3O4/IRMOF-3 (10 mg)
IRMOF-3 (10 mg)
9
10
11
12
13
14
15
Fe3O4 MNPs (10 mol%)
Fe3O4/IRMOF-3/SO3H (5 mg)
Fe3O4/IRMOF-3/SO3H (10 mg)
Fe3O4/IRMOF-3/SO3H (15 mg)
Fe3O4/IRMOF-3/SO3H (20 mg)
No Catalyst
90
95, 95,93c
95
95
-
a Reaction conditions: salicylaldehyde (2 mmol), morpholine (1 mmol), malononitrile (1 mmol), catalyst, solvent (4 mL), room temperature.
b Isolated yields.
C Yields in rt, 40°C, and 70 °C.
The substitution effect was investigated by employing various derivatives of salicylaldehydes and secondary amines under
the optimized reaction conditions, and the results are summarized in Table 2. The reaction can tolerate a wide variety of
salicylaldehyde derivatives carrying either electron-donating substituents such as methoxy group, and electron-
withdrawing groups such as halogens. In addition, aliphatic amines such as diethylamine and dimethylamine react as well
as aromatic amines. However the best yields were achieved with cyclic secondary amines such as morpholine, piperidine
and 4-Methyl piperidine. All products are known compounds,[36,46] and found to be identical with authentic samples through
melting points and spectroscopic data. Almost all the reactions worked quite well and the desired products were obtained
in good to high yields and reasonable turnover numbers (TON) within sustainable reaction times. The TON, defined as
moles of product produced per mole of active site of catalyst (H+).
In order to achieve relatively high yields at optimized conditions, the temperature effect was examined at room
temperature (rt), 40 °C, and 70 °C. As shown in Table 1 (entry 12), by increasing the temperature from ambient
temperature to 40 °C, the conversion rate didn’t increase at all. However, a decrease in yield was observed when
temperature increased from 40 °C to 70 °C. Then, ambient temperature was chosen as the optimum circumstance for the
reaction.
Due to importance of the recyclability and the reusability of catalysts in organic reactions, the catalytic activity of the
recycled Fe3O4/IRMOF-3/SO3H was explored in this system. For this purpose, in each run after 1 h, the catalyst was
separated from the model reaction mixture (3j) by a simple magnetic decantation. The separated catalyst was washed
with methanol several times, dried under vacuum at 90 °C, and then was reused in subsequent cycle. The results showed
(Table 2, entry 10) that the nanocomposite could be successfully used for at least five consecutive runs without significant
loss of its catalytic activity. Also to test for leaching of the catalyst, the model test reaction was carried out in presence of
the Fe3O4/IRMOF-3/SO3H (10 mg) and at the point that yield was 45%, the catalyst was filtered in hot EtOH. The mother
liquor transferred to another screw cap test tube and the reaction procedure allowed to be continued at ambient
temperature, although no further remarkable conversation was observed. On the basis of the obtained results, no
significant active species from the solid catalyst migrates to the supernatant and the catalysis is truly heterogeneous.
Table 2. The pseudo four-component reaction of salicylaldehydes, malononitrile and secondary amines catalyzed by Fe3O4/IRMOF-3/SO3H under
ambient conditions.a
Entry
1
Aldehyde
salicylaldehyde
salicylaldehyde
Secondary amine
N-Methylaniline
N-Eethylaniline
Dimethylamine
Dimethylamine
Dimethylamine
Diethylamine
Diethylamine
Diethylamine
Pyrrolidine
Morpholine
Product
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
Yields (%)
TONb
108
108
119
100
112
111
98
118
112
117
134
138
135
139
121
139
145
165
83
80
90
92
87
78
83
85
2
3
4
5-Chlorosalicylaldehyde
salicylaldehyde
5
6
7
5-Methoxysalicylaldehyde
5-Chlorosalicylaldehyde
salicylaldehyde
8
9
5-Methoxysalicylaldehyde
salicylaldehyde
95
10
11
12
13
14
15
16
17
18
salicylaldehyde
95(95,94,94,93)c
5-Chlorosalicylaldehyde
5-Chlorosalicylaldehyde
5-Methoxysalicylaldehyde
5-Methoxysalicylaldehyde
salicylaldehyde
5-Chlorosalicylaldehyde
5-Methoxysalicylaldehyde
3,5-Dichlorosalicylaldehyde
Pyrrolidine
Morpholine
Pyrrolidine
Morpholine
95
94
98
97
95
92
98
95
4-Methyl piperidine
4-Methyl piperidine
4-Methyl piperidine
4-Methyl piperidine
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
19
20
21
3,5-Dichlorosalicylaldehyde
5-bromosalicylaldehyde
3,5-Dichlorosalicylaldehyde
Diethylamine
Dimethylamine
Morpholine
3s
3t
3u
80
90
94
132
146
160
a Reaction conditions: aldehyde (2 mmol), secondary amine (1 mmol), malononitrile (1 mmol), catalyst (10 mg), EtOH (4 mL), room temperature.
b Turnover number: number of moles of product per mole of active site of catalyst (mole of H+).
c The yields of the model reaction with recycled catalyst after five successive runs.
To investigate the catalytic advantages of Fe3O4/IRMOF-3/SO3H nanocomposite, a comparison table from previously
reported data including yields and reaction conditions for pseudo four-component condensation reaction of
salicylaldehyde, malononitrile, and morpholine (3j) is presented in Table 3. As a whole, the results demonstrate the
benefits of the present protocol over some of the other former reported methods in terms of product yields, reaction times
or reaction conditions.
Table 3. Comparison of the catalytic activity of Fe3O4/IRMOF-3/SO3H with some of the other catalysts reported in the literature for the synthesis
of 3j.
Entry
Catalyst
Silica-bonded N-propylpiperazine sodium n-
propionate
Conditions
Time (h)
6
Yield (%)
85
ref
1
Solvent-free, rt
[47]
2
3
4
5
6
7
8
Fe(II)-BTU-SNPs
Sodium formate
Tetrabromobenzene-1,3-disulfonamide
LiClO4
Ethanol, rt
Ethanol, rt
Ethanol, rt
4
93
83
90
84
92
87
95
[36]
[48]
[49]
[50]
[51]
12
24
24
0.1
0.2
1
Ethanol, rt
Piperidine
[Hnhp][HSO4]
Fe3O4/IRMOF-3/SO3H
MW, 100 C
Solvent free, rt
Ethanol, rt
[52]
This work
A proposed mechanism for the formation of the benzopyranopyrimidines with the aim of catalytic activity of Fe3O4/IRMOF-
3/SO3H is represented in Scheme. 2. The Knoevenagel condensation reaction initiates with assistance of the Bronsted
sulfamic acid sites (-SO3H) though activation of the carbonyl group in salicylaldehyde towards nucleophilic attack of
malononitrile. At the next step, the pinner reaction progress (5→6) though activating the triple bond with the aim of
Bronsted acid sites, concluding in cyclization, in which continues by the amine attack to the activated intermediate 6.
Finally, another salicylic aldehyde molecule interacts with the intermediate 7, following by proton transfer to achieve the
benzopyranopyrimidine product.
Scheme 2. A proposed mechanism for synthesis of benzopyranopyrimidine through catalytic activation of Fe3O4/IRMOF-3/SO3H nanocomposite
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
Conclusions
In summary, Fe3O4/IRMOF-3/SO3H nanocomposite was synthesized through the post-modification of magnetic IRMOF-
3 with chlorosulfonic acid, then was introduced for the synthesis of the benzopyranopyrimidines through one-pot
multicomponent condensation reaction of secondary amines, malononitrile and salicylaldehydes under mild conditions.
The magnetism with nanoparticles, besides post modification of IRMOF-3 with acidic groups produces a nanocomposite
containing high potentials for catalytic application purposes. The Fe3O4/IRMOF-3/SO3H nanocomposite was fully
characterized and its stability was verified even after acidic treatment of the magnetic MOF with chlorosulfonic acid. The
as-reported procedure contains some advantages such as accessible active Brønsted acid sites supported on high
surface area magnetic MOF, applicability to a desired range of substituted salicylaldehyde and secondary amines, short
reaction times, use of small amounts of catalytic resources, ease of separation, recycling and reusability of the catalyst,
and simple reaction workup.
Experimental section
Materials and methods
All reagents with synthetic reagent grade were purchased from merck or sigma and used without further purification. The
particle sizes and morphologies were studied by field emission scanning electron microscope (FE-SEM, MIRA3TESCAN-
XMU with an accelerating voltage of 15 kV) equipped with an energy dispersive spectrometer (EDS) and an optical
microscope (Nikon Eclipse LV 100). The Brunauer–Emmett–Teller (BET) surface area of the catalyst was investigated
using a nitrogen adsorption instrument (Micrometrics ASAP 2020). Pore size was calculated using Density Functional
Theory (DFT). Total pore volume was taken by a single point method at P/P0 = 0.98. X-ray diffraction (XRD) was measured
in a Philips PW 1730 instrument. FT-IR measurements were performed using KBr disc on a Thermo IR-100 infrared
spectrometer (Nicolet). The thermogravimetric analysis (TGA) measurements were taken using SDT Q600. The acid
capacities of the catalyst were determined by acid-base titration using NaCl solution as an ion-exchange agent.[53] A 200
mg sample in powder form was ion-exchanged with an aqueous NaCl saturated solution at ambient temperature for at
least 24 h, followed by filtration and washing with 3 mL of deionized (DI) water. The filtrates were then titrated with NaOH
solution (0.01 M). The 1 H- and 13 C-spectra were measured (CDCl3) with a Bruker DRX 500-Avance FT-NMR instrument
at 500.1 and 125.7 MHz, respectively.
Catalyst preparation
Synthesis of Fe3O4 nanoparticles
Initially Fe3O4 NPs were synthesized by a co-precipitation method.[54] Briefly, a mixture of FeCl2·4H2O (10.8 mmol, 54.3
mg) and FeCl3·6H2O (21.6 mmol, 79.9 mg) were dissolved in distilled water (100 mL). Then, the reaction was continued
under mechanical stirrer for 30 min at 85 °C in an argon atmosphere for homogeneity. Afterwards, ammonium hydroxide
25% (10 mL) was added in one portion into the reaction mixture, which immediately resulted in the formation of the
magnetic black precipitates. The reaction was stirred for further 30 minutes, and then it was cooled to ambient
temperature. The black as-prepared product was separated by an external magnetic decantation, washed several times
with brine and distilled water, then was dried at 80 °C in vacuum, overnight.
Synthesis of Fe3O4@SiO2 core-shell nanoparticles
For preparation of the Fe3O4-SiO2 core-shell; firstly, Fe3O4 NPs (1.0 g) were sonicated in an ethanol solution (150 mL).
Then, ammonium hydroxide 25% (5 mL) was added to the magnetic dispersed solution and the reaction was stirred for
30 minutes. Subsequently, the Fe3O4 NPs were coated with SiO2 through condensation and hydrolysis of 1 mL tetraethyl
orthosilicate (TEOS), in which added dropwise into the reaction mixture over 10 minutes. The reaction was stirred
vigorously for 24 h at room temperature. Finally, the obtained Fe3O4@SiO2 NPs were collected by an external magnet,
centrifuged and washed several times with DI water and ethanol, then dried in a vacuum oven at 80 °C for 24 h.
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
Synthesis of magnetic IRMOF-3 (Fe3O4/IRMOF-3)
Magnetic IRMOF-3 (Fe3O4/IRMOF-3) nanocomposite was obtained via a solvothermal method as follows: In a solution of
Zn(NO3)2 (134 mg, 0.7 mmol) in pure DMF (8 mL), Fe3O4@SiO2 NPs (8 mg) were dispersed by sonication for 30 minutes.
To the above mixture, 2-aminoterephthalic acid (33 mg, 0.18 mmol) was added and sonicated for another 10 minutes at
room temperature. Subsequently, the dispersed mixture was transferred into a 50 mL Teflon-lined stainless steel
autoclave and heated in stable conditions at 100 °C for 24 h. Finally, the obtained brownish precipitate was isolated by
magnetic decantation and was washed several times with pure DMF and methanol, then dried in vacuum oven at 80 °C
for 24 h.
Post-synthetic modification of Fe3O4/IRMOF-3 nanocomposite (Fe3O4/IRMOF-3/SO3H)
The Fe3O4/IRMOF-3 (1g) was sonicated in CH2Cl2 (20 mL) for 30 minutes. Afterwards, chlorosulfonic acid (0.5 mL) was
added dropwise to the reaction vessel under stirring over a period of 30 minutes and kept at room temperature, overnight.
The obtained brownish precipitate was isolated by magnetic decantation and washed several times with pure CHCl3. For
more activation, the nanocomposite was rinsed in 20 mL methanol twice in two days to remove all solvents trapped in
pores. Finally, Fe3O4/IRMOF-3 was separated from methanol by magnetic decantation and dried at 90 °C under vacuum,
for 24 h (Scheme. 3).
Scheme 3. Preparation of Fe3O4/IRMOF-3/SO3H nanocomposite.
General procedure for the preparation of benzopyranopyrimidines
In a screw cap test tube, a mixture of salcilaldehydes 1 (2 mmol), malononitrile 2 (1 mmol), secondary amines 3 (1 mmol)
and Fe3O4/IRMOF-3/SO3H (10 mg) in EtOH (4 mL) was stirred at room temperature for 3 h. After completion of the
reaction as monitored by TLC (eluent: EtOAc/n-hexane, 1:3), 10 mL hot ethanol was added and the catalyst was
separated by magnetic decantation instantly. After cooling of the organic phase, the crude product was precipitated, then
was filtered and washed with DI water and cold EtOH several times to afford the pure product.
Keywords: Magnetic metal-organic framework • Functionalized IRMOF-3 • Nanocomposite catalyst • Multicomponent
reaction • Heterogeneous catalysis
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10.1002/ejic.201801054
European Journal of Inorganic Chemistry
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