Choline chloride-coated UiO-66-Urea MOF: A novel multifunctional heterogeneous catalyst for efficient one-pot three-component synthesis of 2-amino-4H-chromenes

Article abstract of DOI:10.1016/j.molliq.2020.115228

A new Zr-based MOF, namely, UiO-66-Urea, was prepared through polymerization between the 2-aminoterephthalate linkers of UiO-66-NH₂ MOF and 1,4-phenylene diisocyanate under mild reaction conditions. Post-synthetic coating of UiO-66-Urea with ch

Full text of DOI:10.1016/j.molliq.2020.115228

Journal of Molecular Liquids 325 (2021) 115228
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Choline chloride-coated UiO-66-Urea MOF: A novel multifunctional
heterogeneous catalyst for efficient one-pot three-component
synthesis of 2-amino-4H-chromenes
Mohadeseh Akbarian, Esmael Sanchooli ⁎, Ali Reza Oveisi ⁎, Saba Daliran
Department of Chemistry, University of Zabol, P.O. Box: 98615-538, Zabol, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A new Zr-based MOF, namely, UiO-66-Urea, was prepared through polymerization between the 2-
Received 22 September 2020
Received in revised form 19 December 2020
Accepted 26 December 2020
Available online 30 December 2020
2
aminoterephthalate linkers of UiO-66-NH MOF and 1,4-phenylene diisocyanate under mild reaction conditions.
Post-synthetic coating of UiO-66-Urea with choline chloride (ChCl), as easily available, inexpensive, and nontoxic
reagent, under thermal and solvent-free conditions resulted in in-situ formation of a deep-eutectic solvent-like
6 4 4
on the UiO-66-Urea's surface, called here ChCl@UiO-66-Urea. The presence of Zr O (OH) nodes and urea groups
may capable of strong hydrogen bond formation with ChCl. The porous and bioinspired ChCl@UiO-66-Urea was
characterized using FT-IR, powder XRD, SEM, EDX elemental mapping, TGA, and BET surface area measurements.
Choline chloride-coated UiO-66-Urea was successfully promoted one-pot three-component synthesis of
2-amino-4H-chromenes, as biologically active heterocycles, through reactions of aldehydes, malononitrile, and
α-naphthol or 4-hydroxycoumarin under solvent-free conditions. The catalytic activity of the respective solid
was superior than UiO-66, UiO-66-NH , UiO-66-Urea, and even ChCl-2Urea due to synergistic effect between
2
actives sites of UiO-66-Urea and ChCl. The reaction includes a consecutive three-step Knoevenagel condensa-
tion/Michael addition/cyclization mechanism.
Keywords:
Metal-organic frameworks
Zirconium-based MOF
Ionic liquid incorporation in MOF
Deep-eutectic solvent
Hybridization
Multi-component reactions (MCRs)
©
2020 Elsevier B.V. All rights reserved.
1. Introduction
span because of their high surface area, high thermal and chemical
stability, and low toxicity.
Porous metal–organic frameworks (MOFs) are a class of micro/
Ionic liquids (ILs) are environment-friendly and new class of sol-
vents with significant properties such as low volatility, high thermal
and chemical stability, and high polarity which make them as appropri-
ate solvents and/or catalysts for diverse chemical reactions [22]. Deep
eutectic solvents (DESs) are a new emerging class of ionic liquids
which obtained from a eutectic mixture of self-assembling two or
more Brønsted/Lewis acids and bases through hydrogen bonding for-
mation without the need of any solvent and the further purification
[23]. They share many features and properties with ILs but, in contrast,
they can include a wide range of anionic and/or cationic species. As a re-
sult, they have been considered by researchers in significant areas in
concept of green and sustainable chemistry. However, ILs also have
some limitations in industrial applications due to their high viscosity
and their problematic recovery from the reaction mixture, and low effi-
ciency/selectivity. To address these drawbacks, ILs can be confined into
MOFs, namely “IL incorporation in MOFs” [24], collecting the advantages
of both ILs and MOF structures within a new material, IL/MOF composite
mesoporous materials formed in a highly ordered manner by coordi-
nation bond reactions between metal ions/nodes and organic
linkers [1–3]. MOFs are able to be tailored through the choose control
of organic linkers and metal ions for desired chemical process. As a re-
sult, within a short span of time, they have been gained much atten-
tion in a wide research area including catalysis [4–9], photocatalysis
[
10,11], separation [12], chemical sensing [13], drug delivery [14,15],
toxic compounds remediation [16] and so on. Surface functionality
and incorporation of a variety of functional moieties in MOFs are the
other key advantages of them [17]. The organic struts and the clusters
can be post-synthetically modified (PSM) with different species to
make functionalized MOFs which offers advantages over the pristine
MOFs [18]. Zr-based MOFs and at the top of them, UiO-66 (UiO =
University of Oslo) series [19–21] have dramatically gained attention
[
25,26]. They have thus recently emerged as promising materials for po-
⁎
Corresponding authors.
E-mail addresses: Esmael_sanchooli@uoz.ac.ir (E. Sanchooli), aroveisi@uoz.ac.ir
tential applications including adsorption [27,28] and catalysis [8,24,29].
Nevertheless, in spite of these achievements, this strategy mainly is
(
A.R. Oveisi).
https://doi.org/10.1016/j.molliq.2020.115228
167-7322/© 2020 Elsevier B.V. All rights reserved.
0

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
limited to the use of ILs and further the integrating the two individual
components together by PSM procedures to give the desired material.
Also, the simple inclusion of ILs into MOFs void space can be led to the
lack of maximum accessibility to internal pores.
installed onto the UiO-66-NH
2
by PSM, is used as hydrogen donor
and the ChCl is used as hydrogen acceptor. As schematically presented
in Scheme 1, the presence of urea groups and ChCl may induce strong
hydrogen bond interactions between both as observed for the homog-
Chromenes are an important class of heterocyclic compounds with
enormous variety of biologically activities such as antimicrobial, anti-
cancer, antibacterial, anti-rheumatic and anti-allergic activities
enous ChCl-2Urea mixture [23,57]. UiO-66-NH
robustness, high surface area, and reproducible synthesis [21,58]. The
node of UiO-66-NH is a Zr (OH) cluster that comprises Lewis-
2
was selected due to its
2
6
O
4
4
[
30–37]. They also have been used in agrochemicals, pharmaceutical
acidic Zr(IV) sites which are settled in the framework as same as ac-
tive sites of phosphotriesterase enzymes [59]. By such a design, a
novel and bioinspired porous deep eutectic solvent like-MOF is con-
structed. The resulted organic-inorganic hybrid solid was then used
for the one-pot three-component synthesis of 2-amino-4H-
chromenes through reactions of aldehydes, malononitrile, and α-
naphthol or 4-hydroxycoumarin under environmentally-benign
conditions. To the best of our knowledge, this is the first report on
the synthesis and use of such DES/MOF or IL/MOF as heterogeneous
catalyst for a multicomponent reaction.
and synthetic drugs such as Alzheimer's disease and Huntington's dis-
ease [31,38–41]. Some of relevant biological and pharmacological active
structures are presented in Fig. 1.
3 2 2 3
Thus, over the years, many catalysts such as InCl [42], I /K CO [43],
nanostructured diphosphate Na CaP (DIPH) [44], sodium-modified
2
2 7
O
hydroxyapatite [45], KG-60-piperazine [46], alkylaminopyridine-
grafted on HY Zeolite [47], heteropolyacid [48], triazine functionalized
ordered mesoporous organosilica [49], and Laccase immobilized on
CoFe
2 4
O -KCC-1 [50] have been reported for the synthesis of 2-amino-
4H-chromenes. On other hand, porous materials such as tungstic acid
functionalized mesoporous SBA-15 [51], zinc-based MOF [52],
mordenite zeolite/MIL-101(Cr) composite [53], Er-based MOF [54],
and triazine-based porous organic polymer (POP) [55] have been used
to promote the synthesis of other chromene derivatives with different
compositions. However, these methods suffer from some drawbacks
such as the use of additive/toxic reaction media and/or toxic reagent,
not easily available catalyst/reagent, low efficiency, long reaction
times, high loading and/or non-reusability of used catalyst, and tedious
procedure. In addition, MOFs with divalent Zn(II) ions are not stable
under many conditions, which has become a major concern for the
their applications in divers areas [56].
2. Experimental section
2.1. Materials
Zirconium chloride (ZrCl4, Sigma-Aldrich, ≥99.5%), 2-
aminoterephthalic acid (ACROS Organics, 99%), 1,4-phenylene
diisocyanate (TCL Chemicals, >98%), choline chloride (ChCl,
Sigma-Aldrich, ≥99%), N,N′-dimethylformamide (DMF, Merck,
≥99.8%), 4-hydroxycoumarin (Sigma-Aldrich, 98%), 1-naphthol
(Merck, ≥99%), and other reagents were purchased from Merck
and/or Sigma-Aldrich and used as received.
Taking into consideration of the above-mentioned, we present
herein, for the first time, an effective design of porous and bioinspired
ChCl@UiO-66-Urea, deep eutectic solvent like-UiO-66 (DES-UiO-66)
composite, through in-situ forming strong hydrogen bonds directly
between the MOF and cheap and safe choline chloride. The urea func-
2.2. Characterization
Thermogravimetric analysis (TGA, Mettler Toledo) was measured
under nitrogen atmosphere (T = 25–700 °C with heating rate of
1
13
tionality was covalently introduced into the UiO-66-NH
2
through po-
10 °C/ min). H NMR and C NMR spectra were recorded in a Bruker
1
13
lymerization between the 2-aminoterephthalate linkers and 1,4-
phenylene diisocyanate toward formation a new urea functionalized
UiO-66-NH , named here UiO-66-Urea. Then, PSM of UiO-66-Urea
2
with choline chloride (ChCl) under thermal and solvent-free condi-
tions resulted in in-situ formation of ChCl@UiO-66-Urea. The urea
Advance 300 or 250 MHz (300 or 250 MHz for H, 62.9 MHz for C)
using deuterated DMSO as solvent. Powder X-ray diffraction (PXRD)
data were collected on a Philips X'pert diffractometer using Cu Kα radi-
ation (λ = 1.5418 Å). The morphology and chemical composition of the
samples were investigated by field emission scanning electron
Fig. 1. Biological and pharmacological active 2-amino-4H-chromenes.
2

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
Scheme 1. Schematic representative of synthesis of ChCl@UiO-66-Urea.
microscopy (FE-SEM, MIRA3 TESCAN) equipped with an energy disper-
sive X-ray spectrometer (EDX). Nitrogen adsorption isotherms at 77 K
were gained by using a volumetric adsorption analyze (Micromeritics
TriStar II. 3020 Version 3.02). The Fourier-transformed infrared (FT-IR)
spectra were obtained by a Perkin Elmer Spectrum-FTIR.
2.4. Synthesis of urea covalently introduced into UiO-66-NH
Urea)
2
(UiO-66-
The UiO-66-NH
2
2
(activated, 100 mg, 0.349 mmol NH ) in dry DMF
(2.5 mL) was magnetically stirred for 5 min under N
2
atmosphere at
room temperature. 1,4-phenylene diisocyanate (176 mg, 1.1 mmol)
was dissolved in dry DMF (5 mL) and added to the suspension,
2
.3. Synthesis of UiO-66-NH
2
while the mixture was stirred under N
mixture was heated at 40 °C and stirred for 48 h under N
2
atmosphere. The resultant
condition.
2
UiO-66-NH
procedure [58,60]; In a 250-mL round-bottom flask, ZrCl
.7 mmol) in DMF (75 mL) was sonicated at 50–60 °C for 10 min, and
acetic acid (2.85 mL) was added to the clear solution. A solution of 2-
aminoterephthalic acid (0.311 g, 1.7 mmol) in DMF (25 mL) was then
discharged to the earlier solution before being sonicated for additional
2
was synthesized according to the previously reported
Finally, the reaction mixture was cooled down to room temperature
and acetone was added and stirred for 60 min. After that, the partici-
pate was isolated by centrifugation and washed several times with ac-
etone and ethanol. The precipitate was soaked in acetone for 24 h and
then collected by centrifugation. Lastly, the solid was dried at room
temperature under reduced pressure, then at 80 °C for 12 h, and fi-
nally, at 130 °C for 4 h (Yield = 230 mg). FT-IR (ATR, cm ): 3295,
1630, 1565, 1510, 1430, 1389, 1300, 1219, 1106, 1068, 1015, 823,
766, 664, 519, 480, 417.
4
(0.4 g,
1
−1
10 min. Next, water (0.125 mL, 0.007 mmol) was discharged to the re-
sultant solution followed by sonication for 5 min. The flask was capped
tightly and sonicated at ~50 °C for 20 min and then heated at 120 °C for
2
4 h without stirring. After the time, the solution was cooled down to
room temperature and the solid was collected by filtration, washed
2
2.5. Synthesis of deep eutectic solvent-like into UiO-66-NH (ChCl@UiO-66-
with DMF (3 times) and then ethanol (4 times). Lastly, the participate
Urea)
was dried (90 °C, 3 h, under reduced pressure) to give the Zr
6
O
4
(OH)
MOF (580 mg). FT-IR (ATR, cm ): 3469, 3359, 1657,
573, 1494, 1434, 1383, 1336, 1258, 1157, 1096, 764, 664, 572, 476, 430.
4
−
1
(
BDC-NH
2
)
6
The obtained UiO-66-Urea (50 mg) and ChCl (31 mg, 0.3 mmol)
were added in a test tube and the mixture was magnetically stirred
1
3

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
for 4 h at 80 °C, before being cooled to room temperature. After that, a
−1
dark yellow solid was obtained. FT-IR (ATR, cm ): 3293, 3024, 1630,
1
8
557, 1508, 1434, 1406, 1382, 1298, 1258, 1080, 1013, 1006, 952, 865,
23, 767, 644, 518, 473, 416.
2
.6. General procedure for the one-pot three-component synthesis of
chromenes
A typical mixture of aldehyde (1 mmol), malononitrile (1 mmol), 4-
hydroxycoumarin or α-naphthol (1 mmol), and ChCl@UiO-66-Urea
10 mg) in a test tube was stirred magnetically under solvent-free con-
(
dition at 80 °C for the indicated time (see Table 2). After the completion
of the reaction, monitored by thin layer chromatography (TLC) using n-
hexane/ethyl acetate (7:3 v/v), the organic compounds were dissolved
in low amount of chloroform. Then, the MOF-based catalyst was isolated
by centrifugation. After evaporation of the solvent, the residue was re-
crystallized from ethanol to afford the desired product. The products
were characterized by physical and spectroscopic data (Melting point,
1
13
FT-IR, H NMR, and C NMR) as given in supporting information (SI).
. Result and discussion
.1. ChCl@UiO-66-Urea characterization
4
UiO-66-NH was firstly synthesized starting from ZrCl and 2-
Fig. 2. Large-angle XRD patterns form bottom to up: UiO-66-NH
synthesized UiO-66-NH (green), UiO-66-Urea (blue), ChCl@UiO-66-Urea (brown), and
reused ChCl@UiO-66-Urea (gray).
2
(simulated, red), as-
3
2
3
2
aminoterephthalic acid via solvothermal condition according to the pre-
viously reported procedure [58,60]. Subsequently, the free amino
groups were reacted with 1,4-phenylene diisocyanate at 40 °C under ni-
trogen atmosphere for 48 h to yield urea moieties which are covalently
linked to UiO-66-NH (named UiO-66-Urea) (Scheme 1). Further, post-
2
synthetic modification of UiO-66-Urea with choline chloride (ChCl) re-
2
Subsequently, the crystallinity of as-synthesized UiO-66-NH , UiO-
66-Urea, and ChCl@UiO-66-Urea were evaluated by powder X-ray dif-
fractometer (PXRD). As shown in Fig. 2, all of the XRD patterns clearly
showed the reflection peaks of 2θ = 7.36, 8.50, 12.06, 14.12, 14.77,
17.06, 18.59, 19.08, 20.96, 22.20, 25.35, 25.69, and 30.68, which
corresponded, respectively, to (111), (200), (220), (311), (222), (400),
(331), (420), (422), (511), (531), (600), and (711) Bragg planes as the
sulted in in-situ formation of a deep eutectic solvent, might be similar to
+
−
ChCl-2Urea [23], [Choline] [Cl(urea)
2
] , into the UiO-66-Urea MOF
same those of the simulated and reported UiO-66-NH
2
[20,58,59,61].
(
named DES-UiO-66 or ChCl@UiO-66-Urea), in which urea comes
This result was proved that these three MOF structures are the same
from UiO-66-Urea and can act as hydrogen-bond donor whereas ChCl
can act as hydrogen-bond acceptor (Scheme 1).
2
and the pristine UiO-66-NH remained obviously intact after the post-
synthetic modifications.
The successful post-synthetic modifications can be initially assessed
Besides, the morphology, shape, and size of UiO-66-NH
Urea, and ChCl@UiO-66-Urea were assessed by SEM (Fig. 3a–i). The im-
ages showed that the pristine UiO-66-NH particles have octahedral
morphology in the size range of 90 to 200 nm (Fig. 3a–c). In addition,
as given in the Fig. 3d–i, the primary MOF particles are remained un-
changed after the modification procedures. Further, the polymerization
of MOF particles through reacting with the diisocyanate in the second
process, and subsequently, their integration with ChCl, yielding the
2
, UiO-66-
by IR spectroscopy. FT-IR spectra of UiO-66-NH
2
, UiO-66-Urea, and
ChCl@UiO-66-Urea are shown in Fig. S1-S3. The peaks at 3469 and
2
−1
~
3360 cm are assigned to asymmetric and symmetric vibrations of
the amino groups in UiO-66-NH (Fig. S1). The peaks appeared at
657, 1573, 1494, 1383, and 1258 cm are attributed respectively to
2
−1
1
the stretching modes of C=O, O-C=O (asymmetric carboxylate), C=
C, O-C=O (symmetric carboxylate), and Caromatic-N bonds [58,61]. The
−1
observed intense peak at ~764 cm is ascribed to N-H wagging band
2
ChCl@UiO-66-Urea, deep eutectic solvent over the UiO-66-NH , are no-
−1
[
62]. Further peaks at lower frequencies between 475 and 664 cm
ticeable in the Fig. 3d–i. Next, energy dispersive X-ray (EDX) analysis of
the ChCl@UiO-66-Urea revealed the presence of the elemental composi-
tion of C (46.26 wt%), N (23.23 wt%), O (19.71 wt%), Zr (4.79 wt%), and
particularly Cl (6.01 wt%) in the material, approving the successful post-
synthetic modifications (Fig. S4). Moreover, the elemental mapping im-
ages of the respective MOF confirmed that the all elements (notably Cl)
were distributed homogenously in the whole framework (Fig. 4).
Nitrogen adsorption-desorption measurements indicated that
ChCl@UiO-66-Urea is prominently porous with a Brunauer-Emmett-
are related to -OH and -CH bending and Zr-O vibrations. The band cen-
−
1
tered at 664 cm is assigned to stretching mode of μ
20,62]. In IR spectrum of UiO-66-Urea (Fig. S2 in the Supporting Infor-
mation), the complete removal of the stretching band of -N=C=O of
3
−O in Zr-O-Zr
[
−1
the isocyanate at ~2250 cm was associated with appearance of the
new characteristic stretching bands of the urea moiety, N-H at
295 cm , C=O at 1630 cm , and N-C-N at 1300 cm [63]. At the
−1
−1
−1
3
same time, the bands related to the N–H-stretching vibrations of the
amino group are clearly diminished. These data confirm the urea forma-
tion and its linkage to the MOF, namely, UiO-66-Urea. After the last
post-synthetic modification of UiO-66-Urea with choline chloride, the
new characteristic bands of the ChCl are observed at 3024, 1080, 952,
2
−1
Teller (BET) surface area of 350 m
g
and a total pore volume of
3
−1
0.26 cm g (Fig. 5). The observed decrease in BET surface area from
UiO-66-NH to ChCl@UiO-66-Urea, respectively, from 850 m g of
2
350 m g , is due to the formation of urea linkages and their merging
with ChCl toward synthesis of the DES-UiO-66. Furthermore, the iso-
therm curve of the DES-UiO-66 is a typical type I shape which is repre-
sentative of a microporous material.
2
−1
2
−1
−1
and 865 cm , which are respectively related to the asymmetric bend-
ing -OH, rocking CH , asymmetric stretching of CCO, and stretching N-
CH [64] (Fig. S3). Additionally, the absorption band of UiO-66-Urea at
295 cm is moved to the lower wavenumber of 3293 cm and be-
2
3
−1
−1
3
Porosity distribution calculated from nitrogen sorption data by using
DFT model confirmed the presence of micropores (1–1.2 and ~1.5 nm)
in the framework (Fig. 6).
come broader as shown in the Fig. S3. It could be due to the strong hy-
drogen bonds formed between UiO-66-Urea and ChCl. These results
suggest the successful UiO-66-NH
the ChCl@UiO-66-Urea.
2
modifications toward formation of
Further, thermogravimetric analysis (TGA) was employed to evalu-
ate the thermal stability of MOFs. TG curves of UiO-66-NH , UiO-66-
2
4

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
2
Fig. 3. SEM images of UiO-66-NH (a-c), UiO-66-Urea (d-f), and ChCl@UiO-66-Urea (g-i).
Urea, and ChCl@UiO-66-Urea are presented in Fig. 7. For the all samples,
the initial mass loss before 200 °C was due to the elimination of physi-
cally adsorbed water and solvents trapped in the pores of the MOFs.
of 280 to 340 °C, might be due to the decomposition of the DES compo-
nents [64] and the beginning cleavage of the MOF framework. This ther-
mal stability of ChCl@UiO-66-Urea (around 300 °C) is promising for its
use as a heterogeneous catalyst.
For the UiO-66-NH
was due to dihydroxylation of the [Zr
Mass loss above 380 °C was related to the thermal decomposition of
-aminoterephthalic acid ligands and the breakdown of the UiO-66-
NH , which finally resulted in the formation of solid ZrO [58]. Compa-
rably, the UiO-66-Urea showed a mass loss ~36 wt% between 200 and
80 °C which might be due to the dehydroxylation of Zr nodes associ-
2
, mass loss (~19 wt%) between 200 and 360 °C
1
2+
6
O
4
(OH)
4
]
nodes [60,65].
3.2. Catalytic reactions for the synthesis of chromenes
2
2
2
As part of our efforts in developing MOF catalysis [6,58,61], we de-
cided to examine the catalytic performance of ChCl@UiO-66-Urea for
the multicomponent synthesis of chromenes. Thus, the reaction be-
tween benzaldehyde, malononitrile, and α-naphthol was chosen as a
model reaction and optimized by the variation of temperature, catalyst
loading, and reaction medium as the results shown in Table 1. Initially,
the effect of reaction temperature on the yield of the reaction toward
synthesis of 2-amino-4-phenyl-4H-benzo[h]chromene-3‑carbonitrile
3
6
ated with the cleavage of the installed urea moieties. Further, the ChCl@
UiO-66-Urea exhibited two distinct mass loss regions in the tempera-
ture ranges of 200–340 °C (200 to 280 °C and 280 to 340 °C). Mass
loss of ~16 wt% in the region of 200 to 280 °C, might be due to the dehy-
6
droxylation of Zr nodes, and a major mass loss of ~42 wt% in the region
5

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
2
Fig. 4. Energy dispersive X-ray spectroscopy (EDX) elemental mapping images of UiO-66-NH , UiO-66-Urea, and ChCl@UiO-66-Urea.
was investigated (Table 1, entries 1–3). When the reaction was carried
out under solvent-free condition at 50 °C in the presence of the catalyst,
the product yield reached 41%, (Entry 1). With the increasing tempera-
ture from 50 °C to 80 °C, the observed yield was dramatically increased
to 92% (Entry 2) and the highest yield obtained at this temperature after
obviously decreased. The highest yield was achieved in the amount of
catalyst of 10 mg (Entry 2). With the increasing the catalyst loading
from 10 mg to 15 mg, no significant improvement in the product yield
was obtained (Entry 5). Therefore, in view of the less use of the catalyst,
10 mg of the ChCl@UiO-66-Urea was chosen as the best amount of cat-
alyst. Then, the catalytic activity of ChCl@UiO-66-Urea was tested under
identical conditions in different reaction media including solvent-free or
solvent conditions such as ethanol, ethanol/water, and ethyl acetate, as
the results given in the Table 1 (Entry 2 vs. Entries 7–9). As shown in the
Table 1, the highest yield was reached under solvent-free condition at
3
1
h. However, after the further increase of reaction temperature to
00 °C, the product yield was slightly decreased to 91% (Entry 3).
Next, the effect of the catalyst loading (5–15 mg) on the yield of the
product was examined (Table 1, entry 2 vs. entries 4 & 5). As shown
in Entry 4, in low amount of the catalyst, the yield of product was
2 2
Fig. 5. N adsorption-desorption isotherms of UiO-66-NH (top) and ChCl@UiO-66-Urea
(bottom) at 77 K.
Fig. 6. DFT pore size distribution for the ChCl@UiO-66-Urea sample.
6

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
further study the role of Zr
UiO-66-Urea, ZrCl
6
-nodes on the catalytic activity of ChCl@
as the Zr-node precursor was also examined as cat-
4
alyst for the model reaction (Entry 15), which resulted in 24% yield of
the product. These experiments evidently reveal that the catalytic activ-
ity of ChCl@UiO-66-Urea comes from its ChCl@Urea moiety, although
the Lewis acid Zr(IV) nodes can serve as active sites as well. In addition,
the experiments further confirmed synergistic effects between ChCl and
UiO-66-Urea interactions which resulted in the enhancement of cata-
lytic activity of ChCl@UiO-66-Urea compared to the others (Table 1, en-
tries 10–14).
Next, under the optimized reaction conditions, the substrate scope
of the multicomponent reactions was checked. Therefore, several aryl
aldehydes were verified under the optimized reaction conditions
(
Table 2). As shown in Table 2, the aldehydes with a wide range of
electron-donating and electron-withdrawing substituents reacting
with α-naphthol (or 4-hydroxycoumarin instead of α-naphthol) all
afforded the desired products in good to excellent yields. In addition,
electron-poor aromatic aldehydes provided the corresponding products
in slightly higher yield and/or faster reaction time (Table 2). Besides, the
steric hindrance effect of ortho-chloro groups showed no significant in-
fluence on the reaction efficiency (Table 2, entries 3 and 9).
2
Fig. 7. TG curves of UiO-66-NH (top), UiO-66-Urea (middle), and ChCl@UiO-66-Urea
(bottom).
According to our experimental results and previously reported pro-
cedures [47–49], the proposed mechanism for the one-pot three-
component reactions was represented in Scheme 2. Accordingly, the
process is initiated with the activation of aldehyde and malononitrile
with porous ChCl@UiO-66-Urea catalyst due to Lewis acidity of Zr-
MOF [21,58], Brønsted basicity and hydrogen bonding ability of urea
groups [23,66,67]. The hydroxyl group of choline also may act as a hy-
drogen bond catalyst [68] for the reaction. In addition, the impregnation
of UiO-66-Urea with choline chloride greatly facilitates the contact be-
tween the ChCl@UiO-66-Urea and starting materials, due to in-situ for-
mation a deep eutectic or low-melting mixture [23,67]. Subsequently,
the catalytic cycle is most probably continued with the Knoevenagel
condensation reaction between the activated aldehyde and
malononitrile to give the intermediate I (Knoevenagel reaction). The
next step involves the regioselective nucleophilic addition of α-
naphthol/4-hydroxycoumarin (C-addition) to the intermediate I to
form the intermediate II (Michael addition). Finally, the intermediate
8
0 °C after 3 h (Entry 2). To further understand the active sites of the
was examined as catalyst for the model reaction
under the optimal reaction conditions. The observed yield was 32%
with UiO-66-NH (Entry 10, Table 1) which was comparatively lower
MOF, UiO-66-NH
2
2
than using ChCl@UiO-66-Urea as catalyst. The reaction under similar
conditions in the presence of UiO-66 afforded 25% yield of the product
(
Entry 11, Table 2). The use of UiO-66-Urea as catalyst resulted in 46%
yield of the product under identical conditions (Entry 12). Also, ChCl
as catalyst produced a much lower yield compared to that of the
ChCl@UiO-66-Urea (Entry 13). When homogenous ChCl-2urea, mixing
urea and ChCl (ratio 2:1) at 80 °C for 3 h, was used as the catalyst, the
product yield was remarkably increased to 69% (Entry 14), but is still
comparatively lower than using ChCl@UiO-66-Urea as catalyst. To
Table 1
a
Optimization of the reaction conditions for the three-component synthesis of 2-amino-4H-chromenes.
Entry
Catalyst
Catalyst amount (mg)
Time (h)
T)°C(
Solvent
Yield (%)b
1
2
3
4
5
7
8
9
ChCl@UiO-66-Urea
ChCl@UiO-66-Urea
ChCl@UiO-66-Urea
ChCl@UiO-66-Urea
ChCl@UiO-66-Urea
ChCl@UiO-66-Urea
ChCl@UiO-66-Urea
ChCl@UiO-66-Urea
10
10
10
5
3
3
3
3
3
5
5
5
3
3
3
3
3
3
50
80
100
80
80
80
80
80
80
80
80
80
80
80
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
EtOH
41
92
91
60
92
72
59
41
32
25
46
18
69
24
15
10
10
10
10
10
10
10
10
8
EtOH/H
EtOAc
2
O
10
11
12
13
14
15
UiO-66-NH
UiO-66
2
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
Solvent-free
UiO-66-Urea
ChCl
ChCl-urea
ZrCl
4
a
Reaction conditions: benzaldehyde (1 mmol), malononitrile (1 mmol), α-naphthol (1 mmol), and catalyst.
Yields refer to isolated and purified products.
b
7

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
Table 2
a
One-pot three-component synthesis of 2-amino-4H-chromene derivatives using ChCl@UiO-66-Urea catalyst.
Entry
Product
Time
h)/
Yield
%)b
m.p.
(°C)c
Entry
Product
Time
(h)/
m.p.
(°C)c
(
Yield
(%)b
(
1
2
3
4
5
6
7
3/92
3/91
213-215
240-242
245-247
217-219
218-220
180-183
203-205
8
3/91
4.5/85
3.5/91
3/92
245-247
270-273
266-270
260-262
247-249
231-232
9
4/89
10
11
12
13
2.5/91
2.5/92
3/92
4/87
4/84
4.5/91
a
b
c
Reaction conditions: aromatic aldehyde (1 mmol), malononitrile (1 mmol), α-naphthol/4-hydroxycoumarin (1 mmol), and ChCl@UiO-66-Urea (10 mg) under solvent-free condition at 80 °C.
Yields refer to isolated and purified products.
Observed melting points.

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
Scheme 2. Proposed mechanism for the three-component synthesis of chromenes using ChCl@UiO-66-Urea as the catalyst.
II undergoes intramolecular ring closure to produce the corresponding
chromene (Cyclization) and the regenerated catalyst is simultaneously
used in the next cycle.
Further, the stability and reusability of ChCl@UiO-66-Urea were
checked using the model reaction. After the completion of the reaction,
the catalyst was removed from the reaction mixture with chloroform
and dried at 90 °C under vacuum. The catalyst was reused in next cycle
without significant loss in its catalytic efficiency. As exhibited in Fig. S5,
the decrease in efficiency of ChCl@UiO-66-Urea catalyst after the third
and fifth cycles were 4 and 7%, respectively. However, the catalytic activ-
ity was still highof85%evenafter five times use. Tofurther checkthesta-
bility of the catalyst, the reused ChCl@UiO-66-Urea was then
characterized by PXRD, FT-IR, and EDX elemental analysis. Accordingly,
the PXRD of the reused catalyst was indicated that its structure was
Table 3
Comparison of the catalytic activity of ChCl@UiO-66-Urea with catalysts reported for the one-pot three-component reaction of benzaldehydes, malononitrile, and α-naphthol.
Entry
Catalyst (amount)
Solvent
Temperature (°C)
Time (h)
Yield (%)
Ref.
1
2
3
4
5
6
Nanostructured diphosphate Na
Sodium-modified hydroxyapatite (100 mg)
Silica-supported piperazine (185 mg) (for 4-chlorobenzaldehyde)
2
CaP
2
O
7
(DIPH) (0.3 g)
H
H
2
O
O
Reflux
Reflux
Reflux
100
Reflux
110
4
3
7
90
96
74
90
91
90
44
45
46
47
48
49
2
CHCl
Solvent-free
H
3
Alkylaminopyridine-grafted on HY Zeolite (Z-HY@SiO
14[NaP 110] (30 mg)
2D-hexagonal mesoporous material functionalized with a triazine moiety
40 mg) (for 4-chlorobenzaldehyde)
ChCl@UiO-66-Urea (10 mg)
2
-Pr-Py) (30 mg)
80 min
3
4
H
W
5 30
O
2
O
Solvent-free
(
7
Solvent-free
80
3
92
This work
9

M. Akbarian, E. Sanchooli, A.R. Oveisi et al.
Journal of Molecular Liquids 325 (2021) 115228
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Mohadeseh Akbarian: Investigation, Visualization, Formal analysis;
Esmael Sanchooli: Validation, Investigation, Resources, Methodology,
Funding acquisition, Co-supervision; Ali Reza Oveisi: Supervision, Pro-
ject administration, Writing - review & editing; Saba Daliran: Concep-
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Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
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Acknowledgment
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