Ni0 NPs anchored on acid-activated montmorillonite (Ni0-Mont) as a highly efficient and reusable nanocatalyst for synthesis of biscoumarins and bisdimedones

Article abstract of DOI:10.1007/s11164-018-3671-y

Ni⁰ nanoparticles were immobilized on acid-activated montmorillonite (Ni⁰-Mont) by anchoring Ni(OAc)₂·4H₂O on modified micro/mesoporous montmorillonite followed by reduction with ethylene glycol. The prepared cl

Full text of DOI:10.1007/s11164-018-3671-y

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-018-3671-y
0
Ni NPs anchored on acid‑activated montmorillonite
0
(
Ni ‑Mont) as a highly efcient and reusable nanocatalyst
or synthesis oꢀ biscoumarins and bisdimedones
ꢀ
Soleiman Rahmani · Behzad Zeynizadeh1
1
Received: 18 May 2018 / Accepted: 18 November 2018
©
Springer Nature B.V. 2018
Abstract
0
0
Ni nanoparticles were immobilized on acid-activated montmorillonite (Ni -Mont)
by anchoring Ni(OAc) ·4H O on modifed micro/mesoporous montmorillonite ꢀol-
2
2
lowed by reduction with ethylene glycol. The prepared clay composite system was
then characterized using Fourier-transꢀorm inꢀrared (FT-IR) spectroscopy, scanning
electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray
diꢁraction (XRD) analysis, and Brunauer–Emmett–Teller (BET) analysis. SEM
analysis revealed perꢀect dispersion oꢀ metallic nickel nanoparticles with size distri-
bution oꢀ 6‒41 nm on the clay matrix. Micro/mesoporous montmorillonite was pre-
+
pared by activation oꢀ Na -montmorillonite with HCl (4 M) under controlled condi-
0
tions. The catalytic activity oꢀ the prepared Ni -Mont clay was studied in one-pot
microwave-assisted synthesis oꢀ biscoumarins and bisdimedones via Knoevenagel
reaction oꢀ aromatic aldehydes with 4-hydroxycoumarin or dimedone in solvent-
ꢀ
(
ree conditions. All reactions were carried out at room temperature within 5‒15 min
ꢀor biscoumarins) and 5–20 min (ꢀor bisdimedones) to aꢁord the products in high
0
to excellent yield. The reusability oꢀ the Ni -Mont catalyst was also investigated in
seven consecutive cycles, without signifcant loss oꢀ catalytic activity.
Keywords Biscoumarins · Bisdimedones · Knoevenagel · Microwave ·
0
Montmorillonite K10 · Ni -Mont
Introduction
Transition-metal nanoparticles (NPs) are currently attracting a great deal oꢀ atten-
tion due to their prominent properties such as antiꢀungal and antibacterial activities,
being widely used in optical, electrical, magnetic, and sensor devices as well as drug
*
Behzad Zeynizadeh
bzeynizadeh@gmail.com
1
Faculty oꢀ Chemistry, Urmia University, Urmia 5756151818, Iran
Vol.:(012
1
3456789)
3

S. Rahmani, B. Zeynizadeh
delivery systems [1–5]. In addition, their huge surꢀace area and nanosize dimension
accompanied by electronic eꢁects oꢀ the metal species make them attractive cata-
lysts ꢀor promotion oꢀ numerous organic reactions [6]. In this context, because oꢀ
their unique chemical characteristics, air stability, high catalytic activity, easy prep-
aration, and perꢀect recyclability, application oꢀ nickel nanoparticles has attracted
attention ꢀrom chemists in many felds [7–9]. Review oꢀ the literature shows that
applications oꢀ nickel nanoparticles in Suzuki coupling [10–12], reductive amina-
tion oꢀ aldehydes [13], Mizoroki–Heck reaction [14, 15], oxidative Heck reaction
[
16], Hantzsch 1,4-dihydropyridine synthesis [17], synthesis oꢀ 2-arylbenzimida-
zoles, 2-arylbenzothiazoles, and azomethines [18], and pyran derivatives [19] has
also been documented.
In spite oꢀ the great convenience oꢀ transition-metal nanoparticles ꢀor promotion
oꢀ chemical reactions, they have a strong tendency ꢀor agglomeration, which dimin-
ishes their active surꢀace area [20, 21]. Incorporation oꢀ numerous stabilizers or
solid supports to immobilize transition-metal nanoparticles plays an important role
in preventing agglomeration and to control their shape, morphology, and size distri-
bution. In this feld, alkylammonium salts [22], organic ligands [23], carbohydrates
[
24], flamentous carbon [25], and surꢀactants [26, 27] are the most commonly used
stabilizers. Moreover, mesoporous materials including SBA-12 [28], resins [29],
nanocrystalline MgO [30], and clay minerals [31–36] can also be applied as media
ꢀ
or supporting transition-metal nanoparticles.
Clays are a class oꢀ materials that are widely available in Nature, generally being
categorized into two groups, viz. cationic (clay minerals) and anionic clays (known
as layered double hydroxides, LDHs). Cationic clays are constituted ꢀrom colloidal
layered hydrous aluminosilicates including Si(O,OH) tetrahedral and M(O,OH)
4
6
3+
2+
3+
2+
octahedral (M=Al , Mg , Fe or Fe ). In addition, they can be ꢀurther classifed
on the basis oꢀ the layer type and charge as well as the appearance oꢀ both Brønsted
3
+
and Lewis acid properties produced by OH groups and Al ions, respectively, in
tetrahedral sheets. Various combinations oꢀ tetrahedral and octahedral layers result
in clays with diꢁerent properties [33]. Clay minerals oꢀ the smectite group such as
montmorillonite K10, hectorite, saponite, and laponite are suitable solid supports ꢀor
metal nanoparticles, which can be immobilized into the interlamellar spaces. Mont-
morillonite K10, in both its natural and modifed ꢀorms, possesses both Brønsted
and Lewis acid characteristics, which enables it to ꢀunction as a perꢀect solid support
or promoter. In addition, treatment oꢀ montmorillonite with acids or organic materi-
als can dramatically improve properties such as its surꢀace area and porosity [34,
3
5].
Biscoumarins (dicoumarols) are widely used precursors in synthesis oꢀ acridin-
ediones (as laser dyes) and heterocyclic compounds [37]. Review oꢀ the literature
shows that many coumarin and biscoumarin (dicoumarol) compounds exhibit a
broad spectrum oꢀ biological activities, including antiinꢂammatory, antibacterial,
anticancer, antiviral, anti-human immunodefciency virus (HIV), and antiproliꢀ-
erative properties [38–44]. It has also been reported that some dicoumarol-based
inhibitors exhibit activity against Gram-positive bacteria [45, 46]. Accordingly,
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
synthesis oꢀ dicoumarols is a subject oꢀ high interest. Generally, dicoumarols
are prepared by condensation oꢀ 4-hydroxycoumarin with aromatic aldehydes in
various solvents. Molecular iodine [47], piperidine [48], 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU) [49], n-dodecylbenzene sulꢀonic acid (DBSA) [50], sodium
dodecyl sulꢀate (SDS) [51], Zn(proline) [52], tetra-n-butylammonium bromide
2
(
TBAB) [53], ionic liquids [54], and nanosilica chloride [55] are some oꢀ the cat-
alysts/reagents reported ꢀor promotion oꢀ the title reaction. As well as synthesis oꢀ
biscoumarin compounds, preparation oꢀ bisdimedones as raw materials to aꢁord
xanthan products has also attracted attention ꢀrom research groups in laboratory
and industrial settings [56, 57]. Due to their antibacterial, antiviral, antiinꢂamma-
tory, and analgesic activities, xanthene derivatives are very important compounds
[
58], being variably used as dyes [59] in laser technology [60] and as ꢂuorescent
probes ꢀor measuring pH values oꢀ living chondrocytes [61]. As well, some xan-
thenediones are important building blocks in natural products [62]. Although the
mentioned methods have their own merits, most oꢀ them suꢁer ꢀrom disadvan-
tages such as prolonged reaction time, tedious workup procedure, unsatisꢀactory
yield, high temperature, or use oꢀ expensive and unrecoverable catalysts. Thus,
development oꢀ new and more eꢃcient catalytic systems ꢀor use under green
reaction conditions is still required.
In line with the outlined strategies, we introduce herein a highly eꢃcient pro-
tocol ꢀor one-pot microwave-assisted synthesis oꢀ biscoumarins and bisdimedones
by Knoevenagel condensation reaction oꢀ 4-hydroxycoumarin or dimedone with
0
aromatic aldehydes in presence oꢀ Ni NPs anchored on acid-activated montmo-
0
rillonite (Ni -Mont) as a green, eꢃcient, and easily reusable clay-based catalyst
(
Scheme 1).
0
Scheme 1 Synthesis oꢀ biscoumarin 4 and bisdimedone 5 catalyzed by Ni -Mont NPs system
1
3

S. Rahmani, B. Zeynizadeh
Experimental
Materials and methods
All chemicals were purchased ꢀrom chemical companies with best quality and
1
13
were used without ꢀurther purifcation. H and C nuclear magnetic resonance
NMR) and FT-IR spectra were recorded on 300 MHz Bruker Avance and Thermo
(
Nicolet Nexus 670 spectrometers. Particle size and morphology were determined
by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX)
spectroscopy. Melting points were recorded on Electrothermal 9100 melting point
apparatus and are uncorrected. All products are known and were characterized by
comparison oꢀ their physical and spectral data with reported values. Yields reꢀer
to isolated pure products. Thin-layer chromatography (TLC) over silica gel 60
F254 aluminum sheet was used to monitor the reactions. Microwave irradiation
was carried out in a domestic microwave oven (LG MS-2344B, 1250 W). Mont-
morillonite K10 was purchased ꢀrom Sigma-Aldrich company (art. no. 69866,
2
pH ~ 3‒4, surꢀace area 250 m /g).
+
+
Preparation of homoionic Na ‑exchanged montmorillonite (Na ‑Mont)
In a beaker (250 mL) containing distilled water (200 mL), montmorillonite K10
(
5 g) was added and the mixture was stirred vigorously at room temperature ꢀor
2
0 h. The mixture was then allowed to settle, and the aqueous phase was decanted.
To the obtained solid residue, aqueous solution oꢀ NaCl (2 M, 200 mL) was added
and stirring was continued ꢀor 2 h at room temperature. The aqueous phase was
decanted, and the solid residue was again charged with aqueous solution oꢀ NaCl
(
2 M, 200 mL). Aꢀter stirring ꢀor 2 h at room temperature, the aqueous phase was
decanted. The procedure was repeated an additional two times. Finally, the solid
residue was washed ꢀrequently with distilled water until the conductivity oꢀ the
liquid fltrate reached the conductivity oꢀ distilled water. The solid residue was
+
dried at 50 °C under air atmosphere to aꢁord homoionic Na -exchanged montmo-
+
rillonite (Na -Mont) [32].
+
Preparation of acid‑activated montmorillonite (H ‑Mont)
To a round-bottomed ꢂask (250 mL) containing aqueous solution oꢀ HCl (4 M,
+
1
00 mL), Na -Mont (5 g) was added. The mixture was stirred under reꢂux condi-
tions ꢀor 2 h. Aꢀter cooling, the aqueous phase was decanted, and the residue was
−
washed ꢀrequently with distilled water. When the liquid fltrate was ꢀree oꢀ Cl
(
tested with AgNO ), the solid material on flter paper was collected and dried at
3
+
5
0 °C to aꢁord acid-activated montmorillonite (H -Mont).
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
0
0
Preparation of Ni NPs immobilized on acid‑activated montmorillonite [Ni ‑Mont]
In a beaker (100 mL) containing aqueous solution oꢀ Ni(OAc) ·4H O (0.05 M,
2
2
1
0 mL), acid-activated montmorillonite (0.5 g) was added portionwise, and the
resulting mixture was stirred vigorously at room temperature ꢀor 6 h. The aqueous
phase was then evaporated under reduced pressure. The dried Mont-Ni(OAc) was
2
dispersed in ethylene glycol (50 mL) within a double-necked round-bottomed ꢂask.
The mixture was stirred under reꢂux conditions ꢀor 6 h (N atmosphere). Ethylene
2
glycol was then removed by decantation, ꢀollowed by washing the solid residue with
MeOH to remove remaining ethylene glycol. The solid material was then dried at
0
4
0 °C ꢀor 12 h (N ꢂow), giving Ni NPs anchored on acid-activated montmorillon-
2
0
ite (Ni -Mont).
0
General procedure for synthesis of biscoumarins/bisdimedones using Ni ‑Mont
NPs
In a watch glass (diameter 5 cm), a mixture oꢀ 4-hydroxycoumarin/dimedone
0
(
2 mmol), aromatic aldehyde (1 mmol), Ni -Mont (0.02 g), and 3–4 drops absolute
ethanol was well mixed, and the resulting mushy mixture was irradiated in a domes-
tic microwave oven (850 W) ꢀor an appropriate time as mentioned in Tables 4 and
5
. Aꢀter reaction completion (monitored by TLC), the mixture was cooled to room
temperature. Ethyl acetate (5 mL) was then added, and the mixture was stirred ꢀor
5
min. The catalyst was removed ꢀrom the reaction mixture using a flter paper. The
fltrate was evaporated, and the solid material was recrystallized ꢀrom hot ethanol to
aꢁord pure biscoumarin/bisdimedone materials (yield 75–95 %).
Cation‑exchange capacity (CEC) of the clay mineral
The cation-exchange capacity (CEC) oꢀ the clay mineral was determined accord-
ing to the reported procedure [21]. To do this, clay mineral (such as Mont K10)
(
0.5 g) was dispersed in standard alcoholic solution oꢀ CaCl (10 mL, 0.05 M), and
2
the prepared mixture was stirred at room temperature ꢀor 24 h. The suspension was
fltered, washed with EtOH (20 mL), and dried at room temperature ꢀor 12 h. The
2
+
Ca -exchanged clay mineral was then transꢀerred to a volumetric ꢂask (250 mL).
The volume in the ꢂask was increased by adding distilled water to reach the standard
2
+
limit (250 mL). The amount oꢀ Ca was titrated with standard solution oꢀ ethyl-
2
+
enediaminetetraacetic acid (EDTA). The diꢁerence between the Ca concentration
beꢀore and aꢀter cation exchange aꢁords the CEC (meq/g) value oꢀ the clay mineral.
Spectral data ꢀor prepared biscoumarin and bisdimedone materials
3
,3′‑(Phenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (4a) FT-IR (KBr,
ʋ
−
1
1
cm ): 3400, 3067, 2737, 1659, 1609, 1564, 1336, 1089, 755; H NMR (300 MHz,
CDCl ): δ (ppm) 6.11 (s, 1H, CH), 7.25–8.07 (m, 13H, ArH), 11.32 (s, 1H, OH),
3
1
3

S. Rahmani, B. Zeynizadeh
1
3
1
1
1
1.55 (s, 1H, OH); C NMR (75 MHz, CDCl ): δ (ppm) 36.16, 103.88, 105.62,
3
16.42, 116.65, 124.39, 124.91, 126.89, 128.77, 132.88, 135.17, 152.27, 164.60,
65.02.
3
,3′‑(2,4‑Dichlorophenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (4b) FT-IR
−1
1
(
KBr, ʋ cm ): 3068, 2719, 2594, 1649, 1565, 1497, 1097, 759; H NMR (300 MHz,
CDCl ): δ (ppm) 6.12 (s, 1H, CH), 7.24–8.02 (m, 11H, ArH), 11.67 (s, 2H, OH);
3
1
3
C NMR (75 MHz, CDCl ): δ (ppm) 35.46, 116.51, 124.48, 124.87, 126.9, 130.33,
3
1
32.92, 134.1, 152, 164.22, 166.8.
3
,3′‑(4‑Chlorophenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (4c) FT-IR (KBr,
−1
1
ʋ cm ): 3428, 3073, 2730, 1664, 1614, 1565, 1494, 1344, 1094, 770; H NMR
(
300 MHz, CDCl ): δ (ppm) 6.04 (s, 1H, CH), 7.15–8.06 (m, 12H, ArH), 11.32 (s,
3
1
3
1
1
1
H, OH), 11.55 (s, 1H, OH); C NMR (75 MHz, CDCl ): δ (ppm) 35.7, 103.69,
3
05.24, 116.34, 124.41, 125.01, 127.97, 128.77, 132.77, 133.04, 133.83, 152.26,
64.53, 166.02.
3
,3′‑(2‑Chlorophenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (4d) FT-IR (KBr,
−1
1
ʋ cm ): 3069, 2720, 1649, 1556, 1498, 1444, 1340, 1097, 760; H NMR (300 MHz,
CDCl ): δ (ppm) 6.16 (s, 1H, CH), 7.27–8.04 (m, 12H, ArH), 10.93 (s, 1H, OH),
3
1
3
1
1.64 (s, 1H, OH); C NMR (75 MHz, CDCl ): δ (ppm) 35.72, 116.59, 124.42,
3
1
24.87, 126.76, 128.59, 129.24, 130.81, 132.83, 133.49, 162.33.
3
,3′‑(4‑Bromophenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (4e) FT-IR (KBr,
−1
ʋ cm ): 3428, 3068, 2930, 1663, 1612, 1563, 1490, 1445, 1342, 1315, 1200, 1096,
1
1
022, 767; H NMR (300 MHz, CDCl ): δ (ppm) 6.02 (s, 1H, CH), 7.09–8.06 (m,
3
1
3
1
2H, ArH), 11.32 (s, 1H, OH), 11.54 (s, 1H, OH); C NMR (75 MHz, CDCl ): δ
3
(
ppm) 35.86, 103.64, 105.18, 116.36, 116.66, 120.87, 124.4, 124.97, 128.3, 131.69,
1
34.4, 152.28, 162.34, 164.63, 166.02.
3
,3′‑(4‑Methoxyphenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one)
(4f) FT-IR
−1
(
KBr, ʋ cm ): 3064, 2944, 2842, 2727, 1666, 1612, 1562, 1507, 1447, 1343, 1309,
1
1
094, 768; H NMR (300 MHz, CDCl ): δ (ppm) 3.80 (s, 3H, OMe), 6.05 (s, 1H,
3
1
3
CH), 6.84–8.05 (m, 12H, ArH), 11.34 (s, 1H, OH), 11.52 (s, 1H, OH); C NMR
(
75 MHz, CDCl ): δ (ppm) 33.37, 110.93, 116.5, 116.7, 120.4, 123.5, 124.3, 124.7,
3
1
28.2, 128.4, 132.44, 152.13, 157.56, 163.7, 165.2.
3
,3′‑(2‑Methoxyphenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one)
(4g) FT-IR
−1
(
KBr, ʋ cm ): 3412, 3069, 2981, 2724, 1654, 1620, 1550, 1494, 1448, 1337, 1305,
1
1
094, 758; H NMR (300 MHz, CDCl ): δ (ppm) 3.5 (s, 3H, OMe), 6.09 (s, 1H,
3
1
3
CH), 6.85–8.04 (m, 12H, ArH), 11.22 (bs, 2H, OH); C NMR (75 MHz, CDCl ):
3
δ (ppm) 35.48, 104.18, 105.74, 113.98, 116.62, 116.89, 124.36, 124.86, 126.90,
1
27.61, 132.83, 152.25, 152.47, 164.51, 165.69, 169.25.
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
−
1
3
3
,3′‑(p‑Tolylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (4h) FT-IR (KBr, ʋ cm ):
1
100, 2992, 2919, 1665, 1614, 1563, 1502, 1440, 1094, 765; H NMR (300 MHz,
CDCl ): δ (ppm) 2.34 (s, 3H, CH ), 6.07 (s, 1H, CH), 7.12–8.04 (m, 12H, ArH),
3
3
1
3
1
3
1
1.34 (s, 1H, OH), 11.48 (s, 1H, OH); C NMR (75 MHz, CDCl ): δ (ppm) 20.97,
3
5.87, 116.61, 116.93, 124.37, 124.84, 126.36, 129.33, 132.77, 136.46, 152.47,
62.34, 164.5, 165.67.
3
,3′‑(4‑Hydroxyphenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one)
(4i) FT-IR
−1
1
(
KBr, ʋ cm ): 3361, 3072, 2731, 1660, 1614, 1565, 1509, 1443, 1096, 762; H
NMR (300 MHz, CDCl ): δ (ppm) 6.02 (s, 1H, CH), 6.77–8.02 (m, 12H, ArH),
3
1
3
1
1
1.48 (bs, 2H, OH); C NMR (75 MHz, CDCl ): δ (ppm) 35.49, 104.16, 115.64,
3
16.61, 124.37, 126.78, 127.75, 152.41, 154.66, 162.32.
3
,3′‑(4‑Nitrophenylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (4j) FT-IR (KBr,
−1
1
ʋ cm ): 3427, 3075, 2935, 1652, 1562, 1343, 1095, 762; H NMR (300 MHz,
CDCl ): δ (ppm) 6.14 (s, 1H, CH), 7.27–8.17 (m, 12H, ArH), 11.39 (s, 1H, OH),
3
1
3
1
1
1
1.58 (s, 1H, OH); C NMR (75 MHz, CDCl ): δ (ppm) 36.18, 103.22, 104.62,
3
16.26, 116.73, 121.76, 122.12, 124.5, 125.17, 129.59, 132.7, 133.33, 137.9,
48.75, 152.35, 162.34, 166.59, 166.9.
3
,3′‑(2‑Nitrophenyl)methylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one) (4k) FT-IR (KBr,
−1
ʋ cm ): 3433, 3076, 2722, 1652, 1618, 1561, 1532, 1450, 1352, 1309, 1099, 761;
1
H NMR (300 MHz, CDCl ): δ (ppm) 6.64 (s, 1H, CH), 7.27–8.01 (m, 12H, ArH),
3
1
3
1
1
1.55 (bs, 2H, OH); C NMR (75 MHz, CDCl ): δ (ppm) 33.86, 103.71, 116.66,
3
24.57, 125.03, 128.19, 129.49, 131.9, 133.2, 149.76.
3
,3′‑(4‑Pyridylmethylene)‑bis(4‑hydroxy‑2H‑chromen‑2‑one)
(4l) FT-IR
(KBr,
−1
1
ʋ cm ): 3447, 3075, 2880, 1663, 1618, 1543, 1500, 1407, 1102, 757; H NMR
(
300 MHz, DMSO-d ): δ (ppm) 6.47 (s, 1H, CH), 7.21–8.68 (m, 12H, ArH and pyri-
6
dyl-H). It is notable that, due deuterium exchange, hydrogen oꢀ two OH groups at
1
3
region oꢀ δ=11.5 ppm was not observed. C NMR (75 MHz, DMSO-d ): δ (ppm)
6
3
1
8.26, 101.88, 116.20, 119.82, 123.65, 124.67, 125.67, 132.04, 141.35, 153.15,
64.53, 165.34, 168.59.
2
,2′‑(Phenylmethylene)‑bis(3‑hydroxy‑5,5‑dimethylcyclohex‑2‑en‑1‑one) (5a) FT-IR
−1
1
(
KBr, ʋ cm ): 3434, 3038, 2852, 1719, 1593, 1447, 1378, 1405, 858, 746; H NMR
(
300 MHz, CDCl ): δ (ppm) 1.09 (s, 6H, CMe ), 1.23 (s, 6H, CMe ), 2.39 (bs, 8H,
3
2
2
2
CH ), 5.56 (s, 1H, CH), 7.10–7.25 (m, 5H, Ar), 10.1 (br, 1H, OH), 11.91 (s, 1H,
2
OH).
2
,2′‑((2‑Chlorophenyl)methylene)‑bis(3‑hydroxy‑5,5‑dimethylcyclohex‑2‑en‑1‑one)
−1
1
(
5b) FT-IR (KBr, ʋ cm ): 3339, 2954, 1718, 1596, 1458, 1387, 1288, 848, 753; H
NMR (300 MHz, CDCl ): δ (ppm) 1.55 (s, 6H, CMe ), 1.073 (s, 6H, CMe ), 2.05–
3
2
2
2
.53 (m, 8H, 2CH ), 5.63 (s, 1H, CH), 7.12–7.39 (m, 4H, Ar), 11.86 (br, 1H, OH).
2
1
3

S. Rahmani, B. Zeynizadeh
2
,2′‑((4‑Chlorophenyl)methylene)‑bis(3‑hydroxy‑5,5‑dimethylcyclohex‑2‑en‑1‑one)
−1
1
(
5c) FT-IR (KBr, ʋ cm ): 3421, 3055, 2955, 1592, 1373, 1255, 836, 731; H NMR
(
300 MHz, CDCl ): δ (ppm) 1.10 (s, 6H, CMe ), 1.21 (s, 6H, CMe ), 2.38 (bs, 8H,
3
2
2
2
CH ), 5.47 (s, 1H, CH), 7.02 (bs, 2H, Ar), 7.24 (bs, 2H, Ar), 11.76 (bs, 1H, OH),
2
1
1.86 (s, 1H, OH).
2
,2′‑((3‑Hydroxy‑4‑methoxyphenyl)methylene)‑bis(3‑hydroxy‑5,5‑dimethylcy‑
−1
clohex‑2‑en‑1‑one) (5d) FT-IR (KBr, ʋ cm ): 3425, 2951, 2643, 1721, 1594, 1520,
1
1
1
373, 1270, 821, 758; H NMR (300 MHz, CDCl ): δ (ppm) 1.31 (bs, 6H, CMe ),
3
2
.40 (s, 6H, CMe ), 2.73–2.49 (m, 8H, 2CH ), 3.84 (bs, 3H, OCH ), 5.47 (s, 1H,
2
2
3
CH), 6.55–7.22 (m, 3H, Ar), 11.96 (bs, 1H, OH).
2
,2′‑((4‑nitrophenyl)methylene)‑bis(3‑hydroxy‑5,5‑dimethylcyclohex‑2‑enone)
−1
(5e) FT-IR (KBr, ʋ cm ): 3425, 2956, 2882, 1592, 1533, 1451, 1369, 1253, 887,
1
7
2
1
43; H NMR (300 MHz, CDCl ): δ (ppm) 1.12 (s, 6H, CMe ), 1.27 (s, 6H, CMe ),
3
2
2
.37–2.47 (m, 8H, 2CH ), 5.54 (s, 1H, CH), 7.26 (m, 2H, Ar), 8.01 (s, 1H, Ar),
2
1.85 (s, 1H, OH).
Results and Discussion
0
Synthesis and characterization of Ni NPs anchored on micro/mesoporous
0
acid‑activated montmorillonite (Ni ‑Mont)
Following the outlined strategies and due to the lack oꢀ inꢀormation on montmoril-
lonite-catalyzed synthesis oꢀ biscoumarins, we investigated the title transꢀormation
0
using Ni NPs immobilized on acid-activated montmorillonite K10 as a novel reus-
able clay-based catalyst. The study started with synthesis oꢀ the clay catalyst in a
fve-step procedure: (1) Preparation oꢀ swelled (hydrated) montmorillonite through
vigorous stirring oꢀ commercially available montmorillonite K10 in distilled water.
Similar to other clay minerals, montmorillonite K10 can absorb water between inter-
lamellar spaces, moving the layers apart and swelling the clay, which expands the
surꢀace area oꢀ montmorillonite and exposes the cations oꢀ interlayers to contribute
to the Brønsted and Lewis acid properties oꢀ the clay mineral [6]; (2) Preparation oꢀ
+
homoionic Na -exchanged montmorillonite by adequate stirring oꢀ swollen mont-
morillonite in aqueous solution oꢀ NaCl. Through this and simple ion exchange,
+
many cations oꢀ interlayers (oꢀ montmorillonite K10) are exchanged with Na ions.
+
+
Diꢁusion oꢀ Na ions aꢁords high capacity to the clay mineral ꢀor exchanging Na
ions with various guest species (transition-metal ions/nanoparticles, complexes,
+
and H ions) and their encapsulation in interlamellar spaces. Moreover, by altering
the cations oꢀ the interlayers, the acidity (Brønsted and Lewis) oꢀ the clay mineral
can be changed ꢀor diꢁerent purposes; (3) Preparation oꢀ acid-activated montmo-
+
rillonite by stirring homoionic Na -exchanged montmorillonite in aqueous solution
oꢀ hydrochloric acid; (4) Preparation oꢀ immobilized Ni(OAc) on acid-activated
2
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
0
Scheme 2 Preparation oꢀ Ni -Mont NPs system
montmorillonite by simply mixing and stirring oꢀ acid-activated montmorillonite in
aqueous solution oꢀ nickel acetate; (5) Reduction oꢀ nickel acetate to nickel nanopar-
0
ticles with ethylene glycol to obtain Ni -Mont clay system (Scheme 2).
The concentration oꢀ exchangeable cations in a clay mineral is called its cation-
exchange capacity (CEC), measured in milli-equivalent per 100 g oꢀ dried clay [36].
The measurement results ꢀor the CEC were 85 meq/g ꢀor Mont K10 and 110 meq/g
+
+
ꢀ
or Na -Mont, indicating that replacement oꢀ Na ions oꢀ other cations in the interla-
mellar spaces increased the cation-exchange capacity oꢀ the clay mineral.
0
Aꢀter successꢀul synthesis oꢀ the Ni -Mont clay system, the size and morphol-
+
0
ogy oꢀ Mont K10, acid-activated Mont (H -Mont), and Ni -Mont clays were studied
using FT-IR, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX)
spectroscopy, and X-ray diꢁraction (XRD) analysis.
FT‑IR analysis
Fourier-transꢀorm inꢀrared spectroscopy as a primarily tool was utilized ꢀor struc-
tural elucidation oꢀ montmorillonite K10 (Mont K10), acid-activated montmorillon-
+
0
0
ite (H -Mont), and Ni immobilized on acid-activated montmorillonite (Ni -Mont)
(
Fig. 1). The FT-IR spectrum oꢀ Mont K10 shows a wide absorption band at
−1
3
433 cm due to stretching vibration oꢀ hydroxyl groups bonded to Si, Al, and other
−
1
metals that are present, a small absorption band at 1630 cm due to deꢀormation
−
1
vibration oꢀ hydroxyl groups, a strong absorption band at 1054 cm derived ꢀrom
stretching vibration oꢀ Si–O bonds in tetrahedral sites, a small absorption band at
1
−1
7
95 cm− due to the amorphous silica that is present, and bands at 522 and 464 cm
1
3

S. Rahmani, B. Zeynizadeh
+
0
Fig. 1 FT-IR spectrum oꢀ Mont K10, H -Mont, and Ni -Mont clays
due to bending vibration oꢀ Si–O–Al and Si–O–Si bonds. In this context, the FT-IR
+
0
spectrum oꢀ the H -Mont and Ni -Mont clay systems shows that, although they
exhibited the same pattern as montmorillonite alone, the position oꢀ the wide stretch-
−
1
ing vibration oꢀ Si–O bonds oꢀ montmorillonite alone at 1054 cm was shiꢀted to
−
1
+
1
080 cm aꢀter acid activation, confrming successꢀul ion exchange oꢀ the H -Mont
0
system. In the case oꢀ the Ni -Mont system, the mentioned absorption peak shiꢀted
−1
0
to 1042 cm , indicating dispersion oꢀ Ni NPs on the surꢀace oꢀ the montmorillon-
ite clay. Also, the shape oꢀ the absorption band was modifed, becoming narrower. In
−
1
this context, the bands around 2948, 2865, and 1476 cm also confrm immobiliza-
tion oꢀ nickel nanoparticles in the clay matrix through the conꢀormational changes
in metal-linked clay interactions [63–65]. It is notable that the structure oꢀ the clay
matrix was unaꢁected when embedding nickel nanoparticles.
SEM and EDX analysis
Further investigation towards elucidation oꢀ the clay composite systems was car-
ried out by SEM and EDX spectroscopy to determine the elements presents. SEM
+
images and EDX spectra oꢀ Mont K10 and H -Mont clays are shown in Fig. 2. Com-
paring the SEM images (Fig. 2a, c) shows that, aꢀter acid activation, adjacent layers
oꢀ Mont K10 were exꢀoliated to tiny segments. This phenomenon is attributed to
3
+
elimination oꢀ many Al ions ꢀrom octahedral sites in montmorillonite on reaction
3
+
with HCl. It is notable that, due to the removal oꢀ Al ions ꢀrom interlayers, numer-
ous new pores were generated on the surꢀace and in interlamellar spaces, increasing
+
the surꢀace area oꢀ the H -Mont system compared with montmorillonite alone. In
0
this context, the SEM analysis (Fig. 3) oꢀ the Ni -Mont system exhibited anchored
metallic nickel nanoparticles with spherical shape, well distributed on the surꢀace
oꢀ tiny segments or into interlamellar spaces, with particle size ranging ꢀrom 6 to
4
1 nm. Accordingly, the illustrated EDX spectrum clearly demonstrates the presence
0
oꢀ Ni content as well as other elements in the Ni -Mont system.
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
+
Fig. 2 a SEM image and b EDX spectrum oꢀ Mont K10, c SEM image and d EDX spectrum oꢀ H -Mont
system
XRD analysis
In continuation, structural analysis oꢀ the clay composite systems was carried out
by plotting the wide-angle XRD spectrum oꢀ the prepared samples (Fig. 4). Along
with hkl and two-dimensional hk reꢂections, a number oꢀ sharp peaks correspond-
ing to impurities (quartz, cristobalite, and ꢀeldspar) were observed in the diꢁracto-
+
gram oꢀ Mont K10 (Fig. 4a). Accordingly, the XRD spectrum oꢀ the Na -Mont sys-
tem (Fig. 4b) clearly shows a signifcant increase in the intensity oꢀ the absorption
+
peaks. This reveals that, through the simple ion-exchange process, Na ions were
successꢀul incorporated into the interlamellar spaces, leading to a dramatic increase
+
in the occupation oꢀ Na ions [66, 67]. In spite oꢀ this, however, the intensity oꢀ the
+
absorption peaks in the XRD pattern oꢀ the H -Mont system (Fig. 4c) was clearly
decreased. This phenomenon can be attributed to exꢀoliation and destruction oꢀ
+
0
sheets in the Na -Mont system by the HCl activation processing [68]. In the XRD
pattern oꢀ the Ni -Mont system (Fig. 4d), three characteristic peaks at 2θ=44.5°,
5
1.8°, and 76°, marked with (111), (200), and (222) indices, respectively, reveal
1
3

S. Rahmani, B. Zeynizadeh
0
Fig. 3 SEM and EDX spectrum oꢀ Ni -Mont system
0
ꢀ
ormation oꢀ pure Ni NPs with ꢀace-centered cubic (ꢀcc) structure on the surꢀace oꢀ
the clay matrix [69]. This means that no oxide or hydroxide oꢀ nickel was produced
0
during the preparation oꢀ the Ni -Mont system, confrming its phase purity [70].
Ultraviolet–visible analysis
0
The immobilization oꢀ Ni nanoparticles on acid-activated montmorillonite was also
clarifed using ultraviolet–visible (UV–Vis) spectroscopy. To do this, the UV–visible
2
+
spectrum oꢀ Ni immobilized on acid-activated montmorillonite (beꢀore reduction)
2
+
was plotted in the range oꢀ 630–780 nm (Fig. 5). As shown, the prepared Ni -Mont
2
+
system exhibited a broad absorption band due to Ni species. Accordingly, when
2
+
0
reduction oꢀ Ni species by polyethylene glycol was carried out to obtain Ni NPs,
the UV–Vis spectra did not show any absorption band. This analysis clearly demon-
0
strates immobilization oꢀ Ni NPs on the clay matrix [69, 70].
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
Fig. 4 Wide-angle XRD
patterns oꢀ a Mont K10, b
+
0
+
Na -Mont, c H -Mont, and d
Ni -Mont systems
BET analysis
To investigate the porosity and specifc surꢀace area oꢀ the clay composite sys-
+
tems, the N adsorption–desorption isotherms oꢀ the Mont K10, H -Mont,
2
0
and Ni -Mont systems are illustrated in Fig. 6. Analysis oꢀ this plot reveals
that the pattern oꢀ isotherms is similar ꢀor all samples; according to the
Brunauer–Deming–Deming–Teller (BDDT) classifcation, it is oꢀ type IV with
H3 hysteresis loop. It is well known that this type oꢀ isotherm is characteristic oꢀ
micro/mesoporous materials [71, 72]. As well, the parameters obtained ꢀor the
examined samples (Table 1) show that the BET surꢀace area and total pore vol-
+
ume oꢀ the H -Mont system were increased compared with those oꢀ Mont K10
1
3

S. Rahmani, B. Zeynizadeh
Fig. 5 UV–Vis spectrum oꢀ
2+
0
Ni -Mont and Ni -Mont clays
in ethanol
alone. This can be attributed to acid activation oꢀ Mont K10, leading to exꢀolia-
tion/destruction oꢀ adjacent sheets to tiny segments. Thereꢀore, this action gener-
ated more new pores, aꢁording the rise in pore volume and specifc surꢀace area
0
+
[
ꢀ
73, 74]. In contrast, anchoring Ni NPs on H -Mont clay reduced the BET sur-
+
ace area and total pore volume (due to blocking oꢀ pores in the H -Mont system
0
by Ni NPs) accompanied with a signifcant increase in the average pore radius
oꢀ particles. This increase could also arise due to rupture oꢀ some smaller pores
towards bigger ones [21, 63, 75].
0
Synthesis of biscoumarins and bisdimedones catalyzed by Ni ‑Mont system
0
Next, the catalytic activity oꢀ the Ni -Mont clay system was studied in synthesis
oꢀ biscoumarins via Knoevenagel condensation reaction oꢀ aromatic aldehydes
with 4-hydroxycoumarin. To optimize the reaction conditions, the progress oꢀ the
reaction oꢀ 4-hydroxycoumarin (2 mmol) and 4-chlorobenzaldehyde (1 mmol)
0
in presence oꢀ Ni -Mont clay was investigated under diꢁerent conditions. The
+
0
Fig. 6 N adsorption–desorption isotherms oꢀ a Mont K10, b H -Mont, and c Ni -Mont systems
2
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
Table 1 Surꢀace properties oꢀ examined clay composite systems
SBET (m g−1)
2
Vm (cm g−1)
3
Average pore
diameter (nm)
V (cm g−1)
3
Total pore
volume
Sample
p
3
−1
(
cm g
)
Mont K10
250.11
280.52
161.62
51.835
50.313
37.132
6.427
6.7483
7.5016
0.4016
0.419
0.2965
0.4298
0.5081
0.3031
+
H -Mont
0
Ni -Mont
results oꢀ this investigation are illustrated in Table 2. As seen, perꢀorming the
model reaction in various solvents and under reꢂux conditions led to poor yield
oꢀ the fnal product. However, irradiation under microwaves (850 W) in solvent-
ꢀ
ree conditions dramatically accelerated the reaction rate to aꢁord biscoumarin
4
c, 3,3′-(4-chlorophenylmethylene)-bis(4-hydroxy-2H-chromen-2-one), in 95 %
0
yield within 5 min. It is notable that use oꢀ larger quantities oꢀ Ni -Mont catalyst
did not accelerate the rate oꢀ reaction. In addition, carrying out the model reac-
0
tion with lower amounts oꢀ Ni -Mont prolonged the reaction time. So, the condi-
tions mentioned in entry 6 oꢀ Table 2 were selected as the optimum ꢀor complete
conversion oꢀ 4-hydroxycoumarin (2 mmol) and 4-chlorobenzaldehyde to the cor-
responding biscoumarin 4c.
0
The useꢀulness and catalytic activity oꢀ the Ni -Mont system were also high-
0
lighted by comparing the synthesis oꢀ biscoumarin 4c in the presence oꢀ Ni nan-
oparticles alone as well as other modifed montmorillonites under the optimized
reaction conditions. The results oꢀ this investigation are illustrated in Table 3. This
0
table shows that, among the examined catalyst systems, only the Ni -Mont system
eꢃciently catalyzed the reaction within 5 min aꢁording the product in high yield.
3
+
In this context, the Fe -Mont system could also be used ꢀor promotion oꢀ the title
reaction. However, the transꢀormation took a longer reaction time to give the prod-
uct in slightly lower yield (Table 3, entry 5).
The scope and generality oꢀ this synthetic method were ꢀurther studied by syn-
thesis oꢀ structurally diverse biscoumarin compounds through microwave-assisted
Knoevenagel condensation reaction oꢀ 4-hydroxycoumarin with substituted aromatic
0
Table 2 Optimization experiments ꢀor synthesis oꢀ biscoumarin 4c in presence oꢀ Ni -Mont catalyst
0
Entry
Ni -Mont (mg)
Solvent (2 mL)
Condition
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
20
20
20
20
10
20
30
20
EtOH
Reꢂux
Reꢂux
Reꢂux
Reꢂux
Microwave (850 W)
Microwave (850 W)
Microwave (850 W)
Microwave (600 W)
40
120
30
120
10
5
35
30
70
20
83
95
95
80
H O
2
EtOH–H O (1:1)
2
CH CN
3
Solvent-ꢀree
Solvent-ꢀree
Solvent-ꢀree
Solvent-ꢀree
5
20
1
3

S. Rahmani, B. Zeynizadeh
aldehydes under solvent-ꢀree conditions. The results illustrated in Table 4 show the
general trends and versatility oꢀ this synthetic protocol. As shown, all reactions were
carried out within 5‒15 min to aꢁord the products in high to excellent yield.
0
The catalytic ability oꢀ the Ni -Mont system in Knoevenagel reaction oꢀ 1,3-dicar-
bonyl compounds with aromatic aldehydes was ꢀurther explored using the condensa-
tion reaction oꢀ 4-chlorobenzaldehyde (1 mmol) with dimedone (2 mmol) as model
reaction. The results showed that the optimized reaction conditions ꢀor synthesis
oꢀ biscoumarin 4c were also eꢃcient ꢀor synthesis oꢀ bisdimedone 5c. Thereꢀore,
the reaction oꢀ arylaldehydes containing electron-withdrawing or electron-releasing
ꢀ
unctionalities with dimedone under solvent-ꢀree conditions with microwave irradia-
tion (850 W) was investigated; The results are illustrated in Table 5, showing that
all reactions were carried out successꢀully within 5–20 min to aꢁord bisdimedones
5
a–e in high to excellent yield.
Although the exact mechanism oꢀ this synthetic method is not clear, the mecha-
0
nism depicted in Scheme 3 could illustrate the role oꢀ Ni -Mont clay in promoting
the condensation reaction oꢀ 1,3-dicarbonyl compounds with aromatic aldehydes.
0
The mechanism shows that, through polarization oꢀ ꢀormyl group with Ni -Mont
clay, ꢀormation oꢀ intermediate I is ꢀacilitated. Subsequently, by reaction oꢀ
1
,3-dicarbonyl compound with intermediate I, intermediate II is produced. Finally,
Michael addition oꢀ intermediate II with a second molecule oꢀ 1,3-dicarbonyl com-
pound aꢁords the fnal product III.
0
The useꢀulness and potentiality oꢀ the Ni -Mont/microwave system ꢀor one-pot
synthesis oꢀ biscoumarins are highlighted by comparison oꢀ the result obtained ꢀor
biscoumarin 4c with previously reported protocols to accomplish this transꢀorma-
tion in Table 6. This survey reveals that, in terms oꢀ reaction time, reusability oꢀ the
nanocatalyst, and yield oꢀ the desired products, the present work exhibits greater or
comparable eꢃciency to previous systems.
0
Recycling of Ni ‑Mont catalyst
The green and economical ꢀeatures oꢀ the current protocol were ꢀurther examined
0
by studying the reusability oꢀ the Ni -Mont catalyst in synthesis oꢀ biscoumarin
Table 3 Microwave-assisted
Entry
Catalyst (20 mg)
Time (min)
Yield (%)
synthesis oꢀ biscoumarin 4c
0
catalyzed by Ni NPs and
0
1
2
3
4
5
6
7
Ni NPs
5
20
15
20
10
5
70
40
60
40
85
95
70
other modifed clay composite
systems
Mont K10
+
H -Mont
+
Na -Mont
3
+
Fe -Mont
0
Ni -Mont
Mont-SO H
10
3
All reactions carried out under microwave irradiation (850 W)
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
0
Table 4 Microwave-assisted synthesis oꢀ biscoumarins in presence oꢀ Ni -Mont system
Product Ni -Mont (mg) Time (min) Yield (%)a M.p. (°C)
0
Entry Ar-
Found
Reported
1
2
3
4
5
6
7
8
9
1
1
1
C H
4a
20
20
20
20
20
20
20
20
20
20
20
20
5
10
5
10
5
5
5
5
5
95
90
95
85
90
90
82
90
85
90
90
90
213–217 215–216 [76]
265–266
255–257 258–259 [47]
202–204
264–267 264–266 [47]
247–249 249–250 [47]
6
4
2,4-ClC6H3 4b
4-ClC H
2-ClC H
4-BrC H
4-MeOC H
2-MeOC H
4-MeC H
4-OHC H
–
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
6
4
–
6
4
6
4
6
4
226–228
267–269 269–270 [77]
222–225
–
6
4
6
4
–
6
4
0
1
2
4-O NC H
5
15
5
232–234 238–239 [47]
200–202 200–202 [76]
2
6
4
2-O NC H
2
6
4
4-Pyridyl
214–215
–
The condensation reactions were carried out with 1 mmol arylaldehyde and 2 mmol 4-hydroxycoumarin
under microwave irradiation (850 W) under solvent-ꢀree conditions
a
Yields reꢀer to isolated pure products
4
c. Aꢀter completion oꢀ the reaction, the catalyst was separated, washed with
EtOH, then dried under air atmosphere. The reaction vessel was again charged
0
with 4-chlorobenzaldehyde, 4-hydroxycoumarin, and the recycled Ni -Mont clay
to run the condensation reaction ꢀor a second time. The results shows that the
clay catalyst could be reused in seven consecutive cycles without signifcant loss
oꢀ catalytic activity (Fig. 7). In this context, XRD analysis showed that, through
0
the recycling steps oꢀ Ni -Mont catalyst, the clay matrix lost the anchored nickel
content ꢀrom interlamellar spaces (Fig. 8). It is clearly seen that the absorption
signals ꢀor nickel species decreased aꢀter seven recycling steps.
1
3

S. Rahmani, B. Zeynizadeh
Table 5 Microwave-assisted synthesis oꢀ bisdimedones catalyzed by Ni -Mont clay
0
Entry
Ar-
Product
Time (min)
Yield (%)a
M.p. (°C)
1
2
3
4
5
C H
2-ClC H
4-ClC H
3-OH,4-MeOC H
5a
5b
5c
5d
5e
15
8
5
20
10
90
95
95
75
95
195–196
136–137
140–142
170–172
196–197
6
4
6
4
6
4
6
3
4-O NC H
2
6
4
The condensation reactions were carried out with 1 mmol aromatic aldehyde and 2 mmol dimedone
under microwave irradiation (850 W) under solvent-ꢀree conditions
a
Yields reꢀer to isolated pure products
Scheme 3 Proposed mechanism ꢀor Knoevenagel reaction oꢀ arylaldehydes with 1,3-dicarbonyl com-
0
pounds catalyzed by Ni -Mont clay
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
0
Table 6 Comparison oꢀ one-pot synthesis oꢀ biscoumarin 4c with Ni -Mont and other reported catalysts
Entry Catalyst
Time (min) Yield (%) Condition Reusability Reꢀer-
ences
0
a
1
Ni -Mont/microwave
5
95
Solvent-
7
ꢀ
ree
2
3
4
Polyvinyl pyrrolidone-Ni NPs
Sulꢀated titania
15
15
60
92
96
87
r.t.
80 °C
40 °C
4
5
‒
[78]
[79]
[80]
n-Dodecylbenzene sulꢀonic acid
(
DBSA)
5
Silica-bonded N-propyl piperazine
15
92
Reꢂux
5
[81]
sodium n-propionate
6
7
8
9
1
Sodium dodecyl sulꢀate (SDS)
Boiling EtOH
150
750
120
30
95
44
96
95
95
60 °C
Reꢂux
70 °C
Reꢂux
r.t.
5
‒
2
‒
‒
[51]
[82]
[83]
[53]
[48]
SO H-ꢀunctionalized ionic liquids
3
TBAB
Piperidine
0
240
aPresent work
0
Fig. 7 Reusability oꢀ Ni -Mont system in synthesis oꢀ biscoumarin 4c
1
3

S. Rahmani, B. Zeynizadeh
0
Fig. 8 Wide-angle XRD pattern oꢀ Ni -Mont catalyst a beꢀore recycling and b aꢀter seven recycling steps
Conclusions
0
We investigated immobilization oꢀ Ni NPs on acid-activated montmorillonite
0
(
Ni -Mont). The prepared clay composite system was then characterized using
FT-IR spectroscopy, SEM, EDX spectroscopy, XRD analysis, and BET analysis.
0
The catalytic activity oꢀ the Ni -Mont system was studied in microwave-assisted
Knoevenagel condensation reaction oꢀ 4-hydroxycoumarin/dimedone with struc-
turally diverse aromatic aldehydes under solvent-ꢀree conditions. All reactions
were carried out in presence oꢀ 20 mg oꢀ the clay composite, aꢁording the prod-
0
ucts in high to excellent yield. The examined Ni -Mont system was recovered
and reused in seven consecutive cycles without signifcant loss oꢀ catalytic activ-
ity. This protocol exhibits some advantages in terms oꢀ short reaction time, high
0
product yield, and excellent reusability oꢀ the Ni -Mont system, as well as the
advantage oꢀ solvent-ꢀree conditions. It can thus be considered as a prominent
choice ꢀor synthesis oꢀ biscoumarin and bisdimedone materials.
Acknowledgements The authors grateꢀully acknowledged fnancial support oꢀ this work by the research
council oꢀ Urmia University.
1
3

0
Ni NPs anchored on acid-activated montmorillonite…
References
1
2
.
.
X. Xie, Y. Li, Z.Q. Liu, M. Haruta, W. Shen, Nature 458, 746 (2009)
C.N. Ramachandra Rao, G.U. Kulkarni, P.J. Thomas, P.P. Edwards, Chem. Soc. Rev. 29, 27
(
2000)
3
4
5
6
7
8
9
.
.
.
.
.
.
.
E. Formo, E. Lee, D. Campbell, Y. Xia, Nano Lett. 8, 668 (2008)
N. Zheng, G.D. Stucky, J. Am. Chem. Soc. 128, 14278 (2006)
Z. Huang, F. Cui, H. Kang, J. Chen, X. Zhang, C. Xia, Chem. Mater. 20, 5090 (2008)
B. Suresh Kumar, A. Dhakshinamoorthy, K. Pitchumani, Catal. Sci. Technol. 4, 2378 (2014)
S. Bai, X. Shen, G. Zhu, M. Li, H. Xi, K. Chen, ACS Appl. Mater. Interꢀaces 4, 2378 (2012)
F. Davar, Z. Fereshteh, M. Salavati-Niasari, J. Alloys Compd. 476, 797 (2009)
L.K. Yeung, R.M. Crooks, Nano Lett. 1, 14 (2001)
1
1
1
0. F.S. Han, Chem. Soc. Rev. 42, 5270 (2013)
1. L. Wu, J. Ling, Z.Q. Wu, Adv. Synth. Catal. 353, 1452 (2011)
2. Y.L. Zhao, Y. Li, S.M. Li, Y.G. Zhou, F.Y. Sun, L.X. Gao, F.S. Han, Adv. Synth. Catal. 353,
1
543 (2011)
1
1
1
1
1
1
1
2
2
3. F. Alonso, P. Riente, M. Yus, Synlett 9, 1289 (2008)
4. S.Z. Tasker, A.C. Gutierrez, T.F. Jamison, Angew. Chem. Int. Ed. 53, 1858 (2014)
5. W. Zhang, H. Qi, L. Li, X. Wang, J. Chen, K. Peng, Z. Wang, Green Chem. 11, 1194 (2009)
6. C. Zheng, S.S. Stahl, Chem. Commun. 51, 12771 (2015)
7. S.B. Sapkal, K.F. Shelke, B.B. Shingate, M.S. Shingare, Tetrahedron Lett. 50, 1754 (2009)
8. J.M. Khurana, K.Vij Sneha, Synth. Commun. 42, 2606 (2012)
9. M. Saha, B. Das, A. Kumar Pal, C. R. Chim. 16, 1079 (2013)
0. T. Tsukatani, H. Fujihara, Langmuir 21, 12093 (2005)
1. D. Dutta, B.J. Borah, L. Saikia, M.G. Pathak, P. Sengupta, D.K. Dutta, Appl. Clay Sci. 53, 650
(
2011)
2
2
2
2
2
2. J.D. Aiken, R.G. Finke, J. Am. Chem. Soc. 121, 8803 (1999)
3. M. Tamura, H. Fujihara, J. Am. Chem. Soc. 125, 15742 (2003)
4. V.K. Sharma, R.A. Yngard, Y. Lin, Adv. Colloid Interꢀace Sci. 145, 83 (2009)
5. N. Mahata, A.F. Cunha, J.J.M. Orꢀao, J.L. Figueiredo, Appl. Catal. 351, 204 (2008)
6. F. Schröder, D. Esken, M. Cokoja, M.W. van den Berg, O.I. Lebedev, G. Van Tendeloo, B.
Walaszek, G. Buntkowsky, H.H. Limbach, B. Chaudret, R.A. Fischer, J. Am. Chem. Soc. 130,
6
119 (2008)
2
2
7. D.H. Chen, C.H. Hsieh, J. Mater. Chem. 12, 2412 (2002)
8. J.M. Campelo, T.D. Conesa, M.J. Gracia, M.J. Jurado, R. Luque, J.M. Marinas, A.A. Romero,
Green Chem. 10, 853 (2008)
2
9. S. Pande, A. Saha, S. Jana, S. Sarkar, M. Basu, M. Pradhan, A.K. Sinha, S. Saha, A. Pal, T. Pal, Org.
Lett. 10, 5179 (2008)
3
3
3
0. M.L. Kantam, R. Chakravarti, U. Pal, B. Sreedhar, S. Bhargava, Synꢀacts 7, 767 (2008)
1. Z. Király, I. Dékány, Á. Mastalir, M. Bartók, J. Catal. 161, 401 (1996)
2. P. Sharma, S.K. Bhorodwaj, D.K. Dutta, in Journal of Scientiꢀc Conference Proceedings (American
Scientifc Publishers, 2009), p. 40
3
3. A. Gil, S.A. Korili, R. Trujillano, M.A. Vicente, Pillared Clays and Related Catalysts (Springer,
Heidelberg, 2010)
3
3
3
3
3
3
4
4
4. O.S. Ahmed, D.K. Dutta, Langmuir 19, 5540 (2003)
5. P.B. Malla, P. Ravindranathan, S. Komarneni, R. Roy, Nature 351, 555 (1991)
6. R.S. Varma, Tetrahedron 58, 1235 (2002)
7. I. Manolov, C. Maichle-Moessmer, N. Danchev, Eur. J. Med. Chem. 41, 882 (2006)
8. E. Adami, U.E. Marazzi, C. Turba, Arch. Ital. Sci. Farmacol. 9, 61 (1959)
9. Z.H. Chohan, A.U. Shaikh, A. Rauꢀ, C.T. Supuran, J. Enzyme Inhib. Med. Chem. 21, 741 (2006)
0. N. Hamdi, M.C. Puerta, P. Valerga, Eur. J. Med. Chem. 43, 2541 (2008)
1. A.C. Luchini, P. Rodrigues-Orsi, S.H. Cestari, L.N. Seito, A. Witaicenis, C.H. Pellizzon, L.C. Di
Stasi, Biol. Pharm. Bull. 31, 1343 (2008)
4
4
2. D.H. Mahajan, C. Pannecouque, E. De Clercq, K.H. Chikhalia, Arch. Pharm. (Weinheim) 342, 281
(
2009)
3. M.A. Velasco-Velázquez, J. Agramonte-Hevia, D. Barrera, A. Jiménez-Orozco, M.A.J. Garcı ́a -
Mondragón, N. Mendoza-Patiño, A. Landa, J. Mandoki, Cancer Lett. 198, 179 (2003)
1
3

S. Rahmani, B. Zeynizadeh
4
4. D. Završnik, S. Muratović, D. Makuc, J. Plavec, M. Cetina, A. Nagl, E.D. Clercq, J. Balzarini, M.
Mintas, Molecules 16, 6023 (2011)
4
4
4
5. M. Gersch, J. Kreuzer, S.A. Sieber, Nat. Prod. Rep. 29, 659 (2012)
6. K. Petnapapun, W. Chavasiri, P. Sompornpisut, Sci. World J. 2013, 178649 (2013)
7. M. Kidwai, V. Bansal, P. Mothsra, S. Saxena, R.K. Somvanshi, S. Dey, T.P. Singh, J. Mol. Catal. A
Chem. 268, 76 (2007)
4
8. K.H. Khan, S. Iqbal, M.A. Lodhi, G.M. Maharvi, Z. Ullah, M.I. Choudhary, A.U. Rahman, S. Per-
veen, Bioorgan. Med. Chem. 12, 1963 (2004)
4
5
5
5
5
5
9. H. Hagiwara, N. Fujimoto, T. Suzuki, M. Ando, Heterocycles 53, 549 (2000)
0. A. Shamsaddini, E. Sheikhhosseini, Int. J. Org. Chem. 4, 135 (2014)
1. H. Mehrabi, H. Abusaidi, J. Iran. Chem. Soc. 7, 890 (2010)
2. Z.N. Siddiqui, T.N. Mohammed Musthaꢀa, S. Praveen, F. Farooq, Med. Chem. Res. 20, 1438 (2011)
3. J.M. Khurana, S. Kumar, Tetrahedron Lett. 50, 4125 (2009)
4. A. Tzani, A. Douka, A. Papadopoulos, E.A. Pavlatou, E. Voutsas, A. Detsi, ACS Sustain. Chem.
Eng. 1, 1180 (2013)
5
5
5. R. Karimian, F. Piri, A.A. Saꢀari, S.J. Davarpanah, J. Nanostruct. Chem. 3, 52 (2013)
6. A.M. Al-Majid, M. Shahidul Islam, A. Barakat, N.J. Al-Qahtani, S. Yousuꢀ, M. Iqbal Choudhary,
Arab. J. Chem. 10, 185 (2017)
5
5
7. D. Arora, J. Dwivedi, S. Kumar, D. Kishore, Synth. Commun. 48, 115 (2018)
8. A.G. Banerjee, L.P. Kothapalli, P.A. Sharma, A.B. Thomas, R.K. Nanda, S.K. Shrivastava, V.V.
Khatanglekar, Arab. J. Chem. 9, S480 (2016)
5
6
6
6
6
6
6
9. S.A. Hilderbrand, R. Weissleder, Tetrahedron Lett. 48, 4383 (2007)
0. G. Pohlers, J. Scaiano, R. Sinta, Chem. Mater. 9, 3222 (1997)
1. C.G. Knight, T. Stephens, Biochem. J. 258, 683 (1989)
2. S. Hatakeyama, N. Ochi, H. Numata, S. Takano, J. Chem. Soc. Chem. Commun. 17, 1202 (1988)
3. M.A. Mekewi, A.S. Darwish, M.S. Amin, G. Eshaq, H.A. Bourazan, Egypt. J. Petrol. 25, 269 (2016)
4. R. Das, S.S. Nath, R. Bhattacharjee, J. Fluoresc. 21, 1165 (2011)
5. B. Bagchi, S. Kar, S.K. Dey, S. Bhandary, D. Roy, T.K. Mukhopadhyay, S. Das, P. Nandy, Colloid
Surꢀ. B Biointerꢀaces 108, 358 (2013)
6
6
6
6
7
7
7
6. B. Sahin, T. Kaya, Appl. Surꢀ. Sci. 362, 532 (2016)
7. E. Şennik, S. Kerli, Ü. Alver, Z.Z. Öztürk, Sens. Actuators B 216, 49 (2015)
8. S.K. Bhorodwaj, D.K. Dutta, Appl. Catal. A 378, 221 (2010)
9. L. Saikia, D. Dutta, D.K. Dutta, Catal. Commun. 19, 1 (2012)
0. A. Dhakshinamoorthy, K. Pitchumani, Tetrahedron Lett. 49, 1818 (2008)
1. S. Brunauer, L.S. Deming, W.E. Deming, E. Teller, J. Am. Chem. Soc. 62, 1723 (1940)
2. G.B.B. Varadwaj, S. Rana, K. Parida, Chem. Eng. J. 215–216, 849 (2013)
7
3. P.K. Saikia, P.P. Sarmah, B.J. Borah, L. Saikia, K. Saikia, D. Kumar Dutta, Green Chem. 18, 2843 (2016)
7
7
7
7
4. J. Ji, P. Zeng, S. Ji, W. Yang, H. Liu, Y. Li, Catal. Today 158, 305 (2010)
5. S.K. Bhorodwaj, M.G. Pathak, D.K. Dutta, Catal. Lett. 133, 185 (2009)
6. S. Qadir, A. Ahmad Dar, K. Zaman Khan, Synth. Commun. 38, 3490 (2008)
7. N. Tavakoli-Hoseini, M.M. Heravi, F.F. Bamoharram, A. Davoodnia, M. Ghassemzadeh, J. Mol.
Liq. 163, 122 (2011)
7
7
8
8
8
8
8. J.M. Khurana, K. Vij, J. Chem. Sci. 124, 907 (2012)
9. B. Karmakar, A. Nayak, J. Banerji, Tetrahedron Lett. 53, 4343 (2012)
0. B. Pawar, V. Shinde, A. Chaskar, Green Sustain. Chem. 3, 56 (2013)
1. K. Niknam, A. Jamali, Chin. J. Catal. 33, 1840 (2012)
2. I. Manolov, C. Maichle-Moessmer, I. Nicolova, N. Danchev, Arch. Pharm. 339, 319 (2006)
3. W. Li, Y. Wang, Z. Wang, L. Dai, Y. Wang, Catal. Lett. 141, 1651 (2011)
1
3