Electrochemical synthesis of three-dimensional flower-like Ni/Co–BTC bimetallic organic framework as heterogeneous catalyst for solvent-free and green synthesis of substituted chromeno[4,3–b]quinolones

Article abstract of DOI:10.1002/jccs.202000314

In this research, a new flower-like Ni_0.77/Co_0.23– benzene–1,3,5–tricarboxylate (BTC) bimetallic organic framework (Ni/Co–BTC BMOF) is synthesized via the cathodic electrosynthesis (CE) method, based on nickel and cobalt metals and BTC linker. The synthesized BMOF is characterized by several methods, including Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray analysis (EDX). The catalytic activity of the resulting Ni/Co is evaluated in a one-pot four-component reaction of dimedone, aromatic aldehyde, 4–hydroxycoumarin, and ammonium acetate for the synthesis of chromeno[4,3–b]quinolone derivatives under solvent-free condition. The Ni/Co–BTC BMOF catalyst showed very good activity in the tested reaction, and a wide scope of starting materials gave the desired products in high isolated yields in the presence of the Ni/Co–BTC BMOF catalyst. The recovery of Ni/Co BMOF was achieved by a centrifuge, and it was reused at least six times without any significant decrease in catalytic activity.

Full text of DOI:10.1002/jccs.202000314

Received: 18 July 2020
Revised: 7 November 2020
Accepted: 13 November 2020
DOI: 10.1002/jccs.202000314
A R T I C L E
Electrochemical synthesis of three-dimensional flower-like
Ni/Co–BTC bimetallic organic framework as heterogeneous
catalyst for solvent-free and green synthesis of substituted
chromeno[4,3–b]quinolones
Mohammad Hosein Sayahi1 | Matineh Ghomi1 | Samir M. Hamad2
|
Mohammad Reza Ganjali3,4 | Mustafa Aghazadeh3 | Mohammad Mahdavi5
Saeed Bahadorikhalili6
|
1Department of Chemistry, Payame Noor University (PNU), Tehran, Iran
2Scientific Research Center, Soran University, Soran, Iraq
3Center of Excellence in Electrochemistry, School of Chemistry, College of Science, University of Tehran, Tehran, Iran
4Biosensor Research Center, Endocrinology and Metabolism Molecular–Cellular Sciences Institute, Tehran University of Medical Sciences,
Tehran, Iran
5Endocrinology and Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences,
Tehran, Iran
6School of Chemistry, College of Science, University of Tehran, Tehran, Iran
Correspondence
Mohammad Hosein Sayahi, Department
Abstract
of Chemistry, Payame Noor University
(PNU), P.O. Box 19395–3697, Tehran,
Iran.
In this research, a new flower-like Ni0.77/Co0.23– benzene–1,3,5–tricarboxylate
(BTC) bimetallic organic framework (Ni/Co–BTC BMOF) is synthesized via
the cathodic electrosynthesis (CE) method, based on nickel and cobalt metals
and BTC linker. The synthesized BMOF is characterized by several methods,
including Fourier transform infrared spectroscopy (FT-IR), powder X-ray dif-
fraction (PXRD), field emission scanning electron microscopy (FE-SEM), and
energy dispersive X-ray analysis (EDX). The catalytic activity of the resulting
Ni/Co is evaluated in a one-pot four-component reaction of dimedone, aro-
matic aldehyde, 4–hydroxycoumarin, and ammonium acetate for the synthesis
of chromeno[4,3–b]quinolone derivatives under solvent-free condition. The
Ni/Co–BTC BMOF catalyst showed very good activity in the tested reaction,
and a wide scope of starting materials gave the desired products in high iso-
lated yields in the presence of the Ni/Co–BTC BMOF catalyst. The recovery of
Ni/Co BMOF was achieved by a centrifuge, and it was reused at least six times
without any significant decrease in catalytic activity.
Email: sayahymh@pnu.ac.ir
Saeed Bahadorikhalili, School of
Chemistry, College of Science, University
of Tehran, Tehran, Iran.
Email: saeed.bahadorikhalili@khayam.ut.
ac.ir
Funding information
University Research Council, Payame
Noor University
K E Y W O R D S
chromeno[4,3–b]quinolone, electrochemical synthesis, flower-like Ni/Co–BTC bimetallic organic
framework, MOF catalyst, multicomponent reaction
J Chin Chem Soc. 2020;1–10.
http://www.jccs.wiley-vch.de
© 2020 The Chemical Society Located in Taipei & Wiley-VCH GmbH
1

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SAYAHI ET AL.
1 | INTRODUCTION
emission scanning electron microscopy (FE-SEM) and
energy dispersive X-ray analysis (EDX), and was used
as a heterogeneous catalyst for the one-pot and
solvent-free synthesis of chromeno[4,3–b]quinolone
via four-component reaction of dimedone, aromatic
aldehyde, 4–hydroxycoumarin, and ammonium acetate
at room temperature. The general route of this pro-
posed research is illustrated in Scheme 1.
Metal–organic frameworks (MOFs) are known as a new
class of nanoporous crystalline solids. They comprise
metal cations/clusters and organic linkers, which gen-
erate crystals with three-dimensional (3D) structures
via self-assembly.[1–3] Up to now, various chemical-
based methods have been adopted to fabricate nano-
sized MOFs, which include sonochemical,[4,5] microwave–
assisted,[6,7] coordination modulation,[8,9] solvothermal,[10,11]
microemulsion,[12,13] hydrothermal, and template
methods[14] and electrochemical synthesis.[15–18] Due to
the easy synthesis process of MOFs and their remarkable
properties, they have attracted interest in many different
fields such as catalysis, sensors, gas storage, drug delivery,
separation, and optics.[19–23]
Recent research has focused on the potential of the
synthesis of bimetallic MOFs (BMOFs) as a new type of
MOFs to enhance framework stability, gas sorption, and
catalytic activity and magnetic and luminescence
properties.[24–28] BMOFs include two different metal ions
as a reactant with a ligand during the synthesis process,
which leads to the pure phase of MOFs.[21] Among differ-
ent reported processes for the synthesis of BMOFs, the
cathodic electrosynthesis (CE) method, based on the
cathodic electrodeposition procedure, has attracted atten-
tion due to the efficient and controllable synthesis of
MOF nanostructures.[29] Through an electrochemical
route, cathodic electrodeposition via base generation onto
the cathode surface is a simple and inexpensive tech-
nique for nanostructured materials.[30–33]
2 | RESULTS AND DISCUSSIONS
2.1 | Morphology, characterization,
and sensing strategy
In order to ensure the synthesis of Ni0.77/Co0.23–BTC
BMOF, several characterization methods were applied.
The morphology and characterization of Ni0.77/Co0.23
–
BTC BMOF was obtained through various techniques
such as XRD, FT-IR, FE-SEM, and EDS.
Figure 1a shows the XRD pattern of Ni0.77/Co0.23
–
BTC BMOF. The main observed diffraction peaks in this
pattern are easily indexed to the crystal planes of
[Ni3(BTC)2]. Furthermore, this pattern is identical to the
pattern reported for Ni/Co–MOF in the literature.[49,50]
In addition, the XRD result is in good agreement with
the single-crystal data of [M3(BTC)2. 12H2O] (M = Ni,
Co) with CCDC number of 1274034. It should be noted
that no impurity diffractions were observed in the XRD
patterns. These observations indicate the pure crystalline
nature of the synthesized BMOF.
As BMOFs have catalytic centers and can be easily
recycled and reused several times, they have been inter-
estingly applied in catalytic processes.[34–39] The catalytic
effects of many BMOFs have been previously reported in
different fields, including multicomponent reactions,[39]
photocatalytic performance,[40] coupling,[41,42] and oxida-
tive degradation reactions.[43] In addition, the synthesis
of 2,4–disubstituted quinoline,[44] cyclohexenones,[45]
functionalized dihydro–2–oxopyrroles,[46] and Suzukie
Miyaura cross-coupling[47] has been made possible by
BMOFs.
The FT-IR spectrum of the sample is shown in
Figure 1b. The bands at 3,440 cm−1 and 3,108 cm−1 are
caused by the stretching vibration of water molecules,
confirming the existence of coordinated H2O molecules
within the structure. The strong absorption bands at
1,648, 1,606, 1,546, 1,435, and 1,373 cm−1 were assigned
to the asymmetric and symmetric stretching modes of the
coordinated (–COO−) group.[51,52] It should be noted that,
after doping of Co ions, the band at 1,648 cm−1 appeared
in Ni0.77/Co0.23–BTC BMOF, indicating that the Co2+
ions are successfully doped in the structure of the BMOF,
and therefore, the surrounding environment of –COO−
group has been changed. The absence of absorption
bands from 1,730 cm−1 to 1,690 cm−1 associated with the
–COOH is indicative of the deprotonation of H3BTC
upon its contact with metal ions.[49,50]
Here, the CE method was applied for the synthesis of
Ni0.77/Co0.23–BTC BMOF from nickel nitrate, cobalt
nitrate, and benzene–1,3,5–tricarboxylate (BTC). In this
method, electrochemical generation of base anions
(OH−) was achieved by the reduction of pro-base species
like water molecules. The OH− anions cause in situ
deprotonation of the ligand and the deposition of nano-
Surface morphology (i.e., FE-SEM images) for the fab-
ricated Ni0.77/Co0.23–BTC BMOF is given in Figure 2a,b.
3D flower-like blocks are observed for the deposited
Ni0.77/Co0.23–BTC BMOF powder (Figure 2a). Each
observed 3D binding block is composed of many leaf-
shaped nanoscale rods (Figure 2b).
sized MOFs onto the cathode.[48] The prepared Ni0.77
/
Co0.23–BTC BMOF was characterized by various tech-
niques, including powder X-ray diffraction (PXRD), Fou-
rier transform infrared spectroscopy (FT-IR), field

SAYAHI ET AL.
3
SCHEME 1 The general route of this proposed research
FIGURE 1 (a) XRD pattern and (b) FT-IR spectrum of Ni0.77/Co0.23–BTC BMOF
The elemental analysis profile is also presented in
Figure 2c. For the fabricated Ni0.77/Co0.23–BTC BMOF sam-
ple, the elements of carbon, oxygen, nickel, and cobalt are
detected in its chemical composition. The EDS result proves
the successful synthesis of a bimetallic structure by the pres-
ence of both nickel and cobalt in the structure of the
BMOF. The weight percentages of C, O, Co, and Ni are
36.04wt%, 43.53wt%, 4.59wt%, and 15.48wt%, respectively.
The carbon and oxygen percentages confirmed the BTC
content of the fabricated BMOF. The nickel and cobalt
percentages also demonstrated the bimetallic composition
of the electrosynthesized Ni0.77/Co0.23–BTC BMOF.
In order to study the surface area and the pore size of
Ni0.77/Co0.23–BTC BMOF, BET analysis was applied. The
Brunauer–Emmett–Teller (BET) and nitrogen adsorption–
desorption results are presented in Table 1. It could be
observed that Ni0.77/Co0.23–BTC has a high surface area of
721.73 m2/g. In addition, the pore width and pore volume
of the synthesized BMOF are 3.11 nm and 0.69 cm3/g,
respectively.

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SAYAHI ET AL.
FIGURE 2 (a) 3D image of flower-like blocks of Ni0.77/Co0.23–BTC BMOF, (b) 3D and leaf-shaped image of each block, and (c) EDAX
analysis of Ni0.77/Co0.23–BTC BMOF
TABLE 1 Surface area and pore size results of Ni0.77/Co0.23
BTC BMOF
–
of dimedone, aromatic aldehyde, 4–hydroxycoumarin, and
ammonium acetate for the synthesis of chromeno[4,3–b]
quinolone derivatives. To find the optimal reaction condi-
tions, the reaction of dimedone, benzaldehyde, 4–
hydroxycoumarin, and ammonium acetate was selected
as a model reaction, and different factors affecting the
reaction performance were optimized. Various amounts
of the catalyst (0–10 mg) and different solvents, such as
MeOH, EtOH, THF, CHCl3, and CH2Cl2, were investi-
gated for the model of the four-component reaction of
dimedone, benzaldehyde, 4–hydroxycoumarin, and
ammonium acetate. The optimization results are
Surface area (m2/g)
721.73
3.11
Pore width (nm)
Pore volume (cm3/g)
0.69
2.2 | Catalytic study
The catalytic activity of the fabricated Ni0.77/Co0.23–BTC
BMOF was evaluated in a one-pot four-component reaction

SAYAHI ET AL.
5
TABLE 2 Influence of solvents
and catalyst concentration on the
synthesis of 4aa
Entry
Catalyst
Catalyst loading (mg)
Solvent
EtOH
Yield (%)
1
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni0.77/Co0.23–BTC BMOF
Ni-BTC
—
10
10
10
10
10
10
10
10
10
10
10
10
10
None
62
58
37
55
70
91
30
49
40
81
77
42
37
2
EtOH
3
MeOH
4
Et2O
5
H2O
6
H2O, EtOH
Solvent free
CHCl3
7
8
9
CH2Cl2
10
11
12
13
14
THF
Solvent free
Solvent free
Solvent free
Solvent free
Co-BTC
Ni(NO3)2
Co(NO3)2
aThe reaction was carried out using 4-chlorobenzaldehyd (1.0 mmol), dimedone (1.0 mmol), 4–
hydroxycoumarin (1.0 mmol), ammonium acetate (1.5 mmol), and 10-mg catalyst at room temperature
under solvent-free condition.
TABLE 3 Synthesis of chromeno[4,3–b] quinolone derivatives catalyzed by Ce0.47/Ni0.53–BTCa
Entry
Substrate
Product
5a
M.p (ꢀC)
Yield (%)
1
2-methoxyphenylbenzaldehyde
3–nitrobenzaldehyde
160–162[53]
137–139[53]
183–184[54]
190–192[53]
179–181[53]
279–281[55]
261–263[53]
301–303[53]
302–303[52]
290–292[52]
237–239
93
88
91
87
90
93
92
85
91
89
90
2
5b
3
4–chlorophenyl
5c
4
3–chlorobenzaldehyde
3–hydroxybenzaldehyde
4–nitrobenzaldehyde
5d
5
5e
6
5f
7
4-methoxyphenylbenzaldehyde
2-methoxyphenylbenzaldehyde
3,4,5-trimethoxyphenyl
2–hydroxybenzaldehyde
Thiophene-2-carbaldehyde
5g
8
5h
5i
9
10
11
5j
5k
aReaction conditions: aldehyde (1.0 mmol), dimedone (1 mmol), 4–hydroxycoumarin (1 mmol), ammonium acetate (1.5 mmol) and 10 mg catalyst, solvent–
free at room temperature.
presented in Table 2. It can be observed that the catalytic
activity was examined for different amounts of catalyst
under solvent-free condition (Entries 1–5). When the
reaction was run without any catalyst, no product was

6
SAYAHI ET AL.
obtained (Entry 1). This observation proves that the pres-
ence of the Ni0.77/Co0.23–BTC BMOF catalyst is essential
for the reaction performance. The yield of the product
was increased by increasing the amount of catalyst.
Hence, the best yield of the product was obtained in the
presence of 10 mg Ni0.77/Co0.23–BTC, and this weight was
selected for the investigation of solvent effect (Entries
6–12). It should be noted that increasing the amount of
the catalyst to values greater than 10 mg did not raise the
yield of the reaction. According to the yield percentages
of the product, which were obtained from various sol-
vents, the best yield was achieved in the solvent-free con-
dition (Entry 4). Performing the reaction in different
temperatures did not affect the yield of the product. In
addition, the efficiency of the Ni0.77/Co0.23–BTC catalyst
was compared to other catalysts. For this purpose, the
reaction was performed in the presence of other catalytic
agents, including Ni-BTC, Co-BTC, Ni(NO3)2, and
Co(NO3)2. The results showed that the Ni0.77/Co0.23–BTC
catalyst is the most efficient catalyst for the reaction per-
formance. Therefore, 10 mg of the catalyst was selected
as the optimal reaction conditions at room temperature
under solvent-free condition.
Considering the efficiency of the above reaction
protocol, a novel four-component and one-pot syn-
thesis was designed with various functionalized
aromatic aldehydes. The results are shown in Table 3.
The compound structures were fully characterized by
1H, 13C NMR, FT-IR, mass spectroscopy, elemental
analysis, and melting point. It can be observed that
several aldehydes were used in the reaction conditions,
and all of them gave the desired products in good iso-
lated yields.
With these outstanding results in hand, the mecha-
nism of the reaction was proposed. The mechanism
involves Knoevenagel condensation, Michael addition,
and intramolecular cyclization.[43] The proposed mech-
anism for the four-component reaction of dimedone,
aromatic aldehyde, 4–hydroxycoumarin, and ammo-
nium acetate in the presence of Ni0.77/Co0.23–BTC is
presented in Scheme 2. According to the suggested
mechanism, the bimetallic centers act as the catalyst of
the reaction. At the beginning of the reaction, the car-
bonyl groups of dimedone and aldehyde could be activated
by the mentioned active sites. A Knoevenagel reaction
takes place between dimedone and aldehyde, and by
removing one water molecule, the 2–benzylidene–5, 5–
dimethylcyclohexane–1, 3–dione intermediate is formed.
4–Hydroxycoumarine is separately reacted with ammonium
acetate and forms 4–aminooumarine. In the next step of the
reaction mechanism, the Ni0.77/Co0.23–BTC-catalyzed
Michael-type addition reaction of 2–benzylidene–5, 5–
dimethylcyclohexane–1,3–dione, and 4–aminooumarine
leads to the formation of 2–((4–imino–2–oxochroman–3–
yl)(phenyl)methyl)–5,5–dimethylcyclohexane–1,3–dione
intermediate. This intermediate then converts to the
desired product through an intramolecular condensation.
2.3 | Reusability of the catalyst
A great advantage of the Ni0.77/Co0.23–BTC catalyst is its
reusability. The reusability of the catalyst was screened by
the separation of the catalyst from the reaction mixture
SCHEME 2 The proposed mechanism for the reaction of four
components in the presence of Ni0.77/Co0.23–BTC
FIGURE 3 Reusability of Ni0.77/Co0.23–BTC BMOF catalyst
after six sequential runs

SAYAHI ET AL.
7
after the reaction was completed and used in the next reac-
tion. This recovery was repeated six times. The results are
presented in Figure 3. It can be observed that the catalyst
was active after six sequential runs, and no decrease in the
catalytic activity of Ni0.77/Co0.23–BTC was observed.
For studying the stability of the catalyst under the reac-
tion conditions, the Ni0.77/Co0.23–BTC catalyst was charac-
terized by the XRD method after the fifth recovery. For this
purpose, the catalyst was used in sequential reactions. After
the fifth cycle, the Ni0.77/Co0.23–BTC catalyst was separated
from the reaction mixture, washed with ethanol, and dried
in a vacuum oven. Then, the crystalline structure of the
Ni0.77/Co0.23–BTC catalyst was studied by the XRD method.
The result is presented in Figure 4. It could be seen that the
structure of the catalyst remained unchanged during the
reaction, and a similar XRD pattern is observed.
3 | EXPERIMENTAL
3.1 | Chemicals and materials
All precursors including Ni(NO3)2Á6H2O, Co(NO3)2Á6H2O,
ethanol (96%), sodium nitrate (NaNO3, 99%), and benzene–
1,3,5–tricarboxylic acid (H3BTC, 95%) were purchased from
Sigma–Aldrich and used as received. All of solutions were
made with Milli-Q water in the experimental sections.
3.2 | Instruments
The size and morphology of the synthesized BMOF were
observed through field-emission scanning electron micro-
scopy (FE-SEM, Model TE–SCAN MIRA3, operating
FIGURE 4 CRD pattern of Ni0.77/Co0.23–BTC BMOF catalyst
after fifth cycle of recovery
SCHEME 3 The general
route of CE of 3D flower-like
Ni0.77/Co0.23–BTC BMOF

8
SAYAHI ET AL.
voltage 30 kV), and the elemental data were collected
using energy-dispersive spectroscopy (EDS) on this system.
The crystal phase and structure of the sample were deter-
mined by XRD, using a model Phillips PW–1800 diffrac-
tometer with Cu Kα radiation (λ = 1.5406 Å). The FT-IR
spectrum of the sample was acquired using the Bruker
Vector 22 IR instrument.
3.5 | Spectral data for the selected
products
7–(3–metoxyphenyl)–10,10–dimethyl–7,10,11,12–
tetrahydro–6H–chromeno[4,3–b]quinoline–6,8(9H)–
dione
Solid white, M.p: 271–273ꢀC; 1H–NMR (250 MHz,
DMSO–d6): δ = 9.69 (s, NH), 8.27 (1H, d, Ar–H,
J = 7.5 Hz), 7.61 (1H, t, Ar–H, J = 7.5 Hz), 7.39 (2H, q,
Ar–H, J = 11.5 Hz), 7.10 (1H, t, Ar–H, J = 7.75 Hz), 6.68
(2H, d, Ar–H, J = 8.75 Hz), 6.67 (1H, d, Ar–H, J = 7 Hz),
3.64 (3H, s, CH3), 4.91 (1H, s, CH), 2.63 (2H, s, CH2), 2.26
(1H, d, CH2, J = 32.0 Hz), 2.05 (1H, d, CH2, J = 32.0 Hz),
1.19 (3H, s, CH3), 0.85 (3H, s, CH3) ppm; 13C NMR
(60 MHz, DMSO–d6): δ = 196.1, 161.7, 160.4, 153.5,
151.2, 148.6, 143.6, 133.4, 130.5, 125.5, 124.4, 121.4, 118.3,
115.5, 114.5, 112.4, 112.1, 103.1, 56.3, 51.6, 41.9, 41.6,
41.3, 40.9, 40.6, 40.3, 39.9, 35.7, 33.6, 30.5, 28.0 ppm; IR
(KBr) cm−1:3,220.92, 2,945.79, 1,666.13, 1,656.08,
1,644.64, 1,605.93, 1,581.90, 1,571.65, 1,508.17, 1,473.67,
1,305.49, 1,305.49, 1,261.02, 1,238.73, 1,196.02, 1,158.72,
1,045.81, 766.42, 752.20, 691.92; Mass (Mz+): 401; Anal.
Calcd for C25H23NO4: C, 74.80; H, 5.77; N, 3.49,
Found: C, 74.76; H, 5.79; N, 3.54.
3.3 | Electrochemical preparation of
flower-like Ni0.77/Co0.23–BTC BMOF
The CE method was implemented between two elec-
trodes in constant current conditions. To set up the elec-
trochemical cell, a cell composed of a graphite sheet
(as anode, size = 7 cm × 7 cm) and stainless steel sheet
(as cathode, size = 5 cm × 5 cm) was used. To obtain
deposit on both sides of the cathode electrode, the steel
cathode was centered between two graphite anodes. The
electrolyte bath was prepared by dissolving 150 mg of
nickel nitrate, 50 mg of cobalt nitrate, 100 mg of BTC,
and 50 mg NaNO3 in 200 ml of ethanol. For electrode-
position of Ni/Co–BTC, a cathodic current density of
10 mA/cm2 was applied for 30 min to the above-
mentioned electrochemical system. It was observed that
a violaceous deposit was formed on both sides of stain-
less steel cathode at the end of the deposition time. After
this step, the steel cathode was removed from the elec-
trochemical bath and washed several times with etha-
nol. Then, the deposit was separated from the cathode
surface and dried at 70ꢀC for 2 hr. The obtained powder
7–(3–nitrophenyl)–10,10–dimethyl–7,10,11,12–
tetrahydro–6H–chromeno[4,3–b]quinoline–6,8(9H)–
dione
1
Solid white, M.p: 289–296ꢀC. H–NMR (250 MHz, DMSO–
d6): δ = 9.80 (s, NH), 8.29 (1H, d, Ar–H, J = 6.5 Hz), 8.02
(1H, s, Ar–H), 7.96 (2H, d, Ar–H, J = 7.25 Hz), 7.677–7.324
(5H, m, Ar–H), 5.02 (1H, s, CH), 2.66 (2H, s, CH2), 2.26
(1H, d, CH2, J = 34 Hz), 20.5 (1H, d, CH2, J = 34 Hz), 1.16
(3H, s, CH3), 0.97 (3H, s, CH3) ppm; 13C NMR (60 MHz,
DMSO–d6): δ = 161.7, 153.6, 151.8, 149.2, 149.0, 144.0,
136.1, 133.7, 131.0, 125.6, 124.6, 123.8, 122.8, 118.4, 114.3,
111.5, 102.4, 51.4, 42.0, 41.6, 41.3, 41.0, 40.6, 40.3, 40.0, 36.5,
33.7, 30.5, 27.9 ppm; IR (KBr) cm−1: 3,222.34, 3,090.63,
2,969.76, 2,941.76, 1,654.97, 1,605.42, 1,570.86, 1,524.30,
1,507.96, 1,470.96, 1,365.56, 1,344.38, 1,312.96, 1,299.38,
1,236.01, 1,191.27, 1,161.68, 1,150.36, 1,124.30, 1,084.31,
1,044.74, 1,026.52, 6,885.01, 897.00, 863.42, 809.57, 784.81,
761.62, 747.18, 737.84, 720.09, 710.81, 667.28, 652.60, 626.88,
616.51, 511.37, 496.89; Mass (Mz+): 416; Anal. Calcd for
C24H20N2O5: C, 69.22; H, 6.73; N, 6.73, Found: C, 69.27; H,
6.69; N, 6.71.
was the final product and named flower-like Ni0.77
/
Co0.23–BTC BMOF. The general route of CE of the 3D
flower-like Ni0.77/Co0.23–BTC BMOF is illustrated in
Scheme 3.
3.4 | General procedure for the synthesis
of compounds of 5a–5j
A mixture of dimedone (1 mmol), aromatic aldehyde
(1 mmol), hydroxycoumarin (1 mmol), and ammonium
acetate (1.5 mmol) was mixed together in a round-bottomed
flask, and the flower-like Ni0.77/Co0.23–BTC BMOF (10 mg)
was added. The mixture was stirred under solvent-free con-
dition at room temperature for 45 min. The reaction evolu-
tion was controlled by the TLC (hexane: ethyl acetate, 4:1).
Then, hot ethanol was added to the reaction mixture and
stirred at room temperature for 15 min. The catalyst was
centrifuged and separated. The solution was placed in a
cooling bath until a solid white product was obtained. Then,
it was recrystallized with ethanol.
7–(4–chlorophenyl)–10,10–dimethyl–7,10,11,12–
tetrahydro–6H–chromeno[4,3–b]quinoline–6,8(9H)–
dione
1
Solid white, M.p: 256–259ꢀC. H–NMR (250 MHz, DMSO–
d6): δ = 9.70 (s, NH), 8.27 (1H, d, Ar–H, J = 6.5 Hz), 7.59

SAYAHI ET AL.
9
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(1H, d, Ar–H, J = 6.5 Hz), 7.407–7.224 (6H, m, Ar–H), 4.90
(1H, s, CH), 2.62 (2H, s, CH2), 2.24 (1H, d, CH2, J = 34 Hz),
20.4 (1H, d, CH2, J = 34 Hz), 1.03 (3H, s, CH3)–0.89 (3H,
3, CH3) ppm. 13C NMR (60 MHz, DMSO–d6): δ = 196.2,
161.7, 153.5, 151.3, 146.2, 143.7, 133.5, 132.2, 131.1, 129.4,
125.5, 124.5, 118.3, 114.4, 111.9, 102.8, 51.5, 41.9, 41.6, 41.2,
40.9, 40.6, 40.2, 39.9, 35.7, 33.6, 30.5, 28.0 ppm; IR (KBr)
cm−1:3,308.66, 2,959.95, 2,933.95, 1,682.68, 1,670.76, 1,645.25,
1,605.98, 1,568.74, 1,505.03, 1,464.94, 1,449.09, 1,425.59,
1,362.49, 1,362.49, 1,312.63, 1,235.63, 1,235.95, 1,194.67,
1,159.55, 1,147.33, 1,089.62, 1,041.56, 1,014.03, 874.87, 851.79,
830.13, 758.58, 733.91, 712.93, 650.59, 585.58, 571.41, 539.79,
461.42, 432.13, 417.00; Anal. Calcd for C24H20ClNO3: C,
71.02; H, 4.97; N, 3.45, Found: C, 71.06; H, 4.99; N, 3.41.
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4 | CONCLUSIONS
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A simple, convenient, and safe synthetic methodology has
been introduced for the synthesis of chromeno[4,3–b]quino-
lone derivatives at room temperature under solvent-free
conditions. The method is based on the use of the Ni0.77
/
Co0.23–BTC BMOF as a heterogeneous catalyst for the one-
pot multicomponent reaction of dimedone, aromatic alde-
hyde, 4–hydroxycoumarin, and ammonium acetate. The
presented 3D flower-like Ni0.77/Co0.23–BTC BMOF was syn-
thesized via the CE method, which provides many advan-
tages such as milder synthesis conditions, shorter reaction
times, and the ability to control the rate of synthesis. The
catalytic activity of the prepared BMOF in the synthesis of
chromeno[4,3–b]quinolone derivatives was very good, and
the starting materials gave the desired products in high iso-
lated yields. The simplicity of the BMOF synthesis and mild
reaction conditions will also make this synthetic protocol
marvelous and beneficial at an industrial scale. The catalyst
showed very good reusability in the reaction conditions,
and no loss in the activity of the catalyst was observed after
six sequential reactions.
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ACKNOWLEDGMENTS
The authors thank the University Research Council for
financial support of this work.
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How to cite this article: Sayahi MH, Ghomi M,
Hamad SM, et al. Electrochemical synthesis of
three-dimensional flower-like Ni/Co–BTC
bimetallic organic framework as heterogeneous
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