Silver phosphate supported on metal–organic framework (Ag3PO4@MOF-5) as a novel heterogeneous catalyst for green synthesis of indenoquinolinediones

Article abstract of DOI:10.1002/aoc.5176

A new Ag₃PO₄@MOF-5 catalyst has been synthesized and successfully applied in the green synthesis of a library of indenoquinolinediones via one-pot, multi-component reaction of aldehyde, indanedione and enaminone under solvent-free co

Full text of DOI:10.1002/aoc.5176

Received: 20 April 2019
DOI: 10.1002/aoc.5176
Revised: 23 July 2019
Accepted: 24 July 2019
F U L L P A P E R
Silver phosphate supported on metal–organic framework
(Ag3PO4@MOF‐5) as a novel heterogeneous catalyst for
green synthesis of indenoquinolinediones
Ryhan Abdullah Rather | Zeba N. Siddiqui
Department of Chemistry, Aligarh Muslim
A new Ag3PO4@MOF‐5 catalyst has been synthesized and successfully applied
University, Aligarh 202002, India
in the green synthesis of a library of indenoquinolinediones via one‐pot,
Correspondence
Zeba N. Siddiqui, Department of
multi‐component reaction of aldehyde, indanedione and enaminone under
solvent‐free conditions at room temperature. The catalyst was characterized
Chemistry, Aligarh Muslim University,
Aligarh, 202002, India.
using various spectroscopic techniques and elemental analysis. The catalyst
Email: siddiqui_zeba@yahoo.co.in
can be easily separated and exhibits significant recyclability, with insignificant
Funding information
loss of activity after four consecutive runs. The protocol presented has
advantages like green reaction conditions, high yield of products, no need for
column chromatography and good recyclability.
Council of Science and Technology,
Lucknow, U.P., Grant/Award Number:
CST/SERPD/D‐283 (Dated, 14 May 2015)
KEYWORDS
Ag3PO4, grinding, indenoquinolinediones, MOF‐5, solvent‐free
1 | INTRODUCTION
encapsulated. Furthermore, the synthetic flexibility of
MOFs gives considerable control over the size and envi-
In recent years there have been remarkable developments
in the synthesis of porous hybrid materials.[1,2] One such
interesting category of porous material is metal–organic
frameworks (MOFs).[3] They find budding applications
in gas storage and separation, nonlinear optics,
photoluminescence, biomedicine, magnetic and elec-
tronic materials, etc.[4–9] The striking features of MOFs
are their crystalline nature, high specific surface area
ronment of the pores, permitting selectivity to be tuned
more effectively.[16] MOF pores can serve as hosts for
small guest molecules (active homogeneous catalysts) or
as supports for metal or metal oxide nanoparticles.[17]
These properties distinguish MOFs from other porous
materials such as zeolites and activated carbons, and
hence they have found increasing applications as hetero-
geneous solid catalysts for the synthesis of organic
compounds.[18]
(up to 4000 m2 −1),[10] large pore aperture (98°Å)[11]
g
and low density (0.13 g cm−3).[12] The most substantial
feature of MOFs is their potential inner porosity so that
guest molecules can access the pores which are important
for catalytic purposes.[13] A variety of heterogeneous
MOF‐based catalysts has been reported over the past
few decades obtained by hosting various types of catalytic
sites.[9,14] The active sites, both metal centres and organic
linkers, contribute to catalytic activities.[15] Especially,
organic bridging linkers may be used as frameworks with
which various catalytic complexes, biomolecules and
homogeneous catalysts can be immobilized or
A variety of metal‐based MOFs have been designed
and screened in heterogeneous catalysis for various
organic transformations.[19–22] In this context particular
attention has been paid to silver salts due to high
carbophilicity of silver compounds.[23] Silver‐mediated
reactions have emerged as a frontier area in organic
chemistry. The excellent reactivity and high selectivity
exhibited by silver salts in the activation of various
organic substrates place them among the most prominent
reagents in the organic field. Various silver salts have
been used in a variety organic reactions like Mannich,
Appl Organometal Chem. 2019;e5176.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5176

2 of 14
RATHER AND SIDDIQUI
SCHEME 1 Schematic representation of synthesis of catalyst
cycloaddition, aldol, coupling, Michael addition,
profound chemical and biological significance. Thus the
development of efficient methodologies for the synthesis
of such compounds has attracted considerable
attention.[36]
With the increasing application of MOFs as solid cata-
lysts for the synthesis of nitrogen‐containing heterocycles
and in continuation of our ongoing research,[37] herein
we report the synthesis of MOF‐5‐immobilized Ag3PO4
as a novel solid catalyst. The catalyst efficiently catalysed
multicomponent reactions resulting in the formation of
indenoquinolines in excellent yield under solvent‐free
conditions.
alkynylation,
allylation,
domino
and
tandem
reactions.[24,25] Silver‐catalysed organic transformations
feature high functional group tolerance, excellent regio‐,
diasterio‐ or enantioselectivity and high product turnover
numbers under mild reaction conditions.[24] However,
Ag3PO4 catalysts always suffer from stability concerns
because they can be photochemically decomposed if no
sacrificial reagent is involved, which leads to their limited
practical application. Thus, much research has focused
on ways of increasing Ag3PO4 stability through surface
modification.[26,27]
Indenoquinoline derivatives have received consider-
able attention because of their broad range of applica-
tions in medicinal, bioorganic and industrial chemistry
as well as in the field of synthetic organic chemistry.
Their derivatives have been found to exhibit various bio-
logical activities like 5‐HT‐receptor binding[28] and anti‐
inflammatory activities,[29] and are antitumor agents,[30]
steroid reductase inhibitors,[31] acetylcholinesterase
inhibitors,[32] antimalarials,[33] new potential topo I/II
inhibitors[34] and antituberculosis agents.[35] Because of
the biological activities they exhibit, these compounds
have distinguished themselves as heterocycles of
2 | EXPERIMENTAL
2.1 | Preparation of MOF‐5
MOF‐5 was synthesized according to a reported proce-
dure with slight modification.[38] In a typical procedure,
terephthalic acid (5.065 g, 30.5 mmol) and
trimethylamine (8.5 ml) were dissolved in 400 ml of
dimethylformamide (DMF). Zn (OAc)2⋅2H2O (16.99 g,
FIGURE 1 FT‐IR spectral analysis of (a) of MOF‐5, (b)
Ag3PO4@MOF‐5and (c) recycled Ag3PO4@MOF‐5
FIGURE 2 XRD analysis of (a) MOF‐5, (b) fresh Ag3PO4@MOF‐
5 and (c) recycled Ag3PO4@MOF‐5

RATHER AND SIDDIQUI
3 of 14
FIGURE 3 Solid‐state 13C MAS NMR
spectrum of Ag3PO4@MOF‐5
77.4 mmol) was dissolved in DMF (500 ml) and gradually
added to the organic solution with constant stirring over
15 min, forming a precipitate. After the formation of the
precipitate, the mixture was stirred further for 2.5 h.
The precipitate was filtered and immersed in DMF
(250 ml) overnight. It was then filtered again and
immersed in CHCl3 (350 ml, HPLC grade). The solvent
was exchanged three times over 7 days: after 2 days,
3 days and 7 days. The bulk of the solvent was decanted
and the product evacuated overnight to a pressure of
10 mTorr. The product was activated at 120°C for 6 h.
β‐aminoketone 3a–k (1 mmol) and a catalytic amount
of Ag3PO4@MOF‐5 (200 mg) was ground together in a
mortar with a pestle at room temperature for a specified
period. On completion of reaction (as monitored by
TLC), methanol (20 ml) was added and the reaction
mixture filtered. The catalyst was washed with methanol
several times. The solvent was evaporated under reduced
pressure to afford the product in almost pure form,
which was further purified by crystallization from
suitable solvents (Supporting information).
3 | RESULTS AND DISCUSSION
2.2 | Preparation of Ag3PO4@MOF‐5
Scheme 1 illustrates the synthesis of the catalyst.
The prepared MOF‐5 (2 g) was suspended in 50 ml of water
in a 100 ml round‐bottom flask and stirred for 30 min at
room temperature. To this was added disodium phosphate
(Na2HPO4; 0.1 g) and again stirred for 30 min at room
temperature. Then in a separate 50 ml beaker, AgNO3
(1 g) was dissolved in water (20 ml) and added to the
round‐bottom flask containing the solution of MOF‐5
and Na2HPO4. The reaction mixture was stirred for 6 h at
room temperature. The resultant precipitate was filtered,
washed repeatedly with ethanol and dried at 120°C under
vacuum for 24 h. The amount of silver incorporated into
MOF‐5 was found to be 4.4% using inductively coupled
plasma atomic emission spectroscopy (ICP‐AES).
The catalyst was characterized thoroughly using
Fourier transform infrared (FT‐IR) spectroscopy, powder
X‐ray diffraction (XRD), solid‐state NMR spectroscopy,
scanning electron microscopy (SEM), energy‐dispersive
2.3 | General procedure for synthesis of
indenoquinolinediones (4a–n)
A mixture of aromatic aldehyde 1a–k (1 mmol), active
methylene compound 1,3‐indanedione (2; 1 mmol),
FIGURE 4 Raman spectra of (a) MOF‐5 and (b) Ag3PO4@MOF‐5

4 of 14
RATHER AND SIDDIQUI
FIGURE 5 SEM images of (a, b) MOF‐5, (c) Ag3PO4@MOF‐5 and (d) recycled Ag3PO4@MOF‐5
X‐ray spectrometry (EDX), elemental mapping, transmis-
sion electron microscopy (TEM), Brunauer–Emmett–
Teller (BET) measurements, thermogravimetric analysis
(TGA), differential thermal analysis and ICP‐AES.
FT‐IR spectra (Figure 1) confirmed the presence of all
functional groups present in MOF‐5. Two peaks obtained
at 1601 and 1388 cm−1 (Figure 1a) were due to symmetric
and asymmetric stretching of C─O bonded to Zn.[39] Sev-
eral small peaks occurring in the range 1135 to 952 cm−1
corresponded to in‐plane bending of C─H bond present
in the benzene ring of the BDC linker. Similarly, the
small peaks occurring between 900 and 670 cm−1 were
assigned to out‐of‐plane bending of C─H bond of the
benzene ring of the BDC linker.[40] The peaks occurring
at ca 500 cm−1 were characteristic of Zn─O stretching.
The sharp peak at 550 cm−1 (Figure 1b) in the spectrum
of the Ag3PO4@MOF‐5 catalyst corresponded to bending
vibrations of O═P─O. Two other peaks at 821 and
1027 cm−1 corresponded to symmetric and asymmetric
stretching vibrations of P─O─P bond whereas that at
1386 cm−1 were due to stretching vibrations of P═O
bond.[41] The broad peak at 3342 cm−1 indicated the
minor quantity of adsorbed O─H groups on the MOF‐5
structure.
The XRD pattern of MOF‐5 (Figure 2a) displayed char-
acteristic peaks at 2θ = 6.1°, 9.1°, 17.2° and 27.1°.[42] The
peaks at 2θ = 21.1°, 29.6°, 33.1°, 36.5°, 47.7°, 52.3°, 57.4°,
61.5° and 71.4° were due to Ag3PO4 (Fig. 2b) in addition
to peaks due to MOF‐5.[43]
The solid‐state 13C MAS NMR spectrum of
Ag3PO4@MOF‐5 is depicted in Figure 3. The signals
FIGURE 6 TEM image of Ag3PO4@MOF‐5
FIGURE 7 EDX analysis of Ag3PO4@MOF‐5

RATHER AND SIDDIQUI
5 of 14
FIGURE 8 Elemental mapping of (a) Ag3PO4@MOF‐5, (b) carbon, (c) oxygen, (d) zinc, (e) silver and (f) phosphorus
The peak at 254 cm−1 may be attributed to
[46]
observed in the spectrum corresponded to 28.32, 34.92,
126.34, 134.02 ppm (4C, CH), 138.87 and 144.08 ppm
(2C) and 168.30 and 171.48 ppm (2C, 2C═O) supporting
the structure of MOF‐5 in the catalyst. The signals at
29.32 and 34.92 ppm were due to trapped DMF in
Ag3PO4@MOF‐5.[44]
In the Raman spectra of MOF‐5 and Ag3PO4@MOF‐5
(Figure 4), a noticeable peak at 1640 cm−1 was attributed
to C═O stretching of carboxylate group[45] whereas the
peaks at 1460 and 1164 cm−1 were due to in‐plane vibra-
tions of benzene ring. Another peak at 892 cm−1
appeared as caused by out‐of‐plane deformation modes
of C─H bond. The peaks at 575 and 715 cm−1(Figure 4b)
were attributed to P─O bending stretching vibration of
Ag3PO4.
H─O─H.
SEM images (Figure 5a,b) illustrated the preservation
of characteristic cubic symmetry of MOF‐5. It was evident
from the image that Ag3PO4 had efficiently doped on the
surface of MOF‐5 (Figure 5c). TEM observations also
clearly showed the deposition of Ag3PO4 (black dots) on
the surface of MOF‐5 (Figure 6). Furthermore EDX
confirmed the presence of C, O, P, Ag and Zn elements
in the structure of the material (Figure 7), while the
elemental mapping of individual elements C (Figure 8b),
O (Figure 8c), Zn (Figure 8d), Ag (Figure 8e) and P
(Figure 8f) showed their uniform distribution on the
surfaces of MOF‐5. ICP‐AES analysis of the material
showed that the amount of Ag in the material was
FIGURE 9 BET analysis of Ag3PO4@MOF‐5
FIGURE 10 TGA ofAg3PO4@MOF‐5

6 of 14
RATHER AND SIDDIQUI
SCHEME 2 Effect of catalyst on the
model reaction
TABLE 1 Effect of various catalysts on reaction under solvent‐
3.1 | Optimization of reaction conditions
free conditionsa
To optimize the catalytic reaction conditions for the syn-
thesis of indenoquinoline derivatives, we chose 2, para‐
chlorobenzaldehyde (1a) and β‐aminoketone 3a as model
substrates. Several silver salts were tested as source of sil-
ver to enhance the reaction under solvent‐free conditions
by grinding at room temperature (Scheme 2; Table 1). As
evident from the table, most silver salts afforded moder-
ate yield of product. The best result was obtained in terms
of yield and reaction time with silver phosphate (Table 1,
entry 5) as compared to silver nitrate, silver sulfate, silver
carbonate and silver tungstate (Table 1, entries 1–4). The
reaction with MOF‐5 alone afforded good yield of
indenoquinoline derivative 4a but took a longer time
period (Table 1, entry 6). However, the yield of the prod-
uct was enhanced markedly in a very short period of time
when MOF‐5‐supported silver phosphate was tested as
catalyst for the model reaction (Table 1, entry 7). To
explore the viability of our solvent‐free, grinding protocol
at room temperature for the synthesis of
indenoquinolinediones, various solvents like ethanol,
methanol, water, acetonitrile, chloroform, acetic acid,
acetone and isopropyl alcohol were screened. It was
observed that these solvents could not produce
satisfactory results in terms of yield of product and time
period (Scheme 3; Table 2, entries 1–10). Solvents like
poly(ethylene glycol) (PEG) also did not work (Table 2,
entries 11–13). Finally when the reaction was carried
out by grinding under solvent‐free conditions at room
temperature, product formation occurred within 7 min
with 96% yield (Table 2, entry 14). In order to determine
the optimized amount of the catalyst, the model reaction
was carried out with varying amounts of the catalyst
Entry
Catalyst
Time (h)b
Yield (%)c
1
2
3
4
5
6
7
AgNO3
4
62
60
58
58
68
72
96
Ag2SO4
5
Ag2CO3
6
Ag2WO4
6.5
2
Ag3PO4
MOF‐5
1.5
7 min
Ag3PO4@MOF‐5(200 mg)
aReaction of para‐chlorobenzaldehyde (1a; 1 mmol), indane‐1,3‐dione (2;
1 mmol) and β‐aminoketone (3a; 1 mmol) in presence of different catalysts
(10 mol%) under solvent‐free grinding conditions at room temperature.
bReaction progress monitored by TLC.
cIsolated yield.
4.4 wt% which corresponds to a loading amount of
0.40 mmol g−1 of the catalyst.
The specific surface area of Ag3PO4@MOF‐5 was cal-
culated using the BET method and was found to be
721 m2 g−1 (Figure 9) which was lower than that of
MOF‐5, i.e. 890 m2 g−1 [47]
The appreciable decrease in
.
surface area may be due to deposition of Ag3PO4 on the
surface of MOF‐5.
The thermal stability of Ag3PO4@MOF‐5 was studied
by carrying out TGA experiments. As shown in Figure 10,
two main steps of weight loss were observed. The first
step displayed a weight loss of 12.38%, which was caused
by loss of adsorbed solvent or water molecules before
254.30°C. The second step showed a weight loss of about
1.58 wt% from 254.30 to 471.82°C, resulting from thermal
decomposition of MOF‐5.[48]
SCHEME 3 Effect of solvent on the
model reaction

RATHER AND SIDDIQUI
7 of 14
TABLE 2 Comparative study of various solvents versus the sol-
vent‐free methoda
TABLE 3 Effect of catalyst loading on reactiona
Entry
Catalyst (mg)
Time (min)b
Yield (%)c
Temperature
(°C)
Time
(h)b
Yield
(%)c
1
2
3
4
5
6
60
120
60
45
30
7
45
60
72
82
96
96
Entry
Solvent (5 ml)
100
140
180
200
220
1
Ethanol
Reflux
RT
3
62
55
60
48
50
45
44
76
42
40
38
38
38
96
94
90
2
Ethanol
5
3
Methanol
Methanol
Water
Reflux
RT
4
4
6
7
5
Reflux
Reflux
RT
5
aReaction of para‐chlorobenzaldehyde (1a; 1 mmol), indane‐1,3‐dione (2;
1 mmol) and β‐aminoketone (3a; 1 mmol) in presence of various catalyst
loading under solvent‐free grinding conditions at room temperature.
bReaction progress monitored by TLC.
cIsolated yield.
6
Acetonitrile
Chloroform
Acetic acid
Acetone
6
7
7
8
Reflux
RT
2.5
9
7
10
11
12
13
14
15
16
Isopropyl alcohol
PEG‐200
Reflux
Reflux
Reflux
Reflux
Grinding (RT)
Grinding (RT)
Grinding (RT)
7
indole‐3‐carboxaldehye, 5‐methyl‐2‐thiophenecarboxal-
dehyde
8
and
chloro‐3‐pyrazolecarboxaldehyde
as
PEG‐400
8
substrates, giving products in excellent yields (Table 4).
In order to show the superiority of our protocol, a
comparison with reported methods was done (Table 5).
In comparison to reported procedures, our catalytic sys-
tem was found to be more efficient in terms of time
period and product yield.
PEG‐600
8
Solvent free
Solvent free
Solvent free
7 min
15 min
20 min
aReaction of para‐chlorobenzaldehyde (1a; 1 mmol), indane‐1,3‐dione (2;
1 mmol) and β‐aminoketone (3a; 1 mmol) in presence of Ag3PO4@MOF‐5
(200 mg) under various conditions.
bReaction progress monitored by TLC.
cIsolated yield.
3.3 | Reaction mechanism
The mechanism of the synthesis of indenoquinoline
derivatives has been studied carefully by many chem-
ists.[52] Based on these reports, a mechanism (outlined
in Scheme 6) can be selected as the most probable one.
From a mechanistic point of view, first the aldehyde
group of 1 is activated by the catalyst after which the first
step is the formation of Knoevenagel product A. The
second key intermediate is enamine 3, produced by the
condensation of dimedone with aromatic amine.
Condensation of these two fragments gives the acyclic
Michael adduct intermediate B, which undergoes
intramolecular cyclization with participation of the
amino function and one of the indanedione carbonyl
groups to form C, and subsequent loss of water molecule
leads to the formation of indenoquinolone derivative 4.
The catalyst could be regenerated in the last step and
reused for further catalytic cycles.
(Scheme 4; Table 3). It was found that the formation of
indenoquinolinedione derivative increased linearly with
an increase in the amount of catalyst from 60 to 200 mg.
3.2 | Catalytic reaction
After optimization of reaction conditions, the choice of
substrate for the Ag3PO4@MOF‐5‐catalysed synthesis of
indenoquinolinedione derivatives was examined. The
results showed that the reaction tolerated both aldehydes
and β‐aminoketones with electron‐withdrawing as well
as electron‐releasing groups efficiently (Scheme 5;
Table 4). The reaction also significantly tolerated
heteroaromatic aldehydes like 4‐pyridinecarboxaldehyde,
SCHEME 4 Effect of catalyst loading
on the model reaction

8 of 14
RATHER AND SIDDIQUI
SCHEME 5 General scheme for
formation of indenoquinolinedione
derivatives
TABLE 4 Synthesis of various indenoquinolinedione derivatives
Entry
1a–f
3a–f
Product
Time (min)a
Yield (%)b
TON
TOFc
1
7
96
12
102.85
1a
3a
4a
2
8
94
11.75
88.12
1a
3b
4b
3
7
96
12
102.85
1b
3a
4c
4
9
96
12
80.00
1a
3c
4d
(Continues)

RATHER AND SIDDIQUI
9 of 14
TABLE 4 (Continued)
Entry
1a–f
3a–f
Product
Time (min)a
Yield (%)b
TON
TOFc
5
8
96
12
90.00
78.33
102.85
1a
3d
4e
6
9
94
11.75
1a
3e
4f
7
7
96
12
1a
3f
4 g
8
7
96
12
12.85
1c
3e
4 h
9
7
96
12
102.85
1c
3a
4i
10
7
94
11.75
100.71
1c
3d
4j
(Continues)

10 of 14
RATHER AND SIDDIQUI
TABLE 4 (Continued)
Entry
1a–f
3a–f
Product
Time (min)a
Yield (%)b
TON
TOFc
11
7
92
11.5
98.57
1d
3d
4 k
12
7
96
12
102.85
1d
3a
4 l
13
14
15
8
8
8
96
94
96
12
90.00
88.12
90.00
1e
3d
4 m
11.75
1f
3d
4n
12
1g
3f
4o
16
8
96
12
90.00
1g
(Continues)

RATHER AND SIDDIQUI
11 of 14
TABLE 4 (Continued)
Entry
1a–f
3a–f
Product
Time (min)a
Yield (%)b
TON
TOFc
3a
4p
17
8
94
11.75
88.12
1h
3c
3c
3a
4q
18
12
92
11.50
57.50
1i
4r
19
12
92
11.50
57.50
1j
4 s
20
7
96
12
102.85
1k
3d
4 t
aReaction progress monitored by TLC.
bIsolated yield.
cTOF = TON/reaction time (h); TON = no. of moles of the starting materials being converted per mole of active site of the catalyst.

12 of 14
RATHER AND SIDDIQUI
TABLE 5 Comparison of efficiency of Ag3PO4@MOF‐5 catalyst with that of other reported procedures
Entry
Catalyst
Condition
Solvent
Yield (%)
Time
Ref.
1
2
3
4
Ag3PO4@MOF‐5
Grinding, RT
Reflux
—
96
56
80
75
7 min
Present work
[49]
—
Ethanol
Acetic acid
Ethanol
24 h
[50]
[51]
—
Microwave
Reflux
20 min–4 h
3–4 h
PTSA
SCHEME 6 Plausible mechanism for
synthesis of indenoquinoline derivatives
conditions at room temperature using Ag3PO4@MOF‐5
(200 mg) as a catalyst was chosen as model reaction. After
completion of the reaction, the catalyst was recovered by
extracting the mixture with ethyl acetate followed by
3.4 | Leaching study of catalyst
The leaching of the catalyst before and after five catalytic
cycles was studied using ICP‐AES analysis. The analysis
showed that the Ag concentration before (4.4 wt% Ag)
and after recycling experiments (3.7 wt% Ag) was in fair
agreement (within the experimental error). This indicates
that Ag is tightly bound to the support and very little
leaching of the catalyst occurs upon its reuse. To establish
the heterogeneity of the catalyst, ICPAES analysis of the
filtrate after extracting the product and filtering the cata-
lyst was carried out, and the result revealed the absence
of Ag in the filtrate. These results confirmed that the struc-
ture of the catalyst is stable and Ag is tightly bound to the
support, which in turn facilitates efficient recycling.
3.5 | Catalyst recycling
Catalyst recycling experiments were performed in order
to explore the extent of the recyclability of our catalytic
system. The reaction between para‐chlorobenzaldehyde,
indane‐1,3‐dione and β‐aminoketone under grinding
FIGURE 11 Recycling data for Ag3PO4@MOF‐5 catalyst

RATHER AND SIDDIQUI
13 of 14
[10] O. K. Farha, I. Eryazici, N. C. Jeong, B. G. Hauser, C. E.
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Yazaydın, J. T. Hupp, J. Am. Chem. Soc. 2012, 134, 15016.
filtration. The catalyst was then washed with ethyl
acetate and reused for subsequent cycles. The catalyst
was found to retain its activity for a minimum of four
reaction cycles displaying a high catalytic performance
with over 90% yield of the product (Figure 11).
[11] H. Deng, S. Grunder, K. E. Cordova, C. Valente, H. Furukawa,
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4 | CONCLUSIONS
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In summary, we have easily synthesized a new supported
catalyst, Ag3PO4@MOF‐5, and used it for the green and
sustainable synthesis of indenoquinoline derivatives.
The catalyst was found to be highly efficient and could
be reused for four catalytic cycles. No need for column
chromatography for purification of compounds, solvent‐
free conditions, substrate tolerance and good yield of
products are some of the clear achievements of this
protocol. This newly developed energy‐sustainable
strategy provides a good alternative to reported methods.
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The authors are grateful to the Council of Science and
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SERPD/D‐283 (14 May 2015), for financial assistance in
the form of major research project. The authors also
acknowledge DRS II (UGC, New Delhi), University
Sophisticated Instrument Facility (USIF), AMU, Aligarh
for SEM–EDX and TEM facilities, IIT Mumbai for 13C
MAS NMR analysis, IIT Guwahati for BET analysis and
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