A Zn based metal organic framework as a heterogeneous catalyst for C-C bond formation reactions

Article abstract of DOI:10.1039/c8nj05953e

Herein, we report the synthesis and application of a Zn-Bp-BTC MOF (Bp-4,4′-bipyridine; BTC-1,3,5-benzene tricarboxylic acid; MOF-metal organic framework) as a heterogeneous catalyst for mediating organic reactions. Initially, conditions were optimized for the Knoevenagel condensation reaction using Zn-Bp-BTC as a heterogeneous catalyst by varying the solvent, temperature and catalyst loading. Although the reaction proceeded at room temperature using methanol as the solvent, 60 °C offered the best yield in a shorter duration. Under optimized reaction conditions, a wide range of α,β-unsaturated dicyano compounds were prepared from the corresponding carbonyl precursor and malononitrile, the active methylene counterpart. Systematic investigation was also carried out to assess the role of the ligand and metal salt in the Knoevenagel condensation reaction. It was found that the Zn-Bp-BTC MOF catalyzed the reaction efficiently in comparison to its analogue Zn-BTC MOF and precursor Zn(NO₃)₂·6H₂O. Finally, catalytic recycling and stability studies showed that the catalyst is able to mediate the reaction for up to five consecutive cycles without undergoing any significant chemical or morphological changes. Further, the catalyst was tested for its efficacy in a multi-component reaction (MCR). A MCR with the Zn-Bp-BTC MOF as the catalyst afforded good yields and there was no reaction in the absence of the catalyst. Similarly, the catalyst was tested for its efficiency in benzimidazole synthesis.

Full text of DOI:10.1039/c8nj05953e

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Zn based Metal Organic Framework as a Heterogeneous Catalyst for C-C
Bond Formation Reactions
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Kanagaraj Madasamy,a,b Shanmugasundaram Kumaraguru,a Velayutham Sankar,c
Subramaniyan Mannathan,c,d* Murugavel Kathiresana,b*
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a
Mr.
M.
Kanagaraj,
Mr.
S.
Kumaraguru
and
Dr.
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Kathiresan
Electro Organic Division, CSIR - Central Electrochemical Research Institute, Karaikudi-
630003, Tamilnadu, India.
E-mail: kathiresan@cecri.res.in
b
Mr. M. Kanagaraj, and Dr. M. Kathiresan
AcSIR - Academy of Scientific & Innovative Research
Anusandhan Bhavan, Rasi Marg
New Delhi 110001, India.
c
Mr. V. Sankar and Dr. S. Mannathan
SRM Research Institute, SRM Institute of Science and Technology, Kattankulathur, Chennai
603203, India
d
Dr. S. Mannathan
Department of Chemistry, SRM University-AP, Amaravati 522502, Andhra Pradesh, India
Email: mannathan.s@srmap.edu.in

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Abstract
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Herein, we report the synthesis and application of Zn-Bp-BTC MOF (Bp – 4,4ʹ-bipyridine;
BTC – 1,3,5-benzene tricarboxylic acid; MOF – metal organic framework) as a
heterogeneous catalyst for mediating organic reactions. Initially, conditions were optimized
for Knoevenagel condensation reaction using Zn-Bp-BTC as a heterogeneous catalyst by
varying the solvent, temperature and catalyst loading. Although the reaction proceeded at
room temperature using methanol as the solvent, 60 °C offered the best yield in shorter
duration. Under optimized reaction conditions, a wide range of α,β-unsaturated dicyano
compounds were prepared from the corresponding carbonyl precursor and malononitrile, the
active methylene counterpart. Systematic investigation was also carried out to assess the role
of ligand and metal salt in Knoevenagel condensation reaction. It was found that Zn-Bp-BTC
MOF catalyzed the reaction efficiently in comparison to its analogue Zn-BTC MOF and
precursor Zn(NO3)2•6H2O. Finally, catalytic recycling and stability studies showed that the
catalyst is able to mediate the reaction up to five consecutive cycles without undergoing any
significant chemical or morphological changes. Further the catalyst was tested for its efficacy
in multi-component reaction (MCR). MCR with Zn-Bp-BTC MOF as the catalyst afforded
good yields and there was no reaction in the absence of catalyst. Similarly, the catalyst was
tested for its efficiency in benzimidazole synthesis.
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Introduction
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Metal–organic frameworks (MOFs), a family of porous organic-inorganic polymer has
fascinating applications in the areas of catalysis,1 sensors,2 gas storage and separation,3
energy storage and conversion,4, 5 magnetic and ion-conducting properties,6 etc. These
extended porous assemblies are generally composed of metal ions that are inter-connected by
organic linkers.7 Reticular synthetic strategies allow precise tuning in their structural design
and control by proper selection of metal ions and ligands. Post-synthetic modification
strategy allows lateral functionalization of pores and control over their architecture.8 Unique
chemical environment inside the pores provides the necessary binding force for the
adsorption/trapping of guest molecules and the multi-valency of the metal ion plays a key
role in catalyzing chemical reactions. However, their applications in catalysis are restricted to
low temperatures owing to their low chemical and thermal stability at high temperatures,
when compared with inorganic micro and mesoporous materials.9 Despite these facts, MOFs
were successfully employed as heterogeneous catalysts for various organic reactions. The
catalytic activity of MOF is attributed to the reversible interactions between the metal ion
centre and the ligands with the substrate molecules. Moreover, its porous nature and larger
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surface area made them a suitable catalyst for various reactions including Michael addition,10
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cyanosilylation,11 Knoevenagel condensation,12,
aldol condensation,14 C-C and C-
heteroatom coupling,15 transesterification,1 Friedel-Crafts alkylation,7 and others.16, 17 Despite
these developments, the organic transformation reactions using bifunctional (acid & base
active sites present in the architectures) heterogeneous catalyst is scanty.18
In recent years, MOFs with active acid and base sites are shown to be more effective catalyst
for many organic conversions than either of individual base or acid based catalysts.1, 17, 19 In
2002, Kim and coworkers reported NH2-MIL-101(Al) MOF as an effective bifunctional
catalyst for the Meinwald rearrangement–Knoevenagel condensation reaction with significant
substrate selectivity.20 In the reaction, it was demonstrated that the use of both acidic and
basic functional groups was essential to catalyze the tandem reaction effectively. However, in
the absence of basic functional group, the reaction stopped at Meinwald rearrangement. In
addition to this report, He et al. also described the application of bifunctional MOF with open
metal sites and lewis basic sites for selective gas adsorption and heterogeneous cascade
catalysis.21

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Previously, Qin et al. reported that the synthesis of bifunctional Zn metal based MOF
[(Zn(HBTC)(4,4ʹ-bpy) [(where HBTC = 1,2,4-tricarboxylic acid, 4,4ʹ- bipyridine)].22
Different structural arrangements of this material were studied using crystallography. Later,
Li et al. described the synthesis of related MOFs using similar linkers (4,4ʹ-bpy & BTC)
coordinated to transition metals such as Ni and Co with distinct surface areas that are useful
for hydrogen storage.23 Very recently, Kim et al. reported the solvothermal and microwave
synthesis of Zn(HBTC)(4,4ʹ-bpy)•3DMF MOF. In the reaction, the catalytic efficiency of the
Zn MOF was also tested by performing a cycloaddition reaction of CO2 and epoxides.24 The
authors observed that the bifunctional catalyst (possessing acidic and basic sites) obtained
from both of these methods depict identical catalytic properties towards cycloaddition of
CO2.24 Similarly Zn based MOF networks containing various ligands were synthesized and
their applications towards Knoevenagel condensation, dye degradation, etc. were investigated
in detail.13, 25, 26 Though the synthesis of Zn-Bp-BTC is known, its catalytic activity towards
different organic transformation reactions such as Knoevenagel condensation or
benzimidazole synthesis or multicomponent reactions (2-amino 4H-chromene synthesis) are
not reported till date. Herein, we report the synthesis and application of bifunctional Zn-Bp-
BTC MOF as an effective heterogeneous catalyst for Knoevenagel condensation reaction,
benzimidazole synthesis and multi-component reactions.
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Experimental Section
Materials and Methods
All reagents are of analytical grade (Sigma Aldrich and Alfa Aesar) and were used without
any further purification. The X-ray diffraction (XRD) patterns were measured in room
temperature using a BRUKER D8 ADVANCE instrument. The powder diffraction covered
the angle ranges from 10-80o, with a step angle of 0.02o. The morphological structures of the
prepared fabrics were captured using Scanning Electron Microscope (SEM) of TESCAN,
VEGA 3 with Bruker Detecter, Zeck Republic. Thermo gravimetric analysis (TGA) was used
to study the thermal degradation of synthesized materials was determined by using a TGA /
SDT Q600, TA instruments, USA at a scanning rate of 5o C/min, from room temperature to
o
600 C under nitrogen atmosphere. FT-IR analysis was carried out in BRUKER - TENSOR
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27 (Optik GmbH) using RT DLaTGS (Varian) Detector. NMR experiments (1H NMR, C
NMR) were carried out on a Bruker 400 MHz spectrometer at 25° C using CDCl3 as a solvent
and internal reference.
Synthesis of Zn-Bp-BTC MOF

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Reported procedure was followed for this synthesis.23 A mixture of 1,3,5-benzene
tricarboxylic acid (1.05 g, 5.0 mmol), 4,4′-bipyridine (0.78 g, 5.0 mmol) and Zn(NO3)2·6H2O
(1.48 g, 5.0 mmol) were added in 100 mL of DMF (N,N′-dimethylformamide) in a glass
sealed flask. This reaction mixture was heated at 120 °C for 4 h. After completion of the
reaction, the reaction mixture was cooled and filtered. The obtained white color solid was
then washed with DMF and ethanol to remove unreacted starting materials. Finally the pure
white precipitate was dried at 60 °C for 12 h to afford the Zn-Bp-BTC MOF (1.3 g).
General procedure for Knoevenagel condensation
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A mixture of 1-naphthaldehyde (0.06 g, 0.38 mmol) and malononitrile (0.025 g, 0.38 mmol)
were dissolved in 10 ml of MeOH. The reaction mixture was stirred at 60°C for 3 h. The
reaction was carried out using Zn-Bp-BTC MOF as a heterogeneous catalyst. The progress of
the reaction was monitored by TLC (Thin layer chromatography) using EtOAc:PET mixture
as eluent (20%). After completion of the reaction, solvent was evaporated under reduced
pressure. The residue was re-dissolved in EtOAC to remove the undissolved catalyst by
filtration. The crude filtrate was then concentrated and purified by flash column
chromatography using EtOAc:PETmixture (20%) as eluent.
Results and Discussion
Synthesis and Characterization of Heterogeneous catalyst
Zn-Bp-BTC MOF was synthesized by reacting Zn(NO3)2•6H2O, 1,3,5-benzene tricarboxylic
acid and 4,4ʹ-bipyridine in DMF following a reported procedure with slight modifications
(Scheme 1)23 and the details are given in the supporting information. The MOF catalyst was
then characterized for its chemical composition, morphology, etc.
Scheme 1. Synthesis of Zn-Bp-BTC MOF: Reaction conditions; DMF, 120 °C, 4 h.

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Figure 1. FT-IR spectrum of Zn-Bp-BTC MOF
Figure 1 shows the FT-IR spectrum of Zn-Bp-BTC MOF (black line), Zn-BTC MOF (blue
line) and their precursors (red (BTC) and grey line (4,4'-bpy)). Zn-Bp-BTC showed an
absorption peak at 1604 cm−1 corresponding to the C=C stretching vibrations of the benzene
ring. The strong peak at 1708 cm−1 is attributed to the stretching frequency of carbonyl group
(C=O) and the peak at 824 cm−1 is ascribed to the out of plane bending vibrations of C−H
(aromatic ring). C-H stretching and asymmetric bending bands appeared at 3080 cm-1 and
1430 cm-1 respectively. C-O-C stretching vibration band appeared at 1109 cm-1. The
appropriate peak shift of carbonyl group present in 1,3,5-benzene tricarboxylic acid (BTC)
from 1708 to 1639 cm-1 confirms that the Zn metal is coordinated with –COO– moiety. The
presence of strong O–H absorption peak around 3430 cm-1 indicates that some of the carboxyl
groups (possibly terminal carboxyl and some of the inner carboxyl groups) are not
coordinated to the metal center. Besides, the stretching frequency of C=N group in 4,4ʹ-
bipyridine ligand was observed at 1597 cm-1, upon coordination to metal ion, it appeared at
1569 cm-1 (denoted in blue line) confirming the coordination to metal centre. From these, it
can be concluded that both the building blocks such as BTC and 4,4ʹ-bipyridine were
coordinated to Zn metal center as evident from their characteristic peaks.

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Figure 2. Simulated22 and XRD pattern of the as synthesized Zn-Bp-BTC MOF catalyst.
Powder X-ray diffraction (XRD) pattern of Zn-Bp-BTC MOF was performed at room
temperature and is shown in Figure 2. The XRD pattern of the synthesized Zn-Bp-BTC MOF
matches with the simulated XRD pattern. The XRD pattern displays characteristic peaks
below and above 20° (2θ value).27, 28 The XRD pattern of Zn-BTC MOF was compared with
the 2θ values of Zn-BTC, and it reveals that the 2θ values are much closer in both the cases
and in addition, characteristic peaks for 4,4ʹ-bipyridine pattern is also observed in the case of
Zn-Bp-BTC.23 These results clearly indicate the successful formation of Zn-Bp-BTC MOF.23

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Further based on the available r
e
e
ports,23 BTC ligand has the tendency to act b
o
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th as a mono
4
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(one negative charge) and bidenntate (two negative charge) ligand. 4,4ʹ-bipyri ine acts as a
d
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neutral ligand with zero charge The amorphous nature of Zn-Bp-BTC MOF oobtained from
.
.
this method could be attributed tto the decreased coordination ability of Zn2+
which is smaller when comparedd to other transition metals in the same row.23
wwith the ligand
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Figure 3. SEM imagges of as synthesized Zn-Bp-BTC MOF (a and bb).
The SEM images of Zn-Bp-BT
EDX (Energy Dispersive X-ray) is given in the ESI. A closer look at the SEM image shows
rod like morphology. EDX specctrometric studies revealed the presence of Z metal which
offers further support for the co position of Zn-Bp-BTC MOF.
CC MOF are shown in Figure 3a and b and the ccorresponding
nn
m
Catalytic properties of Zn-Bp-BBTC MOF
After synthesizing the Zn-Bp-BTTC MOF, we next studied the catalytic activity of the catalyst
using the following reactions:
Scheme 2. Zn-Bp-BTC catalyzed Knoevenagel condensation reactioon.
Knoevenagel condensation reacction
Knoevenagel reaction is a distin
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t class of organic reaction which is frequently employed for
reacted with
the synthesis of α,β-unsaturated ccarbonyl compounds, where a carbonyl group i
ss

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an active methylene compound to afford the corresponding α,β-unsaturated carbonyl
compounds under suitable reaction conditions.29 This C-C bond forming reaction is
frequently employed as a benchmark reaction to examine the activity of any newly
synthesized homogeneous/heterogeneous catalysts.12, 30-34 Soluble base catalysts in excess
quantity under homogeneous conditions usually catalyze the reaction. On contrary, Lewis
acid catalysts such as ZnCl2, AlCl3, KF-Al2O3 and K10 montmorillonite were also used as
catalysts under heterogeneous conditions.35, 36 Among these two methods, heterogeneous
catalysis is preferred over homogeneous catalysis owing to its simplicity in product isolation.
Wang et al reported the oxidation of aromatic alcohol followed by the condensation of
aromatic aldehyde with malononitrile using bifunctional Au@Cu-MOF heterogeneous
catalyst.37 Although excellent performance of the catalyst is reported, incorporation of
expensive metal like Au into MOF drops its importance. Yang et al reported amine
functionalized Zr based MOF, possessing acidic (Zr) and basic (-NH2) sites depicting
excellent catalytic behavior towards Knoevenagel condensation reaction.19 Apart from these,
reports are available on the MOF, and post-modified MOF catalyzed Knoevenagel
condensation reaction with varying substrates, yield and selectivity.12, 30-32, 34, 38-40
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Thus, the catalytic property of Zn-Bp-BTC MOF was studied using Knoevenagel
condensation as a benchmark reaction as shown in Scheme 2.
Table 1. Role of solvent in Zn-Bp-BTC catalyzed Knoevenagel condensation reaction.a,b
S.No
Solvent
Temperature,
Duration,
Yield,
%
°C
80c
40
h
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3
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THF
DCM
CHCl3
EtOH
DMF
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87
80
99
60
80d
80e
60
MeOH
aZn-Bp-BTC (0.06 mmol), 1-naphthaldehyde (0.64 mmol), malononitrile (0.70 mmol).
b isolated yield.
c reaction carried out at 60 °C also showed no conversion.
d reaction carried out at 60 °C took 10 h to attain the same yield.
e reaction carried out at 60 °C took 12 h to attain the same yield.

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Initial studies were carried out with 1-naphthaldehyde and malononitrile as model
compounds; here malononitrile was used as an active methylene compound and 1-
naphthaldehyde as its carbonyl partner. Control experiments revealed that no condensation
product 1 was formed in the absence of the catalyst. Next, we tested the reaction with various
solvents such as THF, dichloromethane, chloroform, ethanol, DMF and methanol. Among
them, reaction with methanol gave excellent yield of 99% at 60 °C in 3 h (Table 1, entry 6). It
is noteworthy that the reaction did not proceed in THF (Table 1, entry 1). Other solvents such
as ethanol and DMF afforded good yield of about 87 and 80 % respectively (entry 4 and 5),
whereas dichloromethane (DCM) and chloroform (CHCl3) gave moderate yield of 53 and 58
% respectively (entry 2 and 3).
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Figure 4. Effect of temperature on product conversiona,b
a
Zn-Bp-BTC (0.06 mmol), 1-naphthaldehyde (0.64 mmol), malononitrile (0.70 mmol) in
MeOH from RT – 80 °C.
b isolated yield.
Subsequently with the same substrates (1-naphthaldehyde and malononitrile) in MeOH, the
temperature was varied from RT to 80 °C to assess the effect of temperature on product yield
under heterogeneous conditions. When the reaction was carried out at RT, 99% yield was

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obtained at 6 h, whereas when the temperature was increased to 40°C, the same yield was
obtained in 5 h. Then the reaction was carried out at 60 °C, 99% yield was obtained in 3 h.
Further increase in temperature to 80 °C had no effect in the reaction yield (Figure 4). From
this study, it can be concluded that the optimal reaction temperature is 60 °C. Similar studies
were carried out with substituted benzaldehydes and anthraldehyde and the details are given
in supporting information (Table S1-S4).
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Figure 5. Effect of catalyst loading on product conversiona
a1-Naphthaldehyde (0.64 mmol), malononitrile (0.70 mmol) in MeOH, 60 oC.
Then the effect of catalyst loading was studied by varying the amount of catalyst under
optimized reaction conditions as shown in Figure 5. When the catalyst loading was 0.01
mmol, compound 1 was obtained in 91 % yield in 9 h. Similarly, when the catalyst loading
was 0.03 mmol, 98% yield was obtained in 9 h, whereas when the loading was doubled to
0.06 mmol, 99 % yield was obtained in 3 h. Further increase in catalyst loading from 0.12 to
0.25 mmol had no impact on the desired product yields (Figure 5).
With these optimized conditions, we further expanded the scope of this reaction to different
aldehydes and active methylene compounds with 0.06 mmol Zn-Bp-BTC catalyst using
MeOH as a solvent at 60 °C and the results are summarized in Table 2.
Table 2. Zn-Bp-BTC catalyzed Knoevenagel condensation of different substrates with
malononitrile.a

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S.No
1
Starting Material
Product
Duration,
h
Yield,b
%
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99
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2
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4
99
95
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3
8
97
51
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7
41
7
8
4
4
92
93
9
4
3
85
85
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a Zn-Bp-BTC (0.06 mmol), aldehyde (1 equiv), malononitrile (1.1 equiv) in MeOH at 60 C.
4
5
b isolated yield.
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From Table 2, it is evident that the aromatic aldehydes gave excellent yields under optimized
conditions. Simple system such as benzaldehyde gave 99% yield. Fused aromatic systems
such as 1-naphthaldehyde and 1-anthraldehyde provided better yields, 99 and 97%
respectively. In the case of substituted benzaldehydes, the yield varied tremendously
depending on the substituent. Particularly, electron donating group substituted aromatic
aldehydes gave better yield than electron withdrawing group substituted aldehydes. For
instance, di- and tri- methoxy, hydroxy substituted benzaldehydes gave excellent yields 92,
93 and 85 % respectively. Similarly, bromo substituted benzaldehyde afforded the desired
product in 95 % yield. On the other hand, the electron withdrawing 4-carboxy and nitro
substituted benzaldehyde gave 41 and 51% respectively. It is also evident that 2-
naphthaldehyde gave fair yield of 85% when compared with 1-naphthaldehyde under similar
conditions. This indicates the reduced reactivity of 2-naphthaldehyde under these conditions.
It could be concluded that under our experimental conditions with Zn-Bp-BTC as a
heterogeneous catalyst, the Knoevenagel condensation gave better yields for benzaldehyde
and fused aromatic aldehydes, high yields were obtained for aldehydes with electron donating
substituents and moderate to low yields for aldehydes and ketones with strong electron
withdrawing groups.
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Evaluation of the role of metal ion and ligand in catalysis
To assess the role of metal ion in catalysis, an experiment was performed with
Zn(NO3)2•6H2O (precursor used for the synthesis of Zn-Bp-BTC MOF) as a catalyst under
identical conditions. As evident from Table 3, 80% yield was obtained in 8 h with some of
the starting material (aldehyde) remaining unreacted. No significant change in the yield was
observed even when the reaction was carried out over longer duration. Similarly the role of
4,4ʹ-bipyridine present in Zn-Bp-BTC MOF was assessed by performing an experiment with
Zn-BTC MOF under identical conditions, 89% yield was obtained in 5 h with traces of
unreacted aldehyde. Prolonged duration (reaction time) had no effect in conversion. These
results clearly indicate that MOF is necessary for improved catalytic activity and the role of
4,4ʹ-bipyridine as a ligand is essential in the further enhancement of the catalytic activity.
Table 3. Comparison of catalytic activities of Zn-Bp-BTC MOF, Zn-BTC MOF and
Zn(NO3)2 under optimized conditions.a

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S.No
Catalyst
Duration,
YY
ield,b
%
h
8
5
3
1
2
Zn(NO )
)
3 2•6H2O
80
Zn-BTC MOF
89
3
Zn-Bp-
B
TC MOF
99
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a
Catalyst (0.06 mmol), 1-naphthaldehyde (0.64 mmol), malononitrile (0.70 mmol) in MeOH
at 60 oC.
b isolated yield.
Stability and recyclability of thhe catalyst
One of the essential requiremennts of a heterogeneous catalyst is that the catalyst should be
stable, recyclable and reusablee over few cycles. In order to evaluate the stability and
recyclability of Zn-Bp-BTC catalyst, experiments were performed und
eer optimized
conditions. At the end of the reacction, the catalyst was centrifuged, washed wit
hh MeOH three
times and reused in the consecuutive reaction. This cycle was repeated for fivee consecutive
times under identical conditionss and the product yield was identified by HPL
CC. The results
are summarized in Figure 6a.
Figure 6. a) Catalyst recyclabilii
tya and b) stability studies, SEM image of MOF sample after
5 cycles.
a yield as determined by HPLC (
The catalyst was subjected to
hhigh performance liquid chromatography).
mm
orphological analysis (SEM) after five cons
e
e
cutive cycles
(Figure 6b). SEM image after five consecutive reaction cycles showed no signi
in the morphology indicating thaat the catalyst is stable over five cycles.
fficant changes

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Figure 7. XRD pattern of fresh Zn-Bp-BTC MOF and Zn-Bp-BTC MOF after five
consecutive cycles of catalysis
Further, XRD pattern of Zn-Bp-BTC MOF after five consecutive cycles was performed at
room temperature and it indicates no significant changes. Finally, a plausible mechanism for
the formation of α,β-unsaturated dicyano compounds using Zn-Bp-BTC heterogeneous
catalyst has been proposed and discussed in the supporting information (Scheme S2).
Synthesis of Benzimidazole
Benzimidazole is a valuable intermediate for the construction of natural products.[30] The
synthesis of benzimidazole using heterogeneous catalyst incorporating inexpensive metal like
Zn have attracted great attention in the field of pharmaceuticals. In this regard, we have tested
the efficiency of Zn-Bp-BTC MOF catalyst towards the synthesis of benzimidazoles from
readily available starting materials in ethanol at room temperature (Table 4, entry 1-5). The

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reaction between benzaldehyde and o-phenylenediamine in the absence of catalyst did not
afford any product, however in the presence of Zn-Bp-BTC, we obtained benzimidazole in
good yield (84 %) in 5 h. Subsequently, 4-bromo benzaldehyde also afforded the
corresponding product in 87 %. When the reaction was carried out with electron donating (-
OMe) substituted benzaldehyde, the desired product was obtained 83 % yield. Chloro
substituted o-phenylenediamine also gave good yield (85 %). From these results, it can be
concluded that Zn-Bp-BTC MOF exhibit good catalytic activity towards the synthesis of
benzimidazole from substituted o-phenylenediamine and substituted benzaldehydes.
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Table 4. Synthesis of benzimidazole derivatives using Zn-Bp-BTC MOF catalyst.a
S.No
1
Aldehyde
Product
Duration, h
5
Yield, % b
c
-
2
3
5
4
84
87
4
5
5
5
83
85
a)
Zn-Bp-BTC (0.06 mmol), o-phenylenediamine (1.0 equiv.), aldehyde (1.1equiv),
malononitrile (1.1 equiv) in EtOH at RT.
b) isolated yield.
c) absence of catalyst.
Multicomponent reaction
Multicomponent reactions (MCRs), implemented with heterogeneous catalyst have emerged
as an important tool in the field of organic synthetic chemistry. MCRs can be defined as a

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process in which three or more reactants are introduced subsequently in a reaction to form a
single product. Complicated molecules can be synthesized in one-pot reaction and hence the
isolation and purification of intermediates in individual steps are reduced to a single step.
MCRs lower the expenses, time and energy.41 With these advantages, we tested the catalytic
behavior of Zn-Bp-BTC in one-pot synthesis of 2-amino-4H-chromene, an important motifs
present in many pharmaceutically useful compounds.42, 43 Thus, we began the investigation
by treating benzaldehyde, malononitrile and active methylene dimedone in the presence of
Zn-Bp-BTC using ethanol as the solvent. The reaction did not proceed in the absence of
catalyst; however the addition of catalyst facilitated the one-pot reaction and gave 93 % yield
(Entry 2, Table 5). Under identical conditions, 2,5-dimethoxy benzaldehyde afforded the best
yield (95 %) in 5 h. From these observations, it can be concluded that Zn-Bp-BTC
heterogeneous catalyst shows promising catalytic activity for the one-component synthesis of
2-amino-4H-chromene.
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Table 5. Synthesis of 2-amino-4H-chromene derivatives using Zn-Bp-BTC MOF catalyst.a
S.No
1
Aldehyde
Product
Duration, h
6
Yield, % b
c
-
2
3
6
5
93
95
a)
Zn-Bp-BTC (0.06 mmol), aldehyde (1 equiv.), malononitrile (1.1 equiv.) and dimedone (1
equiv.) in EtOH, 80 °C.
b) isolated yield.
c) absence of catalyst.

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Conclusions
In summary, we reported the synthesis, characterization and application of Zn-Bp-BTC MOF
as a heterogeneous catalyst for mediating Knoevenagel condensation reaction, multi-
component reaction and benzimidazole synthesis. Though its synthesis is known in literature,
this is the first report where we employed successfully Zn-Bp-BTC MOF as the catalyst for
various organic reactions. Reactions even preceded at room temperature, however, 60 °C in
methanol offered the best yield in shorter duration. The role of ligand and metal salt in
Knoevenagel condensation reaction was assessed by performing the reaction under optimized
conditions using the Zn-BTC MOF analogue and Zn(NO3)2•6H2O metal salt. It was found
that Zn-Bp-BTC MOF catalyzed the reaction efficiently in comparison to its analogue Zn-
BTC MOF and precursor Zn(NO3)2•6H2O. Finally, catalytic recycling and stability study was
carried out to assess the role of catalytic efficiency over five consecutive cycles and it was
found that the catalyst mediates the reaction efficiently without undergoing significant
chemical and morphological changes. Further applications towards other organic reactions
are underway in our laboratory.
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Conflict of Interest
The authors declare no conflict of interest.
Acknowledgements
M. Kanagaraj thanks DST-INSPIRE for his project assistantship; Dr. M. K and Dr. S. M.
thanks DST-INSPIRE for the faculty award and DST-SERB Start-up Research grant for
research funding. Director and support staffs of CSIR-CECRI are gratefully acknowledged
for their constant support and encouragement.
Electronic Supplementary Information
Electronic Supplementary Information available.
References
1.
2.
L. Zhu, X.-Q. Liu, H.-L. Jiang and L.-B. Sun, Chem. Rev., 2017, 117, 8129-8176.
W. P. Lustig, S. Mukherjee, N. D. Rudd, A. V. Desai, J. Li and S. K. Ghosh, Chem.
Soc. Rev., 2017, 46, 3242-3285.

Page 19 of 22
New Journal of Chemistry
View Article Online
DOI: 10.1039/C8NJ05953E
1
2
3
4
5
6
7
8
9
3.
4.
N. S. Bobbitt, M. L. Mendonca, A. J. Howarth, T. Islamoglu, J. T. Hupp, O. K. Farha
and R. Q. Snurr, Chem. Soc. Rev., 2017, 46, 3357-3385.
S. Suriyakumar, M. Kanagaraj, N. Angulakshmi, M. Kathiresan, K. S. Nahm, M.
Walkowiak, K. Wasinski, P. Polrolniczak and A. M. Stephan, RSC Adv., 2016, 6,
97180-97186.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
5.
S. Suriyakumar, M. Kanagaraj, M. Kathiresan, N. Angulakshmi, S. Thomas and A.
M. Stephan, Electrochim. Acta, 2018, 265, 151-159.
6.
7.
8.
9.
S. Horike, D. Umeyama and S. Kitagawa, Acc. Chem. Res., 2013, 46, 2376-2384.
N. T. S. Phan, K. K. A. Le and T. D. Phan, Appl. Catal. A Gen., 2010, 382, 246-253.
Z. Wang and S. M. Cohen, Chem. Soc. Rev., 2009, 38, 1315-1329.
J. B. DeCoste, G. W. Peterson, H. Jasuja, T. G. Glover, Y.-g. Huang and K. S.
Walton, J. Mater. Chem. A, 2013, 1, 5642-5650.
10.
K. D. Nguyen, C. Kutzscher, F. Drache, I. Senkovska and S. Kaskel, Inorg. Chem.,
2018, 57, 1483-1489.
11.
12.
13.
14.
S. Neogi, M. K. Sharma and P. K. Bharadwaj, J. Mol. Catal. A Chem., 2009, 299, 1-4.
U. P. N. Tran, K. K. A. Le and N. T. S. Phan, ACS Catal., 2011, 1, 120-127.
Y. Li, Y. Su, J. Xu, Z.-l. Xu and H. Xu, Bull. Chem. Soc. Jpn., 2017, 90, 1152-1156.
F. Vermoortele, R. Ameloot, A. Vimont, C. Serre and D. De Vos, Chem. Commun.,
2011, 47, 1521-1523.
15.
16.
17.
18.
19.
20.
21.
A. Dhakshinamoorthy, A. M. Asiri and H. Garcia, Chem. Soc. Rev., 2015, 44, 1922-
1947.
G. Jia, Y. Gao, W. Zhang, H. Wang, Z. Cao, C. Li and J. Liu, Electrochem. Commun.,
2013, 34, 211-214.
M.-L. Hu, V. Safarifard, E. Doustkhah, S. Rostamnia, A. Morsali, N. Nouruzi, S.
Beheshti and K. Akhbari, Microporous Mesoporous Mater., 2018, 256, 111-127.
G. Postole, B. Chowdhury, B. Karmakar, K. Pinki, J. Banerji and A. Auroux, J.
Catal., 2010, 269, 110-121.
Y. Yang, H.-F. Yao, F.-G. Xi and E.-Q. Gao, J. Mol. Catal. A Chem., 2014, 390, 198-
205.
R. Srirambalaji, S. Hong, R. Natarajan, M. Yoon, R. Hota, Y. Kim, Y. Ho Ko and K.
Kim, Chem. Commun., 2012, 48, 11650-11652.
H. He, F. Sun, B. Aguila, J. A. Perman, S. Ma and G. Zhu, J. Mater. Chem. A, 2016,
4, 15240-15246.

New Journal of Chemistry
Page 20 of 22
View Article Online
DOI: 10.1039/C8NJ05953E
1
2
3
4
5
22.
C. Qin, X. Wang, L. Carlucci, M. Tong, E. Wang, C. Hu and L. Xu, Chem. Commun.,
2004, 1876-1877.
6
7
8
9
23.
24.
Y. Li, L. Xie, Y. Liu, R. Yang and X. Li, Inorg. Chem., 2008, 47, 10372-10377.
S.-H. Kim, R. Babu, D.-W. Kim, W. Lee and D.-W. Park, Chin. J. Catal., 2018, 39,
1311-1319.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
25.
26.
J. Wang, Y. Han, H. Xu and Z.-L. Xu, Appl. Organomet. Chem., 2018, 32, e4097.
J. Wang, X. Wang, H. Xu, X. Zhao, Z. Zheng and Z.-l. Xu, ChemPlusChem, 2017, 82,
1182-1187.
27.
28.
L. Xu, E.-Y. Choi and Y.-U. Kwon, Inorg. Chem. Commun., 2008, 11, 1190-1193.
J. Zheng, J. Tian, D. Wu, M. Gu, W. Xu, C. Wang, F. Gao, M. H. Engelhard, J.-G.
Zhang, J. Liu and J. Xiao, Nano Lett., 2014, 14, 2345-2352.
E. Knoevenagel, Ber. Dtsch. Chem. Ges., 1894, 27, 2345-2346.
V. N. Panchenko, M. M. Matrosova, J. Jeon, J. W. Jun, M. N. Timofeeva and S. H.
Jhung, J. Catal., 2014, 316, 251-259.
29.
30.
31.
32.
33.
J. Wang, X. Wang, H. Xu, X. Zhao, Z. Zheng and Z. l. Xu, ChemPlusChem, 2017, 82,
1182-1187.
J. Gascon, U. Aktay, M. D. Hernandez-Alonso, G. P. M. van Klink and F. Kapteijn, J.
Catal., 2009, 261, 75-87.
K. Das Raj, A. Aijaz, K. Sharma Manish, P. Lama and K. Bharadwaj Parimal, Chem.
Eur. J., 2012, 18, 6866-6872.
34.
35.
Z. Miao, Y. Luan, C. Qi and D. Ramella, Dalton Trans., 2016, 45, 13917-13924.
M. Almáši, V. Zeleňák, M. Opanasenko and I. Císařová, Catal. Today, 2015, 243,
184-194.
36.
37.
38.
E. M. Schneider, M. Zeltner, N. Kranzlin, R. N. Grass and W. J. Stark, Chem.
Commun., 2015, 51, 10695-10698.
J.-S. Wang, F.-Z. Jin, H.-C. Ma, X.-B. Li, M.-Y. Liu, J.-L. Kan, G.-J. Chen and Y.-B.
Dong, Inorg. Chem., 2016, 55, 6685-6691.
S. Hasegawa, S. Horike, R. Matsuda, S. Furukawa, K. Mochizuki, Y. Kinoshita and S.
Kitagawa, J. Am. Chem. Soc., 2007, 129, 2607-2614.
39.
40.
M. Hartmann and M. Fischer, Microporous Mesoporous Mater., 2012, 164, 38-43.
M. Opanasenko, A. Dhakshinamoorthy, M. Shamzhy, P. Nachtigall, M. Horacek, H.
Garcia and J. Cejka, Catal. Sci. Technol., 2013, 3, 500-507.
D. Das, ChemistrySelect, 2016, 1, 1959-1980.
41.
42.
P. Sharma, M. Gupta, R. Kant and V. K. Gupta, RSC Adv., 2016, 6, 32052-32059.

Page 21 of 22
New Journal of Chemistry
View Article Online
DOI: 10.1039/C8NJ05953E
1
2
3
43.
J. Safari, M. Heydarian and Z. Zarnegar, Arabian J. Chem., 2017, 10, S2994-S3000.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
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26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
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Table of Contents Entry
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Zn-Bp-BTC MOF was synthesized and characterized. Zn-Bp-BTC MOF was successfully
employed as a catalyst Knoevenagel condensation, Multicomponent reaction and in
Benzimidazole synthesis.
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