Zn@ZIF-67 as Catalysts for the Knoevenagel Condensation of Aldehyde Derivatives with Malononitrile

Article abstract of DOI:10.1007/s10562-017-2153-y

Abstract: Three different bimetallic zinc-cobalt zeolitic imidazolate frameworks (ZIFs) were successfully synthesized at room temperature in water through a green and simple procedure and tested as catalysts for the Knoevenagel condensation reaction betwe

Full text of DOI:10.1007/s10562-017-2153-y

Catal Lett
DOI 10.1007/s10562-017-2153-y
Zn@ZIF-67 as Catalysts for the Knoevenagel Condensation
of Aldehyde Derivatives with Malononitrile
Adriano Zanon1 · Somboon Chaemchuen1 · Francis Verpoort1,2,3
Received: 1 April 2017 / Accepted: 26 July 2017
© Springer Science+Business Media, LLC 2017
Abstract Three different bimetallic zinc-cobalt zeolitic
imidazolate frameworks (ZIFs) were successfully synthe-
sized at room temperature in water through a green and
simple procedure and tested as catalysts for the Knoev-
enagel condensation reaction between p-Br-benzaldehyde
and malononitrile as model reaction. The materials were
characterized with various techniques (XRD, ICP-AES,
SEM, N2 adsorption–desorption, TGA) and displayed
excellent activities and selectivities. Moreover, the crys-
talline structure was preserved and the catalysts could be
reused at least four times with negligible loss of activity.
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-017-2153-y) contains supplementary
material, which is available to authorized users.
* Francis Verpoort
francis.verpoort@ugent.be; Francis@whut.edu.cn
1
Laboratory of Organometallics, Catalysis and Ordered
Materials, State Key Laboratory of Advanced Technology
for Materials Synthesis and Processing, Wuhan University
of Technology, Wuhan, China
2
National Research Tomsk Polytechnic University, Lenin
Avenue 30, 634050 Tomsk, Russian Federation
3
Ghent University, Global Campus Songdo, 119
Songdomunhwa-Ro, Yeonsu-Gu, Incheon 406-840,
South Korea
Vol.:(0123456789)
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A. Zanon et al.
Graphical Abstract
identified as crystalline structures and widely employed
for many different applications such as gas separation and
storage [12–15], sensors [16], drug delivery and catalysis
[17–20]. Compared to the conventional microporous and
mesoporous materials, MOFs exhibited a flexible rational
design, which can be controlled trough the size and func-
tionalization of the organic linker [21, 22]. Metal organic
frameworks have also been reported as active catalysts for
the Knoevenagel condensation [23–25] Recently, a new
subclass of MOFs called zeolitic imidazolate frameworks
(ZIFs) have attracted considerable attention since, resem-
bling the typical channel structure of zeolites, ZIFs can
combine both properties of MOFs and zeolites in one mate-
rial. Being also environmentally friendly, since their syn-
thesis can easily be carried out in water [26, 27], these new
crystalline materials are potential candidates as catalyst for
industry, in which nowadays the minimization of the chem-
ical waste is a utmost important feature to achieve.
Keywords Heterogeneous catalysis · Metal–organic
framework · Knoevenagel condensation · Zeolitic
imidazolate frameworks (ZIFs)
1 Introduction
Knoevenagel condensation reaction between a carbonyl
group and a methylene-activated group is known as a pow-
erful tool in organic chemistry to form new C–C bonds and
applied widely in pharmaceutical intermediates synthesis
[1]. One of the major drawbacks of the aforementioned
reaction is the employment of conventional homogeneous
catalyst such alkali metal hydroxides and organic bases [2,
3], with consequent difficulties in separation and recycling
and production of large amounts of waste. For this reason,
many efforts have been done towards the implementation
of heterogeneous catalysts for this reaction with the explicit
advantages in terms of ease of separation, recycling,
cleaner products and minimum waste.
Only limited literature employing ZIFs as active catalyst
for the Knoevenagel condensation has been provided till
now [28–31]. Tran et al. for example, employed the ZIF-8
for the same reaction and found that the catalytic system
provided high conversion, although after the first cycle it
decreased dramatically [31]. Another recent report showed
the catalytic activity of ZIF-8 in the synthesis of cyanoacr-
ylates and 3-cyanocoumarins, achieving excellent yields
although higher reaction times and temperatures had been
used [32]. We believe that having two different metal sites
with different coordination behaviour may enhance the
reaction rate, since the synergistic effect of the two metals
plays a key role on the activation of the substrates. This idea
Many examples can be found of solid heterogeneous
catalysts for the Knoevenagel condensation which include
amino-functionalized mesoporous silica [4], diamine-
functionalized mesopolymers [5], amine-functionalized
mesoporous zirconia [6], superparamagnetic mesoporous
Mg–Fe bi-metal oxides [7], mesoporous titanosilicate
[8], basic MCM-41 silica [9], acid–base bifunctional
mesoporous MCM-41 silica [10] and zeolites [11]. In
the past few years, a new class of ordered materials has
emerged. Metal organic frameworks (MOFs) have been
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Zn@ZIF-67 as Catalysts for the Knoevenagel Condensation of Aldehyde Derivatives with…
is also supported by a recently published article in which a
bimetallic ZIF (ZnCo-ZIF) was successfully employed for
the synthesis of cyclic carbonates, starting from epoxides
and carbon dioxide as substrates, outperforming all the
catalysts already reported for the reaction [33]. Hence our
goal was to evaluate the activity and the selectivity of three
different new bimetallic Zn@ZIF-67. Excellent conversions
were generated at room temperature and the Zn@ZIF-67
catalysts retained their crystalline structure and were able
to be reused at least four times without significant loss of
activity.
was observed, proving the fact that Zn ions can substitute
Co ions in the lattice, in which the two metals are likely to
interact well, since the ionic radii of Zn-ions and Co-ions
are comparable (0.74 and 0.72 Å respectively). Moreover,
no alteration or damage was found for the as-synthesized
Zn@ZIF-67, proving the homogeneous nature of the net-
work. The FT-IR (Fig. 2) analysis also confirmed the struc-
tural similarity between the bimetallic and monometallic
ZIFs (ZIF-8 and ZIF-67).
The spectra report typical bands at 1350–1500 cm−1 for
all samples that are assigned to the stretching vibration of
the imidazole ring, while the bands observed in the region
of 1000–1350 cm−1 are attributed to the plane vibration of
the imidazole ring. The bands below 800 cm−1 are attrib-
uted to the out-of-plane vibration of the imidazole ring,
whereas the bands at 400 cm−1 are assigned to the metal-N
stretching.
2 Results and Discussion
2.1 Characterization
The synthesis of the catalysts was achieved using cobalt
nitrate and zinc nitrate as metal sources and 2-methylimi-
dazole as ligand, following the procedure reported by Qin
et al. [34] The textural properties of the three Zn@ZIF-67
were analyzed by X-ray diffraction (XRD), thermal analy-
sis (TGA), Fourier transform infrared (FTIR), N2 adsorp-
tion–desorption and scanning electron microscopy (SEM).
The metal content of Zn@ZIF-67 samples (before and
after reaction) was analyzed by inductively coupled plasma
atomic emission analyses spectroscopy (ICP-AES). The
XRD patterns are shown in Fig. 1.
Consistent with the XRD patterns, SEM images,
depicted in Fig. 3, also proved the crystallinity of the as-
synthesized ZIFs.
The resulting particles adopted a well-defined truncated
rhombic dodecahedral morphology. The SEM images
clearly demonstrate that the nanoparticles are homogene-
ously dispersed and that the crystalline morphology of the
recycled samples is preserved. Preservation of the mor-
phology and thus the composition is also confirmed by
ICP-AES, showing that negligible leaching occurred during
the reaction and proving that the desired metal molar ratios
were successfully achieved (Table 1).
The two sharp peaks below and above 10 degrees con-
firms the crystallinity of the structure suggesting that the
synthesized frameworks possess the same sodalite topology
of ZIF-8. Furthermore, the material was homogeneously
distributed and no segregation of cobalt or zinc clusters
TGA-DSC analysis disclosed no substantial differ-
ences between the three Zn@ZIF-67 materials, suggest-
ing the similarity of the networks and indicating that their
crystalline structures are stable up to 400°, with a slight
mass loss for the 25Zn@ZIF-67 and 50Zn@ZIF-67 due
Fig. 1 XRD patterns comparison of Zn@ZIF-67
Fig. 2 FT-IR spectra comparison of the as-synthesized ZIFs
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A. Zanon et al.
Fig. 3 SEM images of fresh
(a–c) and spent (d–f) of 10Zn@
ZIF-67, 25Zn@ZIF-67 and
50Zn@ZIF-67 respectively
Table 1 ICP-AES analysis for
10Zn@ZIF-67
Fresh
25Zn@ZIF-67
Fresh
50Zn@ZIF-67
Zn@ZIF-67
Recycled
Recycled
Fresh
Recycled
Zn
Co
3.33
24.46
3.30
24.41
7.14
20.14
7.09
20.12
13.72
14.22
13.70
14.20
to the evaporation of the solvent molecules and possible
unreacted 2-methylimidazole molecules (see Supporting
information).
suggesting that the three Zn@ZIF-67 materials possess
a small percentage of mesoporous domains. Interestingly,
the surface area decreases with the increasing of the Zinc
content. This effect may be due to the different growth of
the particles in the as-synthesized materials: bigger parti-
cles lead to smaller surface areas. The highest surface area
was found for 10Zn@ZIF-67, with 1881 and 2021 m2/g for
BET and Langmuir respectively, which is consistent with a
recent paper in which a series of bimetallic ZIFs have been
synthesized [35], although the materials in this study (espe-
cially the 10 and 25%) present an higher surface area.
As expected for the N2 adsorption–desorption analysis,
the properties of the three Zn@ZIF-67 materials are simi-
lar and comparable to the isotherms of ZIF-8 and ZIF-67
(Table 2).
All three as-synthesized Zn@ZIF-67 materials exposed
a type I isotherm (see Supporting information), which
can be related to the microporous nature of the materials.
At relative high pressures very small loops are present,
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Zn@ZIF-67 as Catalysts for the Knoevenagel Condensation of Aldehyde Derivatives with…
Table 2 Summarized surface
Sample
ZIF-8
10Zn@ZIF-67
25Zn@ZIF-67
50Zn@ZIF-67
ZIF-67
areas and porosity properties for
ZIF-8, ZIF-67 and Zn@ZIF-67
BET (m2/g)
1131
1153
129
0.58
12.93
1881
2021
103
0.63
12.68
1726
1725
41
0.72
12.60
1447
1450
100
0.70
12.72
1888
1996
55
0.71
12.55
Langmuir (m2/g)
External surface area (m2/g)
Pore volume (cm3/g)
Pore size (Å)
Fig. 4 Knoevenagel condensa-
tion of p-Br-benzaldehyde and
malononitrile
p-Br-benzaldehyde and malononitrile was selected as
model reaction (Fig. 4).
Compared with the previous reports the substrate
amount used in this study was twice the amount as has
been reported [30]. The reaction was studied at room tem-
perature and the kinetics of the reaction were monitored
by withdrawing aliquots from the reaction mixture at the
desired time intervals (50 µL) and analyzed by GC. The
results are presented in Fig. 5 and Table 3.
A blank test without catalyst was performed to under-
stand the reactivity of the substrates however no product
could be detected. Subsequently, homogeneously catalyzed
reactions with the metal salts were screened to test their
activity. A conversion of 11% after 90 min was achieved
when a mixture of the metal salts, Co(NO3)2·6H2O and
Zn(NO3)2·4H2O was applied. Thereafter, ZIF-8 and ZIF-
67 were tested in order to assess the activity of the single
metal ZIFs, see Table 3. While ZIF-8 reached a conversion
of 37% after 90 min, the cobalt counterpart achieved 91%
conversion within the same time window. The difference in
activity between ZIF-8 ad ZIF-67 can be observed already
from the beginning of the reaction, at 5 and 10 min the con-
version of p-Br-benzaldehyde is twice as high for ZIF-67
compared to ZIF-8. Comparing the three different Zn@
ZIF-67, the best performing Zn@ZIF-67 corresponds to
the molar ratio Co:Zn of 9:1, Fig. 5. Introducing the cata-
lyst to the reaction mixture, high conversions are achieved,
e.g. after the first minute 33% conversion is obtained.
Within 45 min complete conversion was obtained, tackling
all other systems. Considering the other two bimetallic ZIF
systems, 25Zn@ZIF-67 and 50Zn@ZIF-67, the increment
of the zinc content in the lattice did not cause any beneficial
effect to the reaction rate, proceeding slower even though
after 90 min the conversion of 90 and 83% respectively
were obtained which are comparable with the 10Zn@
Fig. 5 Kinetic plots of the different catalysts for Knoevenagel con-
densation of p-Br-benzaldehyde with malononitrile
Table 3 Catalytic data of the catalyst screening
Catalysts
Time (min)
Conversion
Selectivity
ZIF-67
90
45
90
90
90
91.13
97.36
83.21
82.92
37.42
>99
>99
>99
>99
>99
10Zn@ZIF-67
25Zn@ZIF-67
50Zn@ZIF-67
ZIF-8
Reaction conditions: 3.9 mmol aldehyde, 7.2 mmol malononitrile,
2.5 mol% catalyst
2.2 Catalytic Studies
In order to assess the activity of three Zn@ZIF-67 mate-
rials, the Knoevenagel condensation reaction between
1 3

A. Zanon et al.
ZIF-67. The reason of this behavior could be surmised by
taking in consideration the two different electronic environ-
ments that the two metal atoms, Zn and Co, posses. It is
known that Zn(II) species possess strong Lewis acid prop-
erties, while for cobalt, originating its acidity from Co(II)
and Co(III) species, exerts a milder acidic behavior than the
counterpart, as supported by TPD analysis reported by Chi-
zallet et al. [36]. Yang et al. as well proved this behaviour
[37] as reported for the synthesis of ethylmethylcarbonate.
Exhibiting different CO2 and NH3 desorption properties,
zinc showed a broader desorption peak at 440 °C, while
for cobalt a sharp peak at 330° was observed. Hence, the
substrate mildly coordinates to Co-species and is more apt
to desorb at the end of the catalytic cycle. For this reason,
increasing the percentage of zinc in the as-synthesized ZIFs
decreases the rate of reaction and consequently the overall
activity of the catalyst.
reaction rate is attained when the polarity of the solvent
increased with the following observed trend in catalytic
activity: toluene<THF<MeOH≅DMSO. This effect can
be rationalized taking in consideration the nature of the
catalyst and the mechanism of the reaction. Since Zn@ZIF-
67 is hydrophobic, increasing the polarity of the reaction
medium may encourage the polar substrates to leave the
catalyst and transfer into the reaction media. On the other
hand, the reaction mechanism is based on a nucleophilic
addition–elimination following the SN1 path in which the
carbocation and the nucleophile are stabilized by the sol-
vent hydrogen bonds. For this reason, since these two
effects are synergistic, the reaction readily occurs in MeOH
and DMSO, achieving quantitative conversion after 15 min.
It is noteworthy to mention that even though the conver-
sions are comparable, a higher reaction rate was achieved
using DMSO (75% conversion after 1 min) and could be
due to the solvatation of the substrate, which in MeOH is
much more sterically hindered and therefore less reactive,
see Fig. 7.
2.3 Effect of the Solvent
The influence of the solvent was also investigated since het-
erogeneous catalyzed reactions can be the extremely sen-
sitive to the solvent [38, 39]. Four different solvents with
increasing polarity were selected [toluene, tetrahydrofuran
(THF), methanol (MeOH), dimethylsulfoxide (DMSO)].
The obtained results are displayed in Fig. 6.
From the comparison of the obtained TOFs using dif-
ferent solvents, it is obvious that a higher reaction rate is
achieved applying DMSO. Therefore, a polar solvent could
stabilizes the carbocation and enhances the nucleophilicity
of the malononitrile. However, the issue is still under fur-
ther investigations to confirm the trend.
Different results are reported in literature regarding the
solvent influence on the condensation reaction. For exam-
ple, MacQuarrie and co-workers reported that non-polar
solvents resulted in the optimum catalytic performance
[40], while Gaston et al. reported an enhanced reaction rate
using polar solvents, while non-polar solvents had a nega-
tive effect on the overall activity of the catalyst [41, 42].
In these work the obtained results indicate that a higher
2.4 Effect of the Substrate
Kinetic plots for the Knoevenagel condensation of dif-
ferent substrates in toluene catalyzed by 10Zn@ZIF-67.
Having determined the influence of the polarity of dif-
ferent solvents, the catalytic performance of Zn@ZIF-67
applying different substrates bearing both electron-with-
drawing (activating) and electron-donating (deactivating)
groups was investigated. A series of different substrates
in combination with malononitrile were employed for the
2500
2000
1500
1000
500
0
THF
MeOH
Toluene
Solvents
DMSO
Fig. 6 Solvents effect on the Knoevenagel condensation of p-Br-ben-
Fig. 7 Initial TOFs of the Knoevenagel reaction using different sol-
zaldehyde with malononitrile
vents
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Zn@ZIF-67 as Catalysts for the Knoevenagel Condensation of Aldehyde Derivatives with…
Table 5 Obtained results for Knoevenagel condensation using differ-
ent substrates catalyzed by 10Zn@ZIF-67
Knoevenagel condensation and the obtained results are
given in Table 4.
The kinetic plots given in Fig. 8 demonstrate an unex-
pected behavior for the different substrates that can be
explained based on the different substituents present on the
phenyl ring, see Table 5.
Substrate
Conversion
Selecꢀvity
50,02
53,79
>99
Since electron-withdrawing and electron-donating
groups are present on the applied substrates the different
effect these moieties exert on the carbonylic carbon has to
be considered. Firstly the electronegativity plays an impor-
tant role on the activation of the substrate. A more electron-
egative substituent present on the phenyl ring of the sub-
strate will result in a higher polarization of the electronic
cloud and consequently drained the electron density from
the aldehyde carbon, which becomes more electrophilic
and apt to react with the activated methylene group of the
malononitrile. Secondly, the presence of a hydroxyl group
e.g. salicylaldehyde affects the reaction rate since the unco-
ordinated metal sides present in the framework can coor-
dinate with the oxygen atoms and hinders the nucleophile
attack on the carbonyl group. A comparison of 10Zn@
ZIF-67 with other reported heterogeneous catalysts clearly
demonstrates that nearly all of them require higher temper-
ature and all the reported systems necessitate a longer reac-
tion time to achieve good yields. A more detailed study of
Table 4 reveals that the reported metal organic frameworks
all demand the presence of basic moieties such as primary
amines to be able to activate the methylene nucleophile,
while for the new catalyst, 10Zn@ZIF-67 the synergistic
role played by the uncoordinated metal nodes (defects) and
the uncoordinated imidazole ligands on the activation of
the malononitrile requires milder basic conditions to exert
the catalytic activity.
>99
>99
19,56
92,43
38,33
>99
>99
Substrate: 3.8 mmol; malononitrile: 7.2 mmol; catalyst: 2.5 mol%
based on the aldehyde, reaction time: 90 min.
2.5 Recyclability Studies
When employing a solid catalyst, a crucial point that
needs to be taken in consideration is whether possible spe-
cies could migrate into the reaction medium and affects
the reaction rate by homogeneous contributions. Hence,
the catalyst was recovered and reused to test its stability.
10Zn@ZIF-67 can catalyze the Knoevenagel condensation
Table 4 Comparison of the initial TOFs for reported ZIFs catalysts26
and Zn@ZIF-67 for the Knoevenagel condensation reaction
Catalyst
Solvent
TOF (s−1
)
ZIF-8
ZIF-8
ZIF-8
ZIF-9
THF
12
5
4
Toluene
EtOAc
THF
16
ZIF-9
ZIF-9
ZIF-10
Toluene
EtOAc
THF
14
5
48
ZIF-10
ZIF-10
10Zn@ZIF-67
10Zn@ZIF-67
10Zn@ZIF-67
10Zn@ZIF-67
Toluene
EtOAc
THF
Toluene
MeOH
DMSO
24
12
111
721
534
2279
Fig. 8 Kinetic plots for the Knoevenagel condensation of different
substrates in toluene catalyzed by 10Zn@ZIF-67
1 3

A. Zanon et al.
reaction at least four times without significant loss of activ-
ity. This recycling study demonstrates that high conversion
can still be achieved and no homogeneous leached species
contributes to the catalytic performance. Furthermore, the
crystalline structure of 10Zn@ZIF-67 was retained, as con-
firmed by the XRD (see Supporting information), SEM and
ICP analysis. The results of the recycling study are depicted
in Fig. 9.
likely on the zinc atoms, since the coordination bond that
is generated between the d orbitals and the p orbitals of the
substrates is much stronger than with the cobalt, as proved
by the study of Gao and coworkers [37]. Finally the last
step occurs, and while losing a molecule of water, simulta-
neously the C=C bond is formed, releasing the product and
closing the catalytic cycle (Fig. 10).
2.6 Mechanism
3 Experimental
To interpret the mechanism of the Knoevenagel conden-
sation between p-Br-benzaldehyde and malononitrile, the
external active sites are to be taken in consideration, as
already reported by Chizallet and coworkers. [36] They
found that at ambient temperature and pressure, the active
sites located on the external surface are likely to be Zn(II)
and Zn(III) together with OH and NH groups. Therefor
in this study, it is reasonable to believe that the reaction
occurs on the uncoordinated surface species, which are
readily available to react in the presence of the substrate.
Consequently, a plausible mechanism could involve the
interaction between the Co and the Zn species in a syner-
gistic adsorption of the aldehyde compound through the
coordination of the oxygen, which attracts the electronic
density and activates the carbonyl carbon making it par-
tially positively charged and apt it to the nucleophilic attack
of the malononitrile. The dicyano derivative, on the other
hand, is activated by the coordination of the metal ions
with the N atoms of the malononitrile, inducing the depro-
tonation of the –CH2– by non-coordinated 2-methylimida-
zole ligands, in which the α-H of the methylene group is
much more positively charged and exhibit stronger acidity
[43]. The coordination of the aldehyde would occur most
All chemicals were purchased from Aladdin Chemical Co.
and Sigma-Aldrich and used without any further purifica-
tion unless otherwise noted.
3.1 Zn-ZIF-67 Synthesis
Zn@ZIF-67 was synthesized at room temperature accord-
ing to the procedure reported for ZIF-67 [34] using zinc
nitrate tetrahydrate [Zn(NO3)2·4H2O] cobalt nitrate hexa-
hydrate [Co(NO3)2·6H2O], and 2-methylimidazole as
ligand. The desired amount of cobalt nitrate was dis-
solved in 8 mL of ultrapure H2O and mixed with a solu-
tion of Zn(NO3)2·4H2O in 8 mL of ultrapure H2O, obtain-
ing three different final molar ratios Zn:Co of 1:9; 2.5:7.5;
5:5 respectively. Another solution of 67 mmol of 2-methyl
imidazole in 8 mL of water was prepared and subsequently
added to the metal solution resulting in a instant precipi-
tation of the product. The mixture was then stirred vigor-
ously for 4 h. Afterwards, the precipitates were separated
by centrifugation at 8000 rpm and washed with methanol
three times. The solid crystals were dried at room tempera-
ture in a vacuum oven for 12 h. The catalyst was activated
at 150 °C, for 3 h under vacuum before use.
Fig. 9 Catalyst recycling stud-
ies using Zn@ZIF-67 as catalyst
for the Knoevenagel condensa-
Recycle tests
10Zn@ZIF-67
25Zn@ZIF-67
50Zn@ZIF-67
tion of p-Br-benzaldehyde and
100
malononitrile
90
80
70
60
50
40
30
20
10
0
1
2
3
4
Cycles
1 3

Zn@ZIF-67 as Catalysts for the Knoevenagel Condensation of Aldehyde Derivatives with…
Fig. 10 Schematic representation of the mechanism for the Knoevenagel condensation reaction catalyzed by Zn@ZIF-67
3.2 Catalytic Studies
vacuum for 200 min. The micropore surfaces were ana-
lyzed using the Brunauer–Emmett–Teller (BET) and Lang-
muir methods. The linearized BET and Langmuir equations
were fit to data within the range 0.003<P/P0 <0.05. The
morphology of Zn-ZIF-67 was measured using a FE-SEM
(FEI Nova 600). Thermal analysis (TGA) was performed
on a Netzsch STA 409 thermal analyzer. A certain amount
of compound was placed inside a crucible and heated from
room temperature to 800 °C under a flow of nitrogen gas.
The FI-IR was performed with a Bruker Vertex 80 V FT-IR
spectrometer. Substrate conversions were determined by
GC (Agilent) with a HP-5 column and a flame ionization
detector; the temperature program for the GC analysis
was as follow: 60–150 °C at 20° min−1, at 150 °C the T
was held for 1 min and then heated from 150 to 160 °C at
1° min−1 and held for 1 min.
In a typical procedure reported by Phan’s research group
[30] (although the quantities have been doubled in order
to overcome aliquots withdrawn problems during the reac-
tion), 3.8 mmol of p-Br-benzaldehyde was transferred in a
two-neck round bottom flask and dissolved in 5 mL of tolu-
ene. Another solution containing 7.6 mmol of malononi-
trile in 5 mL of toluene was prepared and transferred in the
previous solution achieving a total volume of 10 mL. After
the introduction of 2.5 mol% of catalyst based on the alde-
hydes substrates (the initial time for the reaction) the mix-
ture was let to react for 90 min while aliquots were with-
drawn at different time intervals and analyzed them by GC.
At the end of the reaction the catalyst was then separated
by centrifugation and washed several times with methanol
and dried at 80 °C under vacuum.
3.3 Characterization Methods
4 Conclusions
The characterization of Zn@ZIF-67 was performed by
XRD (Bruker D8 advance diffractometer, Bragg–Brentano
geometry) using a Cu Kα radiation source (λ=1.54056 Å)
at 40 kV and 45 Ma. The data were collected at a 5° s−1
scanning speed. Gas adsorption–desorption isotherms and
pore size distributions of products were measured using the
volumetric method on a Micrometrics instrument (ASAP
2020 analyzer). N2 and CO2 gas with purity of 99.999%
was applied for the measurements. For degassing of the
samples, the samples were evacuated at 200 °C under
In summary, it is demonstrated in this study that three dif-
ferent bimetallic Zn@ZIF-67 are highly potent heteroge-
neous catalyst for the Knoevenagel condensation between
benzaldehyde derivatives and malononitrile. The catalysts
were tested using p-Br-benzaldehyde as model substrate
and displayed excellent conversion and selectivity. Fur-
thermore, the catalytic materials could be recycled up to at
least four times without considerable loss of activity while
maintaining their crystalline structure. In comparison with
other different reported catalysts, the Zn@ZIF-67 materials
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A. Zanon et al.
14. Chae HK, Siberio-Perez DY, Kim J, Go Y, Eddaoudi M, Matzger
AJ, O’Keeffe M, Yaghi OM (2004) A route to high surface area,
porosity and inclusion of large molecules in crystals. Nature
427:523–527
exhibited higher reaction rates and excellent activities,
which make them potent candidates to be employed in
organic chemistry to achieve the synthesis of new car-
bon–carbon bonds.
15. Tranchemontagne DJ, Ni Z, O’Keeffe M, Yaghi OM (2008)
Reticular chemistry of metal–organic polyhedra. Angew Chem
Int Ed 47:5136–5147
Acknowledgements The authors are grateful to the State Key Lab
of Advanced Technology for Materials Synthesis and Processing for
financial support (Wuhan University of technology). S. C. appreciates
the National Natural Science Foundation of China (No. 21502146),
The Fundamental Research Funds for the Central Universities (WUT:
2016IVA092) and the Research Fund for the Doctoral Program of
Higher Education of China (471-40120222).
16. Horcajada P, Chalati T, Serre C, Gillet B, Sebrie C, Baati
T, Eubank JF, Heurtaux D, Clayette P, Kreuz C, Chang J-S,
Hwang YK, Marsaud V, Bories P-N, Cynober L, Gil S, Ferey
G, Couvreur P, Gref R (2010) Porous metal-organic-framework
nanoscale carriers as a potential platform for drug delivery and
imaging. Nat Mater 9:172–178
17. Yoon M, Srirambalaji R, Kim K (2012) Homochiral metal–
organic frameworks for asymmetric heterogeneous catalysis.
Chem Rev 112:1196–1231
18. Valvekens P, Vermoortele F, De Vos D (2013) Metal-organic
frameworks as catalysts: the role of metal active sites. Catal Sci
Technol 3:1435–1445
References
19. Dhakshinamoorthy A, Opanasenko M, Cejka J, Garcia H (2013)
Metal organic frameworks as heterogeneous catalysts for the pro-
duction of fine chemicals. Catal Sci Technol 3:2509–2540
20. Corma A, García H, Llabrés i Xamena FX (2010) Engineering
metal organic frameworks for heterogeneous catalysis. Chem
Rev 110:4606–4655
1. Simon C, Constantieux T, Rodriguez J (2004) Utilisation of
1,3-dicarbonyl derivatives in multicomponent reactions. Eur J
Org Chem 2004:4957–4980
2. Balalaie S, Bararjanian
M (2006) Tetra-n-butylammonium
hydroxide (TBAH)–catalyzed Knoevenagel condensation:
a
facile synthesis of α-cyanoacrylates, α-cyanoacrylonitriles, and
α-cyanoacrylamides. Synth Commun 36:533–539
21. Li H, Eddaoudi M, O’Keeffe M, Yaghi OM (1999) Design and
synthesis of an exceptionally stable and highly porous metal-
organic framework. Nature 402:276–279
3. Dalessandro EV, Collin HP, Valle MS, Pliego JR (2016) Mecha-
nism and free energy profile of base-catalyzed Knoevenagel con-
densation reaction. RSC Adv 6:57803–57810
22. Rowsell JLC, Yaghi OM (2004) Metal–organic frameworks: a
new class of porous materials. Microporous Mesoporous Mater
73:3–14
4. Mondal J, Modak A, Bhaumik A (2011) Highly efficient
mesoporous base catalyzed Knoevenagel condensation of differ-
ent aromatic aldehydes with malononitrile and subsequent non-
catalytic Diels–Alder reactions. J Mol Catal A 335:236–241
5. Xing R, Wu H, Li X, Zhao Z, Liu Y, Chen L, Wu P (2009) Mes-
opolymer solid base catalysts with variable basicity: preparation
and catalytic properties. J Mater Chem 19:4004–4011
6. Parida KM, Mallick S, Sahoo PC, Rana SK (2010) A facile
method for synthesis of amine-functionalized mesoporous zir-
conia and its catalytic evaluation in Knoevenagel condensation.
Appl Catal A 381:226–232
23. Hartmann M, Fischer M (2012) Amino-functionalized basic cat-
alysts with MIL-101 structure. Microporous Mesoporous Mater
164:38–43
24. Luan Y, Qi Y, Gao H, Andriamitantsoa RS, Zheng N, Wang G
(2015) A general post-synthetic modification approach of amino-
tagged metal-organic frameworks to access efficient catalysts
for the Knoevenagel condensation reaction. J Mater Chem A
3:17320–17331
25. Burgoyne AR, Meijboom R (2013) Knoevenagel condensation
reactions catalysed by metal-organic frameworks. Catal Lett
143:563–571
7. Gao Z, Zhou J, Cui F, Zhu Y, Hua Z, Shi J (2010) Superpara-
magnetic mesoporous Mg–Fe bi-metal oxides as efficient mag-
netic solid-base catalysts for Knoevenagel condensations. Dalton
Trans 39:11132–11135
26. Kida K, Okita M, Fujita K, Tanaka S, Miyake Y (2013) Forma-
tion of high crystalline ZIF-8 in an aqueous solution. CrystEng-
Comm 15:1794–1801
8. Karmakar B, Chowdhury B, Banerji J (2010) Mesoporous tita-
nosilicate Ti-TUD-1 catalyzed Knoevenagel reaction: an efficient
green synthesis of trisubstituted electrophilic olefins. Catal Com-
mun 11:601–605
27. Jian M, Liu B, Liu R, Qu J, Wang H, Zhang X (2015) Water-
based synthesis of zeolitic imidazolate framework-8 with
high morphology level at room temperature. RSC Adv
5:48433–48441
9. Parida KM, Rath D (2009) Amine functionalized MCM-41: an
active and reusable catalyst for Knoevenagel condensation reac-
tion. J Mol Catal A 310:93–100
28. Zhang G, Zhang T, Zhang X, Yeung KL (2015) Continuous flow
ZIF-8/NaA composite membrane microreactor for efficient Kno-
evenagel condensation. Catal Commun 68:93–96
10. Shang F, Sun J, Wu S, Yang Y, Kan Q, Guan J (2010) Direct
synthesis of acid–base bifunctional mesoporous MCM-41 silica
and its catalytic reactivity in deacetalization–Knoevenagel reac-
tions. Microporous Mesoporous Mater 134:44–50
29. Li Q, Jiang S, Ji S, Ammar M, Zhang Q, Yan J (2015) Synthe-
sis of magnetically recyclable ZIF-8@SiO
2@Fe3O4 catalysts and
their catalytic performance for Knoevenagel reaction. J Solid
State Chem 223:65–72
11. Chaves TF, Carvalho KTG, Urquieta-González EA, Cardoso D
(2016) One-step synthesis of functionalized ZSM-12 zeolite as a
hybrid basic catalyst. Catal Lett 146:2200–2213
30. Nguyen LTL, Le KKA, Truong HX, Phan NTS (2012) Metal-
organic frameworks for catalysis: the Knoevenagel reaction
using zeolite imidazolate framework ZIF-9 as an efficient hetero-
geneous catalyst. Catal Sci Technol 2:521–528
12. Furukawa H, Ko N, Go YB, Aratani N, Choi SB, Choi E, Yazay-
din AÖ, Snurr RQ, O’Keeffe M, Kim J, Yaghi OM (2010)
Ultrahigh porosity in metal-organic frameworks. Science
329:424–428
31. Tran UPN, Le KKA, Phan NTS (2011) Expanding applications
of metal–organic frameworks: zeolite imidazolate framework
ZIF-8 as an efficient heterogeneous catalyst for the Knoevenagel
reaction. ACS Catal 1:120–127
13. Kaye SS, Dailly A, Yaghi OM, Long JR (2007) Impact of
preparation and handling on the hydrogen storage properties of
32. Kolmykov O, Chebbat N, Commenge J-M, Medjahdi G, Sch-
neider R (2016) ZIF-8 nanoparticles as an efficient and reusable
Zn
4O(1,4-benzenedicarboxylate)3 (MOF-5). J Am Chem Soc
129:14176–14177
1 3

Zn@ZIF-67 as Catalysts for the Knoevenagel Condensation of Aldehyde Derivatives with…
catalyst for the Knoevenagel synthesis of cyanoacrylates and
3-cyanocoumarins. Tetrahedron Lett 57:5885–5888
39. Phan NTS, Jones CW (2006) Highly accessible catalytic sites on
recyclable organosilane-functionalized magnetic nanoparticles:
an alternative to functionalized porous silica catalysts. J Mol
Catal A 253:123–131
33. Zanon A, Chaemchuen S, Mousavi B, Verpoort F (2017) Zn-
doped ZIF-67 as catalyst for the CO2 fixation into cyclic carbon-
ates. J CO2 Util 20:282–291
40. Macquarrie DJ, Jackson DB (1997) Aminopropylated MCMs as
base catalysts: a comparison with aminopropylated silica. Chem
Commun 1781–1782
34. Qian J, Sun F, Qin L (2012) Hydrothermal synthesis of zeolitic
imidazolate framework-67 (ZIF-67) nanocrystals. Mater Lett
82:220–223
41. Gascon J, Aktay U, Hernandez-Alonso MD, van Klink GPM,
Kapteijn F (2009) Amino-based metal-organic frameworks as
stable, highly active basic catalysts. J Catal 261:75–87
42. Juan-Alcañiz J, Ramos-Fernandez EV, Lafont U, Gascon J,
Kapteijn F (2010) Building MOF bottles around phosphotungstic
acid ships: one-pot synthesis of bi-functional polyoxometalate-
MIL-101 catalysts. J Catal 269:229–241
35. Zaręba JK, Nyk M, Samoć M (2016) Co/ZIF-8 heterometallic
nanoparticles: control of nanocrystal size and properties by a
mixed-metal approach. Crystal Growth Design 16:6419–6425
36. Chizallet C, Lazare S, Bazer-Bachi D, Bonnier F, Lecocq V,
Soyer E, Quoineaud A-A, Bats N (2010) Catalysis of transes-
terification by a nonfunctionalized metal–organic framework:
acido-basicity at the external surface of ZIF-8 probed by FTIR
and ab initio calculations. J Am Chem Soc 132:12365–12377
37. Yang L, Yu L, Sun M, Gao C (2014) Zeolitic imidazole frame-
work-67 as an efficient heterogeneous catalyst for the synthesis
of ethyl methyl carbonate. Catal Commun 54:86–90
43. Položij M, Rubeš M, Čejka J, Nachtigall P (2014) Catalysis by
dynamically formed defects in a metal–organic framework struc-
ture: Knoevenagel reaction catalyzed by copper benzene-1,3,5-
tricarboxylate. ChemCatChem 6:2821–2824
38. Langhendries G, De Vos DE, Baron GV, Jacobs PA (1999)
Quantitative sorption experiments on Ti-zeolites and relation
with α-olefin oxidation by H2O2. J Catal 187:453–463
1 3