Efficient and recyclable novel Ni-based metal–organic framework nanostructure as catalyst for the cascade reaction of alcohol oxidation–Knoevenagel condensation

Article abstract of DOI:10.1002/aoc.3995

A novel Ni-based metal–organic framework (Ni-MOF) with a Schiff base ligand as an organic linker, Ni₃(bdda)₂(OAc)₂?6H₂O (H₂bdda?=?4,4′-[benzene-1,4-diylbis(methylylidenenitrilo)]dibenzoic acid), was synthesized and characterized using powder X-ray powder diffraction, thermogravimetric analysis, Brunauer–Emmett–Teller measurements, inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, elemental analysis and Fourier transform infrared spectroscopy. The synthesized Ni-MOF exhibited a high catalytic activity in benzyl alcohol oxidation using tert-butyl hydroperoxide under solvent-free conditions. Also, the efficiency of the catalyst was investigated in the cascade reaction of oxidation–Knoevanagel condensation under mild conditions. The Ni-MOF catalyst could be recovered and reused four times without significant reduction in its catalytic activity.

Full text of DOI:10.1002/aoc.3995

Received: 15 May 2017
DOI: 10.1002/aoc.3995
Revised: 27 June 2017
Accepted: 27 June 2017
F U L L P A P E R
Efficient and recyclable novel Ni‐based metal–organic
framework nanostructure as catalyst for the cascade
reaction of alcohol oxidation–Knoevenagel condensation
Sima Aryanejad | Ghodsieh Bagherzade
| Alireza Farrokhi
Department of Chemistry, Faculty of
A novel Ni‐based metal–organic framework (Ni‐MOF) with a Schiff base ligand
as an organic linker, Ni3(bdda)2(OAc)2⋅6H2O (H2bdda = 4,4′‐[benzene‐1,4‐
Sciences, University of Birjand, PO Box
97175‐615, Birjand, Iran
diylbis(methylylidenenitrilo)]dibenzoic
acid),
was
synthesized
and
Correspondence
characterized using powder X‐ray powder diffraction, thermogravimetric
analysis, Brunauer–Emmett–Teller measurements, inductively coupled plasma
atomic emission spectroscopy, transmission electron microscopy, elemental
analysis and Fourier transform infrared spectroscopy. The synthesized Ni‐MOF
exhibited a high catalytic activity in benzyl alcohol oxidation using tert‐butyl
hydroperoxide under solvent‐free conditions. Also, the efficiency of the catalyst
was investigated in the cascade reaction of oxidation–Knoevanagel
condensation under mild conditions. The Ni‐MOF catalyst could be recovered
and reused four times without significant reduction in its catalytic activity.
Ghodsieh Bagherzade, Department of
Chemistry, Faculty of Sciences, University
of Birjand, PO Box 97175‐615, Birjand,
Iran.
Email: bagherzadeh@birjand.ac.ir;
gbagherzade@gmail.com
KEYWORDS
alcohol oxidation, cascade reaction, Knoevenagel, metal–organic framework
1 | INTRODUCTION
systems require the incorporation of noble‐metal centres,
high temperature and soluble base as an additive for
Nowadays, due to increasing environmental concerns, the
design of uncomplicated and practical chemical syntheses
of drugs and useful chemicals is very important. Therefore,
researchers have focused on the design of synthetic sys-
tems that satisfy economic and ecological criteria for pro-
viding the goals of green chemistry.[1–4] One‐pot cascade
reactions are strategies aligned with green chemistry that
reduce production wastes and energy consumption by the
implementation of several consecutive reactions.[5–7] The
use of new catalytic systems is a possible way for the effec-
tive progress of cascade reactions. For this purpose, a wide
diversity of catalysts has been proposed to date. Neverthe-
less, many of these reports are based on homogeneous cat-
alysts that are associated with some problems such as
difficult separation from the reaction medium.[8,9] Also,
effective heterogeneous catalysts for cascade reactions
have been reported.[10,11] The reported heterogeneous
achieving high yields of products in a reasonable time.[10–
12]
Therefore, the development of exceedingly efficient
heterogeneous catalysts that can operate without
additives (e.g. base) under mild conditions should be the
subject of research for one‐pot cascade reactions.
In the past decade, metal–organic frameworks (MOFs),
constructed from metal clusters or ions and organic linkers
through covalent bonds, have attracted great attention
because of their adjustable highly porous structures and
large specific surface areas that make them suitable for
various applications in catalysis,[13] gas storage,[14,15]
adsorption[16] and biomedicine.[17] In fact, MOFs as
heterogeneous catalysts possess the useful combined
features of both homogeneous and heterogeneous
catalysts.[18,19] Also, the large surface area and pore size
of MOFs allow the easy accessibility of organic substrates
to transition metal ions inside the crystal structure.
Appl Organometal Chem. 2017;e3995.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3995

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ARYANEJAD ET AL.
Because of the highly dispersed metal ions in the crystal
structure of MOFs, they can interact with organic
substrates and can be active sites for catalysing organic
reactions,[13,20,21] for example in carbon–carbon[22–25]
and carbon–nitrogen[26,27] bond formation and
oxidation[28–30] transformations. Anyway, a variety of
MOFs with the controllable particle size and morphology
can be achieved by replacing the many organic coordi-
nated ligands with different metal cations of diverse oxida-
tion states and coordination geometries.[31] Actually, the
synthesis of MOFs can be propounded as a construction
game in that, by selecting appropriate components and
their compatibility, MOFs can be synthesized with
favourable and appropriate structural and chemical prop-
erties for particular applications.
Also, the scaling down of MOFs has provided the same
rich variety of compositions, structures and properties of
bulk types with the advantages of nanomaterials. These
compounds are a new class of materials known as
nanoscale MOFs (NMOFs). It should be noted that the
chemical properties, reactivity and catalytic activities of
nanomaterials can be affected not only by their chemical
composition but also by their morphological properties
such as size, shape and surface properties.
Notwithstanding an increasing interest in developing
new synthesis routes to produce MOF nanoparticles, types
of NMOFs are still quite rare.
Aldrich. All chemicals were used without any further
purification. The progress of the reactions and the purity
of the products were determined by TLC on silica‐gel
Polygram SILG/UV254 plates. Fourier transform infrared
(FT‐IR) spectra were recorded with a Nicolet system 800
beam splitter KBr SCAL = 800 in the range 400–
4000 cm−1. The FT‐IR spectrometer used a room
temperature detector. NMR spectra were recorded in
DMSO‐d6 using a Bruker Advance DPX‐400 and 250
instrument using tetramethylsilane as internal standard.
The powder X‐ray diffraction pattern of UoB‐2 was
obtained with an X'Pert Pro MPD diffractometer with a
Cu Kα (λ = 1.54060 Å) radiation source between 2θ = 2°
and 50.0°. Transmission electron microscopy (TEM)
images were obtained using a Philips CM120 microscope.
Thermogravimetric analysis (TGA) of nanopowders was
carried out using a Shimadzu Thermoanalyzer between
30 and 710 °C with a heating rate of 10 °C min−1 under
a nitrogen atmosphere. Elemental analysis was performed
with a PerkinElmer CHNS‐O elemental analyser for
determining the C, H and N contents. Inductively coupled
plasma (ICP) atomic emission spectroscopy was
conducted with an OPTIMA 7300DV. The Brunauer–
Emmett–Teller (BET) surface area and pore size of UoB‐
2 were measured utilizing N2 adsorption–desorption
isotherms at 77 K with a Belsorp Mini II instrument.
The UoB‐2 nanostructures were degassed at 300 °C for
12 h under conditions of dynamic vacuum before BET
analysis. The specific surface areas for N2 were calculated
using the BET model over a relative pressure (P/P0) range
of 0.001–0.1. Total pore volumes were calculated from the
Literature survey reveals only a few examples of MOFs
that catalyse alcohol oxidation reactions[28–30] and cascade
reactions.[32–35] Despite highly efficient and stable catalytic
activity, some of the reported systems are associated with
problems such as high cost and cumbersome synthesis pro-
cess for the catalyst. Therefore, numerous challenges and
opportunities still remain in this domain.
uptake at
a relative pressure of 0.95. Pore size
distributions were calculated from the adsorption
isotherms using the density functional theory method.
As a continuation of our work with the synthesis of
NMOFs,[36] we report herein the fabrication of a novel
Ni‐MOF nanostructure (UoB‐2) with the Schiff base
4,4′‐[benzene‐1,4‐diylbis(methylylidenenitrilo)]dibenzoic
acid (H2bdda) as an organic linker under ultrasound
irradiation. Notably, UoB‐2 is demonstrated as a highly
active heterogeneous catalyst to promote benzyl alcohol
oxidation and as well as the cascade reaction of
oxidation–Knoevenagel condensation under mild
conditions. Moreover, the catalyst could be easily
recovered and reused for a number of times without
significant loss in activity.
2.1 | Preparation of Schiff Base ligand
(H2bdda)
To a solution of terephthaldehyde (1 mmol, 268 mg) in
EtOH was added gradually a solution of 4‐aminobenzoic
acid (2 mmol, 137 mg) in EtOH (10 ml) at room
temperature under magnetic stirring. The reaction
mixture was maintained under the same conditions for
60 min. After that, the yellow crystalline precipitate of
H2bdda was filtered, washed with EtOH three times and
then dried in an oven under vacuum. The structural
assignments of the synthesized Schiff base were based
on FT‐IR, CHN, 1H NMR and 13C NMR data. Anal. Calcd
for H2bdda (C22H16N2O4) (%): C, 70.96; H, 4.33; N, 7.23;
found: C, 70.30; H, 4.46; N, 7.23. FT‐IR (KBr pellet,
selected bands, ν, cm−1): 1681 s, 1623 w, 1585 s, 1422 m,
2 | EXPERIMENTAL
Terephthalaldehyde (CAS no. 623–27‐8; 99% purity), 4‐
aminobenzoic acid (CAS no. 150–13‐0; ≥99% purity) and
all solvents and reagents were obtained from Sigma‐
1
1288 m, 1265 m. HNMR (DMSO, δ, ppm): 6.555 (d, 2H,
3
3JHH = 8.8 Hz, Ar), 7.400 (d, 2H, JHH = 8.4 Hz, Ar),

ARYANEJAD ET AL.
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3
7.626 (d, 2H, JHH = 8.4 Hz, Ar), 8.025 (d, 2H,
3 | RESULTS AND DISCUSSION
3JHH = 8.4 Hz, Ar), 8.080 (d, 1H, JHH = 8.4 Hz, Ar),
3
3
8.132 (s, 2H, CH═N), 8.188 (d, 1H, JHH = 8 Hz, Ar),
3.1 | Synthesis and characterization of
UoB‐2 nanostructure
8.776 (d, 1H, 3JHH = 8 Hz, Ar), 8.950 (d, 1H, 3JHH = 8 Hz,
Ar), 12.521 (b, COOH).
As shown in Scheme 1, the Schiff base ligand was prepared
by the condensation of terephthaldehyde and 4‐
aminobenzoic acid in EtOH at room temperature, which
was then used as an appropriate organic linker for the
novel MOF. The Ni‐MOF nanostructure was synthesized
by the combination of H2abdda with Ni(OAc)2 in water
at room temperature under ultrasonic irradiation. Elemen-
tal CHN and ICP analyses suggested a molecular formula
of Ni3(bdda)2(OAc)2⋅6H2O (calcd (%): C, 50.46; N 4.83; H,
3.89; Ni, 15.04), which reasonably agrees with the real
amounts (%) of C (50.64), N (4.83), H (3.89) and Ni (14.04).
TGA was performed at a heating rate of 10 °C min−1 in
nitrogen atmosphere over a range of 20–700 °C for
investigation of the thermal behaviour of UoB‐2
(Figure 1). The recorded curve showed the following two
marked and well‐separated weight loss steps: a first weight
loss of 9.19% (calcd: 9.46%) from 45 to 250 °C, which can be
ascribed to removal of water molecules, then followed by
2.2 | Preparation of Ni‐MOF (UoB‐2)
At first, H2bdda (1 mmol, 0.372 g) was sonicated in NaOH
(10%, 1 ml)–deionized water (20 ml) to obtain a yellow
and a clear solution. For a period of 15 min, a solution
of nickel acetate (2 mmol, 0.353 g) in deionized water
(10 ml) was added dropwise to the solution of H2bdda at
room temperature under ultrasonic irradiation. The
reaction mixture remained in the sonicator under the
same conditions for 30 min. The resulting light‐green
crystalline material was isolated by centrifugation and
washed with water. Finally, Ni3(bdda)2(OAc)2⋅6H2O
(UoB‐2) was obtained after drying for 5 h at 100 °C.
2.3 | General procedure for benzyl alcohol
oxidation
A mixture of benzyl alcohol (2 mmol), tert‐butyl
hydroperoxide (TBHP; 2 mmol) and UoB‐2 (2 mol%)
was stirred at 65 °C for an appropriate time in solvent‐free
conditions to afford the corresponding aldehyde. After
cooling the reaction mixture to room temperature, UoB‐
2 was separated by centrifuging followed by washing
several times with EtOAc. It was then dried and reused
for the next run.
SCHEME 1 Synthesis of UoB‐2 nanostructure from Schiff base as
organic linker
2.4 | General procedure for benzyl alcohol
oxidation–Knoevenogel reaction
A mixture of benzyl alcohol (2 mmol), TBHP (2 mmol)
and UoB‐2 (2 mol%) was stirred at 65 °C for an
appropriate time under solvent‐free conditions. After
completion of the reaction, the reaction mixture was
allowed to cool to room temperature. Then, an ethanolic
solution (1 ml) of malononitrile (1 mmol) was added to
the mixture and stirred for an additional appropriate time
at room temperature to afford the corresponding
products. At the end of the reaction, UoB‐2 was recovered
by centrifugation, then washed several times with EtOAc,
dried and reused for the next run under the same reaction
conditions. After evaporation of the solvent under
vacuum, the crude product was exposed to silica gel plate
chromatography eluted with n‐hexane–EtOAc (3:1) to
afford pure product.
FIGURE 1 TGA curve of UoB‐2 catalyst

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ARYANEJAD ET AL.
the strong and broad band at 3450 cm−1 was attributed
to the stretching vibrations of coordinated water
molecules. Also, the band at 1697 cm−1 established the
presence of a coordinated acetate ligand. There were two
strong bands at 1594 and 1396 cm−1 due to the
asymmetric and symmetric vibrations of the COO groups.
It should be noted that the values of Δν (Δν = νas(COO) −
νs(COO)) for metal carboxylates are a powerful tool for
classifying coordination modes.[37] According to this, the
carboxylate group binds in a monodentate fashion if
Δν(COO) of the complex is much greater than that of
the ligand; a bidentate coordination is present if Δν(COO)
is significantly less than that of the ligand; and bridging
can be considered when close to the ionic values.
Therefore, the observed Δν values for Ni‐MOF
nanostructure indicated a bridging coordination mode
for the carboxylate groups.
The details of the nanostructure of the synthesized
UoB‐2 were determined from TEM images as shown in
Figure 3. The TEM images indicated clearly that UoB‐2
nanostructure consisted of roughly spherical particles
with uniform morphology. Also, the TEM images
revealed no amorphous component in the synthesized
nanostructure.
In order to investigate the surface area, pore volume
and pore structure of UoB‐2, standard N2 adsorption–
desorption measurements were carried out at 77 K, as
shown in Figure 4. It can be seen that UoB‐2 featured a
type IV isotherm which is typical for mesoporous
materials.[38] The BET surface area was found to be
FIGURE 2 FTIR spectra of (a) ligand and (b) UoB‐2
another weight loss of 41.83% at 420 °C, which can be
related to the decomposition of the organic parts.
118 m2 −1. The total pore volume was estimated as
g
0.28 cm3 g−1 at relative pressure P/P0 = 0.95 single point.
The mesopore size distribution curve, calculated from
Barrett–Joyner–Halenda analysis, displayed an average
pore diameter distribution at 9.44 nm (Figure 4, inset).
Despite the very best efforts, the size of the crystallites
was too small for single‐crystal structure determination.
The FT‐IR spectra of UoB‐2 nanostructure and Schiff
base ligand are shown in Figure 2. A comparison of these
FT‐IR spectra displayed clearly a significant spectral shift
of the carboxylate group that confirmed the coordination
of Schiff base ligand to metal. In the spectrum of UoB‐2,
FIGURE 3 TEM images of UoB‐2 nanostructure

ARYANEJAD ET AL.
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which indicated the presence of a crystalline structure.
Also, the pattern of UoB‐2 was very similar to the
simulated pattern reported for IRMOF‐74‐IV,[39]
confirming the formation of isostructural MOF.
3.2 | Oxidation of benzyl alcohol
One of the most important chemical transformations in
industrial and modern chemistry is the selective catalytic
oxidation of alcohols to the corresponding carbonyl
compounds, so there is considerable interest in the
development of environmentally benign, high‐perfor-
mance and safe heterogeneous catalysts for alcohol
oxidation.
To evaluate the catalytic activity of UoB‐2, the
selective oxidation of benzyl alcohol was chosen as a
model reaction for optimization of reaction conditions.
As a preliminary experiment, the model reaction under
neat conditions did not proceed in the absence of the
catalyst. Therefore, the use of an effective catalyst for
the promotion of benzyl alcohol oxidation is essential.
The effect of solvent was investigated using solvents
such as water, EtOH, EtOAc and CH3CN and also
under solvent‐free conditions. As shown in Figure 6,
the solventless condition is ideal for this selective oxida-
tion. In the absence of any solvent, the influence of
temperature on the catalytic performance was also
examined for this reaction system (Figure 7). The con-
version to benzaldehyde was significantly increased with
increasing reaction temperature from room temperature
to 65 °C, but using higher temperature decreased in the
selectivity of the reaction. In the screening of various
catalyst amounts, the presence of 2 mol% UoB‐2 was
sufficient for excellent conversion (Figure 8). A similar
reaction was performed in the presence of Ni(OAc)2,
FIGURE 4 Adsorption–desorption isotherm (inset showing the
pore width) of UoB‐2
Therefore the further investigation of the structure of
UoB‐2 was not possible. However, the powder X‐ray
diffraction pattern of this material is shown in Figure 5,
FIGURE 5 X‐ray diffraction patterns of (a) UoB‐2 and (b)
IRMOF‐74‐IV
FIGURE 6 Screening of solvent for oxidation reaction with molar
ratio of benzyl alcohol:TBHP = 1:2 and UoB‐2 (2 mol%), 65 °C

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ARYANEJAD ET AL.
FIGURE 9 Screening of TBHP amount for the oxidation reaction
with molar ratio of benzyl alcohol:TBHP = 1:X and UoB‐2 (2 mol%),
solvent free, 65 °C, 75 min
FIGURE 7 Screening of temperature for oxidation reaction with
molar ratio of benzyl alcohol:TBHP = 1:2 and UoB‐2 (2 mol%),
solvent free, 75 min
FIGURE 10 Screening of different oxidants for the oxidation
reaction of benzyl alcohol:oxidant = 1:2 and UoB‐2 (2 mol%),
solvent free, 65 °C, 75 min
FIGURE 8 Screening of catalyst amount for the oxidation
reaction with molar ratio of benzyl alcohol:TBHP = 1:2, solvent
free, 65 °C, 75 min
heterogeneous nature of UoB‐2, the hot leaching test
was carried out for benzyl alcohol oxidation in EtOAc
as solvent at 65 °C. For this experiment, the catalyst
was separated after 50% of the reaction time and the
remaining solution was stirred in the absence of UoB‐
2 for an additional 6 h. The result indicated that no fur-
ther increase in either the conversion or selectivity
occurred in the absence of the catalyst. For further con-
firmation, ICP analysis of the remaining solution exhib-
ited a negligible amount of Ni in the reaction mixture.
This finding established that UoB‐2 is a typical hetero-
geneous catalyst (Figure 11).
and the reaction proceeded only 30% after 75 min. The
oxidation of benzyl alcohol with UoB‐2 was examined
in solvent‐free conditions at 65 °C for determining the
amount of oxidant (Figure 9). The model reaction was
also studied in the presence of different oxidants with
2 mol% of the catalyst at 65 °C under solvent‐free
conditions (Figure 10). The results of this study
suggested that TBHP gave the highest conversion of
benzaldehyde.
One of the special properties of MOFs is the stability
of the framework under reaction conditions, which
leads to a decrease of the percentage of metal leaching
into the organic solution and preservation of the hetero-
geneous nature of the system. In order to evaluate the
The reusability of a heterogeneous catalyst is very
significant, particularly in industrial and chemical
applications. Accordingly, the recyclability and reusability
of UoB‐2 were investigated in the oxidation of benzyl

ARYANEJAD ET AL.
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TABLE 1 UoB‐2‐catalysed oxidation reaction of various alcoholsa
Entry Substrate
Product
Time (h) Yield (%)b
1
1
95
90
85
85
2
3
4
2
1.5
1.5
FIGURE 11 Hot leaching test for benzyl alcohol oxidation
reaction using UoB‐2 under optimized conditions
5
1
85
alcohol with TBHP under the optimized reaction
conditions. After each run, the catalyst was separated
easily from the ethanolic reaction solution by
centrifuging. Then, the catalyst was washed with EtOH,
dried for 1 h at 100 °C and used for the next run under
the same reaction conditions. The stability of UoB‐2, as
well as the ease of recovery, permitted the catalyst to be
recovered and reused effectively for at least four runs
without significant loss of its activity (Figure 12). A
comparison of the FT‐IR spectra of used UoB‐2 and fresh
catalyst indicated that the structure of the catalyst
remained substantially unchanged after four runs.
To explore the scope of this method, the oxidation
reaction of a series of substituted benzyl alcohols was
studied under optimal reaction conditions (Table 1). The
results indicated clearly that the oxidation of different
benzyl alcohols regardless of the types and position of
the substituted functional groups proceeded with
excellent conversion and reasonable selectivity in the
presence of UoB‐2.
6
7
1.5
1.5
91
92
8
2
2
2
90
93
87
9
10
aReaction conditions: alcohol (1 mmol), TBHP (2 mmol), UoB‐2 (2 mol%) at
65 °C and solvent‐free.
bIsolated yield.
3.3 | Benzyl alcohol oxidation–
Knoevenagel reaction
Knoevenagel condensation is one of the most well‐known
carbon–carbon bond coupling reactions which has been
widely utilized for the preparation of a range of
substituted olefins, coumarin derivatives,[40] cosmetics,[41]
perfumes[42] and pharmaceutical chemicals.[43] Therefore,
the catalytic behaviour of UoB‐2, in addition to oxidation
of alcohols, was investigated in Knoevenagel
condensation. To a solution of benzaldehyde (1 mmol)
in EtOH, malononitrile (1 mmol) was added and stirred
in the presence of 3 mol% UoB‐2. After 30 min, the
reaction was completed and afforded the desired product.
From this observation combined with the obtained results
FIGURE 12 Recycling potential of UoB‐2

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ARYANEJAD ET AL.
TABLE 2 One‐pot oxidation–Knoevenagel cascade reaction with
various substrates catalysed by UoB‐2a
of the oxidation reaction, it could be concluded that the
Ni‐MOF nanostructure could be a bifunctional catalyst.
In other words, UoB‐2 could catalyse benzyl alcohol
oxidation and the following Knoevenagel reaction in a
successive manner.
Time
(min)b
Yield
(%)c
Entry Substrate
Product
1
90
45
45
30
94
91
93
93
2
3
4
5
6
7
8
30
45
45
45
95
88
91
93
FIGURE 13 Hot leaching test for benzyl alcohol oxidation–
Knoevenagel reaction using on UoB‐2
9
45
45
92
93
10
11
12
75
60
80
83
13
60
80
aReaction conditions. First step: various substituted benzyl alcohols (1 mmol),
TBHP (2 mmol), UoB‐2 (2 mol%), 65 °C; second step: active methylene com-
pound (1 mmol), EtOH (1 ml), room temperature.
bTime of Knoevenagel reaction.
cIsolated yield.
FIGURE 14 FT‐IR spectra of (a) fresh UoB‐2, (b) after four
recycles in alcohol oxidation and (c) after four recycles in cascade
reaction. Right: TEM image of UoB‐2 after four catalytic runs in
cascade reaction

ARYANEJAD ET AL.
9 of 11
For this investigation, benzyl alcohol in the presence
activated and deactivated benzyl alcohols with
malononitrile. In addition to malononitrile, ethyl
cyanoacetate as the active methylene compound was
examined in oxidation–Knoevenagl reaction. The
results the examination demonstrated that the desired
products were obtained in good yields (Table 2, entries
11–13). It should be noted that the condensation reac-
tion between carbonyl compound and ethyl
cyanoacetate was somewhat slow compared to the reac-
tion with malononitrile because malononitrile is more
reactive than ethyl cyanoacetate.
After the confirmation that UoB‐2 nanoparticles were
active for the given cascade reaction, the recyclability of
the catalyst was investigated. Ni‐MOF nanoparticles can
be easily recovered and reused for the promotion of the
cascade reaction. As shown in Figure 12, the activity of
of UoB‐2 was stirred with TBHP at 65 °C. After
completion of the reaction, the mixture was allowed to
cool to room temperature. Then, an ethanolic solution of
malononitrile was added to the system and was stirred
again for 30 min at room temperature to afford
benzylidene malononitrile with excellent yield.
In order to extend the generality of this method,
the efficiency of UoB‐2 for a selective oxidation–
Knoevenagl reaction of various benzyl alcohols was
examined under the same conditions. The results are
presented in Table 2, confirming the effectiveness of
UoB‐2 in simplifying oxidation–Knoevenagl reaction to
afford
corresponding
substituted
benzylidene
malononitriles based on a cascade reaction. Also, this
heterogeneous catalytic system was effective for both
SCHEME 2 Proposed mechanism for
Knoevenagel condensation using UoB‐2
nanocatalyst
TABLE 3 Comparison of catalytic activity in oxidation–Knoevenagel reaction with previously reported catalysts
Yield (%)
Catalyst
amount Conditions
Time
(h)
Benzylidene
Benzaldehyde malononitrile Ref.
Entry Catalyst
[48]
1
2
3
4
5
6
7
8
9
Zr‐MOF‐NH2
100 mg
100 mg
100 mg
p‐xylene/O2/UV irradiation
48
48
48
2
91
7
[48]
[48]
[49]
[49]
[49]
[50]
[51]
Zn‐MOF‐NH2
Ti‐MOF‐NH2
p‐xylene/O2/UV irradiation
p‐xylene/O2/UV irradiation
28
51
5
32
72
4.6
3.3
95
99
94
NH2‐MIL‐101(Fe) 20 mg
NH2‐UiO‐66(Zr) 20 mg
NH2‐MIL‐125(Ti) 20 mg
Cu3TATAT‐3a
Au@cu(II)‐MOF
UoB‐2
Trifluorotoluene/O2/UV irradiation 40
CH3CN/O2/70 °C
40
40
12
22
1.5
29
39
0
CH3CN/O2/70 °C
8 mol%
3 mol%
2 mol%
CH3CN/O2/75 °C
Toluene–MeOH/O2/110 °C
Solvent‐free/EtOH/TBHP
98
95
This work
aH6TATAT = 5,5′,5″‐(1,3,5‐triazine‐2,4,6‐triyl)tris(azanediyl)triisophthalate.

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ARYANEJAD ET AL.
the catalyst was not changed significantly after the fourth
catalytic run. In order to gain insight into the
4 | CONCLUSIONS
heterogeneous nature of UoB‐2,
a
hot leaching
We carried out the synthesis and characterization of a
novel Ni‐MOF nanostructure (UoB‐2) using a new Schiff
base ligand (H2bdda) obtained under ultrasound
conditions. UoB‐2 exhibited high catalytic performance
for benzyl alcohol oxidation and Knoevenagel
condensation as a cascade reaction. This heterogeneous
catalyst was used in both reaction steps leading to high
yield under ambient conditions, being environmentally
benign. UoB‐2 can be recovered and reused for four runs
without a significant loss in its activity. Most significantly,
the ability of catalyst for performing the one‐pot cascade
reaction, with a decrease in production wastes and energy
consumption, should be advantageous, and it could be a
potential catalyst for applications in chemical industry.
experiment was carried out. For this, after 50% of the
reaction time of benzyl alcohol with malononitrile,
the mixture was centrifuged to remove the solid catalyst.
The reaction was continued in the absence of UoB‐2 for
an additional 4 h. As indicated in Figure 13, no further
increase in the conversion was detected, confirming the
catalysis was heterogeneous in nature. In addition, the
FT‐IR spectrum and TEM image of the reused UoB‐2
illustrated the retention of its structural integrity
(Figure 14). According to the obtained results from the
hot leaching test, FT‐IR spectrum and TEM, the minor loss
of the activity of UoB‐2 in the given cascade reaction is
probably owing to the loss of solid during the separation
process.
As the results show, the title methodology is
economical and industrially important by reason of its
being a one‐pot cascade reaction under solvent‐free
conditions and in ethanol as a safe reaction medium.
Also, UoB‐2 has potential industrially because of its reus-
ability as an active catalyst. Therefore, it is expected that
this method is readily scalable. For testing the potential
ACKNOWLEDGEMENT
The authors are grateful to the University of Birjand for
financial support.
ORCID
practicality, under
a
semi‐scaled‐up procedure
Ghodsieh Bagherzade http://orcid.org/0000-0002-7417-2214
Alireza Farrokhi http://orcid.org/0000-0003-2015-7841
(10.0 mmol) benzylidene malononitrile was obtained in
78% yield in the one‐pot cascade reaction of benzyl
alcohol with malononitrile in the presence of UoB‐2
within 90 min.
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How to cite this article: Aryanejad S,
Bagherzade G, Farrokhi A. Efficient and recyclable
novel Ni‐based metal–organic framework
nanostructure as catalyst for the cascade reaction of
alcohol oxidation–Knoevenagel condensation. Appl
Organometal Chem. 2017;e3995. https://doi.org/
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