Nickel containing ionic liquid based ordered nanoporous organosilica: A powerful and recoverable catalyst for synthesis of polyhydroquinolines

Article abstract of DOI:10.1039/c7ra10758g

A novel nickel containing alkyl-imidazolium ionic liquid based ordered mesoporous organosilica (Ni@IL-OMO) is prepared, characterized and applied as an efficient nanocatalyst in the one-pot synthesis of polyhydroquinolines through the Hantzsch reaction. T

Full text of DOI:10.1039/c7ra10758g

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Nickel containing ionic liquid based ordered
nanoporous organosilica: a powerful and
recoverable catalyst for synthesis of
polyhydroquinolines
Cite this: RSC Adv., 2017, 7, 54789
a
Hamideh Khanmohammadia and Davar Elhamifarbc
*
Dawood Elhamifar,
A novel nickel containing alkyl-imidazolium ionic liquid based ordered mesoporous organosilica (Ni@IL-
OMO) is prepared, characterized and applied as an efficient nanocatalyst in the one-pot synthesis of
polyhydroquinolines through the Hantzsch reaction. The Ni@IL-OMO was prepared via immobilization of
nickel chloride on IL-OMO at room temperature. This was characterized using transmission electron
microscopy (TEM), FTIR-spectroscopy, nitrogen adsorption–desorption analysis, scanning electron
microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The polyhydroquinolines were
obtained in high to excellent yield and selectivity in the presence of a low loading of Ni@IL-OMO with
short reaction times. This catalyst was recovered and reused several times while keeping its efficiency
under the applied conditions. The recovered catalyst was analyzed by TEM to study its structural stability
during reaction process.
Received 28th September 2017
Accepted 22nd November 2017
DOI: 10.1039/c7ra10758g
rsc.li/rsc-advances
organosilica supported metal catalysts and studied their appli-
cations in a set of different organic processes.21–24 These showed
1. Introduction
highly performance and stability under applied reaction
conditions.
The use of ordered mesoporous organosilicas (OMOs) as
supports in organic transformations is a valuable concept
among chemists due to the high surface area, excellent stability
and good selectivity of these materials.1–3 Especially, OMO-
supported transition metals are more interesting owing to
their widespread catalytic applications in several organic
processes such as C–C bond formation.3–6 Among these, metal
containing periodic mesoporous organosilicas (M@PMOs) are
more attractive due to the advantages of PMOs such as high
lipophilicity, high thermal and mechanical stability, and easy
diffusion of organic substrates in the mesochannels of these
noble materials.7,8 M@PMOs are prepared via impregnation of
metallic salts with PMO nanomaterials and/or by simultaneous
hydrolysis and condensation of metal/ligand complexes with
PMO precursors under acidic or basic conditions.7–14 Address-
ing some of these issues in the context of green manufacturing,
several M@PMOs such as V@PMO, Cu@PMO,7,15 Co@PMO,7,16
Pd@PMO,17 Rh@PMO,18 Ru@PMO,7,17b,18 Au@PMO,7,17b
Mo@PMO,19 Fe@PMO,20 Sn@PMO,7,15b and Mn@PMO7 have
been prepared and applied as effective nanocatalysts in
a number of organic transformations. More recently we have
also prepared some ionic liquid based periodic mesoporous
On the other hand, since discover of the Hantzsch reaction
in the organic synthesis, many strategies have been developed
for this important process due to its key role in the formation of
biologically active and pharmacology useful compounds.25–28
This reaction usually is performed via one-pot condensation of
aldehydes, alkylacetoacetates and amines in the presence of
both Lewis and Brønsted acid catalysts.25–27 To date a lot of
catalysts such as TMSI, Yb(OTf)3, cerium(IV) ammonium nitrate,
Bu4NHSO4, ionic liquids, bismuth(III) bromide and boronic
acids have been reported for this process under homogeneous
conditions.29–36 However, due to problems concerted to homo-
geneous catalytic systems such as separation and purication of
desired products and catalyst recovery, a lot of heterogeneous
catalysts with advantages of easy recoverability and reusability
have been recently used for the production of poly-
hydroquinolines via Hantzsch reaction.37–48 Some of developed
heterogeneous systems include supported metallic and organic
catalysts on the surfaces of polymer, silica, carbon and
alumina.37–48 In continuous of aforementioned studies and
according to importance of PMOs in catalytic processes,49–51
herein, for the rst time the nickel chloride is immobilized
onto/into an ionic liquid based ordered mesoporous organo-
silica to prepare a novel nanocatalyst named Ni@PMO-IL. This
catalyst was easily and successfully prepared at room tempera-
ture in DMSO solvent via impregnation method (Scheme 1). The
aDepartment of Chemistry, Yasouj University, Yasouj, 75918-74831, Iran. E-mail: d.
elhamifar@yu.ac.ir
bDepartment of Chemical Engineering, Isfahan University, Isfahan, Iran
cMehr Petrochemical Company, Phase 2 of PSEEZ, Assaluyeh, Bushehr, Iran
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Scheme 1 Preparation of Ni@IL-OMO nanocatalyst.
Ni@PMO-IL catalyst was characterized using several techniques
including TEM, nitrogen adsorption–desorption analysis, FT-
IR-spectroscopy, SEM and EDX. The catalytic performance of
Ni@PMO-IL was developed in the one-pot Hantzsch synthesis of
different polyhydroquinolines. The study showed that the
catalyst is very active in the preparation of a set of different
polyhydroquinoline derivatives under solvent-free media as well
as it is highly recoverable and stable under applied reaction
conditions.
2.3. Procedure for the recovery of Ni@IL-OMO in the
Hantzsch reaction
To do this, the reaction of benzaldehyde, dimedone, ethyl-
acetoacetate and ammonium acetate was selected as a test
model. Aer the reaction was completed in the presence of
catalyst, hot ethanol (10 mL) was added and the obtained
mixture was hotly ltered. The catalyst was washed carefully
with ethanol and dried at 70 ꢀC. The recovered catalyst was
reused in another reaction charged with starting materials in
the same amounts as the rst run. These steps were repeated
several times and it was observed that the catalyst could be
recovered and reused at least 9 times with keeping its efficiency.
2. Experimental section
2.1. Preparation of Ni@IL-OMO nanocatalyst
Firstly, ionic liquid based mesoporous organosilica (IL-OMO)
was prepared according to our recent reported procedure with
a slight modication.21–24 The IL-OMO was then used as support
material as following: typically, 1 g of IL-OMO was added into
DMSO (20 mL) and stirred at room temperature. Aer uniform
distribution of IL-OMO, a DMSO solution of NiCl2$6H2O (2
mmol) was added to the reaction vessel and stirred at room
temperature for 24 h. Aer that, the reaction mixture was
ltered and washed completely with DMSO to remove unreacted
nickel chloride complex. The obtained solid was then dried at
70 ꢀC for 12 h to deliver a powder material called Ni@IL-OMO.
The loading of the nickel was obtained to be 0.6 mmol gÀ1 by
the means of the Ni-content obtained from inductively coupled
plasma/optical emission spectroscopy (ICP-OES).
2.4. Procedure for the hot ltration test
This test was also performed on the condensation reaction of
benzaldehyde, dimedone, ethylacetoacetate and ammonium
acetate in the presence of Ni@IL-OMO. Aer about 40 mol% of
reaction was completed, it was stopped and 10 mL of hot EtOH
was added. This was ltered to remove heterogeneous catalyst.
The solvent of ltrate was removed and the residue was allowed
to continue under standard reaction as above. Interestingly,
aer about 2 h, only a little conversion (<5%) was observed
indicting the catalyst operates in a heterogeneous pathway.
2.2. Synthesis of Hantzsch products in the presence of
Ni@IL-OMO nanocatalyst
For this, aldehyde (1 mmol), dimedone (1 mmol), ethyl/
methylacetoacetate (1 mmol) and ammonium acetate
(1.5 mmol) were mixed in a reaction vessel and 0.5 mol percent of
Ni@IL-OMO nanocatalyst was added to the mixture. This was
stirred at 70 ꢀC without solvent for an appropriate time indicated
in Table 2. Aer the reaction was completed, it was stopped and
hot ethanol (10 mL) was added. The obtained mixture was hotly
ltered to remove heterogeneous Ni-based catalyst. Then, some
ice species were added into ltrate to precipitate or crystallize of
desired crude products. The pure products were obtained aer
recrystallization of crude ones in EtOH.
Fig. 1 FTIR spectrum of Ni@IL-OMO nanocatalyst.
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Fig. 2 TEM image of Ni@IL-OMO nanocatalyst.
3. Results and discussion
Fig.
nanocatalyst.
4
The BJH pore size distribution isotherm of Ni@IL-OMO
The nickel-containing ionic liquid based ordered mesoporous
organosilica was prepared by treatment of Ni(Cl)2$6H2O with IL-
OMO in DMSO at room temperature (Scheme 1).
corresponded to stretching vibration of C–Si bonds. These data
successfully conrm well incorporation and immobilization of
ionic liquid groups in the material network.
TEM image of the nickel-containing IL-OMO was performed
to study mesoporosity of the material (Fig. 2). This image
showed a hexagonally ordered mesoporous structure with high
regularity in the framework for the material. This is character-
istic of SBA-15-type materials and conrms high mesoporosity
and structure order of the material.
The nitrogen adsorption–desorption analysis showed a type
IV isotherm with H1 hysteresis loop (Fig. 3). According to this
analysis, the BET surface area and pore volume were, respec-
tively, 565 m2 gÀ1 and 0.91 cm3 gÀ1. The BJH pore size distri-
bution isotherm of the catalyst illustrated a sharp peak centered
at mean pore diameter of 7.5 nanometer (Fig. 4). These results
The Ni@IL-OMO was rstly characterized by FTIR-
spectroscopy to show the presence of expected organic func-
tional groups in the material framework (Fig. 1). The strong
signals cleared at 1074 and 965 cmÀ1 are assigned to asym-
metric and symmetric stretching vibrations of Si–O–Si bonds.
The peaks of 2952 and 3052 cmÀ1 are assigned, respectively, to
aliphatic and aromatic C–H stretching vibrations of the propyl-
imidazolium moieties. The C]N and C]C stretching vibra-
tions of imidazolium ring are observed, respectively, at 1636
and 1565 cmÀ1. The broad peak cleared about 3392 cmÀ1 is also
attributed to O–H stretching vibration of material surface.
Moreover, the other signals observed at 700–900 cmÀ1 are
Fig. 3 The nitrogen adsorption–desorption isotherms of Ni@IL-OMO
nanocatalyst.
Fig. 5 SEM image of Ni@IL-OMO nanocatalyst.
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immobilization, the signals of oxygen, silicon, nitrogen, chlo-
rine and carbon were observed (Fig. 6a). While for Ni@IL-OMO
(Fig. 6b), the signal of Ni was also seen conrming successful
incorporation and/or immobilization of ionic liquid and nickel
complex moieties into/onto material framework.
The loading of nickel was calculated using Ni-content ob-
tained from inductively coupled plasma/optical emission spec-
troscopy (ICP-OES) and also EDX analysis. The result of these
two techniques were in good agreement with each other and
showed a loading of 0.6 mmol gÀ1 (3.5% wt) for nickel.
Aer characterization, the catalytic application of Ni@IL-
OMO nanocatalyst was investigated in the one-pot Hantzsch
condensation of benzaldehyde, ammonium acetate, ethyl-
acetoacetate and dimedone as a test model. The effect of several
parameters such as temperature, solvent, and catalyst loading
was studied to obtain optimal conditions (Table 1). The study
showed that in the absence of catalyst only a trace amount of
product was obtained, while in the presence of 0.2 and
0.35 mol% of catalyst, respectively, low to moderate yield was
delivered (Table 1, entries 1–3). Interestingly, using 0.5 mol% of
Ni@IL-OMO at 70 ꢀC an excellent yield of corresponding
Hantzsch product was obtained at very short reaction time
(Table 1, entry 4). The solvent effect also illustrated that in
toluene low yield, in EtOH and DMF moderate yield, while
under solvent-free media excellent yield was achieved under the
same reaction conditions (Table 1, entry 4 versus entries 5–7). It
Fig. 6 Energy-dispersive X-ray (EDX) spectrum of (a) IL-OMO and (b)
Ni@IL-OMO nanomaterials.
ꢀ
is also important to note that at 25 and 50 C low to moderate
conversion whereas at 70 ꢀC excellent conversion of starting
material were obtained (Table 1, entry 4 versus entries 8 and 9).
To show the neat effect of supported nickel species in the
catalytic process, the efficiency of Ni-free IL-OMO nanomaterial
was next studied and the result compared with that of Ni@IL-
OMO (Table 1, entry 4 versus entry 10). Interestingly, the latter
case yielded only 18% of desired product indicating the main
catalytic process is affected by supported nickel species.
According to these results, the use of 0.5 mol% Ni@IL-OMO
nanocatalyst under solvent-free media at 70 ꢀC were selected
as optimum conditions.
are in good agreement with TEM image and conrm the pres-
ence of well-ordered mesostructure for the material.
The SEM image of the Ni@IL-OMO nanocatalyst also showed
the presence of particles with uniform morphology and size
(Fig. 5) that is an advantage of the material especially in the
catalytic and adsorption processes.
The high stability and successful immobilization of ionic
liquid groups and Ni-complex were next conrmed by energy-
dispersive X-ray (EDX) spectrum (Fig. 6). Before nickel
In the next stage the efficiency of the present catalyst was
studied in the Hantzsch condensation of different aldehydes
Table 1 Effect of temperature, type of catalyst, catalyst loading and
with
ammonium
acetate,
dimedone
and
ethyl/
solvent in the Hantzsch reactiona
methylacetoacetate (Table 2).
This demonstrated that the Ni@IL-OMO can convert
aromatic aldehydes containing both electron donating and
electron-withdrawing substituents to corresponding Hantzsch
products under the same conditions and short times. The
aliphatic aldehydes such as isobutylaldehyde also delivered
corresponding adduct in good yield. These results successfully
conrm potent efficiency of the present catalyst for the
production of different polyhydroquinoline derivatives appli-
cable in pharmacology and medical sciences.
The recoverability and reusability of the catalyst were then
studied to show its stability under applied conditions (Fig. 7).
For this, aer reaction was completed, hot ethanol was added to
the reaction vessel and obtained mixture was centrifuged to
precipitation of catalyst. The supernatant solution was removed
and the catalyst was recovered and reused in the next run under
Catalyst loading Temperature
(mol%)
Yieldb
Solvent (%)
Entry Catalyst
(ꢀC)
1
2
3
4
5
6
7
8
9
10
No catalyst
—
70
70
70
70
70
70
70
50
25
70
—
—
—
—
EtOH
DMF
<5
25
55
96
68
44
Ni@IL-OMO 0.2
Ni@IL-OMO 0.35
Ni@IL-OMO 0.5
Ni@IL-OMO 0.5
Ni@IL-OMO 0.5
Ni@IL-OMO 0.5
Ni@IL-OMO 0.5
Toluene 23
—
—
—
55
20
18
Ni@IL-OMO 0.5
c
IL-OMO
—
a
Conditions: benzaldehyde (1 mmol), dimedone (1 mmol),
ethylacetoacetate (1 mmol) and ammonium acetate (1.5 mmol),
15 min. b Isolated yields. c The same mg as Ni@IL-OMO was used.
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Table 2 Preparation of polyhydroquinolines in the presence of Ni@IL-OMO catalyst under solvent free conditionsa
Entry
R1
R2
Product
Time (min)
Yieldb (%)
Mp (ꢀC)
1
C6H5
OEt
15
96
202–204
2
2-CH3C6H5
OEt
20
95
205–208
3
4
5
4-CH3OC6H5
3-NO2C6H5
2-ClC6H5
OMe
OMe
OMe
OMe
15
10
20
25
95
92
86
72
260–261
235–237
212–214
200–202
6
(CH3)2CH
a
Conditions: aldehyde (1 mmol), dimedone (1 mmol), methyl/ethylacetoacetate (1 mmol), ammonium acetate (1.5 mmol) and catalyst (0.5 mol%).
Isolated yields.
b
the same conditions as the rst run. The result showed that this was performed in the reaction of benzaldehyde, dimedone,
could be recovered and reused at least 9 times without signi- ethylacetoacetate and ammonium acetate. For this, aer about
cant decrease in its efficiency.
40% completion of the reaction, hot ethanol was added and the
To illustrate whether the catalyst operates in a homogeneous obtained mixture was hotly ltered. Then the solvent of ltrate
or heterogeneous manner, in the next study a hot ltration test was removed and the reaction of residue was allowed to
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continue under optimized conditions. Interestingly, aer 2 h
a conversion of only about 5% was observed. The atomic
adsorption of the ltrate also showed that the amount of nickel
species in the solution is lower than 1 ppm. These observations
successfully conrm high stability of the supported Ni-catalyst
under applied conditions and prove it works in a heteroge-
neous pathway. The TEM image of the recovered catalyst also
showed a well-ordered mesostructure with two dimensional
symmetry the same as its fresh parent (Fig. 8) indicating high
stability of material structure during reaction process.
In the next, a comparison study was performed between our
designed catalyst and recently reported heterogeneous catalytic
systems on the Hantzsch reaction (Table 3). The result showed
that the present catalytic system was better and/or comparable
with those of previous works. Especially, our work were
accomplished under solvent free media under moderate
conditions and the catalyst was more recoverable than previous
catalysts indicating high efficiency of ionic liquid based mate-
rial for powerful immobilization of active nickel centers.
Fig.
reaction.
7 Reusability of Ni@IL-OMO nanocatalyst in the Hantzsch
4. Conclusion
In summary, for the rst time a new ionic liquid based meso-
porous organosilica supported nickel complex (Ni@IL-OMO)
was prepared, characterized and used in the Hantzsch reac-
tion. The TEM and nitrogen-sorption analyses successfully
conrmed the presence of a uniform ordered mesostructure for
this catalyst. The IR and EDX spectroscopies also showed the
well incorporation of ionic liquid and nickel moieties in the
material network. This novel nanocatalyst demonstrated excel-
lent performance in the preparation of different derivatives of
polyhydroquinolines through Hantzsch reaction. The Ni@IL-
OMO was recovered at least nine times with keeping its effi-
ciency and stability under applied reaction conditions. Other
advantages of the present study were low loading and easy
recoverability of the catalyst, solvent-free conditions, easy work-
up and low reaction time. Accordingly, some applications of this
catalyst in other organic processes are underway in our
laboratory.
Fig. 8 TEM image of the recovered Ni@IL-OMO nanocatalyst in the
Hantzsch reaction.
Table 3 A comparison study between our designed catalyst and
recently reported heterogeneous catalytic systems on the Hantzsch
reaction
Recycling
Entry Catalyst
Conditions
times
References
Conflicts of interest
1
2
3
4
5
6
SnO2
nanoparticle
PPA–SiO2
SnO2 (1 mol%)
C2H5OH, r.t.
4
2
3
4
5
2
52
53
44
54
55
38
There are no conicts to declare.
a
Solvent-free
(1.5 mol%), 80 ꢀC
Acknowledgements
Ni0-nanoparticle Solvent free,
25 mg, r.t.
FeF3
The authors thank the Yasouj University and the Iran National
Science Foundation (INSF) for supporting this work.
FeF3 (5 mol%),
EtOH, 75–80 ꢀ
C
TiO2 nanoparticle TiO2 NPs (10 mol%)
EtOH, reux
References
ZnO
ZnO NPs (5 mol%)
solvent-free,
nanoparticle
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