Cross-Linked Polyamine from Imidazolium-Based Materials: A Simple Route to Useful Catalytic Materials

Article abstract of DOI:10.1002/ejoc.201800040

Cross-linked polyamine-based materials were easily prepared by reduction of the corresponding cross-linked imidazolium-based materials with sodium borohydride in hot ethanol. Overall, the synthetic procedure is based on the polymerization of a suitable bis-vinylimidazolium salt with or without a suitable support, such as silica or silica-coated magnetic nanoparticles (γ-Fe₂O₃@SiO₂), followed by reduction. This simple approach allows the synthesis of materials based on a network of secondary and tertiary amines. Materials were characterized by ¹³C cross-polarization magic angle spinning NMR (¹³C CPMAS NMR), proton spin-lattice relaxation times in the rotating frame (T_1ρH) and thermogravimetric analysis (TGA). Cross-linked polyamine-based materials were used as recoverable catalyst for Knoevenagel reaction. High yields of the condensation products were obtained and up to 11 cycles were carried out.

Full text of DOI:10.1002/ejoc.201800040

A Journal of
Accepted Article
Title: Cross-linked polyamine from imidazolium-based materials. A
simple route to useful catalytic materials
Authors: Michelangelo Gruttadauria, Vincenzo Campisciano, Anna
Maria Pia Salvo, Leonarda Francesca Liotta, Alberto Spinella,
and Francesco Giacalone
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201800040
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10.1002/ejoc.201800040
European Journal of Organic Chemistry
FULL PAPER
Cross-linked polyamine from imidazolium-based materials. A
simple route to useful catalytic materials
Vincenzo Campisciano,[a] Anna Maria Pia Salvo,[a] Leonarda Francesca Liotta,[b] Alberto Spinella,[c]
Francesco Giacalone,*[a] and Michelangelo Gruttadauria*[a]
Abstract: Cross-linked polyamine-based materials were easily
prepared by reduction of the corresponding cross-linked imidazolium-
based materials with sodium borohydride in hot ethanol. Overall, the
synthetic procedure is based on the polymerization of the proper bis-
research group has developed and tested different SILs materials
for a wide range of applications.[4] The advantage of such systems
relies in their very straightforward production and huge versatility
of application. We have successfully employed SILs as catalysts
vinylimidazolium salt with or without the presence of a suitable support, themselves for the fixation of CO2 into cyclic carbonates[5] and for
such as silica or silica coated magnetic nanoparticles (γ-Fe2O3@SiO2), etherification of benzylic alcohols,[6] as support material for
followed by reduction. This simple approach allows the synthesis of
materials based on a network of secondary and tertiary amines.
Materials were characterized by 13C Cross-Polarization Magic Angle
Spinning NMR (13C CPMAS NMR), proton spin-lattice relaxation times
in the rotating frame (T1ρH) and thermogravimetric analysis (TGA).
Cross-linked polyamine-based materials were used as recoverable
catalyst for Knoevenagel reaction. High yields of the condensation
products were obtained and up to 11 cycles were carried out.
different organo-[7] and metal-based catalysts,[8] and also as metal
scavenger.[9] Among SILs, those based on cross-linked bis-
imidazolium salts have shown to be the most promising materials.
Herein, we decided to exploit this useful class of materials as
source of highly cross-linked polymers with a high content of
amines following a straightforward approach. A series of poly-
imidazolium salts supported onto silica or silica coated magnetic
nanoparticles (γ-Fe2O3@SiO2), as well as a homopolymerized
bis-imidazolium salt, served as starting materials for the
preparation of the amine cross-linked polymers. The treatment of
cross-linked imidazolium based materials with a large excess of
sodium borohydride causes the reduction of the imidazolium
moieties and the subsequent rings opening,[10] producing highly
cross-linked polymers containing both secondary and tertiary
amines. Due to the presence of numerous amine groups, we
decided to employ the new obtained amine cross-linked polymers
as catalysts for the Knoevenagel condensation reaction.
Knoevenagel condensation reaction is widely employed in the
Introduction
Ionic liquids (ILs), especially those based on imidazolium salts,
can boast a remarkable number of applications in many fields of
chemistry.[1] The reason for such great interest in ILs is mainly due
to their advantageous combination of a series of unique properties
such as low vapor pressure, wide liquid range, lack of
inflammability, high ionic conductivity, and excellent thermal and
chemical stability. Furthermore, the possibility to anchor ILs onto
inert materials providing the so-called supported ionic liquids
(SILs), both physisorbed[2] or covalently[3] linked to a support
material, allows to increase the appeal of ILs in the light of the
advantages arising from the transferring of bulk properties of ILs
to the support material and the limitation of IL leaching in the case
of covalently functionalized support materials. Over the years, our
synthesis of electron-poor olefins and
a wide range of
pharmaceuticals and fine chemicals.[11] Moreover, the current
deep interest aroused by this kind of reaction is also witnessed by
the intense research efforts aimed to the development of different
heterogeneous catalysts for the Knoevenagel condensation as
alternative to homogenous catalysis. The Knoevenagel reaction
is usually catalysed by bases, such as organic amines, but can
be also catalysed by acids and catalysts containing both basic
and acidic sites.[12] The anchoring of organic amines onto a solid
support material is an efficient way to produce heterogeneous
catalysts for the Knoevenagel reaction but, just focusing on the
very recent reported examples concerning the heterogeneous
basic catalysis of Knoevenagel condensation reaction, it is
possible to enumerate a plethora of catalytic systems involving
the use of catalysts based on chitosan,[13] polyoxometalates,[14]
amine functionalized graphene oxide and MOF,[15] among
others.[16] Usually, the choice of the support material of
heterogeneous catalysts is mainly dictated by its robustness and
cost, as well as the ease of recovery and reuse of the obtained
catalyst. For the aforementioned reasons, among the different
solid materials, silica and magnetic nanoparticles are probably the
most employed supports for amine based heterogeneous
catalysts. However, the reported examples of heterogeneous
catalysts, supported either on silica[17] or magnetic support
[a]
Dr. V. Campisciano, Dr. A.M.P. Salvo, Dr. F. Giacalone, Prof. M.
Gruttadauria
Dipartimento Scienze e Tecnologie Biologiche, Chimiche e
Farmaceutiche (STEBICEF)
Università degli Studi di Palermo
Viale delle Scienze, Ed. 17, 90128 Palermo, Italy
E-mail: francesco.giacalone@unipa.it
michelangelo.gruttadauria@unipa.it
http://www.unipa.it/persone/docenti/g/michelangelo.gruttadauria
Dr. L. F. Liotta
Istituto per lo Studio dei Materiali Nanostrutturati ISMN-CNR
Via Ugo La Malfa 153, 90146 Palermo, Italy
Dr. A. Spinella
[b]
[c]
Centro Grandi Apparecchiature-ATeN Center
Università degli Studi di Palermo
Via F. Marini 14, 90128 Palermo, Italy
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejoc.201800040
European Journal of Organic Chemistry
FULL PAPER
materials,[18] concern on the use of supported primary amines or
hybrid systems based on the presence of different amines
(primary, secondary or tertiary) with the latter systems showing a
higher catalytic activity than the former. The superior activity can
be ascribed to the presence of different amines that can
synergistically cooperate to the imine activation of the carbonyl
compound and to the abstraction of an acidic proton from the
methylene compound.[17a] Therefore, the careful selection of the
proper amine derivatives as well as their distribution onto the solid
support material represent fundamental key points to produce an
efficient catalyst. In this regard, amine highly cross-linked
polymers could represent ideal candidates for this purpose. In fact,
the cross-linking nature gives rise to unique properties, such as
Scheme 1. Synthetic procedure of materials 4a-c, 7 and 9.
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10.1002/ejoc.201800040
European Journal of Organic Chemistry
FULL PAPER
high chemical and thermal stability, and high mechanical strength,
ensuring to obtaining polymeric materials with a high content of
basic sites per mass unit of catalyst. There are few examples in
which basic cross-linked polymers[19] or hyperbranched
polyamidoamine or poly(ethyleneimine) dendrimers based
materials[20] are successfully applied as heterogeneous catalysts
for the Knoevenagel condensation. However, the preparation of
such catalytic materials involves multi-step and high time
consuming synthetic procedures. On the other hand, our aim was
to obtain readily and easily accessible amine cross-linked
polymers active in the catalysis of Knoevenagel reaction by
means of a simple reduction process.
Results and Discussion
Scheme 1 shows the synthesis of the catalytic materials 4a-c, 7
and 9. All the bis(1-vinylimidazolium) salts derivatives (1a-c) were
prepared following
a
procedure reported earlier.[21] 3-
Mercaptopropyl-modified silica SiO2-SH 2[22] (1.09 mmol/g SH –
see Figure S1) was functionalized with imidazolium salts 1a-c by
Figure 1. 13C CPMAS NMR spectra of materials 4a', 4a-c, 9 and those of their
precursors 3a-c and 8 before treatment with NaBH4. Asterisks indicate spinning
sidebands.
radical
polymerization in
presence of
2,2′-azobis(2-
methylpropionitrile) (AIBN) as radical initiator, obtaining materials
3a-c. Conversely, γ-Fe2O3@SiO2-SH 5 (1.04 mmol/g SH – see
Figure S1) was reacted with imidazolium salt 1b obtaining
material 6. The imidazolium salt 1b was also homopolymerized to
produce material 8.[23] Subsequently, all the obtained materials
3a-c, 6 and 8 were treated with an excess of NaBH4 giving rise to
the reduction of imidazolium moieties and the ring opening of the
resultant imidazolidine derivatives obtaining highly cross-linked
materials 4a-c, 7, and 9 containing both secondary and tertiary
amines.
13C Cross-Polarization Magic Angle Spinning NMR (13C CPMAS
NMR) of materials 4a-c and 9 and those of their precursors
before treatment with NaBH4 (3a-c and 8) are compared in Figure
1. Solid-state NMR revealed to be a very useful technique for the
optimization of the synthetic procedure of the highly cross-linked
materials. Indeed, NMR spectrum of compound 4a' (Figure 1a)
shows the presence of signals attributed to traces of aromatic
protons belonging to the imidazolium moieties in the 110-150
ppm range, revealing how the treatment of material 3a with a
stoichiometric amount of NaBH4 to give 4a' was not sufficient for
its complete reduction. Conversely, treatment of 3a and the other
materials 3b-c using a not optimized large amount of reductant
(11 equiv. of NaBH4) resulted in their complete reduction
(compare red lines with blue lines - Figure 1a-c). The residual
signals in the 110-150 ppm range, visible in the spectrum of
material 4c (Figure 1c), are attributed to the aromatic protons of
the phenyl moieties of the linker that are not involved in the
reduction process. Conversely, in the same reaction conditions
material 8 was almost completely reduced. The small residue of
aromatic carbons revealed by solid-state NMR measurement is
likely due to the highly cross-linked network of this material that
does not allow free accessibility to some imidazolium units.
Materials 6 and 7 were not analysed by NMR spectroscopy
because of the magnetic nature of the support material.
The proton spin-lattice relaxation times in the rotating frame
(T1ρH) were obtained in order to have information on the protons
spin diffusion that is the propagation of the magnetization of
protons with anti-parallel spins by an energy conserving
process.[24] In particular the higher is the number of protons
around a carbon nucleus the faster is the proton spin diffusion
thus resulting in shorter T1ρH values. The T1ρH values for all the
analysed materials are reported in Table 1. From the analysis of
the relaxation times of the aliphatic protons of all the spectra a
strong decrease of the T1ρH values is evident for the reduced
Table 1. T1ρH values of materials 3a-c before and after the reduction (4a-c) with NaBH4.
3a
Chemical
4a'
Chemical
4a
Chemical
3b
Chemical
4b
Chemical
3c
Chemical
4c
Chemical
T1ρ
H
T1ρ
H
T1ρ
H
T1ρ
H
T1ρ
H
T1ρ
H
T1ρH
shift
(ppm)
136.9
124.0
54.7
48.0
40-44
20-33
(ms)
shift
(ppm)
136.9
124.0
54.7
48.0
40-44
20-33
(ms)
shift
(ppm)
(ms)
shift
(ppm)
135.5
124.3
55.1
(ms)
shift
(ms)
shift
(ppm)
136.7
124.5
74-48
48-33
27.5
(ms)
shift
(ppm)
-
(ms)
(ppm)
139.4
129.9
73-47
47-23
2.2
2.6
2.9
2.7
2.9
2.1
-
2.7
2.6
2.8
2.6
2.0
2.2
1.4
1.3
2.6
3.0
3.0
3.0
3.1
1.5
1.7
1.7
1.7
1.5
-
79-50
50-18
1.2
1.3
74-48
48-33
27.5
1.6
1.1
1.8
50-29
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10.1002/ejoc.201800040
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consequent partial dissolution of the silica supports can occur.
The extent of silica dissolution process may depend on the nature
of the starting imidazolium-based material and on the use of
aqueous or anhydrous ethanol (see Figure S3 and Table S1).
That make useless the direct comparison of the TG curves of
materials 4a-c and 7 with those of their precursors 3a-c and 6
before reduction with NaBH4 (Figure 2 and Figure S2). Indeed,
the TG profiles of the reduced materials (Figure 2) show organic
contents, which depend on the above aspects and they are not
correlated to the starting materials. Nevertheless, the analysis of
the TG curves of the materials 4a-c and 7 allowed to estimate
their amine groups content considering the weight losses at
650 °C (Figure 2). All the calculated catalytic loadings by TG
analysis are reported in Table S1, whereas the amine groups
content of the homopolymerized material 9 corresponds to 15.73
mmol/g. Material 4b was chosen to carry out the initial screening
of the reaction conditions and, at the same time, to test its
recyclability in the Knoevenagel reaction between 4-
bromobenzaldehyde and ethyl cyanoacetate (Table 2). The
reactions were carried out in ethanol at 30 °C for 4 h.
Eventually, in the sixth cycle, using increasing amounts of
substrates and recycling the catalyst, it was gradually possible to
reduce the catalytic loading down to 1.4 mol% (based on amine
groups). Subsequently, the catalytic activities of the silica
supported materials 4a-c, prepared starting by imidazolium salts
1a-c having different linkers between imidazolium moieties, were
compared in the Knoevenagel condensation reaction between 4-
bromobenzaldehyde and ethyl cyanoacetate (Table 3). When the
reaction time was 1.5 h, no difference in catalytic activities was
revealed, obtaining a complete conversion into the corresponding
Figure 2. TGA under oxygen flow of materials 4a-c and 7.
samples. This finding confirms the good outcome of the reduction
process that results in the increased number of protons linked to
the carbons belonging to the reduced imidazolium rings and in the
formation of the primary and secondary amines. Therefore, all
these additional protons contribute to a faster spin diffusion.
In order to determine catalytic loadings, the supported catalysts
4a-c and 7 and their precursors 3a-c and 6 were examined by
thermogravimetric analysis (TGA) under oxygen flow (Figure
2 and Figure S2). For the calculation of the amine groups
content of the different catalytic materials, some assumptions
have to be made. As stated above, solid-state NMR experiments
allowed to assume that in the optimized reaction conditions a total
reduction process, it is expected a weight loss mainly due to the
loss of a bromide ion per imidazolium moiety. However, because
of the basic medium due to the large excess of NaBH4, the
Table 3. Comparison of catalytic activities of materials 4a-c and 4c' in
the Knoevenagel reaction between 4-bromobenzaldehyde and ethyl
cyanoacetate.[a]
Table 2. Screening of the reaction conditions and recycling tests of
catalyst 4b.
Entry
Catalyst
t
Yield
TON[b]
1
2
4a
4b
4c
1.5 h
1.5 h
>99%
>99%
>99%
92%
36
70
54
33
66
51
50
Entry
Aldehyde/Ethyl
cyanoacetate
(mmol/mmol)
Cycle
Yield
3
1.5 h
4
4a
45 min.
45 min.
45 min.
45 min.
1
2
3
4
5
6
0.5/0.5
0.5/0.5
0.5/0.5
1.0/1.0
2.0/2.0
3.5/3.5
1st
2nd
3rd
4th
5th
6th
>99%
>99%
>99%
>99%
>99%
>99%
5
4b
4c
94%
6
95%
7[c]
4c'[d]
90%
[a] Reaction conditions: 4-bromobenzaldehyde (1.55 mmol), ethyl
cyanoacetate (1.55 mmol), ethanol (222 µL), catalyst (4 mg), 30 °C. [b]
TON = mol of product/mol of amine groups. [c] Reaction conditions: 4-
bromobenzaldehyde (1.55 mmol), ethyl cyanoacetate (1.55 mmol),
ethanol (222 µL), catalyst (4.7 mg), 30 °C. [d] Reduction carried out in
absolute ethanol (see Figure S4 for 13C CPMAS NMR spectrum).
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10.1002/ejoc.201800040
European Journal of Organic Chemistry
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olefin 10a (Entries 1-3). Reducing the reaction time to 45 minutes, amine loaded material (Figure S3), showed no difference in
catalysts still showed a similar behaviour being the yields in the
range 92-95% (Entries 4-6), although, in terms of TON, catalyst
4b appears to be more active. A comparison with material 4c’
obtained after reduction in wet ethanol, which gave a higher
catalytic activity (Entries 6-7). Further catalytic tests were carried
out with materials 4b, 7, and 9. We started testing their catalytic
activity in the Knoevenagel condensation (reaction conditions
were not optimized) between a broad substrates scope, including
Table 4. Knoevenagel reaction between aldehydes/ketone and ethyl cyanoacetate/malononitrile catalysed by 4b, 7, or 9. [a]
Entry
Catalyst
Aldehyde/ketone
Methylene
compund
Product
t
Yield
TON[b]
1a
1b
1c
2a
2b
2c
3a
3b
3c
4a
4b
4c
5a
5b
5b
6a
6b
6c
7a
7b
7c
8a
8b
8c
9a
9b
9c
4b
7
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
22 h
1 h
1 h
22 h
1 h
1 h
22 h
1 h
1 h
22 h
1 h
>99%
>99%
>99%
>99%
>99%
>99%
>99%
>99%
>99%
>99%
>99%
>99%
>99%
>99%
>99%
97%
55
96
64
55
96
64
55
96
64
55
96
64
55
96
64
53
64
58
38
48
21
45
91
21
46
96
62
10a
10b
10c
9
4b
7
9
4b
7
9
4b
7
10d
9
4b
7
10e
10f
9
4b
7
67%
9
92%
4b
7
69%
>99%
97%
10g
9
4b
7
83%
95%
10h
10i
9
>99%
84%
4b
7
>99%
98
9
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10b
9
2 h
98%
62
10j
11a
11b
11c
4b
7
22 h
22 h
22 h
87%
92%
91%
48
88
58
10k
9
[a] Reaction conditions (not optimized): aldehyde or ketone (1 mmol), methylene compound (1 mmol), catalyst 1.0  4.7 mol% (4b: 3.3 mg; 7: 2 mg; 9: 1
mg), ethanol (150 µL), 30 °C. [b] TON = mol of product/mol of amine groups.
both electron deficient and electron rich aromatic aldehydes, and
two methylene compounds, namely malononitrile and ethyl
cyanoacetate (Table 4). Examining the results obtained with
activated aromatic aldehydes and ethyl cyanoacetate or using the
Conclusions
highly reactive malononitrile all the catalysts showed no
differences, giving quantitative yields in all cases (Entries 1-5).
When less reactive aromatic aldehydes were used with ethyl
cyanoacetate, catalyst 7 showed to be less active than 4b and 9
(Entries 6-8). High yields were also observed using biphenyl or
2,2’-bithiophenyl systems (Entries 9-10). Conversely, using a
ketone as carbonyl compound, namely cyclopentanone, and
reacting it with malononitrile, all the catalysts required a longer
reaction time to reach good yields (Entry 11). The small
differences observed in the catalytic activity could be mainly
ascribed to the different morphology of the materials.
In the light of the magnetic nature of the support material, which
considerably simplify the recovery of the catalytic system,
material 7 was chosen to carry out recycling tests in the
Knoevenagel condensation between 4-bromobenzaldehyde and
ethyl cyanoacetate (Table 5).
In summary, a straightforward method to produce highly cross-
linked polyamine based materials starting from readily available
cross-linked imidazolium-based materials was reported. The
treatment of
a series of SILs materials, as well as a
homopolymerized bis-imidazolium salt, with an excess of NaBH4
leads to the reduction of the imidazolium moieties and the rings
opening with the simultaneous formation of both secondary and
tertiary amines. The so obtained cross-linked polyamine-based
materials were tested in the Knoevenagel reaction between a
series of carbonyl compounds with two active methylene
compounds, namely malononitrile and ethyl cyanoacetate. Good
to excellent yields into the corresponding olefins were obtained
and it was possible to recycle one of the prepared materials up to
11 cycles.
Because of the magnetic nature of the material, a mechanical
stirring was adopted. This magnetic recovery considerably
simplified the recycling operations. The 8th and 9th cycles showed
a lower yield probably because of the partial deactivation of
catalyst 7. Indeed, the regeneration of material 7 after treatment
with formic acid, restored the catalytic activity affording good
yields into the corresponding olefin in the next two cycles.
Experimental Section
General aspects: Chemicals and solvents were purchased from
commercial suppliers and used as received without further purification. 1H
NMR spectra were recorded with a Bruker 300 MHz spectrometer.
Thermogravimetric analysis (TGA) was performed under oxygen flow from
100 to 800 °C with a heating rate of 10 °C/min in a Mettler ToledoTGA/DSC
STAR System. 13C CPMAS NMR spectra were acquired with a Bruker
Avance II 400 MHz spectrometer with a MAS speed of 5 kHz, 1024 scans,
a contact time of 1.5 ms, a delay time of 3 sec and an excitation pulse of
5.4 μs on the 1H nucleus. The optimization of the Hartmann-Hahn
condition was obtained using an adamantane standard sample. This
compound was also used as the external chemical shift reference. The
spin-lattice relaxation times in the rotating frame (T1ρH) were determined
by the variable spin lock (VSL) pulse sequence. Data were acquired using
spin-lock pulses ranging from 0.1 to 7.5 ms with a spin lock B1 field of 57.6
kHz and a contact time of 1.5 ms.
Table 5. Recycling tests of catalyst 7.
4
5
6
7
8
9
10
97
11
92
Cycle
1
2
3
Synthesis of material 5: γ-Fe2O3@SiO2 (1 g), 3-mercapto-
propyltrimethoxysilane (10.77 mmol, 2 mL) and toluene (7 mL) were
placed in a round bottom flask. The reaction mixture was stirred for 24 h
at reflux, then cooled and filtered under reduced pressure. The obtained
brown powder was washed with hot methanol to remove the residual
unreacted silane. Material 5 was obtained as a brown powder (1.150 g).
Yield
(%)
95
93
97
81
50
57
97
97
95
Reaction conditions: 4-bromobenzaldehyde (2 mmol), ethyl cyanoacetate (2
mmol), catalyst (4 mg), ethanol (300 µL), r.t., 3 h.
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10.1002/ejoc.201800040
European Journal of Organic Chemistry
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Synthesis of material 6: mercaptopropyl modified γ-Fe2O3@SiO2 5 (300
mg, SH loading 1.04 mmol g-1, 0.31 mmol), bis-vinylimidazolium salt 1b
(3.62 equiv., 1.12 mmol, 452 mg), ethanol (9 mL) and AIBN (18 mg, 0.11
mmol) were placed in a two-necked round bottom flask. The suspension
was degassed by bubbling argon for 20 min. The mixture was heated at
78 °C under an argon atmosphere and under stirring. After 20 h, the
reaction mixture was allowed to reach the room temperature, filtered under
reduced pressure and washed with methanol and diethyl ether. The
obtained brown powder (507 mg) was dried overnight under vacuum at
40 °C.
J. Sep. Sci. 2011, 34, 888-900; g) S. N. Riduan, Y. Zhang, Chem. Soc.
Rev. 2013, 42, 9055-9070; h) M. D. Joshi, J. L. Anderson, RSC Adv.
2012, 2, 5470-5484; i) D. R. MacFarlane, N. Tachikawa, M. Forsyth, J.
M. Pringle, P. C. Howlett, G. D. Elliott, J. H. Davis, M. Watanabe, P.
Simon, C. A. Angell, Energy Environ. Sci. 2014, 7, 232-250; j) B. Scrosati,
J. Hassoun, Y.-K. Sun, Energy Environ. Sci. 2011, 4, 3287-3295; k) G.
Gebresilassie Eshetu, M. Armand, B. Scrosati, S. Passerini, Angew.
Chem. Int. Ed. 2014, 53, 13342-13359.
[2]
a) C. P. Mehnert, E. J. Mozeleski, R. A. Cook, Chem. Commun. 2002,
3010-3011; b) A. Riisager, K. M. Eriksen, P. Wasserscheid, R. Fehrmann,
Catal. Lett. 2003, 90, 149-153; c) A. Riisager, P. Wasserscheid, R. van
Hal, R. Fehrmann, J. Catal. 2003, 219, 452-455.
General procedure for the synthesis of materials 4a-c, 7 and 9:
materials 3a-c, 6 or 8 (400 mg), NaBH4 (11 equiv. with respect to
imidazolium moieties) and absolute (for catalysts 4a and 4c') or azeotropic
(for catalysts 4b-c, 7 and 9) ethanol (12 mL) were placed in a round bottom
flask. The mixture was heated at 60 °C under an argon atmosphere and
under stirring. After 20 h, the reaction mixture was allowed to reach the
room temperature, diluted with methanol, transferred into a centrifuge tube,
sonicated for several minutes and then centrifuged. After removing of the
supernatant, the whole washing process was repeated three times with
water, methanol and finally with diethyl ether. The obtained powder was
dried overnight under vacuum at 40 °C.
[3]
[4]
[5]
a) C. P. Mehnert, R. A. Cook, N. C. Dispenziere, M. Afeworki, J. Am.
Chem. Soc. 2002, 124, 12932-12933; b) M. H. Valkenberg, C. deCastro,
W. F. Holderich, Green Chem. 2002, 4, 88-93.
a) V. Campisciano, F. Giacalone, M. Gruttadauria, Chem. Rec. 2017, 17,
918-938; b) F. Giacalone, M. Gruttadauria, ChemCatChem 2016, 8, 664-
684.
a) C. Calabrese, L. F. Liotta, E. Carbonell, F. Giacalone, M. Gruttadauria,
C. Aprile, ChemSusChem 2017, 10, 1202-1209; b) M. Buaki-Sogó, A.
Vivian, L. A. Bivona, H. García, M. Gruttadauria, C. Aprile, Catal. Sci.
Technol. 2016, 6, 8418-8427; c) C. Aprile, F. Giacalone, P. Agrigento, L.
F. Liotta, J. A. Martens, P. P. Pescarmona, M. Gruttadauria,
ChemSusChem 2011, 4, 1830-1837.
General procedure for the Knoevenagel reaction: aldehyde or ketone
(1 mmol), methylene compound (1 mmol), the appropriate amounts of
catalyst and ethanol (150 µL) were placed in a vial with screw cap. The
reaction mixture was heated at 30 °C under stirring for the required time,
then the solvent was evaporated under reduced pressure and the residue
analysed by 1H NMR.
[6]
[7]
L. A. Bivona, F. Quertinmont, H. A. Beejapur, F. Giacalone, M. Buaki-
Sogo, M. Gruttadauria, C. Aprile, Adv. Synth. Catal. 2015, 357, 800-810.
a) E. Montroni, M. Lombardo, A. Quintavalla, C. Trombini, M.
Gruttadauria, F. Giacalone, ChemCatChem 2012, 4, 1000-1006; b) H. A.
Beejapur, F. Giacalone, R. Noto, P. Franchi, M. Lucarini, M. Gruttadauria,
ChemCatChem 2013, 5, 2991-2999; c) H. A. Beejapur, V. Campisciano,
F. Giacalone, M. Gruttadauria, Adv. Synth. Catal. 2015, 357, 51-58.
a) F. Giacalone, V. Campisciano, C. Calabrese, V. La Parola, L. F. Liotta,
C. Aprile, M. Gruttadauria, J. Mater. Chem. A 2016, 4, 17193-17206; b)
C. Petrucci, G. Strappaveccia, F. Giacalone, M. Gruttadauria, F. Pizzo,
L. Vaccaro, ACS Sustain. Chem. Eng. 2014, 2, 2813-2819; c) C. Pavia,
F. Giacalone, L. A. Bivona, A. M. P. Salvo, C. Petrucci, G. Strappaveccia,
L. Vaccaro, C. Aprile, M. Gruttadauria, J. Mol. Catal. A: Chem. 2014, 387,
57-62.
General procedure for the recycling tests in the Knoevenagel
reaction: aldehyde or ketone (1 or 2 mmol), methylene compound (1
equiv.) and the appropriate amounts of catalyst and ethanol were placed
in a vial with screw cap. The reaction was stirred at 30 °C or at r.t. for the
required time. The mixture was then diluted with dichloromethane
magnetically decanted using an external magnet removing the
supernatant and washing the residue with dichloromethane. The combined
organic layers were evaporated under reduced pressure and the residue
was analysed by 1H NMR. The recovered catalyst was dried in an oven at
40 °C and subjected to the next cycles.
[8]
Procedure for the regeneration of catalyst 7: the recovered catalyst was
treated with 200 µL of formic acid. The resulted mixture was stirred for 3 h
at room temperature, then centrifuged and washed with water, aqueous
NaHCO3, water, methanol and diethyl ether. Finally, the catalyst was dried
at 60 °C for 1 h and used in the next cycle.
[9]
R. Buscemi, F. Giacalone, S. Orecchio, M. Gruttadauria,
ChemPlusChem 2014, 79, 421-426.
[10] a) A. Salerno, V. Ceriani, I. A. Perillo, J. Heterocycl. Chem. 1992, 29,
1725-1733; b) E. F. Godefroi, J. Org. Chem. 1968, 33, 860-862.
[11] a) F. M. Moghaddam, Z. Mirjafary, M. J. Javan, S. Motamen, H. Saeidian,
Tetrahedron Lett. 2014, 55, 2908-2911; b) R. H. Vekariya, H. D. Patel,
Synth. Commun. 2014, 44, 2756-2788; c) I. Rodriguez, S. Iborra, F. Rey,
A. Corma, Appl. Catal. A Gen. 2000, 194, 241-252; d) F. Borges, F.
Roleira, N. Milhazes, L. Santana, E. Uriarte, Curr. Med. Chem. 2005, 12,
887-916.
Acknowledgements
Financial support from the University of Palermo is gratefully
acknowledged.
Keywords: Amines • Heterogeneous catalysis • Ionic liquids •
Material science • Polymers
[12] a) M. a. J. Climent, A. Corma, S. Iborra, A. Velty, J. Mol. Catal. A: Chem.
2002, 182, 327-342; b) J. R. Harjani, S. J. Nara, M. M. Salunkhe,
Tetrahedron Lett. 2002, 43, 1127-1130.
[1]
a) P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. 2000, 39, 3772-
3789; b) R. Sheldon, Chem. Commun. 2001, 2399-2407; c) J. P. Hallett,
T. Welton, Chem. Rev. 2011, 111, 3508-3576; d) P. Domínguez de María,
Z. Maugeri, Curr. Opin. Chem. Biol. 2011, 15, 220-225; e) V. Pino, A. M.
Afonso, Anal. Chim. Acta 2012, 714, 20-37; f) C. F. Poole, S. K. Poole,
[13] a) A. Franconetti, P. Domínguez-Rodríguez, D. Lara-García, R. Prado-
Gotor, F. Cabrera-Escribano, Appl. Catal. A Gen. 2016, 517, 176-186; b)
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201800040
European Journal of Organic Chemistry
FULL PAPER
B. Sakthivel, A. Dhakshinamoorthy, J. Colloid Interface Sci. 2017, 485,
75-80.
Isobe, T. Hoshi, T. Suzuki, H. Hagiwara, Molec. Divers. 2005, 9, 317-
320; j) H. Hagiwara, K. Isobe, A. Numamae, T. Hoshi, T. Suzuki, Synlett
2006, 2006, 1601-1603.
[14] a) W. Ge, X. Wang, L. Zhang, L. Du, Y. Zhou, J. Wang, Catal. Sci.
Technol. 2016, 6, 460-467; b) K. Liu, Y. Xu, Z. Yao, H. N. Miras, Y.-F.
Song, ChemCatChem 2016, 8, 929-937.
[18] a) J. B. M. de Resende Filho, G. P. Pires, J. M. G. de Oliveira Ferreira,
E. E. S. Teotonio, J. A. Vale, Catal. Lett. 2017, 147, 167-180; b) R. Maleki,
E. Kolvari, M. Salehi, N. Koukabi, Appl. Organomet. Chem., e3795; c) A.
Ying, L. Wang, F. Qiu, H. Hu, J. Yang, C. R. Chimie 2015, 18, 223-232;
d) F. Shahbazi, K. Amani, Catal. Commun. 2014, 55, 57-64; e) N. T. S.
Phan, C. W. Jones, J. Mol. Catal. A: Chem. 2006, 253, 123-131.
[19] a) Z. Jia, K. Wang, B. Tan, Y. Gu, ACS Catal. 2017, 7, 3693-3702; b) N.
Zohreh, S. H. Hosseini, A. Pourjavadi, C. Bennett, RSC Adv. 2014, 4,
50047-50055.
[15] a) S. Rana, S. B. Jonnalagadda, Catal. Commun. 2017, 92, 31-34; b) C.
S. Hinde, W. R. Webb, B. K. J. Chew, H. R. Tan, W.-H. Zhang, T. S. A.
Hor, R. Raja, Chem. Commun. 2016, 52, 6557-6560; c) H. He, F. Sun,
B. Aguila, J. A. Perman, S. Ma, G. Zhu, J. Mater. Chem. A 2016, 4,
15240-15246; d) A. Taher, D.-J. Lee, B.-K. Lee, I.-M. Lee, Synlett 2016,
27, 1433-1437.
[16] a) G. Tuci, L. Luconi, A. Rossin, E. Berretti, H. Ba, M. Innocenti, D.
Yakhvarov, S. Caporali, C. Pham-Huu, G. Giambastiani, ACS Appl.
Mater. Interfaces 2016, 8, 30099-30106; b) J. Xu, Y. Wang, J.-K. Shang,
D. Ma, Y.-X. Li, Appl. Catal. A Gen. 2017, 538, 221-229; c) S. K. Dey, N.
de Sousa Amadeu, C. Janiak, Chem. Commun. 2016, 52, 7834-7837; d)
W. Jiang, J. Yang, Y.-Y. Liu, S.-Y. Song, J.-F. Ma, Inorg. Chem. 2017,
56, 3036-3043; e) H. Zhang, L. Xiong, Z. He, A. Zhong, T. Wang, Y. Xu,
M. Zhou, K. Huang, Polym. Chem. 2016, 7, 4975-4982.
[20] a) G. R. Krishnan;, J. Thomas;, K. Sreekumar, ARKIVOC 2009, 10, 106-
120; b) H. Hagiwara, M. Sekifuji, N. Tsubokawa, T. Hoshi, T. Suzuki,
Chem. Lett. 2009, 38, 926-927; c) G. R. Krishnan, K. Sreekumar, Eur. J.
Org. Chem. 2008, 2008, 4763-4768; d) T. Wu, X. Wang, H. Qiu, J. Gao,
W. Wang, Y. Liu, J. Mater. Chem. 2012, 22, 4772-4779; e) S. Omar, B.
Dutta, S. Natour, R. Abu-Reziq, J. Organomet. Chem. 2016, 818, 48-57.
[21] M. Gruttadauria, L. F. Liotta, A. M. P. Salvo, F. Giacalone, V. La Parola,
C. Aprile, R. Noto, Adv. Synth. Catal. 2011, 353, 2119-2130.
[17] a) S. M. Ribeiro, A. C. Serra, A. M. d. A. R. Gonsalves, Appl. Catal. A
Gen. 2011, 399, 126-133; b) E. Angeletti, C. Canepa, G. Martinetti, P.
Venturello, Tetrahedron Lett. 1988, 29, 2261-2264; c) K. Komura, Y.
Mishima, M. Koketsu, Appl. Catal. A Gen. 2012, 445–446, 128-132; d)
S.-G. Wang, Catal. Commun. 2003, 4, 469-470; e) Y. Peng, J. Wang, J.
Long, G. Liu, Catal. Commun. 2011, 15, 10-14; f) N. Aider, A.
Smuszkiewicz, E. Pérez-Mayoral, E. Soriano, R. M. Martín-Aranda, D.
Halliche, S. Menad, Catal. Today 2014, 227, 215-222; g) E. Angeletti, C.
Canepa, G. Martinetti, P. Venturello, J. Chem. Soc., Perkin Trans. 1 1989,
105-107; h) S. L. Hruby, B. H. Shanks, J. Catal. 2009, 263, 181-188; i) K.
[22] C. Aprile, F. Giacalone, M. Gruttadauria, A. M. Marculescu, R. Noto, J.
D. Revell, H. Wennemers, Green Chem. 2007, 9, 1328-1334.
[23] P. Agrigento, M. J. Beier, J. T. N. Knijnenburg, A. Baiker, M. Gruttadauria,
J. Mater. Chem. 2012, 22, 20728-20735.
[24] S. Schantz, N. Ljungqvist, Macromolecules 1993, 26, 6517-6524.
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Simply cross-linked: secondary
and tertiary cross-linked polyamine-
based materials were simply
obtained by reduction of
imidazolium-based materials. Such
materials were used as recyclable
catalysts for Knoevenagel reaction.
This easy synthetic approach can
pave the way to other cross-linked
polyamine-based materials for
further applications.
Vincenzo Campisciano, Anna Maria
Pia Salvo, Leonarda Francesca
Liotta, Alberto Spinella, Francesco
Giacalone,* and Michelangelo
Gruttadauria*
Page No. – Page No.
Cross-linked polyamine from
imidazolium-based materials. A
simple route to useful catalytic
materials
This article is protected by copyright. All rights reserved.