Copper–birhodanine complex immobilized on Fe3O4 nanoparticles: DFT studies and heterogeneous catalytic applications in the synthesis of propargylamines in aqueous medium

Article abstract of DOI:10.1002/aoc.4120

Heterogeneous magnetic nanocatalyst, Fe₃O₄@SiO₂–Ligand–Cu (II) MNPs, reveals high catalytic performance within the synthesis of propargylamines using the multicomponent coupling reaction of aldehydes, phenylacetylene and s

Full text of DOI:10.1002/aoc.4120

Received: 7 June 2017
DOI: 10.1002/aoc.4120
Revised: 23 August 2017
Accepted: 25 August 2017
F U L L P A P E R
Copper–birhodanine complex immobilized on Fe O4
3
nanoparticles: DFT studies and heterogeneous catalytic
applications in the synthesis of propargylamines in aqueous
medium
Manuchehr Rezaei | Khaled Azizi | Kamal Amani
Department of Chemistry, Faculty of
Heterogeneous magnetic nanocatalyst, Fe O @SiO –Ligand–Cu (II) MNPs,
Sciences, University of Kurdistan,
617715175 Sanandaj, Iran
3
4
2
6
reveals high catalytic performance within the synthesis of propargylamines
using the multicomponent coupling reaction of aldehydes, phenylacetylene
and secondary amines in water as a solvent. The substantial feature of this
organic–inorganic hybrid magnetic nanocatalyst is the capability of straightfor-
ward separation of the reaction mixture by an external magnet which was
retrieved ten times without significant loss of catalytic activity. This methodol-
ogy has other advantages such as subordination to the principles of green chem-
istry and avoiding the use of expensive and harmful organic solvents. To study
the stability and actual structure of birhodanine derivative–copper (II) complex,
DFT calculations were also performed.
Correspondence
Kamal Amani, Department of Chemistry,
Faculty of Sciences, University of
Kurdistan, 6617715175, Sanandaj, Iran.
Email: amani_71454@yahoo.com;
k.amani@uok.ac.ir
KEYWORDS
copper, DFT calculations, heterogeneous catalysis, magnetic nanoparticle, organic–inorganic hybrid
nanocatalyst
1
| INTRODUCTION
In recent years, to solve these problems,
superparamagnetic nanoparticles have attracted particu-
Due to the increasing need for green and economical
routes in the chemical industry, the use of catalytic sys-
tems with higher selectivity is an important principle in
lar attention because they can be used both as a catalyst
and support to facilitate separation by an external mag-
[
4]
net. These materials have been applied in various fields
such as catalysis, drug delivery, magnetic resonance
imaging (MRI) contrast enhancement, data storage,
targeted drug, magnetic bioseparation, enzyme immobili-
zation and environmental protection because of their
extraordinary properties of superparamagnetism, low
toxicity, retrievability, biocompatibility, and high satura-
[1]
green chemistry. Although homogeneous catalysis has
attracted greater attention than heterogeneous catalysis,
their applications in industrial processes are hindered by
the high cost and difficult separation from the reaction
[2]
mixture. On the contrary, the utilization of either het-
erogeneous catalysis or heterogenized homogeneous cata-
lysts on solid supports such as carbon, polymers, silica and
other metal oxides has received significant attention and
separates from the reaction medium by conventional sep-
aration methods such as filtration or centrifugation. How-
ever, these methods have problems such as the need for
[
5]
tion magnetization. However, pure magnetic nanopar-
ticles (MNPs) have certain defects such as large
[6]
aggregation and altering of magnetic properties. In
order to overcome these problems, magnetic core–shell
structured nanoparticles have been widely accepted as a
feasible approach. Magnetic nanoparticles coated with a
[
3]
expensive equipment and loss of catalyst and product.
Appl Organometal Chem. 2017;e4120.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
1 of 9
https://doi.org/10.1002/aoc.4120

2
of 9
REZAEI ET AL.
layer of silica contribute to the improvement of chemical
stability and dispersibility, also responsive magnetic core
and as much as possible surface–functionalized silica
[7]
shell.
Propargylamines are important compounds that are
found in various natural products and synthetic pharma-
[
8,9]
ceuticals.
These compounds particularly have a neu-
[10]
roprotection role in Parkinson's disease.
The most
common method for preparation of these compounds is
a catalytic coupling of aldehydes, terminal alkynes, and
[11]
amines.
In recent years, the three–component cou-
pling reaction was catalyzed by homogeneous and het-
[12,13]
erogeneous catalyst systems.
However, some of
these catalytic systems have drawbacks such as the use
[14]
of high cost and perilous transition metals , toxic and
[15]
hazardous solvents
catalysts.
and difficulty in retrieving
[16]
More recently, we have designed a new heterogeneous
magnetic nanocatalytic system consisting of Fe O nano-
3
4
particles coated with silica double–charged organic ligand
(birhodanine derivative) complexes of copper ions
(
Fe O @SiO –Ligand–Cu (II) (Scheme 1) which was short
3
4
2
[17]
communicated.
In continuance, further investigation
was carried out by using DFT calculations to confirm
the stability and structure of birhodanine derivative–cop-
per (II) complex. This organic–inorganic hybrid magnetic
nanocatalyst has shown high catalytic performance in one
pot synthesis of propargylamines at 100 °C in water and
with good to excellent yields.
2
2
| EXPERIMENTAL
SCHEME 1 The step by step synthesis of Fe
II) as MNPs
3 4 2
O @SiO ‐ligand‐Cu
(
.1 | Materials, methods and
computational details.
All chemicals were purchased from chemical companies
and used without further purification. FT–IR spectra were
recorded on Bruker FT–IR, Vector–22 spectrophotometer
in the range of 400–4000 cm using KBr pellets tech-
nique. Melting points of products were measured by an
Electrothermal 9100 apparatus. The progress of the reac-
tion was controlled by thin layer chromatography (TLC)
and the resulting products were confirmed by comparing
the physical properties and spectral data with existing
studies.
The geometries of the linker ligand and complexes
were fully optimized without any constraints at the
DFT level in conjunction with the M06‐2X exchange–
correlation functional and 6‐311G (d, p) basis sets for
nonmetal atoms. Copper atoms were treated by
LanL2DZ basis set which uses a pseudo‐potential func-
tion for the non‐valence electrons and is widely used in
study of compounds and clusters containing heavy ele-
[
18]
ments.
The M06‐2X functional was found to be a good
−
1
descriptor for both covalent and non‐covalent interac-
tions and its results are in agreement with the experi-
[
19]
mental data.
The nature of optimized geometries was
verified as real minima through frequency calculations.
The M062X functional along with lanl2dz basis set (for
Cu atoms) and the standard Pople's split valence basis
set of triple zeta quality adding polarization and diffuse
[20]
functions on all nonmetal atoms (6–311++G(2d,2p))
were used for calculation of the energies and electronic
properties of moieties. Finally, the natural bond orbital
(NBO) calculations were performed to analyze the
amount of charges on atoms. All calculations were car-
ried out within the DFT algorithm by using the GAMESS
[
21]
package.

REZAEI ET AL.
3 of 9
2
.2 | Synthesis of silica–coated Fe O
precipitate was filtered and washed with water and etha-
3
4
−
1
MNPs
nol and dried at 60 °C. IR (cm ): 1675 (C = O), 1342
C–N), 1151 (C = S), 744 (C–S).
(
The silica–coated MNPs were prepared via modified
processes.
[22]
2
.5 | Synthesis of metal–complex
a. Typically, 11.68 g FeCl .6H O and 4.30 g FeCl .4H O
3
2
2
2
immobilized MNPs [Fe O @SiO –ligand–
Cu (II)]
3
4
2
were dissolved in 200 ml deionized water under nitro-
gen gas with vigorous stirring at 85 °C. 15 ml 25%
NH .H O was then added to the solution. The color
Fe O @SiO (0.2 g) was added to the solution of Ligand–
3
4
2
3
2
Cu (1 mmol) in ethanol (10 ml) and the reaction mixture
was stirred for 6 h. The cross–linked magnetic nanoparti-
cles were separated from the solution by an external mag-
net, washed with water and then ethanol and dried at
of the bulk solution turned from orange to black
immediately. After stirring and sonication for
3
0 min, the magnetite precipitates were washed twice
with deionized water and once with 0.02 M sodium
chloride by magnetic decantation. Then MNPs were
dried into powder at 50 °C under vacuum.
60 °C.
b. 0.7 g of Fe O was dispersed in a mixture solvent of
3
4
2
.6 | General procedure for the synthesis
ethanol (32 ml) and deionized water (8 ml) by sonica-
tion for 30 min. Then, 0.6 ml of a 25% aqueous solu-
tion of ammonia (NH .H O) and 0.4 ml Tetraethyl
of propargylamines
3
2
Metal–complex immobilized MNPs (25 mg, 2.5 mol% Cu)
was added to a mixture of aldehyde (1 mmol),
phenylacetylene (1 mmol), secondary amine (1 mmol),
in water (2 ml) and heated at 100 °C in a sealed tube with
thorough stirring on an oil bath. The progress of the reac-
tion was monitored by TLC. After completion of the reac-
tion and cooling to rt., the catalyst was separated by using
an external magnet and washed twice with ethyl acetate.
The combined organic layer was washed with brine, dried
over anhydrous Na SO . After removal of organic solvent
under vacuum, the crude products were further purified
by column chromatography on silica gel using ethyl ace-
tate and n–hexane mixture in 2:8 ratio as an eluent. The
structure of all obtained products was identified by com-
parison of spectral data and physical properties with the
existing literature.
orthosilicate (TEOS) were added and stirred for 24 h
at rt. The obtained Fe O @SiO NPs was washed with
3
4
2
deionized water and then ethanol several times by
magnetic decantation and then dried at 60 °C. IR
−
1
(
cm ): 567 (Fe–O), 805 and 1066 (Si–O–Si).
2
.3 | Synthesis of birhodanine derivative
2
4
(ligand)
Birhodanine derivative was synthesized according to the
[
23]
previously reported method with some modification.
Dropwise 3–(triethoxysilyl)propan–1–amine (APTMS)
4 mmol, 0.72 g) was added to a stirred solution of carbon
(
disulfide (4.8 mmol, 0.36 g) and dimethyl acetylene
dicarboxylate (DMAD) (2 mmol, 0.28 g) in acetonitrile
(4 ml) in 5 min. After further stirring for 5 min, the solu-
tion color changed to dark orange. Followed by addition
of ethanol to the reaction mixture, the product was pre-
cipitated down as orange crystals. Finally, the resulting
solid was filtered, washed with ethanol and dried at room
temperature under vacuum. mp = 330 °C (decomposed).
3
| RESULTS AND DISCUSSIONS
As can be seen from Scheme 1, our magnetic catalytic sys-
tem was prepared in several steps. The structure of syn-
thesized catalyst was characterized by different
physicochemical techniques like FT–IR, XRD, EDX, ICP,
−
1
IR (cm ): 1698 (C = O), 11349 (C–N), 1157 (C = S), 786
C–S).
[
17]
(
FE–SEM, TGA, and AGFM.
The size details, particles
shape, and surface morphology were investigated by FE–
SEM, and TEM. The TEM image and their size distribu-
tion curve of Fe O @SiO –Ligand–Cu (II) NPs clearly
2
.4 | Synthesis of birhodanine derivative–
3
4
2
copper (II) complex [ligand–Cu(II)]
indicate that the NPs obtained had an average size of
Copper (II) acetate (2 mmol) was added to the orange
solution of the birhodanine derivative as the Ligand
40 nm (Figure 1).
[
17]
As previously mentioned,
the FT–IR spectrum of
(
1 mmol) in ethanol (20 ml) and refluxed for 1 h. Upon
birhodanine derivative–copper (II) ions complex forma-
tion was along with shifting the peaks of C = O, C–S
and C–S; indicating covalent interactions between copper
addition of metal, the color of the solution changed from
orange to dark brown. The resulting dark brown

4
of 9
REZAEI ET AL.
bonds in S1–Link state are decreased. At applied level of
computation, the S1–Link configuration is more stable
−
1
than S2–Link by about 30 kcal mol . This is in agree-
ment with the fact that in the majority of cases the bond
lengths within S1–Link state are shorter than that of cor-
responding ones in S2–Link. It is interesting that despite
more stabilization of S1–Link configuration, S2–Link
one is preferred upon complexation. Assuming that the
same situation as the gas phase is established in water sol-
vent, the effect may be attributed to the fact that sur-
2+
rounding water molecules of Cu
prefer to interact
with O atom in the vicinity of S2–Link rather than S1–
Link.
In Table 2 the electrical charge of ligand and S2–Link
state of the complex are shown. The results revealed that
by complexation, charge density is transferred from elec-
tropositive C and S atoms to Cu and electronegative O
and N atoms.
The energies of HOMO and LUMO are calculated as
−6.41 and −16.21 eV which led to 0.213 eV HOMO–
LUMO energy gap. According to Koopman's theorem, a
low chemical stability is expected for this complex. A typ-
ical illustration of the electron density distribution (EDD)
of HOMO, HOMO–1, LUMO and LUMO+1 for ligand
and the S2–Link state of the complex are shown in Figure
ESI‐2. As it can be seen from this figure, for both of
HOMO and LUMO of ligand, the EDD is concentrated
on middle S–included region of ligand and has no contri-
bution from Si(OMe)3 groups. Therefore, it might be
expected that this region is attacked by both electrophiles
2+
as Cu and nucleophiles. It is interesting that in compar-
ison with a ligand, in both HOMO and LUMO of the com-
FIGURE 1 TEM image and size distribution of Fe
ligand–Cu (II) NPs
3 4 2
O @SiO –
plex the EDD has concentrated on Si(OMe) groups and
3
and lone pairs of oxygen and sulfur. However, further
investigations were needed. To study the stability and
actual structure of birhodanine derivative–copper (II)
complex, DFT calculations were also performed. The opti-
mized structure of [(MeO) SiCH CH CH ] C N O S
2 2 6 2 2 4
has no contribution from Cu or its neighbor atoms. This
makes the Cu–included region of complex unsuitable for
attacking either electrophiles or nucleophiles. Therefore,
despite the small HOMO–LUMO gap, this gives stability
to the system.
3
2
2
2+
ligand and [(MeO) SiCH CH CH ] C N O S *Cu com-
The experimental and calculated vibrational spectrum
of [(MeO) SiCH CH CH ] C N O S ligand and S1–Link
3
2
2
2 2 6 2 2 4
plex in two states, either Cu linked to 5–member ring
excluded S atom (S1–Link) or Cu linked to 5–member
ring included S atom (S2–Link) are shown in Figure 2
and the structural properties of these moieties are sum-
marized in Table 1. As can be seen from Figure ESI‐1
3
2
2
2 2 6 2 2 4
and
S2–Link
configurations
of
2+
[(MeO) SiCH CH CH ] C N O S *Cu
complex are
3
2
2
2 2 6 2 2 4
shown in Figure ESI‐3. As shown, irrespective of the
height of peaks, the calculated spectrum is in agreement
with experimental one. In order to achieve more consis-
tencies, the intensity of high peaks is reduced by the same
ratio.
Table 2 revealed that a considerable amount of elec-
tron density of atoms of 5–member ring has been lost
upon complex formation. Therefore, it is expected that
the frequency of in–plane distortion mode of vibration of
the 5–member ring is decreased from ligand to complex.
As shown in Figure ESI‐4, while both experimental and
[24]
and inconsistent with previous reports,
a configuration
in which carbonyl groups arranged far from each other is
selected by ligand. Moreover, in both S1–Link and S2–
Link states, Cu atoms are located out of the 5–member
rings including plane and the effect is more evident for
S2–Link configuration.
In comparison with the ligand, the data given in
Table 1 indicates that the C = S bond length for the S1–
Link is increased while the lengths of C1–N and C = O

REZAEI ET AL.
5 of 9
S1-Link
S2-Link
2
+
3 2 2 2 2 6 2 2 4
FIGURE 2 The modest structures as S1–link and S2–link of [(MeO) SiCH CH CH ] C N O S *Cu complex
3 2 2 2 2 6 2 2 4
TABLE 1 The bond lengths and atomic distances (Å) in [(MeO) SiCH CH CH ] C N O S ligand and S1–link and S2–link configurations
2
+
3 2 2 2 2 6 2 2 4
of [(MeO) SiCH CH CH ] C N O S *Cu complex
S1 = C1
C1 = N
C1‐S2
N‐C2
C2 = O1
S2‐C3
C2‐C3
C3‐C3’
S2…O1’
Si‐O
S…Cu*
Ligand
S1‐link
S2‐link
1.636
1.372
1.771
1.388
1.412
1.368
1.217
1.740
1.474
1.353
2.872
1.649
1.678
1.606
1.352
1.389
1.754
1.803
1.206
1.238
1.744
1.749
1.477
1.485
1.353
1.365
2.879
3.049
1.649
1.648
2.211
2.288
*
For S1‐Link configuration is S1 atom and in S2‐Link configuration is S2 atom.
3 2 2 2 2 6 2 2 4
TABLE 2 The electrical charge of atoms in [(MeO) SiCH CH CH ] C N O S ligand and S1 and S2 configurations of
*
2+
[
(MeO)
3
SiCH
2
CH
2
CH
2
]
2
C
6
N
2
O
2
S
4
Cu complex
a
b
C1
C2
C3
S1
S2
N
O
Cu
Si
O
C
Ligand
−0.118
0.492
0.858
−0.275
−0.017
0.492
0.451
−0.498
−0.462
−0.564
‐‐‐
2.263
−0.915
−0.758
−0.201
−0.21
S2‐link
0.066
−0.126
0.287
−0.686
0.849
2.253
a
An average value for O atoms linked to Si.
b
An average value for C atoms within OMe groups.
calculated (S2–Link state) cases confirm this expectation,
the S1–Link case shows a different behavior. This strongly
confirms the priority of formation of S2 on S1.
Link against S1–Link configuration is strongly confirmed
by this evidence. It should be noted that the reduction of
the frequency of C = O is in complete agreement with
increasing the length of this bond and transforming of
electrical charge from C = O to Cu.
After determination the structure and morphology of
the catalyst, their catalytic activity was studied in the
three–component synthesis of propargylamines from
aldehydes, amines and terminal alkynes. For this purpose,
the reaction of benzaldehyde, phenylacetylene, and
The peak of C = O may be treated as the greatest proof
for determination of the true structure of complex among
S1–Link and S2–Link. This peak appears at 1697 and
−
1
1
681 cm for ligand and complex, respectively. Figure
ESI‐3 illustrates that this mode appears at 1788, 1836
−
1
and 1700 cm for ligand, S1–Link and S2–Link states of
complex, respectively. Therefore, the formation of S2–

6
of 9
REZAEI ET AL.
morpholine were chosen to optimize the reaction condi-
tions as a model reaction. The temperature, time, the
amount of catalyst and the kind of solvent were evaluated.
In the first step, the variation in yield of propargylamines
by changing the amount of magnetic nanocatalyst was
investigated. The maximum yield was obtained in the
presence of 25 mg of catalyst. With a further increase in
the amount of catalyst a significant increase in the yield
of the reaction was not observed. The most likely reason
for this phenomenon, the restrictions on the transfer of
reactants to the active sites of the catalyst, was due to
the low distribution of the catalyst in the reaction medium
(Figure 3).
Further optimization studies on the effect of various
solvents on the reaction showed that water as solvent
gives the best performance of the catalyst and maximum
yield of product (Figure 4). A decrease in the yield was
observed when using the DMF and THF as a solvent.
The effects of reaction time and temperature on the cata-
lyst efficiency in the model reaction were also studied
FIGURE 4 Effect of type of solvent on model reaction (Reaction
conditions: Benzaldehyde (1 mmol), morpholine (1 mmol),
phenylacetylene (1 mmol), and nanocatalyst (25 mg) at 100 °C for
1.5 h
(Figure 5). The results showed that at room temperature,
even after a period of 2 hours, no product was formed,
but by increasing the reaction temperature, the yield of
product also increased. The highest yield of the product
was obtained at 100 °C. Furthermore, increases in the
reaction temperature do not lead to a significant increase
in the reaction yield.
In order to evaluate the generality of catalyst, conden-
sation of a variety of aldehydes, piperidine or morpholine,
and phenylacetylene were conducted under the optimized
reaction conditions and the results are shown in Table 3.
As is evident from the results, type and the position of
the substituent on the aldehydes have the greatest effect
on both the reaction times and the yields. Aldehyde
FIGURE 5 Effect of temperature and time parameters on the
model reaction (Reaction conditions: Benzaldehyde (1 mmol),
morpholine (1 mmol), phenylacetylene (1 mmol), nanocatalyst
(
2
25 mg) and H O (2 ml)
derivatives with electron–donating groups such as methyl
and methoxy have longer reaction times than nitro,
bromo, and chloro electron–withdrawing substituents
(
Table 3, entries 1–15). There are no great differences
between the reaction speeds with morpholine compared
to piperidine.
FIGURE 3 Effect of amount of the catalyst on the yield of model
reaction (Reaction conditions: Benzaldehyde (1 mmol), morpholine
(
1 mmol) and phenylacetylene (1 mmol) and H
2
O (2 ml) at 100 °C
The efficiency of the catalytic activity of Fe O @SiO –
3
4
2
for 1.5 h
Ligand–Cu (II) in the synthesis of propargylamine

REZAEI ET AL.
7 of 9
TABLE 3 MNPs–ligand–Cu (II) catalyzed the one–pot synthesis of propargylamines
b
−1
Entry
R
Amine
Time (h)
Yield (%)
TON
TOF (h
)
[
[
[
[
[
[
[
[
[
12c]
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
H
Piperidine
1.5
90
600
400
25]
4‐Cl
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Piperidine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
Morpholine
1.5
1.7
1.4
1.2
2.0
2.2
2.0
2.5
1.5
2.2
1.5
2.0
1.4
2.0
93
91
95
91
89
92
620
607
633
607
593
613
587
5937
640
627
613
580
653
573
413
357
452
506
297
279
293
297
427
285
279
290
467
287
25]
4‐Br
25]
4‐NO
3‐NO
4‐Me
2
2
13c]
25]
25]
4‐OMe
4‐CHO
2‐Cl
13d]
12c]
c
88
89
96
94
92
87
98
[
[
[
[
[
[
13c]
0
1
2
3
4
5
H
26]
27]
27]
28]
13d]
4‐OMe
4‐Cl
4‐Me
4‐NO
2
c
4‐CHO
86
a
Reaction conditions: aldehyde (1 mmol), amine (1 mmol), phenylacetylene (1 mmol), Cat. (25 mg), water (2 ml) at 100 °C.
b
Isolated yields.
c
Disubstituted product.
derivatives with a few previous similar catalytic systems
was also provided (Table 4). The results obtained show
that this new catalytic system is comparable or superior
to some previous reports, including the higher yield of
the product, shorter reaction time, more gentle reaction
conditions, and the use of the catalyst with the ability to
retrieve and reuse, and avoiding the use of toxic and vol-
atile organic solvents.
Stability and ease of recycling the heterogeneous cata-
lyst are very important features of the environmental and
3 4 2
TABLE 4 Comparison of catalytic activity of Fe O @SiO –ligand–Cu(II) with some heterogeneous catalysts for coupling reaction of
benzaldehyde, morpholine, and phenylacetylene
Entry
Catalyst and conditions
Polystyrene–supported Cu (II) complex, toluene, 110 °C
Cu NPs/TiO , neat, 70 °C
Time (h)
Yield (%)
[
[
[
[
[
[
[
[
[
15c]
13c]
29]
1
2
3
4
5
6
7
8
9
1
1
6
82
91
93
95
80
95
85
84
97
90
96
2
7
Cu–Ni, neat, 90 °C
3
30]
Cu (ΙI) salen, neat, 80 °C
Cu@SBA–15, toluene, 110 °C
2.5
6
31]
32]
Cu
2
O/nano–CuFe
2
O
4
, neat, 90 °C
1
13b]
33]
Cu–MCM–41, neat, 100 °C
3
CuNPs/MagSilica, neat, 100 °C
1
13a]
Cu@PMO–IL, CHCl
3
, 60 °C
24
24
1.5
[
[
16b]
0
2
*
This work]
Cu–MOF
3 4 2 2
Fe O @SiO –ligand–Cu (II) NPs, H O, 100 °C
*
With piperidine

8
of 9
REZAEI ET AL.
amounts of catalyst leached are other proof for the hetero-
geneous nature of the nanomagnet supported catalyst.
Based on the similar reported mechanism in the liter-
ature, C–H bond in terminal alkyne is activated by
Fe O @SiO –Ligand–Cu (II). In the next step, the cop-
3
4
2
per–acetylide intermediate undergoes nucleophilic addi-
tion to the iminium ion generated in situ from the
reaction between the aldehyde and the amine to produce
[
11]
the corresponding product (Scheme 2).
4
| CONCLUSION
In summary, Fe O @SiO nanoparticles functionalized
3
4
2
with Cu (II)–birhodanine complex were employed as a
heterogeneous and reusable catalyst for the synthesis of
propargylamines. The nanocatalyst can be reused 10
times without loss of catalytic activity and with negligible
metal leaching. Other advantages of this methodology are
as follows: the employment of water as a green solvent
rather than expensive, toxic and harmful organic solvents,
excellent yields and general in scope. DFT calculations
have confirmed the stability of the complex and the metal
binding ligand.
FIGURE
6
Catalyst reusability for the synthesis of
propargylamines (reaction conditions: Benzaldehyde (1 mmol),
morpholine (1 mmol), phenylacetylene (1 mmol), nanocatalyst
(
2
25 mg) and H O (2 mL) at 100 °C
economic aspects. Therefore, the Fe O @SiO –Ligand–
3
4
2
3
Cu (II) was applied for A coupling reaction in benzalde-
hyde, morpholine, and phenylacetylene under the opti-
mized reaction conditions (Figure 6). After each
reaction, the magnetic nanocatalyst was readily separated
from the reaction mixture by an external magnet and
washed with ethyl acetate and dried in a vacuum. The
recycled catalyst was reused 10 times without a significant
reduction in its catalytic activity. The reusability of the
catalyst affirms that copper ion is effectively immobilized
on magnetic nanoparticles. The leaching out of Cu ions
from the supporter within the reaction was evaluated by
ICP analysis. The quantity of copper ions washed out after
the seventh run of the reaction was only 1%. Trace
ACKNOWLEDGEMENTS
The authors are grateful for the financial support of the
University of Kurdistan and Iran Nanotechnology Initia-
tive Council.
ORCID
Kamal Amani http://orcid.org/0000-0001-8717-7893
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