Magnetic CuO nanoparticles supported on graphene oxide as an efficient catalyst for A3-coupling synthesis of propargylamines

Article abstract of DOI:10.1016/j.cclet.2015.05.021

Magnetically separable CuO nanoparticles supported on graphene oxide (Fe₃O₄ NPs/GO-CuO NPs) is synthesized and characterized for the preparation of propargylamines in EtOH, at 90 °C. Fe₃O₄ NPs/GO-CuO NPs is foun

Full text of DOI:10.1016/j.cclet.2015.05.021

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Chinese Chemical Letters xxx (2015) xxx–xxx
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Chinese Chemical Letters
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Original article
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Magnetic CuO nanoparticles supported on graphene oxide as an
efficient catalyst for A3-coupling synthesis of propargylamines
Q1 Maryam Mirabedini a, Elaheh Motamedi b, Mohammad Zaman Kassaee b,
*
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a Department of Chemistry, Tarbiat Modares University, P.O. Box 14155-175, Tehran, Iran
b Department of Agronomy and Plant Breeding, Division of Molecular Plant Genetics, Collegeof Agricultural & Natural Resources, University of Tehran, Karaj, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
Magnetically separable CuO nanoparticles supported on graphene oxide (Fe3O4NPs/GO–CuONPs) is
synthesized and characterized for the preparation of propargylamines in EtOH, at 90 8C. Fe3O4NPs/GO–
CuONPs is found to be an efficient catalyst for the A3-coupling of aldehydes, amines, and alkynes through
C–H activation. Both aromatic and aliphatic aldehydes and alkynes are combined with secondary amines
to provide a wide range of propargylamines in moderate to excellent yields.
Received 8 February 2015
Received in revised form 15 April 2015
Accepted 29 April 2015
Available online xxx
ß 2015 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences.
Published by Elsevier B.V. All rights reserved.
Keywords:
CuO
Graphene oxide
Fe3O4
A3-coupling
Nano-catalyst
Magnetic nanoparticles
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1. Introduction
[3,16]. The alkyne C–H bond can be activated by employing 30
different complexes and salts of transition metal catalysts such as 31
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A3-coupling of an aldehyde, alkyne, and amine, is considered as
one of the best instances of acetylene-Mannich multicomponent
reactions which has also been well recognized as a synthetic
method toward propargylic amines [1–5]. The latter are versatile
key intermediates in total synthesis of some biologically active
gold complexes [17], silver [18], copper [19–21], zinc [22], iron 32
[23], indium [24,25], iridium [26], mercury [27], nickel [15], 33
zirconium [28], and rhenium [29], but among them the most 34
employed metal has been copper, especially with secondary 35
amines [1,2,30]. Although the majority of the catalytic systems are 36
homogeneous, their loss at the end of the reaction reduces their 37
utility especially for industrial applications. Nowadays, metal 38
nanoparticles are considered as heterogeneous catalysts which 39
possess a high surface-to-volume ratio. Because of enhanced 40
activity and selectivity, they could be competitive alternative to 41
classical catalysis [31,32]. Particularly, the immobilization of 42
metallic salts on high-surface-area nanoparticles causes better 43
stability, dispersity, and recyclability of the catalyst [33]. Recently, 44
such heterogeneous catalysts including silica-immobilized CuI 45
[34], silica gel anchored copper chloride [35], copper ferrite 46
nanoparticles [36], copper nanoparticles [37], nanocrystalline 47
copper (II) oxide [38], impregnated copper on magnetite [39], 48
have also been employed for A3-coupling preparation of propar- 49
compounds such as b-lactams, allylamines, oxotremorine analogs,
isosteres, oxazoles, and other natural products, as well as
therapeutics [6–8]. Furthermore, propargylamines are utilized as
precursors in the synthesis of numerous heterocyclic compounds
such as quinolines [9], phenanthrolines [10], pyrroles [10],
pyrrolidines [11], indolizines [12], and oxazolidinones [7]. Classical
methods for the preparation of these compounds are nucleophilic
attack of lithiumacetylides or Grignard reagents on imines or their
derivatives [13,14]. However, this approach involves stoichiomet-
ric amounts of reagents, requires strict control of the reaction
conditions due to its moisture sensitive nature and its application
is limited in the presence of the more reactive functional groups
such as esters [15]. A3-coupling is an alternative atom-economical
method to synthesis of propargylamines by catalytic C–H
activation, where water is only the theoretical by-product
gylamines.
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On the other hand, Fe3O4NPs is a good support for other 51
catalysts and can facilitate their separation effectively from the 52
liquid products of the reaction via an external magnet [40]. 53
However it is especially difficult to obtain relatively disaggregated 54
Fe3O4NPs, due to its inherent magnetism. This results in losing the 55
*
Corresponding author. Tel.: +98 912 1000392; fax: +98 21 88006544.
Q2
E-mail address: Kassaeem@Modares.ac.ir (M.Z. Kassaee).
http://dx.doi.org/10.1016/j.cclet.2015.05.021
1001-8417/ß 2015 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
Please cite this article in press as: M. Mirabedini, et al., Magnetic CuO nanoparticles supported on graphene oxide as an efficient catalyst
for A3-coupling synthesis of propargylamines, Chin. Chem. Lett. (2015), http://dx.doi.org/10.1016/j.cclet.2015.05.021

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M. Mirabedini et al. / Chinese Chemical Letters xxx (2015) xxx–xxx
chloride (FeCl2Á6H2O, 300 mg) is added at room temperature.
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The temperature is raised to 85 8C and a 30% ammonia solution is
gradually added to increase the pH up to 10. After being rapidly
stirred for 45 min, the solution is cooled at room temperature.
Subsequently, the resulting black precipitate is centrifuged and
washed three times with DI water and lastly dried at 60 8C. For
preparation of Fe3O4NPs/GO–CuONPs nano-catalyst, 30 mg of
prepared Fe3O4NPs/GO in 100 mL of water and CuCl2Á2H2O
(20 mg) is ultrasonicated for 60 min. Then 10 mL NaBH4 solution
(1 wt%) is added and the solution heated in an oil bath at 100 8C
under a water-cooled condenser for 24 h. After that, the solution
was cooled at room temperature and subsequently, the resulting
precipitates are centrifuged and washed three times with DI water
and lastly dried at 60 8C.
Scheme 1. Fe3O4NPs/GO–CuONPs catalyses the A3-coupling leading to
propargylamines.
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dispersibility and specific properties which eventually decreases
its activity [41]. Therefore, immobilization of such magnetic NPs is
required [42]. Two dimensional graphene (G) and its oxidized
derivatives (GO) are extensively used as supports for the
preparation of free-standing magnetic NPs. Unique two-dimen-
sional lamellar structure, high surface area as well as full surface
accessibility, chemical inertness and edge reactivity of GO make it
a promising candidate in preventing aggregation of Fe3O4NPs. It
improves the overall catalytic activity owing to the strong
synergistic interaction between GO and NPs [43].
As part of our ongoing research on the synthesis and application
of Fe3O4NPs/GO nanocomposites [44,45], here we wish to present
our results on the performance and scope of Fe3O4NPs/GO–CuONPs
as a novel nano-catalyst, in the A3-coupling preparation of
propargylamines (Scheme 1).
3. Results and discussion
91
3.1. Characterization of synthesized Fe3O4NPs/GO–CuONPs nano-
catalyst
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In the FTIR (Thermo spectrometer) spectrum of the synthesized
GO (Fig. 1a), the peak at 1710 cmÀ1 corresponds to the stretching
band of C55O in carboxylic acid or carbonyl moieties. The intense
band at 3418 cmÀ1 is attributed to stretching of the O–H and the
deformation of the C–O is observed at 1167 cmÀ1 [47]. FTIR
spectrum of Fe3O4NPs/GO (Fig. 1b) differs from that of GO as
evidenced by the disappearing of C55O bond and weakening of the
O–H bond at 3415 cmÀ1. The peak at 1625 cmÀ1 (aromatic C55C)
may be assigned to the skeletal vibrations of graphitic domains of
GO. Also it shows the band around 558 cmÀ1 that is attributed to
Fe–O, confirming the existence of Fe3O4NPs [37]. FTIR spectrum of
Fe3O4NPs/GO–CuONPs (Fig. 1c) is almost similar to Fe3O4NPs/GO
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2. Experimental
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The synthesized GO (from purified natural graphite using
modified Hummer’s method [46]) is coated with Fe3O4 NPs as
described in our previous report [44,45]. Briefly, 30 mg of GO in
25 mL of water was ultrasonicated for 30 min. 50 mL aqueous
solution of ferric chloride (FeCl3Á6H2O, 800 mg) and ferrous
Fig. 1. Characterization of graphene oxide (GO) supported CuO and Fe3O4 by FTIR (a–c), SEM (d) and EDX analysis (e) and TEM image (f).
Please cite this article in press as: M. Mirabedini, et al., Magnetic CuO nanoparticles supported on graphene oxide as an efficient catalyst
for A3-coupling synthesis of propargylamines, Chin. Chem. Lett. (2015), http://dx.doi.org/10.1016/j.cclet.2015.05.021

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Table 1
dark background represents graphenic substrate and black dots 117
displays metal oxide nanoparticles distributed over the GO 118
Optimization of A3-coupling the reaction conditions for synthesis of propargyla-
mines.a
(Fig. 1f).
119
Entry
Temperature (8C)
Solvent
Catalyst (mg)
Yield (%)
3.2. A3-coupling of aldehydes, amines, and alkynes catalyzed by
Fe3O4NPs/GO–CuONPs
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121
1
2
3
4
5
6
7
8
9
110
80
PhMe
MeCN
MeOH
H2O
20
20
20
20
20
20
15
10
5
85
65
45
–
65
100
25
Firstly, a screening is carried out in order to optimize the 122
temperature of the reaction, solvent and catalyst amount with the 123
coupling of benzaldehyde (1), morpholine (2), and phenylacety- 124
lene (3) as a model reaction (Scheme 1). To check the solvent effect 125
on the product yield, the model reaction is carried out with 20 mg 126
of Fe3O4NPs/GO–CuONPs nano-catalyst in six different solvents 127
such as toluene, MeOH, EtOH, CH2Cl2, CH3CN and DI-water for 24 h 128
(Table 1, entries 1–6). The results show that EtOH is the most 129
effective solvent, since the reaction proceeds smoothly giving the 130
maximum yield (Table 1, entry 6). It is noteworthy that when water 131
and CH2Cl2 is used as the solvent, only a trace amount of product is 132
observed (Table 1, entries 4, 5). Employing lower amounts of nano- 133
catalyst reduces the yield (Table 1, entries 6–9). A higher dosage of 134
the nano-catalyst neither increases the yield nor decreases the 135
reaction time. Thus, all the reactions are performed in EtOH with 136
CH2Cl2
EtOH
EtOH
EtOH
EtOH
–
90
87
70
63
45
90
90
90
a
Phenylacetylene:morpholine:benzaldehyde = 1.5:1.2:1.
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spectrum despite of a little change in the position of Fe–O bond
(567 cmÀ1) that maybe attributed to the presence of Cu–O along
with Fe–O bond in the chemical composition of nano-catalyst. SEM
image (Philips XL30 microscope) indicates the fair dispersity and
spherical morphology of the nanoparticles anchored on the surface
of GO, with average particles sizes between 36 nm and 53 nm
(Fig. 1d). The chemical composition of Fe3O4NPs/GO–CuONPs
nano-catalyst is also examined by EDX analysis which shows peaks
corresponding to C, O, Fe and Cu elements with weight percentages
of 1.16%, 8.20%, 80.77 and 9.87%, respectively (Fig. 1e). In the TEM
image (Philips, EM208S) of Fe3O4NPs/GO–CuONPs catalyst, the
20 mg of Fe3O4NPs/GO–CuONPs at 90 8C for 24 h.
Once the efficiency of nano-catalyst is established, using the 138
optimized reaction conditions, the scope of the reaction is probed. 139
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Scheme 2. Tentative mechanism for the A3-coupling reaction catalyzed over Fe3O4NPs/GO–CuONPs, where small spheres (*) represent CuONPswhile larger ones ( ) indicate
Fe3O4NPs.
Please cite this article in press as: M. Mirabedini, et al., Magnetic CuO nanoparticles supported on graphene oxide as an efficient catalyst
for A3-coupling synthesis of propargylamines, Chin. Chem. Lett. (2015), http://dx.doi.org/10.1016/j.cclet.2015.05.021

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Table 2
A3-coupling of aldehydes (1), amines (2), and alkynes (3) catalyzed by Fe3O4NPs/GO–CuONPs nano-catalyst for production of propargylamines (4).a
Entry
A
Aldehyde
Amine
Product
Yield (%)
4a
1
2a
2b
4a
4b
4b
69
77
B
C
50
78
81
84
D
E
F
87
71
71
80
88
55
G
H
a
50
67
61
51
Phenylacetylene (3):amine (2):aldehyde (1) =1.5:1.2:1.
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Excellent results are encountered for the different combinations of
aldehydes, amines, and alkynes. To generalize the applicability of
our synthesized nano-catalyst in promoting the A3-coupling
reaction, a variety of structurally divergent aldehydes and amines
are used (Table 2).
The results indicate that the aromatic aldehydes with both
electron-donating and electron-withdrawing substituents display
high reactivity with two different amines (2a and 2b)and generate
the corresponding products (4a and 4b) in good yields (Table 2,
entries A–E). Aliphatic aldehydes are also able to undergo addition
to afford the corresponding 4 effectively. However, the reaction is
found to be affected by the nature of 1 as aromatic aldehyde show
higher reactivity, giving higher yields under the same conditions
(Table 2, entries F, G). Similarly, heteroaromatic aldehyde also
participated well in this protocol (Table 2, entry H). A tentative
mechanism for the catalyzed A3-coupling over Fe3O4NPs/GO–
CuONPs is proposed involving the activation of the C–H bond of
alkyne by nano-catalyst. The generated catalyst–acetylide inter-
mediate subsequently reacts with the iminium ion generated in
situ from catalyst activated 1 and 2 to give the corresponding
propargylamine 4 (Scheme 2). In particular, the reaction proceeds
via the initial formation of an iminium intermediate from the
starting amine and aldehyde. However, the iminium formation is
equilibrated, and this equilibrium could be influenced by the
catalyst. The presence of Fe3O4NPs in the catalyst composition
could indeed favor iminium formation. Iron cations acts as Lewis
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Please cite this article in press as: M. Mirabedini, et al., Magnetic CuO nanoparticles supported on graphene oxide as an efficient catalyst
for A3-coupling synthesis of propargylamines, Chin. Chem. Lett. (2015), http://dx.doi.org/10.1016/j.cclet.2015.05.021

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Fig. 2. Yields obtained with recycledFe3O4NPs/GO–CuONPs catalyst.
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acid and play a significant role in increasing the electrophilic
character of the starting aldehyde and stabilizing the immonium
salt by the coordination of the oxygen or nitrogen lone electron
pair [14]. Moreover, there are some reports on iron-catalyzed
coupling of aldehyde, alkyne and amine which proposed the
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(without Fe3O4NPs). In the optimum conditions only 53% yield is
obtained showing the important role of magnetite NPs in the
efficiency of catalyst. The copper ions present in the Fe3O4NPs/GO–
CuONPs act as the C–H activation catalyst. Upon coordination, the
alkyne is probably deprotonated, and copper–acetylide thus
formed which could then add concomitantly to the iminium
compound produced within the Fe3O4NPs/GO [38].
Each of separation and possible reusability is an important
factor in the heterogeneous catalyst effectiveness. In order to
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isolated simply using an external magnet and washed with ethanol
and after air-drying it reused directly for the next trial. The yield of
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less than 6% detected in the next three cycles, indicating the high
efficiency of the recovered Fe3O4NPs/GO–CuONPs catalyst (Fig. 2).
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An efficient Fe3O4NPs/GO–CuONPs-catalyzed three-component
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achieved. The process is simple and generates a diverse range of
propargylamines in good yields. The reaction has high atom
efficiency, since water is the only byproduct. All these facts together
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substrates, and cost effectiveness of the catalyst permit us to
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