Excellent catalytic activity of magnetically recoverable Fe3O4-graphene oxide nanocomposites prepared by a simple method

Article abstract of DOI:10.1039/c5dt01260k

An Fe₃O₄-graphee oxide nanocomposite has been synthesized via a chemical reaction with a magnetite particle size of 18-25 nm. The resulting nanocomposite can be easily manipulated by an external magnetic field, exhibits excellent cat

Full text of DOI:10.1039/c5dt01260k

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An easy-to-prepare Fe3O4-graphene oxide nanocomposite which works well as reusable catalyst
for A3-coupling reaction
Fe3O4 NP
SDS, RT
NaNO3, KMnO4
Conc. H2SO4, H2O2
Aldehyde + Alkyne + Amine
Propargylamine

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DOI: 10.1039/C5DT01260K
ARTICLE TYPE
Excellent catalytic activity of magnetically recoverable Fe3O4-graphene
oxide nanocomposites prepared by a simple method
Prasenjit Mandal and Asoke P. Chattopadhyay*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
Fe3O4-graphene oxide nanocomposite has been synthesized via a chemical reaction with magnetite particle size of 18-25 nm. The
resulting nanocomposite can be easily manipulated by an external magnetic field, exhibit excellent catalytic activity and may be reused
for several cycles with marginal loss of activity. This recyclable nanocomposite provides an efficient, economic, novel route for multi-
component A3 coupling reaction of aldehyde, amine and alkyne and gives the propargylamine in excellent yields.
excellent catalytic activity in the A3-coupling reaction.
10 Introduction
The development of a clean synthetic procedure has become
crucial and demanding because of increasing environmental
50 concerns. Heterogeneous organic reactions have many advantages
in this respect, such as ease of separation and handling, recycling,
and environmentally safe disposal.16 The heterogeneous catalysts
such as graphene oxide-Fe3O4 have attracted a great deal of
attention in recent years because of their high catalytic activity
55 and interesting structures.17 The Fe3O4-GO magnetic
nanoparticles have been most useful as heterogeneous catalysts
because of their numerous applications in biotechnology,
nanocatalysis, and medicine.18 In this context the magnetic
properties19 make possible the complete recovery of the catalyst
60 by means of an external magnetic field.20 On the other hand,
performing organic reactions in aqueous media has several
benefits because water would be considerably safe, nontoxic and
economical compared to organic solvents, abundant, and
environmentally friendly. Moreover, water exhibits selectivity
65 and unique reactivity, which is different from those in
conventional organic solvents.21 Therefore, the development of a
catalyst that is not only stable toward water but also simply
recyclable seems highly desirable.
In continuation of efforts to develop new synthetic methods for
70 the synthesis of propargylamines containing important
biologically active compounds,22 herein we report our
contribution to it viz. using GO-Fe3O4 nanocomposites as
excellent A3 coupling catalysts for its production. These materials
are robust, inexpensive, and easy to make. They are highly active
75 in the coupling reaction of aldehydes, amines, and alkynes, giving
propargylamines selectively with water as the only by-product
(Scheme-1). This feature is of importance for purity requirement,
especially in pharmaceutical industry. Simple mild and low-cost
reusable methods are highly desirable to avoid toxicity.
The highly efficient multi-component reactions in one-pot
syntheses play an important role in current organic synthesis1
since they not only exhibit selectivity and higher atom economy,
but allow construction of molecules of more diversity and
15 complexity and are thus highly valued among synthetic
methodologies. Furthermore, in many cases, multi-component
reactions are easy to perform leading to simple experimental
procedures as well as lower cost, time and energy. The catalytic
coupling reaction of aldehyde, amine and alkyne (A3 coupling) is
20 one of the best examples, where propargylamine is obtained as
the major product. During the past decade, much effort has been
spent to develop one-pot multi-component reactions to make new
carbon–carbon bonds.2 These are typically carried out using a
host of stoichiometric reagents and protecting groups, often
25 generating much waste in the process.
Propargylamines are important components of useful synthetic
precursors3 and biologically active compounds.4 This is reflected
in the interest shown in its synthesis.5-10 The particular coupling
reaction (A3 coupling) can be successful using various types of
30 catalyst such as copper-doped alumina with microwave
assistance,11 copper in solid phase systems,5 gold,12 silver,13
ruthenium–copper cocatalyst5 and iridium.10 The last two in the
list are toxic in nature and have low turnover numbers in their
respective reactions, are difficult to prepare and are not
35 environmentally friendly. Fe3O4 nanoparticles and Fe3O4-
graphene oxide (Fe3O4-GO) nanoparticle catalysts,14-15 on the
other hand, are prepared from iron-salts and graphite powder,
which are both cheap and readily available. They are also
moisture-sensitive, and environmentally friendly. Fe3O4
40 nanoparticles are superparamagnetic, with interesting magnetic
and biological activities. Such a novel composite with high
specific surface area and strong magnetic sensitivity exhibits
80
*Department of Chemistry, University of Kalyani, Kalyani
741235, India; Email: asoke@klyuniv.ac.in; Fax: +91-33-
45
25828282; Tel: +91-33-25828750
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Dalton Transactions
Experimental
of GO in water. SDS was added to the prepared Fe3O4
nanoparticle, which was then added slowly to the GO
solution, along with ammonia solution, with constant stirring
for 30 min to make all materials dissolve completely. The
temperature was raised to 85 0C, and a 30% ammonia
solution was added to adjust the pH to 10. After being rapidly
stirred for 30 min, the solution was cooled to room
temperature. The dark black coloured solution was then
filtered and washed with Milli-Q water/ethanol and dried in
vacuum at 70 0C. In this powdered Fe3O4-GO nanocomposite,
the weight ratio of Fe3O4 to GO was 2:1. (See Scheme 1)
Materials
55
Graphite powder (70 μm, Qingdao Graphite Company),
KMnO4, FeCl3.6H2O, H2SO4, sodium dodecylsulfate (SDS),
FeSO4.7H2O, ammonia solution, H2O2. All chemicals were
reagent grade and purchased from Sinopharm Chemical
Reagent Co. Ltd. Milli-Q (Millipore, Billerica, MA, USA)
and nanopure (double distilled water, filtered through 200 μm
filter) water was used in all experiments.
5
60
10
Preparation
of
water-soluble
magnetic
Fe3O4
Typical procedure for the A3 coupling reaction
nanoparticles
Magnetically active Fe3O4 nanoparticles were synthesized by
chemical co-precipitation of Fe3+ and Fe2+ ions in an alkaline
65
70
75
The reactions were carried out under conventional heating in
a conventional round bottomed flask (rbf), under constant
stirring. The typical A3 coupling reaction was performed as
follows. 0.50 mmol aldehyde, 0.60 mmol amine and 0.75
mmol alkyne were taken in a 50 ml rbf with 6 ml water. 0.05
mmol catalyst was added to it. The reaction mixture was
solution, followed by
a treatment under hydrothermal
15
20
25
30
conditions.23-24 5.7 g FeCl3.6H2O and 2.7 g FeSO4.7H2O were
dissolved in 10 mL nanopure water separately. These two
solutions were thoroughly mixed and added to 20 mL 10 M
ammonium hydroxide with constant vigorous stirring for 1 h
0
stirred for 16 h at 80- 90 C. Progress of the reaction was
0
to make all materials dissolved completely at 25 C. Colour
monitored by sampling aliquots of reaction mixture and
subsequent analysis by GC/GC-MS (VB-1 column, FID),
and/or purified by column chromatography (hexane, silica
gel:EtOAc = 4:1). Product identity and purity were confirmed
by 1H NMR spectroscopy and GC-MS spectrometry.
(Scheme 2)
of the solution changes from dark green to black indicating
the formation of Fe3O4 and completion of the reaction. Then
the dark black slurry of Fe3O4 particles was heated at 80 0C in
a water bath for 30 min. The particles thus obtained exhibited
a strong magnetic response. Impurity ions such as sulphates
and chlorides were removed by washing the particles several
times with nanopure water. Then the particles are dispersed in
20 mL nanopure water and sonicated for 10 min at 60 MHz.
The yield of precipitated magnetic nanoparticles was
determined by removing known aliquots of the suspension
and drying to a constant mass in an oven at 70 0C. The
prepared magnetic nanoparticles were stable at room
temperature (25-30 0C) without getting agglomerated.
R3
R2
O
N
Solvent/Neat ,900c
16hr.Catalyst.
H
Ph
R2R3NH
R1
H
R1
Ph
80
Conditions: aldehyde (1 eq.), amine (1.2 eq.), alkyne (1.5
eq.),GO-Fe3O4 (50 mg, 0.3 mol% Fe3O4 NP) in 5 mL solvent or
neat for 16 h, temperature above 90 0C; conversions were
determined by GC-MS and 1H NMR of crude reaction mixture.
Preparation of graphene oxide
Graphene oxide (GO) was prepared according to the modified
Hummers’ method from graphite powder.25 In detail, 1 g of
graphite powder and 300 mg of NaNO3 in 22 mL of
concentrated H2SO4 were vigorously stirred in an ice bath. 3
g of KMnO4 was added gradually with constant stirring, to
prevent the temperature of the mixture from exceeding 8-10
0C. The ice bath was then removed and the mixture was
stirred at 30 ±3 0c for 35 min. After completion of the
reaction, 45 mL of distilled water was added, and the
35
40
45
85 Results and discussion
Characterization
All synthesized nanoparticles were characterized in the usual
manner, viz. powder XRD, FT-IR, SEM, TEM,
thermogravimetric analysis (TGA) and Raman Spectroscopy.
90 Available data for different systems are given below.
Fe3O4 NP
NaNO3, KMnO4
0
temperature was kept at 95 C for 18 min. The reaction was
Conc. H2SO4, H2O2
SDS, RT
terminated by adding 140 mL of distilled water and 15 mL of
30% H2O2 solution. The reaction product was centrifuged
and washed successively with deionized water and 5% HCl
solution repeatedly until sulfate could not be detected with
BaCl2. Finally, graphene oxide was obtained after drying
under vacuum at 60 0C for 24 h.
Graphene
GO
Fe3O4-GO
Scheme 1. Synthesis of Fe3O4-GO nanocomposites. Red dots
95 indicate oxygen atoms, blue dots indicate Fe3O4 nanoparticles,
green lines represent SDS.
FTIR Study
50
Preparation of Fe3O4-GO nanocomposite.
The FTIR spectra of GO and GO–Fe3O4 hybrid are shown in Figs
1 and 2. The peak at 1711 cm−1 corresponding to ν(C O) of –
100 COOH on the GO shifts to 1634 cm−1 due to the formation of –
The Fe3O4-GO nanocomposite was synthesized by co-
precipitation26 of prepared Fe3O4 nanoparticle in the presence

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DOI: 10.1039/C5DT01260K
ARTICLE TYPE
35.31
35.2
35.0
34.8
34.6
34.4
34.2
34.0
33.8
33.6
33.4
481.50
786.18
5
10
15
20
25
30
35
40
1634.50
2922.77
1099.57
%T
33.2
33.0
32.8
32.6
32.4
32.2
32.0
31.8
3384.97
623.94
579.17
556.12
31.54
4000.0
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
450.0
cm-1
16.873
16.80
16.75
16.70
16.65
16.60
16.55
16.50
16.45
16.40
1711.25
492.55
%T
1569.11
16.35
16.30
16.25
16.20
16.15
16.10
16.05
16.00
15.95
3408.28
545.86
1092.26
15.877
4000.0
3600
3200
2800
2400
2000
1800
1600
1400
1200
1000
800
600
450.0
cm-1
FT-IR spectra of (Fig. 1, top) Fe3O4-GO nanocomposite and (Fig. 2, bottom) graphene oxide
-COO− after coating with Fe3O4. The characteristic peak
corresponding to the stretching vibration of Fe–O bond is also
shifted to 786.2 cm−1 compared to 545.9 cm−1 reported for bulk
Fe3O4,27-29 suggesting that Fe3O4 is bound to the -COO− on the
GO surface.
nanoparticles and in Fig. 4(b) that of Fe3O4-GO nanocomposite
are shown.
55
60
65
SEM Study
45
In Fig 3, SEM images of iron oxide nanoparticles, and
nanocomposites of iron oxide and graphene oxide (GO) are
shown. The images are clearly distinguishable, with the image
of iron oxide nanoparticles showing more cluster-like
compositions having larger grains, and its nanocomposite with
GO showing more uniform structure with smaller particles. In
Fig 4(a), energy dispersive X-ray analysis (EDX) of Fe3O4
Fig. 3. SEM images of Fe3O4 nanoparticles (left) and Fe3O4-
GO nanocomposite (right)
50
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ARTICLE TYPE
Atom
Normalized
wt %
76.26
Atom
%
47.93
52.07
Error
wt %
4.1
5
Fe
O
23.74
7.0
10
x 0.001 cps/eV
600
15
20
25
500
400
300
200
100
0
Atom
Normalized
wt %
88.45
Atom
%
63.68
29.29
7.03
Error
wt %
7.1
9.4
3.4
O
Fe
C
O
C
Fe
Fe
8.75
2.80
2
4
6
8
10
12
14
keV
Fig. 4. EDX images of Fe3O4 nanoparticles (top) and of Fe3O4-GO nanocomposites (bottom)
XRD Study
800
700
600
500
400
300
200
100
(002)
Next, the powder XRD data of iron oxide-GO nanocomposite
is presented in Fig. 5. The most striking feature is the typical
graphene (002) signature at 26.60. Usually, it is expected that,
as graphene is oxidized to graphene oxide, this peak disappears
and another one at much smaller angle (around 10-110)
appears. Also, as GO is made into a composite with metallic
nanoparticles, the peak at 26.60 is supposed to become broader,
with sharper peaks appearing at larger angles due to metal (or
metal oxide). The peaks at 24.30, 33.20 and 49.50 (marked in
blue) may be ascribed to (012), (104) and (024) lines of α-
haematite.30 The peak at 30.60, 35.70 and 41.10 may be
identified as (220), (311) and (400) of Fe3O4 (marked in red).10
Thus, beside the peak at 26.60 of graphene (002), the broader
peak centred at 43.50 is most probably composed of the (100)
peak of graphene, which is usually followed immediately by
the (101) peak.31 This may explain the broadness of the peak.
Please note that the (311) peak is expected to reduce much
upon formation of composite with GO,10 which is observed
here. While the peak at 24.30 could also be ascribed to a
different interplanar distance between graphene sheets, i.e. to
the (002) peak usually observed at 26.60, that would also lead
to a much broader peak in this region,32 which is not seen.
(311)
55
60
65
30
35
40
45
50
(104)
(024)
(100)(101)
(400)
(012) (220)
10
20
30
40
50
2 (degrees)
Fig. 5. Powder XRD spectrum of iron oxide GO
nanocomposite. Black, red and blue denote GO, Fe3O4 and α-
Fe2O3 respectively.
TGA Study
70
We next present thermogravimetric analysis of iron oxide and
iron oxide-graphene oxide nanocomposites. The TGA data of
the two systems are shown in Fig. 6 below. The TGA curve of
iron oxide nanoparticles show a 5% weight loss till 200 C,
followed by a further weight loss of 3.5% till 300 C, and a
0
0
0
0
75
slow loss of 1.5% from 300 C to 800 C. These indicate loss
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DOI: 10.1039/C5DT01260K
of moisture, some of it more tightly bound. The curve for iron
oxide-GO nanocomposite shows two shoulders, one around
GO can be clearly observed. This fact suggests the formation
of GO-Fe3O4 nanocomposites.
102
60
Raman spectrum of the Fe3O4-graphene oxide
nanocomposite
Fe3O4 nanoparticles
5
10
15
20
25
Fe3O4- Graphene oxide composite
100
Raman spectrum of the Fe3O4-graphene oxide nanocomposite
is given below (Fig. 9). Characteristic peaks of Fe3O4 alone,
which are seen in the range 200 – 600 cm-1, are absent in the
present spectrum. Only, the typical D and G peaks of graphene
oxide are seen at 1355.5 and 1585 cm-1 respectively. The ID/IG
ratio is 1.037, showing onset of disorder induced by iron
oxide.
98
96
94
92
90
88
65
70
75
80
85
0
200 400 600 800
5000
4000
3000
2000
1000
t (C)
Fig. 6. Thermogravimetric analysis of Fe3O4
nanoparticles and Fe3O4-GO nanocomposite
0
0
375 C (wt loss 1.5%) and another ~535 C (wt loss 2.7%).
The remaining weight loss upto 800 0C is ~5.6%. This
behaviour is clearly different from most known samples of
GO, which show upto 15% wt loss till 100 C33 and over 30%
0
wt loss beyond, in the 100-200 0C range.34 The nanocomposite
0
500
1000
1500
2000
2500
3000
3500
4000
4500
Raman shift (cm-1
)
0
shows far greater stability upto 800 C, most probably due to
binding of iron oxide nanoparticles to the carboxylate groups
etc. of GO platelets.
Fig. 9. Raman spectrum of Fe3O4-GO nanocomposite
The harmonics are also seen at 2711 and 3170 cm-1. Absence
of the iron oxide peaks in Raman spectrum may indicate low
concentration of Fe3O4 particles in GO. The actual amount of
Fe3O4 in GO was ascertained by Atomic Absorption
Spectroscopy (AAS) as 8.232% of Fe3O4 in GO (w/w).35
30
TEM Study
Fig.7 shows transmission electron micrographs of graphene
oxide-Fe3O4 nanocomposites. Low magnification TEM images
(Fig. 7(a) and (b)) reveals the clean images of small Fe3O4
nanoparticles distributed homogeneously in the flexible two
dimensional graphene oxide nanosheets. These images are the
direct proof of the formation of graphene oxide-Fe3O4
nanocomposites. Moreover, high resolution TEM images (Fig.
7(c), (d) and (e)) shows high crystallinity of Fe3O4 nano-
particles with the appearance of lattice fringes distributed in
the graphene oxide nanosheets matrix. The distance between
two lattice fringes are calculated by using the line profile (a
line drawn to the perpendicular of lattice fringes) graph shown
in Fig. 7(f). It shows that the distance between two lattice
fringes is 0.252 nm which corresponds to the (311) plane of
Fe3O4 crystal. Interestingly, the distinction among the
composites and the two constituents can be clearly made by
analyzing the selected area electron diffraction (ED) patterns.
Fig. 8 shows the ED patterns of Fe3O4 nanoparticles, graphene
oxide nanosheets and Fe3O4-GO nanocomposites. Fig. 8(a)
shows the ED pattern of Fe3O4 nanoparticles with the
appearance of rings indicates the polycrystalline nature of the
particles. Fig 8(b) shows the ED pattern of graphene oxide
taken from a single sheet. Hexagonal ED pattern of GO
indicates the single crystalline nature. Fig. 8(c) shows the ED
pattern taken from a Fe3O4-GO composite. Both ring like ED
pattern of Fe3O4 nanoparticles and hexagonal ED pattern of
90
Catalytic activity
35
40
45
50
55
Propargylic amines, products of the A3-coupling, are important
synthetic intermediates for natural products and potential
therapeutic agents.36 There is some report of single Fe3O4
nanoparticles catalyzing A3-coupling.37,38 As a comparison, we
used graphene oxide–Fe3O4 nanocomposite as a catalyst in A3-
coupling reaction.
95
100
105
110
Optimization of the performance of the catalyst with different
amounts of GO-Fe3O4 nanocomposite was carried out. The A3
coupling reaction of aryl aldehyde, amine and benzene alkyne
was examined by various catalysts of varying amounts was
examined (Table 1). In the absence of the nanocomposite, no
A3 coupling product was observed (Table 1, entry 10). As
expected, in the presence of catalyst, yield of the coupling
product was 93% for 5 wt% loading of GO-Fe3O4 nano-
composite catalyst. The catalytic activity increased with the
increase of the GO-Fe3O4 amount up to 5 wt% (Table 1, 1-7).
On the other hand, in a control experiment when homogeneous
phase Fe3O4, GO and an iron salt was used as the catalyst
under optimized conditions, only 19% , 25% and 83% yields
of the propargylamines (Table 1 Entry 8,9,11 ) were obtained.
Thus GO-Fe3O4 nanocomposite catalyst was more efficient in
A3 coupling reaction than the other substances used.

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(b)
(e)
(a)
(d)
(c)
5
10
15
20
25
30
35
200 nm
10 nm
100 nm
(f)
(311)
0.252 nm
10 nm
Fig. 7. (a) and (b) Low magnification TEM images, (c), (d) and (e) HRTEM images
of graphene oxide-Fe3O4 nanocomposites. (f) Line profile of Fig. 6 (e)
(a)
(b)
(c)
(440)
(a) (311)
(111)
(220)
Fig. 8. (a), (b) and (c) Electron diffraction patterns of Fe3O4, graphene oxide and
Fe3O4-graphene oxide nanocomposites respectively.
Table 1. Effect of catalyst in the 3-component coupling of
cyclohexanecarbaldehyde, piperidine, and phenylacetylene.
Conversions were determined by GC-MS and 1H NMR
analysis of crude reaction mixture.39
We also investigated the effects of reaction temperature,
solvents and reaction time on the catalytic efficiency. At a
lower reaction temperature (25 0C), the GO-Fe3O4
nanocomposite (0.0050 mmol) showed lower conversion
due to an incomplete reaction. We obtained excellent
50
55
60
65
N
CHO
40
Catalyst
N
H
0
Entry Catalyst
Catalyst amt (g)
0.0020
0.0025
0.0030
0.0035
0.0040
0.0045
0.0050
0.0050
Yield (%)
63
70
76
81
84
89
93
19
conversion at a higher reaction temperature (above 90 C).
1
2
3
4
5
6
7
8
GO-Fe3O4
GO-Fe3O4
GO-Fe3O4
GO-Fe3O4
GO-Fe3O4
GO-Fe3O4
GO-Fe3O4
Fe3O4
Solvent-free conditions proved to be the most effective for
the A3-coupling reaction (Table 2) and the conversion was
comparable to that of the homogeneous catalyst (Table 1).
As shown in Table 2, one could conclude from the influence
of the reaction time on the activity that the A3-coupling
reaction reaches completion after 24 h under the present
conditions. We obtained the products in moderate or low
conversions when using ethanol, dichloromethane (DCM),
N,N-dimethylformamide (DMF), tetrahydrofuran (THF),
acetonitrile, dimethyl sulfoxide (DMSO), and ethyl acetate
(Table 2). We also obtained slightly lower conversions when
using water or toluene as the solvent (Table 2). The
optimized reaction conditions include 0.5 equiv of aldehyde,
0.6 equiv of amine, 7.5 equiv of alkyne, and 0.0050 mmol of
GO-Fe3O4 nanocomposite at 90 0C, solvent-free in air.
9
10
11
GO
GO-Fe3O4
0.0050
0.0000
25
trace
83%
Salt of Iron 0.0100
Conditions of the above reaction were as follows. Aldehyde
(1 equiv), amine (1.2 equiv), alkyne (1.5 equiv) and GO-
Fe3O4 (50mg, 0.3 mol% Fe3O4 np) were taken in 5 mL
solvent or neat for 16 h, at temperature above 90 0C.
45

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reactants, which require low temperatures for storage, while
0
our optimum condition was above 90 C. We are currently
Table 2. Effects of various solvents in the 3-component
coupling of cyclohexanecarbaldehyde, piperidine, and
phenylacetylene catalyzed by the graphene–Fe3O4 catalyst.
investigating reaction with such substrates further.
50
We also investigated the effect of adding a mixture of GO
and Fe3O4 nanoparticles, instead of the nanocomposite, for
the reaction of cyclohexanecarbaldehyde, piperidine and
phenylacetylene. The yield obtained was 34.5%, less than
for nanocomposite (Table 3, entry 7). Also, in O2 and N2
atmosphere, the yields of the same reaction were 62% and
75% respectively. This may be related to the stability of
intermediate species involved.40, 41
5
N
CHO
Catalyst
Solvent/Neat
N
H
55
10
Entry Solvent (ml) Conversion (%)
1
2
Ethanol
DCM
48
70
Catalyst recycling
3
4
DMF
THF
Trace
09
60
The magnetically active GO-Fe3O4 nanoparticles were
adsorbed onto the magnetic stirring bar when the magnetic
stirring was stopped. The nanoparticles were then washed
with ethyl acetate, air-dried and used directly for the next
round of reactions without further purification. It was shown
that the nanocomposite catalyst could be recovered and
reused 12 times without significant loss of catalytic activity
(Table 4 and Fig. 10).
5
6
7
8
9
10
Acetonitrile
DMSO
ethyl acetate Trace
Water
Tolune
Neat
46
44
78
84
93
65
On the other hand the reaction depends on temperature and
time (data given in Supplementary Information). When
reaction time increases, the product yield also increases in
water and in solvent. In addition, it was found that at higher
temperatures GO-Fe3O4 nanaocomposite show good
catalytic activity; at 90 0c-120 0c, a 93% yield were obtained,
however at room temperature lower yields are obtained even
after longer reaction times.
Table 4. The reuse of catalyst in A3-coupling
Cycle
%
Yield by Cycle
%
Yield by
15
20
25
30
35
40
GC-MS
93
87
86
84
GC-MS
79
77
75
74
1
2
3
4
5
6
7
8
9
10
11
12
To expand the scope of this A3-coupling, we used various
aldehydes, alkynes, and amines were used as substrates
under the optimized reaction conditions, and the results are
summarized in Table 3. In general, both aliphatic and
aromatic aldehydes underwent the addition reaction
smoothly to provide the desired product in moderate to
excellent yields. As shown in Table 3 (entry 1), only a trace
of A3-coupling product was observed by NMR. Note that the
reactions proceeded smoothly to give the corresponding
propargylamines in a excellent yield. The presence of
electron-rich groups on the benzene ring (Table 3, entries 2–
5) increased the reactivities of the alkynes whereas electron-
withdrawing groups (Table 3, entry 6) on the benzene
decreased the yield. However, aliphatic aldehydes such as
83
82
72
71
70
75
80
85
90
100
80
60
40
20
0
cyclohexanecarboxaldehyde,
2-ethylbutanal
and
formaldehyde all give both higher conversions and greater
yields (Table 3, entries 7-10). It was important to notice that
formaldehyde provides excellent yield than other carbon
chain aliphatic aldehyde (Table 3, entry 10). Good yields
were observed when cyclic dialkylamines such as
pyrrolidine and morpholine were used (Table 3, entries 11
and 12).
The effect of electron-withdrawing groups on the alkyne was
also investigated (Table 3, entries 13 and 14). For 2-
ethynylpyridine and 2-ethynylthiophene, yields were 58%
and 37% respectively. The reaction failed with 2-
ethynylfuran. One problem could be the high volatility of the
1
2
3
4
5
6
7
8
9
10
11
12
No. of cycles
Fig. 10. Recycling of GO-Fe3O4 (3 mol %) catalyst for the t
A3-coupling of aldehyde, amine and alkyne in air in solvent-
free conditions.
Further examination of the catalyst after recycling it 12
times in the above reaction produced interesting results. The
FTIR and XRD spectra, given in Supplementary Information
(Figs. S1 and S2) have the following general features.
45
95

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DOI: 10.1039/C5DT01260K
Page 9 of 14
Dalton Transactions
►
ARTICLE TYPE
Table 3. Effect of substituents on the Fe3O4-GO nanocomposite catalysed A3 coupling reaction
R2
R3
N
GO-Fe3O4
NHR2R3
R1CHO
R4
R1
R4
Product
Entry
1
Aldehyde
Amine
Alkyne
Yield(%)
Trace
CHO
N
N
H
1a
2
3
81
84
CHO
Me
N
N
H
Me
2a
CHO
MeO
N
N
H
OMe
3a
4
5
6
76
70
64
CHO
CHO
CHO
N
N
H
4a
N
OMe
N
H
MeO
5a
Cl
N
N
H
Cl
6a
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 8

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Dalton Transactions
DOI: 10.1039/C5DPT0a12g6e0K10 of 14
7
93
CHO
N
N
H
7a
8
83
CHO
N
N
H
8a
9
70
CHO
N
N
H
9a
10
Formaldehyde
90
N
N
H
H
10a
11a
12a
O
N
O
11
83
CHO
N
H
12
78
CHO
N
N
H

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Page 11 of 14
Dalton Transactions
O
N
O
13
58
CHO
N
N
H
N
13a
14
37
CHO
N
N
H
S
S
14a
1
Most notably, the Fe-O bond, at 786.2 cm-1 in pristine
Fe3O4-GO nanocomposite, shifts to 772.50 cm-1 (Fig. S1 in
Supplementary Information). This shows that the Fe—O is
weakened after recycling the nanocomposite 12 times, but is
still intact. This is true of other features of the
nanocomposite (See Figs. S1 and S2 in Supplementary
Information). In other words, the essential features of the
nanocomposite remain intact after recycling a dozen times.
H-NMR (400MHz, CDCl ): δ= 7.36 (d, 2H), 6.80 (d, 2H),
3.81 (s, 3H), 3.07 (d, 1H), 32.65-2.58 (m, 2H), 2.38 (br, 2H),
2.10-2.02 (m, 2H), 1.76-1.56 (m, 8H), 1.45-1.40 (m, 2H),
1.30-1.01 (m, 3H), 1.00-0.86 (m, 2H),
1-(1-cyclohexyl-3-(3-methoxyphenyl)-prop-2-ynyl)
1piperidine (4a)
5
10
15
20
40
45
50
55
60
65
70
H-NMR (400MHz, CDCl ): δ= 7.20-7.17 (m, 1H), 7.05 (d,
3
1H), 6.97 (d, 1H), 6.81-6.80 (d, 1H), 3.81 (s, 3H), 3.10(d,
1H), 2.63-2.58 (m, 2H), 2.38 (br, 2H), 2.10-2.01(m, 2H),
1.76-1.53 (m, 8H), 1.45-1.40 (m, 2H), 1.31-1.01 (m, 3H),
1.01-0.85 (m, 2H)
1-(3-(4-chlorophenyl)-1-cyclohexylprop-2-ynyl)
1piperidine (5a)
H-NMR (400MHz, CDCl ): δ= 7.34 (d, 2H), 7.27 (d, 2H),
3.07 (d, 1H), 2.60-2.57(m,32H), 2.36 (br, 2H), 2.07-2.00 (m,
2H), 1.84-1.73 (m, 2H), 1.66-1.50 (m, 6H), 1.45-1.40 (m,
2H), 1.32-1.13 (m, 3H), 1.04-0.85 (m, 2H)
Conclusion
Nanocomposites of graphene oxide, doped with Fe3O4
nanoparticles, were prepared by a simple and robust method.
These particles were characterized by the usual manner.
They display excellent catalytic activity, which was used in
the one-pot synthesis of propargylamines following the A3-
coupling protocol.
Magnetic
behaviour
of the
nanocomposites may be employed to reuse the catalyst.
Currently, we are engaged in examining how both product
yield and catalyst life may be increased using easily
available means.
11-(1-Cyclohexyl-3-phenyl-2-propynyl]piperidine (6a)
H-NMR (CDCl , 400MHz, ppm): δ 7.46-7.44 (m, 2H),
3
7.30-7.24 (m, 3H), 3.09 (d, 1H), 2.65-2.60 (m, 2H), 2.44-
2.40 (m, 2H), 2.14-2.04 (m, 2H), 1.80-1.70 (m, 2H), 1.65-
1.51(m, 6H), 1.45-1.40 (m, 2H), 1.34-1.15 (m, 3H), 1.07-
0.88 (m, 2H).
Characterization of compounds
1-(1,3-diphenylprop-2-ynyl)piperidine (1a)
1H NMR (CDCl3, 250 MHz) δ: 1.57-1.63 (m, 2H), 1.72-
1.83 (m, 4H), 2.71-2.73 (m, 4H), 4.96 (s, 1H), 7.42-7.53 (m,
6H), 7.66-7.69 (m, 2H), 7.82 (d, j= 7.2 HZ, 2H),
1-[1-Cyclohexyl-3-(4-methylphenyl)-2-propynyl]
1piperidine (2a)
H-NMR (CDCl , 400MHz): δ 7.30 (d, 2H), 7.06 (d, 2H),
3.08 (d, 1H), 2.636-2.58 (m, 2H), 2.40-2.32 (m, 2H), 2.30 (s,
3H), 2.10-1.96 (m, 2H), 1.77-1.67 (m, 2H), 1.64-1.47 (m,
6H), 1.44-1.35 (m, 2H), 1.31-1.10(m, 3H), 1.06-0.88 (m,
2H),
N-(1-Isopropyl-3-phenyl-2-propynyl) piperidine (7a)
1
H-NMR (CDCl , 400MHz, ppm): δ= 7.47–7.44 (m, 2H),
7.34–7.30 (m, 3H), 3.01 (d, 1H), 2.69–2.65 (m, 2H), 2.43
(br, 2H), 1.97-1.93 (m, 1H), 1.68–1.57 (m, 4H), 1.49–1.46
(m, 2H), 1.10 (d, 3H), 1.02 (d, 3H).
3
25
30
35
1-[1-(1-Ethylpropyl)-3-phenyl-2-propynyl]
1(8a)
piperidine
H-NMR (CDCl , 400MHz, ppm): δ= 7.44-7.41 (m, 2H),
3
7.33-7.23 (m, 3H), 3.21 (d, 1H), 2.65-2.61 (m, 2H), 2.43-
2.39 (m, 2H), 1.78-1.65 (m, 1H), 1.61-1.50 (m, 6H), 1.51-
1.40 (m, 4H), 0.91 (t, 3H), 0.83 (t, 3H)
N-(3-Phenyl)-prop-2-ynyl) piperidine (9a)
1-(1-cyclohexyl-3-(4-methoxyphenyl) prop-2-ynyl)
piperidine (3a)

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DOI: 10.1039/C5DPT0a12g6e0K12 of 14
1
H-NMR (CDCl , 400MHz, ppm): δ= 7.44-7.42 (m, 2H),
7.31-7.28 (m, 3H), 3.47 (s, 2H), 2.56 (br, 4H), 1.69-1.60 (m,
55
Garcia, A. Tillack, C. G. Hartung and M. Beller,
Tetrahedron Lett., 2003, 44, 3217–3221
3
4H), 1.45 (br, 2H).
5 (a) M. A. Youngman and S. L. Dax, J. Comb. Chem.,
2001, 3, 469–472; (b) S. L. Dax, M. A. Youngman, P. Kocis
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4-(1,3-Diphenyl-prop-2-ynyl)-morpholine (10a)
1H NMR (300 MHz,CDCl3): ı 7.63 (d, J = 6.9 Hz, 2H),7.50
(d, J = 6.9 Hz, 2H), 7.36–7.31 (m, 6H), 4.78 (s, 1H), 3.71–
3.64 (m,4H), 2.62–2.56 (m, 4H);
5
60
11-[1-Cyclohexyl-3-phenyl-2-propynyl] pyrrodine (11a)
H-NMR (CDCl , 400MHz, ppm): δ= 7.43-7.42 (m, 2H),
3
10
7.31-7.24 (m, 3H), 3.33 (d, 1H), 2.74-2.70 (m, 2H), 2.64-
2.63 (m, 2H), 2.08 (d, 1H), 1.94 (d, 1H), 1.75-1.74 (m, 6H),
1.68-1.64 (m, 1H), 1.60-1.51 (m, 1H), 1.31-1.04 (m, 5H).
Besides these, 1H-NMR and HRMS data of several products
are given in Supplementary Information.42
65
6 (a) G. W. Kabalka, L. Wang and R. M. Pagni, Synlett,
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15
Acknowledgements
The authors would like to acknowledge help and assistance
received from Prof. K. Ghosh of the Dept. of Chemistry, and
from Prof. T. Basu of the Dept. of Biochemistry &
Biophysics, University of Kalyani. Help from DST-FIST,
DST-PURSE programs are gratefully acknowledged. PM
acknowledges financial support from RGNF from UGC,
New Delhi. Prof. A. Kaviraj, Dept. Of Zoology, University
of Kalyani must be acknowledged for help with AAS. The
authors gratefully acknowledge suggestions from the
anonymous referees, which not only improved the content,
but also pointed to new lines of investigation, esp. with
substituted alkynes.
75
20
80
10 S. Satoshi, K. Takashi and Y. Ishii, Angew. Chem., Int.
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25
11 For examples, see: (a) V. Polshettiwar, B. Baruwati and
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Dalton Transactions
DOI: 10.1039/C5DPT0a12g6e0K14 of 14
39 Reaction products were quantified using a Varian 3400
Gas Chromatograph equipped with a 30-m CP-SIL8CB
capillary column and flame ionization detector and
identified by Trace DSQIIGC equipped with a 60-m TR-50
MS capillary column
40 A. Berrichi, R. Bachir, M. Benabdallah and N.
Choukchou-Braham, Tetrahedron Lett., 2015, 56, 1302-
1306
5
10
15
41 J. Lim, K. Park, A. Byeun and S. Lee, Tetrahedron Lett.,
2014, 55, 4875-4878
42 1H NMR spectra (Fig. S3 - Fig. S12, Supplementary
Information) were recorded on a Bruker DRX-300A Vance
Spectrometer, with CDCl3 as solvent and TMS as the
internal standard. HRMS spectra of 13a and 14a (the last
two products) (Fig. S13 and S14, Supplementary
Information) were taken with a Xevo G2-SQTof Mass
Spectrometer (Waters).