NiO nanoparticles catalyzed three component coupling reaction of aldehyde, amine and terminal alkynes

Article abstract of DOI:10.1016/j.catcom.2015.09.031

This work reports a simple, microwave assisted facile and efficient protocol for the synthesis of nickel oxide nanoparticles (NiO NPs) by using only two reagents i.e. nickel acetate and benzylamine. Nickel acetate reacts with benzylamine to give nickel hydroxide and which on calcination give NiO NPs. Benzylamine plays various role in this reaction such as solvent, reactant and stabilizer. The developed protocol is faster, economically viable and environmentally benign as it is additive free. Transmission electron microscope (TEM) reveals the particles are in nano range and X-ray diffraction (XRD) data shows crystalline nature of NiO NPs. The prepared NiO NPs were used as heterogeneous catalyst for three component coupling reaction of aldehyde, amine with terminal alkynes. The catalyst could be recycled up to fourth run without significant loss in the catalytic activity.

Full text of DOI:10.1016/j.catcom.2015.09.031

Catalysis Communications 72 (2015) 174–179
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
NiO nanoparticles catalyzed three component coupling reaction of
aldehyde, amine and terminal alkynes
a
b
a,
Aravind L. Gajengi , Takehiko Sasaki , Bhalchandra M. Bhanage ⁎
a
Department of Chemistry, Institute of Chemical Technology, Matunga, Mumbai 400 019, India
Department of Complexity Science and Engineering, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 April 2015
Received in revised form 18 September 2015
Accepted 29 September 2015
Available online xxxx
This work reports a simple, microwave assisted facile and efficient protocol for the synthesis of nickel oxide nano-
particles (NiO NPs) by using only two reagents i.e. nickel acetate and benzylamine. Nickel acetate reacts with
benzylamine to give nickel hydroxide and which on calcination give NiO NPs. Benzylamine plays various role
in this reaction such as solvent, reactant and stabilizer. The developed protocol is faster, economically viable
and environmentally benign as it is additive free. Transmission electron microscope (TEM) reveals the particles
are in nano range and X-ray diffraction (XRD) data shows crystalline nature of NiO NPs. The prepared NiO NPs
were used as heterogeneous catalyst for three component coupling reaction of aldehyde, amine with terminal al-
kynes. The catalyst could be recycled up to fourth run without significant loss in the catalytic activity.
© 2015 Elsevier B.V. All rights reserved.
Keywords:
NiO NPs
Microwave
Benzylamine
Propargylamines
Coupling reaction
1
. Introduction
Synthesis of metal and metal oxide nanoparticles is important due to
Propargylamines are the products of three-component aldehyde-al-
kyne-amine coupling (A -coupling) reaction. They are useful building
3
blocks and important skeletons in biologically active compounds [16,
17]. They also serve as an important intermediate for natural product
synthesis [18]. In recent years, great efforts have been made with the
C–H bond activation reaction of terminal alkynes. The C–H bond of al-
kynes can be activated by employing various homogeneous transition
their extraordinary chemical and physical properties with their applica-
tions in diverse areas. Nickel oxide nanoparticles (NiO NPs) are used in
sensors [1], catalysis [2,3], electrochromic windows [4], glycerol stream
reforming [5], photocatalyst [6], energy storage [7] etc. Various research
groups have paid their attention towards the synthesis of NiO NPs using
several methods such as solvothermal [8], sol–gel technique [9], colloi-
dal precipitation [10], thermal decomposition method [11], and micro-
wave [12] etc.
Microwave-assisted synthesis has attracted much attention because
it has advantages of being faster, simpler, easy operation and more en-
ergy efficient [13]. The microwave process is more efficient than the
conventional processes for preparation of various metal oxide nanopar-
ticles [14,15]. The microwave associated synthesis enhances the kinetics
of reactions by one or two orders of magnitude over conventional
methods due to rapid initial heating and generation of localized high
pressure zones at reaction sites. The microwave power dissipated per
I
III
metal catalysts such as Ag salts [19], Au salen complexes [20], Au/
I
III
CeO
2
[21], Cu salts [22], Fe salts [23], Zn salts [24], Hg
2 2 3
Cl [25], InCl
[26], and InBr
3
[27]. These catalysts are expensive and suffer from one
or more drawbacks such as longer reaction time and difficulty in recov-
ery of the catalyst. The heterogeneous catalysts have numerous advan-
tages over the homogeneous catalysts because recyclability of catalysts
such as mesoporous copper silicate [28], mesoporous copper–alumi-
num based nanocomposites [29], Ag nanoparticles supported on nickel
metal organic framework [30], Ni–Y–Zeolite [31], Cu/C nanoparticles
3 4
[32], Co O nanoparticles [33], copper–zeolites [34] nanocrystalline
copper oxide [35], gold nanoparticles [36,37] has been reported for
the synthesis of three component coupling reaction of aldehyde,
amine and terminal alkynes.
2
unit volume is solvent is P = cE ƒε′′, where c, E, ƒ and ε′′ are respectively
radiation velocity, electric field in the material, radiation frequency and
dielectric loss constant, the most vital parameter which decides the abil-
ity of heating material in the microwave field.
Herein, we report a facile, rapid, template free and additive free
method for synthesis of NiO NPs by benzylamine alone which acts as
solvent, promoter and base under microwave irradiation. Furthermore,
we have shown the catalytic applications of synthesized NiO NPs as a
heterogeneous catalyst for three component coupling reaction of alde-
hyde, amine and terminal alkynes. To the best of our knowledge there
is no report on the three component coupling of aldehyde, amine and
terminal alkynes using NiO NPs.
⁎
Corresponding author.
E-mail addresses: bm.bhanage@gmail.com, bm.bhanage@ictmumbai.edu.in
(B.M. Bhanage).
http://dx.doi.org/10.1016/j.catcom.2015.09.031
566-7367/© 2015 Elsevier B.V. All rights reserved.
1

A.L. Gajengi et al. / Catalysis Communications 72 (2015) 174–179
175
Fig. 1. (a,b) TEM, (c) SAED Pattern. (d) EDAX (e) particle size histogram of NiO NPs.
It was observed that NiO NPs as a catalyst exhibits remarkable activ-
ity for a wide variety of substrates with good to excellent yields of de-
sired products along with catalyst recyclability.
aldehyde, amine and terminal alkynes are included in the supporting
information.
3. Results and discussion
2
. Experimental
3.1. Characterization of NiO NPs
The details regarding materials, catalyst preparation, catalyst charac-
terization and typical procedure for the three component coupling of
The morphology of prepared NiO NPs was observed by transmission
electron microscopy (TEM), which shows the particles are in nano
Fig. 2. XRD pattern of (a) nickel hydroxide and (b) NiO NPs.

176
A.L. Gajengi et al. / Catalysis Communications 72 (2015) 174–179
3 2
Fig. 3. (a) TPR spectrum (b) NH -TPD spectrum (c) N adsorption–desorption of NiO NPs.
Fig. 4. (a,b) XPS of Ni 2p and O 1s of NiO NPs. (c,d) TEM and XRD of NiO NPs after fourth run.

A.L. Gajengi et al. / Catalysis Communications 72 (2015) 174–179
177
Fig. 5. (a) Proposed reaction mechanism for synthesis of NiO NPs (b) GC of final organic reaction solution (c) mass spectra of final organic reaction solution.
range with well dispersion as shown in Fig. 1a and b. The selected
area electron diffraction (SAED) pattern (Fig. 1c) indicates the
crystalline nature of NiO NPs. Energy-dispersive X-ray spectrum
sample was pre-treated with argon gas at 400 °C for 1 h to remove
adsorbed water and other impurities. Then 5% H in argon was used
2
from 25 °C to 800 °C with temperature ramp of 10 °C/min having flow
3
(
EDAX) of NiO NPs (Fig. 1d) indicates the presence of Ni, oxygen
rate of 20 cm /min for the reduction of NiO. TPR reduction peak observed
and carbon elements. The carbon comes from the carbon tape
used for the EDAX analysis which indicates the purity of NiO NP
and distribution of nanoparticles are shown in particle size histo-
gram (Fig. 1e), it shows that most of the particles are in the range
of 4 to 12 nm.
at 432 °C as shown in Fig. 3a. The number of acidic sites on the catalyst
was studied by NH
at 400 °C for 30 min then cooled to room temperature. Then sample
was saturated with NH and thereafter desorbed from room temperature
3
-TPD. In this analysis, firstly the NiO NPs pre-treated
3
to 800 °C with the temperature ramp of 10 °C/min with helium gas. Two
acidic sites were noted at 165 °C and 605 °C as shown in Fig. 3b with 7334
μmol/g desorbed amount of NH3. The available surface area of NiO NPs
X-ray diffraction (XRD) analysis were performed with X-ray wave-
length of Cu Kα radiation at λ = 1.5405 Ǻ with the scanning rate of
2
°/min from 10° to 80° for Ni(OH)
2
and 20° to 80° for NiO NPs as
2
was calculated from N adsorption and desorption isotherms (Fig. 3c).
2
shown in Fig. 2. The average crystallite size of synthesized Ni(OH)
2
The BET surface area of the NiO NPs was found to be 39.89 m /g. Fig.
4(a,b) shows the XPS spectra for NiO NPs. The peaks appeared at 854.4
and 860.4 eV belong to Ni 2p3/2 level and peaks at 872.4 and 879.3 eV be-
long to Ni 2p1/2 level (Fig. 4a). The peak at 529.4 eV attributed to oxygen
(O 1s) (Fig. 4b).
and NiO NPs was determined according to Scherrer's equation: D =
kλ/βcosθ, where θ is Bragg angle, β is the full width at half maximum
in radians, it was found to be ~4 nm and ~6 nm respectively. The lattice
planes of (001), (100), (101), (011), (110) which are the characteristic
peak of hexagonal β-Ni(OH)
311), (222) planes of hexagonal NiO (JCPDS 78-0429).
The number of reducible species of NiO NPs was studied by tem-
perature programmed reduction (H -TPR). Before TPR analysis
2
(JCPDS 74-2075) and (111), (200), (220),
A plausible mechanistic pathway for the formation of NiO NPs has
been illustrated in Fig. 5a. The proposed mechanism was further sup-
ported by GC–MS analysis report of mother liquor and it shows the for-
(
2
mation of N-benzylacetamide as a by-product (Fig. 5b, c). Firstly, −NH
2
Scheme 1. NiO NPs catalyzed three component coupling reaction of aldehyde, amine with terminal alkynes.

178
A.L. Gajengi et al. / Catalysis Communications 72 (2015) 174–179
Table 1
Table 2
a
a
Optimization of reaction parameter for the synthesis of propargylamine.
NiO NPs catalyzed three-component coupling of aldehydes, alkynes and amines. a
Entry
Catalyst
mol%)
Solvent
Temp.
(°C)
Time
(h)
Yield
[%]
Entry Aldehydes
Amine
Alkyne
Product
Yield
[%]
b
b
(
Effect of catalyst screening
1
2
3
4
5
Ni(OAc)
NiCl ·6H
NiNO (15)
NiO bulk (15)
NiO NPs (15)
2
·4H
2
O (15)
Toluene
Toluene
Toluene
Toluene
Toluene
120
120
120
120
120
22
22
22
22
22
4
3
8
30
90
O (15)
1
95
2
2
3
2
3
96
98
Effect of catalyst loading
6
7
8
9
1
1
No catalyst
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
120
120
120
120
120
120
22
22
22
22
22
22
NR
NR
56
90
86
60
NiO NPs (05)
NiO NPs (10)
NiO NPs (15)
NiO NPs (20)
NiO NPs (50)
0
1
Effect of solvent
4
48
12
13
14
15
16
17
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
Neat
Water
Toluene
Ethylene-glycol
THF
120
100
120
120
100
120
22
22
22
22
22
22
NR
NR
95
NR
55
5
6
99
97
DMSO
NR
Effect of temperature
18
19
20
21
22
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
Toluene
Toluene
Toluene
Toluene
Toluene
RT
22
22
22
22
22
NR
55
94
90
95
100
120
130
140
Effect of time
7
8
41
98
23
24
25
26
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
NiO NPs (15)
Toluene
Toluene
Toluene
Toluene
120
120
120
120
24
22
20
18
90
95
93
44
a
Reaction conditions: aldehyde (1.0 mmol), amine (1.2 mmol), phenylacetylene (1.5
2
mmol), NiO NPs (15 mol%, 11.2 mg) at 120 °C for 22 h under N atmosphere. NR: No
reaction.
b
GC Yield. The GC yield was quantified with external standard using 1-(1,3-
diphenylprop-2-yn-1-yl)piperidine.
9
97
group of benzylamine reacts with nickel acetate to give A, which on re-
arrangement leads to the formation of nickel hydroxide and N-
benzylacetamide takes place. A similar type of mechanism has also
been reported in literature [14,38].
a
Reaction conditions: aldehyde (1.0 mmol), amine (1.2 mmol), phenylacetylene (1.5
2
mmol), NiO NPs (15 mol%, 11.2 mg) at 120 °C for 22 h under N atmosphere. NR: No
reaction.
b
GC Yield. The GC yield was quantified with external standard using 1-(1,3-
diphenylprop-2-yn-1-yl)piperidine.
3
.2. Catalytic activity of NiO NPs
The prepared NiO NPs were used as a catalyst for three component
The aromatic amine aniline provided less yield of 41% (Table 2, entry
7). This may be due to difference in nucleophilicity of aniline. When 4-
methyl phenylacetylene, ethynylcyclohexane were used in place of
phenylacetylene, the corresponding propargylamines were isolated in
good yields (Table 2, entries 8 and 9). A plausible reaction mechanism
for the three component coupling reaction is shown in Scheme 2 [33,
39]. Next, we examined the reusability of NiO NPs and catalyst shows
reusability up to fourth run without much loss in the catalytic activity
(Table 3). The leaching study of the NiO catalyst was carried out after
fourth run using ICP-AES analysis and only 1.2 ppm of the nickel was
noted in the reaction mixture. To know the morphological changes oc-
curred in the catalyst after fourth run we have carried out TEM and
XRD analysis of NiO NPs (Fig. 4c, d). This analysis indicates there are
no changes in the morphology and lattice planes of the NiO NPs.
coupling reaction of aldehyde, amine and terminal alkynes i.e.
propargylamines synthesis (Scheme 1). The coupling of bezaldehyde,
piperidine and phenylacetylene was selected as a model reaction. Vari-
ous reaction parameters such as catalyst screening (Table 1, entries 1–5)
catalyst loading (Table 1, entries 6–11), solvent (Table 1, entries 12–17),
temperature (Table 1, entries 18–22), time (Table 1, entries 23–26),
were studied. The final optimal reaction conditions are catalyst (15 mol%),
solvent: toluene (2 mL), temp: 120 °C and time 22 h for the reaction. On
the basis of the above optimized reaction conditions, the scope of substrates
for three-component coupling reaction was evaluated (Table 2). By
considering the above optimized reaction conditions, the three-component
coupling reaction proceeded smoothly and generated the desired product
of propargylamines in 95% yield, representing one of the best result
(
Table 2, entry 1). The various substrates of bezaldehyde bearing fluoro,
methoxy preceded smoothly providing desired products in good yield
Table 2, entries 2 and 3). However, the heterocyclic aldehyde gave
4. Conclusion
(
moderate yield as 48% (Table 2, entry 4). Further, cyclic aliphatic
amines such as pyrrolidine, morpholine were studied and it was found
that they also afforded excellent yield of respective products (Table 2,
entries 5 and 6).
In summary, we have prepared NiO NPs using benzylamine via
microwave method. Benzylamine exhibited versatile reagent such as
stabilizer, promoter and solvent. The preparation method for NiO NPs
is easy, inexpensive, rapid and economical. We have developed an

A.L. Gajengi et al. / Catalysis Communications 72 (2015) 174–179
179
Scheme 2. Mechanistic pathway of three component coupling reaction of aldehyde, amine with terminal alkynes using NiO NPs.
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