Clay entrapped nickel nanoparticles as efficient and recyclable catalysts for hydrogenation of olefins

Article abstract of DOI:10.1016/j.tetlet.2008.01.061

Nickel nanoparticles are prepared in the interlamellar spaces of K10-Montmorillonite clay by chemical reduction at moderate temperatures. These clay entrapped nickel nanoparticles are characterized by UV-vis, powder XRD, EDX and HRTEM studies. The resultant ecofriendly supramolecular assembly with nickel content (2.84 wt %) has good catalytic efficiency in hydrogenation of alkenes and alkynes with hydrazine as a reducing agent in ethanol medium. Advantages of the present study include absence of an external hydrogen source, catalyst reusability and a green medium.

Full text of DOI:10.1016/j.tetlet.2008.01.061

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 1818–1823
Clay entrapped nickel nanoparticles as efficient and recyclable
catalysts for hydrogenation of olefins
Amarajothi Dhakshinamoorthy, Kasi Pitchumani *
School of Chemistry, Madurai Kamaraj University, Madurai 625 021, India
Received 24 October 2007; revised 3 January 2008; accepted 10 January 2008
Available online 15 January 2008
Abstract
Nickel nanoparticles are prepared in the interlamellar spaces of K10-Montmorillonite clay by chemical reduction at moderate
temperatures. These clay entrapped nickel nanoparticles are characterized by UV–vis, powder XRD, EDX and HRTEM studies. The
resultant ecofriendly supramolecular assembly with nickel content (2.84 wt %) has good catalytic efficiency in hydrogenation of alkenes
and alkynes with hydrazine as a reducing agent in ethanol medium. Advantages of the present study include absence of an external
hydrogen source, catalyst reusability and a green medium.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Nickel; Nanoparticles; K10-Montmorillonite; Hydrogenation; Olefins
1
3b
13c
Recent advances in organic synthesis in which smectite
clays are used as catalysts or catalyst supports have led
to a rational approach to the design of new heterogeneous
tion of ketones,
aldehydes
and semihydrogenation
1
3d
(ethanol as hydrogen source) of alkynes.
Surprisingly,
until now there has been no report of hydrogenation of ole-
fins and enones. Also, a general problem of metal nanopar-
ticles is their tendency to undergo agglomeration, which
increases their particle size, and therefore, dramatically
1
catalysts. Amongst the advantages of pillared smectite
clays, the most significant is their large size and hence they
can accommodate a greater number of reagents for better
2
14
catalytic activity under controlled conditions. A number
reduces the catalytic activity. Two general strategies have
of methods have been used to prepare nickel nanoparticles
both in solution as well as in heterogeneous media. In a
seminal approach, Rao et al. prepared nickel nanoparticles
in Montmorillonite clays via in situ reduction of Ni(II)
been developed to stabilize the particle size of the metal,
namely, supporting the metal nanoparticles on suitable
1
5
solid surfaces or by using suitable ligands. New possibil-
ities for nickel catalysis can be developed when the nickel
nanoparticles could be stabilized by encapsulating them
in a structured host to combine the unique catalytic prop-
erties of nickel nanoparticles with reaction shape-selectivity
effects.
3
with boiling ethylene glycol. In subsequent studies, nickel
nanoparticles were also prepared via various approaches
4
such as in water-in-oil microemulsions, aqueous hydra-
5
6
7
zine, ethylene glycol, N,N-dimethylformamide as well
8
9
as on heterogeneous media like carbon nanotubes, silica,
surfactant, activated carbon, and on protein.
This prompted us to develop nickel(0) entrapped in a
clay matrix from cheap precursors (Scheme 1) in a simple
experimental protocol, using hydrazine as a reducing
agent. This selective and active hydrogenation catalyst
1
0
11
12
Recently, catalytic applications of nickel nanoparticles
have gained significance and they have been used effectively
1
3a
16
for chemoselective oxidative coupling of thiols,
reduc-
can replace Raney nickel and other common hetero-
geneous hydrogenation catalysts such as Pt and Pd, and
also reduce costs since these catalysts are normally used
in excess and generate poisonous waste end-products after
*
Corresponding author. Tel.: +91 452 2456614; fax: +91 0452 2459181.
E-mail address: pit12399@yahoo.com (K. Pitchumani).
0
040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.01.061

A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron Letters 49 (2008) 1818–1823
1819
0
.09
Ni2+-K10 clay
N2H4, NH3
0.05
0
(
a)
Ni(0)-K10 clay
alkene/alkyne/enone
alkane/ ketone
o
EtOH, 8 h, 70 C
(
b)
Scheme 1. Hydrogenation of unsaturated substrates with clay entrapped
nickel nanoparticles.
-
0.05
-
0.068984
5
the reaction is complete. Our method is also expected to
result in the following advantages: (a) Ni -exchanged
K10-Montmorillonite acts a source for metallic nickel,
40
600
700
800
900
2
+
Wavelength [nm]
2
Fig. 2. (a) UV–vis spectrum (in ethanol) of the NiCl solution from nickel
supported on K10-Montmorillonite and (b) UV–vis spectrum (in ethanol)
of the reduced nickel.
(
b) hydrazine not only acts as a reducing agent but also
generates an inert atmosphere by releasing nitrogen, (c)
ethanol or water can be used as a solvent, (d) one of the
most significant advantages of this methodology is that it
avoids the risk of handling external molecular hydrogen.
We report here the preparation, characterization and
hydrogenating properties of nickel nanoparticles entrapped
in K10-Montmorillonite clay. The catalyst was prepared by
reduction with hydrazine in an aqueous alkaline medium
(Fig. 1). The catalyst was characterized by UV–vis, powder
XRD and also by high resolution transmission electron
2
+
microscopy. The reduction of Ni was considered com-
plete after the disappearance of a broad band at 630–
680 nm (Fig. 2). A powder XRD study was undertaken
for the estimation of phases present in the prepared mate-
rials (Fig. 3).
2
+
using Ni -exchanged K10-Montmorillonite clay as a pre-
cursor. The black suspension after centrifugation was
washed with deionized water and dried at 100 °C for 6 h.
The Ni content of these clay entrapped nanoparticles was
found to be 2.84 wt %, by using energy dispersive X-ray
analysis (EDX, a technique used in conjunction with
SEM). Importantly, EDX analysis also indicated that,
within the detection limits, nickel was the only element
present in these particles. The recovered catalyst (after
the third cycle) was also subjected to EDX analysis and
the nickel content was only marginally decreased
All the reflection peaks can be indexed as face centered
cubic Ni. Three characteristic peaks for nickel (2h = 44.5,
51.8 and 76.4), marked by their indices, [(111), (200) and
(222)] were observed. In accordance with the above two
analyses, it can be concluded that the nanoparticles pre-
pared in this method are pure nickel of fcc structure. No
oxides or hydroxides of nickel were observed, as was
evident from the phase analysis by XRD. This may be
explained by the nitrogen gas which is produced continu-
ously during the reaction, which in turn created an inert
atmosphere. A typical high-resolution transmission elec-
tron micrograph (HRTEM) and the size distribution of
the nickel nanoparticles obtained in a layer of the clay
matrix are shown in Figure 4. The particles are essentially
mono-dispersed with an average diameter of 15–20 nm
(Fig. 4a–d). The corresponding electron diffraction
patterns for the particles (Fig. 4e) revealed that the
(
2.82 wt %). Though a change in shape and size of the
nanoparticles may have occurred, this, however, does not
affect the catalytic activity. It is relevant to note here that
1
7
El-Sayed has established that changes in the size and
shape of the nanoparticles could occur during the course
of their catalytic function. The absence of chlorine in the
sample, showed that the entrapped nickel is zerovalent
Fig. 1. EDX spectra of clay entrapped nickel nanoparticles.

1820
A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron Letters 49 (2008) 1818–1823
Table 1
Optimization of the reaction conditions for the hydrogenation of styrene
a
using clay entrapped nickel nanoparticles as catalyst
Ni(0)-K10 (2.84%)
b
Run
Catalyst
mg)
Hydrazine
(mL)
Solvent
Time
(h)
Yield
(%)
(
1
2
3
4
5
6
7
8
9
None
None
0.1
0.2
0.1
None
0.1
0.1
0.1
0.2
0.2
ACN
ACN
EtOH
ACN
ACN
ACN
ACN
ACN
ACN
ACN
EtOH
EtOH
ACN/H
Hexane
8
8
8
—
—
—
—
—
—
39
91
78
100
62
100
100
91
c
100
100
d
e
50
50
None
100
100
50
100
100
100
100
100
24
8
8
3
8
8
8
8
8
8
8
10
11
12
13
14
a
0.1
0.2
0.2
0.2
f
2
O
Reagents and reaction conditions: styrene (0.45 mmol), solvent (3 mL),
atb 70 °C.
Yield determined by GC.
c
d
e
f
K10-Montmorillonite clay used as catalyst.
Ni –K10 clay used as catalyst.
Reaction carried out in rt.
Acetonitrile–water (1:1) mixture.
2+
Fig. 3. (a) Powder XRD pattern of K10-Montmorillonite clay. (b)
Powder XRD pattern of nickel nanoparticles entrapped on K10-Mont-
morillonite clay matrix.
Fig. 4. (a–c) HRTEM images of highly dispersed nickel nanoparticles embedded in clay matrix. (d) A HRTEM image of a selected portion of nickel
nanoparticles on clay matrix. (e) Selected area electron diffraction pattern for the nanoparticles shown in (a) and also the electron intensity profile expected
for fcc nickel nanocrystallites.

A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron Letters 49 (2008) 1818–1823
1821
Table 2
Catalytic reduction of various unsaturated substrates with nickel nanoparticles embedded in clay matrix
a
b
Entry
Substrate
Product
Yield (%)
c
1
82 (84)
2
3
74
68
4
5
88
OCH3
OCH3
c
79 (81)
OCH3
OCH3
d
6
7
8
52
91
84
N
N
O
O
9
74
81
COOMe
COOMe
1
1
0
1
O
O
d
48
1
2
3
Ph
C
C
S
H
Ph CH2CH3
S
78
79
1
a
b
c
Reaction conditions: Substrate (0.9 mmol), hydrazine hydrate (0.4 mL), ethanol (3 mL), Ni–K10 (100 mg), 8 h, 70 °C.
Yield of isolated product characterized by H NMR.
Yield after third cycle.
Yield determined by GC.
1
d

1822
A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron Letters 49 (2008) 1818–1823
1
8
composition of the nickel nanoparticles was fcc and the
diffraction line width is consistent with a mean crystallite
size of 4 nm. The high intensity spot clearly indicates the
nanocrystalline nickel nanoparticles (Fig. 4e).
Preparation of nickel nanoparticles entrapped on K10-
2
+
Montmorillonite clay: Ni -supported on K10-clay
(500 mg) was suspended in 1 mL of 25% aqueous ammonia.
Then, 2 mL of hydrazine hydrate was added to the solution
and the mixture was stirred at 60 °C for 5 h, cooled and cen-
trifuged with continuous washing with distilled water until
the mother liquor was neutral. The solid was then dried
and stored.
Hydrogenation of styrene as a model system was used to
study the efficiency of the material as a catalyst. Without
any catalyst and hydrazine, with hydrazine alone and cat-
alyst alone, no reduction occurred at room temperature
or at reflux (Table 1, entries 1, 5–6). Furthermore, experi-
ments performed on native clay as well as Ni exchanged
K10 clay did not yield any reduced product, highlighting
the key role of the nickel nanoparticles (Table 1, entries
General procedure for the hydrogenation of alkene, alkyne
or enone: The catalyst (100 mg) was suspended in 3 mL of
ethanol followed by the addition of substrate (0.1 mL,
0.9 mmol). To this heterogenous solution, hydrazine
hydrate (0.4 mL) was added slowly and the resulting mix-
ture was heated with stirring for about 8 h at 70 °C. The
reaction was monitored by gas chromatography. The cooled
solution was filtered, dried with anhydrous sodium sulfate
and the solvent was removed to give the pure product. In
some cases, the product was purified by column chromato-
graphy (silica gel 60–120 mesh size). The structure of the
2
+
2
–3). On the other hand, with clay-entrapped nickel nano-
particles, hydrogenation was successful at reflux tempera-
ture in the presence of hydrazine (Table 1, entries 7–10).
However, lowering the amount of hydrazine caused an
increase in the reaction time and hence an excess quantity
of hydrazine was used in all the cases. Good to high yields
were obtained in refluxing ethanol, acetonitrile (ACN) or
an acetonitrile/water mixture (Table 1, entries 11–13), thus
this catalytic system works efficiently in polar protic, polar
aprotic and non-polar solvents without the detectable
formation of byproducts. Ethanol proved to be the best
solvent in this study.
To extend the scope, various other olefins (Table 2,
entries 1–4) were examined. Simple olefins such as styrene
and its derivatives reacted very efficiently. Surprisingly,
a,b-unsaturated carbonyl compounds, except cyclohexe-
none, were also selectively reduced to the corresponding
ketone in good yields. Furthermore, an ester also under-
went selective hydrogenation. Phenylacetylene was reduced
completely to ethylbenzene. Allyl phenyl sulfide was also
efficiently reduced without loss in catalytic activity. Other
functional groups such as nitro, carbonyl and aromatic
rings were not reduced.
1
product was confirmed from H NMR and GC analyses.
In conclusion, we have shown that nickel nanoparticles
entrapped in a clay matrix can be easily prepared and were
found to exhibit good catalytic activity for the reduction of
a wide range of substrates. This catalytic system is economic
and ecofriendly as it requires neither high temperature nor
harsh acids or bases, and produces high yields with excellent
chemoselectivity. The work-up and product isolation from
the catalyst is easy. Catalyst poisoning, a common problem
with heterogeneous catalysts, is significantly reduced (the
catalytic efficiency remaining unaltered even after the third
run).
Acknowledgements
K.P. thanks the University Grants Commission (for
sanctioning UPE programme to Madurai Kamaraj Univer-
sity) and the Department of Science and Technology, New
Delhi for financial assistance. A.D.M. thanks the Council
of Scientific and Industrial Research, New Delhi for the
award of Senior Research Fellowship.
The recyclability of the clay entrapped nickel nanoparti-
cles was also surveyed. After the reaction, the solution was
filtered, washed with CH Cl (2 Â 5 mL) and dried at
2
2
6
0 °C. The catalyst could be reused directly without further
purification and was used for three consecutive runs with-
out the loss of activity (Table 2).
References and notes
We suggest that the efficient catalytic activity of the
present system can be attributed to the very homogeneous
dispersion of nickel nanoparticles (as evidenced from
HRTEM) inside the clay matrix due to stabilization of
the particles, thus avoiding their aggregation and allowing
control of the particle size. Moreover, the substrate diffu-
sion rate to the active sites of the nickel nanoparticles
may also be increased due to the large size of the clay
matrix.
Preparation of Ni -exchanged clay: K10-Montmorillon-
ite clay (Fluka) was used as received. The nickel ions were
exchanged into the K10-Montmorillonite clay (10 g) by
stirring with nickel chloride (1 M in 25 mL of water for
1
2
. Balogh, M.; Laszlo, P. Organic Chemistry Using Clays; Springer:
Berlin/Heidelberg, 1993.
. Pinnavaia, T. J. In Laszlo, P., Ed.; Preparative Chemistry Using
Supported Reagents; Academic Press: San Diego/London, 1987;
Chapter 25, p 483.
3
. (a) Ayyappan, S.; Subbanna, G. N.; Gopalan, R. S.; Rao, C. N. R.
Solid State Ionics 1996, 84, 271–281; (b) Ahmed, O. S.; Dutta, D. K.
Langmuir 2003, 19, 5540–5541.
4
5
. Chen, D.-H.; Wu, S.-H. Chem. Mater. 2000, 12, 1354–1360.
. Boudjahem, A.-G.; Monteverdi, S.; Mercy, M.; Bettahar, M. Lang-
muir 2004, 20, 208–213.
2
+
6
7
. Wu, S.-H.; Chen, D.-H. J. Colloid Interf. Sci. 2003, 259, 282–286.
. Zhang, Z.; Chen, X.; Zhang, X.; Shi, C. Solid State Commun. 2006,
1
39, 403–405.
1
g of clay) solution at room temperature for 72 h. The clay
8
. Zhang, Z. J. Mater. Res. 2003, 18, 604–608.
was filtered, washed thoroughly with distilled water and
then dried.
9
. (a) Martınez, S.; Manas, M. M.; Vallribera, A.; Schubert, U.; Roigc,
A.; Molinsc, E. New J. Chem. 2006, 30, 1093–1097; (b) Oyamada, H.;

A. Dhakshinamoorthy, K. Pitchumani / Tetrahedron Letters 49 (2008) 1818–1823
1823
Akiyama, R.; Hagio, H.; Naito, T.; Kobayashi, S. Chem. Commun.
006, 4297–4299.
0. Chen, D.-H.; Hsieh, C.-H. J. Mater. Chem. 2002, 12, 2412–
415.
1. (a) Wojcieszak, R.; Zielinski, M.; Monteverdi, S.; Bettahar, M. M. J.
Colloid Interf. Sci. 2006, 299, 238–248; (b) Jacob, D. S.; Genish, I.;
Klein, L.; Gedanken, A. J. Phys. Chem. B 2006, 110, 17711–
15. (a) Haruta, M.; Date, M. Appl. Catal., A 2002, 222, 427–437; (b)
Haruta, M. Stud. Surf. Sci. Catal. 2003, 145, 31–39; (c) Hornstein, B.
J.; Finke, R. G. Chem. Mater. 2003, 15, 899–909; (d) Astruc, D.; Lu,
F.; Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 117, 8062–8063;
Astruc, D.; Lu, F.; Aranzaes, J. R. Angew. Chem., Int. Ed. 2005, 44,
7852–7872; (e) Ghosh, S. K.; Nath, S.; Kundu, S.; Esumi, K.; Pal, T.
J. Phys. Chem. B 2004, 108, 13963–13971; (f) Praharaj, S.; Ghosh, S.
K.; Nath, S.; Kundu, S.; Panigrahi, S.; Basu, S.; Pal, T. J. Phys.
Chem. B 2005, 109, 13166–13174; (g) Budroni, G.; Corma, A. Angew.
Chem., Int. Ed. 2006, 118, 3406–3409; Budroni, G.; Corma, A. Angew.
Chem., Int. Ed. 2006, 45, 3328–3331.
2
1
1
2
17714.
1
1
2. Okuda, M.; Iwahori, K.; Yamashita, I.; Yoshimura, H. Biotechnol.
Bioeng. 2003, 84, 187–194.
3. (a) Saxena, A.; Kumar, A.; Mozumdar, S. J. Mol. Catal. A: Chem.
2
007, 269, 35–40; (b) Kidwai, M.; Mishra, N. K.; Bansal, V.; Kumar,
A.; Mozumdar, S. Catal. Commun. doi:10.1016/j.catcom.2007.
6.010; (c) Kidwai, M.; Bansal, V.; Saxena, A.; Shankar, R.;
16. (a) Latif, K. A.; Choudhury, D. R. Tetrahedron Lett. 1968, 9, 1735–
1739; (b) Petit, G. R.; Van Tamelen, E. E. Organic Reactions XII;
John Wiley: New York, 1964; p 521; (c) Wolfrom, M. L.; Karabinos,
J. V. J. Am. Chem. Soc. 1946, 68, 724–725.
17. Narayanan, R.; El-Sayed, M. A. J. Phys. Chem. B 2005, 109, 12663–
12676.
0
Mozumdar, S. Tetrahedron Lett. 2006, 47, 4161–4165; (d) Alonso,
F.; Osante, I.; Yus, M. Adv. Synth. Catal. 2006, 348, 305–308.
4. (a) Daniel, M.-C.; Astruc, D. Chem. Rev. 2004, 104, 293–346; (b)
Wolf, A.; Schuth, F. Appl. Catal., A: Gen. 2002, 226, 1–13.
1
18. Zach, M. P.; Penner, R. M. Adv. Mater. 2000, 12, 878–882.