Pd on amine-terminated ferrite nanoparticles: A complete magnetically recoverable facile catalyst for hydrogenation reactions

Article abstract of DOI:10.1021/ol070290p

The present communication reports a facile route for Pd(0) immobilization on the surface of amine-terminated Fe₃O₄ and NiFe ₂O₄ nanoparticles for a series of hydrogenation reactions. The catalysts are completely recoverable with the simple application of an external magnetic field, and the efficiency of the catalyst remains unaltered even after 10 repeated cycles for each of the reactions.

Full text of DOI:10.1021/ol070290p

ORGANIC
LETTERS
2
007
Vol. 9, No. 7
419-1421
Pd on Amine-Terminated Ferrite
Nanoparticles: A Complete Magnetically
Recoverable Facile Catalyst for
1
†
Hydrogenation Reactions
Debanjan Guin, Babita Baruwati, and Sunkara V Manorama*
Nanomaterials Laboratory, Inorganic and Physical Chemistry DiVision,
Indian Institute of Chemical Technology, Hyderabad 500 007, India
manorama@iict.res.in
Received February 5, 2007
ABSTRACT
3 4 2 4
The present communication reports a facile route for Pd(0) immobilization on the surface of amine-terminated Fe O and NiFe O nanoparticles
for a series of hydrogenation reactions. The catalysts are completely recoverable with the simple application of an external magnetic field, and
the efficiency of the catalyst remains unaltered even after 10 repeated cycles for each of the reactions.
Conventionally, heterogeneous catalysis is favored over
homogeneous catalysis for a large number of applications
in both fundamental research and industrial applications due
sites, an associated higher surface energy unfavorably in-
creases the particles’ tendency to agglomerate and hence nul-
lifies the high surface area advantage. Thus, to derive maxi-
mum benefit, surface-modified catalysts have been designed.5
Surface modification with appropriate capping agents
offers better dispersion of the catalyst in appropriate solvents,
and thus better performance can be anticipated in their
various applications. Surface-modified nanoparticles can be
used as noble metal supports to prepare heterogeneous
catalysts that are more accessible to the reactants. Tamura
1
to its ease of handling, simple workup, and regenerability.
Despite their synthetic simplicity, heterogenized catalysts are
2
typically less effective than their homogeneous counterparts.
To overcome this limitation, nanosized catalysts have been
1
introduced, as they are endowed with larger surface area
when compared to their bulk counterparts. Recently, nano-
crystalline metals and metal oxides have been efficiently used
as environmentally friendly solid catalysts and also as solid
supports for organic transformation reactions such as epoxi-
6
et al. have shown that BINAP- capped Pd nanoparticles
possess the ability to catalyze asymmetric hydrosilylation
1
3
4
dation, benzylation, coupling reactions, etc. Although a
higher surface area affords nanomaterials with more active
(
3) Mertins, K.; Iovel, I.; Kischel, J.; Zapf, A.; Beller, M. Angew. Chem.,
Int. Ed. 2005, 44, 238.
4) (a)Yang, Q.; Ma, S.; Li, J.; Xiao, F.; Xionga, H. Chem. Commun.
(
†
IICT Communication Number: 061010.
2006, 2495. (b) Andrews, P. S.; Stepan, F. A.; Tanaka, H.; Ley, V. S.;
Smith, D. M. AdV. Synth. Catal. 2005, 347, 647.
(1) (a) Choudary, B. M.; Kantam, M. L.; Ranganath, K. V. S.; Mahendar,
K.; Sreedhar, B. J. Am. Chem. Soc. 2004, 126, 3396. (b) Choudary, B. M.;
Ranganath, K. V. S.; Pal, U.; Kantam, M. L.; Sreedhar, B. J. Am. Chem.
Soc. 2005, 127, 13167. (c) Kantam, M. L.; Shiva Kumar, K. B.; Sridhar,
Ch. AdV. Synth. Catal. 2005, 347, 1212. (d) Choudary, B. M.; Ravichandra,
S. M.; Klabunde, K. J. J. Am. Chem. Soc. 2005, 127, 2020.
(5) (a) Mandal, S.; Roy, D.; Chaudhari, R. V.; Sastry, M. Chem. Mater.
2004, 16, 3714. (b) Tatumi, R.; Akita, T.; Fujihara, H. Chem. Commun.
2006, 3349. (c) White, A. M.; Johnson, A. J.; Koberstein, T. J.; Turro, J.
N. J. Am. Chem. Soc. 2006, 128, 11356. (d) Niu, Y.; Yeung, K. L.; Crooks,
R. M. J. Am. Chem. Soc. 2001, 123, 6840. (e) Lewis, L. N. Chem. ReV.
1993, 93, 2693. (f) Underhill, R. S.; Liu, G. J. Chem. Mater. 2000, 12,
3633.
(2) Abu-Reziq, R.; Alper, H.; Wang, D.; Post, M. L. J. Am. Chem. Soc.
2
006, 128, 5279.
1
0.1021/ol070290p CCC: $37.00
© 2007 American Chemical Society
Published on Web 02/27/2007

of styrene to give chiral alcohols. The primary formidable
task in using such nanoparticles for heterogeneous catalysis
is the problem associated with the separation of the catalyst
after the reaction. It is here that nanoparticles, especially
superparamagnetic particles amenable for magnetic separa-
tion, come as a redeemer.7 Magnetic separation is an
attractive alternative to filtration or centrifugation as it
prevents loss of the catalyst and the reusability increases.
This makes the catalyst cost-effective and promising for
2 4 3 4
The concentration of Pd in NiFe O -DA-Pd and Fe O -
DA-Pd as estimated by inductively coupled plasma atomic
emission spectroscopy (ICP-AES) analysis is 8.54 and 5.87
wt %, respectively. To monitor the changes in the composi-
tion, Pd concentration was estimated after five cycles in both
the catalysts and found to be 8.49 and 5.84, respectively.
This proves that there is no loss of Pd due to leaching during
the reaction. This explains the unaltered efficiency of the
catalyst even after 10 cycles.
industrial applications. Recently, Hu et al. reported a Fe
3
O
4
-
X-ray photoelectron spectroscopy studies were carried out
to establish the oxidation state of Pd in the catalyst. Figure
1 is the Pd 3d5/2 binding energy spectrum that consists of a
immobilized chiral Ru catalyst for the asymmetric hydro-
8
9
genation of aromatic alcohols. Yi et al. reported the
synthesis of nano Pd on SiO -coated Fe and their
application in the hydrogenation of nitrobenzene.
2
2 3
O
The present communication reports a facile route for
Pd(0) immobilization on the surface of amine-terminated
Fe O and NiFe O nanoparticles for a series of hydrogena-
3 4 2 4
tion reactions. These include aromatic nitro and azide
compounds to their respective amine derivatives with better
efficiency than earlier reports10 and saturation reaction of
double- and triple-bond compounds. To the best of our
knowledge, this is a first report for the use of these catalysts
for the named reactions with high efficiency. The catalysts
are completely recoverable with the simple application of
an external magnetic field and remain active even after 10
repeated cycles for each of the reactions.
Figure 1. Binding energy spectra of Pd 3d5/2 in the as synthesized
catalysts showing the presence of only Pd(0) in them.
The synthesis and characterization of the nanosized
1
1,12
NiFe
Anchoring of dopamine molecules on the surface of
NiFe and Fe has been achieved by refluxing and
2 4 3 4
O and Fe O have been reported previously.
2
O
4
3 4
O
single peak at 334.42 eV with a full width at half-maximum
sonication, respectively. The procedure for the synthesis of
the materials is provided as Supporting Information. Here-
(fwhm) of 1.6 attributed to the Pd in the zero oxidation state.
This unambiguously establishes that Pd exists as Pd(0), a
primary requirement for the Pd-catalyzed hydrogenation
reactions.
The magnetization Vs applied field plot shows that the
particles are superparamagnetic at room temperature. The
magnetization does not saturate up to 8000 and 20 000 G
after, the two catalysts will be referred to as NiFe
2 4
O -
DA-Pd and Fe -DA-Pd.
3
O
4
The FTIR spectra of surface-functionalized nanoparticles
and pure dopamine are given in the Supporting Information.
In the FTIR spectrum, the peak at 3410 cm-1 has been
assigned to the surface-adsorbed water and peaks at 2924
for NiFe
almost negligible. The magnetizations for the as synthesized
NiFe and Fe nanoparticles at the highest applied fields
are 43.3 and 57.10 emu/g, respectively. The magnetization
results indicate the suitability of nanosized NiFe and
Fe as catalyst supports for the magnetic separation.
Figure 2a,b shows the TEM micrographs of the NiFe
DA-Pd and Fe -DA-Pd catalysts before reaction. Figure
c,d shows the micrographs of the NiFe -DA-Pd catalyst
2 4 3 4
O and Fe O , respectively, and the coercivity is
-1
and 2848 cm are assigned to the C-H stretching vibrations
-
1
of aromatic groups. The peak at 1616 cm is due to the
O
2 4
3 4
O
-
1
N-H bending. The peak at 1486 cm is due to C-H
bending of aromatic groups, whereas peaks at 1263 and 1121
2 4
O
-1
cm are due to C-O stretching and aliphatic C-H bending,
3 4
O
-
1
respectively. The sharp peak at 594 cm is the IR signature
2
4
O -
for ferrite particles.
3 4
O
2
2 4
O
(
6) Tamura, M.; Fujihara, H. J. Am. Chem. Soc. 2003, 125, 15742.
after three and five reactions. It is observed that the
synthesized particles are spherical, about 10-12 nm in size,
and nearly monodisperse.
The morphology and size of the particles do not change
considerably even after five reactions. This result again
supports the unaltered efficiency of the catalyst. The figure
also shows the photograph of the catalyst being pulled
magnetically.
In a typical reaction, 2 mmol of the reagent is dissolved
in 10 mL of ethyl acetate or ethanol with 0.025 g of catalyst
under 1 atm of hydrogen pressure. Completion of the reaction
is monitored by thin-layer chromatography (TLC). After
(7) (a) B o¨ nnemann, H.; Brijoux, W.; Brinkmann, R.; Dinjus, E.; Jou aˆ en,
T.; Korall, B. Angew. Chem., Int. Ed. Engl. 1991, 30, 1312. (b) Lu, P.;
Toshima, N. Bull. Chem. Soc. Jpn. 2000, 73, 751. (c) Tsang, S. C.; Caps,
V.; Paraskevas, I.; Chadwick, D.; Thompsett, D. Angew. Chem., Int. Ed.
2
004, 43, 5645. (d) Stevens, P. D.; Fan, J.; Gardimalla, H. M. R.; Yen, M.;
Gao, Y. Org. Lett. 2005, 7, 2085. (e) Lu, A.-H.; Li, W. C.; Kiefer, A.;
Schmidt, W.; Bill, E.; Fink, G.; Sch u¨ th, F. J. Am. Chem. Soc. 2004, 126,
8
616.
(
(
(
8) Hu, A.; Yee, G. T.; Lin, W. J. Am. Chem. Soc. 2005, 127, 12486.
9) Yi, K. D.; Lee, S. S.; Ying, Y. J. Chem. Mater. 2006, 18, 2459.
10) Raja, R.; Glovko, B. V.; Thomas, M. J.; Berenguer-Murcia, A.;
Zhou, W.; Xie, S.; Johnson, G. F. B. Chem. Commun. 2005, 2026.
11) Baruwati, B.; Reddy, K. M.; Manorama, S. V.; Singh, R. K.; Om
Parkash. Appl. Phys. Lett. 2004, 85, 2833.
12) Guin, D.; Baruwati, B.; Manorama, S. V. J. Mol. Catal. A, Chem.
005, 242, 26.
(
(
2
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Org. Lett., Vol. 9, No. 7, 2007

Table 1. Summary of the Observations from the Different
a
2 4
Reactions Carried Out on the NiFe O -DA-Pd Catalyst
Figure 2. TEM micrographs of the NiFe
DA-Pd (b) catalyst before reaction. NiFe
(c) and 5 reactions (d), respectively.
2
O
4
-DA-Pd (a) and Fe
4
3 4
O -
2
O -DA-Pd catalyst after
3
a
Reactant amount, 2 mmol; catalyst amount, 0.025 g; and solvent
amount, 10 mL; respectively, in each case. a Yield after 5 reactions.
completion, the catalyst is separated by a small magnet
placed at the bottom of the reaction vessel. Thereafter, the
catalyst is washed with ethyl acetate and used for the next
reaction. The catalytic reactions have been repeated, and even
after 10 cycles there is no deterioration in the catalytic
efficiency. The time required for the completion of the
reactions using ethanol as a solvent was less than that using
ethyl acetate. This is because of the complete heterogeneous
behavior of the catalyst in ethyl acetate, whereas in the case
of ethanol, the catalyst is readily dispersible thereby provid-
ing more active sites. This latter phenomenon may therefore
In summary, we have synthesized an efficient Pd(0)
catalyst immobilized on amine-modified NiFe O and Fe O
2 4 3 4
nanoparticles highly suitable for the hydrogenation of
aromatic nitro and azide compounds to their respective
amines as well as saturation of different kinds of unsaturated
compounds. The catalyst is completely magnetically recover-
able because of the superparamagnetic behavior of NiFe
2 4
O
and Fe nanoparticles. The efficiency of the catalysts
3
O
4
remains unaltered even after 10 cycles making them remark-
able catalysts for industrial applications because of their
efficiency, ease of handling, and cost effectiveness.
1
3
be termed as “solubilized heterogeneous catalysis”. The
detailed observations of all the reactions are given in Table
1
. The unaltered efficiency of the catalyst even after 10 cycles
Acknowledgment. D.G. and B.B. acknowledge CSIR,
India, for the Senior Research Fellowships. The authors are
thankful to Dr. K. Rajender Reddy for the help in recording
is obvious from our TEM micrographs and AES studies
where no significant change in the catalyst is observed even
after five reactions. All the above reactions have also been
13
GCMS spectra and to Dr. B. Jagadeesh for C NMR spectra.
3 4
repeated using the Fe O -DA-Pd catalyst, and except for the
extended time period, no other difference is observed. The
lower Pd concentration as determined from ICP-AES in the
latter catalyst explains the longer reaction period.
Supporting Information Available: Experimental meth-
1
13
ods, FTIR spectra, VSM plots, GCMS spectra, H and
C
spectra, and table for the Fe O -DA-Pd catalyst. This material
3
4
is available free of charge via the Internet at http://pubs.acs.org.
OL070290P
(
13) Price, E. K.; Mason, P. B.; Bogdan, A. R.; Broadwater, J. S.;
Steinbacher, L. J.; McQuad, D. T. J. Am. Chem Soc. 2006, 128, 10376.
Org. Lett., Vol. 9, No. 7, 2007
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