Highly active Pd nanoparticles dispersed on amine functionalized layered double hydroxide for Suzuki coupling reaction

Article abstract of DOI:10.1039/c1dt10697j

The synthesis of well dispersed palladium nanoparticles (1-5 nm) on diamine functionalized LDH is reported. The heterogeneous catalyst displayed unprecedented activity in Suzuki coupling reaction.

Full text of DOI:10.1039/c1dt10697j

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
Dalton
Transactions
Cite this: Dalton Trans., 2011, 40, 7130
www.rsc.org/dalton
COMMUNICATION
Highly active Pd nanoparticles dispersed on amine functionalized layered
double hydroxide for Suzuki coupling reaction†
Sudarshan Singha, Mitarani Sahoo and K. M. Parida*
Received 18th April 2011, Accepted 27th April 2011
DOI: 10.1039/c1dt10697j
The synthesis of well dispersed palladium nanoparticles (1–
5 nm) on diamine functionalized LDH is reported. The
heterogeneous catalyst displayed unprecedented activity in
Suzuki coupling reaction.
A heterogeneous system with the catalysts such as Pd/SiO2,11
Pd/C,12 Pd complex grafted on SiO2,13 Pd complex intercalated in
montmorillonite,14 Pd/Al2O3 and Pd/resin,15 Pd modified zeolite16
is a desired option for commercial realization but affords poor to
moderate conversion and selectivities in C–C coupling reactions.
Herein we describe a simple and efficient method for synthesis
of monodispersed Pd nanoparticles on diamine functionalised
LDH. The investigation of the reactivity of the resulting heteroge-
neous catalyst in Suzuki coupling would provide new information
in fine chemical synthesis.
The layer double hydroxide containing Zn–Al with Zn:Al molar
ratio 3 : 1 was prepared by the co-precipitation method at a
constant pH.17 ZnAl-LDH/SDS precursor was synthesized with
3 : 1 ratio of Zn(II) and Al(III) salts together with sodium dodecyl
sulfate (SDS) as an intercalated anion. The synthesis was carried
out by the co-precipitation method under a constant pH of ~7.10
LDH/SDS and CTAB (cetyl trimethyl ammonium bromide) were
dried at 80 ◦C overnight to maintain an anhydrous condition.
30 ml of methylene dichloride was added to 1.75 g of dried
CTAB (0.16 M) under nitrogen atmosphere. 4.6 ml of N-[3-
(trimethoxysilyl)-propyl] ethylenediamine (abbreviated as TPED)
was added to the dried LDH precursor containing SDS. Then the
CTAB solution containing methylene dichloride was added to the
mixture of TPED and LDH/SDS. The whole mixture was allowed
to react for two days at room temperature. Finally the product
was filtered, washed thoroughly with methylene dichloride. The
functionalized product was dried at room temperature and
abbreviated as LDH/TPED.
0.2 g of PdCl2 was dissolved in 10 ml of 2 M HCl solution of
methanol. The whole Pd solution was transferred to a solution
of 0.5 g functionalized LDH in 20 ml of methanol. The mixed
solution was stirred for 2 h at room temperature and cooled
overnight to 4 ◦C. The colored precipitate was filtered, washed
several times with methanol and dried in air. The prepared
Pd/LDH-complex (0.26 g) was reduced with NaBH4 (0.25 g,
7 mmol) in tetrahydrofuran (10 ml) with constant stirring for
3 h at room temperature. Finally the product was separated by
filtration and washed with tetrahydrofuran to give an air stable
black colored powder. The final product was abbreviated as LDH-
Pd0 (Scheme 1).
Palladium catalyzed Suzuki coupling is a fascinating reaction
from a catalysis science perspective.1 Pd nanoparticles as catalysts
have led to a growing interest which in turn has resulted in
an exponential growth in the number of nanoparticle synthesis
procedures reported for this metal.2 To date Pd nanoparticles have
been prepared by methods like inverse micelle system,3 reduction
of palladium acetate,4 electrochemical synthesis5 or sonochemical
reduction.6 Noble metal nanoparticles have a characteristic large
surface-to-volume ratio, and consequently large fractions of metal
atoms are accessible to reactant molecules, which in turn greatly
enhances the catalytic activity. However, small sized nanoparticle
have the tendency to aggregate which makes the preparation
procedure more laborious. Hence a major demand exists for the
ability to produce well-defined monodispered Pd nanoparticles in
the range of 1–4 nm. A key challenge in the application of these
materials in catalysis is agglomeration of the nanoparticles, which
can be overcome through surface functionalization/stabilization.7
The use of a heterogeneous catalyst in the liquid phase offers
several advantages over homogeneous ones such as ease of
recovery, and atom utility. Hydrotalcite of layered materials consist
of cationic brucite layers and anionic compounds in the interlayer.
The properties of the layered double hydroxide can be altered by
incorporating different anionic complexes and enzymes through
electrostatic interaction.8 LDH supported nanopalladium catalyst
for C–C coupling reactions has been reported by Choudary et al.9
However, to the best of our knowledge reports on covalent attach-
ment of various organic functionalities to the interlayer surface of
LDH are rather scarce. But modification of the LDH surface with
(3-aminopropyl) triethoxysilane by covalent attachment have been
reported by Park et al.10 by which unprecedented properties like
a matrix and affinities for various organic and inorganic species
other than conventional anionic guest can be obtained.
C& MC Department, Institute of Minerals & Materials Technology,
Bhubaneswar, 751013, Orissa, India. E-mail: paridakulamani@yahoo.com;
Fax: 91674-2581637
† Electronic Supplementary Information (ESI) available: XRD patterns,
FTIR studies, mechanism responsible for covalent attachment, catalytic
coupling reaction and catalytic reusability test up to four cycles. See DOI:
10.1039/c1dt10697j
The TEM images (Fig. 1) clearly revealed that most of the
particles are uniformly dispersed; particle size and morphology are
nearly identical. Some particles are in the range of 6–10 nm, but
most had a size in the range of 2–5 nm. TEM image confirms the
7130 | Dalton Trans., 2011, 40, 7130–7132
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
29Si CP MAS NMR spectra (Fig. 3) provide significant infor-
mation about the degree of functionalization and to evaluate the
nature of the M–O–Si bond around Si atom. Peaks in the T
region (deconvolution data) are contributed by Si atoms of the
triethoxy silane and are denoted by Tn (n = 0, 1, 2, 3), which are
used to describe the extent of cross-linking depending on M–O–Si
bond types. T3 represents the formation of three Si–O–M bonds,
which indicates complete cross-linking in the hybrid materials,
while T2 represents formation of two Si–O–M bonds bearing one
uncoordinated Si-OEt group. High intensity of T3 peak reveals the
high degree of condensation of the original triethoxy silane with
LDH.
Scheme 1 Schematic synthesis approach towards Pd0 nanoparticles.
Fig. 3 29Si CP MAS NMR spectra of LDH/TPED.
Fig. 1 (a) TEM image of Pd nanoparticles and histogram showing the size
distribution for the Pd nanoparticles. (b) TEM image of Pd nanoparticles
with electron diffraction pattern (inset, bottom right). (c) TEM image of
the recycled catalyst.
We choose a basic support, Zn–Al LDH as the material of
choice, not only to stabilize the nanopalladium particles but also
to provide adequate electron density to anchored Pd0 species to
facilitate the oxidative addition of halobenzene to Pd0. It is well
Table 1 Coupling of chloroarenes with arylboronic acid in the presence
highly crystalline nature of Pd particles. The interplanar spacing
of 0.22 nm, obtained from the fringes of the lattice, agrees well
with the (111) lattice spacing of face centered cubic (fcc) Pd.
The electron diffraction pattern exhibits (Fig. 1(b), inserted) four
diffuse rings that match well with the (111), (200), (220) and (311)
reflections of the fcc metal.
The X-ray photoelectron spectrum (XPS) data was recorded
(Fig. 2) in order to evaluate the exact oxidation state of palladium
before and after reduction. The binding energy of Pd 3d5/2 for the
sample before reduction (PdII) was observed at 336.9 eV. After
reduction 3d5/2 and 3d3/2 peaks appear at 335.4 and 340.7 eV
respectively which are similar to the previously reported value for
Pd0.18 This is an indication that PdII is reduced to Pd0.
of LDH-Pd(0)
Entry
R, X
R¢
Yield (%)
1
2
3
4
5
6
7
8
H, Br
H
H
H
H
4-MeO
4-Me
H
H
H
94
86
75
91
65
76
96
83
81
90
72
78
88
77
70
82
64
71
4-Me, Br
4-MeO, Br
4-NO2, Br
H, Br
H, Br
H, I
4-Me, I
4-MeO, I
4-NO2, I
H, I
H, I
H, Cl
9
10
11
12
13
14
15
16
17
18
H
4-MeO
4-Me
H
H
H
H
4-MeO
4-Me
4-Me, Cl
4-MeO, Cl
4-NO2, Cl
H, Cl
H, Cl
Reaction conditions: Haloarene (1 mmol), aryl boronic acid (1.5 mmol),
potassium carbonate (3 mmol), Pd(0) catalyst (0.03 g), 1,4-dioxane–
water(5 : 1) = 10 ml, T = 80 ◦C, time = 10 h.
Fig. 2 X-ray photoelectron spectra of LDH-Pd(0).
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 7130–7132 | 7131
©

View Article Online
known that the activation of the C–Cl bond is much more difficult
than the C–Br and C–I bonds and in general requires harsher
conditions in a heterogeneous catalytic system. But in the present
study the reaction results are quite impressive for aryl chlorides
(Table 1). The LDH supported Pd0 catalyst is potent enough to
activate the C–Cl bond to produce biaryl compounds showing
great potential for practical applications. The possible mechanistic
pathway is depicted in Scheme 2. The reaction is believed to pass
through the oxidative addition of aryl halides to Pd0 followed by
the formation of transient organo-metallic species reaction with
boronic acid.19
reaction and the result clearly showed that Pd particles remains
homogeneously dispersed on the support, without any appreciable
change in size and morphology. It is envisaged that palladium
nanoparticles stabilized by TPED could potentially be exploited
more extensively in the field of catalysis in contrast to bulky
stabilizers such as dendrimers, polymers and alkanethiols.
In conclusion, we have shown that functionalization provides
a better control of the loading of palladium and a relatively
uniform distribution of nanoparticles in the layered material. Most
importantly, the catalyst was reusable without Pd leaching and
agglomeration which is an important step towards a simple system
with the potential for commercial exploitation of heterogeneous
catalysts in water-mediated C–C coupling reactions.
References
1 D. Zim, A. L. Monteiro and J. Dupont, Tetrahedron Lett., 2000, 41,
8199.
2 (a) D. Astrue, Inorg. Chem., 2007, 46, 1884; (b) H. Bonnemann and
R. M. Richards, Eur. J. Inorg. Chem., 2001, (10), 2455.
3 J. E. Martin, J. P. Wilcoxon, J. Odinek and P. Provencio, J. Phys. Chem.
B, 2002, 106(5), 971.
4 G. Schmid, M. Harms, J. O. Malm, J. O. Bovin, J. V. Ruitenbeck, H. W.
Zandbergen and W. T. Fu, J. Am. Chem. Soc., 1993, 115, 2046.
5 M. T. Reetz and W. Helbig, J. Am. Chem. Soc., 1994, 116, 7401.
6 Y. Mizukoshi, K. Okitsu, Y. Maeda, T. A. Yamamoto, R. Oshima and
Y. N a g at a , J. Phys. Chem. B, 1997, 101(36), 7033.
7 (a) L. N. Lewis, Chem. Rev., 1993, 93, 2693; (b) R. S. Underhill and G.
Liu, Chem. Mater., 2000, 12, 3633.
8 S. Bhattacharjee, T. J. Dines and J. A. Anderson, J. Phys. Chem. C,
2008, 112, 14124.
9 B. M. Choudary, S. Madhi, N. S. Chowdari, M. L. Kantam and B.
Sreedhar, J. Am. Chem. Soc., 2002, 124, 14127.
10 A.-Y. Park, H. Kwon, A. J. Woo and S.-J. Kim, Adv. Mater., 2005, 17,
106.
Scheme 2 Plausible mechanistic pathway for Suzuki coupling.
Generally, mineral bases are such as alkali metal carbonates or
K3PO4 are used as bases in Suzuki coupling. The use of water either
as a solvent or additive 20 help with the solvation of these organic-
insoluble materials. Also, as organoboron compounds are quite of-
ten stable to protolytic decomposition by water.21 Cammidge and
co-workers have reported heterogeneous Pd phosphine catalysts
and used these in Suzuki coupling in a DME:water (3 : 1) solvent
mixture.22 Low yields are obtained with nonpolar solvents such as
toluene and o-xylene, while polar solvents such as tetrahydrofuran,
1,4-dioxane and 1,4-dioxane–water (5 : 1) gave good yields.
Notably, it was reported that the reduced Pd0 species were
more easily leached into the solution than PdII species.23 Hence
the use of heterogeneous catalyst, free from Pd leaching and
agglomeration, is highly desirable for achieving high activity and
catalyst reusability. In this context, the catalyst was removed from
the solution after approximately 50% conversion at the reaction
temperature. The isolated solution did not exhibit any further
reactivity under similar reaction conditions. These studies indicate
that the loss of the palladium active site is negligible, which could
account for the preservation of catalytic activity. The used catalyst
was examined by TEM (Fig. 1(c)) after the completion of the
11 F. Zhao, B. M. Bhanage, M. Shirai and M. Arai, Chem.–Eur. J., 2000,
6, 843.
12 M. Julia, M. Duteil, C. Grard and E. Kuntz, Bull. Soc. Chim. Fr., 1973,
2791.
13 B. M. Bhanage, M. Shirai and M. Arai, J. Mol. Catal. A: Chem., 1999,
145, 69.
14 (a) B. M. Choudary, M. R. Sarma and K. K. Rao, Tetrahedron Lett.,
1990, 31, 5781; (b) R. S. Varma, K. P. Naicker and P. J. Leisen,
Tetrahedron Lett., 1999, 40, 2075.
15 A. Biffis, M. Zecca and M. Basato, Eur. J. Inorg. Chem., 2001,
1131.
16 L. Djakovitch and K. Koehler, J. Am. Chem. Soc., 2001, 123, 5990.
17 Y. Zhao, F. Li, R. Zhang, D. G. Evans and X. Duan, Chem. Mater.,
2002, 14, 4286.
18 W. P. Zhou, A. Lewera, R. Larsen, R. I. Masel, P. S. Bagus and A.
Wieckowski, J. Phys. Chem. B, 2006, 110, 13393.
19 B. M. Choudary, S. Madhi, M. L. Kantam, B. Sreedhar and Y. Iwasawa,
J. Am. Chem. Soc., 2004, 126, 2292.
20 J. A. Anderson, A. Athawale, F. E. Imrie, F.-M. McKenna, A. McCue,
D. Molyneux, K. Power, M. Shand and R. P. K. Wells, J. Catal., 2010,
270, 9.
21 N. E. Leadbeater, Chem. Commun., 2005, 2881.
22 A. N. Cammidge, N. J. Bates and R. K. Bellingham, Chem. Commun.,
2001, 2588.
23 F. Zhao, B. M. Bhanage, M. Shirai and M. Arai, Chem. Eur. J., 2000,
6, 843.
7132 | Dalton Trans., 2011, 40, 7130–7132
This journal is
The Royal Society of Chemistry 2011
©