Controllable synthesis of palladium nanoparticles and their catalytic abilities in Heck and Suzuki reactions

Article abstract of DOI:10.1016/j.ica.2014.01.041

The monodisperse palladium nanoparticles with the size of about 5.0 nm were prepared by the thermal decomposition of palladium acetylacetonate in the presence of oleylamine and borane tributylamine complex. The palladium nanoparticles were loaded on the a

Full text of DOI:10.1016/j.ica.2014.01.041

Inorganica Chimica Acta 414 (2014) 59–62
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Controllable synthesis of palladium nanoparticles and their catalytic
abilities in Heck and Suzuki reactions
Yong Li a, , Yu Dai , Zhengyin Yang , Tianrong Li
⇑
a
b
b
a
Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan 430074, PR China
College of Chemistry and Chemical Engineering and State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 October 2013
Received in revised form 13 January 2014
Accepted 22 January 2014
Available online 8 February 2014
The monodisperse palladium nanoparticles with the size of about 5.0 nm were prepared by the thermal
decomposition of palladium acetylacetonate in the presence of oleylamine and borane tributylamine
complex. The palladium nanoparticles were loaded on the active carbon black by the sonication followed
by the acetic acid cleaning, and then they are used as the nanocatalysts for carbon coupling reactions,
such as Heck reactions and Suzuki reactions. The nanocatalysts can promote Heck reactions and Suzuki
reactions efficiently with the high catalytic activity and stability. The nanocatalysts can be recycled for at
least six times and their morphologies almost have no great changes. In addition, the catalytic perfor-
mances of nanocatalysts would decrease with the repeated usages due to the increasing sizes of the pal-
ladium nanoparticles.
Keywords:
Palladium nanoparticles
Transmission electron microscope
Catalytic ability
Heck reaction
Ó 2014 Elsevier B.V. All rights reserved.
Suzuki reaction
1
. Introduction
Carbon–carbon bonds are found in many compounds that exhi-
tion, alkylation, hydrodealkylation, polymerization so on [12–14].
Recently, the investigations of NPs with precisely controlled shape
and size have attracted great interest due to their great surface areas,
and their wide applications, such as medicine industry, catalysis,
energy, pollution controlling and so on [15–17]. Among the NPs,
Pd NPs have gained considerable interest in the last few decades
[18,19]. Furthermore, Pd NPs loaded on the inorganic supports can
increase the stability of NPs, and thus the catalytic efficiency would
increase greatly [20].
Herein, we described a simple method for preparing Pd NPs and
carbon loaded Pd NPs (denoted as Pd/C NPs) by high-temperature
decomposition method. Furthermore, the catalytic efficiencies of
Pd/C catalysts were evaluated by Heck and Suzuki reactions.
bit very important biological, pharmaceutical and materials prop-
erties [1–3]. Classically, the synthesis of carbon–carbon bonds
always involved the nucleophilic aromatic substitution reactions,
which required the use of electron-deficient aryl halides or N2 as
a leaving group [4–8]. The synthetic procedure is fussy and rigor-
ous, so new mild and general methods should be developed. The
discovery of transition-metal mediated reactions was important
for the synthesis. Palladium (Pd) catalysts are usually used in
cross-coupling reaction which can generate carbon–carbon bonds
efficiently and simply [9]. While homogeneous Pd catalysts are
not used in industrial application due to the difficulty in separating
and recycling, low catalytic efficiency, and the high leaching of me-
tal species [10,11]. In order to solve the problem, new strategies
should be developed.
Metallic nanoparticles (NPs) are of wide interest since they lead
to many interesting size-dependent electrical, chemical, and optical
properties. Pd related NPs, such as Pd NPs, PdM (M = Cu, Ag, Ni, Co,
Pt) alloy NPs and Pd core/shell (Au/Pd, Ag/Pd, Pd/Pt) NPs on various
supports were most widely applied to many important reactions,
such as carbon coupling reactions, small molecule electro-oxida-
tion/reduction reactions, hydrocarbon hydrogenations, isomeriza-
2
. Experimental
2.1. Materials and instrumentation
2
All the reagents, such as palladium acetylacetonate (Pd(acac) ),
oleylamine (OAm, technical grade, 70%), carbon black (Kejen EC
00J), acetic acid, borane tributylamine complex (BTB), Et N, aryl
3
3
halides, styrene, phenylboronic acid were purchased and used
without further purification. Water used in the experiments was
deionized (DI) and doubly distilled prior to use. Unless otherwise
stated, all the experiments were performed under air atmosphere.
Transmission electron microscope (TEM) images and selected
area electron diffraction (SAED) patterns were acquired on a Philips
⇑
Corresponding author. Tel.: +86 027 67883739.
E-mail address: liyong07@126.com (Y. Li).
http://dx.doi.org/10.1016/j.ica.2014.01.041
020-1693/Ó 2014 Elsevier B.V. All rights reserved.
0

6
0
Y. Li et al. / Inorganica Chimica Acta 414 (2014) 59–62
CM 20 (200 kV) transmission electron microscope. X-ray powder
diffraction (XRD) patterns of the samples were recorded on a Bruker
In this reaction, OAm is acted as the reaction solvent, surfactant
and reductant. And BTB served as a coreductant. The NPs became
monodisperse during the 1 h growth at 90 °C due to Ostwald ripen-
ing. In the synthetic procedure, the use of OAm is very important. If
anthor alkylamine, such as hexadecylamine, octadecylamine, or
dodecylamine was used, no high quality Pd NPs can be obtained,
showing that the double bond present in oleylamine plays a critical
in Pd NP stabilization and growth with a narrow size distribution.
However, oleylamine alone cannot be used to prepare monodis-
perse Pd NPs. The weak reducing power offered by oleylamine pro-
longs the reduction process, causing multinucleation and an
uneven growth rate over differently sized Pd nuclei. BTB fared bet-
ter than other borane reductants we tested, such as borane–mor-
AXS D8-Advanced diffractometer with Cu
k = 1.5418 Å). The yields of Heck and Suzuki reactions were deter-
mined by GC analysis.
K
a
radiation
(
2.2. Synthesis of Pd NPs
2
Under a nitrogen flow, 75 mg of Pd(acac) was mixed with
1
5 mL OAm. The formed solution was heated to 60 °C in 10 min,
resulting in a near colorless solution. 60 °C is the injection temper-
ature, at this temperature, and 300 mg of BTB was solvated in min-
imum amount of OAm (about 3–4 mL) and quickly injected into
the Pd–OAm solution. A visible color change from colorless to a
brown-black was observed. The temperature was raised to 90 °C
4
pholine complex and NaBH . It offers an ideal combination with
oleylamine for the facile synthesis of monodisperse Pd NPs. As
shown in Fig. 1a, the size of Pd NPs is about 5.0 nm, and Pd NPs
show a narrow size distribution with a standard derivation of
about 8% with respect to the diameter of the Pd NPs. XRD patterns
of Pd NPs have been determined by X-ray diffraction apparatus. As
shown in Fig. 2, the obvious peak (111) has been found, and the
peak is corresponding to the characteristic peak of Pd NPs. The
polycrystalline structure of the NPs can be confirmed by the
X-ray diffraction pattern of the Pd NP assembly, from which the
average NP size was estimated to be about 4.0 nm, which is smaller
than the value of 5.0 nm measured from the TEM images in Fig. 1a.
(
3 °C/min) and kept at this temperature for 60 min. The solution
was cooled down to room temperature. 30 mL of ethanol was
added and the product was separated by centrifugation. The prod-
uct was then dispersed in hexane for next step.
2.3. Synthesis of Pd/C NPs
1
0 mg of Pd NPs were dissolved in hexane in a 20 mL vial and an
equal amount of carbon support was added to it. This colloidal
mixture was sonicated for 2 h to ensure complete adherence of
Pd NPs onto the carbon support. After evaporation of hexane,
[
21] In addition, in order to differentiate the crystalline model of Pd
nanoparticles, its selected area electron diffraction (SAED) image
was performed (Fig. 1c). Its SAED pattern exhibited several diffused
rings, which confirms the polycrystalline nature of Pd nanoparti-
2
0 mL of acetic acid was added to the Pd/C dispersion and heated
for 10 h at 70 °C. The reaction mixture was cooled down to room
temperature. 30 mL of ethanol was added and the mixture was
centrifuged at 8000 rpm for 8 min. This procedure was repeated
for three times. The Pd/C NPs were recovered by adding acetone.
Acetone was vaporated and the resultant Pd/C NPs were weighed.
A measured amount of de-ionized water was added, resulting in a
2
mg/mL solution. This mixture was sonicated for 1 h to ensure
uniform distribution. The Heck and Suzuki reactions were carried
out using 4 mg of this catalyst.
2.4. General procedure for Heck reaction
Typically, the as-prepared 4 mg catalyst was added into the
mixture solution of 10 mmol aryl halide, 20 mmol Et
DMF. The mixture solution was preheated for 1 h, and then
2 mmol styrene was added. Then the solution was heated and
3
N and 5 mL
1
Fig. 1. TEM images of Pd NPs (a), Pd/C NPs (b) and SAED pattern of polycrystalline
stirred at 140 °C for 6 h. After cooling down to the room tempera-
ture, the catalyst was recycled for next reaction cycle by acetone
precipitation and centrifugation. The organic phase was collected,
dried and used for GC analysis. The experiments were repeated
with the catalyst recycled from previous reaction.
Pd NPs (c).
(
111)
2.5. General procedure for Suzuki reaction
Pd NPs
Typically, the as-prepared 4 mg catalysts was dispersed in 5 mL
DMF, and then 10 mmol aryl halide, 15 mmol phenylboronic acid
and 20 mmol Et N were added into a 100 mL round-bottom flask.
3
The flask was sealed, stirred, and heated at 140 °C for 2 h. After
cooling down to the room temperature, the catalyst was recycled
for next reaction cycle by acetone precipitation and centrifugation.
And the filtrated solution was collected and dried. The presence of
the product was determined by GC analysis. The experiments were
repeated with the catalyst recycled from previous reaction.
(111)
Pd/C NPs
3
. Results and discussion
20
30
40
50
60
70
80
90
Degree (2θ)
The Pd NPs were prepared by the high-temperature decomposi-
tion of palladium acetylacetonate in the presence of OAm and BTB.
Fig. 2. XRD patterns of Pd NPs and Pd/C NPs.

Y. Li et al. / Inorganica Chimica Acta 414 (2014) 59–62
61
Table 1
Heck and Suzuki reactions of aryl halides and styrene or phenylboronic acid catalyzed by Pd/C NPs.
Pd/C NPs
2Pd/C NPs
B(OH)
X
+
X
+
R
R
R
R
Entry
R
X
Yield (%)a
Yield (%)a
1
2
3
4
5
H
H
H
m-Me
m-Me
Cl
Br
I
Br
I
61
91
95
75
82
41
92
98
69
87
a
Yields were determined by GC analyses.
Table 2
Repeated uses of Pd/C NPs for catalyzing Heck and Suzuki reactions, respectively.
Entry
Reagent 1
Reagent 2
Yield of each round (%)a
1
2
3
4
5
6
1
2
91
88
84
82
78
72
Br
Br
92
86
82
80
71
69
B(OH)
2
a
Yields were determined by GC analyses.
cles. In order to prepare nanocatalysts for Heck and Suzuki reac-
tions, Pd NPs were loaded on the Ketjen carbon black by the soni-
cation followed by the acetic acid cleaning. As shown in Fig. 1b, the
Pd NPs are well dispersed on the carbon support. The size and
morphology of Pd NPs on carbon black have no great changes. In
addition, the XRD patterns of Pd/C NPs have been obtained. As
shown in Fig. 2, the peak (111) of Pd/C NPs is corresponding to
the characteristic peak of Pd NPs, which indicated that Pd NPs were
well-dispersed onto the carbon black.
The Pd/C NPs were tested for catalyzing carbon–carbon coupling
reactions-Heck and Suzuki reactions. The reaction variables such as
the temperature, reaction time, and base were optimized. For Heck
3
reactions catalyzed by Pd/C NPs, Et N as the base and DMF as the
reaction solvent were used. Furthermore, we investigated that the
and phenylboronic acid is best. When the substituted group, such
as methyl group exists, the reaction yield would decrease accord-
ingly due to its hindrance ability.
We also investigated the feasibility of repeated use of Pd/C NPs
on Heck and Suzuki reactions. In Table 2, we present the experi-
mental results from the investigations of recycling of Pd/C NPs for
six consecutive rounds under the same experimental conditions.
After each round, the Pd/C NPs were centrifugated, dried and used
directly for the next round without any further purifications. The
yields of Heck and Suzuki reaction decrease slowly. For Heck
reaction of bromobenzene and styrene, TEM images of Pd/C NPs
after each round were exhibited in Fig. 3. As seem, the morphol-
ogy of Pd/C NPs after every round has no great changes. But the
size of Pd NPs loaded on carbon black is increasing subtly with
the increasing cycles, and that is why the reaction yield is
decreasing [25,26]. Similarly, the yield of Suzuki reaction also de-
creases due to the same reason. We have compared the activities
of prepared Pd/C nanoparticles with other similar catalysts
according to your suggestion. Pd nanoparticles immobilized on
amine-functionalized zeolite can promote Heck reaction greatly,
but we found the morphologies of the nanoparticles have chan-
reaction time for 6 h and reaction temperature for 140 °C are the
optimal reaction conditions. For Suzuki reactions, the base is Et N
3
and the reaction solvent is DMF. When the reactions were termi-
nated, the reaction solutions were removed from the flask and then
subjected to GC analyses. Pd/C NPs were washed and dried for next
recycle reactions, and more than 95% of Pd/C NPs could be recov-
ered based on the calculations of weights of Pd/C NPs.
The yields of Heck reactions for aryl halides and styrene were
showed in Table 1. The yields of chlorobenzene, bromobenzene
and iodobenzene with styrene increase with the stronger of electron
donating ability. For the reaction of 2-bromotoluene and styrene,
the yield is 75%. While when the substituted group is iodide, the
yield increases greatly. All these indicated that the electron donat-
ing ability of the substituted groups has a great importance on the
reaction yields [22–24]. The yields of Suzuki reactions for aryl ha-
lides and phenylboronic acid were shown in Table 1. For Suzuki
reactions, the yield of reaction for chlorobenzene and phenylbo-
ronic acid is the worst, while the yield of reaction for iodobenzene
3 4
ged a lot with its repeated use [27]. Pd–Fe O heterodimer nano-
crystals exhibited good activities for various Suzuki coupling
reactions. The yield is only 81%, which is lower than that of our
nanocatalysts [28]. Pd catalyst on amorphous silica for Suzuki
couplings was prepared, which was efficient in coupling of aryl
iodides and aryl bromides but not active enough toward aryl
chlorides. The catalyst could be reused only three times without
losing activity [29]. Compared with these similar catalysts, we
found our nanocatalysts are easy to prepare, and they can pro-
mote Heck and Suzuki reactions greatly with its repeated uses
without losing its activity.

6
2
Y. Li et al. / Inorganica Chimica Acta 414 (2014) 59–62
Fig. 3. TEM images of Pd/C NPs after catalyzing Heck reaction of bromobenzen and styrene for the first cycle (a), second cycle (b), third cycle (c), fourth cycle (d), fifth cycle (e)
and sixth cycle (f).
[
[
[
5] J. Lindley, T.J. Mason, J.P. Lorimer, Ultrasonics 25 (1987) 45.
6] J.L. Sessler, M.C. Hoehner, Synlett 3 (1994) 211.
7] S. Zhang, D. Zhang, L.S. Liebeskind, J. Org. Chem. 62 (1997) 2312.
4
. Conclusions
In summary, the monodisperse Pd NPs were synthesized via the
[8] F.M. Hauser, P.J. Gauuan, Org. Lett. 1 (1999) 671.
high-temperature decomposition of Pd(acac)
2
in the presence of
[9] J. Sävmarker, J. Lindh, P. Nilsson, Tetrahedron Lett. 51 (2010) 6886.
10] D.J. Cole-Hamilton, Science 299 (2003) 1702.
11] A.F. Littke, G.C. Fu, Angew. Chem., Int. Ed. 41 (2002) 4176.
12] R.R. Tykwinski, Angew. Chem., Int. Ed. 42 (2003) 1566.
[13] A.C. Frisch, M. Beller, Angew. Chem., Int. Ed. 44 (2005) 674.
14] A. Zapf, Angew. Chem., Int. Ed. 42 (2003) 5394.
[
[
[
OAm and BTB with the size of about 5.0 nm. Pd NPs were loaded
on carbon black to be used as nanocatalysts for carbon coupling
reactions, such as Heck and Suzuki reactions. Pd/C NPs showed
great catalytic ability on Heck and Suzuki reactions. In addition,
Pd/C NPs can be recycled in Heck and Suzuki reactions for at least
six cycles without any changes of their morphologies. Pd/C NPs are
good and efficient nanocatalysts for carbon coupling reactions such
as Heck reaction and Suzuki reactions.
[
[
15] R.J. Aitken, M.Q. Chaudhry, A.B. Boxall, M. Hull, Occup. Med. (Lond.) 56 (2006)
300.
[16] Y.M. Lu, H.Z. Zhu, W.G. Li, B. Hu, S.H. Yu, J. Mater. Chem. A 1 (2013) 3783.
17] Y. Li, E. Boone, M.A. El-Sayed, Langmuir 18 (2002) 4921.
18] S. Guo, E. Wang, Nano Today 6 (2011) 240.
19] M. Cao, J. Lin, H. Yang, R. Cao, Chem. Commun. 46 (2010) 5088.
20] R.J. White, R. Luque, V.L. Budarin, J.H. Clark, D.J. Macquarrie, Chem. Soc. Rev. 38
[
[
[
[
(
2009) 481.
21] Y. Liu, C. Sun, T. Bolin, T. Wu, Y. Liu, M. Sternberg, S. Sun, X.M. Lin, Nano Lett. 13
2013) 4893.
[22] C.W. Allen, Chem. Rev. 91 (1991) 119.
Acknowledgement
[
(
This work is supported by Fundamental Research Funds for the
Central Universities (CUG120802).
[
[
23] C. Zhang, J. Huang, M.L. Trudell, S.P. Nolan, J. Org. Chem. 64 (1999) 3804.
24] A.C. Hillier, G.A. Grasa, M.S. Viciu, H.M. Lee, C. Yang, S.P. Nolan, J. Organomet.
Chem. 653 (2002) 69.
References
[25] W. Li, Y. Fu, Y. Fu, X. Wang, J. Zhang, Catal. Lett. 143 (2013) 578.
[
26] F. Coccia, L. Tonucci, N. d’Alessandro, P. D’Ambrosio, M. Bressan, Inorg. Chim.
Acta 399 (2013) 12.
[
[
[
[
1] N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457.
2] P.E. Fanta, Chem. Rev. 64 (1964) 613.
3] H. Mayr, B. Kempf, A.R. Ofial, Acc. Chem. Rev. 36 (2003) 66.
4] J. Hassan, M. Sévignon, C. Gozzi, E. Schulz, M. Lemaire, Chem. Rev. 102 (2002)
[27] S. Mandal, D. Roy, R.V. Chaudhari, M. Sastry, Chem. Mater. 16 (2004) 3714.
[28] Y. Jang, J. Chung, S. Kim, S.W. Jun, B.H. Kim, D.W. Lee, M. Kim, T. Hyeon, Phys.
Chem. Chem. Phys. 13 (2011) 2512.
1
359.
[29] N. Kim, M.S. Kwon, C.M. Park, J. Park, Tetrahedron Lett. 45 (2004) 7057.