Tetrahedron Letters
Hybrid Au/Pd nanoparticles as reusable catalysts for Heck coupling
reactions in water under aerobic conditions
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Mahmoud Nasrollahzadeh , Alireza Banaei
Department of Chemistry, Payame Noor University (PNU), PO Box 19395-3697, Tehran, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 June 2014
Revised 3 December 2014
Accepted 9 December 2014
Available online 15 December 2014
This work reports the synthesis and application of Au/Pd nanoparticles as separable catalysts for Heck
coupling reactions in water under aerobic conditions. This method provides high yields, mild reaction
conditions, and an easy work-up. Catalytic efficiency remains unaltered even after several repeated
cycles.
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Heck
Gold
Palladium
Reusable catalyst
Water
The Heck coupling reaction provides a powerful and straightfor-
ward method for C–C bond formation, which has been widely
applied to diverse areas such as natural product synthesis, pharma-
developing an efficient and heterogeneous hybrid Au/Pd catalyst
that is air and moisture stable and highly active.
We recently described the preparation of various nanoparticles
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ceuticals, biologically active molecules, and materials science.
(NPs). We believe that Au/Pd bimetallic NPs can play an important
Among various palladium catalysts used for this coupling reac-
tion, homogeneous catalysts have been widely investigated, while
less expensive heterogeneous catalysts have received less atten-
role in coupling reactions for the synthesis of organic compounds.
As part of our ongoing interest in heterogeneous catalysts and cou-
pling reactions, we now report the application of Au/Pd bimetallic
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tion. A disadvantage of homogeneous catalysis is the difficulty
NPs in Heck coupling reactions in water under aerobic conditions.
The shape and size of the Au/Pd bimetallic NPs was determined
by scanning electron microscopy (SEM). Figure 1 shows an SEM
image of the Au/Pd bimetallic NPs. The, Pd particles appear as
bright dots over the surface of the Au nanoparticles with average
sizes of less than 80 nm. Moreover, palladium nanoparticles show
different morphologies such as wires and attached nanoparticles.
The length and diameter of these Pd wires are about 300 and
80 nm, respectively. The elemental composition of the catalyst
was analyzed by energy dispersive X-ray spectroscopy (EDS). In
the EDS spectrum of the catalyst (Fig. 2), peaks related to O, Au
and Pd were observed. The EDS results showed that the Au, Pd,
and oxygen concentrations were about 7%, 16%, and 77%, respec-
tively. The excess oxygen is due to physical absorption of oxygen
from the environment during sample preparation.
in separating the catalyst from the reaction mixture, and the fact
that it cannot be used in subsequent reactions. Therefore, the
development of mild, highly efficient, and environmentally benign
methods for ligand- and copper-free coupling reactions remains an
active research area.
Nanotechnology has emerged as a cutting edge technology
interdisciplinary in biology, chemistry, and materials science.
Metal nanoparticles have been used widely due to their interesting
electronic, optical, mechanical, magnetic, and chemical properties,
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which differ greatly from those of bulk substances. For these rea-
sons, metallic nanoparticles have found uses in many applications
in different fields, such as catalysis, photonics, and electronics.
Among various metal catalysts, palladium and gold are able to cat-
alyze a wide variety of chemical reactions under homogeneous and
heterogeneous conditions.4 Due to their higher available catalytic
surface, heterogeneous catalysts are used more and more in the
form of nanoparticles. Thus, it was decided to concentrate on
Next, the catalytic activity of the Au/Pd bimetallic NPs in the
copper- and ligand-free Heck coupling reaction in water was
examined. Initial studies were performed in order to optimize
the conditions for the reaction between iodobenzene (1.0 mmol)
and styrene (1.5 mmol) in the presence of the Au/Pd bimetallic
NPs, CTAB (cetyltrimethylammonium bromide) as an additive
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040-4039/Ó 2014 Elsevier Ltd. All rights reserved.
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