Tetrahedron Letters
Pd/CuO nanoparticles as a highly effective catalyst for the cyanation
of aryl halides under ligand-free conditions
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Mahmoud Nasrollahzadeh
Department of Chemistry, Faculty of Science, University of Qom, PO Box 37185369, Qom, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Copper oxide supported palladium nanoparticles have been used as a separable catalyst for the cyanation
of a range of aryl iodides and bromides under ligand-free conditions. The effect of solvent, base, and cat-
alyst loading was investigated. The catalyst can easily be recovered and reused several times without sig-
nificant loss of catalytic activity.
Received 22 March 2015
Revised 18 November 2015
Accepted 3 December 2015
Available online 7 December 2015
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
Copper oxide
Palladium
Cyanation
Ligand-free
Aryl nitriles are valuable intermediates in organic chemistry
and constitute the key components of a range of pharmaceuticals,
herbicides, agrochemicals and dyes.1 They can also be transformed
into other functional groups such as aldehydes, nitrogen-contain-
ing heterocycles, carboxylic acids and their derivatives.2
Nitriles can be conventionally synthesized by the reaction of
aryl halides with stoichiometric amounts of CuCN,3a–c the
diazotization of anilines and subsequent Sandmeyer reaction or
the transition metal-catalyzed cyanation of aryl halides using
various cyanide sources which include the alkali-metal cyanides,
Me3SiCN and Zn(CN)2.3d–g,2d,3h–j However, in many cases these
methods suffer from drawbacks that restrict their use including;
long reaction times and use of reagents that are toxic, hazardous,
sensitive to moisture or expensive.3
Recently, K4Fe(CN)6 has received attention as an alternative cya-
nation agent due to favorable properties such as being nonexplosive,
nonflammable and inexpensive.4 Additionally, it is not volatile and
is stable in the presence of moisture allowing easy storage. Among
the various catalysts examined for the transition metal-catalyzed
cyanation of aryl halides using K4Fe(CN)6, homogeneous catalysts
in the presence of various ligands have been widely investi-
gated.3i,4e–g However, heterogeneous catalysts proceeding under
ligand-free conditions have received significantly less attention.4
Homogeneous catalysts are more difficult to separate from the
reaction mixture and cannot be reused in consecutive reactions.5
Therefore, the development of a heterogeneous and highly efficient
method for the ligand-free synthesis of nitriles is still an interesting
research area.
Recently, our laboratory described the cyanation reaction of aryl
iodides using carbon supported4c and Natrolite zeolite supported
copper nanoparticles.4d However, the high cost of preparation of
these catalysts may restrict their application, especially in large-
scale processes. Additionally, this method was limited to the
cyanation of aryl iodides.
Catalysis using nanoparticles (NPs) is typically more efficient
than their particulate metal counterparts due to the small particle
sizes and large surface areas. Therefore, heterogeneous catalysts
are increasingly being used in nanoparticle form.6
Various methods have been reported for the synthesis of
nanoparticles.7 Recently, we reported the preparation of Pd/CuO
nanoparticles using the extract of Theobroma cacao L. seed and
their catalytic performance in the reduction of 4-nitrophenol and
the phosphine-free Heck coupling under aerobic conditions.8
Based on our interest in copper, palladium, gold, iron and silver
nanoparticle catalyzed reactions,6 we began to develop an efficient
and heterogeneous Pd/CuO catalyst that was air and moisture
stable.
Pd/CuO NPs were synthesized according to the literature proce-
dure using Theobroma cacao L. seed extract as both reducing and
stabilizing agents (Fig. 1). No surfactant, capping agent, and/or
template were used in this method for the synthesis of Pd/CuO
NPs.8,9
In order to examine the feasibility for the cyanation of aryl
halides (Scheme 1) and determine the optimum conditions, we
examined the reaction of iodobenzene with K4Fe(CN)6 in the
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