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DOI: 10.1002/cplu.201402169
Poly(vinylpyridine)-Grafted Silica Containing Palladium or
Nickel Nanoparticles as Heterogeneous Catalysts for the
Sonogashira Coupling Reaction
Fatemeh Farjadian*[a, b] and Bahman Tamami*[b]
Efficient catalytic systems based on palladium and nickel nano-
particles supported on poly(4-vinylpyridine) (P4VPy)-grafted
silica were prepared. After preparation of P4VPy-grafted silica,
complexation with PdCl2 and NiCl2 was carried out to obtain
the heterogeneous catalytic systems. Scanning and transmis-
sion electron microscopy (SEM and TEM) showed that palladi-
um and nickel particles on the nanoscale were dispersed
throughout the surface. Under copper-, amine-, and phos-
phine-free conditions, the palladium catalyst exhibited excel-
lent activity in the Sonogashira cross-coupling reaction. An
amine- and phosphine-free nickel-catalyzed Sonogashira reac-
tion in the presence of CuI as a cocatalyst was also performed
successfully. In both systems phenylacetylene reacted with aryl
iodides, bromides, and chlorides in high yield and over short
reaction times.
Introduction
Palladium-catalyzed CÀC coupling reactions are one of the
most frequently employed organic transformations.[1–3] The So-
nogashira reaction of terminal alkynes with aryl halides is one
of the CÀC coupling reactions that is employed for the synthe-
sis of substituted arylated alkyne compounds, that is,
C(sp2)ÀC(sp) bonds. These compounds are important inter-
mediates for the synthesis of natural products, pharmaceutical
compounds, organic materials for optical applications, and
polymeric materials.[4,5]
methods were economically and environmentally problematic,
and modifications were carried out by introducing systems
such as those that were phosphine-free,[12–14] copper- and
amine-free,[15,16] copper-catalyzed Pd-free,[17–19] and the use of
other transition metals such as Fe,[20] Co,[21] Ni,[22–28] Ru,[29] and
In,[30] as well as the use of a solid supported catalyst.[15,31–33]
Nickel is a promising and cheaper alternative to the use of
palladium as a transition-metal catalyst in coupling reactions.
There are many reports in the literature on the use of nickel as
an alternative to palladium in homocoupling[34–36] and cross-
coupling reactions such as Heck, Suzuki, and Kumada,[37–43] but
there are only a few reports on Ni-catalyzed Sonogashira reac-
tions.[22–28] A nickel-catalyzed Sonogashira reaction was report-
ed by Beletskaya et al. using homogeneous NiII species.[22]
Wang et al. reported the use of Ni0 particles[21] and also
nickel(0)-powder-doped KF/Al2O3.[22] In 2009, Hu et al. reported
an NiII pincer complex and its efficient use in the Sonogashira
reaction of alkyl halides; following this study, they introduced
nickamine as an efficient precatalyst for the same purpose.[25,26]
In 2010, Bakherad et al. described NiÀCu-catalyzed Sonogashira
coupling of terminal acetylenes with aryl iodides in the pres-
ence of sodium lauryl sulfate as the surfactant,[27] and recently,
an Ni/Cu catalytic system for the coupling of aryl iodides with
various terminal alkynes in the presence of chiral amino alco-
hol was developed by Yang et al.[28] These Ni catalysts require
the use of CuI as cocatalyst, and most of them are effective in
the presence of phosphine ligands. The diversity of aryl halides
used in these reactions is limited to iodides and bromides.
Immobilization of homogeneous catalysts on a solid support
can provide advantages such as product separation, inhibition
of metal loss, catalyst recovery, and recycling. Several methods,
including supporting metal complexes on polymers,[44,45] silica,
and modified silica,[46,47] have been reported in the literature.
Silica- or modified-silica-supported catalysts are good alterna-
The Sonogashira reaction is mostly catalyzed by homogene-
ous Pd complexes in the presence of phosphine ligands, a cata-
lytic amount of CuI as a cocatalyst, and amine as a solvent or
as a base on a large scale.[6,7] Phosphorous ligands are usually
poisonous, air-sensitive, unrecoverable, and can degrade at
elevated temperatures.[1–3] Copper salt is used to facilitate the
oxidative addition of acetylene to palladium metal, but it re-
sults in dangerous waste materials that are difficult to sepa-
rate.[8,9] An amine as a solvent or base is used to enhance the
reaction rate and is not recovered. Furthermore, a problem
that accompanies soluble Pd complexes is the loss of the ex-
pensive metals.[10,11] Consequently, most of the traditional
[a] Dr. F. Farjadian
The Center for Nanotechnology in Drug Delivery
Shiraz University of Medical Sciences
Shiraz 71345 (Iran)
[b] Dr. F. Farjadian, Prof. B. Tamami
Chemistry Department, College of Sciences
Shiraz University, Shiraz 71454 (Iran)
Supporting information for this article is available on the WWW under
1
and 13C NMR data.
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ChemPlusChem 2014, 79, 1767 – 1773 1767