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PAPER
A new functionalized mesoporous matrix supported Pd(II)-Schiff base
complex: an efficient catalyst for the Suzuki–Miyaura coupling reaction†
Koushik Dhara,*a Krishanu Sarkar,b Dipankar Srimani,c Subrata Kumar Saha,d Pabitra Chattopadhyaye and
Asim Bhaumik* f
Received 15th February 2010, Accepted 7th May 2010
First published as an Advance Article on the web 7th June 2010
DOI: 10.1039/c003142a
A new Pd(II) bounded 2D-hexagonally ordered functionalized MCM-41 type material (IV) has been
synthesized. Functionalization was carried out by the anchoring of 3-aminopropyltriethoxysilane in the
MCM-41 type mesoporous material, followed by grafting with 2,6-diacetylpyridine (DAP) to give a
N3-type Schiff base chelating attachment for the Pd(II) species. Fourier transform infrared (FTIR),
powder X-ray diffraction (PXRD) and high resolution transmission electron microscopy (HRTEM)
studies have been used to characterize the material. Material IV behaves as a highly active catalyst
towards Suzuki–Miyaura cross-coupling reaction for the synthesis of biaryl organics. In addition, IV
acts as a true heterogeneous catalyst in coupling reaction. It was found that this catalyst is highly
efficient and recyclable towards Suzuki–Miyaura reaction with high turn over frequencies. X-Ray
photoelectron spectroscopic (XPS) analysis was employed to understand the oxidation state of the
palladium atom in the catalyst (IV) and its loading in the material.
offers considerable complexity to the reaction that may render
Introduction
it industrially unacceptable.4 Thus the heterogenization of a Pd-
Palladium is one of the most crucial metals in catalysis and it
catalyst is a logical step to avoid these problems, as it allows
is commonly used to catalyze a large variety of carbon–carbon
for easy removal from the reaction mixture. However, inorganic
bond forming reactions.1 Of these reactions, the Suzuki–Miyaura
heterogeneous Pd-catalysts show low stability due to leaching of
palladium from the surfaces.5 In fact the leached homogeneous
Pd species is responsible for the catalytic activity in most of
the cases.6 Therefore the search for new efficient and recyclable
heterogeneous catalysts has received much attention.7 Different
approaches like encapsulation or immobilization of catalytically
active metal complexes in solid supports such as zeolites,8 covalent
grafting of such active complexes onto reactive polymer surfaces9
or inorganic porous matrices10 etc. have been utilized in developing
an efficient heterogeneous catalyst. Thus, functionalized ordered
mesoporous silica with high surface area, e.g. MCM-41, MCM-
48 and SBA-15 having attractive nanoscale pore structure are the
natural choice for heterogenization.11
Modified Pd-silica catalysts have been investigated by Molnar
et al.12 and found that Pd immobilized on silica modified with
methyl or phenyl groups exhibited high activity and selectivity in
the Mizoroki–Heck coupling reaction. So the choice of ligand
for functionalization of silica matrices has an important role
on catalytic activity and stability. Mandal et al.13 and Bedford
et al.14 reported the immobilization of Pd nanoparticles on amine-
functionalized zeolites and mesoporous silica, respectively, and
observed high activity and stability of both catalysts in the
Mizoroki–Heck reaction. Tsai et al.15 and Gonzalez-Arellano
et al.16 investigated the nanosized Pd-bipyridyl complex and a
Pd(II)-Schiff base complex anchored onto MCM-41 which showed
high reactivity and recyclability for the Mizoroki–Heck reaction.
An active catalyst for the Ullmann reaction of iodobenzene was
phenyl-PMO supported Pd(II) complex that was reported by
Wan et al.17 Recent developments on the mesoporous material
reaction is very important for constructing unsymmetrical biaryl
compounds compared to other coupling reactions, which employ
more reactive organometallics such as organozinc or Grignard
reagents. Complexes of palladium(II) with nitrogen containing
ligands are well-known catalysts for Suzuki–Miyaura coupling
reactions and thus there is a large interest to employ this reaction
in the formation of C–C bonds.2 The organoboronic acids (and
esters) commonly employed in the Suzuki–Miyaura reaction,
which are air- and moisture-stable and have relatively low toxicity.3
However, common catalysts for the Suzuki–Miyaura reaction are
generally based on homogeneous palladium complexes of Pd(0)
or Pd(II), which causes difficulties in purification of the final
product, recycling of the catalyst, and deactivation via aggregation
into Pd nanoparticles. Further removal of residual palladium
aDepartment of Chemistry, Sambhu Nath College, Labpur, Birbhum,
731303, West Bengal, India. E-mail: koushikdhara@rediffmail.com;
Fax: +913324732805; Tel: +919433125327
bDepartment of Chemistry, Netaji Mahavidyalaya, Arambagh, Hooghly,
712601
cDepartment of Organic Chemistry, Indian Association for the Cultivation
of Science, Kolkata, 700 032, India
dDepartment of Physics, Sambhu Nath College, Labpur, Birbhum, 731303,
West Bengal, India
eDepartment of Chemistry, Burdwan University, Golapbug, Burdwan, 713
104, West Bengal, India
f
Department of Materials Science, Indian Association for the Cultivation of
Science, Jadavpur, Kolkata, 700 032, India. E-mail: msab@iacs.res.in
† Electronic supplementary information (ESI) available: Detailed 1H and
13C data of the coupling products. See DOI: 10.1039/c003142a
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6395–6402 | 6395
©