Epoxy resins cured with ionic liquids as novel supports for metal complex catalysts

Article abstract of DOI:10.1016/j.crci.2012.12.005

In this work, the application of an epoxy resin cured with ammonium ionic liquids as a support for palladium complex catalyst is reported. Supports based on epoxy resin were obtained as a result of the use of ionic liquids: didecyldimethylammonium tetrafluoroborate [d₂m₂am][BF ₄], 1-methyltheobromine tetrafluoroborate [mthb][BF₄], didecyldimethylammonium theobrominate [d₂m₂am][thb], didecyldimethylammonium theophyllinate [d₂m₂am][thp] as cross-linking agents. The characterization of polymeric supports and heterogenized palladium catalysts has involved research methods like time-of-flight secondary ion mass spectrometry (TOF-SIMS), infrared spectroscopy (IR), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS). The activity and stability during long-term use of the investigated catalytic systems were tested in a model Heck reaction. The influence of the type of ILs used as epoxy hardeners on the catalytic properties of epoxy-supported palladium catalysts is discussed.

Full text of DOI:10.1016/j.crci.2012.12.005

C. R. Chimie 16 (2013) 752–760
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´
Full paper/Memoire
Epoxy resins cured with ionic liquids as novel supports for metal complex
catalysts
Sylwia Ostrowska a, Bartosz Markiewicz b, Karolina Wa˛sikowska a, Natalia Ba˛czek a,
Juliusz Pernak b, Krzysztof Strzelec a,
*
a Institute of Polymer and Dye Technology, Faculty of Chemistry, Lodz University of Technology, Stefanowskiego 12/16, 90-924 Lodz, Poland
b Institute of Technology and Chemical Engineering, Faculty of Chemical Technology, Poznan University of Technology, 2M. Sklodowska-Curie Square, 60-965
Poznan, Poland
A B S T R A C T
A R T I C L E I N F O
In this work, the application of an epoxy resin cured with ammonium ionic liquids as a
support for palladium complex catalyst is reported. Supports based on epoxy resin were
obtained as a result of the use of ionic liquids: didecyldimethylammonium tetrafluoroborate
[d2m2am][BF4], 1-methyltheobromine tetrafluoroborate [mthb][BF4], didecyldimethylam-
monium theobrominate [d2m2am][thb], didecyldimethylammonium theophyllinate
[d2m2am][thp] as cross-linking agents. The characterization of polymeric supports and
heterogenized palladium catalysts has involved research methods like time-of-flight
secondary ion mass spectrometry (TOF-SIMS), infrared spectroscopy (IR), scanning electron
microscopy (SEM), X-ray photoelectron spectroscopy (XPS). The activity and stability during
long-termuseoftheinvestigatedcatalyticsystemsweretestedinamodelHeckreaction. The
influence of the type of ILs used as epoxy hardeners on the catalytic properties of epoxy-
supported palladium catalysts is discussed.
Article history:
Received 27 October 2012
Accepted after revision 4 December 2012
Available online 15 January 2013
Keywords:
Epoxy resin
Heterogeneous catalysis
Supported catalysts
Coordination modes
Curing agent
Ionic liquids
Heck reaction
´
ß 2012 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
A homogeneous catalyst deposited on the support can
be easily separated from the reagents and solvents at the
The widespread use of synthetic polymers as catalyst
supports has started to be looked at as an alternative to
typical inorganic carriers. The popularity of employing
macromolecular compounds results mainly from their
availability and wide range of occurrence in the form of
membranes, beads, fibers, films or powders. An unques-
tionable advantage of these organic supports is the ability
to control the cross-linking density, the degree of
crystallinity and the pore size. The chemical structure of
the polymeric matrix influences the catalytic properties of
the metal complex immobilized on it. A properly carried
out synthesis of the carrier allows us to control the
mechanical properties and thermal stability as well.
same time preserving its specific properties such as
activity and selectivity while working under mild pressure
and temperature conditions. The procedure of hetero-
genization of metal complex catalysts on the polymeric
carriers generally involves the displacement of ligands
attached to the metal and their substitution by groups
chemically bonded to the polymer chain [1]. Styrene-
divinylbenzene copolymers, equipped with appropriate
functional groups, are commonly used as supports for the
immobilization of many types of complex catalysts. Their
porosity, surface area and solution characteristics can be
altered by varying the degree of cross-linking. The main
disadvantage of this group of polymers are poor heat
transfer ability, insufficient heat resistance and in many
cases their poor mechanical properties which prevent
them from being used in stirred reactors in which they are
pulverized.
* Corresponding author.
E-mail address: krzysztof.strzelec@p.lodz.pl (K. Strzelec).
1631-0748/$ – see front matter ß 2012 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.crci.2012.12.005

S. Ostrowska et al. / C. R. Chimie 16 (2013) 752–760
753
Epoxy resins are the main materials used as coating
materials, adhesives and composites. Although the poly-
merization process using the opening of the epoxide ring
creates many possibilities for easy functionalization, as
well as direct input of metal complexes into the structure
of the cured matrix, there have been only few reports on
the use of epoxy resins as carriers of metal complex
catalysts in organic synthesis. One of the not numerous
examples of their use in heterogeneous catalysis are the
reports of obtaining molybdenum-doped epoxy resin [2,3].
Such a procedure involves the use of the metal complex as
the polymerization initiator and the precursor of the
catalytic centres in the cured resin. Epoxy resins doped
with Mo, Pd, and Rh complexes manifest high catalytic
stability in the processes of epoxidation, hydrogenation
and hydroformylation [4]. The use of epoxy resins as
carriers of catalysts has been limited so far to the
application of various matrices functionalized with epoxy
groups for the immobilization of proteins and enzymes to
improve their biocatalytic properties [5]. The Sepabeads-EP
epoxide carrier used in industry allows for the highly
efficient immobilization of proteins via the multipoint
covalent bonding with the carrier. This carrier is produced
in the process of curing in the presence of expanding
agents and provides both suitable properties for the
multipoint immobilization and the mechanical character-
istics necessary in the usage of the final biocatalyst [6,7]. In
obtaining of bi-functional epoxy-thiol carriers, in which
the thiol groups are designed to speed up the process of
physical adsorption and the epoxy groups are involved in
the multipoint bonding of proteins [8].
The increasing usage of ionic liquids in synthesis and
catalysis is reflected in a number of monographs dedicated
to application of ionic liquids as solvents in many chemical
reactions and as substances with catalytic properties
[9,10]. Immobilization of organometallic complexes in
thin films of heterogenized ionic liquids has been proposed
as a new concept combining a high diversity of homoge-
neous catalysis with an easy separation of heterogeneous
catalysts [11]. Ionic liquids fixed onto solid organic or
inorganic carriers such as polymers or silica, are heteroge-
neous catalysts exhibiting the properties of ionic liquids
found free in nature. Such a structure of catalytic systems
allows for easier separation, recovery, and recycling of the
catalysts from reaction mixtures [12].
In the nineties, a new catalyst containing the N-
methylimidazole-based chloroaluminate ionic liquid im-
pregnated on silica was patented and it proved to be more
active than the free chloroaluminate ionic liquids [13,14].
The research on this catalytic system showed many defects
in the structure of the carriers. This resulted in loss of
activity during the process due to loss of the active ionic
liquid. This disadvantage was removed during the immo-
bilization by introducing the alkyl bridge between the
carrier and the ionic liquid [15–17].
2005,
a report was published which describes the
Table 1
Description of ionic liquids used.
Cation
Anion
Acronym
CH3
H21C10 N+ C10H21
CH3
O
N
N
[d2m2am][thb]
N
O
N
O
N
N
[d2m2am][thp]
[d2m2am][BF4]
[mthb][BF4]
N
O
N
ꢀ
ꢀ
BF4
O
BF4
N
N
N+
O
N
H

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S. Ostrowska et al. / C. R. Chimie 16 (2013) 752–760
In the present study, we describe our approach to
prepare the polymer-supported catalysts by immobilizing
the palladium complex on the epoxy resin cured with
ammonium ionic liquids. These catalysts were evaluated
for their performance in the Heck reaction. Our aim was to
study the influence of the type of ionic liquid on the
reaction activity. Tests of catalysts stability during their
prolonged use have also been described. Special emphasis
has been stressed on the characterization of metal
distribution on the surface of polymer matrix and its
leaching during subsequent cycles of the reaction. The X-
ray photoelectron spectroscopy (XPS) and IR spectroscopy
were used to gain more information about the mode of
bonding between the metal atom and the functional
groups of the cured epoxy resin.
2. Experimental
Scheme 1. Synthesis of ionic liquids.
2.1. Materials
Epoxy resin bisphenol
A
epichlorohydrin medium
product was finally dried under reduced pressure at 60 8C
molecular weight ꢁ 700 Epidian 5 (EP5), epoxy equivalent
200, (viscosity 20000–30000 mPas at 23 8C), Organika
Sarzyna, Poland and epoxy resin a high purity bisphenol A
diglycidylether D.E.R.TM332 (DER), epoxy equivalent 170,
(viscosity 4000–6000 mPas at 25 8C), the Dow Chemical
Company, USA, were used. Iodobenzene (Aldrich), triethy-
lamine (Organika Sarzyna), methyl acrylate (Aldrich) and
N-metylhylpyrrolidone (ABCR) were used for the Heck
reaction. Tetrafluoroboric acid, theophylline, theobromine,
caffeine, potassium hydroxide, didecyldimethylammo-
nium chloride as well as all solvents were purchased from
commercial suppliers (Sigma-Aldrich, Fluka, Lonza) and
used for synthesis of ionic liquids without further
purification. The ionic liquids applied are collected in
Table 1.
for 24 h (Scheme 1).
2.2.2. Didecyldimethylammonium theophyllinate
[d2m2am][thp]
1H NMR (DMSO-d6)
d
(ppm) 0.86 (t, J = 13.6 Hz, 6H),
1.25 (s, 28H), 1.61 (t, J = 11.3 Hz, 4H), 3.02 (s, 6H), 3.19 (s,
4H), 3.38 (s, 6H), 7.13 (s, 1H). 13C NMR (DMSO-d6)
(ppm)
d
13.9, 21.7, 22.1, 25.8, 27.3, 28.5, 28.7, 28.9, 29.8, 31.3, 49.9,
62.7, 114.8, 146.3, 149.7, 151.8, 157.4.
Elemental analysis calc. (%) for C29H55N5O2 (505.78): C
68.87, H 10.96, N 13.85. Found: C 68.75, H 10.81, N 13.68.
2.2.3. Didecyldimethylammonium tetrafluoroborate
[d2m2am][BF4]
1H NMR (DMSO-d6)
d
(ppm) 0.86 (t, J = 7 Hz, 6H) 1.26
(m, 28H), 1.63 (m, 4H), 2.98 (s, 6H), 3.22 (m, 4H); 13C NMR
(DMSO-d6) (ppm) 13.8, 21.5, 22.0, 25.7, 28.4, 28.6, 28.7,
2.2. Synthesis of ionic liquids
d
28.8, 31.2, 49.9, 62.7.
2.2.1. Synthesis of didecyldimethylammonium and 1-
methyltheobromine (caffeine) salts
Elemental analysis calc. (%) for C22H48BF4N (413.4): C
63.91, H 11.70, N 3.39. Found: C 64.15, H 12.07, N 3.13.
Method
I – Didecyldimethylammonium chloride
(0.05 mol) was dissolved in methanol and a stoichiometric
amount of saturated methanolic solution of KOH was
added. The solutions were stirred at room temperature for
5 min, after which the partially precipitated KCl was
filtrated. Then a stoichiometric amount of an appropriate
theophylline or theobromine or tetrafluoroboric acid was
added. The solutions were stirred again at room tempera-
ture for 15 min and after evaporation of the solvent at a
temperature of 40 8C, the product was dissolved in 20 ml of
anhydrous acetone. The inorganic salt was separated by
filtering and acetone was evaporated to give the product,
which was finally dried under reduced pressure at 80 8C for
24 h (Scheme 1).
2.2.4. Didecyldimethylammonium theobrominate
[d2m2am][thb]
1H NMR (DMSO-d6)
d (ppm) 0.86 (t, J = 11.6 Hz, 6H),
1.26 (s, 28H), 1.62 (t, J = 11,3 Hz, 4H), 3.01 (s, 6H), 3.18 (s,
4H), 3.35 (s, 3H), 3.85 (s, 3H) 7.9 (s, 1H). 13C NMR (DMSO-
d6)
d (ppm) 13.9, 21.66, 22.1, 25.75, 28.48, 28.7, 28.92,
29.15, 31.3, 34.05, 49.9, 62.74, 108.75, 143.11, 149.9,
152.07, 155.4.
Elemental analysis calc. (%) for C29H55N5O2 (505.78): C
68.87, H 10.96, N 13.85. Found: C 68.95, H 10.84, N 13,78.
2.2.5. 1-methyltheobromine (caffeine) tetrafluoroborate
[mthb][BF4]
Method II – 1-methyltheobromine (caffeine) (0.1 mol)
was dissolved in water at 40 8C. Then a stoichiometric
amount of an appropriate tetrafluoroboric acid was added.
The solutions were stirred at 40 8C for 24 h and after
evaporation of the solvent at temperature of 40 8C, the
1H NMR (DMSO-d6)
3.98 (s, 3H), 7.58 (s, 1H); 13C NMR
d
(ppm) 3.39 (s, 3H), 3.57 (s, 3H),
(ppm) 27.82, 29.63,
d
33.57, 107.49, 141.42, 148.51, 151.56, 155.28.
Elemental analysis calc. (%) for C8H11BF4N4O2 (282.00):
C 34.07, H 3.93, N 19.87. Found: C 34.16, H 4.05, N 19.73.

S. Ostrowska et al. / C. R. Chimie 16 (2013) 752–760
755
2.3. Preparation of the carriers
(reduced power 10 kV, 10 mA). The pressure in the
spectrometer chamber was about 5 ꢂ 10–9 mbar. Samples
were pressed to pellets under a pressure of 100 kbar for
10 min before these measurements. The C 1s, N 1s, O 1 s, Cl
2p and Pd 3d core level spectra were recorded. The
analyzer pass energy was set at 20 eV. A take-off angle of
90o was used in all XPS studies. Curve fitting was
performed using the ECLIPSE data system software. This
software describes each of the components of a complex
envelope as a Gaussian-Lorentzian sum function. The
background was fitted using non-linear model function
proportional to the integral of the elastically scattered
electrons (Shirley backgrounds). All binding energies (BEs)
were referenced to the C 1s neutral carbon peak at
284.6 eV.
The carrier was prepared by mixing (3 g) the Epidian 5
or D.E.RTM322 epoxy resin with (1.2 g) the relevant ionic
liquid ([d2m2am][thb], [d2m2am][thp], [d2m2am][BF4],
[mthb][BF4]). After obtaining homogenous consistency,
the mixture was transferred onto a Teflon1 mold and
cured at a temperature of 298 to 423 K over a period of
1 hour to 48 hours. The cured resin was then frozen by
immersion in liquid nitrogen and mechanically ground to a
powder. Average particle size of crushed resins was
measured by sieve analysis. These measurements yield a
median size ranging from 0.5 to 1.0 mm.
2.4. Catalyst preparation
A typical procedure was followed. To a known amount
of polymer matrix (0.1 g) in a round-bottom flask, a known
amount of PdCl2(PhCN)2 dissolved in 10 ml of toluene was
added. The mixture was stirred at room temperature for 2–
3 days when all Pd complex had reacted with the polymer.
The yellow product was filtrated off, extracted with
toluene under nitrogen in order to remove the complex
that was non-chemically bound to the polymer and finally
dried under vacuum. For all supported catalysts, the Pd
content was fixed below the metal uptake capacity for a
polymer. The dry catalysts could be stored in air for many
months without change.
2.8. Morphology studies
The morphology of samples was investigated with a
scanning electron microscope JEOL 5500 LV, working in
high vacuum and accelerating voltage of 10 kV. Energy-
dispersive X-ray microscope (SEM–EDX), JEOL JSM 840A,
Japan, was used to observe the elemental distribution. The
white points in the figures denote Pd atoms.
Pore size distribution parameters were determined by
application of the BET method on Sorptomatic 1900
FISONS Instrument.
2.9. Study of Pd leaching
2.5. Catalytic tests
TOF-SIMS measurements were performed using an
ION-TOF GmbH instrument (TOF-SIMS IV) equipped with
25 keV pulsed Bi+ primary ion gun in the static mode
(primary ion dose about 1.5 ꢂ 1011 ions/cm2). The
The typical Heck reaction was carried out in 50 ml
laboratory reactor. The reactor was charged with 0.05 g of
supported palladium catalyst, 0.28 ml (2.5 mmol) of iodo-
benzene, 0.23 ml (2.5 mmol) of methyl acrylate, 0.15 ml
(1.4 mmol) of toluene, 0.35 ml (2.5 mmol) of triethylamine
and 1.00 ml (10.4 mmol) of N-methylpyrrolidone (NMP).
The reaction was conducted at a temperature of 80 8C for
1.5 hours. Samples were taken every 5, 15, 30, 60 and
90 minutes. The composition of the samples was analyzed
by GC. The reaction products were quantitatively analyzed
by gas chromatography (GC) on a Hewlett-Packard 5990 II
gas chromatograph equipped with a thermal conductivity
detector. The GC column was HP-50+ (cross-linked 50% Ph
analyzed area corresponds to a square of 500 ꢂ 500
mm
in case of secondary ion mass spectra collecting and
surface imaging. For each sample three spectra from
different surface areas were made. To obtain the plain
surface of catalysts (then better mass resolution could be
achieved), powder samples were tableted before the
measurements. In order to compare the quantity of
palladium present on the surface of the catalysts before
and after reaction, the number of counts of selected ions
obtained from collected mass spectra were normalized on
the basis of the value of total counts.
Me silicone) 30 m ꢂ 0.63 mm ꢂ 1.0
mm film thickness. The
product was identified by matching retention times with
those of authentic samples.
3. Results and discussion
2.6. Catalyst recycling
3.1. Spectroscopic characteristics of the polymer supports and
the immobilized Pd catalysts
In the recycling tests, when reaction was completed, the
catalyst was filtered off from the reaction mixture, washed
with 3 ꢂ 25 ml of toluene, vacuum dried and used for the
next reaction.
Currently, there is a growing number of works on the
usage of cured polymers as potential carriers for immo-
bilizing the catalytic complexes of the transition metals
groups. This is due to a number of advantages they possess,
such as: resistance to most organic solvents, ease of
introduction of functional groups without additional
functionalization or the possibility of shaping the final
product. For the purpose of our research, we decided to
select a new type of polymer supports based on epoxy
2.7. Spectroscopy characterization
The FT-IR spectra were measured with a BIORAD 175 C
spectrophotometer in an air atmosphere. XPS measure-
ments were made on a VG ESCALAB 210 spectrometer with
Mg Ka (hn = 1253.6 eV) excitation from an X-ray tube

756
S. Ostrowska et al. / C. R. Chimie 16 (2013) 752–760
Fig. 1. FT-IR spectra of: a) EP5/[d2m2am][thp] support; b) EP5/[d2m2am][thp]/Pd catalyst.
resins with various epoxide numbers, cured with ammo-
nium ionic liquids. We prepared two sets of carriers, one
for the Epidian 5 resin, and the other for the D.E.RTM322
resin (DER), which were cured with the ionic liquids
presented in Table 1.For reasons of clarity and capacity of
this article, we decide to focus on the carrier of the Epidian
5 epoxy resin (EP5) cured with didecyldimethylammo-
nium theophyllinate (EP5/[d2m2am][thp]), which serves as
an example of spectroscopic characterization.
from the EP5/[d2m2am][thp]/Pd spectrum (Fig. 1b.), which
indicates the bonding of the metal by the O atom with a
free pair of electrons (Scheme 2b). We can also observe a
decrease and the shift of the absorption bands from
1661 cmꢀ1 to 1656 cmꢀ1 and 1705 cmꢀ1 to 1701 cmꢀ1
.
This may attest to a particular disorientation of the purine
ring under the influence of Pd(II), which indicates the
possibility of the metal coordination to the N– nitrogen
atom (Scheme 2a). No change was observed for strong
bands at 1581 cmꢀ1 and 1606 cmꢀ1, considered to be due
to asymmetric and symmetric stretching vibrations of two
carbonyl groups of theophylline moiety, which indicates
that the palladium complex is not bonded to the epoxide
support through theophylline carbonyl groups. The new
vibrations band corresponding to the coordinate bond
palladium-theophylline emerge in the FTIR spectra of the
catalyst at 730 cmꢀ1, probably due to the metal-N valence
vibrations.
X-ray photoelectron spectroscopy (XPS) analysis gives a
better indication of the chemistry of the surface of the
heterogenized catalyst particle, whereas the other analysis
methods are more relevant to the composition of the
particles as a whole. XPS analyses the outer surface of
particulates and enables significant information to be
extracted concerning the coordination of a catalytic metal
The FTIR spectrum of the EP5/[d2m2am][thp] carrier
(Fig. 1a) reveals a shift of the characteristic peaks observed
in spectrum of pure didecyldimethylammonium theo-
phyllinate (not presented here), such as the shift of the
absorption bands from 1683 cmꢀ1 to 1705 cmꢀ1 and
1630 cmꢀ1 to 1661 cmꢀ1, corresponding to the stretching
vibrations of the –C N– groups of the purine ring. There
was also a new absorption band at 1743 cmꢀ1, correspond-
ing to the carbonyl group resulting presumably from the
polymerization of the epoxy resin. IR bands in the region of
1740–1750 cmꢀ1 have been found by Spychaj studying the
epoxy resin curing mechanism with imidazolium ionic
liquids [18,19]. These IR absorption bands were explained
by the proposed mechanism of epoxy resin anionic
polymerization initiated by thermal decomposition pro-
ducts of 1,3-dialkylimidazolium ionic liquids. In this
mechanism, assuming regeneration of imidazole deriva-
tives, unsaturated structure of epoxy polymer is formed
and finally transformed by tautomerization into the
structure with the carbonyl group. Our observations
indicate similar mechanism of anionic polymerization
initiated by the anion derived from the ionic liquid used.
The ionic liquid appears to be incorporated into the
network, resulting in a cross-linked polymer stabilized
with bulky counterions.
By comparing the spectra of the EP5/[d2m2am][thp]
carrier and the EP5/[d2m2am][thp]/Pd catalyst (Fig. 1a,b),
we can assume that there are two ways of coordinating the
metal to the matrix. They are shown in Scheme 2. At
1743 cmꢀ1, the absorption band, corresponding to the
vibrations of the carbonyl group of epoxide chain, vanishes
Scheme 2. Mode of coordination of Pd(II) complex by EP5/[d2m2am][thb]
support.

S. Ostrowska et al. / C. R. Chimie 16 (2013) 752–760
757
Table 2
The surface atomic composition of EP5/[d2m2am][thp] support and EP5/[d2m2am][thp]/Pd catalyst obtained from XPS measurements.
EP5/[d2m2am][thp]
Element/band
EP5/[d2m2am][thp]/Pd
Element/band
At, %a
Suggested state
At, %
Suggested state
C1s
C1s
C1s
C1s
C1s
4.16
21.03
27.51
24.5
C
C
C1s
4.11
20.86
27.1
C C
C–C
C1s
C–C
C–N
C1s
C–N
C–OH
C1s
22.82
5.91
C–OH
6.05
C
O
C1s
C O
Cl2p3/2
4.95
Pd–Cl
¼O
¼O
N1s
1.62
1.11
NꢀCꢀN
N1s
1.58
1.03
0.37
1.35
NꢀCꢀN
N–C
N1s
N–C
d
+
Pd3d5/2
Pd3d5/2
Pd
Pd (II)
¼O
¼O
O1s
O1s
O1s
O1s
1.98
5.58
6.23
4.98
NꢀCꢀN
O1s
O1s
O1s
O1s
1.95
5.86
6.10
4.80
NꢀCꢀN
C
O
C O
C–O
OH
C–O
OH
a
The percentage of the element in the support/catalyst.
to the polymer support and the mechanism of catalytic
reaction. The surface composition of catalyst particles can
be determined for species present down to 0.1 atomic
percent, shallow from 1.5 to 10 nm, depth profiling. Major
functional groups for carbon and oxygen can be identified
as well as oxidation states for other species. These
characteristics are important sources of information about
the interfacial chemistry governing catalytic properties.
The percentage data obtained by means of the XPS
technique are summarized in Table 2. In the epoxy resin
carrier sample cured with the [d2m2am][thp] ionic liquid,
the highest percentage has carbon, which is determined by
the use of organic compounds. The C O bond is less
common than the others and amounts to 6%. A low
percentage of nitrogen bonds with carbon and oxygen
(nearly 3%) results from the application of the ammonium
binding energy BE for purine nitrogen atoms and OC O 1s
electrons after the Pd attachment. These data are consis-
tent with the results of FTIR measurements. The XPS
spectrum of the freshly prepared EP5/[d2m2am][thp]/Pd
catalyst shows that palladium appears dominantly in the
d
form of Pd(II). Minor fractions of Pd + nanoclusters are also
observed. It indicates that this polymeric support chains
might stabilize such a catalytically active monovalent
metastable species with a binding energy larger than that
of the Pd metal. The recovered EP5/[d2m2am][thp]/Pd
catalyst after a Heck reaction contained also some minor
fraction of Pd(0). Since the epoxide matrix cured with
[d2m2am][thp] ionic liquid possesses coordination sites of
different coordination ability, it seems very likely that the
zero-valent palladium, Pd(0), comes from the reduction of
Pd(II) coordinated to the carbonyl oxygen, the weaker of
the three coordination sites, whereas new species formed
after each reaction run, Pd clusters, come from the
reduction of Pd(II) coordinated to the purine nitrogen
atoms. The binding energy of Cl 2p3/2 in the XPS spectra, in
the region of 201.7–201.9 eV, indicates the presence of a –
PdCl2 structure.
ionic liquid. As
a result of the immobilization of
PdCl2(PhCN)2, nearly 5% of Pd–Cl bonds and 1.35% of the
divalent palladium bonds emerged. There is also a low
d
+
percentage (0.37%) of the electron-deficient Pd bond,
which formed due to the lateral overlapping of the d
atomic orbitals. This valence state is also referred to Pd
clusters [20]. They are not stable under normal conditions,
but their prolonged life is related to the protection afforded
by the polymer matrix. The lack of distinct changes in
composition of catalyst surface after subsequent catalytic
cycles indicates permanent binding of the ionic liquids
particles.
3.2. Morphology analysis
The characterization of palladium distribution on the
surface of the catalysts and the distribution of the size of
the nanoparticles were performed by means of a scanning
electron microscope (SEM) and energy-dispersive X-ray
spectroscopy (EDX) (Figs. 2–5). The average size of the
palladium nanoparticles for each sample was determined
The XPS data summarized in Table 3 show that three
possible coordination sites participate in binding the Pd to
the epoxide support. This is indicated by the increase of the
Table 3
Binding energy values from XPS measurements.
Sample
Binding energy (eV)
N 1s
O 1s
Pd 3d5/2
Cl 2p3/2
d
+
¼O
–N
NꢀCꢀN
Pd
Pd(0)
Pd(II)
EP5/[d2m2am][thp]
403.4
406.3
406.2
401.3
403.7
403.5
532.0
536.1
536.3
–
–
–
–
EP5/[d2m2am][thp]/Pd before use
EP5/[d2m2am][thp]/Pd after 3 runs
339.7
339.5
–
341.5
341.3
201.9
201.7
335.9

758
S. Ostrowska et al. / C. R. Chimie 16 (2013) 752–760
Fig. 2. SEM micrograph and EDX Pd-mapping of the surface of the DER/[d2m2am][thp]/Pd catalyst before use.
carrier and the steric restrictions imposed by the different
microporosities of these supports. The support micropo-
rous structure can influence the activity of catalyst. The
steric demands of a catalytic centre bound to a support can
be very different from those of its homogeneous analogue.
The porous structure of the support affects the accessibility
of the interior of the swollen resin by increasing diffusional
restrictions for reaction species. The results determined by
the nitrogen BET adsorption method indicate that DER and
EP5-based supports have different pore size distribution
which probably arise from differences in crosslink densi-
ties. These materials show different ratio of micropores
and very low volume of meso- and macropores. The EP5
resins had pore size distribution with the majority of the
micropores of radii below 2 nm. The DER resins exhibit the
lower value of pore specific volume, the lower surface area
and porosity than EP5-based supports.
Fig. 3. SEM micrograph of the surface of the DER/[d2m2am][thp]/Pd
catalyst before use.
3.3. Catalytic tests
by counting the size of about 100 particles from several
SEM pictures. The DER/[d2m2am][thp]/Pd X-ray micro-
probe (Figs. 2 and 3) indicates a uniform distribution of the
palladium particles with an average size of 0.1 nm. A less
regular distribution is observed for the DER/
[d2m2am][thb]/Pd catalyst with an average particle size
of 0.6 nm (Figs. 4 and 5). These differences may be
explained by referring to the morphology of the polymeric
The activity and stability of the palladium catalysts
were researched during their multiple usage in the model
Heck reaction (Scheme 3). The reaction entailed coupling
iodobenzene with methyl acrylate, occurring in the
solution of N-methylpyrrolidone (NMP) in the presence
of triethylamine. The only observed product was methyl
trans-cinnamate. Results in Table 4 show that for the
Fig. 4. SEM micrograph and EDX Pd-mapping of the surface of the DER/[d2m2am][thb]/Pd catalyst before use.

S. Ostrowska et al. / C. R. Chimie 16 (2013) 752–760
759
Table 4
The Heck reaction of iodobenzene with methyl acrylate over epoxide-
supported palladium catalysts.
Catalyst
Run
Conversiona [%]
EP5/[d2m2am][BF4]/Pd
1
2
3
88
91
98
EP5/[d2m2am][thb]/Pd
EP5/[d2m2am][thp]/Pd
EP5/[mthb][BF4]/Pd
1
2
3
95
98
83
1
2
3
56
34
29
1
2
3
89
92
91
Fig. 5. SEM micrograph of the surface of the DER/[d2m2am][thb]/Pd
DER/[d2m2am][thb]/Pd
DER/[d2m2am][thp]/Pd
DER/[mthb][BF4]/Pd
1
2
3
92
79
51
catalyst before use.
1
2
3
56
38
27
samples of the EP5/[d2m2am][thb]/Pd and EP5/
[d2m2am][thp]/Pd catalysts, where in both cases the
organic anion is present in the used ionic liquid, a
significant increase of activity can be seen in the second
cycle of the reaction. This is probably caused by the
increasing volume of the sample (swelling), hence allow-
ing for an easier access to the active spots in the open pores
of the catalyst. In the case of the catalysts based on EP5/
[d2m2am][BF4] and EP5/[mthb][BF4] carriers which have
an inorganic anion in their structure, a high activity in all
reaction runs is observed. We ascribe the lower catalytic
activity of the catalysts supported on the DER resins to
fewer Pd sites being accessible to the reactants when these
are attached to the polymer of lower microporosity. The
better availability of the catalytic sites situated in a EP5
resin having a greater volume of micropores and higher
surface area increases the activity of supported Pd systems.
The activities of most tested catalyst decrease with the
subsequent usage probably due to the leaching of the
palladium. We applied time-of-flight secondary ion mass
spectrometry (TOF-SIMS) to investigate the deactivation
process and to observe a deterioration of the Pd distribu-
tion on the surface of catalysts after a third reaction run in
comparison with the fresh sample. This technique permits
the evaluation of the chemical composition of the catalyst
surface and the distribution of metal or other catalyst
components on the surface. However, the quantitative
analysis by TOF-SIMS method is relatively difficult. TOF-
SIMS may be very useful in the studies of catalyst
deactivation processes. In such a case changes in the
composition of the upper layer of the investigated surface
can be determined. Owing to TOF-SIMS, a considerable
drop in the amount of surface accessible Pd was observed
for EP5/[d2m2am][BF4]/Pd and EP5/[d2m2am][thb]/Pd
catalysts after the Heck reaction in comparison with the
fresh samples (Table 5). The drop of Pd content was at safe
level and slightly affects the catalysts activity within
1
2
3
12
86
92
Reaction conditions: temperature 80 8C; substrates: iodobenzene 0.28 ml
(2.5 mmol), methyl acrylate 0.23 ml (2.5 mmol); solvent: toluene 0.15 ml
(1.4 mmol), triethylamine 0.35 ml (2.5 mmol), N-methylpyrrolidone
(NMP) 1.00 ml (10.4 mmol); catalyst: 0.05 g (Pd content ꢃ 0.07 mM/g);
the conversion refers to GC analysis.
a
Conversion of iodobenzene after 1.5 h.
acceptablelimits,andcanbeexplainedbytheoftenreported
enhancement of the activity for a catalyst containing mixed
valence states of Pd(II) and Pd(0) [21]. Some metal leaching
is often observed when supported catalysts are employed,
usually higher in the first two runs and lower in the next
ones. It mostly comes from the detachment of the weakly
bound metal species via, for example, physical forces. These
are still present after washing the catalyst during the
preparation procedure. Observed decreaseof activity during
prolonged use can be also connected with poor chemical
resistance of epoxy supports to polar solvents like NMP.
However, this solvent was used for the model Heck reaction,
which we chose only to preliminary characterization of
catalytic properties of these catalysts. The performed
catalysts showed good activity and stability comparing to
other catalysts. For example, Cypryk et al. reported that the
activity of the polysiloxane-supported Pd catalysts in the
Mizoroki–Heck arylations of methyl acrylate, butyl acrylate,
and acrylonitrile by iodobenzene and of styrene by
Table 5
Normalized intensity of 106Pd+ selected from the mass spectra of
palladium catalysts.
Catalyst
Run
Intensity of 106Pd+
EP5/[d2m2am][BF4]/Pd
0
3
8.2 ꢂ 10ꢀ3
4.4 ꢂ 10ꢀ3
EP5/[d2m2am][thb]/Pd
0
3
3.3 ꢂ 10ꢀ3
2.3 ꢂ 10ꢀ3
Scheme 3. The Heck reaction of iodobenzene with methyl acrylate.

760
S. Ostrowska et al. / C. R. Chimie 16 (2013) 752–760
bromobenzene was comparable to that of homogeneous
PdCl2(PhCN)2 and maintained through five to ten reaction
cycles [22]. Sudalai reported the use of Pd-exchanged
montmorillonite clays in the Heck reaction. Investigated
catalysts were reused three times without significant loss of
activity [23].
The ionic liquid used at the curing stage has a decisive
influence on the catalytic activity of the catalysts. This was
also confirmed by the results of TOF-SIMS measurements
of the EP5/[d2m2am][BF4]/Pd and EP5/[d2m2am][thb]/Pd
samples (Table 5). The disparity of the intensities of the
palladium ions for the EP5/[d2m2am][BF4]/Pd and EP5/
[d2m2am][thb]/Pd catalysts just after the immobilization
shows that more palladium complex is deposited on the
carrier with an inorganic anion in the structure of the ionic
liquid used as hardener.
To determine the nature of the active species, the effect
of catalyst poisoning has also been investigated. To rule out
the possibility of catalysis by microparticles (colloids or
nanoclusters) of zero-valent palladium formed from
leached and reduced Pd(II) precursor, a mercury poisoning
experiment was carried out by adding mercury to the
reaction mixture before the catalytic test. The mercury
poisoning of metal(0) particles, by amalgamating the
metal or adsorbing on the metal surface is a widely used
test for the heterogeneity/homogeneity of catalysis [24].
An epoxide-supported palladium catalyst vigorously
stirred with a large excess of metallic mercury for 24 h
prior reaction shows almost the same catalytic activity for
the Heck reaction as before poisoning. It is known that
trace amounts of leached metal particles or soluble
palladium complex can be very catalytically active [25].
As additional evidence for the identity of the true catalyst,
hot filtration technique has also been employed, and no
catalytic activity was observed, confirming the absence of
active species (soluble Pd(0)) in the hot filtrate.
of the epoxide-supported palladium catalyst. The studied
catalysts showed different activity in the Heck reaction,
which was related to the different structure of the ionic
liquid used. Based on the recycling efficiency tests, it was
found that prepared polymer-supported palladium cata-
lysts have good catalytic stability. The usage of ionic
liquids with a different structure of ions as curing agents
enables us to obtain carriers which do not require
additional functionalization to control the ligand-binding
affinity to metal complexes.
Acknowledgement
This work was supported by the National Science
Centre (Poland) (grant No 0255/B/H03/2011/40) and by the
Faculty of Chemistry, Lodz University of Technology,
Young Scientist Fund (grant 28.05.2012).
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