Macrocellular Pd@ionic liquid@organo-Si(HIPE) heterogeneous catalysts and their use for Heck coupling reactions

Article abstract of DOI:10.1039/c2nj40527j

Supported ionic liquid phases (SILPs) within macrocellular silica-based foams are prepared by a simple impregnation in organic solvents. Thin ionic liquid layers with thicknesses of 6 to 12 nm were obtained. The SILs mobility has been evidenced through NMR solid state spectroscopy. Subsequently, palladium salts are efficiently trapped within the SILPs, while an in situ palladium hydrogenation allowed an efficient reduction and formation of 10 nm diameter palladium metal nanoparticles. These hybrid foams are used as heterogeneous macrocellular catalysts for the Heck coupling reaction of iodobenzene and cyclohexyl acrylate, where palladium leaching appears to be very low. Despite recyclability minimized through the entrapment of detrimental ammonium salts within the macroporous network during the reaction, competitive TONs and TOFs were reached, while separation of the products can be reached at ease, due to the fact that both palladium species and by-products are trapped within the monolithic foams.

Full text of DOI:10.1039/c2nj40527j

NJC
View Article Online
View Journal | View Issue
PAPER
Macrocellular Pd@ionic liquid@organo-Si(HIPE)
heterogeneous catalysts and their use for Heck
coupling reactions†
Cite this: NewJ.Chem., 2013,
3
7, 157
ab
c
d
d
Nicolas Brun, Peter Hesemann, Guillaume Laurent, Cl e´ ment Sanchez,
b
b
a
Marc Birot, Herv e´ Deleuze* and R e´ nal Backov*
Supported ionic liquid phases (SILPs) within macrocellular silica-based foams are prepared by a simple
impregnation in organic solvents. Thin ionic liquid layers with thicknesses of 6 to 12 nm were obtained. The
SILs mobility has been evidenced through NMR solid state spectroscopy. Subsequently, palladium salts are
efficiently trapped within the SILPs, while an in situ palladium hydrogenation allowed an efficient reduction
and formation of 10 nm diameter palladium metal nanoparticles. These hybrid foams are used as
heterogeneous macrocellular catalysts for the Heck coupling reaction of iodobenzene and cyclohexyl acrylate,
where palladium leaching appears to be very low. Despite recyclability minimized through the entrapment of
detrimental ammonium salts within the macroporous network during the reaction, competitive TONs and
TOFs were reached, while separation of the products can be reached at ease, due to the fact that both
palladium species and by-products are trapped within the monolithic foams.
Received (in Montpellier, France)
1st June 2012,
2
Accepted 4th September 2012
DOI: 10.1039/c2nj40527j
www.rsc.org/njc
3
and thermal stabilities, offering a broad range of applications,
from electrochemistry to catalysis. However, economical aspects
Introduction
4
Due to environmental and ecological issues, optimization of still restrict industrial uses.
chemical synthetic processes in laboratories and industry is essen-
Therefore, supported ionic liquid phases (SILPs) onto porous
5
1
tial. Beyond yield and selectivity, environmental considerations, hosts have recently received much attention as media for reuse of
such as catalyst recovery or volatile organic compounds (VOCs) semi-heterogeneous catalysts, such as palladium compounds for
6
substitution, have to be considered in detail. Thus, both design of carbon–carbon coupling reactions. In these systems, metallic
original catalytic supports and eco-friendly alternatives to VOCs complexes or nanoparticles can be easily stabilized within adsorbed
constitute attractive answers. In this context, ionic liquids (ILs) ionic liquid phases strongly reducing catalyst leaching. Moreover,
appear as a rising option to substitute VOCs and preserve catalytic SILPs enable us to work with smaller amounts of costly ionic liquid
2
4f
entities from leaching. Ionic liquids, which are composed entirely than conventional homogeneous or multiphasic catalytic systems,
of ions, can be distinguished from molten salts by a liquidus state potentially leading to large-scale reactors conception. In most of the
below 100 1C combined with a relatively low viscosity. Particularly, works reported so far, SILPs are limited to thin films of less than
7
quaternary ammonium and phosphonium salts exhibit, for 1 nm either grafted or simply adsorbed on the host surface. This
instance, a stable wide electrochemical window, high ionic typical thickness corresponds more closely to a monomolecular
mobility, negligible vapour pressure, and excellent chemical layer than to a real liquid supported phase. Furthermore, supports
6
a–c,8
are most often mesoporous silica powders
ionogels,
or monolithic
6d,9
within which ionic liquids are encapsulated, limiting
a
b
c
Universit ´e de Bordeaux, Centre de Recherche Paul Pascal, UPR 8641 CNRS,
F-33600 Pessac, France. E-mail: backov@crpp-bordeaux.cnrs.fr
thereby the accessibility of catalysts. Consequently, the design of
supported ionic liquid phases onto macrocellular monoliths would
appear as a promising alternative to conventional heterogeneous
catalysts in order to optimize accessibility and mass transport. To
address this issue, our group has recently developed the design of
macrocellular silica-based hybrid foams made from concentrated
Universit ´e de Bordeaux, Institut des Sciences Mol ´e culaires, UMR 5255 CNRS - Univ.
Bordeaux, F-33400 Talence, France. E-mail: h.deleuz@ism.u-bordeaux1.fr
Institut Charles Gerhardt de Montpellier, UMR 5253 CNRS - ENSCM - Univ.
Montpellier 1-2, F-34000 Montpellier, France
d
Laboratoire de Chimie de la Mati `e re Condens ´e e de Paris, UMR 7574 CNRS - ENSCP
-
Coll `e ge de France, F-75231 Paris, France
10
direct emulsion. These macrocellular materials, named Si(HIPE)
(HIPE is an acronym for High Internal Phase Emulsion), can be
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c2nj40527j
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 157--168 157

View Article Online
Paper
easily functionalized to stabilize for instance palladium particles,
NJC
11a,b
Si(HIPE) preparation. Typically, tetraethylorthosilicate (TEOS,
11c
11d,e
europium complexes or crude enzymes.
Nevertheless, in spite 5.0 g) was added to an aqueous solution of TTAB (16 g, 35 wt%)
of efficient stabilisation, catalyst leaching cannot be totally avoided, previously acidified with concentrated hydrochloric acid solution
11a
leading to an inevitable loss of activity.
(7.0 g). Hydrolysis was left going on until a homogeneous medium
With the aim to circumvent this feature, we describe in the was obtained. The hydrophilic continuous phase was then emulsi-
present contribution a facile route to obtain SILPs onto Si(HIPE) fied drop by drop by dodecane (35 g) using a mortar. The emulsion
monoliths by impregnation under soft vacuum. This approach has was then allowed to condense for 1 week at room temperature. The
allowed the facile immobilization of either Palladium salts or as-synthesized monoliths were washed three times with a THF/
metallic nanoparticles, depending on the post-treatment applied, acetone mixture (1 : 1 v/v) to extract the oily phase. Drying of the
in the supported ionic liquid layer. Catalytic performances toward materials for a week at room temperature was followed by a
À1
the Heck coupling reaction between iodobenzene and cyclohexyla- thermal treatment at 650 1C (heating rate of 2 1C min ) for 6 h,
crylate, according to the supported ionic liquid, and the encapsu- with a 2 h-plateau at 200 1C to remove all organic compounds.
lated catalyst, are also discussed.
g-Imidazole-Si(HIPE) (grafting method). A piece of Si(HIPE)
(300 mg) was added to a solution of 1-[3-(triethoxysilyl)propyl]-
imidazole (0.1 M) in 100 mL of a toluene/isopropanol mixture
at 50 vol%/50 vol%). For a good impregnation, the suspension
was placed under vacuum (8 kPa in a desiccator), until the
Experimental
Materials
(
Tetradecyltrimethylammonium bromide 98% (TTAB) and sodium effervescence disappears. After 72 h aging at room temperature,
hydride (NaH) were purchased from Alfa Aesar. Tetraethylortho- the solution was filtrated. The monoliths were then washed
silicate 98% (TEOS), imidazole, (3-chloropropyl)triethoxysilane three times with 100 mL of a toluene/isopropanol mixture (at
and palladium acetate (Pd(OAc)
) were purchased from Aldrich. 50 vol%/50 vol%) and dried in air. Resulting monoliths are
2
Acetone, toluene, isopropanol, ether, and dodecane 99% were labelled g-imidazole-Si(HIPE).
purchased from Rectapur. Tetrahydrofuran (THF) and hydro-
Representative procedure for catalysts preparation. Solvents
chloric acid 37% (HCl) were purchased from AnalaR Normapur. were degassed for 20 min under an argon flow before use, to
Ionic liquids 1-butyl-3-methylimidazolium bis(trifluoromethane- avoid oxidation of palladium. Typically, a piece of native
sulfonyl)imide, hexafluorophosphate and tetrafluoroborate Si(HIPE) or pre-functionalized g-imidazole-Si(HIPE) (300 mg)
(
labelled later in the text, respectively, as [Bmim]NTf
2
, [Bmim]PF
6
was introduced in a solution of ionic liquid (0.2 M) and
) were all purchased from Solvionic SA. 3,4- palladium acetate (10 M) in THF (or in a 50/50 vol% water/
À2
and [Bmim]BF
4
Epoxycyclohexylmethyl-3,4-epoxycyclohexyl carboxylate (ERL 4221), THF mixture for the hydrophilic IL, [Bmim]BF ). The suspension
4
dipropyleneglycoldiglycidylether (DER 736), nonenyl succinic was placed under vacuum in a desiccator (12 kPa) for a good
anhydride (NSA) and dimethylaminoethanol (DMAE) were pur- impregnation until the effervescence disappears. After 72 h aging
chased from Sigma. Except opposite indication, reactants were at room temperature under static vacuum, the suspension was
used as received without further purification.
filtered, and the macrocellular monoliths were dried under dynamic
vacuum (1–2 kPa) at room temperature for 10 h, to remove residual
Syntheses
solvent. The as-synthesized hybrid foams are named Pd(OAc) @
2
Triethoxysilylated precursors preparation. (3-Chloropropyl)- [Bmim]X@Si(HIPE) or Pd(OAc) @[Bmim]X@g-imidazole-Si(HIPE),
2
triethoxysilane and (THF) were purified by distillation before use. depending on the use of unmodified or pre-functionalized silica
4 6 2
NaH dispersed in oil was rinsed in pentane, then dried in vacuum. monoliths (X = BF , PF or NTf ). The reduction of palladium(II)
NaH (2.4 g, 0.1 mol) was suspended in 100 mL of dry THF under an acetate in metallic palladium(0) was performed by using dihydrogen
0
2
inert atmosphere. To this suspension, 4.8 g of imidazole (0.07 mol) (10 bars, 80 1C, 1 h). Sample was then named Pd @[Bmim]NTf @g-
in 50 mL THF was added dropwise over 30 min and stirred for imidazole-Si(HIPE).
further 2 h at room temperature. Freshly distilled 3-iodopropyl
Catalytic Heck coupling reactions
triethoxysilane (23.3 g, 0.07 moles) was then added dropwise over
0 min and the reaction mixture was stirred for 2 days at room Catalytic tests were realized in 20 mL glass tubes with a side-armed
3
temperature. After completion of the reaction, THF was evaporated. frit. Typically, a piece of hybrid foam (100 mg) was firstly intro-
The reaction product was then extracted with diethyl ether and duced in the reactor, closed with a septum. Then, triethylamine
filtered. After removal of ether from the filtrate, the crude 1-[3- (11 mmol), diluted in octane (1.0 mL), was injected via a syringe.
(
(
triethoxysilyl)propyl]imidazole was purified by vacuum distillation The reaction media was gently purged with argon for 10 min, and
0.1 mm Hg/140 1C) to yield 12.7 g of the title compound (66%). then immersed into a preheated oil bath at 136 1C. Then a mixture
FT-IR (neat): 3110, 2974, 2929, 2888, 1506, 1391, 1228, 1104, 957, of iodobenzene (10 mmol), cyclohexyl acrylate (12 mmol) and
À1
1
7
83, 664 cm ; H NMR (CDCl3): d (ppm) 0.49 (2H, m), 1.15 (9H, t, dodecane (as a GC internal standard; 5 mmol), diluted in octane
J = 6,9 Hz), 1.81 (2H, m), 3.73 (6H, q, 6,9 Hz), 3.87 (2H, t, J = 7,2 Hz), (3.0 mL), was quickly added. Stirring was carried out by octane
1
3
6
1
.84 (1H, s), 6.98 (1H, s), 7.41 (1H, s); C NMR (CDCl ): d (ppm) 7.2, boiling. Aliquots were periodically withdrawn from the reaction
3
29
8.2, 24.8, 49.0, 58.4, 118.7, 129.2, 137.1; Si RMN (CDCl
3
) d À46.5; mixture and diluted with ice-cooled THF (1.0 mL) before GC
+
HRMS (FAB+): Calcd for C12
73.1631.
25 3 2
H O N Si [M + H] 273.1634; found, analysis. Between each catalytic cycle, the pieces of monolith were
2
profusely rinsed out with octane, then immersed for a few minutes
1
58 New J. Chem., 2013, 37, 157--168
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

View Article Online
NJC
Paper
À1
À1
in an aqueous NaOH solution (0.05 M, 10 mL), to remove any an oxygen flux (5 mL min ) using a heating rate of 5 1C min . The
insoluble side-product (mainly triethylammonium iodide). apparatus was a Setaram TAG-1750 thermogravimetric analyser.
Monolithic catalysts were finally dried at 80 1C in an oven.
Results and discussion
Instrumentation
Syntheses and characterization
Scanning electron microscopy (SEM) observations were performed Macrocellular monoliths were obtained using a concentrated
with a Hitachi TM-1000 apparatus at 15 kV. The specimens were direct emulsion, i.e. dispersion of oil in water, where the
gold–palladium-coated in a vacuum evaporator prior to examina- hydrophilic continuous phase contains hydrolyzed silane pre-
tion. Transmission electron microscopy (TEM) experiments were cursors. For synthetic details see the Experimental section.
performed with a Jeol 2000 FX microscope (accelerating voltage of
Characterization at the macroscopic length scale. As
200 kV). High Resolution TEM (HR-TEM) micrographs were observed by SEM, (Fig. 1b, inset), the macroscopic texture of these
obtained with a Jeol 2200 FS microscope. Ultramicrotomy were monoliths resembles a ‘‘hollow spheres’’ aggregation, usually named
performed, using a Reichert-Jung Ultracut E. Typically, a piece of ‘‘cells’’. These ‘‘cells’’, induced by the oil droplets template removed
hybrid foam (20 mg) was previously immersed in 5.0 mL of ERL after intensive washing, are rather polydisperse in size, ranging from
4221 for 3 h. Then, a mixture of ERL 4221 (18 mL), DER 736 (14 mL), 1 mm up to 10 mm. This feature is unchanging, whatever the step of
NSA (48 mL) and DMAE (0.6 mL) was prepared. Afterwards, 1.0 mL functionalization, meaning that the integrity of the materials was
of this mixture was added to the impregnation solution. Then, well preserved during the various reaction steps. As previously
10
polymerisation was performed at 70 1C for 10 h in an oven, and the mentioned, it is obvious that mineralization starts at the oil–water
impregnated sample was finally cut to get 70 nm thin slices.
interface (the interface acting as a defect where the nucleation
Intrusion/extrusion mercury measurements were performed enthalpy is lowered) and then extends moderately to the water
using a Micromeritics Autopore IV 9500 porosimeter, this to reach phase, without polymerizing throughout the hydrophilic continuous
the scaffolds macrocellular cells characteristics. Surface areas and phase. More quantitative information about macroporosity is
pore characteristics on a mesoscale were obtained with a Micro- accessible through mercury intrusion porosimetry (Fig. 1 and
meritics ASAP 2010 apparatus. Small angle X-ray scattering (SAXS) Table 1). Two sets of windows are obtained, clearly highlighted
experiments were carried out with a 18 kW rotating anode X-ray both by SEM and pore size distribution extracted from mercury
source (Rigaku-200) with use of a Ge (111) crystal as a monochro- porosimetry experiments. Firstly, windows that intrinsically connect
mator. The scattered radiation was collected on a two-dimensional two adjacent ‘‘cells’’ can be distinguished that we have previously
detector (Imaging Plate system from Mar Research, Hamburg). The referred to as ‘‘internal junctions’’. These windows diameters are
sample to detector distance was 500 mm.
situated between 30 and 40 nm, as shown by the pore size distribu-
FTIR spectra were obtained with a Nicolet 750 FTIR spectro- tion (Fig. 1). A second class of windows emerging from aggregation
meter. Solid-state NMR was carried out on a Bruker Avance III 300 between several ‘‘cells’’ has also to be considered. These have been
1
13
29
operating at 300 MHz for H, 75 MHz for C and 60 MHz for Si. previously named ‘‘external junctions’’. This contribution induces
Samples were packed into a 7 mm zirconia rotor, put into a larger pores, of 3–4 mm in diameter. It is interesting to notice that
1
3
standard Bruker double-resonance probe and spun at 5 kHz.
Power Gated (PG) spectra were obtained using a 901 pulse of 5 ms, a organosilane species, or by the ionic liquid phase impregnation.
relaxation delay (RD) of 10 s, 256 scans, and a low power decoupling
Nevertheless, looking more precisely at the mercury porosimetry
of n1H = 2.5 kHz during relaxation. C High Power DECoupling data collected in Table 1, it is obvious that both bulk and skeletal
HPDEC) spectra were acquired under the same conditions without densities increase after functionalization and more importantly
C
this feature is not affected either by the functionalization with
1
3
(
13
decoupling during the relaxation. C cross polarization (CP) spectra after impregnation steps. Moreover, the intrusion volume is strongly
13
used n1H = n1C = 50 kHz, RD = 1 s and 26624 scans. In all
C
affected by the IL-impregnation step, since a large decrease can be
experiments a decoupling of n1H = 50 kHz was applied during the pointed out in the material Pd(OAc) @[Bmim]NTf @g-imidazole-
2
2
12
acquisition. The spectra were simulated with the DMFIT program.
Si(HIPE). These characteristics suggest an effective encapsulation
X-ray photoelectron spectroscopy (XPS) experiments were performed and/or coating of ionic liquid phases within the silica-based porous
using an Escalab VG 220i XL apparatus. X-ray diffraction (XRD) framework. To confirm the presence of the ionic liquid phase within
measurements were carried out using X’pert MPD Philips using Cu the macroporous framework, hybrid foams were thoroughly char-
Ka radiation with an average current of 50 mA. Chromatography acterized at meso- and microscopic scales.
experiments were performed using a Varian 3800 and the Star
Characterization at the mesoscopic and microscopic length
chromatography software. The capillary column was a DB5 (5% scales. In Si(HIPE)s synthesis, TTAB, used in large excess in
phenyl groups) column. Iodobenzene (IDB) conversion was calcu- order to be above its critical micelle concentration (CMC), plays
1
0
lated from the peak area ratio of IDB relative to dodecane (D) as two important roles. Firstly, it acts as a stabilizer of the direct
obtained from GC analysis. Elemental analyses of carbon, nitrogen emulsion adsorbing at the oil–water interface. Secondly, it
and palladium were determined by laser ablation inductively generates a supramolecular assembly throughout the hydro-
coupled plasma mass spectrometry (ICP-MS) and carried out by philic continuous phase, promoting, after washing and thermal
the SCA of the Centre National de la Recherche Scientifique (Solaize, treatment, an ordered porosity at the mesoscopic length scale.
France). Thermogravimetric analyses (TGA) were carried out under This is confirmed by both TEM (Fig. 2a) and SAXS (Fig. 2b).
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 157--168 159

View Article Online
Paper
NJC
Fig. 1 Pore size distribution of connecting windows obtained by mercury
Fig. 2 (a) TEM micrograph of a SILPs onto Si(HIPE) macrocellular hybrid material.
(b) SAXS spectrum obtained for ’ a native silica monolith, J an hybrid foam
g-imidazole-Si(HIPE), and K a SILP onto Si(HIPE) monoliths,
porosimetry. (a) g-imidazole-Si(HIPE) and (b) Pd(OAc)
g-imidazole-Si(HIPE). The inset corresponds to a SEM micrograph of the
Pd(OAc) @[Bmim]NTf @g-imidazole-Si(HIPE) macrocellular foam.
2 2
@[Bmim]NTf @
Pd(OAc)
2
@[Bmim]NTf
2
@g-imidazole-Si(HIPE).
2
2
À1
Table 1 Mercury porosimetry data obtained for the silica monolith, the hybrid
foam after covalent grafting of imidazole groups, and one of the SILPs onto
Si(HIPE) macrocellular material
a wave vector q = 0.19 Å ), including both pore diameter and
hybrid silica-based wall in between. Despite the proof of a constant
mesostructure, these techniques do not allow quantifying the
accessibility of the mesoporosity in this series of hybrid foams.
With this purpose, we performed nitrogen sorption measurements
before and after impregnation of the ionic liquid phase. Thereby, it
clearly appears that the functionalization step induces a decrease of
the meso- and micropores surface area (Table 2, entries 1 and 2),
while the ionic liquid impregnation generates a large drop of the
micro- and mesoporous contributions (Table 2, entries 3–6), which
is consistent with the increase of skeletal densities depicted by
mercury porosimetry experiments (Table 1).
2 2
g-imidazole- Pd(OAc) @[Bmim]NTf @
Si(HIPE) Si(HIPE)
g-imidazole-Si(HIPE)
Porosity (%)
92
91
10.4
89
5.6
Intrusion volume 10.9
3
À1
(
cm g )
Bulk density
0.08
0.85
0.09
0.99
0.16
1.50
À3
(g cm
)
Skeletal density
À3
(g cm
)
TEM observations highlight a pore diameter close to 2 nm
Hence, the encapsulation and/or coating of SILPs seems to
ordered in a vermicular mesostructure. SAXS data confirm the be efficient within the macrocellular silica-based monoliths. To
presence of a vermicular structure, exhibiting a unit cell para- check the integrity of both the organosilane molecules grafted and
meter of 3.3 nm (corresponding to the constant peak centred at the ionic liquid coated, a qualitative study by Fourier-transformed
1
60 New J. Chem., 2013, 37, 157--168
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

View Article Online
NJC
Paper
Table 2 Nitrogen sorption data obtained for the silica-based hybrid foams
Nitrogen sorption data
a
b
c
BET surface area
Mesoporous surface area
Total pore volume
2
À1
2
À1
3
À1
Entry
Hybrid foams Si(HIPE)
(m g
)
(m g
)
(cm g
)
1
2
3
4
5
6
Si(HIPE)
g-imidazole-Si(HIPE)
620
462
133
110
117
187
209
139
79
63
77
0.31
0.39
0.13
0.10
0.11
0.19
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
2
@[Bmim]NTf
@[Bmim]NTf
2
@g-imidazole-Si(HIPE)
@Si(HIPE)
2
@[Bmim]BF
@[Bmim]BF
4
@g-imidazole-Si(HIPE)
@Si(HIPE)
4
119
a
b
c
Brunauer, Emmett and Teller method. Mesoporous surface area extracted from the BJH method (Barret, Joyner and Halenda). Single point
adsorption total pore volume.
À1
infrared spectroscopy (FTIR), together with quantitative studies 1390 cm for the spectrum associated with g-imidazole-Si(HIPE)
À1
by elemental analysis and solid-state NMR, was performed.
hybrid foam (Fig. 3b). A small shoulder around 3100 cm
,
First, the integrity of imidazole groups within the silica-based corresponding probably to u (Q C–H) vibration modes, is also visible
À1
foams was checked by FTIR spectroscopy (Fig. 3). It is necessary to (Fig. 3b). Moreover, a shoulder centred at 2957 cm , assigned to
differentiate absorption bands related to the silica framework from u(CH
those associated with functional organic groups. Concerning silica ethoxy groups, coming from an incomplete hydrolysis of the
Fig. 3c), we can distinguish three absorption bands centered at organosilane precursors, or the presence of residual isopropanol/
3
) asymmetrical valence vibration, suggests the presence of
(
1
À1
080, 800 and 460 cm , corresponding, respectively, to Si–O–Si toluene molecules of the impregnation solution (see Experimental
13
antisymmetric and symmetric stretching modes and rocking section). The presence of imidazole groups is also confirmed by
motions, and a broader band between 3200 and 3600 cm
C
À1
,
solid-state NMR study (Fig. 4).
associated with u(OH) and stretching modes of the physisorbed
water molecules and silanol groups.
Thus, the cross polarization (CP) spectrum shows six major peaks
centred at 9.0, 23.8, 50.0, 121.0, 126.6 and 136.5 ppm (Fig. 4a). The
2 3
In addition to these major absorption bands of the silica first three correspond to the Si–(CH ) silicopropyl chain and the
framework itself, signals related to imidazole groups (Fig. 3a) are others to the imidazole ring. A little narrow peak is visible at
clearly noticeable in the FTIR spectrum of the g-imidazole-Si(HIPE) 64.9 ppm, more intense in the high-power decoupling (HPDEC)
2
hybrid foam (Fig. 3b). Thus, u(CH ) symmetrical and antisymme- quantitative spectrum in which another intense narrow peak is
trical stretching modes and d(CH ) rocking motions, related to the visible at 23.6 ppm (Fig. 4b). Both correspond to isopropanol, which
2
silicopropyl chain (propyl segment between Si atom and imidazole is confirmed by the relative decrease in the CP spectrum, showing
À1
group), can be noticed, respectively, at 2928, 2870 and 1451 cm . In the high mobility of these species. Henceforth, it seems obvious that
addition, vibration modes associated with imidazole heterocycles, the methyl groups shown by FTIR comes from isopropanol trapped
u(CQN), u(C–N), u(C–C) and u(CQC), are noticeable from 1549 to within the hybrid foam. Subsequently, to check the local chemical
environment around silicon atoms, and quantify both grafting ratio
and condensation degree of imidazole groups within silica-based
29
foams, Si solid-state NMR study was carried out (Fig. 5).
2
9
At this stage, we have to specify that Si sites are labelled
with the conventional Tn and Qn notation. Thus, T refers to
À1
Fig. 3 FTIR spectra focused on 4000–400 cm wavenumber region. (a) imidazole
1
3
triethoxysilane precursor, (b) g-imidazole-Si(HIPE) hybrid foam and (c) native
Si(HIPE).
Fig. 4 C solid-state NMR study of the g-imidazole-Si(HIPE). (a) Cross polarization
(CP) spectrum. (b) High-power decoupling (HPDEC) spectrum.
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 157--168 161

View Article Online
Paper
NJC
29
Fig. 5 Si HPDEC solid-state NMR study of the g-imidazole-Si(HIPE) hybrid foam
deconvoluted bottom).
(
functional RSiO
of organosilane precursors, while Q species are associated with
SiO -units from the silica framework. In this notation, n corre-
3
-units resulting from hydrolysis and condensation
4
sponds to the number of bridging oxygen atoms surrounding the
silicon and R to the organic chain (i.e., imidazole groups). There-
fore, in this study, Tn signals clearly confirm the presence of [Bmim]NTf
À1
Fig. 6 FTIR spectra focused on 4000–900 cm wavenumber region. (a)
ionic liquid, (b) hybrid foam Pd(OAc) @[Bmim]NTf @g-imidazole-
2
2
2
Si(HIPE) and (c) g-imidazole-Si(HIPE).
imidazole-based organosilane derivatives. Then, after a Lorent-
13
zian/Gaussian deconvolution of these spectra, a molar ratio of
around 5% in T species was determined. This feature was also
n
À1
supported by elemental analysis of nitrogen (Table 3). Moreover, 2854 and 1465 cm (Fig. 6b). Concerning the sample previously
2 1
due to the presence of both T and T
species, we can consider that functionalized with imidazole groups (Fig. 6b), these signals, coming
+
the organosilane precursors used in this study were subjected to an from both chemically grafted imidazoles and physisorbed [Bmim]
incomplete condensation. This feature can be mainly explained cations non-covalently anchored, are largely enhanced, compared
from geometrical constraints on the surface of the silica frame- with the initial g-imidazole-Si(HIPE) hybrid foam (Fig. 6c). Moreover,
work. Thus, considering the lack of catalyst in the impregnation concerning the SILPs within macrocellular silica-based foams, two
À1
solution, partial hydrolysis of ethoxy groups and condensation is intense signals centred at 2968 and 2882 cm , related to antisym-
3
largely promoted by superficial silanol groups and residual physi- metrical and symmetrical u(CH ) stretching modes from short alkyl
+
sorbed water. Henceforth, steric obstructions, involving a limited chain segments of the [Bmim] cation, are clearly visible (Fig. 6b). In
access to superficial groups, are likely to prevent organosilanes addition, u(CQN), u(C–N), u(C–C) and u(CQC) vibration modes
from complete condensation. Nevertheless, organosilane deriva- associated with the imidazole ring are discernible between 1575
À1
À1
tives are mainly grafted onto the inorganic structure by one or two and 1390 cm . Two intense peaks at 3162 and 3128 cm , probably
oxygen atoms, suggesting a rigid anchoring.
corresponding to u (Q C–H) stretching modes, are also revealed.
Non-covalent anchoring and integrity of ionic liquid phases Concerning the anionic part of ILs, a few signals are also noticeable
onto macrocellular foams surface was firstly highlighted by for the SILPs. In the case of bis(trifluoromethanesulfonyl)imide
À
À1
FTIR spectroscopy (Fig. 6).
anion NTf
2
, two peaks between 1354 and 1138 cm suggest the
–N) and trifluoromethyl (–CF )
3
Thus, for each sample, the 1-butyl-3-methylimidazolium presence of both sulfonamide (–SO
cation [Bmim] IRTF typical signature (Fig. 6a) was clearly groups. The integrity of the ionic liquid has also been checked by H
2
+
1
13
displayed. Antisymmetrical and symmetrical u(CH
) stretching and C solid-state NMR (not shown herein). Due to the high ionic
2
modes, together with d(CH ) rocking motions, related to carbons mobility of this phase, very narrow lines are observed and the
2
1
of the silicopropyl chain, are, respectively, noticeable at 2941, spinning side bands have almost disappeared, even on the
spectra at a spinning speed of 5 kHz. All the characteristic reso-
nances are observed, including the CF quadruplet of the counter-
ion that is not visible under CP.
H
3
Table 3 Stoichiometry determined after the covalent grafting of imidazole
groups
Secondly, stoichiometries of this SILPs onto Si(HIPE) series
were determined combining elemental and thermogravimetric
analysis (Table 4).
Wt%
a
a
b
Hybrid foam
C
N
H
2
O
Stoichiometry
The molar ratio Pd/ILs, experimentally fixed at 1/20, was
maintained for each sample, whatever the synthetic route in
use. Thus, it appears, to a first extent, that previous covalent
g-imidazole-Si(HIPE) 4.80 1.60 2.70 SiO1.96(C
6
N
2
H
9
)
0.04Á0.10H
2
O
a
b
By elemental analysis (ICP-MS). And thermogravimetric analysis.
1
62 New J. Chem., 2013, 37, 157--168
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

View Article Online
NJC
Paper
Table 4 Elemental and thermogravimetric analysis for the SILPs onto Si(HIPE)s macrocellular monoliths
Wt%
a
a
a
b
Entry
Hybrid foams Pd(OAc)
2
@Organo-Si(HIPE)
Pd
C
N
2
H O
1
2
3
4
5
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
2
2
@[Bmim]NTf
@[Bmim]NTf
2
@g-imidazole-Si(HIPE)
@Si(HIPE)
0.72
0.68
0.91
0.99
0.71
18.75
15.92
17.64
20.28
17.91
5.92
4.85
4.84
5.18
4.57
1.20
1.40
1.80
2.00
1.50
2
@[Bmim]BF
@[Bmim]BF
4
@g-imidazole-Si(HIPE)
@Si(HIPE)
@Si(HIPE)
4
@[Bmim]PF
6
a
b
Palladium, carbon and nitrogen contents determined by elemental analysis. Water physisorbed content determined by thermogravimetric
analysis.
2
grafting of imidazole groups onto the inorganic support did not coupling reaction. The starting material was Pd(OAc) @
influence the encapsulation of the palladium salt. However, it [Bmim]NTf @g-imidazole-Si(HIPE)s.
2
seems that a previous functionalization enhances subsequent
Palladium reduction characterization. As observed by XPS
[
Bmim]NTf2 physisorption, while generates a decrease in the carried out on Pd(OAc) @[Bmim]NTf @Si(HIPE) (Fig. 7a and b),
2
2
4
amount of [Bmim]BF onto the silica-based support (Table 5). two main peaks centered at 343.5 and 338.3 eV and related to Pd
3
/2
5/2
This feature suggests that the anchoring of hydrophobic ionic 3d and Pd 3d can be noticed. These signals are associated
II
liquids ([Bmim]NTf
stacking with imidazole groups, while the coating of hydrophilic their chemical integrity within the SILP.
ILs ([Bmim]BF ) is promoted via hydrogen bonds between super- Weak contributions at lower binding energies, corresponding to
2 2
) is probably enhanced via a potential p–p with Pd (OAc) species, suggesting that the palladium salts kept
4
ficial oxygen of the silica framework and the imidazolium cation. palladium oxide PdO (341.8 and 336.6 eV) and zerovalent palladium
Finally, average SILPs thickness onto the surface of the macro- (metallic) (340.6 and 335.2 eV), can also be noticed. Different
pores of the hybrid foams were determined (Table S1, ESI†), methods, such as self-induced reduction in alcoholic solvent or
combining nitrogen sorption and mercury porosimetry data hydrogenation under high pressure, are mentioned in the literature
together with calculated stoichiometries. Depending on the starting to generate palladium metallic nanoparticules encapsulated within
porous support used, that is, the unmodified Si(HIPE) or the hybrid the SILPs. However, the first method induced a fast reduction
g-imidazole-Si(HIPE), different adsorption behaviours are assumed. followed by a precipitation of the metallic particles during the
In the first case, a complete filling of the mesoporous volume impregnation step of the silica-based porous support. Therefore,
by the ionic liquid phase is supposed, while we consider that hydrogenation of Pd(OAc) @[Bmim]NTf @Si(HIPE) hybrid foams
2
2
the remaining ionic liquid forms a homogeneous thin film on was preferred. After this treatment, Pd(OAc) @[Bmim]NTf @
2
2
2
À1
the surface of macropores (surface of 65 m g , determined by Si(HIPE) monoliths turned black, highlighting an efficient reduction
mercury porosimetry). In contrast, in the case of SILP@g-imidazole- of the palladium salt (Fig. 7d). This feature is clearly supported from
Si(HIPE), considering the size of the grafted molecules, making the XPS spectrum (Fig. 7c), which displays a shift of the two main
the smallest pores less accessible, and the viscosity of the ionic peaks related to Pd 3d and Pd 3d , initially centred at 343.5 and
liquid impregnated, the ILs cannot fill the mesoporous volume. 338.3 eV, toward lower binding energies (respectively 340.6 and
However, we still assume that the nanometric ILs film onto the 335.2 eV). After deconvolution of the raw spectrum, a weak super-
3/2
5/2
0
macropores is homogeneous. Therefore, depending on the sam- ficial oxidation of the Pd nanoparticles can be noticed, via the
ples, the thickness of the SILPs is estimated between 6 and presence of two contributions related to PdO (341.8 and 336.6 eV).
12 nm. In summary, the presence of macropores in the support These characteristics have been supported by XRD (Fig. 7e–f).
allows us to reach thickness of ILs coating largely higher than Indeed, beyond an intense and broad peak associated with
the ones reported so far in the literature, particularly for meso- amorphous silica, centered at 2y = 211 (Fig. 7e), clear signals
0
II
porous silica-based powders.
related to palladium metallic Pd and palladium oxide Pd O
Reduction of the palladium(II) acetate species encapsulated are also noticed. Particularly, XRD peaks centered at 39.81,
within the supported ionic liquid phase onto palladium(0) 46.31 and 681 (Fig. 7f) correspond, respectively, to (111), (200)
nanoparticles have been performed, with a view to compare and (220) planes of the typical face centered cubic (fcc) struc-
the catalytic performances of both species toward the Heck ture of palladium metal. Therefore, the in situ reduction of
Table 5 Stoichiometries calculated from elemental and thermogravimetric analysis for the SILPs onto Si(HIPE)s macrocellular monoliths
Entry
2
Hybrid foams Pd(OAc) @organo-Si(HIPE)
Stoichiometries
1
2
3
4
5
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
2
2
@[Bmim]NTf
@[Bmim]NTf
2
@g-imidazole-Si(HIPE)
@Si(HIPE)
Pd0.009LI0.19 SiO1.96(C
6
N
2
O
N H
2
O
2
H
9
)
)
0.04Á0.09H
2
2
O
O
2
Pd0.008LI0.16 SiO
Pd0.008LI0.14 SiO1.96(C
Pd0.01LI0.23 SiO
Pd0.008LI0.21 SiO
2
Á0.09H
@[Bmim]BF
@[Bmim]BF
4
@g-imidazole-Si(HIPE)
@Si(HIPE)
@Si(HIPE)
6 2
9
0.04Á0.09H
4
2
Á0.12H
@[Bmim]PF
6
2
Á0.10H
2
O
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 157--168 163

View Article Online
Paper
NJC
Fig. 8 (a) TEM, (b) HR-TEM, and (c) particle size distribution of the
0
Pd @[Bmim]NTf
2
@g-imidazole-Si(HIPE) hybrid foam. The particle size
distribution was determined on 180 nanoparticles.
0
2
Fig. 9 (a–b) TEM of 70 nm-thickness thin sections of the Pd @[Bmim]NTf @
g-imidazole-Si(HIPE).
observation of the micrograph (Fig. 9b) allows us to notice that
the nanoscopic clusters are embedded within a viscous and
heterogeneous thin layer, probably the SILP. Nevertheless, the
observation of the SILP is still delicate, since the 1,3-dialkyli-
midazolium salts are soluble in the mixture used to impregnate
the hybrid foam before the microtome cutting process. To get
2 2
Fig. 7 XPS and pictures carried out on Pd(OAc) @[Bmim]NTf @g-imidazole-
Si(HIPE) (a–b) before and (c–d) after treatment under 10 bar of hydrogen at 80 1C
during 1 h. (e–f) X-ray diffraction spectrum obtained for the
0
Pd @[Bmim]NTf
2
@g-imidazole-Si(HIPE).
palladium(II) yields metallic palladium nanoparticles. This more information concerning the supported ionic liquid phase
feature can be induced by an enhancement of the mass transfer and the interaction with the palladium nanoparticles, a mobi-
at the gas-SILP interfaces, related to the interconnected macro- lity study had to be carried out by solid-state NMR.
porous framework together with the nanometric thickness of
Mobility of the supported ionic liquid phase and influence
the ionic liquid layer. Moreover, the presence of palladium of the palladium reduction. A way of checking the mobility
metallic nanoparticles was highlighted by TEM (Fig. 8a), while inside a sample is to quantify the Nuclear Overhauser Effect
1
3
the planes of the fcc structure were noticed via HR-TEM (NOE) enhancement that can be observed on the C with or
Fig. 8b). The particle size distribution was determined for without irradiation on the neighboring protons during the
(
0
14
2
the Pd @[Bmim]NTf @g-imidazole-Si(HIPE) hybrid foam, by relaxation delay (Fig. 10). The results are summarized in Table
TEM observations carried out on 180 particles (Fig. 8c). A broad S2, ESI.† The higher is the NOE enhancement, the bigger is the
distribution, probably related to the absence of the stabilizing mobility, with a maximum of 2, denoting a very mobile ionic
agent, underlines an average diameter of (11 Æ 6) nm. Never- liquid phase. In the presence of reduced palladium, the mobility
theless, due to the experimental procedure to prepare TEM decreases, especially for the methyl and the imidazolium ring of
grids (see Experimental section), this technique did not offer the cation (Table S2, ESI†). Nevertheless, the NOE increases for
8
the opportunity to observe the supported ionic liquid phase the C of the butyl chain, which can be explained by steric
immobilized within the silica-based foams.
constrains on the counter-ions mobility. Thus, we can assume
In order to circumvent this drawback, a microtome section that the mobility of the ionic liquid phase is largely affected by
0
has been carried out on Pd @[Bmim]NTf @g-imidazole- the palladium species. Another interesting feature concerns the
2
Si(HIPE) samples (Fig. 9). TEM performed on the 70 nm thin influence of the grafting of imidazole groups on the SILP
sections thus prepared, beyond the observation of the macro- mobility (Fig. 10b and c and Table S2, ESI†). Thus, concerning
0
0
2 2
scopic structure made of aggregated hollow spheres (Fig. 9a), Pd @[Bmim]NTf @Si(HIPE) and Pd @[Bmim]NTf @g-imidazole-
9
underlined the presence of palladium metal nanoparticles and Si(HIPE), the grafted carbon C is less mobile but the mobility is
clusters on the macrocellular scaffold (Fig. 9b). A more careful more pronounced on the methyl group.
1
64 New J. Chem., 2013, 37, 157--168
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

View Article Online
NJC
Paper
0
more pronounced for the Pd @[Bmim]NTf
2
@g-imidazole-
Si(HIPE) sample obtained after grafting of imidazole species
and reduction of palladium (Fig. 11c), confirming the influence
of the grafting on the SILP mobility.
Overall, stabilisation of palladium-based catalysts within
supported ionic liquid phases within macrocellular silica-based
monoliths is effective and has been proved by different
techniques.
Catalytic properties toward Heck coupling reaction
The use of ionic liquids to replace organic solvents in metal
catalysed reactions has recently gained much attention and
great progress has been accomplished in this area in the last
few years. Also, we have to underline that to really assess
heterogeneous catalyst efficiency; it is important working in
worst conditions that is to say in a non-reductive atmosphere.
As a direct consequence olefin reductions occurring with
hydrogen have already been tested within Pd@PolyHIPE mate-
1
3
Fig. 10 Solid-state NMR C, (A) HPDEC, (B) PG of (a) [Bmim]NTf
2
@Si(HIPE),
0
0
(
b) Pd @[Bmim]NTf @Si(HIPE) and (c) Pd @[Bmim]NTf @g-imidazole-Si(HIPE).
2 2
1
5a
rials
and show high efficiency, efficiency extrinsically
enhanced by hydrogen that helps maintaining the Palladium
nanoparticles at the zero-valent state. Therefore, we turned our
choice toward chemical reactions occurring in a non-reductive
1
3
These results can also be confirmed using C CP experi-
ments (Fig. 11). Despite the high number of scans, a very low
signal to noise ratio is obtained, because of the mobility
averaging of the H– C dipolar interaction. By addition and
reduction of the palladium (Fig. 11b), we can notice a widening
of the resonances and an increase of the signal to noise ratio,
which both confirm the mobility decrease. This feature is much
11a,b
atmosphere (Myzoroki–Heck
or Suzuki–Myaura C–C coupling
15b
1
13
reactions ) where Palladium nanoparticles will have to endure
both oxidation and leaching processes. In this context, it is
significant that the first well documented palladium-catalysed
16
reaction performed in ILs was the Heck reaction. To increase
catalyst performance and develop more sustainable and environ-
mental benign reaction conditions, immobilisation of Pd(OAc)
silica gel pores, with the aid of [Bmim]PF and the application of
this catalytic system in recyclable Heck reaction has been reporte-
2
in
6
6a,b
d.
The use of a hydrocarbon solvent was necessary to prevent
removal of the IL layer from the silica. Catalytic performances of
different heterogeneous catalysts disclosed in this work have been
tested in the Heck coupling reaction (Scheme 1) using the same
reagents and similar experimental conditions (excepted that dode-
cane was replaced by octane) than in the work cited above in order
of comparison (Fig. 12).
Divergences in catalytic performances appear according to
4 6 2
the IL’s counterion used (BF , PF or NTf ) when using palla-
dium acetate as catalytic species : the conversion level of
iodobenzene after 24 hours is almost two times lower when
performed in an hydrophilic supported ionic liquid such as
[
Bmim]BF , than in [Bmim]PF and [Bmim]NTf that are more
4 6 2
1
3
hydrophobic. Constraints associated with wettability differ-
ences on the surface of the SILPs with the apolar co-solvent
Fig. 11 Solid-state NMR C CP of (a) [Bmim]NTf
2
@Si(HIPE), (b)
0
0
Pd @[Bmim]NTf
2
@Si(HIPE) and (c) Pd @[Bmim]NTf @g-imidazole-Si(HIPE).
2
Scheme 1 Heck coupling reaction addressed in this study: (A) Iodobenzene, (B) Acrylate cyclohexyl, (C) Benzyl cyclohexyl acrylate, (D) Triethylammonium iodate.
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 157--168 165

View Article Online
Paper
NJC
Catalytic performances of the different (Si)HIPEs SILs on the
Heck coupling between iodobenzene and cyclohexyl acrylate
are reported in Table 6 and compared with results of similar
6
a,b
literature experiments.
Pd(OAc) entrapped in the hydrophobic [Bmim]NTf (Table 6,
Best performances are obtained with
2
2
entry 1), grafting of imidazole moieties onto the (Si) HIPE
surface seems to have no apparent effect (Table 6, entry 2).
As mentioned above, the use of an hydrophilic IL such as
0
[
Bmim]BF
4
leads to reduced performances. Pd appears to be less
efficient than Pd(OAc)
2
(Table 6, entries 2 and 3), an inactivation
induced by the formation of ‘‘black’’ palladium during the
reduction step may be the main cause of this behavior. Finally,
the best results obtained in this work appears somewhat lower than
6a,b
data reported by H. Hagiwara et al. for a similar catalytic system
using SILPs within mesoporous silica-based hybrid under similar
6a,b
experimental conditions (entries 1, 4 and 6).
It has to be
Fig. 12 Catalytic properties of the SILPs within silica-based hybrid foams obtained
enlightened that in this latter case, the support used was high
specific surface area finely powdered silica which could enhance
the diffusion of substrates in solution toward the catalytic species
in comparison with millimetre-size monoliths used in the present
work. A better exploitation of the monoliths nature of (Si)HIPE-
based catalyst would be continuous flow reactors.
for the first cycle toward Heck coupling reaction of iodobenzene and cyclohexyl
acrylate. (a) Pd(OAc)
g-imidazole-Si(HIPE), (c) Pd(OAc)
g-imidazole-Si(HIPE), and (e) Pd(OAc)
2
@[Bmim]NTf
@[Bmim]PF
4
@[Bmim]BF -Si(HIPE).
2
-Si(HIPE), (b) Pd(OAc)
2
@[Bmim]NTf
2
@
0
2
6
-Si(HIPE), (d) Pd @[Bmim]NTf
2
@
2
used, e.g. octane, can explain this behaviour. Indeed, a hydro-
Catalysts exhibiting higher performances in the first cycle
philic layer induces most probably a more difficult diffusion of were reused up to four times as shown in Fig. 13.
the reagents from octane toward SIL than a hydrophobic layer.
A significant drop of the conversion yield, from 25 up to
As a direct consequence, the accessibility to the palladium- 50%, is observed in each experiment between the first and the
based catalysts is largely restricted.
second use even if catalysts pieces have been washed between
Table 6 Catalytic data toward Heck coupling reaction of iodobenzene and cyclohexyl acrylate
À1
Entry
Hybrid foams
Molar ratio Pd/iodobenzene
Conversion (%)
Time (h)
TON
TOF (h )
1
2
3
4
5
6
Pd(OAc)
2
@[Bmim]NTf
@[Bmim]NTf
2
2
@Si(HIPE)
@g-imidazole-Si(HIPE)
0.00064
0.00068
0.00064
0.00067
0.00093a
0.00130
65
62
43
56
36
24
24
24
24
24
1015
910
670
835
390
720
42
38
28
35
16
Pd(OAc)
Pd @[Bmim]NTf
2
0
2
@g-imidazole-Si(HIPE)
@[Bmim]PF @Si(HIPE)
@[Bmim]BF
@[Bmim]PF
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
6
4
@Si(HIPE)a
@silica gel
a
a
a
a
6
94
8.5
85
a
From data reported in ref. 6a and b.
Fig. 13 Catalytic properties of the macrocellular hybrid foams obtained on a few cycles toward Heck coupling reaction of iodobenzene and cyclohexyl acrylate. (a) ’
Pd(OAc) @[Bmim]PF -Si(HIPE). (b) m Pd(OAc) @[Bmim]NTf @Si(HIPE), and D Pd(OAc) @[Bmim]NTf @g-imidazole-Si(HIPE). The numbers on the right of the curves
represent the cycle numbers.
2
6
2
2
2
2
1
66 New J. Chem., 2013, 37, 157--168
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

View Article Online
NJC
Paper
hydrogenation allowed an efficient reduction and formation of
10 nm diameter palladium metal nanoparticles. These hybrid
foams were used as heterogeneous macrocellular catalysts
toward Heck coupling reaction of iodobenzene and cyclohexyl
acrylate. Despite a minimized recyclability related to the entrap-
ment of detrimental ammonium salts within the macroporous
network, catalytic performances appear, competitive with best
literature results.
Acknowledgements
Fig. 14 SEM obtained after the first catalytic cycle toward Heck coupling reaction
of iodobenzene and cyclohexyl acrylate for the Pd(OAc)
g-imidazole-Si(HIPE) sample.
2 2
@[BMIM]NTf @
Acknowledgments are made to Christine Labrug `e re (CeCaMA –
Institute for Solid State Chemistry Bordeaux, ICMCB, Pessac)
for XPS experiments, Eric Lebraud (ICMCB) for XRD measure-
ments, Marie-France Achard (CRPP, Pessac) for SAXS, Elisabeth
Sellier (CREMEM, University Bordeaux 1) for HR-TEM observa-
tions, Isabelle Ly (CRPP) for microtomy experiments and
Laetitia Etienne (ICMCB) for ICP-AES assessments. The authors
would like to gratefully acknowledge Dr Simona Ungureanu
and Annick Babeau-Garcia for fruitful discussions.
each cycle with a 0.05 M NaOH aqueous solution, in order to
prevent the detrimental effect associated with the formation of
the triethylammonium iodide by-product. Moreover, a random
evolution of the conversion yield from use to use can be noticed
2 6
for the Pd(OAc) @[Bmim]PF -Si(HIPE) sample, suggesting a
large dependence of the washing step conditions on the catalytic
properties. Indeed, an increase of the immersion duration in the
basic solution after use 3, leads to a large rise of the conversion
in the fourth use, more than 100%. Consequently, the
by-product formation seems to be the main detrimental factor
of the catalytic system used in this study. This feature is
supported by SEM observations performed on hybrid foams after
the first catalytic cycle and the first washing step (Fig. 14).
Beyond the fact that the typical macromorphology of aggre-
gated hollow spheres is preserved despite the use of a basic
solution the washing step (Fig. 14a and b), the presence of
triethylammonium iodide crystals is clearly highlighted within
the macrocellular framework (Fig. 14c). Thus, the hybrid mono-
liths kept the by-products entrapped in the cells, which could
represent a great advantage in view of products separation. This
References
1
2
R. A. Sheldon, J. Chem. Technol. Biotechnol., 1997, 68, 381.
(a) G. W. Parshall, J. Am. Chem. Soc., 1972, 94, 8716;
(b) R. Sheldon, Chem. Commun., 2001, 2399.
3
(a) P. Bonh oˆ te, A.-P. Dias, N. Papageorgiou,
K. Kalyanasundaram and M. Gr ¨a tzel, Inorg. Chem., 1996,
3
5, 1168; (b) J. G. Huddleston, A. E. Visser, W. M. Reichert,
H. D. Willauer, G. A. Broker and R. D. Rogers, Green Chem.,
001, 3, 156.
(a) P. Wasserscheid and W. Keim, Angew. Chem., Int. Ed.,
000, 39, 3772; (b) A. P. Umpierre, G. Machado,
G. H. Fecher, J. Morais and J. Dupont, Adv. Synth. Catal.,
005, 347, 1404; (c) G. Machado, J. D. Scholten, T. de Vargas,
S. R. Teixeira, L. H. Ronchi and J. Dupont, Int. J. Nanotechnol.,
007, 4, 541; (d) J. Dupont, R. F. de Souza and P. A. Z. Suarez,
2
4
2
6d
feature has already been reported by S. Volland et al. using
Pd(OAc) @SILPs confined in silica gels. A very interesting char-
2
2
acteristic of these devices concerns the low leaching of palladium
species. Inductively coupled plasma atomic emission spectroscopy
2
Chem. Rev., 2002, 102, 3667–3692; (e) V. I. P ˆa rvulescu and
C. Hardacre, Chem. Rev., 2007, 107, 2615; ( f ) A. J.
Carmichael, M. J. Earle, J. D. Holbrey, P. B. Mc-Cormac and
K. R. Seddon, Org. Lett., 1999, 1, 997.
(ICP-AES) performed on the catalytic media after the first catalyst
use revealed a palladium release between 0.2 and 0.6 molar% of
the palladium initially trapped within the SILPs. This result is in
6a,b
good agreement with the values reported by H. Hagiwara et al.
5
(a) C. P. Mehner, R. A. Cook, N. C. Dispenziere and
M. Afeworki, J. Am. Chem. Soc., 2002, 124, 12932–12933;
(
b) M. H. Valkenberg, C. deCastro and W. F. H o¨ lderich,
Green Chem., 2002, 4, 88.
Conclusion
Overall we have combined emulsion-based porous materials,
syntheses of Ils, Palladium nanoparticles heterogeneous
nucleation to promote efficient heterogeneous catalysts when
test for Heck coupling reactions. With this endeavor this work
falls into the Integrative Chemistry synthetic path. Particularly,
supported ionic liquid phases within emulsion-templated
macrocellular silica-based monoliths were prepared by a simple
impregnation in organic solvents. Thin ionic liquid layers, from
6 (a) H. Hagiwara, Y. Sugawara, K. Isobe and T. Hoshi, Org.
Lett., 2004, 6, 2325; (b) H. Hagiwara, Y. Sugawara, K. Isobe,
T. Hoshi and T. Suzuki, Org. Lett., 2006, 8, 1749; (c) P. Han,
H. Zhang, X. Qiu, X. Ji and L. Gao, J. Mol. Catal. A: Chem.,
2008, 295, 57; (d) S. Volland, M. Gruit, T. R ´e gnier, L. Viau,
O. Lavastre and A. Vioux, New J. Chem., 2009, 33, 2015.
7 (a) J. Huang, T. Jiang, H. Gao, B. Han, Z. Liu, W. Wu,
Y. Chang and G. Zhao, Angew. Chem., Int. Ed., 2004, 43,
1397–1399; (b) C. P. Mehnert, E. J. Mozeleski and R. A. Cook,
Chem. Commun., 2002, 3010.
1
7
6
up to 12 nm, were obtained. Moreover, palladium salts were
efficiently trapped within the SILPs, while an in situ palladium
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 157--168 167

View Article Online
Paper
NJC
8
9
M. S. Sarkar, H. Qiu and M.-J. Jin, J. Nanosci. Nanotechnol.,
007, 7, 3880.
(a) F. Shi, Q. Zhang, D. Li and Y. Deng, Chem.–Eur. J., 2005,
(c) Y. Chevalier, A.-C. Grillet, M.-I. Rahmi, C. Li `e re,
M. Masure, P. H ´e mery and F. Babonneau, Mater. Sci. Eng.,
C, 2002, 21, 143.
2
1
1, 5279; (b) A. Vioux, L. Viau, S. Volland and J. Le Bideau, C. 13 D. Massiot, F. Fayon, M. Capron, I. King, S. Le Calv ´e ,
R. Chim., 2010, 13, 242.
0 F. Carn, A. Colin, M.-F. Achard, M. Birot, H. Deleuze and
R. Backov, J. Mater. Chem., 2004, 14, 1370.
B. Alonso, J. O. Durand, B. Bujoli, Z. Gan and G. Hoatson,
Magn. Reson. Chem., 2002, 40, 70–76.
14 T. Azais, G. Hartmeyer, S. Quignard, G. Laurent and
F. Babonneau, J. Phys. Chem. C, 2010, 114, 8884.
1
1
1 (a) S. Ungureanu, M. Birot, L. Guillaumme, H. Deleuze,
O. Babot, B. Julian, M.-F. Achard, M. I. Popa, C. Sanchez and 15 (a) A. Desforges, H. Deleuze, O. Mondain-Monval and
R. Backov, Chem. Mater., 2007, 19, 5786; (b) S. Ungureanu,
H. Deleuze, M. I. Popa, C. Sanchez and R. Backov, Chem.
Mater., 2008, 20, 6494; (c) N. Brun, B. Julian-Lopez,
R. Backov, Ind. Eng. Chem. Res., 2005, 44, 8521;
(b) A. Desforges, R. Backov, H. Deleuze and O. Mondain-
Monval, Adv. Funct. Mater., 2005, 15, 1689.
P. Hesemann, L. Guillaume, M.-F. Achard, H. Deleuze, 16 D. Kaufmann, M. Nouroozian and H. Henze, Synlett, 1996,
C. Sanchez and R. Backov, Chem. Mater., 2008, 20, 7117; 1091.
d) N. Brun, A. Babeau-Garcia, H. Deleuze, F. Duran, 17 (a) R. Backov, Soft Matter, 2006, 2, 452; (b) N. Brun,
(
C. Sanchez, V. Ostreicher and R. Backov, Chem. Mater.,
S. Ungureanu, H. Deleuze and R. Backov, Chem. Soc. Rev.,
2011, 40, 771; E. Prouzet, Z. Khani, M. Bertrand,
M. Tokumoto, V. Gyuot-Ferreol and J.-F. Tranchant, Micro-
porous Mesoporous Mater., 2006, 96, 369; (c) C. Sanchez,
C. Boissi `e re, D. Grosso, C. Laberty and L. Nicole, Chem.
Mater., 2008, 20, 682; (d) E. Prouzet, S. Ravaine, C. Sanchez
and R. Backov, New J. Chem., 2008, 32, 1284.
2010, 22, 4555; (e) N. Brun, A. Babeau Garcia,
M.-F. Achard, C. Sanchez, F. Durand, G. Laurent, M. Birot,
H. Deleuze and R. Backov, Energy Environ. Sci., 2011,
4
, 2840.
2 (a) R. K. Harris and M. L. Robbins, Polymer, 1978, 19, 1123;
b) F. Babonneau, New J. Chem., 1994, 18, 1065;
1
(
1
68 New J. Chem., 2013, 37, 157--168
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013