An imidazolium ionic liquid having covalently attached an oxime carbapalladacycle complex as ionophilic heterogeneous catalysts for the Heck and Suzuki-Miyaura cross-coupling

Article abstract of DOI:10.1016/j.tet.2004.06.121

An oxime carbapalladacycle, analogous to that used as catalyst in homogeneous phase, has been derivatized to increase its ionophilicity by introducing an imidazolium group covalently attached through a chain at the complex. The resulting complex is soluble in 1-butyl-3-methylimidazolium ionic liquid (bmimPF₆) and not extractable by ether. The catalytic activity of this palladium complex in bmimPF₆ is, however, unsatisfactory and only increases marginally in bmimPF₆/supercritical CO₂. This limitation has been overcome by supporting this imidazolium palladium complex on high surface area Al/MCM-41 aluminosilicate, whereby a solid active catalyst for the Suzuki cross-coupling has been obtained. Reusability and stability over reuse for this Al/MCM-41-supported catalyst have been studied. Graphical abstract.

Full text of DOI:10.1016/j.tet.2004.06.121

Tetrahedron 60 (2004) 8553–8560
An imidazolium ionic liquid having covalently attached an oxime
carbapalladacycle complex as ionophilic heterogeneous catalysts
for the Heck and Suzuki–Miyaura cross-coupling
*
Avelino Corma, Hermenegildo Garcıa and Antonio Leyva
*
´
´
´
Instituto de Tecnologıa Quımica CSIC-UPV, Av. De los Naranjos s/n, 46022 Valencia, Spain
Received 9 March 2004; revised 31 May 2004; accepted 18 June 2004
Available online 6 August 2004
Abstract—An oxime carbapalladacycle, analogous to that used as catalyst in homogeneous phase, has been derivatized to increase its
ionophilicity by introducing an imidazolium group covalently attached through a chain at the complex. The resulting complex is soluble
in 1-butyl-3-methylimidazolium ionic liquid (bmimPF6) and not extractable by ether. The catalytic activity of this palladium complex in
bmimPF6 is, however, unsatisfactory and only increases marginally in bmimPF6/supercritical CO2. This limitation has been overcome by
supporting this imidazolium palladium complex on high surface area Al/MCM-41 aluminosilicate, whereby a solid active catalyst for the
Suzuki cross-coupling has been obtained. Reusability and stability over reuse for this Al/MCM-41-supported catalyst have been studied.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
in which the catalyst is soluble in ionic liquids, but insoluble in
alkanes or ethers, it would be also possible to develop a
heterogeneoussystem in whichthereaction is carried outin the
ionic liquid, and the reaction products recovered by simple
liquid–liquid extraction using alkanes or ethers.
A general tendency in catalysis is to transform a successful
homogeneous catalytic reaction into a heterogeneous process
in which the catalyst can be easily separated from the reaction
mixture, allowing its reuse and the design of continuous flow
operation.1–3 Among the different approaches for this
homogenous-to-heterogeneous transformation, one estab-
lished strategy is to take advantage of the property offluorous
solvents to be immiscible with typical organic solvents at
room temperature, but to become totally soluble at higher
temperatures. In addition, fluorous liquids are normally poor
solvents at room temperature, but the room-temperature
solubility in them increases considerably by appending to the
molecules a perfluorinated chain that accounts for above 20%
ofthemolecularweight.Thethermotropicpropertyoffluorous
solvents has been applied in heterogeneous catalysis by
modifying conventional catalysts introducing fluorous pony
tails, whose exclusive role is to increase the solubility in the
fluorous phase while decreasing simultaneously the solubility
in conventional organic solvents.
Following a parallel strategy to that used in fluorous-phase
catalysis,6–13 our work here describes the modification of a
carbapalladacycle catalyst aimed at increasing the
‘ionophilicity’ of the complex.14–16 This has been achieved
by introducing an imidazolium pony tail. The effect caused
by the introduction of an imidazolium moiety in the catalyst
can be termed as ‘ionophilicity’ (in analogy with the term
‘fluoricity’17) and is used to describe the alteration of
molecular properties of the catalysts, particularly their
solubility, by increasing its affinity to ionic liquids and its
ionic liquid behaviour. There are precedents in which
molecules have been modified to enhance their iono-
philicity.18,19 This imidazolium-substituted carbapallada-
cycle has also been supported on a large-surface area
support. Related precedents are those reporting the use of
chloroaluminates of N,N0-dialkylimidazolium supported on
MCM-41 silicate as solid Lewis acid catalysts.20 In our case
the counter-anion does not play the role of Lewis acid and
the major point of our work being to devise a synthetic route
to link covalently the imidazolium moiety and the palladium
complex. We will show the results achieved with this
cationic complex as heterogeneous catalysts under various
conditions, addressing its reusability and stability.
The use of ionic liquids is another topic of much interest in
heterogenous catalysis.4,5 Ionic liquids can dissolve many
organic compounds but they are in turn immiscible in some
apolar organic solvents such as alkanes or ethers. In those cases
Keywords: Palladium catalyst; Heterogeneous catalysis; Ionic liquids.
* Corresponding authors. Tel.: C3496-387-7807; fax: C3496-387-7809
(H.G.); e-mail: hgarcia@qim.upv.es
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.06.121

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A. Corma et al. / Tetrahedron 60 (2004) 8553–8560
Scheme 1. Synthetic route followed for the preparation of oxime carbapalladacycle 5. (a) NH2OH, NaOAc, H2O, reflux, 1 h; (b) 1,5-dibromopentane, K2CO3,
acetone, reflux, 48 h; (c) Li2PdCl4, NaOAc, methanol, rt, 72 h; (d) 1-methylimidazole, THF, 50 8C, 72 h.
2. Results and discussion
palladium–carbon bonds in the carbapalladacycle complex
4 produces a change in the number and pattern of the
aromatic protons from A2B2 to ABM. Figure 1 shows the IR
spectra of carbapalladacycles 4 and 5 compared to those of
Oxime carbapalladacycle with structure Pd-2 has been
´
reported by Najera and co-workers as one of the most
´
the parent complex Pd-2 reported by Najera and the starting
active palladium catalysts for the Suzuki–Miyaura cross-
coupling of aryl halides and arylboronic acids.21–24 The
synthetic route followed to prepare its derivative
palladium complex 5 is indicated in Scheme 1. Starting
from 4-hydroxyacetophenone, the corresponding oxime
was obtained and then reacted with 1,5-dibromopentane
to obtain compound 3. Of the various possibilities
tested, the introduction of Pd2C after formation of
compound 3 was found as the most convenient.
Palladium metal ion and its complexes are prone to
undergo reduction with formation of black palladium
metal under very mild conditions.25 Therefore, the step
in which the palladium complex is formed in the
synthetic route has to be carefully selected to avoid
palladium reduction. In our case, other alternatives and,
particularly introduction of palladium in the last step
after formation of the imidazolium moiety were found
less desirable due to the formation of black palladium
metal.
oxime 2. The most salient common feature is the absence of
the C]N stretching vibration of the palladium complexes
as compared to 1670 cmK1 recorded for the oxime
precursors.
Besides ligand centred absorption bands, most transition
metal complexes have in the visible region of the UV–Vis
spectrum charge transfer transition bands that are specific
of the metal-ligand orbital overlapping. As expected in
view of the reports on the optical spectrum of the parent
oxime carbapalladacycle, Figure 2 presents the UV–Vis
spectra of complexes 4 and 5 showing two broad
absorption bands at lmax 300 and 350 nm that are absent
in the ligand 3. This is indicative that the co-ordinative
ligand–metal bound has survived the nucleophilic substi-
tution using N-methylimidazole.
All the intermediates in the synthesis of complex 5 were
characterized analytically and spectroscopically. As the
most salient feature, we have seen that formation of the
Figure 2. Transmission UV–Vis spectra in dichloromethane of 3 (a), 4 (c)
and 5 (b).
When submitted to FAB-MS analysis, complexes 4 and 5
appear as monomeric species and the most characteristic
feature corresponds to the molecular ion cluster arising from
the natural isotopic distribution of Pd or Pd and Br. Based on
FAB-MS, it has been reported that the simplest carba-
palladacycles are dimeric species, in agreement with the
Figure 1. IR spectra of oxime carbapalladacycles recorded at room
temperature in KBr (a) or dissolved in dichloromethane (b, c); (a) oxime
carbapalladacycle Pd-2, (b) compound 4, (c) compound 5.

A. Corma et al. / Tetrahedron 60 (2004) 8553–8560
8555
tendency of palladium to form tetra co-ordinated com-
plexes. In our case, it may very well occur that the
monomeric nature of complexes 4 and 5 arises from the
co-ordination of palladium with terminal groups (Br in
complex 4 and imidazolium in complex 5), thus satisfying
all the co-ordination positions around palladium. As
expected, complex 5 is soluble in 1-butyl-3-methylimado-
zolium hexafluorophosphate (bmimC PF6K) as well as in
halogenated organic solvents.
Complex 5 was also supported on Al/MCM-41 (Si/Al
13). The presence of AlO54K tetrahedra replacing
isomorphically SiO44K in the framework of a silicate
produces and excess of negative charge that requires the
presence of charge balancing cations to maintain the
electroneutrality of the solid.3,26 Aluminosilicates are
particularly suited as solid supports to adsorb and
incorporate positively-charged organic cations such as
complex 5. It is expected that after adsorption,
Coulombic interactions between complex 5 and the
aluminosilicate will occur. The strength of this electro-
static interaction between complex 5 and Al/MCM-41
was determined by following the intensity of the IR
bands corresponding to complex 5 after thermal
treatment of 5@Al/MCM-41 in a sealed cell under
reduced pressure. It was observed that 5 remains
adsorbed after thermal treatment at 300 8C under 10K
2 Pa for prolonged periods. The diffuse reflectance UV–
Vis spectrum shows the two characteristic charge
transfer transition bands of the palladium complex
(Fig. 3). Table 1 provides a comparison of the chemical
analysis (Pd, C and N) and porosity of Al/MCM-41
before and after adsorption of complex 5. In agreement
with the assumption that 5 becomes adsorbed into the
mesoporous channels of Al/MCM-41, the micropore
volume and BET surface area becomes somewhat
reduced with respect to the initial values measured for
pristine Al/MCM-41, although the resulting 5@Al/
MCM-41 catalyst still exhibits the large surface area
and porosity characteristic of the original support.
Figure 3. IR spectra of the 5@Al/MCM-41 recorded at room temperature
after outgassing for 1 h at: room temperature (a), 100 8C (b), 200 8C (c) and
300 8C (d) at 10K2 Pa. For the sake of comparison the IR spectrum of 5
recorded at room temperature is included (e). The inset shows the diffuse
reflectance UV–Vis spectra (plotted as the Kubelka-Munk function of the
reflectance, R) of 5@Al/MCM-41.
Table 1. Relevant analytical and physicochemical parameters of the
Al/MCM-41 and 5@Al/MCM-41
Solid
Al/MCM-41
5@Al/MCM-41
Si/Al atomic ratio
BET surface area
13
781
13
692
(m2!gK1
Micropore volume
)
0.419
38.3
518
0.358
33.9
439
Pd: 0.042; C: 2.56; N: 0.42
(cm3!gK1
Average pore
)
˚
diameter (A)
Micropore area
(m2!gK1
)
Elemental analysis
(mmol!gK1
–
)
Table 2. Results for the Heck or Suzuki reaction of halobenzenes (1 mmol),
styrene (Heck, 156 mg, 1.5 mmol) or tolylboronic acid (Suzuki, 102 mg,
1 mmol) and NaOAc (164 mg, 2 mmol) in a 5 wt% solution of 5 in
(bmim)PF6 (25 mg in 500 mg)) at 130 8C
Entry
Halobenzene
Bromobenzene
Time (h)
Yield (%)
3.4
1
2
3
4
5
6
7
8
24
72
5
5
5
5
20
5
As indicated above, carbapalladacycle complex 5 was
soluble in bmimPF6 and it could not be extracted from
this solution upon extensive liquid–liquid extraction with
diethyl ether. A control using unmodified Najera’s complex
Pd-2 showed that this procedure extracts a significant
fraction of the parent complex from bmimCPF6K as
evidenced visually by the observation of a yellow extract,
thus, demonstrating that the ionophilicity principle based on
the introduction of an imidazolium tag attached to the
palladium complex serves to increase its affinity for
imidazolium ionic liquids.
Bromoacetophenone
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
25.7
17.3
1.6a
7.8b
8.1c
26.3d
8.4e
a
BmimClK1 as solvent.
K2CO3 as base.
Six equivalents of NaOAc.
Supercriticcl CO2.
Suzuki coupling.
b
c
d
e
The activity of complex 5 as reusable catalyst for the Heck
reaction (Eq. (1)) between styrene and halobenzenes was
initially tested in bmimCPF6K and NaAcO as a base. A
summary of the results are shown in Table 2. As it can be
seen there, the results were in general disappointing in terms
of conversion. The use of iodobenzene or deactivated
bromobenzenes as reagents, an excess of NaAcO or a
stronger base does not lead to satisfactory improvements in
conversion. The best results were obtained using supercriti-
cal CO2 as co-solvent in bmimPF6 to decrease the viscosity
of the medium and to promote diffusion. Unfortunately,
even under these conditions the conversion was still far
from optimum. Besides the Heck reaction, Suzuki coupling
(Eq. (2)) of iodobenzene was also inefficiently catalyzed by
complex 5 in ionic liquid (conversions below 10%, see
Table 2 entry 8) and no further tests were carried out,
particularly considering that iodobenzene is the most
reactive reagent.

8556
A. Corma et al. / Tetrahedron 60 (2004) 8553–8560
(1)
(2)
One possible explanation for the low activity of complex 5
in ionic liquids is based on the poor stability of imidazolium
ionic liquids to bases. We and others have previously shown
that ionic liquids have a limitation for NaOH catalyzed
reactions due to the formation of a carbene arising from
deprotonation of bmimC at the 2 position (Eq. (3)).27,28 This
carbene would co-ordinate with complex 5 and eventually
would lead to its decomposition and formation of black
palladium. Whatever the reasons, we tried to circumvent
this problem by supporting complex 5 in Al/MCM-41. The
resulting 5@Al/MCM-41 powder can be used as solid
catalyst in conventional organic solvents.
p-haloacetophenone and phenylboronic acid either in
toluene or DMF in the presence and absence of TBAB.
The use of TBAC as additive was already reported by
23,29
´
Najera
and a likely rationalization of its influence
compatible with our observations will be provided
below.
(3)
The activity of 5@Al/MCM-41 was tested in toluene and
dimethylformamide (DMF). These solvents were selected to
determine the influence of polarity on the catalytic activity
of 5@Al/MCM-41. Table 3 lists conversion and selectivity
data measured using this solid catalyst and tributylamine
(TBA) as base for the Suzuki–Miyaura cross coupling
between halobenzenes and phenylboronic acid (Eq. (4)).
Noteworthy is the positive influence of the presence of
tetrabutylammonium bromide (TBAB) on the activity and
stability of the solid catalyst. Figures 4 and 5 compare the
time conversion plot for the Suzuki coupling of
(4)
As expected in view of the precedents, the activity of
5@Al/MCM-41 was higher in a polar solvent like DMF
than in toluene (see Table 3). Using DMF as solvent,
bromo and even chlorobenzenes undergo Suzuki coup-
ling promoted by 5@Al/MCM-41. As expected, we
notice however that the catalytic activity of 5@Al/
MCM-41 for chlorocompounds is lower than for
bromoderivatives (see footnote a in Table 3). Moreover,
Table 3. Results for the Suzuki reaction of halobenzene (0.2 mmol), phenylboronic acid (36.6 mg, 0.3 mmol), tributylamine (95 mL, 0.4 mmol), TBAB
(32.2 mg, 0.1 mmol) in toluene at 110 8C or DMF at 156 8C (5 mL) for 72 h in the presence of 5@Al/MCM-41 (85.1 mg)
Run
X
R
Solvent
Conversion (%)
Suzuki:homocoupling
products
1
2
3
4
I
I
I
Br
Br
Cl
COCH3
H
Br
COCH3
H
COCH3
Toluene
Toluene
Toluene
DMF
DMF
DMF
O99
51
75
O99
57
87
32:68
51 (the same)
13:62
O99:0
57:0
87:0
5
6a
a
Double amount of catalyst.

A. Corma et al. / Tetrahedron 60 (2004) 8553–8560
8557
while the presently reported 5@Al/MCM-41 is
obviously inappropriate for reactions in water due to
the ionic nature of the bonding between 5 and the Al/
MCM-41 support.
The catalyst can be recovered from the reaction mixture by
simple filtration and after washing with fresh solvent can be
reused. Similar activity and selectivity were measured for
5@Al/MCM-41 either in toluene or DMF after four
consecutive reuses. Palladium analyses of the liquid phase
and activity data upon reuse are given in Table 4.
Figure 4. Time conversion plot for the Suzuki reaction of 4-haloaceto-
phenone (49.2 mg, 0.2 mmol), phenylboronic acid (36.6 mg, 0.3 mmol) and
tributylamine (95 mL, 0.4 mmol) in toluene (5 mL) at 110 8C in the
presence (a, 32.2 mg, 0.1 mmol) or absence (b) of TBAB, using 5@Al/
MCM-41 (85.1 mg) as catalyst.
When dealing with heterogeneous catalysts an important
issue is to confirm that the activity is really due to the solid
catalyst and not to a minor fraction of the active sites that
under the reaction conditions migrates from the solid to the
solution. To address the possibility of leaching, a reaction
was initiated in the presence of 5@Al/MCM-41, then the
suspension filtered while still hot at 50% conversion and the
clear solution after removal of the solid allowed to react
further. If the activity is completely due to the solid catalyst,
the reaction should stop in the absence of the solid. Figure 7
shows the results of the leaching study for 5@Al/MCM-41
in where it can be considered that a percentage of 30% of the
total conversion is due to the palladium dissolved from the
solid into the solution. This leaching is confirmed by a
gradual loss of palladium from the catalyst after being
subject to several recycles (see Table 4).
The diffuse reflectance UV–Vis spectra of reused 5@Al/
MCM-41 shows a considerable decrease and eventually
disappearance of the 350 nm band characteristic of the
initial complex 5 in the first uses. This fact indicates that the
complex is not completely stable under the reaction
conditions and undergoes a progressive decomposition
upon use probably by reduction and formation of palladium
metal. Importantly, a reused 5@Al/MCM-41 sample in
which most of the complex has disappeared, as evidenced
by the disappearance of the 350 nm band in the diffuse
reflectance UV–Vis spectra, still contains over 70% of the
initial palladium and showed high activity towards the
Suzuki coupling (see Table 4, run 3). These data agree with
the transformation during the reaction of most the palladium
complex into highly-dispersed palladium metal particles on
Figure 5. Time conversion plot for the Suzuki reaction of 4-haloaceto-
phenone (39.8 mg, 0.2 mmol), phenylboronic acid (36.6 mg, 0.3 mmol) and
tributylamine (95 mL, 0.4 mmol) in DMF (5 mL) at reflux temperature in
the presence (a, 32.2 mg, 0.1 mmol) or absence (b) of TBAB, using 5@Al/
MCM-41 (85.1 mg) as catalyst.
the activity of 5@Al/MCM-41 in DMF was very similar
to that observed for the parent complex Pd-2 in
homogeneous phase in the same solvent and signifi-
cantly higher under these conditions than an analogous
catalyst previously prepared by us in which an oxime
carbapalladacycle oxime was covalently bonded to
MCM-41 through a chain30 (Fig. 6). The latter catalyst
can be used, however, for reactions in aqueous media,
Figure 7. Time conversion plot for the Suzuki reaction of 4-haloaceto-
phenone (39.8 mg, 0.2 mmol), phenylboronic acid (36.6 mg, 0.3 mmol),
tributylamine (95 mL, 0.4 mmol), TBAB (32.2 mg, 0.1 mmol) in DMF
(5 mL) at reflux temperature in the presence of 5@Al/MCM-41 as catalyst
(a, 85.1 mg) and a twin run in which the solid was filtered in hot at 90 min
(ca. conversion 40%) and allowing the clear solution to continue the
reaction (b).
Figure 6. Time conversion plot for the Suzuki reaction of 4-haloaceto-
phenone (49.2 mg, 0.2 mmol), phenylboronic acid (36.6 mg, 0.3 mmol),
tributylamine (95 mL, 0.4 mmol), TBAB (32.2 mg, 0.1 mmol) in toluene
(5 mL) at 110 8C in the presence of 5@Al/MCM-41 (a, 85.1 mg), 5
anchored covalently to MCM-41 (b, 121.2 mg) and the acetophenone
carbapalladacycle oxime Pd-2 (c, 1.16 mg) as catalysts.

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A. Corma et al. / Tetrahedron 60 (2004) 8553–8560
Table 4. Activity upon reuse of 5@Al/MCM-41 for the Suzuki coupling of 4-iodoacetophenone (0.2 mmol) and phenylboronic acid (3.6 mg, 03 mmol) adding
tributylamine (95 mL, 0.4 mmol) and TBAB (32.2 mg, 0.1 mmol) as co-catalysts in toluene at 110 8C
Run
Reuse
Conversion (%)
Suzuki:homocoupling
products
Pd (mmol!gK1
)
Loss of Pda (% vs
original)
1
2
3
4
0
1
2
3
88
86
90
86
17:71
24:62
20:70
18:70
0.043
0.044
0.033
0.028
!1
!1
21
33
a
Fresh solid catalyst: 0.042 mmol!gK1
.
the high surface area Al/MCM-41 support. This hypothesis
is also in agreement with the positive influence of TBAB on
the catalytic activity. Recent reports25,31–33 have shown that
quaternary ammonium surfactants can be used to stabilize
colloidal Pd nanoparticles that can be active for C–C
coupling reactions provided that palladium agglomeration
and the corresponding particle size growth is prevented.
Large palladium metal particles, as those obtained when this
noble metal is supported on activated carbon, are inert or
considerably less active as Suzuki catalyst.
solution in water (30 mL) and measuring by quantitative
atomic absorption spectroscopy (Varian SpectrAA 10 plus).
The Pd content in organic molecules was determined in the
same way but dissolving the compound in a mixture of
HCl/HNO3 conc. (3 mg in ca. 1:1 mL) and diluting the
solution in water/acetonitrile (95:5 v/v, 30 mL).
3.1. Preparation procedure of Al/MCM-41
To a solution of cetyl trimethylammonium bromide
(3.68 g), tetramethylammonium hydroxide (8.49 g) in
water (32.6 g) aluminium hydroxide (0.48 g) was added
and the mixture was stirred (200 rpm) for 1 h. Silica (5 g,
Aerosil, Degussa) was added and the mixture was stirred for
1 h more until homogeneous gelation was observed. A pH of
13.6 was measured and the gel was submitted to
hydrothermal crystallization at 150 8C for 24 h. After this
time the final pH was measured (11.6) and the solid was
washed with distilled water (0.5 L per g). The solid was
dried at 60 8C for 24 h and calcined (from room temperature
up to 540 8C at a rate of 5 8C!minK1, then the temperature
maintained 10 h of which the first 4 h were purged under
nitrogen flow and the rest under air flow) before use. The
loss of weight in the calcination was ca. 40% and the final
Si/Al molar ratio was ca. 15. The Si/Al atomic ratio was
determined by chemical analysis.
In summary, while the ionophilicity of an oxime carbapal-
ladacycle can be significantly increased by introducing in
the noble metal complex an imidazolium tag, the use of this
catalyst in ionic liquid for the Heck and Suzuki reactions is
limited by the requirement of basic conditions. Supporting
this imidazolium modified carbapalladacycle catalyst on
Al/MCM-41 is a viable methodology to increase the activity
and reusability of the palladium catalyst in organic solvents.
However, the oxime carbapalladacycle complex is not
totally stable under the reaction conditions and as a result
some palladium leaching from the solid to the solution
occurs. These factors play a negative role on the long-term
reusability of the system.
3. Experimental
3.1.1. Synthesis of 2. 4-Hydroxyacetophenone (3 g,
0.022 mol) was added to a solution of hydroxylamine
hydrochloride (5.13 g, 0.074 mol) and sodium acetate
(10.26 g, 0.125 mol) in water (26 mL). The solution was
stirred at reflux temperature for 1 h. After this time, the
aqueous solution was extracted exhaustively with diethyl
ether. The organic phase was dried and the solvent
evaporated under vacuum. To the resulting crude, hexane
was added and 1-(4-hydroxyphenyl)ethanone oxime (2)
starts to precipitate as a white solid (3.25 g, 0.0215 mol,
98%). IR (KBr, cmK1): 3324, 1642, 1603, 1514, 1444,
1316, 1240, 1176, 940, 825, 589. 1H NMR dH (ppm,
300 MHz, CD3OD): 7.49 (2H, d, JZ5 Hz), 6.77 (2H, d, JZ
5 Hz), 2.18 (3H, s). 13C NMR dC (ppm, 300 MHz, CD3OD):
159.9, 156.7, 130.2, 128.9, 116.5, 12.55. MS: m/z 151. Anal.
calcd for C8H9NO2 (151.15): C 63.5; H 5.95; N 9.26. Found:
C 63.19; H 6.22; N 9.35.
The reagents and solvents were obtained from commercial
sources and were used without further purification. GC was
carried out on an HP 5890 instrument equipped with a 25 m
capillary column of 5% phenylmethylsilicone. GC-MS was
performed on an Agilent 5973N instrument equipped with
1
the same column and conditions as GC. H and 13C NMR
were recorded in a 300 MHz Bruker Avance instrument
using CDCl3 or d6-DMSO as solvents and TMS as internal
standard. Diffuse reflectance UV–Vis spectra were recorded
on a Cary 5G adapted with a praying mantis accessory using
BaSO4 as reference. IR spectra were recorded on a Jasko
460plus spectrophotometer using sealed greaseless quartz
cells with CaF2 windows. Self-supported wafers (10 mg)
were obtained by pressing the solid at 1 Ton!cmK1 for
5 min. Thermal treatments were carried out in sealed IR
cells and the spectra recorded in a Nicolet 710 instrument at
room temperature after outgassing at the corresponding
temperature under 10K2 Pa. BET surface area and micro-
pore volume were measured by isothermal nitrogen
adsorption using a Micromeritics ASAP2000. The C and
N content of the solids was determined by combustion
chemical analysis using a Fisons CHNSO analyzer. The Pd
content in Al/MCM-41 catalysts was determined by
3.1.2. Synthesis of 3. A solution of 4-hydroxyacetophenone
oxime (1.51 g, 10 mmol) in acetone (100 mL) was added
dropwise (2 mL/min) to a dispersion of 1,5-dibromopentane
(10 mL, 73 mmol) and K2CO3 (4.14 g, 30 mmol) in acetone
(20 mL) at reflux temperature. After complete addition, the
mixture was heated 48 h. At this time the mixture was
filtered, the solvent evaporated under vacuum and the crude
dissolving the aluminosilicate in
a
HF/HCl/HNO3 conc. (30 mg in ca. 1:1:1 mL), diluting the
mixture of

A. Corma et al. / Tetrahedron 60 (2004) 8553–8560
8559
was submitted to partition in CH2Cl2/water. The organic
3.2. Adsorption of 5 on Al/MCM-41
phase was collected and CH2Cl2 evaporated under vacuum.
The residue was treated with hexane (200 mL) and the
product obtained by filtration under vacuum as a white solid
(yield: 42%, purity by GC O99%). IR (KBr, cmK1): 2939,
2866, 1674, 1599, 1575, 1560, 1510, 1311, 1255, 1170, 833,
588. 1H NMR dH (ppm, 300 MHz, CDCl3): 8.8 (1H, s), 7.6
(2H, d, JZ9 Hz), 6.8 (2H, d, JZ9 Hz), 4.0 (2H, t), 3.3 (2H,
t), 2.3 (3H, s), 1.9 (2H, s), 1.8 (2H, s), 1.6 (2H, s). 13C NMR
dC (ppm, 300 MHz, CDCl3): 159.9, 155.6, 129.0, 127.4,
114.4, 67.7, 33.5, 32.5, 29.0, 24.8, 12.1. MS (FAB): m/z
301–299 (peaks at 151, 134, 120, 94, 77, 69). Anal. calcd for
C13H18NO2Br (300.22): C 52.0; H 6.0; N 4.7. Found: C
51.6; H 5.7; N 2.8.
Palladium complex 5 (200 mg) was dissolved in ethanol/
dichloromethane (2:1 v/v, 24 mL) and the solution was
magnetically stirred (500 rpm) in a pre-heated bath oil at
40 8C in the presence of 2 g of previously dehydrated Al/
MCM-41. After 24 h the mixture was filtered under vacuum
and the solid was exhaustively Soxhlet-extracted with
dichloromethane. The palid yellow solid was kept into a
desicator for 24 h.
3.3. Typical procedure for reactions in ionic liquid
A 5 wt% mixture of complex 5 (25 mg) in bmimPF6
(500 mg) was dissolved in dichloromethane (1 mL). The
solvent was evaporated under reduced pressure and
bromobenzene (105 mL, 157 mg, 1 mmol), styrene
(172 mL, 156 mg, 1.5 mmol) and sodium acetate (164 mg,
2 mmol) were added. The mixture was magnetically stirred
(200 rpm) in a pre-heated oil bath at 130 8C for 24 h. Then,
the solution was cooled, extracted with diethyl ether (5!
5 mL) and the ethereal phase was concentrated and analysed
by CG using nitrobenzene as external standard.
3.1.3. Synthesis of 4. To a methanolic solution (5 mL) of
Li2PdCl4 (786 mg, 3 mmol) and sodium acetate (246 mg,
3 mmol), a solution of 3 (602 mg, 2 mmol) in methanol
(15 mL) was added. The mixture was stirred at room
temperature for 72 h. Then, water was added (20 mL) and,
after cooling, the cyclopalladate complex started to
precipitate as a green solid (yield: 95%, purity by NMR
75%). IR (KBr, cmK1): 3350, 2937, 2862, 1574, 1531,
1454, 1429, 1373, 1342, 1275, 1223, 1215, 1101, 1018, 966,
3.4. Typical procedure for reactions using
5@Al/MCM-41
1
872, 804, 638, 555. H NMR dH (ppm, 300 MHz, DMSO-
d6): 10.4 (1H, s), 9.8 (1H, s), 7.4 (1H, s), 7.2 (1H, d, JZ
15 Hz), 6.7 (1H, d, JZ15 Hz), 4.0 (2H, s), 3.6 (2H, t), 2.2
(3H, s), 1.9 (2H, m), 1.7 (2H, m), 1.5 (2H, m). 13C NMR dC
(ppm, 300 MHz, DMSO-d6): 167.5, 157.3, 154.7, 133.1,
128.3, 122.1, 111.8, 67.6, 35.5, 32.3, 29.1, 28.1, 24.6, 11.7.
MS (FAB): isotopic distribution for M-Cl compatible with 1
Pd and 1 Br (%): m/z 402 (11), 403 (22), 404 (38), 405 (22),
406 (53), 407 (0), 408 (38), 409 (0), 410 (12); found: 19, 29,
43, 28, 53, 14, 37, 16, 13. Anal. calcd for C13H17NO2ClPd
(441.08): C 35.0; H 3.8; N 3.2; Pd 24.0. Found: C 35.4; H
4.1; N 3.2; Pd 22.3.
4-Haloacetophenone (0.1 mmol), phenylboronic acid
(18.3 mg, 0.15 mmol) and tetrabutylammoniun bromide
(TBAB, 16.1 mg, 0.05 mmol) were placed into a double-
necked round-bottom vessel. Toluene (2.5 mL) and tribu-
tylamine (47.5 mL, 37.1 mg, 0.2 mmol) were added and the
solution was magnetically stirred in a pre-heated oil bath at
110 8C in the presence of 5@AlMCM-41 (42.6 mg, 2 mol%
of Pd). The course of the reaction was followed periodically
by stopping the stirring for half a minute and taken aliquots
(0.1 mL) that were analysed by GC. All the products were
confirmed by CG-MS.
3.1.4. Synthesis of 5. To a dark green solution of complex 4
(441 mg, 1 mmol) in THF (50 mL), 1-methylimidazole
(239.1 mL, 246.3 mg, 3 mmol) was added. The solution
turned bright green and was magnetically stirred in a pre-
heated bath oil at 50 8C for three days. After this time the
solvent was evaporated under vacuum. Then, diethyl ether
was added (15 mL), the mixture was filtered. The crude of 5
obtained was dissolved in dichloromethane and filtered in
order to remove any generated Pd black. The organic
solvent was evaporated under vacuum and, after washing
with diethyl ether (3!20 mL), a viscous green oil was
obtained. The product was stored in dry atmosphere
(480 mg, yield: 92%). IR (KBr, cmK1): 3400, 3120, 2941,
2868, 1580, 1596, 1539, 1525, 1458, 1421, 1375, 1336,
1308, 1287, 1277, 1229, 1209, 1167, 1107, 1043, 1028, 962,
818, 741, 699, 660, 640, 621. 1H NMR dH (ppm, 300 MHz,
DMSO-d6): 8.9 (1H, s), 8.2 (1H, s), 7.5 (1H, t, JZ1.5 Hz),
7.4 (1H, s), 7.2 (1H, t, JZ9 Hz), 6.9 (1H, d, JZ9 Hz), 6.7
(1H, dd, JZ3, 1.5 Hz), 3.9 (2H, t, JZ7 Hz), 3.8 (2H, s), 3.7
(3H, d, JZ1.5 Hz), 2.2 (3H, s), 1.7 (2H, m), 1.6 (2H, m), 1.4
(2H, m). 13C NMR dC (ppm, 300 MHz, DMSO-d6): 159.5,
154.7, 151.8, 140.5, 138.4, 136.9, 135.6, 122.6, 121.1,
109.4, 65.3, 55.3, 49.0, 45.6, 34.5, 32.1, 22.4. Anal. calcd
for C17H23N3O2BrClPd (523.20): C 39.0; H 4.4; N 8.0; Pd
20.3. Found: C 40.8; H 5.3; N 10.9; Pd 14.3.
3.5. Leaching tests
Leaching of catalytically active species from the solid to the
solution (which would act as homogeneous catalysts) was
studied filtering the reaction at the time in which 25–50% of
the expected yield was achieved. Filtration was carried out
in a glass syringe coupled with a swinney 13 mm filter
(Millipore) while the reaction was still hot in order to avoid
palladium precipitation upon cooling. Then, the clear
solution was allowed to react for additional 48 h. The
course of the reaction was followed by analysing period-
ically the reaction mixture by GC. The results were
compared with those obtained in the same conditions
without removing the solid catalyst from the reaction
mixture.
3.6. Recovery and reuse of the catalyst
After a typical reaction run (four times the amounts of
reagents and catalyst than in a typical reaction procedure),
the solid was separated by vacuum filtration in hot. Then,
the solid was washed with dichloromethane (300 mL per
100 mg of solid) and was dried 30 min under reduced
pressure. The dry solid was weighed and reused in a next run

8560
A. Corma et al. / Tetrahedron 60 (2004) 8553–8560
13. Gladysz, J. A.; Curran, D. P. Fluorous Chemistry, Tetrahedron
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substrate-to-catalyst and the solvent-to-catalyst ratios con-
stant throughout the series of reuses.
Acknowledgements
16. Schneider, S.; Bannwarth, W. Helv. Chim. Acta 2001, 84,
735–742.
Financial support by the Spanish Ministry of Science and
Technology (MAT2003-01226) and Generalidad Valencia
(grupos 03-020) is gratefully acknowledged. A. L. thanks
the Spanish Ministry of Education for a postgraduate
scholarship.
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