Copper-free heterogeneous catalysts for the Sonogashira cross-coupling reaction: Preparation, characterisation, activity and applications for organic synthesis

Article abstract of DOI:10.1016/j.molcata.2005.05.046

Heterogeneous copper-free catalysts supported on microporous ([Pd(NH ₃)₄]²⁺/NaY) and mesoporous materials ([Pd]/SBA-15) have been prepared, characterised and evaluated in the Sonogashira coupling reaction of aryl halides w

Full text of DOI:10.1016/j.molcata.2005.05.046

Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
Copper-free heterogeneous catalysts for the Sonogashira cross-coupling
reaction: Preparation, characterisation, activity and applications
for organic synthesis
a
a
Patrick Rollet , Wolfgang Kleist , Veronique Dufaudb,∗∗, Laurent Djakovitcha,∗
´
a
Institut de Recherches sur la Catalyse, UPR-CNRS 5401, 2 Avenue Albert Einstein, F-69626 Villeurbanne, France
b
Laboratoire de Chimie, UMR 5182, Ecole Normale Supe´rieure de Lyon, 46 Alle´e d’Italie, F-69364 Lyon Cedex 07, France
Received 29 April 2005; accepted 30 May 2005
Available online 8 August 2005
Abstract
Heterogeneous copper-free catalysts supported on microporous ([Pd(NH3)4]2+/NaY) and mesoporous materials ([Pd]/SBA-15) have
been prepared, characterised and evaluated in the Sonogashira coupling reaction of aryl halides with phenyl acetylene. Gener-
ally, these catalysts showed high activity and selectivity, somewhat comparable to that of homogeneous catalysts (i.e. {Pd[P(o-
C6H4CH3)2(C6H4CH2)[OCOCH3]}2 and PdCl2(PPh3)2). In addition, it was found that the catalyst based on the SBA-15 material (i.e.
[Pd]/SBA-15), was particularly active when using large aryl halides such as bromonaphtalene and bromoanthacene, whereas, the hetero-
geneous catalyst based on microporous support (i.e. [Pd(NH3)4]2+/NaY) was inactive. The recycling of various catalyst and X-ray diffraction
and 31P CP-MAS NMR studies of fresh and recycled catalyst are also briefly discussed.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Heterogeneous catalysts; Microporous support; Mesoporous support; Palladium; Sonogashira cross-coupling
1. Introduction
Generally the Sonogashira reaction is carried out in an
organic solvent such as toluene, THF or DMF, using at least
a stoichiometric amount of base, and a Pd(0)/Cu(I) catalytic
system [22]. To extend the Sonogashira reaction for fine
chemical applications, numerous studies have been reported
in the literature over the last 10 years including the use
of a phase transfer agent [23], reaction in aqueous media
or without solvent [24–29], reaction in ionic-liquids [30],
copper-free versions [31–42], and the use of promoters such
as Zn, Mg, Sn and R4NI [43–46].
Nickel catalysed Sonogashira reactions have been
described by Beletskaya et al. for homogeneous Ni(II)-
species [47] and Wang et al. for Ni(0)-particles [48].
However, these catalysts require the use of CuI as co-catalyst
and PPh3 in order to achieve high activities. Alternatively,
Leadbeater et al. reported a transition-metal free procedure
for the Sonogashira coupling reactions of aryl iodides
and bromides with phenylacetylene under phase-transfer
conditions and using microwave irradiation to efficiently
The Sonogashira cross-coupling of aryl halides and
terminal alkynes or arylenes is a useful tool for the syn-
thesis of alkyl-aryl and diaryl-susbtituted acetylenes [1–8].
Functionalised alkynes are important building blocks for the
synthesis of biologically active molecules and, surprisingly,
have common structural features with natural products that
have been isolated from plants and in the marine organisms,
or synthetic drugs [2,4,9–12]. Therefore, the Sonogashira
reaction is frequently used as a key step in the synthesis of
pharmaceuticals, such as the enediyne antibiotics or oral
contraceptives [13–21].
∗
∗∗
Corresponding author. Tel.: +33 4 72 44 53 81; fax: +33 4 72 44 53 99.
Corresponding author. Tel.: +33 4 72 72 88 57; fax: +33 4 72 72 88 60.
E-mail addresses: veronique.dufaud@ens-lyon.fr (V. Dufaud),
laurent.djakovitch@catalyse.cnrs.fr (L. Djakovitch).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.05.046

40
P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
activate the aryl halides [49]. Nevertheless, while interesting,
these Pd-free methodologies remain limited by the narrow
choice of the reactants and reaction conditions, which lead
to high conversions.
reaction using zeolites as supports [39,63]. In these studies,
zeolite supports were found to be particularly effective in
the stabilisation of active Pd-species during the reaction,
leading to highly active, easily separable and recyclable
heterogeneous palladium catalysts. However, for synthetic
applications such as those encountered in the pharmaceutical
and agrochemical industries, these catalysts remain limited,
since the pore structure of the zeolite support restricted
the size of the molecule that could be involved over the
syntheses.
The present contribution describes the remarkable
catalytic activity of a Pd-modified mesoporous catalyst
([Pd]/SBA-15) for the Sonogashira cross-coupling reaction
of aryl-iodides and -bromides with phenylacetylene and
the potential application of this system to the synthesis of
relatively large molecules. Particular attention has been
paid to the comparison of the activity and selectivity of this
[Pd]/SBA-15 to other metal oxide supported Pd-catalysts
and to homogenous palladium complexes.
The most important improvement concerned the elimina-
tion of CuI as co-catalyst, as CuI can induce homocoupling
reactions of terminal alkynes to diynes in the presence of oxy-
gen (Glaser-type reactions) [50]. This improvement is also
of importance for industrial applications of the Sonogashira
cross-coupling reactions, since copper is very tedious to
recycle. As a solution, several efficient copper-free homoge-
neous catalytic systems have been reported since 1992 for the
cross-coupling reaction of alkynes with aryl- or vinyl-halides
[41,42,51–58]. While these examples contributed to the
improvement of the Sonogashira reaction, the use of homo-
geneous Pd-catalysts makes the separation and the recovery
of the catalysts difficult, if not impossible, and might result
in unacceptable palladium contamination of the products.
As an answer to these problems Astruc and co-workers
[59,60] recently reported the use of a dendritic material to
support the homogeneous [Pd{t-Bu2PCH2N(CH2Ph)CH2Pt-
Bu2}(OAc)2] complex [35], which they had previously
applied to the Sonogashira reaction (79% yield for the
reaction of iodobenzene with phenylacetylene under reflux
in the presence of Et3N using 1 mol% of the Pd-dendritic
catalyst after 24 h). The authors claimed that the dendritic
catalysts could be recovered by precipitation and reused
without significant loss of activity. Although interesting,
this method required the precipitation of the catalyst by a
co-solvent (generally pentane), which increased the amount
of effluent waste during the process.
2. Experimental
2.1. General
All manipulations were conducted under a strict inert
atmosphere or vacuum conditions using Schlenk techniques
including the transfer of the catalysts to the reaction vessel.
All glassware was base- and acid-washed and oven dried.
Thesolventsweredriedusingstandardmethodsandstored
˚
over activated 4 A molecular sieves. The toluene used for the
Few reports describe the Sonogashira reaction heteroge-
neously catalysed by supported palladium catalysts, exam-
plesbeinggenerallylimitedtohighlyreactivearyliodidesand
synthesis of the “palladacyle” catalyst {Pd[P(o-C6H4CH3)2-
(o-C6H4CH2)(CH3CO2)]}2 was distilled under argon before
use over sodium from purple benzophone ketyl.
¨
2-halopyridines. Separately, Kohler et al. [61] and Kotschy et
Tetraethoxysilane (TEOS), poly(ethyleneoxide)-poly(pr-
opyleneoxide)-poly(ethyleneoxide) block copolymer (Plur-
onic 123, Mw: 5000) and diethoxymethylvinylsilane were
purchased from Aldrich Chemical and used without fur-
ther purification. PdCl2 and PdCl2(PPh3)2 were obtained,
respectively, from Alfa and Strem Chemicals. Diphe-
nylphosphine was supplied from Fluka. 2-(diphenylpho-
al. [62] have described the Pd/C catalysed Sonogashira reac-
tion of aryl halides with acetylenes in presence of CuI. When
optimised, using 5 mol% Pd/C, 10 mol% CuI as co-catalyst
and diisopropylamine as the base, Kotschy and co-workers
achievedthequantitativeconversionof2-bromopyridinewith
various acetylenes, such as 1-hexyne, after 24 h under reflux
in DMAc/H2O. However, the success of these examples
remained linked to the use of CuI as co-catalyst. Kotschy and
co-workers clearly demonstrated that the overall activity of
the [Pd/C + CuI] catalytic system was related to the leaching
of the active Pd-species in the solution during the reaction,
thus contaminating the reaction mixture (≤2% of Pd) [62].
The intensive application of the Sonogashira reaction in
the chemical industry depends on the development of new,
stable and recyclable heterogeneous copper-free palladium
catalysts. With this aim, the use of palladium supported on
metal-oxides appears to be the most appropriate heteroge-
neous catalyst to perform this cross-coupling reaction on a
large scale.
sphino)ethyldiethoxymethylsilane,
PPh2-(CH2)2-SiCH3
(OCH2CH3)2, was synthesized by adapting the procedure
reported by Schmid et al. [64]. Equimolar quantities of
HPPh2 and diethoxymethylvinylsilane were irradiated for
4 days using a UV light (high pressure Hg lamp) and a
water-cooled quartz reactor; the product was purified by
distillation under vacuo (b.p. 170–180 ◦C/0.1 Torr, 85%
yield). All the chemicals (organic reagents and solvents)
were deaerated by an argon flow before they were used.
The supports (TiO2 {P25}, SiO2 {Aerosil 200}, Al2O3
{Aluminium oxide C}), were donated by Degussa AG. The
NaY zeolite (LZ-Z-52) was purchased from Sigma–Aldrich
Chemicals. Silica Aerosil 200 was agglomerated prior to use
by treatment with water. After evaporation and drying at
120 ◦C for 3 days the resulting material was crushed and
Some of us have previously reported the first very
efficient heterogeneous Pd-catalyst for the Sonogashira

P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
41
sieved to give a selected fraction with a particle size of
40–60 mesh. BETofasilicasampledehydroxylatedat500 ◦C
under 10−5 mmHg for 6 h gave the following characteristics:
specific surface = 240 4 m2/g. The support materials AlF3
and MgF2 were prepared by a modified procedure given in the
literature [65,66] and calcined for 4 h at 200 ◦C. The result-
ing fluorides were characterized by X-ray powder diffraction
and IR spectroscopy. The specific surface area of the materi-
als (determined via N2 physisorption at 77 K; BET method)
was 180 m2/g (AlF3) and 250 m2/g (MgF2). The Pd/C cata-
lyst (5.1 wt.% on dry basis, 49% water) was purchased from
Aldrich Chemicals.
2.2.2.3. Preparation of [Pd(0)]/NaY [72]. The Pd(0)
exchanged zeolite was obtained by reduction of the
[Pd(II)]/NaY in a U-reactor under a pure hydrogen flow
(70 mL/min) using a heating rate of 8 ◦C/min from room tem-
peratureto350 ◦C. Thetemperaturewasmaintainedat350 ◦C
for 15 min and the reactor was cooled to room temperature
under a flow of argon to give the Pd(0) modified zeolite as a
black powder. The [Pd(0)]/NaY was then stored under argon
to prevent re-oxidation. ICP-AES analysis: 5.5 wt.% Pd.
2.2.2.4. Preparation of [Pd(0)]/SiO2 [74]. A solution of
Pd(acac)2 in benzene (made from 143.1 mg of Pd(acac)2 in
15 mL of benzene) was added to 1.0 g of SiO2. After stir-
ring the mixture for 1 h at room temperature, the toluene was
evaporated to give a slightly yellow material. This latter was
reduced under H2 flow (150 mL/min) in a U-reactor at 70 ◦C
for 2 h to give the desired [Pd(0)]/SiO2 catalyst as grey mate-
rials. ICP-AES analysis: 4.4 wt.% Pd.
2.2. Catalyst preparation
2.2.1. Homogeneous catalysts
PdCl2(PhCN)2 was prepared according procedures previ-
ously described in the literature [67]. The homogeneous “pal-
ladacycle” {Pd[P(o-C6H4CH3)2(C6H4CH2)[OCOCH3]}2
catalyst was prepared from Pd(OAc)2 and Tri(o-
tolyl)phosphine following the procedure reported by
Herrmann and co-workers [68]. PdCl2{PPh2-(CH2)2-
SiCH3(OCH2CH3)2}2 was synthesized by reacting two
equivalents of PPh2-(CH2)2-SiCH3(OCH2CH3)2 with
bis(benzonitrile)palladium dichloride at room temperature
in methylene chloride by adapting a procedure reported
elsewhere [69].
2.2.2.5. Preparation of the [Pd]/AlF3, [Pd]/MgF2, [Pd]/
Al2O3 catalysts: general procedure. These catalysts were
prepared according to a modified precipitation method of
Pd(OH)2 on the fluorides or oxides supports from a PdCl2-
HCl solution by controlled addition of a base like a procedure
originally described by Pearlman [75]. ICP-AES analysis of
the resulting catalysts gave: 1.0 wt.% Pd.
2.2.2.6. Preparation of PdCl2{PPh2-(CH2)2-SiCH3(OCH2
CH3)2}2/SBA-15. Mesoporous SBA-15 type silica was used
as support and was prepared by the acid catalyzed, non-
ionic assembly pathway described by Margolese et al. [76].
The structure-directing agent (Pluronic 123) was removed by
calcination under air at 500 ◦C and the surfactant-free meso-
porous silica was rigorously dried under a flow of nitrogen at
200 ◦C prior to the grafting reaction. Typically, PdCl2{PPh2-
(CH2)2-SiCH3(OCH2CH3)2}2 (∼500 mg) dissolved in dry
toluene was added dropwise to a suspension of calcined SBA-
15 (1 g) in toluene and stirred at 25 ◦C for 2 h to allow the
diffusion of the molecular precursor into the channels of
the pores. The reaction mixture was then heated at 85 ◦C
overnight. After filtration of the solid, the unreacted palla-
dium precursor was removed by a soxlhet extraction with
CH2Cl2 during 10 h. Finally, the resulting solid was dried in
vacuo at 25 ◦C. The organometallic-inorganic hybrid mate-
rial, denoted [Pd]/SBA-15, has been characterized by several
analytical, physical and spectroscopic techniques including
small-angle X-ray powder diffraction and nitrogen sorption
isotherms. Solid-state 1H, 13C, 31P and 29Si NMR spectra as
well as the TGA profile are given in Supporting information.
ICP-AES analysis: 2.1 wt.% Pd and 1.3 wt.% P. MAS
1H NMR ␦: 0.6 ( SiCH3, SiCH2CH2P, OCH2CH3),
3.3 ( SiCH2CH2P, OCH2CH3), 6.7 (phenyl ring). CP-
MAS 13C NMR ␦: −4.6 ( SiCH3), 10.5 ( SiCH2CH2P),
18.7–20.1 ( OCH2CH3 and SiCH2CH2P, respectively),
58.2 ( OCH2CH3), 129.7–137.8 (phenyl ring). CP-MAS
29Si NMR ␦: −12.6 (D1 and D2 sites), −91.6 (Q2 sites),
2.2.2. Heterogeneous catalysts
All catalyst supports were dried prior to use at 120 ◦C
for 48 h under dynamic vacuum (5.10−2 mmHg). After the
synthesis, the catalysts obtained were stored under argon.
2.2.2.1. Preparation of [Pd(NH3)4]2+/NaY [70–73]. A
0.1 M ammonia solution of [Pd(NH3)4]Cl2 prepared from
PdCl2 and a commercial ammonia solution was added drop-
wise (4 mL/g zeolite, corresponding to ca. 5 wt.% Pd in the
final catalyst) to a suspension of the zeolite NaY in bidis-
tilled water (100 mL/g zeolite). The mixture was stirred
for 24 h at room temperature and the exchanged zeolite
was filtered off and washed until no trace of chloride was
detected in the filtrate (AgNO3 test). Then the zeolite was
allowed to dry at room temperature to give the entrapped
[Pd(NH3)4]2+/NaY catalyst as slightly yellow material. ICP-
AES analysis: 5.4 wt.% Pd.
2.2.2.2. Preparation of [Pd(II)]/NaY [72]. The Pd(II)
exchanged zeolite was obtained by calcination of the
entrapped [Pd(NH3)4]2+ zeolite in a U-reactor under a pure
oxygen flow (180 mL/min) using a heating rate of 2 ◦C/min
fromroomtemperatureto500 ◦C. Thetemperaturewasmain-
tainedat500 ◦Cfor30 minandthereactorwascooledtoroom
temperature under a flow of argon to give the modified Pd(II)
zeolite as a golden brown powder. The [Pd(II)]/NaY was then
stored under argon to prevent hydration. ICP-AES analysis:
5.5 wt.% Pd.

42
P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
−101.4 (Q3 sites), −108.2 ppm (Q4 sites). CP-MAS 31P
NMR ␦: 20.7 (trans-isomer), 30.9 (cis-isomer).
2.4. Catalytic tests
The catalytic reactions were carried out in a three-necked
flask, or alternatively in pressure sealed tubes, under argon.
The qualitative and quantitative analysis of the reactants and
the products was made by gas chromatography. Conversion
and yields were determined by GC based on the relative area
of GC-signals referred to an internal standard (diethylene
glycol di-n-butyl ether) calibrated to the corresponding pure
compound. All catalysts were handled and transferred under
argon.
2.3. Characterisation
All solid-state NMR spectra were recorded on a BRUKER
DSX-300 or Avance-500 spectrometers equipped with a
standard 4 mm probehead. The spinning rate was typically
10 kHz. 13C, 29Si and 31P NMR spectra were obtained by
use of cross-polarisation (contact time 5 ms). To achieve a
good polarisation transfer, a ramp was used on the X chan-
1
nel. Recycle delays were typically 1 s (a study on the H
nucleus showed that it was sufficient to allow all protons to
fully relax). 1H, 13C and 29Si MAS spectra were referenced to
tetramethylsilane. 31P MAS spectra were referenced to 85%
H3PO4.
2.4.1. General procedure for the first runs of the
catalysts
A total of 5 mmol of aryl halide, 8 mmol of pheny-
lacetylene, 10 mmol of base and 1 mol% [Pd]-catalyst was
introduced in a three-necked flask under argon. Then 10 mL
of solvent (previously deaerated) was added and the mixture
was further deaerated by an argon flow for 5 min. The reactor
was placed in a preheated oil bath at 80 ◦C. The reaction
was conducted under vigorous stirring for 6 h and then the
reaction mixture was cooled to room temperature before GC
analysis.
X-ray powder diffraction (XRD) data were acquired
on a Bruker D5005 diffractometer using Cu K␣ radiation
˚
(λ = 1054184 A). A TA instruments thermoanalyser 2950 HR
V5.3. was used for simultaneous thermal analysis combining
thermogravimetric (TGA) and differential thermoanalysis
(DTA) at a heating rate of 5 ◦C/min in air. Nitrogen adsorp-
tion and desorption isotherms were measured at 77 K. The
organometallic-inorganic hybrids were evacuated at 160 ◦C
for 24 h before the measurements. Specific surface areas were
calculated following the BET procedure. Pore size distribu-
tion was obtained by using the BJH pore analysis applied to
the desorption branch of the nitrogen adsorption/desorption
isotherm.
The palladium content determinations of the heteroge-
neous catalysts {[Pd(NH3)4]2+/NaY, [Pd(II)]/NaY, [Pd(0)]/
NaY, [Pd(0)]/SiO2, [Pd]/AlF3, [Pd]/MgF2, [Pd]/Al2O3 and
[Pd]/SBA-15} were performed by ICP-AES spectroscopy
from a solution obtained by treatment of the catalysts with
a mixture of HBF4, HNO3 and HCl in a Teflon reactor at
180 ◦C.
2.4.2. General procedure for the recycling of separated
catalysts
For recycling experiments the catalyst used in a first run
was separated by centrifugation, washed two times with
10 mL DMF/H2O (4:1) and reused after drying at room tem-
perature as described for the fresh catalyst.
2.4.3. General procedure for the evaluation of the
catalytic activity of non-separated catalysts
A total of 10 mmol of p-iodotoluene (2.18 g), 15 mmol
of phenylacetylene (1.53 g), 20 mmol of Et3N (2.02 g) and
1 mol% [Pd]-catalyst was introduced in a three-necked flask
under argon. Then 20 mL of DMF/H2O (4:1) previously
deaerated was added and the mixture was further deaerated
by an argon flow for 5 min. The reactor was placed in a
preheated oil bath at 80 ◦C. The reaction was conducted
under vigorous stirring and followed by GC analysis until
completion of the reaction. At completion of the first run (i.e.
2 h) new amounts of reagents (10 mmol of p-iodotoluene,
15 mmol of phenylacetylene, 20 mmol of Et3N) were added,
and the volume of solvent adjusted in order to restore the
concentrations of reagents to that of the initial run. Immedi-
ately after addition, based on GC analysis, the concentration
of the p-iodotoluene was considered as 100% and the
concentration in 1-methyl-4-phenylethynyl-benzene to 0%.
The reaction was followed by GC until 80% conversion and
the procedure was repeated once.
Liquid NMR spectra were recorded on a Bruker AC-250
spectrometer. All chemical shifts were measured relative
1
to residual H or 13C NMR resonances in the deuterated
solvents: C6D6, ␦ 7.15 ppm for 1H, 128 ppm for 13C;
1
CD2Cl2, ␦ 5.32 ppm for H, 53.8 ppm for 13C; CDCl3, ␦
7.25 ppm for 1H, 77 ppm for 13C. Flash chromatography was
performed at a pressure slightly greater than atmospheric
pressure using silica (Merck Silica Gel 60, 230–400 mesh).
Thin layer chromatography was performed on Fluka Silica
Gel 60 F254
.
GC analyses were performed on a HP 4890 chromato-
graph equipped with a FID detector, a HP 6890 autosampler
and a HP-5 column (cross-linked 5% phenyl-methylsiloxane,
30 m × 0.25 mm i.d. × 0.25 ␮m film thickness). Nitrogen is
used as carrier gas. The mass spectra were obtained on a
HP 6890 gas chromatograph equipped with a HP 5973 mass
detector and a HP-5 MS column (cross-linked 5% phenyl-
methylsiloxane, 30 m × 0.25 mm i.d. × 0.25 ␮m film thick-
ness). Helium is used as carrier gas. The experimental error
2.4.4. General procedure for leaching studies by
hot-filtration
A total of 10 mmol of p-iodotoluene, 15 mmol of pheny-
lacetylene, 20 mmol of Et3N and 1 mol% [Pd]-catalyst was
was estimated to be ꢀrel
= 5%.

P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
43
(m, 3 H, CH-C6H5). 13C NMR (62.9 MHz, CDCl3): ␦
(ppm): 133.00 (Cq-C10H7), 132.78 (Cq-C10H7), 131.64 (CH-
C6H5), 131.41 (CH-C10H7), 128.40 (CH-C10H7), 128.36
(CH-C6H5), 128.29(CH-C6H5), 127.98(CH-C10H7), 127.75
(CH-C10H7), 126.64 (CH-C10H7), 126.53 (CH-C10H7),
123.27 (Cq-C6H5), 120.56 (Cq-C10H7), 89.78 (C C), 89.72
(C C). C9H8O: mol. wt.: 228.09 g mol−1. MS: m/z (%) [M+]
228 (100).
introduced in a three-necked flask under argon. Then 20 mL
of DMF/H2O (4:1) previously deaerated was added and the
mixture was further deaerated by an argon flow for 5 min.
The reactor was placed in a preheated oil bath at 80 ◦C. The
reaction was conducted under vigorous stirring for 10 min of
reaction. The supernatant solution was filtered through a can-
nula with a microglass Whatman filter (in order to remove all
fine particles) and then treated for further 5 h under the stan-
dard reaction conditions.
The reaction was monitored over the total period by GC
and the results compared to a standard catalytic reaction.
3.3. 9-(Phenylethynyl)anthracene 11
Eluant petroleum-ether (40–60)/CH2Cl2 = 80/20, Rf =
2.4.5. GC analysis
1
0.58, 76% as a yellow solid. H NMR (250 MHz, CDCl3):
A 3 mL sample of the reaction mixture was quenched with
3 mL of water in a test tube. The mixture was extracted with
2 mL of CH2Cl2 and the organic layer was filtered through
a MgSO4 pad. The resulting dry organic layer was then ana-
lyzed by GC. GC-rate program: 2 min at 100 ◦C, heating
15 ◦C/min up to 170 ◦C, 2 min at 170 ◦C, heating 35 ◦C/min
up to 240 ◦C, 10 min at 240 ◦C, heating 50 ◦C/min up to
270 ◦C and 2 min at 270 ◦C.
3
␦ (ppm): 8.63 (d, J(HH) = 8.4 Hz, 2H, CH-C14H9), 8.39
(s, 1H, CH-C14H9), 7.98 (d, 3J(HH) = 8.6 Hz, 2H, CH-
C6H5), 7.75 (dd, 3J(HH) = 8.1 Hz, 4J(HH) = 1.9 Hz, 2H, CH-
C14H9), 7.57 (td, 3J(HH) = 7.9 Hz, 4J(HH) = 1.3 Hz, 2H, CH-
C14H9), 7.45 (td, 3J(HH) = 7.9 Hz, 4J(HH) = 1.49 Hz, 2H,
CH-C14H9), 7.37 (m, 3H, CH-C6H5). 13C NMR (62.9 MHz,
CDCl3): ␦ (ppm): 132.61 (Cq-C14H9), 131.66 (CH-C6H5),
131.20 (Cq-C14H9), 128.69 (CH-C14H9), 128.53 (CH-
C6H5), 128.49 (CH-C6H5), 127.72 (CH-C14H9), 126.78
(CH-C14H9), 126.61 (CH-C14H9), 125.69 (CH-C14H9),
123.64 (Cq-C6H5), 117.28 (Cq-C14H9), 100.75 (C C), 86.31
(C C). C9H8O: mol. wt.: 278.35 g mol−1. MS: m/z (%) [M+]
278 (100).
2.4.6. Purification of the products 3–11
Thereactionmixturewasdilutedwith250 mLofwaterand
the resulting mixture was extracted with 4 × 20 mL CH2Cl2.
The combined organic layers were washed three times with
15 mL H2O, one time with 15 mL brine, dried over MgSO4
and evaporated. The residue was then purified by flash chro-
matography on silica gel.
4. Results and discussion
Products 3–4, 6–9 gave 1H and 13C NMR data in accor-
dance with the literatures [11,63,77–82].
4.1. Preparation and characterisation of
PdCl2{PPh2-(CH2)2-SiCH3(OCH2CH3)2}2/SBA-15
3. Data for the compounds 5, 10, 11
We chose to prepare catalyst on the base of ordered meso-
porous materials, a class of oxides which, given their wide
pore size range, have shown to be of great use as catalyst sup-
ports in chemical transformations involving bulky molecules.
In addition to accurate control of pore shapes and dimensions,
organic fonctionalisation of the internal surface of the support
can produce precisely controlled active site microstructures
[83–85]. In this study, we chose to support our catalysts on
mesoporous SBA-15 type silicas, as these supports can be
3.1. Trimethyl(3-phenylprop-2-ynyloxy)silane 4
Eluant petroleum-ether (40–60)/CH2Cl2 = 70/30, Rf =
0.68, 57% as a colourless oil. 1H NMR (250 MHz, CDCl3):
␦ ppm: 7.48 (m, 2H, o-C C-C6H5), 7.29 (m, 3H, m-
C C-C6H5; p-C C-C6H5), 4.51 (s, 2H, CH2OH), 0.09
(s, 9H, CH3Si). 13C NMR (62.9 MHz, CDCl3): ␦ (ppm):
131.69 (o-C C, C6H5), 128.48 (p-C C, C6H5), 128.32
(m-C C, C6H5), 122.71 (Cq-C C, C6H5), 87.29 (C C-
CH2OH), 85,62 (C C-CH2OH), 51.50 (CH2OH). C9H8O:
˚
prepared with a pore size up to 80 A and they tend to be ther-
mally and mechanically very stable (due to their relatively
thick walls). The transition metal complex integrated into this
material, the PdCl2{PPh2-(CH2)2-SiCH3(OCH2CH3)2}2
complex, was chosen on the basis of literature reports
that analogous palladium trisarylphosphine complexes were
active and efficient catalysts for the Sonogashira reaction
[35,86].
mol. wt.: 204.34 g mol−1. MS: m/z (%) [M+] 204 (100), [M+
Si(CH3)3] 131 (85) [M+ OSi(CH3)3] 115 (22), [C6H5
77 (32).
]
+
3.2. 2-(Phenylethynyl)naphthalene 10
The SBA-15 type silica was synthesized following a pro-
tocol adapted from Zhao’s report [87–89] by acid catalyzed
polycondensation of TEOS in the presence of the non-ionic
tri-block copolymer, pluronic 123. The oxide support was
calcined at 500 ◦C under flowing air to remove the tem-
plate molecule and liberate the pores. The metal precursor,
Eluant petroleum-ether (40–60)/CH2Cl2 = 80/20, Rf =
0.58, 99% as a white solid. H NMR (250 MHz, CDCl3):
␦ (ppm): 7.99 (brs, 1 H, CH-C10H7), 7.76 (m, 2H, CH-
C10H7), 7.73 (m, 1H, CH-C10H7), 7.51 (m, 3H, CH-
C10H7 and CH-C6H5), 7.42 (m, 2H, CH-C10H7), 7.30
1

44
P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
transition metal precursor has been integrated into the mate-
rial without significant change in its coordinative structure.
The elemental analysis of [Pd]/SBA-15 showed a palladium
loading of 2.1 wt.%. The phosphorous analysis (1.3 wt.%)
corresponds to a molar ratio of P:Pd of 2.1 (expected 2.0). The
31P CP-MAS NMR (see Supporting information) exhibits
two peaks at ␦ 20.7 and ␦ 30.9, which can be attributed respec-
tively to the trans- and cis-isomers of the grafted species (the
solid state NMR spectrum of the molecular precursor showed
two peaks at ␦ 20.6 and ␦ 26.6). This result clearly indicates
that the phosphine ligands have survived the grafting reac-
tion and are still coordinated by pairs to the palladium central
atom. The 1H MAS NMR and the 13C CP-MAS NMR spectra
also show no significant modification of the organic ligand
of the metal complex after the grafting reaction. One should
note the presence of signals in the 13C spectrum of [Pd]/SBA-
15 corresponding to unreacted alkoxysilane groups (␦ 17,
OCH2CH3, and ␦ 58, OCH2CH3). This observation is
also indicated by the overbroad peak at ␦ −12.6 in the 29Si
CP-MAS NMR spectrum which would correspond to the
presence of D1 sites (containing the ligand grafted in the
form PPh2-(CH2)2-SiCH3(OCH2CH3)(OSi )).
Several other types of catalysts were prepared and used
for comparison with these new catalytic materials. Supported
palladium catalysts used for this comparison have previously
been described in the literature, including zeolite supported
[Pd(NH3)4]2+/NaY [73], silica supported palladium(0)
([Pd(0)]/SiO2) [74], [Pd]/AlF3, [Pd]/MgF2 and [Pd]/Al2O3
[75] and a commercial catalyst, Pd/C (type Degussa E101
NE/W, 5.1 wt.% Pd – 49 wt.% water). Furthermore, two
homogeneous catalysts were tested, the “palladacycle”
{Pd[P(o-C6H4CH3)2(C6H4CH2)[OCOCH3]}2 [68] and
PdCl2(PPh3)2 (Strem).
PdCl2{PPh2-(CH2)2-SiCH3(OCH2CH3)2}2, which contains
four condensable siloxane groups per molecule was reacted
with the oxide support in a toluene slurry at 85 ◦C overnight.
The complex presumable reacted with the surface by
condensation of surface silanol of the oxide support with
the alkoxysilane groups of the metal precursor. After the
reaction period, the solid was washed by soxhlet extraction
with CH2Cl2 for 15 h, which assured the total removal of
physisorbed metal precursor ([Pd]/SBA-15).
The catalyst was characterized by a variety of spectro-
scopic and quantitative methods, namely 1H, 13C, 29Si, 31
P
NMR, X-ray diffraction, nitrogen sorption, thermogravimet-
ric analysis and elemental analysis. The small angle X-ray
diffractogram of SBA-15 exhibits a series of three peaks
between 1◦ and 2◦ (2θ, Fig. 1a) which corresponds to a hexag-
onal mesoporous structure with d(1 0 0) spacing of 9.0 nm.
After the grafting reaction, the diffractogram of [Pd]/SBA-15
shows little change excepting a slight decrease in the intensity
of the d(1 0 0) peak.
The results of the analysis of the nitrogen adsorption–
desorption isotherms and the pore size distribution curves
of the calcined SBA-15 and hybrid material [Pd]/SBA-15
are shown in Fig. 2. Both samples show a type IV isotherm
characteristic of mesoporous solids. Relatively narrow pore
diameter distributions were observed for both materials and
the median pore diameter varies somewhat between the two
samples (6.2 and 5.4 nm, respectively), undoubtedly due to
the incorporation of the palladium complex in the cavity. Not
surprisingly, the BET specific surface area also decreased
significantly due to the grafting of the metal precursor, from
920 m2/g for SBA-15 to 520 m2/g for [Pd]/SBA-15.
On the molecular level, it is apparent from the NMR spec-
tra and from the comparative elemental analyses that the
Fig. 1. XRD patterns of (a) calcined SBA-15; (b) (a) after the grafting of PdCl2{PPh2-(CH2)2-SiCH3(OCH2CH3)2}2.

P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
45
Fig. 2. Nitrogen adsorption/desorption isotherms and pore size distributions (from the BJH calculations) of calcined SBA-15 and palladium modified SBA-15
silica (2.1 wt.% Pd).
4.2. Catalytic activity and kinetic studies
(10–60%) under standard reaction conditions [22]. Gener-
ally, when using heterogeneous supported palladium species
(particles, organometallic complexes), the use of CuI as co-
catalyst is required in order to attain reasonable activities
[62]. Therefore, the coupling reaction of bromobenzene with
phenyl acetylene appears to be of interest for developing new
heterogeneous copper-free palladium catalysts and to demon-
strate effects related to the nature/structure of the Pd-species
as well as related to the support.
In previous studies, the reactivity of [Pd(NH3)4]2+/
(NH4)Y towards the Sonogashira reactions of various aryl
iodides and bromides with phenyl acetylene was evaluated.
Remarkable catalytic activity was observed for this specific
catalyst independently of the aryl halides used.
In the present contribution, we limited our experiments
to the Sonogashira coupling reaction of bromobenzene with
phenyl acetylene (Scheme 1: R = H, X = Br). In the litera-
ture, aryl bromides as substrates using homogeneous copper-
free palladium catalysts led generally to low conversions
Generally, all heterogeneous catalysts based on molecular
palladium complexes ([Pd(NH3)4]2+/NaY, [Pd(II)]/NaY,
[Pd]/SBA-15) and homogeneous catalysts gave reasonable

46
P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
Scheme 1. Sonogashira coupling reaction of aryl halides with phenyl acetylene catalysed by copper-free Pd-catalysts.
to high conversions in bromobenzene under our stan-
dard reaction conditions {5 mmol bromobenzene, 7 mmol
phenylacetylene, 10 mmol Et3N, 1 mol% [Pd]-catalyst,
80 ◦C, DMF/H2O = 4:1, 6 h} (Table 1). On the contrary,
the heterogeneous catalysts based on Pd-particles led to
low product yields (≤10%) while giving, comparatively, at
the same time high yield in benzene due to the relatively
rapid dehalogenation of bromobenzene. Surprisingly, the
catalysts prepared following the procedure described by
Pearlman ([Pd]/AlF3, [Pd]/MgF2 and [Pd]/Al2O3) gave low
conversions.
Clearer insight into the behavior of the different copper-
free palladium catalysts was obtained by following the
evolution of the reaction mixture for the coupling reaction
of p-iodoanisole with phenylacetylene with the time (Fig. 3;
Scheme 1: R = p-OCH3, X = I). This reaction was chosen in
order to achieve a complete conversion of the aryl halide over
a relatively short reaction time. As expected, homogeneous
catalysts and heterogeneous catalysts involving immobilised
molecular Pd-species ([Pd(NH3)4]2+/NaY and [Pd]/SBA-
15) gave nearly complete conversion of iodoanisole within
less than 2 h. On the contrary, the [Pd(II)]/NaY catalyst
showed a lower activity, giving only 53% conversion
after 6 h.
Fig. 3. Sonogashira coupling reaction of p-iodonanisole with phenyl acety-
lene.
The initial activities observed for the different hetero-
geneous catalysts further account for these observations
(Table 2). As expected, the “palladacycle” {Pd[P(o-C6
H4CH3)2(C6H4CH2)[OCOCH3]}2 and the PdCl2(PPh3)2
Table 2
Sonogashira coupling reaction of p-iodonanisole with phenyl acetylene
Catalyst
Conversion
(%)a
GC-yield
(%)a
Initial ratec
(mmol/gPd × min)
Table 1
Sonogashira coupling reaction of bromobenzene with phenyl acetylene
[Pd(PPh3)2Cl2]
“Palladacycle”
[Pd]/SBA-15
[Pd(NH3)4]/NaY
[Pd(II)]/NaY
[Pd(0)]/NaY
[Pd(0)]/SiO2
[Pd]/Al2O3
86
89
100
92
53
35
27
85
64
73
96
85
87
100
91
235
272
127
125
37
23
17
171
125
106
94
Catalyst
Conversion (%)a
GC-yield (%)a
[Pd(PPh3)2Cl2]
“Palladacycle”
[Pd]/SBA-15
[Pd(NH3)4]/NaY
[Pd(II)]/NaY
[Pd(0)]/NaY
[Pd(0)]/SiO2
[Pd]/Al2O3
86
92
74
42
22
17
16
10
11
12
17
85
90
73
42
20
10b
4b
50
27b
13b
71b
57b
63b
88b
[Pd]/AlF3
[Pd]/MgF2
[Pd(0)]/C
5b
[Pd]/AlF3
[Pd]/MgF2
[Pd(0)]/C
4b
Reaction conditions: 5 mmol p-iodoanidale, 8 mmol phenylacetylene,
7b
10 mmol Et3N, 1 mol% [Pd]-catalyst, 80 ◦C, DMF/H2O = 4:1, 6 h.
3b
a
Conversions based on unreacted bromobenzene and yields were deter-
Reaction conditions: 5 mmol bromobenzene, 8 mmol phenylacetylene,
10 mmol Et3N, 1 mol% [Pd]-catalyst, 80 ◦C, DMF/H2O = 4:1, 6 h.
Conversions based on unreacted bromobenzene and yields were deter-
mined by GC with an internal standard (diethylene glycol di-n-butyl ether)
mined by GC with an internal standard (diethylene glycol di-n-butyl ether)
after 1 h reaction time (ꢀrel
= 5%).
a
b
The mass balance between conversions and yields is related to the rela-
tively high formation of anisole.
c
(ꢀrel
= 5%).
Initial rates were determined from the kinetic experiments by tracing the
b
The mass balance between conversions and yields is related to the rela-
tively high formation of benzene.
tangent at t = 0 (see Fig. 3) and account only for the formation of the coupling
product.

P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
47
catalysts showed the highest initial activity (>230 mmol/
gPd × min) as expected for a homogeneous catalyst. The
[Pd(NH3)4]2+/NaY and [Pd]/SBA-15 heterogeneous cata-
lysts led to high initial activity (>125 mmol/gPd × min) and
gave quantitative conversions. As predictable from the lower
palladium dispersion, the [Pd(II)]/NaY catalyst exhibited
a lower initial activity, with only 37 mmol/gPd × min and
the supported Pd(0) catalysts ([Pd(0)]/NaY and Pd(0)/SiO2)
showed the lowest initial activity. However, as was already
observed for C C coupling reactions, the related commer-
cially available Pd(0)/C catalyst gave remarkably good con-
versions. Again, surprisingly, while showing a relatively
high initial activity (>106 mmol/gPd × min), the [Pd]/AlF3,
[Pd]/MgF2 and [Pd]/Al2O3 catalysts, did not give very high
product yields, probably due to a lack of stability of the sup-
ported Pd-species.
After demonstrating the applicability of heterogeneous
copper-free palladium catalysts for the Sonogashira reac-
tion of bromobenzene with phenyl acetylene, the questions
regarding the leaching of active Pd-species in solution and the
recyclability of the heterogeneous catalysts were addressed.
Leaching was examined for the coupling reaction of p-
iodoanisole with phenylacetylene under optimised reaction
conditions (10 mmol p-iodoanisole, 15 mmol phenylacety-
lene, 20 mmol Et3N, 1 mol% [Pd]-catalyst, 80 ◦C, 20 mL
DMF/H2O = 4:1) using the hot-filtration method: a catalytic
run was started as for a standard reaction, and after 10 min
of reaction, corresponding to ca. 55% yield, the reaction
mixture was filtered through a celite pad to afford a clear
filtrate. The composition of the clear filtrate was followed
by GC and compared to that of a standard catalytic run.
We particularly studied the behaviour of [Pd(NH3)4]2+/NaY
and [Pd]/SBA-15 for which a high initial activity was
observed.
Fig. 4. Residual catalytic activity of [Pd(NH3)4]2+/NaY after hot filtration
(ꢀ) after 10 min reaction vs. standard catalytic (᭹) run. Reaction conditions:
10 mmol p-iodoanisole, 15 mmol phenylacetylene, 20 mmol Et3N, 1 mol%
[Pd(NH3)4]2+/NaY, 80 ◦C, 20 mL DMF/H2O (4:1).
of the Pd/C catalyst was linked to dissolved (leached) Pd-
species. They seem to indicate that, in our case, pore confine-
ment (the micro- and meso-environment) may participate to
the stabilisation of the immobilised molecular Pd-complexes,
i.e. the {[Pd(NH3)4]2+} and the {PdCl2(PPh2R)2}fragments,
thus preventing leaching.
The remarkable activity and stability toward leaching of
the [Pd(NH3)4]2+/NaY and [Pd]/SBA-15 catalysts make the
study of their recycling particularly interesting. As both cat-
alysts gave comparable results, the study on [Pd]/SBA-15 is
described, here, in details (see Supporting information for the
[Pd(NH3)4]2+/NaY catalyst).
The recycling was first examined for the coupling reac-
tion of bromobenzene with phenylacetylene under optimised
reaction conditions (5 mmol bromobenzene, 7 mmol pheny-
lacetylene, 10 mmol Et3N, 1 mol% [Pd]/SBA-15, 80 ◦C, 6 h,
10 mL DMF/H2O = 4:1). The method used corresponds to
Some of us previously demonstrated the heterogeneity
of a [Pd(NH3)4]2+/(NH4)Y catalyst in the Heck reaction
[73] and, recently, in the Sonogashira reaction [63]. As
expected, the [Pd(NH3)4]2+/NaY catalyst used in the present
experiments gave very similar results: after hot filtration,
the filtrate exhibited further reactivity with a slow increase
of conversion of ca. 5%, which is interpreted as evidence
of leaching (Fig. 4). However, leaching cannot explain the
overall activity of the [Pd(NH3)4]2+/NaY catalyst for which
a quantitative conversion was obtained after ca. 180 min of
reaction under the same conditions.
Generally, Pd-phosphine complexes grafted onto metal
oxide support are reputed to lead to high leaching. For these
reasons, we studied in detail the leaching of the [Pd]/SBA-15
heterogeneous catalyst. As depicted in Fig. 5, no progres-
sion of the conversion was observed after the hot filtration of
the catalyst indicating that no leaching of active Pd-species
occurred. For all catalysts, including the Pd-supported zeo-
lites, AAS analyses of the clear filtrates gave a palladium
concentration <7 ppm.
Fig. 5. Residual catalytic activity of [Pd]/SBA-15 after hot filtration (ꢀ)
after 10 min reaction vs. standard catalytic (᭹) run. Reaction conditions:
10 mmol p-iodoanisole, 15 mmol phenylacetylene, 20 mmol Et3N, 1 mol%
[Pd]/SBA-15, 80 ◦C, 20 mL DMF/H2O (4:1).
These results are very different from those reported by
Kotschy and co-workers where 80% of the overall activity

48
P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
the following procedure: after the first run of the catalyst, the
reaction mixture was allowed to cool to room temperature and
the catalyst was separated by centrifugation and washed with
DMF/H2O(4:1). Therecycled[Pd]/SBA-15catalystwasthen
used without any regeneration as the fresh catalyst under the
same reaction conditions giving 44, 18 and 17% conversion
of bromobenzene for the first, second and third runs, respec-
tively. These results showed that significant deactivation of
thecatalystoccurredduringthefirstrun, butnotsubsequently.
To confirm that the loss of activity was not due to the filtra-
tion and washing of the catalyst between runs, a second type
of recycling study was performed. For this study, we chose to
use the more reactive substrate, p-iodotoluene. At the com-
pletion of the first run (∼2 h), a fresh portion of substrates
and solvent was added directly to the product/solvent/catalyst
slurry, and the conversion of this fresh substrate into 1-
methyl-4-phenylethynyl-benzene, 3, was followed by GC
over a period of 5 h. This procedure was repeated once. The
initial rate observed for the first run (126 mmol/gPd × min)
falls to a stable much lower activity for the second and third
runs (5.5 mmol/gPd × min, Fig. 6).
Fig. 7. CP-MAS 31P NMR of (a) PdCl2{PPh2-(CH2)2-SiCH3(OCH2
CH3)2}2 grafted on SBA-15; (b) (a) after catalysis in the presence of water;
(c) (a) after catalysis in the absence of water.
catalyst used in the second recycling test protocol (no
separation of products between cycles) was isolated by
filtration, washed with fresh solvent mixture and dried under
vacuum prior to CP-MAS NMR characterisation (Fig. 7b). A
dramatic decrease in the signal of the coordinated phosphine
ligands, in particular the signal associated with the cis-
isomer, was observed with the appearance of a new peak at ␦
40, which would generally be associated with the formation
of a phosphine oxide. The oxidation of phosphine in the
presence of water leading to the very weakly coordinating
phosphine oxide is often cited as a deactivation pathway
for such complexes [90]. Thus, we wished to examine the
activity and stability of the same catalyst under anhydrous
conditions.
The Sonogashira reaction of p-iodotoluene with pheny-
lacetylene was performed as above in dry DMF, but major
catalyst deactivation was observed. The fresh catalyst showed
an initial activity of 57 mmol/gPd × min, somewhat lower
than that seen when using the H2O/DMF solvent mixture.
One should also note the inflection point in the product yield
versus time curve at about 10 min (25% yield, see Supporting
information) which may suggest that the active centers are
encumbered by the build-up of the organic salt biproduct (at
this conversion, 110 mg of salt have been formed, to be com-
pared with the 48 mg of catalyst). In the second and third
runs, the activity maintains relatively constant, much lower
activities of 1.6 mmol/gPd × min and 1.2 mmol/gPd × min,
respectively. The catalyst was then filtered, washed and dried
prior to X-ray and NMR analysis (Fig. 7c). Again, the X-
ray diffractogram showed no significant change due to the
catalytic reaction (see Supporting information), indicating
that the overall structural order material was maintained,
and thus activity loss cannot be attributed to mesostruc-
tural degradation (which might lead to diffusional inhibition).
The fresh catalyst peaks have totally disappeared and a new,
sharper peak at ␦ 21 appeared. We cannot determine exactly
what has occurred, but one might postulate the reduction of
the chelated palladium to a tetrahedral, stable and catalyti-
cally less active species. We cannot exclude the effect of the
In order to explain the observed deactivation, we stud-
ied the fresh and the recycled catalyst by X-ray powder
diffraction and by 31P CP-MAS NMR (Fig. 7). The X-ray
diffractogram of the used catalyst showed no significant
change from the diffractogram of the fresh catalyst, that
is it shows three clear peaks in the 0◦–3◦ (2θ) range (see
Supporting information), indicating that the structural order
of the mesoporous material was not perturbed by the cat-
alytic reaction. The 31P NMR spectrum of the fresh catalyst
(Fig. 7a) exhibited two principle peaks at ␦ 20.7 and 30.9,
which indicates that the phosphine ligands are coordinated to
palladium and can be attributed to the cis- and trans-isomers
of the square planar grafted transition metal complex. The
Fig. 6. Recyclability of [Pd]/SBA-15 for the Sonogashira coupling reaction
of p-iodotoluene with phenylacetylene. Reaction conditions: 10 mmol p-
iodotoluene, 15 mmol phenylacetylene, 20 mmol Et3N, 1 mol% [Pd]/SBA-
15, 80 ◦C, 20 mL DMF/H2O (4:1).

P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
49
precipitation of organic salt as a factor, which may prevent
the diffusion of the reagents to the catalytic species. In any
case, water induced phosphine oxidation is clearly not the
only catalyst deactivation route available.
as those encountered in various natural or synthetic biologi-
cally active molecules.
As reported in Table 3, except for specific reagents like the
propargylic alcohol, the [Pd]/SBA-15 catalyst is generally
more active than the zeolite supported [Pd(NH3)4]2+/NaY
catalyst. This could be reasonably attributed to the larger
aperture of the channels in the SBA-15 material, improv-
ing thus the diffusion of the reagents and products to
and from the active centres. The lack of reactivity of
Regarding the high activity of the [Pd(NH3)4]2+/NaY and
the [Pd]/SBA-15 catalysts in the Sonogashira cross-coupling
reaction, we were interested in evaluating and comparing
their catalytic performances for the synthesis of important
substructure, namely propargylic alcohols, indoles or furans,
Table 3
Sonogashira coupling reaction catalysed by [Pd(NH3)4]2+/NaY or [Pd]/SBA-15 applied to the synthesis of target organic molecules
Substrates
Product
[Pd(NH3)4]2+/NaY
[Pd]/SBA-15
Time [h]
Time [h]
Conversiona [%]
Conversiona [%]
0
6
100(73)
6
–
6
–
24
80 (57)
93
99
2
4
100 (72)
6
6
100 (78)
100 (69)
2
100
3
100 (95)
1
100
24
0
24
100 (99)
24
0
24
100 (76)
Reaction conditions: 5 mmol aryl- or vinyl-halide, 8 mmol alkyne, 10 mmol Et3N, 1 mol% [Pd]-catalyst, 80 ◦C, DMF/H20 (4:1).
a
Conversion were determined by GC with an internal standard (diethylene glycol di-n-butyl ether) (ꢀrel
= 5%). Values in parentheses correspond to isolated
product yields.

50
P. Rollet et al. / Journal of Molecular Catalysis A: Chemical 241 (2005) 39–51
the propargylic alcohol using the [Pd]/SBA-15 catalyst,
compared to the [Pd(NH3)4]2+/NaY, could be related to a
relatively strong adsorption of this reagent at the surface of
the catalyst’s support (specific surface = 520 4 m2/g),
resulting to a deactivation of the catalytic centres,
since the corresponding silated derivative lead to good
conversion.
Acknowledgements
Financial support provided by the Re´gion Rhoˆne-
Alpes, France(contract“NAHMOVCA”number301439201/
E038131747/ENS006) is gratefully acknowledged. WK
gratefully acknowledge the European Community (Marie-
Curie Program, contract number HPMT-2000-00164) for a
research grant (3 months). The authors would also like to
thank Fre´de´ric Lefebvre for his help in the solid state NMR
measurements.
Probably, the most interesting results concern the dif-
ferences observed in the catalytic activities when relatively
large educts are engaged into the reaction. Whereas the
2-bromonaphtalene and the 9-bromoanthracene did not react
when using the [Pd(NH3)4]2+/NaY catalyst due to the rela-
˚
tively small apertures (ø = 7.4 A), they did give a complete
Appendix A. Supplementary data
conversion using the [Pd]/SBA-15. These results are particu-
larly stimulating for developing further these catalysts toward
industrial applications for the fine chemical syntheses.
Supplementary data associated with this article can be
found, in the online version at doi:10.1016/j.molcata.2005.
05.046.
5. Conclusion
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[Pd(NH3)4]2+/NaY) are more active than classical Pd(0)-
based catalysts, probably due to higher dispersion and sta-
bility of the active species.
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