Anchoring of Pd on silica functionalized with nitrogen containing chelating groups and applications in catalysis

Article abstract of DOI:10.1016/S1381-1169(01)00478-2

Pd-complexes of silica-anchored nitrogen containing chelating compounds were prepared by the following reactions: (a) synthesis of the Schiff-bases from 3-aminopropyltriethoxysilane and 2-acetylpyridine, 2-acetylpyrazine or 2,6-diacetylpyridine; (b) reduction of the Schiff-bases with NaBH₄ in methanol; (c) cogelification with tetraethyl orthosilicate (TEOS); (d) reaction of the obtained functionalized silica with [PdCl₂(PhCN)₂] in CH₂Cl₂. The corresponding model ligands and palladium complexes were also prepared from the reaction of n-propylamine with the pyridine or pyrazine compound, followed by the reduction with NaBH₄ and the reaction with [PdCl₂(PhCN)₂]. The products were characterized by BET, FTIR, GC-MS, ¹H-NMR and elemental C-H-N analysis. The anchored Pd-complexes were tested as catalysts in: (a) the Heck reaction of iodobenzene with ethyl acrylate or styrene in the presence of tributylamine, as base, and toluene or p-xylene, as solvent; (b) the carbonylation reaction of iodobenzene with CO, at atmospheric pressure, in methanol in the presence of triethylamine or potassium acetate, as base. The catalysts were separated from the reaction mixtures and re-used many times. The best results were obtained in both reactions with the anchored Pd-complexes prepared from 2-acetylpyridine: 14 cycles in the Heck reaction (TON ? 4100 mmol product/mmol Pd) and 20 cycles in the carbonylation of iodobenzene (TON ? 2300 mmol product/mmol Pd).

Full text of DOI:10.1016/S1381-1169(01)00478-2

Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
Anchoring of Pd on silica functionalized with nitrogen containing
chelating groups and applications in catalysis
Matteo Lagasi, Pietro Moggi∗
Department of Organic and Industrial Chemistry, University of Parma, Parco Area delle Scienze 17/A, 43100 Parma, Italy
Received 2 July 2001; accepted 22 October 2001
Abstract
Pd-complexes of silica-anchored nitrogen containing chelating compounds were prepared by the following reactions: (a)
synthesisoftheSchiff-basesfrom3-aminopropyltriethoxysilaneand2-acetylpyridine, 2-acetylpyrazineor2,6-diacetylpyridine;
(b) reduction of the Schiff-bases with NaBH4 in methanol; (c) cogelification with tetraethyl orthosilicate (TEOS); (d) reac-
tion of the obtained functionalized silica with [PdCl2(PhCN)2] in CH2Cl2. The corresponding model ligands and palladium
complexes were also prepared from the reaction of n-propylamine with the pyridine or pyrazine compound, followed by the
reduction with NaBH4 and the reaction with [PdCl2(PhCN)2]. The products were characterized by BET, FTIR, GC–MS,
1H-NMR and elemental C–H–N analysis. The anchored Pd-complexes were tested as catalysts in: (a) the Heck reaction of
iodobenzene with ethyl acrylate or styrene in the presence of tributylamine, as base, and toluene or p-xylene, as solvent;
(b) the carbonylation reaction of iodobenzene with CO, at atmospheric pressure, in methanol in the presence of triethy-
lamine or potassium acetate, as base. The catalysts were separated from the reaction mixtures and re-used many times.
The best results were obtained in both reactions with the anchored Pd-complexes prepared from 2-acetylpyridine: 14 cycles
in the Heck reaction (TON ꢀ 4100 mmol product/mmol Pd) and 20 cycles in the carbonylation of iodobenzene (TON ꢀ
2300 mmol product/mmol Pd). © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Silica-anchored palladium; Schiff-bases; Heck arylation; Carbonylation; Methyl benzoate
1. Introduction
acids, aldehydes, esters or amides. The Heck reaction
between aryl halides and alkenes [2,3], or the carbony-
lation of aryl halides with carbon monoxide and al-
cohols [4], are significant examples of carbon–carbon
bond forming reactions, using palladium homo-
geneous catalysts, whose industrial importance is
well-known. The use of palladium metal catalysts in
Heck C–C coupling reactions has been very recently
overviewed [5]. As well as conventional catalysts,
e.g. Pd–C and Pd–Al2O3 [6], palladium dispersed on
MgO [7,8], or supported on other metal oxides and ze-
olites [9,10] has been successfully tested in the Heck
reaction for the arylation of styrene and acrylonitrile.
However, the progressive deactivation as a result of
The use of heterogeneous catalysts for commonly
homogeneously catalyzed organic reactions may help
to resolve some industrially important problems, such
as the recovery of the catalyst from the reaction mix-
ture and its re-use in order to lower production costs.
Palladium-based homogeneous catalysts are very ac-
tive and selective in industrial organic syntheses [1]
to make a wide range of important products like aryl
∗
Corresponding author. Tel.: +39-521-905464;
fax: +39-521-905472.
E-mail address: pietro.moggi@unipr.it (P. Moggi).
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(01)00478-2

62
M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
Table 1
the palladium leaching during the reaction could be
a serious disadvantage for these supported catalysts.
Instead, the anchoring of palladium complexes on
polymers or inorganic substrates could assure a more
lasting catalytic activity. High catalytic activities, se-
lectivities and stabilities have been reported in the
Heck reaction catalyzed by sulfur-containing poly-
meric palladium complexes [11,12], or by amino- and/
or pyridine-functionalized silica-supported palladium
catalysts [13–15]. Polymer-anchored palladium cat-
alysts have also been used in the carbonylation of
organic halides to oxo esters at mild pressure [16].
This paper mainly deals with the preparation and
characterization of palladium complexes anchored
on silica functionalized with chelating nitrogen lig-
ands. These systems have been successfully tested as
many times re-usable catalysts for the Heck reaction
of iodobenzene with ethyl acrylate and styrene, and
for the carbonylation of iodobenzene in methanol to
methyl benzoate at atmospheric pressure.
Reactions of the formation of the Schiff-bases
Carbonyl
compound (CC)
CC
(mmol)
APS
(mmol)
Conversion,
CC (%)
2-Acetylpyridinea
2,6-Diacetylpyridinea
2-Acetylpyrazinea
2-Acetylpyridineb
2,6-Diacetylpyridineb
2-Acetylpyrazineb
25.8
10.0
9.0
13.4
4.9
24.5
20.0
7.2
12.8
10.1
4.2
99
91
71
94
100
99
6.3
a Catalyst: NH3 aq. 0.2 N.
b Catalyst: NH4F.
The reaction (1) was performed under nitrogen in dry
toluene (40 ml) over 3 Å molecular sieves at room tem-
perature for up to 7 days. The amounts of the reagents
are reported in Table 1. The conversion of CH3COX
was monitored by GC. After removal of the molecu-
lar sieves, the products were isolated by evaporation
of toluene at reduced pressure. The formation of the
Schiff-bases was confirmed by FTIR spectroscopy.
2.1.2. Reduction of the Schiff-bases
The Schiff-bases were reduced to secondary amines
by the following reaction:
2. Experimental
2.1. Catalyst preparation
(EtO)3Si(CH2)3N = C(CH3)X + H2
⇒ (EtO)3Si(CH2)3NHCH(CH3)X
(2)
The silica-anchored palladium catalysts were pre-
pared by the following steps:
A suspension of an excess of NaBH4 in methanol
(30 ml) was quickly dropped in a flask containing the
Schiff-base at 40 ◦C, then the mixture was heated in
refluxing methanol until the development of hydrogen
ceased.
(a) synthesis of the Schiff-bases from 3-aminopropy-
ltriethoxysilane (APS) and 2-acetylpyridine, 2-ace-
tylpyrazine or 2,6-diacetylpyridine, respectively;
(b) reduction of the Schiff-bases with NaBH4 in
methanol;
2.1.3. Formation of the functionalized silica gels
(EtO)3Si(CH2)3NHCH(CH3)X was mixed in a
two-necked flask with tetraethoxysilane, Si(OEt)4
(TEOS) in a 1:9 M ratio, then ethanol (25 ml) was
added and an excess of 0.2 N ammonia solution was
dropped into [mmol H2O = 7(4x + 3y), where x =
mmol TEOS and y = mmol (EtO)3Si(CH2)3NHCH
(CH3)X]. The amounts of reagents and catalyst used
are reported in Table 2. The reaction mixture was
stirred for 1 h, then allowed to stand for several hours
until gelation. The gelified product was filtered on
Buchner, then washed with water and ethanol, dried
overnight at 60 ◦C in vacuo, finally crushed and sieved
to >40 mesh.
(c) cogelification with tetraethyl orthosilicate (TEOS);
(d) reaction of the functionalized silica with
[PdCl2(PhCN)2].
2.1.1. Synthesis of the Schiff-bases
Schiff-bases were prepared from APS by the
following reaction:
(1)

M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
63
Table 2
Preparation of the functionalized silica gels
Functionalized gel
Functionalized silane
Silane (mmol)
TEOS (mmol)
Catalyst (ml)
SILPYa
(EtO)3Si(CH2)3NHCH(CH3)pyc
(EtO)3Si(CH2)3NHCH(CH3)pzd
[(EtO)3Si(CH2)3NHCH(CH3)]2pyc
(EtO)3Si(CH2)3NHCH(CH3)pyc
(EtO)3Si(CH2)3NHCH(CH3)pzd
[(EtO)3Si(CH2)3NHCH(CH3)]2pyc
8.4
5.1
9.1
12.0
4.2
4.9
76.2
47.1
81.9
48.0
38.2
43.9
45
27
48
10
10
10
SILPZa
SILDIPYa
SILPYb
SILPZb
SILDIPYb
a Catalyst: NH3 aq. 0.2 N.
b Catalyst: NH4F.
c Pyridine radical.
d Pyrazine radical.
In another way of preparation, after mixing in
a crystallizer (EtO)3Si(CH2)3NHCH(CH3)X with
TEOS in the 1:9 M ratio, ethanol (30 ml) and an
excess of water containing previously dissolved
NH4F in a 1:100 M ratio to the sum (EtO)3Si(CH2)3
NHCH(CH3)X + TEOS were added. Gelation oc-
curred almost immediately. The obtained gel was
allowed to stand for several days in air, then crushed
up to >40 mesh, washed with water and ethanol,
finally dried overnight at 60 ◦C in vacuo.
2.1.4. Preparation of the anchored palladium
complexes
[PdCl2(PhCN)2] was previously prepared, by dis-
solving PdCl2 at 100 ◦C in a minimum amount
of benzonitrile (15 ml PhCN/g PdCl2), then cool-
ing and adding hexane to precipitate the complex.
[PdCl2(PhCN)2] was then isolated by filtering, washed
twice with hexane and pentane, finally dried at 40 ◦C
at moderately reduced pressure.
To prepare the anchored palladium complexes,
[PdCl2(PhCN)2] was dissolved in CH2Cl2 and the
calculated amount of the functionalized silica was
added. The suspension was maintained 4 h under
stirring, then the only physiadsorbed complex was
extracted in a Soxhlet apparatus with refluxing
The three functionalized silica gels prepared
from 2-acetylpyridine (SILPY) (a), 2-acetylpyrazine
(SILPZ) (b) and 2,6-diacetylpyridine (SILDIPY) (c)
have the following structures:

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M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
CH2Cl2 for 3 h. The solid was finally dried overnight
at 50 ◦C in vacuo. The amount of anchored palladium
was determined by the weight increase of the func-
tionalized support.
The reduction was performed by dropping a sus-
pension of NaBH4 in methanol into the flask con-
taining the Schiff-base previously heated at 40 ◦C.
When the development of hydrogen has ceased
the mixture was cooled to room temperature and
water (30 ml) was added to extinguish the reac-
tion. The amine ligands were recovered by adding
few drops of NaOH 0.1 N, then extracting with
CH2Cl2. The organic extract, after evaporation of
the solvent, was analyzed by FTIR, GC–MS and
1H-NMR spectra.
2.1.5. Reduction of palladium to Pd (0)
The functionalized silica-anchored Pd (II) was re-
duced to metal Pd (0) by a suspension of NaBH4
in methanol. The reduction was performed at 40 ◦C,
by dropping the reducing reagent into a flask con-
taining an amount of the anchored complex corre-
sponding to 0.015 g of palladium suspended in 10 ml
of methanol. When the development of hydrogen has
ceased, few milliliters of water were added to extin-
guish the reaction. The black reduced catalyst was then
filtered, washed with water, methanol and CH2Cl2, fi-
nally dried under nitrogen at 40 ◦C at reduced pressure.
(c) Reaction of the amine bidentate ligand, L, with
[PdCl2(PhCN)2], under stirring, in a minimum
amount of CH2Cl2. The exchange reaction (3):
L + [PdCl2(PhCN)2] ⇒ LPdCl2 + 2PhCN
(3)
occurred almost immediately and gave rise to the
precipitation of the palladium complex, which was
recovered by filtering, washed with CH2Cl2, hex-
ane and pentane, finally dried overnight at 50 ◦C
in vacuo. The model palladium complexes were
characterized by FTIR, 1H-NMR and elemental
C–H–N analysis.
2.2. Preparation of the model ligands
and palladium complexes
The model ligands and palladium complexes were
prepared by the following reaction steps:
(a) Preparation of the Schiff-bases from the reaction of
n-propylamine with the pyridine or pyrazine com-
pound, e.g. for 2-acetylpyridine:
2.3. Reaction tests
The catalytic activity of the prepared silica-anchored
palladium complexes has been tested for:
The reaction was performed under nitrogen with an
excess of amine in dry toluene over 3 Å molecular
sieves at room temperature for up to 7 days. The
conversion of carbonyl compound was monitored
by GC. After removal of the molecular sieves, the
products were isolated by evaporation of unreacted
amine and toluene at reduced pressure. The for-
mation of the Schiff-bases was confirmed by FTIR
spectroscopy.
(a) The Heck reaction from iodobenzene and ethyl
acrylate to ethyl cinnamate, or styrene to stilbene,
in toluene or p-xylene as solvent, with tributy-
lamine as base, for 2 h at 110 ◦C, e.g.:
(b) Reduction of the Schiff-bases to secondary
amines with NaBH4, e.g. for the ligand with
2-acetylpyridine (LIPY):
An amount of catalyst corresponding to 0.015 g Pd
was always used. At the end of the reaction the cat-
alysts were separated from the reaction mixture by
filtration at about 30 ◦C, washed with the reaction

M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
65
solvent and re-used. The filtered liquid was then
cooled in an ice-bath to precipitate the ammonium
salt (Bu)3NHI. After a second filtration the conver-
sions of reagents and the selectivities to products
were determined by GC analyses by adding iso-
propylbenzene as internal standard.
instrument, equipped with a SE-52 packed column,
and interfaced with a MS quadrupole HP 5971 ana-
lyzer. The GC analyses of the reaction products were
performed with a DANI 3400 instrument equipped
with a thermal conductivity detector. As packed
columns the following were used: 2 m 20% Apiezon
L on Chromosorb W-DMCS 100/120 mesh, for the
arylation of ethyl acrylate; 1 m 10% SE-30 on Chro-
mosorb W-AW 80/100 mesh, for the arylation of
styrene; 2 m 20% OV 101 on Chromosorb W-DMCS
60/80 mesh, for the carbonylation of iodobenzene. He
(80 ml/min) as carrier gas was always used. Elemental
C–H–N analyses were performed with a Carlo Erba
EA 1108 analyzer, based on GC separation.
(b) The carbonylation reaction at atmospheric pres-
sure of iodobenzene by bubbling CO, in refluxing
methanol for 8 h, with triethylamine or CH3COOK
as base, to methyl benzoate:
An amount of catalyst corresponding to 0.015 g Pd
was always used. At the end of the reaction the cat-
alysts were separated from the reaction mixture by
filtration and re-used many times. The conversions
of reagents and the selectivities to the product were
determined by GC analyses, by adding isopropyl-
benzene as internal standard.
3. Results and discussion
3.1. Preparation of the Schiff-bases
and amine ligands
The conversions of the carbonyl compounds are
given in Table 1. The condensation reactions with
APS were almost complete. The formation of the
Schiff-bases was demonstrated by the presence in
the FTIR spectra of the absorption peak at about
2.4. Characterization of products
The specific surface area of the functionalized silica
gels was determined with a Micromeritics 2200 ana-
lyzer, by the one-point modified BET method, from
the nitrogen volume adsorbed at the liquid nitrogen
temperature.
1640 cm−1, due to the C N imine double bond, and
=
=
the reduced intensity of the C O absorption peak at
1700 cm−1
.
To prepare the model ligands an excess of
n-propylamine in the preparation of the Schiff-bases
was always used; therefore, the conversion of car-
bonyl compounds was complete. After reduction with
NaBH4 in methanol, the model ligands were char-
FTIR spectra were measured with a Nicolet 5PC
1
spectrometer. H-NMR spectra were recorded with a
Bruker AC 100 spectrometer by using CDCl3 as dilu-
ent for the liquid samples and deuterated DMSO as
solvent for the solid ones.
1
acterized by GC–MS analyses, FTIR and H-NMR
GC–MS analyses of samples, diluted with an ex-
cess of CH2Cl2, were performed with an HP 5890
spectra. The GC–MS analyses evidenced the absence
of by-products.
Table 3
Elemental analyses of the functionalized silica gels
Functionalized silica
C/N ratioa
Elemental analysisa (%)
C
N
H
SILPY
SILPZ
SILDIPY
4.3 (4.3)
2.6 (2.8)
4.4 (4.0)
16.14 (15.90)
8.40 (14.30)
11.41 (17.00)
3.72 (3.71)
3.24 (5.49)
2.58 (3.99)
4.33 (4.28)
2.10 (2.79)
2.56 (2.90)
a Theoretical values in brackets.

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M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
Table 4
Surface area values and anchored palladium amounts on the func-
tionalized silica gels
Functionalized
silica
Surface
area (m2/g)
mmol
Pd/g gel
Pd (%)
SILPYa
335.5
270.0
365.4
18.0
75.4
54.2
0.99
0.72
0.50
0.79
0.65
0.56
9.5
6.8
4.9
7.4
6.2
6.0
SILDIPYa
SILPZa
SILPYb
SILDIPYb
SILPZb
a Catalyst: NH3 aq. 0.2 N.
b Catalyst: NH4F.
gels. Moreover, the formation of soluble oligomers in
sol–gel processes is known from the literature [17].
In Fig. 1 a comparison is made between the
FTIR spectra of the functionalized silica gel SILPY
and the corresponding model ligand in the range
1800–1300 cm−1, where the absorption peaks of aro-
matic C–H and N–H bonds are present. Even though
the intensity of peaks is weakened by the lower con-
centration of the functionalizing groups on silica,
there are at least four absorption peaks in perfect
agreement.
The surface area values of the functionalized silica
gels are reported in Table 4. The use of ammonia
instead of ammonium fluoride as gelification catalyst,
then a slower progress of the gelification process,
clearly produced higher surfaces.
Fig. 1. FTIR spectra in the region 1800–1300 cm−1: (a) function-
alized silica gel prepared from 2-acetylpyridine (SILPY: peaks at
1599, 1574, 1485 and 1444 cm−1); (b) corresponding model lig-
and (LIPY: peaks at 1590, 1571, 1471 and 1435 cm−1).
3.3. Preparation of anchored palladium complexes
The anchored palladium amounts from the com-
plexation reactions of the functionalized silica gels
with [PdCl2(PhCN)2] are reported in the last two
columns of Table 4. The highest amounts were ob-
tained with the functionalized silica gel SILPY. The
formation of the complex is evidenced, both in the
FTIR spectrum of the functionalized silica SILPY
(Fig. 2a) and of the model ligand (Fig. 2b) from a
20 cm−1 shift to lower wavenumbers of the 1600 cm−1
peak.
3.2. Preparation of the functionalized silica gels
The elemental analyses of the functionalized sil-
ica gels prepared with aqueous ammonia as catalyst
(Table 3) were according to the theoretical values
only in the case of the product from 2-acetylpyridine
(SILPY). It is evident, for the other products, a C/N
ratio near to the theoretical one, but in the presence
of a silica excess, with a SiO2/SiO3/2(CH2)3NHCHX
ratio higher than 9:1. There was a lower concentra-
tion of functionalizing groups in the recovered prod-
uct because soluble oligomers probably formed in the
hydrolysis and condensation steps, which remained in
solution after washing and filtering the functionalized
3.4. Catalytic activity tests
The catalytic activity of all prepared anchored pal-
ladium complexes in the arylation reaction of ethyl
acrylate was studied. The best proven catalyst was

M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
67
Fig. 2. FTIR spectra in the region 1800–1300 cm−1 of the palladium complexes prepared from: (a) the functionalized silica gel prepared
from 2-acetylpyridine (SILPY: peaks at 1618 and 1483 cm−1); (b) the corresponding model ligand (LIPY: peaks at 1615 and 1492 cm−1).
then tested for the arylation of styrene and the car-
bonylation of iodobenzene in methanol. A molar ratio
of iodobenzene/palladium about 350:1, corresponding
to about 0.2 g of anchored palladium complex, was
always used.
3.4.1. Heck reaction: arylation of ethyl acrylate
In
(10.8 g
a
typical reaction test, iodobenzene
51.6 mmol), ethyl acrylate (6.4 g
=
=
64.2 mmol), tributylamine (10.1 g = 54.3 mmol),
catalyst (0.2 g ꢀ 0.015 g Pd ꢀ 0.15 mmol Pd)

68
M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
Fig. 3. Catalytic activity tests in the arylation of ethyl acrylate (toluene as solvent). Reaction time is 2 h: (a) conversion of iodobenzene;
(b) net production of ethyl cinnamate (TON, mmol product/mmol Pd).
and solvent (20 ml of toluene, or p-xylene) were
used.
Anchored palladium complexes were generally
more active and more stable than the commercial
Pd/C catalyst, probably due to the higher dispersion
of the metal and the better resistance to leaching by
the reaction solution. A better stability was observed
in refluxing toluene as solvent, probably due to the
lower reaction temperature, which also allowed a bet-
ter control of temperature, then a less easy leaching.
The results of the catalytic activity tests, both ex-
pressed as conversion of iodobenzene and net produc-
tion of ethyl cinnamate (TON, mmol product/mmol Pd)
are reported in Fig. 3 (toluene, as solvent) and Fig. 4
(p-xylene, as solvent), respectively. A commercial 5%
Pd/C (Fluka) catalyst as comparison was tested.

M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
69
Fig. 4. Catalytic activity tests in the arylation of ethyl acrylate (p-xylene as solvent). Reaction time is 2 h: (a) conversion of iodobenzene;
(b) net production of ethyl cinnamate (TON, mmol product/mmol Pd).

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M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
Fig. 5. Catalytic activity tests in the arylation of styrene: conversion of iodobenzene and net production of stilbenes (TON,
mmol products/mmol Pd). Reaction time is 2 h, catalyst used is SILPY·Pd.
Fourteen reaction cycles before deactivation were
performed with SILPY·Pd catalyst, prepared from
SILPY·PdCl2, corresponding to a calculated TON
(mmol ethyl cinnamate/mmol Pd) of about 4100.
Therefore, SILPY·Pd catalyst was selected for testing
in the arylation reaction of styrene to stilbene and
in the carbonylation reaction of iodobenzene with
methanol to methyl benzoate.
trans-stilbene/cis-stilbene ratio was always higher
than 8:1. The conversion of iodobenzene was lower
than in the arylation of ethyl acrylate, due to the ster-
ical hindrance of the styrene molecule, which slows
down the reaction. A double length test (reaction
time = 4 h) actually gave a very higher conversion
(89%) of iodobenzene with a 97% selectivity to stil-
benes.
3.4.2. Heck reaction: arylation of styrene
3.4.3. Carbonylation of iodobenzene
In a typical reaction test, iodobenzene (10.8 g =
51.6 mmol), styrene (6.4 g = 60.5 mmol), tributy-
lamine (10.1 g = 54.3 mmol), catalyst (0.2 g SILPY Pd
ꢀ 0.015 g Pd ꢀ 0.15 mmol Pd) and toluene (20 ml)
as solvent were used.
The results of the catalytic activity tests, both
expressed as conversion of iodobenzene and net pro-
duction of stilbenes (TON, mmol product/mmol Pd)
are reported in Fig. 5. The catalytic activity prac-
tically kept constant during 10 reaction cycles and
the selectivity to stilbenes was always much higher
than 90%. The TON value (mmol stilbenes/mmol Pd)
achieved about 2000 after the 10th test. The
In a typical reaction test, iodobenzene (8.2 g =
39.4 mmol), triethylamine (4.1 g = 40.9 mmol) or
potassium acetate (4.6 g = 46.8 mmol) as base, cata-
lyst (0.2 g SILPY · Pd ꢀ 0.015 g Pd ꢀ 0.15 mmol Pd)
and methanol (30 ml) as reagent and solvent were
used. The reaction tests were performed at 70 ◦C and
atmospheric pressure under flowing CO for 8 h.
The results of the catalytic activity tests, both ex-
pressed as conversion of iodobenzene and net produc-
tion of methyl benzoate (TON, mmol product/mmol Pd)
are reported in Fig. 6. Using triethylamine, rather
than potassium acetate, as base promoter, it was pos-
sible to perform 20 reaction cycles with a quite high

M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
71
Fig. 6. Catalytic activity tests in the carbonylation of iodobenzene in methanol to methyl benzoate. Reaction time is 8 h, catalyst used is
SILPY·Pd: (a) conversion of iodobenzene; (b) net production of methyl benzoate (TON, mmol product/mmol Pd).

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M. Lagasi, P. Moggi / Journal of Molecular Catalysis A: Chemical 182–183 (2002) 61–72
conversion of iodobenzene and a very high selectivity
to methyl benzoate. The TON value (mmol methyl
benzoate/mmol Pd) achieved about 2300 after the 20th
test. A last test was performed with a higher reaction
time (15 h): a 83% conversion of iodobenzene with a
97% selectivity to methyl benzoate was measured, so
proving that the catalyst was still active.
Acknowledgements
This research was supported by MIUR (Cofin 1998
and Cofin 2000: “Metal clusters, basic and functional
aspects”). The authors are grateful to Mr. P.A. Bonaldi
for his technical assistance to GC analyses.
References
4. Conclusions
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