Heck Reaction over Pd-Loaded ETS-10 Molecular Sieve

Article abstract of DOI:10.1246/bcsj.76.1989

ETS-10 molecular sieve has been used as a catalyst in the shape-selective photo catalytic decomposition of aromatic molecules, Aldol-type condensations, aniline oxidation, acylation reactions, and alcohol dehydrogenation. The carbon-carbon coupling of different aryl halides with ethyl acrylate over Pd-loaded ETS-10 was presented. The influences of the Pd content, nature of the base and reactivity of the different substrates and reactants on the coupling reaction were presented. The catalyst exhibited high activity and selectivity towards the carbon-carbon coupling of aryl halides with olefins, even at low concentrations of palladium (0.009 to 1.4 mole % with respect to the substrate). In the case of the coupling of ethyl acrylate with iodobenzene, 96% conversion of iodobenzene with > 98% selectivity could be obtained within 1 hr over a 0.2 wt % Pd-loaded catalyst. The catalyst activated aryl bromide and chloride substrates, and was heterogeneous. Aryl bromide, chloride and their derivatives exhibited moderate activity with ethyl acrylates. Organic bases led to higher catalytic activity than inorganic bases. The catalysts could be reused and reactivated by washing with a moderate decrease in activity. The substrate reactivity increased with electron-withdrawing substituents.

Full text of DOI:10.1246/bcsj.76.1989

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 1989–1992 (2003) 1989
Heck Reaction over Pd-Loaded ETS-10 Molecular Sieve
#
Suresh Babasaheb Waghmode, Smita Girish Wagholikar,and Subramanian Sivasanker
ꢀ;
Catalysis Division, National Chemical Laboratory, Pune-411 008, India
Received April 4, 2003; E-mail: suresh ncl@yahoo.com
Apalladium-loaded ETS-10 molecular sieve has been used as a catalyst in Heck reaction. The catalyst exhibits
high activity and selectivity towards the carbon–carbon coupling of aryl halides with olefins, even at low concentrations
of Pd (0.009 to 1.4 mol% with respect to the substrate). In the case of the coupling of ethyl acrylate with iodobenzene,
96% conversion of iodobenzene with greater than 98% selectivity could be obtained within 1 h over a 0.2 wt % Pd-
loaded catalyst. The catalyst activates aryl bromide and chloride substrates, and appears to be heterogeneous. The
reaction has been investigated with different alkyl halides, olefins and bases.
abled loading of the required amount of Pd. The Pd is expected to
be partly exchanged and partly deposited. Pd-loaded samples
were dried at 110 ꢁC (6 h), calcined at 400 ꢁC (6 h) in air, reduced
at 350 ꢁC in H2 for 6 h and stored under nitrogen. Though metal
dispersion was not measured on the samples, based on one earlier
our study concerning similarly prepared Pt-ETS-10 samples,20 the
dispersions are expected to be moderate in the range of 0.5–0.8 for
samples containing 0.2–2% Pd. The ETS-10 molecular sieve used
The palladium catalyzed carbon–carbon bond forming reac-
tion of aryl halides with olefins (the Heck reaction) in a single
step has become an excellent tool for the synthesis of numer-
ous styrene derivatives due to its tolerance for a wide variety
of functional groups on both reactants.1 The use of homoge-
neous Pd catalysts to promote this reaction is well
established.1,2 For economic reasons, industrial applications
of homogeneous Heck reactions are limited.3 In order to over-
come the problems arising from the separation, recovery and
reuse of Pd complexes, a variety of heterogeneous catalysts
have been developed for the Heck reaction.4–6 These include
Pd supported on carbon, different metal oxides,7,8 clays, meso-
porous silica, zeolites9,10 and Pd nanoparticles.11 The use of
Cu, Ni, Co, and Mn heterogeneous catalysts for Heck reactions
is also known.12 However, only a few reports are available on
the use of metal supported basic catalysts for the Heck reac-
tion.10,13
ETS-10 molecular sieve has been used as a catalyst in the
shape-selective photo catalytic decomposition of aromatic
molecules,14 Aldol-type condensations,15 aniline oxidation,16
acylation reactions17 and alcohol dehydrogenation.18 The car-
bon–carbon coupling of different aryl halides with ethyl acry-
late over Pd-loaded ETS-10 is reported in this paper. The in-
fluences of the Pd content, nature of the base and reactivity of
the different substrates and reactants on the coupling reaction
are presented.
in this study had the chemical composition [Na16:60K14:40
-
(Ti16:21Si79:74O208)] (by atomic absorption spectroscopy) and a
N2 adsorption surface area of 460 m2/g.
Reaction Procedure. The reactions were carried out in the
liquid phase in a 50 mL two neck round-bottomed flask fitted with
a reflux condenser. The flask was charged with the substrate (1
mmol), olefin (5 mmol), base (typically, tributylamine (TBA); 2
mmol), solvent (dimethylformamide (DMF); 5 g) and the catalyst
(0.025 g), and placed in an oil bath kept at 130 ꢁC. The progress of
the reaction was monitored by a gas chromatograph (Varian CX)
using a capillary column, CP Sil 5CB, (i.d. 0.53 mm and 30 m
long). Conversions were calculated on the basis of the substrate
(aryl halide).
Results and Discussion
ETS-10 is a large pore titanosilicate molecular sieve, first
synthesized at Engelhard.21 The framework structure of
ETS-10 consists of corner shared oxygen ions of [TiO6]2ꢂ oc-
tahedra and [SiO4] tetrahedra. ETS-10 possesses a three-di-
mensional pore system made up of 12-membered ring (12-
Experimental
ꢀ
MR) channels with a pore diameter of 7.6 A.
Preparation of Pd-ETS-10. The hydrothermal synthesis of
ETS-10 using TiCl4 was carried out following a published proce-
dure19 with a gel of molar composition: 3.70 Na2O:0.95 K2O:1.0
TiO2:5.70 SiO2:171 H2O. After crystallization, the product was
filtered, washed, dried at 110 ꢁC for 10 h and calcined at 450
ꢁC in dry air for 6 h. Pd (0.2 to 6 wt %) was loaded on the molec-
ular sieve using a solution of [Pd(NH3)4]Cl2 at 80 ꢁC. The proce-
dure involved the stirring of ETS-10 powder with a solution of the
salt (10 mL/g of ETS-10) at 80 ꢁC for 2 h, and then slowly evap-
orating the mixture on a water bath to dryness. This procedure en-
Pd-loaded ETS-10 samples with different Pd contents (0.2
to 6 wt %) were used in the studies. The reaction of iodoben-
zene with ethyl acrylate was chosen as the model reaction to
test the catalytic activity of different samples. The catalytic
activities of different Pd-ETS-10 samples are plotted as a func-
tion of the duration of the run in Fig. 1. The general observa-
tion is that the catalytic activity increases with increasing Pd
loading. The selectivity for Heck products was >98% over
all the catalysts.
The results of studies on the coupling of ethyl acrylate and
iodobenzene carried out over 1 wt % Pd-ETS-10 are presented
in Table 1. Aconversion of about 97% was obtained in about
# Present address: Department of Materials Science and Technol-
ogy, Gifu University, Gifu 501-1193
Published on the web October 15, 2003; DOI 10.1246/bcsj.76.1989

1990 Bull. Chem. Soc. Jpn., 76, No. 10 (2003)
Heck Reaction over Pd-ETS-10 Molecular Sieve
of the clear filtrate was determined by GC. This homogeneous
reaction mixture was heated at 130 ꢁC, and the progress of the
reaction was monitored by GC by following the iodobenzene
conversion. Conversions of 8.1% and 14.6% were observed
in the case of 0.2% and 1 wt % Pd catalysts, after 2 h
(Table 1; entries 7 and 3). Asimilar experiment was conduct-
ed with 1-bromo-4-nitrobenzene, and no conversion was ob-
served in the homogeneous reaction mixture (Table 1; entry
9). The conclusion of these leaching experiments is that some
leaching of Pd occurs in iodobenzene and not in 1-bromo-4-ni-
trobenzene, and the leached Pd is less active than the heteroge-
neous Pd (in ETS-10).
The Heck reaction was also carried out using the Pd salts,
[(NH3)4Pd]Cl2 H2O and Pd(OAc)2. In these experiments,
ꢃ
Fig. 1. Conversion of the substrate over different Pd-ETS-
10 molecular sieves (Reaction conditions: catalyst = 25
mg, temperature = 130 C, substrate = 1 mmol iodoben-
zene, reactant = 5 mmol ethyl acrylate, base = 2 mmol
TBA, and solvent = 5 g DMF).
the amount of Pd used was equivalent to the Pd present when
1 wt % Pd-ETS-10 was used as the catalyst. These complexes
were less active compared to the (1 wt %) Pd-loaded ETS-10
(Table 1). Pd-ETS-10 catalyst is phosphine free, and easy to
prepare compare to homogeneous catalysts. Acomparison
of the results of the present study with those published in the
literature concerning Pd supported over other supports reveals
that Pd-ETS-10 is more active and efficient than the other
catalysts. The reaction takes place in about 1 h over ETS-
10, as compared to 2–14 h over Pd supported on Al2O3,
MOR and SAPO-31 (over Al2O3–iodobenzene/acrylonitrile/
ꢁ
0.75 h of run duration. The catalyst was found to be recyclable
without any loss of activity, the TOF values being 549 for a
fresh catalyst and 572 after one recycle (Table 1; entries 1
and 2). Experiments carried out on the 0.2 wt % Pd catalyst
are also reported in Table 1 (entry 4). The catalyst is quite ac-
tive in spite of the low (0.2 wt %) Pd-loading; a TOF of about
10000 was achieved when 5 mmol of iodobenzene was used
(Table 1; entry 5). The 0.2 wt % catalyst is also recyclable
(Table 1; entry 6).
ꢁ
Et3N, 140 C, 14 h: yield = 72%; over Pd-MOR and SAPO-
31–iodobenzene/Bun N, 130 ꢁC, 2 h: conversion = 97%; with
3
promoter Bun Br (0.413 mmol) and Pd-SAPO-31–iodoben-
4
ꢁ
Leaching studies were carried out to verify the heterogene-
ous nature of the reaction. The tests were performed on both
0.2 and 1 wt % Pd catalysts (Table 1; entries 7 and 3). As the
zene/Bun N, 120 C, 3 h: conversion = 99.5%). The amount
3
of supported Pd is also lower in the Pd-ETS-10 catalysts (0.2
wt %), as compared to published reports, e.g. Al2O3 (5 wt %),
MOR (4 wt %) and SAPO-31 (3 wt %).23
ꢁ
catalysts were reduced in H2 at 350 C, the Pd is expected to
be present mainly as the Pd0 species, which are not soluble in
organic solvents. However, Pd0 may slowly react with a polar
solvent (DMF) and/or an organic base, and form complexes
that can be leached into the solution, as reported by Arai and
others.22
The influence of different bases on the conversion and selec-
tivity was investigated (Table 2). The reaction was faster
when tributylamine and triethylamine were used in the case
of both iodobenzene and 1-bromo-4-nitrobenzene (Table 2).
The reactivities of different olefins (different acrylates and sty-
rene) are compared in Table 3. Ethyl acrylate is found to be
the most reactive and selective among the acrylates (96.5%
in 0.75 h). The reactivities of the acrylates are in the order, eth-
yl acrylate > t-butyl acrylate > methyl acrylate > butyl meth-
In a typical leaching experiment, the catalyst was refluxed
ꢁ
with iodobenzene at 130 C for 15 min, and separated from
the organic layer by centrifuging under hot condition. Ethyl
acrylate was then added to the organic layer. The composition
Table 1. Studies on Heck Reaction Using Pd-ETS-10 and Pd-salts
No.
Substrate
CatalystaÞ
TOS/h
Sel./%
Conv./%
TOFbÞ
PdcÞ=ꢄ10ꢂ3
g
1
2
3
4
5
6
7
8
9
Iodobenzene
IodobenzenedÞ
Pd-ETS-10 (1.0)
Pd-ETS-10 (1.0)
Pd-ETS-10 (1.0)
Pd-ETS-10 (0.2)
Pd-ETS-10 (0.2)
Pd-ETS-10 (0.2)
Pd-ETS-10 (0.2)
Pd-ETS-10 (1.0)
Pd-ETS-10 (1.0)
[(NH3)4Pd]Cl2 (1.0)
Pd(OAc)2 (1.0)
0.75
0.75
2.00
1.00
1.00
1.00
2.00
9.00
6.00
6.00
6.00
98.2
99.1
99.2
98.0
99.1
98.3
98.2
100
96.7
95.9
14.6
95.7
95.7
92.1
8.1
84.3
—
16.1
6.9
549
572
170
2037
10023
9799
287
40
0.250
0.240
0.012
0.050
0.050
0.050
0.001
0.250
0.001
0.250
0.250
IodobenzeneeÞ
Iodobenzene
IodobenzenefÞ
Iodobenzened,fÞ
IodobenzeneeÞ
1-Bromo-4-nitrobenzene
1-Bromo-4-nitrobenzeneeÞ
Iodobenzene
—
72.7
69.0
—
11
5
11
12
Iodobenzene
Reaction conditions: catalyst = 0.025 g; temperature = 130 ꢁC; substrate = 1 mmol iodobenzene; reactant = 5 mmol
ethyl acrylate; base = 2 mmol tributylamine (TBA); solvent = 5 g dimethylformamide (DMF). a) wt % of Pd in the
catalyst is given in brackets. b) TOF = [(mole of iodobenzene converted/mole of Pd)/h]. c) Pd present in the reaction
mixture, in catalyst/in solution. d) First recycle. e) Leaching test. f) 5 mmol iodobenzene, 25 mmol TBA, 20 g DMF.

S. B. Waghmode et al.
Bull. Chem. Soc. Jpn., 76, No. 10 (2003) 1991
Table 2. Influence of Different Bases on the Catalytic
Activity of Pd-ETS-10
aryl chloride derivative (Table 4; entries 4, 5 and 6). The re-
activities of different halobenzenes are in the following order:
iodobenzene > bromobenzene > chlorobenzene (Table 4). In
the case of 1-halo-4-nitrobenzenes, the conversion and selec-
tivity decrease in the following order: 1-iodo-4-nitrobenzene
> 1-bromo-4-nitrobenzene > 1-chloro-4-nitrobenzene. In
general, it is noticed that electron-withdrawing substituents in-
crease the conversion.
The mechanism of the Heck vinylation of iodobenzene with
supported palladium catalyst in a polar solvent (NMP) and an
organic base (Et3N) or Na2CO3 bases has been proposed.24 As
the first step, palladium complexes are formed by coordination
with the polar solvent and/or the organic base, and these are
the catalytically active species. The superior activity of Pd-
ETS-10 could be a result of the support influencing the elec-
tronic property of the Pd metal enhancing its ability to coordi-
nate with the basic ligand, and probably also to form a more
active surface complex. It is also likely that the support, itself,
acts as a basic ligand, making the supported Pd metal very ac-
tive.
No.
Base
TOS
/h
Sel.
/%
Others
/%
Conv.
/%
1
2
3
4
5
6
Triethylamine
Tributylamine
K2CO3
1.00
0.75
2.00
12.00
12.00
9.00
100
98.2
100
97.3
100
98.1
—
1.8
—
2.7
—
95.3
96.7
96.7
77.2
24.5
84.3
NaOAc
K2CO3
aÞ
TriethylamineaÞ
1.9
Reaction conditions: catalyst = 0.025 g (1 wt % Pd); temper-
ature = 130 ꢁC; substrate = 1 mmol iodobenzene; reactant =
5 mmol ethyl acrylate; base = 2 mmol TBA; solvent = 5 g
DMF. a) 1-Bromo-4-nitrobenzene.
Table 3. Reactivities of Different Olefins in the Heck
Reaction Catalyzed by Pd-ETS-10
No.
Olefin
TOS
/h
Sel.
/%
Others Conv.
/%
/%
1
2
3
4
5
6
Methyl acrylate
Ethyl acrylate
1.50 100
0.75 98.2
Methyl methacrylate 2.00 100
—
1.8
—
23.5
—
99.7
96.7
95.2
77.5
100
96.7
Conclusions
Pd-ETS-10 (reduced in H2) exhibits a high activity towards
the Heck coupling of aryl iodides with acrylates under the typ-
ical reaction conditions. ATON value of ꢅ10000 is achieved
for a 0.2 wt % Pd-ETS-10 catalyst for iodobenzene. Though a
small amount of Pd leaches out into solution when iodoben-
zene is used as the substrate and DMF as a solvent, the reaction
is found to proceed mainly by a heterogeneous route. When 1-
bromo-4-nitrobenzene is used as the substrate, the reaction is
totally heterogeneous. Aryl bromide, chloride and their deriv-
atives exhibit moderate activity with ethyl acrylates. Organic
bases lead to higher catalytic activity than inorganic bases.
The catalysts can be reused and reactivated by washing with
a moderate decrease in activity. The substrate reactivity in-
creases with electron-withdrawing substituents.
Butyl methacrylate
t-Butyl acrylate
StyreneaÞ
2.00
1.00 100
3.00 80.2
76.5
19.8
Reaction conditions: catalyst = 0.025 g (1 wt % Pd); temper-
ature = 130 ꢁC; substrate = 1 mmol iodobenzene; reactant =
5 mmol ethyl acrylate; base = 2 mmol TBA; solvent = 5 g
DMF. a) 2 mmol iodobenzene used.
acrylate > methyl methacrylate. Styrene is also quite reactive
(conv. = 96.7% and sel. = 80.2%).
Another important issue concerning a heterogeneously cata-
lyzed Heck reaction is the possibility to activate the industrial-
ly more interesting aryl bromides and chlorides. Acomparison
of the reactivities of different halobenzenes is presented in
Table 4. As expected, the results reported in Table 4 (entries
1, 2 and 3) show that aryl chloride is less active than aryl bro-
mide and aryl iodide. Asimilar trend is also observed for the
SBW and SGW thank CSIR, New Delhi, for senior research
fellowship and Prof. Y. Sugi for discussion.
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Table 4. Reactivities of Different Substrates in the Heck
Reaction Catalyzed by Pd-ETS-10
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acrylate; base = 2 mmol TBA; solvent = 5 g DMF.

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