Pd-SAPO-31, an efficient, heterogeneous catalyst for Heck reactions of aryl chlorides

Article abstract of DOI:10.1016/S0040-4039(03)00706-8

Pd-SAPO-31 exhibits high activity for Heck reactions of aryl chlorides. These catalysts with activities superior to most known solid catalysts can be recovered and reused with negligible loss in activity.

Full text of DOI:10.1016/S0040-4039(03)00706-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 3649–3651
Pd-SAPO-31, an efficient, heterogeneous catalyst for Heck
reactions of aryl chlorides
Rajendra Srivastava, N. Venkatathri, D. Srinivas* and Paul Ratnasamy*
Catalysis Division, National Chemical Laboratory, Pune-411 008, India
Received 30 January 2003; revised 3 March 2003; accepted 14 March 2003
Abstract—Pd-SAPO-31 exhibits high activity for Heck reactions of aryl chlorides. These catalysts with activities superior to most
known solid catalysts can be recovered and reused with negligible loss in activity. © 2003 Elsevier Science Ltd. All rights reserved.
Palladium catalyzed CꢀC bond formation (the Heck
In this work we have prepared 3 wt% of Cu, Ni and Pd
containing SAPO-31 materials, characterized them and
studied their catalytic activity in the Heck reactions of
reaction) is one of the most versatile and useful tools in
1
,2
9
modern organic chemistry. The recent applications of
Heck reactions include the manufacture of Novartis’
Prosulfuron™—an agrochemical, octyl-p-methoxycin-
namate—a sun-screen agent, Albemarle’s Naproxen—
an antibiotic and Singulair—an anti-asthma drug. To
minimize the cost of production, efforts are in progress
to (1) replace Pd with less expensive Ni catalysts, (2)
replace aryl bromides and iodides with the cheaper
chlorides, (3) eliminate the use of phosphine ligands, (4)
employ waste-free production methods by using aro-
matic anhydrides as aryl donors, and (5) utilize hetero-
geneous, reusable catalytsts in place of the present
aryl halides. Metal incorporation did not alter the
crystallinity and framework structure of SAPO-31
(XRD). Cu-SAPO-31 (before reduction with hydrogen)
exhibited a weak, broad band at 600–800 nm in the
diffuse reflectance UV–vis spectrum that could be
2
2
assigned to the E (D)“ T spin allowed, Laporte-for-
g
2g
2+
bidden transition of Cu in an octahedral geometry
Fig. 1). An intense band due to a ligand-to-metal
10
(
charge transfer (LMCT) transition was observed at 310
nm. Calcined Ni-SAPO-31 showed characteristic bands
3
3
3
at 410 and 700 nm due to A “ T (P) and A “
2g
1g
11
g
3
homogeneous systems. Metal catalysts on different
3
T (F) transitions, respectively (Fig. 1). Pd-SAPO-31
1g
supports, e.g. carbon, inorganic oxides, molecular
showed a LMCT band at 250–300 nm. This band
disappeared and an increased absorbance in the visible
region was observed when treated with hydrogen indi-
3–6
sieves, polymeric materials etc. have been explored.
Unfortunately, most are efficient for reactions of aryl
iodides and bromides but not for chlorides. We have
found that palladium-containing silico aluminophos-
2+
cating that all the Pd ions had been converted to
12
metallic Pd (Fig. 1). EPR spectroscopy revealed that
7
,8
phate-31 (Pd-SAPO-31) is highly active even for the
reactions of aryl chlorides (Scheme 1).
2
+
the metal ions are highly dispersed. The Cu in Cu-
SAPO (before hydrogen reduction) is characterized by
signals with spin Hamiltonian parameters, g =2.388,
ꢀ
ꢀ
Cu
gÞ=2.088 and A =118.1 G. Ni-SAPO-31 showed a
ꢀꢀ
perpendicular signal at g=2.345 corresponding to a
highly distorted octahedral environment around the
2+
13
Ni ions. Pd-SAPO-31 reduced with hydrogen exhib-
ited a broad signal at g=2.12 characteristic of dispersed
14
metallic Pd.
The Ni and Cu catalysts, as expected, exhibited lower
activity than the Pd catalyst in the Heck reactions.
Complete conversion of iodobenzene in the Heck cou-
pling reaction with methyl acrylate (CꢀC product selec-
tivity :97–98%) was achieved in 1.5 h with a
Pd-SAPO-31 catalyst, DMF solvent and K CO base.
Scheme 1.
*
0
Corresponding authors. Fax: +91-20-589-3761; e-mail: srinivas@
cata.ncl.res.in; prs@ems.ncl.res.in
2
3
040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)00706-8

3
650
R. Sri6asta6a et al. / Tetrahedron Letters 44 (2003) 3649–3651
9
6.7%) was achieved in 24 h with Pd-SAPO-31, while
only 9.8% conversion was observed with the Ni and Cu
catalysts (CꢀC product selectivity=89.7 and 97%,
respectively). Only the Pd catalyst was active for the
reactions of chlorobenzene and its derivatives (Table 1).
The catalysts can be used effectively for the arylation of
a variety of olefins. In the reaction of iodobenzene and
methyl acrylate, the trans-product was predominant
with selectivity greater than 96%. However, with sty-
rene, a-methylstyrene and ethyl cinnamate both the cis-
and trans-products were detected (Table 1, runs 13–15).
Solvent and base markedly influenced the activity of
Pd-SAPO-31 (Table 1). Among the various solvents,
N,N-dimethyl acetamide (DMA) yielded higher
amounts of the CꢀC product. Among the bases, potas-
sium or cesium carbonate were more effective affording
complete conversion of iodobenzene in 1.5 h with 98%
selectivity for the CꢀC product. The reaction is also
more facile in the presence of electron withdrawing
substituents, such as a nitro group (compare runs 4–6).
During the reaction, metal ions leached out of the
support (Fig. 2; Pd was estimated by atomic absorption
spectroscopy). However, when the reaction was com-
plete (beyond 6 h for iodobenzene) the metal ions could
not be detected in the liquid phase indicating that all
the leached Pd was apparently redeposited onto the
SAPO-31 support. Such a phenomenon of Pd leaching
and redeposition has also been observed by others with
Figure 1. Diffuse reflectance UV–vis spectra of Cu/Ni/Pd-
SAPO-31 catalysts.
15
PdꢀC catalysts.
With the Ni and Cu catalysts, however, the reactions
had to be carried out for 24 h. In the case of bromobenz-
ene, about 92% conversion (CꢀC product selectivity=
As a consequence of this redeposition phenomenon, the
Pd-SAPO-31 catalyst could be recovered from the reac-
Table 1. Heck reactions of aryl halides and methyl acrylate over Pd-SAPO-31 at 120°C
Runa Aryl halide
Base
Solvent
Run time (h)
Aryl halide conversion (mol%)
CꢀC product selectivity (mol%)
1
2
3
4
5
Chlorobenzene
Chlorobenzene
Chlorobenzene
Chlorobenzene
NEt3
NEt3
NEt3
NEt3
DMF
NMP
NMP
DMA
DMA
24
24
70
70
70
29.5
32.6
50.3
70.1
77.5
79.9
98.6
94.6
96.7
96.2
o-Nitrochlorobenzen NEt3
e
6
p-Nitrochlorobenzen NEt3
DMA
70
87.9
97.3
e
7
8
9
1
1
1
1
1
1
1
1
1
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Na CO
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
6
1.5
1.5
2
2
2
2
3
3
2
99.8
100
99.8
100
97.9
98.8
98.3
96.8
96.3
97.2
96.8
84.0
76.8
2
3
K CO
2
3
Cs CO
2
3
0
NEt3
NEt3
NEt3
NEt3
NPr3
NBu3
K CO
0a
0b
0c
1
100
98.9
98.3
98.9
99.5
99.2
96.7
99.4
2
b
e
3
93.7 (14/86)
80.0 (36/64)
78.1 (29/71)
2
3
c
e
4
K CO
12
8
2
3
d
e
5
K CO
2
3
a
Runs 10a–10c are the 1st, 2nd and 3rd recycles of run 10. DMF=N,N-dimethyl formamide, NMP=N-methyl-2-pyrrolidinone, DMA=N,N-
dimethyl acetamide.
Styrene was used in place of methyl acrylate.
a-Methyl styrene was used in place of methyl acrylate.
Ethyl cinnamate was used in place of methyl acrylate.
b
c
d
e
Values in parentheses are distributions of cis-/trans-isomers.

R. Sri6asta6a et al. / Tetrahedron Letters 44 (2003) 3649–3651
3651
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dure similar to that reported for VAPO-31 (see reference
8
), using a reactive gel of the following molar composi-
Figure 2. Pd leached into the solution at different reaction
times; Heck reaction of iodobenzene and methyl acrylate over
Pd-SAPO-31.
tion: Al O :P O :1.16 di-n-propylamine (DPA):0.3
SiO :45 H O. The composition of the final product was
Al O : 0.875 P O : 0.25 SiO . SAPO-31 with 3 wt% of Pd
2
3
2
5
2
2
2
3
2
5
2
was prepared by the ion exchange method using an
tion mixture by filtration and recycled without signifi-
cant loss in activity or selectivity for a minimum of
three cycles (Table 1, runs 10a–10c). The Pd-SAPO-31
is a phosphine-free and easy to prepare catalyst. A
comparative study reveals that Pd-SAPO-31 is more
active and efficient than other heterogeneous catalysts.
The reaction takes place in about 1.5 h as compared to
aqueous solution (10 ml) of (NH ) PdCl ·H O (74.46 mg)
3
4
2
2
and SAPO-31 (1 g). The suspension was stirred for 10 h
at 90°C. The solid (Pd-SAPO-31) was calcined at 550°C
for 6 h and then reduced at 400°C under hydrogen flow
for 6 h. Ni-SAPO-31 and Cu-SAPO-31 were prepared in
a similar manner using the nitrate salts of Ni and Cu,
respectively.
4
–14 h with Pd supported on carbon, graphite, MgO
8
9
. Venkatathri, N.; Hegde, S. G.; Sivasanker, S. J. Chem.
Soc., Chem. Commun. 1995, 151.
and Al O (for carbon–iodobenzene/methyl acrylate/
2
3
Na CO ; 150°C; 4 h, yield 70%; for MgO–iodobenzene/
2
3
. The Heck reactions were carried out in a glass, round
bottom flask (25 ml) fitted with a water-cooled condenser.
In a typical reaction, the halobenzene (1 mmol), methyl
acrylate (2 mmol), base (1.5 mmol) and catalyst (4 wt%
with respect to halobenzene) were taken in 5 g of solvent.
The reaction was conducted at 60–120°C under a nitro-
gen atmosphere. The progress and completion of the
reaction was monitored by gas chromatography. The
products were identified by GC–MS.
acrylonitrile/Et N; 140°C; 14 h, yield 78%; for
3
Al O –iodobenzene/acrylonitrile/Et N; 140°C; 14 h,
2
3
3
yield 72% and for graphite–37 wt%; iodobenzene/sty-
3a
rene/K CO ; 100°C; 95 h, yield 82%). The amount of
2
3
supported Pd is also lower in the SAPO-31 catalysts (3
wt%) as compared to carbon, MgO and Al O (5 wt%)
2
3
3
a
and graphite (37 wt%) catalysts. Further, the reaction
for non-activated aryl halides takes place at relatively
lower temperatures (60–120°C) with Pd-SAPO-31 than
3
10. Velu, S.; Wang, L.; Okazaki, M.; Suzuki, K.; Tomura, S.
with the other solid catalyst systems (100–150°C).
Micropor. Mesopor. Mater. 2002, 54, 113.
1
1
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chlorides.
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R.S. acknowledges UGC, New Delhi for the award of a
Junior Research Fellowship.