Layered double hydroxide-supported nanopalladium: An efficient and reusable catalyst for Suzuki coupling of aryl iodides and bromides at room temperature

Article abstract of DOI:10.1055/s-2006-932478

Layered double hydroxide-supported nanopalladium (LDH-Pd⁰) is an effective catalyst for Suzuki cross-coupling of a wide range of aryl iodides and bromides with arylboronic acids at room temperature. The catalyst is reused for four cycles with consistent activity. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-932478

LETTER
633
Layered Double Hydroxide-Supported Nanopalladium: An Efficient and
Reusable Catalyst for Suzuki Coupling of Aryl Iodides and Bromides at Room
Temperature
L
M
ayered
D
ouble-Hydro
.
xide-Suppor
L
ted
N
anopallad
a
ium kshmi Kantam,* M. S. Subhas, Sarabindu Roy, Moumita Roy
Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad-500007, India
Fax +91(40)27160921; E-mail: lkmannepalli@yahoo.com
Received 25 July 2005
product even after 24 hours. Then we performed the same
Abstract: Layered double hydroxide-supported nanopalladium
0
reaction with different combinations of solvent/base at
(LDH-Pd ) is an effective catalyst for Suzuki cross-coupling of a
0
room temperature using 0.5 mol% of LDH-Pd catalyst
wide range of aryl iodides and bromides with arylboronic acids at
room temperature. The catalyst is reused for four cycles with con- and the results are summarized in Table 1. The yield of
sistent activity.
coupling product depends on the combination of the sol-
vent/base and the same effect is observed in case of Pd/C
catalyzed Suzuki coupling.2 Ethanol–water (1:1) and
Na CO combination was found to be the most effective
Key words: layered double hydroxides, nanopalladium, room tem-
perature, Suzuki cross coupling, aryl iodides, arylboronic acids
f
2
3
system in terms of yield (Table 1, entry 6).
1
The palladium-catalyzed Suzuki cross-coupling reaction
Table 1 Effect of Solvent and Base on the Suzuki Coupling of 1a
of aryl halides with arylboronic acids represents one of the
most well-established methodologies in modern organic
synthesis to synthesize biaryl compounds, important in-
termediates for pharmaceuticals, herbicides and natural
products. Most of the catalytic systems, mainly the com-
bination of palladium salts with various phosphine ligands
or N-heterocyclic carbene ligands, result in excellent
yields with high efficiency. Despite the synthetic elegance
and high turnover numbers, the non-reusability of the pre-
cious palladium precludes wide synthetic applications in
the pharmaceutical industry. In an effort to address the
non-reusability of the catalyst and use of air-sensitive and
expensive ligands, several groups reported different
0
and 2a Catalyzed by LDH-Pd
LDH–Pd0
(
0.5 mol%)
Me
Br + (HO) B
2
Me
solvent, base,
r.t., 12 h
2a
3
a
1a
Entry
Solvent
Base
Isolated yield
%)a
(
1
2
3
4
5
6
7
8
9
Dioxane
KF
10
Dioxane–H O (1:1)
KF
10
2
MeOH
MeOH
EtOH
KF
25
2
ligand-free heterogeneous systems. However, most of
Na CO
55
2
3
3
3
them require elevated reaction temperatures. But from the
practical point of view, it is desirable to develop an oper-
ationally simple system, which has the ability to operate
at room temperature and at low levels of catalyst loading.
Na CO
65
2
EtOH–H O (1:1)
Na CO
90
2
2
2
f
EtOH–H
2
O (1:1)
K
2
CO
3
88
Recently, H. Sajiki et al. reported an efficient protocol
for the phosphine-free Suzuki reaction catalyzed by palla-
dium on carbon at room temperature with 3.5 mol% of
palladium. Earlier, we reported the preparation, character-
EtOH–H O (1:1)
NaOH
80
2
EtOH–H O (1:1)
Et N
15
2
3
ization of layered hydroxide supported nanopalladium
1
1
1
1
1
0
1
2
3
4
EtOH–H O (1:1)
KF
35
2
0
(
LDH-Pd ) catalyst, and its activity in Heck, Suzuki and
i-PrOH
Na CO
38
Sonogashira coupling reactions of chloroarenes at high
2
3
3
3
3
3
3
2
c
temperatures. Impressed with the high catalytic activity
i-PrOH–H O (1:1)
Na CO
80
2
2
0
of the LDH-Pd with chloroarenes at high temperatures,
DMF
THF
Na CO
10
we tried the Suzuki cross-coupling of 4-methylbromoben-
zene with phenylboronic acid under our optimized condi-
tions for chloroarenes [e.g., dioxane–water = 5:1; 5 mL;
KF (3 equiv)], except at room temperature using 0.5 15
mol% of catalyst and obtained 10% yield of the desired
2
Na CO
trace
trace
25
2
MeCN
Na
CO
2
1
6
H O
Na CO
2
2
a
Reaction conditions: 1a (1 mmol), 2a (1.5 mmol), LDH-Pd0
SYNLETT 2006, No. 4, pp 0633–0635
Advanced online publication: 20.02.2006
0
2.
0
3.
2
0
0
6
(0.5 mol%), base (3 mmol), solvent (2 mL), r.t.
DOI: 10.1055/s-2006-932478; Art ID: D21005ST
©
Georg Thieme Verlag Stuttgart · New York

6
34
M. L. Kantam et al.
LETTER
0
To evaluate the scope and limitations of this system, a Table 3 LDH-Pd -Catalyzed Suzuki Coupling of Aryl Halides with
Different Arylboronic Acids
variety of aryl iodides and bromides were reacted with0
phenylboronic acid in presence of 0.5 mol% of LDH-Pd
R
LDH-Pd0
R
3
in ethanol–water (1:1) at room temperature and the re-
(
0.5 mol%)
X +
B(OH)2
sults are summarized in Table 2. From Table 2 it is appar-
ent that aryl iodides react at a faster rate than aryl
bromides, which is as per expectation due to the facile ox-
idative addition of aryl iodides over the bromides. From
Table 2, it is also evident that the presence of electron-do-
nating groups in the aryl halides retards the reaction rate
whereas the electron-withdrawing moiety acts oppositely
by facilitating the oxidative addition step. The amount of
EtOH–H2O (1:1),
Na2CO3, r.t.
1
2
3
Yield (%)a
Entry
R
X
I
Time (h) Product
1
2
3
4
5
6
7
4-OCH3
4
5
3f
98
95
96
97
80
78
88
86
4-OCH3
Br
I
3f
0
.25 mol% of the catalyst also catalyzes the reaction but
4-Me
4-Me
3-NO2
3-NO2
4-F
4
3a
3a
3g
3g
3h
3h
requires longer reaction time (Table 2, entry 8).
Br
I
6
0
Table 2 LDH-Pd -Catalyzed Suzuki Coupling of Different Aryl
10
24
8
Halides with Phenylboronic Acid
Br
I
R
LDH–Pd0
(
0.5 mol%)
X
+
B(OH)2
EtOH–H2O (1:1),
Na2CO3, r.t.
8
4-F
Br
18
1
2
R
3
a
Isolated yields.
Entry
R
X
I
Time (h) Product Yield (%)a
1
2
3
4
5
6
7
8
4-Me
H
6
6
3a
3b
3c
3d
3e
3f
95
95
75
96
96
90
94
bromobenzene and phenylboronic acid is terminated at
0% conversion and the catalyst is separated by a simple
2
I
filtration. The reaction is continued for an additional 12
hours and the conversion almost remain unchanged.
These studies clearly demonstrate that no leaching of
palladium has taken place from the catalyst and through
out the reaction palladium is bound to the support.
2-Me
I
12
6
4-COCH3
I
4-NO2
I
6
4-OCH3
I
6
In conclusion, we have developed an efficient and simple
protocol for Suzuki coupling of aryl iodides and bromides
with arylboronic acids at room temperature using LDH-
H
Br
Br
8
3b
3a
b
d
0
4-Me
10
90, 78,
Pd catalyst. Moreover, the catalyst can be easily re-
c
8
8, 53
covered by simple filtration and reused with consistent
activity. The reusability of the catalyst makes the reaction
economical and commercially viable.
9
4-NO2
Br
Br
6
3e
3f
95
85
1
0
4-OCH3
10
a
b
c
d
Isolated yields.
.25 mol% LDH-Pd was used, reaction time 24 h.
Yield of the product after the fifth cycle.
.5 mol% Pd/C (10%) was used as a catalyst.
Acknowledgment
0
0
We wish to thank the CSIR for financial support under the Task
Force Project CMM-0005. Both M.S. and S.R. thank the Council of
Science and Industrial Research, India, for the award of research
fellowship and M.R. thanks UGC, India for providing a research
0
To widen the scope of our system, we performed the fellowship.
coupling of iodo- and bromobenzene with different aryl-
boronic acids under the same conditions and the results
References and Notes
are recorded in Table 3. Compared with arylboronic acids
containing electron-withdrawing groups, arylboronic
acids containing electron-donating groups afforded better
yields.
(1) (a) Miyaura, N. Top. Curr. Chem. 2002, 219, 11.
(
b) Hassan, J.; Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire,
M. Chem. Rev. 2002, 102, 1359. (c) Kotha, S.; Lahiri, K.;
Kashinath, D. Tetrahedron 2002, 58, 9633. (d) Zapf, A.;
Jackstell, R.; Rataboul, F.; Riermeier, T.; Monsees, A.;
Fuhrmann, C.; Shaikh, N.; Dingerdissen, U.; Beller, M.
Chem. Commun. 2004, 38. (e) Leadbeater, N.; Marco, M.
Angew. Chem. Int. Ed. 2003, 42, 1407; Angew. Chem. 2003,
0
The LDH-Pd catalyst is removed from the reaction mix-
ture by simple filtration and washed with water followed
by acetone and dried in air. The recovered catalyst is used
for four consecutive cycles with consistent activity
115, 1445. (f) Bedford, R. B.; Blake, M. E.; Craig, C. P.;
(Table 2, entry 8). The filtrate is tested for palladium after
Holder, D. Chem. Commun. 2003, 466. (g) Bedford, R. B.;
Cazin, C. S. J.; Coles, S. J.; Gelbrich, T.; Horton, P. N.;
the first cycle by ICP-AES and it is negligible (0.03%). To
check the heterogeneity of the catalyst, a reaction between
Synlett 2006, No. 4, 633–635 © Thieme Stuttgart · New York

LETTER
Layered Double Hydroxide-Supported Nanopalladium
635
0
2c
Hursthouse, M. B.; Light, M. E. Organometallics 2003, 22,
87. (h) Stambuli, J. P.; Kuwano, R.; Hartwig, J. F. Angew.
Chem. Int. Ed. 2002, 41, 4746. (i) Zapf, A.; Ehrentraut, A.;
Beller, M. Angew. Chem. Int. Ed. 2000, 39, 4153.
Preparation of LDH-Pd Catalyst.
9
LDH-Cl (Mg: Al = 3:1, 1.5 g) was suspended in 150 mL of
aq Na PdCl (0.441 g, 1.5 mmol) solution and stirred at
25 °C for 12 h under a nitrogen atmosphere. The solid
catalyst was filtered, washed thoroughly with 500 mL of
H O, and vacuum-dried to obtain 1.752 g of LDH-PdCl
2
4
(
j) Walker, S. D.; Barder, T. E.; Martinelli, J. R.; Buchwald,
S. L. Angew. Chem. Int. Ed. 2004, 43, 1871.
2
4
(
2) (a) LeBlond, C. R.; Andrews, A. T.; Sowa, J. R.; Sun, Y.
Org. Lett. 2001, 3, 1555. (b) Mubofu, E. B.; Clark, J. H.;
Macquarrie, D. J. Green Chem. 2001, 3, 23. (c) Choudary,
B. M.; Madhi, S.; Chowdari, N. S.; Kantam, M. L.; Sreedhar,
B. J. Am. Chem. Soc. 2002, 124, 14127. (d) Pittelkow, M.;
Moth-Poulsen, K.; Boas, U.; Christensen, J. B. Langmuir
(0.86 mmol of Pd/g). Subsequently, LDH-PdCl (1 g) was
4
reduced with hydrazine hydrate (1 g, 20 mmol) in EtOH (10
mL) for 3 h at r.t., filtered, and washed with EtOH to give
0
LDH-Pd as an air-stable black powder (0.95 mmol of Pd/g).
0
Typical Procedure for Suzuki Coupling Using LDH-Pd
as Catalyst.
2
003, 19, 7682. (e) Schimizu, K.; Maruyama, R.; Komai, S.;
Kodama, T.; Kitayama, T. J. Catal. 2004, 227, 202.
f) Sajiki, H.; Kurita, T.; Kozaki, A.; Zhang, G.; Kitamura,
In an oven-dried 10 mL round-bottom flask 4-methylbromo-
benzene 1a (1 mmol), phenylboronic acid 2a (1.5 mmol),
0
(
Na CO (3 mmol), LDH-Pd (0.5 mol%), and EtOH–H O
2
3
2
Y.; Maegawa, T.; Hirota, K. Synthesis 2005, 537.
3) For preparation of LDH-Cl, see: (a) Miyata, S. Clays Clay
Miner. 1975, 23, 369. (b) Typical Procedure. A mixture of
MgCl ·6H O (30.49 g, 0.15 mmol) and AlCl ·6H O (12.07
(1:1, 2 mL) are taken and stirred at r.t. under nitrogen
(
atmosphere and the reaction is monitored by TLC. After the
completion of the reaction, the catalyst is filtered and reused.
The filtrate is diluted with EtOAc and washed with 10% aq
NaOH solution and finally with sat. aq NaCl solution. The
organic layer is dried with Na SO and concentrated to get
2
2
3
2
g, 0.05 mmol) was dissolved in 200 mL of deionized H O.
2
To this solution was slowly added 100 mL of NaOH (2 M)
solution at 25 °C, and a further amount of 2 M NaOH
solution was added to maintain a pH of 10 under nitrogen
flow. The resulting suspension was stirred overnight at
2
4
the crude product. Then it is subjected to column
chromatography to get the pure product. Isolated yield of
1
4-methylbiphenyl 3a was 90%. H NMR: d = 2.39 (s, 3 H),
70 °C. The solid product was isolated by filtration, washed
7.16–7.21 (m, 2 H),7.24–7.30 (m, 1 H), 7.33–7.40 (m, 2 H),
7.40–7.45 (m, 2 H), 7.48–7.54 (m, 2 H).
thoroughly with deionized H O, and dried at 80 °C. All the
2
synthetic steps were carried out using decarbonated H O.
2
Synlett 2006, No. 4, 633–635 © Thieme Stuttgart · New York