Suzuki cross-coupling reaction catalyzed by palladium-supported sepiolite

Article abstract of DOI:10.1016/S0040-4039(02)01132-2

Palladium-supported sepiolite clay has effectively catalyzed the Suzuki cross-coupling reaction of phenylboronic acid with aryl halide including less reactive electron-rich aryl bromides.

Full text of DOI:10.1016/S0040-4039(02)01132-2

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 5653–5655
Suzuki cross-coupling reaction catalyzed by palladium-supported
sepiolite
a,
a
b
a
Ken-ichi Shimizu, * Toshiki Kan-no, Tatsuya Kodama, Hisahiro Hagiwara and
b
Yoshie Kitayama
a
Graduate School of Science and Technology, Niigata University, Ikarashi-2, Niigata 950-2181, Japan
b
Department of Chemistry & Chemical Engineering, Faculty of Engineering, Niigata University, Ikarashi-2, Niigata 950-2181,
Japan
Received 2 May 2002; accepted 7 June 2002
Abstract—Palladium-supported sepiolite clay has effectively catalyzed the Suzuki cross-coupling reaction of phenylboronic acid
with aryl halide including less reactive electron-rich aryl bromides. © 2002 Elsevier Science Ltd. All rights reserved.
The palladium-catalyzed cross-coupling reaction of aryl
halides and arylboronic acids (Suzuki reaction) repre-
sents one of the most important methods for forming
Sepiolite is a fibrous natural clay mineral with ideal
formula of Mg Si O (OH) ·4H O·nH O. Its structure
8
12 30
4
2
2
is formed of talc-like ribbons arranged in such a way
that tetrahedral sheet is continuous but inverts in apical
directions in adjacent ribbons, generating uniform size
2
2
sp –sp carbonꢀcarbon bonds both in modern synthetic
1
chemistry and in industrial application. In the past few
years, attempts have been devoted to the development
of new soluble Pd complexes as highly active catalyst
parallel-piped intracrystalline tunnels (10.8×4.0 A)
,
5
along the fibre. The magnesium ion on the tunnel wall
2
6
for this reaction. In general, the presence of specific
can be substituted with various transition metal ions
which can act as the catalytic active site. Here, we
7
ligands, such as electron-rich and sterically-demanding
phosphines, are necessary to promote the reaction with
the less reactive aryl chlorides and electron-rich aryl
report a novel heterogeneous palladium catalyst, palla-
dium(II) supported on the sepiolite clay, as a highly
active and stable catalyst for Suzuki cross-coupling
reaction of aryl bromides (Scheme 1).
2
bromides. Regarding industrial applications, however,
these ligands and Pd precursors are expensive. Homo-
geneous catalyst is generally connected with the prob-
lem of separation and wasted inorganics which are too
difficult to reuse. In addition, deactivation of the solu-
ble palladium complex catalysts by forming inactive
metal particles is often encountered at high reaction
temperature. These problems could be principally mini-
mized by a heterogeneously catalyzed Suzuki reaction.
To overcome these problems, heterogeneous palladium
catalysts such as palladium complexes immobilized on
The preparation method of the catalyst is simple.
8
According to our previous report, natural sepiolite
(
Konan, China) was treated with dilute HCl aqueous
−3
solution (0.59 mol dm ) to eliminate impurities (calcite
and dolomite) without a decomposition of sepiolite
itself. The Pd -complex immobilized catalyst (Pd -
sepiolite) was prepared by exchanging the sepiolite with
aqueous solution of [Pd(NH ) ]Cl at 298 K for 48 h,
2+
2+
3
4
3 4
2
polymer or inorganic supports have been developed.
However, a large amount of the catalysts were required
for these heterogeneous catalytic systems, whose
turnover numbers were several orders of magnitude
lower than those of the homogeneous catalysts, and
these aspects limit industrial application of Suzuki
reaction.
Keywords: Suzuki reaction; palladium catalysts; sepiolite.
*
Corresponding author.
Scheme 1.
0
040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)01132-2

5
654
K. Shimizu et al. / Tetrahedron Letters 43 (2002) 5653–5655
followed by centrifuging and washing with deionized
water, and subsequently drying in vacuo at 298 K. The
metal content of the catalyst (0.18 wt%) was determined
using ICP. XRD patterns of the catalysts were essen-
tially the same as that of sepiolite. The surface area of
ing step in the Suzuki reaction of aryl bromides on
2+
Pd -sepiolite is not the oxidative addition of aryl
halides to the palladium catalyst.
We performed the leaching test for the reaction of
4-bromoanisole at 100°C; when the solid catalyst was
removed before a completion of the reaction (reaction
time=1 h), the reaction did not proceed any further.
2
+
2
−1
Pd -sepiolite (240 m g by BET method) was very
2
−1
close to that of the original sepiolite (248 m g ). These
results suggest that the palladium complex is immobi-
lized on the surface of sepiolite, without changing tun-
nel structure of sepiolite.
2
+
This proves heterogeneous catalytic activity of Pd -
sepiolite and no contribution from homogenous cataly-
sis. The catalyst could be easily separated from the
reaction mixture by simple filtration and recycled with-
out loosing its activity in the reaction of 4-bromoan-
isole (entry 4). For a comparison, commercially
available palladium catalyst (Pd/C) was also tested for
The catalyst was tested for the cross-coupling between
aryl halide and phenylboronic acid (Scheme 1). Typi-
cally, the reaction was carried out by stirring the reac-
tion mixture containing aryl halide (2.5 mmol),
phenylboronic acid (3.7 mmol), potassium carbonate (5
2
+
this reaction. Compared to Pd -sepiolite (entry 4),
Pd/C showed lower yield and significantly lower TOF
(entry 12). Palladium acetate in bulk solution (entry
13), i.e. homogeneous catalysis, gave higher initial rate
mmol) and the catalyst (0.5 mmol of Pd) in DMF (5
3
cm ) at 100°C under N . As shown in Table 1, the
2
2
+
Pd -sepiolite catalyzed the Suzuki cross-coupling reac-
tion of an aryl iodide or aryl bromides with various
substituents and provided the corresponding coupling
products in excellent yields using a small amount of the
catalyst (0.02 mol%). As expected, aryl chloride was
most inactive (entry 8). Variation of the substituents in
the aryl bromides was also tested. Electron-donating
and electron-withdrawing substituents were both well
tolerated by the catalytic system and the coupling prod-
ucts were obtained in excellent yields. However, the
initial rate of the reaction depended on the substituents;
the ‘non-activated’ substrate (entry 2) and ‘deactivated’
2+
(TOF) than Pd -sepiolite, but resulted in a lower yield
2+
after 24 h than that of Pd -sepiolite.
2+
To evaluate the durability of the Pd -sepiolite catalyst,
we have examined the Suzuki reaction of several aryl
bromides with low catalysts concentration (entries 9–
11). In the cross-coupling of bromobenzene at 130°C, a
yield of 39% was obtained after 1 h with 0.001 mol% of
−
1
palladium, corresponding to TOF value of 39000 h .
After 24 h, the reaction proceeded in 65% yield
(TON=65000). As for 4-bromoanisole and 4-bro-
moacetophenone, under the same reaction conditions,
the products were obtained after 24 h in yields of 56
and 94%, respectively, corresponding to TONs of 56000
and 94000, respectively. To the best of our knowledge,
these are the highest activities for the heterogeneously
catalyzed Suzuki cross-coupling of aryl bromides.
(
4
electron-rich) substrates, such as 4-bromoaniline and
-bromoanisole (entries 3–5) gave better initial rates
than the ‘activated’ (electron-poor) substrates (entries 6
and 7). This reactivity tendency is in contrast to that
generally observed for palladium-catalyzed cross-cou-
9
pling reactions, which suggests that the rate-determin-
2+
a
Table 1. Reactions of aryl halides with phenylboronic acid over Pd -sepiolite catalyst
Entry
Substrate
C H I
T (°C)
Yield (%)b
TONc
TOFd (h−1
)
1
2
3
4
5
6
7
100
100
100
100
100
100
100
100
130
130
130
100
100
80
81
77
4000
4050
3850
4250
4550
4150
4550
230
65000
56000
94000
2000
2200
1595
2098
2380
1633
1532
819
1033
63
39000
9292
7163
74
6
5
C H Br
6
5
4-NH C H Br
2
6
4
e
4-MeOC H Br
85 (84)
6
4
3-ClC H Br
91
83
91
23
65
56
94
40
44
6
4
4-CH COC H Br
3
6
4
4-NO C H Br
2
6
4
f
8
4-CH COC H Cl
3
6
4
g
9
C H Br
6
5
g
1
1
1
1
0
4-MeOC H Br
6 4
g
1
4-CH COC H Br
3
6
4
h
2 (Pd/C)
3 (Pd(OAc)2)
4-MeOC H Br
6 4
i
4-MeOC H Br
1987
6
4
a
b
c
d
e
f
3
Reaction conditions: aryl halide (2.5 mmol), phenylboronic acid (3.7 mmol), K CO (5 mmol), catalyst (0.5 mmol of Pd), DMF (5 cm ).
2
3
GC yield using benzonitrile as internal standard after 20–24 h.
TON=(mol of product/mol of catalyst).
Turnover-frequency calculated at reaction time of 1 h.
Cycle 2.
Amount of the catalyst was 2.5 mmol of Pd.
g
h
i
3
Reaction conditions: aryl halide (25 mmol), phenylboronic acid (37 mmol), K CO (50 mmol), catalyst (0.25 mmol of Pd), DMF (25 cm ).
2
3
Pd/C catalyst (Pd=0.5 wt%) was used.
Palladium(II) acetate was used as homogeneous catalyst.

K. Shimizu et al. / Tetrahedron Letters 43 (2002) 5653–5655
5655
In conclusion, the cross-coupling of aryl bromides with
4. (a) Mubofu, E. B.; Clark, J. H.; Macquarrie, D. J. Green
Chem. 2001, 3, 23; (b) Kosslick, H.; Monnich, I.; Paetzold,
E.; Fuhrmann, H.; Fricke, R.; Muller, D.; Oehme, G.
Microporous Mesoporous Mater. 2001, 44–45, 537; (c)
Varma, R. S.; Naicker, K. P. Tetrahedron Lett. 1999, 40,
439.
2+
phenylboronic acid are efficiently catalyzed by Pd -
sepiolite prepared by simple ion-exchanging. This novel
catalyst provides clean and convenient alternative for
Suzuki reaction in view of the following advantages:
(
1) higher TON than previously reported hetero-
geneous Pd catalysts, (2) simple reaction procedures
and (3) low-cost, waste-minimizing and recyclable cata-
lyst.
5. Preisinger, A. Clay and Clay Minerals, Earth Science
Series; Pergamon: Oxford, 1963; Vol. 12, p. 365.
6. (a) Kitayama, Y.; Muraoka, M.; Kodama, T.; Omi, N.;
Oizumi, M. J. Clay Sci. Soc. Jpn. 1996, 35, 188; (b)
Corma, A.; Perex-Pariente, J.; Soria, J. Clay Minerals
1985, 20, 467; (c) Brigatti, M. F.; Lugli, C.; Poppi, L. Appl.
Clay Sci. 2000, 16, 45.
References
1
. (a) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun.
7. (a) Kitayama, Y.; Michishita, A. J. Chem. Soc., Chem.
Commun. 1981, 401; (b) Corma, A.; Martin-Aranda, R. M.
J. Catal. 1991, 130, 130; (c) Aramendia, M. A.; Borau, V.;
Jimenez, C.; Marinas, J. M.; Sempere, M. E.; Urbano, F.
J. Appl. Catal. 1990, 63, 375; (d) Aramendia, M. A.;
Borau, V.; Jimenez, C.; Marinas, J. M.; Sempere, M. E.;
Urbano, F. J. Synth. Commun. 1990, 20, 3519; (e) Aramen-
dia, M. A.; Borau, V.; Jimenez, C.; Marinas, J. M.; Porras,
A.; Urbano, F. J. J. Mol. Catal. 1994, 94, 131.
8. Kitayama, Y.; Hayakawa, M. J. Clay Sci. Soc. Jpn. 1992,
31, 196.
1981, 11, 513; (b) Miyaura, N.; Suzuki, A. Chem. Rev.
1995, 95, 2457; (c) Suzuki, A. J. Organomet. Chem. 1999,
576, 147.
2
. (a) Wolfe, J. P.; Singer, R. A.; Yang, B. H.; Buchwald, S.
L. J. Am. Chem. Soc. 1999, 121, 9550; (b) Littke, A. F.;
Dai, C.; Fu, G. C. J. Am. Chem. Soc. 2000, 122, 4020; (c)
Andreu, M. G.; Zapf, A.; Beller, M. Chem. Commun.
2
000, 2475; (d) Liu, S.; Choi, M. J.; Fu, G. C. Chem.
Commun. 2001, 2408.
. (a) Uozumi, Y.; Danjo, H.; Hayashi, T. J. Org. Chem.
3
1
999, 64, 3384; (b) Cammidge, A. N.; Baines, N. J.;
9. Beletskaya, I. P.; Cheprakov, A. V. Chem. Rev. 2000, 100,
3009.
Bellingham, R. K. Chem. Commun. 2001, 2588.