H. Bulut et al. / Tetrahedron Letters 44 (2003) 289–291
291
phenylboronic acid in the presence of (CH CO ) Pd as
Mol. Catal. A: Chem. 1999, 142, 275; (c) Djakovitch, L.;
K o¨ hler, K. J. Am. Chem. Soc. 2001, 123, 5990.
8. Djakovitch, L. M.; K o¨ hler, K. J. Organomet. Chem.
2000, 606, 101.
3
2 2
a homogenous catalyst, with the amount of 0.025 mmol
and with the concentration of 1.4 ppm, at 0.5 h reaction
time under the conditions of entry 1. While the cou-
pling product formation was quantitative in the former,
in the lower concentration of Pd its formation was only
9. Djakovitch, L.; Wagner, M.; K o¨ hler, K. J. Organomet.
Chem. 1999, 592, 225.
2+
3%. These may indicate that the leaching of Pd cannot
10. Pd(NH ) -NaY has been shown to be an active catalyst
3 4
explain the overall activity of the catalysts.
precursor for Heck reactions (Refs. 6 and 7). However it
showed no activity in the Suzuki reaction of 4-bromoan-
isole under the reaction conditions used for entry 1.
1. Catalyst preparation: NaY zeolite was prepared from
Some ligand additives, particularly phosphines, are
used in many Pd catalysed reactions. Benzothiazolium
salts were also found to activate palladium as a lig-
1
NH Y (Zeolyst International, Si/Al: 2.5, 70$/pound) by
4
1
4
ion exchange method: NH Y zeolite (25 g) was suspended
and. However, in our case, the addition of PPh(CH3)2
or 3-methylbenzothiazolium iodide which possess suit-
able molecular sizes to be able to penetrate through the
4
in 250 ml water containing 10 wt% of NaNO . After
3
stirring and refluxing the suspension for 24 h, the solid
phase was isolated by filtration. This procedure was
zeolite apertures (ꢀ7 A), in an amount that is twofold
,
+
repeated twice and the Na exchanged zeolite was finally
molar equivalent with respect to the Pd amount,
brought the coupling reaction to a halt.
washed with a large amount of water and calcined at
2+
4
00°C for 10 h. Pd(NH3)4 was introduced into the NaY
zeolite by ion exchange with 0.1 M NH OH solution of
4
In summary, we have found that aryl bromides and aryl
iodides, in general, can be coupled with arylboronic
acids in excellent yield using Pd(II)-exchanged NaY
zeolite. The catalyst can be recycled and reused subse-
quent to regeneration.
Pd(NH ) Cl , corresponding approximately to 1 wt% of
3
4
2
Pd on the zeolite, by following the procedure given in
References 6–8. Pd(II)-NaY was obtained by calcination
2+
of Pd(NH3)4 -NaY in a vertical quartz tube under a flow
of oxygen (200 ml/min), using a heating rate of 1°C/min
from room temperature to 500°C and maintaining the
maximum temperature for 2 h. In order to analyse the
palladium content of the zeolite, Pd(II)-NaY was dis-
solved in a mixture of concentrated HBF , HNO , and
Acknowledgements
4
3
HCl (3:3:2) in a Teflon reactor by heating at 180°C and
subjecting it to 600–650 Watt microwave power. The
AAS gave 1.0±0.1 wt% of Pd.
This work was financially supported by the Research
Funding Office of IZTECH with project No. FEN 2000
0
1. Authors would like to thank Dr. A. Ero g˘ lu, Mr. S.
Yilmaz and Ms. A. Erdem for AAS analysis.
1
2. Typical reaction procedure: In a 50 ml flask equipped with
a magnetic stirring bar was charged aryl halide (1 mmol),
Na CO3 (4 mmol), arylboronic acid (1.2 mmol) and
2
Pd(II)-NaY (0.025 mmol Pd) in succession. The flask was
attached to an argon line and subsequently the reaction
was started by the addition of a 10 ml DMF/water
mixture (1/1). The mixture was vigorously stirred for 1 h
at room temperature. The catalyst was filtered off and
washed with dichloromethane and 0.6 mmol of tetra-
decane was added to the solution as an internal standard.
The organic phase was separated from the aqueous phase
and dried over Na SO . Products were analysed by GC
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3
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and GC/MS and isolated by column chromatography on
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4
5
6
13. Biaryl product (:0.05 mmol) was determined in the
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boronic acid.
6
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