1
782
L. Lin et al.
LETTER
results were obtained in this Pd micelle catalyzed reac- In conclusion, a GIL-mediated aqueous Suzuki coupling
tion.
procedure has been developed using ligand-free Pd cata-
lysts. The Pd micelles stabilized by guanidinium IL bear-
ing long alkyl chains, behave efficiently in Suzuki
coupling reaction. The Pd micelles play a key role in en-
hancing the activity, owing to the highly dispersed Pd ac-
tive sites and the phase-transfer function of GIL, which
ensures the adsorption of reactants and facilitates transla-
tion of intermediates to the surface of the micelle. In addi-
When using IL to stabilize Pd nanoparticles, the stability
of the IL becomes crucial issue. To explore the stability of
the guanidinium IL, the Suzuki reaction of 4-bromoace-
tophenone with benzenboronic acid was carried out in
GIL3 aqueous in the presence of 2.5 equivalents KOH at
6
0 °C for 2 hours. After cooling to room temperature, the
reaction mixture was extracted with diethyl ether. The ex-
tracted phases were monitored by GC using ethyl acetate
as the internal standard. There were no IL decomposition
tion, the GIL/H O catalytic system was more stable than
2
the TBAB/H O catalytic system, enabling the recycling of
2
the Pd catalysts.
products in GIL3/H O catalytic system, but around 6
2
mol% of trialkylammine deriving from the IL decomposi-
tion was detected in TBAB/H O catalytic system under
2
Supporting Information for this article is available online at
the similar conditions. Afonso have studied the stability of
http://www.thieme-connect.com/ejournals/toc/synlett.
1
13
GIL by H NMR and C NMR spectroscopy under basic
2
2
conditions (KOH) at 60 °C. No change in the basic skel-
eton was observed, which was in accordance with our re-
Acknowledgment
sults. Therefore, it is worthy of mention that our GIL/H O
2
We thank the National Science Foundation of China (No.
catalytic system is more stable than TBAB/H O catalytic 20802071, 21074133) for the financial support.
2
system. The studies presented here give strong support
that the guanidinium is a good candidate for aqueous re-
action under basic conditions.
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served after five catalytic recycles (Figure 4).
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(
(
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Synlett 2011, No. 12, 1779–1783 © Thieme Stuttgart · New York