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ACKNOWLEDGMENTS
confirmed that base plays important role in the type reaction
after catalyst.31,32 After completion of the reaction, the solid
residue was filtered off and washed with ethyl acetate to
remove the adherent organic composites. The combined
organic phase was concentrated under reduced pressure and
purified by thin-layer chromatography (TLC, SiO2) to collect
the corresponding products. Isolated amides were character-
We thank the Institute of Chemical and Engineering Sciences,
Agency for Science, Technology, and Research, Singapore, and
“Singapore-EDB-GSK Partnership for Green and Sustainable
Manufacture” for financial support.
1
ized by H, 13C NMR and compared with literature results to
REFERENCES AND NOTES
identify their structures.
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ꢁ
at 50 C for 12 h before next run. The catalyst can be reused
at least four times with the yield of 87, 89, 86, and 87% for
the aminocarbonylation between iodobenzene and aniline in
the presence of K2CO3. To study the leached Pd, the samples
of the filtrate plus washings obtained from above standard
reactions were subjected to ICP analysis that shown the con-
centrations of Pd were to be less than 6.5 ppm. In addition,
the standard reaction was conducted in recovered filtrate
with same loading amounts of substrates as detailed in
Table 1, but no product could be isolated. The results sug-
gested that the supported Pds, rather than the leached Pds,
provide the high catalytic performance. The nanocomposite
of the cyclic PLLA stabilized nano-Pds was also examined for
the aminocarbonylation between iodobenzene and aniline in
the presence of K2CO3. A yield of 81% of was achieved
under same conditions. However, the catalyst composite of
nano-Pd on cyclic PLLAs was not recyclable due to partial
dissociation of the nonsupported cyclic PLLAs. The sup-
ported palladium nanoparticles were also found to be active
for the aminocarbonylation of both aryl bromide and chlo-
ride to form corresponding amides as summarized in Table
2. In the procedure, a strong base, potassium tert-butoxide
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CONCLUSIONS
Biodegradable cyclic PLLA was employed to stabilize palla-
dium nanoparticles and demonstrated unique and suitable
property for the specific application. The cyclic PLLA was also
successfully intercalated into clay by the zwitterionic ROP cat-
alyzed by in situ generated NHC to form the biodegradable
cyclic PLLA-clay hybrid material. Palladium (0) nanoparticles
were successfully supported and well dispersed on the hybrid
to form the new catalyst nanocomposite. The composite was
found to be a highly efficient and recyclable catalyst for ami-
nocarbonylation reaction of aryl halides with various amines.
Considering the sustainability and biodegradability of the sup-
port and high activity of the catalyst nanocomposite, we
expect our prototype catalyst to find broader applications
both in academia and fine chemical industry.
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