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RSC Advances
layers were washed with water, dried over MgSO4, and puried
using column chromatography on silica gel to afford the cor-
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Three phase test
Bromide functionalized silica was prepared using the reported
procedure.22 The test was carried out by taking 4-bromoaceto-
phenone (100 mg, 0.5 mmol), phenylboronic acid (135.3 mg,
1.11 mmol), and K2CO3 (173 mg, 1.25 mmol) in 10 mL aqueous
ethanol (1 : 1) along with 4-BrPhCONH-propyl silica gel (500
mg), and 0.02 mol% catalyst (1 or 2) at 55 ꢀC for 10 h. The
supernatant liquid was extracted with ethyl acetate, dried over
Na2SO4 and puried using column chromatography (90% for 1
and 92% for 2). Aer ltration, the solid product was collected,
washed with ethanol, extracted with CH2Cl2 and hydrolysed
with 2 M KOH for three days at 90 ꢀC. The resulting mixture was
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concentrated and the resulting mixture was analysed using H
and 13C NMR.
€
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Conclusion
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In summary, we have successfully synthesised a self-assembled
Pd6L4 Td-symmetric cage and a Pd4L4 square assembly using
a cis-clipped palladium anchor and semi-rigid ligands with
pyridyl terminals. The assemblies were characterized using
NMR and ESI-MS spectroscopic methods, while HR-TEM
measurements and theoretical calculations gave an idea about
the size and dimension characteristics. Furthermore, both the
assemblies efficiently catalyse Suzuki–Miyaura coupling reac-
tions heterogeneously under mild, aerobic and phosphine free
reaction conditions with low catalyst loading. The work thus
provides a new insight into the ability of discrete self-assembled
palladium cages and cycles to act as reusable heterogeneous
catalysts for Suzuki–Miyaura cross coupling reactions.
Acknowledgements
SP and RJ thank DST-SERB for funding (Grant no. SR/S1/2010/
IC-27), SAIF, IIT Mumbai for ICP AES, STIC-SAIF Cochin, SAIF
Panjab University for 1D and 2D NMR analyses and NRC, IISc
Bangalore for DOSY-NMR. The authors gratefully acknowledge
Dr Dibyendu Sain for theoretical calculations.
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