An Economical, Green Pathway to Biaryls: Palladium Nanoparticles Catalyzed Ullmann Reaction
the solid sample with Pd loading was collected after thor-
ough washing with ethanol and deionized water so that the
unsupported Pd(II) cation can be removed completely. The
sample was vacuum-dried at 608C for 24 h, affording the
supported catalyst Pd NPs/carbon.
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Typical Procedure for Ullmann Reactions in IL/
ScCO2
Aryl halide (2 mM), Al(0) (108 mg), [bmimACHTNUTRGNE(UNG HSO3C4)]
[HSO4] (3 mL) and Pd NPs (3.0% w/w, 186.2 mg) were
added into a 10.0-mL high-pressure stainless vessel, which
was sealed and connected to a CO2 supply. The vessel was
charged with CO2 gradually until a pressure of 5.0 MPa was
obtained and heated at 458C to a stabilized pressure of
7.0 MPa, then more CO2 was added to obtain a pressure of
15.5 MPa. The system were stirred under above conditions
for 10 h, successively, the stirrer and temperature controls
were then switched off, CO2 was gradually released into the
solvent trap (20.0 mL). The IL and Pd NPs/carbon remain-
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droxy-4-pyridone (DHPO, 3 mL, recycled by ion exchange)
for 3 times, and then distilled under reduced pressure to
remove DHPO residues, affording the active catalyst IL so-
lution for further reaction. The solvent trap vessel was then
disconnected and allowed to cool. By simple further decom-
pression of the CO2, the obtained product was collected
through the valve on the bottom of the solvent trap conven-
iently. The resulting organic solid was washed with ethanol
and purified with TLC to give the biaryl products.
ˇ
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Supporting Information
Materials and characterization, synthesis procedure for the
oxidized graphite, supplementary characterization of the re-
cycled catalyst together with details of the spectroscopic
data of the biaryls 2a–h are given in the Supporting Infor-
mation.
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We are grateful to the Shanghai Science Foundation
(10ZR1432000) and Foundation of Guangxi Zhuang Auton-
omous Region of China (NOs. 200626152, 200508193,
200925066) for financial support.
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