(
(
Fig. 2e) to Cu(CH
3
COOH)
2
(Fig. S9a, ESIw) and CuSO
is used, copper
4
Table 1 and the yield of desired product was 85%, which suggests
the considerable stable activity of the material. The yield of biaryl
Fig. S9b, ESIw). However, when Cu(NO
3 2
)
particles cannot totally cover the core Cu O (Fig. S9c, ESIw),
implying a low reaction speed in the case of NO3 anions.
acetylene on Cu (obtained at 40 min), Cu O (obtained at 2 min),
2
2
À
the mixture of Cu and Cu O, cubical and hexapodal Cu O@Cu is
2
2
The effect of solvent was also studied (Fig. S10, ESIw). At low
ethylene glycol amounts (0 and 10 mL), the diameter of Cu particles
on the surface is more than 100 nm, and cannot form a shell. When
ethylene glycol amount is increased to 20 mL, the core–shell
structure can be generated with an external diameter of
B1.5 mm. The diameter of the core–shell structure decreases with
the ethylene glycol dose. The external diameters of obtained
particles are B800 nm with 30 mL ethylene glycol, and the structure
is still core–shell (Fig. S11a, ESIw). However, in the absence of
water, the particles are just hollow spheres with diameters of
B200 nm (Fig. S11b, ESIw). The results suggest that not only does
the reaction become faster at higher ethylene glycol doses, but also
the size of core–shell structure can be controlled to a certain range
by the water and ethylene glycol ratio. The present methodology is
also applied to the synthesis of nonspherical structures. As
7%, 5%, 45%, 92%, and 89%, respectively. These results indicate
that the Cu O@Cu structure is helpful to the Sonogashira
2
coupling reaction, and core–shell materials possess similar catalytic
activity in spite of different shapes. This noble metal- and ligand-
free protocol for the Sonogashira coupling reaction can be a good
alternative to the classical Cu–Pd catalyzed methods, thus provid-
ing an economic and sustainable pathway to biarylacetylenes.
In summary, a facile solution-phase strategy is developed to
2
construct the Cu-outside core–shell structures (Cu O@Cu) with a
Cu O core and a Cu shell, which is the inside-out architecture of
2
usually reported Cu@Cu O. In addition to spherical Cu O@Cu
2
2
core–shell structures, the successful fabrication of square and
hexapod structures demonstrates the generality of our strategy.
2
Moreover, the Cu O@Cu core–shell structure shows high
catalytic activity in the Sonogashira coupling reactions, despite
the absence of the noble metal Pd. Our strategy may open up a
route for the design and synthesis of new functional materials.
Dr Jiahui Kou and Dr Amit Saha are postdoc research
participants at the National Risk Management Research
Laboratory, Environmental Protection Agency, administered
by the Oak Ridge Institute for Science and Education
(ORISE). The support from colleagues, Dr R. Venkatapathy,
Mr C. Han, and Prof. D. D. Dionysiou is appreciated.
depicted in Fig. S12 (ESIw), Cu
hexapod morphology are first prepared. Based on these pre-
designed morphologies, Cu O on the outer surface can be reduced
2
O particles with square and
2
to Cu gradually by using the same method as spherical ones. The
SEM and TEM images shown in Fig. S13 (ESIw) demonstrate that
the Cu shell can be formed clinging to the high-curvature surfaces
of the core Cu O, and the shape of the template Cu O can be well
2
2
preserved. These results, in combination with the spherical data,
give evidence of the generality of our strategy for the fabrication of
Cu
According to the experimental results above, a plausible synthetic
mechanism of Cu O@Cu core–shell structure is proposed
Scheme S1, ESIw). In the ethylene glycol–water system, spherical
Cu O particles, which subsequently act as a sacrificial template
for the generation of Cu O@Cu, are formed immediately after
glucose was added to the reaction solution. Then, the Cu
2
O@Cu core–shell structures with tunable shapes.
Notes and references
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17
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2
2
structures can also be produced through the similar mechanism.
1
1
The obtained Cu O@Cu material was employed to catalyze the
2
2
Sonogashira coupling reactions of aryl iodides with phenyl-
acetylenes. It is fascinating to observe that biarylacetylenes can be
produced with excellent yields (85–94%) in the absence of noble
metal Pd and ligand (Table 1). Moreover, different functional
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1
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2
, and –OMe) are compatible with
O@Cu after reaction
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2
2
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good stability of the structure. The recovered catalyst was reused
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2
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864 Chem. Commun., 2012, 48, 5862–5864
This journal is c The Royal Society of Chemistry 2012