Journal of the American Chemical Society
Article
decreased rapidly to 0 and 2.1%, respectively (Table 2, entries
15 and 16, respectively), indicating the unique catalytic
property of AuCN for such C−C bond formation reaction.
Notably, relatively good yield is obtained at a lower
temperature (403 K) as compared to previous work (423
K),17 which is supposed to be caused by the size effect of our
nanoparticulate catalysts. It is well accepted that, in gold
catalysis, the catalytic properties of AuNPs largely depend on
their supports.44−46 However, it is still an open question
whether Au(I) catalysis follows this rule. Obviously, the
versatility of the present radical pathway potentially allows us
to improve the catalytic properties of AuCN by using different
kinds of supports. Primary results showed that mesoporous
silica is the best support for AuCN oligomers to catalyze the
annulation transformation (Table 2, entries 12 and 17−20),
which is possibly ascribed to the confinement effect of
mesopores. However, it is difficult to suppress the diffusion
of active AuCN/PBu3 species into the reaction solution due to
the homogeneous character of the reaction and the large
entrance size of mesoporous silica (∼10 nm). Therefore, the
engineering of the entrance size (less than 2 nm) is a possible
way to encapsulate or immobilize the active catalytic species
within the porous structure and prevent their leaching problem,
as evidenced in the case of heterogenization of homogeneous
chiral catalysts in SBA-16.47 Additionally, Corma and co-
workers have reported that cationic Au(III) species can be
stabilized on CeO2 and ZrO2 rather than on silica and carbon.48
It is thus expected that large-scale screening of the supports to
find an optimal one is able to turn the current Au(I) based
homogeneous system into heterogeneous with possibility.
Accordingly, further works on gaining insights into the reaction
mechanism using different metal sources and supports and their
applications for both homogeneous and heterogeneous catalysis
are now underway in our laboratory.
This material is available free of charge via the Internet at
AUTHOR INFORMATION
■
Corresponding Author
Present Address
∥Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai, China.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge helpful discussions with Prof. L. M. Zhang at
UCSB and Prof. Y. H. Zhang at ZJU. This work was supported
by the National Science Foundation of China (20873122,
21222307, and 21003106), Fok Ying Tung Education
Foundation (131015), and the Fundamental Research Funds
for the Central Universities (2012QNA3014).
REFERENCES
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4. CONCLUSIONS
In summary, we have developed a radical-involved photo-
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ASSOCIATED CONTENT
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S
* Supporting Information
Synthesis of materials; material characterization; EPR experi-
1
ments; H NMR results; DFT calculations; XRD patterns of
various supported metal cyanides; and TEM images of
monodispersed AuNPs, AgNPs, PtNPs, PdNPs, and RuNPs.
18293
dx.doi.org/10.1021/ja305198p | J. Am. Chem. Soc. 2012, 134, 18286−18294