Further study to clarify the role of Cs2CO3 and other
applications of this system are under way in our group.
The authors acknowledge IASBS Research Councils and
Iran National Science Foundation (INSF) for support of
this work.
Notes and references
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Fig. 1 TEM image of Au/Cs2CO3 after recovery.
3 J.-E. Backvall, Modern Oxidation Methods, Wiley-VCH,
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4 For some related examples of transition-metal-catalyzed aerobic
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nanoparticles on hybrid mesoporous silica, see: (l) Z. Hou,
Fig. 2 X-Ray photoelectron spectra of Au/Cs2CO3 matrix.
To gain more information about the nature of the Au
nanoparticles in the Au/Cs2CO3 matrix, a thin film of the
same recovered catalyst was prepared and studied using XPS.
Fig. 2 shows the XPS spectra of the region corresponding to
the binding energy range of 66–90 eV, which include Cs 4d,
Au 4f5/2, and Au 4f7/2 peaks.
N. Theyssen, A. Brinkmann, K. V. Klementiev, W. Grunertr,
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M. Buhl, W. Schmidt, B. Spliethoff, B. Tesche, C. Weidenthaler
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The peaks located around 83.4 eV were assigned to the
spin–orbit split components of the Au 4f7/2 level in the pure Au
metallic form.15,17 This binding energy (BE) clearly supports
the fact that the Au nanoparticles in our recovered samples
contained only Au0 species. It is very important to note that
due to the absence of any peak at higher energy for the
Au 4f7/2 level, the formation of gold oxides is less probable.
The work up of the reaction was performed using simple
filtration and the recovered Au–Cs2CO3 matrix was readily
used in 3 subsequent reactions (1st = 499%, 2nd = 98,
3rd = 98, 4th = 45% yield) and exhibited consistent catalytic
activity for the aerobic oxidation of benzyl alcohol without
further purification and/or reactivation. However, owing
to extensive agglomeration, the activity of the catalyst
dramatically decreased after the third run.
9 A. Abad, C. Concepcion, A. Corma and H. Garcıa, Angew. Chem.,
´ ´
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In conclusion, NaAuCl4/Cs2CO3 was found to be a simple,
recyclable, and efficient catalyst system for the aerobic
oxidation of alcohols at room temperature without the need
for any further polymeric or oxidic support. Of particular
note, this system gave excellent selectivities to aldehydes for a
wide range of primary alcohols and no evidence of acid
formation was observed with any of the primary alcohols
used. The catalyst also showed significant catalytic activity
for the oxidation of alcohols under normal air atmosphere.
15 See supporting information for detailsw.
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ꢀc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 5555–5557 | 5557