consistent with the high durability of AuHAP in the recycling
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The scope of the substrate silanes using the present AuHAP
catalyst system is exemplified in Table 2. In all cases, AuHAP
efficiently catalyzed the oxidation of silanes to silanols without
the formation of any disiloxane condensation products.
Various aliphatic silanes were successfully oxidized to the
silanols (Table 2, entries 1–9). Triisopropylsilane, a sterically
bulky aliphatic silane, was also oxidized (Table 2, entry 6).
Only the Si–H function of dimethylpropenylsilane was
oxidized to a silanol, while the CQC double bond remained
intact under the reaction conditions (Table 2, entry 8).
Phenylsilanes were also found to be good substrates for the
AuHAP catalyst, and the corresponding silanols were formed
in excellent yields (Table 2, entries 10–12 and 15–19), except
for triphenylsilane (Table 2, entries 13 and 14).
In conclusion, the HAP-supported gold nanoparticle
(AuHAP) catalyst was developed for the oxidation of silanes
in water. This catalytic methodology is a highly potential
candidate for the environmentally friendly oxidation of silanes
with the following advantages: (1) no requirement for organic
solvents, (2) use of water as a clean oxidant, (3) simple
work-up procedure, (4) high activity and selectivity for
silanols, (5) a wide scope of substrate silanes, including various
aliphatic silanes, and (6) reusability of the catalyst.
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This investigation was supported by a Grant-in-Aid for
Scientific Research from the Ministry of Education, Culture,
Sports, Science, and Technology of Japan. This work was also
supported by a Grant-in-Aid for Scientific Research on
Priority Areas (No. 18065016, ‘‘Chemistry of Concerto
Catalysis’’) from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan. Some experiments were
carried out using the facilities at the Research Center for
Ultrahigh Voltage Electron Microscopy, Osaka University.
We thank Dr Uruga, Dr Tanida, Dr Honma, Dr Taniguchi
and Dr Hirayama (SPring-8) for XAFS measurements.
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29 In a separate experiment, the AuHAP-catalyzed oxidation of 1 was
conducted using isotopic H2O18 and 18O-labeled silanol was
formed in 99% selectivity, suggesting that the oxygen atom
incorporated in silanol products were derived not from air (O2)
but water.
Notes and references
1 A. Chanda and V. V. Fokin, Chem. Rev., 2009, 109, 725.
2 S. Minakata and M. Komatsu, Chem. Rev., 2009, 109, 711.
3 P. A. Grieco, Organic Synthesis in Water, Blackie, London, 1998.
30 In the oxidation of 1 at 80 1C for 30 min, the following yields of 2
were obtained with over 99% selectivity: AuHAP, 68%; Au/Al2O3,
62%; Au/SiO2, 51%, Au/MgO, 28%, and Au/TiO2, 27%.
ꢀc
This journal is The Royal Society of Chemistry 2009
5304 | Chem. Commun., 2009, 5302–5304