10.1002/cctc.201800663
ChemCatChem
FULL PAPER
(190 µmol) in a Pyrex test tube. The tube was sealed with a rubber
septum and then photoirradiated at a wavelength > 300 nm by a 400 W
high-pressure mercury arc (Eiko-sha, Osaka) under Ar with magnetic
stirring at 298 K. After the reaction, the gas phase (H2) was analyzed
using a gas chromatograph (Shimadzu, GC-8A equipped with MS-5A).
After the suspension had been filtered to remove the particles, toluene (5
µL) as an internal standard was added. The amounts of TESA and the
products, vinyltriethylsilane (VTES) and tetraethylsilane (TES), were
determined using a gas chromatograph (Shimadzu, GC-2025 equipped
with a DB-1 column).
Figure 7. Although VTES was obtained in a high yield (166
µmol) with no FAD being added to the system, the yield of VTES
linearly decreased with an increase in the amount of FAD added.
The results indicate that FAD directly suppresses photocatalytic
hydrogenation of TESA.
Conclusions
We achieved almost complete semihydrogenation of an alkynyl
group to an alkenyl group in oragnosilane and hydrocarbon in
methanolic suspensions of a Pd-TiO2 photocatalyst. Pd particles
worked as a co-catalyst for semihydrogenation and, in the case
of 4-octyne, the reaction rate over Pd-TiO2 was 11 times larger
than that over Cu-TiO2. Over the Pd co-catalyst, alkyne
hydrogenation had priority to alkene hydrogenation. The Pd co-
catalyst was temporarily deactivated during the reaction and the
capacity of hydrogenation of the unsaturated C-C bond is limited,
which greatly contributed to semihydrogenation of an alkynyl
group. This process provides environmentally friendly, i.e., 1)
additive-free, 2) hydrogen-free, and 3) highly selective,
hydrogenation. In semihydrogenation, a Pd-TiO2 works as a
photocatalyst because the Pd-TiO2 can be re-generated and re-
used.
Acknowledgements
This work was partly supported by JSPS KAKENHI Grant
Numbers 17H03462 and 17H04967. This work was also
supported by MEXT-Supported Program for the Strategic
Research Foundation at Private Universities 2014-2018, subsidy
from MEXT and Kindai University. A.T. is grateful for financial
support from the Faculty of Science and Engineering, Kindai
University.
Keywords: hydrogenation • photocatalysis • alkynes • TiO2
•
palladium
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Experimental Section
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