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This result is different from ordinary MPV reduction
because it proceeds in a hydride reductive manner through the
six-membered transition state formed among carbonyl
compound, alcohol and catalyst as the rate-determining step
as reported by Komanoya et al. . They demonstrated the
presence of the six-membered transition state based on the
kinetic isotope effect using various deuterated 2-propanol as
sacrificial alcohol in addition to FT-IR analysis. In the case of
DOI: 10.1039/C7CC00645D
8a
(
CH ) CHOD, no kinetic isotope effect was observed (k /k =
3
2
H
D
1
.1), whereas (CH ) CDOH gave a large k /k of 1.9. The result
3 2 H D
indicates the -H elimination of 2-propanol participated in the
reduction of carbonyl compound.
Figure 5 Proposed photocatalytic mechanism over DHN/TiO for
reduction of an aldehyde group.
2
1
5
0
5
2
R =0.99
m-CN
m-Cl
environmentally-friendly material transformation system
working under sunlight. Since the reaction rate is still small
compared with the reaction rates over homogeneous and
heterogeneous thermocatalysts (Table S2), engineering
approaches such as efficient light irradiation to the
photocatalyst system are also important.
1
p-Cl
m-CH3
H
p-CH3
p-OCH3
This study was partially supported by Grant-in-Aid for
Scientific Research (No. 26289307 and 15K18269) from the
Japan Society for the Promotion of Science (JSPS) and Program
for the Strategic Research Foundation at Private Universities
0
-
0.4
0
0.4
0.8
Hammett constant
Figure 4 Hammett correlation study for photocatalytic
reduction of various aromatic aldehydes to corresponding
aromatic alcohols in an acetonitrile suspension of DHN/TiO2
under irradiation of visible light.
2
014-2018 from MEXT and Kindai University.
Notes and references
1
2
M.A. Fox and M.T. Dulay, Chem. Rev., 1993, 93, 341.
M.R. Hoffman, S.T. Martin, W. Choi and D.W. Bahnemann,
Chem. Rev., 1995, 95, 69.
Based on the results of the action spectrum and the linear
Hammett correlation described above, we can consider the
mechanism of chemoselective reduction of an aldehyde group
3
G. Palmisano, E. García-López, G. Marcì, V. Loddo, S. Yurdakal,
over DHN/TiO under irradiation of visible light as shown in
V. Augugliaro and L. Palmisano, Chem. Commun., 2010, 46,
2
Figure 5. First, the surface complex species formed by DHN
4
5
6
7
Org. Chem., 1990, 55, 5551.
and TiO functions as a site for absorbing visible light, and the
2
generated electrons are injected into the conduction band of
M. Fukui, A. Tanaka, K. Hashimoto and H. Kominami, Chem.
Lett., 2016, 45, 985.
T. Kamegawa, H. Seto, S. Matsuura and H. Yamashita, ACS
Appl. Mater. Interfaces, 2012, 4, 6635.
TiO . These electrons are used for reduction of the aldehyde
2
group of benzaldehydes adsorbed on the TiO2 surface.
Detailed analysis using the Hammett equation indicated that
an anionic intermediate was formed during reduction of the
aldehyde group. It is expected that the generated anionic
(a) E. J. Campbell, H. Zhou and S. T. Nguyen, Org. Lett., 2001,
, 2391; (b) P. Nandi, Y. I. Matvieiev, V. I. Boyko, K. A.
1
5
Durkin, V. I. Kalchenko and A. Katz, J. Catal., 2011, 284, 42;
(c) D. A. Evans, S. G. Nelson, M. R. Gagne and A. R. Muci, J.
Am. Chem. Soc., 1993, 115 (21), 9800.
+
species is stabilized by protons (H ) formed by oxidation of
triethanolamine used as a hole scavenger.
8
(a) T. Komanoya, K. Nakajima, M. Kitano and M. Hara, J. Phys.
Chem. C, 2015, 119, 26540; (b) J. Wang, K. Okumura, S.
In summary, we succeeded in visible light-induced
Meerwein-Ponndorf-Verley-type
reduction
of
various
Jaenicke and G. K. Chuah, Appl. Catal. A: General, 2015, 493
12.
,
benzaldehydes having other reducible functional groups to
corresponding benzyl alcohols over an organically modified
1
9
1
(a) K. Fuku, K. Hashimoto and H. Kominami, Chem. Commun.,
2010, 46, 5118; (b) K. Fuku, K. Hashimoto and H. Kominami,
Catal. Sci. Technol., 2011, 1, 586.
TiO (OMT) photocatalyst prepared by a simple impregnation
2
method without any special care. This is the first report of
chemoselective reduction of an aldehyde group under
irradiation of visible light. The results obtained in this study
satisfy three important requisites in material transformation,
0 (a) K. Imamura, T. Yoshikawa, K. Nakanishi, K. Hashimoto and
H. Kominami, Chem. Commun., 2013, 49, 10911; (b) H.
Kominami, M. Higa, T. Nojima, T. Ito, K. Nakanishi and K.
Hashimoto, ChemCatChem, 2016, 8, 2019.
i.e., 1) catalyst preparation based on an element strategy that 11 L. P. Hammett, J. Am. Chem. Soc., 1937, 59, 96.
1
2 (a) A. Tanaka, K. Hashimoto and H. Kominami, J. Am. Chem.
Soc., 2012, 134, 14526; (b) S. Kitano, A. Tanaka, K. Hashimoto
and H. Kominami, Phys. Chem. Chem. Phys., 2014, 16, 12554.
uses abundant elements, 2) environmental friendliness that
uses no harmful chemicals and 3) efficient utilization of
sunlight. This paper provides a new concept for an
4
| J. Name., 2012, 00, 1-3
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