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New Journal of Chemistry
DOI: 10.1039/C7NJ03057F
LETTER
Finally, we turned our attention to the investigation of the
Journal Name
2
(a) M. D. Tzirakis, I. N. Lykakis and M. Orfanopoulos, Chem.
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substrate scope for the photocatalytic deoxygenation of
pyridine N-oxides with II (Fig. 3). When the deoxygenation was
Fagnoni and A. Albini, Angew. Chem., Int. Ed., 2007, 46
531; (f) X.-B. Han, Y.-G. Li, Z.-M. Zhang, H.-Q. Tan, Y. Lu and
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,
2
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(a) K. Suzuki, F. Tang, Y. Kikukawa, K. Yamaguchi and N.
Mizuno, Angew. Chem., Int. Ed., 2014, 53, 5356; (b) K. Suzuki,
F. Tang, Y. Kikukawa, K. Yamaguchi and N. Mizuno, Chem.
Lett., 2014, 43, 1429; (c) K. Suzuki, T. Hanaya, R. Sato, T.
Minato, K. Yamaguchi and N. Mizuno, Chem. Commun.,
2
016, 52, 10688.
5
6
(a) K. Suzuki, J. Jeong, K. Yamaguchi and N. Mizuno, Chem.
Asian J., 2015, 10, 144; (b) K. Suzuki, J. Jeong, K. Yamaguchi
and N. Mizuno, New J. Chem., 2016, 40, 1014; (c) J. Jeong, K.
Suzuki, M. Hibino, K. Yamaguchi and N. Mizuno,
ChemistrySelect, 2016, 1, 5042; (d) K. Suzuki, K. Yamaguchi
and N. Mizuno, Chem. Lett., 2017, 46, 1379.
Fig. 3 Scope of the II-catalyzed deoxygenation of pyridine N-oxides by
irradiation with visible light. Reaction conditions: II (5.0 mol%), pyridine N-
oxides (0.1 mmol), 4-methoxybenzyl alcohol (0.5 mmol), acetone (1.0 mL),
photo-irradiation (λ > 400 nm) for indicated times at room temperature (ca.
3
0°C) under Ar (1 atm). Yields were determined by GC using naphthalene as
a
(a) K. Suzuki, R. Sato and N. Mizuno, Chem. Sci., 2013, 4, 596;
(
an internal standard. In acetonitrile (1.0 mL).
b) T. Minato, K. Suzuki, K. Yamaguchi and N. Mizuno,
Angew. Chem., Int. Ed., 2016, 55, 9630; (c) T. Minato, K.
Suzuki, Y. Ohata, K. Yamaguch and N. Mizuno, Chem.
Commun., 2017, 53, 7533.
(a) R. Sato, K. Suzuki, T. Minato, M. Shinoe, K. Yamaguchi and
N. Mizuno, Chem. Commun., 2015, 51, 4081; (b) R. Sato, K.
carried out in acetone, the reaction was completed in a
significantly shorter reaction time (4 h) comparing with that in
acetonitrile (20 h) (Table 1, entry 1 vs. entry 2). This is likely
because the reactants can efficiently coordinate to the vacant
site and/or the zinc site of II in the absence of the coordinating
solvent, like acetonitrile. Pyridine N-oxide and its derivatives
possessing electron-donating as well as electron-withdrawing
substituents were all efficiently converted into the
7
8
9
Suzuki, M. Sugawa and N. Mizuno, Chem. Eur. J., 2013, 19
12982.
,
(a) A. Yoshida, M. Yoshimura, K. Uehara, S. Hikichi and N.
Mizuno, Angew. Chem., Int. Ed., 2006, 45, 1956; (b) A.
Yoshida, S. Hikichi and N. Mizuno, J. Organomet. Chem.,
2
007, 692, 455.
corresponding pyridines in high yields (2a–2j). Even sterically
P. Sobota, M. Kimowicz, J. Utko and L. B. Jerzykiewicz, New J.
Chem., 2000, 24, 523.
hindered 2,6-dimethylpyridine N-oxide was efficiently
converted into the corresponding pyridine (2e). Importantly, 10 The CSI mass spectrum of II in acetone showed signal sets at
2
+
m/z 3543 and 6843 assignable to [TBA
[
9
H(ZnSi
2 20
W O69)] and
pyridine N-oxides possessing other reducible functional groups
were selectively deoxygenated to the corresponding pyridines,
and the reducible functional groups completely remained
intact. For example, hydrogenation of the phenyl ring (2f) and
the C=C double bond (2g) did not occur at all. No
dechlorination of the chloride group (2h) and no reduction of
the carbonyl group (2i) occurred. The cyano group (2j) also
completely remained intact. The structure of II was preserved
after the reaction (Fig. S15, ESI†), and II could be reuse for the
deoxygenation of pyridine N-oxide several times.
+
TBA H(ZnSi W O69)] , respectively (Fig. S16, ESI†). These
8 2 20
results showed that the acetimidate ligand and acetonitrile
ligand on II easily dissociated in the solution. Thus, it was
estimated that the formula of II in the solution was
TBA
1 Several geometric parameters, such as τ’, τ , and THCDA, for
7 3 34 2 2
H [Zn(γ-SiW10O ) (μ-O) ].
1
1
4
Zn1 also suggested that the coordination geometry of Zn1
was close to trigonal monopyramidal (Table S4, ESI†)
2 (a) M. Ray, B. S. Hammes, G. P. A. Yap, A. L. Rheingold and A.
S. Borovik, Inorg. Chem., 1998, 37, 1527; (b) F. Gross and H.
Vahrenkamp, Inorg. Chem., 2005, 44, 3321; (c) J. M.
Blacquiere, M. L. Pegis, S. Raugei, W. Kaminsky, A. Forget, S.
This work was supported in part by JSPS KAKENHI Grant
Numbers 26708009 and 17H03037. We thank Dr. X. Jin (The
University of Tokyo) for fruitful discussion.
A. Cook, T. Taguchi and J. M. Mayer, Inorg. Chem., 2014, 53
242.
3 When using
It was likely because of the low solubility of
4 J. J. Chen and M. A. Barteau, Ind. Eng. Chem. Res., 2016, 55
857.
,
9
1
1
1
I
, the white precipitation due to
I
was observed.
I
.
,
Notes and references
9
5 We have recently synthesized the alkoxides of POMs by the
reaction of trivacant lacunary Keggin-type POMs and
alcohols, and their structures were determined by the X-ray
crystallographic analysis, NMR and CSI mass spectra: T.
Minato, K. Suzuki, K. Yamaguchi and N. Mizuno, Chem. Eur.
J., DOI: 10.1002/chem.201702883.
6 (a) E. Ochiai, J. Org. Chem., 1953, 18, 534; (b) T. Kubota and
H. Miyazaki, Bull. Chem. Soc. Jpn., 1962, 35, 1549; (c) L.
Castro, A. Yahia and L. Maron, Dalton Trans., 2010, 39, 6682.
1
(a) M. T. Pope, Heteropoly and Isopoly Oxometalates,
Springer, Berlin, 1983; (b) N. Mizuno and M. Misono, Chem.
Rev., 1998, 98, 19; (c) Thematic Issue on POMs (Ed.: C. L.
Hill), Chem. Rev., 1998, 98, 1; (d) D.-L. Long, R. Tsunashima
and L. Cronin, Angew. Chem., Int. Ed., 2010, 49, 1736; (e) J.
Tucher, S. Schlicht, F. Kollhoff and C. Sterb, Dalton Trans.,
1
2
2
014, 43, 17029; (f) M. Dave and C. Sterb, Dalton Trans.,
015, 44, 18919.
4
| J. Name., 2012, 00, 1-3
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