Iridium-Catalyzed Reductive Amination of Levulinic Acid to Pyrrolidinones under H2 in Water

Article abstract of DOI:10.1002/cjoc.201600726

The synthesis of pyrrolidinones from reductive amination of levulinic acid (LA) with primary amines is reported. Pyrrolidinones have various applications such as surfactants, pharmaceutical intermediates, dispersants, and solvents. The half-sandwich Cp*Ir complex (Cp* is 1,2,3,4,5-pentamethylcyclopenta-1,3-diene) coordinated by bipyridine ligand bearing both dimethylamino and ortho-hydroxyl groups showed high catalytic activity for the reductive amination of LA. A range of primary amines, such as aromatic and benzyl amines, were readily converted to corresponding pyrrolidinones in good yields.

Full text of DOI:10.1002/cjoc.201600726

COMMUNICATION
DOI: 10.1002/cjoc.201600726
Iridium-Catalyzed Reductive Amination of Levulinic Acid to
Pyrrolidinones under H2 in Water
Zhanwei Xu, Peifang Yan, Hong Jiang, Kairui Liu, and Z. Conrad Zhang*
Dalian National Lab for Clean Energy, State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, Dalian, Liaoning 116023, China
The synthesis of pyrrolidinones from reductive amination of levulinic acid (LA) with primary amines is report-
ed. Pyrrolidinones have various applications such as surfactants, pharmaceutical intermediates, dispersants, and
solvents. The half-sandwich Cp*Ir complex (Cp* is 1,2,3,4,5-pentamethylcyclopenta-1,3-diene) coordinated by bi-
pyridine ligand bearing both dimethylamino and ortho-hydroxyl groups showed high catalytic activity for the re-
ductive amination of LA. A range of primary amines, such as aromatic and benzyl amines, were readily converted to
corresponding pyrrolidinones in good yields.
Keywords iridium, reductive amination, hydrogenation, levulinic acid, biomass
Introduction
Cp*Ir complex, and studied the reaction as shown in
Scheme 1 using formic acid. They further developed the
formic acid assisted reductive amination without cata-
lyst in dimethyl sulfoxide (DMSO).[25] As the silica gel
column was used to separate the product from DMSO,
separation could be an issue in a large scale synthesis.
Hydrosilane was also successfully applied as a hydro-
gen source for the synthesis of pyrrolidinones from LA.
Both boric compound[26] and In complex[27] could effi-
ciently catalyze the reductive amination by using hy-
drosilane. However, hydrosilane is not an ideal reducing
reagent owing to its high price and low atom-economy.
Compared with both formic acid and hydrosilane, H2 is
the most atom-economic hydrogen source (Scheme 1).
However, homogeneous catalysis for pyrrolidinones
synthesis from LA and amines by using H2 was rarely
studied so far.
The abundant and renewable lignocellulosic biomass
is an alternative feedstock to fossil resources for the
production of specialty fine chemicals. However, the
selective transformation of bio-based chemicals to fuels
and fine chemicals still faces big challenges. Levulinic
acid (LA), a versatile platform chemical from selective
hydrolysis of cellulose,[1-5] is regarded as one of the
most promising building blocks to produce value-added
products.[6-16] For example, γ-valerolactone, a hydro-
genation product of LA, can serve as a solvent and pre-
cursor to 1,4-pentanediol. Selective hydrogenation of
LA can also produce 2-methyltetrahydrofuran, a fuel
additive or solvent. The reductive amination of LA can
produce pyrrolidinones, which can be applied as surfac-
tants, pharmaceutical intermediates, dispersants, and
solvents.
Recently, heterogeneous catalyst,[17-22] including Pd,
Rh, Pt, and Au, showed high activity for the reductive
amination of LA with various kinds of amines. However,
high reaction temperature (＞120 ℃) and H2 pressure
are required for the heterogeneous catalysis. In general,
pyrrolidinones may be produced through homogeneous
catalysis in high selectivity under mild conditions.[23-27]
Formic acid, a byproduct generated from the LA pro-
duction process, is a promising hydrogen source. Fu and
coworkers[23] reported the first example of homogene-
ous Ru-catalyzed reductive amination of LA with aro-
matic or aliphatic amines by using formic acid. Xiao
and coworkers[24] prepared the imine ligand coordinated
Scheme 1 Previous work and this work
We previously reported the Cp*Ir complex catalyzed
hydrogenation/hydrolysis of bio-based 5-hydroxymeth-
ylfurfural by using H2 as a hydrogen source.[28-30] In that
work, the product 1-hydroxyhexane-2,5-dione was con-
*
E-mail: zczhang@yahoo.com
Received October 27, 2016; accepted December 18, 2016; published online XXXX, 2017.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201600726 or from the author.
In Memory of Professor Enze Min.
Chin. J. Chem. 2017, XX, 1—5
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Xu et al.
COMMUNICATION
sidered as a potential platform to produce value-added
chemicals. The impact of bipyridine ligand’s structure
on the activity of Cp*Ir complex was systematically
researched. The hydrogenation rate extremely increased
when the bipyridine ligand was modified by both dime-
thylamino (NMe2) and ortho-hydroxyl groups (o-OH)
(Scheme 2). The o-OH group assisted the H2 heterolytic
dissociation,[31-43] and the electron-donating ability of
both NMe2 and o-OH increased the hydrogenation ac-
tivity of the Cp*Ir-L complex. In this work, we investi-
gated the reductive amination of LA by Cp*Ir-L com-
plex under H2 atmosphere.
(m, 1H), 1.21－1.19 (m, 3H); 13C NMR (100 MHz,
CDCl3) δ: 174.2, 137.6, 129.0, 125.7, 124.0, 55.6, 31.4,
26.8, 20.2.
5-Methyl-1-(p-tolyl)pyrrolidin-2-one (2b, 179.8 mg,
95%):[25] 1H NMR (400 MHz, CDCl3, TMS) δ: 7.24－
7.17 (m, 4H), 4.28－4.19 (m, 1H), 2.66－2.47 (m, 2H),
2.40－2.30 (m, 4H), 1.78－1.68 (m, 1H), 1.19－1.17
(m, 3H); 13C NMR (100 MHz, CDCl3) δ: 174.2, 135.6,
135.0, 129.6, 124.2, 55.8, 31.3, 26.8, 21.0, 20.2.
1-(4-Methoxyphenyl)-5-methylpyrrolidin-2-one (2c,
191.0 mg, 93%):[25] 1H NMR (400 MHz, CDCl3, TMS)
δ: 7.25－7.21 (m, 2H), 6.93－6.89 (m, 2H), 4.21－4.13
(m, 1H), 3.78 (s, 1H), 2.63－2.46 (m, 2H), 2.38－2.28
(m, 1H), 1.76－1.67 (m, 1H), 1.15 (d, J＝6.24 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ: 174.1, 157.5, 130.3,
125.9, 114.2, 55.9, 55.3, 31.0, 26.7, 20.1.
Scheme 2 Structure of Cp*Ir-L complex of this work. OTf is
trifluoromethanesulfonate
2+
Me2N
1-(4-Fluorophenyl)-5-methylpyrrolidin-2-one (2d,
173.5 mg, 90%):[25] 1H NMR (400 MHz, CDCl3, TMS)
δ: 7.35－7.29 (m, 2H), 7.10－7.04 (m, 2H), 4.27－4.19
(m, 1H), 2.66－2.48 (m, 2H), 2.40－2.32 (m, 1H),
1.79－1.70 (m, 1H), 1.18 (d, J＝6.24 Hz, 3H); 13C
NMR (100 MHz, CDCl3) δ: 174.3, 160.4 (d, J＝244
Hz), 133.5 (d, J＝3 Hz), 126.0 (d, J＝8 Hz), 115.8 (d,
J＝22 Hz), 55.9, 31.2, 26.7, 20.1.
Cp*
N
IrIII
2 OTf-
N
H2O
OH
Cp*Ir-L
1-(4-Chlorophenyl)-5-methylpyrrolidin-2-one (2e,
187.0 mg, 89%):[25] 1H NMR (400 MHz, CDCl3, TMS)
δ: 7.36－7.31 (m, 4H), 4.30－4.22 (m, 1H), 2.66－2.46
(m, 2H), 2.39－2.30 (m, 1H), 1.78－1.69 (m, 1H), 1.19
(d, J＝6.24 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ:
174.1, 136.2, 130.6, 128.9, 124.8, 55.3, 31.2, 26.5, 19.9.
Experimental
General methods
NMR spectra were run in CDCl3 on a 400 MHz in-
strument and recorded at the following frequencies:
proton (1H, 400 MHz), carbon (13C, 100 MHz). H
1
1-(4-Bromophenyl)-5-methylpyrrolidin-2-one
(2f,
NMR chemical shifts were reported using tetrame-
thylsilane (TMS) as the internal standard. 13C NMR
spectra were reported using CDCl3 as the internal
standard.
223.6 mg, 88%):[25] 1H NMR (400 MHz, CDCl3, TMS)
δ: 7.51－7.47 (m, 2H), 7.31－7.28 (m, 2H), 4.32—4.24
(m, 1H), 2.67－2.48 (m, 2H), 2.41－2.32 (m, 1H),
1.79－1.71 (m, 1H), 1.20 (d, J＝6.24 Hz, 3H); 13C
NMR (100 MHz, CDCl3) δ: 174.2, 136.8, 132.1, 125.2,
118.7, 55.4, 31.3, 26.6, 20.0.
Preparation of Cp*Ir-L
The Cp*Ir-L was prepared according to the litera-
ture.[30] 1H NMR (400 MHz, CD3OD) δ: 1.65 (s, 15H),
3.29 (s, 6H), 7.02—7.05 (m, 1H), 7.21—7.23 (m, 1H),
7.58 (d, J＝2.88 Hz, 1H), 8.09—8.13 (m, 2H), 8.53 (d,
J＝6.96 Hz, 1H); 13C NMR (100 MHz, CD3OD) δ: 8.1,
38.6, 88.8, 105.8, 109.9, 113.3, 114.8, 120.4 (q, J＝317
Hz), 143.6, 149.6, 154.5, 155.9, 156.1, 163.9.
Ethyl 4-(2-methyl-5-oxopyrrolidin-1-yl)benzoate (2g,
160.7 mg, 65%):[25] 1H NMR (400 MHz, CDCl3, TMS)
δ: 8.08－8.04 (m, 2H), 7.57－7.54 (m, 2H), 4.45－4.34
(m, 3H), 2.73－2.51 (m, 2H), 2.43－2.35 (m, 1H),
1.88－1.74 (m, 1H), 1.39 (t, J＝7.12 Hz, 3H), 1.26 (d,
J＝6.24 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ: 174.4,
166.2, 141.9, 130.5, 126.8, 122.0, 61.0, 55.1, 31.5, 26.5,
19.9, 14.4.
Synthesis of pyrrolidinone 2
To a solution of LA (162.4 mg, 1.4 mmol) in water
(2.0 mL) at room temperature was added Cp*Ir catalyst
(0.43 mg, 0.0005 mmol) and aniline (1.0 mmol). The
high pressure reactor (20 mL) was purged with H2 (20
bar) four times, and was heated to 80 ℃ for 10 h. The
aqueous solution was extracted by CH2Cl2 (5.0 mL)
three times. After removing the combined CH2Cl2, the
crude residue was purified on a silica gel column to af-
ford the product 2.
5-Methyl-1-phenylpyrrolidin-2-one (2a, 166.3 mg,
95%).[25] 1H NMR (400 MHz, CDCl3, TMS) δ: 7.41－
7.36 (m, 4H), 7.22－7.18 (m, 1H), 4.33－4.27 (m, 1H),
2.68－2.49 (m, 1H), 2.41－2.32 (m, 1H), 1.79－1.70
1-(4-Benzylphenyl)-5-methylpyrrolidin-2-one
(2i,
217.5 mg, 82%):[25] 1H NMR (400 MHz, D2O) δ: 7.50－
7.45 (m, 5H), 4.26－4.16 (m, 2H), 3.36－3.28 (m, 1H),
2.40－2.21 (m, 2H), 2.07－1.98 (m, 1H), 1.84－1.75
(m, 1H), 1.36 (t, J＝6.64 Hz, 3H); 13C NMR (100 MHz,
D2O) δ: 181.4, 131.2, 129.6, 129.5, 129.3, 54.4, 48.4,
33.6, 29.0, 15.5.
1-Butyl-5-methylpyrrolidin-2-one (2j, 97.8 mg,
63%):[27] 1H NMR (400 MHz, D2O) δ: 3.10－2.97 (m,
2H), 2.75－2.36 (m, 3H), 2.02－1.66 (m, 4H), 1.42－
1.34 (m, 5H), 0.96 (t, J＝6.64 Hz, 3H); 13C NMR (100
MHz, D2O) δ: 179.4, 55.1, 44.5, 35.7, 29.4, 28.4, 20.2,
17.3, 13.7.
2
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Chin. J. Chem. 2017, XX, 1—5

Iridium-Catalyzed Reductive Amination of Levulinic Acid to Pyrrolidinones under H2 in Water
Results and Discussion
amines was performed under optimized conditions. The
results are shown in Table 2. The aromatic amines with
electron-donating methyl or methoxyl groups smoothly
proceeded to generate the corresponding products 2b
and 2c in high yields (95% and 93%). Good yields of 2d,
2e, and 2f (90%, 89%, and 88%, respectively) were also
obtained when the amines bore with electron-with-
drawing groups. Compared to the amines with electron-
donating groups (Me and OMe), the amines with elec-
tron-withdrawing groups (F, Cl, and Br) required longer
reaction time to achieve high yields. The electron-
withdrawing groups probably slowed down the imina-
tion of amines with LA, resulting in a longer time for
electron-deficient amines to convert. The low yields of
2g (65%) and 2h (0%) were owing to the strong elec-
tron-withdrawing effects of CO2Et and CN, respectively.
We also tried the reductive amination of LA with benzyl
amine, and the product 2i was obtained with an 82%
isolated yield. The product 2j was obtained with a 63%
isolated yield, while none of product 2k was obtained
probably because of the steric hindrance effect. The
product 2l was also not obtained.
Based on the literatures [30,37] and experiments, the
proposed mechanism of Cp*Ir-L catalyzed reductive
amination is shown in Scheme 4. The Cp*Ir-L first re-
leases a proton to form intermediate A, followed by H2
heterolytic dissociation on A to form intermediate B.
The imination of LA with amine generates imine prod-
uct C. C reacts with B through an 8-membered ring
transition state[30,44,45] D to form E and A'. The intramo-
lecular amidation of E produces the product. A' reso-
nates to form B to undergo the next catalytic cycle. The
amine with electron-withdrawing groups might slow
down the formation rate of C, resulting in a low reactive-
Because water was environmentally friendly and the
desired product 2a could easily be separated from water
through extraction, the optimization of LA with aniline
was carried out in aqueous solution (Table 1). The re-
ductive amination of aniline with LA was firstly opti-
mized under 20 bar of H2 at 80 ℃, and 75% of 2a was
isolated (Entry 1). Compared to the result of Entry 1, the
yield of 2a decreased at lower H2 pressure (60%, Entry
2), while the yield of 2a was slightly increased with in-
creasing H2 pressure from 20 bar (75%, Entry 1) to 25
bar (77%, Entry 3). Thus, the subsequent optimizations
were carried out under 20 bar of H2. As the byproduct
γ-valerolactone can consume a small amount of LA, the
excess amount of LA was optimized. The yield of 2a
reached 95% when 1.4 equiv. of LA was used (Entry 5).
The yield of 2a decreased to 85% when the temperature
was increased to 100 ℃ (Entry 6), because the
γ-valerolactone formation rate probably increased faster
than the reductive amination rate with increasing the
temperature. The yield of 2a decreased to 43% when the
temperature was decreased to 60 ℃ (Entry 7). In the
presence of 1.4 equiv. of LA, the yield of 2a decreased
to 83% with lower pressure of H2 (15 bar, Entry 8),
while the yield of 2a did not significantly increased with
higher pressure of H2 (20 bar, Entry 9). Finally, the re-
ductive amination of LA was studied in the presence of
a small amount of Cp*Ir-L, and the turnover number
(TON) of catalyst reached 8800 (Entry 7). The subse-
quent synthesis of pyrrolidinones from LA and various
amines was performed with Cp*Ir-L as the catalyst in
water at 80 ℃ under a H2 atmosphere (Entry 5).
Table 1 Optimization of reaction conditionsa
Scheme 4 Proposed reductive amination mechanism
Cp*Ir complex, H2
O
PhNH2
LA
+
N
water
1a
2+
Ph
Me2N
2a
Me2N
Cp*
+
N
N
Cp*
- H+
N
N
Entry
LA (equiv.) Pressure/bar Yieldb/%
IrIII
Temperature/℃
IrIII
1
2
80
80
80
80
80
100
60
80
80
80
1.0
1.0
1.0
1.2
1.4
1.4
1.4
1.4
1.4
1.4
20
15
25
20
20
20
20
15
25
20
75
60
77
89
95
89
43
83
96
88
OH
H2
Cp*Ir-L
O
A
3
+
+
Me2N
Me2N
4
Cp*
H
Cp*
N
N
5
R1
IrIII
IrIII
N
C
6
+
N
R
N
H
H
Ir
N
7
O
H
O
O
B
A'
N
8
9
10c
D: The N linked to Ir is
the N-atom of
D
a Reaction conditions: LA, aniline (1.0 mmol), water (2.0 mL),
and Cp*Ir-L (0.05 mol%), under H2, for 10 h. b Isolated yields
were given. c Cp*Ir-L (0.01 mol%), and for 24 h.
ligand
R
N
H
O
OH
O
R
R
LA
N
OH
R
N
NH2
C
O
E
The direct reductive amination of LA with various
Chin. J. Chem. 2016, XX, 1—5
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
3

Xu et al.
COMMUNICATION
Table 1 Reaction of LA with different aminesa
Compd.
Time/h Yield/%
Compd.
Time/h Yield/%
Compd.
Time/h Yield/%
N
N
Cl
10
7
95
95
93
90
16
14
12
89
88
65
0
10
24
24
24
82
63
0
O
O
2e
2i
N
9
O
2k
16
16
0
a Isolated yields were given for all products.
51, 548.
ity of the relative amines.
[5] Mukherjee, A.; Dumont, M.-J.; Raghavan, V. Biomass Bioenergy
2015, 72, 143.
[6] Gallezot, P. Chem. Soc. Rev. 2012, 41, 1538.
[7] Omoruyi, U.; Page, S.; Jason Hallett, D.; Miller, P. W. ChemSus-
Chem 2016, 9, 2037.
[8] Gilkey, M. J.; Xu, B. ACS Catal. 2016, 6, 1420.
[9] Zhang, Z. ChemSusChem 2016, 9, 156.
[10] Yan, K.; Jarvis, C.; Gu, J.; Yan, Y. Renew. Sustain. Energy Rev. 2015,
51, 986.
[11] Démolis, A.; Essayem, N.; Rataboul, F. ACS Sustainable Chem. Eng.
2014, 2, 1338.
[12] Alonso, D. M.; Wettstein, S. G.; Dumesic, J. A. Green Chem. 2013,
15, 584.
[13] Wright, W. R. H.; Palkovits, R. ChemSusChem 2012, 5, 1657.
[14] Bozell, J. J.; Petersen, G. R. Green Chem. 2010, 12, 539.
[15] De, S.; Saha, B.; Luque, R. Bioresource Technol. 2015, 178, 108.
[16] Pace, V.; Hoyos, P.; Castoldi, L.; Domínguez de María, P.; Alcántara,
A. R. ChemSusChem 2012, 5, 1369.
Conclusions
In summary, we developed a simple and efficient
procedure to synthesize pyrrolidinones by Cp*Ir com-
plex catalyzed reductive amination of LA with amines
under H2 in water. Aromatic amines bearing electron-
donating groups show good reactivity and yield to form
the corresponding pyrrolidinones, while the aromatic
amines bearing electron-withdrawing groups require
longer time to reach good yields. Further extension of
substrate scope and the research on the catalyst recycle,
as well as the large scale synthesis, are underway.
Acknowledgement
This research was supported by the CAS/SAFEA
International Partnership Program for Creative Research
Teams, and the Chinese Government “Thousand Talent”
program funding.
[17] Shilling, W. L. US 19620169656, 1966 [Chem. Abstr. 1966, 64,
67709].
[18] Crook, L. R.; Jansen, B. A.; Spencer, K. E.; Watson, D. H. GB
1036694, 1966 [Chem. Abstr. 1966, 65, 90458].
[19] Manzer, L. E. US 20030396212, 2004 [Chem. Abstr. 2004, 141,
7018].
[20] Manzer, L. E.; Herkes, F. E. US 20030396046, 2004 [Chem. Abstr.
2004, 141, 295854].
References
[21] Du, X. L.; He, L.; Zhao, S.; Liu, Y. M.; Cao, Y.; He, H. Y.; Fan, K. N.
Angew. Chem., Int. Ed. 2011, 50, 7815.
[1] Ahmad, E.; Imteyaz Alam, M.; Pant, K. K.; Ali Haider, M. Green
Chem. 2016, 18, 4804.
[22] Vidal, J. D.; Climent, M. J.; Concepcion, P.; Corma, A.; Iborra, S.;
Sabater, M. J. ACS Catal. 2015, 5, 5812.
[23] Huang, Y. B.; Dai, J. J.; Deng, X. J.; Qu, Y. C.; Guo, Q. X.; Fu, Y.
[2] Pileidis, F. D.; Titirici, M.-M. ChemSusChem 2016, 9, 562.
[3] Deng, W.; Zhang, Q.; Wang, Y. Sci. China, Chem. 2015, 58, 29.
[4] Morone, A.; Apte, M.; Pandey, R. A. Renew. Sust. Energ. Rev. 2015,
4
www.cjc.wiley-vch.de
© 2017 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2017, XX, 1—5

Iridium-Catalyzed Reductive Amination of Levulinic Acid to Pyrrolidinones under H2 in Water
ChemSusChem 2011, 4, 1578.
[35] Fujita, K.; Kawahara, R.; Aikawa, T.; Yamaguchi, R. Angew. Chem.,
[24] Wei, Y.; Wang, C.; Jiang, X.; Xue, D.; Li, J.; Xiao, J. Chem. Com-
mun. 2013, 49, 5408.
[25] Wei, Y.; Wang, C.; Jiang, X.; Xue, D.; Liu, J.-T.; Xiao, J. Green
Chem. 2014, 16, 1093.
[26] Fu, M.-C.; Shang, R.; Cheng, W.-M.; Fu, Y. Angew. Chem., Int. Ed.
2015, 54, 9042.
[27] Ogiwara, Y.; Uchiyama, T.; Sakai, N. Angew. Chem., Int. Ed. 2016,
55, 1864.
Int. Ed. 2015, 54, 9057.
[36] Kawahara, R.; Fujita, K.; Yamaguchi, R. Angew. Chem., Int. Ed.
2012, 51, 12790.
[37] Wang, W.-H.; Himeda, Y.; Muckerman, J. T.; Manbeck, G. F.; Fujita,
E. Chem. Rev. 2015, 115, 12936.
[38] Wang, W.-H.; Ertem, M. Z.; Xu, S.; Onishi, N.; Manaka, Y.; Suna, Y.;
Kambayashi, H.; Muckerman, J. T.; Fujita, E.; Himeda, Y. ACS
Catal. 2015, 5, 5496.
[28] Xu, Z.; Yan, P.; Zhang, Z. C. Chin. J. Org. Chem. 2017, 37, 40.
[29] Xu, Z.; Yan, P.; Xu, W.; Liu, X.; Xia, Z.; Chung, B.; Jia, S.; Zhang,
Z. C. ACS Catal. 2015, 5, 788.
[30] Xu, Z.; Yan, P.; Li, H.; Liu, K.; Liu, X.; Jia, S.; Zhang, Z. C. ACS
Catal. 2016, 6, 3784.
[31] Fujita, K.; Tanaka, Y.; Kobayashi, M.; Yamaguchi, R. J. Am. Chem.
Soc. 2014, 136, 4829.
[32] Zeng, G.; Sakaki, S.; Fujita, K.; Sano, H.; Yamaguchi, R. ACS Catal.
2014, 4, 1010.
[39] Hull, J. F.; Himeda, Y.; Wang, W.-H.; Hashiguchi, B.; Periana, R.;
Szalda, D. J.; Muckerman, J. T.; Fujita, E. Nat. Chem. 2012, 4, 383.
[40] Wang, W.-H.; Xu, S.; Manaka, Y.; Suna, Y.; Kambayashi, H.; Muck-
erman, J. T.; Fujita, E.; Himeda, Y. ChemSusChem 2014, 7, 1976.
[41] Onishi, N.; Xu, S.; Manaka, Y.; Suna, Y.; Wang, W.-H.; Muckerman,
J. T.; Fujita, E.; Himeda, Y. Inorg. Chem. 2015, 54, 5114.
[42] Wang, W.-H.; Hull, J. F.; Muckerman, J. T.; Fujita, E.; Himeda, Y.
Energy Environ. Sci. 2012, 5, 7923.
[43] Suna, Y.; Ertem, M. Z.; Wang, W.-H.; Kambayashi, H.; Manaka, Y.;
Muckerman, J. T.; Fujita, E.; Himeda, Y. Organometallics 2014, 33,
6519.
[33] Kawahara, R.; Fujita, K.; Yamaguchi, R. J. Am. Chem. Soc. 2012,
134, 3643.
[34] Fujita, K.; Yoshida, T.; Imori, Y.; Yamaguchi, R. Org. Lett. 2011, 13,
2278.
[44] Wang, R.; Ma, J.; Li, F. J. Org. Chem. 2015, 80, 10769.
[45] Li, F.; Ma, J.; Wang, N. J. Org. Chem. 2014, 79, 10447.
(Zhao, C.)
Chin. J. Chem. 2016, XX, 1—5
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