Application of alkoxide in catalytic transfer hydrogenation of unsaturated nitrogen compounds

Article abstract of DOI:10.1007/s11164-012-0542-9

Alcoholate was utilized in catalytic transfer hydrogenation of unsaturated nitrogen compounds. In the reduction of nitro compounds, oximes and imines, alkoxide was used as the promoter, with alcohol as the hydrogen source, while in the reduction of nitriles, alkoxide was used as the hydrogen source. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11164-012-0542-9

Res Chem Intermed (2012) 38:2255–2269
DOI 10.1007/s11164-012-0542-9
Application of alkoxide in catalytic transfer
hydrogenation of unsaturated nitrogen compounds
•
Xinzhi Chen Shaodong Zhou Yuehan Chen
•
•
•
•
Zehan Dong Yeyu Gao Chao Qian Chaohong He
•
Received: 17 February 2012 / Accepted: 23 March 2012 / Published online: 10 April 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Alcoholate was utilized in catalytic transfer hydrogenation of unsatu-
rated nitrogen compounds. In the reduction of nitro compounds, oximes and imines,
alkoxide was used as the promoter, with alcohol as the hydrogen source, while in the
reduction of nitriles, alkoxide was used as the hydrogen source.
Keywords Transfer hydrogenation ꢀ Alkoxide ꢀ Amines
Introduction
Transfer hydrogenation using alcohol as the hydrogen source is a clean method to
reduce unsaturated compounds such as ketones, imines, nitriles, etc. [1–4]. Various
alcohols have already been proved to be efficient hydrogen sources for catalytic
reduction of ketones [5–9]. However, the application of alcohol in transfer
hydrogenation of unsaturated nitrogen compounds is limited. Xiang et al. [10] and
Xu et al. [11] have reported transfer hydrogenation of nitro compounds, with
methanol/water as the hydrogen source. But their method suffered from high
temperatures and low yield of primary amines. Zhou et al. [12] has reported Ru–Fe/
C catalyzed transfer hydrogenation of nitro compounds using ethanol/water as the
hydrogen source, which also suffered from the reaction temperature. Actually, only
isopropanol has been proved to be an efficient hydrogen source that can be widely
used in the reduction of unsaturated nitrogen compounds under relatively milder
conditions. The focus of this work is to expand the utilization of various alcohols in
transfer hydrogenation.
X. Chen ꢀ S. Zhou ꢀ Y. Chen ꢀ Z. Dong ꢀ Y. Gao ꢀ C. Qian (&) ꢀ C. He
Department of Chemical and Biological Engineering, State Key Laboratory of Chemical
Engineering, Zhejiang University, Hangzhou 310027, China
e-mail: supmoney@163.com
123

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X. Chen et al.
Recently, we found that dehydrogenation from the a-carbon of alcohol can be
easier when the hydroxyl is deprotonated. So the deprotonated alcohol, which is
alkoxide, may be a better hydrogen source than alcohol in transfer hydrogenation.
Investigations on transfer hydrogenation of unsaturated nitrogen compounds were
performed with various alkoxides present.
Results and discussion
Transfer hydrogenation of nitro
Transfer hydrogenation of 4-chloronitrobenzene catalyzed by different metals was
first investigated, with sodium ethylate as the hydrogen source. Fry et al. [13] have
reported uncatalyzed reduction of nitrobenzene by sodium alkoxide. Ogata et al.
[14] also reported the kinetic study of this process. Prato et al. [15] revealed the
details of the uncatalyzed reduction of substituted nitrobenzene. All the previous
studies have one conclusion in common: the product composition was complicated.
Our recent study indicated that some catalysts may greatly affect the product
distribution. Four commonly used catalysts, Raney Ni, Pd/C, Pt/C, and Cu, were
selected to perform comparative reactions. A coupling reaction between nitroben-
zene and aniline can be catalyzed by particular catalysts [16, 17], and coupling
products were detected with different yields in the reductive environments employed.
As dechlorination could also be available, reactions in the investigated system may be
complicated. The possible products are listed in Eq. 1. It is clear from Table 1 that
reduction of nitrobenzene catalyzed by Pd/C gave the highest selectivity of aniline,
while Pt/C was more effective in catalyzing the coupling reaction. Both reduction of
the nitro group and dechlorination proceeded easily in Raney Ni catalyzed reaction at
323 K, but aniline was the only product if the reaction temperature is decreased to
298 K. It is notable that Cu showed different catalysis effects at different
temperatures; dechlorination was available only at a high temperature.
Cl
Cl
O-
N+
NH2
N
N
N
+
+
Cl
Cl
Cl
C1
B1
NO2
A1
Cat.
ð1Þ
R: C2H5ONa
Solv.: C2H5OH
O-
N+
Cl
NH2
N
N
N
+
+
B2
C2
A2
The oxidized product of sodium ethylate detected in the experiments was
acetaldehyde; then there was an extra proton participating in the reaction. The
proton source in the above systems should be ethanol, so the catalytic transfer
hydrogenation of nitrobenzene with sodium ethylate in ethanol can be expressed as
Eq. 2. According to Eq. 2, the actual cost of sodium ethylate in reducing per mole
123

Application of alkoxide in catalytic transfer hydrogenation
2257
Table 1 Catalytic transfer hydrogenation of 4-chloronitrobenzene with sodium ethylate as hydrogen
source
Entry
Catalyst
Conversion (%)
Selectivity (%)
A1
A2
B1
B2
C1
C2
1
2a
Raney Ni
Raney Ni
Pd/C
92.6
69.4
85.5
90.7
84.3
98.8
–
89.5
[99
–
8.2
–
–
–
–
–
–
–
2.3
–
–
–
–
–
–
–
–
3
[99
–
–
–
4
Pt/C
–
[99
0.7
4.4
–
5
6b
Cu
96.1
40.7
3.2
54.9
–
Cu
–
Reaction conditions: 4-chloronitrobenzene (5 mmol), sodium ethylate (20 mmol), solvent (ethanol,
50 mL), temperature (323 K), time (2 h), catalyst (0.2 g)
a
The reaction temperature is 298 K
b
The reaction temperature is 343 K
nitrobenzene is 2 mol. In order to verify this conclusion, we performed Pd/C
catalyzed transfer hydrogenation of nitrobenzene in ethanol with sodium ethylate of
two times moles. The conversion of nitrobenzene was eventually higher than 99 %,
in agreement with our conclusion. Therefore, the actual role that the alkoxide plays
in the catalytic transfer hydrogenation of nitrobenzene is as a promoter, though most
of the alkoxide is consumed due to the production of water.
Cat.
+ 3C2H5ONa + 3C2H5OH
NO2
+ 3CH3CHO + 2NaOH + C2H5ONa + 2C2H5OH
NH2
ð2Þ
We compared different catalyst–alkoxide/alcohol hydrogen donating systems
with previously used catalyst–alcohol systems. Reduction of nitrobenzene was selected
as the model reaction, and the results are summarized in Table 2. The high yields of
aniline given by catalytic hydrogenation of nitrobenzene in a short time (Table 2,
Entries 19, 20) indicates that the rate-limiting step in catalytic transfer hydrogenation of
nitrobenzene was the dehydrogenation of donor. Among all the previously proposed
transfer hydrogenation systems, NiHMA–CH3CH(CH3)OH was the most efficient one
(Table 2, Entry 11), which gave 97 % yield of aniline in 1.5 h at 356 K. The Raney Ni–
CH3CH(CH3)ONa/CH3CH(CH3)OH system, however, could give a similar yield in a
shorter time, indicating its superiority of dehydrogenation on the Ni surface. The other
hydrogen donating systems, which are shown in Table 2 (Entries 16, 17 and 18) gave
considerably lower yields of aniline than the respective catalyst–alkoxide/alcohol
systems. The advantage of the alkoxide/alcohol combination over alcohol as the
hydrogen source was thus verified. Comparison of different alkoxide/alcohol
combinations provided us with more information. It can be found in Table 2 that
C3H7ONa/C3H7OH and C4H9ONa/C4H9OH were more efficient hydrogen sources
than CH3CH(CH3)ONa/CH3CH(CH3)OH and C2H5CH(CH3)ONa/C2H5CH(CH3)OH,
respectively. So a conclusion can be made that dehydrogenation of primary alkoxides is
more favored than that of secondary alkoxides on the Pd surface. It is can also be found
123

2258
X. Chen et al.
Table 2 Catalytic transfer hydrogenation of nitrobenzene
Cat.
H-donating system
NO2
NH2
Entry H-donating system
Catalyst
Temperature Reaction time Yieldh
(K)
(h)
(%)
1
CH3ONa/CH3OH
Pd/C
333
333
333
333
333
333
333
333
333
356
333
333
333
333
333
356
353
2.5
2
90
87
91
0
2
CH3ONa/CH3OH
Raney Ni
Pd/C
3
CH3OK/CH3OH
2.5
3
4
CH3OH
Pd/C
5
C2H5ONa/C2H5OH
C2H5OK/C2H5OH
Pd/C
2.5
2.5
2.5
2.2
3
96
96
0
6
Pd/C
7
C2H5OH
Pd/C
8
C3H7ONa/C3H7OH
CH3CH(CH3)ONa/CH3CH(CH3)OH
CH3CH(CH3)ONa/CH3CH(CH3)OH
CH3CH(CH3)OK/CH3CH(CH3)OH
CH3CH(CH3)OH
Pd/C
99
88
96
85
30
97
89
98
97
80
30
14
[99
[99
9
Pd/C
10
11
12
13
14
15
16a
17b
18c
19e
20g
21g
Raney Ni
Pd/C
1.0
3
Pd/C
3
C4H9ONa/C4H9OH
Pd/C
2.0
3
C2H5CH(CH3)ONa/C2H5CH(CH3)OH Pd/C
C5H11ONa/C5H11OH
CH3CH(CH3)OH
CH3CH(CH3)OH
CH3OH/H2Of
CH3OH
Pd/C
1.6
1.5
6
NiHMA
c-Fe2O3
Pd–Ba/Al2O3 393
4/hd
Raney Ni
Raney Ni
Pd/C
353
333
333
5
H2
0.25
0.3
H2
For the alkoxide/alcohol system, the reaction conditions are as follows: nitrobenzene (20 mmol), alkoxide
(40 mmol), alcohol (20 mL)
a
Refs. [2, 3]
b
Ref. [20]
c
Ref. [10]
d
The reaction was carried out in a fix-bed reactor
e
Ref. [20]
f
The molar ratio of methanol and water is 1:1
g
The reaction was carried out with toluene–water mixture(volumetric ratio 2:1, 50 mL) as solvent
h
GC yield
that dehydrogenation of alkoxide becomes easier as the carbon chain increases. To
explain the experimental results, we proposed the mechanism of alkoxide promoted
dehydrogenation of alcohol, as shown in Scheme 1. The initial oxidation of the
alkoxide takes place to form an aldehyde or an acetone. Then, aldehyde can react with
another molecule of alkoxide to form a hemiacetal which is subsequently oxidized
irreversibly to the more stable ester; this process is known as the Tishchenko reaction
123

Application of alkoxide in catalytic transfer hydrogenation
2259
O
-H-
O
O
O
O
O
R1
R1
H
R1
O
R1
R1
O
R1
R1
O
-H-
R2
R2
R2
O
O
R1
R1
R2
R1
O
R1
R1
R2
Scheme 1 The proposed mechanism of alkoxide promoted dehydrogenation of alcohol
Table 3 Pd/C catalyzed transfer hydrogenation of different nitro compounds
Cat.
R
R
H-donating system
NO2
NH2
Entry
R
Reaction time (h)
Yieldb (%)
1
2
4-Me
3
3
3
6
3
92
93
90
89
95
3-MeO
3-Cl
3
4a
3-NO2
3-NH2
5
Reaction conditions: substrate (5 mmol), sodium propanolate (11 mmol), propanol (30 mL), temperature
(323 K), catalyst (Pd/C, 0.2 g)
a
For which 20 mmol sodium propanolate was added, and the product was benzene-1,3-diamine
b
GC yield
[18, 19], while similar reactions cannot proceed between acetone and alkoxide, and the
reduction is prone to reverse due to the accumulated acetone. The a-carbon of alkoxide
with a longer carbon chain is easier to be dehydrogenated, so it gave a better
performance in the transfer hydrogenation. Sodium alkoxide and potassium alkoxide
showed almost identical performances in the reactions, indicating that the cation has
little influence on the adsorption and dehydrogenation of alkoxide anion on the Pd
surface. The blank experiments in which the alkoxide was absent gave much lower
yields of amines, indicating the promotion effect of alkoxide.
Our investigation was subsequently expanded to Pd/C catalyzed reduction of
various nitro compounds. C3H7ONa/C3H7OH was employed as the hydrogen
source, and the results are shown in Table 3. Generally, the substituted group on the
benzene ring has little effect on the reduction of nitro. Various substituted anilines
were obtained with high yield under mild conditions.
Now that alkoxide has been proved to be an efficient promoter in alcohol
participated transfer hydrogenation, a question came to us whether alkoxide can be a
hydrogen source without an extra proton donor. Transfer hydrogenation of
123

2260
X. Chen et al.
nitrobenzene was then carried out in aprotic solvents, with just sodium butanolate as
the hydrogen source. To our delight, nitrobenzene could still be reduced, with good
yields of aniline. There was no extra proton donor, so here came another question,
of where the other proton comes from. A phenomenon should be noted that only a
little butyraldehyde was detected all through the reactions, so the oxidization
product of sodium butanolate might be butyryl sodium. After adding water into the
products mixture, butyraldehyde of almost the same quantity with the added sodium
butanolate was detected, which verified our assumption. Table 4 summarizes the
experimental results. Compared to sodium butanolate/butanol participated transfer
hydrogenation, the reaction using only sodium butanolate as the hydrogen source
cost more time to give a similar yield at a higher temperature. Apparently,
butyraldehyde was not such an efficient proton donor as butanol. A reduction in 1,2-
dimethoxyethane (Table 4, Entry 3) gave a higher yield of aniline than those in toluene
and cyclohexane (Table 4, Entries 1, 2), probably because sodium butanolate has a
higher solubility in 1,2-dimethoxyethane.
According to the above conclusion, the alkoxide which can be used singly as a
hydrogen source must has two hydrogen atoms on the a-carbon, when secondary
alcohols should not be available. We next carried out Pd/C catalyzed reduction of
nitrobenzene in toluene, using only isopropanolate as reductant. No aniline was
detected even after 3 h reaction at 343 K, in agreement with our conclusion.
Transfer hydrogenation of nitriles
After investigation on the transfer hydrogenation of nitro, our focus turned to the
reduction of nitriles. The triple bond between carbon and nitrogen in nitriles is
stable and more difficult to be hydrogenated, so that only a few reported transfer
hydrogenation systems are available for the reduction of nitriles. The most efficient
hydrogen source reported until now is hydrazinium monoformate, with which the
transfer hydrogenation of nitriles can be accomplished in a short time with good to
excellent yields of the corresponding amines [21, 22]. However, there is not an
efficient method for reducing nitriles using alcohol as the hydrogen source. Mebane
et al. [4] have reported Raney nickel catalyzed two-step transfer hydrogenation of
aliphatic nitriles by 2-propanol, and fine yields of corresponding amines were
Table 4 Transfer hydrogenation of nitrobenzene in aprotic solvents
Cat.
C4H9ONa
NO2
NH2
Entry
Solvent
Reaction time (h)
Yielda (%)
1
2
3
Toluene
4.5
5
90
88
92
Cyclohexane
1,2-Dimethoxyethane
3.5
Reaction conditions: substrate (5 mmol), sodium butanolate (16 mmol), temperature (343 K), catalyst
(Pd/C, 0.2 g)
a
GC yield
123

Application of alkoxide in catalytic transfer hydrogenation
2261
obtained. But when we transposed this method of reduction to aromatic nitriles, only
a\30 % yield of the respective amines was obtained. A similar result was reported
by Mizushima et al. [23], who have investigated RuH2(PPh3)4 catalyzed reduction
of benzonitrile with the same hydrogen donor, 2-propanol, and found a ow yield of
benzylamine (6 %) after a long reaction (80 h).
A comparison of different catalysts was first performed, with reduction of
benzonitrile as the model reaction. To avoid the effect from the extra proton donor,
all the reactions were carried out in toluene with only sodium propanolate as the
hydrogen source. The results are shown in Table 5. Apparently, Raney Ni has
the highest activity, so it was chosen as the catalyst for further investigation on the
reduction of nitriles.
The influences of different solvents on the reaction were explored next. Another
three solvents, cyclohexane, 1,2-dimethoxyethane, and propanol, were investigated.
Propanol was employed in order to examine the influence of an active proton on the
reaction. The results are summarized in Table 6. Among all the aprotic solvents,
1,2-dimethoxyethane is the most favorable to the reaction, and that can be attributed
to its higher dissolubility of sodium propanolate. It is notable that the reaction in
propanol gave the highest conversion and the lowest selectivity. The probable
reaction is that alcoholysis of benzonitrile in propanol proceeds more easily than
transfer hydrogenation, and there was little reducing product detected. Similar
Table 5 Catalytic transfer hydrogenation of benzonitrile with sodium propanolate as hydrogen source
Entry
Catalyst
Conversion (%)
Selectivity of
benzylamine (%)
1
2
3
4
Raney Ni
Pd/C
60
7
[99
[99
–
Pt/C
0
Cu
5
[99
Reaction conditions: benzonitrile (5 mmol), sodium propanolate (20 mmol), solvent (toluene, 50 mL),
Raney Ni (0.1 g) or Pd/C (0.2 g), temperature (343 K), time (2 h)
Table 6 Raney Ni catalyzed transfer hydrogenation of benzonitrile in different solvents with sodium
propanolate as hydrogen source
Entry
Solvent
Conversion (%)
Selectivity of
benzylamine (%)
1
2
3
4
Toluene
60
58
[99
[99
[99
32
Cyclohexane
1,2-Dimethoxyethane
Propanol
71
[99
Reaction conditions: benzonitrile (5 mmol), sodium propanolate (20 mmol), solvent (50 mL), tempera-
ture (343 K), time (2 h) Raney Ni (0.1 g)
123

2262
X. Chen et al.
results were also obtained in the previous reports [24–27]. So, 1,2-dimethoxyethane
was selected as the solvent for further investigation.
With the selected reaction system, transfer hydrogenation of various nitriles was
investigated. Generally, all the reactions gave good yields of the corresponding
amines. Reduction of aliphatic nitriles (Table 7, Entries 1, 2) took a much shorter time
than that of aromatic nitriles. That can be attributed to the conjugation effect between
the benzene ring and the nitrile triple bond, which reduced the electron density around
the nitrile group and made it more difficult to be hydrogenated. The substituted chloro
and nitro on benzene could also be reduced, according to the experimental results in
‘‘Transfer hydrogenation of nitro’’ section. It can be seen in Table 7 that reduction of
4-chlorobenzonitrile and 4-nitrobenzonitrile (Table 7, Entries 6, 9) did not take an
obviously longer time that that of other substituted benzonitriles, indicating that
dechlorination and reduction of nitro proceeded much faster than reduction of cyano.
The experiment using propanol as hydrogen donor gave no yield of the corresponding
amine (Table 7, Entry 12), and the comparative result in Table 7 (Entry 3) proved the
high efficiency of alkoxide as the hydrogen donor.
In the reduction of nitriles, alkoxide is used as the hydrogen source, and the
oxidating product is acyl sodium, which can be removed by filtration. Compared to
the previous transfer hydrogenation systems, alkoxide participated reduction of
nitrile avoids the introduction of water and alcohol, so that the amines produced can
be easily purified.
Transfer hydrogenation of C=N bond
Alcoholysis of the C=N bond in imine and oxime is not feasible, so alcohol was
employed as the hydrogen source with alkoxide as the promoter in the transfer
hydrogenation of imine and oxime. Various complexes are used as catalyst in the
transfer hydrogenation of imine [28–32], and there are only a few reports on metal
catalyzed reduction of imine [33–35]. Oxime is capable of beingreduced so that
several transfer hydrogenation systems are available [36, 37]. In this work,
reduction of both imine and oxime was performed in the same system, which used
propanolate as the promoter and propanol as the hydrogen source. The results are
summarized in Table 8. Generally, all the selected substrates could be reduced with
good yields of the corresponding amines. For reduction of both oxime and imine,
Raney Ni showed higher catalytic activity than Pd/C. One mole of water is produced
when reducing 1 mol of oxime, so the molar ratio of n(oxime)/n(propanolate)
should not be [1. As no water is produced in the reduction of imine, the catalytic
dose of propanolate is enough to obtain high conversion. Taking account of the
reaction rate, the optimum ratio of n(imine)/n(propanolate) is 1:0.5. In the reduction
of imine, the consumption of propanolate is theoretically 0. Next, the reusability of
the catalyst and propanolate was investigated, and only a slight decrease of yield
was observed when they were reused for the third time. The blank experiments that
proceeded without sodium propanolate give no yield of the corresponding amines,
indicating the high efficiency of alkoxide as the hydrogen donor in the reduction of
imine and oxime. It can also be concluded that sodium propanolate and potassium
propanolate gave almost identical performances.
123

Application of alkoxide in catalytic transfer hydrogenation
2263
Table 7 Catalytic transfer hydrogenation of different nitriles
Cat.
R
R
NH2
CN
propanolate
Reaction conditions: nitrile (5 mmol), sodium propanolate (11 mmol), solvent (1,2-dimethoxyethane,
50 mL), temperature (343 K), Raney Ni (0.1 g)
a
For which 16 mmol sodium propanolate was added
b
For which 27 mmol sodium propanolate was added
c
For which 22 mmol sodium propanolate was added
d
For which sodium propanolate was replaced by propanol (11 mmol)
e
GC yield
123

2264
X. Chen et al.
Table 8 Catalytic transfer hydrogenation of C=N bond
H
R1
N
R1
N
Cat.
R3
R3
C3H7OM/C3H7OH
R2
R2
123

Application of alkoxide in catalytic transfer hydrogenation
2265
Table 8 continued
Reaction conditions: substrate (5 mmol), propanol (50 mL), temperature (343 K), Raney Ni (0.1 g)
a
For Entry 1–12 the alkoxide added was sodium propanolate, for Entries 15 and 16 the alkoxide added
was potassium propanolate
b
GC yield
c
For which Raney Ni and propanolate was reused for the third time
d
For which no sodium propanolate was added
Conclusion
In this work, we utilized alkoxide in the catalytic transfer hydrogenation of
unsaturated nitrogen compounds. Various alkoxide/alcohol systems were used as
the hydrogen source in the reduction of nitro compounds. Primary alkoxide/alcohol
is a more efficient hydrogen source than secondary alkoxide/alcohol, and its activity
increases as the carbon chain increases. The alkoxide/alcohol system could also be
used to reduce oxime and imine. The actual role that alkoxide played in alkoxide/
alcohol participated transfer hydrogenation is as a promoter. Especially in the
reduction of imine, the catalytic dose of alkoxide is enough for a high yield of
the corresponding amine. To avoid alcoholysis of cyano, alkoxide was used alone as
the hydrogen source in the reduction of nitriles, and the corresponding amines were
obtained with good to excellent yields. The utilization of alkoxide can help spread
the application of alcohol as the hydrogen source in transfer hydrogenation.
Experimental section
General procedure for reduction of nitro compounds
To a 100-mL three-necked flask was added alcohol (50 mL), nitro compounds
(5 mmol), alkoxide (11 mmol), and Pd/C (0.2 g). Then, the mixture was heated to
323 K and reacted for 3 h under stirring. After the reaction was completed, the
123

2266
X. Chen et al.
mixture was cooled to 20 °C and filtrated, and then the amine produced can be
distilled from the filtrate.
General procedure for reduction of nitriles
To a 100-mL three-necked flask was added aprotic solvent (50 mL), nitrile
(5 mmol), alkoxide (11 mmol), and Raney Ni (0.1 g). Then, the mixture was heated
to 343 K and reacted for 6 h under stirring. After the reaction was completed, the
mixture was cooled to 20 °C and filtrated, and then the amine produced can be
distilled from the filtrate.
General procedure for reduction of oximes and imines
To a 100-mL three-necked flask was added alcohol (50 mL), substrate (5 mmol),
alkoxide (5 mmol for reduction of oximes, and 0.25 mmol for reduction of imines),
and Raney Ni (0.1 g). Then, the mixture was heated to 343 K and reacted for 8 h
under stirring. After the reaction was completed, the mixture was cooled to 20 °C
and filtrated, and then the amine produced can be distilled from the filtrate.
Product characterization data
Aniline
1H NMR (CDCl3, 400 MHz, ppm): d = 3.64 (brs, 2H), 6.72 (d, 2H, J = 7.6 Hz),
6.76 (t, 1H, J = 7.2 Hz), 7.17 (2H, d, J = 8.0 Hz); 13C NMR (CDCl3, 100 MHz,
ppm): d = 114.9, 118.2, 129.0, 146.3 [38].
4-Methylaniline (Entry 1; Table 3)
1H NMR (CDCl3, 400 MHz, ppm): d = 2.22 (s, 3H), 3.49 (brs, 2H), 6.56 (d, 2H,
J = 7.8 Hz), 6.95 (d, 2H, J = 8.0 Hz); 13C NMR (CDCl3, 100 MHz, ppm):
d = 21.0, 114.9, 126.9, 129.8, 145.8 [39].
3-Methoxyaniline (Entry 2; Table 3)
1H NMR (CDCl3, 400 MHz, ppm): d = 3.68 (brs, 2H), 3.78 (s, 3H), 6.27 (s, 1H),
6.30–6.35 (m, 2H), 7.11 (t, 1H, J = 8.0 Hz); 13C NMR (CDCl3, 100 MHz, ppm):
d = 54.8, 100.5, 103.7, 107.4, 130.0, 147.1, 160.3 [39].
3-Chloroaniline (Entry 3; Table 3)
1H NMR (CDCl3, 400 MHz, ppm): d = 3.72 (brs, 2H), 6.47–6.49 (m, 1H), 6.62 (s,
1H), 7.02 (dd, 1H, J = 8.0, 7.8 Hz), 7.01(t, J = 8.0 Hz, 1H); 13C NMR (CDCl3,
100 MHz, ppm): d = 113.2, 114.9, 118.3, 130.4, 134.5, 147.2 [40].
123

Application of alkoxide in catalytic transfer hydrogenation
2267
Benzene-1,3-diamine (Entries 4, 5; Table 3)
1H NMR (CDCl3, 400 MHz, ppm): d = 3.54 (brs, 4H), 6.01 (t, 1H, J = 2.1 Hz),
6.10 (dd, 2H, J = 7.9, 2.1 Hz), 6.91(t, 1H, J = 7.9 Hz); 13C NMR (CDCl3,
100 MHz, ppm): d = 101.8, 106.0, 130.2, 147.5 [41].
Benzylamine (Entry 3; Table 7)
1H NMR (CDCl3, 400 MHz, ppm): d = 1.34 (s, 2H), 3.62 (s, 2H), 7.07–7.19 (m,
5H); 13C NMR (CDCl3, 100 MHz, ppm): d = 46.2, 126.5, 126.9, 128.3, 143.4 [42].
4-Methylbenzylamine (Entry 4; Table 7)
1H NMR (CDCl3, 400 MHz, ppm): d = 1.45 (brs, 2H), 2.32 (s, 3H), 3.89 (s, 2H),
7.12 (d, 2H, J = 8.0 Hz), 7.20 (d, 2H, J = 8.0 Hz); 13C NMR (CDCl3, 100 MHz,
ppm): d = 21.2, 46.0, 126.8, 129.7, 136.0, 140.7 [43].
2-Methylbenzylamine (Entry 5; Table 7)
1H NMR (CDCl3, 400 MHz, ppm): d = 1.64 (brs, 2H), 2.31 (s, 3H), 3.78 (s, 2H),
7.15–7.22(m, 3H), 7.27 (d, 1H, J = 6.7 Hz); 13C NMR (CDCl3, 100 MHz, ppm):
d = 18.7, 43.9, 126.1, 126.7, 126.9, 130.2, 135.4, 141.1 [44].
4-Methoxybenzylamine (Entry 7; Table 7)
1H NMR (CDCl3, 400 MHz, ppm): d = 1.52 (brs, 2H), 3.73 (s, 3H), 3.76 (s, 2H),
6.84 (d, 2H, J = 8.8 Hz), 7.17 (d, 2H, J = 8.5 Hz); 13C NMR (CDCl3, 100 MHz,
ppm): d = 45.7, 55.2, 114.0, 128.5, 134.1, 158.7 [42].
Phenylmethanamine (Entry 8; Table 7)
1H NMR (CDCl3, 400 MHz, ppm): d = 1.19 (s, 2H), 2.75 (t, 2H), 2,89 (t, 2H),
7.02–7.37 (m, 5H) [45]; 13C NMR (CDCl3, 100 MHz, ppm): d = 40.5, 44.2, 126.1,
128.0, 128.7, 140.2 [46].
4-Aminobenzylamine (Entry 9; Table 7)
1H NMR (CDCl3, 400 MHz, ppm): d = 2.02 (brs, 2H), 3.61 (s, 2H), 4.79 (s, 2H),
6.52 (d, 2H, J = 8.0 Hz), 6.98 (d, 2H, J = 8.0 Hz) [47]; 13C NMR (CDCl3,
100 MHz, ppm): d = 46.1, 115.0, 128.4, 132.9, 147.2 [48].
(1H-indol-2-yl)methanamine (Entry 10; Table 7)
1H NMR (DMSO-d6, 400 MHz, ppm): d = 3.84 (s, 2H), 6.22 (s, 1H), 6.93 (t, 1H,
J = 8.0 Hz), 7.01 (t, 1H, J = 7.8 Hz), 7.30 (d, 1H, J = 7.8 Hz), 7.44 (d, 1H,
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J = 8.0 Hz), 8.57 (s, 2H), 10.94 (brs, 1H); 13C NMR (DMSO-d6, 100 MHz, ppm):
d = 57.4, 98.2, 111.1, 118.9, 119.6, 120.4, 128.5, 136.4, 141.8 [49].
Cyclohexylamine (Entry 4; Table 8)
1H NMR (CDCl3, 400 MHz, ppm): d = 0.92–1.34 (m, 5H), 1.47–1.56 (m, 1H),
1.58–1.75 (m, 4H), 2.42–2.56 (m, 1H), 2.78 (brs, 2H); 13C NMR (CDCl3, 100 MHz,
ppm): d = 24.4, 24.8, 36.0, 49.5 [50].
N-benzylaniline (Entries 5–8; Table 8)
1H NMR (CDCl3, 400 MHz, ppm): 1H NMR (CDCl3, 400 MHz, ppm): d = 4.03 (brs,
1H), 4.32 (s, 2H), 6.62 (d, 2H, J = 7.8 Hz), 6.72 (t, 1H, J = 7.2 Hz), 7.13–7.20 (m,
2H), 7.27 (dd, 1H, J = 8.0, 5.4 Hz), 7.32–7.39 (m, 4H); 13C NMR (CDCl3, 100 MHz,
ppm): d = 48.4, 113.0, 117.7, 127.4, 127.6, 128.7, 129.4, 139.5, 148.3 [51].
N-benzylbutan-1-amine (Entry 9; Table 8)
1H NMR (CDCl3, 400 MHz, ppm): d = 0.88 (t, 3H, J = 7.2 Hz), 1.32–1.42 (m,
2H), 1.48–1.56 (m, 2H), 2.70 (brs. 1H), 3.84 (s, 2H), 7.25–7.39 (m, 5H); 13C NMR
(CDCl3, 100 MHz, ppm): d = 14.1, 20.6, 31.0, 50.2, 56.3, 126.7, 128.5, 128.7,
140.5 [52].
N-ethylaniline (Entry 10; Table 8)
1H NMR (CDCl3, 400 MHz, ppm): d = 1.26 (t, 3H, J = 7.2 Hz), 3.16 (q, 2H,
J = 7.2 Hz), 3.60 (brs, 1H), 6.60–6.64 (m, 2H), 6.70–6.73 (m, 1H), 7.17–7.26 (m,
2H); 13C NMR (CDCl3, 100 MHz, ppm): d = 15.0, 38.6, 113.0, 117.3, 129.4, 148.5
[53].
Acknowledgments We acknowledge the funding support by a grant from the National Natural Science
Foundation of China (No. 21076183), the Zhejiang Provincial Natural Science Foundation of China
(Y4090045), and the Student Research Training Program of Zhejiang University (14th, 7551).
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