Selective and recyclable rhodium nanocatalysts for the reductive N-alkylation of nitrobenzenes and amines with aldehydes

Article abstract of DOI:10.1039/c5ra05243b

Rhodium nanocatalysts were prepared and applied for the reductive N-alkylation of nitrobenzenes and amines to the corresponding secondary amines with aldehydes and ketones. Functional nitrobenzenes, such as nitrobenzenes with F, Cl, Br, CH₃O and CH₃ were transformed to the corresponding secondary amines in good to excellent yields. Moreover, the Rh@CN catalyzed N-alkylation of a series of primary amines with aldehydes and ketones also gave the corresponding secondary amines in high yields. The Rh@CN is heterogeneous, and can be reusable several times (at least 4 times) for the reductive N-alkylation of nitroarenes.

Full text of DOI:10.1039/c5ra05243b

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Selective and Recyclable Rhodium Nanocatalysts for the
Reductive N-Alkylation of Nitrobenzenes and Amines with
Aldehydes
Received 00th January 20xx,
Accepted 00th January 20xx
Lei Huang, Zhi Wang, Longfei Geng, Rizhi Chen, Weihong Xing, Yong Wang and Jun Huang a
DOI: 10.1039/x0xx00000x
Rhodium nanocatalysts were prepared and applied for the reductive N-alkylation of nitrobenzenes and amines to the
corresponding second amines with aldehydes and ketones. Functional nitrobenzenes, such as nitrobenzenes with F, Cl, Br,
CH3O and CH3 were transformed to the corresponding secondary amines in good to excellent yields. Moreover, the
Rh@CN catalyzed N-alkylation of a series of primary amines with aldehydes and ketones gave the corresponding
secondary amines in high yield also. The Rh@CN was heterogeneous, and can be reusable several times (at least 4 times)
for the reductive N-alkylation of nitroarenes.
www.rsc.org/
However, these catalysts are not selective enough for the N-
alkylation of nitrobenzenes with aldehydes, and aldehydes
Introduction
Secondary amines and their derivatives exist in many
biologically active molecules, and are important intermediates
for the synthesis of pharmaceuticals, dyes and fine chemicals1,
so the C-N bond formation becomes an important area in pure
and applied chemistry. The nucleophilic substitution of alkyl
halides with amines in the presence of stoichiometric amounts
of inorganic bases is one of the most common methods of C-N
bond formation2. However, the nucleophilic substitution
process has some problems, for example, the toxic nature of
alkyl halides, low selectivity of monoalkylation of primary
amines. Additionally, the process produces large amounts of
waste salts (stoichiometric amount of salts). The alkylation of
amines with alcohols is a good way for the C-N bond
formation, but the reaction conditions are harsh and the
catalysts are difficult to be reused3. The reductive N-alkylation
of amines with aldehydes (or ketones) is an attractive
procedure for C-N bond formation reaction4. The method
includes two synthetic steps: the C=N bond formation and the
hydrogenation of the imines to the corresponding N-alkylated
amines. Most anilines are produced by the reduction of
nitrobenzenes. Therefore, the reductive N-alkylation using
nitrobenzenes is considered to be an attractive idea as it does
not require prior reduction of nitrobenzenes. The selectivity of
the reaction is a challenging issue, so the development of
effective catalysts is highly desirable. Several catalysts based
on Pd5, Pt6, Ir7 and Au8 catalysts have be reported for the
reductive N-alkylation of nitrobenzenes with aldehydes.
cannot be used efficiently in the N-alkylation. Benzyl alcohol
and toluene are always found as the by-products in the
reaction. Recently, Fe9 and Co10 complexes with N contained
ligands were pyrolysed in activated carbon as heterogeneous
catalysts for the hydrogenation of nitro aromatics efficiently.
The 1, 10-phenanthroline (Phen) can be linked with the
activated carbon to form stable N-doped carbon materials,
which were used as good catalyst supports. And the Fe11 or
Co12 catalysts can also be used for the reductive N-alkylation of
nitrobenzenes with aldehydes. However, the efficiency of the
catalysts was not high enough.
Scheme 1. Rh@CN catalyzed reductive alkylation of nitrobenzenes
with aldehydes
We have reported the transfer hydrogenation of C=O bond
and the selective hydrogenation of nitroaromatics recently, 13
and we are also interested in the direct N-alkylation of
nitrobenzenes with aldehydes. Here rhodium nanoparticles
were supported on N-doped carbon materials as
heterogeneous catalysts, which were highly selective and
efficient for the reductive N-alkylation of nitrobenzenes and
amines with aldehydes and ketones (Scheme 1). Functional
nitrobenzenes, such as nitrobenzenes with F, Cl, Br, CH3O and
CH3 groups, were reductive alkylated with aldehydes efficiently
to the corresponding amines in good to excellent yields.
Moreover, the Rh@CN catalyzed N-alkylation of a series of
a.State Key Laboratory of Materials-Oriented Chemical Engineering,College of
Chemistry and Chemical Engineering; Nanjing Tech University, Nanjing 210009
(China) ,Fax: (+86) 25-83172261; E-mail: junhuang@njtech.edu.cn.
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primary amines with aldehydes and ketones gave the
corresponding secondary amines in high yields also.
Results and discussions
TEM analysis
The Rh@CN catalyst was characterized by TEM and the Rh
particles were highly dispersed in the CN materials (Figure 1).
Although the catalyst Rh@CN was prepared through high
temperature (up to 800 °C), the Rh nanoparticles were kept at
about only 6 nm (Figure 1-a), which indicated that the Rh@CN
was highly thermal stable, and the Phen structure was
profitable for the stabilization of Rh nanoparticles in the
Rh@CN catalyst.
Experimental section
The preparation of the Rh@CN
RhCl3·3H2O (52.6mg) was dissolved in ethanol (100 mL) with
stirring, then 1,10-phenanthroline monohydrate (108mg) was
added into the solution at room temperature (Rh: Phen=1:3
molar ratio). After stirring for another 1 h, activated carbon (1
g) was added into the solution and the mixture was stirring for
10 hours at 60 °C. After the mixture cooled to room
temperature, the ethanol was removed by the rotary
evaporation under vacuum. The black solid was dried in a
drying oven at 60 °C under vacuum for 12 hours, and then the
solid (the precursor of Rh@CN) was transferred into a quartz
boat and placed in the tube furnace under N2. The tube
furnace was heated to 800 °C at the rate of 10 °C per minute,
and kept at 800 °C for 2 hours under N2. After the tube furnace
cooled to room temperature, the catalyst Rh@CN (containing
Rh 2.01 wt %, detected by ICP) was obtained as black powders.
The preparation of the Rh@CN-5
Figure 1. (a)TEM image of the fresh Rh@CN nanocatalyst; (b)
TEM image of Rh@CN nanocatalyst recovered for the 4th time;
scale bar=20 nm.
BET&BJH analysis
The same procedure as that described above for the
preparation of Rh@CN was followed, except RhCl3·3H2O
increased to 131.5mg (containing Rh 4.95 wt %, detected by
ICP).
Based on the nitrogen adsorption-desorption analysis, the BET
(Brunauer-Emmett-Teller) surface area of the Rh@CN was
1128 m2 g-1 reduced from 1706 m2 g-1 (the parent AC), which
implied the CN materials (from Phen) with Rh nanoparticles
were formed inside the AC. And the total pore volume of the
Rh@CN was reduced to 0.82cm3/g from 1.16cm3/g. But the
average pore size increased to 2.9nm from 2.7nm (Figure 2).
The preparation of the Ru@CN
The precursor of Ru@CN was RuCl3 with 1, 10-phenanthroline
monohydrate (Ru: Phen=1:3 molar ratio) in activated carbon.
The same procedure as that described above for the
preparation of Rh@CN was followed, except Ru was used
instead of Rh as the metal catalyst (containing Ru 1.98 wt %,
detected by ICP).
0.6
800
600
400
200
0
AC
Rh@CN
0.5
0.4
0.3
0.2
0.1
0.0
General procedure for the reductive N-alkylation reactions
The reductive N-alkylation of nitrobenzenes (or amines) with
aldehydes was carried out in an autoclave. Typically, an
aldehyde (0.5mmol), a nitrobenzene (or amine) (0.55 mmol),
ethanol (4.0 mL), Rh@CN 14 mg (0.5% mol Rh) were added
into the autoclave with a stir bar. Then the autoclave was
flushed with H2 more than three times to remove the air, and
0.0
0.2
0.4
0.6
0.8
1.0
Relative Pressure (P/P
)
0
AC
Rh@CN
o
filled with H2 (3Mpa). The mixture was stirred under 80 C for
the given time. When the autoclave cooled to the room
temperature, 50 μL C16H34 was added to the reaction mixture
as internal standard for GC analysis. The Rh@CN catalyst was
filtrated off and washed with ethanol (3×4.0 mL). The products
(in the filtrate mixture) were analyzed by GC. The products
were purified by column chromatography on silica gel
(petroleum ether: ethyl acetate=20:1) and identified by 1H-
NMR.
0
10
20
30
40
50
Pore Diameter (nm)
Figure 2. Nitrogen adsorption-desorption isotherms of AC and
Rh@CN (shown in the inset) and BJH pore size distribution
TG analysis
The TG curve (see the Supporting Information, Figure S1) of
the precursor of Rh@CN showed that small amount of water
was desorbed and slight weight loss (about 1.8 %) was
The reusability of the Rh@CN
When the reaction completed and the reaction mixture was
cooled, the catalyst was collected by filtration. The catalyst
was washed by ethanol (3×4.0 mL) and dried under vacuum at
o
observed at temperature less than 200 C. About 8.0% weight
loss was observed at temperature between 200 to 500 °C,
which was attributed to the sublimation of the excess of Phen.
At temperature from 500 to 800 °C, about 2.5% of weight loss
o
the 25 C for 12 h, and then used again for the next reaction
cycle.
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was observed, which was attributed to the formation of Rh
nanoparticles with the escape of the chlorine and the EDX analysis
formation of N-doped graphene layers by carbonization of the
The element contents of the Rh@CN were evaluated by EDS
(Energy Dispersive X-Ray Spectroscopy), and the contents of C, N,
and Rh were 98.68%, 0.67%, 0.65%, respectively (see the
remained Phen ligand 11
.
XPS analysis
In order to find insights to the structures of the Rh Supporting Information, Figure S3). The content of Rh from EDX
nanocatalyst, the Rh@CN was characterized by XPS (X-ray analysis was lower than that from ICP analysis, which was due to
photoelectron spectroscopy) (Figure 3). Two N1s peaks were the enrichment of Rh nanoparticles inside the pores of the CN
found at 398.3 eV and 399.3 eV for the Rh@CN precursor, material, and not all Rh can be detected by EDS in the Rh@CN.
which were assigned to the free pyridinic nitrogen (from free Reaction condition screening for the reductive N-alkylation of
Phen) and the coordinated nitrogen (coordinated phen with Rh nitrobenzene with benzaldehyde
centers) respectively (Fig. 3, the left below) 14. The two N1s
The reductive N-alkylation of nitrobenzene with benzaldehyde was
peaks at 398.3 eV and 399.5 eV for the Rh@CN catalyst were
used as the model reaction, and the optimization of reaction
remained, and two other peaks were found at 400.4 eV and
conditions was performed. The results are listed in Table 1. The
401eV, which should be attributed to “pyrrole-type” and
Rh@CN catalyst was highly active for the reductive alkylation of
“graphite enclosed-type” nitrogen (Fig. 3, the left up). 9 These
nitrobenzene with benzaldehyde in ethanol (Table 1, entry 4).
results suggested that the Phen structure was inserted into the
Ethanol was helpful for Rh@CN catalyzed hydrogenation of the
activated carbon structure on the surface. The Phen structure
nitrobenzene and beneficial for the condensation of aniline with
retained and coordinated with Rh in the Rh@CN catalyst, and
benzaldehyde to form the corresponding imine. THF was also good
it was highly beneficial for the dispersion of the Rh
solvent (Table 1, entry 3), but toluene and cyclohexane were less
nanoparticles and also useful for the stability of the
effective solvents for the transformation (Table 1, entry 1-2). The
nanocatalyst Rh@CN.
added nitrobenzene and benzaldhyde remained and no conversion
The Rh peaks of the precursor of the Rh@CN at 309.2 eV
was detected when 1, 4-dioxane was used as solvent (Table 1, entry
(Rh3d5/2) and at 313.9 eV (Rh3d3/2 Δ=4.7 eV) were from the
5). No benzyl aniline was found when H2O was used as solvent
coordinated complex Rh(Phen)Cl3 (Fig. 3, the right below). As
(toluene, benzyl alcohol and aniline were detected as by-products)
the Rh peaks of Rh@CN for Rh3d5/2 at 307.2 eV and for Rh3d3/2
(Table 1, entry 6). The reductive N-alkylation of nitrobenzene
at 311.9 eV (Δ=4.7 eV) were found, the rhodium in the catalyst
afforded benzyl aniline in 75% yield without solvent (Table 1, entry
Rh@CN was metallic state Rh (0) with the protection of the
10). The Rh/C, Ru@CN were not good catalysts for the
o
Phen structure after treated at 800 C (Fig. 3, the right up)15.
transformation (Table 1, entry 7, 9), as both the activity and
The RhCl3 was decomposed into Rh metal and the Cl was
selectivity were not good. No benzyl aniline was found with Pd/C
released as no reducer was added.
catalyst under similar reaction conditions, only toluene, benzyl
alcohol and aniline were detected (Table 1, entry 8). The Rh@CN-5
307.2
399.5
398.3
311.9
Rh@CN
400.4
catalyst was similarly active to the Rh@CN for the reductive N-
alkylation of nitrobenzene with benzaldehyde in ethanol (Table 1,
entry 11). No reduction was detected using N2 instead of H2, which
indicated that H2 was the reducer and ethanol was only as solvent
(Table 1, entry 12). Under milder reaction conditions, the reductive
N-alkylation gave low yields (Table 1, entry 13-16). No benzyl aniline
was detected using the precursor of Rh@CN as catalyst, which
indicated the Rh complex was not active for the transformation
(Table 1, entry 17). The gram-scale reaction was performed using
the model reaction, and benzyl aniline was obtained in good yield
(Table 1, entry 18).
401
Rh3d
N1s
398.3
399.3
309.2
the precursor of Rh@CN
313.9
The reusability of the Rh@CN nanocatalyst
320
Binding energy (ev)
315
310
305
410
405
400
395
The reusability of the Rh@CN nanocatalyst was tested for the
reductive N-alkylation of nitrobenzene with benzaldehyde and
the results are shown in Figure S4. The Rh@CN nanocatalyst
was easily recycled by filtration and reused for the next
reaction cycle. After removal of the Rh@CN nanocatalyst by
filtration, the filtrate was investigated by ICP, and no Rh was
detected (below the detection limitation of 7 ppb). The filtrate
was inactive towards further reductive N-alkylation reactions.
The Rh@CN can be reused at least 4 times without obvious
deactivation, and benzyl aniline was obtained in good yield (in
92% yield at the 4th time). The 4th time recovered Rh@CN
was analyzed by TEM also and the mean diameter of the
Figure 3. The XPS spectra of the precursor and Rh@CN catalyst
XRD analysis
The presence of metallic state Rh (0) was also confirmed by
XRD (the X-ray diffraction) analysis. Three characteristic peaks
(2θ=41.1, 47.8 and 69.9o) were observed for the metal
rhodium particles. These peaks were assigned to Rh (111), Rh
(200) and Rh (220), respectively (see the Supporting
Information, Figure S2).
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recovered Rh nanoparticles were increased a little (about 8nm, see Figure 1b).
Table 1 Screening of the reductive N-alkylation of nitrobenzene with benzaldehyde a
Journal Name
Entry
Catalyst
Solvent
T/ oC
Pressure/ Mpa
Conv./%
Selsectivity/%b
1
2
3
0
0
0
0
4
0
0
0
0
1
2
3
4
5
6
7
8
Rh@CN
Rh@CN
Rh@CN
Rh@CN
Rh@CN
Rh@CN
Rh/C
Toluene
Cyclohexane
THF
Ethanol
1,4-Dioxane
H2O
Ethanol
Ethanol
Ethanol
Solvent free
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
80
80
80
80
80
80
80
80
80
80
80
80
rt
3
3
3
3
3
3
3
3
3
3
3
3
3
3
0.1
1
3
3
76
100
94
100
0
100
66
100
100
100
99
0
50
89
83
95
100
0
11
17
5
0
0
0
0
0
58
0
0
42
0
60
25
1
70
0
82
0
0
0
0
0
0
0
30
0
18
0
0
0
0
0
0
0
Pd/C
9
Ru@CN
Rh@CN
Rh@CN-5
Rh@CN
Rh@CN
Rh@CN
Rh@CN
Rh@CN
Rh@CN
Rh@CN
40
75
99
0
72
86
26
91
0
10
11
12c
13
14
15
16
17d
18e
0
28
14
74
9
0
3
60
80
80
80
80
90
15
92
0
0
0
0
0
0
0
100
97
a Reaction conditions: benzaldehyde 0.5 mmol; nitrobenzene, 0.55 mmol; solvent 4.0 mL；Rh@CN 14 mg (0.5 mol % Rh, or other catalysts
b
containing 0.5 mol% noble metal); in 6 hours; Conversion (of benzaldehyde) and selectivity were determined by GC (C16H34 used as
;
internal standard); c N2 instead of H2; d the precursor of the Rh@CN used as catalyst e the reaction was scaled up to 20 times.
Table 2. Rh@CN catalyzed the reductive N-alkylation of The reductive N-alkylation of nitrobenzenes with aldehydes
nitrobenzenes with aldehydes.a
The scope of the reductive N-alkylation was then explored
using a number of nitrobenzenes and aldehydes, and the
results are shown in Table 2. The Rh@CN was highly active and
selective for the reductive N-alkylation of nitrobenzenes with
aldehydes, and halides (F, Cl and Br), CH3, CH3O groups were
tolerated well during the transformation. The corresponding
N-alkyl aniline were obtained in good to excellent yields (Table
2, entry 2-14). The steric effects related to the substituents
Entry R1
R2
Time/h
6
Yield/%
99
1
H
H
2
4-F
2-Cl
3-Cl
4-Cl
4-Br
4-CH3
4-OCH3
H
H
6
94
3
H
8
98
4
H
6
94
were
low,
and
2-nitrochlorobenzene
and
2-
5
H
6
96
methylbenzaldehyde were converted to the corresponding
amines in high yields also (Table 2, entry 3, 11). Moreover, the
6
H
12
10
12
6
91
7
H
98
aliphatic
aldehyde
(such
as
octanal,
8
H
94
cyclohexanecarboxaldehyde, 3-phenylpropanal) can also be
converted to the N-alkyl aniline in good yield (Table 2, entry
15-17). When the heterocyclic aldehyde, furfural was used as
the substrate, N-phenyl furfurylamine was obtained in excllent
yield (96%) (Table 2, entry 18).
9
4-F
95
10
11
12
13
14
15
16
H
4-Cl
2-CH3
3-CH3
4-CH3
4-OCH3
octanal
6
94
H
15
10
10
10
12
89
H
92
H
97
H
95
The reductive N-alkylation of amines and aldehydes
H
85
H
cyclohexanecarbo 12
xaldehyde
91
As the reductive N-alkylation of nitrobenzenes should go
through the reduction of the nitrobenzenes to the
corresponding anilines firstly, the reductive N-alkylation of
amines with aldehydes was also studied with the Rh@CN
catalyst. And the results are shown in Table 3. Indeed, the
alkylation of anilines was performed rapidly with
benzaldehyde, and the corresponding secondary amines were
obtained in high yield (Table 3, entry 1-2). Alkylamines (e.g.,
17
H
H
3-phenylpropanal
furfural
12
8
86
96
18
a
Reaction conditions: aldehyde, 0.5 mmol; nitrobenzene, 0.55
o
mmol; Rh@CN 14 mg (0.5 mol % Rh); 80 C; H2 3Mpa; 4.0mL
ethanol. The conversions and yields were determined by GC
(C16H34 used as internal standard).
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benzyl amine, 2-chlorobenzyl amine, β-phenylethylamine, n- benzyl alcohol were detected. As nitrobenzene was excess
octyl amine) can also be used for the N-alkylation, and the (10% excess), aniline increased slowly to about 10% in the end.
corresponding secondary amines were obtained in high yields
also (Table 3, entry 3-6). Moreover, the N-alkylation of aniline
1.2
with cyclohexanone and cyclopentanone gave the
corresponding secondary amines in good yields respectively
1.0
(Table 3, entry 7, 8).
0.8
benzaldehyde
Table 3 Rh@CN catalyzed the reductive N-alkylation of amine
and aldehyde a
aniline
nitrobenzene
0.6
imine
benzyl aniline
0.4
0.2
Entry
1
R1
R2
Time/h
1
Yield/%
97
0.0
0
1
2
3
4
5
6
Time/h
2
3
4
99
99
Figure 4. The reaction sequence of the reductive N-alkylation
of nitrobenzene with benzaldehyde. Reaction conditions:
benzaldehyde, 0.5 mmol; nitrobenzene, 0.55 mmol; Rh@CN 14
mg (0.5 mol % Rh); at 80 oC; H2 3Mpa; 4.0 mL ethanol.
12
4
5
12
12
98
99
The reaction pathway discussion
6
7
n-C8H17NH2
12
12
12
90
96
92
Nitrobenzene should be reduced to aniline firstly, and the
aniline can be detected as the reduced intermediate.
Moreover, the imine from the condensation of aniline with
benzaldehyde was detected also at the beginning of the
reductive N-alkylation of the nitrobenzene with benzaldehyde.
But no benzyl alcohol was found, which implied that the
reduction of nitrobenzene is faster than the reduction of
benzaldehyde. Afterwards, the imine was formed by the
condensation of benzaldehyde with aniline, and then the imine
was further reduced to the corresponding amine. The
reduction of imine was faster than the reduction of
benzaldehyde also since no benzyl alcohol or toluene was
detected in the whole reduction process. In addition, we found
that the reductive N-alkylation of aniline was faster than the
reductive alkylation nitrobenzene (The reductive alkylation of
aniline with benzaldehyde was finished in about 1 h, which is
less than that (4 h) using nitrobenzene) (Table 1, entry 4 and
Table 3, entry 1).
8
a
Reaction conditions: aldehyde, 0.5 mmol; amine, 0.55 mmol;
Rh@CN 14 mg (0.5 mol % Rh); 80 oC; H2 3Mpa; 4.0mL ethanol.
The conversions and yields were determined by GC (C16H34
used as internal standard).
Encouraged by above results, 6-benzylaminopurine (a plant
growth regulator) was prepared by the reductive N-alkylation
of adenine with benzaldehyde using the Rh@CN catalyst. To
our delight, 6-benzylaminopurine was obtained in 80% yield
(Scheme 2). Since adenine and 6-benzylaminopurine are
poorly soluble in ethanol, higher reaction temperature and
higher H2 pressure were required.
+
CH2OH
CH3
Scheme 2 Rh@CN catalyzed synthesis of 6-benzylaminopurine
The reaction sequence of the reductive N-alkylation of
nitrobenzene with benzaldehyde
CHO
+
NO2
NH2
The reaction sequence of the reductive N-alkylation of
nitrobenzene with benzaldehyde was investigated, and the
time-concentration profile was followed (Figure 4). Aniline, the
imine and benzyl aniline can be detected at the first 3 hours.
Then benzyl aniline was increased smoothly, and the imine
was decreased along. Finally, the imine was transformed to
benzyl aniline completely. Benzaldehyde was converted to
benzyl aniline in 100% yield in 6 hours, and no toluene or
N
HN
H2/Rh@CN
Fast
H2/Rh@CN
Fast
Fast
Scheme 3. A possible pathway for the reductive N-alkylation of
nitrobenzene with benzaldehyde.
Based on these experimental results, we proposed the possible
pathway of the Rh@CN catalyzed reductive N-alkylation of
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5
6
(a) J. Zhou, Z. Dong, P. Wang, Z. Shi, X. Zhou, R. Li, J. Mol.
Catal. A-Chem. 2014, 382, 15-22; (b) L.Li, Z. Niu, S. Cai, Y. Zhi,
H. Li, H. Rong, L. Liu, L. Liu, W. He, Y. Li, Chem. Commun.
2013, 49, 6843-6845; (c) B. Sreedhar, P. S. Reddy, D. K. Devi,
J. Org. Chem. 2009, 74, 8806-8809.
(a) L. Hu, X. Cao, D. Ge, H. Hong, Z. Guo, L. Chen, X. Sun, J.
Tang, J. Zheng, J. Lu, H. Gu, Chem. Eur. J. 2011, 17, 14283-
14287; (b) F. G. Cirujano, A. Leyva-Perez, A. Corma, F.
Xamena, ChemCatChem 2013, 5, 538-549.
M. Pintado-Sierra, A. M. Rasero-Almansa, A. Corma, M.
Iglesias, F. Sanchez, J. Catal. 2013, 299, 137-145.
Y. Yamane, X. Liu, A. Hamasaki, T. Ishida, M. Haruta, T.
Yokoyama, M. Tokunaga, Org. Lett. 2009, 11, 5162-5165.
R. V. Jagadeesh, A. Surkus, H. Junge, M. Pohl, J. Radnik, J.
Rabeah, H. Huan, V. Schunemann, A. Bruckner, M. Beller,
Science 2013, 342, 1073-1076.
nitrobenzene with benzaldehyde to the corresponding
secondary amine (Scheme 3). Nitrobenzene was reduced to
aniline firstly, and the aniline was condensed with
benzaldehyde to the imine, and then the imine was reduced to
benzyl aniline. During the reaction, the reaction rate was the
control factor for the reductive alkylation of nitrobenzene with
benzaldehyde, and the reaction rate determined the catalytic
selectivity. No benzyl alcohol or toluene were found from the
hydrogenation of benzaldehyde, which indicated that the
added benzaldehyde fully participated into the reductive N-
alkylation of the nitrobenzene.
7
8
9
Conclusions
10 F. A. Westerhaus, R. V. Jagadeesh, G. Wienhofer, M. Pohl, J.
Radnik, A. Surkus, J. Rabeah, K. Junge, H. Junge, M. Nielsen,
In summary, Rh nanocatalysts were prepared and applied for
the reductive N-alkylation of nitrobenzenes with aldehydes.
The Rh@CN catalyst was found to be highly selective and
efficient for the reductive N-alkylation of nitrobenzenes, and
functional groups, such as F, Cl, Br, CH3O and CH3 were well
tolerated during the transformation, and the corresponding
secondary amines were obtained in good to excellent yields.
Furthermore, the Rh@CN catalyst was highly active and
selective for the reductive N-alkylation of primary amines with
aldehydes and ketones, and the corresponding secondary
amines were obtained rapidly in high yields. Moreover, the
Rh@CN was heterogeneous, and can be reused several times
for the reductive N-alkylation of nitrobenzene.
A. Bruckner, M. Beller, Nat. Chem. 2013,
11 T. Stemmler, A. Surkus, M. Pohl, K. Junge, M. Beller,
ChemSusChem, 2014, , 3012-3016.
12 T. Stemmler, F. A. Westerhaus, A. Surkus, M. Pohl, K. Junge,
M. Beller, Green Chem. 2014, 16, 4535-4540.
13 (a) Z. Wang, L. Huang, L. Geng, R. Chen, W. Xing, Y. Wang and
J. Huang, Catal. lett. 2015, 145, 1008-1013; (b) L. Huang, P.
Luo, M. Xiong, R. Chen, Y. Wang W. Xing and J. Huang, Chin.
J. Chem. 2013, 31, 987-991; (c) L. Huang, Pi. Luo, W. Pei, X.
Liu, Y. Wang, J. Wang, W. Xing, J. Huang, Adv. Synth. Catal.
2012, 354, 2689-2694; (d) P. Luo, K. Xu, R. Zhang, L. Huang, J.
5, 537-543.
7
Wang, W. Xing, J. Huang, Catal. Sci. Technol., 2012, 2, 301-
304; (e)K. Xu, Y. Zhang, X. Chen, L. Huang, R. Zhang, J. Huang,
Adv. Synth. Catal. 2011, 353, 1260-1264.
14 F. Jaouen, J. Herranz, M. Lefevre, J. Dodelet, U. I. Kramm, I.
Herrmann, P. Bogdanoff, J. Maruyama, T. Nagaoka, A.
Garsuch, J. R. Dahn, T. Olson, S. Pylypenko, P. Atanassov and
Acknowledgements
E. A. Ustinov., ACS Appl. Mater. Interfaces 2009, 8, 1623–
1639.
15 Y. Zhang, M. E. Grass, S. E. Habas, F. Tao, T. Zhang, P. Yang,
G. A. Somorjai, J. Phys. Chem. C 2007, 111, 12243-12253.
This work was supported by the National Natural Science of
Foundation of China (grant No. 21136005), the National High
Technology Research and Development Program of China (No.
2012AA03A606) and the Project of Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD,
38701001).
Notes and references
1
A. Seayad, M. Ahmed, H. Klein, R. Jackstell, T. Gross, M.
Beller, Science 2002, 297, 1676-1678.
2
(a) A. Shafir, S. L. Buchwald, J. Am. Chem. Soc. 2006, 128
8742-8743; (b) D. S. Surry, S. L. Buchwald, Chem. Sci. 2011,
,
2,
27-50; (c) S. E. Creutz, K. J. Lotito, G. C. Fu, J. C. Peters,
Science 2012, 338, 647-651.
3
4
(a) R. Kawahara, K. Fujita, R. Yamaguchi, Adv. Synth. Catal.
2011, 353, 1161-1168; (b) W. Zhang, X. Dong, W. Zhao, Org.
Lett. 2011, 13, 5386-5389; (c) Y. Zhao, S. W. Foo, S. Saito,
Angew. Chem. Int. Ed. 2011, 50, 3006-3009; (d) R. Kawahara,
K. Fujita, R. Yamaguchi, Adv. Synth. Catal. 2011, 353, 1161-
1168; (e) M. Bala, P. K. Verma, U. Sharma, N. Kumar, B.
Singh, Green Chem. 2013, 15, 1687-1693.
(a) S. C. A. Sousa, A. C. Fernandes, Adv. Synth. Catal. 2010,
352, 2218-2226; (b) M. Zhang, H. Yang, Y. Zhang, C. Zhu, W.
Li, Y. Cheng, H. Hu, Chem Commun, 2011, 47, 6605-6607; (c)
D. B. Bagal, R. A. Watile, M. V. Khedkar, K. P. Dhake, B. M.
Bhanage, Catal. Sci. Technol. 2012, 2, 354-358; (d) V. Kumar,
S. Sharma, U. Sharma, B. Singh, N. Kumar, Green Chem. 2012,
14, 3410-3414.
6 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5RA05243B
Heterogeneous Rh@CN nanocatalysts were prepared and applied for the reductive N-alkylation of nitrobenzenes
with aldehydes selectively.