A Reusable CNT-Supported Single-Atom Iron Catalyst for the Highly Efficient Synthesis of C?N Bonds

Article abstract of DOI:10.1002/chem.201905468

C?N bond formation is regarded as a very useful and fundamental reaction for the synthesis of nitrogen-containing molecules in both organic and pharmaceutical chemistry. Noble-metal and homogeneous catalysts have frequently been used for C?N bond formatio

Full text of DOI:10.1002/chem.201905468

A Journal of
Accepted Article
Title: A reusable CNTs-supported single-atom iron catalyst for the
highly efficient synthesis of C-N bonds
Authors: Qifeng Ding, Yang Yu, Fei Huang, Lihui Zhang, Jian-Guo
Zheng, Mingjie Xu, Jonathan Baell, and He Huang
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To be cited as: Chem. Eur. J. 10.1002/chem.201905468
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A reusable CNTs-supported single-atom iron catalyst for the
highly efficient synthesis of C-N bonds
Qifeng Ding[a,†], Yang Yu[c,†], Fei Huang*[a,b], Lihui Zhang[b], Jian-Guo Zheng[e], Mingjie Xu[e], Jonathan B.
Baell[a,d], and He Huang*[a,b]
Abstract: C-N bond formation is regarded as a very useful and
fundamental reaction, which is important for the synthesis of
nitrogen-containing molecules in both organic and pharmaceutical
chemistry. Noble metal and homogeneous catalysts have been used
for C-N bond formation frequently, however, there are still some
problems for these catalysts such as high cost, serious pollution and
low atom economy. Herein the low-toxic and cheaper iron complex
was loaded on CNTs and the heterogenous single-atom catalyst
(SAC) named Fe-Nx/CNTs was prepared. We applied this SAC to the
synthesis of C-N bonds for the first time. It was found that
Fe-Nx/CNTs was an efficient catalyst for the synthesis of C-N bonds
from aromatic amines and ketones. The catalytic performance is
markedly excellent with the yield up to 96%, 6-fold higher than that of
noble metal catalysts such as AuCl3/CNTs and RhCl3/CNTs. It was
suitable for up to 13 aromatic amine substrates with no additives and
17 enaminones were obtained. By using high-angle annular darkfield
scanning transmission electron microscopy (HAADF-STEM) in
combination with X-ray adsorption spectroscopy (XAS), we have
observed iron species of Fe-Nx/CNTs were in good dispersion as
single atoms and Fe-Nx might be the catalytic active site. This
Fe-Nx/CNTs catalyst has potential industrial application for its seven
runs without any significant loss of activity.
transition metals exhibited a much-enhanced activity in the
oxygen reduction reactions (ORR).[7-14] In addition, some
CNTs-supported metals like Pd, Ru, Pt and Ni can be used for
hydrogen production from hydrogen iodide and ammonia
decomposition.[15-20] Apart from these many inorganic reactions,
some organic reactions involving the application of CNTs were
also reported.[21-24] For instance, Kobayashi and coworkers[24]
developed a nickel-based Lewis acid integrated with CNTs for
the asymmetric synthesis of nitrones in water. So we envisioned
that more non-noble-metals-CNTs could be prepared to
efficiently synthesize some important compounds in organic
chemistry or pharmaceutical chemistry.
Single-atom catalysts (SACs) are
a type of atomically
dispersed catalysts with mono-nuclear metal complexes or single
metal atoms anchored on supports. Due to the metal single
atoms are easy to anchor to substrates and form strong
interactions with the support,[25] the SACs have demonstrated
superior catalytic performances, such as high activity and
selectivity. Since Zhang firstly reported about the application of
SACs on the CO oxidation in 2011,[26] various types of metal
SACs have been successfully designed and used in the field of
fuel processing, chemicals production and environmental
remediation etc.[27-32] To date, several literature report that single
atom Fe-Nx materials exhibit promising catalytic performances in
a variety of reactions.[33-36] Fe-Nx materials would discard the
noble-metal usage and perform high utilization potential for
industry. Taking into consideration the excellent activity of SACs
as well as the excellent adsorption property of carbon materials,
anchoring single atom Fe-Nx materials on CNTs is thus expected
to be effective to improve the catalyst performance in organic
synthesis.
The nitrogen-containing molecules is very prevalent in
pharmaceutical agents, natural products, functional materials
and synthetic intermediates. The key to the synthesis of
nitrogen-containing molecules is the formation of C-N bonds.[37]
Many strategies have been continuously developed to achieve
efficient synthesis of C-N bonds. However, these strategies
involve many noble metal catalysts and non-recyclable
homogeneous catalysts[38-42] which increase the cost of catalysts
and violate the concept of green chemistry and atom economy.
So cheap and easily recyclable heterogeneous catalysts are
attracting much more attention.
Introduction
Carbon nanotubes (CNTs), with thin planar sheet of sp2-bonded
carbon atoms densely packed in a honeycomb crystal lattice,
was first reported by Lijima in 1991.[1] Due to the high surface
area and excellent electronic conductivity,[2-6] CNTs are good
supports for metals to promote some chemical reactions. Several
reports in the literature have shown that CNTs-supported
[a]
Q. F. Ding, Dr. F. Huang, Prof. J. B. Baell, Prof. H. Huang
School of Pharmaceutical Sciences, Nanjing Tech University
Nanjing, 211816, China
E-mail: huangfei0208@yeah.net; huangh@njtech.edu.cn
Dr. F. Huang, L. H. Zhang, Prof. H. Huang
School of Food Science and Pharmaceutical Engineering, Nanjing
Normal University, Nanjing, 210023, China
Dr. Y. Yu
School of Environmental Science and Engineering, Nanjing Tech
University, Nanjing, 211816, China
Prof. J. B. Baell
Medicinal Chemistry Theme, Monash Institute of Pharmaceutical
Sciences, Monash University, Parkville, Victoria 3052, Australia
Prof. J. G. Zheng, M. J. Xu
Irvine Materials Research Institute, University of California, Irvine, CA
92697-2800, USA
[b]
[c]
[d]
[e]
[†]
In this study we report a reusable and heterogeneous SAC
named Fe-Nx/CNTs, which shows high activity to promote the
synthesis of β-enaminones by the efficient construction of C-N
bonds. Notably, this is the first time that the SAC has been
applied to the C-N bonds construction. The catalytic performance
of Fe-Nx/CNTs is markedly better than that of noble metal
catalysts such as AuCl3/CNTs and RhCl3/CNTs, with the yield up
to 96%, 6-fold higher than that of AuCl3/CNTs and RhCl3/CNTs.
More importantly, by using high-angle annular darkfield scanning
These authors contributed to this work equally.
Supporting information for this article is given via a link at the end of
the document.
1
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10.1002/chem.201905468
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transmission
electron
microscopy
(HAADF-STEM)
in
were presented in Fig. 2b. The peaks at 710.5 eV and 724.5 eV
were assigned to Fe2+ and the peaks at 712.3 eV and 727.0 eV
were assigned to Fe3+. This indicated that different coordinated
Fe-Nx species co-existed in the sample, and some Fe oxides
may also be included due to the hydrothermal preparation
process. In addition, the deconvolution of Fe 2p spectrum (Fig.
S5b) for FeSO4/CNTs also showed the presence of Fe2+ and
Fe3+ species, which could be attributed to Fe-Ox species (maybe
Fe oxides or FeSO4). Therefore, the distinct difference between
Fe-Nx/CNTs and FeSO4/CNTs was about Fe coordination
environment, and Fe-Nx exhibited higher activity than Fe-Ox as
shown in Table 2, entries 1 and 7. Considering that only on the
catalyst surface the iron species can be detected by XPS,[54]
more specific chemical environment of Fe in our catalyst need to
be explored.
combination with X-ray adsorption spectroscopy (XAS), we
observe that iron species of Fe-Nx/CNTs are in good dispersion
as single atoms and Fe-Nx might be the catalytic active site.
Results and Discussion
The iron complex was prepared according to the reported
literature (see the Experimental Section for more details).[43-45] To
demonstrate that the iron complex was formed successfully,
fourier transform infrared spectroscopy (FTIR) and X-ray
diffraction (XRD) were used. As shown in Fig. S1, the FTIR
spectrum showed four characteristic peaks (2974, 2910, 1601,
1085 cm-1), which were identical with those reported
previously.[43] Also, the XRD peaks of iron complex (Fig. S2)
match well with the simulated one (JCPDS 51-2309). Then the
obtained iron complex was supported on CNTs to form
Fe-Nx/CNTs. The Fe and N mass contents of Fe-Nx/CNTs were
(a)
(b)
3.3% and 3.7% respectively through the test of
X ray
fluorescence (XRF), indicating that the iron loading of
Fe-Nx/CNTs was low and the molar ratio of Fe:N was about 1:4.
Brunauer-Emmett-Teller (BET) measurement has been
performed to analyze specific surface area and pore diameter of
related catalysts. N2 isotherms as shown in Figure S3 were close
to Type IV curve and the surface area of the catalysts was shown
in Table S1. Fe-Nx/CNTs exhibited the smaller surface area (171
m2·g −1) and total pore volume (0.267 cm3·g -1) than the CNTs
which resulted from the loading of iron complex.
The morphology and microstructure of the prepared catalyst
Fe-Nx/CNTs were investigated by scanning electron microscopy
(SEM) and high-resolution transmission electron microscopy
(HRTEM) measurements. As shown in the Fig. 1a, no-load CNTs
exhibited a smooth and tubular structure. After iron complex was
supported on CNTs, the surface of CNTs became rough (Fig. 1b).
However, we didn’t detect any obvious metallic Fe species from
HRTEM images (Fig. 1d), suggesting that the size of Fe species
may be reduced to below the resolution of HRTEM with iron
element in good dispersion. In addition, from the XRD pattern of
Fe-Nx/CNTs (Fig. S4), amorphous and graphitic carbon
characteristic peaks were observed without distinct Fe3C and
metallic Fe peaks. This consistently indicated that the Fe species
were dispersed well in the CNTs.[46,47] To our delight, the
HAADF-STEM images showed individual Fe atoms were well
dispersed in the CNTs (Fig. 1e and 1f), indicating that the
Fe-Nx/CNTs was a kind of SACs.
(c)
(e)
(d)
(f)
Figure 1. (a) SEM image of CNTs. (b) SEM image of Fe-Nx/CNTs. (c) TEM
image of CNTs. (d) TEM image of Fe-Nx/CNTs. (e) HAADF-STEM image
showing individual Fe atoms of Fe-Nx/CNTs. (f) Enlargement of image (e).
(a)
(b)
Fe-Nx Species
C-N
Fe (II) 2p 3/2
Fe (III) 2p 3/2
Fe (II) 2p 1/2
Fe (III) 2p 1/2
Satellite
Fe 2p
N1s
For comparison, the catalyst FeSO4/CNTs which showed low
catalytic activity (Table 2, entry 7) was prepared through similar
conditions. Elemental analysis of the catalysts were then carried
out by X-ray photoelectron spectroscopic (XPS) measurements.
As revealed in Fig. S5a, the survey of Fe-Nx/CNTs demonstrated
the presence of C, N, O and Fe elements, while the survey of
FeSO4/CNTs confirms the presence of C, O, S and Fe. The
presence of the oxygen was the result of oxidation of carbon
materials when handled under catalyst preparation conditions.[48]
The deconvolution of the N 1s spectrum for Fe-Nx/CNTs (Fig. 2a)
showed the presence of two types of nitrogen species, which
could be attributed to C-N (at around 401.1 eV)[49,50] and Fe-Nx
( at around 399.8 eV) species.[51-53] The presence of two types of
nitrogen species were obviously due to the loading of the iron
complex. Moreover, the XPS Fe2+ and Fe3+ peaks of Fe-Nx/CNTs
410
405
400
B.E. (eV)
395
390
385 740 735 730 725 720 715 710 705 700
B.E.(eV)
Figure 2. (a) High-resolution spectra of
High-resolution spectra of Fe 2p for Fe-Nx/CNTs.
N 1s for Fe-Nx/CNTs. (b)
XAS is a unique tool for studying the local structure around a
selected element even with low element content. Herein, the
Fe-Nx/CNTs and FeSO4/CNTs were further characterized by
XAS for obtaining the oxidation state, structural and coordination
2
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environment of Fe-absorbing atom. The k3-weighted extended
X-ray absorption fine structure (EXAFS) spectra at the Fe K-edge
for our catalysts were measured and the corresponding fourier
transform spectra in R space were shown in Fig. 3a and 3b.
From the data fitting results in Table 1, we found the
FeSO4/CNTs, which had low catalytic activity in the synthesis of
C-N bonds (Table 2, entry 7) showed a distinct Fe-O coordination
with a coordination number of 1.9. This result suggested that the
Fe-Ox structure could be attributed to FeSO4 and may include
small amount of Fe2O3. For the Fe-Nx/CNTs catalyst, a primary
peak was found at about 1.5 Å which corresponded to the Fe-N
scattering path with a coordination number of 4 suggesting that
most of Fe species were well dispersed in the Fe-Nx/CNTs and
were four-fold coordinated by N atoms. Considering that Fe2+ and
Fe3+ species co-existed according to the XPS analysis, the Fe-Nx
delight, in the presence of Fe-Nx/CNTs, at 110 °C in toluene
under air, the desired product (Z)-1-phenyl-3-(phenylamino)
but-2-en-1-one (3a) was obtained in 94% GC yield (Table 2,
entry 1). Further experiments indicated that catalysts were
important in this aromatic amines involved condensation reaction,
as none of the desired product was detected in the absence of
catalyst or only using CNTs (Table 2, entry 2-3). This result
prompted us to explore other catalysts. The yields of 3a
decreased to 13% and 15% when noble metal catalysts
AuCl3/CNTs and RhCl3/CNTs were used (Table 2, entries 4-5),
indicating the high efficiency of Fe-Nx/CNTs. Notably, using iron
complex as the catalyst obviously reduced the reaction efficiency
(Table 2, entry 6). This could be due to the fact that the iron
complex was difficult to coordinate with other elements for its
saturated six-fold coordinated structure, however, the initiation of
structure could be assigned to Fe2+-N4 and Fe3+-N4.[47] In addition, this reaction required the coordination of metals with the carbonyl
Fe-O coordination also existed with a coordination number of 3,
revealing the presence of Fe oxides (may be Fe2O3). But the
content of Fe-Ox species was relatively low (~6%) from the
EXAFS data fitting results, so Fe-Nx species could be the real
active site in Fe-Nx/CNTs.
oxygen of the substrate 1 (Fig. 8).[56] In addition, due to the
absence of active site Fe-Nx species, FeSO4/CNTs could provide
the product, but in an unsatisfactory yield (Table 2, entry 7). The
yield of 3a improved to 96% when the amount of Fe-Nx/CNTs
was lowered to 150 mg. But the yield of 3a reduced to 91%,
using a smaller loading of Fe-Nx/CNTs (Table 2, entries 8-9). The
effect of solvents (1,4-dioxane, DMF, EtOH and DCE) were then
examined and found that DCE could improve the yields (96% GC
yield and 88% isolated yield, Table 3, entries 10-13). Lowering
the reaction temperature to 70 or 60 °C deteriorated the yield
(Table 2, entries 14-15). Thus, it was concluded that the
optimized reaction conditions were achieved with Fe-Nx/CNTs
(150 mg) as the catalyst in DCE at 80 °C (Table 2, entry 13). In
addition, the TON values of related catalysts were also shown in
the Table S2. It was obvious that the catalytic activity of
Fe-Nx/CNTs was highest.
Fig. 3c shows the normalized X-ray absorption near-edge
structure (XANES) spectra at the Fe K-edge of the Fe Foil,
FeSO4/CNTs and Fe-Nx/CNTs. White-line intensity can reflect
the oxidation state of the Fe species. We found the white-line
intensity of FeSO4/CNTs was strongest, indicating most Fe
species were oxidized. This is consistent with the formation of
Fe-O coordination from FeSO4/CNTs EXAFS fitting results.
Moreover, the white-line intensity of Fe-Nx/CNTs was higher than
that of Fe foil, suggesting that the Fe species in Fe-Nx/CNTs
became more positively charged and were coordinated with
some elements. Meanwhile, the pre-edge peak at about 7115 eV
for Fe-Nx/CNTs, which was different from those of FeSO4/CNTs
and Fe foil in position, shape and intensity, can be assigned to
Fe 1s→3d transition, a quadruple allowed transition, and it was
considered as a possible fingerprint of the Fe-Nx structure.[55]
This is consistent with the analysis about Fe-N4 coordination
formation of EXAFS.
Table 1. EXAFS Data Fitting Results at Fe K-Edge for the Fe Foil,
FeSO4/CNTs, and Fe-Nx/CNTs Catalysts.
σ2
Samples
Shell
CNa
R (Å)b
R factor
(102 Å2)c
FeSO4/CNTs
Fe-Nx/CNTs
Fe-O
Fe-N
Fe-O
1.9
4.0
3.0
2.16
2.08
1.98
0.94
0.09
0.19
0.0097
0.0089
FeSO4/CNTs
Fit
(c)
(a)
Fe-Nx /CNTs
Fe Foil
FeSO4/CNTs
FeSO /CNTs
4
Fe Foil
1.0
1.2
1.6
1.8
2.0
1.4 R (Å)
[a] Coordination number for the absorber−backscatterer pair. [b] Average
absorber-backscatterer distance. [c] Debye-Waller factor. The accuracies of
the above parameters were estimated as follows: CN, ±20%; R, ±1%; σ2,
±20%.
(b)
Fe-N /CNTs
x
Fit
Fe Foil
Fe-Nx/CNTs
Fe-Nx
1.0
1.2
1.6
1.8
2.0
1.4 R (Å)
With these optimized reaction conditions in hand, we further
aimed to apply the catalyst Fe-Nx/CNTs to synthesize diverse
β-enaminones for their significance in organic synthesis.[57-63] As
summarized in Scheme 1, the reaction went smoothly between
various aromatic amines with the substrates 1 and afforded the
corresponding β-enaminones products in moderate to good
isolated yields. It's worth mentioning that all scope reactions
were performed on 2 mmol scale. Aromatic amines 2 with
electron-donating substituents on the aromatic ring, such as
methyl or methoxy, were well tolerated for this process (3b-e,
85-90%). Electron-withdrawing substituents 4-fluoro, 4-chloro,
4-bromo, 4-trifluoromethyl groups lessened the yields of the
desired products 3f-g (73-75%), 3j-k (56-79%). These results
showed an obvious electronic effect. 4-Cl, 3-Cl, 2-Cl groups on
0
1
2
3
4
5
6
7110
7120
7130
7140
7150
7160
R (Å)
Photon Energy (eV)
Figure 3. Fourier-transformed K-edge EXAFS of Fe for (a) FeSO4/CNTs and (b)
Fe-Nx/CNTs. The data ranges used for data fitting in R space (ΔR) are 1.0-2.0
Å. (c) Normalized XANES spectra at Fe K-edge of Fe foil, FeSO4/CNTs and
Fe-Nx/CNTs.
In order to investigate the application of this type of catalyst for
synthesis of C-N bonds. 1-Phenylbutane-1,3-dione (1a) and
aniline (2a) were taken as model substrates to synthesize
β-enaminones through the construction of C-N bonds. To our
3
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the aryl group of substrates 2 prove a positive steric effect on the
yield of 3g (75%), 3h (54%) and 3i (50%), respectively. To our
delight, naphthylamine 2l underwent this reaction as well and the
desired product 3l was obtained in good yield (78%), without
exhibiting steric hindrance. However, the target product 3m was
formed in a relatively low yield (47%) owing to the increased
steric hindrance of substrates 1b (R2 = Ph). The substrates
pentane-2,4-dione (1c) and ethyl 3-oxobutanoate (1d) revealed
good reactivity to obtain efficiently the target products 3n-o
(80-89%).
acid atmosphere,[68] so trifluoroacetic acid was used as the
strong acid to promote the cyclization and the isoxazoles 5a and
5b were obtained in excellent yields. Furthermore, the internal
olefin
of
β-enaminones
could
be
chlorination
by
N-chlorosuccinimide (NCS) to give the products 6a and 6b in
excellent yields.[69]
Table 2. Optimization of Reaction Conditionsa.
Yieldc
(%)
Entry
Catalystb
Solvent
Temp. (oC)
1
2
3
4
5
6
7
8
9
Fe-Nx/CNTs
-
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
110
110
110
110
110
110
110
110
110
94
trace
trace
13
CNTs
AuCl3/CNTs
RhCl3/CNTs
Iron complex
FeSO4/CNTs
Fe-Nx/CNTsd
Fe-Nx/CNTse
15
16
45
96
91
1,4-dioxa
ne
10
Fe-Nx/CNTsd
100
95
11
12
13
14
15
Fe-Nx/CNTsd
Fe-Nx/CNTsd
Fe-Nx/CNTsd
Fe-Nx/CNTsd
Fe-Nx/CNTsd
DMF
EtOH
DCE
DCE
DCE
110
80
80
70
60
86
86
96(88f)
Scheme 1. Substrate Scope for the synthesis of β-enaminones. Reaction
conditions: 1 (2 mmol), 2 (4 mmol), Fe-Nx/CNTs (600 mg), DCE (20 mL), 80 oC,
24 h, 0.1 MPa air. Isolated yields are given.
95
90
[a] Conditions: 1a (0.5 mmol), 2a (1.0 mmol), catalyst (200 mg), solvent (5 mL),
air, 13 h. [b] The metal contents are equimolar with Fe-Nx/CNTs. [c] GC yield
with mesitylene as the internal standard. [d] 150 mg. [e] 100 mg. [f] Isolated
yield given in parentheses.
The substrate scope reactions were carried out on 2 mmol
scale, and encouraged by their success, Fe-Nx/CNTs was used
in a larger scale preparative reaction to demonstrate its practical
utility. The condensation of 1-phenylbutane-1,3-dione (8 mmol)
and p-toluidine (16 mmol) was carried out on 1.30 gram scale to
give target product (3b) in 83% isolated yield (eq 1, Scheme 2).
To further demonstrate the value of this catalyst, the Fe-Nx/CNTs
catalyst system was used for the synthesis of some
pharmacologically active compounds. As shown in the Scheme 2,
the condensation reactions proceed smoothly to give
corresponding products DM27 and H2L4 in good yields (eq 2-3).
DM27 is a P-gp efflux inhibitor which can enhance the oral
bioavailability of antiviral drugs[64] and H2L4 is a non-cytotoxic
compound with antibacterial activity.[65]
Scheme 2. Application research on Fe-Nx/CNTs.
To demonstrate that the β-enaminones are a kind of very
versatile key intermediates in organic synthesis, as shown in
Scheme 3, compounds 3a and 3b were treated with tosyl azide
by employing t-BuOK as the base promoter to give the
1,2,3-triazole 4a and 4b in good yields which could be used in
chemical biology and medicinal chemistry.[66,67] Moreover,
β-enaminones could be cyclized to form the isoxazoles under the
Scheme 3. Functionalization of β-enaminones.
4
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Finally, the suspension liquid was transfered to the muffle furnace at 180
oC for 1 h to give the catalyst Fe-Nx/CNTs as black powder.
Preparation of AuCl3/CNTs, RhCl3/CNTs and FeSO4/CNTs. 270 mg
AuCl3 (0.89 mmol), 202 mg (0.89 mmol) RhCl3·H2O or 248 mg (0.89 mmol)
FeSO4·7H2O and 1 g of CNTs were stirred in EtOH (30 mL) for 2 h. The next
loading process was the same as Fe-Nx/CNTs. Notably, the metal contents of
these catalysts were equimolar with Fe-Nx/CNTs for catalytic activity
comparison.
The recycling of the catalyst is very important for industrial
applications. After filtration and washing with DCE, we could
reuse
the
Fe-Nx/CNTs
for
(1a)
the
with
condensation
aniline (2a)
of
or
1-phenylbutane-1,3-dione
4-methoxyaniline (2e). The results were shown in Fig. 4. The
condensation reaction was carried out six times under identical
reaction conditions with the recycling of Fe-Nx/CNTs. The yields
of the products were 85% and 75% respectively when using
fresh Fe-Nx/CNTs. No significant decrease was observed in the
next six runs and the sixth yields of the product were 82% and
72% respectively. So the catalyst Fe-Nx/CNTs showed a good
reactivity up to 6 cycles without any significant loss of activity or
yield of the desired products.
Acknowledgements
We are grateful to National Natural Science Foundation of China
(21901124), Natural Science Foundation of the Jiangsu Higher
Education Institutions of China (19KJB150032, 19KJB610013),
Postdoctoral Research Foundation of China (2019M651809),
Jiangsu Planned Projects for Postdoctoral Research Funds
(2019K110) and Jiangsu Synergetic Innovation Center for
Advanced Bio-Manufacture (XTE1850) for support of this
research. HAADF STEM work was performed at the UC Irvine
Materials Research Institute (IMRI).
100
4-Methoxyaniline
Aniline
80
60
40
20
0
Keywords: Single atom catalysts • Fe-Nx materials• CNTs • C-N
bond formation
[1]
[2]
S. Lijima, Nature 1991, 354, 56-58.
0
1
2
3
4
5
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Fresh
Number of cycles
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Figure 4. Catalyst Reusability. 1-phenylbutane-1,3-dione (2 mmol), aniline or
4-methoxyaniline (4 mmol) and catalyst Fe-Nx/CNTs (600 mg) at 80 oC in DCE.
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Conclusion
In summary, a SAC Fe-Nx/CNTs was prepared by a simple
method for the highly efficient synthesis of C-N bonds. The
catalytic performance of Fe-Nx/CNTs is superior to noble metal
catalysts like AuCl3/CNTs and RhCl3/CNTs. Such outstanding
performance originates from the introduction of SAC and
electronic coupling between iron species and CNTs. By using
HAADF-STEM in combination with XAS, we have observed iron
species of Fe-Nx/CNTs were in good dispersion as single atoms
and Fe-Nx might be the catalytic active site. In addition, the
Fe-Nx/CNTs catalyst system can be run on a gram-scale and the
product β-enaminones can be functionalized to form some
important nitrogen-containing compounds. Furthermore, the
Fe-Nx/CNTs has stable catalytic activity, evidenced by the
reusability of the catalyst for seven runs with minimal loss in
activity. This work should shed light on the design of more
effective metal-CNTs SAC to be applied in organic synthesis.
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6
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10.1002/chem.201905468
Chemistry - A European Journal
FULL PAPER
Full Paper
A reusable single atom catalyst
Fe-Nx/CNTs is prepared and can be
applied to the synthesis of C-N
bonds. The catalytic performance of
Fe-Nx/CNTs is superior to noble
metal catalysts like AuCl3/CNTs and
RhCl3/CNTs. Such outstanding
performance originates from the
introduction of SAC and electronic
coupling between iron species and
CNTs.
Qifeng Ding, Yang Yu, Fei
Huang*, Lihui Zhang, Jian-Guo
Zheng, Mingjie Xu, Jonathan B.
Baell, and He Huang*
Page No. – Page No.
A reusable CNTs-supported
single-atom iron catalyst for
the highly efficient synthesis
of C-N bonds
7
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