Zn(0)-Catalysed mild and selective hydrogenation of nitroarenes

Article abstract of DOI:10.1039/d0gc01202e

The hydrogenation of nitroarenes is one of the most important strategies for the preparation of anilines. However, it is still a great challenge to develop mild and efficient synthetic routes toward aniline synthesis, particularly those employing both non-precious metal catalysts and low-pressure H2. Herein, we report a highly efficient protocol for the selective hydrogenation of nitroarenes in neutral H2O using H2 (1 atm) over a heterogeneous Zn(0) catalyst under mild conditions. The nitro groups of an array of nitroarenes can be converted into -NH2 with up to 99percent conversions and a selectivity of >99percent, even when functionalized with easily reducible substituents, or in the presence of aromatic ketones or styrene. This study might open an avenue for the selective hydrogenation of nitroarenes over a zinc catalyst using 1 atm H2.

Full text of DOI:10.1039/d0gc01202e

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DOI: 10.1039/D0GC01202E
ARTICLE
Zn(0)-Catalysed mild and selective hydrogenation of nitroarenes
a
c
a
a
a
a
a,b
Shuting Sun, † Muyao Du, Ruixiang Zhao, Xinchun Jv, Pan Hu, Qun Zhang, and Bo Wang*
Received 00th January 20xx,
Accepted 00th January 20xx
The hydrogenation of nitroarenes is one of the most important strategies for preparation of anilines. However, it is still a
great challenge to develop mild and efficient synthetic routes toward aniline synthesis, particularly those employing both
DOI: 10.1039/x0xx00000x
non-precious metal catalysts and low-pressure H
hydrogenation of nitroarenes in neutral H O using H
The nitro groups of an array of nitroarenes can be converted to -NH
when functionalized with easily reducible substituents, or in presence of aromatic ketones or styrene. This study might open
an avenue for the selective hydrogenation of nitroarenes over a zinc catalyst using H of 1atm.
2
. Herein, we report a highly efficient protocol for the selective
(1atm) over a heterogeneous Zn (0) catalyst under mild conditions.
in up to 99% conversions with selectivity of >99%, even
2
2
2
2
Table 1．Some recently developed metal catalyst promoted chemoselective
hydrogenations
1
. Introduction
Anilines are important building blocks for the production of
agrochemicals, pigments, dyes, pharmaceuticals and polymers.
Hitherto, extensive efforts have been made to develop various
catalytic systems for efficient converting nitroarenes into anilines,
nevertheless, most of them rely on noble metal catalysts mediated
Metal Catalyst
R
R
H2
1
hydrogenation using pressurized molecular hydrogen (Entry 1-3,
o
2
a
2b
Entry
Metal
Pressure of
(bar)
Sel.(%)
T ( C)
Ref.
Table 1) or stoichiometric amounts of sodium hydrosulfite, iron,
2
c
2d
H
2
tin, or zinc/ammonia as reductants to get a preferential selectivity
to the nitro group, leading to increased expense on preparation or
large wasted stream of metal salts/muds which might cause seriously
environmental concerns. Some others focused on developing non-
noble metal catalysts for efficient and selective transformation of
nitroarenes into anilines, however, the majority of the procedures
1
2
3
4
5
6
Pt
Pd
Ru
Ni
6-40
6-20
6-40
3-20
3-50
50
95–100
21–>99
86–100
85–96
5–96
60
[1a,1c]
[1b,1f]
[1d,1e]
[3d]
40–210
100–275
40–60
110–150
120
2
are found with low selectivity but requiring pressurized H or/and
3
elevated temperatures (Entry 4-6, Table 1). Currently, the
environmentally benign commercial production of anilines
functionalized with other easily reducible groups, such as
unsaturated bonds, or carbonyl groups, remains as an important
challenge, particularly those over non-precious metal catalysts and
Co
Fe
[3a,3b]
[3c]
20–80
2
using low pressurized H , and processing under mild conditions, are
highly desirable. As has been illustrated in our previous work that
compared with homogeneous catalysts, catalytic hydrogenation over
easier recyclable heterogeneous ones are preferable, particularly for
industrial purposes. The efficient and chemoselective hydrogenation
ofnitroarenes using normal atmospheric hydrogen (1atm) over
heterogeneous non-precious metal catalysts under mild conditions
has been less studied.
Our laboratory recently reported
approaches for the hydrogenation of nitroarenes, ketones,
aldehydes, and nitriles with heterogeneous palladium-based
nanoparticles using normal atmospheric H
reaction conditions can be extended to the selectively reductive
hydrogenation of nitroarenes using non-precious metal catalysts.
Herein, we detail how our envisagement was translated in
experimental reality, leading to the development of a novel non-
precious metal Zn(0)-catalyzed chemoselective hydrogenation of
a complementary mild
4
2
, we wonder if similar
a. S. Sun, Dr. X. Jv, R. Zhao, P. Hu, Q. Zhang, and Prof. Dr. Bo Wang
Key Lab of Advanced Materials of Tropical Island Resources, Ministry of Education
Hainan University
nitroarenes in base- or acid- free H
low-pressure H at 1atm , representing an alternation to currently
developed ones for environmentally benign preparation of anilines.
2
O under mild conditions using
No.58, Renmin AVE, Haikou 570228, P.R.China.
2
E-mail: wangbo@hainanu.edu.cn, bowang2@kth.se (Prof. Dr. B. Wang)
School of Chemistry and Environmental Engineering, Shandong University of
b.
Science and Technology No. 579, Qianwangang Road, Qingdao 266590, P.R.
China.
M. Du
College of Science and Engineering, Shandong Agricultural University
No.7, Panhe AVE, Tai’an 271017, P.R.China.
Electronic Supplementary Information (ESI) available: [details of any supplementary
information available should be included here]. See DOI: 10.1039/x0xx00000x
2
. Results and discussion
c.
In order to find suitable catalyst(s) and conditions,
nitrobenzene was selected as the model substrate. Four
different metal salts and ligands were tested to prepare a list of
metal-ligands (Table 2). It was found through experiments that
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ARTICLE
Journal Name
the catalysts prepared by the four metal salts and the pattern of Zn-NPs shows that the peaks at 31.7°, 34.4°, 36.2°,
View Article Online
DOI: 10.1039/D0GC01202E
1 2 3
corresponding three ligands L , L , and L did not play a role in 47.5°, 56.5°, 62.7°, 67.8° exhibit diffraction lines (hkl)
during the hydrogenation reduction of nitrobenzene. With corresponding to the crystal planes at (100), (002), (101), (102),
o
which, reactions were initially carried out at 25 C, and Zn-L
4
was (110), (103), and (112), respectively, indicating the existence of
found the best as the yield of the desired product aniline was the metal Zn in Zn-NPs (Fig. 2).
5% and the selectivity was >99% (Entry 2, Table 2). Elevated
3
temperatures and pHs were as well investigated, results
o
indicated the best yield was 99% when proceeded at 35 C
o
(
Entry 5, Table 2), a higher temperature at 40 C or a lower one
o
at 30 C would lead to poorer yields (Entries 4,6, Table 2).
Table 2. Optimization studies for hydrogenation of nitrobenzene.a
N
L1-4
H2 (1 atm), rt.
,
Metal salt + L1-4
M
H2O (solvent)
Ligand: NH2
NH2
NH2
NH2
NH2
NO2
NO2
NH2NH2
N
Fig. 1 TEM image of the Zn-L
4
L1
L2
L3
L4
Catalytic hydrogenation
N
O
H
To further characterize the chemical state of catalyst, XPS
analyses were performed (Fig.3), which proved the presence of zinc,
hydrogen and carbon in Zn-NPs. The peak of Zn 2p1/2 and 2p3/2 at
Yield/Selectivity
%/%)
o
Entry
M-L
T ( C)
(
1
046.08 and 1022.98eV correlated well with the peak of Zn (0),
1
Cu-L
4
25
12/99
35/99
5/99
Nitrogen affected Zn (0), causing its binding energy to change,
thereby confirming the presence of Zn (0).5, 6
2
3
4
5
6
7
Zn-L
4
25
25
30
35
40
45
Ni-L
Zn-L
Zn-L
Zn-L
Zn-L
4
4
60/99
99/>99
73/99
30/99
4
4
4
aConditions: Reactions were carried out in 10mL H
magnetic bar; pH, 7.0; H
O stirred with a
2
2
was filled in a balloon; Metal-ligands, 2.5mg;
Nitrobenzene, 20mM; Reaction time, 20h; Yields and selectivities were
determined by HPLC analysis.
2
.1 Characterization of Zn-NPs (Zn-L
To better understand the
diaminonaphthalene (Zn-L ), transmission electron microscopy
4
)
zinc-bound
1,8-
4
Fig. 2 XRD pattern of heterogeneous catalyst Zn-NPs
images indicated that they were not well dispersed
nanoparticles (Fig.1), with an average distribution of particle
diameter of 4.18 nm, which can thus be classified as
nanoparticles (NPs).
EA showed that an average of one zinc atom were found for each
ligand 1,8-diaminonaphthalene (Table S1). NMR spectroscopic
studies on 1,8-diaminonaphthalene functionalized Zn-NPs dispersed
The Zn-NPs were further characterized by X-ray diffraction
2
in alkaline D O to demonstrate that 1,8-diaminonaphthalene was
(XRD), elemental analysis (EA), inductively coupled plasma-
successfully bound to the particle surface.
optical emission spectrometer, X-ray photoelectron
1
13
spectroscopy (XPS), H NMR, C NMR and HH-COSY. The XRD
2
| J. Name., 2012, 00, 1-3
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Journal Name
Table 3. Catalytic hydrogenation of nitroarenes over Zn-NPs.View Article Online
DOI: 10.1039/D0GC01202E
Zn 2p
Conv. Dehal.
Sel.a
(%）
Ent
ry
Nitroare Time
ne (h)
Product
(%)
>99
99
(%）
1
1
5
--
>99
>99
>99
2
3
1
020 1025 1030 1035 1040 1045 1050
Binding Energy (eV)
15
--
Fig. 3 The XPS analyses of Zn-NPs
1
2
2
2
2
5
0
0
5
0
99
--
In order to demonstrate that these signals originate from Zn-
bound 1,8-diaminonaphthalene while not from desorbed ligand
molecules, a certain amount of 1,8-diaminonaphthalene was
4
5
6
7
98
99
99
98
--
13
39
--
>99
>99
>99
>99
1
mixed at an unequal equivalent (Figure S2). the H signals of -
NH at 4.46ppm in free 1,8-diaminonaphthalene was chemically
2
1
3
shifted to 4.52 after bound to Zn and the fact that C signals of
Zn-bound 1,8- diaminonaphthalene were chemically shifted
confirmed the chemically binding state of Zn-bound 1,8-
diaminonaphthalene as well (Figure S4).
NO2
NH
O
H3CO
H3CO
O
N
H
Zn
H
Ar
H2
H
N
R
N
R
H
8
9
3
2
98
0
>99
C
Zn
B
N
Ar
O
H
N
R
N
R
H
O
H
H
Zn
H
N
N
R
H
R
35
32
98
99
99
55
19
--
>99
>99
>99
H2O
A
H2O
H
H
NH2
Cl
N
10
H
O
O
Ar
N
H
N
D
Ar
Ar
H
H
Zn
Zn
N
H
N
R
N
H
H
N
N
R
H
1
1
1
2
R
R
2
0
H3C
O
H2
H
Zn
H
25
20
15
28
99
99
99
98
--
--
--
--
>99
>99
>99
>99
H
Zn
H
H
N
R
N
R
H
H
N
R
N
R
H
F
H
O
13
N
H
N
Zn
Ar
O
Ar
H
N
N
R
H
H
Zn
H
H2
R
H
N
N
H
1
1
4
5
R
R
E
Fig. 4 The proposed catalytic mechanism for Zn(0)-catalysed selective
hydrogenation of nitroarenes.
Conditions: Reactions were carried out in H2O of 10 mL as the solvent
stirred with a magnetic bar; pH, 7.0; H2 was filled in a balloon; Metal-
ligands, 2.5mg; Nitrobenzene, 20mM; Reaction time, 20h; Temperature,
35oC; Conversions were determined by HPLC analysis; a Selectivity was
Several control reactions (Figure S7) were performed to
explore the possible mechanism of the Zn(0)-catalyzed
4
hydrogenation. Based on reaction facts and some references,
the catalytic cycle of our proposed mechanism is outlined in Fig. calculated by comparing the proposed anilines (including the halogenated
. The catalyst B was incubated with H
, and activated to form and dehalogenated) with nitroarenes.
C, which later reacted with nitroarene to form A, and
simultaneously, H O was released, accompanied with which
4
2
2
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Table 4. Selective hydrogenation of nitroarene in the presence of
carbonyl compounds.
were nitrosoarene (D) and B, which was activated again into C
after absorbing H , followed is the combination of D with C to
2
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DOI: 10.1039/D0GC01202E
generate intermediate E, then F was released and formed back
to catalyst B, which was activated a third time by H to form C,
2
which combined again with F to generated back to the catalyst
B and the final product aniline.
With the optimized conditions described in Table 2, the scope
of substrates was investigated (Table 3). All reactions were
proceeded well with excellent conversions of up to >99% (Entry
Entr
y
Conv.
Nitroarene
Aryl ketone
Product
Sel. (%)
>99
(%)
1
, Table3). Several nitroarenes bearing halogen substituents
were tested as well, results indicated that when the substituent
is fluorine, dehalogenation reaction did not occur (Entry 8,
Table 3), nevertheless, when it was chlorine or bromine,
dehalogenation took place, leading to reduced product yields
though conversions kept excellent. It seems that progress
degree of dehalogenation depended on its position on the aryl
ring, an example is when the bromine is at the para position,
about 39% of products are the dehalogenated ones (Entry 6,
Table 3), however when it is at the meta position, about 55% of
substrates would undergo dehalogenation process (Entry 9,
Table 3). It seems that when the halogen atom is closer to the
carbon where nitro group connects, more products are the
dehalogenated ones (Entries 6, 9, Table 3), and it is the same
rule to chloride substituent (Entries 5, 10, Table 3).
Interestingly, when nitroarenes functionalized with easily
reducible groups, for example, carbonyl- or unsaturated C=C
groups, the hydrogenation reaction occurs specifically toward
the nitro group, resulting in excellent selectivity of substrates or
products (Entries 11, 15, Table 3), this promotes us to further
explore whether the chemoselective reactions occur and how
the selectivity will be when nitroarenes are mixed with
reducible aryl ketones or aryl olefins.
1
99
2
3
99
>99
>99
9
9
4
5
99
99
>99
>99
6
7
8
9
99
98
98
98
99
99
99
>99
>99
>99
>99
>99
>99
>99
Table 5. Selective hydrogenation of nitroarene mixed with aryl ethylene.
10
11
12
13
14
15
Entr
y
Aryl
ethylene
Conv.
(%)
Sel.
(%)
Nitroarene
Product
1
2
3
4
99
99
99
99
>99
>99
>99
>99
99
99
99
>99
>99
>99
Conditions were described in the footnote of Table 3.
Conditions are identical with which described in the footnote of Table 3.
An array of mixtures (½ nitroarene + ½ aryl ketone) were then
subjected, and all reactions could afford satisfied conversions and
excellent selectivity (Table 4). Results showed there were basically
4
| J. Name., 2012, 00, 1-3
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no aryl alcohols deriving from the hydrogenation of aryl ketones
were formed, proving the excellent performance of Zn-NPs in
catalytic hydrogenation of nitroarenes even in the presence of easily
reducible carbonyl compounds. Later, several different mixtures
consisting of equal equivalents of nitroarene and aryl ethylene were
evaluated as well (Table 5). Similarly, Zn-NPs showed excellent
selectivity in hydrogenating nitroanilines and specific activity toward
nitro groups, the result agreed well with which the reaction
Acknowledgements
View Article Online
DOI: 10.1039/D0GC01202E
Financial support from the National Natural Science Fundation of
China (21868011), and the National Key R&D Program of China
(2017YFC1103800) is gratefully acknowledged.
Notes and references
employing 4-nitrosyene, whose unsaturated C=C bonds remained 1 (a) K. Xu, Y. Zhang, X. Chen, L. Huang, R. Zhang, J. Huang, Adv.
unchanged (Entry 15,Table 3).
Synth. Catal., 2011, 353, 1260 – 1264; (b) X. Chen, K. Shen, D.
Ding, J. Chen, T. Fan, R. Wu, and Y. Li, ACS Catal., 2018, 8,
1
0641-10648; (c) Z. Sun, Y. Zhao, Y. Xie, R. Tao, H. Zhang, C.
Huang, Z. Liu, Green Chem., 2010, 12, 1007 – 1011; (d) S. Zhao,
H. Liang, Y. Zhou, Catal. Commun., 2007, 8, 1305–1309; (e) K.
Chary, C. S. Srikanth, Catalysis Letters, 2008, 128, 164–170; (f)
X. Shi, , X. Wang, , X. Shang, , X. Zou, , W. Ding, X. Lu,
ChemCatChem, 9, 3743–3751.
3
. Conclusions
In conclusion, we have, for the first time, under normal
atmospheric pressure and over a heterogeneous non-precious
Zn-based catalyst, achieved the highly chemoselective
hydrogenation of nitroarenes using H in H O under mild
2 2
2
3
(a) F. Kovar, F. E. Armond, U.S. Patent, 1976, 3, 975, 444; (b)
M. Suchy, P. Winternitz, M. Zeller, World (WO) Patent, 1991,
conditions. The Zn-NPs are proved to possess excellent
selectivity and stability in high-efficiency and selective
hydrogenation of nitroarenes, making the hydrogenation
extremely easy and environmentally benign. The corresponding
product anilines functionalized with easily reducible
unsaturated C=C bonds or carbonyl groups were provided in
excellent yields of up to > 99% with selectivity of >99%. Besides,
when mixed with carbonyl compounds or olefins, the selectivity
can still make us satisfied though dehalogenation occur when
substrates bearing halogen (F is excluded) atoms on aromatic
ring. The Zn-NPs and its developed methodologies are
applicable for a wide range of nitroarenes. In addition, due to
chemically binding state of ligands to the surface of Zn atoms,
the stable heterogeneous Zn-NPs could be easily recycled and
reused for many times without losing its major activity and
selectivity.
9
9
5
1/00278; (c) J. Butera, J. Bagli, World (WO) Patent, 1991,
1/09023; (d) A. Burawoy, J. P. Critchley, Tetrahedron, 1959,
, 340-351.
(a) F. Westerhaus, R. Jagadeesh, G. Wienhoer, M. Pohl, J.
Radnik, A. Surkus, J. Rabeah, K.Junge, H. Junge, M. Nielsen,
A.Bruckner and M. Beller, Nature Chemistry, 2013, 5, 537–
5
5
43; (b) T. Schwob, R. Kempe, Angew. Chem. Int. Ed., 2016,
5, 15175-15179; (c) Kailong Zhu, M. Shaver, S. Thomas, Chem.
Sci., 2016,7, 3031-3035 ; (d) R. V. Jagadeesh, T. Stemmler, A.-
E. Surkus, H. Junge, K. Junge, M. Beller, Nat. Protoc., 2015, 10,
5
48; (e) Y. Ren, H. Wei, G. Yin, L. Zhang, A. Wang, T. Zhang,
Chem. Commun., 2017, 53, 1969-1972; (f) U. Sharma, P.
Kumar, N. Kumar, V. Kumar, B. Singh, Adv. Synth. Catal., 2010,
3
52, 1834–1840.
4
(a) Y. Liu, S. He, Z ；. Quan, H. Cai, Y. Zhao, B. Wang, Green
Chem., 2019, 21, 830-838; (b) Y. Liu Z. Quan, S. He, Z. Zhao, J.
wang, B. Wang, React. Chem. Eng., 2019, 4, 1145-1152.
J. Sun, P. Zan, L. Ye, X. Yang, L. Zhao, J. Mater. Chem. A, 2017,
5
6
5
, 9815-9823.
(a) J. Wu, Y. Lin, J.Wang, P. Chang, C. Tasi, C. Lu, H. Chiu, and
Y. Yang, Inorg. Chem. 2003, 42, 4516−4518; (b) J.Yang,
E.H.Sargent, S.O.Kelley, J.K.Ying, Nature Materials, 2009, 8,
Conflicts of interest
There are no conflicts to declare.
6
83–689.
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J. Name., 2013, 00, 1-3 | 5
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