The Direct Synthesis of Imines, Benzimidazoles and Quinoxalines from Nitroarenes and Carbonyl Compounds by Selective Nitroarene Hydrogenation Employing a Reusable Iron Catalyst

Article abstract of DOI:10.1002/chem.201801525

The “replacement” of noble metals by earth abundant metals is a desirable aim in catalysis and a possible way of conserving rare elements. The “replacement” is especially attractive if novel selectivity patterns are observed permitting the development of novel coupling reactions. Herein, we report on a novel, robust and reusable iron catalyst, which permits the selective hydrogenation of nitroarenes in the presence of hydrogenation-sensitive functional groups. Based on the selectivity pattern observed, the direct iron-catalyzed synthesis of imines and benzimidazoles from nitroarenes and aldehydes becomes feasible. In addition, we introduce the direct synthesis of quinoxalines from nitroarenes and diketones applying our catalyst.

Full text of DOI:10.1002/chem.201801525

A Journal of
Accepted Article
Title: The Direct Synthesis of Imines, Benzimidazoles and
Quinoxalines from Nitroarenes and Carbonyl Compounds via
Selective Nitroarene Hydrogenation Employing a Reusable Iron
Catalyst
Authors: Rhett Kempe and Christoph Bäumler
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
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To be cited as: Chem. Eur. J. 10.1002/chem.201801525
Link to VoR: http://dx.doi.org/10.1002/chem.201801525
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The Direct Synthesis of Imines, Benzimidazoles and Quinoxalines from Nitroarenes
and Carbonyl Compounds via Selective Nitroarene Hydrogenation Employing a
Reusable Iron Catalyst
Christoph Bäumler and Rhett Kempe*
Abstract: The “replacement” of noble metals by earth abundant
metals is a desirable aim in catalysis and a possible way of conserving
rare elements. The “replacement” is especially attractive if novel
selectivity patterns are observed permitting the development of novel
coupling reactions. Herein, we report on a novel, robust and reusable
iron catalyst, which permits the selective hydrogenation of nitroarenes
in the presence of hydrogenation-sensitive functional groups. Based
on the selectivity pattern observed, the direct iron catalyzed synthesis
of imines and benzimidazoles from nitroarenes and aldehydes
becomes feasible. In addition, we introduce the direct synthesis of
quinoxalines from nitroarenes and diketones applying our catalyst.
similarly important as well as the development of protocols for
their synthesis. We have recently introduced a variety of SiCN-
metal nanocomposite catalysts[, 16 ] and have, very recently,
introduced highly active, selective and reusable cobalt
catalysts.[7,8]
Our iron nanocomposite catalyst has been synthesized in a two-
step procedure. A Fe aminopyridinato complex (Figure 1, top left)
and the commercially available polysilazane HTT1800 were
dissolved in tetrahydrofuran (THF) and dicumylperoxid (DCP)
was added to initiate crosslinking. After removal of the solvent,
the generated green body undergoes pyrolysis under a nitrogen
atmosphere at 750 °C, resulting in a Fe@SiCN nanocomposite.
Magnetic measurements confirmed the superparamagnetic
properties of the pyrolyzed nanocomposite (Figure 1, bottom
right) indicating the presence of small iron nanoparticles (NP).
Prior to pyrolysis, Fe3+ have been identified via magnetic
measurements (Figure 1, bottom left). The generation of iron NPs
was also verified by transmission electron microscopy (TEM;
Figure 1, top right). Homogeneously distributed particles with an
average particle size of 5 nm could be detected. The synthesized
Fe@SiCN catalyst was washed with an aqueous basic solution,
followed by a temperature-programmed reduction (TPR; Figure
S3). The first TPR run indicated the presence of iron oxide
species, due to the increased H2 uptake between 350-600 °C. X-
ray photoelectron spectroscopy (XPS) verified the presence of
metallic Fe and iron oxide species (Figure S4) with about a 1 to 2
ratio in the as synthesized Fe@SiCN material. Nitrogen sorption
measurements (Figure 1, center left) of the Fe@SiCN
nanocomposite indicated the presence of mesopores. A specific
surface area of 101 m2g-1 was calculated by the Brunauer-
Emmet-Teller (BET) method. The pore-size distribution calculated
exhibited the presence of micro- and mesopores, whereby 91 %
of the surface area is caused by mesopores < 10 nm (Figure 1,
center right).
The conservation of our rare element resources is of fundamental
importance to guarantee attractive living conditions for future
generations. The replacement of noble metals by earth abundant
metals in key technologies, such as catalysis, is one of the options
and especially attractive if the “replacement” permits novel
selectivity patterns and/or even novel catalytic transformations.
Hydrogenation reactions play an important role in catalysis and,
thus, are of high interest to the chemical industry and academic
research.[1] The hydrogenation of aromatic nitro compounds is the
method of choice for the production or synthesis of aniline
derivatives, an important class of compounds.[2] In 2006, Corma
and coworkers reported a breakthrough regarding the tolerance
of functional groups applying heterogeneous gold catalysts.[3 ]
Recently, Beller and coworkers could show that heterogeneous
catalysts based on abundantly available transition metals, such
as iron [4] and cobalt,[5] can also mediate the highly selective
hydrogenation of nitroarenes. Based on these initial findings, a
variety of groups developed Co catalysts for the selective and
efficient hydrogenation of nitroarenes.[6, 7,8] Efficient and selective
iron catalysts are essentially unknown beside the initial key
contributions.[4]
Herein, we report on
a
novel reusable and robust
Next, we were interested in applying our Fe catalyst in the
reduction of nitroarenes. The reduction of nitrobenzene was
chosen as the benchmark reaction. Therefore, various reaction
parameters such as pressure, temperature, solvent and catalyst
loading were varied to find conditions for a complete conversion
to aniline. A 3:1 water/TEA (triethylamine) mixture, 6.0 MPa
hydrogen pressure and 120 °C (Figure S5, Table S1) were found
to be optimal. Our catalyst needs more drastic conditions for the
nitroarene hydrogenation than the Fe catalyst developed by Beller
and coworkers,[4] which works well with 4.5 mol% catalyst loading,
90 to 120 °C and 3 to 5 MPa H2 pressure. Investigation of the
substrate scope revealed a broad applicability of our Fe catalyst.
Various substituents, e.g. all halogenides were tolerated (Table 1;
Entries 2-9). The reaction conditions for 1-iodo-4-nitrobenzene
(Table 1; Entry 9), had to be modified slightly. Other
hydrogenation-sensitive functional groups, such as aldehyde,
amide, ketone, and nitrile, could be tolerated too (Table 1). The
temperature and the pressure were slightly increased to ensure
full conversion of sterically more demanding substrates (Table 1;
Entries 15-17). We also investigated (E)-(2-nitrovinyl)benzene but
siliconcarbonitrite (SiCN)-based Fe catalyst. Our catalyst permits
the selective hydrogenation of nitroarenes in the presence of iodo,
aldehyde, ketone and nitrile functional groups. Based on the
tolerance of carbonyl compounds, our catalyst can mediate the
direct synthesis of imines and benzimidazoles from nitroarenes
and aldehydes. Furthermore, we introduce the direct synthesis of
quinoxalines from nitroarenes and diketones.
Imines are important compounds and have been used extensively
as ligands[9] and for the synthesis of materials,[10] fragrances,
fungicides, pharmaceuticals and agricultural chemicals[11]. Thus,
the development of novel imine synthesis protocols is of high
interest. [7, 12 , 13 ] Benzimidazoles[7, 14 ] and quinoxalines[ 15 ] are
[*]
C. Bäumler, Prof. Dr. R. Kempe
Anorganische Chemie II - Katalysatordesign
Universität Bayreuth, 95440 Bayreuth (Germany)
E-mail: kempe@uni-bayreuth.de
Supporting information for this article is given via a link at the end of
the document.
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observed a mixture of products since the C-C double bond was
hydrogenated. Heterocyclic nitro compounds work as well as
demonstrated for isoquinolin-5-amine (Table 1, Entry 18).
were obtained in 72 and 84 % isolated yield, respectively. In
addition, sterically demanding substituents had no negative effect
on the direct imine synthesis (Table 2, Entries 2a,b, 5, 6, 7).
Figure 2: Top: Benchmark reaction with optimized reaction conditions.
Bottom: Recycling of the Fe@SiCN catalyst over six consecutive runs
(conditions for 80 % yield). The activity could be restored completely through
TPR treatment.
The direct synthesis of benzimidazoles from nitroarenes and
aldehydes was investigated next (Table 3) with the reductive
coupling of 4,5-dimethyl-2-nitroaniline and benzaldehyde as the
benchmark reaction. The corresponding benzimidazole was
obtained in 87 % isolated yield under optimized reaction
conditions (Table 3, Entry 1a). Aryl halide as well as heterocyclic
based aldehydes gave similarly high yields (Table 3, Entries 1c,d,
2) and even aliphatic aldehyde can be employed (Table 3, Entry
3).
Finally, the direct synthesis of quinoxalines from nitroarenes and
diketones was investigated (Table 4). The formation of 6,7-
dimethyl-2,3-diphenylquinoxaline from 4,5-dimethyl-2-nitroaniline
and benzil was used as the benchmark reaction. Some of the
quinoxalines synthesized were obtained in isolated yields > 90 %
(Table 4, Entry 1a and c). Again, an attractive functional group
tolerance including a hydrogenation sensitive substituent, nitrile,
was observed.
Figure 1: Top (left): Synthesis of the novel Fe@SiCN nanocomposite. The iron
complex and the commercial available polysilazane HTT 1800 are dissolved in
THF, followed by crosslinking with DCP as an external initiator at 105 °C. The
greenbody obtained undergoes pyrolysis under nitrogen atmosphere at 750 °C,
resulting in an amorphous Fe@SiCN nanocomposite. Top (right): TEM analysis
verified the presence of small iron nanoparticles with a homogenous particle
size distribution centered at 5 nm. Center left: Pore characterization of the
Fe@SiCN nanocomposite via nitrogen sorption measurements. Center right:
Calculated pore-size distribution. Bottom: Magnetic measurements confirm the
transition of Fe3+ ions in the greenbody (left) to iron nanoparticles
(superparamagnetic properties) in the final nanocomposite (right).
Six consecutive runs were performed (conditions for 80 % yield)
to confirm the recyclability of our catalyst. The catalytic activity
declines after the fifth run but can be regained by TPR treatment
(Figure 2). We propose the formation of inactive oxide species
during catalyst separation and handling. Routinely, we used TPR
activation not prior to each use but after three or four times use of
a catalyst sample.
Next, we looked for catalytic transformations that include a
nitroarene hydrogenation step but involve further C-N and/or C-C
bond formation steps for direct syntheses based on the selectivity
patterns discovered above, here especially the tolerance of
carbonyl compounds. The direct synthesis of imines from
nitroarenes and aldehydes was investigated first and we discover
that the condition optimal for the hydrogenation of nitroarenes
work for the imine synthesis as well. We see up to 8 % aryl-alkyl
amine by-product formation, which reduces the (isolated) yields
of the imines.[17] Various aldehydes and nitroarenes were linked
directly. Halogenated substrates (Table 2, Entries 1c, 2b)
achieved isolated yields between 87 and 89 %. Keto and nitrile
functionalities were investigated to confirm the tolerance of
hydrogenation sensitive functional groups. The resulting imines
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Table 1: Chemoselective hydrogenation of substituted nitroarenes; substrate
Table 2: Selective synthesis of substituted imines from nitroarenes and
aldehydes; substrate scope[a]
.
scope[a]
.
Yield[b]
[%]
Entry
Product
Yield[b]
[%]
Entry
1
Product
1a: R1 = H
83
88
89
1
2
3
4
5
6
7
8
9
10
R = H
> 99
91
1b: R1 = OMe
1c: R1 = Cl
1d: R1 = CN
R = 2-Cl
R = 3-Cl
R = 4-Cl
R = 2-Br
R = 3-Br
R = 4-Br
R = 4-F
R = 4-I
[c]
84
> 99
> 99
87
2a: R2 = H
2b: R2 = Br
92
87
2
92
97
92
70 [c]
92 [d]
3
4
5
82
79
89
R = 3-CN
11
12
80
85
13
14
95
89
6
72
15
16
> 99 [e]
95 [e]
17
18
94 [e]
7
81
89
19
88
[a] Reaction conditions: 0.5 mmol substrate, 120 °C, 6.0 MPa H2, 10 mol %
catalyst (2.8 mg Fe, 0.05 mmol, 70 mg), 1 mL TEA, 3 mL H2O , 20 h. [b] Yields
of isolated products. [c] 4 mL H2O.
[a] Reaction conditions: 0.5 mmol substrate, 120 °C, 6.0 MPa H2, 10 mol %
catalyst (2.8 mg Fe, 0.05 mmol, 70 mg), 1 mL TEA, 3 mL H2O , 20 h. [b] Yields
were determined by GC using n-dodecane as an internal standard. [c] 100 °C,
6.5 MPa, 11 mol % catalyst. [d] 4 mL H2O. [e] 125 °C, 6.5 MPa, 24 h.
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Table 3: Selective synthesis of substituted benzimidazoles; substrate scope[a]
.
2
3
75
76 [c]
Entry
1
Product
Yield[b]
[%]
1a: R1 = H
87
81
84
83
1b: R1 = 4-OMe
1c: R1 = 4-F
1d: R1 = 4-Cl
[a] Reaction conditions: 0.5 mmol substrate, 125 °C, 6.5 MPa H2, 10 mol %
catalyst (2.8 mg Fe, 0.05 mmol, 70 mg), 1 mL TEA, 3 mL H2O , 24 h. [b] Yields
of isolated products. [c] 4 mL H2O, 11 mol % catalyst.
2
3
72
69
In summary, we have developed a novel, robust, reusable,
easy to synthesize and easy to handle iron catalyst. The Fe-SiCN
nanocomposite catalyst is highly selective in the hydrogenation of
nitroarenes in the presence of hydrogen-sensitive functional
groups. The tolerance of aldehydes permits the direct iron
catalyzed synthesis of imines and benzimidazoles from
nitroarenes and aldehydes. Again, hydrogenation sensitive
functional groups can be tolerated. The direct synthesis of
quinoxalines from nitroarenes and diketones is a novel way of
accessing this important class of N-heterocyclic compound.
[a] Reaction conditions: 0.5 mmol substrate, 125 °C, 6.5 MPa H2, 10 mol %
catalyst (2.8 mg Fe, 0.05 mmol, 70 mg), 1 mL TEA, 3 mL H2O , 24 h. [b] Yields
of isolated products.
Table 4: Selective synthesis of substituted quinoxalines; substrate scope[a]
.
Acknowledgements
We thank Katja Dankhoff and Prof. Dr. Birgit Weber for magnetic
measurements, John Kannan Mohanraj and Dr. Sven Hüttner for
XPS analysis, Tobias Schwob and Gabriela Hahn for TEM
analysis. We thank the Deutsche Forschungsgemeinschaft, SFB
840, B1 for financial support.
Entry
1
Product
Yield[b]
[%]
1a: R3/4 = H
95
86
92
89
Keywords: benzimidazoles • imines • iron • nitroarene
hydrogenation • quinoxalines
1b: R3/4 = 4-OMe
1c: R3/4 = 4-F
1d: R3/4 = 4-Cl
[1] B. Cornils, W. A. Hermann, R. Schlögle, C.H. Wong (Eds.), Catalysis from A
to Z, 2nd edition, Wiley-VCH, Weinheim, 2002.
Baramov, J. Barry, T. Godiawala, J. Hassfeld, N. Steinfeldt, ChemCatChem
2017, 9, 3210-3217; f) I. Sorribes, L. Liu, A. Corma, ACS Catalysis 2017, 7,
2698-2708; g) F. Zhang, C. Zhao, S. Chen, H. Li, H. Yang, X.-M. Zhang, J.
Catal. 2017, 348, 212-222; h) L. Jiang, P. Zhou, Z. Zhang, Q. Chi, S. Jin, New
J. Chem. 2017, 41, 11991-11997; i) X. Cui, K. Liang, M. Tian, Y. Zhu, J. Ma, Z.
Dong, J. Colloid Interface Sci. 2017, 501, 231-240; j) B. Sahoo, D. Formenti, C.
Topf, S. Bachmann, M. Scalone, K. Junge, M. Beller, ChemSusChem 2017, 10,
3035-3039; k) Li. Liu, F. Gao, P. Concepción, A. Corma, J. Catal. 2017, 350,
218-225; l) Z. Wei, S. Mao, F. Sun, J. Wang, B. Mei, Y. Chen, H. Li, Y. Wang,
Green Chem. 2018, 20, 671-679; m) X. Sun, A. I. Olivos-Suarez, D. Osadchii,
M. J. V. Romero, F. Kapteijn, J. Gascon, J. Catal. 2018, 357, 20-28.
[7] T. Schwob, R. Kempe, Angew. Chem. Int. Ed. 2016, 55, 15175-15179.
[8] M. Eckardt, M. Zaheer, R. Kempe, Sci. Rep. 2018, 8, 2567-2572.
[9] V. C. Gibson, S. K. Spitzmesser, Chem. Rev. 2003, 103, 283-315.
[10] A. W. Bosman, H. M. Janssen, E. W. Meijer, Chem. Rev. 1999, 99, 1665-
1688.
[2] a) H.-U. Blaser, H. Steiner, M. Studer, ChemCatChem. 2009, 1, 210-221.
[3] a) A. Corma, P. Serna, P. Concepcion, J. J. Calvino, J. Am. Chem. Soc.
2008, 130, 8748-8753; b) A. Corma, P.Serna, Science 2006, 313, 332-334.
[4] a) R. V. Jagadeesh, A.-E. Surkus, H. Junge, M.-M. Pohl, J. Radnik, J.
Rabeah, H. Huan, V. Schunemann, A. Brückner, M. Beller, Science 2013, 342,
1073-1076; b) R. V. Jagadeesh, T. Stemmler, A.-E. Surkus, H. Junge, K. Junge,
M. Beller, Nat. Protoc. 2015, 10, 548-557; c) D. Formenti, C. Topf, K. Junge, F.
Ragaini, M. Beller, Catal. Sci. Technol. 2016, 6, 4473-4477.
[5] a) F. A. Westerhaus, R. V. Jagadeesh, G. Wienhofer, M.-M. Pohl, J. Radnik,
A.-E. Surkus, J. Rabeah, K. Junge, H. Junge, M. Nielsen, A. Brückner, M. Beller,
Nat. Chem. 2013, 5, 537-543; b) R. V. Jagadeesh, T. Stemmler, A.-E. Surkus,
M. Bauer, M.-M. Pohl, J. Radnik, K. Junge, H. Junge, A. Brückner, M. Beller,
Nat. Protoc. 2015, 10, 916-926.
[6] For selected examples see: a) Z. Wei, J. Wang, S. Mao, D. Su, H. Jin, Y.
Wang, F. Xu, H. Li, Y. Wang, ACS Catal. 2015, 5, 4783-4789; d) L. Liu, P.
Concepción, A. Corma, J. Catal. 2016, 340, 1-9; b) B. Chen, F. Li, Z. Huang, G.
Yuan, ChemCatChem. 2016, 8, 1132–1138; c) P. Ji, K. Manna, Z. Lin, X. Feng,
A. Urban, Y. Song, W. Lin, J. Am. Chem. Soc. 2017, 139, 7004-7011; d) P.
Zhou, Z. Zhang, ChemSusChem 2017, 10, 1892-1897; e) H. Alex, P. Loos, T.
[11] D. J. Hadjipavlou-Litina, A. A. Geronikaki, Drug Des. Discov. 1998, 15, 199-
206.
[12] For selected examples of catalytic imine syntheses, please see: (oxidation
of amines) a) H. Yuan, W.-J. Yoo, H. Miyamura, S. Kobayashi, J. Am. Chem.
Soc. 2012, 134, 13970-13973; b) T. Sonobe, K. Oisaki, M. Kanai, Chem. Sci.
This article is protected by copyright. All rights reserved.

10.1002/chem.201801525
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11624-11627; b) K. Bahrami, M. M. Khodaei, A. Nejati, Green Chem. 2013, 12,
1237-1241; c) T. B. Nguyen, L. Ermolenko, A. Al-Mourabit, J. Am. Chem. Soc.
2013, 135, 118-121; d) T. Hille, T. Irrgang, R. Kempe, Chem. Eur. J. 2014, 20,
5569-5572; e) C. Xu, Z.-Q. Xiao, H.-M. Li, X. Han, Z.-Q. Wang, W.-J. Fu, B.-M.
Ji, X.-Q. Hao, M.-P. Song, Eur. J. Org. Chem. 2015, 7427-7432; f) C. Chaudhari,
S. H. Siddiki, K.-i. Shimizu, Tetrahedron Lett. 2015, 56, 4885-4888; g) Z. Sun,
G. Bottari, K. Barta, Green Chem. 2015, 17, 5172-5181; h) D. Mahesh, P.
Sadhu, T. Punniyamurthy, J. Org. Chem. 2016, 81, 3227-3234; i) X. Cui, K.
Liang, M. Tian, Y. Zhu, J. Ma, Z. Dong, J. Colloid Interface Sci. 2017, 501, 231-
240.
[15] Selected examples of recent publications reporting catalytic syntheses of
quinoxalines: a) D. J. Klein, D. A. Modarelli, F. W. Harris, Macromolecules 2001,
34, 2427-2437; b) K. M. Evans, A. M. Z. Slawin, T. Lebl, D. Philp, N. J.
Westwood, J. Org. Chem. 2007, 72, 3186-3193; c) A. Go, G. Lee, J. Kim, S.
Bae, B. M. Lee, B. H. Kim, Tetrahedron 2015, 71, 1215-1226; d) B. Roy, S.
Ghosh, P. Ghosh, B. Basu, Tetrahedron Lett. 2015, 56, 6762-6767; e) N.
Kolmer-Anderl, A. Kolmer, C. M. Thiele, M. Rehahn, Chem. Eur. J. 2016, 22,
5277-5287.
[16] For selected examples, please see: a) D. Forberg, T. Schwob, M. Zaheer,
M. Friedrich, N. Miyajima, R. Kempe, Nature Commun. 2016, DOI:
10.1038/ncomms13201. b) S. Sachau, M. Zaheer, A. Lale, M. Friedrich, C
Denner, U. B. Demirci, S. Bernard, G. Motz, R. Kempe, Chem. Eur. J. 2016, 43,
15508-15512; c) G. Hahn, J.-K. Ewert, C. Denner, D. Tilgner, R. Kempe,
ChemCatChem 2016, 8, 2461-2465; d) J.-K. Ewert, D. Weingarth, C. Denner,
M. Friedrich, M. Zeiger, A. Schreiber, N. Jäckel, V. Presser, R. Kempe, J. Mater.
Chem. A 2015, 3, 18906-18912; e) M. Zaheer, J. Hermannsdörfer, W. P.
Kretschmer, G. Motz, R. Kempe, ChemCatChem 2014, 6, 91-95; f) D. Forberg,
J. Obenauf, M. Friedrich, S.-M. Hühne, W. Mader, G. Motz, R. Kempe, Catal.
Sci. Technol. 2014, 4, 4188–4192; g) M. Zaheer, T. Schmalz, G. Motz, R.
Kempe, Chem. Soc. Rev. 2012, 41, 5102-5116.
2012, 3, 3249-3255. (self-condensation of primary amines upon oxidation) c) F.
Su, S. C. Mathew, L. Mohlmann, M. Antonietti, X. Wang, S. Blechert, Angew.
Chem. Int. Ed. 2011, 50, 657-660; d) B. Chen, L. Wang, S. Gao, ACS Catal.
2015, 5, 5851-5876; e) B. Chen, L. Wang, W. Dai, S. Shang, Y. Lv, S. Gao, ACS
Catal. 2015, 5, 2788-2794. (oxidative coupling of alcohols and amines) f) M.
Tamura, K. Tomishige, Angew. Chem. Int. Ed. 2015, 54, 864-867; g) L. Geng,
J. Song, Y. Zhou, Y. Xie, J. Huang, W. Zhang, L. Peng, G. Liu, Chem. Commun.
2016, 52, 13495-13498; h) B. Chen, S. Shang, L. Wang, Y. Zhang, S. Gao,
Chem. Commun. 2016, 52, 471-484; i) X. Huang, L. Liu, H. Gao, W. Dong, M.
Yang, G. Wang, Green Chem. 2017, 19, 769-777.
(acceptorless dehydrogenative coupling of alcohols and amines) j) B.
Gnanaprakasam, J. Zhang, D. Milstein, Angew. Chem. Int. Ed. 2010, 122, 1510-
1513; k) L. Tang, H. Sun, Y. Li, Z. Zha, Z. Wang, Green Chem. 2012, 14, 3423-
3428; l) S. Ruch, T. Irrgang, R. Kempe, Chem. Eur. J. 2014, 20, 13279-13285;
m) J. Bain, P. Cho, A. Voutchkova-Kostal, Green Chem. 2015, 17, 2271-2280;
e) A. Mukherjee, A. Nerush, G. Leitus, L. J. W. Shimon, Y. Ben David, N. A.
Espinosa Jalapa, D. Milstein, J. Am. Chem. Soc. 2016, 138, 4298-4301; n) M.
Mastalir, M. Glatz, N. Gorgas, B. Stoger, E. Pittenauer, G. Allmaier, L. Veiros,
K. Kirchner, Chem. Eur. J. 2016, 22, 12316-12320; o) D.-W. Tan, H.-X. Li, M.J.
Zhang, J.-L. Yao, J.-P. Lang, ChemCatChem 2017, 9, 1113-1118.
(hydrogenative cross-coupling of nitriles and amines) p) S. Chakraborty, G.
Leitus, D. Milstein, Angew. Chem. Int. Ed. 2017, 56, 2074-2078. (hydrogenation
of nitriles to imines) q) S. Chakraborty, D. Milstein, ACS Catal. 2017, 7, 3968-
3972.
[13] For selected examples for the reductive synthesis of imines from niroarenes
and aldehydes, please see: a) Y. Zheng, K. Ma, H. Li, J. Li, J. He, X. Sun, R. Li,
J. Ma, Catal. Lett. 2009, 128, 465-474; b) L. L. Santos, P. Serna, A. Corma,
Chem. Eur. J. 2009, 15, 8196-8203; c) F. G. Cirujano, A. Leyva-Pérez, A.
Corma, F. X. Llabrés i Xamena, ChemCatChem. 2013, 5, 538-549; d) Y.-Z.
Chen, Y.-X. Zhou, H. Wang, J. Lu, T. Uchida, Q. Xu, S.-H. Yu, H.-L. Jiang, ACS
Catal. 2015, 5, 2062-2069.
[17] T. Stemmler, F. A. Westerhaus, A.-E. Surkus, M.-M. Pohl, K. Junge, M.
Beller, Green Chem. 2014, 16, 4535-4540.
[14] Selected examples of recent publications reporting catalytic syntheses of
benzimidazoles: a) N. T. Jui, S. L. Buchwald, Angew. Chem. Int. Ed. 2013, 52,
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10.1002/chem.201801525
Chemistry - A European Journal
COMMUNICATION
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COMMUNICATION
A novel reusable iron catalyst has
been introduced. It is easy to
synthesize and to handle. Beside the
selective hydrogenation of
nitroarenes, the catalyst efficiently
mediates the direct synthesis of
imines, benzimidazoles and
quinoxalines from nitroarenes and
carbonyl compounds. Functional
groups regarded as highly
Christoph Bäumler and Rhett Kempe*
Page No. – Page No.
The Direct Synthesis of Imines,
Benzimidazoles and Quinoxalines
from Nitroarenes and Carbonyl
Compounds via Selective
Nitroarene Hydrogenation
Employing a Reusable Iron Catalyst
hydrogenation sensitive can be
tolerated.
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