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Green Chemistry
Page 7 of 9
DOI: 10.1039/C5GC02460A
Journal Name
ARTICLE
H
H
O
Acknowledgements
O
O
O
Mo
Mo
Mo
Mo
Mo
O
Mo
Mo
O
O
This work was supported by the National Natural Science
Foundation of China (21303189, 21233008, 21422308), and
Dalian Excellent Youth Foundation (2014J11JH126).
O
Step 2
Step 3
HN=NH
H
H
O
H2NHN
H
O
O
O
Mo
Mo
Mo
O
O
O
Mo
Mo
Mo
Mo
Mo
Mo
Mo
Mo
Mo
O
O
O
O
Mo
Mo
O
O
Notes and references
O
H
O
O
1 (a) A. Noujima, T. Mitsudome, T. Mizugaki, K. Jitsukawa, K.
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94.
N=NH
Step 4
Step 1
O
H
H
O
H-NHNH2
N2
O
O
O
Mo
O
O
Mo
Mo
Mo
Mo
Mo
Mo
O O
Mo
Mo O
Mo
O
Mo
O
Mo
O
O
Mo
Step 5
O
H
Mo
H
O
2 (a) X. Liu, L. He, Y. M. Liu, Y. Cao, Acc. Chem. Res., 2014, 47, 793-
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NO2
NH2
Scheme 2. The possible mechanism of the catalytic N-H and N-N bonds cleavage of
hydrazine at the surface of the MoO2 in the nitrobenzene reduction
proton on basic sites (Mo–OH, Hδ+) and a Mo–NHNH2. Step 2:
the Mo–NHNH2 decomposes to an active hydrogen species
(Moδ+–Hδ–) and releases a HN=NH via a β-hydrogen elimination
pathway. Step 3: the released HN=NH attacks another Mo ion
and generates a Mo–OH (Hδ+) and a Mo–N2H. Step 4: the Mo–
N2H releases a N2 and generates another active hydrogen
species (Moδ+–Hδ–). Step 5: the Hδ– and Hδ+ species react with 3 (a) F. Alonso, P. Riente, M. Yus, Acc. Chem. Res., 2011, 44, 379-
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3428.
nitro to generate amine or with hydrazine to generate NH3,
restoring catalytic active sites to the original state.
As shown in Figure S7, without nitrobenzene, surface
proton and hydride unlikely recombine to form hydrogen,
hydrazine decomposition (3N2H4 → N2 + 4NH3) takes place
weakly [0.0165 L gas (g·cat)-1 in 5 min reaction]. Because of the
transfer hydrogenation of the nitrobenzene (2PhNO2 + 3N2H4
→ 2PhNH2 + 3N2 + 4H2O), the addition of nitrobenzene
triggered the gas emission burst [0.625 L gas (g·cat)-1 in 5 min].
Therefore it is clear that MoO2 has two key roles. (1) It
abstracts hydrogen and stabilizes it on surface, restricting
active H* recombination. (2) It catalyzes the hydrogen transfer
to nitrobenzene, which is an oxidant to clean adsorbed hydride.
Such ability of co-existing proton and hydride on MoO2 is
usually attributed to precious metal catalysts, and seldom for
metal oxides. The unique metallic function assured by the
delocalized electrons above the metal atoms at the Fermi level
may account for the excellent catalytic activity of MoO2.
4 Conclusions
5 (a) D. Cantillo, M. Baghbanzadeh, C. O. Kappe, Angew. Chem. Int.
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Kim, B. M. Kim, Chem. Asian J., 2011, 6, 1921-1925; (d) P. S.
Kumbhar, J. Sanehez-Valente, F. Figueras, Tetrahedron Lett.,
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Nanoscale, 2013, 5, 7219-7223; (f) A. S. Kulkarni, R. V. Jayaram, J.
Mol. Catal. A: Chem., 2004, 223, 107-110; (g) A. Maltha, S. C.
Vanwermeskerken, B. Brunet, V. Ponec, J. Mol. Catal., 1994, 93,
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In summary, we report the metallic-basic property of
crystalline MoO2 in generating and stabilizing active hydrogen
species (Hδ+ and Hδ–) at very mild reaction conditions.
Crystalline MoO2 exhibits extremely high active for transfer
hydrogenation of various nitroarenes to arylamines. Detailed
hydrogen transfer mechanism is revealed by experiments and
DFT calculations, which lays a firm foundation for further
catalytic applications of the catalytic system hydrazine and
MoO2.
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