FULL PAPER
DOI: 10.1002/chem.201100818
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Ultrathin Platinum Nanowire Catalysts for Direct C N Coupling of
Carbonyls with Aromatic Nitro Compounds under 1 Bar of Hydrogen
Lei Hu,[a] Xueqin Cao,[a] Danhua Ge,[a] Haiyan Hong,[a] Zhiqiang Guo,[a] Liang Chen,[b]
Xuhui Sun,[c] Jianxin Tang,[c] Junwei Zheng,[d] Jianmei Lu,*[a] and Hongwei Gu*[a]
Abstract: Traditionally important in
the pharmaceutical, agrochemical, and
and hydrogen as the reducing agent, N-
alkylamines were achieved in high
yields. Debenzylation products were
not detected after prolonged reaction
times. Time-dependent analysis, Reac-
tIR spectroscopy and DFT calculations
À
revealed that the C N coupling pro-
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synthetic dye industries, C N coupling
ceeded through a different mechanism
than traditional “reductive amination.”
N-Alkylamines were directly obtained
by intermolecular dehydration over
platinum nanowires under a hydrogen
atmosphere, instead of intramolecular
water elimination and imine hydroge-
nation.
has proved useful for the preparation
of a number of valuable organic com-
pounds. Here, a new method for the
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direct one-pot reductive C N coupling
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Keywords: amination · C N cou-
from carbonyl and aromatic nitro com-
pounds is described. Employing ultra-
thin platinum nanowires as the catalyst
pling · heterogeneous catalysis ·
nanowires · platinum
Introduction
aromatic nitro compounds) with aldehydes (or ketones)[4] is
another attractive procedure for N-alkylamine formation
which includes two synthetic steps: C=N double-bond for-
mation and hydrogenation of the imine derivatives. Several
catalysts have demonstrated their efficiency in reductive
amination reactions. Yamane et al.[5] reported a direct reduc-
tion over Au/Fe2O3 under a 2 MPa hydrogen atmosphere.
Sreedhar et al.[6] reported that gum-acacia-stabilized Pd
nanoparticles could be used as the catalyst with excellent
The importance and widespread use of N-alkylamines in
dye, pharmaceutical, and agrochemical industries have led
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C N coupling to become a core interest in organic synthe-
sis.[1] The reaction of amines with alkyl halides or similar al-
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kylation agents is one of the most common methods of C N
coupling.[2] However, these processes have significant draw-
backs such as alkylation agent toxicity and a lack of mono-
alkylation selectivity. The alkylation of amines with alcohols
through a hydrogen auto-transfer or oxidation process[3] is
an important reaction class that follows three steps to gener-
ate the N-alkylamines. Reductive amination of amines (or
yield. Decaborane Pd/C and HCOOÀNH4+/Pd/C systems
[7]
À
have also been used for C N bond formation. These meth-
ods are encouraging; however, the Au/Fe2O3 system needs
high pressure and the Pd catalysts system causes debenzyla-
tion,[8] which is an side reaction to N-alkylamine formation.
Herein, we report on the use of ultrathin platinum nano-
wires (Pt NW) as nonsupported catalysts for N-alkylation
from aromatic nitro compounds and various carbonyls in a
one-pot reaction under 1 bar of hydrogen. Time-dependent
[a] L. Hu, Prof. Dr. X. Cao, D. Ge, H. Hong, Z. Guo, Prof. Dr. J. Lu,
Prof. Dr. H. Gu
Key Laboratory of Organic Synthesis of Jiangsu Province
College of Chemistry,
Chemical Engineering and Materials Science
Soochow University, Suzhou, 215123 (P. R. China)
Fax : (+86)512-65880905
À
analyses and DFT calculations revealed that C N bonds are
directly formed through intermolecular dehydration instead
of C=N intermediate formation through intramolecular
water elimination and C=N double-bond hydrogenation.
This mechanism is different than previously reported molec-
ular catalysts or “Pd” nanocatalysts. Debenzylation products
were not detected even after prolonged reaction times, up
to 24 h.
[b] Prof. Dr. L. Chen
Institute of Materials Technology & Engineering
Chinese Academy of Sciences
Ningbo, 315201 (P. R. China)
[c] Prof. Dr. X. Sun, Prof. Dr. J. Tang
Functional Nano & Soft Materials Laboratory (FUNSOM) &
Jiangsu Key Laboratory for Carbon-Based
Functional Materials and Devices
Results and Discussion
Suzhou, Jiangsu, 215123 (P. R. China)
[d] Prof. Dr. J. Zheng
Ultrathin Pt NW catalysts were obtained from the acidic
etching of FePt NW under an air atmosphere. Compared
with the starting material, FePt NW (Fe atomic ratio
ꢀ50%, Figure S1, Supporting Information), Fe not was de-
Institute of Chemical Power Sources
Soochow University, Suzhou, 215123 (P. R. China)
Supporting information for this article is available on the WWW
Chem. Eur. J. 2011, 17, 14283 – 14287
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
14283