DOI: 10.1002/cssc.201500869
Communications
Gold-Catalyzed Reductive Transformation of Nitro
Compounds Using Formic Acid: Mild, Efficient, and
Versatile
[
a]
Lei Yu, Qi Zhang, Shu-Shuang Li, Jun Huang, Yong-Mei Liu, He-Yong He, and Yong Cao*
Developing new efficient catalytic systems to convert abun-
dant and renewable feedstocks into valuable products in
a compact, flexible, and target-specific manner is of high im-
portance in modern synthetic chemistry. Here, we describe
a versatile set of mild catalytic conditions utilizing a single
gold-based solid catalyst that enables the direct and additive-
free preparation of four distinct and important amine deriva-
tives (amines, formamides, benzimidazoles, and dimethlyated
amines) from readily available formic acid (FA) and nitro start-
ing materials with high level of chemoselectivity. By controlling
the stoichiometry of the employed FA, which has attracted
considerable interest in the area of sustainable chemistry be-
cause of its potential as an entirely renewable hydrogen carrier
is pertinent to point out that the use of H is not perfectly
2
atom-economical as it might seem owing to current industrial
production of H relying overwhelmingly on fossil fuels and
2
the fact that the associated emissions have led to a net in-
[
6]
crease in global CO levels.
2
There is considerable current interest in exploiting formic
acid (FA) as a promising molecule for hydrogen storage and
delivery, which has been advocated as a carbon-neutral energy
source to meet the ever-increasing demand for a sustainable
[
7]
and affordable energy supply. Of the most attractive features
of FA, apart from its accessibility as a major product from bio-
mass processing, is the possibility to establish an integrated
energy storage scheme for a dispatchable solar- and wind-
and as a versatile C source, a facile atom- and step-efficient
powered energy system based on a reversible FA–CO inter-
1
2
[
8]
transformation of nitro compounds can be realized in a modu-
lar fashion.
conversion. Given the fact that FA easily undergoes selective
dehydrogenation to yield H , FA can be envisioned as an ap-
2
[
9]
pealing terminal reductant. With regard to green organic syn-
thesis, this approach is particularly attractive in light of the ap-
parent and compelling advantage of using FA as a biorenewa-
Chemical reduction of unsaturated bonds of readily available
chemical feedstocks is one of the most fundamental transfor-
[
10]
ble C source for attaching CO, CHO, or methyl groups. In
1
[1]
mations in organic chemistry. In particular, the reductive
transformation of molecules containing nitro functional groups
is of special interest since the reduced products (amines and
related derivatives) are key intermediates or targets in the syn-
thesis of pharmaceuticals, dyes, agrochemicals, pigments, and
this regard, reductive transformation using FA may bring
about new opportunities for the construction of molecular
[
10b,c]
complexity.
Despite the prospects for contributions to
both flexibility and step economy of such types of transforma-
tions, progress in this area, especially expanding the scope of
the FA–nitro reaction, has been largely limited to nitro-to-
[
2,3]
polymers.
Despite many known methods, there are unceas-
[
11]
ing efforts to develop new clean, facile, cost-effective, green,
and chemoselective procedures that eliminate the use of large
excess of expensive and perilous stoichiometric reducing
amine transformations.
Moreover, the reported reactions
[
11a–d]
generally necessitate the use of FA in large excess,
adversely affects the overall atom efficiency.
which
[
4]
agents. In this respect, H gas is arguably one of the most
Heterogeneous Au catalysis has recently emerged as an im-
portant and powerful tool for clean and resource-efficient
2
popular and attractive means to effect reduction, thereby lead-
ing to a number of catalytic hydrogenation procedures amena-
[
12]
chemical synthesis. In particular, various supported Au cata-
lysts have been reported to show distinct reactivity, activity,
and selectivity in a number of industrially important process-
[5]
ble to reduce nitro compounds. However, application of
these processes is constrained by the need for specialized
equipment, limited functional group tolerance, and potential
[
13]
es, complementing and expanding the existing areas of tra-
ditional platinum-group metal (PGM) catalysis. As part of our
continuing exploration into new reaction chemistry by sup-
safety issues regarding H handling. Even more importantly, it
2
[
14]
ported Au nanoparticles (NPs), we recently discovered the
outstanding catalytic ability of Au NPs for FA activation, where-
in we found that subnanomeric gold NPs (ca. 0.8 nm) finely
dispersed on ZrO can promote efficient and selective H gen-
+
+
[
a] L. Yu, Q. Zhang, S.-S. Li, Dr. J. Huang, Dr. Y.-M. Liu, Dr. H.-Y. He,
Prof. Dr. Y. Cao
Department of Chemistry
Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials
Fudan University
Handan Road 220, Shanghai 200433 (P.R. China)
Fax: (+86)21-65643774
E-mail: yongcao@fudan.edu.cn
2
2
eration from FA dehydrogenation under ambient condition-
[14a]
s.
Realizing the advantages of adopting the Au-based re-
duction protocols and also utilizing the excellent catalytic ac-
[
12–14]
+
tivity of supported Au toward FA activation,
we became
[
] These authors contributed equally to this work.
intrigued by the catalytic utility of the Au–FA protocol to de-
velop innovative catalytic processes that enable direct and ad-
ChemSusChem 2015, 8, 3029 – 3035
3029
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim