Tetrahedron Letters
Solid supported rhodium(0) nanoparticles: an efficient catalyst
for chemo- and regio-selective transfer hydrogenation of nitroarenes
to anilines under microwave irradiation q
Nitul Ranjan Guha a,b, Dhananjay Bhattacherjee a, Pralay Das a,b,
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a Natural Plant Products Division, CSIR-Institute of Himalayan Bioresource Technology, Palampur 176061, H.P., India
b Academy of Scientific & Innovative Research, New Delhi, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A Solid-supported rhodium(0) (SS-Rh) catalyst has been developed and applied for the chemo- and regio-
selective reduction of nitroarenes functionalized with CAC multiple bonds and dinitroarenes to their cor-
responding amines respectively using hydrazine hydrate (N2H4ÁH2O) as a reducing source under mild
microwave irradiation (MWI) conditions. The present methodology also shows excellent compatibility
with a broad range of structurally diverse reducible functional groups. The catalyst can be recovered
by simple filtration and reused for 13 cycles with consistent activity hence reduces the cost of the catalyst
assertively.
Received 31 December 2013
Revised 10 March 2014
Accepted 10 March 2014
Available online 17 March 2014
Keywords:
Solid-supported rhodium(0) (SS-Rh)
Heterogeneous catalyst
Nano-catalysis
Ó 2014 Elsevier Ltd. All rights reserved.
Chemo- and regio-selective reaction
Nitro reduction
Recyclable catalyst
Among the hydrogenation reactions, catalytic reduction of
nitroarenes to its corresponding amines represents one of the most
powerful techniques because functionalized anilines are industri-
ally valuable intermediates for pharmaceuticals, dyes polymers,
rubbers, herbicides, and other fine chemicals.1 Non catalytic pro-
cesses involve either Bechamp or sulfide reduction of nitroarenes
generating a large amount of environmental waste.2 A variety of
transition metals such as Au,3 Fe,4 Pt,5 Pd,6 and Ru7 have been re-
ported for the reduction of nitro compounds to their corresponding
amines. However, in comparison to other transition metals, Rh-cat-
alyzed hydrogenation of nitroarenes has not yet been extensively
explored with vast substrate scope.8 A homogenous Rh carbonyl
cluster has been reported as an active catalyst for the selective
reduction of the nitro group in the presence of alkenyl functional-
ity,9 but the homogenous catalyst causes difficulty in product iso-
lation as well as recovery of catalyst for recycling from the reaction
mixture and its air and moisture sensitivity limit the process usage.
Recently, easily-separable and recyclable heterogeneous cata-
lysts in the form of nanoparticles (NPs) are being utilized exten-
sively for the catalytic hydrogenation of nitroarenes to anilines to
override the existing limitations associated with homogenous
counterparts.10 However, only a few examples of heterogeneous
rhodium catalyzed reduction of nitroarenes have been reported
employing N2H4ÁH2O as reducing source.11 Despite their utility,
these methods offered very limited chemo- and regio-selective
reduction of alkenyl as well as alkynylnitroarenes, and dinitroa-
renes, respectively, and suffer from longer reaction time, and nar-
rower substrate scope. Therefore, the development of nano-
impregnated environmentally sustainable and low cost heteroge-
neous catalyst for the selective reduction of nitroarenes is highly
anticipated. Presently, our group is dedicated to the development
and application of solid supported transition metal NPs as hetero-
geneous catalyst in different areas of organic transformations.12 In
continuation to our previous work,13 herein we report further
application of the SS-Rh catalyst for chemo- and regio-selective
reduction of nitroarenes in the presence of most challenging CAC
multiple bonds and highly reducible functional groups to the cor-
responding anilines.
In continuation of our earlier study, SS-Rh NPs were synthesized
following in situ reduction–deposition technique. Amberlite IRA
900 chloride form of resin (1 g) as a solid surface was partially ex-
changed with –BHÀ4 ions from NaBH4 (30 mg) and then washed
with water and acetone. Further it was treated with catalytic quan-
tity of RhCl3, 3H2O (10 mg) in THF for 1 h at 80 °C. After complete
deposition of Rh(0), the white solid surface of resin turned into
black/metallic luster (Fig. 1). When full immobilization of Rh(0)
q
IHBT communication no. 3568.
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Corresponding author. Tel.: +91 1894 233339; fax: +91 1894 230433.
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.