Gold(I)-Thiolate Oligomers for Catalytic Hydrogenation of Nitroaromatics in Aqueous and Organic Medium

Article abstract of DOI:10.1002/cctc.202000885

Thiolated gold nanoclusters (AuNCs) have been introduced to efficiently and selectively catalyze the hydrogenation of nitroaromatics due to the strong interaction of their S?Au-S staple motifs with the nitro groups of nitroaromatics. However, without a gold core, gold(I)-thiolate oligomers (AuSOs) with S?Au-S staple motifs are rarely explored as catalysts for nitroaromatics. Here, we report a straightforward strategy for the synthesis of AuSOs through hydroxyl radical-induced leaching of glutathione-capped gold nanoparticles (GSH-AuNPs). Raman spectroscopy and matrix-assisted laser desorption/ionization-time of flight mass spectrometry demonstrated that hydroxyl radical-triggered etching of the GSH-AuNPs resulted in the production of AuSOs, including Au₄(GSH)₇ and Au₇(GSH)₉. The AuSOs were found to catalyze NaBH₄-mediated hydrogenation of 4-nitrophenol to 4-aminophenol with a chemoselectivity of ～100 percent and a normalized rate constant (Knor) of 4.8×10⁵ s^? g^?1. In addition to the high affinity of the S?Au?S staple motifs for 4-nitrophenol, the unusual catalytic activity of the AuSOs was attributable to the fact that they efficiently catalyzed the production of H₂ from NaBH₄ and the reaction of dissolved oxygen and NaBH₄. The chemoselectivity and applicability of the AuSOs were further verified by performing the catalytic reaction of methyl 2-(2-nitrophenyl) acetate or methyl 4-nitrobenzoate with NaBH₄.

Full text of DOI:10.1002/cctc.202000885

The European Society Journal for Catalysis
Supported by
Accepted Article
Title: Gold(I)-Thiolate Oligomers for Catalytic Hydrogenation of
Nitroaromatics in Aqueous and Organic Medium
Authors: Jyun-Guo You, Dun-Yuan Jin, Wei-Bin Tseng, Po-Chiao Lin,
and Wei-Lung Tseng
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0
1/2020

ChemCatChem
10.1002/cctc.202000885
FULL PAPER
Gold(I)-Thiolate Oligomers for Catalytic Hydrogenation of
Nitroaromatics in Aqueous and Organic Medium
[
a]
[a]
[a]
*[a, b]
*[a]
Jyun-Guo You, Dun-Yuan Jin, Wei-Bin Tseng, Wei-Lung Tseng,
and Po-Chiao Lin
J.-G. You and D.-Y. Jin contributed equally to this work.
[
[
a]
b]
Dr. J.-G., D.-Y. Jin , Dr. W.-B. Tseng, Prof. W.-L. Tseng and Prof. Po-Chiao Lin
Department of Chemistry, National Sun Yat-sen University No.70 Lien-hai Rd., Kaohsiung 80424, Taiwan, R.O.C.
E-mail: tsengwl@mail.nsysu.edu.tw; pclin@mail.nsysu.edu.tw.
Prof. W.-L. Tseng
School of Pharmacy, Kaohsiung Medical University, No. 100, Shiquan 1st Road, Sanmin District, Kaohsiung 80708, Taiwan
Supporting information for this article is given via a link at the end of the document.
Abstract: Thiolated gold nanoclusters (AuNCs) have been
introduced to efficiently and selectively catalyze the hydrogenation of
nitroaromatics due to the strong interaction of their S-Au-S staple
motifs with the nitro groups of nitroaromatics. However, without a
gold core, gold(I)-thiolate oligomers (AuSOs) with S-Au-S staple
motifs are rarely explored as catalysts for nitroaromatics. Here, we
report a straightforward strategy for the synthesis of AuSOs through
hydroxyl radical-induced leaching of glutathione-capped gold
nanoparticles (GSH-AuNPs). Raman spectroscopy and matrix-
assisted laser desorption/ionization-time of flight mass spectrometry
demonstrated that hydroxyl radical-triggered etching of the GSH-
theoretical hydrogen gravimetric density (10.8 wt%), large
3
volumetric density (115 kg H /m ), long shelf-life and good
2
resistance to air exposure, commercial availability as a salt with
[
10]
a high purity (>98%), low cost, and safe use. The reduction of
nitroaromatics involves the [1h1y] drolysis of aqueous NaBH
solutions at room temperature, which is expressed as follows:
4
NaBH
4
+ 2H
2
O → NaBO
2 2
+ 4H + heat (217 kJ)
-
1
Since the solubility of NaBO
2
(3.5 mol L ) and NaBH
4
is quite
low in aqueous solutions, excess water is needed to liberate 4
AuNPs resulted in the production of AuSOs, including Au
and Au (GSH) . The AuSOs were found to catalyze NaBH -mediated
hydrogenation of 4-nitrophenol to 4-aminophenol with
chemoselectivity of ~100% and a normalized rate constant (Knor) of
4 7
(GSH)
moles of hydrogen in real hydrolysis conditions and lowers the
7
9
4
[12]
theoretical hydrogen gravimetric density of NaBH
Additionally, the hydrolysis of NaBH
at generating hydrogen due to the gradual increase in the pH of
4
.
a
4
in pure water is ineffective
5
-1
-1
4
.8 х 10 s g . In addition to the high affinity of the S-Au-S staple
[13]
the mixture during the reaction process.
presence of acid additives (e.g., HCl, H
HCOOH) efficiently accelerates the hydrolysis of NaBH
Although the
motifs for 4-nitrophenol, the unusual catalytic activity of the AuSOs
was attributable to the fact that they efficiently catalyzed the
2
SO
4
, HNO , and
3
[
14]
4
,
this
production of H
and NaBH . The chemoselectivity and applicability of the AuSOs
were further verified by performing the catalytic reaction of methyl 2-
2-nitrophenyl) acetate or methyl 4-nitrobenzoate with NaBH
2 4
from NaBH and the reaction of dissolved oxygen
treatment has drawbacks in terms of the large quantities of acids
required and the difficulty in controlling the reaction process. In
response to these drawbacks, numerous heterogeneous and
homogeneous catalysts have been developed to enhance the
4
(
4
.
reaction kinetics of NaBH
application of NaBH
4
hydrolysis, opening the door for the
in the catalytic hydrogenation of
4
nitroaromatics. The previously reported catalysts are exemplified
by different types (including nanoparticles, nanoclusters, and
single atoms) of noble metals, non-noble metals, alloy metals,
Introduction
Aromatic amines are one of the most essential intermediates for
the synthesis of industrial compounds, such as pharmaceutical
organics (antipyretic and analgesic drugs), cosmetics products
and metal oxides (e.g., Fe
3 4 3 4 2
O , Co O , and CeO ) in the absence
and presence of different supporting materials (e.g., graphene
[
1]
[4, 15]
oxide, carbon nanotube, and mesoporous silica).
It is well-
[
2]
(
3-aminophenol and 4-phenylenediamine), and anticorrosion
documented that that the activity and chemoselectivity of the
catalyst is heavily interrelated with a series of factors such as
[3]
agents (polyaminophenol and polyaniline). For example, the
preparation of paracetamol is conducted by the acetylation of 4-
[16]
the particle morphology (shape, size, and facets),
electronic
stability,
[
4]
aminophenol with acetic anhydride. Aromatic amines are, in
general, produced from the direct reductive amination of
alcohols and aldehydes with the assistance of hydrogen sources.
The catalyst-triggered reduction of nitroaromatics that proceeds
in the presence of hydrogen sources is an alternative to
preparing aromatic amines.
aromatic amines is routinely performed via the catalyst-mediated
hydrogenation of nitroaromatics with molecular hydrogen under
high temperature and pressure conditions. Although hydrazine
hydrate is known to be frequently used for the efficient reduction
[17]
[18]
and
geometrical
structures,
colloidal
[19]
catalyst−reactant/solvent interaction,
interaction.
and catalyst−support
Among the catalysts above-mentioned, gold
nanoparticles have been recognized as useful materials for
catalyzing the NaBH -mediated hydrogenation of nitroaromatics
due to their outstanding chemoselectivity.
[20]
[
4]
4
The production of industrial
[21]
However, in
contrast to other metal-based nanomaterials, the catalytic
activity of gold nanoparticles is relatively poor owing to their low
[
5]
[22]
catalytic activity for the hydrolysis of NaBH
4
to H
2
.
In contrast,
atomically precise gold nanoclusters (AuNCs) exhibited an
enhanced activity for catalyzing the NaBH -mediated reduction
of nitroaromatics and still provided an excellent
chemoselectivity. For example, Li et al. demonstrated that
Au44(SC Ph)32 exhibited an excellent chemoselectivity (97%
[
6]
of nitroaromatics under mild conditions,
an undesirable
4
hydrogenation reaction could occur in the case of nitroaromatic-
bearing carbon-carbon double bonds. For the sake of creating
an environmentally friendly conditio[9n] , alcohols, including
[18, 23]
H
4
[
7]
[8]
2
glycerol, ethanol, and isopropanol, have been shown to
serve as hydrogen donors for the catalyst-mediated reduction of
nitroaromatics to aromatic amines in basic media. However, the
alcohol-mediated hydrogenation process suffers from salt
production, a slow reaction rate, and poor selectivity.
yield of 4-aminophenol) and stability for the catalytic
[23b]
hydrogenation of 4-nitrophenol at low temperatures.
Yamamoto et al. reported that Au25(glutathione)18 provided a
relatively higher catalytic activity for catalyzing the NaBH
4
-
mediated hydrogenation of 4-nitrophenol than thiolate-protected
[
23c]
gold nanoparticles.
Considering that the S–Au–S staple
Recently, sodium borohydride (NaBH
appealing chemical for use as a hydrogen source due to its high
4
) has been seen as an
motifs of thiolated AuNCs serve as an active site for catalyzing
[23d]
[24]
Sonogashira coupling
and aldehyde hydrogenation,
we
1
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ChemCatChem
10.1002/cctc.202000885
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suggest that gold(I)-thiolate oligomers (AuSOs) without a gold
Results and Discussion
core could be promising catalysts for the NaBH
hydrogenation of 4-nitrophenol.
4
-mediated
Formation of AuSOs by Etching GSH-AuNPs.
GSH-AuNPs were synthesized via the reduction of an aqueous
This study introduces
preparation of AuSOs based on the etching of glutathione-
capped gold nanoparticles (GSH-AuNPs) by Fenton's reagent
a
simple approach for the
-1
solution of 2.5 mM HAuCl
4
with 1 mg mL NaBH
4
in the
presence of 0.8 mM GSH. The as-synthesized GSH-AuNPs
possess an average particle size of 47 ± 7 nm, a hydrodynamic
diameter of 54 ± 9 nm, a surface plasmon peak at 533 nm, and
2
+
(
Fe
normalized rate constant (Knor
chemoselectivity (~100%) for the hydrogenation of 4-nitrophenol
to 4-aminophenol using NaBH as a hydrogen source. To our
knowledge, the Knor values of the previously reported thiolated
AuNCs and other nanomaterials used for catalyzing the NaBH
and H O ). The formed AuSOs exhibited a large
2 2
5 -1 -1
=
4.8
х
10
s
g ) and
only Au(0) surface atoms (Figure S1, Supporting Information).
2+
2 2
Fenton’s reagent consisting of 20 mM Fe and 10 mM H O was
4
introduced to react with the GSH-AuNPs, which were monitored
by a UV-Vis absorption spectrometer over time (Figure 1A). The
SPR peak of the GSH-AuNPs rapidly disappeared within 1 min
4
-
5
-1 -1
mediated hydrogenation of 4-nitrophenol are less than 10 s
Table S1, Supporting Information). The experimental results
suggest that the outstanding catalytic activity and
chemoselectivity of the AuSOs could result from two factors: (i)
the motif structure of the AuSOs strongly interacts with the nitro
g
because the hydroxyl radicals efficiently etched the GSH-AuNPs
(
[26]
via the oxidation of gold atoms.
At 5 min, the resulting
products exhibited a broad absorption band across the visible
[27]
region, which is characteristic of the AuSOs. After 5 min, the
absorption band of the resulting products progressively
intensified in the wavelength range of 400 to 500 nm as the
reaction progressed. This observation reflects that incubating
groups of nitroaromatics, thus accelerating the NaBH
hydrogenation reaction, and (ii) the AuSOs efficiently catalyze
the hydrolysis of NaBH and the consumption of dissolved
4
-mediated
4
the GSH-AuNPs for
a longer time with Fenton’s reagent
oxygen, facilitating the hydrogenation of 4-nitrophenol with short
induction period (< 6 s). Given that the hydrogenation of methyl
-nitrobenzoate has been recognized as a model process for
produces more abundant AuSOs. The hydroxyl radical-induced
etching of the GSH-AuNPs was further verified by transmission
electron microscopy (TEM) (Figure 1B–1E). As the GSH-AuNPs
reacted with Fenton’s reagent for 1, 10, 30, and 60 min, the
particle size of the resulting products reduced from 13 ± 5 to 4 ±
4
evaluating the catalytic activity and chemoselectivity of
[
25]
catalysts,
NaBH -mediated reduction of methyl 2-(2-nitrophenyl) acetate
and methyl 4-nitrobenzoate.
the AuSOs were further used to catalyze the
4
Figure 1. Leaching of the AuSOs from the etching of the GSH-AuNPs. (A) Time evolution of UV-Vis absorption spectra of the GSH-
-
1
2+
2 2
AuNPs (4 μg mL ) upon the addition of Fenton’s reagent (20 mM Fe and 10 mM H O ). (B–E) TEM images taken from the reaction of
the GSH-AuNPs with Fenton’s reagent at ambient temperature for (B) 1, (C) 10, (D) 30, and (E) 60 min. (F) MALDI-TOF mass spectrum
of the AuSOs. (G) Raman spectra of the AuSOs obtained from three independent reactions of the GSH-AuNPs with Fenton’s reagent at
ambient temperature for 120 min. (H) XPS spectra of the AuSOs.
2
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ChemCatChem
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previous studies have demonstrated the lost GSH fragments in
[
29]
MALDI-TOF MS analysis of GSH-capped AuNCs,
recommend that the leached AuSOs could contain two
molecular formulas, including Au (GSH) and Au (GSH)
we
4
7
7
9
.
Moreover, Raman spectroscopy was utilized to examine the
formation of Au–S and S–S bonds in the AuSOs, which could be
helpful for clarifying the molecular structure of the AuSOs. The
three repeated Raman measurements performed for the leached
-
1
AuSOs revealed two peaks centered at 305 and 423 cm
(
Figure 1G), which are attributable to Au–S and S–S stretching
[30]
vibrations, respectively.
Treatment of the AuSOs with tris(2-
Figure 2. Optimized geometry of Au
simulated from the Chem3D with Gaussian 09 Interface. Color
legends: dark gray, Au; yellow, S; blue N; red, O; light gray, C; white,
H)
4
(GSH)
7
7 9
and Au (GSH)
carboxyethyl)phosphine (TCEP) resulted in the disappearance
of the S–S peak due to the TCEP-induced cleavage of the S–S
[31]
bonds (Figure S2, Supporting Information).
This result
demonstrates the existence of S–S bonds in the chemical
structure of the AuSOs. As the existence of Au–Au bonds was
confirmed in the AuSOs, their oxidation state was measured
using X-ray photoelectron spectroscopy (XPS). You et al.
reported that the XPS spectrum of GSH-Au(I) complexes,
1
, 2 ± 0.5, and 1.6 ± 0.4 nm. This result confirms the observation
made from the etching experiment measured by UV-Vis
absorption spectroscopy. Once the reaction time was extended
to 120 min, the particle size of the resulting products was too
small to image with TEM. The hydroxyl radicals completely
converted the GSH-AuNPs to the corresponding AuSOs that
were leached into the aqueous solution. Matrix-assisted laser
desorption/ionization-time of flight mass spectrometry (MALDI-
TOF MS) was implemented to measure the molecular weight of
the leached AuSOs. All-trans retinoic acid, used as a nonpolar
matrix, was selected for the MALDI-TOF MS analysis of the
obtained from the direct mixing of GSH and HAuCl
peak corresponding to Au(I) with a binding energy of 84.1 eV.
4
, exhibited a
[29b]
By fitting the Au 4f7/2 peak of the AuSO spectrum with the same
binding energy, the AuSOs were suggested to consist of almost
1
00% Au(I) (Figure 1H). This finding reflects that no Au–Au
bonds are present in the AuSOs. Considering the relative
sensitivity factors of Au4f (4.9) and S2p (0.54) and their peak
areas (Figure 1H; Figure S3, Supporting Information) in the
XPS spectrum, the molar ratio of Au to S for the AuSOs is near
[
28]
nonpolar AuSOs.
Note that polar matrices, such as 2,5-
dihydroxybenzoic acid and α-cyano-4-hydroxycinnamic acid,
were inappropriate for the MALDI-TOF MS detection of AuSOs.
The mass spectrum of the leached AuSOs consisted of two
major peaks at m/z 1010.8 and 1665.4, which are attributed to
0
.69, which is in line with the results obtained from the MALDI-
TOF-MS analysis of the molecular weight of the AuSOs.
According to the above-mentioned findings, we conclude that
hydroxyl radicals efficiently etch the GSH-AuNPs, leading to the
production of numerous AuSOs with molecular formulas of
+
+
[
4 7 7 9
Au S ] and [Au S ] , respectively (Figure 1F). Considering that
Figure 3. Kinetics analysis of NaBH
of solutions (2 mL) of 42 mM NaBH
temperature for 0.3 min. (B) Time-dependent absorbance changes at 400 nm collected from a mixture (2 mL) of 0.4 μg AuSOs, 42 mM
NaBH , and 140 μM 4-nitrophenolate. (C) Percent conversion of 4-nitrophenolate and chemoselective formation of 4-aminophenol
obtained from obtained from three independent reactions of with 42 mM NaBH and 140 μM 4-nitrophenolate in the presence of 0.4 μg
AuSOs. (D) Pseudo-first-order reaction kinetics for 42 mM NaBH -mediated reduction of 140 μM 4-nitrophenolate in the presence of 0.1,
.2, and 0.4 μg AuSOs. (E) UV-Vis absorption spectra and photographs of 100 mL of 42 mM NaBH and 140 μM 4-nitrophenolate before
and after the injection of 20 μg AuSOs. (F) Time-evolution Raman spectra of solutions (2 mL) of 50 mM 4-nitrophenolate and 42 mM
NaBH after the injection of 4 μg AuSOs.
4
-mediated reduction of 4-nitrophenolate in the presence of the AuSOs. (A) UV-Vis absorption spectra
4
and 140 μM 4-nitrophenolate (a) before and (b) after incubation with 0.4 μg AuSOs at ambient
4
4
4
0
4
4
3
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ChemCatChem
10.1002/cctc.202000885
FULL PAPER
Au
four Au–S bonds and two S–S bonds, while Au
contain seven Au–S bonds and one S–S bond. Figure 2 shows
the structures of Au (GSH) and Au (GSH) that were
4
(GSH)
7
and Au
7
(GSH)
9
; Au
4
(GSH)
7
could be composed of
AuSO-catalyzed hydrogenation of 4-nitrophenolate with
[
32]
7
(GSH) might
9
borohydride ions in an aqueous solution. After incubating 0.4
μg AuSOs with a mixture of 42 mM NaBH and 140 μM 4-
nitrophenol for 0.3 min, the obtained result revealed
4
4
7
7
9
a
constructed by the Chem3D Gaussian interface under energy
minimization and geometry optimization conditions.
tremendous reduction in the absorbance of 4-nitrophenolate and
a concomitant rise in the absorbance of 4-aminophenol (Figure
3
A). Moreover, the absorbance of 4-nitrophenolate at 400 nm
sharply reduced with increased time and leveled off after 0.3 min,
reflecting the end of the catalytic reaction (Figure 3B). As a
4
AuSO-Catalyzed Reaction of NaBH and 4-Nitrophenol.
control experiment, the treatment of 4-nitrophenolate with NaBH
4
(
5
Figure 5A, Supporting Information) or Fenton’s reagent (Figure
B, Supporting Information) led to a slight reduction in the
The catalytic activity of the AuSOs was explored by the
hydrogenation of 4-nitrophenol to 4-aminophenol in the
absorbance of 4-nitrophenolate, indicating the essential role of
the AuSOs in the NaBH -mediated reduction of 4-nitrophenolate.
presence of excess NaBH
4
at ambient temperature. Note that
4
the NaBH -mediated reduction of 4-nitrophenol has been utilized
4
The catalytic chemoselectivity of the AuSOs and the percent
conversion of 4-nitrophenolate associated with the above-
mentioned catalytic reaction were evaluated by a reversed-
phase high-performance liquid chromatography (RP-HPLC)
system coupled to a UV-Vis multi-wavelength detector. The RP-
HPLC analysis of the 4-nitrophenolate and 4-aminophenol
standards at different concentrations generated an external
calibration curve that was used for the quantification of the
produced 4-aminophenol (Figure S6, Supporting Information).
Figure S7 (Supporting Information) reveals the chromatograms
as a model reaction to evaluate the catalytic activity of the
nanomaterials toward nitroaromatic compounds because this
[
15a, 21]
reaction is easy to measure.
Information) shows that the treatment of 4-nitrophenol with
freshly prepared NaBH led to a red shift in the absorption peak
from 317 to[ 400 nm, reflecting the formation of 4-
Figure S4 (Supporting
4
31-32]
nitrophenolate.
nitrophenol to 4-nitrophenolate stems from the generation of
NaBO , which raised the solution pH to approximately 11. Given
4
The NaBH -induced conversion of 4-
2
that 4-nitrophenolate and 4-aminophenol have characteristic
absorption peaks centered at 400 and 300 nm, respectively,
real-time UV-vis spectroscopy was implemented to track the
of the products obtained from the NaBH
4
-mediated
hydrogenation of 4-nitrophenolate in the absence and presence
Figure 4. Quantification of H
volumes of H gas in N gas. (B, C) GC chromatogram of the gas sample collected from (B) the hydrolysis of NaBH
catalyzed hydrolysis of NaBH . (D) Illustration of the catalytic mechanism of the AuSOs for the production of H , and the consumption of
2
gas from the AuSO-catalyzed hydrolysis of NaBH
4
. (A) A plot of the peak area of H
2
gas versus the known
2
2
4
and (C) the AuSO-
4
2
dissolved O
2
, and NaBH
4
-mediated hydrogenation of 4-nitrophenolate.
4
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ChemCatChem
10.1002/cctc.202000885
FULL PAPER
of AuSOs. This result indicates that the catalytic treatment of 4-
AuSOs, the hydrogenation reaction of 140 μM 4-nitrophenolate
nitrophenolate and NaBH
than 99% 4-aminophenol without other byproducts (Figure 3C),
such as nitroso compounds and azocompounds.
side reactions rarely occur in the AuSO-catalyzed hydrogenation
reaction of 4-nitrophenolate and NaBH , reflecting that AuSOs
4
with 0.4 μg AuSOs produced more
with 42 mM NaBH
temperature (Figure 3E; Video S1, Supporting Information).
Although a large amount of NaBH is not economic for large-
scale synthesis, NaBH can be regenerated by reacting its
byproducts (i.e., NaBO
4
was complete within 15 s at ambient
[
33]
Evidently,
4
4
[
34]
4
2
) with MgH
2
.
4
The NaBH -triggered
deliver a high catalytic activity and an excellent chemoselectivity
toward 4-nitrophenolate. The kinetics of the AuSO-catalyzed
hydrogenation reaction was investigated under a pseudo-first-
reduction of the nitro group of 4-nitrophenolate catalyzed by the
AuSOs was monitored by Raman spectroscopy. Given that the
intensities of the Raman peaks at 1180, 1336, and 1572 cm
−
1
order condition, in which the NaBH
surpassed the 4-nitrophenolate concentration. The NaBH
concentration remained almost constant throughout the catalytic
process. Plotting the ln(A/A ) value against the reaction time
yielded a linear relationship with a slope of 0.19 s , which is
equal to the apparent rate constant of 0.4 μg AuSOs (Figure
4
concentration largely
corresponding to 140 μM 4-nitrophenolate were too low to be
detected, the 4-nitrophenolate concentration was adjusted to 50
4
-
1
mM. Noted that the peaks at 1180 and 1336 cm stem from O–
–
1
0
N–O stretching vibrations, while the peak at 1572 cm was
−
1
[32, 35]
attributable to aromatic ring vibrations.
μg AuSOs with a mixture of 50 mM 4-nitrophenolate and 42 mM
NaBH , the intensities of the identified Raman peaks gradually
When incubating 4
3
4
D). Note that the A/A
-nitrophenolate at 400 nm and is normalized to the A/A
0
value is expressed as the absorbance of
value
4
0
reduced with increased time (Figure 3F). This observation
agrees with the occurrence of the hydrogenation of nitro groups
in the proposed reaction.
at the initial reaction time. Since the concentration of 4-
nitrophenolate is proportional to the absorbance of 4-
0
nitrophenolate according to Beer’s law, the A/A value directly
We next proposed the possible mechanism for why the
AuSOs rapidly catalyzed the conversion of 4-nitrophenolate to 4-
reflects the ratio of the concentration of 4-nitrophenolate at an
initial time to that at any other time. Additionally, the apparent
rate constants of 0.1 and 0.2 μg AuSOs were estimated to be
aminophenol in the presence of NaBH
4
. In the case of the metal
and 4-nitrophenolate,
-
3
−1
-2 −1
nanoparticle-catalyzed reaction of NaBH
4
8
.4 x 10 and 5.4 s x 10 s , respectively, implying that the
Menumerov et al. demonstrated that the content of dissolved
oxygen governed the induction period due to the rapid reaction
of the formed 4-aminophenol and dissolved oxygen, in which 4-
apparent rate constant is highly correlated with the amount of
the catalyst. The Knor values of 0.1, 0.2, and 0.4 μg AuSOs were
4
5
5
separately determined to be 8.4 x 10 , 2.7 x 10 , and 4.8 x 10
[
36]
−
1
−1
aminophenol was converted back to 4-nitrophenolate.
Once
s
g , which are superior to the reported Knor values collected
the formation rate of 4-aminophenol exceeded the
transformation rate, the catalytic reduction of 4-nitrophenol
occurred after the induction period. According to the above-
from more than 100 studies (Table S1, Supporting Information).
The scalability of the AuSOs was examined by enlarging the
reaction volume from 2 to 100 mL. Upon the addition of 20 μg
Figure 5. The synthetic pathway for the preparation of (A) oxindole, indole, and over-reduced products from methyl 2-(2-nitrophenyl)
acetate and (B) 4-nitrobenzylalcohol, 4-aminobenzylalcohol, and 4-aminobenzoate from methyl 4-nitrobenzoate.
5
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4
Table 1. Synthesis of oxindole (1) by AuSOs-catalyzed reaction of NaBH and methyl 2-(2-nitrophenyl) acetate.
Entry
NaBH
4
(eq.)
AuSOs(mol%)
Conv.(%)a
I(%)a
42
II(%)a
III(%)a
IV(%)a
1
2
3
4
1
0.1
0.3
0.1
0.3
79
100
93
33
25
-
-
4
-
1
3
3
75
-
17
69
73
7
-
94
21
3
a)
The conversion were determined by GC-MS analysis
mentioned observation, the short induction time (< 6 s) observed
in Figure 3B implies that the concentration of dissolved oxygen
rapidly drops during the AuSO-catalyzed reaction of 4-
the strong polar interaction between 4-nitrobenzaldehyde and
thiolated AuNCs through the simulation density functional theory
simulation.
[
24b]
nitrophenolate and NaBH
the oxidation reaction of NaBH
tremendous consumption of dissolved O
this finding, the detection of O gas from the AuSO-catalyzed
reaction of NaBH and dissolved O was conducted using a gas
chromatography system coupled to thermal conductivity
detector. If dissolved O completely reacts with NaBH in the
presence of the AuSOs, H gas from the hydrolysis of NaBH4
will force no or limited O gas to be removed from water. Figure
S8 (Supporting Information) reveals that the addition of the
AuSOs into an aqueous solution of NaBH caused the
tremendous consumption of dissolved O . Thus, no peak was
observed at the retention time of O gas in the presence of
AuSOs. Moreover, the previously reported studies have
4
. The presence of AuSOs enhances
with dissolved O , causing the
. In an effort to support
4
2
2
Extensive application of the AuSOs as a catalyst in organic
synthesis.
2
4
2
a
The efficient and chemoselective conversion of 4-nitrophenate to
2
4
4
-aminophenol encouraged us to exploit the AuSOs for another
2
related organic synthesis process. The AuSO-mediated catalytic
reaction exemplified a chemical transformation from methyl 2-(2-
nitrophenyl) acetate to oxindole (I), which was detected by gas
chromatography coupled to mass spectrometry (GC-MS). Table
2
4
2
1
4
shows the effects of the amounts of NaBH and AuSOs on the
2
yield of oxindole (1). According to the analysis of the four
possible products (compounds I, II, III, and IV shown in Table 1)
performed by gas chromatography coupled to mass
spectrometry, the hydrogenation reaction of methyl 2-(2-
nitrophenyl) acetate, 0.1 mol% AuSOs, and 1.0 equivalent
revealed that the evolution of H
NaBH
nitrophenolate to 4-aminophenol.
2
gas from the hydrolysis of
4
is a determining factor in the rapid conversion of 4-
[37]
Thus, we suggest that the
AuSOs could efficiently catalyze the hydrolysis of NaBH
gas. In confirmation of this hypothesis, the analysis of H
from the AuSO-catalyzed hydrolysis of NaBH was performed by
the same gas chromatography system. A linear calibration curve
was established to quantify the H gas by plotting the peak area
of H gas against the volumes of H gas in N gas, as shown in
Figure 4A. In contrast to when only NaBH was in an aqueous
solution (Figure 4B), the production of H gas from NaBH was
enhanced by approximately 5.6-fold upon the addition of the
AuSOs (Figure 4C). This efficient generation of H gas not only
4
to H
2
NaBH
intramolecular aminolysis. Under the condition of using 0.3
mol% AuSOs and 1.0 equivalent NaBH , the yield of oxindole (I)
was considerably raised up to 75%, and complete conversion
was achieved. While the amount of NaBH was set to 3.0
4
resulted in a 42% yield of oxindole (I) through
2
gas
4
4
2
4
2
2
2
equivalents, the over-reduced products (III) were obtained in
yields of 69% for 0.1 mol% AuSOs (entry 3) and 73% for 0.3
mol% AuSOs (entry 4). Surprisingly, a small amount of indole
4
2
4
(
IV) was observed, which suggests the reduction of an ester and
2
subsequent formation of imine bonds. NaBH3CN has also
been used as hydrogen sources but showed poor reaction
efficiency. When we repeated the above-mentioned reaction
promotes the hydrogenation of 4-nitrophenolate but also purges
dissolved oxygen from the solution. In short, the rapid
conversion of 4-nitrophenolate to 4-aminophenol, as catalyzed
by the AuSOs, is heavily connected to three main reactions: (i)
under the same condition using NaBH
yield of the related products was poor.
4 3
instead of NaBH CN, the
the AuSOs catalyze the oxidation reaction of dissolved O
NaBH , suppressing the back conversion of 4-aminophenol to 4-
nitrophenol; (ii) the AuSOs catalyze the hydrolysis of NaBH to
gas, which forces the removal of dissolved O from water;
2
and
We further examined the catalytic applicability of the AuSOs
for the chemoselective reduction of benzoate ester and nitro
groups. The AuSO-catalyzed reaction of methyl 4-nitrobenzoate
4
4
H
2
2
(
V) and NaBH
4
was studied in a series of 6 solvents (Table 2;
and (iii) the AuSOs induce the catalytic hydrogenation of 4-
nitrophenolate to 4-aminophenol through the strong interactions
between the nitro group of 4-nitrophenol and the S-Au-S motifs
entries 1-6). The identification of the main products was
1
13
conducted using H and C nuclear magnetic resonance (NMR)
spectroscopy. It is noted that the concentration of the purified
by-products was too low to be detected by NMR. In contrast to
[
24b]
of the AuSOs.
(Figure 4D). Likewise, Li et al. demonstrated
6
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ChemCatChem
10.1002/cctc.202000885
FULL PAPER
polar aprotic solvents (tetrahydrofuran, 1.4-dioxane, acetonitrile,
and dimethylformamide), polar protic alcohols (methanol and
ethanol) achieved the complete conversion of methyl 4-
nitrobenzoate (V) to methyl 4-aminobenzoate (VI) in the
nitro group to amine group. Once the AuSOs is absent, their
ester group underwent hydride reduction to form the hydroxyl
group in the presence of NaBH . To our delight, the proposed
4
catalysts, AuSOs, can elegantly control the chemoselective
reduction reaction, producing the exclusive products under the
optimal condition.
presence of 0.3 mol% AuSOs and 3.0 equivalents NaBH
entries 3 and 4) within 1 h. Therefore, ethanol was selected as
4
(
a medium for further investigation. Note that a traditional organic
synthetic procedure would take at least 6 h to obtain a similar
result. While increasing the amount of NaBH and AuSOs, the
4
Conclusion
main products were found to be methyl 4-aminobenzoate (VI)
rather than 4-nitrobenzyl alcohol (VII) and over-reduced 4-
aminobenzyl alcohol (VIII) (entries 7-9). In the absence of the
We have demonstrated that the treatment of GSH-AuNPs with
Fenton’s reagent leached water-soluble and gold core-free
Au
Au
4
(GSH)
(GSH)
7
and Au
and Au
7
(GSH)
(GSH)
9
oligomers. The chemical structures of
9
were confirmed by combined MALDI-
AuSOs, the reduction of methyl 4-nitrobenzoate (V) with NaBH
4
4
7
7
led to the exclusive production of 4-nitrobenzyl alcohol (VII), with
a yield of 72% (entry 10). We next explored the replacement of a
one-step catalytic reaction by a two-step catalytic procedure.
After methyl 4-nitrobenzoate (V) was completely reduced with
TOF MS and Raman spectroscopy analyses. The S–Au–S
staple motifs of the AuSOs exhibited active sites for the NaBH
4
-
mediated hydrogenation of 4-nitrophenol to 4-aminophenol in
aqueous solutions, with an excellent chemoselectivity (~100%).
Moreover, the experimental results disclosed that the AuSOs
4
NaBH , the subsequent addition of 0.3 mol% AuSOs allowed the
exclusive formation of 4-aminobenzyl alcohol (VIII) with a yield
of 68% (entry 12). The above-discussed results point out the
detailed pathway associate with AuSO-catalyzed reaction of
methyl 2-(2-nitrophenyl) acetate and methyl 4-nitrobenzoate with
NaBH , as shown in Figures 5A and 5B, respectively. It is
4
evident that the AuSOs are capable of protecting the ester group
of methyl 2-(2-nitrophenyl) acetate and methyl 4-nitrobenzoat
efficiently catalyzed the production of H
2 4
from NaBH and
consumed the dissolved oxygen, facilitating the rapid and
selective conversion of 4-nitrophenol to 4-aminophenol. The Knor
value of AuSOs (0.4 µg) is tremendously higher than that of the
previously reported thiolated AuNCs and other nanomaterials.
By exploiting their advantages of an outstanding catalytic activity
and chemoselectivity, the AuSOs have been identified to
4
from NaBH reduction, accompanied with the reduction of the
promote the NaBH
4
-mediated conversion of methyl 2-(2-
Table 2. Optimization of reaction conditions for chemoselective hydrogenation of methyl 4-nitrobenzoate(5)
V
VI
VII
VIII
ꢀ
a
a
a
a
Entry
Solvent
THF
NaBH
4
(eq.)
AuSOs(mol%)
Conv.(%)
VI(%)
78
67
100
100
77
67
95
89
92
-
VII(%)
VIII(%)
1
2
3
4
5
6
7
8
9
3
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.3
-
90
-
-
-
-
Dioxane
MeOH
EtOH
ACN
3
3
3
3
3
5
85
100
100
97
-
-
-
-
-
-
DMF
100
100
100
100
100
100
100
-
-
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
-
-
10
10
10
-
-
-
-
-
10
72
-
-
11
0.3
0.3
-
-
b
2
1
10
-
-
68
a)
b)
The conversion were determined by NMR
NaBH
4
-mediated reduction of methyl-4-nitrobenzoate, followed the addition of the AuSOs
7
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ChemCatChem
10.1002/cctc.202000885
FULL PAPER
nitrophenyl) acetate to oxindole in a THF/water mixture and
methyl 4-nitrobenzoate to methyl 4-aminobenzoate in polar
protic alcohols. This economical and straightforward synthetic
strategy is projected to be applicable to other metal
nanoparticles (e.g., Cu and Ag) and thiols (e.g., cysteine).
2-(2-nitrophenyl) acetate (5 mg, 0.0256 mmol) was dissolved in H
0.384 mL/0.256 mL) cosolvent. The resultant solution (0.6 mL) was
placed in an eppendorf tube, followed by the injection of a mixture of
NaBH (0.0075-0.0225 mmol, 0.0284-0.851 mg) and AuSOs (0.128 mL
and 0.384 mL, 80 μg mL ). The obtained mixture was sonicated in the
closed tube for 12 h at ambient temperature. The reaction vessel was
cooled down, and the final products were analyzed by GC-MS (Figure
S9, Supporting Information).
2
O/THF
(
4
-1
Experimental Section
Synthesis of Methyl 4-Nitrobenzoate
To a solution of 4-nitrobenzaldehyde (2000 mg, 13.23 mmol) in acetone
Chemicals
(
3.0 mL) at 0 °C was added a solution of Na
mmol) in H SO /H O (1.84 mL/20.0 mL). The resultant mixture was
gently stirred at 25°C for 6 h. Subsequently, this reaction was quenched
with a saturated aqueous NaHCO solution, followed by the extraction of
the formed products with ethyl acetate. The obtained organic phase was
washed with a mixture of H O and brine, dried with Mg SO , filtered, and
2 7
CrO (5836 mL, 19.84
HAuCl
4
•3H
2
O, 4-nitrophenol, NaBH
4
, FeCl
2
, H
2
O
2
, methyl (2-
potassium
2
4
2
nitrophenyl)
acetate, 4-nitrobenzaldehyde,
dichromate, and glutathione were purchased from Sigma-Aldrich
St. Louis, MO, USA). 1,4-dioxane and acetonitrile were ordered
3
(
from J. T. Baker (PA, USA). Methanol, ethanol
dimethylformamide, and tetrahydrofuran were bought from
Merck (Darmstadt, Germany). Other reagents and chemical
were of analytical grade.
2
2
4
then concentrated under reduced pressure. Purification of the residue by
flash chromatography afforded the products corresponding to 4-
nitrobenzoic acid, which was used in the next reaction immediately. R
f
1
=
2
1
2
0.1(EA/Hex = 1:5); H NMR (400 MHz, MeOD) δ 8.32 (d, J = 8.7 Hz,
H, (H4)), 8.23 (d, J =8.7 Hz ,2H, (H3)); C NMR (100 MHz, MeOD) δ
13
Characterization
UV-Vis absorption and Raman spectra were collected on a double-beam
UV-vis spectrophotometer (JASCO V-670, Tokyo, Japan) and an alpha
67.52(C1), 151.96(C5), 131.97(C2, C3), 124.54(C4); IR (KBr) 3112,
−1
957, 2844, 1698, 1645, 1550, 1589, 1327, 923 cm ; HRMS (EI) calcd
+
for C
7
H
5
NO
4
[M] , 167.0219, found 167.0219. Figure S10 (Supporting
3
00 WITec Raman microscope (WITec Inc., Ulm, Germany) equipped
1
13
Information) shows H and C NMR spectra of 4-nitrobenzoic acid.
with 532 nm laser, respectively. TEM image was taken on a JEM-2100
microscope (JEOL, Tokyo, Japan) attached with an EDS spectrometer
(
X-Max 80T, Oxford, U.K). XPS analyses were carried out using a PHI
Quantera SXM system (ULVAC-PHI Inc., Japan). The RP-HPLC-UV
system was composed of an isocratic pump (Spectra Series P100,
Thermo Separation products, Waltham, MA, USA), a manual injector, a
SCpak ODS-P column (2504605-ODSP, Analab Corp. Taipei, Taiwan;
particle size, 5 μm; inner diameter, 4.6 mm; length, 250 mm), and an UV-
absorption detector (Spectra Series UV100, Thermo Separation Products,
A solution of 4-nitrobenzoic acid in MeOH (20.0 mL) at 25 °C was mixed
with H
quenching the reaction with saturated aqueous NaHCO
rest of the steps for obtaining methyl 4-nitrobenzoate (2163 mg, 2 step
0%).are the same as those described above in the synthesis of 4-
2
SO
4
(1.4 mL) under gentle stirring at 70°C for 12 h, followed by
3
solution. The
1
13
Waltham, MA, USA). H and C NMR spectra were acquired in CDCl
room temperature (JEOL ECZS 400 MHz NMR, Japan). The production
of H gas was detected by a GA-8A chromatograph (Shimadzu, Japan)
3
at
9
1
nitrobenzoic acid. R
f
= 0.25 (EA/Hex = 1:5); H NMR (400 MHz, MeOD)
2
δ 8.32 (d, J = 8.7 Hz, 2H, (H4)), 8.21 (d, J = 9.2 Hz ,2H, (H3)), 3.96 (s,
consisting of argon as a carrier gas, a 5 Å molecular sieve column, and a
thermal conductivity detector. Mass spectra were recorded on a MALDI-
TOF/ TOF-MS instrument (AXIMA Performance, Shimadzu, Japan)
equipped with a nitrogen UV laser (337 nm) and HREI-MS instrument
1
3
3
H, (H6)); C NMR (100 MHz, MeOD) δ 166.59 (C1), 152.04(C5),
136.76(C2), 131.76(C3), 124.62(C4), 53.24(C6); IR (KBr) 3094, 2948,
−
1
1715, 1609, 1527, 1411, 1284, 1050 cm ; HRMS (EI) calcd for
+
(
JEOL JMS-700, Japan). GC-MS was carried on an Agilent 6890N
8 7 4
C H NO [M] , 181.0375, found 181.0379.
Network Gas Chromatograph system (Agilent Technologies, USA)
equipped with 5975 mass spectrometry. Fourier-transform infrared
spectroscopy (FT-IR) data was acquired on a PerkinElmer Spectrum 100
FT-IR spectrometer (PerkinElmer, USA).
AuSOs-Catalyzed Reduction Reaction of methyl 4-nitrobenzoate
and NaBH
4
.
Preparation of the AuSOs
(
1
a) Synthesis of methyl 4-aminobenzoate. A mixture of NaBH
4
(62 mg,
.65 mmol) and AuSOs (2.75 mL, 80 μg mL ) was injected into a
O/EtOH
An aqueous solution of HAuCl
mL of mM GSH under gentle stirring for 30 min.
Subsequently, freshly prepared NaBH
4
(25 mM, 2 mL) was poured into
-1
1
6
1
solution of methyl 4-nitrobenzoate (100 mg, 0.55 mmol) in H
2
-
1
4
(10 mg mL , 2 mL) was
(5.5 mL/5.5 mL) cosolvent. The resultant solution was gently stirred at
25°C for 1 h and then quenched with 1 N HCl solution. The following
steps for obtaining methyl 4-aminobenzoate (84 mg, 100%) are
identical to those mentioned above in the synthesis of 4-nitrobenzoic
acid. R
rapidly injected into the resulting solution. The mixed solution
was continuously stirred at ambient temperature for 12 h,
followed by centrifugation at 17500 rpm for 10 min to remove an
1
f
= 0.25 (EA/Hex = 1:3); H NMR (400 MHz, MeOD) δ 7.73 (d, J =
excess of GSH and HAuCl
4
. The as-synthesized GSH-AuNPs
1
3
8
.5 Hz, 2H, (H3)), 6.63 (d, J = 9.2 Hz ,2H, (H4)), 3.79 (s, 3H, (H6));
C
were incubated with different ratios of Fenton reagent (0−20 mM
2
+
NMR (100 MHz, MeOD) δ 169.26 (C1), 154.60(C5), 132.46 (C3), 118.54
(
1
151.0633, found 151.0634. Figures S11 and S12 (Supporting
Information) display H and C NMR spectra of methyl 4-nitrobenzoate
and methyl 4-aminobenzoate.
Fe and 0−100 mM H
2 2
O ) at ambient temperature for 0−3 h.
C2), 114.32 (C4), 51.94 (C6); IR (KBr) 3412, 3307, 3173, 2980, 2858,
−
1
+
The concentration of the formed AuSOs was determined to be
8 9 2
699, 1467, 1091, 723 cm ; HRMS (EI) calcd for C H NO [M] ,
-
1
8
2
0 μg mL using atomic absorption spectrometer (Model Analyst
00, PerkinElmer, USA).
1 13
NaBH
Freshly prepared NaBH
4
-mediated reduction of 4-nitrophenol
(420 mM, 0.2 and 10 mL) was mixed with an
4
aqueous solution of 4-nitrophenol (1.4 mM, 0.2 and 10 mL) at ambient
temperature, followed by the injection of the AuSOs (0.1 and 5 mL, 4 μg
-
1
mL ). Afterward, the absorption and Raman spectra of the as-prepared
solution were collected as a function of time. The kinetic measurement
4
for NaBH -mediated reduction of 4-nitrophenol was performed by
monitoring the intensity of absorption peak at 400 nm with a time interval
of 10 s.
(
b) Synthesis of 4-nitrobenzyl alcohol. To a solution of methyl 4-
nitrobenzoate (100 mg, 0.55 mmol) in H O/EtOH (8.25mL/5.5 mL)
cosolvent was added NaBH (208 mg, 5.5 mmol). The obtained mixture
2
4
was gently stirred at 25°C for 1 h, followed by quenching with 1 N HCl
solution. The subsequent steps followed the procedure used in the
AuSO-Catalyzed Reduction Reaction of methyl 2-(2-nitrophenyl)
acetate and NaBH .
4
synthesis of 4-nitrobenzoic acid. The formed products correspond to 4-
1
nitrobenzyl alcohol (60 mg, 72%). R
f
= 0.37 (EA/Hex = 1:1); H NMR
(
400 MHz, MeOD) δ 8.19 (d, J = 9.2 Hz, 2H, (H4)), 7.57 (d, J = 9.2
8
This article is protected by copyright. All rights reserved.

ChemCatChem
10.1002/cctc.202000885
FULL PAPER
1
3
Hz ,2H, (H3)), 4.72 (s, 2H, (H1)); C NMR (100 MHz, MeOD) δ 150.84
[13] M. Yadav and Q. Xu, Energy Environ. Sci. 2012, 5, 9698-9725.
[14] a) H. I. Schlesinger, H. C. Brown, A. E. Finholt, J. R. Gilbreath,
H. R. Hoekstra and E. K. Hyde, J. Am. Chem. Soc. 1953, 75, 215-
(
3
C2), 148.44 (C5), 128.20 (C3), 124.42 (C4), 64.00 (C1); IR (KBr) 3670,
029, 2887, 1559, 1347, 1021, 823 cm
C7H7NO3 [M] , 153.0426, found 153.0424. Figure S13 (Supporting
Information) shows H and C NMR spectra of 4-nitrobenzyl alcohol.
−
1
; HRMS (EI) calcd for
+
2
2
19; b) P. P. Prosini and P. Gislon, J. Power Sources 2006, 161,
90-293.
1
13
[
15] a) K. Zhang, J. M. Suh, J.-W. Choi, H. W. Jang, M.
Shokouhimehr and R. S. Varma, ACS Omega 2019, 4, 483-495; b) J.
Song, Z.-F. Huang, L. Pan, K. Li, X. Zhang, L. Wang and J.-J. Zou,
Appl. Catal. B Environ. 2018, 227, 386-408.
[
16] P. Suchomel, L. Kvitek, R. Prucek, A. Panacek, A. Halder, S.
Vajda and R. Zboril, Sci. Rep. 2018, 8, 4589.
17] Y. Zhang, Z. Cui, L. Li, L. Guo and S. Yang, Phys. Chem. Chem.
Phys. 2015, 17, 14656-14661.
18] A. Shivhare, S. J. Ambrose, H. Zhang, R. W. Purves and R. W.
[
(
c) Synthesis of 4-aminobenzyl alcohol. To a solution of methyl 4-
nitrobenzoate (100 mg, 0.55 mmol) in EtOH (5.5 mL) was added NaBH
208 mg, 5.5 mmol), and the resultant mixture was stirred at 25°C for 1 h.
After that, the reaction mixture was incubated with AuSOs (8.25 mL, 80
μg mL ) under gentle stirring at 25°C for 1 h. The reaction was quenched
with 1 N HCl solution. The further steps are the same as those described
above in the preparation of 4-nitrobenzoic acid. The final products were
4
[
(
J. Scott, Chem. Comm. 2013, 49, 276-278.
[19] L. Liu and A. Corma, Chem. Rev. 2018, 118, 4981-5079.
-
1
[
20] J. Fang, J. Li, B. Zhang, X. Yuan, H. Asakura, T. Tanaka, K.
Teramura, J. Xie and N. Yan, Nanoscale 2015, 7, 6325-6333.
21] L. Qin, G. Zeng, C. Lai, D. Huang, C. Zhang, M. Cheng, H. Yi, X.
[
found to be methyl (4-aminophenyl) methanol (46 mg, 68%). R
f
= 0.12
1
Liu, C. Zhou, W. Xiong, F. Huang and W. Cao, Sci. Total Environ.
2019, 652, 93-116.
(
(
EA/Hex = 1:1); H NMR (400 MHz, MeOD) δ 7.10 (d, J = 8.7 Hz, 2H,
H3)), 6.70 (d, J = 8.7 Hz ,2H, (H4)), 4.45 (s, 2H, (H1)); C NMR (100
1
3
MHz, MeOD) δ 148.07 (C5), 132.16 (C2), 129.62 (C3), 116.48 (C4),
5.33 (C1); IR (KBr) 3546, 3329, 3267, 2896, 1689, 1467, 1110, 933
[22] A. Corma and P. Serna, Science 2006, 313, 332-334.
[23] a) Y. Song, J. Zhong, S. Yang, S. Wang, T. Cao, J. Zhang, P. Li,
D. Hu, Y. Pei and M. Zhu, Nanoscale 2014, 6, 13977-13985; b) M.-B.
Li, S.-K. Tian, Z. Wu and R. Jin, Chem. Comm. 2015, 51, 4433-
4436; c) H. Yamamoto, H. Yano, H. Kouchi, Y. Obora, R. Arakawa
and H. Kawasaki, Nanoscale 2012, 4, 4148-4154; d) J. Li, R. R.
Nasaruddin, Y. Feng, J. Yang, N. Yan and J. Xie, Chem.: Eur. J.
6
−
1
+
cm ; HRMS (EI) calcd for C
Figure S14 (Supporting Information) shows H and C NMR spectra of
-aminobenzyl alcohol.
7 9
H NO [M] , 123.0684, found 123.0685.
1 13
4
2
016, 22, 14816-14820; e) S. Zhao, A. Das, H. Zhang, R. Jin, Y.
Song and R. Jin, Pro. Nat. Sci.- Mater. 2016, 26, 483-486.
24] a) G. Li, H. Abroshan, Y. Chen, R. Jin and H. J. Kim, J. Am.
[
Chem. Soc. 2015, 137, 14295-14304; b) G. Li, D.-e. Jiang, S. Kumar,
Y. Chen and R. Jin, ACS Catal. 2014, 4, 2463-2469.
[
3
25] a) J. Tuteja, S. Nishimura and K. Ebitani, RSC Adv. 2014, 4,
8241-38249; b) J. Camacho-Bunquin, M. Ferrandon, H. Sohn, D.
Acknowledgements
Yang, C. Liu, P. A. Ignacio-de Leon, F. A. Perras, M. Pruski, P. C.
Stair and M. Delferro, J. Am. Chem. Soc. 2018, 140, 3940-3951; c)
M. Baron, E. Métay, M. Lemaire and F. Popowycz, Green Chem.
The authors would like to thank the Ministry of Science and
Technology (MOST107-2811-M-110-009) of Taiwan for the
financial support of this study.
2
013, 15, 1006-1015.
26] T.-H. Chen, C.-C. Nieh, Y.-C. Shih, C.-Y. Ke and W.-L. Tseng,
RSC Adv. 2015, 5, 45158-45164.
27] C. Lavenn, L. Okhrimenko, N. Guillou, M. Monge, G. Ledoux, C.
[
[
Dujardin, R. Chiriac, A. Fateeva and A. Demessence, J. Mater.
Chem. C 2015, 3, 4115-4125.
Keywords: gold(I)-thiolate oligomers • 4-nitrophenol • gold
[
[
28] D. C. Schriemer and L. Li, Anal. Chem. 1996, 68, 2721-2725.
29] a) Z. Wu, C. Gayathri, R. R. Gil and R. Jin, J. Am. Chem. Soc.
nanoparticles• nitroaromatics • Fenton’s reagent
2
009, 131, 6535-6542; b) J. G. You, C. Y. Lu, A. S. Krishna Kumar
[
1] B. Laksmi, K. N. Shivananda, Puttaswamy, K. N. Mahendra, N. M.
M. Gowda and R. V. Jagadeesh, Chem. Eng. J. 2010, 163, 403-412.
2] U. Vincent, G. Bordin and A. Rodríguez, Int. J. Cosmet. Sci. 2002,
3, 101-119.
3] A. Guenbour, A. Kacemi and A. Benbachir, Prog. Org. Coat. 2000,
9, 151-155.
4] D. Formenti, F. Ferretti, F. K. Scharnagl and M. Beller, Chem.
Rev. 2019, 119, 2611-2680.
5] a) V. R. Jumde, E. Petricci, C. Petrucci, N. Santillo, M. Taddei
and W. L. Tseng, Nanoscale 2018, 10, 17691-17698.
[
[
30] Z. Zhang and M. Lin, RSC Adv. 2014, 4, 17760-17767.
31] W.-B. Tseng, C.-H. Lee and W.-L. Tseng, ACS Appl. Nano
[
5
[
3
Mater. 2018, 1, 6808-6817.
32] J.-G. You, C. Shanmugam, Y.-W. Liu, C.-J. Yu and W.-L. Tseng,
J. Hazard. Mater. 2017, 324, 420-427.
33] S. Zhang, C.-R. Chang, Z.-Q. Huang, J. Li, Z. Wu, Y. Ma, Z.
Zhang, Y. Wang and Y. Qu, J. Am. Chem. Soc. 2016, 138, 2629-
637.
34] L. Kong, X. Cui, H. Jin, J. Wu, H. Du and T. Xiong, Energy Fuels
009, 23, 5049-5054.
35] J. Li, J. Liu, Y. Yang and D. Qin, J. Am. Chem. Soc. 2015, 137,
039-7042.
36] E. Menumerov, R. A. Hughes and S. Neretina, Nano Lett. 2016,
6, 7791-7797.
37] Z. Wu, X. Mao, Q. Zi, R. Zhang, T. Dou and A. C. K. Yip, J.
Power Sources 2014, 268, 596-603.
[
[
[
[
2
[
2
[
7
[
1
[
and L. Vaccaro, Org. Lett. 2015, 17, 3990-3993; b) R. Kadyrov and T.
H. Riermeier, Angew. Chem. Int. Ed. 2003, 42, 5472-5474; c) R. J.
Kalbasi and O. Mazaheri, Catal. Comm. 2015, 69, 86-91.
[
3
6] P. L. Gkizis, M. Stratakis and I. N. Lykakis, Catal. Comm. 2013,
6, 48-51.
7] M. B. Gawande, A. K. Rathi, P. S. Branco, I. D. Nogueira, A.
[
Velhinho, J. J. Shrikhande, U. U. Indulkar, R. V. Jayaram, C. A. A.
Ghumman, N. Bundaleski and O. M. N. D. Teodoro, Chem.: Eur. J.
2
[
012, 18, 12628-12632.
8] S. Chandrappa, K. Vinaya, T. Ramakrishnappa and K. S.
Rangappa, Synlett 2010, 2010, 3019-3022.
9] T. Subramanian and K. Pitchumani, ChemCatChem 2012, 4,
917-1921.
10] P. Brack, S. E. Dann and K. G. U. Wijayantha, Energy Sci. Eng.
015, 3, 174-188.
11] V. G. Minkina, S. I. Shabunya, V. I. Kalinin, V. V. Martynenko
and A. L. Smirnova, Int. J. Hydrog. Energy 2012, 37, 3313-3318.
12] U. B. Demirci and P. Miele, Energy Environ. Sci. 2011, 4, 3334-
341.
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1
[
2
[
[
3
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ChemCatChem
10.1002/cctc.202000885
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Gold(I)-Thiolate Oligomers: A new class of gold-based catalysts, prepared from the etching of glutathione-capped gold
nanoparticles with Fenton’s reagent , for catalyzing NaBH reduction of nitroaromatics to aminoaromatics with high catalytic activity
normalized rate constant > 10 S g ) and excellent chemoselectivity (~100%)
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This article is protected by copyright. All rights reserved.