One-pot reductive amination of aldehydes with nitroarenes using formic acid as the hydrogen donor and mesoporous graphitic carbon nitride supported AgPd alloy nanoparticles as the heterogeneous catalyst

Article abstract of DOI:10.1039/c8nj01569d

Herein, we report a one-pot protocol for the synthesis of secondary amines via a tandem reductive amination of aldehydes with nitroaromatics utilizing mesoporous graphitic carbon nitride (mpg-C₃N₄) supported AgPd alloy nanoparticles (mpg-C₃N₄/AgPd) as the catalyst, FA as the hydrogen donor and water as the sole solvent, which is a protocol in harmony with the green chemistry rules. In the present one-pot catalytic reductive amination protocol, a variety of secondary amines (11 examples) were yielded by using nitroarenes as a nitrogen source and benzaldehyde in the presence of the mpg-C₃N₄/AgPd nanocatalyst, which is the first example in the literature. Monodisperse AgPd alloy NPs (2.5 ± 0.5 nm) were synthesized by using our established protocol via the co-reduction of silver(i) acetate and palladium(ii) acetylacetonate in the presence of oleylamine and oleic acid as surfactants in a hot organic solvent. The as-prepared AgPd alloy nanoparticles were then deposited on mpg-C₃N₄via a liquid phase self-assembly method. After the structural characterization of the mpg-C₃N₄/AgPd nanocatalyst using TEM, PXRD, BET and ICP-MS analyses, they were directly tested in one-pot direct reductive amination reactions in which they showed superior activity. The applicability of the present one-pot reductive amination strategy was demonstrated over a variety of aldehydes and nitroarenes (11 examples). Moreover, the mpg-C₃N₄/AgPd catalyst was a reusable catalyst in the reductive amination reactions providing 99% yield even after five consecutive runs.

Full text of DOI:10.1039/c8nj01569d

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
rsc.li/njc

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ARTICLE
One-pot reductive amination of aldehydes with nitroarenes using
formic acid as the hydrogen donor and mesoporous graphitic
carbon nitride supported AgPd alloy nanoparticles as the
heterogeneous catalyst
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
a
b,c*
a,*
Seda Ergen, Bilal Nişancı, Önder Metin,
www.rsc.org/
We reported herein one-pot protocol for the synthesis of secondary amines via a tandem reductive amination of
aldehydes with nitroaromatics utilizing mesoporous graphitic carbon nitride (mpg-C supported AgPd alloy
nanoparticles (mpg-C /AgPd) as the catalyst, FA as the hydrogen donor and water as the sole solvent, which is a protocol
3
4
N )
3
N
4
in harmony with the green chemistry rules. In the presented one-pot catalytic reductive amination protocol, a variety of
secondary amines (11 examples) were yielded by using nitroarenes as nitrogen source and benzaldehyde in the presence
3 4
of mpg-C N /AgPd nanocatalyst, which is the first example in the literature. Monodisperse AgPd alloy NPs (2.5 ± 0.5 nm)
were synthesized by using our established protocol comprising the co-reduction of silver(I) acetate and palladium(II)
acetylacetonate in the presence of oleylamine and oleic acid as surfactants in a hot organic solvent. As-prepared AgPd
alloy nanoparticles were then deposited on mpg-C
3 4
N via liquid phase self-assembly method. After the structural
characterization of mpg-C /AgPd nanocatalyst by using TEM, PXRD, BET and ICP-MS, they were directly tested in the
3 4
N
one-pot direct reductive amination reactions in which they showed a superior activity. The applicability of the presented
one-pot reductive amination strategy was demonstrated over a variety of aldehydes and nitroarenes (11 examples).
Moreover, the mpg-C
3 4
N /AgPd catalyst was reusable catalyst in the reductive amination reactions providing 99% yielded
even after five consecutive runs.
comprising the use of nitroarenes as a nitrogen source instead
of primary amines and the tandem transfer hydrogenation
could be very efficient strategy for the synthesis of secondary
amines in the green chemistry context. Because
aforementioned strategy does not require preliminary ex-situ
reduction of nitroarenes that requires intermediate separation
and further purification steps and the use of explosive H gas
2
that is needed to use a specific equipment under potential
safety concerns.
To realize such a reductive amination protocol, a suitable
hydrogen donor molecule and a catalyst that is active in both
catalyzing the dehydrogenation of the hydrogen donor
molecule and the transfer hydrogenation reaction are
required. In other words, a catalyst is needed to activate
tandem dehydrogenation of hydrogen donor molecule and
transfer hydrogenation reaction. Similar to this approach, we
have recently reported a facile one-pot protocol including a
1
. Introduction
Reductive amination is one of the most common methods
used for the conversion of carbonyl compounds (aldehydes or
ketones) into the amine derivatives which are significant
building blocks for the production of various natural products,
1
,2
agrochemicals, pharmaceuticals, dyes and pigments.
In
general, the corresponding secondary amines are yielded by
the reductive amination reactions of a primary amine and a
carbonyl compound in the presence of a suitable reducing
3
,4
agent such as metal hydrides and a transition metal catalyst.
The catalyst plays a key role for the reductive amination
protocols, in which Pd is a metal of choice in general. In this
regard, a variety of reductive amination methods catalyzed by
heterogeneous Pd or several other transition metals have
5
-10
been developed in recent years.
Although these type of
amine-carbonyl reductive amination reactions have several
advantages over other methodologies for the synthesis of
secondary amines such as N-alkylation of primary amines and
three-component cascade reaction performed in
a
commercially available pressure tube for the reduction of
nitroarenes using ammonia borane as a hydrogen source and
in situ generated mesoporous graphitic carbon nitride
1
1
1
2
Buchwald-Hartwig , a one-pot reductive amination protocol
1
3
3 4
supported Pd NPs (mpg-C N /Pd) as catalysts. However, AB is
relatively expensive compared to other potential hydrogen
donor molecules such as formic acid (FA) which has been
regarded as a promising hydrogen storage material owing to
its advantageous features such as being liquid at room
temperature, nontoxic and having high volumetric hydrogen
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1
4,15
capacitiy (53 g/L) and very low cost.
However, hydrogen applicability of the presented one-pot reductive amination
generation from the FA is kinetically inert and suffers the strategy was demonstrated over a variety of aldehydes and
product selectivity problem due to the proceeding of the nitroarenes (11 examples). Moreover, the mpg-C /AgPd
dehydrogenation in two pathways (Eq. (1) and (2), which catalyst was reusable catalyst in the reductive amination
3 4
N
1
6,17
introduce a need of an efficient and selective catalyst.
reactions providing 99% yielded even after five consecutive
runs.
HCOOH
HCOOH
ꢀ
ꢀ
CO
CO(g) + H
2
(g) + H
2
(g) (1)
O (2)
2
2
. Results and discussion
Monodisperse AgPd alloy NPs were synthesized by using
Selective FA dehydrogenation without CO generation could be
achieved by homogeneous catalysts at near-ambient
temperature. However, due to the well-known difficulties in
separating, controlling and recycling of homogeneous catalysts
the heterogeneous catalysis nowadays attracts tremendous
research interests for the selective FA dehydrogenation.
1
8
our previously reported protocol comprising the one-pot co-
reduction of silver(I) acetate and palladium(II) acetylacetonate
in the presence of oleylamine and oleic acid as surfactants in a
1
9
,
2
6
2
0
hot organic solvent.
Although the detailed structural
When the literature on the FA dehydrogenation is examined, it characterization of colloidal AgPd alloy NPs was reported in
can be easily concluded that palladium (Pd) is metal of choice our previous report, the several essential characterization
26
2
1,22
among the heterogeneous catalytic systems.
However, Pd- data including transmission electron microscopy (TEM),
based catalysts suffer from the deactivation problem during
the FA dehydrogenation due to the strong adsorption of
formate anion. To overcome this deactivation problem, Pd has
been combined with various metals including Ag, Au, Ni, Cu
and Mn in bimetallic or multimetallic alloy or core-shell
powder X-ray diffraction (PXRD) and elemental analysis by ICP-
MS are also presented herein for providing convenience to the
readers. Figure 1 shows representative TEM images of colloidal
AgPd alloy NPs taken their hexane dispersion at different
magnifications revealing that the NPs have a monodisperse
particle size distribution with a particle diameter of 2.5 ± 0.5
nm. The composition of as-synthesized AgPd alloys NPs were
found to be Ag40Pd60 by ICP-MS analysis conducted on several
2
3-24
structure.
Among these bimetallic catalysts, AgPd alloy
NPs provided the highest catalytic activity and selectivity for
FA dehydrogenation near ambient conditions as we reported
earlier. Our 2.2 nm AgPd alloy NPs supported on commercial
2
5
carbon black were provided the highest turnover frequency NP samples. Additionally, three other compositions of AgPd
-
1
(
380 h ) among the all heterogeneous catalysts tested in the alloy NPs, namely Ag25Pd75, Ag50Pd50 and Ag60Pd40 NPs, were
dehydrogenation of FA by that time.
On the other hand, the support material has a remarkable
effect on the catalytic activity and selectivity of NPs. For
example, we have demonstrated that reduced graphene oxide
synthesized by using the current recipe and their catalytic
performance was evaluated in the reductive amination
reactions (vide infra).
2
6
(rGO) is a very suitable support material for the metal NPs in
the organic reactions because it enables a closer contact
between the substrates and catalysts via π-π interaction owing
2
7,28
to its empty p-orbitals.
mesoporous graphitic carbon nitride (mpg-C
Besides rGO, in very recently,
) has been
3 4
N
regarded as a suitable support material for the metal NPs
owing to its advantageous properties such as being a visible-
light active semiconductor with a band gap of 2.7 eV (454 nm)
and highly dispersed in polar solvents, having both basic and
3
0, 31
acidic sides and large surface area.
In this respect, we have
recently demonstrated that AgPd alloy NPs showed enhanced
catalytic activity in the dehydrogenation of ammonia borane
3
.
2
when they were supported on mpg-C
3
N
4
According to the Figure 1. Representative TEM images of colloidal Ag40Pd60 alloy
as a visible-light active NPs taken their hexane dispersion at two different
proposed mechanism, mpg-C N
3 4
+
-
semiconductor material generates h /e pairs upon its magnifications.
irradiation under sunlight and the excited electrons will flow
through the d-band of metals (Ag or Pd) with the lower energy
Figure 2 shows the PXRD patterns of monometallic Ag and
Pd NPs along with bimetallic Ag40Pd60 NPs recorded their thin
films formed over amorphous glass. Upon the comparison of
three XRD patterns, it can be easily concluded that all the NPs
than conduction band of mpg-C
Inspired by the results of our aforementioned three studies
we have reported herein a novel one-pot strategy for
the synthesis of secondary amines comprising the reductive
amination of aldehydes with nitroarenes in the presence of
3 4
N .
1
3, 26, 32,
have face centered cubic (fcc) crystal structure and the peak at
o
2
θ= 38.9 attributed to (111) plane of AgPd NPs is located
mpg-C
catalyst, FA as the hydrogen donor and water as the sole
solvent. In the presented study, we have combined the high 04–0783) and Pd NPs (2θ= 39.5 , JCPDS Card No: 87-0638)
3 4 3 4
N supported AgPd alloy NPs (mpg-C N /AgPd) as
o
between those of monometallic Ag (2θ= 38.2 , JCPDS Card No:
o
2
6
catalytic activity of AgPd alloy NPs in FA dehydrogenation
,
confirming the solid solution (alloy) formation between two
the enhanced catalytic activity of AgPd alloy NPs over mpg- metals. Additionally, a very broad peak attributed to the (111)
3
2
C
3
N
4
and the one-pot transfer hydrogenation protocol in a
plane of AgPd alloy NPs reveals the very small crystalline size
of the alloy NPs which is in good agreement with the TEM
image.
1
3
pressure tube . It should be noted that this is the first
example of one-pot reductive amination reaction including the
3 4
mpg-C N /AgPd catalyst and FA as a hydrogen donor. The
2
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In order to use AgPd alloy NPs as reusable catalysts in the
reductive amination reactions along with the enhancement of
their stability, they were supported on several high-surface
area carbon-based support materials including commercial
available
Figure 3. Representative TEM images of mpg-C
3 4
N /Ag40Pd60
nanocatalyst recorded at two different magnifications.
Figure 2. PXRD patterns of colloidal Ag, Pd and Ag Pd alloy
58
4
2
NPs.
mesoporous graphitic carbon nitride (mpg-C N ) via a liquid
3
4
phase self-assembly method. On account of the fact that the
AgPd alloy NPs provided the highest catalytic performance
over the mpg-C N (vide infra), the structural characterization
3
4
of pristine mpg-C N and/or mpg-C N /AgPd catalyst by using
3 4
3
4
TEM and BET surface area were presented herein. Figure 3
shows the representative TEM images of mpg-C N /Ag Pd
60
3
4
40
nanocatalyst recorded at different magnifications. As can be
clearly seen by the TEM images that Ag Pd alloy NPs
4
0
60
homogeneously distributed over mpg-C N nanosheets by
4
3
preserving their initial particle size and morphology. Moreover,
there were no agglomeration or clumps observed over the
examination of almost entire TEM grid revealing the
effectiveness of liquid-phase self-assembly method for the
deposition of AgPd alloy NPs over mpg-C N . It is noteworthy
3
4
mentioned that the CNHS elemental analysis of pristine mpg-
C N revealed that it consists mainly C (32 wt%) and N (53
3
4
wt%) along with a tiny amount of H (2 wt%) as expected.
Additionally, ICP-Ms analysis performed on the several batches
of mpg-C N /Ag Pd catalysts revealed that it contains
Figure 4.
Joyner-Halenda (BJH) pore size distribution plots for (A)
pristine mpg-C and (B) mpg-C /Ag40Pd60 nanocatalyst.
2
N adsorption-desorption isotherms and Barrett-
3
4
40
60
3
N
4
3 4
N
approx. 15wt% total metal.
To further proving the mesoporous structure of mpg-C N4
3
2
with a BET surface area of 205 m /g, average BJH adsorption
3
pore width of 15.5 nm and pore volume of 0.78 cm /g (Figure
and successful assembly of AgPd NPs on it, the surface area
and pore size analysis of mpg-C
3 4
N were studied by taking the
4A
). After the assembly of Ag40Pd60 alloy NPs, the mesoporous
structure of mpg-C is still preserved with the surface area,
average pore size and pore volume were lowered to 139 m /g,
N
2
adsorption-desorption isotherms before and after the
3 4
N
Ag40Pd60
2
NPs deposition. As can be concluded by the N
2
adsorption-
has a
3
1
2.6 nm and 0.47 cm /g (Figure 4B), respectively, which
indicates the deposition of some Ag40Pd60 NPs on the
mesopores of mpg-C
After the catalyst preparation and characterization, based
desorption isotherms, in Figure 4, pristine mpg-C
3 4
N
typical type-IV isotherm revealing its mesoporous structure
3 4
N .
3
3,
on our earlier success on the reductive amination reactions
3
4
3 4
we turned our attention to apply mpg-C N /Ag40Pd60
nanocatalyst in one-pot reductive amination reaction including
nitroarenes as the starting substrate and formic acid as a
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hydrogen source. Compared to the conventional synthesis of eV (454 nm). Then, other minor optimization experiments
N-alkylated aromatic amines starting from readily available including amount of solvent and the temperature were studied
aromatic nitro compounds via a two-step procedure including and the results showed that neither using lower amount of
first the reduction of aromatic nitro compounds under high- water (3 mL) nor performing the reaction at room lower
pressure traditional hydrogenation and then following temperature (RT) did not provide stoichiometric conversion
amination
conversion of nitroarenes to the corresponding aniline it was found that the best conversion yield can be obtained by
derivatives provides a great advantageous regarding step using mpg-C /Ag40Pd60 catalyst and performing the reaction
(
Figure
5), the presented straightforward (Table 1, entry 11,12). As a result of optimization experiments,
3 4
N
3
5
o
economy (one-pot) and cost of reagents.
At the beginning of our study, mpg-C
in 5 mL water at 50 C for 20 h under sunlight.
3
N
4
/Ag40Pd60 catalyst
With the optimized reaction conditions in hands, the
was evaluated by the test reaction of nitrobenzene with efforts were made to show the substrate scope of the
benzaldehyde for finding optimized reaction conditions.
presented one-pot reductive amination protocol and the
results were depicted in Table 2. As clearly concluded by the
Table 2, the mpg-C N /
3
4
Table 1. Optimization of mpg-C N /AgPd catalyzed one-pot
3
4
[a]
reductive amination reactions
Figure 5. The comparison of our one-pot reductive amination
protocol and traditional work representing two step reaction
for the synthesis of secondary amines.
o
T ( C)
[b]
Entry
1
Catalyst
-
t (h)
Conversion
48
50
-
In a serial of optimization studies, the effect of various
reaction parameters including alloy composition, support
material, temperature, reaction time and light were examined
to clarify the best reaction conditions. The reaction
optimization data are summarized in Table 1. First of all, it is
quite obvious that the presented one-pot reductive amination
reactions did not occur at all in the absence of mpg-
mpg-
2
3
4
20
20
20
50
50
50
19
10
93
C N /Ag Pd
3
3
3
4
25
75
mpg-
C
C
N
N
4
/Ag60Pd40
C
3
N
4
/Ag40Pd60 catalyst even for a reaction time of 48 h (Table
, entry 1). Next, the effect of AgPd alloy composition on the
catalytic activity of mpg-C /AgPd catalyst was examined by
mpg-
1
4
/Ag50Pd50
3 4
N
o
mpg-
performing the catalytic reaction in water for 20 h at 50 C
under sunlight. It was concluded that Ag40Pd60 composition
provided the best conversion yield (Table 1, entries 2-5). Next,
the effect of reaction time on the catalytic activity of mpg-
5
6
20
50
≥99
C
3
N
4
/Ag40Pd60
mpg-
15
50
90
C
3
N
N
4
/Ag40Pd60
3 4
C N /Ag40Pd60 catalyst was examined by performing the
mpg-
o
7
5
50
75
catalytic reactions in water at 50 C for different reaction times
and the results revealed that 20 h is the optimum reaction
time for obtaining the stoichiometric conversion yield (Table 1,
entries 5-7). As it is aforementioned in the introduction, the
type of support materials has a significance effect on the
catalytic activity of metal NPs. Therefore, the catalytic activity
of Ag40Pd60 alloy NPs in one-pot reductive amination reaction
were tested by supporting them on rGO, Ketjen Black (KB)
C
3
4
/Ag40Pd60
8
9
rGO-Ag40Pd60
20
20
20
50
50
50
36
17
Ketjen-
Ag Pd
60
4
0
mpg-
[c]
10
65
C
3
3
N
N
4
/Ag40Pd60
along with mpg-C
3 4
N and the results clearly indicated that the
mpg-
[d]
mpg-C N /Ag40Pd60 catalyst provided the best performance in
4
3
11
20
20
50
25
77
C
4
/Ag40Pd60
terms of conversion yield (Table 1, entries 7-9). To understand
mpg-
the scientific reason behind the higher catalytic activity of
12
10
C N /Ag Pd
60
mpg-C
Ag40Pd60 catalysts, the catalytic one-pot reductive amination
reaction was performed in dark and a much lower conversion mmol formic acid, 10 mg mpg-C N /Ag Pd catalyst, 5 mL H O, under
3
N
4
/Ag40Pd60 catalyst than that of rGO-Ag40Pd60 and KB-
3
4
40
[
a]
Reaction conditions: 1 mmol nitrobenzene, 1.2 mmol aldehyde, 4
3
4
40
60
2
[
b]
1
yield (65%) was obtained (Table 1, entry 10), which clearly sunlight. Conversion yields were calculated by H-NMR spectra taken
c]
[
reveals the role of mpg-C N support as a polymeric by using dipenylmethane as an internal standard.
3
Reaction
4
semiconductor material with a visible-region band gap of 2.7
4
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[
d]
performed in dark. The catalytic reaction was performed in 3 mL the reductive amination of benzaldehyde with nitrobenzene
O. was selected as a test reaction. Figure 6A shows a five-run
reusability test of mpg-C /Ag40Pd60 catalysts in the reductive
Ag40Pd60 catalyzed one-pot reductive amination protocol was amination of benzaldehyde with nitrobenzene. As can be easily
3 4
found to be highly effective for the conversion of a variety of concluded by the reusability test, the mpg-C N /Ag40Pd60
H
2
3 4
N
substituted nitroarenes and benzaldehyde derivatives. As a catalyst are highly durable in the test reaction by providing
general case for 4-methylnitroarene analogues, the 99% yield even after five consecutive runs in the one-pot
corresponding alkylamines were yielded nearly quantitative reductive amination of nitrobenzene with benzaldehyde.
(
Table 2, 3b, 3h and 3k) except for 3e (Table 2, 3a, 3d, 3g and Moreover, the characterization of the mpg-C
j). However, in the case of methoxy-substituted nitroarene catalyst by TEM (Figure 6B) and PXRD (Figure S1) after the
derivates, the expected alkylamines were obtained by reusability test revealed that there is almost no change on the
moderate yields (Table 2, 3c and 3i). Surprisingly, the initial morphology and crystal structure of mpg-C
3 4
N /Ag40Pd60
3
3 4
N /Ag40Pd60
presented catalytic protocol worked efficiently for the catalyst, which clearly indicates that the catalyst is highly
synthesis of the most bulky compound, 2-methoxy-N-(4- durable in the presented one-pot reductive amination
methoxybenzyl)aniline (3f), with the conversion yield of 92% protocol.
(Table 2, 3f). Upon these results, it can be concluded that the
presented one-pot catalytic reductive amination methodology
works efficiently for a wide array of substrates as well as being
in harmony with the green chemistry rules because of using
formic acid as a hydrogen source and just water as a solvent in
the reaction process. Although
a variety of reductive
amination protocols is existed in the literature, application of
these protocols have several limitations such as having limited
functional-group tolerance, the need of organic solvents as
well as the dangers posed by the use of molecular hydrogen
3
6-38
gas as the reducing agent and recyclability of the catalyst.
With the presented method, we believe that all of the aabove- Figure 6. (A) The results of a five-run reusability test of mpg-
mentioned disadvantages have been abolished.
C
3
N
4
/Ag40Pd60 nanocatalyst in the one-pot reductive amination
methodology and (B) a representative TEM image of mpg-
/Ag40Pd60 nanocatalyst after the reusability test.
Table 2. Substrate scope of mpg-C N /Ag Pd catalyzed
60
3 4
C N
3
4
40
[a]
reductive amination of aldehydes with nitrobenzenes
3
. Conclusions
Development of new heterogeneous catalytic systems for
the organic transformations is a significant task for the modern
synthetic chemistry. In this respect, we have reported a new
heterogeneous catalytic system for the synthesis of a variety of
secondary amines via one-pot reductive amination protocol
which uses nitroaromatics as the starting substrate, mpg-
C N /Ag Pd as the reusable heterogeneous catalyst, FA as
3
4
40
60
the hydrogen donor and water as the solvent. It should be
noted that this is the first example of one-pot reductive
amination reaction including the mpg-C
FA as a hydrogen donor. In the presented protocol, the mpg-
/Ag40Pd60 nanocatalyst were used for activating both
3 4
N /AgPd catalyst and
3 4
C N
hydrogen generation from the dehydrogenation of FA and the
transfer of the generated hydrogen to the related substrates,
which were succeeded in deed. On the other hand, FA was
preferred as the hydrogen donor because it represents an
economical, safe and straightforward hydrogen carrier and
have been demonstrated that it really works efficiently in the
reductive amination reaction. Moreover, the synthesis of
secondary amines via a directly starting from nitroaromatics as
precursors is really advantageous for the synthetic organic
chemistry in terms of the step economy and cost of substrates.
This reductive amination methodology tolerates a variety of
functional groups and is a green and simple to perform
[
a]
Reaction conditions: 1 mmol nitrobenzene, 1.2 mmol benzaldehyde,
mmol formic acid, 10 mg mpg-C /Ag40Pd60 nanocatalyst, 5 mL H O,
H-NMR
4
3
N
4
2
[
b] 1
reaction time 20 hour and the temperature 50°C
conversions.
3 4
After presenting the applicability of mpg-C N /Ag40Pd60
catalyzed one-pot reductive amination over a variety of
substrates, we then tested its reusability, which is another
important criteria for showing the practicability of
a
heterogeneous catalyst in a certain reaction. For this purpose,
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ARTICLE
alternative to classic two step reductive amination methods.
Journal Name
The presented catalytic reductive amination protocol for the 4.3. The synthesis of monodisperse AgPd alloy NPs
synthesis of secondary amines has several advantageous over
the existing methodologies in the literature such as providing
Monodisperse AgPd alloy NPs were synthesized according
2
6
atom economy by the elimination of extra reaction steps along to our established protocol which is reported elsewhere. In a
with high product yields, being hydrogen pressure free and typical synthesis, silver(I) acetate (0,5 mmol, 84 mg) and
operable under mild reaction conditions along with the use of palladium(II) acetylacetonate (0.5 mmol, 150 mg) were
a bimetallic alloy nanocatalyst with the high activity and dissolved in a mixture of oleic acid (4.5 mL), oleylamine (0.5
reusability. Owing to these advantageous features, we mL) and 1-octadecene (10.0 mL) and the mixture was then
believed that the presented catalytic one-pot reductive heated to 60°C for 5 min. Next, the resultant mixture was
amination protocol has a high potential to be applied for the heated to 180 °C under a gentle argon flow and kept kept at
other synthetic methodologies and used in industry.
this temperature for 20 min following by cooling down to
room temperature. The NP product was separated from the
reaction mixture by adding isopropanol (40 mL), followed by
centrifugation (9000 rpm, 10 min). The resultant NPS were
collected by dispersing them into hexane. The composition of
the yielded NPs was determined by ICP-MS analysis as
4
. Experimental
4.1. Chemicals
Ag40Pd60
.
Besides Ag40Pd60 alloy NPs, three other composition of the
AgPd NPs, namely Ag25Pd75, Ag50Pd50 and Ag60Pd40) could be
synthesized by using the current recipe by only tuning the
All the chemicals used for the synthesis of AgPd alloy NPs
(
(
(
silver(I) acetylacetonate (99%), palladium(II) acetylacetonate
99%), oleylamine (70%), oleic acid (90%), 1-octadecene
90%)), several of the chemical used in the synthesis of mpg-
Ag(ac)/Pd(acac)
2
molar ratio. Under the same reaction
molar ratio of 0.33, 1.5
conditions, using the Ag(ac)/Pd(acac)
2
3 4
C N
(Ludox® HS-40 and ammonium hydrogendifluoride
95%)), all the substrates used in the reductive amination
reactions, and all organic solvents (hexanes(99%), methanol
99%) and ethanol (99%)) were purchased from Sigma-
and 3 yielded to Ag25Pd75, Ag50Pd50 and Ag60Pd40 NPs,
respectively. All the alloy compositions were determined by
ICP-MS analyses of several batches of the colloidal alloy NPs.
(
(
®
Aldrich . On the other hand, the amine precursor for the
synthesis of mpg-C (guanidine hydrochloride (98%)) was
4
.4. Preparation of mpg-C
3 4
N /AgPd catalysts via liquid phase
3 4
N
®
self-assembly method
purchased by Alfa Aesar . It should be noted that all the
chemicals were used as received.
1
3 4
00 mg of mpg-C N was dispersed in 25 mL of ethyl
alcohol via sonication for 1 hours. Next, 10 mL of hexane
solution of AgPd alloy NPs containing 50 mg of NPs (the
amount of AgPd NPs in the hexane solution was determined by
evaporating hexane solution and weighting the dry NP
Instrumentation
The morphology and the particle size analysis of the mpg-
3 4 3 4
C N , AgPd alloy NPs and mpg-C N /AgPd catalysts were
residual) was added into the mpg-C
sonication for 1 hours (mpg-C /AgPd NPs ratio= 33.3 wt%).
The resulted mixture was sonicated for 2 hours to ensure
complete NP adsorption onto the mpg-C support. Finally,
the mpg-C /AgPd catalysts were separated by centrifugation
at 7500 rpm for 10 minutes after ethanol addition.
3 4
N support mixture under
conducted by transmission electron microscope (TEM, Hitachi
HT7700 with EXALENS, 120 kV) working at high-resolution (HR)
mode with the magnification range of 10-800k. The crystal
structure of the samples were studied by using powder X-ray
diffractometer (PXRD, Pananalytical Empyrean with the Cu-Kα
radiation of 40 kV, 15 mA, 1.54051 A°). The surface area and
the pore analysis were characterized by Micromeritics 3Flex
surface characterization analyzer according to the Brunauer-
Emmett-Teller method. The composition of AgPd alloy NPs and
3 4
N
3 4
N
3 4
N
4
.5. General procedure for one-pot reductive amination of
aldehydes with nitroarenes in the presence of mpg-
/AgPd catalysts
3 4
C N
3 4
the metal content of the mpg-C N /AgPd catalyst were
determined by using inductively coupled plasma mass
spectrometer (ICP-MS, Agilent 7800) after digesting the all
samples by microwave oven in aqua regia solution.
3 4
In a typical procedure, 10 mg of as-prepared mpg-C N -
Ag40Pd60 catalyst was well-dispersed in water (5 mL) by the
help of sonication in a glass pressure tube. Next, 1 mmol of
nitroarenes and 4 mmol of formic acid were injected into the
4.2. The synthesis of mesoporous graphitic carbon nitride
o
catalyst solution at 50 C. The resultant mixture first allowed to
(mpg-C
3 4
N )
react for 30 min under vigorous stirring before the injection of
1
mmol benzaldehyde and 1 mmol diphenylmethane into the
3 4
mpg-C N was synthesized by the polycondensation of
catalyst solution. Next, the final mixture was allowed to react
for 20 hours under vigorous stirring. After end of the reaction,
the resulting mixture was allowed to cool down to room
guanidine hydrochloride in the presence of Ludox® HS-40 as a
silica template. The details of the synthesis procedure and the
3 4
detailed characterization of mpg-C N can be found in our
1
3, 32
3 4
temperature. The mpg-C N -Ag40Pd60 catalysts were separated
previous reports
.
6
| J. Name., 2012, 00, 1-3
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Pl Ne ae swe Jdoo u nr no at l ao df j Cu sh te mm ai sr tgr iyn s
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DOI: 10.1039/C8NJ01569D
Journal Name
ARTICLE
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2 4
SO and concentrated
7
by rotary-evaporation. Finally, the sample for NMR analysis
1
was prepared. All the secondary amines yielded herein are 13 B. Nisanci, M. Turgut, M. Sevim, Ö. Metin, ChemistrySelect.,
known compounds in the literature and their recorded spectral
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5
,
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8
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, 12-
test was initiated by using nitrobenzene and benzaldehyde as
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3 4
N /Ag40Pd60
catalyst was separated from the reaction solution via
2
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amination reaction was started with the purified mpg-
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Conflicts of interest
4
3
0 X.H. Li, X. C. Wang, M. Antonietti, Chem. Sci., 2012, 3, 2170-
2174.
There are no conflicts to declare.
3
3
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TABLE OF CONTENTS ENTRY
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