Selective hydrogenation of aromatic compounds using modified iridium nanoparticles

Article abstract of DOI:10.1002/aoc.4260

Till now, Ionic liquid-stabilized metal nanoparticles were investigated as catalytic materials, mostly in the hydrogenation of simple substrates like olefins or arenes. The adjustable hydrogenation products of aromatic compounds, including quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes, are always of special interest, since they provide more choices for additional derivatization. Iridium nanoparticles (Ir NPs) were synthesized by the H₂ reduction in imidazolium ionic liquid. TEM indicated that the Ir NPs is worm-like shape with the diameter around 12.2?nm and IR confirmed the modification of phosphine-functionalized ionic liquids (PFILs) to the Ir NPs. With the variation of the modifier, solvent and reaction temperature, substrate like quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes could be hydrogenated by Ir NPs with interesting adjustable catalytic activity and chemoselectivity. Ir NPs modified by PFILs are simple and efficient catalysts in challenging chemoselective hydrogenation of quinoline and relevant compounds, aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes. The activity and chemoselectivity of the Ir NPs could be obviously impacted or adjusted by altering the modifier, solvent and reaction temperature.

Full text of DOI:10.1002/aoc.4260

Received: 30 October 2017
DOI: 10.1002/aoc.4260
Revised: 10 December 2017
Accepted: 12 December 2017
F U L L P A P E R
Selective hydrogenation of aromatic compounds using
modified iridium nanoparticles
He‐yan Jiang
| Jie Xu | Bin Sun
Key Laboratory of Catalysis Science and
Technology of Chongqing Education
Commission, Chongqing Key Laboratory
of Catalysis and New Environmental
Materials, College of Environmental and
Resources, Chongqing Technology and
Business University, Chongqing 400067,
China
Till now, Ionic liquid‐stabilized metal nanoparticles were investigated as
catalytic materials, mostly in the hydrogenation of simple substrates like
olefins or arenes. The adjustable hydrogenation products of aromatic
compounds, including quinoline and relevant compounds, aromatic nitro
compounds, aromatic ketones as well as aromatic aldehydes, are always
of special interest, since they provide more choices for additional derivati-
Correspondence
zation. Iridium nanoparticles (Ir NPs) were synthesized by the H reduction
2
He‐yan Jiang, Key Laboratory of Catalysis
Science and Technology of Chongqing
Education Commission, Chongqing Key
Laboratory of Catalysis and New
Environmental Materials, College of
Environmental and Resources, Chongqing
Technology and Business University,
Chongqing 400067, China.
in imidazolium ionic liquid. TEM indicated that the Ir NPs is worm‐like
shape with the diameter around 12.2 nm and IR confirmed the modifica-
tion of phosphine‐functionalized ionic liquids (PFILs) to the Ir NPs. With
the variation of the modifier, solvent and reaction temperature, substrate
like quinoline and relevant compounds, aromatic nitro compounds,
aromatic ketones as well as aromatic aldehydes could be hydrogenated by
Ir NPs with interesting adjustable catalytic activity and chemoselectivity.
Ir NPs modified by PFILs are simple and efficient catalysts in challenging
chemoselective hydrogenation of quinoline and relevant compounds,
aromatic nitro compounds, aromatic ketones as well as aromatic aldehydes.
The activity and chemoselectivity of the Ir NPs could be obviously
impacted or adjusted by altering the modifier, solvent and reaction
temperature.
Email: orgjiang@163.com
Funding information
Chongqing Technology and Business Uni-
versity, Grant/Award Numbers: CQCM‐
2016‐02 and 1751039; National Natural
Science Foundation of China, Grant/
Award Number: 21201184
KEYWORDS
aromatic ketone, chemoselective hydrogenation, ionic liquids, iridium nanoparticles, quinoline
1
| INTRODUCTION
volatility, excellent thermal stability, remarkable solubil-
ity and a variety of available structures, ionic liquids
The metal nanoparticles with characteristics of small
diameter and narrow size distribution are receiving
more and more attention in both academic and
industrial research because of their inherent large
can act as both the solvent and the stabilizer in the
preparation of metal nanoparticles. Up to now, ionic
liquid stabilized nanometal particles were tested as
catalysts generally in the hydrogenation of olefins or
[
1–5]
[3,4,13–16]
surface‐to‐volume ratio and quantum size effect.
arenes.
Additional stabilize or modify effects, generally provided
by amines, phosphines and thiols, to nanoparticles
influence the catalytic activity, selectivity and recyclabil-
The selective hydrogenation of aromatic compounds
(quinoline and its analogues, aromatic nitro compounds,
aromatic ketones, aromatic aldehydes etc.) by means of
heterogeneous catalysis is among the most important
[6–12]
ity.
With many advantages, such as negligible
Appl Organometal Chem. 2018;e4260.
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Copyright © 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4260

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JIANG ET AL.
subjects in industrial organic chemistry. 17–26] The con-
[
2 | RESULTS AND DISCUSSION
trollable hydrogenation products of aromatic
compounds are always of interest, as they offer various
2.1 | Synthesis and characterization of Ir
NPs
options for further derivatization. Dupont and co‐
[27]
workers
prepared well‐dispersed transition metal
nanoparticles with narrow size distribution in a variety
of imidazolium‐based ionic liquids, which showed very
interesting activity and selectivity in the hydrogenation
The synthesis of Ir NPs was achieved through the reduc-
tion of [Ir(cod)Cl] in [BMIM]PF (BMIM=1‐butyl‐2,3‐
2
6
dimethylimidazolium), which afforded a dark suspension.
A black powder could be isolated from the black suspen-
sion by adding acetone and then centrifuging (8000 rpm
for 10 min). Washed three times with acetone and dried
under reduced pressure, the isolated powder was analyzed
by transmission electron microscopy (TEM), X‐ray photo-
electron spectroscopy (XPS), X‐ray diffraction (XRD), and
infrared spectroscopy (IR).
[18]
of ketones. Leitner and co‐workers
successfully used
Ru(0) nanoparticles prepared in ionic liquids in the
chemoselective hydrogenation of biomass‐derived
substrates. Herein, we report originally that iridium
nanoparticles (Ir NPs), with the modification of
phosphine‐functionalized ionic liquids (PFILs), exhibit
interesting chemoselectivity in the hydrogenation of
quinoline and its analogues, aromatic nitro compounds,
aromatic ketones and aromatic aldehydes.
The Ir NPs isolated before or after catalytic
hydrogenation were placed as a thin film on a carbon‐
FIGURE 1 TEM images of (a) Ir NPs as prepared, (b) Ir NPs after three consecutive recycles of styrene hydrogenation, (c) Ir NPs after three
consecutive recycles of styrene hydrogenation in the presence of phosphine‐functionalized ionic liquid modifier [BMIM][tppm]

JIANG ET AL.
3 of 8
The surface characteristics of Ir NPs were investigated
by XPS. XPS analysis of Ir NPs prepared in [BMIM]PF6
showed the presence of iridium, nitrogen and carbon,
which signified the presence of the [BMIM]PF in the Ir
6
NPs. The BEs for Ir, 60.7 eV and 63.6 eV, indicated Ir NPs
were composed of Ir(0) (Figure S1 in supporting informa-
tion). XRD analysis (Figure 2) showed the presence of
broad reflection lines indicating the diffraction by very
small crystals. The three diffraction peaks were assigned
as the Ir(0) (111), (220) and (311) reflection planes.
IR is effective for the investigation of the mutual
ligand‐metal interactions of nanometal catalysts.
Information on the interaction between the Ir NPs and
the phosphine‐functionalized ionic liquid modifier
FIGURE 2 X‐Ray diffraction pattern of isolated Ir NPs as
prepared
[
BMIM][tppm] was confirmed by FTIR methods in which
‐1
the red shift of the P‐C H deformation around 1469 cm
6
5
was an indication of the coordination of [BMIM][tppm] to
coated copper grid and characterized by TEM analysis,
which was employed to characterize the obtained Ir
NPs and determine their mean diameters (Figure 1).
The TEM image of Ir NPs as prepared exhibited a
worm‐like shape, with an average diameter of 12.2 nm
the metal Ir(0) (Figure S2 in supporting information).
2.2 | Catalytic hydrogenation
Hydrogenation of quinoline and its analogues is of
considerable industrial interests for the production of pet-
(Figure 1, image A). After three consecutive recycles of
[20,21]
styrene hydrogenation, the TEM image showed a trend
toward agglomeration of the particles (Figure 1, image
B). However, Ir NPs (Figure 1, image C) remained
almost the same shape in the presence of phosphine‐
functionalized ionic liquid modifier [BMIM][tppm] after
three consecutive hydrogenation recycles.
rochemicals, fine chemicals, and pharmaceuticals.
The effect of different reaction factors on the
chemoselective hydrogenation of quinoline is listed in
Table 1. The phosphine‐functionalized ionic liquid
modifiers were fairly important in the catalytic system;
without the modifier, the hydrogenation resulted in a
a
TABLE 1 Optimization of reaction conditions for the chemoselective hydrogenation of quinoline
Selectivity (%)
Yield
Entry
Catalyst
1
(%)
Aa
Ab
Ac
1
94.4
100.0
0.0
0.0
2
3
4
5
6
2
92.0
32.8
18.8
93.0
90.9
100.0
100.0
100.0
100.0
100.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
3
Ir/C
b
1
c
1
a
6 2
Reaction was carried out at 50 °C. Substrate: in a 1 ml [BMIM]PF at [1.8 M], PH :3.0 MPa. Substrate/Ir=100:1, Ir/C (5 wt%, 68 mg). Reaction time: 10 h. 1=Ir
NPs modified by [BMIM][tppm], 2=Ir NPs modified by [BMIM][tppt], 3=Ir NPs as prepared. Products were analyzed by a GC instrument with an FID detector
and HP‐5 column.
b
Third run in the quinoline hydrogenation.
c
Fifth run in the quinoline hydrogenation.

4
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JIANG ET AL.
a
TABLE 2 Hydrogenation of quinoline and its analogues catalyzed by Ir NPs modified by [BMIM][tppm]
Selectivity (%)
Yield
Entry
Substrate
(%)
A‐Ga
A‐Gb
A‐Gc
1
A
94.4
100.0
0.0
0.0
2
3
4
5
6
7
B
C
D
100.0
90.0
81.0
33.4
22.5
0.0
100.0
100.0
100.0
46.1
100.0
‐
0.0
0.0
0.0
0.0
0.0
‐
0.0
0.0
0.0
53.9
0.0
‐
b
E
F
G
a
The reaction conditions are the same as in Table 1.
b
Reaction time: 15 h.
conversion of 32.8% to 1,2,3,4‐tetrahydroquinoline
Table 1, entry 3). Ir NPs modified by [BMIM][tppm]
showed higher activity to 1,2,3,4‐tetrahydroquinoline
without obvious loss in catalytic activity and
chemoselectivity during the quinoline hydrogenation
(Table 1, entries 5‐6).
(
than Ir NPs modified by [BMIM][tppt] (Table 1, entries
We investigated the catalytic performance of [BMIM]
[tppm] modified Ir NPs for the hydrogenation of quino-
line and its analogues (Table 2). Quinoline could be easily
hydrogenated to 1,2,3,4‐tetrahydroquinoline with abso-
1
‐2). The dramatically activity increase of Ir(0) particles
in the chemoselective hydrogenation of quinoline
Table 1, entries 1‐2 vs 3) should be ascribed to the modi-
(
fication effect of PFILs to Ir(0) particles and the modifica-
lute chemoselectivity in [BMIM]PF (Table 2, entry 1).
6
tion effect may be good for the rate‐determining
The hydrogenation activity of 2‐, 3‐ or 8‐methylquinoline
was similar to quinoline. Interestingly, the presence of
substituent in quinoline had no influence on the
hydrogenation chemoselectivity (Table 2, entries 2‐4).
Other substrates, including indole, 2,3‐benzofuran and
1‐benzothiophene, were also tested. In comparison to
[26]
dissociative adsorption of H on the Ir(0) site.
In com-
2
parison, the commercially available Ir/C was utilized as
a catalyst for the selective hydrogenation of quinoline, it
showed poor activity to 1,2,3,4‐tetrahydroquinoline
(Table 1, entry 4). The catalyst 1 could be reused 5 times
a
TABLE 3 Hydrogenation of aromatic nitro compounds by Ir NPs
Entry
Substrate
Catalyst
1
Product
Yield (%)
1
nitrobenzene
aniline
100.0
2
3
4
5
6
7
8
9
nitrobenzene
2
aniline
100.0
98.2
nitrobenzene
3
aniline
nitrobenzene
Ir/C
1
aniline
85.1
m‐methylnitrobenzene
p‐methylnitrobenzene
o‐methoxylnitrobenzene
p‐methoxylnitrobenzene
p‐fluoronitrobenzene
o‐chloronitrobenzene
p‐chloronitrobenzene
m‐methylaniline
p‐methylaniline
o‐methoxyaniline
p‐methoxyaniline
p‐fluoroaniline
o‐chloroaniline
p‐chloroaniline
96.0
1
100.0
72.0
1
1
6.0
1
100.0
100.0
100.0
1
0
1
1
1
1
a
6 2
Reaction was carried out at 50 °C. Substrate: in a 1 ml [BMIM]PF at [1.8 M], PH :3.0 MPa. Substrate/Ir=100:1, Ir/C (5 wt%, 68 mg). Reaction time: 5 h. 1=Ir
NPs modified by [BMIM][tppm], 2=Ir NPs modified by [BMIM][tppt], 3=Ir NPs as prepared. Products were analyzed by a GC instrument with an FID detector
and HP‐5 column. Only corresponding amino aromatic products were detected during all the catalytic reactions.

JIANG ET AL.
5 of 8
quinoline, indole, 2,3‐benzofuran and 1‐benzothiophene
exhibited lower catalytic activity. Indole could be
all the substrates could be efficiently converted into the
corresponding substituted amino aromatic compounds
under mild conditions except substrates with a methoxy
substituent (Table 3, entries 7‐8). The methyl‐ or chloro‐
substituted nitrobenzene afforded the corresponding
amino aromatic compounds and showed comparable
reactivity as that of unsubstituted nitrobenzene.
[BMIM][tppm] modified Ir NPs 1 catalyst showed high
activity for chemoselective hydrogenation of nitroben-
zene and its derivatives, which was not apparently
affected by the steric effect, but possibly by the elec-
tronic effects. In comparison, commercially available
Ir/C catalyst was also tested under similar reaction con-
ditions in the hydrogenation of nitrobenzene (Table 3,
entry 4). However, Ir/C catalyst showed poor activity
towards aniline.
hydrogenated with
complete hydrogenation product (Table 2, entry 5).
,3‐benzofuran could be hydrogenated with the
a
high chemoselectivity to
2
complete chemoselectivity to 2,3‐dihydrobenzofuran. 1‐
Benzothiophene was not reduced (Table 2, entry 7), and
the absence of activity may be attributed to the affinity
1
of sulfur atoms for its classical ƞ ‐S adsorption onto the
surface of Ir NPs 1 catalyst.
Selective hydrogenation of aromatic nitro com-
pounds by metal nanoparticles have seen remarkable
[28,29]
growth in recent years
, we also investigated the
hydrogenation of aromatic nitro compounds over PFILs
modified Ir NPs. As shown in Table 3, with the superior
[
BMIM][tppm] modified Ir NPs 1 as the catalyst, almost
a
TABLE 4 Chemoselective hydrogenation of aromatic ketones by Ir NPs
Selectivity (%)
Yield
Entry
Substrate
Catalyst
3
(%)
H‐L a
H‐L b
H‐L c
b
1
H
0.0
‐
‐
‐
2
3
4
H
H
H
H
H
H
H
I
3
89.0
39.3
19.8
96.6
90.2
0.0
12.6
88.0
85.4
89.5
94.8
‐
0.0
1.8
7.6
0.0
0.9
‐
87.4
10.2
7.0
10.5
1.7
‐
1
2
c
5
3
c
6
1
7
Ir/C
c
8
Ir/C
3
60.0
60.8
20.0
17.7
8.0
83.5
71.5
93.5
54.8
89.1
‐
0.0
13.7
4.0
24.9
5.9
‐
16.5
14.8
2.5
20.3
5.0
‐
9
c
10
11
12
13
14
15
16
I
1
J
3
c
c
c
J
1
K
K
L
L
3
0.0
1
0.0
‐
‐
‐
3
86.8
37.0
89.0
96.2
9.2
3.0
1.8
0.0
1
a
Reaction was carried out at 75 °C. Substrate: in a 1 ml [BMIM]PF
6
2
solution at [1.8 M], PH :3.0 MPa. Substrate/Ir=100:1. Ir/C (5 wt%, 68 mg). Reaction time:
10 h. 1=Ir NPs modified by [BMIM][tppm], 2=Ir NPs modified by [BMIM][tppt], 3=Ir NPs as prepared. Products were analyzed by a GC instrument with an
FID detector and β‐DEX120 capillary column.
b
Reaction was carried out at 30 °C.
c
1
ml water was introduced to catalytic reaction.

6
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JIANG ET AL.
The chemoselective reduction of aromatic ketones by
catalytic activity than catalyst 3 (Table 4, entries 2‐4),
above comparison indicated that all interactions between
PFILs modifiers, substrates, as well as the corresponding
hydrogenation products and Ir(0) particles have impor-
tant influence on the rate‐determining dissociative
adsorption of H2 on the Ir(0) site. Additionally, the
chemoselectivity adjustment in acetophenone hydroge-
nation with 1, 2 and 3 (Table 4, entries 2‐4) suggested
that the PFILs modifiers had influence on preferential
adsorption of acetophenone to the Ir(0) catalysts
followed by reduction with H atoms on the Ir(0) site
means of heterogeneous catalysis is of considerable
importance in the synthesis of fine chemicals, particu-
larly intermediates in the fragrance and pharmaceutical
[17–19]
industries
. Additionally, tuning the hydrogenation
chemoselectivity of aromatic ketones compounds on
heterogeneous catalysis remains a formidable scientific
challenge. The effect of different reaction factors on the
chemoselective hydrogenation of acetophenone is listed
in Table 4 (entries 1‐8). The Ir NPs had no catalytic
activity under ambient temperature in the hydrogenation
of acetophenone (Table 4, entry 1). The phosphine‐func-
tionalized ionic liquid modifiers had important influence
on the catalytic system. Without the modifier, the hydro-
genation resulted in a conversion of 89.0% and a
chemoselectivity as high as 87.4% to cyclohexylethanol
[
26]
. Water is an attractive alternative to traditional
organic solvents because it is cheap, readily available,
[30]
nontoxic, non‐flammable and safe to environment.
Water was introduced to catalytic system to improve
the catalytic performance (Table 4, entries 5‐6). To our
surprise, in the presence of water, the catalytic activity
of Ir NPs catalysts 1 and 3 sharply increased with
improved chemoselectivity to 1‐phenylethanol. We spec-
ulate that C=O in acetophenone not only interacts with
Ir(0) particles, but it also forms the hydrogen bond
with water. As a result, the hydrogen bond between
C=O and water improves the activity and
chemoselectivity of Ir(0) particles for the hydrogenation
of acetophenone to 1‐phenylethanol. Commercially
available Ir/C catalyst was also tested under similar
(
Table 4, entry 2). Interestingly, with the PFILs modi-
fiers, the acetophenone hydrogenation showed low activ-
ity with high chemoselectivity switched to 1‐
phenylethanol (Table 4, entries 3‐4). Ir NPs modified by
[
BMIM][tppm]
1
showed higher activity and
chemoselectivity to 1‐phenylethanol than Ir NPs modi-
fied by [BMIM][tppt] 2. Different from activity change
in quinoline hydrogenation with catalysts 1, 2 and 3
Table 1, entries 1‐3), chemoselective reduction of
acetophenone with catalysts 1 and 2 showed lower
(
a
TABLE 5 Chemoselective hydrogenation of aromatic aldehydes by Ir NPs
Selectivity (%)
T
(°C)
Yield
(%)
Entry
Substrate
Catalyst
1
M‐P a
M‐P b
M‐P c
1
M
30
100.0
100.0
83.0
100.0
0.0
0.0
b
2
M
M
M
N
N
O
O
P
1
75
30
75
30
75
30
75
30
75
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
100.0
2.5
3
Ir/C
97.5
97.0
100.0
99.8
100.0
100.0
100.0
0.0
b
4
Ir/C
81.9
3.0
5
1
1
1
1
1
1
100.0
99.0
0.0
b
6
0.2
7
42.0
0.0
b
8
82.0
0.0
9
100.0
90.2
0.0
b
1
0
P
100.0
a
Substrate: in a 1 ml [BMIM]PF
6 2
solution at [1.8 M], PH :3.0 MPa. Substrate/Ir=100:1. Ir/C (5 wt%, 68 mg). Reaction time: 10 h. 1=Ir NPs modified by [BMIM]
[tppm]. Products were analyzed by a GC instrument with an FID detector and β‐DEX120 capillary column.
b
1
ml water was introduced to catalytic reaction.

JIANG ET AL.
7 of 8
reaction conditions in the hydrogenation of
acetophenone (Table 4, entries 7‐8). Ir/C catalyst showed
poor activity and chemoselectivity during the test.
Some representative examples are also listed in
Table 4 (entries 2, 6, 9‐16) for the chemoselective hydroge-
nation of aromatic ketones catalyzed by Ir NPs 3 in
4 | EXPERIMENTAL SECTION
4.1 | Materials
All manipulations involving air‐sensitive materials were
carried out using standard Schlenk line techniques under
an atmosphere of nitrogen. [Ir(cod)Cl] and Ir/C were
2
[
BMIM]PF or by [BMIM][tppm] modified Ir NPs 1 in a
6
purchased from Acros. Various substrates and other
reagents were analytical grade. The purity of hydrogen
was over 99.99%. Phosphine‐functionalized ionic liquids
mixture of [BMIM]PF6 and water. In comparison to
acetophenone, other substrates generally exhibited lower
catalytic activity with major chemoselectivity to aromatic
ethanols during the test. The activity and chemoselectivity
decreased by increasing the bulkiness of the alkyl group
from methyl or primary alkyl to isopropyl (Table 4, entries
[
31,32]
were synthesized according to literature.
Products
were analyzed by GC instrument with an FID detector
and HP‐5 column (30 m × 0.25 mm) or Chrompack
Chirasil‐DEX column (25 m × 0.25 mm). Products were
confirmed by GC–MS and NMR. The TEM analyses were
performed in a JEOL JEM 2010 transmission electron
microscope operating at 200 kV with nominal resolution
of 0.25 nm. The X‐ray photoelectron spectroscopy (XPS)
measurements were performed on a Thermo ESCALAB
2
, 6, 9‐12). When the substituent was in the para position,
substrate with electron‐donating group showed no
reaction activity (Table 4, entries 13‐16).
The chemoselective hydrogenation of aromatic
aldehydes were also tested (Table 5). In comparison to
the chemoselective hydrogenation of aromatic ketones,
aromatic aldehydes could be hydrogenated to correspond-
ing C=O hydrogenation products easily. Benzaldehyde
could be hydrogenated to corresponding benzyl alcohol
250 spectrometer. The XRD analysis was performed in a
D/MAX 2550 VB/PC using a graphite crystal as
monochromator.
in [BMIM]PF at 30 °C (Table 5, entry 1). Complete
6
hydrogenation product of benzaldehyde could also be
4.2 | Synthesis of Ir NPs
obtained in the mixture solvent of [BMIM]PF and water
6
In a typical experiment, [Ir(cod)Cl] (0.009 mmol) was
(
Table 5, entry 2). Commercially available Ir/C catalyst
2
well dispersed in [BMIM]PF (1 ml) (BMIM=1‐butyl‐2,3‐
was also tested under similar reaction conditions in the
hydrogenation of benzaldehyde (Table 5, entries 3‐4). Ir/
C catalyst showed poor activity during the test. When
the substituent was in the para position of benzaldehyde,
C=O and full hydrogenation could be achieved in elec-
tron‐drawing group substituted substrate (Table 3, entries
6
dimethylimidazolium) and the reaction mixture was
placed in a 20 ml stainless‐steel high pressure reactor.
After stirring the mixture at room temperature under an
atmosphere of argon for 30 min, a constant pressure of
H (g) (1 MPa) was admitted to the system and the content
2
was stirred for 10 min at 75 °C. The reactor was cooled to
ambient temperature and carefully vented. A dark solu-
9
‐10). With electron‐donating group in the para position,
p‐anisaldehyde could be hydrogenated with absolute
chemoselectivity to C=O hydrogenation product
tion was obtained. The Ir NPs embedded in [BMIM]PF6
were employed for hydrogenation studies (see below). Iso-
(Table 3, entries 7‐8).
lation of the Ir NPs for TEM, XPS and XRD analysis was
achieved by dissolving the mixture in acetone (5 ml),
centrifuging (8000 rpm for 10 min), washing with acetone
(3 × 5 ml) and drying under vacuum.
3
| CONCLUSION
In summary, we have demonstrated that Ir NPs
modified by PFILs are simple, efficient and recyclable
catalysts for the challenging selective hydrogenation
of quinoline and its analogues, aromatic nitro
compounds, aromatic ketones and aromatic aldehydes.
The activity and chemoselectivity of the Ir NPs can be
obviously influenced or controlled by variation of
the modifier, solvent and reaction temperature. The
catalytic performance is complementary to both
classical homogeneous and heterogeneous catalysts.
Additional work is currently in progress in this and
related areas.
4
.3 | General procedure for the
heterogeneous chemoselective
hydrogenation
In stainless steel autoclave, PFIL (0.018 mmol) was dis-
persed in previously prepared Ir(0) catalyst. After stirring
at room temperature under an atmosphere of argon for
60 min, the mixture was charged with the appropriate
substrate, and then the autoclave was sealed and purged
with pure hydrogen several times. After the reactants
were heated to predetermined temperature, the reaction
timing began. After completion of the reaction and

8
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JIANG ET AL.
cooling to ambient temperature, the products were iso-
lated by liquid‐liquid extraction with diethyl ether and
analyzed by gas chromatography. Isolation of the Ir NPs
for TEM analysis after catalytic cycles was achieved by
dissolving the reaction mixture in acetone (5 ml),
centrifuging (8000 rpm for 10 min), washing with acetone
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(
3 × 5 ml) and drying under vacuum.
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ACKNOWLEDGEMENTS
[20] M. Yan, T. Jin, Q. Chen, H. E. Ho, T. Fujita, L. Y. Chen, M. Bao,
This work was financially supported by National Natural
Science Foundation of China (No. 21201184), Chongqing
Technology and Business University (1751039) and
Chongqing Key Laboratory of Catalysis and New Envi-
ronmental Materials (CQCM‐2016‐02).
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ORCID
He‐yan Jiang http://orcid.org/0000-0003-1239-7861
[25] M. J. Sharif, P. Maity, S. Yamazoe, T. Tsukuda, Chem. Lett.
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