A Porous Organic Poly(triphenylimidazole) Decorated with Palladium Nanoparticles for the Cyanation of Aryl Iodides

Article abstract of DOI:10.1002/asia.201800681

A new porous organic poly(triphenylimidazole), PTPI-Me, was prepared through a Yamamoto self-coupling reaction of 2,4,5-tris-(4-bromophenyl)-1-methyl-1H-imidazole (TPI-Me) in the presence of bis(1,5-cyclooctadiene)nickel(0). The polymer was subsequently decorated with Pd nanoparticles (NPs) to afford a heterogeneous cyanation catalyst, Pd@PTPI-Me. Pd NPs with an average diameter of 2.7 nm were grown within the PTPI-Me framework, owing to the coordination of the imidazole rings to the Pd species. The resultant Pd@PTPI-Me catalyst, with a Pd loading of 0.13 mmol g^?1, exhibited superior catalytic activity for the cyanation of aryl iodides. More importantly, the heterogeneous catalyst was also readily recycled and displayed negligible deactivation after five cycles.

Full text of DOI:10.1002/asia.201800681

CHEMISTRY
AN ASIAN JOURNAL
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Accepted Article
Title: Porous Organic Polytriphenylimidazole Decorated with Palladium
Nanoparticles for Cyanation of Aryl Iodides
Authors: Haiwen Yu, Siqi Xu, Yijiang Liu, Hongbiao Chen, and
Huaming Li
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Chemistry - An Asian Journal
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Porous Organic Polytriphenylimidazole Decorated with Palladium
Nanoparticles for Cyanation of Aryl Iodides
[
a]
[a]
[a]
[a]
[a][b]
Haiwen Yu, Siqi Xu, Yijiang Liu,* Hongbiao Chen,* and Huaming Li
Abstract: A novel porous organic polytriphenylimidazole (PTPI-Me)
was prepared by Yamamoto self-coupling of 2,4,5-tris-(4-
bromophenyl)-1-methyl-1H-imidazole (TPI-Me) in the presence of
bis(1,5-cyclooctadiene)nickel(0), which was subsequently decorated
with Pd nanoparticles (NPs) to afford a heterogeneous cyanation
catalyst (Pd@PTPI-Me). Pd NPs with an average diameter of 2.7 nm
were well-grown in the PTPI-Me frameworks due to the coordination
of imidazole ring to Pd species. The resultant Pd@PTPI-Me catalyst
mentioned POPs have been synthesized via Pd-catalyzed Heck,
Sonogashira, or Suzuki-Miyaura coupling reactions. Considering
that ligand-complexed Pd catalysts were used in these coupling
processes, the complete removal of Pd residues from the POPs
was bound to be difficult because of the ionic or coordinative
interactions between the synthesized POPs and Pd species.
Undoubtedly, the residual Pd species can significantly interfere
with the catalytic performance of POP-supported metal NPs in
heterogeneous catalysis. In this regard, it is important to employ
other strategies to synthesize POPs that metal residues can be
thoroughly removed or without using any metal catalysts.
As an alternative strategy for POPs synthesis, Ni(0)-induced
Yamamoto coupling is more attractive as compared with Pd-
catalyzed coupling reactions due to the mild reaction conditions
together with the easy removal of metal residues. Indeed, Ni
species in Yamamoto coupling systems can be readily removed
by washing with a mineral acid in the work-up procedure as
−
1
with a Pd loading of 0.13 mmol g exhibited superior catalytic
activity towards cyanation of aryl iodides. More importantly, the
heterogeneous catalyst was readily recycled and displayed
negligible deactivation after five cycles.
Introduction
In recent years, porous organic materials (POMs) including
hyper-crosslinked polymers (HCP ), polymers of intrinsic
S
proved by inductively coupled plasma atomic emission
spectrometry (ICP-AES) analysis.[15] In this manner, the
microporosity (PIMs), covalent organic frameworks (COFs), and
porous organic polymers (POPs), are gained considerable
interest in gas adsorption/separation, luminescent materials,
sensing, and catalysis.[1-10] Among them, POPs are of special
concern in the field of heterogeneous catalysis due to their high
stability, high surface area, designable porosity and flexible
synthetic approaches. Up to now, various functionalized POPs
with N- or P-containing moieties have been successfully used to
prepare heterogeneous catalysts through loading precious metal
nanoparticles (NPs) in their frameworks, which showed superior
catalytic performance with excellent recyclability and reusability.
For example, Ding and co-workers[11] reported the preparation of
interference of metal residues can be excluded. At present, a
(metal)porphyrin[16-18],
variety
of
POPs
based
on
triphenylamine[19],
tetraphenylphosphonium[20]
,
tetraphenylmethane[21], triphenylbenzene[22]
triptycene[24], pyrene[25], imidazolium[26], and triazole skeletons
,
spriobifluorene[23],
[27]
have been successfully synthesized by Yamamoto self-coupling
or cross-coupling reactions. Among them, imidazolium- and
triazole-containing POPs are considered as the most promising
catalyst supports. For example, ultrafine Pd NPs with an
average diameter of 1.39 ± 0.31 nm had been effectively loaded
in the cavities of 1,2,3-triazole-containing POP.[27] Such
supported catalyst exhibited high activity and recyclability in the
hydrogenation of olefins. In addition, Au NPs with an average
diameter of 3.42 nm were also immobilized in imidazolium-
containing POP that fabricated by Yamamoto cross-coupling
reaction, which showed high activity, selectivity, and recyclability
in the reduction of nitrobenzene.[15] Notably, the catalytic activity
3
Ph P-containing POP for Pd NPs loading. The as-synthesized
heterogeneous catalyst exhibited high chemoselectivity and
efficiency towards hydrogenation of nitroarenes and olefins
under gentle conditions. Li et al.[12] synthesized N-heterocyclic
carbene gold(I) complex-incorporated POPs and investigated
their catalytic performance in hydration of phenylacetylenes.
of metal NPs is closely related to their particle size, and the
Wang et al.[
13-14]
have synthesized a series of imidazolium-
smaller particulate is usually thought to have higher catalytic
containing POPs for loading Pd NPs and explored the catalytic
activities in the reduction of nitroarenes. However, all the above-
[28-29]
activity due to the larger reactive area.
On the other hand, it
is also very important to lower the metal NPs loading while
maintaining the high catalytic activity considering that precious
metals are much expensive. In this context, it is highly desirable
to design and synthesize POP supports at a molecular level that
can achieve these goals mentioned above.
[
a]
H Yu, S Xu, Dr. Y Liu, Prof. H Chen, Prof. H Li
College of Chemistry
Xiangtan University
Xiangtan 411105 (P.R. China)
E-mail: liuyijiang84@163.com, chhb606@163.com
Prof. H Li
Key Laboratory of Polymeric Materials & Application Technology of
Hunan Province, Key Laboratory of Advanced Functional Polymeric
Materials of College of Hunan Province, and Key Laboratory of
Environment-Friendly Chemistry and Application in Ministry of
Education
Herein, we demonstrated a novel polytriphenylimidazole-
containing POP (PTPI-Me) that fabricated by Yamamoto self-
coupling of 2,4,5-tris-(4-bromophenyl)-1-methyl-1H-imidazole
[
b]
(
TPI-Me), which was then employed as the support for Pd NPs
loading (Pd@PTPI-Me). The choice of triphenylimidazole as the
building block is based on the fact that it has a rigid molecular
structure on the one hand, and on the other hand, imidazole ring
can complex with metal ions, which facilitates to load metal NPs.
In addition, previous investigations have demonstrated that
Xiangtan University
Xiangtan 411105 (P.R. China)
Supporting information for this article is given via a link at the end of
the document.
triphenylimidazole-containing linear polymers possess high
thermal and chemical stabilities.[
30-31]
Due to the coordinative
1
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FULL PAPER
interaction between imidazole ring and Pd precursor, Pd NPs
with an average diameter of 2.7 nm were well-grown in the
PTPI-Me frameworks. The resultant Pd@PTPI-Me catalyst with
a Pd loading of 0.13 mmol g−1 exhibited superior catalytic activity
towards cyanation of aryl iodides. More importantly, the
heterogeneous catalyst was readily recycled and displayed
negligible deactivation after five cycles.
Scheme 1. Schematic representation of the synthesis of Pd@PTPI-Me.
Figure 1, PTPI-Me is composed of spherical particles (Figure 1a),
and no morphological change is observed after Pd NPs loading
(
Figure 1b). TEM images demonstrate that ultrafine Pd NPs are
Results and Discussion
uniformly distributed in the polymeric frameworks due to the
coordination effect between Pd NPs and the imidazole moieties
in PTPI-Me scaffold (Figure 1c, d). The average size of Pd NPs
is evaluated through statistical analysis of TEM image and is
found to be 2.7 nm (Figure 1c, inset). However, some Pd
aggregates are still observed (Figure 1d).
The synthetic route of the porous organic polymer PTPI-Me was
shown in Scheme 1. The monomer TPI-Me was synthesized by
a one-step condensation reaction between 4,4’-dibromobenzil,
4-bromobenzaldehyde and ammonium acetate, and followed by
a substitution reaction with methyl iodide (Scheme S1). The
1
structure of TPI-Me was fully characterized by H NMR (Figure
S1), 13C NMR (Figure S2) and FT-IR (Figure S3, black line). The
Yamamoto self-coupling of TPI-Me in the presence of bis(1,5-
cyclooctadiene)nickel(0) (Ni(COD)
powder PTPI-Me. The as-synthesized PTPI-Me was then
dispersed in DMF followed by incubation with an H PdCl
, the brown power
2
) generated a light yellow
2
4
aqueous solution. After reduction with NaBH
of Pd@PTPI-Me was obtained (Scheme 1).
4
The structure of PTPI-Me was initially characterized by solid
state 13C NMR spectrum. As illustrated in Figure 2a, the signal at
δ = 139.2 ppm confirmed the success of Yamamoto phenyl–
phenyl coupling among TPI-Me monomers. The signals at δ =
137.5−151.1 ppm were ascribed to carbon atoms of imidazolyl
ring, and the broad signals at 118.2−137.6 ppm were attributed
to the carbon atoms of phenyl ring, In addition, the methyl
carbon also appeared at δ = 35.4 ppm. The FT-IR spectra of
PTPI-Me and Pd@PTPI-Me are shown in Figure S3. As seen,
the strong C-Br stretching vibration band at 513 cm−1 that
corresponded to TPI-Me building block almost disappeared in
the FT-IR spectrum of PTPI-Me, indicating that homocoupling of
TPI-Me occurred (Figure S3, black and blue line). After Pd NPs
was immobilized onto the PTPI-Me skeleton, the symmetric
stretching vibration of C=N-C=C bond in imidazolyl ring shifted
−
1
−1
from 1450 cm to 1445 cm , indicating the strong coordination
interaction between Pd and imidazolyl ring (Figure S3, red line).
Thermogravimetric analyses showed that both PTPI-Me and
Pd@PTPI-Me are stable below 300 °C, and the thermal stability
of Pd@PTPI-Me is somewhat higher than that of PTPI-Me
Figure 1. (a) TEM image of PTPI-Me; (b-e) SEM (b), TEM (c, d), and HRTEM
(
Figure S4). The morphologies of PTPI-Me and Pd@PTPI-Me
(e) images of Pd@PTPI-Me, inset of c shows Pd NPs size distribution; (f) EDX
were then investigated by scanning electron microscopy (SEM)
and transmission electron microscope (TEM). As shown in
mapping image of Pd@PTPI-Me.
2
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The HRTEM image of Pd@PTPI-Me revealed that the
lattice-fringe spacing of Pd NPs was found to be 0.21 nm (Figure
2e, the isotherms of PTPI-Me showed a type IV behavior. The
rapid uptake of N at low pressure (P/P < 0.1) indicated the
2 0
1
e), which corresponded to the Pd (111) plane. In addition,
existence of micropores in PTPI-Me, and the obvious hysteresis
between the adsorption/desorption branch confirmed the
presence of mesopores. The coexistence of micropores and
mesopores in PTPI-Me was further confirmed by the pore size
distribution (Figure 2f). The Brunauer-Emmett-Teller (BET)
surface area of PTPI-Me is 712 m g−1, and the total pore
volume is 0.52 cm g . After loading of Pd NPs, Pd@PTPI-Me
exhibited a type IV isotherms, and the pore size distribution also
suggested the existence of mesopores. The BET surface area
and the total pore volume of Pd@PTPI-Me were decreased to
457 m2 g−1 and 0.33 cm3 g−1, respectively, owing to the pore
filling and mass increment of Pd NPs in the polymer scaffold.
However, the Pd@PTPI-Me still remained mesoporous structure
and could be applicable to heterogeneous catalysis.
energy-dispersive X-ray (EDX) mapping clearly confirmed that
Pd NPs were homogeneously distributed in the PTPI-Me
frameworks (Figure 1f).
Powder X-Ray diffraction (PXRD) showed almost no peak
for PTPI-Me support, while weak peaks at 2θ = 40.0°, 46.1° and
2
3
−1
67.5° were observed for Pd@PTPI-Me, indicating the successful
immobilization of Pd(0) NPs (Figure 2b). The Pd content in
Pd@PTPI-Me was 0.13 mmol g−1 as determined by inductively
coupled plasma atomic emission spectroscopy (ICP-AES). The
chemical composition of Pd@PTPI-Me was further confirmed by
X-ray photoelectron spectroscopy (XPS). As shown in Figure 2c,
the binding energies at around 285 eV, 339 eV, 398 eV and 532
eV corresponded to C 1s, Pd 3d, N 1s and O 1s, respectively.
The Pd 3d spectrum was split into double peaks. The peaks at
around 340.1 eV (Pd 3d3/2) and 334.2 eV (Pd 3d5/2) are assigned
Table 1. Optimization of reaction conditions in the cyanation of iodobenzene [a]
to Pd(0) species, while the peaks at around 341.3 eV (Pd 3d3/2
)
and 335.2 eV (Pd 3d5/2) are attributed to Pd(II) species that may
be resulted from the reoxidation of Pd(0) owing to air contact
(
Figure 2d). The ratio of Pd(0) to Pd(II) in Pd@PTPI-Me is
Pd
(mol %)
---
Temp.
(°C)
120
120
120
80
Time
(h)
10
10
10
10
7
entry
solvent
alkali
yield (%) [b]
calculated to be 1.71 according to their relative peak area,
indicating that Pd(0) is predominant, which is consistent with
PXRD analysis.
1
2
3
4
5
6
7
8
9
DMF
DMF
DMF
DMF
DMF
DMSO
DMAC
DMF
DMF
DMF
DMF
DMF
Na
2
Na
2
Na
2
Na
2
Na
2
Na
2
Na
2
CO
CO
CO
CO
CO
CO
CO
3
3
3
3
3
3
3
No reaction
0.2
90
0.3
99
0.3
No reaction
0.3
120
120
120
120
120
120
120
120
88
95
94
30
98
87
90
95
0.3
10
10
10
10
10
10
10
0.3
0.3
---
CO
NaOH
PO
COOK
[Fe(CN) ], 0.05 mmol;
0.3
K
2
3
10
11
12
0.3
0.3
K
3
4
0.3
CH
3
[
a] Reaction conditions: iodobenzene, 0.2 mmol; K
4
6
Pd@PTPI-Me, 4.5 mg, 0.3 mol % of Pd; solvent, 2 mL; alkali, 0.08 mmol. [b]
GC yield.
Aromatic nitriles are extensively used in agrochemical and
pharmaceutical industries due to their flexible nature of nitrile
moiety, which can be easily converted to versatile functionalities
such as aldehyde, ketone, amine and so forth. Cyanation of aryl
halides under the catalysis of transition metals is a general and
powerful approach to achieve aromatic nitriles. Pd-catalyzed
cyanation is of special interest because of its milder reaction
conditions, economical cost and good recyclability.[32] To
evaluate the catalytic ability of Pd@PTPI-Me, the transformation
of iodobenzene to benzonitrile has been selected as the model
Figure 2. (a) Solid-state 13C NMR spectrum of PTPI-Me; (b) PXRD patterns of
PTPI-Me, Pd@PTPI-Me and Pd(0); (c, d) XPS survey (c) and Pd 3d (d)
4 6
reaction. K [Fe(CN) ] was used as cyanide source because it is
2
spectra of Pd@PTPI-Me; (e) N adsorption/desorption isotherms of PTPI-Me
nontoxic and inexpensive. After the reaction was completed, the
mixture was extracted with ethyl acetate, and the yield was
determined by GC-MS. When the reaction was carried out in the
absence of Pd@PTPI-Me, no desired product was obtained
and Pd@PTPI-Me; (f) Pore size distribution of PTPI-Me and Pd@PTPI-Me.
The porous properties of PTPI-Me and Pd@PTPI-Me were
finally investigated by N isotherms at 77 K. As shown in Figure
2
(
Table 1, entry 1). The yield of benzonitrile was improved with
increasing the amount of Pd@PTPI-Me. For example, 0.2 mol%
3
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Pd gave nearly 90% of benzonitrile (Table 1, entry 2). When Pd
was increased to 0.3 mol%, a yield of 99% was achieved,
indicating that almost all iodobenzene has been converted to
benzonitrile (Table 1, entry 3). The optimal reaction conditions
were selected by a serial of experiments with varying reaction
time, temperature, alkali and solvent. The reaction temperature
was considered to be the most crucial factor for the cyanation of
iodobenzene. No product was obtained when the reaction
proceeded at 80 °C, while other reaction parameters kept
unchanged (Table 1, entry 4). The possible reason is that the
contrary, obvious change of yield was observed with different
alkalis. A quite low yield was obtained in the absence of alkali
(Table 1, entry 8). We are glad to found that carbonates such as
K
2
CO
(Table 1, entry 9, 3), while NaOH can lower the yield from 99%
to 87% (Table 1, entry 10). In the case of K PO , the yield of the
3 2 3
and Na CO give rise to high yield of 98% and 99%
3
4
desired product is slightly reduced to 90% (Table 1, entry 11).
Previous investigation indicated that alkalis such as carbonates
4 6 6
can help to dissolve K [Fe(CN) ] and to promote [Fe(CN)
]4−
species to form intermediates.[ These results suggested that
33]
4 6
K [Fe(CN) ] has low solubility at low temperature. Meanwhile,
the highest yield (~ 99%) was achieved in DMF with 0.3 mol%
the change of reaction time from 10 h to 7 h reduces the yield
from 99% to 88% (Table 1, entry 5). The solvent has less
influence on the yield of benzonitrile (Table 1, entry 6, 7). On the
Pd as the catalyst and Na
120 °C for 10 h.
2
CO
3
as the alkali after heating at
Table 2. Cyanation reaction of substituted aryl iodides catalyzed by Pd@PTPI-Me [a]
.
entry
1
aryl iodide
time
10
product
yield (%) [b]
95
2
3
10
10
93
91
4
5
6
7
8
9
10
10
10
10
12
12
90
93
88 [c]
99
87
90
[
a] Reaction conditions: substrate (0.40 mmol), K
4
[Fe(CN)
6
] (0.10 mmol), Na
2
CO
3
(0.16 mmol), DMF (4 mL), temperature 120 °C, 9 mg Pd@PTPI-Me (0.3 mol%
of Pd). [b] Isolated yield. [c] K [Fe(CN) ] = 0.2 mmol.
4
6
As we all known, the catalytic properties of heterogeneous
Pd catalysts supported on porous materials are closely related
to the active Pd species, Pd particle size/morphology, specific
surface area/pore volume, and the characteristics of the porous
supports.[34-39] By comparison with other reported heterogeneous
Pd catalysts, for example, Pd-metalated porous polycarbazole
same cyanation reaction, in which above 70% product yield was
obtained for ligand-, base-, and additive-free cyanation of aryl
4 6
bromides with K [Fe(CN)
] in the presence of 0.2 mol% Pd.[ In
41]
our case, it is not surprised that Pd@PTPI-Me catalyst shows a
99% product yield in the cyanation of highly active aryl iodides
with 0.3 mol% Pd. The porous-structured Pd@PTPI-Me catalyst
had a relatively high BET surface area and a small Pd particle
size, which facilitated the accessibility to the catalytic site as well
as effective mass transfer.[34] Meanwhile, the electron-donating
nature of TPI-Me also helped to improve catalytic efficiency and
(
Pd-CNP-2) catalyst with 8.7 wt% Pd loading showed 99% yield
4 6
in the cyanation of 1,4-dibromobenzene with K [Fe(CN) ] in the
presence of 0.41 mol% Pd.[40] Another example is porous ZnO-
supported Pd catalyst with only 0.11 mmol g−1 Pd loading for the
4
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Chemistry - An Asian Journal
10.1002/asia.201800681
FULL PAPER
stability.[36] Last but not least, the Pd(0)/Pd(II) ratio in Pd@PTPI-
Me was much higher than that of previous reported Pd catalysts,
which also played an important role in cyanation reaction.[27,29]
The excellent catalytic activity of Pd@PTPI-Me in cyanation
of iodobenzene promoted us to investigate the generality of such
catalytic system. A series of aryl iodides with different electronic
groups and steric hindrances were explored. As shown in Table
reaction. Due to the well-incorporated imidazole moieties in the
PTPI-Me frameworks, the Pd NPs were successfully grown and
uniformly dispersed on the polymeric scaffold, affording a stably
heterogeneous Pd@PTPI-Me catalyst. This Pd catalyst with only
.13 mmol g−1 Pd loading was highly active in the cyanation of
0
aryl iodides. Notably, the heterogeneous Pd@PTPI-Me catalyst
was recyclable without sacrificing the catalytic performance. This
study provides an effective strategy for the construction of POPs
supported Pd catalysts, which is general and applicable for other
heterogeneous catalysts.
2
, a promising yield was observed at 10 h when para-position of
iodobenzene was substituted by electron-withdrawing groups,
such as -NO , -CN, -COCH and -COOCH (Table 2, entry 1, 2,
, 5). However, the conversion of 2-iodobenzonitrile was slightly
2
3
3
4
decreased compared with 4-iodobenzonitrile owing to the steric
hindrance in the ortho-position (Table 2, entry 3). As expected,
the electron-donating substrates including 4-iodoanisole and 4-
iodoaniline gave slightly low yields even at a longer reaction time
Experimental Section
Materials and Instruments
(
Table 2, entry 8, 9). Most importantly, p-diiodobenzene could be
converted to 1,4-benzodinitrile at a relatively high yield with only
increasing K [Fe(CN) ] while keeping the same amount of Pd
Table 2, entry 6), which was promising for the application in
cyanation reaction.
All chemicals were purchased from Aladdin Reagent (Shanghai)
Co., Ltd. and used without further purification unless otherwise
noted. H NMR and 13C NMR spectra were recorded with a 400
MHz Bruker AV-400 NMR spectrometer. Solid-state 13C CP/MAS
NMR was performed on a Bruker SB Avance III 500 MHz
spectrometer with a 4 mm double-resonance MAS probe. FT-IR
4
6
1
(
spectra were recorded on
a Nicolet 6700 spectrometer.
Inductively coupled plasma atomic emission spectrometry (ICP-
AES) analyse was carried out on a Perkin Elmer Optima 5300
DV spectrometer. Thermogravimetric analysis (TGA) was carried
o
–1
out on a STA 449C instrument with a heating rate of 5 C min
–
1
under a N
2
flow rate of 60 mL min . The powder X-ray
diffraction (PXRD) patterns of the samples were collected on a
Rigaku/Max-2500PC X-ray diffractometer with Cu Kα radiation,
the operation voltage and current were maintained at 40 kV and
2
25 mA, respectively. The N adsorption/desorption isotherms
were characterized at 77 K using Micromeritics TriStar II 3020.
The specific surface area was obtained by Brunauer-Emmett-
Teller (BET) method. The pore size distribution was calculated
from the adsorption branches of the isotherms using the DFT
model. Scanning electron microscopy (SEM) images were
recorded using S-4800 (JEOL) operated at an acceleration
voltage of 10 kV. The transmission electron microscopy (TEM)
images were recorded on a JEM-1011 (JEOL) transmission
electron microscope operating at 100 kV. The X-ray
photoelectron spectroscopy (XPS) was performed on a K-Alpha
Figure 3. Recyclability of the Pd@PTPI-Me catalyst.
Recyclability is an important character for the heterogeneous
catalysts, which is also an intrinsic advantage of such catalysts
as compared to their homogeneous counterparts. With this in
mind, the recyclability of Pd@PTPI-Me was further studied using
the model reaction of iodobenzene transforming to benzonitrile.
In this case, the used Pd@PTPI-Me was simply recovered by
centrifugation, washing, followed by drying, and added to a new
reaction. As shown in Figure 3, the recovered catalyst displayed
a negligible decrease in catalytic activity after five cycles. The
TEM image of the collected Pd catalyst after five consecutive
cycles revealed no distinct aggregation of Pd NPs, indicating the
good stability of Pd NPs in the PTPI-Me frameworks (Figure S5).
These results demonstrated that the as-fabricated Pd@PTPI-Me
was an efficient heterogeneous Pd catalyst for the cyanation
reaction.
1063 photoelectron spectrometer (Thermo Fisher Scientific,
England) with Al-Kα X-ray radiation as the X-ray source for
excitation. The conversion of the iodobenzene was calculated
with an Agilent 5975 GC-MS instrument.
Synthesis of monomer (TPI-Me)
In a typical procedure, 4,4’-dibromobenzil (3.68 g, 100 mmol), 4-
bromobenzaldehyde (1.85 g, 100 mmol), ammonium acetate
(
2.31 g, 300 mmol) and 50 mL of acetic acid were added into
round-bottom flask successively. The mixture was refluxed for 6
h and a light yellow solution was obtained. After cooling to
ambient temperature, excessive deionized water was added to
the mixture and white precipitates was formed. After filtration
and recrystallized from ethyl acetate, the product TPI was
collected. Subsequently, methyl iodide (0.85 g, 6.0 mmol) was
Conclusions
In summary, we have prepared a triphenylimidazole-based
porous organic polymer (PTPI-Me) via Yamamoto homocoupling
2 3
added to the mixture of TPI (3.2 g, 6.0 mmol), K CO (2.5 g, 18
5
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Chemistry - An Asian Journal
10.1002/asia.201800681
FULL PAPER
mmol) and 20 mL of dry DMF at 0 °C for 0.5 h. Afterward, the
reaction was heated to reflux for 6 h. After the reaction was
complete, excessive water was added and a white solid was
precipitated. The TPI-Me monomer was obtained by filtration,
drying overnight and recrystallization from ethyl acetate (yield:
Keywords: porous organic polymers • polytriphenylimidazole •
Pd nanoparticles • heterogeneous catalyst • cyanation
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1
700263.
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Synthesis of porous organic polymer (PTPI-Me)
[
The porous organic polymer (PTPI-Me) was synthesized by
Yamamoto coupling reaction (Scheme 1). Typically, under the
protection of nitrogen, TPI-Me (0.55 g, 1.0 mmol), bis(1,5-
cyclooctadiene)nickel(0) (1.0 g, 3.6 mmol), 2,2’-bipyridyl (0.40 g,
[
[
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3.6 mmol), 1,5-cyclooctadiene (0.60 g, 3.6 mmol) and dry DMF
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(
38 mL) were added into a flask with a stirrer. The mixture was
1833-1839.
[
8] Y. Yuan, F.X. Sun, H. Ren, X.F. Jing, W. Wang, H.P. Ma, H.J. Zhao, G.S.
heated to 80 °C for 72 h, and a purple suspension was obtained.
After cooling to ambient temperature, the mixture was treated
with concentrated HCl, and the derived milky white suspension
was filtered and successively washed with NaOH solution (10%),
dichloromethane, methanol and petroleum ether. Finally, a light
yellow PTPI-Me (yield: 90.7%) was obtained after drying under
vacuum at 80 °C for 24 h.
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Synthesis of Pd@PTIP-Me
PTPI-Me (100 mg) was first dispersed in 5 mL of DMF, and then
1
−
1
0
.8 mL H
The mixture was refluxed at 100 °C for 5 h. After cooling to 0 °C,
excessive NaBH was added and stirred. The mixture was
2 4
PdCl aqueous solution (0.2 mol mL ) was added.
2
[
4
4
collected by centrifugation, and then washed with deionized
water and ethanol. Finally, the targeted catalyst Pd@PTIP-Me
was achieved by drying under vacuum at 80 °C for 24 h.
[
Chem. Int. Ed. 2014, 53, 2433-2437.
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[
General procedure for the catalytic reaction
The catalytic performance of the Pd@PTIP-Me was evaluated
by cyanation of aryl iodides. In a typical procedure, iodobenzene
[
3
(
9
0.4 mmol), K
mg of Pd@PTIP-Me and DMF (4 mL) were added into a
Schlenk tube under N atmosphere, and the mixture was heated
4 6 2 2 3
[Fe(CN) ]·3H O (0.1 mmol), Na CO (0.16 mmol),
[
[
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to 120 °C for 12 h. After the reaction was completed (monitored
by TLC), the mixture was cooled to room temperature, and the
solid catalyst was separated by centrifugation. The solution was
extracted with ethyl acetate, and the combined organic layer
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[
4
was dried over anhydrous MgSO . After evaporating off the
[
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solvent, the crude product was further purified by column
chromatography, and the structure was confirmed by 1H NMR
and 13C NMR spectra. The separated solid catalyst was washed
with ethanol and water for several times, and the recovered
catalyst was directly used for the next run with the addition of
fresh substrates. Conversion was estimated by an Agilent 5975
GC-MS instrument (EI).
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This work was financially supported by the National Natural
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Chemistry - An Asian Journal
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FULL PAPER
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Entry for the Table of Contents
FULL PAPER
Haiwen Yu, Siqi Xu, Yijiang Liu, *
Hongbiao Chen* and Huaming Li
Page 1. – Page 6.
Title: Porous Organic Polytriphenyl-
imidazole Decorated with Palladium
Nanoparticles for Cyanation of Aryl
Iodides
A novel porous organic polytriphenylimidazole (PTPI-Me) synthesized by Yamamoto
coupling was utilized as a heterogeneous platform for loading of ultrafine Pd NPs (2.7
−
1
nm). The resultant Pd@PTPI-Me catalyst with a Pd loading of 0.13 mmol g exhibited
superior catalytic activity and recyclability towards cyanation of aryl iodides, which is one
of the most efficient POP-supported Pd catalysts with such a low Pd loading.
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