Phenanthroline functionalized polyacrylonitrile fiber with Pd(0) nanoparticles as a highly active catalyst for the Heck reaction

Article abstract of DOI:10.1016/j.reactfunctpolym.2021.104843

A series of polyacrylonitrile fibers (PANF) functionalized with nitrogen-containing ligands were prepared and then used to synthesize fiber-supported Pd(0) nanoparticle catalysts. The phenanthroline-functionalized PANF with immobilized Pd(0) nanoparticles (PAN_PhenF-Pd(0)) had the best catalytic activity for the Heck reaction under solvent-free conditions. The PAN_PhenF-Pd(0) efficiently stabilized the nanoparticles and they were well-dispersed with Pd(0) particle sizes of about 3 nm. The PAN_PhenF-Pd(0) structure was further characterized by a variety of instrumental methods. A probable mechanism based on the fiber's microenvironment is proposed for the Heck reaction catalyzed by PAN_PhenF-Pd(0). The PAN_PhenF-Pd(0) catalyst is easily recovered from the reaction system and can be used up to six times with only a slight decrease in catalytic activity and with low Pd leaching. The PAN_PhenF-Pd(0) catalyst also has excellent catalytic activity for gram-scale use.

Full text of DOI:10.1016/j.reactfunctpolym.2021.104843

Reactive and Functional Polymers 161 (2021) 104843
Contents lists available at ScienceDirect
Reactive and Functional Polymers
journal homepage: www.elsevier.com/locate/react
Perspective Article
Phenanthroline functionalized polyacrylonitrile fiber with Pd(0)
nanoparticles as a highly active catalyst for the Heck reaction
*
Jian Xiao, Haonan Zhang, Anyaegbu Chima Ejike, Lu Wang, Minli Tao , Wenqin Zhang
Department of Chemistry, School of Sciences, Collaborative Innovation Center of Chemical Science and Engineering, Tianjin University, Tianjin 300072, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
A series of polyacrylonitrile fibers (PANF) functionalized with nitrogen-containing ligands were prepared and
then used to synthesize fiber-supported Pd(0) nanoparticle catalysts. The phenanthroline-functionalized PANF
with immobilized Pd(0) nanoparticles (PANPhenF-Pd(0)) had the best catalytic activity for the Heck reaction
under solvent-free conditions. The PANPhenF-Pd(0) efficiently stabilized the nanoparticles and they were well-
dispersed with Pd(0) particle sizes of about 3 nm. The PANPhenF-Pd(0) structure was further characterized by
a variety of instrumental methods. A probable mechanism based on the fiber’s microenvironment is proposed for
the Heck reaction catalyzed by PANPhenF-Pd(0). The PANPhenF-Pd(0) catalyst is easily recovered from the re-
action system and can be used up to six times with only a slight decrease in catalytic activity and with low Pd
leaching. The PANPhenF-Pd(0) catalyst also has excellent catalytic activity for gram-scale use.
Polyacrylonitrile fiber
Palladium nanoparticles
Heck reaction
Solvent-free
Gram-scale production
1
. Introduction
catalytic properties than homogenous catalysts, many of them have
chemical stability and poor recyclability. Therefore, preparing improved
The Heck reaction is an important method for forming C
–
C bonds
supports for Pd(0) nanoparticles is a valuable research area.
[
1], and has been used for the synthesis of many new types of drugs
Polyacrylonitrile fiber (PANF) is a cheap commercially available
synthetic fiber that has a soft texture and good mechanical strength [41].
It is made from at least 85% acrylonitrile and a copolymer which pro-
duces many cyano groups in the fibers. This makes PANF easy to modify
using common reactions. These excellent properties make PANF an ideal
carrier for heterogeneous catalysts. In our previous work, many func-
tionalized PANF-catalysts have been designed including PANF-
supported acid and base catalysts [42–48], PANF-supported inexpen-
sive metal catalysts [49,50], and PANF-supported phase transfer cata-
lysts [51]. All of these catalysts have excellent catalytic abilities with
good recyclability.
including montelukast (antiasthma agent), naproxen (anti-inflamma-
tory) [2], eletriptan (antimigraine) [3] and rilpivirine (anti-AIDS) [4].
Many organometallic catalysts have been used to efficiently catalyze
Heck reactions, such as compounds containing copper [5], nickel [6,7],
cobalt [8,9], and palladium [10–21]. Among them, palladium catalysis
are the most efficient and have been widely studied by researchers.
However, palladium is expensive and these catalysts are difficult to
recycle in homogeneous reaction systems. Additionally, as a heavy
metal, palladium is poisonous and can cause serious environmental
problems if it is released into nature [22]. From an economical and
environmental standpoint, it is of great importance to develop a recy-
clable palladium catalyst.
Interestingly, it has been shown that carriers containing organic li-
gands have a very positive impact on the dispersion and stability of Pd
(0) nanoparticles and on the catalytic activity of these Pd catalysts
[52–58]. Although aza ligands have weaker coordination abilities than
phosphine ligands, they are much cheaper than phosphine ligands and
can be easily immobilized on PANF [59–62]. Therefore, in this work, a
series of PANFs functionalized with aza ligands were prepared using a
simple method and then Pd(0) nanoparticles were stabilized on each of
these samples (Scheme 1). The catalytic activities of these PANF-Pd(0)
nanoparticle catalysts were investigated for the Heck reaction. The
Traditionally Pd(0) has played a vital role in catalyzing Heck re-
actions and the preparation of catalysts with supported Pd(0) particles
catalysts has found many applications [23,24]. Various carriers
including silica [25], GO [26,27], polymers [28–30], magnetic Fe
3 4
O
[
[
31–33], MOFs [34–36], carbon nanotube [37] and composite materials
38–40] have all been used to prepare heterogeneous palladium cata-
lysts. Compared with supported Pd(II) catalysts, these carriers can hold
Pd(0) more tightly. Although these heterogeneous catalysts have better
*
Corresponding author.
E-mail address: mltao@tju.edu.cn (M. Tao).
https://doi.org/10.1016/j.reactfunctpolym.2021.104843
Received 24 September 2020; Received in revised form 21 January 2021; Accepted 29 January 2021
Available online 3 February 2021
1
381-5148/© 2021 Elsevier B.V. All rights reserved.

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
[
a]
Scheme 1. PANF-supported Pd(0) nanoparticle catalysts
[
a] PANSAF-Pd(0) – secondary amine functionalized PANF with Pd(0) nanoparticles; PANTACDF-Pd(0) – 1,4,7,10-tetraazacyclododecane functionalized fiber with Pd
0) nanoparticles; PANPYF-Pd(0) – pyridine functionalized fiber with Pd(0) nanoparticles; PANIM-PYF-Pd(0) – o-pyridyl imino functionalized fiber with Pd(0)
nanoparticles; PAN
(
S
F-Pd(0) – salen ligand functionalized fiber with Pd(0) nanoparticles; PANPhenF-Pd(0) – phenanthroline functionalized fiber with Pd(0) nano-
particles; PANIMF-Pd(0) – imidazole functionalized fiber with Pd(0) nanoparticles; PANTETAF-Pd(0) – triethylenetetramine functionalized fiber with Pd(0)
nanoparticles.
Table 1
The functionalities of the different functionalized fibers.
Entry
Functionalized fibers
Functionality (mmol/g)
Entry
Functionalized fibers
Functionality (mmol/g)
1
2
3
4
5
6
7
8
9
PANSA
F
F
1.39
0.88
1.36
1.15
1.01
1.01
1.21
0.77
0.04
10
11
12
13
14
15
16
17
PANSAF-Pd(0)
PANPYF-Pd(0)
PANIM-PYF-Pd(0)
0.29
0.28
1.18
0.63
0.69
0.42
1.02
0.35
PANPY
PANIM-PY
PAN
PANPhen
PANOX
F
S
F
S
PAN F-Pd(0)
F
PANPhenF-Pd(0)
PANOXF-Pd(0)
PANTEPAF-Pd(0)
PANTACDF-Pd(0)
F
PANTETA
F
PANTACD
F
PANF-Pd(0)
catalysts were characterized and a possible mechanism is proposed.
. Results and discussion
by loading different aza ligands onto PANF and then chelating Pd(0)
nanoparticles to those ligands (Scheme S1). The amount of aza ligand
immobilized on the PANFs was calculated using the formula: function-
ality = [w%/[M×(1 + w%)] × 1000, where M is the molecular weight of
the corresponding aza ligands and w% is the weight gain of the original
fiber. The results are presented in Table 1 (Entries 2–8). The Pd(0)
content was measured by inductively coupled plasma optical emission
2
2
.1. Preparation and characterization of PANF-immobilized Pd catalysts
Nine PANF-immobilized Pd(0) nanoparticle catalysts were prepared
2

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
Fig. 1. The FTIR spectra of (a) PANF, (b) PANSAF, (c) PANPhenF, (d) PANPhenF-Pd(0), (e) PANPhenF-Pd(0)-1, (f) PANPhenF-Pd(0)-6.
Fig. 2. The XRD spectra of (a) PANF, (b) PANSAF, (c) PANPhenF, (d) PANPhenF-Pd(0) and (e) PANPhenF-Pd(0)-6.
spectrometry (ICP-OES) and those results are also shown in Table 1
Entries 9–17). These results show that the Pd(0) nanoparticles were
immobilized on all the PANFs functionalized with aza ligands
PANPhenF, PANPhenF-Pd(0), PANPhenF-Pd(0)-1 (PANPhenF-Pd(0) was
used for one time) and PANPhenF-Pd(0)-6 (PANPhenF-Pd(0) used 6 times)
are shown in Fig. 1. The two strong absorption peaks at 2244 and 1734
(
ꢀ 1
(
0.28–1.18 mmol/g) but not on the original PANF.
Fourier transform infrared spectroscopy (FTIR) was used to investi-
cm in the original fiber (Fig. 1a) can be attributed to the stretching
–
–
vibrations of C
–
N and C
–
O (in the methoxycarbonyl), respectively
′
gate the structures of the fibers and the FTIR spectra of PANF, PANSAF,
[44]. After the original fiber was modified by N,N -dimethyl-1,3-
3

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
Fig. 3. XPS (a) Survey spectrum of PANPhenF-Pd(0), (b) Pd 3d spectrum of PANPhenF-Pd(0), (c) Cl 2p spectrum of PANPhenF-Pd(0), (d) N 1 s spectrum of PANPhenF-Pd
(
0), (e) C 1 s spectrum of PANPhenF-Pd(0) and (f) O 1 s spectrum of PANPhenF-Pd(0).
4

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
Table 2
The elemental analysis data.
Entry
Fiber
Elemental analysis data
C (%)
H (%)
N (%)
1
2
3
4
5
PANF
66.19
58.91
60.13
53.25
53.49
5.98
6.65
6.45
5.60
5.75
24.38
20.78
20.38
17.21
17.35
PANSA
F
PANPhen
F
PANPhenF-Pd(0)
PANPhenF-Pd(0)-6
propanediamine (SA), two new peaks at 3414 and 1670 cm 1 appear
ꢀ
–
H and C
in the amide) respectively [44]. The peak at 1549 cm can be attrib-
N stretching and the N H bending
vibrations of C-N-H. The spectrum of PANPhenF has two new peaks at
–
O
(
Fig. 1b). These are due to the stretching vibrations of N
ꢀ 1
(
uted to interactions between the C
–
–
ꢀ
1
8
13 and 735 cm , which can be attributed to the deformation vibra-
–
tions of C C and the out-of-plane bending vibrations of the aromatic
–
C H respectively (Fig. 1c) [63]. There are no apparent changes in the
–
spectra of the recycled fibers, indicating that the catalyst have not
changed much after being used (Fig. 1d-1f).
X-ray diffraction (XRD) was used to determine the crystal structure of
the fibers and the XRD patterns of PANF, PANSAF, PANBAF, PANBAF-Pd
◦
(
0) and PANBAF-Pd(0)-6 are shown in Fig. 2. The two peaks at 16.8 and
◦
2
7.8 in PANF (curve a) can be attributed to the (100) and (110)
crystallographic planes of the PANF hexagonal lattice [41]. The spectra
for PANSAF and PANBAF (curves b and c) also contain these peaks
indicating the functionalized fibers have the same structure as the un-
modified PANF. The catalyst PANBAF-Pd(0) has a strong diffraction peak
◦
◦
◦
at 39.6 and two weak peaks at 46.6 and 67.1 (curve d), which can be
attributed to the (111), (200) and (220) facets of palladium, respectively
[
64,65]. The reused catalysts have the same characteristic Pd diffraction
peaks as the unused catalyst which demonstrates that the crystal
structures of the Pd(0) nanoparticles remains the same after being used
in six catalytic cycles.
Fig. 5. The TEM images of PANPhenF-Pd(0). Top row 4,000,000× and bottom
row 8,000,000× magnification.
X-ray photoelectron spectroscopy (XPS) was used to determine the
chemical properties of the surface of PANPhenF-Pd(0) and the results are
shown in Fig. 3. The full range XPS spectrum contains a peak due to Pd
two weak peaks at 342.9 and 337.9 eV can be attributed to Pd 3d3/2 and
Pd 3d5/2 from the residual Pd(II) in the fiber. The Cl 2p spectrum
(
Fig. 3a) which proves that Pd is present in the PANF. The Pd 2d spec-
(
Fig. 3c) contains no obvious peaks indicating that almost all the PdCl
2
trum in Fig. 3b contains two strong peaks at 340.7 and 335.4 eV which
corresponds to Pd 3d3/2 and Pd 3d5/2 of Pd(0), respectively [56]. The
in the fiber was reduced to Pd(0). The N 1 s spectra (Fig. 3d) has peaks at
Fig. 4. The SEM images of (a) PANF, (b) PANSAF, (c) PANPhenF, (d) PANPhenF-Pd(0) and (e) PANPhenF-Pd(0)-6. Top row 200×, middle row 2000× and bottom row
0,000× magnification.
2
5

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
Fig. 6. The thermal stability of (a) PANF, (b) PANSAF, (c) PANPhenF and (d) PANPhenF-Pd(0).
4
01.4 and 399.6 eV which can be attributed to the O=C-N and C
bonds in the functionalized fibers. The C 1 s spectrum (Fig. 3e) contains
two peaks at 286.0 and 284.7 eV which are due to the C O and C
bonds, respectively. Finally the O 1 s spectrum (Fig. 3f) has a strong peak
O, C–O and O–
–
N
Table 3
The catalytic activities of different fiber catalysts for the Heck reaction.
a, b
–
–
C
–
–
at 532.0 eV which is from the C
H bonds in PANPhenF-
Pd(0) [44]. These XPS spectra prove the successful preparation of the
functionalized fiber with immobilized Pd nanoparticles.
Entry
Catalyst
Catalyst loading
mol %)
Temp.
Time
(h)
Yield
(%)
In order to investigate the elemental composition of the fibers,
elemental analysis (EA) was performed and the results for PANF, PAN-
SAF, PANPhenF, PANPhenF-Pd(0) and PANPhenF-Pd(0)-6 are shown in
Table 2. Compared to PANF, PANSAF has less C and N and more H
◦
(
( C)
c
1
2
3
4
5
–
0.5
0.5
0.5
0.5
0.5
110
110
110
110
110
3
3
3
3
3
N.R.
PdCl
2
76
3
PANSAF-Pd(0)
PANPYF-Pd(0)
PANIM-PYF-Pd
(
Table 2, entries 1, 2). This is because the immobilized
CH NHCH CH CH N(CH )CO moiety contains less C and N and more H
than PANF. The PANPhenF sample containing an immobilized 5,6-epoxy-
,6-dihydro-[1,10]-phenanthroline moiety has more C and less N and H
76
86
3
2
2
2
3
(
0)
6
7
PAN
S
F-Pd(0)
0.5
0.5
110
110
3
3
79
97
5
PANPhenF-Pd
(0)
than PANSAF (entry 3) which again corresponds to the chemical makeup
of the moiety. When Pd nanoparticles were immobilized on the sample
to give PANPhenF-Pd(0), the amounts of C, H and N all significantly
decreased (entry 4). This can be attributed to the increased proportion
of palladium. The amounts of C, H and N after use in six catalytic cycles
did not change significantly indicating that the Pd(0) nanoparticles in
PANPhenF-Pd(0) remained relatively intact (Table 2, entry 5).
8
9
PANOXF-Pd(0)
PANTETAF-Pd
0.5
0.5
110
110
3
3
74
80
(
0)
PANTACDF-Pd
0)
1
a
0
0.5
110
3
73
(
General conditions: iodobenzene (1 mmol), acrylic acid (1.5 mmol), N(n-
(1.5 mmol).
The yields of the Heck reaction were determined using HPLC with naph-
4 9 3
C H )
b
In order to observe the microscopic appearance of the fiber surfaces,
scanning electron microscopy (SEM) images of PANF, PANSAF, PANPhen
F
thalene as the internal standard. The results are the average of three reaction
results.
and PANPhenF-Pd(0) are shown in Fig. 4. Under a magnification of 2000,
it can be seen that PANPhenF is thicker than PANF and PANPhenF-Pd(0) is
even thicker (a, c and d). This indicates that the fiber is swollen by the
solvent and chemical reagents during the modification process. After
being used in six catalytic cycles, PANPhenF-Pd(0)-6 became rougher as
seen under 20,000× magnification but no significant damage can be
seen at either 200× and 2000× magnification (Fig. 4e). This proves that
PANPhenF-Pd(0) has good tolerance for reuse.
c
N.R. is the abbreviation for no reaction.
8
,000,000× magnification to be about 3 nm. This confirms that the
nano-sized Pd(0)-immobilized fiber catalyst was prepared.
The thermal stability of PANF, PANSAF, PANPhenF and PANPhenF-Pd
(
0) were tested by thermogravimetric analysis (TGA) and the results are
shown in Fig. 6. The functionalized fibers only have a slight mass loss
Transmission electron microscopy (TEM) was used to determine the
particle size of the palladium nanoparticles in the fibers. The (TEM)
images of PANPhenF-Pd(0) under different magnifications are shown in
Fig. 5. The average size of Pd particles was determined under
◦
below 200 C, which is indicative of their excellent thermal stability.
Both PANSAF and PANPhenF had higher mass losses than PANF when the
◦
◦
temperature was increased from 30 to 670 C but they retained more
mass than PANF when further heated to 800 C. PANPhenF-Pd(0) had the
6

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
Table 4
a, b
Optimization of various parameters for the Heck reaction.
◦
c
Entry
Solvent
Catalyst loading
Dosage of acrylic acid
Base
Temp. ( C)
Time (h)
Yield (%)
TONs
1
2
3
4
5
6
7
8
9
H
2
O
0.5 mol%
0.5 mol%
0.5 mol%
0.5 mol%
0.5 mol%
0.5 mol%
0.5 mol%
0.5 mol%
0.1 mol%
0.1 mol%
0.1 mol%
0.05 mol%
0.1 mol%
0.1 mol%
0.1 mol%
0.1 mol%
1.5 eq
1.5 eq
1.5 eq
1.5 eq
1.5 eq
1.5 eq
1.5 eq
1.5 eq
1.5 eq
1.5 eq
1.5 eq
1.5 eq
2 eq
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
N(n-C
4
4
4
4
4
4
4
4
4
4
4
4
4
4
H
H
H
H
H
H
H
H
H
H
H
H
H
H
9
9
9
9
9
9
9
9
9
9
9
9
9
9
)
)
)
)
)
)
)
)
)
)
)
)
)
)
3
3
3
3
3
3
3
3
3
3
3
3
3
3
Reflux
110
3
3
3
3
3
3
3
3
3
2
3
3
3
3
3
3
3
6
DMF
96
1
192
2
MeOH
EtOH
Reflux
Reflux
reflux
reflux
reflux
110
3
6
CH
3
CN
4
8
1,4-dioxane
Cyclohexane
None
6
12
2
4
97
96
89
97
26
97
61
85
97
323
960
890
970
520
970
610
850
970
DMF
110
1
1
1
1
1
1
1
0
1
2
3
4
5
6
None
110
None
110
None
110
None
110
None
1.2 eq
1.5 eq
1.5 eq
110
None
N(C
2
H
5
)
3
110
d
None
N(n-C
4
H
9
)
3
110
a
b
c
General conditions: iodobenzene (1 mmol), base (1.5 mmol).
The yields of the Heck reaction were determined using HPLC with naphthalene as the internal standard. The results are the average of three reaction results.
The TON values were calculated by dividing the dosage of iodobenzene by the catalyst loading.
d
4 9 3
The dosage of N(n-C H ) is 2 eq.
◦
highest mass residue when heated to 800 C, which can be attributed to
the excellent thermal stability of the phenanthroline-Pd(0) complex.
These results indicate that PANPhenF-Pd(0) may be potentially useful for
use in heated reactions..
2
when there was no catalyst (Table 3, entry 1). Using PdCl as the
catalyst gave a moderate yield of 76% (entry 2). The different fiber-
supported Pd(0) nanoparticle catalysts gave yields between 3% and
99% (entries 3–11) with the highest yield being obtained for PANPhenF-
Pd(0) (entry 7). The differences may be attributed to the different sta-
bilities of the Pd(0) nanoparticles and the different Pd dispersions
caused by the various aza ligands. So the TEM Image of PANSAF-Pd(0)
has been detected, the result is shown in Fig. S1. Compared with
PANPhenF-Pd(0), it is obviously that Pd(0) nanoparticle was agglomer-
ated and has large particle size (over than 10 nm). The test can verify the
effect of ligands on Pd(0) nanoparticle. PANPhenF-Pd(0) was selected as
the optimal catalyst and used for further study.
2
.2. Catalytic activities of PANF-immobilized Pd(0) nanoparticle
catalysts
2
.2.1. The catalytic activities of various PANF-catalysts for the Heck
reaction
The catalytic activities of the different PANF-supported Pd(0) cata-
lysts for the Heck reaction were investigated using solvent-free condi-
tions and the results are shown in Table 3. The reaction did not proceed
Table 5
a,b
PANPhenF-Pd(0)-catalyzed Heck reaction of various substrates.
c
◦
Entry
X
R
1
R
2
Dosage of catalyst (mol%)
T ( C)
Time (h)
Product
Yield (%)
1
2
3
4
5
6
7
8
9
I
H
-COOH
-COOH
-COOH
-COOH
-COOH
-COOH
-COOH
-Ph
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
1.0
0.2
0.2
0.2/0.5
0.2
1.0
1.0
110
110
110
110
110
110
120
110/120
110
110
140
140
140
140
140
140
140
3
1a
1b
1c
1d
1e
1f
92
I
3-CN
4-CN
3
90
I
3
93
I
3-CF
4-NO
4-Br
3
3
95
I
2
3
95
I
3
94
I
3-CH
H
3
3
1 g
1 h
1i
91
I
3/1
3
43/90
91
I
H
-COOMe
-COO(CH
-COOH
-COOH
-COOH
-COOH
-COOH
-COOH
-COOH
10
11
12
13
14
15
16
17
I
H
2
) CH
3 3
2
1j
99
Br
Br
Br
Br
Br
Cl
Cl
H
24
5
1a
1b
1c
1e
1 g
1a
1e
23
3-CN
4-CN
92
4.5
1/0.5
5
94
4-NO
2
97/96
8
3-CH
H
3
5
N.R.
N.R.
4-NO
2
5
a
b
c
◦
4 9 3
H ) (1.5 mmol), PANPhenF-Pd(0) catalyst (0.1 mol%), 110 C.
General conditions: halogenated aromatics (1 mmol), olefins (1.5 mmol), N(n-C
Isolated yield.
◦
Reaction temperature 120 C.
7

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
Scheme 2. Possible mechanism for PANPhenF-Pd(0) catalyzed Heck reaction.
2
.2.2. The optimization of Heck reaction
and the results are shown in Table 5. These results show that the reac-
tivity of different halogenated aromatics is: iodo aromatics (entries 1
and 5) > brominated aromatics (entries 11 and 14) > chlorinated ar-
omatics (entries 16 and 17). In all cases, iodoaromatics were produced
with satisfactory isolated yields (90%–99%) (entries 1–10) under
solvent-free condition. Generally, the halogenated aromatics with
electron-withdrawing groups (entries 2–6, 12–14) had higher yields
than the substrates with electron-donating groups (entries 7 and 15).
Compared with other olefins (entries 1, 9 and 10), styrene (entry 8)
The conditions for the Heck reaction catalyzed by PANPhenF-Pd(0)
were optimized and the results shown in Table 4. First a variety of sol-
vents were tested and the only “solvents” that gave good results were
DMF and solvent-free conditions (Table 4, entries 1–9). Both N(n-
C
C
4
H
H
9
)
)
3
2 5 3
and N(C H ) were tested as bases and with no solvent N(n-
4
9
3
gave a higher yield (entries 11, 15). Next different catalyst
loadings were evaluated and the highest TON (970) was obtained for a
catalyst loading of 0.1 mol% (entry 8, 11 and 12). A longer reaction
time (3 h versus 2 h) is more conducive to the reaction (entries 10, 11).
Additionally, various of dosages of acrylic acid were investigated and
the optimal dosage is 1.5 eq (entries 12–14). Finally, different dosage of
◦
with a large steric hindrance had a low yield at 110 C (43%), but when
◦
the reaction temperature was increased to 120 C, a satisfactory yield of
90% was obtained. PANPhenF-Pd(0) can also selectively catalyze iodo-
benzenes that also contain another low-activity bromine atom with a
selectivity close to 100% under relative mild reaction conditions (entry
6). In summary, PANPhenF-Pd(0) has many advantages as a catalyst such
as low catalyst loading (0.1 mol%), short reaction times (1–5 h) and a
wide range of substrate applicability.
4 9 3
N(n-C H ) were explored, and the optimal dosage is 1.5 eq (entries 11
and 16). In summary, the highest yield and TON for the PANPhenF-Pd(0)
catalyst in the Heck reaction were achieved with 0.1 mol% catalyst
◦
loading, 1.5 eq alkenes, 1.5 eq base, no solvent, 110 C and 3 h (entry
1
1).
2
.3. Heck reaction catalyzed by PANPhenF-Pd(0)
2.4. Possible mechanism for PANPhenF-Pd(0) catalyzed Heck reaction
In order to determine the substrate scope for PANPhenF-Pd(0) in the
A possible catalytic mechanism based on the fiber microenvironment
is shown in Scheme 2. When no solvent is present, the concentration of
Heck reaction, several halogenated aromatics and olefins were tested
8

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
Fig. 7. Reusability test of PANPhenF-Pd(0). Reaction conditions: iodobenzene (10 mmol), acrylic acid (15 mmol), 15 mmol N(n-C
4
H
9
)
3
, 20 mL DMF, 0.1 mol%
◦
PANPhenF-Pd(0), 110 C. The yield was determined using HPLC.
Scheme 3. Gram-scale experiment of Heck reaction catalyzed by PANPhenF-Pd(0).
reactant is high. The organic amine and the Brønsted acid react to
generate an ionic liquid, which facilitates the reaction. The ionic liquid
endows the reaction system with a high concentration of anions and
cations, which can stabilize the reaction intermediates and increase the
activity of the reaction. When the high-polarity solvent DMF was used,
the fiber catalyst swelled causing the substrates and the Pd(0) nano-
particles to make good contact so the reaction proceed smoothly and a
high yield was obtained.
2.5. Reusability and gram-scale experiments
Reusability is a vital factor in evaluating the performance of the
catalyst. After each use, the fiber catalyst was taken out by tweezer,
washed with ethyl acetate and dried. The fiber was then used for the
next catalytic cycle. The PANPhenF-Pd(0) catalyst was reused for six re-
action cycles and the results are shown in Fig. 7. With each successive
cycle the yield decreased slightly from 96% to 87% after six uses. The
reused fiber has been characterized to determine if there were structural
or chemical changes in the fiber (Figs. 1, 2 and 4; Table 2).
Then ICP-MS was used to compare the amounts of Pd in PANPhenF-Pd
Table 6
Comparison of the Heck reaction of iodobenzene and acrylic acid with different catalyst systems.
◦
a
Entry
Catalyst
Catalyst Amount
Solvent
T ( C)
Time (h)
Yield (%)
Reuse times
Ref.
TON
1
2
3
4
5
AOFs-Pd(0)
0.8 mol%
2 mol%
DMF
110
100
90
3
95.5
96
3
[66]
[67]
[68]
[69]
[70]
119
49.5
1960
47
Pd (PNODAM-5)
heptane
22
2
3
Fe
3
O
4
@PCA/Pd(0)-b-PEG
0.05 mol%
2 mol%
H
2
O
98
10
5
PdNPore
MeOH
DMF
80
18
1
94
Pd/APS-MIL-101
0.93 wt%
120
about
–
–
9
7
6
7
8
9
Pd-MPTAT-1
0.97 mol%
3 mol%
H
2
O:EtOH = 1:1
reflux
140
80
6
95
81
99
96
96
95
92
97
2
4
–
[71]
98
Fe
Pd-SP-CMP
(Fe @ PUNP) magnetic microge
3
O
4
/SiO
2
/HPG-NCs
DMF
12
12
12
12
4
[72]
27
0.6 mol%
0.1 mol%
0.0229 mol%
0.5 mol%
1 mol%
1,4-dioxane/H
2
O = 1:1
[73]
165
960
1266
190
93
O
3 4
H
H
2
O
O
reflux
100
80
–
[74]
10
11
12
13
(Pd@IPN)
2
11
9
–
[75]
b
b
SBA-15/PrSO
3
Pd
toluene
DMF
[76]
TiO
2
@Pd NPs
140
110
10
3
[77]
PANPhenF-Pd(0)
0.1 mol%
Solvent-free or DMF
5
This work
970
a
b
Reuse times – number of times the catalyst can be reused before the yield drops 6%.
The reactants are iodobenzene and butyl acrylate.
9

J. Xiao et al.
Reactive and Functional Polymers 161 (2021) 104843
(
0) and PANPhenF-Pd(0)-6. The values were 0.69 mmol/g and 0.49
Acknowledgements
mmol/g respectively so there was a decrease of Pd of 29% indicating
that the fiber supported palladium catalyst still had many of its catalytic
sites after reuse. All of these results indicate that PANPhenF-Pd(0) has
good catalytic stability for repeated use.
This work was financially supported by the National Natural Science
Foundation of China (no. 21777111).
To demonstrate the practical applicability of this method for larger-
scale use, the Heck reaction catalyzed by PANPhenF-Pd(0) was carried
out on a gram-scale and the results are shown in Scheme 3. The dosage of
substrates were increased to 50 eq. The main product cinnamic acid was
washed with water and recrystallized in petroleum ether to give the final
product in 91% isolated yield.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.reactfunctpolym.2021.104843.
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Xiao Jian: Conceptualization, Data curation, Formal analysis,
Writing - original draft, Writing - review & editing. Haonan Zhang,
Anyaegbu Chima Ejike and Lu Wang: Writing - review & editing.
Minli Tao: Conceptualization, Writing - review & editing, Funding
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