Polymeric microsphere-loaded palladium-iminodiacetic acid complex as an efficient and easily recycled catalyst for Suzuki reaction in ionic liquid

Article abstract of DOI:10.1007/s11164-019-03738-y

Core-crosslinked shelled-core microspheres of poly(styrene-co-methyl acrylic acid) (PS-co-PMAA), with cores rich in PS and the shell rich in PMAA, were synthesized by one-stage soap-free emulsion polymerization. A palladium (Pd)-iminodiacetic acid (IDA) complex catalyst is loaded on the shell of the PS-co-PMAA microsphere, which results in the advantage of high dispersion degree and, therefore, high activity. The resultant polymeric microspheres catalyst systems are then applied to catalyze the Suzuki reaction of aryl halides with phenylboronic acid in an ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF₄]). Our catalyst systems are proved to be efficient and active for both aryl bromides and aryl iodides. Compared to traditional Pd(Ph3)₄ catalyst, the PS-co-PMAA-IDA-Pd catalyst used here affords higher yield of Suzuki reaction at even lower catalyst concentration. In addition, our polymeric-microsphere based catalytic system can be easily recycled at least four times with high activity in ionic [bmim][BF₄] liquid.

Full text of DOI:10.1007/s11164-019-03738-y

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-03738-y
Polymeric microsphere‑loaded palladium‑iminodiacetic
acid complex as an efcient and easily recycled catalyst
ꢀor Suzuki reaction in ionic liquid
1
2
1
1
Jianzheng Zhang · Jingshuai Chen · Qiuyu Zhang · Rumin Wang ·
Songhua Wu3
Received: 5 September 2018 / Accepted: 12 January 2019
©
Springer Nature B.V. 2019
Abstract
Core-crosslinked shelled-core microspheres of poly(styrene-co-methyl acrylic acid)
(
PS-co-PMAA), with cores rich in PS and the shell rich in PMAA, were synthesized
by one-stage soap-free emulsion polymerization. A palladium (Pd)-iminodiacetic
acid (IDA) complex catalyst is loaded on the shell of the PS-co-PMAA microsphere,
which results in the advantage of high dispersion degree and, therefore, high activ-
ity. The resultant polymeric microspheres catalyst systems are then applied to cata-
lyze the Suzuki reaction of aryl halides with phenylboronic acid in an ionic liquid
of 1-butyl-3-methylimidazolium tetraꢀuoroborate ([bmim][BF ]). Our catalyst sys-
4
tems are proved to be eꢁcient and active for both aryl bromides and aryl iodides.
Compared to traditional Pd(Ph3) catalyst, the PS-co-PMAA-IDA-Pd catalyst used
4
here aꢂords higher yield of Suzuki reaction at even lower catalyst concentration. In
addition, our polymeric-microsphere based catalytic system can be easily recycled at
least four times with high activity in ionic [bmim][BF ] liquid.
4
Keywords Iminodiacetic acid · Ionic liquid · Microsphere · Palladium · Suzuki
reaction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4
-019-03738-y) contains supplementary material, which is available to authorized users.
Jianzheng Zhang and Jingshuai Chen have contributed equally to this work.
*
Jingshuai Chen
chen_jshuai@ahu.edu.cn
*
Qiuyu Zhang
qyzhang@nwpu.edu.cn
Extended author information available on the last page of the article
Vol.:(012
1
3456789)
3

J. Zhang et al.
Introduction
The palladium-catalyzed cross-coupling of aryl halides with arylboronic acids,
known as the Suzuki reaction, represents a straightforward and highly eꢂec-
tive method for carbon–carbon bond formation in synthesis of biaryl com-
pounds [1–3]. Since their discovery in 1981, extensive eꢂorts have been made to
develop highly active and selective catalytic systems for Suzuki reactions [4–6].
The traditional Suzuki reaction usually proceeds using phosphine-based pal-
ladium catalysts [7–10]. The phosphine-based ligands are highly toxic and dif-
ꢃcult to manipulate since they are air/moisture sensitive. Many attempts have
been made to develop phosphine-free ligands. Alternative suitable ligands such
as thioether–NHC [11] , nucleophilic carbene [12], carbapalladacycle [13], phos-
phanylferrocene ligand [14], mesoionic carbine [15] amide ligand [16] and meta-
hydroxylated imine ligand [17] for palladium catalysts were reported. Moreover,
various scaꢂolds such as silica [18, 19], ZrIV organophosphonate [20], function-
alized grapheme [21], magnetic particles [22, 23], polymeric microspheres and
microcapsules [24], and soluble single polymer chains [25] have been employed
to immobilize palladium to enhance the reusability of the ligand-stabilized pal-
ladium catalyst.
A concern of the Suzuki reaction is extensive use of environmentally harmful
organic solvents. Recently, there has been considerable interest in the use of ionic
liquids as an environmentally benign reaction medium [26–29]. Numerous chemi-
cal reactions, including some enzymatic reactions [28], can be carried out in ionic
liquids. Room temperature ionic liquids have also been widely explored as media
for electrochemical technologies, chemical extractions, and other industrial pro-
cesses. This is due to several intriguing properties of ionic liquids: high thermal
and chemical stability, no measurable vapor pressure, inꢀammability. Ionic liq-
uids, such as 1-butyl-3-methylimidazolium tetraꢀuoroborate ([bmim][BF ]), have
4
also proved to be environmentally benign choices. Moreover, the products can be
separated from the ionic liquid phase through simple extraction with ether or hex-
ane, while the catalytic systems remain in the ionic liquid phase.
Many groups have focused on using polymeric colloid as a catalyst scaꢂold
and found that a colloid-loaded palladium catalyst combines the merits of a read-
ily recovered heterogeneous catalyst and a highly eꢁcient homogeneous catalyst
[
30, 31]. Here, poly(styrene-co-methylacrylic acid) (PS-co-PMAA) shelled-core
microspheres were synthesized by one-stage soap-free emulsion polymerization
[
32]. Then, the catalyst of palladium-iminodiacetic acid (Pd-IDA) complex was
immobilized on the shell of the polymeric microsphere (Scheme 1). Finally, the
activity of the resultant microsphere-loaded Pd-IDA catalyst was evaluated by
the Suzuki reaction, performed in an ionic liquid of [bmim][BF ]. The catalysis
4
demonstrates the eꢁciency of the shelled-core Pd-IDA complex-loaded PS-co-
PMAA microspheres and that they are easily reused in ionic [bmim][BF ] liquid.
4
By comparison, the catalyst presented here has three advantages. First, cheap and
stable iminodiacetic acid, instead of a toxic and air/moisture sensitive phosphine-
based ligand, is used. Second, the Pd-IDA catalyst complex is loaded on the outer
1
3

Polymeric microsphere‑loaded palladium‑iminodiacetic…
1
) EDC, sulf-NHS
1) pH=9.5
2) PdCl
2) IDA
2
Scheme 1 Schematic synthesis of the shelled-core IDA-Pd complex-loaded PS-co-PMAA microspheres
PS-co-PMAA-IDA-Pd)
(
shell of the core–shell microspheres, which is helpful for mass transition dur-
ing the Suzuki reaction. Last, the 480-nm core–shell microsphere scaꢂold can be
fully dispersed in the ionic [bmim][BF ] liquid, which results in the advantage of
4
high dispersion degree and, therefore, high activity.
Experimental details
Materials
An ionic liquid of 1-butyl-3-methylimidazolium tetraꢀuoroborate ([bmim][BF ])
4
was synthesized as described elsewhere [33]. Monomers of styrene (St,>98%,
Tianjin Chemical Company, China) and methyl acrylic acid (MAA,>99%, Tianjin
Chemical Company) were distilled under vacuum before being used. Divinylben-
zene (DVB,>80%, Alfa Aesar) was washed in 5% aqueous sodium hydroxide solu-
tion and water, followed by drying with MgSO . Iodobenzene (>98%, Alfa Aesar),
4
4
-iodophenol (>99%, Shanghai Bangcheng Chemical Co., Ltd., China), 4-iodoben-
zoic acid (>99%, Shanghai Bangcheng Chemical), 4-iodobenzaldehyde (>99%,
Shanghai Bangcheng Chemical), 4-iodoanisole (>99%, Shanghai Bangcheng Chem-
ical), bromobenzene (>99%, China National Pharmaceutical Group Corporation),
4
4
4
4
-bromoacetophenone (>99%, Alfa Aesar), 3-bromotoluene (>99%, Alfa Aesar),
-bromophenol (>99%, Tianjin Guangfu Fine Chemical Research Institute, China),
-bromobenzoic acid (>99%, Beijing Henye Fine Chemical Co., Ltd., China),
-bromoanisole (>99%, Tianjin Chemical Company, China), 4-chloronitrobenzene
(
>99%, China National Pharmaceutical Group Corporation), PdCl (>99.99%, Alfa
2
Aesar), phenylboronic acid (>99%, Beijing Wisdom Chemicals Co., Ltd., China),
-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl,>99%,
Shanghai Convachem Co., Ltd., China), N-hydroxysulfosuccin-imide sodium salt
sulfo-NHS,>99%, Shanghai Convachem Co., Ltd.), iminodiacetic acid (IDA,
1
(
>
99%, Tianjin Guangfu Fine Chemical Research Institute), tetrabutylammonium
bromide (TBAB,>99%, Tianjin Guangfu Fine Chemical Research Institute) and
triethylamine (NEt ,>99%, Tianjin Chemical Company) were all used as received.
3
Double-distilled water was used in the following experiments. Other analytical rea-
gents were used as received.
1
3

J. Zhang et al.
Synthesis of shelled‑core PS‑co‑PMAA‑IDA microspheres
The shelled-core PS-co-PMAA microspheres were synthesized from styrene and
MAA by one-stage soap-free polymerization, and the synthetic route is similar to
that introduced in a previous paper [32]. The resultant colloid was diluted and the
carboxyl group concentration in the dispersion was calculated to be 0.12 mol/L.
The functionalization method of PS-co-PMAA-IDA microspheres has been
reported in our published article [34]. After the reaction was over, the dispersion
was kept at room temperature for 36 h. Next, the dispersion was centrifuged and
the precipitate phase was collected.
Synthesis of palladium‑iminodiacetic‑acid‑complex‑loaded PS‑co‑PMAA
microspheres
After dispersing the collected precipitate in 100 mL of distilled water, 0.408 g
PdCl was added and the mixture was allowed to stand for 12 h at room tempera-
2
2
+
ture. The dispersion was then centrifuged to concentrate the Pd in the upper
liquid phase, which was measured by atomic absorption spectrum (AAS), and the
collected precipitate was again dispersed in 200 mL water. The resulting micro-
sphere palladium-loading concentration was calculated to be 0.745 mg/mL.
General procedures for the Suzuki reaction
Aliquots of 1.0 mmol aryl halide, 3.0 mL of the catalytic dispersion and 3.0 mL
[
emim] [BF4] were added to a screw-capped vial with a side tube. The mixture
was degassed under nitrogen purge for 10 min at room temperature, then slowly
heated to 110 °C with vigorous stirring for 0.5 h to activate the reactants, as
described elsewhere [35]. Next, the mixture was cooled to room temperature.
Then, then 0.18 g phenylboronic acid (1.5 mmol) and, 0.40 mL NEt (3.0 mmol)
3
were added. The mixture was again degassed under nitrogen purge for 10 min.,
after which the vial was bathed in preheated oil at a set temperature and mag-
netically stirred under nitrogen. After the reaction was complete, the mixture was
cooled to room temperature rapidly. Using diethyl ether (3 × 20 mL), the product
was extracted from the reaction mixture, then washed with water. The organic
phase was collected, concentrated, and the subsequent product dried under vac-
1
uum at 40 °C, before weighing and analysis by HNMR.
Characterization
Transmission electron microscopy (TEM) was employed to observe the morphol-
ogy of the microsphere and the polymeric-microsphere-supported catalyst. A
small drop of the sample was deposited onto a carbon-coated copper grid and
dried at room temperature under atmospheric pressure, then TEM was conducted
using a Philips T20ST electron microscope at an acceleration voltage of 200 kV.
1
3

Polymeric microsphere‑loaded palladium‑iminodiacetic…
The IR measurements were performed on a Bio-Rad FTS-6000 IR spectrometer.
1
Using CDCl or DMSO as solvent, H NMR spectra was applied and recorded on
3
2
+
a UNITY PLUS-400 spectrometer to measure the yield of the reaction. The Pd
concentration in aqueous solution was measured by atomic absorption spectrum
AAS), using a Solaar AAS 2 atomic absorption spectrometer.
(
Results and discussion
Synthesis and characterization of shelled‑core, palladium‑catalyst‑loaded
PS‑co‑PMAA microspheres
By one-stage soap-free polymerization with styrene (St) and methyl acrylic acid
(
MAA) in water, the shelled-core PS-co-PMAA microspheres containing a PS-
rich core and a PMAA-rich shell were fabricated. A 5 wt% cross-linker of DVB
was added in order to enhance the stability of the polymeric scaꢂold. As shown
in Fig. 1, the cross-linked PS-co-PMAA microspheres with a shelled-core struc-
ture can be clearly distinguished. The average diameter of the cross-linked PS-co-
PMAA is 480 nm and the diameter of the core is about 350 nm. Before loading
the iminodiacetic acid (IDA) ligand onto the thin shell of PMAA to form IDA-
functionalized shelled-core microspheres (PS-co-PMAA-IDA), part of the car-
boxyl groups in the PMAA shell were pre-activated with 1-ethyl-3-(3-dimethyl-
aminopropyl)carbodiimide hydrochloride (EDC·HCl). This intermediate product
was followed by treatment with N-hydroxysulfosuccin-imide sodium salt (sulfo-
NHS) [34]. The IR spectra of the shelled-core PS-co-PMAA microspheres before
and after being functionalized (Figure S1) indicate the characteristic absorption
Fig. 1 TEM image of the PS-co-PMAA mircrospheres
1
3

J. Zhang et al.
at 1650 cm− and 860 cm is due to C=O stretching-vibration of the acylamide
group in the pendant IDA. Thus, the formation of functionalized microspheres of
PS-co-PMAA-IDA is conꢃrmed.
1
−1
2
+
It is well known that IDA can strongly coordinate with Pd [36], so the IDA-
Pd-complex-loaded PS-co-PMAA microsphere (PS-co-PMAA-IDA-Pd) cata-
lyst forms when the functionalized microspheres of PS-co-PMAA-IDA are dis-
persed in PdCl aqueous solution. To further conꢃrm loading of IDA-Pd complex
2
on the shell of the PS-co-PMAA microspheres, excess NaBH aqueous solution
4
was added to the dispersion of the IDA-Pd-complex-loaded PS-co-PMAA micro-
2
+
spheres to reduce the ions of Pd to Pd(0). As shown in Fig. 2, the 3-nm nano-
particles synthesized in situ are mainly embedded in the shell of the shelled-core
PS-co-PMAA microspheres where IDA was mainly distributed.
As introduced in the Experimental section, the molar ratio of PdCl to PMAA
2
was 1:1. The added PdCl is excessive for IDA, because the PMAA segment on
2
the surface of the PS-co-PMAA microspheres cannot completely react with IDA.
2
+
In the experimental process, the concentration of Pd loaded onto the functioned
microspheres of PS-co-PMAA-IDA is 0.85 mmol/g, which is calculated based on
2
+
the Pd concentration in the centrifugal aqueous solution as measured by atomic
absorption spectrum (AAS). AAS suggests that only 60% carboxyl groups in the
shell-forming PMAA segment of the PS-co-PMAA microspheres are modiꢃed by
IDA. The unmodiꢃed carboxyl groups in the shell-forming PMAA segment are
useful to disperse the IDA-Pd catalyst in polar solvents, such as water (especially
in basic aqueous solution), ethanol and in ionic [bmim][BF ] liquid, forming a
4
stable colloidal dispersion. In fact, the concentration of the functionalized PS-co-
PMAA-IDA microspheres in colloidal dispersion of [bmim][BF ]/H O mix (1:1
4
2
by volume) is as high as 25 mg/mL at room temperature.
Fig. 2 TEM images of the palladium nanoparticles loaded on a shell-layer of the functioned micro-
spheres of PS-co-PMAA-IDA microspheres
1
3

Polymeric microsphere‑loaded palladium‑iminodiacetic…
Suzuki reaction via the PS‑co‑PMAA‑IDA‑Pd catalyst in [bmim][BF ]/H O mixture
4
2
As a model system in preliminary catalytic studies, we observed the Suzuki reaction
of 4-bromoacetophenone and phenylboronic acid in a mixture of [bmim][BF ]/H O
4
2
(
1:1 by volume) at temperatures ranging 80–110 °C, in the presence of 1.0 mol%
PS-co-PMAA-IDA-Pd catalyst and 3 equiv. of various bases [Na CO , NaOH and
2
3
triethylamine (NEt )]. Here, it should be pointed out that the mixture of [bmim]
3
[
BF ]/H O instead of the pure ionic liquid of [bmim][BF ] is used as the reaction
4
2
4
medium since the PS-co-PMAA-IDA-Pd catalyst is dispersed in aqueous solution.
We found that the PS-co-PMAA-IDA-Pd catalyst can be “homogenously” dispersed
in the [bmin][BF ]/water solvent mix just as a homogenous catalyst does at or above
4
room temperature. By contrast, the substrates of aryl halides and the resultant biar-
yls cannot be dissolved in [bmin][BF ]/water solvent mix at room temperature. At
4
or above 80 °C, the aryl halides and the resultant biaryls become soluble. The great
diꢂerence in the solubility between the aryl halides and biaryls with the PS-co-
PMAA-IDA-Pd catalyst is very useful in separating the resultant product from the
reaction mixture, and reuse of the catalyst. The catalysis results are recorded in
Table 1, and show that the bases used have little eꢂect on the biaryl yields. Of the
bases tested, NaOH and NEt resulted in highest coupling yields after 4 h (Table 1,
3
entries 1–3). Compared with the bases, temperature has much greater eꢂect on
biaryl yields (Table 1, entries 4–6). For example, the yield of 4-acetylbiphenyl is just
5
8% at 80 °C in 1 h. (Table 1, entry 4), which increases to 99% at 110 °C in 30 min
(
Table 1, entry 6).
In following experiment, unless otherwise speciꢃed, the Suzuki reactions were
performed in the [bmim][BF ]/H O mix at 110 °C in the presence of 1.0 mol %
4
2
PS-co-PMAA-IDA-Pd catalyst and 3 equiv. NEt .
3
With the optimized conditions in hand, the Suzuki coupling reaction of phenylbo-
ronic acid was tested with a wide range of substrates, such as iodinated, brominated
and chlorinated aromatic compounds. The results are summarized in Table 2 and
indicate that the catalytic system is highly active for both aryl bromides and aryl
iodides, especially aryl iodides. Corresponding biaryl yields are greater than 95%
between 0.5 and 4 h (Table 2, entries 1–11). Furthermore, we found the catalytic
activity of PS-co-PMAA-IDA-Pd is almost as eꢁcient as the homogeneous IDA-
Pd catalyst (data not shown). However, respective yields for the aryl chlorides of
Table 1 Suzuki reactions on
Yield (%)a
Entry
Base
Time (h)
T (°C)
4
-bromoacetophenone by
phenylboronic acid in [bmim]
BF ]/H O under various
1
2
3
4
5
6
Na CO
4
4
4
1
1
0.5
80
80
80
80
95
92
99
99
58
86
99
2
3
[
4
2
NEt3
NaOH
NEt3
NEt3
NEt3
reaction conditions
110
a
1
Isolated yield and purity of the isolated product being conꢃrmed by
H NMR
1
3

J. Zhang et al.
a
Table 2 Suzuki reactions via the catalyst of PS-co-PMAA-IDA-Pd in [bmim][BF ]/H O
4
2
1
.0 mol.% Pd catalyst
R
X
B(OH)
2
R
NEt , [Bmim][BF
3
4
]
Entry
Substrate
Product
Time (h)
0.5
Yield (%)b
99 (95c)
99
1
2
3
4
5
I
I
CHO
CHO
0.5
0.5
74 (99d)
97
I
COOH
OH
COOH
OH
I
0.5
3
0.5
84 (95e)
I
OCH
Br
OCH
3
6
7
8
0.5
0.5
1
99 (95c)
99 (97c)
25 (99f)
Br
COCH
3
COCH
3
Br
COOH
OH
COOH
d
g
9
Br
1
77 (98 , 98 )
1
0
1
Br
OH
1
1
99
c
h
1
Br
OCH
3
OCH3
51 (92 , 96 )
1
2
3
Cl
NO
2
NO
2
12
12
68i
13i
1
Cl
COCH
3
COCH
3
a
Reaction conditions: aryl halide (1.0 mmol) and boronic acid (1.5 mmol, 1.5 eq.), NEt3 (3.0 mmol,
3
eq.), 3.0 mL of colloidal dispersion containing 1.0 mol% Pd catalyst, oil bath temperature at 110 °C
b
1
Isolated yield and purity of the isolated product was conꢃrmed by H NMR
c
The data are from Ref. [35]. Reaction conditions: aryl halide (2.5 mmol), boronic acid (2.75 mmol),
Na CO (5.28 mmol), 2.5.0 mL of H O, 5 mL of [bmim][BF ], 1.2 mol % Pd(Ph ) catalyst, 110 °C, 3 h
2
3
2
4
3 4
d
e
f
The reaction time was extended to 2 h
The reaction time was extended to 1 h
The reaction time was extended to 6 h
g
The data are from Ref. [37]. Reaction conditions: aryl halide (0.5 mmol), boronic acid (0.75 mmol),
K PO ·3H O (1.5 mmol), PdCl (5 mol %), toluene 3 mL, 100 °C, 8 h
3
4
2
2
h
The reaction time was extended to 4 h
i1.0 mmol of TBAB was used
1
3

Polymeric microsphere‑loaded palladium‑iminodiacetic…
4
-chloronitrobenzene and 4-chloroacetophenone (Table 2, entries 12 and 13), are
only 68% and 13%, despite adding one equiv. of TBAB and prolonging reaction time
to 12 h.
As shown in Table 2, the activity of the aryl halides decreases in the order of
I>Br>Cl. Moreover, the substituting groups of aryl halides have signiꢃcant inꢀu-
ence on their activity. The electron-deꢃcient aryl halide is generally more active
than the electron-rich one, excepting 4-iodobenzoic acid and 4-bromobenzoic acid
(
Table 2, entries 3 and 8). A possible cause is electrostatic repulsion between the
electronegative substrates and the catalyst scaꢂold of the PS-co-PMAA micro-
spheres in basic conditions.
Catalysis results were compared with those obtained by Mathews et al. using a
homogeneous Pd(Ph3) catalyst under very similar conditions. The PS-co-PMAA-
4
IDA-Pd catalyst used here aꢂords slightly higher yield than the Pd(Ph3) catalyst
4
of Mathews et al. [35] and does so at lower Pd catalyst concentration (1.0 mol% vs.
1
.2 mol%). When iodobenzene (Table 2, entry 1), bromobenzene (Table 2, entry 6)
and 4-bromoacetophenone (Table 2, entry 7) were used as substrate, the novel cata-
lyst also yielded much more quickly (0.5 h vs.. 3 h). When 4-bromoanisole is sub-
strate, PS-co-PMAA-IDA-Pd and Pd(Ph3) catalyst activity is similar (Table 2, entry
4
1
1). Compared with PdCl catalyst [37], the PS-co-PMAA-IDA-Pd catalyst have
2
higher activity. For example, when m-bromomthyl benzene (Table 2, entry 9) were
used as substrate, The PS-co-PMAA-IDA-Pd catalyst had the same yield at lower Pd
catalyst concentration (1.0 mol % vs. 5.0 mol %) and shorter time (2 h vs. 8 h). As
anticipated, the nature of PS-co-PMAA-IDA markedly inꢀuences the reaction out-
come. As the well-accepted mechanism of the Suzuki reaction [38], the ꢃrst key step
is the formation of a PdII(aryl)(halide) species. The IDA-Pd catalyst dispersed on
the surface of the PS-co-PMAA microspheres is favorable for the formation of PdII
species which are stabilized in the ILs. Yield eꢁciency and activity results suggest
that this novel PS-co-PMAA-IDA-Pd catalyst is a promising alternative.
For heterogeneous catalysts, an essential insight is whether the active metal
migrates from solid to liquid phase, since thus-leached Pd will become signiꢃcantly
responsible for the extent of catalytic activity. To explore possible catalyst leaching,
a Suzuki reaction on 4-bromoacetophenone with benzeneboronic acid was carried
out in [bmim][BF ]/H O mix (1:1 by volume), in the presence of 0.10 mol % of
4
2
PS-co-PMAA-IDA-Pd catalyst until conversion reached 64% at 1 h. At that point,
the PS-co-PMAA-IDA-Pd catalyst solid was ꢃltered out at reaction temperature.
The remaining liquid phase was allowed to react again, with conversion slightly
increasing from 64 to 71% in 2 h, as shown in Fig. 3. These observations indicate
that minimal Pd catalyst leaches into the liquid phase of [bmim][BF ]/H O. Herein,
4
2
it should be pointed out that a relatively low PS-co-PMAA-IDA-Pd catalyst con-
tent of 0.10 mol% was used to perform the Suzuki reaction of 4-bromoacetophe-
none with benzeneboronic acid, in sustained steady conditions over 3 h, as shown in
Fig. 3. When a high PS-co-PMAA-IDA-Pd catalyst content of 1.0 mol % was used,
the relative catalyst leached was negligible.
Last, we transfer our attention to recycling of the PS-co-PMAA-IDA-Pd cat-
alyst. As discussed, the catalyst of PS-co-PMAA-IDA-Pd exists as a colloid in
the [bmin][BF ]/water mix at room temperature, while most of aryl halides and
4
1
3

J. Zhang et al.
1
00
8
6
4
2
0
0
0
0
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (hour)
Fig. 3 Time conversion plot for the Suzuki reaction of 4-bromoacetophenone with benzenboronic acid in
the presence of 0.10 mol % PS-co-PMAA-IDA-Pd catalyst (triangle) and after removal of the catalyst by
ꢃltration (square) at 90 °C
Table 3 Reuse of the catalyst
Cycles
Fresh
99
1st
99
2nd
97
3rd
96
of PS-co-PMAA-IDA-Pd in
a
[
bmim][BF ]/H O
Yield (%)b
4
2
a
Reaction condition is as same as shown in entry 7, Table 2
b
1
Isolated yield and purity of the isolated product being conꢃrmed by
H NMR
the synthesized biaryls are not at all soluble, which makes reuse of the catalyst
easy. After the catalytic reaction was stopped, the reaction system was cooled to
room temperature, and extraction was performed with diethyl ether. The residual
aryl halides and the synthesized biaryls transfer to ether phase, while the PS-co-
PMAA-IDA-Pd catalyst remains in the [bmin][BF ]/water mix. To test the reus-
4
ability of the PS-co-PMAA-IDA-Pd catalyst in [bmim][BF ], a Suzuki reaction
4
on 4-bromoacetophenone by phenylboronic acid was chosen as a typical example.
Catalysis results for this reaction appear in Table 3, where the isolated yield of
4
-acetylbiphenyl is as high as 96% in the fourth cycle, conꢃrming high reusability
for PS-co-PMAA-IDA-Pd catalyst in [bmin][BF ]/water mix.
4
Conclusions
In summary, shelled-core PS-co-PMAA microspheres were prepared via one-stage
soap-free polymerization method. Through modiꢃcation of the shelled-core PS-co-
PMAA microspheres, an IDA-Pd complex was loaded on the microsphere shell to
1
3

Polymeric microsphere‑loaded palladium‑iminodiacetic…
form a PS-co-PMAA-IDA-Pd-loaded microsphere catalyst. This catalytic system
can be used as a highly eꢁcient and easily recycled catalyst for Suzuki reaction
performed in ionic 1-butyl-3-methylimidazolium tetraꢀuoroborate ([bmim][BF ])
4
liquid.
Acknowledgements This work was supported by the National Natural Science Foundation of China
(
Grant Nos. 21706002), Natural Science Foundation of Anhui Province (1808085QB53), and the
Research Fund of School of Chemistry and Chemical Engineering (Anhui University).
References
1
2
3
4
5
6
.
.
.
.
.
.
N. Miyaura, T. Yanagigand, A. Suzuki, Synth. Commun. 11, 513 (1981)
A. Suzuki, J. Organomet. Chem. 576, 147 (1999)
J. Hassan, M. Sevignon, C. Gozzi, E. Schulz, M. Lemaire, Chem. Rev. 102, 1359 (2002)
L. Yin, J. Liebscher, Chem. Rev. 107, 133 (2007)
Z.C. Xiong, N.D. Wang, M. Dai, A. Li, J.H. Chen, Z. Yang, Org. Lett. 6, 3337 (2004)
L.L. Zhang, Y.L. Guo, A. Iqbal, B. Li, M. Deng, D.Y. Gong, W.S. Liu, W.W. Qin, J. Nanopart. Res.
1
9, 150 (2017)
7
8
9
.
.
.
R.B. Bedford, S.J.C. Cazin, S.L. Hazelwood, Angew. Chem. Int. Ed. 114, 4294 (2002)
J.P. Stambuli, R. Kuwano, J.F. Hartwig, Angew. Chem. Int. Ed. 41, 4746 (2002)
R.B. DeVasher, L.R. Moore, K.H. Shaughnessy, J. Org. Chem. 69, 7919 (2004)
1
1
1
0. J.H. Kirchhoꢂ, C. Dai, G.C. Fu, Angew. Chem. Int. Ed. 114, 2025 (2002)
1. K.N. Sharma, N. Satrawala, R.K. Joshi, Eur. J. Inorg. Chem. 16, 1743 (2018)
2. M. Ibrahim, I. Malik, W. Mansour, M. Sharif, M. Fettouhi, B.E. Ali, J. Organomet. Chem. 859, 44
(
2018)
1
1
1
1
1
3. O. Navarro, R.A. Kelly, S.P. Nolan, J. Am. Chem. Soc. 125, 16194 (2003)
4. O. Bárta, I. Císařová, P. Štěpnička, Eur. J. Inorg. Chem. 2, 489 (2016)
5. R. Maity, A. Verma, M. van der Meer, S. Hohloch, B. Sarkar, Eur. J. Inorg. Chem. 1, 111 (2016)
6. H.Y. Liu, X.S. Li, F. Liu, Y. Tan, Y.Y. Jiang, J. Organomet. Chem. 794, 27 (2015)
7. A. Avila-Sorrosa, H.A. Jiménez-Vázquez, A. Reyes-Arellanoa, J.R. Pioquinto-Mendoza, R.A. Tos-
cano, L. González-Sebastiánb, D. Morales-Morales, J. Organomet. Chem. 819, 69 (2016)
8. M. Khajehzadeh, M. Moghadam, J. Organomet. Chem. 863, 60 (2018)
1
1
9. H.H. Zhang, J. Han, F. Tian, Q.Z. Chen, C.Z. Wang, H. Jin, G.Y. Bai, Res. Chem. Intermed. 41,
6
731 (2014)
2
2
2
2
0. S. Borah, S. Mishra, L. Cardenas, G. Nayanmoni, J. Inorg. Chem. 6, 751 (2018)
1. Y.L. Huang, Q. Wei, Y.Y. Wang, L.Y. Dai, Carbon 136, 150 (2018)
2. S. RoyKula, K.K. Senapati, P. Phukan, Res. Chem. Intermed. 41, 5753 (2014)
3. C. Biglione, A.L. Cappelletti, M.C. Strumia, S.E. MartínPaula, M. Uberman, J. Nanopart. Res. 20,
1
27 (2018)
2
2
2
4. J. Chen, J. Zhang, D.J. Zhu, T. Li, J. Porous Mater. 24, 847 (2017)
5. X. Liu, X.H. Zhao, M. Lu, J. Organomet. Chem. 768, 23 (2014)
6. B.H. Zhang, Y.G. Xue, A.N. Jiang, Z.M. Xue, Z.H. Li, J.C. Hao, A.C.S. Appl, Mater. Interfaces 9,
7
217 (2017)
2
2
2
3
3
7. Y.C. Hu, N. Li, G.Y. Li, A.Q. Wang, Y. Cong, X.D. Wang, T. Zhang, ACS Catal. 7, 2576 (2017)
8. T. Itoh, Chem. Rev. 117, 10567 (2017)
9. A. Mondal, A. Das, B. Adhikary, D.K. Mukherjee, J. Nanopart. Res. 16, 2366 (2014)
0. P.W. Zheng, W.Q. Zhang, J. Catal. 250, 324 (2007)
1. X.W. Jiang, G.W. Wei, X. Zhang, W.Q. Zhang, P.W. Zheng, F. Wen, L.Q. Shi, J. Mol. Catal. A:
Chem. 277, 102 (2007)
3
2. X.W. Jiang, Y. Wang, W.Q. Zhang, P.W. Zheng, L.Q. Shi, Macromol. Rapid Commun. 27, 1833
(
2006)
3
3
3. S.T. Handy, X. Zhang, Org. Lett. 3, 233 (2001)
4. J.Z. Zhang, W.Q. Zhang, Y. Wang, M.C. Zhang, Adv. Synth. Catal. 350, 2065 (2008)
1
3

J. Zhang et al.
3
3
3
3
5. C.J. Mathews, P.J. Smith, T. Welton, Chem. Commum. 1249 (2000)
6. M. Pesavento, R. Biesuz, M. Gallorini, A. Profumo, Anal. Chem. 65, 2522 (1993)
7. C. Pan, M. Liu, L. Zhang, H. Wu, J. Ding, J. Cheng, Catal. Commun. 9, 508 (2008)
8. A. Fihri, M. Bouhrara, B. Nekoueishahraki, J.-M. Basset, V. Polshottiwar, Chem. Soc. Rev. 40, 5181
(
2011)
Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional aꢁliations.
Aꢀliations
1
2
1
1
Jianzheng Zhang · Jingshuai Chen · Qiuyu Zhang · Rumin Wang ·
Songhua Wu3
1
Department of Applied Chemistry, School of Science, Northwestern Polytechnical University,
Xi’an 710072, China
2
College of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, Anhui,
China
3
AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China
1
3