Cyclodextrin-supported palladium complex: A highly active and recoverable catalyst for Suzuki–Miyaura cross-coupling reaction in aqueous medium

Article abstract of DOI:10.1002/aoc.3592

A water-soluble, cyclodextrin-supported palladium complex (DACH-Pd-β-CD) catalytic system was designed and synthesized, which can efficiently catalyze Suzuki–Miyaura cross-coupling reactions between aryl halides and arylboronic acid in water under mild conditions. The catalyst was successfully characterized using the methods of transmission electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction, thermogravimetric analysis, and Fourier transform infrared and NMR spectroscopies. Furthermore, the catalyst can be easily separated from the reaction mixture and still maintain high catalytic activity after ten cycles. No leaching of palladium into the reaction solution occurred. The advantages of green solvent (water), short reaction times (2–6?h), low catalyst loading (0.001?mol%), excellent yields (up to 99%) and reusability of the catalyst mean it will have potential applications in green chemical synthesis.

Full text of DOI:10.1002/aoc.3592

Received: 4 May 2016
DOI 10.1002/aoc.3592
Revised: 18 July 2016
Accepted: 31 July 2016
F U L L PA P E R
Cyclodextrin‐supported palladium complex: A highly active and
recoverable catalyst for Suzuki–Miyaura cross‐coupling reaction
in aqueous medium
1
,2
2
1
1
1
1
1
Yafei Guo | Jiuling Li | Xiwei Shi | Yang Liu | Kai Xie | Yuqi Liu | Yubo Jiang |
2
1
*
Bo Yang | Rui Yang
1
Faculty of Science, Kunming University of
Science and Technology, Kunming 650500,
People's Republic of China
A water‐soluble, cyclodextrin‐supported palladium complex (DACH‐Pd‐β‐CD) cat-
alytic system was designed and synthesized, which can efficiently catalyze Suzuki–
Miyaura cross‐coupling reactions between aryl halides and arylboronic acid in water
under mild conditions. The catalyst was successfully characterized using the
methods of transmission electron microscopy, energy‐dispersive X‐ray spectrome-
try, X‐ray diffraction, thermogravimetric analysis, and Fourier transform infrared
and NMR spectroscopies. Furthermore, the catalyst can be easily separated from
the reaction mixture and still maintain high catalytic activity after ten cycles. No
leaching of palladium into the reaction solution occurred. The advantages of green
solvent (water), short reaction times (2–6 h), low catalyst loading (0.001 mol%),
excellent yields (up to 99%) and reusability of the catalyst mean it will have poten-
tial applications in green chemical synthesis.
2
Faculty of Life Science and Technology, Kunming
University of Science and Technology, Kunming
6
50500, People's Republic of China
Correspondence
Rui Yang, Faculty of Science, Kunming University
of Science and Technology, Kunming 650500,
People's Republic of China.
Email: yangrui9111@163.com
KEYWORDS
Cyclodextrin, green catalysis, palladium, Suzuki–Miyaura cross‐coupling reaction
1
|
INTRODUCTION
large number of researchers, who have recently been inter-
ested in the Suzuki–Miyaura coupling reaction, have focused
Carbon–carbon cross‐coupling reactions catalyzed by transi-
their attention on three issues: (1) endeavoring to minimize
the quantity of precious metal catalysts; (2) improving the
recovery and recycling efficiency; and (3) using environmen-
tion metals play an important role in modern synthetic chem-
[1]
istry for the synthesis of complex molecules. In particular,
the Suzuki–Miyaura coupling reaction has a wide range of
applications from the synthesis of natural products and phar-
maceutical intermediates to functional materials with mild
reaction conditions, use of low‐toxicity organic boron
[
6]
tally friendly and cheap solvents.
With these issues in mind, various carriers have been
employed to immobilize Pd catalysts, such as magnetic
[
7]
[8]
[9]
[10]
nanoparticles, Pd/C, silica, carbon nanotubes,
gly-
Most of
phospho-
so as to form stable com-
[
2]
[11]
[12]
[13]
reagents, stability and a wide range of substrates. It is
reported that palladium (Pd) catalysts are most frequently
used in Suzuki–Miyaura coupling reactions and often lead
cosyls,
other polymers
the carriers were functionalized with amine,
and nanomaterials.
[
14]
[
15]
[16]
rus
and sulfydryl groups
[3]
to high reaction rates and yields. With its great advantages,
the Pd‐catalyzed Suzuki–Miyaura coupling reaction made a
significant contribution to the 2010 Nobel Prize in Chemis-
plexes with Pd catalysts. On the one hand, the Pd
complexes are very easy to recycle and reuse. On the other
hand, the quantities of Pd catalysts required are minimal
and the solvents are environmentally friendly, such as water
and ethanol.
[4]
try. However, the Suzuki–Miyaura coupling reaction also
has some drawbacks, such as the difficulty of recycling and
separating precious metals, expensive ligands and pollution
Cyclodextrin (CD)‐supported Pd catalytic systems
recently have attracted much attention for green Suzuki–
[5]
to the environment. As a result, the disadvantages are
conflicting with the conception of green chemistry. Thus, a
[
17]
Miyaura coupling reactions.
CD is a kind of cyclic
Appl. Organometal. Chem. 2016; 1–7
wileyonlinelibrary.com/journal/aoc
Copyright © 2016 John Wiley & Sons, Ltd.
1

2
GUO ET AL.
oligosaccharide and consists of (α‐1,4)‐linked α‐D‐
glucopyranose units which possess a special structure of
lipophilic central cavity and hydrophilic outer surface. The
special structure endows it with various functions, such as
[
18]
[19]
drug delivery,
tion.
catalysis in water
and selective recogni-
[
20]
The superb catalytic performance of CD in water is
probably due to organic substances being able to spontane-
ously form inclusion complexes with CD and the organic
[
21]
reactions may happen in the central lipophilic cavity.
In
recent years, a few functionalized CD ligands were synthe-
sized for Suzuki–Miyaura coupling reactions which were
[
22]
usually grafted with amine and phosphorus groups.
For
and
[
23]
example, Pd supported by triazolyl β‐cyclodextrin
[24]
tetraphosphine α‐cyclodextrin showed wonderful catalytic
properties in Suzuki–Miyaura coupling reactions in neat
water and also showed high turnover numbers and turnover
frequencies. However, the synthesis of CD‐based ligands in
most reports involved complex multi‐steps and the reusability
of the catalysts was not studied. Moreover, metal leaching
experiments were not considered. Hence, we hypothesized
that it would be meaningful to use a simple and cheap CD‐
based water‐soluble catalyst to accomplish Suzuki–Miyaura
coupling reactions in water. In addition, it will be better if
the catalyst has both high catalytic activity and shows easy
catalyst separation/reuse in aqueous media without signifi-
cant catalyst leaching.
SCHEME 1 Synthesis of DACH‐Pd‐β‐CD. Reaction conditions: (a) TosCl,
3 2 2
NaOH, CH CN, H O; (b) DMF, 80°C; (c) Pd(OAc) , toluene, room tem-
perature, 24 h
this study has been calculated based on the Pd content of
DACH‐Pd‐β‐CD.
2
.2 | Characterization of DACH‐Pd‐β‐CD catalyst
NMR spectroscopy is a useful way to demonstrate the forma-
tion of ligand and catalyst. The NMR spectra of DACH‐β‐CD
and DACH‐Pd‐β‐CD are shown in Figure 1. As illustrated in
Figure 1, the characteristic peaks of DACH appear from 3.0
to 1.0 ppm. This result demonstrates the formation of
DACH‐β‐CD. Comparing the spectrum of DACH‐β‐CD with
that of DACH‐Pd‐β‐CD, the peak of acetyl in DACH‐Pd‐β‐
CD is extremely obvious and it could provide probable evi-
dence that the DACH‐Pd‐β‐CD catalyst has been synthesized.
High‐resolution (HR)‐MS was used to confirm the successful
synthesis of DACH‐β‐CD (Fig. S4; m/z calcd for
In our previous report, a type of cheap CD‐based water‐
soluble catalyst, namely DACH‐Pd‐β‐CD (where DACH is
1
,2‐cyclohexanediamine), was used to catalyze the reduction
[25]
of nitroarenes in water.
In the present paper, we report the
synthesis and characterization of DACH‐Pd‐β‐CD and its
application in other Suzuki–Miyaura reactions in water. The
ligand is cheap and can be easily synthesized with the most
common β‐CD derivative (Tos‐β‐CD) and DACH, which
may significantly increase its application in industry. In addi-
tion, the excellent catalytic activity, recycling performance,
metal leaching and catalytic mechanism were studied.
+
[C H N O ] 1230.47, found 1231.4848 [M + H] ,
4
8 82 2 34
+
1253.4670 [M + Na] ). The NMR and HR‐MS results indi-
cate that the degree of substitution of DACH‐β‐CD is 1.
The X‐ray diffraction (XRD) patterns of DACH‐β‐CD
and DACH‐Pd‐β‐CD are presented in Figure 2. Compared
with each other, it is obvious that DACH‐β‐CD (the red
curve) and DACH‐Pd‐β‐CD (the black curve) are both amor-
phous and show a strong and wide characteristic diffraction
peak at 2θ of 15–30°. In addition, the new peaks in the
XRD pattern of DACH‐Pd‐β‐CD at 2θ of 39.6° and 47.1°,
2
2
|
RESULTS AND DISCUSSION
.1 | Preparation of DACH‐Pd‐β‐CD catalyst
The DACH‐Pd‐β‐CD catalyst was prepared following the
procedure shown in Scheme 1. At first, 6‐O‐monotosyl‐β‐
CD was synthesized with a frequently used method in our
groups. Then, DACH was grafted on 6‐O‐monotosyl‐β‐CD
2
corresponding to 110 and 200 crystalline planes of Pd , indi-
cate the existence of Pd in DACH‐Pd‐β‐CD. As a result, the
XRD patterns demonstrate that the catalyst had been synthe-
sized without damaging the crystal structure of the DACH‐β‐
CD ligand and Pd is present in the DACH‐Pd‐β‐CD catalyst.
Transmission electron microscopy (TEM) images of
DACH‐β‐CD and DACH‐Pd‐β‐CD and HR‐TEM image of
DACH‐Pd‐β‐CD are shown in Figure 3. The sample was
put on a piece of copper grid and dried at room temperature
under vacuum. Comparing Figure 3(A) and (B), the main dif-
ference is that many black spots are apparent in the latter, but
[26]
according to previous methods.
Finally, Pd(OAc) and
2
DACH‐β‐CD were added in toluene and stirred at room tem-
perature for 24 h. The pure DACH‐Pd‐β‐CD catalyst was
obtained as a light yellow powder. Moreover, the catalyst is
soluble in water to form a light yellow clear solution. The pal-
ladium content of DACH‐Pd‐β‐CD is 0.1625 mmol g−
1
(determined using inductively coupled plasma optical emis-
sion spectrometry (ICP‐OES)) and the amount of catalyst in

GUO ET AL.
3
used to study the elementary composition of DACH‐Pd‐β‐
CD (Figure 4). Ignoring the peaks of the Cu grid, DACH‐
Pd‐β‐CD consists of O, C, N and Pd. All the results show
the presence of Pd in the DACH‐Pd‐β‐CD catalyst.
2
.3 | Catalytic performance studies
The catalytic performance of DACH‐Pd‐β‐CD for the
Suzuki–Miyaura coupling reaction was evaluated with the
model reaction of 4‐bromoacetophenone and phenylboronic
acid. As is known, base has a significant influence on the
Suzuki–Miyaura coupling reaction. Hence, seven bases were
chosen to test the catalytic activity and the results are summa-
rized in Table 1. Except for the different bases, the other reac-
tion conditions are identical. In the absence of base, the yield
is only about 3% (entry 1). Therefore, the presence of base is
required for the reaction to occur. The coupling reaction
yields using the seven bases were very good, from 82 to
1
FIGURE 1
H NMR spectra of DACH‐β‐CD and DACH‐Pd‐β‐CD
9
3% (entries 2–8). However, using the base Cs CO , the
2
3
product is very clean and without any other byproducts.
Moreover, the isolated yield is up to 93%. All the results in
Table 1 indicate that Cs CO is the optimal base.
2
3
The temperature and the mount of catalyst are very signif-
icant to the catalytic performance. The screening results are
listed in Table 2. As is evident, the Suzuki–Miyaura coupling
reaction can occur at room temperature with a yield of 32%
(entry 1). With the temperature rising from 50 to 80°C, the
yields gradually increase to 93% (entries 2 and 3). In addi-
tion, at higher temperature, the yields show nearly no change
FIGURE 2 XRD patterns of DACH‐β‐CD and DACH‐Pd‐β‐CD
(entries 4 and 5). As a result, 80°C is the optimum tempera-
ture. Considering the amount of catalyst, the quantity of
DACH‐Pd‐β‐CD was selected from 0 to 0.1 mol%.
FIGURE 3 TEM images: (A) DACH‐β‐CD at 100 nm; (B) DACH‐Pd‐β‐
CD at 200 nm; (C) DACH‐Pd‐β‐CD at 50 nm. (D) HR‐TEM image of
DACH‐Pd‐β‐CD at 5 nm
not in the former. When the image is enlarged to 50 nm in
Figure 3(C), the black spots become much clearer. The black
spots are likely to be Pd atoms. In order to further demon-
strate the presence of Pd, a HR‐TEM image of DACH‐
Pd‐β‐CD was obtained (Figure 3D). From Figure 3(D), the
average interplanar distance of DACH‐Pd‐β‐CD is measured
to be ca 0.22 nm, which corresponds well to the plane of Pd.
In addition, energy‐dispersive X‐ray spectrometry (EDS) was
FIGURE 4 EDS pattern of DACH‐Pd‐β‐CD

4
GUO ET AL.
a
TABLE 1 Optimization of base
TABLE 3 Suzuki–Miyaura coupling reactions between aryl halides and
a
arylboronic acid using DACH‐Pd‐β‐CD
b
Entry
Base
Yield (%)
1
2
b
Entry
R
X
R
Time (h)
Yield (%)
1
—
3
82
85
78
93
92
89
82
1
2
H
H
I
H
H
H
H
H
H
1
1
99
98
93
96
95
65
96
98
95
94
96
97
95
76
96
97
90
96
94
95
2
3
4
5
6
7
8
Na
CO
NaHCO
Cs CO
NaOH
PO
2
CO
3
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
I
K
2
3
3
4‐COCH
3
2
3
4
4‐OCH
4‐CHO
2‐CHO
3
2
2
3
5
4
6
24
2
K
3
4
7
4‐COCH
3
3
4‐CH
4‐CH
4‐CH
3‐CH
3‐CH
3
3
3
3
3
3
Et N
8
4‐OCH
4‐CHO
3
2
a
Reaction conditions: aryl halide(1.0 mM), arylboronic acid (1.5 mmol), H
2 ml), DACH‐Pd‐β‐CD (1 × 10−3 mol%), base (1.5 eq.), 80°C, 2 h.
2
O
9
4
(
b
10
4‐COCH
4‐OCH
6
Isolated by column chromatography.
11
3
6
a
12
4‐OCH3
3‐CH3
3
TABLE 2 Optimization of temperature and catalyst loading
13
14
15
16
17
18
19
20
4‐CHO
Br
I
3‐CH
4‐F
4‐F
4‐F
4‐F
4‐F
4‐F
3
6
b
Entry
Temperature (°C)
Catalyst (mol%)
Yield (%)
2‐OCH
4‐COCH
4‐OCH
3‐NO
4‐CHO
3
4
1
2
3
4
5
6
7
8
r.t.
50
0.001
0.001
0.001
0.001
0.001
0
32
68
93
92
93
—
92
93
—
—
6
3
Br
Br
Br
Br
I
6
3
6
80
2
8
100
110
80
6
4‐CH
4‐CH
3
4
3
I
4‐COCH
3
8
80
0.1
a
Reaction conditions: aryl halide (1.0 mmol), arylboronic acid (1.5 mmol),
80
0.01
2 3 2
CO (1.5 mmol), H
O (2 ml), DACH‐Pd‐β‐CD (1 × 10− mol%), 80°C.
3
Cs
b
c
9
80
0.001
0.001
0.001
Isolated by column chromatography.
d
1
1
0
1
80
e
80
Comparing the reactions between various aryl bromides
(entries 3–6) and boronic acid, it turns out that the yields of
para‐substituted aryl bromides (entries 3–5) are much higher
than that of ortho‐substituted aryl bromide (entry 6). In par-
ticular, for entries 5 and 6, the yields of the same substituent
of ─CHO, respectively at para‐position and ortho‐position,
are quite different. This may be due to the regioselectivity
of DACH‐Pd‐β‐CD. Because of the constant cavity size of
DACH‐Pd‐β‐CD, the para‐substituted aryl bromides proba-
bly combine more easily with Pd than ortho‐substituted aryl
bromides. Therefore, the yield of 2‐phenylbenzaldehyde is
only 65%. In addition, a series of arylboronic acid derivatives
(entries 7–13) was also studied. Regardless of using
4‐methylphenylboronic acid and 3‐methylphenylboronic
acid, all the yields are very good at about 96–98%. The only
difference was the time of the coupling reactions;
4‐methylphenylboronic acid took less time. Furthermore,
para‐substituted aryl halides were also tested with
4‐fluorophenylboronic acid and excellent yields are obtained
(entries 14–19). The presence of F in the products was char-
acterized using F NMR spectroscopy. For the coupling
reactions of other substrates, we used 3‐nitrobromobenzene
(entry 17) to study the catalytic activity of meta‐substituted
aryl bromide and the yield is up to 90%. In conclusion, the
DACH‐Pd‐β‐CD catalyst possesses excellent catalytic activ-
ity in Suzuki–Miyaura coupling reactions. Substituents (elec-
tron‐withdrawing or electron‐donating groups) have a slight
influence on the yields. Also, DACH‐Pd‐β‐CD shows a
a
Reaction conditions: aryl halide (1.0 mM), arylboronic acid (1.5 mmol), Cs
1.5 eq.), H O (2 ml), DACH‐Pd‐β‐CD, 2 h.
Isolated by column chromatography.
2
CO
3
(
b
2
c
β‐CD was used to instead of DACH‐β‐Pd‐CD.
d
DACH‐β‐CD was used to instead of DACH‐β‐Pd‐CD.
e
2
β‐CD was used to instead of DACH‐β‐CD, Pd(OAc) (0.001 mmol%).
Entry 6 reveals that the DACH‐Pd‐β‐CD catalyst is quite
important and the coupling reaction cannot happen without
catalyst. Furthermore, the yield for the minimum quantity
(
the same performance with higher quantities (entries 7 and 8).
In addition, considering the influence of CD itself, β‐CD
and DACH‐β‐CD were used to test their catalytic activity
0.001 mol%) of DACH‐Pd‐β‐CD is very good and shows
(
entries 9 and 10), no product being detected. However, when
we added β‐CD and Pd(OAc) to replace the DACH‐Pd‐β‐
CD catalyst (entry 11), the yield is reduced to 6%.
2
In order to investigate the generality of this cross‐cou-
pling reaction, various arylboronic acids were used to react
with aryl halides (iodide or bromide) under the optimized
conditions. The catalytic results are summarized in Table 3.
Overall, the catalyst shows good catalytic activity leading to
excellent yields in the Suzuki–Miyaura coupling reactions.
As indicated in entries 1 and 2, simple aryl halides, such as
iodobenzene and bromobenzene, have a high reactivity with
boronic acid and the reactions are quickly completed in 1 h.
Moreover, the yields of diphenyl are up to 98–99%.
19

GUO ET AL.
5
regioselectivity to aryl halides, the strength of the
regioselectivity being: para‐substituted aryl halides and
meta‐substituted aryl halides > ortho‐substituted aryl halides.
The detailed reasons for the regioselectivity are still under
investigation by our groups.
2.4 | Recyclability of DACH‐Pd‐β‐CD
It is well known that the main advantage of metal catalysts is
their high catalytic efficiency, but unfavorable factors, such as
high price, difficulty in recycling and pollution to the envi-
ronment, seriously limit their applications in industry. There-
fore, in order to expand the applications of DACH‐Pd‐β‐CD,
the recycling of the catalyst was carried out. The general pro-
cedure for recycling the catalytic system is described in
Figure 5. Furthermore, the reaction was conducted with the
optimum reaction conditions: 4‐bromoacetophenone
FIGURE 7 TEM image of DACH‐Pd‐β‐CD after ten cycles
(
1.0 mmol), phenylboronic acid (1.5 mmol), DACH‐Pd‐β‐
−3
CD (1 × 10 mol%), Cs CO (1.5 mmol), 80°C and H O
2
3
2
The content of Pd in the product was determined using ICP‐
OES and no leaching of Pd is detected. The excellent reus-
ability of the catalyst could be due to the strong binding
capacity between Pd and DACH‐β‐CD.
(
2.0 ml). After completion of each cycle, 3 × 5 ml of ethyl
acetate was added to separate the organic phase and the aque-
ous phase was used in the next run without changing the reac-
tion conditions. The recycling results are shown in Figure 6.
In the first cycle, the yield is 93% and the DACH‐Pd‐β‐CD
catalyst still shows high catalytic activity giving a yield of
2
.5 | Proposed mechanism for Suzuki–Miyaura
8
8% after ten cycles. Moreover, after ten cycles, the Pd in
coupling reaction
the TEM image of DACH‐Pd‐β‐CD is still obvious (Figure 7).
Given the results of this work and previous literature, a pos-
sible catalytic mechanism is proposed as shown in Figure 8.
The mechanism is the same as reported previously and
involves three sequential steps: oxidative addition,
[
27]
transmetalation and reductive elimination.
We studied
the two‐dimensional ROESY spectrum (Fig. S7). The results
indicate that the spectrum shows a correlation between the
aromatic protons of 4‐bromoacetophenone and internal
DACH‐Pd‐β‐CD protons (H‐3 and H‐5 of CD), which
FIGURE 5 Recycling procedure for DACH‐Pd‐β‐CD
FIGURE 8 Possible catalytic mechanism of Suzuki–Miyaura cross‐cou-
pling reaction using DACH‐Pd‐β‐CD
FIGURE 6 Recycling of DACH‐Pd‐β‐CD

6
GUO ET AL.
implies that the DACH‐Pd‐β‐CD catalyst is able to recognize
the substrate and insert it into the cavity of β‐CD. Hence, the
catalyst can probably recognize the substrate in water and
promote the Suzuki reaction to occur in its cavity. At first,
DACH‐Pd‐β‐CD is activated to Pd(0) and the aryl halide
reacts with the active DACH‐Pd‐β‐CD (oxidative addition)
to produce the intermediate II. The coordinated halide ion is
weak, and then activated arylboronic acid forms the diaryl
complex with the progress of transmetalation. Finally, the
desired reductive elimination product is released from the
cavity. Afterward, the catalytic cycles can be repeated.
2θ = 0.02° between 2θ = 5° and 90°. TEM and EDS were
conducted using a Tecnai G TF30 S‐Twin. NMR spectra
2
were obtained with a Bruker Avance DRX spectrometer at
500 MHz, with tetramethylsilane as internal reference,
298 K, at Yunnan University, Kunming, China. ICP‐OES
was carried out with an Agilent 5100 instrument.
Thermogravimetric measurements were performed with a
Netzsch STA449F3 instrument, at a heating rate of 10°
C min− from room temperature to 450°C in a dynamic nitro-
1
−
1
gen atmosphere (flow rate = 100 ml min ).
4
.3 | Synthesis of DACH‐β‐CD ligand
3
| CONCLUSIONS
6‐O‐Monotosyl‐β‐CD was synthesized according to proce-
[
26]
dures in the literature.
6‐O‐Monotosyl‐β‐CD (3.22 g,
In this study, a new kind of water‐soluble, macromolecular
Pd complex catalyst, DACH‐Pd‐β‐CD, for Suzuki–Miyaura
coupling reactions was successfully prepared and character-
ized using NMR spectroscopy, XRD, TEM, HR‐TEM and
EDS. The catalyst showed excellent activity in the Suzuki–
Miyaura cross‐coupling reaction and the yields of most
desired products ranged from 88 to 99%. The advantages of
this catalyst are mainly divided into the following several
aspects. Firstly, the catalytic efficiency was strongly
enhanced by the minimum catalyst amount of 0.001 mol%.
Secondly, the reaction solvent of water is very beneficial to
the environment. Thirdly, after the reaction finished, a simple
operation of extraction is used to get the desired products.
Fourthly, the catalytic performance is still very good and
without catalyst loss after ten cycles. In conclusion, the
advantages of the DACH‐Pd‐β‐CD catalyst fully meet the
requirements of green chemistry.
2.5 mmol) and DACH (1.14 g, 10.0 mmol) were dissolved
in anhydrous DMF. The mixture was stirred for 12 h at 80°
C. Then, the reaction solution was added dropwise in acetone
(3 × 500 ml) to remove the excess DACH. The final pure
DACH‐β‐CD was dried overnight in vacuum at 50°C. Yield:
82%.
4
.4 | Synthesis of DACH‐Pd‐β‐CD catalyst
Pd(OAc) (0.0225 g, 0.1 mM) was dissolved in toluene
2
(15 ml) and DACH‐β‐CD (0.369 g, 0.3 mM) was added.
The suspension was stirred at room temperature for 24 h.
Then, the precipitate was washed three times with a large
amount of acetone (300 ml) to remove the tiny amounts of
free Pd(OAc) . Then, the catalyst was dried in vacuum at
2
5
0°C for 24 h, and a light yellow powder was obtained.
4
.5 | General procedure for Suzuki–Miyaura coupling
reaction
4
4
|
EXPERIMENTAL
Aryl halide (1.0 mM), arylboronic acid (1.5 mmol), DACH‐
Pd‐β‐CD (1 × 10− mol%) and Cs CO (1.5 mmol) were
added in a sealed tube with 2.0 ml of water. The mixture
was stirred at 80°C for a few hours and monitored by TLC.
After the reaction completed, the aqueous phase was
extracted with ethyl acetate (3 × 5 ml). Then the combined
3
2
3
.1 | Materials
β‐CD (AR, 98%, MW = 1134.98), DACH (AR, 99%,
MW 114.19), Pd(OAc)2 (metals basis, 99.9%,
MW = 224.51) and p‐toluenesulfonyl chloride (AR, 99%,
MW = 190.65) were purchased from Aladdin Industrial Cor-
poration, Shanghai, China. NaOH, dimethylformamide
=
organic layers were dried using anhydrous MgSO and fur-
ther purified by column chromatography.
4
(
DMF) and CH CN were purchased from Tianjin Fengchuan
3
Chemical Reagent Technologies, China. Aryl halides and
arylboronic acid (AR) were obtained from Macklin Biochem-
ical Technology Co. Ltd. All experiments were carried out in
ultrapure water and all chemicals were used without further
purification.
4
.6 | Separation of catalyst and recycling procedure
Once each Suzuki–Miyaura reaction was finished, ethyl ace-
tate (3 × 5 ml) was added to separate the organic phase and
the aqueous phase was used in the next run with the optimum
reaction conditions.
4.2 | Instrumentation
ACKNOWLEDGMENTS
XRD patterns were obtained using a PHI 5000 VersaProbe II
This work was supported by the National Natural Science
Foundation of China (NSFC) (no. 21362016) and the Science
and Technology Planning Project of Yunnan Province (no.
KKSY201207140), which are gratefully acknowledged.
with Cu Kα radiation (k = 1.5460 Å, 40 kV, 100 mA), at a
−1
scanning rate of 5° min . Powder samples were mounted
on a vitreous sample holder and scanned with a step size of

GUO ET AL.
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How to cite this article: Guo, Y., Li, J., Shi, X.,
Liu, Y., Xie, K., Liu, Y., Jiang, Y., Yang, B., and
Yang, R. (2016), Cyclodextrin‐supported palladium
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for Suzuki–Miyaura cross‐coupling reaction in
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