Preparation and Reactivation of Heterogeneous Palladium Catalysts and Applications in Sonogashira, Suzuki, and Heck Reactions in Aqueous Media

Article abstract of DOI:10.1002/open.201800139

A new type of heterogeneous palladium catalyst, PdMgAl-LDH, was facilely prepared by the immobilization of Pd²⁺ species in the layers of a Mg-Al layered double hydroxide (LDH) with co-precipitation, and then fully characterized by using powder XRD, thermogravimetric differential thermal analysis, TEM, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques. These catalysts can efficiently catalyze copper-free Sonogashira, Suzuki and Heck coupling reactions of various aryl iodides, bromides, and chlorides in aqueous media under phosphine-ligand- and organic-base-free conditions. These catalysts feature easy recovery through simple filtration and could be reused at least six times without a marked loss in activity. Notably, they can be facilely reactivated by a combination of nitrolysis with co-precipitation. The basic LDH skeletons could effectively stabilize the Pd⁰ species created in situ and donate electron density to the Pd⁰ center to facilitate the oxidative addition of aryl halides, thus the PdMgAl-LDH catalysts are stable during catalysis.

Full text of DOI:10.1002/open.201800139

DOI: 10.1002/open.201800139
Preparation and Reactivation of Heterogeneous Palladium
Catalysts and Applications in Sonogashira, Suzuki, and
Heck Reactions in Aqueous Media
Sheng-Yan Zhang+, Kai Yu+, Yu-Shuang Guo, Rui-Qi Mou, Xiao-Fan Lu, and
Dian-Shun Guo*[a]
A new type of heterogeneous palladium catalyst, PdMgAl-LDH,
was facilely prepared by the immobilization of Pd2+ species in
the layers of a Mg-Al layered double hydroxide (LDH) with co-
precipitation, and then fully characterized by using powder
XRD, thermogravimetric differential thermal analysis, TEM,
energy-dispersive X-ray spectroscopy, and X-ray photoelectron
spectroscopy techniques. These catalysts can efficiently cata-
lyze copper-free Sonogashira, Suzuki and Heck coupling reac-
tions of various aryl iodides, bromides, and chlorides in aque-
ous media under phosphine-ligand- and organic-base-free con-
ditions. These catalysts feature easy recovery through simple
filtration and could be reused at least six times without a
marked loss in activity. Notably, they can be facilely reactivated
by a combination of nitrolysis with co-precipitation. The basic
LDH skeletons could effectively stabilize the Pd0 species creat-
ed in situ and donate electron density to the Pd0 center to fa-
cilitate the oxidative addition of aryl halides, thus the PdMgAl-
LDH catalysts are stable during catalysis.
1. Introduction
Palladium-catalyzed Sonogashira, Suzuki, and Heck reactions
are powerful tools for the formation of carbon–carbon bonds
in modern organic synthesis and can boost greater diversity in
natural products, biological molecules, and functional materi-
als.[1] In general, homogeneous Pd catalysts are used with vari-
ous phosphine ligands, which results in several limitations,
such as a lack of catalyst reuse and residual heavy metals in
the final products.[2] However, the application of heterogene-
ous Pd catalysts could avoid such limitations.[3] A popular strat-
egy is to immobilize Pd species onto a suitable solid support,
such as activated carbon,[4] metal oxide,[5] silica,[6] zeolite,[7] or
organic polymers.[8] These catalysts could be applied to pro-
mote some coupling reactions, but their preparation and reac-
tivation are laborious and difficult. In particular, the loss of Pd
species from the solid supports is a serious issue. Thus, it is es-
sential to develop well-defined heterogeneous Pd catalysts
that feature high catalytic performance and facile preparation
and regeneration.
Recently, layered double hydroxides (LDHs), a class of 2D
anionic clays composed of positively charged brucite-like
layers with an interlayer region that consists of charge-com-
pensating anions and solvent molecules,[9] were shown to be a
promising support for heterogeneous catalysts, largely because
of their high dispersion, preferential orientation, abundant
basic sites as potential donors, and high catalytic per-
formance.[10] To date, a majority of LDH-based heterogeneous
Pd catalysts have been prepared through two strategies: 1) in-
sertion of Pd species into the interlayer region of the LDH to
give a Pd/MgAl-LDH catalyst (Figure 1a)[11] or 2) by implanting
Pd species into the layers of the LDH through bonding to
create a PdMgAl-LDH catalyst (Figure 1b).[12] Choudary et al.[11a]
reported that the Pd/MgAl-LDH catalyst can catalyze the Heck
reaction of aryl chlorides under high temperature or micro-
wave radiation in the presence of an organic base. Ruiz
et al.[11b] demonstrated that the Pd/MgAl-LDH catalyst exhibits
high catalytic performance in the Suzuki reaction. Moreover,
Corma et al.[11c] developed a family of PdCu/MgAl(O) catalysts
[a] S.-Y. Zhang,+ K. Yu,+ Y.-S. Guo, R.-Q. Mou, X.-F. Lu, Prof. Dr. D.-S. Guo
College of Chemistry, Chemical Engineering and Materials Science
Collaborative Innovation Center of Functionalized Probes for
Chemical Imaging in Universities of Shandong
Shandong Normal University
Jinan 250014 (China)
E-mail: chdsguo@sdnu.edu.cn
[+] These authors contributed equally to this work
Supporting Information and the ORCID identification number(s) for the
author(s) of this article can be found under: https://doi.org/10.1002/
open.201800139.
ꢀ 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
This is an open access article under the terms of the Creative Commons
Attribution-NonCommercial-NoDerivs License, which permits use and
distribution in any medium, provided the original work is properly cited,
the use is non-commercial and no modifications or adaptations are
made.
Figure 1. The structures of two types of LDH-based Pd catalysts: a) Pd/MgAl-
LDH and b) PdMgAl-LDH.
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that were prepared through wetness impregnation of calcined
MgAl-LDH with Cu2+ and Pd2+ nitrates, and found that these
catalysts have good activity in the Sonogashira reaction. How-
ever, these catalysts are still difficult to prepare and inefficient
to reactivate.
Currently, few PdMgAl-LDH catalysts (Figure 1b) have been
developed and applied in coupling reactions.[12] Sivasanker
et al.[12a] reported that the PdMgAl-LDH catalyst, obtained by a
co-precipitation method, was only used for the Heck reaction
in the presence of an organic base and at high temperature.
Ruiz et al.[12b,c] synthesized the PdMgAl-LDH catalyst in the
same way and used it to catalyze the Suzuki reaction, which
gave less than 10% conversion. Liu et al.[12d] reported that a
Pd2+-doped colloidal LDH catalyst, obtained by delamination
of glycinate-intercalated PdMgAl-LDH, showed high efficiency
in the Heck reaction, but was difficult to recycle.
Figure 2. Powder XRD patterns of a) PdMgAl-LDH-1, b) PdMgAl-LDH-2, and
c) MgAl-LDH.
Our strategy is to implant Pd species in the layers of an LDH
to create PdMgAl-LDH catalysts because they can efficiently
avoid the loss of Pd during the catalytic process. Herein, we
present a series of PdMgAl-LDH catalysts that can efficiently
catalyze the Sonogashira, Suzuki, and Heck reactions of aryl
halides in greener media under P-ligand- and organic-base-free
conditions. Moreover, they can be easily prepared by co-pre-
cipitation and reactivated by a combination of nitrolysis and
co-precipitation.
in parameter c may be ascribed to the distortion of the struc-
ture caused by the larger Pd2+ ions, which affects the layer
thickness.[16c] These results confirmed that Pd2+ ions were suc-
cessfully implanted in the layers of MgAl-LDH. The XRD pat-
terns and a and c parameters of the Pd/MgAl-LDH catalysts
(Figure S1, Table S2) are consistent with results reported previ-
2À
ously,[14] which indicated that PdCl4 was successfully ex-
changed into the interlayer region of the MgAl-LDH.
The TG-DTA results of PdMgAl-LDH-1, PdMgAl-LDH-2, and
MgAl-LDH are shown in Figure 3. All compounds showed obvi-
ous weight loss in two consecutive endothermic stages.[17] The
destructive temperatures of PdMgAl-LDH-1 (Figure 3a) and
PdMgAl-LDH-2 (Figure 3b) at the second weight-loss process
are distinctly ahead of MgAl-LDH (Figure 2c), presumably due
to the structural distortion caused by the larger Pd2+ ions. This
is in agreement with the results from the powder XRD analysis.
TEM images of PdMgAl-LDH catalysts and MgAl-LDH are
shown in Figure 4. The expected hexagonal-plate-like nature of
the crystallites is obviously apparent in each sample, and the
diameters ranged from 60 to 80 nm. The TEM images of
PdMgAl-LDH-1 (Figure 4a) and PdMgAl-LDH-2 (Figure 4b) are
2. Results and Discussion
2.1. Preparation and Characterization of Catalysts
PdMgAl-LDH and MgAl-LDH (Pd-free) catalysts were facilely
prepared by co-precipitation with a double-drop technique.[13]
Given the stability of the brucite layers, two PdMgAl-LDH cata-
lysts, PdMgAl-LDH-1 (0.50% Pd w/w) and PdMgAl-LDH-2
(2.58% Pd w/w), were synthesized and characterized by using
powder XRD, thermogravimetric differential thermal analysis
(TG-DTA), TEM, energy-dispersive X-ray spectroscopy (EDX),
FTIR, and X-ray photoelectron spectroscopy (XPS) techniques.
Additionally, two Pd/MgAl-LDH catalysts, Pd/MgAl-LDH-1
(0.56% Pd w/w) and Pd/MgAl-LDH-2 (2.64% Pd w/w) were pre-
2À
pared by exchanging proportional PdCl4 ions into the inter-
layer region of the MgAl-LDH.[14]
From powder XRD patterns of the PdMgAl-LDH catalysts,
both PdMgAl-LDH-1 (Figure 2a) and PdMgAl-LDH-2 (Figure 2b)
exhibit typical diffraction peaks similar to MgAl-LDH (Fig-
ure 2c),[15] although the ionic radius of Pd2+ is different from
that of Mg2+. Because LDH has a hexagonal structure, lattice
parameters a and c indicate the average distance between
metal ions within the layers and the separation of the neigh-
boring layer centers, respectively,[16a] and can be calculated
from the (110) and (003) reflections of the XRD spectra
(Figure 2) based on a=2d110 and c=3d003. Parameters a and c
of the PdMgAl-LDH catalysts are slightly larger than those of
MgAl-LDH and increase as the amount of Pd is increased
(Table S1, see the Supporting Information). The increase in pa-
rameter a results from larger Pd2+ ions (0.086 nm) in the octa-
hedral coordination site[16b] compared with Mg2+. The increase
Figure 3. Differential thermal analysis (DTA) curves for a) PdMgAl-LDH-1,
b) PdMgAl-LDH-2, and c) MgAl-LDH.
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Pd2+ ions were successfully immobilized in the brucite layers
and show morphology similar to that of MgAl-LDH.
2.2. Catalyst Evaluation
To examine their catalytic activity, the prepared PdMgAl-LDH
catalysts were applied to Sonogashira, Suzuki, and Heck cou-
pling reactions. In view of its environmental safety and com-
patibility with the PdMgAl-LDH catalysts, we tried water as the
reaction solvent.
2.2.1. Application in the Sonogashira Reaction
Figure 4. TEM images of a) PdMgAl-LDH-1, b) PdMgAl-LDH-2, c) MgAl-LDH,
and d) PdMgAl-LDH-1R.
The Sonogashira reaction is a powerful method to create a
carbon–carbon bond between a terminal alkyne and an aryl or
vinyl halide by using a palladium catalyst and a copper co-cat-
alyst; however, the latter could result in a homocoupling prod-
uct upon oxidation. To avoid this byproduct, a copper-free So-
nogashira reaction has been developed.[20] Therefore, the
PdMgAl-LDH catalysts were first applied in a copper-free Sono-
gashira reaction.
similar to that of MgAl-LDH (Figure 4c), which indicates that
the morphology is well retained after a small amount of Mg is
replaced by Pd species in the MgAl-LDH layers. This was also
confirmed by the EDX spectrum (Figure S2). The FTIR spectra
of PdMgAl-LDH-1 and PdMgAl-LDH-2 are similar to that of
MgAl-LDH in the 400 to 4000 cmÀ1 region (Figure 5), and show
typical bands for hydrotalcite with intercalated carbonate
counterions.[12b,18]
To optimize the coupling conditions, we used bromoben-
zene and phenylacetylene as model substrates (Table 1). First, a
coupling reaction was conducted in water at 808C for 24 h
with PdMgAl-LDH-1 (0.20 mol% Pd) as the catalyst and K2CO3
(200 mol%) as the base, which gave a 47% yield of diphenyla-
cetylene (Table 1, entry 1). However, with sodium ascorbate
(NaVc) as the reducing agent, the reaction gave diphenylacety-
lene in 89% yield (Table 1, entry 2) under identical conditions.
This may be ascribed to the fact that Pd2+ in PdMgAl-LDH-1
was reduced to Pd0 in situ by NaVc, which accelerated the oxi-
dative addition of Pd0 to the CÀBr bond.[21] This reduction was
also confirmed by using XPS analysis (Figure S3b). The binding
Table 1. Optimization of Sonogashira reactions catalyzed by using
PdMgAl-LDH-1.[a]
Entry
Base
Additive[b]
Pd [mol%]
T [h]
Yield [%][c]
Figure 5. FTIR spectra for a) PdMgAl-LDH-1, b) PdMgAl-LDH-2, and c) MgAl-
LDH.
1
2
3
4
5
6
7
8
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Na2CO3
K3PO3
Et3N
none
none
CTAB
TBAB
TPAB
TEBAC
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
CTAB
0.20
0.20
0.20
0.20
0.20
0.20
0.30
0.10
0.20
0.20
0.20
0.20
0.20
24
24
12
15
16
16
10
24
12
12
12
16
16
47[d]
89
93
89
87
85
95
72
65[e]
85
82
87
To assess the Pd oxidation state in the PdMgAl-LDH cata-
lysts, XPS analyses were carried out for PdMgAl-LDH-1
and PdMgAl-LDH-11 (after one run). The binding energies of
Pd3d5/2 and 3d3/2 for PdMgAl-LDH-1 were 337.5 and 342.8 eV,
respectively (Figure S3a), which indicated that the implanted
Pd is in the II state.[19] Note that the XPS signal of Pd3d3/2 is
weak due to the low loading of palladium. Moreover, the bind-
ing energy of Pd3d5/2 in PdMgAl-LDH-1 (337.5 eV) is different
from that in Pd/MgAl-LDH (337.1 eV[11a]) and Pd(OH)2 (336.8 eV;
Figure S4).[19]
9
10
11
12
13
pyridine
89
[a] Reagents and conditions: bromobenzene (1.00 mmol), phenylacety-
lene (1.10 mmol), base (2.00 mmol), NaVc (0.01 mmol), additive
(0.10 mmol), and H2O (3 mL). [b] TBAB=tetrabutylammonium bromide,
TPAB=tetrapropylammonium bromide, TEBAC=benzyltriethylammoni-
um chloride. [c] Isolated yield. [d] NaVc-free. [e] Reaction at 608C.
In brief, two PdMgAl-LDH catalysts, with Pd loadings of 0.50
and 2.58%, respectively, were prepared and fully characterized.
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energies of Pd were 335.4 (3d5/2) and 340.7 eV (3d3/2), and were
assigned to the Pd0 species.[19]
Table 2. Scope of Sonogashira reactions catalyzed by PdMgAl-LDH-1.[a]
We found that the use of some tetraalkylammonium salts as
an additive could facilitate the coupling reaction (Table 1, en-
tries 3–6); cetyltrimethylammonium bromide (CTAB) was the
best additive for the coupling reaction (Table 1, entry 3). We
presume that CTAB may act as both a phase-transfer catalyst
and an interlayer regulator of the PdMgAl-LDH because the
powder XRD analysis (Figure S5) indicated that CTAB was
partly incorporated into the interlayer region of PdMgAl-LDH,
which extended the interlayer separation from 0.765 to
2.386 nm (Table S1, entry 5) and allowed the substrates to
enter the interlayer region more easily.
Entry
1
Aryl bromide/iodide
Alkyne
T [h]
1
Yield [%][b]
94
93
92
93
87
85
96
93
95
94
92
93
2
12
1.5
10
1.5
12
2
3
4
5
Furthermore, the bases, catalyst loadings, and reaction tem-
perature were also screened. Of the bases tested (Table 1, en-
tries 2 and 10–13), K2CO3 was found to be the most efficient
base and resulted in a 93% yield. If the loading of the catalyst
was changed to 0.30 mol%, the yield did not increase signifi-
cantly (Table 1, entry 7), whereas a decrease in the catalyst
loading to 0.10 mol% gave only a 72% yield (Table 1, entry 8).
When the temperature was decreased from 80 to 608C, the
yield of product reduced from 93 to 65% (Table 1, entry 9), so
the reaction temperature was maintained at 808C.
6
7
8
15
10
10
14
14
9
10
11
12
To expand the scope of the reaction, we investigated the
copper-free Sonogashira coupling of various aryl halides and
terminal alkynes under the optimized conditions; the results
are shown in Table 2. In most cases the desired products were
obtained in excellent yields with both aryl iodides and aryl bro-
mides and the reactions proceeded rapidly (1–15 h). In particu-
lar, aryl bromides with an electron-rich or -deficient group
could proceed smoothly to give the desired products in 92 to
95% yields (Table 2, entries 9–12). In view of the steric hin-
drance, the products were obtained in moderate yields with 2-
bromotoluene (82%, Table 2, entry 13) and 2-bromo-p-xylene
(80%, Table 2, entry 14) as the starting materials. Moreover, the
coupling of 4-bromopyridine and 5-bromopyrimidine also gave
the products in 91 and 92% yields (Table 2, entries 15 and 16).
The copper-free Sonogashira reactions of some aryl chlorides
were also studied (Table 3). We found that the reaction of
chlorobenzene and phenylacetylene proceeded sluggishly and
gave a lower yield under the same conditions (Table 3,
entry 1). Remarkably, the yield was greatly improved when the
loading of Pd was increased (1.00 mol%) with PdMgAl-LDH-2
in place of PdMgAl-LDH-1 (Table 3, entry 2). However, addition
of a catalytic amount of Na2H2EDTA as a chelating ligand nota-
bly shortened the reaction time (Table 3, entry 5) compared
with other ligands, such as l-proline (Table 3, entry 3) and gly-
cine (Table 3, entry 4). This may be ascribed to the fact that the
ligand binds to the Pd0 species and facilitates oxidative addi-
tion to the CÀCl bond.[21] Different aryl halides were used to
assess the scope of the copper-free Sonogashira reaction and
all gave moderate yields (Table 3, entries 5–10).
13
14
14
14
82
80
15
16
12
12
91
92
[a] Reagents and conditions: aryl halide (1.00 mmol), terminal alkyne
(1.10 mmol), K2CO3 (2.00 mmol), NaVc (0.01 mmol), CTAB (0.10 mmol), and
H2O (3 mL). [b] Isolated yield.
alysts. Similarly, parallel results were obtained for the reaction
of chlorobenzene with phenyl acetylene catalyzed by PdMgAl-
LDH-2 (Table 3, entry 5) and Pd/MgAl-LDH-2 (Table 3, entry 11),
respectively. Pd in the PdMgAl-LDH catalysts is implanted in
the layers of the LDH, whereas Pd in the Pd/MgAl-LDH cata-
lysts is found in the interlayer region of the LDH. This differ-
ence means that it is more difficult for aryl halide molecules to
reach the Pd0 species in PdMgAl-LDH than in Pd/MgAl-LDH.
To verify that the catalytic activity originated from Pd species
implanted in the LDH layers rather than Pd species leached
into solution, the Sonogashira reaction of bromobenzene and
phenylacetylene in the presence of PdMgAl-LDH-1 was con-
ducted. Two parallel reactions were stirred at 808C for 4 h,
then the catalyst was removed from the solution by simple fil-
tration. In one reaction the conversion was found to be 48%,
whereas the other reaction was continued with the filtrate for
a further 8 h; the conversion was found to be almost un-
changed. ICP-MS analysis of the filtrate indicated that only
For comparison, catalysts PdMgAl-LDH-1,2 and Pd/MgAl-
LDH-1,2 were used to catalyze the same model reaction
(Table 4). We found that the activity of PdMgAl-LDH-1 was
slightly lower than that of Pd/MgAl-LDH-1, which can be as-
cribed to the different locations of the Pd species in these cat-
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Table 3. Sonogashira reactions of aryl chlorides with phenylacetylene cat-
alyzed by MgAl-LDH-2.[a]
Table 5. Changes in Pd loading in two catalysts after five cycles of Sono-
gashira reactions.[a]
Catalyst
Pd [%] (w/w)
Fresh catalyst
Used catalyst
Leached Pd
Entry
1
Aryl chloride
Additive
T [h]
72
72
48
48
48
36
36
48
48
48
36
Yield [%][b]
PdMgAl-LDH-1
Pd/MgAl-LDH-1
0.50
0.56
0.48
0.44
0.02
0.12
none
45[c]
75
[a] Reagents and conditions: bromobenzene (1.00 mmol), phenyl acety-
lene (1.10 mmol), K2CO3 (2.00 mmol), NaVc (0.01 mmol), CTAB
(0.10 mmol), and H2O (3 mL).
2
none
3
l-proline
glycine
72
4
75
With a viable protocol in hand, we propose a plausible
mechanism for the copper-free Sonogashira reaction mediated
by PdMgAl-LDH (Figure 6), which proceeds similarly to that in
homogeneous catalysis and involves a typical Pd0/PdII cycle.[22]
The cycle is initiated by the creation of Pd0 species I, followed
by oxidative addition with aryl halide to II, in which the basic
layers of the LDH increase the electron density around the Pd
center to accelerate oxidative addition.[11a,23] Then, coordination
with the terminal alkyne leads to III with a subsequent depro-
tonation to give IV, which undergoes reductive elimination to
yield the final product and restart the catalytic cycle.
5
Na2H2EDTA
Na2H2EDTA
Na2H2EDTA
Na2H2EDTA
Na2H2EDTA
Na2H2EDTA
Na2H2EDTA
82
6
85
7
79
8
84
9
81
10
11
76
84[d]
[a] Reagents and conditions: aryl chloride (1.00 mmol), phenyl acetylene
(1.10 mmol), K2CO3 (2.00 mmol), NaVc (0.05 mmol), CTAB (0.10 mmol), ad-
ditive (0.10 mmol), and H2O (3 mL). [b] Isolated yield. [c] PdMgAl-LDH-1
(0.20 mol% Pd). [d] Pd/MgAl-LDH-2 (1.00 mol% Pd).
Table 4. Comparison of the Sonogashira reaction between bromoben-
zene and phenylacetylene, catalyzed by various catalysts.[a]
Catalyst
T [h]
Yield [%][b]
TON[c]
TOF[d]
PdMgAl-LDH-1
Pd/MgAl-LDH-1
12
8
93
92
465
460
38.8
57.5
[a] Reagents and conditions: bromobenzene (1.00 mmol), phenyl acety-
lene (1.10 mmol), K2CO3 (2.00 mmol), NaVc (0.01 mmol), CTAB
(0.10 mmol), and H2O (3 mL). [b] Isolated yield. [c] TON=turnover
number=mmol of product per mmol of Pd catalyst. [d] TOF=TON/time.
Figure 6. A plausible mechanism for the PdMgAl-LDH-catalyzed copper-free
Sonogashira reaction.
2.2.2. Application in the Suzuki Reaction
about 0.005% of the total Pd had leached into the solution.
These results strongly confirmed that coupling reactions cata-
lyzed by PdMgAl-LDH proceed heterogeneously.
To extend the application scope, the PdMgAl-LDH catalysts
were then applied in the Suzuki coupling reaction. Most condi-
tions optimized for the copper-free Sonogashira reaction were
used directly and the results are shown in Table 6. Similar to
the Sonogashira reaction, if 0.20 mol% Pd loading of PdMgAl-
LDH-1 was used, aryl iodides and aryl bromides with either
electron-rich (Table 6, entries 7,8) or electron-deficient groups
(Table 6, entries 5–6 and 9–10) gave the coupling products in
yields of 91 to 96% over 2 to 15 h. As expected, with
1.00 mol% Pd in PdMgAl-LDH-2 and with Na2H2EDTA as the
ligand, the desired products were obtained from aryl chlorides
Next, the degree of leaching of Pd from two different cata-
lysts, PdMgAl-LDH-1 and Pd/MgAl-LDH-1, was tested after the
fifth Sonogashira reaction cycle of bromobenzene with phenyl
acetylene. In all cases, the catalyst was exhaustively removed
by filtration and the amount of Pd species leached into solu-
tion was determined by using ICP-MS. As shown in Table 5,
PdMgAl-LDH-1 is a very stable catalyst that leached only
0.02% Pd after five cycles.
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Table 6. Evaluation of the PdMgAl-LDH-1 catalyst applied to Suzuki reac-
tions of aryl halides with aryl boronic acid.[a]
Table 7. Evaluation of the PdMgAl-LDH-1 catalyst applied to Heck reac-
tions of aryl halides with alkenes.[a]
Entry
Aryl halide
Arylboronic acid
T [h]
2
Yield [%][b]
Entry
1
Aryl halide
Alkene
T [h]
5
Yield [%][b]
92
1
2
3
4
5
6
7
8
9
93
90
96
94
96
93
91
93
93
12
2
2
16
4
90
3
93
10
8
4
12
10
10
16
16
48
36
48
48
91
5
94
8
6
93
15
15
10
7
92
8
94
10
10
95
9
67[c]
75[c]
69[c]
62[c]
10
11
12
11
12
13
14
15
48
32
36
48
48
80[c]
86[c]
84[c]
78[c]
76[c]
[a] Reagents and conditions: aryl halide (1.00 mmol), acrylate or styrene
(1.10 mmol), K2CO3 (2.00 mmol), NaVc (0.01 mmol), CTAB (0.10 mmol), and
H2O/DMF (2:1, 3 mL). [b] Isolated yield. [c] PdMgAl-LDH-2 (1.00 mol% Pd),
NaVc (0.05 mmol) and Na2H2EDTA (0.10 mmol).
[a] Reagents and conditions: aryl halide (1.00 mmol), arylboronic acid
(1.10 mmol), K2CO3 (2.00 mmol), NaVc (0.01 mmol), CTAB (0.10 mmol), and
H2O (3 mL). [b] Isolated yield. [c] PdMgAl-LDH-2 (1.00 mol% Pd), NaVc
(0.05 mmol), and Na2H2EDTA (0.10 mmol).
yields of 62 to 94%. These results are better than those report-
ed previously,[12a] and some reactions were conducted under
relatively mild conditions.
In summary, heterogeneous PdMgAl-LDH catalysts were suc-
cessfully applied for copper-free Sonogashira, Suzuki, and Heck
reactions of various aryl halides with good-to-excellent yields
in most cases. The chemical structures of all target products
were identified by using IR, 1H, 13C NMR spectroscopies and
HRMS (see the Supporting Information).
in yields of 76 to 86% (Table 6, entries 11–13). This is markedly
different from the result reported previously,[12b] in which the
reaction of bromobenzene and phenylboronic acid catalyzed
by PdMgAl-LDH obtained through co-precipitation by using a
single-drop method only gave a 10% yield. However, the yield
of the same reaction catalyzed by our catalyst was 90%
(Table 6, entry 2). This can be attributed to the fact that our
catalyst was prepared through co-precipitation by using a
double-drop technique, which gives higher catalytic activity.
Additionally, sodium ascorbate and CTAB play a vital role in
the present protocol.
2.3. Catalyst Reusability
Reusability is an important feature for heterogeneous catalysts.
To assess the reusability of PdMgAl-LDH, repeated model So-
nogashira, Suzuki, and Heck reactions were carried out. In all
cases, the catalyst could be recovered easily from the terminat-
ed reaction mixture by filtration or centrifugation. The recov-
ered catalyst was washed with hot EtOH before it was used for
the next cycle under the same conditions. As shown in
Figure 7, the catalyst can be recycled six times without a
marked loss in catalytic activity. Additionally, the morphology
of PdMgAl-LDH-1 used in the Sonogashira reaction was moni-
tored by using TEM analysis. The results revealed that there
2.2.3. Application in the Heck Reaction
To extend the application scope, we also assessed the Heck
olefination of various aryl halides mediated by PdMgAl-LDH
catalysts in the presence of K2CO3 in H2O/DMF (2:1 v/v;
Table 7). Satisfyingly, all aryl halides with iodide, bromide, and
chloride were converted into the corresponding products in
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Table 8. Evaluation of the PdMgAl-LDH-1R catalyst applied to Sonoga-
shira, Suzuki, and Heck reactions.[a]
Reaction
Sonogashira
Suzuki
PhY
T [h]
12
Yield [%][b]
92 (93)
12
89 (90)
Heck
16
88 (90)
&
*
Figure 7. Reusability of PdMgAl-LDH-1 in the Sonogashira ( ), Suzuki ( ),
~
and Heck ( ) coupling reactions.
[a] Reagents and conditions: bromobenzene (1.00 mmol), PhY
(1.10 mmol), K2CO3 (2.00 mmol), NaVc (0.01 mmol), CTAB (0.10 mmol), and
H2O (3 mL). Note: for Heck reaction, H2O/DMF (2:1 v/v, 3 mL) and 1008C.
[b] Isolated yield, data in parentheses refer to yields obtained with
PdMgAl-LDH-1.
was no obvious aggregation of Pd species in the catalyst after
the fifth cycle; however, the Pd species essentially cluster to-
gether after the tenth cycle (Figure S6), which is the key
reason for catalyst deactivation.
Furthermore, these catalysts are easy to prepare and reactivate,
and showed low loss of Pd species.
2.4. Catalyst Reactivation
For practical applications of a promising heterogeneous cata-
lyst, easy reactivation is very significant because deactivation is
inevitable. In fact, it is very difficult to reactivate the original
morphology and catalytic activity of most heterogeneous Pd
catalysts. However, we have successfully developed a tech-
nique that can efficiently reactivate the deactivated PdMgAl-
LDH catalyst, in which deactivated PdMgAl-LDH-1 (after ten
cycles) was washed thoroughly with hot EtOH to remove or-
ganic contaminants, then the amount of Pd was determined
by using ICP-MS, followed by a co-precipitation process to pro-
duce the PdMgAl-LDH-1R catalyst.
Experimental Section
General Information
All chemical reagents were purchased and used without further
purification. H2O was boiled for 3 h to remove oxygen. DMF was
distilled under reduced pressure over CaH2. All reactions were car-
ried out under an N2 atmosphere by using standard Schlenk tech-
niques. The powder XRD patterns were recorded by using a Bruker
D8 Advance X-ray diffractometer. The DTA analyses were recorded
by using a thermogravimetric analysis instrument (SDTQ 600). The
TEM images were obtained by using TEM apparatus (JEM-2100).
FTIR spectra were recorded by using a Bruker Alpha FT-IR spectro-
photometer. The ICP-MS data were recorded by using an IRIS Ad-
vantage Radial instrument under standard conditions. 1H and
13C NMR spectra were recorded by using a BRUKER ADVANCE 300
spectrometer. Mass spectrometric data were collected by using a
maXis UHR-TOF mass spectrometer. Melting points were measured
by using a Yanaco MP-500 micro melting point apparatus and are
uncorrected.
The morphology of PdMgAl-LDH-1R is almost the same as
the original PdMgAl-LDH-1 catalyst, as identified by using
powder XRD (Figure S7) and TEM (Figure 4d) analyses. More-
over, ICP-MS data revealed that the PdMgAl-LDH-1R catalyst
contained 0.44% Pd (w/w) and only 0.02% Pd was lost in the
reactivation procedure.
The catalytic performance of the PdMgAl-LDH-1R catalyst
was evaluated in copper-free Sonogashira, Suzuki, and Heck re-
actions (Table 8) and is very similar to the original PdMgAl-
LDH-1 catalyst in all cases. This confirmed that our reactivation
method for PdMgAl-LDH catalysts is reliable and facile.
General Procedure for the Preparation of Catalysts
Solution A, which contained Mg, Al, and Pd nitrates in an appropri-
ate ratio, and solution B, which contained proportional NaOH and
Na2CO3 bases, were made up. Solutions A and B were then simulta-
neously added dropwise to stirred, deionized H2O (9 mL) at such a
rate that the pH of the reaction mixture was maintained at 9.5. The
mixing process was performed at RT. The resulting slurry was aged
for 13 h at 1008C, then the precipitate was filtered, washed fully
with deionized H2O, and dried for 24 h at 1008C to give the
PdMgAl-LDH catalyst.
3. Conclusions
Two new heterogeneous catalysts, PdMgAl-LDH-1 and
PdMgAl-LDH-2, were prepared by a co-precipitation method
with the double-drop technique and characterized by using
powder XRD, TG-DTA, TEM, EDS, and XPS techniques. The cata-
lysts can efficiently catalyze copper-free Sonogashira, Suzuki,
and Heck reactions for diverse aryl iodides, bromides, and
chlorides with K2CO3 base in aqueous media. The Pd species
within the PdMgAl-LDH layers are stable enough to be cycled
in at least six consecutive runs with high catalytic performance.
PdMgAl-LDH-1 (0.50% Pd w/w)
Pd(NO3)2·2H2O (0.027 g, 0.10 mmol), Mg(NO3)2·6H2O (4.590 g,
17.90 mmol), and Al(NO3)3·9H2O (2.251 g, 6.00 mmol) were dis-
solved in deionized H2O (10 mL) to give solution A, to which
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0.10 molLÀ1 HNO3 (1 mL) was added to avoid hydrolysis of palladi-
um nitrate. NaOH (1.540 g, 38.50 mmol) and Na2CO3 (1.272 g,
12.00 mmol) were dissolved in deionized H2O (11 mL) to form
mixed-base solution B. Then, following the general procedure,
PdMgAl-LDH-1 was prepared as a grey solid (yield: 1.954 g, 0.50%
Pd w/w).
General Procedure for Heck Reactions
mixture of aryl halide (1.00 mmol), acrylate or styrene
A
(1.10 mmol), K2CO3 (2.00 mmol), PdMgAl-LDH-1 (0.043 g,
0.20 mol% Pd) or PdMgAl-LDH-2 (0.041 g, 1.00 mol% Pd), CTAB
(0.10 mmol), sodium ascorbate (0.01 mmol or 0.05 mmol) in DMF/
H2O (3 mL, 1:2) was placed in a 25 mL round-bottom flask and
stirred at 1008C under an N2 atmosphere. After completion, the re-
action mixture was cooled to RT and diluted with ethyl acetate,
then the slurry was ultrasonicated to remove the product from the
catalyst surface. The catalyst was separated by centrifugation, and
the centrifugate was washed with brine, dried over anhydrous
MgSO4, and the crude product was purified by using flash column
chromatography (hexane/ethyl acetate) to obtain the desired
purity.
PdMgAl-LDH-2 (2.58% Pd w/w)
Following the same procedure as for PdMgAl-LDH-1,
Mg(NO3)2·6H2O (4.487 g, 17.50 mmol) and Pd(NO3)2·2H2O (0.133 g,
0.50 mmol) were used to give PdMgAl-LDH-2 as a dark-grey solid
(yield: 2.012 g, 2.58% Pd w/w).
Diphenylacetylene
General Procedure for the Reactivation of PdMgAl-LDH
White solid; eluent: ethyl acetate/hexane (1:20), Rf =0.6; m.p.: 58–
1
598C; H NMR (300 MHz, CDCl3, TMS): ä=7.58–7.55 (m, 4H; ArH),
The deactivated catalyst was first washed twice with hot EtOH to
remove organic contaminants, then dried and used in the reactiva-
tion procedure.
7.39–7.30 ppm (m, 6H; ArH); 13C NMR (75 MHz, CDCl3, TMS): ä=
131.66, 128.39, 128.29, 123.37, 89.47 ppm; IR (neat): ímax =1596,
1492, 748, 681 cmÀ1; HRMS (APCI): m/z calcd for C14H11 [M+H]+:
179.0861; found: 179.0865.
Deactivated PdMgAl-LDH-1 (2.000 g, 0.46% Pd w/w, as confirmed
by ICP) was treated with 20% HNO3 (11 mL) and heated to give
transparent solution A. NaOH (3.200 g, 80.00 mmol) and Na2CO3
(1.272 g, 12.00 mmol) were dissolved in deionized H2O (11 mL) to
create mixed-base solution B. Then, following the general proce-
dure for the preparation of the catalysts, PdMgAl-LDH-1R was ob-
tained as a grey solid (yield: 1.966 g, 0.44% Pd w/w).
2-Methyl-4-phenylbut-3-yn-2-ol
Yellow oil; eluent: ethyl acetate/hexane (1:3), Rf =0.5; 1H NMR
(300 MHz, CDCl3, TMS): ä=7.43–7.40 (m, 2H; ArH), 7.39–7.29 (m,
3H; ArH), 2.01 (s, 1H; -OH), 1.62 ppm (s, 6H; -CH3); 13C NMR
(75 MHz, CDCl3, TMS): ä=131.63, 128.22, 122.76, 93.82, 82.14,
65.60, 31.49 ppm; IR (neat): ímax =3271, 2207, 1596, 1486, 753,
690 cmÀ1; HRMS (ESI): m/z calcd for C11H13O [M+H]+: 161.0966;
found: 161.0970.
General Procedure for Sonogashira Reactions
CTAB (0.10 mmol), sodium ascorbate (0.01 mmol or 0.05 mmol),
and H2O (3 mL) were added to
a mixture of aryl halide
(1.00 mmol), terminal alkyne (1.10 mmol), K2CO3 (2.00 mmol), and
PdMgAl-LDH-1 (0.043 g, 0.20 mol% Pd) or PdMgAl-LDH-2 (0.041 g,
1.00 mol% Pd) in a 25 mL round-bottom flask The resulting mix-
ture was stirred at 808C under an N2 atmosphere. After comple-
tion, the mixture was cooled to RT and diluted with ethyl acetate,
then the slurry was ultrasonicated to remove the product from the
catalyst surface. The catalyst was separated by centrifugation, and
the centrifugate was washed with brine, dried over anhydrous
MgSO4, and the final products were purified by using flash column
chromatography (hexane/ethyl acetate) to obtain the desired
purity.
1-n-Propyl-2-phenylacetylene
Yellow oil; eluent: ethyl acetate/hexane (1:20), Rf =0.5; 1H NMR
(300 MHz, CDCl3, TMS): ä=7.42–7.39 (m, 2H; ArH), 7.32–7.28 (m,
3H; ArH), 2.40 (t, J=6.90 Hz, 2H; -CH2), 1.71–1.59 (m, 2H; -CH2),
1.06 ppm (t, J=7.35 Hz, 3H; -CH3); 13C NMR (75 MHz, CDCl3, TMS):
ä=131.53, 128.14, 127.42, 124.13, 90.21, 80.71, 22.21, 21.38,
13.50 ppm; IR (neat): ímax =2235, 1598, 1498, 753, 689 cmÀ1; HRMS
(APCI): m/z calcd for C11H13 [M+H]+: 145.1017; found: 145.1021.
1-Ferrocenyl-2-phenylacetylene
Orange solid; eluent: ethyl acetate/hexane (1:15), Rf =0.6; m.p.:
117–1198C; 1H NMR (300 MHz, CDCl3, TMS): ä=7.53–7.49 (m, 2H;
ArH), 7.36–7.32 (m, 3H; ArH), 4.53 (s, 2H; FcH), 4.27 ppm (s, 7H;
FcH); 13C NMR (75 MHz, CDCl3, TMS): ä=131.43, 128.30, 127.68,
General Procedure for Suzuki Reactions
A mixture of aryl halide (1.00 mmol), arylboronic acid (1.10 mmol),
K2CO3 (2.00 mmol), PdMgAl-LDH-1 (0.043 g, 0.20 mol% Pd) or
PdMgAl-LDH-2 (0.041 g, 1.00 mol% Pd), CTAB (0.10 mmol), sodium
ascorbate (0.01 mmol or 0.05 mmol), and H2O (3 mL) was placed in
a 25 mL round-bottom flask and stirred at 808C under an N2 at-
mosphere. After completion, the reaction mixture was cooled to
RT and diluted with ethyl acetate, then the slurry was ultrasonicat-
ed to remove the product from the catalyst surface. The catalyst
was separated by using centrifugation, and the centrifugate was
washed with brine, dried over anhydrous Mg2SO4, concentrated
under reduced pressure, and purified by using flash column chro-
matography (hexane/ethyl acetate) to give the desired product.
123.98, 88.33, 85.76, 71.50, 70.09, 68.93, 65.44 ppm; IR (neat): ímax
=
2196, 1593, 1488, 690, 751 cmÀ1; HRMS (APCI): m/z calcd for
C18H15Fe [M+H]+: 287.0523; found: 287.0528
4-Nitrophenyl-2-phenylacetylene
Pale yellow solid; eluent: ethyl acetate/hexane (1:10), Rf =0.6; m.p.:
1
118–1198C; H NMR (300 MHz, CDCl3, TMS): ä=8.22 (d, J=8.40 Hz,
2H; ArH), 7.67 (d, J=8.40 Hz, 2H; ArH), 7.57–7.55 (m, 2H; ArH),
7.41–7.39 ppm (m, 3H; ArH); 13C NMR (75 MHz, CDCl3, TMS): ä=
147.02, 132.25, 131.84, 130.26, 129.26, 128.53, 123.61, 122.13,
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94.70, 87.55 ppm; IR (neat): ímax =2207, 1586, 1508, 1339, 853, 756,
685 cmÀ1; HRMS (ESI): m/z calcd for C14H10NO2 [M+H]+: 224.0712;
found: 224.0715.
2,5-Dimethylphenyl-2-phenylacetylene
Pale yellow solid; eluent: ethyl acetate/hexane (1:20), Rf =0.5; m.p.:
80–828C; 1H NMR (300 MHz, CDCl3, TMS): ä=7.56–7.55 (m, 2H;
ArH), 7.38–7.36 (m, 4H; ArH), 7.15 (d, J=7.80 Hz, 1H; ArH), 7.07 (d,
J=7.80 Hz, 1H; ArH), 2.50 (s, 3H; -CH3), 2.34 ppm (s, 3H; -CH3);
13C NMR (75 MHz, CDCl3, TMS): ä=137.12, 135.06, 132.34, 131.53,
129.39, 129.24, 128.36, 128.11, 123.70, 122.80, 92.98, 88.59, 20.78,
20.25 ppm; IR (neat): ímax =2915, 2203, 1594, 1485, 810, 895, 749,
684 cmÀ1; HRMS (APCI): m/z calcd for C16H15 [M+H]+: 207.1174;
found: 207.1178.
4-Phenylethynylacetophenone
White solid; eluent: ethyl acetate/hexane (1:10), Rf =0.5; m.p.: 94–
1
968C; H NMR (300 MHz, CDCl3, TMS): ä=7.96 (d, J=8.40 Hz, 2H;
ArH), 7.63 (d, J=8.40 Hz, 2H; ArH), 7.59–7.56 (m, 2H; ArH), 7.40–
7.38 (m, 3H; ArH), 2.63 ppm (s, 3H; -CH3); 13C NMR (75 MHz, CDCl3,
TMS): ä=197.24, 136.23, 131.7, 131.74, 128.80, 128.43, 128.26,
122.68, 92.70, 88.60, 26.57 ppm; IR (neat): ímax =2216, 1674, 1594,
1515, 830, 754, 688 cmÀ1; HRMS (ESI): m/z calcd for C16H13O
[M+H]+: 221.0966; found: 221.0962.
4-(Phenylethynyl)pyridine
Pale yellow solid; eluent: ethyl acetate/hexane (1:3), Rf =0.6; m.p.:
93–958C; 1H NMR (300 MHz, CDCl3, TMS): ä=8.62 (d, J=6.00 Hz,
2H; PyH), 7.59–7.56 (m, 2H; PyH), 7.41–7.39 ppm (m, 5H; ArH);
13C NMR (75 MHz, CDCl3, TMS): ä=149.66, 131.90, 131.52, 129.24,
128.52, 125.81, 122.12, 94.04, 86.68 ppm; IR (neat): ímax =2214,
1577, 1533, 1406, 754, 689 cmÀ1; HRMS (ESI): m/z calcd for C13H10N
[M+H]+: 180.0813; found: 180.0815.
4-Phenylethynylaniline
Brown solid; eluent: ethyl acetate/hexane (1:3), Rf =0.5; m.p.: 123–
1
1258C; H NMR (300 MHz, CDCl3, TMS): ä=7.54–7.51 (m, 2H; ArH),
7.38–7.31 (m, 5H; ArH), 6.66 (d, J=8.40 Hz, 2H; ArH), 3.83 ppm (s,
2H; -NH2); 13C NMR (75 MHz, CDCl3, TMS): ä=146.66, 132.96,
131.36, 128.25, 127.64, 123.96, 114.75, 112.69, 90.14, 87.34 ppm; IR
5-(Phenylethynyl)pyrimidine
Yellow oil; eluent: ethyl acetate/hexane (1:3), Rf =0.5; 1H NMR
(300 MHz, CDCl3, TMS): ä=9.14 (s, 1H; PyrimH), 8.86 (s, 2H;
PyrimH), 7.57–7.54 (m, 2H; ArH), 7.40–7.35 ppm (m, 3H; ArH);
13C NMR (75 MHz, CDCl3, TMS): ä=158.63, 156.71, 131.80, 129.39,
128.57, 121.80, 119.96, 96.35, 82.31 ppm; IR (neat): ímax =2212,
1598, 1482, 1408, 759, 687 cmÀ1; HRMS (ESI): m/z calcd for C12H9N2
[M+H]+: 181.0766; found: 181.0761.
(neat): ímax =3472, 3375, 2207, 1611, 1508, 822, 751, 685 cmÀ1
;
HRMS (ESI): m/z calcd for C14H12N [M+H]+: 194.0970; found:
194.0972.
4-Methylphenyl-2-phenylacetylene
White solid; eluent: ethyl acetate/hexane (1:20), Rf =0.5; m.p.: 68–
1
708C; H NMR (300 MHz, CDCl3, TMS): ä=7.55–7.51 (m, 2H; ArH),
Biphenyl
7.43 (d, J=8.10 Hz, 2H; ArH), 7.37–7.33 (m, 3H; ArH), 7.16 (d, J=
8.10 Hz, 2H; ArH), 2.37 ppm (s, 3H; -CH3); 13C NMR (75 MHz, CDCl3,
TMS): ä=138.41, 131.58, 131.53, 129.14, 128.34, 128.10, 123.53,
120.24, 89.60, 88.76, 21.53 ppm; IR (neat): ímax =2917, 2210, 1584,
1500, 814, 752, 687 cmÀ1; HRMS (APCI): m/z calcd for C15H13
[M+H]+:193.1017; found: 193.1022.
White solid; eluent: ethyl acetate/hexane (1:20), Rf =0.6; m.p.: 69–
708C; H NMR (300 MHz, CDCl3, TMS): ä=7.61 (d, J=6.90 Hz, 4H;
ArH), 7.46 (t, J=7.35 Hz, 4H; ArH), 7.36 ppm (t, J=7.35 Hz, 2H;
ArH); 13C NMR (75 MHz, CDCl3, TMS): ä=141.30, 128.80, 127.30,
127.22 ppm; IR (neat): ímax =1569, 1470, 723, 688 cmÀ1; HRMS
(APCI): m/z calcd for C12H11 [M+H]+: 155.0861; found: 155.0866.
1
4-Methylbiphenyl
4-Methoxyphenyl-2-phenylacetylene
White solid; eluent: ethyl acetate/hexane (1:20), Rf =0.5; m.p.: 46–
488C; H NMR (300 MHz, CDCl3, TMS): ä=7.63 (d, J=7.20 Hz, 2H;
White solid; eluent: ethyl acetate/hexane (1:15), Rf =0.5; m.p.: 56–
588C; H NMR (300 MHz, CDCl3, TMS): ä=7.55–7.48 (m, 4H; ArH),
1
1
ArH), 7.54 (d, J=8.10 Hz, 2H; ArH), 7.47 (t, J=7.50 Hz, 2H; ArH),
7.36 (t, J=7.35 Hz, 1H; ArH), 7.30 (d, J=8.10 Hz, 2H; ArH),
2.44 ppm (s, 3H; -CH3); 13C NMR (75 MHz, CDCl3, TMS): ä 141.24,
138.43, 137.06, 129.54, 128.77, 127.23, 127.04, 21.16 ppm; IR (neat):
7.37–7.33 (m, 3H; ArH), 6.90 (d, J=9.00 Hz, 2H; ArH), 3.85 ppm (s,
3H; -CH3); 13C NMR (75 MHz, CDCl3, TMS): ä=159.65, 133.07,
131.47, 128.32, 127.94, 123.64, 115.43, 114.02, 89.39, 88.08,
55.32 ppm; IR (neat): ímax =2931, 2207, 1595, 1501, 832, 751,
687 cmÀ1; HRMS (APCI): m/z calcd for C15H13O [M+H]+: 209.0966;
found: 209.0970.
í
max =2912, 1600, 1478, 821, 749, 685 cmÀ1; HRMS (APCI): m/z calcd
for C13H13 [M+H]+: 169.1017; found: 169.1013.
4-Nitrobiphenyl
3-Methylphenyl-2-phenylacetylene
Pale yellow solid; eluent: ethyl acetate/ hexane (1:15), Rf =0.5;
m.p.: 114–1168C; 1H NMR (300 MHz, [D6]DMSO, TMS): ä=8.30 (d,
J=9.00 Hz, 2H; ArH), 7.96 (d, J=8.70 Hz, 2H; ArH), 7.80–7.77 (m,
2H; ArH), 7.56–7.45 ppm (m, 3H; ArH); 13C NMR (75 MHz,
[D6]DMSO, TMS): ä=147.15, 147.09, 138.29, 129.68, 129.50, 128.30,
127.71, 124.52 ppm; IR (neat): ímax =1591, 1506, 1396, 847, 733,
691 cmÀ1; HRMS (ESI) : m/z calcd for C12H10NO2 [M+H]+: 200.0712;
found: 200.0717.
Colorless oil; eluent: ethyl acetate/hexane (1:20), Rf =0.6; 1H NMR
(300 MHz, CDCl3, TMS): ä=7.58–7.51 (m, 3H; ArH), 7.41–7.36 (m,
3H; ArH), 7.26–7.16 (m, 3H; ArH), 2.54 ppm (s, 3H; -CH3); 13C NMR
(75 MHz, CDCl3, TMS): ä=140.22, 131.88, 131.55, 129.50, 128.39,
128.34, 128.20, 125.62, 123.61, 123.07, 93.39, 88.39, 20.78 ppm; IR
(neat): ímax =2919, 2214, 1597, 1491, 750, 686 cmÀ1; HRMS (APCI):
m/z calcd for C15H13 [M+H]+: 193.1017; found: 193.1014.
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4-Phenylacetophenone
(E)-4-Nitrophenyl-2-styrene
White solid; eluent: ethyl acetate/hexane (1:10), Rf =0.5; m.p.: 120– Pale yellow solid; eluent: ethyl acetate/hexane (1:15), Rf =0.5; m.p.:
1
1
1228C; H NMR (300 MHz, CDCl3, TMS): ä=8.06 (d, J=8.40 Hz, 2H;
159–1608C; H NMR (300 MHz, CDCl3, TMS): ä=8.22 (d, J=9.0 Hz,
ArH), 7.71 (d, J=8.10 Hz, 2H; ArH), 7.65 (d, 2H; J=6.90 Hz, 2H;
ArH), 7.40–7.52 (m, 3H; ArH), 2.66 ppm (s, 3H; -CH3); 13C NMR
(75 MHz, CDCl3, TMS): ä=197.75, 145.81, 139.90, 135.89, 128.97,
128.93, 128.25, 127.29, 127.24, 26.67 ppm; IR (neat): ímax =2919,
1672, 1592, 1477, 835, 759, 683 cmÀ1; HRMS (ESI): m/z calcd for
C14H13O [M+H]+: 197.0966; found: 197.0961.
2H; ArH), 7.64 (d, J=8.70 Hz, 2H; ArH), 7.55 (d, J=7.20 Hz, 2H;
ArH), 7.43–7.33 (m, 3H; ArH), 7.28 (d, J=16.20 Hz, 1H; CH=CH),
7.15 ppm (d, J=16.20 Hz, 1H; CH=CH); 13C NMR (75 MHz, CDCl3,
TMS): ä=146.81, 143.87, 136.21, 133.34, 128.92, 128.87, 127.05,
126.88, 126.31, 124.16 ppm; IR (neat): ímax =3077, 2934, 1593, 1504,
1335, 832, 765, 691 cmÀ1; HRMS (ESI): m/z calcd for C14H12NO2
[M+H]+: 226.0868; found: 226.0863.
4-Methoxybiphenyl
(E)-4-Styrylbenzonitrile
White solid; eluent: ethyl acetate/hexane (1:12), Rf =0.5; m.p.: 86–
1
White solid; eluent: ethyl acetate/hexane (1:12), Rf =0.5; m.p.: 115–
878C; H NMR (300 MHz, CDCl3, TMS): ä=7.60–7.55 (m, 4H; ArH),
1
117 8C; H NMR (300 MHz, CDCl3, TMS): ä=7.64 (d, J=8.10 Hz, 2H;
7.45 (t, J=7.50 Hz, 2H; ArH), 7.33 (t, J=7.20 Hz, 1H; ArH), 7.02 (d,
J=8.70 Hz, 2H; ArH), 3.88 ppm (s, 3H; -CH3); 13C NMR (75 MHz,
CDCl3, TMS): ä=159.19, 140.86, 133.81, 128.72, 128.16, 126.74,
126.66, 114.24, 55.34 ppm; IR (neat): ímax =2961, 1600, 1518, 831,
755, 683 cmÀ1; HRMS (APCI): m/z calcd for C13H13O [M+H]+:
185.0966; found: 185.0969.
ArH), 7.59 (d, J=8.40 Hz, 2H; ArH), 7.54 (d, J=7.50 Hz, 2H; ArH),
7.41–7.29 (m, 3H; ArH), 7.22 (d, J=16.20 Hz, 1H; CH=CH),
7.09 ppm (d, J=16.50 Hz, 1H; CH=CH); 13C NMR (75 MHz, CDCl3,
TMS): ä=141.87, 136.32, 132.51, 132.45, 128.88, 128.66, 126.93,
126.89, 126.76, 119.04, 110.63 ppm; IR (neat): ímax =3024, 2924,
2222, 1596, 1497, 823, 756, 690 cmÀ1; HRMS (ESI): m/z calcd for
C15H12N [M+H]+: 206.0970; found: 206.0966.
4-Phenylpyridine
Pale yellow solid; eluent: ethyl acetate/hexane (1:1); m.p.: 77–
788C; 1H NMR (300 MHz, [D6]DMSO, TMS): ä=8.64 (d, J=6.00 Hz,
2H; PyH), 7.80 (d, J=6.00 Hz, 2H; PyH), 7.71–7.69 (m, 2H; PyH),
7.56–7.45 ppm (m, 3H; ArH); 13C NMR (75 MHz, [D6]DMSO, TMS):
ä=150.68, 147.45, 137.63, 129.67, 129.64, 127.24, 121.66 ppm; IR
(neat): ímax =1581, 1474, 755, 678 cmÀ1; HRMS (ESI): m/z calcd for
C11H10N [M+H]+: 156.0813; found: 156.0809.
(E)-4-Methylphenyl-2-styrene
White solid; eluent: ethyl acetate/hexane (1:20), Rf =0.6; m.p.: 121–
1
1238C; H NMR (300 MHz, CDCl3, TMS): ä=7.51 (d, J=6.90 Hz, 2H;
ArH), 7.42 (d, J=8.10 Hz, 2H; ArH), 7.35 (t, J=7.35 Hz, 2H; ArH),
7.26–7.24 (m, 1H; ArH), 7.17 (d, J=7.80 Hz, 2H; ArH), 7.08 (s, 2H;
CH=CH), 2.36 ppm (s, 3H; CH3); 13C NMR (75 MHz, CDCl3, TMS): ä=
137.55, 134.59, 129.42, 128.67, 127.74, 127.42, 126.45, 126.42,
21.27 ppm; IR (neat): ímax =3020, 2915, 1587, 1502, 804, 752,
686 cmÀ1; HRMS (APCI): m/z calcd for C15H15 [M+H]+: 195.1174;
found: 195.1176.
5-Phenylpyrimidine
Pale yellow solid; eluent: ethyl acetate/hexane (2:3), Rf =0.5; m.p.:
1
50–528C; H NMR (300 MHz, CDCl3, TMS): ä=9.22 (s, 1H; PyrimH),
8.97 (s, 2H; PyrimH), 7.61–7.45 ppm (m, 5H; ArH); 13C NMR
(75 MHz, CDCl3, TMS): ä=157.49, 154.91, 134.36, 134.29, 129.44,
(E)-4-Methoxylphenyl-2-styrene
White solid; eluent: ethyl acetate/hexane (1:20), Rf =0.5; m.p.: 135–
129.02, 127.00 ppm; IR (neat):
ímax =1577, 1497, 1408, 760,
1
1378C; H NMR (300 MHz, CDCl3, TMS): ä=7.49 (t, J=9.15 Hz, 4H;
693 cmÀ1; HRMS (APCI): m/z calcd for C10H9N2 [M+H]+: 157.0766;
ArH), 7.36 (t, J=7.50 Hz, 2H; ArH), 7.24–7.22 (m, 1H; ArH), 7.09 (d,
J=16.20 Hz, 1H; CH=CH), 6.99 (d, J=16.50 Hz, 1H; CH=CH), 6.92
(d, J=8.70 Hz, 2H; ArH), 3.85 ppm (s, 3H; CH3); 13C NMR (75 MHz,
CDCl3, TMS): ä=159.34, 137.68, 130.18, 128.65, 128.24, 127.72,
127.22, 126.65, 126.26, 114.16, 55.34 ppm; IR (neat): ímax =3056,
2918, 1595, 1503, 814, 750, 686 cmÀ1; HRMS (APCI): m/z calcd for
C15H15O [M+H]+: 211.1123; found: 211.1119.
found: 157.0762.
(E)-1,2-Diphenylethene
White solid; eluent: hexane, Rf =0.5; m.p.: 126–1278C; 1H NMR
(300 MHz, CDCl3, TMS): ä=7.53 (d, J=7.20 Hz, 4H; ArH), 7.37 (t, J=
7.35 Hz, 4H; ArH), 7.26 (t, J=7.20 Hz, 2H; ArH), 7.12 ppm (s, 2H;
CH=CH); 13C NMR (75 MHz, CDCl3, TMS): ä=137.39, 128.75, 128.73,
127.66, 126.56 ppm; IR (neat): ímax =3021, 2923, 1595, 1498, 757,
684 cmÀ1; HRMS (APCI): m/z calcd for C14H13 [M+H]+: 181.1017;
found: 181.1020
Acknowledgements
Methyl Cinnamate
We are grateful for financial support from the National Natural
Science Foundation of China (grant no. 21372147) and the Un-
dergraduate Innovative Research Training Program of China
(grant no. 201710445059).
Pale yellow solid; eluent: ethyl acetate/hexane (1:10), Rf =0.6; m.p.:
1
34–368C; H NMR (300 MHz, CDCl3, TMS): ä=7.70 (d, J=16.20 Hz,
1H; CH=CH), 7.54–7.51 (m, 2H; ArH), 7.39–7.37 (m, 3H; ArH), 6.45
(d, J=15.90 Hz, 1H; CH=CH), 3.81 ppm (s, 3H; CH3); 13C NMR
(75 MHz, CDCl3, TMS): ä=167.43, 144.88, 134.42, 130.30, 128.91,
128.08, 117.84, 51.70 ppm; IR (neat): ímax =3065, 2923,1711, 1632,
1489, 769, 713 cmÀ1; HRMS (APCI): m/z calcd for C10H11O2 [M+H]+:
163.0759; found: 163.0763.
Conflict of Interest
The authors declare no conflict of interest.
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ꢀ 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

[10] a) W. Y. Hernµndez, J. Lauwaert, P. Van Der Voort, A. Verberckmoes,
Green Chem. 2017, 19, 5269–5302; b) M. Daud, M. S. Kamal, F. Shehzad,
M. A. Al-Harthi, Carbon 2016, 104, 241–252; c) G. L. Fan, F. Li, D. G.
Evans, X. Duan, Chem. Soc. Rev. 2014, 43, 7040–7066; d) C. M. Li, M.
Wei, D. G. Evans, X. Duan, Small 2014, 10, 4469–4486; e) S. He, Z. An,
M. Wei, D. G. Evans, X. Duan, Chem. Commun. 2013, 49, 5912–5920;
f) Q. Wang, D. O’Hare, Chem. Rev. 2012, 112, 4124–4155; g) Z. P. Xu, J.
Zhang, M. O. Adebajo, H. Zhang, C. Zhou, Appl. Clay Sci. 2011, 53, 139–
150; h) S.-Y. Zhang, S.-G. Sun, Y.-S. Guo, X.-F. Lu, D.-S. Guo, Tetrahedron
Lett. 2018, 59, 3719–3723.
[11] a) B. M. Choudary, S. Madhi, N. S. Chowdari, M. L. Kantam, B. Sreedhar, J.
Am. Chem. Soc. 2002, 124, 14127–14136; b) M. I. Burrueco, M. Mora, C.
JimØnez-Sanchidriµn, J. R. Ruiz, Appl. Catal. A 2014, 485, 196–201; c) A.
Corma, H. García, A. Primo, J. Catal. 2006, 241, 123–131; d) H. Zhou,
G. L. Zhuo, X. Z. Jiang, J. Mol. Catal. A: Chem. 2006, 248, 26–31.
[12] a) T. H. Bennur, A. Ramani, R. Bal, B. M. Chanda, S. Sivasanker, Catal.
Commun. 2002, 3, 493–496; b) M. Mora, C. JimØnez-Sanchidriµn, J. R.
Ruiz, J. Colloid Interface Sci. 2006, 302, 568–575; c) M. Mora, C. JimØnez-
Sanchidriµn, J. R. Ruiz, J. Mol. Catal. A: Chem. 2008, 285, 79–83; d) S.
Liu, X. Jiang, G. Zhuo, J. Mol. Catal. A 2009, 290, 72–78.
Keywords: Heck reaction · heterogeneous catalysis
palladium · Sonogashira reaction · Suzuki reaction
·
[1] a) I. Paterson, R. D. M. Davies, R. Marquez, Angew. Chem. Int. Ed. 2001,
40, 603–607; Angew. Chem. 2001, 113, 623–627; b) K. C. Nicolaou, P. G.
Bulger, D. Sarlah, Angew. Chem. Int. Ed. 2005, 44, 4442–4489; Angew.
Chem. 2005, 117, 4516–4563; c) J. Magano, J. R. Dunetz, Chem. Rev.
2011, 111, 2177–2250; d) E. V. Vinogradova, B. P. Fors, S. L. Buchwald, J.
Am. Chem. Soc. 2012, 134, 11132–11135; e) Y. Yang, N. J. Oldenhuis, S. L.
Buchwald, Angew. Chem. Int. Ed. 2013, 52, 615–619; Angew. Chem.
2013, 125, 643–647.
[2] a) R. B. Bedford, C. S. J. Cazin, D. Holder, Coord. Chem. Rev. 2004, 248,
2283–2321; b) A. F. Littke, G. C. Fu, J. Am. Chem. Soc. 2001, 123, 6989–
7000; c) K. H. Shaughnessy, P. Kim, J. F. Hartwig, J. Am. Chem. Soc. 1999,
121, 2123–2132; d) C. J. Welch, J. Albaneze-Walker, W. R. Leonard, M.
Biba, J. DaSilva, D. Henderson, B. Laing, D. J. Mathre, S. Spencer, X. Bu,
T. Wang, Org. Process Res. Dev. 2005, 9, 198–205.
[3] a) A. Del Zotto, D. Zuccaccia, Catal. Sci. Technol. 2017, 7, 3934–3951;
b) F. Meemken, A. Baiker, Chem. Rev. 2017, 117, 11522–11569; c) .
Molnµr, Chem. Rev. 2011, 111, 2251–2320; d) L. Yin, J. Liebscher, Chem.
Rev. 2007, 107, 133–173; e) D. Zhang, Z. Wei, L. Yu, Sci. Bull. 2017, 62,
1325–1330; f) C. Chen, K. Cao, Z. Wei, Q. Zhang, L. Yu, Mater. Lett. 2018,
226, 63–66.
[13] Y. Zhao, F. Li, R. Zhang, D. G. Evans, X. Duan, Chem. Mater. 2002, 14,
4286–4291.
[14] X.-Z. Zhang, D.-Q. Li, M. Pu, D. G. Evans, X. Duan, Chin. J. Inorg. Chem.
2004, 20, 267–272.
[15] a) W. T. Reichle, S. Y. Kang, D. S. Everhardt, J. Catal. 1986, 101, 352–359;
b) M. R. Weir, J. Moore, R. A. Kydd, Chem. Mater. 1997, 9, 1686–1690.
[16] a) F. Li, J. Liu, D. G. Evans, X. Duan, Chem. Mater. 2004, 16, 1597–1602;
b) R. D. Shannon, Acta Crystallogr. 1976, A32, 751–767; c) F. Basile, G.
Fornasari, M. Gazzano, A. Vaccari, Appl. Clay Sci. 2000, 16, 185–200.
[17] a) F. Basile, G. Fornasari, M. Gazzano, A. Vaccari, Appl. Clay Sci. 2001, 18,
51–57; b) V. Rives, Mater. Chem. Phys. 2002, 75, 19–25.
[4] a) M. Seki, Synthesis 2006, 18, 2975–2992; b) Y. Kitamura, S. Sako, A.
Tsutsui, Y. Monguchi, T. Maegawa, Y. Kitade, H. Sajiki, Adv. Synth. Catal.
2010, 352, 718–730; c) M.-G. Hu, Z.-W. An, W.-S. Du, J. Li, A.-A. Gao,
Chin. J. Chem. 2007, 25, 1183–1186; d) S.-Y. Liu, H.-Y. Li, M.-M. Shi, H.
Jiang, X.-L. Hu, W.-Q. Li, L. Fu, H.-Z. Chen, Macromolecules 2012, 45,
9004–9009.
[5] a) M. Hosseini-Sarvari, Z. Razmi, M. M. Doroodmand, Appl. Catal. A 2014,
475, 477–486; b) D. Yuan, Q. Zhang, J. Dou, Catal. Commun. 2010, 11,
606–610; c) S. Shylesh, V. Schünemann, W. R. Thiel, Angew. Chem. Int.
Ed. 2010, 49, 3428–3459; Angew. Chem. 2010, 122, 3504–3537; d) A.
Grirrane, H. Garcia, A. Corma, J. Catal. 2013, 302, 49–57.
[6] a) V. Polshettiwar, C. Len, A. Fihri, Coord. Chem. Rev. 2009, 253, 2599–
2626; b) A. Khalafi-Nezhad, F. Panahi, Green Chem. 2011, 13, 2408–
2415; c) G. Park, S. Lee, S. J. Son, S. Shin, Green Chem. 2013, 15, 3468–
3473; d) T. Iwai, R. Tanaka, T. Harada, M. Sawamura, Chem. Eur. J. 2014,
20, 1057–1065.
[18] S. Velu, V. Ramkumar, A. Narayanan, C. S. Swamy, J. Mater. Sci. 1997, 32,
957–964.
[19] a) J. F. Moulder, W. F. Stickle, P. E. Sobol, K. D. Bomben, Handbook of X-
ray Photoelectron Spectroscopy, Physical Electronics Inc, USA 1995,
pp. 118–119; b) A. Gniewek, A. M. Trzeciak, J. J. Ziókowski, L. KÞpiÇski, J.
Wrzyszcz, W. Tylus, J. Catal. 2005, 229, 332–343; c) J. Yang, D. Wang, W.
Liu, X. Zhang, F. Bian, W. Yu, Green Chem. 2013, 15, 3429–3437; d) S.
Zhou, M. Johnson, J. G. C. Veinot, Chem. Commun. 2010, 46, 2411–
2413.
[20] a) R. Chinchilla, C. Nµjera, Chem. Rev. 2007, 107, 874–922; b) P. Siemsen,
R. C. Livingston, F. Diederich, Angew. Chem. Int. Ed. 2000, 39, 2632–
2657; Angew. Chem. 2000, 112, 2740–2767.
[21] a) X. Cui, Z. Li, C.-Z. Tao, Y. Xu, J. Li, L. Liu, Q. X. Guo, Org. Lett. 2006, 8,
2467–2470; b) Y.-C. Lai, H.-Y. Chen, W.-C. Hung, C.-C. Lin, F.-E. Hong, Tet-
rahedron 2005, 61, 9484–9489.
[22] a) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–2483; b) C. E. I.
Knappke, A. J. von Wangelin, Chem. Soc. Rev. 2011, 40, 4948–4962.
[23] K. Kaneda, M. Higuchi, T. Imanaka, J. Mol. Catal. 1990, 63, 33–36.
[7] a) L. Djakovitch, K. Koehler, J. Am. Chem. Soc. 2001, 123, 5990–5999;
b) L. Djakovitch, P. Rollet, Tetrahedron Lett. 2004, 45, 1367–1370.
[8] a) P. Lu, J. Lu, H. You, P. Shi, J. Dong, Prog. Chem. 2009, 21, 1434–1441;
b) A. Ohtaka, T. Yamaguchi, T. Teratani, O. Shimomura, R. Nomura, Mole-
cules 2011, 16, 9067–9076; c) M. H. Nguyen, A. B. Smith, Org. Lett. 2013,
15, 4258–4261; d) L. Yu, Y. Huang, Z. Wei, Y. Ding, C. Su, Q. Xu, J. Org.
Chem. 2015, 80, 8677–8683; e) L. Yu, Z. Han, Mater. Lett. 2016, 184,
312–314; f) L. Yu, Z. Han, Y. Ding, Org. Process Res. Dev. 2016, 20, 2124–
2129; g) Q. Wang, X. Jing, J. Han, L. Yu, Q. Xu, Mater. Lett. 2018, 215,
65–67; h) Y. Liu, D. Tang, K. Cao, L. Yu, J. Han, Q. Xu, J. Catal. 2018, 360,
250–260.
[9] a) F. Cavani, F. Trifirò, A. Vaccari, Catal. Today 1991, 11, 173–301; b) F.
Geng, R. Z. Ma, T. Sasaki, Acc. Chem. Res. 2010, 43, 1177–1185.
Received: July 6, 2018
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