Pyridinyl functionalized MCM-48 supported highly active heterogeneous palladium catalyst for cross-coupling reactions

Article abstract of DOI:10.1039/c4ra16677a

An MCM-48 supported 2-pyridinylmethanimine Pd-catalyst was found to be a highly efficient catalyst in the Mizoroki-Heck, Suzuki-Miyaura and copper-free Sonogashira cross-coupling reactions of aryl halides under aqueous reaction conditions. The catalyst efficiently promoted these coupling reactions with ppm levels of palladium to afford the corresponding coupling products in up to 98% yield. The supported Pd-catalyst was readily recovered and reused several times without significant loss of its catalytic activity. This journal is

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Pyridinyl Functionalized MCM-48 Supported Highly Active
Heterogeneous Palladium Catalyst for Cross-Coupling
Reactions
Cite this: DOI: 10.1039/x0xx00000x
Shaheen M. Sarkar,* Md. Lutfor Rahman, Mashitah Mohd Yusoff
Received 00th January 2012,
Accepted 00th January 2012
MCMꢀ48 supported 2ꢀpyridinylmethanimine Pdꢀcatalyst was found to be a highly efficient catalyst in the
MizorokiꢀHeck, SuzukiꢀMiyaura and copperꢀfree Sonogashira crossꢀcoupling reactions of aryl halides in
aqueous reaction conditions. The catalyst was efficiently promoted these coupling reactions with ppm
level of palladium to afford the corresponding coupling products in up to 98% yield. The supported Pdꢀ
catalyst was readily recovered and reused several times without significant loss of its catalytic activity.
DOI: 10.1039/x0xx00000x
www.rsc.org/
Keywords: Pyridinecarboxaldehyde, MizorokiꢀHeck reaction, SuzukiꢀMiyaura reaction,
Sonogashira reaction, PdꢀCatalyst.
[66, 67]. On the other hand, cubicꢀstructured mesoporous MCMꢀ48
silica has received less attention due to difficulties in the synthesis
1. Introduction
[68ꢀ70]. Owing to its unique threeꢀdimensional pore structure,
MCMꢀ48 may be more advantageous than MCMꢀ41. MCMꢀ48 with
threeꢀdimensional nanosized pore networks and high specific surface
areas would be highly interesting in this area. Herein, we report
MCMꢀ48 supported Pdꢀcatalyzed MizorokiꢀHeck, SuzukiꢀMiyaura
and Sonogashira crossꢀcoupling reactions where the quantitative
products were achieved with 130 to 400 mol ppm of catalyst in
aqueous reaction conditions. The ease preparation of the catalyst, its
long shelfꢀlife, its stability toward air, and its compatibility with a
wide variety of aryl halides make it ideal for the aboveꢀmentioned
reactions.
Palladium is the most popular metal catalyst widely used in
numerous organic syntheses due to their applications in organic
synthesis [1–3] materials science [4] photochemistry [5], and in the
pharmaceutical industry [6ꢀ10]. Among them, the MizorokiꢀHeck
[11ꢀ15], SuzukiꢀMiyaura [16ꢀ20], and Sonogashira [21ꢀ25] coupling
reactions play important roles in modern synthetic chemistry. These
crossꢀcoupling reactions are generally proceed in the presence of a
homogeneous palladium catalyst. One practical limit to perform
homogeneous catalysis reactions is difficult to separate the product
from catalyst and reuse of the catalyst. From the standpoint of
environmentally benign organic synthesis, the development of highly
active and easily reusable immobilized catalysts, solventꢀfree
reactions are significant interest to chemists. To overcome these
problems, chemists have investigated the employment of various
heterogeneous palladium species [26, 27]. The development of
heterogeneous metal supported on materials such as carbon [28]
nanotubes [29, 30] graphene [31ꢀ33] silicates [34ꢀ37], polymers [38,
39], metal oxides [40, 41] and various hybrid nanocrystals composed
of different materials have been reported [42ꢀ45]. Alternatively,
metal complexes bound to a ligand anchored on a support have also
been studied as a recyclable catalyst [46, 47]. Palladacycles have
recently emerged as one of the most promising classes of catalysts or
catalyst precursors in the Pdꢀcatalyzed CꢀC bond formation reactions
such as the MizorokiꢀHeck [48ꢀ51], SuzukiꢀMiyaura [52ꢀ55], and
Sonogashira reactions [56ꢀ58]. Nevertheless, only a few examples of
SuzukiꢀMiyaura, MizorokiꢀHeck, and Sonogashira reactions by
using water as the solvent have been reported in the literature [59,
60]. The common strategy to prepare a heterogeneous catalyst
consists of anchoring the conveniently modified transition metal
complexes onto an insoluble support provided the anchoring
procedure and maintains the intrinsic activity and selectivity of the
catalytic center [61, 62].
2. Experimental
2.1 General Information
All manipulations were performed under atmospheric conditions
unless otherwise noted. Reagents and solvents were obtained from
commercial suppliers and used without further purification. Water
was deionized with a Millipore system as a MilliꢀQ grade. PdCl2 was
purchased from Aldrich chemical industries, Ltd. Proton nuclear
magnetic resonance (1H NMR, 500/400 MHz) and carbon nuclear
magnetic resonance (13C NMR, 125 MHz) spectra were measured
with a JEOL JNM ECAꢀ500/400 spectrometer. The 1H NMR
chemical shifts were reported relative to tetramethylsilane (TMS,
0.00 ppm). The 13C NMR chemical shifts were reported relative to
deuterated chloroform (CDCl3 77.0 ppm). Elemental analyses were
performed on a Yanaco CHN Corder MTꢀ6 elemental analyzer by
the chemical analysis team in Rikagaku Kenkyūjo (RIKEN), Wako,
Japan. Inductively coupled plasma atomic emission spectrometry
(ICPꢀAES) was performed on a Shimadzu ICPSꢀ8100 equipment by
the chemical analysis team in RIKEN Wako, Japan. N2 adsorptionꢀ
desorption isotherms were measured with a BEL SORP mini II
analyzer at liquid N2 temperature. Surface area (SBET) was calculated
by the BET method, the pore volume (Vp) was determined by
nitrogen adsorption at a relative pressure of 0.98, and average pore
Recently, mesoporous MCM materials with uniform nanosized
pore diameters and high specific surface areas have become of high
interest as inorganic supports [63ꢀ65]. MCMꢀ41 silica has recently
been used as a solid support for the immobilization of the catalysts
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size (D) was determined from the desorption isotherms using the dried over MgSO4 and evaporated under reduced pressure. The
BarrettꢀJoynerꢀHalenda (BJH) method. XPS spectra were measured residue was purified by short column chromatography on silica gel
with an ESCALA 250 (Thermo Fisher Scientific K.K.) by the eluted with nꢀhexane/EtOAc afforded the desired coupling products
cooperative support team in RIKEN. The energy dispersive in 87ꢀ96% isolated yields.
spectroscopy (EDX) was examined using JEMꢀ2100F, Inha
University, Korea. The gas chromatographyꢀmass spectrometry (GCꢀ
MS) was measured by an Agilent 7860A/JEOL JMSꢀT100GC
2.7 General procedure for the Suzuki reaction
equipped with a capillary column (DBꢀWax, 0.25 mm i.d. × 30 m or A mixture of aryl halide (1 mmol), boronic acid (1.1 mol equiv),
HPꢀ1, 0.32 mm i.d. × 30 m). Thin layer chromatography (TLC) K2CO3 (2 mol equiv), and the Pdꢀcatalyst 3 (0.013ꢀ0.025 mol%) in
analysis was performed on Merck silica gel 60 F254. Column aqueous ethanol (1:1) was stirred at 90 ºC for 5 h. The reaction was
chromatography was carried out on silica gel (Wakogel Cꢀ300).
monitored with GC until the complete consumption of the aryl
halide. The Pdꢀcatalyst 3 was separated by filtration and the reaction
mixture was diluted with H2O and EtOAc. The organic layer was
separated, dried over MgSO4 and evaporated under reduced pressure.
2.2 Preparation of the MCM-48 silica
MCMꢀ48 silica was prepared according to the literature method [71]. The residue was purified by short column chromatography on silica
The resultant silicate mixture was stirred for 1 h at room temperature gel to give the corresponding coupling products in up to 96% yield.
and the samples were then collected by filtration and transferred to a
Teflon lined steel vessel. The sample was then heated at 100 °C for 4
days. The mixture was cold at room temperature and the precipitated
2.8 General procedure for the Sonogashira reaction
products were washed with DI water and calcinated at 500 °C for 8 Aryl halide (1 mmol), phenylacetylene (1.1 mol equiv), piperidine (2
h. The MCMꢀ48 was characterized by XRD and TEM.
mol equiv) and the Pdꢀcatalyst 3 (0.013ꢀ0.025 mol%) was stirred at
80 °C for 4 h and the reaction progress was monitored periodically
by GC analysis. The reaction mixture was cold at room temperature
and diluted with EtOAc and the immobilized Pdꢀcatalyst was
2.3 Preparation of the 3-aminopropylated MCM-48 silica 1
Fresh calcinated MCMꢀ48 silica (1.0 g) was added to a solution of 3ꢀ separated by filtration. The organic layer was washed by H2O, dried
(aminopropyl)triethoxysilane (0.65 mmol) in toluene (20 mL). The over MgSO4 and solvent was evaporated under reduced pressure.
mixture was stirred at 105 ºC for 12 h. The amino functionalized The residue was purified by short column chromatography on silica
MCMꢀ48 silica 1 was collected by filtration, washed repeatedly with gel eluted with nꢀhexane/EtOAc to afford the corresponding
CH2Cl2, and dried under vacuo at 70 ºC. Weight gain showed that coupling products in up to 96% yield.
0.43 mmol of aminopropyl moiety was immobilized on 1.0 g of
MCMꢀ48 silica 1.
3. Results and discussion
3.1 Characterization of the MCM-48 supported Pd-catalyst 3
2.4
Preparation
of
the
MCM-48
supported
2
pyridinylmethanimine
The immobilization of Pdꢀcatalyst onto nanostructured mesoporous
MCMꢀ48 silica was performed in three steps (Scheme 1). Treatment
of MCMꢀ48 silica with (3ꢀaminopropyl)triethoxysilane in refluxing
To a stirred solution of 2-carboxypyridine (0.5 mmol) and Et3N (0.5
mmol) in toluene (25 mL) was added 3-aminopropylated MCMꢀ48
silica 1 (1 g, 0.43 mmol). The mixture was stirred at 50 C for 3 h.
After filtration, the powder was washed several times with
methylene chloride and dried under vacuum at 70 oC to give 3ꢀ
aminopropylated MCMꢀ48 silica supported pyridinylmethanimine 2.
Weight gain showed that 0.38 mmol of 2ꢀcarboxypyridine was
immobilized on 1.0 g of mesoporous MCMꢀ48 silica 2.
o
toluene gave aminopropylated silica gel
1
(0.43 mmol,
(CH2)3NH2/g). The loading ratio of the aminoproplylated moiety can
be
adjusted
by
changing
the
amount
of
(3ꢀ
aminopropyl)triethoxysilane in the immobilization process. The 13C
NMR is indicated that the bond formation between triethoxysilane
and MCMꢀ48 silica (Fig. 1c).
OH
OH
OH
O
2.5 Preparation of the MCM-48 supported Pd-catalyst 3
Si
NH2
O
(EtO)3Si(CH2)3NH2
O
MCM-48
MCM-48
To a stirred solution of 2 (1 g, 0.38 mmol) in CH2Cl2 (25 mL) was
added 0.3 mmol of PdCl2 and stirred at 50 °C for 6 h. The MCMꢀ48
supported Pd catalyst was then collected by filtration and washed
with CH2Cl2 and methanol. After drying in vacuo at 80 °C, the
MCMꢀ48 supported Pdꢀcatalyst 3 was obtained as a reddish color
solid. Weight gain and ICP analyses showed that 0.26 mmol of Pd
was immobilized onto 1.0 g of MCMꢀ48 supported 3.
toluene, 105 °C, 12 h
OH
OH
OH
O
O
N
O
Si
NH2
1
O
Si
O
H
N
O
O
N
MCM-48
Et3N
toluene, 50 °C, 3 h
O
N
O
O
Si
N
2.6 General procedure for the Heck reaction
2
O
All reactions were carried out in a 4 mL glass vial equipped with a
Teflon screw cap. A mixture of aryl halide (1 mmol), olefin (1.2 mol
equiv), Na2CO3 (2 mol equiv), and the Pd catalyst 3 (0.5 mg, 0.013
mol%, 130 mol ppm) in aqueous DMA (1:1) was stirred at 130 °C
for 5 h, and monitored periodically by GC analysis. After completion
of the reaction, it was cold at room temperature and diluted with
EtOAc. The immobilized Pdꢀcatalyst 3 was separated by filtration
and washed by EtOAc. The organic layer was washed by H2O, brine,
Si
N
O
PdCl2
THF, 50 °C, 6 h
O
N
MCM-48
Pd
O
N
O
O
Si
N
3
Scheme 1. Preparation of the MCMꢀ48 supported heterogeneous Pdꢀ
catalyst 3.
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Reaction of 1 with 1.16 equiv excess of 2-carboxypyridine in toluene
at 50 ºC afforded MCMꢀ48 supported 2ꢀpyridinylmethanimine 2
(0.38 mmol/g). The MCMꢀ48 supported Pdꢀcatalyst 3 was prepared
by treatment of 2 with PdCl2 in CH2Cl2 at 50 °C for 6 h. Based on
the inductively coupled plasma (ICP) analysis, the loaded Pd content
was 2.71% (0.26 mmol/g). The TEM images were obtained before
(Fig 1a) and after (Fig. 1b) modification of the MCMꢀ48 silica. Both
Table 1. Loading information of the MCMꢀ48
Pore
diameter
(nm)
Pore
Functional
group
(mmol/g)
Surface
Sample
volume
area (m2/g)
(cm3/g)
MCMꢀ48
1250
865
790
465
3.25
2.82
2.35
2.12
0.71
0.62
0.48
0.35
ꢀ
0.43
0.38
0.26
1
2
3
3.2 Mizoroki-Heck reaction
The prepared MCMꢀ48 supported heterogeneous Pdꢀcatalyst 3 was
first used in the MizorokiꢀHeck coupling reaction of iodobenzene.
The coupling of iodobenzene with methyl acrylate in the presence of
Na2CO3 in aqueous DMA with 0.1 mol% of 3 was initially studied as
a model reaction, which delivered 99% conversion with 96%,
isolated yield of the product within 5 h without using any additive.
(Table 2, entry 1). The reaction conditions were then systematically
optimized, and the results are presented in Table 2. The catalyst
loading could be decreased even further 0.013 to 0.01 mol% (130 to
100 mol ppm), where the catalyst was still efficiently promoted the
coupling reaction (entries 2, 3). High conversion could be still
maintained at 0.01 mol% of ultraꢀlow Pdꢀcatalyst loading (entry 3).
Then we surveyed this coupling reaction using 130 mol ppm of 3 by
changing solvents and bases. When the reaction was conducted in
DMSO, NMP, DMF instead of DMA, in the presence of different
bases similar results were obtained under the same reaction
conditions (entries 4ꢀ10). In the presence of nonꢀpolar solvent
octane, the reaction showed slow conversion rate compare to other
polar solvents used (entry 11).
Table 2. Optimization of the Heck reactiona
Fig. 1 (a) TEM image of Parent MCMꢀ48; (b) TEM image of MCMꢀ48
supported Pdꢀcatalyst 3; (c) 13C NMR of MCMꢀ48 supported 1; (d)
XRD of MCMꢀ48 and Pdꢀcatalyst 3; (e) XPS and (f) EDX image of 3.
Pd-Catalyst 3
I
+
CO2Me
base, solvent
130 °C, 5 h
CO2Me
4a
images showed the hexagonal symmetry of the pore arrays is
conserved after immobilization of the Pdꢀcatalyst onto the MCMꢀ48
silica. The 3D cubic structure and the pore arrays are conserved after
the anchoring of the MCMꢀ48 silica, which is also confirmed by
XRD (Fig. 1d). The fresh MCMꢀ48 shows a strong diffraction peak
and five small diffraction peaks for the 211, 220, 321, 400, 420 and
332 planes. The presence of Pd 3d3/2 (343 eV) and Pd 3d5/2 (337 eV)
peaks in XPS image (Fig 1e) suggested that the successful
incorporation of the Pd(II) onto the MCMꢀ48 supported Pdꢀcatalyst
3. Moreover, EDX image also revealed that the presence of Pdꢀmetal
onto the Pdꢀcatalyst 3. The presence of guest moieties on the
mesoporous framework of MCMꢀ48 resulting in the decrease of
intensity of the peaks. However, the surface area, pore volume and
pore size decreased due to the grafting of organic moieties onto the
mesoporous MCMꢀ48 silica (Table 1).
Entry
Solvent (1:1)
Base
3 (mol%) Yield (%)b
1
2
3
4
Na2CO3
Na2CO3
Na2CO3
K2CO3
0.1
0.013
0.01
0.03
99(96)c
98(95)c
86(82)c
93
DMA:H2O
DMA:H2O
DMA:H2O
DMA:H2O
5
6
7
NaOMe
Na2PO4
K2PO4
Na2CO3
Na2CO3
Na2CO3
Na2CO3
0.03
0.03
0.03
0.03
0.03
0.03
0.03
93
94
92
91
92
93
78
DMA:H2O
DMA:H2O
DMA:H2O
DMSO:H2O
NMP:H2O
DMF:H2O
Octane:H2O
8
9
10
11
a All reactions were carried out using 1 mmol of iodobenzene, 1.2 mmol of
methyl acrylate, a catalytic amount of 3 and 2 mmol of base in 2 mL of
solvent. b GC yield determined using nꢀdodecane as an internal standard and
based on the amount of iodobenzene employed. c Isolated yield.
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The complex is very stable to oxygen and moisture; less change of [72] observed moderate yields in the Heck reaction of aryl bromides
its activity was observed when the Pdꢀcatalyst was exposed to air with various olefins but the reaction rates were quite slow. By
and water in the Heck reaction. With these results in hand, several observing the promising catalytic activity of 3 for various aryl
Heck coupling of aryl halides with different olefins were then tested, iodides, the catalyst was investigated for the coupling of aryl
and the results are summarized in Table 3. Aryl iodides react with bromides with olefins. It was found that the catalyst showed
methyl, ethyl, butyl acrylate, isopropyl acrylamide, and styrene, to outstanding activity in the coupling of aryl bromides with acrylates
give the corresponding coupling products with high yield. Excellent (Table 4, entries 4a-e, g, k). A catalyst loading of 0.04 mol% was
catalytic activity was observed in the couplings of deactivated sufficient to achieve the high conversion within 5 h. Moreover, the
iodotoluene, 4ꢀiodoanisole (4b-h) as well as activated 4ꢀ catalyst also showed outstanding activity in the coupling of
chloroiodobenzene, 4ꢀnitroiodobenzene, 4ꢀiodoacetophenone and 4ꢀ arylbromides with isopropyl acrylamide and styrene smoothly
trifluoromethyl iodobenzene with acrylates (4i-l). The deactivated afforded the corresponding coupling products in up to 90% yield
aryl iodides possessing electronꢀdonating group showed a slight drop (4o-q, s-u). Recently, R. Pleixats et. al [73] have been reported
in reactivity compared to the activated aryl iodides possessing hybrid silica materials containing diꢀ(2ꢀpyridyl)methylamineꢀ
electronꢀwithdrawing group. The heterocyclic compound such as 3ꢀ palladium dichloride complex catalyzed (0.2 mol%) Heck reaction
iodopyridine was efficiently promoted the coupling reaction to give of activated aryl bromide (4ꢀbromoacetophenone) with butyl acrylate
the corresponding predicts (4m) in 92% yield. Moreover, the catalyst in refluxing DMF with significance decreased of catalytic activity
showed outstanding activity in the coupling of iodobenzene with (1st run 100%, 4th run 47% yield). Hence, our catalyst (0.04 mol%)
isopropyl acrylamide and styrene to give the corresponding coupling showed better activity (1st run 96%, 5th run 83% yield) compared to
products in up to 94% yield (4n-u).
their hybrid silica supported Pdꢀcomplex.
Table 3. Heck reaction of aryl iodides with olefins using Pdꢀcatalyst Table 4. Heck reaction of aryl bromides with olefins using Pdꢀ
3a
catalyst 3a
Pd-Catalyst 3
(0.013 mol%)
Pd-Catalyst 3
(0.04 mol%)
Olefins/R1
R1
Br +
O
Olefins/R1
R1
I
+
Na2CO3, DMA:H2O (1:1)
130 °C, 5 h
Na2CO3, DMA:H2O (1:1)
130 °C, 5 h
R
R
R
R
4
4
O
O
O
O
O
Me
OMe
OMe
OEt
Me
OMe
OMe
OEt
Me
4a: 95%
4b: 91%
4c: 90%
Me
Me
4a: 96%
4b: 93%
4c: 91%
O
O
O
O
O
O
OEt
OEt
OBu
NH
OBu
OEt
O
OEt
Me
Me
4g: 90%
4d: 92%
4e: 89%
4f: 94%
4d: 94%
4e: 92%
O
O
O
O
O
OBu
NH
OBu
OEt
OBu
O
Me
MeO
4k: 93%
Ph
4o: 90%
4p: 88%
Me
Cl
MeO
O
4g: 92%
4i: 92%
4h: 93%
O
O
O
Ph
Ph
Ph
OBu
OBu
OBu
Me
MeO
NC
O2N
F3C
4q: 89%
4s: 87%
4t: 82%
4u: 90%
4j: 96%
4k: 95%
4l: 93%
aAll reactions were carried using 1 mmol of aryl bromide, 1.2 mol equiv of
olefin, 0.04 mol% of 3, 2 mol equiv of Na2CO3, in 2 mL of DMA/H2O (1:1)
at 130 °C for 5 h.
O
O
O
OBu
NH
NH
N
Me
4m: 92%
4n: 94%
4o: 93%
4r: 88%
3.3 Suzuki-Miyaura cross-coupling reaction
O
NH
Heterogeneous silicaꢀsupported Pdꢀcatalysts are extensively studied
for the CꢀC bond formatin reaction of aryl halides with aryl boronic
acids, often referred as SuzukiꢀMiyaura crossꢀcoupling reaction [74].
The properties of such Pdꢀcatalysts can be tuned by ligands, such as
phosphines, amines, carbenes, dibenzylideneacetone, imidazolꢀ2ꢀ
ylidenes and so on [75]. Silicaꢀimmobilized Nꢀheterocyclic carbineꢀ
Pdꢀcomplex has recently been reported as a catalyst for Suzuki
crossꢀcoupling reaction [76, 77]. By observing the high catalytic
activity of MCMꢀ48 supported Pdꢀcatalyst 3 in the Heck reaction
hence, we turned our attention to further testify our Pdꢀcatalyst 3 for
the SuzukiꢀMiyaura crossꢀcoupling reaction. With the heterogeneous
Pdꢀcatalyst 3 (0.013 mol%) in hand, we then tested SuzukiꢀMiyaura
cross coupling reaction of 4ꢀiodoanisole with phenylboronic acid in
aqueous ethanol at 90 ºC to for 5 h to give the corresponding biaryl
4q: 93%
MeO
4p: 90%
F3C
4t: 87%
4s: 91%
Me
MeO
NC
4u: 92%
aAll reactions were carried out using 1 mmol of aryl iodide, 1.2 mol equiv
of olefin, 0.013 mol% of 3, 2 mol equiv of Na2CO3, in 2 mL of DMA/H2O
(1:1) at 130 °C for 5 h.
The development of effective catalysts for the CꢀC bond formation
of olefins with aryl bromides is highly important, since these are
interesting substrates for industrial applications. Using diolꢀ
functionalized imidazolium ionic liquids along with PdCl2, Cai et al.
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product in 96% yield (Table 5, 5a). High catalytic activity was 5th run 79% yield). Therefore, our catalyst showed better results
observed in the coupling of deactivated aryl iodides such as 4ꢀ compared to their report.
iodotoluene, 4ꢀiodophenol and 4ꢀiodoaniline as well as activated 4ꢀ
iodoacetophenone (5b-e). In order to investigate the scope of aryl
halides in the coupling with phenylboronic acid, various aryl Table 6. SBAꢀ16 supported Pdꢀcatalyst 3 catalyzed Sonogashira
bromides were used in the coupling reaction. The coupling of reactiona
activated or deactivated aryl bromides proceeded cleanly with 0.025
mol% of Pd to give the corresponding coupling product in up to 96%
yield (5a-e). J. H. Clark [76] reported pyridinyl functionalized silica
Pd-Catalyst 3
(0.013-0.025 mol%)
X
+
Ph
Ph
Ph
piperidine
80 °C, 4 h
gel supported Pd(OAc)2 catalyzed (0.4 mol%) SuzukiꢀMiyaura
crossꢀcoupling reaction of aryl bromide in oꢀxylene at 110 °C under
N2 atmosphere. The reaction proceeded smoothly but the catalytic
activity was decreased (1st run 1.5 h 100%, 4th run 2.5 h 95% yield).
Hence, we used 0.025 mol% of the catalyst which is sixteen times
lower loading of catalyst. Moreover, we performed this crossꢀ
coupling reaction in aqueous condition at 90 °C with no significance
loss of catalytic activity (1st run 5 h, 95%, 4th run 5 h 87% yield).
R
R
X = I/Br
6
Ph
Me
Ph
MeO
6a: X = I, 95%
6b: X = I, 93%
6c: X = I, 94%
X = Br, 91%
X = Br, 92%
X = Br, 92%
O
Ph
O2N
Ph
NC
Ph
6d: X = I, 96%
6f: X = I, 96%
X = Br, 94%
Table 5. SuzukiꢀMiyaura coupling reaction with MCMꢀ48 supported
Pdꢀcatalyst 3a
6e: X = I, 95%
X = Br, 93%
X = Br, 92%
aAll reactions were carried using 1 mmol of aryl halide, 1.2 mol equiv of
phenyl acetylene, Pdꢀcatalyst 3 (0.013 mol% for aryl iodides, 0.025 mol%
for aryl bromides), 2 mol equiv of piperidine under solvent free reaction
conditions at 80 °C for 4 h.
Pd-Catalyst 3
(0.013-0.0250 mol%)
X +
B(OH)2
K2CO3
EtOH/H2O (1:1)
90 °C, 5 h
R
R
5
X = I/Br
4. Recycling of the catalyst
MeO
Me
HO
The recycling of the catalyst is an important issue in heterogeneous
catalysis system. Again, we turn our attention to reuse our Pdꢀ
catalyst. The catalyst was used five times without significance loss
of its catalytic activity. The Pdꢀcatalyst 3 was recovered and reused
by the following steps: the reaction mixture was cooled to room
temperature and diluted with EtOAc and filtered. The solid catalyst
was washed with dichloromethane and dried at 80 °C under vacuum,
and then used it in the next run without changing of the reaction
conditions.
5b: X = I, 95%
5c: X = I, 93%
5a: X = I, 96%
X = Br, 94%
X = Br, 90%
X = Br, 92%
Me
H2N
O
5d: X = I, 92%
X = Br, 89%
5e: X = I, 96%
X = Br, 94%
aAll reactions were carried using aryl halide (1 mmol), Pdꢀcatalyst 3 (0.013
mol% for aryl iodides, 0.025 mol% for aryl bromides), boronic acid (1.1
mol equiv), K2CO3 (2 mol equiv), EtOH/H2O (1:1) at 90 °C for 5 h.
Table 7. Heck, Suzuki and Sonogashira reactions catalyzed by
recycled Pdꢀcatalyst 3
3.4. Heterogeneous Sonogashira cross-coupling reaction
Sonogashira crossꢀcoupling of an aryl halides and a terminal alkynes
are useful tool for the synthesis of arylꢀsubstituted acetylene
compounds [78]. This method has been widely used for the synthesis
of natural products [79], biologically active molecules [80] nonlinear
optical materials and molecular electronics [81] dendrimeric and
polymeric materials [82] macrocycles with acetylene links [83] and
polyalkynylated molecules [84]. With the heterogeneous Pdꢀcatalyst
3 in hand, we investigated its catalytic activity towards Sonogashira
coupling reaction of various aryl halides with phenylacetylene in the
presence of piperidine. The results are summarized in Table 6. The
supported Pdꢀcatalyst 3 with 0.013 mol% efficiently promoted the
Sonogashira coupling reaction of aryl iodides under solvent and
copper free reaction conditions within 4 h. It is worth to note that the
catalytic activities (0.025 mol%) in the coupling of bromobenzene
and substituted bromobenzenes were also excellent (6a-f). R.
Pleixats et. al [73] reported hybrid silica materials containing diꢀ(2ꢀ
pyridyl)methylamineꢀpalladium dichloride complex catalyzed (0.2
mol%) Sonogashira crossꢀcoupling reaction of 4ꢀiodoanisole with
phenylacetylene in refluxing DMF with significance decreased of
catalytic activity (1st run 100%, 5th run 43% yield). Hence, we used
0.013 mol% of the catalyst which is fifteen times lower loading of
catalyst. Moreover, we performed this crossꢀcoupling reaction
without presence of copper salt under solvent free reaction condition
at 80 °C with no significance loss of catalytic activity (1st run 95%,
MizorokiꢀHeck SuzukiꢀMiyaura
Sonogashira
yield (%)c
95
Cycle
yield (%)a
96
yield (%)b
1
2
3
4
95
93
90
87
94
90
88
90
86
81
83 (<0.16 mol
ppm Pd was
leached out)
5
84
79
aReaction was carried out according to Table 3, 4a using 0.5% of 3.
bReaction was carried out according to Table 5, 5b, X = I, using 0.5% of
c
3. Reaction was carried out according to Table 6, 6a, X = I, using 0.5%
of 3.
After carrying out the reaction, the catalyst had consistent catalytic
activity as shown in Table 7. Only slight loss of catalytic activity
was observed under the same reaction conditions as for initial run.
The slight loss of catalyst activity after five cycles due to the loss of
palladium from the support during reaction time (<0.16 mol ppm of
Pd, ICPꢀAES). Thus, it is reasonable to believe that the immobilized
catalyst can be repeatedly used for largeꢀscale production without
significant loss of its catalytic activity.
5. Heterogeneity test
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DOI: 10.1039/C4RA16677A
6
7
M. Ghedini, I. Aiello, A. Crispini, A. Golemme, M. L. Deda, D. Pucci,
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Y. Wakatsuki, H. Yamazaki, P. A. Grutsch, M. Santhanam, C. Kutal, J.
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X. F. Wu, H. Neumann, M. Beller, Chem. Rev. 2013, 113, 1.
In order to check the heterogeneity of the Pdꢀcatalyst 3 we were
carried out in a similar manner as the general procedure for Suzuki
reaction (Table 5, 5a, X = I). After 52% conversion the reaction
mixture was filtered off at hot condition and the aqueous solution
was heated under identical reaction conditions for 2 h and GC
analyzed for the further conversions. No starting material was
converted to the corresponding product after removal of the catalyst
(Fig. 2). This experiment is indicated that the SuzukiꢀMiyaura
reactions were followed a heterogeneous pathway.
8
9
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100
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6. Conclusions
26 C. W. Lim, I. S. Lee, Nano Today 2010, 5, 412.
27 A. Molnar, Chem. Rev. 2011, 111, 2251.
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In conclusion, we have developed nanostructured MCMꢀ48
supported Pdꢀcatalyst 3 for MizorokiꢀHeck, SuzukiꢀMiyaura and
Sonogashira cross coupling reactions. The heterogeneous Pdꢀcatalyst
was found to be highly active for these coupling reactions of aryl
iodide and bromide in aqueous conditions. The Sonogashira cross
coupling reaction was performed under copper and solventꢀfree
reaction conditions. Furthermore, this catalytic system was simply
recovered and reused several times without a significant loss of its
activity.
32 A. R. Siamaki, A. E. R. S. Khder, V. Abdelsayed, M. S. ElꢀShall, B. F.
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Acknowledgments
33 B. Kılıç, S. Sencanlı, Ö. Metin, J. Mol. Catal. A: Chem. 2012, 104, 361.
34 Y. Wan, H. Wang, Q. Zhao, M. Klingstedt, O. Terasaki, D. Zhao, J. Am.
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This work is supported by Ministry of Education Malaysia, fund no.
RDU140124. The authors are grateful to Professor MyungꢀJong Jin,
Inha University, South Korea and Professor Yasuhiro Uozumi,
RIKEN, Wako, Japan for giving us valuable guidelines in this work.
36 W. Zhu, Y. Yang, S. Hu, G. Xiang, B. Xu, J. Zhuang, X. Wang, Inorg.
Chem. 2012, 51, 6020.
& Technology, University 37 S. M. Sarkar, M. L. Rahman, M. M. Yusoff, RSC Adv. 2015, 5, 1295.
Notes and references
Faculty of Industrial Sciences
Malaysia Pahang, 26300 Gambang, Kuantan, Pahang, Malaysia.
Fax: +609 5492766; Tel: +609 5492399; E-mail:
sha_inha@yahoo.com
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