Heck, Suzuki and Sonogashira cross-coupling reactions using ppm level of SBA-16 supported Pd-complex

Article abstract of DOI:10.1039/c4nj02319f

SBA-16 supported 1,2-diaminocyclohexane Pd-complex (100-500 mol ppm of Pd) was found to be an efficient catalyst in the palladium-catalyzed Mizoroki-Heck, Suzuki-Miyaura and copper-free Sonogashira cross-coupling reactions of aryl halides under mild reaction conditions. The Pd-complex efficiently promoted all of these coupling reactions with appropriate coupling partners to afford the corresponding coupling products with almost quantitative yield. The supported Pd-complex was readily recovered and used five times without a significant loss of its catalytic activity.

Full text of DOI:10.1039/c4nj02319f

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ARTICLE
Heck, Suzuki and Sonogashira Cross-Coupling Reactions
using ppm Level of SBA-16 Supported Pd-Complex
Cite this: DOI: 10.1039/x0xx00000x
Shaheen M. Sarkar,* Md. Lutfor Rahman, Mashitah Mohd Yusoff
SBAꢀ16 supported 1,2ꢀdiaminocyclohexane Pdꢀcomplex (100ꢀ500 mol ppm of Pd) was found to be an
efficient catalyst in the palladiumꢀcatalyzed MizorokiꢀHeck, SuzukiꢀMiyaura and copperꢀfree
Sonogashira crossꢀcoupling reactions of aryl halides under mild reaction conditions. The Pdꢀcomplex
was efficiently promoted all of these coupling reactions with apporpiate coupling partners to afford the
corresponding coupling products with almost quantitative yield. The supported Pdꢀcomplex was readily
recovered and used five tiemes without significance loss of its catalytic activity.
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
Keywords: 1,2ꢀdiaminocyclohexane, MizorokiꢀHeck, SuzukiꢀMiyaura, Sonogashira, SBAꢀ16,
Pdꢀcomplex
reactions under aerobic conditions. Our approach is guided by three
imperatives: (i) the solid support should be easily accessible; (ii)
1. Introduction
developing an efficient synthetic route for the facile conversion of
the Heck, Suzuki, and Sonogashira coupling reactions; and (iii) the
ligand anchored on the support should have thermal and airꢀstable at
room temperature. The ease of preparation of the Pdꢀcomplex, its
long shelf life, its stability toward air, and its compatibility with a
wide variety of aryl halides make it ideal for the aboveꢀmentioned
reactions.
Palladium catalyst is the most popular transition metal catalyst
widely used in numerous organic syntheses and synthetic
transformations [1ꢀ3]. Palladium catalyzed SuzukiꢀMiyaura [4, 5],
MizorokiꢀHeck [6ꢀ8], and Sonogashira [9ꢀ11] crossꢀcoupling
reactions play important roles in modern synthetic chemistry. The
original Heck, Suzuki, and Sonogashira reactions are generally
proceed in the presence of homogeneous palladium catalyst.
Purification of the product and reuse of catalyst are quite difficult
when homogeneous catalyst is used. In this context, heterogeneous
metal catalysts are emerging as an alternative to the homogeneous
one that suffers various limitations both commercially and
environmentally. On the otherhand heterogeneous catalysts have
many advantages such as heat stability, reusability, and ease to
purify the product. One common strategy to prepare a heterogeneous
catalyst by covalently anchoring of transition metal complexes onto
an insoluble support provided the anchoring procedure and maintains
the intrinsic activity and selectivity of the catalytic center [12ꢀ14].
From these perspectives, heterogeneous metal catalysts are
particularly well suited since the metal catalyst immobilized on a
support could be easily removed by filtration leaving products
virtually free of metal residues. A number of supports such as zeolite
[15], metal oxides [16], silicaꢀstarch [17], polymers [18, 19], carbon
nanofiber [20], clay [21], montmorillonite [22], and magnetic
mesoporous silica [23ꢀ25] have been used. Alternatively, metal
complexes anchored to a solid support have also been studied as a
recyclable catalyst [26ꢀ30]. Palladacycles have recently emerged as
one of the most promising classes of catalyst or catalyst precursors
in the Pdꢀcatalyzed CꢀC bond formation reactions such as Mizorokiꢀ
Heck [31, 32], SuzukiꢀMiyaura [33ꢀ36], and Sonogashira crossꢀ
coupling reactions [37ꢀ41]. Nevertheless, only a few examples of
SuzukiꢀMiyaura, MizorokiꢀHeck, and Sonogashira reactions were
carried out using water as the solvent [42, 43].
2. Experimental
2.1 General Information
All manipulations were performed under atmospheric conditions
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
size (D) was determined from the desorption isotherms using the
BarrettꢀJoynerꢀHalenda (BJH) method. The gas chromatographyꢀ
mass spectrometry (GCꢀMS) was measured by an Agilent
Here we report the synthesis of SBAꢀ16 supported Pd(II)
complex and its application to the crossꢀcoupling reactions of
MizorokiꢀHeck, SuzukiꢀMiyaura, and copper free Sonogashira
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7860A/JEOL JMSꢀT100GC equipped with a capillary column (DBꢀ with nꢀhexane/EtOAc afforded the desired coupled products in in up
Wax, 0.25 mm i.d. × 30 m or HPꢀ1, 0.32 mm i.d. × 30 m). Thin to 97% yield.
layer chromatography (TLC) analysis was performed on Merck
silica gel 60 F254. Column chromatography was carried out on silica
gel (Wakogel Cꢀ300).
2.7 General procedure for the Suzuki reaction
A mixture of aryl halide (1 mmol), arylboronic acid (1.1 mol equiv),
K2CO3 (2 mol equiv), and the Pdꢀcomplex 3 (0.5 mg, 0.01 mol%,
100 mol ppm) in aqueous ethanol (1:1) was stirred at 90 ºC for 6 h.
2.2 Preparation of the SBA-16 silica
SBAꢀ16 silica was synthesized at room temperature under acidic The reaction was monitored by GC until the complete consumption
condition using Puronic F127 (EO106PO70EO106, Mw = 12.6 K) as a of the aryl halide. The Pdꢀcomplex 3 was separated by filtration and
structureꢀdirecting agent (SDA) [44]. The acidic solution was made the reaction mixture was diluted with H2O and ether. The organic
by adding 1.5 g of deionized (DI) water to 120 g of 2 M HCl layer was separated, dried over MgSO4 and evaporated under
solution at room temperature. Subsequently, 8.5
g
of reduced pressure. The residue was purified by short column
Tetraethoxysilane (TEOS) was added onto the solution and chromatography on silica gel to give the corresponding coupling
continued to stirring for 20 h. The reaction mixture was kept at 100 product in up to 94% isolated yield.
°C for 48 h. During this time the solid SBAꢀ16 was produced under
static conditions in a Teflonꢀlined vessel. The solid product was
recovered and washed with DI water. The calcination was carried
out at 500 °C for 6 h.
2.8 General procedure for the Sonogashira reaction
Aryl halide (1 mmol), phenylacetylene (1.2 mol equiv), piperidine (2
mol equiv) and the Pdꢀcomplex 3 (1 mg, 0.02 mol%, 200 mol ppm)
was stirred at 80 °C for 2 h and reaction progress was monitored by
GC analysis. After completion of the reaction it was cold at room
2.3 Preparation of the 3-chloropropylated SBA-16 silica 1
To a solution of 3ꢀ(chloropropyl)triethoxysilane (200 mg, 0.9 mmol) temperature and diluted with EtOAc and the immobilized Pdꢀ
in toluene (15 mL) was added mesoporous silica SBAꢀ16 (1.0 g) and complex 3 was separated by filtration. The organic layer was washed
the mixture was stirred at 105 ℃ for 12 h. The modified silica was by H2O and dried over MgSO4. Solvent was evaporated under
reduced pressure and the residue was purified by short column
chromatography on silica gel eluted with nꢀhexane/EtOAc to afford
the corresponding coupling products in up to 96% yield.
collected by filtration and washed with CH2Cl2. After drying in
vacuo at 80 ℃, 3ꢀchloropropylated silica 1 was obtained. Weight
gain showed that 0.73 mmol of 3ꢀchloropropyl moiety was
immobilized onto 1.0 g of SBAꢀ16 mesoporous silica 1.
3. Results and discussion
2.4 Preparation of the SBA-16 supported bis-cyclodiamine 2
3.1 Characterization of the SBA-16 supported Pd-complex 3
To a starred solution of 1 (1 g, 0.73 mmol) in CH2Cl2 (30 mL) was
added 1.5 mol equiv of DIPEA and 1.3 mol equiv of 1,2ꢀ
diaminocyclohexane at room temperature and stirred was continued
for 8 h. The modified silica was then collected by filtration and
washed with CH2Cl2. After drying in vacuo at 80 ℃, the SBAꢀ16
supported diamine 2 was obtained as a lite yellow color solid.
Weight gain showed that 0.40 mmol of cyclodiamine was
immobilized on 1.0 g of SBAꢀ16.
The immobilization of Pdꢀcomplex 3 onto mesoporous SBAꢀ16
silica was performed in three steps (Scheme 1). Treatment of SBAꢀ
16 silica with (3ꢀchloropropyl)triethoxysilane in refluxing toluene
gave chloropropylated silica 1 with 0.73 mmol/g of chloropropyl
moiety. In the FTꢀIR spectra bands ware observed at 752 (CꢀCl),
1074 (SiꢀOꢀSi), 1275 (OꢀSiꢀC), 1474 (CꢀC) and 2924 cmꢀ1 (CꢀH)
which indicate the presence of chloropropyl group onto the SBAꢀ16.
The loading ratio of the chloroproplylated moiety can be adjusted by
changing the amount of (3ꢀchloropropyl)triethoxysilane in the
immobilization process. Reaction of 1 with 1.3 equiv excess of 1,2ꢀ
diaminocyclohexane in CH2Cl2 at room temperature afforded SBAꢀ
16 supported 1,2ꢀdiaminocyclohexane 2 (0.4 mmol/g).
2.5 Preparation of the SBA-16 supported Pd-complex 3
To a solution of 2 (1 g, 0.4 mmol) in THF (20 mL) was added 0.2
mmol of PdCl2 and stirred at 50 °C for 6 h. The SBAꢀ16 supported
Pdꢀcomplex was then collected by filtration and washed with THF
and methanol. After drying in vacuo at 80 °C, the SBAꢀ16 supported
Pdꢀcomplex 3 was obtained as an orange color solid. Weight gain
and ICP analyses showed that 0.25 mmol of Pd was immobilized on
1.0 g of SBAꢀ16 supported 3.
2.6 General procedure for the Heck reaction
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 (1.3 mol
equiv), Na2CO3 (2 mol equiv), and the Pdꢀcomplex 3 (2.5 mg, 0.05
mol%, 500 mol ppm) in aqueous DMA (1:1) was stirred at 125 °C
for 4 h. The reaction progress was monitored periodically by GC
analysis. After completion of the reaction, it was cold at room
temperature and diluted with ethyl acetate (EtOAc). The
immobilized Pdꢀcomplex 3 was separated by filtration and washed
with EtOAc. The organic layer was washed by H2O, brine and dried
over MgSO4 and evaporated under reduced pressure. The residue
was purified by short column chromatography on silica gel eluted
2 | RSC Adv., 2014, 00, 1-3
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DOI: 10.1039/C4NJ02319F
O
OH
OH
OH
OH
OH
OH
50000
Si
Si
O
O
O
O
O
CI
CI
(EtO)3Si(CH2)3Cl
H2N
NH2
40000
30000
20000
10000
0
toluene
105 °C, 12 h
DIPEA, CH2Cl2
r.t, 8 h
1
O
O
O
O
O
O
O
Si
Si
O
O
O
O
O
Si
Si
N
H
H
N
N
H
PdCl2
THF
H
N
50 °C, 6 h
0.5
1.5
2.5
3.5
4.5
2
2θ
Fig. 2 Small angle XRD patterns of SBAꢀ16 and SBAꢀ16
supported Pdꢀcomplex 3
O
O
O
O
O
O
O
O
O
O
O
O
Si
Si
Si
Si
N
N
250
200
150
100
50
Pd
N
N
3
Scheme 1 Preparation of the SBAꢀ16 supported heterogeneous Pdꢀ
complex 3
The FTꢀIR bands of 2 ware observed at 1065 (SiꢀOꢀSi), 1152 (CꢀN),
1255 (OꢀSiꢀC), 1457 (CꢀC), and 2912 (CꢀH) cmꢀ1 which indicate the
incorporation of the cyclohexane moieties. The SBAꢀ16 supported
Pdꢀcomplex 3 was prepared by the treatment of 2 with PdCl2 in THF
at 50 °C for 6 h [45]. The content of Pd in the SBAꢀ16 supported 3
0
0
0.2
0.4
0.6
0.8
1
Relative Pressure (P/Po)
was determined (2.46 wt%, 0.25 mmol/g) by weight gain and Fig. 3 Nitrogen absorption isotherm of SBAꢀ16 supported Pdꢀ
inductive coupled plasma emission spectrometer (ICP) analyses and complex 3
no chlorine atom was found by the elemental analysis.
The TEM images of SBAꢀ16, Pdꢀcomplex 3 and after five runs of
Pdꢀcomplex 3 are shown in Fig 1. For fresh SBAꢀ16 (a), the highly
(a)
(b)
(c)
ordered arrangements of mesopores reveal that the material consists
of a highꢀquality bodyꢀcentered cubic mesostructure. In Fig. (b), Pdꢀ
complex 3 presents a wellꢀordered mesopores structure characteristic
of the SBAꢀ16 material, which indicates the mesostructure of SBAꢀ
16 can be substantially conserved after grafting process. Moreover,
the TEM images of reused Pdꢀcomplex 3 were also conserved the
hexagonal symmetry of the pore arrays (c, d & e). The smallꢀangle
Xꢀray diffraction patterns of SBAꢀ16 and the Pdꢀcomplex 3 are
shown in Fig. 2. The fresh SBAꢀ16 shows a strong diffraction peak
at 110 and two small diffraction peaks at 200 and 211 planes. The
intensity of these peaks are decreased due to incorporation of organic
moieties onto the mesoporous SBAꢀ16 but not collapse of the pore
structure [46]. The structural information about the solid catalyst on
a mesoscopic scale, the N2 sorption isotherm plot for Pdꢀcomplex 3
show a typeꢀIV isotherm with H2 hysteresis loop, indicating that the
Pdꢀcomplex 3 still maintains a good mesoporous cageꢀlike structure
(Fig. 3). The BET surface area and pore volume of SBAꢀ16 is 820
m2/g and 0.73 cm3/g, whereas for Pdꢀcomplex 3, these values
decrease to 465 m2/g and 0.28 cm3/g, respectively (ESI, Table 1).
The surface area, pore volume and pore size in Pdꢀcomplex 3 are
reduced during the functionalization of organic moiety into the
parent SBAꢀ16 [47].
(d)
(e)
Fig. 1 (a) Parent SBAꢀ16; (b) SBAꢀ16 supported Pdꢀcomplex 3;
(c), (d), (e) After five cycles of Heck, Suzuki, and Sonogashira
couplings respectively.
3.2 Mizoroki-Heck reaction
The prepared heterogeneous Pdꢀcomplex 3 was first used in Heck
coupling reaction. The coupling of iodobenzene with butyl acrylate
in the presence of Na2CO3 in aqueous DMA with 1.5 mol% of Pdꢀ
complex 3 was initially studied as a model reaction which delivered
100% conversion of the product within 0.8 h (ESI, Table 2, entry 1).
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O
O
O
The catalyst loading could be decreased even further 1 to 0.01
mol%, when 1.5 to 5 h reaction times were required to complete the
reaction (entries 2ꢀ6). High conversion could be still maintained at
0.01 mol% (100 mol ppm) of ultraꢀlow Pdꢀcomplex 3 loading (entry
6). Solvents and bases effect on the activity of Pdꢀcomplex 3 were
surveyed. When the reaction was conducted in DMF, DMSO, NMP
instead of DMA, and using different bases similar results were
obtained under the same reaction conditions (ESI, entries 7ꢀ13). The
reaction showed slow conversion rate when nonꢀpolar solvent
dodacane was used (entry 14). The complex is very stable to oxygen
and moisture and less change of its activity was observed when the
Pdꢀcomplex was exposed to air and water in the Heck reaction. With
these results in hand, several Heck coupling of aryl iodides with
different olefins were then tested, and the results are summarized in
Table 1. Aryl iodides react with butyl acrylate, isopropylacrylamide,
and styrene, to give the corresponding coupling products with high
yield. Excellent catalytic activity was observed in the couplings of
deactivated 4ꢀiodotoluene (4b), 4ꢀ iodoanisole (4c) as well as
activated 1ꢀiodoꢀ4ꢀnitrobenzene (4d), 4ꢀ iodoacetophenone (4e) and
4ꢀtrifluoromethyl iodobenzene (4f) with butyl acrylates. The
deactivated aryl iodides possessing electronꢀdonating group showed
a slight drop in reactivity compared to the activated aryl iodides
possessing electronꢀwithdrawing group. The heterocyclic compound
such as 3ꢀiodopyridine was efficiently promoted the coupling
reaction to give the corresponding product (4g) in 94% yield.
Moreover, the catalyst showed outstanding activity in the coupling
of iodobenzene with isopropyl acrylamide and styrene to give the
corrersponding coupling products in up to 95% isolated yield (4h-o).
The development of effective catalysts for the carbonꢀcarbon
bond formation of olefins with aryl bromides is highly important,
since these are interesting substrates for industrial applications.
Using diolꢀfunctionalized imidazolium ionic liquids along with
PdCl2, Cai et al. [48] observed moderate yields in the Heck reaction
of aryl bromides with various alkenes but the reaction rates were
quite slow. By observing the promising catalytic activity of 3 to
various aryl iodides, the catalyst was then investigated for the
coupling of aryl bromides and olefins. It was found that the Pdꢀ
OBu
O
OBu
OBu
OBu
4a: 95%
Me
MeO
F3C
4b: 93%
4c: 92%
O
O
OBu
OBu
O
O2N
4d: 96%
4e: 97%
4f: 95%
O
O
O
OBu
O
NH
NH
N
Me
4h: 95%
4g: 94%
4i: 95%
4l: 93%
NH
4k: 95%
MeO
Me
4j: 92%
F3C
NC
4n: 91%
4m: 93%
MeO
4o: 93%
aAll reactions were carried out using 1 mmol of aryl iodide, 1.3 mol equiv of
olefin, 500 mol ppm of 3, 2 mol equiv of Na2CO3, in 2 mL of DMA/H2O
(1:1) at 125 °C for 4 h.
Table 2. Pdꢀcomplex 3 catalyzed Heck reaction of aryl halides with
olefinsa
SBA-16 supported
3 (500 mol ppm)
X
Olefins/R1
R1
+
Na2CO3, DMA:H2O (1:1)
125 °C, 4 h
R
R
X = Br/Cl
4
O
O
O
OBu
OBu
OBu
O2N
Me
4a: X = Br, 93%
X = Cl, 51%
4b: X = Br, 90%
X = Cl, 48%
4d: X = Br, 94%
X = Cl, 71%
O
O
O
complex
3 showed outstanding activity in the coupling of
OBu
Me
NH
NH
bromobenzene, 4ꢀbromotoluene, 4ꢀnitroꢀbromobenzene and 4ꢀ
bromoacetophenone with butyl acrylate (Table 2, 4a, b, d, e). A
catalyst loading of 0.05 mol% (500 mol ppm) was sufficient to
achieve the high conversion within 4 h reaction time.
O
MeO
4e: X = Br, 96%
4i: X = Br, 92%
4j: X = Br, 90%
X = Cl, 54%
X = Cl, 68%
Ph
Ph
Ph
Ph
Table 1. Heck reaction of iodobenzene with olefins using Pdꢀ
complex 3a
Me
MeO
NC
4k: X = Br, 93%
4m: X = Br, 90%
4n: X = Br, 89%
4o: X = Br, 92%
aAll reactions were carried using 1 mmol of aryl halide, 1.3 mol equiv of
olefin, 500 mol ppm of 3, 2 mol equiv of Na2CO3, in 2 mL of DMA/H2O
(1:1) at 125 °C for 4 h.
SBA-16 supported
3 (500 mol ppm)
I
Olefins/R1
R1
+
Na2CO3, DMA:H2O (1:1)
125 °C, 4 h
R
R
4
The Heck reaction was also efficiently promoted of aryl bromides
with isopropyl acrylamide and styrene to give the corresponding
coupling products in up to 93% yield (4i-k, m-o). Interestingly, aryl
chlorides were also promoted this coupling reaction under the
similar reaction conditions (4a, b, d, e, j) with relatively poor yields.
Recently, C. Nájera et al. [42] reported styreneꢀmaleic anhydride coꢀ
polymer supported di(2ꢀpyridyl)methylamineꢀpalladium dichloride
complex catalyzed Heck reaction of aryl bromides in water using
0.1 mol% of catalyst at 160 °C for 2 days. Here we used only 500
mol ppm of SBAꢀ16 supported Pdꢀcomplex 3 which was efficiently
promoted Heck reaction and exhibit higher catalytic activity
compared to their newly prepared catalyst. Moreover, our catalyst
also worked well in the aryl chloride systems.
3.3 Suzuki-Miyaura cross-coupling reaction
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Heterogeneous silicaꢀsupported Pdꢀcatalysts are extensively studied Sonogashira crossꢀcoupling of an aryl halides and a terminal alkynes
for the CꢀC bond formation reaction of aryl halides with arylboronic are useful tool for the synthesis of arylꢀsubstituted acetylene
acids, often referred as SuzukiꢀMiyaura cross coupling reaction. The compounds [52, 53]. This method has been widely used for the
properties of such Pdꢀcatalysts can be tuned by ligands, such as synthesis of biologically active molecules [54] and nonlinear optical
phosphines, amines, carbenes, dibenzylideneacetone, imidazolꢀ2ꢀ materials and molecular electronics [55]. With the heterogeneous
ylidenes and so on. Silicaꢀimmobilized Nꢀheterocyclic carbine Pdꢀ Pdꢀcomplex 3 in hand, we investigated its catalytic activity towards
complex has recently been reported as a catalyst for Suzuki crossꢀ Sonogashira coupling reaction of various aryl halides with
coupling reaction [49, 50]. By observing the high catalytic activity of phenylacetylene in the presence of piperidine. The results are
SBAꢀ16 supported Pdꢀcomplex 3 in the Heck reaction hence, we summarized in Table 4. The supported Pdꢀcomplex 3 with only 0.02
turned our attention to further testify our Pdꢀcomplex 3 for the mol% (200 mol ppm) efficiently promoted the Sonogashira coupling
Suzukiꢀ Miyaura cross coupling reaction. With the heterogeneous reaction of aryl iodides and bromides under solvent and copper free
Pdꢀcomplex 3 (0.01 mol%, 100 mol ppm) in hand, we then tested reaction conditions within 2 h (6a-f) reaction time. It is worth to note
SuzukiꢀMiyaura cross coupling reaction of 4ꢀiodoanisole with that the catalytic activities in the coupling of aryl chlorides were also
phenylboronic acid in aqueous ethanol at 90 ºC for 6 h provided the excellent (6d-f). Recently B. Movassagh et al [56] reported Pd(II)
corresponding biaryl product in 92% yield (Table 3, 5a). High Schiff base complex supported on multiꢀwalled carbon nanotubes for
catalytic activity was observed in the coupling of deactivated aryl Sonogashira crossꢀcoupling reaction of aryl iodide using 1.2 mol%
iodides such as 4ꢀiodotoluene, 4ꢀiodophenol and 4ꢀiodoaniline as of Pd under copper free reaction conditions at 90 °C with prominent
well as activated 4ꢀiodoacetophenone (5b-f). In order to investigate decreased of the catalytic activity (1st cycle 99, 4th cycle 82%).
the scope of aryl halides in the coupling with phenylboronic acid, However our catalyst efficiently (200 mol ppm) promoted the
various aryl bromides were used in the coupling reaction. The Sonogashira reaction without significance loss of its catalytic
coupling of activated or deactivated aryl bromides proceeded cleanly activity (1st cycle 100, 4th cycle 96%).
with 0.01 mol% of Pdꢀcomplex 3 to give the corresponding coupling
products in up to 93% yield (5b, e, f). It should be noted that Table 4. SBAꢀ16 supported Pdꢀcomplex 3 catalyzed Sonogashira
activated 4ꢀchloroacetophenone and deactivated 4ꢀchloroanisole and reaction of aryl halidesa
4ꢀchlorotoluene were also efficiently promoted the crossꢀcoupling
reaction to provide the corresponding coupling products in up to
73% yields (5a, b, f).
SBA-16 supported
3 (200 mol ppm)
X
+
Ph
Ph
piperidine
80 °C, 2 h
R
R
Table 3. SuzukiꢀMiyaura coupling reaction with Pdꢀcomplex 3a
X = I/Br/Cl
6
Ph
6a: X = I, 94%
Me
Ph
Ph
MeO
Ph
SBA-16 supported
3 (100 mol ppm)
X +
B(OH)2
Me
K2CO3
EtOH/H2O (1:1)
90 °C, 6 h
6b: X = I, 93%
6c: X = I, 95%
R'
R'
R
R
X = Br, 90%
5
X = I/Br/Cl
MeO
O
O2N
Ph
Ph
NC
HO
6f: X = I, 96%
X = Br, 93%
X = Cl, 72%
6d: X = I, 95%
X = Br, 93%
X = Cl, 68%
5b: X = I, 94%
5c: X = I, 91%
5a: X = I, 92%
6e: X = I, 92%
X = Br, 90%
X = Cl, 68%
X = Br, 88%
X = Cl, 64%
X = Cl, 53%
Me
aAll reactions were carried using 1 mmol of aryl halide, 1.2 mol equiv of
phenyl acetylene, 200 mol ppm of 3, 2 mol equiv of piperidine under solvent
free reaction condition at 80 °C for 2 h.
H2N
Me
Me
O
5d: X = I, 90%
5e: X = I, 90%
X = Br, 90%
5f: X = I, 93%
X = Br, 93%
X = Cl, 73%
3.5 Recycling of the catalyst
aMolar ratio: aryl halide (1 mmol), Pdꢀcomplex 3 (100 mol ppm), aryl
boronic acid (1.1 mol equiv), K2CO3 (2 mol equiv), EtOH/H2O (1:1) at 90 °C
for 6 h.
The recycling of the catalyst is an important issue in heterogeneous
catalysis system. Again, we turn our attention to reusability of our
Pdꢀcomplex 3. The complex was used five times without
significance loss of its catalytic activity. The Pdꢀcomplex 3 was
recovered and reused by the following steps: the reaction mixture
was cold to room temperature and diluted with EtOAc and filtered.
The solid catalyst was washed with EtOAc and dried at 80 °C under
vacuum, and then used it in the next run without changing the
reaction conditions. After carrying out the reaction, the catalyst had
consistent catalytic activity as shown in Table 5. 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
case due to the loss of palladium (<0.18 ppm Pd, ICPꢀAES) from the
support during the reaction. Thus, it is reasonable to believe that the
immobilized catalyst can be repeatedly used for largeꢀscale
production without significant loss of its catalytic activity.
The SBAꢀ16 supported heterogeneous palladium catalyst (0.01
mol%) showed better result compared to our previously reported
silicaꢀsupported NHCꢀPd (0.1 mol%) catalyst [51]. Moreover H.
Yang et. al [24] reported that 0. 1 mol% of SBAꢀ16 supported Pdꢀ
guanidine complex catalyzed SuzukiꢀMiyaura crossꢀcoupling
reaction of aryl iodides and bromides under aqueous conditions at 50
°C but their catalyst does not work well (8% yield) in the aryl
chloride system also their catalyst quickly decreased the reactivity
(1st run 99%, 35 min; 7th run 77%, 15 h). Herein our catalyst (100
mol ppm) efficiently promoted Suzuki reaction of aryl halides
(iodo/bromo/chloro) using only 100 mol ppm of Pd without
significance loss of catalytic activity (1st run 94%, 6 h; 5th run 87%,
6 h). From this data our SBAꢀ16 supported Pdꢀcomplex 3 is superior
than their SBAꢀ16 supported Pdꢀguanidine complex.
Table 5. Heck, Suzuki and Sonogashira reactions catalyzed by
recycled Pdꢀcomplex 3
3.4 Heterogeneous Sonogashira cross-coupling reaction
This journal is © The Royal Society of Chemistry 2012
J. Name., 2014, 00, 1-3 | 5

New Journal of Chemistry
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ARTICLE
Journal Name
DOI: 10.1039/C4NJ02319F
reaction conditions. Furthermore, this Pdꢀcomplex was simply
recovered and reused several times without a significant loss of its
activity. Currently we are preparing heterogeneous chiral
cyclohexyldiamine ligand for asymmetric transfer reactions.
Sonogashira
yield (%)c
94
Cycle
Heck yield (%)a
Suzuki yield (%)b
1
2
3
4
95
95
93
92
94
93
94
92
92
91
88
Acknowledgments
This work is supported by Ministry of Education Malaysia, fund no.
RDU 140124. The authors are grateful to Professor MyungꢀJong Jin,
Inha University, South Korea and Professor Yasuhiro Uozumi,
RIKEN, Wako, Japan for giving us valuable guidelines and
laboratory facilities.
88 (<0.18 ppm Pd
was leached out)
aReaction was carried out according to Table 1, 4a. Reaction was
carried out according to Table 3, 5b, X = I). Reaction was carried
out according to Table 4, 6a.
5
89
86
b
c
Notes and references
Faculty of Industrial Sciences
3.6 Heterogeneity test
& Technology, University
Malaysia Pahang, 26300 Gambang, Kuantan, Pahang, Malaysia.
Fax: +609 5492766; Tel: +609 5492399; E-mail:
sha_inha@yahoo.com
Electronic Supplementary Information (ESI) available: [Loading amount
of organic moieties onto the mesoporous silica SBAꢀ16, optimization
reaction conditions of Heck reaction and NMR data of the coupling
In order to check the heterogeneity (Table 1, 4a) of the Pdꢀcomplex
3 we were considered two experiments; (a) to determine the Pd
content in the solution, a part of the filtrate was placed in a 50 mL
crucible after removing the solvent it was calcined at 600 °C for 3 h.
The residue was dissolved in 20 mL aquaꢀregia and diluted to 50
mL. The Pd leaching in solution was determined by inductively
coupled plasma atomic emission spectrometry (ICPꢀAES) analysis. products]. See DOI: 10.1039/b000000x/
It revealed that the leaching of Pd from the complex into the solution
was lower than 0.18 ppm, which suggests the heterogeneous nature
of the prepared Pdꢀcomplex 3. (b) The reaction was carried out in a
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This journal is © The Royal Society of Chemistry 2012
J. Name., 2014, 00, 1-3 | 7

New Journal of Chemistry
Page 8 of 17
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DOI: 10.1039/C4NJ02319F
Graphical abstract
SBA-16-supported Pd-complex (100-500 mol ppm) catalyzed the Heck, Suzuki and
Soonogashra cross-coupling reactions under mild reaction conditions without significance
loss of its activity.
Pd-complex
500 mol ppm
R1
R1
R1
R
R
Pd-complex
100 mol ppm
+
X
B(OH)2
R2
R1
R2
X = I, Br, Cl
Pd-complex
200 mol ppm

Page 9 of 17
New Journal of Chemistry
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DOI: 10.1039/C4NJ02319F
O
OH
OH
OH
OH
OH
OH
Si
Si
O
O
O
O
CI
CI
(EtO)3Si(CH2)3Cl
H2N
NH2
toluene
105 °C, 12 h
DIPEA, CH2Cl2
r.t, 8 h
O
1
O
O
O
O
O
O
O
Si
Si
O
O
O
O
O
Si
Si
N
H
H
N
N
H
PdCl2
THF
50 °C, 6 h
H
N
2
O
O
O
O
O
O
O
O
O
O
O
O
Si
Si
Si
Si
N
N
Pd
N
N
3
Scheme 1 Preparation of the SBA-16 supported heterogeneous Pd-complex 3

New Journal of Chemistry
Page 10 of 17
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DOI: 10.1039/C4NJ02319F
(a)
(b)
(c)
(d)
(e)
Fig. 1 (a) Parent SBA-16; (b) SBA-16 supported Pd-complex 3;
(c), (d), (e) After five cycles of Heck, Suzuki, and Sonogashira
couplings respectively.

Page 11 of 17
New Journal of Chemistry
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DOI: 10.1039/C4NJ02319F
50000
40000
30000
20000
10000
0
0.5
1.5
2.5
3.5
4.5
2θ
Fig. 2 Small angle XRD patterns of SBA-16 and SBA-16
supported Pd-complex 3

New Journal of Chemistry
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DOI: 10.1039/C4NJ02319F
250
200
150
100
50
0
0
0.2
0.4
0.6
0.8
1
Relative Pressure (P/Po)
Fig. 3 Nitrogen absorption isotherm of SBA-16 supported
Pd-complex 3

Page 13 of 17
New Journal of Chemistry
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DOI: 10.1039/C4NJ02319F
100
80
60
40
20
0
0
1
2
3
4
5
6
Time (h)
Fig. 4 Hot filtration test of Suzuki-Miyaura reaction (Table 3,
5f).

New Journal of Chemistry
Page 14 of 17
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DOI: 10.1039/C4NJ02319F
Table 1. Heck reaction of iodobenzene with olefins using Pd-complex 3a
SBA-16 supported
3 (500 mol ppm)
Olefins/R1
R1
I
+
Na2CO3, DMA:H2O (1:1)
125 °C, 4 h
R
R
4
O
O
O
O
OBu
O
OBu
OBu
OBu
4a: 95%
Me
MeO
4b: 93%
4c: 92%
O
OBu
OBu
O
O2N
F3C
Me
4d: 96%
4e: 97%
4f: 95%
O
O
O
OBu
NH
NH
N
4h: 95%
4g: 94%
4i: 95%
4l: 93%
O
NH
4k: 95%
MeO
Me
4j: 92%
F3C
NC
4n: 91%
4m: 93%
MeO
4o: 93%
aAll reactions were carried out using 1 mmol of aryl iodide, 1.3 mol equiv of
olefin, 500 mol ppm of 3, 2 mol equiv of Na2CO3, in 2 mL of DMA/H2O
(1:1) at 125 °C for 4 h.

Page 15 of 17
New Journal of Chemistry
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DOI: 10.1039/C4NJ02319F
Table 2. Pd-complex 3 catalyzed Heck reaction of aryl halides with olefinsa
SBA-16 supported
3 (500 mol ppm)
X
Olefins/R1
R1
+
Na2CO3, DMA:H2O (1:1)
125 °C, 4 h
R
R
X = Br/Cl
4
O
O
O
OBu
OBu
OBu
O2N
Me
4a: X = Br, 93%
X = Cl, 51%
4b: X = Br, 90%
X = Cl, 48%
4d: X = Br, 94%
X = Cl, 71%
O
O
O
OBu
Me
NH
NH
O
MeO
4e: X = Br, 96%
X = Cl, 68%
4i: X = Br, 92%
4j: X = Br, 90%
X = Cl, 54%
Ph
Ph
Ph
Ph
Me
MeO
NC
4k: X = Br, 93%
4m: X = Br, 90%
4n: X = Br, 89%
4o: X = Br, 92%
aAll reactions were carried using 1 mmol of aryl halide, 1.3 mol equiv of
olefin, 500 mol ppm of 3, 2 mol equiv of Na2CO3, in 2 mL of DMA/H2O
(1:1) at 125 °C for 4 h.

New Journal of Chemistry
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DOI: 10.1039/C4NJ02319F
Table 3. Suzuki-Miyaura coupling reaction with Pd-complex 3a
SBA-16 supported
3 (100 mol ppm)
X +
B(OH)2
K2CO3
EtOH/H2O (1:1)
90 °C, 6 h
R'
R'
R
R
5
X = I/Br/Cl
MeO
Me
HO
5b: X = I, 94%
X = Br, 88%
5c: X = I, 91%
5a: X = I, 92%
Me
H2N
Me
Me
O
5d: X = I, 90%
5e: X = I, 90%
X = Br, 90%
5f: X = I, 93%
X = Br, 93%
X = Cl, 73%
aMolar ratio: aryl halide (1 mmol), Pd-complex 3 (100 mol ppm), aryl
boronic acid (1.1 mol equiv), K2CO3 (2 mol equiv), EtOH/H2O (1:1) at 90
°C for 6 h.

Page 17 of 17
New Journal of Chemistry
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DOI: 10.1039/C4NJ02319F
Table 4. SBA-16 supported Pd-complex 3 catalyzed Sonogashira reaction of aryl halidesa
SBA-16 supported
3 (200 mol ppm)
X
X = I/Br/Cl
Me
+
Ph
Ph
Ph
piperidine
80 °C, 2 h
R
R
6
Ph
MeO
Ph
6a: X = I, 94%
6b: X = I, 93%
6c: X = I, 95%
X = Br, 90%
O
Ph NC
Ph O2N
Ph
6f: X = I, 96%
X = Br, 93%
X = Cl, 72%
6d: X = I, 95%
X = Br, 93%
X = Cl, 68%
6e: X = I, 92%
X = Br, 90%
X = Cl, 68%
aAll reactions were carried using 1 mmol of aryl halide, 1.2 mol equiv of phenyl acetylene, 200 mol ppm of
3, 2 mol equiv of piperidine under solvent free reaction condition at 80 °C for 2 h.