Suzuki-Miyaura C-C coupling reactions catalysed by a homogeneous and nanosilica supported palladium(ii) N-heterocyclic carbene complex derived from 3,5-di(1-imidazolyl)pyridine

Article abstract of DOI:10.1039/c5nj01517k

A new palladium N-heterocyclic carbene complex using 3,5-di(1H-imidazol-1-yl)pyridine (1) as a precursor was prepared. The complex was immobilized on 3-chloropropylated nanosilica as a support and characterized by FT-IR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X-ray analysis, transmission electron microscopy and elemental analysis. The prepared catalyst was used as a heterogeneous catalyst in the Suzuki-Miyaura coupling reactions of various aryl halides with phenylboronic acid and the corresponding biphenyls were being produced in a high yield. The catalyst was recyclable under aerobic conditions without significant loss of activity. Also, the catalytic activity of homogeneous catalyst was investigated.

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ARTICLE
Suzuki-Miyaura C-C coupling reaction catalysed
by homogeneous and nanosilica supported
palladium(II) N-heterocyclic carbene complex
derived from 3,5-di(1-imidazolyl)pyridine
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2015,
Accepted 00th January 2015
DOI: 10.1039/x0xx00000x
Zari Pahlevanneshan, Majid Moghadam,* Valiollah Mirkhani,* Shahram
Tangestaninejad,* Iraj Mohammadpoor-Baltork, Saghar Rezaei
www.rsc.org/
A new palladium N-heterocyclic carbene complex using 3,5-di(1H-imidazol-1-yl)pyridine(1) as
precursor was prepared. The complex was immobilized on3-chloropropylated nanosilica as
support and characterized by FT-IR spectroscopy, thermogravimetric analysis, field emission
scanning electron microscopy, energy dispersive X-ray analysis, transmission electron
microscopy and elemental analysis
. The prepared catalyst was used as a heterogeneous
catalyst in the Suzuki–Miyaura coupling reaction of various aryl halides with phenylboronic acid
and the corresponding biphenyls were produced in high yield. The catalyst was recyclable under
aerobic condition without significant loss of activity
Introduction
Interestingly, applying these reactions minimize the steps
compared to classical organic syntheses.16-27
Application of N-heterocyclic carbenes (NHCs) as ligands and
their metal complexes have received wide attention recently.
However, homogeneous catalysts have wide applications in
organic transformations but these catalysts are not often used in
industrial processes mainly due to their low chemical and
thermal stability and their low potential to provide recyclable
systems. Application of supported catalysts can solve this
problem. In this regard, polymer supported catalysts have
received much attention due to the stability and uniformity of
the obtained materials, and the possibility of easier
product/catalyst separation, combining the advantages of
homogeneous and heterogeneous catalysis.28-31 For instance, the
immobilization of Pd–NHCs on polystyrene32 or silica33 has
been reported. Meanwhile, utilizing of nano-supports in this
case has attracted considerable interest due to their high activity
and environmental acceptability.34 Silica or modified silica-
supported catalysts are good alternatives to traditional
homogeneous catalysts; they are environmentally friendly, have
excellent (chemical and thermal) stability, good accessibility,
and good dispersion of catalytic active sites.35
The strong
‎–‎donor ability, ease of preparation and effective
binding ability of these ligands to most transition metals make
them the only class of ligands that has been able to challenge
the widely employed tertiary phosphines.1–8 N-Heterocyclic
carbenes (NHCs) derived from the replacement of the proton at
C-2 in an imidazolium salt by a metal have been known for
many years but interest was dormant until Arduengo et al.
isolated the free imidazolidene carbene in 1991. NHCs
transition metal complexes as homogeneous catalysts have been
wildly employed in organic transformations such as coupling
reactions such as Suzuki-Miyaura,9–11 Heck,12,13 and Kumada
reactions,14 as well as the Buchwald–Hartwig amination.15 In
particular, discovery of catalytic properties of Pd–NHC
complexes in the Mizoroki–Heck and Suzuki–Miyaura cross‎–
‎coupling reactions is of great importance since these reactions
provide opportunities for the synthesis of substituted arenes
which are used for production of pharmaceuticals and
agrochemicals.
In continuation of our previous work using supported catalysts
in organic synthesis,36-40, here we report the synthesis and
characterization of a new NHC palladium complex, its
immobilization on 3-chloropropylated nanosilica and
Department of Chemistry, Catalysis Division, University of
Isfahan, Isfahan 81746-73441, Iran. Fax: +98-31-36689732;
Tel: +98-31-37934920.
E-mail: moghadamm@sci.ui.ac.ir; mirkhani@sci.ui.ac.ir;
stanges@sci.ui.ac.ir
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application of homogeneous and heterogeneous catalysts in the characterization of (
Suzuki-Miyaura C-C coupling reactions (Scheme 1)
4
) was performed by transmission electron
.
microscopy (TEM). The TEM images of (4) showed well-
defined particles of Pd complex dispersed in nanosilica matrix
(Fig. 4).
Scheme 1 Suzuki-Miyaura C-C coupling reaction catalyzed by Pd(PyBNHC) or
Pd(PyBNHC)@Nano-SiO2
Results and discussion
Preparation and characterization of catalysts
The preparation route for homogeneous catalyst is shown in
Scheme 2. As can be seen, the 3,5-di(1H-imidazol-1-
yl)pyridine was prepared and methylated by methyl iodide.
Finally this methylated compound, 1,1'-(pyridine-3,5-
diyl)bis(3-methyl-1H-imidazol-3-ium) iodide, was complexed
with Pd(OAc)2 to produce the homogeneous diiodo-3,5-di(3-
methylimidazol-1-yl)methylpyridinium iodide) palladium(II).
Scheme 3 Preparation route for the Pd(PyBNHC)@Nano-SiO2 catalyst
The ICP analysis showed that 0.30 mmole of Pd was anchored
on 1 g of heterogeneous catalyst. The nitrogen content of the
catalyst was 2.22% that shows the amount of ligand on the
nanosilica is 0.32 mmol/g. In the diffuse reflectance FT-IR, the
bands at 1094 cm−1 (Si–O–Si), 808 cm−1 (C–Pd), 1605 cm−1
(C=N), and 2956 cm−1 (C–H stretching vibration) proved the
attachment of catalyst on the surface of nano SiO2. The TGA–
DTG analysis of the catalyst shows thermal stability below 260
°C and the weight loss is 16.4 below 600 °C. This observation
can be attributed to the formation of a stable Pd species (Fig. 1).
Scheme
2 Preparation route for the diiodo-(3,5-di(3-methylimidazol-1-
yl)methylpyridinium iodide)palladium(II) catalyst
1
The catalyst was characterized by FT-IR, H- and 13C NMR
spectroscopies and also elemental analysis (see experimental
section).
The preparation path for heterogeneous catalyst is depicted in
Scheme 3. First, 3,5-di(1H-imidazol-1-yl)pyridine was attached
to the surface 3-chloropropylated nanosilica and methylated
with MeI for preparation of NHC ligand. In the next step, the
heterogeneous catalyst, Pd(PyBNHC)@Nano-SiO2
obtained by the reaction of nanosilica supported NHC ligand
with Pd(OAc)2.
(4), was
Fig. 1. TGA curve for compound (3)
Investigation of catalytic activity of both catalysts in the C-
C coupling reactions
The size and surface morphologies of the (4) were directly
visualized by FE-SEM (Fig. 2). As can be seen, the nano-SiO2
particles are spherical and have diameters in the range of 40 to
80 nm. The presence of the palladium was also confirmed by
the EDX detector coupled to the SEM (Fig. 3). Further
The catalytic activities of both homogeneous and
heterogeneous catalysts were investigated in the Suzuki–
Miyaura cross-coupling of aryl halides with phenylboronic
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acid. As shown in Table 1, the reaction conditions such as kind When the model reaction was carried out at room temperature,
of base and solvent, temperature and catalyst amount were only 48% of corresponding product was observed (entry 6). A
º
optimized in the coupling of 4-iodoanisole with phenylboronic reaction temperature of 65 C was found to be optimal for the
acid in the presence of Pd(BNHC)@Nano-SiO2. Different model reaction. Different bases such as NEt3, Na3PO4 and
amount of catalyst was used and the best result was obtained K2CO3 were used in the model reaction. Amongst them, K2CO3
with 0.15 mol% of the catalyst (entries 1-4). In the absence of was found to be the most efficient base. Comparison of
catalyst, no product was detected in the reaction mixture. This inorganic bases utilized showed that carbonate base was more
coupling reaction was found to be highly sensitive to the stable than the other one and an organic base like NEt3 was not
reaction temperature (entries 4-7).
as efficient as K2CO3 (entries 4 and 8-10). Then, the same
reaction was carried out in different aqueous/organic media.
Different aqueous solvents such as DMF, DMSO, EtOH and i-
PrOH and toluene were used as reaction media and the best
result was obtained in aqueous DMF (entries 4 and 11-14).
Table 1. Optimization of conditions in the Suzuki-Miyaura reaction of 4-
iodoanisole and phenylboronic acid catalyzed by Pd(PyBNHC)(@Nano-
SiO2.a
Row
Solvent
Pd
(mol%)
0
0.01
0.15
0.5
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
0.15
Base
T
(oC)
65
65
65
65
85
r.t.
40
65
65
65
65
65
65
65
Time
(h)
6
1.7
0.8
0.6
0.6
5
2.3
5
1.5
2
Yield
(%)b
0
32
99
100
100
48
89
9
77
34
92
78
81
37
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DMF: H2O
DMF: H2O
DMF: H2O
DMF: H2O
DMF: H2O
DMF: H2O
DMF: H2O
DMF: H2O
DMF: H2O
DMF: H2O
DMSO: H2O
EtOH: H2O
i-PrOH: H2O
Toluen: H2O
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
No Base
Na3PO4
NEt3
Fig. 2. SEM image of Pd(PyBNHC)@Nano-SiO2
K2CO3
K2CO3
K2CO3
K2CO3
1
1
1
1
aReaction conditions: 4-Iodoanisole (1 mmol), phenylboronic acid (1.4
mmol), base (3 mmol), solvent/H2O (5 ml, 2:1) under air atmosphere.
bYields were determined by GC.
Fig. 3. SEM-EDX spectrum of Pd(PyBNHC)@Nano-SiO2 catalyst
Therefore, aryl halide (1 mmol), phenylboronic acid (1.4
mmol), K2CO3 (3 mmol) and Pd(BNHC)@Nano-SiO2 (4) (0.15
o
mol%Pd) in DMF/H2O (5 ml, 2:1) at 65 C were selected as
optimized conditions. Under these optimized conditions,
different aryl halides were reacted with phenylboronic acid to
produce the substituted biphenyls. Aryl iodides, bromides and
chlorides bearing electron-donating and electron-withdrawing
groups reacted efficiently with phenylboronic acid and the
desired cross-coupling products were produced in high yields.
As expected; aryl iodides were found to be more reactive than
aryl bromides and chlorides. When, 4-chloroanisole was used in
this reaction, only 21% of the corresponding product was
produced (entry 12).
In order to show the effect of supporting on the catalytic
activity, all reactions were repeated using diiodo-(3,5-di(3-
methylimidazol-1-yl)methylpyridiniumiodide)palladium(II)
complex as homogeneous catalyst using aryl halide (1 mmol),
Fig. 4. TEM image of heterogeneous Pd(PyBNHC)@Nano-SiO2 catalyst
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phenylboronic acid (1.4 mmol), K2CO3 (3 mmol) and reactive than the homogeneous one. This can be attributed to
homogenous palladium (II) complex (1 mol% Pd) in the dispersion of catalyst on nanosilica bearing high surface
DMF/H2O (5 ml, 2:1) (Table 3). The same trend observed for area which in turn facilitates the accessibility of catalytic active
heterogeneous catalyst was also observed for homogeneous sites. To stress this point, some of the reactions were carried out
counterpart.
at equal times (0.3 and 0.8 h) and also using 0.15 mol% of
catalyst. The results showed that the heterogeneous catalyst is
much more efficient than the homogeneous counterpart (Table
4).
Table 2. Suzuki-Miyaura cross-coupling reaction of aryl halides and
phenylboronic acid catalyzed by Pd(PyBNHC)@Nano-SiO2.a
Table 4. Comparison of catalytic activity of both catalysts in the Suzuki-
Miyaura reaction.a
Aryl halide
Pd(PyBNHC)
Yield (%)b
Pd(PyBNHC)@Nano-SiO2
Yield (%)b
0.3 h
0.8 h
0.3 h
0.8
Entry
1
2
3
4
5
6
7
8
X
I
I
I
I
Br
Br
Br
Br
Cl
Cl
Cl
R
H
Me
MeO
NO2
H
MeO
NO2
Ac
Time (h)
0.8
0.93
0.8
1
1.4
1.5
1
0.93
1.7
1.5
1.5
2
Yield (%)b,c
96(92)
98(93)
99(96)
99(92)
92(89)
87(82)
91(87)
98(93)
69(65)
98(92)
97(91)
21(18)
TOF (h-1)
800
702
825
660
438
387
606
653
270
435
431
70
I
38
63
57
96
MeO
Br
Cl
22
2
49
15
34
12
71
43
9
H
Ac
NO2
10
11
12
aReaction conditions: Aryl halide (1 mmol), phenylboronic acid (1.4
mmol), K2CO3 (3 mmol), catalyst (0.15 mol% Pd), DMF/H2O (2:1,
ml)
Cl OMe
aReaction conditions: Aryl halide (1 mmol), phenylboronic acid (1.4
mmol), K2CO3 (3 mmol), catalyst (0.15 mol% Pd), DMF/H2O (2:1,
ml)
5
.
5
.
bYields were determined by GC.
bYields were determined by GC.
Catalyst recovery and reuse
cThe yields in the parentheses refer to isolated yields.
The recovery and reuse of a heterogeneous catalyst are of great
importance from industrial, economical and green chemistry
points of view. Therefore, the reusability of the catalyst was
investigated using a mixture of 4-iodoanisole (1.0 mmol),
phenylboronic acid (1.4 mmol), K2CO3 (3 mmol), and catalyst
Table 3. Suzuki-Miyaura cross-coupling reaction of aryl halides and
phenylboronic acid catalyzed by Pd(PyBNHC).a
o
(0.15 mol%) at 65 C. After completion of the reaction, the
catalyst was filtered and washed thoroughly with acetone,
diethyl ether and water, successively, and reused with fresh 4-
iodoanisole and phenylboronic acid. The results are
summarized in Table 5. As can be seen, the catalyst was
recovered and recycled several times without remarkable loss
of its catalytic activity. The amount of Pd leached was
determined by ICP analysis. It was observed that only small
amounts of Pd are leached in the first run.
Entry
1
2
3
4
5
6
7
8
X
I
I
I
I
Br
Br
Br
Br
Cl
Cl
Cl
R
H
Me
MeO
NO2
H
MeO
NO2
Ac
Time (h)
0.3
0.31
0.2
0.37
0.45
0.5
Yield (%)b
TOF (h-1)
323
316
495
267
182
174
102
102
76
97
98
99
99
82
87
92
82
76
98
81
0.9
0.8
1
1.4
Conclusion
9
10
11
H
Ac
NO2
In conclusion, Suzuki-Miyaura C-C coupling reaction catalysed
by homogeneous and nanosilica supported palladium(II) N-
heterocyclic carbene complex derived from 3,5-di(1-
imidazolyl)pyridine was carried out. Both homogeneous and
heterogeneous catalysts were applied in the Suzuki–Miyaura
coupling of aryl iodide, bromides and chlorides with
phenylboronic acid and the corresponding biphenyls were
produced in good to excellent yield (69-99% except for 4-
chloroanisole). As expected, aryl iodides and bromides were
more reactive than chloride one. Despite the higher catalytic
70
54
1.5
aReaction conditions: Aryl halide (1 mmol), phenylboronic acid (1.4
mmol), K2CO3 (3 mmol), catalyst (1 mol% Pd), DMF/H2O (2:1, 5 ml),
65 oC.
bYields were determined by GC.
cThe yields in the parentheses refer to isolated yields.
Comparison of the turnover frequencies of (TOF) of both
catalysts showed that the heterogeneous catalyst is more
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activity of homogeneous catalyst, it could not be reused even then dried under reduced pressure. Yield: 0.554 g (87%). M.p.:
one time while the heterogeneous catalyst was reused five 270 oC. FT-IR (KBr pellet): absorption frequency in 1634 cm−1
consecutive times without significant loss of its activity.
(C=N), 1605 cm−1(C=C) and 2869 cm−1(C–H stretching
vibration).1H NMR (D2O, 400 MHz): 9.74 (s, 1H), 9.39 (s,
1H), 9.01 (d, J= 2.4 Hz, 1H), 8.54 (t, J= 2 Hz, 1H), 8.11 (d, J=
2.4 Hz, 1H), 7.94 (d, J= 2.0 Hz, 2H), 7.77 (d, J= 2.4 Hz, 1H),
7.66 (d, J= 2.0 Hz, 1H), 4.02 (s, 3H), 3.98 (s, 6H).13C NMR
(D2O, 100 MHz): 34.5, 36.5, 37.0, 121.8, 121.9, 124.9, 125.0,
125.8, 126.2, 132.5, 133.4, 136.2, 141.6, 144.3. Anal. found: C,
27.17;H, 2.93; N,11.35. Calc. for C14H18N5I3: C, 27.05; H, 2.89;
N, 11.27.
Table 5. Investigation of recycling of Pd(PyBNHC)@Nano-SiO2 in the
Suzuki-Miyaura reaction.a
B(OH)2
I
Pd(PyBNHC)@Nano-SiO2
OMe
+
K2CO3, H2O/ DMF
65 °C
OMe
Entry
Yield (%)b
Pd leached (%)c
1
2
3
4
5
99
93
92
90
87
0.11
The palladium complex of 1,1'-(pyridine-3,5-diyl)bis(3-methyl-
1H-imidazol-3-ium) iodide was straightforwardly synthesized
by in situ deprotonation of the imidazolium salt precursor
-
-
-
-
(L)(318 mg, 0.5 mmol) with palladium acetate (112 mg, 0.5
o
mmol) in DMSO. The mixture was stirred for 5 h at 60 C and
then allowed to proceed for an additional 40 min at 100 oC until
a red mixture was obtained. The remaining DMSO was then
removed in vacuo to give an orange solid which was washed
with ethanol and CH2Cl2 (3×20 mL) to remove the unreacted
aReaction conditions: 4-Iodoanisole (1 mmol), phenylboronic acid (1.4
mmol), K2CO3 (3 mmol), catalyst (0.15 mol% Pd), DMF/H2O (2:1, 5 ml),
65oC, 0.8 h.
bYields were determined by GC.
cDetermined by ICP.
1
Pd(OAc)2, and finally dried under air. Yield:185 mg (50%). H
NMR (DMSO-d6, 400 MHz): 6.78 (d, J= 2.0 Hz, 1H), 6.69 (d,
J= 2.0 Hz, 1H), 6.13 (t, J= 2.0 Hz, 1H), 5.71 (d, J= 2.0 Hz, 1H),
5.69 (d, J= 2.0 Hz, 1H), 5.43 (d, J= 2.0 Hz, 1H), 5.41 (d, J= 2.0
Hz, 1H), 1.75 (s, 9H). 13C NMR (DMSO-d6, 100 MHz): 35.2,
Experimental
Materials and methods
All the reagents were obtained from commercial sources. The 37.3, 37.8, 122.8, 122.9, 125.3, 125.9, 126.7, 127.1, 135.2,
DRFT-IR spectra were recorded by
a
Jasco 6300 140.1, 140.3 163.4, 165.2. LC-MS (ESI+) m/z): 742.77
spectrophotometer.1H and 13C NMR (400 and 100 MHz) [M+H+1]+. Anal. found: C, 22.71; H, 2.28; N, 9.52. Calc. for
spectra were recorded on a Bruker Avance 400 MHz C14H16N5I3Pd: C, 22.68; H, 2.18; N, 9.45.
spectrometer. The morphological features were obtained on a
Synthesis of Pd(PyBNHC)@Nano-SiO2
Hitachi S–4700 field emission–‎ ‎scanning electron microscope
(FE–SEM), equipped with an energy dispersive X-ray analysis The silica was activated and chloropropylated by known
(EDAX) detector. Thermogravimetric analysis (TGA) was procedures.42 In a round-bottomed flask equipped with a
carried out on a Mettler TG50 instrument under air flow at a condenser and a magnetic stirrer, chloropropylated nanosilica
o
o
uniform heating rate of 10 Cmin-1 in the range 30-600 C. (1 g), 3,5-di(1H-imidazol-1-yl)pyridine (211 mg, 1 mmol) and
Elemental analysis was performed on a LECO, CHNS-932 NaI (3 mmol, 450 mg) in dry THF (40 mL) was stirred under
analyzer. The mass spectrum of palladium complex was reflux conditions overnight. The yellow solid material was
recorded on a Shimadzo LCMS-2010 EV. The transmission separated by filtration, washed with hot THF for12 h in a
electron microscopy (TEM) was carried out on a Zeiss EM10C Soxhlet apparatus to remove the unreacted starting materials,
o
transmission electron microscope operating at 100 kV. GC and then dried in a vacuum oven at 50 C. For preparation of
analyses were performed on an Agilent GC 6890 equipped with supported NHC ligand, the nanosilica supported 3,5-di(1H-
a 19096C006 80/100 WHP packed column and a flame imidazol-1-yl)pyridine (1 g) was reacted with methyl iodide in
o
ionization detector (FID). The GC yields were calculated by the dry THF (30 mL). The slurry was stirred at 80 C for 24 h and
“internal standard addition” method and in this manner anisole then filtered off. The corresponding solid was washed with
was used as internal standard. The compound of 3,5-di(1H- DMF and ethanol, and then dried under reduced pressure. C:
imidazol-1-yl)pyridine was prepared according to the literature 8.53, H: 1.49, N: 2.22. The final nanocatalyst,
method.41
Pd(PyBNHC)@Nano-SiO2, was obtained by addition of
Pd(OAc)2 (100 mg, 0.44 mmol) to a dispersed mixture of silica
supported NHC (1 g)in DMSO (10 mL) under argon
atmosphere at room temperature. Next, the mixture was stirred
Synthesis
of
diiodo-3,5-di(3-methylimidazol-1-
yl)methylpyridiniumiodide)palladium(II) complex
For preparation of NHC ligand, (
L
), 3,5-di(1H-imidazol-1- for 5 h at 60 oC and then allowed to proceed for an additional
o
yl)pyridine (211 mg, 1 mmol) was reacted with excess methyl 40 min at 100 C. The resulting catalyst washed with ethanol
iodide in dry THF (30 mL) to produce the 1,1'-(pyridine-3,5- (3×20 mL) to remove the unreacted Pd(OAc)2, and finally dried
diyl)bis(3-methyl-1H-imidazol-3-ium) iodide. The mixture was under air.
stirred at 80 oC for 24 h and then filtered off. The
General procedure for Suzuki–Miyaura cross-coupling reaction
corresponding solid was washed with DMF and ethanol, and
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A mixture of aryl halide (1 mmol), phenylboronic acid (1.4 [14] L. Anastasia, E.-I. Negishi, in: E.-I. Negishi (Ed.), Organopalladium
mmol), K2CO3 (3 mmol) and Pd(PyBNHC)@Nano-SiO2, (0.15
mol% Pd) in DMF/H2O (5 ml, 2:1) was stirred at 65 °C under
Chemistry for Organic Synthesis, vol. 1, Wiley-Interscience, New
York, 2002, p. 311.
air atmosphere. After completion of the reaction, the catalyst [15] J. F. Hartwig, in: E.-I. Negishi (Ed.), Organopalladium Chemistry
was separated by centrifugation and the products were extracted for Organic Synthesis, vol. 1, Wiley-Interscience, New York, 2002.
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Page 7 of 7
New Journal of Chemistry
View Article Online
DOI: 10.1039/C5NJ01517K
Efficient Suzuki-Miyaura C-C coupling reaction catalysed by palladium(II) NHC complex
derived from 3,5-di(1-imidazolyl)pyridine under homogeneous and heterogeneous conditions
is reported.