A new N–heterocyclic carbene palladium complex immobilized on nano silica: An efficient and recyclable catalyst for Suzuki–Miyaura [Formula presented] coupling reaction

Article abstract of DOI:10.1016/j.jorganchem.2016.02.019

A new catalytic system based on Pd–NHC complex utilizing (4–pyridyl)bis(imidazolyl)methane as a bidentate NHC ligand supported on nano?silica is introduced. The catalyst was characterized by FT–IR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X–ray analysis, transmission electron microscopy and elemental analysis. This heterogeneous catalytic system exhibited excellent activity in the Suzuki–Miyaura coupling reaction of various aryl halides with phenylboronic acid, and was reusable several times without significant loss of its catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2016.02.019

Accepted Manuscript
A new N‒heterocyclic carbene palladium complex immobilized on nano silica:ꢀ An
efficient and recyclable catalyst for Suzuki–Miyaura C–C coupling reaction
Zari Pahlevanneshan, Majid Moghadam, Valiollah Mirkhani, Shahram
Tangestaninejad, Iraj Mohammadpoor-Baltork, Hossein Loghmani-Khouzani
PII:
S0022-328X(16)30052-3
10.1016/j.jorganchem.2016.02.019
JOM 19403
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 27 April 2015
Revised Date: 3 February 2016
Accepted Date: 11 February 2016
Please cite this article as: Z. Pahlevanneshan, M. Moghadam, V. Mirkhani, S. Tangestaninejad, I.
Mohammadpoor-Baltork, H. Loghmani-Khouzani, A new N‒heterocyclic carbene palladium complex
immobilized on nano silica:ꢀ An efficient and recyclable catalyst for Suzuki–Miyaura C–C coupling
reaction, Journal of Organometallic Chemistry (2016), doi: 10.1016/j.jorganchem.2016.02.019.
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ACCEPTED MANUSCRIPT
A new catalytic system based on Pd-NHC complex of
(4-pyridyl)bis(imidazolyl)methane
supported
on
nanosilica is introduced. This heterogeneous catalytic
system exhibited excellent activity in the Suzuki–
Miyaura coupling reaction of various aryl halides with
phenylboronic acid, and was reusable several times
without significant loss of its catalytic activity.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
A new N‒heterocyclic carbene palladium complex immobilized on nano
silica:ꢀ An efficient and recyclable catalyst for Suzuki–Miyaura C–C
coupling reaction
∗
Zari Pahlevanneshan, Majid Moghadam, Valiollah Mirkhani,* Shahram Tangestaninejad, Iraj
Mohammadpoor‒Baltork, Hossein Loghmani‐Khouzani
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746‒73441, Iran
Abstract‒
A
new
catalytic
system
based
on
Pd‒NHC
complex
utilizing
(4‒pyridyl)bis(imidazolyl)methaneas a bidentate NHC ligand supported on nano‒silica is introduced.
The catalyst was characterized by FT‒IR spectroscopy, thermogravimetric analysis, field emission
scanning electron microscopy, energy dispersive X‒ray analysis, transmission electron microscopy
and elemental analysis. This heterogeneous catalytic system exhibited excellent activity in the Suzuki–
Miyaura coupling reaction of various aryl halides with phenylboronic acid, and was reusable several
times without significant loss of its catalytic activity.
Keywords: Palladium(II) N‒heterocyclic carbene complex; Heterogeneous catalyst; Nano‒silica; C‒C
coupling reactions; Aaryl halides.
1
. Introduction
N‒Heterocyclic carbene (NHC) ligands with strong σ‒donor and weak π‒acceptor properties have
received much attention in the design of homogeneous catalysts because of their binding ability to any
transition metal regardless of their oxidation states that lead to stronger bonds with metal centers
compared to most classical ligands. The NHC complexes are resistant to decomposition, and thermally
∗
Corresponding authors: Tel: +98‒31‒3793‒4920; fax: +98‒31‒36689732; e‒mails: moghadamm@sci.i.ac.ir (M.
Moghadam); mirkhani@sci.ui.ac.ir (V. Mirkhani).
1

ACCEPTED MANUSCRIPT
stable. On the other hand, the catalytic active site is better protected within the inner metal
coordination sphere [1–5]. These properties make them the only class of ligands that can be used
instead of widely used phosphine ligands [6]. Due to their unique catalytic activity, these compounds
have attracted increasing attention in both academic and industrial fields [7,8]. NHC complexes as
homogeneous catalysts have been used in a number of organic transformations such as olefin
metathesis, and C–C and C–N bond formation reactions [9‒13]. Therefore, 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 many vast applications in the synthesis of natural
products, numerous drugs and high performance modern organic materials [14‒18].
Despite the wide application of these homogeneous catalysts inorganic transformations, their recycling
is almost complicated and their separation is very difficult. Moreover, in consequence of toxicity of
palladium residuals, acceptable limits of palladium traces in pharmaceuticals were set usually as ppm
level. Application of supported catalysts can solve this problem [19‒22]. In this regard, the
immobilization of Pd‒NHC complexes on polystyrene [23] or silica [24,25] has been reported.
Meanwhile, utilizing of nano‒supports in this case has attracted considerable interest due to their high
activity and environmental acceptability [26]. 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 [27].
In continuation of our previous work using supported catalysts in organic synthesis [28‒32], here we
wish to describe the synthesis of a new NHC palladium complex supported on nano‒silica,
Pd(PBIM)(OAc) @Nano‒SiO , and its application as a new heterogeneous and recoverable catalyst in
2
2
the Suzuki‒Miyaura C‒C coupling reaction (Scheme 1)
.
2

ACCEPTED MANUSCRIPT
B(OH)2
X
Pd(PBIM)(OAc) @Nano-SiO
2
2
+
ο
DMF:H O/K CO / 60 C
2
2
3
R
R
Scheme 1. Suzuki‒Miyaura C‒C Coupling reaction catalyzed by Pd(PBIM)(OAc) @Nano‒SiO
2
2
2
. Experimental
The chemicals used in this work were purchased from Fluka and Merck chemical companies. The DR
1
13
FT‒IR spectra were recorded by a Jasco 6300 spectrophotometer. H and C NMR (400 and 100
MHz) spectra were recorded on a Bruker Avance 400 MHz spectrometer using CDCl as solvent.
3
Thermogravimetric analysis (TGA) was carried out on a Mettler TG50 instrument under air flow at a
o
‒1
o
uniform heating rate of 10 Cmin in the range 30‒600 C. The scanning electron micrographs,
equipped with an energy dispersive X‒ray analysis (EDX) detector were taken on a Hitachi S‒4700
field emission‒scanning electron microscope (FE‒SEM). The Pd content of the catalyst was
determined by a Perkine Elmer ICP analyzer. Substances were quantified by gas chromatography (GC)
on an Agilent GC 6890 equipped with a 19096C006 80/100 WHP packed column and a flame
ionization detector (FID). Elemental analysis was performed on a LECO, CHNS‒932 analyzer. The
transmission electron microscopy (TEM) was carried out on a Zeiss EM10C transmission electron
microscope operating at 100 kV. The silica was activated and chloropropylated by known procedures
[33,34]
2
2
.1. Synthesis ofPd(PBIM)(OAc) @Nano‒SiO2
2
.1.1. Synthesis of (4‒pyridyl)bis(imidazolyl)methane (1)
The (4‒pyridyl)bis(imidazolyl)methane was prepared using the procedure reported for preparation of
(
2‒pyridyl)bis(imidazolyl)methane [35]. In a typical procedure, a mixture of 1,1‒carbonyldiimedazole
0.88 g, 5.42 mmol), 4‒pyridinecarboxaldehyde (0.52 mL, 5.42 mmol) and CoCl .6H O (6.2 mg, 0.026
(
2
2
3

ACCEPTED MANUSCRIPT
ο
mmol) was stirred at 80 C for 14 h. The mixture was allowed to cool to room temperature, dissolved
in CH Cl (6 mL) and extracted with water (2×6 mL). Then, the organic layer was dried over Na SO
2
2
2
4
and the solvent was evaporated. The crude product was purified by column chromatography, eluted
with CH Cl /CH OH (9:1) afforded the desired compound as a red oil. Yield: 0.158 g (80%).
2
2
3
1
H NMR (CDCl , 400MHz): 8.84 (s, 2H), 8.46 (d, J= 6.0 Hz, 1H), 7.81 (s, 1H), 7.52 (d, J= 31.6 Hz,
3
1
3
2
H), 6.92 (d, J= 33.2, 2H), 6.86 (d, J= 7.2 Hz, 2H), 6.79 (d, J= 5.2, 1H). C NMR (CDCl , 100
3
MHz):150.6, 144.0, 136.8, 135.1, 130.4, 121.7, 121.2, 118.0, 68.4. FT‒IR (KBr disc): 1599 (m), 1480
‒
1
(
m), 1224 (s), 1069 (s), 823 (m), 776 (s), 724 (s) cm .
.1.2. Preparation of Pd(PBIM)(OAc) @Nano‒SiO
The chloropropylated nano‒SiO (1 g) was added to a solution of compound (1)(675 mg, 3 mmol) and
2
2
2
2
NaI (3 mmol, 450 mg) in dry THF (40 mL). The reaction mixture was stirred under reflux conditions
overnight. The yellow solid material was separated by filtration, washed with hot THF for 12 h in a
Soxhlet apparatus to remove the unreacted starting materials, and then dried in a vacuum oven at 50
o
C. For preparation of NHC ligand, the silica supported (4‒pyridyl)bis(imidazolyl)methane (1 g) was
o
reacted with methyl iodide in dry THF (30 mL). The slurry was stirred at 80 C for 20 h and then
filtered off. The corresponding solid was washed with DMF and ethanol, and then dried under reduced
pressure. C: 10.5 H: 3.3 N: 2.01.
2 2 2
The final nano catalyst, Pd(PBIM)(OAc) @Nano‒SiO , was obtained by addition of Pd(OAc) (100
mg, 0.44 mmol) to a dispersed mixture of silica supported NHC (1 g) in DMSO (10 mL) under argon
o
atmosphere at room temperature. Next, the mixture was stirred for 5 h at 60 C and then allowed to
o
proceed for an additional 40 min at 100 C. The resulting catalyst washed with ethanol (3×20 mL) to
remove the unreacted Pd(OAc) , and finally dried under air.
2
2
.2. General procedure for Suzuki–Miyaura cross‒coupling reaction catalyzed by
Pd(PBIM)(OAc) @Nano‒SiO
2
2
4

ACCEPTED MANUSCRIPT
2 3
A mixture of aryl halide (1 mmol), phenylboronic acid (1.3 mmol), K CO (276 mg, 2 mmol) and
2
catalyst (0.004 g, 0.1 mol% Pd) in DMF/H O (4 ml, 2:1) was stirred at 60 °C under air atmosphere.
The progress of the reaction was monitored by GC. After completion of the reaction, ethyl acetate (15
ml) was added and the catalyst was filtered. The organic phase was washed with H O (2×10 ml), dried
2
over anhydrous MgSO and evaporated. The residue was recrystallized from ethyl acetate: ether (1:3)
4
to afford the pure product.
3
. Results and discussion
3
.1. Characterization of Pd(PBIM)(OAc) @Nano‒SiO catalyst
2
2
The preparation of the catalyst follows the steps shown in Scheme 2. First, 4‒pyridinecarbaldehyde
was reacted with 1,1‒carbonyldiimidazole to produce the (4‒pyridyl)bis(imidazolyl)methane (1).
Then, this compound was attached to 3‒chloropropylated nano‒silica. In the next step, this solid was
treated with MeI for preparation of NHC ligand. Finally, the supported palladium catalyst,
2 2
Pd(PBIM)(OAc) @Nano‒SiO , was obtained by the reaction of nano‒silica supported NHC ligand
with Pd(OAc)
2
.
Previously, it is reported that in the methylation of (2‒pyridyl)bis(imidazolyl)methane, only the
nitrogens of imidazole rings were methylated while the pyridyl nitrogen was not methylated [35]. This
can be attributed to the steric hindrance at 2-position for methylation. While this is not true in the case
of (4‒pyridyl)bis(imidazolyl)methane and all nitrogens can be methylated (Scheme 3). Therefore, we
proposed two probable structures for supported catalyst.
The prepared catalyst was characterized by elemental analysis, FT‒IR spectroscopy, SEM, TEM, ICP
and thermal analyses. The nitrogen content of the catalyst was 1.44 mmol/g. This value shows that the
amount of ligand on the nano‒silica is 0.29 mmol/g. The Pd loading of the catalyst, measured by ICP,
showed a value of about 0.25 mmol/g of catalyst. The FT‒IR spectrum of the catalyst showed
5

ACCEPTED MANUSCRIPT
−
1
−1
−1
absorption bands at 1106 cm (Si–O–Si), 798 cm (C–Pd) absorption frequency, 1653 cm (C=N),
−
1
−1
−1
1
623 cm (C=C), 1741 cm (C=O) and 2935 cm (C–H stretching vibration).
The thermal stability of the catalyst was also evaluated by TGA–DTG. As the thermogram shows, the
weight loss below 600 °C is 15.2 for Pd(PBIM)(OAc) @Nano‒SiO . The weight loss begins from 250
2
2
°
C which approved that the catalyst is thermally stable below 250 °C. This observation can be
attributed to the formation of a stable Pd complex (Fig. 1). The SEM image showed that the shape of
silica nanoparticles is spherical (Fig. 2). The presence of the palladium was also confirmed by the EDX
detector coupled to the SEM (Fig. 3). Transmission electron microscopy (TEM) confirmed the
nanometer dimensions of the catalyst particles and also shows that the Pd catalyst has been dispersed
on the silica nanoparticles (Fig. 4). As shown in the particle size histogram, the average size of the
nanoparticles is about 8–12 nm (Fig. 5).
3
.2. Suzuki–Miyaura cross‒coupling of aryl halides with phenylboronic acid in the presence of
Pd(PBIM)(OAc) @Nano‒SiO2
2
The catalytic activity of prepared catalyst was investigated in the Suzuki–Miyaura cross‒coupling of
aryl halides with phenylboronic acid. The coupling of 4‒iodoanisole with phenylboronic acid was
chosen as model reaction and the reaction conditions such as kind of base and solvent, temperature and
catalyst amount were optimized (Table 1). Different amount of catalyst was used and the best result
was obtained with 0.1 mol% of the catalyst (entries 1‒4). In the absence of catalyst, no product was
detected. When the model reaction was carried out at room temperature, only 49% of corresponding
product was observed (entry 6). The highest yield was observed at 60 ºC. Different bases such as NEt3,
Na PO and K CO were used in the model reaction. Amongst them, K CO was found to be the most
3
4
2
3
2
3
efficient base. Comparison of inorganic bases utilized showed that carbonate base was more stable
than the other one and an organic base like Et N was not as efficient as K CO (entries 3, 8‒10).
3
2
3
6

ACCEPTED MANUSCRIPT
Different aqueous solvents such as DMF, DMSO, EtOH and toluene were used as reaction media and
the best result was obtained in aqueous DMF (entries 3 and 11‒13).
o
To confirm the thermal stability of the catalyst, the catalyst was heated for 1 h at 250 C in an oven and
then, this catalyst was used in the reaction of 4‒iodoanisole with phenylboronic acid under the
optimized reaction conditions. No obvious decrease in the catalytic activity was observed.
The applicability of this method was examined in Suzuki‒Miyaura cross‒coupling of aryl halides with
phenylboronic acid. As can be seen from Table 2, under the optimized reaction conditions, different
aryl halides were reacted with phenylboronic acid to produce the substituted biphenyls. Different 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 2-bromotoluene (a more sterically crowded aryl halide) was used for the reaction with
phenylboronic acid, the yield decreased to 80% (entry 9) while in the case of bromobenzene the yield
was 93% (entry 8). On the other hands, when 4‒methoxyphenylboronic acid was used instead of
phenylboronic acid, the reaction times were longer compared to unsubstituted aryl halides (entries 6,
1
2 and 14).
3
.3. Catalyst recovery and reuse
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 (1.3 mmol), K CO (2.0 mmol), and catalyst
2
3
o
(
0.1 mol%) at 60 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 3. As can be seen, the catalyst was recovered
and recycled several times without loss of its catalytic activity remarkably. The amount of Pd leached
7

ACCEPTED MANUSCRIPT
was determined by ICP analysis. It was observed that only small amounts of Pd are leached in the first
run and no Pd was detected in the filtrates after first run.
Acknowledgements
The authors are grateful to the Research Council of the University of Isfahan for financial support of
this work.
References:
[
[
[
[
[
1] W. A. Herrmann, Angew. Chem. Int. Ed. 41 (2002) 1291‒1309.
2] W. A. Herrmann, C. Kocher, Angew. Chem. Int. Ed. Engl. 36 (1997) 2162‒2187.
3] E. Peris, R. H. Crabtree, Coord. Chem. Rev. 248 (2004) 2239‒2246.
4] S. Díez‒Gonzalez, N. Marion, S. P. Nolan, Chem. Rev. 109 (2009) 3612‒3676.
5] M. Alcarazo, T. Stork, A. Anoop, W. Thiel, A. Fürstner, Angew. Chem. Int. Ed. 49 (2010)
2
542‒2546.
6] F. Glorius (Ed.) N‒Heterocyclic Carbenes in Transition Metal Catalysis, Topics in Organomettalic
Chemistry, Springer‒Verlag, Berlin/Heidelberg, Germany, 2007, Vol. 21.
[
[7] S. Budagumpi, R. A. Haque, A.W. Salman, Coord. Chem. Rev. 256 (2012) 1787‒1830.
[8] L. R. Titcomb, S. Caddick, F. G. N. Cloke, D. J. Wilson, D. McKerrecher, Chem. Commun. (2001)
1
388‒1389.
[
[
[
[
[
9] M. Poyatos, J. A. Mata, E. Peris, Chem. Rev. 109 (2009) 3677‒3707.
10] A. H. Hoveyda, J. Org. Chem. 79 (2014) 4763‒4792.
11] J. S. Kingsbury, A. H. Hoveyda, J. Am. Chem. Soc. 127 (2005) 4510‒4517.
12] W. J. Sommer, M. Weck, Coord. Chem. Rev. 251 (2007) 860‒873.
13] N. Debono, A. Labande, E. Manoury, J. C. Daran, R. Poli, Organometallics 29 (2010) 1879‒1882.
8

ACCEPTED MANUSCRIPT
[14] Y. H. Chang, Z. Y. Liu, Y. H. Liu, S. M. Peng, J. T. Chen, S. T. Liu, Dalton Trans. 40 (2011)
4
89‒494.
[
[
[
[
[
[
[
[
[
[
[
[
[
[
15] T. Tu, H. Mao, C. Herbert, M. Z. Xu, K. H. Dotz, Chem. Commun. 46 (2010)7796‒7798.
16] S. Gu, H. Xu, N. Zhang, W. Chen, Chem. Asian J. 5 (2010) 1677‒1686.
17] N. Marion, S. P. Nolan, Acc. Chem. Res. 41 (2008) 1440‒1449.
18] G. C. Fortman, S. P. Nolan, Chem. Soc. Rev. 40 (2011) 5151‒5169.
19] Y. Uozumi, Top. Curr. Chem. 242 (2004) 77‒112.
20] D. Z. Yuan, Q. Y. Zhang, J. B. Dou, Catal. Commun. 11 (2010) 606‒610.
21] M. Choi, D. H. Lee, K. Na, B. W. Yu, R. Ryoo, Angew. Chem. Int. Ed. 48 (2009) 3673‒3676.
22] D. K. Yi, S. S. Lee, J. Y. Ying, Chem. Mater. 18 (2006) 2459‒2461.
23] N. T. S. Phan, D. H. Brown, P. Styring, Tetrahedron Lett. 45 (2004) 7915‒7919.
24] N. Gurbuz, I. Ozdemir, B. Cetinkaya, T. Seckin, Appl. Organomet. Chem. 17 (2003) 776‒780.
25] S. Paul, J. H. Clark, J. Mol. Catal. A: Chem. 215 (2004) 107‒111.
26] J. Y. Jung, J. B. Kim, A. Taher, M. J. Jin, Bull. Korean Chem. Soc. 30 (2009) 3082‒3084.
27] P. M. Price, J. H. Clark, D. J. Macquarrie, J. Chem.Soc., Dalton Trans. (2000) 101‒110.
28] M. Moghadam, S. Tangestaninejad, V. Mirkhani, B. Karami, N. Rashidi, H. Ahmadi, J. Iran.
Chem. Soc. 3 (2006) 64‒68.
29] A. Landarani Isfahani, I. Mohammadpoor‒Baltork, V. Mirkhani, A. R. Khosropour, M.
Moghadam, S. Tangestaninejad, R. Kia, Adv. Synth. Catal. 355 (2013) 957‒972.
30] F. Sadegh, O. Bagheri, M. Moghadam, V. Mirkhani, S. Tangestaninejad, I.
Mohammadpoor‒Baltork, J. Organomet. Chem. 759 (2014)46‒57.
31] M. Ghotbinejad, A. R. Khosropour, I. Mohammadpoor‒Baltork, M. Moghadam, S.
[
[
[
Tangestaninejad, V. Mirkhani, J. Mol. Catal. A: Chem. 385 (2014) 78‒84.
9

ACCEPTED MANUSCRIPT
[32] Z. Pahlevanneshan, M. Moghadam, V. Mirkhani, S. Tangestaninejad, I. Mohammadpoor‒Baltork, A.
R. Khosropour, Appl. Organomet. Chem. 2015, DOI 10.1002/aoc.3297
[33] B. Karimi, A. A. Safari, J. Organomet. Chem. 693 (2008) 2967‒2970.
[34] M. E. Mahmoud, M. M. El‒Essawi, S. A. Kholeif, E. M. I. Fathalla, Anal. Chim. Acta 525 (2004)
1
23‒132.
[35] E. Mas‒Marza, M. Sanau, E. Peris, J. Organomet. Chem. 690 (2005) 5576‒5580.
O
C
N
N
CoCl2
N
N
+
1
8
2 h
O
O
O
N
N
0 o
N
N
Nano
SiO2
(Me3O)3SiCH2CH2CH2Cl
Nano
SiO2
C
Si
CHO
(1)
Cl
N
N
NaI
Dry THF
12 h, reflux
N
I-
N
Cl-
N+
+
N
N
Cl-
N+
N
O
Nano
SiO2
N
N
O
O
Si
Si
N
and/or
O
O
O
Nano
SiO2
N+
I
Si
and/or
Cl-
N+
-
MeI
48 h
N
N+
Cl-
I-
N+
O
O
O
N
Nano
SiO2
N
(
2)
O
O
O
(
3)
N
Nano
SiO2
N
Si
N+
-
I
Pd(OAc)2
DMSO
N
Cl-
N+
N
N
N+
I
OAc
OAc
-
Pd
N
N
O
O
O
and/or
O
O
O
AcO
Nano
SiO2
Nano
SiO2
N
Si
N
Si
Pd
(4)
(
4)
AcO
N
Scheme 2. Preparation route for the catalyst
1
0

ACCEPTED MANUSCRIPT
Scheme 3. Methylation of (2‒pyridyl)bis(imidazolyl)methane and (4‒pyridyl)bis(imidazolyl)methane
1
2

ACCEPTED MANUSCRIPT
Fig. 1. TGA curve for compound (3)
1
3

ACCEPTED MANUSCRIPT
Fig. 2. SEM images of catalyst
1
4

ACCEPTED MANUSCRIPT
Fig. 3. SEM‒EDX spectrum of catalyst
1
5

ACCEPTED MANUSCRIPT
Fig. 4. TEM image of catalyst
1
6

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Fig. 5. Particle size distribution histogram of catalyst
1
7

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Table 1. Optimization of conditions in the Suzuki‒Miyaura reaction of 4‒iodoanisole and
a
2 2
phenylboronic catalyzed by Pd(PBIM)(OAc) @Nano‒SiO .
B(OH)2
I
Pd(PBIM)(OAc) @Nano-SiO
2
2
OMe
+
Catalyst, Solvent,
OMe
o
b
Entry
Solvent
DMF: H O (2:1)
Pd (mol%)
0
Base
T ( C)
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
K CO3
2
60
60
60
60
90
r.t.
40
60
60
60
60
60
60
5
2
0
30
2
DMF: H
DMF: H
DMF: H
2
2
2
O (2:1)
O (2:1)
O (2:1)
0.01
0.1
K
2
K
2
K
2
CO
CO
CO
3
3
3
1
99
0.5
0.7
0.5
4
100
8vhl7
49
DMF: H O (2:1)
0.1
K CO3
2
2
DMF: H O (2:1)
0.1
K CO3
2
2
DMF: H O (2:1)
0.1
K CO3
2
2
89
2
DMF: H O (2:1)
0.1
No Base
4
6
2
DMF: H O (2:1)
0.1
Na PO4
1.5
2
75
2
3
1
1
1
1
0
1
2
3
DMF: H
DMSO: H
EtOH: H
Toluene: H O (2:1)
2
O (2:1)
O (2:1)
O (2:1)
0.1
NEt
3
32
2
0.1
K
2
2
CO
3
3
1
90
2
0.1
K
CO
1
75
0.1
K CO3
2
1
34
2
a
Reaction conditions: 4‒Iodoanisole (1 mmol), phenylboronic acid (1.3 mmol), base (2 mmol), solvent
(
4 ml) under air atmosphere.
b
Yields determined by GC.
1
8

ACCEPTED MANUSCRIPT
Table 2. Suzuki‒Miyaura cross‒coupling reaction of aryl halides and phenylboronic acid
a
catalyzed by Pd(PBIM)(OAc) @Nano‒SiO .
2
2
d
Entry Aryl halide
Product
Time (h)
0.9
Yield (%)
1
I
98
2
Me
MeO
MeO
I
I
0.92
1.7
1
97
93
99
99
91
93
93
d
3
I
I
MeO
OMe
4
5
OMe
NO2
OMe
NO2
0.8
1.5
1.7
1.3
d
6
I
7
8
MeO
I
MeO
OMe
Br
Br
9
1.3
1.4
80
87
1
0
1
MeO
Br
Br
OMe
NO2
1
NO2
1
93
81
d
1
2
MeO
Br MeO
OMe
2.5
1
9

ACCEPTED MANUSCRIPT
O
O
O
1
3
0.95
1.8
99
90
Br
Br
d
1
4
1
1
5
6
Cl
1.6
1.5
68
99
O
O
Cl
1
1
7
8
MeO
Cl
Cl
OMe
NO2
2
31
NO2
1.4
97
a
Reaction conditions: Aryl halide (1 mmol), phenylboronic acid (1.3 mmol), K
2
CO
3
(2 mmol),
DMF/H O (2:1, 4 ml) under air.
2
b
c
o
6
0 C, catalyst (0.1 mol% Pd).
Yields determined by GC.
Using 4‒methoxyphenylboronic acid.
d
2
0

ACCEPTED MANUSCRIPT
Table 3. Recycling and reuse of Pd(PBIM)(OAc)
2
@Nano‒SiO
2
in the
a
Suzuki‒Miyaura reaction.
b
Entry
Pd(PBIM)(OAc) @Nano‒SiO2
2
c
d
Yield (%)
Pd leached (%)
1
2
3
4
5
99
92
92
90
88
0.12
‒
‒
‒
‒
a
Reaction conditions: 4‒Iodoanisole (1 mmol), phenylboronic acid (1.3
mmol), K CO (2 mmol), DMF/H O (2:1, 4 ml) under air.
2
3
2
b
c
o
6
0 C, catalyst (0.1 mol% Pd), 60 min.
Yields determined by GC.
Determined by ICP.
d
2
1

ACCEPTED MANUSCRIPT
u A new NHC palladium complex supported on nano‒silica was prepared u This
heterogeneous catalyst was characterized u This catalyst was highly active in the Suzuki-
Miyaura reaction u The catalyst was reusable.