Recyclable palladium(II) imino-pyridine complex immobilized on mesoporous silica as a highly active and recoverable catalyst for Suzuki-Miyaura coupling reactions in aqueous medium

Article abstract of DOI:10.1016/j.tet.2012.11.042

A new mesoporous silica supported palladium imino-pyridine complex was successfully prepared by attaching palladium acetates to a novel imino-pyridine ligand functionalized MCM-41. The as-prepared catalyst was characterized by ICP-AES, XRD, FTIR, SEM, and TEM. It was found to be an efficient catalyst for Suzuki-Miyaura coupling reactions in aqueous medium. The reactions of various aryl bromides with arylboronic acids could be carried out under aerobic and low Pd loading (0.1 mol %) conditions with good to excellent yields, and very low Pd leaching (<0.2 ppm) was detected. Moreover, the supported catalyst could be simply recovered and reused several times without significant loss of efficiency.

Full text of DOI:10.1016/j.tet.2012.11.042

Accepted Manuscript
Recyclable palladium(II) imino-pyridine complex immobilized on mesoporous silica
as a highly active and recoverable catalyst for Suzuki-Miyaura coupling reactions in
aqueous medium
Qiang Zhang, Hong Su, Jun Luo, Yunyang Wei
PII:
S0040-4020(12)01735-8
10.1016/j.tet.2012.11.042
TET 23743
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 22 September 2012
Revised Date: 1 November 2012
Accepted Date: 9 November 2012
Please cite this article as: Zhang Q, Su H, Luo J, Wei Y, Recyclable palladium(II) imino-pyridine complex
immobilized on mesoporous silica as a highly active and recoverable catalyst for Suzuki-Miyaura
coupling reactions in aqueous medium, Tetrahedron (2012), doi: 10.1016/j.tet.2012.11.042.
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ACCEPTED MANUSCRIPT
Recyclable palladium( ) imino-pyridine complex immobilized
on mesoporous silica as a highly active and recoverable catalyst
for Suzuki-Miyaura coupling reactions in aqueous medium
Qiang Zhang, Hong Su, Jun Luo* and Yunyang Wei
School of Chemical Engineering, Nanjing University of Science & Technology, Nanjing, 210094,
PR China
E-mail: luojun@njust.edu.cn; Fax: (+)86-25-84315030
Recyclable palladium( ) imino-pyridine complex immobilized on mesoporous silica as
a highly active and recoverable catalyst for Suzuki-Miyaura coupling reactions in
aqueous medium
Qiang Zhang, Hong Su, Jun Luo* and Yunyang Wei
School of Chemical Engineering, Nanjing University of Science & Technology, Nanjing,
210094, PR China
Abstract: A new mesoporous silica supported palladium imino-pyridine complex was
successfully prepared by attaching palladium acetates to a novel imino-pyridine ligand
functionalized MCM-41. The as-prepared catalyst was characterized by ICP-AES, XRD, FT-IR,
SEM and TEM. It was found to be an efficient catalyst for Suzuki-Miyaura coupling reactions in

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aqueous medium. The reactions of various aryl bromides with arylboronic acids could be carried
out under aerobic and low Pd loading (0.1 mol%) conditions with good to excellent yields, and
very low Pd leaching (<0.2 ppm) was detected. Moreover, the supported catalyst could be simply
recovered and reused several times without significant loss of efficiency.
Keywords: imino-pyridine complex; supported palladium catalyst; mesoporous silica;
Suzuki-Miyaura coupling
1. Introduction
The palladium-catalyzed Suzuki-Miyaura coupling of aryl halides with arylboronic acids, is
one of the most successful methods for the construction of carbon-carbon bonds in organic
synthesis.1 And the produced biaryl units are important and versatile building blocks in the field of
natural products, pharmaceuticals, agrochemicals, and functional materials.2 Catalysts used in the
reaction process are usually based on homogenous palladium-phosphine complexes3 or
oxime-carbapalladacycles.4 More recently, palladium-N-heterocyclic carbene complexes have
attracted considerable attention as valuable catalysts for this transformation.5 However, separation
of the catalyst from the product is often problematic in the homogeneous systems. Moreover, from
environmental and economic points of view, catalyst recovery is highly desirable, in particular, if
precious metal catalysts are used in large-scale synthesis. In this regard, heterogeneous catalysis
seems particularly well suited since the palladium catalyst immobilized on a support could be
easily separated from the product free of metal residues and recycled. Thus, a variety of supports,
such as polymers,6 silica,7 metal oxides,8 carbon,9 and ionic liquids,10 have been explored. Among
silica supports, the mesoporous silica MCM-41 has aroused considerable interest because it has a

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regular large pore and a extremely high surface area.11 To date, a few palladium complexes on
functionalized MCM-41 support have been prepared and used in the Suzuki coupling.12
Schiff bases, a sort of powerful organic ligands in coordination chemistry, have been widely
used in transition metal-catalyzed reactions.13 Furthermore, some supported Pd Schiff base
complex were prepared and used as heterogeneous catalysts in Suzuki-Miyaura coupling.14
Nevertheless, most of these transformations catalyzed by the supported Pd Schiff base complexes
were performed in high Pd loading, toxic organic solvents or longer reaction time. In recent years,
imino-pyridine chelating ligands, a new kind of Schiff bases, have emerged as attractive ligands
for Cu catalyzed C-O or C-N coupling 15 and Pd catalyzed Heck reactions, cyclization, or ethylene
polymerization.16 In continuation of our efforts in designing greener supported catalysts, herein,
we would like to present a simple preparation of mesoporous silica MCM-41 supported Pd
imino-pyridine complex via anchoring a novel silane-functionalized imino-pyridine ligand onto
MCM-41 by covalent bonds and its application for Suzuki-Miyaura coupling reactions in aqueous
medium. High activity was observed and the catalyst could be simply recovered and reused
several times without significant loss of efficiency.
2. Results and discussion
2.1 Preparation and characterization of the catalyst
It should be mentioned at this point that Clark and co-workers previously prepared similar
imino-pyridine ligands immobilized on amino-functionalized silica and amino-modified starch,
respectively.17 However, the propyl chain as the linker between the bidentate nitrogen donor and
the silicon based anchoring group is short, which might favor additional interactions between the

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framework walls and active sites. Additionally, the results of application for the Suzuki reaction
were not representing the best of advance in this area, due to the harsh conditions, such as the use
of toxic xylene, high reaction temperature and Pd loading. Thus, we focused on immobilizing a
novel imino-pyridine ligand onto silica via a prolonged alkyl chain contained a aryl ring and its
application for a milder Pd-catalyzed process.
The MCM-41 supported palladium catalyst was prepared following the simple procedure
shown in Scheme 1. The precursor silane-functionalized imino-pyridine ligand 2 was synthesized
by nucleophilic substitution of imino-pyridine ligand 1 and (3-chloropropyl)triethoxysilane under
basic conditions. Then the MCM-41 with a toluene solution of complex 2 was refluxed for 24 h to
undergo a condensation reaction, which afforded imino-pyridine ligand functionalized MCM-41 3.
The loading amount of the imino-pyridine ligand was then determined to be 0.25 mmol·g-1 by
elemental analysis of the nitrogen content, which was also supported by TGA analysis (see
Supporting Information).
Scheme 1 Preparation of MCM-41 supported Pd catalyst
In order to warrant the successful functionalization of MCM-41, FT-IR was firstly employed
to give a detailed investigation of the blank MCM-41, free precursor 2, and functionalized
MCM-41 3 (Fig. 1). The Si-O-Si stretching modes of the MCM-41 could be observed as a strong
peak at 1078 cm-1 and broad peaks at around 3440 and 1635 cm-1, which are attributed to the

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Si-OH group and adsorbed water, respectively. The IR curve of free precursor 2 shows typical
bands at around 1590 cm-1 (C=N vibration), 1500 cm-1 (C=C vibration of aryl ring), 2930, 2880
and 1468 cm-1 (alkyl chain stretching and deformation vibrations). While in the spectrum of
functionalized MCM-41 3, these characteristic peaks are at the same wavenumbers, with a small
shift because of the interaction with the support. However, all of these significant features cannot
be observed in the blank MCM-41. The functionalized MCM-41 3 was further confirmed by
solid-state 13C NMR spectra (see Supporting Information). The 13C CP/MAS NMR spectrum
clearly shows the signals for saturated C at 6, 22 and 69 ppm, and for the aryl and pyridine rings in
the range of 115-160 ppm. The resonances at 58 and 16 ppm are attributed to (EtO)3Si- groups that
did not completely hydrolyze. Thus, the above results indicate that the precursor 2 was
successfully grafted onto the MCM-41.
Fig.1 FT-IR spectra of blank MCM-41 (a), free precursor 2 (b), functionalized MCM-41 3 (c).
Ultimately, the obtained 3 was reacted with palladium acetate in acetone at room temperature
for 12 h to give the target catalyst, MCM-41 supported Pd imino-pyridine complex 4, with a
loading of 0.18 mmol of Pd per gram based on inductively coupled plasma (ICP) analysis. X-ray
power diffraction (XRD) patterns of the parent MCM-41 and the catalyst 4 are shown in Fig. 2.

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Small angle XRD of the parent MCM-41 gives the peaks corresponding to hexagonally ordered
mesoporous phases. The characteristic (100) reflection of the parent MCM-41 is remained after
functionalized, indicating that the basic mesoporous structure is not damaged in the whole process
of catalyst preparation. While the (110) and (200) reflections become weak and diffuse, which can
be due to the organic moieties anchored inside the channel of MCM-41.12c Furthermore, the
morphology of the catalyst 4 was investigated by TEM and SEM. Periodic hexagonal porous
tubules can be clearly observed, further confirming that the highly ordered mesopores are present
and these findings are well consistent with the XRD results (Fig. 3). This catalyst exhibited an
ellipsoidal particle shape with a range of particle size from 150 to 250 nm as depicted in the SEM
micrograph (see Supporting Information). The as-prepared catalyst 4 was also characterized by
FT-IR, and the IR spectrum of the catalyst 4 demonstrates that no obvious change occurs after
immobilization of Pd salts on the functionalized MCM-41 3 due to the low Pd loading on the
support (see Supporting Information).18
Fig. 2 XRD patterns of MCM-41 (a), MCM-41 supported Pd catalyst 4 (b).

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Fig. 3 TEM image of the catalyst 4
For comparison, an analogous mesoporous silica supported Pd catalyst (Clark’s catalyst) was also
prepared using the previously reported procedure (Scheme 2).17a The ICP analysis of this
silica-bound catalyst showed there to be 2.13% Pd on the silica, corresponding to a catalyst
loading of 0.20 mmol Pd per gram.
Scheme 2 Preparation of the Clark’s catalyst
2.2 Catalytic activity of the catalyst in Suzuki-Miyaura coupling
The catalytic property of the MCM-41 supported Pd imino-pyridine complex 4 was initially
tested in Suzuki-Miyaura coupling. The coupling of bromobenzene and phenylboronic acid was
chosen as the model reaction. Firstly, the effect of solvent was examined, and a significant effect
was observed (Table 1). The aprotic solvent such as DMF, toluene, THF, CH3CN, acetone, and
dioxane, gave low to moderate yields for this model reaction (Table 1, entries 1-6). While the

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reactions were carried out in ethanol and pure water, moderate to good yield were obtained (Table
1, entries 7 and 8). Interestingly, the use of organic/aqueous co-solvent, resulted in good to
excellent yields for a shorter time (Table 1, entries 9-12). It was worth noting that the best result
was observed when the reaction was performed in EtOH/H2O (1:1, v/v) (Table 1, entry 10).
Table 1 Effect of the solvent on Suzuki–Miyaura reaction a
Pd Cat. (0.1 mol%)
B(OH)2
Br +
K2CO3, solvent, 50
Entry
Solvent
DMF
Time (h)
Yield b (%)
1
3
41
26
7
2
Toluene
THF
3
3
3
4
CH3CN
Acetone
Dioxane
EtOH
3
13
10
<5
90
54
89
96
72
93
5
3
6
3
7
3
8
H2O
6
9
EtOH/H2O (3:1, v/v)
EtOH/H2O (1:1, v/v)
EtOH/H2O (1:3, v/v)
DMF/H2O (1:1, v/v)
1.5
1.5
2
10
11
12
1.5
a
Reaction conditions: bromobenzene (1.0 mmol), phenylboronic acid (1.2 mmol), K2CO3 (2.0
mmol), catalyst 4 (0.1 mol% Pd) in 6.0 mL of solvent at 50 under air.
b Isolated yield.
Secondly, a series of bases were taken into consideration for the model reaction in the
aqueous EtOH. With regard to other bases, K2CO3 was found to act as an excellent base (Table 2,
entry 1). Na2CO3, Cs2CO3, and K3PO4 were also effective (Table 2, entries 2-4). Moreover, the
organic bases, NEt3 and dimethylaminopyridine (DMAP), were also studied, the unsatisfied yields
were obtained (Table 2, entries 7 and 8). Lastly, the different catalyst loading were also
investigated, and 0.1 mol% loading of Pd was found to be optimal (Table 2, entries 9-11). In

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addition, the model reaction could be well carried out in the presence of even much less amount of
Pd (0.005 mol%) for a extended time, which corresponds to a turnover number of 15200,
indicating that this novel MCM-41 supported Pd catalyst 4 is highly efficient for the
Suzuki-Miyaura coupling.
Table 2 Effect of the base and catalyst loading on Suzuki–Miyaura reaction a
Pd Cat.
B(OH)2
Br +
base, EtOH/H2O, 50
Entry
Base
Time (h)
Yield b (%)
1
K2CO3
Na2CO3
Cs2CO3
K3PO4
KOAc
KF
1.5
1.5
1.5
1.5
1.5
1.5
3
96
93
89
92
25
47
23
36
98
92
76
2
3
4
5
6
7
NEt3
8
DMAP
K2CO3
K2CO3
K2CO3
3
9 c
10 d
1
8
11 e
24
a
Reaction conditions: bromobenzene (1.0 mmol), phenylboronic acid (1.2 mmol), base (2.0
mmol), catalyst 4 (0.1 mol% Pd) in 6.0 mL of EtOH/H2O (1:1, v/v) at 50 under air.
b Isolated yield.
c Catalyst (0.5 mol% Pd) was used.
d Catalyst (0.01 mol% Pd) was used.
e Catalyst (0.005 mol% Pd) was used.
With the optimized reaction conditions in hand, several representative coupling reactions of a
variety of aryl halides with arylboronic acids were investigated in the presence of 0.1 mol% of
supported Pd catalyst 4 and 2 equiv of K2CO3 in aqueous EtOH (1:1, v/v) at 50 ꢀ under air, and
the results are summarized in Table 3. The coupling between aryl bromides and phenylboronic
acid, which contained electron-donating as well as electron-withdrawing groups, proceeded

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effectively to afford the corresponding products in good to excellent yields (Table 3, entries 1-12).
And a wide range of functional groups, such as nitryl, acyl, cyano, methoxy and aldehyde, could
be well tolerated in the reaction. Some substituted arylboronic acids were also tested, and they all
reacted smoothly with aryl bromides and generated the desired products in high yields (Table 3,
entries 13-19). Unfortunately, the catalytic system was less effective with the challenging substrate
such as aryl chloride, aryl tosylate, or aryl mesylate. Although the coupling of phenyl tosylate with
phenylboronic acid could generate a 21% yield of biphenyl, it might be caused by homocoupling
of the phenylboronic acid (Table 3, entries 20-23).
Table 3 Suzuki–Miyaura coupling reaction of aryl halide with arylboronic acid a
Pd Cat. (0.1 mol%)
X
(HO)2B
+
R2
R1
R2
Time (h) Product Yield b (%)
R1
K2CO3, EtOH/H2O, 50
Entry
Aryl halides
Arylboronic acids
Br
B(OH)2
1
2
3
1.5
1
3a
3b
3c
96
94
97
Br
Br
B(OH)2
B(OH)2
F3C
OHC
1.5
Br
B(OH)2
B(OH)2
4
5
1.5
1.5
3d
3e
95
OHC
O
97 (69)d
Br
Br
Br
B(OH)2
B(OH)2
B(OH)2
6
7
8
1
1
2
3f
3g
3h
98
94
O2N
NC
93 (56)d
Br
Br
B(OH)2
9
2.5
3i
92
MeO

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91 (50)d
86
Br
B(OH)2
B(OH)2
10
11
3
3j
MeO
Br
OMe
4.5
3k
Br
B(OH)2
B(OH)2
12
13
F
1.5
1.5
3l
90
92
Br
3h
O
B(OH)2
14
1.5
3m
97
Br
Br
B(OH)2
15
16
1.5
2
3j
91
87
MeO
MeO
Br
B(OH)2
B(OH)2
B(OH)2
B(OH)2
3n
O
17
18
19
1.5
2
3o
3p
3q
97
92
97
MeO
Cl
Br
Br
O
O
Cl
1.5
Br
Cl
20 c
12
3e
0 (15)
B(OH)2
21 c
22 c
24
24
3a
3f
21
OTs
B(OH)2
B(OH)2
OTs
O2N
O2N
<5 (19)
23 c
24
3f
<5 (17)
OMs
B(OH)2
a
Reaction conditions: aryl halide (1.0 mmol), arylboronic acid (1.2 mmol), K2CO3 (2.0 mmol),
catalyst 4 (0.1 mol% Pd) in 6.0 mL of EtOH/H2O (1:1, v/v) at 50 under air.
b Isolated yield.
c Catalyst (0.5 mol% Pd) was used (yield of biphenyl in parentheses).
d
The corresponding yields were given in parentheses when Clark’s catalyst (0.1 mol% Pd) was
used.
Interestingly, although the Clark’s catalyst with a shorter propyl chain possesses the similar active

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sites, while it was used for some above Suzuki reactions, the corresponding products were
obtained in only moderated yields (Table 3, entries 5, 8 and 10). We carried out an further effect of
the time on the reaction of p-methylbromobenzene with phenylboronic acid using 0.1 mol% Pd of
our catalyst 4 and Clark’s catalyst, respectively (Fig. 4). Obviously, the Clark’s catalyst was less
active than our designed catalyst 4. These results can be rationalized by our designed catalyst 4
possesses the active sites which are more accessible to the reactants due to a extended
hydrocarbon chain as compared to the Clark’s catalyst.
Fig. 4 effect of the time on Suzuki-Miyaura reaction
The recovery and reuse of a catalyst is highly preferable for a greener process. Thus, the
recyclability of this supported Pd catalyst 4 was investigated by using p-bromoacetophenone and
phenylboronic acid as model substrates. After the reaction, the catalyst 4 was separated by simple
filtration and washed. After drying, it could be reused in the next run directly without further
purification. It was found that the recovery can be successfully achieved in a test of five cycles
with a slight loss of its activity (Fig. 5). Darkening of the recovered catalyst in successive runs
took place under the reaction conditions and the morphology of the recovered catalyst was then
investigated by TEM (see Supporting Information). After the first cycle, Pd nanoparticles with a

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size of about 5 nm were formed and well distributed inside the regular meso-channels. However,
after the fifth cycle, few parts of the mesopores were collapsed in a longtime basic aqueous
medium and then some Pd nanoparticles aggregated outside the meso-channels, which might be a
main reason responsible for a slight deactivation of the catalyst after several cycles.
Furthermore, Pd leaching in the catalyst 4 was also determined. ICP analysis of the clear
filtrate showed that the Pd content was less than 0.2 ppm, which revealed that the immobilized Pd
catalyst 4 was very stable and could endure this coupling conditions. For comparison, we also
examined the reusability of a similar Pd catalyst supported on the pristine MCM-41 without
functionalized by imino-pyridine 2 (designated as Pd@MCM-41). In this case, the catalyst
Pd@MCM-41 was extensively deactivated after the first run and more Pd leaching was found in
the filtrates, which indicated that the imino-pyridine nature within the catalyst 4 played a crucial
role in anchoring active Pd pieces. In order to exclude that the catalyst 4 was only an initial source
for the homogeneous Pd, a new reaction was carried out in the clear filtrate at 50 ꢀ for 24 h,
whereas no desired product 3e was detected.
Fig. 5 Recycling experiment of supported Pd catalyst 4
3. Conclusions

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In summary, we have prepared a novel MCM-41 supported Pd imino-pyridine complex 4,
which was used as a heterogeneous catalyst for Suzuki-Miyaura coupling reactions in aqueous
medium under air. The catalyst was proved to be highly efficient in the synthesis of a diverse
range of biphenyls in excellent yields. Moreover, it offered many practical advantages, such as
oxygen insensitivity, thermal stability, and recyclability. The catalyst could be recovered by simple
filtration and reused for several runs without obvious loss of activity. It was worth noting that the
presence of the imino-pyridine 2 was necessary for the excellent recyclability of the catalyst and
the catalytic activity could be improved when the chain tether in the catalyst structure was
prolonged.
4. Experimental
4.1 General
Melting points were determined with a WRS-1B apparatus and were uncorrected. The IR
spectra were run on a Nicolete spectrometer (KBr). Thermogravimetric analysis was carried out in
1
nitrogen using a Shimadzu TGA-50 spectrometer. H NMR spectra were recorded on a Bruker
DRX500 (500MHz) and 13C NMRspectra on Bruker DRX500 (125 MHz) spectrometer.
Solid-state 13C CP/MAS NMR spectra were measured on a Bruker DRX-400 spectrometer with a
4.0 mm zirconia rotor spinning at 5 kHz. Mass spectra were obtained with an automated Fininigan
TSQ Advantage mass spectrometer. Elemental analysis was performed on an Elementar Vario EL
recorder. Palladium content of the catalyst was measured by inductively coupled plasma (ICP)
on L-PAD analyzer (Prodigy). Transmission electron microscopy (TEM) images were performed
with a JEM-2100 instrument. The mesoporous silica MCM-41 was prepared according to a

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literature procedure.19 All solvents used were strictly dried according to standard operations and
stored over 4A molecular sieves. All other chemicals (AR grade) were commercially available and
used without further purification.
4.2 Synthesis of imino-pyridine ligand (1): 4-[(Pyridine-2-ylmethylene)amino]phenol
Pyridine-2-carbaldehyde (5.35 g, 50.0 mmol) and p-aminophenol (5.46 g, 50.0 mmol) were
added into 25 mL of Methanol and the resulting mixture was stirred under reflux for 3 h. The
mixture was slowly cooled to room temperature and the pure solid product 1 (6.44 g, 32.5 mmol)
was obtained by filtration immediately (yield: 65%). Yellow crystals, Mp (ꢀ): 186-187; 1H NMR
(500 MHz, DMSO-d6): δ 9.64 (s, 1H), 8.63 (s, 1H), 8.67-8.58 (m, 1H), 8.50 (s, 1H), 8.09 (d, J =
8.0 Hz, 1H), 7.92-7.88 (m, 1H), 7.48-7.45 (m, 1H), 7.30-7.26 (m, 2H), 6.82-6.79 (m, 2H).
4.3
Synthesis
of
silane-functionalized
imino-pyridine
ligand
(2):
N-(pyridin-2-ylmethylene)-4-(3-(triethoxysilyl)propoxy)benzenamine
A round-bottom flask was charged with compound 1 (3.97 g, 20.0 mmol), NaH (0.72 g, 30.0
mmol) and dry DMF (30 mL) and the solution was stirred at room temperature for 2 h.
3-chloropropyltriethoxysilane (5.06 g, 21 mmol) was then added dropwise. The resulting mixture
was stirred at 85 ꢀunder nitrogen atmosphere for 24 h, and then cooled and filtered. Finally, the
solvent was removed by rotatory evaporation under reduced pressure, and the crude oil was
purified by flash chromatography (5:1 hexane-EtOAc) to give 5.80 g of product (yield: 72%).
FT-IR (KBr, cm-1): 3055.2, 2079.1, 2926.5, 2879.6, 1627.7, 1589.0, 1497.5, 1466.8, 1231.3,
1169.9, 1085.0, 963.6, 780.8, 543.9; 1H NMR (500 MHz, CDCl3): δ 8.69 (d, J = 4.4 Hz, 1H), 8.63
(s, 1H), 8.18 (d, J = 7.5 Hz, 1H), 7.78 (t, J = 7.5 Hz, 1H), 7.34-7.31 (m, 3H), 6.94 (d, J = 8.5 Hz,

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2H), 3.97 (t, J = 6.5 Hz, 2H), 3.84 (q, J = 7.0 Hz, 6H), 1.95-1.89 (m, 2H), 1.23 (t, J = 7.0 Hz, 11H),
0.78 (t, J = 8.0 Hz, 2H); 13C NMR (125 MHz, CDCl3): δ 158.51, 157.96, 154.88, 149.58, 143.45,
136.62, 124.76, 122.66, 121.62, 115.03, 70.09, 58.41, 22.77, 18.30, 6.47; ESI-MS: m/z 425.0
[M+Na]+.
4.4 Synthesis of MCM-41 supported imino-pyridine ligand (3)
The compound 2 (1.00 g, 2.48 mmol) and pyridine (0.5 mL, 6.15 mmol) were added
dropwise to a suspension of MCM-41 (2.00 g) in dry toluene (20 mL), under nitrogen atmosphere.
The resulting mixture was refluxed for 24 h. After cooling, the suspension was filtered and the
solid residue was washed with acetone and ether. The resulting solid was dried under vacuum at
room temperature, giving a pale yellow powder (2.35 g). FT-IR (KBr, cm-1): 3444.4, 2929.4,
2885.5, 1634.9, 1588.4, 1506.2, 1468.2, 1077.7, 795.4, 543.8.
4.5 Preparation of supported Pd catalyst (4)
To a round-bottomed flask, palladium acetate (67.2 mg, 0.30 mmol) and acetone (30 mL)
were added. The solution was stirred at room temperature for 30 min under nitrogen atmosphere,
and then 1.0 g of the above imino-pyridine ligand functionalized MCM-41 3 was added. The
mixture was stirred at room temperature for 24 h, and filtered. The solid was washed several times
with acetone, dried under vacuum for 4 h to afford the corresponding supported Pd catalyst 4 (1.02
g). The loading of Pd was 1.88 % as determined by ICP-AES. For comparison, palladium salts
were also immobilized on unmodified mesoporous MCM-41 via wet impregnation under the
above conditions. The resulting sample was designated as Pd@MCM-41.
4.6 Preparation of Clark’s catalyst17a
Anchoring the amino group onto MCM-41 was achieved by the stirring of 1.0 g of

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mesoporous silica with 1.8 g of 3-aminopropyltriethoxysilane in toluene at reflux temperature for
18 h under nitrogen. A white solid was obtained, filtered and washed with dichloromethane. This
solid was then reacted with an excess pyridine-2-carbaldehyde (1.0 g) in ethanol at room
temperature for 18 h. The resulting yellowish solid was then collected by filtration and was dried
overnight at 90 ꢀ. Lastly, a solution of palladium acetate (67.2 mg, 0.30 mol) in acetone was
added to the above obtained yellowish solid (1.0 g) and the mixture was stirred at room
temperature for 24 h, and filtered. The solid was washed several times with acetone, dried
overnight at 90 ꢀ to afford the corresponding Clark’s catalyst. The loading of Pd was 2.13 % as
determined by ICP-AES.
4.7 General procedure for Suzuki-Miyaura coupling reaction
Under air atmosphere, a round-bottom flask was charged with aryl halide (1.0 mmol),
arylboronic acid (1.2 mmol), Pd catalyst (5.6 mg, 0.1 mol%), K2CO3 (2.0 mmol) and EtOH/H2O
(1:1, v/v, 6.0 mL). The reaction mixture was stirred at 50 ꢀfor a certain time as monitored by GC.
After completion of the reaction, water (5 mL) and ether (10 mL) was added. The catalyst was
separated by filtration, washed with ether and water, and dried under vacuum for the next run. The
combined organic layers were dried over Na2SO4, filtered, concentrated, and the residue was
purified by flash chromatography on silica gel to afford the corresponding products.
4.8 Analytical data for the Suzuki-Miyaura coupling products
4.8.1. 1,1′-Biphenyl (3a). White solid, Mp (ꢀ): 70-71; 1H NMR (500 MHz, CDCl3): δ 7.61 (d, J =
7.5 Hz, 4H), 7.44 (t, J = 7.5 Hz, 4H), 7.35 (t, J = 7.5 Hz, 2H).
4.8.2. 4-(Trifluoromethyl)biphenyl (3b). White solid, Mp (ꢀ): 69-70; 1H NMR (500 MHz, CDCl3):
δ 7.69 (s, 4H), 7.60 (d, J = 7.5 Hz, 2H), 7.48 (t, J = 7.5 Hz, 2H), 7.41 (t, J = 7.5 Hz, 1H).

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1
4.8.3. 1,1′-Biphenyl-4-carbaldehyde (3c). White solid, Mp (ꢀ): 58-59; H NMR (500 MHz,
CDCl3): 10.09 (s, 1H), 7.98 (dd, J = 8.0, 1.5 Hz, 2H), 7.78 (d, J = 8.0 Hz, 2H), 7.68-7.66 (m, 2H),
7.53-7.49 (m, 2H), 7.46-7.43 (m, 1H).
1
4.8.4. 1,1′-Biphenyl-3-carbaldehyde (3d). White solid, Mp (ꢀ): 53-54; H NMR (500 MHz,
CDCl3): 10.11 (s, 1H), 8.13 (d, J = 1.5 Hz, 1H), 7.89 (dd, J = 7.5, 1.5 Hz, 2H), 7.66-7.62 (m, 3H),
7.52-7.49 (m, 2H), 7.43 (t, J = 7.5 Hz, 1H).
1
4.8.5. 1-(Biphenyl-4-yl)ethanone (3e). White solid, Mp (ꢀ): 120-121; H NMR (500 MHz,
CDCl3): δ 8.06 (d, J = 8.0 Hz, 2H), 7.71 (d, J = 8.0 Hz, 2H), 7.65 (d, J = 7.5 Hz, 2H), 7.50 (t, J =
7.5 Hz, 2H), 7.43 (t, J = 7.5 Hz, 1H), 2.67 (s, 3H).
1
4.8.6. 4-Nitrobiphenyl (3f). Pale yellow solid, Mp (ꢀ): 114-115; H NMR (500 MHz, CDCl3): δ
8.33 (d, J = 8.5 Hz, 2H), 7.77 (d, J = 8.5 Hz, 2H), 7.65 (d, J = 7.5 Hz, 2H), 7.53 (t, J = 7.5 Hz, 2H),
7.48 (t, J = 7.5 Hz, 1H).
4.8.7. 1,1′-Biphenyl-4-carbonitrile (3g). White solid, Mp (ꢀ): 85-86; 1H NMR (500 MHz, CDCl3):
δ 7.74-7.68 (m, 4H), 7.59 (d, J = 7.0 Hz, 2H), 7.50-7.43 (m, 3H).
4.8.8. 4-Methylbiphenyl (3h). White solid, Mp (ꢀ): 47-48; 1H NMR (500 MHz, CDCl3): δ 7.57 (d,
J = 7.5 Hz, 2H), 7.49 (d, J = 8.0 Hz, 2H), 7.42 (t, J = 7.5 Hz, 2H), 7.32 (t, J = 7.5 Hz, 1H), 7.24 (d,
J = 8.0 Hz, 2H), 2.39 (s, 3H).
1
4.8.9. 3-Methoxybiphenyl (3i). Colorless oil; H NMR (500 MHz, CDCl3): δ 7.63 (d, J = 7.0 Hz,
2H ), 7.47 (t, J = 7.5 Hz, 2H), 7.41-7.37 (m, 2H), 7.22 (d, J = 8.0 Hz, 1H), 7.17 (t, J = 7.0 Hz, 1H),
6.94 (dd, J = 8.0, 2.5 Hz, 1H), 3.89 (s, 3H).
1
4.8.10. 4-Methoxybiphenyl (3j). White solid, Mp (ꢀ): 87-88; H NMR (500 MHz, CDCl3): δ
7.59-7.55 (m, 4H), 7.44 (t, J = 7.5 Hz, 2H), 7.33 (t, J = 7.5 Hz, 1H), 7.01 (d, J = 8.5 Hz, 2H), 3.88

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(s, 3H).
4.8.11. 2-Methoxybiphenyl (3k). Colorless oil; 1H NMR (500 MHz, CDCl3): δ 7.59 (d, J = 8.0 Hz,
2H ), 7.47 (t, J = 7.5 Hz, 2H), 7.39-7.36 (m, 3H), 7.09 (t, J = 7.5 Hz, 1H), 7.04 (d, J = 8.5 Hz, 1H),
3.86 (s, 3H).
1
4.8.12. 4-Fluorobiphenyl (3l). White solid, Mp (ꢀ): 73-74; H NMR (500 MHz, CDCl3): δ
7.72-7.69 (m, 4H ), 7.59 (s, 2H), 7.49-7.43 (m, 3H).
1
4.8.13. 1-(4'-Methylbiphenyl-4-yl)ethanone (3m). White solid, Mp (ꢀ): 120-121; H NMR (500
MHz, CDCl3): δ 8.04 (d, J = 8.5 Hz, 2H ), 7.70 (d, J = 8.5 Hz, 2H), 7.56 (d, J = 8.0 Hz, 2H), 7.30
(d, J = 8.0 Hz, 2H), 2.66 (s, 3H), 2.43 (s, 3H).
1
4.8.14. 4-Methoxy-4'-methylbiphenyl (3n). White solid, Mp (ꢀ): 109-110; H NMR (500 MHz,
CDCl3) δ 7.53 (d, J = 8.5 Hz, 2H), 7.47 (d, J = 8.0 Hz, 2H), 7.25 (d, J = 8.0 Hz, 2H), 6.99 (d, J =
8.5 Hz, 2H), 3.87 (s, 3H), 2.41 (s, 3H).
1
4.8.15. 1-(4'-Methoxybiphenyl-4-yl)ethanone (3o). White solid, Mp (ꢀ): 154-155; H NMR (500
MHz, CDCl3) δ 8.01 (d, J = 8.5 Hz, 2H), 7.65 (d, J = 8.5 Hz, 2H), 7.60 (d, J = 8.5 Hz, 2H), 7.0 (d,
J = 8.5 Hz, 2H), 3.87 (s, 3H), 2.64 (s, 3H).
4.8.16. 4-Chlorobiphenyl (3p). White solid, Mp (ꢀ): 76-77; 1H NMR (500 MHz, CDCl3): δ 7.56
(d, J = 7.5 Hz, 2H ), 7.52 (d, J = 8.5 Hz, 2H), 7.46-7.40 (m, 4H), 7.36 (t, J = 7.5 Hz, 1H).
1
4.8.17. 1-(4'-Chlorobiphenyl-4-yl)ethanone (3q). White solid, Mp (ꢀ): 102-103; H NMR (500
MHz, CDCl3): δ 8.05 (d, J = 8.0 Hz, 2H ), 7.67 (d, J = 8.5 Hz, 2H), 7.58 (d, J = 8.0 Hz, 2H), 7.46
(d, J = 8.5 Hz, 2H), 2.66 (s, 3H).
Acknowledgements

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We are grateful for the financial support from the Natural Science Foundation of Jiangsu Province
of China (No.BK2010485), and the Science and Technology Development Fund of Nanjing
University of Science and Technology (No. XKF09066).
Supporting Information
Supporting information related to this article can be found online at…
References and notes
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