An efficient and recyclable heterogeneous palladium catalyst utilizing naturally abundant pearl shell waste

Article abstract of DOI:10.1039/c0gc00780c

An efficient and recyclable ligand-free heterogeneous catalyst has been prepared by the immobilization of palladium onto ground pearl shell powders (Pd/shell powders, Pd/SP). The catalytic activity and recyclability of the prepared Pd/SP along with the charcoal and calcium carbonate supported palladium (Pd/C and Pd/CaCO₃) catalysts have been evaluated using the reductive homocoupling of aromatic halides. Pd/SP not only has higher catalytic activity, but also exhibits much stronger stability than Pd/C and Pd/CaCO ₃. The remarkable Pd/SP stability has been attributed to the chelation of palladium species with the surface chitin and protein molecules of the supported pearl shell powders. The X-ray photoelectron spectroscopy (XPS) studies show that the reductive Pd⁰ species can be regenerated in situ from the oxidative Pd²⁺ species for the Pd/SP catalyzed reductive homocoupling of aromatic halides in ethanol/DMSO solution, suggesting that the heterogeneous and homogeneous palladium catalysis proceeds through a similar Pd⁰/Pd²⁺ cycle catalytic mechanism.

Full text of DOI:10.1039/c0gc00780c

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PAPER
An efficient and recyclable heterogeneous palladium catalyst utilizing
naturally abundant pearl shell waste
Minfeng Zeng, Yijun Du, Chenze Qi,* Shufeng Zuo, Xiudong Li, Linjun Shao and Xian-Man Zhang*
Received 5th November 2010, Accepted 25th November 2010
DOI: 10.1039/c0gc00780c
An efficient and recyclable ligand-free heterogeneous catalyst has been prepared by the
immobilization of palladium onto ground pearl shell powders (Pd/shell powders, Pd/SP). The
catalytic activity and recyclability of the prepared Pd/SP along with the charcoal and calcium
carbonate supported palladium (Pd/C and Pd/CaCO3) catalysts have been evaluated using the
reductive homocoupling of aromatic halides. Pd/SP not only has higher catalytic activity, but also
exhibits much stronger stability than Pd/C and Pd/CaCO3. The remarkable Pd/SP stability has
been attributed to the chelation of palladium species with the surface chitin and protein molecules
of the supported pearl shell powders. The X-ray photoelectron spectroscopy (XPS) studies show
that the reductive Pd0 species can be regenerated in situ from the oxidative Pd2+ species for the
Pd/SP catalyzed reductive homocoupling of aromatic halides in ethanol/DMSO solution,
suggesting that the heterogeneous and homogeneous palladium catalysis proceeds through a
similar Pd0/Pd2+ cycle catalytic mechanism.
alkaline deacetylation of chitin, has high affinity for transition
Introduction
metals due to plenty of amine, hydroxyl and carbonyl functional
Palladium has been demonstrated to be one of the most powerful
groups.5 Recently, chitosan has received much attention as an
and versatile catalysts in synthetic organic chemistry, but the
environmentally friendly solid support for the immobilization
majority of palladium catalysis is limited to homogeneous
of palladium catalysts.6–8 But the preparation of chitosan is
reaction systems.1 It is difficult to recycle the catalyst from a
homogeneous process, leading to the loss of the expensive and
complicated and time-consuming primarily due to its relatively
low content of chitin (<5% weight).9 Although millions of tons
toxic transition metals. Furthermore, the final products are fre-
of pearl shells are generated annually from the pearl and animal
quently contaminated with the residual transition metals, which
feedstock industries, most of the pearl shells end up in landfills
are usually difficult to remove, especially in the pharmaceutical
as environmentally toxic waste because of the slow degradation
industry where metal contaminations are closely monitored.2
of crustacean shells at ambient temperature. In an on-going
From both an economic and environmental point of view, it
effort to explore the potential applications for pearl shell waste,10
is crucial to develop an environmentally benign heterogeneous
we have demonstrated that the incorporation of the pearl shell
process.3 Catalyst reuse will not only improve the overall produc-
powders could significantly improve the mechanical properties
tivity and cost effectiveness of the chemical transformation, but
of the epoxy resin composites.10a The improvement of mechan-
will also minimize their environmental impact, and ultimately
ical performance has been attributed to the intermolecular
contribute to the sustainability of chemical process.4 Indeed,
interactions between the surface chitin and protein molecules of
relatively few homogeneous systems have been commercialized.4
the pearl shell powders with the surrounding epoxy resin matrix
Nevertheless, it is also critical to enhance the catalytic activities
molecules.10a Thus, we hypothesized that the pearl shell powders
of the heterogeneous systems due to the catalytic site limitation
should be an excellent solid matrix to support palladium catalyst
only at the interface, rather than all accessible catalytic sites in
the homogeneous systems.4
A great variety of solid matrices have been employed to
support transition metal catalysts.3 Chitosan, prepared by
since the surface chitin and protein molecules can strongly
chelate palladium species. To the best of our knowledge, pearl
shell powders have not yet been applied to immobilize palladium
catalysts.
The palladium catalyzed reductive homocoupling of aromatic
halides is much more convenient than the traditional copper-
mediated Ullmann reaction for the synthesis of symmetric
biaryls because the Ullmann reaction not only consumes
a stoichiometric amount of copper, but also generates a
Institute of Applied Chemistry and Department of Chemistry, University
of Shaoxing, Shaoxing, Zhejiang, 312000, P. R. China.
E-mail: qichenze@usx.edu.cn, xian-man.zhang@usx.edu.cn;
Fax: +86-575-8834-5682
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stoichiometric amount of copper halide waste.11 However,
the palladium catalyzed reductive homocoupling requires an
excess auxiliary reducing reagent to regenerate in situ the Pd0
active species. Otherwise, a stoichiometric amount of metallic
palladium is needed. Recently, we have demonstrated that
the palladium catalyzed reductive homocoupling of aromatic
halides can be readily performed in dimethyl sulfoxide (DMSO)
and alcohol solutions without the need for additional reducing
reagents.12 In the present paper, we will present the preparation
and characterization of the novel pearl shell powders supported
palladium catalyst (Pd/SP). The catalytic activity, stability and
recyclability of the heterogeneous Pd/SP catalyst have been
examined using the Ullmann-type reductive homocoupling of
aromatic halides.
Table 1 Solvent effects on the Pd/SP catalyzed reductive homocou-
pling of iodobenzenea
Yield (%)b
Added
Conv.
Entry ethanol/ml Time/h (%)
1
2
3
4
5
6
7
8
9
0
0
0
0
5
10
15
20
5
5
5
41
63
80
41
62
77
82
97
88
87
82
75
1
1.3
2.3
1.7
3
12
13
18
25
93
0.2 (4%)
0.5 (9%)
0.7 (12%)
1.0 (17%)
1.5 (23%)
100
100
100
100
100
5
5
a Reaction conditions: iodobenzene (1.0 mmol), Pd/SP catalyst (0.05
mmol), potassium acetate (7.5 mmol), in DMSO (5.0 ml) solution at
120 ◦C unless otherwise indicated. b Biphenyl and benzene yields, based
on the amount of iodobenzene, were determined from the GC-MS
measurements.
Results and discussion
Pearl shell powders with particle size of 150–200 mesh were
used to prepare the heterogeneous palladium catalyst (Pd/shell
powders, Pd/SP). Palladium deposition onto the pearl shell
powders was achieved by wetness impregnation with disodium
tetrachloropalladate (Na2PdCl4) aqueous solution.
Table 2 Comparison of the heterogeneous Pd/SP, Pd/CaCO3 and
Pd/C catalyzed reductive homocoupling of iodobenzenea
The initial reaction conditions for the Pd/SP catalyzed reduc-
tive homocoupling of iodobenzene were adapted from our pre-
vious studies of the homogeneous palladium catalysis: 1.0 mmol
iodobenzene, 0.05 mmol Pd/SP catalyst, 7.5 mmol potassium
acetate in 5.0 ml DMSO solution.12a Reaction progress was
monitored by thin layer chromatography (TLC) and/or gas
chromatography/mass spectroscopy (GC-MS) analysis, which
revealed the gradual decrease of the starting material, and
increase of the biphenyl (1) along with a small amount of
dehalogenation product (2) (Scheme 1; R H, X I).
Yield (%)c
Entry Catalysts
Palladium contentb
1
2
3
5% Pd/SP
5% Pd/CaCO3
5% Pd/C
5.6 0.3%
6.1 0.2%
6.3 0.3%
97
90
88
3
3
3
a Reaction conditions: iodobenzene (1.0 mmol), palladium catalyst (0.05
mmol), potassium acetate (7.5 mmol), in ethanol (0.2 ml)/DMSO (5.0
ml) solution at 120 ◦C for five hours. b Palladium weight percentage was
determined from SEM/EDX analysis. c Biphenyl and benzene yields,
based on the amount of iodobenzene, were determined from GC-MS
measurements.
when the reactions are performed in alcohol solvents.12b,c The
yielded aldehyde can be further oxidized into acid.12b,c Base has
been shown to be essential for the Pd/SP catalyzed reaction,
which is similar to the homogeneous catalysts.12 A series of
frequently used inorganic and organic bases have been screened
for the heterogeneous Pd/SP catalyzed reductive homocoupling
of iodobenzene. Caesium fluoride is the most efficient base
for the homogeneous Pd(dppf)Cl2 catalyzed homocoupling of
iodobenzene.12a,b Surprisingly, caesium fluoride is not the most
efficient base, but the relatively cheaper potassium acetate
is the most efficient base for the Pd/SP catalyzed reductive
homocoupling of iodobenzene.
The commercial charcoal supported palladium (Pd/C) cat-
alyst is one of the most frequently investigated heterogeneous
catalysts in the literature.1,3 Thus, Pd/C is an ideal candidate
for comparing the catalytic activity and recyclability of the
prepared Pd/SP catalyst. For comparison, calcium carbonate
supported palladium (Pd/CaCO3) catalyst has also been pre-
pared since the natural crustacean shells contain over 90%
weight of calcium carbonate.10a Table 2 presents the results for
the 5% Pd/SP, 5% Pd/C and 5% Pd/CaCO3 catalyzed reductive
homocoupling of iodobenzene. The palladium contents of these
heterogeneous catalysts were confirmed by the scanning electron
Scheme 1
Table 1 shows that the biphenyl yields (entries 1–4) are 41,
62, 77 and 82% as the reaction time increases from 5, 10, 15 to
20 h, respectively. Complete conversion of iodobenzene can be
obtained in ~5 h using the homogeneous Pd(dppf)Cl2 catalyst
under similar conditions,12a suggesting that the heterogeneous
Pd/SP catalyst has relatively lower catalytic activity than the
homogeneous Pd(dppf)Cl2 catalyst. Interestingly, the Pd/SP
catalyzed homocoupling can be significantly accelerated by
the addition of a small amount of ethanol (0.2 ml) (entry 5).
For example, an excellent biphenyl yield (97%) was obtained
with 5% Pd/SP catalyst loading in ethanol/DMSO (v/v: 2 : 50)
solution in 5 h. Similar acceleration has been observed for the
heterogeneous Pd/C catalysts.13 But the dehalogenation by-
product increased with higher ethanol concentration (entries
6–9), presumably due to the reaction of ethanol with the
monoarylpalladium intermediate.12 Also, the optimum Pd/SP
catalyst loading was found to be about 5% for the reductive
homocoupling of iodobenzene.
Recently, we have demonstrated that the palladium catalyzed
reductive homocoupling of aromatic halides is stoichiometri-
cally coupled with oxidation of alcohol into aldehyde/ketone
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microscopy/energy dispersive X-ray spectroscopy (SEM/EDX)
analysis. Clearly, Pd/SP has slightly higher catalytic activity
than Pd/C and Pd/CaCO3 for the reductive homocoupling of
iodobenzene.
The inherent advantage of the heterogeneous over homo-
geneous catalysis is the catalyst reuse and easier separation
from the reaction mixture.1,3 The homocoupling yields have
been determined to evaluate the relative catalytic activities of
the recycled Pd/SP, Pd/C and Pd/CaCO3 catalysts for five
consecutive runs and the results are summarized in Fig. 1
and 2. While the biphenyl yields progressively decrease, the
dehalogenation by-product increases with the recycled numbers
for the Pd/C and Pd/CaCO3 catalysts. For example, the
biphenyl yield of the fifth recovered Pd/C catalyst is only about
30% relative to the fresh Pd/C catalyst. The catalytic activity
reduction of the recovered Pd/C and Pd/CaCO3 catalysts could
be attributed to the palladium leaching from the supported
matrix surface as well as the morphological change of palladium
species.14 The morphological change such as crystallization of
the palladium active species may also be associated with the
progressive increase of the dehalogenation by-product (benzene)
as catalyzed by the recycled Pd/C and Pd/CaCO3 catalysts
(Fig. 2). In addition, the similar catalytic activities of the recycled
Pd/C and Pd/CaCO3 catalysts indicate that the adsorption
interactions should be comparable for palladium species with the
supported charcoal and calcium carbonate particles. In striking
contrast to the Pd/C and Pd/CaCO3 catalysts, the biphenyl
and benzene yields for the recycled Pd/SP catalyst remain
essentially unchanged for five cycles (Fig. 1 and 2), suggesting
that palladium leaching is not significant for the heterogeneous
Pd/SP catalyst.
Fig. 2 Dependence of the dehalogenation product (benzene) yields
with the recycled numbers for the palladium catalyzed reductive
homocoupling of iodobenzene in ethanol/DMSO solution.
species with the surface chitin and protein molecules of the
pearl shell particles. This conclusion is supported by the IR
spectroscopic results. Fig. 3 shows that the palladium deposition
onto the pearl shell powders results in significant shifts of
the characteristic IR absorption peaks, i.e. at 877.7 cm-1 by
18.9 cm-1, at 1424.2 cm-1 by 50.7 cm-1 and at 3436 cm-1 by
18.9 cm-1. In contrast, the palladium deposition onto calcium
carbonate has no observable peak shift on the characteristic IR
absorption peaks as shown in Fig. 4.
Fig. 1 Dependence of biphenyl yields with the recycled numbers for
the palladium catalyzed reductive homocoupling of iodobenzene in
ethanol/DMSO solution.
Fig. 3 FTIR spectra of pearl shell powders and 5% Pd/SP catalyst.
Transition metal leaching is a common problem for hetero-
geneous catalysts, but it can be minimized through surface
derivatization by the introduction of special ligand groups
to enhance the affinity with transition metals.3 However, the
ligand synthesis and solid surface modification are usually very
challenging.15 Thus, it is not surprising that relatively few low-
leaching and ligand-free heterogeneous palladium catalysts have
been reported in the literature.16 The remarkable stability of the
Pd/SP catalyst can be attributed to the chelation of palladium
Furthermore, the scanning electron microscopy/energy dis-
persive X-ray spectroscopy (SEM/EDX) analysis shows that
palladium is much more evenly dispersed onto pearl shell
powders (Fig. 5) than onto charcoal (Fig. 6) and onto calcium
carbonate particles (Fig. 7). The X-ray diffraction (XRD)
studies provide additional evidence that palladium dispersion
onto pearl shell powders is more uniform than dispersion
onto charcoal powders as shown in Fig. 8. There is a sharp
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Fig. 4 FTIR spectra of calcium carbonate and 5% Pd/CaCO3 catalyst.
Fig. 7 Scanning electron image of palladium dispersion for 5%
Pd/CaCO3 catalyst.
Fig. 5 Scanning electron image of palladium dispersion for 5% Pd/SP
catalyst.
Fig. 8 X-Ray diffraction (XRD) pictures: (A) shell powders, (B) pearl
shell powders supported palladium catalyst (Pd/SP) and (C) charcoal
supported palladium catalyst (Pd/C).
peaks are essentially identical for the pearl shell powders and the
palladium loaded pearl shell powders, suggesting that the size of
the palladium particles of Pd/SP should be well below the XRD
detection limit.
Finally, X-ray photoelectron spectroscopic (XPS) technique
has been employed to examine the palladium oxidation state
change during the Pd/SP catalyzed reductive homocoupling of
iodobenzene. The results of these studies are summarized in
Fig. 9. Fig. 9A shows that the precatalyst Pd2+/SP has the char-
acteristic palladium 3d5/2 electron binding energy at 337.9 eV,
which is identical to that of the divalent palladium of palladium
chloride (PdCl2) (Fig. 9D), suggesting that the valence state of
palladium is conserved during immobilization onto the surface
of the pearl shell powders. The reductive Pd0 active species could
be in situ regenerated in DMSO12a or an alcohol solution12b in
the presence of base at the elevated temperature. Fig. 9B and 9C
show the similar reduction of the oxidative Pd2+ species into the
Fig. 6 Scanning electron image of palladium dispersion for 5% Pd/C
catalyst.
characteristic diffraction peak of palladium at 40.03◦ for the
Pd/C catalyst (Fig. 8C). Fig. 8A and 8B show that the diffraction
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The Pd/SP catalyzed reductive homocoupling protocol of
iodobenzene is also applicable to a wide variety of aromatic
halides as evident in Table 3. The Pd/SP catalyzed reductive ho-
mocoupling reactions work well for the aromatic halides bearing
electron donating and electron withdrawing groups in the para-
or meta-position (entries 2–10). Excellent homocoupling yields
are also obtained for the heteroaryl halides (entries 13 and 14).
Relative lower homocoupling yields are obtained for 2-chloro-1-
iodobenzene (entry 11) and 2-methyl-1-iodobenzene (entry 12),
presumably due to the steric hindrance for the homocoupling
on the heterogeneous catalyst surface.
In summary, we have developed a novel low-leaching and
ligand-free heterogeneous palladium catalyst utilizing the natu-
rally abundant pearl shell powders. The prepared Pd/SP catalyst
has been shown to be highly active, selective and recyclable for
the reductive homocoupling of aromatic halides. The remarkable
stability of the heterogeneous Pd/SP catalyst has been attributed
to the chelation of palladium species with the surface chitin and
protein molecules of the pearl shell powders. The preparation of
the environmentally benign heterogeneous palladium catalyst
is simple and straightforward, and will have the potential for
production on a large industrial scale.
Fig. 9 X-Ray photoelectron spectra (XPS): (A) Precatalyst Pd2+/SP;
(B) Pd/SP catalyst after heating in ethanol/DMSO solution in the
presence of potassium acetate at 120 ◦C for three hours; (C) Pd/SP
catalyst isolated from the ethanol/DMSO solution of iodobenzene and
potassium acetate at 120 ◦C for 3.0 h; (D) Fresh divalent palladium
(Pd2+) species.12a
Experimental
General
Charcoal supported palladium (Pd/C) catalyst, aromatic sub-
strates, and solvents were all commercially available and used
without further purification. Gas chromatography/mass spec-
troscopy (GC-MS) analysis was carried out on a GC 6890/5975
MSD instrument with a temperature ramp from 140 ◦C to
Pd0 species during the Pd/SP catalyzed reductive homocoupling
of iodobenzene in ethanol/DMSO solution, suggesting that
the heterogeneous Pd/SP catalyzed homocoupling of aromatic
halides proceeds via a mechanism similar to that proposed for the
homogeneous palladium catalysis.12 The Pd0 species undergoes
oxidative insertion with aromatic halide substrates to form
monoarylpalladium (3) and diarylpalladium (4) intermediates.12
Elimination of the biaryl product from the diarylpalladium
intermediate 4 is accompanied with formation of the oxidative
Pd2+ species, which furnishes the catalytic redox cycle as shown
in Scheme 2.
◦
270 ◦C at 10 C min-1. Proton NMR spectra were recorded
in CDCl3 on an AVANCE III 400M Hz spectrometer. Proton
chemical shifts are reported in parts per million (ppm) relative
to tetramethylsilane (TMS) with the residual solvent peak as
the internal reference. Multiplicities are reported as: singlet (s),
doublet (d), and multiplet (m). Melting points were measured
on a Buchi 510 in an open capillary tube and were not
calibrated. Infrared (IR) spectra were recorded in the range
of 500–4000 cm-1 on a Nicolet Nexus Fourier Transformed
Infrared (FTIR) spectrometer (Nicolet Instrument Company,
Madison, WI, USA). X-Ray diffraction (XRD) measurements
were performed on an Xppert 2 MRD (Philips Company,
Washington DC, USA) with Cu-Ka as a radiation source,
operating at 40 kV and 30 mA.
Preparation of the shell powders and calcium carbonate
supported palladium (Pd/SP and Pd/CaCO3) catalysts
Crustacean pearl shells were first cleaned to remove debris and
then ground into powders with a particle size range from 150–
200 mesh, which were used to immobilize palladium catalysts. A
known concentration solution of disodium tetrachloropalladate
(Na2PdCl4) (50 ml) was slowly added into 50 gram of pearl shell
powders in 150 ml water. The resulting mixture was allowed to
stir at room temperature until the solution turned from brown
to colorless. The collected powders were then washed until free
of chloride anion, followed by reduction in a hydrogen gas flow
Scheme 2
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Table 3 Heterogeneous Pd/SP catalyzed reductive homocoupling of various aromatic halide substratesa
Yield (%)b
Entry
Aromatic halides
Time/h
1
2
3
4
5
6
7
8
C6H5I
5
3
3
6
3
3
6
6.5
6
18
13
30
6
97
97
89
97
98
84
99
93
97
80
77
55
98
88
3
3
3
1
0
13
0
0
0
12
0
p-MeOC6H4I
p-MeC6H4I
p-BrC6H4I
p-FC6H4I
p-MeCOC6H4I
m-ClC6H4I
m-FC6H4I
9
m-MeOC6H4I
p-CF3C6H4Br
o-ClC6H4I
10
11
12
13
14
o-MeC6H4I
19
0
0
2-IC5H4Nc
2-BrC5H4Nd
30
a Reaction conditions: aromatic halide (1.0 mmol), Pd/SP catalyst (0.05 mmol), potassium acetate (7.5 mmol), in ethanol (0.2 ml)/DMSO (5.0
ml) solution at 120 ◦C. b Biphenyl and benzene yields, based on the amount of aromatic halide, were determined from the GC-MS measurements.
c 2-Iodopyridine. d 2-Bromopyridine.
at 80 ◦C for one hour. Calcium carbonate supported palladium
(Pd/CaCO3) catalyst was prepared by the same procedure.
XPS measurement. Relative elemental ratios were determined on
an Al/Mg anode with a power of 250 W (14.0 kV). The pressure
of the analysis chamber was maintained at <1 ¥ 10-8 Torr. The
complete scan diagram of 0~12000 eV (currency energy 93.9
eV) was obtained by RBD147 data collecting fiche from US
RBD using Auger Scan 3.21 software. The final electron binding
energies were calibrated using C1s of 284.6 eV as the internal
reference and the electron binding energy peaks were secluded
using the XPS Peak 4.1 software.
General procedure for the reductive homocoupling of aromatic
halides
Aromatic halide (1.0 mmol), heterogeneous palladium catalyst
and base were added into a 20 ml round-bottom flask containing
ethanol/DMSO solution under an argon atmosphere. The
resulting mixture was allowed to stir at the elevated temperature.
When the reaction was complete, the mixture was quenched with
10 ml water, and then extracted with ethyl acetate three times
(3 ¥ 20 ml). The combined organic layer was washed with water
and saturated brine, and then dried with anhydrous Na2SO4.
Solvent was removed under a reduced pressure, and the reaction
products were purified by silica gel chromatography with a
mixture of n-hexane and ethyl acetate.
General procedure for scanning electron microscopy/energy
dispersive X-ray spectroscopy (SEM/EDX) analysis
The elemental analysis of the Pd/C, Pd/CaCO3 and Pd/SP
catalysts was determined with a HITACHI S-4800 scanning
electron microscopy equipped with HORIBA energy dispersive
X-ray (SEM/EDX) spectroscopy. The sample (ca. 5 mg) was
activated under vacuum. A typical setup consisted of a 20 kV
accelerating voltage, a 35 degree takeoff angle, and a working
distance of 15 mm. The duration of the EDX scans on each
individual samples was about 30 s.
General procedure for recycling and reuse of heterogeneous
palladium catalysts
The heterogeneous palladium catalyst was separated from the
reaction mixture by filtration. The recycled palladium catalyst
was washed with ethyl acetate, water and ethanol, and then
returned back to the reactor with 5 ml ethanol. The reaction
system was kept under a hydrogen flow for 20 min, followed by
removal of the solvent under a reduced pressure before the next
catalytic reaction.
Characterization data of the homocoupling products
4,4¢-Dimethoxybiphenyl17 m.p. 178–180 ◦C; 1H NMR: d 7.47 (q,
4 H, J = 6.0 Hz), 6.95 (q, 4 H, J = 6.1 Hz), 3.84 (s, 6 H); MS
(EI) = m/z (%): 182 (100) [M+], 167 (55), 152 (12), 89 (11), 76(3).
Biphenyl18 m.p. 70–71.5 ◦C; 1H NMR: d 7.60 (d, 4 H, J = 7.4
Hz), 7.44 (d, 4 H, J = 7.8 Hz), 7.35 (d, 2 H, J = 7.3); MS (EI) =
m/z (%): 154 (100) [M+], 76 (7).
Procedures for X-ray photoelectron spectroscopic (XPS)
measurements
A 1.5 inch silicon (100) slice with single polishing face was boiled
in sulfuric acid/hydrogen peroxide (v/v, 2/1) for 5 min after
rinsing with water, and then dipped in 10% hydrofluoric acid for
a minute. The silicon slice was further cleaned by sonication
in ethanol and water for 5 min, respectively. The palladium
catalyst samples were then applied on the polished surface for
4,4¢-Dimethylbiphenyl19 m.p. 122–123 ◦C; 1H NMR: d 7.66 (d,
4 H, J = 8.0 Hz), 7.41 (d, 4 H, J = 8.0 Hz), 2.56 (s, 6 H); MS
(EI): m/z (%) = 182 (100) [M+], 167 (55), 152 (12), 89 (11), 76(3).
4,4¢-Diacetylbiphenyl20 m.p. 178–180 ◦C; 1H NMR: d 8.06 (d,
2 H, J = 8.4 Hz), 7.90 (d, 2 H, J = 8.4 Hz), 7.72 (d, 2 H, J = 8.4
Hz), 7.27 (d, 2 H, J = 8.4 Hz), 2.66 (s, 3 H), 2.58 (s, 3 H); MS
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(EI): m/z(%) = 238 (43) [M+], 223(100), 224(16), 152(18), 104(7),
4 (a) D. J. Cole-Hamilton, Science, 2003, 299, 1702; (b) P. Barbaro
and F. Liguori, Chem. Rev., 2009, 109, 515; (c) S. Bhaduri and D.
Mukesh, Homogenous Catalysis: Mechanism and Industrial Applica-
tions, Wiley-Interscience, New York, 2000. pp 1–8.
5 T. Vincent and E. Guibal, Ind. Eng. Chem. Res., 2002, 41, 5158.
6 D. J. Macquarrie and J. J. E. Hardy, Ind. Eng. Chem. Res., 2005, 44,
8499.
7 N. V. Kramareva, A. Y. Stakheev, O. P. Tkachenko, K. V. Klementiev,
W. Grunert, E. D. Finashina and L. M. Kustov, J. Mol. Catal. A:
Chem., 2004, 209, 97.
8 E. Guibal, Prog. Polym. Sci., 2005, 30, 71.
9 W. J. Jung, G. H. Jo, J. H. Kuk, K. Y. Kim and R. D. Park, Appl.
Microbiol. Biotechnol., 2006, 71, 234.
10 (a) G. Ji, H. Zhu, X. Jiang, C. Qi and X.-M. Zhang, J. Appl. Polym.
Sci., 2009, 114, 3168; (b) G. Ji, H. Zhu, C. Qi and M. Zeng, Polym.
Eng. Sci., 2009, 49, 1383; (c) X. Sun, M. Zeng, Y. Wang, G. Ji, X.
Yao, Y. Shen, N. Chen, F. Yan, B. Wang and C. Qi, J. Appl. Polym.
Sci., 2008, 109, 3932; (d) X. Sun, M. Zeng, Y. Lu, X. Yao, Y. Wang,
H. Xiao, F. Yan and C. Qi, He Jishu/Nuclear Techniques, 2007, 30,
735.
43(22).
◦
1
4,4¢-Dibromobiphenyl20 m.p. 164–165 C; H NMR: d 7.60–
7.48 (m, 4 H), 7.40–7.35 (m, 4 H); MS (EI): m/z (%) = 312 (100)
[M+], 152 (75), 76 (25).
4,4¢-Difluorobiphenyl21 m.p. 87–88 ◦C; 1H NMR: d 7.48 (m, 4
H), 7.09 (t, 4 H, J = 8.6); MS (EI): m/z (%) = 190 (100) [M+],
170 (20).
2,2¢-Dichlorobiphenyl22 m.p. 58–59 ◦C; 1H NMR: d 7.01–
7.03(m, 1 H), 7.15–7.22 (m, 1 H), 7.27–7.29 (m, 1 H), 7.30–7.37
(m, 3 H), 7.39–7.42 (m, 1 H), 7.47–7.51 (m, 1 H); MS (EI): m/z
(%) = 222 (59) [M+], 152 (100), 187 (4◦3), 75(18).
3,3¢-Dichlorobiphenyl22 m.p. 28–29 C; 1H NMR: d 7.31–7.37
(m, 4 H), 7.40 (t, 1 H, J = 1.8 Hz), 7.42 (t, 1 H, J = 1.6 Hz), 7.52
(s, 2 H); MS (EI): m/z (%) = 222 (100) [M+], 152 (57), 93 (9),75
(14).
11 D. D. Hennings, T. Iwama and V. H. Rawal, Org. Lett., 1999, 1, 1205.
12 (a) C. Qi, X. Sun, C. Lu, J. Yang, Y. Du, H. Wu and X.-M. Zhang,
J. Organomet. Chem., 2009, 694, 2912; (b) M. Zeng, Y. Du, L. Shao,
C. Qi and X.-M. Zhang, J. Org. Chem., 2010, 75, 2556; (c) M. Zeng, L.
Shao, C. Qi and X.-M. Zhang, in Ferrocenes: Compounds, Properties
and Applications, ed. E. S. Phillips, Nova Science Publishers, Inc.,
Chapter 7, 2010.
3,3¢-Difluorobiphenyl23 m.p. 7–8 ◦C; 1H NMR: d 7.05 (tdd, 2
H, J = 8.0, 2.4 and 0.4 Hz), 7.24 (t, 1 H, J = 2.0 Hz), 7.27 (t, 1
H, J = 2.0 Hz), 7.32 (t, 1 H, J = 1.2 Hz), 7.34 (t, 1 H, J = 1.6
Hz), 7.36–7.42 (m, 2 H); MS (EI): m/z (%) = 190 (100) [M+], 189
(24), 170 (6), 94(5).
2,2¢-Dimethylbiphenyl24 m.p. 16–17 ◦C; 1H NMR: d 7.27–7.20
(m, 6 H), 7.11–7.09 (d, 2 H, J = 7.2 Hz), 2.05 (s, 6 H); MS (EI):
m/z (%) = 182 (70) [M+], 167 (100), 152◦(20), 89 (11).
3,3¢-Dimethoxybiphenyl25 m.p. 41–42 C; 1H NMR: d 3.86 (s,
6 H), 6.90 (dd, 2 H, J = 8.2, 2.6 Hz), 7.12 (d, 2 H, J = 1.6 Hz),
7.17 (d, 2 H, J = 7.6 Hz), 7.34 (d, 2 H, J = 8.0 Hz); MS (EI): m/z
(%) = 214 (100) [M+], 171 (16), 128 (10).
13 L. Shao, Y. Du, M. Zeng, X. Li, W. Shen, S. Zuo, Y. Lu, X.-M. Zhang
and C. Qi, Appl. Organometal. Chem., 2010, 24, 421.
14 (a) F. Zhao, M. Sjirai, Y. Ikushima and M. Arai, J. Mol. Catal. A:
Chem., 2002, 180, 211; (b) M. Dams and P. A. Jacobs, J. Catal.,
2002, 209, 225; (c) Z. Novak, A. Szabo, J. Repasi and A. Kotschy,
J. Org. Chem., 2003, 68, 3327; (d) T. N. Glasnov, S. Findenig and
C. O. Kappe, Chem.–Eur. J., 2009, 15, 1001; (e) B. M. Bhanage and
M. Arai, Catal. Rev. Sci. Eng., 2001, 43, 315.
15 (a) J. A. Gladysz, Chem. Rev., 2002, 102, 3215; (b) N. T. S. Phan,
M. V. D. Sluys and C. W. Jones, Adv. Synth. Catal., 2006, 348, 609.
16 (a) N. Hoshiya, N. Isomura, M. Shimoda, H. Yoshikawa, Y.
Yamashita, K. Iizuka, S. Tsukamoto, S. Shuto and M. Arisawa,
Chem. Catal. Chem., 2009, 1, 279; (b) C. M. Crudden, M. Sateesh
and R. Lewis, J. Am. Chem. Soc., 2005, 127, 10045; (c) J. D. Webb, S.
MacQuarrie, K. McEleney and C. M. Crudden, J. Catal., 2007, 252,
97; (d) J. Artner, H. Bautz, F. Fan, W. Habicht, O. Walter, M. Do¨ring
and U. Arnold, J. Catal., 2008, 255, 180.
17 J. Bergman, R. Carlsson and B. Sjoberg, Org. Synth., 1977, 57, 18.
18 (a) Kirk-Othmer, Encycl. Chem. Technol. 3rd Ed. 1978, 17, 782;
(b) A. C. Silva, A. L. F. Souza and O. A. C. Antunes, J. Organomet.
Chem., 2007, 692, 3104.
19 (a) M. Kuroboshi, Y. Waki and H. Tanaka, J. Org. Chem., 2003, 68,
3938; (b) L. F. Elsom, A. McKillop and E. C. Taylor, Org. Synth.,
1976, 55, 48.
◦
1
2,2¢-Bipyridinyl26 m.p. 71–72 C; H NMR: d 7.34 (dd, 2 H,
J = 7.2, 5.2 Hz), 7.85 (td, 2 H, J = 8.0 and 1.6 Hz), 8.73 (d, 2 H,
J = 8.0 Hz), 7.34 (d, 2 H, J = 4.4 Hz). MS (EI): m/z (%) = 156
(100) [M+], 128 (26), 78 (17), 51 (18).
2,2¢-Dimethoxybiphenyl18 m.p. 178–180 ◦C; 1H NMR: d 7.77
(d, 2 H, J = 7.6 Hz), 7.30 (td, 4 H, J = 7.2 and 0.8 Hz), 6.83 (d, 2
H, J = 8.0 Hz), 6.71 (t, 2 H, J = 7.2 Hz), 3.87 (s, 6 H); MS (EI):
m/z (%) = 214 (100) [M+],184(33),164(24),1◦29(19).
4,4¢-Trifluoromethylbiphenyl27 m.p. 82–83 C; 1H NMR: d 7.72
(q, 8 H, J = 16.0 Hz); MS (EI): m/z (%) = 190 (100) [M+], 172
(50), 85 (10).
20 Y. Miyake, M. Wu, M. J. Rahman, Y. Kuwatani and M. Iyoda, J. Org.
Chem., 2006, 71, 6110.
Acknowledgements
21 (a) G. Cahiez, C. Chaboche, F. Mahuteau-Betzer and M. Ahr, Org.
Lett., 2005, 7, 1943; (b) S. K. Taylor, S. G. Bennett, K. J. Heinz and
L. K. Lashley, J. Org. Chem., 1981, 46, 2194.
22 C. T. Chiou, D. W. Schmedding and M. Manes, Environ. Sci. Technol.,
2005, 39, 8840.
We greatly appreciate the financial support from the Natural
Science Foundation (Y-4080450) of Zhejiang Province, China
and University of Shaoxing.
23 K. Fukui, H. Kitano, T. Osaka, Y. Inamoto and S. Shioji, Nippon
Kagaku Zashi, 1958, 79, 1120.
24 Y. Yuan and Y. B. Bian, Appl. Organomet. Chem., 2008, 22, 15.
25 L.-R. Yang, J.-L. Zhang, M.-P. Song, S.-S. Zhang, N. Yu and Y.-J.
Wu, Huaxue Xuebao, 2003, 61, 959.
26 W. H. F. Sasse, Org. Synth., 1966, 46, 5.
27 T. D. Nelson and R. D. Crouch, Org. React. (Hoboken, NJ USA),
2004, 63, 265.
References
1 J. Tsuji, Palladium Reagents and Catalysts, Wiley, 2nd Ed., New York,
2004.
2 C. E. Garrett and K. Prasad, Adv. Synth. Catal., 2004, 346,
889.
3 L. Yin and J. Liebscher, Chem. Rev., 2007, 107, 133.
356 | Green Chem., 2011, 13, 350–356
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