An efficient and recyclable magnetic-nanoparticle-supported palladium catalyst for the suzuki coupling reactions of organoboronic acids with alkynyl bromides

Article abstract of DOI:10.1055/s-0030-1260138

A highly active, air- and moisture-stable and easily recoverable magnetic-nanoparticle-supported palladium catalyst has been developed for the Suzuki cross-coupling reaction of organoboron derivatives with alkynyl bromides. In the presence of palladium catalyst (0.5 mol%), organoboron derivatives including aromatic and aliphatic boronic acids, potassium aryltrifluoroborates, and sodium tetraphenylborate reacted smoothly with 1-bromo-2-substituted acetylenes to generate the corresponding cross-coupling products in good to excellent yields in ethanol. In addition, it is possible to recover and reuse the supported palladium catalyst at least 16 times without significant loss of its catalytic activity. Georg Thieme Verlag Stuttgart - New York.

Full text of DOI:10.1055/s-0030-1260138

PAPER
2975
An Efficient and Recyclable Magnetic-Nanoparticle-Supported Palladium
Catalyst for the Suzuki Coupling Reactions of Organoboronic Acids with
Alkynyl Bromides
M
agnetic-Nanopa
i
ticle-S
u
d
Pal
l
ladium
i
Catalyst in
C
Z
oupling Reactio
h
ns ang,a,b Pinhua Li,c Yong Ji,a Lei Zhang,c Lei Wang*b,c
a
Department of Chemistry, Anhui Agricultural University, Hefei, Anhui 230036, P. R. of China
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, P. R. of China
Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000, P. R. of China
Fax +86(561)3090518; E-mail: leiwang@chnu.edu.cn
b
c
Received 8 April 2011; revised 15 June 2011
In the past decades, significant progress in this area has
been achieved with a variety of homogeneous palladium
catalysts.2e,5 However, homogeneous catalysis suffers
from the problematic separation of the expensive catalyst.
Abstract: A highly active, air- and moisture-stable and easily re-
coverable magnetic-nanoparticle-supported palladium catalyst has
been developed for the Suzuki cross-coupling reaction of organobo-
ron derivatives with alkynyl bromides. In the presence of palladium
catalyst (0.5 mol%), organoboron derivatives including aromatic Furthermore, homogeneous catalysis might result in
and aliphatic boronic acids, potassium aryltrifluoroborates, and so-
heavy metal contamination of the desired isolated prod-
dium tetraphenylborate reacted smoothly with 1-bromo-2-substitut-
uct. These problems are of particular environmental and
ed acetylenes to generate the corresponding cross-coupling
economic concern in large-scale syntheses. Heteroge-
products in good to excellent yields in ethanol. In addition, it is pos-
neous catalysts, especially expensive and/or toxic heavy
sible to recover and reuse the supported palladium catalyst at least
metal complexes could be an attractive solution to this
problem.2c,6 There has been considerable interest in the
development of supported catalytic systems that can be ef-
ficiently recycled and reused whilst keeping the inherent
catalytic activity. Various inorganic and organic supports
have been explored, such as silica,7 ionic liquids,8 and
polymers.9
16 times without significant loss of its catalytic activity.
Key words: palladium catalyst, Suzuki coupling reaction, organo-
boronic acids, alkynyl bromides, magnetic nanoparticles
The palladium-catalyzed carbon–carbon cross-coupling
of organometallic nucleophiles with organoelectrophiles
is an important synthetic reaction in modern organic syn-
thesis.1 However, most organometallic compounds are
sensitive to air and moisture, or toxic, and often will not
tolerate functional groups, which may be important in
complex syntheses. Constituting one of the few organo-
metallic reagents that tolerate a wide range of functional
groups, boronic acids are conveniently available and gen-
erally environmentally benign. In addition, they are inert
to air and moisture, and resistant to heat.
Magnetic nanoparticles have been studied widely for var-
ious biological and medical applications,10 and most re-
cently, they have emerged as smart and promising
supports with great industrial potential for immobiliza-
tion. This is because magnetic-nanoparticle-supported
catalysts can be easily separated from the reaction medi-
um by an external permanent magnet, which achieves
simple separation of the catalysts without filtration.11
As one of the substrates for the Suzuki reactions, organo-
electrophiles, which contain Csp2–X bonds (such as aryl
and alkenyl halides), Csp2–OTf and Csp3–OTf (aryl and
alkyl triflates) bonds, and even Csp3–X bonds (alkyl ha-
lides) were employed to couple with organoboron deriva-
tives in the Suzuki reactions.12 In contrast, organic halides
possessing Csp–X bonds are rarely used as organoelectro-
philes due to the formation of a mixture of cross-coupling
and homo-coupling products.13
The Suzuki coupling reaction of organoboronic acids with
Csp2–X bonds has become a mainstay of modern synthetic
organic chemistry for the preparation of biaryl com-
pounds.2 It has also been applied to the synthesis of natu-
ral products, agrochemicals, pharmaceuticals, polymers,
and other materials.3 Since its invention, the development
of efficient catalytic systems for the Suzuki coupling reac-
tion has attracted much attention. Classic Suzuki coupling
reactions generally employ palladium catalysts along with
phosphine ligands in the presence of a base.2e,4 However,
the expensive palladium complexes tend to be difficult to
manipulate and recover.
In continuation of our efforts to develop economical and
eco-friendly synthetic pathways for organic transforma-
tions from the viewpoint of green chemistry, we wish to
report here the synthesis of a simple, highly active, air-
and moisture-stable and magnetically recoverable palladi-
um-catalyzed Suzuki cross-coupling reaction of organo-
boron compounds, such as aryl- and alkylboronic acids,
potassium aryltrifluoroborates and sodium tetraphenylbo-
rate with alkynyl bromides with Csp–Br bonds to generate
the corresponding cross-coupling products in good to ex-
SYNTHESIS 2011, No. 18, pp 2975–2983
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Advanced online publication: 27.07.2011
DOI: 10.1055/s-0030-1260138; Art ID: H38111SS
© Georg Thieme Verlag Stuttgart · New York

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PAPER
cellent yields in ethanol (Scheme 1). Moreover, easy cat- For optimization of the Suzuki coupling reaction condi-
alyst recovery and excellent recycling efficiency of the tions, the reaction of 4-methoxyphenylboronic acid (1a)
catalyst make it an ideal system for the reaction, and it is with 1-bromo-2-phenylacetylene (2a) was chosen as a
possible to recover and reuse the grafted catalysts at least model reaction for the exploration in the presence of the
16 times without significant loss of its catalytic activity.
magnetic-nanoparticle-supported palladium catalyst
Fe3O4@SiO2-Pd. The results are summarized in Table 1.
Initially, our investigation was focused on the effect of
solvent on the model reaction. As shown in Table 1,
among the solvents tested, ethanol was the most suitable
reaction media for the model reaction carried out in the
presence of Fe3O4@SiO2-Pd (0.5 mmol%) and Na3PO4
(2.0 equiv) at room temperature for 12 hours (Table 1).
Methanol, isopropanol, acetonitrile, N,N-dimethylform-
amide, 1,4-dioxane, tetrahydrofuran, dimethyl sulfoxide,
toluene, and hexane were inferior and generated the de-
sired cross-coupling product 3a in 90, 78, 66, 54, 62, 71,
58, 30, and 17% yield, respectively (Table 1, entries 2–
10). Unfortunately, no cross-coupling product was isolat-
ed when the reaction was carried out in water (Table 1, en-
try 11). For the model reaction using nanoparticle-
supported palladium catalyst derived from PdCl2,
Pd(dba)3, or Pd(OTFA)2 instead of Pd(OAc)2, the yields
of 3a obtained were comparable with that of the yield of
3a by using nanoparticle-supported palladium catalyst de-
rived from Pd(OAc)2 (Table 1, entries 12–14 vs 1). The
effects of other palladium sources, such as PdCl2,
Pd(OAc)2, Pd(PPh3)2Cl2, and Pd(PPh3)4 on the model re-
action were also examined under the present reaction con-
ditions and the results are also summarized in Table 1.
The coupling reaction could be catalyzed by PdCl2,
Pd(OAc)2, Pd(PPh3)2Cl2, or Pd(PPh3)4, but their catalytic
activity is inferior to that of Fe3O4@SiO2-Pd (Table 1, en-
tries 15–18 vs 1). The amount of Fe3O4@SiO2-Pd catalyst
was also screened and the experimental data indicated that
the reaction was complete when 0.5 mol% loading of pal-
ladium was used at room temperature for 12 hours.
The magnetic-nanoparticle-supported palladium catalyst
Fe3O4@SiO2-Pd was prepared according to the synthetic
route listed in Scheme 1. The silica-coated Fe3O4
[Fe3O4@SiO2] was prepared following the literature pro-
cedures.11b,c,14 Commercially available Fe3O4 nanoparti-
cles with average diameter of 10 nm after sonication, were
coated with a thin layer of silica using a sol-gel method to
generate silica-coated Fe3O4 [Fe3O4@SiO2]. TEM images
of the Fe3O4@SiO2 show the core-shell structure of the
particles, and the silica coating, which has a uniform
thickness of ca. 10 nm. Next, the phosphine ligand can be
anchored easily onto the surface of Fe3O4@SiO2 using 2-
(diphenylphosphino)ethyltriethoxysilane in anhydrous
toluene at 120 °C for 24 hours, with a loading of 0.18
mmol of phosphine per gram, which was quantified via
CHN microanalyses based on the carbon content determi-
nation. Subsequently, the supported palladium catalyst,
Fe3O4@SiO2-Pd was obtained by dissolving palladium(II)
acetate in tetrahydrofuran and treating it with the above
phosphine-functionalized Fe3O4@SiO2. The generated
Fe3O4@SiO2-Pd was found to have a loading of 0.049
mmol of palladium per gram determined via inductively
coupled plasma (ICP) analysis. XRD measurements of
Fe3O4@SiO2-Pd exhibit diffraction peaks corresponding
to the typical spinel maghemite structure and the diffrac-
tion peak of the layered amorphous silica was not obvious,
and no peaks characteristic for palladium(0) nanoparticles
were observed, which proves the excellent dispersion of
the palladium sites on the magnetic nanoparticles. The en-
ergy dispersive X-ray (EDX) analysis showed the pres-
ence of palladium with a loading of 0.056 mmol/g in
Fe3O4@SiO2-Pd (see Supporting Information).
Next, the effect of base on the model reaction was exam-
ined at room temperature by using 0.5 mol% of
(EtO)3SiCH2CH2PPh2
O
O
Si(OEt)4
PPh2
Fe3O4
SiO2
Fe3O4
SiO2
Fe3O4
Si
OEt
Pd(OAc)2
O
PPh2
2
Fe3O4
SiO2
Si
OEt
O
Pd(OAc)2
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd (0.5 mol%)
EtOH
R1B(OH)2
R2
R1
R2
2 = aromatic
Br
+
R1 = aromatic
aliphatic
R
aliphatic
Scheme 1 Preparation of magnetic-nanoparticle-supported palladium catalyst Fe3O4@SiO2-Pd and its application
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Magnetic-Nanoparticle-Supported Palladium Catalyst in Coupling Reactions
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Table 1 Effect of Solvents and Palladium Catalysts on the Suzuki Reactiona
Pd cat.
Br
MeO
MeO
B(OH)2
+
Na3PO4
solvent
1a
2a
3a
Entry
1
Catalyst
Solvent
EtOH
MeOH
i-PrOH
MeCN
DMF
Yield (%)b
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pd
Fe3O4@SiO2-Pdc
Fe3O4@SiO2-Pdd
Fe3O4@SiO2-Pde
PdCl2
96
90
78
66
54
62
71
58
30
17
0
2
3
4
5
6
1,4-dioxane
THF
7
8
DMSO
toluene
hexane
H2O
9
10
11
12
13
14
15
16
17
18
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
95
93
97
28
36
40
51
Pd(OAc)2
Pd(PPh3)2Cl2
Pd(PPh3)4
a Reaction conditions: 4-methoxyphenylboronic acid (1 mmol), 1-bromo-2-phenylacetylene (1 mmol), Pd catalyst (0.005 mmol), and Na3PO4
(2 mmol) in solvent (2 mL) at r.t. for 12 h.
b Isolated yields.
c Fe3O4@SiO2-Pd derived from PdCl2.
d Fe3O4@SiO2-Pd derived from Pd(dba)3.
e Fe3O4@SiO2-Pd derived from Pd(OTFA)2.
Fe3O4@SiO2-Pd as catalyst in ethanol. Sodium phosphate phenylacetylene (2a) was used as one of the model sub-
was found to be the most effective base. Other bases, such strate and a variety of organoboronic acids were examined
as sodium carbonate, potassium phosphate, potassium for the coupling reactions (Table 3, entries 1–13). As can
carbonate, cesium carbonate, triethylamine, and sodium be seen from Table 3, the reactivity of both aromatic and
acetate were substantially less effective (Table 2, entries alkenylboronic acids was observed, in which aromatic bo-
1–7); and tert-butoxide and sodium hydroxide were no ronic acids were much more reactive than the alkenyl one
longer the effective bases in the model reaction due to (Table 3, entries 1–12 vs 13). Aromatic boronic acids with
their strong basicity. It should be noted that the cross- electron-donating groups (such as Me, MeO, and t-Bu) or
coupling of the model substrates could not occur in the ab- electron-withdrawing groups (such as F, Cl, Br, and I) on
sence of a suitable base.
the aromatic rings, as well as 1-naphthaleneboronic acid,
reacted with 1-bromo-2-phenylacetylene (2a) completely
and generated the corresponding cross-coupling products
in excellent yields. In most cases, almost quantitative
yields were obtained (Table 3, entries 1–12). It is impor-
tant to note that the location of the substituents on the
aromatic rings in arylboronic acids had little effect on the
reaction, or even on the ortho-position (Table 3, entries 9–
With the optimized reaction conditions [0.50 mol% load-
ing of Fe3O4@SiO2-Pd, Na3PO4 as base, EtOH as solvent,
r.t.], we examined the scope of the supported-palladium
catalyzed Suzuki coupling reactions of arylboronic acids
and alkynyl bromides on a series of different substrates.
The results are listed in Table 3. At the beginning of the
search for the organoboron substrate scope, 1-bromo-2-
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Table 2 Effect of Bases on the Suzuki Reactiona
Fe3O4@SiO2-Pd
(0.5 mol%)
MeO
B(OH)2
Br
MeO
+
EtOH
base ?
1a
3a
2a
Entry
Base
Yield (%)b
1
2
3
4
5
6
7
Na3PO4
Na2CO3
K3PO4
K2CO3
Cs2CO3
Et3N
96
93
90
87
81
62
37
NaOAc
a Reaction conditions: 4-methoxyphenylboronic acid (1 mmol), 1-bromo-2-phenylacetylene (1 mmol), Fe3O4@SiO2-Pd catalyst (102 mg, con-
taining 0.005 mmol of Pd), and base (2 mmol) in EtOH (2 mL) at r.t. for 12 h.
b Isolated yields.
11). It is noteworthy that the reactivity of Csp–Br in 1-bro- lize in a number of organic transformations.15 When the
mo-2-phenylacetylene is more than that of Csp2–Br in 4- reaction of potassium aryltrifluoroborates with 2a was
bromophenylboronic acid, and that of Csp2–I in 4-io- performed under the present reaction conditions, as ex-
dophenylboronic acid (Table 3, entries 7 and 8). Fortu- pected, excellent yield of the desired product was ob-
nately,
the
cross-coupling
reaction
involving tained (Table 3, entry 14). In addition, as a stable and
alkenylboronic acid also gave the desired product in 77% commercially available borate source, sodium
isolated yield (Table 3, entry 13). As an alternative to or- tetraphenylborate16 was also coupled with 2a completely
ganoboronic acids and esters, organotrifluoroborate salts to generate the corresponding product in 93% yield
have emerged as a new class of air-stable boron deriva- (Table 3, entry 15).
tives, facile to prepare, easy to handle, and feasible to uti-
Table 3 Fe3O4@SiO2-Pd-Catalyzed Suzuki Coupling Reactions of Organoboronic Acids with Alkynyl Bromidesa
Fe3O4@SiO2-Pd (0.5 mmol%)
R1B(OH)2
R2
Br
R2
R1
+
Na3PO4, EtOH
Entry
1
Arylboronic acid
Alkynyl bromide
Product
Yield (%)b
96
B(OH)2
Br
2
3
97
96
B(OH)2
Br
Br
MeO
MeO
B(OH)2
B(OH)2
4
93
Br
5
6
7
89
91
90
Br
Br
Br
F
F
B(OH)2
Cl
Br
B(OH)2
B(OH)2
Cl
Br
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Magnetic-Nanoparticle-Supported Palladium Catalyst in Coupling Reactions
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Table 3 Fe3O4@SiO2-Pd-Catalyzed Suzuki Coupling Reactions of Organoboronic Acids with Alkynyl Bromidesa (continued)
Fe3O4@SiO2-Pd (0.5 mmol%)
R1B(OH)2
R2
Br
R2
R1
+
Na3PO4, EtOH
Entry
8
Arylboronic acid
Alkynyl bromide
Product
Yield (%)b
90
I
B(OH)2
Br
I
B(OH)2
9
10
11
94
93
90
Br
Br
Br
MeO
MeO
B(OH)2
Cl
Cl
B(OH)2
Cl
Cl
B(OH)2
12
96
Br
Cl
B(OH)2
13
14
15
16
17
77
94
93
95
98
Br
Br
Br
Cl
MeO
BF4K
MeO
BNa
4
MeO
MeO
B(OH)2
B(OH)2
MeO
MeO
Br
MeO
Br
Br
OMe
18
19
20
21
93
93
92
73
MeO
MeO
MeO
MeO
MeO
B(OH)2
B(OH)2
B(OH)2
B(OH)2
MeO
MeO
Br
Br
N
Br
Br
N
Br
MeO
a Reaction conditions: alkynyl bromide (1 mmol), organoboron compound (1 mmol), Fe3O4@SiO2-Pd catalyst (102 mg, containing 0.005 mmol
of Pd), and Na3PO4 (2 mmol) in EtOH (2 mL) at r.t. for 12 h.
b Isolated yields.
Next, a series of 1-bromo-2-substituted acetylenes were conditions and good to excellent yields of desired cross-
surveyed for the scope of Csp–Br substrates and the results coupling products were obtained (Table 3, entries 16–21).
in Table 3 indicate that 2-aryl- and 2-alkylethynyl bro- It is evident that the reactivity of 1-bromo-2-arylacety-
mides, including 1-bromo-2-(4-methylphenyl)acetylene, lenes was more than that of 1-bromo-2-alkylacetylenes
1-bromo-2-(4-methoxyphenyl)acetylene,
1-bromo-2- (Table 3, entries 3, and 16–20 vs 21). For 1-bromo-2-aryl-
(tert-butylphenyl)acetylene, 1-bromo-2-(4-bromophe- acetylenes, the presence of electron-donating groups
nyl)acetylene, 1-bromo-2-(m-pyridyl)acetylene, and 1- (MeO, Me, and t-Bu), electron-withdrawing groups (Br),
bromo-2-hexylacetylene displayed high reactivity to 4- and their location on the benzene rings also had little ef-
methoxyphenylboronic acid under the present reaction fect on the reactions (Table 3, entries 16–19).
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Table 4 Reuse of Fe3O4@SiO2-Pd Catalyst for the Model Suzuki Reactiona
reused
Fe3O4@SiO2-Pd
MeO
MeO
B(OH)2
Br
+
Cycle
Yield (%)b
Cycle
9
Yield (%)b
1
2
3
4
5
6
7
8
96
96
96
95
96
95
96
95
94
95
95
94
93
93
92
92
10
11
12
13
14
15
16
a Reaction conditions: 4-methoxyphenylboronic acid (1 mmol), 1-bromo-2-phenylacetylene (1 mmol), reused Fe3O4@SiO2-Pd catalyst (102
mg, containing 0.005 mmol of Pd), and Na3PO4 (2 mmol) in EtOH (2 mL) at r.t. for 12 h.
b Isolated yields.
The magnetic-nanoparticle-supported palladium catalyst tives with ethynyl bromides by using a recyclable magnet-
Fe3O4@SiO2-Pd was tested for recoverability and reus- ic-nanoparticle-supported palladium catalyst. The
ability. After the reaction, Fe3O4@SiO2-Pd was recovered supported catalyst Fe3O4@SiO2-Pd could be reused for 16
by magnetic separation, washed with ethanol (2 mL), wa- consecutive cycles without significant loss of catalytic ac-
ter (2 mL), ethanol (2 mL), and diethyl ether (2 mL), re- tivity through a simple magnetic separation. Further in-
spectively, dried in air and reused for the next reaction. vestigation on the application of magnetic-nanoparticle-
For the model reactions of Suzuki coupling, results in supported catalysts in organic synthesis is still underway
Table 4 indicate that Fe3O4@SiO2-Pd catalyst can be re- in our laboratory.
covered and reused for 16 consecutive trials without sig-
nificant loss of its activity. In addition, palladium leaching
in the supported catalyst was also determined. ICP analy-
sis of the ethanol solution (3 mL) of the Suzuki reaction
showed that the palladium content was less than 0.20
ppm. It was found that more than 99.64 wt% of palladium
was recovered after the Suzuki reaction. To investigate
the heterogeneity of the catalyst systems, filtration test
was performed. However, no additional amount of the de-
sired product was obtained for the model reaction by add-
ing substrates to the filtrate obtained from the separation
of the immobilized palladium catalyst after the reaction.
The heterogeneous character of the catalytically active
species is confirmed in this reaction.
All 1H and 13C NMR spectra were recorded on a Bruker Avance FT-
NMR spectrometer (400 MHz or 100 MHz, respectively). Chemical
shifts are given as d values with reference to TMS as internal stan-
dard. The C, H, and N analyses were performed with a Vario El III
elementar apparatus. The Pd content was determined by a Jarrell-
Ash 1100 ICP analysis. Transmission electron micrograph (TEM)
images were obtained on a Jeol-2010 transmission electron micro-
scope. X-ray diffraction (XRD) measurements were carried out us-
ing a Bruker D8 Advance X-ray powder diffractmeter. IR spectra
were recorded on a Nicolet 6700 FT-IR spectrophotometer using
KBr pellets. Products were purified by flash chromatography on
200–300 mesh silica gel. All the reactions were carried out under an
air atmosphere, and the chemicals were purchased from commercial
suppliers and were used without purification prior to use.
In summary, an efficient and recyclable magnetic-nano-
particle-supported palladium catalyst for the Suzuki cou-
pling reactions of organoboron derivatives with alkynyl
bromides to form 1,2-disubstituted acetylenes have been
developed. In the presence of Fe3O4@SiO2-Pd (0.5
mol%), organoboron compounds, including aryl and alk-
enyl boronic acids, potassium aryltrifluoroborates, and
sodium tetraphenylborate reacted smoothly with 1-bro-
mo-2-substituted acetylenes to generate the correspond-
ing cross-coupling products in good to excellent yields.
This methodology provides an efficient, alternative and
environmentally friendly process for the synthesis of sym-
metric and nonsymmetric 1,2-disubstituted acetylenes
through Suzuki coupling reaction of organoboron deriva-
Silica-Coated Magnetic Nanoparticles Fe3O4@SiO2
Fe3O4 (0.50 g, with an average diameter of 20 nm, purchased from
Aldrich) was diluted with deionized H2O (7 mL) and propan-2-ol
(30 mL), and the mixture was sonicated for approximately 30 min
(the average diameter of Fe3O4 was about 10 nm according to the
TEM image). To this well dispersed magnetic nanoparticle solution,
NH3·H2O (2 mL) followed (EtO)4Si (2 g) slowly added and stirred
for further 4 h at r.t. The material was washed repeatedly with H2O
until the solution was neutral, then the solid material was magneti-
cally separated, washed with EtOH (3 mL) and Et2O (3 mL), respec-
tively, and dried under vacuum.
IR (KBr): 3396 (O–H), 1080 cm–1 (Si–O).
Phosphine-Functionalized Fe3O4@SiO2
2-(Diphenylphosphino)ethyltriethoxysilane (0.38 g) dissolved in
anhyd toluene (5 mL) was added to a suspension of Fe3O4@SiO2
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Magnetic-Nanoparticle-Supported Palladium Catalyst in Coupling Reactions
2981
(0.50 g) in anhyd toluene (30 mL). The mixture was then shaken at
100 °C under a N2 atmosphere for 24 h. The solid material,
Fe3O4@SiO2-P, was magnetically separated, washed repeatedly
with toluene (3 × 2 mL) and CH2Cl2 (3 × 2 mL) to remove unan-
chored species, and dried under vacuum. The loading of phosphine
in phosphine-functionalized Fe3O4@SiO2 was quantified via CHN
microanalyses and found to be 0.18 mmol·g–1 based on the carbon
content determination.
(4-Chlorophenyl)phenylacetylene20
1H NMR (400 MHz, CDCl3): d = 7.54–7.51 (m, 2 H), 7.50–7.44 (m,
2 H), 7.37–7.30 (m, 5 H).
13C NMR (100 MHz, CDCl3): d = 134.23, 132.79, 131.58, 128.67,
128.47, 128.38, 122.90, 121.76, 90.29, 88.22.
(4-Bromophenyl)phenylacetylene20
1H NMR (400 MHz, CDCl3): d = 7.53–7.50 (m, 2 H), 7.48–7.45 (m,
5 H), 7.39–7.36 (m, 2 H), 7.35–7.31 (m, 3 H).
IR (KBr): 3396 (O–H), 2923, 2862 (C–H), 1517, 1469 (C=Carom),
1080 cm–1 (Si–O).
13C NMR (100 MHz, CDCl3): d = 132.99, 131.58, 131.56, 128.47,
128.37, 122.89, 122.44, 122.22, 90.49, 88.29.
Fe3O4@SiO2-Pd
To a sealable reaction tube, Pd(OAc)2 (11.2 mg, 0.05 mmol) and
THF (5 mL) were added. The solution was shaking at r.t. under N2
atmosphere for 10 min, and then 1 g of the above phosphine-func-
tionalized magnetic nanoparticles Fe3O4@SiO2-P was added. The
mixture was shaken at r.t. for 4 h, then the solid catalyst was mag-
netically separated, the solid washed thoroughly with THF (4 × 2.5
mL), and dried under vacuum at 50 °C for 3 h. The Fe3O4@SiO2-Pd
catalyst was obtained with a loading of Pd 0.049 mmol·g–1 deter-
mined via inductively-coupled plasma (ICP) analysis.
(4-Iodophenyl)phenylacetylene21
1H NMR (400 MHz, CDCl3): d = 7.67 (d, J = 8.2 Hz, 2 H), 7.52–
7.50 (m, 2 H), 7.35–7.32 (m, 3 H), 7.23 (d, J = 8.4 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 137.48, 133.05, 131.57, 128.48,
128.36, 122.87, 122.76, 94.09, 90.77, 88.43.
(3-Methoxyphenyl)phenylacetylene17
1H NMR (400 MHz, CDCl3): d = 7.55–7.54 (m, 1 H), 7.53–7.52 (m,
1 H), 7.37–7.34 (m, 4 H), 7.14–7.12 (m, 1 H), 7.07–7.06 (m, 1 H),
6.91–6.88 (m, 1 H), 3.83 (s, 3 H).
IR (KBr): 3396 (O–H), 2978, 2895 (C–H), 1649, 1520 (C=Carom),
1080 cm–1 (Si–O).
13C NMR (100 MHz, CDCl3): d = 159.34, 132.49, 131.62, 129.39,
128.33, 124.25, 124.17, 123.17, 116.32, 114.94, 89.28, 89.17,
55.29.
Catalytic Suzuki Reactions; General Procedure
A mixture of alkynyl bromide (1 mmol), organoboron compound (1
mmol), Na3PO4 (2 mmol), Fe3O4@SiO2-Pd catalyst (102 mg, con-
taining 0.005 mmol of Pd), and EtOH (2 mL) was stirred at r.t. for
4 h. The reaction solution was vacuum-filtered and washed with
EtOH (3 mL) and Et2O (3 mL), concentrated, and the residue was
purified by flash chromatography on silica gel (eluent: PE–EtOAc,
9:1) to obtain the desired product (Table 3).
Phenyl-o-tolyacetylene18
1H NMR (400 MHz, CDCl3): d = 7.53–7.48 (m, 3 H), 7.34–7.29 (m,
3 H), 7.21–7.20 (m, 2 H), 7.16–7.13 (m, 1 H), 2.50 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 140.11, 132.44, 131.79, 131.46,
129.42, 128.30, 128.11, 125.54, 123.51, 122.98, 93.33, 88.33,
20.69.
Diphenylacetylene17
1H NMR (400 MHz, CDCl3): d = 7.54–7.52 (m, 4 H), 7.33–7.31 (m,
(2,4-Dichlorophenyl)phenylacetylene17
1H NMR (400 MHz, CDCl3): d = 7.59–7.56 (m, 2 H), 7.48 (d,
J = 8.4 Hz, 1 H), 7.46 (d, J = 2.0 Hz, 1 H), 7.39–7.36 (m, 3 H), 7.23
(dd, J = 2.0, 8.4 Hz, 1 H).
6 H).
13C NMR (100 MHz, CDCl3): d = 131.58, 128.31, 128.22, 123.24,
89.36.
13C NMR (100 MHz, CDCl3): d = 136.63, 134.46, 133.71, 131.70,
129.28, 128.82, 128.39, 126.95, 122.57, 121.83, 95.44, 85.20.
Phenyl-p-tolyacetylene17
1H NMR (400 MHz, CDCl3): d = 7.53–7.51 (m, 2 H), 7.42 (d,
J = 8.0 Hz, 2 H), 7.34–7.32 (m, 3 H), 7.14 (d, J = 8.0 Hz, 2 H), 2.35
(s, 3 H).
1-(Phenylethynyl)naphthalene18
1H NMR (400 MHz, CDCl3): d = 8.35 (d, J = 8.4 Hz, 1 H), 7.73 (t,
J = 9.2 Hz, 2 H), 7.66 (d, J = 7.2 Hz, 1 H), 7.56–7.54 (m, 2 H), 7.49
(t, J = 8.0 Hz, 1 H), 7.42 (t, J = 7.2 Hz, 1 H), 7.34 (t, J = 7.2 Hz, 1
H), 7.31–7.25 (m, 3 H).
13C NMR (100 MHz, CDCl3): d = 138.35, 131.52, 131.47, 129.09,
128.28, 128.04, 123.45, 120.16, 89.54, 88.70, 21.48.
(4-Methoxyphenyl)phenylacetylene17
13C NMR (100 MHz, CDCl3): d = 133.22, 133.16, 131.63, 130.33,
128.73, 128.40, 128.35, 128.28, 126.74, 126.39, 126.18, 125.25,
123.35, 120.84, 94.29, 87.50.
1H NMR (400 MHz, CDCl3): d = 7.54–7.52 (m, 2 H), 7.37–7.32 (m,
3 H), 7.25–7.23 (m, 1 H), 7.14–7.11 (m, 1 H), 7.06 (t, J = 1.2 Hz, 1
H), 6.95–6.90 (m, 1 H), 3.82 (s, 3 H).
7-Chloro-1-phenylhept-3-en-1-yne22
13C NMR (100 MHz, CDCl3): d = 159.32, 131.61, 129.39, 128.33,
124.16, 123.16, 116.30, 114.93, 89.28, 89.17, 55.27.
1H NMR (400 MHz, CDCl3): d = 7.45–7.41 (m, 2 H), 7.33–7.30 (m,
3 H), 6.24–6.16 (m, 1 H), 5.77 (d, J = 16.4 Hz, 1 H), 3.57 (t, J = 6.8
Hz, 2 H), 2.34 (q, J = 3.6, 10.8 Hz, 2 H), 1.95–1.88 (m, 2 H).
(4-tert-Butylphenyl)phenylacetylene18
1H NMR (400 MHz, CDCl3): d = 7.54–7.51 (m, 2 H), 7.47 (d,
J = 8.0 Hz, 2 H), 7.37–7.30 (m, 5 H), 1.32 (s, 9 H).
13C NMR (100 MHz, CDCl3): d = 142.54, 131.41, 128.27, 128.03,
123.32, 111.07, 88.46, 87.80, 44.10, 31.42, 30.17.
13C NMR (100 MHz, CDCl3): d = 151.50, 131.56, 131.32, 128.28,
4-Methyl-4¢-methoxydiphenylacetylene23
128.04, 125.33, 123.51, 120.23, 89.52, 88.71, 34.77, 31.17.
1H NMR (400 MHz, CDCl3): d = 7.45 (d, J = 9.2 Hz, 2 H), 7.40 (d,
J = 8.0 Hz, 2 H), 7.14 (d, J = 8.0 Hz, 2 H), 6.87 (d, J = 8.8 Hz, 2
H), 3.82 (s, 3 H), 2.36 (s, 3 H).
(4-Fluorophenyl)phenylacetylene19
1H NMR (400 MHz, CDCl3): d = 7.53–7.48 (m, 4 H), 7.35–7.32 (m,
3 H), 7.05–7.00 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 159.46, 138.00, 132.95, 131.32,
129.06, 120.48, 115.58, 113.95, 88.63, 88.17, 55.27, 21.47.
13C NMR (100 MHz, CDCl3): d = 162.45 (d, J = 247.9 Hz), 133.44
(d, J = 8.3 Hz), 132.47, 131.52, 128.32, 123.05, 119.31 (d, J = 3.6
Hz), 115.60 (d, J = 21.9 Hz), 89.02, 88.28.
Synthesis 2011, No. 18, 2975–2983 © Thieme Stuttgart · New York

2982
X. Zhang et al.
PAPER
Bis(4-methoxyphenyl)acetylene17
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1H NMR (400 MHz, CDCl3): d = 7.44 (d, J = 8.8 Hz, 4 H), 6.85 (d,
J = 8.8 Hz, 4 H), 3.78 (s, 6 H).
13C NMR (100 MHz, CDCl3): d = 159.31, 132.80, 115.63, 113.89,
87.91, 55.18.
1-tert-Butyl-4-[(4-methoxyphenyl)ethynyl]benzene24
1H NMR (400 MHz, CDCl3): d = 7.47–7.43 (m, 4 H), 7.34 (d,
J = 8.4 Hz, 2 H), 6.86 (d, J = 8.8 Hz, 2 H), 3.79 (s, 3 H), 1.31 (s, 9
H).
13C NMR (100 MHz, CDCl3): d = 159.45, 151.12, 132.96, 131.14,
125.27, 120.54, 115.61, 113.93, 88.66, 88.15, 55.22, 34.71, 31.15.
1-Bromo-4-[(4-methoxyphenyl)ethynyl]benzene25
1H NMR (400 MHz, CDCl3): d = 7.47–7.45 (m, 4 H), 7.36 (d,
J = 8.4 Hz, 2 H), 6.88 (d, J = 8.4 Hz, 2 H), 3.83 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 159.77, 133.05, 132.83, 131.54,
122.56, 122.03, 114.96, 114.03, 90.53, 87.03, 55.29.
3-[(4-Methoxyphenyl)ethynyl]pyridine23
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1H NMR (400 MHz, CDCl3): d = 8.75 (s, 1 H), 8.51 (dd, J = 1.6, 4.8
Hz, 1 H), 7.77–7.74 (m, 1 H), 7.47 (d, J = 8.4 Hz, 2 H) 7.25–7.21
(m, 1 H), 6.87 (d, J = 8.8 Hz, 2 H), 3.80 (s, 3 H).
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13C NMR (100 MHz, CDCl3): d = 159.88, 151.95, 148.06, 138.04,
133.04, 122.84, 120.65, 114.42, 113.96, 92.65, 84.61, 55.13.
1-(4-Methoxylphenyl)oct-1-yne17
1H NMR (400 MHz, CDCl3): d = 7.32 (d, J = 8.8 Hz, 2 H), 6.81 (d,
J = 8.8 Hz, 2 H), 3.80 (s, 3 H), 2.38 (t, J = 7.2 Hz, 2 H), 1.61–1.55
(m, 2 H), 1.48–1.41 (m, 2 H), 1.34–1.29 (m, 4 H), 0.90 (t, J = 6.8
Hz, 3 H).
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88.80, 80.20, 55.23, 31.38, 28.84, 28.61, 22.56, 19.41, 14.05.
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Recycling of the Supported Palladium Catalyst
In Suzuki coupling reactions, the possibility of recycling the recov-
ered catalyst was investigated using 1-bromo-2-phenylacetylene
and 4-methoxyphenylboronic acid as substrates. After each round,
the supported catalyst was magnetic separated, and washed
thoroughly with Et2O (3 × 2 mL), then dried, and used directly for
the next run.
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Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.
Acknowledgment
We gratefully acknowledge financial support from the National Na-
tural Science Foundation of China (No. 20972057).
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Synthesis 2011, No. 18, 2975–2983 © Thieme Stuttgart · New York