Magnetic nanoparticles-supported palladium: A highly efficient and reusable catalyst for the Suzuki, Sonogashira, and heck reactions

Article abstract of DOI:10.1002/adsc.201100725

A highly efficient, air- and moisture-stable and easily recoverable magnetic nanoparticle-supported palladium catalyst has been developed for the Suzuki, Sonogashira and Heck reactions. A wide range of substrates was coupled successfully under aerobic conditions. In particular, the performance of the magnetic separation of the catalyst was very efficient, and it is possible to recover and reuse it at least eight times without significant loss of its catalytic activity. Copyright

Full text of DOI:10.1002/adsc.201100725

FULL PAPERS
DOI: 10.1002/adsc.201100725
Magnetic Nanoparticles-Supported Palladium: A Highly Efficient
and Reusable Catalyst for the Suzuki, Sonogashira, and Heck
Reactions
a,b
a,c,
a
b,
Pinhua Li, Lei Wang, * Lei Zhang, and Guan-Wu Wang *
a
Department of Chemistry, Huaibei Normal University, Huaibei, Anhui 235000, Peopleꢀs Republic of China
Fax : (+86)-561-3090-518; phone: (+86)-561-3802-069; e-mail: leiwang@chnu.edu.cn
Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, Peopleꢀs Republic of
b
China
E-mail: gwang@ustc.edu.cn
c
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai 200032, Peopleꢀs Republic of China
Received: September 17, 2011; Revised: January 17, 2012; Published online: April 26, 2012
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201100725.
Abstract: A highly efficient, air- and moisture-stable cient, and it is possible to recover and reuse it at
and easily recoverable magnetic nanoparticle-sup- least eight times without significant loss of its catalyt-
ported palladium catalyst has been developed for the ic activity.
Suzuki, Sonogashira and Heck reactions. A wide
range of substrates was coupled successfully under Keywords: Heck reaction; magnetic nanoparticles-
aerobic conditions. In particular, the performance of supported palladium; reusable catalyst; Sonogashira
the magnetic separation of the catalyst was very effi- reaction; Suzuki coupling
Introduction
complexes could be an attractive solution to these
problems. There has been considerable interest in
[
6]
Transition metal-catalyzed cross-coupling reactions the development of supported catalytic systems that
have contributed greatly to the facile and efficient can be efficiently recycled and reused whilst keeping
construction of carbon-carbon and carbon-heteroatom the inherent catalytic activity. Various inorganic and
[1]
bonds, and they have emerged as powerful tools for organic supports have been explored, such as mesopo-
[
2]
[7]
[8]
[9]
advanced organic synthesis in both academic and in- rous silica, ionic liquids and polymers. It is pleas-
[
3]
dustrial laboratories. It is well known that the palla- ing to find that the covalent grafting of such supports
dium-catalyzed Suzuki coupling, Sonogashira reac- with homogeneous catalysts often provides good cata-
tions and Heck reactions are all very important and lytic activity together with the possible recovery of
powerful strategies for the formation of carbon- the catalyst system by a simple process.
carbon bonds, and the 2010 Nobel Prize in chemistry
Magnetic nanoparticles have been studied widely
[10]
was awarded to three scientists, Heck, Negishi and for various biological and medical applications, and
Suzuki for their work on palladium-catalyzed cross- most recently, they have emerged as smart and prom-
[
4]
couplings in organic synthesis. In the past decades, ising supports with great industrial potential for im-
significant progress in this area has been achieved mobilization because the magnetic nanoparticles-sup-
[
5]
with a variety of homogeneous palladium catalysts.
ported catalysts can be easily separated from the reac-
However, homogeneous catalysis suffers from the tion medium by application of an external permanent
problematic separation of the expensive catalyst. Fur- magnet, which achieves simple separation of the cata-
[
11]
thermore, homogeneous catalysis might result in lysts without filtration.
During recent years, mag-
heavy metal contamination of the desired isolated netic nanoparticles-supported palladium catalysts
product. These problems are of particular environ- have been developed for the carbon-carbon bond for-
mental and economic concern in large-scale syntheses. mation reactions. In 2005, Gao and his co-workers
Heterogenization of the existing homogeneous cata- have prepared super-paramagnetic nanoparticles-sup-
lysts, especially expensive and/or toxic heavy metal ported NHC-Pd complexes, which were efficient cata-
Adv. Synth. Catal. 2012, 354, 1307 – 1318
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Pinhua Li et al.
FULL PAPERS
Scheme 1. Preparation of the magnetic nanoparticle-supported palladium catalyst and its applications in Suzuki, Sonogashira
and Heck reactions.
lysts for Suzuki, Heck, and Sonogashira cross-cou- classic carbon-carbon bond formation reactions. In
[12]
pling reactions. Subsequently, Zhu et al. have also particular, easy catalyst recovery and excellent recy-
developed a magnetic nanoparticles-supported ultra cling efficiency of the catalyst make it an ideal system
small palladium catalyst for Suzuki couplings and for these reactions under mild reaction conditions. We
Heck reactions, but merely moderate to good yields demonstrated that it is possible to recover and reuse
[
13]
of the desired products were obtained. In 2008, Xia the grafted catalyst at least eight times without signifi-
and his colleagues have developed a magnetically-sep- cant loss of its catalytic activity.
arable palladium catalyst for carbonylative Sonoga-
shira reactions in the synthesis of a,b-alkynyl ke-
[14]
tones. It is worth noting that Manorama et al. have Results and Discussion
developed a magnetically separable palladium cata-
lyst, which was highly active in Suzuki and Heck cou- The magnetic nanoparticles-supported palladium cat-
pling reactions with a range of aryl halides, moreover, alyst was synthesized according to the procedure sum-
the catalyst was equally active towards the chloro de- marized in Scheme 1. The silica-coated Fe O4
3
[
15]
rivatives.
Most recently, Thiel and his co-workers (SiO @Fe O ) was prepared according to the litera-
2 3 4
[11c,16,18]
have reported the synthesis of a magnetically recover- ture method:
commercially available Fe O4
3
able palladium(II)-phosphine catalyst for the Suzuki nanoparticles, with an average diameter of 10 nm
reactions, however, the preparation of the supported after sonication, were coated with a thin layer of
[
16]
catalyst was not convenient. More importantly, all silica using a sol-gel process to give silica-coated
the above-mentioned supported catalysts could be Fe O . TEM images of the SiO @Fe O showing the
3
4
2
3
4
easily separated from the reaction mixture by simple structure of the particles and the silica coating, which
magnetic attraction, and no significant loss of the cat- has a thickness of about 10 nm, are presented
alytic activity was observed after several consecutive in Figure 1. The phosphine can be anchored easily
reaction cycles. It is thus desirable to develop more onto the surface of the SiO @Fe O
by
2-(diphenylphosphino)ethyltriethoxysilane
2
3
4
efficient and simple magnetic nanoparticles-supported using
[
19]
palladium catalysts for the carbon-carbon bond for-
mation reactions.
A
H
U
G
R
N
U
G
A
H
U
G
R
N
N
(CH ) Si
A
H
U
G
E
N
N
(OEt) ]
under reflux in toluene for
2
2
2
3
24 h, with a loading of 0.18 mmol of phosphine per
In continuation of our efforts to develop economi- gram, which was quantified via CHN microanalysis
cal and eco-friendly synthetic pathways for organic on the basis of the carbon content determination. The
transformations from the viewpoint of green chemis- supported Pd catalyst (Figure 1) was obtained by
[17]
try,
here we wish to report the synthesis of simply dissolving Pd ACHNUTGERTNNUNG( OAc) in THF and treating it
2
a simple, highly efficient, air- and moisture-stable and with the above phosphine-functionalized SiO @Fe O ,
2
3
4
magnetically recoverable palladium-phosphine cata- with a loading of 0.049 mmol of palladium per gram
lyst for the Suzuki, Sonogashira and Heck reactions determined via inductively coupled plasma atomic
under aerobic conditions (Scheme 1). The catalyst emission spectrometry (ICP-AES). XRD measure-
shows a high catalytic activity in the above-mentioned ments of the supported catalyst are shown in Figure 2
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Adv. Synth. Catal. 2012, 354, 1307 – 1318

Magnetic Nanoparticles-Supported Palladium: A Highly Efficient and Reusable Catalyst
Figure 1. TEM images: (a) Fe O nanoparticles; (b) SiO @Fe O ; (c) SiO @Fe O –Pd catalyst; (d) recycled SiO @Fe O –Pd
3
4
2
3
4
2
3
4
2
3
4
catalyst.
and exhibit diffraction peaks corresponding to the fraction peak of the layered amorphous silica was not
typical spinel maghemite structure whereas the dif- obvious, and no peaks characteristic for palladium(0)
nanoparticles were observed, which proves the excel-
lent dispersion of the palladium sites on the magnetic
nanoparticles. The structure of supported palladium
catalyst was also verified by X-ray photoelectron
spectroscopy (XPS) determination. The electron bind-
ing energy analysis shown in Figure 3 indicates that
the oxidation state of palladium in freshly prepared
catalyst was Pd(II), which coordinated to two phos-
[
11d,16]
phorus atoms.
However, the state of palladium in
the used catalyst was mainly Pd(0), which could be
coordinated to four P-ligands.
First, the Suzuki coupling reaction was investigated
in the presence of the magnetic nanoparticle-support-
ed catalyst. Initial experiments with 4-bromoanisole
and phenylboronic acid were performed to optimize
the reaction conditions (base, solvent, and reaction
temperature, see Table 1 in the Supporting Informa-
tion for details). For the base, K PO gave better con-
3
4
versions than other bases, such as Na PO , K CO ,
3
4
2
3
Figure 2. XRD of the supported Pd catalyst.
Na CO , Cs CO , KOH, KF, NaOAc, Et N and DBU.
2
3
2
3
3
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Pinhua Li et al.
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generate the corresponding di-coupled products in
90% yields (Table 1, entry 15).
Moreover, the less reactive and less expensive aryl
chlorides also showed moderate reactivity in the pres-
ence of the supported palladium catalyst
SiO @Fe O –Pd: 4-cyanochlorobenzene and 4-nitro-
2
3
4
cholorobenzene reacted with phenylboronic acid to
generate the corresponding cross-coupling products in
moderate yields, but the reaction of 4-choloroanisole
with phenylboronic acid gave a poor result (Table 1,
entries 16–18). On the other hand, arylboronic acids
bearing electron-withdrawing and electron-donating
groups on the aryl rings, also coupled efficiently with
4-bromoanisole, 2-bromoanisole and bromobenzene,
and the excellent yields of the corresponding products
were obtained (Table 1, entries 19–24).
It is important to note that the supported palladi-
um-catalyzed Suzuki cross-coupling could tolerate
ortho-substituted aryl halides, as well as arylboronic
acid (Table 1, entries 2, 20 and 22–24). The reactions
of 2-bromoanisole with phenylboronic acid, 2-chloro-
phenylboronic acid with 4-bromoanisole, 2-methoxy-
Figure 3. XPS of the supported Pd catalyst
On the other hand, for the solvent, methanol is the phenylboronic acid with 4-bromoanisole, 2,4-dime-
first choice among a series of other solvents, such as thoxyphenylboronic acid with bromobenzene, and 2-
ethanol, i-PrOH, CH CN, DMF, DMA, DMSO, THF, methoxyphenylboronic acid with 2-bromoanisole,
3
dioxane, NMP, DCE, toluene, benzene, hexane, H O were carried out under the present reaction condi-
2
and MeOH/H O (1/1, v/v), and for the temperature, tions, and the desired products were obtained in ex-
2
6
08C is the best choice. The coupling reaction could cellent yields (Table 1, entries 2, 20 and 22–24).
be catalyzed by PdCl , Pd(OAc) , Pd(PPh ) Cl , or Next, we examined the Sonogashira coupling reac-
(PPh ) , but, their catalytic activities are inferior to tion of various aryl iodides and bromides with termi-
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
2
2
3
2
2
Pd
ACHTUNGTRENNUNG
3
4
that of Fe O @SiO –Pd. The reactions were generally nal alkynes in the presence of the supported catalyst
3
4
2
complete within 1–2 h at 608C. It was worthy of note SiO @Fe O –Pd (Table 2). Gratifyingly, we were able
2
3
4
that the reactions could also be completed in 12 h at to perform the efficient copper-free Sonogashira cou-
room tempreture. We have also screened the amount pling reactions of aryl iodides and activated aryl bro-
of supported palladium catalyst, and a 0.50 mol% mides under the optimized reaction conditions
loading of palladium in SiO @Fe O -Pd was found to (1.0 mol% loading of palladium, K CO , DMF, 1008C,
2
3
4
2
3
be optimal.
6 h, see Table 2 in the Supporting Information for de-
With the optimized reaction conditions (0.50 mol% tails), and most of the coupling reactions proceeded
loading of palladium, K PO , MeOH, 608C, 1.5 h), we completely and generated the corresponding products
3
4
examined the scope of the supported palladium-cata- in good to excellent yields (Table 2, entries 1–8, 10–
lyzed Suzuki coupling reactions on a series of differ- 12, and 14–19), while with an ortho-substituted aryl
ent substrates (Table 1). A wide array of electronically iodide, a relatively lower yield was isolated under the
diverse aryl bromides, and chlorides in the reaction present reaction conditions (Table 2, entry 2 vs. 4).
with phenylboronic acid was examined. As can be For the Sonogashira cross-coupling of a neutral aryl
seen from Table 1, aryl bromides bearing electron- bromide with terminal alkyne, for example, the cou-
withdrawing and electron-donating groups, as well as pling of bromobenzene and 1-bromonaphthalene with
1-bromonaphthalene, coupled efficiently with phenyl- phenylacetylene, generated the corresponding prod-
boronic acid, and generated the corresponding prod- ucts in 71 and 79% yields under the optimized condi-
ucts in excellent yields at 608C within 1.5 h (Table 1, tions respectively, which is inferior to the reactions of
entries 1–11). And also, 2-bromopyridine, 3-bromo- aryl iodides and activated aryl bromides with phenyla-
pyridine and 3-bromoquinoline were also able to un- cetylene (Table 2, entries 9 and 13 vs. 1–8 and 10–12).
dergo the coupling reactions with phenylboronic acid
However, this catalytic system was no longer effec-
smoothly and generate the desired cross-coupling tive for the couplings of aryl chlorides with terminal
products in excellent yields under the present reaction alkynes. No desired Sonogashira coupling product
conditions (Table 1, entries 12–14). Notably, 1,4-dibro- was obtained for the reactions of aryl chlorides with
mobenzene (1.0 equiv.) could also undergo the cou- phenylacetylene, and the starting materials were re-
pling reaction with arylboronic acid (2.4 equiv.) to covered unchanged under the present reaction condi-
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Magnetic Nanoparticles-Supported Palladium: A Highly Efficient and Reusable Catalyst
[a]
Table 1. Suzuki coupling reactions of aryl halides with arylboronic acids.
[b]
Entry
1
Arylboronic acid
Aryl halide
Product 3
Yield [%]
3a
99
2
3
3b
3c
99
99
4
5
6
7
8
9
3d
3e
3f
3g
3h
3i
99
99
99
98
99
98
99
1
1
0
1
3j
3k
97
1
1
2
3
3l
92
99
3m
14
3n
95
[
[
[
[
c]
1
1
1
1
1
5
6
7
8
9
3o
3f
3e
3a
3p
90
52
41
26
99
d]
d]
d]
2
2
2
0
1
2
3q
3r
3s
94
99
98
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Pinhua Li et al.
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Table 1. (Continued)
[b]
Entry
Arylboronic acid
Aryl halide
Product 3
Yield [%]
2
3
4
3t
97
2
3u
91
[
a]
Reaction conditions: aryl halide (0.50 mmol), arylboronic acid (0.60 mmol), SiO @Fe O –Pd catalyst (50 mg, containing
2
3
4
Pd 0.0025 mmol), K PO (1.0 mmol) in MeOH (2.0 mL) at 608C for 1.5 h.
Isolated yields.
3
4
[
[
b]
c]
1,4-Dibromobenzene (0.25 mmol), 4-methoxyphenylboronic acid (0.60 mmol), SiO @Fe O –Pd catalyst (50 mg, containing
2 3 4
Pd 0.0025 mmol) in MeOH (2.0 mL) at 608C for 6 h.
Aryl chloride (0.50 mmol), arylboronic acid (0.60 mmol), SiO @Fe O –Pd catalyst (100 mg, containing Pd 0.005 mmol) in
[
d]
2
3
4
DMF (2.0 mL) at 1108C for 10 h.
tions. To the terminal alkynes, regardless of their elec- More than 99% of the catalyst could simply be recov-
tronic characters, both aromatic alkynes and aliphatic ered by fixing a magnet near to the reaction vessel.
alkynes could be coupled smoothly with iodobenzene, For the model reactions of Suzuki coupling, Heck re-
as well as 4-iodoanisole to produce the desired prod- action and Sonogashira reaction, the supported palla-
ucts in good to excellent yields, and the reactions of dium catalyst SiO @Fe O –Pd could be recycled and
2
3
4
aromatic alkynes with 4-iodoanisole gave the superior reused for 8 consecutive trials without loss of its cata-
yields of the products to that of aliphatic alkynes with lytic activity (Table 4). Moreover, palladium leaching
4-iodoanisole (Table 2, entries 14–16 vs. 18 and 19).
in SiO @Fe O –Pd catalyst was determined and ICP
2 3 4
Encouraged by the above satisfactory results of analyses of the methanol solution (3.0 mL) of
Suzuki and Sonogashira reactions, the synthetic po- a Suzuki reaction, the DMF solutions (3.0 mL) of
tential of the supported palladium catalyst, Heck and Sonogashira cross-coupling reactions indi-
SiO @Fe O –Pd was then evaluated for the Heck re- cated that the Pd contents were less than 0.20 ppm in
2
3
4
action. The Heck reactions of a variety of aryl iodides the above solutions, respectively. It is indicated that
and activated aryl bromides with vinyl substrates more than 99.64 wt% of Pd was recovered after the
were performed in the presence of SiO @Fe O –Pd Suzuki reaction, and more than 99.79 wt% of Pd was
2
3
4
(
1.0 mol%) in DMF at 1008C, see Table 3 in the Sup- recovered after the Heck or Sonogashira cross-cou-
porting Information for details). The coupling reac- pling reaction. Meanwhile, iron leaching in
tions proceeded smoothly and generated the corre- SiO @Fe O –Pd catalyst was also determined and
2
3
4
sponding products in good to excellent yields analysis of the reaction solution (3.0 mL) of Suzuki,
Table 3, entries 1–21). Meanwhile, the reaction of Heck or Sonogashira cross-couplings indicated that
(
bromobenzene with n-butyl acrylate, p-bromotoluene the Fe content was less than 0.10 ppm in the solution,
with styrene, and p-bromoanisole with styrene, gave which also demonstrated that there was almost no
the corresponding products in 73, 64, and 51% yields, corrosion on the silica layer of the supported catalyst
[20]
respectively (Table 3, entries 10, 20 and 21). However, in the anhydrous weak basic reaction medium.
no Heck reaction product was detected when aryl Although the Suzuki coupling reaction could be
chlorides were used as one of the substrates in reac- carried out in the presence of a palladium catalyst
tions with methyl acrylate under the standard reaction down to a level of ppm, the leached palladium in the
conditions. The scope of this catalytic system with solution failed to catalyze the reaction under the pres-
vinyl substrates including methyl acrylate, ethyl acry- ent reaction conditions. The key to the success of the
late, n-butyl acrylate, tert-butyl acrylate, acrylonitrile ultra-low palladium method was the use of tetrabuty-
and styrene was also examined. Good to excellent re- lammonium bromide and using controlled microwave
[
21]
sults were obtained when the reactions of the above heating.
vinyl substrates with aryl iodides and activated aryl
bromides were carried out under the identical reac-
tion conditions (Table 3, entries 1–9, and 11–19).
For investigations on the recyclability of the cata-
Conclusions
lyst, it was recovered by magnetic separation, washed In summary, we have developed a highly active, air-
with ethanol, H O, ethanol and diethyl ether respec- and moisture-stable and easily recoverable magnetic
2
tively, dried in air and reused for the next reaction. nanoparticle-supported palladium catalyst for the
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Magnetic Nanoparticles-Supported Palladium: A Highly Efficient and Reusable Catalyst
[a]
Table 2. Sonogashira coupling reaction of aryl halides with terminal alkynes .
[b]
Entry
1
Alkyne
Aryl halide
Product 5
Yield [%]
5a
95
2
3
5b
5c
85
94
4
5
6
7
8
5d
5e
5f
5g
5h
93
95
91
97
96
9
5i
71
1
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
9
5j
89
87
85
79
94
92
96
93
85
82
5h
5g
5e
5k
5l
5m
5n
5o
5p
[
a]
Reaction conditions: aryl halide (0.50 mmol), terminal alkyne (0.60 mmol), SiO @Fe O –Pd catalyst (100 mg, containing
2
3
4
Pd 0.0050 mmol), K CO (1.0 mmol) in DMF (2.0 mL) at 1008C for 6 h.
Isolated yields.
2
3
[
b]
Suzuki, Sonogashira and Heck reactions. A wide ty. It should represent a more simple, efficient, reusa-
range of substrates was coupled successfully under ble and widely applicable magnetic nanoparticles-sup-
aerobic conditions. In particular, the performance of ported palladium catalyst for the classic carbon-
the catalyst was fully retained during the reuse pro- carbon bond formation reactions through the cross-
cess, and it is possible to recover and reuse at least coupling reactions in comparison with the recent re-
[
12–16]
eight times without significant loss of catalytic activi- ported literature.
Adv. Synth. Catal. 2012, 354, 1307 – 1318
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Pinhua Li et al.
FULL PAPERS
[a]
Table 3. Heck reaction of aryl halides with alkenes.
[b]
Entry
1
Alkene
Aryl halide
Product 7
Yield [%]
7a
98
2
3
7b
7c
97
98
4
5
6
7
8
9
7d
7e
7f
7g
7g
7h
7e
7i
98
97
98
98
90
88
73
98
97
96
95
90
93
98
97
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
7j
7k
7l
7m
7n
7o
7p
19
7q
88
2
2
0
1
7n
64
51
7m
[
a]
Reaction conditions: aryl halide (0.50 mmol), vinyl substrate (0.60 mmol), SiO @Fe O –Pd catalyst (100 mg, containing Pd
2
3
4
0
.0050 mmol), K CO (1.0 mmol) in DMF (2.0 mL) at 1008C for 8 h.
2 3
[
b]
Isolated yields.
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Magnetic Nanoparticles-Supported Palladium: A Highly Efficient and Reusable Catalyst
[a]
Table 4. Successive trials by using recoverable SiO @Fe O –Pd catalyst.
2
3
4
[b]
[b]
[b]
Trial
Yield [%] of 3a
Yield [%] of 5a
Yield [%] of 7a
1
2
3
4
5
6
7
8
99
99
97
95
96
95
95
94
95
93
93
91
90
91
89
90
98
94
95
96
93
93
91
92
[
a]
Reaction conditions for Suzuki coupling: 4-bromoanisole (94 mg, 0.50 mmol), phenylboronic acid (72 mg, 0.60 mmol),
reused SiO @Fe O –Pd catalyst (50 mg, containing Pd 0.0025 mmol), K PO (212 mg, 1.0 mmol) in MeOH (2.0 mL) at
2
3
4
3
4
6
1
08C for 1.5 h. Reaction conditions for Heck reaction: 4-iodoanisole (118 mg, 0.50 mmol), ethyl acrylate (86 mg,
.0 mmol), reused SiO @Fe O –Pd catalyst (100 mg, containing Pd 0.005 mmol), K CO (138 mg, 1.0 mmol) in DMF
2
3
4
2
3
(
2.0 mL) at 1008C for 8 h. Reaction conditions for Sonogashira coupling reaction: 4-iodoanisole (118 mg, 0.50 mmol), phe-
nylacetylene (56 mg, 0.60 mmol), reused SiO @Fe O –Pd catalyst (100 mg, containing Pd 0.005 mmol), K CO (138 mg,
2
3
4
2
3
1
.0 mmol) in DMF (2.0 mL) at 1008C for 6 h.
Isolated yields.
[
b]
Experimental Section
ized water and 50 mL of 2-propanol, and the mixture was
sonicated for approximately 30 min. To this well dispersed
magnetic nanoparticles solution, 2.0 mL of NH ·H O fol-
General Remarks
3
2
lowed by 1.6 g of tetraethoxysilane were slowly added and
stirred for further 4 h at room temperature. The material
was washed repeatedly with water until the solution was
neutral, then the solid material was magnetically separated,
washed with ethanol and diethyl ether, respectively, and
dried under vacuum. The silica-coated magnetic nanoparti-
cles, SiO @Fe O (1.36 g) was thus obtained. IR (KBr):
The chemicals were purchased from commercial suppliers
Aldrich, USA and Shanghai Chemical Company, China)
(
and were used without purification prior to use. All
1
H NMR spectra were recorded at 400 MHz on Bruker FT-
NMR spectrometers. Chemical shifts are given as d values
with reference to tetramethylsilane (TMS) as internal stan-
dard. The CHN analysis was performed on a Vario El III el-
ementar. The Pd content was determined by a Jarrell-Ash
2
3
4
À1
nOÀH =3397, nSiÀO =1082 cm .
1
100 ICP analysis. Transmission electron micrograph (TEM)
images were obtained with a JEOL-2010 transmission elec- Synthesis of Phosphine-Functionalized SiO
tron microscope. X-ray diffraction (XRD) measurements
were carried out at room temperature using a Bruker D8
Advance X-ray powder diffractmeter. Infrared (IR) spectra
were measured on a Nicolet 6700 FT-IR spectrophotometer
using KBr pellets. Products were purified by flash chroma-
tography on 200–300 mesh silica gel, SiO2.
@Fe O
3 4
2
[19]
According to the similar procedure, 2-(diphenylphosphi-
no)ethyltriethoxysilane (0.38 g) dissolved in 5.0 mL of dry
toluene, was added to a suspension of 1.0 g of SiO @Fe O
4
2
3
in 30.0 mL of dry toluene. The mixture was then shaken at
008C under a nitrogen atmosphere for 24 h. Then the solid
material (SiO @Fe O –P) was magnetically separated,
1
2
3
4
washed repeatedly with toluene and CH Cl to remove any
2
2
unanchored species and dried under vacuum. The phos-
phine-functionalized SiO @Fe O (brown nanoparticles) was
Synthesis of the Silica-Coated Magnetic Nano-
particles (SiO @Fe O )
2
3
4
2
3
4
obtained; yield: 1.05 g. The loading of phosphine was quan-
À1
Fe O particles (0.50 g, with an average diameter of 20 nm,
tified via CHN microanalysis and found to be 0.18 mmolg
3
4
purchased from Aldrich) were diluted with 5.0 mL of deion-
based on the carbon content determination. IR (KBr):
Adv. Synth. Catal. 2012, 354, 1307 – 1318
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1315

Pinhua Li et al.
FULL PAPERS
1
13
nOÀH =3396,
nSiÀO =1081 cm .
n
CÀH =2925, 2863, nAr,CÀC =1518, 1469,
comparison of their H and C NMR spectral data with the
values of authentic samples.
À1
Synthesis of SiO @Fe O –Pd
Typical Procedure for Catalyst Recovery and
2
3
4
Palladium Leaching of SiO @Fe O -Pd in the Suzuki
Reaction
2
3
4
To a sealable reaction tube, palladium acetate (22.4 mg,
.10 mmol) and THF (15.0 mL) were added. The solution
0
was shaken at room temperature under an inert atmosphere
for 10 min, and then 2.0 g of the above phosphine-function-
alized magnetic nanoparticles (SiO @Fe O –P) were added.
In a reaction vessel, 4-bromoanisole (94 mg, 0.50 mmol),
phenylboronic acid (72 mg, 0.60 mmol), K PO (212 mg,
3
4
2
3
4
1
.0 mmol), and the supported palladium catalyst
The mixture was shaken at room temperature for 4 h, then
the solid catalyst was magnetically separated, and the solid
was washed thoroughly with THF, and dried under vacuum
at 508C for 3 h. The supported Pd catalyst, SiO @Fe O –Pd
(
SiO @Fe O –Pd, 50 mg, containing Pd 0.0025 mmol) were
2
3
4
mixed in MeOH (2.0 mL). The mixture was shaken at 608C
in an air atmosphere for 1.5 h. The supported catalyst was
magnetically separated, and washed with ethanol (2.0 mL),
2
3
4
(
0
brown nanoparticles) was obtained with a loading of
.049 mmol of palladium per gram determined via inductive-
H O (2.0 mL), ethanol (2.0 mL) and diethyl ether (2.0 mLꢂ
2
2
) respectively, then dried, and used directly for the next
ly coupled plasma atomic emission spectrometry (ICP-
run. In addition, palladium leaching from the SiO @Fe O –
2
3
4
AES); yield: 2.01 g. IR (KBr): nOÀH =3397, nCÀH =2978,
Pd catalyst was determined. ICP analysis of the methanol
solution (3.0 mL) of a Suzuki reaction indicated that Pd con-
tents were less than 0.20 ppm.
À1
2
896, nAr,CÀC =1650, 1521, nSiÀO =1080 cm .
General Procedure for the Suzuki Coupling Reaction
Aryl halide (0.5 mmol), arylboronic acid (0.6 mmol), K PO
Typical Procedure for Catalyst Recovery and
3
4
(
(
212 mg, 1.0 mmol), and the supported palladium catalyst Palladium Leaching of SiO @Fe O -Pd in the Heck
2 3 4
SiO @Fe O –Pd, 50 mg, containing Pd 0.0025 mmol) were Reaction
2
3
4
mixed in MeOH (2.0 mL). The mixture was shaken at 608C
in an air atmosphere for 1.5 h. After magnetic separation of
the catalyst, the organic material was twice extracted with
diethyl ether. The organic phase was evaporated under re-
duced pressure. The product was purified by short-column
chromatography on silica gel. All the products have been
previously reported, and their identities were confirmed by
In a reaction vessel, 4-iodoanisole (118 mg, 0.50 mmol),
ethyl acrylate (86 mg, 1.0 mmol), K CO (138 mg, 1.0 mmol),
2
3
and the supported palladium catalyst (SiO @Fe O -Pd,
2
3
4
1
00 mg, containing Pd 0.0050 mmol) were mixed in DMF
(
2.0 mL). The mixture was shakeng at 1008C in an air at-
mosphere for 8 h. The supported catalyst was magnetically
1
13
separated, and washed with ethanol (2.0 mL), H O (2.0 mL),
2
comparison of their H and C NMR spectral data with the
values of authentic samples.
ethanol (2.0 mL) and diethyl ether (2.0 mLꢂ2) respectively,
then dried, and used directly for the next run. In addition,
palladium leaching from the SiO @Fe O –Pd catalyst was
2
3
4
General Procedure for the Sonogashira Coupling
Reaction
determined. ICP analysis of the DMF solution (3.0 mL) of
a Heck reaction indicated that Pd contents were less than
0
.20 ppm.
Aryl halide (0.50 mmol), terminal alkyne (0.60 mmol),
K CO3 (138 mg, 1.0 mmol), and the supported palladium
2
catalyst
(SiO @Fe O –Pd,
100 mg,
containing
Pd Typical Procedure for Catalyst Recovery and
2
3
4
0.0050 mmol) were mixed in DMF (2.0 mL). The mixture
Palladium Leaching of SiO @Fe O -Pd in the
2
3
4
was shaking at 1008C in an air atmosphere for 6 h. After
magnetic separation of the catalyst, the organic material was
twice extracted with diethyl ether. The organic phase was
evaporated under reduced pressure. The product was puri-
fied by short-column chromatography on silica gel. All the
products have been previously reported, and their identities
Sonogashira Reaction
In a reaction vessel, 4-iodoanisole (118 mg, 0.50 mmol), phe-
nylacetylene (56 mg, 0.60 mmol), CO (138 mg,
1.0 mmol), and the supported palladium catalyst
(SiO @Fe -Pd, 100 mg, containing Pd 0.0050 mmol) were
K
2
3
O
3 4
2
1
13
were confirmed by comparison of their H and C NMR
spectral data with the values of authentic samples.
mixed in DMF (2.0 mL). The mixture was shaken at 1008C
in an air atmosphere for 6 h. The supported catalyst was
magnetically separated, and washed with ethanol (2.0 mL),
H O (2.0 mL), ethanol (2.0 mL) and ethyl ether (2.0 mLꢂ2),
2
General Procedure for the Heck Reaction
respectively, then dried, and used directly for the next run.
In addition, palladium leaching in the SiO @Fe O –Pd cata-
Aryl halide (0.50 mmol), vinyl substrate (1.0 mmol), K CO
2
3
2
3
4
(
(
138 mg, 1.0 mmol), and the supported palladium catalyst
SiO @Fe O –Pd, 100 mg, containing Pd 0.0050 mmol) were
lyst was determined. ICP analysis of the DMF solution
(3.0 mL) of a Sonogashira reaction indicated that Pd con-
tents were less than 0.20 ppm.
2
3
4
mixed in DMF (2.0 mL). The mixture was shaken at 1008C
in an air atmosphere for 8 h. After magnetic separation of
the catalyst, the organic material was twice extracted with
diethyl ether. The organic phase was evaporated under re-
duced pressure. The product was purified by short-column
chromatography on silica gel. All the products have been
previously reported, and their identities were confirmed by
Supporting Information
Optimization of the reaction conditions for Suzuki reaction,
Sonogashira reaction, and Heck reaction (Table 1, Table 2
and Table 3), general procedure for the recycling of the sup-
1316
asc.wiley-vch.de
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2012, 354, 1307 – 1318

Magnetic Nanoparticles-Supported Palladium: A Highly Efficient and Reusable Catalyst
1
13
ported palladium catalyst, and H and C NMR data of all
products are available in the Supporting Information.
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