Hydrothermal Heck reaction catalyzed by Ni nanoparticles

Article abstract of DOI:10.1039/b900697d

A novel environmentally benign Heck reaction using Ni nanoparticles as catalysts under hydrothermal conditions has been developed in the absence of phosphine ligands without the protection of an inert atmosphere. The results showed that the aryl iodides and bromides could carry out the coupling reaction with a variety of alkenes by hydrothermal treatment. More importantly, the cheap catalysts are stable under the reaction conditions and retain good to moderate activity for at least six successive runs without any additional activation treatment. This approach would be very useful from a practical viewpoint.

Full text of DOI:10.1039/b900697d

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www.rsc.org/greenchem | Green Chemistry
Hydrothermal Heck reaction catalyzed by Ni nanoparticles
Wu Zhang,* Hongling Qi, Liusan Li, Xiang Wang, Jie Chen, Kaishan Peng and Zhenghua Wang*
Received 14th January 2009, Accepted 28th April 2009
First published as an Advance Article on the web 26th May 2009
DOI: 10.1039/b900697d
A novel environmentally benign Heck reaction using Ni nanoparticles as catalysts under
hydrothermal conditions has been developed in the absence of phosphine ligands without the
protection of an inert atmosphere. The results showed that the aryl iodides and bromides could
carry out the coupling reaction with a variety of alkenes by hydrothermal treatment. More
importantly, the cheap catalysts are stable under the reaction conditions and retain good to
moderate activity for at least six successive runs without any additional activation treatment. This
approach would be very useful from a practical viewpoint.
in heterogeneous systems may be promoted under hydrothermal
Introduction
conditions.
The vinylation of aryl and vinyl halides, called the Heck reaction,
In this work, we report a hydrothermal Heck reaction
is extensively used in organic synthesis.1 Soluble palladium
using Ni nanoparticles as catalysts which were prepared by
compounds, generally phosphine palladium complexes, are the
direct reduction of NiCl2 with NaBH4 in aqueous medium
most efficient catalysts for the Heck reaction. However, phos-
under sonication in the absence of surfactants. The coupling
phine ligands are expensive, toxic, unrecoverable and sensitive
reactions of a variety of aryl halides with different alkenes were
to oxygen and water. Additionally, catalyst recycling is often
investigated under optimum reaction conditions (Scheme 1).
hampered by early precipitation of palladium and recovery of
More importantly, the cheap catalysts are stable under the
the expensive palladium is difficult. The problems could, in
reaction conditions and retain good to moderate activity for
principle, be minimized using heterogeneous catalysts.2 Recently,
at least six successive runs without any additional activation
Mart´ınez and Vallribera prepared Ni nanoparticles embedded
treatment in the absence of the phosphine ligands.
in silica and carbon aerogels which were active and recoverable
catalysts for Mizoroki–Heck reactions.3 Therefore, study on the
Heck reaction using much cheaper heterogeneous catalysts such
as Ni,4 Co5 and Cu6 is of great importance and significance from
industrial and scientific viewpoints.
The Heck reaction is traditionally carried out in organic sol-
vents such as dimethyl formamide (DMF), N-methylpyrrolidone
(NMP) and acetonitrile, which often creates significant safety,
health and environmental issues due to their flammability,
Scheme 1 C–C coupling reaction.
toxicity and volatility. From an economic and environmental
standpoint, it is desirable to avoid any use of hazardous and
expensive organic solvents. There have been a number of reports
on C–C bond formations in aqueous medium in recent years,7–11
which can be attributed to the development of the field of
green chemistry. It is well known that in hydrothermal processes
the temperature is much higher than the boiling point of
water and the self-engendered high pressure takes the water
to a critical or subcritical state. The special properties of
supercritical water make it possible to realize organic reactions
that cannot be attained in organic solvents. It had also been
reported that high-pressure techniques can activate the Heck
reaction.1b,12 So it is expected that the Heck reaction carried out
Results and discussion
Catalyst characterization
The obtained Ni was characterized by X-ray powder diffraction
analysis (XRD). It did not show any peaks that could be
associated with a crystalline phase, which indicates that it is
poorly crystalline or amorphous. In order to further identify the
samples, energy-dispersive spectrometry analysis (EDS, Fig. 1)
was carried out. It reveals that the sample is essentially pure
nickel and the absence of boron. Only a small amount of oxygen
is present, probably due to the existence of air atmosphere
or the oxidation of the sample surface. The morphologies
of the sample were determined by field emission scanning
electron microscopy (FE-SEM) as shown in Fig. 2a. It can
be seen that the sample is mainly composed of small nano-
particles.
Anhui Laboratory of Molecule-Based Materials, Anhui Key Laboratory
of Functional Molecular Solids, College of Chemistry and Materials
Science, Anhui Normal University, Wuhu, 241000, P R China.
E-mail: zhangwu@mail.ahnu.edu.cn; Fax: +86-553-3869310;
Tel: +86-553-3869310
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140 ◦C (Table 1, entries 1 and 9, 10). When the temperature
was raised to 150 ◦C, the yield did not increase significantly
(Table 1, entry 11) and hence 140 ◦C was chosen for the further
study. Experiments showed that 2 mol% of catalyst provided
the best yield of product (Table 1, entries 1 and 12–14). Time-
dependent experiments indicated that the reaction time has a
strong influence on the yield (Table 1, entries 1 and 15–17),
16 h was chosen as the ideal reaction time for the coupling of
iodobenzene with ethyl acrylate. Superior results were obtained
when the molar ratio of iodobenzene with ethyl acrylate was
1 : 1.2. All results were obtained without the protection of an
inert atmosphere.
Thus, the optimized reaction conditions for this Heck reac-
tion were aryl halide (1 mmol), alkene (1.2 mmol), catalysts
(0.02 mmol), K2CO3 (1 mmol), tetrabutylammonium bromide
◦
(TBAB) (0.5 mmol) and water (10 mL) at 140 C in a 15 mL
Teflon-lined stainless-steel autoclave for 16 h.
Fig. 1 EDS image of the Ni nanoparticles.
Testing of the catalysts
We next explored the scope and limitations of this hydrother-
mal Heck reaction for different substrates using Ni nanoparticles
as catalyst under the optimum reaction conditions, and the
results are summarized in Table 2. The yields depended on
the nature of halides and their substituents. It was found that
the yields were generally high for both electron-donating and
electron-withdrawing aryl iodides (Table 2, entries 5–13) and
all of the products were easily separated by the extraction
with ether. The results were comparable to the results obtained
with palladium catalysts in water.8c Furthermore, the yields
in heterogeneous systems were even higher than the yields
obtained in homogeneous ones with nickel catalysts in the
presence of phosphine ligands.4b It is worth mentioning that the
hydrothermal system could tolerate a broad range of functional
groups, such as OMe, OH, NO2 and COOH.
In the case of aryl bromides the catalytic system presented
moderate activity for activated aryl bromobenzenes (Table 2,
entries 14, 15), but only 35% yield of the product was obtained
with bromobenzene (Table 2, entry 16) although the reaction
time was prolonged and a higher reaction temperature was
necessary for the electron-rich aryl bromides (Table 2, entry
17). Unfortunately, the catalytic system was inactive for aryl
chlorides (Table 2, entry 18) and only trace product was
observed. All coupling products were purified and characterized;
only E-isomers were obtained which was confirmed by NMR
(3JH–H = 16 Hz).
During the course of further optimization of our reaction
conditions, the vinylation of iodobenzene with ethyl acrylate was
studiedas model reaction using the as-prepared Ninanoparticles
as catalysts in an autoclave. The effects of solvent, base, temper-
ature, amount of catalyst and reaction time were investigated
and the results are summarized in Table 1. It can be seen that
84% of the product was obtained in pure water in an autoclave
(Table 1, entry 1). A parallel experiment was carried out in
aqueous medium under reflux conditions (Table 1, entry 2),
but only a trace of the product was obtained due to the lower
temperature and pressure compared to hydrothermal conditions.
However, we obtained comparatively better yields with mixed
solvent (Table 1, entry 3) possibly due to the increased solubility
of the organic substrates. Although a better yield was observed
in DMF/H2O = 1/2, water was chosen as the solvent of choice
for our reaction system for economic and environmental reasons.
The basic environment is indispensable for the Heck reaction and
among the bases examined (Table 1, entries 1 and 4–8), K2CO3
showed the best effect on the coupling reaction. It is well-known
that heterogeneous Heck reactions can run better at higher
temperatures if reagents, products, and catalyst can survive such
a harsh treatment. As expected, the yield significantly increased
from 20% to 84% as the temperature increased from 100 ◦C to
Fig. 2 (a) FE-SEM image of the Ni nanoparticles; (b) FE-SEM image of the Ni catalyst after the sixth cycle.
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Table 1 The effects of solvent, base, temperature, amount of catalyst and reaction time on the Heck coupling of iodobenzene and ethyl acrylate
Entry
Solvent
Base
T/◦C
Ni (mol%)c
Time/h
Yield (%)a
1
2b
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
H2O
H2O
K2CO3
K2CO3
K2CO3
KOH
NaOH
Na2CO3
NaOAc
Et3N
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
140
100
140
140
140
140
140
140
120
100
150
140
140
140
140
140
140
2
2
2
2
2
2
2
2
2
2
2
1
1.5
4
2
2
2
16
16
16
16
16
16
16
16
16
16
16
16
16
16
8
84
trace
89
62
55
71
72
64
65
20
85
72
79
86
68
76
85
DMF/H2O = 1/2
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
12
20
H2O
a Isolated yields. b Under reflux conditions. c The amount of the catalysts was relative to the amount of iodobenzene.
Table 2 Heck reactions of aryl halides with alkenes catalyzed by Ni nanoparticlesa
Entry
1
Aryl halide
Alkene
Product
Time/h
Yield (%)b
81
16
16
16
16
2
3
4
84
80
78
5
6
16
16
79
83
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Table 2 (Contd.)
Entry
7
Aryl halide
Alkene
Product
Time/h
16
Yield (%)b
78
8
9
16
16
75
78
10
11
12
13
16
24
24
24
79
76
77
72
14
15
16
17
18
20
61
20
55
30
35
30 (150 ◦C)
30 (150 ◦C)
20
trace
a Reaction conditions: aryl halide (1 mmol), alkene (1.2 mmol), Ni catalysts (0.02 mmol), K2CO3 (1 mmol), TBAB (0.5 mmol), water (10 mL) at
140 ◦C in a 15 mL Teflon-lined stainless-steel autoclave. b Isolated yields.
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Table 3 Successive trials using recycled Nia catalysts
Trial
Yield (%)b
Trial
Yield (%)b
1
2
3
84
82
81
4
5
6
78
76
75
a Reaction conditions: iodobenzene (1 mmol), ethyl acrylate (1.2 mmol), recycled Ni catalysts, K2CO3 (1 mmol), TBAB (0.5 mmol), water (10 mL) at
140 ◦C in a 15 mL Teflon-lined stainless-steel autoclave. b Isolated yields.
Catalysts recycling
(FE-SEM) image and the energy-dispersive spectrometry (EDS)
were obtained on an S-4800 field-emission scanning electron
microscope with an accelerating voltage of 5 kV. NMR spectra
were obtained at 25 ◦C on a Bruker Avance-300 at 300 MHz for
Experiments were also conducted to examine the recyclability
of Ni catalysts. As can be seen from Table 3, Ni nanoparticles
were reused successfully and minor decreases in reaction yields
were observed after the fourth catalytic coupling reactions of
iodobenzene with ethyl arylate (Table 3). Elemental analysis of
the filtrate after the reaction demonstrated no leaching of Ni,
implying that the reaction proceeded through a heterogeneous
catalytic process. After the sixth cycle, Ni nanoparticles were
much larger in size (Fig. 2b) because of aggregation and
precipitation of the catalysts.
1H, and at 75 MHz for 13C NMR, chemical shifts for 1H and 13
were both referenced to CDCl3.
C
Preparation of the catalysts
In a typical synthetic process 0.0952 g NiCl2·6H2O (0.4 mmol)
and 0.012 g NaBH4 (0.3 mmol) were each dissolved in 10 mL
de-ionized water to form aqueous solutions. Then the NiCl2
solution was injected dropwise into the NaBH4 solution under
sonication at 30–40 ◦C. After the addition was complete, the
mixture was sonicated continuously for 10 min. Finally, the
mixture was separated by centrifugation. The black precipitate
was collected and washed with de-ionized water several times,
then dried in a vacuum oven at 60 ◦C for 4 h.
Conclusions
In summary, Ni nanoparticles were prepared by a facial method
under sonication. It was found that the as-prepared Ni nanopar-
ticles exhibited superior catalytic activity in the Heck reaction
simply by environmental benign hydrothermal treatment and
provides the corresponding coupling products with moderate to
good yields in the absence of phosphine ligands. Furthermore,
the cheap catalysts are stable under the reaction conditions and
retain good to moderate activity for at least six successive runs
without any additional activation treatment. Fortunately, it was
found that other metals such as Fe and Cu nanostructures
prepared by the same method also show the similar activities
under hydrothermal conditions. The results of these studies will
be reported in due course.
Procedures for the Heck reaction
In a typical experimental procedure 0.02 mmol Ni was added to
5 mL de-ionized water in a 10 mL beaker, and then 1 mmol of
aryl halide and 1.2 mmol of alkene, followed by 0.5 mmol TBAB
and 1 mmol of K2CO3 were added sequentially, mixed with
vigorous stirring. After five minutes, the mixture was transferred
into a 15 mL Teflon-lined stainless-steel autoclave and de-
ionized water was added up to 80% of the total volume. The
autoclave was maintained at 140 ◦C for an appropriate time, then
cooled down to room temperature and then centrifuged. The
aqueous solution was separated and the precipitate was washed
sufficiently with ethyl ether. The solutions were combined and
extracted with ethyl ether (3 ¥ 5 mL). The organic phases
were then dried with anhydrous magnesium sulfate, filtered and
concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel with a mixture of ethyl
acetate and petroleum ether as eluent.
Experimental
Chemicals
All starting materials and reagents were commercially available
and used without further purification. All products have been
previously reported and characterized. All known products
gave satisfactory analytical data corresponding to the reported
literature values.
Recycling procedure of the catalysts
Apparatus
In the recycling experiment, when the reaction was complete
and allowed to cool down to room temperature naturally,
the precipitate was separated by centrifugation and washed
sufficiently with ether and de-ionized water, each three times,
then dried in a vacuum oven at 60 ◦C for 4 h. The catalysts were
recovered and reused in the next run without further activation
treatment.
The as-prepared Ni products were characterized by X-ray pow-
der diffraction (Shimadzu XRD-6000) with graphite monochro-
matized Cu-Ka radiation (l = 0.154060 nm), employing a
scanning rate of 0.02◦ s-1 in the 2q range from 10◦ to 80◦. All the
experiments were conducted in a 15 mL Teflon-lined stainless-
steel autoclave. The field-emission scanning electron microscopy
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The NMR data of the products are presented below
75 MHz) d: 170.9, 157.9, 148.1, 141.6, 128.6, 123.2, 117.5, 61.0,
14.3.
7.
1.
(E)-Methyl cinnamate: 1H NMR (CDCl3, 300 MHz, ppm) d:
7.70 (d, J = 16.1 Hz, 1H), 7.53–7.50 (m, 2H), 7.38–7.36 (m, 3H),
6.45 (d, J = 16.1 Hz, 1H), 3.80 (s, 3H); 13C NMR (CDCl3, 75
MHz) d: 167.5, 144.9, 134.4, 130.5, 128.9, 128.2, 117.8, 51.7.
2.
(E)-Butyl 3-(2-nitrophenyl) acrylate: 1H NMR (CDCl3,
300 MHz, ppm) d: 8.10 (d, J = 15.9 Hz, 1H), 8.03 (d, J = 8.1 Hz,
1H), 7.64 (d, J = 8.1 Hz, 1H), 7.56–7.54 (m, 1H), 7.54–7.52 (m,
1H), 6.36 (d, J = 15.9 Hz, 1H), 4.16 (t, J = 6.6 Hz, 2H), 1.71–
1.66 (m, 2H), 1.46–1.37 (m, 2H), 0.93 (t, J = 7.2 Hz, 3H); 13C
NMR (CDCl3, 75 MHz) d: 166.2, 148.3, 146.2, 139.6, 133.9,
130.5, 128.9, 124.8, 123.2, 64.5, 30.8, 19.2, 13.7.
8.
1
(E)-Ethyl cinnamate: H NMR (CDCl3, 300 MHz, ppm) d:
7.68 (d, J = 16.0 Hz, 1H), 7.49–7.47 (m, 2H), 7.35–7.33(m, 3H),
6.42 (d, J = 16.0 Hz, 1H), 4.25 (q, J = 7.2 Hz, 2H), 1.31 (t,
J = 7.1 Hz, 3H); 13C NMR (CDCl3, 75 MHz) d: 166.9, 144.5,
134.5, 130.1, 128.9, 128.0, 118.3, 60.4, 14.3.
3.
(E)-4-(3-Butoxy-3-oxoprop-1-enyl)benzoic acid: 1H NMR
(CDCl3, 300 MHz, ppm) d: 12.8 (s, 1H), 8.13 (d, J = 7.9 Hz,
2H), 7.72 (d, J = 16.0 Hz, 1H), 7.63 (d, J = 7.9 Hz, 2H), 6.56 (d,
J = 16.0 Hz, 1H), 4.24 (t, J = 6.5 Hz, 2H), 1.73–1.66 (m, 2H),
1.48–1.41 (m, 2H), 0.97 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3,
75 MHz) d: 169.3, 166.7, 143.0, 139.6, 130.7, 130.3, 128.0, 121.1,
64.8, 30.7, 19.2, 13.8.
(E)-n-Butyl cinnamate: 1H NMR (CDCl3, 300 MHz, ppm) d:
7.69 (d, J = 16.0 Hz, 1H), 7.53–7.50 (m, 2H), 7.38–7.36 (m, 3H),
6.44 (d, J = 16.0 Hz, 1H), 4.21 (t, J = 6.6 Hz, 2H), 1.74–1.64
(m, 2H), 1.50–1.40 (m, 2H), 0.97 (t, J = 7.3 Hz, 3H); 13C NMR
(CDCl3, 75 MHz) d: 167.0, 144.5, 134.5, 130.2, 128.9, 128.0,
118.3, 64.4, 30.8, 19.2, 13.8.
9.
4.
(E)-Butyl 3-(4-chlorophenyl)acrylate: 1H NMR (CDCl3,
300 MHz, ppm) d: 7.59 (d, J = 16.0 Hz, 1H), 7.45 (d, J = 7.5 Hz,
2H), 7.31 (d, J = 7.5 Hz, 2H), 6.37 (d, J = 16.0 Hz, 1H), 4.18 (t,
J = 6.4 Hz, 2H), 1.68–1.64 (m, 2H), 1.44–1.37 (m, 2H), 0.94 (t,
J = 7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz) d: 166.7, 143.0,
136.1, 132.9, 129.1, 128.8, 118.8, 64.9, 30.7, 19.2, 13.7.
10.
1
(E)-1,2-Diphenylethene: H NMR (CDCl3, 300 MHz, ppm)
d: 7.61 (d, J = 7.2 Hz, 4H), 7.46 (t, J = 7.2 Hz, 4H), 7.36 (t,
J = 7.2 Hz, 2H), 7.21 (s, 2H); 13C NMR (CDCl3, 75 MHz) d:
137.4, 128.8, 128.6, 127.7, 126.7.
5.
(E)-Ethyl 3-(4-chlorophenyl)acrylate: 1H NMR (CDCl3,
300 MHz, ppm) d: 7.63 (d, J = 15.9 Hz, 1H), 7.46 (d, J = 8.5 Hz,
2H), 7.36 (d, J = 8.5 Hz, 2H), 6.41(d, J = 15.9 Hz, 1H), 4.27 (q,
J = 7.2 Hz, 2H), 1.34 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3,
75 MHz) d: 166.2, 142.5, 135.6, 132.5, 128.8, 128.7, 118.5, 61.4,
14.3.
(E)-Butyl 3-(4-nitrophenyl)acrylate: 1H NMR (CDCl3,
300 MHz, ppm) d: 8.25 (d, J = 8.6 Hz, 2H), 7.70 (d, J = 16.0 Hz,
1H), 7.68 (d, J = 8.6 Hz, 2H), 6.56 (d, J = 16.0 Hz, 1H), 4.24 (t,
J = 6.6 Hz, 2H), 1.75–1.66 (m, 2H), 1.48–1.38 (m, 2H), 0.97 (t,
J = 7.2 Hz, 3H); 13C NMR (CDCl3, 75 MHz) d: 166.1, 146.6,
141.5, 140.6, 128.6, 124.1, 122.7, 64.9, 30.7, 19.1, 13.7.
6.
11.
(E)-Butyl 3-(4-methoxyphenyl)acrylate: 1H NMR (CDCl3,
300 MHz, ppm) d: 7.62 (d, J = 16.0 Hz, 1H), 7.45 (d, J = 8.3 Hz,
2H), 6.87 (d, J = 8.3 Hz, 2H), 6.29 (d, J = 16.0 Hz, 1H), 4.18 (t,
J = 6.6 Hz, 2H), 3.79 (s, 3H), 1.71–1.62 (m, 2H), 1.46–1.38 (m,
2H), 0.95 (t, J = 7.3 Hz, 3H); 13C NMR (CDCl3, 75 MHz) d:
167.3, 161.3, 144.2, 129.6, 127.1, 115.7, 114.3, 64.2, 55.3, 30.8,
19.2, 13.7.
(E)-Ethyl 3-(4-nitrophenyl) acrylate: 1H NMR (CDCl3,
300 MHz, ppm) d: 8.25 (d, J = 8.5 Hz, 2H), 7.71 (d, J = 16.0 Hz,
1H), 7.67 (d, J = 8.5 Hz, 2H), 6.59 (d, J = 16.0 Hz, 1H), 4.30
(q, J = 7.2 Hz, 2H), 1.36 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3,
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7.18 (d, J = 7.2 Hz, 2H), 6.40 (d, J = 16.0 Hz, 1H), 4.30 (t,
J = 6.6 Hz, 2H), 2.36 (s, 3H), 1.74–1.65 (m, 2H), 1.50–1.41 (m,
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167.3, 144.6, 140.6, 129.6, 128.9, 128.1, 117.2, 64.4, 30.8, 21.5,
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(E)-Butyl 3-(4-hydroxyphenyl)acrylate: 1H NMR (CDCl3,
300 MHz, ppm) d: 7.69 (d, J = 16.0 Hz, 1H), 7.52 (d, J = 8.0 Hz,
2H), 7.38 (d, J = 8.0 Hz, 2H), 6.45 (d, J = 16.0 Hz, 1H), 4.22 (t,
J = 6.3 Hz, 2H), 1.72–1.65 (m, 2H), 1.48–1.41 (m, 2H), 0.97 (t,
J = 7.1 Hz, 3H); 13C NMR (CDCl3, 75 MHz) d: 167.1, 144.6,
134.5, 130.2, 128.9, 128.1, 118.3, 64.5, 30.8, 19.2, 13.8.
Acknowledgements
Financial support from the National Natural Science Foun-
dation of China (20701001, 20872001) and a grant from the
Education Department of Anhui province (TD200707) are
appreciated.
10 (a) R. Breslow, Acc. Chem. Res., 2004, 37, 471–478; (b) U. M.
Lindstroˆm and F. Andersson, Angew. Chem., 2006, 118, 562–565;
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