Entangled Cu Complex over Fe3O4@SiO2 as Supported Catalyst for Synthesis of Alkenyl Nitriles with Aromatic Aldehydes and Acetonitrile

Article abstract of DOI:10.1007/s10562-015-1602-8

An efficient, green and practical approach to synthesize alkenyl nitriles using new supported Cu(II) catalyst via aromatic aldehydes and acetonitrile was developed. The novel catalyst was characterized by FT-IR, XRD, SEM/EDX, TEM, TGA and VSM. Interestingly, the catalyst was found to be active for synthesis of alkenyl nitriles, which were readily obtained in good yields under mild conditions. But most importantly, the original catalyst could be conveniently recovered and recycled from the reaction system by applying an external magnet and reused in four cycles without significant loss in catalytic activity. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-015-1602-8

Catal Lett
DOI 10.1007/s10562-015-1602-8
Entangled Cu Complex Over Fe3O4@SiO2 as Supported Catalyst
for Synthesis of Alkenyl Nitriles with Aromatic Aldehydes
and Acetonitrile
Zhen Gu1 Yanfang Wang1 Yuan Yao1 Xiaofeng Xia1 Haijun Wang1
Wei Li1
•
•
•
•
•
Received: 1 April 2015 / Accepted: 30 July 2015
Ó Springer Science+Business Media New York 2015
Abstract An efficient, green and practical approach to
synthesize alkenyl nitriles using new supported Cu(II)
catalyst via aromatic aldehydes and acetonitrile was
developed. The novel catalyst was characterized by FT-IR,
XRD, SEM/EDX, TEM, TGA and VSM. Interestingly, the
catalyst was found to be active for synthesis of alkenyl
nitriles, which were readily obtained in good yields under
mild conditions. But most importantly, the original catalyst
could be conveniently recovered and recycled from the
reaction system by applying an external magnet and reused
in four cycles without significant loss in catalytic activity.
Graphical Abstract
Keywords Supported catalyst Á Aldehydes Á Acetonitrile Á
Alkenyl nitriles Á Catalytic recycling
1 Introduction
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-015-1602-8) contains supplementary
material, which is available to authorized users.
In addition to being versatile intermediates and building
blocks for chemical synthesis, [1] alkenyl nitriles are
commonly found in natural products [2] and can be
transformed into a variety of functional groups such as
amines, ketones, acids, amides etc. A number of synthetic
routes to alkenyl nitriles are known [3–9], however, in
practice, most of them still display some limitations, such
as require harsh conditions and/or highly toxic reagents or
involvement of expensive metal complexes, oxidants and
ligands. Consequently, the exploration of an innovative
& Haijun Wang
wanghj329@outlook.com
& Wei Li
liweixuxi@126.com
1
The Key Laboratory of Food Colloids and Biotechnology,
Ministry of Education, School of Chemical and Material
Engineering, Jiangnan University, Wuxi 214122, Jiangsu,
China
123

Z. Gu et al.
Fig. 1 Olefination of aromatic
aldehydes
catalytic system is a crucial task for organic chemists and
engineers to overcome these shortcomings and achieve the
criteria of a mild, efficient, and environmentally friendly
solution for the synthesis of substituted alkenyl nitriles.
Metal nanoparticles have attracted much attentionin recent
years due to their potential for applications in biomedicine,
electronic devices, spectroscopy, and especially in catalytic
performances [10–12]. As metal nanoparticles, copper
nanoparticles have been extensively studied because of their
high catalytic activity in different types of organic reactions
due to the large surface area and high utilization of surface
atoms [13–15]. Unfortunately, there are two major disad-
vantages that greatly impede them from being applied in
catalytic processes. On the one hand, the copper nanoparticles
easily aggregate to large clusters owing to their high surface
energy, whichresults in thedeactivationofthecatalyst. Onthe
other hand, it is very difficult to separate and reuse the copper
nanoparticles in subsequent reactions because of their small
size [16–18]. Therefore, developing a facile and efficient
approach to solve these two issues is highly desirable. It has
been affirmed through much investigation that the utilization
of a catalyst support to entangle the metal nanoparticles is a
resultful method in catalytic reactions. For this reason, many
materials have been explored to be candidates for catalyst
supports, such as microporous polymers, mesoporous silica,
amorphous silica and carbon [19–22]. Compared with other
solid supports, the magnetic supports show significant supe-
riority. Fe3O4-supported nanoparticles can be simply sepa-
rated, recovered and reused with an external permanent
magnet due to the paramagnetic property, thus significantly
reducing the cost and production of waste [23–27]. Unluckily,
unprotected magnetic nanoparticles are often unstable and
tend to aggregate during the catalytic transformations [28],
surface coating modification has been explored to tackle the
above problems [29–31]. The SiO2 coating is an elegant way
to improve dispersibility and chemical stability, primarily
because silica displays some advantageous properties, such as
fine chemical inertness and thermal stability, good accessi-
bility, porosity, non-toxicity, and the ease of further surface
functionalization [32–34].
the best of our knowledge, only a few approaches from
aromatic aldehydes to alkenyl nitriles have been reported
[38]. Herein, we reported a direct transformation of aromatic
aldehydes to the corresponding (E)-alkenyl nitrile products at
room temperature (Fig. 1). The significance and advantages
of the present protocol can be summarized as follows: (1)
Aromatic aldehydes are used as substrates and acetonitrile as
a nitrile grouping source, which are inexpensive and easily
available or prepared. (2) There are no poisonous oxidants
and costly ligands in the strategy. (3) The catalyst can be
simply recovered and recycled from the reaction system by
applying an external permanent magnet and reused at least
four cycles with no significant decreases in the yields. The
synthetic procedure for XL–CuCl2–Fe3O4@SiO2 core–shell
structured nanocomposites is illustrated in Fig. 2.
2 Experimental
2.1 Preparation of Catalyst
2.1.1 Synthesis of the N1, N2-bis(3-
(trimethoxysilyl)propyl)oxalamide (XL-APTS)
0.7 mL aminopropyltrimethoxysilane (APTS) was treated
with a solution of triethylamine (0.3 mL) in dry dichlor-
omethane (15 mL), and oxalyl dichloride (150 lL) was
added drop by drop and reaction mixture was stirred for 6 h
at room temperature. Then the mixture was concentrated
and the product was extracted with petroleum ether.
Finally, the resultant was obtained after distilling the pet-
roleum ether.
2.1.2 Synthesis of the SiO2 Nanoparticles
The SiO2 nanoparticles were prepared using a published
method with a slight modification [39]. 1.04 g of CTAB
was added to deionized water (200 mL) at 70 °C and then
5 mL TEOS was added dropwise for 1 h and the mixture
was allowed to cool to room temperature. Then aqueous
ammonia (28 wt%) was added until the pH of the solution
was adjusted to 10.5 and the mixture was stirred for 12 h.
The gel was separated by vacuum filter and washed with
distilled water (20 mL) and EtOH (2 9 10 mL), respec-
tively. The gel was vacuum-dried 50 °C for 12 h and then
calcined at 550 °C for 6 h.
In this work we synthesized a new Cu-catalyst based on
Fe3O4@SiO2 nanoparticles, and the leaching of the copper
minimized by cross-linking [35–37]. Excitingly, a novel and
valid methodology to alkenyl nitriles from aromatic alde-
hydes and acetonitrile was developed when the new sup-
ported Cu(II) catalyst was involved in this transformation. To
123

Entangled Cu Complex Over Fe3O4@SiO2 as Supported Catalyst for Synthesis of Alkenyl Nitriles…
Fig. 2 Preparation of the
catalyst
2.1.3 Synthesis of the ‘‘XL–SiO2–NH2’’
alternately with distilled water and ethanol thrice. After
that, the magnetic NPs were dried under vacuum to obtain
the product for further use.
XL-APTS (200 mg) was added to SiO2 (300 mg) in dry
toluene (20 mL) and refluxed for 24 h at 117 °C under a N2
atmosphere. The solid product was then filtered off, rinsed
three times with ethanol. Finally, the resultant was dried in
vacuum at 50 °C over night.
2.1.6 Synthesis of ‘‘XL–CuCl2–Fe3O4@SiO2’’
XL–CuCl2–SiO2–NH2 (100 mg) and Fe3O4 (20 mg) were
dispersed into 20 mL dry ethanol under mechanical stirring
for 12 h to make sure the Fe3O4 was coated uniformly, and
the color of the particles gradually changed from black to
gray. The product was obtained with the help of a magnet,
rinsed thoroughly with ethanol, and dried in vacuum at
room temperature overnight. The weight percentage of Cu
in the catalyst, as determined by Inductively Coupled
Plasma-Atomic Emission Spectrometry (ICP-AES) analy-
sis, was 3.38 wt%.
2.1.4 Synthesis of the ‘‘XL–CuCl2–SiO2–NH2’’
300 mg of the above-synthesized XL–SiO2–NH2 was
mixed with 30 mg of copper chloride in 20 mL of dry
methyl alcohol. The mixture was refluxed for 24 h at 64 °C
under a N2 atmosphere. The solid product was filtered by
suction, cleaned three times with ethanol, and dried at
50 °C under vacuum for 12 h to give the copper com-
plex[XL–CuCl2–SiO2–NH2].
2.2 Characterisation Techniques
2.1.5 Synthesis of Fe3O4 Nanoparticles
FT-IR spectra were recorded on a Nicolet 360 FT-IR
instrument (KBr discs) in the 4000–500 cm-1 region. XRD
measurements were performed on a BRUKERAXSGMBH-
D8 diffractometer using Cu-Ka radiation as the X-ray
source in the 2h range of 10–70°. The morphologies of the
nanocomposites were obtained using a Hitachi S-4800
filedemission scanning electron microscope/energy dis-
persive X-ray (SEM/EDX) and a JEOL JEM-2100 trans-
mission electron microscope (TEM). Thermogravimetric
The Fe3O4 nanoparticles were prepared via a coprecipita-
tion method [32]. Firstly, 3.3 g of FeCl3 and 2.0 g FeCl2Á
4H2O were added to 35 mL of ethanol under vigorous
stirring. Secondly, 10 mL of ammonium hydroxide (28
wt%) was added to the solution drop by drop. Thirdly, the
mixture solution was heated to 78 °C and stirred for 5 h.
Finally, the products were collected via magnetic separa-
tion after cooling to room temperature and were washed
123

Z. Gu et al.
d
b
analysis (TGA) was performed on a TG/DSC1/1100 Met-
tler Toledo thermogravimetric analyzer under a nitrogen
atmosphere from 25 to 800 °C at a heating rate of 20 °C/
min. Magnetic measurements were performed using a
superconducting quantum interface device magnetometer
(SQUID VSM) at room temperature in an applied magnetic
C-H
c
a
Fe-O
1
C=O
field sweeping from -10 kOe to 10 kOe. H NMR spectra
Si-O-Si
were recorded on 400 MHz in CDCl3, 13C NMR spectra
were recorded on 100 MHz in CDCl3 and CD3COCD3.
Si-O-Si
1000 500
3500
3000
2500
2000
1500
)
3 Results and Discussion
3.1 FT-IR Studies
-1
Wavenumber(cm
Fig. 4 FT-IR spectra of a SiO2, b XL–SiO2–NH2, c XL–CuCl2–
SiO2–NH2 and d XL–CuCl2–Fe3O4@SiO2
FT-IR was used to characterize the compositions of the
synthesized materials, as shown in Figs. 3 and 4. The
strong absorption bands at around 1661 cm-1 can be
ascribed to the vibration of C=O bonds from the XL-APTS,
which indicates that amino groups were successfully ‘‘tied
and tangled’’ by cross-linking [36]. In Fig. 4, all the sam-
ples show broad peaks at around 3400 cm-1, which are
attributed to the stretching vibration of O–H. Meanwhile,
the bands at 812, and 1086 cm-1 correspond to Si–O–Si
bending, and Si–O–Si stretching, respectively [40]. More-
over, Fig. 4b, c, d exhibit new adsorption bands in the
2926–2854 cm-1 region which are assigned to the
stretching of C–H bonds and the bands in the range of
1465–1380 cm-1 are due to the bending vibrations of H–
C–H bonds [41]. Thus, it can be confirmed that surface
modification of the silica shell by XL-APTS was success-
ful. As can be seen by comparing, Fig. 4c shows that the
XL–CuCl2–SiO2–NH2 catalyst didn’t change considerably
after attachment of the copper chloride onto the surface of
the silica nanoparticles. In addition, the typical bands at
573 cm-1 (Fe–O vibration) are observed in Fig. 4d, which
shows that Fe3O4 particles were possibly embedded in XL–
CuCl2–Fe3O4@SiO2.
3.2 XRD Studies
The crystallinity and phase composition of the as-synthe-
sized products were investigated by high-angle X-ray
powder diffraction (XRD). As shown in Fig. 5a, six
diffraction peaks (2h = 30.1°, 35.5°, 43.1°, 53.4°, 57.0°,
and 62.5°) corresponding to (220), (311), (400), (422),
(511) and (440) planes of cubic inverse spinel Fe3O4
nanoparticles are obtained [42]. The same diffraction peaks
can also be found in Fig. 5b, which illustrates that the
diffraction peaks did not change but only the peak intensity
and width changed after being coated with SiO2 and sup-
ported CuCl2 nanoparticles, showing that the crystalline
structure of the composite nanoparticles did not vary [43].
Moreover, Fig. 5b displays a broad diffraction peak at
2h = 22.8° assigned to amorphous silica coated on the
311
220
440
400
511
422
b
a
b
SiO2
1661
(a)
10
20
30
40
2θ(°)
50
60
70
3500
3000
2500
2000
1500
1000
500
-1
Wavenumber(cm
)
Fig. 5 The wide-angle XRD patterns of a Fe3O4 microspheres,
b XL–CuCl2–Fe3O4@SiO2 microspheres
Fig. 3 FT-IR spectra of a APTS, b XL-APTS
123

Entangled Cu Complex Over Fe3O4@SiO2 as Supported Catalyst for Synthesis of Alkenyl Nitriles…
3.4 TGA Studies
surface of Fe3O4 nanospheres. No diffraction peaks for
CuCl2 nanoparticles are observed which proved the
excellent dispersion of the CuCl2 sites on the magnetic
nanoparticles [44, 45].
The thermogravimetric (TG) curves obtained for the
Fe3O4, XL–CuCl2–SiO2–NH2, XL–CuCl2–Fe3O4@SiO2
under a N2 atmosphere are presented in Fig. 7. As can be
seen from the diagram, XL–CuCl2–SiO2–NH2 and XL–
CuCl2–Fe3O4@SiO2 were relatively stable around or
below 300 °C. The thermal stability of XL–CuCl2–Fe3
O4@SiO2 was higher than XL–CuCl2–SiO2–NH2, indicat-
ing Fe3O4 particles have been embedded in XL–CuCl2–
Fe3O4@SiO2. It was in agreement with the above-
3.3 SEM/EDX and TEM Studies
The morphology and size of the synthesized materials were
investigated by scanning electron microscopy (SEM) and
transmission electron microscope (TEM). According to
Fig. 6a, the obtained XL–CuCl2–SiO2–NH2 particles have
an approximate diameter of 50 nm with a rough surface.
The Fe3O4 nanoparticles exhibited spherical particles with
an average size 200 nm in diameter Fig. 6b. SEM of the
Fe3O4 particles after functionalization revealed agglomer-
ates of spherical particles with a larger average size of
300 nm Fig. 6c. The core–shell structure of nanocatalysts
can be visualized by TEM characterization as shown in
Fig. 6e, and the Fe3O4 particles are uniformly coated by the
XL–CuCl2–SiO2–NH2 shell with a thickness of ca. 50 nm.
In addition, Fig. 6f displays a dark nano-Fe3O4 core sur-
rounded by a grey silica shell and the obtained particles are
uniformly dispersed. From Fig. 6d, g, it can be seen that
the catalyst did not show significant change in the mor-
phology or in the size after being reused 4 times. In the last,
the elementary composition of XL–CuCl2–Fe3O4@SiO2
was further analysed by EDX, and the result was consistent
with the expected (see supporting information Fig. S1).
100
a
90
80
c
b
70
100
200
300
400
500
600
700
800
Temperature(°C)
Fig. 7 TGA curves of a Fe3O4, b XL–CuCl2–SiO2–NH2 and c XL–
CuCl2–Fe3O4@SiO2
Fig. 6 SEM images of
b Fe3O4 microspheres, c XL–CuCl2–Fe3O4@SiO2 microspheres,
d XL–CuCl2–Fe3O4@SiO2 after 4 cycles of use; TEM images of
a
XL–CuCl2–SiO2–NH2 microspheres,
(e) and f XL–CuCl2–Fe3O4@SiO2 microspheres and g XL–CuCl2–
Fe3O4@SiO2 after 4 cycles of use
123

Z. Gu et al.
Table 1 Optimization of reaction conditionsa
a
80
60
40
20
b
0
Entry Catalyst
Base
Solvent Yield
(%)b
TONg
-20
-40
-60
-80
1
2
3
4
5
6
CuCl2
Cu(OAc)2
CuBr2
Cu(Otf)2
–
KOH
KOH
KOH
KOH
KOH
KOH
DMA
DMA
DMA
DMA
DMA
DMA
40
8.9
10.8
2.6
35
\10
\10
n.d.
86
-10000
-5000
0
5000
10000
3.4
Applied magnetic field (Oe)
–
XL–CuCl2–
Fe3O4@SiO2
107.9
Fig. 8 Room temperature magnetization curves of a Fe3O4, b XL–
CuCl2–Fe3O4@SiO2
7
XL–CuCl2–
SiO2–NH2
KOH
DMA
DMA
86
\5
26
95.9
mentioned discussion. The curve for Fe3O4, XL–CuCl2–
SiO2–NH2, XL–CuCl2–Fe3O4@SiO2 the residue yield was
about 99.3 wt%, 71.3 and 74.4 wt% at 800 °C, respec-
tively. From these numbers the mass of Fe3O4 in XL–
CuCl2–Fe3O4@SiO2 was estimated to be about 11 wt%.
8
XL–CuCl2–
Fe3O4@SiO2
t-BuOK
9
XL–CuCl2–
Fe3O4@SiO2
CH3CH2Ona DMA
10
11
12
13c
14d
15e
16
17
18
19f
XL–CuCl2–
Fe3O4@SiO2
NaH
NaOH
–
DMA
DMA
DMA
DMA
DMA
DMA
THF
\5
57
XL–CuCl2–
Fe3O4@SiO2
3.5 Magnetic Measurements
XL–CuCl2–
Fe3O4@SiO2
n.d.
81
The magnetic properties of the samples were measured
using a vibrating sample magnetometer (VSM) at room
temperature (300 K) in an applied magnetic field up to 10
kOe, as shown in Fig. 8. The samples show a ferromag-
netic nature, the magnetization saturation (Ms) values for
Fe3O4 microspheres and XL–CuCl2–Fe3O4@SiO2 micro-
spheres are 76.9 and 11.4 emu g-1, respectively. Moreover,
the room temperature magnetization curves of the magnetic
nanoparticle, before and after functionalization, exhibit no
hysteresis which demonstrates its superparamagnetic
characteristics [46, 47]. The magnetic behavior of XL–
CuCl2–Fe3O4@SiO2 nanoparticles could not only benefit
their dispersibility and redispersibility in the solution, but
also guarantee that they can be easily separated with the
help of the external magnetic field.
XL–CuCl2–
Fe3O4@SiO2
KOH
KOH
KOH
KOH
KOH
KOH
KOH
XL–CuCl2–
Fe3O4@SiO2
75
XL–CuCl2–
Fe3O4@SiO2
50
XL–CuCl2–
Fe3O4@SiO2
n.d.
XL–CuCl2–
Fe3O4@SiO2
Toluene n.d.
XL–CuCl2–
Fe3O4@SiO2
DMF
DMA
82
79
XL–CuCl2–
Fe3O4@SiO2
Bold row indicates the optimal experimental conditions
a
Conditions: 1a (0.4 mmol), 2a (4 mmol), catalyst (10 mg), base (3
equiv), solvent (3 mL), at room temperature, in air, 6 h
3.6 Catalytic Study
b
Yields of isolated product after chromatography on silica gel
A novel approach to alkenyl nitriles from aromatic alde-
hydes and acetonitrile has been developed. In order to
investigate the optimized conditions, the catalytic activities
of homogeneous and heterogeneous catalysts were exam-
ined in a model reaction using benzaldehyde and acetoni-
trile as representative substrates under room temperature.
The results are summarized in Table 1. As can be seen, the
homogeneous catalysts, including CuCl2, Cu(OAc)2,
CuBr2, and Cu(OTf)2 were evaluated. Unfortunately, the
catalytic effects were not ideal (see Table 1, entries 1, 2, 3
and 4). To our delight, the heterogeneous XL–CuCl2–
c
Catalyst (20 mg)
d
Base (2 equiv) was used
e
Base (4 equiv) was used
f
Under a nitrogen atmosphere
g
TON: (turnover numbers) moles of substrate converted per mole of
metal ion
Fe3O4@SiO2 was chosen to catalyze the reaction displayed
high catalytic activity (see Table 1, entry 6). Subsequently,
using the heterogeneous XL–CuCl2–SiO2–NH2 to catalyze
123

Entangled Cu Complex Over Fe3O4@SiO2 as Supported Catalyst for Synthesis of Alkenyl Nitriles…
Table 2 Conversion of substituted benzaldehydes to alkenyl nitrilesa,b
a
Reaction conditions: substituted benzaldehydes (0.4 mmol), CH3CN (4 mmol), XL–CuCl2–Fe3O4@SiO2 (10 mg), KOH (1.2 mmol) in DMA
(3 mL) at room temperature
b
Isolated yields
c
2-phenylacetonitrile was used instead of CH3CN
the reaction gave the same yield of 86 % (see Table 1,
entry 7), so nano-Fe3O4 particles will not be involved in
catalytic reaction. In addition, through comparing the
turnover numbers achieved by the different catalysts (see
Table 1), there is no doubt that the most efficient catalyst is
the heterogeneous XL–CuCl2–Fe3O4@SiO2. It was found
that a base additive is crucial to achieve the conversion (see
Table 1, entry 12). However, it is not the fact that the
stronger bases reach the higher yields of reactions. When
strong bases, such as t-BuOK and NaH, were used, the
yields of 3a were less than 5 % (see Table 1, entries 8 and
10). In fact, potassium hydroxide (KOH), an easily avail-
able and inexpensive modest strong base, resulted in an
86 % isolated yield of 3a in the reactions (see Table 1,
entry 6). A selection of solvent systems was also investi-
gated. A survey of reaction media (see Table 1, entries 6
and 18) established that polar solvents such as dimethy-
lacetamide (DMA) or dimethylformamide (DMF) were
essential to maintain higher yields. Nevertheless, the
tetrahydrofuran (THF) and toluene were unfavorable to the
reaction (see Table 1, entries 16 and 17). The observations
could be rationalized in terms of the KOH having relatively
high solubility in a strong polar aprotic solvent. Thus, the
optimal reaction conditions were considered to included
benzaldehyde (1 equiv), CH3CN (10 equiv), XL–CuCl2–
Fe3O4@SiO2 (10 mg), KOH (3 equiv), and DMA as the
solvent at room temperature for 6 h. In addition, we have
carried out the reaction with benzaldehyde and acetonitrile
under standard reaction conditions in nitrogen environ-
ment, and the result was nearly unchanged (see Table 1,
entry 19). This means that the reaction doesn’t require the
participation of oxidant.
To extend the scope of this reaction, a variety of aromatic
aldehydes were subjected to standard reaction conditions
(Table 2). It is worth nothing that this method was proved to
be versatile as a variety of aromatic aldehydes with electron-
withdrawing and electron-donating substituents on the phe-
nyl ring at the different positions were converted to their
corresponding alkenyl nitriles (3a–3 h) in good yields.
Furthermore, heterocyclic aromatic aldehyde such as 1i
performed well, producing corresponding alkenyl nitrile 3i
in 50 % yield. In addition, when the 2-phenylacetonitrile
was used as a nitrile group source, and the yield of the
product 3j was also satisfactory.
A plausible mechanism for the formation of alkenyl
nitriles catalyzed by XL–CuCl2–Fe3O4@SiO2 is shown in
Fig. 9. On the one hand, aromatic aldehyde 1 is activated
by XL–CuCl2–Fe3O4@SiO2 to form the intermediate A, on
123

Z. Gu et al.
Fig. 9 A plausible mechanism
for the synthesis of alkenyl
nitriles using XL–CuCl2–
Fe3O4@SiO2
indicated no significant decreases in yields after 4 cycles
(86–77 %). And after four cycles of catalyst circulation,
the Cu content from the original 3.38 wt% fell to 2.95 wt%.
The loss of activity was probably due mainly to the
agglomeration of catalysts and a small amount of leaching
of the copper. Looking from a global perspective, the
heterogeneous catalyst XL–CuCl2–Fe3O4@SiO2 has a
great potential to be used as a stable and highly active
recyclable solid catalyst in the synthesis of alkenyl nitriles.
80
60
40
20
0
4 Conclusion
1
2
3
4
Number of cycles
In summary, a series of alkenyl nitriles were synthesized
using XL–CuCl2–Fe3O4@SiO2 as catalyst via aromatic
aldehydes and acetonitrile at room temperature. The reac-
tions were carried out in a shorter reaction time under
ligand-free condition, and did not require the participation
of oxidant, which gave good to excellent yields. In this
system, using the surface ‘‘cross-linked’’ to increase the
stability of the Cu(II) nanoparticles and prevent metal
leaching during the reaction appears to be the best logical
solution. Moreover, XL–CuCl2–Fe3O4@SiO2 not only has
the very high catalytic activity but also can be recovered
and reused in 4 recycles without significant loss of catalytic
activity. Besides the synthesis of alkenyl nitriles, such an
environmentally benign catalyst should find a wider
application in various organic reactions, which is an
ongoing project.
Fig. 10 Recyclability results of XL–CuCl2–Fe3O4@SiO2
the other hand, acetonitrile 2 reacts with KOH to generate
B. Subsequently, A is attacked by B to give C, which can
capture H? to produce D. Finally, D occurs the reaction of
dehydration under alkaline conditions, resulting in the
product 3.
3.7 Reuse Test of XL–CuCl2–Fe3O4@SiO2
For practical applications of such heterogeneous systems,
the lifetime of the catalyst and its level of reusability are
very significant factors. To clarify this issue, the reuse of
XL–CuCl2–Fe3O4@SiO2 in the model reaction was
investigated. XL–CuCl2–Fe3O4@SiO2 could be easily
recovered through by an external magnet, washed thor-
oughly with EtOH, and drying in an oven at 50 °C over-
night, then new substrates were added for the next cycle.
Figure 10 shows a summary of the obtained results, which
Acknowledgments The authors are grateful to the National Natural
Science Foundation of China (21402066), the Natural Science
Foundation of Jiangsu Province, China (BK2012547), (BK2012547)
and (BK20140139), MOE & SAFEA for the 111 Project (B13025) for
financial support.
123

Entangled Cu Complex Over Fe3O4@SiO2 as Supported Catalyst for Synthesis of Alkenyl Nitriles…
25. Ludwig W, Savara A, Brandt B, Schauermann S (2011) Phys
Chem Chem Phys 13:966
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