Fe3O4@Boehmite-NH2-CoII NPs: An inexpensive and highly efficient heterogeneous magnetic nanocatalyst for the Suzuki-Miyaura and Heck-Mizoroki cross-coupling reactions

Article abstract of DOI:10.1039/c7gc02647a

Herein we report the synthesis of a magnetically separable core-shell-like Fe₃O₄@Boehmite-NH₂-Co^II NPs as an environmentally friendly heterogeneous catalyst. The as-prepared nanocatalyst was well characterized by various techniques such as FT-IR, XRD, BET, TEM, FE-SEM, EDX, TGA, H₂-TPR, VSM, ICP-OES and elemental analysis and evaluated for the Suzuki-Miyaura and Heck-Mizoroki cross-coupling reactions in a green solvent (H₂O). The results of characterization studies revealed the superparamagnetic behavior of the Fe₃O₄ NP core encapsulated by a Boehmite NP shell. Also, it was clearly found that the size of the particles was about 13-54 nm. In comparison with previously reported catalysts, Fe₃O₄@Boehmite-NH₂-Co^II NPs exhibited perfect catalytic efficiency for the Suzuki-Miyaura and Heck-Mizoroki cross-coupling reactions under mild conditions without using toxic solvents. The concerted effects between individual components of the catalyst and also its unique egg-like nanostructure led to the high catalytic performance of Fe₃O₄@Boehmite-NH₂-Co^II NPs. Also, the introduction of Co significantly lowers the cost of the catalyst. More importantly, the longevity of the nanocatalyst was studied and it was found that the magnetic nanocatalyst was stable under the reaction conditions and could be easily reused for at least seven consecutive cycles without a discernible decrease in its catalytic activity or metal leaching.

Full text of DOI:10.1039/c7gc02647a

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CoII immobilized on aminated Fe3O4@Boehmite nanoparticles
(Fe3O4@Boehmite-NH2-CoII NPs): a novel, inexpensive and highly
efficient heterogeneous magnetic nanocatalyst for Suzuki–
Miyaura and Heck–Mizoroki cross-coupling reactions in green
media
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Arezou Mohammadinezhada , Batool Akhlaghiniaa,*
Herein we report the synthesis of
a
magnetically separable core-shell-like Fe3O4@Boehmite-NH2-CoII NPs as an
environmentally friendly heterogeneous catalyst. The as-prepared nanocatalyst was well characterized by various
techniques such as FT-IR, XRD, BET, TEM, FE-SEM, EDX, TGA, H2-TPR, VSM, ICP-OES and elemental analysis and evaluated
for the Suzuki–Miyaura and Heck–Mizoroki cross coupling reactions in green solvent (H2O). The results of characterizations
revealed the superparamagnetic behavior of the Fe3O4 NPs core encapsulated by a Boehmite NPs shell. Also, it was clearly
found that the size of the particles was about 13-54 nm. In comparison to the previous reported catalysts,
Fe3O4@Boehmite-NH2-CoII NPs exhibited perfect catalytic efficiency for the Suzuki–Miyaura and Heck–Mizoroki cross
coupling reaction under mild conditions without using toxic solvents. The concerted effects between the individual
components of catalyst and also its unique egg-like nanostructure caused the high catalytic performance of
Fe3O4@Boehmite-NH2-CoII NPs. Also, the introduction of Co significantly lowers the cost of catalyst. More importantly, the
longevity of nanocatalyst was studied and found that the magnetic nanocatalyst is stable under the reaction conditions
and could be easily reused for at least seven consecutive cycles without a discernible decrease in its catalytic activity or
metal leaching.
1. Introduction
been shown that transition metal catalysts, including nickel [13],
copper [14], iron [15] and cobalt [16-18], might be employed as
Among the most fundamental reactions in organic chemistry,
generating carbon–carbon bond as a powerful synthetic tool and a
major area in multiple organic transformations has received great
attention [1, 2] owing to, the resulting coupling products are widely
used for academic and industrial process including pharmaceuticals,
agrochemicals, natural products and fine chemical industries [3-6].
Undoubtedly, Suzuki–Miyaura [7] and Heck–Mizoroki [8] cross
coupling reactions are the most beneficial and extensively used
reactions for C-C bond formation due to their high efficiency and
atom economy. In this context, novel transition metal complexes
have been the most extensively studied catalytic systems for
Suzuki–Miyaura [9] and Heck–Mizoroki [10] cross coupling
reactions. During the last decades, Suzuki–Miyaura [11] and Heck–
alternatives to toxic, air sensitive and expensive precious metal
such as palladium in cross coupling reactions. Although, compared
to nickel, palladium, and copper catalysts [19] coupling reaction
under cobalt catalysis is rare [20, 21], but to date, cobalt catalysts
have attracted substantial attention in organic synthesis owing to
their higher reactivity for various C–C bond forming reactions, low
cost, nontoxicity, availability and their interesting mode of action
[22, 23]. There have been a number of important studies focused
on the development of new catalytic systems and methodologies
(including homogeneous and heterogeneous catalysts) based on
cobalt in combination with different ligands to improve Suzuki–
Miyaura and Heck–Mizoroki cross coupling reactions [16-18, 24-28].
Mizoroki [12] coupling reactions were catalyzed by Pd based For the past few years stabilized metallic nanoparticles (NPs) have
catalysts. More recently, in modern organic synthesis, considerable probably been the most frequently employed in modern organic
interest has been focused on palladium-free conditions and it has synthesis. Meanwhile, it has been demonstrated repeatedly that
appropriate particle size, crystal structure and nature of ligand are
crucial to access of metallic NPs with proper catalytic activity [29-
31]. On the other hand, up to now magnetic nanocatalysts have
attracted remarkable attention of organic chemists due to their
feasible removal and recycling by means of an external magnetic
field which is not time-consuming and prevents losing of catalyst
during the separation process. Kinetic problems such as
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aggregation/ oxidation of metal particles and reduction in catalytic
activity which are often caused by having very active surface atoms
can be removed by a well-chosen stabilizer. The stabilizer can
control the particle size, shape and magnetic features of the hybrid
materials, improve the chemical stability, prevent the
agglomeration and serve as the catalyst platform as well [32, 33].
HO
HO
OH
OH
OH
OH
HO
OH
OH
OH
HO
H2
O
NaOH (5%), Ar
HO
Room Temperature
NaOH, H2
Fe3O4
HO
HO
HO
OH
OH
OH
O
HO
OH
HO
OH
HO
HO
Fe3O4@Boehmite NPs (II)
Boehmite NPs (I)
Cl
Cl
Boehmite NPs as a component of aluminium ore bauxite is an
aluminum oxide hydroxide (γ-AlOOH) mineral. Boehmite NPs with
orthorhombic unit cells consists of octahedral double sheets
centered with aluminum ions. Extra hydroxyl groups on its surface
provide the capability of reaction with different linkers and ligands
which could be available for immobilization of metal ions [34].
Nontoxicity, availability, thermal and mechanical stability of
Boehmite NPs makes it an excellent support, especially in
heterogeneous catalysis [35-41]. With these considerations in mind,
and to solve the problem of regeneration and reusing of the
expensive catalyst, the use of Fe3O4/Boehmite NPs hybrids is thus
one of the most elegant and efficient way. As a part of our ongoing
work towards the development of efficient green catalysts [42] we
designed a novel procedure for the synthesis of Fe3O4@Boehmite
NPs with high magnetic feature and very small particle size
compared to the previous reports in literature [43, 44]. In the
following step, functionalization of Fe3O4@Boehmite NPs was
performed by the treatment with (3-choloropropyl)triethoxysilane
and further reaction with triethylenetetramine to afford aminated
Fe3O4@Boehmite. With particular emphasis on the Suzuki–Miyaura
and Heck–Mizoroki cross coupling reactions [43m, 43p]
immobilization of CoII were subsequently carried out via the
reaction of Fe3O4@Boehmite-NH2 with ethanolic solution of
CoCl2.6H2O. A schematic illustration of the preparation strategy of
the CoII immobilized on aminated Fe3O4@Boehmite nanoparticles
(Fe3O4@Boehmite-NH2-CoII NPs) was shown in Scheme 1.
Si
EtO
EtO
EtO
Si
O
O
O
O
O
O
O
O
O
Cl
Si
Fe3O4
Si
Cl
N
H
O
O
O
H2
N
NH
Si
Fe3O4@Boehmite-Pr-Cl (III)
NH2
Cl
N
H
NH
HN
N
H2
N
H
Si
O
NH2
H
N
O
O
NH
H
N
H
N
O
O
O
O
CoII
H2
NH
Si
Fe3O4
O
O
Cl
H
Si
N
N
Cl
N
H
Si
O
NH2
Cl
CoII
NH
HN
O
O
HN
O
O
O
H2
N
Si
H
N
Cl
O
O
O
O
NH2
Si
Fe3O4
O
O
Si
NH
Cl
NH
HN
Cl
NH
O
CoII
H
O
O
N
H2
N
Si
H2
N
Cl
N
H
Cl
CoII
H
N
Fe3O4@Boehmite-NH2 (IV)
HN
N
H
Fe3O4@Boehmite-NH2-CoII NPs (V)
Al(NO3
)
3.9H2
O
FeSO4.7H
FeCl3.6H2
O
Fe3O4
Scheme 1. The magnetic nanocatalyst preparation.
and 1069 cm-1. Fig. 1b displays a weak absorption band at 571 cm-1
related to the Fe-O bond of Fe3O4@Boehmite NPs. Successful
coupling of (3-choloropropyl)triethoxysilane to the surface of
Fe3O4@Boehmite NPs was demonstrated by the characteristic
bending and stretching vibrations of the C-H and Si-O bonds which
were appeared at 1292 and 1074 cm-1 respectively (Fig. 1c) [35, 39,
40, 45]. The existence of grafted TETA could be authenticated by
the appearance of three new absorption bands at 2492, 1637 and
1447 cm-1 which can be assigned to N-H (primary and secondary
amine) bending vibrations (Fig. 1d). Also, the stretching vibration
band of N-H bond (3300-3000 cm-1) could not be precisely defined,
because of covering with the broad absorption band of OH···OH
bond. Upon CoII coordination, the intensity of the characteristic
absorption band related to N-H bending vibration was decreased
considerably (Fig. 1e) [46]. Moreover, the bands at 3555 and 1638
cm-1 were attributed to the O-H stretching of the lattice water
molecule in the cobalt complex [47, 48].
Results and Discussion
Characterization of Fe3O4@Boehmite-NH2-CoII NPs
The catalytic system was well characterized using various
techniques including Fourier transform infrared spectroscopy (FT-
IR), X-ray powder diffraction (XRD), Brunauer, Emmett and Teller
(BET) surface area analysis, transmission electron microscopy
(TEM), field emission scanning electron microscopy (FE-SEM),
energy-dispersive X-ray (EDX), thermogravimetric analysis (TGA),
hydrogen temperature-programmed reduction (H2-TPR), vibrating
sample magnetometer (VSM), inductively coupled plasma optical
emission spectroscopy (ICP-OES) and elemental analysis (CHN).
Fourier transform infrared (FT-IR) spectroscopy evidences the
modification of Fe3O4@Boehmite NPs surface. Fig. 1 demonstrates
the FT-IR spectra of Boehmite NPs (a), Fe3O4@Boehmite NPs (b),
Fe3O4@Boehmite-Pr-Cl
(c),
Fe3O4@Boehmite-NH2
(d),
Fe3O4@Boehmite-NH2-CoII NPs (e) and 7th reused Fe3O4@Boehmite-
NH2-CoII NPs (f). As shown in Fig. 1a, two strong absorption bands at
3294 and 3095 cm-1 correspond to both asymmetric and symmetric
vibrational modes of the O-H bonds of Boehmite NPs. Three
distinctive bands at 752, 630 and 522 cm-1 were attributed to Al-O
vibrations. Existence of hydrogen bonded hydroxyl groups (OH…OH)
was confirmed by the appearance of two absorption bands at 1154
2 | J. Name., 2012, 00, 1-3
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on IUPAC classification) which is the characteristic of mesoporous
materials. The specific surface area, pore volume and mean pore
diameter of Boehmite NPs (a), Fe3O4@Boehmite NPs (b) and
Fe3O4@Boehmite-NH2-CoII NPs (c) were shown in Table 1. Based on
the Brunauer–Emmett–Teller (BET) analysis the average surface
area of Boehmite NPs, Fe3O4@Boehmite NPs and Fe3O4@Boehmite-
NH2-CoII NPs were 20, 46 and 34 m2 g-1, respectively. It is interesting
to note that the low surface area of Boehmite NPs was attributed to
the effect of NaOH:Al(NO3)3.9H2O molar ratio and pH during the
synthetic process [52, 53]. As can be concluded from Table1, the
increased in the BET surface area and decreased in the pore volume
of Fe3O4@Boehmite NPs confirmed the entrance of Fe3O4 NPs into
the Boehmite NPs pores. Likewise, owing to blocking of some pores
by organic linkers upon functionalization process, the surface area
of Fe3O4@Boehmite-NH2-CoII NPs was decreased. Also, the mean
pore diameter and pore volume of Fe3O4@Boehmite NPs were
increased after modification process, according to the data
summarized in Table 1. These results clearly verify the well grafting
of organic segments on the surface of Boehmite NPs (Fig. S2 and
Table 1, Supplementary Material, page 4).
a
630
522
1069
500
752
3095
3294
1154
1292
450
400
350
300
250
200
150
100
50
b
571
c
d
1074
1637
1447
2492
e
f
1638
3555
0
3500
3000
2500
2000
1500
1000
500
-
1
Wave numbers (cm )
Fig. 1. FT-IR spectra of Boehmite NPs (a), Fe3O4@Boehmite NPs (b),
Fe3O4@Boehmite-Pr-Cl
(c),
Fe3O4@Boehmite-NH2
(d),
Fe3O4@Boehmite-NH2-CoII NPs (e) and 7th reused Fe3O4@Boehmite-
NH2 -CoII NPs (f).
The size and morphology of the fresh Fe3O4@Boehmite-NH2-CoII
NPs and 7th recovered Fe3O4@Boehmite-NH2-CoII NPs were studied
by TEM technique. Typical TEM images and particle size
distributions of core-shell Fe3O4@Boehmite-NH2-CoII NPs are shown
in Figure S3 and S4. It was easily observed in Figure S3a, that the
Fe3O4 NPs core is well encapsulated by a Boehmite NPs coating and
a clear boundary between the Boehmite NPs shell and the Fe3O4
NPs core is observed in the egg-like nanostructure. As shown in
Figure S3 (a and b) and Figure S4, the particle sizes of
Fe3O4@Boehmite-NH2-CoII NPs in irregular geometric shape were
about 13-54 nm (Fig. S3 and S4, Supplementary Material, page 5) .
The crystallographic structures of Boehmite NPs (Fig. S1a),
Fe3O4@Boehmite NPs (Fig. S1b) and Fe3O4@Boehmite-NH2-CoII NPs
(Fig. S1c) were investigated by XRD technique. As shown in Fig. S1a,
the Boehmite NPs phase was identified by the peak positions at 2θ
= 14.64˚ (0 2 0), 28.36˚ (1 2 0), 38.50˚ (0 3 1), 46.01˚ (1 3 1), 49.41˚ (0
5 1), 51.79˚ (2 0 0), 55.41˚ (1 5 1), 60.76˚ (0 8 0), 64.15˚ (2 3 1), 65.14˚
(0 0 2), 67.86˚ (1 7 1), and 72.07˚ (2 5 1) which can be confirmed the
crystallization of Boehmite NPs with an orthorhombic unit cell (Ref.
Code: 98-004-6842). In Fig. S1b, the appearance of the
characteristic peaks at 2θ = 30.27˚ (2 2 0), 35.74˚ (3 1 1), 43.27˚ (4 0
0), 53.78˚ (4 2 2), 57.29˚ (5 1 1) and 62.87˚ (4 4 0) are imputed to the
cubic structure of Fe3O4 MNPs (Ref. Code: 98-007-7842). Similarly
(in Fig. S1c), the crystalline peaks occurring at 2θ = 14.87˚ (0 2 0),
28.61˚ (1 2 0), 38.76˚ (0 3 1), 45.95˚ (1 3 1), 49.37˚ (0 5 1), 51.99˚ (2 0
0), 72.37˚ (2 5 1) and 2θ = 30.6˚ (2 2 0), 35.97˚ (3 1 1), 57.57˚ (5 1 1)
The size and morphology of Fe3O4@Boehmite-NH2-CoII NPs was also
studied by field emission scanning electron microscopy (FE-SEM)
technique. As can be seen in Fig. S5, the synthesized nanocatalyst
showed good dispersity with an average size about 20-30 nm which
is very close to the particle size as determined using TEM and XRD
analysis (Fig. S5, Supplementary Material, page 6).
are associated to the Boehmite NPs (Ref. Code: 98-000-6538) and To survey the type of elements in Fe3O4@Boehmite-NH2-CoII NPs,
Fe3O4 NPs (Ref. Code: 98-001-7260), respectively [35, 39, 49, 50]. the energy-dispersive X-ray (EDX) spectrum was taken and shown in
The intensity of all peaks was decreased due to the chemical Fig S6. The composition of as-synthesized catalyst
modifications. In comparison, the crystallinity value of the (Fe3O4@Boehmite-NH2-CoII NPs) was confirmed by the presence of
Fe3O4@Boehmite NPs and Fe3O4@Boehmite-NH2-CoII NPs was O, Fe, Co, Al and Cl in the EDX spectrum (Fig. S6, Supplementary
diminished because of deformation of hydrogen bonding in Material, page 6).
Boehmite NPs upon chemical modifications. Moreover, the X-ray
The thermogravimetric analysis (TGA) was used to determine the
diagram of the Fe3O4@Boehmite-NH2-CoII NPs showed four new
thermal stability and the amount of organic moieties on the surface
peaks at 2θ = 16.53˚ (1 1 0), 32.14˚ (2 2 0), 54.09˚ (1 4 1) and 63.16˚
of Fe3O4@Boehmite NPs. The TGA thermograms of
(5 0 3) which can be attributed to CoII species (Fig. S1c) [51].
Fe3O4@Boehmite
NPs
(a),
Fe3O4@Boehmite-Pr-Cl
(b),
Besides, the average crystalline size of Fe3O4@Boehmite-NH2-CoII
NPs which was calculated using Debye–Scherrer equation (d =
Kλ/(βcosθ)) is estimated to be 33 nm (Fig. S1, Supplementary
Material, page 3) .
Fe3O4@Boehmite-NH2-CoII NPs (c) and 7th reused Fe3O4@Boehmite-
NH2 -CoII NPs (d) were shown in Fig. S7. As can be observed in Fig.
S7a, the negligible weight loss (0.46%) from 20 to 100 ˚C was
attributed to the removal of adsorbed and interstitial water [38].
The nitrogen adsorption-desorption isotherm of Boehmite NPs (a), Also, the observed weight loss (8.54%) at 410 to 600 ˚C corresponds
Fe3O4@Boehmite NPs (b) and Fe3O4@Boehmite-NH2-CoII NPs (c) are to the transformation of γ- AlOOH into γ-Al2O3 [52]. The well
depicted in Fig. S2. As can be seen in Fig. S2, the appearance of H3- crossbred
of
the
organic
spacer
groups
((3-
type hysteresis loops can be identified as type IV isotherm (based choloropropyl)triethoxysilane) on the surface of Fe3O4@Boehmite
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Fe3O4@Boehmite-NH2-CoII NPs
NPs were confirmed by the appearance of a new weight loss (9%)
˚
X
B(OH)2
from 120 to 250 C (Fig. S7b). In the profile of Fe3O4@Boehmite-
KOH, H2O, 80 ºC
R
R
NH2-CoII NPs, the TGA thermogram (Fig. S7c) depicted two-step
thermal decomposition. The first step of weight loss (9 %) from 120
to 250 ˚C was caused by the disintegration of the grafted (3-
choloropropyl)triethoxysilane. The second weight loss (24 %) from
R= H, 4-Cl, 4-NO2, 4-Me, 4-OMe, 2Me-4-NO2, 2-Thienyl, 3-CHO, 4-CHO,
4-CN, 4-NH2, 2-NH2
X= I, Br, Cl
˚
250 to 600 C is ascribed to the transformation of γ-AlOOH into γ-
Al2O3 and also decomposition of the grafted triethylenetetramine. A
good agreement was observed between the elemental analysis and Scheme 2. Suzuki–Miyaura cross coupling reaction in the presence
TGA data, according to the results summarized in Table 2 (Table 2, of Fe3O4@Boehmite-NH2-CoII NPs.
Supplementary Material, page 7). These results clearly corroborated
In our first set of experiments, a DMF solution of 4-iodobenzene
that organic functional groups incorporated on the surface of
(1mmol) was allowed to react with phenylboronic acid (1.2 mmol)
in the presence of 0.33 mol% of Fe3O4@Boehmite-NH2-CoII NPs and
Fe3O4@Boehmite NPs(Fig. S7, Supplementary Material, page 7) .
˚
H2-TPR was used to investigate the type of Co species on the 2 equivalents of K2CO3. Warming the reaction mixture to 100 C,
surface of Fe3O4@Boehmite NPs. The TPR curves of afforded the cross-coupling product with 65% yield after 60 min
Fe3O4@Boehmite-NH2-CoII NPs (a) and 7th reused Fe3O4@Boehmite- (Table 3, entry 1). To access the best optimal catalyst conditions,
NH2-CoII NPs (b) were shown in Fig. S8. Two distinct reduction peaks the effect of various solvents on the model reaction was
˚
were recognized. The first observed peak centered at 550 C can be investigated in-depth (Table 3, entries 2-10). The results of these
attributed to the reduction of immobilized CoII to the metallic experiments reveal that among the different solvents screened
cobalt [54]. The second-step reduction peak may be assigned to the (DMSO, PEG, THF, n-hexane, toluene, 1,4-dioxane, CH3CN, EtOH and
adsorbed cobalt species on the surface of Fe3O4@Boehmite NPs. H2O), H2O can be used as a green, inexpensive and efficient solvent
Formation of cobalt aluminate due to strong interaction between for the Suzuki–Miyaura cross coupling reaction. The results of Table
CoII and AlIII ions caused the reduction of surface CoII at higher 3 confirmed that a basic environment was also crucial to the
temperature (710 ˚C) [55, 56] (Fig. S8, Supplementary Material, Suzuki–Miyaura cross coupling reaction (Table 3, entry 11). Several
page 8).
common bases were tested for the Suzuki–Miyaura cross coupling
reaction in the presence of Fe3O4@Boehmite-NH2-CoII NPs (Table 3,
entries 12-15). KOH afforded higher yield than the other bases.
Then it was selected as the base for the subsequent experiments of
the Suzuki–Miyaura cross coupling reaction. Not surprisingly, the
results depended on the amount of the base used. After a few
attempts, it was found that 3 equivalents of KOH were required to
obtain the best yield of the corresponding product in short reaction
time (Table 3, entries 15-17). It was found that temperature has an
essential effect in this catalytic system, when the model reaction
was carried out at different temperatures. As can be seen in Table
3, the most suitable temperature for Suzuki–Miyaura cross coupling
reaction in the presence of Fe3O4@Boehmite-NH2-CoII NPs was 80 ˚C
(Table 3, entries 18-21). Afterwards, the catalyst loading was also
optimized by performing the model reaction in the presence of
different amounts of catalyst. Higher yield of the desired product in
short reaction time was afforded by employing 0.33 mol% of
nanocatalyst. A significant decrease in the yield of reaction was
observed by applying 0.22 mol% of catalyst, whereas additional
amounts of catalyst (0.44 mol%) was not effective on the yield and
rate of reaction significantly (Table 3, entries 22-23). To clarify the
especial catalytic activity of Fe3O4@Boehmite-NH2-CoII NPs in
Suzuki–Miyaura cross coupling reaction, in a set of experiments the
model reaction was carried out in the absence of any catalyst and
also in the presence of Fe3O4 NPs, Fe3O4@Boehmite NPs,
Fe3O4@Boehmite-Pr-Cl, Fe3O4@Boehmite-NH2 and CoCl2.6H2O
respectively (Table 3, entries 24-29). All of cases were relatively
insufficient for the coupling of 4-iodobenzene with phenylboronic
acid as a benchmark reaction with observed conversion yields of
20%, 20%, 5%, 5%, 5% and 40% after 24 h, respectively (Table 3,
Supplementary Material, page 9).
Magnetic
properties
of
Fe3O4@Boehmite
NPs
and
Fe3O4@Boehmite-NH2-CoII NPs were investigated by a vibrating
sample magnetometer (VSM). As illustrated in Fig. S9, both samples
are superparamagnetic nanoparticles. It can be seen that the
saturation magnetization value of Fe3O4@Boehmite NPs and
Fe3O4@Boehmite-NH2-CoII NPs were 37.52 and 25.1 emu g
-1
,
respectively. Compared with Fe3O4@Boehmite NPs, the saturation
magnetization (MS) intensity of Fe3O4@Boehmite-NH2-CoII NPs was
decreased drastically upon functionalization of Fe3O4@Boehmite
NPs by organic segments. However, this magnetic property was
high enough to provide easy and quick separation of the
nanocatalyst from the reaction mixture with an external magnet
(Fig. S9, Supplementary Material, page 8).
Catalytic performance of the Fe3O4@Boehmite-NH2-CoII NPs for
the Suzuki–Miyaura and Heck–Mizoroki cross coupling reactions
Here, to evaluate the efficiency of the Fe3O4@Boehmite-NH2-CoII
NPs catalyst system, the catalytic property of Fe3O4@Boehmite-
NH2-CoII NPs was investigated in C─C bond formaꢀon via Suzuki–
Miyaura cross coupling reaction (Scheme 2). Initially, the reaction
between 4-iodobenzene and phenylboronic acid was chosen as a
model reaction. To obtain the optimal conditions, the critical
parameters to the outcome of the reaction such as solvent, base,
temperature and catalyst loading were compared. The results of
the optimization of conditions are summarized in Table 3 (Table 3,
Supplementary Material, page 9) .
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The generality of this nanoparticles CoII catalyst was investigated on Scheme 3. Heck–Mizoroki cross coupling reaction in the presence
the substrate scope for Suzuki–Miyaura cross coupling reaction.
of Fe3O4@Boehmite-NH2-CoII NPs
Under the optimized reaction conditions (Table 3, Supplementary
Material, page 9, entry 19), a variety of structurally divergent aryl
iodides, bromides, and chlorides reacted with phenylboronic acid to
generate the desired coupling products (Table 4). The coupling
reactions of aryl iodides and aryl bromides took place in short
period of time with good to high yields whereas aryl chlorides due
to the low reactivity of C–Cl bond cannot produce the satisfactory
yields of coupling products even after prolonged reaction times
(compare entries 1-18 with 19-23). Although aryl bromides required
longer times to afford the same result as aryl iodides (compare
entries 1-9 with 10-18)). This might be due to the leaving group
ability of halogens (I > Br > C l> F). In the present catalytic system,
the electronic and steric effects on the yields and reaction rates
were also studied. This catalytic system showed a good efficiency
with a range of both electron-rich and electron-poor substituted
aryl halides (such as 4-NO2C6H4, 4-ClC6H4, 4-OMeC6H4, 4-MeC6H4, 4-
CNC6H4, 3-CHOC6H4, 4-CHOC6H4, 4-NH2C6H4 and 2-NH2C6H4).
Electron-withdrawing groups accelerated the Suzuki–Miyaura cross
coupling reaction and exhibited better conversions as well, in
comparison with the electron-donating substituents (compare
entries 2,3 with 4,5,8,9 and entries 11, 12, 13 with 16, 17, 18 and 21
with 22, 23). It was observed that the ortho substituted aryl halides
afforded the corresponding products with acceptable yield in longer
reaction time than those obtained with para-substituted ones
reflecting steric effects (Table 4, compare entries 6, 9, 18, 23 with 8,
17, 22).
To test the feasibility of CoII-catalyzed Heck–Mizoroki cross coupling
reaction, 4-iodobenzene (1 mmol) and methyl acrylate (1.2 mmol)
were used as the benchmark substrates. For this purpose, reaction
conditions such as solvent, base, reaction temperature and catalyst
quantity were optimized (Table 5). In surveying of common solvents
(DMF, DMSO, PEG, THF, n-hexane, toluene, 1,4-dioxane, CH3CN,
EtOH and H2O), it was found that only poor yields were obtained
with solvents such as THF, n-hexane, toluene, 1,4-dioxane and
CH3CN while the yield and reaction rate was enhanced in DMF,
DMSO, PEG, EtOH and H2O (Table 5, entries 1-10). Considering
economic and environmental factors H2O was chosen as the best
solvent for the Heck–Mizoroki cross coupling reaction in the
presence of Fe3O4@Boehmite-NH2-CoII NPs. We further turned our
attention to study the effect of base in the Heck–Mizoroki cross
coupling reaction. Our studies revealed that K3PO4 was optimal.
Lower yields were provided with Li2CO3, NaHCO3 and KOH (Table 5,
entries 11-14). As can be seen in Table 5, the role of base is mainly
in the Heck–Mizoroki cross coupling reaction and the desired
product was obtained in highest yield by applying 1/4 molar ratio of
4-iodobenzene
/ K3PO4 (Table 5, entries 15-18). Further
optimization was examined on the effect of temperature and
catalyst loading (Table 5, entries 19-25). The finding suggests that
the yield and reaction rate were enhanced drastically (95% in 45
min) in the presence of 0.44 mol% of Fe3O4@Boehmite-NH2-CoII
NPs at 80 ˚C. To demonstrate the efficiency catalytic activity of
In addition to improving conditions for the Suzuki–Miyaura cross Fe3O4@Boehmite-NH2-CoII NPs in the Heck–Mizoroki cross coupling
coupling reaction, the possibility of performing Heck–Mizoroki cross reaction, the model reaction was performed without using catalyst.
coupling reaction in the presence of Fe3O4@Boehmite-NH2-CoII NPs After long period of time, poor yield of product was gained as well
was strategically explored (Scheme 3).
as in the presence of Fe3O NPs, Fe3O4@Boehmite NPs,
Fe3O4@Boehmite-Pr-Cl, Fe3O4@Boehmite-NH2 and CoCl2.6H2O
respectively (Table 5, entries 26-30) (Table 5, Supplementary
Material, page 11) .
Table 4. Suzuki–Miyaura cross-coupling reactions of different aryl halides with phenylboronic acid catalyzed
by Fe3O4@Boehmite-NH2-CoII NPs.
Entry
1
R
X
I
Product
Time (min)
Isolated Yield
(%)
H
30
95
95
1a
1b
2
4-NO2
I
25
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Journal Name
3
4
5
4-Cl
4-OMe
4-Me
I
25
70
65
93
93
95
1c
I
1d
I
1e
6
7
2-Me-4-NO2
I
50
90
1f
2- Thienyl
I
90
85
1g
8
9
4-NH2
I
2 (h)
98
60
1h
2-NH2
I
3 (h)
1i
10
11
12
13
14
H
Br
35
40
40
35
75
95
95
90
93
95
1a
4-NO2
4-Cl
Br
1b
Br
1c
4-CN
4-CHO
Br
1j
Br
1k
15
3-CHO
Br
90
95
1l
16
17
4-OMe
4-NH2
Br
160
85
90
1d
Br
3 (h)
1h
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18
2-NH2
Br
4 (h)
50
1i
19
20
21
22
H
Cl
3 (h)
4 (h)
2 (h)
7 (h)
45
50
65
20
1a
4-CHO
4-CN
4-NH2
Cl
1k
Cl
1j
Cl
1h
23
2-NH2
Cl
9 (h)
15
1i
Subsequently, to explore the scope and generality of the present expected the reactivity of C-halogen bond have influence that
method in the Heck–Mizoroki cross coupling reaction, the interfere with the reaction, the coupling reaction appears sluggish
optimized reaction conditions were applied for the reaction of a with aryl bromides, gives lower yield under optimized conditions
wide variety of aryl halides including electron-donating and (compare entries 1-8 with entries 9-15). The present strategy can be
electron-withdrawing groups on the aromatic ring with various further extended to the coupling reaction of aryl chlorides with
olefins. The results of this study are summarized in Table 6. By methyl acrylate
/ or n-butyl acrylate under similar catalytic
analyzing Table 6, it was found that all reactions of different conditions. Table 6 obviously reveals that the Heck–Mizoroki cross
substituted aryl iodides with methyl acrylate / or n-butyl acrylate coupling reaction of aryl chloride in the presence of
generated products with yields considered high in short reaction Fe3O4@Boehmite-NH2-CoII NPs leads to unusually less product yield
time (Table 6, entries 1-8 and entries 20-25). Notably aryl iodides even after long period of time (Table 6, entries 16-19 and entries
with electron-withdrawing substituents react with olefins more 29-32).
quickly than those with electron-donating substituents. But as
Table 6. Heck–Mizoroki cross cross-coupling reactions of different aryl halides with olefins catalyzed by Fe3O4 @
Boehmite-NH2-CoII NPs.
Entry
1
R1
H
R2
X
I
Product
Time (min)
Isolated
Yield (%)
Me
45
95
2a
2
4-NO2
Me
I
25
95
2b
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Journal Name
3
4
5
6
7
4-Cl
4-OMe
4-Me
Me
Me
Me
Me
Me
I
35
60
92
80
85
98
25
2c
I
2d
I
55
2e
4-NH2
I
2 (h)
2f
2-NH2
3 (h)
I
2g
8
2-Thienyl
Me
I
85
75
2h
9
H
Me
Me
Br
100
85
90
2a
10
4-NO2
Br
90
2b
11
12
13
4-Cl
Me
Me
Me
Br
90
70
87
90
75
2c
4-CN
Br
2i
4-OMe
Br
3 (h)
2d
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14
4-NH2
Me
Br
4 (h)
70
2f
15
16
17
2-NH2
Me
Me
Me
Br
5 (h)
4 (h)
3 (h)
40
25
40
2g
H
Cl
2a
4-CN
Cl
2i
18
4-NH2
Me
Cl
6 (h)
25
2f
19
20
21
2-NH2
Me
Bun
Bun
Cl
7 (h)
15
95
95
2g
H
I
30
2j
4-NO2
I
30
2k
22
23
24
4-Cl
4-OMe
4-Me
Bun
Bun
Bun
I
30
40
40
90
85
88
2l
I
2m
O
Bun
O
I
Me
2n
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25
2-Thienyl
Bun
I
70
80
2o
26
27
H
Bun
Br
95
95
85
85
2j
4-NO2
Bun
Br
2k
28
29
4-OMe
Bun
Br
2 (h)
77
30
2m
H
Bun
Cl
3 (h)
2j
30
31
4-CN
Bun
Cl
3 (h)
5 (h)
35
30
2p
4-CHO
Bun
Cl
2q
32
4-NH2
Bun
Cl
7 (h)
15
2r
All of the synthesized compounds were known and isolated as oil or instance methyl 3-(4-chlorophenyl) acrylate (Fig. S10,
solid products. The obtained products were characterized by Supplementary Material, page 13), the coupling constant (J) of Ha
comparing their melting points with those reported in the and H was estimated to be ~ 18 Hz, which is the characteristic of
b
literature. Molecular ion peaks of all prepared products exhibited trans isomers.
their respective m/e, according to the mass spectrometric data. In In analogy with the previous reports [57-59] and based on our
addition, the structure of the selected compounds was further findings a plausible mechanism for the Suzuki–Miyaura and Heck–
1
investigated by surveying their high-field H NMR, 13C NMR and FT- Mizoroki cross coupling reactions is proposed in scheme 4. At the
IR spectral data. The disappearance of starting materials confirmed begining, the reaction was thought to be initiated by an in situ
the completion of the reaction which was monitored by TLC.
reduction of CoII complexes to CoI or 0 species (I) in the presence of
Based on the 1HNMR spectral data (Fig. 1-22, Supplementary KOH/ K3PO4 [60] (To probe whether CoI or 0 species fulfilled the cross
Material, page 15-55), Fe3O4@Boehmite-NH2-CoII NPs catalyzed the coupling reactions, we performed the model reactions in the
Heck–Mizoroki cross coupling reaction in a stereospecific manner presence of CoBr and Co(0). The coupling products were produced
and in all of the reactions E-isomers were produced predominately. with satisfactory yields in the presence of CoBr whereas under the
By considering the 1H NMR spectrum of product in details for same reaction conditions, no significant yields were observed in the
10 | J. Name., 2012, 00, 1-3
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presence of Co(0). This finding suggests that the reactions proceeds new olefin and hydridocobalt (VI) was produced. Finally, a reductive
via the formation of the active CoI species). elimination regenerated the active CoI species (I) in the presence of
Then, upon the oxidative addition of aryl halide to low valent CoI, K3PO4. Subsequent aerobic oxidation furnished CoII complexes [61].
aryl cobalt intermediate (II) was afforded. In the following step,
transmetalation of (II) with arylbronic acid in the presence of KOH
afforded Ar-Co (III)-Ar' intermediate (III). Finally, reductive
elimination produced the biaryl product and regenerated the CoI
species (I). Completion of the catalytic cycle for the Suzuki–Miyaura
cross coupling reaction was achieved by aerobic oxidation of the CoI
species (I) to the CoII complexes [61].
In our working suggestion for the Heck–Mizoroki cross coupling
reaction, it was expected that low valent CoI species (I) can be
added to an olefin to afford adduct (IV) via the formation of
(III')(upon olefin coordination). Following β-hydride elimination, a
transmetallation
Ar'-B(OH)2
KOH
H3BO3
KX
Ar
Ar
Co III
Co III
Ar'
X
(II)
(III)
Suzuki-Miyaura
reductive elimination
oxidative addition
Ar-X
Ar-Ar'
Base
[CoI]
(I)
aerobic oxidation
CoII
CoII
Ar-X
K2HPO4
KX
[CoI]
(I)
oxidative addition
reductive elimination
K3PO4
H
Ar
Co III
X
(VI)
R'
(II)
X
O
O
R'
O
Ar
Heck-Mizoroki
O
O
R'
X
Co III
H
O
O
Ar
R'
Ar
X
O
(III)'
(V)
X
Co III
O
Ar
R'
-hydride elimination
migratory insertion
O
H
(IV)
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Scheme. 4. Proposed mechanism for the Suzuki–Miyaura and Heck–Mizoroki cross coupling reactions in the presence of Fe3O4@Boehmite-
NH2-CoII NPs.
From the green chemistry viewpoint, reusability is one of the most The TEM images of the 7th recovered Fe3O4@Boehmite-NH2-CoII NPs
important properties of metal catalysis that should be studied. In were shown in Fig. S3 (c and d) (Fig. S3, Supplementary Material,
this regard, the reusability of Fe3O4@Boehmite-NH2-CoII NPs was page 5). Interestingly, no agglomeration or increase in the particle
studied by consecutive the Heck–Mizoroki cross coupling reaction size was observed even after 7 consecutive recycle runs.
of 4-iodobenzene with methyl acrylate under the optimized
Furthermore, by comparing the TGA thermogram of the fresh
Fe3O4@Boehmite-NH2-CoII NPs with the 7th recovered nanocatalyst,
reaction conditions. After the first catalytic cycle, the nanocatalyst
was easily separated by means of an external magnetic field from
it could be concluded that no significant differences were observed
the reaction mixture, washed with ethanol and acetone (3 × 5 mL)
in the decomposition pattern (compare Fig. S7c with S7d,
and dried at 50 ˚C overnight. Then a new coupling reaction of fresh
Supplementary Material, page 7). However, the weight loss of the
reactants was started using the recovered catalyst. The catalyst was
grafted organic motif was decreased from 33% (in the fresh
nanocatalyst) to 32% in the 7th recycled nanocatalyst. Accordingly,
stable and reusable for up to 7 runs during the catalytic reaction as
it afforded almost identical results in each cycle and slightly
the amount of the grafted (3-choloropropyl)triethoxysilane was
decreased from 1.16 to 1.03 mmol g -1 after 7 cycles, which might
decrease in the yields was observed in 6th and 7th cycles (Table 7).
The turn over frequency (TOF) and turn over number (TON) of the
be ascribed to the diminutive leaching of organic segments during
catalyst were also calculated and the results are shown in Table 7.
recycling process.
As can be seen the supreme catalytic activity of Fe3O4@Boehmite-
As can be inferred from H2-TPR of the 7th recovered
NH2-CoII NPs was not significantly decrease even after 7 recycle
Fe3O4@Boehmite-NH2-CoII NPs (Fig. S8b, Supplementary Material,
runs.
page 8), the oxidation state of Co was not changed even after 7
Table 7. Reusability of Fe3O4@Boehmite-NH2-CoII NPs in the Heck–
recycle runs.
Mizoroki reaction of 4-iodobenzene with methyl acrylate under the
In order to quantitative analysis and realize the exact amount of
cobalt in the fresh and reused Fe3O4@Boehmite-NH2-CoII NPs, ICP-
optimized reaction conditions.
OES technique has been applied in the model Heck–Mizoroki cross
coupling reaction. The ICP-OES analysis showed that 1.1 and 1.04
mmol of cobalt were anchored on 1.000 g of the fresh and 7th
reused nanocatalyst, respectively. According to the obtained data,
no significant leaching of cobalt from the surface of
Fe3O4@Boehmite-NH2-CoII NPs was observed.
Time
(min)
Entry
Isolated Yield (%)
TOF (h-1
)
TON
1
2
45
95
2.87
2.87
2.87
2.15
2.15
45
95
3
45
95
2.15
The obtained results from FT-IR, XRD, TEM, TGA and H2-TPR
undoubtedly confirmed that the physical properties of
Fe3O4@Boehmite-NH2-CoII NPs including functional groups,
crystallographic structure, shape, morphology, particle size, thermal
stability and oxidation sate were preserved in the reaction media
even after 7 recycle runs.
4a
5a
6a
7a
45/50
45/53
45/55
45/60
91/95
90/95
88/95
85/95
2.74/2.58
2.72/2.43
2.66/2.34
2.57/2.15
2.06/2.15
2.04/2.15
2/2.15
1.93/2.15
Heterogeneity studies
a The second numbers in the second columns correspond to the isolated yield after 50,
53, 55 and 60 min.
In the present study, to investigate the homogeneity/heterogeneity
nature of the catalyst, we introduced the hot filtration test, kinetic
study and three-phase test. In the following, all of them were
discussed in details.
To elucidate the long-term durability of the catalyst as an important
issue, after seven cycles in the Heck–Mizoroki cross coupling
reaction, any structural changes of Fe3O4@Boehmite-NH2-CoII NPs
was investigated by FT-IR, XRD, TEM, TGA, H2-TPR and ICP-OES
techniques. It is clearly evident from the FT-IR spectrum of the 7th
reused Fe3O4@Boehmite-NH2-CoII NPs that the metallic ions were
strongly bounded to the surface of Fe3O4@Boehmite NPs through
the coordination of the organic segments and also, no important
changes in the frequencies, intensities and shapes of absorption
bands were observed (Fig.1f).
Hot filtration test
A
hot filtration test was performed to find out whether
Fe3O4@Boehmite-NH2-CoII NPs acts as a heterogeneous catalyst or
solely serves as a CoII ion source by leaching out into the solution to
form the active catalyst species. Toward this point, the Suzuki–
Miyaura and Heck-Mizoroki cross coupling reactions were studied
under the optimal conditions. In half time of the Suzuki–Miyaura
/and Heck-Mizoroki cross coupling reaction of 4-iodobenzene with
phenylboronic acid/ and methyl acrylate, the catalyst was
separated using an external magnetic field and the reaction was
then permitted to continue without catalyst for further 2/ and 3 h.
The reaction progress was followed by thin layer chromatography.
Interestingly, comparing the XRD pattern of fresh and 7th reused
Fe3O4@Boehmite-NH2-CoII NPs exhibited that no significant
broadening or shifting was happened in the characteristic
diffraction peaks (Fig. S1d, Supplementary Material, page 3).
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There was no further coupling reaction, even after an extended To gain insight into the nature of the nanocatalyst, a three-phase
time, indicated that a negligible amount of active species (less than test was designed. Three-phase test is a powerful technique that
0.31 mol% according to the ICP-OES analysis) leached out during allows the catalyst to be in its nature habitat. To conduct the test,
the catalytic reaction. The results established the strong attachment the model Heck-Mizoroki cross coupling reaction was carried out in
of cobalt nanoparticles to the Fe3O4@Boehmite NPs surface. It is the absence and in the presence of Boehmite-NH2 NPs (Scheme 5)
worth to mention that although a positive hot-filtration test as a strong scavenger to capture the homogeneous soluble cobalt
highlights the homogeneity of the catalyst, but a negative test does ions. The reaction progress was monitored by GC. The results are
not allude to the heterogeneous nature of the catalyst due to the depicted in Fig. S12. As it is evident in Fig. S12b, the presence of
quickly re-deposition of soluble active species. Therefore, to assess scavenger has no effect on the yield of the reaction. According to
the homogeneity/heterogeneity of the catalyst further experiments the above observation, it could be concluded that there is no
are required [50].
soluble cobalt ions in solution and the reaction arguably proceeds in
heterogeneous pathway. All of the results obtained from
heterogeneity tests confirmed that the Fe3O4@Boehmite-NH2-CoII
NPs had a high catalytic activity with a truly stable heterogeneous
nature under the described reaction conditions (Fig. S12,
Supplementary Material, page 14).
a
Kinetic study
In order to further explore the possibility of the heterogeneous
nature of Fe3O4@Boehmite-NH2-CoII NPs, a kinetic study was
performed. To this end, two different parameters (reaction yield
and cobalt leaching) were investigated on the model Heck-Mizoroki
cross coupling reaction under the optimized reaction condition. To
determine the cobalt concentration in solution, 4 samples of the
reaction mixture were taken during the reaction. In each case, the
samples were analyzed by ICP-OES as well as the yield of the
reaction was monitored by GC. The results were described in Fig.
S11. No obvious leaching was observed, according to the ICP-OES Scheme 5. Boehmite-NH2 NPs.
data (Fig. S11b). In the other word, the cobalt concentration in
To attain further evaluation of the efficiency of Fe3O4@Boehmite-
NH2-CoII NPs, we compared the catalytic activity of the catalyst with
some of the previously reported heterogeneous (Ni, Fe and Co)
catalysts in the Heck–Mizoroki cross coupling reaction (Table 8).
Although all of the listed catalysts can produce the desired product
in good to excellent yield, but it can be clearly found that
Fe3O4@Boehmite-NH2-CoII NPs is superior to most of the well-
known supported catalyst systems in terms of reaction conditions
(solvent (entries 1-9), temperature (entries 1-5 and entries 7 and 9),
reaction time (entries 1-7 and 9), recovery and reusability (entries
1-7 and 9) as well as price and toxicity.
solution is presumably very small (0.000084, 0.000088, 0.000096
and 0.000096 mol % after 15, 30, 45 and 60 min, respectively). It
could be found that a negligible amount of cobalt in solution had
not a considerable effect on the reaction progress and a notable
increase in the reaction yield could be attributed to the
heterogenous cobalt species. According to the obtained results, the
conclusion could be derived that the heterogenous cobalt species
are the catalyst promoter in this reaction (Fig. S11, Supplementary
Material, page 13).
Three-phase test
Table 8. Comparison of the catalytic activity of Fe3O4@Boehmite-NH2-CoII NPs with literature precedents using Ni, Fe and Co based
heterogeneous catalysts for the Heck–Mizoroki cross coupling reaction.
Entry
Catalyst
Ni(II)–DABCO@SiO2
SiO2-Fe(acac)
Solvent
DMF
PEG
Temperature (˚C)
Time (h)
Yield (%)
97
Reference
1
2
100
130
130
140
150
80
3
10
1.5
85
15
3
Co hollow nanospheres
Nano Co
NMP
NMP
NMP
PEG
16
73
24
4
16
85
25
5
Co/Al2O3
24
56
28
6
Co–NHC@MWCNTsa
Co-IL@MWCNTsb
Co-MS@MNPs/CSc
Nano Co
5
85
27
7
Toluene
PEG
100
80
3
87
26
8
1
8
88
62
63
9
NMP
H2O
120
80
90
10
Fe3O4@Boehmite-NH2-CoII NPs
45 (min)
95
Present study
a Multi walled carbon nanotubes supported N-heterocyclic carbene–cobalt (ΙΙ).
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b Cobalt nanoparticles supported on ionic liquid-functionalized multiwall carbon nanotubes.
c
Cobalt immobilized on MNPs-chitosan functionalized with methyl salicylate (Co-MS@MNPs/CS).
programmed reduction (H2-TPR) was carried out using
a
Quantachrome ChemBET 3000. The magnetic property of catalyst
was measured using a vibrating sample magnetometer (VSM,
Magnetic Danesh Pajoh Inst). Inductively coupled plasma optical
Conclusion
In the present study Fe3O4@Boehmite-NH2-CoII NPs was
synthesized and characterized as an environmentally-friendly
nanocatalyst for the Suzuki–Miyaura and Heck–Mizoroki cross
coupling reactions with various electronically diverse substrates.
The experimental results displayed the core-shell structure of the
synthesized catalyst with a mean size range of 13-54 nm. Owing to
emission spectroscopy (ICP-OES) was carried out on
a
76004555 SPECTRO ARCOS ICP-OES analyzer. All yields refer to
isolated products after purification by thin layer chromatography/
or column chromatography .
Preparation of the Boehmite NPs (I)
the
cooperative
interaction
of
the
four
dentate
triethylenetetramine anchored on aminated Fe3O4@Boehmite, the To a solutions of NaOH (162 mmol, 6.490 g) in 50 mL distilled
nanocatalyst presented high cobalt content with negligible metal water, a solution of Al(NO3)3·9H2O (53 mmol, 20 g) in distilled
leaching during the course of reaction. Subsequently, high yields in water (30 mL) was added drop wise by the rate of 2.94 mL/min
short reaction times were achieved without the need for an under vigorous stirring. After 18 min the resulting milky mixture
˚
expensive palladium catalyst as well as excellent reusability for at was subjected to mixing in ultrasonic bath for 3 h at 25 C. The
least seven times in the corresponding reaction without a reduction obtained Boehmite NPs (I) was filtered and washed by distilled
in catalytic activity. Notably, the superior catalytic activity of using water and was kept in the oven at 220 ˚C for 4 h [64].
Fe3O4@Boehmite-NH2-CoII NPs in C-C bond formation was
Preparation of Fe3O4@Boehmite NPs (II)
characterized by using a chemically stable and magnetic recyclable
Boehmite NPs (I) (2 g) was dispersed in 100 mL of deionized water
nanocatalyst (which can replace Pd ,Ni and Fe complexes for the
for 30 min. Then, FeCl3.6H2O (11.5 mmol, 3.1 g) and FeSO4.7H2O
Suzuki–Miyaura and Heck–Mizoroki cross coupling reactions), using
(7.5 mmol, 2.1 g) were added to the white suspension. The resulting
a benign solvent system without the need for any special conditions
mixture was mechanically stirred for 3 min at room temperature
and minimal Co usage. The use of this new catalyst in organic
under Ar atmosphere. Afterwards, 50 mL NaOH (5%) was added
synthesis will be extended in our laboratory.
very slowly into the mixture under vigorous stirring. The resulting
˚
Experimental
black mixture was continuously stirred for 2 h at 90 C under Ar
General
atmosphere. Finally, the mixture was permitted to cool to room
temperature and then Fe3O4@Boehmite NPs (II) was separated by
an external magnet and washed with deionized water several times
before dried at 50 ˚C overnight.
The purity determinations of the products and the progress of the
reactions were accomplished by TLC on silica gel polygram STL
G/UV 254 plates (preparative TLC was carried out using a Merck GF
254 silica gel on a glass support) or column chromatography on Preparation of Fe3O4@Boehmite-Pr-Cl (III)
silica gel 60 (230-400 mesh) and GC-17A Shimadzu device. The
Fe3O4@Boehmite NPs (II) (1.5 g) was dispersed in dry toluene (50
melting points of products were determined with an Electrothermal
Type 9100 melting point apparatus. The FT-IR spectra were
recorded on an Avatar 370 FT-IR Therma Nicolet spectrometer. The
NMR spectra were provided on Brucker Avance 300, 400 and 500
MHz instruments in CDCl3. Elemental analysis was performed using
a Thermo Finnigan Flash EA 1112 Series instrument. Mass spectra
were recorded with a CH7A Varianmat Bremem instrument at 70 eV
mL) for 30 min. Thereafter, (3-choloropropyl)triethoxysilane (2.5
mmol, 0.6 g) was added to the resulting suspension. The mixture
was refluxed for 28 h. Then, the obtained Fe3O4@Boehmite-Pr-Cl
˚
(III) was filtered, washed with ethanol (5×10 mL) and dried at 50 C
overnight [40].
Preparation of Fe3O4@Boehmite-NH2 (IV)
electron impact ionization, in m/z (rel %). X-ray powder diffraction To a suspension of Fe3O4@Boehmite-Pr-Cl (III) (1 g) in 50 mL
(XRD) was performed on a PANalytical Company X'Pert Pro MPD ethanol, triethylenetetramine (2.5 mmol, 0.365 g) was added at
diffractometer with Cu Ka radiation ((λ = 0.154 nm) radiation. BET room temperature. The resulting mixture was stirred at 80 ˚C for 28
surface area and pore size distribution were measured on a Belsorp h. Then, Fe3O4@Boehmite-NH2 (IV) was filtered, washed with
mini II system at –196° C using N2 as the adsorbate. Transmission ethanol (5×10 mL) and dried at 50 ˚C overnight.
Preparation of Fe3O4@Boehmite-NH2-CoII NPs (V)
electron microscopy (TEM) was performed with a Leo 912 AB (120
kV) microscope (Zeiss, Germany). FE-SEM images were recorded
To a solution of CoCl2·6H2O (4.2 mmol, 0.99 g) in absolute EtOH (5
using a TESCAN, Model: MIRA3 scanning electron microscope
˚
mL), Fe3O4@Boehmite-NH2 (IV) (1 g) was added and stirred at 60 C
operating at an acceleration voltage of 30.0 kV (manufactured
for 18 h. The resulting Fe3O4@Boehmite-NH2-CoII NPs (V) was then
by the Czech Republic). Elemental compositions were determined
filtered, washed with ethanol (3 × 10 mL) to remove the unreacted
materials, and finally dried at 50 ˚C overnight.
with an SC7620 energy-dispersive X-ray analysis (EDX) presenting a
133 eV resolution at 20 kV. Thermogravimetric analyses (TGA and
DTG) were carried out using
a Shimadzu Thermogravimetric Typical procedure for Suzuki–Miyaura cross coupling reaction
Analyzer (TG-50) in the temperature range of 25–950 ˚C at a heating
rate of 10˚C min-1, under air atmosphere. Hydrogen temperature-
Potassium hydroxide (3 mmol, 0.168 g) was added to a mixture of
4-iodobenzene (1.0 mmol, 0.203 g) and phenylboronic acid (1.2
14 | J. Name., 2012, 00, 1-3
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°
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To a mixture of K3PO4 (4 mmol, 0.849 g), methyl acrylate (1.2 mmol,
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The authors gratefully acknowledge the partial support of this study
by Ferdowsi University of Mashhad Research Council (Grant no.
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