Efficient nickel(II) immobilized on EDTA‐modified Fe3O4?SiO2 nanospheres as a novel nanocatalyst for amination of heteroaryl carbamates and sulfamates through the cleavage of C-O bond

Article abstract of DOI:10.1016/j.mcat.2020.110915

In this report, there was immobilized Nickel(II) on EDTA‐modified Fe₃O₄?SiO₂ nanospheres and catalytic activity of which was described in the arylation reaction of nitrogen nucleophiles via carbon-oxygen bond cleavage of (hetero)aryl carbamates and sulfamates. This protocol was applied to various nitrogen nucleophiles such as amines, anilines and N-heterocyclic compounds (pyrroles, indoles and imidazoles) in good to excellent yields. This reaction was promoted without the use of any external ligands under simple and mild conditions. The synthesized catalyst was well characterized by FT‐IR, XRD, TEM, FE-SEM, TGA, DLS,XPS, VSM, EDX, ICP and nitrogen adsorption-desorption isotherm analysis. The recycling studies revealed that the catalyst could be easily recovered by used the external magnetic field and directly reused for at least 7 times without the significant decrease in its catalytic activity.

Full text of DOI:10.1016/j.mcat.2020.110915

MolecularCatalysis492(2020)110915
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Efficient nickel(II) immobilized on EDTA‐modified Fe3O4@SiO2
nanospheres as a novel nanocatalyst for amination of heteroaryl carbamates
and sulfamates through the cleavage of C-O bond
Iman Dindarloo Inalooa,*, Sahar Majnoonib, Hassan Eslahia, Mohsen Esmaeilpoura
a Chemistry Department, College of Science, Shiraz University, Shiraz 71454, Iran
b Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
Magnetic nanoparticle support
Nickel catalyst
N-Arylation
Carbon–oxygen bond cleavage
Carbamates
In this report, there was immobilized Nickel(II) on EDTA‐modified Fe3O4@SiO2 nanospheres and catalytic ac-
tivity of which was described in the arylation reaction of nitrogen nucleophiles via carbon-oxygen bond cleavage
of (hetero)aryl carbamates and sulfamates. This protocol was applied to various nitrogen nucleophiles such as
amines, anilines and N-heterocyclic compounds (pyrroles, indoles and imidazoles) in good to excellent yields.
This reaction was promoted without the use of any external ligands under simple and mild conditions. The
synthesized catalyst was well characterized by FT‐IR, XRD, TEM, FE-SEM, TGA, DLS,XPS, VSM, EDX, ICP and
nitrogen adsorption-desorption isotherm analysis. The recycling studies revealed that the catalyst could be easily
recovered by used the external magnetic field and directly reused for at least 7 times without the significant
decrease in its catalytic activity.
Sulfamates
1. Introduction
attention is the extensive effort for finding suitable and green alter-
natives for aryl halides due to the disadvantages were listed above [14].
Nitrogen–carbon bond formations have become efficient and useful
processes for the preparation of various functionalized natural and ar-
tificial products [1–3]. Due to our growing requirement for the synth-
esis of such classes of compounds that have widespread applications in
pharmaceutical and agricultural industries [1–3], many efforts have
been carried out to provide effective and efficient CeN formation
methodologies for finding new compounds [4–7]. In1983, Toshihiko
Migita reported the synthesis of anilines with cross-coupling of tin
amides and aryl bromides in the presence of palladium for the first time
[8] and then, these catalytic amination reactions of aryl halides (I, Br,
Cl, F) have been attracted many attentions as the most common and
powerful systems for cross-coupling reactions [9,10]. Although these
reactions have been gotten significant advancements over the last
decade, the high cost and toxicity of aryl halides preparation and the
stoichiometric waste of halide generated from these reactions limit
their applications in both academic research and industrial productions,
especially in the drug design process [11,12].
In this regard, phenolic derivatives such as methyl ethers [15–17], pi-
valate esters [18,19], mesylate [20–22], tosylates [23,24], phosphate
[25,26], sulfamates [27–29], carbonates [30–32] and carbamates
[33–35] are the most common groups that have been received con-
siderable attention. Although the phenolic derivatives as electrophiles
are less reactive than aryl halides in the catalytic amination reactions,
the use of these compounds have several extraordinary advantages in-
cluding the wide scope, availability from natural sources and un-
conventional synthetic strategies, high stability and safety [36–41].
In continuous research to find the effective, eco-friendly and simple
methodology, different transition-metals including Cu [42–45], Ni
[46–50], Fe [51,52], Mn [53–55] and Co [56,57] have been in-
vestigated. However, most studies have been focused on copper-based
complexes as catalysts at the beginning of the twenty-first century
[42–45]. Recently, nickel has been widely applied as the catalyst for
designing the new methodology in organic synthesis as a non-toxic
metal with relatively high natural abundance and desirable reactivity
properties [58–63]. In this field, Bolm reported the amination reaction
of tosylates in the presence of Ni catalyst to explore the cross-coupling
reactions of phenolic derivatives [64]. Subsequently, many efforts have
also been devoted towards the finding of the effective approach of CeN
Thus, the designing and development of eco-friendly, facile and
efficient methods for the direct N-arylation reactions through transi-
tion-metal catalyzed approaches were highly desired and beneficial in
recent decades [13]. One of the new strategies that attracted a lot of
⁎ Corresponding author.
E-mail address: iman.dindarlooinaloo@gmail.com (I. Dindarloo Inaloo).
https://doi.org/10.1016/j.mcat.2020.110915
Received 11 December 2019; Received in revised form 17 February 2020; Accepted 22 March 2020
2468-8231/©2020ElsevierB.V.Allrightsreserved.

I. Dindarloo Inaloo, et al.
MolecularCatalysis492(2020)110915
Scheme 1. N-Arylation of nitrogen-containing compounds
with nickel-based catalysis via CeO bond activation of phenol
derivatives.
Scheme 2. Preparation of the Fe3O4@SiO2-EDTA-Ni (II) nanocatalyst.
couplings using the nickel catalysts [65–68]. These studies and in-
vestigations have led us to construct a lot of nickel catalysts to make
these reactions so effective and notably efficient [69–72].
Superparamagnetic Fe3O4 cores at the centre of the initial silica colloids
and the obtained catalysts have recently been received significant at-
tention due to their high stability and efficiency, simple work-up, effi-
cient recovery and good reusability [85–88].
In continuation of our interests in the synthesis and using efficient
superparamagnetic nanocatalysts in various interesting and important
reaction [89–92], we reported the synthesis, characterizations and
employment of nickel(II) nanoparticles immobilized on EDTA‐modified
Fe3O4@SiO2nanospheres (Fe3O4@SiO2-EDTA-Ni(II)) as reusable and
efficient catalyst for the N-arylation of nitrogen-containing compounds
with a library of amines, anilines, indoles and imidazoles via CeO bond
activation of aryl carbamates and sulfamates as phenol derivatives
under mild conditions (Scheme 1).
These reactions have amazing and fantastic results; however, most
of them suffer from some limitations such as using high catalyst
amounts in addition to the presence of some expensive and unrecycl-
able external ligands including N-heterocyclic carbine or phosphine
ligands. As a result, the development of novel and effective Ni-based
CeN bond formation methods is of great importance [65–72]. On the
other hand, the synthesis of the economical catalytic system that can be
easily recovered and reused several times without losing efficiency has
been intensively investigated over the last years due to environmental
and conservation points of view [73–76]. Magnetic separation is a
green and eco-friendly process to recover magnetic heterogeneous
catalysts without filtering or centrifuging [77–79]. Therefore, the pre-
paration of recoverable magnetic catalysts bearing magnetic materials
has been widely investigated [80–82]. Among all magnetic materials,
iron oxides are usually being applied as the popular magnetically ma-
terial because of their special properties such as non-toxicity, low-cost
preparation, amenable to functionalization and easy to handle [83,84].
2. Materials and methods
2.1. Chemicals and instrumentation
All chemicals were purchased from the Flucka, Merck and Aldrich
Chemical Companies with high purity. The products were characterized
2

I. Dindarloo Inaloo, et al.
MolecularCatalysis492(2020)110915
Fig. 2. XRD diffraction pattern of (a) Fe3O4, (b) Fe3O4@SiO2 and (c) Fe3O4@
SiO2-EDTA-Ni(II) NPs.
2.2. Materials synthesis
2.2.1. Preparation of Fe3O4 NPs
Considering the reported method [89–92], 0.9 g of FeCl2⋅4H2O
4.5 mmol), 1.3 g of FeCl3⋅6H2O (4.8 mmol) and 1 g of surfactant poly
(vinyl alcohol) (PVA 15,000) were dissolved in 40 mL deionized water.
The mixture was vigorously stirred at 80 °C for 30 min and then, hex-
amethylenetetramine (1.0 mmol) was slowly added to the solution to
adjust the pH of the solution (∼10.0). After stirring the mixture for 2 h,
the black magnetite was finally collected by an external magnetic field,
rinsed with ethanol several times and dried under vacuum at 80 °C for
10 h.
Fig. 1. FT-IR spectra of (a) Fe3O4@SiO2, (b) Fe3O4@SiO2-NH2, (c) Fe3O4@SiO2-
TCT, (d) Fe3O4@SiO2-TCT-NH2, (e) Fe3O4@SiO2-EDTA and (f) Fe3O4@SiO2-
EDTA-Ni(II) NPs.
and analyzed by comparison of their spectral and physical data such as
melting point, FT-IR, NMR, MS and CHNS with available literature
data. 1H and 13C NMR spectra were recorded with Bruker Avance
DPX250 MHz instruments with Me4Si or solvent resonance as the in-
ternal standard. Fourier transforms infrared (FTIR) spectra were ob-
tained using a Shimadzu FT-IR 8300 spectrophotometer. Powder X-ray
diffraction (XRD) patterns were recorded in a Bruker AXS D8-advance
X-ray diffract to the meter using Cu Kα radiation (λ = 1.5418).
Transmission electron microscopy (TEM) images were taken on a
Philips EM208 microscope with an accelerating voltage of 100 kV. The
hydrodynamic size of the particles was measured by dynamic light
scattering (DLS) techniques, using a HORIBA-LB550 particle size ana-
lyzer. The surface composition was investigated using an X-ray photo-
electron spectroscopy (XPS) on XR3E2 (VG Microtech) spectrometer
using Mg and Al twin anode X-ray gun with the multichannel detector
and a hemispherical analyzer with a resolution of 1.0 eV. The nickel
loading and leaching test were carried out with an inductively coupled
plasma (ICP) analyzer (Varian, vista-pro). Determination of the purity
of the substrate and monitoring of the reactions was accomplished by
thin-layer chromatography (TLC) on a silica-gel polygram SILG/UV 254
plates.
2.2.2. Preparation of Fe3O4@SiO2 NPs [89–92]
The silica coating over the Fe3O4 nanoparticles was achieved via a
well-known Stober method in which 50 mL solvent bearing ethanol/
deionized water (10:1) was applied to disperse 0.5 g of synthesized
Fe3O4 nanoparticles using ultrasound irradiation followed by the ad-
dition of 0.2 mL of tetraethoxysilane (TEOS). During the next step, 5 mL
of NaOH (10 wt%,) solution was added to the mixture at room tem-
perature and it was stirred for 30 min. The resulting Fe3O4@SiO2 MNPs
were collected by an external magnet, washed with distilled water and
ethanol, and dried in a vacuum oven at 80 °C for 10 h.
2.2.3. Synthesis of Fe3O4@SiO2-NH2NPs [89–92]
The functionalization of prepared core-shell was started with adding
0.25 mL of 3-aminopropyl(triethoxy)silane (1 mmol) to a suspension of
Fe3O4@SiO2(1 g) in 10 mL of ethanol and stirring for 12 h under the
reflux conditions. Then, after cooling the crude to room temperature,
the obtained brown precipitate was collected with an external magnet
washed with water and ethanol (1:1) and dried under vacuum at 80 °C.
2.2.4. Synthesis of Fe3O4@SiO2-TCT NPs
1 g of Fe3O4@SiO2-NH2 NPs was dispersed in 10 mL of THF having
dissolved 1 mmol (0.185 g) of cyanuric chloride (TCT) and 1 mmol
(0.17 mL) of diisopropylethylamine (DIPEA). The crude was stirred for
16 h at room temperature and then, Fe3O4@SiO2-TCT NPs were
3

I. Dindarloo Inaloo, et al.
MolecularCatalysis492(2020)110915
Fig. 3. TEM images of (a) Fe3O4, (b) Fe3O4@SiO2, and (c) Fe3O4@SiO2-EDTA-Ni(II); FE-SEM images of (d) Fe3O4, (e) Fe3O4@SiO2, and (f) Fe3O4@SiO2-EDTA-Ni(II)
and the size distributions of (g) Fe3O4, (h) Fe3O4@SiO2, and (i) Fe3O4@SiO2-EDTA-Ni(II) NPs, respectively.
2.2.6. Synthesis of Fe3O4@SiO2-TCT-EDTANPs
The solution of thionyl chloride (SOCl2) (2 mmol) in DMSO (5 mL)
was added dropwise into the solution of EDTA (2 mmol) in DMSO
(15 mL) and the obtained mixture was vigorously stirred for 3 h. Then,
Fe3O4@SiO2‐TCT‐NH2 (1.5 g) was added to the mixture at room tem-
perature. After 2 h, the magnetic moiety was separated by an external
magnet, washed with an aqueous solution of Na2CO3 (0.1 mol L−1) and
subsequently, with acetone. Finally, they were dried at 60 °C to obtain
Fe3O4@SiO2-EDTA NPs.
2.2.7. Synthesis of Fe3O4@SiO2-TCT-EDTA-Ni(II)NPs
In this step, 1.5 g of as-prepared Fe3O4@SiO2-EDTA and 1 g of nickel
(II) acetate tetrahydrate (4 mmol) were dispersed in 10 mL of THF by
ultrasonication and stirred for 4 h under the reflux conditions. Fe3O4@
SiO2-EDTA-Ni NPs were collected by a magnet, washed with water and
ethanol several times and dried at 60 °C overnight.
Fig. 4. EDX spectrum ofFe3O4@SiO2-EDTA-Ni(II)NPs.
collected by a magnet, washed with distilled water and ethanol (1:1)
solution three times and dried at 60 °C.
2.2.8. General procedure for the N-arylation of nitrogen-containing
compounds with C–O activation of aryl carbamate and/or aryl sulfamate
Aryl carbamate and/or aryl sulfamate (1.0 mmol), nitrogen-con-
taining compounds (1.0 mmol), sodium tert-butoxide (2.0 mmol),
Fe3O4@SiO2-EDTA-Ni(II) NPs (0.018 g, 1 mol %) and ethylene glycol
(3.0 mL) were added into a round-bottomed flask and stirred at 100 °C
for 12 h under the inert nitrogen atmosphere. The reaction progress was
monitored by TLC using petroleum ether/ethyl acetate and/or GC
(argon in 5.0 grades or 99.999% purity as carrier gas and PEG as sta-
tionary phase). After the completion of the reaction, the reaction
2.2.5. Synthesis of Fe3O4@SiO2-TCT-NH2 NPs
At the first, cyanuric chloride immobilized Fe3O4@SiO2‐NH2NPs
(1.0 g) was dispersed in 5 mL of DMF and 0.25 mL of bis(3‐amino-
propyl)amine (2 mmol) and DIPEA (2 mmol, 0.35 mL) were added to
the mixture. After stirring at 80 °C for 12 h, the precipitate (Fe3O4@
SiO2-TCT-NH2) was magnetically collected from the solution, washed
with water and ethanol several times and dried at 70 °C for 4 h.
4

I. Dindarloo Inaloo, et al.
MolecularCatalysis492(2020)110915
Fig. 5. TGA spectrum of (a) Fe3O4@SiO2‐NH2, (b) Fe3O4@SiO2‐TCT, (c) Fe3O4@SiO2‐TCT‐NH2 and (d) Fe3O4@SiO2‐EDTA‐Ni(II) NPs; andMagnetic hysteresis loops
of (a) Fe3O4 and (b) Fe3O4@SiO2-EDTA-Ni(II) NPs.
respectively. In the case of Fe3O4@SiO2 NPs, the sharp band at
1090 cm−1 corresponds to overlapped Si–O–Si symmetric and asym-
metric stretching vibrations (Fig. 1a). The characteristic absorption
bands at 2810–2986, 1489, 1123, and 576 cm−1 correspond to the C–H
(stretching vibration), CH2 (bending), Si–O–Si (stretching vibration),
and Fe–O (stretching vibration), respectively, proving the existence of
3‐aminopropyl(triethoxy)silanefunctional groups on the surface of
Fe3O4@SiO2 NPs. Furthermore, the peaks at about 3300−3400 cm−1
can be ascribed to NH2 stretching vibrations (Fig. 1b). In the spectrum
of Fe3O4@SiO2-TCT NPs, the characteristic adsorptions at 1711, 1564
and 1511 cm-1are attributed to C]N stretching vibrations (Fig. 1c). The
peak at 1091 cm-1 was attributed to the C–Cl groups of cyanuric
chloride, which is overlapped by the stretching vibration of Si-O–Si
groups (Fig. 1c). The FT-IR spectra of Fe3O4@SiO2‐TCT‐NH2 NPs
(Fig. 1d) were characterized by the following absorption bands:
stretching vibrations of CeN arising at 1257 cm−1, CH2 (bending) at
1451 cm−1, and the C–H (symmetric and asymmetric stretching vi-
brations) at 2871−3057 cm−1 (Fig. 1d). As can be seen, the typical
absorption peak at 3397 cm−1 indicated the stretching vibrations of
NeH and OeH bonds (overlap) (Fig. 1d). According to Fig. 1e, the
successful Fe3O4@SiO2‐TCT‐NH2 surface modification with EDTA
moieties is verified. In the FT-IR spectra of Fe3O4@SiO2-EDTA (Fig. 1e),
basic characteristic vibrations of CeH bands (asymmetric and sym-
metric stretching)at 2885−3070 cm−1, SieOeSi asymmetric stretching
and symmetric stretching at 1095 and 801 cm−1 and the stretching
vibration of Fe–O were observed at 578 cm−1. Furthermore, the char-
acteristic bands of the carbonyl groups were observed at 1736 cm−1
(C]O carboxylic acid stretching vibration) and 1629 cm−1 (C]O
amide stretching vibration). Eventually, in terms of Fe3O4@SiO2-EDTA-
Ni(II) (Fig. 1f), a redshift of the band at 1736 cm−1 is observed
(1736 cm−1 → 1724 cm−1), which probably is the characteristic of
carbonyl group after interaction with the nickel ions. The observed
results indicate that the functional groups were successfully grafted
onto the surface of the magnetic Fe3O4@SiO2 NPs.
The crystalline structure of magnetic nanoparticles was identified
with the XRD technique. As it can be found in Fig. 2a, the XRD pattern
exhibited the reflection peaks at 30.1°, 35.4°, 43.1°, 53.4°, 57.0° and
62.6° that are indexed to (220), (311), (400), (422), (511) and (440)
crystallographic planes of crystalline Fe3O4 (JCPDS 88-0866) though,
the peak positions of synthesized composites remained unchanged re-
vealing that the crystalline phases of magnetic particles is maintained
after coating. These results present more evidence for the successful
functionalization of nanomagnetite. However, according to Fig. 2b, c,
the crystallinity of the samples decreases after the coating process.
Furthermore, the XRD pattern of Fe3O4@SiO2 shows an obvious diffu-
sion peak at 10−20° because of the presence of the amorphous silica
shell (Fig. 2b). In the case of Fe3O4@SiO2-EDTA-Ni(II) MNPs, the broad
peak was transferred to lower angles due to the synergetic effect of the
Table 1
Selected properties of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-EDTA-Ni(II) NPs.
Sample
Fe3O4 crystal
structure
Specific surface
Magnetite particle
size (nm)b
area (m2/g)a
Fe3O4
Fe3O4@SiO2
Fe3O4@SiO2-
Cubic spinel
Cubic spinel
Cubic spinel
480
430.3
371.6
11.33
12.64
14.97
EDTA-Ni(II)
a
b
Calculated by the BJH method.
Calculated by the Scherrer equation based on powder X-ray diffraction
(XRD) patterns.
Table 2
TGA and elemental analysis for Fe3O4@SiO2‐NH2, Fe3O4@SiO2‐TCT, Fe3O4@
SiO2‐TCT‐NH2 and Fe3O4@SiO2‐EDTA-Ni(II) NPs.
Sample
C (%)
H (%)
N (%)
Total (%)a
Fe3O4@SiO2‐NH2
Fe3O4@SiO2‐TCT
Fe3O4@SiO2‐TCT‐NH2
Fe3O4@SiO2‐EDTA-Ni(II)
TGA (wt%)
EA (wt%)
TGA (wt%)
EA (wt%)
TGA (wt%)
EA (wt%)
TGA (wt%)
EA (wt%)
6.746
6.614
7.377
7.468
16.172
15.946
22.821
21.611
1.501
1.475
0.717
0.750
2.918
2.871
2.853
2.871
2.627
2.532
5.736
5.627
10.564
10.377
9.112
9.232
10.874
10.621
13.830
13.845
29.654
29.194
34.786
33.714
a
Total (%) = C (%) + H (%) + N (%).
mixture was cooled to room temperature and the nanocatalysts sepa-
rated from the mixture with an external magnetic field. Then, water
(10 mL) was added and the crude mixture was subsequently extracted
with ethyl acetate (3
×
10 mL). The organic phases were dried over
anhydrous MgSO4 and the crude product was obtained after removing
the ethereal solution by a rotary evaporator. The product was finally
purified by column chromatography on silica gel using petroleum
ether/ethyl acetate (10:2) as the solvent or recrystallized.
3. Results and discussion
The prepared Fe3O4@SiO2-EDTA-Ni(II) NPs were synthesized via
the multistep procedure (Scheme 2) and well-characterized by the fol-
lowing instrumental techniques: FT-IR, XRD, TEM, FE-SEM, DLS, EDX,
XPS, TGA, VSM, BET, ICP and elemental analysis.
The successful functionalization of the MNPs surface was confirmed
by examination of the FTIR spectra. Fig. 1 shows the FT-IR spectra of
the Fe3O4@SiO2, Fe3O4@SiO2-NH2, Fe3O4@SiO2-TCT, Fe3O4@SiO2-
TCT-NH2, Fe3O4@SiO2-EDTA and Fe3O4@SiO2-EDTA-Ni(II) NPs. All
spectra shows broad bands at around 3400 cm−1 and 580 cm−1, which
are the characteristic of stretching bands of OeH and Fe–O bonds,
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MolecularCatalysis492(2020)110915
Table 3
Optimization of N-arylation of pyrrole with phenyl carbamates using Ni(II) catalyst.
Entry
Catalyst (mol%)
Base (equiv.)
T (°C)
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
1
1
1
NaOtBu(2.0)
NaOAc(2.0)
Na2CO3(2.0)
K3PO4(2.0)
NaOH(2.0)
K2CO3(2.0)
Cs2CO3(2.0)
DBU(2.0)
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
r.t
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
4
8
12
91
41
49
72
51
45
78
62
0
71
80
91
90
66
90
91
15
63
84
85
83
71
90
91
9
–
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
NaOtBu(1.0)
NaOtBu(1.5)
NaOtBu(2.5)
NaOtBu(3.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
NaOtBu(2.0)
1
0.5
1.5
2
1
1
1
1
1
1
80
90
110
120
100
100
100
1
1
a
Isolated yield.
Table 4
Ni catalyst effect in N-arylation of pyrrole with phenyl diethylcarbamate.a
Entry
Catalyst
Yield (%)b
1
Ni(acac)2
0
2
NiCl2
0
3
4
5
6
7
8
9
10
11
NiCl2(DME)
NiBr2bipy
58
61
57
76
81
74
79
82
91
Ni(PCy3)2Cl2
Ni(COD)2
(dppe)Ni(o-tolyl)Cl
(PCy2Ph)2Ni(o-tolyl)Cl
(PCy3)2Ni(o-tolyl)Cl
EDTA-Ni(II)
Fe3O4@SiO2‐EDTA-Ni(II)
a
Reaction conditions: pyrrole (1 mmol), phenyl diethylcarbamate (1 mmol), catalyst (0.018 g, 1 mol% Ni(II)), NaOtBu(2 mmol),
EG (3 cm3), 100 °C, 6 h.
b
Isolated yield.
amorphous silica and the dendrimer (Fig. 2c). In the end, the mean
diameter of nanoparticles was calculated using Scherrer's equation to be
around 12 nm.
Moreover, these results were consistent with the particle size distribu-
tion histogram of magnetic nanoparticles, which were in a narrow
distribution in the range of 8−16 nm, 16−24 nm and 23−37 nm and
average size distribution of 12 nm, 20 nm and 31 nm for Fe3O4, Fe3O4@
SiO2 and Fe3O4@SiO2‐EDTA‐Ni(II) NPs, respectively (Fig. 3g–i).
EDX detector coupled to the SEM was exploited to confirm the ex-
istence of nickel in the Fe3O4@SiO2-EDTA-Ni(II) nanocatalyst (Fig. 4).
Besides, the presence of C, N and O peaks along with the higher in-
tensity of the Si peak compared with the Fe peaks indicates that the
magnetite nanoparticles were trapped by silica and also, the Fe3O4@
SiO2-EDTA-Ni(II) has been successfully synthesized.
The morphology of the final magnetic nanocatalyst can be observed
in TEM and FE-SEM images (Fig. 3a–c). As revealed, the magnetite
nanoparticles possess uniform spherical shape (Fig. 3a, d). The TEM
image of Fe3O4@SiO2 shows the well-defined core-shell structure
(Fig. 3b). Furthermore, Fig. 3c indicates the explicit structure of
Fe3O4@SiO2-EDTA-Ni(II) NPs after being coated with the organic layer.
The FE-SEM photographs demonstrate that the Fe3O4@SiO2 and
Fe3O4@SiO2-EDTA-Ni(II) NPs are almost regular spherical (Fig. 3e, f).
6

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MolecularCatalysis492(2020)110915
Table 5
Evaluation of various phenol derivatives as the electrophile.a
Entry
X
Yield (%)b
1
2
3
4
5
6
7
8
9
Me
Ac
Piv
Ms
Ts
Tf
10 <
46
51
54
57
56
78
87
91
CO2tBu
SO2NEt2
CONEt2
a
Reaction conditions: pyrrole(1 mmol), phenol derivatives (1 mmol), catalyst (0.018 g, 1 mol% Ni(II)), NaOtBu (2 mmol), EG (3
cm3), 100 °C, 6 h.
b
Isolated yield.
removing the external magnetic field (Fig. 5C). These results reveal that
the nanocomposite exhibits good magnetic responsible as an advantage
in the synthesized magnetic separable catalytic system.
Table 6
Reagent scope of amines in the N-arylation reaction.a
The N2 adsorption-desorption isotherms were conducted to in-
vestigate the porous structure and surface area of the nanoparticles. The
measured specific surface areas were 480, 430.3 and 392.6 m2/g for
Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2-EDTA-Ni(II), respectively
(Table 1). Also, the mean particle size of the magnetic nanocatalyst was
calculated using the Scherrer equation to be 11.33, 12.64, and
14.97 nm for Fe3O4, Fe3O4@SiO2, and Fe3O4@SiO2-EDTA-Ni(II), re-
spectively (Table 1).
a
Reaction conditions: phenol derivatives (1 mmol), amines (1 mmol), Ni cata-
lyst (1 mol %, 0.018 g), NaOtBu (2 mmol), EG (3 cm3), 100 °C, 12 h.
b
Isolated yield.
Elemental analysis (EA) for Fe3O4@SiO2‐NH2, Fe3O4@SiO2‐TCT,
Fe3O4@SiO2‐TCT‐NH2 and Fe3O4@SiO2‐EDTA-Ni(II) were carried out
and the data were tabulated in Table 2, which is in good agreement
with the results obtained from TGA. The results displayed that the
contents of C, H and N for Fe3O4@SiO2‐EDTA-Ni(II) are 21.61%, 2.87%
and 9.23%, respectively.
Table 7
Reagent scope of aryl sulfamates and carbamates in the N-arylation reaction.a
Additionally, the loading of Ni particles on the catalyst was con-
firmed by the Inductively Coupled Plasma (ICP) analyzer. For this
purpose, 1 g of the catalyst was stirred in HCl (37%) and then, the
magnetic nanocomposite was separated by an external magnetic field.
The remaining solution was analyzed by inductively coupled plasma
(ICP) to determine the content of nickel. The amount of Ni on the
support was determined as 0.55 mmol per gram of the catalyst.
After the preparation of the catalyst, the activity of which was in-
vestigated in the N-arylation of nitrogen-containing compounds. The
presence of Ni(0) based catalyst is necessary in most cases to obtain the
best results. In recent years, some effective achievement has been re-
ported when Ni(I) complexes had been used for the N-arylation reaction
in which the main challenge in developing the desired N-arylation re-
action is using Ni(II) precatalytic moiety and difficulty reducing Ni(II)
content to Ni(0). In most methodologies, some reducing agents have
been applied such as Zn, Mn or triethylsilane [93–96]. It has recently
been reported that even without any reducing agent for the generation
of Ni(0) catalyst, the Heck and Sonogashira cross-coupling reactions
proceeded well in the presence of NiCl2.6H2O as the catalyst and
ethylene glycol as solvent [97]. This interesting result indicated that
ethylene glycol could reduce the Ni(II) to the lower valent nickel spe-
cies. Therefore, the N-arylation of pyrrole with phenyl carbamates in
the presence of Ni catalyst and ethylene glycol as solvent was chosen as
model reactions.
aReaction conditions: phenol derivatives (1 mmol), amines (1 mmol), Ni cata-
lyst (1 mol %, 0.018 g), NaOtBu (2 mmol), EG (3 cm3), 100 °C, 12 h.
bIsolated yield.
Thermogravimetric analysis (TGA) of the magnetic nanocatalyst
was performed over the temperature range of 25−700 °C. The first
weight loss for all samples are shown in Fig. 5A have been detected
below 150 °C in which the adsorbed water and other solvents on the
surface of the nanomaterials have been lost. The second step was ob-
served between 150 °C and around 600 °C that shows the decomposition
of coating organic layers. Moreover, a significant weight loss of nearly
42.7% in the range of 150−600 °C was obtained due to the elimination
of organic material over Fe3O4@SiO2 NPs (Fig. 5Ad).
The magnetic properties of magnetic nanostructures especially the
final magnetic heterogeneous nanocatalyst was investigated using a
vibrating sample magnetometer (VSM) at room temperature (Fig. 5B).
The hysteresis loops of magnetite and functionalized magnetic catalyst
show no elimination in magnetic properties in the loops and the re-
manence of superparamagnetic behavior for all samples. The magne-
tizations of Fe3O4 and Fe3O4@SiO2-EDTA-Ni(II) MNPs were 64.8 and
28.7 emu/g, respectively (Fig. 5B). The coating with silica and the or-
ganic compounds results in a decrease in the magnetic strength of the
composite. Nevertheless, Fe3O4@SiO2-EDTA-Ni(II) possesses excellent
magnetic responsibility and suitable magnetization values, which can
quickly respond to the external magnetic field and disperse again after
To explore an efficient catalytic system, the model reaction was
investigated in detail by different parameters including the amount of
catalyst, base, time and temperature to develop appropriate reaction
conditions (Table 3).
7

I. Dindarloo Inaloo, et al.
MolecularCatalysis492(2020)110915
Scheme 3. A proposed catalytic cycle for the N-arylation reaction.
With an active catalyst in hand and reliable conditions, we decided
to study the application and efficiency of this Ni-based catalyst in the N-
arylation reaction and the results summarized in Table 4. Un-
fortunately, the model reaction did not work with the catalysts such as
Ni(acac)2 and NiCl2(Table 4, entries 1 and 2). When NiCl2(DME),
NiBr2bipy and Ni(PCy3)2Cl2 were used as the catalyst, about 70% of the
desired product was observed (Table 4,entries 3–5). As expected, the
model reaction catalyzed by other nickel complexes including Ni
(COD)2, (dppe)Ni(o-tolyl)Cl, (PCy2Ph)2Ni(o-tolyl)Cl and (PCy3)2Ni(o-
tolyl)Cl presented a significant increase in the yield (Table 4, entries
6–9). However, these catalysts were not as effective as Fe3O4@
SiO2–EDTA–Ni(II) NPs (Table 4, entry 11). Even using EDTA–Ni(II)
complex as homogeneous catalyst under the optimized reaction con-
ditions, did not result in a better performance (Table 4, entry 10).
The next investigation was focused on the effect of various phenol
derivatives. Hence, the most general, common and highly reactive
phenol derivatives were studied in the optimal reaction conditions
(Table 5). This study showed the insignificant N-acylation results when
the anisole was used as the coupling partner (Table 5, entry1). How-
ever, the corresponding acetate, mesylate, tosylates and triflate sub-
strates gave only modest yields of the desired product (Table 5, entries
2–6). The use of a carbonate coupling partner created the final product
in good yield (Table 5, entry7). Finally, we found that the corre-
sponding carbamate and sulfamate substrates gave the best yields of the
N-acylation products (Table 5, entries 8 and 9). Thus, we elected these
two types of electrophiles to evaluate the scope of the methodology.
After identifying the optimal conditions of the N-arylation reaction,
we examined the scope of alkyl, aryl and heterocyclic amines using
phenyl sulfamates and carbamates (Table 6). It was found that the N-
arylation of various amines resulted good to excellent yields depending
on the steric and electronic nature of the amine substrates. Heterocyclic
Fig. 6. XPS spectra of the (a) fresh and (b) reused catalyst.
At the outset, different bases were screened to determine their ef-
ficacy in the model reaction (Table 3, entries 1–8). These studies de-
monstrate that no N-arylation product in the absence of the base
(Table 1, entry 9) and the use of sodium tert-butoxide lead to the best
performance (Table 3, entry 1). Subsequently, the effect of other im-
portant factors including the amount of the catalyst and NaOtBu, time
and temperature were studied in the model reaction(Table 3, entries
11–25).These investigations indicated that the highest yield of the
product in the model reaction can be obtained using NaOtBu (2.0
equiv.) as a base, 0.018 g of catalyst (1 mol% Ni(II)) and EG as both
solvent and reducing agent at 100 °C after 6 h (Table 3, entry 1).
8

I. Dindarloo Inaloo, et al.
MolecularCatalysis492(2020)110915
Fig. 7. Reusability of the Fe3O4@SiO2-EDTA-Ni(II) NPs.
Fig. 8. TEM (a), FE-SEM (b) and DLS (c) images of Fe3O4@SiO2-EDTA-Ni(II) after seventh recycling experiment.
substrates containing pyrrole, imidazole, pyrazole, indole and benzi-
midazoles underwent coupling with phenyl sulfamates and carbamates
under the optimized conditions and the desired products were synthe-
sized in excellent yields (Table 6, entries 3aa–3af).Aryl amines are also
efficient nucleophiles in the reaction (Table 6, entries 3ag–3ai). Aniline
was also coupled in good yields (Table 6, entry 3ag). The presence of
the electron-donating groups on the phenyl ring of aniline led to the
more desired product (Table 6, entry 3ah)and the electron-withdrawing
groups produced a slightly adverse influence (Table 6, entry 3ai).Be-
sides, the performance of secondary aromatic amines might be affected
by steric factors. N-Ethylaniline as aryl amines with a little steric hin-
drance reacted very well in this reaction conditions (Table 6, entry 3aj),
but diphenylamine with a high steric hindrance did not undergo into
the product very effectively (Table 6, entry 3ak).Although, the primary
and secondary aliphatic amines that are the difficult class of nucleo-
philic substrates in the usual N-arylation reactions, worked well in this
optimal reaction conditions(Table 6, entries 3al–3ao). However, sec-
ondary aliphatic amines showed significantly low performances due to
the steric hindrance (Table 6, entries 3an–3ao).It should be emphasized
that in the case of primary amines, good regioselectivity was observed
and just the mono-aminated product was solely obtained under these
reaction conditions without the formation of di-aminated product.
Furthermore, the coupling of various aryl carbamates and sulfa-
mates as the electrophile with heterocyclic amines was examined under
the optimal conditions (Table 7). Both aryl sulfamates and carbamates
with electron-withdrawing or electron-donating substituents on the aryl
ring were successfully compatible in the reaction showing the
functional group compatibility that could be coupled with heterocyclic
amines to provide the products in good to excellent yields (Table 7,
entries 3ba–3bq). In addition, the sterically hindered ortho-substituted
aryl carbamates and sulfamates reacted with various amines and pre-
sented the good results (Table 7, entries 3bd–3bf and 3bq). It should be
noted that the strong electron-withdrawing substituents such as NO2
showed a bit better performances than other substituents in these re-
action conditions (Table 7, entries 3bo–3bp). Fortunately, the reaction
showed good tolerance toward fluoride substituent and the satisfactory
result was obtained (Table 7, entry 3bl). More importantly, the het-
eroaromatic substrates of carbamate and sulfamate could also partici-
pate smoothly in these reaction conditions and produced the corre-
sponding products in excellent yields (Table 7, entries 3bs–3bu).
In the end, we proposed the plausible catalytic mechanism for the N-
arylation coupling of nitrogen-containing compounds via CeO bond
activation of aryl carbamates and sulfamates according to the reported
researches in the literature, (Scheme 3) [93–97]. Initially, the process
begins with the reduction of Ni(II) by nitrogen-containing compounds
or ethylene glycol as the reducing agents to provide the active Ni(0)
species. Subsequently, the catalytic cycle starts with the oxidative ad-
dition of Ni(0) to aryl carbamates or aryl sulfamates for the in situ
generations of the intermediate (1). This complex subsequently reacts
with the nitrogen-containing compound and base (NaOtBu) to form the
intermediate (2). Finally, the CeN bond formation was occurred
through the reductive elimination step generates Ni(0) catalyst.
To determine the oxidation state of nickel, high resolution X-ray
photoelectron spectroscopy (XPS) spectra of Ni 2p core levels were
9

I. Dindarloo Inaloo, et al.
MolecularCatalysis492(2020)110915
obtained from the catalyst before and after the reaction (Fig. 6). Ac-
cording to the fitted data, the deconvoluted peaks at binding energy
855.9 eV and 861.8 eV are attributed to Ni 2p3/2 and peaks at 872.2 eV
and 879.8 eV constitutes to Ni 2p1/2 for fresh catalyst that can be in-
dexed to Ni2+ (Fig. 6a). [98] Besides, the XPS patterns of recovered
catalyst show the peaks of both Ni2+ and Ni(0) (Fig. 6b). The peaks at
around 852.4 eV and 872.2 eV were assigned to the Ni 2p3/2 and Ni 2p1/
industries as well as in the synthesis of biologically significant com-
pounds in which the safety, environmental and financial issues are of
greater concern.
Funding
No funding was received for this work.
Intellectual property
levels in the Ni(0) which are in good agreement with the literature
2
report [99]. The above phenomena supported that the reaction pro-
ceeded via the traditional Ni2+/Ni(0) cycle mechanism.
The recyclability and high stability of the economically and eco-
friendly catalytic systems are so important in the industry and de-
signing the green and effective synthetic pathways. Therefore, we fo-
cused on the investigation of stability and reusability of catalyst under
the optimal reaction conditions. Therefore, the model reaction was
chosen to be tested in the efficiency of catalyst behavior. After com-
pleting the model reaction, the magnetic heterogeneous catalyst was
separated by using an external magnet and washed with ethanol, dried
at 60 °C under vacuum and prepared for using in the next runs. As
shown in Fig. 7, after seven cycles just the insignificant decrease in the
catalytic activity was observed. Surprisingly, the decrease in the effi-
cacy of catalyst after 7 runs is only 3%.
The morphology and stability of catalyst against the aggregation
have been investigated after seventh run (Fig. 8). As shown in Fig. 8a
and 8b, the TEM and FE-SEM images of recovered magnetic nano-
particles after the seventh cycle revealed that almost all Fe3O4@SiO2-
EDTA-Ni(II) particles are spherical in shape as the same as fresh catalyst
indicating that the aggregation of nanoparticles is venial. Moreover, the
hydrodynamic diameter of the catalyst was studied by the DLS tech-
nique (Fig. 8c) in which insignificant aggregation was observed for
reused nanocatalyst and the size distribution is centered at around
37 nm.
Additionally, the catalyst was investigated by Inductively Coupled
Plasma (ICP) analysis after the last run to determine the amount of
nickel leaching. Accordingly, the amount of loaded nickel on the re-
covered catalyst was measured to be 0.54 mmol/g. Propitiously, the ICP
analysis after the seventh run showed less than 1% nickel leaching.
Moreover, to determine the responsibility of nickel moiety for carrying
out the model reaction, the hot filtration test was performed. When the
reaction time of the model reaction reached the half time of reaction
quenching, the catalyst nanoparticles were taken out from the reaction
mixture by an external magnetic field and the residue was allowed to be
stirred under the reaction conditions. The monitoring of reaction mix-
ture by TLC did not show any considerable progress. These results
showed that only a few species of nickel may exist in the solution phase
and the main responsible species that catalyzes the model reaction, is
the Fe3O4@SiO2-EDTA-Ni(II) nanoparticles. All of these data confirmed
the high stability and reusability of the catalyst under these reaction
conditions.
We confirm that we have given due consideration to the protection
of intellectual property associated with this work and that there are no
impediments to publication, including the timing of publication, with
respect to intellectual property. In so doing we confirm that we have
followed the regulations of our institutions concerning intellectual
property.
Research ethics
We further confirm that any aspect of the work covered in this
manuscript that has involved human patients has been conducted with
the ethical approval of all relevant bodies and that such approvals are
acknowledged within the manuscript.
IRB approval was obtained (required for studies and series of 3 or
more cases)
Written consent to publish potentially identifying information, such
as details or the case and photographs, was obtained from the patient(s)
or their legal guardian(s).
Authorship
The International Committee of Medical Journal Editors (ICMJE)
recommends that authorship be based on the following four criteria:
Substantial contributions to the conception or design of the work; or
the acquisition, analysis, or interpretation of data for the work; AND
Drafting the work or revising it critically for important intellectual
content; AND
Final approval of the version to be published; AND
Agreement to be accountable for all aspects of the work in ensuring
that questions related to the accuracy or integrity of any part of the
work are appropriately investigated and resolved.
Declaration of Competing Interest
We wish to confirm that there are no known conflicts of interest
associated with this publication and there has been no significant fi-
nancial support for this work that could have influenced its outcome.
Acknowledgments
4. Conclusion
The authors gratefully acknowledge the financial support of this
work by the Research Council of Shiraz University.
We have demonstrated a general, convenient and highly efficient
protocol for the N-arylation of nitrogen-containing compounds in-
cluding aliphatic and aromatic amines, indole and imidazole through
CeO activation of phenol derivatives (aryl carbamates and sulfamates)
in the presence of Fe3O4@SiO2-EDTA-Ni(II) NPs. The main benefits of
the application of phenolic derivatives in the N-arylation reaction are
being highly rewarding because these compounds serve not only as
more eco-friendly alternatives rather than aryl halides and also, they
can be easily produced from cheap and available phenols. The other
features of this catalytic system are the significant improvement of the
substrate and functional group tolerance, high selectivity, en-
vironmentally friendly, and being economical, recoverable and reusable
compared to previously published methods. Despite these unique fea-
tures, this catalytic system has special applications in pharmaceutical
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2020.110915.
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