Ionic liquid-functionalized mesoporous silica nanoparticles ([pmim]FeCl4/MSNs): Efficient nanocatalyst for solvent-free synthesis of N,N′-diaryl-substituted formamidines

Article abstract of DOI:10.1002/aoc.3800

We report the synthesis of ionic liquid-functionalized mesoporous silica nanoparticles ([pmim]FeCl₄/MSNs) via a method of post-grafting on parent MSNs. This hybrid material was characterized using scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy, powder X-ray diffraction and thermal analyses. The material was utilized as an efficient heterogeneous catalyst for the synthesis of N,N′-diaryl-substituted formamidines through the reaction of triethyl orthoformate with arylamines under solvent-free conditions. The catalyst was recovered easily and reused several times without significant loss of its catalytic activity.

Full text of DOI:10.1002/aoc.3800

Received: 15 November 2016
DOI: 10.1002/aoc.3800
Revised: 17 January 2017
Accepted: 14 February 2017
F U L L PA P E R
Ionic liquid‐functionalized mesoporous silica nanoparticles
[pmim]FeCl /MSNs): Efficient nanocatalyst for solvent‐free
(
4
synthesis of N,N′‐diaryl‐substituted formamidines
Zahra Nasresfahani | Mohammad Zaman Kassaee
| Esmaiel Eidi
Department of Chemistry, Tarbiat Modares
University, PO Box 14155‐175, Tehran, Iran
We report the synthesis of ionic liquid‐functionalized mesoporous silica
nanoparticles ([pmim]FeCl /MSNs) via a method of post‐grafting on parent
4
Correspondence
MSNs. This hybrid material was characterized using scanning and transmission
electron microscopies, energy‐dispersive X‐ray spectroscopy, nitrogen adsorption–
desorption analysis, Fourier transform infrared spectroscopy, powder X‐ray
diffraction and thermal analyses. The material was utilized as an efficient heteroge-
neous catalyst for the synthesis of N,N′‐diaryl‐substituted formamidines through
the reaction of triethyl orthoformate with arylamines under solvent‐free conditions.
The catalyst was recovered easily and reused several times without significant loss
of its catalytic activity.
Mohammad Zaman Kassaee, Department of
Chemistry, Tarbiat Modares University, PO
Box 14155‐175, Tehran, Iran.
Email: kassaeem@modares.ac.ir
KEYWORDS
formamidines, ionic liquids, mesoporous materials, nanocatalyst, reusable catalyst
1
| INTRODUCTION
of N,N′‐dimethylformamidines or acetamidines by various
[
12]
amines.
Other methods involve the use of acid
[
13]
[14]
[15]
Formamidines are a relatively new group, both in their range
of biological activities and in fields related to organic and
medicinal chemistry. They are used as bioactive molecules,
in various chemical transformations, chelating or bridging
modes, building blocks in polymer synthesis, bleaching
agents for paper, ligands in transition metal catalysts for
asymmetric synthesis,
amines, support linkers in solid‐phase synthesis and in
chlorides,
aldehydes,
o‐dinitrobenzene,
Gold's
as the starting materials.
[
16]
[17]
reagent
and 2‐nitroanilines
[
1]
Also, for the advancement of this protocol various catalytic
[2]
[18]
systems have been investigated such as FeCl , β‐cyclodex-
3
[
3]
[4]
[19]
[20]
[21]
trin,
sulfated zirconia,
ceric ammonium nitrate
and
[
5]
[22]
fluorinated solvents. Nevertheless, some of these methods
require long reaction times, tedious purification processes
and use of inorganic metal catalysts and hazardous organic
solvents. Therefore, there is strong demand for a highly
efficient environmentally benign method for the preparation
of N,N′‐diarylformamidines.
[6]
protecting groups for primary
[
7]
[8]
[9]
dynamic NMR studies. Moreover, some cryoscopic molec-
ular weight determination experiments utilize the molecular
association property of diarylformamidines in benzene
[
10]
solution.
Thus, due to the importance of formamidines,
In this regard, mesoporous materials due to their large
and well‐defined pore sizes, plus high surface areas, have
attracted increasing interest for their applications in the fields
several methods have been developed for their synthesis.
Taylor and Ehrhart have reported a general synthetic method
for the synthesis of formamidines by the reaction of triethyl
orthoformate or orthoacetate with a number of aliphatic
and aromatic amines in acetic acid, under reflux at 140–
[
23]
[24]
of heterogeneous catalysis,
separation gas storage,
Surface functionalization with
[
25]
[26]
sensing
and catalysis.
catalytic homogeneous systems, especially metal complexes,
has been widely applied in order to generate active sites
on the surfaces of these mesoporous silica materials. The
[
11]
150 °C. One of the most popular methods for the synthesis
of symmetric and unsymmetric formamidines is the exchange
Appl Organometal Chem. 2017;e3800.
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Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3800

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NASRESFAHANI ET AL.
immobilization of catalytically active metal complexes onto
the surfaces offers the advantages of a combination of high
catalytic activity, selectivity and stability with easier separa-
tion of the catalysts from reaction media, thus making them
Thermogravimetric analysis (TGA) and differential thermal
analysis (DTA) were done with a thermal analyser at a
−
1
heating rate of 10 °C min . Particle morphology was
examined via scanning electron microscopy (SEM; Hitachi
S‐4160) and transmission electron microscopy (TEM; Philips
CM30, 300 kV). Simultaneous inductively coupled plasma
(ICP)–optical emission spectrometer (Varian Vista‐PRO,
Springvale, Australia) with a radial torch coupled to a
concentric nebulizer and Scott spray chamber and equipped
with a charge coupled device detector was used for ICP
measurements.
[27]
reusable and efficient systems. An active organic fragment
of the organocatalyst in the mesoporous silica framework can
be preserved due to the strong Si─C covalent bonding. The
periodicity of nanoscale pores in these materials could favour
the easy accessibility of organic functions in addition to the
possible diffusion of solvent‐soluble reactants within the
insoluble solid matrix and is thus very attractive for liquid–
solid phase catalytic reactions. Therefore, the covalent
grafting of catalytically active centres onto the surface of
functionalized mesoporous silica becomes of considerable
2
.2 | Synthesis of 1‐methyl‐3‐
(
(
trimethoxysilylpropyl)imidazolium chloride
[pmim]cl)
[
28]
technological interest in the field of molecular catalysis.
Taking into account the advantage of mesoporous
silica, here we present the option of covalent immobiliza-
tion of imidazolium salts on the surface of mesoporous
silica. The resulting materials have highly ionized surfaces
and large surface areas that could be suitable for efficient
scavenging of novel metal salts and maybe used as catalyst
supports. Herein, we report the synthesis and characteriza-
tion of ionic liquid‐functionalized mesoporous silica
A mixture of 5 mmol of 1‐methylimidazole and 5 mmol of
(3‐chloropropyl)trimethoxysilane was refluxed at 95 °C for
24 h under inert atmosphere. Then, the reaction mixture
was cooled. The crude product was additionally washed with
Et O and dried under vacuum affording the product (slightly
2
[
27]
yellow viscous oil).
−
1
FT‐IR (KBr, cm ): 2926, 1633, 1522, 1442, 1120,
1
nanoparticles ([pmim]FeCl /MSNs) and their catalytic
1036,798. H NMR (500 MHz, DMSO, TMS, δ , ppm):
4
H
applications for the synthesis of N,N′‐diaryl‐substituted
formamidines (Scheme 1).
9.63 (1H, NCHN), 8.02 (1H, NCHCH), 7.77 (1H, NCHCH),
4.50 (2H, CH N), 3.89 ((3H, NCH ), 3.82 (9H, OCH ), 1.82
2
3
3
13
(
2H, CH CH Si), 0.5 (2H, SiCH ). C NMR (125 MHz,
2 2 2
DMSO, TMS, δ , ppm): 138.04, 123.88, 122.70, 52.53,
C
2
2
| EXPERIMENTAL
51.24, 36.27, 24.11, 10.13.
.1 | Materials and instrumentation
2.3 | Synthesis of [pmim]FeCl /MSNs catalyst
4
Chemicals were purchased from Merck and Aldrich. Prod-
ucts were characterized through comparison of their melting
point and Fourier transform infrared (FT‐IR) and NMR spec-
tra with those of authentic samples and those reported in the
literature. Melting points were determined in open capillaries
using an Electrothermal 9100 apparatus and are uncorrected.
FT‐IR spectra were recorded using KBr pellets in the range
First, we synthesized MSNs according to the sol–gel
[29]
method.
In order to prepare [pmim]FeCl /MSNs, 1 g
4
(2.7 mmol) of [pmim]Cl was dissolved in 25 ml of dry
toluene and treated with 2 g of MSNs. The mixture was
refluxed for 24 h under inert atmosphere. Then, the reac-
tion mixture was cooled to room temperature. The solid
was isolated by filtration and washed with 20 ml of boiling
dichloromethane to remove the unreacted ionic liquid. In
the next step, the material was dried under high vacuum
to give powder of [pmim]Cl/MSNs. The latter was mixed
with mole amounts of anhydrous FeCl3 in acetone at
−1
4
00–4000 cm with a Nicolet IR‐100 infrared spectrometer.
1
The H NMR spectra were recorded with a Bruker DRX 500‐
Avance spectrometer operating in DMSO‐d and CDCl with
6
3
tetramethylsilane (TMS) as an internal standard. X‐ray dif-
fraction (XRD) was performed using a Philips XPert 1710
diffractometer with Co Kα radiation (λ = 1.79285 Å) at a
voltage of 40 kV. Surface area and isotherms were deter-
mined using nitrogen adsorption–desorption (Micrometritics
TriStar II 3020 surface area and porosity analyser).
3
0 °C for 3 h. The obtained catalyst was filtered and
washed with ethanol, then dried under vacuum at 60 °C
for 24 h (Scheme 2).
2
.4 | General procedure for synthesis of N,N′‐
Diaryl‐substituted Formamidines
The [pmim]FeCl /MSNs catalyst (10 mg) was added to a
4
mixture of aniline (2 mmol) and triethyl orthoformate
(1 mmol). The mixture was magnetically stirred under
SCHEME 1 Synthesis of N,N′‐diaryl‐substituted formamidines

NASRESFAHANI ET AL.
3 of 9
SCHEME 2 Synthesis of nanocatalyst
([pmim]FeCl4/MSNs)
thermal solvent‐free conditions in a preheated oil bath at
0 °C for the appropriate time. After completion of the
reaction (monitored by TLC), the mixture was diluted with
acetone. The used catalyst was separated by filtration and
the product was purified by simple recrystallization from
ethanol.
3 | RESULTS AND DISCUSSION
3.1 | Characterization of [pmim]FeCl /MSNs
8
4
3.1.1 | FT‐IR
The FT‐IR spectra of MSNs, [pmim]Cl/MSNs and [pmim]
N,N′‐Diphenylformamidine (Table 2, entry 1). M.p. 138–
FeCl /MSNs are shown in Figure 1. For the parent MSNs,
4
−
1
1
1
8
40 °C. FT‐IR (KBr, cm ): 3435 (NH), 3046 (CH, Ar),
asymmetric and symmetric Si─O─Si characteristic stretching
1
−1
674 (C═N). H NMR (500 MHz, CDCl , TMS, δ , ppm):
vibrations at 1086 and 801 cm along with Si─OH at
3
H
962 cm− and Si─O─Si bending at 461 cm are observed.
1
−1
.24 (s, 1H), 7.40–7.35 (m, 4H), 7.11–7.10 (m, 6H). MS,
+
[18]
−1
m/z: 196 (M) .
The broad band at around 3450 cm is attributed to the
N,N′‐Bis‐(4‐chlorophenyl)formamidine (Table 2, entry 2).
surface silanols and adsorbed water molecules. The band
at 1635 cm is assigned to the H─O─H bending vibration
of free or absorbed water molecules. In the case of [pmim]
−1
−1
M.p. 178–179 °C. FT‐IR (KBr, cm ): 3419 (NH), 3048 (CH,
1
Ar), 1684 (C═N). H NMR (500 MHz, CDCl , TMS, δ ,
3
18]
H
[
ppm): 8.08 (s, 1H), 7.27 (d, 4H), 6.97 (d, 4H).
N,N′‐Bis(4‐bromophenyl)formamidine (Table 2, entry 3).
−
1
M.p. 184–186 °C. FT‐IR (KBr, cm ): 3439 (NH), 3051
1
(
CH, Ar), 1657 (C═N). H NMR (500 MHz, CDCl , TMS,
3
21]
[
δH, ppm): 8.08 (s, 1H), 7.41 (d, 4H), 6.90 (d, 4H).
N,N′‐Di‐p‐tolylformamidine (Table 2, entry 4). M.p.
−
1
1
39–141 °C. FT‐IR (KBr, cm ): 3435 (NH), 3051 (CH,
1
Ar), 1668 (C═N). H NMR (500 MHz, CDCl , TMS,
3
δ , ppm): 8.17 (s, 1H), 7.12 (d, 4H), 6.98 (d, 4H), 2.33
H
[
18]
(
brs, 6H).
N,N′‐Bis(4‐acetylphenyl)formimidamide (Table 2, entry
−
1
9
(
). M.p. 169–172 °C. FT‐IR (KBr, cm ): 3420 (NH), 3022
1
CH, Ar), 1668 (C═N). H NMR (500 MHz, CDCl , TMS,
3
δH, ppm): 8. 82 (s, NH), 8. 25 (s, CH), 8.14–7.91 (m, 4H),
.44–7.00 (m, 4H).
FIGURE 1 FT‐IR spectra of (a) MSNs, (b) [pmim]cl/MSNs and (c)
[pmim]FeCl /MSNs
4
7

4
of 9
NASRESFAHANI ET AL.
Cl/MSNs and [pmim]FeCl /MSNs, the peaks at 1575 and
4
636 cm− are assigned to C═N and C═C of the
1
1
imidazolium ring. Also, additional bands at 3150, 2932 and
455 cm− are due to C─H stretching, confirming the
1
1
[30]
functionalization of MSNs with the ionic liquid.
3
.1.2 | XRD
The ordered porous structures of MSNs, [pmim]Cl/MSNs
and [pmim]FeCl /MSNs were further confirmed using
4
XRD. The XRD pattern of MSNs exhibits a high peak in
the low‐angle region at 2θ of approximately 2.55° and two
small peaks at 2θ = 3.80° and 4.50°, which are indexed
respectively to the (100), (110) and (200) diffractions of the
typical hexagonal mesoporous structure. For [pmim]Cl/
4
FIGURE 3 Wide‐angle XRD pattern of [pmim]FeCl /MSNs
shows the presence of C, O, Si, Cl and Fe in the [pmim]
MSNs and [pmim]FeCl /MSNs, two intense reflections
4
FeCl /MSNs nanocatalyst (Figure 4b).
4
disappear and only a reflection associated with (100) is
observed. The intensity of this reflection after functionalizing
is obviously lower than that of the original MSNs and shifted
to higher angles (Figure 2). So, the XRD pattern of the func-
tionalized MSNs suggests not only a significant degree of
short‐range ordering of the structure and well‐formed hexag-
onal pore arrays, but also the maintenance of the structural
3.1.4 | TEM
The TEM images of [pmim]FeCl /MSNs provide structural
4
evidence for the organization of the material into ordered
arrays of two‐dimensional hexagonal mesopores, and
show the presence of uniformly distributed iron species
[
30]
order of the synthesized materials after functionalization.
[
30]
(dark spots) (Figure 5).
In the wide‐angle XRD pattern for [pmim]FeCl4/MSNs,
a broad peak appears at 2θ from approximately 20° to 30°
clearly indicating that the silica is mainly in the amorphous
form and no iron oxide is formed (Figure 3).
3
.1.3 | SEM and EDX
The morphology of the synthesized [pmim]FeCl /MSNs
4
particles was investigated using SEM (Figure 4a). The SEM
image shows nanoparticles of spherical shape with rather
uniform sizes. The particle size distribution is narrow and
centred at the range 40–50 nm. The components of [pmim]
FeCl /MSNs were analysed using EDX. The EDX analysis
4
FIGURE 2 Low‐angle XRD patterns of (a) MSNs, (b) [pmim]cl/
4
FIGURE 4 (a) SEM image and (b) EDX spectrum of [pmim]FeCl /
MSNs and (c) [pmim]FeCl
4
/MSNs
MSNs

NASRESFAHANI ET AL.
5 of 9
4
FIGURE 5 TEM images of [pmim]FeCl /MSNs
3
.1.5 | TGA and DTA
losses in different temperature ranges. The TGA curve
of the material shows the first 3% weight loss at 25–
The organic content and the framework stability of the
pmim]FeCl /MSNs sample were estimated quantitatively
1
00 °C corresponding to remove of water and solvents
[
4
remaining from the extraction process. The main weight
loss (30%), observed in the range 260–450 °C, accompa-
nied by an exothermic peak in the DTA curve, is attrib-
uted to the removal of organic functional groups
incorporated in the material framework. These data indi-
cate the successful incorporation of organic and inorganic
functional moieties and confirm the high thermal stability
of the material.
from TGA/DTA (Figure 6). The results show weight
3
.1.6 | Nitrogen adsorption–desorption
isotherms
The nitrogen adsorption–desorption results for MSNs and
[
pmim]FeCl /MSNs are plotted in Figure 7. The nitrogen
4
adsorption–desorption isotherms show typical type IV
TABLE 1 Optimization of reaction conditions for synthesis of N,N′‐
a
diarylformamidines
4
FIGURE 6 Thermal analyses (TGA/DTA) of [pmim]FeCl /MSNs
Temp.
(°C)
Catalyst
(mg)
Yield
(%)
b
Entry
Solvent
Time
1
2
3
4
5
6
7
8
9
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
Solvent‐free
r.t.
50
—
—
—
5
18 h
Trace
30
18 h
80
18 h
50
80
60 min
10 min
10 min
60 min
10 min
2 h
75
80
10
20
20
20
10
10
10
10
95
80
96
r.t.
40
100
96
H
2
O
Reflux
Reflux
Reflux
Reflux
45
10
11
12
EtOH
CH CN
Toluene
2 h
60
3
2 h
65
2 h
70
a
Reaction conditions: aniline (2 mmol), triethyl orthoformate (1 mmol), solvent‐
FIGURE 7 Nitrogen adsorption–desorption isotherms of (a) MSNs
and (b) [pmim]FeCl /MSNs
free or with solvent (5 ml).
b
4
Isolated yield.

6
of 9
NASRESFAHANI ET AL.
isotherms with an H1 hysteresis loop, characteristic of
mesoporous materials with uniform cylindrical pores.
The total surface area, pore volume and average pore
3.2 | Catalytic activity of [pmim]FeCl /MSNs
4
A preliminary investigation of the title reaction was carried
2
−1
3
−1
diameter are 796 m g , 0.490 cm
for MSNs, and 425 m g , 0.459 cm g and 2.9 nm
g
and 3.9 nm
out using [pmim]FeCl /MSNs as the catalyst, while aniline
4
2
−1
3
−1
and triethyl orthoformate were chosen as reactants in a model
reaction to optimize the reaction conditions. The results are
summarized in Table 1. The reaction does not proceed in
the absence of the catalyst at room temperature under neat
conditions (Table 1, entry 1). Stirring the mixture at 50 or
for [pmim]FeCl /MSNs, respectively. Such a decrease in
4
these parameters may indicate the ionic liquid successful
anchored on the surface of the ordered mesoporous
channels.
TABLE 2 Synthesis of N,N′‐diarylformamidines
a
Entry
Amine
Product
Time (min)
Yield (%)
M.p. (°C) (found)
M.p. (°C) (reported)
[18]
1
10
95
138–140
139–140
[
18]
2
3
4
5
5
5
93
95
95
88
178–179
184–186
139–141
126–128
179–180
[
[
[
21]
18]
19]
188–189
140–141
126–128
15
20
[
[
19]
19]
6
7
20
20
85
87
159–161
252–254
159–160
254–256
[18]
8
9
15
15
90
89
240–245
169–172
239–240
—
[
[
18]
22]
1
0
1
10
10
84
90
198–200
169–170
200–201
170–171
1
a
Isolated yield.

NASRESFAHANI ET AL.
7 of 9
8
0 °C also does not result in the formation of product even
amount and temperature does not improve the product yield
(Table 1, entries 6 and 8). In order to determine the effect
of media on the reaction, several solvents, namely water,
after prolonging the reaction time (Table 1, entries 2 and 3).
These negative results indicate the necessity of a catalyst.
Next, we investigated the reaction using various amounts of
EtOH, CH CN and toluene, were screened. The results reveal
3
[
pmim]FeCl /MSNs (5, 10, 20 mg) under solvent‐free
that polar solvents (e.g. water) do not promote the reaction
and non‐polar solvents (e.g. toluene) give the products in
moderate yields. This might be due to greater stability of
the catalyst in non‐polar solvents. However, the reactions
are sluggish and give poor yields with longer reaction times
in comparison with solvent‐free conditions (Table 1, entries
4
conditions at 80 °C. To our surprise, [pmim]FeCl /MSNs
4
(10 mg) shows outstanding activity in the formation of the
desired product in excellent yield within a much shorter
time (Table 1, entry 5). A further increase in the catalyst
9
–12). In other words, the optimal conditions for this reaction
TABLE 3 Comparison of result obtained for synthesis of N,N′‐
are 10 mg of [pmim]FeCl /MSNs under solvent‐free
4
diphenylformimidamide in the presence of [pmim]FeCl
4
/MSNs with
conditions at 80 °C.
those obtained using other methods
After optimizing the reaction conditions, the generality
of the method was evaluated using the reaction of
different substituted anilines with triethyl orthoformate in
Entry
Condition
Time Yield (%)
Ref.
[
[
[
18]
19]
21]
1
2
3
FeCl
3
, toluene, r.t.
3 h
87
95
93
the presence of [pmim]FeCl /MSNs under solvent‐free
β‐Cyclodextrin, H
2
O, r.t. 10 h
4
conditions (Table 2). Anilines substituted with either
electron‐releasing or electron‐withdrawing groups afford
high yields of products with excellent selectivity. So, this
procedure not only preserves the simplicity of the reaction
but also affords good yields of N,N′‐diarylformamidines.
Cerium(IV) ammonium
nitrate, H O, r.t.
15 min
2
[31]
4
5
Ultrasound, r.t.
[pmim]FeCl /MSNs
50 min
10 min
98
95
4
This work
4
SCHEME 3 Plausible mechanism for the synthesis of N,N′‐diaryl‐substituted formamidines in the presence of [pmim]FeCl /MSNs nanocatalyst

8
of 9
NASRESFAHANI ET AL.
In order to confirm that the catalytic activity arises from
pmim]FeCl /MSNs, we compared our results with those
[
4
previously reported in the literature (Table 3). It is clear that
the present method is superior in terms of reaction time and
amount of catalyst.
3
.3 | Plausible mechanism
Scheme 3 shows a plausible reaction pathway for the synthe-
sis of N,N′‐diarylformamidines. It is clear that the
nanocatalyst activates ethoxy groups and facilitates C─O
bond cleavage to generate oxonium ion I that easily
undergoes nucleophilic attack of aromatic amine and inter-
mediate II is formed. Intermediate II is activated by the cat-
alyst to afford oxonium ion III, which is followed by the
nucleophilic addition of aromatic amine to give intermediate
IV. Finally, the removal of EtOH from activated intermediate
FIGURE 9 FT‐IR spectra of fresh catalyst and that after the fifth run
[18,21]
IV affords the expected N,N′‐diarylformamidines.
3
.4 | Leaching of catalyst
A hot filtration test was performed to determine whether iron
is leached from catalyst during the reaction. The reaction
mixture was collected by filtration at the reaction temperature
(80 °C), and then washed with deionized water and diethyl
ether. The content of iron in the catalyst is 8.67 ppm. The
analysis of the reaction mixture using the ICP technique
shows that the leaching of iron is negligible and that the
catalyst is heterogeneous in nature.
FIGURE 10 SEM image of catalyst recovered after the fifth cycle
filtration after the reaction and washed with acetone. The
filtrates were subjected to a vacuum and the resulting cata-
lyst was reused directly for the next run. The procedure
was repeated, and the results indicate that the catalyst can
be recycled five times with a slight loss of its catalytic
activity (Figure 8).
The FT‐IR spectrum of the catalyst recovered after the
fifth reaction cycle gives a pattern similar to that of the
fresh catalyst (Figure 9). A SEM image of the catalyst
recovered after five runs shows there is no obvious change
in the morphology and size in comparison to the fresh
catalyst (Figure 10).
3
.5 | Recyclability of catalyst
The recovery of catalysts is highly preferable for green
processes. Thus, the reusability of the nanocatalyst was
investigated using aniline and triethyl orthoformate as
model substrates. The catalyst was easily recovered by
4
| CONCLUSIONS
We have introduced [pmim]FeCl /MSNs as a heterogeneous
4
nanocatalyst for the direct conversion of primary arylamines
to N,N′‐diaryl‐substituted formamidines. Compared to other
methods, this protocol is much more environmentally
friendly due to solvent‐free conditions. In addition, the proce-
dure provides some advantages like easy work‐up, short
reaction times and high isolated yields.
FIGURE 8 Reusability of [pmim]FeCl
N,N′‐diaryl‐substituted formamidines
4
/MSNs for the synthesis of

NASRESFAHANI ET AL.
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