A novel hydrophobic copper complex supported on γ-Fe2O3 as a magnetically heterogeneous catalyst for one-pot three-component synthesis of α-aminophosphonates

Article abstract of DOI:10.1002/aoc.3877

A novel hydrophobic copper complex supported on γ-Fe₂O₃ is synthesized and characterized by different methods such as FT-IR, XRD, TEM, SEM, TGA, VSM, ICP and CHN analysis. It was used as a magnetically recyclable heterogeneous cataly

Full text of DOI:10.1002/aoc.3877

Received: 30 January 2017
DOI: 10.1002/aoc.3877
Revised: 8 April 2017
Accepted: 12 April 2017
F U L L PA P E R
A novel hydrophobic copper complex supported on γ‐Fe O as a
2
3
magnetically heterogeneous catalyst for one‐pot three‐component
synthesis of α‐aminophosphonates
Sara Sobhani
| Fatemeh Khakzad
Department of Chemistry, College of
Sciences, University of Birjand, Birjand, Iran
A novel hydrophobic copper complex supported on γ‐Fe O is synthesized and
2 3
characterized by different methods such as FT‐IR, XRD, TEM, SEM, TGA,
VSM, ICP and CHN analysis. It was used as a magnetically recyclable heteroge-
neous catalyst for the efficient synthesis of α‐aminophosphonates via a one‐pot
three‐component reaction under solvent‐free conditions. The present catalytic
system worked extremely well for the synthesis of α‐aminophosphonates even up
to five subsequent trails without significant loss of its catalytic activity or copper
leaching. The TEM image and FT‐IR spectrum of the catalyst after five times
recovery showed that the structure of the catalyst was stable under the reaction
conditions with no change being observed. The strong magnetic properties of the
reused catalyst were revealed by complete and easy attraction using an external
magnet and also by VSM curve. This work represents the first and unique example
of a hydrophobic copper complex for catalysis in water generating reactions.
Correspondence
Sara Sobhani, Department of Chemistry,
College of Sciences, University of Birjand,
Birjand, Iran.
Email: ssobhani@birjand.ac.ir;
sobhanisara@yahoo.com
KEYWORDS
copper, heterogeneous catalysts, hydrophobic catalysts, magnetic nanoparticles, water generating reactions
1
| INTRODUCTION
handling and stability of the catalyst and improve the cata-
lyst regenerability and minimize the amount of waste
[
7,8]
In recent years, extensive efforts have been made to the
research dedicated to the development of environmentally
compatible processes. In this regard, elimination of the sol-
vent of the reaction is a safety issue especially when the
formed.
Along this line, a wide range of different hetero-
geneous catalysts have been synthesized by the immobiliza-
tion of homogeneous catalysts and complexes on the surface
[
9–15]
of different supporting materials.
[
1,2]
solvents are potentially toxic and flammable.
Hence,
Within the reported solid supports, magnetic nanoparti-
cles (MNPs) are one of the most outstanding supporting
material because of their magnetic nature, which allows the
facile recovery and recycling of the catalyst without use of
the traditional filtration method. Moreover, MNPs have
unique physical properties including high surface area,
surface modification ability, excellent thermal and chemical
the implementation of solvent‐free processes is one of the
favorable options. Moreover, the use of one‐pot multi‐step
reactions provides opportunities for reducing energy
consumption and waste production as well as decreasing
the quantities of reagents and solvents used.
processes become green, sustainable and attractive with
[
3–5]
These
[
16–30]
low‐cost, step‐saving, reduce the number of purification
stability.
In comparison with the mesoporous
[6]
steps and improve the overall efficiency. On the other
hand, the synthesis and application of heterogeneous cata-
lysts which is the current interest in chemistry and industry
offers more advantages such as simplicity in removal,
nanomaterials, there is not any mass transfer limitation
towards the active sites on the surface of MNPs. However,
considering the hydrophilic nature of MNPs, if the water
generates as a by‐product, it is adsorbed physically on the
Appl Organometal Chem. 2017;e3877.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.3877

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SOBHANI AND KHAKZAD
surface of the catalyst and poisons it. The adsorbed water on
the surface of the catalyst produces more hydrophilic envi-
ronment, reducing the mass transfer of hydrophobic starting
material towards the active sites of the catalyst and decreases
methods such as fourier transform infrared spectroscopy
(FT‐IR), X‐ray diffraction (XRD), transmission electron
microscopy (TEM), scanning electron microscopy (SEM),
thermogravimetric analysis (TGA), vibrating sample
magnetometer (VSM), inductively coupled plasma (ICP)
and elemental analysis (CHN). It was also used as a magnet-
ically recyclable heterogeneous catalyst for the one‐pot three‐
component synthesis of α‐aminophosphonates. This work
represents the first and unique example of a hydrophobic
copper complex for catalysis in water generating reactions.
[31–39]
the activity of the catalyst.
In particular, for one‐pot
multi‐step reactions in which water sensitive intermediates
should be subjected to further reaction, the presence of
adsorbed water on the catalyst surface retards the progress
of the reaction. In fact, the hydrophilic/hydrophobic balance
of the catalyst surface could significantly influence the
catalytic performance. Therefore, the design of heteroge-
neous catalysts with suitable surface polarity is an ultimate
goal in the development of solid catalysts. Recent
investigations have set out to address these issues by
immobilizing inert organic groups on the surface to alter
2
2
| EXPERIMENTAL
.1 | General information
[40–48]
the hydrophobicity of the heterogeneous catalysts.
In
Chemicals were purchased from Merck Chemical Company.
this context, several techniques for the synthesis of heteroge-
neous hydrophobic sulfonic acid catalysts have been
developed. As far as we know, there is not any report on
the synthesis of hydrophobic metal complexes supported on
solid materials.
NMR spectra were recorded on a Bruker Advance DPX‐250
in CDCl as solvent and TMS as internal standard. The purity
3
of the products and the progress of the reactions were accom-
plished by TLC on silica‐gel polygram SILG/UV254 plates.
FT‐IR spectra were recorded on a Shimadzu Fourier
Transform Infrared Spectrophotometer (FT‐IR‐8300). TEM
analysis was performed using TEM microscope (Philips
CM30). Scanning electron microscopy (SEM) by using a
SEM Phenom, model PROX. Thermo gravimetric analysis
(TGA) was performed using a Shimadzu thermo gravimetric
analyzer (TG‐50). Elemental analysis was carried out on a
Costech 4010 CHNS elemental analyzer. Power X‐ray
diffraction (XRD) was performed on a X'Pert Pro MPD
diffractometer with Cu Kα (λ = 0.154 nm) radiation.
Magnetic isotherms by using a vibrating sample magnetome-
ter VSM (LakeShore 7400). The content of Cu in the catalyst
was detemined by OPTIMA 7300DV ICP analyzer.
α‐Aminophosphonates as isoelectronic analogues of the
natural α‐aminoacids, constitute an important class of
compounds owing to their biological and physical properties
as well as their utility as synthetic intermediates. Their
biological applications as herbicides, fungicides, enzyme
inhibitors, plant growth regulators, antitumor, antibiotics,
peptide mimics, antiviral and pharmacological agents are
well documented. These enormous applications have
encouraged the development of a number of techniques for
[49,50]
the synthesis of α‐aminophosphonates.
Kabachnik‐
Fields reaction is one of the most direct and efficient routes
for the synthesis of α‐aminophosphonates. It involves one‐
pot three‐component reaction of aldehydes, amines and
[51–54]
phosphites catalyzed by different catalysts.
Although,
2
.2 | Synthesis of Schiff base supported on
the reported methods are acknowledging, most of them suffer
from one or more of the following drawbacks: high
temperature, low yields of the products, prolonged reaction
times, tedious work‐up procedures, use of air or moisture
sensitive catalysts, requiring stoichiometric amounts of toxic
and non‐recyclable catalysts, using hazardous solvents,
generating large amounts of waste and needing strictly
anhydrous conditions. Therefore, developing water tolerant,
highly efficient and recyclable catalyst for the one‐pot
three‐component synthesis of α‐aminophosphonates via
Kabachnik‐Fields reaction as a water generating protocol is
still desirable.
γ‐Fe O
2
3
[
62]
A mixture of amine‐functionalized γ‐Fe O3
(2 g) in dry
2
MeOH (50 mL) was sonicated for 30 min. A solution of
2,4‐dihydroxybenzaldehyde (0.12 g) in dry MeOH
(5 mL) was added dropwise to the dispersed amine‐func-
tionalized γ‐Fe O3 in MeOH and slowly heated to be
2
refluxed. The reaction mixture was stirred at this temper-
ature for 12 h. Schiff base supported on γ‐Fe O3 was
2
separated by an external magnet and washed with MeOH,
EtOH and Et O (3 × 15 mL) and dried under vacuum at
2
80 °C for 2 h.
As part of our ongoing research on the development of
[55–61]
new heterogeneous catalysts based on MNPs,
herein,
2
.3 | Synthesis of copper‐complex supported
we report the synthesis of a novel hydrophobic copper
on γ‐Fe O (γ‐Fe O ‐cu‐complex)
2
3
2
3
complex supported on MNPs (hydrophobic γ‐Fe O ‐Cu‐
2
3
complex) as a water tolerant heterogeneous catalyst. This
Schiff base supported on γ‐Fe O (2 g) was sonicated in
2
3
newly synthesized catalyst was characterized using various
dry MeOH (50 mL) for 30 min. A solution of CuCl .2H O
2
2

SOBHANI AND KHAKZAD
3 of 9
(0.08 g) in dry MeOH (5 mL) was added to the dispersed
silica gel column chromatography with n‐hexane/EtOAc
Schiff base supported on γ‐Fe O in MeOH and stirred
(2:1) as the eluent.
2
3
under reflux conditions for 10 h. The reaction mixture
was cooled to room temperature. The solid was separated
using an external magnet, washed with MeOH, EtOH
3
3
| RESULTS AND DISCUSSION
.1 | Synthesis and characterization of
and Et O (3 × 15 mL) and dried under vacuum at 80 °C
2
for 15 h.
hydrophobic copper complex supported on
MNPs (hydrophobic γ‐Fe O ‐cu‐complex)
2
3
2
.4 | Synthesis of hydrophobic copper‐complex
The route for the synthesis of hydrophobic copper
supported on γ‐Fe O
complex supported on MNPs (hydrophobic γ‐Fe O ‐Cu‐
2
3
2 3
complex) is schematically illustrated in Scheme 1. At
Copper‐complex supported on γ‐Fe O (2 g) was sonicated
2
3
first, amino‐functionalized γ‐Fe O was reacted with 2,4‐
2
3
in dry MeOH (50 mL) for 30 min. A solution of NaOH
0.04 g) in dry MeOH (5 mL) was added to the dispersed
copper‐complex supported on γ‐Fe O in MeOH and stirred
dihydroxybenzaldehyde to obtain Schiff base immobilized
(
on γ‐Fe O . The treatment of Schiff base immobilized on
2
3
2
3
γ‐Fe O with CuCl .2H O led to the formation of copper
2
3
2
2
at 50 °C for 5 min. 1‐Bromooctane (0.579 g) was added to
the resulting mixture and stirred under reflux conditions for
complex supported on MNPs. To end, the reaction of
Schiff base immobilized on γ‐Fe O with 1‐bromooctane
2
3
20 h. The solid was separated using an external magnet,
provided hydrophobic γ‐Fe O ‐Cu‐complex. The prepared
2
3
washed with MeOH, EtOH and Et O (3 × 15 mL) and dried
under vacuum at 80 °C for 24 h.
2
catalyst was characterized by various techniques including
FT‐IR, XRD, TEM, SEM, TGA, VSM, ICP and CHN.
FT‐IR spectrum of hydrophobic γ‐Fe O ‐Cu‐complex is
2
3
shown in Figure 1. The bands at around 550–670 and
1
2
.5 | General procedure for the synthesis of α‐
020–1040 cm− was attributed to the stretching vibration
1
aminophosphonates catalyzed by hydrophobic
of Fe‐O and Si‐O. The C‐H stretching mode of methylene
2
copper‐complex supported on γ‐Fe O3
−1
can be observed at 2900 cm . The absorption bands at
1
Hydrophobic copper‐complex supported on γ‐Fe O3
1610 and 1455 cm− were allocated to the stretching
vibration of C = N and C = C, respectively. These results
indicated that organic compound was successfully grafted
onto γ‐Fe O MNPs.
2
(0.0015 mmol, 0.0065 gr, 0.015 mol%) was added to the
mixture of aldehyde (1 mmol), amine (1 mmol) and
trialkylphosphite (1 mmol) and stirred at room temperature
for an appropriate time (Table 2. EtOAc (10 mL) was added
to the reaction mixture. The catalyst was separated using an
external magnet, washed several times with EtOAc, dried
and reused for a new trail. The resulting mixture after
evaporation of the solvent under vacuum was purified using
2
3
Powder X‐ray diffraction (XRD) pattern of hydrophobic
γ‐Fe O ‐Cu‐complex is shown in Figure 2. The reflection
2
3
planes of (220), (311), (400), (422), (511) and (440) at
2θ = 30.3°, 35.7°, 43.4°, 53.8°, 57.4° and 63.0° were
recognized from the XRD pattern. These observed diffraction
2 3
SCHEME 1 Synthesis of hydrophobic γ‐Fe O ‐cu‐complex

4
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SOBHANI AND KHAKZAD
2 3
FIGURE 1 FT‐IR spectrum of hydrophobic γ‐Fe O ‐cu‐complex
2 3
FIGURE 2 XRD of hydrophobic γ‐Fe O ‐cu‐complex
peaks are attributed to the diffraction scattering of γ‐Fe O .
2
3
°
The diffraction plane of (111) at 2θ = 37.4 in XRD pattern
of hydrophobic γ‐Fe O ‐Cu‐complex is ascribed to Cu.
2
3
The size and morphology of hydrophobic γ‐Fe O ‐Cu‐
2
3
complex were evaluated by TEM and SEM images
(Figure 3). According to the TEM images, nanoparticles have
an average diameter of 15 nm. The SEM image showed
uniform spherical morphology of MNPs.
The thermal behavior of hydrophobic γ‐Fe O ‐Cu‐com-
2
3
plex was investigated by TGA (Figure 4). As shown in
Figure 4, the weight loss at around 150 °C was related to
the loss of adsorbed water molecules. Other decreasing peak
from 200 to 800 °C due to the decomposition of the organic
groups was also seen in the TGA.
The amount of loading of hydrophobic Cu‐complex on
γ‐Fe O was determined by elemntal analysis, and it was
2
3
FIGURE 3 (a) SEM, (b,c) TEM images, and (d) particle size
distribution histogram of hydrophobic γ‐Fe O ‐cu‐complex
2 3
0
.46 mmol/g based on the nitrogen and carbon amounts
0.65% and 20.30%, respectively). The Cu content of
hydrophobic γ‐Fe O ‐Cu‐complex was quantified by ICP.
(
The magnetic properties of the hydrophobic γ‐Fe O ‐Cu‐
2
3
2 3
The ICP analysis showed that 0.23 mmol of Cu was
complex and γ‐Fe O3 were measured using a vibrating
2
anchored on 1 g of hydrophobic γ‐Fe O ‐Cu‐complex.
sample magnetometer (VSM) at 300°K (Figure 5). The
2
3

SOBHANI AND KHAKZAD
5 of 9
TABLE 1 One‐pot three‐component synthesis of α‐
aminophosphonates under different conditions
Time Yielda
Entry
Catalyst (mol%)
Solvent (min)
(%)
1
Hydrophobic γ‐Fe
complex (0.015)
2
O
O
O
O
O
O
O
3
‐cu‐
3
‐cu‐
3
‐cu‐
3
‐cu‐
3
‐cu‐
3
‐cu‐
3
‐cu‐
‐
70
120
150
135
105
120
120
95
2
3
4
5
6
7
Hydrophobic γ‐Fe
2
H
2
O
75
87
70
85
81
79
complex (0.015)
Hydrophobic γ‐Fe
2
DMF
complex (0.015)
Hydrophobic γ‐Fe
2
CH
CH
3
CN
OH
2 3
FIGURE 4 TGA of hydrophobic γ‐Fe O ‐cu‐complex
complex (0.015)
Hydrophobic γ‐Fe
2
3
complex (0.015)
Hydrophobic γ‐Fe
2
EtOAc
complex (0.015)
Hydrophobic γ‐Fe
2
‐
complex (0.012)
8
9
‐
‐
‐
‐
70
70
70
49
69
80
γ‐Fe
Hydrophobic cu‐complex
0.015)
2 3
O ‐cu‐complex (0.015)
1
0
(
a
Isolated yield. Benzaldehyde (1 mmol), aniline (1 mmol), triethylphosphite
1 mmol).
(
FIGURE 5 VSM curves of γ‐Fe
complex
2
O
3
and hydrophobic γ‐Fe
2
O
3
‐cu‐
of the product was obtained under solvent‐free conditions
(entry 1). By lowering the amount of the catalyst to
0
.012 mol%, the desired product was obtained in lower
yield (entry 7). Similar reactions in the absence of the cat-
samples showed a ferromagnetic nature. The saturation
alyst and in the presence of γ‐Fe O ‐Cu‐complex and
2
3
magnetization of γ‐Fe O was found to be 68.9 emu/g. As
hydrophobic Cu‐complex were also examined (entries 8–
10). The higher catalytic efficiency of hydrophobic γ‐
Fe O ‐Cu‐complex compared to these conditions, showed
2
3
expected after functionalization with hydrophobic Cu‐com-
plex, it was reduced to 52.7 emu/g. The magnetization curves
of the magnetic nanoparticles exhibit no hysteresis, which
demonstrates its superparamagnetic characteristic. The
magnetic behavior of hydrophobic γ‐Fe O ‐Cu‐complex
2
3
the role of this catalyst as a hydrophobic heterogeneous cat-
alyst for the one‐pot synthesis of α‐aminophosphonates. The
great catalytic performance is largely attributed to the
improvement of the active site accessibility by using n‐octyl
groups bounded on the Cu‐complex, which enabled the
repulsion of water from the proximity of the active sites.
Thus, the mass transfer of hydrophobic starting material
towards the active sites of the catalyst and the formation
of water‐sensitive imine in the first step of the reaction were
not retarded.
2
3
nanoparticles guarantees that they can be easily separated
with the help of an external magnetic field.
3
.2 | One‐pot three‐component synthesis of α‐
aminophosphonates catalyzed by hydrophobic
γ‐Fe O ‐cu‐complex
2
3
To explore the generality and scope of this method,
the reaction of various aldehydes, anilines and
trialkylphosphites was studied under optimal reaction con-
ditions (Table 2).
To find the optimized reaction conditions, one‐pot three‐
component reaction of benzaldehyde, aniline and
triethylphosphite in the presence of hydrophobic γ‐Fe O ‐
2
3
Cu‐complex (0.015 mol%) was chosen as a model reaction
Table 1). This reaction was investigated under solvent‐free
As indicated in Table 2, the catalytic reaction of
benzaldehyde and aniline with different trialkylphosphites
proceeded well and the desired products were produced in
88–95% yields (entries 1–3). A number of different
(
conditions and in different solvents such as H O, DMF,
2
CH CN, CH OH and EtOAc (entries 1–6). The best yield
3
3

6
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SOBHANI AND KHAKZAD
TABLE 2 One‐pot three‐component synthesis of α‐aminophosphonates catalyzed by hydrophobic γ‐Fe
2
O
3
‐cu‐complex
Entry
Aldehyde
Benzaldehyde
Amine
Aniline
Phosphite ester
P(OEt)
P(OMe)
P(O‐iso‐Pr)
Time (min)
Yield (%)
TON
TOF
[
[
[
[
[
[
[
[
[
63]
64]
65]
63]
63]
63]
66]
63]
63]
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
3
70
105
120
140
100
140
60
95
88
90
72
80
82
75
98
98
95
90
97
95
98
85
90
6333
5866
6000
4666
5333
5333
5000
6533
6533
6333
6000
6466
6333
6533
5666
6000
5459
3352
3000
2002
3212
2288
5000
5631
4355
7602
3000
6466
4222
5631
4018
2250
Benzaldehyde
Aniline
3
Benzaldehyde
Aniline
3
4‐methoxybenzaldehyde
4‐chlorobenzaldehyde
2‐nitrobenzaldehyde
2,6‐dichlorobenzaldehyde
Benzaldehyde
Aniline
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
P(OEt)
3
3
3
3
3
3
3
3
3
3
3
3
3
Aniline
Aniline
Aniline
4‐chloroaniline
p‐toluidine
2‐chloroaniline
4‐chloroaniline
Aniline
70
Benzaldehyde
90
[
[
[
[
[
[
[
63]
0
1
2
3
4
5
6
Benzaldehyde
50
67]
64]
66]
64]
65]
63]
4‐methoxybenzaldehyde
Cinnamaldehyde
120
60
Thiophene‐2‐carbaldehyde
Furan‐2‐carbaldehyde
2‐naphthaldehyde
Butyraldehyde
Aniline
90
Aniline
70
Aniline
60
Aniline
160
a
Isolated yield. Aldehyde (1 mmol), aniline (1 mmol), trialkylphosphite (1 mmol).
substituted benzaldehyde and anilines reacted with
triethylphosphite to afford the corresponding products in
good to high yields (entries 4–11). Acid‐sensitive aldehydes,
such
as
furfural,
thiophene‐2‐carbaldehyde
and
cinnamaldehyde underwent successful reaction with aniline
and triethylphosphite without any decomposition or
polymerization (entries 12–14). The present catalytic system
also offered promising results for the synthesis of α‐
aminophosphonates from naphtalaldehyde and butyralde-
hyde (entries 15 and 16). In all of the studied reactions, α‐
aminophosphonates were exclusively formed without any
formation of the products such as α‐hydroxyphosphonates.
This observation indicated excellent selectivity of this
method for the synthesis of α‐aminophosphonates. The reac-
tion of ketones with aniline and triethylphosphite was also
studied. However, the results were not as positive as those
above.
SCHEME 2
component synthesis of α‐aminophosphonates catalyzed by
hydrophobic γ‐Fe ‐cu‐complex
A plausible mechanism for the one‐pot three‐
2 3
O
A plausible mechanism for the one‐pot three‐component
reaction of aldehyde, aniline and trialkylphosphite in the
presence of hydrophobic γ‐Fe O ‐Cu‐complex is depicted
in Scheme 2. In the initial step of the catalytic cycle, imine
formation occurs via the reaction of aniline with the
activated aldehydes by the catalyst. n‐Octyl groups bounded
on the Cu‐complex enabled the repulsion of water from the
proximity of the active sites. Thus, the formation of water‐
2
3

SOBHANI AND KHAKZAD
7 of 9
sensitive imine in the first step of the reaction was not
retarded. In the second step, the addition reaction of
trialkylphosphite to the activated imine produced the desired
product. The process represents a typical water‐sensitive
intermediate formation in a one‐pot water generating
reaction.
The most important factors concerning a heterogeneous
catalyst are its stability and reusability along with the ease
of separation. In this regards, the recyclability of hydrophobic
γ‐Fe O ‐Cu‐complex was investigated in the Kabachnik‐
2
3
Fields
reaction
of
benzaldehyde,
aniline
and
triethylphosphite under optimized reaction conditions. After
the reaction was completed, EtOAc was added to the reaction
mixture. The catalyst was separated by an external magnet,
washed several times with EtOAc, dried and reused for a con-
secutive run under the same reaction conditions. As depicted
in Figure 6, the catalytic system worked extremely well even
up to five subsequent trails without significant loss of its cat-
alytic activity or copper leaching (ICP analysis of the catalyst
after five times reuse was investigated). Considering the
results of the leaching experiment, a slight decrease in the
product yield after five times reuse of the catalyst was attrib-
uted to the loss of the catalyst within the recovery and wash-
ing process. The TEM image of the catalyst after five times
recovery (Figure 7a), showed that the structure of the catalyst
was stable under the reaction conditions with no change
being observed. The FT‐IR spectrum of the catalyst showed
all the characteristic peaks of the fresh one (Figure 7b). As
illustrated in Figure 7c, the magnetization curve of hydropho-
bic γ‐Fe O ‐Cu‐complex after five times reuse exhibits no
2
3
hysteresis loop which demonstrates its superparamagnetic
characteristics. Moreover, the strong magnetic properties of
the reused catalyst were revealed by complete and easy
attraction using an external magnet (Figure 7d).
Finally, the catalytic efficiency of this catalyst for one‐pot
three‐component synthesis of α‐aminophosphonates was
compared with some of the reported magnetically recyclable
[68–75]
heterogeneous catalysts
in Table 3. The results in
Table 3 revealed the advantages of the present catalyst over
the other reported catalysts in terms of TON and TOF.
FIGURE 7 (a) TEM image, (b) FT‐IR spectrum and (c) VSM curve
FIGURE 6 Reusability of hydrophobic γ‐Fe
one‐pot three‐component synthesis of α‐aminophosphonates
2
O
3
‐cu‐complex in the
of hydrophobic γ‐Fe
separation of hydrophobic γ‐Fe
2
O
3
‐cu‐complex after five times reuse, and (d) easy
‐cu‐complex
2 3
O

8
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SOBHANI AND KHAKZAD
TABLE 3 Comparison of efficiency of hydrophobic γ‐Fe
the one‐pot synthesis of α‐aminophosphonates
2
O
3
‐cu‐complex with some reported magnetically recyclable heterogeneous catalysts for
a
TONb
TOFc
Entry
Catalyst (mol%)
Conditions
Time (min)
Yield (%)
[
[
[
[
[
[
[
[
68]
d
1
2
3
4
5
6
7
8
9
PTA/Si‐MNPs (20)
Solvent‐free, r.t.
Ultrasonic, r.t.
40–15
7–5
68–94
91–95
70–96
76–94
75–92
94–81
79–91
80–94
70–95
3–5
91–95
103–388
784–1439
60–575
69]
Nano‐γ‐Fe
Fe @Zr
Nano‐Fe
DHAA‐Fe
MgFe (1)
MNP@DSO
Fe @SiO
Hydrophobic γ‐Fe
0.015)
2 3
O (1)
70]
2−
3
O
4
2
O/SO
4
(1)
Solvent‐free, 80 °C
Solvent‐free, 50 °C
EtOH, 40 °C
120–20
55–48
60–15
120–120
35–25
70–20
140–90
6–8
71]
3
O
4
(5)
e
15–19
83–278
72]
3
O
4
(0.9)
83–102
94–81
40–95
73]
2
O
4
Solvent‐free, 35 °C
Solvent‐free, r.t.
Solvent‐free, r.t.
Solvent‐free, r.t.
37–83
74]
f
3
H (0.2)
‐2mimSO
‐cu‐complex
395–455
400–470
4666–6333
134–450
54–290
75]
g
3
O
4
2
3
H (0.2)
This work
2
O
3
2002–7602
(
a
Isolated yield.
b
TON = turnover number (mol of the product/mol of the catalyst).
c
TOF = TON per hour.
d
2 4
PTA/Si‐MNPs = 3‐chloromethoxypropylsilane and imidazole coated by CoFe O
e
f
DHAA‐Fe
3
O
4
= dehydroascorbic acid capped magnetite nanoparticle
H = poly(amidoamine)dendrimer supported on magnetic nanoparticle.
‐2mimSO H = chlorosulfonic acid supported on Fe @SiO
MNP@DSO
3
g
Fe
3
O
4
@SiO
2
3
3
O
4
2
4
| CONCLUSIONS
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How to cite this article: Sobhani S, Khakzad F. A
novel hydrophobic copper complex supported on
γ‐Fe O as a magnetically heterogeneous catalyst for
one‐pot three‐component synthesis of
α‐aminophosphonates. Appl Organometal Chem.
2017;e3877. https://doi.org/10.1002/aoc.3877
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