Synthesis of a copper(ii) complex covalently anchoring a (2-iminomethyl)phenol moiety supported on HAp-encapsulated-α-Fe2O3 as an inorganic-organic hybrid magnetic nanocatalyst for the synthesis of primary and secondary amides

Article abstract of DOI:10.1039/c5ra03977k

A novel hydroxyapatite-encapsulated-α-Fe₂O₃-based Cu(ii) organic-inorganic hybrid (interphase) catalyst was prepared. The prepared nanocatalyst provided an efficient, useful and green method for the oxidative amidation of aromatic aldehydes with ammonium hydrochloride and aniline hydrochloride, in short reaction times and good yields. The magnetic nature of the catalyst led to its easy recovery by an external magnetic field and convenient reuse.

Full text of DOI:10.1039/c5ra03977k

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Synthesis of copper(ΙΙ) complex covalently
anchoring (2ꢀiminomethyl)phenol moiety
supported on HApꢀencapsulatedꢀαꢀFe2O3 as an
inorganic–organic hybrid magnetic nanocatalyst
for the synthesis of primary and secondary
amides
Cite this: DOI: 10.1039/x0xx00000x
Received,
Accepted
DOI: 10.1039/x0xx00000x
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M. Mamaghani*, F. Shirini, M. Sheykhan, M. Mohsenimehr
A novel hydroxyapatiteꢀencapsulatedꢀαꢀFe2O3ꢀbased Cu(II) organicꢀinorganic hybrid (interphase) catalyst
was prepared. The prepared nanocatalyst provided an efficient, useful and green method for the oxidative
amidation of the aromatic aldehydes with ammonium hydrochloride and aniline hydrochloride, in short
reaction times and good yields. Magnetic nature of the catalyst led to its easy recovery by an external
magnetic field and convenient reuse.
Introduction
carboxylic acids or coupling with carboxylic acids mediated by
a coupling reagent.8,9 However, these methods have the innate
Homogeneous catalysts have some advantages due to their
uniform and well defined reactive centres which lead to their
high activity and selectivity. Also, homogeneous catalysts
allow for more effective mixing of the catalyst with the reaction
mixture (occupy the same phase as the reactants), which in turn
creates problems of catalyst separation from the reaction
mixture and therefore the catalyst is difficult to reuse. To solve
this problem, several methods have been checked out to
combine the advantages of homogeneous and heterogeneous
catalysis.1 In this respect, nanoparticles (NPs), especially
magnetic NPs (MNPs) have appeared as a bridge between
homogeneous and heterogeneous catalysts. The magnetic
nature of these particles allows for easy recovery (green
chemistry) and recycling of the catalysts by an external
magnetic field.2 To improve the chemical stability as well as to
achieve some advantages as the versatility in surface
modification, MNPs commonly coat with different organic or
inorganic compounds, precious metals and recently calcium
hydroxyapatite Ca10(PO4)6(OH)2 (HAp).3
Covalently combining an active site onto a large surface area
solid through a flexible spacer to create an organicꢀinorganic
hybrid (interphase) catalyst is known as a way to simulate
homogeneous reaction conditions together with having the
advantage of recyclability.1,4,5
On the other hand, amide bonds have been found in many
natural important polymers such as peptides and proteins and in
a wide range of biological compounds, such as pharmaceuticals
and is also employed as synthetic intermediates for fine
chemical industry and agrochemicals.6,7 Commonly, the amide
bond is synthesized by acylation of amines with either activated
problems of producing waste products, use of hazardous
reagents and poor atom economy.10 To solve these problems in
amide synthesis, novel methods were developed, such as direct
amide synthesis from alcohols with amines or nitroarenes,11
amino carbonylation of haloarenes,12 hydroamination of
alkynes, amidation of thioacids with azides,13 transamidation of
primary amides,14 and C–H oxidative amidation.15
Among these, oxidative amidation of aldehydes with amine
salts is synthetically useful and less hazardous than those
traditionally used such as acid halides, which was first reported
by Nakagawa et al. in 1966 using stoichiometric amounts of
nickel peroxide as the oxidant.16 Subsequently, other
researchers have used new oxidants and novel catalysts for the
direct conversion of aldehydes to amides.
More recently, Yoo and Li introduced a copperꢀcatalyzed
procedure for oxidative amidation of aldehydes with amine
hydrochlorides using CuI−AgIO3 as the catalyst and tertꢀbutyl
hydroperoxide as the oxidant.17
In the years since, other copper catalysts such as Cu(OAc)2 and
CuSO4.5H2O have been reported for the amidation reactions.18
Silicaꢀcoated magnetic carbon nanotubes (MagCNTs@SiO2)ꢀ
immobilized imine–Cu(I) was also introduced as a magnetic
heterogeneous catalyst for the synthesis of different types of
amides.19 Although, significant advances have been achieved in
this field, but introduction of an efficient, economical and
greener catalyst is still desirable.
On the basis of the above concerns, we report herein a novel
copper(ΙΙ)
complex
covalently
anchoring
(2ꢀ
iminomethyl)phenol moiety supported on HApꢀencapsulatedꢀαꢀ
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DOI: 10.1039/C5RA03977K
Fe2O3 (denoted as catalyst
4) (Scheme 1) as an inorganicꢀ diffractometer with CoKα radiation. The ICP analysis showed
organic hybrid magnetic nanocatalyst for efficient oxidative that 4.9% of Cu was anchored on catalyst 4. It means that there
amidation of aromatic aldehydes with amine hydrochloride and is about 0.8 mmol (Cu) per gram of the catalyst.
aniline hydrochloride.
HAP
HAP
P
O
i
iii
α-Fe2O3
NH2
FeCl2.4H2
O
P
O
Si
iv
ii
P
O
FeCl3.6H2
O
2
3
HAP
HAP
1
P
O
P
O
v
α-Fe2O3
α-Fe2O3
P
O
P
O
N
Si
Si
N
Cl
Cl
P
O
P
O
Cu
HO
O
H
4
Scheme
1.
i) Ca(NO3)2, (NH4)2HPO4, NH4OH, ii) calcination, iii) 3-
Wavenumber (cm-1
)
aminopropyltrimethoxysilane, toluene, reflux, 48 h, iv) 2-hydroxy benzaldehyde,
dry EtOH, reflux, 24 h, v) CuCl2, EtOH, r.t., 12 h.
Fig. 1. FT-IR spectrum of catalysts
3 and 4
Results and discussion
In continuation of our research devoted to the development of
new benign methodologies for the preparation of magnetic
nanoparticles,3a,20 we were interested in the synthesis of amide
derivatives using nanocatalyst
4 (Scheme 1). The magnetic
nanoparticles (Fe3O4) were synthesized by a chemical coꢀ
precipitation technique using ferric and ferrous ions. Based on
our previous report,3a after coating a layer of hydroxyapatite on
the surface of the Fe3O4 nanoparticles and its calcination at
450oC, it was functionalized by 3ꢀaminopropyltrimethoxysilane
to produce an organic–inorganic hybrid. Then, the prepared
hybrid was reacted with 2ꢀhydroxybenzaldehyde to obtain a biꢀ
dentate ligand functionalized coreꢀshell magnetic nanocatalyst
Fig.2. XRD spectra of catalyst 4
(named as catalyst
complexed with copper(ΙΙ) by using CuCl2 (Scheme 1). The
nanocatalyst was characterized by various microscopic and
3). Finally, surfaceꢀbound ligands were
4
spectroscopic techniques such as XRD, FTꢀIR, ICP, SEMꢀ
EDX, VSM. In the FTꢀIR spectrum (Fig. 1), the absorption
peak at 464 cmꢀ1 can be assigned to the FeꢀO absorption in the
hematite.21 The O–P–O surface phosphate groups in the
hydroxyapatite shell appeared at 570 and 604 cmꢀ1 which were
in overlap with Fe–O stretching. Also, the P–O stretching
appeared at 1040 cmꢀ1. Signals at around 1419 and 1458 cmꢀ1
related to the aromatic C=C stretching as well as a signal at
1629 cm−1 produced by C=N double bond confirm that the
organic linker was properly immobilized onto the surface. Note
that the C=N signal is shifted to a lower wavenumber than the
C=N stretching frequency of
3
(1629 cmꢀ1 rather than 1634
cm−1). It is implying that C=N bond is coordinated to copper
through the lone pair of nitrogen and oxygen. In XRD analysis
Fig. 3. SEM image of catalyst
4
(Fig. 2), the resulted patterns can be readily referred to αꢀFe2O3
The morphology and size details were investigated by SEM
measurement (Fig. 3). The SEM image of the catalyst clearly
showed the nano size of the particles (with an average about 50
nm) and their morphology is spherical. The SEM image of the
catalyst taken after the fifth cycle of the reaction did not show
significant change in the morphology or in the size of the
(JCPDS no. 33ꢀ0664), and hydroxyapatite (JCPDS no. 24ꢀ
0033). Diffraction peaks at around 28.0o, 38.6o, 41.6o, 47.8o,
58.0o, 63.6o, 66.8o, 68.0o, 72.8o and 74.2o correspond to the
(012), (104), (110), (113), (024), (116), (122), (018), (214) and
(300) reflections patterns of hematite. No other phase except
the hematite and hydroxyapatite is detectable. The
measurements were carried out on
a
Philips X’Pert
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catalyst nanoparticles (58 nm) (Fig. 4), which indicates the amidation of aromatic aldehydes and the reaction conditions,
retention of the catalytic activity after recycling.
such as temperature, reaction time, oxidant and molar ratio of
Fig. 6. VSM curve of catalyst 4.
Fig. 4. SEM image (after the fifth cycle of the reaction) of catalyst
4
the catalyst to substrate was optimized (Table 1). We found that
The EDX spectrum of the nanocatalyst is presented in Fig. 5,
atoms such as Fe, Si, Ca, P, Cu and Cl related to the catalyst
structure, are seen in the spectrum. Based on the EDX spectrum
the copper:chlorine:nitrogen content of the catalyst were found
to be in ratio of 1.2 : 2.03 : 1.0.
the reaction of
pꢀchlorobenzaldehyde (1 mmol), ammonium
chloride (2 mmol) and tertꢀbutylhydroperoxide (TBHP) (0.4
mL) as oxidant in CH3CN (1 mL ) in the presence of
nanocatalyst (10 mg, 0.8 mol%) and Na2CO3 (2 mmol) as base,
at 50°C under Ar atmosphere, produce the desired primary
amide 5a in 40 min and 78% yield (Table 1, entry 1). As shown
in Table 1, entry 1, TBHP, based on the reaction time and yield,
was proved as selected oxidant at 50°C. In comparison, the
reaction at room temperature resulted in a pronounced
reduction in the yield of product 5a and increasing the reaction
time did not change the efficiency of the reaction significantly
(Table 1, entry 4).
The oxidation efficiency of TBHP was also compared against
H2O2 (Table 1, entry 2), and the effect of various solvents was
examined (Table 1). The results revealed that TBHP in CH3CN
produce a better result and in most of the cases it is not
necessary to use the chromatographic methods for separation of
the products.
The procedure led to a green method for the synthesis of
primary and secondary amides (5a-k, 6a-e, Scheme 2, Table 2).
Table1. Optimization of reaction conditions for synthesis of 4ꢀ
chlorobenzamide in the presence of nanocatalyst 4.
Fig. 5. EDX spectra of catalyst
4
Entry
Oxidant
Solvent
Temperature Yield Time
Magnetic characterization of the nanoparticles, which accounts
for its easy recovery, was done using a vibrating sample
magnetometer (VSM) at room temperature, with the field
sweeping from ꢀ8500 to +8500 Oersted. The M(H) hysteresis
loop for the sample was completely reversible and the ratio of
magnetic remanence (Mr)/magnetic saturation (Ms) is about
0.0005, Ms=3.71 emu.gꢀ1, showing that the nanoparticles
exhibit superparamagnetic characteristics (Fig. 6).
(°C)
(%)a
78
50
40
45
45
39
47
24
54
(min)
1
2
3
4
5
6
7
8
9
TBHP
H2O2
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
50
40
50
40
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
r.t.
r.t.
r.t.
50
40
90
120
40
H2O+CH3CN(1:1)
THF
50
40
DMF
Toluene
50
40
50
40
After characterization, catalytic activity of the catalyst was
tested in the oxidative coupling of the aromatic aldehydes with
ammonium chloride and aniline hydrochloride. In a preliminary
a Isolated yield. b Reaction conditions: pꢀchlorobenzaldehyde (1 mmol),
ammonium chloride (2 mmol), nanocatalyst 4 (10 mg, 0.8 mol%), solvent (1
mL), Na2CO3 (2 mmol), oxidant (0.4 mL.), Ar atmosphere.
experiment the reaction of
pꢀchlorobenzaldehyde and
ammonium chloride was chosen as a model reaction for
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VJieowuArrtnicalelONnlainme e
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O
Cu(II)
Cu(I)
t-BuOOH
t-BuOOH
Ar
H
O
t-BuOO
PhNH2
t-BuO
Ar
Scheme 2. Synthesis of amide derivatives in the presence of nanocatalyst 4.
t-BuO
+
+
PhNH2
t-BuO
Ar
As shown in the Table 2, aromatic aldehydes having both
electronꢀdonating and electronꢀwithdrawing groups were
converted to the related amides in good yields. Also in some
cases the yield of secondary amides is slightly higher than the
primary amides.
O
O
PhNH2
+
+
H
PhHN
Ar
Reusability of the catalyst was also reꢀchecked in the
preparation of 5a. After completion of the reaction, the
nanocatalyst was separated from the reaction medium simply
by an external magnetic field, washed with ethyl acetate, dried
under vacuum and reused for the next run. After 5 successive
runs the catalytic activity of the catalyst was almost remained
unchanged (Fig. 2).
Scheme 3. The Postulated mechanism for the catalytic amidation in the presence
of the catalyst
4
On the basis of the reaction conditions, we propose that in the
first step (Scheme 3) catalyst reacts with TBHP generating a
4
tertꢀbutylperoxy radical following the mechanism proposed in
25
literature and a Cu(I)–anchored on the catalyst surface is reꢀ
Table 2. Synthesis of amide derivatives
oxidized by another TBHP. The aniline hydrochloride is then
converted into an amino radical by the resulting tertꢀbutyloxy
radical. The reaction between aldehyde and tertꢀbutylperoxy
lead to an acyl radical, as reported previously.26 Finally, a
terminative coupling reaction occurs between the acyl radical
and the amino radical to form the desired amide. To confirm the
radical pathway of the reaction, it was repeated in the air
(absence of argon atmosphere). In these conditions, no product
was obtained after 24 h.
Entry
1
2
3
4
5
6
7
8
Ar
4ꢀClC6H4
4ꢀHOCC6H4
Thiophenꢀ2ꢀyl
4ꢀCNC6H4
Cinnamaldehyde
4ꢀFC6H4
Product Yield (%)a,b
m.p.
5a
5b
5c
5d
5e
5f
78
76
77
76
75
77
78
75
75
77
74
83
84
81
79
80
177ꢀ179 [16]
178ꢀ181
126ꢀ128 [22]
146ꢀ148 [22]
147ꢀ149 [22]
138ꢀ140 [22]
192ꢀ194 [18]
165ꢀ167 [18]
141ꢀ143 [22]
128ꢀ130 [24]
189ꢀ191 [18]
192ꢀ193 [23]
204ꢀ206 [23]
164ꢀ166 [23]
178ꢀ180
4ꢀBrC6H4
5g
5h
5i
4ꢀ H3COC6H4
3ꢀO2NC6H4
C6H5
4ꢀCF3C6H4
4ꢀClC6H4
4ꢀBrC6H4
C6H5
Thiophenꢀ2ꢀyl
2,4ꢀCl2C6H3
9
10
11
12
13
14
15
16
5j
5k
6a
6b
6c
6d
6e
In order to show the efficiency of present protocol, we
compared our results for amidation of
pꢀchlorobenzaldehyde
with previously reported methods and the results are shown in
Table 3. As it is evident from the results this method avoids the
disadvantages of some other methods such as longer reaction
time and harsh reaction conditions.
199ꢀ201
aIsolated yield, bReaction times 40ꢀ42 min, [ ] reported references.
Table 3. Comparison of various catalysts for the amidation of pꢀ
chlorobenzaldehyde with ammonium chloride.
Yield
(%)
Entry
Time
Catalyst
reference
1
2
3
4
4
89.4
4 h
4 h
6 h
5 h
40 min
Nickel peroxide
[16]
[18]
[19]
This work
This work
48
52
46
78
Cu2O
MagCNTs@SiO2–linker–CuI
CuCl2
Catalyst 4
Experimental section
Material and method
Melting points were measured on an Electrothermal 9100
apparatus. FTꢀIR spectra were determined on a Bruker Alfa FTꢀ
IR spectrometer. 1H NMR (400 MHz) and 13C NMR (100
MHz) spectra were recorded on a Bruker DRXꢀ400 in DMSOꢀ
d6 as solvent and TMS as an internal standard. Chemical shifts
Fig. 2. The reusability of the catalyst
compound 5a.
4 in five runs for the preparation of
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1
on H and 13C NMR were expressed in ppm downfield from Hz, 1H), 7.87 (d,
J
= 5.2 Hz, 1H), 7.72 (d,
J = 7.6 Hz, 2H), 7.36
tetramethylsilane. Elemental analyses were performed on a (t, = 7.6 Hz, 2H), 7.23 (dd,
J
J
= 5.2, 3.6 Hz, 2H), 7.12 (t, J =
CarloꢀErba EA1110CNNOꢀS analyzer and agreed (within 0.30) 7.2 Hz, 1H); 13C NMR (100 MHz, DMSOꢀd6) δC: 159.8, 140.0,
with the calculated values. XRD was carried out on a Philips Xꢀ 138.7, 131.8, 129.1, 128.6, 128.0, 123.7, 120.3; Anal. Cald. for
Pert diffractometer using Co tube. Scanning electron C11H9NOS (203.3): C, 65.00; H, 4.46; N, 6.89; Found: C,
microphotographs (SEMꢀEDX) were obtained on a PHILIPS 65.16; H, 4.35 ; N, 6.75 %.
XL30 electron microscope. ICP analysis was accomplished 2,4ꢀDichloroꢀ
using
VISTAꢀPRO, CCD simultaneous ICP analyzer. (KBr) νmax/cm−1: 3342 (NꢀH), 1659 (CONH); 1H NMR (400
Magnetic properties of catalyst were obtained by vibrating MHz, DMSOꢀd6) δH: 10.54 (s, br., 1H, NH), 7.78 (d, = 2.0
sample magnetometer/Alternating Gradient Force Hz, 1H), 7.70 (d, = 8.0 Hz, 1H), 7.64 (d, = 8.0 Hz, 2H), 7.56
Magnetometer (VSM/AGFM, MDK Co, Ltd, Iran). All the (dd, = 8.2, 2.0 Hz, 1H), 7.35 (m, 2H), 7.13 (t, = 7.4 Hz, 1H);
Nꢀphenylbenzamide (6e): yellow powder, IR
a
J
J
J
J
J
chemicals were purchased from Merck and used without further 13C NMR (100 MHz, DMSOꢀd6) δC: 164.0, 138.8, 135.8, 134.8,
purification. All solvents used were dried and distilled 130.3, 129.2, 128.8, 128.7, 127.4, 124.0, 119.5; Anal. Cald. for
according to standard procedures.
C13H9Cl2NO (266.1): C, 58.67; H, 3.41; N, 5.26; Found: C,
58.77 ; H, 3.52 ; N, 5.11 %.
General procedure for the synthesis of catalyst 4
[αꢀFe2O3@HApꢀSiꢀ(CH2)3ꢀNH2] was synthesized according to Conclusion
the references3a,27 with a few modification and then was
allowed to react with equimolar amount of 2ꢀ
hydroxybenzaldehyde in super dry ethanol for 24 h under Ar
atmosphere. Then, the solid product was magnetically separated
by an external magnet and washed with dry ethanol to produce
In conclusion, a novel heterogeneous HApꢀencapsulatedꢀαꢀ
Fe2O3ꢀbased Cu(II) organicꢀinorganic hybrid nanocatalyst was
successfully produced and its catalytic activity was explored in
the synthesis of amide derivatives from aromatic aldehydes
with ammonium chloride and aniline hydrochloride in good
yield and lower reaction time. The magnetic nature of this
nanaocatalyst allows its easy recovery and recycling by an
external magnetic field.
the catalyst
3 (Scheme 1). A stirring mixture of catalyst 3 and
CuCl2 in ethanol were heated at room temperature for 12 h. The
resultant light brown precipitate formed was filtered, washed
repeatedly with ethanol, and airꢀdried under vacuum at room
temperature to produce catalyst 4.
Acknowledgment
General procedure for the synthesis of amide derivatives (5a-k,
6a-e)
The authors are grateful to the Research Council of University
of Guilan for the financial support of this research work.
A mixture of ammonium chloride or aniline hydrochloride (2
mmol), aryl aldehyde (1 mmol), Na2CO3 (0.21 g, 2 mmol) and
nanocatalyst (0.01 g, 1.4 mol%) in acetonitrile (1 mL) was
stirred at room temperature. Then tertꢀbutyl hydroperoxide
(TBHP) (0.4 mL) was added under argon atmosphere. The
reaction mixture was stirred at 50°C for 40 min. The progress
Notes and reference
Department of Chemistry, Faculty of Sciences, University of Guilan, P.
O. Box 41335ꢀ1914, Rasht,
chem41@guilan.ac.ir;Tel.: (+98) 13 33770899; Fax:(+98) 13 33333262
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Iran. Eꢀmail address: mꢀ
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After completion of the reaction, the reaction mixture was
diluted with ethyl acetate and the catalyst was easily separated
by an external magnet and was washed several times with ethyl
acetate. The mixed organic solvents were concentrated under
vacuum to furnish the desired products (5a-k, 6a-e). All
isolated products were identified by spectroscopic analysis (FTꢀ
1
IR, H NMR and 13C NMR). The spectral data and melting
points of known compounds were compared with those
reported in the literature.
4ꢀFormylbenzamide (5b): white powder, IR (KBr) νmax/cm−1:
3375, 3178 (NH2), 1664 (CONH); 1H NMR (400 MHz, DMSOꢀ
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d6) δH: 10.09 (s, br., 1H, CHO), 8.24 (s, br., 2H, NH), 8.07 (d,
J
= 8.0 Hz, 1H), 7.98 (d,
J
= 8.0 Hz, 1H); 13C NMR (100 MHz,
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,
441ꢀ447.
DMSOꢀd6) δC: 192.9, 167.6, 132.3, 129.3, 128.1, 127.3; Anal.
Cald. for C8H7NO2 (149.1): C, 64.42; H, 4.73; N, 9.39; Found:
C, 64.51 ; H, 4.55 ; N, 9.20 %.
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View Article Online
DOI: 10.1039/C5RA03977K
Graphical abstract
Synthesis of copper(ΙΙ) complex covalently anchoring (2ꢀ
iminomethyl)phenol moiety supported on HApꢀencapsulatedꢀαꢀ
Fe2O3 as an inorganic–organic hybrid magnetic nanocatalyst for
the synthesis of primary and secondary amides
M. Mamaghania,*, F. Shirinia, M. Sheykhana, M. Mohsenimehra
aDepartment of Chemistry, Faculty of Sciences, University of Guilan, P. O. Box 41335-1914, Rasht, Iran. E-mail address: m-
chem41@guilan.ac.ir; Tel.: (+98) 13 33770899; Fax: (+98) 13 33333262
catalyst 4
Na2CO3, TBHP
CH3CN, 50oC, 40 min
O
O
+
RNH2HCl
Ar
H
Ar
R = H,
R
5a-k
6a-e
16 examples
R = Ph,