A manganese Schiff base complex immobilized on copper–ferrite magnetic nanoparticles as an efficient and recyclable nanocatalyst for selective oxidation of alcohols

Article abstract of DOI:10.1007/s11243-018-0244-2

A magnetically recoverable nanocatalyst was synthesized by covalent binding of a Schiff base ligand, namely N,N′-bis(Salicylidene)-1,3-diaminopropane-2-ol (H₂salpn), onto the surface of silica-coated magnetic CuFe₂O₄ nanoparticles, followed by complexation with MnCl₂. The resulting core–shell nanoparticles were characterized by spectroscopic and microscopic methods, including FTIR, XRD, VSM, TGA elemental analysis, TEM, and SEM. The Mn content was determined by ICP analysis. The nanoparticles were investigated as a catalyst for the selective oxidation of alcohols to the corresponding carbonyl compounds with tertiary-butyl hydrogen peroxide. The catalyst can be magnetically separated for reuse, with no noticeable loss of activity in subsequent reaction cycles. FTIR, VSM, and leaching experiments after three successive cycles confirmed that the catalyst was strongly anchored to the magnetic nanoparticles. A suitable mechanism for the reaction is proposed.

Full text of DOI:10.1007/s11243-018-0244-2

Transition Metal Chemistry
https://doi.org/10.1007/s11243-018-0244-2
A manganese Schif base complex immobilized on copper–ferrite
magnetic nanoparticles as an efcient and recyclable nanocatalyst
for selective oxidation of alcohols
Mahmood Tavakoli Hafshejani1 · Samira Saeednia1 · Mehdi Hatef Ardakani1 · Zahra Pakdin Parizi2
Received: 18 February 2018 / Accepted: 2 May 2018
© Springer International Publishing AG, part of Springer Nature 2018
Abstract
A magnetically recoverable nanocatalyst was synthesized by covalent binding of a Schif base ligand, namely N,N′-
bis(Salicylidene)-1,3-diaminopropane-2-ol (H2salpn), onto the surface of silica-coated magnetic CuFe2O4 nanoparticles,
followed by complexation with MnCl2. The resulting core–shell nanoparticles were characterized by spectroscopic and
microscopic methods, including FTIR, XRD, VSM, TGA elemental analysis, TEM, and SEM. The Mn content was deter-
mined by ICP analysis. The nanoparticles were investigated as a catalyst for the selective oxidation of alcohols to the
corresponding carbonyl compounds with tertiary-butyl hydrogen peroxide. The catalyst can be magnetically separated for
reuse, with no noticeable loss of activity in subsequent reaction cycles. FTIR, VSM, and leaching experiments after three
successive cycles confrmed that the catalyst was strongly anchored to the magnetic nanoparticles. A suitable mechanism
for the reaction is proposed.
Introduction
Oxidation reactions are generally carried out in homoge-
neous systems. Although homogeneous catalysts often show
higher catalytic activities than their heterogeneous counter-
parts, they can also sufer from difculties of separation
and recovery of the catalyst from both the reaction mixture
and the products [8–13]. Therefore, the immobilization of
homogeneous catalysts on solid supports has attracted sub-
stantial interest. Recently, various supports have been used
for the immobilization of homogeneous catalysts, includ-
ing mesoporous silica [14–18], polymers [19, 20], activated
carbon [21, 22], and inorganic nanoporous materials [23].
Magnetic nanoparticles have attracted considerable attention
due to their unique properties. They have been used in vari-
ous felds such as magnetically assisted drug delivery, mag-
netic resonance imaging, contrast agents and hyperthermia
treatments [24–29]. One of the most frequent applications
of magnetic nanoparticles is as a substrate for catalysts [30,
31].
Oxidation reactions are among the most useful processes
in organic synthesis, since the products of these reactions
are widely used as intermediates in the pharmaceutical and
fne chemical industries [1, 2]. Among the various kinds of
oxidations, the oxidation of alcohols to carbonyl compounds
is an essential transformation in the laboratory as well as
industry [3, 4]. Traditional oxidation methods are associated
with heavy metals, toxic and environmentally polluting rea-
gents, high temperatures, and moderate chemoselectivities.
Therefore, much research has been focused on the develop-
ment of economical and environmentally benign oxidation
processes [5–7].
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11243-018-0244-2) contains
supplementary material, which is available to authorized users.
Ferrites are a class of magnetic nanoparticles which have
found various applications as image contrast agents [32],
bioseparation sensors [33, 34], and biomedicines [35, 36].
There have been widespread studies on the synthesis of mag-
netic core–shell nanostructures because of their particular
magnetic properties [37–39]. Coating a silica shell around
magnetic nanoparticles provides several advantages, such
as improving the dispersion and enhancement of catalytic
* Samira Saeednia
sami_saeednia@yahoo.com; s.saeednia@vru.ac.ir
1
Department of Chemistry, Faculty of Science, Vali-e-Asr
University of Rafsanjan, Rafsanjan 77188-97111, Iran
2
Department of Nuclear Medicine and Molecular Imaging,
Razavi Hospital, Mashhad 9198613676, Iran
Vol.:(0123456789)
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Transition Metal Chemistry
activity [40]. The silica layer can also protect the core from
corrosion during oxidation and epoxidation reactions [41].
The immobilization of manganese complexes on solid
supports has already received much attention. Manganese
complexes are often easily synthesized, with mild reaction
conditions and short reaction times [42–46]. Given that fer-
rites require an inert atmosphere for synthesis [42, 43], in
this study copper–ferrite was used as a magnetic core. The
magnetism of this material is almost the same as that of fer-
rites, but the preparation is easier, with no need for an inert
atmosphere. To the best of our knowledge, this is the frst
report on the synthesis of a Mn Schif base complex immo-
bilized on copper–ferrite nanoparticles as a magnetic core.
This report describes a simple and efcient synthesis of a
copper–ferrite supported magnetically recyclable and inex-
pensive manganese Schif base catalyst and its application
for the oxidation of alcohols to the corresponding carbonyl
compounds using tertiary-butyl hydrogen peroxide (TBHP)
in ethanol. The catalyst can be easily and completely sep-
arated from the reaction mixture by the application of an
external magnetic feld.
plates. TEM analysis was performed with a TEM micro-
scope (Philips CM30). FTIR spectra were recorded in the
4000–400 cm−1 region, using KBr disks, on a Thermo
SCIENTIFIC model NICOLET iS10 spectrophotometer.
Elemental analyses were obtained on a LECO CHNS-932
analyzer. Thermogravimetric analysis (TGA) was performed
on a computer-controlled Rheometric Scientifc model STA
1500 instrument. Powder X-ray diffraction (XRD) was
performed on a Philips X’pert difractometer with Cu Kα
(λ=0.154 nm) radiation. Room-temperature magnetization
isotherms were obtained using a vibrating sample mag-
netometer (VSM, LakeShore 7400). The Mn content in the
catalyst was determined with an ICP-OES Optima DV7300
inductively coupled plasma analyzer. Gas chromatography
experiments were performed with a Shimadzu 16A chroma-
tograph using a column packed with silicon DC-200 and a
fame ionization detector (FID).
Preparation of CuFe2O4 nanoparticles
CuFe2O4 nanoparticles were prepared by thermal decom-
position of copper and iron salts in water in the presence of
NaOH [44]. In a generic experiment, a solution of NaOH
(3 g) in deionized water (15 mL) was added to a solution
of Fe(NO3)3·9H2O (3.34 g, 8.2 mmol) and Cu(NO3)2·3H2O
(1 g, 4.1 mmol) in deionized water (15 mL) at room tem-
perature over 10 min. After forming a reddish-brown
precipitate, the mixture was warmed to 90 °C and stirred
under ultrasonic irradiation for 2 h and then cooled to room
Experimental
Chemicals were purchased from Merck or Fluka and used
without further purifcation. The purities of the reaction
products and the overall progress of the reactions were
checked by TLC on silica gel polygram SILG/UV254
SiO2
40°C
O
Si
Cl
Si(OCH3)3
24h
O
CuFe2O4
+
O
CuFe2O4
O
EtOH,H2O
105°C, 24h
Toluene
HO
N C
OH
H
CH
H
C
N
C N
OH
OH
H
C
OH
SiO2
SiO2
H
H
O
O
O
Si
Cl
Si
O
O
CuFe2O4
CuFe2O4
O
80°C
, 24h
O
Acetonitrile
N
C
80°C, 24h
Acetonitrile
SiO2
MnCl2.4H2O
N
O
O
O
Mn
Cl
O CH
Si
O
CuFe2O4
O
N
Scheme 1 Synthesis of CuFe2O4@SiO2–MnClsalpn
1 3

Transition Metal Chemistry
Fig. 1 FTIR spectra of (a) CuFe2O4@SiO2–salpnH2 and (b)
CuFe2O4@SiO2–MnClsalpn
temperature. The resulting particles were separated by an
external magnet, then washed three times with deionized
water, and dried under vacuum at 80 °C for 12 h. The nano-
particles were then ground in an agate mortar and kept in a
furnace at 400 °C for 5 h and then cooled to room tempera-
ture. CuFe2O4 particles of about 45–55 nm diameters were
so obtained.
Fig. 2 XRD patterns of (a) CuFe2O4 and (b) CuFe2O4@SiO2–
MnClsalpn
Preparation of silica‑coated magnetite (CuFe2O4@
SiO2 core–shell)
Concentrated aqueous ammonia (3.5 mL) was added slowly
to a sonicated mixture of CuFe2O4 nanoparticles (3.5 g)
suspended in deionized water–ethanol (40:160 mL), and
the resulted mixture was stirred at 40 °C for 30 min. Tetra-
ethyl orthosilicate (TEOS, 2.0 mL) was then added, and
the mixture was stirred at 40 °C for 24 h. The silica-coated
copper–ferrite magnetic nanoparticles (CuFe2O4@SiO2)
were isolated with a magnet. The collected solid was washed
several times with EtOH and diethyl ether and then dried at
100 °C in a vacuum oven for 24 h [45].
Synthesis of chloro‑functionalized CuFe2O4@SiO2
CuFe2O4@SiO2 (3.5 g) was sonicated in dry toluene (50 mL)
for 30 min. 3-Chloropropyltriethoxysilane (3.5 mL) was
Fig. 3 Magnetization curves of (a) CuFe2O4 and (b) CuFe2O4@SiO2–
MnClsalpn
1 3

Transition Metal Chemistry
then added to the suspension, and the mixture was stirred at
105 °C for 24 h. The solid was separated with an external
magnet, washed several times with ethanol, and dried under
vacuum [46].
was separated with an external magnet, washed with EtOAc,
dried, and reused for a sequential run under the same reac-
tion conditions. Evaporation of the solvent from the fltrate
gave the crude product, which was purifed by chromatog-
raphy on silica gel with n-hexane/EtOAc (2:5).
Synthesis of supported Schif base (CuFe2O4@SiO2–
salpnH2)
Results and discussion
SalpnH2 (N,N′-bis(Salicylidene)-1,3-diaminopropane-2-ol)
was prepared according to the reported method [47]. A por-
tion of salpnH2 (1 g, 3.2 mmol) was added to a sonicated
suspension of CuFe2O4@SiO2 (2 g) in acetonitrile (100 mL),
and the resulting mixture was refuxed for 24 h. The solid
was separated magnetically, washed thoroughly with etha-
nol, and dried under vacuum.
Scheme 1 shows the chemistry employed for the functionali-
zation of CuFe2O4 magnetic nanoparticles (MNPs) with the
manganese Schif base complex. In the frst step, the MNPs
were coated with a silica shell to obtain CuFe2O4@SiO2
core–shell. This outer shell of silica serves to improve the
dispersibility of the nanoparticles and also provides surface
Si–OH groups for further surface functionalization. Hence,
the treatment of the silanol groups of CuFe2O4@SiO2 with
chloropropyl trimethoxysilane gives chloropropylated mag-
netite nanoparticles. In the next step, the chloro-functional-
ized CuFe2O4@SiO2 was substituted by the alkoxide groups
of salpnH2 Schif base to yield the CuFe2O4@SiO2–salpnH2,
a tetradentate Schif base ligand supported on CuFe2O4@
SiO2. Finally, the reaction of excess MnCl2·4H2O with
CuFe2O4@SiO2–salpnH2 in dry acetonitrile gave CuFe2O4@
SiO2–MnClsalpn. The fnal product was subjected to Soxhlet
extraction in order to remove unreacted MnCl2.
Synthesis of MnCl2 salpn‑modifed CuFe2O4@SiO2
(CuFe2O4@SiO2–MnClsalpn)
CuFe2O4@SiO2–salpnH2 (2.5 g) was sonicated in dry
acetonitrile (100 mL) for 30 min. To the resulting suspen-
sion, MnCl2.4H2O (2 g) was added, and the mixture was
refuxed for 24 h. The solid was separated with an external
magnet and was subjected to Soxhlet extraction with etha-
nol and then dried under vacuum at 90 °C for 12 h to give
CuFe2O4@SiO2–MnClsalpn.
General procedure for oxidation of alcohols
Characterization of the nanoparticles
All catalytic experiments were performed in a 5-mL test
tube. In a typical procedure, to a solution of benzyl alcohol
(1 mmol) in solvent (0.5 mL), CuFe2O4@SiO2–MnClsalpn
(0.0014 g, 2 mol %) and TBHP (2 mmol) were added. The
reaction mixture was stirred for 1 h at 80 °C, and the prod-
ucts were tracked by TLC or GC. After completion of the
reaction, the mixture was diluted with EtOAc. The catalyst
In order to confrm the modifcation of the magnetite sur-
face, FTIR spectra of the prepared CuFe2O4@SiO2–salpnH2
and CuFe2O4@SiO2–MnClsalpn materials were recorded,
as shown in Fig. 1. The observation of two broad bands at
around 466–581 cm−1 indicates the presence of the mag-
netite core in both samples. The silica coating of magnetite
nanoparticles was confrmed by observation of a broad band
Fig. 4 a SEM image of CuFe2O4 and b EDAX analysis of CuFe2O4
1 3

Transition Metal Chemistry
Fig. 5 a–d HRTEM images of
CuFe2O4@SiO2–MnClsalpn
core–shell nanoparticles and e
the particle size distribution of
CuFe2O4@SiO2–MnClsalpn
at about 1000–1100 cm−1 assigned to Si–O–Si and Si–OH
stretching vibrations. In the FTIR spectrum of CuFe2O4@
SiO2–salpnH2 (Fig. 1a), a band at 1636 cm−1, assigned to
the C=N stretching vibration of salpnH2 [48, 49], and some
weak bands at 1400–1500 cm−1 assigned to the aromatic
rings of salpnH2 were observed; these were not present in the
parent CuFe2O4@SiO2. Upon reaction with MnCl2, the C=N
band at 1636 cm−1 shifted to lower frequency (1620 cm−1)
(Fig. 1b), indicating complexation of the C=N groups to
manganese. Further evidence for formation of CuFe2O4@
SiO2–MnClsalpn was also provided by the observation of
1 3

Transition Metal Chemistry
Table 1 Oxidation of benzyl alcohol to benzaldehyde under diferent
conditions
Entry
Oxidants
T (°C)
Solvent (0.5 ml)
Yielda (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
O2b
80
80
80
65
55
60
80
60
80
80
50
80
80
80
80
80
80
80
80
80
80
80
80
80
–
65
90
85
80
60
60
90
20
60
EtOH
Toluene
CH3OH
THF
CHCl3
CH3CN
CH2Cl2
H2O
DMSO
EtOH
EtOH (1 ml)
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
20
50
40
Fig. 6 TGA curve for CuFe2O4@SiO2–MnClsalpn
H2O2
UHP
–
Trace
30
Trace
60
50
85
Trace
10
15
ν(Mn–O) and ν(Mn–N) bands at ca. 570 and ca. 410 cm−1,
respectively [50, 51].
16c
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
17d
18e
Figure 2 depicts the XRD pattern of the MNPs. The dif-
fraction peaks can be assigned to the planes of inverse cubic
spinel-structured CuFe2O4 (JCPDS no. 034-0425). The same
confrming characteristic peaks were observed in the XRD
pattern of CuFe2O4@SiO2–MnClsalpn, confirming the
stability of the crystalline phase during surface modifca-
tion of the nanoparticles. The XRD pattern of CuFe2O4@
SiO2–MnClsalpn shows an obvious peak at 2θ = 5–20,
assigned to amorphous silica (Fig. 2b). The broadening of
each peak indicates the nanocrystalline nature of the as-
prepared CuFe2O4@SiO2–MnClsalpn. The average size of
CuFe2O4@SiO2–MnClsalpn deduced from Scherrer’s for-
mula was 36.4 nm.
19f
20g
21h
22i (1st)
23i (2nd)
24i (3rd)
30
90
88
85
aIsolated yield, reaction conditions: benzyl alcohol (1 mmol), oxi-
dant (2 mmol, except for entries 12–16), CuFe2O4@SiO2–MnClsalpn
(2 mol%, except for entries 17–21), reaction time: 1 h
b60 bubble/min
c1 mmol TBHP
dCatalyst: 1 mol%
In order to characterize the magnetic properties of the
magnetite nanoparticles before and after surface modifca-
tion, we recorded their hysteresis loops at room temperature
using vibrating sample magnetometry (VSM). The magneti-
zation curves are shown in Fig. 3. The MNPs exhibited no
remaining efects (superparamagnetic properties) with satu-
ration magnetization of about 25 emu/g. The surface-modi-
fed nanoparticles also showed superparamagnetic behavior,
with decreased saturation magnetization of about 7 emu/g.
The CuFe2O4@SiO2–MnClsalpn nanoparticles showed a sat-
uration magnetization of about 18 emu/g, sufcient for them
to be separated easily and rapidly from the reaction mixture
by use of an external magnet. Also, the superparamagnetic
properties of the CuFe2O4@SiO2–MnClsalpn nanoparticles
are suitable to prevent aggregation and enable them to re-
disperse quickly when the magnetic feld is removed.
A SEM micrograph of the synthesized CuFe2O4 nanopar-
ticles is shown in Fig. 4. It is evident that the particles have
almost uniform spherical morphology with a narrow size
distribution. The size of the nanoparticles calculated from
eCatalyst: 3 mol%
fNo catalyst
gCatalyst: CuFe2O4(2 mol%)
hCatalyst: MnCl2.4H2O (2 mol%)
iCatalytic test with frst, second and third recovered catalyst
the SEM micrographs was in the range of 45–55 nm, which
is in good agreement with the value obtained from the XRD
data (the average size from Scherrer’s formula was about
48.5 nm). The obtained EDAX spectrum (Fig. 4b) confrms
the presence of Cu, Fe and O in the sample, with a Cu/Fe
stoichiometry of 1:1.82 (semiquantitative analysis).
The efect of surface modifcation on the size and struc-
ture of the MNPs was evaluated by high-resolution transmis-
sion electron microscopy (HRTEM), which showed a spheri-
cal shape for CuFe2O4@SiO2–MnClsalpn with diameter of
ca. 50 nm (Fig. 5). It also confrmed the core–shell structure
1 3

Transition Metal Chemistry
TBHP
gave the best results. The model reaction was also carried
out in the absence of the catalyst, in the presence of CuFe2O4
and MnCl2.4H2O rather than CuFe2O4@SiO2–MnClsalpn
(entries 19–21); under these conditions, the amount of the
desired product was signifcantly decreased.
MnII
Ph-CHO + H2O
OH
OH
Metal-catalyzed oxidations by alkyl peroxides may pro-
ceed through homolytic or heterolytic mechanisms. Transi-
tion metal complexes of Co, Cu, Fe, and Mn are usually
involved in hemolytic mechanisms [52–54]. Hence, an
oxidation mechanism for benzyl alcohol by TBHP in the
presence of CuFe2O4@SiO2–MnClsalpn can be proposed
as shown in Scheme 2.
.
.
MnIII
tBuO
Ph-CH-OH
MnIII
+
+
Ph-CH2-OH
tBuOH
In order to test the generality of this method, the oxida-
tions of several primary and secondary alcohols under the
optimized reaction conditions were investigated (Table 2).
Substituted benzyl alcohols bearing either electron-releas-
ing or withdrawing groups were also oxidized selectively,
afording the corresponding aldehydes in good-to-excel-
lent yields (entries 1–6). Moderately sterically hindered
benzyl alcohols were also transformed to the correspond-
ing aldehydes in good yields, without any over-oxidation
to the corresponding carboxylic acid (entries 2, 3, 5). In
particular, the heteroaromatic furfuryl alcohol, which is
known to be a challenging substrate in most transition
metal catalyst systems, was oxidized selectively to furfural
in this system (entry 7). Meanwhile, secondary alcohols
gave the corresponding ketones in good yields (entries
8–14).
Scheme 2 Proposed mechanism for oxidation of benzyl alcohol with
TBHP catalyzed by CuFe2O4@SiO2–MnClsalpn
of the particles and confrmed the presence of a silica shell
of uniform thickness (Fig. 5).
Thermogravimetric analysis (TGA) was used to investi-
gate the thermal stability of CuFe2O4@SiO2–MnClsalpn,
as shown in Fig. 6. A weight loss of about 9 wt% between
25 and 600 °C can be attributed to decomposition of the
organic component attached to the surface. According to the
TGA, the amount of organic component functionalized on
CuFe2O4@SiO2 was about 9 wt%.
These results are in good agreement with the elemental
analysis (N= 0.53%) and the ICP analysis, which showed
that 0.19 mmol of manganese was anchored on 1.0 g of
CuFe2O4@SiO2–MnClsalpn nanoparticles.
The chemoselectivity of this system was investigated by
means of a competitive reaction system. A mixture of equal
amounts of benzyl alcohol and 2-phenyl ethanol was oxi-
dized under the conditions given in Table 2 (Scheme 3). In
this experiment, benzyl alcohol was quantitatively oxidized
to benzaldehyde, while the 2-phenyl ethanol remained unre-
acted. In the absence of catalyst, only trace amounts of both
oxidation products were obtained.
Catalytic oxidation of alcohols
The catalytic activity of CuFe2O4@SiO2–MnClsalpn for
the oxidation of alcohols to the corresponding aldehydes
or ketones has been investigated. The oxidation of benzyl
alcohol to benzaldehyde was chosen as a test reaction, with
TBHP as the terminal oxidant. Our initial experiments
focused on the choice of reaction solvent (Table 1, entries
1–10). The reaction was also investigated under solvent-free
conditions. The best product yields were obtained in ethanol
and acetonitrile at 80 °C (entries 2 and 7). Since ethanol is
cheaper and less toxic, it was chosen as solvent for subse-
quent experiments. On lowering the temperature, the product
yield was decreased (entry 11). Next, the infuence of difer-
ent oxidants on the oxidation of benzyl alcohol in ethanol
at 80 °C was investigated (entries 12–14). TBHP proved to
be the best option (entry 2). The reaction gave only a trace
amount of the desired product in the absence of any added
oxidant (entry 15). A similar reaction with 1 mmol of the
oxidant gave a low yield (entry 16). Next, the infuence of
diferent amounts of CuFe2O4@SiO2–MnClsalpn was stud-
ied. Entries 2, 17, and 18 show that 2 mol% of the catalyst
In order to show that nanocatalyst is truly heterogeneous,
a hot fltration test was performed. In this experiment, benzyl
alcohol was oxidized for 30 min (ca. 60% yield, Table 1).
The nanocatalyst was then recovered magnetically at the
reaction temperature to avoid re-adsorption of the solubi-
lized species, and the solution was decanted into a clean
test tube. The decantate was heated at 80 °C for 24 h to
elucidate whether oxidation resulted from a homogeneous
catalyst leached from the support, or from the surface-bound
manganese catalyst. The yields were determined after 1 and
24 h, and it was found that the product amount increased
only slightly and then remained constant (Table 1). When
CuFe2O4@SiO2–MnClsalpn was employed as catalyst, ICP
analyses showed that only a very small amount of Mn (less
than 2%) had been lost after the frst run. The recyclabil-
ity of a heterogeneous catalyst provides a critical advantage
1 3

Transition Metal Chemistry
Table 2 Oxidation of alcohols with TBHP catalyzed by CuFe2O4@SiO2–MnClsalpn
1 3

Transition Metal Chemistry
Table 2 (continued)
Reaction conditions: alcohol (1 mmol), TBHP (2 mmol), catalyst (2 mol %), temperature: 80° C
aAll products are identifed by comparison of their physical data with those of authentic samples
bIsolated yield. Yields are determined by TLC and GC based on the starting alcohol
c1H NMR (500 MHz, CDCl3) δ: 2.31 (s, 3H, CH3), 7.20 (d, J=15 Hz, 2H, ArH), 7.66 (d, J=15 Hz, 2H, ArH), 9.95 (s, 1H, aldehyde H)
d1H NMR (500 MHz, CDCl3) δ: 7.26–7.82 (m, 4H, ArH), 9.96 (s, 1H, aldehyde H)
eTBHP (4 mmol)
fThe alcohols were synthesized according to Ref. [55]
after the second recovery, by means of VSM analysis. The
OH
OH
O
saturation magnetization of the recovered nanocatalyst is
about 17.5 emu/g, hence there is negligible change in its
magnetic properties (see Supplementary Materials Fig. S1).
The FTIR spectrum of the reused catalyst also showed no
detectable changes compared to the fresh catalyst (see Sup-
plementary Materials Fig. S2).
quantitative
trace
CuFe2O4@SiO2-MnClsalpn
80 °C, ETOH, TBHP
H
O
Table 3 compares the catalyst used in the present study
with some other catalysts used for oxidation of benzyl alco-
hol, as reported in the literature. It can be observed that the
catalyst employed here is comparable to, or even superior
to, other examples as previously reported.
Scheme 3 Chemoselectivity of the catalyst
over homogeneous catalysts. The recovered nanocatalyst
was therefore reused for the oxidation of benzyl alcohol,
with the results presented in Table 1. The catalytic activity
showed only a small reduction for three consecutive uses of
the catalyst. We conclude that the manganese species are
strongly bonded to the surface of the nanoparticles, such
that the nanocatalyst is stable under the reaction conditions
and the oxidation is truly heterogeneous. Also, the magnetic
properties of the recovered nanocatalyst were investigated
Conclusions
In this study, a magnetically recoverable nanocatalyst with
high thermal stability (> 200 °C) was synthesized from a
manganese Schif base complex anchored on functionalized
Table 3 Comparison of this
Catalyst
Oxidant
Reaction
time (h)
Tempera- Solvent
ture (°C)
References
work with systems described in
the literature for the oxidation
of benzyl alcohol
Mn@MNP
TBHP
TBHP
Oxone
TBHP
TBHP
TBHP
4
8
0.5
8
8
110
90
25
90
90
80
DMSO
Acetonitrile
Ethanol
Acetonitrile
Acetonitrile
Ethanol
[56]
[52]
[57]
[58]
[59]
This work
SBA-15-pr-NH2-Mn(Salen)
Mn(salen)Cl-cellulose
Mn(II)2,2-bipyridine complexes/HMSa
[Mn(bpy)2]2+/HMS
CuFe2O4@SiO2–MnClsalpn
1
aHexagonal molecular sieves
1 3

Transition Metal Chemistry
15. Kureshy RI, Ahmad I, Noor-ul HK, Abdi SH, Pathak K, Jasra
RV (2006) Chiral Mn(III) salen complexes covalently bonded on
modifed MCM-41 and SBA-15 as efcient catalysts for enan-
tioselective epoxidation of nonfunctionalized alkenes. J Catal
238(1):134–141
silica-coated magnetic nanoparticles. The oxidations of alco-
hols to the related aldehydes or ketones with good-to-excel-
lent yields were efciently mediated by this material. This
system is both cost-efective and environmentally benign,
and the catalyst can be readily separated from the reaction
mixture and reused.
16. Ma L, Su F, Zhang X, Song D, Guo Y, Hu J (2014) Epoxidation
of alkenes catalyzed by highly ordered mesoporous manganese–
salen-based hybrid catalysts. Microporous Mesoporous Mater
184:37–46
Acknowledgements The support of this work by Vali-e-Asr University
17. Zhang H, Wang YM, Zhang L, Gerritsen G, Abbenhuis HC,
van Santen RA, Li C (2008) Enantioselective epoxidation of
β-methylstyrene catalyzed by immobilized Mn (salen) catalysts
in diferent mesoporous silica supports. J Catal 256(2):226–236
18. Zhang H, Zhang Y, Li C (2006) Enantioselective epoxidation of
unfunctionalized olefns catalyzed by the Mn (salen) catalysts
immobilized in the nanopores of mesoporous materials. J Catal
238(2):369–381
of Rafsanjan is acknowledged.
References
1. Shambayati S, Schreiber S, Trost B, Fleming I (1991) In: Trost
BM (ed) Comprehensive organic synthesis. Pargamon Press, New
York
19. Gong B, Fu X, Chen J, Li Y, Zou X, Tu X, Ding P, Ma L (2009)
Synthesis of a new type of immobilized chiral salen Mn(III) com-
plex as efective catalysts for asymmetric epoxidation of unfunc-
tionalized olefns. J Catal 262(1):9–17
2. Sheldon R (2012) Metal-catalyzed oxidations of organic com-
pounds: mechanistic principles and synthetic methodology includ-
ing biochemical processes. Elsevier, Amsterdam
20. Tang X, Tang Y, Xu G, Wei S, Sun Y (2008) Highly enantiose-
lective epoxidation of styrene and α-methylstyrene catalyzed by
new doubly-immobilized chiral (salen) Mn(III) catalysts. Catal
Commun 10(3):317–320
3. Carey JS, Lafan D, Thomson C, Williams MT (2006) Analysis of
the reactions used for the preparation of drug candidate molecules.
Org Biomol Chem 4(12):2337–2347
21. Silva AR, Freire C, de Castro B (2004) Jacobsen catalyst anchored
onto an activated carbon as an enantioselective heterogeneous
catalyst for the epoxidation of alkenes. Carbon 42(14):3027–3030
22. Tu X, Fu X, Hu X, Li Y (2010) Chiral salen Mn(III) immobi-
lized on sulfoalkyl modifed ZSP-IPPA as an efective catalyst for
asymmetric epoxidation of unfunctionalized olefns. Inorg Chem
Commun 13(3):404–407
4. Dugger RW, Ragan JA, Ripin DHB (2005) Survey of GMP bulk
reactions run in a research facility between 1985 and 2002. Org
Process Res Dev 9(3):253–258
5. Arends IW, Sheldon RA (2011) Modern oxidation of alcohols
using environmentally benign oxidants. ChemInform 42(44)
6. Sheldon RA, Arends I, Dijksman A (2000) New developments
in catalytic alcohol oxidations for fne chemicals synthesis. Catal
Today 57(1):157–166
23. Silva AR, Budarin V, Clark JH, Freire C, De Castro B (2007)
Organo-functionalized activated carbons as supports for the cova-
lent attachment of a chiral manganese(III) salen complex. Carbon
45(10):1951–1964
7. Sheldon RA, Arends IW, ten Brink G-J, Dijksman A (2002) Green,
catalytic oxidations of alcohols. Acc Chem Res 35(9):774–781
8. Amato ME, Ballistreri FP, Pappalardo A, Tomaselli GA, Toscano
RM, Williams DJ (2005) Novel chiral (Salen) MnIII complexes
containing a Calix [4] arene unit as catalysts for enantioselec-
tive epoxidation reactions of (Z)-aryl alkenes. Eur J Org Chem
16:3562–3570
24. Chomoucka J, Drbohlavova J, Huska D, Adam V, Kizek R,
Hubalek J (2010) Magnetic nanoparticles and targeted drug deliv-
ering. Pharmacol Res 62(2):144–149
25. Laurent S, Dutz S, Häfeli UO, Mahmoudi M (2011) Magnetic
fuid hyperthermia: focus on superparamagnetic iron oxide
nanoparticles. Adv Coll Interface Sci 166(1):8–23
9. Moghadam M, Tangestaninejad S, Mirkhani V, Mohammadpoor-
Baltork I, Mirjafari A, Mirbagheri NS (2010) Multi-wall carbon
nanotubes supported molybdenum hexacarbonyl: an efcient and
highly reusable catalyst for epoxidation of alkenes with tert-butyl
hydroperoxide. J Mol Catal A Chem 329(1):44–49
26. Mahmoudi M, Sant S, Wang B, Laurent S, Sen T (2011) Super-
paramagnetic iron oxide nanoparticles (SPIONs): development,
surface modifcation and applications in chemotherapy. Adv
Drug Deliv Rev 63(1):24–46
10. Ulmann PA, Braunschweig AB, Lee O-S, Wiester MJ, Schatz GC,
Mirkin CA (2009) Inversion of product selectivity in an enzyme-
inspired metallosupramolecular tweezer catalyzed epoxidation
reaction. Chem Commun 34:5121–5123
27. Sun C, Lee JS, Zhang M (2008) Magnetic nanoparticles
in MR imaging and drug delivery. Adv Drug Deliv Rev
60(11):1252–1265
28. Veiseh O, Gunn JW, Zhang M (2010) Design and fabrication of
magnetic nanoparticles for targeted drug delivery and imaging.
Adv Drug Deliv Rev 62(3):284–304
11. Wei S, Tang Y, Xu X, Xu G, Yu Y, Sun Y, Zheng Y (2011) A new
heterogeneous chiral (salen) manganese(III) system for enantiose-
lective epoxidation of non-functionalized olefns. Appl Organomet
Chem 25(2):146–153
29. Zhao X, Bao XY, Guo W, Lee FY (2006) Immobilizing catalysts
on porous materials. Mater Today 9(3):32–39
12. Yang JY, Liu SY, Korendovych IV, Rybak-Akimova EV, Nocera
DG (2008) Hangman salen platforms containing dibenzofuran
scafolds. Chemsuschem 1(11):941–949
30. McCarthy JR, Weissleder R (2008) Multifunctional magnetic
nanoparticles for targeted imaging and therapy. Adv Drug Deliv
Rev 60(11):1241–1251
13. Yu K, Lou L-L, Ding F, Wang S, Wang Z, Liu S (2006) Highly
enantioselective epoxidation of olefns by Mn(III) salen complex
immobilized on MCM-48. Catal Commun 7(3):170–172
14. Kureshy RI, Ahmad I, Noor-ul HK, Abdi SH, Pathak K, Jasra
RV (2005) Encapsulation of a chiral Mn III (salen) complex in
ordered mesoporous silicas: an approach towards heterogenizing
asymmetric epoxidation catalysts for non-functionalized alkenes.
Tetrahedron Asymmetry 16(21):3562–3569
31. Shokouhimehr M, Piao Y, Kim J, Jang Y, Hyeon T (2007) A mag-
netically recyclable nanocomposite catalyst for olefn epoxidation.
Angew Chem Int Ed 46(37):7039–7043
32. Saeednia S, Ardakani MH, Parizi ZP, Hafshejani MT (2016)
Synthesis and characterization of a magnetically recoverable
molybdenum(VI) nanocatalyst for eco-friendly oxidation of alco-
hols. Transit Met Chem 41(7):767–774
33. Garza-Navarro M, González-González V, Torres-Castro A, Hino-
josa M, García-Loera A, José-Yacamán M (2010) Elaboration of
1 3

Transition Metal Chemistry
superparamagnetic cobalt–ferrite nanocomposites from flms of
chitosan chelates. J Appl Polym Sci 117(2):785–792
34. Hu C, Gao Z, Yang X (2008) One-pot low temperature synthesis
of MFe2O4 (M=Co, Ni, Zn) superparamagnetic nanocrystals. J
Magn Magn Mater 320(8):L70–L73
47. Masteri-Farahani M, Tayyebi N (2011) A new magnetically
recoverable nanocatalyst for epoxidation of olefns. J Mol Catal
A Chem 348(1):83–87
48. Coleman W, Taylor L (1971) Pentadentate ligands. I. Nickel(II)
complexes of the linear Schif base ligands derived from substi-
tuted salicylaldehydes and diethylenetriamine and 2,2′-bis (ami-
nopropyl) amine. Inorg Chem 10(10):2195–2199
35. Gadkari AB, Shinde TJ, Vasambekar PN (2011) Ferrite gas sen-
sors. IEEE Sens J 11(4):849–861
36. Pershina A, Sazonov A, Ogorodova L (2010) Evaluation of the
resistance of DNA immobilized on ferrimagnetic particles of
cobalt ferrite nanopowder against nuclease cleavage. Bull Exp
Biol Med 149(1):67–69
49. Jia M, Thiel WR (2002) Oxodiperoxo molybdenum modifed
mesoporous MCM-41 materials for the catalytic epoxidation of
cyclooctene. Chem Commun 20:2392–2393
50. Mukhopadhyay R, Bhattacharjee S, Bhattacharyya R (1994)
Ligand control on the synthesis and redox potency of mononu-
clear manganese-(III) and-(IV) complexes with tridentate ONS
co-ordination. J Chem Soc Dalton Trans 19:2799–2804
51. Panella B, Vargas A, Baiker A (2009) Magnetically separable Pt
catalyst for asymmetric hydrogenation. J Catal 261(1):88–93
52. Mahdavi V, Mardani M (2015) Mn (Salen) Cl complexes immo-
bilized on SBA-15 functionalized with amine as an efcient,
selective and recyclable catalyst for benzyl alcohol oxidation by
TBHP: the efects of Mn loading and reaction conditions. Res
Chem Intermed 41(11):8907–8927
37. Esmaeilpour M, Sardarian AR, Javidi J (2012) Schif base com-
plex of metal ions supported on superparamagnetic Fe3O4@SiO2
nanoparticles: an efcient, selective and recyclable catalyst for
synthesis of 1,1-diacetates from aldehydes under solvent-free
conditions. Appl Catal A 445:359–367
38. Kapilevich L, D’yakova EY, Nosarev A, Zaitseva T, Petlina
Z, Ogorodova L, Ageev B, Magaeva A, Itin V, Terekhova AO
(2010) Efect of nanodisperse ferrite cobalt (CoFe2O4) particles
on contractile reactions in guinea pigs airways. Bull Exp Biol Med
149(1):70–72
39. Yi DK, Lee SS, Ying JY (2006) Synthesis and applica-
tions of magnetic nanocomposite catalysts. Chem Mater
18(10):2459–2461
53. Oh NY, Suh Y, Park MJ, Seo MS, Kim J, Nam W (2005)
Mechanistic insight into alcohol oxidation by high-valent iron–
oxo complexes of heme and nonheme ligands. Angew Chem
117(27):4307–4311
40. Yoon TJ, Yu KN, Kim E, Kim JS, Kim BG, Yun SH, Sohn BH,
Cho MH, Lee JK, Park SB (2006) Specifc targeting, cell sorting,
and bioimaging with smart magnetic silica core–shell nanomateri-
als. Small 2(2):209–215
54. Rahimi R, Ghoreishi SZ, Dekamin MG (2012) Immobilized
metalloporphyrins on 3-aminopropyl-functionalized silica sup-
port as heterogeneous catalysts for selective oxidation of primary
and secondary alcohols. Monatshefte für Chemie-Chem Mon
143(7):1031–1038
41. Ge Q, Huang Y, Qiu F, Li S (1998) Bifunctional catalysts for
conversion of synthesis gas to dimethyl ether. Appl Catal A
167(1):23–30
55. Mavis ME, Yolacan C, Aydogan F (2010) An investigation of the
catalytic potential of mono-and dicationic imidazolium N-heter-
ocyclic carbenes in the benzoin condensation. Tetrahedron Lett
51(34):4509–4511
42. Bagherzadeh M, Mortazavi-Manesh A (2015) Immobilized man-
ganese porphyrin on functionalized magnetic nanoparticles via
axial ligation: efcient and recyclable nanocatalyst for oxidation
reactions. J Coord Chem 68(13):2347–2360
56. Zhou Q, Wan Z, Yuan X, Luo J (2016) A new magnetic nanopar-
ticle-supported Schif base complex of manganese: an efcient
and recyclable catalyst for selective oxidation of alcohols. Appl
Organomet Chem 30(4):215–220
43. Esmaeilpour M, Javidi J, Dodeji FN, Abarghoui MM (2014) M (II)
Schif base complexes (M=zinc, manganese, cadmium, cobalt,
copper, nickel, iron, and palladium) supported on superparamag-
netic Fe3O4@SiO2 nanoparticles: synthesis, characterization and
catalytic activity for Sonogashira-Hagihara coupling reactions.
Transit Met Chem 39(7):797–809
57. Nasseri MA, Mohammadinezhad A, Salimi M (2015) A cellulose-
supported Mn (salen) Cl complex as an efcient heterogeneous
catalyst for the selective oxidation of benzylic alcohols. J Iran
Chem Soc 12(1):81–86
44. Sun W, Wang H, Xia C, Li J, Zhao P (2003) Chiral-Mn (Salen)-
complex-catalyzed kinetic resolution of secondary alcohols in
water. Angew Chem Int Ed 42(9):1042–1044
58. Mahdavi V, Mardani M (2012) Selective oxidation of benzyl alco-
hol with tert-butylhydroperoxide catalysed via Mn(II) 2,2-bipy-
ridine complexes immobilized over the mesoporous hexagonal
molecular sieves (HMS). J Chem Sci 124(5):1107–1115
59. Mahdavi V, Mardani M, Malekhosseini M (2008) Oxidation of
alcohols with tert-butylhydroperoxide catalyzed by Mn(II) com-
plexes immobilized in the pore channels of mesoporous hexagonal
molecular sieves (HMS). Catal Commun 9(13):2201–2204
45. Dandia A, Jain AK, Sharma S (2013) CuFe2O4 nanoparticles as a
highly efcient and magnetically recoverable catalyst for the syn-
thesis of medicinally privileged spiropyrimidine scafolds. RSC
Adv 3(9):2924–2934
46. Sobhani S, Pakdin-Parizi Z (2014) Lanthanum(III) trifate sup-
ported on nanomagnetic γ-Fe2O3: a new magnetically recy-
clable heterogeneous Lewis acid for the one-pot synthesis of
β-phosphonomalonates. RSC Adv 4(25):13071–13077
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