A supported manganese complex with amine-bis(phenol) ligand for catalytic benzylic C(sp3)-H bond oxidation

Article abstract of DOI:10.1039/c9ra02284h

With regards to the importance of direct and selective activation of C-H bonds in oxidation processes, we develop a supported manganese amine bis(phenol) ligand complex as a novel catalyst with the aim of obtaining valuable products such as carboxylic acids and ketones that have an important role in life, industry and academic laboratories. We further analyzed and characterized the catalyst using the HRTEM, SEM, FTIR, TGA, VSM, XPS, XRD, AAS, and elemental analysis (CHN) techniques. Also, the catalytic evaluation of our system for direct oxidation of benzylic C-H bonds under solvent-free condition demonstrated that the heterogeneous form of our catalyst has high efficiency in comparison with homogeneous ones due to more stability of the supported complex. Furthermore, the structural and morphological stability of our efficient recyclable catalytic system has been investigated and all of the data proved that the complex was firmly anchored to the magnetite nanoparticles.

Full text of DOI:10.1039/c9ra02284h

RSC Advances
View Article Online
View Journal | View Issue
PAPER
A supported manganese complex with amine-
bis(phenol) ligand for catalytic benzylic C(sp3)–H
bond oxidation†
Cite this: RSC Adv., 2019, 9, 14343
a
b
a
*
and Babak Karimi
Touraj Karimpour,
Elham Safaei
With regards to the importance of direct and selective activation of C–H bonds in oxidation processes, we
develop a supported manganese amine bis(phenol) ligand complex as a novel catalyst with the aim of
obtaining valuable products such as carboxylic acids and ketones that have an important role in life,
industry and academic laboratories. We further analyzed and characterized the catalyst using the
HRTEM, SEM, FTIR, TGA, VSM, XPS, XRD, AAS, and elemental analysis (CHN) techniques. Also, the
catalytic evaluation of our system for direct oxidation of benzylic C–H bonds under solvent-free
condition demonstrated that the heterogeneous form of our catalyst has high efficiency in comparison
with homogeneous ones due to more stability of the supported complex. Furthermore, the structural
and morphological stability of our efficient recyclable catalytic system has been investigated and all of
the data proved that the complex was firmly anchored to the magnetite nanoparticles.
Received 25th March 2019
Accepted 25th April 2019
DOI: 10.1039/c9ra02284h
rsc.li/rsc-advances
In the past decade, immobilization of metal complexes on
various supports has been introduced and investigated to
Introduction
overcome the problems pertaining to unsupported complexes.
So this catalytic system has the privileges of both homogeneous
and heterogeneous catalysts. From a sustainable point of view,
the core–shell magnetic nanoparticles (MNPs) are quite
favourable supports.14 These magnetized catalysts can be easily
isolated by applying an appropriate magnetic eld. This unique
characteristic of MNPs eliminates the necessity of procedures
such as centrifugation or ltration for the recycling of the
catalysts. Despite of several interesting reports15 for activation
of the inert C–H bonds, there are limited publications that
address the issue of heterogeneous C–H oxidation catalysis
using Earth-abundant iron16 and manganese catalysts.17
Due to the special importance of C–H bond oxidation in the
pharmaceutical and chemical industries, and ideal properties
of both manganese complexes and magnetic nanoparticles, our
main aim is designing a novel, sustainable and selective
heterogeneous system for benzylic C–H bond oxidation.
Regarding the fact that amine bis(phenol) ligands consist of N
and O atoms, and different substituents on the phenol groups,
they are able to tune the Lewis acidity of the metal centres which
plays a crucial role in the catalytic activity of metal complexes.
Consequently, an amine bis(phenol) ligand was applied to
design our catalyst. The immobilized amine bis(phenolate)
ligand on the magnetite nanoparticles (Fe3O4@SiO2-APTES-
H2LGDC) was prepared according to the previous report in our
group.18 Manganese as an inexpensive, Earth-abundant and
non-toxic metal was applied for metalation of these nano-
particles. It is interesting to note that we found the high coop-
eration between silica-coated Fe3O4 nanoparticles and
From the environmental and economic points of view, the
functionalization of the organic substrates is one of the best
strategic approaches for the preparation of broad ranges of new
chemicals as a novel and attractive way in organic synthesis.1
Because of the accessibility of carbon–hydrogen bonds in
organic substrates, the activation of these bonds is an attractive
and challenging method for selective synthesis of products with
different functional groups. It is noteworthy that the methane
monooxygenases (MMOs) and cytochrome P-450 are two
important classes of enzymes that are applied by nature to
attain high selectivity in the oxidation of alkanes at elevated
rates.2 Two identied forms of the MMOs which contain iron or
copper ions in their active sites are able to produce methanol
from methane.3 The cytochrome P-450 uses its iron porphyrin
core to catalyze the oxidation of hydrocarbons to alcohols
through the carbon–hydrogen activation method with high
turnover numbers.4 Several interesting homogenous catalytic
systems involving transition-metals (Cu,5 Fe,6 Mn,7 Co,8 Ni,9
Pd,10 Rh,11 Ru12 and Ti13) have been reported for this important
process. These systems have limited applications in comparison
with the heterogeneous catalysis, due to product separation and
catalyst recycling problems.
aDepartment of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), P.
O. Box 45137-66731, Gava Zang, Zanjan, Iran
bDepartment of Chemistry, College of Sciences, Shiraz University Shiraz, 71454, Iran.
E-mail: e.safaei@shirazu.ac.ir
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c9ra02284h
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 14343–14351 | 14343

View Article Online
RSC Advances
Paper
manganese complex for the synthesis of a sustainable catalyst. diffraction (XRD) analysis was performed in order to obtain
In our designed system the stabilized manganese complex information about the phase purity and crystalline structure of
exhibits excellent efficiency in selective benzylic C–H bond Fe3O4@SiO2, Fe3O4@SiO2-APTES, Fe3O4@SiO2-APTES-H2LGDC
oxidation for a wide range of substrates as well as toluene. and Fe3O4@SiO2-APTES-MnLGDC (Fig. 1A). Our results are in
Furthermore, ve successful recoveries of the catalyst line with previous reports of Fe3O4@SiO2 nanoparticles XRD
conrmed the stability of the manganese complex attached to pattern.19 XRD pattern for all nanoparticles show the cubic
the magnetic nanoparticles.
inverse spinel of Fe3O4 nanoparticles and a broad diffraction
peak in the 2q ¼ 20–30ꢀ, demonstrating the presence of silica
shell. Diffraction peaks of [111], [220], [311], [400], [422], [511],
and [440] planes found in 18, 30, 35, 43, 54, 57 and 63 degree,
respectively.
Results and discussion
Synthesis and characterization of Fe3O4@SiO2-APTES-MnLGDC
FT-IR analysis was used to investigate the successful func-
tionalization and modication of particles. As can be seen in
Fig. 1B, broad peak at 3423 cmꢁ1 is related to the O–H and N–H
vibrations and the presence of stretching vibration of Fe–O in
all samples was found (at around 544 cmꢁ1). Moreover,
symmetric stretching (at about 400 and 800 cmꢁ1, respectively),
asymmetric stretching of Si–O–Si (at about 1200 cmꢁ1) and
Using the presented route in Scheme 1, immobilized amine
bis(phenol) ligand on the magnetite nanoparticles (Fe3O4@-
SiO2-APTES-H2LGDC) was prepared according to the previously
report in our group,18 aerward for metalation of these nano-
particles MnCl2$4H2O was applied (Scheme 1).
Both chemical nature and structure of our catalyst have been
investigated via the common methods. The powder X-ray
Scheme 1 A schematic illustration of catalyst (Fe3O4@SiO2-APTES-MnLGDC).
Fig. 1 (A) The XRD pattern, (B) the FTIR spectra of Fe3O4@SiO2 (a), Fe3O4@SiO2-APTES (b), Fe3O4@SiO2-APTES-H2LGDC (c) and Fe3O4@SiO2-
APTES-MnLGDC (d).
14344 | RSC Adv., 2019, 9, 14343–14351
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
without any coercivity eld (Hc) and remanent magnetism (Mr).
The resulted data in Fig. 3A shows the high saturation magneti-
zation (Ms) of about 22 emu gꢁ1 for the catalyst that enables it to
be easily separated via an external magnet from the reaction
mixture.21 According to TGA curve of catalyst initial weight at 0–
ꢀ
200 C can be related to trapped solvent on the surface of the
catalyst (Fig. S3B†). As can be seen in Fig. 3B, main weight loss for
the catalyst (Fe3O4@SiO2-APTES-MnLGDC) is observed at high
temperature of about 300–600 ꢀC which proved thermal stability
of the nal catalyst. Thermal behaviour of Fe3O4@SiO2-APTES-
H2LGDC and Fe3O4@SiO2-APTES-MnLGDC samples under N2
atmosphere showed same decomposition pattern indicating that
under metalation with Mn the total structure was preserved. A
noticeable point in this matter is that aer metalation with Mn
the temperature range of main weight loss has been shied to the
lower temperatures (compare diagrams c and d in Fig. 3B). This
issue can be attributed to the catalytic role of Mn on the
decomposition process of organic moieties in the circumstance
of TG experiment. Furthermore, the loading of aminopropyl in
Fe3O4@SiO2-APTES and ligand in Fe3O4@SiO2-APTES-H2LGDC
achieved about 1.43 and 0.5 mmol gꢁ1, respectively. Further tests
such as CHN analysis corroborated these results (1.35 mmol gꢁ1
of APTES in Fe3O4@SiO2-APTES and 0.56 mmol gꢁ1 of H3LGDC in
Fe3O4@SiO2-APTES-H2LGDC). In an attempt to do the estimation
of manganese loading, we used the AAS technique (was found to
be 0.49 mmol gꢁ1).
Chemical state and composition of Mn, Si, C, Cl and O of the
mentioned synthesis catalyst were investigated via X-ray
Photoelectron Spectroscopy (XPS), as well as Fe in the core
(Fe3O4) (Fig. 4). Achieved data suggest Mn has +3 oxidation state
and at 641, and 653 eV we can see lines regarding Mn 2p3/2 and
Mn 2p1/2, respectively. The presence of iron(III) and (II) in the
catalyst was conrmed according to the peaks at 55 (Fe 3p), 710
(Fe 2p3/2), and 724 eV (Fe 2p1/2) in Fig. 4D. In addition, appeared
peak at 200 eV (Cl 2p) truly proves successful attachment of
mentioned ligand (H3LGDC) on the magnetic nanoparticles
(Fig. 4B). As we can see in Fig. 4, peaks related to C 1s, O 1s, Si
Fig. 2 HRTEM (A and B) and FESEM (C and D) images of Fe3O4@SiO2-
APTES-MnLGDC
.
stretching vibrations of Si–OH (at around 900 cmꢁ1) are
evidence to support the existence of silica shell in all magnetic
nanoparticles.20 Bending peak of –CH2 at 1400 cmꢁ1 and
stretching vibrations peaks related to –CH2 and N–H groups at
about 2840–3000 cmꢁ1 and 3400 cmꢁ1, respectively, conrmed
stabilization of amino propyl groups on the particles.
The HRTEM and FESEM analyses played a crucial role in the
investigation of size, structure, and morphology of nano-
magnetic particles. Our results show that nanoparticles are
smaller than 45 nm and core size is about 15 nm that sur-
rounded via 15 nm uniform grey silica shell. HRTEM images of
obtained catalyst (Fig. 2A and B) conrmed the stability of the
core–shell system in Fe3O4@SiO2 nanoparticles aer modica-
tion. Moreover, FESEM analysis indicated our mentioned cata-
lyst has a spherical uniform morphology and smooth surface
(Fig. 2C and D).
We also explored the magnetization of magnetic nanoparticles
by vibrating sample magnetometer (VSM) at room temperature
(Fig. 3A). The superparamagnetic behavior for our catalyst was
conrmed with the eld-dependent magnetization curves
Fig. 3 (A) Magnetization curves of Fe3O4@SiO2-APTES-MnLGDC. Inset: the enlarged image near the coercive field. (B) Thermo-gravimetric
analysis (TGA) of Fe3O4@SiO2 (a), Fe3O4@SiO2-APTES (b), Fe3O4@SiO2-APTES-H2LGDC (c), Fe3O4@SiO2-APTES-MnLGDC (d).
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 14343–14351 | 14345

View Article Online
RSC Advances
Paper
duo to the decomposition of homogeneous form of the catalyst
(MnLGDC) during the oxidation process. This result clearly
conrms the positive effect of nanoparticles on the stability of
manganese complex and proves our complex has a good
structural stability on the magnetic nanoparticles in the
heterogeneous form of our catalyst. It is important to note that,
the mentioned reaction in the presence of manganese(II) chlo-
ride salt as a catalyst has not a good conversion (Table 1, entry
21). Consequently, the last results strongly proved the dramat-
ically inuence of magnetic nanoparticles supported ligand on
the activity of catalyst system. It is more notable, in the absence
of the catalyst but in the presence of 4 eq. of TBHP, slightly
progress in the modal reaction truly conrms the eligibility of
our system (Table 1, entries 22 and 23).
In the process of investigation, the high efficiency of
mentioned catalyst in the aerobic oxidation of the ethylbenzene
in the presence of air and O2 was checked. In the presence of 2
eq. of TBHP and O2 our catalyst showed same activity similar to
3 mmol of TBHP without O2 (Table 1 entries 8 and 10) but at
60 ꢀC and in the absence of TBHP trace conversion was achieved
(Table 1, entry 24). Our results show that this oxidant (O2) can
act at a higher temperature and longer time. This point of view
is supported by good resulted data in Scheme 2 (Scheme 2b and
Fig. 4 The X-ray photoelectron spectroscopy (XPS) spectrum of
catalyst (Fe3O4@SiO2-APTES-MnLGDC).
2s, Si 2p, and N 1s prove the presence of these elements in our
catalyst.22
Catalytic activity evaluation
On the basis of the main goal of our studies, we have investi- c, Fig. S29 and 30†). These data conrm the eligibility of our
gated the efficiency of our designed system for activation of catalyst not only by TBHP (Scheme 2a, Fig. S28†) but also by O2.
a broad range of substrates with different ability to activation.
Into conrming the efficiency of the proposed system as an
In an attempt to achieve an optimized condition, we selected ideal candidate for C–H bond activation, further investigations
oxidation of ethylbenzene to corresponding products as were continued for a broad range of substrates (Table 2,
a model reaction (The results are summarized in Table 1, and Fig. S31–S39† and 1H NMR spectrum of products Fig. S42–
Fig. S3–S27†). We began our investigation into the effect of S49†). 1-Ethyl-4-methoxybenzene (Table 2 entry 1) and 1-ethyl-4-
solvents such as dioxan, EtOH, THF, and CH3CN during 5 h; as bromobenzene (Table 2, entry 2) were chosen to peruse the
we can see in Table 1 (entries 1–4) CH3CN acts as a suitable effect of electron donating (MeOꢁ) and electron withdrawing
solvent and the activity of the mentioned catalyst was increased (Brꢁ) groups in comparison with ethylbenzene. Based on Table
in the smaller amount of CH3CN (Table 1, entries 4–7). Given 2, the substrate with the electron donating group, converted to
the high activity of the catalyst in the absence of solvent, so we products easier than substrates contain electron withdrawing
evaluated the eligibility of our proposed system in the solvent groups. The harder reaction of C–H bond in 1-ethyl-2-
free condition (Table 1, entry 8). The model reaction in the bromobenzene (Table 2 entry 3) in comparison with 1-ethyl-4-
presence of H2O2 cannot progress (Table 1, entry 15); therefore bromobenzene, causes by the steric effect of bromo group.
other green oxidants such as O2 and TBHP were selected.
For bulky molecule such as diphenylmethane, our catalyst
According to the Table 1 (entries 8–11), our catalyst has the showed high activity and selectivity (Table 2 entry 4). It should
best activity in the presence of 3 eq. TBHP. In order to nd the be noted that high selectivity of the catalyst in a catalytic reac-
ꢀ
optimized temperature at room temperature, and 70 C about tion is as important as high activity. This point of view was
13 and 65% conversion was achieved, respectively. Hence, 60 ꢀC conrmed in the oxidation of 1,2,3,4-tetrahydronaphthalene to
was selected as optimized temperature (Table 1 entries 12 and a-tetralone with high conversion and selectivity in 10 h in the
13). By reducing the amount of catalyst to 1 mol% (20 mg) presence of 2 eq. of TBHP (Table 2, entry 5). Furthermore, the
catalytic activity was decreased (Table 1, entry 14) so 2 mol% designed catalyst showed a good efficiency for oxidation of 1-
catalyst chosen as the optimum amount of catalyst. The exper- indanone without any C–C bond cleavage (Table 2 entry 6).
iment was continued by investigation the effect of Fe3O4, Fe3-
With respect to the industrial application of caprolactam, so
O4@SiO2, Fe3O4@SiO2-APTES, and Fe3O4@SiO2-APTES-H3LGDC direct oxidation of toluene to benzoic acid as one of the
(Table 1, entries 16–19). Slightly progress in the model reaction important steps for synthesis of caprolactam is so remarkable.23
in the presence of them proves that these particles do not have Therefore we investigated the competency of our introduced
any catalytic activity in this reaction. Moreover, by synthesizing system for direct oxidation of toluene to benzoic acid as inter-
the homogeneous catalyst (MnLGDC), we explored the catalytic esting transformation. As we can see in Table 2 (entries 7 and 8)
activity of this form of catalyst and just about 19% conversion our catalyst demonstrated high activity in mentioned reaction
was achieved (Table 1 entry 20). As shown in Fig. S41,† the and 71% benzoic acid was achieved with 100% selectivity at
absorption spectra for the fresh reaction mixture in the pres- 20 h. Moreover, to further investigation direct oxidation of 4-
ence of MnLGDC aer an hour has been changed, this can be methylanisole was performed (Table 2 entry 9) and 83% 4-
14346 | RSC Adv., 2019, 9, 14343–14351
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
Table 1 Optimization for the oxidation of ethylbenzene
Selectivityp (%)
Entry
TBHP (eq.)
Solvent (mL)
Time (h)
Conv.o (%)
A
B
C
TONq
16
1
16
87
13
2
3
4
5
6
7
8
9
3
3
3
3
3
3
3
2
2
4
3
3
3
—
3
3
3
3
3
3
4
4
—
2
3
THF, 3
EtOH, 3
5
5
5
5
5
5
5
5
5
5
5
5
5
5
10
10
10
10
10
10
10
10
10
10
10
Trace
Trace
39
41
47
55
62
49
71
65
13
65
50
Trace
Trace
Trace
Trace
Trace
19
CH3CN, 3
CH3CN, 2
CH3CN, 1
CH3CN, 0.5
97
95
96
96
95
94
97
97
92
97
92
3
5
4
4
2
6
1
1
8
3
6
39
41
47
55
61
49
70
65
13
65
49
n
—
3
—
—
—
—
—
—
—
—
—
—
—
—
—
—
10a
11
12b
13c
14d
15e
16f
17g
18h
19i
20j
21k
22l
23l
24m
25
26
2
2
2
89
90
11
10
19
30
30
Trace
Trace
Trace
70
CH3CN, 0.5
CH3CN, 0.5
—
—
99
1
70
96
98
2
96
a
TBHP (2 eq., 70%), O2 balloon. b T ¼ RT. c T ¼ 70 ꢀC. d Cat. (20, 1 mol%). e H2O2 (3 eq., 30%). f Fe3O4, 40 mg. g Fe3O4@SiO2, 40 mg. h Fe3O4@SiO2-
APTES, 40 mg. i Fe3O4@SiO2-APTES-H2LGDC, 40 mg. j MnLGDC (10 mg, 2 mol%). k MnCl2$4H2O (4 mg, 2 mol%). l In the absence of catalyst. m O2
balloon, in the absence of TBHP. Solvent free. Conversions were determined by GC (anisole as internal standard (1 mmol, 1/1, substrate/
anisole)). p Selectivity to product ¼ [product%/(products%)] ꢂ 100. q TON ¼ (substrate/catalyst) ꢂ conversion.
n
o
methoxybenzoic acid as the main product was obtained and this
percentage of conversion proves the positive effect of electron
donating group (MeOꢁ).
Monitoring, hot ltration test and recovery of the catalyst
As we can see in Fig. 5A the oxidation reaction of ethylbenzene
was monitored as a function of time and 97% of conversion was
achieved aer 10 h. Moreover, aer removal of the catalyst at
the half of the completion reaction time (5 h) less than 10%
progress in conversion was observed. Also, the amount leaching
of manganese into the nal aqueous phase was checked and
negligible leaching based on the ICP-AES analysis (less than the
detection limit) was detected. These results truly conrmed the
heterogeneous nature of our catalytic system.
It is noteworthy that simple separation and good recovery of the
catalyst is one of the important branches of green chemistry,
accordingly, to further validation of our catalytic system the feasi-
bility of catalyst recovery was investigated for oxidation of ethyl-
benzene under optimal condition (Fig. 5B). Five successive recycling
of catalyst is a good validation on the durability of our catalyst. In
addition, XRD patterns (Fig. 1A and S1B†), FESEM image (Fig. 2C
and D and S1A†), VSM data (Fig. 3A and S2A†) as well as TGA
analysis (Fig. 3B and S2B†) of pristine and recovered catalysts clearly
show the high chemical and physical stability of our catalysts. The
Scheme 2 Oxidation of ethylbenzene catalyzed by catalyst (Fe3O4@-
SiO2-APTES-MnLGDC) in the presence of (a) TBHP (aq. 70%). (b) O2. (c) Air.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 14343–14351 | 14347

View Article Online
RSC Advances
Paper
Table 2 Substrate scope catalyzed by Fe3O4@SiO2-APTES-MnLGDC
Selectivityd (%)
Major product
Entry
1
Substrate
Major product
Time (h)
Conv.c (%)
Other product
TONe
92
91
98
9
2
2
10
10
10
10
96
64
93
91
95
47
93
89
3
48
100
91
52
—
9
4
5a
6
10
80
100
—
80
7b
8b
10
20
57
71
100
100
—
—
86
107
9b
20
87
92
8
131
a
TBHP (2 eq., 70%). b TBHP (4 eq., 70%). c Conversions were determined by GC. d Selectivity to product ¼ [product%/(products%)] ꢂ 100. e TON ¼
(substrate/catalyst) ꢂ conversion.
Mn content of the recovered catalyst was determined by AAS tech- 0.47 mmol gꢁ1 for recovered catalyst). It may be concluded that the
nique. The result indicated a small leaching in the Mn content at negligible decreasing of catalytic activity aer the 5th run could be
the end of recovery process (0.49 mmol gꢁ1 for fresh catalyst vs. attributed to this minimal leaching of Mn species and/or small
losing of catalyst mass during the recovery process.
Proposed mechanism
According to the previous studies, the oxidation mechanism of
C–H bond in the presence of a non-heme manganese complex
involves a high-valent manganese-oxo species.
Therefore, we think that our system containing a non-heme
manganese complex can produce metal-oxo species which can
generate short-lived alkyl radicals in this reaction (Scheme 3,
cycle A). As can be seen in following Scheme (cycle B), the
formed alcohol converts to the aldehyde or ketone form. Also,
Fig. 5 (A) Monitoring and hot filtration test, (B) recycling for oxidation
of ethylbenzene.
14348 | RSC Adv., 2019, 9, 14343–14351
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
Scheme 3 Proposed mechanism for our non-heme manganese complex-catalyzed benzylic C–H bond oxidation reaction.
further oxidation of prepared benzaldehydes by using of PW1730 (step size: 0.05, time per step: 1 s). The content of
oxidant (TBHP) or H2O can be done (Scheme 3, cycle C).24
manganese in the catalyst was determined using an Atomic
Absorption Spectrometer Varian Spectre AA 110. The organic
composition of the modied MNPs base materials was determined
by thermogravimetric analysis (TGA) and differential thermoanal-
ysis (DTG), heating from room temperature to 800 ꢀC under
nitrogen ow using a STA 409 PC/PG analyser (Netzsch). The
magnetic properties of the prepared materials were measured
using a homemade vibrating sample magnetometer (Meghnatis
Daghigh Kavir Company, Iran) at room temperature from ꢁ10 000
to +10 000 Oe. The electronic states of powders were evaluated
using X-ray photoelectron spectroscopy (was performed using
a Thermo Scientic, ESCALAB 250Xi with Mg X-ray resource). The
content of Mn in nal aqueous phase was determined by applying
an inductively coupled plasma-optical emission spectrometer (ICP-
OES). Furthermore, the products were determined and analysed
using a VARIAN CP-3800 gas chromatograph equipped with
a capillary column and a ame-ionization detector.
Conclusions
In conclusion, our reported system consisting of three parts,
Mn(III) ion, amine bis(phenol) ligand (H3LGDC) and magnetic
nanoparticles. These components showed a good cooperation
effect acting as an efficient, recyclable and environmentally
friendly catalyst under solvent-free and mild conditions in
benzylic C–H bond oxidation reaction for a variety of substrates
as well as toluene. The chemical nature and structural stability
of the catalyst were conrmed by various techniques. Further-
more, both the leaching experiment and ve successive recy-
cling of the catalyst, proved the strong attachment of the
manganese complex onto the magnetite nanoparticles.
Experimental section
Materials and methods
Synthesis of Mn(III) complex of Fe3O4@SiO2-APTES-H2LGDC
(Fe3O4@SiO2-APTES-MnLGDC
)
All reagents and solvents were purchased from commercial sour-
ces and used without further purication. Fourier transform For synthesis of our catalyst, triethylamine (2 mmol, 0.20 g) was
infrared spectroscopy on KBr pellets of the compounds was added to a stirred mixture of Fe3O4@SiO2-APTES-H2LGDC (1.00
recorded on a Bruker Vector 22 in the range of 400 and 4000 cmꢁ1
.
g) and MnCl2$4H2O (1 mmol, 0.20 g) in ethanol (80 mL) under
UV-vis absorbance digitized spectra were collected using a CARY continuous stirring. The mixture reaction was stirred at room
100 spectrophotometer. The morphological features of particles temperature for 4 days. Final product was separated from the
were characterized by using eld emission transmission electron reaction mixture by applying an external magnetic eld and
microscopy (JEOL, JEM-2100F, 200 kV TEM) and Field emission washed with ethanol and acetone. The resulting solid was dried
scanning electron microscopy (JEOL, JSM-7610F). Elemental at 80 ꢀC overnight and used for high selective oxidation of
analyses (C, H and N) were performed by the Elementar, Vario EL benzylic C–H bonds. The resulting material was denoted as
III. The X-ray powder patterns were recorded using a PHILIPS Fe3O4@SiO2-APTES-MnLGDC
.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 14343–14351 | 14349

View Article Online
RSC Advances
Paper
´
7 (a) A. Conde, G. Sabenya, M. Rodrıguez, V. Postils, J. M. Luis,
General procedure in the C–H bond oxidation
´
´
M. M. Dıaz-Requejo, M. Costas and P. J. Perez, Angew. Chem.,
Int. Ed., 2016, 55, 6530–6534; (b) L. Carroll, H. L. Evans,
A. C. Spivey and E. O. Aboagye, Chem. Commun., 2015, 51,
8439–8441.
Under atmosphere of argon in a 5 mL glass ask were placed
catalyst (0.04 g, 2 mol%) and substrate (1 mmol) in solvent free
condition, TBHP as oxidant was added. The reaction mixture
ꢀ
was continuously stirred at 60 C for the desired time and the
8 (a) H. Ren, Y.-P. Zhou, Y. Bai, C. Cui and M. Driess, Chem.–
Eur. J., 2017, 23, 5663–5667; (b) F. Yang, J. Yu, Y. Liu and
J. Zhu, Org. Lett., 2017, 19, 2885–2888.
9 (a) Z. Ruan, D. Ghorai, G. Zanoni and L. Ackermann, Chem.
Commun., 2017, 53, 9113–9116; (b) Y. He, Y. Cai and S. Zhu, J.
Am. Chem. Soc., 2017, 139, 1061–1064.
10 (a) M. D. K. Boele, G. P. F. van Strijdonck, A. H. M. de Vries,
P. C. J. Kamer, J. G. de Vries and P. W. N. M. van Leeuwen, J.
Am. Chem. Soc., 2002, 124, 1586–1587; (b) R. Shi, H. Niu,
L. Lu and A. Lei, Chem. Commun., 2017, 53, 1908–1911; (c)
J. L. Nallasivam and R. A. Fernandes, J. Am. Chem. Soc.,
2016, 138, 13238–13245.
reaction was monitored by TLC, aer completion of the reac-
tion, anisole (1 mmol, 1/1 substrate and anisole) as internal
standard was added. In continue the mixture was extracted with
ethyl acetate and then the catalyst was magnetically recovered
by placing a permanent magnet in the reactor wall. Products
were collected with a syringe and analyzed by gas chromatog-
raphy (GC). The catalyst was washed several times with ethanol
and acetone and then dried at 80 ꢀC overnight before being used
again for the next reaction.
Conflicts of interest
11 C.-Q. Wang, L. Ye, C. Feng and T.-P. Loh, J. Am. Chem. Soc.,
2017, 139, 1762–1765.
There are no conicts to declare.
12 X. Wu, B. Wang, S. Zhou, Y. Zhou and H. Liu, ACS Catal.,
2017, 7, 2494–2499.
13 B. C. Bailey, H. Fan, J. C. Huffman, M.-H. Baik and
D. J. Mindiola, J. Am. Chem. Soc., 2007, 129, 8781–8793.
Acknowledgements
The authors are grateful to the Institute for Advanced Studies in
Basic Sciences (IASBS), the chemistry department of Shiraz
University and Bahman Farnoudi for proofreading of the
manuscript.
¨
14 (a) A.-H. Lu, E. L. Salabas and F. Schuth, Angew. Chem., Int.
¨
Ed., 2007, 46, 1222–1244; (b) S. Shylesh, V. Schunemann
and W. R. Thiel, Angew. Chem., Int. Ed., 2010, 49, 3428–3459.
´
´
¨
15 (a) S. Vasquez-Cespedes, K. M. Chepiga, N. Moller,
¨
A. H. Schafer and F. Glorius, ACS Catal., 2016, 6, 5954–
5961; (b) M. Kaur, S. Pramanik, M. Kumar and V. Bhalla,
ACS Catal., 2017, 7, 2007–2021; (c) S. Warratz, D. J. Burns,
C. Zhu, K. Korvorapun, T. Rogge, J. Scholz, C. Jooss,
D. Gelman and L. Ackermann, Angew. Chem., Int. Ed., 2017,
56, 1557–1560; (d) Y. Gao, P. Tang, H. Zhou, W. Zhang,
H. Yang, N. Yan, G. Hu, D. Mei, J. Wang and D. Ma, Angew.
Chem., Int. Ed., 2016, 55, 3124–3128; (e) T. V. Tran,
H. T. N. Le, H. Q. Ha, X. N. T. Duong, L. H. T. Nguyen,
T. L. H. Doan, H. L. Nguyen and T. Truong, Catal. Sci.
Technol., 2017, 7, 3453–3458; (f) X. Tian, F. Yang,
D. Rasina, M. Bauer, S. Warratz, F. Ferlin, L. Vaccaro and
L. Ackermann, Chem. Commun., 2016, 52, 9777–9780; (g)
S. Korwar, M. Burkholder, S. E. Gilliland, K. Brinkley,
B. F. Gupton and K. C. Ellis, Chem. Commun., 2017, 53,
7022–7025; (h) B. Dong, Z. Han, Y. Zhang, Y. Yu, A. Kong
and Y. Shan, Chem.–Eur. J., 2016, 22, 2046–2050; (i)
V. Pascanu, F. Carson, M. V. Solano, J. Su, X. Zou,
Notes and references
1 (a) J. Wencel-Delord and F. Glorius, Nat. Chem., 2013, 5, 369–
375; (b) K. Godula and D. Sames, Science, 2006, 312, 67–72.
2 (a) M. Chen, Y. Pan, H.-K. Kwong, R. J. Zeng, K.-C. Lau and
T.-C. Lau, Chem. Commun., 2015, 51, 13686–13689; (b)
R. Banerjee, Y. Proshlyakov, J. D. Lipscomb and
D. A. Proshlyakov, Nature, 2015, 518, 431–434; (c)
R. Balasubramanian, S. M. Smith, S. Rawat, L. A. Yatsunyk,
T. L. Stemmler and A. C. Rosenzweig, Nature, 2010, 465,
115–119; (d) G. Xue, D. Wang, R. De Hont, A. T. Fiedler,
¨
X. Shan, E. Munck and L. Que, Proc. Natl. Acad. Sci. U. S.
A., 2007, 104, 20713–20718; (e) C. E. Tinberg and
S. J. Lippard, Acc. Chem. Res., 2011, 44, 280–288; (f)
D. Wang, E. R. Farquhar, A. Stubna, E. Munck and L. Que,
Nat. Chem., 2009, 1, 145–150.
3 V. C. C. Wang, S. Maji, P. P. Y. Chen, H. K. Lee, S. S. F. Yu and
S. I. Chan, Chem. Rev., 2017, 117, 8574–8621.
¨
´
M. J. Johansson and B. Martın-Matute, Chem.–Eur. J., 2016,
4 (a) J. Rittle and M. T. Green, Science, 2010, 330, 933–937; (b)
B. Meunier, S. P. de Visser and S. Shaik, Chem. Rev., 2004,
104, 3947–3980.
5 (a) J.-M. Li, Y.-H. Wang, Y. Yu, R.-B. Wu, J. Weng and G. Lu,
ACS Catal., 2017, 7, 2661–2667; (b) S. Tang, P. Wang, H. Li
and A. Lei, Nat. Commun., 2016, 7, 11676.
22, 3729–3737; (j) S. Zhang, H. Wang, M. Li, J. Han, X. Liu
and J. Gong, Chem. Sci., 2017, 8, 4489–4496; (k) X. Wang,
M. Liu, Y. Wang, H. Fan, J. Wu, C. Huang and H. Hou,
Inorg. Chem., 2017, 56, 13329–13336; (l) D.-T. D. Tang,
K. D. Collins and F. Glorius, J. Am. Chem. Soc., 2013, 135,
7450–7453; (m) H. Fei and S. M. Cohen, J. Am. Chem. Soc.,
2015, 137, 2191–2194.
6 (a) S. Rana, A. Dey and D. Maiti, Chem. Commun., 2015, 51,
14469–14472; (b) J. Serrano-Plana, W. N. Oloo, L. Acosta- 16 (a) C. Rajendran and G. Satishkumar, ChemCatChem, 2017,
´
˜
Rueda, K. K. Meier, B. Verdejo, E. Garcıa-Espana,
9, 1284–1291; (b) S. Samanta and R. Srivastava, Appl.
Catal., B, 2017, 218, 621–636.
¨
M. G. Basallote, E. Munck, L. Que, A. Company and
M. Costas, J. Am. Chem. Soc., 2015, 137, 15833–15842.
14350 | RSC Adv., 2019, 9, 14343–14351
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
17 (a) Y. Kuwahara, Y. Yoshimura and H. Yamashita, Catal. Sci. 21 (a) X. Dong, X. Zhang, P. Wu, Y. Zhang, B. Liu, H. Hu and
Technol., 2016, 6, 442–448; (b) S. Singha and K. M. Parida,
Catal. Sci. Technol., 2011, 1, 1496–1505; (c) L. Fu, S. Zhao,
Y. Chen and Z. Liu, Chem. Commun., 2016, 52, 5577–5580;
(d) Y. Aratani, Y. Yamada and S. Fukuzumi, Chem.
G. Xue, ChemCatChem, 2016, 8, 3680–3687; (b)
R. K. Sharma, M. Yadav, Y. Monga, R. Gaur, A. Adholeya,
R. Zboril, R. S. Varma and M. B. Gawande, ACS Sustainable
Chem. Eng., 2016, 4, 1123–1130.
Commun., 2015, 51, 4662–4665; (e) L. Wang, G. Wang, 22 (a) Y. Liu, J.-F. Chen, J. Bao and Y. Zhang, ACS Catal., 2015, 5,
J. Zhang, C. Bian, X. Meng and F.-S. Xiao, Nat. Commun.,
2017, 8, 15240; (f) Y. Li, C. Liu and W. Yang, New J. Chem.,
2017, 41, 8214–8221.
3905–3909; (b) L. Wang, X. Wang, J. Luo, B. N. Wanjala,
C. Wang, N. A. Chernova, M. H. Engelhard, Y. Liu, I.-T. Bae
and C.-J. Zhong, J. Am. Chem. Soc., 2010, 132, 17686–17689.
18 T. Karimpour, E. Safaei, B. Karimi and Y. Lee, ChemCatchem, 23 X. Xu, M. Tang, M. Li, H. Li and Y. Wang, ACS Catal., 2014, 4,
2018, 10, 1889–1899. 3132–3135.
19 (a) S. Sun, H. Zeng, D. B. Robinson, S. Raoux, P. M. Rice, 24 (a) M. Guo, T. Corona, K. Ray and W. Nam, ACS Cent. Sci.,
S. X. Wang and G. Li, J. Am. Chem. Soc., 2004, 126, 273–
279; (b) M. Shao, F. Ning, J. Zhao, M. Wei, D. G. Evans and
X. Duan, J. Am. Chem. Soc., 2012, 134, 1071–1077.
20 Y. Liu, W. Zhang, X. Li, X. Le and J. Ma, New J. Chem., 2015,
39, 6474–6481.
2019, 5, 13–28; (b) X. Wu, M. S. Seo, K. M. Davis, Y.-M. Lee,
J. Chen, K.-B. Cho, Y. N. Pushkar and W. Nam, J. Am.
Chem. Soc., 2011, 133, 20088–20091; (c) A. Gunay and
K. H. Theopold, Chem. Rev., 2010, 110, 1060–1081; (d)
R. Noyori, M. Aoki and K. Sato, Chem. Commun., 2003,
1977–1986.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 14343–14351 | 14351