A recyclable hybrid manganese(III) porphyrin magnetic catalyst for selective olefin epoxidation using molecular oxygen

Article abstract of DOI:10.1142/S108842461850027X

The synthesis and characterization of a hybrid Mn(III)-porphyrin magnetic nanocomposite is described. Moreover, a sustainable methodology for epoxidation of olefins is reported, using O₂ as a green oxidant and the magnetic nanoparticle as a rec

Full text of DOI:10.1142/S108842461850027X

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2018; 22: 1–11
DOI: 10.1142/S108842461850027X
Published at http://www.worldscinet.com/jpp/
A recyclable hybrid manganese(III) porphyrin magnetic
catalyst for selective olefin epoxidation using molecular
oxygen
Lucas D. Diasa◊, Rui M. B. Carrilhoa, César A. Henriquesa, Giusi Piccirilloa,
Auguste Fernandesb, Liane M. Rossic, M. Filipa Ribeirob, Mário J. F. Calvetea
and Mariette M. Pereira*a◊
a CQC, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal
b Centro de Química Estrutural, Instituto Técnico Superior, Universidade de Lisboa, 1049-001 Lisboa, Portugal
c Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo,
05508-000 São Paulo, Brasil
Received 8 January 2018
Accepted 25 January 2018
ABSTRACT: The synthesis and characterization of a hybrid Mn(III)-porphyrin magnetic nanocomposite
is described. Moreover, a sustainable methodology for epoxidation of olefins is reported, using O2 as a
green oxidant and the magnetic nanoparticle as a recyclable catalyst. High activity in alkene oxidation
was observed, with full selectivity for epoxide formation. The magnetic catalyst presented high stability,
being recovered and reused in five consecutive runs without loss of catalytic activity or selectivity in
cyclooctene oxidation. Moreover, the catalytic system showed very good reactivity toward epoxidation
of a range of terminal, substituted, cyclic or acyclic, aliphatic and aromatic olefins, including terpene and
steroid derivatives, affording a range of biologically relevant epoxides in excellent yields. The isobutyric
acid, formed as side-product, was recovered with high yield and purity, which provides the potential
reutilization of this important industrial product.
KEYWORDS: hybrid magnetic nanoparticles, manganese(III) porphyrin, epoxidation, molecular
oxygen, isobutyric acid, terpene, steroids.
metalloporphyrins [13–21]. Pioneering studies on the
INTRODUCTION
application of metalloporphyrins as epoxidation catalysts
The development of green and economically sus-
were performed by Groves [13–15], who described the
tainable synthetic approaches to prepare epoxides is a
use of Fe and Mn complexes of tetraphenylporphyrin
relevant subject in modern chemistry, since epoxides are
(TPP), using iodosylbenzene [13] or a peroxycarboxylic
versatile building blocks, widely used as intermediates
acid (mCPBA) [14, 15] as the oxidants. Since then,
for the synthesis of agrochemicals and pharmaceuticals
porphyrin-derived catalytic epoxidation systems have
[1–3] and are often present in a large array of bioactive
been widely reported, making use of different oxygen-
molecules [4, 5]. Catalytic olefin epoxidation is currently
transfer reagents, including alkyl hydroperoxides [16],
the main synthetic approach toward epoxides [6–8],
iodosylbenzene [17], peroxycarboxylic acids [18],
which may be promoted by different catalysts, such as
sodium hypochlorite [19], periodates [20] and oxone
organocatalysts [9, 10], enzymes [11] or transition metal
[21]. However, most of such approaches suffer from
complexes [12], namely those based on biomimetic
low atom economy, and catalyst degradation is often
observed. Hence, an increasing awareness in developing
sustainable methods for olefin epoxidation has evolved
◊ꢀSPP full member in good standing.
in three parallel strands: (i) search for greener and more
efficient oxidants, such as hydrogen peroxide [22, 23] or
*Correspondence to: Mariette M. Pereira, tel.: +351 239 8545
474, email: mmpereira@qui.uc.pt.
Copyright © 2018 World Scientific Publishing Company

2
L.D. DIAS ET AL.
molecularoxygen[24–27];(ii)developmentofmorerobust
metalloporphyrin catalysts containing halogen atoms in
their structures to increase their stability against oxidation
processes and also to enhance their catalytic activity [28,
29]; (iii) catalysts’ immobilization onto solid supports
[30] in order to enable their recovery and reuse, namely
in polymers [31], clays [32], silica [33], mesoporous
materials [34], layered double hydroxides (LDH’s) [35],
metal organic frameworks [36–38], polyoxometalates
(POM’s) [39, 40], hybrid magnetic nanoparticles [41, 42]
or other mixed materials [43, 44].
regarding the development of reusable catalysts [55–57],
herein we report the synthesis and characterization of
a magnetically recoverable catalyst based on a hybrid
manganese halogenated porphyrin nanocomposite, and
its efficient application in olefin epoxidation, in the
presence of O2 as the oxidant and isobutyraldehyde as the
co-reductant (Scheme 1b), with concomitant recovery of
isobutyric acid.
RESULTS AND DISCUSSION
Although the use of hydrogen peroxide is considered
an interesting green approach [45–48], the use of
abundant molecular oxygen as an eco-friendly and rene-
wable oxidant is still considered the most appealing
alternative [49]. It is well established that selective olefin
epoxidation, in the presence of O2, requires the use of
a “sacrificial” co-reductant, which is often necessary to
promote the electron transfer to the metal center and
generate the oxygen active species [50–52]. Among the
commonly used co-reductant reagents, isobutyraldehyde
is one of the most economically viable and efficient
to promote the generation of acylperoxy radicals,
known as epoxidation intermediates [53]. However, its
large use leads to high waste of isobutyric acid, which
generally turns the processes less cost-effective and
environmentally less sustainable. It is important to note
that isobutyric acid is a useful platform chemical, used
in several plastic and polymer industrial applications
[54], namely in the large-scale production of methyl
methacrylate (2.2 million ton/year) and sucrose acetate
isobutyrate (100000 ton/year), among others. Thus,
the improvement of sustainable epoxidation processes
that allow the recovery/isolation of isobutyric acid is of
upmost importance.
Synthesis and characterization of Mn(III)
porphyrin-based magnetic nanocomposite
The hybrid Mn(III) porphyrin-based magnetic nano-
composite MNP@SiO2[4-NH-Mn-TDCPP] (3) was pre-
pared by the sequential synthetic procedure described in
Schemes 2 and S1. First, meso-tetraarylporphyrin 1 was
synthesized through a one-pot reaction of pyrrole with
one molar equivalent of 4-acetamidobenzaldehyde and
three molar equivalents of 2,6-dichlorobenzaldehyde, in
water, under microwave irradiation, following our recently
reported eco-friendly methodology [58]. Then, hydrolysis
of 1 was performed in acidic medium, followed by the
.
manganese complex formation, using Mn(OAc)2 4H2O, in
DME, which afforded manganese(III) 5-(4-aminophenyl)-
10,15,20-tri(2,6-dichlorophenyl)porphyrinatomanganese
(2Mn) in 81% yield (Scheme S2). The covalent grafting of
2Mn onto the magnetic support was performed by reacting
the metalloporphyrin with 3-chloropropyltriethoxisilane
(CPTES), in twofold excess, using Et3N as a base, followed
by the addition of silica-coated nanoparticles MNP@SiO2
[55, 59], whose magnetic core (MNP) was generated by
the Fe2+/Fe3+ coprecipitation method [60]. Finally, the
hybrid nanocomposite catalyst MNP@SiO2[4-NH-Mn-
TDCPP] (3) was easily collected using an external magnet
and washed with ethyl acetate and acetonitrile to rinse
away the unreacted metalloporphyrin.
In previous work, we have developed hybrid copper
porphyrin nanoparticles [55] which were proven to be
highly active and reusable catalysts for allylic oxidations,
using molecular oxygen as the oxidant, in the absence
of any co-reductant or solvent (Scheme 1a). Concerned
with environmental and sustainability issues, particularly
The manganese content of MNP@SiO2[4-NH-Mn-
TDCPP] (3) was determined by flame atomic absorption
A) Previous work
O
OH
O2
[CAT]
SiO2
+
[CAT]
(M= Cu)
Ar
covalent
grafting
Fe3O4
N
N
N
N
B) This work
O
Ar
Ar
M
O2
[CAT]
(M= Mn)
hybrid metalloporphyrin
magnetic nanocomposite
+
Ar
O
recovery
O
OH
Scheme 1. Catalytic oxidations using hybrid metalloporphyrin magnetic nanocomposites: (a) Previous work; (b) This work
Copyright © 2018 World Scientific Publishing Company
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A RECYCLABLE HYBRID MANGANESE(III) PORPHYRIN MAGNETIC CATALYST FOR SELECTIVE OLEFIN EPOXIDATION
3
O
NH
CHO
HN
O
Cl
Cl
Cl
Cl
N
H
NH
N
N
(1 eq)
MW
H2O
CHO
HN
Cl
Cl
Cl
Cl
(3 eq)
1
1) HCl, THF
2) Mn(II)OAc . 4H2O
X
X
HO
O
Si
Cl
X =
X
DME
X
O
OH
Si
O
Fe3O4
SiO2
NH2
O
X
X
NH
X
X
AcO
Cl
Cl
Cl
Cl
CPTES
N
N
N
toluene, Et3N
AcO
Mn
N
Cl
Cl
Cl
N
N
N
Fe3O4
Mn
Cl
Cl
N
SiO2
Cl
MNP@SiO2
2 Mn
Cl
Cl
MNP@SiO2[4-NH-Mn-TDCPP] (3)
Scheme 2. Synthesis of hybrid Mn(III) porphyrin magnetic nanocomposite 3
spectroscopy (FAAS), indicating a Mn percentage of
0.09%, which corresponds to 1.5% of porphyrin 2Mn
(0.013 mmol per gram of nanocomposite). Transmission
electron microscopy (TEM) images (Figs S1 and S2)
showed that the silica-coated magnetic nanoparticles
(MNP@SiO2) display nearly spherical morphology with
an average diameter of 29 5 nm, which is significantly
higher than that of the simply oleic acid-stabilized
magnetic nanoparticle MNP (8 2 nm), confirming a
uniform silica coating.
The UV-vis absorption spectrum of 3 shows an intense
Soret band at 465 nm, similarity to the non-immobilized
metalloporphyrin 2Mn whose Soret band is at 480 nm
(Fig. 1). This shift can be explained on the basis of the
orientation of the nanoparticle molecular dipole with
respect to the porphyrin-nanoparticle axis [61].
carried out between 25°C and 800°C, comparatively with
the non-immobilized metalloporphyrin 2Mn and with the
“blank” material, i.e. the 3-chloropropyl functionalized
magnetic nanoparticle, denoted Mn@SiO2-CPTES (4)
(Figs 2a–2c) and (Scheme S3). All diagrams present an
endothermic peak between 50°C and 200°C, attributed to
the weight loss of physically adsorbed water, while further
weight losses (with exothermic peaks) occur between
200°C and 800°C due to organic material decomposition.
The metalloporphyrin content in the hybrid porphyrin
magnetic nanocomposite could be directly calculated from
the TG-DSC diagram of MNP@SiO2[4-NH-Mn-TDCPP]
(3) (Fig. 2a), in temperature range 200–800°C, by
substracting the respective “blank” experiment (Fig. 2b).
The value obtained was 1.4%, which was in good agree-
ment with that determined by FAAS.
Thermogravimetry/differential scanning calorimetry
(TG-DSC) was used to quantify the organic content of the
nanocomposite material, with several measurements being
The effectiveness of the metalloporphyrin 2Mn
grafting onto the magnetic nanoparticle was further
demonstrated by infrared measurements (Fig. 3) of the
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4
L.D. DIAS ET AL.
hybrid material MNP@SiO2[4-NH-Mn-TDCPP] (3),
compared with the non-functionalized silica coated
magnetic nanoparticle (MNP@SiO2).
In the interval 4000–2700 cm-1 (Fig. 3, left), both IR
spectra show broad bands between 3750–3300 cm-1, typical
of terminal silanol and hydroxyl groups in interaction, with
the spectrum of 3 showing additional signals at 2950–
2850 cm-1, which are characteristic of C–H stretching
vibrations. In the interval 1300–1700 cm-1 (Fig. 3, right), no
signals were observed in the IR spectrum of MNP@SiO2,
while the spectrum of 3 present several characteristic peaks
at: 1560 cm-1 (N–H bending), 1450 cm-1 (C–H bending),
1410 cm-1 (Si–CH2 bending), 1608 cm-1 (pyrrole C=N
stretching) and 1508–1465 cm-1 (aromatic C=C stretching),
which corroborate the presence of metalloporphyrin 2Mn
in the nanocomposite.
Fig. 1. UV-vis spectra of: (a) MNP@SiO2[4-NH-Mn-TDCPP]
(3), in DMF; (b) 2Mn, in CHCl3
(a)
(b)
(c)
Fig. 2. TG-DSC curves (weight loss — solid line; heat flow — dashed line) for: (a) MNP@SiO2[4-NH-Mn-TDCPP] (3); (b) MNP@
SiO2-CPTES (4) and (c) 2Mn
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A RECYCLABLE HYBRID MANGANESE(III) PORPHYRIN MAGNETIC CATALYST FOR SELECTIVE OLEFIN EPOXIDATION
5
dichloromethane as solvent (Table 1, entry 1). In the
search of a greener solvent for the reaction [63–65],
2-methyltetrahydrofuran and acetonitrile were tested, the
latter giving similar values of conversion and selectivity
for epoxide formation to those obtained with CH2Cl2,
while the conversion was significantly lower when
2-Me-THF was used (Table 1, entries 2–3). Therefore,
acetonitrile was chosen as solvent for the subsequent
experiments. In the absence of aldehyde, no conversion
was observed (Table 1, entry 4). In addition, aromatic
aldehydes, such as 3-furfural and 2-phenylpropanal
were also tested, but no conversion was observed in
any case (Table 1, entries 5–6), which demonstrates
that an aliphatic aldehyde is required as co-reductant to
generate an activated oxygen catalytic species [50–53].
The porphyrin Mn(III)-OAc-TDCPP-NH2 (2Mn), which
is the homogeneous analogue of the hybrid catalyst 3,
was then tested, providing 98% conversion in 1.5 h and
full selectivity for epoxide formation (Table 1, entry
7). Under the same conditions, catalyst 3 also showed
excellent catalytic activity and selectivity, with 99%
conversion in 1.5 h and practically exclusive formation
of cyclooctene oxide (Table 1, entry 8).
The progress of cyclooctene oxidation reactions, using
both homogeneous or heterogeneous catalysts (2Mn and
3, respectively) was studied for 90 min, by analysis of
aliquots taken from the mixtures at regular intervals
(Fig. 4) and (Tables S1 and S2).
For the homogeneous system 2Mn, a sharp increase
of conversion values is observed in the first 30 min of
reaction (until 70%), followed by a slower increase after
that period, which indicates that catalyst degradation
might be occurring. This was confirmed by UV-vis
analysis, which shows a decrease of ca. 80% in the
metalloporphyrin Soret region, after 30 min (Fig. S3).
In contrast, the reaction’s profile obtained with the
hybrid nanocomposite catalyst (3) indicates that catalyst
degradation does not occur, showing its higher stability.
The similar TON values for both 2Mn and the hybrid
catalyst (3) suggest that the latter, although immobilized
in the magnetic nanoparticle, is homogeneous in nature.
In addition, a “blank” experiment was carried out using
3-chloropropyltriethoxysilane functionalized magnetic
nanoparticle MNP@SiO2-CPTES (4) as catalyst, which
led to a conversion of only 2%, while a practically
inexistent conversion (<1%) was observed in the absence
of catalyst (Table 1, entries 9–10). This clearly demonstr-
ates that the Mn(III) porphyrin-containing hybrid magne-
tic nanoparticle (3) effectively acts as catalytic precursor.
Furthermore, the requirement of isobutyraldehyde as
co-reductant and the high chemoselectivity for epoxide
formation suggest that the reaction possibly follows
the mechanism previously described by Feiters and
coworkers [50], depicted in Scheme 3, in which a
peroxyacid species, formed in the presence of molecular
oxygen and the aldehyde (Eqs. 1–3), is assumed to act as
an oxygen donor to generate the high-valent Mn(V)-oxo
Fig. 3. FTIR spectra of: (a) MNP@SiO2 and (b) MNP@
SiO2[4-NH-Mn-TDCPP] (3), in the regions 4000–2700 (left)
and 1700–1300 (right) (previous to spectra acquisition, the
samples were out-gassed under vacuum, at 150°C, for 90 min,
in order to remove physically adsorbed water. The pre-treatment
temperature was chosen according to TG-DSC).
Catalytic epoxidation reactions using
molecular oxygen
Catalytic epoxidation experiments were carried out
using cyclooctene as the model substrate, molecular
oxygen as the oxidant and an aldehyde as the co-reductant,
in the presence of metalloporphyrin-based catalysts.
Typically, a glass vial was loaded with the appropriate
amount of cyclooctene, the desired metalloporphyrin
catalysts (or the magnetic nanocomposite) and the
aldehyde. The solution was magnetically stirred at
room temperature (25°C), under O2 bubbling, for 1.5 h.
Substrate conversion and selectivity was determined by
GC analysis based on chlorobenzene as internal standard
(Eq. S1), and the results are presented in Table 1, along
with TON calculations.
The homogeneous catalyst Mn(III)-OAc-TDCPP
(5) [62] was initially used as model Mn(III)-porphyrin
catalyst, with whom full conversion was obtained along
with 99% selectivity for epoxide formation, using
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L.D. DIAS ET AL.
Table 1. Evaluation of metalloporphyrin-based catalysts in cyclooctene epoxidation, using O2 as the oxidanta
Entry
Catalyst
Solvent
Co-reductant
Conversion (%)b
TONc
1
2
Mn(III)-OAc-TDCPP (5)
Mn(III)-OAc-TDCPP (5)
Mn(III)-OAc-TDCPP (5)
Mn(III)-OAc-TDCPP (5)
Mn(III)-OAc-TDCPP (5)
Mn(III)-OAc-TDCPP (5)
Mn(III)-OAc-TDCPP-NH2 (2Mn)
CH2Cl2
isobutyraldehyde
isobutyraldehyde
isobutyraldehyde
—
99
10532
3830
10532
—
2-Me-THF
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
36
3
99
4
0
5
3-furfural
0
—
6
2-phenylpropanal
isobutyraldehyde
isobutyraldehyde
isobutyraldehyde
isobutyraldehyde
isobutyraldehyde
isobutyraldehyde
0
—
7
98
10426
10532
213
8
MNP@SiO2[4-NH-Mn-TDCPP] (3) CH3CN
99
9
MNP@SiO2-CPTES (4)
CH3CN
CH3CN
2
10
11d
12d
—
<1
99 (53e)
—
MNP@SiO2[4-NH-Mn-TDCPP] (3) CH3CN
MNP@SiO2[4-NH-Mn-TDCPP] (3) C3H7CN
10532
10532
99
a Reaction conditions: catalyst (4.7 × 10-5 mmol), cyclooctene (0.5 mmol), aldehyde (2.5 mmol), solvent (2 mL),
O2 bubbling, T = 25°C, t = 1.5 h. b Conversions calculated by GC, using chlorobenzene (1.95 × 10-1 mmol) as
c
d
internal standard. turnover number calculated as molproducts/molMn. scale-up: catalyst 3 (64.8 mg, 8.42 × 10-4
mmol Mn), cyclooctene (9 mmol), isobutyraldehyde (45 mmol), solvent (36 mL), O2 bubbling, T = 25°C, t =
3.5 h. conversion at 1.5 h. Selectivity for epoxides was >98% in all cases. All data were reproduced at least
e
twice and reported as an average.
(a)
(b)
Fig. 4. Evolution of cyclooctene epoxidation catalysed by: (a) 2Mn; and (b) 3
intermediate, which operates as the catalytically active
epoxidation species (Eqs. 4–5) [66–68].
The magnetic catalyst showed excellent reusability
in 5 consecutive cycles without loss of activity or
selectivity for epoxide formation. Therefore, besides
the high activity and selectivity, it is worth noting the
great stability of Mn(III) porphyrin magnetic hybrid
catalyst (3), with no catalyst leaching being observed, as
demonstrated by UV-vis analyses of the crude reaction
product (Fig. S5). These findings were corroborated by
induced coupling plasma (ICP) analysis, which showed a
negligible metal content in solution (<0.1 mg mL-1). This
stabilizing effect of the magnetic nanomaterial support
on the metalloporphyrin catalyst was similar to that
Recyclability and scale-up
The magnetic nanocomposite was collected in the
side wall of the reaction flask by the simple action of
an external magnet (Fig. S4), and the recyclability of
MNP@SiO2[4-NH-Mn-TDCPP] (3) was examined.After
washing the solid material with CH3CN and subsequent
solvent removal by drying under vacuum at 60°C for
12 h, the catalyst (3) was reused for the next run (Fig. 5).
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A RECYCLABLE HYBRID MANGANESE(III) PORPHYRIN MAGNETIC CATALYST FOR SELECTIVE OLEFIN EPOXIDATION
7
[MnIII] + RCHO
3
[MnII] + RCO + H+ (eq. 1)
RC(O)OO
MnIII
RCO + O2
(eq. 2)
SiO2
RC(O)OO + RCHO
RC(O)OOH + RCO (eq. 3)
Fe3O4
[MnIII] + RC(O)OOH
[MnV=O] + RCOOH (eq. 4)
3
3
O
[MnV=O]
+
R
[MnIII] +
(eq. 5)
3
R
Scheme 3. Mechanism of olefin epoxidation, adapted from [50]
aliphatic and aromatic olefins were subjected to
epoxidation with molecular oxygen, using the hybrid
Mn-porphyrin nanocomposite catalyst (3), isobutyr-
aldehyde as co-reductant and butyronitrile as the
solvent, Table 2. Full conversions (up to 99%) and very
high selectivity (≥97%) for epoxides were obtained
in most cases; the only exception observed was the
aliphatic terminal olefin 1-hexene (Table 2, entry 1),
which presented a conversion of 65%, as expected for
the aerobic epoxidation of terminal alkyl olefins using
metalloporphyrin catalysts [41]. Remarkably, the novel
hybrid heterogeneous magnetic catalyst 3 was effective in
promoting the selective epoxidation of styrene (Table 2,
entry 2), cyclohexene (Table 2, entry 3) and natural-based
trisubstituted olefins, such as cyclic terpenes (alpha-
pinene, limonene) and the D5-steroid, 3b-acetoxy-5-
pregnen-20-one (Table 2, entries 4–6). It should be noted
that the oxidation of limonene was 100% selective for
the internal C=C double bond, affording exclusively
the corresponding epoxide, isolated in 95% yield
(Table 2, entry 5). In addition, the oxidation of 3b-acet-
oxy-5-pregnen-20-one afforded the respective epoxy
steroid in 57% isolated yield, with 71-b to 29-a diaster-
eomeric ratio (Table 2, entry 6). In addition, it is worth
mentioning that efficient recovery of isobutyric acid (up
to 95%) was achieved in all cases.
Fig. 5. Recycling experiments of MNP@SiO2[Mn(III)
TDCPP-NH2] (3) in cyclooctene epoxidation (reaction
conditions: 3 (3.6 mg, 4.7 × 10-5 mmol Mn), cyclooctene (5.0 ×
10-1 mmol), isobutyraldehyde (2.5 mmol), solvent: acetonitrile
(2 mL); O2 bubbling, T = 25°C, t = 1.5 h. Conversion and
selectivity calculated by GC, using chlorobenzene as internal
standard)
previously observed [55], which may be attributed to the
beneficial influence of the magnetic support in preventing
the formation of catalytically inactive oxo-dimeric
metalloporphyrin species [26]. Remarkably, the hybrid
Mn(III) porphyrin magnetic nanocomposite catalyst (3)
was also able to promote cyclooctene oxidation in a gram-
scale, with 99% conversion being observed in 3.5 h and
full selectivity for epoxide formation, achieving a TON of
10532 (Table 1, entry 11). The replacement of acetonitrile
by a water immiscible analogue (butyronitrile) as the
epoxidation solvent enabled similar results in terms of
conversion (99%) and epoxide selectivity (>98%)
(Table 1, entry 12) and further allowed recovery of
isobutyric acid in excellent yield (up to 95%) by water/
solvent extraction. Therefore, the sustainability of the
overall process was ensured by the efficient recovery of
isobutyric acid, obtained with high purity (≤5% H2O),
showing the potentialities of this methododoly regarding
its reutilization for industrial purposes [54].
EXPERIMENTAL
Reagents and instrumentation
All chemical reagents were purchased from Sigma–
Aldrich (Portugal), presenting the highest grade available.
Epoxides were distilled prior to their use. Solvents were
purifiedbystandardmethods[69]. 1Hand13CNMRspectra
were recorded in CDCl3 solutions on a Bruker Avance
III spectrometer, and a Bruker DRX-400 spectrometer,
1
both operating at 400.13 MHz for H, and 100.61 MHz
1
for 13C). Chemical shifts for H and 13C are expressed in
ppm, relatively to a TMS internal standard. The MALDI-
TOF MS data were acquired using a Bruker Daltonics
FlexAnalysis apparatus. UV-vis absorption spectra were
recorded on a Hitachi U-2010. For solid samples, the
Scope
Under optimized reaction conditions, various olefins
including acyclic or cyclic, terminal, di- or tri-substituted,
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8
L.D. DIAS ET AL.
Table 2. Epoxidation reaction’s scope, catalyzed by MNP@SiO2[4-NH-Mn-TDCPP] (3)a
Entry
1
Substrate
Conversionb (%)
Product (isolated yield, %)
65
2
3
99
99
4
5
99
99
6c
99
a Reaction conditions: MNP@SiO2[4-NH-Mn-TDCPP] (3) (3.6 mg, 4.7 × 10-5 mmol Mn), substrate
(0.5mmol) isobutyraldehyde(2.5mmol), butyronitrile (2mL), O2 bubbling, T = 25°C, t= 2 h. b Conversion
calculated by GC, based on the substrate, using chlorobenzene (1.95 × 10-1 mmol) as internal standard.
c 0.25 mmol substrate. Selectivity for epoxide formation was ≥97% in all cases. All data were reproduced
at least twice and reported as an average.
absorption spectra were recorded by diffuse reflectance
using a Cary 5000 UV-vis-NIR spectrophotometer
equipped with an integrating sphere. TEM analyses
were carried out on a Philips CM 200, operating at an
accelerating voltage of 200 kV. Size distributions of the
hybrid materials were determined through manual analysis
of enlarged images with Imagetool softwareVersion 3.0 to
obtain a statistical size distribution and a mean diameter by
curve fitting using Gaussian function. The samples were
prepared in isopropyl alcohol at room temperature, and
then placed onto carbon-covered copper grids with holes
to dry before analysis. The metal content determination in
hybrid materials was measured by FAAS using an atomic
absorption spectrophotometer Shimadzu AA-6300, using
quartz cells. Thermogravimetric analyses were made in
air, using a TG-DSC Setsys Evo16 instrument (Setaram)
with a heating rate of 10 K min-1 to a maximum tempera-
ture of 800°C. Infrared spectra were obtained using a
FTIR Nexus 670 Nicolet spectrometer. The samples were
pressed into thin wafers (20–25 mg cm-2) and heated in an
IR glass cell from room temperature up to 323 K (150°C)
(heating rate of 5 K min-1) for 1.5 h, under vacuum
(10 Pa) before spectra acquisition in transmission mode.
64 scans with a resolution of 4 cm−1 were collected for
each spectrum. Gas chromatography analysis was carried
out in a HP-Agilent 6890 chromatographer equipped
with an ionization detector (FID) and with a non-polar
HP-5 column (5% diphenyl, 95% dimethylpolysiloxane).
GC-MS spectra were obtained in a Hewlett–Packard
5973 MSD spectrometer, using EI (70 eV), coupled
to a Hewlett-Packard Agilent 6890 chromatographer
equipped with a HP-5 MS column (30 m × 0.25 mm ×
0.25 mm). GC analyses were performed using the
following conditions: initial temperature 373 K (100°C),
rate 333 K min-1, final temperature 553 K (280°C); gas
flow 1.63 mL min-1.
Synthesis of catalysts
5-(4-Acetamidophenyl)-10,15,20-tri(2,6-dichloro-
phenyl)porphyrin (1). This compound was synthesized
through our optimized procedure [58] in 9% isolated
yield, with experimental data being in agreement with
that previously reported [70].
Copyright © 2018 World Scientific Publishing Company
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A RECYCLABLE HYBRID MANGANESE(III) PORPHYRIN MAGNETIC CATALYST FOR SELECTIVE OLEFIN EPOXIDATION
9
5-(4-Aminophenyl)-10,15,20-tri(2,6-dichlorophenyl)
porphyrin (2). In a round bottom flask, the porphyrin
1 (510 mg, 0.58 mmol) was dissolved in THF (60 mL).
Then, a solution of hydrochloric acid (33%) (10 mL)
was added and the reaction was conducted at 40°C for
18 h. Upon complete conversion of the starting material
(observed by TLC), the reaction crude was extracted with
ethyl acetate (50 mL). The organic phase was washed
with a sodium hydrogen carbonate solution (10%)
(30 mL) and water (30 mL), dried with anhydrous sodium
sulphate, and the solvent was evaporated under reduced
pressure. After purification by column chromatography
in silica gel, using a n-hexane:ethyl acetate (1:5) mixture
as the eluent. Yield 459 mg (95%). UV-vis (toluene):
(40 mL), was stirred at 110°C for 16 h. Then, MNP@SiO2
(96 mg) was added and the mixture was kept under reflux
(110°C) for 24 h. The product was magnetically collected
and washed several times with ethyl acetate and acetonitrile.
Finally, the material was dried under vacuum for 24 h.
Manganese(III)5,10,15,20-tetrakis(2,6-dichlorophe-
nyl)porphyrin acetate (5). This compound was synthe-
sised following a literature procedure [62], with
experimental data being in agreement with that previously
reported.
General procedure for catalytic epoxidation
with O2
l
máx, nm (log e): 422 (1.8 × 105), 515 (1.4 × 104), 551
A glass vial was charged with the olefin substrate and
metalloporphyrin catalyst, acetonitrile (or butyronitrile),
isobutyraldehyde and chlorobenzene as inert internal
standard (the exact amounts are specified in Tables 1
and 2). The reaction was conducted under stirring, at
room temperature (25°C) for 90 min, with a constant
bubbling of molecular oxygen. Conversion and selectivity
was determined by GC, based on peak areas, using
chlorobenzene as internal standard. Product identification
was performed by GC analysis against standards and by
1H and 13C NMR of isolated products.
(4.9 × 103), 593 (4.9 × 103), 651 (1.4 × 103).1H NMR
(400 MHz; CDCl3): dH, ppm 8.95 (d, J = 4.6 Hz, 2H,
b-H), 8.67–8.65 (m, 6H, b-H), 8.00 (d, J = 8.0 Hz, 2H,
Ar(NH2)-Hortho), 7.79–7.77 (m, 6H,Ar-Hmeta), 7.67 (t, J = 8.0
Hz, 3H, Ar-Hpara), 7.07 (d, J = 8.0 Hz, 2H, Ar(NH2)-Hmeta),
-2.49 (s, 2H, NH) (Fig. S6). HRMS (ESI-FIA-TOF): m/z
833.0241 (calcd. for M+ 833.0236) (Fig. S7).
Manganese (III) 5-(4-aminophenyl)-10,15,20-tris-
(2,6-dichlorophenyl)porphyrin acetate (2Mn). To a
round bottom flask containing porphyrin 2 (300 mg,
0.36 mmol) dissolved in dimethoxyethane (20 mL),
.
Mn(II)OAc 4H2O (880 mg, 3.6 mmol) was added. The
Catalyst recycling
reaction was left stirring at room temperature (25°C), for
18 h. The solution was then concentrated under vacuum
and washed twice with a saturated solution of sodium
hydrogen carbonate and twice with distilled water, and
dried with anhydrous sodium sulphate. After solvent
evaporation, the crude was purified by silica gel column
chromatography using ethyl acetate as the eluent. Yield
276 mg (81%). Anal. calcd. for C46H26Cl6N5O2Mn: C,
58.26; H, 2.76; N, 7.38%. Found: C, 59.17; H, 2.51; N,
7.35. UV-vis (toluene): lmáx, nm (log e): 371 (2.2 × 104),
480 (4.8 × 104), 586 (4.4 × 103), 621 (2.8 × 103). MS
(MALDI-TOF): m/z 929.963 (calcd. for [M]+ 928.990)
(Fig. S8).
MNP@SiO2[4-NH-Mn-TDCPP] (3). A mixture of
2Mn (120 mg, 0.12 mmol) and triethylamine (0.035 mL,
0.25 mmol) in dry toluene (40 mL) was placed
under stirring, at room temperature for 1 h. Then,
3-chloropropyltriethoxysilane (0.05 mL, 0.25 mmol)
was added and the mixture was kept under reflux
(110°C) for 16 h. Finally, the silica coated magnetic
support MNP@SiO2 (960 mg), obtained through a
reverse microemulsion process [59, 60], was added and
the mixture was kept under reflux (110°C) for 24 h. The
product was magnetically collected and washed several
times with ethyl acetate and acetonitrile to rinse away
excess of metalloporphyrin 2Mn. The final material was
dried under vacuum for 24 h.
Catalyst 3 was steadily separated from the reaction
mixture using an external magnetic stirrer bar followed
by decantation of the liquid. The solid material was
washed with CH3CN (2 mL), dried under vacuum at
60°C for 12 h and reused in the next run.
Scale-up and recovery of for isobutyric acid
The procedure was similar to that described in the
general procedure, but using cyclooctene (0.992 g,
9 mmol), isobutyraldehyde (3.245 g, 45 mmol),
nanocatalyst 3 (64.8 mg, 8.42 × 10-4 mmol Mn),
butyronitrile (36 mL) as the solvent and chlorobenzene
(3.51 mmol) as internal standard. Finally, a sodium
bicarbonate saturated solution (50 mL) was added to the
crude mixture, leading to the formation of two phases.
The target epoxide was then isolated from the organic
phase (with up to 99% yield) by simple distillation, while
the aqueous phase was treated with a 33% HCl solution,
to adjust the solution pH value to 3. Finally, extraction
with 2-methyltetrahydrofuran was carried out and, after
distillation, isobutyric acid was obtained with 99% yield
1
(3.921 g, 44.5 mmol) and characterized by H and 13C
NMR spectroscopy (Figs S9 and S10).
Characterization of products
MNP@SiO2-CPTES (4).
A mixture of triethyl-
Products were further purified and characterized by 1H
and 13C NMR spectroscopy (Figs S11–S24).
amine (0.0035 mL, 0.025 mmol) and 3-chloropropyl-
triethoxysilane (0.005 mL, 0.025 mmol), in dry toluene
Copyright © 2018 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2018; 22: 9–11

10
L.D. DIAS ET AL.
CONCLUSIONS
REFERENCES
A hybrid manganese(III)-porphyrin magnetic nano-
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nanocomposite was efficiently applied as catalyst in the
selective epoxidation of olefins, using molecular oxygen
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runs without loss of activity or epoxide selectivity. The
efficient recovery of isobutyric acid paves the way to
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the bulk chemistry industry. The potential applicability
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compounds via olefin epoxidation, using molecular
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