Manganese meso-tetra-4-carboxyphenylporphyrin immobilized on MCM-41 as catalyst for oxidation of olefins with different oxygen donors in stoichiometric conditions

Article abstract of DOI:10.1142/S1088424612500307

Oxidation of olefins with tert-butyl hydroperoxide (TBHP), tetra-n-butylammonium periodate (TBAP) and potassium peroxomonosulfate (Oxone) in the presence of MCM-41 immobilized meso-tetra-4- carboxyphenylporphyrinatomanganese(III) acetate has been studied.

Full text of DOI:10.1142/S1088424612500307

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2012; 16: 260–266
DOI: 10.1142/S1088424612500307
Published at http://www.worldscinet.com/jpp/
Manganese meso-tetra-4-carboxyphenylporphyrin
immobilized on MCM-41 as catalyst for oxidation of olefins
with different oxygen donors in stoichiometric conditions
Saeed Rayati*a◊, Saeed Zakavib, Parisa Jafarzadeha, Omid Sadeghic and
Mostafa M. Aminic
a Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran 15418, Iran
b Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
c Department of Chemistry, Shahid Beheshti University, G.C., Evin, Tehran 1983963113, Iran
Received 14 November 2011
Accepted 21 December 2011
ABSTRACT: Oxidation of olefins with tert-butyl hydroperoxide (TBHP), tetra-n-butylammonium
periodate (TBAP) and potassium peroxomonosulfate (Oxone) in the presence of MCM-41 immobilized
meso-tetra-4-carboxyphenylporphyrinatomanganese(III) acetate has been studied. The results of
this study show better catalytic performance of the heterogonous catalyst using TBHP as oxidant in
comparison with Oxone and TBAP in oxidation of the used olefins with the exception of cyclooctene.
However, different order of reactivity of various olefins has been observed in the presence of Oxone
and TBHP. In spite of the absence of good electron-withdrawing groups at the periphery of porphyrin
ligand, the catalyst was recovered and reused (at least four times) without detectable catalyst leaching or
a significant loss of the catalytic efficiency. All results have been obtained in the absence of using excess
molar ratios of olefin to the oxidant, commonly employed as a strategy to overcome the instability of
metalloporphyrins in oxidative conditions.
KEYWORDS: manganese, porphyrin, mesoporous, olefin, heterogeneous catalyst, oxidation.
[5–8], zeolites [9–14], clays [15], polymers [16, 17] and
INTRODUCTION
resins have been widely used to anchor metalloporphyrins
Metalloporphyrins have been investigated intensely
to solid surfaces. Compared with the zeolite-Y with a
as biomimetic models of cytochrome P450s, catalases,
small pore size, a large and tunable pore size and also very
peroxidases or as transmembrane electron transport
large specific surface area (approximately 1000 m2.g-1) of
agents [1–3]. The use of chemical model systems will
MCM-41 family make them very attractive candidates
help scientists for overcoming the difficulties in working
to host large molecules such as metalloporphyrins [18–
with enzymes in vivo and in vitro. The main problem
20] for heterogeneous catalytic systems. In order to
in developing these model systems is the high cost of
prevent catalyst leaching, the strength of the attachment
synthetic porphyrins that makes their recovery imperative.
to the support surface is a very important factor that
Therefore, immobilization of the methalloporphyrins on
should be considered during immobilization process. In
solid supports not only helps to improve the recyclability
most metalloporphyrin-based biomimetic oxidation of
of these expensive catalysts but also enhances the catalyst
organic compounds, using purely siliceous MCM-41 or
stability toward oxidative degradation.Alumina [4], silica
aluminated MCM-41 to encapsulate metalloporphyrins,
Ru complexes of electron-rich porphyrins or Mn
complexes of electron-deficient porphyrins have been
SPP full member in good standing
used to overcome the problems associated with the
stability of electron-rich metalloporphyrins [21]. In the
case of electron-rich Mn-porphyrins, due to the low
*Correspondence to: Saeed Rayati, email: rayati@kntu.ac.ir
or srayati@yahoo.com, tel: +98 21-22850266, fax: +98 21-
22853650
Copyright © 2012 World Scientific Publishing Company

MANGANESE MESO-TETRA-4-CARBOXYPHENYLPORPHYRIN IMMOBILIZED
261
stability of these complexes towards strong oxidants,
OAc was prepared according to the literature method
[28]. UV-vis (DMF): lmax, nm 477, 577, 609.
large excess molar ratios of substrate to the catalyst
are usually used to decrease the oxidative degradation
of catalyst in reaction conditions [22–26]. However, this
strategy decreases the contribution from the stability of
metalloporphyrin in the efficiency of the catalyst. In the
present work, we have studied the oxidation of olefins with
tert-butyl hydroperoxide (TBHP), tetra-n-butylammonium
periodate (TBAP) and potassium peroxomonosulfate
(Oxone, 2KHSO5.KHSO4.K2SO4) in the presence of a
Mn complex of meso-tetra-4-carboxyphenylporphyrin
(H2TCPP) immobilized in mesoporous MCM-41 using
the stoichiometric ratios of olefin to oxidant.
Preparation of MCM-41. MCM-41 mesoporous silica
was synthesized according to the literature [29] using
the following procedure: 7.48 g tetradecyl(trimethyl)
ammonium bromide was dissolved in 80.0 g water. Then,
an aqueous solution of sodium silicate (9.9 g in 30.0 g
water) was added dropwise under vigorous magnetic
stirring. After 30 min, the pH was adjusted to 10 using 2 M
sulphuric acid solution. This mixture was transferred into
a Teflon lined autoclave and heated statically at 100 °C for
2 days. The obtained solid material was filtered, washed
with water and dried at 60 °C. The sample was then calcined
in flowing nitrogen at 550 °C (2 °C/min), then in air at the
same temperature for 5 h. The formation of MCM-41 was
confirmed by low angle X-ray diffraction pattern.
EXPERIMENTAL
Preparation of MCM-41-Mn(TCPP)OAc. Synthesis
of MCM-41-Mn(TCPP)OAc was carried out as follows:
to a mixture of MCM-41 (250.0 mg) and Mn(TCPP)OAc
(4.0mg,0.005mmol)in25mLDMF,2-(1H-benzotriazole-
Instruments and reagents
1H NMR spectrum was obtained in dimethyl sulfoxide
(DMSO) solutions with a Bruker FT-NMR 500 (500
MHz) spectrometer. The electronic absorption spectra
were recorded on a single beam spectrophotometer (Cam
Spec-M330) in DMF. The standard linear calibration
curve was recorded by using GVC 932 Plus, equipped
with air-acetylene flame. An X-Pert MDP diffractrometer
with cobalt anode, typically run at a voltage of 40 kV
and a current of 30 mA, was used to record the X-ray
diffraction patterns. IR spectra were recorded on an ABB
Bomem: FTLA 2000–100 in the range of 4000–400 cm-1
using spectral-grade KBr. The oxidation products were
analyzed with a gas chromatograph (Shimadzu, GC-14B)
equipped with a SAB-5 capillary column (phenyl methyl
siloxane 30 m × 320 mm × 0.25 mm) and a flame
ionization detector.
1-yl)-1,1,3,3-tetramethyluronium
tetrafluoroborate
(TBTU) (2.0 mg, 0.006 mmol) and N,N’-diisopropylamine
(DIPEA) (2.0 mg, 0.01 mmol) were added and the mixture
was stirred for 2 days at room temperature [30]. The
weakly adsorbed metalloporphyrins on the mesoporous
surface were removed through washing the solid products
with DMF until the filtrate became colorless. The solid
residue was finally dried at room temperature (Scheme 1).
General oxidation procedure
Typically, the reaction was initiated by adding the
oxidant (0.1 mmol) to the solution of substrate (1 mmol)
and the catalyst (4 μmol), in a 10 mL glass flask containing
1 mL acetonitrile, under magnetic stirring at room
temperature. The solid catalyst was then filtered, and the
organic phase was analyzed by GC.
Chemicals were purchased from Merck or Fluka
chemical companies.
Preparation of porphyrin and metalloporphyrin
precursors. H2TCPP was prepared by successive
addition of 4-carboxybenzaldehyde (300 mg, 2 mmol)
and pyrrole (0.12 mL, 1.8 mmol) to refluxing propionic
RESULTS AND DISCUSSION
Characterization of MCM-41-Mn(TCPP)OAc
acid as described by Adler et al. [27]. UV-vis (DMF):
The covalent bonding of Mn-porphyrin to MCM-
41 mesoporous silica is due to the acid-base reaction
between the porphyrin carboxylic acid and hydroxyl
group of MCM-41 mesoporous silica in the presence of
1
l
max, nm 421, 515, 549, 592, 646. H NMR (500 MHz;
DMSO): dH, ppm 8.69 (8H, br, b-pyrrole), 8.31–8.33 (8H,
d, o-phenyl), 8.08–8.11 (8H, d, m-phenyl). Mn(TCPP)
Scheme 1. Preparation of Mn(TCPP)OAC-MCM-41
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262
S. RAYATI ET AL.
achieved to find out the effect of different parameters
such as solvent, oxidant and co-catalyst on the efficiency
of the catalyst. In this regard, TBHP, TBAP and Oxone,
have been used as oxidant. The results are summarized
in Table 1. With the exception of Oxone, little or no
oxidation of cyclooctene has been observed in the absence
of the catalyst, for a reaction time of 24 h. Oxidation
of cyclooctene in this condition led to formation of
cyclooctene oxide with conversions of 19, 5 and 1% for
Oxone, TBHP and TBAP, respectively.
According to Table 1 and in spite of the 19%
contribution of noncatalytic path in the total conversion,
using Oxone gives the highest yield of cyclooctene oxide
as the sole product.
Table 2 shows that the 1:1 molar ratio of cyclooctene
to oxidant gives higher yield of epoxide compared to the
1:2 one. This observation may be due to the decreased
self degradation of the catalyst in the presence of higher
amount of cyclooctene [22].
The catalytic activity of Mn-porphyrins has been
shown to be strongly enhanced in the presence of different
nitrogen donors especially imidazole [31–33]. Different
molar ratios of catalyst:imidazole were examined and
the 1:10 ratio has been found to be the optimized one
(Table 3). The results demonstrate that in the absence of
ImH, no product is formed and 1:10 molar ratio of catalyst
to ImH gives maximum yield of the product. Beyond this
ratio, a decrease in catalytic efficiency is observed which
may be attributed to the formation of a MnTCPP(ImH)2
species [28]. Also, the formation of hydrogen bonds with
HSO5- which prevents the coordination of oxidant to the
metal center may be considered as a possible cause of
this observation. The stability of active intermediates has
been also shown to be significantly increased due to the
formation of such hydrogen bonds [34].
Oxidation of various olefins with Oxone was carried
out in the presence of MCM-41-Mn(TCPP)OAc under
the optimized reaction conditions (Table 4). While
reactivity of cyclohexene, styrene and a-methyl styrene
was lower than cyclooctene in this catalytic system,
the use of TBHP as oxidant led to lower reactivity of
cyclooctene with respect to the other olefins (Table 5).
This finding may be explained by considering different
pathways and active oxidants previously proposed for
metalloporphyrin-catalyzed oxidation of alkenes with
various oxidants (Schemes 1 and 2) [33–38]; a concerted
mechanism with the involvement of a six coordinate
Mn(III) one (Scheme 2, I) or a high-valent Mn-oxo
species (Scheme 2, II) may be considered for oxidation of
cyclooctene with Oxone. On the other hand, in oxidation
of styrene, a-methyl styrene and cyclohexene with
TBHP, allylic products have been obtained in addition to
epoxide. This observation suggests a radical pathway for
the reaction [35, 36]. In the first step, TBHP coordinates
to the manganese center of Mn(TCPP)OAc/MCM-41
to give an oxomanganese(V)porphyrin (Scheme 3, I)
(or oxomanganese(IV) porphyrin π-cation radical
Fig. 1. XRD patterns of: (a) MCM-41 (b) Mn(TCPP)-
OAC-MCM-41
2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium
tetrafluoroborate (TBTU) as a highly effective uronium
salt in the presence of N,N′-diisopropylamine (DIPEA) in
DMF at room temperature. The prepared catalyst, MCM-
41-Mn(TCPP)OAc, was characterized by IR spectroscopy
and X-ray powder diffraction (XRD) studies. XRD pattern
confirms the incorporation of Mn-porphyrin in the MCM-
41 pores. The manganese content of the catalyst was
determined by atomic absorption spectroscopy. Based on
this value, the Mn content of the catalyst was determined
to be about 230 μmol per gram of the catalyst. The XRD
pattern of the calcined MCM-41 (Fig. 1) shows a reflection
in the 2q range of 1.88°, indexed for a hexagonal cell as
d100. Upon the inclusion of the Mn-porphyrin complex
(MCM-41-Mn(TCPP)OAc, a characteristic diffraction
peaks in XRD were still observed at about 2.01° but with
slight shift of the d100 reflection to a higher angle (Fig. 1),
demonstrating that the long range hexagonal symmetry
of the mesoporous host was maintained after inclusion of
Mn-porphyrin.
The IR spectrum of MCM-41 showed three bands at
1093, 810 and 461 cm-1 and they are assigned to stretching
vibrations of Si–O–Si (mesoporous framework). Also IR
spectrum of MCM-41-Mn(TCPP)OAc, showed a strong
band in 1663 cm-1 which was assigned to the formed
esteric bond after immobilization of the manganese
porphyrin into MCM-41. Comparatively, weak bands
observed at 1499 cm-1 and around 1391 cm-1 can be
related to the C-H stretching vibrations of the CH2 groups
immobilized on the pore surface of MCM-41.
Oxidation of olefins
Oxidation of cyclooctene with different oxygen
donors catalyzed by MCM-41-Mn(TCPP)OAc has been
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Table 1. Oxidation of cyclooctene with various
Table 4. Oxidation of various olefins with Oxone in the
presence of Mn(TCPP)OAC/MCM-41a
oxidants in the presence of Mn(TCPP)OAC/MCM-
41 in acetonitrilea
Entry
Alkene
Conversion, % Epoxide
Entry Oxidant Epoxide yield, %b,c Time, h
yield,
%
1
2
3
4
5
6
7
8
9
TBHP
Oxone
TBAP
4
5
16
6
8
56
1
2
4
24
2
4
24
2
1
2
4
0
9
Me
11
2
11
4
24
3
4
68
2
68
2
a Conditions: the molar ratios for catalyst:ImH:cyc-
looctene:oxidant are 1:10:25:50. b GC yields based
on the starting olefin. c Cylooctene oxide is the sole
product.
a
Conditions: the molar ratios for catalyst:ImH:cycloo-
ctene:oxidant are 1:10:50:50 and reaction time: 4 h.
Table 2. Effect of cyclooctene/oxone molar ratio in
oxidation of cyclooctene in acetonitrilea
Table 5. Oxidation of various olefins with TBHP in the
presence of Mn(TCPP)OAC/MCM-41 in acetonitrilea
Entry Cyclooctene:oxidant Epoxide yield, %
(molar ratio)
Entry
Alkene
Conversion, %
Selectivity, %
(epoxide)
1
2
1:2
1:1
56
68
1
2
23
56
35
27
a
Conditions: the molar ratios for catalyst:ImH is:
1:10.
Me
Table 3. Oxidation of cyclooctene with Oxone in
the presence of different amounts of ImHa
3
17
51
100
14
Entry
Mn(TCPP)OAC/
MCM-41:ImH
Epoxide yield, %
4
1
2
3
1:0
trace
68
1:10
1:15
a
51
Conditions: the molar ratios for catalyst:ImH:cycloo-
ctene:oxidant are 1:10:50:50 and reaction time: 4 h.
a Conditions: the molar ratios for catalyst:ImH:cycl-
ooctene:oxidant are 1:X:50:50.
(Scheme 3, II)) which acts as an active species. This
active species can transfer oxygen atom to the double
bond to form epoxide product or cause allylic oxidation
via H-atom abstraction. According to Tables 4 and 5, with
the exception of cyclooctene, TBHP is a stronger oxidant
relative to Oxone in oxidation of the other olefins. One of
the parameters influencing the rate of oxidation reaction
is the solubility of oxidant in the used solvent. TBAP and
TBHP are soluble in acetonitrile but Oxone is completely
insoluble. However, the stability of metalloporphyrin
towards oxidative degradation with different oxidants
should be also considered in this comparison. Our
previous studies demonstrated significant degradation
of the metalloporphyrins in the presence of Oxone as
oxidant [37, 38].
Catalyst reusability
Oxidation of olefins with Oxone catalyzed by
metalloporphyrins is accompanied by extensive
degradation of the catalyst within the first few minutes
of reaction [37, 38]. Mn(TCPP)OAc has been shown
to be remarkably degraded within the first 5 min after
the addition of the oxidant to the reaction mixture.
Interestingly, under the conditions given in Table 1, the
catalyst was consecutively reused at least four times
without detectable catalyst leaching or a significant loss
of epoxide yield (Table 6). In other words, the degradation
of Mn(TCPP)OAc has been significantly decreased by
immobilization of the metalloporphyrin on MCM-41.
The enhanced efficiency of the immobilized catalyst with
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S. RAYATI ET AL.
Scheme 2. Proposed catalytic cycle for oxidation with Oxone in the presence of Mn(TCPP)OAC/MCM-41
Scheme 3. Proposed catalytic cycle for oxidation with TBHP in the presence of Mn(TCPP)OAC/MCM-41
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MANGANESE MESO-TETRA-4-CARBOXYPHENYLPORPHYRIN IMMOBILIZED
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Table 6. Efficiency of the recovered catalyst for
oxidation of cyclooctene with Oxone for a reaction
time of 24 h
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Entry
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1
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—
67
74
63
60
50
CH3CN
CH3CN
CH3CN
CH3CN
a The molar ratios for catalyst:ImH:alkene:oxidant
are 1:10:50:50.
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CONCLUSION
In summary, MCM-41 immobilized meso-tetra-4-
carboxyphenylporphyrinatomanganese(III) acetate,
a
Mn-porphyrins bearing poor electron-withdrawing
groups at the meso-positions, has been used as a reusable
catalyst for efficient oxidation of olefins with TBHP,
TBAP and Oxone using the stoichiometric ratios of olefin
to the oxidant. The results show significant increase
in the stability of the heterogenized Mn-porphyrin
towards oxidative degradation under reaction conditions
compared to the non-immobilized one. Different order of
reactivity of olefins in the case of the Oxone and TBAH
suggests different reaction pathways in the presence of
the two oxidants. With the exception of cyclooctene,
the catalysts have been more efficient in the presence of
TBHP as oxidant compared to Oxone and TBAP.
Acknowledgements
We gratefully acknowledge practical support of this
study by K.N. Toosi University of Technology.
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