Factors influencing the catalytic activity of β-tetrabrominated meso-tetra(para-tolyl)porphyrinatomanganese(III) for oxidation of sulfides and olefins with Oxone

Article abstract of DOI:10.1142/S108842461100301X

Effect of different reaction parameters on the catalytic activity of β-tetrabrominated meso-tetra(para-tolyl)porphyrinatomanganese(III), MnT(4-CH₃P)PBr₄(OAc), for oxidation of different sulfides and hydrocarbons with tetra-n-butylammonium hydrogen monopersulfate (TBAHS) has been studied. In oxidation of sulfides, the chemoselectivity of reaction has been significantly changed in THF as the solvent compared with the common organic solvents. Also, using nitrogenous bases bearing electron-withdrawing groups (-Cl or -CN) clearly increased the ratio of sulfoxide to sulfone relative to the electron-donating ones. Catalytic oxidation of olefins with TBAHS was conducted in protic and aprotic solvents and acetonitrile has been found as the best solvent. A significantly large difference was found between the co-catalytic activity of imidazole (ImH) and pyridine in comparison with that observed in dichloromethane. The competitive oxidation of cis- and trans-stilbene suggests the presence of a high valent manganese oxo as well as a six coordinate (ImH)MnT(4-CH₃P)PBr₄(HSO₅) species as the active oxidants in acetonitrile.

Full text of DOI:10.1142/S108842461100301X

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2011; 15: 131–139
DOI: 10.1142/S108842461100301X
Published at http://www.worldscinet.com/jpp/
Factors influencing the catalytic activity of b-tetrabrominated
meso-tetra(para-tolyl)porphyrinatomanganese(III) for
oxidation of sulfides and olefins with Oxone
Saeed Rayati*a, Saeed Zakavi*b and Hossein Kalantarib,c
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, Gava Zang, Zanjan 45137-66731, Iran
c Department of Chemistry, University of Kurdestan, P.O. Box 66135-416, Sanandaj, Iran
Received 13 December 2010
Accepted 27 January 2011
ABSTRACT: Effect of different reaction parameters on the catalytic activity of β-tetrabrominated
meso-tetra(para-tolyl)porphyrinatomanganese(III), MnT(4-CH3P)PBr4(OAc), for oxidation of different
sulfides and hydrocarbons with tetra-n-butylammonium hydrogen monopersulfate (TBAHS) has been
studied. In oxidation of sulfides, the chemoselectivity of reaction has been significantly changed in
THF as the solvent compared with the common organic solvents. Also, using nitrogenous bases bearing
electron-withdrawing groups (-Cl or -CN) clearly increased the ratio of sulfoxide to sulfone relative
to the electron-donating ones. Catalytic oxidation of olefins with TBAHS was conducted in protic and
aprotic solvents and acetonitrile has been found as the best solvent. A significantly large difference
was found between the co-catalytic activity of imidazole (ImH) and pyridine in comparison with that
observed in dichloromethane. The competitive oxidation of cis- and trans-stilbene suggests the presence
of a high valent manganese oxo as well as a six coordinate (ImH)MnT(4-CH3P)PBr4(HSO5) species as
the active oxidants in acetonitrile.
KEYWORDS: porphyrin, sulfide, sulfone, alkene, catalyst.
monopersulfate (TBAHS) have been utilized as very
INTRODUCTION
efficient oxidant in oxidation of olefins and organosul-
The monooxygenation of substrates by cytochromes
furs in the presence of Mn-porphyrins as catalyst and
P450 has been reproduced by using metalloporphyrins
imidazole (ImH) as the nitrogen donor ligand [4–8]. Sul-
model systems, the most efficient catalysts being Fe(III) or
foxides are important intermediates in organic synthesis
Mn(III) tetraarylporphyrins bearing electron-withdrawing
substituents at the β-pyrrole positions [1]. Introduction of
which are useful in the synthesis of natural products and
biologically significant molecules [9, 10]. Accordingly,
electron-withdrawing substituents at the periphery of por-
the selective oxidation of sulfides to sulfoxides has been
phyrin ring is among the main strategies have been used
an important challenge in synthetic organic chemistry
to reduce degradation of metalloporphyrins in oxidative
conditions [2]. The effect of degree of β-bromination of
porphyrin core on the catalytic efficiency of meso-tetrakis
[11–15]. In oxidation of sulfides with TBAHS in dichlo-
romethane, sulfone has been obtained as the sole product
using Mn-porphyrin/ImH catalytic system [4–8, 16, 17]
(4-carbomethoxyphenyl)porphyrinatomanganese(III)
which limits its application to the oxidation of sulfides
chloride in oxidation of cyclohexene has been studied
to the corresponding sulfone. In the present work, it has
by Silva et al. [3]. Tetra-n-butylammonium hydrogen
been shown that by changing the reaction parameters,
the chemoselectivity of this very fast reaction may be
significantly altered towards the formation of sulfoxide
SPP full member in good standing
as a considerable product compared to the sulfone one.
On the other hand, due to the environmental problems
*Correspondence to: Saeed Rayati, email: rayati@kntu.ac.ir,
fax: +98 21-22853650, tel: +98 21-23064221
Copyright © 2011 World Scientific Publishing Company

132
S. RayatI et al.
associated with the use of halogenated solvents [18] the
optimized reaction conditions for oxidation of olefins
and organosufurs in a green solvent have been investi-
gated. In the present work, factors influencing the cata-
lytic activity of β-tetrabrominated meso-tetra(para-tolyl)
porphyrinatomanganese(III) as a partially β-brominated
meso-tetraarylporphyrin for oxidation of hydrocarbons
and organosulfur compounds with TBAHS have been
studied.
and Et electron donor substituents show better co-cata-
lytic activity but the lower yield for sulfone formation is
due to the existence of the steric strain. Diethyamine and
triethylamine (Entry 4, 5) with pure σ-donor ability show
lower efficiency than those of ImH. The much lower
co-catalytic activity of diethylamine than triethylam-
ine in spite of the lower steric hindrance of diethylam-
ine is due to the intermolecular formation of hydrogen
bonding in the former and caused the lower coordina-
tion of the diethylamine to the metal center. In the case
of pyridine and methyl-substituted pyridines (Entry 7–9),
the observed order of co-catalytic activities of 4-MePy >
3-MePy > 2-MePy > Py seems to be related to both steric
and electronic effect of methyl substituent. The higher
co-catalytic activity of the methyl-substituted pyridines
than pyridine is due to their better electron donation.
The lower activity of the 2-methyl pyridine respect to the
3-and4-methylpyridinesseemstobeduetotheexistenceof
steric hindrance between methyl group and catalyst. Cyano
pyridines (Entry 10, 11) with an electron–withdrawing CN
substituent show lower co-catalytic activity. 2-amino pyri-
dine (Entry 12) with a lone pair on the amino-substituent
that makes the nitrogen atom better σ- and π-donor shows
catalytic activity similar to the 2-methyl pyridine. This
may be due to the steric effect of the substituent on the
ortho position of the pyridine. 2,6-dichloropyridine with
two substituents on the ortho position shows lower activity
than 2-methyl pyridine or 2-amino pyridine.
The effect of ImH concentration. The effect of ImH
concentration on the oxidation of methyl phenyl sulfide
has also been studied (Table 3). Addition of ImH up to
5:1 relative to the catalyst led to an increase in the con-
version of reaction with no effect on the ratio of sulfoxide
to sulfone. Beyond this ratio, a significant decrease in the
ratio of sulfoxide to sulfone has been observed.
The effect of TBAHS concentration. Since oxidation
of axial base can take place in the presence of an oxidant,
optimization of the amount of TBAHS as oxygen source
is necessary. Different molar ratios of methyl phenyl sul-
fide to the oxidant were used (Table 4) and 1:2 molar
ratio has been found to be the optimized one.
RESULTS AND DISCUSSION
Oxidation of sulfides
Oxidation of methyl phenyl sulfide with TBAHS cata-
lyzed by MnT(4-CH3P)PBr4(OAc) gave methyl phenyl
sulfone as the major product. In a search for suitable reac-
tion conditions to achieve the maximum conversion and
product selectivity, effect of different parameters includ-
ing solvent, type and amount of co-catalyst and amount
of TBAHS were studied in details.
Solvent effect. In order to obtain the best reaction
media, protic and aprotic solvents with different dielec-
tric constants [19] have been used (Table 1). According
to Table 1, maximum conversion was obtained in chlo-
roform, ethanol and dichloromethane while the highest
selectivity for sulfone formation was achieved in ethanol.
Consequently, ethanol with highest ability to sulfone for-
mation and as green solvent was selected for the oxida-
tion of sulfides.
Co-catalyst effects of nitrogen donor. Presence
of a nitrogen base, for example ImH, as a co-catalyst
increased not only the conversion of methyl phenyl
sulfide but also selectivity for the formation of sulfone
product. The results of various nitrogen bases on the oxi-
dation of methyl phenyl sulfide are illustrated in Table 2.
The highest yield of sulfone relative to the sulfoxide was
obtained in the case of ImH (Table 2, Entry 1) with a
strong π and σ-donation ability to the metal center. We
expect that 1-MeImH and 2-EtImH (Entry 2, 3) with Me
Table 1. Oxidation of methyl phenyl sulfide with TBAHS catalyzed by 1 in the presence of ImH in
different solvents at room temperaturea
Entry
Solvent
Conversionb (%)
Yield (%)
(sulfoxide)
Yield (%)
(sulfone)
Sulfoxide/
Sulfone ratio
1
2
3
4
5
6
Acetone
Acetonitrile
Chloroform
86
96
26
17
35
46
18
17
60
79
65
48
82
83
0.43
0.21
0.53
# 1
100
94
Tetrahydrofuran
Ethanol
100
100
0.22
0.20
Dichloromethane
a The molar ratios for oxidant:sulfide:ImH:catalyst are 200:100:10:1. b For 2 min reaction time.
Copyright © 2011 World Scientific Publishing Company
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CatalytIC aCtIvIty Of β-tetRabROmInateD meso-tetRa(Para-tOlyl)PORPhyRInatOmanganeSe(III)
133
Table 2. Oxidation of methyl phenyl sulfide with TBAHS catalyzed by 1 in the presence of different
nitrogen donors in ethanol at room temperaturea
Entry
Axial ligand
Conversion (%)
Yield (%)
(sulfoxide)
Yield (%)
(sulfone)
Time (min)
1
2
ImH
2-EtImH
1-MeImH
NHEt2
100
100
100
100
100
100
100
100
100
100
100
100
100
86
17
24
21
22
19
29
25
23
20
39
40
25
31
35
83
76
79
78
81
71
75
77
80
61
60
75
69
51
2
2
2
2
2
2
2
2
2
2
2
2
2
2
3
4
5
NEt3
6
Py
7
2-MePy
3-MePy
4-MePy
3-CNPy
4-CNPy
2-NH2Py
2,6-Cl2Py
none
8
9
10
11
12
13
14
a The molar ratios for oxidant:sulfide:ImH:catalyst are 200:100:10:1.
Table 3. Effect of various ImH/catalyst molar ratios on oxidation of methyl phenyl sulfide with TBAHS
in ethanol at room temperaturea,b
[lm H]
Entry
Conversion (%)
Yield (%)
(sulfoxide)
Yield (%)
(sulfone)
Sulfoxide/
Sulfone
[Cat.]
1
2
3
4
5
0
5
86
100
100
100
100
35
41
17
18
25
51
59
83
82
75
0.69
0.69
0.20
0.22
0.33
10
15
20
a The molar ratios for oxidant:sulfide:ImH:catalyst are 200:100:X:1. b For 2 min reaction time.
Table 4. Effect of various TBAHS/cat. molar ratios on oxida-
tion of methyl phenyl sulfide in the presence of ImH in etha-
nole at room temperaturea
shows that oxidation of various sulfides gives the cor-
responding sulfone as the major product. In the case of
diallyl sulfide (Table 5, Entry 2), no oxidation at carbon-
carbon double bond was observed. This observation may
be due to the facile oxidation of sulfides with respect to
double bonds. Comparison of the sulfone product in the
methyl phenyl sulfide and diphenyl sulfide (Table 5, Entry
1, 5) reflect the steric effects of phenyl substituents in the
diphenyl sulfide. On the other hand, the higher amount
of sulfone in the dipropyl sulfide than diphenyl sulfide
clearly demonstrates σ-electron donation effects of alkyl
groups with respect to the phenyl substituents.
Stability of the catalyst against the degradation with
oxidant. Electronic spectra of a dichloromethane solu-
tion of the catalyst in the presence of sulfide (Fig. 1A)
and in the absence of sulfide (Fig. 1B) were recorded. It
is observed that in the presence of sulfide the catalyst is
more stable than the time that in the absence of sulfide.
Proposed mechanism for oxidation of sulfides. Sta-
bility of the catalyst in the presence of sulfide (up to 4 h)
TBAHS/
Cat.
Conversion
(%)
Yield (%)
(sulfoxide)
Yield (%)
(sulfone)
100
150
200
250
32
76
3
24
17
14
29
52
83
86
100
100
a
The molar ratios for oxidant:sulfide:ImH:catalyst are
X:100:10:1.
Oxidation of different sulfides. To investigate the
general scope of sulfide oxidation a series of sulfides
such as diallyl, dipropyl, diphenyl and phenyl butyl
were used for oxidation with TBAHS in the presence
of catalytic amount of 1 under optimized conditions,
catalyst:ImH:sulfide:TBAHS (1:10:100:200). Table 5
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134
S. RayatI et al.
Table 5. Oxidation of sulfides with TBAHS catalyzed by 1 in the presence of ImH in ethanol at room temperaturea
Entry
1
Substrate
Conversion (%) Yield (%) (sulfoxide) Yield (%) (sulfone) Time (min)
100
17
83
2
S
2
100
-
100
2
S
3
4
100
99
21
5
79
94
2
2
S
S
5
95
30
65
2
S
a The molar ratios for oxidant:sulfide:ImH:catalyst are 200:100:10:1.
Fig. 1. UV-vis spectra of (A) a solution of Mn(T(4-CH3P)PBr4)OAc in CH2Cl2 in the presence of ImH (a), ImH/TBAHS and methyl
phenyl sulfide after 2 min (b), ImH/TBAHS and the sulfide after 60 min (c) and ImH/TBAHS and the sulfide after 240 min (d).
Figure B shows the same spectra in the absence of methyl phenyl sulfide
supposed the formation of a six coordinate intermedi-
ate instead of Mn-oxo species. We have not ruled out
Mn-oxo formation because the absence of a Mn-oxo band
in the electronic spectra may be due to the facile oxidation
of sulfides in the presence of this species. Therefore, it
seems that TBAHS coordinated to the Mn-center via less
steric hindrance peroxo oxygen (Scheme 1) and activation
of this oxygen will occurr on the surface of the catalyst.
of MnT(4-CH3P)PBr4(OAc) were examined. It was
observed that catalytic activity decreases in the order
acetonitrile (94% conversion) ≈ dichloromethane (92%)
> ethanol (81%) > acetone (76%) > chloroform (70%)
>> tetrahydrofuran (15%) and acetonitrile was selected
as the best reaction solvent for the oxidation reactions.
The observed order of catalytic activity in different sol-
vents cannot be simply rationalized on the basis of the
polarity of solvents. It seems that various factors such
as hydrogen bond ability of solvent molecules, steric
effects and their coordination ability to the metal center
are involved in the observed solvent effect [6, 20].
Oxidation of different alkenes. Oxidation of various
olefins with TBAHS was carried out in the presence
of Mn(T(4-CH3P)PBr4)OAc (Table 6). Reactivity of
Oxidation of olefins
Solvent effect in the epoxidation of cyclooctene with
TBAHS. In order to obtain the best reaction solvent, the
influence of various solvents in the catalytic epoxida-
tion of cyclooctene with TBAHS in the catalytic amount
Copyright © 2011 World Scientific Publishing Company
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OSO3H
O
O
TBAO, Im
CH2Cl2, rt
Mn
Mn
Mn
OAc
ImH
ImH
S
O
S
O
OSO3H
S
S
O
S
O
O
Overoxidation of sulfoxide
Mn
Mn
O
S
+ TBAO +
ImH
ImH
Scheme 1. Proposed mechanism for oxidation of sulfides
Table 6. Epoxidation of alkenes with TBAHS catalyzed by MnT(4-CH3P)PBr4(OAc) in the presence
of ImH in acetonitrilea
Entry
1
Alkene
Conversion (%)
95
Epoxide yield
95
Selectivity (%)
100
2
3
59
91
59
91
100
100
CH3
4
5
52
52
100
100
100
100
6
99.6
38b
38
CH3
7
8
100
76
100
76
100
100
MeO
Cl
9
44
93
44
93
100
100
10
11
12
100
64
88.5c
64c
88.5
100
a The molar ratio for oxidant:alkene:ImH:catalyst is 200:100:10:1. b Acetophenone is the by-product.
c Determined by 1H NMR spectroscopy.
Copyright © 2011 World Scientific Publishing Company
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136
S. RayatI et al.
Table 7. Oxidation of cyclooctene with TBAHS catalyzed by 1
in the presence of different nitrogen donors in acetonitrile at
room temperaturea
cyclohexene is less than cyclooctene (Table 6, Entry 1
and 2), because the oxidation product of cyclooctene
(cyclooctene oxide) is more stable than cyclohexene
oxide. The presence of electron donating groups usually
increases the reactivity of olefins [21]. Therefore, 1-methyl
cyclohexene and 4-methoxy styrene were oxidized better
than cyclohexene and styrene, respectively (Table 6, Entry
2, 3 and 5, 7). On the other hand, electron-deficient sub-
stituents at the double bond decrease conversion and con-
sequently epoxide yield (Table 6, Entry 8). Styrene and
their para-substituents derivatives give selectively epoxide
yield as the sole product but α-methylstyrene gives aceto-
phenone as the by product in addition to epoxide (Table 6,
Entry 6). So, due to steric strain, as well as electron-donat-
ing effects of methyl substituent over oxidation of epoxide
to acetophenone will occur. Epoxidation of 1-octene and
norbornene proceeds in moderate yield (52% and 44%)
and due to the observed steric in the norbornene cycle, it
shows the least reactivity than the other alkene (Table 6,
Entry 4, 9). Since double bond acts as nucleophile in these
oxidation reactions, it seems that conjugated double bonds
were reactive than the others. The more reactivity of non-
terminal alkenes with respect to terminal alkenes, in spite
of more stability of non-terminal alkenes demonstrates the
higher nucleophilic nature of these alkenes rather than ter-
minal double bonds.
Due to the sterically demanding properties of trans-
stilbene, its reactivity is less than cis isomer, and its
oxidation product is trans-stilbene oxide while less hin-
dered isomer (cis-stilbene) results in a mixture of cis and
trans isomer. Apparently, before formation of epoxide in
cis isomer (with less steric strain), a free rotation about
the alkene double bond will occur.
Co-catalytic effects of nitrogen donors. Oxidation of
cyclooctene with TBAHS was carried out in the presence
of different nitrogenous bases as co-catalyst (Table 7).
The results demonstrate the importance of π-rather
than σ-interactions. Pyridines are as a class of nitro-
gen donors with weak π-donating ability and also show
weaker σ-donating ability with respect to linear amines.
Pyridines with a methyl group on the 2, 3 or 4 position
(Table 7, Entry 2–4) display the higher co-catalytic activ-
ity than pyridine (Table 7, Entry 1) and also pyridines
with an electron-withdrawing CN substituent show lower
catalytic activity than pyridine (Table 7, Entry 5, 6). The
improved conversion for 2 and 4-MePy than 3-MePy may
result in the presence of electron-donating methyl group
at ortho or para position with respect to the nitrogen and
increasing electron density on the nitrogen atom.
Entry
Axial ligand
Conversion (%)
1
2
Py
49
76
51
77
32
36
82
27
95
85
68
25
56
2-MePy
3-MePy
4-MePy
3-CNPy
4-CNPy
2-NH2Py
2,6-Cl2Py
ImH
3
4
5
6
7
8
9
10
11
12
13
1-MeImH
2-EtImH
NHEt2
NEt3
a
The molar ratios for oxidant:cyclooctene:ImH:catalyst are
200:100:10:1.
2-NH2Py (Table 7, Entry 7) with a lone pair on the
amino group (as a π electron donation substituent) dis-
plays better catalytic activity than Py. On the other hand
2,6-Cl2Py with two electron-withdrawing Cl substituents
(Table 7, Entry 8) essentially displays lower catalytic
activity than Py.The highest co-catalytic activity observed
in the case of ImH (Table 7, Entry 9) with the strongest
π-donor ability and also smallest size. A decrease in the
conversion in the 1-MeImH and 2-EtImH (Table 7, Entry
10,11) displays the steric hindrance effects of methyl and
ethyl substituents. Pure σ-donor amines (diethylamine
and triethylamine) display relatively poor co-catalytic
activities (Table 7, Entry 12,13). Et2NH which is less
sterically hindered and a stronger base than Et3N, shows
lower co-catalytic activity. It seems that the formation
of intramolecular hydrogen bonding in the Et2NH and
consequently the lower coordination ability towards
metal center is the dominant factor in determining the
co-catalytic activitiy of Et2NH.
The effect of co-catalyst/catalyst ratio. The co-
catalytic activitiy of ImH in the presence of MnT(4-CH3P)
PBr4(OAc) at various ImH/catalyst ratios are presented
in Fig. 2 and 10:1 ratio was selected for the oxidation
of cyclooctene. A decrease in cyclooctene conversion
observed in ImH/catalyst ratio ≥50 may be due to the for-
mation of inactive six coordinate [ImH2: MnT(4-CH3P)
PBr4(OAc)] species.
Although 2-MePy with one methyl group near to
the nitrogen donor atom, hindering its coordination to
the metal center, but shows similar catalytic activity
than 4-MePy that may be related to the hyperconjuga-
tion effects of the methyl group. It is observed that the
difference between the co-catalytic activity of ImH and
pyridines significantly increases in acetonitrile compared
with the dichloromethane as the solvent [22].
Oxidant/catalyst molar ratio effects. The amount of
TBAHS in the oxidation of cyclooctene in the presence of
MnT(4-CH3P)PBr4(OAc) in acetonitrile has been tested.
Since a higher amount of oxidant leading to a degrada-
tion of catalyst and also oxidation of nitrogenous bases,
therefore the amount of oxidant should be optimized.
Copyright © 2011 World Scientific Publishing Company
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Table 9. Oxidation of cis- and trans-stilbene with MnT(4-
CH3P)PBr4(OAc)
cis
trans
cis to trans ratio
14.0
2.7
5.2
The molar ratios for MnT(4-CH3P)PBr4OAc:ImH:(cis- and
trans-stilbene):TBAHS are 1:10:(500 and 500):200.
other hand, acetonitrile as a solvent with low dielectric
constant cannot solvate anions and consequently anions
with extended charge are better leaving group.
Proposed mechanism. Competitive epoxidation
reactions of cis- and trans-stilbene with TBAHS in the
presence of MnT(4-CH3P)PBr4OAc using similar molar
ratios of the reagents may be used as an indirect method
to elucidate the nature of active oxidant [21].
The observed ratio [Table 9] of cis- to trans-stilbene
oxide (5.12) suggests the presence of a high valent man-
ganese oxo species (Scheme 2, I) in equilibrium with a
six coordinate one, i.e. (ImH)MnT(4-CH3P)PBr4(HSO5)
(Scheme 2, II) [20].
Fig. 2. Co-catalytic activities of ImH in the presence of MnT(4-
CH3P)PBr4(OAc) as a function of different co-catalyst/catalyst
molar ratio
Different TBAHS:catalyst malar ratios (150:1, 200:1 and
250:1) were used and the 200:1 (TBAHS:catalyst) ratios
has been found to be the optimized one for the oxida-
tion of the cyclooctene in the presence of MnT(4-CH3P)
PBr4(OAc).
Counter ion effects. The catalytic efficiency of MnT-
(4-CH3P)PBr4X with different counter ions (Table 8)
for oxidation of cyclooctene has
OSO3H
been investigated and the following
order has been observed: MnT
O
O
(4-CH3P)PBr4OAc > MnT(4-CH3P)
PBr4SCN ~ MnT(4-CH3P)PBr4N3
~ MnT(4-CH3P)PBr4IO3 ~ MnT(4-
TBAO, Im
CH2Cl2, rt
Mn
Mn
Mn
OAc
ImH
ImH
CH3P)PBr4Br > MnT(4-CH3P)PBr4Cl
> MnT(4-CH3P)PBr4F. Acetonitrile is
an aprotic solvent which does not par-
ticipate in hydrogen bonding with the
counter ion of MnT(4-CH3P)PBr4X.
II
I
It is observed that the efficiency of
catalyst is greatly lower in the case of
Cl or F as the counter ion.
O
OSO3H
In order to obtain active oxidant,
counter ion should be released from
the metal center and oxidant should
be attached to the metal center.
Therefore, soft anions such as acetate
or thiocyanate can remove from the
O
O
Mn
Mn
ImH
ImH
catalyst (Mn(III) act as a hard acid)
more facile than hard anions. On the
Scheme 2. Proposed catalytic cycle for oxidation of alkenes with TBAHS in
acetonitrile
Table 8. The effect of different anions in oxidation of cyclooctene in acetonitrile
MnT(4-CH3P)PBr4X
Conversion (%)
Selectivity (%)
Time (min)
MnT(4-CH3P)PBr4F
MnT(4-CH3P)PBr4Cl
MnT(4-CH3P)PBr4Br
MnT(4-CH3P)PBr4IO3
MnT(4-CH3P)PBr4N3
MnT(4-CH3P)PBr4SCN
MnT(4-CH3P)PBr4OAc
64
76
83
86
87
89
5
100
100
100
100
100
100
100
2
2
2
2
2
2
2
Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 137–139

138
S. RayatI et al.
EXPERIMENTAL
CONCLUSION
In summary, the optimized conditions for oxidation of
olefins and sulfides with TBAHS in the presence of a par-
tially β-brominated meso-tetraarylporphyrin and nitrogen
donors in nonhalogenated solvents have been reported.
Using THF as solvent direct the chemoselectivity of reac-
tion towards the formation of sulfoxide and sulfone in ca.
1:1 molar ratio. Also, using pyridines with electron-with-
drawing groups such as -CN increases the ratio of sulfoxide
to sulfone compared with pyridines bearing electron-do-
nating groups and imidazoles. Indirect evidence obtained
from competitive oxidation of cis- and trans-stilbene sug-
gests the involvement of a high valent Mn-oxo and a six-
coordinate Mn(III)-porphyrin species in the catalytic cycle
of oxidation of olefins in acetonitrile as solvent.
Instruments and reagents
1H NMR spectra were obtained in CDCl3 solutions
with a Bruker FT-NMR 250 (250 MHz) spectrometer.
The residual CHCl3 in conventional 99.8 atom % CDCl3
gives a signal at d = 7.26 ppm, which was used for
calibration of the chemical shift scale. The electronic
absorption spectra were recorded on a double beam
spectrophotometer (Shimadzu, UV-240) in CH2Cl2. The
reaction products were analyzed by gas chromatography
using a HP Agilent 6890 gas chromatograph equipped
with a HP-5 capillary column (phenyl methyl silox-
ane 30 m × 320 mm × 0.25 mm) and a flameionization
detector.
The free base meso-tetrakis(4-methylphenyl)porphy-
rin was prepared and purified as reported previously [23]
Chemicals were purchased from Merck or Fluka chemi-
cal companies. n-Bu4NHSO5 was prepared according to
the literature [7].
Acknowledgements
This work has been supported by the Iran National
Science Foundation (INSF) (Grant no. 87040848).
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Copyright © 2011 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2011; 15: 138–139

CatalytIC aCtIvIty Of β-tetRabROmInateD meso-tetRa(Para-tOlyl)PORPhyRInatOmanganeSe(III)
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J. Porphyrins Phthalocyanines 2011; 15: 139–139