Partial and full β-chlorination of meso-tetraphenylporphyrin: effects on the catalytic activity of the manganese complexes for oxidation of organic compounds with periodate

Article abstract of DOI:10.1080/15533174.2013.862660

A series of β-chlorinated meso-tetraphenylporphyrins, H₂TPPCI_x (x = 2, 4, 6, or 8) have been prepared and the catalytic activity of their manganese(III) complexes in oxidation of cyclooctene, cyclohexene, and methyl phenyl sulfide wi

Full text of DOI:10.1080/15533174.2013.862660

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Partial and Full β-Chlorination of meso-
Tetraphenylporphyrin: Effects on the Catalytic Activity
of the Manganese Complexes for Oxidation of Organic
Compounds with Periodate
a
a
a
b
a
Saeed Rayati , Elaheh Bohloulbandi , Saeed Zakavi , Majid Jafarian & Mehdi Rashvand avei
a
Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315–1618, Tehran
5418, Iran
1
b
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan,
Iran
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Accepted author version posted online: 31 Dec 2014.
To cite this article: Saeed Rayati, Elaheh Bohloulbandi, Saeed Zakavi, Majid Jafarian & Mehdi Rashvand avei (2014): Partial
and Full β-Chlorination of meso-Tetraphenylporphyrin: Effects on the Catalytic Activity of the Manganese Complexes for
Oxidation of Organic Compounds with Periodate, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal
Chemistry, DOI: 10.1080/15533174.2013.862660
To link to this article: http://dx.doi.org/10.1080/15533174.2013.862660
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ACCEPTED MANUSCRIPT
Partial and Full β-Chlorination of meso-Tetraphenylporphyrin: Effects on the Catalytic
Activity of the Manganese Complexes for Oxidation of Organic Compounds with Periodate
a,*
a
b,*
a
a
Saeed Rayati , Elaheh Bohloulbandi , Saeed Zakavi , Majid Jafarian , Mehdi Rashvand avei
a
Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 16315-1618, Tehran
5418, Iran
1
b
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan,
Iran
*
Corresponding author. E-mail address: rayati@kntu.ac.ir
Abstract
A series of β-chlorinated meso-tetraphenylporphyrins, H
2
TPPCl (x = 2, 4, 6 or 8) have been
x
prepared and the catalytic activity of their manganese(III) complexes in oxidation of
cyclooctene, cyclohexene and methyl phenyl sulfide with tetra-n-butylammonium periodate was
studied. The catalytic activity of the manganese porphyrins in oxidation of cylohexene and
cyclooctene decreased in the order MnTPPCl
MnTPPCl (OAc) >> MnTPPCl (OAc). The oxidative stability of the manganese porphyrins
decreased as MnTPP(OAc) > MnTPPCl (OAc) > MnTPPCl (OAc) > MnTPPCl (OAc) >
MnTPPCl (OAc). Oxidation of methyl phenyl sulfide gave the following order: MnTPP(OAc) ~
MnTPPCl (OAc) > MnTPPCl (OAc) ~ MnTPPCl (OAc) > MnTPPCl (OAc).
6
(OAc) ≥ MnTPP(OAc) ~ MnTPPCl
2
(OAc) >
4
8
6
8
4
2
6
4
2
8
Keywords β-Chlorinated manganese porphyrins, Oxidation, Olefins, Organosulfur; tetra-n-
Butylammonium periodate
1
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INTRODUCTION
Many studies on metalloporphyrin-catalyzed oxygenation of organic compounds since the late
[1]
1
980s have been devoted to the modeling of the catalytic cycle of cytochrome P-450. In this
regard, a wide range of metalloporphyrins, terminal oxidants and co-catalysts were used to
[1-7]
mimic P450 enzymes.
Coordination of terminal oxidants to the metal centre is usually
[2]
essential for a metal-catalysed transformation to take place. In other words, in the absence of
steric hindrance, an increase in the Lewis acidity of the metal centre would facilitate the
coordination of oxidant as donor molecule to the metal centre as acceptor one. Also, the
formation of high-valent metal-oxo porphyrin species is accompanied with the metal and/or
[7]
porphyrin centered oxidation of the metalloporphyrins.
On the other hand, the Lewis acidity
and redox potentials of metal center as well as the oxidative stability of metalloporphyrins
depend on the electronic properties of the substituents at the porphyrin periphery [8,9]. Although
electron-deficient metalloporphyrins have been found to be more efficient catalysts than the
[10-11]
electron-rich ones,
there are many reports which show comparable or higher catalytic
[12-17]
activity of the latter in comparison with the former.
The effect of degree of β-bromination
of meso-tetrakis(4-carbomethoxyphenyl)porphyrinato-manganese(III) chloride on its catalytic
efficiency for hydroxylation of cyclohexane with iodosylbenzene and iodobenzene diacetate was
[
18]
[19]
studied by Idemori and co-workers.
Also, in a recent work,
we have compared the
catalytic performance of a series of Mn(III) β-brominated meso- tetraphenylporphyrins for
oxidation of organosulfurs and olefins with tetra-n-butylammonium periodate (TBAP); a
partially brominated Mn-porphyrin, MnTPPBr (OAc) and MnTPP(OAc) shown higher catalytic
4
activity compared to the other analogues. Herein, we report the comparative study of catalytic
2
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activity of a series of β-chlorinated meso- tetraphenylporphyrins in oxidation of some olefins and
methyl phenyl sulfide with TBAP. Also, the half-wave potentials (E1/2) for the metal-centered
one electron reduction of the complexes were used to study the influence of chlorine atoms on
[9]
the distribution of electron density at the manganese atom. Due to the higher electronegativity
[20]
of chlorine substituent with respect to bromine atom,
the introduction of bromine atoms at the
β positions expected to create more electron deficient character on the porphyrin macrocycle and
consequently on the corresponding manganese porphyrin.
EXPERIMENTAL
Materials and Methods
1
H NMR spectra were obtained in CDCl
in conventional 99.8 atom% CDCl
ppm, which was used for calibration of the chemical shift scale. The electronic absorption
spectra were recorded on a single beam spectrophotometer (Camspect, UV-M 330) in CH Cl
Gas chromatographic analyses were performed on a Shimadzu GC-14B flame ionization detector
FID) with a SAB-5 capillary column (phenyl methyl siloxane 30 m × 320 mm × 0.25 mm).
3
solutions with a Bruker FT-NMR 300 (300 MHz)
spectrometer. The residual CHCl
3
3
gives a signal at = 7.26
2
2
.
(
Electrochemical studies were carried out in a conventional three electrode cell powered by an
electrochemical system comprising of an EG&G model 273A potentiostat/galvanostat. The
system was run by a PC through M270 commercial software via a GPIB interface. A coiled
platinum wire served as an auxiliary electrode and an Ag wire conventional reference electrode
°
was employed. All measurements were carried out at the ambient temperature of 25 ± 2 C.
3
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Electrochemical measurements were conducted in CH
2
Cl solutions containing 0.1 M of Tetra-n-
2
-3
butylammonim perchlorate (TBAPC) and 2 × 10 M of manganese porphyrin complexes.
The free base meso-tetraphenylporphyrin was prepared and purified as reported previously.
[21]
Chemicals were purchased from Merck chemical Co. Tetra-n-butylammonium periodate
[22,23]
(
TBAP) was prepared according to the literature.
Synthesis of the chlorinated porphyrins
H
2
TPPCl
x
(x = 2, 4, 6 or 8)
(OAc), MnTPPCl
MnTPPCl
2
4
(OAc), MnTPPCl
6
(OAc) and MnTPPCl (OAc) (Fig. 1) were
8
[24]
prepared from H
2
TPP by the following four step procedure.
NiTPP
H
2
TPP (614 mg, 1mmol) was dissolved in DMF (10 ml). Ni(OAc)
2
.4H O (800 mg, 3mmol)
2
was added to the reaction mixture and refluxed for 4 h. At the end of reaction, the solvent was
evaporated under reduced pressure and the product was washed twice with distilled water to
1
remove the excess of Ni(OAc)
MHz, CDCl
m- and p- phenyl).
2
.4H
2
O. UV-Vis in DMF, max (nm): 414, 527. H NMR (300
3
)  (ppm): 8.74 (s, 8H, β-pyrrole), 8.13-8.20 (m, 8H, o-phenyl), 7.68 (broad, 12H,
NiTPPCl
NiTPPCl
according to the literature
x
(x = 2, 4, 6 or 8)
2
, NiTPPCl
4
, NiTPPCl
6
and NiTPPCl
8
were prepared from NiTPP and NCS
[25]
with some modification. NCS (0.40g, 3mmol for NiTPPCl
2
; 0.80g,
4
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6
mmol for NiTPPCl
4
; 1.20 g, 9 mmol for NiTPPCl
6
; or 2.40 g, 18mmol for NiTPPCl ) was
8
added with stirring to a solution of NiTPP (1.0 g, 1.5 mmol) in 1,2-dichlorobenzene (60 mL).
The solution was brought to reflux for 2-3 h, and the reaction was monitored using UV-Vis
spectroscopy (the soret band shifted from 414 to 419 nm for NiTPPCl
to 430 nm for NiTPPCl and to 439 nm in the case of NiTPPCl ). After the end of reaction, the
solvent was evaporated under reduced pressure and the crude residue was washed using a
2
, to 424 nm for NiTPPCl
4
,
6
8
mixture of solvents, 30 mL of CH
2
Cl
2
/MeOH (1:10 v/v) to remove any soluble succinimide
1
impurities. NiTPPCl , UV-Vis in CH
2
2
Cl
2
, max (nm): 419, 530. H NMR (CDCl
3
, 300 MHz) δ
(
ppm): 8.61-8.74 (m, 6H, β-pyrrole), 7.83-8.05 (m, 8H, o-phenyl), 7.55-7.71 (m, 12H, m- and p-
1
phenyl). NiTPPCl
4
, UV-Vis in CH
2
Cl
2
, max (nm): 424, 542. H NMR (CDCl
3
, 300 MHz) δ
(
ppm): 8.65-8.85 (m, 4H, β-pyrrole), 8.05-8.20 (m, 8H, o-phenyl), 7.75-8.00 (m, 12H, m- and p-
1
phenyl). NiTPPCl
6
, UV-Vis in CH
2
Cl
2
, max (nm): 430, 542. H NMR (CDCl
3
, 300 MHz) δ
(
ppm): 8.65-8.73 (m, 2H, β-pyrrole), 7.83-7.96 (m, 8H, o-phenyl), 7.63-7.70 (m, 12H, m- and p-
1
phenyl). NiTPPCl
8
, UV-Vis in CH
2
Cl
2
, max (nm): 439, 550. H NMR (CDCl
3
, 300 MHz) δ
(
ppm): 7.90-8.00 (m, 8H, o-phenyl), 7.65-7.80 (m, 12H, m- and p- phenyl).
H
2
TPPCl
TPPCl
Ni(II) complexes with H
) was suspended in 100 ml of CH
x
(x = 2, 4, 6 or 8)
, H TPPCl , H
SO
H
2
2
2
4
2
TPPCl
and NH
Cl
6
and H
2
TPPCl
Cl . About 400 mg of NiTPPCl
SO (98%) was added. The mixture
8
were prepared by demetallation of the
2
4
3
in CH
2
2
x
(x = 2, 4, 6 or
8
2
2
, and 30 ml of H
2
4
was rigorously stirred for 3-4 h at room temperature. The progress of the reaction was
followed by UV-Vis spectroscopy. At the end of the reaction, the flask was transferred to an
5
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ice bath, and NH
overheating and violent boiling/evaporation of the organic solvent. The mixture was
extracted several times with H O and washed with a saturated solution of NaHCO until the
TPPCl , UV-
, 300 MHz) δ (ppm):
3
solution (25%) was added drop wise, with great precaution, to avoid
2
3
pH reached a value of 7.0. The organic phase dried for 45 min on Na
2
SO
4
. H
2
2
1
Vis in CH
2
Cl
2
, max (nm): 420, 515, 548, 595, 651. H NMR (CDCl
3
8
.67-8.91 (m, 6H, β-pyrrole), 8.08-8.24 (m, 8H, o- phenyl), 7.72-7.82 (m, 12H, m- and p-
1
phenyl), -2.83 (d, 2H, NH). H
2
TPPCl
4
, UV-Vis in CH
2
Cl , max (nm): 426, 523, 599, 667. H
2
NMR (CDCl , 300 MHz) δ (ppm): 8.65-8.75 (m, 4H, β-pyrrole), 8.00-8.10 (m, 8H, o-
3
phenyl), 7.60-7.80 (m, 12H, m- and p- phenyl), -2.80 (d, 2H, NH). H
2
TPPCl , UV-Vis in
6
1
CH
2
Cl
2
, max (nm): 433, 529, 572, 613, 675. H NMR (CDCl
3
, 300 MHz) δ (ppm): 8.30-8.70
(
m, 2H, β-pyrrole), 8.20-7.92 (m, 8H, o- phenyl), 7.77 (m, 12H, m- and p- phenyl), -2.40 (d,
1
2
H, NH). H
CDCl
phenyl), -1.55 (broad, 2H, NH).
2
TPPCl
8
, UV-Vis in CH
2
Cl
2
, max (nm): 355, 453, 551, 601, 719. H NMR
(
3
, 300 MHz) δ (ppm): 8.10-8.15 (m, 8H, o- phenyl), 7.70-7.80 (m, 12H, m- and p-
MnTPPCl
x
(OAc) (x = 2, 4, 6 or 8)
(OAc),
(OAc) were prepared and purified according to the literature.
(OAc), UV-Vis in CH Cl , max (nm): 472, 590, 615. MnTPPCl
(OAc), UV-Vis in CH Cl , max (nm): 490, 598,
MnTPP(OAc) ,MnTPPCl
2
MnTPPCl
4
(OAc),
MnTPPCl
6
(OAc)
and
[
18,26]
MnTPPCl
8
2
MnTPPCl
2
2
4
(OAc), UV-Vis in
CH
2
Cl
2
, max (nm): 484, 589, 627. MnTPPCl
6
2
2
6
38. MnTPPCl
8
(OAc), UV-Vis in CH
2
Cl
2
, max (nm): 495, 607, 652.
6
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General oxidation procedure
Stock solution of the catalyst (0.003 M) and imidazole (ImH, 0.5 M) were prepared in
CH
2
Cl . In a test tube, the reagents were added in the following order: substrate (0.25 mmol),
2
catalyst (0.003 mmol, 1.0 ml), ImH (0.03 mmol, 60 l), chlorobenzene (1 mmol) as an internal
˚
standard. TBAP (167 mmol) was then added to the reaction solution at 25 C. The reaction
solutions were analyzed by GC after stirring for 4 h.
RESULS AND DISCUSSION
Electrochemical studies
The cyclic voltammograms for MnTPP(OAc), MnTPPCl
MnTPPCl (OAc) in CH Cl (0.1 M TBAP) are presented in Fig. 2, and the redox potential data
for the one-electron process associated with the Mn(III)/Mn(II) couple are summarized in Table
. The half-wave potentials (E1/2) for the first reduction of MnTPP(OAc), MnTPPCl (OAc),
(OAc) corresponding to the Mn /Mn couple were located,
respectively, at E1/2 = -319, -242, -124, -121.005 and -102 mV in CH Cl . The potentials were
4
(OAc), MnTPPCl
6
(OAc) and
8
2
2
1
4
III
II
MnTPPCl
6
(OAc) and MnTPPCl
8
2
2
positively shifted (anodic shift) with successive increase in the number of chlorine atoms. These
complexes showed a quasi-reversible one-electron reduction under the same conditions. The
observed anodic shift on going from MnTPP(OAc) to MnTPPCl (OAc) can be attributed to the
8
steric as well as the electron-withdrawing effects of chlorine atoms. The electron-withdrawing
effects of the chlorine atoms modify the redox properties of the halogenated complexes with
respect to their non-halogenated counterparts due to tuning of the HOMO-LUMO energy gap, as
[27-34]
was evident by UV-Vis spectroscopy.
7
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Oxidation of olefins
x
Oxidation reactions catalyzed by MnTPPCl (OAc) (x = 0, 2, 4, 6 and 8) using TBAP as
oxidant were investigated in order to verify the effect of the -chlorination and the influence of
(III)
(II)
the Mn /Mn reduction potential on the catalytic properties of the Mn-porphyrin series. In a
search for suitable reaction conditions to achieve the maximum conversion and product
selectivity, different reaction parameters were optimized as follows.
Effect of the TBAP/olefine molar ratio
The reaction was performed using different molar ratios of cyclooctene to the oxidant
(
Table 2) and a 1:2 molar ratio has been found to be the optimized one.
The effect of the co-catalyst/catalyst ratio
The co-catalytic activity of ImH in the presence of MnTPPCl
x
(OAc) (x = 0, 2, 4, 6 and 8) at
various ImH/catalyst ratios are presented in Table 3 and a 5:1 molar ratio was selected for the
oxidation of cyclooctene. According to data of Table 3, the 1:5 molar ratio of ImH to catalyst has
been the best one for the oxidation of olefins with TBAP and the use of ImH in molar ratios
higher than this ratio, leads to a decrease in the efficiency of the catalysts, possibly due the
partial formation of an inactive Mn(Porphyrin)(ImH) species.
2
Effect of the number of chlorine atoms at the  position
Oxidation of cyclooctene and cyclohexene with TBAP was carried out in the presence of
MnTPPCl (OAc) (x = 0, 2, 4, 6 and 8) (Table 4).
x
8
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Stability of the catalyst against the degradation with oxidant
Stability of metalloporphyrins toward oxidative degradation by the active oxidation
intermediates or terminal oxidant under the reaction conditions is a major factor influencing their
[
35]
catalytic activity.
in the presence of cyclooctene by UV-Vis spectroscopy at their λmax and the following order of
stability was observed: MnTPP (OAc) > MnTPPCl (OAc) > MnTPPCl (OAc) >
MnTPPCl (OAc) > MnTPPCl (OAc). In comparison of the chlorinated Mn-porphyrins, the
oxidative stability increased with increase in number of chlorine atoms substituted at the 
positions, but MnTPPCl (OAc) was found to be more stable than the other ones. Interstingly,
MnTPP(OAc) demonstrated higher stability than the β-chlorinated Mn-porphyrins. Also,
MnTPPCl (OAc) showed lower degree of oxidative stability compared to MnTPPCl (OAc).
The oxidative degradation of the used metalloporphyrins has been studied
6
8
4
2
6
8
6
Comparison of the manganese porphyrins
The catalytic activity of the manganese porphyrins (Table 4) in oxidation of cylohexene and
cyclooctene with TBAP in the presence of ImH decreased in the order MnTPPCl (OAc) ≥
MnTPP(OAc) ~ MnTPPCl (OAc) > MnTPPCl (OAc) >> MnTPPCl (OAc). No correlation is
observed between the catalytic efficiency of the complexes and their relative oxidative stability.
Also, the partially chlorinated manganese porphyrin i.e. MnTPPCl (OAc) and MnTPP(OAc)
with no chlorine substituents showed the highest catalytic activity. Interestingly, the catalytic
activity of MnTPPCl (OAc) is unusually lower than that of the other complexes. We have
6
2
4
8
6
8
observed such a complex order of catalytic activity for oxidation of different olefins with TBAP
9
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[15-17,19]
in the case of manganese and iron porphyrins.
Apparently, the order of electron donor
ability of substituents at the β and meso positions of metalloporphyrins can be completely
different from that found in many organic reactions and transformations especially in the
[16]
electrophilic substitution of aromatic compounds.
The observed complex order of catalyst
stability for the manganese porphyrins seems to be due to the involvement of different active
oxidants in the catalytic cycle of the complexes.
Comparison with the brominated analogues
In a previous work [19], the catalytic activity of the β-brominated manganese meso-
tetraphenylporphyrins with 2, 4, 6 and 8 bromine atoms in the oxidation of olefins and sulphides
with TBAP has been studied and compared with that of the non-brominated manganese
porphyrin. While in the oxidation of olefins, the stability of the catalysts decreased in the order
MnTPPBr
the case of the chlorinated complexes the following order has been observed: MnTPP(OAc)>
MnTPPCl (OAc)> MnTPPCl (OAc) > MnTPPCl (OAc) > MnTPPCl (OAc). Also, the order of
catalytic activity of the complexes is as MnTPPBr (OAc) ≥ MnTPPBr (OAc)>
MnTPPBr (OAc)≥ MnTPP(OAc)>> MnTPPBr (OAc) and MnTPPCl (OAc)≥ MnTPP(OAc)≈
MnTPPCl (OAc)> MnTPPCl (OAc) >> MnTPPCl (OAc) for the brominated and chlorinated
8
(OAc) > MnTPP(OAc)> MnTPPBr
6
(OAc)> MnTPPBr
2
(OAc) > MnTPPBr
4
(OAc), in
6
8
4
2
4
2
6
8
6
2
4
8
catalysts, respectively. The results show different order of oxidative stability and catalytic
activity for the series of chlorinated and brominated manganese complexes. However, in both
series, the octa-halogenated complex has been found to be the least effective catalyst of the
1
0
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series. Also, in the oxidation of sulfides, with the exception of the octa-halogenated complexes,
different order of catalytic activity was found for the catalysts of the two series.
Oxidation of methyl phenyl sulfide
Oxidation of methyl phenyl sulfide with TBAP in the presence of catalytic amounts of
MnTPPCl (OAc) (x = 0, 2, 4, 6 and 8) in dichloromethane at room temperature led to the
x
selective sulfoxidation of the substrate. In a search for suitable reaction conditions to achieve the
highest selectivity for sulfoxide, the effect of varying a number of reaction parameters has been
studied. In the absence of metalloporphyrin, the reaction gives the sulfoxide and sulfone in
substantially lower yields (0.64 and 0.87%, respectively).
Effect of TBAP /sulfide molar ratio
In synthetic organic chemistry, the selective oxidation of sulfides to sulfoxides has been an
important challenge. The reaction was performed using various equivalents of oxidant for
oxidation of methyl phenyl sulfide (Table 5, Fig. 3). It shows that the highest conversion was
achieved with the 1:2 molar ratio of methyl phenyl sulfide to TBAP .
The effect of the co-catalyst/catalyst ratio
Oxidation of methyl phenyl sulfide in the presence of various ratios of imidazole to catalyst
changes the ratio of sulfoxide to sulfone in the products rather than the total conversion. The
effect of ImH concentration on the oxidation of methyl phenyl sulfide has also been studied (Fig.
4
). Addition of ImH up to 5:1 relative to the catalyst led to an increase in the conversion of
1
1
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reaction with increase the ratio of sulfoxide to sulfone. The addition of ImH beyond this ratio led
to a decrease in the ratio of sulfoxide to sulfone.
Comparison of the catalysts
Oxidation of methyl phenyl sulfide with TBAP in the presence of the manganese porphyrins
gave the corresponding sulfoxide and sulfone as the products (Table 5). The catalytic activity of
the manganese porphyrins was found to decrease as MnTPP(OAc) ~ MnTPPCl
MnTPPCl (OAc) ~ MnTPPCl (OAc) > MnTPPCl (OAc). However, in the case of using the
sulfide and TBAP in 1:1 or 2:1 molar ratios, nearly no catalytic activity was observed for
MnTPPCl (OAc) in comparison with the other manganese porphyrins. Also, the former gave
6
(OAc) >
4
2
8
8
methyl phenyl sulfide sulfoxide as the major product.
CONCLUSIONS
In
this
study,
effect
of
partial
and
full
chlorination
of
meso-
tetraphenylporphyrinatomanganese(III) acetate at the β positions on the catalytic activity of this
manganese porphyrin for the oxidation of cyclohexene, cyclooctene and methyl phenyl sulfide
with TBAP has been studied. The catalytic activity of the manganese porphyrins in the oxidation
of olefins and methyl phenyl sulfide was found to decrease as MnTPPCl
MnTPPCl (OAc) > MnTPPCl (OAc) >> MnTPPCl (OAc) and MnTPP(OAc) ~
MnTPPCl (OAc) > MnTPPCl (OAc) ~ MnTPPCl (OAc) > MnTPPCl (OAc), respectively. No
clear correlation was found between the catalytic activity of the complexes and their relative
oxidation stability in the reaction condition. Interestingly, MnTPPCl (OAc) showed an unusually
6
(OAc) ≥ MnTPP(OAc)
~
2
4
8
6
4
2
8
8
low catalytic activity compared to the other manganese porphyrins of the series. In combination
with the results of previous studies concerning the relative catalytic activity and stability of the β
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halogenated manganese porphyrins, the electronic effects of halogen atoms substituted at the β
positions of metalloporphyrins as aromatic compounds, seem to be completely different from
that found in many organic reactions and transformations especially in the electrophilic
substitution of aromatic compounds. In other words, there is no correlation between the number
of halogen atoms introduced at the β positions and the catalytic activity as well as the stability of
the manganese porphyrins in oxidation conditions.
ACNOWLEDGEMENTS
The financial support of this work by K.N. Toosi University of Technology research council is
acknowledged.
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Table 1
Half-wave potential data for the metal-centered one-electron reduction of
a
the Mn(III) complexes.
b
Mn-porohyrins
Mn(III)(TPP)
E
ox (mV)
E
red (mV)
ΔE
p
(mV)
E
1/2 (mV)
-
-
246
150
-392
-334
-228
-192
-164
146
-319
-242
-124
-121
-102
Mn(III)(Cl
Mn(III)(Cl
Mn(III)(Cl
Mn(III)(Cl
2
TPP)
TPP)
184
208
142
124
4
-
20
50
40
6
TPP)
-
-
8
TPP)
a
-3
-1
Conditions: CH
2
Cl
2
, MnP = 2 ×10 M, TBAP = 0.1 M, scan rate 50 mV.s
.
Versus Ag/AgCl.
b
Potential difference (Eox-Ered).
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Table 2
Effect of various TBAP/cyclooctene molar ratios on the cyclooctene epoxidation in the presence
a
of ImH in dichloromethane.
b
TBAP/
cycloocten
e
Conversion %
MnTPPCl
MnTPPCl
2
MnTPP
35
4
MnTPPCl
6
MnTPPCl
8
2
4
8
3
1:2
1:1
2:1
26
42
56
32
46
62
3
3
4
58
90
5
9
a
The molar ratios for catalyst:ImH:cyclooctene:oxidant are 1:10:83:x .
b
All reactions were run at room temperature for 4 h.
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Table 3
Effect of various ImH/Catalyst molar ratios on the cyclooctene epoxidation rate and selectivity
a
with TBAP in dichloromethane
b
ImH/Catalyst
Conversion %
MnTPPCl
2
MnTPP
35
MnTPPCl
4
MnTPPCl
6
MnTPPCl
8
2
3
8
5
1
0
26
32
3
6
5
36
28
44
a
The molar ratios for catalyst:ImH: cyclooctene: oxidant are 1:x:83:167 .
b
All reactions were run at room temperature for 4 h.
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Table 4
Oxidation of cyclooctene and cyclohexene with TBAP catalyzed by MnTPPCl
x
(OAc) (x = 0, 2,
a
4
, 6 and 8) in the presence of ImH in dichloromethane.
Catalyst
Cyclooctene
Cyclohexene
Conversion %
b
Yield % Conversion %
Yield %
Epoxide
(
Epoxide)
1-ol
1-on
MnTPP(OAc)
36
35
28
44
6
36
35
28
44
6
26
21
8
1
1
1
1
1
4
2
1
3
1
31
MnTPPCl
MnTPPCl
MnTPPCl
MnTPPCl
2
(OAc)
(OAc)
(OAc)
(OAc)
24
10
25
9
4
6
21
7
8
a
The molar ratios for catalyst:ImH:alkene:oxidant are 1:5:83:167 .
b
All reactions were run at room temperature for 4 h.
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Table 5
Effect of various TBAP/sulfide molar ratios on the oxidation of methyl phenyl sulfide in the
a
presence of ImH in dichloromethane .
TBAP/
Sulfide
Conversion
%
Yield %
(sulfoxide) (sulfone)
Yield %
Catalyst
b
Sulfoxide/sulfone
1
1
2
:2
:1
:1
MnTPP
22
18
16
21
2
49
37
39
48
3
58
40
41
57
18
19
17
14
20
2
35
29
30
38
3
26
22
25
31
9
3
1
2
1
0
14
8
9
10
0
32
18
16
26
9
6.3
17
7
20
-
2.5
3.6
3.3
3.8
-
0.8
1.2
1.5
1.1
1
MnTPPCl
MnTPPCl
MnTPPCl
MnTPPCl
MnTPP
MnTPPCl
MnTPPCl
MnTPPCl
MnTPPCl
MnTPP
2
4
6
8
2
4
6
8
MnTPPCl
MnTPPCl
MnTPPCl
MnTPPCl
2
4
6
8
a
The molar ratios for catalyst:ImH:sulfide:oxidant are 1:10:83:x.
b
All reactions were run at room temperature for 4 h.
2
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X
X
X
X
N
N
OAc
N
N
Mn
X
X
X
X
X = 0 MnTPP(OAc)
X = 2Cl MnTPPCl (OAc)
2
X = 4Cl MnTPPCl (OAc)
4
X = 6Cl MnTPPCl (OAc)
6
X = 8Cl MnTPPCl (OAc)
8
Fig. 1. The used metalloporphyrin in this study
2
2
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-3
Fig. 2. Cyclic voltammograms of Mn(III)(Cl
x
TPP) (CH
2
Cl , MnP = 2 × 10 M, TBAP = 0.1 M,
2
-1
scan rate 50 mV s ).
2
3
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6
5
4
3
2
1
0
0
0
0
0
0
0
0
1:02
01:01
02:01
TBAP/Sulfide
Fig. 3. Effect of various TBAP/sulfide molar ratios on the oxidation of methyl phenyl
sulfide in the presence of ImH in dichloromethane. Light color: yield of sulfoxide, dark color:
yield of sulfone.
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4
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sulfoxide Yield (%)
00
sulfone Yield (%)
sulfoxide selectivity (%)
1
90
80
70
60
50
40
30
20
10
0
1;0
1;5
1;10
Fig. 4. Effect of ImH/MnTPPCl (OAc) molar ratios on the oxidation of methyl phenyl sulfide
6
with TBAP in dichloromethane at room temperature. The molar ratios for
catalyst:ImH:sulfide:oxidant are 1:x:83:167.
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5
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