Stereoelectronic effects of the meso-substituents on the catalytic performance of iron(III) meso-tetraarylporphyrins: Pyridyl and N-methylated pyridyl groups compared to phenyl, 4-methoxyphenyl and 4-sulfonatophenyl ones

Article abstract of DOI:10.1016/j.molcata.2012.11.003

The activity of a series of iron(III) meso-tetraarylporphyrins (aryl = phenyl, 4-methoxyphenyl, 4-sulfonatophenyl, 2-pyridyl, 3-pyridyl, 4-pyridyl and N-methyl-pyridyl counterparts) in the catalysis of oxidation reactions of olefins with tetra-n-butylammonium periodate (TBAP) or NaIO₄ in the presence of imidazole (ImH) has been studied. While the presence of ImH has no effect on the catalytic activity of the Fe-porphyrins containing pyridyl or N-methylated pyridyl substituents at the meso-positions, the catalytic performance of the other Fe-porphyrins significantly increased by the use of ImH in 5:1 molar ratio with respect to the catalyst. As was observed in the comparison of the Mn-porphyrins with pyridyl substituents, the oxidative stability of FeT(4-py)P(OAc) is remarkably higher than that of FeT(2-py)P(OAc) and FeT(3-py)P(OAc). Also, the same order of relative stability was found in the case of the N-methylated analogues. It is noteworthy that N-methylation of FeT(py)P(OAc) complexes led to the substantial decrease in their oxidative stability. Competitive oxidation of cis- and trans-stilbene, provides indirect evidence for the involvement of high valent Fe-oxo porphyrins as well as periodato iron porphyrins as the active oxidant in reactions catalyzed by the used iron porphyrins. However, the involvement of a high valent iron-oxo porphyrin species is more pronounced in the case of FeTPPS₄(OAc), FeT(2-py)P(OAc), FeT(3-py)P(OAc), FeT(4-py)P(OAc) and the N-methylated analogues. Also, an unusual preference of trans-stilbene over cis-stilbene was observed in the competitive epoxidation reaction catalyzed by FeT(3-MePy)P(OAc) and FeT(4-MePy)P(OAc) which cannot be described by the cis/trans isomerization. Furthermore, significant cis/trans isomerization observed upon oxidation of cis-stilbene in the reaction catalyzed by FeT(2-MePy)P(OAc) indicates that steric effects due to the presence of methyl groups at the ortho positions of this complex are of minor importance. On the other hand, large differences were observed in the product distribution for oxidation reactions with TBAO performed in dichloromethane and aqueous solvent. In spite of the lack of close correlation between the catalytic activity of the Fe-porphyrins and the electronic properties of the meso-substituents, in comparison with the corresponding Mn-porphyrins, there is a better correlation between the catalytic activity of the Fe-porphyrins and the electronic effects of the meso-groups.

Full text of DOI:10.1016/j.molcata.2012.11.003

Journal of Molecular Catalysis A: Chemical 367 (2013) 108–115
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Stereoelectronic effects of the meso-substituents on the catalytic performance of
iron(III) meso-tetraarylporphyrins: Pyridyl and N-methylated pyridyl groups
compared to phenyl, 4-methoxyphenyl and 4-sulfonatophenyl ones
Saeed Zakavi∗, Tahereh Mokary Yazdeli
Department of Chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan 45137-66731, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2012
The activity of
a series of iron(III) meso-tetraarylporphyrins (aryl = phenyl, 4-methoxyphenyl, 4-
sulfonatophenyl, 2-pyridyl, 3-pyridyl, 4-pyridyl and N-methyl-pyridyl counterparts) in the catalysis of
oxidation reactions of olefins with tetra-n-butylammonium periodate (TBAP) or NaIO4 in the presence
of imidazole (ImH) has been studied. While the presence of ImH has no effect on the catalytic activ-
ity of the Fe-porphyrins containing pyridyl or N-methylated pyridyl substituents at the meso-positions,
the catalytic performance of the other Fe-porphyrins significantly increased by the use of ImH in 5:1
molar ratio with respect to the catalyst. As was observed in the comparison of the Mn-porphyrins
with pyridyl substituents, the oxidative stability of FeT(4-py)P(OAc) is remarkably higher than that of
FeT(2-py)P(OAc) and FeT(3-py)P(OAc). Also, the same order of relative stability was found in the case
of the N-methylated analogues. It is noteworthy that N-methylation of FeT(py)P(OAc) complexes led
to the substantial decrease in their oxidative stability. Competitive oxidation of cis- and trans-stilbene,
provides indirect evidence for the involvement of high valent Fe-oxo porphyrins as well as periodato
iron porphyrins as the active oxidant in reactions catalyzed by the used iron porphyrins. However, the
involvement of a high valent iron-oxo porphyrin species is more pronounced in the case of FeTPPS4(OAc),
FeT(2-py)P(OAc), FeT(3-py)P(OAc), FeT(4-py)P(OAc) and the N-methylated analogues. Also, an unusual
preference of trans-stilbene over cis-stilbene was observed in the competitive epoxidation reaction
catalyzed by FeT(3-MePy)P(OAc) and FeT(4-MePy)P(OAc) which cannot be described by the cis/trans
isomerization. Furthermore, significant cis/trans isomerization observed upon oxidation of cis-stilbene in
the reaction catalyzed by FeT(2-MePy)P(OAc) indicates that steric effects due to the presence of methyl
groups at the ortho positions of this complex are of minor importance. On the other hand, large dif-
ferences were observed in the product distribution for oxidation reactions with TBAO performed in
dichloromethane and aqueous solvent. In spite of the lack of close correlation between the catalytic
activity of the Fe-porphyrins and the electronic properties of the meso-substituents, in comparison with
the corresponding Mn-porphyrins, there is a better correlation between the catalytic activity of the
Fe-porphyrins and the electronic effects of the meso-groups.
Received in revised form 26 October 2012
Accepted 5 November 2012
Available online 13 November 2012
Keywords:
Meso-tetra(pyridyl)porphyrins
N-methylated
meso-tetra(pyridyl)porphyrins
sulfonated-meso-tetra(aryl)porphyrins
Iron porphyrins
Oxidation of olefins
Catalysis
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
same catalytic performance of metalloporphyrins with electron-
donating groups compared to those bearing electron-withdrawing
After the first report on the use of iron porphyrins in oxi-
dation of hydrocarbons with iodosylbenzene by Groves et al. in
1979, different aspects of the catalytic activity of metallopor-
phyrins have been studied and clarified [1–3]. One of the major
results obtained by different studies is the general agreement
on the higher catalytic activity of electron deficient metallo-
porphyrins relative to the electron rich ones [4]. On the other
hand, there are many reports concerning the higher or nearly the
substituents [5–15]. Manganese porphyrin catalyzed oxidation of
hydrocarbons with sodium periodate was pioneered by Mohajer
and Tangestaninejad in 1993 [5]. After that, several studies have
been carried out on the effects of nitrogen donors, solvent, meso-
and/or ␤ substituents and anionic axial bases on the efficiency
of manganese porphyrins [5–7,13,15,16]. We have previously
studied the catalytic activity of a series of meso- and/or ␤ substi-
tuted electron-deficient and electron-rich manganese porphyrins
in oxidation of various olefins with tetra-n-butylammonium peri-
odate (TBAP) and iodosylbenzene (PhIO) and found a complex
order of catalytic activity for the Mn-porphyrins. Interestingly,
the electron rich Mn-porphyrins showed higher or similar
∗
Corresponding author. Tel.: +98 241 4153202; fax: +98 241 4153232.
E-mail address: zakavi@iasbs.ac.ir (S. Zakavi).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.11.003

S. Zakavi, T. Mokary Yazdeli / Journal of Molecular Catalysis A: Chemical 367 (2013) 108–115
109
2.2. Preparation of porphyrins
Ar
Meso-tetra(pyridyl)- [17,18], meso-tetraphenyl- [19], meso-
tetra(4-OCH3phenyl)- [19], meso-tetra(4-sulfonatophenyl)-
N
N
2
3
Fe
Ar
Ar
N
N
[20,21], were prepared and purified according to the literature
methods. The sulfonated meso-tetra(aryl)porphyrins were isolated
as the tetra-n-butylammonium salts by extraction of the sulfonated
porphyrin into dichloromethane using tetra-n-butylammonium
bromide as the phase transfer catalyst. More details (UV–vis
and 1H NMR spectra data) have been described in our previous
work [16]. N-methylated meso-tetra(pyridyl)porphyrins were
prepared by refluxing the corresponding porphyrin with excess
amounts of methyltosylate in dimethylformamide (DMF) and puri-
fied according to the literature [18,22]. H2T(2-Mepy)P: 1H NMR
1
4
Ar
Ar =
2-pyridyl
4-pyridyl
Porphyrins
H2T(2-py)P
H2T(4-py)P
H2T(2-Mepy)P
H2TPP
H2T(4-OCH3)PP
H2TPPS4
H2T(3-py)P
H2T(3-Mepy)P
H2T(4-Mepy)P
Fe-porphyrins
FeT(2-py)P(OAc) (1)
FeT(4-py)P(OAc) (2)
FeT(2-Mepy)P(OAc) (3)
FeTPP(OAc)(4)
2-methylpyridyl
Phenyl
4-methoxyphenyl
4-sulfonatophenyl
3-pyridyl
FeT(4-OCH3)PP(OAc) (5)
FeTPPS4(OAc) (6)
FeT(3-py)P(OAc) (7)
FeT(3-Mepy)P(OAc) (8)
FeT(4-Mepy)P(OAc) (9)
(DMSO-d6, 400 MHz): −2.995 (2H, br, s, NH), 9.681–9.696 (4Hm
,
3-methylpyridyl
4-methylpyridyl
adjacent to heteroatom, m), 8.860–8.964 (4Hm, m), 9.068–9.078
(4Ho, dd), 8.748–8.783 (4Hp, qn), 9.277 (8H␤, s), 4.039–4.15 (12H,
CH3, s). UV–vis (ꢀ/nm) in water: 412 (Soret), 508, 541, 578, 630.
H2T(3-Mepy)P: 1H NMR (DMSO-d6, 400 MHz): −3.124 (2H, br, s,
NH), 8.626–8.661 (4Hm, dd), 10.007 (4Ho, adjacent to heteroatom,
s), 9.323 (4Ho, d), 9.579–9.594 (4Hp, d), 9.266 (8H␤, s), 4.698 (12H,
CH3). UV–vis (ꢀ/nm) in water: 415 (Soret), 512, 540, 577, 628.
H2T(4-Mepy)P: 1H NMR (DMSO-d6, 400 MHz): −3.086 (2H, br, s,
NH), 9.469–9.511 (8Hm, m), 8.993–9.009 (8Ho, d), 9.202 (8H␤, s),
4.741 (12H, CH3). UV–vis (ꢀ/nm) in water: 420 (Soret), 515, 553,
582, 635.
Fig. 1. Porphyrins and the iron(III) complexes used in this study.
catalytic efficiencies compared to the electron-deficient ones in
oxidation of most of the used alkenes [13,14]. Also, the elec-
tronic effects of meso substituent on the activity of a series
of electron-rich and electron-deficient manganese porphyrins
containing (2-, 3-, 4-)pyridyl, 4-sulfonatophenyl, phenyl and 4-
methoxyphenyl groups at the periphery of porphyrin for the
catalysis of oxidation reaction of olefins with TBAP were stud-
ied in our recent work [16]. The results showed that apparently
the well-known electronic effects of these substituents, have been
used in organic chemistry to predict the product distribution and
the kinetics of reactions as well as the linear free energy rela-
tionship, cannot be simply generalized to the groups attached
to the meso- or ␤-positions of the manganese porphyrins. Due
to the important role played by iron porphyrins in the cataly-
sis of oxidation reactions in biological systems, also in order to
judge whether this behavior is general or not in the series of
iron porphyrins, a wide range of iron porphyrins (Fig. 1) and
olefins have been used to investigate the influence of peripheral
substitution on the oxidative degradation and catalytic activity
of the iron porphyrins. Furthermore, in the present work, N-
methylation of pyridyl substituents has been used to increase
the electron deficiency of the porphyrin core of iron(III) meso-
tetra(pyridyl)porphyrin complexes. The competitive oxidation of
cis- and trans-stilbene has been used to gain insights on the nature
of reactive species involved in the catalytic cycles [7,10,16]. Also,
significant differences were found between the product distribu-
tion of oxidation reaction conducted in aqueous and non-aqueous
conditions.
2.3. Preparation of metalloporphyrins
Porphyrins were metalated with FeCl2·4H2O or Fe(OAc)2 in
refluxing DMF according to the method of Kobayashi et al. [23,24].
The progress of reaction was monitored by UV–vis spectroscopy
(see supporting information for more details). With the excep-
tion of the iron porphyrins with anionic and cationic substituents,
the other metalloporphyrins crystallized from the DMF solution
upon cooling. In the case of the former, after the disappear-
ance of the Soret band of the free base porphyrin (vide infra),
DMF was evaporated in vacuo and further purification was per-
formed on the crude product. The Soret (and visible bands, the
data in the parentheses) of FeTPP(OAc), FeT(4-OCH3)PP(OAc),
FeT(2-py)P(OAc), FeT(3-py)P(OAc), FeT(4-py)P(OAc), FeTPPS4(OAc)
(as tetra-n-butylammonium salt), FeT(2-Mepy)P(OAc), FeT(3-
Mepy)P(OAc) and FeT(4-Mepy)P(OAc) appears at 405 (ꢀmax, in
CH2Cl2) (564, 606), 409 (ꢀmax in CH2Cl2) (569, 612), 404 (ꢀmax
,
in CH2Cl2) (563, 605), 409 (ꢀmax, in CH2Cl2) (498, 565, 607), 402
(ꢀmax, in CH2Cl2) (562, 603), 406 (ꢀmax, in CH2Cl2) (565, 604), 420
(ꢀmax, in DMF) (504, 558, 603), 421 (ꢀmax, in DMF) (490, 551, 637),
423 (ꢀmax, in DMF) (495, 548, 639) nm, respectively. The presence
of unreacted porphyrin, especially in the case of iron porphyrins
with ꢀmax values very close to those of the corresponding free base
porphyrins, was monitored by gradual addition of a dilute solution
of CF3COOH to an aliquot of the reaction mixture and recording the
UV–vis spectrum; the existence of free base porphyrin leads to the
significant red shift of the Soret band due to the formation of the
dication species [25].
2. Experimental
2.1. Instrumental
1H NMR spectra were obtained on a Bruker Avance DPX-
400 MHz spectrometer. The absorption spectra were recorded on
a Pharmacia Biotech Ultrospec 4000 UV-vis spectrophotometer.
All reactions were analyzed by a Varian-3800 gas chromatograph
equipped with a HP-5 capillary column (phenylmethyl siloxane
30 m × 320 ␮m × 0.25 ␮m) or a packed column (Chromosorb WHP
80–100 Mesh, 4 mm × (1/4) m × 2 m) and a flame-ionization detec-
tor. 1H NMR has been used to analyze the products in the case of
cis- and trans-stilbene. All reactions were repeated at least three
times.
2.4. General oxidation procedure
Stock solutions of the Fe-porphyrins (0.003 M) and ImH (0.5 M)
were prepared in dichloromethane (or DMF for the cationic iron
porphyrins). In a typical reaction, alkene (0.25 mmol), Fe-porphyrin
(0.003 mmol, 1 ml) and ImH (X ␮l, vide infra) were added into
a 10 ml round bottom flask containing 1 ml of dichloromethane.
Then, 0.5 mmol (0.217 g) TBAP has been added. The mixture was
stirred thoroughly for 4 h at ambient temperature. The opti-
mized molar ratios of catalyst:ImH:alkene:TBAP are 1:0:85:170 in

110
S. Zakavi, T. Mokary Yazdeli / Journal of Molecular Catalysis A: Chemical 367 (2013) 108–115
Table 1
Table 2
Effect of ImH on the catalytic activity of FeT(2-Py)P(OAc), FeT(4-Py)P(OAc),
The comparison of the catalytic activity of FeTPPCl and FeTPP(OAc) in oxidation of
FeTPP(OAc), FeT(4-OCH3)PP(OAc) and FeT(2-Mepy)P(OAc).a
styrene in CH2Cl2.a
1:0
1:5
1:10
FeTPP(X)
Conversion (%)b
Epoxide
Epoxide
selectivity (%)
yield (%)b
FeT(2-Py)P(OAc)b
Conversion (%)
Epoxide yield (%)
FeT(4-Py)P(OAc)c
Conversion (%)
12.433
12.433
7.573
7.573
5.115
5.115
X = OAc
X = Cl
12.963
6.270
12.963
6.270
100
100
a
The molar ratios of catalyst:ImH:olefin:TBAP are 1:10:83:170.
41.842
41.842
25.855
25.855
19.358
19.358
b
The average value of three independent experiments for a reaction time of 4 h.
Epoxide yield (%)
FeTPP(OAc)d
Conversion (%)
29.378
29.378
15.612
15.612
7.150
7.150
3.1.1. FeT(2-, 3-, or 4-Py)P(OAc) and their N-methylated
analogues
Epoxide yield (%)
FeT(4-OCH3)PP(OAc)b
Conversion (%)
Epoxide yield (%)
FeT(2-Mepy)P(OAc)c
Conversion (%)
In spite of the significant increase in the catalytic activity of the
iron and manganese [16] porphyrins (Table 1) with non-pyridyl
substituents, caused by the presence of ImH, no co-catalytic activity
has been found for ImH in reaction catalyzed by the iron porphyrins
with pyridyl and N-methylated pyridyl substituents. Apparently,
the formation of Fe(porphyrin)(ImH)2 causes the decreased cat-
alytic activity of the latter [7,26,27].
1.188
1.188
13.948
13.948
11.384
11.384
Trace
Trace
32.756
32.756
20.990
20.990
Epoxide yield (%)
a
The molar ratios of catalyst:ImH:olefin:TBAP (or NaIO4 for the reactions per-
formed in water) are 1:X:85:170; Reaction time was 4 h. Average of three runs.
b
Oxidation of styrene in CH2Cl2.
Oxidation of indene in CH2Cl2.
Oxidation of indene in water.
c
d
3.1.2. FeTPP(OAc), FeT(4-OCH3)PP(OAc) and FeTPPS4(OAc) (as
tetra-n-butylammonium salt)
As was observed in the case of manganese porphyrins with the
same meso substituents [16], the presence of ImH leads to a signif-
icance increase in the catalytic performance of these series of iron
porphyrins (Table 1), although the maximum conversion is reached
at a smaller molar ratio of ImH to the catalyst.
reactions catalyzed by iron porphyrins with pyridyl substituents
in dichloromethane and the N-methylated counterparts in water
and 1:5(0.015 mmol, 30 ␮l):85:170 in the presence of the other
iron porphyrins. With the exception of cis- and trans-stilbene,
the progress of reaction was followed using TLC and GC analy-
sis. After the required time, 5 ml diethyl ether was added to the
flask and the reaction mixture passed through a short silica gel
column to remove the unreacted tetra-n-butylammonium peri-
odate and any remaining Fe-porphyrins. Low solubility of TBAP
in ether leads to the precipitation of unreacted oxidant follow-
ing the addition of ether to the reaction mixture. Also, the used
Fe-porphyrins are slightly soluble in ether and are separated by
chromatography through a short silica gel column. Oxidation of
olefins with sodium periodate catalyzed by FeT(2-Mepy)P(OAc),
FeT(3-Mepy)P(OAc) and FeT(4-Mepy)P(OAc) were performed in
aqueous solution. Therefore, after stirring the reaction mixture for
the required time at ambient temperature in air, extraction by
CH2Cl2 was used to separate the products of reactions as well as
the unreacted olefin. After drying the organic phase with MgSO4, it
was analyzed by GC.
3.2. Counteranion effect
The nature of epoxidizing intermediates in iron porphyrin cat-
alyzed epoxidation of olefins was shown to be markedly dependent
on the ligating nature of the anionic ligands [28]. In a previous work,
we have studied the effects of anionic counterion on the catalytic
activity of the iron porphyrin of meso-tetra(n-propyl)porphyrin
[27]. The catalytic activity of FeTPPX (X = Cl, OAc) is significantly
influenced by the nature of counterion (Table 2).
3.3. Iron porphyrin catalyzed oxidation of olefins with TBAP
3.3.1. Oxidative stability of the Fe-porphyrins
According to the data of Table 3, stability of the iron por-
phyrins toward oxidative degradation under the reaction
condition decreases as FeT(4-py)P(OAc) ꢀ FeT(4-Mepy)P(OAc) >
FeT(2-py)P(OAc) ∼ FeT(3-py)P(OAc) > FeTPPS4(OAc) > FeT(2-Mepy)
P(OAc) > FeT(4-OCH3)P(OAc) ∼ FeTPP(OAc) > FeT(3-Mepy)P(OAc).
Interestingly, FeT(4-py)P(OAc) and FeT(4-Mepy)P(OAc) are much
more stable compared to the other members of the series which is
in agreement with our previous findings on the relative stability of
Mn-porphyrins with pyridyl and substituted phenyl groups [16].
2.5. Degradation of metalloporphyrins
Degradation of metalloporphyrins for a reaction time of 4 h was
followed by UV–vis spectroscopy at the ꢀmax of the complexes. Gen-
eral procedure for the oxidation reactions and the molar ratios of
catalyst, ImH, alkene and TBAP are as mentioned above (see [16]
for more details).
3. Results and discussion
Table 3
Degradation of the iron porphyrins under reaction conditions.a
3.1. The optimized ImH/iron porphyrin ratios
Fe-porphyrins
Degradation
(%)b
Fe-porphyrins
Degradation
(%)b
The catalytic activity of metalloporphyrins has been found to be
significantly dependent on the presence of nitrogen donors such
as ImH. Previous studies have shown that in manganese porphyrin
catalyzed oxidation of olefins the 1:10 ratio of the catalyst to ImH is
the optimized condition [7,16]. However, the optimization of this
molar ratio is needed to be done for the iron porphyrins. Accord-
ingly, we have studied the influence of molar ratio of catalyst to
ImH, in oxidation reactions conducted in the presence of the iron
porphyrins. The effect of this parameter has been studied for all of
the iron porphyrins but some of them are summarized in Table 1.
FeT(2-py)P(OAc)c
FeT(3-py)P(OAc)c
FeT(4-py)P(OAc)c
FeTPP(OAc)d
28.6
31.6
6.4
80.6
80.0
FeTPPS4(OAc)d
44.0
71.5
100.0
10.8
FeT(2-Mepy)P(OAc)c,e
FeT(3-Mepy)P(OAc)c,e
FeT(4-Mepy)P(OAc)c,e
FeT(4-OCH3)P(OAc)d
a
See the footnotes of Table 1.
On the basis of the absorbance changes (ꢁA) at the ꢀmax of the Fe-porphyrins
b
(ꢁA/A).
c
The molar ratios of catalyst:ImH:styrene:TBAP are 1:0:83:170.
The molar ratios of catalyst:ImH:styrene:TBAP are 1:5:83:170.
For reaction conducted in water.
d
e

S. Zakavi, T. Mokary Yazdeli / Journal of Molecular Catalysis A: Chemical 367 (2013) 108–115
111
Table 4
Furthermore, the present study indicates much higher oxidative
Oxidation of olefins with TBAP in CH2Cl2 using FeTPP(OAc) as catalyst.a
stability of FeT(4-py)P(OAc) with respect to the N-methylated
FeT(py)P(OAc), with the exception of FeT(4-Mepy)P(OAc). On
the other hand, FeT(3-Mepy)P(OAc) has undergone the greatest
degradation among the iron porphyrins. In comparison with the
corresponding Mn-porphyrins [16], there are larger differences
between the stability of the iron porphyrins. While the introduc-
tion of the SO3 groups at the phenyl substituents of FeTPP(OAc)
causes the significant increase in the stability of the iron porphyrin,
N-methylation of the iron meso-tetra(pyridyl)porphyrins does not
necessarily increase the stability of the iron porphyrin. The order
of stability of the iron meso-tetra(pyridyl)porphyrins is exactly
the same as that was observed in the case of the manganese
porphyrins with the same substituents. It is noteworthy that the
order of stability of the N-methylated iron porphyrins is the same
as was observed in the case of non-methylated iron and manganese
[16] porphyrins. However, the comparable extent of degradation
of FeT(4-OCH3)P(OAc) and FeTPP(OAc) (also the manganese por-
phyrins [16]) implies that the substitution of phenyl groups with
the OCH3 substituents has little or no effect on the stability of
the metalloporphyrin. Finally, except for FeT(4-Mepy)P(OAc), the
iron porphyrins with cationic N-methylated pyridyl substituents
are found to be remarkably less stable than the corresponding
non-methylated analogues. It should be noted that, compared to
the aprotic solvents, the protic solvents such as water, are in favor
of the formation of a high valent iron oxo species [7,29].
Olefins
Conversion
(%)b
Epoxide
Epoxide
selectivity (%)
yield (%)b
29.616
13.242
29.616
13.242
100
100
100
100
H
H
12.961c
16.725
12.961
16.725
10.205
13.948
10.205
13.948
100
100
39.507
Trace
34.059
Trace
86d
–
H3CO
3.3.2. Oxidation reactions in presence of the Fe-porphyrins
With the exception of 4-methoxystyrene, FeTPP(OAc)
catalyzed oxidation of olefins with TBAP gives the corre-
sponding epoxide as the sole product (Table 4). Oxidation of
the former gives some 4-methoxystyrene. The order of reac-
tivity of different olefins is as follows: 4-methoxystyrene >
indene ꢀ cyclooctene > styrene ≥ cyclohexene ≥ cis-
a
The molar ratios of catalyst:ImH:olefin:TBAP are 1:5:83:170.
For a reaction time of 4 h; the average value of three independent experiments.
cis-Cyclooctene.
b
c
d
4-Methoxybenzaldehyde was the other product.
cyclooctene > ␣-methylstyrene ꢀ 1-hexene (no reaction).
Also, in the presence of the other Fe-porphyrins, the following
orders were observed:
The observed order of reactivity of olefins depends on differ-
ent factors such as: (i) the nature of active oxidant; (ii) degree of
steric hindrance around the electrophilic oxygen atom of the active
oxidant; (iii) stereoelectronic effects of the groups attached to the
double bond; and (iv) degree of radical or carbocation character
at the carbon atoms of the double bond involved in the oxidation
reaction. In this regards, (i) high valent iron-oxo porphyrin species
have been implicated as the key reactive intermediates in the cat-
alytic cycles of dioxygen activation by heme and non-heme iron
enzymes [10,30] and consequently are expected to be stronger oxi-
dizing species compared to the corresponding (periodato)iron(III)
porphyrin ones. More efficient oxidation of olefins with periodate
observed in a mixed solvent of CH2Cl2 and tert-butanol [29] or wet
CH2Cl2 [31] compared to the reactions conducted in CH2Cl2 was
explained by the formation of high valent manganese oxo species
in the presence of tert-butanol or water [7,29]; (ii) in the absence
of bulky substituents at the meso positions, the steric hindrance
around the electrophilic oxygen atom of an iron-oxo porphyrin
moiety is usually less than that of a (periodato)iron(III) porphyrin
one. Immediate formation of high valent Mn-oxo porphyrin species,
in oxidation of olefins with TBAP carried out in CH2Cl2/H2O mixed
solvent was reported by Mohajer et al. [7]. Also, addition of small
amounts of different alcohols to the reaction mixture leads to the
formation of high valent Mn-oxo porphyrin moieties even in the
case of MnTPP(OAc) [29]; (iv) radical and carbocation stabilizing
substituents are expected to increase the reactivity of the olefins.
FeTPPS4(OAc) (Table S1): indene > cyclooctene > styrene > ␣-meth-
ylstyrene > cis-cyclooctene cyclohexene ꢀ 4-methoxystyrene ꢀ
1-hexene (no reaction).
FeT(4-OCH3)P(OAc) (Table S2): indene > 4-methoxystyrene ꢀ
styrene ∼ cis-cyclooctene ∼ cyclooctene ∼ cyclohexene ∼ ␣-
methylstyrene ꢀ 1-hexene (no reaction).
FeT(2-py)P(OAc) (Table S3): indene > styrene > cyclohexene ∼ ␣-
methylstyrene ≥ cis-cyclooctene ≥ cyclooctene ꢀ 4-
methoxystyrene ꢀ 1-hexene (no reaction).
FeT(3-py)P(OAc) (Table S4): cyclooctene > ␣-methylstyrene ≥
cis-cyclooctene ∼ indene > cyclohexene ꢀ 4-methoxystyrene ≥
styrene ꢀ 1-hexene (no reaction).
FeT(4-py)P(OAc) (Table S5): indene ꢀ cyclohexene > styrene ꢀ
cyclooctene ∼ cis-cyclooctene > ␣-methylstyrene ∼ 4-methoxyst-
yrene ∼ 1-hexene (no reaction).
Also, for the reactions performed in aqueous media:
FeT(2-CH3Py)P(OAc) (Table S6): 4-methoxystyrene > ␣-methylsty-
rene > cyclohexene > styrene ꢀ indene ꢀ cis-cyclooctene ≥ cyclo-
octene ꢀ 1-hexene (no reaction).
FeT(3-CH3Py)P(OAc) (Table S7): 4-methoxystyrene > ␣-methylsty-
rene > cyclohexene > indene > styrene ꢀ cis-cyclooctene ∼ cyclo-
octene ꢀ 1-hexene (no reaction).
FeT(4-CH3Py)P(OAc) (Table S8): 4-methoxystyrene > ␣-methylsty-
rene > styrene > cyclohexene > indene ꢀ cyclooctene ≥ cis-cyclo-
octene ꢀ 1-hexene (no reaction).
3.3.3. The nature of active oxidant
Epoxidation of cis- and trans-stilbene, in a competitive reac-
tion, has been shown to be a useful probe to provide indirect

112
S. Zakavi, T. Mokary Yazdeli / Journal of Molecular Catalysis A: Chemical 367 (2013) 108–115
Table 5
cis/trans isomerization. This observation is indicative of significant
cleavage of the C C double bond. On the other hand, the unusual
preference of trans-stilbene over cis-stilbene observed in the com-
petitive epoxidation reaction catalyzed by FeT(3-MePy)P(OAc) and
FeT(4-MePy)P(OAc) cannot be explained by the cis/trans isomeri-
zation [27]. Nam et al. reported such an unexpected preference for
trans-stilbene over cis-stilbene in the competitive epoxidations of
cis- and trans-stilbenes catalyzed by Fe(TPFPP)Cl which was the
most electron-deficient iron porphyrin complex of the used Fe-
porphyrins [32].
Competitive oxidation of cis- and trans-stilbene in the presence of the Fe-
porphyrins.a,b
Fe-porphyrins
Cis–trans
Cis/trans
isomerizationc
epoxided
FeT(2-py)P(OAc)
FeT(3-py)P(OAc)
FeT(4-py)P(OAc)
FeTPP(OAc)
FeT(4-OCH3)P(OAc)
FeTPPS4(OAc)
FeT(2-MePy)P(OAc)
FeT(3-MePy)P(OAc)
FeT(4-MePy)P(OAc)
6.5
17.0
10.7
2.0
3.8
4.8
34.7
1.0
16.0
2.8 (3.1)
3.3 (4.2)
1.2 (1.5)
8.3 (10.1)
6.7 (7.1)
3.8 (4.0)
0.3 (1.0)
0.03 (0.04)
0.12 (0.3)
3.3.4. Relative catalytic activity of the Fe-porphyrins
Oxidation of indene with TBAP in the presence of different Fe-
porphyrins (Table 6) shows the following order of catalytic activity
of the Fe-porphyrins:
a
The molar ratios for (cis-stilbene, trans-stilbene):oxidant:ImH:catalyst are: (500,
500):170:0 or 5(see the footnotes of Table 3):1.
b
Analyzed by 1H NMR.
Obtained by control reaction using cis-stilbene, TBAO:ImH:catalyst in 500:170:0
c
Indene:
FeT(4-CH3Py)P(OAc) > FeT(3-CH3Py)P(OAc) > FeT(4-Py)
or 5 (see the footnotes of Table 3):1.
The data in parentheses show the corrected cis/trans stilbene oxide considering
the cis to trans isomerization upon the oxidation of cis-stilbene.
d
P(OAc) > FeT(2-Py)P(OAc) > FeT(4-OCH3)PP(OAc) ≥ FeT(4-SO3H)
PP(OAc) ≥ FeTPP(OAc) ≥ FeT(2-CH3Py)P(OAc) > FeT(3-Py)P(OAc).
Also, for the other olefins, the orders are as follows:
evidence on the nature of active oxidant in the metalloporphyrin
catalyzed epoxidation of olefins in the absence of non-bulky ortho-
substituents on the phenyl groups of meso tetraphenylporphyrins
[7,10,16,29]. The results of competitive oxidation of cis- and trans-
stilbene with TBAO in the presence of the Fe-porphyrins are
summarized in Table 5.
Styrene (Table S9): FeT(4-CH3Py)P(OAc) > FeT(2-CH3Py)P(OAc) ꢀ
FeT(3-CH3Py)P(OAc) > FeT(4-SO3H)PP(OAc) > FeTPP(OAc) ≥ FeT(2-
Py)P(OAc) ≥ FeT(4-Py)P(OAc) > FeT(4-OCH3)PP(OAc) > FeT(3-Py)
P(OAc).
Cyclooctene (Table S10): FeT(3-CH3Py)P(OAc) > FeT(4-SO3H)
PP(OAc) > FeTPP(OAc) > FeT(3-Py)P(OAc) > FeT(4-CH3Py)P(OAc) >
FeT(2-Py)P(OAc) > FeT(2-CH3Py)P(OAc) > FeT(4-OCH3)PP(OAc) >
FeT(4-Py)P(OAc).
Cis-cyclooctene (Table S11): FeT(4-SO3H)PP(OAc) > FeTPP(OAc) ≥
FeT(3-Py)P(OAc) > FeT(2-Py)P(OAc) > FeT(4-CH3Py)P(OAc) ≥ FeT
(2-CH3Py)P(OAc) > FeT(4-OCH3)PP(OAc) > FeT(3-CH3Py)P(OAc) >
FeT(4-Py)P(OAc).
Cyclohexene (Table S12): FeT(2-CH3Py)P(OAc) > FeT(3-CH3Py)
P(OAc) > FeT(4-CH3Py)P(OAc) > FeT(4-SO3H)PP(OAc) ≥ FeTPP(OAc)
∼ FeT(4-Py)P(OAc) > FeT(2-Py)P(OAc) ∼ FeT(3-Py)P(OAc) > FeT(4-
OCH3)PP(OAc).
4-Methoxystyrene (Table S13): FeT(4-CH3Py)P(OAc) ≥ FeT(3-
CH3Py)P(OAc) ≥ FeT(2-CH3Py)P(OAc) ꢀ FeTPP(OAc) > FeT(4-
OCH3)PP(OAc) > FeT(4-SO3H)PP(OAc) > FeT(3-Py)P(OAc) ≥ FeT(2-
Py)P(OAc) > FeT(4-Py)P(OAc).
According to the data of Table 5, the involvement of a high
valent iron-oxo porphyrin species is more pronounced in the
case of FeTPPS4(OAc), FeT(2-py)P(OAc), FeT(3-py)P(OAc), FeT(4-
py)P(OAc) and the N-methylated analogues. The observed ratio
of 1.5 for the reaction catalyzed by FeT(4-py)P(OAc), indicates
the nearly exclusive involvement of an iron-oxo moiety as the
active oxidation intermediate [7,10]. In the case of FeTPP(OAc)
and FeT(4-OCH3)P(OAc), the results are in the favor of a periodato
iron(III)porphyrin species. Also, a significant cis- to trans isomeri-
zation associated with the oxidation of cis-stilbene [7,27,28] was
observed in oxidation of cis-stilbene with periodate in the pres-
ence of FeT(2-MePy)P(OAc), FeT(3-MePy)P(OAc) and to a lesser
extent in the case of FeT(4-py)P(OAc). We have previously reported
a high cis- to trans isomerization in oxidation of cis-stilbene with
the same oxidant, using FeT(n-Pr)P(OAc) as catalyst [27]. These
remarkable isomerizations seem to be in agreement with the
involvement of a high-valent Fe-oxo species rather than a six coor-
dinate periodato one as the active oxidant; rotation about the
˛-Methylstyrene (Table S14): FeT(2-CH3Py)P(OAc) > FeT(4-
CH3Py)P(OAc) ≥ FeT(3-CH3Py)P(OAc) ꢀ FeT(4-SO3H)PP(OAc) >
FeT(3-Py)P(OAc) > FeT(2-Py)P(OAc) ≥ FeTPP(OAc) > FeT(4-OCH3)
PP(OAc) > FeT(4-Py)P(OAc).
C
C bond is expected to be more feasible in the presence of an
active oxidant with less steric hindrance around the electrophilic
oxygen atom, i.e. a metal-oxo one. While the presence of bulky
substituents at the ortho positions of the aryl groups of man-
ganese meso-tetra(aryl)porphyrins has been shown to decrease the
cis/trans isomerization [7], oxidation of cis-stilbene in the presence
of FeT(2-MePy)P(OAc) is accompanied with significant degree of
Although the result of degradation experiments showed low
oxidative stability of FeT(2-Mepy)P(OAc) and FeT(3-Mepy)P(OAc)
under reaction conditions, it is observed that a N-methylated
FeT(Py)P(OAc) is usually the most efficient catalyst of the series.
In oxidation of cis-cyclooctene, FeT(4-SO3H)PP(OAc) shows higher
catalytic activity relative to the other Fe-porphyrins. Also, while
the Fe-porphyrins with cationic meso-substituents are more effi-
cient with respect to the other catalysts in the oxidation of
styrene, FeT(4-Mepy)P(OAc) and FeT(2-Mepy)P(OAc) are substan-
tially more efficient than FeT(3-Mepy)P(OAc). In other words, there
is no close correlation between the relative catalytic performance
of the metalloporphyrins and the electronic properties of the meso-
substituents as well as the oxidative stability of the catalysts. Also,
there is large difference between the degree of dependence of the
catalytic activity of Fe-porphyrins to the electronic effects of the
meso-substituents in oxidation of various olefins. In this regard,
FeT(4-SO3H)PP(OAc) with more electron deficient groups at the
meso positions compared to FeTPP(OAc) is not necessarily a bet-
ter catalyst relative to the latter (compare their relative activity
Table 6
Oxidation of indene with TBAP catalyzed by the Fe-porphyrins.a
Fe-porphyrins
Conversion (%)
Epoxide
yield (%)
Epoxide
selectivity (%)
FeTPP(OAc)
29.616
32.756
30.857
38.102
12.285
41.842
29.378
47.701
51.025
29.616
32.756
30.857
38.102
12.285
41.842
29.378
47.701
51.025
100
100
100
100
100
100
100
100
100
FeT(4-OCH3)PP(OAc)
FeT(4-SO3H)PP(OAc)
FeT(2-Py)P(OAc)
FeT(3-Py)P(OAc)
FeT(4-Py)P(OAc)
FeT(2-CH3Py)P(OAc)
FeT(3-CH3Py)P(OAc)
FeT(4-CH3Py)P(OAc)
a
See the footnotes of Table 3 for details.

S. Zakavi, T. Mokary Yazdeli / Journal of Molecular Catalysis A: Chemical 367 (2013) 108–115
113
ImH
FeIII
SV
New catalytic cycle
ImH
-
IO3
OAc
OAc
FeIII
SII
ImH
O
-
IO3-
IO4
-
IO4
-OAc
ImH
FeIII
SIV
ImH
FeIII
FeIII
SI
SIII
(Path A)a
O
ImH
-
Aldehyde and/or ketone
or
-IO3
(Path C)c
O
New catalytic cycle
Ar-C=C
FeV
SVI
ImH
(Path B)b
Species IV
O
OH
O
(Path D)d
SVI
OH
SVI
FeIV
SVII
ImH
O
(Path B)b
(Path C)c
+ SVII
+
+
SIV
OH
OH
SVI
SVI
SVI
C
C
O
SVII
OH
CH
C
O
+
H
H
C
C
OH
C
C
+ OH
OH
OH
C
O
C
O
C
+ CH3OH + SVII
H
+ SVI
H
Scheme 1. Proposed mechanism for oxidation of different olefins with TBAP; different active oxidant species (SIII and SVI) and paths (A–D) are suggested to be involved in
the oxidation reactions. aA six coordinate periodato Fe(III) complex (i.e. SIII) is the active oxidant intermediate. b–dReactions performed with involvement of a high valent
iron(V) oxo porphyrin species (i.e. SVI) or iron(IV)–oxo porphyrin ␲-cation radicals (see Section 3.3.3 for the nature of active oxidants). In path C, H abstraction from H2O to
SVI has been suggested to be responsible of the formation of OH radical.
in oxidation of ␣-methylstyrene, indene and 4-methoxystyrene).
In comparison of the Fe-porphyrins with phenyl and pyridyl sub-
stituents it is found that in spite of the higher oxidative stability
of the latter (Table 3), with the exception of indene, the former is
a more efficient catalyst in the oxidation of the other olefins. Also,
FeT(4-OCH3)PP(OAc) with better electron donating groups relative
to those with pyridyl substituents has been usually more efficient
than the latter. However, in comparison with the corresponding
Mn-porphyrins [16], there is a better correlation between the cat-
alytic activity of the Fe-porphyrins and the electronic properties
of the meso-substituents. The order of catalytic performance of the
Mn-porphyrins with pyridyl substituents was found to decrease as
MnT(4-Py)P(OAc) > MnT(2- or 4-Py)P(OAc). Also, an unusual oxida-
tive stability was observed for the former [16]. In the case of the
Fe-porphyrins, although a similar trend of oxidative stability was
observed, but the different relative activity was found for the three
Fe-porphyrins in oxidation of different olefins. It is noteworthy that
FeT(4-Py)P(OAc) shows no catalytic activity for the oxidation of
4-methoxystyrene and ␣-methylstyrene (see Tables S13 and S14).
From the steric point of view, the steric hindrance due to the
presence of bulky methyl groups at the ortho positions [6,13]
of FeT(2-Mepy)P(OAc) was expected to decrease its catalytic
activity, compared to that of FeT(4-Mepy)P(OAc) and FeT(3-
Mepy)P(OAc). The comparison of conversion rates of the reactions
catalyzed by the three complexes shows that with the excep-
tion of indene and cyclooctene (Tables 6 and S10), in the case
of the other olefins FeT(2-Mepy)P(OAc) has a catalytic activity
greater than that of FeT(3-Mepy)P(OAc) and comparable with
that of FeT(4-Mepy)P(OAc). Accordingly, the steric hindrance
caused by the methyl groups seems to have little effects on the
catalytic performance of the complex. It should be noted that
the introduction of bulky substituents at the ortho positions of
meso-tetraarylporphyrins has been used as a strategy to improve
the stability of metalloporphyrins in oxidative condition [33].

114
S. Zakavi, T. Mokary Yazdeli / Journal of Molecular Catalysis A: Chemical 367 (2013) 108–115
However, the oxidative degradation of FeT(2-Mepy)P(OAc) is
greater than FeT(4-Mepy)P(OAc) and the three FeT(py)P(OAc)
complexes. Also, the observed significant cis- to trans isomeriza-
tion associated with the oxidation of cis-stilbene in the presence
of FeT(2-Mepy)P(OAc) shows the negligible steric hindrance of the
ortho methyl groups; the formation of trans-stilbene oxide as the
thermodynamically more stable isomer in oxidation of cis-stilbene
requires a free rotation about the alkene C C bond which is
expected to be more feasible in the case of the metalloporphyrins
with less steric strain [7].
no close correlation between the stereoelectronic properties of the
meso substituents and their catalytic activity.
4. Conclusions
In this study, the influence of the electronic properties of the
meso-substituents and the molar ratio of ImH/catalyst on the cat-
alytic activity of a series of iron porphyrin in oxidation of olefins
with TBAP was studied and the following results were obtained:
(i) ImH showed no co-catalytic activity in oxidation reactions
catalyzed by Fe-porphyrins containing pyridyl or N-methylated
pyridyl substituents at the meso-positions; (ii) in spite of the
significant increase in the catalytic performance of the other Fe-
porphyrins due to the presence of ImH, the maximum catalytic
efficiency achieved with a smaller molar ratio of ImH to catalyst
(i.e. the 5:1 molar ratio of ImH to catalyst) compared to that in the
case of the corresponding Mn-porphyrins (i.e. 10:1); (iii) as was
observed in the comparison of the Mn-porphyrins with pyridyl sub-
stituents, the oxidative stability of FeT(4-py)P(OAc) is remarkably
higher than that of FeT(2-py)P(OAc) and FeT(3-py)P(OAc). Also, the
same trend was found in the comparison of the N-methylated ana-
logues. However, N-methylation of FeT(2-, 3- or 4-py)P(OAc) led to
the substantial decrease in their oxidative stability; (v) in spite of
the lack of close correlation between the catalytic activity of the Fe-
porphyrins and the electronic properties of the meso-substituents,
in comparison with the corresponding Mn-porphyrins, there is
a better correlation between the catalytic activity of the Fe-
porphyrins and the electronic effects of the meso-groups; (vi) the
competitive oxidation of cis- and trans-stilbene, gave evidence
of the involvement of high valent Fe-oxo porphyrins as well as
periodato iron porphyrins as the active oxidants in reactions cat-
alyzed by the used iron porphyrins. However, the involvement
of a high valent iron-oxo porphyrin species is more pronounced
in the case of FeTPPS4(OAc), FeT(2-py)P(OAc), FeT(3-py)P(OAc),
FeT(4-py)P(OAc) and the N-methylated analogues; (vii) an unusual
preference of trans-stilbene over cis-stilbene observed in the com-
petitive epoxidation reaction catalyzed by FeT(3-MePy)P(OAc) and
FeT(4-MePy)P(OAc) which cannot be described by the cis/trans
isomerization; (viii) large difference has been observed in the prod-
uct distribution for oxidation reactions with TBAO performed in
dichloromethane and aqueous solvent; while in dichloromethane,
the oxidation of olefins gave the corresponding epoxide as the sole
(or nearly the exclusive) product, running the reaction in water led
to the formation of aldehyde and/or ketone as the major product;
(ix) N-methylation of FeT(py)P(OAc) at the ortho position seems to
have little steric effects on the catalytic activity of the Fe-porphyrin
as well as the degree of cis/trans isomerization in the oxidation of
cis-stilbene.
3.3.5. Proposed mechanism
According to the results of the competitive oxidation of cis-
and trans-stilbene, utilized to elucidate the nature of the active
oxidation species as well as the ratio of the high valent iron
oxo porphyrin species and the six coordinate periodato com-
plex, Fe(porphyrin)(ImH)(IO4), as the active oxidants, the product
distribution observed in the presence of the used catalysts and
the mechanistic studies performed on the iron porphyrin cat-
alyzed oxidation of hydrocarbons [34,35] a possible mechanism
(Scheme 1) is proposed for the oxidation of different olefins
with periodate in aqueous and non-aqueous conditions. Paths A
and D show the formation of epoxide with the involvement of
the Fe(porphyrin)(ImH)(IO4) species or a high valent iron oxo
porphyrin intermediate, respectively. The formation of allyl alco-
hol (in the case of cyclohexene), aldehyde and ketone may be
explained by a radical mechanism initiated by high valent iron
oxo species [33,34] through H abstraction from olefins or water.
Formation of SV which leads to the occupation of the fifth and
sixth coordination sites of the iron(III) atom causes the catalyst
deactivation [7,26,27]. H2O has been suggested (path C) to pro-
duce •OH radical in reaction with high valent iron(V) oxo porphyrin
species (SVI). However, the reduced form of this intermediate, i.e.
(porphyrin)(ImH)iron(IV) OH species may also be considered as
the source of •OH radical, needed for the formation of aldehyde
and ketone products; homolytic cleavage of the iron(IV) OH bond
gives •OH radical and the catalyst precursor (SIV).
3.3.6. A comparison between the catalytic activity of the iron and
manganese porphyrins
Very recently, we have reported the oxidation of different
olefins with TBAP in the presence of the manganese complexes
of the title porphyrins, with the exception of the N-methylated
meso-tetra(pyridyl)porphyrins [16]. In comparison with the results
obtained with the manganese porphyrins (i) FeT(2-, 3- or 4-
py)P(OAc), FeTPP(OAc) and FeT(4-OCH3)P(OAc) are more stable
toward oxidative degradation than the manganese counterparts,
although FeT(4-py)P(OAc) and MnT(4-py)P(OAc) have a compa-
rable high stability relative to the other metalloporphyrins. Also,
FeTPPS4(OAc) is as stable as the manganese complex; (ii) sim-
ilar to that observed in the case of the manganese porphyrin
series, FeT(4-py)P(OAc) and the N-methylated analogue are the
most stable iron porphyrins among the series; (iii) greater dif-
ferences were observed between the oxidative stability of FeT(2-,
3- or 4-py)P(OAc) and FeT(phenyl- or 4-methoxyphenyl)P(OAc),
compared to that observed between the manganese ones; (iv) in
spite of the crucial role of ImH on the catalytic performance of the
manganese porphyrins [16] and iron porphyrins with phenyl, 4-
sulfonatophenyl and 4-methoxyphenyl at the meso positions, the
presence of ImH has a negative effect on the activity of FeT(2-, 3- or
4-Py)P(OAc) and the N-methylated analogues; (v) the manganese
porphyrins are generally more efficient catalysts than the iron ones.
However, the iron and manganese porphyrins with pyridyl sub-
stituents may have comparable catalytic activities; (vi) similar to
that observed in the case of the manganese porphyrins, there is
Acknowledgement
Financial support of this work by the Institute for Advanced
Studies in Basic Sciences (IASBS) is acknowledged.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.molcata.2012.11.003.
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