Synthesis of dipyroromethanes in water and investigation of electronic and steric effects in efficiency of olefin epoxidation by sodium periodate catalyzed by manganese tetraaryl and trans disubstituted porphyrin complexes

Article abstract of DOI:10.1142/S108842461950038X

Condensation of pyrrole with various aldehydes in the presence of BF₃?etherate as an acid catalyst in water provides good yield of some dipyrromethanes. Prolongation of the reaction time with aldehydes substituted by electron-donating (mesityl) or electron-withdrawing (2,6-dichlorophenyl) groups on the ortho positions of the phenyl did not lead to decomposition or scrambling. Manganese trans disubstituted porphyrin complexes which derive from various dipyrromethanes and manganese tetraaryl porphyrin complexes including various substituents with different steric and electronic properties show good catalytic activity in epoxidation of alkenes by NaIO₄ in the presence of imidazole (ImH). The study of steric and electronic effects of the catalysts on the epoxidation of olefins shows that Mn-porphyrin complexes with more bulky and electron-releasing groups on meso phenyls could increase the epoxidation yield of most alkenes.

Full text of DOI:10.1142/S108842461950038X

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2019; 23: 1–8
DOI: 10.1142/S108842461950038X
Published at http://www.worldscinet.com/jpp/
Synthesis of dipyroromethanes in water and investigation
of electronic and steric effects in efficiency of olefin
epoxidation by sodium periodate catalyzed by manganese
tetraaryl and trans disubstituted porphyrin complexes
Mojtaba Bagherzadeh*a, Mohammad Adineh Jonaghania, Mojtaba Aminib
and Anahita Mortazavi-Manesha
aChemistry Department, Sharif University of Technology, Tehran, P.O. Box 11155-3615, Iran
bDepartment of Chemistry, Faculty of Science, University of Maragheh, Maragheh, Iran
Received 9 January 2019
Accepted 6 March 2019
ABSTRACT: Condensation of pyrrole with various aldehydes in the presence of BF3·etherate as an
acid catalyst in water provides good yield of some dipyrromethanes. Prolongation of the reaction time
with aldehydes substituted by electron-donating (mesityl) or electron-withdrawing (2,6-dichlorophenyl)
groups on the ortho positions of the phenyl did not lead to decomposition or scrambling. Manganese
trans disubstituted porphyrin complexes which derive from various dipyrromethanes and manganese
tetraaryl porphyrin complexes including various substituents with different steric and electronic
properties show good catalytic activity in epoxidation of alkenes by NaIO4 in the presence of imidazole
(ImH). The study of steric and electronic effects of the catalysts on the epoxidation of olefins shows that
Mn-porphyrin complexes with more bulky and electron-releasing groups on meso phenyls could increase
the epoxidation yield of most alkenes.
KEYWORDS: dipyrromethanes, porphyrin, manganese, epoxidation.
pyrrole readily undergo condensation using homogeneous
acid catalysts such as BF3·etherate, trifluoroacetic acid
INTRODUCTION
Meso or 5-substituted dipyrromethanes are important
(TFA) and propionic acid at room temperature to yield
precursors for synthesis of meso-substituted porphyrins,
meso-substituted dipyrromethanes along with oligomeric
expanded porphyrins and porphyrin analogues [1–3].
byproducts. The yields are reduced due to the formation
Meso-substituted trans-porphyrins are key structural
of oligomers and stringent purification methods are
components found in a wide range of system models in
needed to remove the byproducts [7–9].
biomimetic and material chemistry from [2 + 2] conden-
The formation of N-confused dipyrromethanes and
sation between dipyrromethane and aldehyde which
tripyrromethanes [10–13], difficulty in controlling
imply preparation of pure trans-porphyrins [4–6].
-
the time to stop the reaction when the dipyrromethane
concentration is at its maximum, large excess of
pyrrole and the distillation of the excess pyrrole
[14], decomposition of the dipyrromethane on silica,
purification problems and acidolysis of dipyrromethanes
[8, 15] are important problems in the reaction conditions
as mentioned above.
Several methods have been reported for synthesis
of 5-substituted dipyrromethanes by condensation of
aldehyde and pyrrole using various combinations of acids
and solvents. All these reports claim moderate yields of
meso-substituted dipyrromethanes. Thus, aldehyde and
In this paper, we prepared some meso-substituted
dipyrromethanes by dropwise addition of pyrrole to an
aqueous solution of aldehyde [16] in the presence of
*Correspondence to: Mojtaba Bagherzadeh, tel.: +98 21
66165354, fax: +98 21 66012983, email: bagherzadeh@sharif.
edu.
Copyright © 2019 World Scientific Publishing Company

2
M. BAGHERZADEH ET AL.
R3
The complexes were used in a catalytic system
for epoxidation of various olefins which were
carriedoutinthepresenceofimidazoleasthebest
axial ligand, tetra-n-butylammonium bromide,
Bu4NBr, as the phase transfer agent in a CH2Cl2/
H2O solvent system at ambient temperature
and NaIO4 as an oxidation agent. Steric and
electronic properties of metalloporphyrins and
alkenes substantially affect the yield of the
product and the rate of oxygenation [27, 31–36].
The effects of various axial ligands as
co-catalysts such as piperidine, pyridine, imida-
CHO
R4
R5
R2
R1
R5
R4
R1
R2
H .
O
2
+
N
BF3. etherate
H
R3
NH
HN
1(a-g)
Fig. 1. Synthesis of dipyrromethanes in water
BF3·etherate as the acid catalyst and at temperature of
70–80°C in argon atmosphere after 30–70 min (Fig. 1).
The reactions with electron-withdrawing and bulky
substituents on the phenyl group in dipyrromethanes
prevent the acidolysis and scrambling of these
compounds.
zole and lutidine were investigated in the epoxidation
of cyclooctene by Mn(BDCPDPP)OAc. Among the
co-catalysts listed above, strong π-donor ImH is the best
co-catalyst.
Metal complexes of various ligands such as oxazolines
[17, 18], Schiff bases [19–22] and porphyrins [23–25]
are recognized as catalysts for epoxidation of alkenes.
Among these catalysts, porphyrins are efficient catalysts
for epoxidation purposes as models of cytochrome P-450
enzymes [26–30]. Meso-substituted porphyrins are key
structural components found in a wide range of system
models in biomimetic and material chemistry from [2 + 2]
condensation between a dipyrromethane and an aldehyde
RESULT AND DISCUSSION
Synthesis of meso-substituted dipyrromethanes
One step synthesis of dipyrromethanes in water was
reported [16]. Success of this approach resides on the fact
that the reaction between the pyrrole and the carbonyl
compound occurs at the interface between the pyrrole
and the acidic aqueous aldehyde or ketone solution. The
release of the dipyrromethane from the aqueous layer
when it is formed forces the reaction to be completed and
protects the product from further reactions.
This method provides the corresponding dipyrro-
methanes in good to excellent yield with dropwise
addition of pyrrole to the aqueous solution of the required
aldehyde in the presence of hydrochloric acid after
30–45 min at 90°C.
derivative for preparation of pure trans-porphyrins. At
-
---
-
first, we prepared a number of porphyrins from [2 + 2]
condensation between dipyrromethane and aldehyde
which were used for preparing manganese porphyrin
complexes including: meso-tetrakis(2,6-dichlorophenyl)
porphyrinato manganese(III) acetate, Mn(TDCPP)OAc,
meso-tetra(mesityl)porphyrinato manganese(III) acetate,
Mn(TMP)OAc, 5,15-bis(2,6-dichlorophenyl)-10,20-
di-(phenyl)porphyrinato manganese(III) acetate, Mn(BD
CPDPP)OAc and 5,15-di(mesityl)-10,20-di(phenyl)por-
phyrinato manganese(III) acetate and Mn(DMDPP)OAc
(Fig. 2).
In the above-mentioned method, use of aqueous HCl
as acid catalyst and a temperature of 90°C produces
tripyrromethane and other oligomers. In the present
R4
Mn(Por)OAc
Mn(TPP)OAc
R1
H
R2
H
R3
H
R4
H
R3
R3
R1
R1
R1
R1
OAc
Mn
N
N
N
Mn(TMP)OAc
CH3
Cl
CH3
H
CH3
Cl
CH3
H
R2
R2
N
Mn(TDCPP)OAc
Mn(DMDPP)OAc
Mn(BDCPDPP)OAc
R3
R3
CH3
Cl
CH3
H
Cl
Cl
H
H
R4
Fig. 2. Meso-tetraaryl porphyrinato manganese(III) acetate and meso-trans disubstituted porphyrinato manganese(III) acetate used
as catalysts in this work
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 2–8

SYNTHESIS OF DIPYROROMETHANES IN WATER AND INVESTIGATION OF ELECTRONIC AND STERIC EFFECTS
3
Table 1. Synthesis of various dipyrromethanes in water in the
presence of BF3·etherate
Table 2. Effect of different axial ligands in the epoxidation
of cyclooctene by Mn(BDCPDPP)OAc/NaIO4a
Entry Aldehyde
Total yield of
dipyrromethane
(%)
Entry
Axial ligand
The yield of
epoxide (%)b
1
2
None
12
14
5
1a
1b
1c
1d
1e
1f
Benzaldehyde
65
85
80
70
65
75
60
Piperidine
Mesitaldehye
3
Tert-buthylamine
Pyridine
2,6-dichlorobenzaldehyde
4-bromobenzaldehyde
4
8
5
4-Methylpyridine
4-Cyanopyridin
4-Aminopyridine
2,6-Dimethylpyridine
N,N-dimethylaminopyridine
Imidazole
16
2
4-chlorobenzaldehyde
6
2-hydroxy 4-methoxybenzaldehyde
2,3,4,5,6-pentaflourobenzaldehyde
7
20
7
1g
8
9
28
78
4
10
11
12
13
14
15
16
17
study, we have used the same method for the synthesis
of dipyrromethanes in water but in the presence of the
BF3·etherate as the acid catalyst at temperature of 70°C
in nitrogen or argon atmosphere after 30–70 min (Fig. 1).
Prolonging of the reaction time for the aldehydes
1a, 1d, 1e, 1f and 1g shows no improvement in the
yield of dipyrromethane production and finally leads to
production of byproducts. For aldehydes are 1b or 1c,
yields of the reactions were high and prolongation of
the reaction time for a few minutes does not produce
any byproduct(s). Thus, it is obvious that higher yields
of dipyrromethanes were obtained in the presence of
both electron-withdrawing (2,6-dichlorophenyl) and
electron-releasing (2,4,6 trimethylphenyl; mesityl) bulky
substituents in the meso positions (Table. 1).
2-Methylimidazole
2-Ethylimidazole
1-Methylimidazole
Benzimidazole
3
5
30
18
17
6
4-Nitroimidazole
Pyridine-N-Oxide
2-Methylpyridine
aThe molar ratio for Mn(Por)OAc: axial ligand:cyclooctene:oxid
b
ant:phase transfer catalyst are 1:10:10:83:167. Determined by
GC at 60 min.
amines such as 2-metylpiperidine and tertbuthylamine
have no co-catalytic effect.
Pyridine or 4-substituted pyridines with weak π-donor
abilities or with electron-donor groups show better
co-catalytic effects than s-donor amines. The epoxidation
rate decreases in the following order:
The bulky substituents on the ortho positions of phenyl
groups on the meso or 5-position of dipyrromethanes
suppress the acidolysis of dipyrromethanes. Reaction
time for dipyrromethenes including electron-withdrawing
substituents on the phenyl groups of these compounds
(1g) is low.
N,N-Dimethylaminopyridine > 4-Aminopyridine
> 4-Methylpyridine > Pyridine > 4-Cyanopyridine
Effect of various axial ligands as co-catalysts on the
epoxidation of cyclooctene by Mn(BDCPDPP)OAc
High co-catalytic activity of 4-aminopyridine results in
a π-resonance effect of its p-NH2 group. 4-Cyanopyridine
with an electron-withdrawing CN substituent displays no
co-catalytic activity. 2-Methylpyridine and 2, 6-dimethyl-
pyridine with one or two group(s) near the nitrogen
donor atom prevent the coordination of the Mn(Por)OAc.
Therefore, they have no co-catalytic activity.
Among the nitrogenous bases, which are used as
co-catalysts,imidazoleisthebestco-catalystofthenitrogen
donors (Table 2, entry 10). Binding of 2-metylimidazole
and 2-ethylimidazole are shown in Fig. 3.
Most metal-catalyzed oxidation systems require the
addition of a base which acts as an axial ligand and
remarkably improves both the rate and the selectivity of
the reaction (proximal effect) [37, 38]. In these catalytic
systems, similar to other biomimetic catalysts based on
synthetic metalloporphyrins, presence of axial ligands
remarkably improves the rate of epoxidation [24, 39].
The effect of a number of axial ligands is examined for
the epoxidation of cyclooctene in the Mn(BDCPDPP)
OAc catalytic system (Table 2).
Binding of 2-metylimidazole and 2-ethylimidazole
to the central metal would more severely restrict
displacement of the central metal toward the strong oxo
ligand because of steric repulsion between the 2-methyl
and 2-ethyl substituents and the porphyrin ring.
In the absence of an axial ligand, 12% of cyclooctene
oxide is produced. Pure s-donor amines do not have a
co-catalytic effect. Piperidine with s-donating ability and
with low steric effect, shows great co-catalytic activity
with this Mn(Por)OAc catalyst. Sterically hindered
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 3–8

4
M. BAGHERZADEH ET AL.
O
Mn
H3C
HN
N
O
Mn
O
O
N
N
Mn
Mn
H
CH3CH2
N
B
-
HN
B=ImH, IO4
O
O
Mn
Mn
H3C
O2N
N
N
N
H3C
NH
Fig. 3. A comparison between co-catalytic effects of various imidazole axial ligands
1-methylimidazole is coordinated to the metal center
oxide is formed with higher yield and greater stability,
which indicates that there is low-hindered Mn(TPP)OAc
complex for rotation about the alkene C–C bond at some
intermediate step. In Mn(DMDPP)OAc catalysts, two
groups of trans phenyls of porphyrin have substituents
in contrast to Mn(TPP)OAc, thus steric effect is less only
for two sides of Mn(DMDPP)OAc.
without steric effects like 2-alkyl imidazole but it cannot
form a N–H….B hydrogen bond with nitrogen which has
a methyl group (Fig. 3), so it has no distal effect [39,
40]. The low co-catalyst effect of 4-nitroimidazole which
is related to its electron-withdrawing NO2 substituent
is unable to accelerate electron releasing through its
imidazole group. Thus, imidazole as a strong π donor for
its proximal and distal effects is the best axial ligand in
this catalytic porphyrin system.
Greater reactivity of 1-methylcyclohexene than cyclo-
hexene and styrene derivatives than styrene, clearly
demonstrates an electronic effect of alkenes in a
Mn(DMDPP)OAc catalyst. The long reaction time
for Mn(DMDPP)OAc reflects high steric properties
of Mn(DMDPP)OAc due to the methyl groups in ortho
positions of two trans phenyls of Mn(DMDPP)OAc.
Cis-stilbene gives only 7% trans-stilbene oxide
with Mn(DMDPP)OAc and 14% trans-stilbene with
Mn(TPP)OAc. These results imply that free rotation
about the alkene C–C bond at some intermediate step for
Mn(DMDPP)OAc, due to steric methyl groups, is more
difficult than for low hindered Mn(TPP)OAc complexes.
Mn(TMP)OAc with bulky substituents at ortho and
para positions of the aryl rings require a long reaction time
(18–24 h) for epoxidation of different alkenes. Most alkenes
are completely converted to corresponding epoxides with
Mn(TMP)OAc after a long reaction time compared to
Mn(TPP)OAc (3 h) and Mn(DMDPP)OAc (12 h) catalysts.
These observations indicate that the electronic properties
of the phenyl substituents have an important role in the
epoxidation of most of alkenes and electron-releasing
groups increase the reaction times of the catalysts.
Catalytic epoxidation of alkenes by various
Mn(Por)OAc/ImH/NaIO4 systems
The epoxidation of alkenes and hydroxylation of
alkanes catalyzed by metalloporphyrin complexes is
the subject of many investigations. The epoxidation of
alkenes has been examined with a variety of manganese
porphyrins containing different phenyl groups [30].
Comparison of the catalytic properties of five different
meso-substituted manganese porphyrins in the
epoxidation of various alkenes with NaIO4 and in the
presence of imidazole is presented in Table 3.
Comparison and investigation of epoxidation
of various alkenes with different porphyrin catalysts
InthepresenceofMn(TPP)OAc, 1-methylcyclohexene
is more reactive than cyclohexene, and for styrene
derivatives, 4-methoxystyrene is more reactive than
4-methylestyrene and styrene. Epoxidation of limonene
produces only 1,2-epoxide. All of these observations
indicate that the electronic properties of alkenes
substantially affect the rate of oxygenation. Sterically
demanding trans-stilbene shows less reactivity than the
cis isomer. Compared with the cis isomer, trans-stilbene
Epoxidation of cis- and trans-stilbene in the presence
of bulky Mn(TMP)OAc is 100% stereoselective and
leads to formation of the corresponding epoxides.
The epoxidation yield of alkenes in the presence of
Mn(BDCDPP)OAc with Cl substituents on the ortho
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 4–8

SYNTHESIS OF DIPYROROMETHANES IN WATER AND INVESTIGATION OF ELECTRONIC AND STERIC EFFECTS
5
Table 3. Epoxidation of alkenes with Mn(Por)OAc/NaIO4/imidazole at room temperaturea
Alkene
Epoxide yield (%)b
Mn(TPP)OAc
3 h
Mn(DMDPP)OAc
Mn(BDCPDPP)OAc
Mn(TDCPP)OAc Mn(TMP)OAc
3 h
12 h
3 h
6 h
24 h
3 h
24 h
Cyclooctene
Cyclohexene
1-Methylcyclohexene
Styrene
100
70
85c
40
54
51
40
60
20
24
30
15
20
10
49
25
90
100h
93
70
73
55
72
79
60
52
65
32
70
54
—
86
84
82
85
49
82
94
95
87m
85
36
98
94
24
40
34
35
25
22
25
57
19
25
3
99
76
—
85i
100
100
100
100n
100
100
100n
100n
96n
46
92
100
100
100
100d
100
59e
75
93
a-Methylstyrene
4-Methylstyrene
4-Methoxystyrene
Indene
84
72
90
86j
87k
100
54 (23)g
95
100
100
72 (20)g
63 (7)f
46
Limonene
cis-Stilbene
76 (14)f
trans-Stilbene
1-Octene
65
82l
70
82
—
12
60
trans-2-Octene
60
40
71
4
54
b
c
d
aThe molar ratios of Mn(Por)OAc:imidazole:olefin:NaIO4:n-Bu4NBr were 1:10:10:83:167. GLC yield based on starting alkene. 2 h. 150 min.
e1,2-epoxide is sole product. f Trans-stilbene oxide. g8,9-epoxide. h110 min. i5 h. j3.5 h. k4 h. l4 h. mProducts:25% 1,2-epoxide, 42% 8,9-epoxide and
20% limonene dioxide. n18 h.
positions of phenyl groups as a catalyst is higher than for
Mn(DMDPP)OAc.
The ortho substituents of the meso-phenyl rings protect
the meso-position sterically and electronically from a
bimolecularoxidationprocess.Thestabilityoffivedifferent
manganese porphyrins was studied for cyclooctene
epoxidation with NaIO4 in the presence of imidazole and
the results are illustrated in Fig. 3. The obtained results
show that the ortho substituted catalysts e.g. Mn(TDCPP)
OAc, Mn(TMP)OAc and to some extent Mn(BDCDPP)
OAc were unchanged, but intense degradation of
Mn(TPP)OAc and Mn(DMDPP)OAc was observed.
Study of stability of all catalysts in cyclooctene after
24 h by UV-vis spectroscopy illustrates that the simple
Mn-porphyrins, e.g. Mn(TPP)OAc, Mn(DMDPP)OAc
and to some extent Mn(BDCDPP)OAc with low steric
protection of both faces of the macrocycle, are more
sensitive to destruction through the meso position than
Mn(TDCPP)OAc and Mn(TMP)OAc catalysts which
have substituents on their ortho positions of porphyrin
phenyls.
We found that Mn(DMDPP)OAc was completely
destroyed after 24 h in comparison with Mn(BDCDPP)
OAc. This observation indicates that electron-releasing
groups in the ortho positions of low-hindered Mn(Por)
OAcsuchasMn(DMDPP)OAcacceleratethedegradation
of the porphyrin ring after a long time (Fig. 4).
In fact, electron-releasing or electron-withdrawing
substituents are known to provide a steric protection
to porphyrin rings against the oxidative degradation of
the complex during both thermal and photochemical
catalytic processes.
Low epoxidation yields more electron-rich and
sterically hindered alkenes such as 1-methylcyclohexene,
trans-2-octene and a-methylstyrene demonstrate that
electronic properties of alkenes are not important in the
presence of Mn(BDCDPP)OAc. In fact, electronic effects
of the catalyst are efficient for epoxidation. Epoxidation
of cis- and trans-stilbene with Mn(BDCDPP)OAc is
100% stereoselective.
The long reaction time required for the Mn(TDCPP)
OAc catalyst compared to Mn(TPP)OAc, Mn(BDCDPP)
OAc and Mn(DMDPP)OAc indicates that the steric
properties of Mn(TDCPP)OAc and low epoxide yield for
alkenes in the presence of Mn(TDCPP)OAc compared
with Mn(TMP)OAc are related to electronic effects.
Low epoxide yield for trans-stilbene in the presence of
Mn(TDCPP)OAc obviously demonstrates the effect of
steric properties of catalyst and alkenes. The Mn(TDCPP)
OAc catalyst is more active than Mn(TMP)OAc and
epoxidation of unfunctionalized alkenes was performed
by Mn(TDCPP)OAc in excellent yield. It should be
mentioned that the electronic effect of catalyst has a key
role in the epoxidation intermediate.
Investigation of stability of various Mn porphyrins
used in this work
It is well known that metalloporphyrins suffer from
oxidation at the meso-position which is followed by ring
opening [33].
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 5–8

6
M. BAGHERZADEH ET AL.
1.2
1
Mn(TPP)OAc
Mn(DMDPP)OAc
Mn(TMP)OAc
0.8
0.6
0.4
0.2
Mn(TDC)OAc
Mn(BDCPDPP)OAc
0
0
0.5
1
1.5
2
2.5
3
Time (min)
Fig. 4. Mn-(Por)OAc decomposition measured by UV-vis spectroscopy vs. time for five Mn-(Por)OAc in the epoxidation of
cyclooctene by NaIO4 and in the presence of imidazole
45
40
35
30
Epoxidation of cyclooctene with NaIO4 catalyzed
by Mn(BDCPDPP)OAc in the presence or absence
of 2,6-di tert-butyl p-cresol as an inhibitor
It has been suggested that high valent Mn-oxo species
are considered as the active intermediates during olefin
epoxidation with various single oxygen donors in
biphasic systems [32].
In a typical experiment, addition of an inhibitor in
different molar ratios to cyclooctene was performed.
Figure 5 shows the results of this experiment by use of
radical trapping experiments (with a radical scavenger,
2,6-di tert-butyl p-cresol). It was established that
intermediates with radical character are probably
involved in the epoxidation reactions.
25
20
15
10
5
0
0
0.1
0.2
0.3
0.4
0.5
0.6
mmol of inhibitor
Fig. 5. Addition of inhibitor in different molar ratio to
cyclooctene in epoxidation reaction with Mn(BDCDPP)OAc/
NaIO4/ImH for 30 min
The production of trans-stilbene oxide from cis-
stilbene with low hindered catalysts such as Mn(TPP)
OAc and Mn(DMDPP)OAc requires an intermediate
which leads to its direct formation with a cis/trans
inversion. This may be accounted for by a mechanism
involving radical intermediates.
products of oxidation reactions were determined and
analyzed by an HP Agilent 6890 gas chromatograph
equipped with a HP-5 capillary column (5% phenyl
methyl siloxane 60.0 m × 250 mm × 1.00 mm) and a
flame-ionization detector.
EXPERIMENTAL
Synthesis of dipyrromethanes
Materials
In a typical experiment, a solution of 3.6 mmol of
mesitaldehyde was added to 80 mL boiling water and
stirred under nitrogen or argon atmosphere for 15 min
at room temperature. Then 0.5 mmol BF3·etherate was
added, followed by the dropwise addition of 18 mmol
of pyrrole. After refluxing for 30–70 min, at which point
no aldehyde was detected by TLC analysis (cyclohexane/
ethyl acetate/triethylamine; 80:20:1), the suspension was\
left to cool at 40–50°C and then the reaction mixture was
diluted with CH2Cl2 (50 mL) and 50 mL NaOH (0.1 N)
in order to quench the reaction. Afterwards, the mixture
was extracted with CH2Cl2 and the organic layer was
All used compounds were purchased from Merck or
Fluka in analytical grade. Dichloromethane, chloroform,
pyrrole, benzaldehyde and ethyl acetate were distilled
before reactions.
Physical measurement
1H NMR spectra were collected by a Bruker FT-NMR
500 MHZ spectrometer using CDCl3 as solvent at
ambient temperature. UV-vis spectra were obtained
with a CARY 100 Bio spectrophotometer. The reaction
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 6–8

SYNTHESIS OF DIPYROROMETHANES IN WATER AND INVESTIGATION OF ELECTRONIC AND STERIC EFFECTS
7
dried over Na2SO4. The solvent was then removed under
reduced pressure and the resulting green dipyrromethane
product was washed with a small volume of n-hexane.
Finally, the hexane/residual pyrrole mixture was removed
under vacuum. Recrystallization (water: ethanol 4:1)
gave the dipyrromethane as white crystals (Table1).
Meso-(2,4,6 trimethylphenyl)dipyrromethane (1b).
dipyrromethanes in water was reported in this study.
Unsubstituted aldehyde requires a time control to stop
the reaction when the dipyrromethane concentration is at
its maximum level.
The steric and electronic effects of various
metalloporphyrins, alkenes and axial ligand types affect
the yield of the epoxidation of alkenes. Epoxidation of
various olefins with Mn(TPP)OAc and Mn(BDCDPP)
OAc in this catalytic system shows a high reactivity in
a short time compared to other catalysts. Therefore, the
most efficient time for epoxidation with Mn(TPP)OAc
in this catalytic system is 3 h and the electronic effect of
alkenes is effective in improving the yield of epoxidation.
Greater reactivity of the Mn(BDCDPP)OAc catalyst is
due to its steric effects. Low steric effect and electron
density of two groups of trans phenyls for Mn(DMDPP)
OAc lead to high yield epoxidation in a low reaction time
compared to more steric catalysts such as Mn(TDC)OAc
and Mn(TMP)OAc.
1
mp: 160°C, Yield (80–85%), H NMR (solvent: CDCl3
internal standard: TMS): d ppm): 2.1 (s, 6H), 2.31 (s,
)
3H), 5.94 (s, 1H, meso-H), 5.99 (m, 2H), 6.15 (m, 2H),
6.64 (m, 2H), 6.87 (s, 2H), 7.89 (brs, 2H, NH).
Meso-(2,6-dichlorophenyl)dipyrromethene (1c). mp:
98–99°C, Yellowish solid, Yield (80%), 1H NMR: d
)
ppm): 6.05–6.10 (m, 2H), 6.20 (m, 2H), 6.52 (s, 1H,
meso-H), 6.73–6.77 (m, 2H), 7.13–7.15 (m, 1H), 7.36–
7.37 (d, 2H), 8.28 (bs, 2H, 2NH).
Synthesis of porphyrin ligands and Mn(Por)OAc
complexes
Epoxidation of trans-stilbene by all the catalysts and
epoxidation of cis-stilbene by Mn(BDCDPP)OAc and
the more hindered catalysts, i.e. Mn(TMP)OAc and
Dipyrromethanes 1b and 1c were selected for
synthesis of desired tetraaryl and trans disubstituted
porphyrins. The [2 + 2] condensation reaction between
dipyrromethane and aldehyde was used for preparing pure
tetraaryl and trans disubstituted porphyrins. Synthesis
and characterization of these complexes have been
reported in the literature [37]. We have used literature for
synthesis of manganese porphyrins [38].
It has been observed that when the dipyrromethane
contains an electron withdrawing substituent such as
meso-(2,6-dichlorophenyl)dipyrromethane, high yields
of porphyrins were obtained.
Mn(TDCPP)OAc, are 100% stereospecific It should be
.
mentioned that only pure epoxides of these isomeric
forms are obtained. Whereas cis-stilbene epoxidation
by Mn(DMDPP)OAc and the low hindered catalysts,
i.e. Mn(TPP)OAc lead to a mixture of cis- and trans-
stilbene oxide. These results and the high reactivity of
cis- and trans-stilbene with respect to the trans isomer
can be interpreted by the more difficult approach of
the trans isomer to oxidizing active species. This is
due to the unfavorable interactions between the olefin
and porphyrin substituents. Furthermore, with the aim
of increased catalyst stability, the stability of various
Mn porphyrins used in this work were studied. In fact,
electron-releasing or electron-withdrawing substituents
are known to provide a steric protection to the porphyrin
ring against the oxidative degradation of the complex
during both thermal and photochemical catalytic
processes. More hindered catalysts such as Mn(TMP)
OAc and Mn(TDCPP)OAc are more stable than the low
hindered catalysts in epoxidation reactions because of the
protection of the meso positions of porphyrin rings by
these hindered groups.
Epoxidation of alkenes
Typically, for alkene epoxidation, a solution of
Mn(Por)OAc (0.003 mmol) in CH2Cl2 (2mL), tetra-n-
buthylammonium bromide (0.03 mmol) as the phase
transfer catalyst, imidazole (0.03 mmol) and substrate
(0.25 mmol) were successively added and then a
solution of NaIO4 (0.5 mmol in 5 mL water) was added
to the resulting mixture and the two phases were stirred
thoroughly for an appropriate time at room temperature.
Formation of products and consumption of substrates
were monitored by GC and compared with authentic
samples.
Acknowledgments
CONCLUSIONS
We are grateful to the Faculty of Chemistry of Sharif
University of Technology for financial support of this
project.
In the present research, we prepared some meso-
substituted dipyrromethanes by dropwise addition of
pyrrole to an aqueous solution of aldehyde. It should be
mentioned that high yields of dipyrromethane production
in aqueous media were obtained in the presence of
electron-donating, electron-withdrawing and sterically
bulky substituents on ortho positions of phenyls of
aldehydes that protect dipyrromethanes from acidolysis
or scrambling. In other words, one-step synthesis of
REFERENCES
1. Jasat A and Dolphin D. Chem. Rev. 1997; 97:
2267–2340.
2. Rohand T, Dolusic E, Ngo TH, Maes W and Dehaen
W. Arkivoc 2007; 10: 307–324.
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 7–8

8
M. BAGHERZADEH ET AL.
3. Saito S and Osuka A. Angew. Chem., Int. Ed. 2011;
50: 4342–4373.
24. Bagherzadeh M and Mortazavi-ManeshA. J. Coord.
Chem. 2015; 68: 2347–2360.
4. Richard G and Lindsey JS. Tetrahedron 2004; 60:
11435–11444.
5. Nagarajan S and Gourdon A. Arkivoc 2009; 10:
312–317.
25. Castro KADF, Rodrigues JMM, Mendes RF, Neves
GPMS, Simões MMQ, Cavaleiro JAS, Almeida FA,
Tomé JPC and Nakagaki S. J. Catal. 2016; 344:
303–312.
6. Gryko DT and Tasior M. Tetrahedron Lett. 2003;
44: 3317–3321.
7. Naik R, Joshi P, Kaiwar SP and Deshpande RK.
Tetrahedron 2003; 59: 2207–2213.
8. Vigmond SJ, Chang MC, Kallury KM and Thomp-
son M. Tetrahedron Lett. 1994; 35: 2455–2458.
9. Ló SM, Ducatti DR, Duarte MER, Barreira SM,
Noseda MD and Gonçalves AG. Tetrahedron Lett.
2011; 52: 1441–1443.
10. Zhao H, Liao J, Ning J, Xie Y, Cao Y, Chen L,
Yang D and Wang B. Adv. Synth. Catal. 2010; 352:
3083–3088.
11. Ka JW and Lee CH. Tetrahedron Lett. 2000; 41:
4609–4613.
12. Rao PD, Littler BJ, Geier JR and Lindsey JS. J. Org.
Chem. 2000; 65: 1084–1092.
13. Lindsey JS. Acc. Chem. Res. 2010; 43: 300–311.
14. Durantini EN and Silber JJ. Syn. Commun. 1999;
29: 3353–3368.
26. De Montellano PRO, (Ed.). Cytochrome P450:
Structure, Mechanism, and Biochemistry, Kluwer
Academic/Plenum Publishers: New York, 2005.
27. Bagherzadeh M and Mortazavi-Manesh A. RSC
Adv. 2016; 6: 41551–41560.
28. Bagherzadeh M and Mesbahi E. J. Porphyrins
Phthalocyanines 2018; 22: 972–980.
29. Hajimohammadi M, Mofakham H, Safari N and
Mortazavi Manesh A. J. Porphyrins Phthalocya-
nines 2012; 16: 93–100.
30. Laha JK, Dhanalekshmi S, Taniguchi M, Ambroise
A and Lindsey JS. Org. Process Res. Dev. 2003; 7:
799–812.
31. De Visser SP and Nam W. In Handbook of Porphy-
rin Science. Kadish KM, Smith KM and Guilard R.
(eds). World Scientific Publishing,Singapore, 2010,
Vol. 10, pp. 85–140.
32. Arasasingham RD, He GX and Bruice TC. J. Am.
Chem. Soc. 1993; 115: 7985–7991.
15. Adler AD, Longo FR, Finarelli JD, Goldmacher J,
Assour J and Korsakoff L. J. Org. Chem. 1967; 52:
827–836.
33. Battioni P, Renaud JP, Bartoli JF, Artiles MR, Fort
M and Mansuy D. J. Am. Chem. Soc. 1988; 110:
8462–8470.
16. SobralAJFN, Rebanda NGCL, Silva MD, Lampreia
SH, Silva MR, Beja AM, Paixao JA and Gonsalves
AMDAR. Tetrahedron Lett. 2003; 44: 3971–3973.
17. Bagherzadeh M, Tahsini L, Latifi R and Woo LK.
Inorg. Chim. Acta 2009; 362: 3698–3702.
18. Bagherzadeh M. Latifi R and Tahsini L. J. Mol.
Catal. A: Chem. 2006; 260: 163–169.
34. Collman JP, Brauman JI, Meunier B, Hayashi T,
Kodadek T and Raybuck SA. J. Am. Chem. Soc.
1985; 107: 2000–2005.
35. Nam W. Kim I, Lim MH, Choi HJ, Lee JS and Jang
HG. Chem. — Eur. J. 2002; 8: 2067–2071.
36. Groves JT and Stern MK. J. Am. Chem. Soc. 1987;
109: 3812–3814.
19. Li Z, Liang L, Yang L, Chena H and Zhoua X.
J. Mol. Catal. A: Chem. 2005; 235: 108–113.
20. Bagherzadeh M, Amini M, Parastar H, Jalali-Heravi
M, Ellern A and Woo LK. Inorg. Chem. Commun.
2012; 20: 86–89.
21. Bagherzadeh M, Ataie S, Mahmoudi H and Janczak
J. Inorg. Chem. Commun. 2017; 84: 63–67.
22. Rayati S, Zakavi S, Koliaei M, Wojtczak A and
Kozakiewicz A. Inorg. Chem. Commun. 2010; 13:
203–207.
37. Halterman RL and Mei X. Tetrahedron Lett. 1996;
37: 6291–6294.
38. AdlerAD, Longo FR, Kampas F and Kim J. J. Inorg.
Nucl. Chem. 1970; 32: 2443–2445.
39. Mohajer D, Karimipour G and Bagherzadeh M.
New J. Chem. 2004; 28: 740–747.
40. Yuan LC and Bruice TC. J. Am. Chem. Soc. 1986;
108: 1643–1650.
23. Alemohammad T, Safari N, Rayati S, Gheidi M,
Mortazavimanesh A and Khavasi H. Inorg. Chim.
Acta 2015; 434: 198–208.
Copyright © 2019 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2019; 23: 8–8