Partial and full β-bromination of meso-tetraphenylporphyrin: Effects on the catalytic activity of the manganese and nickel complexes for photo oxidation of styrene in the presence of molecular oxygen and visible light

Article abstract of DOI:10.1016/j.jorganchem.2020.121464

A series of β-brominated meso-tetraphenylporphyrins, H₂TPPBr_x (x = 0, 4, 8) have been synthesized and the photocatalytic activity of their manganese (III) and nickel (II) complexes in photo oxidation of styrene was thoroughly investi

Full text of DOI:10.1016/j.jorganchem.2020.121464

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Partial and Full β-Bromination of meso-Tetraphenylporphyrin: Effects
on the Catalytic Activity of the Manganese and Nickel Complexes for
photo oxidation of styrene in the presence of molecular oxygen and
visible light
Saeedeh Saadati , Milad Esfandiar
PII:
S0022-328X(20)30366-1
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Highlights
 A series of β-brominated meso-tetraphenylporphyrins, H2TPPBrx
(x = 0, 4, 8) have been synthesized and the photocatalytic activity
of their manganese (III) and nickel (II) complexes in photo
oxidation of styrene was thoroughly investigated.
 A new green method was developed for photocatalytic oxidation of
styrene, using molecular oxygen in the presence of visible light.
 UV-VIS and 1H- NMR techniques were used to characterize the
synthesized catalysts.
 The effect of solvent and bromination degree was studied on the
catalytic activity and stability of sensitizers.
 The effect of bromination on the stability of synthesized catalysts
and their photocatalytic oxidation was examined.
1

Partial and Full β-Bromination of meso-Tetraphenylporphyrin: Effects on the
Catalytic Activity of the Manganese and Nickel Complexes for photo
oxidation of styrene in the presence of molecular oxygen and visible light
Saeedeh Saadati1, Milad Esfandiar2*
1. Department of Chemistry, K.N. Toosi University of Technology, P.O. Box 163151618, Tehran,
15418, Iran
2. Department of Mechanical Engineering, K.N. Toosi University of Technology, P.O. Box
163151618, Tehran, 15418, Iran
Abstract
A series of β-brominated meso-tetraphenylporphyrins, H2TPPBrx (x = 0, 4, 8) have
been synthesized and the photocatalytic activity of their manganese (III) and nickel
(II) complexes in photo oxidation of styrene was thoroughly investigated. The
green photo oxidation process was done using molecular oxygen and in the
presence of visible light. The effect of solvent and bromination degree was studied
on the catalytic activity and stability of sensitizers. Based on the obtained results,
free base porphyrins showed better catalytic activity among metallated
counterparts and the order of catalytic activity was as follows:
H2TPPBr4>H2TPPBr8>H2TPP. The order for Ni and Mn metallated porphyrins was
also
obtained
as:
NiTPPBr8>NiTPPBr4>NiTPP
and
MnTPPBr4(OAc)>MnTPP(OAc)>>>MnTPPBr8(OAc), respectively. According to
the stability studies, significant increase was observed after addition of metal in
porphyrin structure; i.e. more than 80% in the case of Ni. Finally, a mechanism
was proposed for photo oxidation of styrene in the presence of H2TPP porphyrin.
* Corresponding author. K.N. Toosi University of Technology, No. 17, Pardis St., Mollasadra Ave., Vanak Sq.,
Tehran 19395-1999, Iran
E-mail address: miladsfandyar2000@gmail.com
Fax: (0098-21)88674748
2

Keywords: β-brominated porphyrins, Photo oxidation, Styrene, molecular oxygen
1. Introduction
Porphyrins, which are characterized by a large number of electrons extended over
the macromolecule have been widely studied in the past two decades. Nonlinear
optical properties as well as possible applications in photosynthesis, transport and
storage of oxygen, electron transfer and biomedical applications bring them to the
center of attentions [1-8]. Various functionalized porphyrins are prepared by
regioselective substitution of meso or beta carbon atom positions [9-11]. One of
the most exploited porphyrins is meso-tetraphenylporphyrin prepared by
substitution of phenyl groups in the meso-positions with versatile applications in
medicine, electronics and optics [12-15]. The physicochemical properties of meso-
tetraphenylporphyrins are highly sensitive to introduction of any substituent (e.g.
bromination, chlorination, nitration and etc.) in beta-positions. In this regard, there
have been an interest for designing different brominated meso-
tetraphenylporphyrin as well as their metalloporphyrins complexes especially due
to the electron-withdrawing nature of final macrocycle, which is desirable for
catalytic applications.
Catalytic activity of meso-tetraphenylporphyrins in oxidation reactions has been
widely studied during the past decade. Oxidation reactions of alkyl benzenes,
cycloalkanes, olefins, alcohols and ketones are the most endeavored reactions. For
instance, Shalit et. al [16] designed an iron meso-tetraphenylporphyrin chloride
(Fe[TPP]Cl) complex as a selective catalyst for oxidative cross-coupling of
phenols. Halogenated meso-tetraphenylporphyrin Mn(III) complexes were also
used as an efficient catalyst for synthesis of polycarbonates and cyclic carbonates
[17]. Nickel(II) tetraphenylporphyrin was also acted as an efficient photocatalyst
for maleimide annulation reactions. According to the observed results, the
3

performance was superior compared to the metal-based photocatalysts in terms of
ready availability and excited state redox properties [18]. Metalloporphyrins has
been used for the treatment of cancer and dermatological disease through
phoyodynamic therapy (PDT), and advanced materials for engineering molecular
antenna for harvesting solar energy [19]. Despite the great potential of
metalloporphyrins complexes as catalyst, the major concern of the community is
avoiding the use of pollutant co-oxidants or co-catalyst. The need of maintainable
advancement in compound industry has persistently caused to notice discover
safe, natural agreeable and atom-economic compound procedures, Thereafter, there
is a huge demand for green oxidants in catalytic oxidation reactions. Among the
mostly common used oxygen donors (e.g. hydrogen peroxide, alkyl peroxides,
sodium hypochlorite and oxygen), the molecular oxygen is, definitely, the most
attractive mainly due to its abundance and easy handling [20, 21, 22]. Also
researches have proposed utilizing engineered polymers as an option because of
their wide synthetic assorted variety and generally straight forward control. There
is a report of new approach to plan arrangement controlled and stereospecific
oligomers chain development and successive photoinduced RAFT single unit
monomer inclusion (Photograph –RAFT SUMI). [23]
In this study, a new green method was developed for photocatalytic oxidation of
styrene using β-brominated meso-tetraphenylporphyrins. Molecular oxygen in the
presence of visible light was used to study the catalytic activity of manganese(III)
and nickel(II) complexes of β-brominated meso-tetraphenylporphyrins, H2TPPBrx
(x =0, 4, 8), in photo oxidation of styrene. The effect of bromination on the
stability of synthesized catalysts and their photocatalytic oxidation was examined.
4

2. EXPERIMENTAL
2.1. Materials and methods
Bruker FT-NMR 300 (300 MHz) spectrometer was used for 1H NMR spectroscopy
in CDCl3 solution (see Table1 and Table 2). The remaining CHCl3 in conventional
99.8 atom% CDCl3 creates a signal at d = 7.26 ppm, which was utilized for the
calibration of the chemical shift scale. The electronic absorption spectra were
recorded on a single beam spectrophotometer (Camspect, UV-M330) in CH2Cl2,
EtOH or DMF. Gas chromatographic analyses were performed on Agilent
Technologies GC-7890B flame ionization detector (FID) with a HB-5 capillary
column.
Table 1. The 1H NMR data of H2TPPBrx (x= 0,4,8 )
Porphyrins
H2TPP
ß-Pyrrole (ppm)
8.85 (s,8H)
o-Phenyl (ppm)
8.20-8.24
(m,8H)
m,p-Phenyl (ppm)
7.73-7.77
(m,12H)
N-H (ppm)
-2.77
(s,2H)
H2TPPBr4
H2TPPBr8
8.69 (s,4H)
8.16-8.19
(m,8H)
7.70-7.90
(m,12H)
-2.82
(s,2H)
8.13-8.15
(m,8H)
7.72-7.75
(m,12H)
-1.25
----
(broad,2H)
5

Table 2. The 1H NMR data of NiTPPBrx (x= 0,4,8 )
Porphyrins
NiTPP
ß-Pyrrole (ppm)
8.74 (s,8H)
o-Phenyl (ppm)
8.13-8.20
(m,8H)
m,p-Phenyl (ppm)
7.73-7.77
N-H (ppm)
----
(broad,12H)
7.65-7.91
NiTPPBr4
NiTPPBr8
8.54-8.85 (s,4H)
8.18-8.37
(m,8H)
----
----
(m,12H)
8.00-8.10
(m,8H)
7.75-7.90
----
(m,12H)
All of the chemicals and solvents were purchased from Merck Company and were
employed without extra purification.
2.1. Synthesis
A schematic for preparation of brominated porphyrins and metalloporphyrins can
be seen in Scheme1.
6

Scheme1. Preparation of brominated porphyrins and metalloporphyrins.
Synthesis procedures of porphyrins and metalloporphyrins are as follow:
2.2.1. H2TPP
Freshly distilled pyrrole (2.58 ml, 37 mmole) and benzaldehyde (3.87 ml, 37
mmole) are added to 25 ml of refluxing propionic acid. After refluxing for 90
minutes, the solution is cooled to room temperature and filtered and the filter cake
is washed with methanol and hot water. The resulting purple crystals are air dried
and finally dried in vacuum oven.
2.2.2. H2TPPBrx (x = 2, 4)
First 250 mgr (0.4 mmole) H2TPP was dissolved in 20 ml of chloroform. Then 144
mgr (0.8 mmole) of freshly crystallized N-bromosuccinimide (NBS) was added to
7

this solution. The reaction left stirring for 24 hrs. The formation of Soret band at
423 nm is the indication of H2TPPBr2 formation (see Table 3). For the synthesis of
H2TPPBr4, 250 mgr (0.4 mmole) H2TPP was dissolved in 20 ml of chloroform.
Then 288 mgr (1.6 mmole) of freshly crystallized NBS was added to this solution.
The reaction left stirring for 24 hrs. The formation of Soret band at 436 nm is the
indication of H2TPPBr4 formation.
Table 3. The soret and Q (0,0) bands of H2TPPBrx (x= 0,4,8 ) in comparison with the bands
of H2TPP
Porphyrins
Soret band
λ(nm)
418
Q(0,0) band
λ(nm)
646
H2TPP
H2TPPBr4
∆ⱴ (cm-1)a
H2TPPBr8
∆ⱴ (cm-1)
440
683
1196
469
838
745
2601
2057
a
7
∆ⱴ= 10 (
) relative to the corresponding band of H2TPP
⁄
⁄
8

2.2.3. NiTPP
First 0.3 gr (0.3 mmole) of pure H2TPP was added to 20 ml of refluxing
dimethylformamide (DMF). Then, 0.8 gr (3 mmole) Ni(OAc)2.4H2O) was added to
the solution and kept refluxing for 2 hrs.
2.2.4. NiTPPBrx (x = 2, 4, 6, 8)
0.13 gr (0.13 mmole) NiTPP was dissolved in 20 ml chloroform and 0.07 gr (0.4
mmole) of freshly crystallized NBS was added to the solution. The reaction left
stirring for 24 hrs. The formation of Soret band at 424 nm is the indication of
NiTPPBr2 formation. For the synthesis of NiTPPBr4, 0.13 gr (0.13 mmole) NiTPP
was dissolved in 20 ml chloroform and 0.14 gr (0.8 mmole) of freshly crystallized
NBS was added to the solution. The reaction left stirring for 24 hrs. The formation
of Soret band at 428 nm is the indication of NiTPPBr4 formation. For the synthesis
of NiTPPBr6, a solution containing 1.0 gr (1.5 mmole) NiTPP was prepared in 60
ml 1,2-dichlrobenzene and 1.58 gr (9.0 mmole) freshly crystallized NBS was
added to this solution and left refluxing for 3-4 hrs. Shifting of Soret band from
414 nm to 440 nm is the indication for NiTPPBr6 formation (see Table 4). For the
synthesis of NiTPPBr8, a solution containing 1.0 gr (1.5 mmole) NiTPP was
prepared in 60 ml 1,2-dichlrobenzene and 3.20 gr (18.0 mmole) freshly crystallized
NBS was added to this solution and left refluxing for 2-3 hrs. Shifting of Soret
band from 414 nm to 445 nm is the indication for NiTPPBr8 formation.
9

Table 4. The soret and Q (0,0) bands of NiTPPBrx (x= 0,4,8 ) in comparison with the bands
of NiTPP
Porphyrins
NiTPP
Soret band λ(nm)
Q(0,0) band λ(nm)
414
428
790
445
1682
527
545
626
555
957
NiTPPBr4
∆ⱴ (cm-1)a
NiTPPBr8
∆ⱴ (cm-1)
2.2.5. NiTPPBrn (n = 6, 8)
For demetallization of nickel porphyrins, 400 mgr of Ni(TPPBrn) was dissolved in
100 ml of CH2Cl2 and 30 ml of H2SO4 (98%) was slowly added to the solution.
This solution was kept stirring for 1-2 hrs.
2.2.6. H2TPPBrx (x = 6, 8)
The same procedure as 2.2.5 was used.
2.2.7. MnTPP(OAc)
1 mmole H2TPP was added to 50 ml of refluxing DMF. Then, 0.8 gr (3 mmole)
Mn(OAc)2.4H2O) was added to the solution and kept refluxing for 2 hrs.
2.2.8. MnTPPBrX(OAc) (x= 2, 4, 8)
For x= 2, 4: 0.11 gr (0.13 mmole) H2TPPBr2 was dissolved in 30 ml chloroform
and 0.25 gr (1.04 mmole) Mn(OAc)2.4H2O) which was dissolved in minimum
amount of methanol was added to the solution and kept refluxing for 2 hrs. For x=
10

8: 0.02 gr (0.13 mmole) H2TPPBr2 was dissolved in 30 ml chloroform and 0.04 gr
(0.1 mmole) Mn(OAc)2.4H2O) which was dissolved in minimum amount of
methanol was added to the solution and kept refluxing for 2 hrs (see Table 5).
Table 5. The soret and Q (0,0) bands of MnTPPBrx(OAc) (x= 0,4,8 ) in comparison with
the bands of MnTPP(OAc)
Porphyrins
MnTPP(OAc)
MnTPPBr4(OAc)
∆ⱴ (cm-1)
Soret band λ(nm)
Q(0,0) band λ(nm)
479
488
380
476
1682
618
641
580
MnTPPBr8(OAc)
∆ⱴ (cm-1)
683
1540
2.2. General oxidation procedure
In a model experiment, 2.5× 10-6 mole of porphyrins and metalloporphyrins were
added to styrene (1× 10-2 mole) in a glass tube without any other solvent. Oxygen
was bubbled via the solution and the sample was irradiated in the presence of
visible light (fluorescent circular lamp, 22 W and 230 V) and (λ > 350 nm) for 6–
72 h at 25 °C; the sample was kept 3 cm from center of the lamp. The products
were identified by GC-chromatography. Scheme 2 shows major products of the
photo oxidation of styrene that used in this study.
Scheme 2. Photocatalytic oxidation of Styrene by molecular oxygen in the presence of
porphyrin or metalloporphyrin sensitizers in solvent free condition at 25 °C
11

3. Results and discussions
The photocatalytic oxidation of styrene in the presence of porphyrin and
metalloporphyrin sensitizers [Mn (III)(TPPBrx)OAc (x = 0, 4 and 8) ] and
[Ni(II)(TPPBrx) (x = 0, 4, and 8)] were thoroughly studied and compared. In the
photocatalytic oxidation process, we used molecular oxygen as a green oxygen
donor and studied the degree of bromination on the photocatalytic oxidation of the
Mn-porphyrin and Ni-porphyrin. Scheme 3 shows the structures of sensitizers
employed in this study.
Scheme3. Free-base (H2TPP, H2TPPBr4 and H2TPPBr8) and their metalated (Mn, and Ni)
porphyrins sensitizers.
12

3.1. The optimal amount of sensitizer
At first, In order to find the optimal conditions for the photo oxidation process,
styrene was selected as a model of the alkene family and meso-tetra
phenylporphyrin (H2TPP) as a sensitizer was used in different concentrations. The
results are presented in Table 6.
Table 6. The effect of different amount of H2TPP in Photo oxidation of styrene in solvent
free conditiona
Entry Styrene/ Cat
Cat: H2TPP
0.25×10-6
2.5×10-6
Conversion % Selectivity % (benzaldehyde) TON*
1
2
3
40000
4000
400
1.3
64
69
60
548
266
9.32
6.66
2.33
25×10-6
* Turnover number
a Photo oxidation of 0.01 mole styrene by O2 in the presence of H2TPP as the photosensitizer
under visible light in 24 hrs reaction time
As shown in Table 6, the highest conversion percentage and also the best
selectivity for benzaldehyde was obtained in (1/4000) styrene to catalyst ratio. So
this ratio was used for all future experiments in the present study.
3.2. The effect of metal in photo oxidation reaction
As mentioned earlier, most porphyrin derivatives in natural environments are
metallic porphyrins due to their tunable photochemical properties. In order to study
the effect of metal in photo oxidation reaction of styrene, nickel and manganese
metals were selected. The photo oxidation reaction of styrene in the presence of
metallic porphyrins was carried out using visible light in free solvent conditions
within 72 hrs. The results are presented in Table 7.
13

Table 7. The effect of metal in Photo oxidation of styrene in optimal concentration in
solvent free conditiona
Entry
Catalyst
H2TPP
Conversion %
4.03 (3.08)b
1.34
Selectivity% (benzaldehyde)
TON
161( 123 )
53
1
2
3
67(79)
72
NiTPP
MnTPP(OAc)
2.28
57
91
a Sensitizers (2.5× 10-6 mole), styrene (0.01 mol and sub/cat = 4000) in 72 hrs reaction time.
b Conversion after 48 hrs reaction time.
According to the obtained results, the highest conversion percentage after 72h
irradiation was obtained with non-metallic porphyrin (H2TPP), while NiTPP
showed the best selectivity for benzaldehyde. In the case of metallated porphyrins,
manganese porphyrin exhibited better activity than nickel-porphyrin. The order of
activity of porphyrins in the photo oxidation reaction of styrene in the presence of
visible light is as follows: H2TPP>NiTPP<MnTPP(OAc)
3.3. Effect of bromination degree at the β positions on catalytic properties
It is well known that the halogenated metalloporphyrins are more robust to
oxidative degradation and show enhanced catalytic activities compared to their
non-halogenated complement [24-26]. The higher metal3+/metal2+ reduction
potential of these halogenated derivatives is the main motivation for developing
plentiful metalloporphyrins with polyhalogen substituents for various catalytic
oxidation systems. In order to study the effect of bromination degree on the
catalytic activity of H2TPP and their Mn and Ni metallated porphyrins, photo
oxidation of styrene was carried out in the presence of visible light and under
moderate condition of O2 blubbing. Figure 1 shows the catalytic activity of
14

H2TPPBrx (X= 0, 4, and 8), MnTPPBrx(OAc) (x = 0, 4, and 8) and NiTPPBrx (X=
0, 4,and 8) in solvent free condition after 72h irradiation.
Fig. 1. The effect of the number of bromine atom on the catalytic activity of porphyrins and
metalloporphyrins in solvent free condition after 72h irradiation.
Based on the obtained results (Fig.1), the catalytic activity of porphyrin sensitizers
was obtained as follows: H2TPP>MnTPP>NiTPP in solvent free condition. It is
worth mentioning that among metallated porphyrins, Mn porphyrins showed better
activity than Ni porphyrins.
3.4. Solvent effect
The effect of bromination degree on activity of porphyrins and metalloporphyrins
in photo oxidation of styrene was also studied in acetonitrile solvent during 24 hrs
and 48 hrs. The results are summarized in Table 8.
15

Table 8. The effect of bromination degree in photo oxidation of styrene using different
sensitizers in the presence of acetonitrile as solventa.
Entry
1
Catalyst
H2TPP
Conversion% Selectivity%(benzaldehyde)
TON
4.74(4.78)b
0.27(0.65)b
0.26(0.58)b
0.72(1.4)b
78(52)c
53(22)c
53(65)c
81(73)c
53(53)c
53(60)c
50(57)c
55(53)c
53(48)c
189(191)d
2
3
4
5
6
7
8
9
H2TPPBr4
H2TPPBr8
10(26)d
10(23)d
28(56)d
12(18)d
6(16)d
5(19)d
8(9)d
NiTPP
NiTPPBr4
0.31(0.45)b
0.16(0.40)b
0.14(0.48)b
0.21(0.24)b
0.24(0.34)b
NiTPPBr8
MnTPP(OAc)
MnTPPBr4(OAc)
MnTPPBr8(OAc)
9(13)d
a Sensitizers (2.5× 10-6 mole), styrene (0.01 mole and sub/cat = 4000), 24 hrs reaction time.
b Conversion after 48h irradiation.
c Selectivity after 48h irradiation.
d TON after 48 h irradiation.
Based on the obtained results, it is observed that the presence of bromine has a
negative effect on the catalytic activity of free base porphyrin sensitizers. In the
steady-state conditions of the air and the visible light and in the presence of
acetonitrile, the catalytic activity of porphyrin sensitizers was obtained as follow
H2TPP> H2TPPBr4>H2TPPBr8 while the NiTPP sensitizer showed the highest
conversion percentage and the highest selectivity versus benzaldehyde (Table 8,
entry 4), bromine had negative effect on Ni(II) porphyrins (Table 8, entries 4, 5
and 6) the catalytic activity of porphyrin sensitizers in the steady-state conditions
16

of the air and the visible light in acetonitrile solvent and the arrangement of
porphyrin activity was obtained as follows: NiTPP>NiTPPBr4>NiTPPBr8.
After 48 hours of reaction, MnTPP(OAc) sensitizer showed the highest conversion
percentage and the highest selectivity of benzaldehyde among Mn(III) porphyrins
and bromine showed positive effect on photo oxidation of styrene (Table 8, entries
7, 8 and 9) as follows:
MnTPPBr8(OAc)>MnTPPBr4(OAc)>MnTPP(OAc)
It is worth mentioning that the obtained results in the presence of solvent, is in
consistent with previous studies that solvents may enhance conversion percent in
photo oxidation reactions [27-30].
3.5. The stability of porphyrin sensitizers
The effect of metal on the stability of porphyrin sensitizers was investigated by
examining UV-Vis spectrum at room temperature and solvent-free conditions. For
the stability study, 2.5×10-6 mole of porphyrin and metalloporphyrin sensitizer and
0.01 mole of styrene were used. According to the UV-Vis spectrum seen in Fig.2,
H2TPP (Fig2(a)) was degraded 94% after 24 hrs of the photo oxidation reaction
while Mn (Fig2(b)) and Ni (Fig2(c)) porphyrins were degraded 23% and 10%,
respectively in the same time. Thus significant stability can be obtained by adding
metal in porphyrin structure.
17

Fig.2 . Stability of porphyrin sensitizers (a) H2TPP, (b) MnTPP(OAc) and (c)
NiTPP after 24 hrs in the solvent free conditions.
18

3.6. Proposed mechanism for photo oxidation of styrene in the presence of
H2TPP
According to the proposed mechanism Scheme 4, In the absence of metal, the
following mechanism can be found when free base porphyrin (H2TPP) is used as a
sensitizer in the reaction of photo oxidation leads to the formation of a single
oxygen, which proceeds from another photochemical pathway.
In the first, a photosensitizer is converted to the lowest single-excitation mode by
absorbing a certain amount of visible light (1PS*), then follow by intersystem
crossing (ISC) sensitizer converted into a triple excited state (3PS*), if energy of
this excited state is as large as about 96 kJ/mole, this amount of energy can be
absorbed by the oxygen in ground state (3Σ-g) and by the electronic excitation
energy transfer (EET) cause formed the lowest excited single oxygen state (1Δg)
+
and the second excited state of oxygen, (1Σg ). The energy of the singlet state or the
triplet state of oxygen is transmitted by photo-induced electron transfer by the light
(PET) into the ground state of oxygen(3Σ-g), and the molecular oxygen is converted
into an anion of superoxide which is a very active radical [31]. Then the anion
peroxide enters the CH bond and forms the radical (Scheme4,I) then with loss of
the radical OH make epoxide (Scheme4,II), which is highly active, and after an
electron transfer, it produces acetophenone. Also, epoxide (Scheme4,II) can absorb
radicals from the environment and forming another radical species (Scheme4,III),
and then with the breakdown of the bonding and exhaust of formaldehyde, the
dominant product (benzaldehyde) is made [32, 33].
19

Scheme4. Proposed mechanism for photo oxidation of styrene in the presence of H2TPP
porphyrin.
20

4. Conclusion
We employed a new sort of green, considerably selective, cost effective and
photocatalytic method for oxidation of styrene. Air as a clean and accessible
oxidant was employed in the presence of visible light irradiation and a series of β-
brominated meso-tetraphenylporphyrins, H2TPPBrx (x = 0, 4, 8) have been
synthesized and the catalytic activity of their manganese(III) and nickel(II)
complexes were studied for photo oxidation of styrene. Based on the obtained
results the free base porphyrins showed superior catalytic activities among
metallated porphyrins. In addition, the bromination degree not only played a
significant role in catalytic activity of synthesized porphyrins but also enhanced the
stability of catalyst up to 8 times.
Acknowledgements
The financial support of this work by K.N. Toosi University of Technology
research council is acknowledged.
21

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