Synthesis and characterization of tetraarylporphyrins in the presence of nano-TiCl4·SiO2

Article abstract of DOI:10.1007/s10593-015-1741-2

[MediaObject not available: see fulltext.] Synthesis of tetraarylporphyrins by the coupling of an aromatic aldehyde and pyrrole using nano-TiCl₄·SiO₂ as mild, inexpensive, and highly efficient catalyst is studied in the present article.

Full text of DOI:10.1007/s10593-015-1741-2

DOI 10.1007/s10593-015-1741-2
Chemistry of Heterocyclic Compounds 2015, 51(6), 578–581
Synthesis and characterization of tetraarylporphyrins
in the presence of nano-TiCl4·SiO2
Leila Zamani1,2*, Bi Bi Fatemeh Mirjalili2
1 Department of Medicinal Chemistry, Faculty of Pharmacy and Pharmaceutical
Sciences Research Center, Shiraz University of Medical Sciences,
Shiraz, I. R. Iran
2 Department of Chemistry, College of Science, Yazd University,
Yazd, PO Box 8915813149, I. R. Iran; e-mail: l.zamani2008@gmail.com
Published in Khimiya Geterotsiklicheskikh Soedinenii,
2015, 51(6), 578–581
Submitted 16.01.2015
Accepted after revision 14.04.2015
Ar
Ar
NH
NH
N
N
H
N
nano-TiO4·SiO2
CAN
4
+ 4ArCHO
Ar
Ar
Ar
Ar
N
H
H
N
HN
HN
Ar
Porphyrinogen
Ar
Porphyrin
Synthesis of tetraarylporphyrins by the coupling of an aromatic aldehyde and pyrrole using nano-TiCl4·SiO2 as mild, inexpensive, and
highly efficient catalyst is studied in the present article.
Keywords: aromatic aldehyde, pyrrole, tetraarylporphyrins, heterogeneous catalyst, nano-TiCl4·SiO2.
Porphyrins as important biogenic structures are found in
various biologically active substances, such as hemoglobin,
chlorophyll, vitamin B12, cytochromes, and are capable of
DNA cleavage.1,2 In recent years substituted porphyrins
have been used in biomimetic chemistry,3,4 medicinal
chemistry,5 analytical chemistry,6 and molecular electronic
devices.7 Also, they are used for optical applications in e.g.
data storage,8 nonlinear optics,9,10 electrochromism,11 etc.,
which are just few of the many areas that have inspired the
synthesis of porphyrin-based compounds. Porphyrins are
used as catalysts,12–14 photosensitizers,15 nonlinear optical
materials,16 liquid crystals,17,18 in photovoltaic cells,19 light-
harvesting complexes,20 as well as in photodynamic
therapy of cancer.21 The increasing importance of these
applications provides a continuous stimulus for intensive
research towards artificial porphyrin assemblies.
In recent years, the application of reusable heterogeneous
catalysts has gained considerable importance in organic
synthesis because of their environmental, economical, and
industrial aspects.22 Up to now, many reusable and
heterogeneous catalysts have been designed and used. In
particular, metal colloids, mineral clays, and immobilized
reagents on silica gel, alumina, and other solid supports are
some common examples of heterogeneous catalysts that have
extensive applications in organic transformations. These
catalysts have attracted a great deal of attention due to their
ease of handling, enhanced reaction rates, greater selectivity,
and simple work-up in most cases.
Several syntheses of meso-tetraarylporphyrins have been
reported to proceed in the presence of catalysts such as
SOCl2/SiO2,23 PCl5,24 CF3SO2Cl,25 silica-supported sulfuric
acid (SSA),26 and HBr/MeOH.27 However, each method
has certain restrictions with regards to scope and reaction
conditions, such as costs of synthesis, unrecoverable
catalysts, strong acidic conditions, long reaction times, low
yields, difficult work-up, and harsh reaction conditions. To
avoid these limitations, we are working towards the
development of more efficient methods, that wood provide
higher yields for the synthesis of tetraarylporphyrins in the
presence of nano-TiCl4·SiO2.
Titanium tetrachloride, as a powerful Lewis acid, is a
liquid that is highly volatile, corrosive, and difficult to
handle. It is readily hydrolyzed to produce HCl in the
presence of moisture. Silica-supported TiCl4 has several
advantages as a catalyst which makes it economically and
environmentally attractive. It can be stored at ambient
temperatures for months without losing its catalytic
activity. This catalyst does not need special precautions for
preparation, handling, storage, and use.28–32
In continuation of our investigations on solid-supported
acids in organic synthesis,28–32 we have investigated the synthe-
sis of tetraarylporphyrins in the presence of various acids.
0009-3122/15/5106-0578©2015 Springer Science+Business Media New York
578

Chemistry of Heterocyclic Compounds 2015, 51(6), 578–581
Ar
Ar
Scheme 1
NH
N
H
NH
N
N
50% nano-TiO4·SiO2
CAN
Ar
+ ArCHO
Ar
Ar
Ar
H
N
N
H
HN
HN
Ar
1a–j
Table 1. Synthesis of tetraphenylporphyrin (2a) under various conditions. Optimization study*
Ar
2a–j
Entry
Catalyst (g)
Quantity, g
Oxidant
Solvent
Tempetature
Time, h
Yield, %
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
SiO2
0.5
0.4
0.2
0.15
0.1
0.05
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.04
0.1 ml
0.05
CAN
CAN
CAN
CAN
CAN
CAN
CAN
DDQ
TCM
Chloranil
CAN
CAN
CAN
CAN
CAN
CAN
CAN
Aair
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Solvent-free
MeOH
rt
rt
rt
rt
rt
rt
rt
rt
rt
1
1
1
1
1
1
1
1
1
1
1
3
1
30
3
2
2
4
4
4
10
70
82
81
81
78
60
70
65
64
50
52
14
10
64
52
47
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
30% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
50% nano-TiCl4·SiO2
PCl5
rt
rt
Reflux
rt**
rt***
Reflux
Reflux
Reflux
Reflux
Reflux
rt
Solvent-free
EtOAc
Acetone
Et2O
THF
CH2Cl2
CH2Cl2
CH2Cl2
6224
6525
6026
CF3SO2Cl
SSA
Air
Air
* The amounts of starting materials: benzaldehyde (0.1 ml, 1 mmol, 10–2 M), pyrrole (0.07 ml, 1 mmol, 10–2 M). The resulted tetraphenylporphyrinogen (1a)
was oxidized into the porphyrin 2a by treating with 0.1 g of the respective oxidant in the presence of air.
** Grinding in MM 400 mixer mill at 25 Hz frequency.
*** Sonication with BANDELIN Sonopulse HD 3200 Ultrasonic apparatus at 20 KHz frequency.
Herein, we report that nano-TiCl ·SiO is an efficient catalyst
presence of 50% nano-TiCl4·SiO2 at room temperature,
while optimal catalyst loading was 0.1 g of 50% nano-
TiCl4·SiO2 per 1 mmol of starting material (Table 1, entry 5).
The initially formed tetraphenylporphyrinogen (1a) was
then aerobically oxidized into tetraphenylporphyrin (2a) in
the presence of various oxidants, among which ceric
ammonium nitrate (CAN) was found to be the best one.
Next, various aldehydes and pyrrole were used as sub-
strates for the synthesis of tetraarylporphyrinogens (Table 2).
All the products are known and were characterized by
1
2
4
2
for the synthesis of tetraarylporphyrinogens, and its efficiency
is comparable with some other catalysts such as SiO /SOCl ,23
3
2
PCl ,24 CF SO Cl,25 and SSA.26 The synthesis and2characte-
4
5
rization of3nan2o-TiCl ·SiO is published in literature.32
5
4
2
To optimize the reaction conditions, the condensation of
benzaldehyde and pyrrole was used as a model reaction
(Scheme 1, Table 1). Performing the process under
different conditions revealed that the best result was
achieved by stirring the reactants in dichloromethane in the
6
7
8
9
10
Table 2. Synthesis of tetraarylporphyrins 2a–j*
Ar
Time, h
Yield, %
Ar
Time, h
Yield, %
Porphyrin
Porphyrin
Ph
1.0
1.5
1.0
1.0
2.0
80
74
87
88
74
4-O2NC6H4
4-(i-Pr)C6H4
2-ClC6H4
2-MeOC6H4
2,4-Cl2C6H3
0.5
1.5
1.0
2.0
1.0
94
60
81
70
91
2a
2b
2c
2d
2e
2f
2g
2h
2i
4-MeC6H4
4-ClC6H4
4-MeOC6H4
4-BrC6H4
2j
* Reaction conditions: pyrrole (1 mmol), arylaldehydes (1 mmol), 50% nano-TiCl4·SiO2 (0.1 g). The resulted tetraarylporphyrinogens 1 were oxidized
into the respective porphyrins 2 by treating with of CAN (0.1 g, 5 mol %) for 20 min in the presence of air.
579

Chemistry of Heterocyclic Compounds 2015, 51(6), 578–581
IR spectra, UV-Visible and 1H NMR spectra and by
δ, ppm: 3.05 (2H, s, 2NH); 2.42 (12H, s, H Ar); 7.35–7.37
(8H, m, H Ar); 7.89–7.91 (8H, m, H Ar); 8.66 (8H, s, H Ar).
5,10,15,20-Tetrakis(4-chlorophenyl)porphyrin (2c).
Mp >300°C (mp >300°C)24. IR spectrum, ν, cm–1: 3350 (br,
N–H), 3050 (C–H aromatic), 1550 (aryl stretch), 1469 (br,
NH bend), 1440 (br, C=N), 1250, 966, 799, 750 (C–Cl).
UV spectrum, λmax, nm (log ε): 422 (4.88), 518 (4.35), 560
comparison of their physical properties with those reported
in the literature.
Thus, 50% nano-TiCl4·SiO2 as an efficient, cheap,
noncorrosive, and available catalyst has been used for the
synthesis of tetraarylporphyrins. High to excellent yields,
ease of work-up, mild reaction conditions, short reaction
times, environmentally friendly procedures, and the ability
to tolerate a diversity of substituents in aldehyde are
features of this new procedure.
1
(4.12), 595 (3.84), 655 (3.62). H NMR spectrum, δ, ppm:
3.15 (2H, s, 2NH); 7.70–7.72 (8H, m, H Ar); 7.87–7.88
(8H, m, H Ar); 8.65 (8H, s, H Ar).
5,10,15,20-Tetrakis(4-methoxyphenyl)porphyrin (2d).
Mp >300°C (mp >300°C)26. IR spectrum, ν, cm–1: 3350 (br,
N–H), 3007 (C–H aromatic), 2931 (C–H aliphatic), 1460
(NH bend, C=N), 1246 (C–O), 832. UV spectrum, λmax (log ε):
424 (4.85), 449 (5.23), 519 (4.47), 555 (4.24), 595 (3.84),
670 (3.36).
5,10,15,20-Tetrakis(4-bromophenyl)porphyrin (2e).
Mp >300°C (mp >300°C)25. IR spectrum, ν, cm–1: 3340 (br,
N–H), 3050 (C–H aromatic), 1585 (aryl stretch), 1486 (br,
NH bend), 1250, 965, 799. UV spectrum, λmax, nm (log ε):
421 (5.17), 518 (5.31), 550 (4.82), 591 (4.61), 649 (3.54).
1H NMR spectrum, δ, ppm: 3.17 (2H, s, 2NH); 7.54–7.55
(8H, m, H Ar); 7.92–7.93 (8H, m, H Ar); 8.65 (8H, s, H Ar).
5,10,15,20-Tetrakis(4-nitrophenyl)porphyrin (2f). Mp
>300°C (mp >300°C)26. IR spectrum, ν, cm–1: 3360 (br, N–H),
3050 (C–H aromatic), 2923 (C–H aliphatic), 1585 (aryl
stretch), 1515 and 1345 (N–O stretch), 1469 (NH bend),
1200 (C=N), 785. UV spectrum, λmax, nm (log ε): 422
(4.75), 517 (4.52), 548 (4.33), 590 (4.15), 650 (3.41), 676
(2.43).
5,10,15,20-Tetrakis(4-isopropylphenyl)porphyrin (2g).
Mp >300°C (mp >300°C)29. IR spectrum, ν, cm–1: 3320 (br,
N–H), 3050 (C–H aromatic), 2959 (C–H aliphatic), 1500
(br, aryl stretch, C=N, NH bend), 1370 and 1380 (CH bend,
i-Pr), 832. UV spectrum, λmax, nm (log ε): 420 (5.21), 518
(4.94), 52 (4.28), 599 (3.43), 652 (2.19).
5,10,15,20-Tetrakis(2-chlorophenyl)porphyrin (2h).
Mp >300°C (mp >300°C)26. IR spectrum, ν, cm–1: 3431 (br,
N–H), 3050 (C–H aromatic), 2924 (C–H aliphatic), 1564
(aryl stretch), 1468 (NH bend), 1432 (C=N), 1044, 965,
747, 707 (C–Cl). UV spectrum, λmax, nm (log ε): 418
(5.80), 515 (5.51), 550 (4.22), 590 (3.81), 643 (1.20).
5,10,15,20-Tetrakis(2-methylphenyl)porphyrin (2i).
Mp >300°C (mp >300°C)26. UV spectrum, λmax, nm (log ε):
418 (5.57), 514 (4.80), 545 (4.63), 591 (4.33), 646 (3.26).
5,10,15,20-Tetrakis(2,4-dichlorophenyl)porphyrin (2j).
Mp >300°C (mp >300°C)26. IR spectrum, ν, cm–1: 3427 (br,
N–H), 3090 (C–H aromatic), 1564 (aryl stretch), 1469 (NH
bend), 1440 (C=N), 997, 725. UV spectrum, λmax, nm (log ε):
418 (5.30), 450 (5.02), 515 (4.83), 550 (4.18), 591 (3.91),
646 (3.44).
Experimental
FT-IR (ATR) spectra were recorded on a Bruker Eqinox 55
spectrometer. UV/Vis spectra were recorded on an
Ultrospec 3000 V/Visible spectrometer in 1 mol/l CH2Cl2
1
solutions. H NMR spectra were recorded on a Bruker
Avance DRX-400 (400 MHz) instrument in CDCl3 using
TMS as internal standard. Melting points were measured
with a Thermo Scientific Electrothermal digital apparatus.
The chemicals were purchased from Merck and used
without any additional purification.
Preparation of 50% nano-TiCl4·SiO2. To a mixture of
silica gel (0.5 g) and CHCl3 (5 ml), TiCl4 (0.5 g, 0.29 ml)
was added dropwise with stirring. The resulting suspen-
sion was further stirred for 1 h at room temperature,
filtered, washed with CHCl3, and dried at room tempe-
rature in air.
Synthesis of porphyrins 2a–j (General method).
Pyrrole (0.07 ml, 1 mmol), aldehyde (1 mmol), 50% nano-
TiCl4·SiO2 (0.1 g), and CH2Cl2 (20 ml) were placed in a
50 ml beaker. The mixture was stirred at room temperature
within the time specified in Table 2. The progress of the
reaction was monitored by TLC. After the reaction was
finished, CAN (0.1 g, 5 mol %) was added to the reaction
mixture and stirred at room temperature for 20 min in the
presence of air while the reaction mixture became dark-
purple indicating porphyrinogen conversion into porphyrin
under aerobic oxidation. The solution was concentrated
under reduced pressure and chromatographed on neutral
alumina column eluting with CH2Cl2–petroleum ether,
1:1.5. Alternatively, crude solid residues obtained by the
evaporation of the corresponding reaction mixtures were
sequentially washed with Et2O, hot H2O, and cold MeOH
to give pure porphyrins as purple solid.
5,10,15,20-Tetraphenylporphyrin (2a). Mp >300°C
(mp >300°C)26. IR spectrum, ν, cm–1: 3311 (br, N–H), 3053
(C–H aromatic), 2923 (C–H aliphatic), 1595 (aryl stretch),
1469 (NH bend), 1440 (C=N), 965, 792, 726, 696.
UV spectrum, λmax, nm (log ε): 418 (4.52), 517 (4.01), 549
1
(3.84), 591 (3.73), 647 (3.42). H NMR spectrum, δ, ppm:
2.98 (2H, s, 2NH); 7.56–7.59 (12H, m, H Ar); 8.01–8.03
(8H, m, H Ar); 8.65 (8H, s, H Ar).
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