Synthesis and solution properties of new metal-free and metallo-phthalocyanines containing four bis(indol-3-yl)methane groups

Article abstract of DOI:10.1016/j.tetlet.2012.07.046

Metallo-phthalocyanines bearing four bis(indol-3-yl)methane groups were successfully prepared by reaction of the corresponding phthalonitriles with anhydrous metal salts [Zn(CH₃COO)₂, NiCl₂ and CoCl₂] in the presence of a catalytic amount of DBU in 2-(dimethylamino)ethanol. The metal-free phthalocyanine was obtained by treating a mixture of the phthalonitrile derivative in similar conditions but in the absence of a metal salt. All of these phthalocyanines are soluble in DMSO, DMF, and pyridine. The products were characterized by IR, NMR, and UV-vis spectroscopy, MALDI-TOF-MS, and thermogravimetric analysis. The aggregation properties of the phthalocyanines were investigated at different concentrations in DMSO. All the phthalocyanines showed monomeric behavior in solution.

Full text of DOI:10.1016/j.tetlet.2012.07.046

Tetrahedron Letters 53 (2012) 5223–5226
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and solution properties of new metal-free and
metallo-phthalocyanines containing four bis(indol-3-yl)methane groups
⇑
Ali Reza Karimi , Azam Khodadadi
Department of Chemistry, Faculty of Science, Arak University, Arak 38156-8-8349, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Metallo-phthalocyanines bearing four bis(indol-3-yl)methane groups were successfully prepared by
reaction of the corresponding phthalonitriles with anhydrous metal salts [Zn(CH3COO)2, NiCl2 and CoCl2]
in the presence of a catalytic amount of DBU in 2-(dimethylamino)ethanol. The metal-free phthalocya-
nine was obtained by treating a mixture of the phthalonitrile derivative in similar conditions but in
the absence of a metal salt. All of these phthalocyanines are soluble in DMSO, DMF, and pyridine. The
products were characterized by IR, NMR, and UV–vis spectroscopy, MALDI–TOF–MS, and thermogravi-
metric analysis. The aggregation properties of the phthalocyanines were investigated at different concen-
trations in DMSO. All the phthalocyanines showed monomeric behavior in solution.
Received 15 April 2012
Revised 27 June 2012
Accepted 11 July 2012
Available online 26 July 2012
Keywords:
Metallo-phthalocyanine
Metal-free phthalocyanine
4-Nitrophthalonitrile
Bis(indol-3-yl)methane
Aggregation
Ó 2012 Elsevier Ltd. All rights reserved.
Phthalocyanines (Pcs) are remarkable compounds possessing
photophysical,1 semiconducting,2 and photoconducting properties3
Therefore, the development of techniques for the synthesis and
functionalization of indoles has been a focus of research over the
years.34 Bis(indol-3-yl)methanes feature extensively in bioactive
metabolites of terrestrial and marine origin.35,36 They also exhibit
potent antibacterial activity.37
Due to our interest in the synthesis of bis(indol-3-yl)meth-
anes38 and phthalocyanines,26 we report the synthesis and charac-
terization of several metal free and metallo-phthalocyanines
bearing four bis(indol-3-yl)methane groups which enabled the
molecules to dissolve in a number of organic solvents such as
DMF, DMSO, and pyridine (Scheme 1). A combination of these
two potentially promising units [phthalocyanine and bis(indol-3-
yl)methane groups] may improve their organosolubility and bio-
logical properties.
due to their 18p
-electron aromatic macrocyclic structure.4 For
many years, phthalocyanines have been used as dyes.5 Recently,
Pc complexes have been investigated in diverse fields such as elec-
tronic displays,6 photocatalysts,7 liquid crystals,8,9 photovoltaic
cells,10 electrochromic devices,11 semi-conductors,12 data storage
systems,13 chemical sensors,14 gas sensors,15 solar cells,16 nonlinear
optics,17 and as photodynamic therapy (PDT) agents.18–20
Another significant aim of research into the chemistry of
phthalocyanines is to enhance their solubility in various solvents.
Although, many Pcs have low solubility in common organic sol-
vents, their solubility can be improved by the incorporation of sub-
stituents, such as long alkyl, alkoxy, alkylsulfanyl, and other bulky
groups.21–24 Among the substituted phthalocyanines, those bearing
a heterocyclic group, have received considerable attention.25 Dif-
ferent heterocyclic phthalocyanines that have been synthesized
Phthalonitrile derivatives 5a–b were synthesized in two steps.
The first involved
a nucleophilic aromatic displacement on
4-nitrophthalonitrile 2 with 4-hydroxybenzaldehyde 1 in the pres-
ence of anhydrous K2CO3 as the base in DMF to give the dicyano
compound 3. Then compound 3 was reacted with 2 equiv of indole
4 in the presence of alum as the catalyst in acetonitrile at room
temperature. Compounds 5a and 5b were obtained in 94% and
96% yields, respectively.
The metal-free phthalocyanine 6 was obtained by cyclotetra-
merization of 5a using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
as the catalyst. The reaction was carried out in refluxing
2-(dimethylamino)ethanol (DMAE) under a nitrogen atmosphere.
The metallo-phthalocyanines 7–12 were prepared by reaction of
phthalonitrile derivatives 5a–b with anhydrous metal salts
[Zn(CH3COO)2, NiCl2 and CoCl2] in the presence of a few drops of
and studied include those with xanthene,26 -prolinol,27 imidaz-
L
ole,28 thiophene,29 pyridine,30 triazole,31 and other heterocyclic
substituents.
Indole and its derivatives are important in organic chemistry and
display a variety of physiological and pharmacological properties.32
The indole scaffold is an important structural motif in medicinal
chemistry.33 Substituted indoles have been referred to as privileged
structures since they are capable of binding to many receptors with
high affinity.
⇑
Corresponding author. Tel.: +98 861 4173400; fax: +98 861 4173406.
E-mail address: a-karimi@araku.ac.ir (A.R. Karimi).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.07.046

5224
A. R. Karimi, A. Khodadadi / Tetrahedron Letters 53 (2012) 5223–5226
R
R
CN
O
NH
NH
CN
O
H
CN
CN
ii
i
+
5a-b
CN
R
2
H
NO2
OH
NH
R: H or CH3
O
O
4
1
2
3
CN
iv
H
N
iii
H
N
R
R
NH
NH
O
O
HN
HN
R
N
N
N
N
N
N
N
H
R
N
N
N
N
N
N
N
M
N
O
O
HN
HN
NH
NH
R
H
O
O
N
R
NH
NH
7-12
6
O
O
R
H
H
M
Zn
Ni
Co
Zn
Ni
Co
7-12
7
8
9
10
11
12
MX
Zn(OAc)2
NiCl2
CoCl2
Zn(OAc)2
NiCl2
CoCl2
HN
HN
H
R
R
N
H
N
H
CH3
CH3
CH3
Yields: 47-57%
Yield: 46%
Scheme 1. Synthesis of the metal-free and metallophthalocyanines 6–12. Reagents and conditions: (i) K2CO3, DMF, 24 h, rt; (ii) alum, CH3CN, 24 h, rt; (iii) DBU, DMAE, N2,
reflux; (iv) Metal salt, DBU, DMAE, N2, reflux.
DBU in a high-boiling solvent (DMAE) under a nitrogen atmo-
sphere. Generally, phthalocyanine complexes are insoluble in most
organic solvents; however the introduction of substituents on the
ring increased their solubility. Phthalocyanine complexes 6–12
showed an excellent solubility in DMF, DMSO, and pyridine. They
were insoluble in ether, ethyl acetate, dichloromethane, and aceto-
nitrile. IR, 1H NMR, MALDI–TOF–MS, and UV–vis spectra were con-
sistent with the proposed structures of the compounds. TGA was
used to determine the thermal stability of these complexes.
The IR spectrum of 3 clearly indicated the disappearance of the
OH band at 3352 cmÀ1 and the NO2 bands at 1538 cmÀ1 and
1355 cmÀ1 and the appearance of a CN peak at 2237 cmÀ1. More-
over, the formation of compounds 5a–b was consistent with disap-
pearance of the C@O band at 1691 cmÀ1 and the appearance of
new bands at 3408 and 3379 cmÀ1 related to the NH groups for
5a and 5b, respectively. After cyclotetramerization of 5a–b, The
IR spectra of phthalocyanines 6–12 lacked the CN band, com-
pletely. The 1H NMR spectrum of 5a exhibited two singlets at d:
10.87 and 5.91, respectively, for the NH and CH protons. The aro-
matic protons resonated in the range of d: 8.07–6.86. The spectrum
of 5b exhibited three singlets at d: 10.79, 5.97, 2.12, respectively,
for NH, CH, and CH3 protons. The aromatic protons appeared in
the range of d: 8.12–6.72. In the 1H NMR spectra of 6, 7, 9, 10,
and 11 resonances for the NH groups were observed at d: 10.82,
10.85, 10.86, 10.80, and 10.76, respectively. Because of the ring
current, the inner N–H proton of compound 6 was shifted to high
field and it could not be observed.39 After the cyclotetramerization,
the aromatic protons were observed as multiplets at d: 6.85–7.72,
6.86–7.94, 6.92–7.35, 6.72–7.37, and 6.88–7.22 for 6, 7, 9, 10, and
11, respectively. The aliphatic CH peaks appeared at d: 5.93, 5.94,
5.87, 5.97, and 5.98 for 6, 7, 9, 10, and 11, respectively. The CH3
signals were observed as a multiplet at d: 2.12–2.33 for 10 and at
d: 1.98–2.13 for 11.
In the electronic spectrum of the metal-free phthalocyanine
6 (Fig. 1) in DMF, the characteristic split Q absorption band was ob-
served with absorptions at kmax = 697 and 669 nm with a shoulder
at 611 nm. These Q band absorptions show the monomeric species
with D2h symmetry and due to the phthalocyanine ring relate to
the fully conjugated 18p
-electron system.40 The presence of a
strong absorption band in the near UV region at kmax = 354 nm also
showed the Soret region B band.
The UV–vis spectra of the metallophthalocyanines 7–12 in DMF
are shown in Figure 2. The UV–vis absorption spectra of phthalocy-
anines 6–12 had intense Q absorptions at kmax = 697, 669, 675,
671, 662, 677, 671, and 663 nm, with weaker absorptions at 611,
609, 605, 599, 611, 613, and 605 nm, respectively. These results
are typical of metallophthalocyanines with D4h symmetry. The B
Figure 1. Absorption spectrum of 6 in DMF (C = 3 Â 10À5 M).

A. R. Karimi, A. Khodadadi / Tetrahedron Letters 53 (2012) 5223–5226
5225
Table 2
Thermal analysis data for 6–12
Pcs Temp of
Mass
loss %
found
Probable
%
calcd
Nature of probable
fragment lost
dec (°C)
6
7
200–496 37.85
496–995 38.96
197–430 23.71
430–976 69.17
37.44
39.13
24.12
69.24
6C8H6N
4C7H5O, C6H3, C7H10
4C8H6N
C8H3N3, C6H3, 2C8H3N3 4C7H5O,
4C8H6N,
O
8
9
195–420 24.15
420–910 68.71
24.20
69.46
4C8H6N
C8H3N3, C6H3, 2C8H3N3 4C7H5O,
4C8H6N,
3C8H7N
2C8H7N
C8H7N
190–384 18.18
384–502 12.41
18.15
12.10
6.05
502–582
6.12
582–915 32.41
210–432 22.87
432–586 21.62
586–905 45.35
30.60
22.94
21.72
45.42
4C7H5O, 2C8H7N
8CH3, 3C8H7N
2C7H5O, 2C8H7N
C8H3N2 C8H3N, C8H3N3, C7H6,
C7H5O, 3C8H7N
4C8H7N, 8CH3
C8H3N3, 4C7H5O 4C8H7N,
4C8H7N, 8CH3
4C8H7N
10
Figure 2. Absorption spectra of metallophthalocyanines 7–12 in DMF
(C = 3 Â 10À5 M).
11
12
192–450 28.88
450–975 50.20
230–471 28.31
471–613 22.56
613–921 43.69
28.68
50.32
28.63
22.68
43.89
Table 1
Absorption spectral data for phthalocyanines 6–12 in DMF (C = 3 Â 10À5 M)
Pcs
kmax/nm (log e)
C8H3N, C6H3 4C7H5O, 2C8H3N3
6
7
8
697(4.17), 669(4.21), 611(3.80), 333(4.34), 275(4.72)
675(4.66), 609(4.02), 354(4.36), 277(4.66)
671(4.47), 605(4.02), 278(4.77)
9
662(3.53), 599(4.02), 323(4.45), 275(4.68)
677(4.36), 611(3.80), 348(4.30), 271(4.60)
671(4.31), 613(3.77), 331(4.30), 272(4.75)
656(4.67), 591(4.00), 321(4.52), 272(4.74)
10
11
12
band absorptions of compound 7, 8, 9, 10, 11, and 12 were ob-
served at kmax = 275, 333, 277, 354, 278, 275, 323, 271, 348, 272,
331, 279 nm, respectively (Table 1). The Q band was attributed to
the
p–
p⁄ transition from the highest occupied molecular orbital
(HOMO) to the lowest unoccupied molecular orbital (LUMO) of
the Pc ring. The B band in the UV region was related to the transi-
tions from the deeper
p
levels to the LUMO.41
In this study, the aggregation behavior of the phthalocyanines
6–12 was investigated in DMSO at different concentrations. All the
phthalocyanines did not show aggregation in this solvent. The
aggregation behavior of 10 in DMSO at different concentrations
is shown in Figure 3. As the concentration was increased, the inten-
sity of absorption of the Q band also increased and there was no
new band (normally blue shifted) due to the aggregated species.
So, these complexes exhibited a monomeric form as deduced from
the absorption spectra in different concentrations.
Figure 3. Aggregation behavior of 10 in DMSO at different concentrations:
6 Â 10À5 M (A), 5 Â 10À5 M (B), 4 Â 10À5 M (C), 3 Â 10À5 M (D).
The MALDI–TOF–MS measurement for compound 10 gave the
characteristic molecular ion peak at m/z: 2035.1 [M]+ confirming
the proposed structure (Fig. 4).
The thermal properties of all the metal-free phthalocyanines
and metallo-phthalocyanines were analyzed by thermal gravimet-
ric analysis (TGA) in the temperature range 30–1000 °C under a
nitrogen atmosphere with a heating rate of 10 °C/min. The initial
weight loss up to 190 °C was related to the residual solvent which
is typical of a TGA heating run. The complexes 6, 7, 8, 11 had two
degradation steps and complexes 10 and 12 had three degradation
steps, while complex 9 had four degradation steps. The initial
decomposition temperatures of the compounds are in the order:
12 > 10 > 6 > 7 > 8 > 11 > 9. No obvious correlation was observed
between the transition metal ions in the phthalocyanine com-
plexes and the initial decomposition temperature (Table 2).
In conclusion, we have synthesized and characterized new
metal-free and metallophthalocyanines 6–12 containing four
bis(indol-3-yl)methane groups.42 All of these phthalocyanines are
soluble in DMSO, DMF, and pyridine and did not show aggregation
in DMSO. The Pcs reported in this work can be considered as
Figure 4. MALDI-TOF-MS spectrum of 10.
efficient candidates for solution studies requiring the monomeric
form of such materials as in the case of the photosensitizers used
in photodynamic therapy.
Acknowledgment
We gratefully acknowledge the financial support from the Re-
search Council of Arak University.

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42. Synthesis of 4-(4-formylphenoxy)phthalonitrile (3):
A
mixture of 4-
hydroxybenzaldehyde 1 (0.122 g, 1 mmol), 4-nitrophthalonitrile 2 (0.173 g,
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1H NMR (400 MHz, DMSO-d6) dH: 10.87 (s, 2H, NH), 8.07 (d, J = 6.6 Hz, 1H,
Harom), 7.76 (d, J = 2.1 Hz, 1H, Harom), 7.47 (d, J = 6.3 Hz, 2H, Harom), 7.30–7.37
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0.21 mmol), Zn(CH3COO)2 (0.013 g, 0.07 mmol), three drops of (DBU), and
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cooling to room temperature the mixture was treated with EtOH (2 mL) in
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1338, 1228, 1095, 742. 1H NMR (300 MHz, DMSO-d6) dH: 10.85 (8H, NH), 6.86–
7.94 (m, 68H, Harom), 5.94 (CH, 4H).
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