Synthesis and Characterisation of Unsymmetrical Porphyrazines Containing Bis(hydroxyethylthio) Substituents

Article abstract of DOI:10.1007/s00706-003-0074-5

Unsymmetrical porphyrazines bearing a single peripheral bis(hydroxyethylthio) moiety were synthesised by mixed condensation of bis(2-hydroxyethylthio)maleonitrile and phthalonitrile. Complexation of the thioether groups of metal-free porphyrazine with PdCl₂ further lowered the intensity of the Q-band absorption of the porphyrazine core. The new compounds were characterised by elemental analyses, IR, ¹H NMR, UV-Vis, and mass spectra.

Full text of DOI:10.1007/s00706-003-0074-5

Monatshefte f€ur Chemie 134, 1555–1560 (2003)
DOI 10.1007/s00706-003-0074-5
Synthesis and Characterisation
of Unsymmetrical Porphyrazines
Containing Bis(hydroxyethylthio) Substituents
ꢀ
Ayfer Kalkan and Zehra A. Bayir
Technical University of Istanbul, Department of Chemistry, Maslak, Istanbul, Turkey
Received May 14, 2003; accepted May 19, 2003
Published online September 18, 2003 # Springer-Verlag 2003
Summary. Unsymmetrical porphyrazines bearing a single peripheral bis(hydroxyethylthio) moiety
were synthesised by mixed condensation of bis(2-hydroxyethylthio)maleonitrile and phthalonitrile.
Complexation of the thioether groups of metal-free porphyrazine with PdCl2 further lowered the
intensity of the Q-band absorption of the porphyrazine core. The new compounds were characterised
1
by elemental analyses, IR, H NMR, UV-Vis, and mass spectra.
Keywords. Porphyrazine; Phthalocyanine; Palladium; Complex.
Introduction
Phthalocyanines and porphyrins have received considerable attention due to inter-
esting applications [1, 2]. In addition to their traditional applications as dyes and
pigments, the special characteristics of phthalocyanines make them suitable as
charge carriers in electrophotography [3] and as the dye component in optical data
storage systems [4]. Furthermore, their properties have been identified as having
potential for exploitation in a number of other fields including gas sensing [5],
photovoltaic cells [6], optical limiting [7], and photodynamic therapy of cancer
[8]. The unique properties of porphyrins lead to their importance in the develop-
ment of molecular optoelectronic gates and switches [9], photo-inducible energy
[10], semiconductors [11], and enzyme models [12].
In comparison to phthalocyanines and porphyrins, porphyrazines have been
studied less frequently for a long period. Starting with the general high-yield route
to octakis(alkylthio)porphyrazine by Hoffmann [13], an extensive series of deriva-
tives with physical and chemical properties comparable to those of phthalocyanines
have been reported [14–17].
ꢀ
Corresponding author. E-mail: bayir@itu.edu.tr

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A. Kalkan and Z. A. Bayir
In contrast to the symmetrical porphyrazines, which are obtained directly by
cyclotetramerization of an unsaturated dinitrile, unsymmetrical ones require the
development of new methods of synthesis and separation. Unsymmetrically sub-
stituted derivatives functionalized with heteroatoms can bind additional metal ions,
have the potential to exhibit novel magnetic and electronic properties, and serve as
building blocks in the assembly of higher order polymetallic arrays. Also the
presence of soft S donor atoms play an important role in affecting the solid state
interactions [18–20].
Our previous papers have described a series of symmetric and unsymmetric
phthalocyanines carrying various substitutents, e.g. triaza or dioxadiaza macro-
cycles, or alkylthio groups on the periphery [21–25]. It has been shown that the
peripheral substituents enhance the solubility in common organic solvents and
provide donor sites for binding transition metal ions leading to heteromultinuclear
complexes.
In the present paper we report the synthesis of unsymmetrical porphyrazines
having a single peripheral bis(hydroxyethylthio) moiety. Also a palladium(II) com-
plex of the metal-free porphyrazine was prepared.
Results and Discussion
Unsymmetrical porphyrazines can be synthesized by co-cyclizing two different
precursors (A and B). When stoichiometric amounts are used, a mixture of all
six possible porphyrazine products is obtained naturally, and separation of the
desired singly substituted AB3 product by column chromatographic techniques
can be very difficult. When one of the precursors, e.g. B, is present in excess, only
two products are obtained, the fully symmetric B4 porphyrazine and the desired
AB3 porphyrazine.
In this work, unsymmetrical magnesium porphyrazine was prepared by the
reaction of bis(2-hydroxyethylthio)maleonitrile (1) [26] with phthalonitrile (2) in
1:25 ratio in a suspension of magnesium butoxide in refluxing butanol. The reason
for using one of the reagents in large excess was to minimize the formation of cross
tetramerization products and to promote the formation of the 3:1 product and
phthalocyanine.
Demetalization of these products by trifluoroacetic acid produced metal-free
phthalocyanine and unsymmetrical metal-free porphyrazine 3. Metal-free phthalo-
cyanine is hardly soluble in most organic solvents, whereas 3 is soluble with the
proper selection of a thioether protecting group. The purple product 3 was isolated
from the reaction mixture by Soxhlet extraction with THF.
Remetallation of the porphyrazine core with Zn(II) or Co(II) proceeds by treat-
ment of the free porphyrazine 3 with a small excess of the appropriate metal
acetate to produce 4 and 5. In contrast to the hexlythio analog, the solubility of
the unsymmetrical porphyrazines 3–5 is very low.
The reaction of the palladium(II) ion with the thioether groups of 3 gave a
product having a five membered chelate ring. The solubility of this four coordinate
palladium complex 6 is even lower than that of the parent porphyrazine 3.
Elemental analysis results, 1H NMR, IR, UV-Vis, and mass spectral data for all
new products were consistent with the assigned formulae. In the IR spectrum of 3,

Unsymmetrical Porphyrazines
1557
Scheme 1
the disappearance of the intense CꢁN stretching vibrations of precursors 1 and 2
can be taken as a clear evidence for tetrapyrrole formation. Also, characteristic NH
stretching vibrations of the inner core and CH stretching vibrations of aliphatic
groups in 3 were observed at ꢀꢀ¼ 3285 and 2930–2800 cmꢂ1. The IR spectra of the
porphyrazine complexes 4 and 5 were very similar to 3, with the exception of a NH
stretching band at ꢀꢀ¼ 3285 cmꢂ1:
The 1H NMR spectrum of 3 exhibited the aromatic protons around ꢁ ¼ 8.32 and
7.24 ppm as multiplet and the OCH2 and SCH2 protons of the hydroxyethylthio
moiety at ꢁ ¼ 3.98 and 3.60 ppm as triplet. The OH group of 3 was observed at
ꢁ ¼ 4.81 ppm. Inner core –NH protons of metal-free porphyrazine 3 appeared as a
deuterium exchangeable broad signal at ꢁ ¼ ꢂ2.42 ppm indicating the 18ꢂ electron
system of the planar molecule. These values are comparable with those for other
substituted porphyrazines [26–28]. In addition to the elemental analysis results the
mass spectral analysis is critical in determining the ratio of the two precursors as
3:1 after the cyclotetramerization reaction. The Mþ ion peak at m=z ¼ 616 (EI) for
3 provides strong evidence for a 3:1 condensation of the precursors.
Phthalocyanines and porphyrazines display similar and characteristic absorp-
tion spectra. Porphyrazines, like phthalocyanines, exhibit two main bands, a Soret
(B band) between ꢃ ¼ 330–375 nm and another one (Q band) beyond ꢃ ¼ 650 nm.
The optical spectra of unsymmetrical metallo porphyrazines 4 and 5 exhibit an
intense absorption in the Soret region at ꢃ ¼ 346 and 326 nm and a broad Q band at

1558
A. Kalkan and Z. A. Bayir
Fig. 1. UV-Vis of unsymmetrical metal-free porphyrazine 3 ( —— ) and its PdCl2 complex 6 (. . . . . .)
ꢃ ¼ 666 and 656 nm, respectively. The spectrum of the metal-free porphyrazine 3 is
quite similar, but with a split Q band having Qx and Qy absorbances at ꢃ ¼ 653 and
690 nm. The electronic spectra of 3 and its Pd complex 6 are shown in Fig. 1. After
complexation a distinct decrease in the Q band has occurred. This can be inter-
preted as a lowering of the electron density in the tetrapyrrole unit after binding a
cationic species directly to the thioether donors on the periphery.
Experimental
IR spectra were recorded on a Mattison 1000 FTIR spectrometer (KBr). UV-Vis spectra were measured
1
on a UNICAM UV-Vis spectrophotometer. H NMR spectra were acquired on a Bruker 250 MHz
€
spectrometer. Elemental analyses (C, H, N) were carried out by the analysis laboratory of the Tubitak
Marmara Research Center. The results were in favourable agreement with the calculated values.
Compound 1 was synthesised according to Ref. [26].
22,23-Di(2-hydroxyethylthio)-ꢄ-27H,29H-tribenzo[b,g,l]porphyrazine (3, C32H24N8S2O2)
A suspension of 0.312 g of Mg powder (13 mmol) in 50cm3 of n-butanol was refluxed overnight after
addition of a few crystals of I2 to initiate the reaction. To this mixture, 0.230 g of bis(2-hyrox-
yethylthio)maleonitrile (1mmol) and 3.2 g of phthalonitrile (25 mmol) were added. The reaction
mixture was kept at reflux under N2 for 12 h. After the hot mixture was filtered, the precipitate was
refluxed with acetone, methanol, and filtered off. The crude magnesium porphyrazine was dissolved in
5 cm3 of trifluoroacetic acid and stirred at room temperature for 3 h. The solution was added dropwise
into ice=H2O in order to precipitate the product and then neutralised with aqueous NH3 (10%). The
resulting precipitate was filtered off and washed first with H2O, ethanol, and dried in vacuo. The solid
product was extracted with THF in a Soxhlet for 24 h. After evaporation of the solvent a pure product
was obtained by washing the residue with methanol and diethyl ether. Yield: 0.073g (12%); IR (KBr):
ꢀꢀ¼ 3330 (OH), 3285 (NH), 2930ꢂ2800 (alkyl CH), 1042 (CO) cmꢂ1
;
1H NMR (DMSO-d6):
ꢁ ¼ ꢂ2.42 (broad s, NH), 3.60 (t, J ¼ 6.82Hz, 4SCH2), 3.98 (t, J ¼ 6.89 Hz, 4OCH2), 4.81 (s,
2OH), 8.32ꢂ7.24 (m, 12Ar-H) ppm; UV-Vis (THF): ꢃ(lg ") ¼ 690 (4.63), 653 (4.57), 339 (4.39) nm.

Unsymmetrical Porphyrazines
1559
22,23-Di(2-hydroxyethylthio)tribenzo[b,g,l]porphyrazinatozinc(II) (4, C32H22N8S2O2Zn)
To a solution of 0.125 g of 3 (0.2mmol) in 20 cm3 of THF a solution of 73 mg of Zn(CH3COO)2
(0.4mmol) in 10 cm3 of absolute ethanol was added under N2. The mixture was heated under reflux for
18h. The crude product was filtered and washed with H2O, methanol, and ethanol. The blueish green
product was dried under vacuum. Yield: 0.120 g (88%); IR (KBr): ꢀꢀ¼ 3310 (OH), 2953–2876 (CH),
1038 (CO) cmꢂ1; UV-Vis (THF): ꢃ(lg ") ¼ 666 (4.84), 346 (4.42) nm.
22,23-Di(2-hydroxyethylthio)tribenzo[b,g,l]porphyrazinatocobalt(II) (5, C32H22N8S2O2Co)
Compound 5 was prepared according to the same procedure as described for 4 by starting from 0.125g
of 3 (0.2mmol) and 71 mg of Co(CH3COO)2 (0.4mmol). Yield: 0.114g (85%); IR (KBr): ꢀꢀ¼ 3300
(OH), 2960ꢂ2870 (CH), 1060 (CO) cmꢂ1; UV-Vis (THF): ꢃ (lg ") ¼ 656 (4.41), 326 (4.30) nm.
22,23-Di(2-hydroxyethylthio)-ꢄ-27H,29H-tribenzo[b,g,l]porphyrazinatopalladium(II) chloride
(6, C32H24N8S2O2PdCl2)
Compound 3 (0.250g, 0.4 mmol) was refluxed in 10 cm3 of THF for 12h under N2 in the presence of
0.153 g of PdCl2(C6H5CN)2 (0.4mmol). The dark blue precipitate was filtered off, washed with
methanol, and dried in vacuo. Yield: 0.079 g (25%); IR (KBr): ꢀꢀ¼ 3330 (OH), 3285 (NH),
2930ꢂ2800 (CH), 1042 (CO) cmꢂ1; UV-Vis (THF): ꢃ (log ") ¼ 690 (4.37), 654 (4.34), 331 (4.41) nm.
Acknowledgement
This work was supported by the Research Fund of the Technical University of Istanbul.
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