Synthesis and characterization of a phthalocyanine-porphyrazine hybrid and its palladium(II) complex

Article abstract of DOI:10.1007/s007060070027

A phthalocyanine-porphyrazine hybrid molecule composed of three phthalonitrile units and one maleonitrile moiety was prepared by cyclomerization of the reactants in the presence of magnesium butoxide. Two thioether groups fused to β-pyrrol positions were complexed with PdCl₂. The compounds were characterized by ¹H NMR, IR, and UV/Vis spectroscopy as well as elemental analysis.

Full text of DOI:10.1007/s007060070027

Monatshefte fuÈr Chemie 131, 1191±1195 (2000)
Synthesis and Characterization of a
Phthalocyanine-Porphyrazine Hybrid
and its Palladium(II) Complex
Ã
SËebnem B. Sesalan and Ahmet GuÈl
_
Technical University of Istanbul, Department of Chemistry, TR-80626 Maslak, Istanbul, Turkey
Summary. A phthalocyanine-porphyrazine hybrid molecule composed of three phthalonitrile units
and one maleonitrile moiety was prepared by cyclomerization of the reactants in the presence of
magnesium butoxide. Two thioether groups fused to ꢀ-pyrrol positions were complexed with PdCl2.
The compounds were characterized by 1H NMR, IR, and UV/Vis spectroscopy as well as elemental
analysis.
Keywords. Macrocycles; Complexes; Palladium; Phthalocyanine; Porphyrazine.
Introduction
As in the case of phthalocyanines, functionalization of the porphyrazine core at the
periphery has attracted increasing attention during the last decade [1, 2]. Whereas
early efforts were mainly directed towards symmetrically substituted derivatives,
the construction of unsymmetrical structures made up of unsaturated 1,2-dinitriles
and phthalonitriles has been developed later [3]. In this context, Hoffmann and
Barrett have provided examples of heteroatom donors directly bound to the
macrocyclic core of the porphyrazine side of the hybrid structure [3±6].
In addition to the peripherally functionalized phthalocyanine derivatives, we have
recently focused on the preparation of novel porphyrazines, making use of the liability
of substituted dithiomaleonitriles to cyclotetramerize in the presence of magnesium
alkoxide [7±11]. We have accomplished to prepare symmetrically octakis-substituted
derivatives with active peripheral substituents, among them crown ethers [12],
ferrocenes [13], dimethylamine, and trimethylammonium groups [14].
Despite the growth of research currently being carried out world-wide on the
synthesis of phthalocyanines and porphyrazines with thioether substituents, to our
knowledge complexation of these donors with palladium(II) has been investigated
only in the solution state, and no product has been isolated [15, 16]. Complexes of
thioethers with Pd(II) have been investigated in detail in the case of thiacyclophanes
[17]. In the present article we report on the synthesis of a new metal-free
phthalocyanine-porphyrazine hybrid structure and its palladium(II) complex on the
peripheral thioether donors directly bound to the 18-Å electron containing inner core.
Ã
Corresponding author

1192
SË. B. Sesalan and A. GuÈl
Results and Discussion
The synthesis of phthalocyanine-porphyrazine hybrid structures started with the
cocyclization of bis-hexylthio-maleonitrile (1) with phthalonitrile (2) [18±19].
Generally, six reaction products would be expected involving six possible structures
with the ratio of 1:2 ranging from 0:4 to 4:0 [20]. In order to make use of both the
insolubility of all phthalonitrile products (i.e. the phthalocyanines) and the solubility
of hexylthio substituted products, the ratio of 1:2 was kept suf®ciently small to
direct the reaction to form derivatives containing mainly phthalocyanine systems
and only a single maleonitrile unit. Demetalization of these products with a strong
acid (e.g. tri¯uoroacetic acid) yielded the insoluble metal-free phthalocyanine
(H2Pc) together with a suf®ciently high amount of the soluble phthalocyanine-
porphyrazine hybrid (3).
The four-coordinate palladium complex 4 was prepared by substitution of the
benzonitrile moieties of bis-benzonitrile-palladium dichloride with 3 to form a ®ve
membered chelate ring. The square planar complexation of the type PdCl2S2 did
not cause apprecible change in the colour of the macrocycle due to the intense
absorption of the 18-Å electron system.

Phthalocyanine-Porphyrazine Hybride Pd Complex
1193
The IR spectrum of 3 showed NH streching vibrations of the inner core at
1
1
3270 cm and CH vibrations of the hexyl groups around 2840±2900 cm . After
complexation with palladium(II), the presence of the inner core NH groups was
1
1
veri®ed by the NH streching absorptions around 3260 cm . The H NMR spectra
of 3 and 4 also con®rm the metal-free state for both structures. The chemical shift
for the NH group in 3 appeared at 4:0 ppm as a broad peak which is a typical
value for porphyrinoid structures [1±5]. In 4, these protons are shifted to 1:3 ppm.
The aromatic protons of 3 were observed between 8.13 and 7.39 ppm as a singlet, a
doublet, and a triplet. These peaks also shifted to 8.87-7.97 ppm after complexation.
For the S-CH2 protons of 3 and 4, a high®eld shift of 0.14 ppm was observed upon
complexation.
The electronic spectra of phthalocyanines and porphyrazines do not extensively
change in their general appearance upon peripheral subtitution, but removal of one
benzo group causes noticeable differences. A single Q band in metallo derivatives
and its splitted form in their metal-free counterparts are characteristic [2]. A
comparison of metal-free phthalocyanine with the metal-free porphyrazine indicates
that the splitted Q bands are extremely broad and of low intensity in the latter. In
this sense, the UV/Vis spectrum of the metal-free phthalocyanine-porphyrazine
hybrid 3 resembles that of metal-free phthalocyanine. However, the position of the
absorption maxima indicates a structure of lower symmetry than D2h. As shown in
Fig. 1, the splitted intense peaks appear at 616 and 708 nm, clearly separated in
contrast to metal-free phthalocyanine, and there are two less intense peaks at 654
and 676 nm in between. The result of complexation with etheral S-donors was
expected to cause apparent changes in the UV/Vis spectrum, since these
heteroatoms are in direct contact with the aromatic Å-electron system. This should
lead to a clear difference with respect to complexation of donor groups on the
periphery of phthalocyanine, where complexation affects the electronic spectra only
indirectly by enhancing or diminishing the aggregation of planar molecules. From
Fig. 1, only slight broadening of the B band can be observed, but the Q band region
Fig. 1. UV/Vis of phthalocyanine-porphyrazine hybrid 3 (Ð) and its PdCl2 complex 4 (- - - - -)

1194
SË. B. Sesalan and A. GuÈl
is completely different for 4. Three peaks at 579, 637, and 684 nm together with a
shoulder at 703 nm indicate that the symmetry of the molecule has changed and that
the planar coordination sites around palladium(II) are no longer located in the plane
of the macrocycle.
Experimental
IR spectra were recorded on a Mattson 1000 FTIR spectrometer using KBr pellets. UV/Vis spectra
1
were measured on a UNICAM UV/Vis spectrophotometer. H NMR spectra were acquired on a
Bruker 250 MHz spectrometer. Elemental analyses were carried out by the analysis laboratory of the
TuÈbitak Marmara Research Center; the results were in good agreement with the calculated values.
1,2-Bis-hexylthio-maleonitrile [18, 19] and bis-benzonitrile-palladium dichloride [21] were prepared
according to literature procedures.
22,23-Di(hexylthio)-ꢁ-27H,29H-tribenzo[b,g,l]porphyrazine (3; C40H40N8S2)
Mg powder (312 mg, 13 mmol) was re¯uxed overnight in 50 cm3 of butanol with the addition of a few
crystals of I2. To this mixture, 310mg bis-hexylthio-maleonitrile (1 mmol) and 3.2 g phthalonitrile
(25 mmol) were added, and the mixture was re¯uxed for 12 h under N2. A dark-blue suspension was
obtained. After ®ltration, the ®ltrate was evaporated to dryness. The crude product was demetallized
with 5 cm3 of CF3COOH and treated with 10 cm3 methanol to precipitate the product. After ®ltering,
washing with methanol, and drying, the solid product mixture was treated with 15 cm3 CHCl3, stirred
for 1 h, and then ®ltered in order to separate the desired product from the insoluble metal-free
phthalocyanine. Evaporation of the solvent to dryness and addition of 10 cm3 methanol resulted in a
dark blue precipitate which was ®ltered, washed with methanol, and dried in vacuo.
Yield: 120 mg (17%); soluble in CH2Cl2, CHCl3, THF, and DMF; UV/Vis (CHCl3): ꢂmax ˆ 708
(48300), 676 (13090), 654 (11940), 616 (26600), 346 (34480) nm ("); IR (KBr): ꢃꢀ ˆ 3280 (NH),
3050 (Ar-CH), 3000-2900 (aliph. CH), 1250 cm 1; 1H NMR (CDCl3, ꢄ, 250 MHz): 8.13-7.39 (m, 12
Ar-H), 3.88 (d, 2 SCH2), 1.92-1.25 (m, 8 CH2), 0.96 (t, 2 CH3), 4.0 (broad s, 2 NH) ppm.
Palladium dichloride complex of 22,23-di(hexylthio)-ꢁ-27H,29H-tribenzo[b,g,l]porphyrazine
(4; C40H40N8S2PdCl2)
3 (696 mg, 1 mmol) was re¯uxed with 383 mg PdCl2(C6H5CN)2 (1 mmol) in 20 cm3 CHCl3 under N2
for 12 h. The mixture was ®ltered, and the ®ltrate was evaporated to dryness. When the residue was
treated with n-hexane, the crude product was precipitated. It was ®ltered, washed ®rst with n-hexane
and then with methanol, and dried in vacuo.
Yield: 200 mg (23%); soluble in CHCl3, CH2Cl2, and THF; UV/Vis (CHCl3): ꢂmax ˆ 703
(15560), 684 (20120), 637 (12920), 579 (11800), 344 (22160) nm ("); IR (KBr): ꢃꢀ ˆ 3280 (NH),
3050 (Ar-CH), 3000-2900 (aliph. CH), 1250 cm 1; 1H NMR (CDCl3, ꢄ, 250 MHz): 8.87-7.97 (m, 12
Ar-H), 3.74 (s, 2 SCH2), 1.56-1.01 (m, 8 CH2), 0.88 (t, 2 CH3), 1.3 (broad s, 2 NH) ppm.
Acknowledgements
È
Financial support of this research from Tubitak-Turkey (TBAG No. 1823) is gratefully acknowledged.
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Phthalocyanine-Porphyrazine Hybride Pd Complex
1195
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Received May 23, 2000. Accepted June 26, 2000