New type of tetrazine-substituted metallophthalocyanines by microwave irradiation: Synthesis and characterization

Article abstract of DOI:10.1002/hc.20623

5,6-bis(4-methylphenyl)-2,3-dihydro-1,2,3,4-tetrazine 2 was synthesized by the dimerization of ethyl p-methylbenzoateformylhydrazone 1 in hydrazinehydrate solution. 2,3-bis(4-methylphenyl)-6,7,14,15-tetrahydro[1,2,3,4]tetrazino [2,3d][1,8, 4,5]benzodithia

Full text of DOI:10.1002/hc.20623

Heteroatom Chemistry
Volume 21, Number 7, 2010
New Type of Tetrazine-Substituted
Metallophthalocyanines by Microwave
Irradiation: Synthesis and Characterization
Ece Tugˇba Saka, Nuri Yıldırım, and Halit Kantekin
Department of Chemistry, Faculty of Arts & Sciences, Karadeniz Technical University,
61080 Trabzon, Turkey
Received 22 February 2010; revised 17 May 2010
veloped around these interesting and advanced
ABSTRACT: 5,6-bis(4-methylphenyl)-2,3-dihydro-
materials [1–3]. Possible technological applications
of phthalocyanines, such as semiconductivity [4],
electrochromic displays [5], chemical sensors [6],
and catalysts [7–9], have encouraged many re-
searchers to synthesize various types of metal
phthalocyanine [4,5,10–12]. The increasing impor-
tance and use of phthalocyanines as advanced
materials have encouraged chemists to design
variables of the central metal ion and the periph-
eral substituents to reach the planned interesting
properties.
A major disadvantage of phthalocyanines and
metallophthalocyanines is their low solubility in or-
ganic solvents or water. The solubility can be in-
creased, however, by introducing crown ethers or
long-chain groups, such as alkyl or alkoxy, into the
peripheral positions of the phthalocyanine frame-
work [13–14]. Tetra-substituted phthalocyanines are
usually more soluble than the corresponding octa-
substituted phthalocyanines due to the formation of
constitutional isomers and the high-dipole moment
that results from the unsymmetrical arrangement of
the substituents at the periphery [15,16]. According
to their substituent positions, two types of tetra-
substituted macrocycles, which show significant
differences in their chemical and physical be-
haviors, can be distinguished. Substitution at
the more sterically crowded (nonperipheral) posi-
tion causes reduced aggregation tendencies more
than substitution at the b (peripheral) position
[17].
1,2,3,4-tetrazine 2 was synthesized by the dimeriza-
tion of ethyl p-methylbenzoateformylhydrazone 1 in
hydrazinehydrate solution. 2,3-bis(4-methylphenyl)-
6,7,14,15
-
tetrahydro[1,2,3,4]tetrazino [2,3d][1,8,
4,5]benzodithia-diazecine-10,11-dicarbonitrile 4 was
sythesized by cyclization reaction of tetrazine
monomer 2 onto 1,2-bis-(2-iodoethylmercapto)-4,5-
dicyanobenzene 3. Co(II) and Cu(II) phthalocyanine
complexes were prepared by reaction of the dinitrile
compound (4) with the chlorides of Co(II), Cu(II),
and DMAE at 175◦C, 350 W in a microwave oven
for 10 min. Zn(II)-phthalocyanine complex was
prepared by reaction of the dinitrile compound 4
with the acetate of Zn(II) and DMAE at 175◦C,
350 W in a microwave oven for 10 min. The new
compounds were characterized by a combination of
1
IR, H-NMR, 13C NMR, UV-vis, elemental analysis,
ꢀ
C
and MS spectral data.
2010 Wiley Periodicals, Inc.
Heteroatom Chem 21:456–461, 2010; View this article
online at wileyonlinelibrary.com. DOI 10.1002/hc.20623
INTRODUCTION
Phthalocyanines have been known as excellent func-
tional materials for a long time, so diverse chem-
ical and technological applications have been de-
Correspondence to: Halit Kantekin; e-mail: halit@ktu.edu.tr.
2010 Wiley Periodicals, Inc.
c
ꢀ
456

New Type of Tetrazine-Substituted Metallophthalocyanines by Microwave Irradiation: Synthesis and Characterization 457
and C S at 2230, 1048, and 963 cm−1, is in agree-
ment with the proposed structure. In the H-NMR
Metallophthalocyanine complexes (MPc) have
proved to be highly promising as photosensitizers for
photodynamic therapy (PDT), due to their intense
absorption in the red region of the visible light. High-
triplet state quantum yields and long-triplet lifetimes
are required for an efficient sensitization. The pho-
tophysical properties of the phthalocyanine dyes are
strongly influenced by the presence and nature of the
central metal ion. Complexation of phthalocyanine
with transition metals gives dyes with short-triplet
lifetimes [18].
In recent years, it has been recognized that
microwave processing has potential as an alterna-
tive to classical processing because of the inherent
advantages of microwave heating, which is selec-
tive, direct, rapid, internal, and controllable [19].
Microwave processing has therefore been applied
in such varied fields as pulp drying, food cook-
ing, organic synthesis, ceramic sintering, compos-
ite joining, chemical analyses, and waste treatment
[20–21].
1
spectrum of 4, the NH group of compound 2 dis-
1
appeared as expected. The H-NMR spectrum of 4
showed new signals at δ = (δ:ppm): 8.25 (s, 2H, Ar–
H), 8.14 (d, 4H, Ar–H), 7.40 (d, 4H, Ar–H), 2.48 (m,
8H, CH2–N, and CH2–S), 2.40 (s, 6H, CH3). In the
13C-NMR, spectrum of 4 indicated the presence of
nitrile carbon atom in 4 at δ = 113.85 ppm. The MS
mass spectrum of 4 shows a peak at m/z = 508 [M]+,
confirming formation of the desired compound. El-
emental analyses data are in good agreement with
this formulation desired.
In the IR spectrum of 5, the disappearance of
C N stretching vibration at 2230 cm−1 in the IR spec-
trum and, opposite this observation, C N stretching
vibration at around 1609 cm−1 satisfied this formula-
tion. The 1H-NMR spectra of tetra-substituted Zn(II)
phthalocyanine 5 show a complex pattern owing to
the mixed isomer character of the compound. The
1
complex 5 was found to be pure by H-NMR spec-
In addition, tetrazines are unique since they con-
stitute the most electron deficient aromatic family
of compounds, providing unusually high electron
affinity and charge transfer potential as conjugated
molecules [22].
Our previous studies have focused on synthesis
of phthalocyanines containing tetraaza [23], dithia-
diaza macrocyclic moieties [24], pyridyl groups
[25], and thiophenyl groups [26]. In the present
work, we describe the synthesis and characteriza-
tion of tetrazine compound 2, tetrazine containing
phthalonitrile compound 4, and then metallo ph-
thalocyanine complexes 5, 6, and 7 by microwave
irradiation.
tra with the substituent and ring proton observed
in their respective region. The resonance belonging
to ring protons was observed at 8.50 (s, 2H, Ar–H),
8.05 (d, 4H, Ar–H), 7.73 (d, 4H, Ar–H). The ethylene
bridge protons signals are at 2.52 (m, 32H, CH2–N
and CH2-S) and methyl protons signals are at 2.48 (s,
24H, CH3). In the 13C-NMR spectrum of compound
5, 12 carbon signals (152.06, 143.50, 137.87, 137.77,
126.77, 126.08, 125.78, 124.33, 123.56, 35.85, 32.71,
30.56) were seen. In the mass sprectrum of com-
pounds 5, the presence of a molecular ion peak at
m/z = 2095 [M+H]+ confirmed the purposed struc-
ture. Elementel analysis data of 5 gave satisfactory
results that were close to calculated values.
The IR spectra of 6 and 7 are similar to com-
pound 5. The disappearance of C N vibration for
compound 5 confirms the formation of these com-
pounds. Due to Cu(II) phthalocyanine 6 and Co(II)
phthalocyanine 7 being paramagnetic, 1H-NMR and
13C-NMR spectra cannot be taken. In the mass spec-
trum of compounds 6 and 7 the presence of molec-
ular ion peaks at m/z: 2095 [M+2H]+, 2090 [M]+, re-
spectively, confirmed the proposed structures. The
elemental analysis confirms the desired compounds
6 and 7.
The UV-vis absorption spectra of metalloph-
thalocyanines 5, 6, and 7 in pyridine show intense
Q absorption at λmax = 713, 707, and 698 nm, with
weaker absorptions at 641, 638, and 620 nm, respec-
tively. The single Q-bands in metallo phthalocyanine
derivatives 5, 6, and 7 are characteristic (Fig. 1). This
result is typical of metal complexes of substituted
and unsubstituted metallophthalocyanines with D4h
symmetry [29]. On the other hand, such split Q-band
RESULTS AND DISCUSSION
Metallophthalocyanine complexes 5, 6, and
7
were synthesized in three steps (Scheme 1).
The first step is the dimerization of ester
formylhydrazones [27]. In the second step, the
base-catalyzed cyclization reaction of 1,2-bis(2-
iodomercapto)-4,5-dicyanobenzene [28] 3 with 5,6-
bis(4-methylphenyl)-2,3-dihydro-1,2,3,4-tetrazine 2
afforded the dinitrile monomer 4. In the final step,
MPc were synthesized by microwave irradiation
(Scheme 1). The metallophthalocyanines 5, 6, and
7 were obtained from dicyano derivative 4 and cor-
responding anhydrous metal salts Zn(CH3COO)2,
CuCl2, and CoCl2, respectively, by microwave irri-
dation in 2-(dimethylamino)ethanol for 10 min.
In the IR spectrum of 4, the disappearance of
NH stretching vibration at 3321 cm−1, along with the
appearance of new bands, respectively, C N, C N,
Heteroatom Chemistry DOI 10.1002/hc

458 Saka, Yıldırım, and Kantekin
H3C
H3C
NNHCHO
C
OC2H5
N
N
H2NNH2.H2O
NH
NH
H3C
-
C2H5OH
(1)
(2)
H3C
H3C
H3C
CN
CN
N
N
N
I
I
S
S
CN
S
S
N
N
NH
NH
i
+
N
CN
H3C
(2)
(3)
(4)
ii
CH3
H3C
CH3
H3C
N
N
N
N
N
N
N
N
S
S
S
S
N
N
N
N
N
N
M
N
N
S
S
S
S
N
N
N
N
N
N
N
N
CH3
H3C
CH3
H3C
5
6
7
Compound
M
Zn
Cu
Co
SCHEME 1 The synthetic pathway for the preparation of the phthalocyanine complexes (5–7): (i) Dry CH3CN, dry K2CO3,
45◦C, (ii) 175◦C, 350 W, DMAE with Zn (CH3COO)2, CuCl2, and CoCl2, respectively.
absorptions in pyridine are due to π–π∗ transition of
this fully conjugated 18π electron systems [30].
reagents were of reagent-grade quality and were
used as purchased from commercial sources. All sol-
vents were dried and purified as described by re-
ported procedures [31]. IR spectra was recorded on
a Perkin Elmer 1600 FT-IR spectrophotometer, us-
ing KBr pellets or NaCl discs. 1H and 13C-NMR spec-
tra were recorded on a Varian Mercury 200 MHz
spectrometer in DMSO-d6; pyridine-d5 and chemical
shifts were reported (δ) relative to Me4Si as internal
standard. Mass spectra were measured on a Micro-
mass Quatro LC/ULTIMA LC-MS/MS spectrometer.
The elemental analyses were performed on a Costech
ECS 4010 instrument. Melting points were measured
EXPERIMENTAL
Chemicals and Instrumentation
Ethyl p-methylbenzoateformylhydrazone [27] and
1,2-bis-(2-iodoethylmercapto)-4,5-dicyanobenzene
[28] were prepared according to the literature. All
syntheses of phthalocyanine reactions were carried
under a dry nitrogen atmosphere using Standard
Schlenk techniques. All chemicals, solvents, and
Heteroatom Chemistry DOI 10.1002/hc

New Type of Tetrazine-Substituted Metallophthalocyanines by Microwave Irradiation: Synthesis and Characterization 459
2
2,3-Bis(4-methylphenyl)-6,7,14,15-tetrahydro-
[1,2,3,4]tetrazino[2,3][1,8,4,5]benzodithiadiazecine-
10,11-dicarbonitrile 4. 5,6-bis(4-methylphenyl)-2,3-
dihydro-1,2,3,4-tetrazine 2 (1.106 g, 4.2 mmol) was
dissolved in dry CH3CN (40 mL) under N2 atmo-
sphere. Then K2CO3 (1.43 g, 10.5 mmol) was added.
The reaction mixture was stirred under N2 at 45◦C for
1 h. To the solution, 1,2-bis(2-iodoethylmercapto)-
4,5-dicyanobenzene 3 (2.10 g, 4.2 mmol) was added
to the reaction mixture, and the system was de-
gased three times and stirred under N2 atmosphere
at 100◦C for 5 days. The end of the reaction was
controlled by thin-layer chromatography by using
methanol:ethylacetate (3:1). Then the reaction mix-
ture was cooled to room temperature. The reac-
tion mixture was filtered from blue filter paper and
the yellowish green precipitate removed. The so-
lution was evaporated, and the dark-yellow prod-
uct was washed with water and diethyl ether and
dried in vacuo over P2O5. The product was puri-
fied by silica gel column chromotograpy with chlo-
roform:methanol:ethylacetate (6:3:1). At the end of
this purification step, the suitable fractions were put
together and their solvent was evaporated under re-
duced pressure to 5 mL. Then the mixture was fil-
tered and washed with cold ethanol. Yield: 1.32 g
(62%), mp: 102–104◦C. Anal. Calcd for C28H24N6S2:
C, 66.14; H, 4.72; N, 16.53%. Found: C, 66.26; H, 4.65;
N, 16.02%. IR (KBr tablet) νmax/cm−1: 3065 (Ar–H),
2917–2850 (Aliph. C–H), 2230 (C N), 1659 (C N),
1594, 1504, 1421, 1396, 1303, 1221, 1186, 1048, 963,
928, 846. 1H-NMR. (DMSO-d6), (δ:ppm): 8.25 (s, 2H,
Ar–H), 8.14 (d, 4H, Ar–H), 7.40 (d, 4H, Ar–H), 2.48
(m, 8H, CH2-N and CH2-S), 2.40 (s, 6H, CH3). 13C-
NMR. (DMSO-d6), (δ:ppm): 143.53, 128.70, 126.43,
126.21, 125.58, 124.38, 122.20, 120.65, 113.85, 38.91,
38.50, 38.07. MS (FAB), (m/z): 508 [M]+.
1.5
1
0.5
0
500
600
700
λ ( nm )
800
900
FIGURE 1 UV-vis spectra of compounds 5 (--), 6 (. . . ), and
7 (–) in pyridine.
on an electrothermal apparatus and are uncorrected.
All reagents and solvents were of reagent-grade qual-
ity and were obtained from commercial suppliers.
All solvents were dried and purified as described by
Perrin and Armarego [31].
Methods
5,6-Bis(4-methylphenyl)-2,3-dihydro-1,2,3,4-tet-
razine 2. Ethyl p-methylbenzoateformylhydra-
zone 1 (2.13 g, 10.9 mmol) was dissolved in a
solution of hydrazine hydrate (1.36 g, 27.25 mmol)
in 60 mL of chloroform, and the reaction mixture
was preheated at 90◦C for 6 h. After that, the
flask was kept under reflux for 48 h. The resulting
solution was evaporated under reduced pressure
until dry, and yellow product was washed three
times with deionized water. The crude product was
crystallized from ethanol. The pale yellow solid
dried in vacuo. Yield: 1.24 g (58%), mp: 250–252◦C.
Anal. Calcd for C16H16N4: C, 72.72; H, 6.06; N, 21.21.
Found: C, 72.18; H, 6.05; N, 21.20%. IR (KBr tablet)
νmax/cm−1: 3321 (N-H), 3029 (Ar–H), 2918–2857
(Aliph. C-H), 1641 (C N), 1570, 1514, 1485, 1395,
1335, 1215, 1190, 1017, 962, 913, 857. 1H-NMR.
(DMSO-d6), (δ:ppm): 7.91 (d, 4H, Ar–H), 7.26 (d,
4H, Ar–H), 3.59 (s, 2H, N-H), 2.33 (s, 6H, CH3).
13C-NMR. (DMSO-d6), (δ :ppm): 143.52, 129.77,
128.71, 126.52, 125.13, 21.60. MS (FAB), (m/z): 264
[M]+.
Zn(II)-Containing Phthalocyanine 5. A mixture
of phthalonitrile 4 (0.3 g, 0.588 mmol), anhy-
drous Zn(CH3COO)2 (52.17 mg, 0.285 mmol), and
2-(dimethylamino)ethanol (DMAE) (3 mL) was ir-
radiated in a microwave oven at 175◦C, 350 W for
8 min. After cooling at room temperature the reac-
tion mixture refluxed with ethanol (40 mL) to precip-
itate the product, which was filtered off. The green
solid product was washed with hot ethanol and di-
ethyl ether and dried in vacuo over P2O5. Preparative
thin-layer chromatography was used with pyridine
as the solvent system for purification of zinc(II) ph-
thalocyanine. This product soluble pyridine, THF,
DMF, DMSO. Yield: 130 mg (43%), mp > 300◦C.
Elemental analyses (C112H96N24S8Zn) (2097.37g
mol−1) calcd: C, 64.00; H, 4.57; N, 18.30; Zn, 3.11.
Heteroatom Chemistry DOI 10.1002/hc

460 Saka, Yıldırım, and Kantekin
nm : [(10−5 ε dm3 mol−1 cm−1)]: 620(4.47), 698(4.72).
Found: C, 62.85; H, 4.37; N, 18.58; Zn, 3.08. IR (KBr
tablet) νmax/cm−1: 3061 (Ar–H), 2917–2853 (Aliph.
C–H), 1609 (C N), 1583, 1481, 1373, 1174, 1111,
1064, 941, 842, 746, 529. 1H-NMR. (DMSO-d6),
(δ:ppm): 8.50 (s, 8H, Ar–H), 8.05 (d, 16H, Ar–H),
7.73 (d, 16H, Ar–H), 2.52 (m, 32H, CH2–N and
CH2-S), 2.48 (s, 24H, CH3). 13C-NMR. (Pyridine-
d5), (δ:ppm): 152.06, 143.50, 137.87, 137.77, 126.77,
126.08, 125.78, 124.33, 123.56, 35.85, 32.71, 30.56.
UV-vis (pyridine): λmax/nm : [(10−5 ε dm3 mol−1
cm−1)]: 641(3.84), 713(4.12). MS (FAB), (m/z): 2095
[M+H]+.
MS (FAB), (m/z): 2090 [M]+.
ACKNOWLEDGMENT
Financial support from the Unit of the Scien-
tific Research Projects of Karadeniz Technical Uni-
versity (Project No.: 2006.111.02.1) is gratefully
acknowledged.
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10 min. After cooling at room temperature the reac-
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itate the product, which was filtered off. The green
solid product was washed with hot ethanol and di-
ethyl ether and dried in vacuo. The green product
was purified by preparative thin-layer chromatog-
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707(4.44). MS (FAB), (m/z): 2095 [M+2H]+.
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