The symmetrical porphyrazine with annulated six membered rings

Article abstract of DOI:10.1016/j.poly.2009.12.012

Tetrakis(cyclohexylpyrazino)porphyrazinato magnesium(II) with annulated six membered rings has been prepared by two different methods. In Method A: cyclotetramerization of 2,3-dicyano-5,6-cyclohexanopyrazine (1) in the presence of Mg(OPr)₂ in n-propanol afforded the tetrakis(cyclohexylpyrazino)porphyrazinato magnesium(II) (2). In Method B: selenodiazole rings on the periphery of tetrakis(selenodiazole)porphyrazinato magnesium(II) were opened by the action of H₂S to yield the vicinal diamino functionalities. The ring closure of the vicinal diamino groups with 1,2-cyclohexanedione afforded the tetrakis(cyclohexylpyrazino) porphyrazinato magnesium(II) (2).

Full text of DOI:10.1016/j.poly.2009.12.012

Polyhedron 29 (2010) 1314–1316
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The symmetrical porphyrazine with annulated six membered rings
*
Hilal Onay, Burak Esat, Ramazan Öztürk
Fatih University, Department of Chemistry, TR 34500, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Tetrakis(cyclohexylpyrazino)porphyrazinato magnesium(II) with annulated six membered rings has
been prepared by two different methods. In Method A: cyclotetramerization of 2,3-dicyano-5,6-cyclohex-
anopyrazine (1) in the presence of Mg(OPr)2 in n-propanol afforded the tetrakis(cyclohexylpyrazino)por-
phyrazinato magnesium(II) (2). In Method B: selenodiazole rings on the periphery of
tetrakis(selenodiazole)porphyrazinato magnesium(II) were opened by the action of H2S to yield the vic-
inal diamino functionalities. The ring closure of the vicinal diamino groups with 1,2-cyclohexanedione
afforded the tetrakis(cyclohexylpyrazino) porphyrazinato magnesium(II) (2).
Received 1 October 2009
Accepted 10 December 2009
Available online 16 December 2009
Keywords:
Porphyrazine
Tetrakis(selenodiazole)porphyrazine
1,2-Cyclohexanedione
1,2-Diaminomaleonitrile
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
porphyrazine and followed by addition of a-diketone (1,2-cyclo-
hexadione) to get the ring closure and (Method B): the Linstead
macrocyclization of the 2,3-dicyano-5,6-cyclohexapyrazine in the
presence of Mg(II)-propylate in n-propanol.
Porphyrazine systems (tetrapyrrolic macrocycles) and their me-
tal complexes are investigated in the field of basic research and as
materials for practical applications [1–4]. One synthetic route to
octakis-functionalized porphyrazine is the cyclization of the func-
tionalized dicyano precursor in the presence of magnesium alkox-
ide (usually propanol and butanol are used) [5–9]. Although, the
amino functionalized derivatives of porphyrazine complexes are
commonly desired, the direct macrocyclization of 1,2-diaminoma-
leonitrile has been unsuccessful. It has been shown that if the ami-
no groups were locked in a cyclic structure they would couple
more strongly and therefore make the corresponding porphyrazine
synthesis more efficient [10]. The ring form of 1,2,5-thiadiazole
and 1,2,5-selenodiazole derivatives of maleonitriles are utilized
in the synthesis tetrakis(thiadiazole)porphyrazine (TTDPz) or tet-
rakis(selenodiazole)porphyrazine (TSeDPz), respectively [10–13].
Tetrakis(selenodiazole)porphyrazines can be reductively converted
into their corresponding octaaminoporphyrazine intermediate by
the action of H2S with release of the Se atoms. These porphyrazines
having vicinal diamino functionalities can also be used as complex
forming scaffolds through peripheral chelating ligands [14–17].
The annulation to the porphyrazine molecule through the ring clo-
sure of the vicinal diamino groups with several diketones opens up
a new synthetic approach to the structural modification of the
symmetrical porphyrazine macrocycle.
2. Experimental
All reagents and solvents were of reagent grade and used as re-
ceived. FT-IR measurements were performed with a Perkin–Elmer
BXII ATR spectrophotometer, UV–vis measurements were carried
out with Unicam double-beam spectrophotometer, elemental anal-
ysis by a Carlo Erba 1106 instrument, and 1H NMR and 13C NMR
measurements were carried out in DMSO-d6 or CDCl3 using a Bru-
ker 400 MHz instrument. The TSeDPz was prepared according to
literature [10].
2.1. Synthesis of ligand (1)
Diaminomaleonitrile (250 mg, 2.31 mmol) and 1,2-cyclohexadi-
one (63 mg, 5.62 mmol) were refluxed for 2 h in absolute ethanol
(20 ml) in the presence of catalytic amount of p-toluene sulfonic
acid. After evaporation of the solvent under reduced pressure, the
ligand was extracted into organic phase from solid material with
20 ml diethyl ether. When the solvent was removed, the ligand
was obtained with 75% yield. IR:
m : 2945m (C–H),
max/cmÀ1
2200m (C„N), 1614m (C@C, in pyrazine), 1376s, 1206m. Calc.
for C10N4H8: 184.12, Found: MALDI-MS (m/z): 183.12. 1H NMR
(400 MHz, DMSO-d6): d/ppm: 3.05 (2H, t) and 1.92 (2H, t). 13C
NMR (400 MHz, DMSO-d6): d/ppm: 114.22 (C„N), 129.89 (C@C),
158.29 (C@N), 21.00(C–C) and 31.75(C–C). Anal. Calc. for
C10H8N4: C, 65.21; H, 4.38; N, 30.41. Found: C, 65.19; H, 4.35; N,
30.38%.
We report here; the synthesis of the symmetrical porphyrazine
with annulated six membered rings by (Method A): the reductive
deselenation of TSeDPzMg with H2S in pyridine to form octaamino-
* Corresponding author. Tel.: +90 212866 33 00; fax: +90 212866 34 02.
E-mail address: rozturk@fatih.edu.tr (R. Öztürk).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.12.012

H. Onay et al. / Polyhedron 29 (2010) 1314–1316
1315
Scheme 1. Synthesis of tetrakis(cyclohexylpyrazino) porphyrazinato magnesium(II) (2).
2.2. Synthesis of tetrakis(cyclohexylpyrazino)porphyrazinato
3. Results and discussion
magnesium(II) (2)
In this work, we have synthesized tetrakis(cyclohexylpyrazi-
no)porphyrazinato magnesium(II) (2) by two different methods.
In the Method A: The reductive deselenation of TSeDPzMg per-
formed through the intermediate formation of octaaminoporphyr-
azine (Pz-(NH2)8Mg) by using H2S in pyridine followed by addition
Method A: Freshly prepared TSeDPz (50 mg, 0.057 mmol) [10]
was suspended in pyridine (20 ml), and gaseous H2S was bubbled
through the suspension for about 5 min. After evaporation of the
solvent under reduced pressure, the solid material was washed five
times with 20 ml of CHCl3. The solid crude product (ca. 300 mg)
was suspended in absolute ethanol (25 ml), then 1,2-cyclohexadi-
one (158 mg, 1.4 mmol) and catalytic amounts of p-toluenesulfonic
acid were added and the reaction mixture was refluxed for 8 h.
After cooling, the solid material was separated by centrifugation,
then washed with ethanol and brought to constant weight in a vac-
uum desiccator. The solid was extracted with several portions (four
to six) of pyridine (10 ml). A dark green solid tetrakis(cyclo-
hexylpyrazino)porphyrazine (2) was obtained from evaporation
of a-diketone (1,2-cyclohexadione) resulting in the ring closure of
the amino groups to yield tetrakis(cyclohexylpyrazino)porphyraz-
inato magnesium(II) (2) (35% yield) (Scheme 1). In the Method B
(Linstead macrocyclization): Firstly, 2,3-dicyano-5,6-cyclohexa-
pyrazine ligand (1) has been prepared by the reaction of diamino-
maleonitrile with 1,2-cyclohexadione in absolute ethanol under
nitrogen with a reasonable yield (77%). After that, the template
of freshly prepared Mg(OPr)2 and 2,3-dicyano-5,6-cyclohexapyr-
azine ligand (1) in n-propanol under reflux for 12 h gave the com-
pound 2 in good yield (ꢀ65%) (Scheme 1). In the 1H NMR spectrum
of the 2,3-dicyano-5,6-cyclohexapyrazine ligand (1), two different
peaks of CH2 groups in the cyclohexyl groups appeared at 3.05 ppm
(t) and 1.92 ppm (t). And also in the 13C NMR spectrum, peaks at
114.22 (C„N), 129.89 (C@C), 158.29 (C@N), 21.00 and 31.75 (C–
C, cyclohexyl ring) are consistent with the structure of the ligand.
In the MALDI-MS spectrum, the molecular ion peak appeared at
184.12 m/z.
of these pyridine solutions (yield: 35%). IR:
(C–H), 1630w (C@C), 1500w ( (CNmeso)), 1238s (
(CN)), 1090 m (d(pyr)). UV–vis (in DMSO) kmax (nm) (log e
m
max/cmÀ1: 2985m
(pyr)), 1142s
):
m
m
(m
352 (0.857), 636 (0.698). Calc. for C40N16H32Mg: 760.42, Found:
MALDI-MS (m/z): 763.05 [M+3H]+. 1H NMR (ppm, in DMSO-d6):
2.28 and 1.23 (–CH2 in pyrazino groups). Anal. Calc. for
C40H32N16Mg: C, 63.12; H, 4.24; N, 29.44. Found: C, 63.15; H,
4.26; N, 29.43%.
Method B: Magnesium metal (93 mg, 3.88 mmol) and a piece
of iodine crystal were refluxed in n-propyl alcohol (15 ml) to
obtain a suspension of magnesium propylate(MgOPr)2. 100 mg,
0.641 mmol of ligand (1) was added into mixture and the
reaction was continued for further 6 h. After cooling to room tem-
perature, the mixture was filtered and the solvent was evaporated.
The solid material was washed with 15 ml of 10% Na2CO3 two
times and with water till neutrality and with ethanol then dried
The tetrakis(cyclohexylpyrazino)porphyrazinato magnesium(II)
(2) molecule has very interesting spectroscopic features resem-
bling the phthalocyanine analogues. The annulation of selenodiaz-
ole rings to the porphyrazine core highly influences the electronic
and vibrational states of the TSeDPzMg. In the FT-IR spectra, the
vibrations of the central porphyrazine core are strongly coupled
with those of annulated heterocycles. The strong C–H stretching
vibration band at around 2934 cmÀ1 corresponds to the presence
of the cyclohexyl groups on the peripheral positions of the por-
phyrazine core. The stretching vibrations of the meso-N bridge
under vacuum (60% yield); IR:
(C@C), 1532w (CNmeso)), 1236m
1148m and 1046w (d(Pyr)). UV–vis (in DMSO) kmax (nm) (log
m
max/cmÀ1: 2934m (C–H), 1630w
(Pyr)), 1148m (CN)),
):
(m
(m
(m
e
(m
(CNmeso)) and the skeleton C@C appear as weak-medium peaks
at around 1530 and 1637 cmÀ1, respectively. The skeletal vibra-
tions of pyrrole rings, (Pyr), are strongly mixed with the (C@N)
352 (0.875), 636 (0.995). Calc. for C40N16H32Mg: 760.42, Found:
MALDI-MS (m/z): 763.0 [M+3H]+. 1H NMR (ppm, in DMSO-d6):
2.29 and 1.24 (–CH2 in pyrazino groups). Anal. Calc. for
C40H32N16Mg: C, 63.12; H, 4.24; N, 29.44. Found: C, 63.14; H,
4.27; N, 29.41%.
m
m
vibrations of the annulated selenodiazole rings and give the in-
tense IR bands at 1235 cmÀ1. The disappearance of the strong
stretching vibrations of the SeN bonds in 1,2,5-selenodiazoles

1316
H. Onay et al. / Polyhedron 29 (2010) 1314–1316
TSeDPzMg (at 676 nm) disappears and a broad band at 530 nm
with a shoulder at 620 nm appears. This can be attributed to the
octaaminoporphyrazine Pz-(NH2)8Mg complex. The coupling reac-
tion between 1,2-cyclohexadione and Pz-(NH2)8Mg gave the target
molecule of tetrakis(cyclohexylpyrazino)porphyrazinato magne-
sium(II) (2).
In the UV–vis spectrum of compound 2 in DMSO, the Q band
absorption is at 636 nm (Fig. 1) shows a hypsochromic shift about
40 nm which may due to the expansion of the porphyrazine ring
via fusing of the pyrazine substitutions to the peripheral positions.
In the MALDI-MS spectrum of the compound 2, the peak at
763.52 m/z is consistent with molecular ion [M+3H]+ peak.
4. Conclusion
In conclusion, we have prepared porphyrazine molecules with
the fused six membered pyrazino rings by two different methods.
The choice of coupling diketones may influence the optical, physi-
cochemical and solubility properties of those macrocyclic com-
pounds. We have chosen the 1,2-cyclohexadione as a-diketone to
overcome the solubility problem of porphyrazines by attachment
of such alicyclic groups on the peripheries.
Fig. 1. UV–vis spectra of TSeDPzMg (- - -), compound 2 (Method A) (
compound 2 (Method B) (—) and Pz-(NH2)8Mg(Á Á ÁÁ Á Á) in DMSO.
),
m
(SeN) at 716 and 640 cmÀ1 shows the deselenation of the
Acknowledgment
TSeDPzMg prepared by Method B. The in-plane deformations of
the pyrrolenine rings, d(Pyr), give a strong IR band at 1084 cmÀ1
and a weak-medium band at 1042 cmÀ1
. The peaks around
This work was supported by the Research Fund of the Fatih Uni-
versity under the Project No. P50020802-2.
1142–1147 cmÀ1 indicates the resonating C–N groups belonging
to six membered rings which were not observed in the spectrum
of TSeDPzMg. The common peaks for the core of the porphyrazine
macrocycle appeared at 149.4, 137.5, 128.9 125.9 and 124.8 ppm.
In the 13C NMR spectrum, the disappearance of the C„N nitrile
at 118 ppm for the ligand and the appearance of the pyrrolic C–N
at 137.5 ppm prove the formation of the porphyrazine molecule.
Also, the C–CH2 peaks for cyclohexyl groups (in the ligand ob-
served at 21.0 and 31.7) appeared at 19.3 and 30.7 ppm in the por-
phyrazine molecule.
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*
*
p–p and n–p transitions
*