Synthesis and spectral parameters of tetra(6-tert-butyl-2,3-quinoxalino) porphyrazine and its metal complexes

Article abstract of DOI:10.1134/S1070363208070293

Tetra(6-tert-butyl-2,3-quinoxalino)porphyrazine and its complexes with bivalent metals were synthesized for the first time by template tetramerization of 6-tert-butylquinoxaline-2,3-dicarbonitrile. The obtained macrocyclic compounds are soluble in hydroph

Full text of DOI:10.1134/S1070363208070293

ISSN 1070-3632, Russian Journal of General Chemistry, 2008, Vol. 78, No. 7, pp. 1447–1451. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © S.V. Efimova, A.B. Korzhenevskii, O.I. Koifman, 2008, published in Zhurnal Obshchei Khimii, 2008, Vol. 78, No. 7, pp. 1214–1218.
Synthesis and Spectral Parameters
of Tetra(6-tert-butyl-2,3-quinoxalino)porphyrazine
and Its Metal Complexes
S. V. Efimovaa, A. B. Korzhenevskiib, and O. I. Koifmanb
a Ivanovo State University of Chemical Technology, pr. F. Engel’sa 7, Ivanovo, 153000 Russia
e-mail: sef@isuct.ru
b Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
Received June 28, 2007
Abstract—Tetra(6-tert-butyl-2,3-quinoxalino)porphyrazine and its complexes with bivalent metals were synthesized for
the first time by template tetramerization of 6-tert-butylquinoxaline-2,3-dicarbonitrile. The obtained macrocyclic
compounds are soluble in hydrophobic solvents. Their electronic absorption spectra in organic solvents and the spectra of
the corresponding protonated forms in sulfuric acid were studied.
DOI: 10.1134/S1070363208070293
Potential structural diversity of tetraarenoporphyr-
azines, as well as diversity of practically useful
properties of already prepared compounds of this
series, determines the necessity of further synthesis of
new derivatives and studies on their properties with a
view to develop materials of new generation for
various fields of practical application. Undoubtedly,
aza analogs of naphthalocyanine attract strong interest
from the viewpoints of both fundamental science and
possible practical use. However, studies and
application of known octaaza-2,3-naphthalocyanines,
i.e., tetra-2,3-quinoxalinoporphyrazines are considerably
limited, or (in some cases) they become impossible
because of very poor solubility of these compounds in
organic solvents [1].
properties of these compounds but also the scope of
their application in various fields, from chemistry and
medicine to optoelectronics. Although some tert-butyl-
substituted tetra(azaareno)porphyrazines, namely tetra
(6-tert-butyl-3,4-pyridino)porphyrazine [3] and tetra(5-
tert-butyl-2,3-pyrazino)porphyrazine [4] and their
metal complexes have been synthesized and character-
ized by spectral methods, syntheses of copper and
vanadyl complexes of tetra(tert-butylquinoxalino)por-
phyrazine have been reported only in [5, 6].
The goal of the present study was to synthesize tetra
(6-tert-butyl-2,3-quinoxalino)porphyrazine (II) and its
complexes III–V with bivalent metals and examine
their spectral parameters. Compounds II–V were
prepared as shown in Scheme 1.
It is known that introduction of various peripheral
substituents into tetraarenoporphyrazine molecules
makes them better or lesser soluble in different
solvents, depending on the substituent nature and their
number. Introduction of tert-butyl groups into the
phthalocyanine molecule is known to considerably
improve the solubility in organic solvents, whereas the
electronic and geometric structure remains almost
unchanged, as follows from almost complete identity
of the electronic absorption spectra of the substituted
and parent compounds in both DMF and H2SO4 [2].
Such liophilization could extend not only the set of
methods applicable for studying physicochemical
Compounds II–V were not reported previously;
they were isolated as dark green powders which did
not melt up to 350°C. Compounds II–V are much
better soluble in DMF and DMSO as compared to
unsubstituted analogs and, unlike the latter, are soluble
in chloroform, benzene, and alcohol. Therefore, it was
possible to purify them by column chromatography on
silica gel. Tetra(6-tert-butyl-2,3-quinoxalino)porphyr-
azine (II) and its metal complexes III–V were isolated
as crystal hydrates. Before studying their spectral
properties, they were subjected to thermal treatment at
423–523 K under a residual pressure of 10–4 MPa. The
1447

1448
EFIMOVA et al.
Scheme 1.
Bu-t
t-Bu
N
N
N
N
N
H2
N
NC
NH
CN
N
N
N
N
N
N
M(OAc)2
C
C
CN
CN
NH2
CF3COOH
N
M
N
+
N
t-Bu
HN
N
t-Bu
I
N
N
NaOH
N
Bu-t
Bu-t
t-Bu
t-Bu
N
N
N
N
N
NH
N
N
N
N
HN
N
N
N
N
N
Bu-t
II, M = H2; III, M = Cu; IV, M = Co; V, M = Zn.
t-Bu
completeness of dehydration was checked by
thermogravimetric analysis.
metal complexes, which lack Soret band, complexes
III–V displayed a strong absorption band at λ ~350 nm.
It was interesting to examine the effects of the
central metal ion and solvent nature on the spectral
parameters of compounds II–V in solution. The
electronic absorption spectra of tetra(6-tert-butyl-2,3-
quinoxalino)porphyrazine (II) and its metal complexes
III–V in aprotic solvents (benzene, chloroform; Fig. 1)
contained strong bands in the yellow–red and UV
regions, which is typical of phthalocyanines.
Unfortunately, among common aprotic solvents, only
DMF and DMSO can be used for studying the spectra
of tetra(2,3-quinoxalino)porphyrazines and their tetra-
tert-butyl-substituted analogs. Therefore, we were able
to estimate the effect of peripheral alkyl groups on the
electronic absorption spectra only in DMF. In the
spectrum of II, as well of its unsubstituted analog, the
first Q-band is not split. The same is characteristic of
phthalocyanine. Unlike the spectra of unsubstituted
Introduction of tert-butyl groups almost does not
change the position of the first absorption band in the
spectra of metal-free compound II and its copper and
zinc complexes III and V, while cobalt complex IV is
characterized by blue shift of that absorption
maximum (Δλmax = 11 nm). On the other hand, its
vibrational satellite in the spectra of copper and zinc
complexes III and V is resolved better, the shift of the
absorption maximum being minimal (Δλmax = 3 and –
7 nm, respectively), but it disappears from the spectra
of ligand II and cobalt complex (IV) (the
corresponding unsubstituted analogs show an
inflection point).
Interestingly, the spectra of modified tetra-2,3-
quinoxalinoporphyrazines (except for zinc complex V)
contain fairly intense absorption bands in the region λ
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 7 2008

SYNTHESIS AND SPECTRAL PARAMETERS
IV
1449
D
III
1.4
V
1.2
1.0
0.8
0.6
0.4
0.2
II
300
400
500
600
700
800
λ, nm
Fig. 1. Electronic absorption spectra of tetra(6-tert-butyl-2,3-quinoxalino)porphyrazines II–V in DMF.
Electronic absorption spectra of tetra(6-tert-butyl-2,3-
quinoxalino)porphyrazines II–V
640–650 nm, whose origin was not identified.
Analogous bands were also observed in chloroform
(II, V) and benzene (III–V). Complexation of
porphyrazine II, as well as of its unsubstituted analog,
with copper and zinc is not accompanied by shift of the
Q-band, while the Q-band in the spectrum of cobalt
complex IV is displaced by 11 nm toward shorter
wavelengths.
λmax, nm (log ε)
Solvent
II
III
IV
V
DMF
707 (4.61)
–
704 (4.52)
670 (4.02)
647 (4.12)
352 (4.65)
707 (4.65)
664 (4.19)
–
695 (4.78) 707 (4.32)
–
669 (4.11)
–
Solvatochromic effect (see table; Figs. 1, 2) for the
alkyl-substituted macrorings is reflected in the
appearance of absorption bands at λ 640–650 nm and
vibrational satellite of the Q-band, position of the Soret
band (the strongest effect is observed for complex III:
Δλmax = –22 nm in going from DMF to benzene), and
absorption intensities. The position of the Q-band in
the spectra of solutions of the ligand and metal
complexes almost does not change: the maximal Δλ
value (+10 nm) was found for complex V in going
from chloroform to benzene.
640 (4.32)
350 (4.78)
712 (4.78)
679 (4.41)
644 (4.32)
347 (4.72)
648 (4.34)
348 (4.79) 347 (4.41)
704 (4.62) 704 (4.58)
660 (4.38) 671 (4.25)
CHCl3
–
645 (4.15)
344 (4.68)
708 (4.12)
–
342 (4.75) 357 (4.78)
698 (4.08) 714 (4.18)
Benzene 710 (4.25)
665 (3.78)
–
–
667 (3.68)
648 (3.63)
329 (4.38)
745 (4.48)
–
647 (3.54) 650 (3.52)
350 (4.28) 348 (4.34)
746 (4.25) 768 (4.72)
603 (4.58) 605 (4.63)
535 (4.62) 560 (4.52)
402 (4.89) 390 (5.12)
268 (4.85) 256 (4.93)
347 (4.45)
H2SO4
750 (4.21)
612 (4.08)
–
Study on the electronic absorption spectra of tetra
(6-tert-butyl-2,3-quinoxalino)porphyrazines II–V in
concentrated sulfuric acid (Fig. 3) showed that
peripheral alkylation almost does not affect the mode
of protonation. Like unsubstituted tetraquinoxalino-
porphyrazine and its metal complexes, the first band in
544 (4.51)
395 (4.88)
251 (4.91)
207 (4.89)
378 (4.86)
264 (4.78)
205 (4.93)
–
–
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 7 2008

1450
EFIMOVA et al.
D
IV
1.2
III
V
1.0
0.8
0.6
0.4
0.2
II
300
400
500
600
700
800
λ, nm
Fig. 2. Electronic absorption spectra of tetra(6-tert-butyl-2,3-quinoxalino)porphyrazines II–V in chloroform.
log ε
5
V
4
IV
III
II
3
150
250
350
450
550
650
750
850
λ, nm
Fig. 3. Electronic absorption spectra of tetra(6-tert-butyl-2,3-quinoxalino)porphyrazines II–V in 17.5 M H2SO4.
the electronic absorption spectra of II–V in sulfuric
acid shifts red relative to its position in the spectra
recorded from organic solutions, which is quite
consistent with the up-to-date concepts on polarization
of the main chromophore upon protonation. The
magnitude of the red shift is almost the same for the
substituted and unsubstituted compounds. As in the
spectra in DMF, coordination of ligand II to the
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 78 No. 7 2008

SYNTHESIS AND SPECTRAL PARAMETERS
1451
examined metals in sulfuric acid solution leads to a
blue shift of the first absorption band whose position is
weakly related to the metal nature.
subjected to chromatography on silica gel using
chloroform was eluent, and the eluate was evaporated
to dryness. Yield 75%. Found, %: C 70.95, 71.00; H
5.26, 5.29; N 23.77, 26.71. C56H50N16. Calculated, %:
C 71.04; H 5.28; N 23.67.
EXPERIMENTAL
(24(5),74(5),124(5),174(5)-Tetra-tert-butyl-5,10,15,20-
tetraazatetraquinoxalino[2,3-b:2′,3′-g:2″,3″-l:2′′′,
3′′′-q]porphyrin) metal complexes III–V (general
The electronic absorption spectra were measured on
a Perkin–Elmer Lambda 20 spectrophotometer using
rectangular cells with a cell path length of 0.1 to 1 cm;
concentration 10–4–10–6 M. The IR spectra were
obtained from samples pelleted with KBr on an Avatar
360 FT-IR ESP spectrometer with Fourier transform.
The elemental compositions were determined on a
FlashEATM 1112 analyzer.
procedure). A mixture of 0.23
g
of 6-tert-
butylquinoxaline-2,3-dicarbonitrile (I), 0.25 mmol of
copper(II), cobalt(II), or zinc(II) acetate, and a
catalytic amount of ammonium molybdate was heated
to 200–220°C, and the melt thus formed was kept for
30 min at that temperature. The mixture was cooled
and treated in succession with boiling 5% hydrochloric
acid and boiling 5% aqueous ammonia, and the
precipitate was filtered off and subjected to
chromatography on silica gel using chloroform as
eluent. Complexes III–V were isolated as dark green
finely crystalline substances with metal luster, which
did not melt up to 400°C; compounds III–V are
readily soluble in organic solvents.
2,3-Diiminosuccinonitrile was synthesized by
oxidation of 2,3-diaminomaleonitrile with dichlorodi-
cyanobenzoquinone [7]. Yield 92%, mp 165–166°C.
Found, %: C 45.55, 45.69; H 1.90, 1.88; N 52.55,
52.43. C4H2N4. Calculated, %: C 45.28; H 1.88; N
52.83.
4-tert-Butylbenzene-1,2-diamine was synthesized
by successive nitration and reduction of 4-tert-
butylaniline [8]. Yield 67%, mp 96–97°C. Found, %: C
71.37, 71.40; H 9.62, 9.61; N 19.01, 18.99. C10H16N2.
Calculated, %: C 71.42; H 1.53; N 19.05.
Complex III. Yield 68%. Found, %: C 66.67,
66.62; H 4.75, 4.79; N 22.25, 22.28. C56H48N16Cu.
Calculated, %: C 66.70; H 4.76; N 22.23.
6-tert-Butylquinoxaline-2,3-dicarbonitrile (I). A
mixture of 0.5 g of 2,3-diiminosuccinonitrile and 0.5 g
of tert-butylbenzene-1,2-diamine was added over a
period of 30 min to 10 ml of trifluoroacetic acid,
maintaining the temperature not exceeding 20°C. The
resulting suspension was left to stand at room
temperature, Trifluoroacetic acid was removed under
reduced pressure, and the residue was washed with
water, dried, and recrystallized from benzene. Yield
0.73 g (52%), mp 110–112°C. IR spectrum (KBr), ν,
cm–1: 3242 (C=N), 2978–2875 (C–H), 2252 (C≡N).
Found, %: C 68.45, 68.58; H 5.02, 5.01; N 26.53,
26.41. C14H12N4. Calculated, %: C 68.85; H 4.91;
N 26.22.
(24(5),74(5),124(5),174(5)-Tetra-tert-butyl-5,10,15,20-
tetraazatetraquinoxalino[2,3-b:2′,3′-g:2″,3″-l:2′′′,
3′′′-q]porphyrin) (II). A mixture of 1 g of 6-tert-
butylquinoxaline-2,3-dicarbonitrile (I) and 1 g of
anhydrous sodium hydroxide was heated to 200–220°
C, and the melt was kept for 10–15 min at that
temperature. The mixture was cooled and ground with
distilled water, and the precipitate was filtered off. The
product was washed on a filter in succession with
distilled water (until neutral washings), 50 ml of
hydrochloric acid (slowly), and water again and
Complex IV. Yield 57%. Found, %: C 66.97, 66.99;
H
4.75, 4.79;
N
22.34, 22.32. C56H48N16Co.
Calculated, %: C 67.00; H 4.78; N 22.33.
Complex V. Yield 74%. Found, %: C 66.62, 66.61;
H
4.73, 4.74;
N
22.22, 22.23. C56H48N16Zn.
Calculated, %: C 66.60; H 4.75; N 22.20.
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