Synthesis and spectral properties of 1,2,5-thiadiazolo-, 1,2,5-selenadiazolo-, and benzo-fused β-phenyl-substituted porphyrazines

Article abstract of DOI:10.1134/S1070428007120202

Cross cyclotetramerization of trans-2,3-diphenylbutanedinitrile with 1,2,5-thia(selena)diazole-3,4-dicarbonitriles or phthalodinitrile in the presence of magnesium butoxide gave mixtures of Mg(II) porphyrazine complexes which were treated with trifluoroac

Full text of DOI:10.1134/S1070428007120202

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 12, pp. 1854–1863. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © P.A. Stuzhin, I.V. Pimkov, A. Ul’-Khak, S.S. Ivanova, I.A. Popkova, D.I. Volkovich, V.A. Kuz’mitskii, M.-P. Donzello, 2007,
published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43, No. 12, pp. 1848–1857.
Synthesis and Spectral Properties
of 1,2,5-Thiadiazolo-, 1,2,5-Selenadiazolo-, and Benzo-Fused
β-Phenyl-Substituted Porphyrazines
P. A. Stuzhina, I. V. Pimkova, A. Ul’-Khaka, S. S. Ivanovaa, I. A. Popkovaa, D. I. Volkovichb,
V. A. Kuz’mitskiib, and M.-P. Donzelloc
a Ivanovo State University of Chemical Technology, pr. F. Engel’sa 7, Ivanovo, 153460 Russia
e-mail: stuzhin@isuct.ru
b Institute of Molecular and Atomic Physics, National Academy of Belarus, Minsk, Belarus
c Universita di Roma “La Sapienza,” Rome, Italy
Received January 26, 2007; revised August 23, 2007
Abstract—Cross cyclotetramerization of trans-2,3-diphenylbutanedinitrile with 1,2,5-thia(selena)diazole-3,4-
dicarbonitriles or phthalodinitrile in the presence of magnesium butoxide gave mixtures of Mg(II) porphyrazine
complexes which were treated with trifluoroacetic acid to isolate unsymmetrical hexaphenyl-substituted
1,2,5-thia(selena)diazolo- and benzo-fused porphyrazines together with diphenyltribenzoporphyrazine. Their
1H NMR and electronic absorption spectra (in the UV and visible regions) were recorded. The effect of benzene
and heteroring fusion on the electronic and steric structure and spectral properties of porphyrazine derivatives
was studied in terms of the molecular orbital perturbation theory and semiempirical quantum-chemical calcula-
tions (AM1, PM3, ZINDO/S, CNDO/S).
DOI: 10.1134/S1070428007120202
Fusion of various heterorings considerably affects
physical and chemical properties of porphyrazines
(PA) [1]. We previously synthesized tetra(1,2,5-thiadi-
azolo)porphyrazine (H2{SN2}4PA) [2], its selenium-
containing analog H2{SeN2}4PA [3], and benzo-
porphyrazines with fused 1,2,5-thiadiazole [4–6] or
1,2,5-selenadiazole fragments [4]. Like phthalocyanine
H2Pc, these compounds possess a 42π-electron chromo-
phore, and they may be regarded as heteroelement-
containing analogs of phthalocyanine. In the present
work we synthesized porphyrazines with a contracted
30π-electron chromophore, namely hexa-β-phenylpor-
phyrazines having only one fused 1,2,5-thiadiazole,
1,2,5-selenadiazole, or benzene ring, and examined
how the nature of the fused ring affects their spectral
parameters. The relations between the size and sym-
metry of π-electron chromophore and spectral param-
eters were studied using porphyrazines having dif-
ferent numbers of fused benzene rings.
with a metal salt, which is carried out by heating the
reactants in melt or in a high-boiling solvent [1, 7, 8].
Metal-free porphyrazines are usually obtained by
demetalation of the corresponding Mg(II) complexes
which are synthesized by either direct fusion of a di-
nitrile {e.g., trans-2,3-diphenylbutanedinitrile (Ia) [9]
or phthalonitrile (IV) [10]} with magnesium or tem-
plate cyclotetramerization of a dinitrile in alcohol in
the presence of magnesium alkoxide (Linstead proce-
dure [11]). Porphyrazines having four fused 1,2,5-thia-
(selena)diazole rings are obtained as Mg(II) complexes
Mg{XN2}4PA by cyclotetramerization of 1,2,5-thia-
(selena)diazole-3,4-dicarbonitrile II or III in the pres-
ence of magnesium propoxide or butoxide in the corre-
sponding alcohol [2, 3]. In order to synthesize hexa-β-
phenylporphyrazines Va–Vc having only one fused
hetero (or benzene) ring, cross template cycloconden-
sations of dinitrile Ia with heterocyclic dinitriles II and
III or phthalodinitrile (IV) in the presence of magne-
sium butoxide in butanol was performed (Scheme 1).
The most convenient and widely used method for
the synthesis of porphyrazine derivatives is based on
template condensation of maleonitrile or phthalonitrile
Taking into account that cross cyclocondensation
of two different dinitriles A and B could give rise to
1854

SYNTHESIS AND SPECTRAL PROPERTIES OF 1,2,5-THIADIAZOLO-...
1855
Scheme 1.
NC
CN
NC
CN
CN
CN
NC
Ph
Ph
N
N
N
N
CN
S
Se
Ia
II
III
IV
CF3COOH
Mg(OBu)2, BuOH, Δ
Ia
+
II–IV
Mixture of Mg porphyrazine complexes
V–X
Ph
Ph
Ph
Ph
Ph
Ph
N
N
N
N
21N
N
N
N
22N
H
22N
22N
Ph
Ph
Ph
H
23
21
N23
NH
N23
21N
Ht
HN
Ht
Ht
Ht
H
Ph
H
N 24
N 24
N 24
N
N
N
N
N
Ht
Ph
Ph
trans-H2{Ht}2PAPh4 (VIIa–VIIc)
Ph
Ph
Ph
H2{Ht}PAPh6 (Va–Vc)
Ph
cis-H2{Ht}2PAPh4 (VIa–VIc)
Ph
Ph
Ht
N
N
N
N
N
N
22N
H
N
H
N
H
Ph
Ph
Ph
N23
N
N
21N
Ht
N
Ht
N
Ht
Ht
H
H
N
H
N
Ph
N 24
N
N
N
N
N
N
Ht
H2{Ht}3PAPh2 (VIIIa–VIIIc)
Ht
Ph
H2PAPh8 (X)
Ph
H2{Ht}4PA (IXa–IXc)
N
N
N
N
V–X,
=
(a),
(b),
Se
(c).
Ht
S
a mixture of two symmetric porphyrazines AAAA and
BBBB and four porphyrazines with a lower symmetry
(AABB, ABAB, AAAB, ABBB), we examined the re-
action in more detail with a view to find optimal condi-
tions for the formation of hexa-β-phenylporphyrazines
having only one fused ring. It is most likely that the
porphyrazine macroring is formed in two steps. In the
first step, condensation of two dinitrile molecules gives
a dimer, and next follows intermolecular cyclization of
two dimeric units [12, 13].
the latter are equally reactive in the subsequent cyclo-
condensation with formation of structures AAAA,
AABB, ABAB, AAAB, ABBB, and BBBB (rate con-
stant kt), porphyrazine ABBB should be formed with
the maximal yield (18.5%) at a dinitrile B-to-A ratio of
3:1 (Fig. 1). However, the fractions of the other low-
symmetry porphyrazines should also be significant
(19.4% of AABB, 7.4% of ABAB, and 4.7% AAAB),
and the fractions of symmetric structures BBBB and
AAAA should be 46.6% and 3.5%, respectively. As
shown in Fig. 1, the yield of ABBB begins to exceed
the yields of all other low-symmetry porphyrazines
starting from a B:A ratio of 4:1, and the value B:A =
7:1 seems to be optimal for the synthesis and isolation
of ABBB. Although the yield of symmetric structure
In terms of the above mechanism, we performed
kinetic and statistical analysis of the cross cyclocon-
densation (Scheme 2). Provided that dinitriles A and B
are equally reactive (rate constant kd) in the processes
leading to dimeric structures AA, AB, and BB and that
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

STUZHIN et al.
1856
Scheme 2.
AA
AA
+
+
AA
AB
AAAA
AAAB
A
A
B
+
+
+
A
B
B
AA
AB
BB
AA
AB
+
+
BB
AB
AABB
kt
kd
AB
AB
BB
+
+
+
AB
BB
BB
ABAB
ABBB
BBBB
BBBB reaches 68%, the theoretical yield of target
structure ABBB (16.3%) is greater than the overall
yield of the other products (15.5%).
value, is likely to result from different reactivities of
the initial dinitriles, which were assumed to be similar
while estimating the theoretical yield. The reactivity of
dinitriles is determined by both polarization of the
C≡N bond (which depends on the charges on the nitro-
gen and carbon atoms) and steric structure of their
molecules. The results of PM3 quantum-chemical cal-
culations showed that the cyano groups in heterocyclic
dinitriles II and III should be more reactive in the
cyclotetramerization process than those in phthalodi-
nitrile (IV): the C≡N bonds in molecules II and III are
polarized more strongly, and the nitrogen atoms are
electron-deficient (Table 1). On the other hand, closure
of pyrrole ring fused to a five-membered heteroring is
expected to involve greater steric hindrances than in
the formation of isoindole fragment from phthalodi-
nitrile [8]. The cyano groups in dinitrile Ia are least
polarized, and their trans configuration is unfavorable
for pyrrole ring closure. Therefore, the cyclocondensa-
tion should be preceded by transformation of trans-
dinitrile Ia into cis isomer Ib (Scheme 3); this process
is accompanied by increase in the polarization of the
cyano groups (Table 1).
Taking into account the above stated, we performed
cross cyclocondensation using 4–7-fold excess of di-
nitrile Ia with respect to dinitrile II–IV. At a Ia-to-II–
IV ratio of 4:1, the yield of porphyrazines Va–Vc
(after demetalation) was 3–4% calculated on the over-
all amount of initial dinitriles and 4–5% calculated on
the minor dinitrile. Insofar as at the given reactant ratio
the maximal theoretical yield of structure ABBB is
18.3% (23% on the minor dinitrile), the experimental
yield is 16–22% of the theoretical value. In the reac-
tion of dinitrile Ia with selenadiazole III at a ratio of
7:1 we isolated 4.7% of H2{SeN2}PAPh6 (Vb), the
conversion of III being 9.4%; these values constitute
29% of the theoretically possible ones (16.3 and 33%,
respectively).
The overall yield of magnesium(II) porphyrazine
complexes in joint condensation of two different di-
nitriles ranged from 90 to 95%, and their demetalation
was also characterized by a high yield (about 90%).
Therefore, the considerably lower yield of hexaphenyl-
porphyrazines Va–Vc, as compared to the theoretical
Theoretically, only 5−10% of dinitrile II−IV
[II−IV-to-Ia ratio 1:(4−7)] should give rise to sym-
metric porphyrazines IXa−IXc. In fact, the yield of
porphyrazines IX was 40−60%. Increased yield was
also observed for diphenylporphyrazines VIIIa−VIIIc
having three fused rings. At a Ia–IV ratio of 4.3:1, the
conversion of phthalodinitrile (IV) into tribenzopor-
phyrazine VIIIc was 24%, and the overall yield of the
latter was 6.1% against theoretical values of 12 and
3.2%, respectively. Under these conditions, the yield of
tetraphenyl derivatives VIa−VIc and VIIa−VIIc and
especially of hexaphenylporphyrazines Va−Vc is lower
than that expected theoretically. Thus dinitriles II−IV,
despite their small fraction in the reaction mixture
[ratio 1:(4−7) with respect to Ia] are consumed mainly
for their self-condensation rather than for the reaction
with dinitrile Ia, and the latter gives rise to a larger
80
60
40
AAAA
AAAB
AABB
ABAB
ABBB
BBBB
20
0
1
2
3
4
5
6
7
8
9
10
Ratio B:A
Fig.1. Plot of the yield of porphyrazines versus the dinitrile
A–B ratio in the cross condensation according to Scheme 2.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

SYNTHESIS AND SPECTRAL PROPERTIES OF 1,2,5-THIADIAZOLO-...
1857
Scheme 3.
Ph
Ph
Mg(OBu)2, 40–60°C
BuO
NH
NH
N
NC
Ph
Ph
NC
Ph
CN
Ph
Ic
Ph
Ph
CN
Ia
Ib
NH3, Na, BuOH, Δ
HN
N
H
Id
amount of symmetric ocaphenylporphyrazine (X)
(70−80%) than it is expected at the given initial di-
nitrile ratio (55−70%).
raphy on aluminum oxide using chloroform as eluent.
Unsymmetrical porphyrazine magnesium complexes
cannot be separated in such a way; therefore, their
mixture was subjected to demetalation by treatment
with trifluoroacetic acid, followed by repeated chroma-
tography. The first fraction contained a small amount
of octaphenylporphyrazine H2PAPh8 (X), hexa-β-phen-
ylporphyrazines Va−Vc were eluted in the second frac-
tion, and the third fraction contained a mixture of cis-
and trans-tetra-β-phenylporphyrazines VIa−VIc and
VIIa−VIIc. Isomers VI and VII are characterized by
very similar Rf values in thin-layer chromatography on
silica gel. Dibenzoporphyrazines VIc and VIIc were
identified by electronic absorption spectroscopy (see
below). We failed to find conditions for preparative
separation of cis and trans isomers VI and VII by
column chromatography. Di-β-phenylporphyrazines
VIIIa and VIIIb having three fused 1,2,5-thia- or
1,2,5-selenadiazole fragments are poorly soluble and
are partially separated together with symmetric prod-
ucts IXa and IXb by Soxhlet extraction and filtration.
The remaining (dissolved) part of VIIIa and VIIIb is
retained in the chromatographic column; the chromato-
graphic mobility of compounds VIIIa and VIIIb is so
low that they cannot be eluted with chloroform con-
taining methanol or even with pyridine or dimethyl-
formamide. By contrast, di-β-phenyltribenzoporphyr-
When dinitrile Ia was added to a suspension of
magnesium butoxide, the mixture was kept for 10−
20 min at 40−60°C, and the other (more reactive) di-
nitrile was then added, the relative yield of the corre-
sponding hexaphenylporphyrazine slightly increased,
while the yield of symmetrically fused product IX de-
creased. Presumably, in the first step dinitrile Ia under-
goes isomerization into cis-dinitrile Ib which reacts
with magnesium butoxide to give intermediate 5-but-
oxy-3,4-diphenyl-2H-pyrrol-2-imine (Ic) (Scheme 3),
as was reported for phthalodinitrile under analogous
conditions [12, 14]. Even better results were obtained
when dinitrile Ia was converted into more reactive di-
hydropyrrole-2,5-diimine Id according to [15]. For this
purpose, gaseous ammonia was bubbled through a sus-
pension of compound Ia in butanol in the presence of
a catalytic amount of sodium butoxide at moderately
elevated temperature. Diimine Id was not isolated
from the reaction mixture but was added together with
dinitrile III to a suspension of magnesium butoxide. In
this case, at a Ia-to-III ratio of 7:1, the experimental
yield of hexa-β-phenylporphyrazine Vb increased up
to the theoretical value (overall yield 16.3%, yield cal-
culated on III 33%).
Table 1. Polarization of the C≡N bond in dinitriles I–IV
according to PM3 calculations
Apart from optimization of conditions for joint con-
densation of dinitriles Ia and II–IV, the problem re-
lated to separation of the porphyrazine mixture thus
formed turned out to be equally important. Symmet-
rically fused porphyrazines IXa−IXc and their Mg(II)
complexes are very poorly soluble in noncoordinating
organic solvents (CH2Cl2, CHCl3, benzene), and they
are separated from the other products by Soxhlet ex-
traction with those solvents. Symmetric Mg(II)–octa-
phenylporphyrazine (MgPAPh8) is readily separated
from the soluble magnesium complexes by chromatog-
Charges on atoms
Polarization of the C≡N
bond Δδ = |δC – δN|
Dinitrile
C
N
−0.096 −0.056
−0.125 −0.024
−0.108 0.022
−0.116 –0.024
−0.114 −0.028
0.040
0.101
0.130
0.140
0.086
Ia
Ib
II
III
IV
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

STUZHIN et al.
1858
659
695
spectroscopy. Their electronic absorption spectra
H2Bz4PA
(h)
showed strong dependence on the nature and position
of the fused fragments, as well as on the size of the
macrocyclic π-chromophore (Fig. 2). Porphyrazines
Va−Vc and tribenzoporphyrazine VIIIc were also
characterized by elemental analyses and H NMR
spectra.
344
345
H2Bz3PAPh2
cis-H2Bz2PAPh4
695
(g)
603
1
In the 1H NMR spectra of β-phenyl-substituted por-
phyrazines, protons in the β-phenyl groups resonate
as multiplets at δ 8.0−8.5 (o-H), 7.5−7.6 (m-H), and
7.7−7.9 ppm (p-H). Protons in the ortho positions ap-
pear most closely to the macroring and are deshielded
more strongly by the π-electron ring current; therefore,
their signals are differentiated to a greater extent than
signals from the para- and meta-protons. In the spectra
of H2{SeN2}PAPh6 (Vb) and H2{Bz}PAPh6 (Vc)
separate doublets are observed from ortho-protons in
different phenyl groups. Protons in the α-positions of
fused benzene rings in compounds Vc and VIIIc suffer
the maximal effect of π-electron ring current in the
porphyrazine macroring, and their signal is located
most downfield (δ 8.8−9.2 ppm); signals from the
corresponding β-protons appear at δ 7.9−8.2 ppm. The
inner NH protons are strongly shielded by π-electron
ring current; their broadened signals are observed at
δ –1.7 to –2.2 ppm.
357
670
(f)
628
*
*
trans-H2Bz2PAPh4
(e)
345
353
721
358
573
*
*
H2BzPAPh6
691
693
(d)
(c)
588
361
353
H2{SeN2}PAPh6
574
679
H2{SN2}PAPh6
574
(b)
(a)
The electronic absorption spectra of unsymmetrical
porphyrazines, as well as of symmetric derivatives,
octaphenylporphyrazine and phthalocyanine, contain
strong bands arising from π–π* transitions in the
macroring (Fig. 2). In keeping with the Gouterman
four-orbital theory [16], two strong absorption bands
(Q1 and Q2) in the visible region (λ 570–730 nm) may
be assigned to electron transitions from the HOMO to
LUMO and LUMO-1. Vibrational satellites of the Q1
and Q2 bands have low intensity. Broadened Soret
band in the UV region (λ 340–360 nm) corresponds
to transitions from the HOMO-1 to LUMO and
LUMO-1; it is characterized by considerable contribu-
tion of electronic excitations other than HOMO-1 →
LUMO, LUMO-1 (see, e.g., [17]).
357
H2PAPh8
664
599
400
600
800
λ, nm
Fig. 2. Electronic absorption spectra of fractions isolated by
chromatographic separation of mixtures of β-phenyl-substi-
tuted porphyrazines in methylene chloride: (a) H2PAPh8 (X,
first fraction); (b) H2{SN2}PAPh6 (Va), (c) H2{SeN2}PAPh6
(Vb), and (d) H2{Bz}PAPh6 (Vc) (second fraction); (e) trans-
H2{Bz}2PAPh4 (VIIc) and (f) cis-H2{Bz}2PAPh4 (VIc) (third
fraction); (g) H2{Bz}3PAPh2 (VIIIc, fourth fraction);
(h) phthalocyanine H2Pc [H2{Bz}4PA] (IXc) in chloroben-
zene. Absorption bands marked with an asterisk correspond
to impurities of other porphyrazines.
Figure 2 (a–d) shows that extension of macrocyclic
chromophore from 26 π-electrons in H2PAPh8 to
30 π-electrons upon fusion of one aromatic fragment
(1,2,5-thiadiazole, 1,2,5-selenadiazole, or benzene)
leads to increased splitting of the Q-bands: from
1630 cm–1 for H2PAPh8 (X) to 2690 cm–1 for H2{SN2}-
PAPh6 (Va), 2990 cm–1 for H2{SeN2}PAPh6 (Vb), and
2540 cm–1 for H2{Bz}PAPh6 (Vc). This is the result of
hypsochromic shift of the Q2 component by 730, 730,
azine H2{Bz}3PAPh2 (VIIIc) is characterized by fairly
high solubility and chromatographic mobility; it was
successfully isolated by column chromatography (in
the fourth fraction).
The purity of porphyrazines isolated by column
chromatography was checked by electronic absorption
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

SYNTHESIS AND SPECTRAL PROPERTIES OF 1,2,5-THIADIAZOLO-...
LUMO+1
1859
and 330 cm–1 and bathochromic shift of the Q1 com-
LUMO
ponent by 330, 660, and 590 cm–1, respectively (here-
inafter, the shifts are given relative to H2PAPh8). The
Soret band maximum shifts by 330 cm–1 toward higher
frequencies for H2{SN2}PAPh6 and H2{Bz}PAPh6 and
by 690 cm–1 toward lower frequencies for H2{SeN2}-
PAPh6. Variations in the electronic absorption spectra
with increase in the number of fused benzene rings in
β-phenyl-substituted porphyrazines H2{Bz}nPAPh8–2n
(Vc–IXc) are fairly similar to those observed for struc-
turally related β-aryl-substituted porphyrazines, β-(3-tri-
fluoromethylphenyl)benzoporphyrazines H2{Bz}nPA-
(3-CF3C6H4)8–2n [18] and β-(4-tert-butylphenyl)(4,5-di-
octyloxybenzo)porphyrazines H2{4,5-(C8H17O)2Bz}n-
PA(4-t-BuC6H4)8–2n [19, 20]. The chromophoric frag-
ment in isomeric tetra-β-phenyldibenzoporphyrazines,
cis- and trans-H2{Bz}2PAPh4, has the same number of
π-electrons (34); however, the electronic absorption
spectra of fractions isolated by thin-layer chromatog-
raphy on silica gel differed considerably (Fig. 2e, f).
The fraction with Rf 0.90 is characterized by red shift
of the Q1 band (λmax 721 nm) and blue shift of the Q2
band (λmax 573 nm), so that splitting of the Q band is
fairly large (3580 cm–1); strong splitting (~1050 cm–1)
is also observed for the Soret band (λmax 345 and
358 nm). By contrast, the fraction with Rf 0.88 dis-
played a weak splitting of the Q-band (990 cm–1;
λmax 670 and 628 nm for Q1 and Q2, respectively),
while the Soret band was not split. Theoretical analysis
(see below) and comparison with published data
[18–20] allowed us to assign the fraction with Rf 0.90
to trans isomer VIIc, and that with Rf 0.88, to cis-VIc.
b2g (egx)
b3g (egy)
HOMO+1
HOMO-1
au (a1u)
b1u (a2u)
Fig. 3. Structure of the frontier molecular orbitals of parent
porphyrazine H2PA (D2h symmetry). In parentheses are given
the theoretical group designations for the D4h symmetry
group.
of molecular orbitals, including the highest occupied
and lowest unoccupied molecular orbitals responsible
for electronic absorption patterns. Fusion affects pri-
marily the contribution of atomic orbitals of the pyr-
role β-carbon atoms. Figure 3 shows the structure of
frontier π-molecular orbitals of porphyrazine (H2PA)
having a D2h symmetry (ZINDO/S or CNDO/S calcu-
lations). It is seen that the LUMO-1 b2g should be
sensitive to annelation to 2H-pyrrole rings, and the
LUMO b3g, to 1H-pyrrole rings (inner NH protons are
located along the horizontal axis). The HOMO au elec-
Table 2. Gas-phase heats of formation (ΔHf) of fused por-
phyrazines according to PM3 and AM1 calculations
Further extension of the chromophore fragment
to 38 π-electrons in tribenzoporphyrazine VIIIc and
42 π-electrons in phthalocyanine (IXc) almost does not
affect the position of the Q1 band as compared to
benzoporphyrazine Vc but is accompanied by red shift
of the Q2 band maximum to λ 603 and 659 nm for
compounds VIIIc and IXc, respectively. As a result,
splitting of the Q bands decreases to 2200 cm–1 in the
spectrum of VIIIc [which is slightly smaller than in
the spectrum of Vc (2540 cm–1)] and to 780 cm–1 in the
spectrum of IXc. The Soret maxima in the spectra of
tri- and tetrabenzoporphyrazines are displaced by
~1000 cm–1 toward higher frequencies relative to that
in the spectrum of octa-β-phenylporphyrazine X
having no fused rings.
ΔHf, kJ/mol
NH
tautomer
β-H
β-Ph
Porphyrazine
PM3
927
904
993
972
920
910
967
947
956
AM1
AM1
H2{SeN2}PA
H2{SN2}PA
21,23
22,24
21,23
22,24
21,23
22,24
21,23
22,24
1386
1364
1215
1211
1257
1247
1252
2029
2004
1858
1851
1686
1672
1679
1509
1501
H2{Bz}PA
trans-H2{Bz}2PA
On a qualitative level, the observed shifts of the
Q-band maxima may be interpreted in terms of the
perturbation theory as applied to π-molecular orbitals.
Fusion of an aromatic ring should change the energies
cis-H2{Bz}2PA
H2{Bz}3PA
21,23
22,24
10040 1295
993 1289
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

STUZHIN et al.
1860
tron density on the β-carbon atoms in 1H-pyrrole rings
is higher than on Cβ in 2H-pyrrole rings. The main
contributions to the HOMO-1 b1u are those of the
meso-nitrogen atoms and nitrogen atoms in the 2H-
pyrrole rings.
2200 cm–1), and bathochromic shift of its Q1 compo-
nent is smaller than that observed for trans-dibenzo-
porphyrazine VIIc but greater than the corresponding
shift for cis isomer VIc. Finally, exhaustive benzene
ring fusion [phthalocyanine (IXc)] leads to increase in
both HOMO and LUMO energies, and splitting of the
Q band becomes smaller due to bathochromic shift of
its short-wave component Q2 (Fig. 2h).
1,2,5-Thia(selena)diazole fragments in molecules
H2{SN2}PA and H2{SeN2}PA contain electronegative
nitrogen atoms and are π-deficient; therefore, fusion of
such heterorings reduces the energy of π-molecular
orbitals, the HOMO au being stabilized to a lesser
extent than the LUMO b3g but to a greater extent than
the LUMO-1 b2g. Increased splitting of the Q band in
electronic absorption spectra indicates greater stabili-
zation of the LUMO rather than LUMO-1. Smaller
distance between the Q1 and Q2 maxima corresponds
to lesser stabilization of the HOMO as compared to the
LUMO but greater as compared to the LUMO-1.
Larger bathochromic shifts of the Q1 and Soret bands
in the electronic spectrum of the selenium-containing
derivative suggest stronger relative stabilization of the
LUMO. A probable reason is smaller contribution to
the conjugation system of selenium 4dπ orbitals com-
pared to sulfur 3dπ orbitals.
Additional information on the structure of fused
porphyrazine derivatives, which is helpful for inter-
pretation of their spectral parameters, can be obtained
by quantum-chemical calculations. We performed
semiempirical AM1, PM3, CNDO/S, and ZINDO/S
calculations for parent porphyrazine H2PA, its benzo-
and 1,2,5-thiadiazolo-fused derivatives containing dif-
ferent numbers of fused rings, and their β-phenyl-
substituted derivatives. The existence of different NH
tautomers of porphyrazines having one, two (trans
isomers), and three fused rings was also taken into
account. The heats of formation of their molecules in
the gas phase are given in Table 2 (the structures were
optimized by the AM1 and PM3 methods). Figure 4
illustrates the effect of 1,2,5-thiadiazole and benzene
ring fusion on the energies of frontier π-molecular
orbitals of most stable tautomers, and Figure 5 shows
theoretical electronic absorption spectra in the region
of Q band maxima, calculated by the ZINDO/S and
CNDO/S methods for AM1-optimized structures.
Fusion of benzene rings destabilizes π-molecular
orbitals, especially those in which the contributions of
π-atomic orbitals of the β-carbon atoms are consider-
able. Therefore, increased splitting of the Q band in the
spectrum of benzoporphyrazine VIc may be attributed
to increased energy of the LUMO-1, and bathochromic
shift of the Q1 band, to somewhat weaker destabiliza-
tion of the HOMO, the LUMO energy changing in-
significantly. Fusion of the second benzene ring at the
trans position may be expected to further destabilize
the HOMO and LUMO-1, which should lead to in-
creased splitting of the Q band as a result of batho-
chromic shift of its long-wave component Q1. By
contrast, cis-fusion increases the HOMO and LUMO
energies, which should be accompanied by an addi-
tional hypsochromic shift of the Q1 component and
hence weaker splitting of the Q band. Taking into
account the above stated, the TLC fractions with
Rf 0.90 and 0.88 (Fig. 2e, f) may be identified,
respectively, as trans-dibenzoporphyrazine VIIc
(λmax 721 and 573 nm for Q1 and Q2; Δν = 3580 cm–1)
and its cis isomer VIc (λmax 670 and 628 nm for Q1 and
Q2; Δν = 990 cm–1). Fusion of the third benzene ring to
the trans isomer increases the energies of both HOMO
and LUMO, and to the cis isomer, the energies of the
HOMO and LUMO-1. Therefore, the Q band in the
electronic absorption spectrum of tribenzoporphyr-
azine VIIIc (Fig. 2g) is split more weakly (Δν =
The data in Table 2 show that in all cases 22,24-NH
tautomer is more stable than the corresponding 21,23-
NH tautomer (ΔΔHf = 10–25 kJ/mol). The calculated
Q-band splittings (Fig. 5) for 22,24-NH tautomers are
consistent with the experimental data (Fig. 2), while
those calculated for 21,23-NH tautomers are consider-
ably lower. The 1H NMR spectra of porphyrazines Va–
Vc contain one signal from NH protons, while triben-
zoporphyrazine H2{Bz}3PAPh2 (VIIIc) displays two
NH signals. These findings indicate that in all cases at
293 K the most stable are 22,24-NH tautomers in
which the maximal number of β-phenyl groups reside
on the 1H-pyrrole rings (four in Va–Vc and two in
VIIIb; see Scheme 1) while aromatic heterorings or
benzene rings are fused to the 2H-pyrrole fragments
(two of three in VIIIb). The presence of only one NH
1
signal in the H NMR spectra of Va–Vc may also be
rationalized in terms of fast interconversion of the
21,23- and 22,24-NH tautomers. However, taking into
account the presence of two NH signals in the spec-
trum of H2{Bz}3PAPh2 (VIIIb) and published data for
pentyloxy-substituted [1,2,5]thiadiazolotribenzopor-
phyrazine which was shown to exist as the only
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

SYNTHESIS AND SPECTRAL PROPERTIES OF 1,2,5-THIADIAZOLO-...
1861
H2{SN}2PA
H2{Bz}PA H2{Bz}2PA H2{Bz}3PA
trans cis
22,24-NH tautomer over a broad temperature range
(210–300 K) [5], such interpretation seems to be less
appropriate. Thus the results of quantum-chemical cal-
culations in combination with the experimental elec-
tronic absorption and 1H NMR spectra indicate that the
most stable is 22,24-NH tautomer.
As shown in Fig. 4, fusion of electron-withdrawing
1,2,5-thiadiazole fragment actually stabilizes all fron-
tier π-molecular orbitals, while benzene ring fusion de-
stabilizes them.
–1
H2PA
LUMO
–2
–3
–4
–5
–6
–7
–8
–9
HOMO
Concerning calculations of the excited states, the
following must be noted. Initially, CNDO/S and
ZINDO/S calculations of electronic absorption spectra
of the compounds under study were performed using
standard sets of parameters. The predicted trends in
variation of the Q1 and Q2 transitions and Q2–Q1 split-
ting for structures having different numbers of fused
benzene rings were consistent with the experimen-
tal data (the results obtained by the CNDO/S and
ZINDO/S methods differed insignificantly). In partic-
ular, the data for dibenzoporphyrazines were repro-
duced especially well: the strongest splitting of the
Q band and the largest bathochromic shift of the Q1
component are observed for the trans isomer, while the
cis isomer is characterized by the lowest values of
these parameters. Nevertheless, the calculations were
not free from some disadvantages typical of porphyrins
on the whole [17]. On the one hand, the energies of
transitions Q1 and Q2 to the two lowest excited singlet
states (S1 and S2) are systematically underestimated
with respect to the experimental data. On the other
hand, the calculated energies of transitions to other
states with higher energies are overestimated. This
applies primarily to transitions in the near UV region,
i.e., to the Soret band. According to the calculations,
the Soret band covers at least six S0→Si transitions
(where i = 3–8) with fairly high probabilities (cf. PM3
and ZINDO/S calculations of the electronic absorption
spectra of benzoporphyrazine zinc complexes [20]).
Fig. 4. Calculated (ZINDO/S) energies of frontier π-molec-
ular orbitals of fused porphyrazines having no substituents in
the β-positions.
reproduction of experimental electronic absorption
spectra of porphyrin and porphyrazine derivatives con-
stitutes a separate problem. In addition, this problem is
considerably complicated by a number of factors. For
example, the experimental spectrum in the UV region
(Fig. 2) looks like a broad diffuse band with no distinct
maxima. Calculations of the low-symmetry fused por-
phyrazine derivatives showed that their excited states
(e)
680
1
0
693
584
586
622
616
670
(d)
668
650
1
0
(c)
(b)
(a)
641
1
0
671
666
717
625
1
0
574
In order to improve agreement between the calcu-
lated and experimental electronic absorption spectra
we changed some parameters in the CNDO/S and
ZINDO/S approximations. In particular, raising the
π–π overlap parameter from the common value 0.585
to 0.67 resulted in increased energies of Q1 and Q2
transitions so that the latter better matched the experi-
mental data (Fig. 5). On the other hand, the transitions
S0→Si (i = 3, 4, 5, 6, 7, 8) were simultaneously dis-
placed to even shorter wavelengths.
633
612
1
0
588
400
500
600
λ, nm
700
800
Fig. 5. Theoretical electronic absorption spectra of β-phenyl-
substituted porphyrazines with fused benzene rings: (a) Vc,
(b) VIc, (c) VIIc, (d) VIIIc, and (e) 1,2,5-thiadiazole
derivative Va (ZINDO/S calculations). Bold solid lines cor-
respond to the 22,24-NH tautomers, and hashed lines, to the
21,23-NH tautomers.
Optimization of parameters involved in CNDO/S
and ZINDO/S calculations to achieve quantitative
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

STUZHIN et al.
1862
Si (i = 3, 4, 5, 6, 7, 8) include a number of configura-
tions. For structurally related molecules having an in-
version center, the Si states (i = 3, 4, 5, 6, 7, 8) are B1,
B2 N1, and N2 with u-symmetry and two states with
g-symmetry [21–24].
added, and dry ammonia was bubbled through the
mixture over a period of 2 h on heating at the boiling
point. A suspension of magnesium butoxide in 25 ml
of butan-1-ol (preliminarily prepared from 0.24 g of
magnesium) and 0.112 g (0.6 mmol) of 1,2,5-selena-
diazole-3,4-dicarbonitrile (III) were added, and the
mixture was heated for 2 h under reflux. The product
was isolated as described in a. Yield 175 mg (33%),
EXPERIMENTAL
1
The electronic absorption spectra were measured in
the range from λ 350 to 900 nm on a Hitachi U-2000
spectrophotometer from solutions with a concentration
of 10–6 to 10–5 M. The 1H NMR spectra were recorded
at 293 K on a Bruker AC-200 spectrometer operating
at 200.13 MHz from solutions in chloroform-d. At
a porphyrazine concentration of 0.005 to 0.01 M, all
1H NMR signals were broadened due to strong inter-
molecular association. Resolved signals were observed
only from dilute solutions (c < 0.002 M).
Rf 0.79 (CH2Cl2, Silufol). H NMR spectrum, δ, ppm:
8.76 m (2H, o-H), 8.33 m (10H, o-H), 7.70 m (6H,
p-H), 7.54 m (12H, m-H), –1.70 br (2H, NH). Found,
%: C 71.20; H 3.77; N 16.08. C52H32N10Se. Calculated,
%: C 71.31; H 3.68; N 15.99. M 875.85.
7,8,12,13,17,18-Hexaphenyl[1,2,5]thiadiazolo-
[3,4-b]-5,10,15,20-tetraazaporphyrin H2{SN2}PAPh6
(Va) was synthesized and isolated as described above
for H2{SeN2}PAPh6 (method a) from 1 g (4.3 mmol)
of dinitrile Ia and 0.135 g (1.0 mmol) of 1,2,5-thia-
diazole-3,4-dicarbonitrile (II). Yield 40 mg (5%),
7,8,12,13,17,18-Hexaphenyl[1,2,5]selenadiazolo-
[3,4-b]-5,10,15,20-tetraazaporphyrin H2{SeN2}-
PAPh6 (Vb). a. Metallic magnesium, 0.24 g (0.01 mol),
was dissolved in 25 ml of boiling butan-1-ol (the reac-
tion was initiated by adding a small crystal of iodine),
1 g (4.3 mmol) of diphenylfumaronitrile (Ia) and
0.112 g (0.6 mmol) of 1,2,5-selenadiazole-3,4-dicarbo-
nitrile (III) were added to the resulting porridge-like
suspension of magnesium butoxide, and the mixture
was heated for 8 h under reflux. The solvent was dis-
tilled off from the dark green mixture, the dry residue
was treated with 20 ml of 50% aqueous acetic acid to
remove excess magnesium butoxide (the mixture was
stirred for 1.5 h), and the precipitate was filtered off,
washed with several portions of water, dried, and ex-
tracted with chloroform in a Soxhlet apparatus. The
extract containing a mixture of soluble Mg(II)–por-
phyrazine complexes was subjected to chromatography
on aluminum oxide to separate the main part of the
Mg(II)–octaphenylporphyrazine complex (about
500 mg, 41%). A fraction containing unsymmetrical
Mg(II)–porphyrazine complexes was evaporated, the
residue was dissolved in 5 ml of trifluoroacetic acid,
the solution was left overnight and evaporated, and the
residue was washed with water until neutral washings,
dried, dissolved in chloroform, and subjected to chro-
matography on aluminum oxide. The first fraction con-
tained octaphenylporphyrazine, and the second fraction
was subjected to repeated chromatography to isolate
50 mg (9%) of H2{SeN2}PAPh6.
1
Rf 0.91 (CH2Cl2, Silufol). H NMR spectrum (CDCl3),
δ, ppm: 8.15–8.35 m (12H, o-H), 7.70 m (6H, p-H),
7.54 m (12H, m-H), –2.24 br (2H, NH). Found, %:
C 75.22; H 3.70; N 17.19; S 3.95. C52H32N10S. Calcu-
lated, %: C 75.34; H 3.89; N 16.90; S 3.87. M 828.95.
7,8,12,13,17,18-Hexaphenylbenzo[b]-5,10,15,20-
tetraazaporphyrin H2{Bz}PAPh6 (Vc) and 17,18-di-
phenyltribenzo[b,g,l]-5,10,15,20-tetraazaporphyrin
H2{Bz}3PAPh2 (VIIIc). Cross condensation of 1 g
(4.3 mmol) of dinitrile Ia and 0.125 g (1.0 mmol) of
phthalodinitrile (IV) was performed as described
above for the synthesis of H2{SeN2}PAPh6 (Vb),
method a. Chromatographic separation of the extract
on aluminum oxide using chloroform as eluent gave
4 fractions. By repeated chromatography of the second
fraction we isolated 30 mg (4%) of compound Vc,
Rf 0.94 (benzene, Silufol). 1H NMR spectrum (CDCl3),
δ, ppm: 9.15 m (2H, α-H), 8.79 d (4H, o-H), 8.42 d
(4H, o-H), 8.25–8.35 m (4H, o-H), 8.03 m (2H, β-H),
7.80–7.95 m (6H, p-H), 7.55 m (12H, m-H), –1.34 br
(2H, NH). Found, %: C 82.30; H 4.63; N 13.78.
C56H36N8. Calculated, %: C 81.93; H 4.42; N 13.65.
M 820.95.
The third fraction contained cis- and trans-tetra-
phenyldibenzoporphyrazines H2{Bz}2PAPh4 which we
failed to separate by column chromatography [Rf 0.88
and 0.90 (benzene, Silufol). By repeated chromatog-
raphy of the fourth fraction (Al2O3, benzene) we isolat-
ed 50 mg (6%) of compound VIIIc, Rf 0.70 (benzene,
Silufol). 1H NMR spectrum (CDCl3), δ, ppm: 8.82 m
(2H, α-H), 8.70 m (4H, α-H), 8.24 d (4H, o-H), 8.15 m
b. Dinitrile Ia, 1 g, was added to 20 ml of butan-1-
ol, a catalytic amount (10 mg) of metallic sodium was
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 12 2007

SYNTHESIS AND SPECTRAL PROPERTIES OF 1,2,5-THIADIAZOLO-...
1863
10. Linstead, R.P. and Lowe, A.W., J. Chem. Soc., 1934,
(4H, β-H), 7.93 m (2H, β-H), 7.64 m (2H, p-H), 7.52 m
(4H, m-H), –1.68 br (1H, NH), –2.24 br (1H, NH).
Found, %: C 77.84; H 4.07; N 18.22. C40H24N8. Calcu-
lated, %: C 77.91; H 3.92; N 18.17. M 616.68.
p. 1022.
11. Linstead, R.P. and Whalley, M., J. Chem. Soc., 1952,
p. 4839.
12. Oliver, S.W. and Smith, T.D., J. Chem. Soc., Perkin
Trans. 2, 1987, p. 1579.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
nos. 05-03-32921, 06-03-81022) and by the Byelorus-
sian Republican Foundation for Basic Research (grant
no. F06R-141). The authors thank Prof. C. Ercolani
(Universitá di Roma “La Sapienza”) for helpful dis-
cussions.
13. Nolan, K.J.M., Hu, M., and Leznoff, C.C., Synlett,
1997, p. 593.
14. Borodkin, V.F., Zh. Prikl. Khim., 1958, vol. 31, p. 813.
15. Vasil’ev, S.I., Kulinich, V.P., Shaposhnikov, G.P., and
Smirnov, R.P., Russ. J. Gen. Chem., 1998, vol. 68,
p. 1264.
16. Gouterman, M., The Porphyrins, Dolphin, D., Ed., New
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