Thiophen-2-yl and bithienyl substituted pyrazine-2,3-dicarbonitriles as precursors for tetrasubstituted zinc azaphthalocyanines

Article abstract of DOI:10.1016/j.poly.2013.02.017

Peripheral thiophen-2-yl substituents extend the macrocyclic conjugation of zinc(II)azaphthalocyanines, (ZnAzaPc), due to coplanarity between the two ring systems, and red-shifted UV-Vis Q-bands are observed. This lowering in energy is favourable for vari

Full text of DOI:10.1016/j.poly.2013.02.017

Polyhedron 54 (2013) 201–210
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Polyhedron
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Thiophen-2-yl and bithienyl substituted pyrazine-2,3-dicarbonitriles
as precursors for tetrasubstituted zinc azaphthalocyanines
a
Eva H. Mørkved a, Trygve Andreassen b,c, Roland Fröhlich d, Frode Mo e, , Susana V. Gonzalez
⇑
a Norwegian University of Science and Technology, Department of Chemistry, N-7491 Trondheim, Norway
b Norwegian University of Science and Technology, Department of Biotechnology, N-7491 Trondheim, Norway
c Norwegian University of Science and Technology, Department of Circulation and Medical Imaging, MR Core Facility, N-7491 Trondheim, Norway
d Organisch-Chemisches Institut, Universität Münster, Corrensstrasse 40, D-48149 Münster, Germany
e Norwegian University of Science and Technology, Department of Physics, N-7491 Trondheim, Norway
a r t i c l e i n f o
a b s t r a c t
Article history:
Peripheral thiophen-2-yl substituents extend the macrocyclic conjugation of zinc(II)azaphthalocyanines,
(ZnAzaPc), due to coplanarity between the two ring systems, and red-shifted UV–Vis Q-bands are
observed. This lowering in energy is favourable for various applications. Pyrazine-2,3-dicarbonitriles
substituted in the 5-position with alkyl-thiophen-2-yl groups or bithienyl groups, were synthesized as
precursors for the parent tetrasubstituted ZnAzaPcs, expected to show further red-shifted Q-bands.
The reagent Zn(quinoline)2Cl2 was used for one-step cyclotetramerizations. None of the bithienyl substi-
tuted precursors gave clean reactions, and mainly polymeric material resulted. Two ZnAzaPcs tetrasub-
stituted with respectively 5-ethyl-thiophen-2-yl and 3,4-dimethyl-thiophen-2-yl groups, were obtained
in fair yields, 40–50%. UV–Vis Q-bands at 660 nm and molar extinction coefficients 111 000 and
89 000 Mꢀ1 cmꢀ1 were observed for the blue-green DMF solutions of the two tetramers. 2D NMR meth-
ods were applied in analyses of DMF-d7 solutions. Broad and partly overlapping 1H NMR signals for both
compounds indicate aggregation. In addition, the extensive number and distribution of sharp peaks in the
spectrum reflect structural isomerism. Molecular ions were determined by mass spectrometry (MALDI-
TOF). Four pyrazino[2,3-b]pyrazine-2,3-dicarbonitriles, substituted with phenyl or alkylated thiophen-
2-yl groups, were synthesized from 5,6-diamino-pyrazine-2,3-dicarbonitrile and aryl glyoxylaldehydes.
These precursors were not sufficiently stable for cyclotetramerization.
Received 19 September 2012
Accepted 2 February 2013
Available online 19 February 2013
Keywords:
Zinc azaphthalocyanine
Tetrapyrazinoporphyrazine
Thiophen-2-yl
2,20-Bithienyl
Pyrazine-2,3-dicarbonitrile
Pyrazino[2,3-b]pyrazine
Crystallography
Dichlorobis(quinoline-N)zinc(II)
Structure analyses of 5-(5-ethylthiophen-2-yl)pyrazine-2,3-dicarbonitrile, and 5-(50-ethyl-2,20-bithio-
phen-5-yl)pyrazine-2,3-dicarbonitrile, reveal extended
degree of electron delocalization in the three-ring system of the latter compound presumably makes
self-association through interactions the greatly preferred mechanism for condensation.
Ó 2013 Elsevier Ltd. All rights reserved.
p-electron systems in both structures. The high
p-p
1. Introduction
therein. Eight additional nitrogen atoms on the periphery of AzaPc
increase the polarity of these macrocycles, and substituents may
be used for tuning solubility, UV–Vis absorptions, i.e. shifts of
Q-bands, and acid–base properties.
Phthalocyanines (Pc), have served as important industrial blue-
green colourants for about one hundred years, and during the last
two decades both properties and numerous sophisticated applica-
tions have been explored for this class of compounds [1]. Tetrapy-
razinoporphyrazines, here named azaphthalocyanines (AzaPc), are
in general considered less important than the parent phthalocya-
nines due to different physical properties such as inferior stability,
colour, and less resistance to oxidation. However, interest in this
class of compounds is steadily increasing, and many potential
applications in materials science have been proposed and in sev-
eral cases realized, for brief overviews see, e.g. [2] and references
A particular area for application of Pc and AzaPc macrocycles are
as photosensitizers (PS) in photodynamic therapy (PDT), e.g. of cer-
tain forms of cancer [2,3]. The biomedical function of a PS depends
on its ability to absorb visible light (optimal range 650–800 nm)
and transfer the energy to oxygen, thereby creating reactive oxygen
species, in particular singlet oxygen, that will readily react with and
damage vital constituents of the malignant cells [4,5]. Aza-substitu-
tion within the Pc macromolecule results in absorption at shorter
wavelengths than for the parent Pc, thus the Q-band of unsubstitut-
ed ZnAzaPc at 636 nm is considerably shifted compared to that of
ZnPc, 674 nm [6]. The optical properties of the macrocycle can be
optimized by introducing suitable substituents in the 2,3-dicyano-
⇑
Corresponding author. Tel.: +47 47 02 12 92.
E-mail address: frode.mo@ntnu.no (F. Mo).
pyrazine moiety that upon cyclotetramerization will extend the p-
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.02.017

202
E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
electron system of the AzaPc macrocycle. However, extension of the
chromophore will also increase the inherent tendency of both Pcs
and AzaPcs to self-aggregation, forming dimeric and oligomeric
species, characterized by lower solubility, weaker absorbance and
fluorescence emission, resulting in reduced efficiency as PS [5].
The tendency to aggregation can be suppressed by various means,
such as introducing bulky substituents in the periphery of the mac-
rocycle, in a water medium by making use of charged substituents
or solvents favouring the monomeric state, cf. [3(e)] and references
therein.
There is limited knowledge regarding the influence of hetero-
atom substituents on both synthesis and properties of AzaPc. In
previous work, we have synthesized some AzaPc where heteroat-
oms (S, O or N) link the substituents to the pyrazine ring [7]. Syn-
theses of AzaPc with various carbon-linked heteroaromatic
substituents have been reported by us [8] and by others
[2(b),(e)]. Important studies have been made recently of the struc-
tural and electronic implications of bulky phenoxyl and pyridin-2-
yl substituents [2(d),9,10] and N,N0-alkyl substituted aniline sub-
stituents, the latter enabling a pH controlled ON–OFF switching
of intramolecular charge transfer which is directly linked to the
PS function [11].
study of the symmetrically bis-substituted 5,6-bis(2,20-bithio-
phen-5-yl)pyrazine-2,3-dicarbonitrile has been carried out previ-
ously [14b]. The pyrazine precursor was obtained in low yield,
and purification of the product was difficult due to its low solubil-
ity and poor stability. Hardly any cyclotetramerization took place
in attempted reactions with zinc salts and quinoline. These results
show that octasubstituted ZnAzaPcs with eight bithienyl groups,
implying further extension of the delocalized electron system,
are unstable and have a strong disposition to aggregation. Clearly,
X-ray structure studies of the precursors could be very useful in
assessing their relative potential wrt. cyclotetramerization, as well
as solubility, location of Q-band and singlet oxygen production of
the tetramer.
In the present work we have investigated how peripheral 2,20-
bithienyl or thiophen-2-yl groups being attached as mono-substit-
uents affect electronic and structural properties of the precursors
and their abilities to undergo cyclotetramerization. Structure anal-
ysis of selected precursors was expected to give additional infor-
mation about the parent substituents as tools for extending the
chromophoric system of ZnAzaPc. The results of these investiga-
tions could indicate if these compounds may be further developed;
application as sensitizers for PDT being one possibility.
Studies of the relative chemical stabilities and measurements of
the singlet oxygen and fluorescence quantum yields that are essen-
tial properties for the function as PS, indicate that of the heteroar-
omatic pyridin-2-yl, furan-2-yl and thiophen-2-yl substituents in
AzaPcs, the latter are the most promising [12,13]. The thiophen-
2-yl groups of octa(thiophen-2-yl)ZnAzaPc [12], induce a red shift
to 673 nm in the Q-band of the UV–Vis spectrum, and also higher
intensity of this absorption. The parent dicarbonitrile precursor
with 5,6-di(thiophen-2-yl) substituents (A) readily tetramerized,
yield 88%. The product had a high value for the singlet oxygen
2. Experimental
2.1. Materials and methods
Accurate mass determinations of compounds 3–7 were ob-
tained on a Finnigan MAT 95XL spectrometer, either with electron
spray ionization (ESI, positive mode), or with electron impact (EI)
at 70 eV electron energy and 1.0 mA electron current. An Agilent
6520 QTOF MS instrument equipped with a dual electrospray ion
source was used for compounds 5c and 7i. The samples were dis-
solved in acetonitrile and injected into the MS using an Agilent
1200 series HPLC. Analysis was performed as a flow injection anal-
ysis without any chromatographic step. MALDI-TOF mass spectra
of compounds 8a–b were recorded on an AutoFlex III TOF/TOF
200 mass spectrometer operated in TOF mode. Each sample was
dissolved in dichloromethane (DCM), spotted onto the target plate,
airdried at ambient temperature and covered with the matrix solu-
quantum yield, / = 0.635, indicating very little aggregation [12].
D
In contrast, the precursor with 5,6-di(5-methylthiophen-2-yl) sub-
stitutents (B) tetramerized in much lower yield, 33%. The parent
tetramer, octa(5-methylthiophen-2-yl)ZnAzaPc (Q-band at
679 nm), showed extensive aggregation, in consonance with a very
small / = 0.196 [6]. In comparison, the tetrasubstituted ZnAzaPc
D
complexes, with thiophen-2-yl or 5-methyl-thiophen-2-yl substit-
uents, cf. structures 9 in [6], were both obtained in good yield from
the corresponding precursors, with Q-bands at 661 and 666 nm,
and / values 0.555 and 0.554, respectively [6].
tion which consisted of a-cyano-4-hydroxycinnamic acid, acetoni-
D
Recently we have shown [14] that octasubstituted ZnAzaPc,
with four peripheral thiophen-2-yl groups and four bulky phenoxy
groups have Q-band absorptions in the range 660–665 nm. Aggre-
gation was effectively suppressed by the ortho-substituted phen-
oxy groups. One obvious next step would be to continue work
with structurally related unsymmetrically octasubstituted ZnA-
zaPcs and explore the properties of variously substituted thio-
phen-2-yl and bithienyl pyrazine substituents. Interestingly, the
results obtained for structures 9 in [6] containing single thiophene
or 5-methylthiophene substituents indicate that tetrasubstituted
complexes without bulky spacer groups are also promising in
terms of singlet oxygen production and solubility, and therefore
suggest another line of research worth pursuing.
The suitability of symmetrically bis-substituted precursors for
tetramerization is not well understood at present. A recent X-ray
structure study of precursor A showed that one of the thiophene
rings was required by symmetry to be disordered and lying in a
quasi-orthogonal orientation to the plane containing the other thi-
ophene and the pyrazine ring [14a]. As noted above this precursor
gave the ZnAzaPc tetramer in good yield with very little aggrega-
tion, suggesting that the initial relative orientation of the thio-
phene rings could explain these findings. An X-ray study of
precursor B would indicate if a more planar structure in this case
is a factor promoting the observed aggregation. A preliminary
trile and trifluoroacetic acid. IR spectra were obtained on a Thermo
Nicolet Nexus FT-IR spectrometer with a Smart Endurance reflex-
ion cell. NMR spectra of all new compounds were recorded on a
Bruker Avance DPX 400 NMR spectrometer at 400.13 (1H) and
100.61 MHz (13C). NMR spectra of compounds 8a–b were recorded
on a Bruker Avance 600 NMR spectrometer, fitted with a TCI cryo-
probe, at 600.18 MHz (1H) and 150.92 MHz (13C). Chemical shifts
are given relative to internal tetramethyl silane (TMS) when CDCl3
was used as solvent. Chemical shifts are calibrated relative to the
DMSO signal at 2.50 ppm for 1H, and 39.51 ppm for 13C when
DMSO-d6 was used as solvent and acetone signal at 2.05 ppm for
1H and 29.92 ppm for 13C when acetone-d6 was used as solvent.
The NMR pulse techniques COSY, HSQC and HMBC were used to
correlate 1H and 13C NMR signals for all new compounds. UV–Vis
spectra were recorded on a Cary 50 UV–Vis spectrophotometer.
Melting points were obtained on a Büchi 530 melting point appa-
ratus and are uncorrected. Merck Kieselgel 60F 254 was used for
thin layer chromatography (TLC) and Merck silica 63–200 lm
was used for column chromatography. 2-Ethylthiophene (1a),
3,4-dibromothiophene and methylmagnesium bromide (3M in
diethylether), were obtained from Aldrich. Thiophene, 2-bromo-
thiophene and (Ni–P), [1,3-bis(diphenylphosphino)propane]-
nickel(II)chloride, were obtained from Acros Organics. 2-Bromo-
5-ethylthiophene was obtained from a reaction of 2-ethylthio-

E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
203
phene and N-bromosuccinimide (NBS) in THF, as in [15]. 5-Bromo-
2,20-bithiophene was obtained from 2,20-bithiophene and NBS in
DMF, as in [16]. 5-Methyl-2-thiopheneglyoxylaldehyde (3g) and
thiophene-2-glyoxylaldehyde (3h) were prepared as in [6], phenyl-
glyoxal hydrate (3i) was obtained from Aldrich. 5,6-Diaminopyr-
azine-2,3-dicarbonitrile (6) was obtained as in [12].
ppm 15.5 (CH3), 24.16 (CH2); thiophene; 125.8 (C3), 135.8 (C2),
137.0 (C4), 160.5 (C5); 89.5 (CH(OH)), 185.3 (C@O).
2.2.1.6. 5-Benzyl-2-thiopheneglyoxylaldehyde (3b). Yield of tan pow-
der (65%), mp. 100–102 °C. ESIMS: m/z: Anal. Calc. for C13H11O2-
S (MH+): 231.0474. Found: 231.0478. Calc. for C14H15O3S
[M(CH3OH)H+]: 263.0736. Found: 263.0736. IR:
m
, cmꢀ1 3358
(broad, H-bonded OH stretch), 2917 (w), 1642 (s, C@O), 1450,
1418, 1146, 1107, 1045 (s, CH–OH, C–O stretch), 997, 803, 743,
698, 600. Dimer of 3b + H2O: 1H NMR (CDCl3): d, ppm 4.16 (4H,
CH2, s), 4.88 (2H, OH, d, J = 10.1 Hz), 6.11 (2H, CH(OH), d,
J = 10.1 Hz); thiophene: 6.86 (2H, H4, d, J4,3 = 3.9 Hz), 7.88 (2H, H3,
d, J3,4 = 3.9 Hz); phenyl: 7.21 (4H, H2, H6, m), 7.25 (2H, H4, m),
7.31 (4H, H3, H5, m). 13C NMR (CDCl3): d, ppm 36.8 (CH2), 89.5
(CH(OH)), 185.3 (C@O); thiophene: 127.2 (C4), 136.8 (C2), 136.9
(C3), 157.1 (C5); phenyl: 127.1 (C4), 128.7 (C2, C6), 128.8 (C3, C5),
138.6 (C1).
2.2. Synthesis
2.2.1. Compounds 3a–f
2.2.1.1. General procedure for the synthesis of compounds 1b–f. The
method of Ni–P catalyzed coupling of Grignard reagents with 2-
bromothiophenes in diethyl ether [17] was used. The compounds
were purified by chromatography on silica with hexane, and were
used for the next step without further purification. Compounds 1b
[17], 1d [15] and 1e [18] were obtained as oils. Compound 1c, mp.
34 °C, mp. 34–35 °C [17]; compound 1f, mp. 30–31 °C, mp. 33 °C
[17].
2.2.1.7. 5-Phenyl-2-thiopheneglyoxylaldehyde (3c). Yield 60%, mp.
120–130 °C decomp., mp.135–138 °C decomp. [24]. ESIMS: m/z:
2.2.1.2. General procedure for the synthesis of compounds 2a–f. A
solution of compound 1 and acetic anhydride (1.1 molar equiva-
lent) was heated with stirring at 100 °C for 2–14 h. The product
was poured onto ice, extracted with DCM and chromatographed
on silica with DCM. 2-Acetyl-5-ethylthiophene (2a) [19], and 2-acet-
yl-5-benzylthiophene (2b) [20], were obtained as oils. 2-Acetyl-5-
phenylthiophene (2c), mp. 110 °C, mp. 114.5–116 °C [21]; 5-acet-
yl-50-ethyl-2,20-bithiophene (2d), mp. 105–106 °C, mp. 106–107 °C
[22]; 5-acetyl-2,20-bithiophene (2f), mp. 105–110 °C, mp. 110–
111 °C [23].
Anal. Calc. for
C
13H13O3S [M(CH3OH)H+]: 249.0580. Found:
249.0590. IR:
m
, cmꢀ1 3409–3353 (broad, H-bonded OH stretch),
1668 (s, C@O), 1443, 1238, 1120, 1076 (s, C–O stretch of CH–
OH), 1033, 802, 756 (s), 687 (s). 1H NMR (DMSO-d6): d, ppm 9.45
(1H, CHO, s); thiophene: 7.76 (1H, H4, d, J4,3 = 4.1 Hz), 8.22 (1H,
H3, d, J3,4 = 4.1 Hz); phenyl: 7.42 (1H, H4, m), 7.50 (2H, H3, H5,
m), 7.84 (2H, H2, H6, m). 13C NMR (DMSO-d6): d, ppm 188.4
(CHO), 178.9 (C@O); thiophene: 125.5 (C4), 135.9 (C2), 138.0 (C3),
154.3 (C5); phenyl: 126.3 (C2, C6), 129.4 (C3, C5), 129.8 (C4),
132.3 (C1). 3c + H2O: 1H NMR (DMSO-d6): d, ppm 5.54 (1H,
CH(OH)2), m), 6.85 (2H, (OH)2, d, J = 6.2 Hz); thiophene: 7.65 (1H,
H4, d, J4,3 = 4.0 Hz), 8.03 (1H, H3, d, J3,4 = 4.0 Hz); phenyl: 7.42
(1H, H4, m), 7.47 (2H, H3, H5, m), 7.78 (2H, H2, H6, m). 13C NMR
(DMSO-d6): d, ppm 89.7 (CH(OH)2), 190.0 (C@O); thiophene:
124.9 (C4), 136.0 (C3), 138.5 (C2), 151.5 (C5); phenyl: 126.0 (C2,
C6), 129.2 (C4), 129.3 (C3, C5), 132.7 (C1).
2.2.1.3. 5-Acetyl-50-benzyl-2,20-bithiophene (2e). Yield of tan powder
(50%), mp. 112–115 °C. ESIMS: m/z: Anal. Calc. for C17H15OS2
(MH+): 299.0559. Found: 299.0558. IR:
m
, cmꢀ1 2359 (w), 1647
(s, C@O), 1467, 1437, 1277, 876, 798 (s), 714, 698. 1H NMR (CDCl3):
d, ppm 2.52 (3H, s), 4.13 (2H, s), thiophene: 7.05 (1H, d,
J3,4 = 4.0 Hz), 7.54 (1H, d, J4,3 = 4.0 Hz), thiophene0: 6.75 (1H, d,
0
0
0
0
J4 ,3 = 3.7 Hz), 7.13 (1H, d, J3 ,4 = 3.7 Hz); phenyl: 7.25 (1H, H4, m),
7.26 (2H, H2, H6, m), 7.32 (2H, H3, H5, m). 13C NMR (CDCl3): d,
ppm 26.5 (CH3), 36.4 (CH2), thiophene: 123.6 (C3), 133.3 (C4),
141.9 (C5), 146.1 (C2); thiophene0: 125.5 (C30), 126.3 (C40), 134.9
(C20), 146.2 (C50); phenyl: 126.8 (C4), 128.6 (C2, C6), 128.7 (C3,
C5), 139.6 (C1); 190.3 (C@O).
2.2.1.8. 50-Ethyl-2,20-bithiophene-5-glyoxylaldehyde (3d). Yield of
tan powder (40%), mp. 112–123 °C decomp. ESIMS: m/z: Anal. Calc.
for
C
12H11O2S2 (MH+): 251.0195. Found: 251.0195. Calc. for
C13H15O3S2 [(M(CH3OH)H+] 283.0457. Found: 283.0462. IR:
m
,
cmꢀ1 3400 (broad, H-bonded OH stretch), 2965 (w), 1655 (s,
C@O), 1470, 1436, 1236, 1114, 1062 (s, CH–OH, C–O stretch),
1029, 797 (s). 1H NMR (CDCl3): d, ppm 1.34 (3H, t, J = 7.5 Hz),
2.87 (2H, q, J = 7.5 Hz), 9.55 (1H, CHO, s); thiophene: 7.19 (1H, H3,
d, J3,4 = 4.1 Hz), 8.19 (1H, H4, d, J4,3 = 4.1 Hz); thiophene0: 6.78 (1H,
2.2.1.4. General procedure for the synthesis of compounds 3a–f. A
mixture of compound 2, selenium dioxide (1.5 molar eq.), dioxane
and water was heated with stirring at 100 °C for 14–16 h. The reac-
tion mixture was filtered and rotary evaporated to dryness. The
residue was chromatographed on silica with DCM to remove unre-
acted material, followed by acetone, which eluted the aryl
glyoxylaldehydes.
H40, d, J4 ,3 = 3.7 Hz), 7.25 (1H, H30, d, J3 ,4 = 3.7 Hz). 13C NMR
(CDCl3): d, ppm 15.7 (CH3), 23.7 (CH2), 178.2 (C@O), 189.2 (CHO);
thiophene: 124.3 (C3), 133.9 (C5), 138.7 (C4), 150.94 (C2); thio-
phene0: 125.1 (C40), 126.7 (C30), 133.2 (C20), 150.89 (C50).
0
0
0
0
2.2.1.9. 50-Benzyl-2,20-bithiophene-5-glyoxylaldehyde (3e). Yield of
tan powder (66%), mp.119–120 °C. ESIMS: m/z: Anal. Calc. for C17-
H13O2S2 (MH+): 313.0351. Found: 313.0350. Calc. for C18H17O3S2
2.2.1.5. 5-Ethyl-2-thiopheneglyoxylaldehyde (3a). Yield of tan pow-
der (40%), mp. 92–94 °C. ESIMS: m/z: Anal. Calc. for C8H9O2S
(MH)+: 169.0318. Found: 169.0320. Calc. for C9H13O3-
[M(CH3OH)H+]: 345.0614. Found: 345.0616. IR:
m
, cmꢀ1 3403
S [(MH+MeOH)+]: 201.0580. Found: 201.0593. IR:
m
, cmꢀ1 3317
(broad, H-bonded OH stretch), 1651 (s, C@O), 1461, 1230, 1112,
1061 (s, CH–OH, C–O stretch), 1024, 818, 801, 738, 699. 1H NMR
(DMSO-d6): d, ppm 4.19 (2H, m), 9.41 (1H, CHO, s); thiophene:
7.43 (1H, d, J3,4 = 4.1 Hz), 8.12 (1H, d J4,3 = 4.1 Hz); thiophene0:
(broad), 2959, 2953 (w), 2370 (w), 1648 (s), 1421, 1250, 1116,
1064, 1043, 995 (s), 899, 809, 609 (s). 1H NMR (CDCl3): d, ppm
1.36 (3H, CH3, t, J = 7.5 Hz), 2.94 (2H, CH2, q, J = 7.5 Hz); thiophene:
6.94 (1H, H3, d, J3,4 = 3.9 Hz), 8.14 (1H, H4, d, J4,3 = 3.9 Hz); 9.54
(1H, CHO, s). 13C NMR (CDCl3): d, ppm 15.4 (CH3), 24.24 (CH2); thi-
ophene: 126.3 (C3), 134.3 (C2), 138.2 (C4), 162.5 (C5); 178.6 (C@O),
189.3 (CHO). Dimer of 3a + H2O: 1H NMR (CDCl3): d, ppm 1.32 (6H,
t, J = 7.5 Hz), 2.89 (4H, q, J = 7.5 Hz); thiophene: 6.88 (2H, H3, d,
J3,4 = 3.9 Hz), 7.90 (2H, H4, d, J4,3 = 3.9 Hz); 4.96 (2H, OH, d,
J = 10.1 Hz), 6.15 (2H, CH(OH), d, J = 10.1 Hz). 13C NMR (CDCl3): d,
6.99 (1H, H40, d, J4 ,3 = 3.6 Hz), 7.48 (1H, H30, d, J3 ,4 = 3.6 Hz); phe-
0
0
0
0
nyl: 7.25 (1H, H4, m), 7.30 (2H, H2, H6, m), 7.32 (2H, H3, H5, m); 13
C
NMR (DMSO-d6): d, ppm 35.35 (CH2), 178.5(C@O), 188.4 (CHO);
thiophene: 124.8 (C3), 134.6 (C2), 138.1 (C4), 147.7 (C5); thiophene0:
127.2 (C30, C40), 133.6 (C20), 147.4 (C5); phenyl: 126.63 (C4), 128.52
(C2, C6), 128.63 (C3, C5), 139.9 (C1). 3e + H2O: 1H NMR (DMSO-d6):
d, ppm 4.17 (2H, CH2, m); thiophene: 7.32 (1H, H3, overlap), 7.93

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E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
(1H, H4, d, J4,3 = 4.0 Hz); thiophene0: 6.94 (1H, H40, d, J4,3 = 3.6 Hz),
2.2.2.4. 5-(5-Phenylthiophen-2-yl)pyrazine-2,3-dicarbonitrile (4c).
7.37 (1H, H30, J3 ,4 = 3.6 Hz); phenyl: 7.25 (1H, H4, m), 7.30 (2H,
H2, H6, m), 7.32 (2H, H3, H5, m); 5.48 (1H, s), 6.83 (2H, OH, broad
s). 13C NMR (DMSO-d6): d, ppm 35.33 (CH2); thiophene: 124.2 (C3),
136.0 (C4), 137.2 (C2), 144.9 (C5); thiophene0: 126.2 (C30), 126.9
(C40), 133.9 (C20), 146.4 (C50); phenyl: 126.59 (C4), 128.51 (C2, C6),
128.60 (C3, C5), 140.0 (C1); 89.7 (CH(OH)), 189.8 (C@O).
Yield of bright yellow fluorescent powder: 0.16 g (57%), mp. 278–
0
0
280 °C. ESIMS: m/z: Anal. Calc. for
306.0808. Found: 306.0806. UV–Vis (DCM): kmax, nm (
275 (12 000), 405 (36 000). IR:
, cmꢀ1 3106 (CH, w), 2238 (CN, w),
C
16H12N5S [(MH+NH4)+]:
e
, Mꢀ1 cmꢀ1
)
m
1546, 1495, 1458 (s), 1442, 1417, 1338, 1086, 818, 766 (s), 689. 1H
NMR (DMSO-d6): d, ppm phenyl: 7.43 (1H, H4, m), 7.49 (2H, H3, H5,
m), 7.84 (2H, H2, H6, m); thiophene: 7.81 (1H, d, J4,3 = 4.1 Hz), 8.35
(1H, d, J3,4 = 4.1 Hz); pyrazine: 9.65 (1H, H6, s). 13C NMR (DMSO-
d6): d, ppm phenyl: 126.0 (C2, C6), 129.36 (C4), 129.37 (C3, C5),
132.4 (C1); thiophene: 126.3 (C4), 133.4 (C3), 137.0 (C2), 151.4
(C5); 113.9 and 114.6 (CN at pyrazine C2 and C3); pyrazine: 129.2
(C2), 133.0 (C3), 143.8 (C6), 149.4 (C5).
2.2.1.10. 2,20-Bithiophene-5-glyoxylaldehyde (3f). Yield of orange
powder (76%), mp.120–128 °C decomp., mp. 126–130 °C [24].
ESIMS: m/z: Anal. Calc. for C11H11O3S2 [(MCH3OH)H+]: 255.0144.
Found: 255.0144. IR:
m
, cmꢀ1 3403–3330 (broad, H-bonded OH
stretch), 2363 (w), 1663 (s, C@O), 1448, 1244, 1115, 1063 (s),
1028, 815, 801 (s). 1H NMR (DMSO-d6): d, ppm 9.42 (1H, CHO, s);
thiophene: 7.53 (1H, H3, d, J3,4 = 4.1 Hz), 8.16 (1H, H4, d,
2.2.2.5. 5-(3,4-Dimethylthiophen-2-yl)pyrazine-2,3-dicarbonitrile (4d).
J4,3 = 4.1 Hz); thiophene0: 7.19 (1H, H40, dd, J4 ,5 = 5.1 Hz, J4 3 = 3.7 -
Yield of bright yellow fluorescent powder: 0.16 g (68%), mp. 178–
0
0
0
0
Hz), 7.65 (1H, H30, dd, J3 ,4 = 3.7 Hz, J3 5 = 1.1 Hz), 7.73 (1H, H50, dd,
180 °C. ESIMS: m/z: Anal. Calc. for
258.0808. Found: 258.0809. UV–Vis (DCM): kmax, nm (
260 (8 000), 370 (28 000). IR:
, cmꢀ1 3102 (CH, w), 2241 (CN, w),
C
12H12N5S [(MH+NH4)+]:
0
0
0
0
J5 ,4 = 5.1 Hz, J5 ,3 = 1.1 Hz). 13C NMR (DMSO-d6): d, ppm 188.3
(CHO), 178.6 (C@O); thiophene: 125.3 (C3), 134.9 (C5), 138.0 (C4),
147.5 (C2); thiophene0: 127.2 (C30), 128.7 (C50), 129.0 (C40), 135.1
(C20). 3f+H2O: 1H NMR (DMSO-d6): d, ppm 5.50 (1H, CH(OH)2, s),
6.87 (2H, broad, (OH)2); thiophene: 7.43 (1H, H3, d, J3,4 = 4.0 Hz),
7.97 (1H, H4, d, J4,3 = 4.0 Hz); thiophene0: 7.16 (1H, H40, dd,
e
, Mꢀ1 cmꢀ1
)
0
0
0
0
m
1545 (s), 1499, 1459 (s), 1420, 1371, 1340, 1187, 1134, 1024, 922,
872, 797. 1H NMR (CDCl3): d, ppm thiophene: 2.26 (3H, CH3 at C4,
d, J = 1.0 Hz), 2.54 (3H, CH3 at C3, s), 7.32 (1H, H5, broad singlet);
pyrazine: 9.02 (1H, H5, s). 13C NMR (CDCl3): d, ppm thiophene:
15.2 (CH3 at C3), 15.3 (CH3 at C4), 128.3 (C5), 131.0 (C2), 141.4
(C4), 143.6 (C3); pyrazine: 113.0 and 113.4 (CN at C2 and C3),
132.9 (C2), 128.4 (C3), 144.4 (C5), 152.1 (C6).
J4 ,5 = 5.1 Hz, J4 3 = 3.6 Hz), 7.54 (1H, H30, dd, J3 ,4 = 3.6 Hz,
0
0
0
0
0
0
J3 ,5 = 1.1 Hz), 7.67 (1H, H50, dd, J5 ,4 = 5.1 Hz, J5 ,3 = 1.1 Hz). 13C
NMR (DMSO-d6): d, ppm 89.8 (CH(OH)2), 189.9 (C@O); thiophene:
124.8 (C3), 136.0 (C4), 137.6 (C5), 144.7 (C2); thiophene0: 126.4
(C30), 127.8 (C50), 128.8 (C40), 135.4 (C20).
0
0
0
0
0
0
2.2.2.6. 5-(50-Ethyl-2,20-bithiophen-5-yl)pyrazine-2,3-dicarbonitrile (5a).
Yield of orange/red fluorescent powder, 0.19 g (60%), mp. 206–207 °C
2.2.2. Compounds 4 and 5
decomp. ESIMS: m/z: Anal. Calc. for
C
16H14N5S2 [(MH+NH4)+]:
2.2.2.1. General procedure for the synthesis of compounds 4a–c and
5a–c. A solution of diaminomaleonitrile (DAMN) (1.5 mmol,
0.16 g) and 3 (1 mmol) in 10 ml glacial acetic acid was heated at
100 °C for 2 h. The reaction mixture was filtered and rotary evapo-
rated to dryness. The solid residue was chromatographed on silica
with DCM. Compound 4d was obtained by the same method; from
a reaction of DAMN with 3,4-dimethyl-2-thiopheneglyoxylaldehyde;
this compound was obtained as an orange oil in appproximately
55% yield from 2-acetyl-3,4-dimethylthiophene [25], which again
was obtained from 3,4-dimethylthiophene [17].
340.0685. Found: 340.0686. UV–Vis (DCM): kmax, nm (e )
, Mꢀ1 cmꢀ1
290 (14 000), 450 (36 000). IR: m
, cmꢀ1 3097 (CH, w), 2229 (CN, w),
1541, 1466 (s), 1414, 1336, 1084, 811 (s). 1H NMR (CDCl3): d, ppm
1.35 (3H, t, J = 7.5 Hz), 2.88 (2H, q, J = 7.5 Hz); thiophene0 : 6.79 (1H,
H40 d, J4 3 = 3.6 Hz), 7.21 (1H, H30, overlap); thiophene: 7.21 (1H, H4,
overlap), 7.80 (1H, H3, d, J3,4 = 4.1 Hz); pyrazine: 9.02 (1H, H6, s). 13C
NMR (CDCl3): d, ppm 15.8 (CH3), 23.7 (CH2); thiophene0: 125.0 (C40),
126.2 (C30), 133.1 (C20), 150.5 (C50); thiophene: 124.7 (C4), 131.8
(C3), 134.9 (C5), 147.6 (C2); 112.8 and 113.4 (CN at pyrazine C2 and
C3); pyrazine: 128.5 (C3), 133.3 (C2), 142.3 (C6), 150.2 (C5).
0
0
2.2.2.2. 5-(5-Ethylthiophen-2-yl)pyrazine-2,3-dicarbonitrile (4a).
Yield of yellow powder, 0.20 g (83%), mp. 137–138 °C. ESIMS: m/
2.2.2.7. 5-(50-Benzyl-2,20-bithiophen-5-yl)pyrazine-2,3-dicarbonitrile
(5b). Yield of orange, fluorescent powder, 0.12 g (31%), mp. 196–
z: Anal. Calc. for
258.0805. UV–Vis (DCM): kmax, nm (
372 (29 000). IR:
, cmꢀ1 2984 (CH, w), 2238 (CN, w), 1550, 1470,
C
12H12N5S [(M+NH4)+]: 258.0808. Found:
198 °C. ESIMS: m/z: Anal. Calc. for
C
21H16N5S2 [(MH+NH4)+]:
e
, Mꢀ1 cmꢀ1) 260 (6 000),
402.0842. Found: 402.0841. UV–Vis (DCM): kmax, nm (e )
, Mꢀ1 cmꢀ1
m
295 (14 000), 445 (37 000). IR: m
, cmꢀ1 2234 (CN, w), 1543, 1446
1339, 1118, 1073, 815. 1H NMR (CDCl3): d, ppm ethyl: 1.39 (3H, t,
J = 7.5 Hz), 2.96 (2H, q, J = 7.5 Hz); thiophene: 6.97 (1H, d,
J4,3 = 3.9 Hz), 7.77 (1H, J3,4 = 3.9 Hz); pyrazine: 9.02 (1H, H6, s). 13C
NMR (CDCl3): d, ppm ethyl: 15.5, 24.1; 112.9 and 113.4 (CN at pyr-
azine C2 and C3); thiophene: 126,6 (C4), 131.4 (C3), 134.9 (C2),
158.7 (C5); pyrazine: 128.6 (C2), 133.2 (C3), 142.3 (C6), 150.6 (C5).
(s), 1449, 1414, 1329, 1073, 802 (s), 790, 735, 701 (s). 1H NMR
(CDCl3): d, ppm 4.16 (2H, CH2, s); phenyl: 7.28 (3H, H2, H4, H6,
m), 7.34 (2H, H3, H5, m); thiophene0: 6.81 (1H, d, J4 ,3 = 3.7 Hz),
0
0
0
0
7.21 (1H, d, J3 ,4 = 3.7 Hz); thiophene: 7.18 (1H, d, J4,3 = 4.1 Hz),
7.78 (1H, d, J3,4 = 4.1 Hz); pyrazine: 9.01 (1H, H6, s). 13C NMR
(CDCl3): d, ppm 36.4 (CH2); phenyl: 126.9 (C4), 128.61 (C2, C6),
128.8 (C3, C5), 139.4 (C1); thiophene0 : 126.1 (C30), 126.6 (C40),
134.3 (C20), 147.2 (C50); thiophene: 124.9 (C4), 131.8 (C3), 135.1
(C5), 147.3 (C2); 113.4 and 112.8 (CN at pyrazine C3, C2 or C2,
C3); pyrazine: 128.59 (C2), 133.3 (C3), 142.3 (C6), 150.2 (C5).
2.2.2.3. 5-(5-Benzylthiophen-2-yl)pyrazine-2,3-dicarbonitrile (4b).
Yield of yellow powder 0.27 g (89%), mp. 127–128 °C. ESIMS: m/
z: Anal. Calc. for
320.0961. UV–Vis (DCM): kmax, nm (
375 (29 000). IR:
, cmꢀ1 3029 (CH, w), 2230 (CN, w), 1542 (s),
C
17H14N5S [(MH+NH4)+]: 320.0964. Found:
e
, Mꢀ1 cmꢀ1) 260 (7000),
m
2.2.2.8.
5-(2,20-Bithiophen-5-yl)pyrazine-2,3-dicarbonitrile
(5c).
1453 (s), 1411, 1335, 1058, 929, 811, 776, 745,735, 709. 1H NMR
(CDCl3): d, ppm 4.22 (1H, s); phenyl: 7.27 (2H, H2, H6, m), 7.28
(1H, H4, m), 7.35 (2H, H3, H5, m); thiophene: 6.97 (1H, d,
J4,3 = 3.9 Hz), 7.76 (1H, d, J3,4 = 3.9 Hz); pyrazine: (1H, H6, 8.99, s).
13C NMR (CDCl3): d, ppm 36.8 (CH2); phenyl: 127.3 (C4), 128.7
(C2, C6), 128.93 (C3, C5), 138.6 (C1); thiophene: 127.9 (C4), 131.3
(C3), 136.0 (C2), 155.4 (C5); 112.8 and 113.3 (CN at pyrazine C2
and C3); pyrazine: 128.87 (C2), 133.2 (C3), 142.3 (C6), 150.4 (C5).
Yield of orange/red powder 0.15 g (51%) mp. 250–258 °C decomp.
ESIMS: m/s: Anal. Calc. for C14H7N4S2 (MH+): 295.0107. Found:
295.0109. UV–Vis (DCM): kmax, nm (
430 (25 000). IR:
, cmꢀ1 2225 (CN, w), 1556, 1499, 1456 (s),
1415, 1336, 1229, 1117, 1071, 838, 812 (s), 733 (s). 1H NMR
e
, Mꢀ1 cmꢀ1) 285 (9 000),
m
(DMSO-d6): d, ppm thiophene0: 7.18 (1H, H40, dd, J4 ,5 = 5.1 Hz,
0
0
J4 ,3 = 3.7 Hz), 7.61 (1H, H30, dd, J3 ,4 = 3.7 Hz, J3 ,5 = 1.1 Hz), 7.70
0
0
0
0
0
0
(1H, H50, dd, J5 ,4 = 5.1 Hz, J5 ,3 = 1.1 Hz); thiophene: 7.58 (1H, H4,
0
0
0
0

E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
205
d, J3,4 = 4.1 Hz), 8.30 (1H, H3, d, J3,4 = 4.1 Hz); pyrazine: 9.63 (1H, H6,
s). 13C NMR (DMSO-d6): d, ppm thiophene0: 126.6 (C30), 128.0 (C50),
128.9 (C40), 135.3 (C20); thiophene: 126.2(C4), 133.3 (C3), 136.2 (C5),
144.5 (C2); 113.9 and 114.6 (CN at pyrazine C2, C3); pyrazine: 129.1
(C2), 132.9 (C3), 143.8 (C6), 149.3 (C5).
134.0 (C4), 135.3 (C1); 114.5 and 114.6 (CN at pyrazine C2 and
C3), 134.2 and 135.8 (pyrazine C2 and C3), 145.6 (C9), 146.3
(C10), 153.7 (C7), 160.2 (C6).
2.2.4. Compounds 8a–b
2.2.4.1. General procedure for the synthesis of compounds 8. Com-
pound 4a or 4d (0.8 mmol), Zn(quinoline)2Cl2 [7(d)] (0.4 mmol)
and freshly distilled quinoline (0.4 ml) were transferred to a round
bottom flask. The stirred reaction mixture was flushed with nitro-
gen for 15 min at ambient temperature, and heated under nitrogen
at 170–175 °C for 30 min. The dark semi-solid was sonicated with
diethyl ether, and the collected dark solid was stirred at ambient
temperature with methanol (20 ml) for 1 h, and subsequently with
acetone for 1 h. The dark powders were dried at 0.1 mm Hg for 5 h
at ambient temperature.
2.2.3. 6-Aryl-substituted pyrazino[2,3-b]pyrazine-2,3-dicarbonitriles,
7a, 7g, 7h and 7i
2.2.3.1. General procedure for synthesis of 7a, 7g, 7h and 7i. A solu-
tion of 0.32 g (2 mmol) of 5,6-diaminopyrazine-2,3-dicarbonitrile
(6) and 3a, 3g, 3h or 3i (2 mmol) in 15 ml of glacial acetic acid
was heated under reflux for 14 h. The red solutions were rotary
evaporated, and the residues were chromatographed on silica with
DCM.
2.2.3.2. 6-(5-Ethylthiophen-2-yl)pyrazino[2,3-b]pyrazine-2,3-dicarbo-
nitrile (7a). Yield of orange powder 0.39 g (66%), mp. 201–210 °C
decomp. ESIMS: m/z: Anal. Calc. for C15H13ON6S [(MH+MeOH)+]:
2.2.4.2.
to)]zinc(II) (8a). Yield of dark blue powder 0.1 g (50%), UV–Vis
(DMF): kmax, nm (
, Mꢀ1 cmꢀ1) 660 (111 000), 602 (28 000), 380
(87 000). UV–Vis (pyridine): kmax, nm (
, Mꢀ1 cmꢀ1) broad shoulder
centred near 740 (10 000), 665 (67 000), 600 (17 000), 385
(82000). IR:
, cmꢀ1 2354 (CH, w), 1528, 1474 (s), 1458, 1313,
[Tetra(5-ethylthiophen-2-yl)-(octazaphthalocyanina-
325.0866. Found: 325.0869. UV–Vis (DCM): kmax, nm (
e )
, Mꢀ1 cmꢀ1
e
460 (22 000), 345 (12 000), 315 (12 500). IR:
m
, cmꢀ1 2353 (CH, w),
e
2240 (CN, w), 1580, 1474 (s), 1436, 1419, 1401 (s), 1345, 1237,
1182, 1077 (s), 824 (s). 1H NMR (CDCl3): d, ppm 1.43 (3H, t,
J = 7.5 Hz), 3.02 (2H, q, J = 7.5 Hz); thiophene: 7.08 (1H, H4, d,
J = 4.0 Hz), 8.07 (1H, H3, d, J = 4.0 Hz); pyrazinopyrazine: 9.63 (1H,
H7, s). 13C NMR (CDCl3): d, ppm 15.4, 24.5; thiophene: 127.4 (C4),
134.1 (C3), 136.9 (C2), 162.3 (C5); 112.5 and 112.7 (CN), 131.0
and 134.6 (pyrazine C2 and C3), 144.1 (C9), 146.1 (C10), 151.6
(C7), 154.8 (C6).
m
1205, 1080, 904 (s), 793, 761, 680. MS (MALDI-TOF) m/z: 1025.08
(MH+). Anal. Calc. for C48H32N16S4Zn: 1024.12 (M), for C48H33N16S4-
Zn: 1025.12 (MH+). The expected isotopic pattern for zinc was
found at m/z (calcd. % rel. int.) 1025.1 (52), 1026.1 (57), 1027.1
(30), 1028.1 (39), 1029.1 (20), 1030.1 (5), 1031.1 (4).
2.2.4.3.
to)]zinc(II) (8b). Yield of dark blue powder 0.08 g (40%), UV–Vis
(DMF): kmax, nm (
, Mꢀ1 cmꢀ1) 660 (89 000), 600 (20 000), 380
(85 000). IR:
, cmꢀ1 2360 (CH, w), 1526, 1473 (s), 1375, 1205,
[Tetra(3,4-dimethylthiophen-2-yl)-(octazaphthalocyanina-
2.2.3.3. 6-(5-Methylthiophen-2-yl)pyrazino[2,3-b]pyrazine-2,3-dicar-
bonitrile (7g). Yield of orange powder 0.17 g (30%), mp. 240–250 °C
decomp. EIMS: m/z: Anal. Calc. for C13H6N6S (M+): 278.0369.
e
Found: 278.0367. UV–Vis (DCM): kmax, nm (
e
, Mꢀ1 cmꢀ1) 455
m
1094, 1077, 911, 758 (s), 672. 1H NMR (DMF-d7): d, ppm 2.0–
2.75 (CH3 at thiophene C3 and C4, broad), 7.4–7.75 (CH at thio-
phene C5, broad), 9.35–9.55 (CH at pyrazine C6). 13C NMR (DMF-
d7): d, ppm 13.5–15 (CH3 at thiophene C3 and C4); thiophene:
124–128 (C5), 131–135 (C2), 140–142 (C3, C4); pyrazine: 144–
145 (C6), 151–152 (C5). MS (MALDI-TOF) m/z: 1025.14 (MH+). Anal.
Calc. for C48H32N16S4Zn: 1024.12 (M), for C48H33N16S4Zn: 1025.12
(MH+). The expected isotopic pattern for zinc was found at m/z
(calcd. % rel. int.) 1025.1 (52), 1026.1 (57), 1027.1 (30), 1028.1
(39), 1029.1 (20), 1030.1 (5), 1031.1 (4).
(29 000), 340 (14 000), 310 (16 000). IR:
m
, cmꢀ1 2360 (CH, w),
2240 (CN, w), 1580, 1477 (s), 1435, 1399 (s), 1337, 1321, 1240,
1211, 1181, 1070 (s), 926, 809 (s). 1H NMR [(CD3)2 C@O]: d, ppm
2.67 (3H, broad s); thiophene: 7.16 (1H, H4, dq, J = 3.9 Hz,
J = 1.0 Hz), 8.37 (1H, H3, d, J = 3.9 Hz), 9.97 (1H, H7, broad s). 13C
NMR [(CD3)2C@O]: d, ppm 16.2; thiophene: 130.0 (C4), 135.6 (C3),
139.3 (C2), 153.7 (C5); pyrazinopyrazine: 114.6 and 114.8 (CN at
C2 and C3), 132.7 and 135.7 (C2, C3), 147.1 and 145.5 (C9, C10),
153.0 (C7), 155.6 (C6).
2.2.3.4. 6-(Thiophen-2-yl)pyrazino[2,3-b]pyrazine-2,3-dicarbonitrile
(7h). Yield of yellow powder 0.2 g (38%), mp. 290–295 °C decomp.
2.3. X-ray crystallographic studies
EIMS: m/z: Anal. Calc. for
264.0207. UV–Vis (DCM): kmax, nm (
325 (12 000), 305 (14 000). IR:
, cmꢀ1 3106 (CH, w), 2241 (CN,
w), 1581, 1509, 1407 (s), 1337, 1210, 1180, 933, 852, 733 (s). 1H
NMR [(CD3)2C@O] d, ppm thiophene: 7.45 (1H, H4, dd,
C
12H4N6S (M+): 264.0213. Found:
e
, Mꢀ1 cmꢀ1) 430 (22 000),
Compounds 4a and 5a were synthesized as described in Sec-
tions 2.2.2.1, 2.2.2.2 and 2.2.2.6. Single crystals of 4a and 5a were
obtained by slow evaporation of solutions in dichloromethane.
Data for both compounds were collected with a Nonius KappaCCD
diffractometer, equipped with a rotating anode generator. Pro-
grams used for the various crystallographic operations were, for
m
:
J4,5 = 4.8 Hz, J4,3 = 4.0 Hz), 8.13 (1H, H5, dd, J5,4 = 4.8 Hz,
J5,3 = 1.0 Hz), 8.56 (1H, H3, dd, J3,4 = 4.0 Hz, J3,5 = 1.0 Hz), 10.0 (1H,
pyrazine H7, s). 13C NMR [(CD3)2C@O]: d, ppm thiophene: 131.0
(C4), 134.7 (C3), 137.3 (C5), 141.4 (C2); pyrazinopyrazine: 114.6
and 114.7 (CN at C2 and C3), 132.7 and 135.8 (C2, C3), 145.6 and
146.9 (C9, C10), 153.1 (C7), 155.8 (C6).
data collection: COLLECT [26], data reduction: DENZO-SMN [27], absorp-
tion correction: DENZO [28], structure solution by direct methods:
SHLXS-97 [29], structure refinement: SHELXL-97 [30], and graphics:
ORTEP-3 [31].
Structure refinement of 4a in space group Pca21 gave a Flack x
parameter 0.40(8) indicating racemic twinning of the crystal struc-
ture as one possibility [32]. Refinement of the inverted structure
yielded a Flack x parameter 0.57(8) thus supporting the initial
choice of handedness. Refining as racemic twins gave a BASF
(BAtch Scale Factor) of 0.41(8), this value refers to the fractional
contribution of the other twin component. The shifts in atomic
and bonding parameters relative to those from the standard refine-
ment were negligible, of the order 1/10 esd. Therefore, we use the
parameters from the standard refinement for the discussion.
2.2.3.5. 6-(Phenyl)pyrazino[2,3-b]pyrazine-2,3-dicarbonitrile (7i).
Yield of yellow powder 0.32 g (62%), mp. 270 °C decomp. ESIMS:
m/z: Anal. Calc. for C14H7N6 (MH+): 259.0727. Found: 259.0731.
UV–Vis (DCM): kmax
,
nm
(e, ) 390 (22 500), 285
Mꢀ1 cmꢀ1
(16 000). IR:
m
, cmꢀ1 2355 (CH, w), 2241 (CN, w), 1570, 1454,
1397 (s), 1320 (s), 1285, 1225, 1172, 780 (s), 689 (s). 1H NMR
[(CD3)2C@O]: d, ppm phenyl: 7.72 (2H, H3, H5, m), 7.76 (1H, H4,
m), 8.58 (2H, H2, H6, m), 10.14 (1H, broad s, pyrazine H7). 13C
NMR [(CD3)2C@O]: d, ppm phenyl: 130.0 (C2, C6), 130.5 (C3, C5),

206
E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
Table 1
Summary of crystallographic parameters, data acquisition and refinement data for 4a and 5a.
Compound
4a
5a
Composition
C12H8N4S
C16H10N4S2
Formula weight (Mr)
Melting point, mp. (K)
Crystal system, space group
Crystal colour
240.285
410–411
322.410
479–480
Monoclinic, P21/n
Bright red in reflected light
Dark yellow in transmitted light
223(2) LT
Orthorhombic, Pca21
Yellow in both reflected and transmitted light
T (K)
223(2) LT
Unit cell dimensions
a (Å)
b (Å)
c (Å)
b (o)
12.5245(2)
12.8778(3)
7.1753(2)
7.9263(2)
13.2200(3)
14.4357(4)
99.830(1)
1490.45(7)
1.437
V (Å3)
1157.29(5)
1.379
Calc. density, Dx (Mg mꢀ3
)
Z
4
4
k (Å)
0.71073
0.36 ꢂ 0.13 ꢂ 0.06
0.261
0.71073
Crystal size (mm)
0.35 ꢂ 0.08 ꢂ 0.07
l
(mmꢀ1
)
0.358
Transmission, minimum/maximum
0.912/0.985
0.885/0.975
Scan modes
x
0.667
and /
x and /
0.668
Resolution, smax sin h=k (Åꢀ1
)
Completeness within smax (%)
98.5
98.3
Reflections collected/unique reflections [Rmerge(all)]
9385/2703 [0.032]
2589
11692/3661 [0.037]
3157
Unique reflections with F2 > 2 (F2) (NO)
r
No. reflections/restraints/variables (NV)
2703/1/155
3661/1/205
Final R indices (F2 > 2 (F2))
r
R(F) = 0.0362, wR(F2) = 0.0874
R(F) = 0.0390, wR(F2) = 0.0905
0.0334/0.45
R(F) = 0.0409, wR(F2) = 0.0964
R(F) = 0.0486, wR(F2) = 0.1030
0.0356/0.81
Final R indices (all data)
Weight parameters wA and wB
Goodness of fit (GOF) on F2
Extrema in final el. density (e Åꢀ3
1.086
ꢀ0.20 to 0.21
1.071
ꢀ0.21 to 0.27
)
w = 1/[
R(F) =
wR(F2) = {
GOF = [
r
2(F02) + (wA ⁄ P)2 + wB ⁄ P], where P = (Max (F02, 0) + 2 ⁄ Fc2)/3.
R
||F0| ꢀ |Fc||/
R|F0|.
2
R
[w(F0 ꢀ Fc2)2]/
R
[w(F02)2]}1/2
.
wF0 ꢀ Fc2)2/(NO ꢀ NV)]1/2
.
2
R
Compound 5a exhibits disorder in the terminal ethyl group hav-
ing two slightly rotated orientations, one major (A ethyl) and one
minor (B ethyl). The occupancies of the two groups refined to
of 1a–f with acetic anhydride and phosphoric acid as catalyst. 5-
Acetyl-50-benzyl-2,20-bithiophene (2e) has not been reported
previously.
0.82(2) and 0.18(2), respectively, corresponding to
a
ratio
Arylglyoxyl aldehydes 3a–f were obtained by selenium dioxide
oxidation of 2a–f and were purified by chromatography on silica
with acetone. Compounds 3a, 3b, 3d and 3e have not been re-
ported previously, but all six compounds 3a–f were analyzed by
high resolution ESIMS. Both protonated molecular ion and proton-
ated molecular ion with added methanol were observed for 3a, 3b,
3d and 3e, whereas only M(CH3OH)H+ was observed for 3c and 3f.
NMR analysis of compounds 3a–f confirm the typical behaviour
of glyoxylaldehydes, (glyoxals), i.e. dimers, addition of water, and
equilibria between monomers and dimers were observed. Due to
low solubility of compounds 3c, 3e and 3f, these compounds were
dissolved in DMSO-d6, whereas CDCl3 solutions were analyzed of
the more soluble compounds 3a, 3b and 3d. 5-Benzyl-2-thiophene-
glyoxylaldehyde (3b) formed a stable dimer with one molecule of
added water in CDCl3 solution. The symmetrical structure
(Scheme 1) was confirmed by observation of two hydroxyl groups
at 4.88 ppm as doublets (J = 10.1 Hz) and two hydrogen atoms at
6.11 ppm as doublets (J = 10.1 Hz). The presence of hydrogen-
bound hydroxyl groups was confirmed by IR spectrometry, i.e. a
broad absorption at 3358 cmꢀ1 was observed. 5-Ethyl-2-thioph-
eneglyoxylaldehyde (3a) in CDCl3 solution appeared initially as
the same type of dimer + H2O as 3b, but on standing increasing
amounts of monomer 3a had formed. A CDCl3 solution of 50-
ethyl-2,20-bithiophene-5-glyoxylaldehyde (3d) showed presence
of monomer only. NMR analysis of DMSO-d6 solutions of the fol-
lowing three compounds, 5-phenyl-2-thiopheneglyoxylaldehyde
(3c), 50-benzyl-2,20-bithiophene-5-glyoxylaldehyde (3e) and 2,20-
bithiophene-5-glyoxylaldehyde (3f) showed presence of equilibria
between monomer and monomer + H2O (Scheme 1). The hydrogen
A:B ꢁ 4:1. The distance between the refined positions for atoms
C(22A) and C(22B) was 0.52 Å. During the refinement the atoms
C(21A) and C(21B) were constrained to superpose, atomic displace-
ment parameters (ADPs) of the other B atoms were set equal to
those of the parent A atoms. A weak restraint was imposed to keep
the terminal C–C bond lengths approximately equal in both
conformations.
Non-H atoms were refined anisotropically. The H atoms were
calculated and refined as riding atoms assuming idealized confor-
mations, applying isotropic ADPs. Full-matrix least-squares refine-
ments were based on F2 using all reflections.
A summary of crystallographic parameters, and parameters for
data collections and structure refinements is given in Table 1. Ta-
ble 2 is a listing of selected bond lengths and angles for both
structures.
3. Results and discussion
3.1. Synthesis and characterization
3.1.1. Pyrazines 4a–d and 5a–c
The pyrazines 4 and 5 were synthesized by condensation of 1,2-
diaminomaleonitrile (DAMN) and arylglyoxylaldehydes 3 in acetic
acid solutions.
2-Substituted thiophenes 1a–f are known compounds and were
either commercially available or were synthesized by the Ni–P cat-
alyzed condensation of a Grignard reagent and a bromothiophene
derivative [17]. Compounds 2a–f were obtained by acylation

E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
207
Table 2
Substituted pyrazine-2,3-dicarbonitriles 4a–d and 5a–c were
obtained in good to fair yields, and were analysed by HR-ESIMS,
UV–Vis, IR and NMR spectrometry.
Selected bond lengths (Å) and bond angles (°) with esd’s in parentheses for 4a and 5a.
4a
5a
UV–Vis absorptions were recorded for DCM solution of com-
pounds 4 and 5, and the expected red shifts, caused by alkylthioph-
ene- or bithienyl substituents on pyrazine-2,3-dicarbonitrile, were
confirmed. The observed absorptions are as follows: kmax = 370 nm
for 5-(5-ethylthiophen-2-yl)pyrazine-2,3-dicarbonitrile (4a) and
Bond lengths
C(1)–C(2)
C(2)–N(3)
N(3)–C(4)
C(4)–C(5)
C(5)–N(6)
N(6)–C(1)
C(4)–C(41)
C(41)–N(42)
C(5)–C(51)
C(51)–N(52)
1.410 (3)
1.320 (3)
1.342 (3)
1.388 (3)
1.334 (2)
1.344 (2)
1.444 (3)
1.132 (3)
1.446 (2)
1.140 (3)
1.412 (2)
1.316 (2)
1.347 (2)
1.390 (2)
1.337 (2)
1.338 (2)
1.442 (3)
1.140 (3)
1.445 (3)
1.140 (2)
5-(3,4-dimethylthiophen-2-yl)pyrazine-2,3-dicarbonitrile
(4d);
kmax = 375 nm for 5-(5-benzylthiophen-2-yl)pyrazine-2,3-dicarbo-
nitrile (4b); kmax = 405 nm for 5-(5-phenylthiophen-2-yl)pyrazine-
2,3-dicarbonitrile (4c). Higher values of red shifts were observed
for the bithienyl substituted pyrazines: kmax = 430 nm for 5-(2,20-
bithiophen-5-yl)pyrazine-2,3-dicarbonitrile (5c); kmax = 445 nm
for 5-(50-benzyl-2,20-bithiophen-5-yl)pyrazine-2,3-dicarbonitrile
(5b); kmax = 450 nm for 5-(50-ethyl-2,20-bithiophen-5-yl)pyrazine-
2,3-dicarbonitrile (5a).
C(1)–C(11)
C(11)–S(12)
S(12)–C(13)
C(13)–C(14)
C(14)–C(15)
C(15)–C(11)
1.447 (2)
1.728 (2)
1.443 (2)
1.731 (2)
1.731 (2)
1.372 (3)
1.398 (3)
1.375 (2)
1.373 (3)
C(13)–C(16)
C(16)–S(17)
S(12)–C(13)a
S(17)–C(18)a
C(13)–C(14)a
C(18)–C(19)a
C(14)–C(15)a
C(19)–C(20)a
C(20)–C(16)
1.446 (3)
1.731 (2)
3.1.2. Pyrazinopyrazines 7a, 7g, 7h and 7i
5,6-Diaminopyrazine-2,3-dicarbonitrile (6) and arylglyoxylal-
dehydes 3a and 3g–i were heated under reflux for 14 h in glacial
acetic acid. Yellow-orange powders of 7 were obtained in moderate
yields, see Scheme 2. The glyoxylaldehydes are remarkably more
reactive towards 6 than the ethanediones which were used for syn-
theses of 6,7-diarylpyrazino[2,3-b]pyrazine-2,3-dicarbonitriles
[12]. Even if compounds 7 appear to be more stable than the tetra-
substituted pyrazinopyrazines [12], compound 7h, 6-(thiophen-2-
yl)pyrazino[2,3-b]pyrazine-2,3-dicarbonitrile, for instance, was
unstable in DMSO, but sufficiently stable in acetone for NMR anal-
ysis. Attempted cyclotetramerizations of compounds 7 gave black
insoluble solids which could not be purified and further
characterized.
1.724 (2)
1.357 (3)
1.408 (3)
1.730 (2)
1.356 (3)
1.409 (3)
1.366 (3)
C(13)–C(21)a
C(18)–C(21)a
C(21)–C(22)
1.505 (3)
1.499 (3)
1.500 (3)/1.500 (3)b
1.503 (4)/1.501(4)b
Bond angles
C(2)–C(1)–N(6)
C(1)–C(2)–N(3)
C(2)–N(3)–C(4)
N(3)–C(4)–C(5)
C(4)–C(5)–N(6)
C(5)–N(6)–C(1)
C(4)–C(41)–N(42)
C(5)–C(51)–N(52)
120.4 (2)
122.9 (2)
116.2 (2)
121.5 (2)
122.6 (2)
116.4 (2)
179.7 (2)
178.9 (2)
120.6 (2)
123.5 (2)
115.6 (2)
121.5 (2)
122.9 (2)
115.9 (2)
178.0 (2)
177.7 (3)
3.1.3. Zinc(II) azaphthalocyanines 8a–b
The reagent Zn(quinoline)2Cl2, prepared from zinc(II) chloride
and quinoline [7(d)], was used to obtain ZnAzaPc 8a–b from pre-
cursors 4a and 4d, as in Scheme 3.
Moderate reaction temperatures, i.e. 170–175 °C, were used for
the cyclotetramerizations in order to suppress possible decomposi-
tion. Attempted cyclizations of compounds 4b and 4c under similar
reaction conditions gave unsatisfactory results. An impure cyclo-
tetramer, as indicated by a UV–Vis Q-band at 665 nm, was ob-
tained in low yield from 4b, whereas 4c decomposed to an
untractable brown solid. Further purification and characterizations
of the cyclization product from 4b were not carried out due to its
instability and low purity.
N(6)–C(1)–C(11)
C(2)–C(1)–C(11)
118.1 (2)
121.5 (2)
120.5 (1)
128.6 (2)
110.8 (2)
118.3 (2)
121.1 (2)
120.8 (1)
128.2 (2)
111.0 (1)
91.7 (1)
110.9 (1)
113.5 (2)
113.0 (2)
120.8 (1)
128.4 (2)
119.5 (1)
130.5 (2)
110.0 (1)
C(1)–C(11)–S(12)
C(1)–C(11)–C(15)
C(15)–C(11)–S(12)
C(11)–S(12)–C(13)
S(12)–C(13)–C(14)
C(13)–C(14)–C(15)
C(14)–C(15)–C(11)
S(12)–C(13)–C(16)
C(14)–C(13)–C(16)
C(13)–C(16)–S(17)
C(13)–C(16)–C(20)
C(20)–C(16)–S(17)
C(11)–S(12)–C(13)a
C(16)–S(17)–C(18)a
S(12)–C(13)–C(14)a
S(17)–C(18)–C(19)a
C(13)–C(14)–C(15)a
C(18)–C(19)–C(20)a
C(19)–C(20)–C(16)
112.5 (2)
Tetrasubstitution of 8a with 5-ethylthiopen-2-yl groups, and of
8b with 3,4-dimethylthiophen-2-yl groups, induced 25 nm red-
shifted UV–Vis Q-bands; observed at 660 nm (
cmꢀ1) for 8a and at 660 nm ( = 89 000 Mꢀ1 cmꢀ1) for 8b, both as
dilute (approx. 10ꢀ5 M) DMF solutions. The red-shifted Q-bands
e -
= 111 000 Mꢀ1
91.9 (1)
110.9 (2)
113.9 (2)
e
92.5 (1)
110.2 (2)
are ascribed to the extended
phene substituents and the 18
p
p
-electron systems between thio-
-electron macrocycles. There was
113.9 (2)
113.4 (2)
no sign of aggregation in the DMF solutions as seen from both
shape and posititon of the Q-bands of these macrocycles. However,
the UV–Vis spectrum of 8a in pyridine shows a much reduced Q-
band at 665 nm and higher absorption at wavelengths >700 nm
including a broad shoulder centred near 740 nm, these features
allegedly relating to aggregation. UV–Vis spectra of 8a and 8b are
shown as Supporting Information.
S(12)–C(13)–C(21)a
S(17)–C(18)–C(21)a
C(14)–C(13)–C(21)a
C(19)–C(18)–C(21)a
C(13)–C(21)–C(22)a
C(18)–C(21)–C(22)a
120.7 (2)
128.5 (2)
114.5 (2)
120.2 (2)/120.2 (2)b
129.6 (2)/129.6 (2)b
114.7 (2)/114.3(3)b
a
NMR analysis of compounds 8a–b was obtained by identifica-
tions of the 1H NMR and corresponding 13C NMR signals using
the pulse techniques COSY, HSQC and HMBC. The DMF-d7 solutions
of macrocycles 8 indicated massive aggregation due to consider-
ably more concentrated solutions than used for the UV–Vis analy-
sis. Only compound 8b could be analyzed by NMR spectrometry.
Upper entry in pair of values applies to structure 4a, lower entry to 5a.
First value applies to A-ethyl (major), second value to B-ethyl (minor) in
b
structure 5a. C(21A) and C(21B) are constrained to superpose.
bound OH-groups were observed as broad IR absorptions at ca.
3400 cmꢀ1 for these three compounds as well.

208
E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
1
1
1
o
1
2
3
4
o
2
3
2
2
2
2
2
3
2
3
2
2
3
2
2
3
2
2
2
2
2
Scheme 1. Synthesis of unsymmetrically substituted pyrazine-2,3-dicarbonitriles 4a–d and 5a–c.
Mass spectrometry (MALDI-TOF) of compounds 8a–b shows the
calculated molecular ions with the expected isotopic clusters char-
acteristic of zinc. The compounds were dissolved in dichlorometh-
ane, spotted onto the target plate and dried at ambient
temperature before being covered with matrix and injected into
the spectrometer. Mass spectra of 8a and 8b are reproduced in
Supporting Information.
H2
H2
Both NMR and mass spectra show the presence of small
amounts of impurities in 8a–b. Their effects on calculated yields
and extinction coefficients are expected to be insignificant.
3.1.4. Crystal structures of compounds 4a and 5a
The two structures with the atomic numbering are shown in
Fig. 1a and b. Common to both are the pyrazine-2,3-dicarbonitrile
ring bonded to one thiophene ring. The pyrazine ring of structure
4a is not strictly planar; the average torsion angle is about 1.5°.
The other rings in both structures are planar, with average torsion
angles in the range 0.15–0.75°. The thiophene ring in 4a is rotated
about 9.5° clockwise about the C(1)–C(11) bond vector. In 5a all
Scheme 2. Synthesis of substituted pyrazinopyrazine-2,3-dicarbonitriles 7.
Broad 1H signals corroborate extensive aggregation; the large
number and distribution of sharp lines reflect the presence of
structural isomers. The NMR spectra are shown as Supporting
Information.

E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
209
Bonding parameters of the pairs of pyrazine and thiophene
rings in 4a and 5a are closely similar. For the pyrazine rings the
average and maximum differences in the six bond lengths are
0.0037 and 0.006 Å, and in the six endocyclic bond angles 0.37°
and 0.6°, respectively. For a more relevant comparison of the thio-
phene geometry near the ethyl substituent we have used the three
bond lengths and three bond angles involving atoms S(12), C(13)
and C(14) in 4a and S(17), C(18) and C(19) in 5a. In Table 2 the
upper entry in each pair relates to 4a, the lower entry to 5a. Aver-
age and maximum deviations in total five bond lengths are 0.0026
and 0.006 Å, and in the five endocyclic bond angles 0.4° and 0.7°,
respectively.
2
2
o
4. Conclusion
5-Substituted pyrazine-2,3-dicarbonitriles 4a–d, 5a–c and 6-
aryl-substituted pyrazino[2,3-b]pyrazine-2,3-dicarbonitriles 7,
were synthesized as potential precursors for ZnAzaPc. Compounds
4a, 5-(5-ethylthiophen-2-yl)pyrazine-2,3-dicarbonitrile, and 4d, 5-
(3,4-dimethylthiophen-2-yl)pyrazine-2,3-dicarbonitrile, gave rea-
sonable yields of tetrasubstituted ZnAzaPc 8a and 8b from reac-
tions with Zn(quinoline)2Cl2. The thiophen-2-yl peripheral
substituents of compounds 8a–b induce red-shifted Q-bands to
660 nm, from 636 nm for unsubstituted ZnAzaPc. Strong aggrega-
tion precluded NMR analysis of 8a in DMF solution. The features of
the 1H NMR spectrum of 8b in DMF solution are consistent with
aggregation and the presence of structural isomers. Molecular ions
of 8a–b were identified by MALDI-TOF spectrometry.
Neither bithienyl substituted pyrazines 5 nor pyrazinopyrazines
7 form cyclotetramers, apparently due to destabilization of the
precursors by the conjugation imposed by bithienyl groups on 5,
or the conjugation within the pyrazinopyrazine skeleton of 7.
The crystallographic study of 4a and 5a shows that both struc-
tures have extended delocalized electron systems, in particular the
latter having three nearly perfectly coplanar rings. It appears that
the terminal ethyl group in the three-ring system of 5a is insuffi-
Scheme 3. Synthesis and structure of unsymmetrical tetrasubstituted zinc azapht-
halocyanines 8a–b. Only one structural isomer is shown for compounds 8.
three rings are very nearly coplanar, the largest deviation from
coplanarity, 1.8°, appears between the two thiophene rings.
Short intramolecular contacts between pyrazine N(6) and S(12)
of the adjacent thiophene ring are approximately equal in both
structures, 2.98 Å. The distance between the nearly eclipsed H(2)
and H(15) atoms is 2.22 Å in 4a, and 2.12 Å in 5a, which has a high-
er degree of ring coplanarity. In 5a there are in addition similar
contacts between the two thiophene rings S(12)ꢃ ꢃ ꢃH(20), 2.99 Å,
and S(17)ꢃ ꢃ ꢃH(14), 2.87 Å. Both structures feature several intermo-
lecular contacts of the type C–Hꢃ ꢃ ꢃA. The acceptor atom A in most
of the cases is the carbonitrile N(42) in two different adjacent mol-
ecules. Three of these Hꢃ ꢃ ꢃN(42) distances are in the range 2.55–
2.58 Å, the shortest is 2.44 Å. Structure 5a has also one contact
where the acceptor atom is S(17), the parent Hꢃ ꢃ ꢃS distance is
2.78 Å. The shortest of the contacts presumably have a certain de-
gree of hydrogen bond character.
cient to prevent self-aggregation via
p–p interactions. Replace-
Contacts involving hydrogen atoms have been calculated with
ment of the H atom bonded to pyrazine with a bulky substituent,
i.e. substitution near the centre of the conjugated system, presum-
C(sp2)–H bonds normalised at 1.09 Å, and C(sp3)–H bonds at 1.10 Å.
Fig. 1. Molecular conformation of compounds 4a in (a) and 5a in (b) with atomic numbering. Disorder in the ethyl group of 5a can be described as a small rotation of the C(22)
methyl about the C(18)–C(21) bond yielding two conformations A and B occurring in the ratio 4:1. ADP ellipsoids represent a 50% probability.

210
E.H. Mørkved et al. / Polyhedron 54 (2013) 201–210
(b) E.H. Mørkved, H. Ossletten, H. Kjøsen, Acta Chem. Scand. 53 (1999) 1117;
(c) E.H. Mørkved, H. Kjøsen, H. Ossletten, N. Erchak, J. Porphyrins
Phthalocyanines 3 (1999) 417;
(d) E.H. Mørkved, N.K. Afseth, H. Kjøsen, J. Porphyrins Phthalocyanines 10
(2006) 1301.
ably would have been more efficient to suppress self-aggregation
and obtain cyclotetramers with larger Q-band red shifts and in-
creased capacity for singlet oxygen production than, e.g. com-
pounds 9 and 10 in Ref. [6].
[8] E.H. Mørkved, H. Ossletten, H. Kjøsen, O. Bjørlo, J. Prakt. Chem. – Chem. Ztg.
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Acknowledgement
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130.
Dr. Kåre A. Kristiansen is thanked for technical assistance with
the MALDI-TOF analyses.
Appendix A. Supplementary data
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treatment with triethylamine in methanol for oxidation of the intermediate
thenoin. Heating under reflux of an acetic acid solution of 1,2-
diaminomaleonitrile with the above diketone for 16 hours gave, after
chromatography on silica with dichloromethane, 5,6-bis(2,20- bithiophen-5-
yl)pyrazine-2,3-dicarbonitrile, m.p. 235–245 °C decomp. This product was
shown by NMR analysis to contain approximately 25 % of unreacted diketone
in addition to the targeted pyrazine-2,3-dicarbonitrile.
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CCDC 901362 and 901363 contain the supplementary crystallo-
graphic data for structures 4a and 5a, respectively. These data can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223 336
033; or e-mail: deposit@ccdc.cam.ac.uk. Various spectral data for
compounds 8a and 8b are given as Supporting Information. Sup-
plementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.poly.2013.02.017.
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