Synthesis of substituted dipyrido[3,2-a:2′,3′-c]phenazines and a new heterocyclic dipyrido[3,2-f:2′,3′-h]quinoxalino[2,3-b]quinoxaline

Article abstract of DOI:10.1016/j.tet.2008.02.097

Three new α,α′-diimine ligands were synthesized based on condensation of 1,10-phenanthroline-5,6-dione with 1,2-phenylenediamine derivatives using different approaches. All compounds were fully characterized by IR, ¹H and ¹³C NMR, UV-visible, and MS spectroscopies. We report the first example of a dipyrido[3,2-f:2′,3′-h]quinoxalino[2,3-b]quinoxaline, which exhibits a strong absorption at 430 nm and an interesting electrochemical behavior. These new molecules may have biological potential and are of synthetic and technological importance.

Full text of DOI:10.1016/j.tet.2008.02.097

Tetrahedron 64 (2008) 5410–5415
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of substituted dipyrido[3,2-a:20,30-c]phenazines and a new heterocyclic
dipyrido[3,2-f:20,30-h]quinoxalino[2,3-b]quinoxaline
*
Fabio da Silva Miranda , Aline Maria Signori, Juliano Vicente, Bernardo de Souza, Jacks Patrick Priebe,
*
Bruno Szpoganicz, Norberto Sanches Gonçalves, Ademir Neves
´
´
Departamento de Quımica, Universidade Federal de Santa Catarina, CP-476, 88040-900 Florianopolis, SC, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 January 2008
Received in revised form 26 February 2008
Accepted 28 February 2008
Available online 4 March 2008
Three new
a,a
0-diimine ligands were synthesized based on condensation of 1,10-phenanthroline-5,6-
dione with 1,2-phenylenediamine derivatives using different approaches. All compounds were fully
characterized by IR, 1H and 13C NMR, UV–visible, and MS spectroscopies. We report the first example of
a dipyrido[3,2-f:20,30-h]quinoxalino[2,3-b]quinoxaline, which exhibits a strong absorption at 430 nm and
an interesting electrochemical behavior. These new molecules may have biological potential and are of
synthetic and technological importance.
Keywords:
1,10-Phenanthroline-5,6-dione
Ó 2008 Elsevier Ltd. All rights reserved.
dppz
dpq
Tetraazanaphthacene
B3LYP
1. Introduction
phenanthroline-5,6-dione (1). Indeed, there are many publications
in the literature on molecules that combine the phenanthroline
Ligands based on 1,10-phenanthroline (phen) and 2,20-bipyr-
idine (bpy) have been reported as potential prototypes in many
applications including optical devices,1,2 DNA intercalating,3,4 with
prospects regarding new drugs5 and catalysts,6 and supramolecular
chemistry.7,8 All these uses are based on the photo-physical and
electrochemical properties of ligands and their metal complexes.9
Molecules like dipyrido[3,2-a:20,30-c]phenazine (dppz)10 and di-
pyrido[3,2-f:20,30-h]quinoxaline (dpq)11 derivatives combine in-
teresting properties, such as bidentate coordination ability, rigidity,
or bipyridine moieties with the phenazine and quinoxaline units,
but none with the tetraazanaphthacene moiety. This is the first
example of a dipyrido[3,2-f:20,30-h]quinoxalino[2,3-b]quinoxaline
ring (dpq-QX), which is a molecule containing the tetraazanaph-
thacene and bipyridine moieties together.
This new heterocyclic compound contains six condensation
rings and six nitrogen atoms, two being coordinate donors at the
phenanthroline moiety and four nitrogens from the tetraaza por-
tion. This site is p-accepting and is able to coordinate metal centers
and planar highly conjugated aromatic structure. Their
p
-accepting
and is also suited for H-bonding with H-donors like DNA-bases. In
addition, this new heterocyclic compound also shows interesting
optical and electrochemical properties. Tetraazanaphthacene has
been described as an important heterocyclic compound in different
areas, such as bridging mixed-valence metal complexes14 and
organic superconductors15 and its photo-emission properties have
been recently reported.16 In this paper the synthesis of two new
asymmetric dppz ligands with 2,1,3-thiadiazole (dppz–BTDZ) and
sulfonic acid groups (dppz–SO3) are also described, both with
interesting optical and electrochemical behavior, and they may also
provide new prototypes for DNA interaction.
character and nitrogen sites enable them to be intercalated into
DNA or promote H-bonds at the phenazine and quinoxaline moi-
eties of these compounds, from the bpy moiety. In the photo-
chemistry of ruthenium(II) and osmium(II) complexes with this
class of ligands an electron excited at the metal center is transferred
rapidly to the phenazine, resulting in an efficient charge separation
useful for solar cells and other applications.
In connection with our interest in the search for new DNA
cleaving agents12,13 we present here the synthesis and complete
characterization of a new polycyclic conjugate derivative from 1,10-
The synthetic route to produce the three new compounds was
based on the condensation of 1,10-phenanthroline-5,6-dione 1
with aromatic 1,2-diamines synthesized in many steps using three
different approaches. All of them were based on the o-phenyl-
enediamine 2 and obtained through adaptations from the literature
* Corresponding authors. Tel.: þ55 48 3721 9852; fax: þ55 48 3721 6850.
E-mail addresses: miranda@qmc.ufsc.br (F. da Silva Miranda), ademir@
qmc.ufsc.br (A. Neves).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.02.097

F. da Silva Miranda et al. / Tetrahedron 64 (2008) 5410–5415
5411
methods.17–20 The o-phenylenediamine 2 has the advantage of
reacting at different positions on the benzene ring or amino groups.
We explored this feature to produce the symmetric 2,3-di-
aminequinoxaline5throughthethree-stepprocedure17 asdescribed
by Carmack and shown in Scheme 1. Firstly, 2 was transformed into
2,3-dihydroxyquinoxaline 3 followed by reaction with thionyl
chloride and DMF as the catalyst resulting in 2,3-dichloroquinoxa-
line 4 and amination with liquid ammonia in 80% yield.
The second amine was the 4,5-diamino-2,1,3-benzothiazole
9 obtained in four steps from 2. The diamine was transformed
into 2,1,3-benzothiadiazole 6, as described by Dupont et al. using
thionyl chloride in dichloromethane.18 Nitration of 6 in a mixture of
nitric and sulfuric acids at 10 ꢀC gave 4-nitro-2,1,3-benzothiadi-
azole 7 in 80% yield as described in the literature.19 The direct
amination of 7 with hydroxylamine in methanolic potassium
hydroxide gave 5-amino-4-nitro-2,1,3-benzothiazole 8, which was
reduced to 4,5-diamine-2,1,3-benzothiazole 9 with sodium di-
thionite in water.20
and 13 in good yields. The reaction of the diamine 5 with 1 resulted
in the new heterocyclic 11, which shows a decreased solubility in
most solvents in relation to dppz, probably due to
p-stacking in-
teractions and other intermolecular forces. Its structure has two
conjugate pyrazines that can promote coordination or H-bonding at
these sites. The reaction of 2,1,3-benzothiadiazole-4,5-diamine 9
with 1 resulted in the asymmetric 12 with high yields. The mole-
cule 12 has a low solubility in most solvents. The diamine 10 was
reacted with 1 in 1:1 water/ethanol v/v resulting in the dipyr-
ido[3,2-a:20,30-c]phenazine-11-sulfonic acid 13, that shows a in-
creased solubility in water and in mixtures of water/ethanol and
water/DMSO, an important feature for biochemistry studies
(Scheme 2).
The 1H NMR spectrum of 11 shows five peaks due to the C2v
symmetry (see Supplementary data, Fig. S1), and the assignment of
the signals are in agreement with the literature, where the Hc
proton is the most shifted to high fields while the Hb proton is less
affected when compared to the other protons in dppz and phen
systems.25,26 On the other hand, the phenanthroline moiety of
compound 12 is considerably affected by the thiadiazole conjugate
The sulfonation of phenylenediamine was performed via a
new route using only concentrated sulfuric acid at 137 ꢀC for 1
day. Cold water was then added resulting in a white precipitate,
that was recrystallized in water affording the pure 3,4-di-
aminobenzenesulfonic acid 10 in 77% yield. The literature methods
reported for the synthesis of 3,4-diaminobenzenesulfonic acid are
more harsh, for example, sulfonation of o-phenylenediamine with
H2SO4/SO3,21 SO3,22 or by reduction of 3-nitro-4-aminobenz-
enesulfonate with HCl/SnCl2.23 Our method offers a more simple
approach to sulfonate 2.
0
group at the 10 and 11 positions, the Hc and Hc are separated by
0.25 ppm (see Supplementary data, Fig. S2). The protons Ha/Ha0 and
0
Hb/Hb are less affected by the geometry of the molecule and occur
in the same peak, each signal in these cases referring to two pro-
tons. It can be noted that there are 18 peaks in the 13C spectrum of
12, which shows that the carbon atoms are more affected by
molecular asymmetry than the hydrogen atoms. The 1H NMR
spectrum of compound 13 shows that it is less affected than com-
pound 12, having six peaks due to its molecular geometry (see
Supplementary data, Fig. S3). The protons in the phenanthroline
moieties are not separated in either case, and the 13C NMR shows 16
peaks, the other two peaks are in the region of CF3CO2D. Also,
The dione 1 was prepared according to the literature24 using
HNO3/H2SO4/KBr to oxidize the 1,10-phenanthroline to 1,10-phe-
nanthroline-5,6-dione 1 in high yields, which was then reacted
with the diamines 5, 9, and 10 to form the new molecules 11, 12,
Scheme 1. Synthesis of diamines.

5412
F. da Silva Miranda et al. / Tetrahedron 64 (2008) 5410–5415
Figure 1. Absorption spectra of 11–13 in DMSO at 3ꢂ10ꢁ5 M.
to the
p
–
p transition of the phenanthroline moiety. The strong
*
absorption between 360–460 nm with two maxima at 409 and
432 nm is due to increased conjugation in the system and these
Scheme 2. Synthesis of new dppz ligands.
maxima represent
exhibited the pattern of the dppz skeleton, the exception in 12 is
the of the thiadiazole ring at 318 nm. The transitions of
p
–
p
*
transitions. Compounds 12 and 13
compound 13 behaves in the same way as compound 12, which
confirms the influence of substituent groups on the carbon atoms
p
–p
*
p–
p
*
in all parts of the extended conjugate
p
-system.
the phenanthroline moiety were observed at 256 and 260 nm, re-
The electrochemical, spectroscopic, and DFT results are sum-
marized in Table 1. The UV–visible spectrum of 11 in DMSO solution
shows a different pattern when compared with the spectra of dpq
and dppz (see Fig. 1), most probably due to the increase in number
of pyrazine rings conjugated in the polycyclic system.27 The spec-
trum shows two main peaks or regions, with three shoulders. The
peaks in the region between 250–330 nm are not well defined and
spectively, for 12 and 13. In the literature, the other peaks are
usually assigned to
p
–
p transitions of the pyrazine moiety. The
*
electronic spectra of dpq,28 dppz,29,30 phenanthroline,31 quinoxa-
line,32 phenazine,32 and tetraazanaphthacence27 have been repor-
ted by many different groups. This information is important in the
assignment of
p
–
p transitions relating to phenanthroline and
*
pyrazine moieties, but a complete study is beyond the scope of this
paper and an experimental and theoretical study on the excited
states of these new compounds and their coordination compounds
will be presented elsewhere.
probably include the contribution of
p
–
p
*
transitions of all parts of
transitions of the
the ring and is also a characteristic of the
p
–
p
*
phenanthroline portion. The peak at 276 nm is tentatively assigned
Table 1
Summary of the results for the spectroscopic, electrochemical, and DFT calculations
Compound
Absorption spectra
Electrochemistry
pKa
Results from DFT calculation at B3LYP/6-31þG(d,p)a
lmax
log
3
Assignment
E1/2, V
Assignment
HOMO
LUMO
Gap
LUMO
LUMO
c
h
I
A
u
þ1
þ2
11
269
276
286
293
310
389
409
432
4.69
4.71
4.68
4.65
4.38
4.15
4.48
4.63
p–
p–
p–
p–
p–
p–
p–
p–
p
p
p
p
p
p
p
p
*
*
*
*
*
*
*
*
phen
phen
phen
phen
taz
taz
taz
taz
ꢁ0.422
ꢁ0.787
ꢁ1.029
ꢁ2.202
ꢁ2.393
p
*
p
*
p
*
p
*
p
*
taz
taz
taz
phen
phen
1.50
2.04
2.68
ꢁ6.75
ꢁ6.78
ꢁ3.59
ꢁ3.68
3.16
3.10
ꢁ2.00
ꢁ2.06
ꢁ1.91
ꢁ2.02
5.17
5.23
1.58
1.55
6.75
6.78
3.59
3.68
8.47
8.83
12
13
256
318
343
351
367
377
387
4.55
4.58
4.40
4.27
4.16
3.97
4.26
p
p
p
p
p
p
–
–
–
–
–
–
p
p
p
p
p
p
*
*
*
*
*
*
phen
Thiadiazole
diaz
diaz
diaz
ꢁ0.902
ꢁ1.174
ꢁ1.568
ꢁ1.865
ꢁ2.159
ꢁ2.460
p
p
p
p
p
p
*
*
*
*
*
*
diaz
diaz
diaz
phen
phen
phen
ND
ꢁ6.83
ꢁ6.80
ꢁ2.87
ꢁ2.87
3.97
3.93
ꢁ2.84
ꢁ2.80
ꢁ1.89
ꢁ1.97
4.85
4.84
1.98
1.96
6.83
6.80
2.87
2.87
5.93
5.95
diaz
273
295
347
355
366
375
386
4.77
4.41
3.97
4.02
4.17
4.12
4.27
p–
p–
p–
p–
p–
p–
p–
p
p
p
p
p
p
p
*
*
*
*
*
*
*
phen
phen
diaz
diaz
diaz
diaz
diaz
ꢁ0.489
ꢁ0.879
ꢁ1.192
ꢁ1.820
ꢁ2.022
ꢁ2.181
ꢁ2.338
ꢁ2.404
ꢁSOꢁ3
ꢁSOꢁ3
3.26
ꢁ5.18
ꢁ7.01
ꢁ7.05
ꢁ6.90
ꢁ2.99
ꢁ6.60
ꢁ4.41
ꢁ3.20
3.29
ꢁ3.12
ꢁ0.44
ꢁ2.76
0.77
3.81
3.77
3.78
2.56
3.84
ꢁ3.74
ꢁ3.15
ꢁ2.31
ꢁ2.15
0.06
ꢁ3.17
ꢁ2.41
ꢁ2.06
ꢁ1.99
0.25
4.80
5.11
5.17
5.01
1.72
4.68
0.38
1.91
1.88
1.89
1.28
1.92
5.18
7.01
7.05
6.90
2.99
6.60
4.41
3.20
3.29
3.12
0.44
2.76
29.96
6.84
7.10
6.63
1.15
p
*
p
*
p
*
p
*
p
*
p
*
diaz
phen
phen
phen
phen
phen
ꢁ1.84
ꢁ1.82
5.71
NDdnot determined; tazdtetraza; diazddiazine.
a
The theoretical results are shown in the following order, first line gaseous phase and below the DMSO phase. In the case of compound 13 the results are expressed as the
two first lines zwitterionic form, the next two lines the neutral form, and the last lines the anionic form.

F. da Silva Miranda et al. / Tetrahedron 64 (2008) 5410–5415
5413
The easy reduction of dipyridophenazines is due to the lower
energy -accepting
orbital of the phenazine moiety.29 Thus, the
p
*
p
site in dipyridophenazine is located on the phenazine portion of the
molecule. DFT calculations are known to provide good geometries,
frequencies, and ground-state energies. We used the B3LYP/6-
31þG(d,p) method to correlate the electronic structure of com-
pounds 11–13 with the electrochemical properties.
For this correlation we used the conceptual DFT,33–35 whereby it
is possible to calculate the theoretical values of electronegativity
(c), hardness (
h), ionization energy (I), electronic affinity (A), and
electrophilicity index (
u
), among other properties. All these prop-
erties are calculated from the energies of frontier orbitals and the
mathematical formalism can be found in the Refs. 33–35. Table 1
shows the values of HOMO, LUMO, LUMOþ1, LUMOþ2, gap, ioniza-
tion energy, electronic affinity, and electrophilicity index in gaseous
and liquid phase (DMSO) calculated by the PCM method. In the case
of compound 13 we decided to explore the three different forms of
protonation: (a) the zwitterionic form with the nitrogen from
the protonated phenanthroline moiety; (b) the anionic form and (c)
the neutral form with the protonation at the sulfonic group. The
zwitterionic form was found to be more stable than the neutral
form by 10.33 kcal molꢁ1 in aqueous phase and 9.86 kcal molꢁ1 in
DMSO phase. An inverse situation is found in the gaseous phase
where the neutral form is 23.83 kcal molꢁ1 more stable than the
zwitterionic form. This situation shows the importance of the in-
clusion of solvent effects in order to obtain correct predictions of
molecules, which can present different possibilities of protonation.
Comparison of the first reduction process of 11–13 with dpq and
dppz shows a shift in the reduction process to positive values in 11
due to the extended conjugate system, which facilitates the re-
duction process. The analysis of the molecular orbital is important
to determine the electrochemically active orbital, since the first
LUMO is called the electrochemical orbital.25,30 For molecule 11, the
first LUMO is tetraza based, and thus the first reduction process will
probably occur at this site. But the other LUMOs have close energy
values allowing, also, the population of these electronic states. This
is currently being investigated by ab initio calculations and exper-
imental techniques and the results will be presented in the future.
The square wave voltammogram of 11 shows five successive
reduction processes (see Fig. 2). The first at ꢁ0.422 V is reversible
while the others at ꢁ0.787, ꢁ1.029, ꢁ2.202, and ꢁ2.393 V are quasi-
reversible. The three empty orbitals of lower energy are very dif-
ferent, the LUMO shows more contribution from tetraza moiety,
Figure 2. Square wave voltammograms of 11–13 at 10ꢁ3 M in DMSO.
voltammetry starting at negative potentials shows two oxidation
peaks at ꢁ0.192 and 0.113 V, due to the re-oxidation of sulfonic
groups reduced at low potentials.
Of the theoretically calculated parameters the best correlation of
the electrochemical results was found between electronic affinity
and the electrophilicity index in the DMSO phase. These parame-
ters expressed the tendencies of a certain molecule to undergo
reduction. The usefulness of electrophilicity index has also been
reported in other contexts.36,37 The comparison shows that mole-
cule 11 possesses a high electron acceptor characteristic because of
while the LUMO is completely extended throughout the system
þ1
and the LUMO has a contribution only from the phenanthroline
þ2
moiety. The LUMO and LUMOþ1 probably participate in the process
between 0.4–1.0 V while the LUMO2þ is in agreement with the high
reduction potentials of the phenanthroline moiety (see Supple-
mentary data, Fig. S5). It is important to note that LUMO and
þ1
LUMO orbitals probably participate in the charge transfer from
the high values of A and u. Molecule 13 shows a tendency to un-
þ2
metal to ligand in the complex, because the symmetry is appro-
priate and the nitrogens of phenanthroline have a significant par-
ticipation in these molecular orbitals. Ligand 12 has six reduction
processes at ꢁ0.902, ꢁ1.174 V (reversible and phenazine based),
ꢁ1.568, ꢁ1.865, ꢁ2.159, and ꢁ2.460 V (quasi-reversible) assigned
to phenanthroline site reduction. The plot of the molecular orbital
of 12 in particularly the LUMOs showed a similar behavior to 11 (see
dergo reduction of the sulfonic group. The best correlation was
found in DMSO due to the instability of the zwitterionic form in
gaseous phases. The molecular orbitals were more affected by
solvent inclusion in 13 than in the cases of 11 where they do not
change forms, and 12, where they showed few modifications in the
LUMO and LUMOþ1. The changes caused by solvent inclusion are
more evident in the ionic forms of 13 where there is high charge
concentration in specific parts.
The pKa’s of 11 and 13 were determined by potentiometric
titration in a 70:30 ethanol/water system. The values found for the
hydrolysis of the phenanthroline moiety were 2.68 and 3.26,
respectively, for 11 and 13. These pKa’s values are in agreement with
the phenanthroline protonation as described in the literature.38
Compound 13 showed a maximum solubility at pH¼3.40, in-
dicating the best pH to work with it. Compound 11 shows two
further pKa’s of 1.50 and 2.04, which are assigned to the tetraza
Supplementary data, Fig. S6), i.e., the LUMO and LUMO
are
þ1
phenazine centered and LUMO
is phenanthroline based. The
þ2
difference is the delocalization caused by the asymmetry of the
molecular shape. Regarding the electrochemistry of 13 there are
two main reduction peaks at ꢁ1.192 and ꢁ2.404 V, the first one
assigned to the phenazine part and the second to the phenan-
throline moiety, however, the molecule has another six peaks from
the reduction reactions of the sulfonic group at ꢁ0.489, ꢁ0.879,
ꢁ1.820, ꢁ2.022, ꢁ2.181, and ꢁ2.338 V. However, the square wave

5414
F. da Silva Miranda et al. / Tetrahedron 64 (2008) 5410–5415
portion. The pKa of 12 was not determined because of the low
solubility of this compound.
2.2. Synthesis
Compounds 10–13 were characterized by 1H and 13C NMR, in-
frared, mass spectroscopy, and elemental analysis. Compounds 1
and 3–9 were prepared according to the literature, giving spectral
data consistent with that reported. Confirmatory characterization is
provided in Supplementary data.
Compounds 11–13 are being tested as DNA intercalating agents,
such as ruthenium complexes ([Ru(phen)2L]2þ) and iron(II) tris-
complexes, and the results will be presented in future papers.
2.2.1. 3,4-Diaminobenzenesulfonic acid (10)
Compound 2 (20 g, 184.94 mmol) was added to 90 mL of sulfuric
acid 96% at ꢁ30 ꢀC under stirring for 1 h, followed by stirring until
room temperature. The green solution was then kept at 137 ꢀC for 1
day. The reaction mixture was cooled and cold water was added to
afford a white precipitate, which was filtered off and recrystallized
in water to afford white crystals. Yield 77%. Anal. Calcd for
C6H8N2O3S$2H2O: C, 32.14; H, 5.39; N, 12.49; S, 14.30. Found: C,
31.98; H, 5.23; N, 12.12; S, 14.28. MS (EI, 70 eV) m/z 188.05 [Mþ],
calcd 188.03. 1H NMR (ppm, 400 MHz, D2O)
1H), 7.17 (dd, J3¼8.4 Hz, J4¼1.8 Hz, 1H), 7.36 (d, J4¼1.8 Hz, 1H), 8.1
d
: 6.82 (d, J3¼8.4 Hz,
2. Experimental
2.1. General
(br s, 4H). 13C NMR (ppm, 100.8 MHz, D2O)
d: 117.1, 118.1, 119.3,
122.5, 133.3, 135.5. IR (KBr, cmꢁ1): 3058, 1682, 1568, 1457, 1411,
1312, 1289, 1202, 1114, 1007, 921, 810, 736.
All reagents and solvents for the synthesis and analysis were of
analytical and/or spectroscopic grade from Sigma or Aldrich and
used without further purification. Infrared spectra were acquired
on a Perkin Elmer FTIR 2000. NMR analysis was performed on
a Varian 400 MHz spectrometer. Elemental analysis for compounds
10–13 was carried out using a Carlo Erba Analyzer Model E-1110.
The UV–visible spectra were obtained using a Perkin Elmer Lambda
19 instrument. Low-resolution mass spectra were obtained for
compounds 1 and 3–12 on a Shimadzu CGMS-QP5050A instrument
using the direct injection mode. The samples were placed in
a sample vial fixed onto the probe. The probe temperatures were
programmed as follows: 5 ꢀC minꢁ1 up to 100 ꢀC and held for 5 min,
increasing from 100 to 300 ꢀC at 20 ꢀC minꢁ1, and held for 5 min.
The quadrupole mass spectrometer was operated in the electron
impact (EI) mode (ionization energy 70 eV) scanning from m/z 20 to
400 in 0.5 s. The mass spectra for compound 13 was obtained by
ESI-MS. The ESI-Q-Tof mass spectrometry (MS) analyses were car-
ried out using a Q-Tof ultima API spectrometer (Waters/Micromass)
equipped with an elecrospray ionization source operated in the
negative mode (ESI(ꢁ)-MS). Typical MS conditions were: source
temperature of 100 ꢀC, dessolvation temperature of 100 ꢀC, capil-
lary voltage of 3.5 kV and cone voltage of 35 V. Mass spectrometer
calibrations were made by using formic acid. Compound 13 was
diluted in water, acetonitrile, and formic acid (50:49.9:0.1, v/v/v).
The sample was injected using a syringe pump at a flow rate of
2.2.2. Dipyrido[3,2-f:20,30-h]quinoxalino[2,3-b]quinoxaline
(dpq-QX) or quinoxalino[20,30:5,6]pyrazino[2,3-f][1,10]-
phenanthroline (11)
Compound 1 (1 g, 4.76 mmol) was dissolved in ethanol under
nitrogen and 0.78 g (4.87 mmol) of 5 dissolved in DMF was added
to this solution and the reaction mixture was then refluxed for 8 h.
The orange solid formed was filtered off and washed with cold
water, ethanol, and acetone. The product was recrystallized in
chloroform to afford an orange material. Yield 85%. Anal. Calcd for
C
20H10H6$0.8H2O: C, 68.87; H, 3.36; N, 24.10. Found: C, 68.58; H,
3.15; N. 24.15. MS (EI, 70 eV) m/z 334.15 [Mþ], calcd 334.10. 1H NMR
(ppm, 400 MHz, CDCl3)
d
: 7.88 (dd, J3¼8.1, 4.4 Hz, 2H, Hb), 8.07 (dd,
J3¼7.0 Hz, J4¼3.3 Hz, 2H, He), 8.52 (dd, J3¼7.0 Hz, J4¼3.3 Hz, 2H, Hd),
9.35 (dd, J3¼4.4 Hz, J4¼1.5 Hz, 2H, Ha), 9.83 (dd, J3¼8.1 Hz,
J4¼1.5 Hz, 2H, Hc). 13C NMR (ppm, 100.8 MHz, CDCl3)
d: 109.7, 124.9,
126.9, 130.2, 133.1, 135.4, 143.7, 146.6, 146.9, 154.2. UV–vis (DMSO,
nm (log 3)): 269 (4.69), 276 (4.71), 286 (4.68), 293 (4.65), 310(4.38),
389 (4.15), 410 (4.48), 432 (4.63). IR (KBr, cmꢁ1): 3079, 1582, 1493,
1412, 1385, 1203, 1080, 894, 753, 740, 503.
2.2.3. Dipyrido[3,2-a:20,30-c]phenazine-10,11-(2,1,3-thiadiazole)
(dppz–BTDZ) (12)
Compound 1 (1 g, 4.76 mmol) was dissolved in ethanol under
nitrogen and 0.80 g (4.81 mmol) 9 was added to this solution and
the reaction mixture was stirred for 15 min at room temperature
and then refluxed for further 2 h. The solid formed was filtered off
and washed with water, cold ethanol, hexane, and acetone. The
product was recrystallized in dichloromethane to afford a pink
material. Yield 88%. Anal. Calcd for C18H10N6S$0.5H2O: C, 61.88;
H, 2.60; N, 24.05; S, 9.18. Found: C, 61.51; H, 2.45; N, 23.91; S, 8.96.
MS (EI, 70 eV) m/z 340.25 [Mþ], calcd 340.05. 1H NMR0 (ppm,
10 m
L minꢁ1. Mass spectra were acquired along m/z 100–1500 range.
Datawere analyzed by MassLynxÒ 4.0 software. The electrochemical
experiments were carried with deaerated 3ꢂ10ꢁ4 mol Lꢁ1 solutions
of compounds 11–13, all in DMSO. The experiments were per-
formed using Pt working and auxiliary electrodes, an Ag/AgCl
reference electrode, and Bu4NPF6 at a concentration of 0.1 mol Lꢁ1
as the supporting electrolyte. The ferrocene–ferrocenium (Fc/Fcþ)
couple served as the internal reference,39 and all potentials were
referenced to normal hydrogen electrode (0.400 V vs NHE). The
instrument used was a BASI Epsilon Model EC Epsilon. The square
wave voltammetry was performed at frequency of 25 Hz and
amplitude of 10 Hz. Cyclic voltammetry used scan rates of 50, 100,
200, 300 mV sꢁ1. The pKa’s of 11 and 13 were determined by
potentiometric titration in an ethanol/water mixture (as described
in literature40), with the aid of the BEST7 program.41 All calcula-
tions reported here were performed by the Gaussian 03 code.42
B3LYP exchange correlation potential,43 in connection with the
6-31þG(d,p) basis set, were used to obtain equilibrium geometries
of the new molecules. Harmonic vibration frequencies were com-
puted to characterize them as minima energy point. To study the
solution behavior of the different species, the polarized continuum
(overlapping spheres) model44 was used, to simulate the water and
DMSO solvents. PCM calculation used radii UAKS and all standard
specifications of Gaussian package, the exception was the electro-
static scaling factor of 1.35 to DMSO.
400 MHz, CF3CO2D)
d
: 8.56 (dd, J3¼8.4, 5.1 Hz, 2H, Hb/Hb ), 8.66
(d, J3¼8.8 Hz,1H, He), 8.72 (d, J3¼8.8 Hz,1H, Hd), 9.54 (dd, J3¼5.1 Hz,
0
J4¼1.5 Hz, 2H, Ha/Ha ), 10.43 (dd, J3¼8.4 Hz, J4¼1.5 Hz, 1H, Hc), 10.67
(dd, J3¼8.4 Hz, J4¼1.5 Hz, 1H, Hc ). 13C NMR (ppm, 100.8 MHz,
0
trifluoroacetic-d1) d: 126.1, 127.6, 127.6, 129.9, 130.1, 132.8, 138.2,
138.4, 139.1, 139.2, 140.1, 140.6, 141.1, 146.7, 148.3, 148.6, 152.1,
156.3; UV–vis (DMSO, nm (log 3)): 256 (4.55), 318 (4.58), 343
(4.40), 351 (4.27), 367 (4.16), 377 (3.97), 387 (4.26). IR (KBr, cmꢁ1):
3024, 1573, 1492, 1422, 1375, 1364, 1129, 1084, 1078, 836, 817,
741, 497.
2.2.4. Dipyrido[3,2-a:20,30-c]phenazine-11-sulphonic acid
(dppz–SO3) (13)
A mixture of 1 g (4.76 mmol) of 1,10-phenanthroline-5,6-dione
and 1.08 g (4.83 mmol) of 10 in 20 mL of water/ethanol 1:1 v/v was
refluxed for 4 h. Upon cooling, the white-yellow precipitate was
collected by filtration and washed with cold water, methanol, and
acetone. Yield 95%. Anal. Calcd for C18N4H9SO3H: C, 59.66; H, 2.78;

F. da Silva Miranda et al. / Tetrahedron 64 (2008) 5410–5415
5415
13. Peralta, R. A.; Neves, A.; Bortoluzzi, A. J.; dos Anjos, A.; Xavier, F. R.; Szpoganicz,
B.; Terenzi, H.; de Oliveira, M. C. B.; Castellano, E.; Friedermann, G. R.; Mangrich,
A. S.; Novak, M. A. J. Inorg. Biochem. 2006, 100, 992–1004.
N, 15.46; S, 8.85. Found: C, 59.35; H, 2.76; N, 15.28; S, 8.66. ESI-MS
(ꢁ) m/z 361.037 [Mꢁ], calcd 361.039. 1H NMR (ppm, 400 MHz,
0
CF3CO2D)
d
: 9.60 (dd, J3¼8.1, 5.1 Hz, 2H, Hb/Hb ), 9.70 (d, J3¼9.0 Hz,
´
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1H, Hf), 9.77 (d, J3¼9.0 Hz, 1H, He), 10.19 (s, 1H, Hd), 10.55 (dd,
15. Tadokoro, M.; Yasuzuka, S.; Nakamura, M.; Shinoda, T.; Tatenuma, T.; Mitsumi,
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Murata, K. Angew. Chem., Int. Ed. 2006, 45, 5144–5147.
0
J3¼5.1 Hz, J4¼1.5 Hz, 2H, Ha/Ha ), 11.40 (dd, J3¼8.1 Hz, J4¼1.5 Hz, 2H,
Hc/Hc ). 13C NMR (ppm, 100.8 MHz, trifluoroacetic-d1)
d: 128.8,
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3
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Supplementary data
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