New viologen analogs: 1,4-bis[2-(pyridin-4-yl)ethenyl]benzene quaternary salts

Article abstract of DOI:10.1134/S1070363209070196

Alkylation of 1,4-bis[2-(pyridin-4-yl)ethenyl]benzene with alkyl p-toluenesulfonates and dimethyl sulfate gave new viologen analogs, 1-alkyl-4-(2-{4-[2-(1-alkylpyridinium-4-yl)ethenyl]phenyl}ethenyl)-pyridinium bis(p-toluenesulfonates) and sulfate. Their

Full text of DOI:10.1134/S1070363209070196

ISSN 1070-3632, Russian Journal of General Chemistry, 2009, Vol. 79, No. 7, pp. 1513–1518. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © A.V. Gutov, E.B. Rusanov, L.V. Chepeleva, S.G. Garasevich, A.B. Ryabitskii, A.N. Chernega, 2009, published in Zhurnal Obshchei
Khimii, 2009, Vol. 79, No. 7, pp. 1156–1161.
New Viologen Analogs: 1,4-Bis[2-(pyridin-4-yl)ethenyl]benzene
Quaternary Salts
a
a
a
b
A. V. Gutov , E. B. Rusanov , L. V. Chepeleva , S. G. Garasevich ,
a
a
A. B. Ryabitskii , and A. N. Chernega
a
Institute of Organic Chemistry, National Academy of Sciences of Ukraine, ul. Murmanskaya 5, Kiev, 02660 Ukraine
e-mail: AVGutov@mail.ru
b
Taras Shevchenko Kiev National University, Kiev, Ukraine
Received June 19, 2008
Abstract—Alkylation of 1,4-bis[2-(pyridin-4-yl)ethenyl]benzene with alkyl p-toluenesulfonates and dimethyl
sulfate gave new viologen analogs, 1-alkyl-4-(2-{4-[2-(1-alkylpyridinium-4-yl)ethenyl]phenyl}ethenyl)-
pyridinium bis(p-toluenesulfonates) and sulfate. Their derivatives with tetrafluoroborate and tetraphenylborate
ions were also obtained. Spectral properties of the synthesized compounds were examined, and their structure
was determined by X-ray analysis.
DOI: 10.1134/S1070363209070196
Viologens or 4,4'-bipyridine double quaternary salts
have long been known, and they have found versatile
applications. Viologens are used in molecular
electronic devices (e.g., matrices for transistors),
photochemistry (solar energy conversion, isolation of
hydrogen from water), electrochromic display devices,
etc. [1, 2]. Diversity of applications of viologens is
determined by their unique physical and chemical
properties both in solution and in crystal. First of all,
this is facile one-electron reduction which generates
stable radical cation [3–5].
It is known that many important properties typical
of viologens, such as one-electron reduction, photo-
chromism, etc., may also be inherent to their analogs in
which two pyridinium fragments are linked through a
spacer [6, 7]. Moreover, variation of the spacer struc-
ture may enhance or weaken some properties.
The properties of some spacer viologen analogs
derived from 1,4-bis(pyridin-4-yl)benzene and 4,4'-bis
(pyridin-4-yl)biphenyl were examined previously [8].
N
N
N
N
Also, viologen analogs possessing a heteroaromatic
spacer were synthesized [7].
+N
N+
X
S
X = O, S.
N
N
1
,4-bis[2-(pyridin-4-yl)ethenyl]benzene (I) with ethyl
and butyl p-toluenesulfonates and dimethyl sulfate
Scheme 1). Compound I was prepared according to
modified procedure [9], by condensation of
terephthalaldehyde with 4-methylpyridine. Other
viologen analogs were obtained by anion exchange in
p-toluenesulfonates II and IV by tetrafluoroborate and
tetraphenylborate. Compound III was synthesized by
N
N
n
(
Viologens in which the pyridinium fragments are
linked through a furan or thiophene fragment were
reported in [6].
In the present work we synthesized novel viologen
analogs having a divinylphenyl spacer by alkylation of
1513

1
514
GUTOV et al.
Scheme 1.
+
N R
HBF4
N
−
(
BF )
+
4 2
R N
III
+
N R
X
R
+
R N
2
X−
II, IV, VI
+
N R
−
(
BF )
4
2
+
R N
N
I
V
4
; V, R = Et; VI, R = Me, 2X = O .
II, R = Bu, X = 4-MeC
6
H
4
SO
3
; III, R = Bu; IV, R = Et, X = 4-MeC
6
H
4
SO
3
treatment of II with tetrafluoroboric acid, while
sodium tetraphenylborate was used in the synthesis of
salt VI.
B which differ by orientation of the terminal ethyl
groups with respect to the central benzene ring. The N-
ethyl groups in dication VA (Fig. 1) are oriented
toward one side of the central fragment: the
Attempts to reduce the dications in salts II–VI to
the corresponding radical cations with sodium
dithionite resulted in decoloration of the initial
aqueous solution (in contrast to the reduction of related
viologens which give rise to violet color [1]).
2
2
21 23 24
pseudotorsion angle C C C C is 9.9°, whereas the
corresponding groups in dication VB appear at the
opposite sides of the central fragment (the
2
2
21 23 24
15
pseudotorsion angle C C C C is 179.1°). The C
14
8
13
and C atoms and the C –C atoms in the central
benzene ring in dication VB are statistically disordered
by two positions a and b with equal populations. As a
result, a superposition of two conformers VBa (Fig. 2)
and VBb (Fig. 3) is observed in crystal.
Numerous attempts were made to obtain crystals of
salts II–VI suitable for X-ray analysis. However, we
succeeded in growing single crystals only of
compound V. Despite their poor quality and instability
at room temperature on exposure to air, they were
subjected to X-ray analysis. The other salts crystallized
as finely dispersed powders, regardless of the solvent
used and temperature conditions. According to the X-
ray diffraction data, a unit cell of crystalline compound
V includes two symmetry-independent dications A and
1
2
1
20
The central N N C –C fragment in all three
conformers is almost planar: deviations of atoms from
the mean-square plane do not exceed 0.06 Å in VA,
0.33 Å in VBa, and 0.31 Å in VBb. Such geometry
implies partial conjugation of the pyridinium rings
2
10
9
1
C
C
C
6
C
1
6
17
C
14
C
C
C
1
N
2
3
2
3
21
1
8
C
N
11
8
C
C
C
7
C
C
13
C
1
5
5
C
4
22
12
C
24
19
C
C
C
C
C
C
2
0
C
Fig. 1. Structure of dication VA according to the X-ray diffraction data. Principal bond lengths (Å) and bond and torsion angles
1
1
5
1
21
1
16
2
20
2
23
2
6
7
14
(
deg): C –N 1.348(2), C –N 1.350(2), C –N 1.485(2), C –N 1.348(2), C –N 1.350(2), C –N 1.485(2), C –C 1.325(3), C –
15
7
6
3
6
7
8
11 14 15
14 15 18
3
6
7
8
11 14 15 18
C 1.330(3); C C C 123.62(19), C C C 127.98(19), C C C 125.14(18), C C C 126.93(18); C C C C 179.4, C C C C –178.5.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

NEW VIOLOGEN ANALOGS
1515
1
6
24
C
17
C
C
1
5
2
3
C
10
9
C
2
C
C
2
N
C
1
8
6
1
C
C
C
2
0
C
19
14
11
C
C
8
3
1
C
C
C
N
7
21
C
C
13
12
C
C
4
C
5
22
C
C
Fig. 2. Structure of dication VBa according to the X-ray diffraction data. Principal bond lengths (Å) and bond and torsion angles
1
1
5
1
21
1
16
2
20
2
23
2
6
7
14
(
C
deg): C –N 1.351(2), C –N 1.347(2), C –N 1.485(2), C –N 1.342(2), C –N 1.343(2), C –N 1.488(2), C –C 1.336(4), C –
1
5
7
6
3
6
7
8
11 14 15
14 15 18
3
6
7
8
11 14 15 18
1.323(8); C C C 124.98(19), C C C 127.48(2), C C C 126.6 (5), C C C 117.0(4); C C C C –174.8, C C C C 178.6.
1
22
2
C
C
C
C
21
3
C
6
C
1
1
0
9
1
C
N
C
C
1
7
5
1
4
1
6
C
4
C
C
C
7
8
1
8
11
C
C
C
C
2
2
3
4
C
1
5
12
3
C
C
2
C
N
1
9
C
2
0
C
C
Fig. 3. Structure of dication VBb according to the X-ray diffraction data. Principal bond lengths (Å) and bond and torsion angles
1
1
5
1
21
1
16
2
20
2
23
2
6
7
14
(
deg): C –N 1.351(2), C –N 1.347(2), C –N 1.485(2), C –N 1.342(2), C –N 1.343(2), C –N 1.488(2), C –C 1.336(3), C –
15
7
6
3
6
7
8
11 14 15
14 15 18
3
6
7
8
11 14 15 18
C 1.340(8); C C C 124.98(19), C C C 127.48(19), C C C 125.87 (5), C C C 117.41(4); C C C C –174.8, C C C C –177.1.
through the π-system formed by double bonds and
etc., were observed in the crystalline structure of
compound V since the dications are spatially separated
by large tetraphenylborate anions and solvate dime-
thylformamide molecules (Fig. 4).
benzene ring. The dihedral angles between the central
8
13
1
1
5
benzene ring (C –C ) and pyridine rings N C –C and
2
16
20
N C –C are, respectively, 2.3 and 2.5° in VA, 7.5
and 2.9° in VBa, and 8.7 and 0.4° in VBb). It should
be noted that the double bonds C –C and C –C in
The luminescence spectra of crystalline compounds
III and VI showed single structureless bands with their
maxima at λ 490 (III) and 545 nm (VI), while
compound IV displayed at least two bands at λ 490
and 514 nm. Interestingly, the luminescence intensity
of compound IV was greater by more than an order of
magnitude than the intensity of luminescence of related
viologens. This may be due to different properties of the
anion and specificity of crystal packing.
6
7
14
15
dication VA are oriented trans relative to the central
6
7
14 15
benzene ring (the pseudotorsion angle C C C C is–
75.9°). Analogous conformation of the central
1
fragment is typical of dication VBb where the
corresponding torsion angle is –176.0°. On the other
6
7
14
15
hand, the double bonds C –C and C –C in VBa are
8
13
oriented cis with respect to the C –C fragment
pseudotorsion angle C C C C 11.9°). The bond
6
7
14 15
(
To conclude, we have synthesized new spacer
viologen analogs extended by a stilbene fragment. Ac-
cording to the X-ray diffraction data, these compounds
in crystal may exist as at least three conformers. The
examined salts exhibit luminescence in the crystalline
state, and its intensity strongly depends on the anion
nature and alkyl groups on the nitrogen atoms.
lengths and bond angles in the pyridinium rings do not
differ significantly from those typical of viologens[1–4].
Dications VA and VB in crystal are arranged almost
parallel to each other, the corresponding dihedral angle
being 12.0°. No shortened intermolecular contacts like
cation–cation, cation–anion, cation–solvent molecule,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

1
516
GUTOV et al.
b
a
0
c
Fig. 4. A fragment of crystal packing of compound V.
EXPERIMENTAL
The H NMR spectra were recorded on a Bruker
procedure in full-matrix anisotropic approximation
using SHELX software package. The refinement was
performed with 15624 reflections with I > 2σ(I) (1602
refined parameters, 9.75 reflections per parameter).
The positions of hydrogen atoms were calculated on
the basis of geometry considerations and were refined
with fixed thermal and positional factors. The
1
spectrometer at 282.2 MHz using DMSO-d as solvent
6
and tetramethylsilane as internal reference. The
electronic absorption spectra were measured on a
Shimadzu UV-3100 spectrophotometer from solutions
in methanol. Luminescence studies were performed on
a Coderg T-800 automated spectrometer (excitation at
λexcit 280 nm with a UV light-emitting diode).
2
2
following weight scheme was applied: w = 1/[s (Fo ) +
2
2
2
(
0.0458P) + 2.6973P] where P = (Fo + 2Fc )/3. The
final divergence factors were R = 0.051 and wR =
1
2
0
.1023; goodness of fit 1.007. The residual electron
The X-ray diffraction data for a single crystal of
compound V as solvate with DMF, V·2DMF, were
density from the Fourier difference series was –0.430
and 0.326 e Å . The complete set of crystallographic
data for compound V was deposited to the Cambridge
Crystallographic Data Centre (entry no. CCDC 653127).
–3
acquired on
a
Bruker Smart Apex II CCD
diffractometer (MoK irradiation, λ = 0.71069 Å) at 88 K;
α
θmax = 25.58, spherical segment–35 ≤ h ≤ 42, –16 ≤ k ≤
2
1, –26 ≤ l ≤ 26. Total of 70269 reflection intensities
1,4-Bis[2-(pyridin-4-yl)ethenyl]benzene (I). Pow-
dered anhydrous zinc chloride, 13.64 g, was added to a
solution of 13.7 g of 4-methylpyridine and 6.7 g of
terephthalaldehyde in 40 ml of acetic anhydride, and
the mixture was heated for 24 h under reflux, cooled to
70°C, and filtered. The precipitate was washed with
acetic anhydride and alcohol to obtain 11 g of the
crude product which was recrystallized from pyridine.
were measured, 24033 of which were independent.
Monoclinic crystals with the following unit cell
parameters: a = 34.9368(14), b = 17.5556(6), c =
2
8
3
1.6119(8) Å; β = 104.451(1)°; V = 12877.6(8) Å ; Z =
3
–1
; dcalc = 1.16 g/cm ; μ = 0.069 cm ; F(000) = 4816;
space group P2 /c. The structure was solved by the
direct method and was refined by the least-squares
1
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 79 No. 7 2009

NEW VIOLOGEN ANALOGS
1517
1
Yield 6.6 g (46%), yellowish powder. H NMR
(2H, J = 16.2 Hz), 8.27 d (4H, J = 6.9 Hz), 9 d (4H,
J = 6.6 Hz). Electronic absorption spectrum, λmax, nm
spectrum, δ, ppm: 7.2 d (2H, J = 16.2 Hz), 7.592 s
4H), 7.65 d (2H, J = 16.2 Hz), 7.92 d (4H, J = 6.6 Hz),
.426 d (4H, J = 7.2 Hz).
–
4
–1
–1
(
8
(ε×10 , l mol cm ): 251 (0.76), 384 (3.86). Found,
%: C 66.29, 66.49; H 5.92, 6.06, S 9.04, 9.24.
C H N O S . Calculated, %: C 66.29; H 5.88; S 9.36.
3
8
40
2
6 2
1
-Butyl-4-(2-{4-[2-(1-butylpyridinium-4-yl)ethenyl]-
phenyl}ethenyl)pyridinium bis(4-methylbenzenesul-
fonate) (II). A mixture of 1.4 g of compound I and
1-Ethyl-4-(2-{4-[2-(1-ethylpyridinium-4-yl)ethenyl]-
phenyl}ethenyl)pyridinium bis(tetraphenylborate) (V).
Quaternary salt IV, 0.68 g, was dissolved in 20 ml of
hot water, and a solution of 0.75 g of sodium tetra-
phenylborate in 15 ml of hot water was added in one
portion. A yellow solid separated. The mixture was
shaken, heated for 5 min at 70°C (oil bath), and left to
stand for 1 h at room temperature. The precipitate was
filtered off, washed with warm water, and dried. The
crude product, 0.95 g, was dissolved in 4 ml of DMF
on heating, the solution was filtered, and 17 ml of hot
alcohol was added. After 2 h, the precipitate was
filtered off and washed with alcohol. Yield 0.78 g
4
2
.6 g (excess) of butyl p-toluenesulfonate was fused at
00°C on heating on an oil bath over a period of 1.5 h.
The hot melt was treated with 20 ml of diisobutyl
ketone, and the precipitate was filtered off, washed
with acetone, and recrystallized from ethanol. Yield
1
2
.76 g (76%), yellow powder. H NMR spectrum, δ,
ppm: 0.9 t (6H), 1.3 m (4H), 1.9 m (4H), 2.3 s (6H),
4
7
1
.5 q (4H), 7.1 d (4H, J = 7.5 Hz), 7.5 d (4H, J = 8.1 Hz),
.64 d (2H, J = 16.2 Hz), 7.9 s (4H), 8.07 d (2H, J =
6.5 Hz), 8.27 d (4H, J = 6.6 Hz), 9 d (4H, J = 6.9 Hz).
–
4
Electronic absorption spectrum, λ , nm (ε×10 ,
max
–1
–1
1
l mol cm ): 251 (0.9), 384 (4.29). Found, %: C
7.94, 67.95; 6.27, 6.28; 8.69, 8.73.
C H N O S . Calculated, %: C 68.08; H 6.53; S 8.65.
(76%). H NMR spectrum, δ, ppm: 1.54 t (6H), 4.54 q
6
H
S
(4H), 6.75 t (8H), 6.9 t (16H), 7.2 m (16H), 7.54 d
(2H, J = 16.4 Hz), 7.8 s (4H), 7.96 d (2H, J = 16.4 Hz),
42
48
2
6 2
8
.2 d (4H, J = 6 Hz), 8.9 d (4H, J = 6 Hz). Electronic
1
-Butyl-4-(2-{4-[2-(1-butylpyridinium-4-yl)ethenyl]-
absorption spectrum: λmax 382 nm. Found, %: C 87.89,
phenyl}ethenyl)pyridinium bis(tetrafluoroborate) (III).
Quaternary salt II, 0.5 g, was dissolved in 30 ml of
water on heating to the boiling point, and 2 ml (excess)
of tetrafluoroboric acid was added. After 5 h, the
precipitate was filtered off, dried, and recrystallized
from 6 ml of acetonitrile. Yield 0.16 g (42%), white
88.09; H 7.98, 7.18. C H B N . Calculated, %: C
72 66 2 2
88.15; H 6.79.
1-Methyl-4-(2-{4-[2-(1-methylpyridinium-4-yl)-
ethenyl]phenyl}ethenyl)pyridinium sulfate (VI). A
mixture of 0.8 g of compound I and 1.4 g of dimethyl
sulfate was heated for 4 h at 180°C on an oil bath. The
mixture was cooled to 100°C, 3 ml of water was
added, the mixture was heated for 10 min at the boiling
point and allowed to cool down, and the precipitate
was filtered off, washed with acetone, and re-
crystallized from aqueous ethanol. Yield 1.01 g (88%),
yellow powder. Found, %: C 64.74, 64.69; H 4.91,
4.95; S 7.49, 7.53. C H N O S. Calculated, %: C
1
powder. H NMR spectrum, δ, ppm: 0.94 t (6H), 1.32 m
(
1
(
4H), 1.92 m (4H), 4.53 q (4H), 7.64 d (2H, J =
6.2 Hz), 7.9 s (4H), 8.05 d (2H, J = 15.9 Hz), 8.27 d
4H, J = 6.6 Hz), 9 d (4H, J = 6.3 Hz). Electronic
absorption spectrum, λmax, nm (ε×10 , l mol cm ):
51 (0.69), 382 (2.6). Found, %: C 58.73, 58.75; H
.71, 5.78; N 5.15, 5.16. C H B N F . Calculated, %:
–
4
–1
–1
2
5
28
34
2
2 8
C 58.77; H 5.98; N 4.89.
2
2
20
2
4
64.31; H 4.87; S 7.80.
1-Ethyl-4-(2-{4-[2-(1-ethylpyridinium-4-yl)ethenyl]-
phenyl}ethenyl)pyridinium bis(4-methylbenzolsul-
fonate) (IV). A mixture of 0.85 g of compound I and
ACKNOWLEDGMENTS
2
(
2
.4 g of ethyl p-toluenesulfonate was fused at 175°C
oil bath) over a period of 1.5 h. The melt was cooled,
0 ml of anhydrous acetone was added, the mixture
The authors thank Yu.L. Slominskii for his help and
fruitful discussions.
was heated for 1 h under reflux and filtered while hot,
and the precipitate was washed with anhydrous
acetone on a filter. Recrystallization from 12 ml of
ethanol gave 1.46 g (71%) of salt IV as a bright yellow
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2
.
.
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powder. H NMR spectrum, δ, ppm: 1.54 t (6H), 2.3 s
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