A New Family of 2(3H)-Thiazolone Azines as Precursors to Air-Stable Radical Cations

Article abstract of DOI:10.1246/bcsj.77.165

A Novel 2(3H)-thiazolone azines family having R_F substituents on the 4,4′-positions were efficiently prepared in good yield. The two-step synthesis involves the preparation of N, N′ -dialkyl-1,2-hydrazinedicarbothioamides and their reaction with bromomethyl perflooroalkyl ketone, resulting in double ring closure. All the members prepared in this new family of compounds form stable radical cations, which enables them to be considered as ideal candidates for electrochemical tuning of light absorption as in electrochromic windows or displays and as redox indicators or mediators.

Full text of DOI:10.1246/bcsj.77.165

Ó 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 165–167 (2004)
165
A New Family of 2(3H)-Thiazolone Azines as Precursors
to Air-Stable Radical Cations
ꢀ
´
Amer Hammami, Hicham Cavalie-Kosheiry, and Michel Armand
´
Laboratoire International sur les Materiaux Electroactifs CNRS - UMR 2289 Universite de Montreal,
´
´
´
B.P. 6128, Montreal, Quebec, Canada H3C3J7
´
Received May 26, 2003; E-mail: armandm@chimie.umontreal.ca
A Novel 2(3H)-thiazolone azines family having RF substituents on the 4,40-positions were efficiently prepared in
good yield. The two-step synthesis involves the preparation of N,N0-dialkyl-1,2-hydrazinedicarbothioamides and their re-
action with bromomethyl perflooroalkyl ketone, resulting in double ring closure. All the members prepared in this new
family of compounds form stable radical cations, which enables them to be considered as ideal candidates for electro-
chemical tuning of light absorption as in electrochromic windows or displays and as redox indicators or mediators.
The viologen type redox couples (X2þ , Xꢁþ , Xꢂ) have
been extensively studied1–5 in recent years, mostly for their po-
tential application in electrochromic devices. While all di-cat-
ions based on quaternized 4,40-bipyridines and homologues
show perfectly reversible redox behavior, the potential at which
the highly colored radical mono-cations form is too negative for
stability in air. Since complete prevention of oxygen ingress in
electrochromic devices based on redox dyes is illusory, espe-
cially for the appealing flexible devices using ITO-on-plastic
substrates (retrofit on existing windows), the achievement of
air/moisture stability is essential. Separating the pyridine moi-
eties by the electronegative –N=N– bridge shifts the potential
by ꢃ þ200 mV, which is still insufficient. 2(3H)-Benzo-thia-
duce the symmetrical N,N0-dialkyl-1,2-hydrazinedicarbothiio-
amides, ii) formation of the thiazole moieties by ring closure
using halomethyl perfloroalkyl ketone.
The synthesis13,14 of compounds 3 and 4 is straightforward
(Scheme 1), and the availability of various isothiocyanates15 al-
lows for the manipulation of their lipophilic character and the
introduction of various functionalities. They were prepared in
two steps. The first step was the synthesis of N,N0-dialkyl-
1,2-hydrazinedicarbothiioamides 2 by direct addition of the
corresponding isothiocyanate 1 to hydrazine in a 2:1 ratio.
ꢂ
The reaction takes place in THF at 0 C, with a quantitative
yield. Then, the target compounds 3 and 4 were obtained by ad-
dition of 2 molar amounts of bromomethyl trifluoromethyl ke-
tone and bromomethyl pentafluoroethyl ketone, respectively, in
refluxing ethanol. Compounds 3 and 4 were obtained in good
yields (70–75%; Table 1). Recrystallization from ethanol gave
analytically pure samples.
For each product, a single crystal suitable for X-ray diffrac-
tion studies was grown by cooling an ethanol solution of com-
pound 3. All 2(3H)-thiazolone azines form colorless rectangu-
lar prismatic crystals, easily isolated and characterized. The
zolone azines discovered by Hunig,6,7 which were made water
¨
soluble by sulphonation, give mono- and dication radicals at
(0.67 V and 1.19 V vs Ag/AgCl), and are used to test peroxi-
dases (laccases).8,9 These compounds, however, are difficult
to prepare and are mutagenic. In addition, the di-sulfonate is in-
soluble in aprotic solvents and polymer electrolytes, possibly
including gelled, of interest for electrochromic devices. The
pristine molecule itself shows poor solubility due to extensive
‘‘ꢀ’’ stacking of this large multi-ring system.
The simple 2(3H)-thiazolone azines have received far less
attention.10,11 Their potential is not strong enough (170 mV),
and the neutral molecule is already highly colored (yellow to
red) due to the chromogenic azo linkage.12
step 1
S
C
S
C
NH2 NH2
2RN
C
1
S
RHN
NH NH
NHR
THF, 0°C
2
R = CH3, C4H9, C6H13
Results and Discussion
step 2
O
O
Br
Br
In this paper, we report a new family of 2(3H)-thiazolone
azines in which a perfluoroalkyl substituent is introduced on
each ring. This strategy was used to raise the redox potential,
influenced by the electron-withdrawing effect of the perfluoro
moieties, resulting also in a non-absorbing neutral state:
S
S
CF3
N
N
N
N
N
R
N
F3C
3
4
CF3
EtOH, 12h
R
2
reflux
S
S
(Ncolorless , Xꢁþ
, X2þweakly absorbing). These new
CF2CF3
absorbing
molecules have been characterized in terms of electrochemis-
try, structure, and absorbance.
The title molecules were prepared in two steps: i) addition of
an alkyl isothiocyanate to hydrazine (quantitative) to pro-
N
R
N
R
CF3F2C
CF2CF3
Scheme 1. Synthesis of 2(3H)-thiazolone azines.
Published on the web January 13, 2004; DOI 10.1246/bcsj.77.165

166 Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
Novel Precursors to Stable Radicals Cations
Table 1. Yields Obtained for 2(3H)-Thiazolone Azines
change resulting from the introduction of the RF group is the
shift in absorption to a colorless starting molecule. The materi-
als, in molecular form or as polymers, are ideal candidates for
electrochemical tuning of light absorption, as in electrochromic
windows and displays. They offer an interesting alternative to
the 2(3H)-thiazolone azines in terms of solubility and stability
of the radical cation as redox shuttles and mediators (indirect
oxygen bleaching . . .), and for laccases assays.
2(3H)-Thiazolone azines
Yield/%
S
S
N
N
N
3a
3b
3c
4d
4e
73
75
70
78
75
N
F3C
F3C
CF3
CH3
S
CH3
S
N
N
N
N
CF3
(CH2)3CH3
S
(CH2)3CH3
S
N
N
N
N
Experimental
F3C
CF3
(CH2)5CH3
S
(CH2)5CH3
S
Material. All chemicals used were reagent grade. A 1 M (= 1
mol dmꢄ3) solution of hydrazine in THF (Aldrich) was used as the
source of the anhydrous base. Isothiocyanates, bromomethyl tri-
fluoromethyl ketone and 1-bromo-3,3,4,4,4-pentafluoro-2-buta-
none were obtained from Lancaster (UK) or TCI (Japan) and were
used as received. All reactions were conducted under dry a argon
atmosphere.
N
N
N
N
CF3F2C
CF3F2C
CF2CF3
CH3
S
CH3
S
N
N
N
N
CF2CF3
(CH2)5CH3
(CH2)5CH3
General. 1H, 13C and 19F spectra were recorded on a Bruker
400 MHz spectrometer in THF-d8 solution. Chemical shifts are re-
ported in ppm with internal reference to TMS. Mass spectra (MS)
were recorded on a Micromass 1212 spectrometer. Infrared (IR)
spectra were recorded in the range 4000–600 cmꢄ1 using a
Perkin-Elmer 298 infrared spectrometer. Spectra were taken with
KBr disks. Melting points (mp) were determined with a capillary
tube Thomas Hoover melting point apparatus and are reported as
uncorrected values.
Synthesis of Dicarbothiothioamides (Compounds 2a–2e). A
1.0 M hydrazine solution in anhydrous THF (10 mL, 10 mmol, 320
mg contained N2H4) was added dropwise over 30 min to a solution
of alkyl isothiocyanate (20 mmol, 1.462 mg for CH3NCS, resp.
2.865 mg for C6H13NCS) in anhydrous THF (35 mL), at 0 ꢂC under
dry argon. After 1 h of vigorous stirring a white precipitate ap-
peared. Stirring was maintained for 3 h. Then, the solvent was re-
moved under reduced pressure, and the crude product was washed
with cold THF to obtain a white powder in pure form and quanti-
tative yield.
rings are co-planar with the two perfluoroalkyl groups in the
eclipsed conformation. For 3b, the hexyl side-chains chose a
trans-gauche-trans-trans conformation. The planearity of the
rings conjugated through the azino linkage is almost a prereq-
uisite for stable radicals.
The azinodi-4-thiazolines previously described in the litera-
ture are yellow compounds, resembling in this respect azo-pyr-
idines, a measure of electron density on the N–N bridge. The
immediate effect of the presence of two perfluoroalkyl groups
ꢀ
(ꢁ
¼ 2:6), reducing the electron density, is the formation
CF3
of colorless derivatives with an absorption shifted to the UV re-
gion. 3a–4e are strictly insoluble in water, especially those with
the longest perfluoroalkyl and/or N-alkyl groups. They dissolve
easily in most organic solvents, however.
All compounds prepared in this study exhibit a well-behaved
electrochemical response in MeCN with a one electron oxida-
tion of the neutral form to the radical cation (Eꢂ ¼ 0:68 and
0.71V for 3 and 4) of intense blue coloration, followed by a sec-
ond electron abstraction leading to the dicationic species (pale
yellow-green) at 1.2 V vs Agꢂ/AgCl. The radical cations thus
prepared where found not only to be air stable, due to their re-
dox potential, which is above that of oxygen, but also water sta-
ble, the redox reaction, taking place before the oxidation of the
latter- and especially light-fast.
When the counter-anion is hydrophobic (e.g., [(CF3SO2)2-
N]ꢄ), the radical salt is water insoluble, but soluble in polar
organic solvents (Ac, MeCN, CH2Cl2. . .). On the other hand,
hydrophilic counter-anions (e.g., Clꢄ, Brꢄ, CF3CO2ꢄ) yield
water soluble salts. The electrochemistry of such materials will
be presented in detail elsewhere.
General Procedure for the Synthesis of Compounds 3a–c
and 4d–e.
N,N0-dialkyl-1,2-hydrazinedicarbothiioamides (3
mmol. 534.8 or 859.5 mg for C1 resp. C6) were dissolved in 60
ꢂ
mL anhydrous ethanol at 50 C over 30 min, 7.5 mmol (1336 or
1807 mg for CF3 resp. C2F5) of bromomethyl trifluoromethyl
ketone or 1-bromo-3,3,4,4,4-pentafluoro-2-butanone were added
slowly at 50 ꢂC over 30 min. The mixture was refluxed overnight.
A white precipitate separated when the mixture was cooled to 0 ꢂC.
The precipitates were filtered and recrystallized from ethanol to
obtain colorless tubular crystals.
3-Methyl-4-trifluꢂoromethyl-2(3H)-thiazolone Azine 3a:
73% yield; mp 181 C; IR (KBr) 3412, 3182, 3103, 2953, 1742,
1607, 1445, 1397, 1332, 1305, 1259, 1198, 1157, 1000, 861,
826, 754 cmꢄ1
;
1H NMR (THF-d8) 6.83 (s, 2H, CH), 3.40 (s,
6H, CH3); 13C NMR (THF-d8) 164.9, 132.7, 110.8, 124.6 (q, JCF
¼
269 Hz), 36.3; 19F NMR (THF-d8) ꢄ60:2 (CF3); HRMS calcd for
C10H8F6N4S2 362.009, found 362.008.
3-Butyl-4-trifluoromethyl-2(3H)-thiazolone Azine 3b: 75%
Conclusions
ꢂ
The new family of 2(3H)-thiazolone azines bearing RF sub-
stituents can be easily synthesized from readily available pre-
cursors. The choice of RF and R allows for fine-tuning of the
properties of the molecules compared to the 2(3H)-thiazolone
azine. Their solubility in ordinary organic solvents is excellent
while their redox potentials are similar. The most striking
yield; mp 104 C; IR (KBr) 3412, 3173, 3114, 2973, 2940, 2881,
2345, 1602, 1583, 1452, 1425, 1375, 1329, 1290, 1272, 1214,
1126, 846 cmꢄ1 1H NMR (THF-d8) 6.81 (s, 2H, CH), 3.78 (m,
;
4H, NCH2), 1.85 (m, 8H, CH2CH2), 0.97 (m, 6H, CH3); 13C NMR
(THF-d8) 160.0, 128.4, 106.6, 120.4 (q, JCF ¼ 269 Hz), 48.5, 21.1,
20.8, 11.4; 19F NMR (THF-d8) ꢄ59:3 (CF3); HRMS calcd for

A. Hammami et al.
Bull. Chem. Soc. Jpn., 77, No. 1 (2004)
167
C16H20F6N4S2 446.102, found 446.103.
3-Hexyl-4-trifluoromethyl-2(3H)-thiazolone Azine 3c: 70%
yield; mp 102 C; IR (KBr) 3122, 2959, 2858, 1603, 1582, 1471,
1452, 1423, 1378, 1332, 1270, 1233, 1185, 1155, 1121, 1011,
988, 857 cmꢄ1 1H NMR (THF-d8) 6.81 (s, 2H, CH), 3.82 (m,
;
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We acknowledge the support of CNRS within the frame of
the International Joint Laboratory on Electroactive Materials
(CNRS UMR 2289).