Novel fluorine containing tetrathiafulvalenes for the preparation of Langmuir-Blodgett films

Article abstract of DOI:10.1023/A:1025647112804

The novel fluorinated tetrathiafulvalenes: tetra(2,3,5,6-tetrafluorobenzylthio)-, dimethyldi(2,3,4,5,6-pentafluorobenzylthio)-, dimethyldi(2,3,5,6-tetrafluorobenzylthio)-, dimethyldi[3,5-di(trifluoromethyl)-benzylthio]-, and dimethyldi(2-fluoro-4-bromobenzylthio)tetrathiafulvalenes have been synthesized in order to prepare Langmuir-Blodgett films. Their cyclic voltamograms have been studied and these show two, reversible, one-electron oxidation waves. A novel series of fluorinated benzylthio- and benzoylthio-1,3-dithiole-2-thiones and -2-ones has been synthesized.

Full text of DOI:10.1023/A:1025647112804

Chemistry of Heterocyclic Compounds, Vol. 39, No. 6, 2003
NOVEL FLUORINE CONTAINING
TETRATHIAFULVALENES FOR THE
PREPARATION OF LANGMUIR–BLODGETT FILMS
G. G. Abashev1, E. V. Shklyaeva1, A. G. Tenishev1, and D. N. Korekov2
The novel fluorinated tetrathiafulvalenes: tetra(2,3,5,6-tetrafluorobenzylthio)-, dimethyldi(2,3,4,5,6-
pentafluorobenzylthio)-, dimethyldi(2,3,5,6-tetrafluorobenzylthio)-, dimethyldi[3,5-di(trifluoromethyl)-
benzylthio]-, and dimethyldi(2-fluoro-4-bromobenzylthio)tetrathiafulvalenes have been synthesized in
order to prepare Langmuir–Blodgett films. Their cyclic voltamograms have been studied and these
show two, reversible, one-electron oxidation waves. A novel series of fluorinated benzylthio- and
benzoylthio-1,3-dithiole-2-thiones and -2-ones has been synthesized.
Keywords: 1,3-dithiol-2-ones, 1,3-dithiole-2-thiones, fluorinated benzylthiotetrathiafulvalenes, cyclic
voltamograms.
In recent times an increasing amount of attention has been focused on studying the electroconductive
properties of organic conductors derived from mono- and multifilms prepared by the Langmuir–Blodgett
method (LB films). These conducting LB films were previously obtained based on amphiphilic
7,7,8,8-tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) derivatives which contained long
aliphatic chains [1-3]. However, in recent times, it has been possible to prepare films based on TTF derivatives
not containing long chains [4] with their stabilization brought about by the addition of aliphatic acids such, for
example, as arachidonic acid [2-4]. In the studies [2, 3] tetra(benzylthio)tetrathiafulvalene was used for the
preparation of the conducting films and di(methylthio)di(benzylthio)tetrathiafulvalene in the report [5]. The
exchange of hydrogen for fluorine in the benzyl radical and the effect of this exchange on the stability of the LB
film had not been investigated at all hence we have prepared a novel series of fluoro-substituted
benzylthiotetrathiafulvalenes. The synthesis of the latter has been performed according to Scheme 1 starting
from the mesoionic salt 1 which was prepared by the methods reported in the studies [6-9]. Alkylation of the salt
1 was carried out with the fluoro-substituted benzyl chlorides or bromides in acetone by heating to the
disappearance of its orange coloration. As a rule, the obtained chlorides (2a,c – oil, and 2b,d – crystals) can be
used for further syntheses without purification. Reduction of these compounds occurs most efficiently in
acetonitrile medium using a small excess of sodium borohydride. The 2-substituted 1,3-dithioles 3a-d obtained
in this way are oily products which can also be used without preliminary purification. The 1,3-dithiolium
perchlorates 4a-d are crystalline products which decompose upon heating.
__________________________________________________________________________________________
1
Natural Sciences Institute, Perm State University, Perm 614600, Russia; e-mail: gabashev@psu.ru.
2
OOO Scientific Introduction Firm "Okta", Perm 614000, Russia. Translated from Khimiya
Geterotsiklicheskikh Soedinenii, No. 6, pp. 888-894, June, 2003. Original article submitted June 4, 2000;
revision submitted May 29, 2001.
760
0009-3122/03/3906-0760$25.00©2003 Plenum Publishing Corporation

Scheme 1
_
S
SCH2Ar
S
S
_
+
S
S
MeCOMe
+
ArCH Hal
+
N
X
2
N
Me
Me
1
2a–d
ArCH2S
SCH2Ar
Me
SCH2Ar
Me
SCH2Ar
+
S
S
S
NaBH4
HClO4
S
NEt3
S
_
ClO4
N
S
Me
S
H
S
Me
3a–d
5a–d
cis / trans
4a–d
2–5 a Ar = C6F5, b Ar = 2,3,5,6-F4C6H, c Ar = 3,5-(CF3)2C6H3, d Ar = 2-F,4-Br–C6H3;
2 a, b, d X = Cl, c X = Br
The tetrathiafulvalenes 5a-d synthesized were obtained as a mixture of the cis and trans forms and are
orange colored crystalline materials.
Alkylation of the bistetraethylammonium bis(1,3-dithiole-2-thione-4,5-dithiolato) zincate (6), which had
been obtained by the method reported in [10], with the fluoro-substituted benzyl chlorides in acetone gave the
4,5-di(2,3,5,6-tetrafluorobenzylthio)- (7a), 4,5-di(2,3,4,5-tetrafluorobenzylthio)- (7b), 4,5-di(2,3,4,5,6-
pentafluorobenzylthio)- (7c), 4,5-di(2-fluoro-4-bromobenzylthio)- (7d), and 4,5-di[3,5-di(trifluoromethyl)-
benzylthio]-1,3-dithiole-2-thione (7e) (see Scheme 2). Upon heating with mercuric acetate for 5-10 min in acetic
acid they are converted to 4,5-di(2,3,5,6-tetrafluorobenzylthio)- (8a), 4,5-di(2,3,4,5,6-pentafluorobenzylthio)-
(8c), 4,5-di(2-fluoro-4-bromobenzylthio)- (8d), and 4,5-di[3,5-di(trifluoromethyl)benzylthio]-1,3-dithiol-2-one
(8e) respectively. The obtained oxygen derivatives do not form the corresponding tetrathiafulvalenes when
heated in triethylphosphite.
Scheme 2
2–
S
S
S
S
+
S
Zn
ArCH2Cl
(NEt4)2
S
+
S
S
S
S
6
S
S
SCH2Ar
SCH2Ar
SCH2Ar
SCH2Ar
Hg(OAc)2 / AcOH
O
S
S
S
7a–e
8a,c–d
S
SCOAr
SCOAr
6 + ArCOCl
S
S
9a–d
7, 8 a Ar = 2,3,5,6-F4C6H; b Ar = 2,3,4,5-F4C6H; c Ar = C6F5; d Ar = 2-F,4-Br–C6H3;
e Ar = 3,5-(CF3)2C6H3; 9 a Ar = 3-F–C6H4; b Ar = 2,3,4-F3C6H2; c Ar = 2,3,4,5-F4C6H;
d Ar = 3,5-(CF3)2C6H3
761

The reaction of the zincate 6 with the fluoro-substituted benzoyl chlorides (see Scheme 2) also gave
4,5-di(3-fluorobenzoylthio)- (9a), 4,5-di(2,3,4-trifluorobenzoylthio)- (9b), 4,5-di(2,3,4,5-tetrafluorobenzoyl-
thio)- (9c), and 4,5-di[3,5-di(trifluoromethyl)benzoylthio]-1,3-dithiole-2-thione (9d) which could not be
converted to the corresponding tetrathiafulvalenes by the standard methods.
Following Scheme 3 [11], the thione 7a gave the tetra(2,3,5,6-tetrafluorobenzylthio)tetrathiafulvalene
(10). Reaction of compound 7a with diethoxycarbenium borofluoride in methylene chloride gave the
2-ethylthio-4,5-di(2,3,5,6-tetrafluorobenzylthio)-1,3-dithiolium borofluoride (11). The latter was reduced using
sodium borohydride in acetonitrile to give 2-ethylthio-4,5-di(2,3,5,6-tetrafluorobenzylthio)-1,3-dithiole (12)
which could be treated with perchloric acid in ether to give the 4,5-di(2,3,5,6-tetrafluorobenzylthio)-1,3-
dithiolium perchlorate (13). The reaction of perchlorate 13 with triethylamine in acetonitrile gave the
tetrathiafulvalene (10) as small, dark red needles.
Scheme 3
ArCH2S
ArCH2S
+
S
NaBH4
MeCN
+
S
_
BF4
CH(OEt)2BF4
7a
Et
S
11
ArCH2S
ArCH2S
ArCH2S
S
NEt3
S
_
HClO4
SEt
H
+
ClO4
MeCN
S
S
ArCH2S
12
13
ArCH2S
ArCH2S
SCH2Ar
SCH2Ar
S
S
S
S
10
10–13 Ar = 2,3,5,6-F4C6H
The characteristics for the synthesized compounds are given in Table 1.
Since compounds 2a,c, 3a,c,d, 4a-d, 12, and 13 were used in subsequent syntheses without purification
their parameters are not reported in Table 1.
In order to measure the electron-donor properties of the synthesized fluoro-containing
tetrathiafulvalenes we obtained their cyclic voltamperograms and observed two reversible, one-electron
oxidation waves. Their potentials are given in Table 2. Comparison with the unsubstituted tetrathiafulvalene
shows that the oxidation of the fluoro-substituted benzylthiotetrathiafulvalenes occurs at higher potentials. The
even higher value of E1/21 for compound 10 can be explained by the presence of the four bulky tetrafluorobenzyl
substituents around the central tetrathiafulvalene fragment which hinders the process of oxidation of the latter.
The obtained compounds could be used for the synthesis of the conductive cation radical salts and for
the formation of LB films.
762

TABLE 1. Characteristics of the Synthesized Compounds
Found S, %
Calculated S, %
3
IR spectrum,
Com-
Empirical
formula
——————
mp, °С
1Н NMR (CDCl3), δ, ppm
ν, cm-1
pound
1
2b
2d
3b
2
4
5
6
C16H16ClF4NS3
22.30
22.37
111-112
162-163
88-89
1.65 (6H, m, 3CH2); 1.67 (3H, d, CH3); 3.50 (2H, s, SCH2); 4.53 (4H, m, 2NCH2);
7.03 (1H, m, HAr
)
C16H18BrFNS3
C16H17F4NS3
21.07
1.84 (2H, s, CH2); 1.96 (4H, m, 2CH2); 2.02 (3H, s, CH3); 4.00 (6H, m, 2NCH2, SCH2);
21.14
7.30 (3H, m, HAr
)
24.25
24.32
1.45 (2H, m, CH2); 1.57 (4H, m, 2CH2); 2.52 (4H, m, 2CH2); 2.02 (3H, s, CH3);
3.97 (2H, s, SCH2); 5.95 (1H, s, СН); 6.99 (1H, m, HAr
)
C22H10F10S6
C22H12F8S6
C26H16F12S6
C20H12Br2F2S6
C17H6F8S5
29.15
165-167
181-182
135-136
157-159
101-102
61-63
2.00 (6H, s, 2CH3); 3.95 (4H, s, 2CH2)
5a
5b
5c
5d
7a
7b
7c
29.29
30.85
30.99
2.00 (6H, s, 2CH3); 3.99 (4H, s, 2CH2); 7.01 (2H, m, HAr
1.73 (6H, s, 2CH3); 3.95 (4H, s, 2CH2); 7.79 (2H, s, HAr); 7.70 (4H, s, HAr
1.75 (6H, m, 2CH3); 3.85 (4H, s, 2SCH2); 7.07 (2H, s, HAr); 7.23 (4H, m, HAr
)
25.53
)
25.69
28.55
28.69
)
30.58
1065 (C=S)
4.07 (4H, s, 2CH2); 7.05 (2H, m, HAr
4.01 (4H, s, 2CH2); 7.00 (2H, m, HAr
4.06 (4H, s, 2CH2)
)
)
30.68
C17H6F8S5
30.51
30.68
1063 (C=S)
1063 (C=S)
C17H4F10S5
28.62
78.5-79.5
28.70

TABLE 1 (continued)
1
2
3
4
5
6
C17H10Br2F2S5
C21H10F12S5
27.83
28.01
102-103
172-173
86-87
1069 (C=S)
1060 (C=S)
1660 (C=O)
1663 (C=O)
1665 (C=O)
1670 (C=O)
3.93 (4H, s, 2CH2); 7.95 (4H, m, HAr); 7.09 (2H, m, HAr)
7d
24.53
4.38 (4H, s, 2CH2); 7.99 (4H, s, HAr); 7.97 (2H, s, HAr
4.05 (4H, s, 2CH2); 7.05 (2H, m, HAr);
4.03 (4H, s, 2CH2)
)
7e
8a
8c
8d
8e
9a
24.64
C17H6F8OS4
25.28
25.32
C17H4F10OS4
C17H10Br2F2OS4
C21H10F12OS4
C17H8F2O2S5
23.53
46-50
23.64
22.97
23.05
Oil
3.90 (4H, s, 2CH2); 7.91 (4H, m, HAr); 7.0 (2H, m, HAr
4.35 (4H, s, 2CH2); 8.37 (4H, s, HAr); 8.16 (2H, s, HAr
7.50 (8H, m, HAr
)
20.10
79-80
)
20.21
36.10
36.22
131-132
1682 (С=O)
)
1085 (C=S)
C17H4F6O2S5
C17H2F8O2S5
C21H6F12O2S5
C34H12F16S8
31.09
123-124
115-117
153-155
159-161
1685 (С=O)
7.69 (2H, m, HAr); 7.16 (2H, m, HAr
7.08 (2H, m, HAr
8.16 (2H, s, HAr); 8.37 (4H, s, HAr
2.05 (8H, s, 4CH2); 7.49 (4H, m, HAr
)
9b
9c
9d
10
31.16
1065 (C=S)
29.01
29.12
1675 (С=O)
)
1060 (C=S)
23.50
1670 (С=O)
)
23.62
1065 (C=S)
26.02
26.15
)

TABLE 2. Cyclic Voltamperogrametric Data*
Com-
pound
Е
1/21, V
Е
1/22, V
Е
1/21, V
Е
1/22, V
Compound
Tetrathiafulvalene
0.55
0.53
0.51
0.48
0.69
0.89
0.89
0.84
0.82
0.94
0.41
0.57
0.82 [12]
0.85 [3]
5a
5b
5c
5d
10
Tetra(benzylthio)-
tetrathiafulvalene
Trimethyl(benzylthio)-
tetrathiafulvalene
0.27
0.81 [8]
_______
*
Voltamperograms were obtained in benzonitrile solution;
tetraethylammonium perchlorate (c = 0.1 molar) electrolyte, Pt working
electrode, AgCl/Cl reference electrode, 50 mV/s scanning rate, 0.1 molar
concentration of tetrathiafulvalene.
EXPERIMENTAL
The fluoro-substituted benzyl and benzoyl chlorides were obtained from OOO "Okta" (Perm city).
1H NMR spectra were taken on a DRX-400 spectrometer (400 MHz). IR spectra were recorded on a UR-20
spectrometer using vaseline oil and the cyclic voltamperograms were obtained using a PI-50-1 potentiostat in a
three electrode cell with a platinum electrode in benzonitrile solution with (C2H5)4NClO4 electrolyte.
Zincate 6 was synthesized by the method in the study [10].
1-{4-[3,5-Di(trifluoromethyl)benzylthio]-5-methyl-1,3-dithiol-2-ylidene}piperidinium Bromide (2c).
3,5-Di(trifluoromethyl)benzyl bromide (10 mmol) was added to a solution of the mesoionic salt 1 (2.33 g,
10 mmol) in acetone (100 ml) and the mixture was heated to its decolorization. Evaporation of the acetone gave
a colorless crystalline product which was used without further purification. Compounds 2a,b,d were prepared
similarly and are oily, hygroscopic materials. The yields of the products are close to quantitative.
5-Methyl-2-piperidino-4-(2,3,5,6-tetrafluorobenzylthio)-1,3-dithiol (3b). Sodium borohydride
(12 mmol) was added portionwise to a solution of compound 2b (10 mmol) in acetonitrile (50 ml), the reaction
mixture was diluted with water, and the separated oil was extracted with ether. The ether extracts were dried
over sodium sulfate, ether was removed, and the product 3b was recrystallized from alcohol to give small,
colorless, fine needles. Yield 85%.
Compounds 3a,c,d were obtained similarly as oily liquids
1,3-Dithiolium Perchlorates (4a-d) (General Method). An ether solution of compound 3a-d (1 mmol)
was stirred with 70% perchloric acid. The ether was evaporated and the residue was cooled in the fridge. The
shining, flaky perchlorate was filtered off and then used without purification. The product yields were 60-70%.
Dimethyldi(arylmethylthio)tetrathiafulvalenes (5a-d) (General Method). Triethylamine was added
dropwise to a solution of compound 4a-d (1 mmol) in dry acetonitrile (3 ml) until precipitation of the product
5a-d ceased. The latter was then recrystallized from acetonitrile. The compounds are formed as small orange or
red needles.
1,3-Dithiol-2-thiones (7a-e) and (9a-d) (General Method). The corresponding fluoro-substituted
benzyl or benzoyl chloride (200 mmol) was added to the zincate 6 (3.6 g, 50 mmol) dissolved in acetone
(100 ml). The mixture was stirred at room temperature for 1.5 h, the solution was diluted with water, and the
yellow crystals were filtered off and recrystallized from alcohol or acetic acid. Yield of thiones 85-95%.
1,3-Dithiol-2-ones (8a,c-e) (General Method). Compound 7a-e (10 mmol) was heated over 15 min in
acetic acid with a small excess of mercuric acetate and the black precipitate of mercuric sulfide was filtered off.
The light yellow filtrate was diluted with water, held at room temperature for about 16 h, and the light yellow
crystalline product of 8a,c-e was separated and purified by recrystallization from alcohol.
765

The work was carried out with the financial support of the Russian Foundation for Fundamental
Research (RFFR), grant No. 99-03-32872a.
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