Synthesis and properties of thiophene and dithiin functionalized tetrathiafulvalenes

Article abstract of DOI:10.1080/10426507.2013.788005

Syntheses of two analogues of tetrathiafulvalene (TTF), fused to 1,4-dithiin and thiophene rings, substituted with thiophene moieties, have been illustrated. The syntheses were accomplished through the reaction of a 1,8-diketone with phosphorus pentasulfide or Lawesson's reagent in boiling dry toluene. Conversion of the thioketones to their the oxo forms with mercury (II) acetate, was followed by self-coupling in freshly distilled boiling triethyl phosphite. Attempts for their electro-polymerizations through the thiophene groups at the peripherals were unsuccessful. Computational chemistry studies revealed that the thiophene groups did not exhibit enough spin densities to perform polymerization. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Full text of DOI:10.1080/10426507.2013.788005

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Synthesis and Properties of
Thiophene and Dithiin Functionalized
Tetrathiafulvalenes
Erdal Ertas a , Hakan Bildirir b , Onur Sahin b & Ipek Oksen b
a TUBITAK Marmara Research Centre, FI , Gebze , Kocaeli , Turkey
b Organic Chemistry, Chemistry Department, Science Faculty,
Istanbul Technical University , Maslak-Istanbul , Turkey
Accepted author version posted online: 05 Apr 2013.Published
online: 03 Oct 2013.
To cite this article: Erdal Ertas , Hakan Bildirir , Onur Sahin & Ipek Oksen (2013) Synthesis and
Properties of Thiophene and Dithiin Functionalized Tetrathiafulvalenes, Phosphorus, Sulfur, and Silicon
and the Related Elements, 188:12, 1835-1844, DOI: 10.1080/10426507.2013.788005
To link to this article: http://dx.doi.org/10.1080/10426507.2013.788005
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Phosphorus, Sulfur, and Silicon, 188:1835–1844, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2013.788005
SYNTHESIS AND PROPERTIES OF THIOPHENE AND
DITHIIN FUNCTIONALIZED TETRATHIAFULVALENES
Erdal Ertas,1 Hakan Bildirir,2 Onur Sahin,2 and Ipek Oksen2
1TUBITAK Marmara Research Centre, FI, Gebze, Kocaeli, Turkey
2Organic Chemistry, Chemistry Department, Science Faculty, Istanbul Technical
University, Maslak-Istanbul, Turkey
GRAPHICAL ABSTRACT
Abstract Syntheses of two analogues of tetrathiafulvalene (TTF), fused to 1,4-dithiin and
thiophene rings, substituted with thiophene moieties, have been illustrated. The syntheses
were accomplished through the reaction of a 1,8-diketone with phosphorus pentasulfide or
Lawesson’s reagent in boiling dry toluene. Conversion of the thioketones to their the oxo forms
with mercury (II) acetate, was followed by self-coupling in freshly distilled boiling triethyl
phosphite. Attempts for their electro-polymerizations through the thiophene groups at the
peripherals were unsuccessful. Computational chemistry studies revealed that the thiophene
groups did not exhibit enough spin densities to perform polymerization.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords Thiophene; tetrathiafulvalene; 1,8-diketone; phosphorus pentasulfide; Lawesson’s
reagent
Received 30 January 2013; accepted 28 February 2013.
Address correspondence to Erdal Ertas, TUBITAK Marmara Research Centre, FI, P.O. Box 21, 41470
Gebze, Kocaeli, Turkey. E-mail: erdal.ertas@tubitak.gov.tr
1835

1836
E. ERTAS ET AL.
INTRODUCTION
The discovery of metallic conductivity of charge transfer complexes of tetrathiaful-
valene (TTF) 1 with tetracyanoquinodimethane (TCNQ) goes back to the end of 1973.1–5
Since then great efforts have been devoted to improve and understand its properties. Various
derivatives, among which the most important one is bis(ethylenedithio)tetrathiafulvalene
(BEDT-TTF, or ET) 2, have been synthesized and their charge transfer salts with TCNQ
or mono anions have been prepared.4,6–10 They displayed interesting properties such as
superconductivity at very low temperatures, conductivity, and semiconductivity.2 As gen-
erally accepted, crystal structures of the charge-transfer salts and π-extension of the
donor molecules are two important parameters for improving the properties of organic
materials.11–15 As TTF is a strong organic donor molecule, various research groups
devoted immense interest in synthesizing π-extended TTF derivatives to improve its
properties.16–21
TTF derivatives, having thiophene groups on the peripherals, are of interest for
research groups. Although some studies have appeared in the literature, among which Bryce
and co-workers reported first TTF linked to thiophene, 22–27 and our group reported first TTF
fused to 1,4-dithiin and thiophene groups, more efforts are required to explore such TTF
derivatives.16,17,20 In the present work, we report syntheses, electronic and electrochemical
properties of new TTF derivatives, consisting of fused thiophene and 1,4-dithiin rings, both
having thiophene groups.

FUNCTIONALIZED TETRATHIAFULVALENES
1837
RESULTS AND DISCUSSION
Syntheses
The syntheses of TTF 3 fused to 1,4-dithiin and TTF 4 fused to thiophene, both
having thiophene moieties, were accomplished with self-coupling reactions of 5-(thien-2-
yl)-[1,3]dithiolo[4,5-b][1,4]dithiin-2-one 8 and 6-(thien-2-yl)thieno[3,2-d][1,3]dithiol-2-
one 9 in boiling dry triethyl phosphite, respectively, which were prepared by converting the
thione groups of 6 and 7 to oxo groups with mercuric acetate in acetic acid (Scheme 1).28
The TTF derivatives 3 and 4 were obtained as mixtures of non-separable cis- and trans-
isomers 3 and 4a and 4b. The syntheses of the crucial compounds, the thiones, 6 and 7,
exhibiting 1,4-dithiin and thiophene rings, respectively, fused to TTF were conducted by
employing the reaction of 1,8-diketone 5 with P4S1029 and Lawesson’s reagent (LR).30 The
diketone 5 was synthesized by reaction of the readily available zinc-complex 1031 with
2-(2-bromoacetyl)thiophene 12, which was obtained by treatment of 2-acetylthiophene 11
with bromine.32 It is an established method now that fused 1,4-dithiins and thiophenes can
be synthesized in a one pot reaction from 1,8-diketones through their reactions with P4S10 or
LR,33 which then require a separation process of the dithiins and the thiophenes, in general
by employing column chromatography. Considering our previous experience,34 it could be
possible to shift the reaction toward the dithiin or the thiophene, by performing the reaction
in acid or base. Thus, the ring closure reaction of 1,8-diketone 5 was conducted in neutral,
acidic, and basic conditions and the results are summarized in Table 1. The reactions were
also conducted in acid and base without P4S10 or LR to demonstrate that these reagents
are required for the ring closure. The best overall yield (82%) and selectivity with 1,4-
dithiine 6 as major product (75%) and thiophene 7 as minor product (7%) was obtained
with P4S10 under basic conditions. Unfortunately, such selectivity could not be achieved
with the thiophene 7. After an intensive study, the best selectivity with the thiophene 7 as
major product (55%) and the dithiin 6 as minor product (10%) was obtained with P4S10
under acidic conditions. A possible mechanism for the formation of 7 is given in Scheme 2,
which may explain how the rearrangement of 6, with the help of acid and through the
Table 1 Reaction conditions and yields for the synthesis of 6 and 7
Reagent
P4S10
Reaction Condition
6 (%)
7 (%)
Total Conversion
neutral
acidic
A: dry toluene, reflux, 3 h
B: dry toluene, reflux, 6 h
35
30
45
42
10
15
75
75
25
20
30
26
35
20
25
55
57
5
61
65
65
67
65
72
80
82
55
60
50
Aa: dry toluene, reflux, p-TSA, 3 h
Ba: dry toluene, reflux, p-TSA, 6 h
Ab: dry toluene, reflux, glacial acetic acid, 3 h
Bb: dry toluene, reflux, glacial acetic acid, 6 h
Ac: dry toluene, reflux, NaHCO3, 3 h
Bc: dry toluene, reflux, NaHCO3, 6 h
dry toluene, reflux, 3 h
basic
7
LR
neutral
acidica
basicc
30
40
20
dry toluene, reflux, p-TSA, 3 h
toluene, reflux, NaHCO3, 3 h
aequal amounts of p-TSA (p-toluenesulfonic acid) and reagent (P4S10 or LR).
b1 mL of glacial acetic acid.
cequal amounts of NaHCO3 and reagent (P4S10 or LR).

1838
E. ERTAS ET AL.
intermediates 13 and 14, to form the thiophene 6 takes place. All efforts using LR did not
yield any better result than P4S10.
Scheme 1
Scheme 2
Cyclic Voltammetry and Polymerization Studies
The electrochemical properties of the compounds 3 and 4 in dichloromethane con-
taining TBABF4 were studied by cyclic voltammetry (CV) (Figure 1). While compound
3 exhibiting a fused 1,4-dithiin ring displayed oxidation at 1.02 V, compound 4 with a
fused thiophene ring showed oxidation at 1.41 V, both of which are irreversible steps. As
they had thiophene groups at the peripherals, their electro-polymerization was attempted.
Unfortunately all our efforts to produce any polymer were not successful. When the CV of

FUNCTIONALIZED TETRATHIAFULVALENES
1839
Figure 1 Cyclic voltammogram of 3 and 4 in 0.1 M TBAPF6/DCM with a scan rate of 100 mV/s.
Figure 2 Spin density and SOMO of 3. (Color figure available online).
Figure 3 Spin density and SOMO of 4. (Color figure available online).

1840
E. ERTAS ET AL.
4 was examined closely, small oxidation and reduction peaks at 1.0 and 0.9 V, respectively,
were observed which could be an indication of the formation of an oligomer. Then, a
computational study was initiated to understand if the thiophene rings at the peripherals
had enough spin density at the carbon atoms next to the sulfur atoms, where polymerization
is expected to take place. Unfortunately, those carbon atoms either exhibited a very small
positive spin density such as 0.003 for the compound 3 (Figure 2) or a negative spin density
of −0.004 for the compound 4 (Figure 3), which explains why the electro-polymerization
did not take place. As the spin density studies are compatible with the experimental results,
no further study was performed for electro-polymerization.
CONCLUSIONS
Analogues of TTF exhibiting fused thiophene and 1,4-dithiin rings which, further-
more, exhibit thien-2-yl substituents were synthesized. The synthesis was achieved by cy-
clization of the 1,8-diketone 5 with both phosphorus pentasulfide and Lawesson’s reagent,
which resulted in the formation of the two analogues 6 and 7 in one batch. In order to obtain
them selectively, neutral, acidic, and basic conditions were applied for the ring closure re-
action, which indicated that the best selectivity for the formation of TTF with fused dithiin
rings is achieved with phosphorus pentasulfide under basic conditions whereas phosphorus
pentasulfide under acidic conditions provided the best selectivity for the formation of the
TTF with a fused thiophene ring. Unfortunately, all attempts to electro-polymerize the
analogues failed. Spin density calculations indicated that the peripheral thiophene moieties
did not exhibit enough spin density at the carbon atoms next to the sulfur atoms, where
electro-polymerizations was expected to take place.
EXPERIMENTAL
Chemicals
All chemical reagents were obtained from Sigma-Aldrich-Fluka Co. Ltd. (Stein-
heim, Germany), unless otherwise stated. Toluene and bromine were obtained from Merck
(Darmstadt, Germany).
Instrumentation
A CH-Instruments Model 400A was used as potentiostat for the CV studies. FTIR
spectrum was recorded on a Thermo Nicolet 6700 FT-IR-ATR spectrometer. UV measure-
ments were performed on a HITACHI U-0080D instrument. NMR spectra were recorded
in CDCl3 on a 400 MHz Bruker DPX system (1H: 400 MHz, 13C: 100 MHz). HR-Mass
spectra were recorded on Bruker Daltonics MicroTof ESI-TOF Mass Spectrometer.
Cyclic Voltammetry (CV)
Cyclovoltamograms were recorded to investigate the electroactivity of 3 and 4. A CV
compartment with Pt-working, Pt-counter, and Ag-wire reference electrodes was employed.
Tetrabutylammonium hexafluorophosphate (TBAPF6) (0.1 M) in dichloromethane was used
as solvent supporting electrolyte. All measurements were recorded at room temperature
under nitrogen atmosphere.

FUNCTIONALIZED TETRATHIAFULVALENES
1841
Computational Studies
Full geometry optimizations of gas-phase stationary points were performed with a
6–311++G(d,p)35 basis set, where the functions of atomic orbital descriptors are aug-
mented with polarization and diffuse functions on both heavy atoms and hydrogens, using
Becke’s three-parameter exchange functional (B3)36 with the Lee–Yang–Parr correlation
functional (LYP)37 as implemented in Gaussian 03.38 While the restricted method was
applied for closed-shell molecules, unrestricted calculations were performed for radical
cations. The minima of calculated structures were verified by analyzing the harmonic vi-
brational frequencies, using analytical second derivatives with NIMAG = 0. Visualization
of spin densities was done with GaussView 5.0839 using an isocontour value of 0.0004
ebohr−3, respectively.
2-(2-Bromoacetyl)thiophene 12. Ketone 12 was synthesized according to the lit-
erature method.32 Bromine (15.6 g, 97.6 mmol) in 10 mL glacial acetic acid was added
drop-wise into the stirred solution of 2-acetylthiophene (11.7 g, 92.8 mmol) in 10 mL
glacial acetic acid. After the addition was completed, the reaction mixture was stirred at
room temperature for 1 h, and then at 45◦C for 2 h. The dark brown mixture was poured into
ice water (2 × 300 mL). Water, formed as a separate layer, was decanted and the remaining
trace amounts of water and 2-acetylthiophene were removed by vacuum distillation at 40◦C
at 25 mbar. The oily brown liquid 12 (16.77 g, 88.21%) was checked with the reference,
purchased from Aldrich (Steinheim, Germany).
4,5-Bis[2-oxo-2-(thien-2-yl)ethylthio]-1,3-dithiol-2-thione 5. A solution of 2-(2-
bromoacetyl)thiophene (5.70 g, 27.8 mmol) 12 in 20 mL acetone was added drop-wise to
a stirred solution of zinc complex 10 (5 g, 7.0 mmol) in 30 mL acetone and the reaction
mixture was stirred at room temperature for 5 h. After filtration, the solvent was removed
by use of a rotary evaporator. The red crude product was extracted with CH2Cl2 (2 ×
200 mL). The organic layer was dried over anhydrous Na2SO4, filtered and evaporated
under reduced pressure. The crude product was crystallized from hexane/CH2Cl2 (1:1) to
1
yield 5 as a yellow powder (4.99 g, 80.6%), mp. 112–113◦C; H NMR: δ 7.76 (dd, J =
3.9/1.1 Hz, 2H), 7.74 (dd, J = 4.9/1.1 Hz, 2H), 7.18 (dd, J = 3.9/4.9 Hz, 2H); 4.23 (s, 4H,
2 CH2); 13C NMR: δ 210.9, 185.7, 142.1, 137.8, 135.7, 133.6, 128.9, 43.3; HRMS (ESI)
m/z C15H10O2S7 (M++1) requires 446.8787, found 446.8799; IR νmax 1656 (C O), 1058
(C S) cm−1
.
5-(Thien-2-yl)-[1,3]dithiolo[4,5-b][1,4]dithiine-2-thione 6 and 6-(Thien-2-
yl)thieno[3,2-d][1,3]dithiole-2-thione 7.
Neutral Reaction: A solution of 0.50 g (1.12 mmol) 1,8-diketone 5 in 20 mL dry
toluene was added to a hot (70◦C) solution (20 mL) of P4S10 (0.75 g, 1.6 mmol). The reaction
mixture was refluxed at 110◦C for 3 h. The solvent was removed by blowing nitrogen gas.
The remaining crude product was dissolved in CH2Cl2 and filtered to remove undissolved
solids. The solvent was evaporated under reduced pressure and the crude product was
purified by column chromatography eluting with hexane/CH2Cl2 (5:1) to obtain 6 as first
fraction as a brown solid (0.12 g, 35%) and 7 as second fraction as a dark brown solid
(0.08 g, 26%). 6: Mp. 144–145◦C; 1H NMR: δ 7.34 (dd, J = 5.1/1.1 Hz, 1H), 7.30 (dd, J =
3.7/1.1 Hz, 1H), 7.1 (dd, J = 5.1/3.7 Hz, 1H), 6.7 (s, 1H); 13C NMR: δ 213.9, 138.5, 135.6,
130.8, 128.8, 128.4, 128.1, 127.5, 116.3; HRMS (ESI) m/z M++1 calculated for C9H4S6
m/z 304.8707, found 304.8710; IR νmax 1062(C S) cm−1. – 7: Mp. 134–136◦C, 1H NMR:

1842
E. ERTAS ET AL.
δ 7.66 (s, 1H), 7.31 (dd, J = 5.1/1.1 Hz, 1H), 7.20 (dd, J = 3.6/1.1 Hz, 1H), 7.10 (dd, J =
5.1/3.6 Hz, 1H); 13C NMR: δ 214.6, 137.2, 135.9, 133.2, 129.6, 128.4, 126.1, 125.2, 124.6;
HRMS (ESI) m/z M++1 calculated for C9H4S5 m/z 272.9002, found 272.8989; IR νmax
1063(C S) cm−1
.
The same procedure was applied for the reactions with LR. Yields are given in Table 1.
Reaction in the Presence of p-TSA or Glacial Acetic Acid. To the mixture of p-TSA
(0.75 g) and P4S10 (0.75 g) dissolved in dry toluene (20 mL) at 70◦C, was drop-wise added
the 1,8-diketone 5 (0.50 g, 1.10 mmol) dissolved in toluene (20 mL). After employing
the same work up and separation techniques described above, 6 and 7 were obtained with
45% and 20% yield, respectively. The same reaction conditions, work up and separation
techniques were applied when glacial acetic acid (1 mL) was used in place of p-TSA. Yields
for each reaction condition are given in Table 1.
Reaction with NaHCO3. The same reaction conditions and separation techniques as
described for the reaction with p-TSA were employed. The yields are given in Table 1.
5-(Thien-2-yl)-[1,3]dithiolo[4,5-b][1,4]dithiin-2-one, 8. Mercuric acetate (1.57 g,
4.95 mmol) was added to a solution of 6 (0.5 g, 1.65 mmol) in CHCl3/glacial acetic acid
(3:1, 30 mL). The reaction was stirred at room temperature for 2 h. It was filtrated through
celite and the filtrate was extracted with NaHCO3 solution (2 × 20 mL) and water (2 ×
20 mL). The organic layer was dried over anhydrous Na2SO4, filtered and the solvent was
removed under reduce pressure to yield 8 as a light yellow powder (0.31 g, 65%). Mp.
1
138–139◦C; H NMR: δ 7.32 (m, 2H), 7.02 (dd, J = 5.04/3.8 Hz, 1H), 6.70 (s, 1H); 13C
NMR: δ 192.2, 138.8, 135.2, 128.3, 127.9, 127.5, 121.3, 119.2, 116.2; HRMS (ESI) m/z
C9H4OS5 (M++1) requires 288.8942, found 288.8938; IR νmax 1682 (C O) cm−1
.
6-(Thien-2-yl)thieno[3,2-d][1,3]dithiol-2-one, 9. The reaction conditions and sepa-
ration techniques described above were employed to obtain 9 as a yellow powder (0.36 g,
1
85%). Mp. 92–94◦C; H NMR: δ 7.52 (s, 1H), δ 7.28 (dd, J = 3.6 / 1.0 Hz, 1H), 7.17
(dd, J = 3.6/1.1 Hz, 1H), 7.14 (s, 1H), 7.04 (dd, J = 5.1/3.6 Hz, 1H); 13C NMR: δ 193.6,
139.3, 135.7, 128.4, 127.9, 125.9, 125.1, 123.9, 117.7; HRMS (ESI) m/z C9H4OS4 (M++1)
requires 256.9221, found 256.9218; IR νmax 1662 cm−1
.
2,2ꢁ-Bi{5-(thien-2-yl)[1,3]dithiolo[4,5-b][1,4]dithiin-2-ylidene} 3. Compound 8
(0.2 g, 0.7 mmol) in freshly distilled (EtO)3P (15 mL) was heated at 110◦C under N2
for 3 h. (EtO)3P was distilled off under reduced pressure to obtain 3 as a brown powder
1
(0.3 g, 80%). Mp. 168–170◦C, H NMR: δ 7.29 (dd, J = 5.1/1.0 Hz, 2H), 7.27 (dd, J =
4.7/1.1, Hz, 2H), 7.01 (dd, J = 5.1/3.8 Hz, 2H), 6.6 (s, 2H); 13C NMR: δ 140.3, 137.3,
135.6, 130.4, 129.5, 128.4, 128.1, 128.0, 123.9; HRMS (ESI) m/z C18H8S10 (M++1) re-
quires 544.7854, found 544.7906.
(E)- and (Z)-2,2ꢁ-Bi{6-(thien-2-yl)thieno[2,3-d][1,3]dithiol-2-ylidene} (4a + 4b).
The same reaction conditions and separation techniques were employed to obtain the
mixture of 4a and 4b as a brown powder (0.21 g, 75%). Mp. 155–159◦C; 1H NMR: δ 7.53
(s, 4H), 7.32 (dd, J = 5.1/1.0 Hz, 4H), 7.23 (dd, J = 3.6/1.0, 4H), 7.10 (dd, J = 5.1/3.6 Hz,
4H), 13C NMR: δ 139.3, 135.7, 128.9, 128.5, 128.3, 125.1, 123.9, 121.3, 117.7; EIMS m/z
479.84 (M++1). Anal. Calcd. for C18H8S8: C 44.97, H 1.68. Found C 44.20, H 1.72.
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