A high yield conversion of tetrathiafulvalene into bis(ethylenedithio)tetrathiafulvalene and derivatives

Article abstract of DOI:10.1039/a707814e

TTF is converted into BEDT-TTF (80%) in a one pot reaction.

Full text of DOI:10.1039/a707814e

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A high yield conversion of tetrathiafulvalene into
bis(ethylenedithio)tetrathiafulvalene and derivatives
Ronald L. Meline and Ronald L. Elsenbaumer*,†
Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington,
TX 76019, USA
TTF is converted into BEDT–TTF (80%) in a one pot
reaction.
S
S
S
S
S
S
2
or
S
S
S
S
S
S
(1) 5 LDA THF
BEDT–TTF 1a has been utilized as the donor in the bulk of
known superconducting organic molecular solids.1,2 Although
commercially available, BEDT–TTF is invariably expensive and
thus a number of synthetic routes to the donor have been
reported.3–6 Literature syntheses most commonly involve the
multistep formation of 4,5-ethylenedithio-1,3-dithiol-2-one,
which is then coupled by trialkyl phosphite. Recently, we have
reported a modest yield synthesis of BEDT–TTF circumvent-
ing this coupling step.7
(2)
O
S
S
S
1a
(80%)
EtO
EtO
S
S
S
S
S
3
O
4a
HS
HS
O
+
In addition to thiones and ketones based on dimercaptoisot-
rithione (DMIT, 1,3-dithiole-2-thioxo-4,5-dithiolate), TTF 2
has been used extensively in recent years as the building block
for extended donors owing to the acidity of its vinylic protons
as first reported by Green, who demonstrated the proton–
lithium exchange by treatment of TTF with BunLi or LDA.8
Tetrakis(alkylchalcogeno)TTFs have been synthesized by util-
izing tetralithiated TTF with subsequent elemental selenium or
tellurium insertion into the carbon᎐lithium bond pairs, or with
the use of disulfide electrophiles.9–12 It should be noted that
insertion of elemental sulfur into the carbon᎐lithium bond
has been reported as difficult13 or essentially non-existent.10
Attempted alkylative ring closure of tetrakis(chalcogeno)TTF
tetraanions with dibromoalkanes leads to polymeric products
(i.e. intermolecular alkylation) even under high dilution
conditions.9,14 Chalcogen analogues based on BEDT–TTF
(i.e. capped donors, BEDSe–TTF, BEDTe–TTF) have been
prepared by Lee and Williams from TTF through the use of
protecting group chemistry and solvent manipulation, respect-
ively.14,15 As a result of the difficulty of sulfur insertion and
subsequent intramolecular alkylation with 1,2-dibromoethane,
a facile conversion of TTF into BEDT–TTF has not been
realized.
Building on prior synthetic routes to alkylthioTTFs from
disulfides, a novel bisdisulfide was synthesized incorporating
an ethyl spacing unit and ester leaving groups. Upon nucleo-
philic attack of tetralithiated TTF or isomerized tetralithiated
tetrathianaphthalene (TTN, 3) onto 1,2-bis(ethoxycarbonyl-
dithio)ethane 4a, BEDT–TTF was produced along with four
equivalents of ethanol and four equivalents of carbon
oxysulfide. The simple by-products facilitated workup, realizing
BEDT–TTF in an overall yield of 80% from TTF.
The bisdisulfide 4a was synthesized from two equivalents of
ethoxycarbonylsulfenyl chloride16 5 and one equivalent of
ethane-1,2-dithiol 6 in quantitative yield. Crystalline 4a is com-
pletely soluble in THF or diethyl ether. Disulfide formation
is based on the chemistry of Brois, who has utilized alkoxy-
carbonylsulfenyl chlorides and a variety of thiols to produce
ester alkyl disulfides [EtOC(O)S᎐SЈR] which selectively yield
unsymmetrical disulfides (RЈ᎐S᎐S᎐RЉ) upon reaction with one
EtO
SCI
5
6
Scheme 1
equivalent of a different thiol (RЉSH).16 In this study, the
carbanions of tetralithiated TTF easily add ethanedithiol units
from 4a producing BEDT–TTF.
The overall utility of this approach can be seen in light of
recent reports of new facile syntheses and even bulk syntheses
of TTF.7,17 The alkoxycarbonylsulfenyl chloride can be used to
prepare a number of alkyl (4a, 4b) and aryl (4c) spaced bis-
disulfides from various dithioles leading to a series of capped
TTFs (1a, 1b, 1c), thereby demonstrating the general utility of
this approach.
S
S
S
S
–
–
–
–
5 LDA
2 or 3
THF, –78 °C
O
O
S
S
4a R = –CH2CH2–
4b R = –CH2CH2CH2–
S
EtO
R
–78 °C
2
EtO
S
4c R =
S
S
1a R = –CH2CH2–
S
S
S
S
1b R = –CH2CH2CH2–
R
R
1c R =
S
S
O
S
Nu–
R
S
OEt
Nu
S
R
+ C(O)S + EtO–
Scheme 2
Experimental
1,2-Bis(ethoxycarbonyldithio)ethane 4a
Ethoxycarbonylsulfenyl chloride 5 was prepared in very high
yield according to a published procedure.18 12.00 g (85 mmol)
of 5 was dissolved in 100 ml of dichloromethane, placed in a
† E-Mail: elsenbaumer@uta.edu
J. Chem. Soc., Perkin Trans. 1, 1997
3575

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250 ml round bottomed flask capped with a septum, and cooled
with a dry ice–isopropyl alcohol bath to ~Ϫ30 ЊC under N2.
4.00 g (42.5 mmol) 6 dissolved in 20 ml of dichloromethane was
syringed into the flask over a 10 min period turning the yellow
solution colorless. The solution was washed with 5% aq.
NaOH, water and dried with MgSO4. The filtered solution was
condensed to give an oil which crystallizes on standing. Yield
12.68 g (98.7%); mp 44–45 ЊC; δH(CDCl3–SiMe4) 1.35 (t, 6H),
3.07 (s, 4H), 4.36 (q, 4H); δC(CDCl3–SiMe4) 14.1, 37.5, 65.2,
168.8; m/z (EI) 302 (Mϩ).
lit.,19 mp >250 ЊC (decomp.)] and 1c [yield 72%, mp 284–287 ЊC
(decomp.), lit.,20 mp 286–287 ЊC (decomp.)] which are identical
to the known organic metals.19–22
Acknowledgements
The authors would like to thank AFOSR for financial support
as well as C. M. Land and V. V. Sorokin for technical assistance.
References
1 J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser,
H. H. Wang, A. M. Kini and H. Whangbo, Organic Super-
conductors, Prentice Hall, New Jersey, 1992.
1,2-Bis(ethoxycarbonyldithio)propane 4b
Same procedure as 4a producing a yellow liquid. Yield 97.0%;
δH(CDCl3–SiMe4) 1.34 (t, 6H), 2.06 (quintet, 2H), 2.93 (t, 4H),
4.35 (q, 4H); δH(CDCl3–SiMe4) 14.1, 26.9, 36.8, 65.0, 169.0; m/z
(EI) 316 (Mϩ).
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1,2-Bis(ethoxycarbonyldithio)benzene 4c
Same procedure as 4a producing crystals. Yield 94.2%; mp 49–
51 ЊC; δH(CDCl3–SiMe4) 1.34 (t, 6H), 4.35 (q, 4H), 7.30 (m, 2H),
7.67 (m, 2H); δC(CDCl3–SiMe4) 14.2, 65.5, 129.0, 131.0, 136.5,
168.1; m/z (EI) 350 (Mϩ).
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BEDT–TTF 1a
BunLi (40 ml of a 2.5  solution in hexanes, 100 mmol) was
syringed through a rubber septum into a solution of diisopro-
pylamine (15 ml, 107 mmol) in dry THF (50 ml) in a 500 ml
round bottomed flask with a stirrer bar at Ϫ78 ЊC (dry ice/
isopropyl alcohol) under nitrogen (purge through rubber sep-
tum) to form lithium diisopropylamide (LDA). After stirring
the solution for 1 h, TTF or TTN (6) (4 g, 19.6 mmol) was
dissolved in dry THF (200 ml) and added to a pressure equal-
izing funnel and placed on top of the flask. Nitrogen was then
transferred to the top of the funnel. The TTF solution was then
added dropwise over a 4 h period to the LDA solution giving a
bright yellow solution. The solution was stirred for an add-
itional 4 h whereupon the funnel was then charged with 12.68 g
of 4a (42 mmol) dissolved in 80 ml of THF. The bisdisulfide
solution was added over a 2 h period, and the reaction flask was
allowed to warm to room temperature overnight. The resulting
red suspension was filtered on a glass sintered funnel, washed
with water (100 ml), methanol (100 ml) and finally diethyl ether
(200 ml) to give pure BEDT–TTF 6.03 g [mp 244–247 ЊC
(decomp.)], in powder form. BEDT–TTF can be recrystallized
from CS2, sulfolane or thiophene.7 Similar reaction procedures
were used to prepare 1b [yield 68%, mp 246–250 ЊC (decomp.),
20 H. Müller, H. P. Fritz, R. Nemetshek, R. Hackl, W. Biberacher and
C. P. Heidmann, Z. Naturforsch., B, 1992, 47, 718.
21 L. C. Porter, A. M. Kini and J. M. Williams, Acta Crystallogr., 1987,
C43, 998.
22 J. P. Parakka, A. M. Kini and J. M. Williams, Tetrahedron Lett.,
1996, 8085.
Paper 7/07814E
Received 22nd October 1997
Accepted 23rd October 1997
3576
J. Chem. Soc., Perkin Trans. 1, 1997