Novel method for the synthesis of functionalized tetrathiafulvalenes, an acceptor-donor-acceptor molecule comprising of two o-quinone moieties linked by a TTF bridge

Article abstract of DOI:10.1016/j.tet.2010.07.038

In search of a synthesis of o-quinone-tetrathiafulvalene-o-quinone triads a novel facile route was developed. Sodium tetrathiooxalate was for the first time used as a synthon in functionalized TTF preparation. The main purpose of this work was to construct an organic compound, which on the one hand possesses a redox-amphotericity, and on the other hand can act as a bridging ligand in construction of linear, 2D and 3D assemblies. Properties of new acceptor-donor-acceptor ligand in respect to application as a building block for the molecular devices have been investigated.

Full text of DOI:10.1016/j.tet.2010.07.038

Tetrahedron 66 (2010) 7605e7611
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Novel method for the synthesis of functionalized tetrathiafulvalenes, an
acceptoredonoreacceptor molecule comprising of two o-quinone moieties
linked by a TTF bridge
,
a
a
a
a
Viacheslav Kuropatov a , Svetlana Klementieva , Georgy Fukin , Aleksander Mitin , Sergey Ketkov ,
*
Yulia Budnikova b, Vladimir Cherkasova, Gleb Abakumov a
a G.A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences, Tropinina str., 49, 603950, Nizhny Novgorod, Russian Federation
b A.E. Arbuzov Institute of Organic and Physical Chemistry of Russian Academy of Sciences, Arbuzov str. 8, Kazan, 420088 Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 April 2010
Received in revised form 24 June 2010
Accepted 15 July 2010
Available online 22 July 2010
In search of a synthesis of o-quinone-tetrathiafulvalene-o-quinone triads a novel facile route was de-
veloped. Sodium tetrathiooxalate was for the first time used as a synthon in functionalized TTF prepa-
ration. The main purpose of this work was to construct an organic compound, which on the one hand
possesses a redox-amphotericity, and on the other hand can act as a bridging ligand in construction of
linear, 2D and 3D assemblies. Properties of new acceptoredonoreacceptor ligand in respect to appli-
cation as a building block for the molecular devices have been investigated.
Keywords:
o-Quinone
Ó 2010 Elsevier Ltd. All rights reserved.
Tetrathiafulvalene
Tetrathiooxalate
Acceptoredonoreacceptor triad
1. Introduction
o-Quinone is a stronger acceptor as compared with p-quinone,
in addition it can act as a chelating ligand to form stable complexes
During the last few years, there has been increasing interest in
the search for organic compounds exhibiting a low HOMOeLUMO
gap1 due to their potential application in molecular electronics and
optoelectronics. A possible way to achieve this aim is a combination
of covalently linked donor and acceptor moieties in one molecule.2
TTF is widely used as an acceptor in the construction of such sys-
tems.3 Here we present the preparation of such AeDeA system
consisting of two sterically hindered o-quinone moieties connected
via fused TTF bridge. An analogous molecule containing p-quinone
1 instead of o-quinone have been studied by Hudhomme et al.4,5
(Fig. 1).
with various transition and non-transition metals. Moreover,
transition metals in such complexes can change their oxidation
state when the metal environment is altered.6e8 In turn, these
properties suggest that the use of these species as building blocks in
the construction of 2D and 3D assemblies may lead to molecular
wires, and perhaps even molecular rectifiers. So, our main purpose
was to synthesize redox-amphoteric, planar, rigid, fully conjugated,
and bridging ligands with the non-Kekulé structure. A molecule
combining redox-amphotericity and ability to act as a ligand is
reported for the first time in this work.
There are several synthetic approaches to TTF.2,9 Most of these
synthetic procedures for preparation of symmetrically functional-
ized TTF proceed with a key intermediate, which already contains
the 1,3-dithiol ring. The final stage is homocoupling of 1,3-dithiol-
2-one or corresponding thione using phosphines or phosphites.
This method includes a prior protection of all other carbonyl and
hydroxyl groups before the dimerization, followed by deprotection
procedures.
O
O
O
O
S
S
S
S
1
In this work fused triad, o-quinoneeTTFeo-quinone, was pre-
pared via a novel synthetic route. In contrast to strategies pre-
viously used for TTF syntheses, our method does not require
complicated and prolonged procedures of protection/deprotection
of carbonyl groups. Moreover, all processes can be conducted
Figure 1. p-QuinoneeTTFep-quinone triad (1).
* Corresponding author. Tel.: þ7 831 462 7682; fax: þ7 831 462 7497; e-mail
address: viach@iomc.ras.ru (V. Kuropatov).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.07.038

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V. Kuropatov et al. / Tetrahedron 66 (2010) 7605e7611
sequentially in one-pot. It seems to us that the analogous route
could be extended for the incorporation of the TTF functionality
between two aromatic fragments.
system directly in the course of the template synthesis. 4-Chloro-
3,6-di-tert-butyl-o-benzoquinone 4 (2 equiv) were combined with
1 equiv of sodium tetrathiooxalate Na2(tto), which already contains
the S2CeCS2 motif. It should be noted that this is the first usage of
a tetrathiooxalate salt as a precursor for TTF syntheses.
2. Results and discussion
Sodium tetrathiooxalate Na2(tto) have been synthesized start-
ing from elemental sodium and sulfur according to the method
proposed by Takata et al.10,11 (Scheme 2) In order to manipulate
a gram scale of anhydrous Na2S2 we optimized the synthetic pro-
cedure and exploited an ultrasonic bath. The interaction between
sodium and sulfur was conducted in a degassed glass ampoule at
80 ꢀC in dimethoxyethane in the presence of catalytic amounts of
benzophenone. Then Na2S2 was treated with tetrachloroethylene to
give Na2(tto) according to the method described by Breitzer et al.12
The anion tto2ꢁ is very labile and tends to transform into C4S26ꢁ in
solution.12 This makes isolation and storage of Na2(tto) inexpedient.
Thus, Na2(tto) should be used instantly after preparation. A solution
of Na2(tto) in methanol/MeCN was gradually added to 2 equiv of
quinone 4 dissolved in MeCN under vigorous stirring. The reaction
proceeds instantly on mixing the reactants (Scheme 3). The color of
the solution of quinone turns from red to deep blue. Intermediate
product 5 was not isolated because subsequent cyclization into
five-membered ring occurs simultaneously. We propose that the
mechanism of this reaction is similar to that reported previously for
the reaction of 4 with sodium xanthate.13 Quinone-catechol 6 was
then oxidized with alkaline potassium ferricyanide to give bis-
quinone 7. Bis-o-quinone 7 was isolated as dark violet prismatic
crystals with a yellowish metallic luster.
At the beginning of the work we chose the classic synthetic
strategy
toward
the
preparation
of
the
conjugated
o-quinoneeTTFeo-quinone system. According to this concept we
considered the quinone 2 as the starting material for the prepara-
tion of a target product. Despite many efforts associated with var-
iation of experimental conditions the dimerization products in the
resulting crude mixture were not observed. Moreover, treatment of
quinone 2 with excess triethylphosphite results only in formation
of dioxaphospholane species 3. It is rather surprising that the car-
bonyl group in the five-membered ring remains unchanged in this
reaction (Scheme 1).
t-Bu
t-Bu
t-Bu
O
O
O
O
O
O
S
S
S
S
S
S
O
t-Bu
t-Bu
t-Bu
2
t-Bu
O
O
S
S
According with the TLC data, the conversion of 4 in this reaction
is close to 100%. Bis-o-quinone 8, containing sulfur bridge was
obtained as the only byproduct together with the main product 7.
Et3P
O
3
t-Bu
Scheme 1. Homocoupling of 2: (EtO)3P, THF, 2 h, 60 ꢀC.
NaS
S
S
a
b
6Na +
6S
3Na2S2
A novel strategy, which allows incorporation of the TTF group in
conjugated and extended AeDeA systems, has been developed.
This strategy gives the opportunity to obtain the desired species in
a good yield. The main idea was to assemble the fused AeDeA
SNa
Scheme 2. Preparation of sodium tetrathiooxalate: (a) DME, 80 ꢀC, ultrasonic bath,
50 h; (b) tetrachloroethylene, MeOH/MeCN, 5 min.
t-Bu
t-Bu
O
O
S
S
O
+
+
NaS
SNa
Cl
O
Cl
t-Bu
t-Bu
4
a
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
S
S
S
t-Bu
O
O
OH
OH
S
S
S
S
O
S
O
O
t-Bu
t-Bu
O
6
5
b
t-Bu
t-Bu
t-Bu
O
O
O
O
S
S
S
S
t-Bu
7
Scheme 3. Preparation of 7: (a) MeOH/MeCN solution, 5 min, rt, ꢁNaCl; (b) ether/H2O, K4[Fe(CN)6], K2CO3, rt, 10 min.

V. Kuropatov et al. / Tetrahedron 66 (2010) 7605e7611
7607
Table 1
Crude mixture consists of two quinones 7 and 8 in the ratio 3:2,
which were separated from each other by crystallization. Forma-
tion of 8 can be attributed to the admixture of Na2S in the parent
disulfide. To prove this hypothesis we conducted the reaction of
Na2S with 4. Quinone 8 was obtained in a quantitative yield. Its
structure was established by X-ray analysis. Compound 8 was iso-
lated as octahedron-shaped dark-brown crystals. Its physical and
chemical properties are very much alike with those of other steri-
cally hindered o-quinones.14e16 Thus, it can be reduced with alkali
metals and thallium to give corresponding semiquinone com-
plexes. All additional information on this compound can be found
in the Supplementary data (Fig. 2).
Wave lengths and extinction molar coefficients of absorption maxima of 7 in dif-
ferent solvents
a
b
Solvent
ETN
lmax (nm)
3
ꢂ10ꢁ4 (Mꢁ1 cmꢁ1
)
Pentane
Et2O
THF
DME
CH3CN
0.009
0.117
0.207
0.231
0.460
518
527
539
542
556
3.04ꢃ0.04
3.17ꢃ0.09
2.70ꢃ0.03
2.53ꢃ0.05
2.69ꢃ0.04
a
ETNdempirical parameter of solvent polarity.21
Extinction
b
3
was measured in the concentration range from 3ꢂ10ꢁ5 to
3ꢂ10ꢁ4 M.
analogue4,5 1, but the observed CT band of 7 is blue-shifted and the
absorption coefficient is almost 40 times as large as those of 1.
In cyclic voltammetry (CV) experiments, 7 showed reduction
behavior consisting of four single-electron waves at ꢁ0.40, ꢁ0.61,
ꢁ1.04, and ꢁ2.56 V (Ered, DMF, vs Hg/Hg2Cl2) (Fig. 4). Two first
waves are fully reversible, the other two waves are quasi reversible.
Oxidation in DMF occurs at Eox¼1.40 V and is irreversible (Fig. 5).
Such behavior can be explained by a partial oxidation of the solvent,
which can take place at this potential.
t-Bu
t-Bu
O
O
O
O
S
t-Bu
t-Bu
8
Figure 2. Bis-o-quinone (8).
Compound7isstabletoairinthesolidstateandinsolution, butitis
relatively photosensitive. Its diluted solutions lose color when being
exposed to visible light over 5e7 h. Crystals of 7 grown from methy-
lene chloride lose the lattice solvent and crumble on air. Its de-
composition starts near the melting point at 243 ꢀC. All the
spectroscopic data (1H and 13C NMR, IR) for 7 are in agreement with
the proposed structure. The IR spectrum shows a well pronounced
downward shift of the carbonyl stretching (1647, 1629 cmꢁ1) with
respect to the corresponding values of 3,6-di-tert-butyl-o-benzoqui-
none (1679, 1656 cmꢁ1).17 This behavior is explained by the partial
charge transfer from TTF fragment toward the quinone moieties. In
CDCl3 the 13C NMR spectrum of 7 consists of a peak at
d 117.2 ppm,
whichischaracteristicfortheC]CatomsintheTTFfunctionality.18e20
Due to the bulky hydrophobic tert-butyl substituents, com-
pound 7 is readily soluble in most polar organic solvents such as
THF, chloroform, dichloromethane, DME or acetone and moderate
soluble in saturated hydrocarbons.
The combination of a strong donor (TTF) and a weak acceptor (o-
quinone) in one molecule results in a facile intramolecular electron
transfer, which is manifested in an intense band in the 370e650 nm
region in the electronic absorption spectrum of 7. The maxima of
absorption is strongly dependent on the solvent used (e.g.,
lmax¼564 nm,
3
¼31,000 Mꢁ1 cmꢁ1 in CH2Cl2) (Fig. 3). Extremely high
extinction values have been observed in all the solvents used. As
a rule, a state with a partial charge transfer is stabilized in polar sol-
vents, which is manifested in a red-shift of absorption band (Table 1).
Very similar behavior was reported for the p-quinone AeDeA
Figure 4. Cyclic voltammogram of 7 (5ꢂ10ꢁ3 M) in DMF (reduction).
Cyclic voltammograms were also recorded in p-di-
chlorobenzene/MeCN mixture. There are three reduction waves at
ꢁ0.48, ꢁ0.72 and ꢁ1.22 V (Ered, vs Hg/Hg2Cl2) and two oxidation
waves at 1.62 and 1.82 V (Eox) (see Supplementary data). The first
and the second reductions are one-electron and these are
reversible. The third reduction wave and both oxidations in o-di-
chlorobenzene/MeCN mixture are irreversible. Compound 7 is
poorly soluble in solvents, which are usually employed in electro-
chemical experiments. It is difficult to find a solvent providing both
a good solubility for the titled compound and a high resistance to
oxidation. Nevertheless, the presence of four distinct reduction
waves in CV recorded in DMF shows that two quinone moieties
effectively interact via the TTF bridge. The extremely high value of
the oxidation potential is not characteristic for tetrathiafulvalenes.
All the TTF derivatives are oxidized in the range 0.32e0.80 V2 (E ),
½
i.e., unsubstituted TTF has a first half-wave oxidation potential of
0.34 V.22 A remarkably large anodic shift, observed for the TTF
oxidation wave in 7, is ascribed to the strong electron-withdrawing
effect of the fused o-quinone moieties.
Figure 3. Solvatochromic shift of absorption maxima of 7 in different solvents.

7608
V. Kuropatov et al. / Tetrahedron 66 (2010) 7605e7611
spectrum. This signal is observed at the same time with the mon-
osemiquinone quartet and is centered at g¼2.0050 and reveals the
HFS constant on sodium (aNa¼0.37 G, Fig. 6b). The intensity of the
first quartet decreases up to full disappearance with simultaneous
growth of the second one (Fig. 6c). We suppose that the second
signal indicates the formation of a triply reduced derivative of 7. A
doubly reduced binuclear complex seems to be EPR silent. Its dia-
magnetism could be explained by the effective coupling of unpaired
electrons situated on the semiquinone termini via the conducting
TTF bridge. Exhaustive reduction of 7 results in formation of an
insoluble tetranuclear sodium complex. This powder exhibits
a weak EPR signal, but taking into account its intensity, it can be
attributed to the admixture of paramagnetic trinuclear species.
Notably, addition of equivalent amounts of 7 to the tetranuclear
complex results in formation of mono-, di-, and trireduced adducts,
respectively.
Figure 5. Cyclic voltammogram of 7 (5ꢂ10ꢁ3 M) in DMF (oxidation).
Like many sterically hindered o-quinones, compound 7 can be
easily reduced in solution with alkali metal or thallium amalgam.
Reduction proceeds stepwise to give mono-, di-, tri, and tetraa-
nionic species, respectively. The color of the solution converts from
violet to deep blue and then to brownish-green. Tri- and tetraan-
ions of 7 are almost insoluble. EPR monitoring of the reduction of 7
with sodium in THF shows formation of a semiquinone radical-
anionic species at the first stage (Fig. 6a). The spectrum is centered
at g¼2.0047, the quartet splitting is due to the coupling of the
electronic spin with the sodium nucleus (aNa¼0.40 G). The spec-
trum lines are rather narrow with the HFS constant value on metal
being typical for sodium complexes with symmetrical sterically
hindered o-quinones.23 Further reduction of monosemiquinone
leads to the appearance of another quartet signal in the EPR
Figure 7. A side view of 7a.
Figure 8. A side view of 7b.
Figure 9. A front view of 7a.
Two polymorph samples of 7 were studied by X-ray crystal-
lography. The first one was grown by slow cooling of a concentrated
solution of 7 in dichloromethane/hexane (7a), the second one was
obtained from an acetone/hexane mixture (7b). Both 7a and 7b
contain dichloromethane and acetone in their crystal lattices, re-
spectively. Molecules of 7a are packed in stacks so that the TTF
planes are parallel to each other (Fig.10). The generatrix of the stack
is normal to the planes of the molecules. Moreover the carbonyl
groups of the adjacent molecules in a stack are situated directly
above the sulfur atoms of the TTF moiety. The intermolecular dis-
tance between the face-to-face planes of the adjacent molecules
Figure 6. Evolution of the EPR spectra of 7 upon reduction with sodium in THF.

V. Kuropatov et al. / Tetrahedron 66 (2010) 7605e7611
7609
(d¼3.66 Å) shows a significant overlap comparable with the plane-
to-plane distances between donor and acceptor molecules in
crystals of mixed-stack intermolecular charge transfer complexes.
The shortest intermolecular atomeatom distance of 3.22 Å in 7a is
observed between the atom O1 of one molecule and the atom S5 of
the adjacent molecule. The intermolecular contacts can be attrib-
uted to the dipoleedipole interaction between the electron-poor
atom O1 and the electron-rich atom S5 (Fig. 9).
direction. Another distortion is observed in the case of 7b. To re-
duce the steric repulsion from the tert-butyl substituents, the car-
bonyl groups of one quinone ring protrude in the opposite direction
from the molecular plane (Fig. 8).
Density Functional Theory (DFT) calculations of the fused
AeDeA system were performed using Gaussian 03 at the B3LYP/6-
31G level of theory for a full geometry optimization, with no
*
symmetry constraints. Even if no symmetry was imposed, the op-
timized geometry obtained was close to the D2h point group. The
optimized structure is very similar to that observed experimentally
in 7b, the carbonyls from one quinone ring are bent in the opposite
dimensions from the plane of the molecule. Calculations of 7 show
that the LUMO is delocalized primarily over the quinone rings and
the oxygen atoms, and the HOMO belongs to the S2C]CS2 frame-
work (Figs. 12 and 13). The calculated energies for HOMO and
LUMO are ꢁ5.81 eV and ꢁ3.39 eV, respectively. The HOMOeLUMO
gap in 7 was estimated to be 2.41 eV. This indicates that the ab-
sorption band at 514 nm (2.41 eV) can be assigned to the intra-
molecular charge-transfer transition HOMO/LUMO. Commonly,
o-quinones are the better acceptors compared with the analogous
p-quinones. Taking this into account we expected the HOMO-
eLUMO gap in 7 to be smaller than value 1.46 eV observed by
Dumur et al. for 1.4 To understand this fact we compared the con-
tribution from the TTF fragments to HOMO for 7 and 1. These values
are 74% and 87%, respectively. A relatively high contribution of
quinone orbitals in HOMO increases the HOMOeLUMO gap value
for 7. These data are in a good agreement with high oxidation po-
tential determined by CV experiments.
Figure 10. A crystal structure of 7a.
The crystal lattice of 7b consists of molecules that are built in
interpenetrating stacks (Fig. 11). The shortest intermolecular dis-
tance in one stack is 8.80 Å but each quinone moiety is placed above
a TTF moiety of a molecule from an adjacent stack, with the dis-
tance between the quinone carbonyl and sulfur atom being 3.32 Å,
which is close to the sum of the Van der Waals radii.
The central CeC bonds of the TTF moiety in both polymorphs 7a
and 7b are longer than the standard double bond (1.34 Å).18e20 This
fact might be ascribed to the contribution of a dipolar structure to
the ground state. An estimated value of CT derived from the
structural parameters according to method proposed earlier18 is 0.3
for 7a and 0.1 for 7b.
Figure 12. LUMO orbital of 7 obtained by DFT calculations.
Figure 11. A crystal structure of 7b.
X-ray crystallography revealed that the molecules of 7a and 7b
are nearly planar. The difference between 7a and 7b is due to dis-
tortion of the quinone rings. The distortion is caused by the steric
repulsion between tert-butyl substituents both from the sulfur and
oxygen atoms. This repulsion forces the quinone ring in 7a to skew
along the axis of tert-butyl substituents, so that carbonyl groups are
bent in the same dimension from the molecule ring (Fig. 7). The
carbonyl groups of the second quinone ring are bent in the opposite
Figure 13. HOMO orbital of 7 obtained by DFT calculations.

7610
V. Kuropatov et al. / Tetrahedron 66 (2010) 7605e7611
Thus, results of X-ray investigations, electrochemical data as
at rt. A color of the mixture turned to deep-blue. The solvent was
removed in vacuum and the residue was gradually extracted with
Et2O (500 mL). The ethereal solution was oxidized on air with a large
excess of alkaline potassium ferricyanide solution. The completeness
of the oxidation was checked by TLC. The ether layer was washed
with water and evaporated. The residue was washed repeatedly with
small portions of hexane to remove 4,40-thiobis(3,6-di-tert-butylcy-
clohexa-3,5-diene-1,2-dione). Di-o-quinone 7 was isolated (1.22 g,
25%) as violet crystals with yellowish metallic luster after crystalli-
zation at ꢁ18 ꢀC from CH2Cl2/hexane. Mp: 243 ꢀC. A sample suitable
for crystallography was obtained after recrystallization from the
mixture CH2Cl2/hexane (1/10) and acetone/hexane (1/5). Anal. Calcd
(%) for C30H36O4S4 (588.86 g molꢁ1): C 61.19, H 6.16, S 21.79; found: C
well as DFT calculations show that the donor ability of the TTF
moiety in 7 is essentially weakened compared with the non-
substituted tetrathiafulvalene. At the same time, the o-quinone
function, which is presumably determined by the energy of LUMO
seems to be only slightly disturbed by an annealed TTF fragment.
3. Conclusion
We have developed a novel synthetic route for the preparation
of functionalized tetrathiafulvalenes. Also we have synthesized the
first o-quinoneeTTFeo-quinone acceptoredonoreacceptor triad.
The presence of both electron donor and acceptor fragments results
in a multistage amphoteric redox behavior. The HOMOeLUMO gap
for compound 7 is estimated from DFT calculations to be 2.41 eV.
Proposed strong charge transfer in compound 7 agrees with an
intense CT band in the electronic absorption spectrum, which can
be assigned as the HOMO/LUMO transition.
60.97, H 6.19, S 21.90; IR:
n
¼1647, 1629, 1496, 1478, 1393, 1363, 1294,
1218, 1091, 1025, 995, 913w, 840, 816, 765, 641, 538, 463 cmꢁ1 1H
;
NMR (200 MHz, CDCl3, 25 ꢀC, TMS):
NMR (50 MHz, CDCl3, 25 ꢀC, TMS):
d
¼1.47 ppm (s, 36H; 4tBu); 13
C
d
¼29.9 (C(CH3)3), 37.5 (C(CH3)3),
117.2 (C]C of TTF core), 140.1, 149.3 (C]C of o-benzoquinone rings),
183.3 ppm (C]O).
4. Experimental section
4.1. General procedures
4.1.4. 4,40-Sulfanediylbis(3,6-di-tert-butylcyclohexa-3,5-diene-1,2-
dione) (8). Compound was extracted with hexane from a crude
product formed in the previous reaction. Solvent was evaporated.
Octahedron-shaped dark-brown crystals were isolated from ace-
tone (1.55 g, 39%). Mp 201e202 ꢀC. Anal. Calcd (%) for C28H38O4S
(470.64 g molꢁ1): C 71.45, H 8.14, S 6.81; found: C 71.31, H 8.07, S
IR spectra were recorded on a FSM-1201 FTIR spectrometer in
Nujol. UV/vis spectra were measured on a PerkineElmer Lambda 25
spectrometer in 0.1 cm quartz cells. CV experiments were carried out
using an E2P Epsilon potentiostat equipped with a three-electrode cell
C3. The scanrateis100 mV/s.1Hand13CNMRspectrawereobtainedon
a Bruker Avance III 400 MHz and Bruker DPX 200 MHz instrument. The
chemical shifts are expressed in parts per million downfield relative to
6.77; IR:
n
¼1671s, 1653s, 1611m, 1535w, 1517m, 1481m, 1360m,
1279m, 1260s, 1212s, 1158s, 1028w, 952m, 931w, 898m, 837m,
795w, 756m, 720w, 647w, 580w, 508w cmꢁ1 1H NMR (200 MHz,
;
CDCl3, 25 ꢀC, TMS):
d
¼1.16, 1.48 (both s, both 18H; 2tBu), 6.64 ppm
13
internal tetramethylsilane (
d
¼0 ppm) or chloroform (
d¼7.26 ppm).
(s, 2H); C NMR (50 MHz, CDCl3, 25 ꢀC, TMS):
d¼28.8, 30.6 (2C
X-band EPR spectra were recorded with Bruker a EMX spectrometer.
The samples for EPR study were prepared according to procedures
described by Prokof`ev et al.23 Elemental analyses were carried out
with a EURO EA machine. X-ray analysis was carried out on a Bruker
Smart Apex diffractometer. Polyethyleneterephthalate sheets covered
by the homogeneous silica gel sorbent layer Sorbfil-TLC-P were used
for TLC analyses. Solvents were purified and dried by standard
(CH3)3, 2C0(C0H3)3), 35.2, 37.4 (2C(CH3)3, 2C0(C0H3)3), 138.9, 142.0,
148.3, 153.2 (C]C, C0]C0), 182.7, 184.1 (2C]O, 2C0]O).
4.2. X-ray crystallographic study
Diffraction data for 7 and 8 were collected at 100 K with a Bruker
SMART Apex diffractometer using Mo K
and graphite monochromator. Crystal data for 7a: C33H42Cl6O4S4,
Mr¼843.61, crystal dimensions 0.33ꢂ0.28ꢂ0.18 mm, orthorhombic,
a
radiation (
l
¼0.71073 Å)
procedures.24 Tetrachloroethylene (CAS N 127e18-4) was used as
ꢀ
received from Aldrich Chemical Co. Unless noted otherwise, synthetic
procedures were carried out under vacuum.
Pnnm,
a¼21.4233(12) Å,
b¼6.3455(4) Å,
c¼14.7914(8) Å,
4-Chloro-3,6-di-tert-butyl-o-benzoquinone was synthesized as
described by Garnov et al.25 starting from 3,6-di-tert-butyl-o-ben-
zoquinone, which was prepared according to a known procedure.17
a
¼
b
¼
g
¼90ꢀ, V¼2010.8(2) Å3, Z¼2, rcalcd¼1.393 g cmꢁ3, F(000)¼
876,
m
¼0.670 mmꢁ1, 2qmax¼26.00ꢀ, 15,275 measured reflections,
1948 independent reflections (Rint¼0.0602) with Iꢄ2
s
(I),
R1¼0.0572 (Iꢄ2
s
(I)) and 0.0765 (all data), wR2¼0.1415 (Iꢄ2
s
(I))
4.1.1. Disodium disulfide. Sodium (1.15 g, 50 mmol) was melted in
dry diglyme, washed from alkali and dried in vacuum. Then sulfur
powder (1.61 g, 50 mmol) and a solution of benzophenone (0.11 g,
0.6 mmol) in DME (40 mL) were added. The reaction mixture was
sealed and then treated for 50 h at 80 ꢀC in an ultrasonic bath until
the sodium completely disappeared.
and 0.1514 (all data), GOF¼1.023, 0.986, and ꢁ0.506 e Åꢁ3 max. and
min. residual electron density.
Crystal data for 7b: C33H42O5S4, Mr¼646.91, crystal dimensions
0.38ꢂ0.28ꢂ0.20 mm,
orthorhombic,
Pbcn,
a¼15.8500(7) Å,
b¼10.1413(4) Å, c¼20.1608(9) Å,
a¼
b
¼
g
¼90ꢀ, V¼3240.6(2) Å3, Z¼4,
rcalcd¼1.326 g cmꢁ3, F(000)¼1376,
m
¼0.333 mmꢁ1, 2qmax¼29.99ꢀ,
23,003 measured reflections, 4570 independent reflections
4.1.2. Disodium tetrathiooxalate. An ampoule of Na2S2 suspension
in DME was opened and the solvent was removed in vacuum. The
residue was dissolved in MeOH (10 mL) and diluted with CH3CN
(50 mL). Then the mixture was filtered to remove unreacted sulfur
to give an orange-brown solution. A tenfold excess of tetrachloro-
ethylene (8.5 mL, 83 mmol) was added to this solution and the
mixture heated for 5 min at 80 ꢀC in a water bath. The color of the
solution changed to dark-brown and sodium chloride precipitated.
Once prepared the solution of Na2(tto) was immediately used in the
following synthesis without purification.
(Rint¼0.0165) with Iꢄ2
s
(I), R1¼0.0348 (Iꢄ2
s (I)), and 0.0404 (all
(I)) and 0.0957 (all data), GOF¼1.048,
data), wR2¼0.0905 (Iꢄ2
s
0.458, and ꢁ0.230 e Åꢁ3 max. and min. residual electron density.
Crystal data for 8: C28H38O4S, Mr¼470.64, crystal dimensions
0.57ꢂ0.42ꢂ0.24 mm, tetragonal, P4(3)2(1)2, a¼10.2539(2) Å,
b¼10.2539(2) Å, c¼25.1993(10) Å,
a
¼
b
¼
g
¼90ꢀ, V¼2649.52 Å3, Z¼4,
rcalcd¼1.180 g cmꢁ3
,
F(000)¼1016,
m
¼0.152 mmꢁ1
,
2
qmax¼25.99ꢀ,
22,029 measured reflections, 2522 independent reflections
(Rint¼0.0351) with Iꢄ2
s
(I), R1¼0.0922 (Iꢄ2
s (I)), and 0.0943 (all
data), wR2¼0.2072 (Iꢄ2 (I)) and 0.2084 (all data), GOF¼1.112, 0.280,
s
and ꢁ0.289 e Åꢁ3 max. and min. residual electron density.
4.1.3. 4,40,7,70-Tetra-tert-butyl-2,20-bi-1,3-benzodithiole-5,50,6,60-te-
trone (7). A solution of Na2(tto) was added to 4-chloro-3,6-di-tert-
butyl-o-benzoquinone (4.32 g, 17 mmol) dissolved in CH3CN (10 mL)
Absorption corrections were made using the SADABS pro-
gram.26 The structures were solved by direct methods and refined
on F2 by full matrix least squares using SHELXTL.27 All non-

V. Kuropatov et al. / Tetrahedron 66 (2010) 7605e7611
7611
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and 8 were placed in calculated positions and were refined in the
riding model. CCDC-743592 (7a), 743593 (7b) and 765938 (8)
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (þ44) 1223 336
033; or deposit@ccdc.cam.ac.uk).
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Acknowledgements
We gratefully acknowledge the financial support of the Russian
Foundation for Basic Research, grants 10-03-00788-a and 09-03-
97034-r_povolzh’e_a and the Program for support of Leading Sci-
entific Schools NSh-7065.2010.3. This work was made according to
FSP “Scientific and scientific-pedagogical cadres of innovation
Russia” for 2009–2013 years (GK-P839 from 25.05.2010).
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Supplementary data
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Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2010.07.038. These data in-
clude MOL files and InChiKeys of the most important compounds
described in this article.
References and notes
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