Tetrathiafulvalene-oligo(para-phenyleneethynylene) conjugates: Formation of multiple mixed-valence complexes upon electrochemical oxidation

Article abstract of DOI:10.1002/chem.201102868

Short monodisperse oligo- (para-phenyleneethynylene) (pOPE) units bearing laterally attached tetrathio-substituted tetrathiofulvalene (TTF) units have been synthesised from functionalised aromatic building blocks by using the Sonogashira cross-coupling me

Full text of DOI:10.1002/chem.201102868

DOI: 10.1002/chem.201102868
Tetrathiafulvalene–Oligo(para-phenyleneethynylene) Conjugates: Formation
of Multiple Mixed-Valence Complexes upon Electrochemical Oxidation
[a]
Sꢀrka Lipnickꢀ, Martin Beˇlohradsky,[a] Viliam Kolivosˇka,[b] Lubomꢁr Pospꢁsˇil,*[a, b]
ˇ
´
Magdalꢂna Hromadovꢀ,[b] Radek Pohl,[a] Jana Vacek Chocholousˇovꢀ,[a] Jaroslav Vacek,[a]
Jan Fiedler,[b] Irena G. Starꢀ,[a] and Ivo Stary*[a]
´
ˇ
Dedicated to Dr. Jirꢀ Zꢁvada on the occasion of his retirement
Abstract: Short monodisperse oligo-
(para-phenyleneethynylene) (pOPE)
units bearing laterally attached tetra-
thio-substituted tetrathiofulvalene
(TTF) units have been synthesised
from functionalised aromatic building
blocks by using the Sonogashira cross-
coupling methodology. The unusual
redox properties of these TTF–pOPE
conjugates were observed by employ-
ing electrochemical methods, such as
cyclic voltammetry and exhaustive
electrolysis. We found that formally
one half of the TTF units in the pOPE
monomer 1, dimer 2, and trimer 3
(with 2, 4, and 6 TTF units, respective-
ly) are electrochemically silent during
the first-step oxidation at 0.49 V. We
propose the formation of persistent
mixed-valence complexes from the
TTF and TTF+ units present in an
C
equal ratio. Such mixed-valence dyads
(single or multiple in the partially oxi-
dised 1–3) exhibit an unusual stability
towards oxidation until the potential of
the second oxidation at 0.84 V is ach-
ieved. This finding suggests that below
this potential the oxidation of the re-
spective mix-valence complexes is ex-
tremely slow.
Keywords: cross-coupling · donor–
acceptor systems · electrochemistry ·
oligomers · tetrathiofulvalene
Introduction
ology has allowed for the preparation of monodisperse
OPEs, the length of which can range from a dimer up to 23-
mer that reaches 15 nm.[6] The inner para-phenylene unit of
the OPEs has been described as bearing alkyl,[5a,7] alkoxyl,[8]
perfluoroalkyl,[9] aryl,[10] alkenyl,[11] alkynyl,[12] cyano,[9,13]
halo,[9,14] nitro,[15] amino,[16] hydroxy,[17] diarylboranyl,[18] car-
Functionalised monodisperse oligo(para-phenyleneethyny-
lene)s[1] (p-OPEs) have recently attracted significant atten-
tion for manifold reasons, namely, they can be synthesised
in a straightforward way by employing the reliable Sonoga-
shira coupling methodology[2] optionally connected with an
effective convergent/divergent approach,[3] they have been
intensively studied as p-conjugated molecular wires,[4] and
they have been cleverly used as shape-persistent, easy-to-
make molecular scaffolds.[5] The effective synthetic method-
bonyl,[19]
alkoxycarbonyl,[20]
carboxyl,[21]
alkoxy-
AHCTUNGTRENNUNG
the realm of the polymeric pOPEs,[23] other structural varia-
tions, such as pendant phosphonate, sulfonate, bis-alkylam-
monium solubilising substituents,[24] or attached biomole-
cules have even been found.[25] Thus, a large portfolio of the
pOPEs bearing diverse functionalities has already been syn-
thesised and various physicochemical properties of these p-
conjugated rods have been studied. However, there are only
scattered examples of monodisperse pOPEs conjugated with
tetrathiofulvalene (TTF) moieties[26] or their parts[22] and, to
the best of our knowledge, there has been no systematic
study on this subject.
ˇ
ˇ
´
ˇ
[a] S. Lipnickꢀ, Dr. M. Belohradsky, Assoc. Prof. Dr. L. Pospꢁsil,
ˇ
Dr. R. Pohl, Dr. J. V. Chocholousovꢀ, Dr. J. Vacek, Dr. I. G. Starꢀ,
´
Dr. I. Stary
Institute of Organic Chemistry and Biochemistry, v.v.i.
Academy of Sciences of the Czech Republic
Flemingovo nꢀm. 2, 16610 Prague 6 (Czech Republic)
Fax : (+)420-220 183 133
Within a long-term program focused on the development
of new zipper-type multiple donor–acceptor (D–A) interac-
tions, we turned our attention to the short pOPE rods
equipped laterally with TTF units. Importantly, the concept
of the zipper assembly has already been demonstrated by
Matile and Sakai in an intriguing series of reports,[27] in
which they have recently described the formation of n/p-het-
erojunction photosystems containing interdigitated pOPE
chromophores (along with para-oligophenyl moieties) bear-
ing pendant and electronically tuned naphthalenediimide
E-mail: stary@uochb.cas.cz
ˇ
ˇ
[b] V. Kolivoska, Assoc. Prof. Dr. L. Pospꢁsil, Dr. M. Hromadovꢀ,
Dr. J. Fiedler
´
J. Heyrovsky Institute of Physical Chemistry, v.v.i.
Academy of Sciences of the Czech Republic
Dolejskova 3, 18223 Prague 8 (Czech Republic)
Fax : (+)420-286 582 307
ˇ
E-mail: lubomir.pospisil@jh-inst.cas.cz
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102868.
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FULL PAPER
(NDI) chromophores. By following this general paradigm of
supramolecular assembly, which has so far scarcely been
studied relative to, for instance, hydrogen-bonding-control-
led self-organisation,[28] promising highly ordered functional
materials might be envisaged in connection with photovolta-
ics and molecular electronics or the development of new
programmable binding motifs.
TTF complexes in solution being elusive.[32,33] These com-
plexes can be detected only under specific circumstances.[34]
Providing that this weak association is supported by addi-
tional forces such as an intermolecular p–p interactions,[32]
physical constriction inside a cage structure,[35] a covalent
junction between the respective TTF units,[36] or a preorgan-
ised zipper-type interaction,[37] the rare mixed-valence com-
Our interest in monodisperse pOPEs with tethered TTF
units stems from the unique redox properties of TTF. The
discovery of the parent TTF molecule in 1970[29] initiated
considerable efforts in the synthesis and application of this
simple compound and its derivatives.[30] Homogeneous or
heterogeneous reversible oxidation of the nonaromatic TTF
plex of the [(TTF)2]+ structure might be observed. More-
C
over, TTF+ can spontaneously self-associate to form a dia-
C
magnetic [(TTF)2]2+ dication (p dimer).[34] The question of
whether the TTF+ moieties coexist independently under
C
partial oxidation along with the parent TTF or the p dimers
such as [(TTF)2]+ or [(TTF)2]2+ are formed relates to the
C
to a half-aromatic radical cation TTF+ and a fully aromatic
solid-state conductivity of p-doped TTF stacks. The strong
C
dication TTF2+ makes this redox system an attractive build-
ing block for larger molecules and functional materials.[31]
electronic coupling inside the [(TTF)2]+ dyad leads to the
C
p-electron delocalisation necessary for effective charge
propagation along the TTF stacks, whereas any strong
p bonding within the [(TTF)2]2+ ion results in nonconduct-
ing states.[34]
Upon generating the radical ion TTF+ from electroneutral
C
closed-shell TTF, an original electron donor (D) is convert-
ed into an electron acceptor (A), as a consequence of which
the formation of a D–A complex represented by the
Herein, we report on the synthesis and physicochemical
properties of the new TTF–pOPE conjugates 1–3 (Figure 1).
These short double-sided combs bear two, four, or six elec-
troactive TTF groups laterally attached to the central phe-
nylene unit or pOPE rod. In particular, we studied their in-
triguing redox properties to observe the spontaneous forma-
[(TTF)2]+ mixed-valence dyad (p dimer) might be anticipat-
C
ed. However, the interaction energy between the filled and
half-filled HOMO orbitals of the individual components is
small, which results in the intermolecular mixed-valence
tion of mixed-valence [(TTF)2]+ -type complexes. Such a
C
multiple D–A interaction might give rise to new interlaced
supramolecular assemblies that bridge the gap between the
solution and solid-state realms.
Results and Discussion
Synthesis of the TTF–pOPE conjugates: The model mono-
mer 1 bearing two TTF units was synthesised in a straight-
forward way from the known dibromide 4[38] and (2-cyano-
AHCTUNGTRENNUNG
ethyl)sulfanyl TTF derivative 5[39] by following the proce-
dure published by Nielsen and co-workers[39] (Scheme 1).
Upon the treatment of 5 with cesium hydroxide, the labile
2-cyanoethyl group was easily removed and the resulting thi-
olate anion readily displaced the bromine atoms in 4 to pro-
vide 1 in an acceptable yield after its purification by liquid
chromatography.
Scheme 1. The synthesis of the TTF monomer 1: a) 5 (2.0 equiv), CsOH
(2.3 equiv), DMF/methanol (10:1), RT, 0.5 h, then 4, RT, 12 h (29%).
Figure 1. The models of the multiple TTF–pOPE conjugates 1–3.
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The general strategy for the synthesis of dimer 2 (and
trimer 3, see below) was first to prepare fully TTF-function-
alised phenylene building blocks and then to combine these
blocks by means of the Sonogashira coupling methodology
(Scheme 2). The iodination of 4 with one equivalent of I2
led to the monoiodide 6, which was isolated as a major
product along with the known diiodide 7.[24a] Satisfactorily,
compounds 6 and 7 could easily be separated by column
chromatography. Compound 6 was fused with two TTF units
to afford a functionalised building block 8. The Sonogashira
coupling between 8 and (triisopropylsilyl)acetylene under
Pd0/CuI catalysis smoothly provided the ethynylated product
9, which was desilylated by treatment with tetrabutylammo-
nium fluoride. The resulting alkyne 10 was coupled with
iodide 8 under Pd0/CuI catalysis to give rise to the desired
dimer 2 in a moderate yield.
The synthesis of the pOPE backbone, such as in trimer 3,
which bears six TTF units, could start either from the cen-
tral phenylene precursor 11 (to grow simultaneously in two
directions) or from the terminal precursor 10 (to grow only
in one direction; Scheme 3). Although the former approach
allowed the preparation of trimer 3 in moderate yield, the
necessity of repeated column-chromatography purification
to separate it from numerous minor byproducts disqualified
this synthetic pathway. Satisfactorily, the latter approach
avoided an arduous purification of the final product. There-
fore, we converted the known diiodide 7[24a] into the sym-
metrical bis-TTF derivative 11. Subsequently, we treated 11
with nearly equimolar amount of (triisopropylsilyl)acetylene
under Pd0/CuI catalysis to obtain a 3:2 mixture of 12 and 13
along with the minor unreacted diodide 11. The desired
monoethynylated product 12 was easily isolated by column
chromatography in a reasonable 45% yield. The Sonoga-
shira coupling of 10 with 12 led to dimer 14, which was desi-
lylated with tetrabutylammonium fluoride to afford the ter-
minal alkyne 15. Finally, cross-coupling of 15 with iodide 8
provided trimer 3 as a clean product in an acceptable yield.
NMR spectroscopic characterisation of the TTF–pOPE con-
jugates: All of the prepared compounds were fully charac-
terised by NMR spectroscopic analysis by means of standard
1H, 13C, H,H-COSY, H,C-HSQC, and H,C-HMBC techni-
ques (complete signal assignment is given in the Supporting
Information). Occasionally, we could see line broadening of
1
the signals in the H NMR spectra for selected TTF deriva-
tives, such as 1 and 14, even if the measurements were per-
formed in acid-free CDCl3 (to prevent TTF protonation).[40]
By changing this solvent to CD2Cl2 with similar solvation
1
properties, sharp lines in the H NMR spectra resulted.
Computational study of the TTF–pOPE conjugates: To shed
light on the molecular shape of the multiple TTF–pOPE
conjugates 1–3, we studied these molecular structures theo-
retically. Because of the system size and computer limita-
tions, we used the AM1 semiempirical method for geometry
optimisation and the Universal Force Field (UFF) for mo-
lecular-dynamics simulations. We focused on the prototypal
TTF dimer 2, the structure of which was first optimised at
the AM1 level. Molecular dynamics (MD) were simulated
by our in-house program TINK to explore the conforma-
tional space. The simulation ran for 1500 ps, and the starting
and final geometries of the dimer system 2 are shown in
Figure 2. As expected, the molecule exhibited significant
conformational freedom to adopt numerous low-lying con-
formations in the course of the simulation (only one of the
Scheme 2. The synthesis of the TTF dimer 2: a) I2 (1.0 equiv), KIO3
(1.0 equiv), acetic acid, 758C, 3 h, 70 % of 6 (23% of 7); b) 5 (2.1 equiv),
CsOH (2.3 equiv), DMF/methanol (10:1), RT, 0.5 h, then 6, RT, 3 h
ꢀ ꢁ
(79%); c) TIPS C CH (2.0 equiv), [PdACHTNUTRGNE(UNG PPh3)4] (5 mol%), CuI
(15 mol%), diisopropylamine/DMF (1:1), 508C, 4 h (92%); d) nBu4NF
(1.1 equiv), THF, RT, 0.5 h (97%); e) [PdACHTNUTRGNE(UNG PPh3)4] (15 mol%), CuI
(40 mol%), diisopropylamine/DMF (1:1), 408C, 3 h (32%). TIPS=triiso-
propylsilyl.
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Redox Properties of Mixed-Valence Complexes
FULL PAPER
Figure 2. The molecular structure of the TTF dimer
2 obtained by
a) AM1 optimisation and B) MD simulation (only one low-lying con-
former shown).
populated conformations is shown). Furthermore, MD simu-
lations were performed to scan the conformational space of
the TTF monomer 1 to inspect the flexibility necessary to
reach a close-to-parallel position of the tethered TTF units
(distance: <4 ꢃ). Both the relaxed conformer of 1 and the
conformer with intramolecularly stacked TTF units, which
were formed during the MD simulation, were treated at the
AM1 and B3LYP/6-31G* levels of theory in vacuum to see
an energy difference of about 3 kcalmolꢀ1 in favour of the
relaxed conformer of 1 (see the Supporting Information for
further details).
Electrochemical analysis of the TTF–pOPE conjugates: The
electrochemical experiments were carried out to identify
possible communication between the TTF multiple redox
centres laterally attached to the pOPE backbone. The TTF–
Scheme 3. The synthesis of the TTF trimer 3: a) 5 (2.1 equiv), CsOH
(2.3 equiv), DMF/methanol (10:1), RT, 0.5 h, then 7, RT, 3 h (70%);
ꢀ ꢁ
b) TIPS C CH (1.1 equiv), [PdACHTNUGTRNEUGN(PPh3)4] (5 mol%), CuI (15 mol%), diiso-
propylamine/DMF (1:1), 508C, 4 h (45, 30, and 21% of 12, 13, and recov-
ered 11); c) 10 (1.0 equiv), 12 (1.0 equiv), [PdACHTNURTGNEUNG(PPh3)4] (15 mol%), CuI
(40 mol%), THF/diisopropylamine/DMF (1:1:1), RT, 3 days (45%);
d) nBu4NF (1.1 equiv), THF, RT, 0.5 h (98%); e) 8 (1.5 equiv), [Pd-
AHCTUNGTRENNUNG
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pOPE conjugates 1–3 were investigated by cyclic voltamme-
try (CV) at various scan rates (0.05–50 Vsꢀ1) by using chro-
noamperometry and exhaustive electrolysis at two different
potentials, which corresponded to the first and second oxi-
dation steps. The cyclic voltammetry of the monomer 1 with
two TTF units showed two simple one-electron oxidation
steps at 0.489 and 0.853 V (Figure 3). The anodic/cathodic
dation step. The presence of such a small overlapped wave
was clearly indicated by the semi-integration followed by
the log-plot analysis (see below).
The analysis of the cyclic voltammograms of compounds
1–3 under the given conditions indicated that, to our sur-
prise, the charge transferred did not correspond to the
number of the TTF units attached. This finding could be in-
ferred from the comparison of the heights of the corre-
sponding peak currents (or the heights of “neo-polaro-
grams”, see below) with the height of the peak current of
ferrocene at the same molar concentration (Figure 3). Such
a controversial observation deserved a detailed study. The
analysis of the voltammograms was substantially facilitated
by the convolution methods, which transformed current–
voltage curves to diagrams identical to those obtained by
the steady-state techniques (polarography or rotating disc
voltammetry). Voltammograms transformed by semi-inte-
gration to “neo-polarograms” (i.e., m(t) vs E)[41] showed the
wave/height ratios of 1:1, 2:1, and 3:1 for 1–3, respectively
(Figure 4A), which reflected an increased number of the ox-
idisable units in a molecule. The potential dependence of
log[m(t)/
G
yielded the log–plot curves with the slope of 59 mVdecadeꢀ1
(Figure 4B, dashed lines), which was characteristic for a
one-electron heterogeneous redox step. Hence, the wave/
height ratio in Figure 4A just reflected an increased amount
of the oxidisable functions present in 1–3. Therefore, the
TTF redox centres did not substantially electronically com-
municate between themselves. Obviously, we observed only
Figure 3. The cyclic voltammetry of 0.2 mm solutions of 1–3 and ferrocene
(in 0.1m tetrabutylammonium hexafluorophosphate in dichloroethane at
the scan rate of 0.5 Vsꢀ1).
peak separations were 60 mV for both of the redox steps.
The other two oligomers 2 and 3 were oxidised practically at
the same potentials (Table 1). The anodic/cathodic peak cur-
rent ratio equalled unity for both the redox steps, and all
the TTF–pOPE conjugates thus confirmed a reversible elec-
tron exchange. The heterogeneous standard rate constant
was very high and outside of the measurement limit. The
impedance spectroscopy yielded no sign of kinetic control
until a frequency as high as 5 kHz. We did not observe any
peak splitting for 1. In contrast, dimer 2 with four TTF units
yielded a voltammogram, in which the first oxidation peak
seemed to be preceded by a small shoulder. Trimer 3 with
six TTF units showed a similar peak overlap for the first oxi-
Table 1. The formal redox potentials and limiting wave heights of the
TTF–pOPE conjugates 1–3 obtained from the semiintegrated cyclic vol-
tammetry.[a]
Compound
E0
E0
m
G
mACHTUNGTRENNUNG
1
2
[V]
[V]
N
]
N
]
1
2
3
0.489
0.482
0.488
0.412
0.853
0.826
0.840
–
0.103
0.173
0.279
0.119
0.096
0.176
0.276
Figure 4. Semiintegration of the positive scans of the voltammograms of
1–3 from Figure 3; the wave of ferrocene is labelled as Fc (A). The loga-
rithmic analysis of the first oxidation wave of the semiintegrated voltam-
mograms of 1–3 from Figure 3A.
ferrocene
[a] CV in 0.1m tetrabutylammonium hexafluorophosphate in dichloro-
ethane at the scan rate of 0.5 Vsꢀ1 referenced to AgjAgClj1m LiCl.
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Redox Properties of Mixed-Valence Complexes
FULL PAPER
around one half of the electrons transferred relative to that
expected. The numerical logarithmic analysis also distin-
guished the contribution of the small overlapped shoulders
present in the first oxidation step of 2 and 3. Small prepeaks
amounted to only few percent of the total current and their
position was shifted towards lower potentials by approxi-
mately 20, 47, and 60 mV for 1–3, respectively (Figure 4B).
For the sake of indisputably determining the number of
electrons n involved in the first oxidation step, we applied
two additional independent approaches: the method devel-
oped by Malachesky[42] and an exhaustive bulk electrolysis.
It is worth noting that the procedure by Malachesky does
not require any knowledge of the diffusion coefficient. It
yields n from the relationship between the scan-rate depend-
ence of voltammetric peak currents ip and the time decay of
a chronoamperometric transient i(t) measured under diffu-
sion control. Both sets of data have to be measured for the
same bulk concentration, the same electrode area, and
within a similar timescale. The estimation of n according to
the method of Malachesky yielded n=1.0ꢂ0.1, 1.9ꢂ0.3,
and ꢃ2.5 for 1–3, respectively (Table 2). These values were
vincingly to the number of TTF units. Such a slow rate of
electrolysis suggests a possible presence of a chemical equili-
brium between redox-inactive and redox-active forms.
It is worth noting that electrochemistry of the TTF deriva-
tive 5 and 1,4-dibutoxybenzene, which represent simplified
models of the key structural elements of 1–3, did not exhibit
irregular behaviour of the multiple TTF derivatives men-
tioned above or did not interfere with the redox-active
groups, respectively. The backbone element 1,4-dibutoxy-
benzene was electrochemically active at potentials at least
0.53 V more positive than the highest oxidation potential of
all the TTF derivatives (see the Supporting Information for
cyclic voltammograms). The TTF compound 5 could reversi-
bly be oxidised in two steps that represent two one-electron
processes, as could be seen from logarithmic analysis of the
neo-polarogram obtained by the semi-integration of the
cyclic voltammetry curve (see the Supporting Information
for further details). The first-step oxidation of 5 was accom-
panied by the appearance of a NIR band at l=2100 nm.
Later, we will show that the half-oxidised 1 yields a similar
NIR band shifted by 150 nm towards longer wavelengths.
Such an anomalous behaviour of the TTF–pOPE conju-
gates 1–3 in the electrochemical oxidation requires an ex-
planation. The determination of the number of electrons
transferred n under given experimental conditions undoubt-
edly indicates that in the first oxidation step at around 0.5 V
formally only one half of the TTF units undergoes a single-
Table 2. The number of electrons n per molecule transferred in the first-
step electrochemical oxidation of 1–3.[a]
Compound
Expected[b]
Method of
Malachesky
Exhaustive
electrolysis
1
2
3
2
4
6
1.0ꢂ0.1
1.9ꢂ0.3
ꢃ2.5
1.1ꢂ0.05
2.3ꢂ0.05
>2.5
electron transfer to form the corresponding TTF+ -type rad-
C
ical ion such as 1+ (Scheme 4) or multiple radical cations
C
[a] The first oxidation step at 0.75 V. [b] The number of the TTF units per
molecule.
derived from 2 or 3. An adequate number of the native TTF
units can form mixed-valence D–A complexes with the
TTF+ radical ion units in the same molecule (such as in A)
C
further confirmed by measuring the faradaic charge con-
sumed during the exhaustive electrolysis at a potential of
the diffusion-limited first oxidation (0.75 V). Thus, we could
conclude that, in the first redox step, formally only one half
of the TTF units of 1–3 were oxidised.
or different one (such as in B–D). Furthermore, the radical–
The next question to be answered was to estimate the
exact number of electrons n transferred in the second oxida-
tion step. The comparable height of the first and second
redox peaks in the cyclic voltammograms or neo-polaro-
grams (Figure 4) of 1–3 implied that again not all the TTF
units were oxidised on the timescale of this process, even at
the higher potential (>1 V) than the respective second oxi-
dation potential (0.8 V; Table 1). The estimation of n in the
second oxidation step was verified again by several inde-
pendent standard electrochemical methods, and the ob-
tained values are consistent. However, the exhaustive bulk
electrolysis of 2 at 1 V indeed consumes a charge that corre-
sponds to its oxidation by the total number of eight elec-
trons, as expected from the number of TTF functions in 2.
Compound 3 was electrolyzed at the potential of the second
oxidation step and also yielded a charge that corresponds to
uptake of twelve electrons, as expected from the presence of
six electroactive groups. Although the electrochemical oxi-
dation of 2 and 3 was very slow (within 2 h), the total
charge needed to complete the reaction corresponded con-
Scheme 4. The possible intra- and intermolecular mixed-valence com-
plexes A–D and p-dimer E formed from the half-oxidised 1+ during the
C
first oxidation step (the characteristic wavelengths of the absorption
bands associated with the corresponding forms of the TTF unit(s) are in-
dicated).
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radical coupling that results in the formation of a p dimer,
such as E, is known to participate in the electrochemistry of
TTF derivatives.[45b,e,h] Thus, the process that leads to the
mixed-valence complexes A–D must practically be instanta-
neous and much faster than the first-step oxidation of the
TTF units (a complete conversion TTF!TTF+ would oth-
C
erwise occur).
The mixed-valence complexes in question seem to be oxi-
datively stable up to the potential of 0.8 V. Obviously, the
second-step preparative-scale exhaustive oxidation of all the
TTF functions is an overall slow process, regardless of the
fact that the electron-transfer rate is very high. It is obvious
that a slow homogeneous equilibrium accounts for a long re-
action period of the exhaustive bulk electrolysis and, on the
other hand, for a smaller height of the peaks of the second
oxidation step (at 0.8 V) in the cyclic voltammetry of 1–3,
which corresponds also to one half of the expected height. It
is worth noting that in this specific case the time scales of
the CV and exhaustive electrolysis differ by about the 2–4
orders of magnitude. However, the mixed-valence com-
plexes, such as A–D, which are rather resistant to oxidation
below 0.8 V, might be further slowly oxidised above 0.8 V to
the 14+ ion most likely after their slow dissociation back to
the 1+ radical ion. Such an equilibrium is absent during the
C
first oxidation step, since the UV/Vis spectra of the solution
in situ held after exhaustive electrolysis at the constant po-
tential of the first oxidation step did not change, even after
2 hours at the applied potential. The UV/Vis spectrum did
not show any signal that corresponds to the original com-
pound that should be there after hypothetical dissociation of
the mixed-valence complex to cation radical and original re-
actant and the integrated charge was still equal to one.
Therefore, a reason for such an unusual behaviour must be
sought elsewhere. One possible suggestion is that the silent
TTF units are indeed blocked in such a complex and behave
differently once the nonsilent TTF units within this complex
are oxidised in the second oxidation step. Assuming that the
equilibrium is shifted completely towards the mixed valence
complex formation (no observation of any UV/Vis signal
from the reactant), only the withdrawal of the second elec-
tron from the nonsilent TTF unit leads to the availability of
the originally electrochemically silent TTF units in the mole-
cule. Therefore, on the time scale of the cyclic voltammetric
measurements, only one half of the TTF units is oxidized.
We propose that the mixed-valence complex should be
formed concomitantly with the first electron-transfer step.
The proposed mechanism of oxidation of the TTF–pOPE
conjugates 1–3 was further supported by spectroelectro-
chemical data for the characteristic changes in the UV/Vis
spectra, which were monitored during the exhaustive elec-
trolysis of 1 and 2 (see Figure 5 for the UV/Vis spectroelec-
trochemistry of 2). Upon setting the first-step oxidation po-
tential to 0.6 V, the original UV/Vis maxima at l=310 and
330 nm gradually decreased while two new absorption bands
at l=450 and 830 nm appeared (Figure 5A).
Figure 5. The UV/Vis spectroelectrochemistry of 0.48 mm 2 and 0.2m tet-
rabutylammonium hexafluorophosphate in dichloroethane during the
electrolysis at A) the first-step redox potential of 0.6 V and B) the subse-
quent electrolysis at the second-step redox potential of 1.0 V.
(Scheme 4). The positions of the absorption maxima ob-
served were in accord with reported data related to the tet-
rathio-substituted TTF+ radical ions.[33,36c,44] Furthermore,
C
the second-step oxidation at 1 V led to the gradual disap-
pearance of the UV/Vis maxima at l=450 and 830 nm. At
the same time, a new strongly absorbing band appeared that
gradually shifted its position from l=775 to 722 nm (Fig-
ure 5B). The presence of such a band indicated oxidation of
the originally neutral TTF units in 2 to TTF2+ units as re-
ported previously (the strong absorption at around l=550–
750 nm is characteristic for the TTF2+ species).[36c,37,45e]
We performed an spectroelectrochemical study of 1 in
situ in the NIR region at the potential of the first oxidation
process (Figure 6) to monitor the formation of the proposed
intermediate mixed-valence [(TTF)2]+ -type complexes. A
C
gradual increase of the broad NIR band at l=2250 nm indi-
cated the formation of the aforementioned mixed-valence
complex, as it was described for related TTF species (l=
1630–2300 nm).[32,34,35b,36a,b,37,45b,e] It is worth noting that
during the electrolysis of 1 at 0.65 V in a thin optical cell
The occurrence of the latter spectral bands is known to
[34,35,36c,d,37,43]
reflect the formation of the TTF+ -type species
C
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Chem. Eur. J. 2013, 19, 6108 – 6121

Redox Properties of Mixed-Valence Complexes
FULL PAPER
Figure 6. The temporary increase of the NIR absorption band (at l=
2250 nm) associated with the proposed formation of a mixed-valence
[(TTF)2]+·-type complex during the first-step oxidation of 1 at the poten-
tial of 0.6 V (12.3 mm 1, 0.1m tetrabutylammonium hexafluorophosphate
in dichloroethane).
this band reached its maximum and later gradually disap-
peared. This behaviour explains why the NIR band can
escape the observation if the NIR spectrum is taken ex situ
in an exhaustively oxidised sample at the same potential.
The first-step oxidation of 1–3 generates the TTF+ -type
C
radical ions, which should be paramagnetic (along with their
mixed-valence complexes) or diamagnetic if they undergo
the radical dimerisation with the formation of a s bond.[34]
Electron spin resonance (ESR) spectroscopy confirmed that
the first-step oxidation of these compounds at 0.7 V led to a
radical species because the ESR signal was observed (see
Figure 7 for the ESR spectrum of oxidized species 2). The
temperature-dependent measurements showed that whereas
a single-line spectrum was observed at 208C, fine splitting of
the signal appeared at ꢀ638C. We propose that this behav-
iour stems from a dynamic equilibrium between inter- and
intramolecular complexes or their conformers, which pro-
ceeds quickly on the ESR timescale at ambient temperature
or is frozen at a low temperature.
Figure 7. The ESR spectrum at A) 20 and B) ꢀ638C of 2 oxidised at
0.7 V in dichloroethane.
oxidised to the TTF+ state (if we consider two limiting sit-
C
uations). The latter case invokes a hypothesis that the oxida-
tion is incomplete but the number of electrons transferred
in the oxidised molecules is twofold greater than observed
(see Table 2 for the oxidation of 1–3). As for 1, the meas-
ured first one-electron oxidation at 0.7 V might involve a
hidden two-electron process, for which a suggested reaction
The observation that upon the first-step oxidation at 0.5 V
formally one half of the TTF units in 1–3 remain, surprising-
ly, electrochemically silent is not in accord with the earlier
mechanism 1!1+ !1
is given in Scheme 5 (possible oli-
C
2+2C
studies on the intramolecular mixed-valence [(TTF)2]+ -type
gomeric mixed-valence complexes were omitted). Its numer-
ical simulation using the finite difference methods[50] showed
that at large values of the rate constant k2 the original two-
electron wave changes to a single-electron wave (Figure 8).
Hence, the first oxidation step involves a stepwise oxidation
of both TTF units in some molecules 1, which is accompa-
nied by the very fast formation of the mixed-valence com-
plexes D and C. The rate of the formation of D is less im-
portant and gives rise to a small shoulder seen on the log–
plot diagrams (see the Supporting Information). The rate
constant for the formation of C is at least k2 ꢄ104 mꢀ1 sꢀ1
(the simulations are not sensitive to a large k2 value and
hence a more accurate estimate is not available). We are
aware that Scheme 5 omits the formation of p dimers, for
which absorption at l=830 nm was observed and consid-
ered in Scheme 4. However, the formation of these dimers
C
complexes. If the two communicating TTF redox centres
generate a mixed-valence complex during the first-step oxi-
dation, then, usually, a broadening or splitting of the corre-
sponding CV wave appears.[36c,45] This finding is generally
explained by facilitating the first single-electron transfer be-
cause the formation of a [(TTF)2]+ -type dyad stabilises a
C
TTF+ -type intermediate. This outcome results in hampering
C
the second single-electron transfer (due to the electrostatic
repulsion in a [(TTF)2]2+-type intermediate).[45g] However,
there is seemingly no substantial splitting of the first-step
oxidation wave in the case of 1.
The fact that formally one half of the TTF units are elec-
trochemically silent at the first-step oxidation potential
means that either one half of the TTF units in all the mole-
cules or all the TTF units in one half of the molecules are
Chem. Eur. J. 2013, 19, 6108 – 6121
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6115

ˇ
´
L. Pospꢁsil, I Stary et al.
modynamically controlled). However, the first and second
oxidation wave in the cyclic voltammograms of 1–3 should
be in a 1:3 ratio but not of the approximately same height as
we observed (Figure 3).[51] Accordingly, the suggested ex-
planation based on the astounding kinetic stability of the
[(TTF)2]+ -type mixed-valence complexes at 0.5 V and their
C
slow oxidation to the TTF2+-type state above 0.8 V seems to
be more probable.
Conclusions
We have synthesised the new TTF–pOPE conjugates 1–3,
which resemble short double-sided combs bearing two, four,
or six electroactive TTF groups laterally attached to the cen-
tral phenylene unit or pOPE rod. The syntheses of dimer 2
and trimer 3 have been based on the Sonogashira coupling
between the TTF-functionalised aryl iodides and aryl acety-
lenes. Compounds 1–3 were characterised in detail by NMR
spectroscopic analysis, and the lowest-energy conformers of
these compounds were identified by using DFT computa-
tional methods.
Scheme 5. The proposed mechanism of the oxidation of 1 in the first oxi-
dation step at 0.5 V. Numerical simulation shows that k2 >1000 leads to a
formal one-electron voltammetric currents.
Intriguingly, the electrochemical oxidation of the TTF–
pOPE conjugates 1–3 provided unexpected results. Despite
the fact that the TTF derivatives are usually oxidised in two
consecutive waves to generate first the TTF+ -type radical
C
ion, which is converted into the TTF2+-type ion at higher
redox potentials, we surprisingly found one half of the TTF
units in solutions of 1–3 to be seemingly electrochemically
silent during the first-step oxidation. The kinetic simulations
and the presence of the NIR mixed-valence band at l=
2250 nm indicated that the first-step oxidation (at 0.5 V) of
the prototypal 1 bearing two TTF units might be a hidden
two-electron process, in which the doubly oxidised mole-
Figure 8. The numerical simulation of the steady state current-voltage de-
pendence for the mechanism given in Scheme 5. Standard heterogeneous
rate constants were assumed to be high (1 cmsꢀ1) and other kinetic con-
stants were k1 =k3 =kꢀ1 =kꢀ2 =0.
cules 12+2 interacted with the nonoxidised species 1 to form
C
the persistent mixed-valence complexes of the TTF–TTF+
C
does not lead to the consumption of the starting material 1
and, therefore, cannot explain the one-electron character of
the waves.
type. The experimental data obtained from cyclic voltamme-
try, exhaustive bulk electrolysis, spectroelectrochemistry,
UV/Vis–NIR, and ESR spectroscopy were consistent with
this observation. Such complexes exhibited a remarkable ki-
netic stability towards oxidation, which, consequently, hin-
To provide a rationale why formally one half of the TTF
units contained in solutions of 1–3 remains electrochemical-
ly silent upon the first-step oxidation at 0.5 V, we suggest
the formation of mixed-valence complexes exemplified by
A–D, as discussed above (Schemes 4 and 5). Two scenarios
might be proposed to explain why all the TTF units in the
dered the oxidation of all the TTF units to the TTF+ radical
C
ions at the first-step oxidation potential.
These results provide new stimuli for further research ac-
tivities focused on the structure of multiple mixed-valence
(or D–A) complexes derived from the TTF–pOPE conju-
gates, on the formation of the intramolecular p-delocalised
mixed-valence complexes are not converted into the TTF+
C
state at the first-step oxidation potential: 1) The mixed-va-
lence complexes derived from 1–3 are unusually resistant to
the further oxidation until the oxidation potential of 0.8 V is
achieved. This behaviour suggests that below this potential
the oxidation of the respective mixed-valence complexes is
extremely slow (kinetically controlled). A large shift of
redox potentials upon complexation of metallic cations has
been well known for decades. 2) Alternatively, by forming
mixed-valence complexes, the first-step oxidation wave is
split to such an extent (ca. l=350 mV) that its higher-poten-
tial part overlaps with the second-step oxidation wave (ther-
stacks of the [(TTF)2]+ dyads, on a possible role of the p-
C
conjugated pOPE backbone in electron-transfer processes
and, last but not least, on designing the proper partners to
control their zipping driven by a multiple intermolecular D–
A interactions.
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Redox Properties of Mixed-Valence Complexes
FULL PAPER
termination better than 0.30% abs. Commercially available catalysts and
reagent-grade materials were used as received. Decane was degassed by
three freeze/pump/thaw cycles before use. Diisopropylamine was distilled
from calcium hydride under argon; THF was freshly distilled from
sodium/benzophenone under nitrogen; DMF was degassed by three
freeze/pump/thaw cycles before use, HPLC-grade methanol was stored
over molecular sieves. The TLC analysis was performed on silica gel 60
F254-coated aluminium sheets (Merck), and the spots were detected by a
Experimental Section
Computational details: Gaussian09 package[46] was used to perform the
AM1 semiempirical calculations. Constant-energy molecular-dynamics
simulations were run with our in-house program TINK[47] and the UFF[48]
force field. The simulation time step was 1 fs; the initial temperature was
300 K. Charges were assigned by the charge equilibration scheme.[49]
Electrochemistry, spectroelectrochemistry, and ESR spectroscopy: Elec-
trochemical measurements were performed using a potentiostat/galvano-
stat Autolab PGSTAT30 equipped with a frequency response module
(Eco Chemie, The Netherlands). A three-electrode electrochemical cell
was used. The reference electrode, AgjAgClj1m LiCl, was separated
from the test solution by a nonaqueous salt bridge. The potential of the
ferrocene/ferrocenium redox couple (Fc/Fc+) was 0.412 V. The working
electrode was a glass-sealed Au disc 0.5 mm in diameter. The auxiliary
electrode was a platinum wire. The scan rate of the applied DC potential
was in the range 0.05–50 Vsꢀ1. Tetrabutylammonium hexafluorophos-
phate (TBAPF6) and dichloroethane were supplied by Sigma Aldrich.
The indifferent electrolyte TBAPF6 was recrystallised and dried under
vacuum. Dichloroethane was dried over activated molecular sieves.
Oxygen was removed from the solution by passing a stream of argon sa-
turated with vapours of the solvent. The spectroelectrochemical data
were obtained in an optically transparent thin-layer cell. The spectra
were recorded using a diode-array UV/Vis spectrometer from Hewlett–
Packard (model 8452A) and a UV/Vis–NIR spectrometer from Perki-
nElmer (Lambda 1050 model). The solutions of the cation radicals for
the ESR spectroscopic analysis were prepared by an exhaustive electroly-
sis in a cell with a separated compartment of the counterelectrode and
transferred under inert atmosphere to a flat quartz cuvette. The ESR
spectra were measured with a Bruker ELEKSYS E-500 spectrometer.
The modulation frequency was 100 kHz. The modulation amplitude was
0.05–0.1 G. Voltammograms (the dependence of the current i on the ap-
plied potential E) were numerically transformed to semi-integrated “neo-
polarograms”, which give the dependence of a semi-integral m(t) as a
function of the applied potential E in the form of a sigmoid wave with a
solution of CeACHTUNRTGNEN(GU SO4)2·4H2O (1%) and H3PAHCTUTGNREN(NUGN Mo3O10)4 (2%) in sulfuric
acid (10%). The chromatography was performed on silica gel 60 (0.040–
0.063 mm; Fluka).
4,4’-[Benzene-1,4-diylbis(oxyethane-2,1-diylsulfanediyl)]bis[4’,5,5’-tris(bu-
tylsulfanyl)-2,2’-bi-1,3-dithiole] (1): A Schlenk flask was charged with tet-
rathiafulvalene 5 (103 mg, 0.186 mmol, 2.0 equiv), flushed with argon,
and DMF (7 mL) was added.
A solution of CsOH·H2O (36 mg,
0.214 mmol, 2.3 equiv) in methanol (0.5 mL) was slowly added to the re-
action mixture, which was stirred at room temperature for 0.5 h. Dibro-
mide 4 (30 mg, 0.093 mmol, 1.0 equiv) dissolved in DMF (3 mL) was
added and the reaction mixture was stirred at room temperature for 12 h.
The solvent was removed in vacuo, and the crude product was purified
by column chromatography on silica gel (hexane/chloroform 70:30) to
provide 1 (31 mg, 29%) as a red amorphous solid. 1H NMR (500 MHz,
CD2Cl2): d=0.90, 0.915, 0.92 (3ꢄt, 18H, Jvic =7.4 Hz), 1.36–1.48, 1.55–
1.65 (2ꢄm, 24H), 2.81, 2.825 (2ꢄt, 12H, Jvic =7.3 Hz), 3.15 (t, 4H, Jvic
=
6.5 Hz), 4.11 (t, 4H,
J
vic =6.5 Hz), 6.83 ppm (s, 4H); 13C NMR
(125.7 MHz, CD2Cl2): d=13.91, 13.93, 13.94 (4ꢄq), 22.2 (t), 32.37, 32.38,
32.39 (3ꢄt), 35.7 (t), 36.52, 36.54 (2ꢄt), 68.0 (t), 110.0, 111.6 (2ꢄs), 116.2
(d), 126.2 (s), 128.3, 128.4, 130.9 (3ꢄs), 153.4 ppm (s); IR (CCl4): n˜ =
2961, 2932, 2875, 2864, 1614, 1593, 1507, 1465, 1380, 1226, 1033 cmꢀ1
;
UV/Vis (ClCH2CH2Cl): lmax (loge)=311 (3.01), 332 (3.05), 350 nm
(3.03); MS (TOF MALDI): m/z: 1162 [M+]; MS (ESI+): m/z: 1201
([M+K]+), 1185 ([M+Na]+), 1162 [M+]; HRMS (ESI+): m/z calcd for
C57H86O2S16: 1162.0584 [M+]; found: 1162.0589.
4,4’,4’’,4’’’-{Ethyne-1,2-diylbis[benzene-2,1,4-triylbis(oxyethane-2,1-diylsul-
fanediyl)]}tetrakis[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiole] (2):
A
Schlenk flask was charged with 10 (97.0 mg, 0.082 mmol), [Pd(PPh3)4]
ACHTUNGTRENNUNG
limiting height of mlim
.
(14.3 mg, 0.012 mmol, 15 mol%), and CuI (6.2 mg, 0.033 mmol,
40 mol%); flushed with argon; and then a solution of 8 (105.6 mg,
0.082 mmol, 1.0 equiv) in diisopropylamine (8 mL) and DMF (8 mL) was
added. The reaction mixture was stirred at 408C for 3 h. The solvent was
removed in vacuo, and the crude product was purified by column chro-
Materials and procedures: The melting points were determined on a
Kofler hot-stage apparatus and are uncorrected. The 1H NMR spectra
were measured at 400.13, 499.88, and 600.13 MHz, the 13C NMR spectra
at 100.61, 125.71, and 150.90 MHz in CDCl3 with TMS as an internal
standard or CD2Cl2. The chemical shifts are given in d and the coupling
constants J are given in Hz. The HMBC experiments were set up for JCꢀ
H =5 Hz. For correct assignment of both the 1H and 13C NMR spectra of
key compounds, COSY, HMQC, and HMBC experiments were per-
formed. The IR spectra were measured in CCl4. The EI mass spectra
were determined at an ionising voltage of 70 eV, the m/z values are given
along with their relative intensities (%). The standard spectra measured
with 70 eV were recorded in the positive ion mode. The TOF EI spectra
were measured by using an orthogonal acceleration time-of-flight mass
spectrometer GCT Premier (Waters). The sample was dissolved in
chloroform, loaded into a quartz cup of the direct probe, and inserted
into the ion source. The source temperature was 2208C. For exact mass
measurement, the spectra were internally calibrated using perfluorotri-n-
butylamine (Heptacosa). The ESI mass spectra were recorded using the
LCQ classic ion-trap mass spectrometer (Thermo) equipped with an elec-
trospray ion source and controlled by Xcalibur software. The mobile
matography on silica gel (chloroform/hexane 40:60) to provide
2
(61.0 mg, 32%) as a red amorphous solid. 1H NMR (400 MHz, CDCl3,
TMS): d=0.897, 0.904, 0.917, 0.923 (4ꢄt, 36H), 1.35–1.49, 1.54–1.66 (2ꢄ
m, 48H), 2.82 (t, 24H, Jvic =7.3 Hz), 3.17 (t, 4H, Jvic =6.5 Hz), 3.23 (t,
4H, Jvic =6.9 Hz), 4.14 (t, 4H, Jvic =6.5 Hz), 4.24 (t, 4H, Jvic =6.9 Hz),
6.86 (m, 4H), 7.07 ppm (dd, 2H, J6,4 =1.7 Hz); 13C NMR (100.6 MHz,
CDCl3, TMS): d=13.55, 13.59 (2ꢄq), 21.59, 21.61 (2ꢄt), 31.69, 31.72,
31.74 (3ꢄt), 35.0 (t), 35.90, 35.92 (2ꢄt), 67.4 (t), 68.8 (t), 89.8 (s), 109.25,
109.32, 111.0 (3ꢄs), 114.5 (s), 115.1 (d), 116.6 (d), 119.0 (d), 125.1, 125.2
(2ꢄs), 127.56, 127.57, 127.8, 130.28, 130.34 (5ꢄs), 152.5 (s), 153.4 ppm
(s); IR (CCl4): n˜ =2961, 2931, 2874, 2863, 2216, 1601, 1577, 1495, 1465,
1380, 1222, 1031 cmꢀ1; UV/Vis (ClCH2CH2Cl): lmax (loge)=263 (4.77),
313 (4.72), 333 nm (4.75); MS (TOF MALDI): m/z: 2346 [M+].
4-{[2-(2,5-BisACTHNUTRGNE{NUG [2,5-bis(2-{[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiol-4-yl]-
sulfanyl}ethoxy)phenyl]ethynyl}-4-(2-{[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-
1,3-dithiol-4-yl]sulfanyl}ethoxy)phenoxy]ethyl}sulfanyl)-4’,5,5’-tris(butyl-
sulfanyl)-2,2’-bi-1,3-dithiole (3): A Schlenk flask was charged with 8
phase consisted of methanol/water (9:1) with a flow rate of 200 mLminꢀ1
.
The samples were dissolved in chloroform, diluted with the mobile phase,
and injected with a 5 mL loop. The exact mass was measured using an
LTQ Orbitrap XL hybrid mass spectrometer (Thermo Fisher Scientific;
Waltham, MA, USA) equipped with an electrospray ion source. The
mobile phase consisted of methanol/water (9:1) with a flow rate of
100 mLminꢀ1. The sample was dissolved in chloroform, diluted with the
mobile phase, and injected using a 2 mL loop. The mass spectra were in-
ternally calibrated by using the known impurities in the mobile phase.
Accurate mass measurements were obtained by EI or ESI mass-spectro-
metric analysis. Combustion analyses were performed by a PE 2400
Series II CHNS/O Analyzer (Perkin Elmer) with an accuracy of CHN de-
(81.4 mg, 0.063 mmol), [PdACHTUNRGTNEUNG(PPh3)4] (11.0 mg, 0.009 mmol, 15 mol%), and
CuI (5.0 mg, 0.028 mmol, 40 mol%); flushed with argon; and then solu-
tion of 15 (100.0 mg, 0.0421 mmol, 1.5 equiv) in diisopropylamine (5 mL),
DMF (5 mL), and THF (5 mL) was added. The reaction mixture was stir-
red at room temperature for 3 days. The solvent was removed in vacuo,
and the crude product was purified by column chromatography on silica
gel (chloroform/hexane 40:60) to provide 3 (101.2 mg, 45%) as a red
amorphous solid. 1H NMR (600 MHz, CDCl3, TMS): d=0.87–0.94 (m,
54H), 1.35–1.47, 1.55–1.65, 2.79–2.86 (3ꢄm, 108H), 3.17, 3.24, 3.27 (3ꢄt,
12H, Jvic =6.5 Hz), 4.15, 4.25, 4.28 (3ꢄt, 12H, Jvic =6.5 Hz), 6.86, 6.87 (2ꢄ
Chem. Eur. J. 2013, 19, 6108 – 6121
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6117

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L. Pospꢁsil, I Stary et al.
m, 4H), 7.089 (s, 2H), 7.090 ppm (dd, 2H,
J
6’,4’ =2.0, J6’,3’ =1.4 Hz);
vacuo, and the crude product was purified by column chromatography on
13C NMR (150.9 MHz, CDCl3, TMS): d=13.61, 13.62, 13.63, 13.7 (4ꢄq),
21.6, 21.68, 21.69 (3ꢄt), 31.7, 31.77, 31.80 (3ꢄt), 34.99, 35.04, 35.2 (3ꢄt),
35.95, 35.97 (2ꢄt), 67.4, 68.6 (2ꢄt), 89.9 (s), 91.6 (s), 109.4, 111.1 (2ꢄs),
114.2 (s), 114.7 (s), 114.9 (d), 116.8 (d), 118.2 (d), 119.0 (d), 125.1, 125.3
(2ꢄs), 127.56, 127.63, 127.8, 130.36, 130.40, 130.43 (6ꢄs), 152.5 (s), 153.1
(s), 153.5 ppm (s); IR (CCl4): n˜ =2961, 2930, 2874, 2862, 2210, 1602, 1578,
1506, 1493, 1465, 1380, 1216, 1027 cmꢀ1; UV/Vis (ClCH2CH2Cl): lmax
(loge)=307 (4.76), 332 (4.72), 350 (4.51), 378 nm (4.47); MS (TOF
MALDI): m/z: 3530 [M+].
silica gel (chloroform/hexane 50:50) to provide 9 (575 mg, 92%) as a red
amorphous solid. H NMR (600 MHz, CDCl3, TMS): d=0.90, 0.91, 0.920,
0.921, 0.924, 0.925 (6ꢄt, 18H, Jvic =7.4 Hz), 1.14 (m, 21H), 1.37–1.48,
1.55–1.65, 2.79–2.84 (3ꢄm, 36H), 3.14 (t, 2H, Jvic =6.6 Hz), 3.15 (t, 2H,
1
J
vic =7.0 Hz), 4.10 (t, 2H, Jvic =6.6 Hz), 4.15 (t, 2H, Jvic =7.0 Hz), 6.80 (d,
1H, J3,4 =8.9 Hz), 6.82 (dd, 1H, J4,3 =8.9, J4,6 =2.9 Hz), 6.97 ppm (d, 1H,
6,4 =2.9 Hz); 13C NMR (150.9 MHz, CDCl3, TMS): d=11.3 (d), 13.6 (q),
J
18.7 (q), 21.6 (t), 31.7 (t), 34.8 (t), 35.0 (t), 35.9 (t), 67.3 (t), 68.4 (t), 95.5
(s), 102.5 (s), 114.4 (s), 114.5 (d), 116.4 (d), 119.5 (d), 125.2, 125.3 (2ꢄs),
127.6, 127.8, 130.2, 130.5 (4ꢄs), 152.3 (s) 154.2 ppm (s); =CS2 not detect-
ed; IR (CCl4): n˜ =2961, 2932, 2875, 2865, 2155, 1603, 1579, 1496, 1465,
1381, 1224, 1031 cmꢀ1; UV/Vis (ClCH2CH2Cl): lmax (loge)=219 (4.79),
262 (4.61), 312 (4.47), 330 nm (4.31); MS (TOF MALDI): m/z: 1342 [M+
]; MS (TOF ESI+): m/z: 1381 ([M+K]+), 1365 ([M+Na]+), 1342 [M+];
HRMS (ESI+): m/z calcd for C57H86O2NaS16Si: 1365.1799 [(M+Na)+];
found: 1365.1821.
1,4-Bis(2-bromoethoxy)-2-iodobenzene (6) and 1,4-bis(2-bromoethoxy)-
2,5-diiodobenzene (7): A round flask was charged with dibromide 4
(9.27 g, 28.6 mmol), KIO3 (6.12 g, 28.6 mmol, 1.0 equiv), iodine (3.63 g,
28.6 mmol, 1.0 equiv) and then acetic acid (300 mL) and conc. H2SO4
(3 mL) were added to the reaction mixture, which was stirred at 758C for
3 h. After cooling, water (100 mL) was added to the reaction mixture, a
saturated solution of Na2SO3 was added, and the organic layer was ex-
tracted with chloroform (5ꢄ200 mL). The organic phases were collected,
washed with water (2ꢄ50 mL), and dried over MgSO4. The solvent was
removed in vacuo, and the crude reaction mixture was purified by
column chromatography on silica gel (chloroform/hexane 30:70) to pro-
vide monoiodide 6 (8.11 g, 65%) as a solid and diiodide 7 (4.27 g, 26%)
as a solid. Compound 6: M.p.: 73–748C (hexane); 1H NMR (500 MHz,
CDCl3, TMS): d=3.60 (t, 2H, Jvic =6.2 Hz), 3.66 (t, 2H, Jvic =6.4 Hz),
4,4’-[(2-Ethynylbenzene-1,4-diyl)bis(oxyethane-2,1-diylsulfanediyl)]-
bis[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiole] (10): A Schlenk flask was
charged with 9 (560 mg, 0.417 mmol), flushed with argon, and solution of
nBu4NF·3H2O (145 mg, 0.459 mmol, 1.1 equiv) in THF (15 mL) was
added. The reaction mixture was stirred at room temperature for 30 min.
The solvent was removed in vacuo, and the crude product was purified
by column chromatography on silica gel (chloroform) to provide 10
1
4.21 (t, 2H, Jvic =6.2 Hz), 4.27 (t, 2H, Jvic =6.4 Hz), 6.78 (d, 1H, J3,4
8.9 Hz), 6.88 (dd, 1H, J4,3 =8.9, J4,6 =3.0 Hz), 7.36 ppm (d, 1H, J6,4
=
(479 mg, 97%) as a red oil. H NMR (500 MHz, CDCl3, TMS): d=0.906,
=
0.908, 0.921, 0.922, 0.926, 0.928 (6ꢄt, 18H, Jvic =7.4 Hz), 1.37–1.48, 1.56–
1.65, 2.80–2.85 (3ꢄm, 36H), 3.14 (t, 2H, Jvic =6.6 Hz), 3.19 (t, 2H, Jvic =
3.0 Hz); 13C NMR (125.7 MHz, CDCl3, TMS): d=28.8 (t), 29.0 (t), 68.7
(t), 70.3 (t), 87.5 (s), 114.3 (d), 115.9 (d), 126.0 (d), 152.0 (s); 153.4 ppm
7.2 Hz), 3.27 (s, 1H), 4.10 (t, 2H, Jvic =6.6 Hz), 4.19 (t, 2H, Jvic =7.2 Hz),
6.83 (d, 1H, J3,4 =9.0 Hz), 6.87 (dd, 1H, J4,3 =9.0, J4,6 =2.9 Hz), 6.99 ppm
(d, 1H, J6,4 =2.9 Hz); 13C NMR (125.7 MHz, CDCl3, TMS): d=13.58,
13.60 (2ꢄq), 21.6 (t), 31.7 (t), 34.6 (t), 35.86 (t), 35.94, 35.96, 35.98 (3ꢄt),
67.3 (t), 68.6 (t), 79.5 s), 81.6 (s), 109.2, 109.4, 111.2 (3ꢄs), 112.9 (s), 114.5
(d), 117.1 (d), 119.6 (d), 125.0, 125.2 (2ꢄs), 127.6, 127.7, 127.78, 127.83,
130.4, 130.7 (6ꢄs), 152.3 (s), 154.0 ppm (s); IR (CCl4): n˜ =3312, 2961,
(s); IR (CCl4): n˜ =2934, 2862, 1598, 1575, 1487, 1456, 1209, 1017 cmꢀ1
;
MS (TOF EI+): m/z (%): 452 ([M+ ] with 81Br81Br, 32), 450 ([M+ ] with
C
C
79Br81Br, 65), 448 ([M+ ] with 79Br79Br, 33), 343 (33), 341 (34), 235 (8),
C
135 (8), 109 (95), 107 (100); HRMS (EI+): m/z calcd for C10H11O279Br2I:
447.8171 [M+]; found: 447.8169. Compound 7: M.p. 1448C (hexane), lit.
141–1428C.[24a]
2930, 2875, 2860, 2108, 1605, 1580, 1497, 1465, 1380, 1223, 1031 cmꢀ1
;
4,4’-[(2-Iodobenzene-1,4-diyl)bis(oxyethane-2,1-diylsulfanediyl)]-
UV/Vis (ClCH2CH2Cl): lmax (loge)=219 (4.82), 263 (4.30), 311 (4.39),
329 nm (4.32); MS (TOF MALDI): m/z: 1186 [M+]; elemental analysis
(%) calcd for C48H66O2S16: C 48.52, H 5.60, S 43.18; found: C 48.26, H
5.48, S 42.95.
bis[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiole] (8): A Schlenk flask was
charged with tetrathiafulvalene 5 (2.72 g, 4.91 mmol. 2.1 equiv), flushed
with argon, and DMF (150 mL) was added. A solution of CsOH·H2O
(861 mg, 5.129 mmol, 2.3 equiv) in methanol (15 mL) was slowly added
to the reaction mixture, which was stirred at room temperature for
30 min. Dibromide 6 (1.0 g, 2.23 mmol) dissolved in DMF (3 mL) was
added to the reaction mixture, which was stirred further at room temper-
ature for 12 h. The solvent was removed in vacuo, and the crude product
was purified by column chromatography on silica gel (chloroform/hexane
60:40) to provide iodide 8 (2.26 g, 79%) as a solid. M.p. 81.0–81.58C
(hexane); 1H NMR (600 MHz, CDCl3, TMS): d=0.89, 0.91, 0.921, 0.922,
0.926, 0.930 (6ꢄt, 18H, Jvic =7.4 Hz), 1.36–1.48, 1.56–1.65, 2.80–2.84 (3ꢄ
m, 36H), 3.13 (t, 2H, Jvic =6.6 Hz), 3.21 (t, 2H, Jvic =6.6 Hz), 4.09 (t, 2H,
4,4’-[(2,5-Diiodobenzene-1,4-diyl)bis(oxyethane-2,1-diylsulfanediyl)]-
bis[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiole] (11): A Schlenk flask was
charged with tetrathiafulvalene 5 (2.59 g, 4.68 mmol, 2.1 equiv), flushed
with argon, and DMF (200 mL) was added. A solution of CsOH·H2O
(0.89 g, 5.29 mmol, 2.4 equiv) in methanol (15 mL) was slowly added to
the reaction mixture, which was stirred at room temperature for 30 min.
Dibromide 7 (1.0 g, 2.23 mmol) dissolved in DMF (50 mL) was added to
the reaction mixture, which was further stirred at room temperature for
12 h. The solvent was removed in vacuo, and the crude product was puri-
fied by column chromatography on silica gel (chloroform/hexane 60:40)
to provide iodide 11 (2.21 g, 70%) as red crystals. M.p. 73–748C
(hexane); 1H NMR (600 MHz, CDCl3, TMS): d=0.90, 0.92, 0.933 (3ꢄt,
18H, Jvic =7.4 Hz), 1.37–1.48, 1.56–1.65, 2.79–2.84 (3ꢄm, 36H), 3.19 (t,
4H, Jvic =6.7 Hz), 4.13 (t, 4H, Jvic =6.7 Hz), 7.19 ppm (s, 2H); 13C NMR
(150.9 MHz, CDCl3, TMS): d=13.59, 13.61, 13.63 (3ꢄq), 21.6 (t), 31.7,
31.75, 31.78 (3ꢄt), 34.8 (t), 35.96, 35.98 (2ꢄt), 69.3 (t), 86.4 (s), 109.5,
111.4 (2ꢄs), 123.4 (d), 124.8 s), 127.6, 127.9, 130.9 (3ꢄs), 152.7 ppm (s);
IR (CCl4): n˜ =2961, 2932, 2875, 2865, 1594, 1576, 1483, 1465, 1458,
J
vic =6.6 Hz), 4.14 (t, 2H, Jvic =6.6 Hz), 6.76 (d, 1H, J3,4 =9.0 Hz), 6.85
(dd, 1H, J4,3 =9.0, J4,6 =2.9 Hz), 7.33 ppm (d, 1H, J6,4 =2.9 Hz); 13C NMR
(150.9 MHz, CDCl3, TMS): d=13.56, 13.59 (2ꢄq), 21.6 (t), 31.7, 31.8 (2ꢄ
t), 34.8, 35.8 (2ꢄt), 35.92, 35.94, 36.0 (3ꢄt), 67.4 (t), 69.2 (t), 87.2 (s),
109.2, 109.5, 111.2, 111.3 (4ꢄs), 113.6 (d), 115.6 (d), 124.8, 125.3 (2ꢄs),
125.7 (d), 127.6, 127.76, 127.78, 130.4, 130.8 (5ꢄs), 151.9 (s), 153.3 ppm
(s); IR (CCl4): n˜ =2961, 2931, 2875, 2864, 1598, 1574, 1478, 1465, 1380,
1212, 1018 cmꢀ1; UV/Vis (CH3CN): lmax (loge)=218 (4.78), 263 (4.34),
308 (4.51), 332 nm (4.31); MS (TOF MALDI): m/z: 1288 [M+]; MS
(TOF ESI+): m/z: 1327 ([M+K]+), 1311 ([M+Na]+), 1288 [M+];
1210 cmꢀ1
, UV/Vis (ClCH2CH2Cl): lmax (loge)=248 (4.62), 308 nm
HRMS (EI+): m/z calcd for C46H65IO2S16
:
1287.9563 [M+]; found:
(4.52); MS (TOF MALDI): m/z: 1414 [M+]; MS (TOF ESI+): m/z: 1453
([M+K]+), 1437 ([M+Na]+), 1414 [M+]; HRMS (ESI+): m/z calcd for
C46H64O2I2NaS16: 1436.8408 [(M+Na)+]; found: 1436.8419.
1287.9555.
ACHTUNGTRENNUNG
A
(9):
A
{[4-Iodo-2,5-bis(2-{[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiol-4-
A
yl]sulfanyl}ethoxy)phenyl]ethynyl}
{[2,5-bis(2-{[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiol-4-yl]sulfanyl}e-
thoxy)benzene-1,4-diyl]diethyne-2,1-diyl}bis[tris(1-methylethyl)silane]
(13): A Schlenk flask was charged with 11 (3.1 g, 2.19 mmol), [Pd(PPh3)4]
(127 mg, 0.110 mmol, 5 mol%), and CuI (62.6 mg, 0.330 mmol,
15 mol%); flushed with argon; and diisopropylamine (20 mL) and DMF
ACHTUNGTRENN[UNG tris(1-methylethyl)]silane (12) and
(26.9 mg, 0.023 mmol, 5 mol%), and CuI (12.7 mg, 0.067 mmol,
15 mol%); flushed with argon; and then diisopropylamine (8 mL) and
DMF (8 mL) were added. (Triisopropylsilyl)acetylene (0.207 mL,
0.932 mmol, 2.0 equiv) was added dropwise over 30 min to the reaction
mixture, which was stirred at 508C for 4 h. The solvent was removed in
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
6118
www.chemeurj.org
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 6108 – 6121

Redox Properties of Mixed-Valence Complexes
FULL PAPER
(20 mL) were added. (Triisopropylsilyl)acetylene (0.536 mL, 2.41 mmol,
1.1 equiv) was added dropwise over 30 min to the reaction mixture,
which was stirred at 508C for 4 h. The solvent was removed in vacuo, and
the crude product was purified by column chromatography on silica gel
(chloroform/hexane 70:30) to provide 12 (1.69 g, 45%) as a red amor-
phous solid, 13 (1.0 g, 30%) as an amorphous solid, and recovered start-
ing diiodide 11 ( 0.65 g, 21%).
Iodide 12: 1H NMR (600 MHz, CDCl3, TMS): d=0.89, 0.915, 0.920,
0.922, 0.925, 0.930 (6ꢄt, 18H, Jvic =7.4 Hz), 1.14 (m, 21H), 1.36–1.48,
1.55–1.65, 2.79–2.85 (3ꢄm, 36H), 3.14 (t, 2H, Jvic =7.0 Hz), 3.22 (t, 2H,
1.54–1.64, 2.80–2.84 (3ꢄm, 72H), 3.18 (t, 2H, Jvic =6.5 Hz), 3.22, 3.242,
3.243 (3ꢄt, 6H, Jvic =6.5 Hz), 3.40 (s, 1H), 4.14 (t, 2H, Jvic =6.5 Hz), 4.22,
4.23, 4.24 (3ꢄt, 6H, Jvic =6.5 Hz), 6.88 (m, 2H), 7.01 (s, 1H), 7.078 (m,
1H), 7.082 ppm (s, 1H); 13C NMR (150.9 MHz, CD2Cl2): d=13.9, 14.0
(2ꢄq), 22.19, 22.21, 22.23 (3ꢄt), 32.35, 32.40, 32.41 (3ꢄt), 35.6, 35.7 (2ꢄ
t), 36.51, 36.53, 36.6 (3ꢄt), 68.1 (t), 69.08, 69.11, 69.2 (3ꢄt), 79.9 (s), 83.6
(d), 90.1 (s), 92.3 (s), 109.7, 109.9 (2ꢄs), 113.5 (s), 114.5 (s), 115.4 (d),
115.8 (s), 117.5 (d), 118.2 (d), 119.3 (d), 119.4 (d), 125.99, 126.00, 126.01
(3ꢄs), 128.25, 128.29, 128.32, 128.36, 128.44, 128.5, 130.9, 131.0, 131.1,
131.3 (10ꢄs), 153.2 (s), 153.5 (s), 154.1 (s), 154.4 ppm (s); IR (CCl4): n˜ =
3312, 2961, 2932, 2875, 2864, 2418, 1601, 1577, 1495, 1465, 1380, 1221,
1031 cmꢀ1; UV/Vis (ClCH2CH2Cl): lmax (loge)=273 (4.69), 298 (4.75),
312 (4.69), 333 nm (4.64); MS (TOF MALDI): m/z: 2370 [M+].
J
vic =6.6 Hz), 4.12 (t, 2H, Jvic =7.0 Hz), 4.14 (t, 2H, Jvic =6.6 Hz), 6.84 (s,
1H), 7.27 ppm (s, 1H); 13C NMR (150.9 MHz, CDCl3, TMS): d=11.3 (d),
13.56, 13.59, 13.60, 13.61 (4ꢄq), 18.7 (q), 21.61, 21.63 (2ꢄt), 31.72, 31.74,
31.8 (3ꢄt), 34.7 (t), 35.0 (t), 35.9, 36.0 (2ꢄt), 68.5 (t), 69.2 (t), 87.5 (s),
97.0 (s), 101.8 (s), 109.2, 109.6, 111.2, 111.3 (4ꢄs), 114.3 (s), 117.0 (d),
124.3 (d), 124.8 (s), 125.3 (s), 127.60, 127.63, 127.9, 130.5, 130.7 (5ꢄs),
151.6 (s), 154.5 ppm (s); IR (CCl4): n˜ =2961, 2931, 2875, 2156, 1587, 1483,
1463, 1373, 1365, 1214, 1023 cmꢀ1; UV/Vis (ClCH2CH2Cl): lmax (loge)=
219 (4.05), 270 (4.78), 313 (4.60), 330 nm (4.53); MS (TOF MALDI): m/
z: 1468 [M+]; MS (TOF ESI+): m/z: 1507 ([M+K]+), 1491 ([M+Na]+),
1468 [M+]; HRMS (ESI+) m/z calcd for C57H85IO2NaS16Si: 1491.0778
[(M+Na)+]; found: 1491.0787.
Acknowledgements
This research was supported by the European Commission under Grant
No. FP7-FUNMOL 213382; the Czech Science Foundation under Grant
Nos P207/10/2214, 203/09/1802, and 203/09/0705; the Ministry of Educa-
tion, Youth and Sports of the Czech Republic under Project No.
7E09054; the Grant Agency of the Academy of Sciences of the Czech
Republic under Grant No. IAA400400802; and the Institute of Organic
Chemistry and Biochemistry, Academy of Sciences of the Czech Repub-
lic (RVO: 61388963).
Bisethynylated product 13: 1H NMR (600 MHz, CDCl3, TMS): d=0.90,
0.918, 0.923 (3ꢄt, 18H, Jvic =7.4 Hz), 1.15 (m, 42H), 1.37–1.47, 1.56–1.64,
2.82 (3ꢄm, 36H), 3.16 (t, 4H, Jvic =6.9 Hz), 4.13 (t, 4H, Jvic =6.9 Hz),
6.88 ppm (s, 2H); 13C NMR (150.9 MHz, CDCl3, TMS): d=11.3 (d),
13.56, 13.58, 13.59 (3ꢄq), 18.8 (q), 21.59, 21.62, 21.63 (3ꢄt), 31.72, 31.73
(2ꢄt), 34.9 (t), 35.9, 35.96, 35.97 (3ꢄt), 68.3 (t), 97.4 (s), 102.3 (s), 109.3,
111.0 (2ꢄs), 114.6 (s), 117.8 (d), 125.3 (s), 127.6, 127.9, 130.2 (3ꢄs),
153.7 ppm (s); IR (CCl4): n˜ =2961, 2932, 2875, 2866, 2153, 1603, 1587,
1496, 1465, 1381, 1367, 1221, 1027 cmꢀ1; UV/Vis (ClCH2CH2Cl): lmax
(loge)=289 (3.85), 334 nm (4.59); MS (TOF MALDI): m/z: 1522 [M+];
MS (TOF ESI+): m/z: 1461 ([M+K]+), 1445 ([M+Na]+), 1422 [M+];
HRMS (EI+): m/z calcd for C68H106O2NaS16Si2: 1545.3155 [(M+Na)+];
found: 1545.3142.
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{[4-
l}ethoxy)phenyl]ethynyl}-2,5-bis(2-{[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-
dithiol-4-yl]sulfanyl}ethoxy)phenyl]ethynyl}[tris(1-methylethyl)]silane]
(14): A Schlenk flask was charged with 12 (837 mg, 0.569 mmol), [Pd-
(PPh3)4] (98.6 mg, 0.085 mmol, 15 mol%), and CuI (43.4 mg, 0.222 mmol,
ACHTUNGTRENNUNG{[2,5-Bis(2-{[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiol-4-yl]sulfany-
[4] a) J. M. Tour, Molecular Electronics, World Scientific, Singapore,
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AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
40 mol%); flushed with argon; and then a solution of 10 (675 mg,
0.569 mmol, 1.0 equiv) in diisopropylamine (10 mL), DMF (10 mL), and
THF (10 mL) was added. The reaction mixture was stirred at room tem-
perature for 3 days. The solvent was removed in vacuo, and the crude
product was purified by column chromatography on silica gel (chloro-
form/ethyl acetate 85:15) to provide 14 (647 mg, 45%) as a red amor-
phous solid. 1H NMR (500 MHz, CDCl3, TMS): d=0.86–0.94 (m, 36H),
1.15 (m, 21H), 1.36–1.48, 1.54–1.66, 2.78–2.85 (3 ꢄ m, 72H), 3.12–3.26
(m, 8H), 4.12–4.26 (m, 8H), 6.86 (m, 2H), 6.95 (s, 1H), 7.03 (s, 1H),
7.08 ppm (m, 1H); 13C NMR (125.7 MHz, CDCl3, TMS): d=11.4 (d),
13.60, 13.62 (2ꢄq), 18.8 (q), 22.7 (t), 31.8 (t), 34.9, 35.0, 35.1, 35.2 (4ꢄt),
35.96, 35.99, 36.00 (3ꢄt), 67.4, 68.3, 68.6, 68.8 (4ꢄt), 89.8 (s), 91.5 (s),
97.6 (s), 104.5 (s), 109.4, 109.5 (2ꢄs), 111.1 (s), 114.2 (s), 114.5 (d), 114.8
(s), 116.9 (d), 117.6 (d), 118.7 (d), 119.0 (d), 125.0, 125.1, 125.4 (3ꢄs),
127.6, 127.8, 127.9, 130.1, 130.4, 130.5 (7ꢄs), 152.5 (s), 153.0 (s), 153.5 (s),
154.0 ppm (s); IR (CCl4,): n˜ =2961, 2931, 2874, 2865, 2151, 1603, 1579,
1503, 1493, 1465, 1380 cm ꢀ1; UV/Vis (ClCH2CH2Cl): lmax (loge)=226
(4.79), 301 (4.82), 333 nm (4.76); MS (TOF MALDI): m/z: 2526 [M+].
4-{[2-(2-{[2,5-Bis(2-{[4’,5,5’-tris(butylsulfanyl)-2,2’-bi-1,3-dithiol-4-yl]sulfa-
nyl}ethoxy)phenyl]ethynyl}-5-ethynyl-4-(2-{[4’,5,5’-tris(butylsulfanyl)-2,2’-
bi-1,3-dithiol-4-yl]sulfanyl}ethoxy)phenoxy)ethyl]sulfanyl}-4’,5,5’-tris(bu-
tylsulfanyl)-2,2’-bi-1,3-dithiole (15): A Schlenk flask was charged with 14
(610 mg, 2.41 mmol), flushed with argon, and a solution of nBu4NF·3H2O
(83.8 mg, 0.266 mmol, 1.1 equiv) in THF (15 mL) was added. The reac-
tion mixture was stirred at room temperature for 30 min. The solvent was
removed in vacuo, and the crude product was purified by column chro-
matography on silica gel (chloroform) to provide 15 (561 mg, 98%) as a
red oil. 1H NMR (600 MHz, CD2Cl2): 0.86–0.93 (m, 36H), 1.34–1.48,
Chem. Eur. J. 2013, 19, 6108 – 6121
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6119

ˇ
´
L. Pospꢁsil, I Stary et al.
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Chem. Eur. J. 2013, 19, 6108 – 6121

Redox Properties of Mixed-Valence Complexes
FULL PAPER
Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A.
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Received: September 13, 2011
Revised: January 8, 2013
Published online: March 13, 2013
Chem. Eur. J. 2013, 19, 6108 – 6121
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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