Synthesis and properties of end-capped bis(oligothienyl) sulfides

Article abstract of DOI:10.1139/V08-128

The synthesis, and the optical and electrochemical properties, of a series of mesitylthio (MesS-) end-capped bis(oligothienyl) sulfides are presented. The target compounds were synthesized principally by convergent protocols, whereby a series of short thiophene oligomers bearing one terminal mesitylthio (MesS-) substituent were first assembled by metal-catalyzed cross-coupling reactions and then coupled via divalent sulfur through reactions with bis(phenylsulfonyl) sulfide. The spectroscopic and electrochemical features of the bis(oligothienyl) sulfides are qualitatively similar to those of the related mesitylthio-capped fully conjugated oligothiophenes, suggesting that the degree of electronic communication between the two oligothiophene chromophores in the bis(oligothienyl) sulfides is low. Cyclic voltammetry studies on the bis(oligothienyl) sulfides reveal that these species can be reversibly oxidized to radical cations, but the reversibility of subsequent oxidations depends on oligothienyl chain length and the presence and position of more electron-rich ethylenedioxythiophene (EDOT) groups. In general, the bis(oligothienyl) sulfides possess fewer than the expected number of reversible oxidations based on comparisons with their corresponding mesitylthio-capped fully conjugated oligothiophenes; excessive charge accumulation at or near the central linking sulfur atom is believed to be responsible for the irreversible behavior. Analysis of the irreversible voltammetric response of one of the bis(oligothienyl) sulfides leads to the suggestion of a decomposition mechanism for the cationic species involving carbon-sulfur bond cleavage and subsequent coupling of thiophene fragments -a finding with potential implications for the poor environmental stability of doped poly(p-phenylene sulfide), one of the prototypical conducting polymers.

Full text of DOI:10.1139/V08-128

982
Synthesis and properties of end-capped
bis(oligothienyl) sulfides
Daniel J. T. Myles, M’hamed Chahma, and Robin G. Hicks
Abstract: The synthesis, and the optical and electrochemical properties, of a series of mesitylthio (MesS-) end-capped
bis(oligothienyl) sulfides are presented. The target compounds were synthesized principally by convergent protocols,
whereby a series of short thiophene oligomers bearing one terminal mesitylthio (MesS-) substituent were first assem-
bled by metal-catalyzed cross-coupling reactions and then coupled via divalent sulfur through reactions with
bis(phenylsulfonyl) sulfide. The spectroscopic and electrochemical features of the bis(oligothienyl) sulfides are qualita-
tively similar to those of the related mesitylthio-capped fully conjugated oligothiophenes, suggesting that the degree of
electronic communication between the two oligothiophene chromophores in the bis(oligothienyl) sulfides is low. Cyclic
voltammetry studies on the bis(oligothienyl) sulfides reveal that these species can be reversibly oxidized to radical cat-
ions, but the reversibility of subsequent oxidations depends on oligothienyl chain length and the presence and position
of more electron-rich ethylenedioxythiophene (EDOT) groups. In general, the bis(oligothienyl) sulfides possess fewer
than the expected number of reversible oxidations based on comparisons with their corresponding mesitylthio-capped
fully conjugated oligothiophenes; excessive charge accumulation at or near the central linking sulfur atom is believed
to be responsible for the irreversible behavior. Analysis of the irreversible voltammetric response of one of the
bis(oligothienyl) sulfides leads to the suggestion of a decomposition mechanism for the cationic species involving car-
bon–sulfur bond cleavage and subsequent coupling of thiophene fragments — a finding with potential implications for
the poor environmental stability of doped poly(p-phenylene sulfide), one of the prototypical conducting polymers.
Key words: conjugated materials, conducting polymers, oligothiophenes, electronic communication.
Résumé : On a effectué la synthèse d’une série de bis(oligothiényl)sulfures fermés aux extrémités par des groupes mé-
sitylthio (MesS–) et on en a déterminé les propriétés optiques et électrochimiques rapportées ici. Les produits recher-
chés ont été synthétisés par des protocoles convergents dans lesquels une série d’oligomères courts du thiophène
portant un substituant terminal mésitylthio sont d’abord assemblés par des réactions de couplage croisées catalysées par
un métal avant d’être couplés avec du soufre bivalent par le biais de réactions avec du sulfure de bis(phénylsulfonyle).
Les caractéristiques spectroscopiques et électrochimiques des sulfures de bis(oligothiényle) sont qualitativement sembla-
bles à celles des oligothiophènes apparentés complètement conjugués et fermés aux extrémités par des groupes mésityl-
thio; ceci suggère que le degré de communication électronique est faible entre les deux chroromophores
oligothiophènes des sulfures d’oligothiényle. Les études de voltampérométrie cyclique sur les sulfures de bis(oligothié-
nyle) révèlent que ces espèces peuvent être oxydées d’une façon réversible en cations radicaux, mais que la réversibi-
lité des oxydations subséquentes dépend de la longueur de la chaîne oligothiényle et de la présence et de la position de
groupes éthylènedioxythiophène (EDOT) plus riches en électrons. En général, les sulfures de bis(oligothiényle) possè-
dent des nombres d’oxydation réversibles inférieurs à ceux qui pourraient être attendus sur la base de comparaison
avec les oligothiophènes apparentés complètement conjugués et fermés aux extrémités par des groupes mésitylthio;
l’accumulation excessive de charge au ou près de l’atome de soufre central pourrait être responsable de ce comporte-
ment irréversible. Une analyse de la réponse voltampérométrique irréversible d’un des sulfures de bis(oligothiényle)
conduit à suggérer un mécanisme de décomposition pour l’espèce cationique impliquant une rupture de la liaison car-
bone-soufre et un couplage subséquent des fragments thiophènes, une observation qui présente des implications poten-
tielles pour la mauvaise stabilité environnementale du poly(sulfure de p-phénylène) dopé, un des prototypes de
polymères conducteurs.
Mots-clés : matériaux conjugués, polymères conducteurs, oligothiophènes, communication électronique.
[Traduit par la Rédaction] Myles et al. 991
Received 11 June 2008. Accepted 26 July 2008. Published on the NRC Research Pres Web site at canjchem.nrc.ca on
13 September 2008.
D.J.T. Myles, M. Chahma,1 and R.G. Hicks.2 Department of Chemistry, University of Victoria, Victoria, BC, V8W 3V6, Canada.
1Present address: Department of Chemistry and Biochemistry, Laurentian University, Sudbury, ON P3E 2C6, Canada.
2Corresponding author (e-mail: rhicks@uvic.ca).
Can. J. Chem. 86: 982–991 (2008)
doi:10.1139/V08-128
© 2008 NRC Canada

Myles et al.
983
Scheme 1.
Introduction
The development of structure–property (electrochemical,
spectroscopic, conducting, emissive) relationships for π-
conjugated oligomers is a well-entrenched field of study (1).
Many of these studies have produced important insights for
the less well-defined — but technologically important —
conjugated polymers. For example, the notion of π stacking
as a mechanism for charge transport in conducting polymers
was largely facilitated by electrochemical and spectroscopic
studies on oligothiophenes (2). In addition, many conjugated
oligomers are emerging as viable components of new elec-
tronic materials in their own right (3).
Scheme 2.
The diversity of functional polymers has increased greatly
through the incorporation of inorganic segments into other-
wise conventional organic systems. Many of these hybrid
polymers are based on transition metals, (4), but there is a
growing body of “organomain group” polymers containing
p-block elements in the main chain (5). Polyaniline can be
considered as a prototypical example (6), but polymers con-
taining group 13 (7), 14 (8), or 15 (9) elements have been
developed as well. Polymers containing group 16 elements
in the main chain have a more sporadic history. Poly(thiazyl)
(SN)x is noteworthy for its conducting and superconducting
properties and as the forerunner to the field of organic con-
ducting polymers (10). Poly(p-phenylene sulfide) (PPS) was
one of the first conducting doped polymers and the first
based on a commodity polymer (11). This material suffers
from serious environmental stability problems in its oxidized
(doped) forms. Related sulfur-bridged polymers are similarly
unstable when doped (12). Nakayama and co-workers (13)
have reported the synthesis of oligomeric analogues of PPS
in which the p-phenylene is replaced by 2,5-thiophenediyl;
no physical properties were presented. Finally, Manners and
co-workers (14) have prepared poly(thiaferrocenes) via the
ring-opening polymerization of [1]thiaferrocenophanes; the
electronic properties of short, well-defined oligomers were
also investigated as models for the polymer — a rare exam-
ple of the application of the “oligomers approach” in conju-
gated main group polymer chemistry.
capped by SR groups and the polymers in which thiophene
chromophores are linked by sulfur prompted us to prepare a
SMes
series of model systems based on MesSTnSTn
where
TnSTn is a bis(oligothienyl) sulfide segment — essentially a
segment of the polymers — in which both terminal positions
are also capped by SR groups to prevent electropolymeriza-
tion (as opposed to the uncapped TnSTn compounds, which
upon electro-oxidation, polymerize to (TnSTn)m.
Results and discussion
Synthesis
Scheme 1 outlines the general synthetic route to the
mesitylthio end-capped bis(oligothienyl) sulfides. The target
compounds were assembled by a convergent protocol,
whereby two equivalents of an unsymmetrically substituted
oligothiophene were metallated and then reacted with
bis(phenylsulfonyl) sulfide; this sulfur transfer reagent has
proven to be better than sulfur dichloride (SCl2), for which
these reactions typically proceed in low yield (14, 19, 20).
(2-Mesitylthio)thiophene 1 was prepared by the reaction of
2-thienylmagnesium bromide with 2-mesitylenesulfenyl
chloride (MesSCl). Subsequent lithiation of 1 with 1 equiv.
of BuLi, followed by treatment with 0.5 equiv. of (PhSO2)2S
We have been investigating small molecule and polymeric
conjugated oligothiophene–sulfur materials. We have dem-
onstrated that mesitylthio- (MesS-) capped oligothiophenes
provided the desired sulfide MesSTSTSMes in 80% yield. The
SMes
MesSTn
(n = 1–4) can be reversibly oxidized to radical
bis(bithienyl) sulfide MesST2ST2
was prepared by
SMes
cations and dications, some of which exhibit exceptional sta-
bility (15). The stability of the oxidized forms arises from
both the blocking of the terminal (α and ω) carbon atoms of
the oligothiophene segment as well as the strong π-donating
nature of the thioether (-SR) group. We separately described
several bis(oligothienyl) sulfides that could be electropoly-
merized to give poly(oligothienyl sulfide)s in which conju-
gated oligothiophene segments are linked together by
divalent sulfur (16, 17); related poly(aryl sulfide)s and disul-
fides have been subsequently reported by other groups (18).
The electrochemical properties of our poly(oligothienyl
sulfide)s varied based on the structure of the monomer; gen-
erally, the polymers based on the electron-rich ethylene-
dioxythiophene (EDOT) building block showed reversible
redox behavior, but those based on unsubstituted thiophenes
showed significant irreversibility in their oxidative electro-
chemistry. The apparent differences between the oligomers
lithiation of bithiophene 2 (synthesized from 2,2′-bithio-
phene by deprotonation and reaction with MesSCl) and sub-
sequent quenching with (PhSO2)2S. The bis(terthienyl)
SMes
sulfide MesST3ST3
required a slightly more elaborate
route. Compound 2 was selectively brominated at the other
terminal position with NBS in DMF (21) and then subse-
quently coupled with 2-tributylstannylthiophene using
Pd(PPh3)4 as a catalyst to give 3 in 88% yield. Terthiophene
SMes
3 was converted to the targeted sulfide MesST3ST3
by
lithiation and quenching with (PhSO2)2S.
Variants of MesSTSTSMes were also targetted in which the
parent thiophene unit is replaced with the well-known (22)
electron-rich 3,4-ethylenedioxythiophene moiety. However,
the preparation of MesSESESMes by a convergent strategy was
abandoned owing to difficulties in preparing the necessary
precursor, namely, 2-mesitylthio-3,4-ethylenedioxythiophene
4. The reaction of α-lithiated EDOT with 1 equiv. of
© 2008 NRC Canada

984
Can. J. Chem. Vol. 86, 2008
Table 1. Lowest energy electronic transitions for bis(oligothienyl) sulfides and related compounds
in various charge states.
Neutral
Radical cation
Dication
Compound
λmax (nm)
λmax (nm)
λmax (nm)
Reference
TST
268
310
302
335
—
—
—
—
—
17
MesSTSTSMes
MesSTSMes
T2ST2
555, 896
412, 638
—
This work
15
15
MesST2ST2
MesST2
MesST4
MesST3ST3
MesST3
360
358
420
395
386
563, 865
572, 905
756, 1420
—
—
This work
SMes
SMes
520
893
680a
696
15
SMes
15
SMes
This work
15
SMes
676, 1170
ESE
270
309
305
362
—
—
—
—
—
17
MesSESESMes
MesSESMes
520, 860
405, 551
509, 900
This work
15
15
MesSE2
SMes
ETSTE
345
375
458
345
375
431
—
—
—
—
—
17
MesSETSTESMes
MesSETTESMes
TESET
788, 892
860
—
—
900
This work
15
17
This work
15
MesSTESETSMes
MesSTEETSMes
725, 1241
721, 1240
monosubstituted 8 in 66% yield. Finally, lithiation of 8, fol-
lowed by introduction of sulfur with (PhSO2)2S, afforded
MesSETSTESMes, in which the EDOT groups occupy the
outer positions of the conjugated moieties, in 72% yield.
Scheme 3.
Electronic spectra
The solution spectra of the bis(oligothienyl) sulfides, to-
gether with the fully conjugated bis(mesitylthio)
oligothiophenes previously reported (15), provide some in-
sights into how the terminal and internal sulfur atoms per-
turb the π chromophores of oligothiophenes. The solution
absorption spectral data are summarized in Table 1.
We have previously shown that mesitylthio (MesS-) sub-
stituents at the terminal (α, ω) positions cause moderate
(~30 nm) red shifts in the lowest energy electronic transi-
tions of oligothiophenes. This effect is apparent in the cur-
rent series of bis(thienyl) sulfides. For example, the low
energy transitions for the uncapped bis(thienyl) sulfides TST
and T2ST2 are at 268 and 335 nm, respectively; the maxima
for the mesitylthio-capped analogues MesSTSTSMes and
SMes
MesST2ST2
are 310 and 360 respectively. The incorpora-
tion of ethylenedioxy groups on the β-carbons also produces
predictably moderate red shifts. On the other hand, the inter-
nal bridging sulfur units have little effect on extending the
overall conjugation length. For example, λmax for
MesSCl preferentially gives the disubstituted compound 5
over the monosubstituted compound 4 (Scheme 2) (15).
The preparation of MesSESESMes was accomplished by
dilithiating bis(3,4-ethylenedioxythienyl) sulfide (6) ESE
followed by treatment with 2 equiv. of MesSCl (Scheme 3).
Two isomeric EDOT containing bis(bithienyl) sulfide deriva-
tives were also prepared using convergent protocols as
shown in Scheme 3. Lithiation of 6 (15) with n-BuLi fol-
lowed by quenching with (PhSO2)2S gave MesSTESETSMes–
with two EDOTs connected to the central sulfide, in 68%
yield. The isomeric species required building block 8, which
was made by lithium–halogen exchange (BuLi) of 7 (25),
followed by reaction with MesSCl to give the
MesST2ST2SMes, with two single bithiophenes flanking a cen-
SMes
tral sulfur, is only red-shifted by 2 nm relative to MesST2
.
which has a single bithiophene chromophore. In contrast,
λ
max for MesST4SMes, a fully conjugated tetrathiophene, is red-
shifted by 50 nm relative to MesST2ST2SMes. Comparisons be-
tween other analogous pairs of oligomers (e.g., MesSTSTSMes
vs. MesSTSMes MesSESESMes vs. MesSESMes) reveal similar trends;
;
overall the lowest energy absorption maxima is dominated
by the nature of the individual thienyl segment: there is little
additional delocalization between the two oligomeric units
© 2008 NRC Canada

Myles et al.
985
Table 2. Oxidation potentials of bis(oligothienyl) sulfides and re-
lated compounds as determined by cyclic voltammetry experi-
ments (see Experimental section for details).
through the central sulfur bridge. This is further corrobo-
rated by the fact that the extinction coefficients of the
SMes
capped bis(thienyl) sulfides MesSTnSTn
(see Experimen-
tal section) are roughly twice as large as the corresponding
Compound
MesSTSTSMes
Oxidation potentials (V)
Reference
coefficients of the straight conjugated capped oligomers
SMes
MesSTn
(15). Thus, although the linking sulfur atom has
+1.14, +1.43*
1.05
+0.99, +1.15, +1.50
This work
(15)
This work
MesSTSMes
two lone pairs of electrons, one of which in principle could
engage in π overlap with the oligothienyl π system, the spec-
troscopic data suggests that the orientation of the thienyl
units with respect to the S lone pair orbitals is not optimal
for overlap and (or) π donation by S into what is already an
electron-rich π system is ineffective.
MesST2ST2
SMes
MesST2
+0.87, +1.25
(15)
SMes
MesST4
+0.83, +0.91
(15)
SMes
MesST3ST3
+0.91, +1.02, +1.13. +1.49*
+0.86, +1.02
This work
(15)
SMes
MesST3
SMes
Electronic spectra of the oxidized forms of several
mesitylthio-capped oligothiophenes and bis (oligothienyl)
sulfides were obtained either by electrochemical oxidation
of the neutral species in solution or by chemical oxidation
with NOBF4. The cationic states of the “uncapped” oligo-
mers are too reactive to observe, as they undergo the ex-
pected rapid coupling to yield polymers (16). Spectra of the
MesSESESMes
+0.90, +1.14*
0.87
+0.57, +0.94
This work
(15)
(15)
MesSESMes
SMes
MesSE2
MesSETSTESMes
MesSETTESMes
MesSTESETSMes
MesSTEETSMes
+0.78, +0.93, +1.31, +1.70*
+0.61, +0.66
+0.78, +0.97*
This work
(15)
This work
(15)
SMes
cationic α,ω-bis-(mesitylthio) oligothiophenes MesSTn
+0.49, +0.73
(n = 1–4) and MesSESMes were obtained by chemical oxida-
tion with NOBF4 in CH2Cl2. Stable radical cations could be
generated for all of these compounds, in accord with closely
related bis(mesitylthio)oligothiophenes reported by us (15).
Note: All potentials are given as formal potentials (E1/2) vs. SCE except
for numbers denoted with an asterisk (*), which correspond to anodic
peak potentials for irreversible oxidations.
sulfide MesSESESMes radical cation absorbs at 520 and
860 nm.
Comparisons between the various compounds containing
Radical cation spectra could not be obtained for
SMes
MesSETSTESMes or MesST3ST3
owing to the small differ-
ence between first and second oxidation potentials for these
compounds (see below); for the former, this problem is com-
pounded by the instability of the dicationic state.
conjugated bithiophene chromophores are more complex.
SMes
The radical cations of MesST2ST2
(563 and 865 nm) and
MesST2SMes (572 and 905 nm) have similar spectroscopic fea-
tures, and in fact the absorption maxima of the former are
actually slightly blue-shifted with respect to the latter. This
indicates that little to no electronic coupling occurs between
The electronic absorption spectrum for the radical cation
of MesSTSMes has two absorption maxima at 412 and 638 nm.
The corresponding EDOT-based compound MesSESMes also
has peaks at 405 and 551 nm. Within the thiophene series
MesSTnSMes (n = 1–4), as the thiophene chain length increases
there is a shift to lower energies for the radical cation series
and the (more limited) dication spectral series. The spectral
features of these radical cations do not show any dependence
on temperature (between –5 and +20 °C) or concentration
(between 10–5 and 10–4 mol/L), suggesting that radical cat-
ion π dimerization does not occur. Dimer formation is most
likely suppressed because of the steric hindrance of the cap-
ping mesityl groups.
Spectra of several of the capped bis(oligothienyl) sulfides
in cationic states were also obtained. The radical cation of
bis(thienyl) sulfide MesSTSTSMes has two major bands at 555
and 896 nm. These are significantly red-shifted in compari-
son to the radical cation spectrum of MesSTSMes (412 and
638 nm). This sharply contrasts comparisons between the
two neutral compounds, which are nearly identical to one
another. This suggests that there may be a strong interaction
between the two thiophene units via the sulfur bridge for
MesSTSTSMes in its radical cation state. This may arise from
the fact that removal of an electron from the oligothiophene
renders it a more electron-deficient π system, thereby facili-
tating stabilization (and hence delocalization) from a sulfur
lone pair orbital. π-Dimer bands can be ruled out, based on
the fact that the intensities of the 555 and 896 nm peaks
show neither a concentration nor temperature dependence.
Similar comparisons can be made for the EDOT analogues
of these species: the radical cation of MesSESMes has peaks at
405 and 551 nm, whereas bis(3,4-ethyelenedioxythienyl)
adjacent bithiophenes via the sulfur bridge, presumably be-
SMes
cause the radical cation in MesST2ST2
is strongly local-
ized in the bithiophene cores. However, this picture is
complicated upon consideration of the spectrum of the radi-
cal cation of MesSTESETSMes; the absorption maxima (725
and 1241 nm) are dramatically red-shifted compared with
the all-thiophene analogue MesST2ST2SMes. This may suggest
that the placement of the more electron-rich EDOT groups
on the “internal” positions serves to concentrate spin and
(or) charge closer to the central sulfur linker, thereby facili-
tating more effective delocalization.
The properties of the mesitylthio- capped model com-
pounds can also be compared with the previously reported
poly(oligothienyl sulfide)s. As a representative example,
SMes
MesSE2
has a S-EE-S unit that is also present in the poly-
mer poly(ESE). Neutral poly(ESE) has its absorption max-
SMes
ima at 455 and 484 nm, whereas MesSE2
absorbs at
362 nm. The fact that poly(ESE) has its absorptions red-
SMes
shifted with respect to MesSE2
provides evidence that the
biEDOT units are electronically coupled in the neutral poly-
mer; in this regard the “capped” molecules are analogous to
the “uncapped” monomers (i.e., ESE) that were actually em-
ployed to synthesize the polymers. Furthermore, the doped
polymer has absorptions at 605 and 1020 nm whereas the
SMes
radical cation of MesSE2
has two absorption bands at 509
and 900 nm. The red-shift is most likely due to strong
intrachain electronic coupling of the biEDOT groups in the
polymer, although interchain effects cannot be ruled out.
© 2008 NRC Canada

986
Can. J. Chem. Vol. 86, 2008
Fig. 1. Cyclic voltammograms of (a) MesSTSTSMes (first oxida-
tion only), (b) MesSTSTSMes (full scan), (c) MesST2ST2SMes; and
(d) MesST3ST3SMes. The redox process labelled with an asterisk in
(c) corresponds to the ferrocene/ferrocenium redox couple (added
as a reference). See Experimental section for details.
Electrochemical studies
The redox properties of the bis(thienyl) sulfides were
studied using cyclic voltammetry. The results of these
studies are summarized in Table 2, which also contains elec-
trochemical data for the previously reported bis(mesitylthio)-
capped oligothiophenes (15). Our previous work on the lat-
ter compounds established that the mesitylthio substituents
provide stability to the oxidized forms of the oligothio-
phenes. This stability arises in part by “blocking” the α and
ω positions, thereby preventing polymerization (via oxidative
coupling) of the thiophene radical cation; the π-donating ef-
fect of the sulfur substituent also contributes to the stability
of the cationic forms of the oligomers. These effects are also
manifested in the bis(thienyl) sulfide compounds presented
here. All of the new compounds exhibit at least one chemi-
cally reversible oxidation process (equivalence of anodic and
cathodic peak currents, peak potentials that are scan-rate-
independent); the anodic and cathodic peak separations for
each compound lie in the range of 60–90 mV, which is com-
parable to that of the ferrocene/ferrocenium redox couple
under the same experimental conditions and suggestive of
quasi-reversible electrochemical behavior. Many of the
bis(thienyl) sulfides can be reversibly oxidized to dications
or even trications in a few cases.
In general, the oxidation potentials of oligothiophene are
influenced by their chain length; longer oligomers are oxi-
dized at lower potentials. Among the homologous series of
SMes
bis(thienyl) sulfides MesSTnSTn
(n = 1–3), this trend
to radical cations and dications, but the corresponding
SMes
bis(thienyl) sulfides MesSTnSTn
(n = 2, 3) have fewer
holds; however, the change in first oxidation potential as a
function of chain length for this series is comparable to the
corresponding changes in the fully conjugated thiophenes.
The first oxidation potential of MesSTSMes is +1.05 V. Ex-
tending the conjugated segment from one to two thiophenes
(i.e., MesST2SMes, E1° = +0.87 V) leads to a drop in first oxi-
than the expected four reversible oxidation waves: the
SMes
bis(bithienyl) sulfide MesST2ST2
has two reversible and
one quasi-reversible wave, and the bis(terthienyl) sulfide
SMes
MesST3ST3
has three very closely spaced reversible oxi-
dations and a fourth irreversible one at higher potentials.
Overall, the charge storage capacity of these compounds is
relatively limited compared with the parent, fully conjugated
counterparts.
dation potential of 0.18 V. Analogous comparisons between
SMes
MesSTSTSMes (E1° = +1.14 V) and MesST2ST2
(E1° =
+0.99 V) produce qualitatively similar results: the first oxi-
dation potential for the longer oligomers is +0.15 V lower.
The
MesSTESETSMes and MesSETSTESMes contain the same fun-
damental chromophore bis(thioether) substituted
two
mixed
thiophene–EDOT
compounds
SMes
Thus, although MesST2ST2
is two thiophene units longer
than MesSTSTSMes, the comparative electrochemical proper-
ties (in conjunction with the electronic spectra, see above)
suggest that the connection of two thiophene segments by a
divalent sulfur linker does not lead to an extension of effec-
tive conjugation length.
—
a
unsymmetric bithiophene RSETSR. Given the analyses of the
electrochemical properties of the other bis(thienyl) sulfides,
it is not surprising that the first oxidation of MesSTESETSMes
and MesSETSTESMes occur at the same potential. However,
the electrochemical behavior of these two isomers beyond
the first oxidations differs markedly. The former compound
can only be reversibly oxidized to a radical cation, whereas
the latter has two fully reversible oxidations and a third that
is quasi-reversible (tending towards reversibility at high scan
rates); it is not until the fourth oxidation that decomposition
occurs. The differences in electrochemical responses be-
tween these compounds can be understood by consideration
of the location of the more electron-rich EDOT moieties.
MesSTESETSMes has the EDOTs directly flanking the central
sulfur atom. The first two oxidations correspond to electron
removal from each of the “ET” moieties, but with the spin
and charge on both components more localized on the
EDOT moieties. Thus the dication of this compound appears
to have sufficient spin and charge concentration to render it
unstable (a proposal of how this compound may degrade is
provided below). In contrast, the isomeric MesSETSTESMes
Given that the bis(thienyl) sulfides contain two thiophene
chromophores sharing a common linker, the electrochemical
responses of these might naïvely be expected to consist of
the sum of the individual processes associated with each
SMes
thiophene segment, i.e., MesSTnSTn
should possess twice
as many oxidations as MesSTnSMes. This is not the case.
SMes
Figure 1 shows the cyclic voltammograms of MesSTnSTn
(n = 1–3). For example, MesSTSMes and MesSESMes both pos-
sess one reversible oxidation process. Given that the
bis(thienyl) sulfide analogues MesSTSTSMes and MesSESESMes
contain two “monothiophenes”, these compounds might be
expected to have two oxidation waves corresponding to one-
electron removal from each of the two thiophene units.
However, both of these can only be reversibly oxidized to
radical cations; the second oxidation process in both com-
pounds is irreversible. In a similar vein, all of the other “par-
SMes
ent” oligomers MesSTn
(n > 1) can be reversibly oxidized
© 2008 NRC Canada

Myles et al.
987
Fig. 2. Multiple cycle CV of MesSTESETSMes. The redox process
at +0.5 V vs SCE appears on the second anodic sweep.
two oligothiophene segments via a sulfur atom connector is
relatively weak. Nonetheless, there are clear sequential one-
electron oxidation processes corresponding to electron loss
from each of the two segments in the cyclic voltammograms
of most of the oligomers. Electrostatic effects are the most
likely reason behind this behavior, (i.e., the proximity of the
first positive charge can make it harder to create a second
positive charge) and can produce the same effect.
The capped bis(oligothienyl) sulfides can all be reversibly
oxidized, but after that, deleterious effects of excessive
charge begin to appear. We have previously established that
MesS-capped oligothiophenes can be oxidized twice, in
some cases affording very stable cationic species. The
bis(oligothienyl) sulfides have two such moieties and also
can be oxidized, though the charge storage capability does
not scale with the doubling of thiophene chromophores. This
may explain why the poly(oligothienyl sulfide)s were not as
well-behaved electrochemically (17) — overoxidation leads
to decomposition (a common fate of fully conjugated poly-
mer redox processes). In fact PPS was one of the first poly-
mers to be doped to conducting form, though the doped
forms are highly reactive. Our electrochemical studies are
consistent with the relatively poor charge storage capacity of
these systems; the suggestion that carbon–sulfur bond cleav-
age as a major decomposition route, which is supported by
the recent description of synthetically useful version of this
reaction (23), may be a possible model for doped PPS (and
relatives) itself.
has the EDOTs located near the ends of the molecule. The
dication of this compound should therefore have its spin and
(or) charge driven towards each end, meaning that the two
cationic chromophores do not perturb one another to the
same extent, and thereby providing stability to the dication.
We have previously rationalized the differences between the
electrochemical properties of fully conjugated mixed
Experimental3
General
EDOT–thiophene
compounds
MesSTEETSMes
and
Unless stated otherwise, all reactions and manipulations
were carried out under an argon atmosphere using standard
Schlenk line or glovebox techniques. Glassware was dried in
an oven at 125 °C for 24 h prior to use. Solvents were dried
and distilled under argon prior to use (acetonitrile, dichloro-
methane, and hexanes from CaH2; diethyl ether, tetra-
hydrofuran, and toluene from sodium benzophenone ketyl).
All reagents were purchased from commercial sources and
used as received except as otherwise stated. The following
compounds were prepared according to literature proce-
dures: 2-mesitylenesulfenyl chloride (15), bis(phenylsulfonyl)
sulfide (19), 2,2′-bithiophene (24), bis(3,4-ethylenedioxy-2-
thienyl) sulfide (ESE) (16), 3,4-ethylenedioxy-5′-mesityl-
thio-2,2′-bithiophene (6, 15), and 3,4-ethylenedioxy-5-
bromo-2,2′-bithiophene (7, 25).
MesSETTESMes based on similar topological arguments (15).
Electrochemical cycling through the second (irreversible)
oxidation of MesSTESETSMes leads to the appearance of a
growth of a new reversible redox couple on the second an-
odic scan at a potential of +0.5 V, substantially lower than
the first oxidation potential of this compound (Fig. 2). The
potential for this new process matches the first oxidation po-
tential of MesSTEETSMes (Table 2). We suggest that this spe-
cies is in fact being formed during the course of the
oxidative decomposition of MesSTESETSMes. Although the
precise mechanistic details are unclear, one possible process
involves decomposition of the dication via carbon–sulfur
bond scission involving the central sulfur atom. The result-
ing “ETSMes” fragments could then couple via CC bond for-
1H NMR spectra were recorded at 300 MHz and 13C
NMR spectra were recorded at 75 MHz, unless otherwise
noted. Melting points are uncorrected. Electronic spectra
were recorded on a Varian Cary 5 spectrometer using 10 mm
quartz cuvettes. All UV–vis and NIR studies were per-
formed in freshly distilled dichloromethane. Voltammetric
measurements were performed at RT (22 2 °C) (except for
variable temperature studies) in dichloromethane containing
1 mmol/L substrate (except for the variable concentration
studies) and 1 mol/L of n-Bu4NBF4 as electrolyte. Platinum
mation between two EDOTs to give MesSTEETSMes
.
Conclusions
Several bis(oligothienyl) sulfides have been prepared and
their redox and spectroscopic properties investigated. The
terminal mesitylthio substituents prevent oxidative polymer-
ization of these species and facilitate the detailed examina-
tion of structure–property relationships. Overall, the
“electronic communication”, i.e., delocalization, between
3 Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of Un-
published Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3816. For more in-
formation on obtaining material refer to cisti-icist.nrc-cnrc.gc.ca/cms/unpub_e.shtml.
© 2008 NRC Canada

988
Can. J. Chem. Vol. 86, 2008
button (diameter 1.6 mm) was used as the working elec-
trode. Platinum wire and silver wire were used as the coun-
ter and quasi-reference electrodes, respectively. The working
electrode was polished on alumina before use. iR compensa-
tions were applied for all experiments for potential measure-
ments. All redox potentials were calibrated by comparing to
ferrocene, which was added as an internal reference and then
reported vs. SCE (Fc/Fc+ Eo = +0.46 V vs SCE in CH2Cl2).
The number of electrons associated with the redox processes
were determined by comparison of the peak current magni-
tudes with those of equimolar quantities of the internal refer-
ence. Solutions of cationic species were generated either
electrochemically (by constant potential bulk electrolysis in
a two-compartment cell using two 3 cm × 3 cm platinum
plates as cathode and anode) or chemically (by additions of
aliquots of substoichiometric quantities, typically 0.2 equiv.
at a time, of NOBF4 solutions as oxidant).
by column chromatography (silica gel, hexanes/ethyl acetate
(9:1 v/v)) to provide
a
slightly yellow solid.
Recrystallization from methanol/chloroform produced white
crystalline flakes of MesSTSTSMes, yield 4.26 g (80%), mp
92 °C. UV–vis (CH2Cl2) λmax (nm): 310 (ε 1.9 × 104). Re-
maining spectroscopic data are identical to those found in
ref. 26.
5-Mesitylthio-2,2′-bithiophene (2)
To a solution of 2,2′-bithiophene (3.00 g, 18.0 mmol) in
THF (60 mL) was added dropwise n-butyllithium (11.3 mL,
18.1 mmol, 1.6 mol/L in hexanes) at 0 °C. The mixture was
warmed to RT and stirred for 1.5 h. The mixture was cooled
to –70 °C, and a solution 2-mesitylenesulfenyl chloride
(3.38 g, 18.1 mmol) in hexanes (25 mL) was then added
dropwise via cannula. Stirring was continued at –70 °C for
0.5 h, then the mixture was allowed to warm to RT, and wa-
ter (50 mL) was added. The aqueous layer was washed with
ether (50 mL), and the organic extracts were washed with
brine (3 × 50 mL), and dried over anhydrous magnesium
sulfate. The solvent was removed by rotary evaporation, and
the green oily residue was purified by column chromatogra-
phy (silica gel, hexanes) to provide a slightly yellow solid.
Subsequent recrystallization from methanol produced white
2-(Mesitylthio)thiophene (1)
2-Bromothiophene (4.00 g, 24.5 mmol) was added to a
slurry of magnesium powder (0.90 g, 37.0 mmol) in diethyl
ether (20 mL). The reaction was initiated with a small
amount of the bromo reagent and a crystal of iodine. Once
the exothermic reaction had started, the remaining bromo re-
agent was added dropwise to the ice-cooled magnesium
slurry over the course of 20 min. The solution was allowed
to warm to RT and then refluxed for 1 h, after which the
brown Grignard solution was recooled to 0 °C, and a solu-
tion of 2-mesitylenesulfenyl chloride (4.57 g, 24.5 mmol) in
hexanes (25 mL) was added dropwise via cannula. The re-
sulting pale brown solution was stirred at 0 °C for an addi-
tional 30 min. The mixture was then warmed to RT and
poured into brine (100 mL). The aqueous layer was ex-
tracted with ether (3 × 50 mL), and the combined organic
extracts were further washed with water (3 × 50 mL) and
dried over anhydrous sodium sulfate. After filtration, re-
moval of the solvent gave a dark brown oil, which was puri-
fied by flash chromatography (silica gel, hexanes) to provide
1
crystalline flakes of 2, yield 3.60 g (63%), mp 46 °C. H
NMR (500 MHz, CDCl3) δ: 7.13 (dd, J = 5.1, 1.1 Hz, 1H),
7.01 (dd, J = 3.6, 1.1 Hz, 1H), 6.96 (s, 2H), 6.94–6.92 (m,
2H), 6.81 (d, J = 3.7 Hz, 1H), 2.53 (s, 6H), 2.28 (s, 3H). 13C
NMR (CDCl3) δ: 142.82, 139.46, 137.77, 137.17, 136.74,
129.55, 129.44, 128.82, 127.71, 124.15, 123.56, 123.44,
21.84, 21.11. MS (LSI) m/z: 316 (M+, 100%). Anal. calcd.
C17H16S3: C 64.51, H 5.10, S 30.39; found: C 64.58, H 5.29,
S 30.07.
Bis(5′-mesitylthio-5,2′-bithien-2-yl) sulfide
SMes
(
MesST2ST2
)
A solution of 2 (6.00 g, 18.9 mmol) in THF (150 mL)
cooled to –70 °C was treated dropwise with n-butyllithium
(11.9 mL, 19.0 mmol, 1.6 mol/L in hexanes). The resulting
bright yellow solution was stirred at –70 °C for 1 h. After
which, a solution of bis(phenylsulfonyl) sulfide (2.98 g,
9.48 mmol) in THF (20 mL) was added dropwise via can-
nula, and the resulting orange solution was stirred at –70 °C
for an additional 1 h. The mixture was warmed to RT and
poured into water (100 mL). The fine yellow precipitate was
filtered off and washed with cold methanol (3 × 50 mL).
1
a pale yellow liquid of 1, yield 4.41 g (77%). H NMR
(CD2Cl2) δ: 7.16 (dd, J = 5.1, 1.5 Hz, 1H), 6.95 (s, 2H),
6.92 (dd, J = 3.7, 1.5 Hz, 1H), 6.88 (dd, J = 5.1, 3.7 Hz,
1H), 2.49 (s, 6H), 2.25 (s, 3H). 13C NMR (CDCl3) δ: 142.82,
139.27, 137.42, 130.03, 129.36, 128.24, 127.09, 126.07,
21.82, 21.09. HRMS (EI) for C13H14S2 [M+]: calcd.
234.0537; found 234.0541.
Bis(5-mesitylthio-2-thienyl) sulfide (MesSTSTSMes
)
This solid was recrystallized from a mixture of chloroform
SMes
and methanol (120 mL, 1:1 v/v) to afford MesST2ST2
as
This compound has been prepared previously by a differ-
ent route (26). A solution of 1 (5.00 g, 21.3 mmol) in THF
(100 mL) cooled to –70 °C was treated dropwise with n-
butyllithium (13.3 mL, 21.3 mmol, 1.6 mol/L in hexanes).
The resulting yellow solution was stirred at –70 °C for 1 h,
after which a solution of bis(phenylsulfonyl) sulfide (3.34 g,
10.6 mmol) in THF (20 mL) was added dropwise via can-
nula, and the resulting golden yellow solution was stirred at
–70 °C for an additional 1 h. The mixture was warmed to RT
and poured into water (100 mL). The aqueous layer was ex-
tracted with ether (3 × 50 mL), and the combined organic
extracts were further washed with water (3 × 50 mL), and
dried over anhydrous sodium sulfate. After filtration, re-
moval of the solvent gave a yellow oil, which was purified
pale yellow needles, yield 4.90 g (78%), mp 154 °C. UV–vis
1
(CH2Cl2) λmax (nm): 360 (ε 3.9 × 104). H NMR (CDCl3) δ:
7.00 (d, J = 3.7 Hz, 2H), 6.94 (s, 4H), 6.86 (d, J = 4.4 Hz,
2H), 6.80 (d, J = 3.7 Hz, 2H), 6.74 (d, J = 4.4 Hz, 2H), 2.48
(s, 12H), 2.27 (s, 6H). 13C NMR (CDCl3) δ: 142.82, 141.33,
139.57, 137.89, 136.72, 133.58, 133.48, 129.46, 129.27,
128.38, 124.02, 123.28, 21.78, 21.10. MS (EI) m/z: 662 (M+,
100%). Anal. calcd. for C34H30S7: C 61.59, H 4.56, S 33.85;
found: C 61.40, H 4.49, S 33.85.
5-Bromo-5 -mesitylthio-2,2 -bithiophene
′
′
5-Mesitylthio-2,2′-bithiophene 2 (6.32 g, 20.0 mmol) was
dissolved in DMF (100 mL). In the absence of light, NBS
© 2008 NRC Canada

Myles et al.
989
(3.91 g, 22.0 mmol) was added portionwise to the solution at
RT. After addition, the solution was stirred at RT overnight
in the dark. The resulting pale yellow solution was diluted
with dichloromethane (100 mL) and poured into brine
(100 mL). The aqueous phase was collected and washed
with a second portion of dichloromethane (100 mL). All
organics were collected and extracted with water (5 ×
100 mL) to remove any remaining DMF. The dichloro-
methane layer was dried over anhydrous sodium sulfate, fil-
tered, and evaporated. The obtained pale orange liquid was
purified by column chromatography (silica gel, hexanes/
dichloromethane (4:1 v/v)) to provide 5-bromo-5′-mesityl-
2,2′-bithiophene as a yellow liquid, yield 7.10 g (90%). This
compound was used in the next step without further purifi-
cation. 1H NMR (CDCl3) δ: 6.94 (s, 2H), 6.87 (d, J =
4.4 Hz, 1H), 6.84 (d, J = 3.7 Hz, 1H), 6.75 (d, J = 3.7 Hz,
1H), 6.72 (d, J = 3.7 Hz, 1H), 2.49 (s, 6H), 2.26 (s, 3H). MS
(LSI) m/z: 394 (M+, 79Br, 90%), 395 (M + 1, 79Br, 28%),
396 (M+, 81Br, 100%), 397 (M + 1, 81Br, 27%).
8H), 6.90 (d, J = 3.7 Hz, 2H), 6.86 (d, J = 3.8 Hz, 2H), 6.78
(d, J = 3.7 Hz, 2H), 2.50 (s, 12H), 2.27 (s, 6H). 13C NMR
(125 MHz, CDCl3) δ: 143.06, 141.51, 139.78, 137.74,
137.22, 136.82, 135.30, 134.07, 133.89, 129.68, 129.54,
128.77, 124.91, 124.14, 123.94, 123.77, 22.01, 21.32. MS
(LSI) m/z: 826 (M+, 10%). Anal. calcd. C42H34S9: C 60.97,
H 4.14, S 34.88; found: C 60.67, H 4.17, S 34.27.
Bis(5-mesitylthio-3,4-ethylenedioxy-2-thienyl) sulfide
(
MesSESESMes
)
A solution of bis(3,4-ethylenedioxy-2-thienyl) sulfide
ESE (2.06 g, 6.55 mmol) was cooled to –40 °C and treated
slowly with n-butyllithium (8.19 mL, 13.1 mmol, 1.6 mol/L
in hexanes). The bright red solution was stirred for 1.5 h at
–40 °C. After which, the solution was cooled to –70 °C, and
a freshly prepared solution of 2-mesitylenesulfenyl chloride
(2.45 g, 13.1 mmol) in hexanes (15 mL) was added dropwise
via cannula. The resulting pale brown solution was stirred at
–70 °C for an additional 30 min. The mixture was then
warmed to RT and poured into water (100 mL). The fine
white precipitate of MesSESESMes was filtered off, washed
with cold methanol (3 × 20 mL), and dried in vacuo. Yield
2.10 g (52%), mp 206 °C. UV–vis (CH2Cl2) λmax (nm) 309
′′
5-Mesitylthio-2,2′:5′,2 -terthiophene (3)
A flask was charged with 2-(tributylstannyl)thiophene
(3.05 mL, 9.59 mmol), 5-bromo-5′-mesitylthio-2,2′-
bithiophene (3.79 g, 9.59 mmol), Pd(PPh3)4 (554 mg), and
toluene (20 mL). The mixture was heated to reflux for 20 h.
After cooling to RT, the black mixture was diluted with
ether (100 mL) and poured into saturated potassium fluoride
(100 mL). The resulting tributyltin fluoride was filtered off
and washed with cold ether (3 × 15 mL). The organic phase
was collected, washed with brine (3 × 100 mL), and dried
over anhydrous sodium sulfate. The solvent was removed by
rotary evaporation, and the dark yellow residue was purified
by column chromatography (silica gel, hexane/EtOAc (9:1
v/v)) to provide a bright yellow solid. Recrystallization from
ethanol produced yellow crystalline plates of 3, yield 3.36 g
1
(ε 2.3 × 104). H NMR (CDCl3) δ: 6.90 (s, 4H), 4.19 (m,
8H), 2.48 (s, 12H), 2.25 (s, 6H). 13C NMR (CDCl3) δ:
143.13, 142.92, 140.55, 139.40, 129.53, 128.99, 113.53,
107.17, 64.95, 64.77, 22.19, 21.27. MS (LSI) m/z: 614 (M+,
18%), 463 ((M
–
C9H11S)+, 100%). Anal. calcd.
C30H30O4S5: C 58.60, H 4.92, S 26.07; found: C 58.21, H
4.72, S 26.07.
Bis(5′-mesitylthio-3,4-ethylenedioxy-5,2′-bithien-2-
yl)sulfide (MesSTESETSMes
)
A
solution of 3,4-ethylenedioxy-5′-mesitylthio-2,2′-
bithiophene 6 (0.85 g, 2.27 mmol) in THF (15 mL) cooled
to –40 °C was treated dropwise with n-butyllithium
(1.42 mL, 2.27 mmol, 1.6 mol/L in hexanes). The bright or-
ange solution was stirred at –40 °C for 1.5 h. After which,
the solution was cooled to –70 °C, and a solution of
bis(phenylsulfonyl) sulfide (0.36 g, 1.15 mmol) in THF
(10 mL) was added dropwise via cannula. The resulting yel-
low solution was stirred at –70 °C for an additional 30 min.
The mixture was then warmed to RT and poured into a cold
mixture of diethyl ether and water (120 mL, 1:5 v/v). The
fine yellow precipitate was filtered off and washed with cold
water (3 × 15 mL). This solid was recrystallized from a mix-
ture of chloroform and methanol (80 mL, 3:5 v/v) to afford
MesSTESETSMes as yellow flakes, yield 0.60 g (68%), mp
1
(88%), mp 80 °C. H NMR (500 MHz, CDCl3) δ: 7.18 (dd,
J = 5.1, 1.1 Hz, 1H), 7.11 (dd, J = 3.6, 1.1 Hz, 1H), 6.99 (d,
J = 3.8 Hz, 1H), 6.98 (dd, J = 5.1, 3.6 Hz, 1H), 6.96 (s, 2H),
6.92 (d, J = 3.7 Hz, 1H), 6.90 (d, J = 3.8 Hz, 1H), 6.80 (d,
J = 3.8 Hz, 1H), 2.52 (s, 6H), 2.28 (s, 3H). MS (LSI) m/z :
398 (M+, 100%). Anal. calcd. C21H18S4: C 63.27, H 4.55, S
32.18; found: C 63.47, H 4.51, S 31.92.
′′
′′
A solution of 3 (765 mg, 1.92 mmol) in THF (25 mL),
Bis(5 -mesitylthio-5,2′:5′,2 -terthien-2-yl) sulfide
SMes
(
MesST3ST3
)
cooled to –70 °C, was treated dropwise with n-butyllithium
(1.20 mL, 1.92 mmol, 1.6 mol/L in hexanes). The resulting
bright orange solution was stirred at –70 °C for 1 h. After
which, a solution of bis(phenylsulfonyl) sulfide (302 mg,
0.96 mmol) in THF (10 mL) was added dropwise via can-
nula, and the resulting orange solution was stirred at –70 °C
for an additional 1 h. The mixture was then warmed to RT
and poured into a cold mixture of diethyl ether and water
(120 mL, 1:5 v/v). The fine yellow precipitate was filtered
off and washed with cold methanol (3 × 15 mL). This solid
1
198 °C. UV–vis (CH2Cl2) λmax (nm) 375 (ε 4.2 × 104). H
NMR (CDCl3) δ: 6.93 d, J = 3.7 Hz, 2H), 6.92 (s, 4H), 6.76
(d, J = 3.7 Hz, 2H), 4.26 (m, 8H), 2.48 (s, 12H), 2.25 (s,
6H). 13C NMR (CDCl3) δ: 143.70, 142.94, 139.45, 136.82,
136.70, 134.90, 129.85, 129.60, 128.86, 123.55, 115.51,
104.47, 65.14, 64.85, 22.07, 21.29. HRMS (LSI) for
C38H34O4S7 [M+]: calcd. 778.0502; found 778.0502. Anal.
calcd. for C38H34O4S7: C 58.58, H 4.40, S 28.81; found: C
58.47, H 4.39, S 28.38.
was recrystallized from a mixture of tetrahydrofuran and
SMes
methanol (40 mL, 1:1 v/v) to afford MesST3ST3
as dark
golden yellow crystals, yield 400 mg (50%), mp 156 °C.
3,4-Ethylenedioxy-5-mesitylthio-2,2′-bithiophene (8)
A solution of 3,4-ethylenedioxy-5-bromo-2,2′-bithiophene
7 (3.90 g, 12.9 mmol) in THF (40 mL) cooled to –78 °C was
1
UV–vis (CH2Cl2) λmax (nm) 395 (ε 6.5 × 104). H NMR
(500 MHz, CDCl3) δ: 7.08 d, J = 3.7 Hz, 2H), 6.93–6.95 (m,
© 2008 NRC Canada

990
Can. J. Chem. Vol. 86, 2008
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treated dropwise with n-butyllithium (8.04 mL, 12.9 mmol,
1.6 mol/L in hexanes). The resulting bright red solution was
stirred for 1.5 h at –78 °C. A solution of 2-mesityl-
enesulfenyl chloride (2.41 g, 12.9 mmol) in hexanes
(20 mL) was added dropwise via cannula, and the resulting
rusty red solution was stirred at –78 °C for an additional
30 min. The mixture was warmed to RT and poured into wa-
ter (100 mL). The aqueous layer was extracted with ether (3
× 50 mL), and the combined organic extracts were further
washed with water (3 × 50 mL) and dried over anhydrous
sodium sulfate. After filtration, removal of the solvent gave
a dark yellow solid, which was purified by column chroma-
tography (silica gel, hexanes/dichloromethane (1:1 v/v)) to
provide a bright yellow solid. Recrystallization from metha-
nol/chloroform produced bright yellow needles of 8, yield
1
3.20 g (66%), mp 120 °C. H NMR (500 MHz, CDCl3) δ:
7.15 dd, J = 5.1, 1.1 Hz, 1H), 7.08 (dd, J = 3.7, 1.1 Hz, 1H),
6.94 (dd, J = 5.1, 3.7 Hz, 1H), 6.92 (s, 2H), 4.29 (m, 4H),
2.56 (s, 6H), 2.25 (s, 3H). 13C NMR (125 MHz, CDCl3) δ:
142.68, 141.51, 138.91, 136.52, 134.25, 129.44, 129.23,
126.93, 123.74, 122.74, 113.00, 107.07, 64.76, 64.69, 21.97,
20.95. MS (EI) m/z: 374 (M+, 100%). Anal. calcd.
C19H18O2S3: C 60.93, H 4.84, S 25.68; found: C 60.75, H
4.92, S 25.67.
Bis(5′-mesitylthio-3′,4′-ethylenedioxy-5-2′-bithien-2-yl)
sulfide (MesSETSTESMes
)
A solution of 8 (1.00 g, 2.67 mmol) in THF (30 mL),
cooled to –40 °C, was treated dropwise with n-butyllithium
(1.67 mL, 2.67 mmol, 1.6 mol/L in hexanes). The dark red
solution was stirred at –40 °C for 1 h. After which, the solu-
tion was cooled to –70 °C, and
a
solution of
bis(phenylsulfonyl) sulfide (0.42 g, 1.34 mmol) in THF
(10 mL) was added dropwise via cannula. The resulting pale
red solution was stirred at –70 °C for an additional 30 min.
The mixture was then warmed to RT and poured into water
(75 mL). The fine yellow precipitate was filtered off and
washed with cold methanol (3 × 20 mL). This solid was
recrystallized from a mixture of chloroform and methanol
(80 mL, 3:5 v/v) to afford MesSETSTESMes as yellow nee-
dles, yield 0.75 g, (72%), mp 213 °C. UV–vis (CH2Cl2) λmax
8. (a) R.J.P. Corriu, C. Guerin, B. Henner, T. Kuhlmann, A. Jean,
F. Garnier, and A. Yassar. Chem. Mater. 2, 351 (1990); (b) P.
Chicart, R.J.P. Corriu, J.J.E. Moreau, F. Garnier, and A.
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8 (1991); (c) K. Tamao, S.
Yamaguchi, and M. Shiro. J. Am. Chem. Soc. 116, 11715
(1994); (d) S. Yamaguchi, T. Goto, and K. Tamao. Angew.
Chem. Int. Ed. 39, 1695 (2000); (e) Y. Lee, S. Sadki, B. Tsuie,
and J.R. Reynolds. Chem. Mater. 13, 2234 (2001).
1
(nm) 375 (ε 4.4 × 104). H NMR (500 MHz, THF-d8) δ:
9. (a) Z. Jin and B.L. Lucht. J. Organometal. Chem. 653, 167
(2002); (b) K. Naka, T. Umeyama, and Y. Chujo. J. Am.
Chem. Soc. 124, 6600 (2002); (c) V.A. Wright and D.P. Gates.
Angew. Chem. Int. Ed. 41, 2389 (2002); (d) R.C. Smith and
J.D. Protasiewicz. Eur. J. Inorg. Chem. 998 (2004); (e) R.C.
Smith and J.D. Protasiewicz. J. Am. Chem. Soc. 126, 2268
(2004); (f) T. Baumgartner and R. Reau. Chem. Rev. 106, 4681
(2006); (g) V.A. Wright, B.O. Patrick, C. Schneider, and D.P.
Gates. J. Am. Chem. Soc. 128, 8836 (2006).
7.05 d, J = 3.9 Hz, 2H), 6.92 (s, 4H), 6.91 (d, J = 3.9 Hz,
2H), 4.27 (m, 8H), 2.51 (s, 12H), 2.22 (s, 6H). 13C NMR
(125 MHz, THF-d8) δ: 143.48, 142.99, 139.84, 139.78,
138.69, 134.03, 133.77, 130.35, 130.10, 123.03, 112.90,
108.54, 65.96, 65.78, 22.26, 21.11. HRMS (LSI) for
C38H34O4S7 [M+]: calcd. 778.0502, found 778.0490. Anal.
calcd. for C38H34O4S7: C 58.58, H 4.40, S 28.81; found: C
58.67, H 4.42, S 28.55.
10. M.M. Labes, P. Love, and L.F. Nichols. Chem. Rev. 79, 1 (1979).
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J.M. Sowa, R.L. Elsenbaumer, and R.H. Baughman. J. Chem.
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K.K. Kanazawa, J.R. Reynolds, and G.B. Street. J. Chem. Soc.
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Acknowledgements
We thank the University of Victoria, the Natural Sciences
and Engineering Research Council of Canada, and Defence
R&D Canada-Atlantic for support of this work.
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