Oxidative bond formation in dithienyl polyphenylenes: Optical and electrochemical consequences

Article abstract of DOI:10.1002/ejoc.201100332

A new set of dithienyl polyphenylenes was prepared with a view of developing sulfur-containing polyaromatic hydrocarbons (PAHs) by oxidative cyclodehydrogenation. The first of these, 1,2-bis(5-methyl-2-thienyl)-3,4,5,6- tetra-(4-tert-butylphenyl)benzene (

Full text of DOI:10.1002/ejoc.201100332

FULL PAPER
DOI: 10.1002/ejoc.201100332
Oxidative Bond Formation in Dithienyl Polyphenylenes: Optical and
Electrochemical Consequences
Colin J. Martin,[a] Belen Gil,[a] Sarath D. Perera,[a,b] and Sylvia M. Draper*[a]
Keywords: Thiophenes / Electrochemistry / C–C coupling / Photophysics / Sulfur
A new set of dithienyl polyphenylenes was prepared with a
view of developing sulfur-containing polyaromatic hydro-
carbons (PAHs) by oxidative cyclodehydrogenation. The first
of these, 1,2-bis(5-methyl-2-thienyl)-3,4,5,6-tetra-(4-tert-but-
ylphenyl)benzene (1) was sterically hindered at the 5-posi-
tions of the thienyl rings and under Lewis acid catalyzed
cyclodehydrogenation gave monomeric intramolecularly
fused dithienyl 3, which was spectroscopically and structur-
ally characterized. Under the same conditions, three unhin-
dered dithienyl polyphenylenes, 1,2-(thienyl)-3,4,5,6-tetra(4-
rected intra- and intermolecular C–C bond fusions. The re-
sulting dimers 4, 7, and 8 were identified through a series of
1H, 13C, and 2D NMR experiments. The electrochemical and
photophysical properties of the dimers were examined. Their
optical properties reflect the coplanarity or otherwise of their
cojoined parts. The electrochemical oxidation of the dithienyl
polyphenylene precursors showed a relationship between
the ease of oxidation and the availability of the 2- and 5-
positions on the thienyl rings. Using spectroelectrochemical
methods the electrochemically oxidized and chemically oxid-
tert-butylphenyl)s 2, 5, and 6, underwent both thiophene-di- ized products were compared.
Introduction
Results and Discussion
The chemical and electrochemical oxidation of thiophene
systems has been extensively studied[1–4] due to the ease
with which thiophenes undergo intermolecular dehydroge-
nation to form polymers.[3,5,6] The propensity of thiophene
systems toward the formation of insoluble products along
with the difficulty of controlling the properties of the re-
sulting polymers have led to the strategy of using monomers
containing multiple thiophene units.[7,8] Substituted bisthi-
enyl-, dithienylethene-, and thiophene-oligomer monomers
have given better control over both the band gap and the
conductivity of the polymers formed upon oxidation. In all
of these systems, the focus has been on the effect of the
structural changes to the monomer on the resulting poly-
mer.[4,6] In comparison, little attention has been paid to the
design of molecular systems containing multiple thiophene
units where both inter- and intramolecular oxidations are
possible.[9] Building on our recent work on monothienyl
polyphenylenes[10] and our established expertise in dehydro-
genation and carbon–carbon bond-forming processes,[11–13]
we now present synthetic strategies for the generation of a
series of dithiophene-containing polyaromatic compounds.
A full discussion of the photochemical and electrochemical
properties of the new molecules is provided.
In recently published work, we presented a monothienyl
polyphenylene that upon oxidation gave a dimeric S-doped
hexabenzocoronene; the photochemical properties of which
were dependent on the twist of each coronene unit around
the newly formed dimer bond.[10] Here we report a series of
disulfur polyphenylenes, similar in structure to our pre-
[a] School of Chemistry, University of Dublin, Trinity College,
Dublin 2, Ireland
Fax: +353-1-671-2826
E-mail: smdraper@tcd.ie
Scheme 1. Synthetic route to thienyl polyphenylenes 1–4. Reagents
and conditions: (i) Tetrakis(4-tert-butylphenyl)cyclopentadienone,
Ph2CO, 300 °C melt, 90 min, 41% (for 1), 66% (for 2); (ii) FeCl3,
CH2Cl2/CH3NO2, 25 °C, 40 min, 90% (for 3), 55% (for 4).
[b] The Chemistry Department, Open University of Sri Lanka,
Nugegoda, Sri Lanka
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100332.
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viously reported nitrogen-containing polyphenylenes. The
latter are known to undergo Lewis acid catalyzed oxidation
to give heterosuperbenzene systems [N-HSB].[11]
The prevalence of intermolecular dehydrogenations in
thienyl oxidation[14,15] and the consequent problem of mul-
tiple isomeric products initially led us to sterically block
the site for intermolecular dehydrogenation. To this end, a
bisthienylacetylene with methyl substituents MeS2CCS2ЈMe
was synthesized and subsequently reacted with tert-butyl-
substituted tetraphenylcyclopentadienone to give
(Scheme 1).
1
Cyclodehydrogenation of this bis(methylthienyl) polyphen-
ylene was carried out by using FeCl3 as oxidant and Lewis
acid to give 3 (Scheme 1). Mass spectral analysis of 3 shows
the loss of two hydrogen atoms, consistent with the one ex-
clusive 3–3Ј intramolecular C–C bond fusion apparent in the
single-crystal X-ray structure (Figure 1, C62–C72).
Figure 1. Single-crystal X-ray molecular structure of 3. H atoms
are omitted for clarity.
In the crystal packing of 3 (Supporting Information, Fig-
ure S1) there are two orientations of the molecule, each one
layering on top of the other so as to avoid steric interactions
To examine the reactivities of unhindered dithienyl poly-
between the tertiary butyl groups. Unlike with other poly- phenylenes under dehydrogenation conditions, symmetric
phenylenes,[16] no π–π interactions are seen between the mole- S2CCS2Ј and S3CCS3Ј and asymmetric S2CCS3Ј dithienyl-
cules in each layer (a minimum π–π distance of 4.95 Å is ob- acetylenes were prepared by Sonogashira coupling of the
served).
appropriate thienyl bromides.[17] Using these alkynes, three
Scheme 2. Synthetic route to partially cyclized thiophene systems 7 and 8. Reagents and conditions: (i) Tetrakis(4-tert-butylphenyl)cyclopen-
tadienone, Ph2CO, 300 °C melt, 90 min, 66% (for 5), 66% (for 6); (i) FeCl3, CH2Cl2/CH3NO2, 25 °C, 40 min, 60% (for 7), 52% (for 8).
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Oxidative Bond Formation in Dithienyl Polyphenylenes
new dithienyl polyphenylene precursors were prepared more reactive 2- and 5-positions on the thiophene rings.
(Scheme 1, Scheme 2).
The more complex asymmetry of precursor 6 dictates that
2,2Ј-Dithiophene 2 was oxidized to give 4 (Scheme 1), here there are significantly more dimeric products possible
whose mass spectrum shows the loss of six hydrogen atoms on dehydrogenation (12 in total); however, NMR spec-
and the formation of a dimer. This is in agreement with the troscopy (Figure 3) again indicates the formation of only
formation of three new C–C bonds, of which one is involved one of two possible isomers (Scheme 2, 8A and 8B). The
in dimer formation. The 1H NMR spectrum of 4 (Figure 2) 1H NMR spectrum clearly shows thienyl ring protons reso-
reveals that the compound has only lost hydrogen on each nating at both high and low field, suggesting inward and
of the thiophene moieties. Unlike other reported polyphen- outward pointing thienyl S atoms.
ylenes,[10] no oxidation occurred at the phenylene rings.
Three thiophene protons remain: an AB pattern at δ = 7.44
and 7.32 ppm and a singlet at δ = 7.41 ppm. The appear-
ance of these signals, supported by additional NMR spec-
troscopic data, conclusively led to the structure of dimeric
species 4 (Scheme 1). Hence dimerization occurred at the
5,5Ј-positions as expected from standard thiophene reactiv-
ities.[18] Comparing the 1H NMR spectrum with that of
blocked species 3 (Figure 2) it can be seen that in both cases
the remaining thienyl hydrogen atoms resonate between δ =
7.45 and 7.15 ppm. These downfield shifts are indicative of
thienyl environments in which the S atoms point toward
the ortho phenyl rings of the polyphenylene (Figure 1) and
indicate that the orientation of the thienyl rings in 3 and 4
is the same.[13]
1
Figure 3. H NMR spectra of 7 and 8 (25 °C, 600 MHz, CDCl3 7,
[D2]-1,1,2,2-tetrachloroethane 8).
In the absence of structural data, definitive characteriza-
tion of compounds 7 and 8 has not been possible; however,
it can be concluded that clean and single products were
formed in both cases. Further exposure of 7 and 8 to condi-
tions of dehydrogenation resulted in either no reaction
(FeCl3) or decomposition (AlCl3).
Photophysical Measurements
Figure 2. 1H NMR spectra (25 °C, 600 MHz, CDCl3) of 3 (top)
and 4 (bottom).
The systematic structural variation in this family of novel
S-containing polyaromatics lent itself to a study of their
A more complex set of polyphenylene bond fusions was optical properties as a function of planarity and the posi-
possible on the dehydrogenation of 3,3Ј- and 2,3Ј-dithienyl tion of their thienyl S atoms. The absorption spectra of
polyphenylenes 5 and 6 (Scheme 2). However, the 1H NMR monomers 1, 2, 5, and 6 (Supporting Information, Table S1,
spectra of 5 and 6 were also dominated by the expected Figure S2) present broad unstructured bands, typical of
thienyl and phenyl ring signals, suggesting the formation of nonplanar polyphenylenes.[19] The molecules present two
similar dimeric products. This conclusion is further sup- broad, weak emission bands (Supporting Information,
ported by the mass spectroscopic data, which again indicate Table S2): one at high energy, which was attributed to the
the formation of three new C–C bonds one of which was polyphenylene core (360–390 nm),[20,21] and one at low en-
the result of dimerization.
ergy, which was attributed to the thiophene rings (420–
For 7, a total of four dehydrogenated dimers are possible; 520 nm;
Supporting
Information,
Table S1,
Fig-
however, only one of these is formed (Figure 3, Scheme 2). ure S3).[22–25] The molecules are clearly structurally flexible
1
The upfield shift in the H NMR spectrum of two of the in both the ground and excited states.
thiophene signals (between δ = 6.45 and 6.25 ppm) indicates
Dimeric systems 4, 7, and 8 also present a set of high-
that in this case the thienyl sulfur atoms point away from energy absorptions (Figure 4, λ = 350–450 nm) that are
their neighboring phenyl rings, that is, the ortho phenyl consistent with reported values for fused thienyl systems.[26]
groups shield the thienyl protons that point towards In addition, their spectra contain a shoulder, similar to the
them.[13] The data are therefore consistent with only two one observed in monothiophene hexabenzocoronenes,[18]
possible dimers 7A and 7B (both shown in Scheme 2). Of that extends to lower energies. It corresponds to the in-
these, 7A is preferred, as in this case both the intermo- creased conjugation arising from the two fused thienyl units
lecular and intramolecular oxidations have occurred at the in the dimer when they are coplanar (Scheme 3B).[14]
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Figure 4. UV/Vis spectra (chloroform, 10–5 m) of 4 (---), 7 (––), and
8 (···).
Scheme 3. Twisted (A) and planar (B) conformations as observed
in dimeric systems 4, 7, and 8.
Figure 5. UV/Vis and excitation spectra of (a) 4 and (b) 7 at room
temperature. UV/Vis (––, grey solid line), solid state (···), chloro-
form (10–3 m; ––, solid black line), chloroform (10–5 m, ---).
The absorptivity of the tail is greatest for 7 in solution,
indicating that the planar conformation (Scheme 3B) is
more easily attained in this case. The sharp-structured ab-
sorption bands (around λ = 350–450 nm) observed for all
three dimers support the idea of a high-energy barrier for
the rotation of monomeric subunits through the newly
formed bond.[22–25]
Systems 4, 7, and 8 are luminescent in the solid state and
in solution at room temperature and at 77 K. They exhibit
dual luminescence, which varies with concentration (Sup-
porting Information, Table S3). In dilute solution (chloro-
form, 10–5 m; Figure 5), the excitation spectra correspond
to the absorption spectra but with the absence of the low-
energy absorption shoulder, suggesting a highly twisted
conformation (Scheme 3A).[22–25] At higher concentrations,
a new low-energy band appears (between 525 and 575 nm)
matching the tail described in the UV/Vis spectra (Figure 5)
and suggesting a planar conformation. This concentration
dependence is thought to be due to excited-state molecules
aggregating more readily than those in the ground state,
giving rise to excimeric species.[25,27,28]
The emission spectra of the dimers (at low concentration,
Figure 6; Supporting Information, Table S3) show a high-
energy band at similar energy to the emission (Supporting
Information, Table S2) attributed to the thienyl rings of the
starting materials. This implies that there is no increase in
the delocalization of electronic density upon dimerization,
and it is consistent with a twisted conformation in dilute
solutions (Scheme 3A). In more concentrated solutions
(chloroform, 10–3 m), 4, 7, and 8 have a new broad lower-
energy emission (Figures 5b and 6b; Supporting Infor-
mation, Table S3) sometimes mixed with the high-energy
bands attributed to the twisted conformation.
Figure 6. Emission spectra of (a) 4 and (b) 7 at room temperature.
Solid state (···), chloroform (10–3 m, ––), chloroform (10–5 m, ---).
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Oxidative Bond Formation in Dithienyl Polyphenylenes
Although all three dimeric systems 4, 7, and 8 present tial of +1.60 V. In the case of the 2,3Ј-thiophene precursor
excimeric emissions at high concentration, the nature of 6, the available sites for intramolecular bond formation are
their excited states is different. In 4, the emission comes 3–2Ј and there is also a possible 5–5Ј intermolecular bond.
from a singlet state (nanosecond range), whereas for 7 and In the UV/Vis spectrum (Figure 7a) we see the formation
8 the emission is of triplet-state origin (microsecond range). of weak absorptions at 396 and 419 nm after 20–25 min,
The difference in the lifetimes seems to indicate that sys- which are similar to those seen in dimeric product 8 (Sup-
tems 7 and 8 can form more stable excimers, as they adopt porting Information, Table S1).
a planar conformation more readily (Scheme 3). This is fur-
ther demonstrated in the solid state where the emissions
of 7 and 8 are slightly redshifted relative to those of the
concentrated solutions (Figure 6b). For 4, however, the exci-
tation spectra of the solid state and dilute solutions coincide
(Figure 6a). The blueshift between the emissions in the solid
state and dilute solutions (Figure 6b) seems to indicate a
twisted conformation (Scheme 3A) for 4 even in the solid
state.
Excimeric species only form in the dimeric systems. In
the case of monomeric 3, the emission spectrum does not
show any change with concentration, having only a sharp
band at 400 nm and a tail to longer wavelengths (to
600 nm). At low temperature, a second structured band is
also observed (495, 525 nm) that can be attributed to emis-
sion from the triplet state (Supporting Information, Fig-
ure S4).
Electrochemical Measurements
The partially fused dithiophene-containing systems 4, 7,
and 8 undergo no oxidation within the potential windows
in both chloroform and acetonitrile. Each polyphenylene (1,
2, 5, and 6; Schemes 1 and 2) undergoes a single irreversible
Figure 7. The changes in the UV/Vis spectrum of (a) 6 and (b) 5
oxidation to form a stable species (chloroform, 10–2 m). The
lowest oxidation potential is observed for 3,3Ј symmetric
species 5 (+1.34 V), where both 2–2Ј intramolecular and 5–
5Ј intermolecular bond formations are possible.
as an open potential of +1.6 V is applied (chloroform, 10–4 m) (vs.
Fc/Fc+).
The formation of these peaks, similar to those seen in
An increase in oxidation potential to +1.44 V is seen for the dimeric species, is even more pronounced in the case of
6 possibly due to the more electrochemically demanding 2– 5 (Figure 7b) where the absorptions are observed after
3Ј or 2–4Ј intramolecular bond fusions available. For both 25 min at 416 and 444 nm; in 5 the thiophenes can undergo
1 and 2 a further increase in oxidation potential is seen, a 2–2Ј intramolecular oxidative bond formation along with
resulting from the 3,3Ј intramolecular bond formations re- a 5–5Ј intermolecular one. Assuming this has occurred in
quired in these systems; however, in 1 where the 5-positions the electrochemical oxidation there are still unoxidized 5-
are blocked, a decrease in the intensity of the oxidation was positions on the thiophene dimer that could undergo fur-
observed.
ther oxidative bond formation. This could explain the ap-
Such a trend implies that electrochemical oxidation to pearance of a new set of absorption bands, after 60 min, in
give C–C bond fusion occurs preferentially at the 2,5-posi- the same region (350–375 nm) as that seen for oligothio-
tions of each thiophene; this data mirrors the chemically phenes containing three or four thienyl units.[30]
obtained products where intramolecular 2,2Ј bond forma-
For 2, electrochemical oxidation results in no change in
tion occurs ahead of intramolecular 2,3Ј fusion (where a the UV/Vis spectrum; as this was the most chemically reac-
choice is available). The presence of the phenyl substituents tive species towards FeCl3 this result seems surprising. If
in our compounds acts to preclude electrochemical polyme- the available oxidation sites (Table 1) are as predicted, intra-
rization or indeed further chemical oxidation of any of the molecular oxidation of 2 can occur exclusively at the 3-posi-
compounds as a result of steric effects and the effect of tion on the thiophene ring. As electrochemical oxidation
substitution on the electron density at the relevant thio- has been widely reported to drastically favor those involving
phene polymer-linking positions.[29]
at least one 2/5-position on the ring[3] it can be assumed
To study the products of these high-voltage oxidations, that under electrochemical conditions the 5–5Ј intermo-
the UV/Vis spectra of polyphenylenes 1, 2, 5, and 6 were lecular oxidation occurs preferentially over the 3–3Ј intra-
observed as the solutions were oxidized by an open poten- molecular one. Oxidation of 2 will not lead to intramolecu-
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C. J. Martin, B. Gil, S. D. Perera, S. M. Draper
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lar bond formation, and as such, the product does not con- dation (Figure 8a). For 6, electrochemical oxidation pro-
tain the new absorptions observed in the cases of 5 and 6. duces an emission spectrum with maxima at 432 and
In the case of 1 in which all the 2/5-positions of the thio- 460 nm (Figure 8b), and again these are very similar to the
phenes are blocked, no observable change in the spectrum emissions observed for 8, the product from chemical oxi-
was seen after 75 min.
dation.
Table 1. Irreversible oxidation potentials of 1, 2, 5, and 6 (chloro-
form, 10–2 m) vs. Fc/Fc+.
Conclusions
Polyphenylene
precursor
Oxidation
[V]
Available sites for
electrochemical oxidation
Examination of oxidative carbon–carbon bond forma-
tions within dithienyl polyphenylenes has led to the synthe-
sis of novel monomeric and dimeric sulfur containing poly-
aromatic products. The reactivity of dithienyl polyphenyl-
ene precursors 1, 2, 5, and 6 shows a preference for the
formation of thiophene–thiophene inter- and intramolecu-
lar carbon–carbon bonds over intramolecular thiophene–
phenylene bonds where possible. This leads to the forma-
tion of partially fused species 3, 4, 7, and 8 upon chemical
oxidation. Electrochemical oxidation gives only bond for-
mation at the more reactive 2- and 5-thiophene positions to
give products that have been monitored spectroelectrochem-
ically.
Dimeric species 4, 7, and 8 have optical properties that
vary with concentration as a result of the orientation of the
systems about the newly formed dimer bond. Blocked fused
monomer 3 does not show the same optical properties as
the dimers, but instead shows a single luminescence at room
temperature.
1
2
6
5
+1.56
+1.52
+1.44
+1.34
3,3Ј intra
3,3Ј intra, 5,5Ј inter
2,3Ј or 2,4Ј intra, 5,5Ј inter
2,2Ј intra, 5,5Ј inter
In order to investigate if the products formed from the
electrochemical oxidations of 5 and 6 were similar to those
seen upon chemical oxidation, the fluorescence spectra of
the electrochemical products were examined at low concen-
tration (chloroform, 10–4 m) and compared to those of the
chemical products (i.e., 7 and 8).
In both cases an increase in fluorescence intensity was
observed upon electrochemical oxidation. For 5, a new vi-
brationally structured fluorescence spectrum was observed.
The maxima at 462 and 489 nm closely match those in the
emission spectrum of 7, the product from chemical oxi-
Experimental Section
General Methods: 2,3,4,5-Tetrakis-(4-tert-butylphenyl)cyclopen-
tadienone was synthesized according to a literature procedure.[31]
Flash chromatography was performed by using silica gel (Aldrich
Chemical) as the stationary phase. IR spectra were recorded neat
or for 7 and 8 in KBr with a Perkin–Elmer Spectrum 100 FTIR
spectrometer fitted with a Universal ATR accessory. NMR spectra
were recorded with a Bruker Avance DPX 400 spectrometer op-
erating at 400.13 MHz for 1H and at 100.62 MHz for 13C, or for 4,
7, and 8 with a Bruker Avance II 600 NMR spectrometer operating
at 600.13 MHz for 1H and at 150.90 MHz for 13C; all samples were
standardized with respect to TMS. ESI MS were recorded with a
micromass LCT electrospray mass spectrometer, EI MS were re-
corded with a Waters GCT Premier electron impact mass spectrom-
eter, MALDI MS were recorded with a MALDI-Q-ToF Premier
mass spectrometer. Accurate MS were referenced against leucine
enkephalin (555.6 gmol–1) and were reported within 5 ppm. UV/
Vis absorption spectra were recorded with a Shimadzu UV-2450
UV/Vis recording spectrophotometer. All electrochemical experi-
ments were performed with a CH Instruments potentiostat model
660B. Cyclic voltammograms were measured on 0.01 m solutions
of the compounds in acetonitrile or chloroform, and open potential
experiments were carried out on 1 mm solutions of the compounds
in chloroform. Tetra-n-butylammonium hexafluorophosphate
(Bu4NPF6, 0.1 m) was used as supporting electrolyte, a glassy car-
bon working electrode, a Pt wire counterelectrode and a SCE refer-
ence electrode were used. Potentials are quoted vs. the ferrocene–
ferrocenium couple (0.0 V), and all potentials were referenced to
internal ferrocene added at the end of each experiment. All solu-
tions were continuously degassed for 10 min by nitrogen bubbling
before the experiments were performed and a flow of nitrogen was
Figure 8. The fluorescence emission on the electrochemical oxi-
dation of (a) 5 at λexc = 421 nm and (b) 6 at λexc = 394 nm, before
(···) and after (---) +1.6 V was applied for 40 min. (chloroform,
10–4 m) vs. Fc/Fc+; along with the relevant chemically oxidized
products 7 (a, ––) and 8 (b, ––). (Note: in both cases the spectra
have been normalized, the emission before oxidation is normalized
relative to the emission after oxidation).
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Oxidative Bond Formation in Dithienyl Polyphenylenes
maintained over the solution for the duration of the experiments.
Emission and excitation spectra were obtained with a Fluorolog
FL-3–11 spectrofluorimeter, in which lifetime measurements were
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 129.4 (CTh), 128.1
(CTh), 124.9 (CTh), 121.7 (Cquat/Th), 85.7 (Cacetyl) ppm. IR (neat): ν
˜
= 2161 (CϵC), 1352, 1076, 960, 868, 828, 774, 693 cm–1. MS (EI,
performed with an IBH Datastation HUB 5000F. All samples were acetonitrile): m/z = 189.9916 [M]+ (calcd. 189.9911). C10H6S2
degassed under an argon atmosphere prior to the experiment being
carried out.
(190.28): calcd. C 63.12, H 3.18; found C 63.21, H 3.21.
S2CCS2Ј: Yield: 0.51 g (2.68 mmol, 14%). M.p. 73–74 °C. 1H NMR
4
CCDC-782261 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(400 MHz, CDCl3, 25 °C, TMS): δ = 7.33 (dd, JH,H = 1.0 Hz,
3JH,H = 5.0 Hz, 2 H, HTh), 7.30 (dd, 4JH,H = 1.0 Hz, 3JH,H = 3.5 Hz,
3
2 H, HTh), 7.03 (dd, JH,H = 3.5, 5.0 Hz, 2 H, HTh) ppm. 13C{1H}
NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 131.7 (CTh), 127.2
2-Thienyl-3-thienylacetylene (S2CCS3Ј): To a mixture of benzyltri-
ethylammonium chloride (25 mg, 0.11 mmol), copper(I) iodide
(34 mg, 0.13 mmol), tetrakis(triphenylphosphane) palladium(0)
(110 mg, 0.09 mmol), 2-bromothiophene (0.305 mL, 3.15 mmol),
and 4-(3-thienyl)-2-methyl-3-butyn-2-ol (0.59 g, 3.32 mmol) in ben-
zene (10 mL) was added 5.5 n NaOH (8 mL, 0.044 mmol). The
mixture was stirred at 80 °C for 3 d, and it was then cooled to room
temperature. A solution of saturated ammonium chloride (40 mL)
was added, and the solution was stirred for 1 h. The phases were
separated, and the aqueous layer was extracted with toluene. The
organic phases were dried with magnesium sulfate, and the solvent
was evaporated. The product was purified by column chromatog-
raphy on silica (hexane/dichloromethane, 3:2) to give a white solid
(0.21 g, 1.11 mmol, 34%). M.p. 75–76 °C. 1H NMR (400 MHz,
CDCl3, 25 °C, TMS): δ = 7.55 (dd, 4JH,H = 1.0, 3.0 Hz, 1 H, HThЈ),
7.33 (dd, 4JH,H = 3.0 Hz, 3JH,H = 5.0 Hz, 1 H, HThЈ), 7.30 (m, 2 H,
(CTh), 126.7 (CTh), 122.4 (CTh/quat), 85.7 (Cacetyl) ppm. IR (neat): ν
˜
= 2186 (CϵC), 1433, 1407, 1199, 1041, 1028, 850, 825, 694 cm–1.
MS (EI, acetonitrile): m/z = 189.9919 [M]+ (calcd. 189.9911).
C10H6S2 (190.28): calcd. C 63.12, H 3.18; found C 63.83, H 3.07.
Synthesis of Thienyl-Substituted Benzenes: A mixture of the rel-
evant acetylene (0.32 mmol), 2,3,4,5-tetrakis-(4-tert-butylphenyl)-
cyclopentadienone (150 mg, 0.25 mmol), and benzophenone (0.5 g)
were heated for 90 min at 300 °C while attached to an air con-
denser, giving a brown mixture. After cooling to room temperature,
this was purified by flash chromatography (SiO2; hexane/diethyl
ether, 9:1) to give the product as a light colored solid (1 and 2,
grey; 5, white; 6, brown). These were recrystallized from a mixture
of chloroform and methanol (2 mL of each).
1: Yield: 82 mg (0.10 mmol, 41%). M.p. 245–246 °C. 1H NMR
3
(400 MHz, CDCl3, 25 °C, TMS): δ = 6.92 (d, JH,H = 8.3 Hz, 4 H,
3
4
3
HAr), 6.80 (m, 8 H, 2*HAr), 6.62 (d, JH,H = 8.6 Hz, 4 H, HAr),
2*HTh), 7.22 (dd, JH,H = 1.0 Hz, JH,H = 5.0 Hz, 1 H, HThЈ), 7.03
(dd, 3JH,H = 3.0, 5.0 Hz, 1 H, HTh) ppm. 13C{1H} NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 131.4 (CTh), 129.3 (CThЈ), 128.4 (CThЈ),
126.8 (CTh), 126.7 (CTh), 125.1 (CThЈ), 122.8 (CTh/quat), 121.5
6.27 (m, 4 H, 2*HTh), 2.26 (s, 6 H, CH3), 1.16 (s, 18 H, CMe3),
1.10 (s, 18 H, CMe3) ppm. 13C{1H} NMR (100 MHz, CDCl3,
25 °C, TMS): δ = 147.9 (Cquat), 147.5 (Cquat), 141.7 (Cquat), 141.6
(Cquat), 139.8 (Cquat), 139.7 (Cquat), 137.8 (Cquat), 137.6 (Cquat),
134.2 (Cquat), 130.8 (CAr), 130.5 (CAr), 128.8 (CTh), 123.7 (CTh),
123.3 (CAr), 123.0 (CAr), 34.2 (CMe3), 34.0 (CMe3), 31.3 (CH3),
(CThЈ/quat), 87.8 (Cacetyl), 81.7 (Cacetyl) ppm. IR (neat): ν = 2163
˜
(CϵC), 1213, 1118, 866, 849, 824, 774, 699, 689, 619 cm–1. MS
(EI, acetonitrile): m/z = 189.9916 [M]+ (calcd. 189.9911). C10H6S2
(190.28): calcd. C 63.12, H 3.18; found C 62.96, H 3.21.
31.2 (CH ), 15.2 (CH ) ppm. IR (neat): ν = 2960, 1511, 1460, 1391,
˜
3
3
1361, 1269, 1118, 1019, 830, 797, 571 cm–1. MS (ESI, acetonitrile):
Synthesis of Bisacetylenes S3CCS3Ј S2CCS2Ј, and MeS2CCS2ЈMe:
,
m/z = 821.4197 [M + Na]+ (calcd. 821.4191).
To a mixture of the appropriate bromothiophene (20 mmol), 2-
methyl-3-butyn-2-ol (2.0 mL, 20 mmol), benzyltriethylammonium
chloride (71 mg, 0.31 mmol), copper(I) iodide (100 mg,
0.53 mmol), and tetrakis(triphenylphosphane) palladium(0)
(200 mg, 0.17 mmol) in benzene (10 mL) was added 5.5 n NaOH
(8 mL, 0.044 mmol), and the mixture was stirred for 3 d. More bro-
mothiophene (20 mmol) in benzene (8.0 mL) was added, and the
solution was heated to 80 °C and stirred at this temperature for
3 d. The mixture was then cooled to room temperature. A solution
of saturated ammonium chloride (40 mL) was added, and the solu-
tion was stirred for 1 h. The phases were separated, and the aque-
ous layer was extracted with toluene. The organic phases were dried
with magnesium sulfate, and solvent was evaporated. Purification
by column chromatography on silica (hexane) gave the desired
products as white solids.
2: Yield: 124 mg (0.16 mmol, 66%). M.p. 270–271 °C. 1H NMR
4
(400 MHz, CDCl3, 25 °C, TMS): δ = 7.02 (dd, JH,H = 1.0 Hz,
3JH,H = 5.0 Hz, 2 H, HTh), 6.92 (d, 3JH,H = 8.0 Hz, 4 H, HAr), 6.83
3
3
(d, JH,H = 8.0 Hz, 4 H, HAr), 6.81 (d, JH,H = 8.0 Hz, 4 H, HAr),
3
3
6.66 (d, JH,H = 8.5 Hz, 4 H, HAr), 6.63 (dd, JH,H = 3.5, 5.0 Hz,
4
3
2 H, HTh), 6.51 (dd, JH,H = 1.0 Hz, JH,H = 3.5 Hz, 2 H, HTh),
1.16 (s, 18 H, CMe3), 1.11 (s, 18 H, CMe3) ppm. 13C{1H} NMR
(100 MHz, CDCl3, 25 °C, TMS): δ = 147.6 (Cquat), 147.2 (Cquat),
141.6 (Cquat), 141.4 (Cquat), 141.4 (Cquat), 137.1 (Cquat), 137.0
(Cquat), 133.4 (CTh/quat), 130.4 (CAr), 1F.0 (CAr), 128.6 (CTh), 125.1
(CTh), 125.0 (CTh), 122.9 (CAr), 122.7 (CAr), 33.7 (CMe3), 33.6
(CMe ), 30.8 (CH ), 30.7 (CH ) ppm. IR (neat): ν = 3031, 2958,
˜
3
3
3
2901, 2866, 1510, 1461, 1390, 1362, 1269, 1019, 827, 699 cm–1. MS
(ESI, acetonitrile): m/z = 793.3842 [M + Na]+ (calcd. 793.3878).
MeS2CCS2ЈMe: Yield: 1.84 g (8.43 mmol, 42%). M.p. 55–56 °C. 1H
NMR (400 MHz, CDCl3, 25 °C, TMS): δ = 7.07 (d, 3JH,H = 3.5 Hz,
2 H, HTh), 6.67 (qd, JH,H = 1.0 Hz, JH,H = 3.8 Hz, 2 H, HTh),
2.50 (d, 4JH,H = 0.8 Hz, 6 H, CH3) ppm. 13C{1H} NMR (100 MHz,
CDCl3, 25 °C, TMS): δ = 142.3 (CTh/quat), 132.2 (CTh), 125.4 (CTh),
5: Yield: 125 mg (0.16 mmol, 66%). M.p. 253–254 °C. 1H NMR
3
(400 MHz, CDCl3, 25 °C, TMS): δ = 6.90 (d, JH,H = 8.5 Hz, 4 H,
4
3
3
HAr), 6.85–6.82 (m, 6 H, HTh and HAr), 6.74 (d, JH,H = 8.0 Hz, 4
3
4
H, HAr), 6.65 (d, JH,H = 8.0 Hz, 4 H, HAr), 6.56 (dd, JH,H = 1.5,
3.0 Hz, 2 H, HTh), 6.51 (dd, 4JH,H = 1.0, 3JH,H = 5.0 Hz, 2 H, HTh),
1.16 (s, 18 H, CMe3), 1.11 (s, 18 H, CMe3) ppm. 13C{1H} NMR
(100 MHz, CDCl3, 25 °C, TMS): δ = 147.4 (Cquat), 147.1 (Cquat),
140.6 (Cquat), 140.4 (Cquat), 140.3 (Cquat), 137.3 (Cquat), 137.2
(Cquat), 134.9 (Cquat), 130.5 (CAr), 130.2 (CAr), 130.0 (CTh), 123.9
120.7 (CTh/quat), 85.8 (Cacetyl), 15.5 (CH ) ppm. IR (neat): ν = 2190
˜
3
(CϵC), 1487, 1439, 1200, 1159, 1044, 804, 789, 720 cm–1. MS (EI,
acetonitrile): m/z = 218.0225 [M]+ (calcd. 218.0224).
S3CCS3Ј: Yield: 1.52 g (7.99 mmol, 40%). M.p.76–77 °C. 1H NMR
(400 MHz, CDCl3, 25 °C, TMS): δ = 7.54 (dd, 4JH,H = 1.5, 3.0 Hz, (CTh), 122.9 (CAr), 122.6 (CAr), 122.1 (CTh), 33.7 (CMe3), 33.6
4
3
2 H, HTh), 7.32 (dd, JH,H = 3.0 Hz, JH,H = 5.0 Hz, 2 H, HTh),
(CMe ) 30.8 (CH ), 30.7 (CH ) ppm. IR (neat): ν = 1511, 1461,
˜
3 3 3
7.21 (dd, 4JH,H = 1.5 Hz, JH,H = 4.5 Hz, 2 H, HTh) ppm. 13C{1H}
1392, 1362, 1269, 1202, 1119, 1018, 853, 803, 763 cm–1. MS (ESI,
3
Eur. J. Org. Chem. 2011, 3491–3499
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3497

C. J. Martin, B. Gil, S. D. Perera, S. M. Draper
FULL PAPER
acetonitrile): m/z = 771.4048 [M + H]+ (calcd. 771.4058). C54H58S2
3
3
4 H, HAr), 7.08 (d, JH,H = 5.3 Hz, 4 H, HAr), 6.96 (d, JH,H =
(771.17): calcd. C 84.10, H 7.58; found C 84.29, H 7.53.
3.8 Hz, 2 H, HTh), 6.83 (m, 8 H, 2*HAr), 6.67 (m, 8 H, 2*HAr),
6.38 (s, 2 H, HThЈ), 6.31 (d, JH,H = 3.8 Hz, 2 H, HTh), 1.44 (s, 18
3
6: Yield: 120 mg (0.16 mmol, 66%). M.p. 248 °C. 1H NMR
H, CMe3), 1.32 (s, 18 H, CMe3), 1.11 (s, 18 H, CMe3), 1.10 (s, 18
H, CMe3) ppm. 13C{1H} NMR (150.9 MHz, CDCl3, 25 °C, TMS):
δ = 149.6 (Cquat), 149.4 (Cquat), 147.3 (Cquat), 147.2 (Cquat), 140.0
(Cquat), 139.9 (Cquat), 139.7 (Cquat), 137.8 (Cquat), 137.7 (Cquat),
137.6 (Cquat), 137.5 (Cquat), 134.3 (Cquat), 134.2 (Cquat), 133.6
(Cquat), 132.3 (Cquat), 130.8 (CAr), 130.7 (CAr), 130.6 (CAr), 129.9
(CAr), 128.1 (CTh), 127.4 (Cquat), 127.3 (Cquat), 127.0 (Cquat), 126.8
(Cquat), 125.1 (CThЈ), 124.8 (CAr), 124.6 (CAr), 122.7 (2*CAr), 120.7
(CTh), 34.7 (CMe3), 34.4 (CMe3), 34.0 (CMe3), 31.9 (CMe3), 31.7
3
(400 MHz, CDCl3, 25 °C, TMS): δ = 7.00 (d, JH,H = 5.0 Hz, 1 H,
3
HThЈ), 6.91 (m, 4 H, 2*HAr), 6.86 (dd, JH,H = 2.9, 5.0 Hz, 1 H,
3
H
Th), 6.81 (m, 6 H, 3*HAr), 6.75 (d, JH,H = 8.0 Hz, 2 H, HAr),
6.66 (m, 4 H, 2*HAr), 6.64–6.59 (m, 3 H, 2*HTh and 1*HThЈ), 6.44
3
(d, JH,H = 3.5 Hz, 1 H, HThЈ), 1.16 (s, 18 H, CMe3), 1.12 (s, 18 H,
CMe3) ppm. 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ =
147.5 (Cquat), 147.4 (Cquat), 147.2 (Cquat), 147.1 (Cquat), 142.0
(Cquat), 141.3 (Cquat), 140.7 (Cquat), 140.4 (Cquat), 140.2 (Cquat),
137.2 (Cquat), 137.2 (Cquat), 137.1 (Cquat), 135.8 (Cquat), 132.4
(Cquat), 130.4 (2*CAr), 130.1 (CAr), 130.0 (CAr), 129.9 (CTh), 128.4
(CThЈ), 125.0 (CThЈ), 124.9 (CTh), 124.0 (CThЈ), 122.9 (CAr), 122.8
(CAr), 122.6 (2*CAr), 122.1 (CTh), 33.7 (CMe3), 33.6 (CMe3), 30.8
(CH ), 31.4 (CH ), 31.2 (CH ), 29.7 (CH ) ppm. IR (KBr): ν =
˜
3
3
3
3
3414, 2963, 1638, 1462, 1363, 1261, 1096, 1022, 801, 610 cm–1. MS
(MALDI, acetonitrile): m/z = 1534.7457 [M]+ (calcd. 1534.7409).
(CH ), 30.7 (CH ) ppm. IR (neat): ν = 2957, 2863, 1461, 1361,
˜
8: Purified by silica (dichloromethane/hexane, 1:4). Yield: 26 mg
(0.017 mmol, 52%). M.p. Ͼ320 °C. 1H NMR (600 MHz, CDCl3,
25 °C, TMS): δ = 7.33 (m, 6 H, HAr and HTh), 7.27 (m, 4 H, HAr
and solv. peak), 7.22–7.16 (m, 10 H, 2*HAr and HTh), 6.82 (m, 8
H, 2*HAr), 6.70 (m, 8 H, 2*HAr), 6.44 (s, 2 H, HThЈ), 1.40 (s, 18 H,
CMe3), 1.33 (s, 18 H, CMe3), 1.11 (s, 18 H, CMe3), 1.10 (s, 18 H,
CMe3) ppm. 13C{1H} NMR (150.9 MHz, CDCl3, 25 °C, TMS): δ
= 150.8 (Cquat), 149.4 (Cquat), 147.3 (Cquat), 140.2 (Cquat), 140.0
(Cquat), 138.0 (Cquat), 137.7 (Cquat), 137.5 (Cquat), 137.4 (Cquat),
137.2 (Cquat), 136.9 (Cquat), 135.4 (Cquat), 134.9 (Cquat), 134.2
(Cquat), 132.8 (Cquat), 132.6 (Cquat), 131.9 (CTh), 130.8 (CAr), 130.6
(2*CAr), 128.9 (Cquat), 128.2 (CThЈ), 126.7 (Cquat), 126.0 (Cquat),
125.1 (CAr), 124.9 (CAr), 124.7 (CAr), 122.7 (CAr), 122.6 (CAr),
120.2 (CTh), 34.5 (CMe3), 34.4 (CMe3), 33.9 (2*CMe3), 31.4 (CH3),
3
3
1270, 1153, 1102, 1019, 828 cm–1. MS (ESI, acetonitrile): m/z =
771.4050 [M + H]+ (calcd. 771.4058).
General FeCl3 Cyclodehydrogenation Procedure: The relevant di-
thienyl benzene (0.065 mmol) was dissolved in dry dichlorometh-
ane (20 mL) and an excess of FeCl3 (0.189 g, 1.12 mmol, 20 equiv.)
in nitromethane (3 mL) was added dropwise under bubbling nitro-
gen. The mixture was stirred for 40 min to give a brown solution.
This was quenched with methanol (30 mL), poured into water, ex-
tracted into chloroform, dried with MgSO4, and concentrated.
3: Purified by column chromatography on silica (dichloromethane/
hexane, 1:3). Yield: 47 mg (0.058 mmol, 90%). M.p. Ͼ320 °C. 1H
NMR (400 MHz, CDCl3, 25 °C, TMS): δ = 7.18 (d, 3JH,H = 6.5 Hz,
3
4 H, HAr), 7.16 (s, 2 H, HTh), 7.09 (d, JH,H = 8.0 Hz, 4 H, HAr),
31.3 (CH ), 31.0 (2*CH ) ppm. IR (KBr): ν = 3414, 2963, 1638,
˜
3
3
3
3
6.72 (d, JH,H = 8.0 Hz, 4 H, HAr), 6.63 (d, JH,H = 8.5 Hz, 4 H,
HAr), 2.36 (s, 6 H, CH3), 1.24 (s, 18 H, CCH3), 1.0 (s, 18 H, CCH3)
ppm. 13C{1H} NMR (100 MHz, CDCl3, 25 °C, TMS): δ = 150.3
(Cquat), 146.8 (Cquat), 141.2 (Cquat), 139.1 (Cquat), 137.3 (Cquat),
136.8 (Cquat), 136.5 (Cquat), 134.6 (Cquat), 133.8 (Cquat), 131.5 (CAr),
130.4 (CAr), 125.1 (Cquat), 124.4 (CAr), 122.3 (CAr), 118.7 (CTh),
34.1 (CMe3), 33.6 (CMe3), 31.0 (CH3), 30.7 (CH3) ppm. IR (neat):
1462, 1363, 1261, 1096, 1022, 801, 610 cm–1. MS (MALDI, acetoni-
trile): m/z = 1534.7480 [M]+ (calcd. 1534.7490).
Supporting Information (see footnote on the first page of this arti-
cle): Crystal packing of 3 along with additional photochemical
data.
ν = 2957, 1520, 1388, 1361, 853, 789, 696 cm–1. MS (MALDI, ace-
˜
Acknowledgments
tonitrile): m/z = 796.4168 [M]+ (calcd. 796.4136).
4: Purified by silica glass plate (dichloromethane/hexane, 1:4).
Yield: 27 mg (0.018 mmol, 55%). M.p. Ͼ320 °C. 1H NMR
(600 MHz, [D2]-1,2-dichloroethane, 25 °C, TMS): δ = 7.44 (d, 3JH,H
C. J. M. thanks the Science Foundation Ireland award SFI-
08RFPCHE1465 and the Trinity College Ussher fellowship for fin-
ancial support. S. P. thanks the Science Foundation Ireland award
SFI-05PICAI819, and B. G. would like to acknowledge funding
from the Marie-Curie EU grant FP5MKTD-014772-SMART. We
thank Dr. Martin Feeney, Dr. J. Bernard Jean-Denis, Dr. John
O’Brien, and Dr. Manuel Ruether for technical assistance. For X-
ray analysis we thank Dr. Sunil Varughese (SFI-05PICAI819) and
Dr. Longsheng Wang (FP5MKTD-014472-SMART).
3
= 5.5 Hz, 2 H, HTh), 7.41 (s, 2 H, HThЈ), 7.35 (d, JH,H = 7.7 Hz,
4 H, HAr), 7.32 (d, 3JH,H = 5.2 Hz, 2 H, HTh), 7.27 (m-with CHCl3
3
3
peak, 4 H, HAr), 7.21 (d, JH,H = 7.9 Hz, 4 H, HAr), 7.18 (d, JH,H
3
= 8.0 Hz, 4 H, HAr), 6.83 (d, JH,H = 7.9 Hz, 4 H, HAr), 6.81 (d,
3JH,H = 8.1 Hz, 4 H, HAr), 6.76 (d, 3JH,H = 8.1 Hz, 4 H, HAr), 6.71
3
(d, JH,H = 8.1 Hz, 4 H, HAr), 1.42 (s, 18 H, CMe3), 1.32 (s, 18 H,
CMe3), 1.08 (s, 36 H, 2*CMe3) ppm. 13C{1H} NMR (150.9 MHz,
CDCl3, 25 C, TMS): δ = 150.9 (Cquat), 150.8 (Cquat), 147.4 (Cquat),
147.3 (Cquat), 140.3 (Cquat), 140.0 (Cquat), 138.3 (Cquat), 137.4
(Cquat), 137.2 (Cquat), 136.8 (Cquat), 136.7 (Cquat), 135.7 (Cquat),
135.2 (Cquat), 134.9 (Cquat), 134.2 (Cquat), 131.9 (CAr), 131.8 (CAr),
130.7 (CAr), 130.6 (CAr), 127.7 (CTh), 126.5 (Cquat), 126.0 (Cquat),
125.7 (CAr), 125.0 (CAr), 124.7 (Cquat), 122.7 (CAr), 122.6 (CAr),
120.4 (CTh), 118.1 (CThЈ), 117.2 (Cquat), 34.5 (CMe3), 34.4 (CMe3),
33.9 (CMe3), 33.8 (CMe3), 31.5 (CH3), 31.3 (CH3), 31.0 (2* CH3)
ppm. MS (MALDI, chloroform): m/z = 1534.7516 [M]+ (calcd.
1534.7490).
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www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 3491–3499

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Received: March 9, 2011
Published Online: May 24, 2011
Eur. J. Org. Chem. 2011, 3491–3499
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3499