Synthesis and characterization of extended tetrathiafulvalenes with di-, tri-, and tetraethynylethene cores

Article abstract of DOI:10.1002/ejoc.200500287

A selection of new acetylenic building blocks has been prepared and employed for construction of extended tetrathiafulvalenes (TTFs) and novel donor-acceptor molecules based on either diethynylethene (DEE), triethynylethene (TriEE), or tetraethynylethene

Full text of DOI:10.1002/ejoc.200500287

FULL PAPER
Synthesis and Characterization of Extended Tetrathiafulvalenes with Di-, Tri-,
and Tetraethynylethene Cores
Asbjørn Sune Andersson,[a] Katrine Qvortrup,[a] Esben Rossel Torbensen,[b]
Jan-Philipp Mayer,[b] Jean-Paul Gisselbrecht,[c] Corinne Boudon,[c] Maurice Gross,[c]
Anders Kadziola,[a] Kristine Kilså,[a] and Mogens Brøndsted Nielsen*[a]
Keywords: Alkynes / Conjugation / C–C coupling / Cross-coupling / Donor–acceptor systems
A selection of new acetylenic building blocks has been pre- were studied for their redox, chromophoric, and structural
pared and employed for construction of extended tetrathia-
fulvalenes (TTFs) and novel donor–acceptor molecules based
on either diethynylethene (DEE), triethynylethene (TriEE), or
tetraethynylethene (TEE) cores. The novel chromophores
properties, which have provided fundamental structure–
property relationships.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
Tetrathiafulvalene (TTF) is a good electron donor that
has been widely exploited in supramolecular and materials
chemistry.[1] The extension of π-electron conjugation in
tetrathiafulvalene by a spacer unit as well as functionaliz-
ation by electron acceptors has attracted considerable atten-
tion in the quest for electrically conducting or non-linear
optical (NLO) materials (Figure 1).[2] We have recently
shown that acetylenic scaffolding is a powerful tool for con-
structing alkyne-extended TTFs by suitable modules, such
as the acetylenic dithiafulvene 1 that is readily desilylated
to provide the terminal acetylene 2.[3]
very useful modules that have been successfully employed
by Diederich and co-workers for the construction of a large
variety of conjugated molecules, such as poly(triacetylene)
oligomers and expanded radialenes.[4] The optical proper-
ties of these scaffolds were strongly enhanced upon func-
tionalization with aryl groups, such as electron-donating
anilino groups and electron-accepting nitrophenyl groups.[5]
Thus, donor–acceptor functionalized TEE scaffolds were
found to exhibit exceptionally high third-order NLO
susceptibilities.[6] For these reasons, we became interested in
functionalizing di-, tri-, and tetraethynylethenes with dithi-
afulvene donor groups. Such target molecules will be
termed DEE-, TriEE-, and TEE-extended TTFs. Here we
present synthetic protocols together with electrochemical
and preliminary photophysical investigations.[7]
Figure 1. Schematic representation of extended TTF and donor–
acceptor (D–A) dyads based hereupon.
Results and Discussion
Silylated derivatives of (E)-diethynylethene [(E)-DEE]
Synthesis: The synthesis of DEE-extended TTFs pro-
ceeds according to Scheme 1. The dialdehyde 3[8] and the
phosphonium salt 4[9] were prepared according to literature
procedures. They were reacted together in a Wittig reaction,
after deprotonation of 4 with nBuLi, which afforded the
DEE-TTF 5 in good yield. This same strategy has found
wide application for preparing polyenic analogues of
TTF.[10] However, treating 3 with the ylide of 6[11] gave only
the mono-coupled product 7. It was not possible to force
and tetraethynylethene (TEE) provide examples of other
[a] Department of Chemistry, University of Copenhagen,
Universitetsparken 5, 2100 Copenhagen Ø, Denmark
Fax: +45-35320212
E-mail: mbn@kiku.dk
[b] Department of Chemistry, University of Southern Denmark,
Campusvej 55, 5230 Odense M, Denmark
[c] Laboratoire dЈElectrochimie et de Chimie Physique du Corps
Solide, UMR 7512, CNRS, Université Louis Pasteur,
67000 Strasbourg, France
3660
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200500287
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Extended Tetrathiafulvalenes with Di-, Tri-, and Tetraethynylethene Cores
FULL PAPER
olefination at both aldehyde positions by treating 3 with microwave heating at 60 °C for 6 min.[18] Hereby TEE-TTF
more than two equivalents of 6. However, a phosphite-me- 12 was obtained in a yield of 38%. The yield was improved
diated cross-coupling with the 1,3-dithiole-2-one 8 gave the further by substituting the microwave heating with ultra-
cross-coupled compound 9 in good yield. Accordingly, this sonification at 30 °C for 4 hours.[19] The TEE core was un-
latter procedure presents a convenient route to unsymmetri- der these conditions constructed in yields as high as 85%.
cal, alkene-extended TTFs, in this case with one end con-
taining cyanoethyl-protected thiolate groups. Cyanoethyl-
thio-substituted TTFs have proven as versatile building
blocks for oligomers and macrocycles via stepwise depro-
tection-realkylation protocols as shown by Becher and co-
workers.[12] The cyanoethyl groups of 9 were removed ac-
cording to the standard procedure by CsOH, leaving the
Si(iPr)3 groups uncleaved. Alkylation with MeI in situ fi-
nally afforded the symmetrical TTF 10.
Scheme 2. Synthesis of TEE-extended TTF. a) [Pd(PhCN)2Cl2],
P(tBu)3, CuI, HN(iPr)2, THF, toluene, microwave heating, 60 °C,
6 min; 38%; b) [Pd(PhCN)2Cl2], P(tBu)3, CuI, HN(iPr)2, THF, tol-
uene, ultrasonification, 30 °C; 85%.
TEE-TTF 12 containing two silyl-protected acetylene
groups possesses the possibility for further acetylenic scaf-
folding. The trimethylsilyl protecting groups were removed
by K2CO3 in THF/MeOH, and the desilylated compound
was hereafter subjected to an oxidative Hay coupling[20]
with an excess of phenylacetylene (Scheme 3). This cross-
coupling reaction provided the large conjugated chromo-
phore 13 in 18%. The rather low yield was partly due to
significant decomposition of the desilylated intermediate.
We experienced similar stability problems in the desilylation
of the DEE-extended TTFs. Attempts of cross-coupling de-
silylated 12 with p-iodonitrobenzene were unsuccessful,
since decomposition took over in this slow reaction (as
compared to the Hay coupling).
Scheme 1. Synthesis of DEE-extended TTFs. a) nBuLi, THF; 60%;
b) NEt3, THF; 69%; c) P(OEt)3; 79%; d) CsOH·H2O, MeI, THF,
MeOH; 82%.
Geminally functionalized TEEs were previously con-
structed from Sonogashira cross-couplings[13] between vi-
Scheme 3. Synthesis of extended TEE-TTF chromophore. a)
K2CO3, THF, MeOH; b) phenylacetylene, CuCl, TMEDA,
CH2Cl2, air; 18%. TMEDA = N,N,NЈ,NЈ-tetramethylethylenedi-
nylic dibromides and arylacetylenes containing either elec-
tron-donating (e.g. NMe2) or withdrawing (e.g. NO2) sub-
amine.
stituents.[14] The couplings usually proceeded smoothly in
the presence of the [Pd(PPh3)2Cl2]/CuI catalyst system. Sur-
In order to construct a TEE core with dithiafulvene do-
prisingly, we find that treatment of 11 (Scheme 2) with 2 nors and p-nitrophenyl acceptors, we decided to incorporate
under these conditions completely failed to provide the the p-nitrophenyl groups first. The synthesis proceeds ac-
TEE-extended TTF 12.[15] Many cross-couplings are en- cording to Scheme 4. Compound 11 was desilylated and
hanced by using bulky, electron-rich phosphanes.[16] Re- then subjected to a Pd-catalyzed coupling with an excess of
cently, Hundertmark et al.[17] developed a versatile catalyst p-iodonitrobenzene to provide the new molecular module
system, [Pd(PhCN)2Cl2]/P(tBu)3/CuI, that allowed room 14. An ultrasound-promoted cross-coupling reaction be-
temperature Sonogashira coupling of aryl bromides with a tween 14 and two equivalents of 2 ultimately afforded the
wide variety of terminal acetylenes. We turned to this sys- donor–acceptor TEE 15 in almost quantitative yield. We
tem and at the same time subjected the reaction mixture to exploited this same procedure for preparing a donor–ac-
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M. B. Nielsen et al.
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ceptor TEE containing one remaining silyl protecting group
(Scheme 5). Thus, selective mono-desilylation of 16 fol-
lowed by a cross-coupling reaction with p-iodonitrobenzene
gave compound 17 that was subsequently coupled with two
equivalents of 2, which provided TEE 18.
Scheme 6. Synthesis of donor–acceptor TriEE. a) CBr4, PPh3, Zn,
CH2Cl2, room temp.; 72%; b) [Pd(PhCN)2Cl2], P(tBu)3, CuI,
HN(iPr)2, THF, toluene, ultrasonification, 30 °C; 30%.
Finally, synthetic protocols were developed for obtaining
DEE-spaced donor–acceptor molecules.[24] The new dibro-
mide 20 conveniently serves as a useful starting material for
such target molecules (Scheme 7). Subjecting 20 to the Pd0-
catalyzed stereoselective hydrogenolysis procedure devel-
oped by Uenishi et al.,[25] followed by in situ cross-coupling
with 2 gave cis-22 in good yield. Diethyl phosphite re-
duction[26] of 20 at 50 °C for 6 h gave trans-23 that was iso-
lated and subsequently cross-coupled with 2 to afford trans-
22. When the reduction of 20 was run instead at 0 °C for
2 h, a mixture of trans/cis-22 (53:47) was obtained in an
overall yield of 87%. The low stereoselectivity as compared
to that reported by Hirao et al.[26] from reduction of β,β-
dibromostyrene (trans/cis, 94:6) is probably due to the pres-
ence of the triple bond between the aromatic ring and the
dibromo-substituted double bond. A lower stereoselectivity
for compounds not having the double bond directly at-
tached to the aromatic ring has been reported by others.[27]
We found that cis-22 conveniently decomposed in prefer-
ence to trans-22 upon prolonged heating at a temperature
of 50 °C or higher. Thus, only trace amounts of the cis-
isomer remained after 6 h at 50 °C.
Scheme 4. Synthesis of donor–acceptor TEE. a) K2CO3, THF,
MeOH; b) p-iodonitrobenzene, [PdCl2(PPh3)2], CuI, Et3N, THF;
54%; c) [Pd(PhCN)2Cl2], P(tBu)3, CuI, HN(iPr)2, THF, toluene,
ultrasonification, 30 °C; 97%.
Scheme 5. Synthesis of unsymmetrical donor–acceptor TEE. a)
K2CO3, THF, MeOH; b) p-iodonitrobenzene, [PdCl2(PPh3)2], CuI,
Et3N, THF; 44%; c) [Pd(PhCN)2Cl2], P(tBu)3, CuI, HN(iPr)2,
THF, toluene, ultrasonification, 30 °C; 48%.
A new donor–acceptor molecule based on the triethyny-
lethene (TriEE) core was prepared according to the proto-
col depicted in Scheme 6. First the aldehyde 19[21] was sub-
jected to a Corey–Fuchs dibromoolefination,[22] which gave
the new building block 20, a vinylic dibromide containing
a p-nitrophenylacetylene substituent. A cross-coupling reac-
tion between 2 and 20 afforded TriEE 21 in a yield of
30%.[23] For comparison, 21 was only obtained in a yield
of 10% with the [Pd(PPh3)2Cl2]/CuI catalyst.
Scheme 7. Synthesis of donor–acceptor DEEs. a) [Pd(PPh3)4],
Bu3SnH, toluene; b) CuI, HN(iPr)2, THF; 39%; c) HPO(OEt)2,
Et3N, 50 °C; 42%; d) [Pd(PPh3)4], CuI, HN(iPr)2, toluene, THF;
67%.
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Extended Tetrathiafulvalenes with Di-, Tri-, and Tetraethynylethene Cores
FULL PAPER
X-ray Crystallographic Analysis: Crystals of cis-22 suit-
able for X-ray crystallographic analyses were grown by slow
evaporation of a CH2Cl2 solution at ca. 8 °C. Crystals of
trans-22 were obtained by recrystallization from MeCN.
The structures of cis-22 and trans-22 (Figure 2 and Figure
3) confirm the postulated isomer designations. Moreover,
the structures reveal that the conjugated section, except for
one of the methoxycarbonyl groups, is almost in the same
plane for both molecules, with root-mean-square deviations
of 0.206 Å and 0.133 Å, respectively. The bond length alter-
nation in the p-nitrophenyl ring can be expressed by the
quinoid character (δr) of the ring defined by[28]
Figure 4. Definition of bond lengths for calculation of quinoid
character (δr).
Electronic Absorption Spectroscopy: The UV/Vis spectro-
scopic data in CHCl3 of the compounds are listed in
Table 1, and some selected spectra are displayed in Figure
5 and Figure 6 in comparison to the butadiyne-extended
δr = [(a – b) + (c – b)]/2 Ϸ [(aЈ – bЈ) + (cЈ – bЈ)]/2,
where a, b and c are defined according to Figure 4. Very
small values of δr = 0.010 Å (cis-22) and 0.011 Å (trans-22)
are obtained, which signal a little permanent dipole mo-
ment in the ground state. The same quinoid character was
determined for the p-NO2Ph ring of p-NO2C6H4–CϵC–
C6H4NH2 (δr = 0.011 Å).[28]
Figure 5. UV/Vis absorption spectra in CHCl3 of extended TTFs.
Figure 2. X-ray crystal structure of cis-22. All atoms, except methyl
hydrogen atoms on C28 together with O7, O8 and the C29 methyl
group, are approximately planar (rmsd = 0.206 Å for 33 atoms).
They make an angle of 78° with the plane formed by O7, O8, C25,
C27 and C29 (rmsd = 0.006 Å). Drawing made by ORTEP-II.[34]
Figure 6. UV/Vis absorption spectra in CHCl3 of donor–acceptor
molecules.
Figure 3. X-ray crystal structure of trans-22. All atoms of trans-22, except methyl hydrogens on C28 together with O7, O8 and the C29
methyl group, are almost planar (rmsd = 0.133 Å for 33 atoms). They make an angle of 65° with the plane formed by O7, O8, C25, C27
and C29 (rmsd = 0.009 Å). Drawing made by ORTEP-II.[34]
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M. B. Nielsen et al.
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Table 1. Absorption band maxima and molar molar absorptivities in the UV/Vis spectra of compounds in CHCl3.[a]
Compound
λmax [nm] (ε [–1 cm–1])
353 (4790) 468 (46000)
287 (sh, 10500) 299 (sh, 8110) 349 (8560)
5
294 (sh, 16400) 303 (19400)
335 (6550)
496 (67500)
365 (sh, 7330) 483 (35300)
7
268 (13200)
273 (19600)
280 (17100)
279 (13800)
263 (42400)
301 (29900)
9
309 (18300)
312 (14900)
293 (15100)
295 (24600)
327 (34600)
339 (sh, 10200) 359 (sh, 7670) 493 (sh, 48100) 519 (67000)
340 (sh, 8840) 358 (sh, 6640) 496 (sh, 40900) 524 (62500)
10
12
303 (15000)
339 (33600)
339 (15400)
389 (17200)
378 (14500)
462 (sh, 27500) 490 (38500)
491 (35400)
471 (33300)
453 (38900)
13
522 (sh, 31100)
15
343 (sh, 33400) 381 (23000)
525 (sh, 29000)
516 (sh, 21700)
18
300 (sh, 22900) 312 (25400)
303 (sh, 20000) 329 (23600)
305 (sh, 16800) 330 (20600)
305 (sh, 16400) 325 (19300)
330 (25400)
437 (26200)
423 (12600)
424 (29800)
375 (18800)
21
cis-22
trans-22
[a] sh = shoulder.
TTF 24.[3b] The longest-wavelength absorption maximum is or trans-22 in CHCl3 at 436 nm, the absorption spectrum
significantly red-shifted along the progression 24 (λmax
429 nm; 2.9 eV) – 12 (λmax = 453 nm; 2.7 eV) – 5 (λmax
=
=
changes as a result of isomerization in less than an hour.
The photostationary state is characterized by a cis/trans ra-
496 nm, 2.5 eV). Nguyen et al.[10a] found a longest-wave- tio of 8:2. Similarly as to what was found by Arai,[24e] the
length absorption at λmax = 420 nm (3.0 eV) for 25, an ana- ratio of quantum yields φtransǞcis/φcisǞtrans can be estimated
logue of 5 devoid of the lateral acetylene appendages. These to 6:4 as judged from the ratio of εtrans/εcis Ϸ 7:3.
absorption properties allow us to deduce the following
1H NMR Spectroscopy: The position of the fulvene pro-
structure-property relationships: i) The HOMO–LUMO ton resonances is strongly influenced by the nature of the
gap decreases upon extending the two-dimensional conju- spacer. Thus, a significant downfield shift is observed when
gation within the spacer (5 vs. 25, 12 vs. 24); ii) a linear proceeding from 24 (δH = 5.53 ppm)[3b] and TEE-TTF 12
conjugation pathway between the two dithiafulvenes pro- (δH = 5.65 ppm) to DEE-TTF 5 (δH = 6.76 ppm). The ful-
vides a smaller HOMO–LUMO gap than a cross-conju- vene proton resonates at δH = 5.41 (d, J = 2.4 Hz) and
gated pathway (5 vs. 12). Moreover, it is worth noting that 5.43 ppm[3b] for 1 and 2, respectively. The presence of the
not only does DEE-TTF 5 exhibit the most red-shifted ab- electron-withdrawing p-nitrophenyl group in cis-22 (δH
=
sorption maximum but also by far the strongest absorption 5.69 ppm, d, J = 2.6 Hz) and trans-22 (δH = 5.59 ppm, d, J
(ε, 67500 –1 cm–1). Substituting the CO2 Me by SMe = 2.6 Hz) results in small downfield shifts.
groups (10) leads to a further red shift (λmax = 524 nm,
2.4 eV).
Computational Study: DFT calculations[29] at the B3LYP/
6-31+G(d) level on PM3 geometry optimized structures re-
veal that trans-22 is slightly more stable than cis-22, namely
by 0.3 kcalmol–1. At the B3LYP/6-311++G(2d,p) level, a
difference of 0.2 kcalmol–1 was obtained.
HOMO–LUMO plots of 12, 13, 15, 21, and cis/trans-22
are depicted in Figure 7. The silyl groups were substituted
by hydrogen atoms in 12 for calculational convenience. The
HOMO of this compound has large coefficients at both the
dithiafulvene rings and the central TEE core. The LUMO
extends from the TEE to the two dithiafulvene rings with
no lobes, however, at the outer C=C sites. The LUMO+1
(and LUMO+2) is located instead at the two outer ethylene
Figure 6 displays the spectra of donor–acceptor dyads biscarbonyl groups. The HOMO and LUMO are further
cis-22, trans-22, 21, and 15, based on DEE, TriEE, and extended in 13 to the two phenyl groups. The HOMO has
TEE spacers, respectively. These compounds exhibit strong major coefficients at the dithiafulvene ring(s) and at the
charge transfer (CT) transitions, in particular TEE 15. spacer system for each of the donor–acceptor molecules 15,
Interestingly, the CT absorption band of trans-22 exhibits 21, and cis/trans-22, whereas the LUMO and LUMO+1
almost twice the molar absorptivity as that of cis-22. This mainly involve the p-nitrophenyl group(s) as well as the
isomeric difference is similar to that exhibited by trans/cis- spacer system. The small lobes at the p-nitrophenyl group
1-(4-dimethylaminophenyl)-6-(4-nitrophenyl)hex-3-ene-1,5- in the HOMO of cis/trans-22 sustains the small quinoid
diyne, as reported by Arai and co-workers.[24e] No decom- character as found by X-ray crystallography. Isomerization
position or thermal isomerization was observed according between cis- and trans-22 is facilitated by light as all MOs
1
to H NMR spectroscopy upon heating any of the isomers participating in the excited state involve the central double
at 125 °C in [D6]DMSO. Further, isomerization between bond. Thus, in order to avoid the π* antibonding character
cis-22 and trans-22 is slow (several days) in artificial day- across this bond, the excited state results in elongation of
light (60-W light bulb). However, upon irradiating either cis- the central bond and a decreased rotational barrier.
3664
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Extended Tetrathiafulvalenes with Di-, Tri-, and Tetraethynylethene Cores
FULL PAPER
Figure 7. HOMO, LUMO, and LUMO+1 of 12 (Me3Si groups replaced by hydrogen atoms), 13, 15, 21, cis-22, and trans-22 calculated
at the B3LYP/6-31+G(d) level.
Electrochemistry: The electrochemical properties were in- optical gaps are significantly smaller than those calculated
vestigated by cyclic (CV) and rotating disk (RDV) voltam- from electrochemistry. Moreover, the best line fitting the
metry. Electrochemical data are collected in Table 2. Com- data is very steep. Interestingly, cis-22 experiences a much
parison of redox potentials of the extended TTFs 5, 12, and larger electrochemical gap than trans-22, whereas the op-
24 reveals a strong dependence on the nature of the spacer. tical gaps of these two isomers are very similar.
We have previously shown by both experimental and theo-
retical studies that the donor strength is significantly dimin-
ished upon replacing double bonds with triple bonds.[3] In
agreement with this finding, 5 is a significantly stronger do-
nor than 24. From the data in Table 2, a significant differ-
ence between linear and cross-conjugated extended TTFs
appears. Thus, cross-conjugated TTF 12 experiences a re-
markable reluctance towards oxidation as compared to
both 2 and 24. In contrast, these three TTFs are reduced at
very similar potentials. The mono-nitrophenyl derivatives
21 and 18 undergo an additional reversible one electron re-
duction occurring on the nitrophenyl moieties at –1.40 V
for 21 and –1.35 V (vs. Fc+/Fc) for 18, whereas the dini-
trophenyl derivative 15 undergoes two reversible one-elec-
tron steps at –1.34 and –1.39 V occurring on the both ni-
trophenyls (Figure 8). It is noteworthy that the oxidation
potential of compounds 15, 18, and 21 are quite similar
to those of 12 and 13, which means that the nitrophenyl
Conclusions
Acetylenic scaffolding is a powerful tool for construction
of large conjugated TTFs and related donor–acceptor mole-
cules that may find interesting materials applications. It is
possible to alter significantly the redox and chromophoric
properties by only minor alterations in the acetylenic scaf-
fold. Thus, notable differences are observed between one-
and two-dimensional π-spacers and between linear and
cross-conjugated π-spacers. Synthetic protocols have been
devised for obtaining a wide range of new acetylenic build-
ing blocks containing the p-nitrophenyl acceptor (14, 17,
20, trans-23).
Experimental Section
substituents have almost no influence on the oxidation po- General Methods: Chemicals were purchased from Aldrich, Fluka,
and GFS chemicals and were used as received. THF was distilled
from Na/benzophenone. All reactions were carried out under Ar or
N2 (except for the Hay coupling reaction forming 13) by applying a
positive pressure of the protecting gas. Thin-layer chromatography
(TLC) was carried out using aluminium sheets pre-coated with sil-
ica gel 60F (Merck 5554). The plates were inspected under UV light
and, if required, developed in I2 vapour. Column chromatography
was carried out using silica gel 60F (Merck 9385, 0.040–0.063 mm).
Desilylation of 1 to provide 2 was carried out according to a pre-
viously published procedure.[3b] Compound 2 was used directly for
tentials of the dithiafulvene moieties. This observation
agrees well with the very similar HOMO orbitals obtained
in the computational study (Figure 7).
For donor–acceptor molecules 15, 18, 21, trans-22, and
cis-22, we find a relatively good linear correlation between
the optical HOMO–LUMO gap (Emax, calculated from
λmax) and the electrochemical HOMO–LUMO gap (calcu-
lated as the difference between first oxidation potential and
first reduction potential) (Figure 9), even though the oxi-
dation occurs irreversibly for all of these compounds. The the coupling reactions after Et2O/H2O extraction (but no further
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M. B. Nielsen et al.
FULL PAPER
Table 2. Electrochemical data observed in CH2Cl2 + 0.1  Bu4NPF6. Potentials vs. Fc+/Fc. Working electrode: glassy carbon electrode;
counter electrode: Pt; reference electrode: Ag/AgCl. Scan rate: 0.1 V s–1.
Compound
Cyclic voltammetry
∆Ep (mV)
Rotating disk voltammetry
E° (V)[a]
Ep (V)[b]
E1/2 (V)
Slope (mV)
5
+0.18 (1 e–)
+0.39 (1 e–)
–1.83 (2 e–)
9
+0.09 (1 e–)
–0.09 (1 e–)
–2.08 (1 e–)
70
70
80
+0.11
–0.10
–2.12
–2.48
+0.18
+0.00
–2.10
–2.45
65
70
80
80
65
–2.47 (1 e–)
10
+0.15 (1 e–)
+0.00 (1 e–)
–2.04 (1 e–)
60
60
65
70
100
100
75
–2.36 (1 e–)
+0.71 (2 e–)[c]
–1.80 (2 e–)
+0.65 (2 e–)
–1.44 (1 e–)
–1.92
12
13
+0.68
[d]
+0.69
–1.42
60
70
90
–1.92
[d]
15
+0.66 (2 e–)
–1.34 (1 e–)
–1.39 (1 e–)
–1.53 (1 e–)
60
60
60
–1.36[e]
100
–1.56
–1.93
+0.66
–1.40
–1.57
–1.92
–
60
130
45
60
60
–1.88[f]
18
21
+0.67 (2 e–)
–1.35 (1 e–)
–1.53 (1 e–)
60
60
–1.95[f]
100
+0.70 (2 e–)
–1.40 (1 e–)
–1.67 (1 e–)
75
85
–1.52[e]
160
–1.99
trans-22
cis-22
24[g]
+0.69 (1 e–)
+0.75
–1.48
–1.94
80
100
100
–1.41 (1 e–)
–1.43 (1 e–)
70
–1.90
–2.00
+0.73 (1 e–)
+0.69
–1.45
–1.92
80
100
100
[d]
–1.89
–2.02
+0.58 (2 e–)
+0.55
–1.87
60
175
–1.81 (2 e–)
[a] Eo = (Epc + Epa)/2, where Epc and Epa = cathodic and anodic peak potentials. Criteria for reversibility are: i. linear peak current
evolution with the square root of the scan rate, ii. anodic to cathodic peak current ratio equal to unity at any scan rate, iii. constant peak
potential with scan rate. [b] Ep = irreversible peak potential. [c] Reversible at scan rates Ͼ 5 V s–1. [d] Spread-out unresolved wave. [e]
Overlapping two one-electron transfers. [f] Multielectron transfer. [g] Ref.[3b]
work-up). A Personal Chemistry, Smith Creator oven was em-
ployed for microwave-assisted reactions. A Bransonic ultrasonic
cleaner, Branson 1510 water bath, was used for ultrasonification.
Melting points were determined with a Büchi melting point appara-
tus and are uncorrected. 1H NMR (300 MHz) and 13C NMR
(75 MHz) spectra were recorded with Gemini or Varian instru-
ments, using the residual solvent as the internal standard. All chem-
ical shifts are quoted on a δ scale, and all coupling constants are
expressed in Hertz (Hz). Samples were prepared using CDCl3 pur-
chased from Cambridge Isotope Labs. Electron impact ionisation
with a Jeol JMS-HX 110 Tandem Mass Spectrometer in the posi-
tive ion mode using 3-nitrobenzyl alcohol (NBA) as matrix. Gas
chromatography–mass spectrometry (GC-MS) was performed with
a HP5890 Series II plus gas chromatograph coupled with a HP5972
Series Mass analysator. Microanalyses were performed at the Mi-
croanalytical Laboratory at the Department of Chemistry, Univer-
sity of Copenhagen and at the Atlantic Microlab, Inc., Atlanta,
Georgia.
Absorption Spectroscopy: UV/Vis spectra were recorded with Cary
50 (Varian Inc.) or Shimadzu UV 1601PC instruments using
CHCl3 (LabScan, HPLC-grade) as the solvent. The absorption of
CHCl3 in the same cuvette (1 cm path length) was used for baseline
correction. The photolysis of cis- and trans-22 was performed using
the 436-nm line (FWHM 5 nm) from a 200 W high-pressure mer-
cury arc lamp equipped with a Bausch & Lomb monochromator
(2700 grooves/mm). The output of this line was 10 mW/cm2 at the
cuvette position, with the beam broadened to 5 cm2 to ensure irra-
mass spectrometry (EI–MS) was performed with
a Varian
MAT 311A instrument. Matrix-assisted laser-desorption/ionization
time-of-flight mass spectrometry (MALDI–TOF–MS) was per-
formed with Kratos Kompact 2 MALDI–TOF and Bruker Auto-
flex instruments with 2,5-dihydroxybenzoic acid (DHB) as matrix.
High resolution (HR) MALDI mass spectrometry was performed
with an IonSpec Fourier Transform mass spectrometer with DHB
as matrix. Fast atom bombardment (FAB) spectra were obtained
3666
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 3660–3671

Extended Tetrathiafulvalenes with Di-, Tri-, and Tetraethynylethene Cores
FULL PAPER
diation of the full sample area (Ϸ 2 cm2). The irradiance was mea-
sured prior to all photolysis experiments using an AvaSpec-2048
diode array spectrometer (Avantes) and a 600 µm optic fiber
equipped with a circular diffuser (diameter 3900 µm). As reference
for the irradiance an Avantes halogen light source, HL-2000, was
used. The photostationary state was obtained from a 40–50 µm
solution of pure isomer which was irradiated for 20 min, and the
resulting absorption spectrum analyzed to a mixture of pure cis-22
and trans-22 spectra.
Electrochemistry: CH2Cl2 was purchased spectroscopic grade from
Merck, dried over molecular sieves (4 Å), and stored under argon
prior to use. Bu4NPF6 was purchased electrochemical grade from
Fluka and used as received. The electrochemical experiments were
carried out at 20 2 °C in CH2Cl2 containing 0.1  Bu4NPF6 in a
classical three-electrode cell. The working electrode was a glassy
carbon disk electrode (3 mm in diameter) used either motionless
for CV (0.1 to 10 V s–1) or as rotating-disk electrode for RDV. The
counter electrode was platinum wire and the reference electrode
either an aqueous Ag/AgCl electrode or a platinum wire used as
pseudo reference. All potentials are referenced to the ferrocenium/
ferrocene (Fc+/Fc) couple used as an internal standard. The access-
ible range of potentials on the glassy carbon electrode was +1.4
to –2.4 V vs. Fc+/Fc in CH2Cl2. All measured potentials are uncor-
rected for ohmic drop. The electrochemical cell was connected to a
computerized multipurpose electrochemical device AUTOLAB
(Eco Chemie BV, Utrecht, The Netherlands) controlled by the
GPSE software running on a personal computer.
X-ray Structure Determination of Complexes cis-22 and trans-22:
Intensity data for cis-22 and trans-22 were collected at 122 K with
a Bruker–Nonius KappaCCD diffractometer equipped with an Ox-
ford Cryostream unit. Data were reduced with EvalCCD,[30] the
structures solved by direct methods using SIR97[31] and refined by
least-squares against F2 with SHELXL97[32] as incorporated in the
maXus program.[33] Both cis-22 and trans-22 crystallize in space
¯
group P1 with one molecule per asymmetric unit. trans-22 co-crys-
tallizes with one molecule of MeCN per asymmetric unit. For both
structures all non-hydrogen atoms were anisotropically refined. All
hydrogen atoms were found in subsequent difference Fourier maps
and refined using a riding model. Experimental parameters and
statistics are summarized in Table 3.
Figure 8. Cyclic voltammetry on a glassy carbon working electrode
of compounds 13, 15, and 18 in CH2Cl2 + 0.1  Bu4NPF6. Scan
rate: 0.1 V s–1.
CCDC-266874 and -266875 contain the supplementary crystallo-
graphic 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.
Computations: The compounds were subjected to a computational
study employing the Gaussian program package.[29] Structures were
optimized at the semiempirical PM3 level. Frequencies were calcu-
lated to verify that the calculated structures are local minima on
the potential energy surface and to correct for zero-point kinetic
energies. Single-point energy and HOMO–LUMO calculations
were carried out at the B3LYP/6-31+G(d) level.
(E)-1,4-Bis[4,5-bis(methoxycarbonyl)-1,3-dithiol-2-ylidene]-2,3-bis-
[triisopropylsilylethynyl]but-2-ene (5): To a solution of phospho-
nium salt 4 (437 mg, 0.86 mmol) in dry THF (20 mL) at –78 °C
was slowly added nBuLi (0.55 mL, 0.88 mmol, 1.6  in hexane),
resulting in a red solution. Then the dialdehyde 3 (182 mg,
0.41 mmol) in dry THF (10 mL) was slowly added. The solution
was stirred at –78 °C for 2 h, whereupon satd. aq. NH4Cl (200 mL)
was added. Then Et2O (200 mL) was added, the organic phase sep-
arated and washed with H2O (200 mL), dried (MgSO4), and con-
centrated in vacuo. Column chromatography (SiO2, CH2Cl2) af-
Figure 9. Correlation between optical and electrochemical
HOMO–LUMO gaps for donor–acceptor molecules. Emax is the
longest-wavelength absorption energy, Eox,1 is the first oxidation
potential, and Ered,1 is the first reduction potential.
1
forded 5 (207 mg, 60%) as an orange solid. M.p. 129–130 °C. H
Eur. J. Org. Chem. 2005, 3660–3671
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M. B. Nielsen et al.
FULL PAPER
Table 3. X-ray diffraction parameters and statistics of compounds cis-22 and trans-22.
cis-22
trans-22
Empirical formula
Mr
T [K]
C20H13NO6S2
427.45
122(2)
C20H13NO6S2/C2H3N
427.45/41.05
122(2)
λ [Å]
0.71073
triclinic
P1
7.6620(4); 111.425(6)
11.3840(9); 91.106(5)
11.7710(9); 94.587(7)
951.40(12)
0.71073
Crystal system
Space group
a [Å]; α [°]
triclinic
¯
¯
P1
7.3880(4); 106.482(5)
11.0070(6); 97.778(6)
14.1940(12); 90.717(7)
1095.06(13)
2
1.421
0.285
b [Å]; β [°]
c [Å]; γ [°]
V [Å3]
Z
2
ρcalcd. [g ×cm–3]
µMo-Kα [mm–1]
F(000)
1.492
0.319
440
0.46×0.34×0.14
1.86–35.05
44333
8375 [Rint = 0.066]
6466
484
Crystal size [mm3]
θ range [°]
0.51×0.28×0.10
1.51–35.01
44097
9611 [Rint = 0.058]
7400
1.039
Reflections collected
Unique data
Obsd. data [I Ͼ 2σ(I)]
GOF on F2
R indices (all data)
Larg.diff.peak/hole [e ×Å–3]
1.097
R1 = 0.064, wR2 = 0.098
0.50/–0.35
R1 = 0.064, wR2 = 0.108
0.53/–0.37
NMR (300 MHz, CDCl3): δ = 1.13/1.14 (2×s, 42 H), 3.79 (s, 6 H), C40H58N2S8Si2 (879.56): calcd. C 54.62, H 6.65, N 3.18, S 29.16;
3.84 (s, 6 H), 6.76 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = found C 54.84, H 6.69, N 3.30, S 29.28.
11.3, 18.7, 53.0, 53.4, 102.5, 112.1, 113.0, 122.1, 131.1, 131.3, 135.1,
(E)-1,4-Bis[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-2,3-bis[triiso-
propylsilylethynyl]but-2-ene (10): Compound 9 (78 mg, 0.089 mmol)
159.5, 160.3 ppm. MS (MALDI-TOF): m/z = 848.5 [M+].
C40H56O8S4Si (849.29): calcd. C 56.57, H 6.65, S 15.10; found C
was dissolved in THF (10 mL), and the solution was degassed with
56.42, H 6.62, S 15.06.
argon. Then MeI (1 mL) was added and hereafter CsOH·H2O
(E)-[4,5-Bis(2Ј-cyanoethylthio)-1,3-dithiol-2-ylidene]-2,3-bis[triiso-
propylsilylethynyl]but-2-enal (7): The phosphonium salt 6 (384 mg,
0.62 mmol) and the dialdehyde 3 (214 mg, 0.48 mmol) were dis-
solved in a mixture of dry THF (30 mL) and dry MeCN (10 mL).
Then Et3N (0.2 mL) was added during 5 min at room temp. After
stirring for 25 min, Et2O (300 mL) was added, and mixture was
extracted with H2O (2×250 mL), dried (MgSO4), and concentrated
in vacuo. Column chromatography (SiO2, CH2Cl2) afforded 7
(55 mg, 0.33 mmol) dissolved in argon-degassed MeOH (3 mL).
The mixture was stirred for 40 min and then concentrated in vacuo.
The residue was subjected to column chromatography (SiO2,
CH2Cl2), affording 10 (58 mg, 82%) as an orange solid. M.p. 186–
1
187 °C. H NMR (300 MHz, CDCl3): δ = 1.15/1.16 (2×s, 42 H),
2.37 (s, 6 H), 2.39 (s, 6 H), 6.81 (s, 2 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 11.5, 18.8, 19.0, 103.2, 110.6, 113.1, 121.5, 126.1,
128.1, 136.4 ppm. MS (MALDI-TOF): m/z = 800 [M+ ].
(233 mg, 69%) as a red oil. 1H NMR (300 MHz, CDCl3): δ = 1.11– C36H56S8Si2 (801.49): calcd. C 53.95, H 7.04, S 32.00; found C
1.16 (m, 42 H), 2.71–2.79 (m, 4 H), 3.05–3.15 (m, 4 H), 7.11 (s, 1 54.22, H 7.27, S 31.87.
H), 10.12 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 11.2,
11.3, 18.7, 31.3 (× 2), 99.9, 100.0, 109.6, 113.6, 115.8, 117.1, 124.0,
7-[4,5-Bis(methoxycarbonyl)-1,3-dithiol-2-ylidene]-4-{[4,5-bis(meth-
oxycarbonyl)-1,3-dithiol-2-ylidene]propynyl}-1-trimethylsilyl-3-[tri-
methylsilylethynyl]hept-3-en-1,5-diyne (12): i) Microwave Heating:
To a mixture of CuI (3.5 mg, 0.018 mmol), [Pd(PhCN)2Cl2] (20 mg,
0.052 mmol) was added argon-degassed THF (0.5 mL), toluene
(0.5 mL), and HN(iPr)2 (0.17 mL). Then P(tBu)3 (0.125 mL, 10%
in hexane) was added and hereafter the dibromide 11 (156 mg,
129.3, 137.7, 148.8, 189.3 ppm (two signals overlapping). MS
(MALDI-TOF): m/z = 701 [M+]. HR-MS (FT-MALDI): m/z =
723.24260 [M + Na]+ (calcd. for C35H52N2NaOS4Si2: 723.23932).
C35H52N2OS4Si2 (701.22): calcd. C 59.95, H 7.47, N 3.99, S 18.29;
found C 59.49, H 7.44, N 4.13, S 18.47.
(E)-1-[4,5-Bis(2Ј-cyanoethylthio)-1,3-dithiol-2-ylidene]-4-[4,5-bis- 0.413 mmol), which resulted in a dark brown mixture. This mixture
(methylthio)-1,3-dithiol-2-ylidene]-2,3-bis[triisopropylsilylethynyl]-
but-2-ene (9): Compounds 7 (79 mg, 0.11 mmol) and 8 (94 mg,
was transferred to a capped vial containing solid 2 (1.27 mmol).
The mixture was subjected to microwave heating (60 °C, 6 min).
0.45 mmol) were dissolved in P(OEt)3 (1.6 mL). The mixture was Then it was filtered through a short plug of silica (SiO2, CH2Cl2).
heated at 120 °C for 15 min. Then CHCl3 (300 mL) was added, and
the mixture was extracted with H2O (2×250 mL), dried (MgSO4),
and concentrated in vacuo. Column chromatography (SiO2,
Column chromatography (SiO2, CH2Cl2 Ǟ CH2Cl2/EtOAc, 10:1)
afforded 12 (113 mg, 38 %) as a red-brown solid. ii) Ultrason-
ification: To a mixture of CuI (3.5 mg, 0.018 mmol) and [Pd-
CH2Cl2) gave 9 (78 mg, 79 %) as a red oily solid. 1H NMR (PhCN)2Cl2] (20 mg, 0.052 mmol) was added argon-degassed THF
(300 MHz, CDCl3): δ = 1.15/1.16 (2×s, 42 H), 2.37 (s, 3 H), 2.40 (0.5 mL), toluene (0.5 mL), and HN(iPr)2 (0.17 mL). Then P(tBu)3
(s, 3 H), 2.67–2.76 (m, H), 3.00–3.08 (m, 4 H), 6.81 (s, 1 H), 6.83 (0.125 mL, 10% in hexane) was added and hereafter the dibromide
(s, 1 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 11.4 (× 2), 18.8, 11 (161 mg, 0.426 mmol), which resulted in a dark brown mixture.
18.9, 30.9, 31.1, 102.8, 103.0, 110.9, 111.2, 112.7, 114.8, 117.3,
120.5, 123.0, 126.4, 126.8, 128.0, 128.2, 132.9, 138.2 ppm; (one sig-
nal overlapping). MS (MALDI-TOF): m/z = 878 [M+ ].
This mixture was transferred to a flask containing solid 2
(1.35 mmol). The mixture was subjected to ultrasonification at
30 °C for 4 h, whereupon it was filtered through a plug of silica
3668
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 3660–3671

Extended Tetrathiafulvalenes with Di-, Tri-, and Tetraethynylethene Cores
(SiO2, CH2Cl2). Column chromatography (SiO2, CH2Cl2
FULL PAPER
as a dark red solid. The solid was dissolved in CH2Cl2 (3 L was
required) and washed with H2O. After concentration in vacuo, the
residue was dissolved in a minimum amount of CH2Cl2 and pre-
cipitated as a red solid upon addition of hexane. Column
Ǟ
CH2Cl2/EtOAc, 10:1) afforded 12 (262 mg, 85%) as a red-brown
1
solid. M.p. 143–146 °C (decomp.). H NMR (300 MHz, CDCl3): δ
= 0.23 (s, 18 H), 3.83 (s, 6 H), 3.84 (s, 6 H), 5.65 (s, 2 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 0.2, 53.4 (two signals overlapping), chromatography (SiO2, CH2Cl2 Ǟ CH2Cl2/EtOAc, 10:1) afforded
92.7, 96.1, 97.4, 101.8, 105.2, 112.5, 118.6, 130.6, 132.2, 148.0,
159.3, 159.7 ppm. MS (MALDI-TOF): m/z = 728 [M+]. HR-MS
(FAB): m/z = 728.0524 [M+] (calcd. for C32H32O8S4Si2: 728.0519).
C32H32O8S4Si2 (729.03): calcd. C 52.72, H 4.42; found C 52.96, H
4.82.
15 (882 mg, 97%) as a dark red solid. M.p. Ͼ 250 °C (decomp. at
ca. 170 °C). H NMR (300 MHz, CDCl3): δ = 3.71 (s, 6 H), 3.85
(s, 6 H), 5.77 (s, 2 H), 7.68 (d, 8.8 Hz, 4 H), 8.23 (d, 8.8 Hz, 4 H)
ppm. MS (FAB): m/z = 826 [M+]. C32H22N2O12S4 (826.85): calcd.
C 55.20, H 2.68, N 3.39; found C 54.84, H 2.45, N 3.29.
1
9-[4,5-Bis(methoxycarbonyl)-1,3-dithiol-2-ylidene]-6-{[4,5-bis(meth- 3-[Dibromomethylidene]-1-triisopropylsilyl-5-[4-nitrophenyl]penta-
oxycarbonyl)-1,3-dithiol-2-ylidene]propynyl}-1-phenyl-5-[phenylbuta-
1,3-diynyl]non-4-en-1,3,7-triyne (13): To a solution of TEE-TTF 12
(204 mg, 0.280 mmol) in THF (7 mL) and MeOH (20 mL) was
added K2CO3 (84 mg, 0.63 mmol). The deprotection was complete
after stirring for ca. 30 min. A difference in Rf values between 12
and its desilylated derivative was difficult to ascertain on TLC, but
the desilylated compound appeared darker. Then Et2O (200 mL)
was added, and the organic phase was washed with aq. NaCl
(150 mL). The organic phase was dried (MgSO4) and concentrated
in vacuo to almost dryness. The residue was dissolved in dry
CH2Cl2 (50 mL), whereupon phenylacetylene (0.7 mL, 6 mmol)
was added. Then Hay catalyst (1 mL) was added. [Hay catalyst:
1,4-diyne (17): To solution of 16 (340 mg, 0.872 mmol) in THF
(14 mL) and MeOH (30 mL) was added K2 CO3 (121 mg,
0.872 mmol). Complete desilylation was accomplished according to
TLC after stirring for 15 min. Then Et2O (250 mL) was added and
the mixture was washed with aqueous NaCl (250 mL), dried
(MgSO4), and concentrated in vacuo to a yellowish oil. The ma-
jority (83%, 0.724 mmol) of this oily residue of 3-(dibromomethyli-
dene)-1-triisopropylsilylpenta-1,4-diyne was dissolved in THF
(15 mL) and Et3N (3 mL). Then p-iodonitrobenzene (1.0 g,
4.0 mmol), [PdCl2(PPh3)2] (30 mg, 0.078 mmol), and CuI (10 mg,
0.053 mmol) were added. The mixture was stirred overnight, where-
upon it was filtered through a short column (SiO2, CH2Cl2). Col-
TMEDA (53 mg, 0.46 mmol), CuCl (43 mg, 0.43 mmol), CH2Cl2 umn chromatography (SiO2, hexane/CH2Cl2, 1:1) afforded 17
(1.5 mL)]. The mixture was stirred under air for ca. 15 min. Then
CH2Cl2 (200 mL) was added, and the organic phase was washed
(164 mg, 44%) as a crystalline off-white solid. M.p. ca. 140 °C (de-
comp.). 1H NMR (300 MHz, CDCl3): δ = 1.1 (s, 21 H), 7.65 (d,
8.8 Hz, 4 H), 8.21 (d, 8.8 Hz, 4 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 11.3, 18.8, 90.9, 93.1, 101.0, 101.5, 111.0, 114.1, 123.8,
129.1, 132.6, 147.7 ppm. HR-MS (FAB): m/z = 510.0105 [M + H]+
(calcd. for C21H26Br2NO2Si: 510.0100).
with H2O (200 mL). Column chromatography (SiO2, CH2Cl2
Ǟ
CH2Cl2/EtOAc, 20:1) afforded 13 (40 mg, 18%) as a dark red solid.
M.p. Ͼ 250 °C (decomp. at ca. 180 °C, turning dark). 1H NMR
(300 MHz, CDCl3): δ = 3.50 (s, 6 H), 3.83 (s, 6 H), 5.73 (s, 2 H),
7.33–7.37 (m, 6 H), 7.50–7.53 (m, 4 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 53.4, 53.6, 74.6, 79.1, 83.9, 87.9, 92.5, 98.1, 98.9, 109.8,
121.3, 121.7, 128.6, 129.7, 130.8, 132.7, 133.0, 150.4, 159.4, 159.7
ppm. HR-MS (FAB): m/z = 784.0359 [M+] (calcd. for C42H24O8S4:
784.0354).
1-[4,5-Bis(methoxycarbonyl)-1,3-dithiol-2-ylidene]-4-{[4,5-bis(meth-
oxycarbonyl)-1,3-dithiol-2-ylidene]propynyl}-1-triisopropylsilyl-3-[4-
nitrophenyl]hept-3-en-1,5-diyne (18): To a mixture of CuI (5.0 mg,
0.026 mmol) and [Pd(PhCN)2Cl2] (30 mg, 0.078 mmol) was added
dibromide 17 (65.0 mg, 0.127 mmol) and then THF (3.00 mL), tol-
3-[Dibromomethylidene]-1,5-bis[4-nitrophenyl]penta-1,4-diyne (14): uene (3.00 mL), HN(iPr)2 (0.30 mL), P(tBu)3 (0.20 mL, 10% in
To a solution of 11 (584 mg, 1.54 mmol) in THF (14 mL) and
MeOH (40 mL) was added K2CO3 (214 mg, 1.55 mmol). Complete
desilylation was accomplished according to TLC after stirring for
hexane). This mixture was transferred to a flask containing com-
pound 2 (1.046 g, 4.08 mmol) and dibromide 17 (193 mg,
0.377 mmol). The mixture was subjected to ultrasonification at
15 min. Then Et2O (250 mL) was added, and the mixture was 30 °C for 4 h, whereupon it was filtered through a short column of
washed with aqueous NaCl (250 mL), dried (MgSO4), and concen- silica (SiO2, CH2Cl2). Column chromatography (SiO2, CH2Cl2 Ǟ
trated in vacuo to a yellowish oil. This oily residue of 3-(dibro-
momethylidene)penta-1,4-diyne was dissolved in THF (15 mL) and
Et3N. Then p-iodonitrobenzene (2.0 g, 8.0 mmol), [PdCl2(PPh3)2]
(50 mg, 0.13 mmol), and CuI (15 mg, 0.079 mmol) were added. Af-
ter stirring overnight, the mixture was filtered through a short col-
umn (SiO2, CH2Cl2). Column chromatography (SiO2, hexane/
CH2Cl2, 1:1) gave 14 (400 g, 54%) as an off-white solid. M.p. ca.
140 °C (decomp.). 1H NMR (300 MHz, CDCl3): δ = 7.71 (d,
9.1 Hz, 4 H), 8.24 (d, 9.1 Hz, 4 H). 13C NMR (75 MHz, CDCl3):
δ = 89.9, 93.9, 112.4, 113.2, 123.9, 128.7, 132.6, 147.9 ppm. MS
(FAB): m/z = 475 [M + H]+.
CH2Cl2/EtOAc, 10:1) afforded 18 (210 g, 48%) as a dark red solid.
M.p. Ͼ 250 °C (decomp. at ca. 180 °C). 1H NMR (300 MHz,
CDCl3): δ = 1.1 (s, 21 H), 3.70 (s, 3 H), 3.84 (s, 3 H), 3.85 (s, 3 H),
3.85 (s, 3 H), 5.60 (s, 1 H), 5.75 (s, 1 H), 7.62 (d, 8.8 Hz, 2 H), 8.20
(d, 8.8 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 11.4, 18.8,
53.6, 53.7, 92.7, 92.8, 93.3, 96.1, 97.1, 97.3, 98.0 (two signals over-
lapping), 103.4, 103.4, 111.8, 118.9, 123.7, 129.8, 130.9, 131.1,
132.3, 132.5, 133.0, 147.2, 149.0, 149.2, 159.4, 159.5, 159.7, 159.9
ppm. HR-MS (FAB): m/z = 861.1241 [M+ ] (calcd. for
C41H39NO10S4Si: 861.1226). C41H39NO10S4Si (862.10): calcd. C
57.12, H 4.56, N 1.62; found C 56.79, H 4.25, N 1.69.
7-[4,5-Bis(methoxycarbonyl)-1,3-dithiol-2-ylidene]-4-{[4,5-bis(meth- 1,1-Dibromo-4-(4-nitrophenyl)but-1-en-3-yne (20): The aldehyde 19
oxycarbonyl)-1,3-dithiol-2-ylidene]propynyl}-1-[4-nitrophenyl]-3-[4- (595 mg, 3.40 mmol) and CBr4 (2.25 g, 6.85 mmol) were dissolved
nitrophenylethynyl]hept-3-en-1,5-diyne (15): To a mixture of CuI
(5.0 mg, 0.026 mmol) and [Pd(PhCN)2Cl2] (30 mg, 0.078 mmol) (0.654 g, 10.0 mmol) was added. Then PPh3 (1.81 g, 6.90 mmol)
was added the dibromide 14 (78.2 mg, 0.164 mmol), and then THF was added, resulting in a dark red solution. After stirring for
(3.00 mL), toluene (3.00 mL), HN(iPr)2 (0.30 mL), and P(tBu)3 45 min, the mixture was filtered through a short plug of silica
in dry CH2Cl2 (50 mL), whereupon fine Zn powder (Ͻ 63 µm)
(0.20 mL, 10% in hexane). After vigorous stirring, this mixture was
transferred to a flask containing compound 2 (979 mg, 3.82 mmol)
and dibromide 14 (173 mg, 0.363 mmol). The mixture was sub-
jected to ultrasonification at 30 °C for 4 h. The product precipitated
(SiO2, CH2Cl2). The filtrate was concentrated in vacuo to a light
yellow powder. The product 20 (802 mg, 72%) was obtained pure
after washing with cold hexane (to remove any remains of CBr4).
Further purification can be performed by column chromatography
Eur. J. Org. Chem. 2005, 3660–3671
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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M. B. Nielsen et al.
FULL PAPER
(SiO2, CH2Cl2) or recrystallization from hexane. M.p. 101–102 °C.
trans-1-Bromo-4-(4-nitrophenyl)but-1-en-3-yne (trans-23): To a solu-
1H NMR (300 MHz, CDCl3): δ = 6.81 (s, 1 H), 7.63 (d, 8.8 Hz, 2 tion of the dibromide 20 (1.01 g, 3.05 mmol) in diethyl phosphite
H), 8.20 (d, 8.8 Hz, 2 H ppm). 13C NMR (75 MHz, CDCl3): δ = (2.0 mL, 15.5 mmol) was added triethylamine (2.0 mL, 14.4 mmol),
90.9, 94.7, 104.7, 119.0, 123.9, 129.4, 132.4, 147.6 ppm. MS (FAB):
and the dark brown mixture was stirred at 50 °C for 6 h. Diethyl
m/z = 329 [M+]. MS (GC): m/z = 329 [M+]. C10H5Br2NO2 (330.96): ether (50 mL) was added, and the Et3N·HBr was removed by fil-
calcd. C 36.29, H 1.52, N 4.23; found C 36.57, H 1.42, N 4.18.
tration. The filtrate was concentrated in vacuo and the residue sub-
jected to column chromatography (SiO2, cyclohexane/CH2Cl2, 3:2),
which afforded trans-23 (320 mg, 42%) as an off-white solid. Re-
moval of trace amounts of the cis-isomer can be done by recrystalli-
zation from hexane. M.p. 133–135 °C. 1H NMR (300 MHz,
CDCl3): δ = 6.45 (d, 14.1 Hz, 1 H), 6.92 (d, 14.1 Hz, 1 H), 7.57 (d,
9.1 Hz, 2 H), 8.19 (d, 9.1 Hz, 2 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 89.6, 90.9, 117.0, 121.3, 123.9, 129.7, 132.4, 147.5 ppm.
7-[4,5-Bis(methoxycarbonyl)-1,3-dithiol-2-ylidene]-4-{[4,5-bis(meth-
oxycarbonyl)-1,3-dithiol-2-ylidene]propynyl}-1-[4-nitrophenyl]hept-3-
en-1,5-diyne (21): To a mixture of CuI (5 mg, 0.03 mmol) and
[Pd(PhCN)2Cl2] (30 mg, 0.078 mmol) was added THF (1.0 mL),
toluene (1.0 mL), HN(iPr)2 (0.3 mL), and P(tBu)3 (0.2 mL, 10% in
hexane) under argon. This mixture was transferred via a syringe to
a flask containing the dibromide 20 (162 mg, 0.489 mmol) and 2
(342 mg, 1.33 mmol) under argon. The reaction mixture was sub-
jected to ultrasonification for 2½ h at ca. 25–30 °C. Then it was
filtered through a short plug of silica (SiO2, CH2Cl2). Column
chromatography afforded the product 21 (91 mg, 30%) as a red
powder. M.p. Ͼ 300 °C (decomp.). 1H NMR (300 MHz, CDCl3):
δ = 3.71 (s, 3 H), 3.85 (2×s, 6 H), 3.87 (s, 3 H), 5.59 (s, 1 H), 5.71
(s, 1 H), 6.24 (s, 1 H), 7.62 (d, 9.0 Hz, 2 H), 8.20 (d, 9.0 Hz, 2 H)
ppm. 13C NMR (75 MHz, CDCl3): δ = 53.7, 91.1, 92.5, 92.8, 93.6,
93.9, 96.8, 97.9, 99.5, 116.6, 118.4, 123.8, 130.1, 131.1, 131.4, 131.9,
132.2, 133.1, 147.2, 148.4, 148.8, 159.5, 159.6, 159.8 (× 2) ppm. MS
(FAB): m/z = 681 [M+]. C30H19NO10S4 (681.74): calcd. C 52.85, H
2.81, N 2.05; found C 52.76, H 2.72, N 1.97.
Acknowledgments
The Danish Technical Research Council (STVF, grant # 26-01-
0033), the Danish Natural Science Research Council (SNF, grants
# 21-04-0084 and # 2111-04-0018), Carlsbergfondet, and Direktør
Ib Henriksens Fond are gratefully acknowledged for financial sup-
port. A. S. Andersson thanks The University of Copenhagen for a
PhD scholarship. We thank Flemming Hansen for collection of X-
ray diffraction data.
cis-7-[4,5-Bis(methoxycarbonyl)-1,3-dithiol-2-ylidene]-1-[4-nitro-
phenyl]hept-3-en-1,5-diyne (cis-22): To a solution of the dibromide
20 (331 mg, 1.00 mmol) in toluene (3 mL) was added [Pd(PPh3)4]
(46.2 mg, 0.040 mmol) followed by Bu3SnH (0.30 mL, 1.1 mmol),
and the mixture was stirred at room temp. for 1 h. Then 1
(1.25 mmol) in THF (1 mL) was added, followed by HN(iPr)2
(0.85 mL). The mixture was degassed with argon, whereupon CuI
(57 mg, 0.30 mmol) was added. The mixture was stirred overnight
and filtered through a short plug of silica (SiO2, CH2Cl2). Column
chromatography (SiO2, CH2Cl2) afforded cis-22 (166 mg, 39%) as
a red solid. M.p. 151–153 °C. 1H NMR (300 MHz, CDCl3): δ =
3.72 (s, 3 H), 3.84 (s, 3 H), 5.69 (d, 2.6 Hz, 1 H), 6.04 (d, 10.8 Hz,
1 H), 6.19 (dd, 10.8/2.6 Hz, 1 H), 7.63 (d, 8.8 Hz, 2 H), 8.20 (d,
8.8 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 53.4, 53.5,
92.6, 93.1, 95.2, 96.0, 98.0, 116.3, 121.0, 123.6, 130.0, 130.9, 131.9,
132.9, 147.0, 147.6, 159.3, 159.7 ppm. MS (FAB): m/z = 427 [M+].
HR-MS (FAB): m/z = 427.0192 [M+] (calcd. for C20H13NO6S2:
427.0184). C20H13NO6S2 (427.45): calcd. C 56.20, H 3.07, N 3.28;
found C 55.80, H 3.01, N 3.02.
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trans-7-[4,5-Bis(methoxycarbonyl)-1,3-dithiol-2-ylidene]-1-[4-nitro-
phenyl]hept-3-en-1,5-diyne (trans-22): To a solution of the bromide
trans-23 (252 mg, 1.00 mmol) in toluene (3 mL) was added
[Pd(PPh3)4] (46.2 mg, 0.04 mmol), and the mixture was stirred at
room temp. for 1 h. Then 2 (1.25 mmol) in THF (1 mL) was added,
followed by HN(iPr)2 (606 mg, 6 mmol). The mixture was degassed
with argon, whereupon CuI (57 mg, 0.30 mmol) was added. After
stirring for 3 h at room temp., the mixture was filtered through a
short plug of silica (SiO2, CH2Cl2). Column chromatography (SiO2,
CH2Cl2) afforded trans-22 (287 mg, 67%) as
a red solid.
Recrystallization from MeCN gave the product as red crystals. M.p.
1
115–117 °C. H NMR (300 MHz, CDCl3): δ = 3.85 (s, 3 H), 3.87
(s, 3 H), 5.59 (d, 2.6 Hz, 1 H), 6.16 (d, 15.8 Hz, 1 H), 6.35 (dd,
15.8/2.6 Hz, 1 H), 7.57 (d, 8.8 Hz, 2 H), 8.19 (d, 8.8 Hz, 2 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 53.5 (two signals overlapping),
92.7 (× 2), 93.5, 93.8, 98.6, 118.0, 122.5, 123.7, 129.8, 131.3, 131.5,
132.2, 147.1, 147.3, 159.4, 159.6 ppm. MS (FAB) m/z = 427 [M+].
C20H13NO6S2 (427.45): calcd. C 56.20, H 3.07, N 3.28; found C
55.96, H 2.72, N 3.13.
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3670
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Extended Tetrathiafulvalenes with Di-, Tri-, and Tetraethynylethene Cores
FULL PAPER
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Received: April 25, 2005
Published Online: July 11, 2005
Eur. J. Org. Chem. 2005, 3660–3671
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3671