The synthesis of molecular rods with a transversal push-pull system

Article abstract of DOI:10.1002/ejoc.200700070

The design and synthesis of the molecular cruciforms 1-4 consisting of an oligophenylene-ethynyl backbone with an acetyl-protected sulfur anchor group on one end and a crossing oligophenylene cross-bar with terminal trifluoromethyl and dimethylamino group

Full text of DOI:10.1002/ejoc.200700070

FULL PAPER
DOI: 10.1002/ejoc.200700070
The Synthesis of Molecular Rods with a Transversal Push-Pull System
Alfred Błaszczyk,[a,b] Matthias Fischer,[a] Carsten von Hänisch,[a] and Marcel Mayor*[a,c]
Keywords: Push-pull system / Molecular rods / Cruciform / Sonogashira coupling / Suzuki coupling
The design and synthesis of the molecular cruciforms 1–4
consisting of an oligophenylene-ethynyl backbone with an
acetyl-protected sulfur anchor group on one end and a cross-
ing oligophenylene cross-bar with terminal trifluoromethyl
and dimethylamino groups as transversal push-pull system
are reported. These cruciforms 1–4 are model compounds to
investigate electronic potential-dependent switching proper-
ties of molecular junctions. While the oligophenylene-
ethynyl backbone is responsible for the electronic transport
properties, the transversal push-pull system should alter the
tilt angle of the rod upon alignment in an electric field. As
the tunnel distance at the rods end to the opposite electrode
depends on the tilt angle of the rod, a considerable depen-
dence of the transport current on the tilt angle is expected.
The investigation of such transport mechanisms with the
model compounds 1–4 may unravel the origin of negative
differential conductance phenomena in devices consisting of
sandwiched self assembled monolayers between two elec-
trodes. The reported cruciform structures display limited sta-
bility features in the presence of acids. Their assembly is
based on metal catalyzed cross coupling reactions with the
chromatographic separation of two, on opposite sides mono-
protected regioisomers as key step.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
central phenyl ring is functionalized with a nitro and an
amino group resulting in a transversal push-pull system
which is tilted by 60° with respect to the axis of the OPE
rod. Variations of the molecular structure unraveled that
the nitro group is crucial for the observation of NDR effects
in such devices.[6]
Introduction
The concept of molecular electronics that considers the
use of molecular structures to build electronic devices exhi-
bits remarkable scientific interest recently.[1] Feasibility of
molecular devices lies in our ability to understand specific
properties of molecules acting individually or in self-
assembled monolayers and to use these properties in the
creation of a new class of devices. Of particular interest
within molecular electronics are switching devices based on
bistable molecular structures.[2] A molecular junction con-
sisting of a laterally limited self-assembled monolayer
between two parallel gold electrodes displayed promising
electronic properties, namely a negative differential resis-
tance (NDR).[3] However, the origin of the effect is still
under investigation and numerous theoretical studies pro-
vide a variety of different hypotheses.[4] In addition, model
compounds for the thorough investigation of a particular
hypothesis have already been reported like e.g. the synthesis
of suitably functionalized macrocycle.[5] The self-assembled
monolayer forming molecule consists of a oligopheneylene-
ethynyl (OPE) backbone with a terminal sulfur group for
the immobilization on a gold substrate. In addition, the
A plausible explanation for the observed decrease of the
current upon applying a particular threshold voltage (NDR
effect) could be the parallel alignment of the push-pull
vector of the SAM-molecule in the electric field. In Figure 1
an upright molecule in the junction is displayed in A) and
a tilted molecule after alignment of its push-pull vector in
the electric field is displayed in B). As in the nanopore set-
up the distance between both electrodes remains constant,
the tilting of the molecular rod increases the distance
between its end and the top electrode considerably (d1 com-
pared with d0 in Figure 1). The tunnel current between the
molecule and the top electrode decreases exponentially with
the distance and hence, an increasing spacing between
molecule and top electrode should decrease the current
through the junction significantly. Electric field-dependent
switching properties have already been reported for scan-
ning tunneling microscope investigations of molecular rods
with tailor-made polarities in an amide containing SAM
host matrix.[7] However, the focus of these studies was
rather the interplay between polarity along the rod axis and
hydrogen bonding in the host environment than the align-
ment of a perpendicular dipole vector.
[a] Institute for Nanotechnology, Forschungszentrum Karlsruhe
GmbH,
Postfach 3640, 76021 Karlsruhe, Germany
E-mail: marcel.mayor@int.fzk.de
[b] Faculty of Commodity Science,
Al. Niepodległos´ci 10, 60-967 Poznan´, Poland
[c] University of Basel, Department of Chemistry,
St. Johannsring 19, 4056 Basel, Switzerland
E-mail: marcel.mayor@unibas.ch
The strength of the dipole moment of the transversal
push-pull system depends not only on its terminal electron-
donating and electron-accepting functional groups, but also
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Molecular Rods with a Transversal Push-Pull System
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Figure 1. Sketch of a hypothetical switching mechanism of the reported NDR device. At low voltages the molecule stands more or less
upright in the SAM with the distance d0 for the tunnel current between the top electrode and the terminal π-system of the molecular rod
(A). Upon applying an electric field, the para nitro aniline push-pull system of the central ring subunit aligns resulting in an increased
distance d1 between the top electrode and the end of the molecule (B).
on their separation. As model compounds to investigate the
proposed electric field-dependent switching mechanism,
molecular rods with a considerable transversal dipole mo-
ment due to an increased spacing between donor and ac-
ceptor group are appealing.
Here we report the synthesis and characterization of cru-
ciform molecules 1–4 (Figure 2) consisting of oligopheny-
lene-ethynylene (OPE) backbones of varying length and
transversal oligophenylene (OP) rods. While one end of the
longer OPE rod substructure is terminally functionalized
with an acetyl-protected sulfur group for immobilization on
noble metal surfaces, the transversal OP substructure acts
as a push-pull system with an electron-donating dimethyl-
amino group on one end and a chemically inert electron-
accepting trifluoromethyl group on the opposite end. A
Figure 2. Cruciform target structures 1–4 consisting of an OP push-
pull system crossing a terminal acetylsulfanyl-functionalized OPE
particular advantage of these cruciforms is that the direc-
tion of the transversal push-pull vector can be inverted by
chemical synthesis allowing a more detailed investigation of
the polarization direction. Furthermore, the length of the
OPE rod can be adjusted to the electrode spacing of a par-
ticular device.
rod.
Synthetic Strategy
Functionalized cruciform π-systems have already been
While the OPE backbone of the cruciform target struc-
reported as test structures for molecular electronics,[8] as tures 1–4 is assembled sequentially by acetylene scaffolding
electro-optically active chromophore in self-assembled thin steps like Sonogashira cross-coupling reactions[15] and
films,[9] as chromophores with tunable bandgaps,[10] as acetylene protection group chemistry, the transversal OP
metal ion sensors[11] and as building blocks of coordination push-pull system is formed gradually by Suzuki cross-coup-
polymers.[12] Some of these cruciform structures have either ling reactions.[16] Both cross-coupling reactions have palla-
an OP-[8] or an OPE-substructure[10–12] in common with the dium catalysts in common and display comparable chemo
here presented cruciforms. Furthermore, the combination selectivities like the preference of iodine as leaving group
of OP and OPE rods in a cruciform structure has been re- compared with bromine. Thus starting with 1,4-dibromo-
ported from Swager and co-workers as precursors of ex- 2,5-diiodobenzene, either the OPE or the OP rod might be
tended fused-ring systems in molecules[13,14] as well as in assembled in first place. In Figure 3 the here investigated
polymers.[14]
fraction of the possible retrosynthetic pathways are dis-
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Figure 3. Retrosynthetic strategy to assemble the target structure 1. Horizontal retrosynthetic arrows represent Suzuki coupling steps and
vertical retrosynthetic arrows represent acetylene scaffolding steps like Sonogashira coupling reactions or acetylene deprotections. The
white retrosynthetic arrows represent the pathway A, while the light grey retrosynthetic arrows display the synthetic path B which led to
the target structure 1.
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Molecular Rods with a Transversal Push-Pull System
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played. While acetylene scaffolding reaction steps are dis- coupling reactions required to assemble the OP and the
played vertically, Suzuki coupling reactions are represented OPE rods.
by horizontal retrosysnthetic arrows. After the introduction
of both silyl-protected acetylenes, the key step of the retro-
Synthesis and Characterization
synthetic Scheme is the differentiation of both acetylene
functions. Distinguishing chemically between both acetyl-
enes is crucial to control the position of the sulfur anchor
group and hence also the direction of the transversal push-
pull rod with respect to the backbone of the immobilized
molecule. This can either be achieved by regioselective de-
protection or by separation of both regioisomers from a
statistical mixture after partial removal of the silyl protec-
tion groups of the acetylenes.
The required starting compound 1,4-dibromo-2,5-di-
iodobenzene 5 was synthesized following a reported syn-
thetic protocol.[17] Our first attempts towards the target
structure 1 were following the retrosynthetic pathway A,
represented by white retrosynthetic arrows in Figure 3. The
synthetic steps are displayed in Scheme 1.
As displayed in Figure 3, the synthetic strategy has been
investigated along two alternative pathways for both shorter
rods 1 and 2. However, the modular synthesis of the OPE
backbone allows to assemble the longer rods 3 and 4 from
the same building blocks.
In pathway A, the OP based push-pull rod was first syn-
thesized by consecutive Suzuki coupling reactions substitut-
ing both iodine atoms of the starting tetrahalobenzene.
Subsequently both bromine atoms were substituted by silyl-
protected acetylenes. After either regioselective deprotec-
tion of one of both acetylenes or separation of the regioiso-
mers, the OPE backbone comprising a sulfur anchor group
on one end should be assembled gradually to provide access
to the desired target structures. However, for the silyl-pro-
tected diacetylene with the perpendicular terphenyl push-
pull system neither suitable reaction conditions for the re-
gioselective deprotection nor a chromatographic system for
the separation of both regioisomers have been found.
To increase the difference between both regioisomers, in
pathway B the perpendicular push-pull system was only
partially assembled. Again starting from 1,4-dibromo-2,5-
diiodobenzene, a subunit of the OPE backbone is first syn-
thesized by substituting both iodines with silyl-protected
acetylenes in a Sonogashira coupling reaction. Sub-
sequently the electron-accepting subunit of the OP push-
pull rod is introduced by a Suzuki coupling. Partial depro-
tection of the silyl-protected acetylenes provides a reaction
mixture containing both regioisomers. The considerable dif-
Scheme 1. Synthetic steps towards 1 following the retrosynthetic
pathway A depicted in Figure 3: a) 4-(trifluoromethyl)phenyl-
boronic acid, Pd(PPh3)4, K2CO3, DME/H2O, 75 °C, 16 h, 48%; b)
4-(dimethylamino)phenylboronic acid, Pd(PPh3)4, K2CO3, DME/
H2O, 75 °C, 16 h, 15%; c) TIPSA, Pd(PPh3)2Cl2, (iPr)2NH, CuI,
THF, room temp., 16 h, 98%; d) TBAF, THF/AcOH, room temp.
Applying Suzuki coupling conditions, commercially
ference of both sides of the OP rod at this stage of the available 4-(trifluoromethyl)phenylboronic acid together
synthesis enhances their physical difference and facilitates with the starting material 5 provided the monosubstituted
their separation and indeed, classical column chromatog- derivative 6. In a 1,2-dimethoxyethane (DME) water mix-
raphy allowed to distinguish between both regioisomers. ture 1.5 equivalents of 5 were treated with an equivalent of
After separation of both regioisomers, the first branch of 4-(trifluoromethyl)phenylboronic acid and a tenfold excess
the OPE backbone is introduced in a Sonogashira coupling of potassium carbonate (K2CO3) in the presence of 5 mol-
reaction to get rid of the rather reactive deprotected acetyl- % tetrakis(triphenylphosphane)palladium(0) (Pd(PPh3)4) as
ene subunit. Subsequently, the OP push-pull system is com- catalyst at 75 °C. After workup, the doubly substituted ter-
pleted by substituting the remaining bromine with a corre- phenyl derivative and the desired singly substituted trihalo-
sponding dimethylaniline boronic acid derivative in a biphenyl compound 6 were isolated as white solids by
Suzuki reaction step. Finally, the second acetylene is column chromatography (CC) in 41% and 48% yield
deprotected and the remaining part of the OPE backbone respectively. To keep the reaction temperature at 75 °C
comprising the acetyl-protected sulfur anchor group is turned out to be crucial as at higher temperature consider-
assembled. In both strategies the acetyl-protected sulfur ter- able deiodination of the starting material was observed.
minus is introduced at the end of the synthesis as this rather Comparable reaction conditions applied to the monoiodo
labile functional group would restrict considerably the pos- derivative 6 and commercially available 4-(dimethylamino)-
sible reaction conditions for both palladium catalyzed phenylboronic acid provides the push-pull terphenyl system
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7 in poor yields of 15%. The assembly of the terphenyl sys-
tem was accompanied by several side products that have
neither been isolated nor identified. Substitution of both
bromines of 7 by (triisopropyl)acetylene (TIPSA) has been
achieved applying Sonogashira coupling conditions. Thus
the dibromide 7 was treated with TIPSA in tetrahydrofuran
(THF) with diisopropylamine ((iPr)2NH) as base and
dichlorobis(triphenylphosphane)palladium (Pd(PPh3)2Cl2)
and copper iodide (CuI) as catalysts at room temperature
to provide the doubly protected diacetylene 8 in 98% yield
as a white solid after CC. Monodeprotection of the doubly
silyl-protected diacetylene 8 was achieved with tertabutyl-
ammonium fluoride (TBAF) as source of fluorine anions.
Compound 8 was dissolved in THF and after addition of a
drop of acetic acid (AcOH) as proton source 0.7 equiv. of
TBAF were added. After stirring overnight at room tem-
perature, a mixture of starting material, both mono-
deprotected regioisomers and traces of the fully deprotected
diacetylene were obtained. While the starting material 8 and
the fully deprotected derivative could be separated by CC,
the very comparable polarities of both regioisomers did not
allow separating them by CC. Even though numerous
Scheme 2. Synthesis of both regioisomers 12 and 13. a) TIPSA,
Pd(PPh3)2Cl2, (iPr)2NH, CuI, THF, room temp., 40 h, 77%; b) 4-
solvent systems have been investigated, hardly any differ- (trifluoromethyl)phenylboronic acid, Pd(PPh3)4, K2CO3, DME/
H2O, 80 °C, 14 h, 46%; c) TBAF, THF/AcOH, room temp.
ences in polarities have been observed for both regio-
isomers.
The difficulties in separation of both regioisomers to- drop of acetic acid 0.74 equiv. of TBAF was added. After
gether with the poor yield in the assembly of the terphenyl work up by filtration through a silica short plug the dif-
push-pull system considerably reduced the attractivity of ferent reaction products were isolated by CC. Fortunately,
the so far followed synthetic pathway A. In order to en- both regioisomers turned out to be separable by CC on
hance the differences between both regioisomers, the grad- silica gel with pure hexane as eluent. Both regioisomers 12
ual assembly of the push-pull system and the OPE rod as and 13 were isolated as colorless oils in 29 and 21% yields,
displayed in Figure 3 as pathway B has been envisaged.
respectively. Both compounds displayed rather limited sta-
In similarity to the synthetic pathway A, also in the sec- bility properties indicated by a color change to brown upon
ond pathway B the desired target structure 1 is developed extended drying. Nevertheless, both compounds were stable
from 1,4-dibromo-2,5-diiodobenzene 5 as starting material. over several weeks when kept at –20 °C in the dark. Due to
As displayed in Scheme 2, first exclusively both iodine’s of these stability restrictions we were not able to provide cor-
the tetrahalo derivative 5 were substituted by TIPSA to pro- rect elemental analysis of these two compounds.
vide the doubly silyl-protected diacetylene 9 in a yield of
Of particular importance is the structural assignment of
77%, demonstrating the chemoselectivity of the Sonoga- both regioisomers 12 and 13 as the further assembly of the
shira coupling. The synthesis of 9 followed the protocol al- target structures is solely based on chemoselectivity and
ready reported by Tovar and Swager.[18]
hence, their structures are developed by chemical arguments
The chemical robustness of both TIPS protection groups from the corresponding regioisomer.
opened a wide space of potential reaction conditions for
As expected, both TIPS-protection groups and both ter-
the subsequent Suzuki coupling reactions. To introduce the minal acetylenic protons displayed considerable differences
1
electron withdrawing trifluoromethylphenyl group equi- for both regioisomers. The chemical shifts in the H NMR
molar amounts of the dibromide 9 and the commercially spectra for the acetylene proton and for the TIPS protons
available 4-(trifluoromethyl)phenylboronic acid with cata- are 1.17 ppm and 3.17 ppm for one regioisomer and 0.98–
lytic amounts of Pd(PPh3)4 and an excess of K2CO3 were 0.99 ppm and 3.48 ppm for the other regioisomer. For the
kept at 80 °C in a DME/water mixture for 14 h. After work chemical shift of these ethynylic groups the functional
up the desired monosubstituted biphenyl derivative 10 and groups in the corresponding ortho-positions are assumed to
the doubly substituted terphenyl system 11 were isolated be the key-players as they are sterically closest and they
both as white solids in 46 and 32% yields respectively by couple electronically stronger than the groups in the corre-
CC. Comparable reaction conditions applied to the doubly sponding meta-positions. Thus, the very comparable chemi-
silyl-protected diacetylene 10 as described above for 8 re- cal shifts of the TIPS groups with model compounds al-
sulted in a statistical mixture of the fully protected starting ready synthesized during the assembly of these structures
material 10, both regioisomers 12 and 13 together with allowed the structural assignment.
traces of the doubly deprotected diacetylene. The starting
The chemical shift of the TIPS protons of the doubly
material 10 was dissolved in THF and after addition of a TIPS-protected diacetylene 9 with bromine substituents in
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Molecular Rods with a Transversal Push-Pull System
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ortho-positions for both acetylenes is with 1.13 and 1.14
After identification of both regioisomers 12 and 13, their
very comparable to the TIPS protons at δ = 1.17 ppm of functional groups allowed the gradual assembly of the de-
one regioisomer and thus, this regioisomer is expected to sired target structures 1–4. The synthesis of the target rods
be compound 13 with a bromine atom in ortho-position of 1–4 is displayed in Scheme 3. As the limited stability of 12
the TIPS acetylene. On the other hand the terphenyl side and 13 was attributed to their free acetylene, this function
product 11 has two TIPS-protected acetylenes each in or- was first caped with an aromatic system in a Sonogashira
tho-position of a para-trifluoromethylphenyl substituent. In coupling reaction. To assemble the shorter target structures
similarity to the other regioisomers the signals of his TIPS 1 and 2, the corresponding regioisomer 12 and 13 together
protons are at δ = 0.98 and 0.99 ppm and thus, the structure with 1.5 equiv. of iodobenzene, catalytic amounts of
of the regioisomer with the TIPS signal at δ = 0.98 and 0.99 Pd(PPh3)4 and CuI in a THF/(iPr)2NH mixture was kept at
ppm is 12 with a para-trifluoromethylphenyl substituent in room temperature overnight. After work up and CC the
ortho-position to the TIPS acetylene. While at this stage of corresponding phenylacetylene derivatives 14 and 15 were
the synthesis the assignment was still questioned to some isolated both in 86% yields as colorless oil and as white
extend, it was confirmed finally by an x-ray structure of a solid, respectively. Subsequently, the terphenyl push-pull
derivative of 13.
system was completed by substituting the remaining bro-
Scheme 3. Synthesis of target structures 1–4. a) iodobenzene, Pd(PPh3)4, (iPr)2NH, CuI, THF, room temp., 16 h, 86% (14) and 86% (15);
b) 4-(dimethylamino)phenylboronic acid, Pd(PPh3)4, K2CO3, DME/H2O, 80 °C, 16 h, 84% (16) and 66% (17); c) TBAF, THF, room
temp., 97% (18) and 94% (19); d) S-(4-iodophenyl) thioacetate, Pd(PPh3)4, (iPr)2NEt, CuI, THF, room temp., 16 h, 80% (1) and 83%
(2); e) 1,4-diethyl-2-iodo-5-(phenylethynyl)benzene, Pd(PPh3)4, (iPr)2NH, CuI, THF, room temp., 16 h, 72% (20) and 90% (21); f) 4-
(dimethylamino)phenylboronic acid, Pd(PPh3)4, K2CO3, DME/H2O, 80 °C, 16 h, 86% (22) and 81% (23); g) TBAF, THF, room temp.,
90% (24) and 96% (25); h) S-(4-iodophenyl) thioacetate, Pd(PPh3)4, (iPr)2NEt, CuI, THF, room temp., 16 h, 44% (3) and 62% (4).
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mine of 14 and 15 with commercially available 4-(dimeth- vent.[21] The acetylene derivatives 18 and 19 and S-(4-iodo-
ylamino)phenylboronic acid in a Suzuki cross-coupling re- phenyl) thioacetate together with catalytic amounts of
action. The corresponding bromines 14 and 15 and the bo- Pd(PPh3)4 and CuI were kept at room temperature over-
ronic acid derivative together with catalytic amounts of night in a THF/(iPr)2NEt mixture. After work up and CC,
Pd(PPh3)4 and an excess of K2CO3 in a DME/water mix- the desired terminally sulfur-functionalized OPE rods com-
ture were kept at 80 °C overnight. After work up, the ter- prising a transversal OP push-pull system 1 and 2 were iso-
phenyl push-pull derivatives 16 and 17 were isolated in 84% lated both as yellow solids in yields of 80 and 83%, respec-
and 66% yields respectively by CC. While 16 was a brown- tively.
ish oil, compound 17 as a derivative of 13 was a crystalline
The assembly of the target structures comprising an elon-
brownish solid. Single crystals suitable for X-ray analysis gated OPE rod 3 and 4 was achieved with very similar reac-
were obtained by slow diffusion of ethanol into a solution tion conditions as described above for the shorter deriva-
of 17 in dichloromethane. The solid-state structure of 17 is tives 1 and 2. Both regioisomers 20 and 21 were first caped
displayed in Figure 4. Compound 17 crystallizes with two with 1,4-diethyl-2-iodo-5-(phenylethynyl)benzene, which
independent molecules in the monoclinic space group was synthesized following the literature procedure.[22] The
P21/n.[19] These two molecules show an almost coplanar but reaction proceeded smoothly in (iPr)2NEt/THF at room
antiparallel arrangement, such that the trifluoromethyl temperature to afford the π-extended systems 20 and 21 in
group of one molecule lies above the dimethylamino group 72% and 90% isolated yield, respectively. Subsequently,
of the other. The distance between the central phenyl rings Suzuki cross-coupling of the commercially available 4-(di-
of these two molecules amounts to 371.4 pm.
methylamino)phenylboronic acid to the bromide atom of 20
or 21 in a DME/water solvent mixture at 80 °C provided
the molecular rods 22 and 23 comprising a terphenyl push-
pull system in 86 and 81% isolated yields after CC. The
task of both ethyl side chains of the OPE rod was to provide
the required solubility and processability of the longer rod
target structures 3 and 4 and of their precursors.
Comparable reaction conditions as described for 16 and
17 allowed the efficient removal of the TIPS protection
group from 22 and 23 and provided the two acetylenes 24
and 25 in yields of 90 and 96% respectively after CC.
Again, a final Sonogashira coupling step of the acetylenes
of 24 and 25 with a slight excess of 1.3 to 1.4 equiv. of
S-(4-iodophenyl) thioacetate in the presence of catalytic
amounts of Pd(PPh3)4 and CuI in a THF/(iPr)2NEt mixture
at room temperature provided the longer terminally sulfur-
functionalized OPE rods comprising a transversal OP push-
pull system 3 and 4, both as yellow solids which were iso-
lated by CC in yields of 44 and 62%, respectively.
Figure 4. Solid state structure of 17 (ORTEP, thermal ellipsoids set
All new compounds were fully characterized by conven-
at the 50% probability level).
1
tional analytical and spectroscopic techniques like H and
13C-NMR spectroscopy and mass spectrometry. However,
The solid-state structure of 17 with the meta relation at superimposition of two 13C-NMR signals has been ob-
the central ring between the para-trifluoromethylphenyl served for several compounds which display one signal less
group and the trisisopropylsilylethynyl substituent confirm than expected in the aromatic region of their 13C-NMR
1
the above suggested H NMR assignment for its precursor spectra. This is the case for compounds 1, 4, 7, 16, 20, 21,
13 and thus, the differentiation between both regioisomers 24 and 25. Furthermore, apart from the too labile interme-
12 and 13.
With both ideally substituted terphenyl structures 16 and pounds was investigated by elemental analysis.
17 in hand, the assembly of the desired target structures 1 The cruciform target structures 1–4 are soluble in aprotic
diates 12 and 13, the purity of the new synthesized com-
and 2 was accomplished in two steps. After fluoride pro- organic solvents and particularly well soluble in haloge-
moted desylilation by TBAF in wet THF the free acetylenes nated organic solvents. However, they display limited sta-
18 and 19 were isolated by CC in yields of 97 and 94%, bility features in particular in chloroform, probably due to
respectively, both as yellowish solids. To complete the OPE traces of acids. These stability restrictions are probably due
rod, a final Sonogshira coupling between the free acetylenes to an electrophilic cyclization reaction of the cruciforms 1–
of 18 and 19 with the known S-(4-iodophenyl) thio- 4 to fused aromatic rings in the presence of catalytic
acetate[20] provided the desired target structures 1 and 2. amounts of acids. This cyclization reaction has been investi-
For this final reaction step (iPr)2NEt was used instead of gated in details by Swager and co-workers for the cruciform
(iPr)2NH as for the acetyl-protected thiophenol improved motive consisting of crossed OP and OPE rods and turned
stability features are reported for the tertiary amine as sol- out to be efficient with electron-rich terminal substituents
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Molecular Rods with a Transversal Push-Pull System
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at the OPE substructure.[13] Thus, the cruciform structures improving the stability features of the cruciform substruc-
1–4 comprising the terminal electron-rich sulfur anchor ture by altering the subsituents in proximity of the central
group at the OPE rod is probably exposed to this unwanted phenyl ring.
cyclization reaction. Furthermore, by TLC traces of several
degradation products emerging from 1–4 were observed
Experimental Section
which may point to several degradation pathways. However,
during attempts to crystallize these cruciforms 1–4 in acid
free solvents in the dark, no degradations of the dissolved
molecules were observed over periods of several months.
Of particular interest will be the applied potential depen-
dence of the electronic transport properties of these cruci-
forms immobilized in nanoscale junctions. The availability
of two different length of the longer OPE cross-bars enables
to bridge gaps between electrodes of various length. Based
on MM+ calculation, the length of the shorter cruciforms
1 and 2 is 1.95 nm between the sulfur atom and the terminal
hydrogen atom at the opposite end of the OPE backbone,
while the length of the longer cruciform structures 3 and 4
is calculated to be 2.63 nm. Furthermore, for both series of
different length both push-pull directions of the transversal
OP cross-bar have been synthesized, enabling the investiga-
tion of both possible polarization directions of the elec-
trodes. While for the cruciforms 1 and 3 their electron-ac-
cepting trifluoromethyl groups of their transversal OP rods
point towards the electrode to which the cruciforms are co-
valently bound, they point towards the opposite electrode
for the cruciforms 2 and 4. We hope to be able to trace
more carefully potential switching mechanisms based on
this variety of the cruciform structure. First attempts to im-
mobilize these cruciforms between nanoscale-spaced elec-
trodes are currently under investigations.
General Remarks: All chemicals were used as received from the
supplier, solvents were p.a. quality and used without further purifi-
cation. If necessary the solvents were dried by standard literature
procedures, THF with Na/benzophenone[23] and (iPr)2NEt,
(iPr)2NH over CaH2. The following instruments were used for the
characterization of the synthesized compounds: 1H NMR and 13C-
NMR spectra were recorded on a Bruker Ultra Shield 300 MHz,
the J values are given in Hz. MALDI-TOF spectra was performed
on a PerSeptive Biosystems Voyager DE PRO time-of-flight mass
spectrometer and EI-MS on a LKB-9000S. Melting points were
measured with a Büchi Melting Point B-540 apparatus. TLC was
carried out on Merck silica gel 60 F254 plates and column
chromatography (CC) using Merck silica gel 60 (0.040–0.063 mm).
Elemental analyses were performed using the ThermoQuest
FlashEA 1112 N/Protein Analyzer.
2,5-Diethyl-1,4-diiodobenzene: Synthesis according to a literature
procedure[22] (42.7 g, 65%). M.p. 70–72 °C (ref.[22] 68–69 °C). 1H
3
NMR (300 MHz, CDCl3, 25 °C): δ = 1.18 (t, JH,H = 7.5 Hz, 9 H,
3
CH3), 2.64 (q, JH,H = 7.5 Hz, 4 H, CH2), 7.62 (s, 2 H) ppm. 13C
NMR (75 MHz, CDCl3, 25 °C): δ = 14.6, 33.3, 100.5, 138.8,
146.0 ppm. MS (EI): m/z (%) = 386.0 (100) [M+], 370.9 (37.5) [M+ –
CH3], 259.0 (9.4) [M+ – I], 132.1 (8.0) [M+ – 2I], 117.1 (23.8) [M+
2I, – CH3].
–
1,4-Diethyl-2-iodo-5-(phenylethynyl)benzene: Synthesis according to
a literature procedure[22] (5.7 g, 76%, colorless oil). 1H NMR
3
(300 MHz, CDCl3, 25 °C): δ = 1.24 (t, JH,H = 7.5 Hz, 3 H, CH3),
3
3
1.31 (t, JH,H = 7.5 Hz, 3 H, CH3), 2.72 (q, JH,H = 7.5 Hz, 2 H,
CH2), 2.83 (q, 3JH,H = 7.5 Hz, 2 H, CH2), 7.27–7.40 (m, 4 H), 7.50–
7.59 (m, 2 H), 7.72 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 14.6, 14.8, 27.0, 33.6, 87.7, 93.8, 101.0, 122.8, 123.4,
128.5, 128.5, 131.6, 131.7, 138.9, 143.9, 145.4 ppm. MS (EI): m/z
Conclusions
The synthesis of four new cruciform molecules 1–4 con-
sisting of a longer oligophenylene-ethynyl (OPE) cross-bar
and a transversal oligophenylene (OP) cross-bar is de-
scribed. One end of the OPE rod bears an acetyl-protected
sulfur as anchor group for metal electrodes. The crossing
OP rod is terminally functionalized with an electron-ac-
cepting trifluoromethyl group and with an electron-donat-
ing dimethylamino group to provide a push-pull system
transversal to the rods main axis. Not only two different
length of the cruciforms OPE backbone have been synthe-
sized, but also both push-pull directions of the transversal
OP rod. The assembly of these cruciforms 1–4 is mainly
(%) = 360.0 (100) [M+], 345.0 (10.4) [M+ – CH3], 233.2 (9.1) [M+
I], 218.1 (14) [M+ – I, – CH3].
–
1,4-Dibromo-2,5-diiodobenzene (5): Compound 5 was synthesized
according to a literature procedure[17] (25.1 g, 52%). M.p. 164–
166 °C (ref.[17] 163–165 °C). 1H NMR (300 MHz, CDCl3, 25 °C): δ
= 8.06 (s, 2 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 101.8,
129.6, 142.7 ppm. MS (EI): m/z (%) = 489.5 (49), 487.6 (100), 485.6
(51) [M+], 362.7 (9), 360.7 (19), 358.7 (9) [M+ – I], 235.8 (7), 233.8
(15), 231.8 (8) [M+ – 2I], 154.9 (10), 152.9 (11) [M+ – 2I, – Br].
2,5-Dibromo-4-iodo-4Ј-(trifluoromethyl)biphenyl (6): To a mixture
of 5 (8.5464 g, 17.5 mmol) in degassed DME (200 mL), 4-(trifluor-
omethyl)phenylboronic acid (2.2158 g, 11.7 mmol), Pd(PPh3)4
based on metal catalyzed cross-coupling reactions. How- (0.6759 g, 0.58 mmol), K2CO3 (16.1928 g, 117 mmol) and degassed
water (50 mL) were added. The reaction mixture was heated to
75 °C and kept at 75 °C for 16 h under a nitrogen atmosphere.
DME was removed by rotary evaporation and the residue was ex-
tracted with CH2Cl2. The solvent was removed and the residue was
absorbed on silica gel. Purification by column chromatography
(CC) (silica gel, hexane) afforded 6 as a white solid (2.81 g, 48%).
M.p. 91–94 °C. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 7.49 (d,
ever, the key step of the synthetic approach is the separation
of two regioisomers by column chromatography.
These cruciforms have been designed as prospective
electronic potential-dependent switching systems integrated
between two electrodes with nanoscale spacing. Limited
stability features of these cruciform structures have been ob-
served in the presence of traces of acids.
3
3JH,H = 8.1 Hz, 2 H), 7.55 (s, 1 H), 7.69 (d, JH,H = 7.8 Hz, 2 H),
8.17 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 101.4,
121.4, 122.3, 124.1 (q, 1JC,F = 270.7 Hz), 125.4 (q, 3JC,F = 3.9 Hz),
pendent transport properties in electronic circuits, we are 129.2, 129.6, 129.8, 130.6 (q, 2JC,F = 32.5 Hz), 134.2, 142.5 (q, 4JC,F
While these cruciforms are currently immobilized on an
electrode surface to investigate their electronic potential-de-
Eur. J. Org. Chem. 2007, 2630–2642
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2637

A. Błaszczyk, M. Fischer, C. von Hänisch, M. Mayor
FULL PAPER
= 1.3 Hz), 142.7, 143.6 ppm. MS (EI): m/z (%) = 507.6 (45), 505.6
(100), 503.6 (47) [M+], 299.9 (24), 297.9 (24) [M+ – Br, – I], 219.0
(15) [M+ – 2Br, – I].
due was fractioned by CC (silica gel, hexane) to afford 10 (4.2622 g,
46%) as a white solid and the side product 11 (3.257 g, 32%) as a
white solid.
1
2Ј,5Ј-Dibromo-4-dimethylamino-4ЈЈ-trifluoromethyl[1,1Ј:4Ј,1ЈЈ]ter-
phenyl (7): Similar reaction conditions as described above for 6 have
been applied for the synthesis of 7. A solution of 6 (2.78 g,
10: M.p. 89–92 °C. H NMR (300 MHz, CDCl3, 25 °C): δ = 0.97
(s, 3 H, CH), 0.98 (s, 18 H, CH3), 1.15 (s, 3 H, CH), 1.16 (s, 18 H,
CH3), 7.46 (s, 1 H), 7.64 (s, 4 H), 7.81 (s, 1 H) ppm. 13C NMR
5.50 mmol), 4-(dimethylamino)phenylboronic acid (1.36 g, (75 MHz, CDCl3, 25 °C): δ = 11.3, 11.4, 18.6, 18.8, 98.5, 99.0,
1
8.2 mmol), Pd(PPh3)4 (0.3172 g, 0.27 mmol), K2CO3 (2.2747 g,
16.5 mmol) in degassed DME/H2O (90/30 mL) was heated to 75 °C
and kept at 75 °C for 16 h under a nitrogen atmosphere. After sim-
ilar work-up as described above for 6, the residue was purified by
CC (silica gel, hexane:CH2Cl2 = 2:1) and gave 7 as beige solid
(402 mg, 15 %). M.p. 171–173 °C. 1H NMR (300 MHz, CDCl3,
25 °C): δ = 3.04 (s, 6 H, CH3), 6.81 (broad d, 3JH,H = 7.8 Hz, 2 H),
103.9, 104.3, 123.3, 124.3 (q, JC,F = 272.4 Hz), 124.8, 125.2 (q,
3JC,F = 3.9 Hz), 125.9, 129.7, 130.1 (q, JC,F = 32.4 Hz), 134.0,
136.8, 141.9, 142.7 (q, JC,F = 1.7 Hz) ppm. C35H48BrF3Si2
(661.83): calcd. C 63.52, H 7.31; found C 63.75, H 7.65. MS (EI):
m/z (%) = 662.3 (6) [M+], 660.3 (5) [M+], 619.2 (100) [M+ – C3H7],
617.3 (87) [M+ – C3H7].
2
4
11: M.p. 215–218 °C. 1H NMR (300 MHz, CDCl3, 25 °C): δ = 0.98
3
3
7.37 (d, JH,H = 8.7 Hz, 2 H), 7.56 (d, JH,H = 8.1 Hz, 2 H), 7.60
(s, 1 H), 7.66 (s, 1 H), 7.72 (d, 3JH,H = 8.1 Hz, 2 H) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 40.6, 111.8, 121.0, 121.9, 124.3 (q,
3
(s, 6 H, CH), 0.99 (s, 36 H, CH3), 7.59 (s, 2 H), 7.68 (d, JH,H
=
8.4 Hz, 4 H), 7.72 (d, JH,H = 8.7 Hz, 4 H) ppm. 13C NMR
3
(75 MHz, CDCl3, 25 °C): δ = 11.3, 18.6, 97.6, 105.0, 122.4, 124.4
3
2
1JC,F = 273.0 Hz), 125.3 (q, JC,F = 3.8 Hz), 129.9, 130.2 (q, JC,F
3
3
(q, JC,F = 270.4 Hz), 125.2 (q, JC,F = 3.7 Hz), 129.8, 130.0 (q,
4
= 32.5 Hz), 130.3, 135.2, 135.5, 140.5, 143.2 (q, JC,F = 1.5 Hz),
3JC,F = 32.7 Hz), 134.2, 142.4, 143.1 (q, JC,F = 1.6 Hz) ppm. MS
4
144.0, 150.3 ppm. C21H16Br2F3N (499.16): calcd. C 50.53, H 3.23,
N 2.81; found C 50.89, H 3.43, N 2.69. MS (MALDI-TOF): calcd.
for C21H16Br2F3N 498.9577; found: 499.4195.
(EI): m/z (%) = 726.3 (6) [M+], 683.3 (100) [M+ – C3H7].
[2-(4-Bromo-6-ethynyl-4Ј-(trifluoromethyl)biphenyl-3-yl)ethynyl]tri-
isopropylsilane (12) and [2-(4-Bromo-5-ethynyl-4Ј-(trifluoromethyl)-
biphenyl-2-yl)ethynyl]triisopropylsilane (13): To a solution of 10
(1.7949 g, 2.71 mmol) in degassed THF (200 mL) with some drops
of acetic acid a solution of TBAF (2 mL, 1  TBAF in THF) was
added. The reaction mixture was stirred at room temperature for
16 h. After filtration through silica gel (hexane) all solvents were
removed. The residue was separated by CC (silica gel, hexane) to
afford 12 (397 mg, 29%) and 13 (288 mg, 21%) both as brown oils.
4-Dimethylamino-4ЈЈ-trifluoromethyl-2Ј,5Ј-bis[2-(triisopropylsilyl)-
ethynyl][1,1Ј:4Ј,1ЈЈ]terphenyl (8): To a solution of 7 (289.5 mg,
0.58 mmol), Pd(PPh3)2Cl2 (20.3 mg, 0.029 mmol), CuI (11 mg,
0.058 mmol), (iPr)2NH (10 mL) in dry and degassed THF
(200 mL) (triisopropylsilyl)acetylene (0.34 mL, 1.52 mmol) was
added. The reaction mixture was kept at room temperature for 16 h
under a nitrogen atmosphere. After removal of the solvent by ro-
tary evaporation the crude product was purified by CC (silica gel,
hexane:CH2Cl2 = 1:1) to provide 8 (399.1 mg, 98%) as a white
solid. M.p. 166–169 °C. 1H NMR (300 MHz, CDCl3, 25 °C): δ =
1.04 (apparent s, 21 H, TIPS), 1.10 (apparent s, 21 H, TIPS), 3.03
12: 1H NMR (300 MHz, CDCl3, 25 °C): δ = 0.98 (s, 3 H, CH),
0.99 (s, 18 H, CH3), 3.48 (s, 1 H), 7.49 (s, 1 H), 7.60–7.70 (m, 4
H), 7.82 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ =
1
3
11.3, 18.6, 81.5, 83.8, 98.9, 103.7, 122.5, 124.1, 124.3 (q, JC,F
=
=
(s, 6 H, NCH3), 6.82 (d, JH,H = 8.7 Hz, 2 H), 7.60 (s, 1 H), 7.63
272.4 Hz), 124.6, 125.3 (q, 3JC,F = 3.7 Hz), 129.7, 129.8 (q, JC,F
2
3
3
(d, JH,H = 8.7 Hz, 2 H), 7.67 (s, 1 H), 7.71 (d, JH,H = 8.4 Hz, 2
H), 7.77 (d, 3JH,H = 8.4 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 11.4, 11.5, 18.6, 18.8, 40.7, 96.1, 96.4, 105.7, 106.4,
4
32.6 Hz), 134.3, 137.0, 142.0, 142.5 (q, JC,F = 1.6 Hz) ppm. MS
(EI): m/z (%) = 506.0 (11), 504.0 (10) [M+], 462.8 (100), 460.8 (84)
[M+ – C3H7].
1
3
112.3, 122.0, 122.1, 124.5 (q, JC,F = 270.5 Hz), 125.1 (q, JC,F
3.7 Hz), 127.4, 129.7 (q, JC,F = 32.2 Hz), 129.9, 130.1, 134.3,
134.5, 140.5, 143.6 (q, JC,F = 1.5 Hz), 143.8, 150.4 ppm.
=
2
1
13: H NMR (300 MHz, CDCl3, 25 °C): δ = 1.17 (apparent s, 21
4
H, TIPS), 3.17 (s, 1 H), 7.49 (s, 1 H), 7.64–7.74 (m, 4 H), 7.85 (s,
C43H58F3NSi2 (702.09): calcd. C 73.56, H 8.33, N 1.99; found C
73. 70, H 8. 21, N 2.09. MS (MALDI-TOF): calcd. for
C43H58F3NSi2 701.4054; found 701.2474.
1 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 11.4, 18.8, 81.0,
3
83.4, 99.4, 104.1, 121.6, 124.3 (q, JC,F = 3.7 Hz), 124.9, 125.3 (q,
1JC,F = 273.2 Hz), 126.6, 129.6, 130.3 (q, JC,F = 32.2 Hz), 134.3,
2
4
137.3, 141.8, 142.2 (q, JC,F = 1.6 Hz) ppm. MS (EI): m/z (%) =
1,4-Dibromo-2,5-bis[2-(triisopropylsilyl)ethynyl]benzene (9): Com-
pound 9 was synthesized according to a literature procedure[18]
(4.63 g, 77 %). M.p. 119–121 °C. 1H NMR (300 MHz, CDCl3,
25 °C): δ = 1.13 (s, 6 H, CH), 1.14 (s, 36 H, CH3), 7.67 (s, 2 H)
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 11.4, 18.8, 99.9,
103.4, 123.9, 126.8, 136.7 ppm. MS (EI): m/z (%) = 598.2 (3.2),
596.2 (5.8), 594.2 (2.6) [M+], 555.1 (58), 553.1 (100), 551.1 (48)
[M+ – C3H7].
(%) 506.0 (3.2), 504.0 (3.0) [M+], 462.9 (100), 460.9 (95) [M+
C3H7].
–
[2-(4-Bromo-5-(2-phenylethynyl)-4Ј-(trifluoromethyl)biphenyl-2-yl)-
ethynyl]triisopropylsilane (14): A similar reaction protocol as de-
scribed above for 8 has been applied for the synthesis of 14. A
solution of iodobenzene (0.593 mmol, 0.07 mL), 12 (200 mg,
0.396 mmol), Pd(PPh3)4 (22.9 mg, 0.022 mmol), CuI (7.5 mg,
0.039 mmol) and (iPr)2NH (3 mL) in degassed THF (50 mL) was
4-Bromo-4Ј-trifluoromethyl-2,5-bis[2-(triisopropylsilyl)ethynyl]bi-
phenyl (10) and 2Ј,5Ј-Bis[2-(triisopropylsilyl)ethynyl]-4,4ЈЈ-bis(tri- stirred for 16 h at room temperature. The solvents were removed
fluoromethyl)[1,1Ј:4Ј,1ЈЈ]terphenyl (11): Similar reaction conditions
as described above for 6 have been applied for the synthesis of 10
and 11. A solution of 1,4-dibromo-2,5-bis(triisopropylsilylethynyl)-
benzene (9) (8.374 g, 14.0 mmol), 4-(trifluoromethyl)phenylboronic
and the residue was purified by CC (silica gel, hexane) to get 14 as
an colorless oil (197.6 mg, 86 %). 1H NMR (300 MHz, CDCl3,
25 °C): δ = 0.99 (s, 3 H, CH), 1.00 (s, 18 H, CH3), 7.35–7.41 (m, 3
H), 7.53 (s, 1 H), 7.56–7.61 (m, 2 H), 7.66 (s, 4 H), 7.85 (s, 1 H)
acid (2.6658 g, 14.0 mmol), Pd(PPh3)4 (0.8089 g, 0.7 mmol), K2CO3 ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 11.3, 18.6, 87.8, 96.2,
(7.7398 g, 56 mmol) in degassed DME/H2O (200/50 mL) was
heated to 80 °C and kept for 14 h at 80 °C under a nitrogen atmo-
sphere. After evaporation of the organic solvent, extraction with
CH2Cl2 and again evaporation of the solvents the remaining resi-
98.5, 104.0, 122.7, 123.3, 124.3 (q, 1JC,F = 270 Hz), 124.6, 125.2 (q,
2
3JC,F = 3.7 Hz), 125.8, 128.6, 129.1, 129.7, 130.1 (q, JC,F
=
32.5 Hz), 131.9, 133.4, 136.9, 142.0, 142.6 (q, 4JC,F = 1.1 Hz) ppm.
C32H32BrF3Si (581.58): calcd. C 66.09, H 5.55; found C 66.13, H
2638
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 2630–2642

Molecular Rods with a Transversal Push-Pull System
FULL PAPER
5.78. MS (MALDI-TOF): calcd. for C32H32BrF3Si 582.1388; found
580.3855.
4-Dimethylamino-5Ј-ethynyl-2Ј-(2-phenylethynyl)-4ЈЈ-trifluorometh-
yl[1,1Ј:4Ј,1ЈЈ]terphenyl (18): To a solution of 18 (181 mg,
0.29 mmol) in degassed THF (30 mL) a solution of TBAF (0.1 mL,
1  TBAF in THF) was added. The reaction mixture was stirred
at room temperature for 1 h. After evaporation of the solvents the
residue was purified by CC (silica gel, hexane:CH2Cl2 = 2:1) to
provide 18 as yellowish solid (131 mg, 97%). M.p. 64–66 °C. 1H
NMR (300 MHz, CDCl3, 25 °C): δ = 3.06 (s, 6 H, NCH3), 3.18 (s,
[2-(4-Bromo-6-(2-phenylethynyl)-4Ј-(trifluoromethyl)biphenyl-3-yl)-
ethynyl]triisopropylsilane (15): A similar reaction protocol as de-
scribed above for 8 has been applied for the synthesis of 15. A
solution of iodobenzene (0.445 mmol, 0.05 mL), 13 (150 mg,
0.297 mmol), Pd(PPh3)4 (17.2 mg, 0.015 mmol), CuI (5.7 mg,
0.03 mmol) and (iPr)2NH (3 mL) in degassed THF (50 mL) was
stirred for 16 h at room temperature. The solvents were removed
and the residue was purified by CC (silica gel, hexane) to afford
15 as a white solid (151.2 mg, 86%). M.p. 112–114 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 1.21 (apparent s, 21 H, TIPS), 7.28–
7.39 (m, 5 H), 7.56 (s, 1 H), 7.76 (s, 4 H), 7.91 (s, 1 H) ppm. 13C
NMR (75 MHz, CDCl3, 25 °C): δ = 11.5, 18.8, 87.3, 95.6, 99.0,
3
1 H), 6.86 (d, JH,H = 8.4 Hz, 2 H), 7.31–7.37 (m, 3 H), 7.43–7.49
(m, 2 H), 7.65–7.82 (m, 8 H) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 40.6, 82.0, 82.7, 89.5, 94.1, 111.9, 120.4, 122.1, 123.4,
1
3
124.4 (q, JC,F = 270.6 Hz), 125.1 (q, JC,F = 3.7 Hz), 126.8, 128.4,
2
128.5, 129.7, 129.7 (q, JC,F = 32.5 Hz), 130.2, 131.6, 134.2, 134.7,
140.3, 143.0 (q, JC,F = 1.5 Hz), 143.2, 150.4 ppm. C31H22F3N
4
1
3
(465.51): calcd. C 79.98, H 4.76, N 3.01; found C 80.17, H 4.89, N
2.89. MS (MALDI-TOF): calcd. for C31H22F3N 465.1699; found
464.8913.
104.4, 123.0, 124.2 (q, JC,F = 271.3 Hz), 125.0, 125.2 (q, JC,F
=
=
2
3.6 Hz), 125.7, 126.1, 128.6, 129.0, 129.7, 130.2 (q, JC,F
32.6 Hz), 131.6, 134.2, 136.3, 141.2, 142.6 (q, 4JC,F = 1.5 Hz) ppm.
C32H32BrF3Si (581.58): calcd. C 66.09, H 5.55; found C 66.17, H
5.64. MS (MALDI-TOF): calcd. for C32H32BrF3Si 582.1388; found
580.4558.
4-Dimethylamino-2Ј-ethynyl-5Ј-(2-phenylethynyl)-4ЈЈ-trifluorometh-
yl[1,1Ј:4Ј,1ЈЈ]terphenyl (19): To a solution of 17 (81 mg, 0.13 mmol)
in degassed THF (20 mL) a solution of TBAF (0.5 mL, 1  TBAF
in THF) was added. The reaction mixture was stirred at room tem-
perature for 1 h. After evaporation of the solvents the residue was
purified by CC (silica gel, hexane:CH2Cl2 = 2:1) to afford 19 as
yellowish solid (57 mg, 94 %). M.p. 189–192 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 3.05 (s, 6 H, NCH3), 3.22 (s, 1 H),
6.83 (d, 3JH,H = 8.4 Hz, 2 H), 7.34 (s, 5 H), 7.61 (d, 3JH,H = 8.4 Hz,
4-Dimethylamino-2Ј-(2-phenylethynyl)-4ЈЈ-trifluoromethyl-5Ј-[2-(tri-
isopropylsilanyl)ethynyl][1,1Ј:4Ј,1ЈЈ]terphenyl (16): A similar syn-
thetic protocol as described for the synthesis of 6 has been applied
for the synthesis of 16. A solution of 14 (228 mg, 0.392 mmol), 4-
(dimethylamino)phenylboronic acid (91 mg, 0.549 mmol),
Pd(PPh3)4 (22.6 mg, 0.019 mmol), K2CO3 (217 mg, 1.57 mmol) in
degassed DME/H2O (30/10 mL) was heated to 70 °C and kept at
70 °C for 16 h under a nitrogen atmosphere. After work-up, the
residue was purified by CC (silica gel, hexane:CH2Cl2 = 2:1) to
afford 16 as brownish oil (206 mg, 84 %). 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 1.07 (apparent s, 21 H, TIPS), 3.07 (s, 6 H,
3
2 H), 7.67 (s, 1 H), 7.71 (s, 1 H), 7.75 (d, JH,H = 8.2 Hz, 2 H),
3
7.83 (d, JH,H = 8.3 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 40.5, 81.8, 83.3, 88.7, 94.3, 111.9, 120.4, 122.3, 123.0,
1
3
124.4 (q, JC,F = 272.0 Hz), 125.1 (q, JC,F = 3.9 Hz), 126.6, 128.5,
2
128.7, 129.6, 129.6 (q, JC,F = 32.2 Hz), 130.1, 131.5, 133.9, 135.0,
139.7, 143.2 (q, JC,F = 1.7 Hz), 144.0, 150.3 ppm. C31H22F3N
3
4
NCH3), 6.89 (d, JH,H = 8.4 Hz, 2 H), 7.28–7.32 (m, 4 H), 7.42–
3
7.49 (m, 2 H), 7.64–7.75 (m, 6 H), 7.79 (d, JH,H = 8.3 Hz, 1 H)
(465.51): calcd. C 79.98, H 4.76, N 3.01; found C 79.66, H 4.80, N
2.97. MS (MALDI-TOF): calcd. for C31H22F3N 465.1699; found
464.6519.
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 11.3, 18.6, 40.6, 89.6,
1
93.9, 96.4, 105.7, 112.0, 121.5, 122.1, 123.5, 124.5 (q, JC,F
=
3
270 Hz), 125.0 (q, JC,F = 3.8 Hz), 127.1, 128.4, 129.8, 129.9 (q,
2JC,F = 32.6 Hz), 130.2, 131.6, 133.8, 134.4, 140.5, 143.2, 143.5 (q,
4JC,F = 1.2 Hz), 150.4 ppm. C40H42F3NSi (621.85): calcd. C 77.26,
H 6.81, N 2.25; found C 77.32, H 6.73, N 1.98. MS (MALDI-
TOF): calcd. for C40H42F3NSi 621.3033; found 620.6691.
5Ј-[2-(4-Acetylsulfanylphenyl)ethynyl]-4-dimethylamino-2Ј-(2-phen-
ylethynyl)-4ЈЈ-trifluoromethyl[1,1Ј:4Ј,1ЈЈ]terphenyl (1): For the syn-
thesis of 1 a similar Sonogashira coupling protocol as described for
8 has been applied. A solution of S-(4-iodophenyl) thioacetate (101
mg, 0.36 mmol), 18 (130 mg, 0.28 mmol), Pd(PPh3)4 (16.2 mg,
0.014 mmol), CuI (5.3 mg, 0.028 mmol) and (iPr)2NEt (2 mL) in
degassed THF (50 mL) was stirred for 16 h at room temperature.
After removing of the solvents the residue was absorbed on silica
gel to charge a column. CC (silica gel, hexane:CH2Cl2 = 1:1) af-
forded 1 (137.5 g, 80%) as yellow solid. M.p. 187–189 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 2.44 (s, 3 H, CH3), 3.05 (s, 6 H,
4-Dimethylamino-5Ј-(2-phenylethynyl)-4ЈЈ-trifluoromethyl-2Ј-[2-(tri-
isopropylsilanyl)ethynyl][1,1Ј:4Ј,1ЈЈ]terphenyl (17): A similar syn-
thetic protocol as described for the synthesis of 6 has been applied
for the synthesis of 17. A solution of 15 (140 mg, 0.241 mmol), 4-
(dimethylamino)phenylboronic acid (47.7 mg, 0.289 mmol),
Pd(PPh3)4 (13.9 mg, 0.012 mmol), K2CO3 (133.2 mg, 0.964 mmol)
in degassed DME/H2O (30/10 mL) was heated to 80 °C and kept
at 80 °C for 16 h under a nitrogen atmosphere. After evaporation
of the organic solvent, extraction with CH2Cl2, drying over MgSO4
followed by evaporation of the solvents the remaining residue was
fractioned by CC (silica gel, hexane:CH2Cl2 = 2:1) to afford 17 as
brownish solid (98.5 mg, 66 %). M.p. 93–96 °C. 1H NMR
(300 MHz, CDCl3, 25 °C): δ = 1.04 (apparent s, 21 H, TIPS), 3.02
3
NCH3), 6.86 (d, JH,H = 8.7 Hz, 2 H), 7.30–7.48 (m, 9 H), 7.67–
3
7.78 (m, 6 H), 7.83 (d, JH,H = 8.1 Hz, 2 H) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 30.4, 40.7, 89.6, 90.6, 93.3, 94.1,
112.0, 121.3, 121.8, 123.4, 124.3, 124.4 (q, 1JC,F = 270.3 Hz), 125.0
3
2
(q, JC,F = 3.6 Hz), 126.9, 128.4, 128.5, 129.7 (q, JC,F = 32.5 Hz),
129.8, 130.2, 131.6, 132.0, 133.8, 134.1, 134.3, 139.8, 143.2 (q, 4JC,F
= 1.6 Hz), 143.3, 150.3, 193.5 ppm. C39H28F3NOS (615.71): calcd.
C 76.08, H 4.58, N 2.27; found C 76.35, H 4.69, N 2.18. MS
(MALDI-TOF): calcd. for C39H28F3NOS 615.1838; found
614.6310.
3
(s, 6 H, NCH3), 6.82 (d, JH,H = 8.4 Hz, 2 H), 7.30 (s, 5 H), 7.57–
3
7.65 (m, 3 H), 7.67 (s, 1 H), 7.73 (d, JH,H = 8.3 Hz, 2 H), 7.81 (d,
3JH,H = 8.6 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ
= 11.5, 18.8, 40.7, 88.9, 94.1, 96.1, 106.5, 112.3, 121.7, 121.9, 123.1,
124.40 (q, 1JC,F = 272.0 Hz), 125.0 (q, 3JC,F = 3.6 Hz), 127.2, 128.5,
2Ј-[2-(4-Acetylsulfanylphenyl)ethynyl]-4-dimethylamino-5Ј-(2-phen-
ylethynyl)-4ЈЈ-trifluoromethyl[1,1Ј:4Ј,1ЈЈ]terphenyl (2): For the syn-
thesis of 2 a similar Sonogashira coupling protocol as described
for 8 has been applied. A solution of S-(4-iodophenyl) thioacetate
(46.6 mg, 0.168 mmol), 19 (50 mg, 0.107 mmol), Pd(PPh3)4 (7.5 mg,
0.0065 mmol), CuI (2.5 mg, 0.013 mmol) and (iPr)2NEt (2 mL) in
2
128.6, 129.7 (q, JC,F = 32.0 Hz), 129.8, 130.1, 131.5, 133.7, 134.8,
4
139.7, 143.4 (q, JC,F = 1.5 Hz), 143.7, 150.3 ppm. C40H42F3NSi
(621.85): calcd. C 77.26, H 6.81, N 2.25; found C 77.47, H 6.64, N
2.10. MS (MALDI-TOF): calcd. for C40H42F3NSi 621.3033; found
620.6773.
Eur. J. Org. Chem. 2007, 2630–2642
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2639

A. Błaszczyk, M. Fischer, C. von Hänisch, M. Mayor
FULL PAPER
degassed THF (25 mL) was stirred for 16 h at room temperature.
After removing of the solvents the residue was absorbed on silica
gel to charge a column. CC (silica gel, hexane:CH2Cl2 = 1:1) af-
forded 2 (54.7 mg, 83 %) as yellow solid. M.p. 214–215 °C. 1H
was heated to 80 °C and kept at 80 °C for 16 h under a nitrogen
atmosphere. After evaporation of the organic solvent, extraction
with CH2Cl2, drying over MgSO4 followed by evaporation of the
solvents the remaining residue was charged on a column. CC (silica
gel, hexane:CH2Cl2 = 1:1) afforded 22 as brown oil that solidifies
NMR (300 MHz, CDCl3, 25 °C): δ = 2.44 (s, 3 H, CH3), 3.05 (s, 6
3
H, NCH3), 6.86 (d, JH,H = 8.2 Hz, 2 H), 7.32 (s, 5 H), 7.36 (d, upon standing (210.7 mg, 86 %). M.p. 94–96 °C. 1H NMR
3
3
3JH,H = 8.2 Hz, 2 H), 7.44 (d, JH,H = 8.2 Hz, 2 H), 7.64–7.77 (m, (300 MHz, CDCl3, 25 °C): δ = 1.05–1.17 (m, 24 H), 1.33 (t, JH,H
3
3
6 H), 7.84 (d, JH,H = 8.1 Hz, 2 H) ppm. 13C NMR (75 MHz, = 7.4 Hz, 3 H, CH3), 2.57 (q, JH,H = 7.5 Hz, 2 H, CH2), 2.87 (q,
3
CDCl3, 25 °C): δ = 30.4, 40.7, 88.9, 91.4, 93.1, 94.3, 112.0, 121.1,
3JH,H = 7.5 Hz, 2 H, CH2), 3.05 (s, 6 H, NCH3), 6.84 (d, JH,H
=
1
3
122.0, 123.0, 124.4 (q, JC,F = 272.0 Hz), 124.7, 125.1 (q, JC,F
=
8.5 Hz, 2 H), 7.23 (s, 1 H), 7.34–7.43 (m, 4 H), 7.55–7.60 (m, 2 H),
2
3
3.9 Hz), 126.9, 128.1, 128.5, 128.7, 129.75 (q, JC,F = 32.7 Hz),
129.8, 130.2, 131.5, 132.2, 133.8, 134.1, 134.3, 139.8, 143.3, 143.5,
150.3, 193.7 ppm. C39H28F3NOS (615.71): calcd. C 76.08, H 4.58,
N 2.27; found C 75.98, H 4.48, N 2.14. MS (MALDI-TOF): calcd.
for C39H28F3NOS 615.1838; found 614.5119.
7.65 (s, 1 H), 7.68 (d, JH,H = 8.2 Hz, 2 H), 7.75 (s, 1 H), 7.78 (d,
3JH,H = 8.4 Hz, 2 H), 7.83 (d, 3JH,H = 8.4 Hz, 2 H) ppm. 13C NMR
(75 MHz, CDCl3, 25 °C): δ = 11.5, 14.6, 14.7, 18.8, 26.9, 27.2, 40.7,
88.3, 93.2, 93.4, 94.5, 96.2, 106.5, 112.3, 121.9, 122.1, 122.3, 122.9,
3
123.5, 124.5 (q, 1JC,F = 271.9 Hz), 125.2 (q, JC,F = 3.7 Hz), 127.3,
2
128.4, 128.5, 129.8 (q, JC,F = 32.3 Hz), 129.9, 130.2, 131.58,
Biphenyl Derivative 20: For the synthesis of 20 a similar Sonoga-
shira coupling protocol as described for 8 has been applied. A solu-
tion of 2,5-diethyl-4-iodotolane (0.591 mmol, 212.8 mg), 12
(248.9 mg, 0.492 mmol), Pd(PPh3)4 (28.4 mg, 0.0246 mmol), CuI
(9.4 mg, 0.0494 mmol) and (iPr)2NH (5 mL) in degassed THF
(50 mL) was stirred for 16 h at room temperature. After evapora-
tion of the solvents, the residue was purified by CC (silica gel, hex-
ane) to get 20 as colorless oil that solidifies into white solid upon
4
131.64, 131.8, 133.7, 134.8, 139.8, 143.4, 143.5, 143.8 (q, JC,F
=
1.1 Hz), 143.9, 150.4 ppm. C52H54F3NSi (778.07): calcd. C 80.27,
H 7.00, N 1.80; found C 80.77, H 6.89, N 1.78. MS (MALDI-
TOF): calcd. for C52H54F3NSi 777.3972; found 776.6136.
5Ј-[2-(2,5-Diethyl-4-(2-phenylethynyl)phenyl)ethynyl]-4-dimethyl-
amino-4ЈЈ-trifluoromethyl-2Ј-[2-(triisopropylsilanyl)ethynyl][1,1Ј:4Ј,-
1ЈЈ]terphenyl (23): For the synthesis of 23 a similar Suzuki coupling
protocol as described for 6 has been applied. A solution of 21
(410 mg, 0.556 mmol), 4-(dimethylamino)phenylboronic acid
(128.4 mg, 0.778 mmol), Pd(PPh3)4 (32.1 mg, 0.028 mmol) and
K2CO3 (307 mg, 2.22 mmol) in degassed DME/H2O (30/10 mL)
was heated to 80 °C and kept at 80 °C for 16 h under a nitrogen
atmosphere. After evaporation of the organic solvent, extraction
with CH2Cl2, drying over MgSO4 followed by evaporation of the
solvents the remaining residue was charged on a column. CC (silica
gel, hexane:CH2Cl2 = 1:1) afforded 23 as yellow solid (350 mg,
1
standing (261.4 mg, 72%). M.p. 106–108 °C. H NMR (300 MHz,
CDCl3, 25 °C): δ = 1.11 (t, 3JH,H = 7.6 Hz, 3 H, CH3), 1.22 (appar-
3
ent s, 21 H, TIPS), 1.32 (t, JH,H = 7.5 Hz, 3 H, CH3), 2.52 (q,
3
3JH,H = 7.5 Hz, 2 H, CH2), 2.86 (q, JH,H = 7.5 Hz, 2 H, CH2),
7.19 (s, 1 H), 7.34–7.42 (m, 4 H), 7.53–7.59 (m, 3 H), 7.71–7.78 (m,
4 H), 7.93 (s, 1 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ =
11.5, 14.6, 14.7, 18.8, 26.9, 27.2, 88.2, 91.7, 94.6, 94.8, 99.1, 104.4,
1
121.6, 123.35, 123.40, 123.42, 124.3 (q, JC,F = 271.8 Hz), 125.0,
3
2
125.3 (q, JC,F = 3.6 Hz), 125.7, 128.5, 129.7, 130.2 (q, JC,F
=
1
4
81%). M.p. 187–189 °C. H NMR (300 MHz, CDCl3, 25 °C): δ =
32.7 Hz), 131.58, 131.64, 131.8, 134.2, 136.3, 141.2, 142.9 (q, JC,F
= 1.1 Hz), 143.53, 143.54 ppm. C44H44BrF3Si (737.80): calcd. C
71.63, H 6.01; found C 71.97, H 6.22. MS (MALDI-TOF): calcd.
for C44H44BrF3Si 738.2332; found 736.4347.
3
1.03 (s, 3 H, CH), 1.4 (s, 18 H, CH3), 1.20 (t, JH,H = 7.5 Hz, 3 H,
3
3
CH3), 1.32 (t, JH,H = 7.6 Hz, 3 H, CH3), 2.69 (q, JH,H = 7.5 Hz,
3
2 H, CH2), 2.86 (q, JH,H = 7.5 Hz, 2 H, CH2), 3.06 (s, 6 H), 6.87
(d, JH,H = 8.8 Hz, 2 H), 7.32 (s, 1 H), 7.33–7.42 (m, 4 H), 7.53–
3
3
Biphenyl Derivative 21: For the synthesis of 21 a similar Sonoga-
shira coupling protocol as described for 8 has been applied. A solu-
tion of 2,5-diethyl-4-iodotolane (0.805 mmol, 289.9 mg), 13
(312.9 mg, 0.619 mmol), Pd(PPh3)4 (35.8 mg, 0.031 mmol), CuI
(11.8 mg, 0.062 mmol) and (iPr)2NH (3 mL) in degassed THF
(50 mL) was stirred for 16 h at room temperature. After evapora-
tion of the solvents, the residue was purified by CC (silica gel, hex-
ane) to afford 21 as yellowish solid (410.3 mg, 90%). M.p. 126–
7.59 (m, 2 H), 7.62–7.74 (m, 6 H), 7.79 (d, JH,H = 8.1 Hz, 2 H)
ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 11.4, 14.7, 14.8, 18.6,
27.0, 27.2, 40.7, 88.4, 92.9, 94.1, 94.4, 96.6, 105.7, 112.1, 121.99,
1
3
122.04, 122.7, 123.5, 124.5 (q, JC,F = 271.8 Hz), 125.1 (q, JC,F
=
2
3.7 Hz), 127.4, 128.4, 128.5, 129.6 (q, JC,F = 32.2 Hz), 129.8,
130.2, 131.5, 131.6, 131.9, 133.7, 134.5, 140.6, 143.33, 143.35,
143.5, 150.4 ppm. C52H54F3NSi (778.07): calcd. C 80.27, H 7.00,
N 1.80; found C 79.90, H 6.93, N 1.99. MS (MALDI-TOF): calcd.
for C52H54F3NSi 777.3972; found 776.6738.
1
128 °C. H NMR (300 MHz, CDCl3, 25 °C): δ = 1.06 (apparent s,
3
21 H, TIPS), 1.37 (t, JH,H = 7.5 Hz, 6 H, CH3), 2.86–3.04 (m, 4
2Ј-[2-(2,5-Diethyl-4-(2-phenylethynyl)phenyl)ethynyl]-4-dimethyl-
amino-5Ј-ethynyl-4ЈЈ-trifluoromethyl[1,1Ј:4Ј,1ЈЈ]terphenyl (24): To a
solution of 22 (210.7 mg, 0.271 mmol) in degassed THF (50 mL) a
solution of TBAF (0.3 mL, 1  TBAF in THF) was added. The
reaction mixture was stirred at room temperature for 30 min. After
evaporation of the solvents, the residue was purified by CC (silica
gel, hexane:CH2Cl2 = 1:1) to provide 24 as whitish solid (152.4 mg,
3
H, CH2), 7.35–7.42 (m, 3 H), 7.48 (d, JH,H = 6.3 Hz, 2 H), 7.54–
7.62 (m, 3 H), 7.71 (s, 4 H), 7.91 (s, 1 H) ppm. 13C NMR (75 MHz,
CDCl3, 25 °C): δ = 11.3, 14.8, 15.2, 18.6, 27.4, 27.4, 88.3, 92.2,
1
94.7, 95.1, 98.5, 104.0, 121.8, 123.2, 123.5, 124.30 (q, JC,F
=
3
271.9 Hz), 124.31, 125.2 (q, JC,F = 3.7 Hz), 126.0, 128.51, 128.52,
129.7, 130.1 (q, JC,F = 32.3 Hz), 131.6, 131.8, 132.0, 133.5, 137.0,
2
142.0, 142.6, 143.6, 144.1 ppm. C44H44BrF3Si (737.80): calcd. C
71.63, H 6.01; found C 71.89, H 6.19. MS (MALDI-TOF): calcd.
for C44H44BrF3Si 738.2332; found 736.4537.
1
90%). M.p. 160–162 °C. H NMR (300 MHz, CDCl3, 25 °C): δ =
3
3
1.14 (t, JH,H = 7.6 Hz, 3 H, CH3), 1.33 (t, JH,H = 7.6 Hz, 3 H,
3
3
CH3), 2.58 (q, JH,H = 7.6 Hz, 2 H, CH2), 2.87 (q, JH,H = 7.5 Hz,
2 H, CH2), 3.06 (s, 6 H, NCH3), 3.25 (s, 1 H), 6.86 (d, JH,H =
3
2Ј-[2-(2,5-Diethyl-4-(2-phenylethynyl)phenyl)ethynyl]-4-dimethyl-
amino-4ЈЈ-trifluoromethyl-5Ј-[2-(triisopropylsilanyl)ethynyl]-
[1,1Ј:4Ј,1ЈЈ]terphenyl (22): For the synthesis of 22 a similar Suzuki
coupling protocol as described for 6 has been applied. A solution of
20 (230.9 mg, 0.313 mmol), 4-(dimethylamino)phenylboronic acid
(72.3 mg, 0.438 mmol), Pd(PPh3)4 (18.1 mg, 0.0157 mmol) and
8.4 Hz, 2 H), 7.24 (s, 1 H), 7.33–7.45 (m, 4 H), 7.54–7.69 (m, 5 H),
7.73–7.83 (m, 5 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ =
14.6, 14.7, 26.9, 27.2, 40.5, 81.8, 83.3, 88.7, 93.1, 93.3, 94.5, 111.9,
120.3, 122.1, 122.6, 123.0, 123.5, 124.4 (q, 1JC,F = 271.0 Hz), 125.1
3
2
(q, JC,F = 3.6 Hz), 126.6, 128.4, 128, 5, 129.81, 129.82 (q, JC,F
=
K2CO3 (172.9 mg, 1.25 mmol) in degassed DME/H2O (30/10 mL) 32.3 Hz), 130.1, 131.58, 131.63, 131.8, 133.9, 134.9, 139.8, 143.47,
2640
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 2630–2642

Molecular Rods with a Transversal Push-Pull System
FULL PAPER
143.49, 144.1, 150.3 ppm. C43H34F3N (621.73): calcd. C 83.07, H
5.51, N 2.25; found C 83.37, H 5.32, N 2.01. MS (MALDI-TOF):
calcd. for C43H34F3N 621.2638; found 620.6378.
H, CH2), 2.87 (q, 3JH,H = 7.4 Hz, 2 H, CH2), 3.06 (s, 6 H, NCH3),
3
6.86 (d, JH,H = 8.8 Hz, 2 H), 7.33 (s, 1 H), 7.34–7.42 (m, 8 H),
3
7.55–7.60 (m, 2 H), 7.68 (d, JH,H = 8.8 Hz, 2 H), 7.71 (s, 1 H),
3
7.74–7.81 (m, 3 H), 7.84 (d, JH,H = 8.2 Hz, 2 H) ppm. 13C NMR
5Ј-[2-(2,5-Diethyl-4-(2-phenylethynyl)phenyl)ethynyl]-4-dimethyl-
amino-2Ј-ethynyl-4ЈЈ-trifluoromethyl[1,1Ј:4Ј,1ЈЈ]terphenyl (25): To a
solution of 23 (310 mg, 0.398 mmol) in degassed THF (50 mL) a
solution of TBAF (0.5 mL, 1  TBAF in THF) was added. The
reaction mixture was stirred at room temperature for 1 h. After
evaporation of the solvents the residue was purified by CC (silica
gel, hexane:CH2Cl2 = 1:1) to get 25 as yellowish solid (238.9 mg,
(75 MHz, CDCl3, 25 °C): δ = 14.7, 14.8, 27.0, 27.2, 30.4, 40.6, 88.3,
90.6, 93.1, 93.3, 94.2, 94.4, 112.0, 121.2, 122.2, 122.6, 122.7, 123.5,
3
124.3, 124.4 (q, 1JC,F = 272.1 Hz), 125.1 (q, JC,F = 3.9 Hz), 127.1,
2
128.4, 128.5, 129.77, 129.76 (q, JC,F = 32.3 Hz), 130.1, 131.5,
131.6, 131.8, 132.0, 133.9, 134.1, 134.3, 140.0, 143.28, 143.32,
143.4, 143.5, 150.3, 193.7 ppm. C51H40F3NOS (771.93): calcd. C
79.35, H 5.22, N 1.81; found C 78.99, H 4.91, N 1.99. MS
(MALDI-TOF): calcd. for C51H40F3NOS 771.2777; found
770.6451.
1
96%). M.p. 170–172 °C. H NMR (300 MHz, CDCl3, 25 °C): δ =
3
3
1.20 (t, JH,H = 7.5 Hz, 3 H, CH3), 1.35 (t, JH,H = 7.5 Hz, 3 H,
3
3
CH3), 2.70 (q, JH,H = 7.5 Hz, 2 H, CH2), 2.86 (q, JH,H = 7.5 Hz,
2 H, CH2), 3.06 (s, 6 H, NCH3), 3.18 (s, 1 H), 6.86 (d, JH,H
3
=
8.8 Hz, 2 H), 7.32 (s, 1 H), 7.34–7.42 (m, 4 H), 7.52–7.59 (m, 2 H),
Acknowledgments
3
7.61–7.68 (m, 3 H), 7.70–7.77 (m, 3 H), 7.80 (d, JH,H = 8.4 Hz, 2
H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 14.7, 14.8, 27.0,
27.2, 40.6, 82.1, 82.6, 88.3, 93.1, 93.9, 94.4, 112.1, 120.4, 122.6,
122.8, 123.5, 124.4 (q, 1JC,F = 271.9 Hz), 125.2 (q, 3JC,F = 3.6 Hz),
We are thankful for financial support by the Volkswagen Founda-
tion (I80-880), German Ministry of Education and Research
within the network project MOLMEM (BMBF-FZK 13N8360)
and by the Swiss National Science Fondation.
2
127.1, 128.4, 128.5, 129.7, 129.8 (q, JC,F = 32.0 Hz), 130.2, 131.5,
131.6, 131.9, 134.1, 134.8, 140.5, 143.0, 143.3, 143.4, 143.5,
150.4 ppm. C43H34F3N (621.73): calcd. C 83.07, H 5.51, N 2.25;
found C 82.70, H 5.57, N 2.34. MS (MALDI-TOF): calcd. for
C43H34F3N 621.2638; found 621.6614.
[1] Reviews on molecular electronics: a) A. Nitzan, M. A. Ratner,
Science 2003, 300, 1384–1389; b) G. Maruccio, R. Cingolani,
R. Rinaldi, J. Mater. Chem. 2004, 14, 542–554; c) R. A. Wassel,
C. B. Gorman, Angew. Chem. Int. Ed. 2004, 43, 5120–5123; d)
D. K. James, J. M. Tour, Chem. Mater. 2004, 16, 4423–4435.
[2] a) Z. K. Keane, J. W. Ciszek, J. M. Tour, D. Natelson, Nano
Lett. 2006, 6, 1518–1521; b) R. Beckman, K. Beverly, A. Bou-
kai, Y. Bunimovich, J. W. Choi, E. DeIonno, J. Green, E. John-
ston-Halperin, Y. Luo, B. Sheriff, J. F. Stoddart, J. R. Heath, J.
Chem. Soc., Faraday Trans. 2006, 131, 9–21; c) D. Dulic, S. J.
van der Molen, T. Kudernac, H. T. Jonkman, J. J. D. de Jong,
T. N. Bowden, J. van Esch, B. L. Feringa, B. J. van Wees, Phys.
Rev. Lett. 2003, 91, 207402.
5Ј-[2-(4-Acetylsulfanylphenyl)ethynyl]-2Ј-[2-(2,5-diethyl-4-(2-phenyl-
ethynyl)phenyl)ethynyl]-4-dimethylamino-4ЈЈ-trifluoromethyl[1,1Ј:4Ј-
,1ЈЈ]terphenyl (3): For the synthesis of 3 a similar Sonogashira
coupling protocol as described for 8 has been applied. A solution
of S-(4-iodophenyl) thioacetate (84.3 mg, 0.303 mmol), 24 (145 mg,
0.23 mmol), Pd(PPh3)4 (13.3 mg, 0.0115 mmol), CuI (4.4 mg,
0.0231 mmol) and (iPr)2NEt (2 mL) in degassed THF (25 mL) was
stirred for 16 h at room temperature. By evaporation of the solvents
the residue was absorbed on silica gel to charge a column. CC
(silica gel, hexane:CH2Cl2 = 1:1) afforded 3 (77.5 mg, 44%) as yel-
[3] J. Chen, M. A. Reed, A. M. Rawlett, J. M. Tour, Science 1999,
286, 1550–1552.
1
low solid. M.p. 210–212 °C. H NMR (300 MHz, CDCl3, 25 °C):
[4] Examples are: a) M. Galperin, M. A. Ratner, A. Nitzan, Nano
Lett. 2005, 5, 125–130; b) F. Zahid, M. Paulsson, E. Polizzi,
A. W. Ghosh, L. Siddiqui, S. Datta, J. Chem. Phys. 2005, 123,
064707; c) H. Dalgleish, G. Kirczenow, Phys. Rev. B 2006, 73,
245431; d) I. Cacelli, A. Ferretti, M. Girlanda, M. Macucci,
Chem. Phys. 2006, 320, 84–94; e) R.-R. Fan, R. Y. Lai, J.
Cornil, Y. Karzazi, J.-L. Bredas, L. Cai, L. Cheng, Y. Yao,
D. W. Price, S. M. Shawn, J. M. Tour, A. J. Bard, J. Am. Chem.
Soc. 2004, 126, 2568–2573; f) Y. Karzazi, J. Cornil, J. L. Bredas,
Nanotechnology 2003, 14, 165–171; g) J. Taylor, M. Brandbyge,
K. Stokbro, Phys. Rev. B 2003, 68, 121101; h) J. M. Seminario,
A. G. Zacarias, P. A. Derosa, J. Chem. Phys. 2002, 116, 1671–
1683; i) E. G. Emberly, G. Kirczenow, Phys. Rev. B 2001, 64,
125318/1–125318/5; j) J. M. Seminario, A. G. Zacarias, J. M.
Tour, J. Am. Chem. Soc. 2000, 122, 3015–3020.
3
3
δ = 1.11 (t, JH,H = 7.4 Hz, 3 H, CH3), 1.30 (t, JH,H = 7.4 Hz, 3
3
H, CH3), 2.44 (s, 3 H, CH3), 2.55 (q, JH,H = 7.5 Hz, 2 H, CH2),
3
2.84 (q, JH,H = 7.5 Hz, 2 H, CH2), 3.07 (s, 6 H, NCH3), 6.87 (d,
3JH,H = 8.5 Hz, 2 H), 7.21 (s, 1 H), 7.30–7.41 (m, 6 H), 7.46 (d,
3JH,H = 8.2 Hz, 2 H), 7.51–7.58 (m, 2 H), 7.65–7.78 (m, 6 H), 7.81
(d, 3JH,H = 8.3 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C):
δ = 14.6, 14.7, 26.9, 27.2, 30.4, 40.6, 88.3, 91.4, 93.2, 93.3, 93.4,
1
94.5, 112.0, 121.1, 122.2, 122.4, 123.0, 123.5, 124.4 (q, JC,F
=
3
271.9 Hz), 124.7, 125.2 (q, JC,F = 3.9 Hz), 126.9, 128.2, 128.4,
128.5, 129.80 (q, JC,F = 32.2 Hz), 129.83, 130.2, 131.57, 131.63,
2
131.8, 132.1, 133.8, 134.1, 134.3, 135.1, 139.9, 143.46, 143.49,
143.6, 150.4, 193.7 ppm. C51H40F3NOS (771.93): calcd. C 79.35, H
5.22, N 1.81; found C 79.66, H 5.66, N 1.93. MS (MALDI-TOF):
calcd. for C51H40F3NOS 771.2777; found 770.5919.
[5] A. Błaszczyk, M. Chadim, C. von Hänisch, M. Mayor, Eur. J.
Org. Chem. 2006, 3809–3825.
2Ј-[2-(4-Acetylsulfanylphenyl)ethynyl]-5Ј-[2-(2,5-diethyl-4-(2-phenyl-
ethynyl)phenyl)ethynyl]-4-dimethylamino-4ЈЈ-trifluoromethyl[1,1Ј:4Ј-
,1ЈЈ]terphenyl (4): For the synthesis of 4 a similar Sonogashira
coupling protocol as described for 8 has been applied. A solution of
S-(4-iodophenyl) thioacetate (144.1 mg, 0.518 mmol), 25 (230 mg,
0.37 mmol), Pd(PPh3)4 (21.4 mg, 0.0185 mmol), CuI (7.1 mg,
0.0373 mmol) and (iPr)2NEt (2 mL) in degassed THF (100 mL)
was stirred for 16 h at room temperature. By evaporation of the
solvents the residue was absorbed on silica gel to charge a column.
CC (silica gel, hexane:CH2Cl2 = 1:1) afforded 4 (177 mg, 62%) as
yellow solid. M.p. 179–182 °C. 1H NMR (300 MHz, CDCl3,
[6] a) J. Chen, W. Wang, M. A. Reed, A. M. Rawlett, D. W. Price,
J. M. Tour, Appl. Phys. Lett. 2000, 77, 1224–1226; b) J. M.
Tour, A. M. R. M. Kozaki, Y. Yao, R. C. Jagessar, S. M. Dirk,
D. W. Price, M. A. Reed, C.-W. Zhou, J. Chen, W. Wang, I.
Campbell, Chem. Eur. J. 2001, 7, 5118–5134; c) J. Chen, W.
Wang, J. Klemic, M. A. Reed, B. W. Axelrod, D. M. Kaschak,
A. M. Rawlett, D. W. Price, S. M. Dirk, J. M. Tour, D. S. Grub-
isha, D. W. Bennett, Ann. N. Y. Acad. Sci. 2002, 960, 69–99.
[7] a) P. A. Lewis, C. E. Inman, Y. Yao, J. M. Tour, J. E. Hutchi-
son, P. S. Weiss, J. Am. Chem. Soc. 2004, 126, 12214–12215; b)
P. A. Lewis, C. E. Inman, F. Maya, J. M. Tour, J. E. Hutchison,
P. S. Weiss, J. Am. Chem. Soc. 2005, 127, 17421–17426.
[8] J. E. Klare, G. S. Tulevski, K. Sugo, A. de Picciotto, K. A.
White, C. Nuckolls, J. Am. Chem. Soc. 2003, 125, 6030–6031.
3
3
25 °C): δ = 1.22 (t, JH,H = 7.6 Hz, 3 H, CH3), 1.33 (t, JH,H
=
3
7.5 Hz, 3 H, CH3), 2.45 (s, 3 H, CH3), 2.72 (q, JH,H = 7.5 Hz, 2
Eur. J. Org. Chem. 2007, 2630–2642
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2641

A. Błaszczyk, M. Fischer, C. von Hänisch, M. Mayor
FULL PAPER
[9] a) H. Kang, P. Zhu, Y. Yang, A. Facchetti, T. J. Marks, J. Am.
Chem. Soc. 2004, 126, 15974–15975; b) H. Kang, G.
Evmenenko, P. Dutta, K. Clays, K. Song, T. J. Marks, J. Am.
Chem. Soc. 2006, 128, 6194–6205.
[10] J. N. Wilson, M. Josowicz, Y. Wang, U. H. F. Bunz, Chem.
Commun. 2003, 2962–2963.
0.113 mm–1, STOE IPDS2, Mo-Kα radiation, λ = 0.71073 Å,
T = 160 K, 2θmax = 52°; 22059 reflections measured, 10381
independent reflections (Rint = 0.0975), 7697 independent re-
flections with Fo Ͼ 4σ(Fo). The structure was solved by direct
methods and refined, by full-matrix least square techniques
against F2, 830 parameters (Si, N, C refined anisotropically, the
CF3 groups are disorderd and were refined with split positions,
H atoms were calculated at ideal positions). R1 = 0.0725 wR2
= 0.2122 (all data); Gof: 1.020; maximum peak 0.506 e·Å–3.
CCDC-634158 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.
[11] J. N. Wilson, U. H. F. Bunz, J. Am. Chem. Soc. 2005, 127,
4124–4125.
[12] W. W. Gerhardt, A. J. Zucchero, J. N. Wilson, C. R. South,
U. H. F. Bunz, M. Weck, Chem. Commun. 2006, 2141–2143.
[13] a) M. B. Goldfinger, K. B. Crawford, T. M. Swager, J. Am.
Chem. Soc. 1997, 119, 4578–4593; b) M. B. Goldfinger, K. B.
Crawford, T. M. Swager, J. Org. Chem. 1998, 63, 1676–1686.
[14] M. B. Goldfinger, T. M. Swager, J. Am. Chem. Soc. 1994, 116,
7895–7896.
[15] K. Sonogashira, Y. Tohda, N. Hagihara, Tetrahedron Lett.
1975, 16, 4467–4470.
[16] N. Miyaura, T. Yanagi, A. Suzuki, Synth. Commun. 1981, 11,
513–515.
[20] D. T. Gryko, C. Clausen, K. M. Roth, N. Dontha, D. F. Bo-
cian, W. G. Kuhr, J. S. Lindsey, J. Org. Chem. 2000, 65, 7345–
7355.
[21] R. P. Hsung, J. R. Babcock, C. E. D. Chidsey, L. R. Sita, Tetra-
hedron Lett. 1995, 36, 4525–4528.
[22] D. V. Kosynkin, J. M. Tour, Org. Lett. 2001, 3, 993–996.
[23] H. G. O. Becker, W. Berger, G. Domschke, E. Fanghänel, J.
Faust, M. Fischer, F. Gentz, K. Gewald, R. Gluch, W. D. Hab-
icher, R. Mayer, P. Metz, K. Müller, D. Pavel, H. Schmidt, K.
Schollberg, K. Schwetlick, E. Seiler, G. Zeppenfeld in Or-
ganikum, Wiley-VCH, Weinheim, 2001, chapter F, p. 741–762.
Received: January 26, 2007
[17] H. Hart, K. Harada, C. F. Du, J. Org. Chem. 1985, 50, 3104–
3110.
[18] J. D. Tovar, T. M. Swager, J. Organomet. Chem. 2002, 653, 215–
222.
[19] 17 (C40H42F3NSi): a = 1616.0(3), b = 2022.0(4), c = 2230.2(5)
pm, α = 90, β = 108.86(3), γ = 90°, V = 6896(2)·106 pm3; mono-
clinic P21,/n, Z = 8, ρcalcd. = 1.2198 gcm–1, µ(Mo-Kα) =
Published Online: March 30, 2007
2642
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 2630–2642