Syntheses, Structures and Conformational Dynamics of 1,3,5-Tris(3-ethynylbiphenyl-2′-yl)benzene Derivatives

Article abstract of DOI:10.1002/ejoc.201500615

Following a route described by Müllen et al. we improved the preparation of 1,2,3-tris(3-iodobiphenyl-2′-yl)benzene (4). During the required iododesilylation with iodine monochloride the unexpected formation of a mono-chlorinated compound 6 as major produ

Full text of DOI:10.1002/ejoc.201500615

FULL PAPER
DOI: 10.1002/ejoc.201500615
Syntheses, Structures and Conformational Dynamics of 1,3,5-Tris-
(3ЈЈ-ethynylbiphenyl-2Ј-yl)benzene Derivatives
Daniel Trawny,[a] Marcel Quennet,[a,b] Nadine Rades,[a] Dieter Lentz,[a] Beate Paulus,[a] and
Hans-Ulrich Reissig*[a]
Keywords: Arenes / Polycycles / C–C coupling / Iodination / Electron transfer / Conformational dynamics / DFT
calculations
Following a route described by Müllen et al. we improved
the preparation of 1,2,3-tris(3ЈЈ-iodobiphenyl-2Ј-yl)benz-
ene (4). During the required iododesilylation with iodine
ing a preferred solid-state conformation (“2-up-1-down”) dif-
ferent from that of the chlorinated compound (“propeller”
conformation). Compound 7 showed remarkable conforma-
monochloride the unexpected formation of a mono-chlorin- tional dynamics in solution as observed by 1H NMR spec-
ated compound 6 as major product was observed, when an
excess of the iodination reagent was employed. The reaction
mechanism for the formation of this compound involving an
oxidizing process is discussed. X-ray crystallography of the
subsequent alkynylated product 7 proves the location of the
chlorine atom at the central benzene ring. The related com-
troscopy. Temperature-dependent measurements allowed
the calculation of an energy difference of two major conform-
ers of ca. 2 kJ/mol and a rotational barrier ΔGrot of ca. 77 kJ/
mol. These values were convincingly confirmed by DFT cal-
culations. A subsequent Sonogashira reaction of 4 with a
suitable bipyridine derivative provided a unique trivalent bi-
pound 5 was likewise investigated by X-ray analysis reveal- pyridine derivative.
tional isomerism and calculated the rotational energy barri-
Introduction
ers as well as the energy differences of the isomers and com-
pare these values with experimentally determined data.
These data will be additionally supported with X-ray crystal
structures.
The tremendous increase of the importance of nano-
graphenes as potential molecular devices[1] requires efficient
and simple strategies for their synthesis. Of particular inter-
est in this area are compounds with a hexa-peri-hexabenzo-
coronene (HBC) core[2] and the few synthetic routes avail-
able are generally based on the oxidation of suitable precur-
sors.[3] Possible HBC precursors are compounds such as A
or B (Scheme 1).[4] Due to our research with C3-symmetri-
cal extended π-systems containing bi- or terpyridine end
groups[5] we envisioned to prepare compounds with a HBC
core that should be particularly suitable for STM investi-
gations[6] of the resulting multivalent molecules.[7] Based on
the protocol of Müllen et al.[8] we report the synthesis of the
novel C3-symmetrical precursor 5 and its chloro-substituted
derivative 7 – obtained by accident – (Scheme 2) that are
ideally suited for investigations of their conformational dy-
namics by experiment and theory. By the application of
computational methods we have analyzed the conforma-
Scheme 1. Two common hexa-peri-hexabenzocoronene (HBC) pre-
cursors A and B.
Results and Discussion
[a] Institut für Chemie und Biochemie, Freie Universität Berlin,
Takustraße 3, 14195 Berlin, Germany
The concept for the preparation of triiodinated precursor
4 was described previously by Müllen et al.,[8,9] but we used
a slightly different approach in the presented work
(Scheme 2). Treatment of 2Ј-bromoacetophenone with sili-
con tetrachloride at 0 °C in ethanol[10] provided the desired
tribrominated precursor 1 in excellent yield. It should be
noted that Müllen et al. report that silicon tetrachloride is
ineffective for this reaction and for this reason they em-
E-mail: lentz@chemie.fu-berlin.de
b.paulus@fu-berlin.de
hans.reissig@chemie.fu-berlin.de
www.bcp.fu-berlin.de/en/chemie/chemie/forschung/OrgChem/
reissig/index.html
[b] Helmholtz-Zentrum Berlin für Materialien und Energie GmbH,
Hahn-Meitner-Platz 1, 14109 Berlin, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500615.
Eur. J. Org. Chem. 2015, 4667–4674
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4667

H.-U. Reissig et al.
FULL PAPER
Scheme 2. Synthesis of trialkynes 5 and 7 starting from simple precursor 2Ј-bromoacetophenone as well as an MM2 optimized molecular
model of 5 in order to illustrate the non-planarity of the compound.
ployed trifluoromethanesulfonic acid. We found that silicon strongly depends on the amount of iodine monochloride.
tetrachloride has to be added very quickly to the reaction Treatment of 3 with a nearly stoichiometric amount of iod-
mixture in order to obtain full conversion of 2Ј-bromo- ine monochloride (3.3 equiv.) gave the desired triiodinated
acetophenone. In this way the yield of compound 1 could precursor 4 in 74% yield. However, in a first experiment we
be strongly improved from 72%[9] to 97%. Following again had used a high excess of iodine monochloride (9 equiv.)
Müllen’s route, the subsequent Suzuki coupling with that also led to the iododesilylation reaction, but an ad-
boronic acid 2 delivered compound 3 in good yield. Sub- ditional chlorine atom was introduced furnishing com-
sequently, the trimethylsilyl groups of 3 were replaced by pound 6. At this stage of our study it was not possible to
iodo substituents employing iodine monochloride.[11] We localize the position of the single chloro substituent by
unexpectedly found that the outcome of this transformation NMR experiments however, the molecular composition was
4668
www.eurjoc.org
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 4667–4674

1,3,5-Tris(3ЈЈ-ethynylbiphenyl-2Ј-yl)benzene Derivatives
clearly proven by mass spectrometry. Therefore we decided ure 1).[14] In the detailed molecular crystal structure of 5 the
to convert both compounds 4 and 6 into the target alkynes “2-up-1-down” conformer is preferred, in which two bi-
5 and 7 in order to proceed with the structural analyses. phenyl moieties point to one side with respect to the plane
Sonogashira reactions of 4 and 6 with (triisopropyl)silyl- of the central benzene ring and one to the opposite side. In
acetylene followed by deprotection with tetra-n-butyl- contrast, the solid-state structure of compound 7 shows a
ammonium fluoride (TBAF) successfully delivered the de- “propeller” conformer with all three biphenyl moieties
sired alkynes 5 and 7 in good yields.
The mechanism of the reaction of compound 3 with an
excess of iodine monochloride leading to the chloro-substi-
tuted compound 6 is puzzling. We could not detect prod-
ucts containing chloro substituents and still trimethylsilyl
groups, and without an excess of iodine monochloride com-
pound 6 was not observed. We therefore conclude that the
chlorination reaction occurs after the complete iodode-
silylation reaction of 3 that is generally very fast.[12] Using
ESR and UV spectroscopy, Eberson et al. demonstrated the
ability of iodine monochloride to act as oxidizing reagent
of aromatic compounds,[13] however to the best of our
knowledge its role as tandem iodination-chlorination rea-
gent has not been reported so far. We propose a mechanism
wherein compound 4 is oxidized by the excess of iodine
monochloride to give the radical cation C (Scheme 3). Sub-
sequent attack of the chloride affords radical D which is
again oxidized to furnish cation E. Deprotonation finally
provides the isolated chloro-substituted product 6. Interme-
diates C, D and E are strongly stabilized due to the conjuga-
tion with the other benzene rings. These substituents are
certainly out of plane but nevertheless they can consider-
ably contribute to the stability of intermediates. The central
benzene ring of precursor 4 bears three biphenyl substitu-
ents and as the electron-richest moiety of the compound its
oxidation as depicted in Scheme 3 is most likely, leading to
the radical cation C with the best stabilization. The fact
that only monochlorination of 4 was observed may be ex-
plained by the deactivation of 6 due to the first introduced
chloro substituent.
Remarkably, a significant difference was observed be-
tween the solid-state structures of compounds 5 and 7 (Fig- 7.
Figure 1. Molecular structure (ORTEP[15]) of compound 5 (top)
and chloro-substituted compound 7 (bottom) showing the “2-up-
1-down” conformation for 5 and the “propeller” conformation for
Scheme 3. Proposed mechanism of the chlorination of 4 to compound 6 by an excess of iodine monochloride.
Eur. J. Org. Chem. 2015, 4667–4674
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4669

H.-U. Reissig et al.
FULL PAPER
pointing to one side of the molecule. None of the biphenyl
units in both compounds are planar, the corresponding di-
hedral angles differ significantly from 0 and 180°, respec-
tively.
The 1H NMR spectrum of chloro-substituted compound
7 recorded at room temperature shows four signals for the
alkynyl proton (ratio ca. 2:1:2:4), whereas the spectrum of
5 exhibits as expected only one signal. In order to further
investigate the conformational behavior of compound 7 we
performed temperature-dependent NMR experiments. Fig-
ure 2 depicts the relevant sections of the NMR spectra at
eight different temperatures. After heating up to 120 °C the
sample was again cooled to 30 °C to ensure that no decom-
position had occurred. It turned out that the observed sig-
nals correspond to two conformational isomers showing
two coalescence temperatures TK with the difference of the
Figure 3. Rotational barrier as a function of the dihedral angle φ
for two different starting conformations with the chloro substituent
at the central benzene ring and for the unsubstituted trialkyne 5.
The dihedral angle is fixed while all other coordinates of the mol-
ecule are optimized. A dihedral angle of 0° corresponds to a struc-
ture, where the external ring system is in plane with the central ring
and the alkynyl-substituted benzene ring is located on the site of
the atom in position Y. By fixing and scanning over the dihedral
angle the multi-dimensional potential energy surface is projected
on a one-dimensional potential energy curve, leading to a non-
smooth potential energy curve for dihedral angles of 100–120° and
a sharp rotational barrier at 180°.
chemical shifts Δν (TK1 = 60 °C, Δν1 = 2.9 Hz and TK2
=
80 °C, Δν2 = 8.3 Hz, respectively). These values were used
to estimate a rotational energy barrier ΔGrot that is in the
range of 77Ϯ3 kJ/mol.[16] The ratio of both conformers was
additionally calculated (32:68) which corresponds to an en-
ergy difference of ca. 2 kJ/mol at 24 °C. It is highly probable
that these two conformational isomers are due to the hin-
dered rotation around the C–C bond of the central biphenyl
The conformational dynamics of the trialkynes 5 and 7
subunits of 7 with two ortho substituents (see Figure 3). All were also investigated by the density functional method
other biphenyl moieties are less substituted and should B97D/def2-SVP and the relative energies [kJ/mol] reported
hence have considerably lower rotational barriers (as shown here refer to the electronic ground state energy at T = 0 K.
by the dynamic behaviour of compound 5 and confirmed The calculated rotational energy barrier ΔErot of 5 con-
by the calculations discussed below). There are no similarly verting the “propeller” conformer into the “2-up-1-down”
complex compounds in the literature, being analyzed with conformer amounts to 35 kJ/mol, a value indicating that
respect to their rotational barrier. However, one may com- these conformers interconvert very fast at room tempera-
1
pare 2-phenylbiphenyl (ΔGrot = 31.4 kJ/mol), 2-chlorobi- ture. Our H NMR experiments support this result since
phenyl (ΔGrot = 32.2 kJ/mol) and a compound with a 2- only one alkyne proton signal was observed for compound
chloro-2Ј-methylbiphenyl moiety (ΔGrot = 78.1 kJ/mol) to 5. The calculated energy difference of the two conformers
recognize that our ΔGrot values are in fair agreement with amounts to only 0.6 kJ/mol. On the contrary, the calculated
these data determined from simpler biphenyl derivatives.[17] rotational energy barrier ΔErot of the conformers of 7,
72 kJ/mol for starting conformation Y = Cl; X = H and
85 kJ/mol for starting conformation X = Cl, Y = H, is sig-
nificantly higher due to the chlorine atom at the central
benzene ring. Comparison of these calculated rotational en-
ergy barriers and energy differences (energy difference of
1.0 kJ/mol for starting conformation Y = Cl and 4.4 kJ/mol
for starting conformation X = Cl) with experimental data
1
in solution as obtained by the temperature-dependent H
NMR spectroscopic experiments (77Ϯ3 kJ/mol, 1.9 kJ/
mol) show a good agreement, proving that the vibrational
and entropic contributions to these energy values are sim-
ilar for the different conformations.
To evaluate the rotational barrier the dihedral angle φ
was changed gradually from 0° to 270°, where the dihedral
angle φ is fixed and all other coordinates of the molecule
are relaxed. Larger angles than 270° yield too very narrow
phenyl rings of two terminal ring systems, leading to non-
converging computations (see Figure 3). At a dihedral angle
of 0° the terminal ring system is in plane with the central
Figure 2. Temperature-dependent 1H NMR spectra of 7 in [D6]-
part, whereby the alkynyl-substituted benzene ring is close
DMSO (only the section of the alkynyl protons is shown). Spectra
to the atom located in position Y of the central ring. With
this definition of the dihedral angle, there are two possible
at temperatures of more than 100 °C are not different from those
recorded at 100 °C and are not depicted.
4670
www.eurjoc.org
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 4667–4674

1,3,5-Tris(3ЈЈ-ethynylbiphenyl-2Ј-yl)benzene Derivatives
starting conformations for a rotation of one outer ring sys-
tem, chlorine at position X or Y (see Figure 3). In starting
conformation Y the outer ring first passes the chlorine in
position Y at 0° and then the hydrogen at 180° in position
X. For starting conformation X the outer ring system first
passes the hydrogen in position Y and then at 180° the
chlorine in position X. The “propeller” conformation corre-
sponds to 235° and the “2-up-1-down” conformation to
125°.
We also performed calculations for compounds with the
chlorine atom at one of the external alkynyl-substituted
benzene rings instead of the central benzene ring. Consider-
ably lower rotational barriers in the range of 26–36 kJ/mol
were found for these constitutional isomers, providing ad-
ditional evidence for the location of the chlorine atom of
compound 7 at the central ring. In contrast to the unsubsti-
tuted compound 5, the computations show for some substi-
tution positions at the outer ring that the “propeller” con-
former is more stable than the “2-up-1-down” conformer
(for further details see Supporting Information), but for all
cases the barrier is nearly identical to the unsubstituted
compound 5.
We also briefly examined the photophysical properties of
compounds 5 and 7. Their UV/Vis absorption and fluores-
cence spectra recorded in chloroform as solvent are de-
picted in Figure 4. As expected the spectra of the two π-
systems hardly differ from each other. The absorption max-
ima of compounds 5 and 7 are essentially identical (245 nm)
whereas the emission maximum of the chlorinated com-
pound 7 (388 nm) is slightly red-shifted in comparison with
5 (374 nm). The calculated Stokes shifts are 14100 cm–1 for
compound 5 and 15000 cm–1 for the chloro-substituted
product 7, respectively.
Scheme 4. Sonogashira reaction of triiodo compound 4 with alkyne
8 leading to trivalent bipyridine derivative 9.
Conclusions
In this report we show that the route originally designed
by Müllen et al. smoothly leads to precursors of com-
pounds with a hexa-peri-hexabenzocoronene (HBC) core.
The simple procedure leading to the crucial starting mate-
rial 1 could be considerably improved. During the iododesi-
lylation of intermediate 3 we surprisingly obtained mono-
chlorinated compound 6 if a large excess of iodine mono-
chloride was employed. The expected compound 4 was
smoothly formed by use of equimolar amounts of the iodin-
ation reagent. By Sonogashira couplings compounds 4 and
6 were converted into the tris(alkynyl)-substituted products
5 and 7 that were carefully analyzed and compared by X-
ray crystallography, by dynamic 1H NMR spectroscopy and
by DFT calculations. All these methods reveal an excep-
Figure 4. UV/Vis and fluorescence spectra of compounds 5 (solid
lines) and 7 (dashed lines) in CHCl3.
The three iodo substituents of compound 4 offer ad- tional conformational behavior of the sterically hindered
ditional options for further functionalization. To demon- chlorinated compound 7. Experimental and computational
strate this potential we prepared trivalent bipyridine deriva- results show remarkable good agreement and give a rota-
tive 9 in good yield by Sonogashira reaction using 4-eth- tional barrier around the C–C bond of the central biphenyl
ynyl-2,2Ј-bipyridine (8)[18] as coupling partner (Scheme 4). subunits of 7 in the range of 77 kJ/mol. Triiodinated com-
Due to its ease availability and unique structure this prod- pounds such as 4 are suitable precursors for other coupling
uct should be an interesting candidate for the generation reactions as demonstrated by its conversion into trivalent
and investigation of new supramolecular complexes. Studies bipyridine derivative 9, thus opening routes to new interest-
in this direction are ongoing.[19]
ing systems with a HBC core.
Eur. J. Org. Chem. 2015, 4667–4674
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4671

H.-U. Reissig et al.
FULL PAPER
General Procedure 1 for Iododesilylation Reactions: Similarly to the
literature procedure,[18] to a solution of 3 in CH2Cl2 was added
dropwise a solution of iodine monochloride. After stirring for 4 d
at room temperature satd. aq. Na2S2O3 was added and the phases
were separated. The organic phase was washed with water, dried
with Na2SO4, filtered and concentrated to a volume of one-tenth
of the starting volume. The solution was cooled to 0 °C and cold
ethanol was added. A solid precipitated, which was collected by
filtration and washed with a small amount of cold CH2Cl2 and
ethanol.
Experimental Section
General Methods: Reactions were performed under an atmosphere
of argon in flame-dried flasks; solvents and reagents were added
by syringe. Solvents were dried by standard procedures. TLC was
performed with pre-coated silica gel plates (Sil G-60 F254) and
detected under UV light at 254 nm. Products were purified by flash
chromatography on silica gel (230–400 mesh, Merck or Fluka). 1H-
and 13C NMR spectra were recorded using either Bruker (AC 500/
AVIII 700) or JEOL (ECX 400/Eclipse 500) instruments. Chemical
shifts (in δ units, ppm) are referenced to TMS by using CHCl3 (δ
= 7.26 ppm) and CDCl3 (δ = 77.0 ppm) as the internal standards
1,3,5-Tris(3ЈЈ-iodobiphenyl-2Ј-yl)benzene (4): Quantities used fol-
lowing general procedure 1: 3 (220 mg, 293 μmol), CH2Cl2 (66 mL),
iodine monochloride (1.0 mL, 1.0 mmol, 1 m in CH2Cl2). Drying
in vacuo provided compound 4 (198 mg, 74%) as pale yellow solid.
Melting range: 107–113 °C. 1H NMR (500 MHz, CDCl3): δ = 6.77
(s, 3 H, 2-H), 6.81–6.85 (m, 3 H, Ar), 6.91–6.94 (m, 3 H, Ar), 7.01–
7.05 (m, 3 H, Ar), 7.32–7.36 (m, 9 H, Ar), 7.60–7.63 (m, 6 H, Ar)
ppm. 13C NMR (126 MHz, CDCl3): δ = 94.1 (s, Ar-I), 127.7, 128.1,
129.7, 130.1, 130.3, 130.7, 135.6, 138.4, 138.6 (9 d, 9 Ar), 138.8,
140.0, 140.4, 144.0 (4 s, 4 Ar) ppm. HRMS (EI, 180 °C, 80 eV):
calcd. for C42H27I3: 911.9241 [M]+·, found 911.9263 [M]+·. The ob-
served analytical data agree with the literature data.[8]
1
for H- and 13C NMR spectra, respectively. IR spectra were mea-
sured with a Nicolet 205 FTIR spectrometer. MS and HRMS
analyses were performed with Finnigan MAT 711 (EI = 80 eV,
8 kV), MAT 95 (EI = 70 eV) or MAT CH7A (EI = 80 eV, 3 kV)
instruments. ESI-TOF MS were measured with an Agilent 6210
ESI-TOF (solvent flow rate was adjusted to 4 μL/min, spray volt-
age set to 4.000 V; drying gas flow rate was set to 15 psi). Elemental
analyses were carried out with a Vario EL instrument. Melting
points were measured with a Büchi 510 apparatus and are uncor-
rected.
1,3,5-Tris(2Ј-bromophenyl)benzene (1): Similar to the literature pro- Chloro-Substituted 1,3,5-Tris(3ЈЈ-iodobiphenyl-2Ј-yl)benzene (6):
cedure,[8] 2Ј-bromoacetophenone (5.17 g, 26.0 mmol) was dissolved
in ethanol (40 mL) and silicon tetrachloride (13.2 g, 77.9 mmol)
was quickly added at 0 °C (the reaction vessel has to be connected
with a tube in order to release hydrogen chloride into the fume
hood). The resulting red solution was stirred at room temperature
overnight. The mixture was quenched with water (100 mL) and the
resulting precipitate was filtered off, washed with water and dried
in vacuo to give compound 1 (4.56 g, 97%) as pale yellow solid,
Quantities used following general procedure 1: 3 (693 mg,
922 μmol), CH2Cl2 (180 mL), iodine monochloride (8.2 mL,
8.20 mmol, 1 m in CH2Cl2). Drying in vacuo provided compound
1
6 (641 mg, 73%) as pale yellow solid. Melting range: 83–88 °C. H
1
NMR: The H NMR spectrum shows no significant difference in
comparison to the spectrum of 4. It is very difficult to distinguish
between 4 (in total 27 aromatic protons) and 6 (in total 26 aromatic
protons). 13C NMR: The 13C NMR spectrum shows no significant
m.p. 157–160 °C (ref.[8] 159–160 °C). 1H NMR (400 MHz, CDCl3): difference in comparison to the spectrum of 4. Nevertheless the
δ = 7.21 (ddd, J = 1.8, 7.5, 8.0 Hz, 1 H, 4Ј-H), 7.37 (dt, J = 1.2,
singlet at δ = 94.1 ppm (Ar-I) splits into two singlets at 94.02 and
7.5 Hz, 1 H, 5Ј-H), 7.46 (dd, J = 1.8, 7.5 Hz, 1 H, 6Ј-H), 7.50 (s, 1 94.09 indicating the missing C3-symmetry. MS (EI, 180 °C, 80 eV):
H, 2-H), 7.68 (dd, J = 1.2, 8.0 Hz, 1 H, 3Ј-H) ppm. The observed
calcd. for C42H26ClI3: 945.9 [M]+·, found 946.0 [M]+·.
analytical data agree with the literature data.[8]
General Procedure 2 for Sonogashira Reactions: Arylhalide, ethynyl-
(triisopropyl)silane, Pd(PPh3)4, triphenylphosphine and CuI were
dissolved in pyridine and triethylamine. The solution was heated to
80 °C overnight under an argon atmosphere. The volatile compo-
nents were removed under reduced pressure and the residue was
diluted with CH2Cl2. Satd. aq. NH4Cl was added, the layers were
separated and the aqueous phase was extracted with CH2Cl2. The
combined organic layers were dried with Na2SO4 and concentrated
to dryness. The residue was filtered through a small pad of silica
(hexanes/ethyl acetate = 10:1) to give a yellow oil. The crude prod-
uct was dissolved in THF and TBAF was added. The mixture was
stirred at room temperature overnight, then quenched with satd.
aq. NH4Cl and extracted with ethyl acetate. The combined organic
layers were dried with Na2SO4 and concentrated to dryness.
1,3,5-Tris[3ЈЈ-(trimethylsilyl)biphenyl-2Ј-yl]ylbenzene (3): Analo-
gously to the literature procedure,[8] a mixture of 1 (220 mg,
405 μmol), boronic acid derivative 2 (472 mg, 2.43 mmol),[20]
Pd(PPh3)4 (47 mg, 41 µmol) and satd. aq. Na2CO3 (1.2 mL,
2.43 mmol, 2 m) in toluene (4 mL) was heated to 130 °C overnight
in an ACE pressure tube. After cooling to room temperature water
(10 mL) and ethyl acetate (20 mL) were added, the phases were
separated and the aqueous phase was extracted with ethyl acetate
(3ϫ 10 mL). The combined organic layers were dried with Na2SO4
and concentrated to dryness. The residue was purified by column
chromatography on silica gel (hexanes) to give compound 3
(271 mg, 89%) as pale yellow solid. Melting range: 131–140 °C, not
1
reported in literature. H NMR (500 MHz, CDCl3): δ = 0.19–0.22
(m, 27 H, CH3), 6.65 (dd, J = 0.9, 7.6 Hz, 3 H, Ar), 6.73 (s, 3 H,
2-H), 6.92 (dt, J = 1.4, 7.5 Hz, 3 H, Ar), 7.25 (dt, J = 1.4, 7.5 Hz,
1,3,5-Tris(3ЈЈ-ethynylbiphenyl-2Ј-yl)benzene (5): Quantities used fol-
lowing general procedure 2: 4 (80 mg, 88 μmol), ethynyl(tri-
3 H, Ar), 7.27 (d, J = 7.5 Hz, 3 H, Ar), 7.35 (td, J = 1.2, 7.4 Hz, isopropyl)silane (56 mg, 307 μmol), Pd(PPh3)4 (10 mg, 8.8 μmol),
3 H, Ar), 7.40 (d, J = 1.4 Hz, 3 H, Ar), 7.41 (d, J = 1.6 Hz, 3 H, triphenylphosphine (2.3 mg, 8.8 μmol), CuI (0.8 mg, 4.4 μmol),
Ar), 7.46 (dt, J = 1.1 Hz, 3 H, Ar) ppm. 13C NMR (126 MHz, pyridine (2 mL), triethylamine (200 μL); THF (3 mL), TBAF
CDCl3): δ = 1.0 (q, CH3), 127.30,* 127.32, 130.0, 130.2, 130.4,
130.8, 131.4, 135.1 (8 d, 9 Ar), 140.3, 140.4, 140.5, 140.9, 141.1 (5
(390 μL, 390 μmol, 1 m in THF). The residue was purified by col-
umn chromatography on silica gel (hexanes/ethyl acetate = 40:1) to
give compound 5 (33 mg, 62%) as colorless solid, m.p. 202–204 °C.
s, 5 Ar) ppm, *signal with higher intensity. IR (ATR): ν = 3055
˜
(=C–H), 2950 (C–H), 1245 (Si–C) cm–1. HRMS (EI, 130 °C, 1H NMR (500 MHz, CDCl3): δ = 3.08 (s, 3 H, CϵCH), 6.77 (s, 3
80 eV): calcd. for C51H54Si3: 750.3533 [M]+·, found 750.3498 [M]+·.
H, 2ЈЈ-H), 6.83 (br. d, J = 7.5 Hz, 3 H, Ar), 6.90 (br. d, J = 7.8 Hz,
The observed analytical data agree with the literature data.[8] It 3 H, Ar), 7.24–7.33 (m, 6 H, Ar), 7.35 (br. s, 3 H, 2Ј-H), 7.35–7.37
should be mentioned that for the reported 1H NMR spectrum only
a multiplet was recorded.
(m, 3 H, Ar), 7.40–7.43 (m, 6 H, Ar) ppm. 13C NMR (126 MHz,
CDCl3): δ = 77.4 (s, CϵC), 83.8 (d, CϵCH), 122.1 (s, Ar), 127.6,
4672
www.eurjoc.org
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 4667–4674

1,3,5-Tris(3ЈЈ-ethynylbiphenyl-2Ј-yl)benzene Derivatives
127.9, 128.0, 130.1, 130.3, 130.4, 130.7, 131.2, 133.3 (9 d, 3 Ar, C-
tution with chlorine at the central ring, rotational barriers for
mono-chloro substituents at one of the external alkynyl-substituted
2ЈЈ, C-2Ј, 4 Ar), 139.4, 140.1, 140.6, 142.0 (4 s, 4 Ar) ppm. IR
(ATR): ν = 3305 (ϵC–H), 3045–3025 (=C–H), 2110 (CϵC) cm–1. benzene rings have been computed, where four different substitu-
˜
UV/Vis (CHCl3, logε): λ = 245 nm (4.60). HRMS (EI, 150 °C, tion positions are possible. The “propeller” conformation corre-
80 eV): calcd. for C48H30: 606.2347 [M]+·, found 606.2325 [M]+·.
sponds to 220°–230° and “2-up-1-down” to 135°–140° (see Sup-
porting Information).
Chloro-Substituted 1,3,5-Tris(3ЈЈ-ethynylbiphenyl-2Ј-yl)benzene (7):
Quantities used following general procedure 2:
6 (640 mg,
676 μmol), ethynyl(triisopropyl)silane (440 mg, 2.41 mmol),
Pd(PPh3)4 (81 mg, 70 μmol), triphenylphosphine (18 mg, 70 μmol),
CuI (7 mg, 35 μmol), pyridine (14 mL), triethylamine (1.5 mL);
THF (28 mL), TBAF (2.3 mL, 2.30 mmol, 1 m in THF). The resi-
due was purified by column chromatography on silica gel (hexanes/
ethyl acetate = 40:1) to give compound 7 (293 mg, 68%) as color-
less solid, m.p. 88–91 °C.
Because of the presence of different conformers the 1H NMR spec-
trum is very complex and only a high temperature NMR spectrum
could be fully interpreted. 1H NMR (500 MHz, [D6]DMSO,
120 °C): δ = 3.86 (s, 2 H, CϵCH), 3.89 (s, 1 H, CϵCH), 6.68 (br.
s, 3 H, 2ЈЈ-H), 6.88–7.48 (5 m, 23 H, Ar) ppm. Because of the
presence of different conformers the 13C NMR spectrum
(126 MHz, CDCl3) is very complex and the signals could not be
Acknowledgments
The generous support by the Deutsche Forschungsgemeinschaft
(DFG) (SFB 765), the Evonik Foundation (PhD fellowship for
D. T.) and Bayer HealthCare is gratefully acknowledged. The au-
thors thank Dr. Reinhold Zimmer for his help during preparation
of this manuscript. Furthermore the preliminary computational
work by K. Sonneberg and N. Passing and the computation time
by the Zentraleinrichtung für Datenverarbeitung (ZEDAT) of the
Freie Universität Berlin are acknowledged.
[1] a) L. Chen, Y. Hernandez, X. Feng, K. Müllen, Angew. Chem.
Int. Ed. 2012, 51, 7640–7654; Angew. Chem. 2012, 124, 7758–
7773; b) S. Fujii, T. Enoki, Acc. Chem. Res. 2012, 46, 2202–
2210; c) H. Seyler, B. Purushothaman, D. J. Jones, A. B.
Holmes, W. W. H. Wong, Pure Appl. Chem. 2012, 84, 1047–
1067.
[2] a) L. Schmidt-Mende, A. Fechtenkötter, K. Müllen, E. Moons,
R. H. Friend, J. D. MacKenzie, Science 2001, 293, 1119–1122;
b) M. D. Watson, A. Fechtenkötter, K. Müllen, Chem. Rev.
2001, 101, 1267–1300; c) A. M. van de Craats, N. Stutzmann,
O. Bunk, M. M. Nielsen, M. Watson, K. Müllen, H. D.
Chanzy, H. Sirringhaus, R. H. Friend, Adv. Mater. 2003, 15,
495–499.
assigned. IR (ATR): ν = 3290 (ϵC–H), 3060 (=C–H), 2160, 2105
˜
(CϵC) cm–1. UV/Vis (CHCl3, logε): λ = 245 nm (4.64). C48H29Cl
(641.2): calcd. C 89.91, H 4.55; found C 89.56, H 4.59. MS (EI,
170 °C, 80 eV): calcd. for C48H29Cl: 640.2 [M]+·, found 640.4 [M]
+·
.
1,3,5-Tris{3ЈЈ-[(2,2Ј-bipyridin-4-yl)ethynyl]biphenyl-2Ј-yl}benzene
(9): A mixture of 4 (110 mg, 110 μmol), alkyne 8 (69 mg, 384 μmol),
Pd(PPh3)4 (13 mg, 11 μmol), triphenylphosphine (3 mg, 11 μmol)
and CuI (2 mg, 11 μmol) in pyridine (7 mL) and triethylamine
(3.5 mL) was heated to 80 °C overnight under an argon atmo-
sphere. The volatile components were removed under reduced pres-
sure and the residue was diluted with CH2Cl2 (10 mL). Satd. aq.
NH4Cl (10 mL) was added, the layers were separated and the aque-
ous phase was extracted with CH2Cl2 (3ϫ 10 mL). The combined
organic layers were dried with Na2SO4 and concentrated to dry-
ness. The residue was purified by column chromatography on alu-
minum oxide (hexanes/ethyl acetate = 1:1) to give compound 9
(68 mg, 58%) as pale yellow solid, m.p. 103–106 °C. 1H NMR
(400 MHz, CDCl3): δ = 6.81 (s, 3 H, 2ЈЈ-H), 6.87 (br. d, J = 7.1 Hz,
3 H, Ar), 6.92 (br. d, J = 7.7 Hz, 3 H, Ar), 7.29–7.34 (m, 6 H, 5Ј-
H, Ar), 7.35–7.37 (m, 6 H, 5-H, Ar), 7.45–7.49 (m, 9 H, Ar), 7.61–
7.71 (m, 3 H, Ar), 7.82 (dt, J = 1.8, 7.8 Hz, 3 H, 4Ј-H), 8.39 (d, J
= 7.8 Hz, 3 H, 3Ј-H), 8.52 (s, 3 H, 3-H), 8.64 (d, J = 5.0 Hz, 3 H,
6-H), 8.69 (br. d, J = 4.7 Hz, 3 H, 6Ј-H) ppm. 13C NMR (126 MHz,
CDCl3): δ = 87.3, 94.2 (2 s, 2 CϵC), 121.3 (d, C-3Ј), 122.3 (s, Ar)
123.4, 124.2, 125.3, 127.7, 128.0, 128.1, 130.1, 130.2, 130.4, 130.7,
131.6 (11 d, C-3, C-5Ј, C-5, 8 Ar), 132.5 (s, Ar), 133.1, 137.1 (2 d,
Ar, C-4Ј), 139.4, 140.2, 140.7, 142.2 (4 s, 4 Ar), 149.3, 149.4 (2 d,
[3] a) A. Halleux, R. H. Martin, G. S. D. King, Helv. Chim. Acta
1958, 41, 1177–1183; b) E. Clar, J. F. Stephen, Tetrahedron
1965, 21, 467–470; c) A. Stabel, P. Herwig, K. Müllen, J. P.
Rabe, Angew. Chem. Int. Ed. Engl. 1995, 34, 1609–1611; Angew.
Chem. 1995, 107, 1768–1770.
[4] S. Ozasa, Y. Fujioka, H. Hashino, N. Kimura, E. Ibuki, Chem.
Pharm. Bull. 1983, 31, 2313–2320.
[5] D. Trawny, V. Kunz, H.-U. Reissig, Eur. J. Org. Chem. 2014,
6295–6302.
[6] a) L. Vandromme, H.-U. Reissig, S. Gröper, J. P. Rabe, Eur. J.
Org. Chem. 2008, 2049–2055; b) D. Trawny, L. Vandromme,
J. P. Rabe, H.-U. Reissig, Eur. J. Org. Chem. 2014, 4985–4992;
c) D. Trawny, P. Schlexer, K. Steenbergen, J. P. Rabe, B. Paulus,
H.-U. Reissig, ChemPhysChem 2015, 16, 949–953; d) J. Dash,
D. Trawny, J. P. Rabe, H.-U. Reissig, Synlett 2015, DOI:
10.1055/s-0034–13807.
[7] Review: C. Fasting, C. A. Schalley, M. Weber, O. Seitz, S.
Hecht, B. Koksch, J. Dernedde, C. Graf, E.-W. Knapp, R.
Haag, Angew. Chem. Int. Ed. 2012, 51, 10472–10498; Angew.
Chem. 2012, 124, 10622–10650.
[8] X. Feng, J. Wu, V. Enkelmann, K. Müllen, Org. Lett. 2006, 8,
C-6, C-6Ј), 155.6, 156.5 (2 s, 2 Ar) ppm. IR (ATR): ν = 3055 (=C–
˜
1145–1148.
H), 2210 (CϵC) cm–1. UV/Vis (CHCl3, logε): λ = 244 nm (4.82).
HRMS (ESI-TOF): calcd. for C78H48N6: 1069.4013 [M + H]+,
found 1069.4061 [M + H]+.
[9] J. Wu, M. Baumgarten, M. G. Debije, J. M. Warman, K.
Müllen, Angew. Chem. Int. Ed. 2004, 43, 5331–5335; Angew.
Chem. 2004, 116, 5445–5449.
[10] S. S. Elmorsy, A. Pelter, K. Smith, Tetrahedron Lett. 1991, 32,
Crystallization Procedure: A small amount of the corresponding
trialkyne (ca. 20 mg) was dissolved in 10 mL of hexanes (test tube).
After the addition of 0.5 mL of ethanol the tube was sealed with a
septum and punctured with a cannula. After two weeks suitable
small crystals were isolated by pipetting of the solution.
4175–4176.
[11] L. M. Stock, A. R. Spector, J. Org. Chem. 1963, 28, 3272–3274.
[12] J. Vcelak, V. Chvalovsky, Collect. Czech. Chem. Commun. 1973,
38, 1055–1072.
[13] L. Eberson, M. P. Hartshorn, F. Radner, O. Persson, Chem.
Commun. 1996, 215–216.
[14] ORTEP-3v2 for windows: L. J. Farrugia, J. Appl. Crystallogr.
1997, 30, 565.
[15] CCDC-1045759 (for 5) and CCDC-1045760 (for 7) contain the
supplementary crystallographic data for this paper. These data
Computational Details: Density Functional Theory (DFT) calcula-
tions have been performed using the B97D[21,22] functional with
the def2-SVP basis set. All calculations where performed with the
Gaussian 09 Rev. A.02 program package.[23] To confirm the substi-
Eur. J. Org. Chem. 2015, 4667–4674
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4673

H.-U. Reissig et al.
FULL PAPER
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via DOI: www.ccdc.cam.ac.uk/data_
request/cif Crystal data for 5: triclinic, a = 10.450(11), b =
12.100(13), c = 14.499(17) Å, α = 78.98(2), β = 82.22(2), γ =
according to mass spectrometry contained an additional equiv-
alent of water.
[20] C. L. Nesloney, J. W. Kelly, J. Org. Chem. 1996, 61, 3127–3137.
[21] A. D. Becke, J. Chem. Phys. 1997, 107, 8554–8560.
68.08(3)°, V = 1665(3) Å3, Z = 2, λ = 0.71073 Å (Mo-Kα), T = [22] S. Grimme, J. Comput. Chem. 2006, 27, 1787–1799.
100 K, 3410 unique reflexions, Rint = 0.141, wR2(all) = 0.288,
R1(obs.) = 0.094. 7: triclinic, a = 10.1125(3), b = 11.2335(4), c
= 15.5723(5) Å, α = 98.298(2), β = 100.739(2), γ = 100.003(2)°,
V = 1682.81(10) Å3, Z = 2, λ = 1.54178 Å (Cu-Kα), T = 100 K,
5882 unique reflexions, Rint = 0.062, wR2(all) = 0.221, R1(obs)
= 0.082.
[23] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B.
Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li,
H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Son-
nenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hase-
gawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M.
Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Starov-
erov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell,
J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M.
Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Ad-
amo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Mar-
tin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B.
Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09,
revision A.02, Gaussian, Inc., Wallingford CT, 2009.
[16] H. Shanan-Atidi, K. H. Bar-Eli, J. Phys. Chem. 1970, 74, 961–
963.
[17] a) G. Bott, L. D. Field, S. Sternhell, J. Am. Chem. Soc. 1980,
102, 5618–5626; b) for a recent data collection for rotational
barriers of biphenyl derivatives, see: L. Lunazzi, M. Mancinelli,
A. Mazzanti, S. Lepri, R. Ruzziconi, M. Schlosser, Org. Bio-
mol. Chem. 2012, 10, 1847–1855.
[18] V. Grosshenny, R. Ziessel, Tetrahedron Lett. 1992, 33, 8075–
8078.
[19] First attempts to oxidize compound 9 with iron(III) chloride[6]
in order to provide a trivalent bipyridine derivative containing
a HBC core provided no clean product. Under the reaction
conditions we mainly obtained an unknown compound which
Received: May 13, 2015
Published Online: June 15, 2015
4674
www.eurjoc.org
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2015, 4667–4674