Structural, optical, and electrochemical properties of three-dimensional push-pull corannulenes

Article abstract of DOI:10.1021/jo302217n

Electrochemically active corannulene derivatives with various numbers of electron-donating 4-(N,N-dimethylamino)phenylethynyl (1-4) or electron-withdrawing cyanobutadienyl peripheral substitutents (5-8) were prepared. The latter derivatives resulted from

Full text of DOI:10.1021/jo302217n

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Structural, Optical, and Electrochemical Properties of
Three-Dimensional Push−Pull Corannulenes
Yi-Lin Wu,† Mihaiela C. Stuparu,‡ Corinne Boudon,§ Jean-Paul Gisselbrecht,§ W. Bernd Schweizer,†
Kim K. Baldridge,*,‡ Jay S. Siegel,*,‡ and Francois Diederich*,†
̧
†Laboratorium fur Organische Chemie, ETH Zurich, Honggerberg, HCI, 8093 Zurich, Switzerland
̈
̈
̈
̈
‡Institute of Organic Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
̈
̈
§Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide, UMR 7177 CNRS, Universite
́
de Strasbourg, 4 rue Blaise
Pascal, 67081 Strasbourg Cedex, France
S
* Supporting Information
ABSTRACT: Electrochemically active corannulene derivatives
with various numbers of electron-donating 4-(N,N-dimethyl-
amino)phenylethynyl (1−4) or electron-withdrawing cyanobuta-
dienyl peripheral substitutents (5−8) were prepared. The latter
derivatives resulted from formal [2 + 2] cycloaddition of
cyanoolefins to 1−4 followed by retro-electrocyclization. Con-
formational properties were examined by variable-temperature
NMR and X-ray diffraction and opto-electronic properties by
electronic absorption/emission spectra and electrochemical
measurements; these analyses were corroborated by dispersion-corrected density functional calculations at the level of B97-D/
def2-TZVPP. In CH2Cl2, 1−4 exhibit intramolecular charge-transfer (ICT) absorptions at 350−550 nm and green (λem ∼ 540 nm) or
orange (600 nm) fluorescence with high quantum yields (56−98%) and are more readily reduced than corannulene by up to 490 mV.
The variation of optical gap and redox potentials of 1−4 does not correlate with the number of substituents. Cyanobutadienyl
corannulenes 5−8 show red-shifted ICT absorptions with end-absorptions approaching 800 nm. Intersubstituent interactions lead to
distortions of the corannulene core and lower the molecular symmetry. NMR, X-ray, and computational studies on 5 and 8 with one
cyanobutadienyl substituent suggested the formation of intermolecular corannulene dimers. Bowl-inversion barriers around ΔG⧧ =
10−11 kcal/mol were determined for these two molecules.
Modification of the peripheral substituents provided the
electrochemically active corannulenes 1−8 in this work. The 4-
(N,N-dimethylamino)phenylethynyl derivatives 1−4 constitute
a new class of electron-rich and highly fluorescent corannulenes
in which the anilinoethynyl substituents extend radially in a star-
burst fashion with limited degrees of conformational freedom.
Reaction of 1−4 with tetracyanoethene (TCNE) or 2-[4-(trifluo-
romethyl)benzylidene]malononitrile proceeds by formal [2 + 2]
cycloaddition (CA) between the electron-deficient alkenes and the
donor-activated acetylenes, followed by retro-electrocyclization
(RE), to yield a contrasting family of electron-poor corannulenes
(5−8) with multiple cyanobuta-1,3-dienyl arms (Chart 1).8
The additional s-cis/s-trans conformational variability of the
cyanobutadienyl arms in 5−8 further modifies the three-
dimensional geometry of corannulene and allows for core-
convergent as well as core-divergent geometries. A recent con-
formational study on nascent 2,3-diphenylbuta-1,3-diene by
single-crystal X-ray analysis and MP2/6-311++G** calculations9
revealed the preference to the synclinal conformer (torsion angle
55.6° by X-ray).10 The corresponding anticlinal conformer
INTRODUCTION
■
Polycyclic aromatic organic molecules have been important
components in the search for highly efficient organic (opto-)-
electronic devices.1 Their large π-surfaces enable regular solid-
state packing and electron transduction; the extended π-conjugation
is responsible for molecular electrical and/or opto-electronic prop-
erties, which are translated into the characteristics of the bulk
materials and are easily tailored by alteration of the substituents on
the periphery of the π-frameworks.
Corannulene is composed of five benzene rings fused to a
central five-membered cycle and has a bowl-shaped π-conjugated
system, adding one more dimension to the chemistry of usually
planar polycyclic aromatics.2 In addition to the interest in the
dynamic stereochemistry3 and organometallic coordination3d,4
associated with this curved structure, there has been growing
attention to the materials applications of corannulene. For in-
stance, lithium can be stored/intercalated between corannu-
lenes, yielding a promising anode material for batteries.5 A
dramatic increase in fluorescence quantum yields from 0.03 to
0.8−0.9 was effected by arylethynylation of corannulene,6 and
wavelength-tunable electrochemiluminescence was achieved
by forming exciplexes with coreactants during electrochemical
processes.7
Received: October 9, 2012
© XXXX American Chemical Society
A
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Chart 1. Corannulene Derivatives 1−8 with Electrochemically Active Peripheral Substituents
(a local minimum, torsion angle 155°) is higher in energy by
1.70 kcal/mol, and the barrier for converting the low energy
conformer into the high energy one is 5.33 kcal/mol. Installation
of the cyanobutadiene motifs on the periphery of corannulenes
5−8 is expected to introduce intersubstituent and/or sub-
stituent−corannulene interactions that influence the materials
properties displayed by this family of chromophores.
electrochemically active corannulenes. Mono- and bis[4-
(dimethylamino)phenylethynyl]corannulenes 1 and 2 were
prepared in 70% and 80% yields, respectively, by Sonogashira
coupling between 4-ethynyl-N,N-dimethylaniline and mono- or
dibromocorannulene, respectively, at elevated temperatures
(Scheme 1). Tetrakis[4-(dimethylamino)phenylethynyl]cor-
annulene 3 was synthesized by Stille cross-coupling, which
proceeded with 80% yield, from the corresponding tetrabromo-
corannulene. For the Stille reaction with the less reactive pen-
tachlorocorannulene precursor, a sterically demanding nucleo-
philic N-heterocyclic carbene6c,14 was employed as the ligand for
Pd(0), and penta-substituted compound 4 was obtained in 30%
RESULTS AND DISCUSSION
■
Synthesis. Previously reported bromo-,6b,11 1,6-dibromo-,6c
1,2,5,6-tetrabromo-,12 and 1,3,5,7,9-pentachlorocorannu-
lenes11,13 allowed access to the peripherally functionalized,
B
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a
Scheme 1. Syntheses of Corannulene Derivatives 1−8
a
TCNE = tetracyanoethene, DME = 1,2-dimethoxyethane, and IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene.
1
yield. The first-order patterns of the H NMR and 13C NMR
spectra (CDCl3, 298 K) of 2−4 indicate signal degeneracy
consistent with C2v, C2v, and C5h symmetries, respectively, in
solution.
8.10 ppm and the singlet at ca. 7.95 ppm from the corannulene
unit shifted downfield (Figure 1). At high concentration (76.7 mM),
some of the corannulene protons in 5 exhibited NOE en-
hancements by irradiation at the N(CH3)2 frequency (Figure 2);
in contrast, such a phenomenon was not observed in the dilute
solution (7.7 mM), even after an acquisition time increased by a
factor of 10. Similarly, the N(CH3)2 signal of the other singly
functionalized corannulene 8 exhibited an upfield shift upon
concentration: δ(N(CH3)2) = 2.863 ppm at 2.14 mM and 2.835
ppm at 36.2 mM (see the Supporting Information). The similar
concentration dependency for 5 and 8 suggested weak inter-
molecular association, where N(CH3)2 groups are situated in a
shielding environment close to a corannulene unit, as indicated
by the upfield shifts of these signals and the NOE results.
The CA−RE reactions between the donor-activated acety-
lenes (1, 2, and 4) and TCNE were conducted with an excess
amount of TCNE (1.5 equiv per ethynyl functionality) at room
temperature in 1,1,2,2-tetrachloroethane to afford the corre-
sponding 1,1,4,4-tetracyanobuta-1,3-dienyl- (TCBD) substituted
corannulenes 5−7 in excellent yields (94−96%). To facilitate the
stereochemical analysis of butadiene-substituted corannulenes
by NMR, 2-[4-(trifluoromethyl)benzylidene]malononitrile15
was allowed to react with 1 at 120 °C for 2 d. (E)-Configured
butadiene 8 was isolated in 89% as the only product due to the
high torquoselectivity of this reaction.8d,e,15b
Compound 8 crystallizes in the triclinic space group P1 with
̅
The analogous reaction of 3 and TCNE did not reach com-
pletion, even with a large excess of TCNE at elevated tem-
perature (120 °C) and reaction times of more than a week. Only
molecules having molecular composition of [3 + 2 TCNE] were
detected by mass spectrometry.16 Prolonged reaction time
resulted in decomposition of these intermediate species. The
sluggish reactivity of aromatic o-diacetylenes has been noticed
previously by Tobe and co-workers17 and our group,8a possibly
resulting from the electron-withdrawing power of the TCBD
moiety formed in the first addition step and from steric hindrance
by this bulky ortho substituent.
two molecules of 8 and two CHCl3 in the asymmetric unit; the
symmetry-independent molecules are essentially superimpos-
able. Four CF3 groups cluster around an inversion center, form-
ing a fluorine-rich region, and the two molecules of 8 arrange in a
dimeric fashion, both related by the center of inversion (Figure 3a).
In each dimeric entity, the N-methyl group of one molecule is
embedded by the concave surface of the corannulene unit of
the symmetry-related molecule (shortest CNMe2-to-Ccorannulene
distance = 3.33 Å) and is proximal to the aniline ring of the
latter.18 Such a dimeric structure, were it to persist at higher solution
concentrations, could explain the shielding and NOE enhancement
observed in the variable concentration NMR spectra.
The butadiene torsion angles are ∼63° for 8. In a related
compound 9, where a phenyl ring replaces the corannulene unit
of 8, the analogous torsion angle is 67° (Figure 3b);15b in TCBD
molecule 10 (2,3-bis[4-(dimethylamino)phenyl]buta-1,3-diene-
1,1,4,4-tetracarbonitrile), related to 5, the corresponding torsion
of 62° was found (Figure 3c).8a This similarity supports the idea
Structural Features of Monocyanobutadienyl Coran-
1
nulenes 5 and 8. The H NMR spectra for singly TCBD-
functionalized 5 (500 MHz, CD2Cl2) showed concentration-
dependent behavior. At high concentrations, the 1H resonances
from the N(CH3)2 group and the aromatic protons ortho to the
N(CH3)2 group shifted upfield (δ(N(CH3)2) = 3.142 ppm at
0.77 mM and 3.113 ppm at 76.7 mM), whereas the doublet at ca.
C
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Figure 1. Partial 1H NMR spectra (500 MHz, CD2Cl2, 293 K) of 5 at concentrations indicated at the upper left corner of each trace. Signal assignments
are given.
Figure 2. Upper trace: partial 1H 1D-NOE difference spectrum (500 MHz, 293 K) of 5 (76.7 mM in CD2Cl2), obtained by irradiation at the NMe2
resonance. Lower trace: the corresponding 1H NMR spectrum for comparison. Signal assignments are given; solid circles indicate two doublets from
corannulene protons.
that the skew, synclinal conformation of 2,3-diarylbuta-1,3-diene
is an easily accessible minimum.
concave side for the more stable bowl-inversion isomers 8b
and 8d; the geometry of the lowest energy 8d resembles the
conformation seen in the X-ray analysis. All four conformers
exhibit synclinal butadiene torsion (44°−50°). Comparison
between the structures of calculated 8d, 8dimer, and 8 (X-ray)
suggests that the molecule can adapt the conformation readily for
dimer formation, but structural changes to widen the torsion
angle of the butadiene and to increase the coplanarity between
the aniline and dicyanovinyl moieties are nevertheless necessary.
The dispersion-enabled density functional, B97-D, together
with the def2-TZVPP basis set was used to study the con-
formation of butadienyl corannulene 8.19,20 Two sets of low-
energy conformers 8a/8b and 8c/8d were found; the conformer
in each set is related to each other by bowl inversion of the
corannulene unit, and the conformers in different sets by the
rotation about the Cbutadiene−Ccorannulene single bond (Table 1).
The N,N-dimethylanilino groups situate at the convex face of the
corannulene bowl for the higher energy 8a and 8c and at the
1
For 8dimer, the computed H NMR chemical shift of the
N(CH3)2 group, which locates inside the corannulene bowl
D
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Figure 3. (a) ORTEP representation of compound 8 with thermal ellipsoids shown at the 40% probability level, 100 K. Color code: gray = C, blue = N,
yellow = F, and green = Cl. Hydrogen atoms are omitted for clarity. (b) Overlay of 8 (orange, torsion angle ϕ = 63°) and 9, a phenyl analog of 8 (purple,
ϕ = 67°).15b (c) Structure of 2,3-bis[4-(dimethylamino)phenyl]buta-1,3-diene-1,1,4,4-tetracarbonitrile (10); torsion angle about the butadiene unit ϕ = 62°.8a
Table 1. Geometric, Energetic, and NMR Parameters of 8, Calculated at the B97-D/def2-TZVPP Level of Theory in the Gas Phase
8a
8b
8c
8d
8dimer
8 (X-ray)
location of aniline relative to corannulene
convex
1.00
concave
0.24
convex
0.87
concave
0.00
concave
concave
a
e
relative energy E0(kcal/mol)
−26.8
57.7
b
butadiene torsion α (deg)
45.7
43.7
49.7
44.3
63.1
30.3
b
aniline−vinyl torsion β (deg)
35.2
46.0
32.2
44.4
25.3
c
N(CH3)2 chemical shift (ppm)
2.92
1.69
2.97
1.61
−2.19
−87.19
0.92
d
CF3 chemical shift (ppm)
−87.40
0.93
−86.99
0.93
−87.34
0.93
−87.07
0.93
bowl depth (Å)
0.88
inversion barrier (kcal/mol)
11.13
11.90
10.38
11.25
10.2, 10.8
a
b
c
d
Zero-point corrected energy, relative to 8d. Absolute values are given. CSGT calculations, relative to Si(CH3)4. CSGT calculations, relative to
e
CFCl3. ZPE (zero-point energy)-uncorrected, calculated as E(8dimer) − 2 × E(8d); value in CH2Cl2: −24.8 kcal/mol. See the Supporting
Information for DFT estimations at other levels of theory.
region, appears at −2.19 ppm (Table 1). This result is qualita-
tively in line with the upfield shifts of the N(CH3)2 resonance for
5 and 8 noticed in the more concentrated solutions (vide supra),
suggesting that a similar kind of intermolecular association
happens in solutions. However, the strength of this interaction is
(B97-D/def2-TZVPP,CH2Cl2//B97-D/def2-TZVPP) down to ca.
+1.72 kcal/mol for DFT/COSMO (B3LYP/def2-TZV-
PP,CH2Cl2//B97-D/def2-TZVPP), one has a wide berth to fill
with interpretation (Table 1 and Supporting Information).
Certainly, a light tendency for 8 to dimerize remains consistent
with the NMR shifts observed, the X-ray structure, and the com-
putational model.
Corannulene undergoes a rapid bowl-to-bowl inversion
process at room temperature, with an estimated barrier of
11.5 kcal/mol.3a,13a Some monosubstituted corannulenes display
barriers to bowl inversion of 10.2−11.3 kcal/mol when studied
by variable-temperature NMR (VT-NMR).2a The trifluorome-
thylphenyl derivative 8 displays two sets of NMR signals with
unequal intensities below Tc = 220 K; reversible (de)coalescence
indicates an equilibrium structural interconversion (Figure 4).
At 183 K, the more stable conformer shows N(CH3)2 NMR
1
weak as indicated by the minor change in H chemical shifts
found experimentally. The calculated dimerization energy in
solution (E(8dimer) − 2E(8d), negative value implies dimer more
stable) at best places extreme limits on the actual dimerization
energy. When using DFT-D in a continuum solvent method like
COSMO, dispersion of the explicit molecules is included but not
for the solvation shell. When using DFT without dispersion then
neither the explicit molecules nor the solvent contribute any
dispersive component. The former tends to strongly overestimate
the binding, whereas the latter is more likely to underestimate the
value. With a range of ca. −24.8 kcal/mol for DFT-D/COSMO
E
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1
Figure 4. Partial H (500 MHz, CD2Cl2, left) and 19F VT-NMR (470 MHz, CD2Cl2, right) spectra of 8. The temperature at which each trace was
recorded is shown on the left. Signal assignments are given.
resonance at upper field (2.62 vs 2.94 ppm) and CF3 at lower
field (−61.92 vs −62.19 ppm) relative to the less stable
conformer. The unequal intensity suggested two structures of
different energy (ΔG ∼ 0.65 kcal/mol at Tc), most likely two
diastereoisomers related by bowl inversion. The assignment is
supported by the calculated upfield N(CH3)2 chemical shifts and
downfield CF3 shifts for the more stable conformers 8b and 8d,
relative to those for 8a and 8c, respectively (Table 1). Bowl-
inversion barriers of ΔG⧧ = 10.2 kcal/mol (minor to major)
and 10.8 kcal/mol (major to minor) were estimated at the
coalescence temperature Tc = 220 K by the Gutowsky−Holm
approximation and the Shanan-Atidi−Bar-Eli method.21
B97-D/def2-TZVPP energies E0 (Table 1) correlate well with
both the bowl-inversion barrier and the relative energy of the
two bowl-inversion forms. For 5, the two bowl-inversion
isomers appear to have similar energies; the inversion barrier
was estimated to be ΔG‡ = 10.2 kcal/mol at Tc = 205 K
(Supporting Information).
Conformation of Multiply Cyanobutadienyl-Function-
alized Corannulenes 6 and 7. As previously mentioned,
multiply functionalized corannulenes 2 and 4 display NMR
spectra consistent with C2v and C5h symmetry at room tem-
perature, respectively; however, these symmetry characteristics
do not persist in the corresponding bis- and pentakis-TCBD
compounds 6 and 7, as a result of substantial intersubstituent
interactions. VT-NMR experiments permitted the character-
ization of these interactions and their interplay with the curved
structure of corannulene in 6 and 7. The presence of multiple
low-symmetric diastereoisomers at low temperatures, however,
hampered the analysis of bowl-inversion processes associated
with these electron-deficient corannulenes.
amino group (Figure 5). Cooperative contributions from the syn-
clinal conformation of TCBD and the curvature of corannulene
result in some of the five peripheral substituents being positioned at
one face. The situation is even more complicated when there are two
and three substituents at either face of the corannulene, since these
two substituents can have 1,3-, 1,5-, or 1,7-relationships, each
resulting in C1 symmetry, the subgroup of C5h. Despite this com-
1
plexity, the H NMR signals from the corannulene moiety are
perceptibly sharper than those from the aniline units at the same
temperature range. At temperatures above 363 K, the increased
rate of interconversion of one C1 conformer into another restores
the “expected” C5 symmetry of 7.
Reducing the number of aniline-TCBD substituents from five
to two reduces the number of possible conformers. For bis-
1
TCBD 6, the H NMR spectra display two singlets around
8.05 ppm, two doublets around 7.85 ppm, and another two doublets
around 7.70 ppm (temperature = 273 30 K) in the region
where 1H signals of corannulene are expected, and these two sets
of signals have roughly equal intensities (Figure 6b). According
to the molecular structure of 6, the two sets of 1H signals were
assigned to two magnetically distinct, 2-fold symmetric isomers
in solution.
One of these 2-fold symmetric molecules has the two TCBD
arms pointing toward the same face of its corannulene unit (syn-6),
and the other one has TCBDs at opposite faces (anti-6) (Scheme 2).
The comparable NMR intensities of syn-6 and anti-6 are reminiscent
of the similar populations of the bowl-inversion pair of mono-TCBD
5. The coexistence of both isomers suggests restricted rotation about
the Cbutadiene−Ccorannulene single bond due to the impedance of the
o-methyl groups. The strong interaction observed between these
neighboring functionalities testifies to the blocked reactivity of
tetraacetylene 3 toward the addition of the third and fourth
equivalents of TCNE (vide supra). At sufficiently high tem-
perature, a single species with a time-averaged 2-fold symmetry
For pentakis-TCBD 7 at temperatures lower than 300 K,
multiple magnetically distinct N-methyl groups were observed
and the same holds true for its aromatic protons ortho to the
F
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1
Figure 5. Partial H VT-NMR spectra (300 MHz, (CDCl2)2) of 7. Temperature at which each trace was recorded is shown on the left. Signal
assignments are given.
Figure 6. Partial 1H VT-NMR spectra (500 MHz) of 6 (a) in (CDCl2)2 at 328−363 K and (b) in CD2Cl2 at 240−300 K. Temperature at which each
trace was recorded is shown on the left. Signal assignments are given.
G
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Scheme 2. Graphic Representation of Various Conformers of 6
Figure 7. UV/vis absorption spectra of 1−4 in CH2Cl2 at 298 K (c ∼ 10−5 M).
was observed by NMR (Figure 6a); a barrier of 19.2 kcal/mol at
Tc = 343 K for this restricted rotation was estimated. Atrop-
isomerism with a similar barrier had been previously observed for
a TCBD−C60 conjugate, in which the rotation about the bond
connecting the two moieties was also hindered by a neighboring
methyl group attached to the carbon sphere.22
It should be noted that the above stereochemical analysis for 6
provides a simplified picture and is only applicable at high
temperatures where the corannulene core is inverting rapidly and
can be considered as a time-averaged planar structure. Taking the
curvature of this core unit into consideration results in four con-
formers, syn-6a, syn-6b, anti-6a, and anti-6b; the former two are
both Cs symmetric molecules, and the latter two are C1 sym-
metric and form a pair of enantiomers (Scheme 2). At lower
temperatures, the bowl-inversion motion slows, and three
magnetically distinct species can be observed and, in principle,
examined with regard to their bowl-inversion dynamics; how-
ever, complicated and unresolvable 1H NMR signals were recorded,
making interpretations about the molecular conformation in this
temperature range difficult (down to 150 K in Freon (CDCl2F) or
down to 200 K in CD2Cl2). The syn-/anticlinal conformational
equilibrium of the butadiene moieties may be one of the sources to
complicate the analysis. The barrier of this process is expected to be
higher than that of 2,3-diphenylbuta-1,3-diene (ca. 5 kcal/mol
by MP2/6-311++G**),9b caused by the neighboring methyl
substituent.
Electronic Absorption and Emission Spectra. Two
absorption bands in the region of 280−350 and 350−550 nm
were observed for 1−4 in dichloromethane (Figure 7). The
broad, long-wavelength absorptions in the latter region are
assigned to have intramolecular charge-transfer (ICT) character
as they diminished when these solutions were treated with
trifluoroacetic acid (TFA); the resulting spectra closely resemble
those of phenylethynyl corannulenes.6c This observation also
suggested that the absorptions in the higher energy region (280−
350 nm) are mostly due to the π−π* transitions of ethynyl-
corannulenes. The optical gaps (ΔEopt) estimated from the
absorption onset (1: 2.44, 2: 2.39, 3: 2.18, and 4: 2.30 eV)
H
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Figure 8. UV/vis absorption spectra of 5−7 in CH2Cl2 at 298 K (c ∼ 10−5 M). Inset shows the changes of absorption spectra of 7 upon addition of
trifluoroacetic acid (up to 105 equiv).
decrease, by and large, as the number of electron-donating group
increases. Excitation energies (ΔEcalc, to the first allowed excited
state) calculated at the level of TD B97-D/def2-TZVPP show the
same trend (1: 2.22, 2: 2.08, 3: 1.75, and 4: 2.00 eV in the gas phase,
and 1: 2.07, 2: 1.89, 3: 1.59, and 4: 1.76 eV in CH2Cl2), but are
systematically underestimated relative to the experimental values.
The larger optical gap of 4 compared to that of 3 signifies that
the exact positioning of the substituents and thus the molecular
symmetry substantially influences the electronic structure of
corannulene derivatives. On the time scale of the UV/vis exper-
iment, the bowl-inversion of 1−3 should be frozen and the
spectra should arise from molecular symmetries C1 or Cs. Hence,
there should be nondegenerate A-type orbitals for 1 or A′- and A″-
type orbitals for 2 and 3. In the case of 4, the C5 symmetry results in
sets of closely separated degenerate E1- and E2-type orbitals.6c The
observation of similar electronic absorption behavior between di-
and penta-substituted compounds 2 and 4 as compared to 3 and 4
reflects a “redistribution” of orbital energies by high molecular
symmetry. According to the TD-DFT calculations, the first two
transitions of 4 are essentially forbidden (oscillator strengths
f = 0.00); the first allowed transition (S3 ← S0) requires 1.76 eV for
excitation, which is close to the value predicted for 2 (1.89 eV).
Similar to their trimethylsilyl, phenyl, alkylphenyl, and alkoxy-
phenyl analogues, anilino compounds 1−4 show strong photo-
luminescence in solution.6c Compared to the parent corannulene
(λem = 423 nm, Φf = 0.03), multivalent phenylethynylcor-
annulenes (λem ∼ 500 nm), and multivalent 3,4,5-trialkoxyphe-
nylethynylcorannulenes (λem ∼ 530 nm), introduction of aniline
groups induces a bathochromic shift of the emission bands to ca.
600 nm. In the present series, emission at λem = 533 nm (Φf =
0.98) for 1, λem = 538 nm (Φf = 0.93) for 2, λem = 593 nm (Φf =
0.76) for 3, and λem = 595 nm (Φf = 0.56) for 4 was observed (see
the Supporting Information for spectra). While many push−pull
chromophores experience the rapid radiationless decay from
their twisted or distorted ICT excited states,23 the inclusion of
cylindrically symmetric acetylene units in peripherally function-
alized corannulenes on the one hand keeps molecular rigidity for
radiative relaxation, and on the other hand allows for the free
choice of functionality around the corannulene core. Thus,
fluorescence compounds with blue, green, and orange colors
could be obtained with reasonable emission quantum yields.
The cyanobutadiene molecules 5−7 exhibit red-shifted ab-
sorption bands compared to their ethynyl precursors (Figure 8).
For 5, the high-energy absorption at 248 nm is attributed to the
local excitation of the aniline and the corannulene groups, the
260−350 nm band originates from the 2,3-diaryl TCBD system,
and the broad and multiband absorption covering 350−700 nm
is dominated by ICT character. In the case of 6, the two higher-
energy transitions present in 5 were similarly observed; however,
two well-separated ICT absorptions at 396 and 600 nm were
recorded. A similar two-band ICT absorption at 384 and 532 nm
was observed in an analogous compound where a 2,2′-diethoxy-
1,1′-binaphthalene-3,3′-diyl unit is used in place of the 2,4-
dimethyl-corannulen-1,6-diyl unit of 6.24 The similarity between
the latter two molecules, in comparison to 5, indicates the critical
steric and electronic effects of the ortho-dimethyl or ortho-
diethoxy groups on modifying HOMO/LUMO manifolds.
For 7, two very intense absorptions at 363 nm (ε 112 500
M−1 cm−1) and 468 nm (ε 199 800 M−1 cm−1) were observed,
with one weak shoulder around 600 nm (Figure 8). As discussed
earlier, the C5 symmetry of its precursor 4 was removed by the
steric interactions between TCBD moieties. Thus, the excep-
tionally high molar absorption of 7 is likely due to the presence of
five push−pull chromophoric units in a single molecule. Even
though the nature of the absorption at 363 nm remains unclear,
the appearance of a strong band at 468 nm together with a shoulder
at 600 nm (nonvanishing until ca. 800 nm) is characteristic of
crowded TCBD molecules having a strong electron-withdrawing
unit at the 2-position of the butadiene. For instance, dialkylanilino-
substituted octacyano[4]dendralenes display absorptions around
490 nm with shoulders at 650 nm for,25 and strong absorptions
around 465 nm with shoulders at 600 nm for, multivalent TCBDs.8a
As mentioned earlier, the ICT absorptions of push−pull
chromophores are diminished by TFA protonation (pKa 0.52 in
H2O) of the electron-donating aniline functionality (for PhNMe2H+,
pKa 5.07 in H2O).26 Larger amounts of TFA are generally needed to
fully quench the ICT bands of 5 and 6 as compared to 1−4 becase of
the reduced basicity of the anilino groups induced by the presence of
electron-withdrawing cyanovinyl moieties. However, the complete
disappearance of the ICT absorptions of 7 upon treatment with TFA
was not observed (Figure 8 inset). The intensities of the ICT
absorptions at 363 and 468 nm were reduced, but a saturation of
I
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spectral change was reached even after the employment of 105
equiv of TFA. The difficulty in achieving global protonation
reflects the combined and strong electron-withdrawing power of
five cyanovinyl groups and of protonated aniline groups. Moreover,
it further underscores the proximity between aniline substituents
caused by the curvature of corannulene and the geometrical pre-
ferences of 2,3-diaryl butadienes; global protonation would
otherwise produce strong and unfavorable Coloumbic repulsions.
Electrochemistry of Conjugates 1−7. Investigations of
1−7 and sym-pentakis(trimethylsilylethynyl)corannulene 116c
were carried out by cyclic voltammetry (CV) and rotating disk
voltammetry (RDV) in CH2Cl2 (+ 0.1 M n-Bu4NPF6); potentials
reported in Table 2 are referenced to the ferricinium/ferrocene
The parent corannulene is known to undergo up to four
reduction steps at rather negative potentials, and these potentials
are strongly dependent on the choice of solvents and supporting
electrolytes, especially for the latter three reductions.27 The first
two reductions occur at roughly E1/2 −2.35 and −3.02 V versus
Fc+/Fc.28 Such processes are made more favorable by the
electron-withdrawing acetylenic substituents in 11 (−1.81 and
−2.18 V). In the case of 1−4, the end-capped aniline groups
counteract the effects of lowering reduction potentials by Csp
Csp units; there is no clear correlation between the first reduction
potentials and the number of ethynyl substituents: E1/2,red: 2
(−1.86) ≈ 4 (−1.86) > 3 (−1.93) > 1 (−2.25 V). The absence of
a second reduction for more easily reduced compounds 2 and 4
suggests relatively large potential gaps between the first and the
second reductions as compared to 3, 11, and corannulene.
On the oxidation side, strong electrode inhibition was often
observed, and a nonmonotonic trend was again observed: Ep,ox: 1
(+0.37) > 2 (+0.35) > 4 (+0.33) > 3 (+0.20 V). Clearly, the ortho
4-(N,N-dimethylaminophenyl)ethynyl groups in 3 together greatly
amplify the electron donating in the molecule; moreover, the oxi-
dation potential of 3 is lower than those of 4,4′-(buta-1,3-diyne-
1,4-diyl)bis(N,N-dialkylanilines), which exhibit oxidation poten-
tials in the range of +0.26 − +0.32 V.25 The observation of a
second oxidation event (at ca. +0.43 V) for 2 and 4 indicates that
the anilino substituents are not independent redox sites; elec-
tronic communication is effective even through the fairly large
π-framework of ethynylcorannulene.
Table 2. Cyclic Voltammetry (CV; scan rate v = 0.1 V s−1) and
Rotating Disk Voltammetry (RDV) Data in CH2Cl2 (+ 0.1 M
a
n-Bu4NPF6)
CV
ΔEp/mV
70
RDV
b
c
d
e
f
compd
E°/V
Ep/V
E1/2/V
slope/mV
11
−1.81
−1.81 (1e−)
−2.18 (1e−)
+0.37 (1e−)
60
60
50
70
g
1
2
+0.37
−2.13
+0.44
+0.35
−2.25 (1e−)
h
−1.86
−1.92
60
60
−1.86 (1e−)
60
60
h
3
4
5
6
7
+0.20
For TCBDs 5−7, the oxidation of aniline is shifted to more
positive potentials by more than 500 mV due to the presence of
cyanovinyl functionalities, which is in agreement with our pre-
vious studies.25 Contrasting with the oxidation behaviors of 2 and
4, the oxidations of 6 and 7 show only one anodic peak whose
characteristics correspond to the oxidation of two (for 6) or five
(for 7) independent anilino centers. Deposition occurs for 6
during oxidation, which gave a sharp redissolution peak at +0.83 V
during the reverse scan.
−1.93 (1e−)
−2.35
+0.42
+0.33
−2.29
h
−1.90
+0.91
−0.83
−1.18
60
70
90
80
−1.86
60
60
70
+0.94 (1e−)
−0.85 (1e−)
−1.23 (1e−)
+0.90 (2e−)
−0.73 (2e−)
−1.36 (2e−)
75
i
i
+0.92
+0.95
First reductions for 5−7 were recorded around −0.71 to −0.83 V;
compounds with higher numbers of cyanovinyl functionalities
are more easily reduced, as one would expect. However, this
effect is marginal going from 6 to 7. Two, well-defined, and
reversible reductions on the TCBD moieties were observed for 5
at any scan rate, while similar but broad reductions were observed
in the case of 6. From the peak shapes and especially from the
peak potential differences, it is clear that, for 6, each step cor-
responds to two overlapping reversible one-electron transfers
separated by about 50 mV for the first reduction and by 75 mV
for the second step. This small, but noticeable peak separation is
suggestive of interactions between the two TCBD moieties.
For highly functionalized 7, the CV was reproducible, but a
series of unresolved redox processes occurs on the reduction
side. Convolution of the experimental curves suggests two sets of
five reversible one-electron transfers (Supporting Information).
In addition to orbital interactions through the π-system of cor-
annulene (cf. the oxidation of 2 and 4), the close proximity of the
TCBD moieties allows for electrostatic interactions between the
reduced TCBDs, and explains the observed splitting of redox
potentials for the latter compounds. It should be mentioned that
for 7, the amplitude of the latter reduction peaks in CV became
smaller and smaller, probably due to the decreasing solubility of
the multianionic species. However, by RDV, the unresolved wave
amplitudes (limiting currents) show similar amplitudes, denoting
that the same number of electrons have been exchanged.
−0.71
−1.24
120
150
100
150
j
j
j
j
j
j
j
j
j
−0.72
−0.80
−0.90
−1.03
−1.31
−1.41
−1.52
−1.64
−1.86
−0.72 (2e−)
−0.82 (1e−)
−0.90 (1e−)
−1.05 (1e−)
−1.45 (5e−)
200
a
All potentials are given vs the Fc+/Fc couple used as the internal
b
standard. Eo = (Epc + Epa)/2, where Epc and Epa correspond to the
c
cathodic and anodic peak potentials, respectively. ΔEp = Epa − Epc.
d
e
Ep = irreversible peak potential. E1/2 = half-wave potential.
f
Logarithmic analysis of the wave obtained by plotting E vs log[I/
g
(Ilim−I)]. A second reversible electron transfer is observed at −2.20 V
for scan rates higher than 1 V/s. Electrode inhibition during
oxidation. Electrode inhibition during oxidation; on the reverse scan
in CV, a redissolution peak is observed at +0.83 V. These potentials
h
i
j
were determined from the cyclic voltammetry convolution.
couple (Fc+/Fc). For some derivatives, reproducible data could
only be observed on freshly polished working electrodes due to
electrode inhibition during redox processes.
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(corresponding R-values based on all 11961 reflections 16.06% and
16.83%). CCDC deposition no. 901534.
CONCLUSION
■
Peripherally functionalized corannulenes with one, two, four, and
five electron-donating and/or electron-withdrawing substituents
were efficiently synthesized. Their electronic absorption spectra
were dominated by ICT absorptions in the visible region of 350−
800 nm. Ethynylanilines 1−4 exhibit strong fluorescence in green
or orange colors, whereas rapid and nonradiative decay might
result from the ICT states for 5−7. Their redox behaviors were
characterized; significantly reduced and diverse reduction
potentials were observed, as compared to the parent corannulene.
The energy required for electronic excitation and the redox
potentials were found not to alter monotonically with respect to the
number of substituents. The exact positioning of the substituents,
molecular symmetry, and the stability of the states formed (oxidized,
reduced, or excited) all make critical contributions.
The multicyanobutadiene motifs of 5−8 enhance the electron-
accepting power of corannulene systems, and their unique geo-
metries were found to provoke the steric interaction between
ortho-functionalities (for 6), transannular steric and electrostatic
interactions (for 7), and intermolecular interactions (for 5 and 8).
Optical and electrochemical properties of functionalized cor-
annulenes are thus subtly modified by such conformational in-
fluences, in addition to the effects from molecular symmetries and
the positioning of substituents.
(4-N,N-Dimethylanilinoethynyl)corannulene (1). A solution of
bromocorannulene (280 mg, 0.856 mmol), 4-ethynyl-N,N-dimethylani-
line (372 mg, 2.56 mmol), [Pd(PPh3)2Cl2] (30 mg, 0.04 mmol), PPh3
(76 mg, 0.29 mmol), and CuI (50 mg, 0.26 mmol) in piperidine (15 mL)
was heated at 100 °C for 1 d under N2. Piperidine was evaporated from
the cooled mixture, and the residue was subsequently passed through a
small SiO2 plug (CH2Cl2). The concentrated CH2Cl2 solution was
added dropwise to hexanes; the precipitate was collected and washed
one more time with hexanes to give 1 (230 mg, 70%) as a yellow solid.
1
Mp: 165−167 °C. H NMR (300 MHz, CDCl3): δ = 3.02 (s, 6 H;
NMe2), 6.76 (d, J = 8.8 Hz, 2 H; PhNMe2), 7.63 (d, J = 8.8 Hz, 2 H;
PhNMe2), 7.69−7.84 (m, 6 H; corannulene), 7.87 (d, J = 8.8 Hz, 1 H;
corannulene), 8.02 (s, 1 H; corannulene), 8.18 ppm (d, J = 8.8 Hz, 1 H;
corannulene). 13C NMR (75 MHz, CDCl3): δ = 40.3, 86.1, 95.1, 110.1,
112.0, 122.7, 126.4, 126.7, 127.16, 127.20, 127.3, 127.4, 127.5, 130.1,
130.7, 131.0, 131.1, 133.1, 134.9, 135.3, 135.7, 135.8, 136.2, 150.4 ppm
(24 out of 27 expected peaks). IR (ATR): ν = 3024 (vw), 2893 (vw),
2804 (vw), 2185 (m), 1605 (m), 1522 (m), 1357 (w), 1228 (w), 1154
(w), 1122 (w), 1098 (w), 1064 (w), 868 (m), 827 (s), 812 cm−1 (s). UV/vis
(CH2Cl2): λmax (ε) = 295 (42 300), 396 nm (21 300 M−1 cm−1). HR-ESI-
MS m/z: calcd for C30H20N+ 394.15903, found 394.15876 ([M + H]+).
1,6-Bis(4-N,N-dimethylanilinoethynyl)-2,5-dimethylcorannulene
(2). A solution of 1,6-dibromo-2,5-dimethylcorannulene (90 mg, 0.206
mmol), 4-ethynyl-N,N-dimethylaniline (209 mg, 1.44 mmol), [Pd-
(PPh3)2Cl2] (30 mg, 0.04 mmol), PPh3 (76 mg, 0.29 mmol), and CuI
(50 mg, 0.26 mmol) in piperidine (15 mL) was heated at 100 °C for 1 d
under N2. Piperidine was evaporated from the cooled mixture, and the
residue was subsequently passed through a small plug (SiO2; CH2Cl2).
The concentrated CH2Cl2 solution was added dropwise to hexanes; the
precipitate was collected and washed one more time with hexanes to give
2 (90 mg, 80%) as a yellow solid. Mp: 285−288 °C. 1H NMR (300 MHz,
CDCl3): δ = 3.00 (s, 6 H; Me), 3.03 (s, 12 H; NMe2), 6.74 (d, J = 8.8 Hz, 4
H; PhNMe2), 7.56 (d, J = 8.8 Hz, 4 H; PhNMe2), 7.81 (d, J = 8.8 Hz, 2 H;
corannulene), 7.91 (s, 2 H; corannulene), 8.07 ppm (d, J = 8.8 Hz, 2 H;
corannulene). 13C NMR (101 MHz, CDCl3): δ = 16.9, 40.3, 85.1, 99.8,
112.1, 120.4, 125.0, 126.2, 127.4, 130.5, 131.7, 132.8, 134.1, 134.3, 135.8,
138.8, 150.3 ppm (17 out of 19 expected peaks). IR (ATR): ν = 2889
(vw), 2802 (vw), 2191 (w), 1605 (s), 1519 (s), 1358 (m), 1229 (m),
1198 (m), 1064 (m), 944 (s), 815 (s), 788 cm−1 (s). UV/vis (CH2Cl2):
λmax (ε) = 300 (54 900), 328 (sh, 40 600), 391 (sh, 23 300), 430 nm (28
The adjustable absorption and fluorescence properties, curved
π-surface for supramolecular interaction and metal ion stabilization/
complexation, multiple reduction states, and the established
and efficient methodologies for derivatization, together,
make corannulenes promising candidates for electrochemically
and/or photophysically active functional materials. The 1,6-
diethynylcorannulene presented here is also a potential synthon
for corannulene-containing polymers or cyclophane-type molecular
baskets.15b
EXPERIMENTAL SECTION
■
Materials, General Methods, and Electrochemistry. See the
Supporting Information.
+
800 M−1 cm−1); HR-ESI-MS m/z: calcd for C42H33N2 565.26383;
Theoretical Calculations. The conformational analyses of the
molecular systems described in this study and property calculations were
carried out using the GAMESS19 software packages at the level of B97-D/
def2-TZVPP.20 Full geometry optimizations were performed and
uniquely characterized via second derivatives (Hessian) analysis to deter-
mine the number of imaginary frequencies (0 = minima; 1 = transition
state). Chemical shifts were calculated by referencing the CSGT29 isotropic
magnetic shielding constants (σ) to SiMe4 (σ = 31.3501 ppm, for 1H) or to
CFCl3 (σ = 144.6463 ppm, for 19F) in vacuum. Time dependent TD-DFT
calculations in CH2Cl2 were performed on the optimized, gas-phase
geometries.
found 565.26339 ([M + H]+); calcd for C42H34N22+ 283.13555, found
283.13509 ([M + 2H]2+).
1,2,5,6-Tetrakis(4-N,N-dimethylanilinoethynyl)corannulene (3).
[Pd(PPh3)4] (20 mg, 0.02 mmol) was added to a solution of 1,2,5,6-
tetrabromocorannulene (245 mg, 0.436 mmol) and N,N-dimethyl-4-[2-
(trimethylstannyl)ethynyl]aniline (810 mg, 2.62 mmol) in anhydrous
dimethoxyethane (40 mL) under N2. The mixture was heated at reflux
for 4 d. The solvent of the cooled mixture was evaporated, and the
residue was passed through a small plug (SiO2; CH2Cl2). The con-
centrated CH2Cl2 solution was added dropwise to hexanes; the pre-
cipitate was collected and washed one more time with hexanes to give 3
(280 mg, 80%) as a red solid. Mp: 202−204 °C. 1H NMR (400 MHz,
CDCl3): δ = 3.02 (s, 24 H; NMe2), 6.73 (d, J = 8.3 Hz, 8 H; PhNMe2),
7.63 (d, J = 8.2 Hz, 8 H; PhNMe2), 7.81 (d, J = 8.7 Hz, 2 H;
corannulene), 8.07 (d, J = 8.7 Hz, 2 H; corannulene), 8.12 ppm (s, 2 H;
corannulene). 13C NMR (101 MHz, CDCl3): δ = 40.3, 86.16, 86.24,
100.4, 100.5, 110.6, 112.0, 124.4, 124.5, 126.5, 126.8, 127.6, 131.0, 131.2,
133.1, 133.8, 134.6, 135.5, 150.3 ppm (19 out of 25 expected peaks). IR
(ATR): ν = 2888 (vw), 2856 (vw), 2799 (vw), 2173 (m), 1602 (s), 1519
(s), 1442 (m), 1353 (s), 1161 (s), 944 (m), 810 cm−1 (s). UV/vis
(CH2Cl2): λmax (ε) = 306 (97 700), 327 (sh, 78 300), 418 (75 600), 469
X-ray Analysis of 8. The scattering intensity data were collected
under MoKa radiation (λ = 0.71073 Å). Cell dimensions were obtained
based on 4040 reflections above 20 σ(I) (qmax = 25.16°). The structure
was solved by direct methods with SHELXS and refined with OLEX2
and SHELXL.30 All non-hydrogen atoms were refined anisotropically,
H-atoms isotropically with some restraints by full matrix least-squares
using experimental weights w = 1/[s2(Fo)2 + (0.07000 P)2], where P =
(Fo + 2 Fc2)/3. One corannulene moiety is partly disordered. No
2
attempt was made to refine multiple atom positions.
Single crystals were obtained by slow diffusion of pentane into the
CHCl3 solution of 8 at 4 °C: C41H24F3N2·CHCl3, Mr = 753.00, crystal
dimensions 0.04 × 0.11 × 0.19 mm, triclinic space group P1, Z = 4, a =
11.817(2) Å, b = 14.954(2) Å, c = 20.549(3) Å, α = 70.961(5)°, β =
84.168(5)°, γ = 88.955(5)°, V = 3414.5(8) Å3, D = 1.430 g/cm3 at
100(2) K. Number of measured and unique reflections 39740 and
11961, respectively (Rint = 8.06%, Rsig = 12.26%). Final R(F) = 6.89%,
wR(F2) = 13.72% for 1119 parameters and 6279 reflections with I > 2σ(I)
+
nm (sh, 41 700 M−1 cm−1). HR-ESI-MS m/z: calcd for C60H47N4
̅
823.37952, found 823.37911 ([M + H]+).
1,3,5,7,9-Pentakis(4-N,N-dimethylanilinoethynyl)corannulene (4).
The mixture of 1,3,5,7,9-pentachlorocorannulene (550 mg, 1.3 mmol),
Pd(OAc)2 (147 mg, 0.65 mmol), IPr·HCl (556 mg, 1.3 mmol), and
potassium tert-butoxide (146 mg, 1.3 mmol) in anhydrous dimethoxyethane
K
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The Journal of Organic Chemistry
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(50 mL) was stirred under N2 at rt for 1 h. N,N-Dimethyl-4-[2-
(trimethylstannyl)ethynyl]aniline (5 g, 15.71 mmol) was added to the
solution and the mixture heated at reflux for 4 d. The solvent was evap-
orated and the residue purified by flash chromatography (FC) (SiO2;
CH2Cl2) to give compound 4 as an orange solid (380 mg, 30%). Mp:
310 °C dec. 1H NMR (400 MHz, CDCl3): δ = 3.03 (s, 30 H; NMe2),
6.73 (d, J = 8.9 Hz, 10 H; PhNMe2), 7.61 (d, J = 8.9 Hz, 10 H; PhNMe2),
8.23 ppm (s, 5 H; corannulene). 13C NMR (101 MHz, CDCl3): δ = 40.4,
86.1, 95.8, 110.2, 112.1, 122.9, 129.7, 131.3, 133.3, 134.4, 150.5 ppm. IR
(ATR): ν = 2887 (vw), 2855 (vw), 2799 (vw), 2176 (m), 1602 (s), 1519
(s), 1442 (m), 1352 (s), 1160 (s), 944 (m), 809 cm−1 (s). UV/vis
(CH2Cl2): λmax (ε) = 313 (114 100), 420 nm (86 300 M−1 cm−1). HR-ESI-
MS m/z: calcd for C70H56N5+ 966.45302, found 966.45278 ([M + H]+);
calcd for C70H57N52+ 483.73015, found 483.72989 ([M + 2H]2+).
[3-[4-(Dimethylamino)phenyl]buta-1,3-diene-1,1,4,4-tetracarbo-
nitrile-2-yl]corannulene (5). Acetylene 1 (23 mg, 0.058 mmol) and
TCNE (23 mg, 0.18 mmol) were dissolved in (CHCl2)2 (2 mL). The
mixture was stirred at 25 °C for 1 h. The solvent was removed, and
the residue was purified by FC (SiO2; CH2Cl2) to give 5 as a red solid
(29 mg, 96%). Mp: 190 °C dec. 1H NMR (400 MHz, CDCl3, 298 K):
δ = 3.16 (s, 6 H; NMe2), 6.75 (d, J = 9.3 Hz, 2 H; PhNMe2), 7.75 (d, J =
8.8 Hz, 1 H; corannulene), 7.79−7.94 (m, 8 H), 7.97 (d, J = 8.9 Hz, 1 H;
corannulene), 8.06 ppm (d, J = 8.9 Hz, 1 H; corannulene). 13C NMR
(100 MHz, CDCl3, 298 K): δ = 40.2, 74.9, 89.8, 111.7, 112.5, 112.8,
113.5, 114.5, 119.1, 125.8, 126.3, 127.1, 127.5, 128.3, 128.5, 129.1, 129.3,
131.5, 131.6, 131.8, 132.8, 133.7, 134.8, 135.7, 135.7, 137.1, 138.3, 154.5,
164.2, 167.3 ppm (30 out of 33 expected peaks). IR (ATR): ν = 3029
(vw), 2923 (vw), 2862 (vw), 2217 (m), 1604 (m), 1492 (m), 1385 (m),
1174 (m), 832 (m), 820 cm−1 (m). UV/vis (CH2Cl2): λmax (ε) = 429
(26 100), 284 nm (28 100 M−1 cm−1). HR-ESI-MS m/z: calcd for
C36H19N5Na+ 544.15327, found 544.15359 ([M + Na]+).
2,5-Dimethyl-1,6-bis[3-[4-(dimethylamino)phenyl]buta-1,3-
diene-1,1,4,4-tetracarbonitrile-2-yl]corannulene (6). Diacetylene 2
(25 mg, 0.044 mmol) and TCNE (28 mg, 0.22 mmol) were dissolved in
(CHCl2)2 (2.5 mL). The mixture was stirred at 25 °C for 2.5 h. The
solvent was removed and the residue purified by FC (SiO2; CH2Cl2/
CH3CN 1:0 → 40:1) to give 6 as a black solid with green luster (34 mg,
94%). Mp > 400 °C. 1H NMR (500 MHz, CD2Cl2, 315 K): for isomer a,
δ = 3.06 (s, 6 H; Me), 3.13 (s, 12 H; NMe2), 6.77 (d, J = 8.5 Hz, 4 H;
PhNMe2), 7.70 (d, J = 8.5 Hz, 4 H; PhNMe2), 7.75 (d, J = 4 Hz, 2 H;
corannulene), 7.87 (d, J = 4 Hz, 2 H; corannulene), 8.09 ppm (s, 2 H;
corannulene); for isomer b, δ = 3.06 (s, 6 H; Me), 3.12 (s, 12 H; NMe2),
6.77 (d, J = 8.5 Hz, 4 H; PhNMe2), 7.70 (d, J = 8.5 Hz, 4 H; PhNMe2),
7.73 (d, J = 4 Hz, 2 H; corannulene), 7.89 (d, J = 4 Hz, 2 H;
corannulene), 8.08 ppm (s, 2 H; corannulene); 13C NMR (125 MHz,
CD2Cl2, 300 K): for both isomers a and b, δ = 18.7, 40.59, 40.60, 80.2,
80.8, 97.2, 97.3, 111.6, 112.66, 112.71, 113.0, 113.2, 113.7, 113.9, 115.3,
115.4, 120.6, 120.8, 125.8, 125.9, 127.10, 127.13, 128.9, 129.0, 129.4,
129.5, 130.7, 130.9, 131.19, 131.22, 131.3, 133.7, 133.8, 135.1, 135.2,
135.7, 135.8, 135.99, 136.04, 142.3, 142.7, 155.0, 155.1, 165.1, 165.2,
167.7, 167.8 ppm (47 out of 50 expected peaks). IR (ATR): ν = 2919
(vw), 2859 (vw), 2809 (vw), 2211 (m), 1599 (m), 1481 (m), 1376 (m),
1169 (m), 817 cm−1 (m). UV/vis (CH2Cl2): λmax (ε) = 600 (15600),
396 (30700), 301 nm (42200 M−1 cm−1). HR-ESI-MS m/z: calcd for
C54H32N10Na+ 843.27036, found 843.27025 ([M + Na]+).
1,3,5,7,9-Pentakis[3-[4-(dimethylamino)phenyl]buta-1,3-diene-
1,1,4,4-tetracarbonitrile-2-yl]corannulene (7). Pentaacetylene 4 (30 mg,
0.031 mmol) and TCNE (48 mg, 0.375 mmol) were dissolved in
(CHCl2)2 (4 mL). The mixture was stirred at 25 °C for 16 h. The solvent
was removed and the residue purified by FC (SiO2; CH2Cl2/CH3CN
40:1 → 15:1) to give 7 as a black solid with green luster (48 mg, 96%).
Mp > 400 °C. 1H NMR (500 MHz, (CDCl2)2, 410 K): δ = 3.22 (s, 30 H;
NMe2), 6.93 (d, J = 9.3 Hz, 10 H; PhNMe2), 7.83 (s, br, 5 H;
corannulene), 8.07 ppm (d, br, 10 H; PhNMe2). 13C NMR (125 MHz,
(CDCl2)2, 410 K): δ = 39.6, 75.5, 91.5, 110.6, 112.5, 113.0, 113.7, 117.6,
126.6, 133.0, 133.1, 134.6, 136.5, 154.9, 160.1, 164.2 ppm (16 out of 17
expected peaks). IR (ATR): ν = 2920 (vw), 2864 (vw), 2807 (vw), 2214
(m), 1603 (m), 1492 (m), 1386 (m), 1173 (m), 820 cm−1 (m); UV/vis
(CH2Cl2): λmax (ε) = 600 (sh.), 468 (199 800), 363 nm (112 500 M−1
cm−1). HR-ESI-MS m/z: calcd for C100H55N25Na+ 1628.49645, found
1628.49631 ([M + Na]+). Anal. Calcd for C100H55N25: C, 74.76; H, 3.45;
N, 21.79. Found: C, 74.63; H, 3.75; N, 21.74.
(E)-2-(2-(Corannulenyl)-1-(4-(dimethylamino)phenyl)-3-(4-
(trifluoromethyl)phenyl)allylidene)malononitrile (8). Acetylene 1 (23 mg,
0.058 mmol) and 2-[4-(trifluoromethyl)benzylidene]malononitrile
(40 mg, 0.18 mmol) were dissolved in (CHCl2)2 (2 mL). The mixture
was stirred at 120 °C for 2 d. The solvent was removed and the residue
purified by FC (SiO2; CH2Cl2) to give 8 as an orange solid (32 mg,
89%). Mp: 230−232 °C. 1H NMR (500 MHz, CD2Cl2, 298 K): δ = 2.86
(s, 6 H; NMe2), 6.50 (d, J = 9.3 Hz, 2 H; PhNMe2), 7.40 (d, J = 8.4 Hz, 2
H; PhCF3), 7.48 (d, J = 8.4 Hz, 2 H; PhCF3), 7.48 (s, 1 H, vinyl), 7.63 (d,
J = 9.3 Hz, 2 H; PhNMe2), 7.65−7.71 (m, 4 H; corannulene), 7.74−7.84
ppm (m, 5 H; corannulene). 13C NMR (125 MHz, CD2Cl2, 298 K): δ =
40.5, 78.2, 112.0, 115.7, 116.1, 121.1, 124.5 (q, J = 272.2 Hz, CF3), 125.8
(q, J = 3.7 Hz, Cipso-CF3), 126.2, 127.3, 127.6, 127.8, 128.0, 128.1,
128.15, 128.21, 128.7, 129.8, 130.5, 130.7 (q, J = 32.5 Hz, Cortho-CF3),
131.2, 131.3, 131.7, 132.0, 132.8, 135.6, 135.7, 135.96, 136.03, 136.2,
136.7, 138.7, 139.1, 139.7, 153.4, 175.3 ppm. 19F NMR (470 MHz,
CDCl3, 303 K): δ = −63.35 ppm (s, 3 F). IR (ATR): ν = 3029 (vw),
2918 (vw), 2857 (vw), 2216 (m), 1600 (m), 1497 (m), 1376 (m), 1320
(m), 1170 (m), 833 (m), 822 cm−1 (m). UV/vis (CH2Cl2): λmax (ε) =
455 (21000), 297 nm (39500 M−1 cm−1). HR-ESI-MS m/z: calcd for
C41H25F3N3+ 616.19951, found 616.19898 ([M + H]+).
ASSOCIATED CONTENT
■
S
* Supporting Information
Torsion angles of buta-1,3-dienes retrieved from Cambridge
Structural Database (CSD), 1H NMR of 8 at variable
1
concentrations, H VT-NMR of 5, emission spectra of 1−4,
cyclic voltammetry of 7, computational details, general and
electrochemistry methods, and NMR spectra of new com-
pounds. This material is available free of charge via the Internet at
http://pubs.acs.org. The crystal structure data for 8 (CCDC
901534) is available from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
AUTHOR INFORMATION
Corresponding Author
*E-mail: (K.K.B.) kimb@oci.uzh.ch, (J.S.S.) jss@oci.uzh.ch,
(F.D.) diederich@org.chem.ethz.ch.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by the ERC Advanced Grant No.
246637 (OPTELOMAC) and the Swiss National Science
■
Foundation. We thank PD Dr. H. P. Luthi (ETH) for valuable
̈
discussions about the properties of 2,3-diphenylbutadienes and Prof.
B. Jaun (ETH) and Dr. B. Bernet (ETH) for valuable discussions
about the conformations of compound 6. Y.-L.W. is grateful for a
fellowship from the Stipendienfonds der Schweizerischen Chem-
ischen Industrie (SSCI). M.C.S. appreciates financial support from
the Swiss National Science Foundation (Ambizione PZ00P2-
126615).
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M
dx.doi.org/10.1021/jo302217n | J. Org. Chem. XXXX, XXX, XXX−XXX