Electron-poor N-substituted imide-fused corannulenes

Article abstract of DOI:10.1039/c2cc32643d

N-Substituted imide-fused corannulenes can be generated from the corresponding tetramethylfluoranthenes. Syntheses, crystal structure and electronic properties are reported. The solid state structure of the pentafluorophenyl derivative shows nearly perfect π-stacking in a convex-concave fashion and is expected to possess useful electronic properties.

Full text of DOI:10.1039/c2cc32643d

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COMMUNICATION
Electron-poor N-substituted imide-fused corannulenesw
Bernd M. Schmidt, Berit Topolinski, Philipp Roesch and Dieter Lentz*
Received 13th April 2012, Accepted 4th May 2012
DOI: 10.1039/c2cc32643d
N-Substituted imide-fused corannulenes can be generated from
the corresponding tetramethylfluoranthenes. Syntheses, crystal
structure and electronic properties are reported. The solid state
structure of the pentafluorophenyl derivative shows nearly perfect
p-stacking in a convex–concave fashion and is expected to possess
useful electronic properties.
been used to change the intermolecular alignment. The group of
Petrukhina showed that the ‘‘hub’’ of corannulene can be
reacted with electrophiles, leading to bowl-shaped carbocations
bearing the counteranion partially.15
Corannulene-bowl based systems offer notionally a large
p–p overlap if aligned in a convex–concave stacked fashion,
comparable to or surpassing the overlapping surface of PBIs.
A dense arrangement in the solid state could prevent the
intrusion of oxygen and moisture into the channel region
and might be important in the design of air-stable n-channel
type semiconductors.
Intensive attention has been paid to the development of organic
semiconducting materials for the fabrication of devices such as
organic thin-film transistors (OTFTs), organic photovoltaic
cells (OPVs) as well as light-emitting diodes. Oligothiophenes,1
fullerenes,2 porphyrins3 and especially (core-substituted) perylene
((C)PBI) and naphthalene bisimide ((C)NBI) dyes gained much
popularity during the last few years.4 In particular electron
deficient PBIs are discussed as promising air-stable organic
n-type semiconductors in thin film transistors. Curved polycyclic
aromatic hydrocarbons are less studied, Seki and co-workers
investigated the anisotropic electron-transport properties of the
needle-like crystals of sumanene in 2009 and showed that high
electron mobility can be examined by time-resolved microwave
conductivity methods.5 Both sumanene (C21H21)6 and the
shallower congener corannulene (C20H10) are non-planar subunits
(buckybowls) of fullerenes. The latter buckybowl has been the
subject of extensive theoretical and experimental research7 and
is now available in the kilogram scale.8
Herein we report the synthesis of corannulene-fused imides, a
comparison with the fluoranthene precursor molecules as well
as the isolation of by-products (Scheme 1). Solvent-free single-
crystals of 1a, 2 and 3a could be obtained and the packing
motifs were studied by X-ray crystal structure analysis.z
N-Substituted maleimides can be easily prepared bearing
various substituents.16 Because of the very low nucleophilicity of
(per)fluorinated amines, a late introduction is unfavorable. In
combination with the method published by Siegel and co-workers17
as well as other groups,18 the corresponding fluoranthenes can
Recently, we investigated some intrinsic molecular properties of
sumanene and corannulene, in particular their charge density
distribution.9 The crystal structure of sumanene is characterized
by 1D columnar p-stacking in a convex–concave fashion,10 whereas
the solid state structure of unsubstituted corannulene is dominated
by C–Hꢀ ꢀ ꢀp interactions.11 Nevertheless, depending on the
substituent attached, different architectures can be formed in the
solid state and have been investigated crystallographically. Siegel
and co-workers showed for example that tetrabromocorannulene
and di-, tetra- and pentasubstituted aryl-alkynylcorannulenes
form columnar structures in the solid state.12 Furthermore
metal–organic assemblies like the binary complex of corannulene
and a trimercury complex13 as well as a Cu(111)14 surface have
Freie Universitat Berlin, Fabeckstrasse 34/36, D-14195, Berlin,
¨
Germany. E-mail: dlentz@zedat.fu-berlin.de;
Fax: +49-30-838-52590; Tel: +49-30-838-52695
w Electronic supplementary information (ESI) available: Syntheses,
X-ray crystallographic details and additional data. CCDC
876633–876635. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2cc32643d
Scheme 1 (a) 4.8 eq. pentan-3-one, 7.5 eq. KOH, MeOH, 1 h rt; then
1.0 eq. of the corresponding maleimide, nitrobenzene, 48 h 180 1C;
(b) 4.8 eq. pentan-3-one, 7.5 eq. KOH, MeOH, 1 h rt; then 1.0 eq.
1-(perfluorophenyl)-1H-pyrrole-2,5-dione, acetic anhydride, 48
h
140 1C; (c) 12.0 eq. NBS, 3.0 mol% DBPO, CCl4, hn, 30 h 80 1C;
then 8.8 eq. nickel powder, DMF, 8 h, 80 1C.
c
6520 Chem. Commun., 2012, 48, 6520–6522
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Fig. 1 Space-filling model of 2 as represented by the asymmetric unit,
created with ORTEP21 and rendered with POV-Ray.22
Fig. 2 ORTEP21 representation (space-filling model) of the crystal
packing in 1a, rendered with POV-Ray.22 The excerpt shows the dense
head-to-tail arrangement which proceeds in infinite columns along the
crystallographic b axis.
be prepared from 3,8-dimethylacenaphthene-quinone.7b The
fluoranthene skeleton is thus constructed by condensation
with pentan-3-one and subsequent Diels–Alder-reaction with
the corresponding maleimides followed by decarbonylation.
In this particular case however, the usage of acetic anhydride
enables the formation of the adduct 2 with a central
bicyclo[2.2.2]oct-2-ene unit, which is obtained as the major
product. It is formed either by reaction of an exo-dimer
from the condensation reaction or by decarbonylation of the
exo-adduct and subsequent reaction with a second equivalent
of maleimide.19 Due to the molecular strain and steric
repulsion,20 the pentafluorophenyl group gives a distinct set
of signals identifiable as the first order ABCDE-type 19F-NMR
spectrum at room temperature (see ESIw). The structure was
ultimately assigned by single-crystal X-ray diffraction and is
shown in Fig. 1.
If the reaction is run in nitrobenzene at 180 1C this adduct is
not observed and the desired product 1a and 1b can be isolated
in 43% and 45% yield, respectively. The steric hindrance in 2
and 1a is expected to be similar, but now a fast C6F5 rotation is
present in 1a at room temperature, whereas no unusual
characteristics are found for 1b. The higher symmetry of 1a
in comparison to 2 now results in a AA0BB0C-type 19F-NMR
spectrum. The solid state structure shows a moderately canted
alignment of the perfluorinated phenyl group in 1a, which
opposes the electron rich lower part (‘‘naphthalene-part’’) of
an adjacent molecule in the twisted stack, see Fig. 2. This
dense head-to-tail crystal packing is supported by C–Hꢀ ꢀ ꢀO
bonding of the carbonyl groups of approximately 2.48 A to the
opposing molecule and furthermore by relevant C–Fꢀ ꢀ ꢀH–C
contacts23 of 2.55 A to the naphthalene-part of the next
column (see ESIw for additional representations).
Wohl–Ziegler reaction and subsequent nickel-mediated
intramolecular coupling involving complete debromination of
the product24 yield the corresponding corannulenes 3a and 3b,
likewise. Single crystals of sufficient quality were obtained by
slow evaporation of a chloroform solution. The bowls of 3a are
aligned into 1D parallel columns (see Fig. 3), but unlike for
example indenocorannulenes,25 in a staggered conformation.
The bowl direction of the same stack is the same, whereas
adjacent columns have an opposite direction. The extended
p-system results surprisingly in a shallower bowl-depth of
about 0.826 A, with the bowls being slightly tilted by 101.
This alignment is facilitated by C–Hꢀ ꢀ ꢀF–C (2.55–2.78 A)
Fig. 3 Space-filling model of the crystal packing in 3a, rendered with
POV-Ray. The concave–convex bowl-in-bowl stacking is apparent, while
the molecule’s orientation and side chains alternate by roughly 1801.
interactions between the anti-parallelly aligned neighboring stacks.
The pentafluorophenyl ring is more canted in comparison to 1a,
with an angle of 761 to the imide ring, probably to maximize
C–Fꢀ ꢀ ꢀH–C contacts, and lacks the very close and flexible
p-electron rich surface of 1a. The 19F-NMR spectrum at room
temperature suggests again free rotation of the pentafluoro-
phenyl ring of 3a and the alkyl chain of 3b. One spoke bond
and one flank bond are the shortest (C016–C031) and longest
(C019–C034) C–C-bonds of 1.3761(1) and 1.4453(1) A in the
corannulene-bowl, respectively. Both are marginally longer
than in the parent corannulene molecule11b as a consequence
of the decreased curvature and similar to the ones of published
PBIs.4e Within the convex–concave stacks no pitch or roll angle
is found, resulting in no transverse shifting. The intermolecular
bowl distance calculated between three molecules along the stack
is 7.34 A, which leads to an average bowl-to-bowl distance of
3.67 A, regardless of the small slipping angle. This difference is
smaller than previously reported for tetra- and penta-substituted
corannulenes, which may result from the steric demand of the
arylalkynyl groups attached.12a
Cyclic voltammetry on a DCM solution reveals only moderate
lowering of the LUMO levels of the fluoranthenes,26 probably
c
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Chem. Commun., 2012, 48, 6520–6522 6521

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because of the electron-donating methyl groups attached for
the following ring-closure. The imide-fused corannulenes, 3a
and 3b, show satisfactory LUMO energies of 3.4 eV for both
compounds, especially when considering that only one section
of the molecule is functionalized and no further bay substituents
are present. The LUMO barrier is comparable to the one of
unsubstituted PBI (3.8 eV)27 and could be significantly lowered
upon introduction of electron-withdrawing cyano substituents
into the corannulene rim. The first reduction wave in dichloro-
methane solution to the monoanion is expected to take place at
the extended node of the molecules. Measurements in THF
show a well separated second reversible reduction wave to the
dianion.
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Imide-fused corannulenes can be generated easily by
using cheap nickel powder, with aromatic or aliphatic imide
substituents at the node of the conjugated system. The new
class of corannulene compounds is promising for n-type
semiconductor applications, because of their non-covalent
interactions in the solid state. The twisted alignment of the bowls
by nearly 1801 provides additional shielding by the separated side
chain. The large p–p overlap from the convex–concave stacked
structure is highly favourable for charge carrier mobility. We will
further investigate the optical and solid state properties of this
new scaffold in due course.
Support from the Graduate School GRK 1582 is gratefully
acknowledged. We thank Dr Holger Ott, Bruker-AXS, for the
data collection of compound 3a and Dr Shuhei Higashibayashi
for valuable discussion.
Notes and references
z Crystal data for 1a: C28H16F5NO2, monoclinic, a = 16.691(5) A,
b = 7.731(2) A, c = 16.655(5) A, a = 90.001, b = 107.022(6)1, g =
90.001, V = 2055.0(11) A3, T = 133(2) K, space group P2(1)/c, Z = 4,
15 784 reflections measured, 3602 independent reflections (Rint
=
0.0566). The final R1 value was 0.0409 (I > 2s(I)). The final wR(F2)
value was 0.1078 (I > 2s(I)). The final R1 value was 0.0725 (all data).
The final wR(F2) value was 0.1324 (all data). The goodness of fit on F2
was 1.038. Crystal data for 2: C38H20F10N2O4, monoclinic, a =
12.407(4) A, b = 27.476(8) A, c = 9.607(3) A, a = 90.001, b =
110.687(6)1, g = 90.001, V = 3063.9(15) A3, T = 133(2) K, space
group Cc, Z = 4, 17 831 reflections measured, 3125 independent
reflections (Rint = 0.0565). The final R1 value was 0.0463 (I >
2s(I)). The final wR(F2) value was 0.1139 (I > 2s(I)). The final
R1 value was 0.0648 (all data). The final wR(F2) value was 0.1235
(all data). The goodness of fit on F2 was 1.061. Crystal data for 3a:
C28H8F5NO2, monoclinic, a = 16.4353(5) A, b = 7.3459(2) A, c =
16.4520(4) A, a = 90.001, b = 108.036(2)1, g = 90.001, V =
1888.68(9) A3, T = 100(2) K, space group P21/n, Z = 4, 17 814
reflections measured, 3883 independent reflections (Rint = 0.0530).
The final R1 value was 0.0373 (I > 2s(I)). The final wR(F2) value was
0.0883 (I > 2s(I)). The final R1 value was 0.0535 (all data). The final
wR(F2) value was 0.0961 (all data). The goodness of fit on F2 was
1.019.
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