π-Extended Diaza[7]helicenes by Hybridization of Naphthalene Diimides and Hexa-peri-hexabenzocoronenes

Article abstract of DOI:10.1002/chem.202003402

The synthesis of an unprecedented, π-extended hexabenzocorene (HBC)-based diaza[7]helicene is presented. The target compound was synthesized by an ortho-fusion of two naphthalene diimide (NDI) units to a HBC-skeleton. A combination of Diels–Alder and Scho

Full text of DOI:10.1002/chem.202003402

Accepted Article
Accepted Article
Title: π-Extended Diaza[7]helicenes by Hybridization of Naphthalene-
imides and Hexa-peri-hexabenzocoronenes
Authors: Andreas Hirsch, Carolin Dusold, dmitry Sharapa, and Frank
Hampel
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To be cited as: Chem. Eur. J. 10.1002/chem.202003402
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01/2020

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π-Extended Diaza[7]helicenes by Hybridization of Naphthalene-
imides and Hexa-peri-hexabenzocoronenes
Carolin Dusold,[a] Dmitry I. Sharapa,[b] Frank Hampel[a] and Andreas Hirsch*[a]
[a]
[b]
Carolin Dusold, Dr. F. Hampel, Prof. Dr. Andreas Hirsch
Department of Chemistry and Pharmacy
Friedrich-Alexander University Erlangen-Nürnberg
Nikolaus-Fiebiger-Straße 10, 91058 Erlangen, Germany
E-mail: andreas.hirsch@fau.de
Dr. Dmitry I. Sharapa
Institute of Catalysis Research and Technology
Karlsruhe Institute of Technology
Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
Supporting information for this article is given via a link at the end of the document.
Abstract: The synthesis of an unprecedented, π-extended
hexabenzocorene(HBC)-based diaza[7]helicene 3 is presented. The
target compound was synthesised by an ortho-fusion of two
naphthalenediimide (NDI) units to a HBC-skeleton. A combination of
Diels-Alder and Scholl-type-oxidation reactions involving a symmetric
di-NDI-tolane precursor were crucial for the very selective formation
of the helical superstructure 3 via the hexa-phenyl-benzene (HPB)
derivative 2. The formation of the diaza[7]helicene moiety in the final
Scholl oxidation is favoured, affording the symmetric π-extended
helicene 3 as the major product as a pair of enantiomers. The
separation of the enantiomers was successfully accomplished by
HPLC involving a chiral stationary phase. The absolute configuration
of the enantiomers was assigned by comparison of the circular
dichroism spectra with quantum mechanical calculations.
of progress has been made on the lateral extension of
helicenes,[10a,12] including π-extended helicenes based on
perylenediimide,[13] pyrene[14] and hexa-peri-hexabenzocoronene
(HBC).[15] Especially the use of HBC subunits enables the design
of new “superhelicenes”[15a], representing new proto-types in the
field of chiral nanographenes. Such helically twisted graphenes
can be considered as promising candidates in the field of chiral
electronics,[16] not only due to their outstanding chiroptical
properties, but also due to an enhanced π−π stacking relative to
the parent helicene, which is crucial to achieve efficient charge
carrier transportation,[17] and an improved solubility compared to
their planar analogues.[18] In this contribution, we will expand the
concept of HBC-based helicenes by introducing additional
aromatic subunits to further extend the conjugated π-system. We
have selected naphthalenediimides (NDIs) as promising
candidates since they feature desirable chemical and
(opto)electronical properties themselves.[19] As a consequence,
we accomplished an ortho-fusion of two NDI units to an HBC-
skeleton, generating an unprecedented, π-extended HBC-based
heterohelicene. The high degree of pre-organization of the
diaza[7]helicene subunit results in the formation of a chiral
compound with two NDI arms lying on top of each other (Figure
1).
Introduction
The development of nonplanar PAHs is currently an emerging
field in synthetic organic chemistry.[1] Among the most important
starting points for this progress is the discovery of the parent
helicenes.[2] Since then, research groups all over the world further
elaborated the investigation and understanding of helicene
chemistry, with great success.[3] Outstanding chiroptical
properties,[4] such as inducing the emission of circularly polarized
light, large optical rotation values and pronounced circular
dichroism bands make them very attractive for applications in
nonlinear optics,[5] asymmetric synthesis,[6] chiroptical switches,[7]
and organic semiconductors[8]. Next to the classical
carbohelicenes, heterohelicenes, which include one or more
heteroaromatic rings such as pyridine, pyrrole, and thiophene are
receiving growing interest and it was realized that their property
combinations can even surpass those of the conventional all-
carbon analogues.[9] Furthermore, the π-extension of the basic
helicene skeleton is of considerable interest since it can notably
tune optical, electronical and supramolecular properties.[10]
Elongation of the spiral arrangement of the conjugated π-system
represents the most common way to prepare higher helicene
derivatives.[11] In contrast to that, the expansion of the conjugated
system on the outer rim is still a challenging issue. Recently, a lot
Figure 1. General structure of a chiral, π-extended diaza[7]helicene based on
HBC and NDI.
This helical superstructure combines not only the advantages of
lateral π-extended helicenes with those of azahelicenes, at the
1
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same time, the fusion of two NDI arms enables the generation of
an extensive conjugated π-surface all over the molecule.
Photophysical investigations were carried out and the
corresponding enantiomers were separated in order to determine
their chiroptical properties.
The first step was the palladium-catalysed Sonogashira cross-
coupling reaction between boc-protected alkyne 4 and 4-bromo-
1,2-naphthaleneimidebenzimidazole 5. The required boc-
protected alkyne building block 4 was prepared according to
literature procedures[20], starting with the protection of diamino-
bromobenzene 11 to enable the successful performance of the
subsequent Sonogashira coupling reactions, followed by
deprotection of the TMS-group (see SI S1 for synthetic details).
The second building block NDI-compound 5 was prepared via
Results and Discussion
condensation of naphthalenemonoimide
bromobenzene 11 (Scheme 3). During this reaction, two
constitutional isomers are formed, the 4-bromo-1,2-
8
with diamino-
Our strategy to synthesise the π-extended HBC-based
diaza[7]helicene HBC 3 relies on the combination of standard
Diels-Alder and Scholl-type reactions (Scheme 1).
naphthaleneimidebenzimidazole
5 as well as 5-bromo-1,2-
naphthaleneimidebenzimidazole 12. The two compounds can
easily be separated by column chromatography, isolating the first
yellow fraction in 42% yield, and the second orange fraction in
36% yield. Although the NMR- and optical spectra of both
compounds differ significantly as shown in Scheme 3 (for further
information see SI S2), clear structural assignment was not
possible at this point.
Scheme 1. Synthetic concept to generate 7-helical HBC 3.
The key intermediate of our synthetic concept is the tolane
derivative 1 containing two symmetrically fused NDI units. The
symmetric constitution of the corresponding di-NDI-hexa-phenyl-
benzene (HPB) 2 is crucial to generate the desired 7-helical
moiety in the final HBC. The synthetic sequence started with the
preparation of the symmetric precursor 1 as illustrated in Scheme
2.
Scheme 3. Synthesis of the naphthaleneimidebenzimidazole isomers
5
(orange) and 12 (black) and their 1H NMR- and UV-vis absorption spectra. a)
Imidazole, 160 °C, 3 h, yield 36% (5) and 42% (12).
However, crystals of the orange fraction suitable for X-ray
diffraction analysis were grown by slow evaporation of a solution
of the compound in DCM at room temperature. Small needles
were obtained, and the quality of the X-ray analysis was sufficient
for unambiguous structure assignment (see SI S2 for further
information). Thus, a secure assignment of the orange fraction to
the 4-bromo-1,2-naphthaleneimidebenzimidazole 5 isomer is
possible as depicted in Figure 2.
Scheme 2. Synthesis of symmetric and unsymmetric di-NDI HPBs 2 and 10. a)
PdCl2(PPh3)2, CuI, Et3N, toluene, 80 °C, 18 h, yield 82% b) TFA, DCM, rt, 3 h
c) DMF, 140 °C, 18 h, yield 56% d) tetrakis-(tert-butyl)tetracyclone, toluene,
220 °C, 24 h, yield 29% (2) and 30% (10).
Figure 2. Crystal structure of 4-bromo-1,2-naphthaleneimidebenzimidazole 5.
2
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The boc-protected NDI-tolane 6 synthesised by Sonogashira
reaction was obtained in a pure form in good yields of 82%
(Scheme 2). The boc-protecting group was removed using TFA[21]
to afford the free di-amino functionality. Due to the sensitivity
towards oxidation of such aminotolane compounds,[22] the crude
product 7 was used directly in the next condensation reaction with
HPLC-separation resulted in exclusive isolation of fraction 3,
which was analysed by NMR spectroscopy. The important
regions of the proton 1H-NMR spectrum are displayed in Figure 3.
The spectrum reveals a defined set of signals, already indicating
the existence of one pure compound instead of a mixture of
isomers. In the aromatic area five signals for the protons of the
HBC are present between 9.32 – 10.03 ppm and four signals
between 8.19 – 9.06 ppm that can be assigned to the NDI
hydrogen atoms. Moreover, only one resonance can be found at
4.92 ppm (N-CH) and the protons of the tert-butyl groups of the
HBC-unit appear as only two singlets at 1.85 and 1.80 ppm. The
appearance of only one set of resonances suggest that the
isolated compound must be symmetrical, which is consistent with
either the desired 7-helical HBC 3 or HBC 13.
naphthalenemonoimide
8
without further purification or
characterisation to generate di-NDI-tolane precursors 1 and 9
with an overall yield of 56%. The new fused naphthalene-
benzimidazole moiety is once again formed as two constitutional
isomers. One the one hand, a symmetrical compound 1 is formed
in which the introduced naphthalenemonoimide is connected to
the tolane in a binding pattern similar to the already existing
naphthalene-benzimidazole unit, highlighted in blue in Scheme 2.
On the other hand, an asymmetric tolane is formed when the
naphthalenemonoimide is fused to the tolane in an alternative
binding pattern, highlighted in red. The asymmetric tolane 9 is not
a suitable precursor for the targeted π-extended HBC-based
diaza[7]helicene HBC 3, since planarization of the corresponding
unsymmetrical HPB 10 would not result in the desired 7-helical
structure in the end. The symmetrical di-NDI tolane 1 with both
NDI units fused to it through the blue binding pattern is essential
for the formation of the helical superstructure in the final
compound. Unfortunately, isomers 1 and 9 could not be separated
at this stage. Hence, the fused di-NDI-tolane was reacted as a
mixture of isomers in the subsequent Diels-Alder reaction with
tetrakis-(tert-butyl)tetracyclone[15a,23] at 220 °C to generate the
corresponding di-NDI HPBs 2 and 10. At this stage the two
isomers could easily be separated by column chromatography in
pure form. Symmetrical HPB 2 was obtained in 29% and
unsymmetrical HPB 10 in 30% yield. For the final transformation
of di-NDI HPB 2 Scholl oxidation conditions using FeCl3 were
applied. After 18 h, complete conversation of the starting material
was observed, and new dark-green compounds were traced by
TLC. The crude mixture was separated by HPLC (see SI S3).
Next to the expected molecules 3, 13 and 14 several minor side-
products were detected, in particular chlorinated side-products as
well as compounds with one bond of the HBC core still not closed.
However, the major fraction of the reaction was identified as the
product by mass spectrometry. In Scheme 4, the structure of the
three constitutional isomers formed during the final Scholl
oxidation, namely, the two symmetrical isomers 13 and 3 and the
unsymmetrical isomer 14 is depicted.
Figure 3. Important regions of the 1H-NMR spectrum of 7-helical HBC 3.
For an unambiguous structural assignment, additional 1D- and
2D-NMR experiments were performed (see SI S4). The 1H-
COSY-NMR spectrum exhibits the coupling of the aromatic
hydrogen atoms, except for the HBC protons at 10.03 ppm, which
features no such correlation. This characteristic is in principle still
compatible for hydrogen atoms H1 (highlighted in orange) for both
symmetrical isomers (Scheme 4). However, 1D-ROESY NMR-
spectroscopy shows that selective excitation of this resonance at
10.03 ppm results in a strong signal at 9.58 ppm. Since hydrogen
atoms H1 of HBC 13 are completely isolated, no NOE signal is
expected, unlike the H-atoms H1 of HBC 3, which exhibit
neighbouring protons at the HBC-rim. Thus, this is a first
indication that the isolated fraction is the desired, isometrically
pure diaza[7]helicene HBC 3. Hence, Scholl oxidation of
symmetric di-NDI HPB 2 favours the formation of the 7-helical
structure. One possible explanation for this could be the π-π
interaction of the two NDI units that is most pronounced once they
lie on top of each other causing a suitable pre-orientation of the
HPB. As a result, 7-helical HBC 3 is formed as the major
compound which was isolated in 43% yield. HBC 13 and 14 were
formed only in minor quantities (< 1 mg) and could not be isolated.
The structural assignment is supported by a very good resolution
of all NMR spectra of HBC 3, which were recorded at room without
the necessity to perform high-temperature measurements. It is
expected that such extended aromatic systems form
intermolecular aggregates due to strong π-π interactions, which
would drastically decrease the solubility. Thus, compound 13
Scheme 4. Final Scholl-oxidation of HPB 2 leading to the three possible
isomers: symmetrical HBC 13, 7-helical HBC 3, and unsymmetrical HBC 14;
hydrogen atoms without COSY-correlation: H1 highlighted in orange a) FeCl3,
CH3NO2, DCM, 0 °C, o.n., yield 43%.
3
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should not be resolvable at room temperature. However, the
nonplanar helicene subunit and the inherent three-dimensional
twist of HBC 3 provides excellent solubility in a very large variety
of organic solvents. In comparison, the symmetrical HPB 2 shows
a much lower solubility and thus, high-temperature NMR
measurement were needed to obtain spectra with good resolution
(see SI S5). The transformation of di-NDI-HPB 2 to the
corresponding HBC 3 can be monitored by UV-vis absorption
spectroscopy as well (Figure 4). After Scholl oxidation, HCB 2
displays a new strong absorption signature due to the HBC unit
Since compound 3 contains a diaza[7]helicene unit, it is a chiral
molecule and can adopt either (M)- or (P)-configuration (Figure
5A). In order to separate the enantiomers, we targeted HPLC
using a chiral Chiralpak 1BN-5 column. Indeed, we were able to
separate the two enantiomers with retention times of tR = 14.7
min and tR =31.3 min. This allowed us to analyse their chiroptical
properties with circular dichroism (CD) spectroscopy (Figure
5B+C). The mirror image spectra display five strong Cotton
effects in the ultraviolet and visible region between 260 – 340 nm,
365 – 390 nm, 390 – 430 nm, 430 – 460 nm and 580 – 730 nm
with corresponding ІΔεІ of 33 M-1cm-1, 25 M-1cm-1, 16 M-1cm-1, 15
M-1cm-1, and 10 M-1cm-1 respectively. The calculated dissymmetry
factors ІgabsІ reach a maximum of 1.5×10-3. In addition, we
conducted DFT calculations (Figure 6) to gain information about
the 3D-structure of 3.
at 372 nm with a high molar extinction coefficient of 54000 M-1cm-
1
.
At the same time, the NDI absorption broadens and
experiences a strong red shift of 100 nm to 571 nm. In addition,
the intensity decreases from extinction coefficient values of
around 25000 M-1cm-1 to 11100 M-1cm-1.
Figure 4. Comparison of UV-vis absorption spectra of HPB 2 (blue) and 7-
helical HBC 3 (green).
Emission properties were investigated upon irradiation at the
corresponding absorption maximum. Although the starting
material 5 exhibits a very strong fluorescence with a maximum at
570 nm, the emission intensity is already drastically decreased for
di-NDI tolane mixture 1/9 as well as for HPB 2. Finally, the
fluorescence of the 7-helical HBC 3 is completely quenched, and
no emission is detected any more (see SI S6).
Figure 6. Geometry optimised structures of HBC 3 at B3LYP/def2-SVP without
dispersion correction; hydrogen atoms, tBu groups and swallow tail are omitted
for clarity; A) top view with relevant distances between the two NDI arms B)
torsion angles of the inner helix C) side view with interplanar angle of the inner
helix D) representation of the highest occupied molecular orbital (HOMO) and
the lowest unoccupied molecular orbital (LUMO).
Traditionally, π-π stacking is better described by dispersion-
corrected than by dispersion-devoid DFT. However, there are
some works claiming that in condensed phase the uncorrected
approach might be more consistent with reality.[24] Thus, we
performed optimisation both with B3LYP/def2-SVP (Figure 6) and
B3LYP-D3/def2-SVP (Figure S28) and for both geometries CD-
spectra were simulated with same methodology (sTD-CAM-
B3LYP/def2-TZVP, see S7+S8 for details). Although the
electronic structure (Figure 6D) is very consistent for both
obtained geometries (the highest occupied molecular orbital
(HOMO) is mainly delocalized on the HBC unit while the lowest
unoccupied molecular orbital (LUMO) is equally localized on both
NDI moieties), the obtained geometries differ significantly in the
interplanar distance of the two NDI-wings. This indeed shifts and
effects the intensity of peaks in the long-wave part of the CD-
spectra that corresponds to excitations with significant role of the
LUMO. Nevertheless, the general pattern of the spectra stays the
Figure 5. A) (M)- and (P)-configuration of 7-helcial HBC 3, tBu groups and
swallow tail are omitted for clarity; B) chiral separation of 3 (Chiralpak 1BN-5, n-
heptane/EtOH/DEA 70/30/0.1, 4ml/min, rt) C) circular dichroism (CD)
spectroscopy measurements of (M)-3 (black) and (P)-3 (blue) and the
corresponding calculated spectra (sTD-CAM-B3LYP/def2-TZVP with D3: grey,
light blue; without D3: red, green).
4
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same for both geometries and is in good agreement with the
experimentally measured spectra (especially in the area between
350 – 500 nm, see Figure 5C). Thus, the first eluted fraction was
assigned as (M)- and the second eluted fraction as (P)-isomer.
Furthermore, characteristic helicity values such as torsion angles
and interplanar angle, were analysed. The inner helix with
corresponding torsion angles as well as the interplanar angle is
shown in Figure 6B and 6C, respectively. The seven rings form a
helicene subunit with an overall sum of torsion angles α–ε of θ =
95° – 106° (with and without dispersion correction). This value is
between the ones of previously reported [7]-helicenes, e.g. all
carbon [7]-helicenes (sum of torsion angles 108° – 134°)[3h,10a] or
Experimental Section
Chemicals were purchased from Sigma-Aldrich and used without any
further purification. Solvents were distilled prior to usage. Thin layer
chromatography (TLC) was performed on Merck silica gel 60 F524,
detected by UV-light (254 nm, 366 nm). Plug chromatography and column
chromatography were performed on Macherey-Nagel silica gel 60 M
(deactivated, 230−400 mesh, 0.04−0.063 mm). NMR spectra were
recorded on a Bruker Avance 400 (1H: 400 MHz, 13C: 101 MHz), a Bruker
Avance 500 (1H: 500 MHz, 13C: 126 MHz), or a Bruker Avance Neo Cryo-
Probe DCH (1H: 600 MHz, 13C: 151 MHz). Deuterated solvents were
purchased from Sigma-Aldrich and used as received. Chemical shifts are
given in ppm at room temperature and are referenced to residual protic
impurities in the solvents (1H: CHCl3: 7.24 ppm, C2H2Cl4: 5.91 ppm) or the
deuterated solvent itself (13C{1H}: CDCl3: 77.16 ppm, C2D2Cl4: 74.20 ppm).
The resonance multiplicities are indicated as “s” (singlet), “bs” (broad
singlet), “d” (doublet), “t” (triplet), “q” (quartet) and “m” (multiplet). Mass
spectrometry was carried out with a Shimadzu AXIMA Confidence
(MALDI-TOF, matrix: 2,5-dihydroxybenzoic acid DHB, trans-2-[3-(4-tert-
butylphenyl)-2-methyl-2-propenyliden]malononitrile, DCTB) or without
matrix (OM). High resolution mass spectrometry (HRMS) was recorded on
a LDI/MALDI-ToF Bruker Ultraflex Extreme machine or on a APPI-ToF
mass spectrometer Bruker maXis 4G UHR MS/MS spectrometer. UV/vis
spectroscopy was carried out on a Varian Cary 5000 UV−vis−NIR
spectrometer. The spectra were recorded at rt in DCM in quartz cuvettes
(edge length = 1 cm) under ambient conditions. Fluorescence spectra
[7]-azahelicenes (sum of torsion angles 80.2°)[9a,25]
.
First titration experiments were performed to examine the
efficiency of 3 to quench the emission of a fluorescent molecule
and it was found that the emission intensity of anthracene
significantly gets quenched after the successive addition of 3.
Theoretical calculations support the idea of anthracene being
enclosed within the NDI units (see SI S9 for further information).
The successful development of the synthetic strategy to HBC 3
opens up the access to a new compound class, which can be
described as HBC based, chiral nano-tweezers having two
structurally similar, π–extended ryleneimide arms. In this series,
HBC 3 with its two NDI wings represents the smallest compound
with promising structural features stemming from the high pre-
organisation of the diaza[7]helicene subunit. Using larger
ryleneimides, to elongate the aromatic tweezer-arms, will further
increase the cavity of such helical tweezers and, as a
were obtained from
a Shimadzu RF-5301 PC and a NanoLog
spectrofluorometer (Horiba Scientific). Circhular dichroism spectroscopy
was measured at rt in DCM on a Jasco J-815 spectrometer. HPLC
separation was carried out using Shimadzu analytical and preparative
HPLC with system controller CBM-20A, solvent delivery unit LC-20A,
autosampler SIL-20A, column oven CTO-20A, photodiode array detector
SPDM20A, on-line degassing unit DGU-20A and low-pressure gradient
unit. All chromatograms were processed with Shimadzu LabSolution(c)
software and exported as ASCII files
consequence,
opens
exciting
opportunities
for
the
supramolecular interaction with interdigitated host molecules.
Conclusion
4/5-Bromo-1,2-naphthaleneimidebenzimidazole (5) (12)
A dry flask was charged with NMI 8 (100 mg, 0.237 mmol, 1.1 equiv.), 4-
bromo-1,2-diaminbenzene 11 (40.0 mg, 0.216 mmol, 1 equiv.) and
imidazole (800 mg) and the mixture was stirred under nitrogen at 160 °C
for 3 h. The reaction mixture was cooled to rt, diluted in DCM and washed
with H2O. The combined organic layers were concentrated under reduced
pressure and the crude was purified by silica gel column chromatography
(SiO2, DCM:hexanes 1:1) to provide the two separated isomers 5 and 12
in a pure form. Yields: 5 (44.0 mg, 0.077 mmol, 36%), 12 (52.0 mg, 0.091
mmol, 42%).
In summary, two NDI unites were fused to a HBC through a
benzimidazole bridge for the first time to generate a π-extended
aza-helicene framework 3 that was investigated with respect to its
photophysical and chiroptical properties. The ortho fusion of the
NDI units to the HBC leads to the formation of a fully conjugated
diaza[7]helicene as a new helical hybrid involving a wide lateral
π-extension of the helicene skeleton. During final Scholl oxidation,
the 7-helical HBC 3 was the only product formed out of three
possible isomers as pair of enantiomers, demonstrating
pronounced stereoselectivity of the formation process. The
enantiomers were separated by HPLC employing a chiral
stationary phase. The chiroptical properties investigated with CD
measurements were supported by theoretical calculations, which
also allowed for an assignment of the absolute configuration of
the isolated enantiomers. For a better understanding as to why
the HPB-precursor is forced to adopt a 7-helical conformation and
in order to prevent the formation of unwanted side products,
improved synthetic protocols for the final Scholl oxidation are
currently studied. The synthetic access to aza[n]helicenes such
as 3 will pave the way for the exploration of unprecedent chiral
nano-tweezers with two rigid functional arms. The use of the
higher rylene-imide analogues, in particular perylene-imides, to
create a tweezer with even longer and more extended π-surface,
is currently under investigation.
4-Bromo-1,2-naphthaleneimidebenzimidazole (5)
1H-NMR (CDCl3, 400 MHz, 25 °C): δ = 8.87 – 8.66 (m, 4H, Ar-CH), 8.54
(d, J = 1.8 Hz, 1H, Ar-CH), 7.64 (d, J = 8.6 Hz, 1H, Ar-CH), 7.51 (dd, J =
8.6, 1.9 Hz, 1H, Ar-CH), 5.37 – 5.01 (m, 1H, N-CH), 2.29 – 2.17 (m, 2H,
CH2), 1.96 – 1.67 (m, 2H, CH2), 1.42 – 1.05 (m, 12H, CH2), 0.92 – 0.68 (m,
6H, CH3) ppm. 13C-NMR (CDCl3, 101 MHz 25 °C): δ = 159.3 (C=O), 148.3,
143.0, 132.9 (Ar-C), 131.6, 130.0 (Ar-CH), 127.7 (Ar-C), 127.1 (Ar-CH),
126.9, 125.9, 125.1 (Ar-C), 121.9 (Ar-CH), 120.5 (Ar-C), 119.1 (Ar-CH),
55.4 (N-CH), 32.4, 31.8, 26.8, 22.7 (CH2), 14.2 (CH3) ppm. MS (MALDI-
TOF, dctb): m/z = 572.2 (100%, C31H31BrN3O3 [M+H]+). HRMS (APPI,
CH2Cl2): calculated for C31H31BrN3O3 ([M+H]+) m/z = 572.1543, found m/z
= 572.1545. UV-Vis (CH2Cl2): λ [nm] (ε [M-1cm-1]) = 304 (23500), 316
(26500), 443 (18500). Fluorescence (CH2Cl2): λexc. [nm] = 443, λemission
[nm] (rel. int.) = 570 (100).
5-Bromo-1,2-naphthaleneimidebenzimidazole (12)
1H-NMR (CDCl3, 400 MHz, 25 °C): δ = 8.97 – 8.56 (m, 4H, Ar-CH), 8.24
(d, J = 8.5 Hz, 1H, Ar-CH), 7.83 (d, J = 1.8 Hz, 1H, Ar-CH), 7.47 (dd, J =
8.7, 1.8 Hz, 1H. Ar-CH), 5.33 – 4.98 (m, 1H, N-CH), 2.34 – 2.11 (m, 2H,
CH2), 2.05 – 1.69 (m, 2H, CH2), 1.41 – 0.96 (m, 12H, CH2), 0.93 – 0.51 (m,
6H, CH3) ppm. 13C-NMR (CDCl3, 101 MHz 25 °C): δ = 159.1 (C=O), 148.8,
145.2 (Ar-C), 131.6 (Ar-CH), 130.9 (Ar-C), 129.8 (Ar-CH), 127.6 (Ar-C),
127.2 (Ar-CH), 126.8, 125.8, 124.8 (Ar-C), 123.7 (Ar-CH), 119.7 (Ar-C),
5
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116.9 (Ar-CH), 55.4 (N-CH), 32.4, 31.8, 26.8, 22.7 (CH2), 14.2 (CH3) ppm.
MS (MALDI-TOF, dctb): m/z = 572.2 (100%, C31H31BrN3O3 [M+H]+).
HRMS (MALDI-TOF, dctb): calculated for C31H31BrN3O3 ([M+H]+) m/z =
572.1543, found m/z = 572.1528. UV-Vis (CH2Cl2): λ [nm] (ε [M-1cm-1]) =
300 (22500), 312 (25500), 420 (16000). Fluorescence (CH2Cl2): λexc. [nm]
= 420, λemission [nm] (rel. int.) = 556 (100).
147.41, 147.36, 141.6, 141.5, 141.4, 141.1, 141.0, 140.7, 140.6, 139.3,
139.1, 137.7, 137.6, 137.4, 131.04, 130.99, 130.71, 130.67, 130.6, 127.50,
127.47, 127.4, 126.1, 125.7, 125.6, 125.5, 123.3, 123.1, 120.4, 119.4,
119.0, 118.7, (Ar-CH, Ar-C), 55.3 (N-CH), 34.0 (CH2), 32.4 (C-CH3), 31.7
(CH2), 31.28, 31.20, 31.18 (CH3), 26.6, 22.5 (CH2), 14.0 (CH3) ppm. MS
(MALDI-TOF, dctb): m/z = 1589.9 (100%, C108H112N6O6 [M+H]+). HRMS:
(MALDI-TOF, dctb): calculated for C108H112N6O6 ([M]+) m/z = 1588.8638
found m/z = 1588.8652. UV-Vis (CH2Cl2): λ [nm] (ε [M-1cm-1]) = 322
(51000), 471 (25000). Fluorescence (CH2Cl2): λexc. [nm] = 471, λemission
[nm] (rel. int.) = 651 (100).
NDI-Tolane (6)
A 20 mL MW vial was charged with Br-Naph 5 (70 mg, 0.12 mmol, 1
equiv.), PdCl2(PPh3)2 (4.2 mg, 0.006 mmol, 0.05 equiv.), CuI (0.5 mg,
0.003 mmol, 0.02 equiv.) and toluene (4 mL) and sealed with a septum.
The solution was degassed for 15 min and subsequently di-tert-butyl(4-
ethynyl-1,2-phenylene)dicarbamate 4 (82.0 mg, 0.25 mmol, 2 equiv.)
dissolved in Et3N (2 mL) was added via a syringe. The reaction mixture
was stirred at 80°C overnight under argon atmosphere. The solvent was
removed under reduced pressure and the crude product was subjected to
column chromatography (SiO2; EtOAc:Hexane 1:4) to provide the pure
product 6 as a red solid (83 mg, 0.10 mmol, 82% yield). 1H-NMR (CDCl3,
400 MHz, 25 °C): δ = 8.91 – 8.86 (m, 2H, Ar-CH), 8.75 (bs, 2H, Ar-CH),
8.61 (d, J = 1.5 Hz, 1H, Ar-CH), 7.79 (d, J = 8.4 Hz, 1H, Ar-CH), 7.69 (bs,
1H, Ar-CH), 7.59 (m, 2H, Ar-CH), 7.34 (dd, J = 8.4, 1.9 Hz, 1H, Ar-CH),
6.84 (bs, 1H, N-H), 6.66 (bs, 1H, N-H), 5.22 – 5.09 (m, 1H, N-CH), 2.28 –
2.13 (m, 2H, CH2), 1.92 – 1.78 (m, 2H, CH2), 1.53 (s, 9H, CH3), 1.52 (s,
9H, CH3), 1.35 – 1.18 (m, 12H, CH2), 0.84 – 0.78 (m, 6H, CH3) ppm. 13C-
NMR (CDCl3, 101 MHz 25 °C): δ = 159.3, 153.9, 153.5 (C=O), 148.7,
143.8, 132.1, 131.5, 130.3, 129.2, 127.8, 127.2, 126.9, 126.0, 125.3,
122.2, 120.8, 119.2 (Ar-CH, Ar-C), 90.6, 89.6 (C≡C), 81.4, 81.3 (C-CH3),
55.4 (N-CH), 32.4, 31.9 (CH2), 28.4 (CH3), 26.8, 22.7 (CH2), 14.2 (CH3)
ppm. MS (MALDI-TOF, dctb): m/z = 824.4 (C49H54N5O7 [M+H]+). HRMS:
(APPI, CH2Cl2) calculated for C49H54N5O7 ([M+H]+) m/z = 824.4018 found
m/z = 824.4011. UV-Vis (CH2Cl2): λ [nm] (ε [M-1cm-1]) = 328 (17100), 480
(6700).
Unsymmetric Di-NDI-HPB (10)
1H-NMR (C2D2Cl4, 400 MHz, 135 °C): δ = 8.82 – 8.49 (m, 8H, Ar-CH),
8.13 (dd, J = 1.6, 0.7 Hz, 1H, Ar-CH), 7.94 (d, J = 8.4 Hz, 1H, Ar-CH), 7.53
(d, J = 1.4 Hz, 1H, Ar-CH), 7.34 (dd, J = 8.4, 0.7 Hz, 1H, Ar-CH), 7.22 (dd,
J = 8.4, 0.8 Hz, 1H, Ar-CH), 7.13 (dd, J = 8.3, 1.6 Hz, 1H, Ar-CH), 6.89 –
6.71 (m, 16H, Ar-CH), 5.15 – 5.02 (m, 2H, N-CH), 2.20 – 2.10 (m, 4H,
CH2), 1.92 – 1.80 (m, 4H, CH2), 1.34 – 1.20 (m, 24H, CH2), 1.13 – 1.08 (m,
18H, CH3), 1.02 (s, 9H, CH3), 0.97 (s, 9H, CH3), 0.84 – 0.76 (m, 12H, CH3)
ppm. 13C-NMR (C2D2Cl4, 101 MHz, 120 °C): δ = 163.4, 163.2, 159.0
(C=O), 148.2, 148.1, 147.0, 147.9, 147.5, 147.4, 147.3, 146.0, 143.4,
141.9, 141.7, 141.6, 140.9, 140.8, 140.3, 140.2, 139.4, 139.2, 137.8,
137.7, 137.6, 131.3, 131.2, 130.6, 130.5, 129.8, 128.1, 128.0, 127.5,
127.4, 126.3, 125.8, 124.8, 124.8, 123.3, 123.2, 122.9, 118.8, 114.2, 113.7
(Ar-CH, Ar-C), 55.4 (N-CH), 34.0 (CH2), 32.9 (C-CH3), 31.4 (CH2), 31.2
(CH2), 31.20, 31.15, 31.09 (CH3), 22.3 (CH2), 13.7 (CH3) ppm. MS
(MALDI-TOF, dctb): m/z = 1590.1 (100%, C108H112N6O6 [M+H]+). HRMS:
(MALDI-TOF, dhb): calculated for C108H112N6O6 ([M]+) m/z = 1588.8638
found m/z = 1588.8681. UV-Vis (CH2Cl2): λ [nm] (ε [M-1cm-1]) = 320
(37500), 450 (18000). Fluorescence (CH2Cl2): λexc. [nm] = 451, λemission
[nm] (rel. int.) = 649 (100).
7-Helical HBC (3)
In a 20 mL MW-vial symmetrical di-NDI-HPB 2 (20.0 mg, 12.6 µmol, 1
equiv.) was dissolved in DCM (20 mL) and cooled to 0 °C with an ice bath.
After degassing with N2 for 20 min a solution of dry FeCl3 (120 mg, 0.378
mmol, 60 equiv.) in MeNO2 (0.1 mL) was added. The mixture was
degassed for further 15 minutes and stirred overnight. The reaction was
quenched via the addition of MeOH. The solvent was removed under
reduced pressure and the crude product was purified by HPLC
chromatography to provide the pure product 3 as a dark green solid (8.2
mg, 5.2 µmol, 43%). 1H-NMR (C2D2Cl4, 600 MHz, 25 °C): δ 10.03 (s, 2H,
Ar-CHCor), 9.58 (s, 2H, Ar-CHCor), 9.40 (s, 2H, Ar-CHCor), 9.35 (s, 2H, Ar-
CHCor), 9.32 (s, 2H, Ar-CHCor), 9.06 (d, J = 7.6 Hz, 2H, Ar-CHNaph), 8.66 (d,
J = 7.6 Hz, 2H, Ar-CHNaph), 8.24 (d, J = 7.1 Hz, 2H, Ar-CHNaph), 8.19 (d, J
= 7.5 Hz, 2H, Ar-CHNaph), 4.97 – 4.85 (m, 2H, N-CH), 2.28 – 2.17 (m, 4H,
CH2), 2.00 – 1.92 (m, 4H, CH2), 1.84 (s, 18H, CH3), 1.79 (s, 18H, CH3),
1.28 – 1.10 (m, 24H, CH2), 0.79 – 0.71 (m, 12H, CH3) ppm. 13C-NMR
(C2D2Cl4, 151 MHz, 25 °C): δ = 156.8, 150.52 150.4, 149.7, 144.2, 130.9,
130.8, 130.7, 130.2, 129.9, 129.7, 128.4, 127.4, 127.3, 127.1, 126.5,
125.4, 124.0, 123.5, 122.1, 121.0, 120.8, 120.6, 120.0, 119.8, 119.7,
119.1, 115.4 (Ar-CH, Ar-C), 55.4 (N-CH), 36.2, 36.1 (C-CH3), 32.4, 32.3
(CH3) 31.8, 30.0, 26.9, 22.8 (CH2) 14.4 (CH3) ppm. MS (MALDI-TOF,
dctb): m/z = 1577.8 (100%, C108H100N6O6 [M]+). HRMS: (MALDI-TOF,
dctb): calculated for (C108H100N6O6 [M]+) m/z = 1576.7699, found m/z =
1576.7696. UV-Vis (CH2Cl2): λ [nm] (ε [M-1cm-1]) = 372 (54000), 571
(11100).
Di-NDI-Tolane (1) (9)
Compound
6 (80.0 mg, 0.097 mmol, 1 equiv.) was dissolved in
DCM/trifluoroacetic acid (8 mL, 1:1 v/v) and stirred at room temperature
for 3 h under nitrogen atmosphere.[21] Et3N was added for neutralization
and the mixture was filtered over silica. The solvent was removed under
reduced pressure and due to the sensitivity towards oxidation of di-amino
tolane 7[22] the crude product was used in the next condensation reaction
without further purification and characterization. Approximately 62 mg
(0.100 mmol,
1 equiv.) of the crude di-amino tolane 7 and
naphthalenemonoimide 8 (130 mg, 0.300 mmol, 3 equiv.) were dissolved
in DMF and heated to 140 °C for 18 h under argon atmosphere. The
mixture was cooled to rt, extracted with DCM and washed with water. The
solvent was removed under reduced pressure and the crude product was
purified by plug chromatography (SiO2; DCM) to provide the title
compounds as an isomeric mixture 1 and 9 (54.0 mg, 0.054 mmol, 56%
yield). MS (MALDI-TOF, dctb): m/z = 1009.5 (100%, C64H60N6O6 [M+H]+).
HRMS: (APPI, CH2Cl2/Tol): calculated for C64H60N6O6 ([M]+) m/z =
1008.4569 found m/z = 1008.4595.
Di-NDI-HPB (2) (10)
A 1 mL MW-vial was charged with the isomeric mixture of di-NDI-tolanes
9 and 10 (54.0 mg, 0.054 mmol, 1 equiv.), tetrakis-(tert-butyl)tetracyclone
[15a,23]
(50.0 mg, 0.081 mmol, 1.5 equiv.) and toluene (1 mL) and sealed
with a septum. The reaction mixture was degassed with N2 for 5 minutes
and heated to 220 °C for 24 h. The solvent was removed under reduced
pressure and the crude was purified by column chromatography (SiO2,
THF:Hexane 1:9) to provide the pure products 2 and 10. Yields: symmetric
di-NDI-HPB 2 (25.0 mg, 0.015 mmol, 29%), unsymmetric di-NDI-HPB 10
(26.0 mg, 0.016 mmol, 30%).
Acknowledgements
The authors thank the Deutsche Forschungsgemeinschaft (DFG
- SFB 953 “Synthetic Carbon Allotropes”, and the Graduate
School Molecular Science (GSMS) for financial support
Symmetric Di-NDI-HPB (2)
1H-NMR (C2D2Cl4, 400 MHz, 135 °C): δ = 8.81 – 8.50 (m, 8H, Ar-CH),
8.14 (s, 2H, Ar-CH), 7.33 (d, J = 8.4, 2H, Ar-CH), 7.20 – 7.11 (m, 2H, Ar-
CH), 6.93 – 6.66 (m, 16H, Ar-CH), 5.17 – 5.02 (m, 2H, N-CH), 2.24 – 2.12
(m, 4H, CH2), 1.94 – 1.78 (m, 4H, CH2), 1.39 – 1.19 (m, 24H, CH2), 1.11
(s, 18H, CH3), 1.00 (s, 18H, CH3), 0.86 – 0.72 (m, 12H, CH3) ppm. 13C-
NMR (C2D2Cl4, 101 MHz, 120 °C): δ = 158.9, 158.6 (C=O), 147.9, 147.7,
Keywords: chirality • helicene • hexabenzocoronene •
naphthalene • π-extension
6
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10.1002/chem.202003402
Chemistry - A European Journal
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Entry for the Table of Contents
A diaza[7]helicene was formed as the only isomer via the fusion of two NDIs to a HBC core, generating a fully conjugated superstructure
with a wide lateral π-extension of the inner heterohelix. The helical twist brings along an attractive spatial arrangement and affects the
chemical and photophysical features. Isolation of the corresponding enantiomers was accomplished by HPLC on a chiral stationary
phase and the absolute configurations were determined by comparison of their CD-spectra with quantum mechanical calculations.
9
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