Fast oxidative cyclooligomerization towards low- and high-symmetry thiophene macrocycles

Article abstract of DOI:10.1002/chem.201503211

Macrocycles with quaterthiophene subunits were obtained by cyclooligomerization by direct oxidative coupling of unsubstituted dithiophene moieties. The rings were closed with high selectivity by an α,β′-connection of the thiophenes as proven by NMR spectroscopy. The reaction of the precursor with terthiophene moieties yielded the symmetric α,α′-linked macrocycle in low yield together with various differently connected isomers. Blocking of the β-position of the half-rings yielded selectively the α,α′-linked macrocycle. Selected cyclothiophenes were investigated by scanning tunneling microscopy, which displayed the formation of highly ordered 2D crystalline monolayers. Heteroaromatic rings: Thiophene macrocycles with an unconventional α,α′- or α,β′-connection are readily synthesized by oxidative cyclooligomerization of the appropriate thiophenes. The actual reaction outcome strongly depends on the precursor structure (see scheme).

Full text of DOI:10.1002/chem.201503211

DOI: 10.1002/chem.201503211
Full Paper
&
Heteroaromatic Macrocycles
Fast Oxidative Cyclooligomerization towards Low- and High-
Symmetry Thiophene Macrocycles
Stefan K. Maier,[a] Georgiy Poluektov,[a] Stefan-S. Jester,*[a] Heiko M. Mçller,*[b] and
Sigurd Hçger*[a]
Abstract: Macrocycles with quaterthiophene subunits were
obtained by cyclooligomerization by direct oxidative cou-
pling of unsubstituted dithiophene moieties. The rings were
closed with high selectivity by an a,b’-connection of the thi-
ophenes as proven by NMR spectroscopy. The reaction of
the precursor with terthiophene moieties yielded the sym-
metric a,a’-linked macrocycle in low yield together with vari-
ous differently connected isomers. Blocking of the b-position
of the half-rings yielded selectively the a,a’-linked macrocy-
cle. Selected cyclothiophenes were investigated by scanning
tunneling microscopy, which displayed the formation of
highly ordered 2D crystalline monolayers.
Introduction
oligo- or polythiophene structures that possess higher solubili-
ty than their linear analogues.[11]
Thiophene-based shape-persistent macrocycles are interesting
compounds owing to their optical properties, and their ability
to form superstructures by non-covalent interactions or to
functionalize solid surfaces.[1–4] As they consist of several units
of the same building block, cyclooligomerization reactions are
the most efficient methods to synthesize macrocyclic mole-
cules. The ring-closure reaction can rely on the oxidative cou-
pling of terminal acetylenes[5] attached to appropriate curved
segments, with the possibility to transform the butadienylene
units to thiophenes.[6,7] Alternatively, the ring closure can also
be performed oxidatively at the thiophene sites after metalla-
tion[8] or by the direct oxidative coupling of thiophenes. Gener-
ally, this leads to cyclothiophenes connected at their a-posi-
tion; b-linked thiophenes are rare in macrocycle chemistry.[7]
Exceptions generally only occur when the a-positions are
either blocked by substituents, or when coupling at the b-posi-
tions leads to the formation of six-membered condensed
cycles.[9] However, a,b’-linkages are known as defects in poly-
thiophenes synthesized by oxidative coupling methods using
oxidants such as FeCl3 or by electrochemical means.[10] More-
over, a,b’- and b,b’-linkages are also part of some non-linear
We recently reported thiophene-containing macrocycles that
are synthesized by direct oxidative coupling of the appropriate
thiophene subunits in cyclodimerization reactions.[12] In a similar
approach, the cyclization of precursor 2 was attempted by
using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as the
oxidant. Contrary to the commonly used FeCl3,[13] DDQ is solu-
ble in dichloromethane, no chlorinated side-products have to
be removed, and the reaction conditions can be fine-tuned by
the choice of the acid used in the reaction.[14]
Results and Discussion
Under Suzuki reaction conditions, dithiophene boronic
ester 1 was coupled with 1-tert-butyl-3,5-diiodobenzene[15]
(Scheme 1) to yield half-ring 2, which was subsequently cyclo-
dimerized by using DDQ and trifluoroacetic acid (TFA) in di-
chloromethane over a period of merely 10 min.[16,17]
Gel permeation chromatography (GPC) of the crude product
showed an elution diagram typical for a cyclooligomerization
[a] Dr. S. K. Maier, G. Poluektov, Dr. S.-S. Jester, Prof. Dr. S. Hçger
KekulØ-Institut für Organische Chemie und Biochemie
Rheinische Friedrich-Wilhelms-Universität Bonn
Gerhard-Domagk-Strasse 1, 53121 Bonn (Germany)
Fax: (+49)228-73-5662
E-mail: stefan.jester@uni-bonn.de
hoeger@uni-bonn.de
[b] Prof. Dr. H. M. Mçller
Institut für Chemie, Universität Potsdam
Karl-Liebknecht-Strasse 24–25, 14476 Golm (Germany)
Fax: (+49)331-977-5092
Scheme 1. Synthesis of the unsymmetric thiophene macrocycle 3 by an oxi-
dative cyclodimerization of half-ring 2. a) [Pd(PPh3)4], Cs2CO3, 808C, 17 h,
73%; b) 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), trifluoroacetic
acid (TFA), 08C, 10 min, 31%.
E-mail: Heiko.Moeller@uni-potsdam.de
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201503211.
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under pseudo-high-dilution conditions with a dimeric species
as the major product of the reaction (see the Supporting Infor-
mation).[15] Purification by using recycling GPC (recGPC) isolat-
ed the main product in 31 % yield, and its exact mass matched
the expected value for a cyclodimer. Contrary to our expecta-
tions, the signals in the aromatic region of the proton and
carbon NMR spectra of the product appear rather broad at
room temperature, but become sharp at elevated tempera-
tures and show a rather complicated signature, as indicative of
a thiophene macrocycle of low symmetry.[16] The nearly com-
plete resonance assignment of the macrocycle was achieved
by analyzing a set of homo- and heteronuclear 2D spectra (see
the Supporting Information), including 2D-COSY, 2D-NOESY,
1H,13C HMQC, and 1H,13C HMBC. Most resonances originating
from the tBu, phenyl, and thiophene groups were readily iden-
Scheme 2. Synthesis of unsymmetric thiophene macrocycles with dodecyl
(7a) and octadecyl (7b) side chains at the corner pieces. a) 4a:
[NiCl2(dppp)], C12H25MgCl, 508C, 14 h, 70%; 4b: [NiCl2(dppp)], C18H37MgCl,
RT, 20 h, 70%; b) 5a: I2, HIO3, 1108C 3 h, 85%; 5b: I2, HIO3, 110!708C, 24 h,
74%; c) 6a: 1, [Pd(PPh3)4], Cs2CO3, 808C, 42 h, 69%; 6b: 1, [Pd(PPh3)4],
Cs2CO3, 808C, 20 h, 78%; d) 7a: DDQ, TFA, 08C, 9 min, 40%; 7b: DDQ, TFA,
08C, 7 min, 35%.
1
tified by the H and 13C chemical shift values and multiplicity.
However, determining the precise connectivity of these build-
ing blocks required the combination of information from all
spectra. The molecule was identified as the cyclodimer 3
(Scheme 1), in which the ring is closed by an a,a’- and an a,b-
connection of the thiophene units on either side (for structural
assignment by NMR analysis and a complete discussion of the
spectra, see the Supporting Information).
As mentioned, it is known that the b-positions of thiophenes
can be addressed in oxidative coupling reactions even in the
presence of free a-positions,[10] and there are also examples re-
ported for the formation of such a,b’-connections as a result
of geometric reasons.[9b] However, in our case, no six-mem-
bered cycle is formed. In fact, the formation of cycle 3 does
not appear very favored, especially as we know from our previ-
ous work that an a,a’-connection is also possible in such rings
with quaterthiophene subunits.[11] Nevertheless, the ring-clo-
sure reaction is apparently fast enough to surpass any reaction
of the nominally more reactive a-positions.
To gain additional insight into the structure of the unsym-
metric cycles from scanning tunneling microscopy (STM) meas-
urements, analogs of 3 carrying four dodecyl (7a) or four octa-
decyl (7b) substituents were synthesized (Scheme 2). Under
Kumada coupling conditions, m-dichlorobenzene was alkylated
to yield 4a/b, which were iodinated with iodic acid to give 5a/
b. Coupling with 1 gave 6a/b, which were subsequently cy-
clized with DDQ to yield, after purification by recGPC, the un-
symmetric cyclodimers 7a/b as the major products (yellow
solids). The synthesis of 7a as well as 7b is proof of how readi-
ly accessible these new macrocycles with this unconventional
structure are. The reaction worked without any difficulties,
even on a 120 mg scale to yield 42 mg of pure product (7b).
STM analysis (Figure 1) showed that 7a and 7b self-assem-
ble at the solid/liquid interface of 1,2,4-trichlorobenzene (TCB)
and highly oriented pyrolytic graphite (HOPG). In both images,
the macrocyclic backbones appear bright (owing to low tun-
neling resistivity) and are separated by darker regions (indicat-
ing higher resistivity at nominally the same height) covered by
dodecyl (7a, Figure 1a) or octadecyl (7b, Figure 1c) side
chains that align along the HOPG main axis directions.[18,19]
Compound 7a packs in pairs with alternating orientations, and
a proposed supramolecular model is shown in Figure 1b. A
Figure 1. STM images and supramolecular models of self-assembled mono-
layers of 7a and 7b at the TCB/HOPG interface. a) and b) 7a (image and
unit-cell parameters: 20.0”20.0 nm2, c=10À5 m, VS =À0.8 V, It =50 pA;
a=(6.4Æ0.2) nm, b=(3.0Æ0.1) nm, g(a,b)=(89Æ2)8; g(a,d)=(1Æ2)8); c)
and d) 7b (image and unit-cell parameters: 20.0”20.0 nm2, c=10À6 m,
VS =À0.79 V, It =10 pA; a=(12.0Æ0.3) nm, b=(3.6Æ0.1) nm,
g(a,b)=(49Æ2)8; g(a,d)=(17Æ2)8). Red and white (black) lines indicate the
unit-cell vectors and HOPG main axis directions, respectively, and the blue
arrows indicate the backbone orientations. Approximate positions of sulfur
atoms are shown in yellow.[20]
unit cell of a=(6.4Æ0.3) nm, b=(3.0Æ0.1) nm and g(a,b)=
(89Æ2)8 is indexed, containing four molecules. Attributed to
its longer side chains, the macrocyclic backbones of 7b (Fig-
ure 1c) are more clearly resolved and appear as bright “D”-
shaped objects in which the a,b’-connected thiophene units
appear as protrusions pointing out of the otherwise oval-
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shaped rings (cf. arrow “1”, Figure 1c). A unit cell of a=(12.0Æ
0.3) nm, b=(3.6Æ0.1) nm and g(a,b)=(49Æ2)8 is indexed,
containing four molecules that adopt two different orienta-
tions (blue arrows).[18,19]
The results led to the question of whether the cyclization of
the thiophene half-rings by using DDQ as the oxidant also
leads to the binding motifs of a,a’- and a,b’-connections for
larger building blocks (as observed in 3 and 7a/b, containing
eight thiophene units), or whether two a,a’-connections
would be favored in less strained systems (as expected for the
cyclization products of larger half-ring structures). Therefore,
we coupled the dioctadecyl-substituted diiodinated corner
piece 5b to terthiophene boronic ester 8 to obtain the half-
ring 9 (Scheme 3). The subsequent cyclization under otherwise
Figure 2. a) STM image and b) supramolecular model of self-assembled
monolayer of 10 at the TCB/HOPG-interface. Image parameters, unit cell,
and additional packing parameters: 20.0”20.0 nm2, c=10À6 m, Vs =À0.8 V,
It =50 pA; a=(3.5Æ0.1) nm, b=(2.6Æ0.1) nm, g(a,b)=(72Æ2)8;
g(b,d)ꢀg(b,c)=(23Æ5)8. Red, white (black), and blue lines indicate unit-cell
vectors, HOPG main axis directions, and directions of the north–south axes
c of the macrocycles, respectively. Approximate positions of sulfur atoms are
shown in yellow.
phene units. However, macrocycle 10 is almost insoluble at
room temperature in any solvent, which is very unfortunate for
the inevitable purification by recGPC.
Another possibility to obtain a macrocycle with sole a,a’-
connections is to block the b-position(s) of the terminal thio-
phene rings of the macrocycle precursor. Therefore, we decid-
ed to synthesize precursor 13 (Scheme 4), which has hexyl sub-
Scheme 3. Synthesis of a thiophene macrocycle with sexithiophene sub-
units. a) 5b, [Pd(PPh3)4], Cs2CO3, 808C, 14 h, 60%; b) DDQ, TFA, 08C, 9 min,
4% (22% unidentified cyclodimers).
identical conditions again proceeded smoothly at first glance,
but MS analysis of the crude product showed that a variety of
cyclodimers (with an overall yield of 26%) were produced in
the reaction, which could not be separated from each other by
recGPC—except for the isomer with the largest hydrodynamic
radius, which could be obtained in pure form. Owing to the
high symmetry shown in the NMR spectrum, this isomer was
identified as macrocycle 10, in which both sides of each of the
two half-rings are connected through the a-positions of the
thiophenes, but contains 12 instead of 8 thiophene rings, as in
3 or 7a/b. Although not isolated, the formation of the respec-
tive isomer with an a,a’- and a,b’-connection cannot be ex-
cluded.
Scheme 4. Synthesis of a thiophene macrocycle with sexithiophene sub-
units. a) 5b, [PdCl2(dppf)], RT, 14 h, 86%; b) 1) BuLi, TMEDA (N,N,N’,N’-tetra-
methylethylenediamine), 2) iPrBpin (Bpin=bis(pinacolato)diboron),
À78!08C; c) [Pd(PPh3)4], Cs2CO3, 808C, 80 h, 23%; d) DDQ, TFA, 08C,
10 min, 4% (28% dimer).
STM analysis (Figure 2) showed that at the solid/liquid inter-
face on HOPG 10 self-assembles into a monolayer pattern in
which the molecules pack into an oblique pattern to which
a unit cell containing one molecule with lattice constants a=
(3.5Æ0.1) nm, b=(2.6Æ0.1) nm, g(a,b)=(72Æ2)8 is indexed.
The C2v symmetric shape of the ovalish backbones (which
appear bright) additionally supports the structural assignment
(based on the NMR data) that the cyclization leads at both
coupling points to a,a’-thiophene connections (compared with
the D-shaped rings observed in Figure 1).
stituents at one of the b-positions of both terminal thiophenes.
Thiophenes were attached to 5b in a Kumada coupling reac-
tion with 2-thienylmagnesium bromide to form 11.[21] Lithia-
tion/borylation of the latter yielded 12, which was coupled
under Suzuki cross-coupling conditions with 2-bromo-3-hex-
ylthiophene to form the half-ring 13.
Thus, it was indeed possible to obtain a highly symmetric
a,a’-connected macrocycles from a precursor with more thio-
Compound 13 was cyclized with DDQ by using similar con-
ditions as before to yield the a,a’-connected macrocycle 14,
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which was the only macrocycle isolated in this reaction. How-
ever, the ring-closure reaction is much slower for 14 than it
was for 7a/b and 10, so after 10 min reaction time there is still
a large amount of open-chain dimer in the reaction mixture,
which was separated by recGPC. As a result of the slight distor-
tions in the planarity owing to the hexyl-groups, 14 is not col-
ored as intensely yellow as the unsymmetric macrocycles 3
and 7a/b, which possess an undistorted quaterthiophene unit
(see the Supporting Information). Contrary to the open-chain
dimer, the cyclodimer 14 is solid at room temperature. The ad-
ditional hexyl substituents make the macrocycle soluble even
in non-polar organic solvents.
Experimental Section
Synthesis, materials, and general equipment
Reagents were purchased in reagent grade quality from commer-
cial sources and used without further purification. All reactions
were performed under argon by using standard Schlenk tech-
niques. Unless stated otherwise, all glassware used for reactions
was evacuated, heated to over 1008C, and flushed with argon
prior to loading with the reagents. Dichloromethane was dried by
distillation over CaH2. Solvents for workup were purified by distilla-
tion. All products were dried under vacuum prior to analysis. 1H
and 13C NMR spectra were recorded by using Bruker DPX 300 (1H:
300 MHz, 13C: 75 MHz), DPX 400 (1H: 400 MHz, 13C: 100.6 MHz), or
DPX 500 (1H: 500 MHz, 13C: 125.8 MHz) spectrometers. Chemical
shifts are given in parts per million (ppm) referenced to the residu-
STM analysis (Figure 3) showed that the molecules form
(again) an oblique pattern (to which a unit cell of a=(4.0Æ
0.1) nm, b=(1.9Æ0.1) nm, g(a,b)=(82Æ2)8 is indexed) in
which rows of “O”-shaped (oval) backbones are separated by
regions covered by the alkyl side chains, which interdigitate in-
termolecularly.
1
al H or 13C signals in deuterated solvents. Mass spectra were mea-
sured by using a Bruker Daltonics autoflex II TOF/TOF (MALDI-MS;
matrix material: DCTB (trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-
propenylidene]malononitrile) or dithranol), a Finnigan Thermo-
Quest MAT 95 XL (EI-MS), or an AEI MS-5 (EI-HRMS) spectrometer.
Peaks (m/z) smaller than 10 % (relative to the basis peak) are not
reported. UV/vis absorption spectra were recorded by using a Per-
kinElmer Lambda 18 spectrophotometer using 0.1, 0.2, 1.0, 10, and
100 mm quartz cuvettes manufactured by Hellma. Fluorescence ex-
periments were run on a PerkinElmer LS 50 B spectrofluorometer
in all-transparent 10 mm quartz cuvettes by monochromatic excita-
tion at the indicated wavelength. Melting points were determined
by using a Leica DMLB microscope with resistive heating socket
controlled by using a Leica LMW transformer and a Testo 925 digi-
tal thermometer. Thin-layer chromatography (TLC) was conducted
on silica-gel-coated aluminum plates (Macherey–Nagel, Alugram
SIL G/UV254, 0.25 mm coating with fluorescence indicator). For pu-
rification by column chromatography, silica gel 60M (Macherey–
Nagel, 0.04–0.063 mm, 230–400 mesh) was used as the stationary
phase, which was suspended in the indicated solvent. Gel permea-
tion chromatography (GPC, also: size-exclusion chromatography
(SEC)) was performed with THF (HPLC grade, Fisher, stabilized with
2.5 ppm 2,6-di-tert-butyl-4-methylphenol (BHT)) at RT. GPC analyses
were run by using an Agilent Technologies system at a flow rate of
1 mL minÀ1 using an IsoPump G1310 A, a G1314B VWD detector,
and PSS columns (Polymer Standards Service (PSS), Mainz, Germa-
ny: 102, 103, 105, and 106 Š; 5m; 8”300 mm). All molecular weights
were determined after polystyrene (PS) calibration (using PS stand-
ards obtained from PSS). For the preparative separation of product
mixtures by means of GPC, a Shimadzu recycling GPC systems was
used, equipped with an LC-20 AD pump, an SPD-20A UV detector,
and a set of three preparative columns from PSS (either 103 Š, 5m,
20”300 mm, or linearS, 5m, 20”300 mm), operated at a flow rate
of 5 mL minÀ1. GC-MS analyses were performed by using a Shimad-
zu system equipped with an AOC-20i autoinjector, a GCMS-QP2010
Plus mass spectrometer, and a GC-2010 gas chromatograph with
an FS-Supreme-5 MS column (length 30 m, internal diameter
0.25 mm, film thickness 0.26 mm). The system was operated with
helium as the carrier gas in the temperature range 50–3408C.
Figure 3. a) STM image and b) supramolecular model of self-assembled
monolayer of 14 at the TCB/HOPG interface. Image parameters, unit cell,
and additional packing parameters: 20.0”20.0 nm2, c=10À6 m, VS =À0.6 V,
It =15 pA; a=(4.0Æ0.1) nm, b=(1.9Æ0.1) nm, g(a,b)=(82Æ2)8;
g(b,c)=(90Æ10)8, g(a,d)=(31Æ2)8. Red, white (black), and blue lines indi-
cate unit-cell vectors, HOPG main axis directions, and directions of the
north–south axes c of the macrocycles, respectively. Approximate positions
of sulfur atoms are shown in yellow.
Conclusion
All in all, we have shown that it is possible to synthesize thio-
phene-containing macrocycles by DDQ-mediated coupling re-
actions of respective half-ring structures that are terminated
by thiophenes. The oxidative coupling does not require other
functional groups such as halogens or metals. However, the
coupling position (a or b) depends on the ring size and may
lead to unexpected results. The high tendency of some of the
molecules to form an a,b’-thiophene structure is remarkable.
However, blocking the b-position of the terminal thiophenes
leads to pure a,a’-isomers. Compounds with long alkyl side
chains self-assemble at the solid/liquid interface on HOPG so
that STM can be used to visualize the D- and O-shaped back-
bones with submolecular resolution.
NMR spectroscopy of 3
Compound 3 was dissolved in 1,1,2,2-[D2]tetrachloroethane to
a concentration of 27 mm. NMR spectra were acquired on Bruker
AVANCE III spectrometers with proton resonance frequencies of
400.13 MHz or 600.13 MHz. The 400 MHz spectrometer was
equipped with a BBFOplus probe. The 600 MHz spectra were re-
1
corded with an inverse H/13C/15N/31P-QXI probe. All spectra were
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recorded at 400 K, adjusted with a sample containing 80% glycol
in [D6]DMSO. Spectra were referenced to the residual solvent
signal (C2D2Cl4, dH =6.00 ppm). Processing and analysis was done
with TopSpin (Bruker, v3.1) and MestreNOVA (Mestrelab Research,
v7.1.0). Assignments are based on 1D-1H, 1D-13C, 2D-COSY, 2D-
tion by recGPC, an orange solid (15 mg, 40 %) was obtained.
1H NMR (400 MHz, CD2Cl2, RT): d=7.67 (s, 1H), 7.58 (s, 1H), 7.37 (d,
J=5.3 Hz, 1H), 7.25–7.13 (m, 11 H), 7.11–7.09 (m, 2H), 7.07 (d, J=
3.6 Hz, 1H), 7.03 (d, J=3.8 Hz, 1H), 7.01–6.99 (m, 2H), 2.89–2.78
(m, 8H), 1.73–1.55 (m, 8H), 1.47–1.20 (m, 72H), 0.93–0.84 ppm (m,
12H); MS (MALDI-pos, DCTB): m/z calcd for C92H120S8: 1480.7;
NOESY, H, 13C HMQC, and H, 13C HMBC spectra (see the Support-
ing Information). Because of conformational exchange processes,
the spectra of this macrocycle are significantly dependent on
sample temperature and spectrometer frequency. To ensure consis-
tency, all assignments reported here were therefore derived from
1
1
found: 1480.6; GPC (THF vs. PS): Mp =1730 gmolÀ1
.
Synthesis of 7b: 6b (120 mg, 0.13 mmol) and DDQ (90 mg,
0.40 mmol) were dissolved in dry dichloromethane (50 mL) and
added to a solution of TFA (1.5 mL) in dry dichloromethane
(100 mL) at 08C over 5 min. After stirring for another 2 min, the re-
action was quenched by addition of methanol and NaHCO3 (aq).
The organic layer was washed twice with water and after purifica-
tion by recGPC, an orange solid (42 mg, 35 %) was obtained.
1H NMR (500 MHz, CD2Cl2, RT): d=7.65 (s, 1H), 7.57 (s, 1H), 7.35 (d,
J=5.3 Hz, 1H), 7.23–7.18 (m, 6H), 7.17–7.14 (m, 4H), 7.14–7.11 (m,
2H), 7.09–7.07 (m, 2H), 7.05 (d, J=3.6 Hz, 1H), 7.01 (d, J=3.7 Hz,
1H), 6.99–6.97 (m, 2H), 2.87–2.77 (m, 8H), 1.70–1.55 (m, 8H), 1.45–
1.21 (m, 1H), 0.88 ppm (t, J=6.9 Hz, 12H); 13C NMR (125 MHz,
CD2Cl2, RT): d=144.26, 143.08, 142.78, 142.37, 141.15, 140.77,
140.36, 139.98, 137.38, 137.27, 136.73, 136.70, 136.61, 136.51,
136.50, 136.42, 135.55, 133.56, 133.19, 132.99, 132.54, 132.09,
131.44, 131.11, 130.96, 130.84, 129.77, 128.61, 128.32, 127.12,
127.10, 126.70, 126.08, 126.02, 124.34, 123.99, 123.84, 123.79,
123.62, 123.60, 123.55, 54.00, 54.00, 34.03, 33.90, 33.69, 32.53,
32.14, 31.85, 31.81, 31.69, 30.34, 30.33, 30.31, 30.29, 30.29, 30.25,
30.23, 30.20, 30.15, 30.09, 30.06, 30.05, 29.97, 29.95, 23.29, 23.29,
14.49 ppm; MS (MALDI-pos, DCTB): m/z calcd for C116H168S8: 1817.1;
1
a 1D-1H and a H,13C HMBC spectrum measured consecutively on
the 600 MHz spectrometer. 13C chemical shifts were measured in
the indirect dimension of the HMBC spectrum.
Scanning tunneling microscopy (STM)
The experimental setup consisted of an Agilent 5500 SPM system
placed on a Halcyonics active vibration damping platform and en-
closed in a home-built acoustic damping box. Mechanically cut Pt/
Ir (80:20) tips were used and further modified in situ by applying
short voltage pulses until high resolution was achieved. Highly ori-
ented pyrolytic graphite (HOPG) substrates were obtained from
MikroMasch in ZYB quality and freshly cleaved prior to each experi-
ment. All STM measurements were performed at the solid/liquid in-
terface (with the tip immersed in the solution). A solution of the re-
spective substance in 1,2,4-trichlorobenzene (TCB, 0.5 mL, 10À5
–
10À6 m) was dropped onto a piece of freshly cleaved HOPG at
808C, the temperature was retained for 20 s, then, the sample was
allowed to cool to RT. The sample was inserted into the STM and
the STM imaging was performed, which was typically completed
within 30 min. Bias voltages between À0.6 V and À0.8 V and cur-
rent set points between 10 pA and 50 pA were applied to acquire
the images shown here. All images were calibrated by subsequent
immediate acquisition of an additional image at reduced bias volt-
age; therefore, the atomic lattice of the HOPG surface is visible,
which is used as a calibration grid. Data processing, also image cal-
ibration, was performed by using the SPIP 5 (Image Metrology)
software package.
found: 1817.2; GPC (THF vs. PS): Mp =2520 gmolÀ1
.
Synthesis of 10: (130 mg, 0.12 mmol) and DDQ (82 mg,
9
0.36 mmol) were dissolved in dry dichloromethane (50 mL) and
subsequently added at 08C to a solution of TFA (1.5 mL) in dry di-
chloromethane (120 mL) over 5 min. After stirring for another
4 min, the reaction was quenched by addition of methanol and
NaHCO3 (aq). The organic layer was washed twice with water and
after purification by recGPC, an orange solid (5 mg, 4 %) was ob-
1
tained. H NMR (500 MHz, C2D2Cl4, 373 K): d=7.60 (s, 2H), 7.28 (s,
2H), 7.26 (d, J=3.7 Hz, 4H), 7.23 (d, J=3.7 Hz, 4H), 7.21–7.18 (m,
12H), 7.10 (d, J=3.7 Hz, 4H), 2.95–2.89 (m, 8H), 1.79–1.71 (m, 8H),
1.53–1.31 (m, 120H), 1.04–0.91 ppm (m, 12H); MS (MALDI-pos,
DCTB): m/z calcd for C132H176S12: 2145.0; found: 2145.0; GPC (THF
Synthesis and characterization
Synthesis of 3: 2 (23 mg, 0.05 mmol) and DDQ (8 mg, 0.15 mmol)
were dissolved in dry dichloromethane (20 mL) and subsequently
added at 08C to a solution of TFA (0.4 mL) in dry dichloromethane
(20 mL) over 5 min. After stirring for another 5 min, the reaction
was quenched by addition of methanol and NaHCO3 (aq). The or-
ganic layer was washed twice with water and after purification by
recGPC, an orange solid (7 mg, 31 %) was obtained. 1H NMR
(500 MHz, C2D2Cl4, 373 K): d=7.76 (dd, J1 =1.6 Hz, J2 =1.6 Hz, 1H),
7.74 (dd, J1 =1.6 Hz, J2 =1.6 Hz, 1H), 7.70 (dd, J1 =1.7 Hz, J2 =
1.7 Hz, 1H), 7.68 (dd, J1 =1.7 Hz, J2 =1.7 Hz, 1H), 7.65 (dd, J1 =
1.6 Hz, J2 =1.6 Hz, 1H), 7.52 (dd, J1 =1.6 Hz, J2 =1.6 Hz, 1H), 7.40 (d,
J=5.2 Hz, 1H), 7.38 (d, J=3.8 Hz, 1H), 7.36 (d, J=3.8 Hz, 1H),
7.32–7.30 (m, 2H), 7.28 (d, J=3.8 Hz, 1H), 7.26–7.24 (m, 2H), 7.23
(d, J=3.7 Hz, 1H), 7.22–7.18 (m, 4H), 7.18 (d, J =3.7 Hz, 1H), 7.05
(d, J=3.7 Hz, 1H), 6.92 (d, J=3.8 Hz, 1H), 1.50 ppm (s, 1H); MALDI
HRMS: m/z calcd for C52H40S8: 920.0891; found: 920.0874; GPC (THF
vs. PS): Mp =2950 gmolÀ1
.
Synthesis of 14: 13 (24 mg, 0.02 mmol) and DDQ (15 mg,
0.07 mmol) were dissolved in dry dichloromethane (30 mL) and
subsequently added at 08C to a solution of TFA (0.7 mL) in dry di-
chloromethane (30 mL) over 5 min. After stirring for another 5 min,
the reaction was quenched by addition of methanol and NaHCO3
(aq). The organic layer was washed twice with water and after pu-
rification by recGPC, the open-chain dimer (6 mg, 28 %) was ob-
tained as a yellow liquid together with 14 as a yellow solid (1 mg,
4 %).
1
Acyclic dimer: H NMR (400 MHz, CD2Cl2, RT): d=7.45 (s, 2H), 7.23
(s, 2H), 7.19 (d, J=5.2 Hz, 2H), 7.13 (d, J=3.7 Hz, 2H), 7.10 (d, J=
3.7 Hz, 2H), 7.04 (s, 2H), 7.02 (d, J=3.9 Hz, 2H), 7.02 (d, J =4.0 Hz,
2H), 6.96 (d, J=5.2 Hz, 2H), 2.81–2.77 (m, 16H), 1.74–1.55 (m,
16H), 1.35–1.13 (m, 144H), 0.93–0.81 ppm (m, 24H); MS (MALDI-
pos, DCTB): m/z calcd for C140H218S8: 2155.5; found: 2155.4; GPC
vs. PS): Mp =630 gmolÀ1
.
Synthesis of 7a: 6a (38 mg, 0.05 mmol) and DDQ (35 mg,
0.15 mmol) were dissolved in dry dichloromethane (30 mL) and
added to a solution of TFA (0.6 mL) in dry dichloromethane
(30 mL) at 08C over 5 min. After stirring for another 4 min, the re-
action was quenched by addition of methanol and NaHCO3 (aq).
The organic layer was washed twice with water and after purifica-
(THF vs. PS): Mp =3030 gmolÀ1
.
1
Cyclodimer: H NMR (400 MHz, CD2Cl2, RT): d=7.46 (s, 2H), 7.26 (s,
2H), 7.19 (s, 4H), 7.11 (d, J=3.7 Hz, 4H), 7.07 (d, J=3.7 Hz, 4H),
2.94–2.59 (m, 16H), 1.65–1.59 (m, 16H), 1.39–1.19 (m, 144H), 0.94–
0.77 ppm (m, 24H); MS (MALDI-pos, DCTB): m/z calcd for
Chem. Eur. J. 2016, 22, 1379 – 1384
www.chemeurj.org
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ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
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H. D. F. Winkler, C. A. Schalley, P. Bäuerle, Angew. Chem. Int. Ed. 2009, 48,
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C140H216S8: 2153.5; found: 2153.3; GPC (THF vs. PS): Mp =
2950 gmolÀ1
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Keywords: cyclooligomers · scanning tunneling microscopy ·
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Received: August 14, 2015
Published online on December 16, 2015
Chem. Eur. J. 2016, 22, 1379 – 1384
www.chemeurj.org
1384
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim