Shape-persistent macrocycles comprising perfluorinated benzene subunits: Synthesis, aggregation behaviour and unexpected μ-rod formation

Article abstract of DOI:10.1039/b817274a

The synthesis of a series of shape-persistent macrocycles (SPMs) (1-4 and 6) comprising different numbers and/or spatial arrangement of meta-substituted tetrafluorobenzene and benzene subunits interlinked with diacetylenes is described. To increase their

Full text of DOI:10.1039/b817274a

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Shape-persistent macrocycles comprising perfluorinated benzene subunits:
synthesis, aggregation behaviour and unexpected l-rod formation†
Lijin Shu,a Marcel Mu¨ri,b Ralph Krupkea and Marcel Mayor*a,b
Received 2nd October 2008, Accepted 24th December 2008
First published as an Advance Article on the web 5th February 2009
DOI: 10.1039/b817274a
The synthesis of a series of shape-persistent macrocycles (SPMs) (1–4 and 6) comprising different
numbers and/or spatial arrangement of meta-substituted tetrafluorobenzene and benzene subunits
interlinked with diacetylenes is described. To increase their solubility, all five SPMs were functionalized
by four peripheral hexyl chains. These SPMs were assembled from common diacetylene building blocks
by a modular synthetic strategy based on palladium and/or copper catalyzed versions of acetylene
coupling reactions (oxidative acetylene coupling and Cadiot–Chodkiewicz coupling). The aggregation
properties in chloroform of SPMs 1–6 were investigated by concentration- and temperature-dependent
1H-NMR investigations and by vapour pressure osmometry studies. Aggregation constants and
thermodynamic data of the process were obtained by least-squares fitting of the NMR data and by van’t
Hoff analysis respectively. Aggregation was only observed for SPMs 2–6 comprising electron deficient
tetrafluorobenzene corner units. While dimerization was the major aggregation process for SPMs 3–6,
the formation of larger aggregates in solution was only observed for SPM 2. The formation of
aggregates is in all cases enthalpically driven. As the largest and the smallest enthalpic contribution and
entropic loss in the series of aggregating SPMs were found for the two SPMs 3 and 4, each comprising
two fluorinated corner units, the spatial arrangement of these subunits within the macrocycle seems to
be at least equally important as the ratio of tetrafluorobenzene and benzene moieties. Interestingly,
micro-scaled hexagonal rods were formed from SPM 3 upon heating in toluene, presumably consisting
of mixtures of oligomers arising from covalently interlinked macrocycles.
We recently reported the synthesis of the SPM 5 consisting
of diyne linked alternating hexylbenzene and tetrafluorobenzene
Shape-persistent macrocycles (SPMs) gained considerable at-
subunits displaying an increased dimerization tendency arising
Introduction
tention during the last decade.1–7 As rigid nanoscale scaffolds
they are not only able to control the intramolecular spatial
arrangement of functional groups and subunits,3,8–15 but also
from quadrupole interactions between the electron rich and
electron poor subunits of the formed dimer.19 The considerable p–
p stacking interactions between fluorinated benzene and benzene
to organize their intermolecular self-assembly in solution2,6,7,16–19
and on 2D substrates.8,20,21 Furthermore, their aggregation pro-
perties make them promising building blocks for nanoscale
objects22,23 and tailor-made functional materials.4,18,24,25 Since
Moore and co-workers reported the dimer formation of SPMs
due to p–p stacking,26,27 numerous new SPM model compounds
were synthesized to investigate the phenomenon in detail. In
particular, SPMs comprising electron-donating28 and electron-
withdrawing14,19 substituents,26,27,29 hydrogen bonding units,30 and
chiral building blocks31,32 were synthesized to examine their aggre-
gation properties. First theoretical models to calculate assembling
properties of SPMs have been reported.33
were first reported by Patrick and Prosser in 1960.34 Since
then, the phenomenon has been investigated in detail35 with
designed model compounds including either intramolecular36,37
or intermolecular38–41 p–p stacking interactions.42,43 In addi-
tion, theoretical models provide further insight into the na-
ture of the intermolecular interactions.33,44 Meanwhile, the
supramolecular synthon has been applied successfully in crystal
engineering,45–58 surface patterning,59 topochemistry60,61 and to
preorganize reactants.62–64 Furthermore, fluorinated benzene sub-
units have been incorporated to tune material properties of liquid
crystals,65–67 polymers,68,69 hydrogels,70 adjustable networks,71 opti-
cally active materials72–74 and even biomolecules75 like DNA76,77 or
peptides.78
Aggregation properties of macrocycles incorporating meta-
ethynyl or -diyne interlinked benzene corner units have already
been investigated. Increased aggregation tendencies were observed
for SPMs comprising electron deficient benzene subunits and,
thus, benzoate based subunits with their electron-withdrawing
exo-annular substituents were used as aggregation favouring
corner units.26,29 In addition, a strong solvent dependence of the
aggregation behaviour was observed.79 The objective of this study
is to investigate the potential of tetrafluoro-substituted benzene
aForschungzentrum Karlsruhe GmbH, Institute for Nanotechnology, P. O.
Box 3640, D-76021 Karlsruhe, Germany. E-mail: marcel.mayor@kit.edu;
Fax: +49 7247 82 5685; Tel: +49 7247 82 6392
bUniversity of Basel, Department of Chemistry, St. Johannsring 19, CH-
4056 Basel, Switzerland. E-mail: marcel.mayor@unibas.ch; Fax: +41 61
267 1016; Tel: +41 61 267 1006
† Electronic supplementary information (ESI) available: Tables of the
temperature and concentration dependent 1H-NMR investigations, de-
scribtion of the solubility studies and the tables of the data displayed in
Fig. 2 and 3. See DOI: 10.1039/b817274a
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corners as aggregation-steering subunits. Thus, the macrocycles
1–6 were synthesized and characterized as a family of SPMs
comprising different numbers and/or different spatial arrange-
ment of perfluorinated subunits (Fig. 1). Their aggregation and
dimerization was investigated in chloroform by concentration
dependent H-NMR experiments and by vapour pressure osmo-
metry studies. Aggregation constants K were determined at
various temperatures, providing further insights into the thermo-
dynamic driving forces of the aggregation process.
1
Results and discussion
Synthesis
All five SPMs 1–5 consist of six aromatic corner units interlinked
with diacetylenes in the meta-position. To increase the solubility
of these structures in organic solvents, particular benzene subunits
are functionalized with additional hexyl chains in the remaining
meta-positions. To keep the series of macrocycles as comparable
as possible, with the obvious exception of 5, each cycle is
functionalized with four alkyl chains. The diacetylene linker allows
for a modular assembly of the SPMs from suitable meta-diyne-
functionalized benzene building blocks. Symmetric diacetylenes
can be obtained by a Glaser-type oxidative acetylene coupling
reaction80,81 while for asymmetric acetylenes both precursors are
distinguished as acetylene and bromoacetylene allowing for a
Cadiot–Chodkiewicz coupling reaction.81,82
The assembly of the SPMs 1–4 is displayed in Scheme 1, while
the synthesis of the SPM 5 with periodically alternating tetrafluo-
robenzene and hexylbenzene subunits has already been reported.19
First, the differently functionalized 1,3-diethynylbenzene build-
ing blocks 8–12 were synthesized. 1,3-Bis(bromoethynyl)benzene
(8) was obtained by brominating the commercially available
1,3-diethynylbenzene (7). The diyne 7 was treated with N-
bromosuccinimide (NBS) and traces of AgNO3 in acetone to
provide the desired dibromoacetylene 8 in 77% yield after purifi-
cation by column chromatography (CC). By applying similar re-
action conditions, 1,3-bis(bromoethynyl)-5-hexylbenzene 10 was
obtained as a slightly yellowish oil in 91% yield from 1,3-diethynyl-
5-hexylbenzene (9). The diyne 9 and the mono protected diyne 11
were obtained in four steps following a published protocol.19 These
precursor syntheses start with 4-hexylaniline which is doubly
brominated to 2,6-dibromo-4-hexylaniline. Deamination followed
by substitution of both bromines with triisopropylsilyl (TIPS)
protected acetylenes in a Sonogashira-type83,84 coupling reaction
provided the doubly protected diyne precursor. Gentle deprotec-
tion gave a mixture of the doubly deprotected diyne 9 and the
mono protected diyne 11 which were isolated by CC. The synthesis
of the 1,2,3,5-tetrafluoro-4,6-bis(bromoethynyl)benzene building
block 12 was reported elsewhere.19 Tetrafluoroisophthalonitrile
was reduced to tetrafluoroisophthalaldehyde and a Corey–Fuchs
reaction sequence85 provided the dibromoacetylene precursor 12.
With the required precursors 7–12 in hand, the stepwise
assembly of the SPMs was undertaken. The semicycles 13, 16 and
18, comprising terminal TIPS protected acetylenes, were obtained
by a palladium and copper catalyzed variation of the Cadiot–
Chodkiewicz coupling reaction.86 Thus, the dibromoacetylene
precursors 8, 10 and 12 were treated with two equivalents of the
mono protected diyne 11 in the presence of Pd2(dba)3·CHCl3 and
CuI as catalysts to provide the doubly TIPS protected semicycles
13, 16 and 18 in 66%, 24% and 67% yields respectively after CC.
The corresponding free acetylenes 14, 17 and 19 were obtained
by treating the TIPS protected precursors with TBAF in wet
Fig. 1 Chemical structures and schematic representation of the SPMs
1–5. White hexagons represent a benzene subunit while coloured hexagons
represent a tetrafluorobenzene subunit.
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Scheme 1 Synthesis of the SPMs 1–4 and their precursors. Reagents and conditions: a) NBS, AgNO3, CH3COCH3, r.t.; b) TBAF, wet THF, r.t.;
c) Pd2(dba)3·CHCl3, CuI, C6H5CH3, EtN(i-Pr)2, r.t.; d) Cu(CH3CO2)2·H2O, C5H5N, C6H6, r.t.; e) PdCl2(PPh3)2, CuI, THF, EtN(i-Pr)2.
THF at room temperature. Thus the diacetylenes 14, 17 and 19
were obtained in 81%, 96% and 79% yields respectively after CC.
The semicycle 15 comprising two terminal bromoacetylenes was
isolated by CC in 94% after treating the diyne semicycle 14 with
NBS and traces of AgNO3.
an oxidative acetylene coupling was applied. A suspension of
Cu(CH3CO2)2·H2O in 300 mL pyridine and 200 mL benzene was
stirred vigorously under air while a solution of the semicyclic
diacetylene 14 dissolved in 100 mL benzene was added dropwise
over a period of 24 hours at room temperature. After stirring
the reaction mixture at room temperature for another 2 days,
the solvents were evaporated and the residue redissolved in
Using these semicycles, the macrocycles 1, 2 and 3 were
assembled. For the SPM 1 a pseudo high dilution variation of
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toluene. Filtration and subsequent separation by size exclusion
chromatography (SEC) provided the macrocycle 1 in 25% yield
as a brown solid. Most likely, the formation of larger open chain
and cyclic oligomers under the applied reaction conditions are
responsible for the moderate yield of isolated SPM 1. These side
products of larger molecular weight were not further investigated.
For the assembly of the macrocycle 2, a pseudo high dilution
variation of the above-described Pd and Cu catalyzed version
of the Cadiot–Chodkiewicz coupling reaction was applied. To a
nitrogen purged mixture of 450 mL toluene and 5 mL diisopropy-
lethylamine containing Pd2(dba)3·CHCl3 and CuI as catalysts, a
solution of equimolar amounts of the semicycles 15 and 19 in
40 mL toluene was added dropwise over a period of 10 hours at
room temperature. The reaction mixture was allowed to stir at
room temperature for another 4 days. The solvents were removed
and the remaining residue redissolved in 15 mL toluene. After
filtration and SEC, the macrocycle 2 was obtained in 9% yield as
a light brown solid. Also in this case, the expected side products
of larger molecular weights were not further investigated.
The successful ring closure between the doubly bromoacetylene-
functionalized pentamer 20 and the diyne 9 to the SPM 4 led
us to investigate similar reaction conditions with the diyne 19
and the dibromoacetylene 21 to obtain the enlarged macrocycle 6
consisting of eight aromatic corner units (displayed in Scheme 2).
In analogy to the SPM 5, the highly symmetric macrocycle
6 consists of alternating tetrafluorobenzene and hexylbenzene
subunits. However, the expansion of the ring no longer allows
for planarity of the cyclic system which might be reflected in its
association behaviour. Applying comparable reaction conditions
to the precursors 19 and 21 as for 9 and 20 during the synthesis of
4, the macrocycle 6 was isolated in an even lower yield of 6% as a
white solid after SEC.
To assemble the macrocycle 3, comparable pseudo high dilution
conditions were applied for a Pd and Cu catalyzed variation of
the oxidative acetylene coupling.87 Thus, a mixture of 15 mL
diisopropylethylamine in 1.2 L dry THF containing PdCl2(PPh3)2
and CuI as catalyst and dry silica gel as a water trap was stirred
under dry air. A solution of the semicycle 19 in 100 mL dry
THF was added dropwise over a period of 10 hours. The reaction
mixture was stirred for another 4 days before the solvents were
removed and the remaining residue was dissolved in 15 mL toluene.
Filtration through a short plug of silica gel and separation by SEC
provided the SPM 3 in 20% yield as a brown solid. The oligomeric
side products were not further investigated.
Scheme 2 Synthesis of the macrocycle 6. Reagents and conditions:
a) Pd2(dba)3·CHCl3, CuI, C6H5CH3, EtN(i-Pr)2, r.t.
In contrast to the SPMs 1–3, the macrocycle 4 was not
assembled from two hemicycles but by a stepwise elongation of
the semicycle 17. Thus, the diyne 17 was treated under the Pd and
Cu catalyzed reaction conditions already described above with
an excess of the bromoethynyl-functionalized tetrafluorobenzene
building block 12. In order to maximize the relative concentration
of the bromoacetylene precursor 12 with respect to the diyne 17,
7.7 equivalents of 12 were dissolved together with the catalysts
in a degassed diisopropylethylamine/toluene mixture to which a
solution of the diyne 17, dissolved in toluene, was added dropwise
over a period of 2% hours at room temperature. After stirring
for additional 2 hours, removal of the solvents and purification
by CC, the terminal bromoethynyl-functionalized pentamer 20
was isolated in 46% yield as a yellow solid. To close the cycle
4, its precursors 20 and 9 were treated under comparable high
dilution conditions as described above for the synthesis of SPM 2.
Thus, to a vigorously stirred and degassed mixture of the catalysts
Pd2(dba)3·CHCl3 and CuI dissolved in 450 mL toluene and 5 mL
diisopropylethylamine a solution comprising equimolar amounts
of the dibromoacetylene 20 and the diacetylene 9 dissolved in
40 mL toluene was added dropwise over 10 hours at room
temperature. After stirring for 4 days, the solvents were removed
and the residue redissolved in toluene. Filtration and purification
by SEC provided the SPM 4 in 9% yield as a brown solid. A
considerable fraction of the crude reaction products passed faster
through the SEC column than the SPM 4 suggesting the presence
of higher molecular weight oligomers which were not further
investigated.
The macrocycles 1–6 and their precursors were fully character-
ized by 1H-, 13C- and 19F-NMR spectroscopy, mass spectrometry
and elemental analysis. However, the limitations in solubility and
availability of the macrocycle 2 combined with its rather low
symmetry and the multiple splitting of the carbon signals of per-
fluorinated benzenes, did not allow to resolve the aromatic carbons
of its tetrafluorobenzene subunit in the 13C-NMR spectrum.
Stacking investigations
1H-NMR investigations. Due to the limited solubility of these
SPMs in polar solvents such as acetonitrile or methanol, their
aggregation properties were investigated exclusively in chloro-
form. Thus, their 1H-NMR spectra were recorded in CDCl3
at various concentrations and temperatures. However, the ob-
servable concentration windows were limited by the solubilities
of these SPMs in chloroform. In particular, the saturation-
concentrations at 25 ◦C in chloroform of the macrocycles 1, 2,
3 and 6 were 2.75 mmol/L, 5.15 mmol/L, 1.96 mmol/L and
2.64 mmol/L respectively. Interestingly, the SPM 4 displayed the
highest saturation-concentration (31 mmol/L). Only the SPM 5
(25 mmol/L) was comparable.
Within the observable concentration window (0.5–2.75 mmol/
L) the chemical shifts of both, the exo- and the endo-annular
protons of SPM 1 were concentration independent. This con-
centration independent behaviour points at dissolved monomeric
molecular species in this concentration regime, as previously
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reported for comparable SPMs like e.g. phenyl ethynyl macrocycles
peripherally functionalized with butylcarboxylates, butylether- or
benzylbutylether-groups.2
the asymptotic branch is cut off due to the solubility restrictions.
A less pronounced upfield shift with increasing concentration was
observed for SPM 2.
1
In contrast to 1, the chemical shifts of the proton signals
of the SPMs 2–6 depended on their concentrations. For all
five SPMs the exo-annular protons displayed a stronger con-
centration dependence (Fig. 2) than the endo-annular proton.
Even in the narrow concentration range required to observe a
detectable 1H-NMR signal and the solubility of the SPM in
CDCl3 at 10 ◦C, a considerable shift towards higher field with
increasing concentration was observed, suggesting intermolecular
p–p stacking. As expected, the presence of both corner units,
benzene and tetrafluorobenzene is required to promote p–p
stacking by quadrupole interactions in the investigated solvent,
temperature and concentration regimes. While the chemical shift
vs. concentration slopes (Fig. 2) of the SPMs 4 and 5 allow to
anticipate an asymptotic approach towards a signal for infinite
concentration, this was not the case for the SPMs 2, 3 and 6 due to
their limited concentration window. However, the slopes of 3 and 6
resemble strongly the more pronounced concentration dependent
initial branch of the slopes of 4 and 5 and thus, it seems likely that
These H-NMR investigations, displaying systematic changes
of the chemical surrounding of the macrocycles comprising
tetrafluorobenzene subunits with concentration, strongly point at
intermolecular stacking events. However, the number of SPMs
involved in the formation of these stacked supermolecules cannot
be determined by these titration experiments.
Vapour pressure osmometry (VPO). The stacking behaviour of
the SPMs 1–4 and 6 was further investigated by VPO to inspect
whether the chemical shifts observed in the 1H-NMR studies arise
from dimerization of these SPMs or from the formation of larger
oligomeric piles consisting of several stacked SPMs. Thus, the
averaged molecular weights of dissolved species were measured
for these SPMs at various concentrations which are listed in
Table 1.
Very comparable molecular weights were obtained at all four
concentrations of SPM 1 in CHCl3 at 37 ◦C. The values between
1302 and 1090 g/mol are comparable with the molecular weight
(1081 g/mol). This suggests the presence of freely dissolved SPMs
without intermolecular stacking, as observed by 1H-NMR studies.
It is noteworthy that several of the SPM solutions listed in
Table 1 are clearly below the critical lower concentration of about
2 mmol/L (~0.003 mol/kg) suggested for the VPO apparatus
(Knauer VPO K-7000) and thus, these data should be considered
as semi-quantitative, diagnostic for stacking interactions.
Due to the poor yield in its synthesis, only very limited
amounts of the SPM 2 comprising a single tetrafluorobenzene
subunit were available for VPO investigations. Thus, only two
concentrations were measured to study its stacking behaviour. A
0.82 mmolar solution of SPM 2 in CHCl3 at 37 ◦C displayed
a value (1139 g/mol) corresponding to the SPM molecular
weight (1153 g/mol), pointing at completely dissolved individual
molecules 2 at this concentration. More surprising was the value of
3780 g/mol at a concentration of 3.38 mmol/L which suggests the
presence of at least trimeric stacked species under the investigated
conditions. As the majority of SPMs reported so far were either
not aggregating or forming only dimers, the observation of larger
oligomers by VPO for SPM 2 was unexpected. Unfortunately,
the available quantity of SPM 2 did not allow investigation of its
stacking behaviour in further detail.
Fig. 2 Concentration dependence of the 1H-NMR chemical shifts of the
exo-annular protons of the macrocycles 1–6 in CDCl3 at 10 ◦C. The dots
are the measured values and the solid lines are the fitted titration curves.
Table 1 Concentration dependent average molecular weight of the aggregates formed by the macrocycles 1–4 and 6 in CHCl3
1a
2a
3b
4b
6a
C84H72
C84H68F4
1153.43 g/mol
C84H64F8
1225.39 g/mol
C84H64F8
1225.39 g/mol
C104H64F16
1617.60 g/mol
1081.47 g/mol
conc.
(mmol/L)
mwt.
(g/mol)
conc.
(mmol/L)
mwt.
(g/mol)
conc.
(mmol/L)
mwt.
(g/mol)
conc.
(mmol/L)
mwt.
(g/mol)
conc.
(mmol/L)
mwt.
(g/mol)
0.31
1.2
2.31
4.99
1302
1120
1124
1090
0.82
3.38
1139
3780
0.57
1.14
2.28
4.65
9.46
623
1022
1619
1930
2133
0.82
1.22
2.69
5.63
10.85
1136
2169
2247
2012
2254
0.32
0.87
1609
2411
a Measured at 37 ◦C. b Measured at 42 ◦C.
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The SPM 3, comprising two tetrafluorobenzene subunits facing
each other on the cycle’s periphery (1,4-position), was available
in larger amounts. To expand the scope of addressable concen-
trations, the solvation of 3 in CHCl3 at 42 ◦C was assisted by
ultrasonic sonication. A maximum concentration of 9.46 mmol/L
was reached as a slightly cloudy solution without observable
precipitation. As displayed in Table 1, an increase of the average
molecular weight of the dissolved species with concentration was
observed for SPM 3. However, even at the maximum concentration
a molecular weight (2133 g/mol) below the one expected for
complete dimer formation (2450 g/mol) was recorded. Thus, the
dominant assembly process of SPM 3 is most likely dimeric.
The SPM 4 comprises, as SPM 3, two tetrafluorobenzene
subunits, but in 1,3-positions with respect to the corner units of the
SPM. Intrestingly, this structural variation makes the SPM about
ten times more soluble. Again, its aggregation in CHCl3 at 42 ◦C
was investigated by VPO. As displayed by the data in Table 1,
the VPO investigations do not really benefit from the increased
solubility of 4. While a molecular weight of 1136 g/mol pointing
to a monomeric dissolved species (1225 g/mol) was observed at
a concentration of 0.82 mmol/L, all investigated concentrations
above 1.22 mmol/L displayed values between 2012 g/mol and
2254 g/mol, pointing at stacked dimers of SPM 4. Again, dimer
formation seems to be the dominant assembly process, as even for
concentrations above 10 mmol/L, only values below the molecular
weight of the dimer were observed.
VPO investigations of the SPM 6 were limited to only two
concentrations due to the limited availability of the compound.
SPM 6 is an expanded structural analog of SPM 5, for which
dimer formation has already been reported as the major assembly
process in CHCl3 at room temperature.19 However, the expansion
by two additional corner units reduces the planarity of 6 con-
siderably and might influence its assembly behaviour. The values
recorded in CHCl3 at 37 ◦C displayed mainly the presence of
dissolved monomeric species at a concentration of 0.32 mmol/L
and its tendency to stack upon increasing the concentration to
0.87 mmol/L. The recorded average molecular weight does not
point towards further aggregation beyond dimer formation. While
the recorded VPO data and the similarity to SPM 5 point towards
dimerization as the dominant aggregation process, the restricted
amount of VPO data available for SPM 6, combined with the
limited accuracy of the method in the investigated concentration
regime, hardly allows us to exclude the formation of larger stacks.
Assuming dimer formation as the major aggregation behaviour,
the average molecular weight of 2411 g/mol at a concentration
of 0.87 mmol/L corresponds to about 50% of the molecules in
solution aggregated as dimers.
the formation of larger aggregates was considered exclusively for
SPM 2.
Association constants and thermodynamic data. The concen-
1
tration dependent H-NMR and VPO investigations allow de-
termination of the association constants for the SPMs 2–4 and
1
6. While the H-NMR data are perfectly suited to extract the
association constant by least-squares curve fitting, the VPO data
are crucial to favour a particular association model for each
SPM.2 Thus, based on the osmometric data, a monomer–dimer
equilibrium has been assumed as the major aggregation process of
SPMs 3–6. To obtain dimerization constants (KDim), eqn (1) with
ctot as the total concentration of the SPM and dMono and dDim as
the chemical shifts of the monomer and the dimer respectively was
used for least-squares curve fitting of the concentration dependent
1H-NMR data.88
8◊ KDim ◊ctot +1 -1
4 ◊ KDim ◊ctot
(1)
d = dDim + dMono - dDim
(
)
While the aggregation by dimerization of SPM 5 has already been
rep◦orted,19 the dimerization constants obtained by curve fitting at
20 C are summarized in Table 2. Furthermore, the fitted curves
at 10 ◦C are presented as solid lines in Fig. 2, displaying the good
correlation between measured data points and calculated curves.
For the larger aggregates of SPM 2 an isodesmic association
model was applied, assuming a general association constant
independent from the extent of the already existing stack towhich a
monomer is aggregating (KDim = K3 = K4 =. . . . . .= Kn = KAss). To
obtain association constants (KAss) of SPM 2, least-squares curve
fitting of the NMR data to eqn (2) was applied.29,79 In eqn (2), d is
the chemical shift at the concentration of SPM 2 (ctot), and dMono
and dAss are the limiting chemical shifts of the monomer and the
aggregate respectively.
4◊KAss ◊ctot +1 -1
2◊KAss ◊ctot
(2)
d=dAss + dMono -dAss
(
)
The association constants obtained for SPM 2 are displayed
tog◦ether with the dimerization constants of◦the other SPMs at
20 C in Table 2 and the fitted curve for 10 C is displayed as a
solid line in Fig. 2.
Furthermore, by varying the temperature of the concentration
dependent 1H-NMR investigations followed by least-squares
curve fitting, association constants at different temperatures were
obtained. The aggregation of each SPM was investigated at
five different temperatures and a subsequent van’t Hoff analysis
Table 2 Aggregation constants at 20 ◦C of SPMs 1–6 in CDCl3 and
thermodynamic data obtained by van’t Hoff analysis
In summary, the VPO studies pointed, in spite of the limited
amounts of SPMs available and the borderline concentrations
of the samples, towards dimerization as the major aggregation
process for most of the studied SPMs. While the lack of
aggregation was expected for SPM 1, the tendency to form
larger aggregates of SPM 2 was rather surprising. However, due
to the limited availability of SPM 2, this behaviour has been
deduced from a single VPO solution which was reproduced in
triplicate. All three measurements provided comparable results
and the measured average molecular weight pointing at about
trimeric species should be outside the variation and imperfection
of the method and the apparatus. Thus, throughout the paper
SPM K293 K (M-1) DG293 K (kJ/mol) DH293 K (kJ/mol) DS (J/mol·K)
1a
2b
3c
4c
5c
6c
~0
33.4 21.2
22.6 12.1
116.1 19.2 -11.6 2.7
1875 605 -18.3 5.2
176.2 35.9 -12.6 4.9
-8.9 4.0
-7.6 4.8
-46.6 2.0
-85.3 4.4
-33.6 1.3
-64.1 2.6
-63.9 2.5
-128.5 6.8
-265.2 16
-75.1 4.6
-156.3 8.9
-172.9 8.3
a No aggregation was observed in CDCl3. b The formation of larger
aggregates was observed by osmometry. c No larger aggregates than dimers
were observed by osmometry.
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provided thermodynamic data of the association process. Thus,
plots of the natural logarithm of their association constants against
the inverse absolute temperature should provide straight lines
with DH/R as slopes and -DS/R as axis intercepts. In Fig. 3
the van’t Hoff plots of the SPMs 2–6 are displayed and the
extracted thermodynamic parameters of the association process
are summarized in Table 2.
fluorobenzene/benzene interactions, a rotational displacement
reduces the distance between repulsive fluorinated corner units.
Finally, the aggregation of SPM 2 displays a comparable weak
enthalpic contribution as was observed for SPM 4. However,
while a rather low enthalpic contribution has been expected
due to the low number of stabilizing interactions arising from
a single fluorinated unit in the macrocycle, the comparison with
the dimerizing SPMs is questionable to some extent due to its
different aggregation mechanism.
The entropies (DS) listed in Table 2 oppose the trend observed
for the enthalpic contributions of the dimerizing SPMs 3–6.
Namely, aggregation systems with a large enthalpic contribution
have a large negative entropy. This is the expected observation
that a strong aggregation tendency tends towards a more ordered
system reflected in a large negative value for its entropy (DS). The
number of solvent molecules released by aggregation is (i) not able
to compensate the entropy loss by aggregation and (ii) assumed to
be comparable for all investigated SPMs.
In addition, the aggregation constants at 20 ◦C are displayed in
Table 2. As displayed by the various slopes in the van’t Hoff plot,
aggregation constants of these SPMs are strongly temperature
dependent and the selection of 20 ◦C as the observation temper-
ature is to some extent arbitrary. However, while the aggregation
constants of SPMs 2–4 and 6 are all within one order of magnitude,
the SPM 5 with a maximized number of stabilizing interactions
and a favourable planar geometry displays a more than ten fold
increased aggregation constant at 20 ◦C (K293 K(5) = 1875
605 M-1).
Fig. 3 Van’t Hoff plots of the SPMs 2–6. While for SPMs 3–6 the natural
logarithm of the dimerization constant KDim was plotted, the natural
logarithm of the association constant KAss obtained assuming an isodesmic
association model was used for the SPM 2. Least-squares fit of the data
points provided the regression lines.
Temperature triggered formation of l-rods
All five aggregating SPMs 2–6 have their enthalpically driven
association with negative free energies at 20 ◦C (DG293 K) in
common. However, the enthalpic contributions to the associations
of these different SPMs vary considerably, as can be seen by their
A surprising observation was made during the characterization of
SPM 3. Recording of the 13C-NMR spectra of these macrocycles
was challenging due to their limited solubility and the extensive
coupling of carbon nuclei with peripheral fluorine substituents.
Thus, 13C-NMR spectra were recorded in d8-toluene, which turned
out to be able to dissolve considerable amounts of different
fluorinated SPMs 2–6. To further increase the amount of dissolved
different slopes in Fig. 3 or their enthalpies at 20 ◦C (DH293 K
)
listed in Table 2. While both macrocycles 5 and 6 consisting
of alternating hexylbenzene and tetrafluorobenzene corner units
display comparable enthalpies at 20 ◦C, the largest and the
lowest enthalpic contributions have both been observed by an
SPM comprising two tetrafluorobenzene corner units, pointing
at the crucial importance of the spatial arrangement of these
subunits. The most negative enthalpy was observed for SPM 3,
having the two fluorinated corner units at opposite corners of the
macrocycle (1,4-position) while the lowest enthalpic contribution
was observed for SPM 4 with its two fluorinated corner units in the
1,3-position. The enlarged enthalpic stabilization of 3 compared
with 5 was surprising at first glance, as the latter enables more
stabilizing fluorobenzene/benzene couples in an aggregated dimer.
However, the finding might be rationalized to some extent by
the theoretically predicted rotational displacement (by 6.5◦) of
these fluorobenzene/benzene couples in an aggregated dimer.33
While in a dimer of 5 the rotational displacement results to
some extent in a reduced distance between repulsive fluorinated
corner units, this is not the case for a dimer of SPM 3. On the
other hand, the weaker enthalpic contribution in the dimer of
SPM 4 can be rationalized by (i) the lower number of stabilizing
fluorobenzene/benzene couples compared with 5 and (ii) by the
fact that for each possible dimer profiting from four stabilizing
◦
SPM 3, the solution was heated to 50 C. Initially, the increased
temperature dissolved 3 completely in toluene. However, after
a few hours, the compound precipitated again at this elevated
temperature. Neither further increase of the temperature nor
sonication of the sample allowed the formed precipitation to be
redissolved.
Closer inspection of the precipitate by scanning electron mi-
croscopy (SEM) revealed well formed rod-like crystallites with a
hexagonal cross-section as displayed in Fig. 4. The diameter of a
typical crystallite is in the order of a few microns and its aspect
ratio (length/diameter) is in the order of 10. Thus, these crystallites
must consist of a large number of well ordered molecules.
Even more surprising than the self-assembly of these macro-
cycles at elevated temperature in well ordered crystallites was
their behaviour during inspection by SEM. The as-prepared rods
have numerous cracks perpendicular to their long axis (Fig. 4A)
which disappear under progressive SEM imaging. As an example,
Fig. 4B displays the same area of a crystallite as Fig. 4A after
irradiation with the electron beam for about 5 minutes. This
behaviour is very surprising for organic materials. Usually organic
materials subjected to electron irradiation are unstable and tend to
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Fig. 4 SEM images of a hexagonal rod-like crystallite formed in a 50 ◦
C
hot solution of SPM 3 in toluene. As-prepared sample (A), after irradiation
for 5 minutes (B).
charge up and disintegrate. Here the opposite is observed, namely
defects in these crystallites are repaired under electron irradiation.
Moreover, these crystallites do not show any sign of charging,
pointing at an efficient charge transport mechanism in these m-
rods.
These observations show (i) that the 10 keV (1.6 ¥ 10-15 J =
1.6 fJ) electrons provide sufficient energy to activate defect healing
without causing significant structural damage and (ii) that charges
can propagate through the material to the conducting substrate.
The healing mechanism is observed on a micron length scale
and thus, it is probably caused by an electron beam induced
rearrangement of the molecular building blocks in the crystallite
and not the result of a reaction on the molecular scale.
Fig. 5 GPC analysis of a solution of 3 in toluene (A) before and (B) after
heating at 50 ◦C for 48 hours.
However, the fact that these crystallites are no longer soluble in
hot toluene whereas freshly prepared samples of SPM 3 are raised
the question concerning the molecular identity of the building
blocks of these crystallites. Fortunately, after the screening of
numerous solvents, dimethylformamide (DMF) turned out to be
able to dissolve small amounts of these crystallites completely.
Thus, a saturated toluene solution of SPM 3 was divided into
two halves. While the first sample was evaporated to dryness, the
second sample was heated to 50 ◦C for 48 hours and the thereby
formed solution comprising considerable amounts of precipitated
crystallites was evaporated to dryness. Subsequently, both samples
were redissolved in equivalent amounts of DMF and investigated
by gel permeation chromatography (GPC). While for the first
sample mainly the signal of the SPM 3 was observed (Fig. 5A), the
solution of these redissolved crystallites (Fig. 5B) displays signals
of twice and three times the molecular weight of the macrocycle
3, pointing at dimers and trimers.
Fig. 6 Infrared spectra of the SPM 3 (top) and of the crystallites obtained
from 3 upon heating in toluene (bottom). Both spectra were recorded as
KBr pellets.
was not possible due to the poor solubility and the polydisperse
nature of the material.
Apparently, heating of a concentrated solution of SPM 3 in
toluene provides covalently interlinked dimeric and trimeric struc-
tures. As a potential interlinking reaction an oligomerization of the
diacetylene units of two stacked macrocycles was hypothesized.
Similar reactions have already been reported triggered by light
in the solid state for diacetylenes organized by supramolecular
interactions of benzene and perfluorobenzene subunits.62,89 Typical
reaction products of diacetylene polymerizations contain but-1-
en-3-yne subunits. Thus, the crystallites were further investigated
by infrared spectroscopy, to search for new double bonds formed,
pointing at these expected subunits. And indeed, the comparison
of the IR spectra of the parent SPM 3 and the resulting crystallites
(Fig. 6) displayed a new signal at l = 1695 cm-1, which can be
assigned to a new carbon–carbon double bond in these crystallites.
Unfortunately, further investigation by 13C-NMR spectroscopy
Conclusion
A series of macrocycles consisting of diacetylene interlinked meta-
benzene corner units was synthesized and fully characterized. The
number and the relative position of perfluorinated corner units
were varied systematically to investigate the strength of inter-
molecular interactions arising from benzene/tetrafluorobenzene
quadrupole interactions. In particular, concentration dependent
1H-NMR experiments and vapour pressure osmometry investi-
gations provided insight into the aggregation behaviour of these
SPMs in CHCl3. While no aggregation tendency was observed
for the unfluorinated SPM 1, already a single fluorinated corner
unit in SPM 2 resulted in the formation of larger aggregates.
Interestingly, the formation of aggregates beyond dimers have
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only been observed for this SPM 2 comprising a single fluorinated
corner subunit while for all the other SPMs 3–6 comprising several
fluorinated corner units, all concentration dependent investiga-
tions pointed towards dimerization as the major aggregation
process. Thermodynamic data of the aggregation processes of
these SPMs were obtained by studying their assembly behaviour
at various temperatures. According to these results, the aggrega-
tion of these SPMs 2–6 comprising fluorinated corner units is
enthalpically driven. The largest enthalpic contribution together
with the largest entropic loss was observed for SPM 3 having
two fluorinated corner units facing each other. Furthermore, by
heating a concentrated solution of SPM 3 in toluene to 50 ◦C
a precipitation of rod-like crystallites with a hexagonal section
was observed. Investigation of these crystallites by SEM displayed
electron beam induced healing features which have – to the
best of our knowledge – not been reported so far for organic
materials. Further analysis of the crystallite forming material
pointed at covalently interlinked macrocycles, probably arising
from temperature induced oligomerization in the supramolecular
stack.
ArH), 7.42 (m, 2H, ArH), 7.53 (s, 1H, ArH). 13C-NMR (75 MHz,
CDCl3) d 51.01, 78.99, 122.98, 128.38, 132.02, 135.24. m/z (EI)
283.8 [M+]. EA calc. for C10H4Br2 (283.95): C 42.30, H 1.42.
Found: C 42.42; H 1.49%.
1,3-Bis(bromoethynyl)-5-hexylbenzene 10. 1,3-Diethynyl-5-
hexylbenzene (9) (700 mg, 3.33 mmol), N-bromosuccinimide
(1.20 g, 6.75 mmol) and silver nitrate (100 mg, 0.589 mmol) were
dissolved in acetone (30 mL). The reaction mixture was stirred
for 2 hours at room temperature, then adsorbed on silica gel and
1
purified by CC to yield 10 (1.11 g, 91%). H-NMR (300 MHz,
3
CDCl3) d 0.89 (t, 3H, JHH = 6.6 Hz, CH3), 1.29 (br, 6H), 1.57
3
(m, 2H), 2.54 (t, 2H, JHH = 7.65 Hz, -CH2Ar), 7.24 (br, 2H,
ArH), 7.34 (t, J = 1.35 Hz, 1H, 3JHH = 1.35 Hz, ArH). 13C-NMR
(75 MHz, CDCl3) d 14.07, 22.54, 28.78, 30.96, 31.61, 35.33, 50.28,
79.25, 122.75, 132.27, 132.59, 143.36. EA calc. for C16H16Br2
(368.11): C 52.21, H 4.38. Found: C 52.55; H 4.17%.
1,3-Bis((3-hexyl-5-((triisopropylsilyl)ethynyl)phenyl)buta-1,3-
diynyl)benzene 13. In degassed diisopropylethylamine (4 mL), 8
(1.42 g, 5.00 mmol), Pd2(dba)3·CHCl3 (80.0 mg, 0.0770 mmol)
and CuI (50.0 mg, 0.260 mmol) were added. Subsequently, to
this mixture a solution of 11 (4.00 g, 11.0 mmol) in dry and
degassed toluene (30 mL) was added dropwise in 2 hours at room
temperature. After stirring for another 2 hours, the solvent was
removed. The residue was purified by CC (silica gel, hexane) to
Currently, we are investigating potential applications of these
crystallites displaying promising conducting properties in the SEM
experiment.
Experimental
1
give the desired product 13 (2.82 g, 66%) as a yellow solid. H-
NMR (300 MHz, CDCl3) d 0.92 (t, 6H, 3JHH = 6.3 Hz, CH3), 1.15
(s, 42H), 1.35 (br, 12H), 1.65 (q, 4H), 2.58 (t, 4H, 3JHH = 7.8 Hz,
ArCH2), 7.30 (br, 5H, ArH), 7.48 (br, 3H, ArH), 7.52 (m, 1H,
ArH), 7.67 (t, 1H, 3JHH = 1.35, ArH). 13C-NMR (75 MHz, CDCl3)
d 11.45, 13.98, 18.68, 22.55, 28.88, 30.99, 31.65, 35.48, 73.90,
74.93, 80.34, 81.70, 91.48, 106.22, 121.77, 122.62, 124.06, 128.69,
132.27, 132.93, 133.00, 133.46, 136.17, 143.51. m/z (MALDI-
TOF) 854.45 [M+]. EA calc. for C60H78Si2 (855.43): C 84.24, H
9.19. Found: C 84.22, H, 9.38%.
General
All reagents were obtained from Aldrich or ABCR and were
used without further purification. Solvents were distilled and –
if mentioned – dried by standard methods.90 Unless otherwise
stated, the reactions were performed under a N2 atmosphere.
Compounds 9, 11, 12, 18, 19 and 20 were prepared according
to already reported procedures.19 Thin layer chromatography
(TLC) was carried out on Merck silica gel 60 F254 plates and
Merck silica gel 60 (0.040–0.063 mm) was used for column
chromatography (CC). Preparative size exclusion chromatography
1,3-Bis((3-ethynyl-5-hexylphenyl)buta-1,3-diynyl)benzene
14.
R
was performed with Bio-Beadsꢀ S-X Beads from BIO RAD and
TBAF (765 mg, 2.93 mmol) in THF (15 mL) was added dropwise,
over a period of 30 minutes, to a stirred solution of 13 (1.00 g,
1.17 mmol) in wet (containing 1% of water) THF (150 mL). After
stirring for 4 hours at room temperature the solvent was removed
and the residue was chromatographed (silica gel, hexane) to give
distilled toluene as eluent. 1H-NMR and 13C-NMR spectra were
recorded on a Bruker Ultra Shield 300 MHz and 500 MHz
NMR spectrometer, the J values are given in Hz. MALDI-
TOF MS spectra were recorded on a PerSeptive Biosystems
Voyager-DE PRO time-of-flight mass spectrometer. EI-MS were
recorded on a Finnigan MAT 95Q mass spectrometer. Elemental
analyses (EA) were recorded using a ThermoQuest FlashEA 1112
N/Protein Analyzer. Vapour pressure osmometry experiments
were performed with a KNAUER vapour pressure osmometer
K-7000. A LEO 1530 scanning electron microscope was used for
scanning electron microscopy (SEM) investigations. Furthermore,
a 10 kV acceleration voltage and a 100 pA beam current were
used to record the sample. The secondary electrons were detected
with an in-lens detector while the sample surface was scanned for
crystallites.
1
the desired product 14 (0.52 g, 81%) as colourless oil. H-NMR
(300 MHz, CDCl3) d 0.89 (t, 6H, 3JHH = 6.75 Hz, CH3), 1.33 (br,
12H), 1.61 (br, 4H), 2.56 (t, 4H, 3JHH = 7.65 Hz, ArCH2), 7.34 (br,
5H, ArH), 7.50 (br, 4H, ArH), 7.68 (t, 1H, 3JHH = 1.5 Hz, ArH).
13C-NMR (75 MHz, CDCl3) d 14.04, 22.53, 28.80, 30.91, 31.60,
35.33, 73.92, 74,76, 77.72, 80.28, 81.30, 82.65, 121.68, 122.28,
122.42, 128.63, 132.76, 132.99, 133.04, 133.24, 136.06, 143.48. EI:
m/z 542.2 [M+]. EA calc. for C42H38 (542.75): C 92.94, H 7.06.
Found: C 92.88, H 7.12%.
1,3-Bis((3-(bromoethynyl)-5-hexylphenyl)buta-1,3-diynyl)ben-
zene 15. 14 (3.13 g, 50.0 mmol), N-bromosuccinimide (19.6 g,
110 mmol) and silver nitrate (1.64 g, 9.66 mmol) were dissolved
in acetone (80 mL). The reaction mixture was stirred for 2 hours
at room temperature, then adsorbed on silica gel and purified by
1,3-Bis(bromoethynyl)benzene 8. 1,3-Diethynylbenzene (7)
(1.50 g, 11.9 mmol), N-bromosuccinimide (6.00 g, 33.7 mmol)
and silver nitrate (354 mg, 2.09 mmol) were dissolved in acetone
(90 mL). The reaction mixture was stirred for 2 hours at room
temperature, then adsorbed on silica gel and purified by CC to
yield 8 (2.60 g, 77%). 1H-NMR (300 MHz, CDCl3) d 7.26 (t, 1H,
1
CC to yield in the desired product 15 (3.29 g, 94%). H-NMR
3
(300 MHz, CDCl3) d 0.92 (t, 6H, JHH = 6.3 Hz, -CH3), 1.33
3
(br, 12H), 1.60 (m, 4H), 2.56 (t, 4H, JHH = 7.7 Hz, -CH2Ar),
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7.28 (m, 2H, ArH), 7.33 (m, 2H, ArH), 7.36 (m, 1H, ArH), 7.43
(m, 2H, ArH), 7.52 (m, 2H, ArH), 7.67 (m, 1H, ArH). 13C-NMR
(75 MHz, CDCl3) d 14.06, 22.54, 28.80, 30.90, 31.61, 35.33, 50.63,
73.97, 74.76, 79.14, 80.31, 81.24, 121.71, 122.27, 122.96, 128.62,
132.67, 133.91, 132.99, 133.05, 136.06, 143.51. m/z (MALDI-
TOF) 698.10 [M+]. EA calc. for C42H36Br2 (700.54): C 72.01, H
5.18. Found: C 71.54, H 5.60%.
TOF) 1079.94 [M+]. EA calc for C84H72 (1081.47): C 93.29, H
6.71. Found: C 92.67, H 6.68%.
SPM 2. To a degassed solution of diisopropylethylamine
(5 mL), dry toluene (450 mL), Pd2(dba)3·CHCl3 (40.0 mg,
0.0390 mmol) and CuI (20.0 mg, 0.100 mmol) a solution of 15
(158 mg, 0.120 mmol) and 19 (139 mg, 0.120 mmol) in dry toluene
(40 mL) was added dropwise over a period of 10 hours under a
nitrogen atmosphere. The reaction mixture was stirred for 4 days
at room temperature, the solvent was removed, and the residue
was dissolved in toluene (15 mL), filtered and purified by SEC
(toluene) to give the desired SPM 2 (10.4 mg, 9%) as a brown
solid. 1H-NMR (300 MHz, CDCl3) d 0.90 (t, 12H, 3JHH = 6.45 Hz,
(5,5¢-(5-Hexyl-1,3-phenylene)bis(buta-1,3-diyne-4,1-diyl)bis(3-
hexyl-5,1-phenylene))bis(ethyne-2,1-diyl)bis(triisopropylsilane) 16.
10 (200 mg, 0.540 mmol), Pd2(dba)3·CHCl3 (80.0 mg,
0.0770 mmol) and CuI (50.0 mg, 0.260 mmol) was suspended in
dry and degassed diisopropylethylamine (4 mL). Subsequently,
a solution of 11 (400 mg, 1.100 mmol) in toluene (30 mL)
was dropped to the reaction mixture over a period of 2 hours.
The reaction mixture was stirred for another 2 hours at room
temperature, the solvent was removed and the crude purified by
CC (silica gel, hexane) to yield the desired product 16 (120 mg,
24%). 1H-NMR (300 MHz, CDCl3) d 0.91 (t, 9H, 3JHH = 6.45 Hz, -
3
CH3), 1.31 (br, 24H), 1.58 (br, 8H), 2.59 (t, 8H, JHH = 7.65 Hz,
CH2Ar), 7.31 (br, 5H, ArH), 7.33 (s, 4H, ArH), 7.46 (br, 2H,
ArH), 7.56 (br, 2H, ArH), 7.58 (s, 2H, ArH), 7.72 (br, 1H, ArH).
13C-NMR (75 MHz, CDCl3) d 14.02, 22.52, 28.87, 30.86, 31.61,
35.39, 65.41, 73.46, 74.25, 74.31, 74.54, 74.79, 80.43, 80.59, 80.93,
81.05, 83.85, 84.75, 121.35, 122.11, 122.35, 122.44, 122.52, 128.61,
132.59, 132.84, 132.92, 133.26, 133.38, 134.38, 134.46, 136.88,
143.69, 143.84. 19F-NMR (376 MHz, CDCl3) d -105.38, -124.85,
-162.15. m/z (MALDI-TOF) 1152.53 [M+]. EA calc. for C84H68F4
(1152.53): C 87.47, H 5.95. Found: C 85.33, H 6.34%.
CH3), 1.15 (s, 42H), 1.32 (m, 18H), 1.62 (m, 6H), 2.60 (t, 6H, 3JHH
=
7.65 Hz, -CH2Ar), 7.33 (br, 6H, ArH), 7.50 (br, 3H, ArH). 13C-
NMR (75 MHz, CDCl3) d 11.25, 14.09, 18.65, 22.57, 28.79, 28.88,
30.93, 31.08, 31.63, 31.64, 35.37, 35.43, 73.84, 74.28, 80.60, 81.29,
91.20, 106.00, 121.60, 122.09, 123.81, 132.24, 132.85, 133.24,
133.39, 143.40, 143.66. m/z (MALDI-TOF) 1875.04 [2M+]. EA
calc. for C66H90Si2 (939.59): C 84.37, H 9.65. Found: C 83.62, H
9.91%.
SPM 3. To a solution of Pd(PPh3)2Cl2 (300 mg, 0.430 mmol),
CuI (400 mg, 2.10 mmol) and dry silica gel in diisopropylethy-
lamine (15 mL) and dry THF (1200 mL), a solution of 19 (200 mg,
0.320 mmol) in dry THF (100 mL) was added dropwise over a
period of 10 hours. The reaction mixture was stirred for 4 days
under dry air at room temperature. The solvent was removed, and
the residue was dissolved in toluene (15 mL), filtered over 1 cm
silica gel and purified by SEC to yield the desired SPM 3 (40 mg,
5,5¢-(5-Hexyl-1,3-phenylene)bis(buta-1,3-diyne-4,1-diyl)bis(1-
ethynyl-3-hexylbenzene) 17. TBAF (379 mg, 1.45 mmol) in THF
(10 mL) was added dropwise, over a period of 30 minutes, to a
stirred solution of 16 (550 mg, 0.580 mmol) in THF (40 mL).
After stirring for 4 hours at room temperature the solvent was
removed and the residue was chromatographed (silica gel, hexane)
to give the desired product 17 (0.35 g, 96%) as a colourless oil.
1H-NMR (300 MHz, CDCl3) d 0.89 (t, 9H, 3JHH = 6.3 Hz, CH3),
1.30 (br, 18H), 1.60 (m, 6H), 2.56 (t, 6H, 3JHH = 7.8 Hz, CH2Ar),
3.08 (s, 2H), 7.32 (m, 6H, ArH), 7.48 (m, 3H, ArH). 13C-NMR
(75 MHz, CDCl3) d 14.06, 22.54, 28.80, 30.90, 30.95, 31.61, 35.36,
74.00, 74.26, 77.68, 80.70, 81.06, 82.67, 121.78, 122.05, 122.42,
132.80, 133.02, 133.26, 133.50, 143.51, 143.67. m/z (MALDI-
TOF) 626.21 [M+]. EA calc. for C48H50 (626.91): C 91.96, H 8.04.
Found: C 91.25, H 8.15%.
1
20%) as a yellow solid. H-NMR (300 MHz, CDCl3) d 0.92 (t,
3
12H, JHH = 6.3 Hz, CH3), 1.33 (br, 24H), 1.65 (m, 8H), 2.57
3
(t, 8H, JHH = 7.5 Hz, CH2Ar), 7.29 (s, 8H), 7.54 (s, 4H). 13C-
NMR (125 MHz, d8-toluene, 50 ◦C) d 14.1, 22.8, 29.2, 31.0, 32.0,
35.5, 66.1, 74.3, 75.5, 81.4, 84.5, 85.5 (m), 100.0 (m), 121.9, 122.8,
132.9, 133.4, 134.9, 137.3 (J 255), 143.9, 152.5 (J 255), 161.0 (J
255). 19F-NMR (376 MHz, CDCl3) d -106.2, -125.7, -162.6. m/z
(EI) 1224.5 [M+]. EA calc. for C84H64F8 (1224.4): C 82.33, H 5.27.
Found: C 81.97, H 5.24%.
6,6¢-(5,5¢-(Perfluoro-1,3-phenylene)bis(buta-1,3-diyne-4,1-diyl)-
bis(3-hexyl-5,1-phenylene))bis(buta-1,3-diyne-4,1-diyl)bis(2-(bromo-
ethynyl)-1,3,4,5-tetrafluorobenzene) 20. 12 (2.00 g, 5.60 mmol),
Pd2(dba)3·CHCl3 (120 mg, 0.110 mmol) and CuI (50.0 mg,
0.260 mmol) were dissolved in dry and degassed
diisopropylethylamine (4 mL). Subsequently, to the reaction
mixture a solution of 17 (450 mg, 0.720 mmol) in dry toluene
(30 mL) was added dropwise over a period of 2 hours at room
temperature. The reaction mixture was stirred for another 2 hours,
the solvent was removed and the residue was purified by CC
(silica gel, hexane) to yield the desired product 20 (380 mg,
46%) as a yellow solid.: 1H-NMR (300 MHz, CDCl3) d 0.90 (m,
Shape-persistent macrocycle (SPM) 1. To a suspension of
Cu(OAc)2·H2O (150 mg, 0.753 mmol) in pyridine (300 mL) and
benzene (200 mL) a solution of 14 (100 mg, 0.180 mmol) in benzene
(100 mL) was added dropwise, at room temperature, over a period
of 24 hours. After addition, the reaction mixture was stirred for an
additional two days at room temperature. The reaction mixture
was concentrated and filtered and evaporated to dryness. The
crude was purified by size exclusion chromatography (SEC) to
yield the desired SPM 1 (25 mg, 25%) as a brown solid. 1H-NMR
(300 MHz, CDCl3) d 0.91 (t, 12H, 3JHH = 6.6 Hz, CH3), 1.25 (br,
3
9H), 1.32 (br, 18H), 1.61 (m, 6H), 2.58 (t, 6H, JHH = 7.65 Hz,
3
24H), 1.56 (m, 8H), 2.57 (t, 8H, JHH = 7.65 Hz, ArCH2), 7.32
CH2Ar), 7.33 (s, 2H, ArH), 7.35 (s, 4H, ArH), 7.46 (m, 1H, ArH),
7.48 (m, 2H, ArH). 13C-NMR (75 MHz, CDCl3) d 14.05, 22.57,
28.84, 30.89, 31.64, 35.36, 62.75 (q), 64.80 (t), 65.43 (t), 73.32 (d),
74.18, 74.45, 80.58, 80.95, 83.74, 84.45 (q), 99.60 (m), 121.19,
121.97, 122.18, 133.28, 133.30, 133.51, 133.60, 133.84, 137.25
(br, 10H, ArH), 7.50 (m, 8H, ArH), 7.74 (m, 2H, ArH). 13C-NMR
(75 MHz, CDCl3) d 14.11, 22.58, 28.81, 30.97, 31.65, 35.43, 74.18,
74.28, 74.75, 80.43, 80.83, 81.05, 121.90, 122.00, 122.40, 128.74,
132.70, 132.80, 132.83, 134.30, 136.95, 143.72. m/z (MALDI-
1090 | Org. Biomol. Chem., 2009, 7, 1081–1092
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(J 254), 143.72, 143.85, 152.35 (J 262.5), 160.0 (J 255.0).
19F-NMR (376 MHz, CDCl3) d -106.9 (d), -125.3 (m), -162.4
(m). EA calc. for C68H48Br2F8 (1176.90): C 69.40, H 4.11. Found:
C 69.24, H 4.45%.
Promotion Agency (CTI). The authors thank Prof. Thomas Ward
for proof reading of the manuscript.
References
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