Structural studies on inclusion compounds and solvent sorption behavior of gradually elongated wheel-and-axle-type diol hosts featuring lateral benzo[b]thiophene units

Article abstract of DOI:10.1016/j.molstruc.2016.02.053

Based on the wheel-and-axle design strategy, a series of six new clathrate hosts featuring two di(benzo[b]thien-2-yl)hydroxymethyl units attached to both ends of a central linear building element of varying length have been synthesized and their capability to form crystalline inclusion compounds with a fixed range of organic solvents are reported. X-ray crystal structures of relevant inclusion compounds have been determined and are comparatively discussed involving structural modification of the host molecules. Organic vapor sorption behavior of the host compounds coated as solid films on the quartz crystal of a QCM device has been studied. Significant differences in the affinities towards solvent vapors dependent both on structural and polarity properties of host and solvent are observed, indicating potential application as mass sensitive materials.

Full text of DOI:10.1016/j.molstruc.2016.02.053

Accepted Manuscript
Structural studies on inclusion compounds and solvent sorption behavior of gradually
elongated wheel-and-axle-type diol hosts featuring lateral benzo[b]thiophene units
Felix Katzsch, Tobias Gruber, Edwin Weber
PII:
S0022-2860(16)30146-6
10.1016/j.molstruc.2016.02.053
MOLSTR 22262
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 26 November 2015
Revised Date: 12 February 2016
Accepted Date: 12 February 2016
Please cite this article as: F. Katzsch, T. Gruber, E. Weber, Structural studies on inclusion compounds
and solvent sorption behavior of gradually elongated wheel-and-axle-type diol hosts featuring lateral
benzo[b]thiophene units, Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.2016.02.053.
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ACCEPTED MANUSCRIPT

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Structural studies on inclusion compounds and solvent sorption
behavior of gradually elongated wheel-and-axle-type diol hosts
featuring lateral benzo[b]thiophene units
Felix Katzscha, Tobias Gruberb,*, Edwin Webera,*
a Institut für Organische Chemie, TU Bergakademie Freiberg, Leipziger Straße 29, 09596
Freiberg/Sachsen, Germany.
b School of Pharmacy, University of Lincoln, Joseph Banks Laboratories, Green Lane,
Lincoln, Lincolnshire, LN6 7DL, United Kingdom.
* Corresponding authors. Tel: +44 (0)1522 837396 (T. Gruber); Tel: +49 (0)3731 39 2386,
Fax: +49 (0)3731 39 3170 (E. Weber)
E -mail addresses. tgruber@lincoln.ac.uk (T. Gruber); edwin.weber@chemie.tu-freiberg.de
(E. Weber).
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HIGHLIGHTS
•
•
•
•
•
The syntheses of gradually elongated wheel-and-axle-type hosts are presented.
A longer central spacer unit does not improve the general inclusion behaviour.
Most efficient solvent inclusion in the crystal is found for a biphenyl spacer.
The ratio of vapor absorption is notably high for the C≡C-Ph-C≡C spacer.
A structure memory effect has been shown.
Keywords:
Diol hosts
Crystalline inclusion compounds
X-ray structural study
Quartz crystal microbalance
Vapor absorption measurement
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ABSTRACT
Based on the wheel-and-axle design strategy, a series of six new clathrate hosts featuring two
di(benzo[b]thien-2-yl)hydroxymethyl units attached to both ends of a central linear building
element of varying length have been synthesized and their capability to form crystalline
inclusion compounds with a fixed range of organic solvents are reported. X-ray crystal
structures of relevant inclusion compounds have been determined and are comparatively
discussed involving structural modification of the host molecules. Organic vapor sorption
behavior of the host compounds coated as solid films on the quartz crystal of a QCM device
has been studied. Significant differences in the affinities towards solvent vapors dependent
both on structural and polarity properties of host and solvent are observed, indicating potential
application as mass sensitive materials.
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Introduction
Aiming at applications such as separation, sensing and storage of chemical substances,
crystalline inclusion compounds are very encouraging [1-4]. In previous studies concerning
this topic respective results are evident. This applies particularly for the inclusions formed of
hosts derived from and ‘wheel-and-axle’ strategy [5,6]. As defined by this strategy,
conventional host compounds feature a structure having two bulky diarylhydroxymethyl
moieties attached to a central linear building element mostly composed of ethynylene, 1,4-
phenylene, 4,4’-biphenylene or combinations of these structural units involving varied
expansions of the rigid central axis. Owing to their irregular shape, corresponding hosts do
not pack efficiently and thus they tend to yield inclusion compounds in the presence of neutral
guest molecules. In a modification of this proven design, wheel-and-axle type geometries
have also been created bipartitely via an association of bulky carboxylic acid fragments [7] or
using ligands of varying length for bridging the metal centers of porphyrins [8,9] or other
metal containing molecules [10]. Hence, it is convincingly shown that the covalently linked
axis of a conventional wheel-and-axle host molecule can be replaced by a system of hydrogen
bonds or by coordination of ligands generating inclusions alike. Moreover, derived from the
existing findings, the length of the central axis is demonstrated to decisively control the void
dimensions as well as the mode of aggregation in the crystal including, e.g., wheel-and-axle
or shish-kebab type shapes of supramolecular scaffolds [8,9], aside from the kind of subunits
that compose the molecular wheels exercising a similar effect. Only recently, steroidal wheel-
and-axle-type hosts [11] as well as the exchange of the lateral aryl groups of respective host
molecules against heterocycles [12] opened up a further new way of structural modification,
showing high potential to control inclusion selectivity of organic guest species. This has been
confirmed by the host molecules BTh1 and BTh2 (Fig. 1) bearing di(benzo[b]thien-2-
yl)hydroxymethyl moieties laterally attached to central ethynylene and 1,4-phenylene units,
respectively [13]. For obvious reasons, an extension of the central axis both of BTh1 and
BTh2 by the insertion of additional ethynylene and 1,4-phenylene units or substitution of a
trigonal benzene-1,3,5-triyl moiety for the linear 1,4-phenylene building element of BTh2 in
order to increase the number of the lateral bulky functional groups seemed very promising,
giving rise to compounds 1-5 and compound 6, respectively (Fig. 1) Hence, all these
compounds being distinguished by a gradually increased linear or geometrically modified
structure were synthesized and comparatively studied with reference to the formation of
crystalline host-guest inclusion behaviour of the prototype hosts BTh1 and BTh2 towards
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organic guests. Moreover, no less than seven crystal structures of solvent inclusions formed of
1 (1a), 2 (2a, 2b), 4 (4a-4c) and 5 (5a), that have been isolated, are described giving detailed
information of the molecular conformations as well as the supramolecular organization and
interactions between host and guest in the solid state. Finally, compounds 1-6 have been
tested as solid coatings of a quartz crystal microbalance (QCM) [14] to reveal their potential
in organic vapor sorption and conclusions are drawn from all the findings.
Fig. 1. Chemical formulae of the studied diol host compounds 1-6 including compounds for
comparison (BTh1 and BTh2) and specification of corresponding inclusion compounds
proven by X-ray structure determination.
Results and discussion
Preparation of compounds
Syntheses of the host compounds 1-6 were performed as illustrated in Fig. 2 (1, 3, 6)
and Fig. 3 (2, 4, 5). For the preparation of 1, this involves reaction of dimethyl biphenyl-4,4'-
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dicarboxylate (7) with in situ generated 2-lithiobenzo[b]thiophene (obtained from
benzo[b]thiophene 8 and n-butyl lithium in dry THF at -30 °C under argon). Analogous
reaction protocols using dimethyl 4,4'-(ethynylene)dibenzoate (9) or trimethyl 3,3',3''-
(benzene-1,3,5-triyl)tripropynoate (11) (prepared from 10) as ester components yielded 3 and
6, respectively. Differing from the literature description [15], the dimethyl dicarboxylate 7
was prepared from 4-(methoxycarbonyl)phenylboronic acid (synthesized by literature
procedures [16,17]) and methyl 4-iodobenzoate in the presence of Pd(PPh3)2Cl2 and NaHCO3
in water/THF following a Suzuki-Miyaura type reaction [18]. The dimethyl dicarboxylate 9
was obtained from methyl 4-ethynylbenzoate and methyl 4-iodobenzoate using a described
Sonogashira-Hagihara coupling method [19]. The triester 11, not yet being mentioned in the
literature before, was synthesized from 1,3,5-triethynylbenzene (10) [20] and methyl
chloroformiate on treatment with n-butyl lithium in dry THF.
Fig. 2. Synthesis of the host compounds 1, 3 and 6.
Pd-catalyzed coupling reactions following the Sonogashira-Hagihara protocol [21]
were applied to 1,1-di(benzo[b]thien-2-yl)prop-2-yne-1-ol (14) and corresponding diiodides
[1,4-diiodobenzene, 4,4'-diiodobiphenyl and bis(4-iodophenyl)ethyne] to yield the respective
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diols 2, 4 and 5. The basic intermediate 14 was synthesized in three steps starting from
benzo[b]thiophene (8) which was reacted with n-butyl lithium and N,N-dimethylcarbamoyl
chloride in dry THF to give di(benzo[b]thien-2-yl)methanone (12). To this latter compound
was then added trimethylsilylacetylene (TMSA) in the presence of n-butyl lithium leading to
the TMS-protected acetylenic alcohol 13 which was deprotected under basic condition
(K2CO3) to yield 14.
Fig. 3. Synthesis of the host compounds 2, 4 and 5.
Inclusion compounds of 1-6 including the studied solvents were obtained as described
in the Experimental.
Capability of inclusion formation
Previously, we demonstrated that the replacement of thien-2-yl groups of a new
prototype host structure [12] by the more bulky benzo[b]thien-2-yl groups giving rise to
BTh1 and BTh2 (Fig. 1) leads to a distinct enhancement of the crystalline inclusion formation
with organic solvent molecules [13]. Following this line of thought, the question arises
whether the intended homologues of BTh1 and BTh2, i.e. 1-6, featuring in their molecular
structure an elongated central axis (1-5) or an increased number of bulky lateral groups (6)
may cause a further improvement of the inclusion behavior. In order to ensure a sound basis
for comparison, a variety of solvents corresponding to those applied to BTh1 and BTh2 were
used for the crystallization of 1-6. They range from dipolar protic (alcohols, amines) to
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largely apolar species (chloroform, 1,4-dioxane, toluene) and involve solvents of acyclic and
cyclic as well as aliphatic and aromatic or heteroaromatic nature. More detailed specification
of the solvents and findings obtained from the crystallization study including the results
recently achieved from BTh1 and BTh2 are listed in Table 1.
In general, compound 1 is the most efficient one in solvent inclusion (11 hits) and,
thus, is comparable with BTh1 (12 hits) and BTh2 (10 hits) by means of the number of
inclusions obtained from solvent crystallization. But also hosts 2-4 (9 hits each) are close to
the efficacy of the references while 5 (5 hits) and 6 (7 hits) show a decreased inclusion ability.
This suggests that increasing the length of the central axis in the molecules (except for 1) is
not always helpful to improve the capacity for solvent inclusion.
Another noticeable point refers to the host:guest stoichiometry of the inclusion
compounds. Whereas BTh1 and BTh2 almost universally use 1:2 stoichiometry in the solvent
inclusion, the present hosts crystallize with solvents in varying stoichiometries including 3:1,
3:2, 1:1, 3:4, 2:3, 1:2, 2:5, 1:3, 1:4 and 1:5, i.e. covering a very broad range. For all that, also
in this series of compounds the stoichiometric ratio of 1:2 is generally preferred
corresponding with the bifunctionality of the host molecules. This is most obviously
demonstrated by the inclusion compounds of 5 being only of a low number but having a
constant 1:2 stoichiometry. Nevertheless, it is noticed that outstandingly high solvent ratios,
up to 1:5, appear rather frequent, and, yet, showing a distinct accumulation for the host
molecule 6 featuring a trigonal structure.
Regarding the variety of solvents being included it is seen that toluene as a clearly
apolar solvent is successfully included from 1, 3, 4 and 6 which is in contrast with BTh1 and
BTh2 since both do not form respective inclusion compounds. Hence, representatives of the
new hosts do not develop such strong limitation to include only solvents of protic and
distinctly polar nature as shown for the former hosts. But with reference to the failure of
chloroform inclusion they are equivalent. Moreover, all the hosts demonstrate conformity in
the inclusion of THF and pyridine followed by acetone which apparently is only unsuccessful
with 5. The whole of the other dipolar aprotic solvents are rather differently included by the
hosts making it difficult to pinpoint a general trend. Remarkably, EtOAc and DMSO are only
included by 3 and 6, respectively, even though the solvent ratio in the case of the DMSO
inclusion is markedly high. Distinct differences are also observed in the inclusion formation
with protic guests, in particular considering the alcohols showing no correspondence among
each other, including BTh1 and BTh2. Virtually, it is obvious from Table 1 that the alcohols
show a rather low tendency to be included, resembling in this respect the facts of the former
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hosts. Hence, in order to provide a more profound basis for drawing conclusion extending
those from the above findings, a detailed X-ray crystallographic structural study performed of
selected inclusion compounds was carried out.
(a)
(b)
(c)
(d)
(e)
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(f)
(g)
Fig. 4. Molecular structures of the studied inclusion compounds 1a (a), 2a (b), 2b (c), 4a (d),
4b (e), 4c (f) and 5a (g) involving atom numbering scheme and specification of disorder sites
in 1a, 2a, 4a, 4b, 4c and 5a. (Ellipsoid plots drawn with 50 % probability level.)
Single crystal X-ray structural study
Unfortunately, crystals of inclusion compounds being in a quality for carrying out an
X-ray structural analysis could only be isolated of the hosts 1, 2, 4 and 5, while the hosts 3
and 6 refrained from suitable crystal formation. Nevertheless, a reasonable structural
comparison including the prototype hosts BTh1 and BTh2 is possible allowing sufficient
insight into the structural circumstances. In detail, the crystalline inclusion compounds which
have been studied via X-ray structural analysis involve 1a (1 · pyridine), 2a (2 · pyridine), 2b
(2 · n-BuOH), 4a (4 · pyridine), 4b (4 · acetone), 4c (4 · THF) and 5a (5 · DMF) being
itemized in Fig. 1. An especially good opportunity presents itself for structural comparison of
the inclusions 1a, 2a and 4a, all containing pyridine, however, showing very different
stoichiometric ratios (1a, 1:2; 2a, 1:5; 4a, 1:3). But also the other inclusion compounds (2b,
4b, 4c, 5a) enable an immediate structural comparison based on the same solvent species,
even if only included in the crystals of the previous hosts BTh1 and BTh2. Crystal data for
the studied compounds are summarized in Table 2. Selected torsion angles of the molecules
are listed in Table 3. Packing properties of the studied inclusion compounds are presented in
Table 4 and relevant non-covalent interactions found in the crystal structures are given in
Table S1 (Supplementary Material). Molecular structures of the inclusion compounds are
illustrated in Fig. 4, corresponding packing diagrams and excerpts of packing modes are
represented with Figs.5-11, respectively.
Irrespective of the particular host molecule, all the inclusion compounds containing
pyridine as the guest solvent (1a, 2a, 4a) crystallize in the triclinic space group P-1. However,
as despite from 1a having half a host molecule and a refined pyridine molecule in the
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asymmetric unit (Fig. 4a), both in 2a (Fig. 4b) and 4a (Fig. 4d) only one of the pyridine
molecules could be refined and the residual electron density was removed by the SQUEEZE
method of the PLATON program [22]. On the other hand, for the inclusion compounds 2b, 4b
and 4c, the monoclinic space group P21/c (or the alternative setting P21/n) was determined. In
2b (Fig. 4c), the n-BuOH molecules could not be refined and as before the SQUEEZE method
was used to remove the residual electron density, while one of the THF molecules of 4c (Fig.
4f) shows twofold disorder with a site occupancy factor (sof) of 0.66. As found for 1a, 2a and
4a, the inclusion compound 5a crystallizes in the space group P-1 (Fig. 4g). Aside from the
specific disorder of solvent molecules, twofold disorder of benzo[b]thiophene units of the host
molecules have been observed in 1a (sof=0.90), 2a (sof=0.83), 4a (sof=0.90), 4b (sof=0.56,
0.66) and 5a (sof=0.74). Moreover, in the case of 2a, the benzene ring of the spacer element
was found to be twofold disordered (sof=0.69).
Molecular structures
For the determination of the molecular conformations of the respective hosts, we
focused on the one hand on the dihedral angles describing the relative orientations of the two
benzo[b]thiophene units and the hydroxyl function. On the other hand, we also incorporated
the relative orientations of the phenylene units of the central spacer element to one another
and with reference to the orientation of the OH function. Corresponding torsion angles of the
host compound conformations in the crystal structures are summarized in Table 3.
In the structure of 1a (Fig. 4a), the benzene rings of the biphenyl unit are coplanar to
each other. The molecular conformation is shown to be stabilized by intramolecular S···O-
contacts [12,23] [d(S1···O1) = 2.846(1) Å, d(S2···O1) = 3.044(1) Å] and can be described by
the torsion angles of the heteroaromatic units with reference to the OH group of 28.3° (S1-C1-
C17-O1) and 43.8° (S2-C9-C17-O1). Regarding the structures of 2a (Fig. 4b) and 2b (Fig.
4c), the alkyne bonds are slightly distorted which is specified by the bond angles of 176.1°
and 177.5° for 2a or 175.0° and 178.4° for 2b. Just as for 1a, the molecule conformations of
the hosts are stabilized by intramolecular S···O-contacts [2a: d(S1···O1) = 2.954(1) Å,
d(S2···O1) = 2.969(2) Å; 2b: d(S1···O1) = 2.904(3) Å, d(S2···O1) = 2.919(3) Å] giving rise
to torsion angles of the heteroaromatic units relative to the OH groups of 41.0°/-35.9° for 2a
and 26.6°/-33.6° for 2b with reference to the atomic sequences S1-C1-C17-O1 and S2-C9-
C17-O1, respectively. The host conformations in the structures of 4a, 4b and 4c (Figs. 4d-4f)
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feature again stabilization via intramolecular S···O-contacts but involve also intramolecular
S···S-contacts [24-26] leading to corresponding torsion angles around the two heteroaromatic
and hydroxyl groups as particularized in Table 3. Probably owing to a packing induced
distortion of the spacer elements, the alkyne bonds are not linear showing bond angles that
range between 176.2 and 179.1 ° (with 4a deviating the most). In contrast to 1a, the biphenyl
unit 4b is not co-planar arranged having an interplanar angle of 38.3.
In the structure of 5a (Fig. 4g) both the terminal (174.0° and 176.1°) and the central
(178.8°) alkyne bonds are slightly distorted while the benzene rings of the tolane fragment are
co-planar. With reference to the conformation including the benzo[b]thiophene units and the
OH group, we notice again the implication of intramolecular S···O-contacts [d(S2···O1) =
2.966(1) Å, d(S1B···O1) = 2.855(5) Å] giving rise to corresponding torsion angles of -28.6°
(S2-C9-C17-O1) and -151.7 (S1-C1-C17-O1).
Packing structures
Emphasizing packing density of the different kinds of host-guest complexes (Table 4),
particularly noticeable observations are as follows. In case of the inclusion compounds 2a and
4c featuring especially high stoichiometric ratios of solvent (5 pyridine and 4 THF molecules
per host, respectively), the guest species occupy parts of the unit cells of 48.5 and 37.3 %,
respectively, which is attended by Kitaigorodskii packing index (KPI) values [27] (without
solvent) of 41.2 and 47.7 %, respectively. The high framework porosity of 2a results from
channel-like voids in all three crystallographic directions while 4c imbeds the THF in solvent
cages (see below). In comparison, the 1:3 pyridine inclusion 4a contains two different solvent
channels (A and B) along the a-axis and possess a KPI value (without solvent) of 51.8 %
offering 31.8 % solvent accessible void (SAV) in the unit cell. The 1:2 inclusion compounds
1a (pyridine), 2b (n-BuOH) and 5a (DMF) form frameworks which show KPI values (without
solvent) of 54.5, 56.9 and 58.4 % and SAVs of 26.9, 22.0 and 17.2 %, respectively, depending
both on the guest volume and property which influence the packing of the host molecules.
The closest packing of the investigated structures is formed of the 1:2 DMF inclusion
compound 5a with a KPI value (with solvent) of 70.6 % followed by the 1:1 acetone host-
guest compound 4b having a KPI value (with solvent) of 70.5 %.
Regarding a more detailed discussion on the molecular arrangement including a
description of intermolecular interactions modes, the structures can be described as follows.
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In the structure of the inclusion compound 1a, the host molecules are lined up in strands along
the crystallographic b-axis connected by weak C‒H···O-hydrogen bonding [28] [d(C19···O1)
= 3.339(2) Å] with the graph set R22(10) [29] (Fig. 5a). The strands are linked in the a-
direction via C‒H···π-interactions [30,31] [d(C2···Cg9) = 3.564(2) Å, d(C7···Cg8) =
3.475(2) Å, d(C15···Cg5) = 3.630(2) Å] while in c-direction C‒H···π- [d(C13···Cg7) =
3.770(2) Å] and C‒H···S-contacts [32] [d(C4···S2B) = 3.485(4) Å (10 %), d(C5···S2B) =
3.459(6) Å (10 %)] participate in the stabilization of the crystal. The pyridine guest molecules
are included cage-like in the packing structure (Fig. 5b) and are fixed to the host hydroxyls by
strong O‒H···N-hydrogen bonds [d(O1···N1G) = 3.339(2) Å] (Fig. 5a), C‒H···π-
[d(C23···Cg10) = 3.650(2) Å, d(C1G···Cg5) = 3.685(2) Å] and π···π-interactions [33,34] (d
= 3.944 Å) among each other.
(a)
(b)
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Fig. 5. Illustration of the structure 1a: (a) Host molecule strand showing hydrogen bond ring
motif R22(10) and linkage of pyridine. (b) Cage-like packing structure. Non-relevant H-atoms
are omitted for clarity.
Strand formation of host molecules is also observed in the structure of 2a with hosts
being connected along the [110]- as well as in b-direction by C‒H···π-interactions
[d(C6···Cg5) = 3.709(2) Å; d(C13···Cg6) = 3.791(2) Å] (Fig. 6a). Furthermore, S···O-
contacts [d(S2···O1) = 3.150(2) Å] give rise to the stabilization of the packing in the [011]-
direction thus featuring a highly porous network structure exhibiting solvent channels in all
three crystallographic directions (Fig. 6b). The refined pyridine guest molecule is included in
the channel along the c-axis being attached to host molecules by O‒H···N-hydrogen bonding
[d(O1···N1G) = 2.748(2) Å] and C‒H···π-interactions [d(C1G···Cg4) = 3.778(2) Å,
d(C2G···Cg1) = 3.675(2) Å, d(C3G···Cg2) = 3.516(2) Å].
(a)
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(b)
Fig. 6. Illustration of the structure 2a: (a) Host molecule strand involving linkage of pyridine.
(b) Channel-like packing structure viewed in two different directions. Non-relevant H-atoms
are omitted for clarity.
Similar to before, host molecules in the structure of 2b form chains (here along the b-
axis) but now being stabilized by strong O‒H···O-hydrogen bonds [d(O1···O1) = 2.773(5) Å]
between the host OH groups (Fig. 7a). In addition, the host chains are stabilized in a-direction
via C‒H···S- [d(C7···S2) = 3.658(4) Å] and C‒H···π-interactions [d(C5···Cg4) = 3.631(4) Å]
while in c-direction only C‒H···S-contacts [d(C12···S1) = 3.657(4) Å] occur. The hydrogen
atoms of the host hydroxyls show twofold disorder (sof = 0.57) and are thus labeled in Fig. 7a
as H1B linking the host molecules and H1A probably connecting the included n-BuOH guest.
It follows from this that the guest molecules are accommodated in host channels extending
along the crystallographic b-axis (Fig. 7b).
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(a)
(b)
Fig. 7. Illustration of the structure 2b: (a) Host molecule chain showing twofold disorder of
the hydroxyl group. (b) Channel-like packing structure in the crystallographic b-direction and
respective Van-der-Waals model. Non-relevant H-atoms were omitted for clarity.
Again, the packing structure of 4a is composed of strand-like connected host
molecules. The strands developed in this way run along the crystallographic a-axis and are
stabilized both by weak C‒H···O-hydrogen bonding [d(C25···O1) = 3.424(3) Å] and C‒
H···S-contacts [d(C12···S2) = 3.511(3) Å] (Fig. 8a). In the b-direction, the strands interact
via C‒H···π-contacts [d(C5···Cg5) = 3.494(3) Å]; in c-direction via C‒H···π- [d(C14···Cg3)
= 3.712(3) Å] and additional C‒H···S-contacts [d(C15···S2) = 3.705(3) Å]. Based on this
arrangement, two different solvent channels (A and B) are formed along the crystallographic
a-axis (Fig. 8b). The refined pyridine molecules are accommodated within the channels of
type A fixed by O‒H···N-host-guest hydrogen bonding [d(O1···N1G) = 3.110(3) Å] which
according to the bond length should only be rated of moderate strength. Nevertheless,
additional C‒H···π-interactions [d(C7···Cg6) = 3.581(2) Å, d(C5G···Cg4) = 3.562(3) Å] take
part in guest fixation. The second guest channel (B) contains the pyridine molecules which
could not be refined.
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(a)
(b)
Fig. 8. Illustration of the structure 4a: (a) Host molecule strand involving linkage of pyridine.
(b) Channel-like packing structure and Van-der-Waals model (channel A = unrefined
pyridine, channel B = refined pyridine). Non-relevant H-atoms are omitted for clarity.
In the crystals of 4b, the host molecules occur as dimers connected by strong O‒
H···O-hydrogen bonds [d(O2···O1) = 3.168(2) Å] and C‒H···S-contacts [d(O2···S1) =
3.550(1) Å] forming a hydrogen bond ring motif with the graph set R21(5) with the hydroxyl
group O2‒H2A being in an inverse bifurcated situation (Fig. 9a). Furthermore, C‒H···π-
interactions [d(C27···Cg9) = 3.484(2) Å, d(C7···Cg16) = 3.517(2) Å] between the biphenyl
as well as between the benzo[b]thiophene units support the dimer stabilization. The host
dimers are linked in the [101]- and [301]-directions, and also along the b-axis via C‒H···π-
interactions [d(C46···Cg12) = 3.509(2) Å; d(C14···Cg11) = 3.706(2) Å; d(C5···Cg4) =
3.495(2) Å, d(C24···Cg7) = 3.673(2) Å, d(C31···Cg14) = 3.538(2) Å] while additional C‒
H···S-contacts [d(C21···S4) = 3.642(2) Å] occur in the b-direction. Against expectation, but
obviously caused by the packing arrangement, the hydroxyl group O1‒H1 of the host is
unable to act as a donor of a conventional hydrogen bond and is pointing towards an aromatic
unit of an adjacent dimer. As a result of this, the acetone guest molecules are included cage-
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like (Fig. 9b) and fixed only by weak C‒H···O-hydrogen bonding [d(C38···O1G) = 3.463(3)
Å] and C‒H···S-contacts [d(C3G···S2) = 3.855(3) Å] involving the benzo[b]thiophene unit
(Fig. 9a).
(a)
(b)
Fig. 9. Illustration of the structure 4b: (a) Host molecule dimer showing hydrogen bond ring
motif R21(5) and linkage of acetone. (b) Cage-like packing structure. Non-relevant H-atoms
are omitted for clarity.
The crystal of 4c is composed of layers of host molecules running parallel to the [-
102]-plane with hosts being stabilized strand-like along the crystallographic b-axis using C‒
H···π-interaction [d(C5···Cg6) = 3.509(2) Å] (Fig. 10a). Adjacent strands within a layer are
oriented in opposite directions and connected among each other again by means of C‒H···π-
interaction [d(C7···Cg2) = 3.509(2) Å, d(C15···Cg7) = 3.509(2) Å]. The THF guest
molecules are intercalated between the host layers (Fig. 10b). One of the solvent molecules
(THF1) is connected via a strong O‒H···O-hydrogen bond [d(O1···O1G) = 3.463(3) Å] (Fig.
10a) and a C‒H···π-interaction [d(C3G···Cg4) = 3.509(2) Å] to a corresponding layer while
connection to the adjacent host layer is enabled also using C‒H···π-interaction [d(C1G···Cg6)
18

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= 3.509(2) Å]. In contrast, the THF molecule 2 is linked to one layer by weak C‒H···O-
hydrogen bonds [d(C10···O1H) = 3.463(3) Å, d(C25···O1H) = 3.463(3) Å] (Fig. 10a) with
the THF oxygen O1H being in a bifurcated situation, thus in a position to connect the adjacent
host layer via C‒H···π-interactions [d(C3HB···Cg6) = 3.497(1) Å, d(C4HA···Cg6) =
3.654(8) Å].
(a)
(b)
Fig. 10. Illustration of the structure 4c: (a) Host layer showing linkage of THF. (b) Layer-like
packing structure. Non-relevant H-atoms are omitted for clarity.
Layers of host molecules are also a main building principle of the crystal formed of
5a. They run parallel to the [001]-plane and, as before, consist of strands of host molecules
(Fig. 11). Along the crystallographic a-axis, the strands are connected by C‒H···π-
[d(C24···Cg4) = 3.497(1) Å] as well as π···π-interaction [d(Cg1···Cg5) = 3.984(1) Å] and in
the b-direction via C‒H···S-contact [d(C15···S1) = 3.642(2) Å]. The intercalated DMF guests
link the host layers (Fig. 11a) resulting in a hydrogen bond ring motif with the graph set
R24(18), which has not been reported before in the literature. Thereby, strong O‒H···O-
[d(O1···O1G) = 3.463(3) Å] and weak C‒H···O-hydrogen bonds [d(C4···O1G) = 3.463(3) Å]
are involved with the DMF oxygen O1G showing inverse bifurcation. In addition, C‒H···π-
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interactions [d(C2G···Cg7) = 3.497(1) Å, d(C3G···C8Ar) = 3.497(1) Å, d(C3G···Cg6) =
3.497(1) Å] between the DMF methyl groups and aromatic units of the hosts as well as a C‒
H···π-interaction [d(C1G···Cg9) = 3.497(1) Å] including the DMF formyl hydrogen and a
terminal alkyne unit of the host give rise to the stabilization of the packing.
(a)
(b)
Fig. 11. Illustration of the structure 5a: (a) Linkage of the host molecules of adjacent layers
by DMF mediated connection. (b) Layer-like packing structure. Non-relevant H-atoms are
omitted for clarity.
Solvent vapor absorption behavior
The diol host compounds 1 - 6 were deposited as solvent-free thin films from CHCl3-
solution on a quartz crystal microbalance [14] and investigated in view of their vapor
absorption. Hereby, the corresponding gas-sensing process, i.e. the solvent vapor sorption, is
represented by the incorporation of the analyte into the chemical layer deposited on the quartz
crystal, leading to a mass increase. As a result, the resonance frequency of the quartz crystal is
shifted delivering information on the amount of the incorporated solvent [35]. To enable a
sound comparison with previous data obtained from BTh1 and BTh2 [13], a series of
different solvent vapors being in correspondence with a former selection of vapors [12,13]
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was used. They involve vapors of n-hexane, CHCl3, THF, acetone, EtOH and Et2NH. The
vapor absorption ratios of 1-6 including those of BTh1 and BTh2 for comparative purpose
are listed in Table 5 and corresponding bar graphs are shown in Fig. 12.
(a)
(b)
Fig. 12. Vapor absorption diagrams of the hosts 1 - 5 in comparison with BTh1 and BTh2 (a)
as well as of the host 6 coated from different solvents (b).
As expected, the vapor of the least polar solvents, i.e. n-hexane and CHCl3 show the
lowest absorption ratio, no matter which host compound is used for coating. In reversal
conclusion, vapors of the more polar and protic solvents feature a much higher absorption
being expressed by increased absorption ratios (100 % equals an inclusion stoichiometry of
1:1, 200 % of 1:2 etc. [36]); this is particularly true for the vapors of EtOH and Et2NH.
Nevertheless, for each coating sorption ratios depend on host structure and its packing in the
solid state. However, since the structures of solvent-free crystals of 1-6 are not known, it is
difficult to deliver a sound reasoning based on an appropriate approach. To specify a few facts
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of noteworthy behavior: BTh1 and compound 5 demonstrate particular high activity of
sorption for EtOH (212 % and 218 % ratios, respectively, equating to approximate 1:2 host-
guest stoichiometries), though both compounds feature very different lengths of the central
molecular axes and appear as rather inefficient referring to their inclusion from solvent
crystallization. The same we found for the sorption of Et2NH by 6 (coated from CHCl3)
showing the highest ratio of vapor uptake on the whole (224 %); though 6 failed to make
accessible a corresponding inclusion complex on solvent crystallization. From another
approach of reasoning one may think that the spatial condition near the binding active
hydroxyl group of the host exercises a controlling influence on the vapor sorption. This would
mean that the hosts featuring an ethynylene unit attached to the hydroxyl substituted carbon
atom (BTh1, 2, 4-6) are favored over hosts having an attached phenylene unit (BTh2, 1, 3);
but also in this respect there is no corresponding trend justified by the data. Hence, the results
once more [12,13,36] make us aware that the vapor sorption behavior and solvent co-
crystallization properties of the present hosts are only limited, if at all, transferable.
In further studies, we observed a preconditioning effect of the sorptive coating. This
has been found working with host compound 6 showing high ratios of included EtOH both on
solvent crystallization (1:4 stoichiometry) and vapor sorption (185 %) when 6 having been
deposited from CHCl3 solution. However, when the quartz crystal was dipped in a 0.01
M
solution of 6 in EtOH and the solvent was evaporated aiming for a solvent-free and loosely
packed coating, sorption measurements with the guest vapors applied before, revealed a
different outcome of the experiment instead. The uptake of all guest vapors is decreased now
in comparison to the coating of 6 from chloroform ranging from -22% for EtOH and -72 %
for n-hexane. Moreover, the sequence of the different solvents has changed. Et2NH which was
taken up in the highest ratio before, is now absorbed only moderately. The smallest change
has been observed for EtOH as a guest vapor (Table 5, Fig. 12b). This remarkable finding
might be explained by a kind of ‘structure memory effect’ [37,38] of the voids remained after
solvent desorption of the initial host-guest coating.
Conclusion
Carbonyl addition reactions of benzo[b]thien-2-yl-lithium to corresponding di- or
triesters in the cases of 1, 3 and 6, respectively, and Sonogashira-Hagihara cross-coupling
reactions between a particular benzo[b]thien-2-yl substituted propynol (14)
and
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corresponding spacer moieties in the cases of 2, 4 and 5 gave the new diol compounds in
respective to high yields (54-96 %). An intensive study of the inclusion property in solid state
by crystallization from a variety of solvents proved their versatile host behavior and inclusion
activity. Other than we expected, elongation of the central spacer unit does not improve the
inclusion behavior in general. This is in line with findings for gradually elongated porphyrin
systems [8,9]. The most efficient solvent inclusion has been found for a biphenyl spacer
showing an inclusion ratio comparable to previously discussed molecules having phenyl or an
ethynlene spacer. By way of interest, for the new compounds, high ratio of included solvent is
rather common, which is especially true for the trigonal host 6.
From seven inclusion compounds X-ray structures could be solved. The structural
investigation revealed the dominance of layers, cages and channels, with the guests being
accommodated in the respective voids. A particular high framework porosity is observed for
the 1:5 pyridine inclusion 2a indicating ideal spacer length for optimal bulkiness of the host;
for this example a KPI of only 41.2 % has been found. As before for the tendency to form
crystalline inclusion compounds, the ability for QCM vapor absorption is rarely depending on
the spacer length, though much more on the spacer components. The ratio of vapor absorption
is notably high for the C≡C-Ph-C≡C spacer occurring either two (2) or three (6) times in the
respective host. For 6 as the most active of the hosts studied here, the use of different solvents
on the quality of the coating has been investigated. Thereby, a ‘structure memory effect`
shown for the inclusion of EtOH instead of CHCl3 is obvious, which could lead to an
interesting concept for construction of a selective sensor material.
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Experimental Section
General
The melting points were measured on a microscope heating stage Thermovar
(Reichert-Jung). IR spectra were recorded on a Nicolet FT-IR 510 spectrometer as KBr pellets
(wave numbers given in cm-1). 1H and 13C NMR spectra were obtained from a Bruker Avance
500 at 500.1 (1H) and 125.8 MHz (13C) using TMS as internal standard. Chemical shifts for
proton and carbon resonances are given in ppm (δ). Mass spectra were recorded on a Hewlett
Packard 5890 Series II/MS 5971 A. Elemental analyses were measured using a Hanau vario
MICRO cube. The TLC analysis was performed with aluminium sheets precoated with silica
gel 60 F254 (Merck). Silica gel (63-100 ꢀm, Merck) was used for column chromatography.
Starting compounds including benzo[b]thiophene (BTh) (8), bibenzyl, 4-bromotoluene, 1,4-
diiodobenzene, 4,4'-diiodobiphenyl, methyl 4-iodobenzoate and other reagents were
purchased from commercial sources and used without further purification. Dimethyl 4,4’-
(ethynylene)dibenzoate (9) [19] and 4,4´-diiodotolane [39] were prepared as described in the
literature. 1,3,5-Triethynylbenzene (10) has been synthesized from commercially available
1,3,5-tribromobenzene applying a Pd-catalyzed cross-coupling with MEBINOL (2-methylbut-
3-yn-2-ol) followed by cleavage of the 2-hydroxypropan-2-yl protection groups [20].
Syntheses
Dimethyl biphenyl-4,4'-dicarboxylate (7)
The synthesis has been carried out differing from the literature procedure [15]. A mixture
of 4-(methoxycarbonyl)boronic acid (2.04 g, 11.4 mmol) and methyl 4-iodobenzoate (3.00 g,
11.4 mmol) in 75 ml THF and 90 ml H2O was degassed (10 min) under an argon atmosphere
followed by the addition of Pd(PPh3)2Cl2 (92.4 mg, 0.132 mmol) and NaHCO3 (9.00 g, 107.1
mmol). After refluxing for 4 h and cooling down to room temperature, the resulting
crystalline solid was collected by vacuum filtration (fraction 1). The residue obtained by the
evaporation of the filtrate was extracted with 200 ml CH2Cl2. Drying of the organic phase
(Na2SO4) and evaporation of the solvent gave a white solid (fraction 2). The two fractions
were combined and crystallized from toluene to yield 7 as a white flaky solid (1.96 g, 64 %).
o
1
Mp: 211 - 212 °C (lit. 212 - 213 C [39]). H NMR (DMSO-d6): δH = 3.89 (s, CH3), 7.91 (d,
Ar-H, J = 8.55 Hz), 8.07 (d, Ar-H, J = 8.55 Hz). 13C NMR (DMSO-d6): δC = 52.2 (CH3),
127.3, 129.2, 129.9, 143.2 (Ar-C), 165.9 (COOMe).
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Trimethyl 3,3',3''-(benzene-1,3,5-triyl)tripropynoate (11)
A solution of n-BuLi (25.8 ml, 41.2 mmol, 1.6
M n-hexane) in 150 ml dry THF was
treated dropwise with 1,3,5-triethynylbenzene (10) (2.00 g, 13.3 mmol) in 50 ml dry THF at -
40 °C under an argon atmosphere. The temperature was decreased to -78 °C and methyl
chloroformiate (3.2 ml, 41.2 mmol) was added slowly. After stirring for 6.5 h at room
temperature, the reaction was quenched with 1M hydrochloric acid (150 ml), the mixture
extracted with CHCl3 (150 ml), the organic phase dried (Na2SO4) and the solvent evaporated.
Column chromatography [SiO2; EtOAC/n-hexane 1:6] of the crude product yielded
compound 11 as a white powder (1.27 g, 29 %). Mp: 127 - 130 °C. Rf = 0.44 (EtOAc/n-
1
13
hexane 1:6). H NMR (CDCl3): δH = 3.86 (s, CH3), 7.80 (s, A-H). C NMR (CDCl3): δC =
52.7 (CH3), 81.7, 82.0 (C≡C), 121.0, 137.6 (Ar-C), 153.2 (COOMe). IR: 3070, 2954, 2226,
1716, 1584, 1430, 1354, 1258, 1217, 1189, 1153, 1031, 933, 921, 894, 869, 829, 740, 677,
599, 558, 543, 462, 436. MS(ESI): m/z calc. for C18H12O6: 324.06, found: 325 [M+H]+. EA:
calc. for C18H12O6: C% 66.67, H% 3.73, found: C% 66.79, H% 3.94.
Di(benzo[b]thien-2-yl)methanone (12)
The synthesis has been performed following the literature procedure [40] but obtaining a
higher yield. To a solution of benzo[b]thiophene (8) (8.05 g, 60 mmol) in 80 ml dry THF at -
30 °C (under argon) was added slowly n-BuLi (37.5 ml, 1.6
M in n-hexane). After having
stirred for 15 min at -30 °C, the mixture was treated with N,N-dimethylcarbamoyl chloride
(2.8 ml, 30 mmol) and stirred again for 5 h at room temperature. Afterwards, the reaction
mixture was cooled to 0 °C, quenched with 1
M hydrochloric acid (120 ml) and extracted with
CH2Cl2 (3x 120 ml). The combined organic phases were dried (Na2SO4) and evaporated. The
obtained crude product was stirred for 30 min in 70 ml refluxing EtOH. The remaining solid
was collected and dried to yield 2 as a white powder (8.07 g, 91 %). Mp: 162 - 164 °C (lit.
165.5 °C [41]). 1H NMR (CDCl3): δH = 7.44, 7.50 (each: td, BTh5/6, J = 8.00, 1.15 Hz), 7.91,
13
7.94 (each: d, BTh4/7, J = 7.85 Hz), 8.19 (s, BTh3). C NMR (CDCl3): δC = 122.9, 125.2,
126.1, 127.5, 130.8, 139.0, 142.2 (BTh), 181.5 (C=O).
1,1-Di(benzo[b]thien-2-yl)-3-(trimethylsilyl)prop-2-yne-1-ol (13)
Under an argon atmosphere, TMSA (1.74 ml, 12.2 mmol) in 60 ml dry THF was treated
slowly at -78 °C with n-BuLi (7.6 ml, 1.6
M n-hexane) followed by dropwise addition of a
solution of di(benzo[b]thien-2-yl)methanone (12) (3.00 g, 10.2 mmol) in 60 ml dry THF. The
mixture was stirred for 3 h at room temperature and quenched with a sat. NH4Cl-solution (90
25

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ml). After evaporation of the solvent, the residue was extracted with CH2Cl2 (3x 90 ml). The
combined organic phases were dried (Na2SO4), the solvent evaporated and the obtained
colourless oil stirred for 30 min in 40 ml n-hexane. Collection and drying of the precipitate
yielded compound 13 as a white powder (3.38 g, 85 %). Mp: 145 - 149 °C. 1H NMR (CDCl3):
δH = 0.28 (s, SiCH3), 3.35 (s, OH), 7.31 (2td, BTh5/6, J = 7.95, 7.15, 1.40, 1.30 Hz), 7.46 (s,
BTh3), 7.72 (d, BTh4, J = 7.00 Hz), 7.77 (d, BTh7, J = 7.70 Hz). 13C NMR (CDCl3): δC = 0.1
(SiCH3), 70.6 (C-OH), 93.1, 105.2 (C≡C), 122.4, 122.7, 124.4, 124.7, 125.0, 139.3, 140.5,
149.0 (BTh). IR: 3563, 3055, 2960, 1456, 1434, 1331, 1301, 1251, 1196, 1141, 1128, 1104,
1071, 1054, 1040, 1013, 941, 835, 787, 761, 741, 726, 707, 688, 674, 628, 584, 484, 443, 437,
429. MS(ESI): m/z calc. for C22H20OS2Si: 392.07, found: 392 [M]+. EA: calc. for
C22H20OS2Si: C% 67.30, H% 5.13, S% 16.33, found: C% 67.56, H% 5.17, S% 16.26.
1,1-Di(benzo[b]thien-2-yl)prop-2-yne-1-ol (14)
A mixture of 13 (3.00 g, 7.6 mmol) and K2CO3 (4.20 g, 30.4 mmol) in 100 ml MeOH
was stirred for 7 h at room temperature, then diluted with CH2Cl2 (100 ml) and quenched with
sat. NH4Cl-solution (100 ml). The separated aqueous phase was extracted with CH2Cl2 (100
ml) and the combined organic phases dried (Na2SO4). Evaporation of the solvent gave a
yellow oily residue which was stirred for 20 min in 25 ml n-hexane/EtOAc (10:1). The
formed precipitate was collected and dried yielding 14 as a beige powder (2.22 g, 91 %). Mp:
1
113 - 116 °C. H NMR (CDCl3): δH = 3.02 (s, C≡CH), 3.37 (s, OH), 7.33 (2td, BTh5/6, J =
7.10, 7.00, 1.55, 1.35 Hz), 7.51 (s, BTh3), 7.73 (dd, BTh4, J = 7.05, 1.65 Hz), 7.78 (d, BTh7, J
= 7.60, 1.75 Hz). 13C NMR (CDCl3): δC = 70.1 (C-OH), 75.8, 84.1 (C≡C), 122.4, 122.5,
124.2, 124.5, 124.9, 138.9, 140.2, 148.1 (BTh). IR: 3496, 3274, 3058, 2114, 1530, 1455,
1433, 1332, 1301, 1250, 1198, 1147, 1098, 1059, 1014, 977, 932, 861, 836, 782, 749, 727,
709, 674, 650, 614, 593, 577, 558, 507, 492, 428, 408. MS(ESI): m/z calc. for C19H12OS2:
320.03, found: 320.0 [M]+. EA: calc. for C19H12OS2: C% 71.22, H% 3.77, S% 20.01, found:
C% 70.92, H% 3.68, S% 20.48.
General procedure for the synthesis of 1, 3 and 6
To a solution of benzo[b]thiophene (8) (2.15 g, 16.0 mmol) in 20 ml dry THF under an
argon atmosphere at -30 °C, n-BuLi (10.0 ml, 16.0 mmol, 1.6M n-hexane) was added slowly.
The mixture was treated with the corresponding ester and stirred at room temperature. After
quenching with saturated aqueous NH4Cl-solution, the residue was extracted with CHCl3. The
26

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organic phase was dried (Na2SO4) and the solvent evaporated. Specific details for each
compound are given below.
4,4'-Bis[di(benzo[b]thien-2-yl)hydroxymethyl]biphenyl (1)
Dimethyl biphenyl-4,4'-dicarboxylate (7) (1.08 g, 4.0 mmol) was added as a solid in
small portions and the reaction mixture was stirred for 6 h at room temperature. The crude
product was crystallized from CHCl3 yielding compound 1 as a white solid (2.14, 72 %). Mp
1
> 284 °C (dec). H NMR (DMSO-d6): δH = 7.24 (s, BTh3), 7.33 (2td, BTh5/6, J = 7.15, 1.60
13
Hz), 7.59 (s, OH), 7.61, 7.70 (each: d, Ar-H, J = 8.55 Hz), 7.80, 7.91 (each: m, BTh4/7). C
NMR (DMSO-d6): δC = 77.2 (C-OH), 122.3, 122.6, 123.9, 124.3, 124.4 (BTh), 126.2, 127.2,
138.9 (Ar-C), 139.0, 139.3 (BTh), 145.0 (Ar-C), 152.6 (BTh). IR: 3417, 3053, 1493, 1433,
1391, 1329, 1303, 1249, 1182, 1153, 1129, 1085, 1061, 990, 941, 894, 860, 825, 776, 744,
725, 653, 613, 567, 466, 432. MS(ESI): m/z calc. for C46H30O2S4: 742.11, found: 765.2
[M+Na]+. EA: calc. for C46H30O2S4: C% 74.36, H% 4.07, S% 17.26, found: C% 74.37, H%
4.13, S% 17.56.
4,4'-Bis[di(benzo[b]thien-2-yl)hydroxymethyl]tolane (3)
Dimethyl tolane-4,4'-dicarboxylate (9) (1.18 g, 4.0 mmol) was added as a solid in small
portions and the reaction mixture was stirred for 8 h at room temperature. The crude product
was heated for 20 min at 50 °C in EtOH (60 ml). Collection of the solid by filtration yielded
1
compound 3 as a yellowish powder (2.10, 68 %). Mp > 190 °C (dec). H NMR (DMSO-d6):
δH = 7.20 (s, BTh3), 7.34 (2td, BTh5/6, J = 7.10, 1.70 Hz), 7.56, 7.59 (each: d, Ar-H, J = 8.75
Hz), 7.67 (s, OH), 7.81, 7.91 (each: m, BTh4/7). 13C NMR (DMSO-d6): δC = 77.2 (C-OH),
89.4 (C≡C), 121.5 (Ar-C), 122.3, 122.8, 124.0, 124.4, 124.5 (BTh), 127.0, 131.0 (Ar-C),
138.9, 139.3 (BTh), 146.2 (Ar-C), 152.1 (BTh). IR: 3535, 3053, 1945, 1910, 1799, 1717,
1701, 1606, 1559, 1511, 1461, 1432, 1404, 1334, 1309, 1252, 1179, 1154, 1131, 1090, 1065,
1017, 1002, 938, 891, 850, 815, 777, 748, 726, 710, 612, 587, 568, 463, 435. MS(ESI): m/z
calc. for C48H30O2S4: 766.11, found: 749.0 [M-OH]+. EA: calc. for C48H30O2S4: C% 75.16,
H% 3.94, S% 16.72, found: C% 75.20, H% 4.02, S% 16.69.
1,3,5-Tris[3,3-di(benzo[b]thien-2-yl)-3-hydroxypropynyl]benzene (6)
Trimethyl 3,3',3''-(benzene-1,3,5-triyl)tripropynoate (11) (0.84 g, 2.6 mmol) in 20 ml dry
THF was added dropwise and the reaction mixture was stirred for 8.5 h at room temperature.
The crude product was heated for 15 min at 50 °C in EtOH (40 ml). Collection of the solid by
27

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filtration yielded compound 6 as a yellowish brown powder (1.45 g, 54 %). Mp: 138 - 142 °C.
1H NMR (DMSO-d6): δH = 7.36 (2td, BTh5/6, J = 7.20, 1.30 Hz), 7.67 (s, BTh3), 7.87 (d,
BTh4, J =7.15 Hz), 7.92 (s, Ar-H), 7.93 (d, BTh7, J =7.15 Hz), 8.08 (s, OH). 13C NMR
(DMSO-d6): δC = 69.2 (C-OH), 83.4, 92.6 (C≡C), 121.4, 122.5, (BTh), 123.0 (Ar-C), 124.1,
124.5, 124.7 (BTh) 134.6 (Ar-C), 138.9, 139.2, 150.2 (BTh). IR: 3441, 3057, 2227, 1625,
1583, 1529, 1458, 1434, 1417, 1332, 1307, 1251, 1187, 1128, 1104, 1056, 1015, 979, 940,
882, 861, 832, 781, 747, 726, 709, 679, 583, 438. MS(ESI): m/z calc. for C63H36O3S6:
1032.10, found: 1015.1 [M-OH]+. EA: calc. for C63H36O3S6·EtOH: C% 72.33, H% 3.92, S%
17.82, found: C% 71.91, H% 3.71, S% 17.73.
General procedure for the synthesis of 2, 4 and 5
A mixture of 1,1-di(benzo[b]thien-2-yl)prop-2-yne-1-ol (14) (1.00 g, 3.1 mmol) and the
corresponding arylhalide in 60 ml triethylamine was degassed for 10 min (under argon). Then,
the catalyst system containing Pd(PPh3)2Cl2 (21.8 mg, 0.031 mmol), CuI (17.7 mg, 0.093
mmol) and PPh3 (16.3 mg, 0.062 mmol) was added and the subsequent reaction carried out
under reflux (TLC controlled). After cooling to room temperature, the reaction mixture was
diluted with CHCl3 (80 ml) and washed with saturated aqueous NH4Cl-solution (80 ml). The
separated organic phase was dried (Na2SO4) and the solvent evaporated.
1,4-Bis[3,3-di(benzo[b]thien-2-yl)-3-hydroxypropynyl]benzene (2)
The reaction was run for 7.5 h using 1,4-diiodobenzene (0.49 g, 1.5 mmol) as the
arylhalide. The crude product was stirred for 15 min in EtOH/acetone (4:1, 30 ml) and the
solid collected by vacuum filtration to yield compound 2 as a white powder (1.02 g, 95 %).
1
Mp >267 °C (dec). Rf = 0.27 (EtOAc/n-hexane 1:2). H NMR (CDCl3): δH = 3.92 (s, OH),
7.33 (2t, BTh5/6, J = 7.10 Hz), 7.53 (s, BTh3), 7.56 (s, Ar-H), 7.74, 7.79 (each: d, BTh4/7, J =
7.25, 7.65 Hz). 13C NMR (CDCl3): δC = 70.8 (C-OH), 86.8, 91.8 (C≡C), 122.4 (Ar-C), 122.4,
122.7, 124.3, 124.7, 125.0 (BTh), 132.1 (Ar-C), 139.3, 140.4, 149.0 (BTh). IR: 3523, 3050,
2872, 2233, 1500, 1455, 1432, 1329, 1303, 1264, 1248, 1192, 1123, 1097, 1056, 1012, 936,
834, 800, 787, 743, 723, 704, 676, 600, 593, 575, 548, 478, 432. MS(ESI): m/z calc. for
C44H26O2S4: 714.08, found: 737.2 [M+Na]+. EA: calc. for C44H26O2S4: C% 73.92, H% 3.67,
S% 17.94 found: C% 73.72, H% 3.60, S% 18.12.
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