Triptycene-derived calix[6]resorcinarene-like hosts: Synthesis, structure and self-assemblies in the solid state

Article abstract of DOI:10.1039/c1cc15895c

A class of novel triptycene-derived calix[6]resorcinarene-like hosts have been designed and synthesized, and they are all cis-isomers with fixed cone conformation and can form head-to-head dimeric structures in the solid state. The Royal Society of Chemis

Full text of DOI:10.1039/c1cc15895c

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COMMUNICATION
Triptycene-derived calix[6]resorcinarene-like hosts: synthesis, structure
and self-assemblies in the solid statew
Peng-Fei Liab and Chuan-Feng Chen*a
Received 22nd September 2011, Accepted 5th October 2011
DOI: 10.1039/c1cc15895c
A class of novel triptycene-derived calix[6]resorcinarene-like
hosts have been designed and synthesized, and they are all
cis-isomers with fixed cone conformation and can form
head-to-head dimeric structures in the solid state.
phenol moieties. It was found that the novel macrocycles are
all cis-isomers with fixed cone conformation, and can self-
assemble into the head-to-head dimeric structures and further
3D microporous architectures in the solid state.
Synthesis of the triptycene-derived calix[6]resorcinarene-like
hosts 5a–c and 6a–c is depicted in Scheme 1. Starting from
2,7-dimethoxyltriptycene,9 compound 2 was prepared in 75%
yield by formylation with hexamethylenamine in refluxed
trifluoroacetic acid, and then reduction of the aldehyde with
sodium borohydride in MeOH and THF gave compound 3.
By the reaction of 3 and excess of p-substituted-phenols in
toluene in the presence of p-toluenesulfonic acid, compounds
4a–c were obtained in 54–78% yields. Finally, the reaction of
compound 3 with equimolar amount of 4 in o-dichlorobenzene
in the presence of p-toluenesulfonic acid gave the target
calix[4]resorcinarenes 5a–c in 20–22% yields. Macrocycles
5a–c were further demethylated by BBr3 in dichloromethane
to give compounds 6a–c in 90–95% yields.
Calixresorcinarenes or resorcinarenes1 are a class of well
defined macrocyclic compounds related to calixarenes, and
they can be mostly obtained by acid-catalyzed condensation
of resorcinol with aldehydes.2 Calix[4]resorcinarenes with
bowl-shaped structures are well known, and they have been
widely used as the building blocks for the construction of
cavitands, carcerands3 and molecular capsules.4 In particular,
Rebek and co-workers5 have developed a new method to
deepen the cavity of calix[4]resorcinarenes by bridging two
adjacent phenoxyl groups with suitable linkers, and found that
the new synthetic hosts have wide potential applications in
molecular recognition, stabilizing reaction intermediates and
catalysis, which thus made a very impressive development in
the chemistry of calixresorcinarene. However, it was noted that
compared with calix[4]resorcinarenes, calix[6]resorcinarenes
have larger cavities but more flexible conformation, which
might make them be less studied.6
The 1H NMR spectrum of 5a showed not only a singlet for
the tert-butyl protons, one singlet for the methoxy protons,
and two singlets for the bridgehead protons of two triptycene
In recent years, we have devoted ourselves to the synthesis
of novel triptycene-derived hosts and their applications in
supramolecular chemistry.7 As a result, we reported a class
of novel triptycene-derived calix[5]arenes and calix[6]arenes,
and found that the triptycene building block played a key role
in fixing the conformation of the calixarenes.8 Thus, we
deduced that if 2,7-dihydroxyltriptycene was used as an alter-
native of resorcinol, novel calixresorcinarene-like hosts with
large cavity and fixed conformation could be obtained. Herein,
we report the preliminary results on the synthesis and structure
of a class of novel triptycene-derived calix[6]resorcinarene-like
hosts containing two triptycene moieties and two p-substituted
a Beijing National Laboratory for Molecular Sciences,
CAS Key Laboratory of Molecular Recognition and Function,
Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, China. E-mail: cchen@iccas.ac.cn;
Fax: +86 10-62554449
b Graduate School, Chinese Academy of Sciences, Beijing 100049, China
w Electronic supplementary information (ESI) available: Synthesis
and characterization data of new compounds. Variable-temperature
1H NMR experiments of macrocycle 5a. Crystal data and packing of
5a and 6a. CCDC 842676–842678. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c1cc15895c
Scheme 1 Synthesis of the macrocycles 5a–c and 6a–c. Reagents
and conditions: (a) hexamethylenamine, CF3CO2H, reflux, 75%;
(b) NaBH4, MeOH, 98%; (c) p-substituted-phenol, p-TsOH, PhMe;
(d) p-TsOH, o-dichlorobenzene; (e) BBr3, dichloromethane.
c
12170 Chem. Commun., 2011, 47, 12170–12172
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Fig. 1 (a) Top view and (b) side view of crystal structure of 5a. (c)
Top view and (d) side view of crystal structure of 6a. Dashed lines
denote the intramolecular hydrogen bonding interactions. Solvent
molecules and hydrogen atoms not involved in the interactions are
omitted for clarity.
moieties, but a pair of doublet signals for the methylene
protons, which are very similar to those of the classical
calix[4]arene with cone conformation.1b Moreover, six signals
for the aliphatic carbons were only observed in the 13C NMR
Fig. 2 Packing of 5a. (a) Side view and (b) top view of the head-
to-head dimer with CH2Cl2 molecules situated in the cavity.
(c) Microporous architecture viewed along the c-axis. Dashed lines
denote the non-covalent interactions between the adjacent molecules.
Solvent molecules and hydrogen atoms not involved in the interactions
are omitted for clarity.
1
spectrum of 5a. Its variable-temperature H NMR experiments
also showed no obvious changes of the methylene proton
signals with the increase of the temperature (Fig. S21, ESIw).
These observations suggested that 5a is the cis-isomer with
highly symmetric structure and fixed cone conformation.
Similarly, it was found that macrocycles 5b–c and the corres-
ponding demethylated macrocycles 6a–c are all the cis-isomers
with fixed cone conformation in solution.10
between the methyl protons of one triptycene moiety and the
methoxyl groups of its adjacent macrocycle with the distances
of 2.45 and 2.46 A, respectively. Two dichloromethane molecules
were positioned inside the dimeric cavity, and there also
existed a C–HÁÁÁCl interaction9 between the methyl proton of
one macrocycle and each dichloromethane molecule with the
distance of 2.46 A, which might play an important role in
formation of the dimeric structure. Moreover, we found that
the dimers can be stacked in pillars to form a tubular structure
with aromatic rings as the wall8c viewed along the c-axis,
which further assemble into a 3D microporous architecture
with the CH2Cl2 molecules located inside each channel (Fig. 2c
and Fig. S22, ESIw).
In the case of 6a, two macrocyclic molecules can also form a
head-to-head dimer, but there is a shift between the two dimer
components. As shown in Fig. 3a and b, besides a pair of
C–HÁ Á ÁO hydrogen bonding interactions between the bridged
hydrogen of triptycene and the phenoxyl oxygen atom of
another macrocycle with the distance of 2.34 A, there existed
a pair of O–HÁ Á ÁO hydrogen bonding interactions between the
phenoxyl proton of one triptycene and the oxygen atom of
acetone situated in the cavity of another macrocycle with the
distance of 1.91 A, and a pair of C–HÁ Á Áp interactions between
the methyl proton of the acetone at the cavity and the
aromatic ring of the adjacent triptycene with the distance of
2.86 A. Moreover, a pair of O–HÁ Á ÁO hydrogen bonding
(1.99 A) and a pair of C–HÁ Á ÁO hydrogen bonding (2.40 A)
interactions between the phenoxyl groups of one macrocycle
and the adjacent acetone above the macrocycle were also
observed. These multiple noncovalent interactions resulted in
the dimeric structure. Furthermore, it was also found that the
Fortunately, we obtained block and colorless crystals11 of
5a and 6a suitable for X-ray analysis by slow diffusion of
CH3OH into a dichloromethane solution of 5a and evaporation
of an acetone solution of 6a, respectively. As shown in Fig. 1,
the crystal structures revealed that macrocycles 5a and 6a are all
cis-isomers, which are consistent with the results in solution.
Besides the rigid triptycene skeletons and the large steric tert-
butyl groups, there existed one pair of intramolecular hydrogen
bonding interactions between the phenol protons and the adjacent
methoxyl groups of one triptycene moiety in 5a with the distance
of 1.99 A. For 6a, two pairs of intramolecular hydrogen bonding
interactions between the tert-butylphenol protons and the adjacent
methoxyl groups of two triptycene moieties with the distances of
1.91–1.99 A are shown. These hydrogen bonding interactions
play an important role in controlling the conformation of the
macrocycles. As a result, it was found that 6a has a more
symmetrical conformation than 5a due to the two-fold hydrogen
bonds to pull two triptycene units of 6a inward. The dihedral
angle between the face-to-face benzene rings of the triptycene
moieties in 6a is 9.471, which is much smaller than that of 5a
(30.061). The dihedral angle (24.411) between two p-tert-butyl-
phenol rings of 5a is also smaller than that of 6a (34.291).
Moreover, 5a shows a wider rim of 9.52 Â 10.67 A2 and a
narrower rim of 7.96 Â 9.30 A2, while 6a has the wider and
narrower rim of 9.10 Â 9.87 and 7.45 Â 9.63 A2, respectively.
We further studied the self-assemblies of macrocycles 5a and
6a in the solid state. As shown in Fig. 2, two macrocyclic
molecules of 5a can form a head-to-head dimeric capsule by
virtue of two pairs of C–HÁ Á ÁO hydrogen bonding interactions
c
This journal is The Royal Society of Chemistry 2011
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We thank the National Natural Science Foundation of
China (20972162) and the National Basic Research Program
(2011CB932501) for financial support.
Notes and references
1 (a) Calixarenes 2001, ed. M. Z. Asfari, V. Bohmer, J. Harrowfield and
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J. Vicens, Kluwer Academic Publishers, Dordrecht, Netherlands, 2001;
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Chemistry, ed. J. F. Stoddart, Royal Society of Chemistry, Cambridge,
1998; (c) Calixarenes and Resorcinarenes: Synthesis, Properties and
Applications, ed. W. Sliwa and C. Kozlowski, Wiley-VCH Verlag
GmbH & Co. KGaA, Weinheim, 2009.
2 (a) J. B. Niederl and H. J. Vogel, J. Am. Chem. Soc., 1940, 62,
2512–2514; (b) A. G. S. Hoegberg, J. Am. Chem. Soc., 1980, 102,
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R. M. Sampson and G. W. Kalleymeyn, J. Am. Chem. Soc., 1988, 110,
2554–2560; (b) Container Molecules and Their Guests, ed. D. J. Cram
and J. M. Cram, Royal Society of Chemistry, Cambridge, 1994.
4 (a) L. R. MacGillivray and J. L. Atwood, Nature, 1997, 389,
469–472; (b) T. Evan-Salem, I. Baruch, L. Avram, Y. Cohen,
L. C. Palmer and J. Rebek, Proc. Natl. Acad. Sci. U. S. A., 2006,
103, 12296–12300.
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1996, 25, 255–264; (e) J. Rebek Jr., Angew. Chem., Int. Ed., 2005,
44, 2068–2078; (f) J. Rebek Jr., Acc. Chem. Res., 2009, 42,
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Fig. 3 Packing of 6a. (a) Top view and (b) side view of the head-to-
head dimeric structure with acetone molecules situated in the cavity.
(c) Microporous architecture viewed along the b-axis. Dashed blue
lines denote the non-covalent interactions between the adjacent
molecules. Solvent molecules and hydrogen atoms not involved in
the non-covalent interactions are omitted for clarity.
macrocyclic molecules of 6a could self-assemble into a micro-
porous architecture viewed along the b-axis (Fig. 3c), and the
acetone molecules were situated inside the channels (Fig. S23,
ESIw), which is similar to that of molecule 5a.
9 C. Zhang and C.-F. Chen, J. Org. Chem., 2007, 72, 3880–3888.
10 See ESIw for details.
11 Crystal data for 5a with the solvents squeezed: C68H64O6, Mw
=
977.19, crystal size 0.30 Â 0.26 Â 0.24 mm, triclinic, space group
In summary, we have designed and synthesized a class
of novel triptycene-derived calix[6]resorcinarene-like hosts,
and found that all of the macrocycles are cis-isomers with
fixed cone conformation in solution and in the solid state.
Moreover, we found that macrocycle 5a and its demethylated
molecule 6a can self-assemble into the head-to-head dimeric
structures and further 3D microporous architectures in the
solid state, in which the solvent guests situated in the cavity
played an important role in formation of the assemblies. The
further applications of these novel triptycene-derived macrocycles
in supramolecular chemistry are in progress in our laboratory.
%
P1, a = 12.717(3) A, b = 17.240(3) A, c = 18.924(4) A, a =
109.86(3)1, b = 100.40(3)1, g = 107.82(3)1, V = 3523(2) A3, T =
173(2) K, Z = 2, m = 0.058 mmÀ1, 31 373 reflections measured,
12 871 unique (Rint = 0.072), final R indices [I > 2s(I)]: R = 0.133,
wR = 0.328, R indices (all data): R = 0.172, wR = 0.345. Crystal
data for 6a: C64H56O6Á3(C3H6O), Mw = 1095.32, crystal size
0.35 Â 0.32 Â 0.21 mm, monoclinic, space group P2(1)/n,
a = 12.531(3) A, b = 38.597(8) A, c = 14.299(2) A, a = 90.001,
b = 97.405(2)1, g = 90.001, V = 6858(2) A3, T = 173(2) K, Z =
4, m = 0.069 mmÀ1, 41 470 reflections measured, 12 518 unique
(Rint = 0.0504), final R indices [I > 2s(I)]: R = 0.117, wR =
0.302, R indices (all data): R = 0.134, wR = 0.314. CCDC 842677
(5a-solvents squeezed) and 842678 (6a).
c
12172 Chem. Commun., 2011, 47, 12170–12172
This journal is The Royal Society of Chemistry 2011