Triptycene-derived calix [6]arenes: Synthesis, structures, and their complexation with fullerenes C60and C70

Article abstract of DOI:10.1002/chem.201000517

Two pairs of novel triptycene-derived calix[6]arenes 4a, b and 5a, b have been efficiently synthesized through both one-pot and two-step fragment-coupling strategies starting from 2,7-bis(hydroxymethyl)-l,8-dimethoxytriptycene 1. Subsequent demethylation of 4a.b and 5a,b with BBr₃ in dry dichloromethane gave the macrocyclic compounds 6a,b and 7a,b. Treatment of either 4a or 6a with AlCl₃ resulted in the same debutylated product 8, while 9 was similarly obtained from either 5 a or 7 a. Structural studies revealed that all of the macrocycles have well-defined structures with fixed conformations both in solution and in the solid state owing to the introduction of the triptycene moiety with a rigid three-dimensional (3D) structure, making them very different from their classical calix [6]arene counterparts. As a consequence, it was found that all of these the triptycene-derived calix [6]arenes could encapsulate small neutral molecules in their cavities in the solid state. Moreover, it was also found that the macrocycles 4 b and 5 b showed highly efficient complexation abilities toward fullerenes C₆₀ and C₇₀, forming 1:1 complexes with association constants ranging from (5.22 ± 0.20) × 10₄ to(8.68±0.30)×l0 ⁴M^-1.

Full text of DOI:10.1002/chem.201000517

DOI: 10.1002/chem.201000517
Triptycene-Derived Calix[6]arenes: Synthesis, Structures, and Their
Complexation with Fullerenes C60 and C70
Xiao-Hong Tian[a, b] and Chuan-Feng Chen*[a]
Abstract: Two pairs of novel tripty-
cene-derived calix[6]arenes 4a,b and
5a,b have been efficiently synthesized
through both one-pot and two-step
fragment-coupling strategies starting
from 2,7-bis(hydroxymethyl)-1,8-dime-
thoxytriptycene 1. Subsequent deme-
thylation of 4a,b and 5a,b with BBr3 in
dry dichloromethane gave the macro-
cyclic compounds 6a,b and 7a,b. Treat-
ment of either 4a or 6a with AlCl3 re-
sulted in the same debutylated product
8, while 9 was similarly obtained from
either 5a or 7a. Structural studies re-
vealed that all of the macrocycles have
well-defined structures with fixed con-
formations both in solution and in the
solid state owing to the introduction of
classical calix[6]arene counterparts. As
a consequence, it was found that all of
these the triptycene-derived calix[6]ar-
enes could encapsulate small neutral
molecules in their cavities in the solid
state. Moreover, it was also found that
the macrocycles 4b and 5b showed
highly efficient complexation abilities
toward fullerenes C60 and C70, forming
1:1 complexes with association con-
stants ranging from (5.22Æ0.20)ꢀ104
to (8.68Æ0.30)ꢀ104 mÀ1.
the triptycene moiety with
three-dimensional (3D)
a
rigid
structure,
making them very different from their
Keywords: calixarenes · fullerenes ·
host–guest systems · synthesis de-
sign · triptycene
Introduction
molecules, while calix[6]arenes and larger calixarenes have
so many conformations that their cavities are also difficult
to utilize.[3] Indeed, only through appropriate functionaliza-
tion on both the lower and upper rims to fix the conforma-
tion were Arduini et al. able to show that triphenylureidoca-
lix[6]arene derivatives could be used as “wheels” for the
synthesis of pseudorotaxanes and rotaxanes.[4] Recently,
The design and synthesis of new classes of hollow host com-
pounds with inner cavities large enough to encapsulate or-
ganic guests is always an interesting and exciting research
topic in supramolecular chemistry.[1] Among the various
known types of macrocyclic molecules, calixarenes,[1,2]
a
class of well-defined phenol-derived cyclic oligomers
bridged by methylene groups, have been the focus of consid-
erable attention in the last two decades. However, it was
noted that the cavities of calix[4]arenes are too small to
complex common organic guests except some small solvent
ACHTUNGTRENRNUGN einaud and co-workers reported a class of calix[6]arene-
based ligands that could act as biomimetic molecular recep-
tors.[5] However, experimental and theoretical studies have
shown that calix[6]arenes display extreme conformational
flexibility due to facile ring inversion of their aromatic units,
which must be restricted in order to obtain suitably pre-or-
ganized subunits. For this reason, several research groups[6]
have developed various strategies for the conformational re-
striction of calix[6]arenes, which have proven to be more
difficult to implement for the larger cyclic oligomers.
[a] X.-H. Tian, Prof. C.-F. Chen
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratory of Molecular Recognition and Function
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190 (China)
Recently, we showed that triptycene derivatives with a
rigid three-dimensional (3D) structure could be used as
useful building blocks for the synthesis of different kinds of
novel macrocyclic compounds with specific structures and
properties.[7] We further envisaged that if one or more
phenol group(s) in the classical calix[4]arene were to be re-
placed by appropriate triptycene moieties, a new class of
triptycene-derived calixarenes with larger cavities and fixed
conformations would be obtained. Consequently, we synthe-
Fax : (+86)10-62554449
E-mail: cchen@iccas.ac.cn
[b] X.-H. Tian
Graduate School, Chinese Academy of Sciences
Beijing 100049 (China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000517: 1H and 13C NMR
spectra of new compounds; variable-temperature H NMR spectra of
4a and 6a; crystal packing of 6a; fluorescence titrations and Job
plots for the complexation of C60 and C70 by 4b and 5b.
1
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FULL PAPER
sized some novel triptycene-derived calix[6]arenes with
fixed conformations and found that they formed tubular as-
semblies in the solid state.[8a] More recently, we also report-
ed a series of triptycene-derived calix[5]arene derivatives
with fixed cone conformations in solution and in the solid
state.[8b] In this paper, we report: 1) the synthesis of a series
of triptycene-derived calix[6]arene derivatives, 2) their well-
defined structures with fixed conformations, 3) their encap-
sulation of small neutral molecules in the solid state, and
4) their highly efficient complexation abilities toward C60
and C70.
Results and Discussion
Synthesis of triptycene-derived calix[6]arenes: The synthesis
of the triptycene-derived calix[6]arenes 4 and 5 is depicted
in Scheme 1. We previously reported that the diastereomeric
triptycene-derived calix[6]arenes 4a and 5a could be con-
veniently synthesized by one-pot reaction of the triptycene
derivative 1 and p-tert-butylphenol in o-dichlorobenzene in
the presence of 4-methylbenzenesulfonic acid.[8a] Following
the same approach, the calix[6]arenes 4b and 5b were syn-
thesized in 17 and 11% yield, respectively, by the one-pot
reaction of 1 and p-phenylphenol. The macrocycles 4 and 5
could also be synthesized by a two-step fragment-coupling
approach. As shown in Scheme 1, reaction of the triptycene
derivative 1 with an excess of p-substituted phenol 2a or 2b
in refluxing toluene in the presence of p-toluenesulfonic
acid gave the trimers 3a and 3b in yields of 89 and 83%, re-
spectively.[8b] The macrocycles 4 and 5 were then obtained in
17–25% yield by the reaction of 1 and 3 in o-dichloroben-
zene in the presence of p-toluenesulfonic acid. Compared
with the one-pot reaction, the ready accessibility of the
[1+2] product 3 and the subsequent higher yields of the cyc-
lization reactions, showed that the fragment-coupling
method may be more practical for the preparation of the de-
sired macrocycles.
Scheme 1. Synthesis of triptycene-derived calix[6]arenes.
Moreover, we found that treatment of 4a,b and 5a,b with
BBr3 in dry dichloromethane further afforded the demethy-
lated compounds 6a,b and 7a,b, respectively, in high yields
(Scheme 2). Treatment of 6a and 7a with AlCl3 in toluene
at room temperature resulted in the debutylated products 8
and 9 in yields of 61 and 54%, respectively. Under the same
conditions, we also found that the macrocycles 4a and 5a
could not only be debutylated, but also demethylated to
yield 8 and 9 in moderate yields (Scheme 3). The new com-
1
pounds were all characterized by H and 13C NMR spectros-
copy, mass spectrometry, and elemental analysis.
Structures of the triptycene-derived calix[6]arenes in solu-
tion: We have previously proved that the macrocycles 4a
and 5a are a pair of diastereomers, with 4a being a cis
isomer with cone conformation and 5a being a trans isomer
with a chair conformation.[8a] Similarly, macrocycles 4b and
1
5b are also a pair of diastereomers, and their H NMR spec-
tra were seen to be very different. As shown in Figure 1, the
Scheme 2. Demethylation of triptycene-derived calix[6]arenes.
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C.-F. Chen and X.-H. Tian
tures and fixed conformations in solution, similar to those of
their respective precursors. The 1H and 13C NMR spectral
features of the debutylated macrocycles 8 and 9 correspond-
ing to their methylene bridges are also quite similar to those
of their precursors 4a–7a, indicating that 8 and 9 adopt the
same fixed conformations as those of their precursors.
In order to further investigate the conformational mobili-
ty, variable-temperature 1H NMR experiments on 5a in
[D6]DMSO were also carried out. As shown in Figure 2, no
obvious changes in the methylene proton signals of 5a were
observed upon increasing the temperature, which is in
accord with its fixed conformation. In addition, the upfield
Scheme 3. Debutylation of triptycene-derived calix[6]arenes.
Figure 2. Variable-temperature 1H NMR spectra of 5a in [D6]DMSO at
300 MHz.
Figure 1. 1H NMR spectra (300 MHz, CDCl3) of a) 4b and b) 5b; * de-
notes the peak of CH3OH.
1H NMR spectra of both 4b and 5b showed two singlets due
to the bridgehead protons of the triptycene moiety and one
singlet due to the methoxy protons, but their corresponding
chemical shifts are very different. In particular, it was noted
that 4b showed a pair of doublet signals at d=3.42 and
4.34 ppm (Dd=0.92) due to the methylene protons, while a
pair of doublets at d=3.78 and 3.90 ppm (Dd=0.12) was ob-
served in the spectrum of 5b. The results indicated that 4b
has a syn orientation of the two triptycene moieties, while in
5b they are in an anti orientation.[9] Moreover, we also
found that only four signals due to the aliphatic carbons
were observed in the 13C NMR spectra of 4b and 5b. These
observations are all consistent with their highly symmetrical
structures and fixed conformations in solution.
shift of the methoxy proton signal and the slight downfield
shift of the triptycene proton signals indicate that the tripty-
cene moieties are continuously stretching out and the four
methoxy groups present on the narrow rim of the calix[6]ar-
ene are oriented inwards toward the cavity with increasing
temperature. Moreover, it was also found that variable-tem-
1
perature H NMR experiments on 4a and 6a gave similar
results to those obtained for 5a. Therefore, it could be con-
cluded that although these triptycene-derived calix[6]arenes
have the cavities of classical calix[6]arenes, they show fixed
conformations similar to those of classical calix[4]arenes,
and the most significant factor responsible for determining
the conformational mobility of these novel calix[6]arenes is
not the bulky tert-butyl groups at the para position of the
phenol groups, but mainly the introduction of the triptycene
moiety with its rigid 3D structure.
As in the case of their precursors 4 and 5, the demethylat-
ed products 6a and 6b are also a pair of diastereomers, as
1
are 7a and 7b. Their H NMR spectra all showed a pair of
doublet signals due to the protons of the methylene bridges
and two singlets due to the bridgehead protons of the tripty-
cene moiety. Meanwhile, five signals due to the aliphatic car-
bons were observed in the 13C NMR spectra of 6a and 7a,
and three signals due to the aliphatic carbons were observed
in the 13C NMR spectra of 6b and 7b. These results indicat-
ed that the macrocycles 6 and 7 each had symmetrical struc-
X-ray crystal structures of the triptycene-derived calix[6]ar-
enes: The X-ray crystal structures of the macrocyclic com-
pounds 4a,[8a] 5a,[8a] 5b, 6a, and 8 were determined, and
their crystallographic data are summarized in Table 1.
Owing to the rigid 3D structure of the triptycene moieties,
the macrocycles 4a, 5a, 5b, 6a, and 8 all have highly sym-
metrical structures and specific fixed conformations in the
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Calix[6]arenes Rigidified with Triptycene Units
FULL PAPER
Table 1. X-ray crystallographic data of 4a, 5a, 5b, 6a, and 8.
Compound
4a·2CH3OH
5a·4CH2Cl2·2CH3OH
5b·3CH2Cl2
6a·2CHCl3·2H2O
8·H2O
formula
Mr
crystal size [mm]
crystal system
space group
a [ꢂ]
b [ꢂ]
c [ꢂ]
a [8]
b [8]
C70H72O8
1041.28
0.59ꢀ0.57ꢀ0.06
monoclinic
C2/c
14.953(3)
13.561(3)
29.634(6)
–
104.15(3)
–
5827(2)
4
C74H80Cl8O8
1380.98
C75H62Cl6O6
1271.95
0.25ꢀ0.23ꢀ0.18
monoclinic
P21/n
16.4382(15)
18.8836(16)
20.9472(19)
–
103.707(6)
–
6317.1(10)
4
C66H58Cl6O8
1189.81
0.20ꢀ0.20ꢀ0.16
monoclinic
C2m
22.281(4)
16.835(3)
19.708(4)
–
99.98(3)
–
7086(2)
4
C56H42O7
826.9
0.25ꢀ0.22ꢀ0.11
monoclinic
P21/c
12.055(7)
11.236(6)
38.750(2)
–
95.588(6)
–
5224(4)
4
1.051
173(2)
1.588
0.25ꢀ0.20ꢀ0.18
triclinic
¯
P1
7.4028(15)
15.554(3)
16.174(3)
78.87(3)
81.79(3)
82.09(3)
1797.0(6)
1
g [8]
V [ꢂ3]
Z
1calcd [gcmÀ3
T [K]
]
1.187
173(2)
1.273
1.276
173(2)
1.809
1.337
173(2)
1.059
1.115
173(2)
1.064
GOF on F2
R1 [I>2s (I)]
wR2 (all data)
0.0769
0.1607
0.1194
0.3979
0.0913
0.2846
0.1029
0.3068
0.1088
0.2928
solid state, which are in agreement with the results obtained
in solution.
Similar to 5a,[8a] the macrocycle 5b is also a trans isomer,
in which the face-to-face benzene rings of the triptycene
moieties are each parallel to one another, and the centroid
distances between the face-to-face benzene rings are 8.205
and 8.649 ꢂ, respectively (Figure 3). Interestingly, it was
found that the two p-phenylphenol rings are opposite and
coplanar, with the distance between the two phenolic
oxygen atoms being 6.051 ꢂ. Moreover, we also found that
À
by virtue of a pair of C H···O hydrogen bonds (dCÀ
=
H···O
2.552 and 2.684 ꢂ) between the aromatic protons of the
phenol ring in one macrocycle and the phenolic oxygen of
its adjacent macrocycle and a p–p interaction (dp–p
=
3.358 ꢂ) between the phenyl rings of adjacent triptycene
moieties, the molecule 5b could self-assemble into a 1D
supramolecular structure (Figure 3c), which could further as-
semble into a microporous architecture (Figure 3d).
In the case of 6a, the crystal structure exhibited a typical
cone conformation with a highly symmetrical C2v space
À
group (Figure 4a, b). There exist two pairs of O H···O hy-
drogen bonds (dO···O =2.757 and 2.829 ꢂ, respectively) be-
tween the phenolic hydroxyl groups and the adjacent phe-
nolic hydroxyl groups of the triptycene moieties. Conse-
quently, two face-to-face p-tert-butylphenol rings are almost
parallel to one another, and the dihedral angle between
them is reduced to 7.448 compared with 138.238 in the pre-
cursor 4a,[7a] mainly because of the enhanced intraannular
hydrogen bonds after demethylation. Moreover, it was
found that the cavity cross-section of 6a ranges from 9.56ꢀ
12.09 ꢂ (upper rim) to 7.91ꢀ8.84 ꢂ (lower rim). The macro-
cycle 8 showed similar structural features to those of 6a
À
(Figure 4c, d). The structure also features two pairs of O
H···O hydrogen-bonding interactions (dO···O =2.752 and
2.830 ꢂ, respectively) between the adjacent phenolic hy-
droxyl groups. The dihedral angle between the face-to-face
phenolic rings is 6.958, which is smaller than that in 6a.
Moreover, the cavity cross-section of 8 ranges from 9.22ꢀ
Figure 3. a) Top view and b) side view of 5b. c) The noncovalent interac-
tions between the adjacent molecules, and d) a microporous structure
viewed along the b axis. Solvents and hydrogen atoms not involved in the
noncovalent interactions are omitted for clarity.
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C.-F. Chen and X.-H. Tian
Figure 6. a) Top view and b) side view of the crystal structure of
2CH3OH@4a. c) Top view and d) side view of the crystal structure of
2CH3OH@5a. Dashed lines show the hydrogen-bonding interactions. Hy-
drogen atoms are omitted for clarity.
Figure 4. a) Top view and b) side view of 6a. c) Top view and d) side view
of 8. Dashed lines show the hydrogen bonds. Hydrogen atoms and sol-
vents are omitted for clarity.
These layers could then further stack into two sets of per-
pendicular channels, as illustrated when viewed along the a
axis (Figure 5b) and the c axis (Figure 5c), in which CHCl3
molecules reside.[10]
Encapsulation of small neutral molecules in the solid state:
As expected, the triptycene-derived calix[6]arenes not only
have large enough cavities to serve as hosts, but also have
specific fixed conformations. By virtue of these structural
features, they can easily encapsulate small neutral guest
molecules within their cavities in the solid state. Conse-
quently, it was found that 4a could encapsulate two CH3OH
molecules in its cavity, mainly due to its conformational ri-
gidification, which is impossible for its corresponding classi-
cal calix[6]arene counterpart. It was found that in the host–
À
guest complex 2CH3OH@4a there exist a pair of O H···O
hydrogen bonds (dOÀH···O =2.115 ꢂ) between the phenolic
oxygen atom and the hydroxyl proton of CH3OH (Figure 6a,
b). As in the case of 4a, it was found that 5a could also ac-
commodate two CH3OH molecules in its cavity (Figure 6ACHTUNGTRENNUNG(c,
À
d)), anchored by three pairs of O H···O hydrogen-bonding
interactions (dOÀH···O =2.363 and 2.573 ꢂ, respectively) be-
tween the hydroxyl group of CH3OH and the phenolic hy-
À
Figure 5. Crystal packing of 6a. The noncovalent interactions between
the adjacent macrocycles in one layer (a); the 3D microporous structure
viewed along the b) a axis and c) c axis. Solvents and hydrogen atoms
not involved in the noncovalent interactions are omitted for clarity.
droxyl group, a pair of C H···O hydrogen bonds (dCÀ
2.556 ꢂ) between the methyl protons of CH3OH and the
=
H···O
À
phenolic oxygen atom, and a pair of C H···p interactions
(dCÀH···p =2.845 ꢂ) between the methyl protons of CH3OH
and the phenyl ring of the triptycene moiety in 5a. More-
11.91 ꢂ (upper rim) to 7.63ꢀ8.87 ꢂ (lower rim), and the
centroid distances between the face-to-face benzene rings in
the triptycene moieties were found to be 9.70 and 9.686 ꢂ,
respectively.
It was further found that macrocycle 6a could arrange al-
ternately to form a 2D layer structure through two pairs of
À
over, in 2CH3OH@5a, a pair of O H···O hydrogen-bonding
interactions between the hydroxyl groups of the two metha-
nol molecules with distances of 1.548 ꢂ are also observed.
These multiple noncovalent interactions play an important
role in the formation of the complex.
À
C H···p interactions (dCÀH···p =2.814 ꢂ) between the methyl-
ene protons of one molecule and the phenyl rings of the
triptycene moieties of the adjacent molecules (Figure 5a).
In the case of 5b, a CH2Cl2 molecule is encapsulated in its
À
cavity (Figure 7a, b), anchored by one pair of O H···Cl hy-
drogen-bonding interactions (dOÀH···Cl =2.60 and 2.654 ꢂ, re-
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Calix[6]arenes Rigidified with Triptycene Units
FULL PAPER
spectively) between the chlorine atoms of CH2Cl2 and the
also of great interest in relation to the development of full-
erene-based functional materials. For this purpose, various
macrocyclic hosts for complexation with fullerenes have
hitherto been reported,[14] and among them calixarenes have
received considerable attention since the pioneering work of
Atwoodꢃs group in purifying fullerenes C60 and C70 by selec-
tive complexation with calix[8]arene.[15]
À
phenolic protons in 5b, one pair of C H···O hydrogen-bond-
ing interactions (dCÀH···O =2.603 and 2.690 ꢂ, respectively)
between the methylene protons of CH2Cl2 and the phenolic
À
oxygen atoms, and one C H···p interaction (dCÀ
=
H···p
2.802 ꢂ) between a proton of CH2Cl2 and the phenyl ring of
the triptycene moiety in 5b. For 6a, it was found that a
CHCl3 molecule is accommodated in its cavity (Figure 7c, d)
Having established that the present triptycene-derived
calix[6]arenes exhibited well-defined fixed conformations
and sufficiently large electron-rich cavities, we reasoned that
they could also serve as efficient hosts for complexation
with fullerenes. Consequently, we investigated the complex-
ation properties of macrocycles 4b and 5b with fullerenes
C60 and C70 by a fluorescence method. As shown in Figure 8,
the fluorescence of 4b at 334 nm was significantly quenched
upon the addition of C60 to a solution of this macrocycle in
toluene. A Job plot and fluorescence titration experiments
showed that a 1:1 complex was formed between 4b and C60.
Accordingly, the association constant Ka of the complex
4b·C60 was calculated from a plot of F0/Fcal (Fcal: the calibrat-
ed fluorescence intensity[16]) versus C60 concentration to be
68970Æ1706mÀ1. Under the same conditions, it was found
that addition of C70 also led to a significant quenching of the
fluorescence of 4b. The fluorescence titration and the Job
plot revealed that 4b formed a 1:1 complex with C70 with an
association constant Ka of 52214Æ2039mÀ1.[10] As in the
case of 4b, we further found that 5b could also form 1:1
complexes with both C60 and C70, and the corresponding as-
sociation constants Ka were calculated to be 86787Æ
2984mÀ1 and 59007Æ3798mÀ1, respectively.[10]
À
by virtue of a pair of C H···p (dCÀH···p =2.841 ꢂ) interactions
between the proton of CHCl3 and the phenyl rings of the
triptycene moiety. Similarly, we also found that one water
molecule could be encapsulated within the cavity of macro-
À
cycle 8 (Figure 7e, f) by one C H···O hydrogen-bonding in-
teraction (dCÀH···O =2.484 ꢂ) between the bridgehead proton
of the triptycene moiety and the oxygen atom of water, and
a pair of O H···O hydrogen-bonding interactions (dOÀ
1.829 and 1.965 ꢂ, respectively) between the phenolic pro-
tons of the triptycene moiety and the oxygen atom of water.
Thus, the present triptycene-derived calix[6]arenes with
fixed conformation could all encapsulate small neutral mole-
cules in their cavities in the solid state, in contrast to their
classical calix[6]arene analogues.[11]
À
=
H···O
Complexation of the triptycene-derived calix[6]arenes with
fullerenes C60 and C70: During the past two decades, ful-
lerenes and their derivatives have been extensively investi-
gated owing to their wide potential applications, for example
in enzyme imitation[12] and material sciences.[13] Constructing
new classes of supramolecular containers for fullerenes is
It is known that classical calix[6]arene and p-tert-butyl cal-
ix[6]arene analogues in the double-cone conformation can
form 1:2 complexes with C60 and C70 through torsion along
[17]
À
À
the CAr CH2 CAr bonds prior to complexation. In con-
trast, macrocycles 4b and 5b can only form 1:1 complexes
Figure 8. Emission spectra (lex =296 nm) of 4b (3.2ꢀ10À6 moldmÀ3) in
the presence of C60 in toluene at 258C. The concentrations of C60 for
curves a–m (from top to bottom) were 0, 0.0512, 0.1024, 0.1536, 0.2048,
0.256, 0.3584, 0.4096, 0.4608, 0.512, 0.5632, 0.6144, and 0.6656 (ꢀ
10À5 moldmÀ3). Inset: The variation of fluorescence intensity F0/Fcal of 4b
with increasing C60 concentration.
Figure 7. a) Top view and b) side view of the crystal structure of
CH2Cl2@5b. c) Top view and d) side view of the crystal structure of
CHCl3@6a. e) Top view and f) side view of the crystal structure of
H2O@8. Dashed lines show the hydrogen-bonding interactions. Hydrogen
atoms are omitted for clarity.
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C.-F. Chen and X.-H. Tian
the products 4a and 5a in yields of 19 and 13%, respectively. Similarly,
4b and 5b were obtained in yields of 17 and 11%, respectively, by the re-
action of 1 and 2b.
with C60 and C70, which may be mainly attributed to the fact
that introduction of the triptycene moiety confines them to
a rigid conformation. Moreover, compared with the com-
plexation of fullerene C60 by the classical calix[5]arene and
calix[6]arene derivatives (Ka =9–1300mÀ1),[18] 4b and 5b ex-
hibited much higher affinities toward C60 and C70, indicating
that the advantage of introducing a triptycene framework
into these novel calix[6]arenes is not only that it fixes their
conformations, but also that it increases the electron density
of the aromatic rings, and therefore might further contribute
to enhancing the interaction of the concave cavities of the
macrocyclic hosts with the electron-deficient convex surface
of the fullerenes.
Method B: Under the same conditions as described in Method A, reac-
tion of 1 and 3a afforded 4a and 5a in yields of 25 and 19%, respective-
ly. Analogously, 4b (20%) and 5b (17%) could be obtained by the reac-
tion of 1 and 3b.
4b: White solid. M.p. >3008C; 1H NMR (300 MHz, CDCl3): d=3.42 (d,
J=15.3 Hz, 4H), 3.96 (s, 12H), 4.34 (d, J=15.3 Hz, 4H), 5.26 (s, 2H),
6.12 (s, 2H), 6.74 (d, J=7.5 Hz, 4H), 6.95–6.98 (m, 8H), 7.29–7.55 (m,
16H), 7.58 ppm (d, J=7.5 Hz, 4H); 13C NMR (75 MHz, CDCl3): d=29.4,
42.6, 53.7, 62.5, 120.0, 123.4, 123.6, 125.2, 125.3, 126.5, 126.6, 126.6, 128.7,
128.8, 129.6, 132.3, 136.7, 140.8, 144.8, 145.9, 146.5, 152.0, 152.4 ppm;
MALDI-TOF MS: m/z: 1016 [M]+, 1039 [M+Na]+, 1055 [M+K]+; ele-
mental analysis calcd (%) for C72H56O6·1.5CH3OH·0.5H2O: C 82.17, H
5.91; found: C 82.34, H 5.99.
5b: White solid. M.p. >3008C; 1H NMR (300 MHz, CDCl3): d=3.24 (s,
12H), 3.78 (d, J=14.5 Hz, 4H), 3.90 (d, J=14.5 Hz, 4H), 5.35 (s, 2H),
5.87 (s, 2H), 6.41 (s, 2H), 6.96–6.98 (m, 4H), 7.01 (d, J=7.5 Hz, 4H),
7.09 (d, J=6.8 Hz, 4H), 7.22–7.36 (m, 13H), 7.49–7.52 ppm (m, 5H);
13C NMR (75 MHz, CDCl3): d=32.3, 42.6, 53.8, 61.9, 119.5, 123.4, 123.6,
125.2, 125.3, 126.4, 126.6, 127.7, 128.0, 128.3, 128.5, 130.5, 133.1, 136.8,
140.8, 144.3, 146.3, 146.5, 152.4, 153.2 ppm; MALDI-TOF MS: m/z: 1016
[M]+, 1039 [M+Na]+, 1055 [M+K]+; elemental analysis calcd (%) for
C72H56O6·1.5CH3OH: C 82.87, H 5.87; found: C 82.96, H 5.79.
Conclusion
In conclusion, we have synthesized two pairs of novel tripty-
cene-derived calix[6]arenes 4a,b and 5a,b through both one-
pot and two-step fragment-coupling strategies starting from
1,8-dimethoxy-2,7-dihydroxymethyltriptycene. Subsequent
demethylation of 4a,b and 5a,b with BBr3 in dry dichloro-
methane gave the macrocyclic compounds 6a,b and 7a,b.
Treatment of either 4a or 6a with AlCl3 resulted in the
same debutylated product 8, while under the same condi-
tions the debutylated compound 9 could be obtained from
either 5a or 7a. Structural studies have revealed that all of
the macrocycles have well-defined structures with fixed con-
formations both in solution and in the solid state owing to
the introduction of the triptycene moiety with a rigid 3D
structure, which are very different from those of their classi-
cal calix[6]arene counterparts. As a consequence, it was
found that all of these triptycene-derived calix[6]arenes
could encapsulate small neutral molecules in their cavities
in the solid state. Moreover, it was also found that macrocy-
cles 4b and 5b showed highly efficient complexation abili-
ties toward fullerenes C60 and C70. We believe that these
novel triptycene-derived calix[6]arenes will find wide appli-
cations in molecular recognition and molecular assembly,
areas that are actively being pursued in our laboratory.
General procedure for the preparation of 6 and 7: A solution of boron
tribromide (0.6 g, 2.4 mmol) in dry dichloromethane was added dropwise
to a solution of 4 or 5 (0.10 mmol) in dry dichloromethane (20 mL). The
mixture was stirred at room temperature for 10 h. Dilute hydrochloric
acid was then added to quench the reaction. The organic layer was dried
over anhydrous MgSO4. The solvent was removed in vacuo, and the resi-
due was submitted to column chromatography (petroleum ether/EtOAc
6:1) and then recrystallized from CH3OH/CH2Cl2 to give the product.
1
6a: Yield 73%. White solid. M.p. >3008C; H NMR (300 MHz, CDCl3):
d=1.06 (s, 18H), 3.42 (d, J=14.4 Hz, 4H), 4.05 (d, J=14.4 Hz, 4H), 5.34
(s, 2H), 6.10 (s, 2H), 6.94–7.03 (m, 18H), 7.27–7.36 (m, 6H), 7.43–
7.46 ppm (m, 2H); 13C NMR (75 MHz, CDCl3): d=31.3, 32.1, 33.9, 40.8,
54.2, 116.7, 123.4, 123.5, 125.1, 125.2, 125.3, 125.9, 127.8, 130.2, 144.2,
145.1, 146.2, 146.5, 147.0, 148.1 ppm; MALDI-TOF MS: m/z: 943
[M+Na]+, 959 [M+K]+; elemental analysis calcd (%) for
C64H56O6·CH3OH: C 81.91, H 6.34; found: C 82.07, H 6.30.
1
6b: Yield 78%. White solid. M.p. >3008C; H NMR (300 MHz, CDCl3):
d=3.49 (d, J=14.6 Hz, 4H), 4.12 (d, J=14.5 Hz, 4H), 5.33 (s, 2H), 6.12
(s, 2H), 6.92–7.07 (m, 13H), 7.14–7.23 (m, 6H), 7.20–7.25 (m, 7H), 7.30–
7.38 (m, 2H), 7.45 (d, J=6.3 Hz, 2H), 8.48 ppm (brs, 6H); 13C NMR
(75 MHz, CDCl3): d=31.8, 54.2, 76.6, 77.0, 77.4, 116.8, 123.5, 124.9, 125.1,
125.2, 126.6, 126.7, 127.0, 127.7, 128.4, 130.2, 134.9, 140.6, 145.0, 146.4,
146.5, 148.0, 148.9 ppm; MALDI-TOF MS: m/z: 983 [M+Na]+, 999
[M+K]+; elemental analysis calcd (%) for C68H48O6·1.3CH3OH: C 83.01,
H 5.35; found: C 83.17, H 5.30.
Experimental Section
1
7a: Yield 74%. White solid. M.p. >3008C; H NMR (300 MHz, CDCl3):
d=1.19 (s, 18H), 3.61 (d, J=14.7 Hz, 4H), 3.90 (d, J=14.7 Hz, 4H), 5.34
(s, 2H), 6.05 (s, 2H), 6.83–7.22 (m, 18H), 7.26–7.77 ppm (m, 8H);
13C NMR (75 MHz, CDCl3): d=31.4, 33.3, 34.0, 40.3, 54.1, 116.7, 116.9,
123.3, 123.6, 125.0, 125.2, 125.4, 126.1, 126.4, 126.8, 131.5, 144.9, 145.4,
146.6, 146.7, 149.8 ppm; MALDI-TOF MS: m/z: 943 [M+Na]+, 957
[M+K]+; elemental analysis calcd (%) for C64H56O6·CH3OH·0.5H2O: C
81.14, H 6.39; found: C 81.32, H 6.36.
General: Melting points, taken on an electrothermal melting point appa-
ratus, are uncorrected. 1H and 13C NMR spectra were measured on a
Bruker DMX300 NMR spectrometer. MALDI-TOF mass spectra were
obtained on a Bruker BIFLEXIII mass spectrometer. Elemental analyses
were performed at the Analytical Laboratory of the Institute of Chemis-
try, Chinese Academy of Sciences.
General procedure for the preparation of 4 and 5
1
7b: Yield 71%. White solid. M.p. >3008C; H NMR (300 MHz, CDCl3):
Method A: A solution of 1 (1 mmol) and 2a (1 mmol) in o-dichloroben-
zene (120 mL) was slowly added to a solution of a catalytic amount of p-
TsOH in o-dichlorobenzene (60 mL) under an argon atmosphere at
1008C. After 24 h, an additional portion of 2a (1 mmol) was added, and
the mixture was heated for a further 24 h. The dark solution was then
concentrated in vacuo, and the residue was separated by column chroma-
tography on silica gel (eluent: ethyl acetate/petroleum ether, 1:10). Re-
crystallization of the appropriate fractions from CH3OH/CH2Cl2 afforded
d=3.71 (d, J=14.7 Hz, 4H), 3.96 (d, J=14.7 Hz, 4H), 5.34 (s, 2H), 5.97
(s, 2H), 6.45 (s, 4H), 6.58 (s, 2H), 6.89–6.97 (m, 4H), 7.00 (s, 8H), 7.29–
7.40 ppm (m, 18H); 13C NMR (75 MHz, CDCl3): d=32.8, 40.5, 54.2,
116.7, 123.4, 123.7, 124.0, 125.0, 125.1, 126.8, 127.0, 127.1, 128.0, 131.3,
134.9, 140.4, 145.0, 146.4, 146.6, 149.1, 151.6 ppm; MALDI-TOF MS:
m/z: 983 [M+Na]+, 999 [M+K]+; elemental analysis calcd (%) for
C68H48O6·1.5CH3OH: C 82.72, H 5.39; found: C 82.54, H 5.48.
8078
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Chem. Eur. J. 2010, 16, 8072 – 8079

Calix[6]arenes Rigidified with Triptycene Units
FULL PAPER
General procedure for the preparation of 8 and 9: Anhydrous aluminum
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a solution of 4a or 5a
(0.13 mmol) and phenol (0.06 g, 0.62 mmol) in toluene (20 mL) under
argon. The mixture was stirred at room temperature for 3 h and then
quenched with dilute hydrochloric acid. The organic layer was separated
and dried over MgSO4. The solvent was removed in vacuo, and the resi-
due was submitted to column chromatography (petroleum ether/EtOAc)
and then further recrystallized from CH3OH/CH2Cl2 to give 8 and 9 in
yields of 61 and 54%, respectively. Following the same procedure as de-
scribed above, macrocycles 8 and 9 could also be obtained from 6a and
7a in yields of 57 and 46%, respectively.
8: White solid. M.p. >3008C; 1H NMR (300 MHz, CDCl3): d=3.45 (d,
J=14.5 Hz, 4H), 4.10 (d, J=14.5 Hz, 4H), 5.35 (s, 2H), 6.10 (s, 2H), 6.70
(t, J=7.5 Hz, 2H), 6.95–7.00 (m, 16H), 7.32–7.41 (m, 2H), 7.40–7.46 (m,
2H), 8.07 (brs, 4H), 8.62 ppm (brs, 2H); 13C NMR (75 MHz, CDCl3):
d=31.7, 40.7, 54.1, 116.8, 121.7, 123.5, 124.9, 125.5, 126.7, 127.7, 128.9,
130.2, 144.9, 146.3, 148.0, 149.3 ppm; MALDI-TOF MS: m/z: 831
[M+Na]+, 847 [M+K]+; elemental analysis calcd (%) for
C56H40O6·CH3OH: C 81.41, H 5.27; found: C 81.22, H 5.34.
9: White solid. M.p. >3008C; 1H NMR (300 MHz, CD3CN): d=3.77 (d,
J=14.2 Hz, 4H), 4.06 (d, J=14.3 Hz, 4H), 5.55 (s, 2H), 6.10 (s, 2H), 6.61
(s, 3H), 6.79 (t, J=7.5 Hz, 3H), 6.95 (s, 2H), 7.07–7.31 (m, 16H), 7.51–
7.52 ppm (m, 4H); 13C NMR (75 MHz, CD3CN): d=31.5, 41.1, 54.3,
117.1, 121.6, 124.26, 124.31, 125.7, 125.8, 127.0, 128.5, 128.8, 129.6, 132.2,
145.8, 146.9, 147.4, 149.4, 152.1 ppm; MALDI-TOF MS: m/z: 831
[M+Na]+, 847 [M+K]+; elemental analysis calcd (%) for
C56H40O6·0.5CH3OH: C 82.26, H 5.13; found: C 82.37, H 5.19.
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Acknowledgements
We thank the National Natural Science Foundation of China (20625206,
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Received: February 27, 2010
Published online: June 25, 2010
Chem. Eur. J. 2010, 16, 8072 – 8079
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8079