The influence of isomerism on the self-assembly behavior and complexation property of 1,3-alternate tetraaminopyridyl-thiacalix[4]arene derivatives

Article abstract of DOI:10.1016/j.tet.2008.04.116

A series of 1,3-alternate conformation thiacalix[4]arenes containing different isomeric aminopyridyl pendent arms have been synthesized. It was found that their self-assembly behaviors and complexation properties strongly depended on the structures of aminopyridyl pendent arms. The crystal structures demonstrate that tetra(meta-aminopyridyl)-thiacalix[4]arene motif is capable of forming intramolecular hydrogen bondings between the sp² nitrogen donors in the meta position of the aminopyridyl groups and the facing amide N-H of the adjacent aminopyridyl groups, and self-assembles via C-H?O weak hydrogen bondings and C-H?π interaction to generate a double stranded rectilineal networks. By contrast, in the case of tetra(para-aminopyridyl)-thiacalix[4]arene, the presence of para-aminopyridyl units enables the formation of N-H?N strong hydrogen bondings between the individual molecules leading to the solid-state structure with water-bridged double strands. Their complexation properties had been also studied by measurement of the stability constants for their complexation in a range of metal cations and investigation of their binding models via ¹H NMR titration and ESI-MS experiments. It was found that the three ligands exhibited high and selective extractability toward Ag⁺, and their stoichiometry of ligand to Ag⁺ was 1:1, while the meta-aminopyridyl derivative showed the best extraction capacity and possessed the most efficient binding sites.

Full text of DOI:10.1016/j.tet.2008.04.116

Tetrahedron 64 (2008) 6230–6237
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
The influence of isomerism on the self-assembly behavior and complexation
property of 1,3-alternate tetraaminopyridyl-thiacalix[4]arene derivatives
,
a
a
b
Xiong Li a, Shu-Ling Gong a , Wei-Ping Yang , Yuan-Yin Chen , Xiang-Gao Meng
*
a College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, PR China
b College of Chemistry, Huazhong Normal University, Wuhan 430079, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 1,3-alternate conformation thiacalix[4]arenes containing different isomeric aminopyridyl
pendent arms have been synthesized. It was found that their self-assembly behaviors and complexation
properties strongly depended on the structures of aminopyridyl pendent arms. The crystal structures
demonstrate that tetra(meta-aminopyridyl)-thiacalix[4]arene motif is capable of forming intramolecular
hydrogen bondings between the sp2 nitrogen donors in the meta position of the aminopyridyl groups
and the facing amide N–H of the adjacent aminopyridyl groups, and self-assembles via C–H/O weak
Received 19 January 2008
Received in revised form 25 April 2008
Accepted 29 April 2008
Available online 1 May 2008
Keywords:
Thiacalixarene
Isomer
Self-assembly
Complexation
hydrogen bondings and C–H/
p interaction to generate a double stranded rectilineal networks. By
contrast, in the case of tetra(para-aminopyridyl)-thiacalix[4]arene, the presence of para-aminopyridyl
units enables the formation of N–H/N strong hydrogen bondings between the individual molecules
leading to the solid-state structure with water-bridged double strands. Their complexation properties
had been also studied by measurement of the stability constants for their complexation in a range of
metal cations and investigation of their binding models via 1H NMR titration and ESI-MS experiments. It
was found that the three ligands exhibited high and selective extractability toward Agþ, and their
stoichiometry of ligand to Agþ was 1:1, while the meta-aminopyridyl derivative showed the best ex-
traction capacity and possessed the most efficient binding sites.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
blocks into solid-state supramolecular architectures, which are
currently investigated extensively in the fields of chemical, bi-
Calixarenes1,2 are synthetic macrocycles derived from the con-
densation of phenols and formaldehyde, which, depending on the
number of aromatic units in the cyclic array and on the function-
alization at the phenolic oxygen atoms (lower or narrow rim), have
been actively studied and utilized as the third generation of host
compounds in addition to the well-known crown ethers3 and cy-
clodextrins.4 The introduction of suitable donor groups at the lower
rim of calixarenes produces powerful and selective ionophores,
particularly for spherical metal ions.5 Extensively studied are the
calix[4]arene podands and the calix[4]crowns showing high effi-
ciency and selectivity toward silver metal6,7 due to its considerable
utility of the noble metal in the fields of anti-bacterial medicine,
catalysis, optoelectronics, microelectronics, and so on.8 The binding
ability of the most Agþ ionophores is based alike on the preferred
interaction between the soft Agþ ion and the donor atoms such as N.
Although the complexation of metal ions continues to occupy
a central place in calixarene chemistry,1–3 more recent attention
has also been devoted to the self-assembly of calixarene building
ological, and materials science and technology.2 One of the most
important features of these supramolecular architectures is the
simultaneous operation of several cooperative weak forces working
between molecular building blocks or tectons9 such as van der
Waals, electrostatic, p–p, CH–p, H-bonding, coordination bonding,
etc.10–12 Among the various types of molecular tectonics, the cal-
ixarenes adorned with hydrogen bonding donor and acceptor
groups at the upper rim or the lower rim are particularly attrac-
tive,12,13 since they can act as building blocks for the noncovalent
synthesis of nanostructures,14 ion channels,15 self-assembled di-
meric capsules, and so on.16–18
In the crystalline phase, molecular networks are defined by the
nature of tectons composing the architecture (shape, interaction
sites, and their localization in space), the type of interaction in-
volved in the interconnection of consecutive tectons, and finally,
the number of independent translations operating on the recog-
nition patterns.19,20 Thus, one strategy that has been used to
modulate the self-assembly behavior is to alter the localization of
interaction sites in the organic tecton. In other terms, one must take
into account the influence of isomerism of the interaction sites on
the self-assembly behavior and design the organic tecton accord-
ingly. There are few examples with this aspect, most notably,
* Corresponding author. Fax: þ86 27 68754067.
E-mail address: gongsl@whu.edu.cn (S.-L. Gong).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.04.116

X. Li et al. / Tetrahedron 64 (2008) 6230–6237
6231
Pansanel and co-worker20 reported that two organic tectons, based
on a 1,4-phenylenediamine backbone functionalized with two
isomeric pyridine units through amide junctions, self-assemble in
the presence of HgCl2 to generate two types of 2-D networks, one of
the purely metallo-organic type, based on only coordination bonds,
and the other combining both coordination and hydrogen bonds.
Thiacalix[4]arenes, in which the four methylene bridges of
‘usual’ calix[4]arenes are replaced by sulfur,21 have a slightly dif-
ferent size and shape.22 Therefore, thiacalix[4]arene derivatives
have (eventually significantly) different complexation properties23
and different self-assembly preferences.18 Herein, we report the
synthesis of thiacalix[4]arene analogs 4a–c in 1,3-alternate con-
formation comprising O and N ligating sites by anchoring isomeric
amidopyridyl groups to the lower rim and the effect of the ami-
dopyridyl side chain’s substitution pattern on their metal ion-
binding properties. In addition, the presence of aminopyridyl
groups in an alternating mode below and above its main plane
provides additional hydrogen bond donors and acceptors, facili-
tating the formation of a H-bonding supramolecular assembly. In
this paper, we also demonstrate the solid-state structural analysis
of the free ligands differing only by the position of connection of the
amide group to the pyridyl group (meta for 4b and para for 4c) and
of two completely different types of 1-D supramolecular self-as-
sembled systems, especially, the analogous thiacalix[4]arene 4c
self-assembles to form ordered arrays containing water-bridged
double strands. By comparing ion-binding and self-assembly
properties of isomers 4a–c, we find that the amidopyridyl’s sub-
stitution pattern is essential for mediating ion-binding and self-
assembly network.
tetraacetate in 1,3-alternate conformation by alkylation with ethyl
bromoacetate in refluxing acetone using Cs2CO3 as a base according
to the known procedures.24 The corresponding acid chloride was
prepared by hydrolysis of ester with aq NaOH in a mixture of eth-
anol and water,25 followed by treatment with thionyl chloride in
refluxing CH2Cl2 for 48 h in good yield. The crude chloride was used
without purification for subsequent condensation with the ami-
nopyridine isomers, and the corresponding tetraamides were
obtained in high yields. In order to explore the complexation be-
havior of ligands, the correlative reference compounds 7a–c were
also synthesized from p-tert-butyl-phenol as shown in Scheme 1.
Structures of the above-mentioned thiacalix[4]arene derivatives
4a–c were proved by the combination of 1H NMR spectroscopy and
mass spectroscopy (ESI-MS). The ESI-MS spectra of all receptors
4a–c showed the only one most intense signals corresponding to
the molecular peak [MHþ] (100% int.), which showed that they
were tetraaminopyridine products. All their 1H NMR spectra
showed a singlet for the tert-butyl groups, a singlet for the aromatic
protons and a singlet for OCH2CO, which precisely reflected its S4
symmetry. It is obvious that all the compounds adopted 1,3-alter-
nate conformation or cone conformation. It was reported that both
in the calix[4]arene and thiacalix[4]arene bearing ester functional
groups, the chemical shift of the tert-butyl protons in the cone
conformation are located at higher field than that in the 1,3-alter-
nate conformation. The signal of tert-butyl protons of 4a–c appears
at
shift of the tert-butyl protons either in the 1,3-alternate confor-
mation (approximately 1.25 ppm) or in the cone conformation
d 0.70–0.80 ppm, which is at much higher field than the chemical
d
(usually >1.00 ppm),7,24–27 the large highfield shift indicates that
the tert-butyl protons are exposed to the ring current shielding
effect operating in the proximal pyridine ring. The result is expli-
cable only by the steric characteristics of 1,3-alternate conforma-
tion that the four tert-butyl and four pyridine groups are
symmetrically distributed on the two side of thiacalixarene cavity
so that the tert-butyl protons can locate at the shielding field of the
pyridine ring. Moreover, the synthetic pathway started from the
2. Results and discussion
2.1. Synthesis and structural assignments
As illustrated in Scheme 1, the synthesis started from parent
thiacalix[4]arene, which was transformed into the corresponding
Scheme 1. (i) BrCH2COOCH2CH3, Cs2CO3/acetone, reflux for 7 days; (ii) NaOH, EtOH/H2O, reflux for 12 h; (iii) SOCl2/CH2Cl2, reflux for 48 h; (iv) THF, reflux for 24 h; (v)
BrCH2COOCH2CH3, Na2CO3/acetone, reflux for 12 h; (vi) KOH, EtOH/H2O, reflux for 12 h.

6232
X. Li et al. / Tetrahedron 64 (2008) 6230–6237
conformationally immobilized 1,3-alternate tetraacetate of known
structure,28 thus we speculated that it also adopted 1,3-alternate
conformation.25,29 The correlative reference compounds 7a–c
were also confirmed by the combination of 1H NMR spectroscopy
ESI-MS.
The final evidence for the 1,3-alternate conformation of thia-
calixarene derivatives 4b and 4c was obtained by single-crystal
X-ray crystallography as shown in the X-ray structures.
aminopyridyl groups to form intramolecular hydrogen bondings
with the facing amide N–H of the adjacent aminopyridyl groups. As
depicted in Figure 1, the amide N1 and N5 atoms in molecule at (x,
y, z) acting as H-bonding donors, to pyridyl N4 and N8 atoms in the
same molecule, respectively, form two intramolecular hydrogen
bonds, thereinto, locating on two ends of the thiacalixarene core. In
this conformation, all the amine NH protons orientate inwardly
with respect to the framework and buried in the cavity of thiaca-
lixarene, thus they could not form strong intermolecular hydrogen
bond with adjacent ligands. In the case of 1,3-alternate thiaca-
lix[4]arene derivative 4c, the potential H-bonded amide N atoms
N1/N3/N5/N7 do not form any intramolecular H-bonds with pyr-
idyl N atoms due to the terminal position of the nitrogen atoms in
the para-pyridyl moieties and are outwardly oriented with respect
to the cavity. Such a conformation ensures that these amide N
atoms in 4c are available for intermolecular interactions with the
pyridyl N atoms, a feature that helps to form infinite strong
H-bonded Networks of 4c.11,15
2.2. Solid-state self-assembly
Single crystals of 4b and 4c suitable for X-ray diffraction ex-
periments were both obtained by slow evaporation of their
dichloromethane/methanol mixed solution. As shown in the X-ray
structures (Fig. 1), the thiacalixarenes are all in a 1,3-alternate
conformation.
The thiacalixarene shape can be characterized by the values of
the dihedral angles between the phenolic rings and the mean plane
defined by the sulfur atoms, while the extent of perpendicularity
differs from aromatic rings to aromatic rings in both of 4b and 4c.
The consecutive four aromatic rings in 4b make a dihedral angle of
approximately 61ꢀ, 70ꢀ, 79ꢀ, and 73ꢀ. Whereas the dihedral angles
defined are comparable to 67ꢀ, 70ꢀ, 82ꢀ, and 70ꢀ, respectively, found
in the structure of 4c. Therefore, the shape of thiacalixarene cores in
4b and 4c is extraordinarily close to each other, and both adopt
a slightly pinched 1,3-alternate conformation, with no crystallo-
graphic symmetry.
In the solid state, compared with the shape of the thiacalixarene
cores in 4b and 4c, their whole molecular structures show much
more unsymmetrical, which could be ascribed to the spatial dif-
ferent outspread of the side chains possessing rotational flexibility.
While the most significant conformational difference for 4b and 4c
was the orientation of aminopyridyl side chain connected to the
thiacalixarene skeleton, which result from the different position of
connection of the amine group to the pyridyl group. For 4b, it is
possible for the sp2 nitrogen donors in the meta position of the
In designing these two structural isomers of receptors, we an-
ticipated that their different conformations would give rise to dif-
ferent self-assembly properties, which was, in fact, the case. As can
be readily seen from Figure 2, the tectons 4b are interconnected via
intermolecular C38–H38A/
p
interaction (dH38A/ ¼2.74 Å) be-
p
tween the O–CH2 group in one of the lower rim substituent and one
of the pyridyl subunit of neighboring thiacalix[4]arene and C35–
H35B/O2 interaction (dO2/H35B¼2.72 Å) between the tert-butyl
group and the carbonyl group, forming along the b axis a 1-D
polymeric chain, in which thiacalixarene cavities are mutually
oriented side-by-side.
Then two adjacent linear networks exhibit a staggered, anti-
parallel, up–down arrangement and are double stranded in-
terwoven, leading thus to double stranded rectilineal networks
(Fig. 3).30 The driving force for the formation of this peculiar ar-
rangement is related to the C62–H62A/O6 interactions (dO6/
¼2.43 Å) between the O–CH2 groups belonging to one strand
H62A
and carbonyl oxygen atoms of the other strand.
Figure 1. A perspective view of the different conformation of the aminopyridyl side chain on thiacalixarene skeleton in solid-state structures of 4b (left) and 4c (right) and its
labeling scheme. Dotted lines indicate hydrogen bonds. The hydrogen atoms not involved in intramolecular H-bonding interaction and the solvent molecules are omitted for clarity.

X. Li et al. / Tetrahedron 64 (2008) 6230–6237
6233
Figure 2. A portion of the X-ray structure showing the formation of single strand obtained by mutual C38–H38A/
p
and C35–H35B/O2 interactions of neighboring thiaca-
lix[4]arene 4b. Dotted lines evidence the intermolecular interactions. For clarity, H atoms not involved in intermolecular interactions, and solvent molecules and anions are not
shown (up, view perpendicular to a axis; down, view perpendicular to c axis).
Figure 3. A portion of the X-ray structure showing the formation of double stranded interwoven rectilineal architecture resulting from the C62–H62A/O6 interactions between
two adjacent single strands of thiacalix[4]arene 4b (view perpendicular the c axis).
Solution of the diffraction data revealed an endo cavity asym-
metric unit that comprises one thiacalix[4]arene and three disor-
dered methanol molecules. Notably, methanol solvent molecules
among the crystal lattice serve to link the individual double
stranded rectilineal networks in the c axis and ab axis, respectively,
which constructed the overall supramolecular assembly of the
building blocks 4b. However, the above solvent disorder features
seemed to have a negligible effect, allowing for a precise de-
termination of the interactions between the host and solvent
molecules, as well as the driving force for the packing of the ad-
jacent double stranded interwoven infinite linear networks.
In the overall crystal architecture of 4c, the building blocks are
held together by intermolecular H-bonds and solvent molecules
play the role of the bridges between the individual thiacalixarenes.
Thiacalix[4]arene neighbors are directly linked to one another via
a strong intermolecular N7–H7/N4 H-bonds (dN4/H7¼2.10 Å)
between the amide N–H and the pyridyl nitrogens forming a 1-D
polymeric chain along the c directions,15 where the individual
molecules of the macrocycle are in a side-by-side orientation
(Fig. 4).31 Two strips of the resulting 1-D networks are further
connected by water molecules via a series of oppositely directed
N2/H–O–H/O2 (dN2/H¼2.20 Å and dO2/H¼2.08 Å) bridges of
hydrogen bonds to give a extended water-bridged double strands
(Fig. 5).
Some solvent molecules such as methanol and dichloromethane
are incorporated into the lattice during crystallization to fill the
void space located among the individual water-bridged double
strands. The overall crystal architecture is characterized by ex-
tended water-bridged double strand that propagate through the
crystal along the b axis and ac axis, respectively, in which the ad-
jacent double strands are indirectly interconnected via dichloro-
methane-mediated bridges.32 However, the disorder of the
Figure 4. A portion of the X-ray structure showing the formation of single strand obtained by mutual N7–H7/N4 interactions of neighboring thiacalix[4]arene 4c (view per-
pendicular the a axis).

6234
X. Li et al. / Tetrahedron 64 (2008) 6230–6237
Figure 5. A portion of the X-ray structure showing the formation of the water-bridged double strand (left, view perpendicular to c axis; right, view perpendicular to a axis).
dichloromethane molecule prevents us from determining the type
of the interactions between the dichloromethane and the building
block 4c, as well as giving an accurate account of the relative weak
interaction fashion between the consecutive neighboring water-
bridged double strands.
2.3. Complexation study
A first estimation of the ionophoric properties of ligands 4a–c
was accomplished by the picrate extraction method developed by
Pedersen.33 The results expressed as an association constants (Ka)
are reported in Table 1, using the picrate extraction method
reported by Lein and Cram,34 which is more quantitative and allows
a direct comparison of the ionophoric properties of compounds
4a–c with each other, the values of association constants (Ka) are
listed in Table 1. A comparison with p-tert-butylthiacalix[4]arene 1
was also provided.
Two-phase solvent extraction experiments reveal that the in-
troduction of the aminopyridine groups into the lower rim of the
thiacalixarene skeleton fixed in the 1,3-alternate conformation
could enhance its selectivity and affinity for Agþ with different
Figure 6. 1H NMR titration of 4b with AgClO4 in CDCl3/DMSO-d6¼1:1 (v/v).
efficiencies depending on the side chain. It is clear from Table 1 that
when the terminal group on the side chain is ortho-pyridyl, the Ka
perchlorate added. The Dd value increased in proportion to the
amount of the perchlorate added and became constant after the
addition of 1.0 mol equiv of the perchlorate, indicating that
the stoichiometry of the complex is 1:1 in the solution. Similar
phenomena also occurred in the case of 4a and 4c. The 1:1 stoi-
chiometry of Agþ complex of the ligands 4a–c was also confirmed
by ESI-MS. After 24 h precomplexation between ligands 4a–c with
4 equiv of AgClO4 in CHCl3/DMSO (1:1), respectively, all of their
electrospray mass spectrometry showed two most intense peaks at
m/z 1363.3 and 1365.3 corresponding to the [ligandþ107Agþ] and
[ligandþ109Agþ] ions, respectively.
value for silver picrate is only twice higher than that of the parent
thiacalix[4]arene 1 (10.62ꢁ106 and 5.09ꢁ106, respectively). How-
ever, when the terminal group is para-pyridyl, there is almost
a fivefold increase in Ka value for silver picrate. The highest increase
in extraction of Agþ is observed when the terminal group is meta-
pyridyl, whose Ka value for silver picrate is nearly 19 times higher
than that of ionophore 1. This data indicate that the efficiency of
ligands 4a–c in the complexation of silver ion should be sensitive
mainly to the position of nitrogen in the pyridine rings.
In order to gain insight into the extraction mechanism, 1H NMR
titration experiments were carried out. Titrations of ligands 4a–c
with silver perchlorate in CDCl3/DMSO-d6¼1:1 (v/v) at 298 K did
not cause the appearance of new signals, but led to the distinct
change in the chemical shifts to indicate fast metal exchange be-
tween complexed and uncomplexed species on the NMR time scale
at room temperature. During the titration of 4b, distinct change in
the chemical shift was observed in the region of the aminopyridyl
group. Figure 6 shows the change in the chemical shift of the
aminopyridyl protons (Dd) plotted against the amount of silver
Although more or less the same situations were found after the
addition of silver perchlorate to ligands 4a–c, there are some dif-
ferences in their Agþ binding sites. Comparison of 1H NMR chemical
shifts between free and Agþ complexed ligands can investigate
their Agþ binding sites and precisely explain the influence of the
structure of the aminopyridyl group on the complexation ability,
which is shown in Table 2. Since the present studies have been
performed in neutral media, it would be anticipated that such
Table 1
Association constants (Kaꢁ10ꢂ5) for complexes of metal picrates with ionophores in CHCl3
Liþ
Naþ
Kþ
Csþ
Co2þ
Ni2þ
Cu2þ
Zn2þ
Agþ
50.9
106.2
937.3
270.8
1
24.2
12.6
13.2
d
9.1
14.8
d
8.7
2.24
d
5.8
d
d
16.2
5.34
57.8
4.26
5.4
2.47
d
4a
4b
4c
9.34
17.5
1.13
d
23.3
13.1
9.16
1.29
d
3.80
1.11
d
‘d’ Denotes the value of Ka less than 105.

X. Li et al. / Tetrahedron 64 (2008) 6230–6237
6235
Table 2
Comparison of 1H NMR chemical shifts (
d
) between free and Agþ complexed ligands in the 1H NMR titration experiments
Side chain
Host
Thiacalixarene
t-BuH
ArH
7.594
OCH2
4.992
4.949
ꢂ0.043
4.686
PyH-1
PyH-2
PyH-3
PyH-4
NH
4a
0.672
0.706
0.034
0.708
0.758
0.05
0.863
0.937
0.074
8.175
8.161
6.959
7.004
0.045
7.425
7.501
0.076
7.507
7.665
0.158
7.618
7.654
0.036
8.424
8.429
0.005
7.507
7.665
0.158
8.204
8.221
0.017
8.319
8.559
0.24
8.457
8.503
0.046
8.841
8.999
0.158
9.191
9.333
0.142
8.757
9.221
0.464
4aþAgþ
Dd
7.592
ꢂ0.02
7.308
7.351
0.043
7.492
7.525
0.033
ꢂ0.014
4b
8.451
4bþAgþ
Dd
4.592
8.330
ꢂ0.121
8.457
8.503
0.046
ꢂ0.094
4c
4.653
4cþAgþ
Dd
4.629
ꢂ0.024
compounds should behave as binding ligands through the amino-
pyridyl oxygen and sp2 nitrogen atoms rather than amide nitrogen
atoms.35 The largest downfield shifts of ligands 4a and 4c were
measured for the amido protons (NH), this could be indicative of
a form of coordination as simple as a two-point ligation, which
occurs with the primary oxygen donors of the amido groups and
form a sandwich-like complex with Agþ. In the case of 4a, it is
unexpected that the sp2 nitrogen atom in the ortho position whose
lone-pair electron oriented toward the cavity center did not play
considerable role in complexation as reflected by the small Dd
values of PyH¼ꢂ0.01 to þ0.05 ppm. The unusual observation may
result from that amide unit, which locates so close to the sp2 ni-
trogen atom in the ortho position that would disturb its binding to
Agþ. In the 1,3-alternate-4c$Agþ system, it is impossible for the
pyridyl nitrogen atoms to interact with Agþ due to the terminal
position of the nitrogen atom in the para-pyridyl moiety, which can
be affirmed by the crystal structures of 4c (Fig. 1). Thus, one can
consider that the downfield shift of the para-pyridyl protons (þ0.05
and þ0.16 ppm, respectively) is due to the inductive effect arising
from the interaction between the amido oxygen donors and Agþ.
On the other hand, it is well known that the electron-withdrawing
effect of the sp2 nitrogen atom toward the amide group in the ortho
position is stronger than that in the para position, so the basicity of
the amide oxygen atom in ligand 4a would be weaker than that in
ligand 4c, thereby it provides a more favorable ligating site for
binding, which is shown by the smaller downfield shift of the NH
proton (0.16 vs 0.46 ppm). This is in agreement with the extraction
results that the association constant (Ka) of 4a$Agþ complex is
lower than that of 4c$Agþ complex.
With ligand 4b a quite different situation was found upon
complexation with Agþ. As indicated in the crystal structures of 4b
(Fig. 1), the meta position of the nitrogen atoms in the aminopyridyl
groups that makes just half of the sp2 nitrogen donors could form
hydrogen bondings with the facing amide N–H of the adjacent
aminopyridyl groups, only if two of the four side chains show
marked distortion. So it is presumable that the weaker hydrogen
bonding system of 4b might be broken and the sp2 nitrogen atom
would complex Agþ when the metal cation approach the cavity of
the ligand. As expected, the most marked downfield shifts are ex-
perienced by the amido proton (0.14 ppm) followed by PyH-4
proton ortho to N of pyridyl (0.24 ppm), thus it is can be inferred
that the ligand 4b binds the silver ion mainly by the pyridyl ni-
trogen atoms with the assistance of carbonyl oxygen donors. We
consider, therefore, that the best Agþ extraction ability of 4b among
the three ligands is attributed to preferred interaction between the
soft nitrogen donor atoms and the soft Agþ ion.7
bind Agþ, but lacking the thiacalixarene’s macrocycle. The standard
extraction assay even in the presence of high excess of 7a–c showed
that no Agþ was extracted into the CHCl3 solution. In addition,
spectroscopy indicated no Agþ binding by 7a–c in CDCl3/DMSO-d6
(1:1). These controls with 4-tert-butyl-(pyridyl-carbamoyl-
methoxy)-benzenes 7a–c support the hypothesis that the 1,3-al-
ternate thiacalixarene’s core is critical for the Agþ binding properties
of 4a–c.
3. Conclusions
Tetraaminopyridyl-thiacalix[4]arene derivatives (4a–c) in the
1,3-alternate conformation were synthesized. It was found that
their self-assembly behavior strongly depended on the structure of
aminopyridyl pendent arms. Two crystal structures demonstrated
that tetra(meta-aminopyridyl)-TCA motif is capable of forming
a double stranded rectilineal networks, where the thiacalixarene is
preorganized in a side-by-side arrangement, by contrast, tetra-
(para-aminopyridyl)-TCA self-assembles via hydrogen bondings to
generate solid-state structure with water-bridged double strand,
which is the first example of encapsulation of water molecules
within an organized network of thiacalixarene derivative. Further
development of this self-assembly motif in the field of crystal en-
gineering to design functional materials is possible since thiaca-
lixarenes offer the potential of controlling the self-assembly
pattern by the nature of the substituents on the thiacalixarene core.
On the other hand, their complexation study indicated that all
the ligands 4a–c show Agþ ion selectivity over other metal cations
and the binding efficiency is influenced by the structures of ami-
nopyridyl pendent arms. In the case of meta-aminopyridyl com-
pound 4b, the sp2 nitrogen and carbonyl oxygen donors in
amidopyridyl unit possess the most advantaged steric arrange-
ment, thus it shows the best extraction capacity. Therefore, in the
design of the tetraaminopyridyl-thiacalix[4]arene derivatives to
optimize the metal ion affinity, amidopyridyl group of the meta-
isomer should be mostly considered.
4. Experimental
4.1. General
Melting points are uncorrected. The 1H NMR and 13C NMR
spectra were recorded at 298 K in CDCl3 at 300 MHz and 75 MHz,
respectively, on
a Varian Mercury-VX300 spectrometer. The
chemical shifts were recorded in parts per million (ppm) with TMS
as the internal reference. ESI mass spectra were determined using
a Finnigan LCQ Advantage mass spectrometer. Elemental analyses
were performed with a Thermo Quest Flash EA1112 apparatus. UV–
vis spectra were recorded on a Shimadzu UV-1601 spectropho-
tometer. X-ray data were recorded using a Bruker SMART CCD
single-crystal diffractometer. compound p-tert-butylthiacalixarene
was synthesized by the method described by Kumagai and
To determine whether Agþ binding is an intrinsic property of
ligands 4a–c or a general property of hydrophobic amidopyridyl
units, 4-tert-butyl-(pyridyl-carbamoyl-methoxy)-benzenes 7a–c
(Fig. 1) were tested in the two-phase solvent extraction experi-
ments. Compounds 7a–c are the respective monomeric analogs of
thiacalixarenes 4a–c, bearing aminopyridyl functions that could

6236
X. Li et al. / Tetrahedron 64 (2008) 6230–6237
co-workers.21 1,3-Alternate p-tert-butylthiacalixarene tetraacetate
was synthesized according to the literature procedure,24 the cor-
responding carboxylic acid 2b was synthesized as described in the
literature.25
a yellow oil in a 99% yield. 1H NMR (300 MHz, CDCl3):
d 1.29 (s, 9H,
C(CH3)3), 1.33 (t, 3H, J¼6.6 Hz, CH2CH3), 4.27 (q, 2H, J¼7.2 Hz,
CH2CH3), 4.60 (s, 2H, OCH2), 6.85 (d, 2H, J¼8.7 Hz, ArH), 7.31 (d, 2H,
J¼8.7 Hz, ArH).
4.2. General procedure for the synthesis of 1,3-alternate
thiacalix[4]arene tetraaminopyridyl derivatives
(compounds 4a–c)
4.4. General procedure for the synthesis of (4-tert-butyl-2,
6-dimethyl)phenoxyacetic acid 6b
A mixture of 6a (2.36 g, 10 mmol) and potassium hydroxide
(1.16 g, 20.7 mmol) in 90 mL of ethanol/water (2:l, v/v) was heated
at 100 ꢀC for 12 h, the solvent was evaporated under reduced
pressure, and 50 mL of HCl (1 mol/L) and 50 mL of CHCl3 were
added. The organic phase was washed with purified water
(3ꢁ50 mL), dried over anhydrous MgSO4, and then all volatiles
were removed at reduced pressure to afford a yellow oil in a 90%
A mixture of acid 2b (0.23 g, 0.24 mmol) and thionyl chloride
(0.8 mL, 11.2 mmol) in dichloromethane (10 mL) was reflux for
48 h. Removal of the solvent and residual thionyl chloride under
reduce pressure furnished the acid chloride 2c as an off-white solid.
The crude product 2c was cooled to room temperature and dis-
solved in THF (15 mL), and then aminopyridine (0.23 g, 2.45 mmol)
was added. The stirred mixture was refluxed under N2 atmosphere,
then approximate half of the solvent was distilled off, and the
residue was treated with 10 mL of distilled water; after filtration,
the precipitate was washed with distilled water (3ꢁ10 mL) to give
a yellow to dark red precipitate and the mixture of products was
then separated by column chromatography (silica gel) to give the
thiacalix[4]arene tetraaminopyridyl derivatives.
yield. 1H NMR (300 MHz, CDCl3):
d 1.30 (s, 9H, C(CH3)3), 4.67 (s, 2H,
OCH2CO), 6.87 (d, 2H, J¼4.5 Hz, ArH), 7.33 (d, 2H, J¼4.5 Hz, ArH).
4.5. General procedure for the synthesis of reference
compounds (compounds 7a–c)
The reaction step was used as described for the preparation of
4a–c. After the reaction finished, the solvent was removed under
reduced pressure and the residue was washed with purified water.
Then all volatiles were removed at reduced pressure to afford the
reference compounds.
4.2.1. 5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetrakis[(2-pyridyl)-
carbamoyl-methoxy]-2,8,14,20-tetrathiacalix[4]arene, 4a
Obtained as a white solid. Yield: 78%, mp>270 ꢀC. 1H NMR
(300 MHz, CDCl3): d 0.74 (s, 36H, C(CH3)3), 5.09 (s, 8H, ArOCH2), 7.01
(dd, J1¼7.2 Hz, J2¼5.1 Hz, 4H, PyH), 7.63–7.66 (m, 12H, ArHþPyH),
8.26 (d, J¼5.1 Hz, 4H, PyH), 8.28 (d, J¼9 Hz, 4H, PyH), 9.01 (br s, 4H,
NH). 13C NMR (75 MHz, CDCl3): 30.5, 34.1, 68.8, 114.7, 120.1, 126.4,
130.0, 137.8, 148.0, 150.9, 155.5, 168.1. MS ESIþ m/z: 1257.4 [MHþ]
(100%). EA calcd for C68H72N8O8S4: C, 64.94; H, 5.77; N, 8.91; S,
10.20%. Found: C, 64.79; H, 5.72; N, 8.86; S, 10.16%.
4.5.1. 4-tert-Butyl-[(2-pyridyl)-carbamoyl-methoxy]benzene, 7a
Obtained as a yellow oil. Yield: 95%. 1H NMR (300 MHz, CDCl3):
d
1.32 (s, 9H, C(CH3)3), 4.62 (s, 2H, ArOCH2), 6.94 (d, 2H, J¼9 Hz,
ArH), 7.08–7.12 (m, 1H, PyH), 7.35 (d, 2H, J¼9 Hz, ArH), 7.74–7.79 (m,
1H, PyH), 8.30–8.35 (m, 2H, PyH), 9.15 (br s, 1H, NH). MS ESIþ m/z:
284.2 [Mþ] (100%).
4.2.2. 5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetrakis[(3-pyridyl)-
carbamoyl-methoxy]-2,8,14,20-tetrathiacalix[4]arene, 4b
4.5.2. 4-tert-Butyl-[(3-pyridyl)-carbamoyl-methoxy]benzene, 7b
Obtained as a yellow oil. Yield: 92%. 1H NMR (300 MHz, CDCl3):
Obtained as a white solid. Yield: 90%, mp>280 ꢀC. 1H NMR
d
1.32 (s, 9H, C(CH3)3), 4.64 (s, 2H, ArOCH2), 6.94 (d, 2H, J¼8.7 Hz,
(300 MHz, CDCl3):
d 0.70 (s, 36H, C(CH3)3), 4.71 (s, 8H, ArOCH2),
ArH), 7.35–7.39 (m, 3H, ArHþPyH), 8.27 (d, 1H, J¼8.7 Hz, PyH), 8.41
(d, 1H, J¼4.5 Hz, PyH), 8.51 (s, 1H, PyH), 8.70 (s, 1H, NH). MS ESIþ
m/z: 284.3 [Mþ] (100%).
7.30 (s, 8H, ArH), 7.39 (dd, J1¼7.5 Hz, J2¼4.8 Hz, 4H, PyH), 8.28 (s, 4H,
PyH), 8.42 (d, J¼4.8 Hz, 4H, PyH), 8.55 (d, J¼8.1 Hz, 4H, PyH), 9.25
(br s, 4H, NH). 13C NMR (75 MHz, CDCl3): 30.6, 34.3, 69.3, 124.5,
127.5, 129.0, 130.1, 136.6, 141.1, 144.8, 148.6, 166.0. MS ESIþ m/z:
1257.5 [MHþ] (100%). EA calcd for C68H72N8O8S4: C, 64.94; H, 5.77;
N, 8.91; S, 10.20%. Found: C, 64.67; H, 5.80; N, 8.90; S, 10.10%.
4.5.3. 4-tert-Butyl-[(4-pyridyl)-carbamoyl-methoxy]benzene, 7c
Obtained as a yellow oil. Yield: 85%. 1H NMR (300 MHz, CDCl3):
d
1.31 (s, 9H, C(CH3)3), 4.65 (s, 2H, ArOCH2), 6.92 (d, 2H, J¼9 Hz,
ArH), 7.39 (d, 2H, J¼7 Hz, ArH), 7.51 (d, 2H, J¼6 Hz, PyH), 8.61 (d,
4.2.3. 5,11,17,23-Tetra-tert-butyl-25,26,27,28-tetrakis[(4-pyridyl)-
carbamoyl-methoxy]-2,8,14,20-tetrathiacalix[4]arene, 4c
2H, J¼6 Hz, PyH), 8.76 (s, 1H, NH). MS ESIþ m/z: 284.1 [Mþ] (100%).
Obtained as a white solid. Yield: 90%, mp>250 ꢀC. 1H NMR
(300 MHz, CDCl3):
d
0.74 (s, 36H, C(CH3)3), 4.86 (s, 8H, ArOCH2),
4.6. X-ray structural determination of 4b
7.47–7.50 (m, 16H, PyH þArH), 8.57 (d, J¼6.0 Hz, 8H, PyH), 8.59 (s,
4H, NH). 13C NMR (75 MHz, CDCl3): 30.6, 34.5, 70.7, 113.7, 127.2,
130.9, 144.2, 149.8, 151.3, 156.2, 166.7. MS ESIþ m/z: 1257.4 [MHþ]
(100%). EA calcd for C68H72N8O8S4: C, 64.94; H, 5.77; N, 8.91; S,
10.20%. Found: C, 64.79; H, 5.81; N, 8.86; S, 10.13%.
C68H72N8O8S4$3CH3OH,
M¼1321.66,
monoclinic,
a¼
37.7549(16) Å, b¼12.7784(6) Å, c¼30.4133(13) Å,
a
¼90ꢀ,
b
¼
108.6850(10)ꢀ,
g
¼90ꢀ, V¼3154.5(4) Å3, space group¼C2/c, Z¼8,
Dc¼1.263 Mg/m3,
m
¼0.199 mmꢂ1. Intensity data were collected up
to
q
¼25.50ꢀ by using 2
q scanning mode with graphite filtered Mo
4.3. General procedure for the synthesis of ethyl
p-tert-butylphenoxyacetate 6a
Ka
radiation (
l
¼0.71073) on a 0.30ꢁ0.20ꢁ0.20 mm3 crystal at
294(2) K. A total of 67,987 reflections were measured, 12,914 were
independent, and of which 8339 [I>2(I)] were considered
observed. The structure was solved by direct methods using
SHELXS9736and refined by Full-matrix least-squares on F2 using
SHELXL97.37 All the non-hydrogen atoms were located directly by
successive Fourier calculations and were refined anisotropically.
Hydrogen atoms were placed in geometrically calculated positions
by using a riding model. No absorption correction was applied. Final
To a mixture of p-tert-butyl-phenol (1.50 g, 10 mmol) and
Na2CO3 (1.06 g, 10 mmol) in dry acetone (100 mL) was added ethyl
bromoacetate (2.00 g, 12 mmol). The mixture was refluxed for 12 h,
cooled at room temperature, and concentrated under reduced
pressure. The residue was dissolved in CHCl3 and washed with
1 mol/L HCl. The organic layer was separated, washed with brine
(2ꢁ15 mL), and dried over anhydrous MgSO4. After filtration, the
solvent was evaporated to dryness to obtain the pure product as
R indices [I>2
s
(I)] R1¼0.0642, wR2¼0.1740, and R indices (all data)
R1¼0.1029, wR2¼0.1928 was found for 12,914 independent

X. Li et al. / Tetrahedron 64 (2008) 6230–6237
6237
6. (a) Ikeda, A.; Shinkai, S. J. Am. Chem. Soc. 1994, 116, 3102; (b) Ikeda, T.; Tsudera,
T.; Shinkai, S. J. Org. Chem. 1997, 62, 3568; (c) Tsudera, T.; Ikeda, A.; Shinkai, S.
Tetrahedron 1997, 53, 13609; (d) Chen, L.; Zeng, X.; He, X.; Zhang, Z. Z.; Frese-
nius, J. Anal. Chem. 2000, 367, 535; (e) Kimura, K.; Yayima, S.; Tatsumu, K.;
Yokoyama, M.; Oue, M. Anal. Chem. 2000, 72, 5290; (f) Zeng, X.; Sun, H.; Chen,
L.; Leng, X.; Xu, F.; Li, Q.; He, X.; Zhang, W.; Zhang, Z. Z. Org. Biomol. Chem. 2003,
1073; (g) Demirel, A.; Dogan, A.; Akkus, G.; Yilmaz, M.; Kilic, E. Electroanalysis
2006, 18, 1019.
reflections,1 restraints, and 876 parameters. The GOF value is 1.003.
Crystallographic data (excluding structural factors) for the struc-
tures in this paper have been deposited with the Cambridge Crys-
tallographic Data Centre as supplementary publication no. CCDC
674705. Copies of the data can be obtained, free of charge, on ap-
plication to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: þ44
(0)1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
´
´
7. Csokai, V.; Gru¨ n, A.; Balazs, B.; Simon, A.; Tothb, G.; Bitter, I. Tetrahedron 2006,
62, 10215.
8. (a) Bozkurt, S.; Karakucuk, A.; Sirit, A.; Yilmaz, M. Tetrahedron 2005, 61, 10443;
(b) Fonta`s, C.; Antic´o, E.; Vocanson, F.; Lamartine, R.; Seta, P. Sep. Purif. Technol.
2007, 54, 322.
4.7. X-ray structural determination of 4c
9. Simard, M.; Su, D.; Wuest, J. D. J. Am. Chem. Soc. 1991, 113, 4696.
10. (a) Burrows, A. D. Struct. Bond. 2004, 108, 55; (b) Metrangolo, P.; Resnati, G.
Chem.dEur. J. 2001, 7, 2511; (c) Casnati, A.; Liantonio, R.; Metrangolo, P.; Res-
nati, G.; Ungaro, R.; Ugozzoli, F. Angew. Chem., Int. Ed. 2006, 45, 1915.
11. Hosseini, M. W. Acc. Chem. Res. 2005, 38, 313.
C
68H72N8O8S4$CH2Cl2$2CH3OH$2H2O, M¼1424.54, monoclinic,
a¼13.7252(16) Å, b¼35.497(4) Å, c¼15.3054(18) Å,
a
¼90ꢀ,
b
¼
93.524(2)ꢀ,
g
¼90ꢀ, V¼7442.8(15) Å3, space group¼P2(1)/n, Z¼4,
Dc¼1.271 Mg/m3,
m
¼0.262 mmꢂ1. Intensity data were collected up
12. Baldini, L.; Sansone, F.; Massera, C.; Casnati, A.; Ugozzoli, F.; Ungaro, R. Inorg.
Chim. Acta 2007, 360, 970.
to
q
¼22.63ꢀ by using 2
q scanning mode with graphite filtered Mo
13. Sansone, F.; Segura, M.; Ungaro, R. Calixarenes in Bioorganic and Biomimetic
Chemistry. In Calixarenes 2001; Asfari, Z., Bo¨hmer, V., Harrowfield, J., Vicens, J.,
Eds.; Kluwer Academic: Dordrecht, The Netherlands, 2001; Chapter 27.
14. (a) Prins, L. J.; Reinhoudt, D. N.; Timmerman, P. Angew. Chem., Int. Ed. 2001, 40,
2383; (b) Casnati, A.; Sansone, F.; Ungaro, R. Acc. Chem. Res. 2003, 36, 246.
15. Seganish, J. L.; Santacroce, P. V.; Salimian, K. J.; Fettinger, J. C.; Zavalij, P.; Davis,
J. T. Angew. Chem., Int. Ed. 2006, 45, 3334.
16. Cho, Y. L.; Rudkevich, D. M.; Shivanyuk, A.; Rissanen, K.; Rebek, J. Chem.dEur. J.
2000, 6, 3788.
17. Rebek, J. Chem. Commun. 2000, 637.
18. Kasyan, O.; Kalchenko, V.; Bolteb, M.; Bo¨hmer, V. Chem. Commun. 2006, 1932.
19. (a) Hosseini, M. W. CrystEngComm 2004, 6, 318; (b) Bosch, E. CrystEngComm
2007, 9, 191.
20. Pansanel, J.; Jouaiti, A.; Ferlay, S.; Hosseini, M. W.; Planeix, J. M.; Kyritsakas, N.
New J. Chem. 2006, 30, 71.
21. Kumagai, H.; Hasegawa, M.; Miyanari, S.; Sugawa, Y.; Sato, Y.; Hori, T.; Ueda, S.;
Kamiyama, H.; Miyano, S. Tetrahedron Lett. 1997, 38, 3971.
22. (a) Iki, N.; Miyano, S. J. Inclusion Phenom. Macrocycl. Chem. 2002, 4, 99; (b)
Lhotak, P. Eur. J. Org. Chem. 2004, 1675.
23. Morohashi, N.; Narumi, F.; Iki, N.; Hattori, T.; Miyano, S. Chem. Rev. 2006, 106,
5291.
Ka
radiation (
l
¼0.71073) on a 0.30ꢁ0.10ꢁ0.10 mm3 crystal at
295(2) K. A total of 77,457 reflections were measured, 14,584 were
independent, and of which 7958 [I>2(I)] were considered ob-
served. Final R indices [I>2
s(I)] R1¼0.0771, wR2¼0.2084, and R
indices (all data) R1¼0.1289, wR2¼0.2348 was found for 14,584
independent reflections, 36 restraints, and 919 parameters. The
GOF value is 0.994. The apparent high R values are possibly due to
the disorder found in one of the tert-butyl groups and the solvent
molecules. The structure was solved by direct methods using
SHELXS9736 and refined by Full-matrix least-squares on F2 using
SHELXL97.37 All the non-hydrogen atoms were located directly by
successive Fourier calculations and were refined anisotropically
except for an oxygen atom of one lattice solvent molecule of
methanol. Hydrogen atoms except for that of the disordered lattice
solvent molecule were placed in geometrically calculated positions
by using a riding model. No absorption correction was applied.
Crystallographic data (excluding structural factors) for the struc-
tures in this paper have been deposited with the Cambridge Crys-
tallographic Data Centre as supplementary publication no. CCDC
674706. Copies of the data can be obtained, free of charge, on ap-
plication to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: þ44
(0)1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).
24. (a) Akdas, H.; Mislin, G.; Graf, E.; Hosseini, M. W.; Cian, A. D.; Fischer, J.
´
´
Tetrahedron 1999, 40, 2113; (b) Lhotak, P.; Stastny, V.; Zlatuskova, P.; Stibor, I.;
Michlova´, V.; Tkadlecova´, M.; Havlicek, J.; Sykora, J. Collect. Czech. Chem.
Commun. 2000, 65, 757.
ˇ
´
´
´
25. Zlatuskova, P.; Stibor, I.; Tkadlecova, M.; Lhotak, P. Tetrahedron 2004, 60, 11383.
26. (a) Lamartine, R.; Bavoux, C.; Vocanson, F.; Martin, A.; Senlisb, G.; Perrinb, M.
Tetrahedron Lett. 2001, 42, 1021.
27. (a) Iki, N.; Narumi, F.; Fujimoto, T.; Morohashi, N.; Miyano, S. J. Chem. Soc., Perkin
Trans. 2 1998, 2, 2745; (b) Iwamoto, K.; Araki, K.; Shinkai, S. Tetrahedron 1991, 47,
4325; (c) Aruand-Neu, F.; Collins, E. M.; Deasy, M.; Ferguson, G.; Harris, W. J.;
Kaituer, B.; Lough, A. J.; Mckervey, M. A.; Marques, E.; Ruhl, B. L.; Weill, M. J. S.;
Seward, E. M. J. Am. Chem. Soc. 1989, 111, 8681; (d) Yamato, T.; Zhang, F. L.;
Kumamaru, K.; Yamamoto, K. J. Inclusion Phenom. Macrocycl. Chem. 2002, 42, 51.
28. van Leeuwen, F. W. B.; Beijleveld, H.; Koojiman, H.; Spek, A. L.; Verboom, W.;
Reinhoudt, D. N. Tetrahedron Lett. 2002, 43, 9675.
Acknowledgements
We are grateful to the National Natural Science Foundation of
China (20772092) and the Hubei Province Natural Science Fund for
Distinguished Young Scholars (2007ABB021) for financial support.
´
ˇ´
´
29. (a) Dudic, M.; Lhotak, P.; Stibor, I.; Dvorakova, H.; Lang, K. Tetrahedron 2002, 58,
ˇ
ˇ´
´
´
5475; (b) Stastny´, V.; Stibor, I.; Dvorakova, H.; Lhotak, P. Tetrahedron 2004, 60,
3383.
References and notes
30. Hosseini, M. W. Chem. Commun. 2005, 5825.
31. Sy´kora, J.; Himl, M.; Stibor, I.; Cı´sarova, I.; Lhotak, P. Tetrahedron 2007, 63, 2244.
ˇ
´
´
´
´
32. Gil-Ramırez, G.; Benet-Buchholz, J.; Escudero-Adan, E. C.; Ballester, P. J. Am.
Chem. Soc. 2007, 129, 3820.
1. (a) Gutsche, C. D. Calixarenes; Stoddart, J. F., Ed.; Monographs in Supramolecular
Chemistry; The Royal Society of Chemistry: Cambridge, 1989; (b) Ikeda, A.;
Shinkai, S. Chem. Rev. 1997, 97, 1713; (c) Calixarenes in Action; Mandolini, L.,
Ungaro, R., Eds.; Imperial College Press: London, 2000; (d) Calixarenes 2001;
Asfari, Z., Bo¨hmer, V., Harrowfield, J. M., Vicens, J., Eds.; Kluwer Academic:
Dordrecht, 2001.
33. Pedersen, C. J. Fedn. Proc. 1968, 27, 1305.
34. (a) Lein, G. M.; Cram, D. J. J. Am. Chem. Soc. 1985, 107, 448; (b) Helgeson, R. C.;
Weisman, G. R.; Toner, J. L.; Tamowski, T. L.; Chau, L.; Mayer, J. M.; Cram, D. J.
J. Am. Chem. Soc. 1979, 101, 4928.
35. (a) Clement, O.; Rapko, B. M.; Hay, B. P. Coord. Chem. Rev. 1998, 170, 203; (b)
Pessoa, J. C.; Correia, I.; Kiss, T.; Jakusch, T.; Castro, M. M. C. A.; Geraldes, C. F. G.
C. J. Chem. Soc., Dalton Trans. 2002, 4440; (c) Singh, N.; Kumar, M.; Hundal, G.
Tetrahedron 2004, 60, 5393; (d) Bhalla, V.; Kumar, M.; Katagiri, H.; Hattoria, T.;
2. Gutsche, C. D. Calixarenes Revisited; Stoddart, J. F., Ed.; Monographs in Supra-
molecular Chemistry; The Royal Society of Chemistry: Cambridge, 1998.
3. (a) Cation Binding by Macrocycles; Inoue, Y., Gokel, G. W., Eds.; Marcel Dekker:
New York, NY, 1990; (b) Gokel, G. W. Crown Ethers and Cryptands; The Royal
Society of Chemistry: London, England, 1991.
´
Miyanoa, S. Tetrahedron Lett. 2005, 46, 121; (e) Oueslati, I.; Thuery, P.;
Shkurenko, O.; Suwinska, K.; Harrowfield, J. M.; Abidie, R.; Vicensf, J. Tetrahe-
dron 2007, 63, 62; (f) Bhalla, V.; Babu, J. N.; Kumar, M.; Hattorib, T.; Miyano, S.
Tetrahedron Lett. 2007, 48, 1581.
4. (a) Wenz, G. Angew. Chem., Int. Ed. Engl. 1994, 33, 803; (b) Szejtli, J. Cyclodextrins
and their Inclusion Complexes; Akademjai Kiado: Budapest, 1982; (c) Compre-
hensive Supramolecular Chemistry; Szejtli, J., Osa, T., Eds.; Pergamon: Elsevier,
Oxford, 1996; Vol. 3, (Cyclodextrins).
5. Casnati, A.; Ungaro, R. Calixarenes in Spherical Metal Ion Recognition. In
Calixarenes in Action; Mandolini, L., Ungaro, R., Eds.; Imperial College Press:
London, 2000; Chapter 4.
36. Sheldrick, G. M. SHELXS97, A Program for Crystal Structure Solution; University of
Go¨ttingen: Go¨ttingen, Germany, 1997.
37. Sheldrick, G. M. SHELXL97, A Program for Crystal Structure Refinement; University
of Go¨ttingen: Go¨ttingen, Germany, 1997.