Synthesis, crystal structures, cation-binding properties and the influence of intramolecular C-H...O interactions on the complexation behaviour of a family of cone p-tert-butylcalix[4]arene-crown-5 compounds

Article abstract of DOI:10.1002/ejic.200600354

A family of cone p-tert-butylcalix[4]arene-crown-5 compounds with various substituents (H, COCH₃, CH₂CO₂C ₂H₅ and CH₂CO₂H) appended at the opposite phenolic oxygen atoms have been synthesised to evaluate their efficiency and selectivity towards different alkali and alkaline-earth metal ions, and also to ascertain the role of the appended side-arms in the complexation process. The selectivity of these ionophores towards Na ⁺, K⁺, Mg²⁺, and Ca²⁺ has been evaluated with an aqueous solution containing an equimolar mixture of these ions. The concentration of metal ion in the extract (organic phase) has been estimated by ion chromatographic assay. Among these ions, K⁺ shows the highest selectivity in all cases except one, where the two phenolic oxygen atoms contain COCH₃ substituents. All the ionophores show poor selectivity towards Mg²⁺ and Ca²⁺. Association constants (K_a) for the binding of Na⁺ and K⁺ to these ionophores have been determined spectrophotometrically. K^a (7.2 × 10⁷) is highest for the binding of K⁺ to the ionophore with CH₂CO₂C₂H₅ substituants. The molecular structures of four of the ionophores and four of the metal complexes have been established by single-crystal X-ray crystallography. Analysis of the structures revealed that in case of the ionophore with two COCH₃ substituents, the C-H...O interactions form an eight-membered zigzag ring almost perpendicular to the crown ring, which prevents entry of the metal ions into the calix-crown cavity. The ionophore with CH₂CO₂C₂H₅ substituents, where no such interaction is observed, forms metal complexes easily and exhibits the highest association constant. ¹H and ¹³C NMR studies have also been, carried out to investigate the conformational behaviour of these ionophores and their metal complexes in solution. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600354

FULL PAPER
DOI: 10.1002/ejic.200600354
Synthesis, Crystal Structures, Cation-Binding Properties and the Influence of
Intramolecular C–H···O Interactions on the Complexation Behaviour of a
Family of Cone p-tert-Butylcalix[4]arene-crown-5 Compounds
Pragati Agnihotri,[a] Eringathodi Suresh,[a] Parimal Paul,*[a] and Pushpito K. Ghosh*[a]
Keywords: Calixarenes / Crown compounds / Selectivity / Association constants
A family of cone p-tert-butylcalix[4]arene-crown-5 com- for the binding of K+ to the ionophore with CH2CO2C2H5
pounds with various substituents (H, COCH3, CH2CO2C2H5
and CH2CO2H) appended at the opposite phenolic oxygen
atoms have been synthesised to evaluate their efficiency and
selectivity towards different alkali and alkaline-earth metal
ions, and also to ascertain the role of the appended side-arms
in the complexation process. The selectivity of these iono-
phores towards Na+, K+, Mg2+, and Ca2+ has been evaluated
with an aqueous solution containing an equimolar mixture of
these ions. The concentration of metal ion in the extract (or-
ganic phase) has been estimated by ion chromatographic as-
say. Among these ions, K+ shows the highest selectivity in
all cases except one, where the two phenolic oxygen atoms
contain COCH3 substituents. All the ionophores show poor
selectivity towards Mg2+ and Ca2+. Association constants (Ka)
for the binding of Na+ and K+ to these ionophores have been
determined spectrophotometrically. Ka (7.2×107) is highest
substituents. The molecular structures of four of the iono-
phores and four of the metal complexes have been estab-
lished by single-crystal X-ray crystallography. Analysis of the
structures revealed that in case of the ionophore with two
COCH3 substituents, the C–H···O interactions form an eight-
membered zigzag ring almost perpendicular to the crown
ring, which prevents entry of the metal ions into the calix-
crown cavity. The ionophore with CH2CO2C2H5 substituents,
where no such interaction is observed, forms metal com-
plexes easily and exhibits the highest association constant.
1H and 13C NMR studies have also been carried out to inves-
tigate the conformational behaviour of these ionophores and
their metal complexes in solution.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
stituents at the upper rim of the calixarene and the ap-
pended functional groups at the two sides of the crown ring.
Among various conformations of the calixarene, 1,3-alter-
nate conformers have been studied more extensively as com-
plexing agent for alkali metal ions.[4b,4c,4f,5] Other conform-
ers have also been prepared but metal ion complexation
studies are rare.[4a,4d] Among various crown ether rings,
crown-5- and crown-6-containing calixarene derivatives
have been found to be more suitable for complexation with
alkali metal ions.[4] A number of calix[4]-bis(crown ethers)
and their complexation behaviour, mainly with cations of
large size, have also been reported.[6]
It has been observed that the substituents at the lower
rim determine the conformations of the calixarenes. Calix-
[4]arene-crown ether derivatives in 1,3-alternate conforma-
tion have been studied most since they are more efficient
and selective in the complexation of potassium ions.[5] The
ionophores p-tert-butylcalix[4]arene-crown derivatives,
which have not been studied extensively, exist in cone, par-
tial cone and 1,3-alternate conformations.[4a,4g,7] In the lat-
ter case, the desired conformation can be obtained by ma-
nipulating the experimental conditions and reagents.[4g,8] It
should be noted that the selectivity and efficiency of extrac-
tion of alkali and alkaline-earth metal ions is maximal with
Calixarenes, which are macrocyclic oligomers made up
of phenol units linked by a methylene bridge, are receiving
increasing attention because of their ability to bind guest
molecules or ions.[1] In the calixarene family, calix[4]arenes
are most popular because of their rigid structures, which
make them ideal candidates for the complexation of neutral
molecules or ions.[1,2] This chemistry has become even more
versatile because of the ease with which calix[4]arenes can
be modified with functional groups at either the lower or
upper rims, or both, depending on the requirements. These
modified calixarenes provide a highly pre-organized archi-
tecture for the assembly of converging binding sites.[3]
Among these calixarene derivatives, calix[4]arene-crown
ethers have attracted intense interest as selective alkali
metal extractants.[4] The ion selectivity of this class of com-
pounds is controlled mainly by the conformation of the ca-
lixarene platform, the size of the crown ether ring, the sub-
[a] Analytical Science Division, Central Salt and Marine Chemi-
cals Research Institute,
Bhavnagar 364002, India
E-mail: ppaul@csmcri.org
pkghosh@csmcri.org
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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FULL PAPER
the cone conformation of p-tert-butylcalix[4]arene-crown
derivatives, except for one report in which a partial cone
conformation was reported to exhibit high K+/Na+ selectiv-
ity.[4a]
Results and Discussion
Synthesis of Ligands 1–5
As part of our effort to identify suitable options for selec-
tive extraction of K+ from natural sources such as brine
and bittern, which mainly contain Na+, K+, Ca2+ and
The compound p-tert-butylcalix[4]arene-crown-5 (1) was
synthesised by the reaction of p-tert-butylcalix[4]arene,
tetraethylene glycol ditosylate and tBuOK (Scheme 1) ac-
cording to a modified literature procedure.[4a] The confor-
mation of the calix-crown products depends on the reaction
conditions and reagents used; the cone conformation
needed for the complexation study could be obtained in
good yield. For the synthesis of acetyl derivatives of 1, we
attempted the reaction at room temperature with acetyl
chloride and acetyl bromide, using NaH as base and diethyl
ether as solvent. However, a mixture of mono- and diacetyl
derivatives was obtained, with the former as the major
product even after extended (3 d) stirring. We optimised the
reaction conditions in diethyl ether to maximize the yield
of the monoacetyl derivative, and compound 2 was ob-
tained in cone conformation after purification by column
chromatography. By switching the solvent from diethyl
ether to THF and conducting the synthesis under reflux
conditions, we were successful in obtaining the diacetyl de-
rivative 3 in good yield. Compound 4 was obtained in cone
conformation by the reaction of 1 with ethyl bromoacetate
in the presence of K2CO3 under reflux in acetonitrile. Hy-
drolysis of 4 yielded the corresponding acid 5 in good yield.
During preparation of this manuscript, a paper has ap-
peared on the synthesis of 4 and 5 and use of the latter as
a proton di-ionisable extractant for Mg2+, Ca2+, Sr2+ and
Ba2+; however, this study is quite different from that re-
ported here.[10]
Mg2+ [9]
we here report our studies on competitive binding
,
of these ions with p-tert-butylcalix[4]arene-crown-5 deriva-
tives in the cone conformation (Figure 1). The effect of ap-
pended substituents on complexation and the structural
features of the ionophores before and after complexation in
solution and the solid state, as probed by NMR spectro-
scopic and single-crystal X-ray studies, are reported. These
studies have enabled us to unravel structural features of the
ionophores and their complexes; in particular, the influence
of intramolecular hydrogen bonding on complexation.
Figure 1. Structures of the ionophores (1–5) used in this study.
Scheme 1. Synthesis of p-tert-butylcalix[4]arene-crown-5 compounds; a) OTsCH2(CH2OCH2)2CH2OTs, tBuOK, benzene; b) CH3COBr,
NaH, diethyl ether; c) CH3COBr, NaH, THF; d) BrCH2CO2C2H5, K2CO3, CH3CN; e) NaOH, ethanol.
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Cone p-tert-Butylcalix[4]arene-crown-5 Compounds
Synthesis of Na+ and K+ Complexes of 1–5
FULL PAPER
thus indicating that the structures of the metal complexes
in solution are close to a regular cone conformation. The
difference between the two signals due to phenyl groups and
also due to tert-butyl groups observed for the free ligand
are significantly reduced (Յ0.1) in the complexed state. This
is presumably because insertion of a metal ion into the
crown cavity provides a similar geometrical shape of the
complexed molecule. It should be noted that the two ap-
pended CH2CO2C2H5 groups of 4·Na+Pic– and 4·K+Pic–
exhibit one set of signals [δ = 4.77 (s), 4.32 (q) and 1.33 (t)
ppm for 4·Na+Pic– and δ = 4.57 (s), 4.32 (q) and 1.33 (t)
ppm for 4·K+Pic– (Figure 2)] thus indicating that both
groups in each compound are chemically equivalent in solu-
tion. A similar observation was also noted for the com-
plexes of 3 and 5, in which two appended COCH3 and
CH2CO2H groups are present, respectively. Interestingly,
the crystal structures of 4·Na+Pic–, 4·K+Pic– and 5·K+Pic–
(see below) show that only one of the two appended groups
in each complex is connected to a metal ion through its
oxygen atom. Therefore, two sets of signals for two non-
equivalent appended groups in each complex are expected.
The appearance of only one set of signals suggests exchange
of coordination between the appended groups and the
metal ion in solution. This exchange process is fast enough
Reaction of the ligands with a ten-fold excess of metal
picrate in chloroform resulted in the formation of 1:1 metal
complexes. In the case of 3, however, the Na+ complex
(3·Na+Pic–, Pic = picrate) was only obtained in poor yield,
and virtually no complex formation took place with K+, as
1
evident from the H NMR spectrum. Hence, the K+ com-
plex of 3 is not discussed further.
All of these ligands and metal complexes gave satisfac-
tory C, H, and N analyses. The mass spectra of all these
ligands and metal complexes were recorded and the ob-
served m/z values show excellent agreement with the calcu-
lated values. It may be noted that the m/z values (100%) of
all ligands correspond to the Na+ adduct [ligand + Na]+,
which is a well-known phenomenon in LC mass spectrome-
try. The potassium and sodium complexes of the ligands
(complex formation was confirmed by NMR studies and
X-ray structure determination; vide infra) exhibit molecular
ion peaks corresponding to [ligand + K]+ and [ligand + Na]+,
respectively.
NMR Study
1
The H and 13C NMR spectra of all compounds were on the NMR timescale to make them indistinguishable. An-
recorded in CDCl3 and the data are presented in the Experi- other unprecedented observation is noted for the signals for
mental Section. The NMR spectroscopic data established the phenyl and tert-butyl protons of the complexes of 1.
the conformation of the ligands and complexes in solution. Ligand 1 shows two signals for the phenyl protons and two
1
The H NMR spectra of these compounds exhibit two sig- signals for the tert-butyl protons. However, in the complexes
nals for the aromatic protons, two doublets for the bridging one of the signals (high-field) of the phenyl protons is found
methylene groups of the calixarene unit and two singlets for to split to produce two signals at δ = 6.73 (1 H) and 6.63
the tert-butyl groups. In the case of 2 and its complexes, (3 H) ppm for 1·Na+Pic– and δ = 6.74 (1 H) and 6.61 (3 H)
however, the spectra are more complex because of asym- ppm for 1·K+Pic–. The high-field signal for tert-butyl is also
metric substituents at the p-hydroxy positions of the oppo- seen to split to produce signals at δ = 1.20 (3 H), 0.92 (3
site benzene rings (OH and COCH3). In all of these ionoph- H) and 0.83 (12 H) ppm for 1·Na+Pic– and δ = 1.20 (3 H),
ores and complexes, a typical AB pattern was observed for 0.93 (3 H) and 0.81 (12 H) ppm for 1·K+Pic–. The possibil-
the methylene bridge (ArCH2Ar) protons, that is, two ity of the formation of other conformations can be ruled
widely separated doublets at δ = 3.90–4.65 and 3.12– out on the basis of full NMR spectroscopic data. The crys-
3.36 ppm (J = 12–13.8 Hz), which suggests that these ion- tal structure of 1·K+Pic– shows that the picrate anion is
ophores exist in a cone conformation in solution.[4a,11] The coordinated to the metal ion in a bidentate fashion through
low-field doublet is due to the axial H atom and the high- the oxygen atoms of the deprotonated phenolic group and
field doublet is due to the equatorial H atom of the methyl- one of the nitro groups. Beer et al. have noted similar obser-
ene bridge. The chemical shift difference (∆δ) between Haxial vations in the lanthanide picrate complexes of their tert-
and Hequatorial serves as a measure of the “flattening” of butylcalix[4]arene diamide ligand.[13]
each phenyl unit.[1a,12] In general, ∆δ = 0.9 ppm for a sys-
Analysis of the crystal structure of 1·K+Pic– shows that
tem in the regular cone conformation, and for a more “flat- the benzene ring of the picrate anion is in proximity, and
tened” conformation the value of ∆δ decreases. For com- almost parallel to, one of the benzene rings of the calixar-
pounds 1–5, the ∆δ values are 0.78, 0.89 (1.31 for another ene (Cg–Cg distance is 3.76 Å and the dihedral angle be-
ring), 0.78, 1.48 and 1.10 ppm, respectively. These data indi- tween the planes of the rings is 13.72°). The structural
cate that the “flattening” of the phenyl rings is greater in 1 analysis shows that one of the phenyl protons and a few of
and 3 and lesser in 4 and 5 than that of the regular cone the tert-butyl protons of one of the benzene rings of the
conformation.[4a] The reduced “flattening” in 4 and 5 is be- calixarene are pointed towards the deshielding zone of the
cause of steric crowding caused by bulky substituents at the benzene ring of the picrate anion, which results in a split-
narrow lower rim of the calix[4]arene-crown moiety. The ∆δ ting of the signals for the phenyl and tert-butyl protons.[14]
values for the metal complexes of 1–3 could not be calcu- Because of this deshielding effect, the signals of one of the
lated because of the overlapping of signals from the high- phenyl protons and two methyl groups of the tert-butyl
field doublet and crown moiety. However, for the complexes moiety are shifted downfield; the shift of one of the methyl
of 4 and 5 these values are in the range 1.07–1.12 ppm, groups is quite pronounced.
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41.10° (82.67° and 35.60° for the other molecule in the unit
cell) for 1, 87.00° and 7.40° for 2, 60.66° and 39.82° for 3
and 78.10° and 29.18° for 4. The opposite benzene rings,
which are connected to the crown moiety, are less flattened,
as evident from their low inter-planar angles. The wide vari-
ations in flattening of the rings are due to steric overcrowd-
ing of the bulky substituents at the lower rim of the rings
and also due to intramolecular C–H···O interactions. It
should be noted that the oxygen atoms of the CO groups of
the COCH3 substituent in 2 and 3 and the CH2COOC2H5
substituent of 4 are directed away from the polyether rings,
which could be due to minimisation of the electrostatic re-
pulsion between the lone pairs of the oxygen atoms of the
CO and polyether rings. Most of the appended groups show
hydrogen-bonding interactions with the oxygen atoms of
the polyether rings. There are many examples of hydrogen-
bonding interactions involving OH groups at the lower rim
of the calixarene,[16] although hydrogen-bonding interac-
tions involving other groups are not common. In case of 1,
the hydrogen atoms of the OH groups (O6–H6 and O7–H7)
make strong O–H···O interactions with O5 and O1, which
act as donors; O7, on the other hand, acts as an acceptor,
making C–H···O interactions with H48A and H50B of the
methylene groups of the polyether ring. The interesting fea-
ture of the packing is the dimeric association of the two
ligands A and B present in the asymmetric unit. This occurs
by an intermolecular C–H···O interaction involving H10K
attached to C101 and the phenolic oxygen atom O6. Two
such hydrogen-bonded dimers are further associated by a
C–H···π interaction to form a tetrameric unit (Figure 5).
Details of C–H···O, C–H···N, and C–H···π interactions of
1–3 and 4 are given in Table S1 in the Supporting Infor-
mation. In the case of 2, the hydrogen atom (H1) of the
phenolic oxygen atom O1 is involved in a strong intramolec-
ular O–H···O interaction with O4. Two of the methyl hydro-
gen atoms of the acetyl moiety (H46B and H46C) make
intramolecular C–H···O interactions with O4 and O8 of the
crown moiety. A packing diagram of 2 showing the one-
dimensional array formed by intermolecular hydrogen-
bonding interactions between adjacent molecules is de-
picted in Figure S1 (Supporting Information).
Figure 2. 1H NMR spectra of ionophore 4 (a), its Na+ (4·Na+Pic–)
(b) and K+ complexes (4·K+Pic–) (c), recorded in CDCl3 at room
temperature.
In the 13C NMR spectra, the signals of the carbon atoms
of the four methylene bridges (ArCH2Ar) appear at the
same position (one peak), with a chemical shift of δ Ϸ
31 ppm, which is typical for the cone conformation of tert-
butylcalix[4]arene derivatives.[4g,15] The other observation is
that the C-1 and C-4 carbon atoms (see Figure 3 for the
numbering scheme) show two signals each, which could be
due to different substituents attached to the carbon atoms
at the lower rim of the calixarene. In the metal complexes,
the 13C NMR signals are consistent with the cone confor-
mation of the calixarene moiety albeit with some changes
in chemical shift for the carbon atoms of the crown moiety,
due to complex formation, compared to the free ligand.
The intramolecular hydrogen-bonding pattern of 3 is
interesting and provides important information regarding
its robustness towards complexation with K+. In this com-
pound, it has been observed that the two H atoms of each
methyl group of the two appended COCH3 groups (H46B,
H48C and H46C, H48B) are close to the oxygen atoms of
the polyether ring and are held strongly by C–H···O interac-
tions with O6 and O8 of the crown moiety (Table 1) In fact,
this hydrogen bonding forms an eight-membered puckered
ring, which is nearly perpendicular to the crown ring
Figure 3. Numbering scheme for carbon atoms of the p-tert-bu-
tylcalix[4]arene used in the NMR discussion.
Crystal Structures
X-ray crystal structures of four ionophores and four (79.33°) and crosses it through the middle (Figure 6). We
complexes have been determined; ORTEP views of the ion- believe this interaction also exists in solution and, therefore,
ophores are displayed in Figure 4. The structures of the ion- metal ions such as K+ cannot enter into the cavity to form
ophores clearly show the flattened cone conformation, as metal complexes. The packing diagram of 3, which shows a
suggested by the NMR spectroscopic data. However, the dimeric association of the molecule through intermolecular
extent of flattening differs from ligand to ligand. The inter- interactions involving surrounding lattice solvent molecules,
planar angles between the two opposite rings are 71.89° and is shown in Figure S2 (Supporting Information).
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Cone p-tert-Butylcalix[4]arene-crown-5 Compounds
FULL PAPER
Figure 4. ORTEP views of compounds 1 (a), 2 (b), 3 (c) and 4 (d).
Figure 5. Packing diagram of 1 viewed along the a-axis showing
the tetrameric association of the compound with acetonitrile (ball-
and-stick model) in the cavity of the calix cone.
Table 1. Intramolecular C–H···O interactions involving methyl hy-
drogen atoms of COCH3 and oxygen atoms of the crown ring for 3.
D–H···A
H···A [Å]
D···A [Å]
Ͻ(D–H···A) [°]
C46–H46B···O6
C46–H46C···O8
C48–H48B···O8
C48–H48C···O6
2.30
2.32
2.44
2.40
3.240(3)
3.269(3)
3.315(4)
3.255(4)
167
168
151
149
Figure 6. Capped stick model of compound 3, showing C–H···O
interactions (dotted line) involving methyl hydrogen atoms of
COCH3 groups and oxygen atoms (O6 and O8) of the crown
moiety.
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In the case of 4 the C–H···O interactions involving the One of the acetonitrile molecules present in the crystal oc-
crown ring are not significant. The only interaction ob- cupies the cone cavity of the calixarene unit in all cases.
served is that between the hydrogen atoms (H49A) of the This acetonitrile molecule is held in the cavity and forms
CH2COOC2H5 moiety and O9 of the crown ring. However, C–H···N interactions with the hydrogen atom of one of the
the oxygen atoms of the CO groups of both CH2COOC2H5 bridging ethylene groups and C–H···π interactions with the
moieties form C–H···O interactions with the hydrogen benzene rings of the calixarene moiety.
atoms of the bridging methylene group. The packing dia-
The crystal structures of the metal complexes reveal that
gram of 4 is also available as Supporting Information (Fig- the K+ ion is coordinated to eight oxygen atoms in all com-
ure S3).
plexes whereas the Na+ ion in 4·Na+Pic– is coordinated to
All of the above ligands contain lattice solvent mole- six oxygen atoms (Figure 7). In 1·K+Pic–, where eight coor-
cule(s) and these appear to play a role in crystal formation. dination sites with oxygen atoms as donor are not available,
Figure 7. ORTEP views of complexes 1·K+Pic– (a), 4·Na+Pic– (b), 4·K+Pic– (c), and 5·K+Pic– (d).
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Cone p-tert-Butylcalix[4]arene-crown-5 Compounds
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the picrate anion acts as a bidentate ligand to make K+ Chromatograms of the original solution and that of the ex-
octacoordinate. For complexes 4·Na+Pic–, 4·K+Pic– and tract obtained using 4 are given in Figure 8. The distribu-
5·K+Pic–, out of two CH2CO2C2H5 and CH2CO2H ap- tions of metal ions in the organic extracts, together with
pended arms, the oxygen atom of the CO group of one arm values of the observed selectivity ratios, are given in Table 3.
is coordinated to K+. In the case of 4·Na+Pic–, however, As can be seen from the data, all ionophores except 3 show
two oxygen atoms (O9 and O10) of the crown moiety are high selectivity towards K+, this selectivity being highest for
not coordinated to Na+. The M–O distances of all com- 4 (82.1%). From the crystal structures it appears that the
plexes are given in Table 2. In the metal complexes, the cone calix-crown cavity fits well with K+, allowing it to coordi-
conformations of the calixarene moieties are more symmet- nate to all the oxygen donors of the cavity. Na+ also coordi-
ric than those of the corresponding free ligands. For exam- nates, but it does not fit well in the cavity and leaves two
ple, all the four phenyl rings of 4·K+Pic– make similar oxygen atoms of the crown ring uncoordinated. Mg2+ and
angles of intersection with the plane of the four rim methyl- Ca2+ show poor selectivity.
ene groups (64.50–69.92°) and the inter-planar angles be-
tween the two opposite rings are 45.63° and 54.25°, which
suggests an almost symmetric cone conformation of the ca-
lixarene unit.
Table 2. Metal–oxygen bond lengths [Å] for complexes 1·K+Pic–,
4·Na+Pic–, 4·K+Pic–, and 5·K+Pic–.
1·K+Pic–
K1–O9
K1–O5
K1–O1
K1–O3
2.700(2)
2.703(2)
2.711(2)
2.726(2)
K1–O2
K1–O4
K1–O8
K1–O6
2.824(2)
2.845(2)
2.890(2)
3.013(2)
4·Na+Pic–
Na1–O5
Na1–O11
Na1–O1
2.367(3)
2.375(3)
2.394(3)
Na1–O7
Na1–O8
Na1–O4
2.405(3)
2.420(3)
2.543(3)
4·K+Pic–
K1–O1
K1–O5
K1–O11
K1–O10
2.657(2)
2.659(3)
2.712(2)
2.758(3)
K1–O7
K1–O4
K1–O9
K1–O8
2.801(2)
2.803(2)
2.836(3)
2.931(3)
5·K+Pic–
K1–O1
K1–O2
K1–O4
K1–O7
2.742(6)
2.561(8)
2.566(5)
2.703(4)
K1–O8
K1–O9
K1–O10
K1–O11
2.760(6)
2.971(8)
2.926(6)
2.704(4)
Figure 8. Ion chromatograms of a) a solution containing an equi-
molar mixture of Na+, K+, Mg2+, and Ca2+ and b) the extract
obtained from the equimolar mixture by two-phase extraction
using ionophore 4.
Analysis of the crystal structures revealed that each of
these structures make a number of intra- and intermo-
lecular C–H···O interactions, leading to layered or zigzag
chain network of packing. Packing diagrams (Figures S4–
S7) and a table of hydrogen-bonding interactions (Table S2)
for all these complexes are available as Supporting Infor-
mation. Some of the solvent molecules and picrate anions
are highly disordered, as discussed in the Experimental Sec-
tion.
Apart from cavity size, the C–H···O interactions involv-
ing oxygen atoms of the crown ring observed in some of
these compounds play an important role in complex forma-
tion. In the ionophores 2–5, the main coordination core
(calix-crown moiety) for all of them is the same, with one
of the appended arms taking part in coordination. How-
ever, the selectivity for a particular metal ion (e.g. K+) dif-
fers significantly. The crystal structures show that in the
case of 2, one side of the crown ring is blocked by strong
Selectivity
The selectivities of these ionophores toward metal ions C–H···O interactions between two of the methyl protons of
such as Na+, K+, Mg2+ and Ca2+ were determined by a COCH3 and the oxygen atoms of the crown rings. For 3,
two-phase extraction method followed by ion chromato- both the sides are blocked (Figure 6), and in this case the
graphic assay of the metal ions in the extract.[9] The experi- effect is so severe that K+ cannot enter into the cavity for
ments were carried out with an aqueous solution containing complex formation. For 4, however, the C–H···O interac-
equimolar amounts of Na+, K+, Mg2+ and Ca2+ as their tion involving oxygen atoms of the crown ring is not signifi-
picrate salts, as described in the Experimental Section. cant and the metal ion can interact easily with the calix-
Eur. J. Inorg. Chem. 2006, 3369–3381
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3375

P. Agnihotri, E. Suresh, P. Paul, P. K. Ghosh
Table 3. Concentration of metal ions in the extract and selectivity ratio with respect to potassium ion.
FULL PAPER
Compound
Concentration [%] of metal ion in extract[a]
Selectivity ratio[b]
K+/Mg2+
Na+
K+
Mg2+
Ca2+
K+/Na+
K+/Ca2+
1
2
3
4
5
22.0
28.3
56.5
17.9
26.6
63.8
57.5
25.3
82.1
69.4
3.2
10.9
12.0
18.1
–
4.2
1.7
1.2
0.3
2.7
1.5
12.2
16.5
–
–
60.9
6.0
4.9
1.4
–
2.15
[c]
–
[c]
[c]
–
0.7
16.9
[a] Concentration [%] of metal ion in the original solution (before extract): Na+ = 18.2, K+ = 30.9, Mg2+ = 19.9, Ca2+ = 31.7. [b] Ratio
calculated by [% of K+ in the extract][% of Mn+ in the original solution]/[% of Mn+ in the extract][% of K+ in the original solution]. [c]
Trace amount.
crown moiety. This is consistent with the selectivity data
and the association constants determined. It should be
noted that apart from the appended arms, the remainder
of all five ionophores is identical, therefore the observed
variation in complex formation/selectivity is obviously due
to the effect of the appended arms. Steric crowding is not a
significant factor in this case as the ionophore with the
most bulky appended arms (4) shows the highest selectivity.
This suggests that the intramolecular hydrogen-bonding in-
teractions involving the lower rim of the ionophore play an
important role in complex formation with metal ions. The
appended functional groups, which are expected to act co-
operatively as an axial ligand to stabilise the complex, may
not always work in this manner and could even inhibit com-
plex formation.
(2)
The distribution constants were determined using Equa-
tion (3).[17]
(3)
The values of association constants (Ka) and R for all
ionophores are given in Table 4. The data show that the
values of Ka for K+ with various ionophores decrease in the
order 4 Ͼ 5 Ͼ 1 Ͼ 2 ϾϾ 3, which is consistent with the
selectivity data and the C–H···O interactions observed in
the crystal structures. For Na+, the values of Ka are approx-
imately 10–100 times lower than those for K+, in line with
the selectivity data.
Association Constants
Table 4. Molar ratio of picrate/host in the organic layer (R) and
association constants (Ka) with Na+ and K+.
The association constants (Ka) of the ionophores 1–5
with Na+ and K+ picrates were determined spectrophoto-
metrically, as described in the Experimental Section. Metal
picrates in aqueous solution were extracted with chloroform
both in the presence and absence of host. The amount of
picrate ion in the chloroform layer was determined from its
extinction coefficient at 380 nm after appropriate dilution
in CH3CN. The association constants were determined
using Equation (1), where Ka is the association constant, Kd
the distribution constant, R the molar ratio of picrate to
Ionophore
R
Ka
Na+
K+
Na+
K+
1
2
3
4
5
0.02
0.02
0.01
0.26
0.34
0.24
0.08
–
0.68
0.66
1.06×104
8.70×104
5.17×104
3.12×106
5.96×106
1.82×106
3.25×105
–
7.20×107
5.80×107
host in the organic layer, [Gi]H O the initial concentration of
Conclusions
2
the guest (metal ion/picrate), [Hi]
the initial concentra-
CHCl3
A series of p-tert-butylcalix[4]arene-crown ethers with
various substituents attached to the opposite phenolic oxy-
gen atoms have been synthesised in the cone conformation
to evaluate their performance as ionophores towards Na+,
K+, Mg2+ and Ca2+. NMR and crystal structure studies
suggest that these ionophores exist in a “flattened” cone
conformation both in solution and the solid state. Na+ and
tion of the host (ionophore) in chloroform, VCHCl the vol-
ume of the organic layer (chloroform) and VH O th3e volume
2
of the aqueous layer.[17]
(1)
The molar ratios of picrate to host (R) were determined K+ complexes of these ionophores have been synthesised
from Equation (2), where A is the observed absorbance in and the crystal structures show that, in all cases, one of the
the aqueous phase, D the dilution factor, ε the extinction two appended substituents coordinates to the metal ion and
coefficient of the picrate salt at 380 nm in CH3CN (ε = the size of the calix-crown cavity is most suited to K+
16900), [Gi+] the initial concentration of guest in the aque- among the ions studied. The H NMR study also revealed
1
ous phase, Vaq the volume of the aqueous phase, Vorg the that there is fast exchange of coordination between the two
volume of the organic phase, and [Hi*] the initial concentra- appended groups and the metal ion in solution. The selec-
tion of the host in the CHCl3 phase.[18]
tivity study with a mixture of cations showed the highest
3376
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 3369–3381

Cone p-tert-Butylcalix[4]arene-crown-5 Compounds
FULL PAPER
selectivity towards K+; the association constants also follow
the same order. The one exception is compound 3, where
access to the metal ion is blocked as a result of strong C–
H···O interactions between the pendant COCH3 substitu-
ents and the crown moiety. Such deleterious interactions
are apparently nonexistent in the case of the CH2CO2C2H5
substituents as the ligand interacts strongly with the metal
ions. Evidently, although appended functional groups (like
“lariat” crown ethers) are known to act as a stabilizing axial
by column chromatography using silica gel as packing material and
ethyl acetate/hexane (1:5) as eluent. Initially, some starting materi-
als were separated and then the desired product was eluted. The
solvent was removed from the desired fraction and the solid com-
pound was dried in vacuo. Yield: 0.11 g (39%). 1H NMR
(200 MHz, [D3]chloroform): δ = 7.20 (s, 2 H, ArH), 7.08 (s, 2 H,
ArH), 6.79 (s, 1 H, OH), 6.64 (d, J = 2.4 Hz, 2 H, ArH), 6.59 (d,
J = 2.4 Hz, 2 H, ArH), 4.55 (d, J = 13.0 Hz, 2 H, ArCH2Ar), 4.13
(d, J = 12.8 Hz, 2 H, ArCH2Ar), 4.07–3.46 (m, 16 H, crown-CH2),
3.24 (dd, J1 = 13.1, J2 = 3.6 Hz, 4 H, ArCH2Ar), 2.90 (s, 3 H,
ligand, these may, in fact, act in the opposite way if strong OCH3), 1.35 (s, 9 H, tBu), 1.34 (s, 9 H, tBu), 0.83 (s, 18 H, tBu)
ppm. 13C NMR: δ = 171.18 (COCH3), 151.45, 151.25, 150.44 (C-
intramolecular hydrogen bond involving the crown ring is
1), 147.43, 146.24 (C-4), 135.71, 135.44, 133.11, 132.01, 131.96 (C-
operational. The X-ray structure determination of the ion-
2, C-6), 128.47, 126.05, 125.58, 125.36, 125.33, (C-3, C-5), 74.98,
ophores therefore provides an insight into the effect of in-
72.39, 71.69, 71.52, 70.99, 70.38, (OCH2CH2OCH2CH2O), 32.49,
tramolecular interactions on the structure–selectivity corre-
lation.
32.29, (C-7), 32.40, 31.62 (C-8), 31.97 (ArCH2Ar), 22.10 (COCH3)
ppm. LC-MS: m/z = 871.7 (calcd. for [2 + Na+]: 871.53).
C54H73O8.5 (2·0.5H2O, 857.53): calcd. C 75.63, H 8.58; found C
75.64, H 8.55.
Experimental Section
Synthesis of 3: NaH (0.02 g, 0.8 mmol) was added to a solution of
Reagents and Methods: The ligand p-tert-butylcalix[4]arene was
synthesised according to a literature procedure.[19] Metal picrate
salts were prepared by the reaction of picric acid and the metal
hydroxide in aqueous media. All the reagents used in this study
were purchased from Aldrich and S. D. Fine Chemicals. All sol-
vents were of analytical grade and purified by standard procedures
before use.[20] Milli-Q (Millipore Corporation) water was used for
extraction and ion chromatographic study. Elemental analyses (C
and H) were performed with a model 2400 Perkin–Elmer elemental
analyzer. NMR spectra were recorded with a model DPX 200
Bruker FT-NMR instrument. Infrared spectra were recorded with
a Perkin–Elmer Spectrum GX FT-IR system. Mass spectra were
recorded with a Q-TOF MicroTM LC-MS instrument. The UV/Vis
spectra were recorded with a model 8452A Hewlett–Packard diode
array spectrophotometer. Cation concentration was measured with
a Dionex 500 ion chromatograph. Single crystal structures were
determined using a Bruker SMART 1000 (CCD) diffractometer.
1 (0.20 g, 0.25 mmol) in THF (70 mL) and the reaction mixture
was refluxed. After 30 min of reflux, a solution (10 mL) of acetyl
bromide (0.5 mL, 7.0 mmol) in THF was added dropwise to the
reaction mixture and refluxing was continued. After 6 h, the solu-
tion was cooled to room temperature, filtered and the solvent of
the filtrate was removed by rotary evaporation. The residue was
treated with 2  HCl (50 mL), the mixture filtered and the solid
mass washed twice with water (25 mL each time). The product thus
obtained was recrystallised from dichloromethane/acetonitrile.
Yield: 0.16 g (81%). 1H NMR (200 MHz, [D3]chloroform): δ = 7.06
(s, 4 H, ArH), 6.48 (s, 4 H, ArH), 4.28–4.06 (m, 8 H, crown-CH2),
3.90 (d, J = 12.8 Hz, 4 H, ArCH2Ar), 3.77–3.61 (m, 8 H, crown-
CH2), 3.12 (d, J = 12.8 Hz, 4 H, ArCH2Ar), 2.56 (s, 6 H, OCH3),
1.25 (s, 18 H, tBu), 0.78 (s, 18 H, tBu) ppm. 13C NMR: δ = 171.39
(COCH3), 154.95, 152.44 (C-1), 146.66, 145.43 (C-4), 135.53 (C-2),
132.16 (C-6), 126.68, 125.51 (C-3, C-5), 74.02, 73.62, 71.89, 71.57
(OCH2CH2OCH2CH2O), 32.42, 31.82, 31.74 (C-7, C-8), 32.04 (Ar-
CH2Ar), 22.25 (COCH3) ppm. LC-MS: m/z = 913.53 (calcd. for [3
+ Na+]: 913.52). C56H76O10 (3·H2O, 908.52): calcd. C 74.03, H
8.43; found C 74.12, H, 8.07.
Synthesis of 1: A mixture of p-tert-butylcalix[4]arene (1.46 g,
2.25 mmol) and tBuOK (0.23 g, 2 mmol) in 150 mL of dry benzene
was refluxed under an inert gas with stirring for 1.5 h, then tetra-
ethylene glycol ditosylate (1.06 g, 2 mmol) was added. After re-
fluxing for 24 h, a second portion of tBuOK (0.23 g, 2 mmol) was
added, and the reaction mixture was refluxed for an additional
24 h. It was then cooled to room temperature, treated with 1  HCl
(125 mL), and extracted five or six times with 30 mL of diethyl
ether each time. The combined organic layers were finally washed
three times with water (100 mL each time) and the solvent was
removed by rotary evaporation. The crude product was purified by
column chromatography using silica gel as packing material and
dichloromethane/ethyl acetate (4:1) as eluent. Yield: 0.75 g (43%).
1H and 13C NMR spectroscopic data are similar to those reported
earlier.[4a,10] LC-MS: m/z = 829.51 (calcd. for [1 + Na+] 829.50).
C52H71O7.5 (1·0.5H2O, 815.50): calcd. C 76.59, H 8.78; found C
76.48, H, 8.69.
Synthesis of 4: A mixture of 1 (0.20 g, 0.25 mmol) and K2CO3
(0.08 g, 0.53 mmol) in 70 mL of acetonitrile was refluxed with stir-
ring for 3 h, then ethyl bromoacetate (0.09 g, 0.53 mmol) was added
dropwise and refluxing was continued for 24 h. The reaction mix-
ture was then cooled to room temperature, treated with 5% HCl
(50 mL) and extracted with 50 mL of dichloromethane. The or-
ganic layer thus obtained was washed twice with water (50 mL in
each time) and the solvent was removed by rotary evaporation. The
crude product was recrystallised from dichloromethane/acetonitrile.
Yield: 0.18 g (71%). 1H NMR (200 MHz, [D3]chloroform): δ = 6.84
(s, 4 H, ArH), 6.74 (s, 4 H, ArH), 5.07 (s, 4 H, OCH2CO), 4.65 (d,
J = 12.6 Hz; 4 H, ArCH2Ar), 4.20–4.05 (m, 8 H, crown-CH2),
3.76–3.66 (m, 8 H, crown-CH2), 3.17 (d, J = 12.6 Hz, 4 H, Ar-
CH2Ar), 1.21 (t, J = 6.8 Hz, 6 H, CH3), 1.13 (s, 18 H, tBu), 1.01
(s, 18 H, tBu) ppm. 13C NMR: δ = 171.53 (OCH2COOCH2CH3)
153.98, 152.79 (C-1), 145.28, 145.13 (C-4), 134.67 (C-2), 134.09 (C-
6), 125.46 (C-3, C-5), 73.40, 71.81, 71.49, 71.18, (OCH2CH2OCH2-
CH2O), 70.98 (OCH2COOCH2CH3), 60.69 (OCH2COOCH2CH3),
34.37, 34.25 (C-7), 32.68 (ArCH2Ar), 32.18, 31.83 (C-8), 14.82
(OCH2COOCH2CH3) ppm. LC-MS: m/z = 1001.58 (calcd. for [4
+ Na+]: 1001.57). C60H86O13 (4·2H2O, 1014.6): calcd. C 71.03, H
8.54; found C 71.01, H, 8.46.
Synthesis of 2: Compound 1 (0.27 g, 0.3 mmol), NaH (0.04 g,
1.75 mmol), and acetyl bromide (0.4 mL, 5.4 mmol) were dissolved
in 70 mL of diethyl ether and the mixture was stirred at room tem-
perature under an inert gas for 3 d. After removing the solvent
with a rotary evaporator, the solid mass was treated with 10% HCl
(50 mL) and extracted with dichloromethane (50 mL). The organic
layer was washed twice with water (50 mL each time) and the sol-
vent was removed by rotary evaporation. The product was purified
Eur. J. Inorg. Chem. 2006, 3369–3381
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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3377

P. Agnihotri, E. Suresh, P. Paul, P. K. Ghosh
FULL PAPER
Synthesis of 5: An aqueous solution (0.25 mL) of NaOH (15%)
was added to an ethanolic solution (70 mL) of 4 (0.10 g, 0.1 mmol)
and the reaction mixture was heated under reflux. After 24 h, it
was cooled to room temperature and the solvent was removed by
rotary evaporation. Then, 50 mL of cold water was added to the
solid mass and 30% HCl was added dropwise with vigorous stirring
until the pH of the solution reached 1. The solid product thus pro-
duced was isolated by filtration. The crude product was then dis-
solved in chloroform (50 mL) and washed with HCl (30%) followed
by concentrated brine. The organic layer was separated, the solvent
removed, and the product dried in vacuo. Yield: 0.065 g (70%). 1H
NMR (200 MHz, [D3]chloroform): δ = 7.12 (s, 4 H, ArH), 6.60 (s,
4 H, ArH), 5.29 (s, 4 H, OCH2CO), 4.37 (d, J = 12.0 Hz, 4 H,
ArCH2Ar), 4.08–3.85 (m, 16 H, crown-CH2), 3.27 (d, J = 12.0 Hz,
4 H, ArCH2Ar), 1.33 (s, 18 H, tBu), 0.83 (s, 18 H, tBu) ppm. 13C
NMR: δ = 172.99 (OCH2COOH), 153.69, 152.18 (C-1), 146.69,
146.19 (C-4), 135.49 (C-2), 132.89 (C-6), 126.39, 126.19 (C-3, C-5),
74.09, 71.13, 71.07, 70.99 (OCH2CH2OCH2CH2O), 70.44 (OCH2-
COOH), 34.89, 34.39 (C-7), 32.89 (ArCH2Ar), 32.39, 31.99 (C-8)
ppm. LC-MS: m/z = 945.52 (calcd. for [5 + Na+]: 945.51).
C56H80O14 (5·3H2O, 976.51): calcd. C 68.87, H 8.26; found C 69.14,
H, 8.32.
H, ArCH2, crown-CH2), 3.30 (d, J = 12.8 Hz, 4 H, ArCH2), 2.27
(s, 3 H, OCH3), 1.35 (s, 9 H, tBu), 1.30 (s, 9 H, tBu), 0.82 (s, 18
H, tBu) ppm. 13C NMR: δ = 171.36 (COCH3), 150.34, 150.06, (C-
1), 148.59, 148.00 (C-4), 132.55 (C-2), 128.51 (C-6), 127.22, 126.44
(C-3, C-5), 125.85 (picrate), 75.88, 71.93, 71.21, 70.22 (OCH2CH2-
OCH2CH2O), 34.57, 32.20 (C-7), 32.30, 31.51 (C-8), 31.83 (Ar-
CH2Ar), 21.74 (COCH3) ppm. LC-MS: m/z = 871.9 (calcd. for [2
+ Na+]: 871.53). C60H76N3NaO16 (with H2O, 1117.5): calcd. C
64.49, H 6.86, N 3.76; found C 64.23, H 6.88, N 3.57.
Potassium Complex of 2 (2·K+Pic–): 1H NMR (200 MHz, [D3]chlo-
roform): δ = 8.72 (s, 2 H, picrate), 7.20 (s, 1 H, ArH), 7.08 (s, 1 H,
ArH), 7.06 (s, 2 H, ArH), 6.79 (s, 1 H, OH), 6.64–6.56 (m, 4 H,
ArH), 4.16–3.46 (m, 20 H, ArCH2, crown-CH2), 3.33–3.19 (m, 4
H, ArCH2), 2.90 (s, 3 H, OCH3), 1.34 (s, 9 H, tBu), 1.30 (s, 9 H,
tBu), 0.83 (s, 18 H, tBu) ppm. 13C NMR:
δ = 174.56
(COCH3),150.56, 150.33 (C-1), 147.88, 146.28 (C-4), 132.80 (C-2),
128.75 (C-6), 127.49, 126.31 (C-3, C-5), 125.73 (picrate), 75.01,
72.39, 71.44, 70.43 (OCH2CH2OCH2CH2O), 34.46, 32.48 (C-7),
32.28, 31.56 (C-8), 31.85 (ArCH2Ar), 21.82 (COCH3) ppm. LC-
MS: m/z = 887.57 (calcd. for [2 + K+]: 887.53). C60H74KN3O15
(1115.5): calcd. C 64.60, H 6.69, N 3.76; found C 65.13, H 6.37, N
3.85.
General Procedure for the Synthesis of Na+ and K+ Complexes of
1–5: A mixture of 0.05 mmol of the required ionophore (1–5) and
Na+/K+ picrate (0.5 mmol, ten-fold excess) was stirred in chloro-
form at room temperature for 24 h. The reaction mixture was then
filtered to remove unreacted picrate salt and the complex was ob-
tained by removing the solvent from the filtrate by rotary evapora-
tion. The yellow complex thus obtained was dissolved in a mini-
mum amount (ca. 3 mL) of dichloromethane (in which Na+/K+
picrate is almost insoluble) and filtered to remove trace quantities
of unreacted Na+/K+ picrate. The solvent was then removed from
the filtrate and the yellow product was dried in vacuo. The 1H
NMR spectra of the product did not show any signal correspond-
ing to free ligand or excess picrate anion. Yield: 90–95%.
Sodium Complex of 3 (3·Na+Pic–): 1H NMR (200 MHz, [D3]chloro-
form): δ = 8.82 (s, 2 H, picrate), 7.16 (s, 4 H, ArH), 6.53 (s, 4 H,
ArH), 4.28–3.72 (m, 20 H, ArCH2, crown-CH2), 3.35 (d, J =
13.0 Hz, 4 H, ArCH2), 2.61 (s, 6 H, OCH3), 1.26 (s, 18 H, tBu),
0.75 (s, 18 H, tBu) ppm. 13C NMR: δ = 171.58 (COCH3), 151.77,
151.51 (C-1), 146.64, 144.50 (C-4), 135.67 (C-2), 132.38 (C-6),
127.20 (picrate), 126.71, 125.88 (C-3, C-5), 75.23, 71.98, 71.17,
70.53 (OCH2CH2OCH2CH2O), 34.70, 32.32, 32.20, 31.93 (C-7, C-
8), 31.49 (ArCH2Ar), 21.34 (COCH3) ppm. LC-MS: m/z = 914.0
(calcd. for [3 + Na+]: 913.52). C62H77N3NaO16.5 (with 0.5H2O,
1150.5): calcd. C 64.73, H 6.75, N 3.65; found C 64.75, H, 6.92, N
3.32.
Sodium Complex of 4 (4·Na+Pic–): 1H NMR (200 MHz, [D3]chloro-
form): δ = 8.80 (s, 2 H, picrate), 7.10 (s, 4 H, ArH), 7.04 (s, 4 H,
ArH), 4.77 (s, 4 H, OCH2CO), 4.48 (d, J = 12.4 Hz, 4 H, Ar-
CH2Ar), 4.32 (q, J = 7.4 Hz, 4 H, OCH2CH3), 4.09 (m, 4 H, crown-
CH2), 3.86 (br., 12 H, crown-CH2), 3.36 (d, J = 12.2 Hz, 4 H,Ar),
1.33 (t, J = 7.0 Hz, 6 H, OCH2CH3), 1.13 (s, 18 H, tBu), 1.10 (s, 18
H, tBu) ppm. 13C NMR: δ = 171.44 (OCH2COOCH2CH3) 151.85,
150.53 (C-1), 148.78, 148.23 (C-4), 134.73 (C-2, C-6), 127.16 (pic-
rate), 126.60 (C-3, C-5), 77.04, 73.93, 71.27, 70.33, (OCH2CH2-
OCH2CH2O), 70.57 (OCH2COOCH2CH3), 62.60 (OCH2-
COOCH2CH3), 34.83, 34.80 (C-7), 31.95 (C-8), 31.10 (ArCH2Ar),
14.84 (OCH2COOCH2CH3) ppm. LC-MS: m/z = 1001.57 (calcd.
for [4 + Na+]: 1001.57). C66H84N3NaO18 (1229.6): calcd. C 64.47,
H 6.89, N 3.42; found C 64.77, H 6.88, N 3.66.
Sodium Complex of 1 (1·Na+Pic–): 1H NMR (200 MHz, [D3]chloro-
form): δ = 8.69 (s, 2 H, picrate), 7.03 (s, 2 H, OH), 7.03 (s, 4 H,
ArH), 6.73 (s, 1 H, ArH), 6.63 (s, 3 H, ArH), 4.22–4.16 (m, 12 H,
ArCH2Ar and crown-CH2 overlapped), 3.98–3.80 (m, 8 H, crown-
CH2), 3.30 (d, J = 13.6 Hz, 4 H, ArCH2Ar), 1.29 (s, 18 H, tBu),
1.20 (s, 3 H, tBu), 0.92, 0.83 (s, 15 H, tBu) ppm. 13C NMR: δ =
150.15, 148.15 (C-1), 143.27, 142.18 (C-4), 132.61 (C-2), 128.62 (C-
6), 127.50 (C-3), 126.35 (C-5), 125.99 (picrate), 75.84, 71.27, 70.24
(OCH2CH2OCH2CH2O), 34.59 (C-7), 32.40, 32.24, 31.60 (C-8),
31.93 (ArCH2Ar) ppm. LC-MS: m/z = 829.10 (calcd. for [1 + Na+]:
829.50). C58H72N3NaO14 (1057.51): calcd. C 65.84, H 6.85, N 3.96;
found C 65.46, H, 6.49, N 3.68.
Potassium Complex of 1 (1·K+Pic–): 1H NMR (200 MHz, [D3]chlo-
roform): δ = 8.70 (s, 2 H, picrate), 7.05 (s, 2 H, OH), 7.05 (s, 4 H,
ArH), 6.74, (s, 1 H, ArH), 6.61 (s, 3 H, ArH), 4.37–4.18 (m, 12 H,
ArCH2Ar and crown-CH2), 3.90–3.73 (m, 8 H, crown-CH2), 3.30
(d, J = 13.8 Hz, 4 H, ArCH2Ar), 1.30 (s, 18 H, tBu), 1.20 (s, 3 H,
tBu), 0.93 (s, 3 H, tBu), 0.81 (s, 12 H, tBu) ppm. 13C NMR: δ =
50.35, 148.17 (C-1), 143.74, 142.15 (C-4), 132.65 (C-2), 129.03 (C-
6), 127.74 (C-3), 126.55 (C-5), 125.89 (picrate), 75.75, 71.56, 71.35,
70.14 (OCH2CH2OCH2CH2O), 34.69, 34.59 (C-7), 32.43, 32.26,
31.62 (C-8), 31.85 (ArCH2Ar) ppm. LC-MS: m/z = 845.41 (calcd.
for [1 + K+]: 845.50). C58H72KN3O14 (1073.5): calcd. C 64.89, H
6.76, N 3.91; found C 65.15, H 6.54, N 3.67.
Potassium Complex of 4 (4·K+Pic–): 1H NMR (200 MHz, [D3]chlo-
roform): δ = 8.82 (s, 2 H, picrate), 7.10 (s, 4 H, ArH), 7.06 (s, 4 H,
ArH), 4.57 (s, 4 H, OCH2CO), 4.46 (d, J = 12.2 Hz, 4 H, Ar-
CH2Ar), 4.32 (q, J = 7.4 Hz, 4 H, OCH2CH3), 4.40–3.84 (m, 16
H, crown-CH2), 3.36 (d, J = 12.6 Hz, 4 H, ArCH2Ar), 1.33 (t, J =
6.8 Hz, 6 H, CH3), 1.13 (s, 18 H, tBu), 1.10 (s, 18 H, tBu) ppm.
13C NMR: δ = 170.76 (OCH2COOCH2CH3) 151.76, 151.12 (C-1),
148.31, 147.74 (C-4), 134.47, 134.37 (C-2, C-6), 127.17 (picrate),
126.68 (C-3, C-5), 77.13, 73.87, 71.50, 70.64, (OCH2CH2OCH2-
CH2O), 70.57 (OCH2COOCH2CH3), 62.63 (OCH2COOCH2CH3),
34.79 (C-7), 31.97 (C-8), 30.16 (ArCH2Ar), 14.86 (OCH2-
COOCH2CH3) ppm. LC-MS: m/z = 1017.1 (calcd. for [4 + K+]:
Sodium Complex of 2 (2·Na+Pic–): 1H NMR (200 MHz, [D3]chloro-
form): δ = 8.78 (s, 2 H, picrate), 7.05 (s, 2 H, ArH), 6.98 (s, 2 H, 1017.6). C66H84KN3O18 (1245.6): calcd. C 63.66, H 6.79, N 3.37;
ArH), 6.66 (br., 2 H, ArH), 6.63 (br., 2 H, ArH), 4.30–3.62 (m, 20 found C 64.15, H, 6.94, N 3.40.
3378
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 3369–3381

Cone p-tert-Butylcalix[4]arene-crown-5 Compounds
FULL PAPER
Sodium Complex of 5 (5·Na+Pic–): 1H NMR (200 MHz, [D3]chloro-
form): δ = 8.85 (s, 2 H, picrate) 7.06 (s, 4 H, ArH), 7.10 (s, 4 H,
ArH), 4.65 (s, 4 H, OCH2CO), 4.43 (d, J = 12.0 Hz, 4 H, ArCH2),
4.08–3.86 (m, 16 H, crown-CH2), 3.36 (d, J = 12.0 Hz, 4 H,
with a Vortex Genie mixer for 5 min. The tubes were then placed
in a centrifuge for 15 min. Aliquots of 0.5 mL of the organic phase
were carefully removed from each phase with a syringe and trans-
ferred to a 10-mL volumetric flask, which was brought to the mark
ArCH2), 1.14 (s, 18 H, tBu), 1.11 (s, 18 H, tBu) ppm. 13C NMR: with acetonitrile. The absorbance of each sample was then deter-
δ = 172.23 (OCH2COOH), 151.61, 150.18 (C-1), 148.77, 148.24 (C- mined (λ = 380 nm) after appropriate dilution (to make absorbance
4), 134.75 (C-2, C-6), 126.69 (picrate), 126.60, 126.49 (C-3, C-5),
within measuring limit). The molar ratio of picrate/host (R) was
74.03, 71.45, 70.68, 69.96 (OCH2CH2OCH2CH2O), 68.25 (OCH2- then calculated from Equation (2).
COOH), 34.81, 34.74 (C-7), 31.93, 31.89 (C-8) 30.37 (ArCH2Ar)
Determination of Distribution Constants (Kd) of Picrate Anion: A
ppm. LC-MS: m/z = 945.0 (calcd. for [5 + Na+]: 945.51).
C62H78N3NaO19 (with H2O, 1191.5): calcd. C 62.50, H 6.60, N
3.52; found C 62.67, H, 6.75, N 3.64.
0.02  metal picrate solution in 100 mL of water was added to
100 mL of chloroform and the mixture was shaken in a separating
funnel for 5–6 h. The layers of the mixture were then allowed to
separate overnight (ca. 12 h). The lower layer (chloroform) was
then carefully transferred into a round-bottomed flask and the sol-
vent evaporated with a rotary evaporator. The residue was quanti-
tatively transferred with acetonitrile to a 10-mL volumetric flask
and diluted with acetonitrile up to the mark. The absorbance of
the organic layer was measured spectrophotometrically and the
value of Kd was determined from Equation (3).
Potassium Complex of 5 (5·K+Pic–): 1H NMR (200 MHz, [D3]chlo-
roform): δ = 8.87 (s, 2 H, picrate), 7.12 (s, 4 H, ArH), 7.04 (s, 4 H,
ArH), 4.65 (s, 4 H, OCH2CO), 4.47 (d, J = 12.0 Hz, 4 H, ArCH2),
4.07–3.82 (m, 16 H, crown-CH2), 3.36 (d, J = 12.2 Hz, 4 H,
ArCH2), 1.17 (s, 18 H, tBu), 1.07 (s, 18 H, tBu) ppm. 13C NMR:
δ = 171.50 (OCH2COOH), 153.81, 152.13 (C-1), 148.43 (C-4),
134.56, 134.38 (C-2, C-6), 126.83, 126.63 (picrate, C-3, C-5), 74.05,
71.62, 70.69, 70.32 (OCH2CH2OCH2CH2O), 68.72, (OCH2-
COOH), 34.77 (C-7), 32.01, 31.90 (C-8) 30.37 (ArCH2Ar) ppm.
LC-MS: m/z = 961.57 (calcd. for [5 + K+]: 961.51). C62H78KN3O19
(with H2O, 1207.5): calcd. C 61.67, H 6.51, N 3.48; found C 61.16,
H, 6.80, N 3.24.
X-ray Crystallography for 1–4, 1·K+Pic–, 4·Na+Pic–, 4·K+Pic– and
5·K+Pic–: Crystal data collection and refinement parameters for all
eight compounds are given in Table 5. A suitable crystal of each
compound was selected, coated with Paratone oil and mounted
with epoxy cement on the tip of a fine glass fibre. Data sets were
obtained with a Bruker Smart APEX diffractometer with a CCD
area detector using graphite-monochromated Mo-Kα radiation (λ
= 0.71073 Å) at liquid nitrogen temperature (100 K). Data frames
were processed using the Bruker SAINT program.[21] Intensities
were corrected for Lorentz, polarisation, decay effects and an ab-
sorption correction was applied using SADABS.[22] The structure
was solved by direct methods using SHELXS-97[23] and refined on
F2 using SHELXL-97.[24] The non-hydrogen atoms were located
directly by successive Fourier calculations and were refined aniso-
tropically in all the solvated ligand structures except for 2. In 2,
three of the tert-butyl groups attached to the phenyl rings were
found to be disordered over two positions (with occupancy factor
0.50) and these disordered tert-butyl groups were refined only iso-
tropically. In the case of 1·K+Pic–, the lattice THF molecule is dis-
ordered extensively, and in the case of 4·K+Pic– two of the tert-
butyl groups, the lattice solvent molecules (benzene and THF) and
the nitrate groups of the picrate anions showed dynamic disorder;
all these disordered atoms were refined isotropically. Since it was
very difficult to determine the dynamic disorder present in both
the tert-butyl groups and lattice solvent molecules, these disorders
were taken care of by assigning a tentative occupancy factor for
the reasonably good peaks appearing in the difference Fourier map
depending upon their peak heights. Anisotropic full-matrix refine-
ment of all atoms, except the disordered atoms, was carried out
using SHELXL-97 until convergence was reached (no significant
peaks in the difference Fourier map). The inclusion of all the disor-
dered atoms with the occupancy factor tentatively assigned, de-
pending upon the peak height, significantly reduced the refinement
parameters, thus implying the correct treatment of the disorder; a
constrained or rigid model refinement was not possible in this case.
In the case of 4·Na+Pic–, it was not possible to locate the picrate
anions and severely disordered solvents (THF and toluene from
which crystals for X-ray study were grown) present in the lattice
from the difference Fourier map. A suitable disorder model was
not obtained and the picrate anion and solvent contribution was
subtracted from the reflection data using the program
SQUEEZE.[25] A combination of SQUEEZE and PLATON was
applied to resolve severely disordered molecules of solvents (THF
and toluene) within the asymmetric unit, which also contains one
Determination of Selectivity of the Ionophores: The selectivity of the
ionophores towards Na+, K+, Mg2+, and Ca2+ was determined
using an equimolar mixture of the picrate salts of these ions accord-
ing to a procedure described in the literature.[9] In a typical pro-
cedure, equal volumes (15 mL) of an aqueous solution of an equi-
molar mixture of picrate salts (Na+, K+, Mg2+, Ca2+; 0.005  each)
and a CH2Cl2 solution (15 mL) of the required ionophore (0.005 )
were mixed and vigorously shaken in a vortex mixer for 15 min.
The solution was then transferred to a separating funnel and al-
lowed to stand for 4–5 h. The dichloromethane layer was then sepa-
rated and transferred to a crucible, stripped of solvent by gentle
heating in a water bath, and then heated in a furnace at 550 °C for
4–5 h. The residue was dissolved in deionized water (ca. 5 mL) and
filtered through 0.2-µm filter paper. The relative concentrations of
the cations in the filtrate were determined by ion chromatography
on an Ion Pac CS12 (2 mm) analytical column and 20 m methyl-
sulfonic acid as eluent with a flow rate of 0.25 mLmin–1. Quantifi-
cation was made using a standard solution containing a mixture of
NaCl, KCl, MgCl2, and CaCl2 (15 ppm each). A blank experiment,
without added ionophore, was carried out under similar experi-
mental conditions; no detectable amount of picrate was observed
in the dichloromethane layer.
Determination of Association Constants (Ka) with Na+ and K+ Pic-
rate: Association constants of the ionophores 1–5 with Na+ and
K+ were determined according to a published procedure using pic-
rate as anion.[17,18] This involves two-phase (water/chloroform) ex-
traction of the metal complex followed by determination of the
ratios of picrate to host (R) in the organic phase and determination
of the distribution constants (Kd) of the picrate salts between water
and chloroform [Equations (1)–(3)].
Determination of Molar Ratio of Picrate/Host in the Organic Layer
(R): Aqueous solutions were prepared that were 0.01  in the pic-
rate of Na+ and K+. Into each of two 10-mL centrifuge tubes was
transferred 1 mL of the appropriate picrate solution with a syringe;
1-mL aliquots of a previously prepared chloroform solution that
was 0.01  in host were then added with a syringe to each tube.
The tube was covered immediately with a rubber septum to prevent
evaporation and the two layers in each tube were mixed thoroughly
Eur. J. Inorg. Chem. 2006, 3369–3381
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3379

P. Agnihotri, E. Suresh, P. Paul, P. K. Ghosh
Table 5. Experimental data for the X-ray diffraction studies on single crystals of 1–4, 1·K+Pic–, 4·Na+Pic–, 4·K+Pic–, and 5·K+Pic–.
FULL PAPER
Compound
1
2
3
4
1·K+Pic–
4·Na+Pic–
4·K+Pic–
5·K+Pic–
Empirical formula
C108H142N2O14 C58H51N2O8 C76H84N3O9 C64H88N2O11 C62H72KN3O15 C60H82NaNO12 C82H70KN3O19 C62H58N3KO19
Formula mass
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
Z
1692.24
12.2085(12)
35.618(4)
46.261(5)
90
90
90
8
904.01
1133.68
1061.36
1138.33
1002.25
13.570(3)
32.711(8)
19.403(5)
90
105.859(5)
90
4
1440.51
15.4140(12)
20.1863(16)
24.673(2)
90
97.7120(10)
90
4
1188.21
19.1372(13)
16.0996(12)
20.0525(14)
90
97.772(2)
90
4
20.9878(13)
12.7867(8)
21.2898(13)
90
111.2090(10) 78.6250(10)
90
14.3741(9)
14.7658(9)
17.2358(11)
66.2500(10)
12.9539(9)
13.7659(9)
16.9973(11)
82.6790(10)
88.1120(10)
80.4720(10)
2
12.4879(11)
15.1378(13)
16.1659(14)
92.793(2)
94.146(2)
100.515(2)
2
67.2500(10)
2
4
V [Å3]
Crystal system
Space group
λ [Å]
20116(4)
orthorhombic monoclinic
5326.4(6)
3084.2(3)
triclinic
P1
0.71073
1.221
0.205
1212
2964.6(3)
triclinic
P1
0.71073
1.189
0.080
1148
2990.8(4)
triclinic
P1
0.71073
1.264
0.157
1208
8285(3)
monoclinic
P21/n
0.71073
0.804
7607.6(10)
monoclinic
P21/n
0.71073
1.258
6121.5(8)
monoclinic
P21/c
0.71073
1.289
¯
¯
¯
Pbca
0.71073
1.118
0.073
7328
P21/c
0.71073
1.127
0.075
1908
ρcalcd. [gcm–3
]
µ [mm–1
F(000)
]
0.059
2164
0.143
3032
0.162
2488
Temp. [K]
100
100
100
100
100
100
100
100
Rflns collected/unique 60303/13142
20483/6939
0.0247
1.195
0.0764/
0.2149
0.0816/
0.2184
18195/13407 25645/13342 18244/13194
39935/14475
0.0981
0.856
0.0910/
0.2134
0.1527/
0.2404
44443/17616
0.0367
1.044
0.0945/
0.2720
0.1360/
0.3056
24283/7976
0.084
1.073
0.1180/
0.3039
0.1631/
0.3356
R(int)
GOF on F2
R1/wR2 ([IϾ2σ(I)]
0.1332
1.065
0.1203/
0.2972
0.1867/
0.3498
0.0172
1.013
0.0160
1.038
0.0247
1.009
0.0651/
0.1669
0.0809/
0.1801
0.0518/
0.1427
0.0592/
0.1492
0.0665/
0.1633
0.0908/
0.1778
R1/wR2 (all data)
crystallographically independent picrate anion. Within the 3460 Å3
void space occupied by solvent molecules and the unresolved
anion, a total of 810 electrons were calculated per unit cell. After
correction for the one unresolved counteranion per asymmetric
unit, corresponding to 115 electrons, the rest of the electron density
per asymmetric unit (87.6) can be equated for by the presence of
approximately one molecule of THF and one molecule of toluene
in the asymmetric unit. A refinement using reflections modified
by the SQUEEZE procedure behaved well, and the geometry of
4·Na+Pic– and, of course, the R factors and GOF values were sig-
nificantly improved. H atoms (except for the H atoms attached to
the disordered non-hydrogen atoms and some of the lattice solvent
hydrogen atoms) were calculated on the basis of geometric criteria
and were treated with a riding model in subsequent refinements
using the SHELXL default parameters. The molecular graphics of
the crystal structures were generated using ORTEP, PLATON and
Mercury.[26–28] CCDC-297554 to -297561 (for complexes 1–4,
1·K+Pic–, 4·Na+Pic–, 4·K+Pic–, and 5·K+Pic–, respectively) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[1] a) C. D. Gutsche, Calixarenes, The Royal Society of Chemistry,
Cambridge, UK, 1989; b) Calixarenes, A Versatile Class of
Macrocyclic Compounds (Eds.: J. Vicens, V. Bohmer), Kluwer,
Dordrecht, Netherlands, 1991; c) V. Boehmer, Angew. Chem.
1995, 107, 785; Angew. Chem. Int. Ed. Engl. 1995, 34, 713; d) A.
Ikeda, S. Shinkai, Chem. Rev. 1997, 97, 1713; e) C. D. Gutsche,
Calixarenes Revisited, The Royal Society of Chemistry, Cam-
bridge, UK, 1998; f) Calixarenes in Action (Eds.: L. Mandolini,
R. Ungaro), Imperial College Press, London, 2000; g) F. Ar-
naud-Neu, M. A. McKervey, M. J. Schwing-Weill, Calixarenes
2001 (Eds.: Z. Asfari, V. Bohmer, J. Harrowfield, J. Vicens),
Kluwer Academic Publishers, Dordrecht, The Netherlands,
2001; h) A. Casnati, F. Sansone, R. Ungaro, Adv. Supramol.
Chem. 2003, 9, 165–218.
[2] a) F. Arnaud-Neu, E. M. Collins, M. Deasy, G. Ferguson, S. J.
Harris, B. Kaitner, A. J. Lough, M. A. McKervey, E. Marques,
B. L. Ruhl, M. J. Schwing-Weill, E. M. Seward, J. Am. Chem.
Soc. 1989, 111, 8681; b) A. Ikeda, S. Shinkai, J. Am. Chem.
Soc. 1994, 116, 3102; c) S. Leon, D. A. Leigh, F. Zerbetto,
Chem. Eur. J. 2002, 8, 4854; d) G. Guillemot, E. Solari, C.
Rizzoli, C. Floriani, Chem. Eur. J. 2002, 8, 2072; e) A. Shivan-
yuk, M. Saadioui, F. Broda, I. Thondorf, M. O. Vysotsky, K.
Rissanen, E. Kolehmainen, V. Boehmer, Chem. Eur. J. 2004,
10, 2138.
[3] a) P. L. H. M. Cobben, R. J. M. Egberink, J. G. Bomer, P.
Bergveld, W. Verboom, D. N. Reinhoudt, J. Am. Chem. Soc.
1992, 114, 10573; b) M. H. B. G. Gansey, W. Verboom,
F. C. J. M. van Veggel, V. Vetrogon, F. Arnaud-Neu, M.-J.
Schwing-Weill, D. N. Reinhoudt, J. Chem. Soc., Perkin Trans.
2 1998, 2351; c) J. Rebek Jr, Chem. Commun. 2000, 637; d) D.
Diamond, K. Nolan, Anal. Chem. 2001, 73, 22A (invited A-
Section article); e) A. F. D. de Namor, D. Kowalska, E. E. Cas-
tellano, O. E. Piro, F. J. S. Velarde, J. V. Salas, Phys. Chem.
Chem. Phys. 2001, 3, 4010; f) S. E. Matthews, P. Schmitt, V.
Felix, M. G. B. Drew, P. D. Beer, J. Am. Chem. Soc. 2002, 124,
1341; g) P. R. A. Webber, A. Cowley, M. G. B. Drew, P. D. Beer,
Chem. Eur. J. 2003, 9, 2439.
Supporting Information Available (see footnote on the first page of
this article): Tables S1 and S2 contain hydrogen-bonding param-
eters of the ionophores and metal complexes, respectively. Figures
S1–S7 show packing diagrams of 2–4, 1·K+Pic–, 4·Na+Pic–,
4·K+Pic–, and 5·K+Pic–, respectively.
Acknowledgments
We are grateful to the Department of Science and Technology
(DST), Government of India, for financial support. We also thank
CSIR, New Delhi for generous support towards infrastructure and
core competency. P. A. gratefully acknowledges CSIR for awarding
a Senior Research Fellowship (SRF).
3380
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 3369–3381

Cone p-tert-Butylcalix[4]arene-crown-5 Compounds
FULL PAPER
[4] a) E. Ghidini, F. Ugozzoli, R. Ungaro, S. Harkema, A. A. El-
Fadl, D. N. Reinhoudt, J. Am. Chem. Soc. 1990, 112, 6979; b)
A. Casnati, A. Pochini, R. Ungaro, F. Ugozzoli, F. Arnaud,
S. Fanni, M.-J. Schwing, R. J. M. Egberink, F. de Jong, D. N.
Reinhoudt, J. Am. Chem. Soc. 1995, 117, 2767; c) A. Ikeda, T.
Tsudera, S. Shinkai, J. Org. Chem. 1997, 62, 3568; d) J. Guillon,
J.-M. Leger, P. Sonnet, C. Jarry, M. Robba, J. Org. Chem. 2000,
65, 8283; e) K. Takahashi, A. Gunji, D. Guillaumont, F. Pichi-
[11] a) D. N. Reinhoudt, P. J. Dijkstra, P. J. A. in’t Veld, K. E.
Bugge, S. Harkema, R. Ungaro, E. Ghidini, J. Am. Chem. Soc.
1987, 109, 4761; b) P. J. Dijkstra, J. A. J. Bbrunink, K. E.
Bugge, D. N. Reinhoudt, S. Harkema, R. Ungaro, F. Ugozzoli,
E. Ghidini, J. Am. Chem. Soc. 1989, 111, 7567.
[12] a) C. D. Gutsche, M. Iqbal, K. Nam, I. Alam, Pure Appl.
Chem. 1988, 60, 483; b) K. Iwamoto, S. Shinkai, J. Org. Chem.
1992, 57, 7066.
erri, S. Nakamura, Angew. Chem. Int. Ed. 2000, 39, 2925; f) [13] P. D. Beer, M. G. B. Drew, A. Grieve, M. I. Ogden, J. Chem.
J. S. Kim, O. J. Shon, J. W. Ko, M. H. Cho, I. Y. Yu, J. Vicens,
J. Org. Chem. 2000, 65, 2386; g) H. Zhou, K. Surowiec, D. W.
Purkiss, R. A. Bartsch, Org. Biomol. Chem. 2005, 3, 1676; h) J.
Luo, Q.-Y. Zheng, C.-F. Chen, Z.-T. Huang, Chem. Eur. J.
2005, 11, 5917; i) I. Oueslati, R. Abidi, P. Thuery, M. Nierlich,
Z. Asfari, J. Harrowfield, J. Vicens, Tetrahedron Lett. 2000, 41,
8263; j) L. Prodi, F. Bolletta, M. Montalti, N. Zaccheroni, A.
Casnati, F. Sansone, R. Ungaro, New J. Chem. 2000, 24, 155; k)
A. Casnati, N. Della Ca, F. Sansone, F. Ugozzoli, R. Ungaro,
Tetrahedron 2004, 60, 7869.
Soc., Dalton Trans. 1995, 3455.
[14] a) R. P. Thummel, Y. Jahng, Inorg. Chem. 1986, 25, 2527; b)
R. P. Thummel, F. Lefoulon, J. D. Korp, Inorg. Chem. 1987, 26,
2370; c) P. Paul, B. Tyagi, A. K. Bilakhiya, M. M. Bhadbhade,
E. Suresh, G. Ramachandraiah, Inorg. Chem. 1998, 37, 5733.
[15] C. Jaime, J. de Mendoza, P. Prados, P. M. Nieto, C. Sanchez,
J. Org. Chem. 1991, 56, 3372.
[16] a) I. Oueslati, R. Abidi, P. Thuery, M. Nierlich, Z. Asfari, J.
Harrowfield, J. Vicens, Tetrahedron Lett. 2000, 41, 8263; b) I.
Oueslati, R. Abidi, P. Thuery, J. Vicens, J. Inclusion Phenom.
2003, 47, 173; c) S. Banthia, A. Samanta, Org. Biomol. Chem.
2005, 3, 1428; d) A. Dubes, K. A. Udachin, P. Shahgaldian,
A. N. Lazar, A. W. Coleman, J. A. Ripmeester, New J. Chem.
2005, 29, 1141.
[17] S. S. Moore, T. L. Tarnowski, M. Newcomb, D. J. Cram, J. Am.
Chem. Soc. 1977, 99, 6398.
[18] a) K. E. Koeing, G. M. Lein, P. Stuckler, T. Kaneda, D. J.
Cram, J. Am. Chem. Soc. 1979, 101, 3553; b) D. J. Cram, G. M.
Lein, J. Am. Chem. Soc. 1985, 107, 3657.
[5] a) R. Ungaro, A. Casnati, F. Ugozzoli, A. Pochini, J.-F. Dozoli,
C. Hill, H. Rouquette, Angew. Chem. Int. Ed. Engl. 1994, 33,
1506; b) V. Lamare, J.-F. Dozol, F. Ugozzoli, A. Casnati, R.
Ungaro, Eur. J. Org. Chem. 1998, 1559; c) J. S. Kim, J. H. Pang,
I. Y. Yu, W. K. Lee, I. H. Suh, J. K. Kim, M. H. Cho, E. T.
Kim, D. Y. Ra, J. Chem. Soc., Perkin Trans. 2 1999, 2, 837; d)
A. Casnati, A. Pochini, R. Ungaro, C. Bocchi, F. Ugozzoli,
R. J. M. Egberink, H. Struijk, R. Lugtenberg, F. D. Jong, D. N.
Reinhoudt, Chem. Eur. J. 1996, 2, 436.
[6] a) J. S. Kim, I. H. Suh, J. K. Kim, M. H. Cho, J. Chem. Soc.,
Perkin Trans. 1 1998, 2307; b) J. S. Kim, W. K. Lee, I. H. Suh,
J.-G. Kim, J. Yoon, J. H. Lee, J. Org. Chem. 2000, 65, 7215; c)
I. Leray, Z. Asfari, J. Vicens, B. Valeur, J. Chem. Soc., Perkin
Trans. 2 2002, 1429; d) J. S. Kim, O. J. Shon, S. H. Yang, J. Y.
Kim, M. J. Kim, J. Org. Chem. 2002, 67, 6514; e) S. H. Lee,
J. Y. Kim, J. Ko, J. Y. Lee, J. S. Kim, Org. Chem. 2004, 69, 2902;
f) Z. Asfari, C. Bressot, J. Vicens, C. Hill, J.-F. Dozol, H. Rou-
quette, S. Eymard, V. Lamare, B. Tournois, Anal. Chem. 1995,
67, 3133; g) F. Arnaud-Neu, Z. Asfari, B. Souley, J. Vicens,
New J. Chem. 1996, 20, 453.
[19] C. D. Gutsche, M. Iqwal, Org. Synth. 1989, 68, 234.
[20] D. D. Perrin, W. L. F. Armarego, D. R. Perrin, Purification of
Laboratory Chemicals, 2nd ed., Pergamon Press, Oxford, U. K.,
1980.
[21] Bruker Analytical X-ray Instruments, Inc., Madison, WI.
[22] G. M. Sheldrick, University of Göttingen, Göttingen, Ger-
many, 1996.
[23] G. M. Sheldrick, SHELXS97, a program for crystal structure
solution, University of Göttingen, Germany, 1997.
[24] G. M. Sheldrick, SHELXL97, a program for crystal structure
refinement, University of Göttingen, Germany, 1997.
[25] A. L. Spek, SQUEEZE, University of Utrecht, The Nether-
lands, 1992.
[7] Z. Brzozka, B. Lammerink, D. N. Reinhoudt, J. Chem. Soc.,
Perkin Trans. 2 1993, 1037.
[8] H. Tsue, T. Takimoto, R. Tamura, C. Kikuchi, S. Tanaka, Lett.
Org. Chem. 2004, 1, 276.
[9] a) E. Suresh, P. Agnihotri, B. Ganguly, P. Bhatt, P. S. Subra-
manian, P. Paul, P. K. Ghosh, Eur. J. Inorg. Chem. 2005, 2198;
b) P. Agnihotri, E. Suresh, B. Ganguly, P. Paul, P. K. Ghosh,
Polyhedron 2005, 24, 1023.
[26] C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
[27] A. L. Spek, PLATON-97, University of Utrecht, The Nether-
lands, 1997.
[28] Mercury 1.3, supplied with Cambridge Structural Database
CCDC, Cambridge, UK, 2003–2004.
[10] H. Zhou, K. Surowiec, D. W. Purkiss, R. A. Bartsch, Org. Bi-
omol. Chem. 2006, Advance Article in Web.
Received: April 20, 2006
Published Online: July 25, 2006
Eur. J. Inorg. Chem. 2006, 3369–3381
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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