Synthesis and inclusion properties of C3-symmetric triazole derivatives based on hexahomotrioxacalix[3]arene

Article abstract of DOI:10.1039/c2nj40599g

A series of metal ion receptors cone-7,15,23-tri-tert-butyl-25,26,27- tris{[1H-(1-arylmethyl)(1,2,3-triazolyl)]-4-methoxy}hexahomotrioxacalix[3] arenes, cone-3-cone-5, have been synthesized from 7,15,23-tri-tert-butyl-25,26, 27-tris(propargyloxy)hexahomotrioxacalix[3]arene 2via click chemistry. The complexation properties of the receptors cone-3-cone-5 toward the selected binding of heavy metal and transition metal ions have been evaluated. The structure of cone-3 was elucidated by single-crystal X-ray crystallography. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012.

Full text of DOI:10.1039/c2nj40599g

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ARTICLE TYPE
Synthesis and inclusion properties of C3-symmetric triazole derivatives
based on hexahomotrioxacalix[3]arene
b
Cheng-Cheng Jina, Takashi Kinoshitaa, Hang Conga, Xin-Long Ni*b, Xi Zeng , David L. Hughesc, Carl
Redshawc and Takehiko Yamato*a
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x6
A series of metal ion receptors cone-7,15,23-tri-tert-butyl-25,26,27-tris{[1H-(1-arylmethyl)(1,2,3-triazolyl)]-4-methoxy} andhexahomo-
trioxacalix[3]arenes cone-3–cone-5 have been synthesized from 7,15,23-tri-tert-butyl-25,26,27-tris(propargyloxy)hexahomotrioxa-
calix[3]arene 2 via Click chemistry. The complexation properties of the receptors cone-3–cone-5 toward the selected binding of heavy
10 metal and transition metal ions have been evaluated. The structure of cone-3 was elucidated by single-crystal X-ray crystallography.
‘click’ reaction) has provided a straightforward molecular
50 linking strategy which has been adopted in a wide range of
Introduction
applications in the biological, materials, and medicinal
chemistry areas. 9 The properties of the 1,2,3-triazole moiety as
Over the last few decades, the development of artificial
receptors for ion recognition, complexation and transportation
has proved to be an important topic in both environmental and
15 supramolecular chemistry.1 Calixarenes and their derivatives
are macrocyclic compounds possessing a hydrophobic cavity,
which can bind various organic, inorganic or biological
molecules and be widely used as convenient and versatile
building blocks in supramolecular chemistry.2 They can be
20 modified to give rise to a great variety of derivatives with
tuneable binding properties. For example, calix[4]arene
derivatives incorporating crown ethers, amides, esters, and
carboxylic acid groups have been shown to selectively extract
metal ions.3 Hexahomotrioxacalix[3]arene is related to
25 calix[4]arene and 18-crown-6 ether; it has a three-dimensional
cavity with a potentially C3-symmetric structure, and is
attractive to supramolecular chemists as a receptor for metal
cations,4 ammonium cations,5 and fullerene derivatives.6
Introduction of larger alkyl groups on the phenolic oxygens of
30 calix[4]arenes led to a situation where the OR groups cannot
rotate through the annulus.7 Although there exist four possible
conformational isomers in calix[4]arenes, viz. cone, partial-
cone, 1,2-alternate and 1,3-alternate, only two different
conformational isomers, "cone" and "partial-cone", should be
35 expected in hexahomotrioxacalix[3]arene. Thus, the
conformational isomerism should be much simpler in O-
alkylated hexahomotrioxacalix[3]arenes. Shinkai et al reported
the conformer distribution of the hexahomotrioxacalix[3]arene
ligand set, and found that the partial-cone is sterically less
40 crowded than the cone and therefore formed predominantly
regardless of the O-alkylation conditions.7d The cone form
results only in the presence of a templating metal such as NaH
which strongly interacts with the phenolic oxygens, with
substituent groups such as ethoxycarbonylmethyl or N,N-
45 diethylamino- carbonylmethyl groups present in the reaction
system.8
the linker in multivalent derivatives can be exploited for the
binding of cations, such as in the accelerated catalysis of the
55 “click” reaction by in situ formation of copper complexes. The
coordination chemistry of triazoles has also been investigated
through the formation of transition metal complexes of a range
of bis-triazoles.10 In calixarene chemistry, the copper-
catalyzed 1,2,3-triazole was first exploited for the
60 functionalization of the calixarene scaffold by Zhao and co-
workers in 2005.11 More relevant to this work has been the
incorporation of functionalized triazoles on to a tailored
calixarene scaffold for the selective binding of various metal
cations.12 Very recently, we also have developed a series of
65 triazole-derived chemosensors for selective binding of heavy
metal ions based on calixarene scaffolds.13 For example,
chemosensors derived from hexahomotrioxacalix[3]arene
exhibited a highly selective affinity for the Pb2+ cation through
enhancement of the monomer emission of pyrene in both
70 organic and organic/aqueous solution,13a whereas a similar
outcome was observed for the Zn2+ ion only in a purely
organic medium.13b Indeed, triazole-appended receptors also
have a strong affinity for other heavy metal ions such as Cu2+
and Hg2+, and substantial binding constants have been
75 evidenced by slightly changing the fluorescence properties of
the pyrene in different solvents. Interestingly, Rao et al
reported a calix[4]arene sensor12f which incorporated two
potential binding sites: one bistriazole binding pocket and
another consisting of two Schiff base groups functionalised
80 with hydroxymethyl groups. The Rao system appeared
extremely sensitive and was selective towards the sensing of
1
Zn2+ over other tested divalent metal ions. However, H NMR
studies revealed that Zn2+ only binds at the Schiff base site.
Similar studies were conducted by Xie and co-workers14 by
85 attaching pyridin-2′-yl-1,2,3-triazole fluorophores to β-
cyclodextrin and calix[4]arene, and their observations
indicated that chemical modification of a calixarene represents
an effective and versatile way of producing receptors with
Recently the application of Cu(I)-catalyzed 1,3-dipolar
cycloaddition of an azide and a terminal alkyne (CuAAC
ciety of Chemistry [year]
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highly selective ion-binding properties. Even minor changes in
the regioselective functionalization or conformation of the
chemically modified calixarenes can be associated with
dramatic changes in the complexation properties. As a part of
our research on the construction of calixarene-derived
chemosensors, we herein report the synthesis and
characterisation of a series of triazole derivatives based on
hexahomotrioxacalix[3]arenes fixed in the cone conformation
using O-propargyl groups, together with their binding
2) revealed that there are two different conformations in the
40 unit cell (1:1 ratio), and that one exhibits a classical partial-
cone structure (Fig. 2a) while the other exhibits an
intermediate between partial-cone and cone structure (Fig. 2b).
5
10 properties towards heavy- and transition-metal ions.
Results and Discussion
A series of triazole derivatives based on hexahomo-
trioxacalix[3]arene was synthesized by the method shown in
Scheme 1.
45
Scheme 2 Complexation of 2 with n-BuNH3ClO4.
1
Fig. 1 (a) Partial H NMR spectra of 2 in a CDCl3/CD3CN (10:1 v/v)
50 solution and (b) in the presence of 1.0 equiv of n-BuNH3ClO4.
15
Scheme 1 Synthesis of triazole derivatives based on hexahomotrioxa-
calix[3]arene with the cone conformation, cone-3–5.
Reaction of the calix[3]arene 1 with propargyl bromide in the
1
presence of Cs2CO3 afforded 2 in 42% yield.13a The H NMR
20 spectrum of 2 shows two singlets for the tert-butyl protons at δ
1.22 and 1.27 ppm (relative intensity 2:1) and multiplet signals
for the bridging methylene protons in the region of δ 4.0 to
4.85 ppm. Furthermore, the resonances of the aromatic protons
appeared at δ 7.23 and 7.30 ppm, consistent with 2 adopting a
25 partial-cone structure. In order to confirm whether compound
2 can be converted from partial-cone to cone structure, 1H
NMR titration experiments of 2 with n-BuNH3ClO4 were
carried out in a solution of CDCl3/CD3CN (10:1 v/v). The
partial 1H NMR spectra of 2 in the absence and presence of n-
30 BuNH3+ClO4 are shown in Fig. 1. Upon interaction with n-
BuNH3 , the bridging methylene protons (Hax and Heq) clearly
appeared at δ 4.98 and 4.29 ppm, and the aromatic protons also
Fig. 2 The X-ray structure of 2 with two different conformations in the
unit cell.13a
1
shifted to a single peak at δ 7.30 ppm. The H NMR changes
indicated that the O-propargyl conformation of 2 also allowed
35 oxygen-through-the-annulus rotation on interaction with the C3
symmetry structure of n-BuNH3 and thus interconversion
+
55 Fig. 3 Plausible reaction pathways for hexahomotrioxacalix[3]arene
derivatives from mobile-structure to cone-structure by the Cu(I)
catalysed ‘click’ reaction.
from partial-cone to cone structure of 2 had occurred (Scheme
2). On the other hand, the X-ray crystal structure of 213a (Fig.
2
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Following on from these observations, we reasoned that
the template effect of the Cu(І) ions should play an important
role in the formation of cone products of hexahomotrioxacalix-
[3]arene (Fig. 3).15 We then showed that a series of cone
‘flattened cone’ shape, with the phenolic O atoms O(1) and
O(3) pointing inwards towards the centre of the ring, and the
30 third O atom, O(2), pointing outwards.
Similarly, the 1H NMR spectra of compounds cone-4 and
cone-5 also suggest that the pyridine triazole derivatives adopt
the cone conformation. Interestingly, the chemical shift of the
protons on the triazole rings of cone-3–cone-5 appeared at δ
35 7.61, 7.85, and 7.77 ppm, respectively; the different chemical
shifts of these protons may be attributed to the interaction of
the pyridine nitrogen atom with the triazole protons. For
example, in cone-4, there are two cavities, i.e. rings of
nitrogen-rich groups, in the lower rim substituents; one is
40 formed from the nitrogen atoms of the triazole ring in each
chain, and the other from the nitrogen atoms of the three
pyridine rings. These artificial receptors, which have electronic
donor and acceptor moieties in their structure, can form intra-
or inter-molecular hydrogen bonds, depending partly on the
45 solvent. For example, DMSO, MeCN, and THF are potential
acceptor molecules with which the triazole C-H groups can
form intermolecular hydrogen bonds. In other solvents, such as
CHCl3, intramolecular hydrogen bonds may be formed. It was
thought that the geometric structure of compound cone-4
50 might make it feasible, in CHCl3, to form intramolecular
hydrogen bonds between the hydrogen atom of the triazole
ring and the nitrogen atom of the pyridine. This appears likely
since the chemical shifts of the protons on the triazole rings
move downfield.
5
conformations
of
triazole
derivatives
based
on
hexahomotrioxacalix[3]arene, cone-3–cone-5, could be
synthesized by the Cu(I)-catalyzed 1,3-dipolar cycloaddition
reaction of 2 with azides under click conditions with yields of
72, 42 and 43 %, respectively. The 1H NMR spectrum of cone-
10 3, for example, showed a singlet for the tert-butyl protons at δ
1.08 ppm, and singlets for ArOCH2-triazole and triazole-CH2-
4-methoxybenzene at δ 4.55 and 5.29 ppm, respectively,
indicating a C3-symmetrical cone structure for this compound.
Moreover, single crystal X-ray diffraction analysis of cone-3
15 confirmed its conformation (but distorted considerably from
C3-symmetry) as shown in Fig. 4. The calixarene ring forms a
55
In order to investigate the ionophoric affinities of the
compounds cone-3–cone-5 for cations, the extraction ability
was determined by solvent extraction from the aqueous phase
to the organic phase (methylene dichloride). The results are
summarized in Fig. 5, and we see that compounds cone-3–
60 cone-5 showed high extractability towards Ag+, Cu2+, Pb2+ and
Hg2+ cations. This pronounced extractability for Ag+ has not
been observed with other triazole-modified calixarene-derived
compounds.12, 13a,b The association constants of receptors cone-
3–cone-5 for the picrates of silver cations were determined in
65 CH2Cl2/THF (99:1, v/v) according to the Benesi-Hildebrand
equation,16 and were calculated, for complexation with Ag+, to
be 3.2 × 103, 2.1 × 104 and 4.7 × 103 M-1, respectively. After
addition of compounds cone-3–cone-5 to the solution of
picrate, the absorption maximum peak was shifted from 358
70 nm to 378 nm, indicating the formation of complexes.
(a)
20
(b)
75 Fig. 5 Liquid-liquid extractability of compounds cone-3–cone-5 with
metal cations ([Host] = 1.25 × 10−4 mol in CH2Cl2, [Guest] = 1.25 ×
10−4 mol in water at 25 °C).
Fig. 4 X-ray structure of compound cone-3 showing (a) the whole
molecule, and (b) the upper-rim groups, viewed on to the calix-ring
25 plane. The thermal ellipsoids of the O and N atoms are drawn at the
50% probability level; C atoms are drawn as spheres and hydrogen
atoms have been omitted for clarity.
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40
Fig. 6 Job plot for complexation of cone-3 with Ag+ ion
Fig. 8 Partial chemical shifts of compounds cone-3–cone-5 (4 × 10−3
M) at 300 MHz in CD3CN solution in the presence of 1.0 equiv. of
45 AgClO4.
complexation with Ag+. Similarly, titration of 1.0 equiv of
AgClO4 with a solution of cone-4 also caused immediate
complexation as shown by the downfield shift of the triazole
50 proton (ꢀδ 0.05 ppm). Moreover, the protons on the pyridine
moieties were also shifted downfield (Fig. 8b), indicating that
the nitrogen atoms not only of the triazole ring but also of the
pyridine moieties were involved in the selective binding of
Ag+ cations. However, titration of 1.0 equiv of AgClO4 with
55 the solution of cone-5 revealed no obvious chemical shift
changes for the OCH2-bridge linker protons, which have
previously been used to track the complex behaviour of the
calixarene with guest by measurement of the tilt angle of the
parent cavity rings.17 Interestingly, some of the protons on the
60 pyridine moieties exhibited larger downfield shifts (while
others shifted upfield) and accompany a slightly downfield
shift of the triazole protons when AgClO4 was added to the
solution of receptor cone-5 (Fig. 8c). This result suggested that
the nitrogen-rich tri-ligand cavities formed by the pyridine
65 moieties have a stronger affinity for Ag+ than do the triazole
groups alone.
5
Fig. 7 Job plot for complexation of cone-4 with Ag+ ion
Due to the existence of three metal-binding sites including
the parent cavities, triazole moieties as well as in the pyridine
moieties, so, there are several possibilities for metal
10 complexation in compounds 3–5 with guest molecules and 1:1
or 1:2 metal complexation might be possible. Therefore, two-
phase picrate extraction (H2O/CH2Cl2) using the continuous
variation method was applied to determine the stoichiometry
of the cone-3 with Ag+ ions. The percentage extraction for
15 cone-3 (Job plot) supports the formation of a 1:1 complex with
Ag+ cation, whilst that for cone-4 indicates the formation of
1:2 complexes. Thus, the percentage extractions reach a
maximum at 0.5 mole fraction when cone-3 and the Ag+ cation
concentrations were varied systematically (Fig. 6), indicating
20 that Ag+ forms a 1:1 complex with cone-3. When cone-4 and
Ag+ cation concentrations were changed systematically, the
percentage extraction reached a maximum between 0.6 and 0.7
mole which indicated that cone-4 formed a 1:2 complex with
Ag+ (Fig. 7). Interestingly, in the case of cone-5, 1:1
25 complexation with Ag+ was observed in spite of the two
different (triazolyl and pyridyl group) binding sites.
Conclusions
A series of metal ion receptors cone-3–cone-5 has been
synthesized via click chemistry, and the binding of transition
70 metal ions has been evaluated by solvent extraction from the
Furthermore, in order to look further into the binding
1
properties of the receptors cone-3–cone-5 with Ag+, H NMR
1
aqueous to the organic phase (methylene dichloride) using H
NMR titration experiments. We have also demonstrated that
the O-propargyl group of the flexible macrocycle 2, on
reaction with azides, gives tri-triazole alkylated products
75 which adopt cone conformations. X-ray crystallographic and
1H NMR spectra studies provided unambiguous information
about the cone structures. The binding studies of cone-3–cone-
5 indicated that the nitrogen-rich tri-ligand cavities formed by
both the triazole ring and the pyridine N atoms show
80 selectivity for Ag+, but the nitrogen atoms on the pyridine
moieties appeared to have a stronger affinity for those cations.
These results give some insight into the molecular design of
new synthetic receptors for metal ions.
titration experiments were carried out in CD3CN solution. The
30 partial chemical shift changes for compounds cone-3–cone-5
on complexation with Ag+ are illustrated in Fig. 8. For
example, on gradual addition of Ag+ salt to a solution of
compound cone-3 (Fig. 8a), the proton on the triazole ring
showed a downfield shift of ∆δ 0.15 ppm, from δ 7.61 to
35 7.76ppm, and the OCH2-bridge linker protons were shifted
upfield by ∆δ 0.18 ppm (Hax: from δ 4.48 to 4.30 ppm; Heq:
from δ 4.35 to 4.18 ppm). The spectral changes suggested that
all three triazole moieties of cone-3 and the parent cavity of
hexahomotrioxacalix[3]arene were involved in the
4
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bridge), 4.55 (6H, s, ArO-CH2-triazole), 5.29 (6H, s, triazole-
CH2-Ar), 6.87 (6H, d, J=9.0 Hz, ArH), 6.92 (6H, s, ArH), 7.23
(6H, d, J= 9.0 Hz, ArH) and 7.61 (3H, s, triazole-H); δC
60 (CDCl3): 31.43, 31.21, 53.36, 55.25, 67.33, 69.36, 114.27,
123.22, 126.10, 127.08, 129.78, 130.96, 144.31, 146.42,
152.07 and 159.74; FAB: m/z 1180.4739 (M+). Anal. calcd.
for C69H81O9N9 (1180.47): C, 70.21; H, 6.92; N, 10.68. Found:
C, 70.38; H, 6.78; N, 10.54%.
Experimental
All melting points are uncorrected. 1H NMR spectra were
recorded at 300 MHz on a Nippon Denshi JEOL FT-300 NMR
spectrometer in deuteriochloroform with Me4Si as an internal
reference. IR spectra were measured as KBr pellets on a
Nippon Denshi JIR-AQ2OM spectrometer. UV-vis spectra
were recorded on a Perkin Elmer Lambda 19 UV/VIS/NIR
spectrometer. Mass spectra were obtained on a Nippon Denshi
JMS-01SA-2 spectrometer at 75 eV using a direct-inlet
5
65 Similarly, compounds cone-4 and cone-5 were prepared as
described above in 42 and 43% yields, respectively.
10 system. Elemental analyses were performed by Yanaco MT-5.
Gas–liquid chromatograph (GLC) analyses were performed by
Shimadzu gas chromatograph, GC-14A; silicone OV-1, 2 m;
programmed temperature rise, 12°C min−1; carrier gas
nitrogen, 25 mL min−1.
cone-7,15,23-Tri-tert-butyl-25,26,27-tris{[1H-(2-
pyridylmethyl)(1,2,3-triazolyl)]-4-methoxy}
hexahomotrioxacalix[3]arene (cone-4): colourless prisms
70 [CHCl3/hexane (1:3, v:v)], mp 81–82 °C; δH (CDCl3): 1.08
(27H, s, tBu), 4.37 (6H, d, J= 13.7 Hz, ether bridge), 4.51 (6H,
d, J= 13.7 Hz, ether bridge), 4.62 (6H, s, ArO-CH2-triazole),
5.52 (6H, s, triazole-CH2-2py), 6.91 (6H, s, ArH), 7.20 (3H, d,
J= 7.9 Hz, 2-py-H3), 7.23 (3H, m, 2-py-H5), 7.70 (3H, dd, J=
75 7.9, 7.2 Hz, 2-py-H4), 7.85 (3H, s, triazole-H) and 8.48 (3H, d,
J= 4.4 Hz, 2-py-H6); δC (CDCl3): 28.87, 31.64, 52.70, 64.72,
66.80, 119.83, 120.62, 122.03, 123.57, 128.45, 134.60, 141.70,
143.83, 147.05, 149.57 and 152.09; FAB: m/z 1093.35 (M+).
Anal. calcd. for C63H72O6N12 (1093.35): C, 69.21; H, 6.64; N,
80 15.37. Found: C, 69.16; H, 6.65; N, 15.59 %.
15 Materials.
7,15,23-tri-tert-Butylhexahomotrioxacalix[3]-
arene 1 was prepared according to the previously reported
procedure.7a
Preparation
of
7,15,23-tri-tert-butyl-25,26,27-
tris(propargyloxy)hexahomotrioxacalix[3]arene (2):
A
20 solution of hexahomotrioxacalix[3]arene (1) (0.3 g, 0.52
mmol) and Cs2CO3 (1.69 g, 5.2 mmol) in dry acetone (15 mL)
was heated at reflux for 1 h. 3-Bromo-1-propyne (propargyl
bromide) (0.62 g, 5.2 mmol) and dry acetone (10 mL) were
added and the mixture was refluxed for 18 h. The solvent was
25 evaporated and the residue partitioned between 10% HCl and
CH2Cl2. The organic layer was separated and dried (MgSO4)
and the solvent was evaporated. The residue was dried to
afford 2 as a colourless oil (0.15 g, 42%) which was
recrystallized from CHCl3/hexane (1:3, v/v) to afford the
30 desired product 2 as colourless prisms, mp 106–108 °C; δH
(CDCl3): 1.22 (18H, s, tBu), 1.27 (9H, s, tBu), 1.98 (1H, t, J=
2.4 Hz, acetylene-H), 2.41 (2H, t, J= 2.4 Hz, acetylene-H),
2.87 (2H, s, ArO-CH2-acetylene), 4.29 (4H, s, ArO-CH2-
acetylene), 4.0–4.85 (12H, m, ether bridge), 7.23 (2H, d, J=
35 2.4 Hz, ArH), 7.30 (2H, d, J= 2.4 Hz, ArH) and 7.31 (2H, s,
ArH); δC (CDCl3): 31.39, 31.46, 34.26, 34.39, 60.087, 61.74,
64.25, 66.50, 69.33, 73.82, 75.04, 79.47, 80.05, 126.57,
128.21, 128.45, 130.14, 130.71, 131.77, 146.81, 146.93,
151.99 and 153.43; FAB: m/z 690 (M+). Anal. calcd. for
40 C45H54O6 (690.9): C, 78.23; H, 7.88; Found: C, 78.48; H,
7.65%.
cone-7,15,23-Tri-tert-butyl-25,26,27-tris{[1H-(3-
pyridylmethyl)(1,2,3-triazolyl)]-4-methoxy}-
hexahomotrioxacalix[3]arene (cone-5) : colourless prisms
[CHCl3/hexane (1:3, v:v)], mp 77–78 °C; δH (CDCl3): 1.09
85 (27H, s, tBu), 4.34 (6H, d, J= 13.4 Hz, ether bridge), 4.48 (6H,
d, J= 13.4, ether bridge), 4.60 (6H, s, ArO-CH2-triazole), 5.46
(6H, s, triazole-CH2-3py), 6.92 (6H, s, ArH), 7.30 (3H, m, 3-
py-H5), 7.61 (3H, d, J= 7.5 Hz, 3-py-H4), 7.77 (3H, s, triazole-
H), 8.50 (3H, d, J= 4.4 Hz, 3-py-H6) and 8.58 (3H, broad s, 3-
90 py-H2); δC (CDCl3): 28.83, 31.63, 48.71, 64.67, 66.83, 121.01,
121.17, 121.22, 123.73, 128.28, 133.35, 141.94, 143.97,
146.83, 147.38 and 149.57; FAB: m/z 1093.35 (M+). Anal.
calcd. for C63H72O6N12 (1093.35): C, 69.21; H, 6.64; N, 15.37.
Found: C, 69.37 H, 6.53; N, 15.27 %.
95 Stoichiometry of metal complexation
The method of continuous variation was employed to
determine the stoichiometry in complexes of hosts cone-3–
cone-5. Two-phase solvent extraction was carried out between
aqueous picrates (5 mL, [metal picrate] = 2 × 10−4 M) and host
100 (5 mL, [host] = 2 × 10−4 M in CH2Cl2). The molar ratios of the
both host and metal picrate were varied from 0 to 1, while the
total concentration was kept at several constant levels. The
two-phase mixture in a glass tube immersed in a thermostated
water bath at 25 °C was shaken at 300 strokes per min for 1 h
105 and then kept, at the same temperature, for 2 h, allowing the
complete separation of the two phases. The absorbance of each
solution was determined by UV spectroscopy (λ= 290 nm).
Job plots were generated by plotting the extracted [M+] versus
the mole fraction of metal.
Preparation
of
cone-7,15,23-tri-tert-butyl-25,26,27-
tris{[1H-(4-methoxybenzyl)(1,2,3-triazolyl)]-4-
methoxy}hexahomotrioxacalix[3]arene (cone-3): Copper
45 iodide (10 mg) was added to a solution of 2 (50 mg, 0.072
mmol) and 4-methoxybenzyl azide (73.5 mg, 0.45 mmol) in
15 mL THF/H2O (2:1), and the mixture was heated at 50°C
for 24 h. The resulting solution was cooled and diluted with
water and extracted twice with CHCl3. The organic layer was
50 separated and dried (MgSO4) and evaporated to give the solid
crude product. The residue was eluted from a column
chromatography of silica gel with hexane/ethyl acetate (v/v=
4:1) to give the desired product cone-3 (64 mg, 72%) as
colourless prisms [CHCl3/hexane (1:3, v:v)], mp 147–149 °C;
55 δH (CDCl3): 1.07 (27H, s, tBu), 3.71 (9H, s, OMe), 4.35 (6H,
d, J= 13.1 Hz, ether bridge), 4.48 (6H, d, J= 13.1 Hz, ether
110 1H NMR complexation experiments
To a CD3CN solution (5 × 10−3 M) of cone-3–cone-5 in the
NMR tube was added a CD3CN solution (5 × 10−3 M) of
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AgSO3CF3. The spectrum was recorded after addition and the
60 Acknowledgments
temperature of the NMR probe was kept constant at 27 °C.
The association constant Kass was calculated by non-linear
fitting analysis of the observed chemical shift changes of the
ArOCH2-triazole protons.18
This work was performed under the Cooperative Research
Program of “Network Joint Research Center for Materials and
Devices (Institute for Materials Chemistry and Engineering,
Kyushu University)”. We would like to thank the OTEC at
65 Saga University and The Royal Society for financial support,
and the EPSRC for an overseas travel grant to C.R.
5
Extraction experiments
Metal picrates (2.5 × 10−4 M) were prepared in situ by
dissolving the metal hydroxide (0.01 mol) in 2.5 × 10−4
M
Notes and references
a
picric acid (100 mL); triply-distilled water was used for all
10 aqueous solutions. Two-phase solvent extraction was carried
out between water (5 mL, [metal picrate] = 2.5 × 10−4 M) and
CH2Cl2 (5 mL, [ionophore] = 2.5 × 10−4 M). The two-phase
mixture was shaken in a stoppered flask for 2 h at 25 °C. We
confirmed that this period was sufficient to attain the
15 distribution equilibrium. This was repeated 3 times, and the
solutions were left standing until phase separation was
complete. The extractability was determined spectrophoto-
chemically from the decrease in the absorbance of the picrate
ion in the aqueous phase, as described by Pedersen.19
Department of Applied Chemistry, Faculty of Science and
Engineering, Saga University, Honjo-machi 1, Saga 840-8502 Japan.
70 Fax: (internat.)
u.ac.jp
+ 81(0)952/28-8548; E-mail: yamatot@cc.saga-
b
Key Laboratory of Macrocyclic and Supramolecular Chemistry of
Guizhou Province, Guizhou University, Guiyang, Guizhou, 550025,
China. E-mail: longni333@163.com
c
75 Energy Materials Laboratory, School of Chemistry, University of
East Anglia, Norwich, NR4 7TJ, UK
† Electronic Supplementary Information (ESI) available: Details of
single-crystal X-ray crystallographic data in CIF. See
DOI: 10.1039/b000000x/
80
20 Crystallographic analysis of cone-3
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the conclusion of the refinement, wR2 = 0.144 and R1
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UK
[fax:
144-1223-336033
or
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Binding modes of cone-3 and cone-4 with Ag+