Metal ions recognition by 1,2,3-triazolium calix[4]arene esters synthesized via click chemistry

Article abstract of DOI:10.1007/s10847-009-9582-1

Two triazole-modified calix[4]arene diesters were synthesized via Huisgen 1,3-dipolar cycloaddition between azides esters and alkynylcalixarenes. Their structures had been deduced from ¹H NMR, element analysis and ESI-MS. Two-phase extraction experiments indicated that triazole-modified calix[4]arene diethylester 3a exhibited Cs⁺ selectivity. Springer Science+Business Media B.V. 2009.

Full text of DOI:10.1007/s10847-009-9582-1

J Incl Phenom Macrocycl Chem (2010) 66:43–47
DOI 10.1007/s10847-009-9582-1
ORIGINAL ARTICLE
Metal ions recognition by 1,2,3-triazolium calix[4]arene esters
synthesized via click chemistry
Haibing Li Æ Junyan Zhan Æ Mingliang Chen Æ
Demei Tian Æ Zhilong Zou
Received: 15 February 2009 / Accepted: 8 April 2009 / Published online: 5 May 2009
Ó Springer Science+Business Media B.V. 2009
Abstract Two triazole-modified calix[4]arene diesters
were synthesized via Huisgen 1,3-dipolar cycloaddition
between azides esters and alkynylcalixarenes. Their struc-
metals ions [6]. Xie and co-workers synthesized 2-pyridyl
triazole substituted b-cyclodextrins via click chemistry as a
Zn2? fluorescent probes [7]. At the same time click reac-
tions have already been used successfully to prepare water-
soluble [8] and other triazole-modified calixarenes as ion
sensors [9–15]. Recently, we synthesized a series of tria-
zole-modified calix[4]crowns [16].
1
tures had been deduced from H NMR, element analysis
and ESI-MS. Two-phase extraction experiments indicated
that triazole-modified calix[4]arene diethylester 3a exhib-
ited Cs? selectivity.
Calixarenes [17–19] are extensively utilized as the most
versatile and useful building blocks for the design and
construction of elaborated supramolecular systems. In
order to preorganize the host it is usually desirable to
prepare the calixarenes with well-defined structural fea-
tures suitable for complexation. Also, the ion selectivity is
dependent on cooperation of the conformation and sub-
stituents. It was reported that OCH2COOR, OCOCH2NR2
etc. are favorable groups for the coordination of alkali
metal ions [20–26]. By skillful combination of conforma-
tion and substituents via kinds of coupling technique, a
series of excellent ionophores for Li? [21], Na? [18] and
K? [20] and Cs? [22–26] ions have been synthesized.
And also the studies of recognition behavior are very sig-
nificative, especially on how to recognize cesium ion
selectively. Therefore, we wanted to introduce the OCH2-
COOR group to the calixarene cavity by the click chem-
istry and investigate its extraction ability towards alkali
metal ions.
Keywords Triazole-modified calix[4]arene Á
Click chemistry Á Extraction
Introduction
The application of click chemistry developed by Meldal [1]
and Sharpless [2] involving the Cu(1)-catalyzed 1,3-dipolar
cycloaddition of an azide and a terminal alkyne is rapidly
growing, especially in the areas of biological, materials,
and medicinal chemistry [3–5]. Besides the advantages of
its high efficiency, regioselectivity, and compatibility with
reaction conditions, the unique properties of the 1,4-
disubstituted 1,2,3-triazole ring in terms of its ability to
participate in hydrogen bond and dipole–dipole interac-
tions has made click chemistry even more attractive in
metal ions-binding. Recently, the role of 1,2,3-triazole in
the formation of stable metal complexes has also been
realized and accordingly some triazole-based receptors. For
instance, Astruc and co-workers reported click assembly of
1,2,3-triazole-linked dendrimers for the recognition of
It is of interest to observe what happens when both tri-
azole spacer and ester groups are incorporated into one
calix[4]arene, due to the coordination of alkali metal ions is
promoted by OCH2COOR residues. In this paper we wish
to report our investigation of triazole-modified calix[4]ar-
ene by 1,3-dipolar cycloaddition between azide esters and
alkynylcalixarenes and as well as the cooperating com-
plexation ability of the triazole and ester groups towards
alkali metal ions. As expected, the complexation ability
H. Li (&) Á J. Zhan Á M. Chen Á D. Tian Á Z. Zou
Key Laboratory of Pesticide and Chemical Biology (CCNU),
Ministry of Education, College of Chemistry, Central China
Normal University, 430079 Wuhan, China
e-mail: lhbing@mail.ccnu.edu.cn
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J Incl Phenom Macrocycl Chem (2010) 66:43–47
General procedure for the synthesis of compounds 3b
varies remarkably according to the triazole spacer and the
different ester groups. Moreover, it was found that one of
the diesters, triazole-modified calix[4]diethylesters 3a
exhibits cesium ion selectivity.
The compound 3a was stirred in methanol and toluene
(50 mL V\V = 1:1) for 10 h under reflux. After the sol-
vent was removed under reduced pressure, a portion of
water was added for precipitation. The solid material was
filtered, washed with water, and dried. Finally, purified by
recrystallization from the chloroform–methanol.
Experimental
Compound 3b: 1H NMR (400 MHz, CDCl3) d: 0.91
(s, 18H, But), 1.34 (s, 18H, But), 2.87 (s, 6H, OCH3), 3.27
(d, 4H, J = 12.4 Hz, ArCH2Ar), 4.37 (d, 4H, J = 12.4 Hz,
ArCH2Ar), 4.87 (s, 4H, NCH2), 5.10 (s, 4H, OCH2), 6.71
(s, 4H, ArH), 7.03 (s, 4H, ArH), 8.01 (s, 2H, ArOH), 8.02
(s, 2H, CH). ESI(?)MS(m/z, %): 954.5 (M?,100). Anal.
calc. for C56H70N6O8: C, 70.42%; H, 7.39%; N, 8.80%;
found: C, 70.23%; H, 7.25%; N, 8.90%.
Materials and methods
1H NMR spectra were recorded on Varian Mercury VX400
at ambient temperature with TMS as the internal standard.
ESI-MS were recorded on a Finnigan LCQ-Advantage
instrument. UV-Vis spectra were obtained using a Scinco
S-3100 UV-Vis recording spectrophotometer. All chemi-
cals were A.R. grade and were purified by standard
procedures.
Solvent extraction experiments
General procedure for the synthesis of compound 1
Picrate extraction experiments were performed by follow-
ing Ho’s procedure [27]. One milliliter 5 9 10-4 M solu-
tion of calixarene in CHCl3 was vigorously shaken with
2 mL of a 5 9 10-5 M aqueous picrate solution in water
and the concentration of picrate ion remaining in the
aqueous phase was then determined by UV spectra from
the resulting absorbance at 380 nm. Blank experiments
showed that no picrate extraction occurred in the absence
of calixarene.
A solution of p-tert-butylcalix[4]arene (4 g, 6.2 mmol) and
BrCH2CCH (1.7 mL, 15.5 mmol) in acetone (150 mL) and
K2C03 (1.8 g, 13.0 mmol) were heated to reflux for 17 h.
The cooled reaction mixture was filtered and washed with
chloroform. The filtrate were removed under vacuum and
the residue was further purified by crystallization by slow
diffusion of methanol into a chloroform solution. The
product was collected by filtration, washed with methanol
(3 9 10 mL) and dried under vacuum.
General procedure for the synthesis of compounds 3a
Results and discussion
1
(290 mg, 0.40 mmol), CuSO4 9 5H2O (100 mg,
The synthetic route is depicted in Scheme 1. As a first step
azide esters 2 was synthesized by reacting bromoethyl-
acetate with NaN3 in DMF at 90 °C in high yield
and without purification [28]. Then The reaction of
alkynylcalixarenes 1 [29] with 2 has been carried out in
DMF at 90 °C with copper(II) sulfate, and sodium ascor-
bate to afford triazole-modified calix[4]arene diesters 3a in
good yield up to 86% after recrystallization from CH2Cl2/
MeOH. The diethylesters 3a was transformed into corre-
sponding the dimethylesters (3b) by ester exchange reac-
tion in near quantitative yield in refluxing MeOH and
toluene (V\V = 1:1). The structures of these compounds
3a, 3b were characterized by ESI-MS spectra, elemental
0.402 mmol) and sodium ascorbate (200 mg, 1.010 mmol)
were added to a solution of 2 (114 mg, 0.88 mmol) in DMF
(15.0 mL). The mixture was heated at 90 °C for 10 h, and
then diluted with ethyl acetate (20 mL) and washed with
water (3 9 10 mL). The organic phase was dried over
MgSO4, filtered and the solvent removed under reduced
pressure. The residue was recrystallized from CH2Cl2/
MeOH to afford 3a as a white solid in 86% yield.
1
Compound 3a: H NMR (400 MHz, CDCl3) d: 1.17 (s,
18H, But), 1.22 (s, 18H, But), 1.25–1.28 (m, 6H, CH3), 3.29
(d, 2H, J = 12.8 Hz, ArCH2Ar), 3.42 (d, 2H, J = 13.2 Hz,
ArCH2Ar), 4.35 (d, 2H, J = 13.2 Hz, ArCH2Ar), 4.46 (d,
2H, J = 12.8 Hz, ArCH2Ar), 4.17–4.26 (m, 4H, CH2CH3),
4.91 (d, 2H, J = 17.6 Hz, OCH2), 4.99 (d, 2H, J = 10 Hz,
NCH2), 5.32 (d, 2H, J = 17.6 Hz, OCH2), 6.19 (d, 2H,
J = 10 Hz, NCH2), 6.87 (d, 4H, J = 7.6 Hz, ArH), 7.06 (d,
4H, J = 7.6 Hz, ArH), 7.36 (s, 2H, CH), 8.00 (s, 2H,
ArOH). ESI(?)MS(m/z, %): 981.2 (M?,100). Anal. calc.
for C58H74N6O8: C, 70.85%; H, 7.59%; N, 8.55%; found:
C, 70.89%; H, 7.53%; N, 8.60%.
1
analyses and H NMR spectra. The ESI-MS spectra of 3a
and 3b show the expected molecular ion peaks, which
indicate that the ester is linked to the calix[4]arene moiety
1
by the triazole groups. In H NMR spectra a pair of two
doublets (d) of ArCH2Ar protons for compound 3a, two
doublets for ArCH2Ar protons for compound 3b and two
singlets for the tert-butyl groups for compounds 3a, 3b
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J Incl Phenom Macrocycl Chem (2010) 66:43–47
45
Scheme 1 Synthesis of
triazole-modified calix[4]arene
esters
O
O
NaN3
DMF
Br
N3
O
O
2
CuSO4
sodium ascorbate
2
DMF
O
OH
O
OH
O
OH
O
OH
N
N
N
N
N
N
1
3a
R
R
3a
3b
CH2CO2Et
CH2CO2Me
R =
MeOH/toluene
Table 1 Percentage extraction of alkali metal ions
suggest that triazole-modified calix[4]arene ester 3a and 3b
keep the cone conformation [30–32].
Host
Li?
Na?
K?
Cs?
Cs?/Na?
Examination of the CPK molecular models reveals that
triazole-modified calix[4]arene ester are well preorganized
to extract cation. The ions binding properties of 3a and 3b
were investigated by extracting the picrate salts from the
aqueous to the organic phase [27]. In order to compare the
influence of the triazole groups on the extraction, the p-
tert-butylcalix[4]arene 1,3-diethylacetate 4 was used as a
reference compound [20]. The result of extraction studies
was listed in Table 1. Arnaud-Neu reported that the ref-
erence compound 4 failed to show any significant extrac-
tion potential. We have investigated the picrate extraction
experiment, compound 4 have a very poor extractants of
alkaline metal picrates and the percentage extraction is up
to 1%. However, it can be seen from Table 1 in comparison
with 4, triazole-modified calix[4]diester 3a showed higher
extraction selectivity towards Cs? and the extraction ratio
Cs?/Na? of compound 3a is up to 10.52 which indicated
that the triazole groups inflected the extraction ability and
selectivity. It is well-known that 1,2,3-triazole groups
containing the nitrogen atom are preferable for complexing
the more polarizable transition metal cations such as the
Pb2?, Cu2?, Cd2?, Zn2? and so on [9–15]. And also, it was
reported that OCH2COOR, OCOCH2NR2 etc. are favorable
groups for the coordination of alkali metal ions. We have
3a
3b
4
3.9
1.9
\1
5.2
8.7
4.9
54.7
16.4
\1
10.52
1.89
37.4
\1
\1
50
40
30
20
10
0
O
OH
O
OH
N
N
N
N
Cs+
N
N
O
O
O
O
Li
Na
K
Cs
Metal Ion
ions by enhancing the flexibility of the cavity formed by
the two ester group. At the same time, it revealed that the
cavity formed by the two moderately rigid ester group is so
larger that the ester groups are preferable for the com-
plexing the much softer and larger alkaline metal ion such
as the Cs?. Meanwhile, the triazole-modified calix[4]die-
thylester 3a and triazole-modified calix[4]dimethylester 3b
display different selectivity towards alkali metal ions.
According to the literature the extraction selectivity
towards alkali metal cations is relative to the cavity
1
also performed the H NMR experiments in CDCl3 in the
presence of the picrates and found that the chemical shift of
proton on the triazole group have no change. Therefore, the
high extraction selectivity towards alkali metal cations for
the triazole-modified calix[4]arene 3a and 3b could
because the flexible triazole groups facilitate the com-
plexation between the ester groups and the soft alkali metal
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J Incl Phenom Macrocycl Chem (2010) 66:43–47
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tilt angle of the aromatic rings. Therefore, for the triazole-
modified calix[4]diethylester 3a the endmost ethyl groups
of the ester groups had the much stronger influence on the
cavity dimensions formed by the two ester groups than the
endmost methyl groups. The ethylester groups may form
the larger cavity to fit the largest Cs? and the methylester
groups may form the small cavity to fit the K? which
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Acknowledgments This work was financially supported by the
National Natural Science Foundation of China (20602015,
20772038), Program for Distinguish Young Scientist of Hubei
Province (2007ABB017) and Program for Chenguang Young Scien-
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