Synthesis and complexing properties of thiacrownophanes

Article abstract of DOI:10.3987/com-01-9262

Novel thiacrownophanes (1) (cis-form) and (2) (trans-form) were prepared by means of intramolecular [2 + 2] photocycloaddition of styrene derivatives. The ratio of 1:2 was significantly dependent on the oxyethylene chain length of the linkage between the two aromatic nuclei of precursors. In a liquid-liquid extraction, thiacrownophanes (1c) possessing three ethereal oxygens showed perfect selectivity with high efficiency toward Ag⁺ ion. From ESI-MS analysis, 1c was found to form a 1:1 complex with Ag⁺ ion in MeCN-H₂O homogeneous system.

Full text of DOI:10.3987/com-01-9262

HETEROCYCLES, Vol. 55, No. 9, 2001, pp. 1635 - 1640, Received, 4th June, 2001
SYNTHESIS
AND
COMPLEXING
PROPERTIES
OF
THIACROWNOPHANES
Seiichi Inokuma, Takashi Funaki, Masayuki Tanakajima, Shinji Nabekura, Keigo
Isawa, and Jun Nishimura*
Department of Chemistry, Gunma University, 1-5-1 Tenjin-cho, Kiryu 376-8515,
Japan
Abstract- Novel thiacrownophanes (1) (cis-form) and (2) (trans-form) were
prepared by means of intramolecular [2 + 2] photocycloaddition of styrene
derivatives. The ratio of 1:2 was significantly dependent on the oxyethylene
chain length of the linkage between the two aromatic nuclei of precursors. In a
liquid-liquid extraction, thiacrownophanes (1c) possessing three ethereal oxygens
showed perfect selectivity with high efficiency toward Ag+ ion. From ESI-MS
analysis, 1c was found to form a 1:1 complex with Ag+ ion in MeCN-H2O
homogeneous system.
Crownophanes possessing both cyclophane and crown ether moieties in the molecule were found to show
unique host-guest interaction with many kinds of metal cations and organic compounds in organic
media.1-9 They were conveniently prepared by efficient intramolecular photocycloaddition of styrene
derivatives. Recently, we found a quite astonishing results in the preparation of thiacrownophanes,
because it formed cis-isomers (1) and/or trans-isomers (2), although the photochemical method has
always exclusively given cis-isomer like 3.6 In this communication, we report the relationship between
the ratio of 1:2 and linkage length of precursors, and complexing ability of the thiacrownophanes toward
heavy metal cations.
Thiacrownophanes (1) and (2) were prepared by the sequence shown in Scheme 1. Thus, compounds
(4a-d) were obtained in good yields from thioetherification of 4-bromothiophenol with
oligoethyleneglycol ditosylate, and then converted to 5a-d by Migita-Kosugi-Stille reaction10 in moderate
yields. Finally thiacrownophanes were synthesized by the photoreaction.1 Analytical data of new
compounds prepared are given.11 Photoreaction of 5a and 5b exclusively afforded cis-isomers (1a)
(18%) and (1b) (15%), respectively. In contrast with these data, irradiation to 5c produced both cis-

isomer (1c) (19%) and trans-isomer (2c) (5%). Surprisingly, 5d exclusively gave trans-isomer (2d)
(12%). Thus, it was found that product isomer ratio significantly depended on the length of oxyethylene
linkage. In the case of prototypical crownophanes, which have only ethereal oxygens in the linkage, cis-
isomer was exclusively formed in the photoreaction even if the precursor has six ethereal oxygens in the
linkage.1
Br
S
Br
S
Br
b)
a)
c)
S
S
SH
O
O
n
n
4
a; n=1 Y. 90%
b; n=2
5
a; n=1 Y. 50%
b; n=2
Y. 90%
Y. 30%
c; n=3 Y. 75%
d; n=4 Y. 75%
c; n=3 Y. 31%
d; n=4 Y. 40%
H
H
H
H
+
S
S
S
S
O
O
n
n
1
a; n=1 Y. 18%
b; n=2
a; n=1 Y. 0%
b; n=2 Y. 0%
2
Y. 15%
c; n=3 Y. 19%
d; n=4 Y. 0%
Y. 12%
d; n=4 Y. 15%
c; n=3
Scheme 1. Reactions and conditions: a) TsO(CH2CH2O)n+1Ts, NaOEt/EtOH, rt; b) CH2=CHSn(n-Bu)3,
2,6-di-tert-butyl-4-methylphenol/toluene, reflux; c) hν (> 280 nm)/MeCN, N2, rt.
Thiacrownophanes obtained were used as extractants for heavy metal
H
H
cations in a liquid-liquid system. A CH2Cl2 solution of a host compound
(1 x 10-4 mol dm-3, 5 mL) and an aqueous solution (0.1 mol dm-3, 5 mL),
whose pH value was adjusted as high as possible not to precipitate the
hydroxides, were shaken in a 20-mL test tube equipped with a ground glass
stopper at room temperature for 2 h. After two phases were separated, an
aliquot (2 mL) of the organic phase was evaporated, and then HNO3
O
O
S
S
3
O

solution (0.1 mol dm-3, 2 mL) was added to the residue. Extracted cation in the acidic aqueous solution
was analyzed by atomic absorption spectrometry. Results are summarized in Table 1 with thiacrown
reference compounds (3 and 6). Both 1a and 2c hardly extracted any heavy metal cations examined.
Although 1b with a small cavity to fit Ag+ ion and 2d with a strained ligating ring showed a little affinity
toward Ag+ ion, 1c efficiently and exclusively extracted Ag+ ion. This efficiency was higher than those
of thiacrownophane 3 and conventional dithia-15-crown-5 (6).
From the frame work investigation using the space-filling model, two large sulfur atoms directly attached
on the aromatic nuclei of 1c form a nicely arranged cyclic polyether cavity with ca. 2.7 Å of diameter.
The cavity size is suitable for Ag+ ion (diameter, 2.32 Å) since an optimaized diameter ratio for cation
and crown ether cavity generally becomes 0.9 at complexation.12
Table 1. Extraction of heavy metal cations with ligands
Extractability (%)a
ligand
Ag+
Pb2+
Cu2+
Mn2+
Zn2+
Ni2+
Co2+
Fe3+
1a
1b
1c
2c
2d
3
0(6.9)
13(4.6)
50(6.5)
2(5.6)
0(4.5)
0(5.3)
0(4.5)
0(4.9)
0(4.5)
6(4.8)
0(5.0)
0(4.5)
0(4.3)
0(4.5)
0(4.5)
0(4.5)
0(4.1)
0(4.3)
0(6.4)
0(4.5)
0(6.0)
0(4.3)
0(5.5)
0(6.1)
0(6.2)
0(6.8)
0(5.7)
0(6.0)
0(5.5)
0(5.5)
0(5.3)
0(5.7)
0(6.8)
0(6.9)
0(7.0)
0(6.6)
0(6.9)
2(6.9)
0(7.0)
0(7.0)
0(7.1)
0(7.0)
0(6.9)
0(7.0)
0(7.0)
0(7.0)
0(1.5)
0(1.9)
0(1.5)
0(1.5)
0(1.9)
0(1.7)
0(1.9)
14(6.9)
43(4.4)
15(5.0)
6
a
Extraction conditions: Aq. phase (5 mL), [metal nitrate]= 1.0 x 10-1 mol dm-3;
Org. phase, CH2Cl2 (5 mL), [ligand]= 1.0 x 10-4 mol dm-3; ca. 20 ˚C, shaken for
1 h. The values were based on the concentration of the crown compounds.
Values in parentheses were equilibrium pH of aqueous phase. Reproducibility
was ±15% which was the average value obtained from three independent runs.
O
O
S
S
O
6
13
The C NMR chemical shift of two linkage carbons attached to sulfur or ethereal oxygen observed
considerably changed with increasing the amount of AgClO4 added to the host solution, but the titration
curve was not reached to a plateau up to the 1c/Ag+ ratio of 3, indicating a difficulty in determining exact
stoichiometric relationships between the host compound and Ag+ ion in the complexation.
Since ESI-MS is an appropriate method to observe cation-complexing behavior in solution,13,14 we
investigated the interaction between 1c and Ag+ ion in MeCN-H2O (1:1) by employing the method to

clarify the complexing behavior of the thiacrownophane to Ag+ ion clearer: The sample solution
contained 1c and AgClO4 salt (1 x 10-4 mol dm-3 in each). Figure 2 showed that 1:1 (1c:Ag+) complex
was quantitatively formed, because free 1c was hardly detected.
100
[M + Ag]+
50
[M]+
0
700
300
500
Mass nunber (m/z)
Figure 2. ESI-MS spectra of pyridinocrownophane (1c) in 1:1 (v/v) MeCN-H2O containing
AgClO4.
In conclusion, thiacrownophanes was prepared by intramolecular [2 + 2] photocycloaddition, and trans-
thiacrownophanes were first prepared in the series of crownophanes. In the liquid-liquid extraction, 1c
showed extraordinarily high efficiency and selectivity toward Ag+ ion. From ESI-MS analysis
compound (1c) was found to form Ag+-complex quantitatively in homogeneous solution.
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2
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m), 2.16 (2H, m). ESI-MS m/z 430.4 (M+), 431.4 ([M + H]+). 2d; pale yellow liquid. 1H NMR (CDCl3,
500 MHz) δ=7.36 (4H, ABq, J=8.2), 7.32 (4H, ABq, J=8.2), 3.74 (2H, m), 3.56 (16H, m), 3.01 (4H, t, J=7.0),
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