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Selective oxidation of thiacalix[4]arenes to the sulfinyl- and sulfonylcalix[4]arenes and their coordination ability to metal ions
TETRAHEDRON LETTERS
Pergamon
Tetrahedron Letters 39 (1998) 7559-7562
Selective Oxidation of Thiacalix[4]arenes to the Sulfinyl- and Sulfonylcalix[4]arenes and Their Coordination Ability to Metal Ions N o b u h i k o Iki, *a H i t o s h i K u m a g a i *b N a o y a M o r o h a s h i , a K o h k i E j i m a , a Mitsuharu Hasegawa, b Setsuko Miyanari, b and
S o t a r o M i y a n o *a
•a Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku Universib,, Aramaki-Aoba 07, Sendai 980-8579, Japan b
Chemical Technology L a ~ ,
Cosmo Research Institute, Satte, Saitama 340-0193, Japan
Received 12 July 1998; revised 30 July 1998; accepted 31 July 1998
Abstract Thiacalix[4]arenes, in which the four methylene bridges of calix[4]arenes are replaced by sulfide linkages, were selectively oxidized to sulfinyl- or sulfonylcalix[4]arene under mild conditions with control of the stoichiometry of the oxidant. Solvent extraction of the transition and alkaline earth metal ions with these hosts showed that the metal binding ability was governed by the oxidation state of the sulfur functionalities. © 1998 Elsevier Science Ltd. All rights reserved. Keywords: Calixarenes; Oxidation; Sulfides; Complexation.
Calixarenes, which are methylene-bridged metacyclophanes derived from p-alkylphenols, are versatile compounds in supramolecular and molecular recognition chemistry [1]. Additional functionalities have been introduced by etherification of the phenolic oxygens (lower rim) and/or substitution of the ppositions (upper rim). For instance, the coordination ability of p-tert-butylcalix[4]arene (1) has been developed by introducing ligating groups such as ester, amide or carboxy groups to the lower rim [2]. On the contrary, the calixarene analogues in which the bridging groups (X) are hetero atoms instead of the methylene groups are very rare due to the difficulty in their synthesis [3,4]. Recently, we reported facile synthesis of p-tertbutylthiacalix[4]arene (2) by base-catalyzed condensation of the phenol and elemental sulfur [5]. As a remarkable result of the replacement of X = CH2 by S, 2 can quantitatively extract
0040-4039•98•5 - see front matter © 1998 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(98)01645-1
R
x. x
R
OH HO
OH
R
/'----'
R calixarenes
X
R
1 2
CH 2 S
Bu t Bu t
3
S
Oct t
4
SO 2
Bu t
5 6
SO 2 SO
Oct t BUt
Octtdenotes 1,1,3,3-tetramethylbutyl group.
7560
transition metal ions such
a s C o 2+, C H 2+
and Zn 2+ from an aqueous phase into chloroform [6].
As had been reported in the literature, we, ourselves, confirmed that 1 has little extraction ability of these metal ions under the comparable extraction conditions [6]. Detailed studies on the structure of 2-Zn 2+ complexes by IH NMR [6] and X-ray crystallography [7] allowed us to conclude that the high binding ability of TCA to the metal ions arises from the involvement of the epithio group, X -- S, for the coordination (vide infra). As is well known, a sulfide function is readily oxidized to the sulfoxide and sulfone, which prompted us to oxidize 2 into the corresponding sulfinyl and sulfonyl derivatives. Herein we report highly selective synthesis of p-tert-butylsulfonylcalix[4]arene (4) and p-(1,1,3,3tetramethylbutyl)sulfonylcalix[4]arene (5) as well as p-tert-butylsulfinylcalix[4]arene (6). Also reported are the results of a solvent extraction study to demonstrate that the coordination ability of the calix[4]arenes depends on the bridging X (= CH2, S, SO, or SO2). The calixarenes 1 [8] and 2 [5] are synthesized as described in the literature, p-(1,1,3,3Tetramethylbutyl)thiacalix[4]arene (3) was obtained by a similar method to that used for the synthesis of 2.1 The oxidation of all four epithio groups into sulfinyl or sulfonyl groups was quite facile. In a typical run, to a solution of 2 (1.0 g, 1.38 mmol) in chloroform (30 ml) were added acetic acid (50 ml) and NaBO3.4H20 (2.0 g, 13 mmol). After the mixture had been stirred at 50°C for 18 hr, 4 was extracted with chloroform (30 ml x 3) and worked up as usual. The product was recrystallized from benzene-methanol and dried in vacuo (80°C, 12 hr) to give a pure sample of 4 (I.06 g, 90.0%). 2 Hydrogen peroxide could be used to oxidize 2 or 3 to the sulfone. 3 By reducing the amount of NaBO3.4H20 to a slight excess (2.0 g, 12 mmol), 2 (2.0 g, 2.76 mmol) was oxidized at 50°C for 4.5 hr to yield 6 (0.67 g, 30.7%). 4 I Compound
3:
mp 260-261 °C; FAB MS m/z 944 (M+); IR (KBr) 33(X) (OH), 2955(CH) cm I; IH NMR (CDCI~) d 0.56 (36H
s, ~2(CH3)2CH2C(CH3)3), 1.24 (24H, s, -C(CH3)2CH2C(CH3)3), 1.59 (8H, s, -C(CH3)2C_H2C(CH3)3), 7.57 (SH, s, Ar H), 9.20 (4H, s, OH); 155.1 (CAr) .
13C NMR (CDCI3) ~5 31.2, 31.7, 32.3, 38.0, 57.0 (-C(CH3)2CH2C(CH3) a) and 120.4, 136.6, 143.4, and
CalcdforC56Hs004S4:C, 71.13; H, 8.53; S, 13.57.
Compound 4:
Found:C, 71.14; H, 8.58; S, 13.53.
mp >360°C; FAB MS m/z 849 (M++I); IR (KBr) 3354 (OH), 2964 (CH), 1319, 1159 (SO 2) c'm I; JH NMR
(CDCI3) 8 1.27 (36H, s, C(CH3)3), 8.03 (SH, s, Ar-H), OH protons (4H) were not detected. 13C NMR (CDCI2CDCI 2) i~ 30.8 . . 34.6 (C_(CH3)3) and 125.9 and 133.2 (CAr). Two of the 13(,-At reson~mces were not observed possibly due to their long (C(C_H3)3), relaxation time. 3
Calcd forC40H48OI2S4: C, 56.58: H, 5.70; S, 15.11.
Found: C, 56.63; H, 5.68; S, 15.01.
For instance, 3 (2.0 g, 1.38 mmol) was dissolved in chlorotbrm (40 ml) and then trifluoroacetic acid (10 ml) and an aq. soln. o! hydrogen peroxide (30%, 20 ml) were added. The mixture was stirred at 80°C lbr 24 hr. After being cooled, the reaction prCuchct was extracted wilh chloroform (30 ml × 3) and washed with 6 M HCI aq. soln. (20 ml x 3). The chlorolorm solution was evaporated to ffyness. The solid residue was triturated well with hexane (150 ml) to remove yellow-colored impurities and then dissolved in chloroform (200 ml). The chlorotorm solution w~t,; washed with 12 M HCI (20 ml × 3) and then evaporated to &yness to give a pure sample of 5 (1.80 g, 79.5%).
Compound 5:
mp 336 °C (&J,:omp.); FAB MS m/z 1074 (M++I); IR
(KBr) 3389 (OH), 2957 (CH), 1306, 1140 (SO 2) cm 1; IH NMR (CDCI 3) 8 0.680 (36H, s, -C(CH3)2CH2C(C_H3)3), 1.32 (24H, s, -C(CH3)2CH2C(CH3)3), 1.73 (8H, s, -C(CH3)2C_H2C(CH~)3), 8.10 (8H, s, Ar H); 13C NMR (CDCI 3) ~ 31.1, 31.8, 32.3, 38.7, 56.5, (-C(CH3)2CH2C(CH3) 3) and 126.9, 133.7, 143.9, and 151.2 (CAr). Calcd for C56H80OI2S4: C, 62.65; H, 7.51; S, 11.95. Found: C, 62.53; H, 7.34; S, 11.76. 4 Compound6: mp 295 °C (decomp.); FAB MS m/z 785 (M++I); IR (KBr) 3188 (OH), 2953(CH), 1001 (SO) cm . I IH NMR
7561
II f~e,-~,O A(q/ ~
/S~o. ~ a xx-. . . 4OII~
~
o
. 8
~ ,,
~
O
~~
0
Fig. 1 The axial-equatorial interconversion of S=O orientation via flip-l'lop inversion of 6. For clarity, p-tert-butylphenol moieties are depicted as hexagons.
The ~H and ~3C NMR spectra of 4, 5, and 6 are uncomplicated and quite similar to those of the parent thiacalix[4]arenes, indicating the structural resemblance, i.e., the cone conformation. In the case of 6, however, ~3C resonance of the two ipso aromatic carbons with respect to H and sulfinyl S=O group splitted into two in each case, suggesting that a pair of distal S=O groups is in the axial orientation while another pair is in the equatorial as shown in Fig. 1. The ax-eq orientation seems to interconvert rapidly via flip-flop inversion on t H NMR time scale to give a single resonance for Ar-H. 4 The proposed C2v configuration of 6 seems to be reasonable as it may be the most stable disposition to minimize the steric and electronic repulsions. The effects of the oxidation state of X on the coordination ability to metal ions were investigated via solvent extraction. 5 The percent extraction, E%, 5 for various metal ions was tabulated in Table 1. 6
Examination of the data in Table 1 reveals several interesting
extraction features characteristic of the calixarenes used. The parent calixarene 1 could hardly extract either transition metal ions or alkaline earth metal ions. On the other hand, thiacalixarenes 2 and 3 extracted the f o r m e r ions very well, while they showed little or no affinity to the latter ions. It can be seen that sulfonylcalixarene 5 behaved in a contrasting manner to the thiacalixarenes (2,3) in that it p r e f e r r e d far more the alkaline earth metal ions, in particular Ca 2÷ ion, than the transition metal ions. As has been reported, the high binding ability of 2 to the transition metal ions can be ascribed to the presence of the the lone pair electrons of one of which can take part in coordinating to the with two phenoxide groups to f o r m two sets of the five-membered chelated 2a) [6,7]. It seems that removal of the lone pair electrons on S by converting
epithio groups, cationic center structure (Fig. to SO2 results
(CDCI3)~5 1.29 (36H, s, C(CH3)3), 7.65 (8H, s, Ar-H), 9.30 (4H, s, OH); t3C NMR (CDCI2CDCI 2) 6 31.1 (C(_C_H3)3), 34.5 (C(CH3)3), 122.5 and 127.7 (_C_Ar-SO), 123.9 and 130.0 (C_Ar-H), 142.1 (C_Ar-But), and 152.4 (C_Ar-OH), which were unambiguously assigned by DEPT. Calcd for C40H4808S4: C, 61.19; H, 6.16; S, 16.34. Found: C, 60.88; H, 6.12; S, 16.06. 5 To a 30 ml vial tube were pipetted a solution of a calixarene (5x 104 M 1, 2, 3, 4, 5, or 6) in chloroform (10 ml) and an a~eous solution (10 ml) containing a metal ion (1×10 ~4 M), pH buffer (5×10 2 M Tris-HCI at pH 8.0 or NH3-HCI at pH 10.0), and tetramethylammonium chloride (0.1 M). The mixture was shaken at 300 strokes/rain for 24 hr. The total concentration of the metal species remaining in the aqueous phase, [Metal]~q, was measured by atomic absorption spectrometer or inductively coupled plasma atomic emission spectrophotometer.
The concentration of the metal ion extracted into the organic phase, [Metal]org, as
the complex was estimated by [Metal]org = [b'Ietal]aq.init - [Metal]aq, where [Metal]aq.init is the initial concentration of the metal ion in the aqueous phase. The percent extraction, E%, was calculated by E% = [Metal]org/ [Metallaq,init× 100°h. 6 In the case of 4, because the aqueous phase was turbid probably due to a reduced solubility in chloroform, the evaluation of the E% was not attempted.
7562
Table 1
The E% values of transition metal and alkaline earth metal ions by calixarenes.
Calixarenes No. X
Co 2+
Transition metal (pH 8.0) Ni 2÷ Cu 2+
Alkaline earth metal(pH 10) Mg 2+ Ca 2+ Ba2+
Zn 2+
1
CH2
5a
1"
Ia
6a
0
0
3
2
S
99 a
97"
69a(99) b
99 a
1
0
7
3
S
99
96
89
99
3
0
0
5
SO2
9
2
4
10
60
100
80
6c
SO
99
(99)
17
(99)
(99)
(91 )
(99)
See reL 6.
c: Except for Co 2+ and Cu 2+, metal-complexes precipitated.
b: At pH 7.0.
in the loss of the coordinating ability to the transition metal ions but the sulfonyl oxygen can in turn bind to the alkaline earth metal ions (Fig. 2b). In this respect, it is quite interesting that sulfinylcalixarene 6 could form complexes with not only the transition metal ions except Cu 2÷ ion but also the alkaline earth metal ions. Thus, it may be said that 6 can switch the coordinating atom between S and O depending on the hardness or softness [9] of the metal ion (Fig. 2c and d). Explanation for the exceptional behavior of Cu 2÷ ion should wait further study. In conclusion, we have shown here selective oxidation of thiacalix[4]arenes to the sulfinyland sulfonylcalix[4]arenes and their characteristic binding behaviors with metal ions by use of the lone pair electrons or oxygen atom on the sulfur moiety. M
M'
O-o. ~
R
/SO~
M
o-"''o o " "
R
M'
O-o~
o- _ o
R
R
(a) 2, 3 (b) 5 (c) 6 (d) 6 Fig. 2 Schematic views of the coordination manner of 2, 3, 5, or 6. Cationic centers M and M' denote transition metal and alkaline earth metal ions, respectively.
References [I] Gutsche CD. Calixarenes: Monographs in Supramolecular Chemistry, Stoddart JF, editor. Cambridge: The Royal Society of Chemistry, 1989; Calixarenes: A Versatile Class of Macrocyclic Compounds, Vicens J, B~hmer V, editors. Dordrecht: Kluwer Academic, 1991; B6hmer V. Angew. Chem. Int. Ed. Engl. 1995; 34: 713-745. [2] See e.g.; Arnaud-Neu F, Collins EM, Deasy M, Ferguson G, Harris S J, Kaitner B, Lough AJ, McKervey MA, Marques E, RuM BL, Schwing-Weill MJ, Seward EM. J. Am. Chem. Soc. 1989; 11 l: 8681-8698; Nagasaki T, Shinkai S. Bull. Chem. Soc. Jpn. 1992; 65: 471-475. [3] Sone T, Ohba Y, Moriya K, Kumada H, Ito K. Tetrahedron 1997; 53:10689 10698. [4] K6nig, B, R6del, M, Bubenitschek, P, Jones, P. G. Angew. Chem. Int. Ed. Engl. 1995; 34: 661~62. [5] Kumagai H, Hasegawa M, Miyanari S, Sugawa Y, Sato Y, Hori T, Ueda S, Kamiyama H, Miyano S. Tetrahedron Lett. 1997; 38: 3971-3972. [6] Iki N, Morohashi N, Narumi F, Miyano S. Bull. Chem. Soc. Jpn. 1998; 71: 1597-1603. 171 Iki N, Morohashi N, Miyano S. to be published elsewhere. [8] Gutsche CD, Iqbal M. Org. Synth. 1990; 68: 234-237. [9] Pearson RG. J. Am. Chem. Soc. 1963; 85: 3533-3539; J. Chem. Edu. 1968; 45: 581-587.
Pergamon
Tetrahedron Letters 39 (1998) 7559-7562
Selective Oxidation of Thiacalix[4]arenes to the Sulfinyl- and Sulfonylcalix[4]arenes and Their Coordination Ability to Metal Ions N o b u h i k o Iki, *a H i t o s h i K u m a g a i *b N a o y a M o r o h a s h i , a K o h k i E j i m a , a Mitsuharu Hasegawa, b Setsuko Miyanari, b and
S o t a r o M i y a n o *a
•a Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku Universib,, Aramaki-Aoba 07, Sendai 980-8579, Japan b
Chemical Technology L a ~ ,
Cosmo Research Institute, Satte, Saitama 340-0193, Japan
Received 12 July 1998; revised 30 July 1998; accepted 31 July 1998
Abstract Thiacalix[4]arenes, in which the four methylene bridges of calix[4]arenes are replaced by sulfide linkages, were selectively oxidized to sulfinyl- or sulfonylcalix[4]arene under mild conditions with control of the stoichiometry of the oxidant. Solvent extraction of the transition and alkaline earth metal ions with these hosts showed that the metal binding ability was governed by the oxidation state of the sulfur functionalities. © 1998 Elsevier Science Ltd. All rights reserved. Keywords: Calixarenes; Oxidation; Sulfides; Complexation.
Calixarenes, which are methylene-bridged metacyclophanes derived from p-alkylphenols, are versatile compounds in supramolecular and molecular recognition chemistry [1]. Additional functionalities have been introduced by etherification of the phenolic oxygens (lower rim) and/or substitution of the ppositions (upper rim). For instance, the coordination ability of p-tert-butylcalix[4]arene (1) has been developed by introducing ligating groups such as ester, amide or carboxy groups to the lower rim [2]. On the contrary, the calixarene analogues in which the bridging groups (X) are hetero atoms instead of the methylene groups are very rare due to the difficulty in their synthesis [3,4]. Recently, we reported facile synthesis of p-tertbutylthiacalix[4]arene (2) by base-catalyzed condensation of the phenol and elemental sulfur [5]. As a remarkable result of the replacement of X = CH2 by S, 2 can quantitatively extract
0040-4039•98•5 - see front matter © 1998 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(98)01645-1
R
x. x
R
OH HO
OH
R
/'----'
R calixarenes
X
R
1 2
CH 2 S
Bu t Bu t
3
S
Oct t
4
SO 2
Bu t
5 6
SO 2 SO
Oct t BUt
Octtdenotes 1,1,3,3-tetramethylbutyl group.
7560
transition metal ions such
a s C o 2+, C H 2+
and Zn 2+ from an aqueous phase into chloroform [6].
As had been reported in the literature, we, ourselves, confirmed that 1 has little extraction ability of these metal ions under the comparable extraction conditions [6]. Detailed studies on the structure of 2-Zn 2+ complexes by IH NMR [6] and X-ray crystallography [7] allowed us to conclude that the high binding ability of TCA to the metal ions arises from the involvement of the epithio group, X -- S, for the coordination (vide infra). As is well known, a sulfide function is readily oxidized to the sulfoxide and sulfone, which prompted us to oxidize 2 into the corresponding sulfinyl and sulfonyl derivatives. Herein we report highly selective synthesis of p-tert-butylsulfonylcalix[4]arene (4) and p-(1,1,3,3tetramethylbutyl)sulfonylcalix[4]arene (5) as well as p-tert-butylsulfinylcalix[4]arene (6). Also reported are the results of a solvent extraction study to demonstrate that the coordination ability of the calix[4]arenes depends on the bridging X (= CH2, S, SO, or SO2). The calixarenes 1 [8] and 2 [5] are synthesized as described in the literature, p-(1,1,3,3Tetramethylbutyl)thiacalix[4]arene (3) was obtained by a similar method to that used for the synthesis of 2.1 The oxidation of all four epithio groups into sulfinyl or sulfonyl groups was quite facile. In a typical run, to a solution of 2 (1.0 g, 1.38 mmol) in chloroform (30 ml) were added acetic acid (50 ml) and NaBO3.4H20 (2.0 g, 13 mmol). After the mixture had been stirred at 50°C for 18 hr, 4 was extracted with chloroform (30 ml x 3) and worked up as usual. The product was recrystallized from benzene-methanol and dried in vacuo (80°C, 12 hr) to give a pure sample of 4 (I.06 g, 90.0%). 2 Hydrogen peroxide could be used to oxidize 2 or 3 to the sulfone. 3 By reducing the amount of NaBO3.4H20 to a slight excess (2.0 g, 12 mmol), 2 (2.0 g, 2.76 mmol) was oxidized at 50°C for 4.5 hr to yield 6 (0.67 g, 30.7%). 4 I Compound
3:
mp 260-261 °C; FAB MS m/z 944 (M+); IR (KBr) 33(X) (OH), 2955(CH) cm I; IH NMR (CDCI~) d 0.56 (36H
s, ~2(CH3)2CH2C(CH3)3), 1.24 (24H, s, -C(CH3)2CH2C(CH3)3), 1.59 (8H, s, -C(CH3)2C_H2C(CH3)3), 7.57 (SH, s, Ar H), 9.20 (4H, s, OH); 155.1 (CAr) .
13C NMR (CDCI3) ~5 31.2, 31.7, 32.3, 38.0, 57.0 (-C(CH3)2CH2C(CH3) a) and 120.4, 136.6, 143.4, and
CalcdforC56Hs004S4:C, 71.13; H, 8.53; S, 13.57.
Compound 4:
Found:C, 71.14; H, 8.58; S, 13.53.
mp >360°C; FAB MS m/z 849 (M++I); IR (KBr) 3354 (OH), 2964 (CH), 1319, 1159 (SO 2) c'm I; JH NMR
(CDCI3) 8 1.27 (36H, s, C(CH3)3), 8.03 (SH, s, Ar-H), OH protons (4H) were not detected. 13C NMR (CDCI2CDCI 2) i~ 30.8 . . 34.6 (C_(CH3)3) and 125.9 and 133.2 (CAr). Two of the 13(,-At reson~mces were not observed possibly due to their long (C(C_H3)3), relaxation time. 3
Calcd forC40H48OI2S4: C, 56.58: H, 5.70; S, 15.11.
Found: C, 56.63; H, 5.68; S, 15.01.
For instance, 3 (2.0 g, 1.38 mmol) was dissolved in chlorotbrm (40 ml) and then trifluoroacetic acid (10 ml) and an aq. soln. o! hydrogen peroxide (30%, 20 ml) were added. The mixture was stirred at 80°C lbr 24 hr. After being cooled, the reaction prCuchct was extracted wilh chloroform (30 ml × 3) and washed with 6 M HCI aq. soln. (20 ml x 3). The chlorolorm solution was evaporated to ffyness. The solid residue was triturated well with hexane (150 ml) to remove yellow-colored impurities and then dissolved in chloroform (200 ml). The chlorotorm solution w~t,; washed with 12 M HCI (20 ml × 3) and then evaporated to &yness to give a pure sample of 5 (1.80 g, 79.5%).
Compound 5:
mp 336 °C (&J,:omp.); FAB MS m/z 1074 (M++I); IR
(KBr) 3389 (OH), 2957 (CH), 1306, 1140 (SO 2) cm 1; IH NMR (CDCI 3) 8 0.680 (36H, s, -C(CH3)2CH2C(C_H3)3), 1.32 (24H, s, -C(CH3)2CH2C(CH3)3), 1.73 (8H, s, -C(CH3)2C_H2C(CH~)3), 8.10 (8H, s, Ar H); 13C NMR (CDCI 3) ~ 31.1, 31.8, 32.3, 38.7, 56.5, (-C(CH3)2CH2C(CH3) 3) and 126.9, 133.7, 143.9, and 151.2 (CAr). Calcd for C56H80OI2S4: C, 62.65; H, 7.51; S, 11.95. Found: C, 62.53; H, 7.34; S, 11.76. 4 Compound6: mp 295 °C (decomp.); FAB MS m/z 785 (M++I); IR (KBr) 3188 (OH), 2953(CH), 1001 (SO) cm . I IH NMR
7561
II f~e,-~,O A(q/ ~
/S~o. ~ a xx-. . . 4OII~
~
o
. 8
~ ,,
~
O
~~
0
Fig. 1 The axial-equatorial interconversion of S=O orientation via flip-l'lop inversion of 6. For clarity, p-tert-butylphenol moieties are depicted as hexagons.
The ~H and ~3C NMR spectra of 4, 5, and 6 are uncomplicated and quite similar to those of the parent thiacalix[4]arenes, indicating the structural resemblance, i.e., the cone conformation. In the case of 6, however, ~3C resonance of the two ipso aromatic carbons with respect to H and sulfinyl S=O group splitted into two in each case, suggesting that a pair of distal S=O groups is in the axial orientation while another pair is in the equatorial as shown in Fig. 1. The ax-eq orientation seems to interconvert rapidly via flip-flop inversion on t H NMR time scale to give a single resonance for Ar-H. 4 The proposed C2v configuration of 6 seems to be reasonable as it may be the most stable disposition to minimize the steric and electronic repulsions. The effects of the oxidation state of X on the coordination ability to metal ions were investigated via solvent extraction. 5 The percent extraction, E%, 5 for various metal ions was tabulated in Table 1. 6
Examination of the data in Table 1 reveals several interesting
extraction features characteristic of the calixarenes used. The parent calixarene 1 could hardly extract either transition metal ions or alkaline earth metal ions. On the other hand, thiacalixarenes 2 and 3 extracted the f o r m e r ions very well, while they showed little or no affinity to the latter ions. It can be seen that sulfonylcalixarene 5 behaved in a contrasting manner to the thiacalixarenes (2,3) in that it p r e f e r r e d far more the alkaline earth metal ions, in particular Ca 2÷ ion, than the transition metal ions. As has been reported, the high binding ability of 2 to the transition metal ions can be ascribed to the presence of the the lone pair electrons of one of which can take part in coordinating to the with two phenoxide groups to f o r m two sets of the five-membered chelated 2a) [6,7]. It seems that removal of the lone pair electrons on S by converting
epithio groups, cationic center structure (Fig. to SO2 results
(CDCI3)~5 1.29 (36H, s, C(CH3)3), 7.65 (8H, s, Ar-H), 9.30 (4H, s, OH); t3C NMR (CDCI2CDCI 2) 6 31.1 (C(_C_H3)3), 34.5 (C(CH3)3), 122.5 and 127.7 (_C_Ar-SO), 123.9 and 130.0 (C_Ar-H), 142.1 (C_Ar-But), and 152.4 (C_Ar-OH), which were unambiguously assigned by DEPT. Calcd for C40H4808S4: C, 61.19; H, 6.16; S, 16.34. Found: C, 60.88; H, 6.12; S, 16.06. 5 To a 30 ml vial tube were pipetted a solution of a calixarene (5x 104 M 1, 2, 3, 4, 5, or 6) in chloroform (10 ml) and an a~eous solution (10 ml) containing a metal ion (1×10 ~4 M), pH buffer (5×10 2 M Tris-HCI at pH 8.0 or NH3-HCI at pH 10.0), and tetramethylammonium chloride (0.1 M). The mixture was shaken at 300 strokes/rain for 24 hr. The total concentration of the metal species remaining in the aqueous phase, [Metal]~q, was measured by atomic absorption spectrometer or inductively coupled plasma atomic emission spectrophotometer.
The concentration of the metal ion extracted into the organic phase, [Metal]org, as
the complex was estimated by [Metal]org = [b'Ietal]aq.init - [Metal]aq, where [Metal]aq.init is the initial concentration of the metal ion in the aqueous phase. The percent extraction, E%, was calculated by E% = [Metal]org/ [Metallaq,init× 100°h. 6 In the case of 4, because the aqueous phase was turbid probably due to a reduced solubility in chloroform, the evaluation of the E% was not attempted.
7562
Table 1
The E% values of transition metal and alkaline earth metal ions by calixarenes.
Calixarenes No. X
Co 2+
Transition metal (pH 8.0) Ni 2÷ Cu 2+
Alkaline earth metal(pH 10) Mg 2+ Ca 2+ Ba2+
Zn 2+
1
CH2
5a
1"
Ia
6a
0
0
3
2
S
99 a
97"
69a(99) b
99 a
1
0
7
3
S
99
96
89
99
3
0
0
5
SO2
9
2
4
10
60
100
80
6c
SO
99
(99)
17
(99)
(99)
(91 )
(99)
See reL 6.
c: Except for Co 2+ and Cu 2+, metal-complexes precipitated.
b: At pH 7.0.
in the loss of the coordinating ability to the transition metal ions but the sulfonyl oxygen can in turn bind to the alkaline earth metal ions (Fig. 2b). In this respect, it is quite interesting that sulfinylcalixarene 6 could form complexes with not only the transition metal ions except Cu 2÷ ion but also the alkaline earth metal ions. Thus, it may be said that 6 can switch the coordinating atom between S and O depending on the hardness or softness [9] of the metal ion (Fig. 2c and d). Explanation for the exceptional behavior of Cu 2÷ ion should wait further study. In conclusion, we have shown here selective oxidation of thiacalix[4]arenes to the sulfinyland sulfonylcalix[4]arenes and their characteristic binding behaviors with metal ions by use of the lone pair electrons or oxygen atom on the sulfur moiety. M
M'
O-o. ~
R
/SO~
M
o-"''o o " "
R
M'
O-o~
o- _ o
R
R
(a) 2, 3 (b) 5 (c) 6 (d) 6 Fig. 2 Schematic views of the coordination manner of 2, 3, 5, or 6. Cationic centers M and M' denote transition metal and alkaline earth metal ions, respectively.
References [I] Gutsche CD. Calixarenes: Monographs in Supramolecular Chemistry, Stoddart JF, editor. Cambridge: The Royal Society of Chemistry, 1989; Calixarenes: A Versatile Class of Macrocyclic Compounds, Vicens J, B~hmer V, editors. Dordrecht: Kluwer Academic, 1991; B6hmer V. Angew. Chem. Int. Ed. Engl. 1995; 34: 713-745. [2] See e.g.; Arnaud-Neu F, Collins EM, Deasy M, Ferguson G, Harris S J, Kaitner B, Lough AJ, McKervey MA, Marques E, RuM BL, Schwing-Weill MJ, Seward EM. J. Am. Chem. Soc. 1989; 11 l: 8681-8698; Nagasaki T, Shinkai S. Bull. Chem. Soc. Jpn. 1992; 65: 471-475. [3] Sone T, Ohba Y, Moriya K, Kumada H, Ito K. Tetrahedron 1997; 53:10689 10698. [4] K6nig, B, R6del, M, Bubenitschek, P, Jones, P. G. Angew. Chem. Int. Ed. Engl. 1995; 34: 661~62. [5] Kumagai H, Hasegawa M, Miyanari S, Sugawa Y, Sato Y, Hori T, Ueda S, Kamiyama H, Miyano S. Tetrahedron Lett. 1997; 38: 3971-3972. [6] Iki N, Morohashi N, Narumi F, Miyano S. Bull. Chem. Soc. Jpn. 1998; 71: 1597-1603. 171 Iki N, Morohashi N, Miyano S. to be published elsewhere. [8] Gutsche CD, Iqbal M. Org. Synth. 1990; 68: 234-237. [9] Pearson RG. J. Am. Chem. Soc. 1963; 85: 3533-3539; J. Chem. Edu. 1968; 45: 581-587.