Sulfonyl-bridged oligo(benzoic acid)s: Synthesis, X-ray structures, and properties as metal extractants

Article abstract of DOI:10.1007/s10847-012-0283-9

Sulfonyl-bridged oligo(benzoic acid)s 7 _n (n = 2-4) are prepared from the corresponding triflate esters (8 _n ) of sulfur-bridged oligophenols by palladium-catalyzed methoxycarbonylation of the triflate moieties, followed by hydrolysi

Full text of DOI:10.1007/s10847-012-0283-9

J Incl Phenom Macrocycl Chem
DOI 10.1007/s10847-012-0283-9
ORIGINAL ARTICLE
Sulfonyl-bridged oligo(benzoic acid)s: synthesis, X-ray structures,
and properties as metal extractants
•
Naoya Morohashi Kazutoshi Nagata
•
•
Tomoko Hayashi Tetsutaro Hattori
Received: 2 November 2012 / Accepted: 22 December 2012
Ó Springer Science+Business Media Dordrecht 2013
Abstract Sulfonyl-bridgedoligo(benzoic acid)s7n (n = 2–4)
are prepared from the corresponding triflate esters (8n) of
sulfur-bridged oligophenols by palladium-catalyzed meth-
oxycarbonylation of the triflate moieties, followed by
hydrolysis of the resulting methyl esters, and subsequent
oxidation of the sulfur bridges. X-ray analysis reveals that
dimer 72 forms supramolecular zig-zag chains through
intermolecular hydrogen bonds between the carboxy groups.
As for the crystal of trimer 73, two molecules are associated
through two couples of intermolecular hydrogen bonds
between terminal and central carboxy groups to form a cyclic
dimer, which connects with two adjacent dimers with the
remaining carboxy groups to construct an infinite columnar
structure. Tetramer 74 adopts a monomolecular cyclic
structure through intramolecular hydrogen bonds between
the terminal carboxy groups, and a molecule connects with
each of two adjacent molecules through two couples of
intermolecular hydrogen bonds between inner carboxy and
sulfonyl groups. Solvent extraction experiments reveal that
the oligo(benzoic acid)s exhibit high extractability toward
lanthanoid ions (Ln3?); the performance follows the order
74 & 73 [ 72. Moderate extraction selectivity is observed
for the extraction of Pr3?, Gd3?, and Yb3? with 72. X-ray
crystallographic analysis of cluster [Tb4L4(H2O)6](Et3NH)4,
which was prepared from 74 (H4L) and Tb(NO3)3ꢀ6H2O in
the presence of Et3N, reveals that no sulfonyl oxygens
coordinate to the metal centers. This indicates that the high
extractability of 74 originates from the electron-withdrawing
nature of the sulfonyl function, which increases the acidity of
two adjacent carboxy groups.
Keywords Oligo(benzoic acid) ꢀ Sulfonyl group ꢀ
Solvent extraction ꢀ Lanthanoid ion
Introduction
Recently, many studies have been focused on the devel-
opment of novel extractants for the separation, purification,
and recycling of lanthanoid ions against the background of
an increasing demand in high-technology industries [1–3].
Calix[n]arenes (e.g., 1) are a versatile platform for devel-
oping metal extractants [4–6]. To capture lanthanoid ions
(Ln3?), binding sites such as 2-(dialkylphosphoryl)acet-
amido [7, 8], phosphono [9, 10], alkoxy(hydroxy)phos-
phoryl [11], and carboxy groups [12–14] have been
introduced either to the hydroxy groups through linking
moieties or, alternatively, at the p-positions with or without
linking moieties. On the other hand, we reported that thi-
acalixarenes 2 and 3, and sulfur-oxidized derivatives 4 and
5 exhibit high extractability toward metal ions [15, 16],
which is attributed to the coordination of the sulfur atomic
groups to metal ions in cooperation with two neighboring
phenoxy oxygens, as evidenced by X-ray structural anal-
ysis [17]. In agreement with this, extraction selectivity
varies depending on the oxidation state of the bridging
moieties. For example, thiacalixarenes 2 and 3 extract very
well so-called ‘‘soft’’ metal ions in the hard and soft acids
and bases (HSAB) principle [18, 19], with the aid of the
coordination of the soft sulfur atoms, whereas sulfonylca-
lixarene 5 prefers ‘‘hard’’ metal ions, including lanthanoid
N. Morohashi (&) ꢀ K. Nagata ꢀ T. Hayashi ꢀ T. Hattori (&)
Department of Biomolecular Engineering, Graduate School of
Engineering, Tohoku University, 6-6-11 Aramaki-Aoba,
Aoba-ku, Sendai 980-8579, Japan
e-mail: morohashi@orgsynth.che.tohoku.ac.jp
T. Hattori
e-mail: hattori@orgsynth.che.tohoku.ac.jp
123

J Incl Phenom Macrocycl Chem
ions, with the aid of the coordination of the hard sulfonyl
oxygen [16]. However, compounds 2–5 require high pH
and long time for extraction [15, 16]. We assumed that
these drawbacks can be improved by replacing the hydroxy
groups with more acidic and more metal-affinitive func-
tions such as carboxy, phosphono, and sulfo groups.
However, such chemical transformations are difficult even
by using transition metal catalysts [20–25], because
calixarenes have sterically crowded cyclic structures and
possess a number of coordination sites. Recently, Ohba
et al. and our group reported that an open-chain analog of
thiacalixarene 2 (64) exhibits almost equal extractability to
that of compound 2 toward soft metal ions [26, 27]. In
addition, linear tetramer 64 with reduced steric hindrance
allowed to replace the hydroxy groups with carboxy and
diphenylphosphino functions [28–30]. In this study, we
have synthesized sulfonyl-bridged bis-, tris-, and tetra-
kis(benzoic acid)s 7n (n = 2–4) and examined their metal
extraction capability in order to develop efficient extract-
ants for lanthanoid ions [29].
and stored under nitrogen. Compounds 6n was prepared
according to the literature procedures [31].
Synthesis
Compound 82: To a solution of 62 (4.00 g, 12.0 mmol) in
CH2Cl2 wasaddedpyridine(d = 0.983;3.9 mL,48.0 mmol),
and the mixture was stirred at room temperature for 30 min.
To the mixture was added trifluoromethanesulfonic anhydride
(d = 1.719; 4.3 mL, 26.4 mmol), and the resulting mixture
was stirred for 2 h. The reaction was quenched with 2 M HCl
(5 mL). The resulting mixture was poured into 2 M HCl
(60 mL) and extracted with CHCl3. The organic layer was
evaporated to leave an oil, which was purified by column
chromatography on silica gel with CHCl3-hexane (1:1) as an
eluent to give 82 (7.10 g, 99 %), mp 120–120.8 °C; FAB-MS
1
594 (M?); H NMR (400 MHz) d 1.23 (s, 18H, C(CH3)3),
7.24 (d, 2H, J = 7.3 Hz, ArH), 7.36 (dd, 2H, J = 7.3, 2.5 Hz,
ArH), 7.41 (d, 2H, J = 2.5 Hz, ArH); 13C NMR (100 MHz) d
31.0, 34.8, 117.0, 120.2, 121.5, 127.0, 127.4, 131.9, 146.9,
152.5; IR (KBr) 2,970, 1,423, 1,215, 1,134 cm-1. Anal. Calcd
for C22H24F6O6S3: C, 44.44; H, 4.07. Found: C, 44.30; H,
4.07.
Compound 83: This compound was prepared by a similar
procedure to that used for the preparation of 82. Hexane–
AcOEt (3:1) was employed for the column chromatography
as an eluent. Starting from 63 (700 mg), 83 (1.08 g, 87 %)
was obtained as a colorless powder, mp 101.3–104.0 °C;
1
FAB-MS 907 (M?); H NMR (400 MHz) d 1.12 (s, 9H,
C(CH3)3), 1.28 (s, 18H, C(CH3)3), 7.23 (s, 2H, ArH),
7.24–7.26 (m, 2H, ArH), 7.39 (dd, 2H, J = 8.7, 2.4 Hz,
ArH), 7.44 (d, 2H, J = 2.4 Hz, ArH); 13C NMR (125 MHz)
d 30.8, 31.2, 35.0, 114.9, 117.5, 120.0, 121.8, 122.6, 127.3,
127.6, 130.0, 131.4, 132.3, 145.5, 147.0, 152.7, 152.8; IR
(KBr) 2,970, 1,421, 1,211, 1,141 cm-1. Anal. Calcd for
C33H35F9O9S5: C, 43.70; H, 3.89. Found: C, 43.66; H, 4.03.
Compound 84: This compound was prepared by a similar
procedure to that used for the preparation of 82. Hexane–
CHCl3 (1:1) was employed for the column chromatography
as an eluent. Starting from 64 (500 mg), 84 (786 mg, 89 %)
was obtained as a colorless powder, mp 128.2–130.9 °C;
FAB-MS 1,218 (M?); 1H NMR (400 MHz) d 1.08 (s, 18H,
C(CH3)3), 1.25 (s, 18H, C(CH3)3), 7.23 (d, 2H, J = 2.4 Hz,
ArH), 7.24 (d, 2H, J = 2.4 Hz, ArH), 7.26 (d, 2H,
J = 8.7 Hz, ArH), 7.41 (dd, 2H, J = 8.7, 2.4 Hz, ArH),
7.46 (d, 2H, J = 2.4 Hz, ArH); 13C NMR (100 MHz) d
30.6, 31.0, 34.9, 117.0, 120.2, 121.7, 123.4, 127.2, 127.3,
130.0, 130.1, 131.1, 131.3, 132.2, 145.3, 146.9, 152.7,
152.7; IR (KBr) 2,970, 1,427, 1,211, 1,138 cm-1. Anal.
Calcd for C44H46F12O12S7: C, 43.34; H, 3.80. Found: C,
43.15; H, 3.80.
Experimental section
General methods
Melting points were taken using Stuart SMP3 and are
uncorrected. 1H and 13C NMR spectra were measured with
tetramethylsilane as an internal standard and CDCl3 as a
solvent, unless otherwise noted. Infrared (IR) spectra were
recorded on a Shimazu FTIR-8300 spectrometer. Microa-
nalyses were carried out in the Microanalytical Laboratory
of the Institute of Multidisciplinary Research for Advanced
Materials, Tohoku University. HRMS spectra were mea-
sured using a Bruker Daltonics APEX III in Research and
Analytical Center for Giant Molecules, Graduate School of
Science, Tohoku University. Inductively coupled plasma
atomic emission spectra (ICP-AES) were measured using a
Thermo scientific iCPA6500. Silica gel (63–200 lm) was
used for column chromatography and TLC. Water- and air-
sensitive reactions were routinely carried out under nitro-
gen. Toluene was distilled from sodium diphenyl ketyl and
stored under nitrogen. DMSO (CaSO4), CH2Cl2 (CaH2),
and MeOH (Mg) were distilled from dehydrating agents
Compound 92: To a solution of 82 (1.15 g, 1.93 mmol)
in DMSO–MeOH (2:1, 45 mL) were added Pd(OAc)2
123

J Incl Phenom Macrocycl Chem
(86.8 mg, 0.390 mmol), DPPB (319 mg, 0.770 mmol),
iPr2NEt (d = 0.742; 1.5 mL, 7.72 mmol). The mixture was
stirred under CO atmosphere (1 atm) at 70 °C for 18 h.
After cooling, the reaction was quenched with 2 M HCl
(50 mL). The mixture was poured into water (50 mL) and
extracted with CHCl3 (100 mL 9 3). The organic layer
was dried over Na2SO4 and concentrated in vacuo. The
residue was purified by column chromatography on silica
gel with AcOEt–MeOH (2:1) as an eluent to give 92
7.80 (d, 2H, J = 8.2 Hz, ArH); 13C NMR (100 MHz,
DMSO-d6) d 30.5, 34.6, 123.9, 129.0, 130.1, 130.2, 136.7,
154.7, 167.7; IR (KBr) 1,697 cm-1. Anal. Calcd for
C22H26O4S: C, 68.37; H, 6.78. Found: C, 68.28; H, 6.77.
Compound 103: This compound was prepared by the
same procedure as used for the preparation of 102. Starting
from 93 (574 mg), 103 (318 mg, 60 %) was obtained as a
colorless powder, mp 269.0–269.3 °C; FAB-MS 594 (M?);
1H NMR (400 MHz, acetone-d6) d 1.16 (s, 18H, C(CH3)3),
1.33 (s, 9H, C(CH3)3), 6.99 (d, 2H, J = 1.8 Hz, ArH), 7.28
(dd, 2H, J = 8.2, 1.8 Hz, ArH), 7.73 (s, 2H, ArH), 7.98 (d,
2H, J = 8.2 Hz, ArH); 13C NMR (100 MHz, DMSO-d6) d
30.5, 30.6, 34.7, 34.7, 121.9, 124.2, 124.9, 129.7, 130.8,
134.1, 140.9, 144.5, 153.8, 155.0, 167.2, 167.7; IR (KBr)
1,684 cm-1. Anal. Calcd for C33H38O6S2: C, 66.64; H,
6.44. Found: C, 66.31; H, 6.55.
1
(773 mg, 97 %) as an oil, FAB-MS 414 (M?); H NMR
(400 MHz) d 1.18 (s, 18H, C(CH3)3), 3.84 (s, 6H,
CO2CH3), 7.20 (d, 2H, J = 1.9 Hz, ArH), 7.30 (dd, 2H,
J = 8.3, 1.9 Hz, ArH), 7.85 (d, 2H, J = 8.3 Hz, ArH); 13
C
NMR (100 MHz) d 30.6, 34.7, 51.8, 123.5, 128.8, 129.7,
130.3, 137.7, 155.4, 166.8; IR (KBr) 1,716 cm-1. Anal.
Calcd for C24H30O4S: C, 69.53; H, 7.29. Found: C, 69.46;
H, 7.33.
Compound 104: This compound was prepared by the
same procedure as used for the preparation of 102. Starting
from 94 (331 mg), 104 (226 mg, 85 %) was obtained as a
colorless powder, mp 297.2–300.9 °C; FAB-MS 803
Compound 93: This compound was prepared by a sim-
ilar procedure to that used for the preparation of 92. Hex-
ane–CHCl3 (3:2) was employed for the column
chromatography as an eluent. Starting from 83 (1.00 g), 93
(574 mg, 83 %) was obtained as an oil, FAB-MS 636
(M?); 1H NMR (400 MHz) d 1.12 (s, 18H, C(CH3)3), 1.23
(s, 9H, C(CH3)3), 3.68 (s, 3H, CO2CH3), 3.93 (s, 6H,
CO2CH3), 6.89 (d, 2H, J = 1.8 Hz, ArH), 7.16 (dd, 2H,
J = 8.2, 1.8 Hz, ArH), 7.62 (s, 2H, ArH), 7.91 (d, 2H,
J = 8.2 Hz, ArH); 13C NMR (100 MHz) d 30.9, 31.1,
35.2, 35.2, 52.2, 52.4, 122.1, 124.6, 126.0, 130.9, 131.6,
134.6, 141.6, 143.4, 154.9, 156.0, 166.9, 167.4; IR (KBr)
1,715 cm-1. Anal. Calcd for C36H44O6S2: C, 67.89; H,
6.96. Found: C, 67.80; H, 7.17.
1
([M ? 1]?); H NMR (400 MHz, CDCl3-DMSO-d6 (4:1))
d 1.12 (s, 18H, C(CH3)3), 1.18 (s, 18H, C(CH3)3), 6.85 (d,
2H, J = 1.8 Hz, ArH), 7.16 (dd, 2H, J = 8.2, 1.8 Hz,
ArH), 7.45 (d, 2H, J = 1.8 Hz, ArH), 7.47 (d, 2H,
J = 1.8 Hz, ArH), 7.92 (d, 2H, J = 8.2 Hz, ArH); 13C
NMR (100 MHz, DMSO-d6) d 30.4, 30.4, 34.6, 34.6,
121.8, 124.1, 124.4, 129.3, 130.0, 130.7, 132.2, 133.2,
141.2, 141.3, 153.5, 154.9, 167.1, 167.7; IR (KBr) 3,427,
1,693 cm-1. Anal. Calcd for C44H52O9S3 (104ꢀH2O): C,
64.36; H, 6.38. Found: C, 64.11; H, 6.12.
Compound 72: To
a solution of 102 (318 mg,
Compound 94: this compound was prepared by a similar
procedure to that used for the preparation of 92. Starting
from 84 (786 mg), 94 (408 mg, 78 %) was obtained as an
0.824 mmol) in CHCl3 (5 mL) were added acetic acid
(5 mL) and NaBO3ꢀ4H2O (507 mg, 3.30 mmol), and the
mixture was refluxed for 24 h. After cooling, the mixture
was poured into 2 M HCl (50 mL) and extracted with
CHCl3 (50 mL 9 3). The combined organic layer was
washed with 6 M HCl and evaporated to leave a residue,
which was crystallized from acetone–hexane to give 72
(318 mg, 92 %), mp 281.3–283.6 °C; FAB-MS 441
1
oil, FAB-MS 858 (M?); H NMR (400 MHz) d 1.12 (s,
18H, C(CH3)3), 1.17 (s, 18H, C(CH3)3), 3.81 (s, 6H,
CO2CH3), 3.93 (s, 6H, CO2CH3), 6.87 (d, 2H, J = 1.8 Hz,
ArH), 7.16 (dd, 2H, J = 8.3, 1.8 Hz, ArH), 7.41 (d, 2H,
J = 1.8 Hz, ArH),7.47 (d, 2H, J = 1.8 Hz, ArH), 7.91 (d,
2H, J = 8.3 Hz, ArH); 13C NMR (100 MHz) d 30.8, 30.9,
35.0, 35.1, 52.1, 52.5, 122.0, 124.5, 126.0, 130.8, 130.8,
131.4, 133.0, 133.9, 139.7, 141.6, 154.5, 155.8, 166.8,
167.3; IR (KBr) 1,732 cm-1. Anal. Calcd for C48H58O8S3:
C, 67.10; H, 6.80. Found: C, 66.92; H, 7.02.
1
([M ? Na]?); H NMR (500 MHz, acetone-d6) d 1.37 (s,
18H, C(CH3)3), 7.64 (d, 2H, J = 8.0 Hz, ArH), 7.79 (dd,
2H, J = 8.0, 1.9 Hz, ArH), 8.45 (d, 2H, J = 1.9 Hz, ArH);
13C NMR (100 MHz, acetone-d6) d 31.2, 35.9, 129.5,
129.7, 131.1, 132.3, 140.0, 154.7, 169.1; IR (KBr) 1,711,
1,293 cm-1. Anal. Calcd for C22H26O6S3: C, 63.14; H,
6.26. Found: C, 62.85; H, 6.18.
Compound 102: A mixture of 92 (921 mg, 2.22 mmol)
and KOH (1.25 g, 22.2 mmol) in EtOH–H2O (10:1,
44.0 mL) was refluxed for 2 h. The mixture was cooled in
an ice-water bath and acidified with 4 M HCl (100 mL) to
liberate the free acid, which was collected by filtration and
washed with water to give 102 (760 mg, 89 %), mp
275.8–277.1 °C; FAB-MS 386 (M?); 1H NMR (400 MHz,
DMSO-d6) d 1.13 (s, 18H, C(CH3)3), 7.06 (d, 2H,
J = 1.8 Hz, ArH), 7.40 (dd, 2H, J = 8.2, 1.8 Hz, ArH),
Compound 73: This compound was prepared by a sim-
ilar procedure to that used for the preparation of 72.
Starting from 103 (220 mg), 73 (195 mg, 80 %) was
obtained as a colorless powder, mp 309.7–311.6 °C; FAB-
1
MS 681 ([M ? Na]?); H NMR (400 MHz, acetone-d6) d
1.35 (s, 18H, C(CH3)3), 1.39 (s, 9H, C(CH3)3), 7.62 (d, 2H,
J = 8.0 Hz, ArH), 7.81 (dd, 2H, J = 8.0, 1.8 Hz, ArH),
123

J Incl Phenom Macrocycl Chem
8.32 (d, 2H, J = 1.8 Hz, ArH), 8.72 (s, 2H, ArH); 13C NMR
(100 MHz, DMSO-d6) d 30.3, 30.6, 35.0, 35.4, 127.6,
128.6, 131.4, 131.5, 132.0, 133.2, 137.0, 138.7, 153.1, 153.5,
166.2, 168.9; IR (KBr) 3,200, 1,706, 1,327 cm-1, HRMS
calcd for C33H37O10S2 [M - H]? 657.1834, found
657.1831.
X-ray crystallographic analysis
X-ray crystallographic analysis was performed with a Bruker
SMART APEX or APEX II diffractometer (graphite
˚
monochrometor, MoKa radiation, k = 0.71073 A). Data
integration and reduction were performed with the SAINT
and XPREP software [32] and the absorption correction was
performed by the semi-empirical method with SADABS
[33]. The structure was solved by the direct method using
SHELXS-97 [34] and refined by using least-squares methods
on F2 with SHELXL-97 [34]. X-ray analysis was undertaken
using the free GUI software of Yadokari-XG 2009 [35, 36].
Crystallographic data have been deposited with Cambridge
Crystallographic Data Centre: Deposition number CCDC
908516–908518 for 72, 73, and 11 and 908785 for 74.
Compound 74: This compound was prepared by a similar
procedure to that used for the preparation of 72. Crystalli-
zation was carried out from CH2Cl2–hexane. Starting from
102 (260 mg), 74 (192 mg, 66 %) was obtained as a color-
less powder, mp 249.9–251.3 °C; FAB-MS 921 ([M ?
Na]?); 1H NMR (400 MHz) d 1.22 (s, 18H, C(CH3)3), 1.46
(s, 18H, C(CH3)3), 7.38 (d, 2H, J = 1.9 Hz, ArH), 7.78 (dd,
2H, J = 8.2, 1.9 Hz, ArH), 7.99 (d, 2H, J = 8.2 Hz, ArH),
8.48 (d, 2H, J = 1.9 Hz, ArH), 8.57 (d, 2H, J = 1.9 Hz,
ArH); 13C NMR (100 MHz, DMSO-d6) d 30.5, 30.7, 35.6,
36.1, 128.9, 129.4, 131.6, 131.9, 132.1, 133.6, 134.6, 138.7,
139.5, 140.3, 154.5, 154.8, 166.7, 168.7; IR (KBr) 3,568,
1,720, 1,331 cm-1. Anal. Calcd for C44H50O14S3: C, 58.78;
H, 5.61. Found: C, 58.70; H, 5.72.
Crystallographic data for 72: C22H26O6S4, fw = 418.49,
˚
˚
orthorhombic, Pbcn, a = 13.049(2) A, b = 10.9020(18) A,
3
˚
˚
c = 14.746(3) A, V = 2,097.9(6) A , Z = 4, T = 173(2)
K, 10,867 reflections measured, 2,395 independent reflec-
tions, 2,147 reflections were observed (I [ 2r(I)), R1 =
0.0418, wR2 = 0.1090 (observed), R1 = 0.0459, wR2 =
0.1154 (all data).
Cluster 11: To a solution of 74 (23.0 mg, 25.0 lmol) in
methanol–toluene (4:1, 20.0 mL) was added Et3N (d =
0.729; 69 lL, 0.50 mmol), and the mixture was stirred for
30 min. To a mixture was added a solution of Tb(NO3)3ꢀ
6H2O (11.0 mg, 25.0 lmol) in methanol–toluene (4:1,
5.0 mL), and the resulting mixture was refluxed for 3 h. The
volatile materials were evaporated to leave a residue, which
was dissolved in CHCl3 (10 mL) and washed with water
(10 mL 9 2). After the organic layer was evaporated, the
residue was crystallized from CH2Cl2–hexane to give 11
(17.0 mg, 59 %) as a colorless powder. Vapor diffusion of
diethyl ether to a solution of 11 in CH2Cl2 afforded single
crystals.
Crystallographic data for 73ꢀH2Oꢀ(CH3CN)0.5: C34H41.5
˚
O11S2, fw = 697.30, monoclinic, C2/c, a = 31.493(9) A,
˚
˚
b = 11.149(3) A, c = 25.511(7) A, b = 119.872(4)°, V =
3
7,767(4) A , Z = 8, T = 173(2) K, 20,953 reflections
˚
measured, 8,720 independent reflections, 3,710 reflections
were observed (I [ 2r(I)), R1 = 0.0872, wR2 = 0.2170
(observed), R1 = 0.2108, wR2 = 0.2991 (all data).
Crystallographic data for 74ꢀCH2ClCH2Clꢀ(CH3OH)0.5
ꢀ
hexane: C52.5H70Cl2O14.5S3, fw = 1,100.17, monoclinic,
˚
P21/c, a = 16.506(6) A, b = 18.365(6) A, c = 20.401(7) A,
˚
˚
3
˚
b = 109.994(11)°, V = 5,811(3) A , Z = 4, T = 100 (2) K,
26,154 reflections measured, 7,599 independent reflections,
2,652 reflections were observed (I [ 2r(I)), R1 = 0.0956,
wR2 = 0.2196 (observed), R1 = 0.2418, wR2 = 0.2643 (all
data).
Solvent extraction
Crystallographic data for 11ꢀCH2Cl2ꢀ(C2H5OC2H5)3ꢀ
General procedure for the extraction experiment is as follows:
An aqueous solution containing indicated concentrations of a
metal ion ([Metal]aq,init = 1.0 9 10-4 M), Me4NCl (0.1 M),
and a pH buffer (0.05 M) was prepared; the pH buffer was
selected from glycine–NH3 (pH = 2.5–3.5), succinic acid–
NH3 (pH = 4.0–5.0), MES–NH3 (pH = 5.5–6.0), PIPES–
NH3 (pH = 6.5–7.0), HEPPSO–NH3 (pH = 7.5–8.5), and
CHES–NH3 (pH = 9.0–10.0). In case of the extraction of
Ag?, Me4NCl was not added to avoid the formation of AgCl.
The aqueous solution (10 mL) was combined with a solution
of an extractant ([72] = 1.0 9 10-3 M, [73] = 6.7 9 10-4 M,
[74] = 5.0 9 10-4 M) in 4-methyl-2-pentanone or CHCl3
(10 mL) in a 30 mL vial tube, and the mixture was shaken at
300 strokes min-1 at room temperature (*20 °C) for 1 h.
After the two layers were separated, [Metal]aq was measured
by ICP-AES.
(H2O)4: C213H300Cl2N4O69S12Tb4, fw = 5,111.87, mono-
˚
clinic, C2/c, a = 46.801(11) A, b = 19.028(5) A, c = 42.
˚
3
˚
˚
374(10) A, b = 121.267(3)°, V = 33,015(14) A , Z = 4,
T = 100 (2) K, 182,210 reflections measured, 37,607 inde-
pendent reflections, 22,968 reflections were observed
(I [ 2r(I)), R1 = 0.0785, wR2 = 0.2212 (observed), R1 =
0.1430, wR2 = 0.2712 (all data).
Results and discussions
Synthesis
Sulfonyl-bridged oligo(benzoicacid)s7n (n = 2–4)werereadily
prepared by using palladium-catalyzed methoxycarbonylation
123

J Incl Phenom Macrocycl Chem
as a key step (Scheme 1) [37–39]. Thus, the esterification of
oligophenols 6n (n = 2–4) with triflic anhydride gave tri-
flate esters 8n, which were subjected to palladium-catalyzed
methoxycarbonylation using MeOH, Pd(OAc)2, dppb, and
Hunig’s base in DMSO under CO atmosphere (1 atm). The
Pd catalyst smoothly replaced all the triflate moieties with
methoxycarbonyl functions to give oligo(benzoate ester)s
9n. Hydrolysis of the methyl esters 9n, followed by the
oxidation of the bridging sulfur moieties using NaBO3ꢀ4H2O
gave sulfonyl-bridged oligo(benzoic acid)s 72, 73, and 74 in
total yields of 79, 35, and 39 %, respectively, based on the
starting oligophenols 6n.
X-ray structural analysis
The novel sulfonyl-bridged oligo(benzoic acid)s were
subjected to single-crystal X-ray analysis. Prerequisite
single crystals were obtained by the vapor diffusion of
hexane (for 72 and 74) or CH3CN (for 73) to an acetone
solution of 72 or 73, or a CH2ClCH2Cl solution of 74.
The crystal of 72 belongs to the orthorhombic system
with Pbcn space group. The molecule has a C2 symmetric
structure (Fig. 1a). The two carboxy groups adopt anti
conformation with respect to the plane defined by the sulfur
and two adjacent carbon atoms. As a result, the carboxy
groups do not form intramolecular hydrogen bonds but
connect with other carboxyl groups of neighboring 72
molecules through intermolecular hydrogen bonds to con-
struct a 21-helical zig-zag structure along the c axis
Fig. 1 X-ray structure of 72: a Molecule and b hydrogen-bond
network viewed along the c-axis. Hydrogen atoms except those of
carboxy groups and disordered carbon atoms are omitted for clarity.
Green dotted lines represent intermolecular hydrogen bonds. (Color
figure online)
dimer is molecularly chiral and two enantiomeric con-
formers connect alternately through intermolecular hydro-
gen bonds between the remaining carboxy groups to form
an infinite columnar structure along the c-axis (Fig. 2c); the
˚
average O–H_O=C distance is 1.767 A. Further, the
˚
columnar structures are arranged parallel to each other
along the b-axis to construct a layer (Fig. 2d), and the
layers pile up along the a-axis (Fig. 2e). Interestingly,
porous channels are created along the b-axis and filled with
CH3CN and H2O molecules.
(Fig. 1b); the average O–H_O=C distance is 1.785 A.
The crystal of 73 belongs to the monoclinic system with
C2/c space group. The molecule adopts a twisted confor-
mation (Fig. 2a) and the central and a terminal carboxy
group connect with a terminal and the central carboxy
group of an adjacent molecule, respectively, through
intermolecular hydrogen bonds to construct a cyclic dimer
structure with C2 symmetry (Fig. 2b); the average O_O
The crystal of 74 belongs to the monoclinic system with
P21/c space group. The molecule has a cyclic structure
with intramolecular hydrogen bonds between the terminal
carboxy groups (Fig. 3a). The conformation is chiral and a
˚
distance is 2.631 A. Interestingly, the conformation of the
Scheme 1 Synthesis of 72, 73,
and 74
123

J Incl Phenom Macrocycl Chem
Fig. 3 X-ray structure of 74: a Molecule and b hydrogen-bond
network viewed along the a-axis. Green dotted lines represent
intermolecular hydrogen bonds. Hydrogen atoms, disordered carbon
atoms, and included solvents are omitted for clarity. (Color figure
online)
for serving as a supramolecular absorbent, which captures
specific molecules in the solid state [40, 41].
Solvent extraction
Solvent extraction was carried out to evaluate the coordi-
nation ability of the sulfonyl-bridged oligo(benzoic acid)s
7n toward lanthanoid ions (Ln3?), as well as several other
metal ions. An aqueous solution (10 mL) containing a
metal ion (1.0 9 10-4 M), Me4NCl (0.1 M), and a pH
buffer (0.05 M) was combined with the same volume of a
solution of an extractant ([72] = 1.0 9 10-3 M,
[73] = 6.7 9 10-4 M, [74] = 5.0 9 10-4 M) in MIBK or
CHCl3 (10 mL); the concentration of the monomer unit
was fixed at 2.0 9 10-3 M for the three extractants. The
mixture was vigorously shaken at room temperature for 1 h
and the metal ion remained in the aqueous phase was
analyzed by ICP-AES. The extraction percent (E %) was
calculated according to the following equation:
Fig. 2 X-ray structure of 73: a Molecule, b dimer, c hydrogen-bond
network viewed along the c-axis, d cross-section of crystal packing
parallel to the bc plane, and e cross-section of crystal packing parallel
to the ac plane. Green dotted lines represent intermolecular hydrogen
bonds. Hydrogen atoms except those of carboxy groups, disordered
carbon atoms, and included solvents (a–c) are omitted for clarity.
Molecules are color-coded to clarify the packing structure (d and e).
(Color figure online)
ꢀ
ꢁ
E% ¼ ½Metalꢁaq;initꢂ½Metalꢁaq =½Metalꢁaq;initꢃ100%
molecule connects with each of two adjacent antipodal
conformers through two couples of intermolecular hydro-
gen bonds between inner carboxy and sulfonyl groups to
construct an infinite columnar structure along the a-axis
(Fig. 3b). The average intramolecular O–H_O=C and
intermolecular C(=O)O_O=S distances are 1.819 and
where [Metal]aq,init and [Metal]aq are the concentrations of
the metal ion in the aqueous phase before and after
extraction. Figures 4 and 5 show the pH dependence of
E % for Ag?, Cu2?, Ni2?, Mg2?, Ho3?, and Tb3?. The
performance of sulfur-bridged tetrakisphenol 64, as well as
that of tetrakis(benzoic acid) 104, was also tested for
comparison.
˚
2.661 A, respectively.
As mentioned above, it was found that the sulfonyl-
bridged oligo(benzoic acid)s change their crystal structures
depending on the number of monomer unit. The crystal of
tri(benzoic acid) 73, bearing porous channels, has a potential
A soft metal ion, Ag?, was extracted only with tet-
rakisphenol 64 in a moderate E % at pH 6.0 (Fig. 4a). On
the other hand, an intermediate metal ion, Cu2?, was
123

J Incl Phenom Macrocycl Chem
Fig. 5 The pH dependence of E % for Mg2? (a), Ho3? (b), and Tb3?
(c) with 64 (open circle), 72 (filled circle), 73 (open square), 74 (filled
square), and 104 (filled triangle). MIBK was used as an organic phase
Fig. 4 The pH dependence of E % for Ag? (a), Cu2? (b), and Ni2?
(c) with 64 (open circle), 72 (filled circle), 73 (open square), 74 (filled
square), and 104 (filled triangle). MIBK was used as an organic phase
high extractability toward lanthanoid ions, Ho3? and Tb3?
,
which were hardly extracted with 64 (Fig. 5b, c). The pH
dependence of E % indicates that 7n, as well as 104,
extracted the metal ions by exchanging their acidic protons.
In this mechanism, extraction becomes difficult as pH
decreases. The pH values, above which 72, 73, and 74
exhibited high E % values, are 7.0, 5.5, and 5.5, respec-
tively. Therefore, the extractability of the oligo(benzoic
acid)s follows the order 74 & 73 [ 72, indicating that the
presence of more than three carboxy units is important for
the efficient extraction of lanthanoid ions. A similar
observation has been made in the extraction of soft to
intermediate metal ions with oligophenols [27]. It should
be noted that Ho3? was quantitatively extracted with 73 and
extracted with not only 64 but also 73, 74, and 104 in high
E % at pH 6.0–7.0 (Fig. 4b). However, another interme-
diate metal ion, Ni2?, was extracted only with 74 among 7n
in a moderate E % even at pH 8.5, whereas 64 completely
extracted this ion at the same pH (Fig. 4c). As mentioned
above, sulfonyl-bridged oligo(benzoic acid)s 7n was infe-
rior to sulfur-bridged tetrakisphenol 64 in extractability
toward soft to intermediate metal ions. It seems that the
replacement of phenolic hydroxy groups with more acidic
and more metal-affinitive carboxy groups cannot cover the
lack of soft sulfur coordination sites.
A hard metal ion, Mg2?, was extracted only with 74 in
moderate E % (Fig. 5a). Interestingly, 7n and 104 exhibited
123

J Incl Phenom Macrocycl Chem
groups, adopts a rigid conformation suited for the dis-
crimination of ion radii. However, the difference of the
pH1/2 values was not sufficient to separate the three ions;
actually, the E % values of Yb3?, Gd3?, and Pr3? were 88,
75, and 30 %, respectively, at pH 6.6.
X-ray structural analysis of a Tb3? cluster of compound
74
In order to gain insight into the origin of the high extract-
ability of oligo(benzoic acid) 74, as well as 73, toward
lanthanoid ions, we prepared a Tb complex, which was
found to be a metal cluster later (vide infra), and analyzed it
by X-ray crystallography. Compound 74 (H4L) was allowed
to react with 1 molar equiv of Tb(NO3)3ꢀ6H2O in the
presence of an excess of Et3N in refluxing toluene–metha-
nol (4:1). After aqueous workup, the mixture was crystal-
lized from CH2Cl2–hexane to give cluster 11 formulated as
[Tb4L4(H2O)6](Et3NH)4. Single crystals suitable for X-ray
analysis were obtained by vapor diffusion of diethyl ether to
a CH2Cl2 solution of cluster 11 (Fig. 7). The cluster adopts
Fig. 6 The pH dependence of E % for Tb3? with 5 (times symbol)
and 74 (filled square). CHCl3 was used as an organic phase
74 at pH 7.0 even by reducing the extraction time (30 min).
The comparison of the extraction performance among
sulfur-bridged tetrakisphenol 64, sulfonyl-bridged tetra-
kis(benzoic acid) 74, and its sulfur-bridged analog 104
indicates that the replacement of the hydroxy groups is
more effective than the oxidation of the bridging sulfur
moieties for the improvement of the extractability toward
lanthanoid ions. The extractability of 74 toward Tb3? was
also compared with that of sulfonylcalixarene 5 (Fig. 6),
which is reported to exhibit high affinity toward hard metal
ions [16]. It was found that Tb3? was quantitatively
extracted with 74 even at pH 3.5, when CHCl3 was used as
an organic phase; the performance is apparently superior to
that of sulfonylcalixarene 5.
a Ci-symmetric cyclic structure composed of four ate
-
complexes [TbL3/4L1/4
]
with four Et3NH? as counter
Our next attention was directed toward the extraction
selectivity of lanthanoid ions with the oligo(benzoic acid)s.
Table 1 summarizes the half-extraction pH (pH1/2) for the
extraction of Pr3?, Gd3?, and Yb3? with dimer 72 and
tetramer 74, as compared to the results with sulfonylca-
lixarene 5 (The E % values somewhat depend on buffering
agents. The pH1/2 values could not be precisely determined
for 73 because they fall around the pH range (pH & 5.5)
where the buffer has to be changed). A distinct difference
in pH1/2 was observed among the three ions when dimer 72
was employed. The extraction selectivity increased in the
order Pr3? \ Gd3? \ Yb3?, which correlates with the
descending order of ion radius. It is easily conceivable that
dimer 72, upon ligation to a metal ion with the two carboxy
Table 1 The pH1/2 values for the extraction of lanthanoid ions
Ligands
pH1/2
Pr3?
Gd3?
Yb3?
5
5.77
6.85
2.70
5.78
6.25
2.71
5.59
6.03
2.75
72
74
Fig. 7 Crystal structure of 11 (a) and its schematic view (b).
t
Hydrogen atoms, Bu groups, and included solvents are omitted for
clarity
CHCl3 was used as an organic phase
123

J Incl Phenom Macrocycl Chem
Conclusion
Sulfonyl-bridged oligo(benzoic acid)s 7n were prepared
from the corresponding sulfur-bridged oligophenols and
analyzed by X-ray crystallography. Solvent extraction
experiments of lanthanoid ions with 7n revealed the rela-
tionship between the number of monomer unit and
extractability, as well as selectivity. The origin of the high
extractability of 74 was explained based on the X-ray
structure of a Tb cluster.
Acknowledgments The authors wish to thank Prof. K. Itaya (Tohoku
University) for courteous permission to use instruments.
Fig. 8 Coordination spheres of Tb1 and Tb2 in X-ray structure of 11.
˚
Selected atomic distances (A): Tb1–O3 2.498(6), Tb1–O4 2.376(6),
Tb1–O5 2.256(5), Tb1–O7 2.338(6), Tb1–O9 2.486(6), Tb1–O10
2.524(5), Tb1–O16 2.317(6), Tb1–O29 2.356(6), Tb2–O10 2.280(5),
Tb2–O10 2.385(5), Tb2–O11 2.394(6), Tb2–O12 2.547(6), Tb2–O13
2.340(6), Tb2–O15 2.303(5), Tb2–O30 2.454(6), and Tb2–O31 2.405(5)
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