Complexation behavior and crystal structure of a dithia[16.3.3](1,2,6)cyclophane: A novel one-dimensional coordination polymer with perchlorate anions as linkers

Article abstract of DOI:10.1016/S0040-4039(02)02243-8

The synthesis of 20,28-dimethyl-24,33-dithia-1,4,7,10,13,16-hexaoxa[16.3.3](1,2,6)cyclophane 3 was achieved by cesium carbonate-assisted high dilution cyclization. Cyclophane 3 exhibited strong complexation towards all alkali metal ions. The change in chemical shift for the bridge methylene protons upon addition of alkali metal ions correlated to log K_a. The crystal structure of cyclophane 3 as well as its sodium and potassium complexes was studied. Cyclophane 3 formed a novel one-dimensional coordination polymer with potassium perchlorate using anions as the linkers, while the complex of 3 with sodium perchlorate had a dimeric structure.

Full text of DOI:10.1016/S0040-4039(02)02243-8

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 9199–9202
Complexation behavior and crystal structure of a
dithia[16.3.3](1,2,6)cyclophane: a novel one-dimensional
coordination polymer with perchlorate anions as linkers†
Jianwei Xu and Yee-Hing Lai*
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
Received 15 July 2002; revised 24 September 2002; accepted 4 October 2002
Abstract—The synthesis of 20,28-dimethyl-24,33-dithia-1,4,7,10,13,16-hexaoxa[16.3.3](1,2,6)cyclophane 3 was achieved by cesium
carbonate-assisted high dilution cyclization. Cyclophane 3 exhibited strong complexation towards all alkali metal ions. The change
in chemical shift for the bridge methylene protons upon addition of alkali metal ions correlated to log Ka. The crystal structure
of cyclophane 3 as well as its sodium and potassium complexes was studied. Cyclophane 3 formed a novel one-dimensional
coordination polymer with potassium perchlorate using anions as the linkers, while the complex of 3 with sodium perchlorate had
a dimeric structure. © 2002 Elsevier Science Ltd. All rights reserved.
The term crownophane is defined as a macrocycle in
which a mobile polyether chain and a rigid cyclophane
unit are present.1 Crownophanes, combining a flexible
moiety with complexation ability, exhibit some interest-
ing properties.2–4 Dithia[3.3]metacyclophane shows con-
formational diversity in solution.5 Besides syn–anti
isomerization, it undergoes bridge-wobbling, ring-
flipping and ring-tilting processes. In this article, we
report the synthesis, complexation properties and struc-
tural study of a syn-dithia[3.3]metacyclophane-fused
crownophane.
pseudochair–pseudochair conformation. Both aromatic
rings do not deviate from planarity, but tilt at an angle
of 12.8°, which is less than that in syn-2,11-
dithia[3.3]metacyclophane (20.6°)10 because the internal
crown ring forces the aromatic rings to be inclined to
favor ‘inward tilting’. The average diameter of the
,
crown part is estimated to be ca. 2.81 A. The
crownophane 3 exhibits strong complexation ability
towards all alkali metal cations. Its logarithm of associ-
ation constants (Ka)11 are 3.57, 4.26, 5.77, 5.21 and
4.55, respectively, for Li+, Na+, Rb+, and Cs+. Log Ka
for K+ is the largest, which is as expected in accordance
with the size complementarity. In comparison with
18-crown-6,12 K+/Na+ selectivity for 3 decreases by a
Crownophane 3 was synthesized as shown in Scheme 1.
Tetraol 2a6 was prepared in a good yield of 66% by the
reaction of bis(2,6-hydroxymethyl)-4-methylphenol 1
with pentaethylene glycol dibromide in dry acetone.
Conversion of 2a to tetrabromide 2b7 could be achieved
in 74% yield using phosphorus tribromide in dry 1,4-
dioxane at low temperature. The corresponding
crownophane 38 was obtained in 51% yield when 2b
underwent intramolecular cyclization with Na2S·9H2O
in the presence of Cs2CO3 under high dilution condi-
tions. The single-crystal X-ray structure of 3 was
determined9 (Fig. 1). The two thia-bridges in 3 adopt a
Keywords: cyclophane; crownophane; synthesis; complexation; crystal
structure.
Scheme 1. Reagents and conditions: (i) 2a, Br(CH2CH2O)4−
CH2CH2Br, acetone, K2CO3; 2b, PBr3, 1,4-dioxane, 0–10°C;
(ii) Na2S·9H2O, Cs2CO3, benzene/ethanol, high dilution con-
ditions.
* Corresponding author. Fax: +65-6779-1691; e-mail: chmlaiyh@
nus.edu.sg
† Taken in part from the J. Xu’s dissertation.
0040-4039/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(02)02243-8

9200
J. Xu, Y.-H. Lai / Tetrahedron Letters 43 (2002) 9199–9202
Figure 1. ORTEP drawing of 3. Hydrogen atoms are omitted
for clarity.
factor of 6.4, indicating that aromatic ring-tilting and
thia-bridge wobbling processes in the cyclophane part
have an effect on the selectivity.
Figure 2. The chemical shift changes for Heq and Hax upon
addition of an alkali cation correlated to log Ka. The Dl are
taken as their absolute values in the plot.
Induced chemical shifts upon addition of alkali metal
ions were measured in CD3CN and the results are
summarized in Table 1. Interestingly, the oxyethylene
protons show only small changes relative to the bridge
methylene protons (axial Hax and equatorial Heq). The
changes in chemical shift of the methylene protons in
the thia-bridges exhibit a correlation to the log Ka for
the alkali metal ions: the higher the log Ka, the larger
the change in chemical shift (Fig. 2). For example,
crownophane 3, which has the largest log Ka for K+,
showed the largest downfield shift (0.21 ppm) for Hax
and the largest upfield shift (−0.27 ppm) for Heq. In fact
the order of the chemical shift changes for Hax in 3
(K+>Rb+>Na+>Cs+>Li+) follows the same trend as the
order of the log Ka values. The thia-bridges in 3
undergo wobbling processes13 in solution, however,
complexation may reduce or disrupt the free wobbling
motion due to steric hindrance thus leading to confor-
mational and geometrical changes in the cyclophane
part. This may account for the large change in chemical
shift for the bridge methylene protons upon addition of
alkali metal ions.
Figure 3. ORTEP drawing of the coordination polymer
formed by 3·KClO4 at the 50% probability level. Hydrogen
atoms are omitted for clarity.
(Fig. 3). The infinite zig-zag chain formed by the potas-
,
sium atoms with K···K distance of 6.75 A and a
K···K···K angle of 102.6° is parallel or antiparallel to
other chains and extends along the crystallographic a
axis. In particular, it is noteworthy that the interlayer
of chains interacts through hydrogen bonding between
O8 of the anion and the HꢀC of the polyether chain
(Fig. 4). The CꢀH···O interaction, with distances of
The complex 3·KClO4 for X-ray crystallographic analy-
sis was obtained by vapor diffusion in a mixture of 1:1
stoichiometric crownophane 3 and KClO4 in acetoni-
trile.14 The drawing of 3·KClO4 is portrayed in Fig. 3.
Each K+ is eight-coordinated to oxygen atoms, five
from six crown ring oxygen atoms and three from two
independent perchlorate anions. Each complex unit is
linked to other two host–guest moieties through the
perchlorate anions to generate an infinite wave chain
,
3.375 and 2.576 A, for the C···O and H···O, respec-
tively, and an angle of 137.7° for CꢀH···O, dominates
the interchain packing and thus stabilizes the crystal.
The K+ in (3·KClO4)n lies significantly above the aver-
age plane defined by O2, O3, O4, O5 and O6 by 1.033
Table 1. Changes in chemical shift (Dl)a upon addition of alkali cations in CD3CN at 25°C
Metal ion
Heq
Hax
Ha (Ar)
H(Me)
Hb
Hc
Hd
He
0.05
0.02
−0.03
−0.03
−0.05
Hf
0.05
0.08
−0.05
−0.05
‘0.21
Li+
Na+
K+
−0.02
−0.15
−0.27
−0.24
−0.16
0.03
0.15
0.21
0.20
0.12
0.01
0.01
0.02
0.02
0.04
0.01
0.03
0.04
0.05
0.05
0.05
−0.01
−0.04
−0.04
−0.04
−0.03
0.05
−0.01
−0.04
−0.05
0.00
0.02
−0.03
−0.04
−0.05
Rb+
Cs+
a Dl (ppm)=l(M+Pic−+Crownophane)−l(Crownophane); [M+Pic−]=[Crownophane].

J. Xu, Y.-H. Lai / Tetrahedron Letters 43 (2002) 9199–9202
9201
polymeric unit consisting of lithium and a bridging
halogen. In this respect, the supramolecular assembly in
(3·KClO4)n observed in our study seems to be a unique
example.
Supplementary material
Crystallographic data for the structures reported in this
paper have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication
numbers CCDC-184025-184027. Copies of the data can
be obtained free of charge upon application to CCDC
12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44)
1223-33603; email: deposit@ccdc.cam.ac.uk).
Figure 4. The packing of (3·KClO4)n along the crystallo-
graphic a axis. The hydrogen bonds are indicated by dashed
lines.
Acknowledgements
+
,
A. This is very different from the 18-crown-6-K
complex15 in which K+ is coordinated to all six oxygen
atoms and embedded perfectly in the plane. On the
other hand, the crown part bends towards one of the
thia-bridges. This steric arrangement in (3·KClO4)n
places the potassium ion in a more favorable spatial
environment able to coordinate to oxygen atoms from
another perchlorate anion thus extending the chain
according to the observed pattern. The thermogravi-
metric analysis of (3·KClO4)n shows that the coordina-
tion polymer was relatively stable and started to
decompose at about 270°C.
This research was sponsored by National University of
Singapore (NUS). We are grateful to Assoc. Professor
J. J. Vittal and Ms. Tan Geok Kheng for determination
of the X-ray single crystal structures in the X-ray
structure laboratory at the Department of Chemistry of
NUS.
References
1. (a) Inokuma, S.; Sakai, S.; Nishimura, J. Top. Curr.
Chem. 1994, 172, 87–118; (b) Nishimura, J.; Nakamura,
Y.; Hayashida, Y.; Kuda, T. Acc. Chem. Res. 2000, 33,
679–686.
For comparison, we also examined the reaction of 3
and NaClO4 and determined the structure of complex
3·NaClO4.16 Since the Na+ ion, with a diameter of 1.90
,
A, is smaller than that of the host cavity, it resulted
2. (a) Helgeson, R. C.; Timko, J. M.; Cram, D. J. J. Am.
Chem. Soc. 1974, 96, 7380–7382; (b) Helgeson, R. C.;
Tarnowski, T. L.; Timko, J. M.; Cram, D. J. J. Am.
Chem. Soc. 1977, 99, 6411–6418; (c) Hiratani, K.; Goto,
M.; Nagawa, Y.; Kasuga, K.; Fujiwara, K. Chem. Lett.
2000, 1364–1365; (d) Tokuhisa, H.; Ogihara, T.; Nagawa,
Y.; Hiratani, K. J. Inclusion Phenom. Macrocyclic. Chem.
2001, 39, 347–352; (e) Allwood, B. L.; Kohnke, F. H.;
Stoddart, J. F.; Williams, D. J. Angew. Chem., Int. Ed.
1985, 24, 581–584; (f) Tsuzuki, S.; Houjou, H.; Nagawa,
Y.; Hiratani, K. J. Chem. Soc., Perkin Trans. 2 2001,
1951–1955; (g) Tokuhisa, H.; Nagawa, Y.; Uzawa, H.;
Hiratani, K. Tetrahedron Lett. 1999, 40, 8007–8010; (h)
Hiratani, K.; Uzawa, H.; Kasuga, K.; Kambayashi, H.
Tetrahedron Lett. 1997, 38, 8993–8996.
instead in the formation of
a dimeric complex
(3·NaClO4)2, in which Na+ is coordinated to four oxy-
gen atoms from the polyether chain and perchlorate
anions again act as linkers (Fig. 5). In 3·NaClO4, the
thia-bridges adopt pseudochair–pseudochair conforma-
tions similar to those observed in the free crownophane
3 and 3·KClO4.
Classic crown ethers form stable complexes with metal
ions, however, crown ethers and main group metal
cations are rarely employed to construct coordination
polymers. Some reported coordination polymers con-
sisting of crown ethers are in fact the inorganic polymer
with organic spaces which on the basis of the help from
the transition metal ions,17 or crown ethers, were used
solely as supporting units.18 A recent paper19 reported
an example of an extended chain structure with the
3. Inokuma, S.; Takezawa, M.; Satoh, H.; Nakamura, Y.;
Sasaki, T.; Nishimura, J. J. Org. Chem. 1998, 63, 5791–
5796.
4. (a) Inokuma, S.; Kimura, K.; Funaki, T.; Nishimura, J.
Heterocycles 2001, 55, 447–451; (b) Inokuma, S.; Kimura,
K.; Funaki, T.; Nishimura, J. Heterocycles 2001, 54,
123–130; (c) Kumar, S.; Bhalla, B.; Singh, P.; Singh, H.
Tetrahedron Lett. 1996, 37, 3495–3496.
5. Mitchell, R. H. In Organic Chemistry, A Series of Mono-
graphs, Vol. 45-I, Cyclophanes; Keehn, P. H.; Rosenfeld,
S. M., Eds.; Academic Press: New York, 1983; Chapter 4,
pp. 239–310.
1
Figure 5. ORTEP drawing of the dimeric (3·NaClO4)2 at the
50% probability level. Hydrogen atoms are omitted for clar-
6. 2a: H NMR (300 MHz) in CDCl3 l 2.28 (s, 6H), 3.16 (t,
J=6.0 Hz, 4H), 3.68–3.71 (m, 12H), 3.73–3.81 (m, 4H),
ity.
4.06–4.08 (m, 4H), 4.64 (d, J=6.0 Hz, 8H) 7.07 (s, 4H);

9202
J. Xu, Y.-H. Lai / Tetrahedron Letters 43 (2002) 9199–9202
12. Ouchi, M.; Inoue, Y.; Kanzaki, T.; Hakushi, T. J. Org.
IR (neat) 3400, 2916, 2876, 1596, 1474, 1456, 1353, 1245,
1209, 1125, 1059, 989, 948, 901, 868 cm−1; MS (EI) (m/z)
502 (M+−2H2O, 0.3), 484 (M+−3H2O, 0.5); anal. calcd for
C28H42O10: C, 62.44; H, 7.86. Found: C, 62.38; H, 7.90%.
Chem. 1984, 49, 1408–1412.
13. (a) Lai, Y.-H.; Tan, C.-W. J. Org. Chem. 1991, 56,
264–267; (b) Mitchell, R. H.; Vinod, T. K.; Bodwell, G.
J.; Weerawarna, K. S.; Anker, W.; Williams, R. V.;
Bushnell, G. W. Pure Appl. Chem. 1986, 58, 15–24.
14. Crystal data for 3·KClO4: C28H38ClKO10S2, 673.25 g
7. 2b: 1H NMR (300 MHz) in CDCl3 l 2.29 (s, 6H),
3.72–3.80 (m, 12H), 3.87–3.90 (m, 4H), 4.23–4.26 (m,
4H), 4.59 (s, 8H), 7.16 (s, 4H); IR (KBr) 3051, 2878,
1589, 1481, 1461, 1246, 1217, 1137, 1109, 1041, 902, 868,
797, 603 cm−1; MS (EI) (m/z) 786 (M+, 0.1) 788 (M++2,
0.2), 790 (M++4, 0.4), 792 (M++6, 0.1), 549 (M+−379Br,
0.4), 470 (M+−479Br, 2.0); anal. calcd for C28H38Br4O6: C,
42.56; H, 4.85. Found: C, 42.78; H, 4.60%.
mol−1, orthorhombic, a=10.5597(2), b=16.5602(3), c=
3
,
,
36.8430(5) A, h=90, i=90, k=90°, V=6442.76(19) A ,
T=293(2) K, Pbca, Z=8, v=0.430 mm−1, 29329 reflec-
tions collected, 5667 independent reflections, Rint
0.0432. The final wR2 (F2)=0.2432 (all data).
=
15. Seiler, P.; Dobler, M.; Dunitz, J. D. Acta Crystallogr.
1
8. 3: H NMR (300 MHz) in CDCl3 l 2.11 (s, 6H), 3.28 (d,
1974, B30, 2744–2745.
16. Crystal data for 3·NaClO4: C28H38ClNaO10S2, 657.14
gmol−1, orthorhombic, a=20.8073(7), b=9.7163(3), c=
4H, J=14.6 Hz), 3.64–3.67 (m, 4H), 3.78–3.84 (m, 16H),
4.45 (d, 4H, J=14.6 Hz), 6.79 (s, 4H); 13C NMR (300
MHz) in CDCl3 l 20.63, 30.19, 70.08, 70.86, 71.06, 71.21,
74.59, 129.93, 130.36, 133.08, 153.53. IR (KBr) 2909,
2878, 1606, 1472, 1419, 1353, 1299, 1259, 1212, 1199,
1117, 1092, 952, 858, 575 cm−1; MS (EI) (m/z) 534 (M+,
66); anal. calcd for C28H38O6S2: C, 62.89; H, 7.16; S,
11.99. Found: C, 63.10; H, 7.00; S, 12.10%.
,
16.2025(6) A, h=90, i=105.930(1), k=90°, V=3149.2(2)
3
A , T=295(2) K, P2(1)/c, Z=4, v=0.321 mm−1, 15611
,
reflections collected, 5531 independent reflections, Rint
=
0.0335. The final wR2 (F2)=0.1566 (all data).
17. (a) Zhang, H.; Wang, X.-M.; Teo, B. K. J. Am. Chem.
Soc. 1996, 118, 11813–11821; (b) Zhang, H.; Wang, X.-
M.; Zhang, K.-C.; Teo, B. K. Coord. Chem. Rev. 1999,
183, 157–195; (c) Zhang, H.; Wang, X.-M.; Zhu, H.;
Xiao, W.; Teo, B. K. J. Am. Chem. Soc. 1997, 119,
5463–5464.
18. (a) Webb, H. R.; Hardie, M. J.; Raston, C. L. Chem. Eur.
J. 2001, 7, 3616–3620; (b) Hardie, M. J.; Raston, C. L.;
Webb, H. R.; Johnson, J. A. Chem. Commun. 2000,
849–850.
9. Crystal data for 3: C28H38O6S2, 534.70 g mol−1, triclinic,
,
a=8.8831(1), b=10.2001(2), c=15.5568(4) A, h=
100.111(1), i=91.664(1), k=90.542(1)°, V=1386.95 (5)
3
−1
,
A , T=293(2) K, P-1, Z=2, v[XJW1](=0.231 mm
8836 reflections collected, 6290 independent reflections,
int=0.0152. The final wR2 (F2)=0.2098 (all data).
,
R
10. Anker, W.; Bushnell, G. W.; Mitchell, R. H. Can. J.
Chem. 1979, 57, 3080–3087.
11. Moore, S. S.; Tarnowski, T. L.; Newcomb, M.; Cram, D.
J. J. Am. Chem. Soc. 1977, 99, 6398–6405.
19. Boulatov, R.; Du, B.; Meyers, E. A.; Shore, S. G. Inorg.
Chem. 1999, 38, 4554–4558.