constant values from the amide proton titration curve data,
analysis of the ortho-pyridinium proton titration data, which
interestingly displayed comparatively larger magnitudes of
downfield perturbations, proved successful (Table 1). Taking into
account the larger size of the bromide anion, the topologically
constrained binding cavity of the catenane and the greater
perturbation of the ortho-pyridinium protons, association of
bromide with the catenane may occur outside of the amide
binding pocket, possibly via favourable electrostatic interactions
with the positively charged pyridinium ring. Downfield shifts of
the amide and ortho-pyridinium protons signals were also observed
in catenane titrations with fluoride and dihydrogenphosphate,
however the data could not be analysed by any EQNMR binding
models. These results suggest the [2]catenane is able to interact
with various anions but importantly, only chloride is bound
strongly and specifically inside the amide binding cavity, whose
size and geometry are suitably designed to accommodate this
anionic guest.
Notes and references
{ Crystal data for 22+(Cl2)(PF62)?2CH2Cl2: C74H96Cl5F6N6O20P, Mr
=
1711.83, crystal dimensions 0.20 6 0.40 6 0.42 mm, monoclinic, space
˚
group C c, a = 21.5488(19), b = 13.3481(9), c = 27.620(3) A, b = 92.313(7)u,
V = 7938.0(11) A , Z = 4, rcalcd = 1.432 g cm23, m(CuKa) = 2.615 mm21
,
3
˚
F000 = 3584, T = 150 K. Final R = 0.0770, wR = 0.0914 with I > 2s(I),
GOF = 1.009 for 1010 parameters and a total of 26601 reflections, of which
13870 were independent (Rint = 0.030). Oxford Diffraction Gemini
˚
diffractometer, graphite-monochromated CuKa radiation (l = 1.54248 A);
collection range 5.0u ¡ h ¡ 74.2u. Details of the structure have been
deposited at the Cambridge Crystallographic Data Centre as supplemen-
tary publication no. CCDC 602960. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b606503a
1 A. R. Pease, J. O. Jeppesen, J. F. Stoddart, Y. Luo, C. P. Collier and
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and F. Vogtle, Acc. Chem. Res., 2001, 34, 465.
2 J.-P. Sauvage and C. Dietrich-Buchecker, Molecular catenanes,
rotaxanes and knots: a journey through the world of molecular topology,
Wiley-VCH, Weinheim; Chichester, 1999.
3 A. L. Vance, N. W. Alcock, J. A. Heppert and D. H. Busch, Inorg.
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Indeed competitive anion complexation studies using electro-
spray mass spectrometry (ESMS) further corroborate the
catenane’s selectivity for chloride. An equimolar aqueous mixture
4 For some examples, see: C. Seel and F. Vogtle, Chem.–Eur. J., 2000, 6,
21; C. M. Keaveney and D. A. Leigh, Angew. Chem., Int. Ed., 2004, 43,
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of the ammonium salts of chloride, fluoride, acetate, dihydrogen-
2
phosphate, hydrogensulfate and nitrate was mixed with 22+(PF6
)
2
in methanol and the resulting ESMS spectrum revealed only the
chloride adduct [22+(Cl2)] and the catenane dication 22+ signal.
This selectivity for chloride has to be attributed to the unique
interlocked chelating structure of the topologically interesting
binding compartment.
5 P. D. Beer and P. A. Gale, Angew. Chem., Int. Ed., 2001, 40, 487;
P. A. Gale, Coord. Chem. Rev., 2003, 240, 191; J. L. Sessler, S. Camiolo
and P. A. Gale, Coord. Chem. Rev., 2003, 240, 17.
In conclusion, we have developed a high yielding anion
templated synthesis of a chloride selective [2]catenane via an
unprecedented novel anion directed interweaving strategy which
assembles two identical anion recognizing motifs into an
orthogonal structure. Catenane formation resulting from a double
RCM reaction is critically dependent on the molar equivalence of
chloride anion template present. 1H NMR, electrospray mass
spectrometry and single crystal X-ray analysis all provide evidence
for the formation of the catenane. The application of mechanically
interlocked cavities as potential binding domains for the selective
recognition and sensing of a range of anionic guest species is
currently under investigation in our laboratories.
6 J. A. Wisner, P. D. Beer and M. G. B. Drew, Angew. Chem., Int. Ed.,
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Chem. Soc., 2002, 124, 12469; D. Curiel and P. D. Beer, Chem.
Commun., 2005, 1909.
8 M. R. Sambrook, P. D. Beer, J. A. Wisner, R. L. Paul and A. R. Cowley,
J. Am. Chem. Soc., 2004, 126, 15364.
9 C. O. Dietrich-Buchecker, J. P. Sauvage and J. P. Kintzinger,
Tetrahedron Lett., 1983, 24, 5095; C. O. Dietrich-Buchecker,
J. P. Sauvage and J. M. Kern, J. Am. Chem. Soc., 1984, 106, 3043;
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10 R. H. Grubbs, S. J. Miller and G. C. Fu, Acc. Chem. Res., 1995, 28, 446.
11 The compound could also be obtained from exchange of chloride in
22+(Cl2)(PF62) to hexafluorophosphate. See supporting information.
12 M. J. Hynes, J. Chem. Soc., Dalton Trans., 1993, 311.
We thank the Clarendon Fund and the Overseas Research
Student (ORS) Awards Scheme for a scholarship (K.-Y. N.).
Oxford Diffraction Ltd is thanked for the generous loan of a
Gemini diffractometer.
3678 | Chem. Commun., 2006, 3676–3678
This journal is ß The Royal Society of Chemistry 2006