A catenane host system containing integrated triazole C-H hydrogen bond donors for anion recognition

Article abstract of DOI:10.1039/c2cc34210c

A 3,5-bis(triazole)-pyridinium motif is integrated into a catenane structural framework via chloride anion templation. The catenane host system displays a high degree of selectivity for halide anions over dihydrogen phosphate.

Full text of DOI:10.1039/c2cc34210c

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2012, 48, 8499–8501
www.rsc.org/chemcomm
COMMUNICATION
A catenane host system containing integrated triazole C–H hydrogen
bond donors for anion recognitionw
Nicholas G. White and Paul D. Beer*
Received 12th June 2012, Accepted 6th July 2012
DOI: 10.1039/c2cc34210c
A 3,5-bis(triazole)-pyridinium motif is integrated into a catenane
structural framework via chloride anion templation. The catenane
host system displays a high degree of selectivity for halide anions
over dihydrogen phosphate.
Table 1 Apparent association constants, Kapp (MÀ1 a
rotaxane formation with isophthalamide macrocycle 2
) for pseudo-
Anion
ClÀ
Triazole thread 1+
Amide thread 3+
800(70)
38(3)
420(15)
170(25)
À
PF6
The ease of synthesis of 1,2,3-triazoles via the copper(I)-catalysed
cycloaddition of azides and terminal alkynes (CuAAC) has led to
this reaction being widely exploited across the chemical sciences.1
Notably, the efficacy, mild reaction conditions and range of
functional group tolerance has proven ideal for use in the
construction of mechanically bonded architectures.2–8
a
Calculated using WINEQNMR218 monitoring the hydroquinone
signal; estimated standard errors are given in parentheses (293 K,
solvent: 1 : 1 CDCl3 : acetone-d6).
macrocycle 216 (Scheme 1, see ESIw for synthesis). Substantial
upfield shifts in the macrocycle’s hydroquinone resonances were
observed, consistent with the formation of an anion-templated
pseudorotaxane,16,17 with these perturbations being caused by
donor–acceptor interactions between electron-rich hydroquinone
groups and the electron-deficient pyridinium threading component.
Further evidence for pseudorotaxane formation was provided by
2D ROESY NMR (see ESIw).
In the analogous titration experiment with 1ÁPF6, only very
minor shifts of the macrocycle’s hydroquinone signals were
observed, demonstrating the crucial importance of the chloride
anion template in stabilising the interpenetrated assembly.
Apparent 1 : 1 stoichiometric association constants were
calculated for pseudorotaxane formation, monitoring the hydro-
quinone proton data, using WINEQNMR2.18 For comparison
purposes, titration experiments were also undertaken with the
The triazole group itself has also been utilised in anion
binding applications as the polarised heterocycle provides an
effective C–H hydrogen bond donor, which is able to bind
anions in organic solvents.9–14 Herein, we demonstrate that the
integration of a new 3,5-bis(triazole)-pyridinium functionality into
a catenane structural framework results in a potent anion host
system that exhibits a pronounced selectivity for halide anions
over dihydrogen phosphate. To the best of our knowledge, a
triazole-containing catenane anion receptor is unprecedented.15
Proton NMR pseudorotaxane assembly investigations were
initially undertaken to establish whether the 3,5-bis(triazole)-
pyridinium motif was capable of penetrating the cavity of an
isophthalamide macrocycle via chloride anion templation.
Aliquots of a solution of the novel compound 1ÁCl were titrated
into a 1 : 1 CDCl3 : d6-acetone solution of the isophthalamide
Scheme 1 Formation of chloride-templated pseudorotaxane between isophthalamide macrocycle and threading component 1ÁCl.
amide thread analogue, N-methyl-3,5-bis(hexylcarbamoyl)-
pyridinium chloride, 3ÁCl.17 As shown in Table 1, the bis(triazole)-
Inorganic Chemistry Laboratory, Department of Chemistry,
University of Oxford, South Parks Road, Oxford, UK OX1 3QR.
E-mail: paul.beer@chem.ox.ac.uk; Fax: +44 (0)1865 272690;
Tel: +44 (0)1865 285142
w Electronic supplementary information (ESI) available: Synthetic
procedures and characterisation of all new compounds, crystallo-
graphic data for 1ÁClÁ2tBu and 5ÁCl, NMR titration protocols and
data. CCDC 885861, 885862. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c2cc34210c
pyridinium receptor 1ÁCl forms
a significantly stronger
pseudorotaxane assembly with 2 than does the bis(amide)-
pyridinium analogue 3ÁCl. Also it is noteworthy that with the
corresponding hexafluorophosphate pyridinium salts, the bis-amide
3ÁPF6 undergoes a significant degree of interpenetration, whereas
the pseudorotaxane assembly with 1ÁPF6 is extremely weak.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 8499–8501 8499

View Article Online
Fig. 2 X-ray crystal structure of 5ÁCl.
The templating chloride anion was removed by repeatedly
washing a dichloromethane solution of 5ÁCl with aqueous
ammonium hexafluorophosphate to afford 5ÁPF6 (see ESIw).
The 1H NMR spectra of 2, 5ÁCl and 5ÁPF6 are shown in Fig. 3.
A large upfield shift of the hydroquinone proton resonances,
e and f, is observed in the interlocked species compared to the
free macrocycle, consistent with inter-ring stacking inter-
actions. Significant downfield shifts are observed for triazole
and amide signals in the catenane’s cavity, due to deshielding
of these protons by hydrogen bonding interactions with the
encapsulated chloride anion.
Fig. 1 X-ray crystal structure of 1ÁClÁ2tBu
.
The solid state structure of the pseudorotaxane 1ÁClÁ2tBu 19
was determined by single crystal X-ray crystallography
(Fig. 1). The pseudorotaxane is stabilised by hydrogen bonds
between the chloride anion and amide and triazole groups, with
additional close hydroquinoneÁ Á ÁpyridiniumÁ Á Áhydroquinone
contacts and hydrogen bonding between the pyridinium methyl
group and macrocycle polyether chain.
The synthesis of the new catenane 5ÁCl was achieved
by chloride anion templated Grubbs’ catalysed ring-closing
metathesis reaction of 1.2 equivalents of 4ÁCl and one equivalent
of isophthalamide macrocycle 2 in dichloromethane (Scheme 2).
The catenane was isolated in 64% yield (following purification by
preparative thin layer chromatography) – significantly higher
than the 45% reported for the analogous bis(amide)-pyridinium
catenane.20 No catenane formation was detected when 4ÁPF6 was
used in place of 4ÁCl, demonstrating the importance of the
templating halide anion.
Catenane 5ÁCl was characterised by 1H, 13C and 2D ROESY
NMR (see ESIw), as well as by high resolution ESI mass
spectrometry and single crystal X-ray crystallography (Fig. 2).
The solid state structure of 5ÁCl shows that both amide and
both triazole groups form hydrogen bonds to the chloride
anion, with the structure stabilised by the packing of electron-poor
and electron-rich aromatic rings, and hydrogen bonding between
the pyridinium methyl group and macrocycle polyether chain.
Preliminary anion binding studies of 5ÁPF6 were conducted
in the competitive solvent mixture 1 : 1 CDCl3 : CD3OD.
Stoichiometric association constants (1 : 1) were calculated
using WINEQNMR2,18 monitoring the triazole proton resonance.
Importantly, while little difference is observed between the
bis-triazole containing catenane and the all-amide catenane
analogue in terms of chloride association strength, dihydrogen
phosphate is bound much more weakly by 5ÁPF6, with an
impressive selectivity of more than an order of magnitude
between the halides and the basic oxoanion (Table 2).21
Presumably, the tetrahedrally shaped dihydrogen phosphate
anion is too large to penetrate the catenane’s unique interlocked
bis-triazole bis-amide hydrogen bond donating cavity.
In summary, we have demonstrated the capability of a new
3,5-bis(triazole)-pyridinium group to form a stronger chloride
anion-templated pseudorotaxane assembly with an isophthalamide
macrocycle than the 3,5-bis(amide)-pyridinium analogue. This
enhanced stability of interpenetration has been exploited in the
Scheme 2 Synthesis of catenane 5. Conditions and reagents: (i) Grubbs’ II catalyst, CH2Cl2, 64%.
c
This journal is The Royal Society of Chemistry 2012
8500 Chem. Commun., 2012, 48, 8499–8501

View Article Online
We thank the Clarendon Fund and Trinity College, Oxford
for funding (NGW) and Oxford Chemical Crystallography for
providing instrumentation.
Notes and references
1 J. E. Hein and V. V. Fokin, Chem. Soc. Rev., 2010, 39,
1302–1315.
2 A. Fahrenbach and J. F. Stoddart, Chem.–Asian J., 2011, 6,
2660–2669.
3 Y. Yamada, M. Okamoto, K. Furukawa, T. Kato and K. Tanaka,
Angew. Chem., Int. Ed., 2012, 51, 709–713.
4 A. Joosten, Y. Trolez, J.-P. Collin, V. Heitz and J.-P. Sauvage,
J. Am. Chem. Soc., 2012, 134, 1802–1809.
5 J. D. Megiatto and D. I. Schuster, J. Am. Chem. Soc., 2008, 130,
12872–12873.
6 H. Lahlali, K. Jobe, M. Watkinson and S. M. Goldup, Angew.
Chem., Int. Ed., 2011, 50, 4151–4155.
7 K. D. Hanni and D. A. Leigh, Chem. Soc. Rev., 2010, 39,
¨
1240–1251.
Fig. 3 Truncated 1H NMR spectra of 5ÁCl (top), 5ÁPF6 (middle) and
2 (bottom) (300 MHz, 293 K, solvent: CDCl3, all species 8 mM).
8 J.-P. Collin, F. Durola, J. Frey, V. Heitz, F. Reviriego,
J.-P. Sauvage, Y. Trolez and K. Rissanen, J. Am. Chem. Soc.,
2010, 132, 6840–6850.
Table 2 Association constants, Ka (MÀ1 a
based catenanes
)
for amide and triazole-
9 Y. Hua and A. H. Flood, J. Am. Chem. Soc., 2010, 132,
12838–12840.
10 Y. Hua and A. H. Flood, Chem. Soc. Rev., 2010, 39, 1262–1271.
11 Y. Li and A. H. Flood, Angew. Chem., Int. Ed., 2008, 47, 2649–2652.
12 Y. Li and A. H. Flood, J. Am. Chem. Soc., 2008, 130, 12111–12122.
13 H. Juwarker, J. M. Lenhardt, D. M. Pham and S. L. Craig, Angew.
Chem., Int. Ed., 2008, 47, 3740–3743.
14 H. Juwarker, J. M. Lenhardt, J. C. Castillo, E. Zhao,
S. Krishnamurthy, R. M. Jamiolkowski, K.-H. Kim and
S. L. Craig, J. Org. Chem., 2009, 74, 8924–8934.
15 For a rare example of a triazole axle containing rotaxane that
binds chloride see H. Zheng, W. Zhou, J. Lv, X. Yin, Y. Li, H. Liu
and Y. Li, Chem.–Eur. J., 2009, 15, 13253–13262.
16 M. R. Sambrook, P. D. Beer, J. A. Wisner, R. L. Paul,
A. R. Cowley, F. Szemes and M. G. B. Drew, J. Am. Chem.
Soc., 2005, 127, 2292–2302.
17 J. A. Wisner, P. D. Beer and M. G. B. Drew, Angew. Chem., Int.
Ed., 2001, 40, 3606–3609.
18 M. J. Hynes, J. Chem. Soc., Dalton Trans., 1993, 311–312.
19 The tbutyl-substituted macrocycle was used because of its increased
solubility.
20 M. R. Sambrook, P. D. Beer, J. A. Wisner, R. L. Paul and
A. R. Cowley, J. Am. Chem. Soc., 2004, 126, 15364–15365.
21 Preliminary 1H NMR binding studies with acetate, benzoate and
nitrate reveal very small perturbations of the catenane’s triazole
and amide cavity proton resonances (0.02–0.04 ppm after 1 equivalent
of anion).
19
Anion
Triazole catenane 5ÁPF6
Amide catenaneÁPF6
730
—
—
ClÀ
BrÀ
IÀ
680(20)
630(50)
510(10)
49(4)
À
H2PO4
K1 = 480, K2 = 520
Calculated using WINEQNMR218 monitoring triazole protons;
estimated standard errors are given in parentheses (293 K, solvent:
1 : 1 CDCl3 : CD3OD).
a
synthesis of the first triazole-containing catenane anion receptor in
an impressive yield of 64%. The triazole catenane host system
binds halides strongly in the competitive 1 : 1 CDCl3 : CD3OD
solvent mixture, and importantly exhibits a high degree of
selectivity for the halides over dihydrogen phosphate, superior
to that of an amide catenane analogue. This serves to illustrate
that the integration of triazole C–H hydrogen bond donor
groups into interlocked host structural design has the exciting
potential to influence significantly the host’s anion recognition
properties.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 8499–8501 8501