Ion-pair recognition by a heteroditopic triazole-containing receptor

Article abstract of DOI:10.1002/chem.201200251

A new heteroditopic calix[4]diquinone triazole containing receptor capable of recognising both cations and anions through Lewis base and C-H hydrogen-bonding modes, respectively, of the triazole motif has been prepared. This ion-pair receptor cooperativel

Full text of DOI:10.1002/chem.201200251

DOI: 10.1002/chem.201200251
Ion-Pair Recognition by a Heteroditopic Triazole-Containing Receptor
Simon C. Picot, Benjamin R. Mullaney, and Paul D. Beer*[a]
Abstract: A new heteroditopic calix[4]-
diquinone triazole containing receptor
capable of recognising both cations and
Cation binding by the calix[4]diqui-
none oxygen and triazole nitrogen
donors enhances the strength of the
halide complexation at the isophthala-
mide recognition site of the receptor.
Conversely, anions bound in the recep-
torꢁs isophthalamide cavity enhance
cation recognition. H NMR investiga-
1
tions in solution suggest that the recep-
torꢁs triazole motifs are capable of co-
ordinating simultaneously to both
cation and anion guest species. Solid-
state X-ray crystallographic structural
analysis of a variety of receptor ion-
pair adducts further demonstrates the
dual cation–anion binding role of the
triazole group.
À
anions through Lewis base and C H
hydrogen-bonding modes, respectively,
of the triazole motif has been pre-
pared. This ion-pair receptor coopera-
tively binds halide/monovalent-cation
combinations in an aqueous mixture,
with selectivity trends being established
Keywords: anions
· calixarenes ·
cations · host–guest systems · ion
pairs · receptors · triazoles
1
by H NMR and UV/Vis spectroscopy.
Introduction
amples of triazole-containing ditopic receptors have been re-
ported.[6] Herein, we describe a novel heteroditopic calix[4]-
diquinone triazole containing receptor, which recognises
alkali metal cation/halide anion ion-pair species. 1H NMR
spectroscopic investigations in solution and solid-state X-ray
crystallographic structural analysis suggest that the triazole
motifs are capable of coordinating simultaneously to both
cation and anion guest species.
The design and construction of heteroditopic receptor mole-
cules for ion-pair recognition is currently an area of intense
research activity.[1] This has been stimulated in part by com-
pelling evidence that the cation and anion binding affinities
and selectivity of monotopic receptor systems have been
demonstrated to be critically influenced by the nature of
counterions. Through favourable cooperative electrostatic
interactions, ion-pair receptors have the potential to signifi-
cantly enhance the efficacy of charged guest recognition and
also to act as superior extraction and membrane transport
agents.[1,2]
The 1,2,3-triazole motif is being used extensively as a cova-
lent linkage in the facile copper(I)-catalysed azide–alkyne
coupling synthesis of an ever increasing range of organic
and biological molecules.[3] Importantly, the heterocycle is
also proving to be a versatile ion recognising unit for both
cations and anions. As a nitrogen-containing Lewis base, tri-
azole-based ligands have been shown to coordinate transi-
tion-metal cations.[4] In contrast, aryl macrocyclic and acyclic
Results and Discussion
Receptor design and synthesis: We have described previous-
ly a series of heteroditopic calix[4]diquinone polyether iso-
phthalamide receptors that exhibit unprecedented coopera-
tive AND ion-pair recognition, displaying little affinity for
ꢀfreeꢁ ions but enhanced binding of contact ion-pairs, such as
NaCl.[7,8]
triazole oligomers recognise halide anions through coopera-
[5]
À
tive triazole C H···anion hydrogen bonds. Hence, the inte-
gration of the triazole motif into the design of heteroditopic
receptors for ion-pair recognition is an attractive proposi-
tion. Surprisingly, to the best of our knowledge, only two ex-
[a] S. C. Picot, B. R. Mullaney, Prof. P. D. Beer
Inorganic Chemistry Laboratory, Department of Chemistry
University of Oxford
South Parks Road, Oxford, OX1 3QR (UK)
Fax : (+44)1865-272690
E-mail: paul.beer@chem.ox.ac.uk
Figure 1. Target heteroditopic ion-pair receptor 1: the triazole groups act
as a) Lewis bases to coordinate a metal cation, and b) hydrogen-bond
donors to bind an anion.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200251.
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Chem. Eur. J. 2012, 18, 6230 – 6237

FULL PAPER
By replacing the polyether chain linkers with triazole
groups, the target heteroditopic receptor 1, shown in
Figure 1, has the potential capability of recognising cations
(Figure 1a), anions (Figure 1b) and ion-pairs through tria-
zole-group participation.
The synthesis of receptor 1 is shown in Scheme 1. The
copper(I)-catalysed azide–alkyne click (CuAAC) reaction of
1,3-bisalkyne lower-rim-functionalised calix[4]arene de-
oxidation of macrocycle 5 with thalliumACTHNGUTERNNU(G III) trifluoroacetate
in trifluoroacetic acid (TFA; Scheme 1).
The ditopic receptor was characterised by 1H and
13C NMR spectroscopy and electrospray mass spectrometry.
Crystals of 1 suitable for X-ray single-crystal structural anal-
ysis were grown by slow evaporation of a solution of 1 in
CD3CN. The structure (Figure 2) shows the calix[4]diqui-
none unit adopting a partial cone conformation, with the
two tert-butylphenyl rings almost parallel (148) and the qui-
none rings are antiparallel but converge on the cavity, with
an interplanar angle of 408. The rest of the macrocycle lies
in a nearly flat conformation, with the isophthalamide and
triazoles adopting syn/anti conformations.
Figure 2. Single-crystal X-ray structure of 1 grown from CD3CN. Non-do-
nating hydrogen atoms and solvent molecules are omitted for clarity.
Thermal ellipsoids are displayed at the 30% probability level.
Cation and anion binding studies: The cation and anion
1
binding properties of 1 were investigated by using H NMR
and UV/Vis spectroscopic analysis. The addition of MPF6
salts (M=K, Na and NH4), in which hexafluorophosphate is
1
used as a non-coordinating anion for H NMR spectroscopic
solutions of 1 in 2% D2O/CD3CN induced, in all cases,
downfield shifts in the triazole protons (H4): with potassium
Dd= +0.08 and sodium Dd= +0.09 ppm, causing relatively
larger perturbations than ammonium, Dd= +0.04 ppm
(Figure 3).
It is noteworthy that the CH2 protons (H3) between the
triazole and calix[4]diquinone motif are also shifted down-
field upon cation addition, whilst the aromatic protons of
the calix[4]diquinone (H7, H8) converge and the AB quartet
of the calix CH2 protons (H1, H2) diverge. This suggests that
the calix[4]diquinone undergoes a conformational change in
order for the lower-rim oxygen and triazole nitrogen donors
to complex with the cation, as depicted in Figure 1a.
UV/Vis spectroscopic titrations were performed in 2%
H2O/CH3CN, monitoring the n–p* quinone absorption of
1 upon addition of cations.[11] Typically, a significant en-
hancement of the n–p* quinone absorption was observed
Scheme 1. Synthetic route to target macrocycle 1.
ACHTUNGTRENNUNG
rivative 2[9] with bisazide-functionalised isophthalamide
compound 4, prepared from reacting the corresponding bis-
bromide 3[10] with sodium azide, afforded the bistriazole-
containing macrocycle 5 in 49% yield. It is noteworthy that
when the cyclisation reaction was carried out in the pres-
ence of one equivalent of tetrabutylammonium chloride, the
yield increased significantly to 77%. This observation indi-
cates that the chloride anion is acting as a template, through
coordination to the isophthalamide motif in 4, which preor-
ganises the azide groups in a syn/syn conformation, favour-
ing the cyclisation process. The target calix[4]diquinone tria-
zole receptor 1 was then prepared in good yield (84%) by
+
with K+ and Na+ (Figure 4). However, addition of NH4
caused little alteration in the spectrum, suggesting very
weak binding. Specfit[12] analysis of the UV/Vis titration
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6231

P. D. Beer et al.
Figure 3. 1H NMR (500 MHz) spectra of receptor
1.5ꢄ10À3 moldmÀ3; titrant [KPF6]=0.075 moldmÀ3
1
upon addition of equivalents of KPF6 in 2% D2O/CD3CN; temperature: 293 K; [1]i =
.
anions added, the isophthalamide (H5), internal phenyl (H6)
and triazole (H4) protons were all found to shift downfield
(Figure 5). For the phenyl proton H6, the halide-induced
shifts Dd were largest for chloride (+0.64 ppm), then bro-
mide (+0.14 ppm), with iodide causing only a modest per-
turbation (+0.06 ppm). These results suggest that the halide
anion is bound in the receptor cavity by cooperative hydro-
gen bonding by the triazole and isophthalamide groups, as
shown in Figure 1b.
Job-plot analysis revealed a 1:1 binding mode for each
halide and association constants were determined by using
1
WinEQNMR2 analysis of the H NMR titration data, moni-
toring the isophthalamide internal proton (H6).[13] Table 2 re-
veals that receptor 1 exhibits a preference for the smaller,
more charge-dense chloride anion,[14] which suggests that the
Figure 4. Enhancement of the n–p* quinone absorbance in response to
addition of KPF6. Solvent: 2% H2O/CH3CN; temperature: 298 K; [1]i =
bistriazole-isophthalamide cavity is of complementary size
3ꢄ10À4 moldmÀ3; titrant [KPF6]=0.09 moldmÀ3
.
for ClÀ.
Crystals of a chloride complex of 1 suitable for X-ray
single-crystal structural analysis were grown by slow evapo-
ration of a solution of 1 in 2% D2O/CD3CN with an excess
of TBACl. The structure (Figure 6) shows that a chloride
anion is bound in an intermolecular manner between tria-
data gave 1:1 stoichiometric association constants (Table 1)
that reveal that Na+ forms the strongest cation complex, fol-
+
lowed by K+, and NH4 is very weakly bound.
À
zoles from different macrocycles, with triazole C H···Cl hy-
drogen-bond lengths of 3.486(9) ꢃ, supporting the H NMR
1
Table 1. UV/Vis spectroscopy K11 values for interactions of 1 with vari-
ous cations[a]
spectroscopy solution-state evidence for triazole CH–anion
interactions.
[b]
Cation
Association K11 [mÀ1
]
The calix[4]diquinone unit is found to adopt a partial
cone conformation, with the two tert-butylphenyl rings
almost parallel and the quinone rings orientated convergent-
ly, with an interplanar angle of 488. Another chloride is
bound within the macrocycle cavity by hydrogen bonding to
K+
155
460
–
Na+
+[c]
[d]
NH4
[a] Solvent:
2%
;
H2O/CH3CN; 298 K;
temperature:
[1]i =
3ꢄ10À4 moldmÀ3
titrant [MPF6]=0.09 moldmÀ3
. [b] Errors <10%.
[c] Titrant as a solution in 5% H2O/CH3CN for solubility. [d] Binding too
weak to be determined.
À
the isophthalamide protons (amide N H···Cl 3.286(6),
À
3.238(6) ꢃ and internal C H···Cl 3.415(6) ꢃ). The bulky
TBA resides outside the macrocycle cavity but proximate to
its chloride counteranion. Hence, the solid-state structure of
the chloride-anion complex of 1 highlights the dominance of
intermolecular triazole and amide halide anion interactions,
whereas H NMR spectroscopy anion-binding investigations
in solution indicate halide recognition by cooperative intra-
molecular triazole and amide hydrogen bonds.
1
Anion binding studies were undertaken by H NMR spec-
troscopy, focusing on the triazole CH protons and the iso-
phthalamide motif. Anions were added as their TBAX salts
(X=Cl, Br and I), in which tetrabutylammonium (TBA) is
a bulky non-coordinating cation. For each of the halide
1
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Ion-Pair Recognition
FULL PAPER
Figure 5. 1H NMR (500 MHz) spectra of receptor 1 upon addition of equivalents of TBACl. In response, cavity triazole (H4), isophthalamide (H5) and in-
ternal CH (H6) protons shift downfield. Solvent: 2% D2O/CD3CN; temperature: 293 K; [1]i =1.5ꢄ10À3 moldmÀ3; titrant [TBACl]=0.075 moldmÀ3
.
Table 2. 1H NMR spectroscopy K11 values for interactions of 1 with vari-
greater downfield shifts by at least 0.1 ppm for addition of
chloride to 1·KPF6 as compared to its addition to 1.
ous anions[a]
[b]
Anion
Association K11 [mÀ1
]
Furthermore, chloride binding to 1·KPF6 concomitantly
caused the calix[4]diquinone aryl protons (H7, H8) to con-
verge, the calix CH2 protons (H1, H2) to diverge and the a-
CH2 triazole proton (H3) to shift downfield. Interestingly,
further addition of chloride after one equivalent induced no
more perturbations in these receptor proton signals, whereas
the isophthalamide protons shifted progressively downfield.
A possible K+ClÀ ion-pair binding mode is the S-shaped
conformation depicted in Figure 8, in which the triazole
motifs function simultaneously as a Lewis base to coordinate
ClÀ
BrÀ
IÀ
178 (16)
67 (5)
31 (3)
[a] 1H NMR (500 MHz); solvent: 2% D2O/CD3CN; temperature: 293 K;
[1]i =1.5ꢄ10À3 moldmÀ3
<10%.
;
titrant [TBAX]=0.075 moldmÀ3
.
[b] Errors
À
the cation and as C H hydrogen-bond donors to bind the
halide anion.
The association constants shown in Table 3 were deter-
mined by monitoring the isophthalamide phenyl proton H6.
In all cases, it was found that halide-anion binding was en-
hanced significantly in the presence of coordinating cations.
Overall, Kobs for halide binding to 1·MPF6 was typically 3–11
times greater than the halide association constants deter-
mined for receptor 1 alone. Chloride appears to be the best
size match for the isophthalamide and triazole cavity, form-
ing the optimal ion-pair with Na+ClÀ, and relatively weaker
cooperative ion-pair associations are observed with the
larger halides, bromide and iodide.
UV/Vis spectroscopic analysis was utilised to monitor the
titration of cations into a solution of receptor 1 with one
equivalent of halide anion in 2% H2O/CH3CN (Table 4).
The n–p* quinone absorption was monitored and showed
enhancement of the band centred at 325 nm in all instances
(Figure 9). For all three cations studied, the presence of
bound halides resulted in enhanced cation binding (Table 4),
with optimal ion-pair cooperativity being observed with Na+
ClÀ, in agreement with the NMR spectroscopic titration re-
sults. Furthermore, the ammonium association, which was
very weak in the absence of coordinating halide anions, is
effectively “switched on” by chloride or bromide binding.
Further evidence for ion-pair binding was then sought in
the solid state.
Figure 6. Single-crystal X-ray structure of 1·2TBACl. Note the chloride
bound intermolecularly by the triazole H4. Hydrogen atoms not involved
in hydrogen bonding and non-coordinating tetrabutylammonium cations
are omitted for clarity. Thermal ellipsoids are displayed at the 30% prob-
ability level.
1
Ion-pair binding studies: H NMR spectroscopy was used in-
itially to monitor titration of halide anions (as TBAX salts)
with solutions of macrocycle 1 in 2% D2O/CD3CN contain-
ing one equivalent of cation (MPF6). The addition of up to
one equivalent of chloride to 1·KPF6 (Figure 7) induced sig-
nificant downfield shifts in the key bistriazole-isophthala-
mide protons, with the triazole proton (H4) undergoing
a larger magnitude of perturbation, Dd= +0.19 ppm for
1·KPF6 compared with Dd= +0.09 ppm for 1. The isophtha-
lamide (H5) and phenyl (H6) protons similarly exhibited
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P. D. Beer et al.
Figure 7. 1H NMR spectra of receptor 1·KPF6 upon addition of equivalents of TBACl in 2% D2O/CD3CN with corresponding KCl ion-pair formation in
the cavity; temperature: 293 K; [1·KPF6]i =1.5ꢄ10À3 moldmÀ3; titrant [TBACl]=0.075 moldmÀ3
.
Table 4. UV/Vis spectroscopy Kobs values for interactions of 1 with vari-
ous ion-pair combinations[a]
Cation salt
titrated
Anion salt
in solution
Association Kobs
Cooperativity
factor[c]
[b]
G
]
K+
none
n/a
2.1
1.6
1.4
n/a
2.2
1.4
n/a
n/a
n/a
K+
TBACl
TBABr
TBAI
330
250
220
460
K+
K+
Na+
Na+
Na+
none
TBACl
TBABr
none
TBACl
TBABr
1000
640
+[d]
[e]
NH4
NH4
NH4
–
+[d]
370
300
+[d]
[a] Solvent: 2% H2O/CH3CN; temperature: 298 K; [1·TBAX]i =
3ꢄ10À4 moldmÀ3 titrant [MPF6]=0.09 moldmÀ3
[b] Errors <10%.
[c] Cooperativity factor is calculated by Kobs(anion, ionpair)/Kobs(anion,free). [d] Ti-
trant as a solution in 5% H2O/CH3CN for solubility. [e] Binding too
weak to be determined.
;
.
Figure 8. Possible solution-state ion-pair binding by heteroditopic recep-
tor 1.
Table 3. 1H NMR spectroscopy Kobs values for interactions of 1 with vari-
ous ion-pair combinations[a]
Anion salt
titrated
Cation salt
in solution
Association Kobs
Cooperativity
factor[c]
[b]
G
]
ClÀ
ClÀ
ClÀ
ClÀ
BrÀ
BrÀ
BrÀ
BrÀ
IÀ
none
KPF6
NaPF6
NH4PF6
none
178 (16)
n/a
9.6
10.9
4.2
n/a
6.2
7.2
4.6
n/a
3.1
1711 (65)
1950 (129)
747 (28)
67 (5)
414 (36)
479 (42)
307 (22)
31 (3)
KPF6
NaPF6
NH4PF6
none
IÀ
KPF6
96 (5)
[a] 1H NMR (500 MHz); solvent: 2% D2O/CD3CN; temperature: 293 K;
[1·MPF6]i =1.5ꢄ10À3 moldmÀ3
;
titrant
[TBAX]=0.075 moldmÀ3
.
[b] Errors <10%. [c] Cooperativity factor is calculated by Kobs(cation,ionpair)
Kobs(cation,free); n/a=not applicable.
/
Figure 9. Enhancement of the n–p* quinone absorbance of 1·TBACl in
response to addition of KPF6; solvent: 2% H2O/CH3CN; temperature:
298 K; [1]i =3ꢄ10À4 moldmÀ3; titrant [KPF6]=0.09 moldmÀ3
.
Ion-pair binding in the solid state: Crystals of macrocycle
1 with various ion pairs were grown by slow evaporation of
a solution of 1·MPF6 (in which M is the desired coordinating
cation) in 2% D2O/CD3CN in the presence of excess TBAX
(in which X is the desired coordinating anion). In all cases
for which crystals were successfully grown, neither TBA+
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Ion-Pair Recognition
FULL PAPER
À
nor PF6 were found in the crystal structure. In each of the
cases in which coordinating cations were bound in the
cavity, the calix[4]diquinone unit was observed to adopt
a pinched-cone conformation; the two tert-butylphenyl rings
were almost parallel and the quinone rings orientated con-
vergently, with an interplanar angle of 688, facilitating
oxygen coordination to the cation.
1·KCl: The K+ and ClÀ ions are bound in the crystal struc-
ture in an unusual contact ion-pair manner, with intermolec-
ular contacts. Importantly, the triazole motif acts as a Lewis
À
base metal-cation binder and as a C H···halide-anion hydro-
gen-bond donor (Figure 10), corroborating the evidence
1
from the solution-state H NMR spectroscopy ion-pair bind-
ing studies. In one position in the crystal, the triazole Lewis
base nitrogen atom binds to the potassium, N···K
3.102(5) ꢃ; in another position in the crystal the triazole CH
À
hydrogen-bonds intermolecularly to chloride, C H···Cl
3.546(6) ꢃ.
Figure 11. Single-crystal X-ray structure of (1·KCl)n, demonstrating inter-
molecular packing and the key K+ClÀ contact ion-pair. Only hydrogen
atoms involved in hydrogen bonding are shown for clarity. Thermal ellip-
soids are displayed at the 30% probability level.
Figure 10. Single-crystal X-ray structure of 1·KCl with the intermolecular
K+ClÀ contact ion-pair shown. Additionally, the triazole lone pair is
shown to interact with K+ and the triazole CH is shown to bind to ClÀ.
Only hydrogen atoms involved in hydrogen bonding are shown for clari-
ty. Thermal ellipsoids are displayed at the 30% probability level.
Figure 12. Single-crystal X-ray structure of 1·NaCl with a water molecule
separating the ion pair in the cavity. The ClÀ is bound by an array of in-
tramolecular hydrogen bonds from the triazole and isophthalamide. Only
hydrogen atoms involved in hydrogen bonding are shown for clarity.
Thermal ellipsoids are displayed at the 30% probability level.
Oxygen interactions with the potassium cation (quinone
O···K 2.643(4), 2.798(4) ꢃ, phenyl O···K 2.949(3), 3.085(3) ꢃ
and an intermolecular quinone O···K 2.747(4) ꢃ) are supple-
mented by the triazole nitrogen lone-pair coordination to
potassium and also a contact ion-pair between the K+ of
one molecule and the ClÀ (centre-to-centre 3.304(2) ꢃ) of
O···Na 2.740(5), 2.530(5) ꢃ). In addition, the sodium ion is
coordinated by a water molecule (Na···O 2.297(5) ꢃ), which
an adjacent molecule in
a pseudo-dimer configuration
(Figure 11).[8] Chloride is held in position intramolecularly
also hydrogen bonds to the chloride in the cavity (O H···Cl
À
À
by the isophthalamide motif (amide N H···Cl 3.291(5),
3.131(5) ꢃ). The chloride is bound intramolecularly by the
À
À
3.296(5) ꢃ and an internal C H···Cl 3.512(6) ꢃ).
isophthalamide motif (amide N H···Cl 3.310(5), 3.419(5) ꢃ
À
and internal C H···Cl 3.515(6) ꢃ) and also by the triazole
1·NaCl: The Na+ and ClÀ ions are separated by a water
molecule in the macrocycle cavity (Figure 12). A triazole
CH forms an intramolecular hydrogen-bonding cavity for
hydrogen bond.
+
1·NH4Cl: The NH4 and ClÀ ions are separated in the cavity
À
chloride (triazole C H···Cl 3.585(6) ꢃ) together with the
isophthalamide motif.
by >6 ꢃ and exhibit no apparent direct, nor even a solvent-
mediated, interaction (Figure 13). In this case, the triazole
motif binds chloride in an intermolecular fashion by a
Calix[4]diquinone oxygen atoms interact with the sodium
cation (quinone O···Na 2.357(5), 2.292(4) ꢃ and phenyl
À
C H···Cl bond.
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6235

P. D. Beer et al.
Experimental Section
All commercial-grade chemicals were used without further purification.
TBAX and MPF6 salts were stored under vacuum prior to use, in a desic-
cator containing phosphorus pentoxide and self-indicating silica. Mass
spectra were obtained on a Bruker MicroTof (ESMS) instrument. NMR
spectra were recorded on a Varian Mercury 300 (13C) or Varian Unity
Plus 500 (1H) spectrometer with the solvent serving as the lock and inter-
nal reference. UV/Vis spectra were recorded on a PG Instruments T60U
Spectrophotometer. Melting points were recorded on a Gallenkamp ca-
pillary melting-point apparatus and are uncorrected.
Dialkyne 2 and dibromide 3 have previously been synthesised.[9,10]
fresh solution of oxidising thallium
(III) trifluoroacetate (0.44 moldmÀ3
in trifluoroacetic acid was prepared as reported by McKillop et al.[15]
N1,N3-bis(3-azidopropyl)isophthalamide (4): Dibromide
(2.00 g,
4.92 mmol) was dissolved in dry, degassed dimethylformamide (50 mL)
and sodium azide (3.20 g, 10 equiv) was then added. The reaction mixture
was stirred under a N2 atmosphere at room temperature overnight and
then added to H2O (250 mL). A white precipitate formed and this was
extracted from the aqueous layer with CH2Cl2 (6ꢄ100 mL). The com-
bined organic fractions were dried over MgSO4 and the solvents carefully
removed in vacuo with no heating to give the desired product as a white
solid (1.47 g, 4.45 mmol, 91%). M.p. 75–778C; 1H NMR (300 MHz,
A
)
G
Figure 13. Single-crystal X-ray structure of 1·NH4Cl with the guest ions
widely separated in the cavity. The triazole forms hydrogen bonds to ClÀ
in an intermolecular fashion. Only hydrogen atoms involved in hydrogen
bonding are shown for clarity. Thermal ellipsoids are displayed at the
30% probability level.
3
The oxygen interactions with the ammonium cation
appear to be electrostatic rather than directed by hydrogen
bonding (quinone O···NH4 2.701(17), 2.758(16) ꢃ and
phenyl O···NH4 2.930(14), 3.074(14) ꢃ). The chloride is
bound intramolecularly by the isophthalamide motif (amide
CDCl3, 298 K): d=8.17 (t, 4J
3J(H,H)=7.8, 4J(H,H)=1.8 Hz, 2H; phenylH), 7.49 (t, 3J
1H; phenylH), 6.74 (brs, 2H; CONH), 3.54 (dt, 3J
(H,H)=6.6, 6.0 Hz,
2H; NHCH2R), 3.43 (t, 3J
(H,H)=6.3 Hz, 2H; N3CH2R), 1.90 ppm (q,
3J(H,H)=6.6 Hz, 2H; RCH2R); 13C NMR (75 MHz, CDCl3, 298 K): d=
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
À
À
N H···Cl 3.453(10), 3.364(10) ꢃ and internal C H···Cl
3.628(12) ꢃ) and also by the intermolecular triazole hydro-
gen bond.
167.2, 134.7, 130.0, 128.8, 125.3, 49.3, 37.7, 28.7 ppm; HRMS (ESI): m/z
calcd for C14H18N8O2Na: 353.1445 [M+Na]+; found: 353.1443.
Macrocycle 5: N1,N3-bis(3-azidopropyl)isophthalamide
4
(100 mg,
0.303 mmol) and dialkyne 2 (220 mg, 0.303 mmol) were dissolved in dry
dichloromethane (100 mL). To this were added tetrabutylammonium
chloride (84 mg, 1 equiv), tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]a-
1·KBr: The crystal structure of the 1·KBr complex can be
found in the Supporting Information.
mine (TBTA; 2 mg, 1 mol%), [CuI
ACTHNUGTRENNUG(MeCN)4PF6] (57 mg, 0.5 equiv) and
diisopropylethylamine (158 mL, 3 equiv). The reaction mixture was stirred
at room temperature under a N2 atmosphere for 3 days. Crude TLC in
4% EtOH/CH2Cl2 showed full consumption of the starting materials.
The reaction mixture was then washed with aqueous HCl (1m; 100 mL),
saturated aqueous NaHCO3 (100 mL) and then H2O (100 mL). The or-
ganic component was dried over MgSO4 and the solvent removed in
vacuo to give a pale yellow solid. This was then purified by column chro-
matography, first by removing a fast-running yellow fraction (CH2Cl2,
1 column volume (CV); 4% EtOH/CH2Cl2, 2.5 CV; 5% EtOH/CH2Cl2,
5 CV; 10% EtOH/CH2Cl2, 5 CV), isolating the pure macrocycle as
a white glassy solid (247 mg, 77%). M.p. 2008C (decomp.); 1H NMR
Conclusion
A new heteroditopic calix[4]diquinone triazole containing
receptor capable of recognising both cations and anions
through respective Lewis base and C H hydrogen-bonding
À
modes of the triazole motif has been prepared. 1H NMR
and UV/Vis spectroscopic titration studies determined that
the ion-pair receptor cooperatively binds halide–monovalent
cation combinations in a polar solvent mixture of 2% water/
acetonitrile. Cation binding by the calix[4]diquinone oxygen
and triazole nitrogen donor groups enhances the strength of
halide complexation in the receptorꢁs isophthalamide site by
up to 11 times in the case of the Na+ClÀ ion pair. Converse-
ly, halide-anion binding in the receptorꢁs isophthalamide
motif enhances cation complexation.
(300 MHz, CDCl3, 298 K): d=8.02 (d, 3J
7.82 (brs, 2H; CONH), 7.68 (brs, 1H; phenylH), 7.60 (s, 2H; triazoleH),
ACHTUNGTNER(NUNG H,H)=6.6 Hz, 2H; phenylH),
3
7.47 (t, JACTHNUTRGNE(NUG H,H)=7.8 Hz, 1H; phenylH), 6.99 (s, 4H; calixH), 6.89 (s, 4H;
calixH), 4.98 (s, 4H; OCH2R), 4.73 (brt, 3J
ACHTUNGTRENNUNG
leCH2R), 4.08 (d, 2J
NHCH2R), 3.24 (d, J
G
2
A
RCH2R), 1.93 (brs, 2H; OH), 1.23 (s, 18H; CCH3), 1.04 ppm (s, 18H;
CCH3); 13C NMR (75 MHz, CDCl3, 298 K): d=166.6, 150.2, 149.3, 147.7,
144.3, 141.9, 133.9, 132.8, 131.4, 129.5, 127.4, 125.8, 125.2, 124.4, 123.2,
69.1, 58.7, 49.2, 37.6, 34.1, 33.8, 32.1, 31.6, 31.0 ppm; HRMS (ESI): m/z
calcd for C64H78N8O6Na: 1077.5937 [M+Na]+; found: 1077.5914.
A number of receptor/ion-pair adduct solid-state struc-
tures have been determined by X-ray crystallography. These
structures further corroborate the findings from the
1H NMR spectroscopy ion-binding investigations in solution,
that the receptorꢁs triazole motifs are capable of coordinat-
ing simultaneously to both cation and anion guest species.
Receptor 1: Macrocycle 5 (500 mg, 0.474 mmol) was added to a solution
of TlACHTUNGTRNEUN(G CF3CO2)3 in TFA (0.44m, 6.45 mL, 6 equiv). The reaction mixture
was stirred under a N2 atmosphere in the dark at room temperature for
2 days. CH2Cl2 (15 mL) was added to the orange reaction mixture, which
was then washed with H2O (3ꢄ15 mL), dried over MgSO4 and the sol-
vent removed in vacuo to give the impure product as a yellow solid
(485 mg). This was then purified by recrystallisation from CH2Cl2/Et2O
and the desired product was collected and dried in vacuo to give a yellow
1
solid (385 mg, 84%). M.p. 1758C (decomp.); H NMR (300 MHz, CDCl3,
298 K): d=8.44 (s, 1H; phenylH), 8.11 (d, 3J
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
6236
www.chemeurj.org
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 6230 – 6237

Ion-Pair Recognition
FULL PAPER
7.8 Hz, 1H; phenylH), 6.94 (s, 4H; quinoneH), 6.39 (s, 4H; calixH), 4.86
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(s, 4H; OCH2R), 4.58 (t, 3J
ACTHNUTRGEN(UGN H,H)=6.0 Hz, 4H; triazoleCH2R), 3.60 (m,
2
8H; quinoneCH2calix, NHCH2R), 3.36 (d, JACTHNUTRGNE(NUG H,H)=13.2 Hz, 4H; quino-
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Acknowledgements
We thank the EPSRC for a D.T.A. studentship (to S.C.P.) and the Dia-
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Received: January 23, 2012
Published online: April 4, 2012
Chem. Eur. J. 2012, 18, 6230 – 6237
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6237