Calix[4]arene-based rotaxane host systems for anion recognition

Article abstract of DOI:10.1002/chem.200902659

The synthesis, structure and anion binding properties of the first calix[4]arene-based [2]rotaxane anion host systems are described. Rotaxanes 9·Cl and 12·Cl, consisting of a calix[4]-arene functionalised macrocycle wheel and different pyridinium axle components, are prepared via adaption of an anion templated synthetic strategy to investigate the effect of preorganisation of the interlocked host's binding cavity on anion binding. Rotaxane 12·Cl contains a conformationally flexible pyridinium axle, whereas rotaxane 9·Cl incorporates a more preorganised pyridinium axle component. The X-ray crystal structure of 9·Cl and solution phase ¹H NMR spectroscopy demonstrate the successful interlocking of the calix[4]arene macrocycle and pyridinium axle components in the rotaxane structures. Following removal of the chloride anion template, anion binding studies on the resulting rotaxanes 9·PF₆ and 12·PF ₆ reveal the importance of preorganisation of the host binding cavity on anion binding. The more preorganised rotaxane 9·PF₆ is the superior anion host system. The interlocked host cavity is selective for chloride in 1:1 CDCl₃/CD₃OD and remains selective for chloride and bromide in 10% aqueous media over the more basic oxoanions. Rotaxane 12·PF₆ with a relatively conformationally flexible binding cavity is a less effective and discriminating anion host system although the rotaxane still binds halide anions in preference to oxoanions.

Full text of DOI:10.1002/chem.200902659

DOI: 10.1002/chem.200902659
Calix[4]arene-Based Rotaxane Host Systems for Anion Recognition
Anna J. McConnell,[a] Christopher J. Serpell,[a] Amber L. Thompson,[a]
David R. Allan,[b] and Paul D. Beer*[a]
Abstract: The synthesis, structure and
anion binding properties of the first
calix[4]arene-based [2]rotaxane anion
host systems are described. Rotaxanes
9·Cl and 12·Cl, consisting of a calix[4]-
arene functionalised macrocycle wheel
and different pyridinium axle compo-
nents, are prepared via adaption of an
anion templated synthetic strategy to
investigate the effect of preorganisa-
tion of the interlocked hostꢀs binding
cavity on anion binding. Rotaxane
12·Cl contains a conformationally flexi-
ble pyridinium axle, whereas rotaxane
9·Cl incorporates a more preorganised
pyridinium axle component. The X-ray
crystal structure of 9·Cl and solution
phase 1H NMR spectroscopy demon-
strate the successful interlocking of the
calix[4]arene macrocycle and pyridini-
um axle components in the rotaxane
structures. Following removal of the
chloride anion template, anion binding
studies on the resulting rotaxanes 9·PF6
and 12·PF6 reveal the importance of
preorganisation of the host binding
cavity on anion binding. The more pre-
organised rotaxane 9·PF6 is the superi-
or anion host system. The interlocked
host cavity is selective for chloride in
1:1 CDCl3/CD3OD and remains selec-
tive for chloride and bromide in 10%
aqueous media over the more basic ox-
oanions. Rotaxane 12·PF6 with a rela-
tively conformationally flexible binding
cavity is a less effective and discrimi-
nating anion host system although the
rotaxane still binds halide anions in
preference to oxoanions.
Keywords: anions
· calixarenes ·
rotaxanes · supramolecular chemis-
try · templation
Introduction
Calixarenes are attractive molecular structural frame-
works renowned for their versatility and ease of functionali-
sation at both the narrow lower, and wide upper rim.[4,5] As
a result a multitude of calixarene derivatives have been uti-
lised as cation,[6] anion[4,7] and ion-pair receptors.[8] They
have also recently begun to be incorporated into interlocked
structures including rotaxanes[9,10] and catenanes.[11–13]
We have undertaken a research programme with the ob-
jective of exploiting the unique topological cavities of rotax-
anes and catenanes in anion host-guest chemistry.[10–12,14–16]
We have previously reported the synthesis of heteroditopic
calix[4]arene receptors which exhibit unprecedented cooper-
ative and ion-pair binding behaviour.[17,18] Through suitable
modification of this heteroditopic receptor design, together
with exploitation of a strategic anion templation methodolo-
gy, calix[4]arene functionalised [2]catenane anion receptors
were assembled.[11,12] Herein we describe the preparation of
the first calix[4]arene-based [2]rotaxane anion host systems,
which consist of a calix[4]arene functionalised macrocycle
wheel and pyridinium axle components, through adaptation
of a new synthetic pathway that involves anion templation
in combination with favourable p–p stacking interactions.[15]
Anion binding investigations reveal the more preorganised
rotaxane exhibits an impressive high affinity for chloride
The imaginative design and construction of rotaxane and
catenane interlocked molecules of increasing complexity
and functionality is an area of intense current interest.[1]
This has been stimulated by their promising applications as
components of molecular machines and switches in which
external stimuli can control the mechanical-bond dynam-
ics.[2] Despite this, the potential of these molecules to func-
tion as selective-host systems in molecular recognition appli-
cations has been largely overlooked, which is somewhat sur-
prising given their unique three-dimensional topological
binding cavities.[3]
[a] A. J. McConnell, C. J. Serpell, Dr. A. L. Thompson, Prof. P. D. Beer
Inorganic Chemistry Laboratory, Department of Chemistry
University of Oxford, South Parks Road, Oxford, OX1 3QR (UK)
Fax : (+44)1865-272-690
E-mail: paul.beer@chem.ox.ac.uk
[b] Dr. D. R. Allan
Diamond Light Source, Harwell Science and Innovation Campus
Didcot, OX11 0QX (UK)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902659.
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Chem. Eur. J. 2010, 16, 1256 – 1264

FULL PAPER
and bromide in aqueous solvent media in preference to
basic oxoanions.
Results and Discussion
Synthetic strategy: The strategy for the synthesis of the
target calixarene-based [2]rotaxanes is depicted in
Scheme 1. Anion templation and favourable p–p stacking
interactions between the calix[4]arene-based macrocycle
precursor and stoppered pyridinium axle component are ex-
ploited prior to reaction with a clipping component to form
the [2]rotaxane. The calix[4]arene macrocycle precursor 1
incorporates electron rich hydroquinone groups to facilitate
p–p stacking interactions with the electron deficient pyridi-
nium axle component. In addition, it is functionalised with
terminal amine groups for the clipping condensation reac-
tion with an appropriate bis-acid chloride derivative. Cal-
ix[4]arene-based rotaxanes containing the two pyridinium
axle components, 2·Cl and 3·Cl, are synthesised to investi-
gate the effect of preorganisation of the axle component on
the anion binding properties of the resulting rotaxane host
systems.
Macrocycle precursor 1[12] and axle component 2·Cl[16]
were prepared according to literature procedures. The syn-
thesis of the new axle component 3·Cl is outlined in
Scheme 2. Compound 6 was synthesised in 79% yield by
heating a suspension of compounds 4[19] and 5[17] and K2CO3
in acetonitrile in a microwave at 1608C for four hours. The
phthalimide protecting groups were removed in 96% yield
using hydrazine monohydrate. The resulting amine 7 was re-
acted with 3,5-bis(chlorocarbonyl) pyridine in CH2Cl2 to
give 8 in 82% yield. Methylation of 8 with methyl iodide af-
forded 3·I in 96% yield. The iodide anion was exchanged
for chloride by repeated aqueous washings with ammonium
chloride to give 3·Cl in 95% yield. In addition the non-coor-
Scheme 1. A diagram of the ion-pair templation strategy for the synthesis
of calix[4]arene-based rotaxanes.
dinating hexaACHTUNGTRENNUNGfluACHTUNGTRENNUNGoroACHTGUNTRENpNNGU hosphate
salt 3·PF6 was prepared for
anion binding studies by repeat-
ed washing of a solution of 3·Cl
in
CHCl3
with
aqueous
NH4PF6.
Synthesis of rotaxanes: The
[2]rotaxane 9·Cl was prepared
by adding isophthaloyl dichlor-
ide to a 1:1 mixture of com-
pounds
CH2Cl2 in the presence of tri-
ethylamine (Scheme 3). Rotax-
1 and 2·Cl in dry
A
ACHTUNGTRENNUNG
ane 9·Cl was isolated in 11%
yield following purification by
preparative thin-layer chroma-
tography and recrystallisation
from CHCl3/MeOH. In addition
the macrocycle by-product 10
Scheme 2. Synthesis of axle component 3·Cl. a) K2CO3, CH3CN, mW, 1608C, 4 hr; b) N2H4.H2O, EtOH, reflux,
was isolated in 30% yield. The 16 hr; c) NEt3, CH2Cl2, RT, 19 hr; d) MeI, acetone, reflux, 3 days; e) Anion exchange.
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1257

P. D. Beer et al.
[16]
phate using AgPF6 to improve the organic solvent solubil-
ity. The hexafluorophosphate anion was not expected to in-
terfere with any anion templation effects due to the large
excess of chloride anions produced in the condensation reac-
tion as a consequence of amide formation. Although the sol-
ubility of the axle component was improved upon anion ex-
change, the yield of the rotaxane did not significantly in-
crease. Despite the solubility problems with 2·Cl, the rotax-
ane synthesis was repeated in the presence of 1.5 equiva-
lents of 2·Cl and the rotaxane was isolated in an improved
yield of 17%. The macrocycle by-product 10 was also isolat-
ed in 23% yield.
Rotaxane 12·Cl was synthesised using an analogous syn-
thetic procedure and owing to the improved solubility of
3·Cl compared to 2·Cl, it was possible to carry out the reac-
tion at a higher concentration (Scheme 4). The rotaxane was
Scheme 3. Synthesis of rotaxane 9·Cl and macrocycle by-product 10.
formation of the macrocycle by-product accounts for the
lower yield of rotaxane as compared with our previously re-
ported rotaxane system where a flexible polyether hydroqui-
none bis-amine is used as the macrocycle precursor compo-
nent instead of the relatively more preorganised calix[4]ar-
ene bis-amine synthon.[15]
Interestingly, whereas the macrocyclisation of bis-amine 1
and isophthaloyl dichloride in the absence of the axle com-
ponent gave macrocycle 10 in
25% yield, the analogous con-
densation reaction in the pres-
ence of the unstoppered 3,5-bis-
amide pyridinium chloride axle
component 11·Cl afforded the
macrocycle in an improved
yield of 38%. This suggests
chloride anion templation in
Scheme 4. Synthesis of rotaxane 12·Cl.
combination with favourable p–
p
donor-acceptor interactions
contribute to the efficacy of
macrocycle formation, and in rotaxane formation using the
stoppered axle. In an effort to improve the yield of the ro-
taxane, a number of the reaction conditions were varied.
Compound 2·Cl has limited solubility in CH2Cl2 and there-
fore the chloride anion was exchanged to hexafluorophos-
isolated in 23% yield following purification by preparative
thin layer chromatography and recrystallisation from
CHCl3/diisopropyl ether (iPr2O). The macrocycle by-product
10 was also formed, but owing to its impure nature it was
not possible to obtain an accurate yield.
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Calix[4]arene-Based Rotaxane
FULL PAPER
1
Rotaxanes 9·Cl and 12·Cl were characterised by H and
13C NMR spectroscopy, high-resolution electrospray mass
spectrometry and melting point analysis.[20] A comparison of
1
the H NMR spectra of the macrocycle 10, axle 2·Cl and ro-
taxane 9·Cl in CDCl3 are shown in Figure 1. The downfield
shifts of the isophthalamide protons a and b are indicative
of halide anion complexation in the rotaxaneꢀs interlocked
host binding cavity. In addition the upfield shifts of the axle
proton e can be attributed to the competitive binding of
chloride in the rotaxane compared with the ion-paired free
axle. The upfield shifts and splitting of the hydroquinone
protons c and d result from p–p stacking interactions be-
tween the electron deficient pyridinium unit of the axle and
electron rich hydroquinone rings of the macrocycle. The
ROESY spectra of 9·Cl and 12·Cl (Figure S10) reveal a
number of through space correlations between the respec-
tive macrocycle and axle components, as illustrated in
Figure 2.
X-ray crystal structure of rotaxane 9·Cl: Single crystals of
rotaxane 9·Cl were obtained by slow evaporation of a solu-
tion of the rotaxane in 45:45:10 CDCl3/CD3OD/D2O. Al-
though of a good size, the crystals were found to diffract
poorly under standard MoKa radiation. Despite these diffi-
culties, it was possible to collect a useable dataset and the
X-ray crystal structure unambiguously confirmed the con-
nectivity and interlocked nature of the structure (Fig-
ure S12).
However, a higher quality dataset was obtained from an-
other crystal from the same sample, analysed using synchro-
tron radiation on beamline I19 at Diamond Light Source
(Figure 3). Interestingly, structural differences were ob-
served as established by examination of the conformation of
Figure 2. Portion of the ROESY spectrum of rotaxane 9·Cl in CDCl3 at
298 K illustrating the through space correlations between the calixarene
macrocycle and ion-pair thread components.
the stopper groups (Figure S12).
Contraction of one of the cell
axes indicates that this results
from solvent loss (Table S1).
However, with respect to the
supramolecular forces involved,
there is little difference be-
tween the two samples. A top-
down view makes it clear that
slippage of the stoppers is im-
possible. The intermolecular
forces used to template the ro-
taxane in solution are still pres-
ent in the solid state: hydrogen
bonds from both components to
the chloride anion; p–p stack-
ing between the electron poor
pyridinium unit and the elec-
tron rich hydroquinone groups
(though with a high degree of
offset); and secondary hydro-
gen bonding of the pyridinium
Figure 1. 1H NMR spectra of a) axle 2·Cl, b) rotaxane 9·Cl and c) macrocycle 10 in CDCl3 at 298 K.
methyl group to calixarene oxy-
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1259

P. D. Beer et al.
Figure 3. X-ray crystal structure of 9·Cl obtained by synchrotron radia-
tion displaying anion coordination. Disorder and non-coordinating hydro-
gen atoms are omitted for clarity.
gens (Table 1). The chloride anion is tetrahedrally coordi-
À
nated with respect to the amide protons (a mean N(H) Cl
distance of 3.36 ꢂ), but central aryl protons also form close
À
contacts with a mean C(H) Cl distance of 3.32 ꢂ.
Figure 4. Portion of the ROESY spectrum of rotaxane 9·PF6 in CDCl3 at
298 K illustrating the through space correlations between the calixarene
macrocycle and ion-pair thread components.
Table 1. Selected crystallographic data for rotaxane 9·Cl. Distances are
given for atoms labelled in numerical order.
[a]
À
N(H) Cl distances [ꢂ]
3.222(11), 3.544(37)
3.340(9),[c] 3.246(9)[c]
3.511(12),[c] 3.273(40)[c]
3.366(14), 3.276(12)
4.015(8), 3.749(8)
17.2(7), 8.7(6)
3.734(16), 3.428(16)
3.113(13), 3.559(14)
taxanes and axle. Chemical shift changes were monitored
upon addition of a variety of anions, added as their tetrabu-
tylammonium (TBA) salts. In the presence of anions such as
chloride and bromide, downfield shifts of the cavity protons
a, f and g were observed for both rotaxanes 9·PF6 and
12·PF6 (Figure 5). However, the addition of acetate and di-
hydrogen phosphate induced an upfield shift of proton f and
downfield shifts of protons a and g. This is suggestive of a
different binding mode for these anions, most likely outside
the interlocked cavity due to their large size. In contrast,
downfield shifts of protons a, f and g were observed upon
addition of all anions to the axle 3·PF6. WinEQNMR2[23]
analysis of the titration data gave association constant
values for the 1:1 rotaxane/anion stoichiometric complexes
shown in Table 2.
The association constant values reveal the more preorgan-
ised rotaxane 9·PF6 is the superior anion discriminating and
complexing host system. Rotaxane 9·PF6 is selective for
chloride over bromide and the more oxobasic anions acetate
and dihydrogen phosphate. This selectivity is due to a com-
plementary size match between the preorganised inter-
locked binding cavity and the chloride anion, as evidenced
in the solid state structure of 9·Cl (Figure 3). Owing to the
[a]
À
C(H) Cl distances [ꢂ]
p–p centroid–centroid distances [ꢂ][b]
p–p stacking angle[b] [8]
Pyr+-C(H3)-O distances [ꢂ][a]
[a] Calculated within CRYSTALS[21] by using the full variance-covariance
matrix. [b] Calculated by using PLATON[22] without inclusion of the co-
variance. [c] Multiplicity of value occurs owing to disorder.
Anion binding studies: To study the anion binding proper-
ties of the rotaxanes, the chloride anion template was re-
moved from the respective interlocked host cavity by wash-
ing a CHCl3 solution of the rotaxanes with aqueous NH4PF6.
The resulting rotaxanes 9·PF6 and 12·PF6 and axle 3·PF6
were characterised by 1H, 19F, 31P, 13C NMR spectroscopy,
electrospray mass spectrometry and melting point analysis.
The ROESY NMR spectra of 9·PF6 (Figure 4) and 12·PF6
(Figure S11) both demonstrate through space correlations
between the macrocycle and axle components indicating
that anion exchange has preserved the interlocked structure.
1H NMR titration experiments in 1:1 CDCl3/CD3OD were
undertaken to study the anion binding properties of the ro-
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Calix[4]arene-Based Rotaxane
FULL PAPER
media were also investigated (Table 2). In a 45:45:10 CDCl3/
CD3OD/D2O solvent mixture the rotaxane binds the halide
anions in preference to the oxoanions and as expected the
association constant values are lower in this more competi-
tive aqueous mixture. It is noteworthy the rotaxane is no
longer selective for chloride over bromide with both anions
exhibiting similar binding affinities in the aqueous mixture.
This loss of chloride anion selectivity is presumably a conse-
quence of the smaller halide anionꢀs larger hydration energy
which effectively competes with the overall anion recogni-
tion process.[24]
The axle 3·PF6 and rotaxane 12·PF6 exhibit significantly
weaker anion binding compared with rotaxane 9·PF6 in 1:1
CDCl3/CD3OD solutions. Rotaxane 12·PF6 has a similar
shaped binding cavity to rotaxane 9·PF6 and as a result, still
binds the halides in preference to the larger oxoanions.
However, it cannot discriminate chloride from bromide
since the binding cavity is more conformationally flexible
and can accommodate the larger bromide in the cavity with
a similar affinity to chloride. The axle 3·PF6 also cannot sig-
nificantly discriminate between the halides and as common-
ly observed for acyclic receptor systems, it binds the basic
dihydrogen phosphate more strongly.
Conclusion
The first calix[4]arene-based [2]rotaxane anion host systems
have been prepared via adaption of a recently discovered
anion templated synthetic methodology. Two rotaxanes, 9·Cl
and 12·Cl, incorporating different axle components were
synthesised to investigate the effect of preorganisation of
the interlocked hostꢀs binding cavity on anion binding. Ro-
Figure 5. 1H NMR spectra of a) 9·Cl, b) 9·PF6 and c) 9.H2PO4 in 1:1
CDCl3/CD3OD at 298 K.
taxane 12·Cl contains
whereas rotaxane 9·Cl incorporates a more preorganised
axle component. Solution phase H NMR spectroscopy ex-
a conformationally flexible axle
Table 2. Anion binding properties of rotaxanes 9·PF6, 12·PF6 and axle
3·PF6.[a]
1
[b]
[c]
[b]
[b]
XÀ
9·PF6
9·PF6
3·PF6
12·PF6
periments provided evidence for the successful interlocking
of the calix[4]arene macrocycle and pyridinium axle compo-
nents in the rotaxane structures. Additionally the first X-ray
crystal structure of a calix[4]arene-based rotaxane anion
host system reveals the axle is threaded through the calix[4]-
arene macrocycle with a chloride anion complexed within
the rotaxane host cavity. Following removal of the chloride
anion template, the anion binding properties of the resulting
ClÀ
3820
1560
1140
530
620
630
70[d]
80
300
440
710
160
650
630
BrÀ
À
H2PO4
420
OAcÀ
140[d]
[a] Association constants derived from winEQNMR2[23] analysis of the
ortho pyridinium proton g data from 1H NMR titration experiments in
[b] 1:1 CDCl3/CD3OD and [c] 45:45:10 CDCl3/CD3OD/D2O at 298 K.
Errors <10%. [d] Errors <20%.
1
rotaxanes 9·PF6 and 12·PF6 were studied by H NMR titra-
tion experiments. These reveal that the degree of preorgani-
sation of the host cavity governs the strength and selectivity
of anion binding. The more preorganised rotaxane 9·PF6 is
the superior anion host system exhibiting selectivity for
chloride in 1:1 CDCl3/CD3OD and selectivity for the halide
anions in 45:45:10 CDCl3/CD3OD/D2O over the more basic
oxoanions. Rotaxane 12·PF6 having a relatively conforma-
tionally flexible binding cavity, however is a less effective
and discriminating anion host system. The rotaxane still
binds halide anions in preference to the oxoanions, unlike
the axle 3·PF6.
lack of conformational flexibility of the binding cavity, the
larger anions bromide, acetate and dihydrogen phosphate
cannot be completely encapsulated within the rotaxane
cavity. As a result, the magnitude of the association con-
stants for these anions is significantly lower than for chlo-
ride. In addition, the large oxoanions most likely associate
on the periphery of the cavity in a different binding mode to
chloride as evidenced by the upfield shift of proton f in
Figure 5.
As the rotaxane displays strong binding of chloride in 1:1
CDCl3/CD3OD, its anion binding properties in aqueous
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P. D. Beer et al.
(30 mL) and H2O (2ꢃ30 mL). The organic layer was dried over MgSO4,
filtered and the solvent was removed. Following purification by silica gel
chromatography (99:1 CHCl3/MeOH), the product 6 was obtained as a
white solid in 79% yield (1.43 g, 2.2 mmol). M.p. 82–848C; 1H NMR
(300 MHz, CDCl3): d=7.81 (dd, 3J=5.4, 4J=3.1 Hz, 2H; PhthH), 7.66
(dd, 3J=5.4, 4J=3.1 Hz, 2H; PhthH), 7.21 (m, 9H; ArH), 7.06 (m, 6H;
Experimental Section
All commercial-grade chemicals and solvents were used without further
purification unless otherwise stated. Where dry solvents were used, they
were degassed with nitrogen, dried by passing through an MBraun
MPSP-800 column and then used immediately. Triethylamine was dis-
tilled over and stored over potassium hydroxide. Thionyl chloride was
distilled over triphenyl phosphite. TBA salts were stored prior to use
under vacuum in a desiccator containing phosphorus pentoxide and self-
indicating silica gel. Deionised water was used in all cases.
1H, 13C, 19F and 31P NMR spectra were recorded by using a Varian Mercu-
ry 300, a Varian Unity Plus 500 or a Bruker AVII500 with cryoprobe
spectrometer. Mass spectra were obtained by using a Bruker micrOTOF
or a MALDI Micro MX spectrometer. Melting points were recorded by
using a Gallenkamp capillary melting point apparatus and are uncorrect-
ed. Elemental analysis was carried out by the service at London Metro-
politan University. Microwave reactions were carried out by using a Bio-
3
ArH), 6.68 (d, J=8.8 Hz, 2H; ArH), 4.04 (t, 3J=4.8 Hz, 2H; CH2), 3.93
(m, 2H; CH2), 3.83 (m, 4H; CH2), 1.31 ppm (s, 18H; tBu); 13C NMR
(75 MHz, CDCl3): d=168.26, 156.43, 148.30, 147.35, 143.92, 139.45,
133.85, 132.07, 132.04, 131.10, 130.64, 127.17, 125.62, 124.09, 123.21,
113.06, 69.06, 67.99, 67.18, 63.40, 37.20, 34.26, 31.34 ppm; ESMS: m/z
calcd for C45H47NO4Na: 688.3397; found: 688.3398 [M+Na]+.
Synthesis of 7: Compound 6 (0.32 g, 0.48 mmol) was suspended in ethanol
(20 mL), hydrazine monohydrate (0.7 mL, excess) was added and the re-
sulting mixture was heated under reflux for 16 hr. The resulting white
suspension was cooled to room temperature, poured in water (50 mL)
and then extracted using CH2Cl2 (3ꢃ50 mL). The combined organic
layers were dried over MgSO4, filtered and the solvent was removed to
give 7 as an off-white solid in 96% yield (0.26 g, 0.48 mmol). M.p. 68–
ACHTUNGTRENNUNGtage Initiator 2.0 microwave.
Compounds 1,[12] 2,[16] 4,[19] 5[17] and 11·Cl[25] were prepared according to
literature procedures. The synthesis and characterisation of macrocycle
10 has been described elsewhere.[12] The characterisation of macrocycle
10 was consistent with the literature data.
1
708C; H NMR (300 MHz, CDCl3): d=7.24 (m, 9H; ArH), 7.10 (m, 6H;
3
ArH), 6.79 (d, J=9.1 Hz, 2H; ArH), 4.11 (t, 3J=4.8 Hz, 2H; CH2), 3.82
(t, 3J=4.8 Hz, 2H; CH2), 3.59 (t, 3J=5.1 Hz, 2H; CH2), 2.91 (br. s., 2H;
CH2N), 1.83 (br. s., 2H; NH2), 1.31 ppm (s, 18H; tBu); 13C NMR
(75 MHz, CDCl3): d=156.50, 148.33, 147.34, 143.92, 139.63, 132.19,
131.11, 130.65, 127.20, 125.65, 124.11, 113.13, 73.11, 69.50, 67.15, 63.43,
41.62, 34.28, 31.35 ppm; ESMS: m/z calcd for C37H46NO2: 536.3523;
found: 536.3539 [M+H]+.
Synthesis of 3·I: A solution of 8 (0.27 g, 0.23 mmol) and methyl iodide
(0.5 mL, excess) in acetone (15 mL) was heated under reflux under a N2
atmosphere for three days. The solvent was removed to give 3·I as an
1
orange solid in 96% yield (0.30 g, 0.22 mmol). M.p. 158–1608C; H NMR
(300 MHz, CDCl3): d=9.87 (s, 1H; py H4), 9.22 (s, 2H; py H2 and H6),
8.79 (br. s., 2H; NH), 7.19 (m, 18H; ArH), 7.08 (m, 12H; ArH), 6.73 (d,
3J=8.8 Hz, 4H; ArH), 4.21 (s, 3H; N+CH3), 4.10 (m, 4H; CH2), 3.85 (m,
8H; CH2), 3.71 (m, 4H; CH2), 1.29 ppm (s, 36H; tBu); 13C NMR
(75 MHz, CDCl3): d=160.63, 156.34, 148.35, 147.33, 146.26, 143.89,
141.57, 139.79, 134.42, 132.16, 131.03, 130.58, 127.26, 125.66, 124.18,
113.20, 69.40, 68.89, 67.41, 63.41, 49.36, 40.19, 34.27, 31.35 ppm; ESMS:
m/z: 1216.7144 [MÀI]+.
Synthesis of 3·Cl: A biphasic mixture of 3·I (0.26 g, 0.20 mmol) in CHCl3
(100 mL) and 1m NH4Cl(aq) (100 mL) was stirred vigorously for 30 mins.
The aqueous layer was decanted and the procedure was repeated a fur-
ther four times. The organic layer was dried over MgSO4, filtered and the
solvent was removed. Compound 3·Cl was obtained as a yellow solid in
95% yield (0.23 g, 0.19 mmol). M.p. 186–1888C; 1H NMR (300 MHz,
CDCl3): d=10.53 (s, 1H; py H4), 9.47 (t, 3J=4.7 Hz, 2H; NH), 9.26 (s,
2H; py H2 and H6), 7.20 (m, 18H; ArH), 7.07 (m, 12H; ArH), 6.72 (d,
3J=8.8 Hz, 4H; ArH), 4.30 (s, 3H; N+CH3), 4.11 (m, 4H; CH2), 3.86 (m,
8H; CH2), 3.71 (t, 3J=5.0 Hz, 4H; CH2), 1.29 ppm (s, 36H; tBu);
13C NMR (75 MHz, CDCl3): d=160.39, 156.34, 148.31, 147.30, 146.65,
143.85, 141.37, 139.72, 133.96, 132.16, 131.03, 130.58, 127.22, 125.64,
124.13, 113.09, 69.41, 69.01, 67.30, 63.39, 49.28, 40.38, 34.25, 31.33 ppm;
ESMS: m/z: 1216.7087 [MÀCl]+.
Synthesis of 8: A suspension of 3,5-pyridinedicarboxylic acid (0.05 g,
0.30 mmol) in SOCl2 with a drop of DMF was heated under reflux under
a N2 atmosphere for 17 hr. The excess SOCl2 was removed by distillation
in vacuo and the resulting solid was redissolved in dry CH2Cl2 (15 mL).
This was added dropwise over 1 hr to a solution of compound 7 (0.32 g,
0.60 mmol) and NEt3 (0.15 mL, 1.1 mmol) in dry CH2Cl2 (20 mL) under a
N2 atmosphere. The reaction mixture was left to stir for 19 hr, then
washed with 1m HCl(aq) (2ꢃ30 mL) and brine (30 mL). The organic layer
was dried over MgSO4, filtered and the solvent was removed to give 8 as
1
a white solid in 82% yield (0.30 g, 0.25 mmol). M.p. 130–1328C; H NMR
4
(300 MHz, CDCl3) d: 9.12 (s, 2H; py H2 and H6), 8.53 (t, J=2.1 Hz, 1H;
py H4), 7.20 (m, 18H; ArH), 7.09 (m, 12H; ArH), 6.86 (br. s., 2H; NH),
6.74 (d, 3J=9.1 Hz, 4H; ArH), 4.06 (m, 4H; CH2), 3.81 (m, 4H; CH2),
3.70 (m, 8H; CH2), 1.30 ppm (s, 36H; tBu); 13C NMR (75 MHz, CDCl3):
d=164.73, 156.16, 150.75, 148.36, 147.30, 143.87, 139.90, 133.31, 132.21,
131.06, 130.61, 129.56, 127.23, 125.67, 124.15, 113.10, 69.76, 69.57, 67.07,
63.43, 39.89, 34.27, 31.35 ppm; ESMS: m/z: 1224.6626 [M+Na]+.
Synthesis of 9·Cl:
A solution of isophthaloyl dichloride (0.015 g,
0.072 mmol) in dry CH2Cl2 (20 mL) was added to a solution of bis-amine
1 (0.070 g, 0.069 mmol), axle 2·Cl (0.11 g, 0.10 mmol) and NEt3 (0.02 mL,
0.14 mmol) in dry CH2Cl2 (15 mL). The reaction mixture was stirred at
room temperature under a N2 atmosphere for 1 hr and then washed with
1m HCl(aq) (2ꢃ10 mL) and brine (10 mL). The organic layer was dried
over MgSO4, filtered and the solvent was removed. Following purification
by preparative thin-layer chromatography (4:1 EtOAc/CHCl3) and re-
crystallisation from CHCl3/MeOH, the rotaxane 9·Cl was isolated as a
yellow solid in 17% yield (0.021 g, 0.0097 mmol). M.p. 2508C (dec.);
1H NMR (300 MHz, CDCl3): d=10.59 (s, 1H; py H4), 10.44 (br. s., 2H;
NH), 9.16 (s, 2H; py H2 and H6), 8.92 (s, 1H; isoH), 8.62 (br. s., 2H;
NH), 8.02 (d, 3J=7.9 Hz, 2H; isoH), 7.81 (d, 3J=8.8 Hz, 4H; ArH), 7.13
(m, 35H; ArH, calix ArH, isoH), 6.67 (s, 4H; calix ArH), 6.47 (d, 3J=
9.0 Hz, 4H; hydroqH), 6.25 (d, 3J=9.0 Hz, 4H; hydroqH), 5.69 (s, 2H;
OH), 4.97 (s, 3H; N+CH3), 4.45 (d, 2J=13.6 Hz, 4H; ArCHinHoutAr),
4.19 (m, 8H; CH2), 4.09 (m, 4H; CH2), 3.82 (m, 4H; CH2), 3.46 (d, 2J=
13.6 Hz, 4H; ArCHinHoutAr), 1.39 (s, 18H, tBu), 1.33 (s, 36H, tBu),
0.87 ppm (s, 18H; tBu); 13C NMR (125 MHz, CDCl3): d=167.11, 158.10,
154.01, 151.70, 150.58, 149.97, 148.32, 147.54, 146.97, 144.99, 144.67,
143.52, 142.78, 134.62, 134.06, 133.21, 131.75, 131.58, 131.09, 130.64,
128.46, 127.33, 125.93, 125.69, 125.52, 125.11, 124.26, 120.85, 114.86,
114.35, 75.19, 67.68, 65.88, 63.77, 50.81, 41.24, 34.30, 34.02, 33.85, 31.75,
31.39, 31.16, 30.90 ppm; ESMS: m/z: 2177.0742 [MÀCl]+; elemental anal-
Synthesis of 3·PF6: 3·Cl (0.066 g, 0.053 mmol) was dissolved in CHCl3
(10 mL) and washed with 0.2m NH4PF6(aq) (5ꢃ10 mL). The organic layer
was separated, dried over MgSO4, filtered and the solvent was removed
to give 3·PF6 as a white solid in 91% yield (0.066 g, 0.049 mmol). M.p.
142–1448C; 1H NMR (300 MHz, CDCl3) d: 9.14 (s, 1H; py H4), 8.94 (s,
2H; py H2 and H6), 7.59 (t, 3J=4.4 Hz, 2H; NH), 7.21 (m, 18H; ArH),
7.08 (m, 12H; ArH), 6.70 (d, 3J=8.8 Hz, 4H; ArH), 4.17 (s, 3H; N+
CH3), 4.03 (m, 4H; CH2), 3.78 (m, 4H; CH2), 3.68 (m, 8H; CH2),
1.29 ppm (s, 36H; tBu); 13C NMR (75 MHz, CDCl3): d=160.56, 156.17,
148.37, 147.33, 145.78, 143.88, 141.21, 139.95, 135.10, 132.18, 131.02,
130.57, 127.27, 125.68, 124.19, 113.19, 69.42, 68.97, 67.29, 63.43, 49.17,
40.41, 34.27, 31.35 ppm; 19F NMR (282.5 MHz, CDCl3): d=À72.01 ppm
(d, 1J=713 Hz, PF6À); 31P NMR (121.6 MHz, CDCl3): d=À144.63 ppm
(septet, J=713 Hz, PF6À); ESMS: m/z: 1216.7160 [MÀPF6]+.
1
Synthesis of 6: A suspension of compounds 4 (1.27 g, 2.8 mmol), 5
(1.33 g, 3.4 mmol) and K2CO3 (0.79 g, 5.7 mmol) in CD3CN (15 mL) was
heated in a microwave for 4 hr at 1608C. The reaction mixture was
cooled to room temperature and the solvent was removed. The crude
material was redissolved in CHCl3 (50 mL), washed with 1m HCl(aq)
1262
www.chemeurj.org
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 1256 – 1264

Calix[4]arene-Based Rotaxane
FULL PAPER
ysis calcd (%) for C146H162N5O12Cl: C 79.19, H 7.37, N 3.16; found C
79.04, H 7.25, N 3.23.
63.39, 49.95, 40.90, 39.80, 34.26, 34.03, 33.85, 31.75, 31.35, 30.91 ppm;
19F NMR (282.5 MHz, CDCl3): d=À70.70 ppm (d, 1J=713 Hz, PF6À);
31P NMR (121.6 MHz, CDCl3): d=À143.76 ppm (septet, 1J=714 Hz,
PF6À); ESMS: m/z: 2353.1877 [MÀPF6]+.
Synthesis of 9·PF6: A solution of 9·Cl (0.048 g, 0.021 mmol) in CHCl3
(10 mL) was washed with 0.2m NH4PF6(aq) (5ꢃ10 mL) and water
(10 mL). The combined organic layers were dried over MgSO4, filtered
and the solvent was removed to give 9·PF6 as a yellow solid in 100%
yield (0.049 g, 0.021 mmol). M.p. 2408C (dec.); 1H NMR (300 MHz,
CDCl3): d=9.40 (br. s., 2H; NH), 9.12 (s, 1H; py H4), 9.00 (br. s., 2H;
py H2 and H6), 8.73 (s, 1H; isoH), 8.02 (dd, 3J=7.9, 4J=1.5 Hz, 2H;
isoH), 7.56 (d, 3J=8.5 Hz, 4H; ArH), 7.45 (t, 3J=7.5 Hz, 2H; NH), 7.15
(m, 35H; calix ArH, ArH), 6.64 (s, 4H; calix ArH), 6.44 (m, 8H; hy-
droqH), 6.18 (s, 2H; OH), 4.77 (s, 3H; N+CH3), 4.44 (d, 2J=13.8 Hz,
4H; ArCHinHoutAr), 4.12 (m, 8H; CH2), 3.79 (m, 4H; CH2), 3.58 (m,
Acknowledgements
We wish to thank the Woolf Fisher Trust and the Overseas Research Stu-
dent (ORS) Awards Scheme for a scholarship (A.J.M) and the EPSRC
and Johnson Matthey for a CASE studentship (C.J.S). We also thank Dr
N. H. Rees for valuable NMR advice.
2
4H; CH2N), 3.38 (d, J=13.8 Hz, 4H; ArCHinHoutAr), 1.36 (s, 18H; tBu),
1.32 (s, 36H; tBu), 0.85 ppm (s, 18H; tBu); 13C NMR (125 MHz, CDCl3):
d=167.05, 158.08, 152.92, 152.12, 150.10, 149.91, 148.54, 147.25, 146.82,
145.27, 144.19, 143.40, 142.52, 141.61, 134.12, 133.93, 133.72, 131.86,
131.64, 131.02, 130.85, 130.59, 128.86, 128.33, 127.39, 125.98, 125.84,
125.74, 125.53, 124.32, 120.37, 115.69, 114.65, 75.11, 67.34, 67.16, 63.82,
50.35, 39.86, 34.31, 33.94, 33.82, 31.74, 31.49, 31.38, 30.91 ppm; 19F NMR
(282.5 MHz, CDCl3): d=À70.10 ppm (d, 1J=715 Hz, PF6À); 31P NMR
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1
m/z: 2177.1363 [MÀPF6]+.
Synthesis of 12·Cl:
A solution of isophthaloyl dichloride (0.014 g,
0.071 mmol) in dry CH2Cl2 (2 mL) was added to a solution of bis-amine 1
(0.070 g, 0.069 mmol), axle 2·Cl (0.13 g, 0.11 mmol) and NEt3 (0.02 mL,
0.14 mmol) in dry CH2Cl2 (5 mL). The reaction mixture was stirred at
room temperature under a N2 atmosphere for 1 hr and then washed with
1m HCl(aq) (2ꢃ5 mL) and brine (5 mL). The organic layer was dried over
MgSO4, filtered and the solvent was removed. Following purification by
preparative thin-layer chromatography (4:1 EtOAc/CHCl3) and recrystal-
lisation by vapour diffusion of iPr2O into a CHCl3 solution of the rotax-
ane, the rotaxane 12·Cl was isolated as a yellow solid in 24% yield
(0.039 g, 0.016 mmol). M.p. 2008C (dec.); 1H NMR (300 MHz, CDCl3):
d=9.82 (br. s., 1H; py H4), 9.28 (br. s., 1H; isoH), 9.03 (br. s., 2H; py H2
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3
and H6), 8.76 (br. s., 2H; NH), 8.68 (br. s., 2H; NH), 8.27 (d, J=7.9 Hz,
2H; isoH), 7.53 (t, 3J=7.9 Hz, 1H; isoH), 7.18 (m, 22H; ArH), 7.04 (m,
12H; ArH), 6.71 (d, 3J=8.8 Hz, 4H; ArH), 6.65 (s, 4H; calix ArH), 6.47
(d, 3J=8.8 Hz, 4H; hydroqH), 6.19 (d, 3J=8.8 Hz, 4H; hydroqH), 5.71
(br. s., 2H; OH), 4.89 (s, 3H; N+CH3), 4.40 (d, 2J=13.6 Hz, 4H; Ar-
CHinHoutAr), 4.24 (m, 4H; CH2), 4.10 (m, 4H; CH2), 4.03 (m, 8H; CH2),
3.87 (m, 4H; CH2), 3.76 (t, 3J=4.4 Hz, 4H; CH2), 3.67 (t, 3J=4.8 Hz,
4H; CH2), 3.57 (m, 4H; CH2), 3.43 (d, 2J=13.6 Hz, 4H; ArCHinHoutAr),
1.39 (s, 18H; tBu), 1.28 (s, 36H; tBu), 0.86 ppm (s, 18H; tBu); 13C NMR
(125 MHz, CDCl3): d=166.83, 159.83, 156.55, 153.78, 151.54, 150.51,
149.97, 148.29, 147.49, 147.36, 144.34, 143.91, 142.75, 139.42, 133.62,
133.53, 132.09, 131.88, 131.51, 131.10, 130.85, 130.63, 128.99, 128.41,
127.17, 125.89, 125.60, 125.51, 124.26, 124.08, 114.74, 114.07, 113.09, 75.21,
69.13, 67.49, 67.16, 65.25, 63.39, 50.61, 41.23, 39.78, 34.25, 34.01, 33.83,
31.74, 31.66, 31.34, 31.08, 30.89 ppm; ESMS: m/z: 2353.0742 [MÀCl]+.
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Synthesis of 12·PF6: A solution of 12·Cl (0.057 g, 0.024 mmol) in CHCl3
(20 mL) was washed with 0.2m NH4PF6(aq) (5ꢃ10 mL) and water
(10 mL). The combined organic layers were dried over MgSO4, filtered
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CDCl3/CD3OD): d=8.95 (s, 2H; py H2 and H6), 8.88 (s, 1H; py H4), 8.64
(s, 1H; isoH), 8.09 (d, 3J=7.8 Hz, 2H; isoH), 7.60 (t, 3J=7.8 Hz, 1H;
isoH), 7.07 (m, 34H; calix ArH, ArH), 6.72 (d, 3J=8.8 Hz, 4H; ArH),
6.64 (s, 4H; calix ArH), 6.38 (m, 8H; hydroqH), 4.69 (s, 3H; N+CH3),
4.37 (d, 2J=13.7 Hz, 4H; ArCHinHoutAr), 4.10 (m, 4H; CH2), 4.01 (m,
8H; CH2), 3.86 (t, 3J=4.6 Hz, 4H; CH2), 3.80 (m, 4H; CH2), 3.70 (m,
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3
2
4H; CH2), 3.60 (t, J=4.9 Hz, 4H; CH2), 3.48 (m, 4H; CH2), 3.35 (d, J=
13.7 Hz, 4H; ArCHinHoutAr), 1.33 (s, 18H; tBu), 1.20 (s, 36H; tBu),
0.81 ppm (s, 18H; tBu); 13C NMR (125 MHz, CDCl3): d=167.00, 160.34,
156.43, 152.85, 151.53, 149.85, 149.62, 148.35, 147.53, 147.28, 143.84,
143.38, 143.07, 142.21, 139.66, 134.00, 133.08, 132.17, 131.65, 131.43,
131.04, 130.59, 129.20, 128.39, 127.20, 125.82, 125.69, 125.65, 124.11,
115.64, 115.53, 114.49, 112.99, 75.28, 69.39, 68.35, 67.30, 67.15, 66.77,
Chem. Eur. J. 2010, 16, 1256 – 1264
ꢁ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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