Halide selective anion recognition by an amide-triazolium axle containing [2]rotaxane

Article abstract of DOI:10.1039/c4ob00801d

A new rotaxane containing the 3-amido-phenyl-triazolium group incorporated into the interlocked structure's axle component has been prepared by a chloride anion templated clipping strategy. Proton NMR titration experiments reveal that the interlocked host displays a high degree of halide anion recognition in competitive 1:1 CDCl₃-CD₃OD solvent mixture. Chloride and bromide anions are bound strongly and selectively, with negligible complexation of the larger, more basic oxoanions, acetate and dihydrogen phosphate being observed. Density functional theory calculations on the related axle motifs 3-amido-phenyl-triazolium, pyridinium bis-triazole and pyridinium bis-amide were performed, and indicate that the new rotaxane axle motif displays much weaker oxoanion binding than the pyridinium based systems. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ob00801d

Organic &
Biomolecular Chemistry
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PAPER
Halide selective anion recognition by an
amide-triazolium axle containing [2]rotaxane†
Nicholas G. White,a Ana R. Colaço,b Igor Marques,b Vítor Félixb and Paul D. Beer*a
Cite this: Org. Biomol. Chem., 2014,
12, 4924
A new rotaxane containing the 3-amido-phenyl-triazolium group incorporated into the interlocked struc-
ture’s axle component has been prepared by a chloride anion templated clipping strategy. Proton NMR
titration experiments reveal that the interlocked host displays a high degree of halide anion recognition in
competitive 1 : 1 CDCl3–CD3OD solvent mixture. Chloride and bromide anions are bound strongly and
selectively, with negligible complexation of the larger, more basic oxoanions, acetate and dihydrogen
phosphate being observed. Density functional theory calculations on the related axle motifs 3-amido-phenyl-
triazolium, pyridinium bis-triazole and pyridinium bis-amide were performed, and indicate that the new
rotaxane axle motif displays much weaker oxoanion binding than the pyridinium based systems.
Received 17th April 2014,
Accepted 15th May 2014
DOI: 10.1039/c4ob00801d
www.rsc.org/obc
incorporating this motif into an axle component, we demon-
strate its use in the anion templated synthesis of a novel rotax-
Introduction
Inspired by the key roles played by anions in numerous bio- ane host system which exhibits a notably high degree of halide
logical and environmental processes,1 the development of arti- anion recognition over oxoanions in competitive 1 : 1 CDCl3–
ficial anion receptors is an area of intense current research CD3OD solvent mixtures. This anion selectivity trend is ration-
interest.2 Seminal reports in 2008 established that readily-pre- alised by computational experiments on anion complexes of
pared 1,2,3-triazole groups could bind anions through polar- the rotaxane’s amido-phenyl-triazolium axle component which
ized C–H hydrogen bonds,3 and a range of triazole containing indicate this motif to be a relatively weak binder of oxoanions
hosts have since been reported,4 as well as a few receptors con- when compared with bis-triazole and bis-amide pyridinium
taining the alkylated triazolium moiety.5 Notably, Pandey has containing axles.
utilized a bile acid scaffold to synthesize a range of acyclic and
macrocyclic bis-triazolium systems that selectively bind
fluoride, chloride, hydrogen sulfate or dihydrogen phosphate,
depending on the host structure.5a,d,e Inspired by this work, we
Results and discussion
Rotaxane synthesis
prepared a triazolium axle containing rotaxane6 via anion tem-
plation, and demonstrated that this interlocked host could
bind anions in competitive solvent media.5b More recently, we
have reported a tetra-triazolium macrocycle5f and tetra-triazo-
lium cage,5g and demonstrated that these highly charged
receptors exhibit strong recognition of sulfate in aqueous
mixtures.
The triazolium-amide containing axle component 1+ was pre-
pared in three steps from commercially available 3-ethynyl-
benzoic acid (Scheme 1). Copper(I)-catalyzed azide–alkyne
cycloaddition (CuAAC) reaction of azide-appended tetraphenyl
compound 2 8 gave acid 3 in 69% yield. Activation of the acid
using refluxing thionyl chloride, followed by condensation
with tetraphenyl amine 4 9 afforded the triazole-amide axle
component 5, again in 69% yield. Alkylation using trimethyl-
oxonium tetrafluoroborate in dry dichloromethane, followed
by anion exchange using Amberlite® resin produced the
triazolium-amide axle component 1·Cl.
Grubbs’-catalysed chloride anion templated ring closing
metathesis of 1·Cl and bis-vinyl macrocycle precursor 6 10 in
dichloromethane followed by purification via preparative
TLC and recrystallization gave rotaxane 7·Cl in 47% yield
(Scheme 2). Anion exchange to 7·PF6 was achieved by repeated
Herein we introduce the novel 3-amido-phenyl-triazolium
motif, containing both amide and triazolium functionality.7 By
aInorganic Chemistry Laboratory, Department of Chemistry, University of Oxford,
South Parks Road, Oxford, OX1 3QR, UK. E-mail: paul.beer@chem.ox.ac.uk
bDepartamento de Química, CICECO and Secção Autónoma de Ciências da Saúde,
Universidade de Aveiro, 3810-193 Aveiro, Portugal
†Electronic supplementary information (ESI) available: General synthetic
remarks, NMR and mass spectra of novel compounds, ROESY NMR spectrum of
7·PF6, titration protocols and binding data and further details of crystallography
and modelling experiments. Full crystallographic data are provided in CIF
format. CCDC 997909. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c4ob00801d
washing with aqueous NH4PF6(aq)
.
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Scheme 1 Synthesis of triazolium-amide containing axle component 1·Cl.
Scheme 2 Synthesis of triazolium-amide axle containing rotaxane 7·PF6.
1
The new rotaxane was characterized by H, 13C, 19F and 31P bonds from triazolium, amide and macrocycle phenylene
NMR spectroscopy, as well as by high resolution ESI mass protons. In the solid state, hydrogen bonds from the axle tria-
spectrometry. The interlocked nature of the compound was zolium and amide groups are of moderate strength, while the
1
also confirmed by 2D ROESY spectroscopy (Fig. S13†). The H anion sits asymmetrically within the macrocycle, forming one
NMR spectra of the chloride and hexafluorophosphate salts of strong and one weak hydrogen bond to amide donors from the
7+ are shown in Fig. 1: the host’s cavity resonances b, c and 2 cycle (more details are given in the ESI†). Donor–acceptor
are observed significantly downfield in 7·Cl compared to 7·PF6, interactions are observed between one of the macrocycle’s
consistent with hydrogen bonding interactions between these hydroquinone rings and the central phenylene ring of the axle
protons and the interlocked cavity encapsulated halide anion. component [centroid⋯centroid = 3.660(17) Å], with a longer
The hydroquinone signals, 3 and 4, are shifted upfield contact between the other hydroquinone ring and the triazo-
relative to the hexafluorophosphate salt, suggesting enhanced lium group [centroid⋯centroid = 3.813(9) Å].
pyridinium⋯hydroquinone aromatic donor–acceptor inter-
Rotaxane anion binding
actions upon anion coordination.
Small single crystals of the rotaxane as its bromide salt
were obtained from a 1H NMR titration sample (vide infra) suit-
able for synchrotron X-ray structural analysis. The bromide
anion is held within the interlocked cavity (Fig. 2) by hydrogen
The anion recognition properties of 7·PF6 were investigated
using 1H NMR titration experiments in competitive 1 : 1
CDCl3–CD3OD solvent mixture (see ESI† for titration protocols
and data). WINEQNMR2 11 analysis of the titration data deter-
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Fig. 1 Partial 1H NMR spectra of 7·PF6 (bottom) and 7·Cl (top). Peak
labelled corresponds to residual CHCl3 signal, unlabelled peaks belong
to bulky stopper groups (1 : 1 CDCl3–CD3OD, 293 K).
Fig. 3 Structures of rotaxanes related to 7·PF6, 8·PF6 8 and 9·PF6.10
Fig. 2 X-ray crystal structure of 7·Br. Minor component of the dis-
ordered macrocycle and most hydrogen atoms are omitted for clarity.
larger shifts than bromide. When the oxoanions acetate and
dihydrogen phosphate are added to the receptor, only very
small movements of the 1H NMR signals were observed (less
than 0.05 ppm over the course of the titration experiments),
suggesting negligible anion binding. The selectivity for the
halide anions over the more basic oxoanions is noteworthy,
and presumably arises due to the preorganised three-dimen-
sional cavity of the interlocked host, which is too small to
accommodate the large oxoanions.
Table 1 Association constants, Ka (M−1), for rotaxanes with halide and
polyatomic anions in 1 : 1 CDCl3–CD3OD
a
8
10c
Anion
7·PF6
8·PF6
9·PF6
Cl−
2035(50)
1948(15)
411(18)
936(40)
186(9)
137(3)
4500
—
1500
725
d
Br−
−
b
H2PO4
OAc−
—
b
—
The pronounced chloride and bromide selectivity of 7·PF6
is particularly noteworthy when compared with the analogous
rotaxanes 8·PF6 8 and 9·PF6 10 (Fig. 3), which contain an identi-
cal macrocycle to 7·PF6 and respectively pyridinium bis-triazole
and pyridinium bis-amide axle components. While both
8·PF6 and 9·PF6 display selectivity for halide anions over
a Anions added as tetrabutylammonium salts, estimated standard
errors given in parentheses, association constants determined using
WINEQNMR2 11 at 293 K. b Peak shifts too small to infer binding event
(<0.05 ppm after 10 equivalents of anion). c Errors estimated to be less
than 10%. d No data reported.
mined 1 : 1 stoichiometric association constants, monitoring oxoanions, significant oxoanion binding is still observed,
the rotaxane’s triazolium resonance (Table 1).
which is not the case with 7·PF6 (Table 1). Further insight
Both chloride and bromide anions are bound strongly by into these results was obtained by quantum calculations, as
the rotaxane, with addition of chloride causing significantly follows.
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DFT calculations on truncated axle motifs
The electrostatic potential computed on a molecule’s electron
density surface (VS) is an excellent tool to evaluate non-
covalent interactions that have a significant electrostatic con-
tribution.12 In particular, the most positive values (VS,max) are
straightforwardly related to hydrogen-bond acidity13 and con-
sequently with the receptor’s anion binding ability.14 In this
context, the structures of the axle components of the inter-
locked hosts 7+, 8+ and 9+ were optimised at B3LYP/6-31G**
followed by calculation of the VS,max at the same level of theory
with Gaussian 09.15 In addition, the VS,max were computed for
the 3-amido-phenyl-triazolium, pyridinium bis-triazole and
pyridinium bis-amide axle motifs generated from the corres-
ponding axles by the complete replacement of the tetraphenyl
stoppers by methyl substituents. DFT calculations on these
+
hypothetical molecules, denoted as 7methyl+, 8methyl and
9methyl+, allow us to ascertain the axle motifs’ contribution to
the electrostatic potential of the entire axle component.
The VS,max for the axles of 7+, 8+ and 9+ are gathered in
Table 2 together with those calculated for the corresponding
+
motifs 7methyl+, 8methyl and 9methyl+. Overall, the VS,max values
for the complete axles are lower than the corresponding
central motif values, as would be expected for the different dis-
tribution of the electrostatic potential on the surfaces of these
molecules. However, the VS,max values computed for the
hypothetical molecules mirror the trend observed for the com-
plete axles, indicating that this quantum descriptor is mainly
dictated by the central core of the axle component.
Fig. 4 Computed electrostatic potentials mapped on the 0.001 elec-
+
+
+
trons per Bohr3 surface of 7methyl (top), 8methyl (middle) or 9methyl
(bottom), with colours ranging between blue (<31.4 kcal mol−1) and red
(>125.5 kcal mol−1). The locations of VS,max are illustrated with red and
purple dots.
Table 2 VS,max (kcal mol−1) calculated for complete and truncated axle
components at B3LYP/6-31G**
affinities. The binding ability of the neutral macrocycle was also
computed at the same theory level (see ESI† for details),
affording two close VS,max of 45.93 and 43.10 kcal mol−1, which
are situated in the vicinity of the N–H binding units of the iso-
phthalamide head (red dots in Fig. S17†). Given that the same
macrocycle is present in rotaxanes 7+, 8+ and 9+, it would seem
reasonable that differences in binding strength are largely due
to variation in the axle component,16 and so we focussed our
modelling on this part of the interlocked structure.
Structure
Entire axlea
Truncated motifb
7+
8+
9+
108.76,c 102.74
99.51, 97.80
122.43, 120.26
116.57,c 106.81
106.82, 106.52
129.31, 129.02
a Starting geometries of the axle components were taken from the
single crystal X-ray structures of related rotaxane systems, as described
in the ESI. b Truncated motif corresponds to the axle fragments
+
+
+
7methyl
,
8methyl or 9methyl as defined in the text. c This VS,max
The VS,max listed in Table 2 are in perfect agreement with
the experimental binding data, following the anion affinity
order 9+ > 7+ > 8+, as given by the association constants for
chloride anion. To investigate the observed selectivity prefer-
ence of 7+, we next modelled the hydrogen bonding arrange-
ments between the three axle motifs and the four anions
under study (Cl−, Br−, H2PO4− and OAc−).
corresponds to the Ctriazolium–H site.
The electrostatic potential mapped on the electron density
surfaces of each central motif is shown in Fig. 4, along with
the position of VS,max. Equivalent depictions are presented in
Fig. S16† for the entire axle components. The symmetric
+
The complexes between axle motifs 7methyl+, 8methyl and
+
+
8methyl and 9methyl entities exhibit two distinct VS,max (single
red dots) with almost identical energies located in the region
of the two binding sites (Ctriazole–H or N–H amide groups). In
9methyl+, and the four inorganic anions were optimised using
the B3LYP functional and the basis set 6-311+G**. The use of
these structural motifs rather than the entire axles com-
ponents is computationally less demanding and is appropriate
given that the axles’ electrostatic potential is largely deter-
mined by the central motif (vide supra). The final geometries
+
contrast, the 7methyl axle motif, with an asymmetric structure,
presents a higher VS,max of 116.57 kcal mol−1 near the C–H
from the positively charged triazolium ring (red dot) and a
second one, with a lower energy of 106.81 kcal mol−1 (purple
dot) close to the N–H binding site. In other words, this entity,
like the complete axle component 7+, exhibits two binding sites
with different acidities and, therefore, with different anion
+
of the anion complexes with 7methyl are shown in Fig. 5
together with the intermolecular hydrogen bonds. Similar
depictions are presented in Fig. S18 and S19† for the anion
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While in general, the oxoanions H2PO4 and OAc− form
−
shorter hydrogen bonds with the axle motifs than the halide
anions, suggesting stronger binding, this analysis neglects the
key contributing factor of the preorganised three-dimensional
interlocked cavity. It has been previously observed, experi-
mentally,18 that the axle component of 9+ displays a strong pre-
ference for basic oxoanions over chloride, but the formation of
the rotaxane host structure overcomes, and indeed reverses,
this trend. Given the computed weaker oxoanion binding of
the axle motif of 7+, it seems that rotaxane formation leads to
almost complete loss of binding for these large oxoanions
in the competitive solvent media used. This feature is being
investigated by means of classical molecular dynamics simu-
lations on the twelve host–guest complexes formed between
rotaxanes 7+, 8+ and 9+ and the anions Cl−, Br−, OAc− and
H2PO4−, and the results of this computational study will be
reported in due course.
Fig. 5 DFT optimised geometries at B3LYP/6-311+G** of the mono-
atomic (top) and polyatomic (bottom) anion complexes with the 7methyl
axle motif.
+
Conclusions
complexes with 8methyl+ and 9methyl+. The distances of two rele-
vant hydrogen bonds between the binding units and the
anions are given in Table 3 along with the second order stabili-
zation energies (E2)17 between the anions’ lone pairs orbitals
and the antibonding orbitals of the axle motif (σ* N–H or
C–H orbitals). The complete dimensions of all intermolecular
bonding interactions for all three axle motifs are summarised
in Tables S1–S3.†
In summary, a new rotaxane incorporating the 3-amido-
phenyl-triazolium motif has been prepared by an anion
templation methodology. The interlocked host is selective for
halide anions over the larger and more basic oxoanions, acetate
and dihydrogen phosphate. Importantly, this selectivity is far
more pronounced than that reported for analogous rotaxanes
incorporating pyridinium bis-triazole or pyridinium bis-amide
axle components. Molecular modelling studies suggest that
this is due to the amido-phenyl-triazolium motif exhibiting
inherently weaker oxoanion binding than the pyridinium con-
taining motifs.
When considering the halide anions, the shortest hydrogen
+
bonds are observed between 9methyl and the anions, while
+
+
8methyl forms the longest hydrogen bonds, and 7methyl is
intermediate between 9methyl and 8methyl+. These hydrogen
+
bond dimensions lead to E2 stabilization energies for the
+
+
+
halide anions following the trend 9methyl > 7methyl > 8methyl
.
These trends are entirely in accordance with the solution
phase anion binding data for the related rotaxane host systems
and the calculated VS,max values.
Experimental
General remarks
General comments, details of instrumentation, 1H NMR,
13C NMR and high resolution mass spectra are provided in
the ESI.†
+
Interestingly though, 7methyl forms much longer hydrogen
bonds to the oxoanions than 9methyl and comparable (OAc−)
+
or longer (H2PO4−) hydrogen bonds than 8methyl+. The E2
values for these anions are highest for 9methyl+, slightly lower
+
for 8methyl and much lower for 7methyl+. Taken together, these
X-ray crystallography
results demonstrate that the central motif of 7+ has a much Diffraction data were collected at Diamond Lightsource, Beam-
weaker affinity for oxoanions than those present in 8+ or 9+,
and corroborate the negligible solution binding of oxoanions
by rotaxane 7+.
line I1919 (λ = 0.6889 Å), at 100 K.20 Raw frame data, including
data reduction, inter-frame scaling, unit cell refinement and
absorption corrections were processed using CrysAlisPro.21
Table 3 Hydrogen bond distances (Å) of two relevant interactions between the truncated axle motifs and anions (X−), along with the corresponding
second order stabilization energies (E2, kcal mol−1
)
+
+
+
7methyl
8methyl
9methyl
Anion
C⋯X−
N⋯X−
E2
C⋯X−
C⋯X−
E2
N⋯X−
N⋯X−
E2
Cl−
3.377
3.575
3.175
2.914
3.191
3.328
2.896
2.879
40.38
32.16
24.62
30.20
3.417
3.573
2.936
2.924
3.418
3.573
2.976
2.948
29.45
27.02
60.18
47.78
3.219
3.381
2.691
2.686
3.220
3.382
2.711
2.709
45.38
35.50
66.75
69.41
Br−
−
H2PO4
OAc−
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The structure was solved with SIR9222 and refined using full- 119.1, 118.3, 118.3, 63.7, 63.5, 34.5, 34.5, 31.5 (one resonance
matrix least-squares on F2 within the CRYSTALS suite.23 All overlapping/not observed). HRESI MS (pos.): 1183.7157, calc.
non-hydrogen atoms were refined with anisotropic displace- for [C83H92NO4·Na]+ = 1183.7163.
ment parameters; hydrogen atoms were generally visible in the
Triazolium axle component 1+
difference map, and were refined with restraints on bond
lengths and angles, after which the positions were used as the The triazole axle component 5 (0.058 g, 0.050 mmol) was
basis for a riding model.24 Crystals were found to be twinned – dissolved in dry CH2Cl2 (10 mL). (Me3O)(BF4) (0.0088 g,
an appropriate twin law was found using the ROTAX25 package 0.060 mmol) was added and the mixture stirred at room temp-
within the CRYSTALS suite. Full crystallographic details are erature under a nitrogen atmosphere for 16 hours. The alkylat-
provided in CIF format as ESI.†
ing agent was quenched by addition of CH3OH (1 mL), and the
colourless solution taken to dryness under reduced pressure.
Column chromatography (5% CH3OH in CH2Cl2) gave 1·BF4 as
Triazole acid 3
The aryl azide 2 8 (0.106 g, 0.200 mmol) and 3-ethynylbenzoic a white powder. Yield: 0.042 g (67%).
acid (0.037 g, 0.25 mmol) were dissolved in CH2Cl2 (10 mL).
1H NMR (CDCl3): 9.15 (s, 1H, amide-H), 9.07 (s, 1H, trz+-H),
DIPEA (0.090 mL, 0.065 g, 0.50 mmol), TBTA (0.011 g, 8.21 (s, 1H, phenyl-H), 8.01 (d, 3J = 7.9 Hz, 1H, phenyl-H),
0.020 mmol) and [Cu(CH3CN)4](PF6) (0.0075 g, 0.020 mmol) 7.61–7.73 (m, 5H, 4 × stopper-H, 1 × phenyl-H), 7.49 (d, 3J =
were added and the yellow solution stirred at room tempera- 8.9 Hz, 2H, stopper-H), 7.40 (app. t, 3J = 7.9 Hz, 1H, phenyl-H),
ture under a nitrogen atmosphere for 3 days. The reaction was 7.09–7.30 (m, 26H, stopper-H), 4.27 (s, 3H, methyl-H), 1.31 (s,
t
t
diluted with further CH2Cl2 (10 mL), washed with HCl(aq) (1 M, 27H, Bu-H), 1.29 (s, 27H, Bu-H). 13C NMR (d6-DMSO): 164.4,
2 × 20 mL) and brine (20 mL), dried (MgSO4), and taken to 151.0, 148.3, 147.8, 143.8, 143.0, 142.6, 142.4, 136.4, 136.1,
dryness under reduced pressure. Column chromatography (5% 132.3, 132.2, 132.1, 130.6, 130.4, 130.0, 129.9, 129.7, 129.1,
CH3OH in CH2Cl2) gave 3 as a white powder. Yield: 0.093 g 127.7, 124.8, 124.5, 122.9, 120.9, 119.7, 63.4, 62.9, 34.1, 34.1,
(69%).
1H NMR (d6-DMSO): 9.36 (s, 1H, trz-H), 8.51 (s, 1H, ph-H), (d6-DMSO): −148.3 (m). HRESI-MS (pos.): 1175.7475, calc. for
31.3, 31.3 (one peak obscured by DMSO signal). 19F NMR
3
3
8.16 (d, J = 7.8 Hz, 1H, ph-H), 7.94 (d, J = 7.8 Hz, 1H, ph-H), [C84H95N4O]+ = 1175.7500.
7.88 (d, 3J = 8.7 Hz, 2H, stopper-H), 7.62 (app. t, 3J = 7.8 Hz,
The tetrafluoroborate salt of 1+ (0.032 g, 0.025 mmol) was
3
1H, ph-H), 7.33–7.41 (m, 8H, stopper-H), 7.15 (d, J = 8.5 Hz, taken up in 9 : 1 CH3CN–H2O (50 mL, required gentle heating).
6H, stopper-H), 1.26 (s, 27H, Bu-H). 13C (d6-DMSO): 148.1, It was repeatedly passed down a Cl−-loaded Amberlite® anion
t
147.7, 146.5, 143.4, 134.2, 131.7, 130.6 130.0, 129.4, 129.4, exchange column. The CH3CN was removed under reduced
129.0, 129.0, 126.0, 124.7, 120.1, 119.5, 63.2, 34.1, 31.1 (one pressure and the remaining aqueous suspension extracted
resonance overlapping/not observed). HRESI-MS (neg.): with CH2Cl2 (3 × 20 mL). The combined organic fractions were
674.3757, calc. for [C46H48N3O2]− = 674.3752.
washed with brine (20 mL), dried (MgSO4), and taken to
dryness under reduced pressure to give 1·Cl as a sparingly-
soluble white powder. Yield: 0.029 g (94%).
Triazole axle 5
The carboxylic acid 3 (0.068 g, 0.10 mmol) was suspended in
1H NMR (5 : 1 CDCl3–CD3OD): 9.79 (s, 1H, trz+-H), 8.49 (s,
SOCl2 (2 mL). A drop of pyridine was added, and the suspen- 1H, phenyl-H), 8.20 (d, 3J = 7.8 Hz, 1H, phenyl-H), 7.82–7.89
sion was heated to reflux under a nitrogen atmosphere for (m, 3H, 2 × stopper-H, 1 × phenyl-H), 7.68–7.75 (m, 3H, 2 ×
3
16 hours, during which time all material dissolved. The SOCl2 stopper-H, 1 × phenyl-H), 7.53 (d, J = 8.9 Hz, 2H, stopper-H),
was removed under reduced pressure and the resulting yellow 7.15–7.27 (m, 14H, stopper-H), 7.04–7.10 (m, 12H, stopper-H),
t
t
solid taken up in dry CH2Cl2 (10 mL). NEt3 (0.056 mL, 0.040 g, 4.44 (s, 3H, methyl-H), 1.27 (s, 27H, Bu-H), 1.26 (s, 27H, Bu-
0.40 mmol) was added followed by the tetraphenyl amine 4 9 H). LRESI-MS (pos.): 1175.77, calc. for [C84H95N4O]+ = 1175.75.
in dry CH2Cl2 (10 mL), and the resulting clear yellow solution
Rotaxane 7+
was stirred at room temperature under a nitrogen atmosphere
for 16 hours. It was washed with 10% HCl(aq) (2 × 20 mL) and The chloride salt of 1+ (0.024 g, 0.020 mmol) and the bis-vinyl
brine (20 mL), dried (MgSO4), and taken to dryness under precursor 6 10 (0.020 g, 0.030 mmol) were dissolved in dry
reduced pressure. Column chromatography (CH2Cl2) gave 5 as CH2Cl2 (5 mL, required gentle heating). Grubbs’ II catalyst
a white powder. Yield: 0.080 g (69%).
(0.0020 g, 10% by weight) was added and the reaction stirred
1H NMR (CDCl3): 8.39 (s, 1H, amide-H), 8.25 (s, 1H, trz-H), at room temperature under a nitrogen atmosphere for 3 days.
3
8.07 (d, J = 8.0 Hz, 1H, phenyl-H), 8.01 (s, 1H, phenyl-H), 7.86 It was taken to dryness under reduced pressure, and purified
(d, 3J = 7.7 Hz, 1H, phenyl-H), 7.65 (d, 3J = 8.8 Hz, 2H, stopper- by preparative TLC (2% CH3OH in CH2Cl2) to give slightly
H), 7.54–7.59 (m, 3H, 1 × phenyl-H, 2 × stopper-H), 7.42 (d, 3J = impure 7+ (yield at this point ∼0.021 g, ∼57%). It was taken up
8.8 Hz, 2H, stopper-H), 7.21–7.29 (m, 14H, stopper-H), in hot CH3OH–CH2Cl2 (4 : 1, 10 mL), and the total volume
t
7.10–7.14 (m, 12H, stopper-H), 1.32 (s, 27H, Bu-H), 1.31 (s, reduced to ∼5 mL by boiling. Cooling the solution resulted in
27H, tBu-H). 13C NMR (CDCl3): 165.4, 148.9, 148.5, 144.0, the precipitation of a white powder, which was isolated by fil-
143.4, 135.9, 135.6, 134.5, 132.7, 132.0, 131.0, 130.8, 130.8, tration and washed with ice-cold CH3OH (2 × 1 mL) to give
130.6, 129.6, 129.1, 127.2, 124.8, 124.8, 124.5, 124.3, 119.5, 7·Cl. Yield: 0.017 g (47%).
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Organic & Biomolecular Chemistry
1H NMR (1 : 1 CDCl3–CD3OD): 10.10 (s, 1H, amide-H), 9.96
3 (a) Y. Li and A. H. Flood, Angew. Chem., Int. Ed., 2008, 47,
2649; (b) H. Juwarker, J. M. Lenhardt, D. M. Pham and
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19, 17751; (l) N. G. White, H. G. Lovett and P. D. Beer, RSC
Adv., 2014, 4, 12133.
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rotaxane, and have since reported several interlocked mole-
cular shuttles and muscles containing triazolium groups:
F. Coutrot and E. Busseron, Chem. – Eur. J., 2008, 14,
4784.
7 Li, Li and co-workers have reported a series of acyclic anion
receptors based on the amide-triazole motif: Y.-J. Li, L. Xu,
W.-L. Yang, H.-B. Liu, S.-W. Lai, C.-M. Che and Y.-L. Li,
Chem. – Eur. J., 2012, 18, 4782.
8 N. G. White and P. D. Beer, Org. Biomol. Chem., 2013, 11,
1326.
9 H. W. Gibson, S.-H. Lee, P. T. Engen, P. Lecavalier, J. Sze,
Y. X. Shen and M. Bheda, J. Org. Chem., 1993, 58,
3748.
(s, 1H, trz+-H), 9.53 (s, 1H, phenyl-H), 8.92 (s, 1H, phenyl-H),
8.72 (s, 2H, phenyl-H), 8.14 (d, 3J = 7.4 Hz, 1H, phenyl-H),
7.63–7.87 (m, 8H, 4 × stopper-H, 2 × amide-H, 2 × phenyl-H),
7.16–7.30 (m, 20H, stopper-H) 7.09 (d, 3J = 8.5 Hz, 6H,
6 stopper-H), 6.95 (d, 3J = 8.5 Hz, 6H, stopper-H), 6.14–6.22 (m,
8H, hydroquinone-H), 5.95 (app. br. s, 2H, vinyl-H), 4.32 (s,
3H, methyl-H), 3.61–4.16 (m, 20H, macrocycle-CH2), 1.33 (s,
t
t
27H, Bu-H), 1.27 (s, Bu-H). HRESI-MS (pos.): 1796.9870, calc.
for [C116H130N7O11]+ = 1796.9823.
The chloride salt of 7+ (0.014 g, 0.0075 mmol) was taken up
in CH2Cl2 (20 mL). The solution was washed with NH4PF6(aq)
(0.1 M, 7 × 20 mL) and H2O (3 × 20 mL). Thorough drying
1
in vacuo gave 7·PF6 as a white powder. Yield: 0.012 g (79%). H
NMR (1 : 1 CDCl3–CD3OD): 9.40 (s, 1H, trz+-H), 8.94 (s, 1H,
phenyl-H), 8.75 (d, 4J = 1.5 Hz, 2H, phenyl-H), 8.04 (d, 3J =
7.9 Hz, 1H, phenyl-H), 7.81 (d, 3J = 8.8 Hz, 2H, stopper-H), 7.74
(t, 4J = 1.5 Hz, 1H, phenyl-H), ∼7.59 (obscured by residual
CHCl3 peak, 1H, phenyl-H), 7.55 (app. t, 3J = 7.9 Hz, 1H,
phenyl-H), 7.43 (d, 3J = 8.8 Hz, 2H, stopper-H), 7.30 (d, 3J =
8.7 Hz, 6H, stopper-H), 7.24 (d, 3J = 8.9 Hz, 6H, stopper-H),
7.20 (d, 3J = 8.9 Hz, 2H, stopper-H), 7.07–7.10 (m, 14H,
stopper-H), 6.21–6.33 (m, 8H, hydroquinone-H), 5.83 (app. br.
s, 2H, vinyl-H), 4.19 (s, 3H, methyl-H), 3.43–4.00 (m, 20H,
t
t
macrocycle-CH2), 1.32 (s, 27H, Bu-H), 1.29 (s, 27H, Bu-H). 13C
NMR (1 : 1 CDCl3–CD3OD): 165.9, 165.7, 153.3, 153.1, 149.8,
149.2, 149.1, 145.1, 144.6, 143.5, 143.3, 136.6, 136.5, 136.1,
133.5, 132.7, 132.2, 131.7, 131.2, 131.0, 130.2, 130.1, 129.7,
127.0, 126.1, 125.3, 124.8, 122.4, 120.7, 120.2, 115.6, 115.0,
71.4, 69.8, 68.4, 66.9, 64.6, 64.1, 40.6, 40.1, 34.9, 34.8, 31.7,
31.6 (3 resonances overlapping/not observed). 19F NMR (1 : 1
2
CDCl3–CD3OD): −73.4 (d, JP,F = 711 Hz). 31P NMR (1 : 1
2
CDCl3–CD3OD): −144.5 (d, JP,F = 711 Hz). LRESI-MS (pos.):
1796.88, calc. for [C116H130N7O11]+ = 1796.98.
Acknowledgements
NGW thanks the Clarendon. Fund, Trinity College Oxford and
the Vice-Chancellors’ Fund for financial support. We thank
Diamond Lightsource for an award of beamtime on Beamline
I19. ARC, IM and VF acknowledge the financial support from
FCT under the project PEst-C/CTM/LA0011/2013 with co-
participation of the European Community funds FEDER,
QREN and COMPETE. IM thanks the FCT for the PhD scholar-
ship SFRH/BD/87520/2012.
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