Anion-templated assembly of [2]rotaxanes

Article abstract of DOI:10.1039/b518178j

Anion templation is used to develop a general method for rotaxane synthesis. The anion-templated synthesis of three new [2]rotaxanes containing positively charged pyridinium axles and neutral isophthalamide macrocyclic components is described. The incorpo

Full text of DOI:10.1039/b518178j

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Anion-templated assembly of [2]rotaxanes
Mark R. Sambrook,† Paul D. Beer,* Michael D. Lankshear, R. Frederick Ludlow and James A. Wisner‡
Received 22nd December 2005, Accepted 9th February 2006
First published as an Advance Article on the web 10th March 2006
DOI: 10.1039/b518178j
Anion templation is used to develop a general method for rotaxane synthesis. The anion-templated
synthesis of three new [2]rotaxanes containing positively charged pyridinium axles and neutral
isophthalamide macrocyclic components is described. The incorporation of electron withdrawing
substituents, such as the nitro group, into the 5-position of an isophthalamide bis-vinyl acyclic
precursor results in a significant improvement in [2]rotaxane assembly yields. Rotaxane anion binding
strengths are also enhanced whilst the rotaxane’s unique interlocked binding domain ensures selectivity
for chloride – the templating anion – is maintained.
[Cu(phen)2]+ complex. Formation of an interpenetrated assembly,
Introduction
or [2]pseudorotaxane, was achieved by incorporation of a neutral
Over the past couple of decades a number of assembling mo-
amide cleft into a macrocyclic component (Fig. 1). Subsequent
tifs have been established for the preparation of mechanically
chloride anion recognition by this hydrogen-bond donor site
bonded supramolecular systems.1 In particular, the use of metal–
results in threading of the organic pyridinium chloride ion-pair
ligand coordination chemistry,2 hydrogen bonding,3 p–p stacking
interactions4 and solvophobic forces5 have become common-place.
In spite of their diffuse nature, pH-dependence and relative high
solvation energies, the field of anion templation is of intense
current interest6 where many serendipitous examples of templated
metal-based cages7 and macrocycles8 reveal the anion filling
an internal void around which the structure is assembled.9 In
sharp contrast, however, the much rarer use of anion templates
in assembling interlocked molecules has focused on the use
of rigorously designed hydrogen-bond donor anion recognition
motifs.10 For example, Vo¨gtle’s anion-mediated rotaxane synthesis
relies upon the complexation and orientation of a negatively
charged phenoxide intermediate by a neutral macrocyclic lactam
to form a semi-rotaxane.11 This assembly, shielded on one side by
a bulky group, subsequently reacts with a sterically demanding
electrophile to form a rotaxane. This imaginative approach has
been exploited by Smith’s group in the preparation of rotaxanes
with ion-pair binding macrocycles and rotaxinated squarine dyes12
and in a related stoppering method of rotaxane formation by
Schalley and co-workers.13
We have recently reported the use of spherical halide anions
as templates for the construction of a number of [2]pseudoro-
taxane assemblies.14 A chloride anion that is tightly ion-paired
to a cationic organic thread, e.g. a pyridinium amide cleft, has
been found, in non-competitive solvents, to be coordinatively
unsaturated and possess an empty meridian available for further
complexation by a second, neutral, anion recognition site.15 Al-
though not possessing the stereochemical preferences inherent in
a transition metal centre, sterics force an orthogonal arrangement
of the two ligands in a manner analogous to, for example, a
and formation of a [2]pseudorotaxane.16
Fig. 1 Anion-templated [2]pseudorotaxane assembly.
The conversion of these types of pseudorotaxanes to interlocked
mechanically-bonded assemblies will produce novel rotaxane
and catenane structures that contain unique, three-dimensional,
topological binding domains for the specific recognition of anionic
guest species. With the goal of using anion templation to develop
a general method for rotaxane synthesis and to understand the
factors that influence the yields and anion recognition properties
of the assembled interlocked species, we report here the synthesis
and anion coordination studies of three new [2]rotaxanes.
Results and discussion
Rotaxane construction strategy
We have recently reported the synthesis of a [2]rotaxane using
an anion-templated approach, illustrated in Scheme 1.17 The axle
component consists of a pyridinium chloride ion-pair motif with
two bulky ‘stopper’ groups. In non-competitive solvent media,
chloride anion association with a suitably designed neutral acyclic
second component that contains an anion recognition site, such as
isophthalamide, and is terminally functionalised with allyl groups
produces an assembly that after a ring-closing metathesis (RCM)
reaction affords the target [2]rotaxane (Scheme 1). RCM has
proved an efficient method in the preparation of catenanes18,19 and
Department of Chemistry, Inorganic Chemistry Laboratory, University of
Oxford, South Parks Road, Oxford, UK OX1 3QR. E-mail: paul.beer@
chem.ox.ac.uk
† Current address: Department of Materials, University of Oxford, Parks
Road, Oxford, UK OX1 3PH.
‡ Current address: Department of Chemistry, The University of Western
Ontario, Chemistry Building, London, Ontario, Canada N6A 5B7.
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bromoacetonitrile in acetone using potassium carbonate as base
afforded the nitrile compound 5 in moderate yield, which was
subsequently reduced using lithium aluminium hydride to give
the amine compound 6. Protection of the amine functionality
using Boc-anhydride followed by the high yielding removal of the
benzyl protecting group via hydrogenation afforded compound
8. The known compound 2-allyloxyethanol-p-toluene sulfonate23
was reacted with compound 8 in the presence of base to give
the allyl-appended naphthalene derivative 9. Removal of the Boc
protecting group using trifluoroacetic acid (TFA) yielded the
deprotected amine as an oil which was more easily handled after
protonation to give the hydrochloride salt 10. Condensation of
10 with isophthalic acid chloride gave the naphthalene-containing
isophthalmide derivative 11.
Scheme 1 Anion-templated synthesis of a [2]rotaxane via ring-closing
The terphenyl-functionalised pyridinium halide and hexafluo-
rophosphate derivatives 12a–d (Fig. 2) was prepared according to
literature procedure.17
metathesis (RCM).
rotaxanes,20 with the latter having also been accessed by related
olefin metathesis strategies.21
In an effort to demonstrate the generality and synthetic ver-
satility of this anion-templated method of rotaxane assembly, an
investigation into the effect of incorporating electron withdrawing
substituents into the 5-position of an isophthalamide anion
binding motif and changing the nature of the aryl spacer motif on
the yields and anion binding properties of the resulting rotaxanes
was undertaken.
Synthesis of bis-vinyl-functionalised isophthalamide derivatives
Condensation of the appropriate 5-substituted isophthalic acid
chloride with two equivalents of the vinyl-functionalised amine
derivative (1)19 in the presence of triethylamine in dry tetrahy-
drofuran solution afforded the corresponding bis-vinyl isophtha-
lamide derivatives 3 and 4 in yields of 40–50% (Scheme 2). The
naphthalene-containing isophthalamide derivative was prepared
according to the synthetic pathway shown in Scheme 3.
Fig. 2 Terphenyl-functionalised pyridinium salts 12a–d investigated as
potential [2]rotaxane thread components.
1H NMR anion-binding studies of isophthalamide derivatives
In order to ascertain which anion may serve as the potential tem-
1
plate in the ensuing rotaxane syntheses, H NMR anion binding
studies were undertaken with bis-vinyl-appended isophthalamide
(2) and 5-nitroisophthalamide (3) compounds. The addition of
tetrabutylammonium (TBA) halide, dihydrogen phosphate and
hydrogen sulfate salts to dichloromethane-d2 solutions of both
derivatives resulted in significant downfield shift perturbations
of the respective compounds’ aryl b and amide c protons.
WinEQNMR 24 analyses of the resulting titration isotherms gave
1 : 1 association constant values as shown in Table 1.
With both derivatives, chloride anions are bound the most
strongly of the halides, as a result of possessing the most effective
hydrogen-bond acceptor ability and a potential size match with
the amide cleft binding site. It is noteworthy that the presence
of an electron withdrawing nitro group in the isophthalamide’s
5-position substantially enhances the anion binding ability of the
ligand for all anionic guests, without altering the selectivity trends.
This increased affinity is postulated to be a result of a decrease
in the pKa of the amide protons and hence an increase in their
hydrogen-bond donor ability. The 5-iodoisophthalamide ligand
Scheme
dervatives.
2
Synthesis of bis-vinyl-functionalised isophthalamide
The starting material 1-benzyloxy-5-hydroxynaphthalene was
prepared according to a literature procedure.22 Reaction with
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Scheme 3 Naphthalene ligand synthesis. Reagents and conditions: i) BrCH2CN, K2CO3, acetone, reflux, 12 h, 69%; ii) LiAlH4, Et2O, 293 K, 1 h, 71%; iii)
Boc-anhydride, CH2Cl2, 293 K, 12 h, 53%; iv) Pd/C, 1 atm H2, DMF–MeOH (4 : 1), 293 K, 12 h, 61%; v) 2-allyloxyethanol-p-toluene sulfonate,23 K2CO3,
EtOH, reflux, 12 h, 64%; vi) TFA, CH2Cl2, 293 K, 12 h, CHCl3, HCl(g), 20 min, 47%; vii) isophthaloylcarbonylchloride, NEt3, CH2Cl2, 0 ◦C, 1 h, 44%.
Table 1 Association constants for ligands 2 and 3 with TBA salts
determined by 1H NMR (CD2Cl2, 293 K)
Association constantsa/M−1
Anion
2
3
Cl−
330
140
30
490
150
180
3550
1500
250
6400
1730
600
Br−
I−
BzO−
H2PO4
−
−
HSO4
a Estimated errors less than 10%.
(4) was found to bind chloride with an association constant of
900 M−1.
Taking into account these findings, chloride was chosen as the
templating anion in subsequent rotaxane formation reactions.
Scheme 4 Anion-templated macrocyclisation facilitated by ring-closing
metathesis (RCM).
Templated macrocyclisation reactions
it is expected that no steric strain will be imposed on this
functionality due to the large ring size. The trans : cis ratio is
calculated from the isomeric olefinic protons in the 1H NMR
spectrum (trans = 5.84, cis = 5.77 ppm) to be 6 : 1.
As a test for the suitability of RCM macrocyclisation reactions
using Grubbs’ catalyst in the presence of a halide anion template,
the isophthalamide derivative 2 was stirred with one equivalent of
TBA chloride and 10% Grubbs’ catalyst by weight. Macrocycle 13
was isolated by preparative TLC in 30% yield (Scheme 4).
A comparison of the 1H NMR spectra of the acyclic and cyclised
isophthalamide compound reveals the expectedchanges in the allyl
proton environments as a result of a completed metathesis reaction
(Fig. 3).
Interestingly, in the absence of a chloride template, or in the
−
presence of the non-coordinating PF6 anion, no cyclisation is
observed, indicating the critical nature of the template in the RCM
process. These results are in agreement with previously reported
observations on related systems in which the lowest energy
conformation of 3,5-isophthalamide systems has been determined
to be the syn–anti.25 Stabilisation of this conformation is through
internal NH · · · O hydrogen bonding. In this conformation the two
terminal allyl groups will be at a considerable spatial separation
The alkene in the cyclised product can exist as either the cis
or trans isomer, with the latter expected to dominate as the
thermodynamic product of the equilibrium process. In addition,
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Scheme 5 Anion recognition forces a change in ligand conformation from syn–anti to syn–syn, thus facilitating ring-closing metathesis.
component with the pyridinium chloride-stoppered thread 12a
in dichloromethane. Of note is the observed solubilisation of the
neutral acyclic amide compounds being enhanced in the presence
of the pyridinium chloride thread, indicative of association of the
two components. Addition of Grubbs’ catalyst (10% by weight)
facilitates the RCM reaction, and isolation of the [2]rotaxanes was
achieved by preparative TLC (Scheme 6).
[2]Rotaxane yields of up to 60% for the 5-nitroisophthalamide
derivative 3 were achieved, which compares with the previously
reported isophthalamide [2]rotaxane yield of 45%.17 This result is
in agreement with the enhanced macrocyclisation yields and the
increased strength of chloride anion binding by 3 in comparison
to 2, suggesting that the predominant interaction driving the
rotaxane assembly process is anion recognition.
Fig. 3 Selected region of 1H NMR of ligand 2 (bottom) and the related
macrocycle 13 (top) in CDCl3.
Importantly, no [2]rotaxane formation was observed using
pyridinium bromide, iodide and hexafluorophosphate salts 12b–d,
indicating the crucial nature of the chloride anion template to the
assembly process. Over an extended period of time no dissociation
of the [2]rotaxane species was observed, indicating that the bulky
stopper groups are large enough to prevent a deslipping process.
A comparison of the 1H NMR spectra of 12a, 3 and the [2]ro-
taxane product 16a is given in Fig. 5. With 5-nitroisophthalamide
derivative 3, downfield shift perturbations are observed for the
aryl, n, and amide, o, proton environments as a result of chloride
anion complexation. Correspondingly, an upfield perturbation in
the pyridinium thread’s aryl, b, and amide, c, proton environments
is observed due to chloride anion polarisation as a result of
complexation by the neutral component. Importantly, upfield
shift perturbations are observed in the neutral component’s
hydroquinone proton environments, s and r, as a result of
a p–p donor–acceptor interaction between these electron-rich
functionalities and the electron-deficient pyridinium ring of the
threading component.26 The completed metathesis reaction is
again observed by the loss of the characteristic terminal allyl
splitting pattern. In addition, high resolution electrospray mass
spectrometry and elemental analysis were used to characterise the
new rotaxane systems (see the Experimental section).
and therefore no cyclisation is observed. Upon addition of a
suitable anion template, however, the higher energy syn–syn
conformation becomes more favoured. In this conformation the
allyl groups are in much closer proximity, thus favouring the RCM
reaction (Scheme 5).
The chloride anion-templated RCM reaction was also at-
tempted with the 5-nitroisophthalamide derivative 3 and the cyclic
product (14) isolated in 60% yield after purification (Fig. 4). This
higher macrocyclisation yield, as compared with the preparation
of macrocycle 13, is a result of more effective chloride anion
1
templation and complements the H NMR association constant
values shown in Table 1.
Fig. 4 Structure of the cyclic product 14.
Anion-templated assembly of [2]rotaxanes
Despite the much poorer solubility of the naphthalene amide
compound (11) solubilisation was observed in dichloromethane
in the presence of pyridinium chloride ion-pair 12a. Addition
of Grubbs’ catalyst once again facilitated RCM and, after
Extension of this cyclisation strategy to the formation of [2]rotax-
anes using the 5-nitro-, 5-iodo- and naphthalene-isophthalamide
derivatives (3, 4 and 11) involved simply mixing the appropriate
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Scheme 6 [2]Rotaxane synthesis.
1
Fig. 5 Selected region of the H NMR of (a) thread molecule 12a, (b) rotaxane 16a and (c) 5-nitroisophthalamide derivative 3 (CDCl3, 298 K). For
proton labelling see Scheme 6.
1
purification by preparative TLC, [2]rotaxane 18 (Fig. 6) was
obtained in 15% yield. This lower [2]rotaxane product yield can
be postulated to arise from both the greater flexibility afforded
to the vinyl-terminated oxyethylene chain as a result of the
unsymmetrical substitution of the naphthalene linker and the
larger resulting macrocycle.
Similar 1H NMR shift perturbations to those noted with
[2]rotaxanes 16a and 17a were observed for rotaxane 18, namely
downfield shifts in environments n and m and upfield shifts
in b and c as a result of anion binding (Fig. 7). Although
inherently more crowded, the aromatic region of the H NMR
spectrum also revealed upfield shift perturbations in the electron-
rich naphthalene proton environment, t, as a result of p–p donor–
acceptor interaction with the electron-deficient pyridinium ring.
Rotaxanes as anion hosts
Whilst the anion-templated assembly of [2]rotaxanes presents a
novel approach to the preparation of interlocked species, the desire
to incorporate a degree of functionality into the final system
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Table 2 Association constants for PF6 thread 12d and PF6 rotaxanes 15b,
16b and 17b determined by 1H NMR (CD3OD–CDCl3, 1 : 1)
Association constantsa/M−1
Anion
Thread 12d
Rot 15b17
Rot 16b
Rot 17b
Cl−
K11
125
1130
4500
4500
−
H2PO4
K11
260
—
300
—
1500
—
1800
180
K12
AcO−
K11
2200
140
100
40
725
—
930
—
K12
a Estimated errors less than 10%.
Fig. 6 Structure of the naphthalene-containing [2]rotaxane (18) as
assembled though anion templation. Additional structural stabilisation is
provided by p–p stacking interactions and N+CH3 · · · O hydrogen bonding.
dominant factor in anion recognition by the free thread is therefore
the oxobasicity of the guest anions, hence the much weaker
coordination of the chloride anion. In sharp contrast, however,
are the binding trends observed for all three hexafluorophosphate
rotaxanes, which are completely reversed: Cl− > H2PO4− > OAc−.
The selectivity change is postulated to be a result of a unique anion
binding site formed by the two orthogonally arranged amide clefts.
A chloride anion can be bound tightly in this pocket due to both
complementary topography and the formation of four NH · · · Cl−
hydrogen bonds. Large anions such as dihydrogen phosphate and
acetate bind weakly as a result of either having to penetrate the
binding pocket, which would be sterically demanding, or forcing a
displacement of the pyridinium thread from the macrocyclic cavity.
Both of these binding mechanisms would be highly unfavourable
and unlikely to be able to present a full complement of hydrogen-
bond donors.
With rotaxanes 16b and 17b the dramatic increase in the
magnitude of the association constants can be explained by
considering the effect of the nitro and iodo substituents of the
isophthalamide ring. As indicated by the 1H NMR binding studies
of 3 and 4, these electron withdrawing functionalities appear to
increase the acidity and hydrogen-bonding ability of the amide
protons and thus result in enhanced anion recognition. It is
noteworthy that whilst the anion association constant values are
larger for rotaxanes 16b and 17b relative to 15b (Table 2), the
unique topology of the interlocked binding domain ensures that
selectivity for chloride, the templating anion, is maintained.
Fig. 7 Selected region of the 1H NMR spectrum of rotaxane 18 (293 K,
acetone-d6). For proton labelling see Fig. 6.
encouraged us to investigate their ability to function as anion
hosts. Removal of the chloride anion template from the cavity
of [2]rotaxanes 16a and 17a using silver hexafluorophosphate
yielded the corresponding hexafluorophosphate [2]rotaxane salts
1
16b and 17b. Although perturbations in the H NMR chemical
shifts of the cleft-sited amide and aryl protons are observed,
very few additional perturbations are seen, indicating a retention
of the [2]rotaxane structure upon template removal. Titration
of chloride, dihydrogen phosphate and acetate anions, as their
TBA salts, gave rise to perturbations in the rotaxane amide
and aryl protons surrounding the pocket previously occupied
by the template. Analysis of the resulting binding curves using
the WinEQNMR 24 software program allowed determination of
1 : 1 association constants for complexation of the anionic
guests by the host [2]rotaxane (Table 2). In order to determine
the effect of rotaxanation upon binding phenomena, analogous
association constant determinations were carried out with the
hexafluorophosphate thread 12d. Owing to a limited supply of
material, [2]rotaxane 18 was not investigated with regard to its
anion binding properties.
Conclusions
Anion templation has been shown to be an effective route to
the preparation of macrocycles and [2]rotaxanes. In particular,
the synthesis of three new [2]rotaxanes has demonstrated the
generality of this anion-templated approach to the assembly
of interlocked species. Importantly, rotaxanes templated in this
manner have a degree of functionality integral to their structure.
The use of unique cavities at the centre of interlocked structures as
host molecules has only recently begun to be explored despite
the unique properties they possess.12b,17,18,27 Dramatic changes
in anion binding selectivities have been demonstrated to occur
upon rotaxanation. Simple modification of just one component
can improve both rotaxane assembly yields and anion binding
strengths significantly. In this instance the incorporation of
electron withdrawing substituents, such as the nitro group, into the
Despite the possibility of a complementary size match between
the amide cleft of the thread and a chloride anion, the pyridinium
hexafluorophosphate thread 12d displays a greater selectivity
preference for both acetate and dihydrogen phosphate anions. The
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5-position of an isophthalamide anion binding motif increases the
acidity of the amide protons which leads to impressive yields of up
to 60% for [2]rotaxane formation, concomitant with the rotaxane
binding domain both augmenting thermodynamic stability and
conserving selectivity for chloride, the templating anion. We are
currently seeking to exploit this anion templation methodology
further in the design of mechanically interlocked species for anion
sensing applications.
136.0, 138.8, 152.5, 153.1 and 165.6; m/z (ESI) 731.1259 (M + H+
requires 731.1829).
Preparation of compound 5
1-Benzyloxy-5-hydroxynaphthalene (1.8 g, 7.2 × 10−3 mol), bro-
moacetonitrile (0.95 g, 7.92 × 10−3 mol) and potassium carbonate
(1.09 g, 7.92 × 10−3 mol) were heated under reflux in acetone
(100 ml) for 12 h. The resulting reaction mixture was cooled to
room temperature and filtered. The solvent was removed to give
a brown oil that was redissolved in dichloromethane and filtered
through a plug of silica. The solvent was removed to give the
product (1.44 g, 69%) as a pale yellow solid; dH(300 MHz, CDCl3,
Me4Si) 4.96 (2H, s, OCH2Ph), 5.25 (2H, s, CNCH2), 6.96 (1H, d,
J = 7.5 Hz, ArH), 7.51–7.53 (2H, m, ArH), 7.33–7.45 (5H, m,
ArH), 7.78 (1H, dt, J 8.7, J 0.8, ArH) and 8.07 (1H, dt, J 8.4, J
0.9, ArH); dC(300 MHz, CDCl3, Me4Si) 53.8, 70.2, 106.1, 106.5,
106.6, 114.0, 114.8, 117.2, 124.8, 125.3, 126.2, 127.5, 128.0, 128.7,
129.1, 137.0, 137.3, 152.2 and 154.4; m/z (ESI) 290.1233 (M + H+
requires 290.1181).
Experimental
The synthesis of compounds 12a–d, 1, 2 and 15a,b have been
previously described.17,19 2-Allyloxyethanol-p-toluene sulfonate
and 5-iodoisophthalic acid were prepared according to literature
procedures.23,28 All starting materials were purchased from Aldrich
Chemicals and used as received with the exception of thionyl
chloride and triethylamine which were distilled from triethyl
phosphite and over potassium hydroxide, respectively, and the
latter stored over potassium hydroxide. All solvents were dried
1
using standard laboratory procedures prior to use. H and 13C
NMR spectra were recorded on Varian 300 MHz VX Works and
500 MHz Unity Plus spectrometers. Mass spectrometry was car-
ried out using a Micromass LCT electrospray mass spectrometer.
Elemental analyses were performed by the Inorganic Chemistry
Laboratory Microanalysis Service, Department of Chemistry,
University of Oxford, and by the Elemental Analysis Service,
London Metropolitan University.
Preparation of compound 6
Compound 5 (0.5 g, 4.84 × 10−3 mol) was dissolved in diethyl ether
(100 ml) and added carefully to a suspension of lithium aluminium
hydride (0.1 g, 2.6 × 10−3 mol) in diethyl ether (150 ml) and stirred
atroomtemperatureforonehour. Aqueous10%sodiumhydroxide
solution was added slowly (approx. 25 ml) until no further gas
production was observed. Saturated aqueous sodium chloride
solution was added (50 ml) and the organic layer decanted. Diethyl
ether (80 ml) was added to the aqueous phase and stirred for 20 min
before being decanted. This procedure was repeated once more.
The organic phases were combined and dried over magnesium
sulfate. Removal of the solvent gave the product (0.36 g, 71%) as a
white solid; dH(300 MHz, CDCl3, Me4Si) 3.12 (2H, t, J = 5.1 Hz,
CH2), 4.05 (2H, t, J 5.1, CH2), 5.13 (2H, s, CH2 benzyl), 6.73 (1H,
d, J 7.8, ArH), 6.81 (1H, d, J 7.5, ArH), 7.21–7.33 (5H, m, ArH
benzyl), 7.41–7.43 (2H, m, ArH), 7.77 (1H, d, J 8.4, ArH) and
7.83 (1H, d, J 8.7, ArH).
Preparation of 5-nitroisophthalamide ligand 3
A solution of synthon 1 (0.82 g, 3.0 mmol) and triethylamine
(8 ml) in THF (100 ml) was prepared and cooled to 0 ◦C. 5-
Nitroisophthaloyl dichloride was added and the solution stirred
for 1 h keeping the temperature below 5 ◦C. The resulting reaction
mixture was filtered and the solvent removed to give an oil. The oil
was then dissolved in dichloromethane (100 ml) and washed with
aqueous 10% HCl solution (3 × 100 ml) and water (3 × 100 ml).
The organic phase was then dried over magnesium sulfate and
the solvent removed to give the product (0.49 g, 50%) as a yellow
solid (Found: C, 62.9; H, 6.1; N, 6.6. Calc. for C34H39N3O10: C,
62.8; H, 6.05; N, 6.5%); dH(300 MHz, CDCl3, Me4Si) 3.89 (4H, t,
J = 4.2 Hz, CH2), 3.89 (4H, m, NHCH2), 4.09 (12H, m, CH2),
Preparation of compound 7
Compound 6 (1.35 g, 4.60 × 10−3 mol) and Boc-anhydride (1.80 g)
were dissolved in dichloromethane (100 ml) and stirred at room
temperature for 12 h. The resulting reaction mixture was filtered
through a plug of silica and the solvent was removed to give a
pale yellow solid. After stirring in hexane (50 ml) for 20 min and
filtering the product (0.96 g, 53%) was obtained as a white solid;
=
=
5.2–5.3 (2H, m, CH CH2), 5.93 (2H, m, CH CH2), 6.83 (8H, m,
ArH), 6.94 (2H, br s, NH), 8.54 (1H, s, 4-H) and 8.73 (2H, s, 2-H);
dC(300 MHz, CDCl3, Me4Si) 40.1, 68.0, 66.9, 68.6, 72.4, 115.3,
115.6, 117.5, 124.6, 131.2, 134.5, 136.3, 148.2, 152.5, 153.3, 164.6;
m/z (ESI) 672.70 (M + H+ requires 672.25).
t
dH(300 MHz, CDCl3, Me4Si) 1.40 (9H, s, Bu), 3.61 (2H, q, J =
5.1 Hz, NHCH2), 4.08 (2H, t, J 5.1, OCH2), 5.06 (1H, br s, NH),
6.62 (1H, br s, OH), 6.69 (1H, d, J 7.5, ArH), 6.81 (1H, d, J
7.5, ArH), 7.26 (2H, t, J 8, ArH) and 7.72 (2H, d, J 8.4, ArH);
dC(300 MHz, CDCl3, Me4Si) 23.4, 40.2, 67.4, 70.1, 105.2, 109.3,
114.4, 124.9, 125.3, 126.7, 127.3, 127.9, 128.5, 151.8, 154.0 and
156.2; m/z (ESI) 304.1563 (M + H+ requires 304.1549).
Preparation of 5-iodoisophthalamide ligand 4
Method as for compound 3, using synthon 1 (0.3 g, 1.15 × 10−3
mol) and 5-iodoisophthaloyl dichloride (0.10 g, 5.73 × 10−3 mol)
to give the product (0.16 g, 40%) as a white solid (Found: C,
55.9; H, 5.4; N, 3.9. Calc. for C34H39IN2O8: C, 55.9; H, 5.4; N,
3.8%); dH(300 MHz, CDCl3, Me4Si) 3.75 (8H, m, CH2), 4.01
=
(12H, m, CH2), 5.16–5.30 (4H, m, CH CH2), 5.84–5.97 (2H,
Preparation of compound 8
=
m, CH CH2), 6.77 (8H, s, ArH), 7.33 (2H, br t, J = 4.4 Hz, NH),
8.11 (1H, s, 4-H) and 8.13 (2H, s, 2-H); dC(300 MHz, CDCl3,
Me4Si) 39.8, 66.8, 67.8, 68.4, 72.2, 94.2, 115.3, 115.4, 117.4, 134.3,
Compound 7 (0.96 g, 2.44 × 10−3 mol) was dissolved in a
suspension of 10% palladium on activated carbon (0.09 g) in
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=
DMF–methanol (100 ml, 4 : 1). The reaction mixture was stirred
overnight under an atmosphere of hydrogen. Filtration through
Celite followed by solvent removal gave a crude brown oil.
Recrystallisation from water gave the product (0.45 g, 61%) as a
white powder; dH(300 MHz, CDCl3, Me4Si) 1.40 (9H, s, tBu Boc),
3.61 (2H, q, J = 5.1 Hz, NHCH2), 4.08 (2H, t, J 5.1, OCH2), 5.06
(1H, br s, NH), 6.62 (1H, br s, OH), 6.69 (1H, d, J 7.5, ArH), 6.81
(1H, d, J 7.5, ArH), 7.26 (2H, t, J 8.0, ArH) and 7.72 (2H, d, J 8.4,
ArH); dC(300 MHz, CDCl3, Me4Si) 28.4, 40.2, 67.4, 70.1, 105.2,
109.3, 113.9, 114.4, 124.9, 125.3, 126.7, 127.3, 127.9, 128.5, 151.8,
154.0 and 156.2; m/z (ESI) 304.1563 (M + H+ requires 304.1549)
m, CH CH2), 6.93 (2H, d, J = 7.2 Hz, ArH), 7.02 (2H, d, J 8.1,
ArH), 7.27–7.44 (5H, m, ArH), 7.55 (2H, t, J 8.8, ArH), 7.71 (2H,
d, J 9.3, ArH), 7.82 (2H, d, J 7.5, ArH), 8.032 (2H, d, J 8.4, ArH),
8.57 (1H, s, ArH), 9.13 (2H, br t, J 5.7, NH); m/z (ESI) 727.3250
(M + H+ requires 727.2995).
Preparation of isophthalamide macrocycle 13
Ligand 2 (75 mg, 0.124 mmol) and tetrabutylammonium chloride
(56 mg, 0.2 mmol) were dissolved in dichloromethane (50 ml) and
stirred for 15 min. Grubbs’ catalyst (7.5 mg) was added and the
resulting solution stirred for 12 h. The resulting reaction mixture
was purified by preparative TLC (SiO2) using dichloromethane–
methanol (93 : 7) as eluent to give the product (21 mg, 30%)
as a white powder (Found: C, 65.3; H, 6.3; N, 4.5. Calc. for
C32H36N2O8·CH3OH: C, 65.1; H, 6.6; N, 4.6%); dH(300 MHz,
CDCl3, Me4Si) 3.76 (4H, m, OCH2CH2O), 3.85 (4H, m, NHCH2),
Preparation of compound 9
A solution of compound 8 (0.43 g, 1.42 × 10−3 mol), 2-
allyloxyethanol-p-toluene sulfonate (0.36 g, 1.42 × 10−3 mol)
and potassium carbonate (0.22 g, 1.56 × 10−3 mol) in ethanol
(50 ml) was heated under reflux for 12 h. After cooling to room
temperature the reaction mixture was filtered and the solvent
removed to give a brown oil. Chloroform (80 ml) was added and
a fine precipitate observed which was subsequently removed by
filtration. Removal of the solvent gave the product (0.35 g, 64%)
=
4.08 (12H, m, CH2), 5.84 (2H, s, CH CH), 6.66 (2H, br s, NH),
6.80 (8H, m, ArH hydroquinone), 7.55 (1H, t, J = 7.6 Hz, Ar-5-
H) and 7.99 (3H, m, ArH); dC(300 MHz, CDCl3, Me4Si) 40.0,
67.4, 68.4, 68.7, 71.1, 104.8, 115.6, 116.1, 129.5, 131.0, 134.9,
135.3, 152.9, 153.6 and 167.0; m/z (ESI) 577.69 (C32H36N2O8 +
H+ requires 577.65).
t
as a brown oil; dH(300 MHz, CDCl3, Me4Si) 1.48 (9H, s, Bu),
3.7 (2H, q, J = 5.2 Hz, NHCH2), 3.97 (2H, t, J 4.8, CH2), 4.17–
4.22 (4H, m, CH2), 4.32 (2H, t, J 4.8, CH2), 5.23–5.40 (2H, m,
CHCH2), 5.93–6.06 (1H, m, CHCH2), 6.84 (1H, t, J 7.5, ArH),
6.88 (1H, d, J 7.5, ArH), 7.37 (1H, t, J 8.0, ArH), 7.39 (1H, t, J
8.0, ArH), 7.85 (1H, d, J 8.4, ArH) and 7.91 (1H, d, J 8.4, ArH);
dC(300 MHz, CDCl3, Me4Si) 28.4, 40.2, 67.5, 67.6, 68.6, 70.1, 72.4,
105.5, 105.7, 114.2, 114.8, 117.3, 125.2, 127.3, 127.9, 128.5, 134.6
and 154.4; m/z (ESI) 410.1945 (M + H+ requires 410.1943).
Preparation of 5-nitroisophthalamide macrocycle 14
Method as for 13 using ligand 3 (100 mg, 1.5 × 10−4 mol),
tetrabutylammonium chloride (42.7 mg, 1.5 × 10−4 mol) and
Grubbs’ catalyst (10 mg). Purification by preparative TLC using
ethyl acetate as eluent furnished the product (52 mg, 54%) as a
pale yellow powder (Found: C, 61.1; H, 6.1; N, 6.5. Calc. for
C32H35N3O10: C, 61.8; H, 5.7; N, 6.8%); dH(300 MHz, CDCl3,
Me4Si) 3.76 (4H, t, J = 4.2 Hz, CH2), 3.86 (4H, m, NHCH2),
4.04 (12H, m, CH2), 5.84 (2H, t, J 2.9, CHCH), 6.73 (8H, m,
ArH), 6.91 (2H, br s, NH), 8.35 (1H, s, ArH p-NO2) and 8.78
(2H, s, ArH o-NO2); dC(300 MHz, CDCl3, Me4Si) 40.2, 68.7, 67.1,
68.4, 71.0, 115.5–115.8 (four peaks), 125.4, 129.3, 136.3, 153.0 and
153.4; m/z (ESI) 622.2300 (M + H+ requires 622.2400).
Preparation of compound 10
Compound 9 (0.33 g, 8.52 × 10−3 mol) was dissolved in
dichloromethane (100 ml) and TFA (5 ml) and stirred for 12 h.
The resulting reaction mixture was washed with water (2 ×
100 ml) and the combined aqueous layers back-extracted with
dichloromethane (100 ml). The organic phases were combined,
dried over magnseium sulfate and the solvent was removed to give
a light brown oil. The oil was dissolved in chloroform (50 ml)
and HCl(g) was bubbled through the solution for 20 min or until
no more precipitate was formed. Diethyl ether (50 ml) was added
and the product (0.11 g, 47%) collected by filtration; dH(300 MHz,
CD3OD, Me4Si) 3.63 (2H, m, CH2), 3.95 (4H, m, CH2), 4.17
Preparation of nitro-rotaxane chloride 16a
Ligand 3 (90 mg, 1.39 × 10−4 mol) and pyridinium chloride thread
12a (100 mg, 9.29 × 10−4mol) were dissolved in dichloromethane
(50 ml) and stirred for 20 min. Grubbs’ catalyst was added (18 mg,
10% by weight) and the reaction mixture stirred overnight. The
solvent was removed and the crude reaction mixture seperated
by preparative TLC (SiO2) using dichloromethane–methanol (93 :
7) as eluent. The product (90 mg, 57%) was isolated as a yellow
powder (Found: C, 75.0; H, 6.8; N, 4.8. Calc. for C106H113ClN6O12:
C, 75.0; H, 6.7; N, 4.95%); dH(300 MHz, CDCl3, Me4Si) 1.31
=
(4H, br t, CH2), 5.15–5.25 (2H, m, CH CH2), 5.77–5.87 (2H,
=
m, CH CH2), 6.86 (2H, m, ArH), 7.79–7.93 (2H, m, ArH) and
7.33–7.45 (2H, m, ArH); m/z (ESI) 274.1574 (M+ − Cl− requires
274.169).
Preparation of naphthalene ligand 11
t
A solution of compound 10 (0.27 g, 9.75 × 10−3 mol) and
triethylamine (3 ml) in dichloromethane (50 ml) was prepared
and cooled to 0 ◦C. Isophthaloylcarbonylchloride was added and
the reaction mixture stirred for one hour, keeping the temperature
below 5 ◦C, during which time a precipitate was observed to form.
The product (0.15 g, 44%) was isolated by filtration; dH(300 MHz,
CDCl3, Me4Si) 3.79–3.83 (8H, m, CH2), 4.08 (4H, m, CH2), 4.23–
(36H, s, Bu), 3.77 (12H, m, NHCH2CH2OArOCH2), 4.11 (8H,
m, CH2OCH2), 4.45 (3H, s, N+CH3), 6.01 (2H, br s, CHCH), 6.18
(4H, d, J = 9.0 Hz, ArH), 6.43 (4H, d, J 9.0, ArH), 7.02 (8H, m,
ArH), 7.19 (2H, m, ArH), 7.23 (12H, m, ArH), 7.81 (4H, d, J 9.0,
ArH), 8.70 (2H, br s, NH mac), 8.90 (2H, s, ArH o-NO2), 9.10
(2H, s, ArH o-N+), 9.34 (1H, s, ArH p-NO2), 9.78 (1H, br s, ArH
p-N+) and 10.23 (2H, br s, NH thread); m/z (ESI) 1662.85 (M+ −
Cl− requires 1161.8416).
=
4.28 (8H, m, CH2), 5.14–5.32 (4H, m, CH CH2), 5.86–5.98 (2H,
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Preparation of iodo-rotaxane chloride 17a
9.70 (2H, br s, NHc); m/z (ESI) 1716.8728 (M+ − Cl− requires
1716.8878).
Method as for rotaxane 16a using ligand 4 (25 mg, 1.41 × 10−5
mol), pyridinium chloride thread 12a (69 mg, 6.39 × 10−5mol) and
Grubbs’ catalyst (7 mg) to furnish the product (43%) as a yellow
powder; dH(300 MHz, CDCl3, Me4Si) 1.31 (36H, s, tBu), 3.74–3.82
(12H, m, CH2), 4.06–4.11 (8H, m, CH2), 4.37 (3H, br s, N+CH3),
Acknowledgements
We thank the EPSRC for a studentship (M. R. S.) and for
a postdoctoral fellowship (J. A. W.). We also acknowledge the
Natural Sciences and Engineering Research Council of Canada
for financial support (J. A. W.).
=
6.02 (2H, br s, CH CH), 6.17 (4H, d, J = 8.7 Hz, ArH), 6.42
(4H, d, J 8.4, ArH), 7.07 (8H, d, J 7.8, ArH stopper), 7.16 (8H,
d, J 7.8, ArH stopper), 7.21–7.26 (14H, m, ArH stopper), 7.81
(4H, d, J 7.5, NHArH), 8.43 (2H, ArH o-N+), 8.50 (2H, br s, ArH
o-CI), 8.92 (1H, br s, ArH p-CI), 9.14 (2H, br s, NH mac), 9.71
(1H, br s, ArH p-N+) and 10.26 (2H, br s, NH thread); m/z (ESI)
1742.7482 (M+ − Cl− requires 1742.7532).
References
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Preparation of nitro-rotaxane hexafluorophosphate 16b
The nitro-rotaxane chloride (40 mg, 2.35 × 10−5 mol) was dissolved
in dichloromethane and stirred with silver hexafluorophosphate
(30 mg, 1.18 × 10−4mol) for 12 h in the absence of light. The
resulting solution was filtered through Celite and the solvent
removed to give the pure product (85%) as a yellow solid (Found:
C, 70.3; H, 6.5; N, 4.8. Calc. for C106H113F6N6O12P: C, 70.4; H,
t
6.3; N, 4.7%); dH(300 MHz, CDCl3, Me4Si) 1.31 (36H, s, Bu),
3.76–3.81 (12H, m, CH2), 4.05–4.10 (8H, m, CH2), 4.31 (3H, br s,
+
=
N CH3), 6.01 (2H, br s, CH CH), 6.19 (4H, d, J = 8.7 Hz, ArH),
6.47 (4H, d, J 8.7, ArH), 7.05–7.21 (14H, m, ArH), 7.78 (4H, d, J
7.8, NHArH), 8.57 (2H, br s, ArH o-N+), 8.96 (2H, m, ArH o-CI,
p-CI), 9.04 (2H, br s, NH mac), 9.26 (1H, br s, ArH p-N+) and
10.19 (2H, br s, NH thread).
Preparation of iodo-rotaxane hexafluorophosphate 17b
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Method as for 16b using the iodo-rotaxane chloride 17a (25 mg,
1.41 × 10−5 mol) and silver hexafluorophosphate (14 mg, 5.62 ×
10−5mol) to give the product (18 mg, 100%) as a yellow powder
(Found: C, 67.4; H, 6.2; N, 3.7. Calc. for C106H113F6IN5O10P: C,
67.4; H, 6.0; N, 3.7%); dH(300 MHz, CDCl3, Me4Si) 1.28 (36H,
tBu), 3.73 (8H, m, CH2), 3.80 (4H, m, CH2), 4.01 (8H, m, CH2),
+
=
4.24 (3H, s, N CH3), 5.94 (2H, CH CH), 6.23 (4H, d, J = 8.0 Hz,
ArH), 6.45 (4H, d, J 8.5, ArH), 7.10 (8H, d, J 8.0, ArH), 7.21
(14H, m, ArH), 7.72 (4H, br s, ArHNH), 8.48 (2H, s, ArH o-N+),
8.71 (1H, br s, ArH p-CI), 8.98 (2H, br s, NH mac), 9.30 (1H, br s,
ArH p-N+) and 10.05 (2H, br s, NH thread).
Preparation of naphthalene-rotaxane chloride 18
Method as for 16a using naphthalene ligand 11 (120 mg, 1.70 ×
10−4 mol), pyridinium chloride thread 12a (120 mg, 1.12 ×
10−4mol) and Grubbs’ catalyst to furnish the product (30 mg,
15%) as a yellow solid (Found: C, 76.7; H, 6.7; N, 3.7. Calc. for
C114H118ClN5O10: C, 78.1; H, 6.8; N, 4.0%); dH(300 MHz, acetone-
t
d6, Me4Si) 1.37 (36H, s, Bu), 3.67–3.71 (4H, m, NHCH2), 3.94–
3.96 (4H, m, CH2), 4.06–4.07 (4H, m, CH2), 4.11 (4H, t, J =
4.5 Hz, CH2), 4.24 (4H, m, CH2CH), 4.66 (3H, s, N+CH3), 6.24
(2H, br s, CHCH), 6.28 (2H, d, J 7.8), ArHt), 6.40 (2H, d, J 7.5,
ArHq) 6.64 (2H, t, J 8.0, ArHr), 6.84 (2H, t, J 8.3, ArHu), 7.10
(2H, d, J 9.0, ArHm), 7.05–7.42 (31H, m, ArHe,f ,g,h,i,j,k), 7.54 (2H, d,
J 8.4, ArHs), 7.90 (4H, d, J 8.7, ArHd ), 8.05 (2H, d, J 7.8, ArHl),
8.88 (2H, br s, NHn), 8.95 (3H, ArHa,m), 9.24 (1H, br s, ArHb) and
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