'Click' functionalised polymer resins: A new approach to the synthesis of surface attached bipyridinium and naphthalene diimide [2]rotaxanes

Article abstract of DOI:10.1039/c3ob27273g

Herein we describe the design and synthesis of a series of solid-tethered [2]rotaxanes utilising crown ether-naphthalene diimide or crown ether-bipyridinium host guest interactions. TentaGel polystyrene resins were initially modified in a two-stage procedure to azide functionalised beads before the target supramolecular architectures were attached using a copper catalysed click procedure. The final assembly was examined using IR spectroscopy and gel-phase ¹H High Resolution Magic Angle Spinning (HR MAS) NMR spectroscopy. The HR MAS technique enabled a direct comparison between the solid-tethered architectures and the synthesis and characterisation of analogous solution-based [2]rotaxanes to be made. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3ob27273g

Organic &
Biomolecular Chemistry
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‘Click’ functionalised polymer resins: a new approach
to the synthesis of surface attached bipyridinium and
naphthalene diimide [2]rotaxanes†
Cite this: Org. Biomol. Chem., 2013, 11,
2105
Hannah Wilson,a Sean Byrne,a Nick Bamposb and Kathleen M. Mullen*a
Herein we describe the design and synthesis of a series of solid-tethered [2]rotaxanes utilising crown
ether-naphthalene diimide or crown ether-bipyridinium host guest interactions. TentaGel polystyrene
resins were initially modified in a two-stage procedure to azide functionalised beads before the target
supramolecular architectures were attached using a copper catalysed “click” procedure. The final assem-
bly was examined using IR spectroscopy and gel-phase 1H High Resolution Magic Angle Spinning
(HR MAS) NMR spectroscopy. The HR MAS technique enabled a direct comparison between the solid-
tethered architectures and the synthesis and characterisation of analogous solution-based [2]rotaxanes
to be made.
Received 23rd November 2012,
Accepted 22nd January 2013
DOI: 10.1039/c3ob27273g
www.rsc.org/obc
confined systems is more difficult, particularly in the absence
of an appropriate redox probe. Various methods including
Introduction
Developments in fundamental concepts such as self-assembly, X-ray photoelectron spectroscopy (XPS), electrochemical tech-
template directed synthesis and dynamic covalent synthesis niques, steady state fluorescence, surface probe microscopy
have transformed the field of supramolecular chemistry, allow- (STM, AFM) and solid-state FT-IR have all been used to analyse
ing for the design and operation of more elaborate interlocked solid tethered supramolecular systems.7,8 However, many of
architectures and molecular machines than would have been these techniques do not provide direct comparisons with solu-
thought possible at its inception. Early statistical approaches tion based systems. Finally, but perhaps most importantly,
to isolate rotaxanes or catenanes in <5% yield, have been aban- fundamental questions remain as to the full effect surface con-
doned in light of these developments allowing [n]rotaxanes, finement has on the dynamic nature of complex molecular
[n]catenanes and even more complex molecular knots and machines.
links to be made reliably and in much higher yields.1–4 Greater
Research attempting to answer many of these questions has
understanding of the inherent dynamic nature of such inter- been ongoing, with notable examples by the groups of Stod-
locked systems has also led to the development of a range of dart, Leigh, and Sauvage, amongst others demonstrating the
molecular switches or shuttles, ratchets, and molecular successful assembly of interlocked architectures on a variety of
motors.5 However, in order to realise the potential these substrates including Langmuir Blogett films,9–12 embedded
systems hold in transforming modern technologies, they need polymer matrixes,13–15 sol gel glass surfaces6 and self
to be incorporated into functionalised materials or deposited assembled monolayers (SAMs) on gold or other surfaces.16–29
onto surfaces.6 These objectives present several challenges. Furthermore, for a series of surface bound multi-station rotax-
Firstly, the chemistry used for surface attachment needs to be anes, Stoddart et al. have demonstrated that while the rate of
compatible with the synthetic requirements of the interlocked shuttling is dependent on the surface medium, the mechan-
assemblies. Secondly, the characterisation of such surface ism for switching between stations is consistent for all mole-
cules, regardless of whether they are in solution, tethered to
solid surfaces (such as gold) or embedded in polymer
matrixes.13 In contrast, Sauvage et al. showed that while redox
aSchool of Chemistry, Physics and Mechanical Engineering, Queensland University of
activated ring circumrotation is observed in solution for a
series of Cu(I)/Cu(II) catenanes, when such systems are
deposited on gold, intramolecular motion is markedly slowed
if not completely frozen.23,30 These examples highlight the
need to be able to accurately characterise and understand the
dynamic behaviour of supramolecular architectures deposited
Technology, Brisbane, Queensland 4001, Australia.
E-mail: kathleen.mullen@qut.edu.au; Tel: +61 (0)7313 82393
bDepartment of Chemistry, Lensfield RoadUniversity of Cambridge, Cambridge,
CB2 1EU, UK
†Electronic supplementary information (ESI) available: UV, IR and HR MAS
NMR studies of both solution and surface based rotaxanes, and full characteris-
ation details for all new compounds. See DOI: 10.1039/c3ob27273g
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on surfaces, as solution behaviour is not always directly
comparable.
As the complexity of supramolecular architectures in solu-
1
tion increases, H NMR is vitally important in understanding
the dynamic behaviour characteristic of interlocked architec-
tures. Attachment of these systems to surfaces such as gold,
prevents investigation of dynamic behaviour by 1H NMR.
However, when using swelling polystyrene resins as the solid
support, 1H NMR spectra can be obtained using HR MAS
(High Resolution Magic Angle Spinning) NMR techniques,
thus providing a direct comparison between solid and solution
dynamics. Previous work has allowed us to monitor the reversi-
ble assembly of a range of pseudorotaxanes incorporating
neutral naphthalene diimide threads, crown ether macrocycles
and ruthenium stoppered porphyrins on polystyrene resins
(such as ArgoGel or TentaGel resins).31–34 In some of these
studies it was found that although pseudorotaxane assembly is
fast relative to the chemical shift timescale in solution, the
binding process was in slow exchange on the polymer
surface.34 Additional binding interactions between the macro-
cycle and the polymer tethers were also observed, which high-
lights the importance of this technique in identifying key
differences between solution and surface based supramolecu-
lar chemistry. Preliminary studies into the assembly of kineti-
cally trapped rotaxanes on polymer resins was also
undertaken; however, to date surface functionalisation has
been limited to ester condensation reactions.32 Herein we
report the use of the Cu(I) catalyzed Huisgen 1,3-dipolar cyclo-
addition or “click” reaction between azides and alkynes as a
means of functionalising polymer resins with [2]rotaxane
Scheme 1 Synthesis of mono-stoppered bipyridinium thread 5. Reagents and
conditions: (i) TBTA, Cu(MeCN)4PF6, acetone, 48 h, RT.
Scheme 2 Attempted synthesis of mono-stoppered naphthalene diimide
thread 7. Reagents and conditions: (i) TBTA, Cu(MeCN)4PF6, DCM : MeOH (9 : 1),
48 h, RT.
1
architectures and their subsequent characterisation by H HR
MAS NMR spectroscopy (see Fig. 1).
Results and discussion
Synthesis of mono-stoppered threads
In this study two electron deficient motifs, one containing the
charged bipyridinium motif and another containing the
neutral naphthalene diimide moiety, were investigated as suit-
able thread components for the assembly of [2]rotaxanes on
polymer supports. The synthesis of the alkyne functionalised
mono-stoppered bipyridinium thread 5 necessary for surface
functionalisation using a click methodology is outlined in
Scheme 1. Bipyridinium 5 was synthesised according to a
modified literature procedure35 in which stopper azide 3 was
reacted with an excess of bipyridinium bis-alkyne 4, in the
presence of Cu(MeCN)4PF6 and TBTA. Purification by reverse
phase medium pressure liquid chromatography (MPLC)
afforded the target mono-stoppered thread in good yield.
A similar strategy was initially employed for the synthesis of
the neutral mono-stoppered naphthalene diimide thread 7
(Scheme 2). However, despite using an excess of diimide bis-
alkyne 6, all attempts to synthesise 7 were unsuccessful with
only the di-stoppered thread and unreacted diimide bis-alkyne
being isolated from the reaction mixtures. This can be
Fig. 1 Target surface bound bipyridinium and diimide [2]rotaxanes, 1 and 2
respectively.
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attributed to the insolubility of the diimide bis-alkyne 6 in 1,4,5,8-naphthalenetetracarboxylic dianhydride in dry DMF, to
almost all organic solvents. Although the first cycloaddition provide the unsymmetrical diimide 8 in statistical yield follow-
between the diimide bis-alkyne and stopper azide is inherently ing purification by column chromatography. A Mitsunobu
slow, upon formation, the soluble mono-stoppered naphtha- reaction between 8 and 4-(tris(4-(tert-butyl)phenyl)methyl)-
lene diimide thread immediately reacts with the remaining phenol36 subsequently afforded the desired mono-stoppered
stopper azide in solution to yield exclusively the di-stoppered thread 9 in 61% yield.
thread.
Control solution based rotaxane experiments
An alternative strategy involving the initial synthesis of
unsymmetrical naphthalene diimide was ultimately used to
synthesise the desired mono-stoppered naphthalene diimide
thread 9 (see Scheme 3). Propargyl amine and 5-amino-1-
pentanol were slowly added to a heated suspension of
Having obtained both the mono-stoppered bipyridinium 5 and
the mono-stoppered naphthalene diimide 9 threads, con-
ditions for rotaxane formation using dinaphtho-38-crown-10
10 as the macrocycle component were investigated. Whilst
similar rotaxanes using these components have been pre-
viously reported, these experiments were important not only to
establish ideal conditions for the surface click reactions, but
were also necessary in order to ensure that the increased solu-
bility of the thread did not significantly affect the yield of
rotaxane as has been seen in related systems.37 A solution of
mono-stoppered thread 5 or 9, was reacted with stopper azide
3 in the presence of one equivalent of dinaphtho-38-crown-10
10. Following purification via column chromatography the
desired bipyridinium rotaxane 11 and the naphthalene
diimide rotaxane 12 were isolated in 25% and 23% yields,
respectively (see Schemes 4 and 5). The reactions were then
repeated using five equivalents of crown 10 and as expected
the yield of interlocked products increased to 36% and 33%
respectively. Both rotaxanes were characterised by 1H NMR,
13C NMR, UV-Vis and ESI-MS (mass peak at m/z 1066.6174
[M − 2PF6]2+ for 11 and 2130.1467 [M]+ for 12). The yields of
the [2]rotaxanes were not significantly different to the yields
expected using double click strategies, indicating that the use
of a more soluble thread should still give reasonable yields of
interlocked products on polymer bead surfaces.
Scheme 3 Synthesis of mono-stoppered diimide thread 9. Reagents and con-
ditions: (i) DMF, 120 °C, 2 h; (ii) 4-(tris(4-(tert-butyl)phenyl)methyl)phenol, PPh3,
DBAD, CHCl3, 50 h, RT.
Unlike the dumbbell and macrocycle non-interlocked
counterparts which are either off-white or pale yellow in
Scheme 4 Synthesis of solution phase bipyridinium [2]rotaxane 11. Reagents and conditions: (i) TBTA, Cu(MeCN)4PF6, CHCl3 : MeOH (95 : 5), 4 days, RT.
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Scheme 5 Synthesis of solution phase naphthalene diimide [2]rotaxane 12. Reagents and conditions: (i) TBTA, Cu(MeCN)4PF6, CHCl3 : MeOH (95 : 5), 4 days, RT.
macrocycle. Similarly, the crown aromatic protons α, β and γ
have been shifted upfield, appearing at 5.98, 6.43 and
6.84 ppm in the bound rotaxane, as compared to their typical
shifts when unbound of 6.52, 7.20 and 7.80 ppm. These
changes in chemical shifts are characteristic of the interlocked
nature of this structure, and are consistent with literature
reports of related [2]rotaxanes.37
Surface attachment and HR MAS analysis
Having established suitable reaction conditions for the syn-
thesis of diimide and bipyridinium [2]rotaxanes in solution,
attention turned to the attachment of these [2]rotaxanes to
polymer resins. Previous surface attachment has involved
Fig. 2 1H NMR spectra of the mono-stoppered bipyridinium thread 5 (top),
bipyridinium rotaxane 11 (middle) and dinaphtho-38-crown-10 10 (bottom) in
CDCl3 at 303 K.
using EDC catalysed ester condensation reactions to success-
fully attach individual rotaxane components to either TentaGel
or ArgoGel beads and monitor the subsequent rotaxane assem-
bly process under thermodynamic control.31,33,34 In addition,
there has been one reported attempt to attach kinetically
stable interlocked architectures to ArgoGel beads using the
same ester condensation reaction, with modest success.32 In
this study we extended the bead attachment protocol to the
Cu(I) catalysed Huisgen 1,3-dipolar cycloaddition ‘click’ reac-
tion between azides and alkynes (see Scheme 6).
Given the mild reaction conditions and typically high
yields, this reaction has gained favour in the synthesis of
supramolecular systems such as catenane and rotaxanes.39–42
Our objective was to attain high loading efficiency of rotaxane
components and a significant proportion of the interlocked
architectures on the bead using this reaction.
The synthesis of azide functionalised TentaGel resins was
achieved via an initial reaction of TentaGel HL-OH beads with
tosyl chloride to generate the tosylated resin 13. This was sub-
sequently reacted with sodium azide to give the desired azide
functionalised beads 14. In both reactions, a large excess of
either tosyl chloride or sodium azide was used in order to
maximise functional group conversion. As a control, the azide
functionalised beads 14 were initially reacted with the mono-
stoppered threads 5 and 9 to give the bipyridinium and
diimide thread functionalised beads 15 and 16 (see Scheme 6).
colour, both rotaxanes are highly coloured (red/pink). This is
attributed to a charge transfer interaction which in the UV can
be seen at 517 nm (ε 1710 M−1 cm−1) and 491 nm (ε 1040 M−1
cm−1) for the bipyridinium rotaxane 11 and the diimide rotax-
ane 12 respectively (see Fig. S1†). This is indicative of the
strong complexation in the mechanically interlocked systems
and has been observed in related bipyridinium-crown and
diimide-crown rotaxanes and catenanes.37,38
1
The partial H NMR spectra of 11 and 12 in CDCl3 are dis-
played in Fig. 2 and S2.† For the bipyridinium rotaxane 11,
significant upfield shifts in the bipyridinium protons a and b
(Δδ = 1.86 ppm and 0.88 ppm respectively), and crown protons
β and γ (Δδ = 0.10 ppm and 0.80 ppm respectively) were
observed due to π–π stacking interactions between the crown
ether macrocycle and bipyridinium thread, indicative of suc-
cessful rotaxane formation (see Fig. 2).
1H NMR analysis of the neutral [2]rotaxane 12 also revealed
significant upfield shifts in both the naphthalene diimide and
macrocycle protons (see Fig. S2†). The naphthalene diimide
proton a is shifted from 8.81 ppm to 8.28 ppm, indicative of
the shielding effect from the aromatic protons in the
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Scheme 6 Synthesis of polymer bound [2]rotaxanes. Reagents and conditions: (i) tosyl chloride, Et3N, DMAP, CH2Cl2, RT, 7 days; (ii) NaN3, H2O, RT, 7 days; (iii) 5,
TBTA, Cu(MeCN)4PF6, CHCl3 : MeOH (95 : 5), RT, 7 days; (iv) 9, TBTA, Cu(MeCN)4PF6, CHCl3 : MeOH (95 : 5), RT, 7 days; (v) 5, 10, TBTA, Cu(MeCN)4PF6, CHCl3 : MeOH
(95 : 5), RT, 7 days; (vi) 9, 10, TBTA, Cu(MeCN)4PF6, CHCl3 : MeOH (95 : 5), RT, 7 days.
Fig. 3 IR spectra of TentaGel-OH beads (blue), azide functionalised TentaGel
beads 14 (red) and diimide thread functionalised beads 16 (green).
Fig. 4 Comparison of the effect of the number of CPMG loops on the quality
of the HR MAS 1H NMR spectrum of 15. Beads were swollen in CDCl3.
IR spectroscopy was used initially to qualitatively monitor
the success of the ‘click’ reaction (see Fig. 3 and S3–S5†). After
conversion of the starting TentaGel-OH beads to the azide
functionalised resin 14, a new peak at 2108 cm−1 was observed
(8.73 ppm) and triazole (7.78 ppm) aromatic peaks for the
diimide functionalised resin 16 visible in the NMR spectra. In
which is characteristic of the N3 moiety.43 Upon ‘click’ reaction
with either the bipyridinium mono stoppered thread 5 or the
diimide mono stoppered thread 9, this resonance disappeared
indicating that the bead functionalisation reaction to give 15
and 16 was successful.
both cases peaks for the tetraphenyl stopper group were
observed at 7.22, 7.08 and 6.72 ppm. Good signal to noise was
achieved when running the basic 1D NMR experiments;
however, for bipyridinium functionalised resins 15, appli-
cation of a standard 32 π-pulse CPMG sequence (used pre-
1H HR MAS NMR analysis of these beads also indicated suc-
cessful attachment of the thread components (see Fig. 4 and
S8†), as evidenced by the expected bipyridinium (8.93 and
8.38 ppm) and triazole (7.68 ppm) aromatic peaks for the
bipyridinium functionalised resin 15, and the diimide
1
viously to improve the quality of the H spectrum by removing
the broad aromatic resonances arising from the polystyrene
bead core) also resulted in the removal of the broad bipyridi-
nium aromatic proton peaks (see Fig. 4). This is due to the fact
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Fig. 5 4× Magnification optical microscope photos of (a) 15, (b) 16, (c) 1, and
(d) 2.
that while the CPMG pulse sequence successfully filters out
any broad resonances due to the bead core, it is an indiscrimi-
nate process and the intensity of signals arising from the
tethered components can also be suppressed, depending on
their relaxation properties. As such, shorter CPMG pulse
sequences with only 8 π-pulses were acquired to identify the
balance between suppression of the bead core resonances
without significantly affecting the proton peaks attributed to
the bipyridinium thread. From these experiments it was clear
that the click reaction was indeed successful in functionalising
the beads with a loading sufficient to record good quality
1H HR MAS NMR spectra.
Fig. 6 HR MAS 1H NMR spectra of bipyridinium rotaxane functionalised beads
1 (top) and solution based bipyridinium rotaxane 11 (bottom) in CDCl3.
The bead functionalisation reaction was then repeated in
the presence of dinaphtho-38-crown-10 10 to generate the
desired rotaxane functionalised beads 1 and 2 (see Scheme 6).
IR spectroscopy revealed that the peak characteristic of the
azide functionality on resin 14 (2108 cm−1) was absent in the
IR spectra for rotaxane functionalised beads 1 and 2 indicating
good bead loading. Visual inspections of the rotaxane functio-
nalised beads 1 and 2 were also promising as unlike the
thread functionalised beads 15 and 16 which were yellow in
appearance, both the rotaxane functionalised beads had a
strong reddish appearance (see Fig. 5). This colouration (which
was also observed in the solution based rotaxanes 11 and 12)
is indicative of donor–acceptor complex formation between
Fig. 7 HR MAS 1H NMR spectra for diimide functionalised beads 16 (top),
diimide rotaxane functionalised beads 2 (middle) and solution based diimide
rotaxane (bottom) in CDCl3.
crown macrocycles and diimide or bipyridinium threads corresponding to unbound diimide appearing at 8.70 ppm,
resulting in this characteristic charge transfer phenomenon.
and those resulting from the complexed rotaxane diimide
Further definitive evidence of rotaxane formation on the appearing upfield at 8.21 ppm (see Fig. 7). In addition, peaks
polymer surface was provided by 1H HR MAS NMR spectro- corresponding to the crown ether aromatic protons were identi-
scopy (see Fig. 6 and 7). For the bipyridinium rotaxane func- fied at 6.81, 6.36 and 5.89 ppm. This clearly indicates that a
tionalised beads 1, two sets of bipyridinium peaks (a and b) mixture of diimide thread and diimide rotaxane were attached
were observed with those belonging to the uncomplexed to the bead, and based on proton integration of the basic 1D
thread appearing at 9.21 and 8.60 ppm, while those indicative NMR spectrum, the percentage of rotaxane was determined to
of rotaxane formation appeared in the upfield position at 8.19 be approximately 20%.
and 6.78 ppm. Likewise peaks for the crown ether macrocycle
Attempts to improve the proportion of interlocked architec-
were observed at 6.78 and 6.56 ppm. Integration of the basic tures on the surface by using an excess of crown 10 (five
1D NMR spectrum suggests that the target bipyridinium rotax- equivalents) were surprisingly unsuccessful. IR and HR MAS
ane species 1 was approximately 40% of the total bead tethered NMR spectroscopy showed a drop in the efficiency of the click
population with the remaining surface functionalised by the reaction as evidenced by the appearance of a residual azide
uncomplexed bipyridinium thread.
peak in the IR at 2108 cm−1, and poor quality HR MAS NMR
For diimide rotaxane functionalised beads 2, again two sets spectra. This is contrary to the solution based control studies
of naphthalene diimide peaks were observed, with those in which increasing the macrocycle concentration had no
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effect on the overall reaction efficiency. Addition of more macrocycle is binding to the polyether tethers in such a way as
copper catalyst did not improve reaction efficiency.
to inhibit the reaction with the diimide or bipyridinium
thread remains unclear. Repeated “click reactions” of these
beads in the presence of excess crown may ultimately lead to
complete bead functionalisation, however more efficient synth-
eses will be the focus of future work. Nevertheless this is a
Conclusion
This study has shown that the Cu(I) catalyzed Huisgen 1,3- clear example of a situation in which solution chemistry has
dipolar cycloaddition or “click” reaction between azides and not been directly transferred to the chemistry of solid sup-
alkynes is an effective reaction for synthesising interlocked ports, therefore highlighting the need to use surfaces and tech-
architectures both in solution and on solid supports. The syn- niques that allow such direct comparison between solution
thesis of mono-stoppered rotaxane thread components was and surface processes. Future work will investigate these obser-
achieved in good yields, and subsequent attempts to syn- vations using dynamic covalent chemistry as a strategy to
thesise rotaxanes in solution proceeded smoothly with inter- increase the percentage of interlocked architectures on these
locked architectures being isolated in yields of 33–36%. These polymer surfaces.
yields are comparable to related literature reports indicating
that the stoppering of one end of each thread had no signifi-
cant effect on its binding to the macrocycle or subsequent
rotaxane formation. Analogous “click” reactions to functiona-
Experimental
lise polymer resins with interlocked architectures were also General considerations
attempted. Initial screening of the azide bead functionalisa-
Unless otherwise stated, reagents were purchased from com-
tion and subsequent reaction with the mono-stoppered
mercial sources and used without further purification. All sol-
diimide or bipyridinium threads was followed using IR
vents were dried before use over type 3 Å or 4 Å molecular
spectroscopy. Clear (qualitative) evidence of the appearance
sieves according to standard procedures. Triethylamine was
and subsequent disappearance of the azide resonance at
dried over KOH. Silica gel column chromatography was carried
out using Merck Silica Gel 60 (grade 9385, 230–400 mesh).
Analytical TLC was carried out on Merck Silica Gel 60 F254 pre-
coated aluminium sheets. Reverse phase chromatography was
carried out using an Agilent SuperFlash C18n (SF 25–55 g)
column.
2108 cm−1 suggested that the click reactions were highly
efficient. 1H HR MAS NMR spectroscopy demonstrated that
the reactions to functionalise the beads with individual stop-
pered thread components were successful with bead loading at
a sufficient level to allow high quality 1H spectra to be
recorded. However, given the inherent broadness in these
Solution NMR spectra were recorded on a Bruker Avance
systems (particularly for the bipyridinium thread) attempts to
400 MHz spectrometer and referenced to the relevant solvent
selectively remove the broad polystyrene resonances also
peak. TentaGel™-HL-OH resins were purchased from Peptides
resulted in the removal of characteristic bipyridinium aromatic
International with a quoted loading of 0.43 mmol g−1 and a
proton peaks. This is due to the non-discriminant nature of
particle size of approximately 90 μm. HR MAS NMR spectra
the CPMG pulse sequences used and thus a careful balance
were acquired on a Bruker DRX400 spectrometer at room
needed to be found such that the quality of the NMR spectra
temperature using a Bruker HR MAS probe. Rotors containing
was improved by removing some of the broadness associated
a suspension of the beads in CDCl3 were spun at 4 kHz. One-
with the polystyrene core without impacting significantly on
dimensional HR MAS spectra were obtained with 64 scans.
the attached thread or rotaxane resonances. When repeating
Unless otherwise stated, the CPMG pulse sequence contained
the bead reactions in the presence of crown, significant pro-
0, 8, 32 or 64 π-pulses with a repetition time of 30 ms.
ESI high-resolution mass spectra were obtained using a
QTOF LC mass spectrometer which utilised electrospray ioniz-
portions of both the bipyridinium rotaxane 1 (40%) and the
diimide rotaxane 2 (20%) were evident in the HR MAS 1H NMR
spectra. Attempts to increase the proportion of rotaxane on the
ation. Melting points were measured on a variable-temperature
bead by using an excess of crown were not successful. In fact
apparatus by the capillary method and are uncorrected. IR
the excess crown impeded the bead functionalisation reaction,
spectra were obtained using a Thermo Nicolet Nexus 870 esp
as evidenced by the residual azide peak in the IR spectrum
spectrometer equipped with a 45° Ge ATR accessory at 4 cm−1
and the poor signal to noise ratios observed in the 1H HR MAS
resolution using 64 scan averaging.
spectra. This is surprising given the fact that the use of excess
Coloured bead images were taken using
a
Leica
crown did not negatively impede the rate of reaction or yield in
our solution control studies. Addition of higher equivalents of
copper catalyst also failed to improve reaction efficiency
suggesting that the poor reaction efficiency is not due to pro-
blems with the copper catalysts (i.e. the excess crown seques-
MZ6 modular stereomicroscope with a Leica CLS 150 light
source and Leica camera mounted at 4× magnification.
Synthetic procedures
tering the copper) as this would have been either observed in The stopper azide 3,37 the bipyridinium alkyne 4,44 the NDI
solution control studies or overcome upon addition of excess alkyne 6,45 and the dinaphtho-38-crown-10 10,46 were
copper to the bead reactions. Whether the excess crown ether synthesised according to literature procedures. Full 1H and
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13C NMR spectra for all key compounds are provided in the ESI chromatography using 100% CHCl3 to 80% CHCl3 : 20% EtOAc
(see Fig. S9–S18†).
as the eluent followed by recrystallisation from CHCl3 and
MeOH to give the pure product as a cream solid (110 mg,
Mono-stoppered BIPY·2PF6 thread (5)
61%); m.p. 275–277 °C; m/z (ESI-MS) [M]+ 876.4587
1
Tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) (0.21 g, C59H60N2O5 (calc. 876.4502); H NMR (400 MHz, CDCl3) δ 8.81
0.40 mmol) and bipyridinium alkyne 4 (2.20 g, 4.0 mmol) and (4H, m, a-H), 7.24 (6H, d, J = 8.0 Hz, Ar-H), 7.10–7.09 (8H, m,
Cu(MeCN)4PF6 (0.15 g, 0.39 mmol) were dissolved in dry Ar-H), 6.75 (2H, d, J = 8.0 Hz, Ar-H), 5.00 (2H, s, CH2), 4.25
acetone (90 mL). Stopper azide 3 (0.61 g, 0.99 mmol) dissolved (2H, t, J = 7.4 Hz, CH2), 3.97 (2H, m, OCH2), 1.85 (2H, m, CH2),
in dry acetone (100 mL) was then added dropwise over a 1.64 (2H, m, CH2), 1.53 (2H, m, CH2), 1.31 (28 H, s, CH and
period of 60 minutes. The reaction mixture was stirred under CH3); 13C NMR (100 MHz, CDCl3) δ 162.7, 162.0, 156.7, 148.2,
argon at room temperature for 48 hours, before the solvent 144.1, 139.4, 132.1, 131.3, 131.0, 130.6, 126.9, 126.7, 126.2,
was removed in vacuo. The crude product was purified by 124.0, 112.8, 77.8, 77.2, 71.2, 67.3, 63.0, 40.8, 34.2, 31.3, 29.8,
RP MPLC using a gradient of 100% H2O to 100% MeCN over 29.0, 27.8, 23.7.
40 min to give the pure product as a pale brown solid
BIPY rotaxane (11)
(0.66 g, 76%); m.p. 246–248 °C; m/z (ESI-MS) [M]2+ 440.2766
C59H70N5O2 (calc. 440.2759); 1H NMR (400 MHz, Acetone-d6) Mono-stoppered BIPY·2PF6 thread 5 (50 mg, 0.057 mmol),
δ 9.44 (4H, d, J = 5.6 Hz, b-H), 8.82 (4H, d, J = 4.0 Hz, a-H), dinaphtho-38-crown-10 (10) (185 mg, 0.29 mmol), TBTA (3 mg,
7.89 (1H, s, c-H), 7.34 (6H, d, J = 8.0 Hz, Ar-H), 7.17–7.13 0.006 mmol) and Cu(MeCN)4PF6 (2 mg, 0.006 mmol) were dis-
(8H, m, Ar-H), 6.83 (2H, d, J = 8.0 Hz, Ar-H), 5.29 (2H, m, CH2), solved in a dry, degassed mixture of 5% MeOH : 95% CHCl3
5.15 (2H, m, CH2), 4.59 (2H, t, J = 5.0 Hz, CH2), 4.08 (5 mL). The stopper azide 3 (35 mg, 0.057 mmol) was then
(2H, t, J = 4.0 Hz, CH2), 3.94 (2H, t, J = 5.0 Hz, OCH2), added and the reaction mixture was stirred under argon at
3.82 (2H, t, J = 4.0 Hz, OCH2), 3.62 (2H, m, CH2), 3.19 room temperature for 4 days. After this time the solvent was
(2H, m, CH2), 2.72 (1H, s, CH), 1.31 (27H, s, CH3); 13C NMR evaporated and the residue purified by column chromato-
(100 MHz, Acetone-d6) δ 156.7, 150.3, 149.9, 148.3, 146.3, graphy using 5% MeOH : 95% CHCl3 as the eluent to give the
144.3, 139.6, 131.9, 130.4, 127.0, 126.9, 124.2, 123.6, 113.2, desired rotaxane as an orange solid (50 mg, 36%);
− 2+
78.1, 74.1, 69.2, 69.1, 67.1, 63.0, 61.3, 60.1, 49.7, 33.9, 30.7, m.p. 223–225 °C; m/z (ESI-MS) [M − PF6
29.5, 26.9, 20.7.
]
1066.6174
C
136H164F12N8O14P2 (calc. 1066.6184); 1H NMR (400 MHz,
CDCl3) δ 8.56 (4H, d, J = 8.0 Hz, b-H), 7.98 (2H, s, c-H), 7.21
(12H, d, J = 8.0 Hz, Ar-H), 7.11–7.00 (24H, m, γ-H, Ar-H and
Unsymmetrical NDI thread (8)
Naphthalene-1,4,5,8-tetracarboxylic acid dianhydride (490 mg, β-H), 6.96 (4H, d, J = 8.0 Hz, a-H), 6.79 (4H, d, J = 8.0 Hz, Ar-H),
1.8 mmol) was dissolved in dry, degassed DMF (2 mL). A solu- 6.51 (4H, d, J = 7.9 Hz, α-H), 5.01 (4H, m, CH2), 4.62 (4H, t, J =
tion of 5-amino-1-pentanol (200 mg, 1.9 mmol) and propargyl 4.0 Hz, CH2), 4.12 (4H, m, OCH2), 3.99 (2H, m, OCH2),
amine (200 mg, 1.9 mmol) dissolved in dry, degassed DMF 3.92–3.87 (36H, m, OCH2), 3.53 (4H, m, CH2), 1.30 (54H, s,
(3 mL) was added dropwise under argon. The reaction mixture CH3); 13C NMR (100 MHz, CDCl3) δ 156.3, 153.0, 148.2, 144.4,
was stirred under argon at 120 °C for 2 hours. The solvent was 144.0, 143.9, 141.2, 139.8, 132.2, 130.6, 126.0, 125.3, 124.0,
evaporated to yield a crude purple solid which was purified by 123.9, 123.5, 113.7, 113.0, 105.8, 77.2, 71.1, 71.0, 70.1, 69.6,
column chromatography using 20% EtOAc : 80% DCM as the 69.3, 67.9, 67.2, 63.0, 60.5, 50.2, 34.2, 31.3, 27.3.
eluent to give the pure product as a cream solid (230 mg,
NDI rotaxane (12)
32%); m.p. 206–208 °C; m/z (ESI-MS) [M]+ 390.1247
1
C22H18N2O5 (calc. 390.1215); H NMR (400 MHz, CDCl3) δ 8.81 Mono-stoppered NDI thread 9 (50 mg, 0.055 mmol) and
(4H, m, a-H), 5.00 (2H, s, CH2), 4.24 (2H, t, J = 7.4 Hz, CH2), dinaphtho-38-crown-10 (10) (180 mg, 0.28 mmol) were dis-
3.69 (2H, m, CH2), 2.25 (1H, s, OH), 1.81 (2H, m, CH2), 1.68 solved in a dry, degassed mixture of 5% MeOH : 95% CHCl3
(2H, m, CH2), 1.55 (2H, m, CH2), 1.31 (1H, s, CH); 13C NMR (6 mL). A solution of Cu(MeCN)4PF6 (2 mg, 0.006 mmol) and
(100 MHz, CDCl3) δ 162.7, 162.0, 131.3, 131.0, 126.9, 126.7, TBTA (3 mg, 0.006 mmol) dissolved in a dry, degassed mixture
126.2, 77.8, 77.2, 71.2, 62.7, 40.8, 32.3, 29.8, 27.8, 23.2.
of 5% MeOH : 95% CHCl3 (0.2 mL) was added to the reaction
mixture, followed by a solution of stopper azide 3 (34 mg,
0.056 mmol) dissolved in dry, degassed 5% MeOH : 95%
Mono-stoppered NDI thread (9)
Unsymmetrical NDI thread 8 (80 mg, 0.21 mmol), 4-(tris- CHCl3 (0.6 mL). The reaction mixture was then stirred under
(4-(tert-butyl)phenyl)methyl)phenol36 (103 mg, 0.21 mmol) argon at room temperature for 4 days. After this time the
and PPh3 (82 mg, 0.31 mmol) were dissolved in dry, degassed solvent was evaporated and the crude material was purified by
CHCl3 (8 mL). Di-tert-butyl azodicarboxylate (105 mg, column chromatography using 50% EtOAc : 50% hexane to
0.46 mmol) in dry, degassed CHCl3 (3 mL) was then added 100% EtOAc as the eluent to give the desired rotaxane as a red
dropwise at 0 °C and the reaction mixture was left to stir under solid (39 mg, 33%); m.p. 166–168 °C; m/z (ESI-MS) [M]+
1
argon at room temperature for 50 hours. The reaction mixture C136H155N5O7 2130.1467 (calc. 2130.1418); H NMR (400 MHz,
then was filtered through a short plug of silica and the filtrate CDCl3)) δ 8.28 (4H, m, a-H), 8.09 (1H, s, c-H), 7.23 (12H, d, J =
evaporated. The crude material was purified by column 8.0 Hz, Ar-H), 7.09–7.06 (16H, m, Ar-H), 6.84–6.80 (6H, m, γ-H
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and Ar-H), 6.73 (2H, d, J = 8.0 Hz, Ar-H), 6.43 (4H, m, β-H), MeOH : 95% CHCl3 (1 mL) was then added to the beads, and
5.98 (4H, m, α-H), 5.41 (2H, s, CH2), 4.64 (4H, m, CH2), 4.08 the reaction mixture was kept under argon at room tempera-
(4H, m, OCH2), 4.00 (12H, m, OCH2), 3.91–3.86 (26H, m, ture for 7 days. The beads were collected by filtration and
OCH2), 3.77 (4H, m, OCH2), 2.05–1.94 (4H, m, CH2), 1.31 (54H, washed with CHCl3 (10 mL), acetone (10 mL), water (10 mL),
s, CH3); 13C NMR (100 MHz, CDCl3) δ 162.9, 162.6, 156.8, sat. NH4Cl (10 mL), CH2Cl2 (10 mL), and hexane (10 mL) to
1
156.2, 154.1, 152.8, 148.2, 148.2, 144.1, 144.0, 139.8, 139.4, give the pale yellow diimide functionalised beads. H HR MAS
132.2, 130.6, 130.6, 130.4, 126.5, 124.9, 124.6, 124.0, 123.9, NMR (400 MHz, CDCl3) δ 8.73 (4H, m, a-H), 7.78 (1H, br s,
123.4, 114.4, 114.0, 112.9, 112.9, 105.4, 103.3, 71.3, 71.1, 70.9, c-H), 7.22 (6H, br m, Ar-H), 7.08 (8H, br m, Ar-H), 6.72 (2H, m,
69.8, 69.7, 67.7, 67.2, 66.8, 62.9, 34.2, 34.2, 33.8, 31.8, 31.3, Ar-H), 5.50 (2H, br s, CH2), 4.50 (2H, br m, CH2), 4.21 (2H, m,
29.6, 29.4, 29.3, 29.2, 29.1, 27.8, 24.1, 22.6, 14.1.
OCH2), 2.75 (2H, m, CH2), 1.63 (4H, m, CH2), 1.29 (27 H, s,
CH3).
Tosyl functionalised TentaGel resins (13)
Bead tethered bipyridinium rotaxane (1)
Under argon TentaGel-OH beads (103 mg, 0.43 mmol g−1 OH
loading), tosyl chloride (103 mg, 0.54 mmol) and a catalytic A solution of mono-stoppered BIPY·2PF6 thread (254 mg,
amount of 4-dimethylaminopyridine were suspended in dry 0.29 mmol) and dinaphtho-38-crown-10 (10) (915 mg,
DCM (3 mL). To this mixture Et3N (100 μL) was added and the 1.4 mmol) dissolved in dry, degassed 5% MeOH : 95% CHCl3
reaction was left for one week with occasional stirring. After (3 mL) was added to a round bottomed flask containing the
this time the beads were filtered and washed sequentially with azide functionalised TentaGel resin 14 (49 mg) under argon.
DCM and hexane several times (5 × 5 mL each), followed by a TBTA (15 mg, 0.029 mmol) and Cu(MeCN)4PF6 (10 mg,
final wash with acetone (5 mL), water (5 mL) and acetone 0.028 mmol) dissolved in dry, degassed 5% MeOH : 95%
(5 mL). The resulting off white beads were dried in vacuo.
CHCl3 (0.5 mL) were then added and the reaction mixture was
kept under argon at room temperature for 7 days. The beads
were collected by filtration and washed with acetone (10 mL),
Azide functionalised TentaGel resins (14)
The tosyl functionalised TentaGel beads 13 were suspended in water (10 mL), sat. NH4Cl (10 mL), CH2Cl2 (10 mL), and
water (3 mL) and sodium azide (351 mg, 5.4 mmol) was then hexane (10 mL). The resulting orange beads were dried
1
added. The reaction was left for one week with occasional stir- in vacuo. H HR MAS NMR (400 MHz, CDCl3) δ 9.21 (m, b-H),
ring, before the beads were filtered, washed with water (10 × 8.60 (m, a-H), 8.19 (m, b-H), 7.68 (br s, c-H), 7.22 (m, Ar-H),
5 mL), acetone (5 mL) and sequential rinsing with DCM and 7.08 (m, γ-H and Ar-H), 6.78 (m, a-H), 6.70 (m, Ar-H), 6.56 (m,
hexane (5 × 5 mL each). The off white beads were then dried α-H), 5.15 (m, CH2), 4.61 (m, CH2), 4.48 (m, CH2), 4.19 (m,
in vacuo.
CH2), 4.00 (m, CH2), 3.96 (m, CH2), 3.85 (m, OCH2), 3.50 (m,
OCH2), 3.40 (m, OCH2), 2.83 (m, CH2), 2.25 (m, CH2), 1.30 (s,
CH3). Note: The characteristic crown-complexed proton peak
Bipyridinium functionalised TentaGel resins (15)
A solution of mono-stoppered BIPY·2PF6 thread 5 (250 mg, assignments are highlighted in bold.
0.28 mmol) dissolved in dry, degassed acetone (2 mL) was
added to a round bottomed flask containing the azide functio-
Bead tethered naphthalene diimide rotaxane (2)
nalised TentaGel resins 14 (40 mg) under argon. TBTA (15 mg,
A
solution of mono-stoppered NDI thread (250 mg,
0.029 mmol) and Cu(MeCN)4PF6 (10 mg, 0.029 mmol) dis- 0.29 mmol) and dinaphtho-38-crown-10 (10) (907 mg,
solved in dry, degassed acetone (1 mL) was then added to the 1.4 mmol) dissolved in dry, degassed 5% MeOH : 95% CHCl3
beads and the reaction was kept under argon at room tempera- (4 mL) was added to a round bottomed flask containing the
ture for 7 days. The beads were collected by filtration and azide functionalised TentaGel resin 14 (52 mg) under argon.
washed with acetone (10 mL), water (10 mL), sat. NH4Cl TBTA (15 mg, 0.029 mmol) and Cu(MeCN)4PF6 (10 mg,
(10 mL), CH2Cl2 (10 mL), and hexane (10 mL). The off white 0.029 mmol) dissolved in dry, degassed 5% MeOH : 95%
beads were then dried under vacuum. 1H HR MAS NMR CHCl3 (0.5 mL) were then added and the reaction mixture was
(400 MHz, CDCl3) δ 8.93 (4H, br m, b-H), 8.38 (4H, br m, a-H), kept under argon at room temperature for 7 days. The beads
7.68 (2H, br s, c-H), 7.22–7.20 (6H, m, Ar-H), 7.08–7.06 (8H, m, were collected by filtration and washed with CHCl3 (10 mL),
Ar-H), 6.72–6.70 (2H, m, Ar-H), 5.01 (2H, br m, CH2), 4.47 (4H, acetone (10 mL), water (10 mL), sat. NH4Cl (10 mL), CH2Cl2
br m, CH2), 4.02 (2H, br m, CH2), 3.88 (2H, m, OCH2), 3.76 (10 mL), and hexane (10 mL). The resulting red beads were
(4H, br m, OCH2), 2.74 (2H, m, CH2), 1.29 (27H, s, CH3).
dried under vacuum. 1H HR MAS NMR (400 MHz, CDCl3)
δ 8.70 (m, a-H), 8.21 (m, a-H), 7.78 (br s, c-H), 7.22 (br m, Ar-H),
7.08 (br m, Ar-H), 6.81 (m, γ-H), 6.73 (m, Ar-H), 6.36 (m, β-H),
Diimide Functionalised TentaGel resins (16)
A
solution of mono-stoppered NDI thread 9 (253 mg, 5.89 (m, α-H), 5.50 (br m, CH2), 5.15 (m, CH2), 4.66 (m, CH2),
0.29 mmol) dissolved in dry, degassed 5% MeOH : 95% CHCl3 4.51 (m, CH2), 4.20 (m, OCH2), 4.07 (m, CH2), 3.93 (m, OCH2),
(2 mL) was added to a round bottomed flask containing the 3.84 (m, OCH2), 3.47 (m, OCH2), 3.33 (m, OCH2), 2.76 (m,
azide functionalised TentaGel resins 14 (53 mg) under argon. CH2), 2.30 (m, CH2), 1.60 (m, CH2), 1.29 (s, CH3). Note: the
A solution of TBTA (15 mg, 0.029 mmol) and Cu(MeCN)4PF6 characteristic crown-complexed proton peak assignments are
(10 mg, 0.029 mmol) dissolved in dry, degassed 5% highlighted in bold.
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Organic & Biomolecular Chemistry
18 F. Cecchet, P. Rudolf, S. Rapino, M. Margotti, F. Paolucci,
J. Baggerman, A. M. Brouwer, E. R. Kay, J. K. Y. Wong and
D. A. Leigh, J. Phys. Chem. B, 2004, 108, 15192–15199.
19 H. Imahori, H. Yamada, S. Ozawa, K. Ushida and Y. Sakata,
Chem. Commun., 1999, 1165–1166.
Acknowledgements
This work was supported by the Australian Research Council.
20 S. S. Jang, Y. H. Jang, Y. H. Kim, W. A. Goddard,
A. H. Flood, B. W. Laursen, H. R. Tseng, J. F. Stoddart,
J. O. Jeppesen, J. W. Choi, D. W. Steuerman, E. DeIonno
and J. R. Heath, J. Am. Chem. Soc., 2005, 127, 1563–1575.
21 E. Menozzi, R. Pinalli, E. A. Speets, B. J. Ravoo,
E. Dalcanale and D. N. Reinhoudt, Chem.–Eur. J., 2004, 10,
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