Dynamic covalent synthesis of donor-acceptor interlocked architectures in solution and at the solution: Surface interface

Article abstract of DOI:10.1002/asia.201403288

Despite advances in the range of mechanically interlocked architectures that can be synthesized and operated as supramolecular machines, motors and sensors in solution, in many cases their synthesis is laborious and expensive requiring long multistep pathways with extensive purification at each stage. Dynamic covalent chemistry has been shown to overcome problems with traditional kinetically controlled synthetic approaches that often afford low yields of interlocked architectures due to irreversible formation of non-interlocked by-products. Herein, we describe the use of reversible disulfide exchange reactions as a means to assemble catenanes and rotaxanes in organic solutions. Moreover, the application of this thermodynamic approach to assemble interlocked architectures at the solution:surface interface, specifically polymer resins, is discussed.

Full text of DOI:10.1002/asia.201403288

DOI: 10.1002/asia.201403288
Full Paper
Supramolecular Chemistry
Dynamic Covalent Synthesis of Donor–Acceptor Interlocked
Architectures in Solution and at the Solution:Surface Interface
[
a]
Hannah Wilson, Sean Byrne, and Kathleen M. Mullen*
Abstract: Despite advances in the range of mechanically in-
terlocked architectures that can be synthesized and operat-
ed as supramolecular machines, motors and sensors in solu-
tion, in many cases their synthesis is laborious and expensive
requiring long multistep pathways with extensive purifica-
tion at each stage. Dynamic covalent chemistry has been
shown to overcome problems with traditional kinetically
controlled synthetic approaches that often afford low yields
of interlocked architectures due to irreversible formation of
non-interlocked by-products. Herein, we describe the use of
reversible disulfide exchange reactions as a means to assem-
ble catenanes and rotaxanes in organic solutions. Moreover,
the application of this thermodynamic approach to assem-
ble interlocked architectures at the solution:surface inter-
face, specifically polymer resins, is discussed.
Introduction
cleophilic substitution, and olefin metathesis reactions, have
been used to prepare mechanically interlocked compounds in
[12,14,16–20]
Significant developments in fundamental supramolecular con-
high yields;
however, the work described herein ex-
[
1,2]
[3]
cepts such as self-assembly,
self-organisation, molecular
ploits disulfide exchange in the dynamic covalent assembly of
catenanes and rotaxanes. Research undertaken by Sanders
et al. have demonstrated the success of such an approach by
synthesizing a range of electron-rich 1,5-dialkoxynaphthalene
and electron-deficient 1,4,5,8-naphthalene tetracarboxylic dii-
[
2,4]
[5]
recognition,
and template-directed synthesis, have un-
locked access to increasingly elaborate interlocked architec-
[
6,7]
[8]
[9]
tures including knots,
suitanes, Borromean rings, and
[
10]
ravels.
With increased topological complexity, however,
[16,18,21,22]
[7]
comes synthetic challenges, and traditional kinetically con-
trolled synthetic approaches prove problematic due to the po-
tential formation of kinetic by-products that decrease the over-
all reaction efficiency. For example, in a clipping protocol for
mide catenanes
and even a trefoil knot via disulfide
exchange from simple building blocks.
This work aims to extend previous research by investigating
the use of disulfide exchange as a means of synthesizing not
only donor–acceptor catenanes but also rotaxanes, with the ul-
timate view of implementing this approach at the solution:sur-
face interface. The dithiol building blocks chosen for investiga-
tion in this work are the p-electron-rich 1,5-dialkoxynaphtha-
lene 1 and the zinc-metallated porphyrin 2 as well as the p-
electron-deficient naphthalene diimide 3 (Figure 1). The poten-
tial for the addition of dinaphtho-[38]-crown-10 ether macrocy-
cles 4 or naphthalene diimide dumbbell 5 components to
direct the dynamic covalent assembly of interlocked architec-
tures will be discussed (Scheme 1).
[2]rotaxane synthesis, the free macrocycle can form in addition
to the desired rotaxane, thus reducing the yield of interlocked
[
11,12]
products.
If, however, reversible or dynamic bonds are
used in the macrocycle formation, any non-interlocked macro-
cycle produced can reopen and reassemble around the dumb-
[13]
bell, thereby introducing a “proof-reading” mechanism. As
mechanically interlocked molecules are typically lower in free
energy than their non-interlocked counterparts, increased
[11,13,14]
yields of interlocked architectures are often observed.
The energetic bias towards interlocked architectures renders
dynamic covalent chemistry—the chemistry of thermodynami-
cally controlled bond formation—a powerful tool in the crea-
Results and Discussion
[
15]
tion of mechanical bonds.
Numerous reversible covalent
bond forming reactions, including imine, acetal, hydrazone,
and ester formation as well as Aldol, Diels–Alder, Michael, nu-
Synthesis of Dithiol Building Blocks. The synthesis of the bis-
thioacetate protected 1,5-dialkoxynaphthalene SAc-1 and the
bis-benzylthioacetate protected zinc porphyrin SAc-2 were car-
[23,24]
[
a] H. Wilson, S. Byrne, Dr. K. M. Mullen
School of Chemistry, Physics and Mechanical Engineering
Queensland University of Technology
ried out according to literature procedures.
Thioacetate
protected naphthalene diimide SAc-3 was synthesised straight-
forwardly according to Scheme 2. A solution of 2-(2-amino-
ethoxy)ethanol and 1,4,5,8-napthalenetetracarboxylic dianhy-
dride in DMF was refluxed overnight to afford the pure bis-al-
cohol 6. This was subsequently reacted with tosyl chloride to
Brisbane, Queensland, 4001 (Australia)
E-mail: kathleen.mullen@qut.edu.au
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/asia.201403288.
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Scheme 2. Synthesis of bis-thioacetate naphthalene diimide SAc-3. Reagents
and conditions: (i) DMF, 908C, argon, 18 h, 84%; (ii) TsCl, TEA, DMAP, CH Cl ,
2 2
RT, 3 days, 88%; (iii) KSAc, DMF, RT, 62 h, 95%.
Figure 1. Building blocks chosen for investigation in dynamic covalent syn-
thesis of mechanically interlocked architectures.
Scheme 3. Synthesis of 1,5-dialkoxynaphthalene thiol building block 1 with
sodium methoxide. Reagents and conditions: (i) NaOMe, CH
argon, RT.
2 2
Cl /MeOH (1:1),
the yields were compromised by concomitant decomposition.
Consequently, the reaction conditions had to be optimized for
each building block to ensure complete deprotection whilst
minimizing monomer decomposition. A summary of the opti-
mal reaction conditions determined for each building block by
1
monitoring the deprotection reactions by H NMR spectrosco-
py is outlined in Table 1.
Table 1. Optimized conditions for deprotection of thioacetate precursors
to dithiols 1–3.
Scheme 1. Cartoon representation of dynamic covalent synthesis of inter-
locked architectures from dithiol building blocks and preformed dumbbell
components.
Dithiol
NaOMe [equiv]
Reaction Time
Yield
1
2
3
8.0
6.0
8.0
5 min
10 min
10 min
89%
88%
57%
afford the tosylate derivative 7 which was then reacted with
potassium thioacetate to give the desired bis-thioacetate di-
imide SAc-3 in 95% yield.
[
23,25]
Initial attempts following literature reports
to deprotect
Control Studies. Having synthesized the dithiol building
blocks 1–3, our attention turned to optimization of disulfide
exchange in organic solvents. In order to better understand
the conditions required to promote disulfide exchange, and
thus replicate literature reports, a series of disulfide-exchange
experiments examining the effect of concentration of both
building blocks and base were investigated. A balance be-
tween reaching equilibrium in reasonable time frames (ideally
3–4 days) by increasing the concentration of DBU, without re-
sulting in the decomposition of the thiol building blocks, was
needed. In general, the optimal balance was achieved by air
the bis-thioacetate precursors SAc-1, SAc-2 and SAc-3 using
hydrazine monohydrate were unsuccessful, with incomplete
deprotection of the thioacetate being observed. A more effi-
cient strategy using sodium methoxide and Zemplꢁn deacety-
[
20,26]
lation conditions was adopted.
In this approach, a solution
of sodium methoxide in dry degassed methanol was added to
the bis-thioacetate dissolved in dry, degassed CH Cl , and the
2
2
reaction was stirred at room temperature (Scheme 3). Whilst
this method proved to be far more efficient, with complete de-
protection occurring within 5–15 min for each building block,
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oxidation of a 5 mm solution of dithiol (1–3) in the presence of
corporating either p-rich crown ether macrocycle 4 or p-defi-
cient naphthalene diimide dumbbell 5 in disulfide libraries in
an effort to synthesize donor–acceptor interlocked architec-
tures. Firstly, solutions containing the p-rich aromatic crown
ether 4 with diimide 3 were examined as it was envisaged that
p-donor/acceptor interactions between diimide 3 and crown 4
could direct the assembly of the [2]catenane 11 (Scheme 4).
1
equivalent of DBU (see Figure S1, Supporting Information).
These conditions were then applied to more complex libra-
ries involving two or three dithiol building blocks. It was envi-
sioned that p-donor/acceptor interactions between these
motifs would direct the assembly of donor–acceptor macrocy-
cles and potentially catenanes, as has been reported in aque-
[
16,17,21]
ous studies (see Scheme S2, Supporting Information).
Li-
braries were set up using the optimized conditions of equimo-
lar solutions of 1 and 3 (5 mm) in CHCl in the presence of
3
1
equivalent of DBU. A gradual color change from pale yellow
to pink was observed in this library, indicative of donor–ac-
ceptor intermolecular interactions between the diimide and
naphthyl motifs. Thermodynamic equilibrium was achieved
after 21 days, and the HPLC analysis indicated that the major
product of the library was the cyclic heterodimer 8 (90%), with
proportions of the cyclic naphthyl dimer 9 (7%) also being ob-
served (Figure 2). The presence of the molecular ion adduct at
Scheme 4. Dynamic covalent synthesis of [2]catenane 11. Reagents and con-
ditions: (i) 1 equiv DBU, CHCl , air, RT, 14 days.
3
In these studies, 1 equivalent of DBU was added to a 2:1
mixture of diimide 3 and crown 4 (5 mm total concentration),
and the library was then monitored daily by reverse-phase
HPLC using 100% MeOH isocratic mobile phase. During its
equilibration, the solution turned intense red, which is indica-
tive of strong complexation between the electron-deficient di-
imide and electron-rich naphthalene motifs in mechanically in-
terlocked assemblies. HPLC analysis indicated that while the
[
2]pseudorotaxane complex dominated, the [2]catenane 11
was produced in a 20% yield (Figure 3). The identity of [2]cate-
nane 11 was confirmed by LC-MS analysis with peaks observed
+
+
at m/z=1603.4288 [M+Na] and 1619.4034 [M+K] .
Figure 2. Comparison of HPLC traces of equilibrating mixtures of one or two
dithiol building blocks: (a) RP-HPLC trace of 5 mm of 1 with 1 equiv DBU,
(
b) RP-HPLC trace of 5 mm of 3 with 1 equiv DBU, (c) RP-HPLC trace of 5 mm
of 1 and 3 with 1 equiv DBU, and (d) NP-HPLC trace of 5 mm of 1+3 with
equiv DBU. Absorbance was recorded at 383 nm for (b) and at 292 nm for
a), (c) and (d).
1
(
Figure 3. Reverse-phase HPLC trace of 5 mm library generated from 3 and 4.
Absorbance was monitored at 292 nm.
+
m/z=861.1601 [M+Na] in the LC-MS confirmed the identity
of heterodimer 8. Smaller amounts of the cyclic naphthyl
trimer (<2%) were observed; however, no traces of donor–ac-
ceptor catenane species were detected in this library. Similarly,
the mixed heterodimer was the dominant species in libraries
containing porphyrin dithiol 2 and naphthoquinol thiol 1 (see
Figure S2).
A second directed library incorporating the electron-defi-
cient dumbbell 5 and the electron-rich 1,5-dialkoxynaphtha-
lene 1 was investigated. It was anticipated that p–donor–ac-
ceptor interactions would direct the cyclization of dimer 9
around dumbbell 5 to afford [2]rotaxane 12 (Scheme 5). Identi-
cal conditions to those described in the [2]catenane synthesis
mentioned above were used.
Dynamic Covalent Synthesis of Interlocked Architectures.
Having investigated the assembly of simple donor–acceptor
macrocycles via disulfide exchange, our attention turned to in-
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Scheme 5. Dynamic covalent synthesis of [2]rotaxane 12. Reagents and con-
ditions: (i) 1 equiv DBU, CHCl , air, RT, 14 days.
3
Pleasingly, over time a color change from pale yellow to
dark pink was observed, suggesting donor–acceptor interac-
tion between the diimide and naphthoquinone motifs. HPLC
analysis revealed the gradual formation of [2]rotaxane 12,
which was confirmed by LC-MS analysis with a mass peak ob-
Scheme 6. Dynamic covalent synthesis of [2]rotaxane 13. Reagents and con-
ditions: (i) 1 equiv DBU, CHCl , air, RT, 14 days.
3
+
served at m/z=2332.0458 [M+Na] . The equilibrium composi-
using the optimized conditions described above. In both cases
the reaction mixtures were allowed to equilibrate for 14 days
and, following purification by column chromatography, the de-
sired [2]catenane 11 and [2] rotaxane 12 were isolated in 21%
and 22% yields, respectively.
tion of this mixture was reached after 14 days, and contained
[
2]rotaxane 12 (22%) as well as non-interlocked compounds,
namely linear dimer (5%), cyclic dimer 9 (34%), cyclic trimer
0 (4%), and diimide dumbbell 5 (27%), in smaller proportions
Figure 4).
1
(
Figure 4. Reverse-phase HPLC trace of library produced by mixing 1 and 5.
Absorbance was monitored at 292 nm.
1
Figure 5. Aromatic region of the H NMR spectra of naphthalene diimide 3
Attempts to prepare porphyrin-containing [2]rotaxanes via
disulfide exchange were also undertaken. It was anticipated
that p–p interactions between diimide and porphyrin motifs
and p-donor/acceptor recognition between naphthalene and
diimide units could be simultaneously exploited to direct the
assembly of heterodimer 14 around diimide dumbbell 5 to
afford [2]rotaxane 13 (Scheme 6); however, no evidence of ro-
taxane was observed when employing the optimized disulfide
exchange conditions. After 3 days, thermodynamic equilibrium
was reached, and the heterodimer 14 (84%) was found to be
the major constituent with smaller amounts of porphyrin
homodimer 15 (9%) and naphthalene homodimer 9 (6%) also
present.
(
top), [2]catenane 11 (middle), and dinaphth-[38]-crown-10 4 (bottom) in
CDCl at 303 K.
3
1
The partial H NMR spectra of [2]catenane 11 in CDCl are
3
1
displayed in Figure 5. In the H NMR spectrum of the [2]cate-
nane 11, the aromatic naphthalene diimide proton a appears
shifted upfield as a broad singlet at d 8.63 ppm as compared
to d 8.78 ppm in the uncomplexed diimide 3. Likewise, the ar-
omatic protons a, b, and g of crown 4 are also shifted upfield.
Moreover, the doublet-triplet-doublet pattern that arises from
coupling of aromatic protons in the 1,5-substituted naphtha-
lene system is noticeably doubled in each case, thereby dem-
onstrating that the symmetry of the crown ether ring is broken
by catenation with the diimide ring, as has been previously re-
Large-Scale Preparation and Characterization of Disulfide-
Linked Interlocked Architectures. Preparative scale synthesis
of [2]catenane 11 and [2]rotaxane 12 was then attempted
[27]
ported in related systems.
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covalent chemistry in the construction of interlocked architec-
tures in solution, the effectiveness of such an approach at the
solution:surface interface remains unexplored. It was hoped
that addition of naphthalene diimide thread functionalized
beads 16 to a solution of 1,5-dialkoxynaphthalene 1 under the
conditions of disulfide exchange would result in the self-as-
sembly of disulfide-linked bead-tethered [2]rotaxane 17
(
Scheme 7).
1
Figure 6. Aromatic region of the H NMR spectra of naphthalene diimide
dumbbell 5 (top), [2]rotaxane 12 (middle), and 1,5-dialkoxynaphthalene
1
(bottom) in CDCl
3
at 303 K.
1
Similarly, in the H NMR spectrum of the naphthalene dii-
mide [2]rotaxane 12, the diimide proton a was shifted upfield
from d 8.74 ppm to d 8.54 ppm as a result of the shielding
effect from the aromatic naphthalene protons (Figure 6). Up-
field shifts of 0.15 ppm, 0.14 ppm, and 0.29 ppm were also ob-
served for the naphthalene aromatic protons a, b, and g, re-
spectively, in comparison to the spectrum of 1,5-dialkoxynaph-
thalene 1. These substantial changes in chemical shifts are
characteristic of the interlocked nature of this architecture, and
correlate with analogous [2]rotaxanes reported in the litera-
Scheme 7. Dynamic synthesis of disulfide-linked naphthalene diimide [2]ro-
taxane 17. Reagents and conditions: (i) 1 equiv DBU, CHCl , air, RT, 14 days.
3
Naphthalene diimide functionalized beads 16 (1 equiv) were
added to a solution of 1,5-dialkoxynaphthalene dithiol 2.1
[
28]
ture.
(2 equiv) in CHCl , and disulfide exchange was initiated by the
3
In contrast to the non-interlocked counterparts which are all
pale yellow or cream in color, both [2]catenane 11 and [2]ro-
taxane 12 possess a vibrant red color. This intense coloration is
evidenced by broad absorption bands in the UV/Vis spectra at
addition of DBU (1 equiv). The reaction was left to stir at ambi-
ent conditions for 14 days to ensure that thermodynamic equi-
librium was reached. After this time the beads were washed
extensively to remove any untethered library components.
Pleasingly, visual inspections of beads 17 showed that, in con-
trast to the yellow thread functionalized resins 16, the rotax-
ane functionalized beads 17 had a distinct red color (Figure S4,
Supporting Information). This red coloration is indicative of
a charge-transfer phenomenon between the p-rich dialkoxy-
naphthalene motifs of the macrocycle and the p-deficient
naphthalene diimide motif in the thread, and has been seen in
À1
À1
5
06 nm (e=1100m cm ) for 11 and at 525 nm for 12 (e=
030m cm ), thereby reflecting strong complexation in the
À1
À1
1
interlocked architectures (Figure S3). Similar charge-transfer
bands have been observed in related crown-diimide catenane
[
28,29]
and rotaxane systems.
Dynamic Covalent Synthesis of a Resin-Tethered Naphtha-
lene Diimide [2]Rotaxane. Given the successful synthesis of
a rotaxane and a catenane using disulfide exchange in solu-
tion, investigations into whether disulfide exchange could be
used to assemble interlocked architectures at the solution–sur-
face interface were carried out. We have previously reported
the controlled self-assembly of rotaxane and pseudorotaxane
[28,30,31]
related solution and surface-bound rotaxanes.
This quali-
tatively suggests at least some rotaxane assembly at the bead–
solvent interface.
1
H HR-MAS NMR analysis indicated that rotaxane formation
had occurred on the surface as evidenced by the diimide peak
at 8.03 ppm; however, peaks for the macrocycle napthoqui-
none protons were obscured under the bead and stopper aro-
matic protons (see Figure 7). The bound diimide proton chemi-
cal shift is consistent with that seen in related surface-bound
[
30,31]
systems on polystyrene TentaGel resins.
This work high-
lighted two important issues; firstly, surface functionalization
using kinetically controlled bond formation can result in mix-
tures of the desired interlocked and undesired non-interlocked
products on the surface, and secondly, the dynamic behavior
of supramolecular architectures deposited on surfaces is not
always directly comparable to that observed in solution, high-
lighting the importance of using characterization tools such as
[30,31]
diimide-containing rotaxanes.
Nevertheless, it is clear that
significant amounts of uncomplexed diimide thread remain on
the surface, and future work will look at optimizing reaction
conditions to favor the formation of interlocked architectures
at the solution:surface interface.
1
H HR-MAS NMR spectroscopy. Despite the success of dynamic
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rification. All solvents were dried before use over type 3 ꢂ or 4 ꢂ
molecular sieves according to standard procedures. 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 Super-
Flash C18n (SF 25–55 g) column.
Solution NMR spectra were recorded on a Bruker Avance 400 MHz
spectrometer and referenced to the relevant solvent peak. Tenta-
Gel-HL-OH resins were purchased from Peptides International with
À1
a quoted loading of 0.43 mmolg and a particle size of approxi-
mately 90 mm. HR MAS-NMR spectra were acquired on a Bruker
DRX400 spectrometer at room temperature using a Bruker HR-MAS
1
Figure 7. Aromatic region of the H HR-MAS NMR spectra of the rotaxane-
functionalized beads 17 (top) and naphthalene diimide tether beads 16
probe. Rotors containing a suspension of the beads in CDCl were
3
3
(bottom) in CDCl at 303 K.
spun at 4 kHz. One-dimensional HR-MAS spectra were obtained
with 64 scans. Unless otherwise stated, the CPMG pulse sequence
contained 0, 8, 32 or 64 p-pulses with a repetition time of 30 ms.
Conclusions
ESI high-resolution mass spectra were obtained using a QTOF LC
mass spectrometer which utilized electrospray ionization. Melting
points were measured on a variable-temperature apparatus by the
capillary method and are uncorrected. IR spectra were obtained
using a Thermo Nicolet Nexus 870 esp spectrometer equipped
Disulfide exchange has been shown to be an effective synthet-
ic route for the synthesis of interlocked architectures both in
solution and at the solution:surface interface. Starting with rel-
atively simple dialkoxynaphthalene, diimide, and porphyrin
thiol building blocks, their disulfide exchange reactions were
explored in organic solutions. Reaction conditions were opti-
mized to find the balance between reaching thermodynamic
equilibrium in reasonable timeframes (up to 21 days) without
concomitant decomposition. As the intermolecular interactions
between naphthalene diimide and dialkoxynaphthalene build-
ing blocks are weaker in organic solvents, due to the absence
of any favorable hydrophobic effects, no interlocked architec-
tures were isolated when using only mixtures of 1, 2 or 3. Ad-
dition of dinaphthocrown ether 4 or diimide stoppered thread
À1
with a 458 Ge ATR accessory at 4 cm resolution using 64 scan
averaging.
Colored bead images were taken using a Leica MZ6 modular ster-
eomicroscope with a Leica CLS 150 light source and Leica camera
mounted at 4x magnification.
Synthetic Procedures. The synthesis of the bis-thioacetate protect-
ed 1,5-dialkoxynaphthalene SAc-1 and the bis-benzylthioacetate
protected zinc porphyrin SAc-2 were carried out according to liter-
[23,24]
ature procedures.
Likewise, the synthesis of the dinapthocrown
4
, diimide stoppered thread 5, and diimide-functionalized TentaGel
[28,31]
resins 16 have all been previously reported.
The synthesis of
the thiol building blocks can be found in the Supporting Informa-
tion.
5
provided sufficient pre-organization to overcome these
issues allowing the [2]catenane 11 and [2]rotaxane 12 to be
isolated in 21 and 22% yields, respectively. The use of reversi-
ble disulfide exchange as a means to assemble interlocked ar-
chitectures on surfaces was then examined. In this case disul-
fide exchange was initiated using dialkoxynaphthalene thiol
Naphthalene diimide disulfide [2]catenane (11). Naphthalene dii-
mide dithiol 3 (35 mg, 0.074 mmol) and dinaphtho-38-crown-10
ether 4 (23 mg, 0.036 mmol) were dissolved in CHCl (20 mL). DBU
3
(11 mL, 0.074 mmol) was added to the red solution which was
stirred at room temperature under air for 14 days. The solution
was then washed with H O (20 mL), dried over Na SO , and the sol-
1
in the presence of polymer resins that had been functional-
2
2
4
ized with a stoppered diimide thread 16. The concentration of
thiol and base were identical to those that had been successful
in synthesizing the [2]rotaxane 12. Pleasingly, evidence of ro-
taxane formation on the polymer resin was observed both
qualitatively by the red coloration of the bead and by the pres-
vent was evaporated to yield a crude red solid. Purification of this
crude material by column chromatography (EtOAc/CH Cl 3:7) af-
2
2
forded the desired [2]catenane as a red solid (13 mg, 21%); m.p.>
+
2
808C
(decomp.);
m/z
(ESI-MS)
[M+Na]
1603.4288
+
1
C H N NaO S (calc. 1603.4352); H NMR (400 MHz, CDCl ): d=
80
84
4
22
4
3
8
.63 (8H, bs, a-H), 7.73 (2H, d, JHH =8.2 Hz, a-H), 7.53 (2H, d, JHH
=
1
ence of peaks for the bound diimide resonance in the H HR-
8
.2 Hz, a-H), 7.12 (2H, t, JHH =7.9 Hz, b-H), 7.01 (2H, t, JHH =7.9 Hz,
MAS NMR spectrum. Clear evidence of the naphthoquinone ar-
omatic protons was obscured by the bead and stopper aro-
matic proton signals. Future work needs to look at optimizing
reaction conditions to increase the proportion of rotaxane on
the surface, which will facilitate characterization. Nevertheless,
these are promising results indicating that dynamic covalent
chemistry can be used to assemble interlocked architectures at
the solution:surface interface.
b-H), 6.44 (2H, d, JHH =8.1 Hz, g-H), 4.48–4.35 (8H, m, CH ), 4.06–
2
3.96 (8H, m, OCH ), 3.95–3.71 (40H, m, OCH ), 2.91–2.78 ppm (8H,
2
2
m, SCH ).
2
Naphthalene diimide disulfide [2]rotaxane (12). 1,5-Dialkoxy-
naphthalene dithiol 1 (50 mg, 0.14 mmol) and naphthalene diimide
dumbbell 5 (107 mg, 0.068 mmol) were dissolved in CHCl (41 mL).
3
DBU (20 mL, 0.14 mmol) was added to the orange solution which
was stirred at room temperature under air for 14 days. During this
time the solution became dark pink. The solution was then
washed with H O (40 mL), dried over Na SO , and the solvent was
2
2
4
evaporated to yield a crude dark pink solid. Purification of this
crude material by column chromatography using (EtOAc/CH Cl
Experimental Section
2
2
General Considerations. Unless otherwise stated, reagents were
purchased from commercial sources and used without further pu-
1:3) as the eluent afforded the desired rotaxane as a pale red solid
(33 mg, 22%); m.p. 178–1818C; m/z (ESI-MS) [M+Na] 2332.0458
+
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C138H156N NaO S
(calc. 2332.04198); H NMR (400 MHz, CDCl3):
d=8.57 (4H, s, a-H), 7.86 (2H, s, c-H), 7.75 (4H, d, JHH =8.2 Hz, g-H),
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16 4
2
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7
7
.39–7.31 (12H, d, JHH =8.0 Hz, Ar-H), 7.24 (4H, t, JHH =7.9 Hz, b-H),
.12–7.03 (16H, m, Ar-H), 6.76 (4H, d, JHH =8.0 Hz, Ar-H), 6.59 (4H,
d, JHH =8.1 Hz, a-H), 4.95 (4H, s, CH ), 4.54–4.52 (4H, m, CH ), 4.32
8H, t, JHH =4.8 Hz, OCH ), 4.09–3.99 (12H, m, OCH ), 3.93–3.89 (4H,
2 2
m, OCH ), 3.81–3.77 (12H, m, OCH ), 3.21–3.16 (8H, m, SCH ),
[
[
[
2
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2
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.31 ppm (54H, s, CH3).
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Gel resin beads 16 (26 mg, 0.027 mmol). DBU (8.1 mL, 0.054 mmol)
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room temperature for 14 days. The beads were collected by filtra-
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9
38–993.
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Keywords: catenanes · dynamic covalent chemistry · HR-MAS
NMR spectroscopy · rotaxanes · supramolecular chemistry
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Received: November 12, 2014
2004, 304, 1308–1312.
Published online on && &&, 0000
Chem. Asian J. 2015, 00, 0 – 0
www.chemasianj.org
7
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
FULL PAPER
Supramolecular Chemistry
Exchange program: The use of disulfide
exchange to reversibly assemble inter-
locked architectures both in solution
and on polymer resins is described.
Hannah Wilson, Sean Byrne,
Kathleen M. Mullen*
&& – &&
Dynamic Covalent Synthesis of
Donor–Acceptor Interlocked
Architectures in Solution and at the
Solution:Surface Interface
&
&
Chem. Asian J. 2015, 00, 0 – 0
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8
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!