Unidirectional threading of triphenylureidocalix[6]arene-based wheels: Oriented pseudorotaxane synthesis

Article abstract of DOI:10.1002/chem.200390089

Triphenylureidocalix[6]arenes 5a,b are heteroditopic receptors having a pinched cone structure able to interact with both the cation and the anion of ion pairs. They are able to act as wheels and form complexes of the pseudorotaxane type with axles derive

Full text of DOI:10.1002/chem.200390089

FULL PAPER
Unidirectional Threading of Triphenylureidocalix[6]arene-Based Wheels:
Oriented Pseudorotaxane Synthesis
Arturo Arduini,* Francesco Calzavacca, Andrea Pochini, and Andrea Secchi[a]
Abstract: Triphenylureidocalix[6]ar-
enes 5a,b are heteroditopic receptors
having a pinched cone structure able to
interact with both the cation and the
anion of ion pairs. They are able to act as
wheels and form complexes of the
pseudorotaxane type with axles derived
from dialkylviologen salts. An investi-
gation into the possibility of exploiting
the different structural and chemical
information present on the two distinct
rims of the calixarene wheel as control
elements to pivot the direction of the
axle threading processes and give access
to oriented pseudorotaxanes is reported.
It was verified that, in C6D6, an asym-
metric dicationic axle derived from 4,4'-
bipyridil bearing two alkyl chains, one of
which has a stopper, and triphenylurei-
docalix[6]arenes 5a or 5b form 1:1
supramolecular complexes belonging to
the class of pseudorotaxanes. The struc-
ture of these complexes has been infer-
red through H NMR techniques. The
data show that the axle accesses the
calixarene cavity only through the wider
rim. To further verify this issue, the new
rotaxane 8, obtained by stoppering the
pseudorotaxane derived from 5b and
the symmetrical axle 7 with diphenyl-
acetyl chloride, was synthesised. In the
1H NMR spectrum of 8, the aliphatic
protons of the axle portion that resides
at the wide rim of the wheel show
chemical shifts that are almost identical
to those observed in pseudorotaxanes 6.
On the other hand, those that stick out
of the narrow rim of 8 experience
chemical shifts that could not be found
in the oriented pseudorotaxanes 6.
1
Keywords: calixarenes
¥
host
guest systems ¥ oriented pseudoro-
taxanes ¥ rotaxanes ¥ unidirectional
threading
wheels, are the cyclodextrins, characterised by a shallow
truncated cone structure.[5]
Introduction
Pseudorotaxanes and rotaxanes[1] are very interesting and
promising tools for the construction of working devices and
molecular machines.[2] In simple instances a pseudorotaxane
can derive from the assembly of two distinct components: a
sufficiently large macrocycle, which acts as a wheel, and an
acyclic component, which, by threading the wheel, acts as an
axle. The insertion of two bulky stoppers at the ends of the
axle inserted into the wheel yields a rotaxane. By exploiting
the principles of supramolecular chemistry, and in particular
of ™organic template synthesis∫,[3] several classes of wheels
and axles that have complementary sizes have been employed
so far for the construction of such complex systems.[4]
Particularly attractive, and consequently widely studied as
In this context, although no systematic studies have been
reported so far, an aspect that is gaining increasing attention is
the threading processes of these wheels with asymmetrical
axles. Almost a decade ago, Kaifer and Isnin[6] succeeded in
the synthesis of two isomeric [2]rotaxanes that differ by the
orientation of the a-cyclodextrin wheel with respect to the
two different stoppers, while Matsuo and co-workers have
shown that cyclodextrines can form ™stable∫ oriented pseudo-
rotaxanes with appropriate asymmetrical axles.[7] More re-
cently, the problem of the direction of guest insertion and
orientation was studied by using axles in which the included
portion of the asymmetric axle pivots the direction of its
insertion into the toroidal wheels.[8] In contrast, the prepara-
tion of polyrotaxanes composed of cyclodextrins and various
polymers that do not control the access to the cavity, afford a
head-to-tail orientation of these wheels along the polymer
chain.[9,10]
[a] Prof. A. Arduini, F. Calzavacca, Prof. A. Pochini, Dr. A. Secchi
Dipartimento di Chimica Organica e Industriale
¡
Universita di Parma, Parco Area delle Scienze 17/a
43100 Parma, Italy.
Calix[n]arenes are phenolic macrocycles widely used in
host guest chemistry as versatile platforms for the synthesis
of versatile and efficient receptors.[11] They are frequently
compared to cyclodextrins because of their truncated cone
structure and their ability to form endo-cavity inclusion
complexes with suitable guests. In solution, however, the
Fax : (‡39)0521-905472
E-mail: arturo.arduini@unipr.it
Supporting information for this article is available on the WWW under
http://www.chemeuj.org or from the author: full spectral character-
isation of new compounds 3b and 8, 2D NMR spectra of pseudorotax-
ane 6b.
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793

A. Arduini et al.
FULL PAPER
cavities of these two types of hosts possess complementary
binding properties. In fact, while cyclodextrins experience
high affinity towards neutral organic species, typically in
aqueous media, calixarenes better host quaternary ammoni-
um cations in apolar media.[12]
The binding properties of the latter macrocycles have
recently been applied by us to the synthesis of the first
example of a rotaxane having a calix[6]arene derivative as a
wheel.[13] We have also shown that, in apolar media, the
triphenylureidocalix[6]arene derivative 5a can be threaded by
dioctylviologen diiodide and yields a pseudorotaxane (I). In
the solid state, pseudorotaxane I (see Figure 1) is stabilised by
Figure 2. Schematic representation of the two possible pseudorotaxane
isomers derived from a calix[6]arene wheel and an asymmetrical axle
carrying only one stopper.
elements to guide the threading process of dicationic axles
derived from 4,4'-bipyridyl (Figure 2).
The starting considerations for the present study arise from
the observation that the calix[6]arene skeleton, because of its
ring size, possesses an annulus that is large enough to allow a
guest having the size of the bipyridyl to cross the two rims.
Therefore in the absence of control elements the threading
process could take place both from the wider or narrower rim
of the macrocycle. In the triphenylureido calix[6]arene 5,
however, the wide rim is rather hydrophilic, because of the
three ureido moieties, while the narrow rim, which bears alkyl
groups, is hydrophobic. This difference could be exploited as a
control element to guide axle-insertion processes.
To address this issue, we synthesised an asymmetric axle
derived from 4,4'-bipyridyl functionalised with two alkyl
chains, one of which bears a stopper, and studied the structure
of the complexes formed with triphenylureidocalix[6]arene
derivatives.
Results and Discussion
Axles 3a,b were obtained through the stepwise synthesis
reported in Scheme 1 by treating diphenylacetyl chloride with
w-bromohexanol to give 1, which was treated with 4,4'-
bipyridine in refluxing CH3CN to give 2. Alkylation of the
Figure 1. X-ray crystal structure of pseudorotaxane I derived from 5a and
dioctylviologen diiodide.[13]
a combination of several supramolecular interactions that
involve all parts of the wheel. In fact, the phenyl groups of the
phenylurea moieties–the aromatic walls of the calixarene
and the oxygen atoms present at the narrow rim–are
involved in stabilising this supramolecular complex. In
addition, the two counteranions are hydrogen bonded to the
six ureido NH groups present at the wide rim of the wheel.
The observation that the cationic portion of the axle is
located at the p-donor calix[6]arene walls reflects the host
guest properties of calixarenes and is opposite and comple-
mentary to that for cyclodextrins, in which the same cationic
portion along analogous axles can be employed as stopper.[14]
We envisaged that because of the large number of
possibilities for inserting functional groups and binding sites
onto both rims of the calixarene skeleton,[11,15] the synthesis of
rotaxanes or pseudorotaxanes having a calixarene as wheel
could contribute to the development of new molecular
devices that have properties governed by a wider range of
control elements.
Scheme 1.
second nitrogen atom of 2 with iodopentane in CH3CN
afforded 3a as a red solid in 33% overall yield. Then, an
anion-exchange reaction with silver tosylate gave axle 3b in
85% yield as pale yellow solid.
Axles 3a,b are not sufficiently soluble in chloroform or
benzene for an accurate NMR analysis.[16] The main common
In this paper we wish to describe a synthetic and structural
study to verify whether the different chemical and structural
information attached to the two distinct rims of triphenylure-
idocalix[6]arene derivatives 5 could be exploited as control
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Oriented Pseudorotaxanes
793 799
1
features of their H NMR spectra taken in CD3CN are that
signal at about d ˆ 2.9 ppm, while those of the pseudo-axial
and pseudo-equatorial bridging methylene resonate as broad
signals at d ˆ 4.5 and 3.5 ppm, respectively (see Figure 3c).
protons 6, 9 and 7, 8 of the bipyridyl system resonate as
doublets at about d ˆ 9.0 and 8.5 ppm, respectively, while
protons 5 and 10 resonate at d ˆ 4.65 and 4.60 ppm, respec-
tively (see Scheme 2 for numbering). Unambiguous assign-
ment of all other signals was achieved through 1H 1H
TOCSY spectra (see Supporting Information).
Initially the ability of 3a to act as axle was evaluated by
using the ready available wheel 5a,[17] through 1H NMR
analysis of the solution obtained by equilibrating a solution of
5a in C6D6 with a slight excess of solid 3a. The NMR spectrum
of the deep red solution obtained after filtration of the
undissolved axle appears as a single set of signals consistent
with a 1:1 host guest complex that is in slow exchange on the
NMR timescale.[18]
In the 1H NMR spectrum of the complex 6a, the protons of
the methoxy groups (e), which are expelled from the
calixarene cavity as consequence of threading,[19] are down-
field shifted of about 1 ppm. The six NH protons i and l suffer
a downfield shift of about 2 ppm because of their involvement
in hydrogen bonding with the two halide counteranions. The
eight protons of the bipyridyl group 6, 7, and 8 and 9 are
substantially upfield shifted by about 2.3, 2.0, 1.5 and 0.7 ppm,
respectively, because of their proximity to the calixarene
cavity and the phenyl rings of the phenylureido groups.
However the extensive peaks overlapping in the spectral
region between 2 and 0.5 ppm, where most of the signals of
the calixarene octyl chains resonate, precluded the unequiv-
ocal assignment of several protons of the axle. Therefore the
new calix[6]arene 5b, in which the basic skeleton of the wheel
remains almost intact and bears the 2-ethoxyethyl groups in
the place of the octyl chains of 5a, was synthesised by treating
4b[17] with phenylisocyanate to give 80% yield (Scheme 2).
Contrary to that of 5a, the 1H NMR of 5b is rather broad,
also at different temperatures, and shows the same features in
all deuterated solvents used, probably because of its con-
formational flexibility. In C6D6 at 300 K, for example, the
protons of the three methoxy groups resonate as a very broad
Figure 3. 1H NMR spectra (300 MHz, 300 K) of a) 3b in CD3CN;[16]
b) pseudorotaxane 6b in C6D6; c) triphenylureidocalix[6]arene 5b in C6D6.
To study the possible effects of the two halides of 3a on the
pseudorotaxane structure, the ditosylate 3b was submitted to
1
complex formation with calix[6]arene 5b. In the H NMR
spectrum of the deep red solution obtained by adding an
equimolecular amount of solid 3b to a 0.01m solution of 5b in
C6D6, the signals of calixarene 5b have a sharper peak pattern
consistent with a cone structure (Figure 3b).
The chemical shift variation (see Figure 4) experienced by
the protons of the axle observed in the spectrum of this
complex parallels those observed in the complex 6a (derived
from 5a and 3a), and the counteranions seem to have only a
negligible effect on the complex structure.
Scheme 2.
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A. Arduini et al.
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Figure 4. Protons downfield (‡) and upfield (À) shifts (Dd, ppm) of
selected signals of pseudorotaxane 6b (for proton assignment and
numbering see Scheme 2).
All signals of the NMR spectrum of 6b were identified and
assigned by 1H 1H DQF-COSY spectra (see Supporting
Information). Particularly informative is the observation that
the chemical shift of protons 1, 2, and 3, belonging to the
pentyl chain of the axle, are downfield shifted upon complex
formation by 0.3, 0.4 and 0.5 ppm, while protons 4 and 5
experience an upfield shift of 0.21 and 0.71 ppm, respectively.
On the other hand, protons 10 are upfield shifted by about
0.9 ppm, and these upfield shifts propagate, with the excep-
tion of protons 13, through the hexyl chain to protons 14; here
this shift had decreased to 0.16 ppm. Protons 15 and 16 remain
almost unaffected by complex formation. These data suggest
that the portion of the axle between protons 5 and 14 is
subjected to the anisotropy shielding effect of the aromatic
domains of the calixarene host, while all the others are
downfield shifted.
Unequivocal information on the relative orientation of the
two components of 6b was deduced from ROESY experi-
ments that, together with the expected intramolecular cross
peaks of both pseudorotaxane components, showed axle
wheel intermolecular cross peaks between protons 8 and 9
with h, 10 and 11 with m and 11 and 12 with n (see Figure 5). In
addition, protons 2, 3 and 4 of the pentyl chain show cross
peaks with protons d and e of the wheel. These ROESY data,
together with the chemical-shift variation experienced by the
protons of both pseudorotaxane components, are consistent
with the hypothesis of a structure in which the axle points its
pentyl chain towards the groups present at the narrow rim of
the calix[6]arene, while the stopper is located in the region of
the phenylureido moieties.
However, the lack of the parent isomeric pseudorotaxane
derived from the access of the axle to the narrow of rim of the
wheel and having the stopper in proximity to the calix[6]arene
alkyl chains, prompted us to synthesise rotaxane 8 (see
Scheme 3) to establish whether the protons of its identical
stoppered arms, because of their different orientation inside
the wheel, resonate as distinguishable set of signals in the
1H NMR spectrum.
In fact in this rotaxane, because of its orientation towards
the phenylureido groups of the calixarene, the portion of the
axle between protons 6 and 1 should manifest chemical-shift
variations comparable with those observed in 6b. On the
Figure 5. Selected expanded portions of 1H 2D-ROESY NMR (300 MHz,
spin-lock 200 ms) spectrum of pseudorotaxane 6b in C6D6, showing the
more representative axle wheel intermolecular cross-peaks (for full 2D
spectrum attribution see Supporting Information).
other hand, the protons of the axle portion between protons 6'
and 1', because of their proximity to the narrow rim of the
wheel, could represent a model for the pseudorotaxane
derived from the insertion of axle 3b from the narrow rim
of the calixarene wheel.
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Oriented Pseudorotaxanes
793 799
Scheme 3.
Rotaxane 8 was synthesised in 20% yield by adding a slight
excess of diphenylacetyl chloride to the homogeneous sol-
ution obtained by heating equimolecular amounts of wheel 5b
and the diol 7 in dry toluene under reflux for 24 hrs. Although
the complete assignment of all signals of the axle was not
possible because of extensive overlapping and broadening of
some signals in the region 0.5 2 ppm, the 1H NMR spectrum
of 8 in C6D6 (see Figure 6) shows that protons a and 1, which
resonate at d ˆ 5.23 and 4.17 ppm, experience chemical shifts
that are almost identical to those of protons 16 (d ˆ 5.24) and
15 (d ˆ 4.15) of pseudorotaxane 6b (see Scheme 3 for
numbering).
resonate at d ˆ 5.28 and 4.44 ppm because of their proximity
to the narrow rim of the wheel and could not be detected in
the spectra of 6b. These data further support the hypothesis
that the formation of complexes derived from the access of
the axle to the narrow rim of the calix[6]arene wheel does not
takes place.
A tentative explanation of this findings could derive from a
combination of the following factors: a) in C6D6, the three
methoxy groups present at the narrow rim of the calix[6]arene
are oriented inwards towards the cavity, occupying it and thus
disfavouring, by repulsive intermolecular interactions, the
access of the axle to the narrow rim. b) The size and binding
ability of the wheel inner volume are suitable only for the
inclusion of the cationic portion of the axle. c) In the apolar
C6D6, axles 3a,b are present as tight ion pairs. It is therefore
reasonable to assume that a process that implies, at least, the
partial separation of the dication from its counteranions
should take place before cation insertion into the wheel.[20]
d) The hydrophilic ureido groups present at the wider rim of
the calix are potent hydrogen-bond-donor groups and partic-
ipate in the overall complexation process by ligating the two
anions of the axle. In this way, the formation of a ligand-
separated ion pair is favoured.
1
In addition, from the H 1H COSY spectrum it emerges
that protons 2, 5 and 6, which resonate at about d ˆ 1.5, 0.8
and 3.5 ppm, respectively, experience chemical shifts that are
very similar to those of protons 14 (d ˆ 1.44), 11 (d ˆ 0.87) and
10 (d ˆ 3.68) of 6b. On the other hand, protons a' and 1'
On these bases, it could be that hydrogen bonding
interactions between the two anions and the phenylureido
NH groups pivot the direction of the cationic axle insertion
from the wider rim of the calixarene wheel.
Conclusion
In summary a new strategy to control the direction of the
threading of heteroditopic calix[6]arene based wheel has been
disclosed. The exploitation of this property for the synthesis of
new molecular machines is under investigation in our
laboratory and will be published in due course.
Figure 6. Partial 1H NMR spectra (300 MHz, 300 K) of rotaxane 8 in C6D6.
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J ˆ 7.5 Hz, 2H; 10-H), 4.14 (t, J ˆ 6.6 Hz, 2H; 15-H), 2.33 (s, 6H; 22-H),
2.05 1.85 (m, 4H; 4,11-H), 1.60 (brt, 2H; 14-H), 1.4 1.3 (m, 8H;
3,2,12,13-H), 0.93 (t, J ˆ 7.2 Hz, 3H; 1-H); 13C NMR (75 MHz, CD3CN),
d ˆ 172.9, 149.5, 146.4, 146.3, 139.9, 139.1, 129.2, 128.9, 127.8, 126.3, 65.3,
62.5, 62.4, 57.3, 31.4, 31.3, 28.5, 28.3, 25.6, 25.4, 22.4, 20.9, 13.7; MS (ESI,
Experimental Section
All reactions were carried out under nitrogen; all solvents were freshly
distilled under nitrogen and stored over molecular sieves for at least 3 h
prior to use. All other reagents were of reagent-grade quality as obtained
from commercial suppliers and were used without further purification.
Column chromatography was performed on silica gel 63 200 mesh. NMR
‡
CH3CN/H2O) m/z: 521.1 [M2‡‡H ]; elemental analysis calcd (%) for
C49H56N2O8S2 ¥ 2H2O (901.18): C 65.31, H 6.71, N 3.11, S 7.12; found: C
65.33, H 6.65, N 3.07, S 7.05.
spectra were recorded in CDCl3 unless otherwise indicated. Mass spectra
Synthesis of wheel 5b: Phenyl isocyanate (0.14 g, 1.0 mmol) and 4b (0.16 g,
0.14 mmol) were mixed in CH2Cl2 (100 mL) and stirred at RT overnight.
The solvent was evaporated, and the residue purified by column
chromatography (hexane/ethyl acetate 3:2) to give 0.16 g (80%) of 5b.
M.p. 174 1768C; 1H NMR (300 MHz, C6D6, 300 K) d ˆ 7.3, 7.25, 6.9, 6.7
(4brs, 33H; m,n,o,f,f',f''-H and i,l-H), 4.5 (brd, 6H; g'-H), 3.9, 3.8, 3.6, 3.4
(4brs, 36H; d,c,b,g-H), 2.9 (brs, 9H; e-H), 1.3 (s, 27H; h-H), 1.1 (brs, 9H;
a-H); 1H NMR (300 MHz, CDCl3, 300 K) d ˆ 7.1 (brs, 21H; m,n,o,l,f',f''-
H), 6.9 (brs, 3H; i-H), 6.3 (brs, 6H; f-H), 4.3 (brs, 6H; g'-H), 4.1, (brs, 6H;
d-H), 3.8 (brs, 6H; c-H), 3.7-3.6 (m, 12H; b,g'-H), 2.9 (brs, 9H; e-H), 1.2 (s,
27H; h-H), 0.85 (t, J ˆ 6.5 Hz, 9H; a-H); 13C NMR (75 MHz, CDCl3) d ˆ
154.7, 152.0, 146.7, 138.2, 135.7, 132.9, 132.4, 128.9, 127.5, 123.3, 123.0, 120.3,
72.3, 70.0, 69.8, 66.8, 60.2, 34.1, 31.4, 30.9, 15.23; MS (ESI, CH3OH) m/z:
[21]
were determined in the CI(CH ) or ESImode as appropriate.
Melting
4
points are uncorrected. Elemental analyses[22] were carried out at the
laboratory of microanalysis of the Instituto di Chimica Farmaceutica e
Tossicologica of the University of Parma. Compounds 5a and 4b were
synthesised according to literature procedures.[17] Attribution and number-
ing of the NMR signals for new compounds 1, 3a,b and 5b follows that
reported throughout the manuscript (see Schemes 2 and 3 and Supporting
Information).
Synthesis of 6-bromohexyl diphenylacetate (1): 6-Bromohexan-1-ol (0.66 g,
3.6 mmol) and diphenylacetyl chloride (1.0 g, 4.3 mmol) were dissolved in
dry THF (100 mL), and the solution was stirred overnight at room
temperature. The solvent was evaporated under reduce pressure, and the
oily residue was purified by column chromatography (hexane/ethyl acetate
‡
‡
1488.7 [M ‡Na ]; elemental analysis calcd (%) for C90H108N6O12
¥
1
9:1) to give 0.99 g (73%) of 1 as a colourless liquid. H NMR (400 MHz,
1
³2CH2Cl2 (1508.4): C 72.07, H 7.28, N 5.57; found: C 72.33, H 7.19, N 5.61.
298 K) d ˆ 7.27 7.36 (m, 10H; 17,18,19-H), 5.05 (s, 1H; 16-H), 4.17 (t, J ˆ
6.6 Hz, 2H; 15-H), 3.36 (t, J ˆ 6.6 Hz, 2H; 10-H), 1.81 (m, 2H; 11-H), 1.65
(m, 2H; 14-H), 1.40 (m, 2H; 12-H), 1.31 (m, 2H; 13-H); 13C NMR
(75 MHz, 298 K) d ˆ 172.4, 138.7, 128.6, 128.5, 127.2, 64.9, 57.2, 33.5, 32.5,
Synthesis of axle 7: 4,4'-bipyridyl (0.5 g, 3.2 mmol) and 6-bromohexan-1-ol
(1.74 g, 9.6 mmol) were heated under reflux in CH3CN (100 mL) for 48 h.
The yellow heterogeneous mixture was filtered, and the solid was collected
and washed with CH3CN (2 Â 20 mL) to give 0.57 g (34%) of 7 as yellow
solid. M.p. 2478C (dec.); 1H NMR (300 MHz, [D6]DMSO) d ˆ 9.41 (d, J ˆ
6.9 Hz, 4H; 7,7'-H), 8.80 (d, 4H; 8,8'-H), 4.71 (t, J ˆ 7.5 Hz, 4H; 6,6'-H),
3.37 (t, J ˆ 4.5 Hz, 4H; 1,1'-H), 1.98 (m, 4H; 5,5'-H), 1.4 1.3 (m, 12H;
2,3,4,2',3',4'-H); 13C NMR (75 MHz, [D6]DMSO) d ˆ 149.4, 146.6, 127.5,
‡
28.3, 27.6, 24.9; MS, CI(‡) m/z: 376 [M ].
Synthesis of 1-[6-(Diphenylacetoxyhexyl)]-4-pyridin-4-yl-pyridinum bro-
mide (2): Bromoester
1 (0.96 g 2.5 mmol) and 4,4'-bipyridyl (0.8 g,
5.1 mmol) were dissolved in dry CH3CN (100 mL), and the solution was
heated under reflux for 24 h to give an heterogeneous mixture. The white
solid was filtered off, and the solvent was completely evaporated under
reduced pressure to give a yellow solid, which was crystallised from CH2Cl2/
hexane and gave 0.67 g (49%) of 2. M.p. 108 1108C; 1H NMR (300 MHz,
CD3CN, 298 K) d ˆ 9.15 (d, J ˆ 5.2Hz, 2H; 9-H), 8.81 (d, J ˆ 4.1 Hz, 2H;
6-H), 8.39 (d, J ˆ 5.2 Hz, 2H; 8-H), 7.82 (d, J ˆ 4.1 Hz, 2H; 7-H), 7.2 7.4
(m, 10H; 17,18,19-H), 5.10 (s, 1H; 16-H), 4.71 (t, J ˆ 7.5 Hz, 2H; 10-H), 4.09
(t, J ˆ 6.4 Hz, 2H; 15-H), 1.93 (m, 2H; 11-H), 1.57 1.52 (m, 2H; 14-H),
1.33 1.25 (m, 4H; 12,13-H); 13C NMR (75 MHz, [D6]DMSO) d ˆ 173.2,
153.1, 151.8, 146.2, 141.7, 139.8, 129.3, 129.2, 127.9, 126.2, 122.8, 65.3, 61.1,
‡
‡
61.8, 61.4, 33.0, 31.7, 26.2, 25.8; MS (ESI, CH3OH) m/z: 357.9 [M2‡ À H ] .
Synthesis of rotaxane 8: Wheel 5b (0.04 g, 0.03 mmol) and axle 7 (0.014 g,
0.03 mmol) were heated under reflux in toluene (50 mL) for 24 h, then
diphenylacetyl chloride (0.018 g, 0.08 mmol) was added. The mixture was
heated under reflux for a further 48 h, then the solvent was completely
removed under reduced pressure. Purification of the resulting red residue
by chromatography (hexane/ethyl acetate/nPrOH 7:2:1) afforded 0.015 g
(20%) of 8 as red solid. M.p. 95 998C; 1H NMR (300 MHz, C6D6) d ˆ 9.8
and 9.6 (2brs, 6H; i,l-H), 7.9 (brd, 2H; 7-H), 7.8 (brd, 6H; m-H), 7.66 (s,
6H; f-H), 7.6 7.5 (m, 18H; b,b',g,g',8-H), 7.3 7.2 (m, 10H; f',f'',d,d'-H), 7.1
(brt, 6H; n-H), 6.9 (brd, 2H; 7'-H), 6.8 6.7 (m, 5H; o,8'-H); 5.28 (s, 1H;
a'-H), 5.23 (s, 1H; a-H), 4.61 (brd, 6H; g'-H), 4.44 (t, J ˆ 6.6 Hz, 2H; 1'-H),
4.17 (t, 2H; J ˆ 6.6 Hz, 1-H), 4.0 (brs, 15H; d,e-H), 3.8 (brs, 2H; 6'-H), 3.7
(brs, 6H; c-H), 3.5-3.3 (m, 14H; 6,b,g-H), 2.1 (brs, 2H; 5'-H), 1.87 (s, 27H;
h-H), 1.5 1.4 (brs, 6H; 2,3',4'-H), 1.23 (t, J ˆ 6.5 Hz, 9H; a-H), 1.1 1.0 (m,
4H; 3,4-H), 0.8 0.6 (m, 2H; 5-H); 13C NMR (75 MHz, C6D6) d ˆ 174.9,
171.0, 162.4, 153.9, 153.3, 148.7, 144.2, 143.3, 141.2, 139.6, 137.3, 132.6, 129.7,
129.3, 129.1, 129.0, 128.4, 128.1, 127.8, 127.4, 125.2, 124.7, 121.4, 117.8, 116.8,
91.8, 72.9, 70.3, 66.7, 65.3, 64.9, 61.4, 60.7, 57.8, 57.7, 35.1, 32.0, 30.2, 29.7, 28.8,
28.0, 26.3, 25.8, 25.4, 15.6, 11.4; MS (ESI, CH3OH) m/z: 1106.0 [M2‡].[23]
‡
56.7, 31.4, 28.5, 25.7, 25.5; MS (ESI, CH3OH) m/z: 451.0 [M ].
Synthesis of 3a: Compound
2 (0.26 g, 0.5 mmol) and an excess of
iodopentane (0.26 mL, 2.0 mmol) were heated under reflux in dry CH3CN
(50 mL) for 10 days to give a deep purple homogeneous solution, which was
evaporate to dryness. The residue was dissolved in the minimum quantity of
CH3OH (ca. 2 mL), then NaI(0.75 g, 5.0 mmol) was added. The resulting
heterogeneous solution was stirred. After 1 h, the solid suspension was
filtered off, and ethyl acetate was added until complete precipitation of 3a,
which was collected by filtration and washed with ethyl acetate. The purity
of 3a was checked by TLC (CH3OH/33% NH4OH 99:1). After drying,
0.34 g (94%) of pure 3a were obtained. M.p. 225 2278C; 1H NMR
(400 MHz, CD3CN, 298 K): d ˆ 9.05 and 9.03 (2d, J ˆ 6.1 Hz, 4H; 6,9-H),
8.50 (d, 4H; 7,8-H), 7.3 7.2 (m, 10H; 17,18,19-H), 5.09 (s, 1H; 16-H), 4.67
(t, J ˆ 7.5 Hz, 2H; 5-H), 4.62 (t, J ˆ 7.5 Hz, 2H; 10-H), 4.13 (t, J ˆ 6.6 Hz,
2H; 15-H), 2.04 (brt, 2H; 4-H), 1.97 (brt, 2H; 11-H), 1.60 (brt, 2H; 14-H),
1.4 1.3 (m, 8H; 3,2,12,13-H), 0.93 (t, J ˆ 7.2 Hz, 3H; 1-H); 13C NMR
(75 MHz, CD3CN), d ˆ 171.7, 150.6, 146.2, 139.9, 129.2, 127.9, 127.8, 65.3,
62.9, 57.3, 31.4, 31.3, 28.5, 28.2, 25.6, 25.4, 22.3, 22.3; UV/Vis (CH3CN):
lmax(Ge) ˆ 447 nm (990.5 molÀ1 dmÀ3 cmÀ1); MS (ESI, CH3OH) m/z: 521.1
Acknowledgements
We are grateful for financial support from the MIUR ™Supramolecular
Devices Project∫ and CIM (Centro Interdipartimentale di Misure) ™G.
Casnati∫ of the University of Parma for NMR and Mass measurements.
‡
‡
[M2‡ À H ] ; elemental analysis calcd (%) for C35H42I2N2O2 (776.54): C
54.14, H 5.45, N 3.61; found: C 53.79, H 5.38, N 3.64.
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¡
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Chem. Eur. J. 2003, 9, No. 3

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¡
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Received: September 12, 2002 [F4417]
Chem. Eur. J. 2003, 9, No. 3
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