Post-assembly processing of [2]rotaxanes

Article abstract of DOI:10.1002/1521-3765(20021115)8:22<5170::AID-CHEM5170>3.0.CO;2-S

The concept of using [2]rotaxanes that carry one or more surrogate stoppers which can subsequently be converted chemically into other structural units, resulting in the formation of new interlocked molecular compounds, is introduced and exemplified. Starting from simple NH₂⁺-centered/crownether-based [2]rotaxanes, containing either one or two benzylic triphenylphosphonium stoppers, the well-known Wittig reaction has been employed to make, 1) other [2]rotaxanes, 2) higher order rotaxanes, 3) branched rotaxanes, and 4) molecular shuttles - all isolated as pure compounds, following catalytic hydrogenations of their carbon-carbon double bonds, obtained when aromatic aldehydes react with the ylides produced when the benzylic triphenylphosphonium derivatives are treated with strong base. The two starting [2]rotaxanes were characterized fully in solution and also in the solid state by X-ray crystallography. The new interlocked molecular compounds that result from carrying out post-assembly Wittig reactions on two [2]rotaxanes were characterized by (dynamic) ¹H NMR spectroscopy. In the case of a molecular shuttle in which the crown ether component is dibenzo[24]-crown-8 (DB24C8), shuttling is slow on the ¹H NMR timescale, even at high temperatures. However, when DB24C8 is replaced by benzometaphenylene[25]-crown-8 as the ring component in the molecular shuttle, the frequency of the shuttling is observed to be around 100 Hz in [D₄] methanol at 63 °C.

Full text of DOI:10.1002/1521-3765(20021115)8:22<5170::AID-CHEM5170>3.0.CO;2-S

FULL PAPER
Post-Assembly Processing of [2]Rotaxanes**
Sheng-Hsien Chiu,[a] Stuart J.Rowan, [a, c] Stuart J.Cantrill, [a, d] J.Fraser Stoddart,* [a]
[b]
[b]
Andrew J.P.White,
and David J.Williams*
Abstract: The concept of using [2]ro-
taxanes that carry one or more surrogate
stoppers which can subsequently be
converted chemically into other struc-
tural units, resulting in the formation of
new interlocked molecular compounds,
is introduced and exemplified. Starting
compounds, following catalytic hydro-
genations of their carbon carbon dou-
ble bonds, obtained when aromatic al-
dehydes react with the ylides produced
when the benzylic triphenylphosphoni-
um derivatives are treated with strong
base. The two starting [2]rotaxanes were
characterized fully in solution and also
in the solid state by X-ray crystallogra-
phy. The new interlocked molecular
compounds that result from carrying
out post-assembly Wittig reactions on
two [2]rotaxanes were characterized by
(dynamic) 1H NMR spectroscopy. In the
case of a molecular shuttle in which the
crown ether component is dibenzo[24]-
crown-8 (DB24C8), shuttling is slow on
the 1H NMR timescale, even at high
temperatures. However, when DB24C8
is replaced by benzometaphenylene[25]-
crown-8 as the ring component in the
molecular shuttle, the frequency of the
shuttling is observed to be around
100 Hz in [D4]methanol at 638C.
‡
from simple NH2 -centered/crown-
ether-based [2]rotaxanes, containing ei-
ther one or two benzylic triphenylphos-
phonium stoppers, the well-known Wit-
tig reaction has been employed to make,
1) other [2]rotaxanes, 2) higher order
rotaxanes, 3) branched rotaxanes, and 4)
molecular shuttles–all isolated as pure
Keywords:
mechanical bond
¥
molecular recognition ¥ molecular
shuttle ¥ template synthesis ¥ Wittig
reactions
anes.[2] They are molecules in which one or more rings become
trapped on a dumbbell-shaped component by two bulky
terminal stoppers. They represent a major subset of inter-
locked molecular compounds[3] and have attracted much
attention in recent years because of their potential shuttling[4]
and switching[5] properties. On account of these properties,
they provide a means[6] of constructing linear motor-mole-
cules[7] and other forms of artificial molecular machinery[8] on
the tiniest of scales, namely the nano one. Also, as a
consequence of their mechanical characteristics and bistable
hysteretic attributes, they are now being fine-tuned and
fashioned for fabrication and incorporation[9] into molecular
electronic devices.[10] So far, these devices have included
electronically configurable[11] and reconfigurable[12] switches,
which have made it possible[13] very recently to create[11, 12]
both memory and logic circuits–two crucial milestones that
must be reached if a finite-state molecular computer[14] is ever
going to become a reality.
During the past 15 years, the exploitation of the funda-
mental aspects of molecular recognition,[15] together with the
development of the concept of self-assembly,[16] also referred
to as noncovalent (supramolecular) synthesis,[17] has led to the
evolution of highly efficient template-directed proce-
dures[18]–sometimes called supramolecular assistance to co-
valent synthesis[19]–for constructing interlocked molecular
compounds.[1]
Introduction
Mechanically interlocked molecules[1] are composed of two or
more components between which there are no covalent
bonds; only noncovalent bonds usually and at least one
mechanical bond are present. Examples include the rotax-
[a] Prof. J. F. Stoddart, Prof. S.-H. Chiu, Prof. S. J. Rowan, Dr. S. J. Cantrill
Department of Chemistry and Biochemistry
University of California, Los Angeles
405 Hilgard Avenue, Los Angeles, CA 90095-1569 (USA)
Fax : (‡1)310-206-1843
E-mail: stoddart@chem.ucla.edu
[b] Prof. D. J. Williams, Dr. A. J. P. White
Chemical Crystallography Laboratory
Department of Chemistry, Imperial College
South Kensington, GB-London, SW7 2AY (UK)
Fax : (‡44)207-594-5835
[c] Prof. S. J. Rowan
Current Address:
Department of Macromolecular Science
Case Western Reserve University
2100 Adelbert Road, Cleveland, OH 44106-7202 (USA)
[d] Dr. S. J. Cantrill
Current Address:
Division of Chemistry and Chemical Engineering
California Institute of Technology
1200 East California Blvd, Pasadena, CA 91125 (USA)
[**] ™Molecular Meccano∫, Part 65. For Part 64, see: S. J. Cantrill, G. J.
Youn, J. F. Stoddart, D. J. Williams, J. Org. Chem. 2001, 66, 6857 6872.
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5170 5183
Although a wide range of supramolecular synthons[20] have
already been employed[1] as recognition motifs to bring
together the separate components of catenanes and rotaxanes,
our discovery[21] in the early 90s, that secondary dialkylam-
fact that the free species and the pseudorotaxane are in slow
exchange on the 1H NMR timescale, the ability of the bromo-
thread[23a] 1a-H ¥ PF6 to form a [2]pseudorotaxane [DB24C8 ꢀ
1a-H]PF6 with DB24C8 was demonstrated by 1H NMR
spectroscopy. A Ka value of 400mÀ1 was calculated, based on
the single-point method[24] in CD3CN. Building on this
complexation, the template-directed synthesis of the [2]ro-
taxane 2a-H ¥ 2PF6 was accomplished in 80% yield, simply by
adding PPh3 to a mixture of 1a-H ¥ PF6 and DB24C8 in
CH2Cl2, followed by counterion exchange.
‡
monium ions (R2NH2 ) will spontaneously thread through the
cavities of appropriately sized crown ethers has led, in
addition to our publishing more than 60 short communica-
tions and full papers, to an enormous amount of interest being
shown by other research workers[22] in this simple and
appealing way to assemble a whole new class of interlocked
molecular compounds from inexpensive or readily available
starting materials. It remains an attractive proposition to look
for new synthetic protocols to aid and abet the further
covalent modification and planned manipulation of inter-
locked molecules constructed originally using this particular
recognition motif.
To demonstrate the generality of this new synthetic
approach toward triphenylphosphonium-stoppered [2]rotax-
anes, we decided to synthesize rotaxanes with the slightly
larger crown ether, benzometaphenylene[25]crown-8
(BMP25C8). Since the p-tert-butylbenzyl group is not large
enough to prevent dethreading of the BMP25C8 macro-
cycle,[25] we prepared 1b-H ¥ PF6 (Scheme 1), a thread-like
dialkylammonium salt,[26] containing a bromomethylphenyl
group, and the sterically more demanding 3,5-di-tert-butyl-
benzyl group. Addition of PPh3 to a solution of BMP25C8 and
1b-H ¥ PF6 in CH2Cl2 yielded the [2]rotaxane 2b-H ¥ 2PF6 in
32% yield. This lower yield, when compared to the formation
of the DB24C8-containing rotaxane 2a-H ¥ 2PF6, is presum-
ably a consequence of the much weaker binding[27] exhibited
We can use [2]rotaxane I (Figure 1), which carries a
surrogate stopper that can be chemically converted into
another terminal group and results in a new interlocked
‡
by BMP25C8 toward DBA ions relative to that exhibited by
DB24C8.
Single crystals, suitable for X-ray crystallography, were
grown by liquid diffusion of MeOH into a CH2Cl2 solution of
the [2]rotaxane 2a-H ¥ 2PF6. The solid-state structure of the
[2]rotaxane 2a-H ¥ 2PF6 shows (Figure 2) that the DB24C8
component has a conventional U-shaped conformation with
the two catechol rings inclined by approximately 558 to each
other. The dicationic dumbbell component is tethered to the
Figure 1. Graphical representation of the threading-followed-by-stopper-
ing approach to [2]rotaxanes and the subsequent stopper-exchange
concept.
molecule II, as a building block
to construct infinitely more
complex interlocked molecules.
Here, we apply the well-known
Wittig reaction, starting from
simple [2]rotaxanes that con-
tain either one or two benzylic
triphenylphosphonium
stop-
pers, to make other 1) [2]rotax-
anes, 2) higher order rotaxanes,
3) branched rotaxanes, and 4)
molecular shuttles. The results,
which amount to an important
and convincing proof of princi-
ple, have already been present-
ed in skeleton format in a
couple of short communica-
tions.[23]
Results and Discussion
The syntheses of two mono(tri-
phenylphosphonium)-ion-stop-
pered [2]rotaxanes are shown in
Scheme 1. On account of the
Scheme 1.
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J. F. Stoddart, D. J. Williams et al.
FULL PAPER
H ¥ PF6 in CH2Cl2 alone. After counterion exchange, 4a-H ¥
3PF6 was isolated in 55% yield. Based on the moderately high
Ka for the formation of the [2]pseudorotaxane precursor
[DB24C8 ꢀ 3-H]PF6 in the reaction solvent, as well as the
relatively high concentration of the host and guest in solution,
>99% of the total amount of 3-H ¥ PF6 is expected to be
complexed as the [2]pseudorotaxane. Nonetheless, we ob-
served a large amount of unthreaded dumbbell being formed
at the expense of a higher yield of the corresponding
[2]rotaxane 4a-H ¥ 3PF6. The mixture of counterions present
after PPh3 displaces bromide ions from 3-H ¥ PF6 results
presumably in the formation of a tight ion-pair between the
BrÀ and the NH2 center of both the 3-H and the
intermediate mono(triphenylphosphonium)-substituted ions,
a situation which reduces the strength of the binding between
them and DB24C8 and, consequently, hinders the formation
of the [2]rotaxane 4a-H ¥ 3X and encourages the production
of the free dumbbell-shaped compound (see Experimental
Section).
‡
‡
Figure 2. The cationic portion of the solid-state structure of the [2]rotax-
ane 2a-H ¥ 2PF6. The hydrogen bonding geometries, X ¥¥¥ O, H ¥¥¥ O [ä],
À
and X H ¥¥¥ O [8]: a) 3.05, 2.21, 156; b) 3.14, 2.30, 154; c) 3.27, 2.40, 150;
d) 3.23, 2.34, 153.
‡
À
crown ether by weak N H ¥¥¥ O
À
and C H ¥¥¥ O hydrogen bonds
(a d in Figure 2), a binding that
is supplemented by p p stacking
between one of the catechol rings
of the DB24C8 component and
the central phenylene ring of the
dumbbell component (centroid ¥¥¥
centroid distance and mean inter-
planar separation: 3.74, 3.49 ä,
respectively). There are no p
p
interactions between the catechol
rings and the phenyl rings of the
‡
Ph3P stopper. There are also no
inter-[2]rotaxane interactions of
note.
After having made and charac-
terized two different mono(tri-
phenylphosphonium)-stoppered
[2]rotaxanes, 2a-H ¥ 2PF6 and 2b-
Scheme 2.
By using a similar protocol to that employed in the
synthesis of 4a-H ¥ 3PF6, the [2]rotaxane 4b-H ¥ 3PF6, in
which the crown ether BMP25C8 is the macrocyclic compo-
nent, was assembled in 43% yield. Again, we believe that the
slightly lower yield of 4b-H ¥ 3PF6, relative to that of the
[2]rotaxane 4a-H ¥ 3PF6, is a consequence of the weaker
binding between the dialkylammonium thread 3-H ¥ X and the
larger BMP25C8 macrocycle relative to that of DB24C8.[28]
Single crystals, suitable for X-ray crystallography, were
grown by slow evaporation of a CH2Cl2/MeOH solution of the
[2]rotaxane 4a-H ¥ 3PF6. The solid-state structure of the
[2]rotaxane 4a-H ¥ 3PF6 shows (Figure 3) that the DB24C8
component adopts a U-shaped conformation, very similar to
that observed in 2a-H ¥ 2PF6, with the two catechol rings
subtending an angle of about 548. The tricationic dumbbell
component is threaded approximately centrally through the
H ¥ 2PF6, we became interested in synthesizing bis(triphenyl-
phosphonium)-stoppered [2]rotaxanes, which are not only
more highly symmetrical, but also carry functionality at both
termini of their dumbbell components. Again, since the free
species and the pseudorotaxane [DB24C8 ꢀ 3-H]PF6 are in
1
slow exchange on the H NMR timescale, the single-point
method[24] was used to obtain Ka values of 350mÀ1 and
1800mÀ1 for the 1:1 complex formed in CD3CN and CD2Cl2/
CD3CN (1:1), respectively. The binding constant in CD2Cl2/
CD3CN of this bis(4-bromomethyl)-substituted thread 3-H ¥
PF6 with DB24C8 is slightly smaller than that (Ka ˆ 2000mÀ1
)
of the bis(4-bromo)-substituted dibenzylammonium salt,[24b]
but larger than that (Ka ˆ 960mÀ1) of the bis(4-methyl)-
substituted one.[24b]
The [2]rotaxane 4a-H ¥ 3PF6 was assembled (Scheme 2) by
adding PPh3 to a mixture of 3-H ¥ PF6 (100mm) and DB24C8
(174mm) in CH2Cl2/CH3CN (1:1). A CH2Cl2/MeCN mixed-
solvent system was utilized because of the poor solubility of 3-
crown ether and is held in position by a combination of weak
‡
À
À
N
H ¥¥¥ O and C H ¥¥¥ O hydrogen bonds (a e in Figure 3).
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[2]Rotaxanes
5170 5183
occur under the basic Wittig reaction conditions, since the
noncovalent stabilizing interactions between DB24C8 and the
dialkylammonium ion will be ™switched off∫ by the deproto-
‡
nation of the NH2 center. We have demonstrated, however,
that the triphenylphosphonium ion stopper on [2]rotaxane
2a-H ¥ 2PF6 can be exchanged for a 4-tert-butyl one to
generate a new [2]rotaxane 5a-H ¥ PF6, while maintaining
the interlocked nature of the [2]rotaxanes. This important
observation can be explained by examining the mechanism
(Scheme 3) of the Wittig reaction. This examination reveals
that at each stage of the reaction–ylide, betaine, oxaphos-
phetane, and alkene–the DB24C8 macrocycle is trapped
along the axle of the dumbbell-shaped component because of
the presence of triphenylphosphine- and tert-butylphenyl-
derived stoppers, irrespective of the presence or lack of
hydrogen bonding interactions between the two components.
To convert both the Z and E isomers into a common product,
hydrogenation of the cis and trans double bonds in the
rotaxane was achieved by using Adams× catalyst[29] (PtO2)/H2,
Figure 3. The cationic portion of the solid-state structure of the [2]rotax-
ane 4a-H ¥ 3PF6. The hydrogen bonding geometries, X ¥¥¥ O, H ¥¥¥ O [ä],
À
and X H ¥¥¥ O [8]: a) 3.05, 2.26, 147; b) 2.96, 2.15, 151; c) 3.33, 2.44, 153;
d) 3.21, 2.41, 156; e) 3.22, 2.33, 156.
In contrast to the near parallel
p
p stacking between one of
the phenylene rings of the di-
cation and one of the catechol
rings observed in 2a-H ¥ 2PF6,
here, the analogous ring sys-
tems are inclined by approxi-
mately 208 (with a centroid ¥¥¥
centroid separation of 4.14 ä),
thus reducing appreciably any
potential
p
p
stabilization.
The only inter[2]rotaxane inter-
action of note is p p stacking
between the phenylene ring on
the convex side of the DB24C8
component in one molecule
and one of the phenyl rings of
‡
the Ph3P stoppers positioned
on the convex face of the crown
ether in another. These rings
are inclined by 68 with cent-
Scheme 3.
and the homogeneous [2]rotaxane 6a-H ¥ PF6 was obtained in
61% yield (Figure 4). H NMR spectra recorded during the
roid ¥¥¥ centroid and mean interplanar separations of 3.75 and
3.56 ä, respectively.
1
transformation become much simpler after hydrogenation of
5a-H ¥ PF6. Two pairs of tert-butyl signals in the region d ˆ
1.21 1.32 of the spectrum of 5a-H ¥ PF6, which indicate that
the ratio of the E/Z isomers is around 1:2, were converted into
only one pair of signals in the spectrum of 6a-H ¥ PF6 after
hydrogenation of the double bonds. The disappearance of the
signals for the olefinic protons and the appearance of the
corresponding signal at d ˆ 2.83 for the bismethylene protons
confirms that the reduction proceeded to completion. The
upfield shifts of the signals for the a-, b-, and g-OCH2 protons
of the DB24C8 macrocycle (d ˆ 4.08, 3.75, and 3.47, respec-
tively), compared to those for uncomplexed DB24C8 (d ˆ
4.24, 3.76, and 3.61), support the interlocked nature of the two
components of 6a-H ¥ PF6 and the existence of strong hydro-
gen bonding interactions between the DB24C8 ring and the
With this selection of triphenylphosphonium-ion-stoppered
[2]rotaxanes (2a-H ¥ 2PF6, 2b-H ¥ 2PF6, 4a-H ¥ 3PF6, and 4b-
H ¥ 3PF6) at our disposal, we were able to start examining
their potential as interlocked synthetic intermediates in Wittig
reactions by treating them with a range of mono-, di-, and tri-
aldehydes in the presence of base.
To demonstrate that the triphenylphosphonium-ion stop-
pers of these rotaxanes can be converted into alternative
stoppers through Wittig reactions, we first examined reactions
with the mono(triphenylphosphonium)-ion-stoppered rotax-
ane 2a-H ¥ 2PF6. Reaction of 2a-H ¥ 2PF6 with p-tert-butyl-
benzaldehyde in the presence of an excess of NaH in CH2Cl2
afforded 5a-H ¥ PF6 (Scheme 3)–as a mixture of E and Z
isomers–in 80% yield, after acidic work up and counterion
exchange (NH4PF6/H2O). One might expect dethreading to
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J. F. Stoddart, D. J. Williams et al.
FULL PAPER
Figure 4. Partial 1H NMR spectra (400 MHz, CD3CN, 298 K) of a) the E/Z isomer mixture of [2]rotaxanes 5a-H ¥ PF6 and b) the hydrogenated [2]rotaxane
6a-H ¥ PF6.
dialkylammonium ion center with dumbbell-shaped compo-
nent.
protecting-group approach, that is, by adding sterically bulky
groups to a small aldehyde in order to increase its steric size
and transform it into a true stopper for the synthesis of a
rotaxane. To demonstrate this approach, 2,5-bis(benzyloxy-
methoxy)benzaldehyde (10) was prepared from methyl 2,5-
dihydroxybenzoate by 1) benzyloxymethoxy (BOM) protec-
tion to give the ester 8, 2) LiAlH4 reduction of the ester to
yield the alcohol 9, and 3) Swern oxidation of the alcohol to
afford the aldehyde 10 in 72% overall yield (Scheme 5). The
After successfully exchanging the one single triphenylphos-
phonium stopper in the [2]rotaxane 2a-H ¥ 2PF6, we decided
to examine the possibility of exchanging two triphenylphos-
phonium ion stoppers in one step to build a symmetrical
[2]rotaxane. And so, the Wittig chemistry was repeated, but
this time with the [2]rotaxanes 4a-H ¥ 3PF6 and 4b-H ¥ 3PF6 as
substrates. Reaction of 4a-H ¥ 3HF6 with p-tert-butylbenzal-
dehyde in the presence of an excess of NaH in CH2Cl2
(Scheme 4) afforded an E/Z mixture of olefins after proton-
ation (1n HCl) and counterion exchange (NH4PF6/H2O). This
isomeric mixture of olefins was hydrogenated with the aid of
PtO2 as a catalyst to produce the [2]rotaxane 7a-H ¥ PF6 from
4a-H ¥ 3PF6 in 50% yield.
The challenge of synthesizing a sterically bulky aldehyde
for the Wittig reaction can easily be resolved by using a
Scheme 5.
[2]rotaxane 4a-H ¥ 3PF6 was treated with the aldehyde 10 to
yield a [2]rotaxane 11a-H ¥ PF6 after catalytic hydrogenation
(Scheme 6); this rotaxane bears potentially removable BOM
groups at its termini. The BMP25C8-derived [2]rotaxane 4b-
H ¥ 3PF6 also undergoes the Wittig reaction with 2,5-bis(ben-
zyloxymethoxy)benzaldehyde, followed by hydrogenation, to
yield the corresponding [2]rotaxane 11b-H ¥ PF6 in 63% yield.
These results suggest that the 2,5-bis(benzyloxymethoxy)-
phenyl groups are sterically impassable by both the DB24C8
and BMP25C8 macrocycles. When the BOM protecting
groups of the rotaxane 11a-H ¥ PF6 were removed under
acidic conditions (5% HCl/THF), substituted hydroquinone
rings were revealed at the termini of the thread. A large
amount of free DB24C8 was observed, however, in the crude
reaction mixture; this suggests that the hydroquinone rings
Scheme 4.
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[2]Rotaxanes
5170 5183
Scheme 6.
are not large enough to serve as mechanical stoppers for
DB24C8 and so decomplexation of the macrocycle from the
thread occurs. Since the BOM-protected hydroquinone units
are true stoppers, while the simple hydroquinone units are
not, the procedures described above represent a simple
method for constructing a [2]rotaxane by a protecting-group
approach and its conversion into a [2]pseudorotaxane by the
removal of the protecting groups under acidic conditions.
Having demonstrated that new [2]rotaxanes can be gen-
erated by reacting mono- and bis(triphenylphosphonium) ion-
stoppered [2]rotaxanes with mono-aldehydes, we turned our
attention to the reaction of these same rotaxanes with
dialdehydes (Scheme 7). When 2,5-dimethoxyterephthalde-
hyde and 2,5-bis(benzyloxymethoxy)terephthaldehyde[30]
were used as the partners to 2a-H ¥ 2PF6 in Wittig reactions,
the [3]rotaxanes 12a-2H ¥ 2PF6 and 13a-2H ¥ 2PF6, respec-
tively, were isolated after hydrogenation. These results
suggest that the 2,5-dimethoxyphenylene unit is also sterically
bulky enough to prevent the dethreading of the DB24C8
macrocycles during the Wittig reaction.
The bulky BOM groups that separate the two DB24C8
macrocycles in 13a-2H ¥ 2PF6 were removed under acidic
conditions to give a [3]rotaxane with a hydroquinone-core:
14a-2H ¥ 2PF6. Since the bridging unit no longer contains the
BOM groups, the DB24C8 macrocycles may be able, in
theory, to traverse the linker between the two ammonium
centers. However, the [3]rotaxane 14a-2H ¥ 2PF6 was not
stable. It decomposed in less than seven days at ambient
temperature. Evidence for free DB24C8 was observed in the
resulting 1H NMR spectrum, suggesting that the backbone of
the dumbbell-shaped component undergoes cleavage. The
hydroquinone ring is most likely to be the site of this cleavage,
possibly as a result of an oxidative free-radical process.
Having treated 2a-H ¥ 2PF6 and 2b-H ¥ 2PF6 with dialde-
hydes to produce [3]rotaxanes, we were intrigued at the
prospect of treating a triphenylphosphonium-ion-stoppered
rotaxane with a trialdehyde, namely triformylbenzene, and so
possibly providing a route to dendrimer-like rotaxanes. When
1,3,5-triformylbenzene[31] was added to a CH2Cl2 solution of
2a-H ¥ 2PF6 in the presence of an excess of NaH, the branched
[4]rotaxane 15a-3H ¥ 3PF6 was isolated as a complex mixture
of stereoisomers (Scheme 8). No rotaxanes were isolated in
which the three Wittig reactions had occurred with the loss of
one or more DB24C8 rings. If it is assumed that the first step is
the addition of a single ylide derived from [2]rotaxane 2a-H ¥
2PF6 to C6H3(CHO)3, then the formyl groups on the 3' and 5'
positions of the benzene ring in the putative intermediate
must presumably be large enough to prevent dethreading of
the DB24C8 macrocycle, otherwise the analogue of 15a-3H ¥
3PF6, having lost one DB24C8, would also have been isolated.
The complicated 1H NMR spectrum (Figure 5) of the olefinic
[4]rotaxane mixture 15a-3H ¥ 3PF6 was dramatically simpli-
fied after hydrogenation, an outcome that suggests the
formation of the highly symmetrical dendritic [4]rotaxane
16a-3H ¥ 3PF6. The interlocked nature of the macrocycles was
confirmed by the upfield shifts of the a-, b-, and g-OCH2
1
proton signals. The H NMR signal of the methylene groups
‡
adjacent to the NH2 center was found to be a triplet and
shifted downfield to d ˆ 4.59, an observation which suggests
the existence of hydrogen bonding between the crown ethers
Scheme 7.
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J. F. Stoddart, D. J. Williams et al.
FULL PAPER
Thus far, we have demonstrat-
ed that, when the hydrogen
bonding between the crown
‡
ether and the NH2 center is
™switched off∫ under basic Wit-
tig reaction conditions, the tri-
phenylphosphonium ion-stop-
pered [2]rotaxanes 2a-H ¥ 2PF6,
2b-H ¥ 2PF6, 4a-H ¥ 3PF6, and
4b-H ¥ 3PF6 can react with steri-
cally bulky aldehydes to form a
variety of new [2]-, [3]-, and
[4]rotaxanes without losing their
macrocyclic components.
We now describe how we ex-
tended our studies of these sys-
Scheme 8.
tems to utilize aldehydes with
little steric bulk in order to take
advantage of the expected dethreading of the rotaxanes×
components during the Wittig reaction (Scheme 9). Interest-
ingly, we discovered that reaction of 2a-H ¥ 2PF6 under basic
conditions with terephthaldehyde–an aldehyde that is not
large enough to prevent the dethreading of DB24C8 after the
first Wittig reaction–affords only a mixture of the unsatu-
rated [2]rotaxanes (Scheme 9). Hydrogenation of this olefin
mixture was achieved by using H2/PtO2 to yield (66% overall
yield from 2a-H ¥ 2PF6) a molecular shuttle 17a-2H ¥ 2PF6,
which contains only one DB24C8 ring that is shared between
‡
its two degenerate NH2 recognition sites. The [3]rotaxane,
Figure 5. Partial 1H NMR spectra (400 MHz, CD3CN, 298 K) of a) the E/Z
isomer mixture of [4]rotaxanes 15a-3H ¥ 3HF6 and b) the hydrogenated
[4]rotaxane 16a-3H ¥ 3HF6.
which would have contained two DB24C8 rings, that is, one
ring located at each recognition site, was not observed as a
product of the reaction sequence outlined in Scheme 9.
The outcome of this reaction sequence is significant for at
least two reasons. Firstly, it demonstrates that the aldehyde
which was used in the Wittig reaction is not large enough to
and the encircled ammonium ion centers in 16a-3H ¥ 3PF6.
The dendritic [4]rotaxane 16a-3H ¥ 3PF6 was obtained in an
impressive 47% yield after the sequence of six reactions,
namely three Wittigs followed by three hydrogenations.
‡
prevent the dethreading of the crown ether once its NH2
binding site has been deprotonated. In the synthesis of
Scheme 9.
5176
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Chem. Eur. J. 2002, 8, No. 22

[2]Rotaxanes
5170 5183
[2]rotaxane 17a-2H ¥ 2PF6, after the first Wittig reaction of
2a-H ¥ 2PF6 with OHCC6H4CHO, the DB24C8 ring slips off
the semirotaxane[32] because the formyl-terminated end of the
rivet-shaped component is not large enough to prevent
dethreading of the macrocycle. However, during the second
Wittig reaction, this time using the formyl-terminated inter-
mediate, with another equivalent of 2a-H ¥ 2PF6, dethreading
is impossible because both ends of the newly created dumb-
bell-shaped component are sufficiently large (tert-butylphen-
yl) to retain the DB24C8 macrocycle. Secondly, it gives
immediate access to [2]rotaxanes that can behave as molec-
ular shuttles[4] and so provides a simple means of building this
kind of prototypical molecular machinery. A previous study[4c]
on bis(dialkylammonium)-ion-containing molecular shuttles
(which was prepared by a more laborious route) has
demonstrated that the passage of a DB24C8 macrocycle
across a p-phenylene ring is slow on the 1H NMR timescale at
400 MHz, even at elevated temperatures and in highly polar
solvents. The slightly larger ring macrocycle BMP25C8 is
expected, however, to shuttle along such a thread with
somewhat greater ease. Therefore, we prepared the analogous
BMP25C8-containing [2]rotaxane 17b-2H ¥ 2PF6 (Scheme 9)
by utilizing the mono(triphenylphosphonium)-ion-stoppered
rotaxane 2b-H ¥ 2PF6 with the Wittig reaction/hydrogenation
protocol. The resulting [2]rotaxane 17b-2H ¥ 2PF6 does be-
have as a molecular shuttle on the 1H NMR timescale.
Consequently, we examined the shuttling of the BMP25C8
macrocycle along the linker, which contains three p-phenyl-
studies in most nonpolar solvents are limited by the slow rate
of exchange of the macrocycle between the NH2 centers, we
‡
investigated the kinetic behavior of molecular shuttle 17b-
2H ¥ 2PF6 in CD3OD, which is polar enough to weaken the
BMP25C8/dialkylammonium-ion interaction and so make
coalescence easier to achieve. The 1H NMR spectrum of 17b-
2H ¥ 2PF6 in CD3OD at ambient temperature also shows two
distinct signals for two pairs of Ar-CH2CH2-Ar groups.
However, these two signals coalesce (Figure 6b) at 336 K
with a limiting frequency difference (Du) of 46.8 Hz, which
corresponds to a value of kc of 104 sÀ1 for the process of the
‡
macrocycle shuttling between the NH2 centers. By using the
Eyring equation, a free energy of activation of 16.6 kcalmolÀ1
was obtained[4c] for the shuttling process at the coalescence
temperature Tc of 336 K.
Conclusion
Unless we can devise the means to modify covalently the
constitutions of rotaxanes by transforming them into yet more
organized and sophisticated arrays, they are destined to
occupy a place in the hall of fame for chemical compounds
that earns them the accolade of being exotic and only very
occasionally, potentially useful. Hence, there is a need to bring
about the ways and means to be able to process rotaxanes
after their initial supramolecularly assisted template-directed
syntheses. In this full paper, we have described how Wittig
chemistry can be called into action to achieve a whole range of
different structural objectives of a post-assembly nature.
Some of the transformations that can be carried out on
‡
ene rings-positioned between the two NH2 centers. The
1
partial H NMR spectrum (Figure 6a) of 17b-2H ¥ 2PF6 in
CD3CN at ambient temperature shows that the dumbbell has
two distinct halves, as highlighted by the observation of two
peaks at d ˆ 2.73 and 2.86 for the two pairs of CH2CH2 groups
that link the three p-phenylene rings of the spacer unit
together, suggesting that the BMP25C8 macrocycle shuttles
‡
benzylic triphenylphosphonium-stoppered, NH2 -centered/
crown-ether-based [2]rotaxanes, although routine in nature,
establish a principle of considerable significance to the
chemistry of interlocked molecular compounds beyond sim-
ple catenanes and rotaxanes: they open up, for example,
completely new pathways to intriguing interlocked macro-
molecules, including polyrotaxanes of the conventional,[33]
dendritic,[34] and daisy chain[35] types. Yet other carefully
designed transformations make
slowly between the NH2 centers on the 1H NMR timescale at
‡
‡
400 MHz. In one of these halves, the NH2 center is encircled,
in characteristic fashion, by the BMP25C8 macrocyclic ring,
while in the other it is free, that is, not encircled. Since kinetic
it possible to construct, with
incredible control, molecular
machines–for example, the
molecular shuttle reported
herein–of a precisely defined
nature that are preordained by
the reagents and conditions
employed in carrying out the
Wittig reactions. The story that
begins to unfold in this full
paper about how Wittig chem-
istry can be used in a post-
assembly fashion to take rotax-
anes, as starting materials in
synthesis, onto a higher level
of structure and function, is
Figure 6. a) Partial 1H NMR spectrum (400 MHz, CD3CN, 298 K) of the two-station molecular shuttle 17b-2H ¥
2PF6 depicting the asymmetrical nature of the shuttle at ambient temperature. b) Partial variable temperature
1H NMR spectra (400 MHz, CD3OD) of molecular shuttle 17b-2H ¥ 2PF6 highlighting the signals of the Ar-
CH2CH2-Ar groups, which coalesce at 336 K.
surely no more than a begin-
ning. Post-assembly processing
of rotaxanes (and catenanes)
Chem. Eur. J. 2002, 8, No. 22
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5177

J. F. Stoddart, D. J. Williams et al.
FULL PAPER
resolved into two partial occupancy orientations and the non-hydrogen
atoms of the major occupancy orientations were refined anisotropically
(those of the minor occupancy orientations were refined isotropically). The
included dichloromethane solvent molecule was also found to be disor-
dered, but over three partial occupancy sites; again only the major
occupancy non-hydrogen atoms were refined anisotropically, the others
will extend far beyond the influence of Wittig chemistry in the
fullness of time. A principle has been established and it is
bound to find expression elsewhere in this branch of
chemistry: it is one in which the mechanical bond can be
preserved totally or modified very precisely, according to the
diktat of the synthetic chemist.
À
isotropically. The C H hydrogen atoms were placed in calculated positions,
assigned isotropic thermal parameters, U(H) ˆ 1.2 Ueq(C) [U(H) ˆ
À
1.5 Ueq(C-Me)], and allowed to ride on their parent atoms. The N H
hydrogen atoms were located from a DF map and refined isotropically
À
subject to an N H distance constraint (0.90 ä). Refinements were by full
Experimental Section
matrix least-squares based on F 2 to give R1 ˆ 0.076, wR2 ˆ 0.208 for 7278
independent observed reflections [jFo j> 4s(jFo j ), 2qX1208] and 850
parameters. All computations were carried out using the SHELXTL PC
program system.[36] CCDC-187101 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(‡44)1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk).
Materials and methods: All glassware, stirrer-bars, syringes, and needles
were either oven- or flame-dried prior to use. All reagents, unless otherwise
indicated, were obtained from commercial sources. Anhydrous CH2Cl2 and
MeCN were obtained by distillation from CaH2 under Ar. Anhydrous THF
was obtained by distillation from Na/Ph2CO under N2. Reactions were
carried out under a N2 or Ar atmosphere. Thin-layer chromatography
(TLC) was performed on Analtech 0.25 mm silica gel GHLF. Column
chromatography was carried out over silica gel 60F (Merck 9385, 0.040
0.063 mm). Melting points were determined on an Electrothermal 9100
apparatus and are uncorrected. 1H and 13C NMR spectra were recorded on
either Bruker AC360 (360 and 90 MHz, respectively) or ARX400 (400 and
100 MHz, respectively) spectrometers. The deuterated solvent was used as
the lock, while either the solvent×s residual protons or TMSwas employed
as the internal standard. Chemical shifts are reported in parts per million
(ppm). Mutiplicities are given as s (singlet), d (doublet), t (triplet), q
(quartet), m (mutiplet), and br (broad). Coupling constants are in hertz.
Fast-atom bombardment (FAB) mass spectra were obtained using a ZAB-
SE mass spectrometer, equipped with a krypton primary atom beam,
utilizing a m-nitrobenzyl alcohol matrix. Microanalyses were performed by
Quantitative Technologies, Inc (USA).
{[2]-{N-(3,5-Di-tert-butylbenzyl)-N-{4-[(triphenylphosphonio)methyl]ben-
zyl}ammonium}(benzometaphenylene[25]crown-8)rotaxane}
bis(hexa-
fluorophosphate) (2b-H ¥ 2PF6): A solution of 1b-H ¥ PF6 (1.0 g, 1.8 mmol)
and BMP25C8 (1.0 g, 2.2 mmol) in MeNO2 (10 mL) was stirred at room
temperature for 10 min. PPh3 (0.6 g, 2.3 mmol) was added and the reaction
mixture was stirred for 12 h at ambient temperature. The solvent was
removed under reduced pressure, and the solid residue was dissolved in
MeCN (30 mL). Aqueous NH4PF6 (2 g) in H2O (30 mL) was added, and the
organic solvent was evaporated under reduced pressure. The residue was
partitioned between CH2Cl2 (50 mL) and H2O (30 mL). The organic layer
was washed with H2O (30 mL), dried (MgSO4), and evaporated to dryness.
The crude product was purified by column chromatography (SiO2; MeCN/
CH2Cl2 (1:9)). The rotaxane 2b-H ¥ PF6 was isolated as a white solid (0.75 g,
1
32%). M.p. 123 1258C; H NMR (400 MHz, CD3CN, 298 K): d ˆ 1.22 (s,
{[2]-{(N-4-tert-Butylbenzyl)-N-{4-[(triphenylphosphonio)methyl]benzyl}-
18H), 3.30 3.97 (m, 20H), 4.01 4.20 (m, 4H), 4.35 4.50 (m, 6H), 6.49
6.53 (m, 3H), 6.59 6.64 (m, 2H), 6.64 6.70 (m, 2H), 6.85 6.90 (m, 2H),
7.09 7.18 (m, 3H), 7.33 (d, J ˆ 1.7 Hz, 2H), 7.46 7.55 (m, 7H), 7.60 7.68
(m, 6H), 7.72 7.88 (m, 5H); 13C NMR (100 MHz, CD3CN, 298 K): d ˆ 30.3
(J(P,C) ˆ 48.3 Hz), 31.5, 35.6, 52.7, 53.8, 68.6, 68.9, 70.1, 71.0, 71.1, 72.0,
104.4, 108.4, 113.1, 118.2 (d, J(P,C) ˆ 85.7 Hz), 122.5, 124.9 (d, J(P,C) ˆ
13.6 Hz), 129.2 (d, J(P,C) ˆ 8.4 Hz), 131.1, 131.2, 131.3, 131.4, 131.6, 132.0
(d, J(P,C) ˆ 5.4 Hz), 132.5 (d, J(P,C) ˆ 3.8 Hz), 135.0 (d, J(P,C) ˆ 9.8 Hz),
136.4 (d, J(P,C) ˆ 2.9 Hz), 147.1, 152.7, 160.8; 31P NMR (162 MHz, CD3CN,
ammonium}(dibenzo[24]crown-8)rotaxane}
bis(hexafluorophosphate)
(2a-H ¥ 2PF6): A solution of 1a-H ¥ PF6 (1.0 g, 2.0 mmol) and DB24C8
(1.0 g, 2.2 mmol) in CH2Cl2 (10 mL) was stirred at room temperature for
10 min. PPh3 (0.6 g, 2.3 mmol) was added, and the reaction mixture was
stirred for 12 h at ambient temperature. The solvent was evaporated under
reduced pressure, and the solid residue was dissolved in MeCN (30 mL),
aqueous NH4PF6 (2 g in 30 mL H2O) was added, and the organic solvent
was evaporated under reduced pressure. The residue was partitioned
between CH2Cl2 (100 mL) and H2O (50 mL), and the organic phase was
washed with H2O (2 Â 50 mL). The organic layer was dried (MgSO4) and
concentrated. The product was purified by column chromatography (SiO2;
MeCN/CH2Cl2 (1:9)). The rotaxane 2a-H ¥ 2PF6 was isolated as a white
solid (2.0 g, 80%). M.p. 229 2318C; 1H NMR (400 MHz, CD3CN, 298 K):
d ˆ 1.22 (s, 9H), 3.45 3.55 (m, 8H), 3.59 3.75 (m, 8H), 3.94 4.00 (m,
8H), 4.39 (d, J ˆ 14.8 Hz, 2H), 4.45 4.52 (m, 2H), 4.70 4.75 (m, 2H), 6.64
(dd, J ˆ 2.4, 8 Hz, 2H), 6.70 6.79 (m, 4H), 6.79 6.88 (m, 4H), 7.15 (d, J ˆ
8 Hz, 2H), 7.23 (s, 4H), 7.43 7.49 (m, 6H), 7.61 7.66 (m, 6H), 7.83 7.87
(m, 3H); 13C NMR (100 MHz, CD3CN, 298 K): d ˆ 29.4 (J(P,C) ˆ 48.2 Hz),
30.5, 34.2, 51.7, 52.2, 67.8, 70.1, 70.6, 112.3, 117.1 (J(P,C) ˆ 85.7 Hz), 121.3,
125.6, 127.6 (d, J(P,C) ˆ 8.3 Hz), 128.7, 129.2, 129.8, 130.2 (d, J(P,C) ˆ
12.5 Hz), 131.0 (d, J(P,C) ˆ 5.3 Hz), 133.0 (d, J(P,C) ˆ 3.3 Hz), 134.1 (d,
J(P,C) ˆ 9.7 Hz), 135.3 (d, J(P,C) ˆ 3 Hz), 147.3, 152.3; 31P NMR (162 MHz,
298 K): d ˆ À143.6 (septet, J ˆ 708 Hz, PF6À), 22.6 (PhP ); MS(FAB): m/z:
‡
‡
‡
1178 [M À PF6] , 1033 [M À H À 2PF6] ; elemental analysis calcd (%) for
C65H80NO8P3F12 (1324): C 58.93, H 6.09, N 1.06; found: C 58.53, H 6.09,
N 0.99.
{[2]-{Bis{4-[(triphenylphosphonio)methyl]benzyl}ammonium}(dibenzo-
[24]crown-8)rotaxane} tris(hexafluorophosphate) (4a-H ¥ 3PF6): PPh3
(287 mg, 1.1 mmol) was added to
a solution of 3-H ¥ PF6 (200 mg,
0.38 mmol) and DB24C8 (508 mg, 0.66 mmol) in CH2Cl2/MeCN (1:1,
3.8 mL), and the reaction was then left to stir at room temperature
overnight. MeCN (50 mL) and NH4PF6 (0.5 g) in H2O (10 mL) were added,
the organic solvent was removed under reduced pressure and then the
milky aqueous solution was partitioned between CH2Cl2 (50 mL) and H2O
(50 mL). The organic layer was dried (MgSO4) and concentrated. The
crude product was purified by column chromatography (SiO2; CH3CN/
CH2Cl2 (1:9)), to yield the [2]rotaxane 4a-H ¥ 3PF6 (340 mg, 55%). M.p.
147 1498C; 1H NMR (400 MHz, CD3CN, 298 K): d ˆ 3.48 3.55 (m, 8H),
3.65 3.66 (m, 8H), 3.91 3.93 (m, 8H), 4.42 (d, J ˆ 14.8 Hz, 4H), 4.55
4.62 (m, 4H), 6.66 6.70 (m, 8H), 6.79 6.85 (m, 4H), 7.13 (d, J ˆ 8 Hz,
4H), 7.45 7.50 (m, 14H), 7.61 7.66 (m, 12H), 7.83 7.87 (m, 6H); 13C NMR
(100 MHz, CD3CN, 298 K): d ˆ 29.4 (J(P,C) ˆ 48.5 Hz), 51.9, 67.6, 70.1, 70.6,
112.2, 117.4 (d, J(P,C) ˆ 85.7 Hz), 121.3, 128.0 (d, J(P,C) ˆ 8.3 Hz), 129.8,
130.2 (d, J(P,C) ˆ 12.5 Hz), 131.2 (d, J(P,C) ˆ 5.4 Hz), 132.6 (d, J(P,C) ˆ
3.8 Hz), 134.1 (d, J(P,C) ˆ 9.7 Hz), 135.4 (d, J(P,C) ˆ 3 Hz), 147.1; 31P NMR
(162 MHz, CD3CN, 298 K): d ˆ À143.6 (septet, J ˆ 708 Hz, PF6À), 22.8
CD3CN, 298 K): d ˆ À143.6 (septet, J ˆ 708 Hz, PF6À), 22.6 (PhP ); MS
‡
‡
‡
(FAB): m/z: 1122 [M À PF6] , 976 [M À H À 2PF6] ; elemental analysis
calcd (%) for C61H72NO8P3F12 (1268): C 57.77, H 5.72, N 1.10; found: C
57.54, H 5.54, N 1.05; Single crystals, suitable for X-ray crystallography,
were grown by liquid diffusion of MeOH into a solution of the [2]rotaxane
2a-H ¥ 2PF6 in CH2Cl2. Crystal data for 2a-H ¥ 2PF6: [C61H72NO8P][PF6]2 ¥
≈
CH2Cl2, Mr ˆ 1353.0, triclinic, space group P1 (no. 2), a ˆ 13.722(1), b ˆ
15.241(1), c ˆ 17.972(1) ä, a ˆ 109.50(1), b ˆ 102.75(1), g ˆ 96.36(1)8, Vˆ
3385.3(3) ä3, Z ˆ 2, 1calcd ˆ 1.327 gcmÀ3
,
m(CuKa) ˆ 22.6 cmÀ1
F(000) ˆ
,
1408, Tˆ 293 K; clear prismatic blocks, 0.47  0.40  0.13 mm, Siemens
P4/RA diffractometer, graphite-monochromated CuKa radiation, w-scans,
9779 independent reflections. The structure was solved by direct methods
and the full occupancy non-hydrogen atoms were refined anisotropically
(the phenyl rings of the triphenylphosphonium moiety were refined as
idealized rigid bodies). Disorder was found in the tert-butyl group of the
thread and in both of the hexafluorophosphate anions; in each case this was
‡
‡
‡
(PhP ); MS(FAB) m/z: 1486 [M À PF6] , 1341 [M À H À 2PF6] ; elemen-
tal analysis calcd (%) for C76H80NO8P5F18 (1631): C 55.92, H 4.94, N 0.86;
found:
C 55.73, H 4.78, N 0.75. Single crystals, suitable for X-ray
crystallography, were grown by slow evaporation of a CH2Cl2/MeOH
solution of the [2]rotaxane 4a-H ¥ 3PF6. Crystal data for 4a-H ¥ 3PF6:
5178
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Chem. Eur. J. 2002, 8, No. 22

[2]Rotaxanes
5170 5183
[C76H80NO8P2][PF6]3 ¥ 5CH3OH, Mr ˆ 1792.5, monoclinic, space group I2/a
(no. 15), a ˆ 29.055(7), b ˆ 16.315(5), c ˆ 38.179(12) ä, b ˆ 102.67(2)8, Vˆ
was added and the mixture was stirred under an H2 atmosphere for 30 min.
The mixture was then filtered, the solvent evaporated, and the residue
purified by flash column chromatography (SiO2; CH2Cl2/MeOH 100:0 !
95:5) to yield the hydrogenated [2]rotaxane 6a-H ¥ PF6 as a clear oil (33 mg,
17659(9) ä3, Z ˆ 8, 1calcd ˆ 1.348 gcmÀ3
,
m(MoKa) ˆ 2.00 cmÀ1
F(000) ˆ
,
7472, Tˆ 293 K; clear blocks, 1.00  0.93  0.83 mm, Siemens P4/PC
diffractometer, graphite-monochromated MoKa radiation, w-scans, 11433
independent reflections. The structure was solved by direct methods and
the non-hydrogen atoms of the [2]rotaxane and the hexafluorophosphate
anions were refined anisotropically (the phenyl rings of the triphenylphos-
phonium moieties were refined as idealized rigid bodies). The included
methanol solvent molecules were found to be both highly disordered and
distributed over numerous full and partial occupancy sites; only the major
occupancy non-hydrogen atoms were refined anisotropically, the others
1
49%). H NMR (400 MHz, CDCl3, 298 K): d ˆ 1.24 (s, 9H), 1.30 (s, 9H),
2.83 (br, 4H), 3.44 3.48 (m, 8H), 3.74 3.76 (m, 8H), 4.05 4.10 (m, 8H),
4.50 4.62 (m, 4H), 6.73 6.78 (m, 4H), 6.85 6.90 (m, 4H), 7.03 (d, J ˆ
8 Hz, 2H), 7.11 (d, J ˆ 8 Hz, 2H), 7.16 7.19 (m, 4H), 7.21 (d, J ˆ 8 Hz, 2H),
7.35 (d, J ˆ 8 Hz, 2H), 7.55 (br, 2H); 13C NMR (100 MHz, CDCl3, 298 K):
d ˆ 31.2, 31.4, 34.4, 34.6, 36.8, 37.0, 52.2, 52.3, 68.2, 70.1, 70.6, 112.6, 121.6,
125.2, 125.5, 128.1, 128.6, 128.7, 128.9, 129.3, 138.3, 143.1, 147.5, 147.8, 148.8,
‡
152.4; HRMS(FAB): m/z calcd for C54H72NO8 [M À PF6] : 862.5258;
À
À
isotropically; their associated C H and O H hydrogen atoms were not
found: 862.5257.
À
located. The C H hydrogen atoms of the [2]rotaxane were placed in
{[2]-{Bis{4-[2-(4-tert-butylphenyl)ethyl]benzyl}ammonium}(dibenzo[24]-
crown-8)rotaxane} hexafluorophosphate (7a-H ¥ PF6): A mixture of 4a-H ¥
3PF6 (100 mg, 60 mmol) and NaH (10 mg, 0.4 mmol) in CH2Cl2 (1 mL) was
stirred at room temperature for 30 min, and then a solution of p-tert-
butylbenzaldehyde solution (28 mg, 0.17 mmol) in CH2Cl2 (1 mL) was
added slowly. The mixture was stirred at room temperature for 18 h before
MeOH (0.2 mL) was added to quench the reaction. The mixture was
partitioned between CH2Cl2 (30 mL) and H2O (30 mL). The organic layer
was washed with 5% HCl (2 Â 30 mL), dried (MgSO4), and concentrated.
The crude product was dissolved in MeCN (1 mL), and saturated aqueous
NH4PF6 was added until no further precipitation was observed. The solid
was filtered, washed with H2O, and dried under vacuum. The dry solid was
dissolved in THF (4 mL), PtO2 (6 mg) was added, and the mixture stirred
under an H2 atmosphere for 30 min. The solvent was removed under
reduced pressure, and the residue was partitioned between CH2Cl2 (30 mL)
and H2O (30 mL). The organic layer was washed with 5% HCl (2 Â 30 mL),
dried (MgSO4), and evaporated to dryness. The crude product was
dissolved in MeCN (1 mL) and saturated aqueous NH4PF6 was added
until no further precipitation was observed. After filtration, the solid was
purified by column chromatography (SiO2; MeOH/CH2Cl2 1:24) yielding
the [2]rotaxane 7a-H ¥ PF6 (30 mg, 50%). 1H NMR (400 MHz, CD3CN,
298 K): d ˆ 1.26 (s, 18H), 2.79 (s, 8H), 3.69 (s, 8H), 3.60 3.70 (m, 8H),
3.95 4.03 (m, 8H), 4.51 4.60 (m, 4H), 6.70 6.86 (m, 8H), 6.98 (d, J ˆ
8.1 Hz, 4H), 7.10 (d, J ˆ 7.5 Hz, 4H), 7.28 (d, J ˆ 7.5 Hz, 4H), 7.46 (d, J ˆ
8.1 Hz, 4H), 7.45 (br, 2H); 13C NMR (100 MHz, CD3CN, 298 K): d ˆ 30.6,
34.0, 36.3, 36.6, 52.1, 67.9, 70.1, 70.5, 112.5, 121.3, 125.1, 128.1, 128.5, 129.3,
129.5, 138.6, 142.9, 147.5, 148.7; HRMS(FAB): m/z calcd for C62H80NO8
calculated positions, assigned isotropic thermal parameters, U(H) ˆ
À
1.2 Ueq(C), and allowed to ride on their parent atoms. The N H hydrogen
atoms were located from a DF map and refined isotropically subject to an
À
N H distance constraint (0.90 ä). Refinements were by full matrix least-
squares based on F 2 to give R1 ˆ 0.092, wR2 ˆ 0.223 for 4889 independent
observed reflections [jFo j> 4s(jFo j ), 2qX458] and 1037 parameters. All
computations were carried out using the SHELXTL PC program system.[36]
CCDC-187102 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (‡44)1223
336 033; or e-mail: deposit@ccdc.cam.ac.uk). The corresponding dumb-
bell compound (179 mg, 35%) was also isolated. M.p. 222 2248C;
1H NMR (400 MHz, CD3CN, 298 K): d ˆ 4.12 (br, 4H), 4.65 (d, J ˆ
14.9 Hz, 4H), 6.99 (dd, J ˆ 2.4, 8 Hz, 4H), 7.29 (d, J ˆ 8 Hz, 4H), 7.50
7.56 (m, 12H), 7.65 7.69 (m, 12H), 7.84 7.89 (m, 6H); 13C NMR
(100 MHz, CD3CN, 298 K): d ˆ 29.4 (J(P,C) ˆ 48.5 Hz), 50.7, 117.3
(J(P,C) ˆ 85.8 Hz), 129.0 (J(P,C) ˆ 8.4 Hz), 130.2 (J(P,C) ˆ 12.5 Hz), 130.9
(J(P,C) ˆ 3 Hz), 131.1 (J(P,C) ˆ 3.9 Hz), 131.5 (J(P,C) ˆ 5.4 Hz), 134.1
(J(P,C) ˆ 9.8 Hz), 135.4 (J(P,C) ˆ 3 Hz); 31P NMR (162 MHz, CD3CN,
298 K): d ˆ À143.6 (septet, J ˆ 708 Hz, PF6À), 23.7 (PhP ); HRMS(FAB):
‡
‡
m/z calcd for C52H47NP3F6 [M À H À 2PF6] : 892.2826; found: 892.2826.
{[2]-{Bis{4-[(triphenylphosphonio)methyl]benzyl}ammonium}(benzome-
taphenylene-[25]crown-8)rotaxane} tris(hexafluorophosphate) (4b-H ¥
3PF6): PPh3 (600 mg, 2.3 mmol) was added to a solution of 3-H ¥ PF6
(400 mg, 0.75 mmol) and BMP25C8 (1.0 g, 2.2 mmol) in MeNO2 (4 mL),
and the reaction was then left to stir at room temperature overnight. MeCN
(50 mL) and NH4PF6 (1.0 g) in H2O (10 mL) were added, the organic
solvent was removed under reduced pressure, and then the milky aqueous
solution was partitioned between CH2Cl2 (50 mL) and H2O (50 mL). The
organic layer was dried (MgSO4) and concentrated. The crude product was
purified by column chromatography (SiO2; MeCN/CH2Cl2 (1:9)). [2]Ro-
taxane 4b-H ¥ 3PF6 (380 mg, 43%) was recovered as a white solid. M.p.
124 1268C; 1H NMR (400 MHz, CD2Cl2, 298 K): d ˆ 3.42 3.51 (m, 8H),
3.53 3.62 (m, 4H), 3.70 3.91 (m, 8H), 4.05 4.15 (m, 4H), 4.30 4.49 (m,
8H), 6.45 (s, 1H), 6.50 6.55 (m, 2H), 6.60 6.70 (m, 2H) 6.75 6.95 (m,
6H), 7.10 7.20 (m, 5H), 7.40 7.50 (m, 12H), 7.60 7.95 (m, 20H); 13C NMR
(100 MHz, CD2Cl2, 298 K): d ˆ 30.3 (d, J(P,C) ˆ 49.4 Hz), 52.2, 68.0, 68.1,
69.7, 70.7, 70.8, 71.7, 103.5, 107.5, 112.2, 116.2, 117.1, 121.7, 128.2 (d, J(P,C) ˆ
8.3 Hz), 130.0, 130.4 (d, J(P,C) ˆ 12.6 Hz), 131.5, 131.6 (d, J(P,C) ˆ 5.3 Hz),
133.9 (d, J(P,C) ˆ 9.6 Hz), 135.6 (d, J(P,C) ˆ 2.8 Hz), 146.0, 159.8; MS
‡
[M À PF6] : 966.5884; found: 966.5910.
Methyl 2,5-bis(benzyloxymethoxy)benzoate (8): A mixture of methyl 2,5-
dihydroxybenzoate (1.5 g, 8.9 mmol) and NaH (0.63 g, 26 mmol) was
cooled to 08C. DMF (25 mL) was added slowly, and the reaction mixture
was stirred at 08C for 1 h. Benzyloxymethyl chloride (3.3 mL) was added to
the reaction mixture dropwise by syringe for 30 min. The solution was
warmed up slowly to room temperature and stirred for 18 h. MeOH (3 mL)
was added to quench the reaction. The mixture was partitioned between
CH2Cl2 (200 mL) and H2O (200 mL). The organic layer was separated,
washed with 5% HCl(aq) (3 Â 100 mL), dried (MgSO4), and concentrated.
Purification by column chromatography using an EtOAc/hexanes (1:2)
1
mixture as the eluent gave the ester 8 (3.36 g, 92%). H NMR (400 MHz,
CD3CN): d ˆ 3.83 (s, 3H), 4.69 (s, 2H), 4.73 (s, 2H), 5.26 (s, 2H), 5.27 (s,
2H), 7.13 7.21 (m, 2H), 7.22 7.40 (m, 10H), 7.41 (s, 1H); 13C NMR
(100 MHz, CD3CN): d ˆ 52.7, 70.9, 71.0, 94.0, 95.0, 118.3, 119.4, 119.8, 122.3,
124.1, 128.7, 128.9, 128.9, 129.3, 138.6, 138.6, 151.9, 152.7, 167.0 (one signal is
™missing∫, presumably because of two overlapping signals); HRMS(EI):
m/z calcd for C24H24O6: 408.1573; found: 408.1573.
‡
‡
(FAB): m/z: 1486 [M À PF6] , 1341 [M À H À 2PF6] ; elemental analysis
calcd (%) for C76H80NO8P5F18 (1631): C 55.92, H 4.94, N 0.86; found: C
55.83, H 4.80, N 0.84. The corresponding dumbbell compound (450 mg,
51%) was also isolated and characterized. See the previous subsection.
2,5-Bis(benzyloxymethoxy)benzylalcohol (9): LiAlH4 (1.43 g, 37.6 mmol)
was added in small portions to a solution of ester 8 (3.1 g, 7.5 mmol) in THF
(30 mL) over a period of 1 h. The reaction mixture was stirred at room
temperature for 18 h. MeOH (10 mL) was slowly added to quench the
reaction. The mixture was partitioned between CH2Cl2 (200 mL) and H2O
(200 mL). The organic layer was separated, washed with 5% HCl(aq) (3 Â
100 mL), dried (MgSO4), and concentrated. Purification by column
chromatography by using an EtOAc/hexanes (1:3) mixture as the eluent
gave the alcohol 9 (2.45 g, 85%). 1H NMR (400 MHz, CD3CN): d ˆ 3.22 (t,
J ˆ 6 Hz, 1H), 4.63 (d, J ˆ 6 Hz, 2H), 4.70 (s, 4H), 5.25 (s, 2H), 5.26 (s, 2H),
6.94 (dd, J ˆ 3 Hz, 8.9 Hz, 1H), 7.06 (d, J ˆ 8.9 Hz, 1H), 7.17 (d, J ˆ 3 Hz,
1H), 7.21 7.41 (br, 10H); 13C NMR (100 MHz, CD3CN): d ˆ 60.1, 70.7,
70.9, 94.1, 94.2, 116.4, 116.5, 117.3, 118.3, 128.7, 128.7, 128.8, 128.9, 129.3,
{[2]-{N-(4-tert-Butylbenyl)-N-{4-[2-(tert-butylphenyl)ethyl]benzyl}ammo-
nium}(dibenzo[24]crown-8]rotaxane} hexafluorophosphate (6a-H ¥ PF6):
4-tert-Butylbenzaldehyde (0.2 mmol) was added to a mixture of 2a-H ¥
2PF6 (100 mg, 80 mmol) and NaH (8 mg, 0.3 mmol) in CH2Cl2 (2.6 mL),
and the mixture was left to stir at ambient temperature for 12 h. The
reaction was quenched with 1n HCl (10 mL) and the aqueous phase was
extracted with CH2Cl2. The solvent was evaporated, the residue was
dissolved in MeCN (10 mL), and saturated aqueous NH4PF6 was added
until no further precipitation was observed. The precipitate was filtered off,
washed with water and then dried under vacuum. Flash column chroma-
tography (SiO2; CH2Cl2/MeOH 100:0 ! 95:5), yielded the rotaxane 5a-H ¥
PF6 as a white solid, which was then dissolved in THF (2 mL). PtO2 (3 mg)
Chem. Eur. J. 2002, 8, No. 22
¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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5179

J. F. Stoddart, D. J. Williams et al.
FULL PAPER
133.5, 138.8, 138.8, 150.2, 153.1; HRMS(FAB): m/z calcd for C23H24O5:
380.1624; found: 380.1623.
(400 MHz, CD3CN, 298 K): d ˆ 2.73 2.88 (m, 8H), 3.44 3.51 (m, 8H),
3.52 3.61 (m, 4H), 3.72 3.85 (m, 8H), 4.10 4.17 (m, 4H), 4.28 4.38 (m,
4H), 4.65 (s, 4H), 4.70 (s, 4H), 5.18 (s, 4H), 5.24 (s, 4H), 6.49 6.59 (m,
3H), 6.60 6.65 (m, 2H), 6.78 6.90 (m, 6H), 7.10 7.35 (m, 31H), 7.64 (br,
2H); 13C NMR (100 MHz, CD3CN, 298 K): d ˆ 32.5, 36.2, 53.0, 68.6, 68.9,
70.3, 70.7, 71.0, 71.1, 71.3, 72.0, 94.2, 94.3, 104.4, 108.4, 113.0, 115.8, 116.5,
119.7, 122.3, 128.7, 128.7, 128.8, 128.8, 129.3, 129.4, 129.5, 129.7, 130.5, 131.4,
132.9, 138.8, 138.9, 144.4, 147.4, 151.2, 152.8, 160.8; MS(FAB): m/z: 1398.8
2,5-Bis(benzyloxymethoxy)benzaldehyde (10): A mixture of oxalyl chlor-
ide (0.31 mL, 3.55 mmol) and CH2Cl2 (10 mL) was cooled to À788C.
DMSO (0.42 mL, 5.9 mmol) was added slowly to the mixture, and the
solution was stirred at À788C for 30 min. Compound 9 (0.89g, 2.17 mmol)
in CH2Cl2 (10 mL) was slowly added into the solution mixture by means of
a syringe. The reaction mixture was stirred at À788C for 40 min. Et3N
(1.4 mL, 10 mmol) was added, and the reaction mixture was slowly warmed
up to room temperature. The mixture was partitioned between CH2Cl2
(200 mL) and H2O (200 mL). The organic layer was separated, washed with
H2O (3 Â 100 mL), dried (MgSO4), and concentrated. Purification by
column chromatography with an EtOAc/hexanes (1:2) mixture as the
eluent gave the aldehyde 10 (0.825 g, 93%). 1H NMR (400 MHz, CD3CN):
d ˆ 4.68 (s, 2H), 4.74 (s, 2H), 5.27 (s, 2H), 5.38 (s, 2H), 7.20 7.38 (m, 12H),
7.44 (d, J ˆ 3 Hz, 1H), 10.37 (s, 1H); 13C NMR (100 MHz, CD3CN): d ˆ
70.9, 71.5, 94.0, 94.4, 114.8, 118.3, 118.3, 125.6, 127.2, 128.7, 128.8, 128.9,
129.0, 129.3, 138.5, 138.6, 152.9, 155.7, 190.0; HRMS(EI): m/z calcd for
C23H22O5: 378.1467; found: 378.1475.
‡
[M À PF6] ; elemental analysis calcd (%) for C86H96NO16PF6 (1545): C
66.87, H 6.26, N 0.91; found: C 66.87, H 6.48, N 0.55.
{[3]-(Dibenzo[24]crown-8){2,5-bis{2-[4-(4-tert-butylbenzylammoniometh-
yl)phenyl]ethyl}-1,4-dimethoxybenzene}(dibenzo[24]crown-8)rotaxane}
bis(hexafluorophosphate) (12a-2H ¥ 2PF6):
A mixture of 2a-H ¥ PF6
(50 mg, 40 mmol) and NaH (6 mg, 0.25 mmol) in CH2Cl2 (2 mL), and the
mixture was stirred at room temperature for 30 min before 2,5-dimethoxy-
terephthaldehyde (4 mg, 20 mmol) in CH2Cl2 (0.5 mL) was added slowly by
means of a syringe. The reaction mixture was stirred for 12 h at ambient
temperature, H2O (0.1 mL) was added to quench the reaction, and the
mixture was partitioned between CH2Cl2 (30 mL) and H2O (30 mL). The
organic layer was washed with H2O (2 Â 30 mL), dried (MgSO4), and
evaporated to dryness. The residue was purified by column chromatog-
raphy (SiO2; MeCN/CH2Cl2 1:9). The [3]rotaxane 12a-2H ¥ 2PF6 was
isolated as a white solid (21 mg, 56%). M.p. 155 1578C; 1H NMR
(360 MHz, CD3CN, 298 K): d ˆ 1.20 (s, 18H), 2.73 (s, 8H), 3.50 (s, 16H),
3.69 (s, 6H), 3.73 3.80 (m, 16H), 3.99 4.08 (m, 16H), 4.53 4.66 (m, 8H),
6.70 (s, 2H), 6.70 6.88 (m, 16H), 7.00 (d, J ˆ 9.1 Hz, 4H), 7.14 7.25 (m,
12H), 7.48 (br, 4H); 13C NMR (90 MHz, CD3CN, 298 K): d ˆ 31.4, 32.4,
35.2, 36.3, 53.1, 53.2, 56.8, 69.0, 71.1, 71.5, 113.5, 114.3, 122.3, 126.4, 129.1,
129.5, 130.1, 130.2, 130.3, 130.5, 144.2, 148.6, 152.3, 153.1; MS(FAB): m/z:
{[2]-{Bis{4-[2-(2,5-bis(benzyloxymethyleneoxy)phenyl]ethyl}benzyl}am-
monium}(dibenzo[24]crown-8)rotaxane} hexafluorophosphate (11a-H ¥
PF6): A mixture of 4a-H ¥ 3PF6 (100 mg, 60 mmol) and NaH (10 mg,
0.4 mmol) in CH2Cl2 (1 mL) was stirred at room temperature for 30 min,
and then a solution of 10 (70 mg, 0.17 mmol) in CH2Cl2 (1 mL) was added
slowly. The mixture was stirred at room temperature for 18 h before MeOH
(0.2 mL) was added to quench the reaction. The mixture was partitioned
between CH2Cl2 (50 mL) and H2O (50 mL). The organic layer was washed
with 5% HCl (2 Â 30 mL), dried (MgSO4), and concentrated. The crude
product was dissolved in MeCN (1 mL), and saturated aqueous NH4PF6
was added until no further precipitation was observed. The solid was
filtered, washed with H2O, and dried under vacuum. The dry solid was
dissolved in THF (4 mL), PtO2 (6 mg) was added, and the mixture stirred
under an H2 atmosphere for 30 min. The solvent was removed under
reduced pressure, and the residue was partitioned between CH2Cl2 (30 mL)
and H2O (30 mL). The organic layer was washed with 5% HCl (2 Â 30 mL),
dried (MgSO4), and evaporated to dryness. The crude product was
dissolved in MeCN (1 mL), and saturated aqueous NH4PF6 was added
until no further precipitation was observed. After filtration, the solid was
purified by column chromatography (SiO2; MeOH/CH2Cl2 1:24) yielding
the [2]rotaxane 11a-H ¥ PF6 as a clear, thick oil (45 mg, 48%). 1H NMR
(400 MHz, CD3CN, 298 K): d ˆ 2.70 2.90 (m, 8H), 3.40 3.52 (m, 8H),
3.68 3.80 (m, 8H), 3.97 4.10 (m, 8H), 4.56 4.64 (m, 4H), 4.65 (s, 4H),
4.70 (s, 4H), 5.18 (s, 4H), 5.24 (s, 4H), 6.70 6.91 (m, 12H), 6.91 7.10 (m,
6H), 7.16 (d, J ˆ 7.8 Hz, 4H), 7.21 7.40 (m, 20H), 7.45 (br, 2H); 13C NMR
(100 MHz, CD3CN, 298 K): d ˆ 32.5, 36.2, 53.1, 68.8, 70.7, 71.0, 71.0, 71.5,
94.2, 94.3, 113.4, 115.8, 116.5, 119.7, 122.2, 128.7, 128.7, 128.8, 128.8, 129.3,
129.4, 129.5, 130.3, 130.5, 133.0, 138.8, 138.9, 143.9, 148.4, 151.2, 152.8; MS
‡
‡
1741 [M À PF6] , 1595 [M À H À 2PF6] .
{[3]-(Dibenzo[24]crown-8){2,5-bis{2-[4-(4-tert-butylbenzylammonio)meth-
ylphenyl]ethyl}-1,4-bis(benzyloxymethyleneoxy)benzene}(dibenzo[24]-
crown-8)rotaxane} bis(hexafluorophosphate) (13a-2H ¥ 2PF6): A mixture
of 2a-H ¥ 2PF6 (150 mg, 0.12 mmol) and NaH (16 mg, 0.67 mmol) in CH2Cl2
(2 mL) was stirred at room temperature for 30 min before 2,5-bis(benzy-
loxymethyleneoxy)terephthaldehyde (24 mg, 60 mmol) in CH2Cl2
(0.75 mL) was added slowly by means of a syringe. The mixture was
stirred overnight at room temperature before H2O (0.3 mL) was added to
quench the reaction. The mixture was partitioned between CH2Cl2 (50 mL)
and H2O (50 mL), and the organic layer was washed with H2O (2 Â 50 mL),
dried (MgSO4), and evaporated to dryness. The residue was purified by
column chromatography (SiO2; MeOH/CH2Cl2 1:19), and the [3]rotaxane
13a-2H ¥ 2PF6 was isolated as a white solid (70 mg, 56%). M.p. 104
1068C; 1H NMR (400 MHz, CD2Cl2, 298 K): d ˆ 1.26 (s, 18H), 2.83 (s,
8H), 3.42 3.52 (m, 16H), 3.68 3.78 (m, 16H), 4.00 4.10 (m, 16H), 4.52
4.63 (m, 8H), 4.75 (s, 4H), 5.28 (s, 4H), 6.72 6.94 (m, 16H), 7.00 (s, 2H),
7.03 7.12 (m, 4H), 7.20 7.40 (m, 22H), 7.55 (br, 4H); 13C NMR (100 MHz,
CD2Cl2, 298 K): d ˆ 31.3, 32.5, 34.8, 36.3, 52.6, 52.6, 68.4, 70.4, 70.6, 71.0,
93.8, 112.8, 116.8, 121.9, 125.8, 128.1, 128.2, 128.7, 129.0, 129.1, 129.3, 129.6,
129.7, 129.8, 138.0, 143.8, 147.9, 150.3, 152.7; MS(FAB): m/z: 1952 [M À
‡
(FAB): m/z: 1399.5 [M À PF6] ; elemental analysis calcd (%) for
C86H96NO16PF6 (1545): C 66.87, H 6.26, N 0.91; found: C 66.56, H 6.47, N
0.82.
‡
‡
PF6] , 1806 [M À H À 2PF6] ; elemental analysis calcd (%) for
C110H138N2O20P2F12 (2098): C 62.96, H 6.63, N 1.33; found: C 62.56, H
6.71, N 1.17.
{[2]-{Bis{4-{2-[2,5-bis(benzyloxymethyleneoxy)phenyl]ethyl}benzyl}am-
monium}(benzometaphenylene[25]crown-8)rotaxane}
hexafluorophos-
phate (11b-H ¥ PF6): A mixture of 4b-H ¥ 3PF6 (100 mg, 60 mmol) and
NaH (10 mg, 0.4 mmol) in CH2Cl2 (1 mL) was stirred at room temperature
for 30 min, and then 10 (70 mg, 0.17 mmol) in CH2Cl2 (1 mL) was added
slowly. The mixture was stirred at room temperature for 18 h, and then
MeOH (0.2 mL) was added to quench the reaction. The mixture was
partitioned between CH2Cl2 (50 mL) and H2O (50 mL). The organic layer
was washed with 5% HCl (2 Â 30 mL), dried (MgSO4), and concentrated.
The crude product was dissolved in MeCN (1 mL), and then saturated
aqueous NH4PF6 was added until no further precipitation was observed.
The precipitate was filtered, washed with H2O, and dried under vacuum.
The dry solid was dissolved in THF (4 mL), PtO2 (6 mg) was added, and the
mixture was stirred under an H2 atmosphere for 30 min. The solvent was
removed under reduced pressure, and the residue was partitioned between
CH2Cl2 (30 mL) and H2O (30 mL). The organic layer was washed with 5%
HCl (2 Â 30 mL), dried (MgSO4) and concentrated. The crude product was
dissolved in MeCN (1 mL) and saturated aqueous NH4PF6 was added until
no further precipitation was observed. After filtration, the solid was
purified by column chromatography (SiO2; MeOH/CH2Cl2 1:24) yielding
the [2]rotaxane 11b-H ¥ PF6 as clear thick oil (60 mg, 63%). 1H NMR
{[3]-(Dibenzo[24]crown-8){2,5-bis{2-[4-(4-tert-butylbenzylammoniometh-
yl)phenyl]ethyl}-2,5-dihydroxybenzene}(dibenzo[24]crown-8)rotaxane}
bis(hexafluorophosphate) (14a-2H ¥ 2PF6): The [2]rotaxane 13a-2H ¥ 2PF6
(20 mg, 10 mmol) in 5% HCl/THF (1:19; 5 mL) was heated under reflux
overnight before being cooled to room temperature. A solution of NH4PF6
(20 mg) in H2O (2 mL) was added, the THF was evaporated, and the
residue was partitioned between H2O (20 mL) and CH2Cl2 (20 mL). The
organic layer was washed with H2O (2 Â 20 mL), dried (MgSO4), and then
the solvent was evaporated. The residue was purified by column
chromatography (SiO2; MeCN/CH2Cl2 1:9), and the [3]rotaxane 14a-
2H ¥ 2PF6 was isolated (11 mg, 64%). 1H NMR (400 MHz, CD3CN, 298 K):
d ˆ 1.21 (s, 18H), 2.60 2.80 (m, 8H), 3.44 3.52 (m, 16H), 3.63 3.72 (m,
16H), 3.93 4.04 (m, 16H), 4.52 4.67 (m, 8H), 6.22 (s, 2H), 6.49 (s, 2H),
6.71 6.87 (m, 16H), 6.99 (d, J ˆ 8.1 Hz, 4H), 7.16 7.23 (m, 12H), 7.55 (br,
4H); 13C NMR (100 MHz, CD3CN, 298 K): d ˆ 31.4, 32.1, 35.1, 36.0, 53.0,
53.1, 68.9, 71.1, 71.5, 113.4, 117.5, 122.2, 126.3, 127.1, 129.5,130.0, 130.2,
‡
130.3, 130.5, 144.2, 148.5, 148.5, 153.0; MS(FAB): m/z: 1711 [M À PF6] ,
‡
1565 [M À H À 2PF6] .
5180
¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/02/0822-5180 $ 20.00+.50/0
Chem. Eur. J. 2002, 8, No. 22

[2]Rotaxanes
5170 5183
{[4]-{1,3,5-Tris{2-[4-(4-tert-butylbenzylammoniomethyl)phenyl]ethyl}ben-
zene}tris(dibenzo[24]crown-8)rotaxane} tris(hexafluorophosphate) (16a-
3H ¥ 3PF6): Benzene-1,3,5-tricarboxaldehyde (8.5 mg, 50 mmol) was added
precipitation was observed. After filtration, the solid was purified by
column chromatography (SiO2; MeOH/CH2Cl2 1:19) to yield the [2]rotax-
ane 17b-2H ¥ 2PF6 as a white solid (16 mg, 24%). 1H NMR (400 MHz,
CD3CN, 298 K): d ˆ 1.21 (s, 18H), 1.31 (s, 18H), 2.73 (s, 4H), 2.86 (s, 4H),
3.35 4.00 (m, 24H), 4.10 4.21 (m, 4H), 4.30 4.40 (m, 2H), 4.42 4.53 (m,
2H), 6.50 6.65 (m, 3H), 6.65 6.80 (m, 2H), 6.81 7.00 (m, 4H), 7.00 7.50
(m, 17H), 7.80 (br, 4H); 13C NMR (90 MHz, CD3CN, 298 K): d ˆ 31.6, 31.7,
35.5, 35.6, 37.4, 37.7, 37.8, 38.1, 53.1, 53.3, 53.6, 53.8, 68.6, 69.0, 70.2, 71.0, 71.2,
71.9, 104.4, 108.4, 113.1, 118.3, 122.4, 122.4, 123.8, 124.8, 124.9, 129.4, 129.5,
129.6, 130.6, 131.5, 131.7, 140.1, 140.4, 147.4, 151.9, 152.5 (seven signals are
™missing∫, presumably because of signal overlap); MS(FAB): m/z: 1344
to
a solution of 2a-H ¥ 2PF6 (200 mg, 0.16 mmol) and NaH (15 mg,
0.6 mmol) in CH2Cl2 (2.6 mL), and the mixture was then left to stir at
room temperature for 16 h. The reaction was quenched with 1n HCl
(10 mL), and the aqueous phase was then extracted with CH2Cl2. The
solvent was removed from the combined organic phases, the residue was
dissolved in MeCN (10 mL) and then saturated aqueous NH4PF6 was added
until no further precipitation was observed. The precipitate was filtered off,
washed with water, and then dried under vacuum. The resulting solid was
further purified by dissolving it in a small amount of CH2Cl2 and then
reprecipitated with Et2O. The crude rotaxane 15a-3H ¥ 3PF6 was dissolved
in THF (1.5 mL), PtO2 (6 mg) was added and the mixture stirred under an
H2 atmosphere for 2 h. The reaction mixture was then filtered and purified
by flash column chromatography (SiO2; CH2Cl2/MeOH 100:0 ! 95:5),
yielding the fully hydrogenated [4]rotaxane 16a-3H ¥ 3PF6 as a clear oil
‡
‡
[M À PF6] , 1198 [M À H À 2PF6] .
Acknowledgement
This research was supported by the National Science Foundation (CHE-
9910199) and the Petroleum Research Fund, administered by the
American Chemical Society. The paper is also based upon work supported
by the National Science Foundation under equipment grant number CHE-
9974928.
1
(67 mg, 47%). H NMR (400 MHz, CDCl3, 298 K): d ˆ 1.21 (s, 27H), 2.72
(br, 12H), 3.44 3.48 (m, 24H), 3.74 3.76 (m, 24H), 3.99 4.01 (m, 24H),
4.56 4.63 (m, 12H), 6.75 6.80 (m, 12H), 6.81 6.88 (m, 12H), 6.88 (s, 3H),
6.99 (d, J ˆ 8 Hz, 6H), 7.15 7.23 (m, 18H), 7.48 (br, 6H); 13C NMR
(100 MHz, CDCl3, 298 K): d ˆ 30.4, 34.2, 36.8, 37.0, 52.1, 67.9, 70.1, 70.5,
112.4, 121.2, 125.3, 126.1, 128.5, 129.0, 129.2, 129.4, 129.6, 141.7, 142.9, 147.5,
152.0 (one signal is ™missing∫, presumably because of two overlapping
‡
‡
signals); MS(FAB): m/z: 2554 [M À PF6] , 2408 [M À H À 2PF6] .
[1] a) D. B. Amabilino, J. F. Stoddart, Chem. Rev. 1995, 95, 2725 2828;
b) F. Vˆgtle, T. D¸nnwald, T. Schmidt, Acc. Chem. Res. 1996, 29, 451
460; c) M. Fujita, Acc. Chem. Res. 1999, 32, 53 61; d) Molecular
Catenanes, Rotaxanes and Knots (Eds.: J.-P. Sauvage, C. Dietrich-
Buchecker), Wiley-VCH, Weinheim, 1999; e) G. A. Breault, C. A.
Hunter, P. C. Mayers, Tetrahedron 1999, 55, 5265 5293; f) T. J. Hubin,
{[2]-{1,4-Bis{2-[4-(4-tert-butylbenzylammoniomethyl)phenyl]ethyl}ben-
zene}(dibenzo[24]crown-8)rotaxane} bis(hexafluorophosphate) (17a-2H ¥
2PF6): A solution of terephthaldehyde (10.5 mg, 80 mmol) in CH2Cl2
(2.5 mL) was added, over a period of 2 h, to a solution of 2a-H ¥ 2PF6
(200 mg, 0.2 mmol) and NaH (15 mg, 0.6 mmol) in CH2Cl2 (2.5 mL). The
reaction was then left to stir at room temperature for 15 h, before being
quenched with 1n HCl (10 mL), and the aqueous phase was then extracted
with CH2Cl2. The solvent was evaporated from the combined organic
phases, the residue was dissolved in MeCN, and then saturated aqueous
NH4PF6 was added until no further precipitation was observed. The
precipitate was filtered off, washed with H2O, and then dried under
vacuum. The resulting solid was further purified by dissolving it in a small
amount of CH2Cl2 and then reprecipitating it by the addition of Et2O. The
crude product was dissolved in THF (3 mL), PtO2 (6 mg) was added, and
the mixture was stirred under an H2 atmosphere for 1 h. The mixture was
then filtered, the solvent evaporated, and the residue purified by flash
column chromatography (SiO2; CH2Cl2/MeOH 100:0 ! 95:5) to yield the
[2]rotaxane 17a-2H ¥ 2PF6 as a clear oil (72 mg, 66%). 1H NMR (400 MHz,
CD3CN, 298 K): d ˆ 1.19 (s, 9H), 1.29 (s, 9H), 2.78 (s, 4H), 2.83 (s, 4H),
3.41 3.54 (m, 8H), 3.70 3.73 (m, 12H), 3.99 4.02 (m, 8H), 4.54 4.62 (m,
4H), 6.75 6.81 (m, 4H), 6.81 6.88 (m, 4H), 6.93 6.98 (m, 2H), 7.01 7.08
(m, 4H), 7.11 7.30 (m, 12H), 7.34 7.39 (m, 2H), 7.48 (br, 2H); 13C NMR
(100 MHz, CDCl3, 298 K): d ˆ 30.4, 30.5, 34.1, 34.2, 36.4, 36.7, 36.8, 37.0,
51.9, 52.0, 52.1, 52.2, 67.9, 70.1, 70.5, 112.5, 121.3, 125.2, 125.3, 128.1, 128.3,
128.4, 128.6, 129.0, 129.2, 129.3, 129.6, 139.0, 139.4, 140.8, 142.8, 147.5, 147.8,
150.1, 152.0 (three signals are ™missing∫, presumably because of signal
D. H. Busch, Coord. Chem. Rev. 2000, 200 202,
5 52; g) J. F.
Stoddart, H.-R. Tseng, Proc. Natl. Acad. Sci. 2002, 99, 4797 4800.
[2] G. Schill, Catenanes, Rotaxanes and Knots, Academic Press, New
York, 1971.
[3] The other archetypal example of an interlocked molecule is
a
catenane–a molecule in which two or more rings are linked
mechanically. For example, see references [1] and [2].
[4] a) P.-L. Anelli, N. Spencer, J. F. Stoddart, J. Am. Chem. Soc. 1991, 113,
5131 5133; b) P.-L. Anelli, M. Asakawa, P. R. Ashton, R. A. Bissell,
¬
G. Clavier, R. Gorski, A. E. Kaifer, S. J. Langford, G. Mattersteig, S.
Menzer, D. Philp, A. M. Z. Slawin, N. Spencer, J. F. Stoddart, M. S.
Tolley, D. J. Williams, Chem. Eur. J. 1997, 3, 1113 1135; c) J. Cao,
M. C. T. Fyfe, J. F. Stoddart, G. R. L. Cousins, P. T. Glink, J. Org.
Chem. 2000, 65, 1937 1946; d) V. Bermudez, N. Capron, T. Gase,
F. G. Gatti, F. Kajzar, D. A. Leigh, F. Zerbetto, S. Zhang, Nature 2000,
406, 608 611; e) S. J. Loeb, J. A. Wisner, Chem. Commun. 2000,
1939 1940; f) M. Belohradsky, A. M. Elizarov, J. F. Stoddart,
Coll. Czech. Chem. Commun. in press. For an interesting quantum-
mechanical description of the shuttling process associated
with
a [2]rotaxane, see: g) D. A. Leigh, A. Troisi, F. Zerbetto,
Angew. Chem. 2000, 112, 358 361; Angew. Chem. Int. Ed. 2000, 39,
350 353.
‡
overlap); MS(FAB): m/z: 1086 [M À H À 2PF6] .
¬
[5] a) R. A. Bissell, E. Cordova, A. E. Kaifer, J. F. Stoddart, Nature 1994,
{[2]-{1,4-Bis{2-[4-(3,5-di-tert-butylbenzylammoniomethyl)phenyl]ethyl}-
369, 133 137; b) M.-V. MartÌnez-DÌaz, N. Spencer, J. F. Stoddart,
Angew. Chem. 1997, 109, 1991 1994; Angew. Chem. Int. Ed. Engl.
1997, 36, 1904 1907; c) P. R. Ashton, R. Ballardini, V. Balzani, I.
benzene}(benzometaphenylene[25]crown-8)rotaxane}
bis(hexafluoro-
phosphate) (17b-2H ¥ 2PF6): A solution of 2b-H ¥ 2PF6 (57 mg, 45 mmol)
and NaH (5 mg, 22 mmol) in CH2Cl2 (0.6 mL) was stirred at room
temperature for 30 min, and then terephthaldehyde (3 mg, 22 mmol) in
CH2Cl2 (0.6 mL) was added slowly. The mixture was stirred at room
temperature for 18 h before MeOH (0.1 mL) was added to quench the
reaction. The mixture was partitioned between CH2Cl2 (30 mL) and H2O
(30 mL). The organic layer was separated, washed with 5% HCl (2 Â
20 mL), dried (MgSO4), and evaporated to dryness. The residue was
dissolved in MeCN (1 mL) and then saturated aqueous NH4PF6 was added
until no further precipitation was observed. The solid was filtered, washed
with H2O, and dried under vacuum. The solid was dissolved in THF (2 mL),
PtO2 (3 mg) was added, and the mixture was stirred under an H2
atmosphere for 40 min. The solvent was evaporated under reduced
pressure, and the residue was then partitioned between CH2Cl2 (30 mL)
and H2O (30 mL). The organic layer was washed with 5% HCl (2 Â 20 mL),
dried (MgSO4), and concentrated. The crude product was dissolved in
MeCN (1 mL), and saturated aqueous NH4PF6 was added until no further
¬
¬
Baxter, A. Credi, M. C. T. Fyfe, M. T. Gandolfi, M. Gomez-Lopez, M.-
V. MartÌnez-DÌaz, A. Piersanti, N. Spencer, J. F. Stoddart, M. Venturi,
A. J. P. White, D. J. Williams, J. Am. Chem. Soc. 1998, 120, 11932
11942; d) P. R. Ashton, R. Ballardini, V. Balzani, A. Credi, K. R.
Dress, E. Ishow, C. J. Kleverlaan, O. Kocian, J. A. Preece, N. Spencer,
J. F. Stoddart, M. Venturi, S. Wenger, Chem. Eur. J. 2000, 6, 3558
3574; e) A. M. Brouwer, C. Frochot, F. G. Gatti, D. A. Leigh, L.
Mottier, F. Paolucci, S. Roffia, G. W. H. Wurpel, Science 2001, 291,
2124 2128; f) A. M. Elizarov, S.-H. Chiu, J. F. Stoddart,J. Org. Chem.
in press.
[6] a) J. A. Preece, J. F. Stoddart, Nanotechnology 1994, 3, 149 166;
¬
¬
b) M. Gomez-Lopez, J. A. Preece, J. F. Stoddart, Nanotechnology
1996, 7, 183 192; c) M. D. Ward, Chem. Ind. 1997, 640 645; d) D. A.
Leigh, A. Murphy, Chem. Ind. 1999, 178 183; e) M. D. Ward, Chem.
¬
¬
Ind. 2000, 22 26; f) M. Gomez-Lopez, J. F. Stoddart, Nanostructured
Materials and Nanotechnology (Ed.: H. S. Nalwa), Academic Press,
Chem. Eur. J. 2002, 8, No. 22
¹ 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/02/0822-5181 $ 20.00+.50/0
5181

J. F. Stoddart, D. J. Williams et al.
FULL PAPER
San Diego, 2000, p 641 689; g) P. A. Gale, Philos. Trans. R. Soc.
London Ser. A 2000, 358, 431 453; h) Molecular Switches (Ed.: B. L.
Feringa), VCH-Wiley, Weinheim, 2001.
Prins, D. N. Reinhoudt, P. Timmerman, Angew. Chem. 2001, 113,
2446 2492; Angew. Chem. Int. Ed. 2001, 40, 2382 2426; c) D. N.
Reinhoudt; M. Crego-Calama, Science 2002, 295, 2403 2407.
[18] a) D. H. Busch, N. A. Stephensen, Coord. Chem. Rev. 1990, 100, 119
154; b) S. Anderson, H. L. Anderson, J. K. M. Sanders, Acc. Chem.
Res. 1993, 26, 469 475; c) R. Cacciapaglia, L. Mandolini, Chem. Soc.
Rev. 1993, 22, 221 231; d) R. Hoss, F. Vˆgtle, Angew. Chem. 1994,
106, 389 398; Angew. Chem. Int. Ed. Engl. 1994, 33, 375 384; e) T. J.
Hubin, A. G. Kolchinski, A. L. Vance, D. L. Busch, Adv. Supramol.
Chem. 1999, 5, 237 357; f) Templated Organic Synthesis (Eds.: F.
Diederich, P. J. Stang), Wiley-VCH, Weinheim, 1999.
¬
¬
[7] a) M. Gomez-Lopez, J. F. Stoddart, Bull. Soc. Chim. Belg. 1997, 106,
491 500; b) J.-P. Sauvage, Acc. Chem. Res. 1998, 31, 611 619; c) J.-C.
Chambron, J.-P. Sauvage, Chem. Eur. J. 1998, 4, 1362 1366; d) M.-J.
¬
Blanco, M. C. Jimenez, J.-C. Chambron, V. Heitz, M. Linke, J.-P.
¬
Sauvage, Chem. Soc. Rev. 1999, 28, 293 305; e) M. C. Jimenez, C.
Dietrich-Buchecker, J.-P. Sauvage, Angew. Chem. 2000, 112, 3422
3425; Angew. Chem. Int. Ed. 2000, 39, 3284 3287; f) J.-P. Collin, C.
¬
Dietrich-Buchecker, P. Galvina, M. C. Jimenez-Molero, J.-P. Sauvage,
Acc. Chem. Res. 2001, 34, 477 487; g) L. Raehm, J.-P. Sauvage, Struct.
[19] M. C. T. Fyfe, J. F. Stoddart, Acc. Chem. Res. 1997, 30, 393 401.
[20] G. R. Desiraju, Angew. Chem. 1995, 107, 2541 2558; Angew. Chem.
Int. Ed. Engl. 1995, 34, 2311 2327.
¬
Bond. 2001, 99, 55 78; h) M. C. Jimenez-Molero, C. Dietrich-
Buchecker, J.-P. Sauvage, Chem. Eur. J. 2002, 8, 1456 1466.
¬
¬
[8] a) V. Balzani, M. Gomez-Lopez, J. F. Stoddart, Acc. Chem. Res. 1998,
31, 405 414; b) V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart,
Angew. Chem. 2000, 112, 3484 3530; Angew. Chem. Int. Ed. 2000, 39,
3348 3391; c) R. Ballardini, V. Balzani, A. Credi, M. T. Gandolfi, M.
Venturi, Acc. Chem. Res. 2001, 34, 445 455; d) R. Ballardini, V.
Balzani, A. Credi, M. T. Gandolfi, M. Venturi, Struct. Bond. 2001, 99,
163 188; e) A. Harada, Acc. Chem. Res. 2001, 34, 456 464; f) C. A.
Schalley, K. Beizai, F. Vˆgtle, Acc. Chem. Res. 2001, 34, 465 476.
[9] A. R. Pease, J. F. Stoddart, Struct. Bond. 2001, 99, 189 236.
[10] a) A. Aviram, M. A. Ratner, Chem. Phys. Lett. 1974, 29, 277 283;
b) Introduction to Molecular Electronic Devices (Eds.: M. C. Petty,
M. R. Bryce, D. Bloor), Oxford University Press, New York, 1995;
c) Molecular Electronics (Eds.: J. Jortner, M. Ratner), Blackwell
Science, Oxford, 1997; d) Molecular Electronics: Science and Tech-
nology (Eds.: A. Aviram, M. Ratner), New York Academy of Science,
New York, 1998; e) J. M. Tour, Acc. Chem. Res. 2000, 33, 791 804;
f) J. M. Tour, A. M. Rawlett, M. Kozaki, Y. Yao, R. C. Jagessar, S. M.
Dirk, D. W. Price, M. A. Reed, C. W. Zhou, J. Chen, W. Wang, I.
Campbell, Chem. Eur. J. 2001, 7, 5118 5134.
[21] a) P. R. Ashton, P. J. Campbell, E. J. T. Chrystal, P. T. Glink, S.
Menzer, D. Philp, N. Spencer, J. F. Stoddart, P. A. Tasker, D. J.
Williams, Angew. Chem. 1995, 107, 1997 2001; Angew. Chem. Int. Ed.
Engl. 1995, 34, 1865 1869; b) P. R. Ashton, E. J. T. Chrystal, P. T.
Glink, S. Menzer, C. Schiavo, J. F. Stoddart, P. A. Tasker, D. J.
Williams, Angew. Chem. 1995, 107, 2001 2004; Angew. Chem. Int.
Ed. Engl. 1995, 34, 1869 1871.
[22] a) A. G. Kolchinski, D. H. Busch, N. W. Alcock, J. Chem. Soc. Chem.
Commun. 1995, 1289 1291; b) A. G. Kolchinski, N. W. Alcock, R. A.
Roesner, D. H. Busch, Chem. Commun. 1998, 1437 1438; c) M.
Montalti, L. Prodi, Chem. Commun. 1998, 1461 1462; d) E. Ishow, C.
Credi, V. Balzani, F. Spadola, L. Mandolini, Chem. Eur. J. 1999, 5,
984 989; e) B. F. G. Johnson, C. M. G. Judkins, J. M. Matters, D. S.
Shephard, S. Parsons, Chem. Commun. 2000, 1549 1550; f) H. W.
Gibson, L. Hamilton, N. Yamaguchi, Polym. Adv. Technol. 2000, 11,
791 797; g) S. A. Duggan, G. Fallon, S. J. Langford, V.-L. Lau, J. F.
Satchell, M. N. Paddon-Row, J. Org. Chem. 2001, 66, 4419 4426; h) T.
Takata, H. Kawasaki, N. Kihara, Y. Furusho, Macromolecules 2001, 34,
5449 5456; i) H. W. Gibson, N. Yamaguchi, L. Hamilton, J. W. Jones,
J. Am. Chem. Soc. 2002, 124, 4653 4665.
[23] a) S. J. Rowan, S. J. Cantrill, J. F. Stoddart,Org. Lett. 1999, 1, 129 132;
b) S. J. Rowan, J. F. Stoddart, J. Am. Chem. Soc. 2000, 122, 164 165.
[24] a) P. R. Ashton, E. J. T. Chrystal, P. T. Glink, S. Menzer, C. Schiavo, N.
Spencer, J. F. Stoddart, P. A. Tasker, A. J. P. White, D. J. Williams,
Chem. Eur. J. 1996, 2, 709 728; b) P. R. Ashton, M. C. T. Fyfe, S. K.
Hickingbottom, J. F. Stoddart, A. J. P. White, D. J. Williams, J. Chem.
Soc. Perkin Trans. 2 1998, 2117 2128; c) P. R. Ashton, R. A. Bartsch,
S. J. Cantrill, R. E. Hanes, Jr., S. K. Hickingbottom, J. N. Lowe, J. A.
Preece, J. F. Stoddart, V. S. Talanov, Z.-H. Wang, Tetrahedron Lett.
1999, 40, 3661 3664.
[11] a) C. P. Collier, E. W. Wong, M. Belohradsky, F. M. Raymo, J. F.
Stoddart, P. J. Kuekes, R. S. Williams, J. R. Heath, Science 1999, 285,
391 394; b) E. W. Wong, C. P. Collier, M. Belohradsky, F. M. Raymo,
J. F. Stoddart, J. R. Heath, J. Am. Chem. Soc. 2000, 122, 5831 5840.
[12] a) C. P. Collier, G. Mattersteig, E. W. Wong, Y. Luo, K. Beverly, J.
Sampaio, F. M. Raymo, J. F. Stoddart, J. R. Heath, Science 2000, 289,
1172 1175; b) C. P. Collier, J. O. Jeppesen, Y. Luo, J. Perkins, E. W.
Wong, J. R. Heath, J. F. Stoddart, J. Am. Chem. Soc. 2001, 123, 12632
12641; c) Y. Luo, C. P. Collier, J. O. Jeppesen, K. A. Nielsen, E.
DeIonno, G. Ho, J. Perkins, H.-R. Tseng, T. Yamamoto, J. F. Stoddart,
ChemPhysChem 2002, 3, 519 525.
[13] J. Perkins, C. P. Collier, J. R. Heath, J. O. Jeppesen, Y. Luo, K. A.
Nielson, A. R. Pease, J. F. Stoddart, E. W. Wong, Mol. Electron.
Bioelectron. 2001, 12, 69 74.
[14] A. R. Pease, J. O. Jeppesen, J. F. Stoddart, Y. Luo, C. P. Collier, J. R.
Heath, Acc. Chem. Res. 2001, 34, 433 444.
[15] a) See Tetrahedron Symposia-in-Print on molecular recognition:
Tetrahedron 1995, 51, 343 648; b) see special issue on molecular
recognition: Chem. Rev. 1997, 97, 1231 1734; c) see Tetrahedron
Symposia-in-Print on recognition-mediated self-assembly of organic
systems: Tetrahedron 2002, 58, 621 844.
[25] S.-H. Chiu, S. J. Rowan, S. J. Cantrill, P. T. Glink, R. L. Garrell, J. F.
Stoddart, Org. Lett. 2000, 2, 3631 3634.
[26] S. J. Rowan, S. J. Cantrill, J. F. Stoddart, A. J. P. White, D. J. Williams,
Org. Lett. 2000, 2, 759 762.
[27] S. J. Cantrill, D. A. Fulton, A. M. Heiss, A. R. Pease, J. F.
Stoddart, A. J. P. White, D. J. Williams, Chem. Eur. J. 2000, 6, 2274
2287.
[28] In order to obtain some information concerning the kinetic acidity of
‡
the NH2 groups in the rotaxanes 4a-H ¥ 3PF6 and 4b-H ¥ 3PF6, we
treated these rotaxanes (60mm) with D2O (7m) in CD3CN and
[16] a) J. S. Lindsey, New J. Chem. 1991, 15, 153 180; b) D. Philp, J, F.
Stoddart, Synlett 1991, 445 458; c) G. M. Whitesides, J. P. Mathias,
C. T. Seto, Science, 1991, 254, 1312 1319; d) D. Philp; J. F. Stoddart,
Angew. Chem. 1996, 108, 1242 1286; Angew. Chem. Int. Ed. Engl.
1996, 35, 1154 1196; e) P. T. Glink, C. Schiavo, J. F. Stoddart, D. J.
Williams, Chem. Commun. 1996, 1483 1490; f) J. Rebek, Jr., Acc.
Chem. Res. 1999, 32, 278 286; g) M. C. T. Fyfe, J. F. Stoddart, Adv.
Supramol. Chem. 1999, 5, 1 53; h) S. J. Cantrill, A. R. Pease, J. F.
Stoddart, J. Chem. Soc. Dalton Trans. 2000, 3715 3734; i) D. H.
Gracias, J. Tien, T. L. Breen, C. Hsu, G. M. Whitesides, Science 2000,
289, 1170 1172; j) P. Ball, Nature 2001, 413, 667 668; k) L. F. Lindoy,
I. M. Atkinson, Self-Assembly in Supramolecular Systems (Ed.: J. F.
Stoddart), Royal Society of Chemistry: Cambridge, 2000; l) G. M.
Whitesides, B. Grzybowski, Science 2002, 295, 2418 2421; m) F. Hof,
S. L. Craig, C. Nuckolls, J. Rebek, Jr., Angew. Chem. 2002, 114, 1556
1578; Angew. Chem. Int. Ed. 2002, 41, 1488 1508.
monitored the H-D exchange reaction. In both cases, we were unable
to observe the NH2 signals after adding D2O. Instead, the kinetic
‡
behavior was estimated by observing the change in the shape of the
signal associated with the proton of the methylene groups adjacent to
‡
NH2 center from a multiplet to a broad singlet during the exchange
process. In contrast to the reported slow kinetic exchange process
(t1/2 ˆ 17 min) of
a similar rotaxane containing a DB24C8 unit
(N. Kihara, Y. Tachibana, H. Kawasaki, T. Takata, Chem. Lett. 2000,
506 507), the exchange rate was much faster for the [2]rotaxane
4a-H ¥ 3PF6 (t1/2 < 3 min) and 4b-H ¥ 3PF6 (t1/2 < 1 min). The stronger
kinetic acidity of the [2]rotaxane 4b-H ¥ 3PF6 compared to
4a-H ¥ 3PF6 may also reflect the fact that interaction between
BMP25C8 and the dialkylammonium ion is weaker than that between
DB24C8 and the dialkylammonium ion. The reason for the difference
in kinetic behavior of the [2]rotaxane 4a-H ¥ 3PF6 and Takata×s
rotaxane is not clear. We suspect, however, that the crown ether unit in
4a-H ¥ 3PF6 has more ™room∫ to move around than in Takata×s
rotaxane–because of the larger distance between the ammonium
[17] a) G. M. Whitesides, E. E. Simanek, J. P. Mathias, C. T. Seto, D. Chin,
M. Mammen, D. M. Gordon, Acc. Chem. Res. 1995, 28, 37 44; b) L. J.
5182
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Chem. Eur. J. 2002, 8, No. 22

[2]Rotaxanes
5170 5183
center and the stopper groups–resulting in less steric hindrance for
the approach of D2O toward the ammonium center.
Yamaguchi, D. S. Nagvekar, H. W. Gibson, Angew. Chem. 1998, 110,
2361 2364; Angew. Chem. Int. Ed. 1998, 37, 2518 2520.
[29] When Pd/C was used as the catalyst for the same hydrogenation,
[34] a) D. B. Amabilino, M. Asakawa, P. R. Ashton, R. Ballardini, V.
Balzani, M. Belohradshy, A. Credi, M. Higuchi, F. M. Raymo, T.
Shimizu, J. F. Stoddart, M. Venturi, K. Yase, New J. Chem. 1998, 22,
959 972; b) F. Osswald, E. Vogel, O. Safarowsky, F. Schwanke, F.
Vˆgtle, Adv. Synth. Catal. 2001, 343, 303 309; c) A. M. Elizarov, S.-H.
Chiu, P. T. Glink, J. F. Stoddart, Org. Lett. 2002, 4, 679 682.
[35] a) P. R. Ashton, I. W. Parsons, F. M. Raymo, J. F. Stoddart, A. J. P.
White, D. J. Williams, R. Wolf, Angew. Chem. 1998, 110, 2016 2019;
Angew. Chem. Int. Ed. 1998, 37, 1913 1916; b) P. R. Ashton, I. Baxter,
S. J. Cantrill, M. C. T. Fyfe, P. T. Glink, J. F. Stoddart, A. J. P. White,
D. J. Williams, Angew. Chem. 1998, 110, 1344 1347; Angew. Chem.
Int. Ed. 1998, 37, 1294 1297; c) P. L. Vidal, M. Billon, B. Divisia-
Blohorn, G. Bidan, J. M. Kern, J.-P. Sauvage, Chem. Commun. 1998,
629 630; d) S. J. Cantrill, G. J. Youn, J. F. Stoddart, D. J. Williams, J.
Org. Chem. 2001, 66, 6857 6872.
‡
À
hydrogenlysis (presumably of the benzylic C N bond) took place, a
reaction which destroys the backbone of the rotaxane and results in
the quantitative isolation of free DB24C8. A similar hydrogenolysis
(H2/PtO2) occurred when the reaction mixture was hydrogenated for a
long period of time.
[30] S.-H. Chiu, S. J. Rowan, S. J. Cantrill, L. Ridvan, P. R. Ashton, R. L.
Garrell, J. F. Stoddart, Tetrahedron 2002, 58, 807 814.
[31] W. P. Cochrane, P. L. Pauson, T. S. Stevens,J. Chem. Soc. C 1968, 630
632.
[32] A semirotaxane has been defined as a pseudorotaxane with a stopper
at one of the two termini of the rod-like component. See, for instance:
a) J.-P. Collin, P. Gavina, J.-P. Sauvage, New J. Chem. 1997, 21, 525
528; b) C. Seel, A. H. Parham, O. Safarowsky, G. M. H¸bner, F.
Vˆgtle, J. Org. Chem. 1999, 64, 7236 7242.
[33] a) A. Harada, J. Li, M. Kamachi, Nature 1992, 356, 325 327; b) S. S.
Zhu, T. M. Swager, J. Am. Chem. Soc. 1997, 119, 12568 12577; c) W.
Herrmann, M. Schneider, G. Wenz, Angew. Chem. 1997, 109, 2618
2621; Angew. Chem. Int. Ed. Engl. 1997, 36, 2511 2514; d) N.
[36] SHELXTL PC version 5.03, Siemens Analytical X-Ray Instruments,
Inc., Madison, WI, 1994.
Received: June 6, 2002 [F4161]
Chem. Eur. J. 2002, 8, No. 22
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