Mechanically linked polyrotaxanes: A stepwise approach

Article abstract of DOI:10.1021/ma034521t

A new synthetic approach for the preparation of mechanically linked polyrotaxanes was developed. Two variations of rotaxane monomers were synthesized, based on diphenylmethane and tetraphenylmethane blocking groups. Both rotaxanes bear a protected phenol

Full text of DOI:10.1021/ma034521t

7004
Macromolecules 2003, 36, 7004-7013
Mechanically Linked Polyrotaxanes: A Stepwise Approach
Mich el P . L. Wer ts, Ma a r ten va n d en Booga a r d , Ger a sim os M. Tsivgou lis,† a n d
Geor ges Ha d ziioa n n ou *,‡
Department of Polymer Chemistry and Materials Science Centre, University of Groningen,
Nijenborgh 4, 9747 AG Groningen, The Netherlands
Received April 23, 2003; Revised Manuscript Received J uly 21, 2003
ABSTRACT: A new synthetic approach for the preparation of mechanically linked polyrotaxanes was
developed. Two variations of rotaxane monomers were synthesized, based on diphenylmethane and
tetraphenylmethane blocking groups. Both rotaxanes bear a protected phenol functionality in the
dumbbell-shaped part and a protected carboxylic acid functionality in the cyclic component. Via a
“stepwise” polymerization, a rotaxane dimer and a rotaxane tetramer have been obtained. The procedure
involves selective deprotection of the two functional groups in separate batches and a subsequent coupling
reaction of the produced monofunctional/monoprotected monomers so that a dimer is formed. Longer
and monodisperse oligomers can easily be obtained by repetition of this procedure. In addition, deprotection
of both functionalities in the dimer and subsequent esterification resulted in the formation of a polymer
with a molecular weight of ca. 400 000. The molecules obtained were isolated and characterized by 1H
NMR and mass spectrometry.
In tr od u ction
perse oligomers of various sizes and for two different
types of rotaxanes.
The past few years, the interest in new topological
structures based on rotaxanes and catenanes has strongly
increased. Starting from “simple” assemblies, more and
more complex structures, such as [5]catenanes1 or tris-
[2]rotaxanes2 have been synthesized. Because of their
unique characteristics, rotaxanes and catenanes have
been proposed as potential candidates in the area of
molecular machineries3 (shuttles, piston/cylinder sys-
tems, switches and logical gates). For example, pH-
driven,4,5 light-driven,6 or redox-driven5 shuttle-type
systems have been synthesized. An important contribu-
tion toward this direction has been realized by the group
of Sauvage and co-workers.7
Three possible strategies that can lead to polyrotax-
anes with mechanically linked repeating units are
depicted in Scheme 1. The first method is based on the
“clipping” procedure, and the second is based on the
“threading” of the linear part through the cyclic part of
the monomer and subsequent blocking. For both meth-
ods, the polymerization is not effective because (a) the
complexation yield of cyclophane tetracation with poly-
ether-based dumbbells is very low and (b) there is a
significant risk of intermolecular reactions, yielding
cyclic monomers, dimers and trimers. This has been
found by Stoddart et al. for both crown ether-py-
ridylpyridinium14 and crown ether-dibenzylammonium
salt15 systems.
Finally, in the third method (Scheme 1), a rotaxane
monomer bearing two functional groups is prepared
which is subsequently polymerized in a more “classical”
way. In this approach the low-yielding step of the
rotaxane-complex formation is eliminated, since the
rotaxane functionality is permanently present in the
monomer. However, attempts based on this approach
did not give any polyrotaxanes;11b the main reason was
the high percentage of intermolecular instead of in-
tramolecular connection leading as before to cyclic
monomers and dimers.
In the field of polymers, a number of fascinating
polyrotaxane structures has been presented.8 The prop-
erties of these compounds are in many cases very
different compared to the “naked” polymers.9 Among the
various structures, one of the most interesting ones
concerns polymers with mechanically linked repeating
units. A significant progress has only been achieved for
mechanically linked polycatenanes.10 In contrast, in the
case of polyrotaxanes, various attempts11 have been
made, but the results in the synthesis of these “daisy
chain” molecules are less spectacular and mainly con-
cern small oligomers (dimers)2,11b and polypseudorotax-
anes.12
Recently, we have reported16 a new procedure to pre-
pare both mechanically linked rotaxane oligomers and
polymers that eliminates the problem of intermolecular
reactions that was present in all the previous cases.
Although, basically the general scheme of the third
strategy (Scheme 1) is followed, now the functionalities
X and Y of the molecule are both orthogonally17 pro-
tected. In particular, in this “stepwise polymerization”
, a rotaxane bearing two protected functional groups
XP 1 and YP 2, is used as the starting material (Scheme
2). The synthesis is based on a step-by-step approach
consisting of sequential deprotection-coupling steps.
The two functional groups in the bifunctional rotaxane
are deprotected selectively in separate batches, leading
to two monofunctional rotaxane monomers, one bearing
Here, we present a new approach for the synthesis of
mechanically linked polyrotaxanes.13 The synthesis is
based on a new step-by-step approach, consisting of
sequential deprotection-coupling steps. The method has
been successfully applied in the synthesis of monodis-
* To whom correspondence should be addressed. E-mail: hadzii@
ecpm.u-strasbg.fr.
† Current address: Department of Chemistry, University of
Patras, Rio-Patra 26500, Greece. E-mail: tsivgoulis@chemistry.
upatras.gr.
‡ Current address: De´partement des Polyme`res, Ecole Europ-
e´enne Chimie Polyme`res Mate´riaux (ECPM), Universite´ Louis
Pasteur Strasbourg, 25 rue Becquerel, F-67087 Strasbourg Cedex
2, France.
10.1021/ma034521t CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/26/2003

Macromolecules, Vol. 36, No. 19, 2003
Mechanically Linked Polyrotaxanes 7005
Sch em e 1. Syn th etic Ap p r oa ch es for th e P r ep a r a tion
of a Mech a n ica lly Lin k ed P olyr ota xa n e
F igu r e 1. Proposed rotaxane monomers for the preparation
of oligorotaxanes via the stepwise “polymerization” procedure.
Sch em e 3. Syn th esis of th e Tw o Block in g Gr ou p s,
Ba sed on Dip h en ylm eth a n e (4a ) a n d
Tetr a p h en ylm eth a n e (4b)
Sch em e 2. Sch em a tic P r esen ta tion of th e Step w ise
“P olym er iza tion ” P r oced u r ea
a
In each step, which consists of two deprotection reactions
and one coupling reaction, the number of repeating units in
the oligomer is doubled.
the functional group Y in the dumbbell and one bearing
the functional group X in the cyclic unit. A coupling
reaction between these two products gives a rotaxane
dimer18 as the sole product. This dimer again contains
the same two protected functional groups XP 1 and YP 2;
therefore, the deprotection-coupling sequence can be
repeated to obtain a tetramer. In this way, any size of
oligomer can be obtained by just continuing the same
deprotection-coupling procedure.19
tetraphenylmethane 14b blocking groups, respectively,
were synthesized. In particular, the blocking groups
(either functionalized or nonfunctionalized) were first
prepared and connected to an ethylene glycol chain.
Next, the middle part 12, which is the same for both
14a and 14b, was synthesized. Its reaction with the
ethylene glycol-extended blocking groups in two steps
yielded the dumbbells.
Resu lts a n d Discu ssion
Design of th e Rota xa n e Mon om er . As a basis for
the rotaxane, we have chosen the cyclophane-polyether
system because it is well-known from literature that
cyclophanes can be functionalized without losing their
complexing properties.20 The cyclophane contains an
allyl-protected carboxylic acid, linked via a butyl spacer.
The dumbbell contains either diphenylmethane or tet-
raphenylmethane end groups. One of them is function-
alized with a tert-butyldiphenylsilyl- (TBDPS-) pro-
tected phenol. Selective deprotection is carried out with
Pd(PPh3)4 and Bu4NF, respectively. A more detailed
description of the selection of the specific groups and
deprotection conditions can be found in the Supporting
Information. The final structures of the two proposed
rotaxane monomers are depicted in Figure 1.
The preparation of the diphenylmethane and tet-
raphenylmethane blocking groups, bearing the TBDPS-
protected phenol moiety is depicted in Scheme 3.
4-Hydroxybenzophenone (2) was reacted with tert-
butyldiphenylchlorosilane as described in the litera-
ture.21 To prevent deprotection, a mild reducing agent
was used (NaBH4) to yield the TBDPS-protected diphen-
ylmethane blocking group 4a (79%). On the other hand,
the tetraphenylmethane-based blocking group was pre-
pared by reaction of phenol with p-anisyldiphenylchlo-
romethane (5). Demethylation of the methoxy group in
6 with BBr3 yielded 4,4′-dihydroxytetraphenylmethane
(7). Protection of one of the phenol groups produced the
desired blocking group 4b.22
Both unsubstituted blocking groups 10a and 10b were
prepared according to literature methods.23,24 These
blocking groups were further reacted to give the final
dumbbell molecules according to the procedure shown
in Scheme 4. Most of the steps are based on the same
general type of reaction, namely etherification of an
alcohol or phenol with a tosylate derivative. NaH/THF
and K2CO3/DMF were used since their efficiency for
these etherifications is well-known.25 For the synthesis
of the diphenylmethane-based dumbbell 14a , the two
blocking groups 4a and 10a were reacted with the bis-
(tosylate) 8. The middle part 12 was prepared via the
Syn th esis of th e Rota xa n e Mon om er s. The “clip-
ping” method was applied for the synthesis of both
-
rotaxane monomers 1a ‚4PF6 and 1b‚4PF6-. The fol-
lowing molecules required for this method were initially
prepared: (a) the dumbbell-shaped molecules, (b) the
bis(pyridylpyridinium) dicationic salt 26‚2PF6-, and (c)
the functionalized and protected p-bis(bromomethyl)-
benzene 19.
(a ) Du m bbell-Sh a p ed Molecu les. On the basis of
the same synthetic approach, two different dumbbell-
shaped molecules bearing diphenylmethane 14a and

7006 Werts et al.
Macromolecules, Vol. 36, No. 19, 2003
Sch em e 4. Syn th esis of th e Du m bbell-sh a p ed
Molecu les 14a a n d 14b, Bea r in g th e TBDP S-P r otected
P h en ol F u n ction a lities
Sch em e 6. Syn th esis of th e Bifu n ction a l Rota xa n es
1a ,b‚4P F 6- a n d th e Sym m etr ic Rota xa n es
27a ,b‚4P F 6- a
a
Key: a ) Diphenylmethane, b ) Tetraphenylmethane.
of sulfuric acid. Subsequent reaction with the acid
chloride 17 gave allyl-4-butanoate-2,5-di(bromomethyl)-
benzoate 19 in a 49% yield.
The rotaxane monomers were produced (Scheme 6)
by reaction of the three components described above
(dumbbells 14a or 14b, the bis(pyridylpyridinium) di-
Sch em e 5. Syn th esis of th e Dibr om id e 19 Bea r in g th e
Allyl-P r otected Ca r boxylic Acid F u n ction a lity
-
cationic salt 26‚2PF6 and the dibromide 19) in the
presence of AgPF6. After 7 days, any polymeric by-
products as well as uncomplexed cyclophane were
precipitated with CHCl3 and removed by centrifugation.
By the addition of Et2O to the redissolved rotaxanes in
CH2Cl2, the diphenylmethane- and tetraphenylmethane-
-
-
based rotaxanes 1a ‚4PF6 and 1b‚4PF6 were precipi-
tated as red solids in 4.0% and 5.4% yields, respectively.
The uncomplexed dumbbell was recovered from the
supernatant liquids by silica column chromatography
and reused. The solubility of the rotaxanes is largely
depended on the counterion salts. The hexafluorophos-
phate salts are soluble in organic solvents of medium-
high polarity such as CH2Cl2, acetone, CH3CN, and
DMF, while the chlorine salts are soluble in H2O and
H2O-MeOH mixtures.
reaction of the bis(tosylate) 8 with an excess of hydro-
quinone in the presence of potassium carbonate and
subsequently reacted with 11a to yield 13a . Because of
bisubstitution, the symmetric dumbbell is formed as a
byproduct. Finally, the dumbbell-shaped molecule 14a
was produced in a 36% yield by reacting the function-
alized blocking groups 9a with 13a . The relatively low
yield can be attributed to silyl migration26 of the silyl
group. Following the same procedure, we have prepared
the tetraphenylmethane-based dumbbell 14b in similar
yields.
(b ) Bis(p yr id ylp yr id in iu m ) Dica t ion ic Sa lt 26‚
2P F 6). This compound was prepared according to a
literature procedure30 by the reaction of R,R′-dibromoxy-
lene with 4,4′-bipyridyl.
(c) F u n ction a lized a n d P r otected p-Bis(br om o-
m eth yl)ben zen e 19. The synthesis of compound 19 is
presented in Scheme 5. This molecule was essential for
the preparation of a functionalized cyclophane since it
contains three structural components: (a) two reactive
bromine atoms necessary for the cyclophane formation,
(b) a carboxylic acid function protected as allyl ester,
and (c) a butyric acid extension for minimization of
steric and electronic effects.
Starting from the unfunctionalized dumbbells 24a
and 24b (byproducts in the synthesis of 13) and using
R,R′-dibromo-p-xylene instead of the intermediate 19,
one can form the “symmetric” analogues 27a ‚4PF6- and
-
27b‚4PF6 in a 19% yield for both cases. The large
difference in yields between the functionalized and
nonfunctionalized rotaxanes can be attributed to steric
hindrance due to the carboxylic acid functionality in the
cyclophane.11a
Rota xa n e Oligom er s. Both rotaxanes 1a ‚4PF6- and
-
1b‚4PF6 bear at appropriate positions two protected
functional groups so that oligomers and/or polymers
with mechanically linked repeating units can be formed.
According to Scheme 3, three steps are necessary to
obtain the dimer, selective deprotection of the carboxylic
acid and phenol group in two separate batches and
subsequent coupling of the produced monofunctional
rotaxane monomers.
Bis(bromomethyl)benzoic acid 16 was prepared via
the bromination of 2,5-dimethylbenzoic acid with
NBS/BPO.28 A detailed description of the byproducts
formed during the bromination is given in the Sup-
porting Information. The acid was converted quantita-
tively to the acid chloride 17 by reaction with thionyl
chloride.
In one batch, the phenol moiety was deprotected
by cleavage of the silyl ether bond with Bu4NF in
MeCN (Scheme 7). Counterion exchange with aqueous
NH4PF6 gave the monomer-OH 29‚4PF6- in a quanti-
tative yield. In another batch, the carboxylic acid
functionality of the rotaxane monomer was deprotected
Compound 18 was prepared29 by reacting γ-butyro-
lactone with an excess of allyl alcohol in the presence

Macromolecules, Vol. 36, No. 19, 2003
Mechanically Linked Polyrotaxanes 7007
Sch em e 7. Syn th esis of Rota xa n e Dim er s 30a ,b‚8P F 6- a n d th e Rota xa n e Tetr a m er 33b‚16P F 6- a
a
Key: a ) Diphenylmethane, b ) Tetraphenylmethane.
with Pd(PPh3)4 in MeCN/CHCl3/NMM/AcOH. Under
these conditions, the monomer-COOH 28‚4PF6 was
formed in 3 h. The deprotections were performed on
both the diphenylmethane- and tetraphenylmethane-
based rotaxanes. All the four monofunctional mono-
mers obtained (28a ‚4PF6-, 28b‚4PF6-, 29a ‚4PF6-, and
29b‚4PF6-) were characterized by 1H NMR spectroscopy
and MALDI-TOF mass spectrometry, indicating com-
plete removal of the protective groups and the absence
of side reactions. Thus, it was confirmed that the func-
-

7008 Werts et al.
Macromolecules, Vol. 36, No. 19, 2003
tional groups on the rotaxane monomers were indeed
orthogonally protected. Because of stability problems in
the diphenylmethane rotaxanes (see Supporting Infor-
mation), oligomers were only prepared with the tet-
raphenylmethane-based compounds.
In the next step, the monomer-COOH 28b‚4PF6- and
the monomer-OH 29b‚4PF6-, both bearing tetraphen-
ylmethane blocking groups, were esterified in CH2Cl2
in the presence of DCC and pyridine. After 7 days at
room temperature, DHU was filtered off and the rotax-
anes precipitated with Et2O. Column chromatography
and subsequent counterion exchange with aqueous
NH4PF6 yielded the rotaxane dimer 30b‚8PF6- in a 30%
yield. The low yield can be attributed to the conversion
of monomer-COOH 28‚4PF6- to the stable N-acylurea
derivative during the reaction, as was revealed by mass
spectrometry. This conversion is a known problem in
esterifications with DCC30 and has also been observed
in the esterification of catenanes.10d Undoubtedly, a low
yielding coupling step would cause severe limitations
in the preparation of longer oligorotaxanes and/or
polyrotaxanes. Therefore, on model compounds as well
as on the rotaxanes, several modifications of the esteri-
fication procedure were tried in order to improve the
yield of this step. The major side-reaction concerns
rearrangement of the O-acylurea intermediate to an
N-acylurea. It was found that this reaction can almost
completely be prevented if pyridine is replaced by a
more powerful catalyst like DMAP in combination with
p-toluenesulfonic acid (ratio compound/DMAP/p-tolu-
enesulfonic acid 1.0/2.0/1.9). The small excess of DMAP
compared to the acid is enough to permit a rapid
esterification while the presence of the acid strongly
suppresses the rearrangement of the O-acylurea to the
N-acylurea. These results are slightly different from
those reported by the group of Stupp31 where it is
mentioned that, in the best conditions, the ratio DMAP/
acid should be exactly one. Use of the optimal condi-
tions, raised the isolated yield for the rotaxane dimer
F igu r e 2. 1H NMR spectra of the tetraphenylmethane-based
rotaxanes: (a) monomer 1b‚4PF6-; (b) dimer 30b‚8PF6-; (c)
tetramer 33b‚16PF6-. The asterisk marks a signal due to
residual solvent.
-
30b‚8PF6 from 30% to 80% without any observable
amount of N-acylurea.
To prove that the stepwise “polymerization” of Scheme
3 can be used for oligomers longer than dimers, the
deprotection and coupling steps were repeated in the
presence of the newly formed ester link. So, next the
synthesis of the rotaxane tetramer was performed. The
phenol and carboxylic acid functionality in the tetra-
-
phenyl-based rotaxane dimer 30b‚8PF6 were depro-
tected in two separate batches. Esterification of the two
monofunctional dimers gave a mixture of unreacted
dimer-OH, some N-acylurea of the dimer-COOH and
the tetramer 33b‚16PF6-. The reaction mixture was
eluted over a silica column with MeCN/MeOH. By the
addition of NH4PF6 at a concentration from 0 to 1.5%
(v/v) we were able to isolate the rotaxane tetramer in a
35% yield. The low yield can be attributed to the difficult
separation of the products.
F igu r e 3. Electron spray mass spectra of the tetraphenyl-
In Figure 2, the 1H NMR spectra of the rotaxane
methane-based rotaxanes: (a) monomer 1b‚4PF6-; (b) dimer
-
30b‚8PF6-; (c) tetramer 33b‚16PF6
.
-
monomer 1b‚4PF6-, dimer 30b‚8PF6 and tetramer
-
33b‚16PF6 are presented. All show typical signals
corresponding to the cyclophane (8.32-8.42 ppm and
9.44-9.60 ppm) and the dumbbell (3.75-4.15 ppm and
7.31-7.45 ppm). Their ratios are the same in each case.
In contrast, the peaks assigned to the protective groups
(allyl at 5.35-5.50 and 6.12 ppm, TBDPS at 7.53-7.63
and 7.87 ppm) decrease, as expected, with a factor of 2
each time since the number of repeating units doubles.
The tetraphenylmethane-based monomer, dimer and
tetramer rotaxanes were characterized by electron spray
-
mass spectrometry (Figure 3). The monomer 1b‚4PF6
shows three peaks at 578 [M - 4PF6 ]
- 4+, 819 [M -
3PF6
]
- 3+, and 1302 [M - 2PF6
]
- 2+. For the dimer
-
30b‚8PF6 six peaks are observed from 541 [M -
- 8+
8PF6
]
to 1689 [M - 3PF6 ]
- 3+, and finally for the

Macromolecules, Vol. 36, No. 19, 2003
Mechanically Linked Polyrotaxanes 7009
F igu r e 4. 1H NMR spectrum of the polyrotaxane 35b‚nPF6
The asterisk marks a signal due to residual solvent.
.
-
Sch em e 8. Sch em a tic P r esen ta tion of th e Syn th esis
F igu r e 5. Zimm plot for the light scattering of the polyro-
taxane 35b‚nPF6 in CH2Cl2.
-
of th e P olyr ota xa n e 35b‚4n P F 6-.
rotaxane dimer. In the monomer, the rotaxane “spends”
some time in an arrangement in which the cyclophane
is located close to the blocking groups. As a result, the
two functional groups are close in space and therefore
easy to couple. In contrast, in the dimer an arrangement
in which the cyclophane is close to the blocking groups,
does not lead to a close proximity of the two functional
groups and therefore the two functions are free to react
intramolecularly. The close spatial proximity of the
cyclophane to the blocking groups is not surprisingly,
taking into account that (i) the tetraphenylmethane
system is rich in electrons (especially the functionalized
one) and (ii) the energy barrier to move from the
hydroquinone group to the blocking group is similar to
the energy barrier to move between the two hydro-
quinone groups.
-
tetramer 33b ‚16PF6
, 11 peaks from 523 [M -
- 16+
- 6+
16PF6
]
to 1635 [M - 6PF6
]
are visible.
Rota xa n e P olym er . Although the molecular weight
of the tetramer is as high as 10 000, it cannot be
considered to be a polymer. Theoretically, polymeriza-
tion can take place when both functional groups X and
-
Y of the rotaxane monomer 1b‚4PF6 are deprotected.
However, from the literature11b it is known that this
leads mainly to low molecular weight cyclic products
instead of a polymer. By using the dimer 30b‚8PF6- as
starting material, the two functional groups are more
separated in space, hereby decreasing the possibility of
intramolecular reactions, and thus a high molecular
weight polymer can be obtained.
Con clu sion s
The preparation of five new rotaxanes is described in
the present article. In particular, two rotaxane mono-
mers, one rotaxane dimer, one tetramer, and a polymer
were obtained. The structure of these rotaxanes was
based on the polyether-cyclophane system. For the
preparation of monodisperse oligorotaxanes, consisting
of either two or four repeating units, we have de-
veloped a new synthetic route, based on a step-by-step
approach. The procedure requires rotaxanes, bearing
two functions orthogonally protected at appropriate
positions. Two rotaxane monomers have been designed,
which bear one protected phenol moiety in the dumbbell
part of the rotaxane and one protected carboxylic acid
moiety in the cyclophane component. As blocking groups,
both diphenylmethane and tetraphenylmethane have
been used.
The synthesis of the polymer 35b‚4nPF6- is depicted
in Scheme 8. Initially, the two functional groups were
deprotected in two sequential steps. The produced
bifunctional dimer 34b‚8PF6 was polymerized under
the optimal conditions used for the preparation of the
-
-
tetramer. After 5 days the polyrotaxane 35b‚4nPF6
was precipitated from CH2Cl2/Et2O.
-
The 1H NMR spectrum of the polyrotaxane 35b‚4nPF6
shows broad peaks as is expected for high molecular
weight compounds, due to slight differences in the
chemical environment for the separate monomer units.
Attempts have been made to determine the molecular
weight by gel permeation chromatography. As calibra-
tion standards, the monomer, dimer, and tetramer could
be used. Despite our efforts, no appropriate gel system
was found. Different materials used were silica, Sephan-
dex, LH-20, and Styragel. Pure solvents or solutions
with salts25b were tested. In all cases, the separation is
dominated by absorption of the rotaxanes on the column
material, instead of separation due to differences in size.
Finally, the molecular weight of the polyrotaxane
35b‚4nPF6- was measured with static light scattering.
A Zimm plot of the results, obtained in CH2Cl2 is shown
in Figure 5. A molecular weight Mw of 400 000 and a
mean-square radius of gyration of 80 ( 10 nm was
found. Assuming a polydispersity of 2 for a polyconden-
sation, the average degree of polymerization is 75
monomer units.
By sequential deprotection and coupling of the car-
boxylic acid and phenol functionalities it was possible
to synthesize the tetraphenylmethane-based rotaxane
dimer in high yield (80%). The same procedure was
repeated with dimer to obtain in this way the rotaxane
tetramer. The advantage of this approach is the syn-
thesis of monodisperse oligomers, and by repetition of
the deprotection-coupling steps, any number of repeat-
ing units can be obtained, which can be used for the
studies of the dynamic properties of mechanically linked
molecules.
The polycondensation of the bisdeprotected rotaxane
dimer gave for the first time a high molecular weight
mechanically linked polyrotaxane with on average 75
mechanically linked repeating units per polymer chain.
We believe that one of the main reasons for the high
molecular weight is related to the configuration of the

7010 Werts et al.
Macromolecules, Vol. 36, No. 19, 2003
mmol) in THF (10 mL) was added to a suspension of NaH (0.35
g, 8.8 mmol) in THF (5 mL) and refluxed for 2 h after which
it was added dropwise to a refluxing solution of 8 (6.03 g, 12
mmol) over a period of 0.5 h. After stirring for 2 h, the reaction
mixture was concentrated, CH2Cl2 was added, and the result-
ing mixture was extracted with water. The organic phase was
dried over MgSO4 and the solvent evaporated in vacuo. After
column chromatography [SiO2, Et2O] the product was isolated
as a gray oil (1.60 g, 39%). 1H NMR: δ 2.43 (s, 3H), 3.54-3.72
(m, 14H), 4.13 (t, 2H), 5.40 (s, 1H), 7.21-7.37 (m, 12H), 7.78
(d, 2H). HRMS C28H34O7S: calcd, 514.2025; found, 514.2018.
1-{p -[2-(2-(2-(2-(Dip h e n ylm e t h oxy)e t h oxy)e t h oxy)-
eth oxy)eth oxy]p h en oxy}-13-{p-h yd r oxyp h en oxy}-3,6,9-
tr ioxa u n d eca n e (13a ): A solution of 11a (0.80 g, 1.5 mmol),
12 (1.14 g, 3 mmol), and K2CO3 (0.41 g, 3 mmol) in dry DMF
(20 mL) was stirred for 20 h at 80 °C. The solvent was removed
in vacuo, and the resulting brown oil was dissolved in CH2Cl2
and washed with water. The organic layer was dried over
Na2SO4, and the solvent removed in vacuo. Column chroma-
tography [SiO2, CH2Cl2:acetone 9:1] yielded the product as a
Exp er im en ta l Section
Ma ter ia ls. Chemicals were used as received from their
commercial sources. All reactions were carried out under a
nitrogen atmosphere. Solvents were dried over molecular
sieves except for THF, which was distilled from NaH and
sodium (benzophenon) and DMF which was distilled twice
from P2O5 under reduced pressure. Benzhydrol (10a ),23 4-hy-
-27
droxytetraphenylmethane (10b),24 and 26‚2PF6
were pre-
pared according to literature procedures.
Ch a r a cter iza tion . 1H NMR spectra were recorded on a 300
MHz Varian (VXR 300) spectrometer or a 500 MHz Varian
(Unity 500) spectrometer. Chloroform-d1 was used as an
internal standard, unless stated otherwise. MALDI-TOF
spectra were taken on a Micromass TofSpec E mass spectrom-
eter using 2,5-dihydroxybenzoic acid (DHB) as matrix. Electron
spray mass spectra were recorded on a Sciex API3000 triple/
quadruple mass spectrometer. High-resolution mass spectra
(HRMS) were obtained from a J EOL MS Route J MS-600H.
Elemental analyses were carried out at the Microanalytical
Department of the University of Groningen.
1
gray oil (0.48 g, 45%). H NMR: δ 3.60-3.84 (m, 26H), 3.95-
Dih yd r oqu in on e Tetr a eth ylen e Glycol (12). Hydro-
quinone (11.0 g, 100 mmol) and 8 (5.03 g, 10 mmol) were
dissolved in dry DMF (50 mL). After the addition of K2CO3
(2.90 g, 21 mmol), the reaction mixture was stirred for 15 h at
80 °C. The solvent was removed in vacuo and the resultant
brown oil was dissolved in CH2Cl2 and extracted with water.
The organic layer was dried over Na2SO4 and the solvent was
removed in vacuo. The resulting oil was dissolved in warm
chloroform, and after cooling, the excess hydroquinone was
filtered off. Column chromatography [SiO2, Et2O:CH2Cl2 (2:
4.08 (m, 6H), 5.40 (s, 1H), 6.71 (s, 4H), 6.78 (d, 4H), 7.21-
7.37 (m, 10H). The disubstituted product could be isolated in
1
a 20% yield. H NMR: δ 3.59-3.73 (m, 32H), 3.78-3.84 (m,
8H), 4.02-4.18 (m, 8H), 5.40 (s, 2H), 6.81 (s, 8H), 7.22-7.38
(m, 20H).
[1-{p -[2-(2-(2-(2-(Dip h e n ylm e t h oxy)e t h oxy)e t h oxy)-
eth oxy)eth oxy]p h en oxy}-13-{p-[2-(2-(2-(2-(4-((d ip h en yl-
t er t -b u t y l)silox y)d ip h e n ylm e t h oxy )e t h o xy )e t h o x y )-
eth oxy)eth oxy]p h en oxy}-3,6,9-tr ioxa u n d eca n e (14a ): A
suspension of NaH (75 mg, 1.87 mmol) in dry THF (8 mL) was
added to a solution of 13a (1.23 g, 1.7 mmol) in dry THF (20
mL). After being stirred at room temperature for 10 min, this
solution was added to a refluxing solution of 9a (1.31 g, 1.7
mmol) in dry THF (25 mL) and refluxing was continued for 2
h. The reaction mixture was concentrated, extracted with
CH2Cl2/H2O, and dried over MgSO4. Concentration of the
organic layer and column chromatography [SiO2, CH2Cl2:
acetone (9:1)] yielded the product as a light-yellow oil (0.80 g,
36%). 1H NMR: δ 1.08 (s, 9H), 3.52-3.73 (m, 32H), 3.78-3.83
(m, 8H), 4.00-4.07 (m, 8H), 5.27 (s, 1H), 5.40 (s, 1H), 6.67 (d,
2H), 6.81 (s, 8H), 7.03 (d, 2H), 7.19-7.40 (m, 13H), 7.67 (d,
4H).
4-Hyd r oxy-4′-m eth oxytetr a p h en ylm eth a n e (6). p-Ani-
sylchlorodiphenylmethane (0.79 g, 2.5 mmol) and phenol (5.1
g, 54 mmol) were stirred for 20 h at 60 °C, cooled, dissolved in
CH2Cl2, and extracted twice with 1 M Na2CO3 and twice with
H2O. The solution was dried over MgSO4 and the solvent
removed in vacuo. Column chromatography [SiO2, hexane:Et2O
(2:1)] yielded the product as a white solid (0.45 g, 68%). 1H
NMR: δ 3.80 (s, 3H), 5.20 (s, 1H), 6.71 (d, 2H), 6.81 (d, 2H),
7.08 (d, 2H), 7.12 (d, 2H), 7.18-7.30 (m, 10H).
1
1)], yielded a clear oil (2.1 g, 55%). H NMR: δ 3.67 (s, 8H),
3.75 (t, 4H), 3.92 (t, 4H), 6.67 (d, 8H).
4-(Dip h en yl-ter t-bu tylsiloxy)ben zop h en on e (3). Pyri-
dine (8.4 mL, 100 mmol) was added to a solution of tert-
butyldiphenylsilyl chloride (7.2 mL, 28 mmol) in dry THF (15
mL) and stirred for 15 min. This solution was added dropwise
to a solution of 4-hydroxybenzophenon (5.0 g, 25 mmol), NEt3
(3.8 mL, 28 mmol), and DMAP (0.15 g, 1.25 mmol) in dry THF
(35 mL) at 0 °C over a period of 0.5 h. After being stirred for
5 h at room temperature, the solution was concentrated, Et2O
was added, and the resulting solution was extracted with 0.1
M HCl and water. The organic layer was dried over MgSO4,
the solvent removed in vacuo, and the product recrystallized
1
from hexane as white crystals (10.0 g, 92%). H NMR: δ 1.11
(s, 9H), 6.81 (d, 2H), 7.33-7.54 (m, 9H), 7.63 (d, 2H), 7.67-
7.74 (m, 6H). Anal. Calcd for C29H28O2Si: C, 79.78; H, 6.47.
Found: C, 79.89; H, 6.57.
4-((Dip h en yl-ter t-bu tyl)siloxy)d ip h en ylm eth a n ol (4a ).
3 (3.20 g, 7.33 mmol) was dissolved in dry THF (25 mL).
NaBH4 (83 mg, 2.20 mmol) was added, and the reaction
mixture was refluxed for 7 h. After cooling, Et2O was added,
and the resulting solution was washed with water and dried
over MgSO4. Evaporation of the solvent in vacuo and column
chromatography [SiO2, hexane:Et2O (3:1)] yielded the product
4,4′-Dih yd r oxytetr a p h en ylm eth a n e (7): BBr3 (0.85 g,
3.4 mmol) in dry CH2Cl2 (3 mL) was added to a solution of 6
(0.50 g, 1.4 mmol) in dry CH2Cl2 (15 mL). After being stirred
for 1.5 h at room temperature, the reaction mixture was
extracted with water and dried over MgSO4, yielding the
product as a white solid (0.5 g, ∼100%). 1H NMR (CDCl3/
CD3OD): δ 6.48 (s, 2H), 6.55 (d, 4H), 6.88 (d, 4H), 7.01-7.15
(m, 10H).
1
as a clear oil (2.54 g, 79%). H NMR: δ 1.13 (s, 9H), 2.19 (d,
1H), 5.74 (d, 1H), 6.76 (d, 2H), 7.11 (d, 2H), 7.24-7.50 (m, 11H),
7.74 (d, 4H). HRMS C29H30O2Si: calcd, 438.2026; found,
438.2015.
2-(2-(2-(2-(4-((Dip h e n yl-t er t -b u t yl)siloxy)d ip h e n yl-
m eth oxy)eth oxy)eth oxy)eth oxy)eth oxy Tosyla te (9a ). A
suspension of NaH (0.25 g, 6.3 mmol) in dry THF (10 mL) was
added to a solution of 4a (2.50 g, 5.7 mmol) in dry THF (15
mL). After stirring for 10 min, this solution was added to a
refluxing solution of 8 (5.73 g, 11.4 mmol) in dry THF (40 mL)
and refluxing was continued for 3 h. The reaction mixture was
concentrated in vacuo, extracted with CH2Cl2/H2O, and dried
over MgSO4. Concentration of the organic layer and column
chromatography [SiO2, CHCl3:Et2O (11:1)] yielded the product
as a light-yellow oil (2.85 g, 65%). 1H NMR: δ 1.13 (s, 9H),
2.41 (s, 3H), 3.54-3.65 (m, 14H), 4.12 (t, 2H), 5.27 (s, 1H),
6.68 (d, 2H), 7.10 (d, 2H), 7.22-7.40 (m, 13H), 7.68 (d, 4H),
7.77 (d, 2H).
4-(Dip h en yl-ter t-b u t ylsiloxy)-4′-h yd r oxyt et r a p h en yl-
m eth a n e (4b). To a solution of 7 (0.82 g, 2.3 mmol) in
triethylamine (7 mL) and pyridine (5 mL) were added DMAP
(71 mg, 0.6 mmol) and tert-butylchlorodiphenylsilane (0.61 mL,
2.3 mmol), and the reaction was stirred overnight at room
temperature. The solution was extracted with water and dried
over MgSO4, and the solvent was removed in vacuo. Column
chromatography [SiO2, hexane:Et2O:CH2Cl2 (3:1:1)] yielded the
1
product as a clear oil (0.76 g, 55%). H NMR: δ 1.08 (s, 9H),
6.64 (d, 4H), 6.87 (d, 2H), 6.93 (d, 2H), 7.08-7.21 (m, 10H),
7.32-7.38 (m, 6H), 7.71 (dd, 4H). HRMS C41H38O2Si: calcd,
590.2641; found, 590.2629.
2-(2-(2-(2-(4-[4-((Dip h en yl-ter t-bu tyl)siloxy)]tr itylp h e-
n oxy)eth oxy)eth oxy)eth oxy)eth oxy Tosyla te (9b). A sus-
pension of NaH (15 mg, 0.39 mmol) in dry THF (0.5 mL) was
2-(2-(2-(2-(Dip h en ylm et h oxy)et h oxy)et h oxy)et h oxy)-
eth oxy Tosyla te (11a ). A solution of benzhydrol (1.47 g, 8

Macromolecules, Vol. 36, No. 19, 2003
Mechanically Linked Polyrotaxanes 7011
added to a solution of 4b (0.20 g, 0.35 mmol) in dry THF (2
mL) This solution was added to a refluxing solution of 8 (0.70
g, 1.4 mmol) in dry THF (7 mL), and refluxing was continued
for 2 h. The reaction mixture was concentrated in vacuo,
extracted with CH2Cl2/H2O, and dried over MgSO4. Concentra-
tion of the organic layer and column chromatography [SiO2,
Et2O:hexane:CH2Cl2 (2:1:1)] yielded the product as a clear oil
(0.18 g, 55%). H NMR: δ 1.08 (s, 9H), 6.58 (d, 2H), 6.69 (d,
2H), 6.81 (d, 2H), 6.94 (d, 2H), 7.04 (dd, 4H), 7.09-7.17 (m,
6H), 7.26-7.39 (m, 8H), 7.64 (d, 4H), 7.74 (d, 2H).
2-(2-(2-(2-(4-Tr it ylp h e n oxy)e t h oxy)e t h oxy)e t h oxy)-
eth oxytosyla te (11b). A suspension of NaH (53 mg, 1.3
mmol) in dry THF (2 mL) was added to a solution of 4-hy-
droxytetraphenylmethane (0.40 g, 1.2 mmol) in dry THF (6
mL). After being stirred for 5 min, this solution was added to
a refluxing solution of 8 (1.2 g, 2.4 mmol) in dry THF (10 mL),
and refluxing was continued for 1.5 h. The reaction mixture
was concentrated in vacuo, CH2Cl2 was added, and the reaction
mixture was washed with water and dried over MgSO4.
Concentration of the organic layer and column chromatogra-
phy [SiO2, Et2O:CH2Cl2:hexane (2:1:1)] yielded the product as
a white solid (0.58 g, 72%). 1H NMR: δ 2.41 (s, 3H), 3.58-
3.70 (m, 10H), 3.81-3.88 (t, 2H), 4.06-4.20 (m, 4H), 6.80 (d,
2H), 7.12 (d, 2H), 7.17-7.26 (m, 15H), 7.33 (d, 2H), 7.81 (d,
2H).
Allyl-4-h yd r oxybu ta n oa te (18). Concentrated sulfuric
acid (0.10 g, 1 mmol) was added to a mixture of butyrolactone
(0.43 g, 5 mmol) and allyl alcohol (2.9 g, 50 mmol) and the
reaction mixture stirred for 1 day at room temperature.
NaHCO3 (0.1 g, 1 mmol) was added and the reaction mixture
stirred for another hour. Et2O was added and extracted twice
with 1 M Na2CO3 solution and water, the resulting solution
dried over MgSO4 and the solvent evaporated in vacuo.
Kugelrohr distillation (73 °C, 0.04 mmHg) yielded the product
1
1
as a clear liquid (0.21 g, 29%). H NMR: δ 1.80 (quintet, 2H),
2.38 (t, 2H), 2.57 (s, 1H), 3.56 (t, 2H), 4.47 (d, 2H), 5.12 (d,
1H), 5.21 (d, 1H), 5.72-5.88 (m, 1H).
Allyl-4-bu ta n oa te-2,5-bis(br om om eth yl)ben zoa te (19).
16 (0.21 g, 0.68 mmol) was suspended in dry toluene (10 mL).
SOCl2 (0.10 mL, 1.43 mmol) was added and the reaction
mixture refluxed for 1 h. The reaction mixture was concen-
trated in vacuo, dissolved in dry CH2Cl2 (7 mL) and NEtiPr2
(0.13 mL, 0.82 mmol) and 18 (0.10 g, 0.68 mmol) were added.
The reaction mixture was stirred overnight at room temper-
ature, extracted with water and dried over MgSO4. Concentra-
tion of the organic layer and column chromatography [SiO2,
hexane:CHCl3:Et2O (8:3:1)] yielded the product as a light-
yellow oil (0.15 g, 49%). 1H NMR: δ 2.08 (m, 2H), 2.46 (m,
2H), 4.34 (m, 2H), 4.47 (dd, 2H), 4.53 (d, 2H), 4.90 (dd, 2H),
5.16 (d, 1H), 5.24 (d, 1H), 5.77-5.90 (m, 1H), 7.36-7.49 (m,
2H), 7.88 (d, 1H).
{[1-{p -[2-(2-(2-(2-(d i p h e n y lm e t h o x y )e t h o x y )e t h -
oxy)e t h oxy)e t h oxy]p h e n oxy}-13-{p -[2-(2-(2-(2-[4-((d i-
p h e n yl-t er t -b u t yl)siloxy)p h e n yl]p h e n ylm e t h oxy)e t h -
oxy)et h oxy)et h oxy)et h oxy]p h en oxy}-3,6,9-t r ioxa u n d e-
ca n e][cyclo(2,5-(p a r a q u a t -p -p h en ylen ep a r a q u a t )(a llyl-
4-bu ta n oa te)ben zoa te)]r ota xa n e} Tetr a k is(h exa flu or o-
p h osp h a te) (1a ‚4P F 6)): The dumbbell 14a (158 mg, 0.12
mmol) and 19 (52 mg, 0.12 mmol) were dissolved in dry MeCN
(0.3 mL). AgPF6 (70 mg, 0.28 mmol) and 26‚2PF6- (85 mg, 0.12
mmol), dissolved in dry MeCN (0.3 mL), were added. After
being stirred for 4 days at room temperature, the reaction
mixture was centrifuged and the solution concentrated to 0.5
mL. By addition of CHCl3 (4 mL), the paraquat dication and
cyclophane precipitated. The solution was concentrated to 3
mL, and Et2O (1 mL) was added. The red precipitate was
1-{p-[2-(2-(2-(2-(4-Tr itylph en oxy)eth oxy)eth oxy)eth oxy)-
eth oxy]ph en oxy}-13-{p-h yd r oxyp h en oxy}-3,6,9-tr ioxa u n -
d eca n e (13b). 11b (0.40 g, 0.6 mmol) and 12 (0.15 g, 0.4 mmol)
were dissolved in dry DMF (7 mL), and K2CO3 (0.09 g, 0.64
mmol) was added. After 20 h at 90 °C, CH2Cl2 was added, and
the reaction mixture was extracted with 0.1 M HCl and water
and dried over Na2SO4. Concentration of the organic layer and
column chromatography [SiO2, CH2Cl2:acetone (9:1)] yielded
the product as a clear oil (0.20 g, 58%). 1H NMR: δ 3.60-3.68
(m, 16H), 3.71-3.78 (m, 8H), 3.89-4.04 (m, 8H), 6.67 (d, 4H),
6.72 (d, 2H), 6.74 (s, 4H), 7.03 (d, 2H), 7.09-7.20 (m, 15H).
1
The disubstituted product could be isolated in 22% yield. H
NMR: δ 3.60-3.68 (m, 24H), 3.71-3. 08 (m, 12H), 3.91-4.04
(m, 12H), 6.67 (d, 4H), 6.73 (s, 8H), 7.03 (d, 4H), 7.09-7.20
(m, 30H).
1-{p-[2-(2-(2-(2-(4-tr itylph en oxy)eth oxy)eth oxy)eth oxy)-
eth oxy]p h en oxy-13-{p-[2-(2-(2-(2-(4-[4-((d ip h en yl-ter t-bu -
tyl)siloxy)]tr itylp h en oxy)eth oxy)eth oxy)eth oxy)eth oxy]-
p h en oxy}-3,6,9-tr ioxa u n d eca n e (14b). A suspension of NaH
(8 mg, 0.2 mmol) in dry THF (0.3 mL) was added to a solution
of 13b (0.16 g, 0.18 mmol) in dry THF (3 mL). This solution
was added to a refluxing solution of 9b (0.17 g, 0.18 mmol) in
dry THF (4 mL), and the refluxing was continued for 2 h. The
reaction mixture was concentrated in vacuo, CH2Cl2 was
added, and the reaction mixture was washed with water and
dried over MgSO4. Concentration of the organic layer and
column chromatography [SiO2, CH2Cl2:acetone (9:1)] yielded
the product as a clear oil (0.13 g, 45%). 1H NMR: δ 1.07 (s,
9H), 3.60-3.68 (m, 16H), 3.72-3.80 (m, 8H), 3.98-4.08 (m,
8H), 6.58 (d, 2H), 6.69 (d, 2H), 6.73 (d, 2H), 6.77 (s, 8H), 6.81
(d, 2H), 6.94 (d, 2H), 7.04 (d, 6H), 7.10-7.21 (m, 21H), 7.27-
7.39 (m, 6H), 7.64 (dd, 4H). Anal. Calcd for C102H112O16Si: C,
75.50; H, 7.00. Found: C, 75.28; H, 7.18.
subjected to column chromatography [SiO2, MeOH:2
M
NH4Cl:MeNO2 (7:2:1)] and after ion exchange with NH4PF6,
1
the product was obtained as a red solid (10 mg, 5%). H NMR
(CD3CN): δ 1.20 (s, 9H), 2.38 (quintet, 2H), 2.77 (t, 2H), 3.60-
4.15 (m, 48H), 4.70-4.76 (m, 4H), 5.22 (d, 1H), 5.28-5.43 (m,
3H), 6.10 (m, 1H), 6.27 (s, 4H), 6.48 (s, 2H), 6.52 (s, 2H), 6.88
(d, 2H), 7.23 (d, 2H), 7.34-7.61 (m, 21H), 7.85 (d, 4H), 8.16 (s,
4H), 8.30-8.40 (m, 10H), 8.71 (s, 1H), 9.43-9.49 (m, 6H), 9.59
(d, 2H). MALDI-TOF (dihydroxybenzoic acid matrix): 2298
[M - 2PF6]+; 2153 [M - 3PF6]+; 2009 [M - 4PF6]+. UV/vis
(solvent): λmax [nm] (ꢀ [M-1 cm-1]) ) 265 (36 000); 466 (650).
{[1-{p -[2-(2-(2-(2-(4-t r it ylp h e n oxy)e t h oxy)e t h oxy)-
et h oxy)et h oxy]p h en oxy-13-{p -[2-(2-(2-(2-(4-[4-((d ip h en -
yl-ter t-b u t yl)siloxy)]t r it ylp h en oxy)et h oxy)et h oxy)et h -
o x y )e t h o x y ]p h e n o x y }-3,6,9-t r io x a u n d e c a n e ][c y c lo -
(2,5-(p a r a q u a t -p -p h e n y le n e p a r a q u a t )(a lly l-4-b u t a -
n oa te) ben zoa te)]r ota xa n e} Tetr a k is(h exa flu or op h os-
p h a te) (1b‚4P F 6)). The dumbbell 14b (157 mg, 0.1 mmol)
2,5-Bis(br om om eth yl)ben zoic Acid (16). 2,5-Dimethyl-
benzoic acid (5.00 g, 33.3 mmol), N-bromosuccinimide (2.52 g,
14.2 mmol), and benzoylperoxide (171 mg, 0.71 mmol) were
dissolved in CCl4 (100 mL) and refluxed. A red color appeared
which disappeared again after 15 min. NBS (2.52 g) and BPO
(171 mg) were added, and refluxing was continued. NBS (2.52
g) and BPO (171 mg) were added two more times after 15 and
45 min. Each time a red color appeared which disappeared
before addition of the next portion. The reaction mixture was
refluxed for 30 min after the last addition and then cooled fast.
The solid was filtered off and the filtrate concentrated in vacuo.
The solid was dissolved in CH2Cl2:acetone (3:1) and precipi-
tated with hexane (30 mL). The precipitate was filtered off,
dissolved in CH2Cl2:acetone (3:1) and again precipitated with
hexane (40 mL). The product was filtered off as an off-white
-
and 26‚2PF6 (68 mg, 0.1 mmol) were dissolved in dry DMF
(0.3 mL). AgPF6 (61 mg, 0.25 mmol) in MeCN (0.4 mL) and
allyl-4-butanoate-2,5-di(bromomethyl) benzoate 19 (42 mg, 0.1
mmol) in MeCN (0.5 mL) were added. After being for 7 days
at room temperature, the reaction mixture was centrifuged
and the solution concentrated to 1 mL. By addition of CHCl3
(5 mL), the free cyclophane precipitated. The solution was
concentrated to 1 mL and the rotaxane precipitated by the
addition of Et2O (3 mL). The solid was dissolved in CHCl3 (1
mL) and again precipitated with Et2O (1 mL), yielding the
1
product as a red solid (18.6 mg, 6.6%). H NMR (acetone-d6):
δ 1.25 (s, 9H), 2.36 (quintet, 2H), 2.75 (t, 2H), 3.75-4.15 (m,
48H), 4.67-4.77 (m, 4H), 5.36 (d, 1H), 5.47 (d, 1H), 6.12 (m,
1H), 6.21 (s, 4H), 6.32 (s, 2H), 6.52 (s, 2H), 6.82-6.98 (m, 6H),
7.03 (d, 2H), 7.12 (d, 2H), 7.18-7.25 (m, 6H), 7.31-7.45 (m,
21H), 7.53-7.63 (m, 6H), 7.87 (d, 4H), 8.18 (s, 4H), 8.32-8.42
1
solid (2.6 g, 25%). H NMR: δ 4.50 (s, 2H), 4.99 (s, 2H), 7.50
(d, 1H), 7.61 (dd, 1H), 8.16 (d, 1 H).

7012 Werts et al.
Macromolecules, Vol. 36, No. 19, 2003
(m, 10H), 8.74 (s, 1H), 9.44-9.50 (m, 6H), 9.60 (d, 2H).
MALDI-TOF: m/z 2603 (M - 2PF6)+, 2458 (M - 3PF6)+, 2313
(M - 4PF6)+. Anal. Calcd for C146H154F24N4O20P4Si: C, 60.62;
H, 5.37; N, 1.94. Found: C, 60.25; H, 5.38; N, 2.02. Thus, 95%
of the unthreaded dumbbell could be recovered by column
chromatography of the ether phase [SiO2, CH2Cl2:acetone (9:
1)].
mmol) in MeCN (0.7 mL). After 30 min at room temperature,
CH2Cl2 was added, and the resulting solution was extracted
twice with H2O/NH4PF6 and twice with water. The rotaxane
was precipitated from the organic phase with Et2O, yielding
the product as a red solid (42 mg, 75%). 1H NMR (acetone-d6):
δ 2.34 (quintet, 2H), 2.76 (t, 2H), 3.75-4.15 (m, 48H), 4.69-
4.75 (m, 4H), 5.35 (d, 1H), 5.47 (d, 1H), 6.10 (m, 1H), 6.20 (s,
4H), 6.31 (s, 2H), 6.52 (s, 2H), 6.85-6.98 (m, 6H), 7.10 (d, 2H),
7.16-7.21 (m, 6H), 7.28-7.45 (m, 21H), 8.18 (s, 4H), 8.32-
8.42 (m, 10H), 8.74 (s, 1H), 9.44-9.50 (m, 6H), 9.60 (d, 2H).
MALDI-TOF (dihydroxybenzoic acid matrix): m/z 2365 (M
- 2PF6)+, 2220 (M - 3PF6)+, 2075 (M - 4PF6)+.
{[1-{p -[2-(2-(2-(2-(D i p h e n y lm e t h o x y )e t h o x y )e t h -
oxy)eth oxy)eth oxy] ph en oxy}-13-{p-[2-(2-(2-(2-[4-((diph en -
yl-t er t -b u t yl)siloxy)p h e n yl]p h e n ylm e t h oxy)e t h oxy)-
eth oxy)eth oxy)eth oxy]p h en oxy}-3,6,9-tr ioxa u n d eca n e]-
[cyclo(2,5-(p a r a q u a t -p -p h en ylen ep a r a q u a t )-4-ca r b oxy-
bu tylben zoate)]r otaxan e} Tetr akis(h exaflu or oph osph ate)
-
Dim er (30b‚8P F6)). 29b‚4PF6- (17 mg, 6.3 µmol), 28b‚4PF6
-
(28a ‚4P F 6)). To a solution of 1a ‚4PF6 (10 mg, 3.9 µmol) in
(18 mg, 6.3 µmol), DMAP (1.6 mg, 13 µmol), and TosH (2.2
mg, 11 µmol) were dissolved in MeCN (0.2 mL), and DCC (4
mg, 19 µmol) was added. After the reaction was stirred for 1
day at room temperature, DHU was removed by centrifugation
and the product precipitated with CH2Cl2/Et2O. Column chro-
matography [SiO2, MeOH:2 M NH4Cl:MeNO2 (7:2:1) f MeOH:
H2O (7:2) f MeCN + 0.5% NH4PF6] yielded the product as a
CHCl3 (0.4 mL) were added acetic acid (13 µL, 230 µmol) and
NMM (13 µL, 115 µmol). A solution of Pd(PPh3)4 (9 mg, 7.7
µmol) in CHCl3 (0.1 mL) was added, and the reaction mixture
was stirred for 3 h at room temperature. After addition of
CHCl3 (3 mL), the rotaxane was precipitated with Et2O (1 mL).
The solid was extracted with CH2Cl2/H2O and the solvent
evaporated in vacuo, yielding the product as a red solid (7.8
mg, 80%). 1H NMR (CD3CN): δ 1.20 (s, 9H), 2.38 (quintet, 2H),
2.77 (t, 2H), 3.60-4.15 (m, 48H), 4.71 (t, 2H), 5.43 (s, 1H), 5.54
(s, 1H), 6.27 (s, 4H), 6.48 (s, 2H), 6.52 (s, 2H), 6.88 (d, 2H),
7.23 (d, 2H), 7.34-7.61 (m, 21H), 7.85 (d, 4H), 8.16 (s, 4H),
8.30-8.40 (m, 10H), 8.71 (s, 1H), 9.43-9.49 (m, 6H), 9.59 (d,
2H).
1
red solid (27 mg, 78%). H NMR (acetone-d6): δ 1.23 (s, 9H),
2.31-2.46 (m, 4H), 2.75 (t, 4H), 3.75-4.22 (m, 96H), 4.67-
4.79 (m, 6H), 5.35 (d, 1H), 5.47 (d, 1H), 6.12 (m, 1H), 6.19 (s,
8H), 6.26 (s, 2H), 6.32 (s, 2H), 6.53 (s, 4H), 6.81-6.97 (m, 12H),
7.01 (d, 4H), 7.10 (d, 4H), 7.18-7.23 (m, 12H), 7.31-7.45 (m,
42H), 7.52-7.63 (m, 6H), 7.86 (d, 4H), 8.17 (s, 8H), 8.30-8.42
(m, 20H), 8.74 (s, 2H), 9.44-9.50 (m, 12H), 9.56-9.60 (m, 4H).
MALDI-TOF: m/z 4923 (M - 4PF6)+, 4778 (M - 5 PF6)+, 4633
(M - 6PF6)+, 4488 (M - 7 PF6)+, 4343 (M - 8PF6)+.
{[1-{p -[2-(2-(2-(2-(D i p h e n y lm e t h o x y )e t h o x y )e t h -
oxy)e t h oxy)e t h oxy]p h e n oxy}-13-{p -[2-(2-(2-(2-[4-h y-
d r oxyp h en yl]p h en ylm et h oxy)et h oxy)et h oxy)et h oxy)-
e t h o x y ]p h e n o x y }-3,6,9-t r io x a u n d e c a n e ][c y c lo (2,5-
(p a r a q u a t -p -p h e n yle n e p a r a q u a t )(a llyl-4-b u t a n oa t e )-
b en zoa t e)]r ot a xa n e} Tet r a k is(h exa flu or op h osp h a t e)
(29a ‚4P F 6)). o-Nitrophenol (0.6 mg, 4.3 µmol) and Bu4NF (9.5
-
Dim er )COOH (31b‚8P F 6)): To a solution of 30b‚8PF6
(27 mg, 4.9 µmol) in CHCl3 (0.1 mL) were added acetone (0.1
mL), acetic acid (17 µL, 0.30 mmol), and NMM (16 µL, 0.15
mmol). A solution of Pd(PPh3)4 (11 mg, 10 µmol) in CHCl3 (0.1
mL) was added, and the reaction mixture was stirred for 7 h
at room temperature. After addition of CH2Cl2 (2 mL), the
rotaxane was precipitated with Et2O (1 mL). PPh3 was
removed by precipitation with acetone. The solution was
extracted twice with CH2Cl2/NH4PF6 and twice with CH2Cl2/
H2O. Column chromatography [SiO2, MeCN:MeOH:NH4PF6 (9:
1:0% f 9:1:1%)] yielded the product as a red solid (11 mg,
40%). 1H NMR (acetone-d6): δ 1.23 (s, 9H), 2.31-2.46 (m, 4H),
2.75 (t, 4H), 3.75-4.22 (m, 96H), 4.67-4.79 (m, 4H), 6.19 (s,
8H), 6.26 (s, 2H), 6.32 (s, 2H), 6.53 (s, 4H), 6.81-6.97 (m, 12H),
7.01 (d, 4H), 7.10 (d, 4H), 7.18-7.23 (m, 12H), 7.31-7.45 (m,
42H), 7.52-7.63 (m, 6H), 7.86 (d, 4H), 8.17 (s, 8H), 8.30-8.42
(m, 20H), 8.74 (s, 2H), 9.44-9.50 (m, 12H), 9.56-9.60 (m, 4H).
MALDI-TOF (dihydroxybenzoic acid matrix): m/z 4738 (M
- 5 PF6)+, 4593 (M - 6PF6)+, 4448 (M - 7 PF6)+;
-
µL, 9.5 µmol) were added to a solution of 1a ‚4PF6 (10 mg,
3.9 µmol) in MeCN (0.2 mL). After 30 min, the rotaxane was
precipitated with water and centrifuged. The solid was dis-
solved in CHCl3 (2 mL) and precipitated with Et2O (1 mL)
twice, yielding the product as a red solid (6.4 mg, 70%). 1H
NMR (CD3CN): δ 2.38 (quintet, 2H), 2.77 (t, 2H), 3.60-4.15
(m, 48H), 4.70-4.76 (m, 4H), 5.22 (d, 1H), 5.28-5.43 (m, 3H),
6.10 (m, 1H), 6.27 (s, 4H), 6.48 (s, 2H), 6.52 (s, 2H), 6.90 (d,
2H), 7.25 (d, 2H), 7.34-7.49 (m, 15H), 8.16 (s, 4H), 8.30-8.40
(m, 9H), 8.61 (s, 1H), 8.71 (s, 1H), 9.43-9.49 (m, 6H), 9.59 (d,
2H).
{[1-{p -[2-(2-(2-(2-(4-Tr it ylp h e n oxy)e t h oxy)e t h oxy)-
e t h o x y )e t h o x y ]p h e n o x y }-13-{p -[2-(2-(2-(2-(4-[4-((d i-
p h e n yl-t er t -b u t yl)siloxy)]t r it ylp h e n oxy)e t h oxy)e t h -
oxy)eth oxy)eth oxy]p h en oxy}-3,6,9-tr ioxa u n d eca n e][cy-
clo(2,5-(p a r a q u a t -p -p h en ylen ep a r a q u a t )-4-ca r b oxyb u -
tylben zoa te)]r ota xa n e} Tetr a k is(h exa flu or op h osp h a te)
Dim er )OH (32b‚8P F 6)): o-Nitrophenol (0.9 mg, 7 µmol)
and Bu4NF (6 µL, 6 µmol) were added to a solution of
30b‚8PF6- (27 mg, 4.8 µmol) in MeCN (0.2 mL). After 30 min,
CH2Cl2 was added and extracted twice with H2O/NH4PF6 and
twice with water. The rotaxane was precipitated from the
organic phase with Et2O, yielding the product as a red solid
(22 mg, 85%). 1H NMR (acetone-d6): δ 2.31-2.46 (m, 4H), 2.75
(t, 4H), 3.75-4.22 (m, 96H), 4.67-4.79 (m, 6H), 5.35 (d, 1H),
5.47 (d, 1H), 6.12 (m, 1H), 6.19 (s, 8H), 6.26 (s, 2H), 6.32 (s,
2H), 6.53 (s, 4H), 6.81-6.97 (m, 12H), 7.01 (d, 4H), 7.10 (d,
4H), 7.18-7.23 (m, 12H), 7.31-7.45 (m, 42H), 8.17 (s, 8H),
8.30-8.42 (m, 20H), 8.74 (s, 2H), 9.44-9.50 (m, 12H), 9.56-
9.60 (m, 4H). MALDI-TOF (dihydroxybenzoic acid matrix):
m/z 4540 (M - 5 PF6)+, 4395 (M - 6PF6)+, 4250 (M - 7 PF6)+.
-
(28b‚4P F 6)): To a solution of 1b‚4PF6 (64 mg, 22 µmol) in
CHCl3 (0.5 mL), were added acetone (0.2 mL), acetic acid (76
µL, 1.33 mmol), and NMM (73 µL, 0.66 mmol). A solution of
Pd(PPh3)4 (51 mg, 44 µmol) in CHCl3 (0.5 mL) was added, and
the reaction mixture was stirred for 3 h at room temperature.
After addition of CHCl3 (3 mL), the rotaxane was precipitated
with Et2O (1 mL). PPh3 was removed by precipitation with
acetone. Evaporation of the solvent in vacuo yielded the
1
product as a red solid (50 mg, 80%). H NMR (acetone-d6): δ
1.24 (s, 9H), 2.33 (quintet, 2H), 2.71 (t, 2H), 3.78-4.21 (m,
48H), 4.71 (t, 2H), 6.20 (s, 4H), 6.31 (s, 2H), 6.54 (s, 2H), 6.82-
6.93 (m, 6H), 7.02 (d, 2H), 7.11 (d, 2H), 7.18-7.23 (m, 6H),
7.30-7.44 (m, 21H), 7.52-7.61 (m, 6H), 7.86 (d, 4H), 8.17 (s,
4H), 8.31-8.41 (m, 10H), 8.73 (s, 1H), 9.46-9.53 (m, 6H), 9.58
(d, 2H). MALDI-TOF (dihydroxybenzoic acid matrix): m/z
2563 (M - 2PF6)+, 2418 (M - 3PF6)+, 2273 (M - 4PF6)+.
{[1-{p -[2-(2-(2-(2-(D i p h e n y lm e t h o x y )e t h o x y )e t h -
oxy)et h oxy)et h oxy]p h en oxy}-13-{p -[2-(2-(2-(2-(4-[4-h y-
d r oxyt r it ylp h e n oxy)e t h oxy)e t h oxy)e t h oxy)e t h oxy]-
p h en oxy}-3,6,9-t r ioxa u n d eca n e][cyclo(2,5-(p a r a q u a t -p-
p h en ylen ep a r a qu a t)(a llyl-4-bu ta n oa te)ben zoa te)]r ota x-
an e} Tetr akis(h exaflu or oph osph ate) (29b‚4P F6)). o-Nitro-
phenol (4.2 mg, 0.03 mmol) and Bu4NF (27 µL, 0.03
-
Tetr a m er (33b‚16P F 6)): Dimer-COOH 31b‚8PF6 (6.9
-
mg, 1.3 µmol) and Dimer-OH 32b‚8PF6 (5.6 mg, 1.1 µmol)
were dissolved in dry MeCN (0.15 mL). DMAP (0.26 mg, 2.1
µmol) in MeCN (10 µL), TosH (0.4 mg, 2.0 µmol) in MeCN (10
µL), and DCC (0.9 mg, 4.2 µmol) in MeCN (10 µL) were added.
After 4 days at room temperature, DCC (2 mg) was added.
After 7 days the reaction mixture was extracted with CH2Cl2/
NH4PF6 and twice with CH2Cl2/H2O, and the product subse-
quently precipitated from CH2Cl2/Et2O. Column chromatog-
raphy [SiO2, MeCN:MeOH:NH4PF6 (9:1:0% f 9:1:1.5%)] yielded
the pure tetramer as a red solid (4.0 mg, 35%). 1H NMR
(acetone-d6): δ 1.23 (s, 9H), 2.31-2.46 (m, 8H), 2.75 (t, 8H),
3.75-4.22 (m, 192H), 4.67-4.79 (m, 10H), 5.35 (d, 1H), 5.47
-
mmol) were added to a solution of 1b‚4PF6 (61 mg, 0.02121

Macromolecules, Vol. 36, No. 19, 2003
Mechanically Linked Polyrotaxanes 7013
1997, 119, 2952. (d) Born, M.; Ritter, H. Angew. Chem., Int.
Ed. Engl. 1995, 34, 309.
(d, 1H), 6.12 (m, 1H), 6.19 (s, 16H), 6.26 (s, 4H), 6.32 (s, 4H),
6.53 (s, 8H), 6.81-6.97 (m, 28H), 7.01 (d, 4H), 7.10 (d, 4H),
7.18-7.23 (m, 28H), 7.31-7.45 (m, 84H), 7.52-7.63 (m, 6H),
7.86 (d, 4H), 8.17 (s, 16H), 8.30-8.42 (m, 40H), 8.74 (s, 4H),
9.44-9.50 (m, 24H), 9.56-9.60 (m, 8H).
(9) Gibson, H. W.; Marand, H. Adv. Mater. 1993, 5, 11-21.
(10) (a) Weidmann, J .-L.; Kern, J .-M.; Sauvage, J .-P.; Muscat, D.;
Mullins, S.; Ko¨hler, W.; Rosenauer, C.; Ra¨der, H. J .; Martin,
K.; Geerts, Y. Chem.sEur. J . 1999, 5, 1841. (b) Hamers, C.;
Kocian, O.; Raymo, F. M.; Stoddart, J . F. Adv. Mater. 1998,
10, 1366. (c) Hamers, C.; Raymo, F. M.; Stoddart, J . F. Eur.
J . Org. Chem. 1998, 2109. (d) Menzer, S.; White, A. J . P.;
Williams, D. J .; B`ılohradsky´, M.; Hamers, C.; Raymo, F. M.;
Shipway, A. N.; Stoddart, J . F. Macromolecules 1998, 31, 295.
(11) (a) Tamaoki, N.; Shimada, S. Acta Chem. Scand. 1997, 51,
1138. (b) Rowan, S. J .; Cantrill, S. J .; Stoddart, J . F.; White,
A. J . P.; Williams, D. J . Org. Lett. 2000, 2, 759. (c) Oku, T.;
Furusho, Y.; Takata, T. J . Polym. Sci., Part A 2003, 41, 119.
(d) Hoshino, T.; Miyauchi, M.; Kawaguchi, Y.; Yamaguchi,
H.; Harada, A. J . Am. Chem. Soc. 2000, 122, 9876.
(12) Yamaguchi, N.; Nagvekar, D. S.; Gibson, H. W. Angew.
Chem., Int. Ed. 1998, 37, 2361.
HO)Dim er )COOH (34b‚8P F 6)): To a solution of the
-
dimer-OH 32b‚8PF6 (22 mg, 4.2 µmol) in CHCl3 (0.1 mL)
were added acetone (0.1 mL), acetic acid (14 µL, 0.25 mmol),
and NMM (14 µL, 0.13 mmol). A solution of Pd(PPh3)4 (10 mg,
8 µmol) in CHCl3 (0.1 mL) was added, and the reaction mixture
was stirred for 3 h. After addition of CH2Cl2 (2 mL), the
rotaxane was precipitated with Et2O (1 mL). PPh3 was
removed by precipitation with acetone. Precipitation from
CHCl3/Et2O yielded the product as a red solid (20 mg, 91%).
1H NMR (acetone-d6): δ 2.31-2.46 (m, 4H), 2.75 (t, 4H), 3.75-
4.22 (m, 96H), 4.67-4.79 (m, 4H), 6.19 (s, 8H), 6.26 (s, 2H),
6.32 (s, 2H), 6.53 (s, 4H), 6.81-6.97 (m, 14H), 7.01 (d, 2H),
7.10 (d, 2H), 7.18-7.23 (m, 14H), 7.31-7.45 (m, 42H), 8.17 (s,
8H), 8.30-8.42 (m, 20H), 8.74 (s, 2H), 9.44-9.50 (m, 12H),
9.56-9.60 (m, 4H). MALDI-TOF: m/z 4051 [M - 8PF6]+, 4196
[M - 7 PF6]+, 4341 [M - 6PF6]+, 4486 [M - 5 PF6]+, 4631 [M
- 4PF6]+.
(13) Werts, M. P. L. Mechanically Linked Oligorotaxanes. Thesis,
2001.
(14) Ashton, P. R.; Parsons, I. W.; Raymo, F. M.; Stoddart, J . F.;
White, A. J . P.; Williams, D. J .; Wolf, R. Angew. Chem., Int.
Ed. Engl. 1998, 37, 1913.
(15) Ashton, P. R.; Baxter, I.; Cantrill, S. J .; Fyfe, M. C. T.; Glink,
P. T.; Stoddart, J . F.; White, A. J . P.; Williams, D. J . Angew.
Chem., Int. Ed. 1998, 37, 1294.
-
P olym er (35b‚n P F 6)). The difunctional dimer 34b‚8PF6
(20 mg, 3.8 µmol), DMAP (0.9 mg, 8 µmol), and TosH (1.3 mg,
7 µmol) were dissolved in dry MeCN (0.05 mL). DCC (2.4 mg,
12 µmol) was added and was again added after 2 days (1.6
mg). After 7 days, the product was precipitated twice from
CH2Cl2/Et2O and subsequently extracted with CH2Cl2/NH4PF6
and twice with CH2Cl2/H2O to yield the polymer as a red solid
(16 mg, 80%).
(16) Werts, M. P. L.; Van den Boogaard, M.; Hadziioannou, G.;
Tsivgoulis, G. M. Chem. Commun. 1999, 623.
(17) Barany, G.; Merrifield, R. B. J . Am. Chem. Soc. 1977, 99,
7363.
(18) This structure could be denoted as a [3]rotaxane, in which
the prefix indicates the number of mechanically linked
components within one molecule. However, we think that it
will be more appropriate for the present article to name our
rotaxanes from a polymer viewpoint as monomers, dimers,
polymers, etc.
(19) It is not necessary to double the molecular weight in each
step; e.g. a dimer can be coupled with a monomer to yield a
trimer.
(20) Ashton, P. R.; Ballardini, R.; Balzani, V.; Boyd, S. E.; Credi,
A.; Teresa Gandolfi, M.; Go´mez-Lo´pez, M.; Iqbal, S.; Philp,
D.; Preece, J . A.; Prodi, L.; Ricketts, H. G.; Stoddart, J . F.;
Tolley, M. S.; Venturi, M.; White, A. J . P.; Williams, D. J .
Chem.sEur. J . 1997, 3, 152.
(21) (a) Chaudhary, S. K.; Hernandez, O. Tetrahedron Lett. 1979,
99. (b) Guindon, Y.; Yoakim, C.; Bernstein, M. A.; Morton,
H. E. Tetrahedron Lett. 1985, 26, 1185.
Ack n ow led gm en t. The authors thank B. Kwant
and J . Drakopoulou for their assistance in the synthetic
work, M. J eronimus-Stratingh for performing the elec-
tron spray MS experiments, and A. Kiewiet for the high-
resolution MS measurements. This work was financially
supported by the Netherlands Foundation for Chemical
Research (NWO-CW).
Su p p or tin g In for m a tion Ava ila ble: Text discussing the
design of the rotaxane monomer, bromination of bis(bromom-
ethyl)benzoic acid, and stability of the rotaxane monomers, a
table giving 1H NMR data for the byproducts formed in the
synthesis of 16, and figures showing the structures of the
byproducts formed in the synthesis of 16 and a MALDI-TOF
spectrum of 1a ‚4PF6-. This material is available free of charge
via the Internet at http://pubs.acs.org.
(22) The more rational logic would be to first protect the phenol
in
6 and subsequently deprotect the second phenol by
cleavage of the methyl ether. Unfortunately, the deprotection
condtions for the methoxy group also gives
deprotection of the TBDPS group.
a complete
(23) Vogel, A. I. In Practical Organic Chemistry, 3rd ed.; Long-
mans, Green and Co. Ltd.: London, 1956.
Refer en ces a n d Notes
(24) Ashton, P. R.; Bissell, R. A.; Go´rski, R.; Philp, D.; Spencer,
N.; J . F. Stoddart, J . F.; Tolley, M. S. Synlett 1992, 919.
(25) For example a) Ashton, P. R.; Bissell, R. A.; Philp, D.; Spencer,
N.; Stoddart, J . F. In Supramolecular Chemistry; Balzani,
V., De Cola, L., Eds.; Kluwer Academic Publishers: Dor-
drecht, The Netherlands, 1992. (b) Anelli, P. L.; Spencer, N.;
Stoddart, J . F. J . Am. Chem. Soc. 1991, 113, 5131.
(26) (a) J ones, S. S.; Reese, C. B. J . Chem. Soc., Perkins Trans 1
1979, 2762; (b) Ko¨hler, W.; Pfleiderer, W. Liebigs Ann. Chem.
1979, 1855. (c) Ogilvie, K. K.; Entwistle, D. W. Carbohydr.
Res. 1981, 89, 203.
(1) Amabilio, D. B.; Ashton, P. R.; Reder, A. S.; Spencer, N.;
Stoddart, J . F. Angew. Chem., Int. Ed. Engl. 1994, 33, 433.
(2) Du¨nnwald, T.; J a¨ger, R.; Vo¨gtle, F. Chem.sEur. J . 1997, 3,
2043.
(3) Balzani, V.; Gomez-Lopez, M.; Stoddart, J . F. Acc. Chem. Res.
1998, 31, 405-414.
(4) Bissell, R. A.; Cordova, E.; Kaifer, A. E.; Stoddart, J . F. Nature
(London) 1994, 369, 133.
(5) Philp, D.; Stoddart, J . F. Angew. Chem., Int. Ed. Engl. 1996,
35, 1154.
(6) (a) Murakami, H.; Kawabuchi, A.; Kotoo, K.; Kunitake, M.;
Nakashima, N. J . Am. Chem. Soc. 1997, 119, 7605. (b)
Beniston, A. C.; Hariman, A.; Lynch, V. M. Tetrah. Lett. 1994,
1473.
(7) (a) Livoreil, A.; Christiane, O.; Buchecker, D.; Sauvage, J . P.
J . Am. Chem. Soc. 1994, 116, 9399. (b) Cardenas, J . P.;
Livoreil, A.; Sauvage, J . P. J . Am. Chem. Soc. 1996, 118,
11980.
(8) For example: (a) Herrmann, W.; Schneider, M.; Wenz, G.
Angew. Chem., Int. Ed. Engl. 1997, 36, 2511. (b) Gong, C.
G.; Gibson, H. W. Angew. Chem., Int Ed. 1998, 37, 310. (c)
Hoskins, B. F.; Robson, R.; Slizys, D. A. J . Am. Chem. Soc.
(27) Geuder, W.; Hu¨nig, S.; Suchy, A. Angew. Chem., Int. Ed. Engl.
1983, 22, 489; Tetrahedron 1986, 42, 1665.
(28) (a) Vo¨gtle, F.; Gru¨tze, J .; Na¨tscher, R.; Wieder, W.; Weber,
E.; Gru¨n, R. Chem. Ber. 1975, 108, 1694. (b) Newcomb, M.;
Moore, S. S.; Cram, D. J . J . Am. Chem. Soc. 1977, 99, 6405.
(29) Brown H. C.; Keblys, K. A. J . Org. Chem. 1966, 31, 485.
(30) (a) Vowinkel, E. Chem. Ber. 1967, 100, 16. (b) Neises, B.;
Steglich, W. Angew. Chem., Int. Ed. Engl. 1978, 17, 522. (c)
Holmberg, K.; Hansen, B. Acta Chem. Scand. B 1979, 33, 410.
(31) Moore, J . S.; Stupp, S. I. Macromolecules 1990, 23, 65.
MA034521T