A photoswitchable rotaxane with an unfolded molecular thread

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DOI: 10.1002/ejoc.200500421

A Photoswitchable Rotaxane with an Unfolded Molecular Thread

Sebastian Schmidt-Schäffer,^[a]Lutz Grubert,^[a]Ulrich W. Grummt,^[b]Karin Buck,^[a]and

Werner Abraham*^[a]

Keywords: Cycloheptatriene / Rotaxanes / Tropylium ion / Supramolecular chemistry

Novel [2]rotaxanes containing the tetracationic cyclophane

cyclobis(paraquat-4,4-biphenylene) and a dumbbell-shaped

molecular thread incorporating a photoactive diarylcyclohep-

tatriene station as well as a photo-inactive aryl station have

been synthesized with yields of nearly 30% by the coupling

of two halves of the molecular thread. Each half incorporates

one of the two stations which are recognized by the tetracat-

ionic ring. The switch principle is based on photoheterolysis

of a diarylcycloheptatriene bearing a suitable leaving group

such as a methoxy substituent. The rotaxanes were trans-

formed into the related rotaxanes incorporating a diaryl trop-

ylium unit by electrochemical oxidation. The co-conforma-

tion of all rotaxanes was determined by ¹H NMR and UV/Vis

spectroscopy. It has been shown that the occupation of the

two different stations by the tetracationic ring depends both

on the electron donor capacity of these stations and on the

chain units between the stations. The desired preferred occu-

pation of the diarylcycloheptatriene station was achieved by

fine tuning both the stopper group at the end of the molecu-

lar thread and the number of oxygen atoms within the chain.

By tuning the chain length it has also been achieved that

both of the rotaxanes incorporating the diarylcycloheptatri-

ene unit and the tropylium-containing rotaxanes adopt an

unfolded structure in solution. The tetracationic ring resides

exclusively on the second aryl station within the tropylium

rotaxanes. Switching between co-conformations of the cyclo-

heptatrienyl-containing rotaxanes and the tropylium-con-

taining rotaxanes can be achieved by photoheterolysis of the

methoxy-substituted diarylcycloheptatriene, yielding the tro-

pylium rotaxane, which reacts thermally back to the cyclo-

heptatriene rotaxane, and thus closes the switching cycle.

Germany, 2006)

anes and rotaxanes have already been used in electronic de-

vices.^[4]

Introduction

Catenanes and rotaxanes are supramolecules, the compo-

nents of which are mechanically interlocked. Nondegener-

ated rotaxanes consist of a ring and a threadlike compo-

nent, incorporating two different recognition sites (sta-

tions). These stations control the interaction between the

ring and the thread components.^[1]Depending on the nature

of the interaction, external stimuli can change the relative

positions of the ring on the molecular thread by changing

the interaction between the ring and the stations. This type

of large-amplitude shuttling process can be triggered by

chemical, electrochemical, and photochemical stimuli.^[2]

Photochemical and electrochemical energy, in particular,

are of great interest as driving forces, because with them,

no waste products are formed during the driving process.

Such bistable rotaxanes can serve as archetypical molecules

for the development of nano-, photo-, or electromechanical

systems.^[3]Nanoelectromechanical systems such as caten-

The tetracationic ring cyclo-bis(paraquat-p-phenylene) 1

is a widely-used ring component (see Scheme 3). We re-

cently reported the synthesis and photochemical switching

of a bistable rotaxane in which the ring component is 1 and

the molecular thread contains a photoactive diarylcy-

cloheptatriene (CHT) station and anisole as the second sta-

tion.^[5]

The noncovalent interactions between the ring and the

two constitutionally different stations are of electrostatic, π-

stacking, charge-transfer, and hydrogen-bonding nature.^[6]

Ring movement along the molecular thread stimulated by

light or electron transfer is expected to occur against an

activation barrier, since only very weak interactions be-

tween the ring and the thread are possible outside of the

recognition stations.^[7]

The different sets of noncovalent interactions are primar-

ily determined by the electron donor capacity of the two

recognition sites.^[8]The ring therefore resides preferentially

on the CHT station. However, NMR spectroscopic investi-

gation has shown that the rotaxane adopts a folded confor-

mation enabling a side-by-side π-π stacking interaction of

the weaker electron donor station with the ring, thus opti-

mizing binding energy. A nonfolded conformation is desir-

able for ring movement over a long distance.

[a] Humboldt-University, Institute of Chemistry,

Brook-Taylor-Str. 2, 12489 Berlin, Germany

Fax: +49-30-20937266

E-mail: abraham@chemie.hu-berlin.de

[b] Friedrich-Schiller-University, Institute of Physical Chemistry,

Helmholtzweg 4, 07743 Jena, Germany

Supporting information for this article is available on the

WWW under http://ww w .eurjoc.org or from the author.

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A Photoswitchable Rotaxane with an Unfolded Molecular Thread

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We therefore attempted to obtain new rotaxanes exhibit-

ing this type of extended structure in solution.

In this paper, we describe the synthesis of several pairs

of CHT-containing and related tropylium (Tr)-containing

bistable rotaxanes, their characterization by NMR and UV/

Vis spectroscopy, and their switching by light and by pro-

tons. Two pairs exhibited unfolded conformations in both

the CHT-state and the Tr-state.

Scheme 1. Principle of photoheterolysis of a methoxy-diarylcy-

cloheptatriene.

Results and Discussion

The switch principle is based on photoheterolysis of a

diarylcycloheptatriene possessing a suitable leaving group to allow movement of the ring. The rate constants of such

such as a methoxy substituent (see Scheme 1).^[9]

shuttling processes in similar rotaxanes have been deter-

Photoheterolysis converts the electron-rich station into mined to be on the order of 10³s^–1.^[1a,10]Furthermore,

an electron-poor recognition site. Due to the generation of NMR studies of degenerated rotaxanes incorporating diaryl

the positively charged tropylium ion, the tetracationic ring cycloheptatriene stations have revealed that the shuttling

1 will be repelled and will move to the weaker electron do- process is fast in relation to the timescale of NMR spec-

nor station present within the bistable rotaxane (see troscopy.^[11]

Scheme 2). By thermal recombination of the ions, the start

In ideal bistable rotaxanes, the ring resides only on one

conformation is restored, thus closing the switching cycle. of the two recognition sites. Both π-stacking and electro-

The lifetime of the tropylium state must be long enough static interactions are controlled by the electron donor ca-

Scheme 2. Rotaxane 2 with numbering of some atoms.

Scheme 3. Principle of rotaxane synthesis.

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pacity of the stations, which is related to the oxidation po-

tential. Therefore, the differences between the oxidation po-

tentials of the diaryl cycloheptatriene station (A-CHT-B in

Scheme 2) and station C should be large. Accordingly, we

chose the xylyl station to be the photoinactive second sta-

tion in a bistable rotaxane (see Scheme 2).

The syntheses of the new rotaxanes were carried out by

a rather unusual pathway: two halves of the molecular

thread, each having one recognition site and a bulky group

at the end (see Scheme 2), were combined in the presence

of ring 1, as outlined in Scheme 3.

The two halves of the molecular thread of rotaxane 2

were synthesized as outlined in Scheme 4 and Scheme 5.

Rotaxane 2 was self-assembled using compounds 9c and

14 as templates for the tetracationic ring 1 and binding to-

gether the two halves of the thread by alkylation of the

amino group of compound 9c in the presence of 2,6-di-tert-

butyl-4-methylpyridine. Rotaxane 2 was isolated in 38%

yield.

¹H NMR spectroscopy is useful for monitoring the dis-

tribution of the ring between the two recognition sites, i.e.,

diaryl cycloheptatriene (A-CHT-B in Scheme 2) and xylene

(C). The chemically-induced shift values were calculated by

comparison of the uncomplexed and complexed recognition

stations, i.e., compounds 9c and 14 vs. rotaxane 2. The pro-

ton signals were attributed to the different aromatic groups

Scheme 5. Synthesis of the eastern half of the molecular thread.

with the aid of two-dimensional NMR spectroscopy, such induced shift (CIS) values determined for rotaxane 2 are

as C–H-COSY, H–H-COSY, and ROESY. The chemically given in Scheme 6.

Scheme 4. Synthesis of the western half of the molecular thread.

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A Photoswitchable Rotaxane with an Unfolded Molecular Thread

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Scheme 6. Chemically-induced shift (CIS) of some proton resonances of rotaxane 2 calculated by comparison of related proton signals

of fragments of the uncomplexed molecular thread and of rotaxane 2 (δ9c-δ2 and δ14-δ2), and of the uncomplexed ring 1 and 2.

The strong upfield shift of the protons of station C

clearly indicates that ring 1 preferentially encircles this re-

cognition site. This behavior is surprising because the CHT

ox

station (E_1/2= 0.5 V^[5]) is a much stronger electron donor

ox

than xylene (E_1/2= 1.3 V^[12]). Indeed, it has recently been

found with other rotaxanes that competition between dialk-

oxybenzene and xylene is decided in favor of the station

derived from hydroquinone.^[13]

In order to gain insight into the interaction between the

xylene station and the tetracationic ring, we studied the

pseudorotaxane formed in a 1:1 mixture (3×10^–2m) of

compounds 14 and 1. The results depicted in Scheme 7 con-

firmed the strong upfield shift of the xylene station.

The CIS values observed with rotaxane 2 and the pseu-

dorotaxane in Scheme 7 are very similar, indicating the rela-

Scheme 7. CIS values of the protons of the pseudorotaxane 1/14

calculated by comparison of the uncomplexed and complexed com-

ponents.

Scheme 8. CIS values of some protons of rotaxane 15 calculated by comparison of related protons of molecular thread 41 (for the

tropylium ion region) and of 14 (for the region of station C).

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tively strong interaction of the xylene station with the tetra- the position of the ring within the rotaxane is not changed

cationic ring. This finding emphasizes that not only the by traversal from 2 to 15, and this pair of rotaxanes is there-

electrostatic, π-stacking, and CT-interaction forces control fore useless for any switching process.

recognition, but that the hydrogen bonds formed between

the oxygen atoms of the oxyethylene chains and the acidic sen, with an oxidation potential also considerably lower

protons of ring 1 play an important role in it as well.^[14]

than that of the A–CHT–B station, but avoiding the

The rotaxane was electrochemically oxidized, providing neighboring of this station by two oxyethylene chains. We

the violet tropylium rotaxane 15 (Scheme 8). decided to incorporate an anisole station bearing an alkyl

For this reason, a photo inactive station had to be cho-

The CIS values of the protons of station C given in chain on one side instead of the oxyethylene chain. For this

Scheme 8 are identical to those in Scheme 6. Accordingly, purpose, the eastern half of the molecular thread had to

Scheme 9. Synthesis of the eastern half of the molecular thread of rotaxane 22.

Scheme 10. Synthesis of rotaxane 22.

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A Photoswitchable Rotaxane with an Unfolded Molecular Thread

be newly designed (see Scheme 9). The rotaxane synthesis

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The CIS values calculated by comparison of the NMR

following the reaction sequence to 2 (Scheme 10) provides spectra of compound 22 and those of compounds 20 and

compound 22 in 27% yield.

9c are given in Scheme 11.

Assignment of the proton resonances observed for 22 in

The expected preferred occupation of the CHT station

acetonitrile solution to the different aromatic groups is dif- can be determined based on CIS values. In addition, how-

ficult because, due to dynamic processes, not all proton res- ever, station C interacts with the ring component by a fast

onances appear at room temperature. However, at 343 K, shuttling process of the ring between the two stations or an

the most important proton resonances appear and can be interaction of C alongside the outer bipyridinium units of

attributed to the two stations involved, with the help of two- the ring due to folding of the thread. The differences in

dimensional methods such as determination of H–H-, C–H- shielding effects found for protons 7 and 8 and 17 and 18,

and NOE-cross peaks. Assignment of the strongly upfield- respectively (see Scheme 10), are most likely related to fold-

shifted resonances of aromatic protons to the substituents ing of the glycol chain between the two stations, thus bring-

A and B is possible based on C–H-COSY cross peaks be- ing the two stations within the vicinity of the tetracationic

1

cause, unlike the H signals, the ¹³C resonances are only ring.^[5]This interpretation is supported by the observation

marginally shifted due to interaction with ring 1. The as- of additional sets of signals (with portion of 40%) for pro-

signments were further confirmed by NOE effects (ROESY tons 17–19 and aromatic protons of C. These protons are

spectra). The extent of participation of station C in the in- shifted strongly upfield, indicating a strong interaction with

teraction of the molecular thread with 1 can be deduced ring 1. Because the integrity of compound 22 is guaranteed

from the resonances of the protons at positions 18 and 19 by mass spectra and elemental analysis, only isomers and

(Scheme 10). These protons are shifted upfield together conformers are possible as origins of the additional signal

with the protons of C, provided that station C is occupied sets. However, isomers of the cycloheptatriene could not be

by the tetracationic ring. The resonances of 18- and 19-H detected. Instead, a second set of CHT-protons was ob-

are easy to identify, because these signals are separated served, less upfield-shifted than that of the main conformer.

from other proton resonances.

Further, isomers of the CHT fragment cannot explain the

Scheme 11. CIS values obtained for rotaxane 22.

Scheme 12. Proton resonances of the two conformers of rotaxane 22 (δ, [D₆]acetone solutions).

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S. Schmidt-Schäffer, L. Grubert, U. W. Grummt, K. Buck, W. Abraham

We expected that the driving forces leading to the inter-

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additional sets of signals in the region of the proton reso-

nances of C. Therefore, additional co-conformers with ring action of station C with the ring could be weakened by

1 residing on station C are most likely present. The proton shortening of the oxyethylene chain between the phenol

resonances of two co-conformers are depicted in oxygen and the bulky stopper group. The trityl stopper

Scheme 12.

should additionally hinder any interaction between the oxy-

Surprisingly, the exchange between these conformers is gen atoms of the chain with the acidic protons of 1 by in-

slow, on the time scale of NMR spectroscopy, even at 65 °C. corporation of methyl groups in the phenol fragment bear-

The temperature-dependent spectra measured between 5 °C ing the trityl group. For this purpose, the eastern half of

and 65 °C (see Supporting Information) reveal a downfield- the molecular thread was newly designed. The sequence of

shift of the protons of station C with increasing temperature synthesis is analogous to that for the molecular thread of

and an upfield-shift of the protons of phenyl group A; how- rotaxane 22 (see Scheme 14).

ever, the ratio of the signals remains constant. Obviously,

The western half of the molecular thread incorporating

the forces driving the interaction between ring 1 and the the CHT station was modified in relation to the stopper

anisole station are not weak enough to yield exclusive occu- fragment. Compound 33c (Scheme 15) was used for the

pation of the diaryl cycloheptatriene station. Again, the synthesis of rotaxane 34 (Scheme 16). Compound 33c, with

electron donor capacity of the station is not the only prop- the trityl-dimethylphenol fragment, has more steric require-

erty governing interaction with the tetracationic ring.

ments than the adamantoyl group present in the western

The oxidation of rotaxane 22 provides the tropylium rot- half of thread 36 (see Scheme 17). However, it was found

axane 23, consisting of only one conformer. As expected, (see below) that the stopper fragment on this side of the

the calculated CIS-values confirmed that ring 1 resides on molecular thread does not affect the co-conformation of the

station C (see Scheme 13). However, because in rotaxane 22 rotaxanes. Indeed, it was found that modification of the

only 60% of the desired co-conformer exists with ring 1 linker at station C was decisive. Both rotaxane 34 and rot-

residing on the CHT station, studies of rotaxane pair 22/23 axane 37 exhibit exclusive occupation of the CHT station.

were not continued.

Additionally, there are no hints of a folded structure of the

Scheme 13. CIS values obtained for the tropylium rotaxane 23 by comparison of compound 41, molecular thread 20, uncomplexed ring

1, and rotaxane 23.

Scheme 14. Synthesis of the eastern half of the molecular thread of rotaxane 34.

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molecular thread resulting in an interaction of station C COSY and ROESY (see Supporting Information). Further-

alongside the bipyridinium units of ring 1. The CIS values more, marginal shifts of 18-H- and 19-H-proton resonances

of the protons both of the CHT ring and the aromatic sub- are a strong indication that interaction of station C with 1

stituents A, B, and C given in Scheme 18 reveal the desired fails.

residence of ring 1 on the CHT station with a clear prefer-

NOE effects observed in the ROESY spectra of rotaxane

ence for the A-substituent.

37 are additionally marked by arrows in Scheme 18. Resi-

Assignment of the signals was performed by two-dimen- dence of ring 1 on the CHT station is indicated by contacts

sional NMR spectroscopy, such as C–H-COSY, H–H- between both the ß-protons (in relation to N) of the bipyri-

Scheme 15. Synthesis of the western half of the molecular thread of rotaxane 34.

Scheme 16. Synthesis of rotaxane 34.

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Scheme 17. Synthesis of rotaxane 37.

Scheme 18. CIS values of proton resonances of rotaxanes 34 and 37 obtained by comparison of the proton resonances of uncomplexed

molecular threads and compound 2 with related proton resonances measured in the rotaxanes. Arrows mark NOEs between protons

observed by ROESY spectra.

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A Photoswitchable Rotaxane with an Unfolded Molecular Thread

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Scheme 19. Electrochemical oxidation of rotaxanes 34 and 37 and molecular thread 38.

Scheme 20. CIS values calculated for rotaxane 40. Arrows mark NOEs between protons observed by ROESY spectra.

dinium unit and the benzylic protons of 1 (see Supporting ring 1 and the methyl groups of the stopper fragment (see

Information).

Scheme 20).

Again, the corresponding tropylium rotaxanes 39 and 40

were obtained by electrochemical oxidation of compounds

34 and 37. The molecular thread 38 was also oxidized in

order to compare the proton resonances of rotaxane 37

with those of compound 41 (Scheme 19).

Switching Cycle

Introduction of the leaving group into the cycloheptatri-

Strong upfield shifts of the proton resonances of station ene ring is very easy. Both the tropylium rotaxanes 39 and

C (for compound 40, see Scheme 20) confirm the change of 40 and compound 41 have only to be dissolved in methanol.

location of 1 in the rotaxane, for example in traversal from The long-wavelength absorption band at 550 nm disappears

37 to 40 (Scheme 19). Thus, the proton resonances of 18-H in solutions with concentrations up to 3×10^–5m (see Fig-

and 19-H, separate from other signals, indicate where the ure 1, a). For solutions of higher concentration, addition of

ring resides. Further, occupation of station C is confirmed a base such as NaHCO₃to an acetonitrile solution contain-

by ROESY-cross peaks between the α- and ß-protons of ing 1 m methanol is necessary.

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Figure 1. a) UV/Vis absorption spectra of rotaxane 43 (2.5×10^–5m) and molecular thread 44 (3×10^–5m) in acetonitrile solution containing

methanol (1 m). b) Partial UV/Vis-absorption spectra of rotaxane 43 (5×10^–4m) and molecular thread 44 (5×10^–4m) in acetonitrile

solution containing methanol (1 m).

Several isomers of the newly-formed 7-methoxycyclohep- is bathochromically shifted by about 1800 cm^–1compared

tatriene derivatives are possible. In the NMR spectra, at with 44. Only rotaxane 43 exhibits a weak absorption band

least three isomers are visible. However, the appearance of around 550 nm (see Figure 1, b), which is assigned to the

an absorption band around 370 nm (see Figure 1, a) corre- charge-transfer absorption band of the rotaxane.

sponds to the formation of the two main isomers a and b

Unfortunately, assignment of all the proton signals of the

aryl groups is not possible. However, the occupation of the

which are thermodynamically favored (Scheme 21).^[5]

There are two important differences between the absorp- methoxy-substituted CHT station can be determined from

tion spectra of rotaxane 43 and the corresponding thread two findings: first, the resonances of 18-H and 19-H are not

44. The shoulder at the long-wavelength site of compound upfield-shifted but are equal to those of molecular thread

43, which is due to the diarylcycloheptatriene chromophore, 41 (Scheme 22, see also Supporting Information). Second,

Scheme 21. Reaction of the tropylium rotaxanes with methanol and the most probable isomers.

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A Photoswitchable Rotaxane with an Unfolded Molecular Thread

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Scheme 22. Some proton resonances of rotaxane 43 and thread 44. Arrows mark NOEs between protons observed by ROESY spectra.

the long-wavelength absorption bands of rotaxanes 42 and the other hand, the ionic state of compound 44 has a longer

43 are bathochromically shifted compared with the absorp- lifetime of 7 s; the positively charged ring in 42 and 43 may

tion band of molecular thread 44 due to the polar environ- accelerate the nucleophilic attack of the methoxide ion on

ment induced by tetracationic ring 1^[5](see Scheme 22 and the tropylium ion.

Figure 1, a).

Quantum yields of photoheterolysis were not deter-

mined. However, it is obvious that the quantum efficiency

of the photoreaction of molecular thread 44 is about one

order of magnitude greater than that of the rotaxanes by

comparing the recorded signal intensity observed with

equal excitation conditions (compare parts a and b in Fig-

ure 2). This is due to the higher rate of non-radiative deacti-

vation of the excited state of the rotaxanes resulting from

the existence of a low-lying charge transfer state within the

rotaxanes. The quantum yields of the photoheterolysis reac-

tion of model compounds such as shown in Scheme 1 were

determined to be in the range of 0.1.^[9]

On the other hand, competing photoreactions such as

the sigmatropic hydrogen shift observed in molecular

thread 44 are quenched in the rotaxanes, allowing more

switching cycles of the rotaxanes compared with the thread.

The irradiation of the model compound and the molecular

thread 44 with 10 laser flashes reduces the intensity of the

transient optical absorption due to the related tropylium

ions by a factor of about 2. A similar result was obtained by

stationary irradiation of diluted solutions of the molecular

thread with the unfiltered light of a high pressure mercury

lamp. In this case only the absorption band of the diaryl

Photoheterolysis of Rotaxanes 42, 43 and Molecular

Thread 44

These three compounds undergo a photoreaction in

methanol solution by excitation at a wavelength between

330 and 370 nm, resulting in the formation of the corre-

sponding tropylium methoxides, as monitored by the ap-

pearance of intermediates at the absorption band around

570 nm (see Figure 2). Because the co-conformation of the

tropylium rotaxanes consists of occupation of station C by

ring 1, movement of the ring from the CHT station to C is

initiated by the photoreaction (see Scheme 23).

The lifetime of the rotaxanes in their “tropylium state”

is limited by the thermal nucleophilic attack of the solvent

on the tropylium in a pseudo-first-order reaction ion-as-

sisted by the methoxide base. In the absence of a base, the

reaction of methanol with the tropylium rotaxanes occurs

within minutes. For rotaxanes 42 and 43, the lifetime of the

ionic state is 3 s. The reaction of the solvent with the tropyl-

ium ion is not hindered by the cationic ring because the

latter resides on station C far from the tropylium ring. On

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Figure 2. a) Transient absorption spectra observed during flash photolysis of molecular thread 44. b) Transient absorption spectra ob-

served during flash photolysis of rotaxane 43.

irradiation using equal excitation conditions as mentioned

above did not reduce the transient intensity and the inten-

sity of the cycloheptatriene chromophore, respectively, by

more than 5%. Accordingly, transient absorption spectra of

tropylium rotaxanes could be obtained point by point from

consecutively recorded kinetic traces. The same signal in-

tensity monitored at 570 nm was observed after the first

and the fifteenth flash.

Besides the light-driven formation of the tropylium rot-

axane 40 (with methoxide as anion) from 43, this reaction

can also be initiated by protons. Addition of trifluoroacetic

acid (TFA) to rotaxanes 42 and 43 in methanol-containing

solutions generates the tropylium rotaxane, and addition of

a base such as solid NaHCO₃yields back 42 or 43

(Scheme 23). The chemically-driven cycle can be followed

by UV/Vis spectroscopy (see Figure 3).

Scheme 23.

methoxycycloheptatriene chromophore can be monitored,

indicating the irreversible degradation of the photoactive

subunit (see Supporting Information). The observed spec-

tral changes support the assumption that a sigmatropic hy-

drogen shift is the competing photoreaction. However, in

Figure 3. UV/Vis absorption spectra of rotaxane 42: 1 – rotaxane

39 in acetonitrile solution; 2 – after addition of methanol (0.5 mL/

9.5 mL); 3 – after addition of NaHCO₃; 4 – addition of TFA; 5 –

the case of the rotaxanes, both the flash and the stationary addition of NaHCO₃; 6 – after addition of TFA.

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A Photoswitchable Rotaxane with an Unfolded Molecular Thread

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Syntheses

Conclusions

Rotaxane 2

We have demonstrated that the conformation of a rotax-

ane incorporating a photoactive electron donor station and

a second photo-inactive and weaker electron donor station

can be fine-tuned in such a way that only one station inter-

acts with the tetracationic cyclophane used as the wheel.

Both the electron-donor capability and the adjacent chain

units govern the strength of the interaction between the

electron-poor ring and the electron-rich photoinactive sta-

tion. In these rotaxanes, reversible switching between two

states is based on the photoheterolysis of methoxycyclohep-

tatrienes incorporated in the molecular thread. The thermal

reaction of the solvent methanol with the tropylium ions

assisted by the methoxide ion generated by photoheterolysis

a: 4-[Tris(p-tolyl)methyl]phenol (3): Tris(p-tolyl)methyl chloride^[16]

(10 g, 17.9 mmol) and phenol (10 g, 106 mmol) were heated at

80 °C for 16 h. The reaction mixture was recrystallized from etha-

nol after cooling down to room temperature, yielding 3 (9.4 g, 80%)

as a white solid, m.p. 213 °C. ¹H NMR (300 MHz, [D₆]acetone,

TMS): δ = 2.30 (s, 9 H, CH₃), 4.70 (s, 1 H, OH), 6.69 [d, 2 H,

J(H,H) = 8 Hz, phenyl], 7.01–7.07 (m, 12 H, phenyl), 7.07 [d,

J(H,H) = 8 Hz, 2 H, phenyl] ppm. C₂₈H₂₆O (378.52): calcd. C

88.95, H 6.92; found C 88.62, H 7.03.

b: 2-{2-[2-(4-Tris(p-tolyl)methylphenoxy)ethoxy]ethoxy}ethyl p-Tol-

uenesulfonate (5): NaOEt (0.55 g, 8.13 mmol) was added to triethy-

lene glycol bis(tosylate) 4 (16.0 g, 34.9 mmol) and 3 (2.20 g, 5.81

mmol) dissolved in acetonitrile (150 mL). The solution was re-

closes the cycle. The switching cycle can be repeated several fluxed for 6 h. After cooling and filtration, the solvent was removed

under vacuum. The crude product was dissolved in acetone, and

the excess of 4 was precipitated by adding diethyl ether. The filtrate

was evaporated and the residue was purified by CC (cyclohexane/

acetone, 10:1). 5 (3.19 g, 83%) was obtained as colorless oil. ¹H

NMR (300 MHz, [D₆]acetone, TMS): δ = 2.28 (s, 9 H, methyl),

2.42 (s, 3 H, tosyl), 3.53 (m, 2 H, oxyethylene), 3.58 (m, 2 H, oxye-

thylene), 3.66 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 3.76 [t, J(H,H)

= 5 Hz, 2 H, oxyethylene], 4.08 [t, J(H,H) = 5 Hz, 2 H, oxyethy-

lene], 4.15 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 6.82 [d, J(H,H) =

9 Hz, 2 H, phenyl], 7.00–7.08 (m, 12 H, phenyl), 7.08 [d, J(H,H) =

9 Hz, 2 H, phenyl], 7.44 [d, J(H,H) = 8 Hz, 2 H, phenyl], 7.80 [d,

J(H,H) = 9 Hz, 2 H, phenyl] ppm. MS: [C₄₁H₄₄NaO₆S]⁺calcd.

687.2751; found 687.2764 [M + Na]. C₄₁H₄₄SO₆(664.86): calcd. C

74.07, H 6.67, S 4.82; found C 74.17, H 6.72, S 4.55.

times without fading the photoactive unit of the rotaxanes.

A switching cycle can also be obtained using acids and

bases. The actual state of the system can conveniently be

determined by UV/Vis-spectroscopic monitoring of the tro-

pylium absorption band around 550 nm. Due to the ex-

tended conformation of the rotaxanes, shuttle movements

of large amplitude are initiated by light and thermal energy.

Work is in progress to fix these types of switchable rotax-

anes onto surfaces.

Experimental Section

General Methods: MeCN was distilled over CaH₂. Silica gel 60

(0.040–0.063 mm) (Fluka) was used for column chromatography

(CC). Melting points (m.p.) were determined with a Boetius heating

microscope. NMR spectra were recorded on a Bruker DPX 300

(300 MHz), a Bruker Advance 400 (400 MHz) or a Bruker AMX

600 (600 MHz) spectrometer. UV/Vis spectra were recorded with a

Shimadzu UV- 2500 PC spectrometer. The flash photolysis appara-

tus used is of conventional design. Briefly, a cylindrical cell of

10 cm length and 10 mm diameter is positioned in the common

focal line of a double elliptical reflector with two flash-lamps. The

electrical energy of the flashes was about 900 J (20 µF capacitor,

6.7 kV) the flash duration amounts to 14 µs. Glass filters are in-

serted between the sample and the flash lamps. In the particular

cases, Schott UG2 (maximal transmission at 365 nm) and Schott

UG11 (maximal transmission at 330 nm) were used. A Xe high-

pressure arc lamp (100 W) serves as the measuring source. The

electrical output of the photomultiplier is recorded with the help

of a digital oscilloscope and transferred to a personal computer.

Data evaluation was performed by non-linear regression using the

ALAU program.^[15]Transient absorption spectra were obtained

point by point from consecutively recorded kinetic traces. Station-

ary absorption spectra of the solutions were recorded before and

after repeated flashing in order to detect irreversible degradation.

Steady state photolysis experiments were carried out with acetoni-

trile solutions by using a 500-W high-pressure mercury lamp. The

solutions were irradiated in 1-cm quartz cuvettes. Thermal switch-

ing between tropylium rotaxanes and methoxycycloheptatrienyl ro-

taxanes was done by alternate addition of solid NaHCO₃and ace-

tonitrile solution of trifluoroacetic acid (TFA). Rapid scan (1 to

c: 7-[4-(2-{2-[2-(4-Tris(p-tolyl)methylphenoxy)ethoxy]ethoxy}-

ethoxy)phenyl]cyclohepta-1,3,5-triene (7): 7-(4-Hydroxyphenyl)-

1,3,5-cycloheptatriene (6)^[17]was synthesized according to a modi-

fied procedure: phenol (5.50 g, 58.5 mmol) and 7-methoxy-1,3,5-

cycloheptatriene (4,0 g, 32.7 mmol) were mixed. The mixture was

immediately cooled to –30 °C. The temperature was held at –30 °C

for 72 h. The excess phenol was removed by washing with warm

water (200 mL, 50 °C). The residue was digested with water (200

mL, 90 °C, ten times). Compound 6 crystallized from the collected

aqueous solutions as white crystals (2.89 g, 48%), m.p. 84–85 °C,

ref.^[17]61.5–62.5 °C.

Compounds 6 (0.79 g (4.26 mmol), 5 (2.70 g, 4.06 mmol), and

NaOEt (0.333 g, 4.90 mmol) in acetonitrile (150 mL) were stirred

at room temperature for 15 min and heated to reflux for 5 h. After

cooling, the solution was filtered and the solvents were evaporated.

Purification of the crude product by CC (cyclohexane/acetone,

10:1) afforded 6 (2.30 g, 84%) as an oil. ¹H NMR (300 MHz, [D₆]-

acetone, TMS): δ = 2.28 (s, 9 H, methyl), 2.59 [t, J(H,H) = 5 Hz,

2 H, CHT, 7-H], 3.68 (s, 4 H, oxyethylene), 3.82 (m, 4 H, oxyethy-

lene), 4.09 (m, 2 H, oxyethylene), 4.12 (m, 2 H, oxyethylene), 5.35

(m, 2 H, CHT, 1-H, 6-H), 6.22 (m, 2 H, CHT, 2-H, 5-H), 6.73 [t,

J(H,H) = 3 Hz, 2 H, CHT, 3-H, 4-H], 6.82 [d, J(H,H) = 9 Hz, 2

H, phenyl], 6.94 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.01–7.09 (m, 14

H, phenyl), 7.27 [d, J(H,H) = 9 Hz, 2 H, phenyl] ppm. MS:

[C₄₇H₄₈Na O₄]⁺calcd. 699.35; found 699.27 [M + Na]. C₄₇H₄₈O₄

(676.90): calcd. C 83.40, H 7.15; found C 83.59, H 6.93.

d: [4-(2-{2-[2-(4-Tris(p-tolyl)methylphenoxy)ethoxy]ethoxy}ethoxy)-

phenyl]tropylium Perchlorate (8): Compound 7 (2.20 g, 3.25 mmol)

50 V/s) cyclic voltammetry was performed using a PG 285 IEV in dichloromethane (50 mL) was treated with trityl perchlorate

potentiostat (HEKA Elektronik). ESI mass spectrometry was car-

ried out with a Finnigan LTQ equipment (Thermo Electron).

(1.46 g, 3.90 mmol). After stirring for 18 h, the precipitate was fil-

tered off and methyl-tert-butyl ether (MTBE, 400 mL) was added

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391

S. Schmidt-Schäffer, L. Grubert, U. W. Grummt, K. Buck, W. Abraham

FULL PAPER

to the filtrate. After 1 d the red oily precipitate was separated. The

phenyl), 7.27 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.49 [d, J(H,H) = 9

Hz, 2 H, phenyl] ppm. MS: [C₅₃H₅₃NNaO₄]⁺calcd. 790.3867;

found 790.3855 [M + Na]⁺. C₅₃H₅₃NO₄(767.99): calcd. C 82.89,

H 6.69, N 1.82; found C 82.89, H 7.11, N 1.93.

oil was washed with MTBE and dried under vacuum affording 8 as

1

a yellow foam (2.40 g, 95%), m.p. 80–82 °C. H NMR (300 MHz,

CDCl₃): δ = 2.26 (s, 9 H, methyl), 3.74 (s, 4 H, oxyethylene), 3.80–

3.89 (m, 4 H, oxyethylene), 4.02–4.07 (m, 2 H, oxyethylene), 4.10–

4.14 (m, 2 H, oxyethylene), 6.68 [d, J(H,H) = 9 Hz, 2 H, phenyl],

6.95 [d, J(H,H) = 9 Hz, 2 H, phenyl] 6.97–7.10 (m, 14 H, phenyl),

7.82 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.97–7.10 (m, 14 H, phenyl),

8.76–8.73 (m, 2 H, tropylium), 8.77–8.85 (m, 2 H, tropylium), 9.04

[d, J(H,H) = 10 Hz, 2 H, tropylium] ppm. MS: [C₄₇H₄₇O₄]⁺calcd.

675.3469; found 675.3494 (M – ClO₄).

2,6-Dimethyl-4-tritylphenol (10): Triphenylmethyl chloride (22 g,

78.9 mmol) and 2,6-dimethylphenol (40 g, 327 mmol) were heated

at 170 °C for 2 h. After cooling to room temperature, the reaction

mixture was recrystallized from ethanol, yielding 10 as a white solid

1

(22.1 g, 77%), m.p. 164 °C. H NMR (300 MHz, CDCl₃): δ = 2.13

(s, 6 H, methyl), 4.51 (s, 1 H, OH), 6.79 (s, 2 H, phenyl), 7.13–7.27

(m, 15 H, phenyl) ppm. C₂₇H₂₄O (364.49): calcd.C 88.97, H 6.65;

found C 88.63, H 6.96.

e) 4-{3-[4-(2-{2-[2-(4-Tris(p-tolyl)methylphenoxy)ethoxy]ethoxy}-

ethoxy)phenyl]cyclohepta-2,4,6-trienyl}phenylamine (9a) and 4-{4-[4-

(2-{2-[2-(4-Tris(p-tolyl)methylphenoxy)ethoxy]ethoxy}ethoxy-

phenyl]cyclohepta-2,4,6-trienylphenylamine (9b): Aniline (1.20 g,

12.9 mmol) in acetonitrile (5 mL) was added to 8 (2.00 g, 2.57

mmol) dissolved in acetonitrile (25 mL). An oily precipitate was

immediately formed. After 20 min the solution was separated from

the oil and evaporated under reduced pressure. The crude product

was purified by CC (toluene/ethyl acetate, 12:1) affording 9a and

9b (975 mg, 49%). The isomers were separated by repeating CC.

2-(2-{4-[2-(2-Tosylethoxy)ethoxymethyl]benzyloxy}ethoxy)ethyl Tol-

uene-4-sulfonate (11): 2-(2-{4-[2-(2-Hydroxyethoxy)ethoxymethyl]-

benzyloxy}ethoxy)ethanol^[18](27.0 g, 85.9 mmol) and p-toluenesul-

fonyl chloride (33.6 g, 176 mmol) in dichloromethane (400 mL)

were treated with solid NaOH at 0 °C for 1 h. After stirring for

20 h at room temperature, the precipitate was filtered off. The sol-

vent was removed under reduced pressure and the remaining prod-

uct was purified by CC (cyclohexane/acetone, 4:1) affording 11 as

white solid (41.7 g, 76%), m.p. 50 °C. ¹H NMR (300 MHz, [D₆]-

9a: Yield 390 mg (20 %), m.p. 72–74 °C. ¹H NMR (300 MHz, [D₆]- acetone, TMS): δ = 2.43 (s, 6 H, methyl), 3.56 (s, 8 H, oxyethylene),

acetone, TMS): δ = 2.26 (s, 9 H, methyl), 2.54 [t, J(H,H) = 6 Hz, 3.68 [t, J(H,H) = 5 Hz, 4 H, oxyethylene], 4.17 [t, J(H,H) = 5 Hz,

1 H, CHT, 1-H], 3.65 (s, 4 H, oxyethylene), 3.75–3.81 (m, 4 H, 4 H, oxyethylene], 4.50 (s, 4 H, H-10),. 7.31 (s, 4 H, phenyl), 7.45

oxyethylene), 4.03–4.11 (m, 4 H, oxyethylene), 4.55 (br. s, 2 H, [d, J(H,H) = 8 Hz, 4 H, phenyl], 7.80 [d, J(H,H) = 8 Hz, 4 H,

NH₂), 5.35 (m, 1 H, CHT, 7-H), 5.37 [d, J(H,H) = 6 Hz, 1 H, phenyl] ppm. C₃₀H₃₈S₂O₁₀(622.75): calcd. C 57.86, H 6.15; S

CHT, 2-H], 6.22 (m, 1 H, CHT, 6-H), 6.70 [d, J(H,H) = 9 Hz, 2 10.30; found C 57.67, H 6.19, S 10.23.

H, phenyl], 6.79 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.84 (m, 1 H,

2-[2-(4-{2-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]ethoxy-

CHT, 5-H), 6.88 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.92 [d, J(H,H)

methyl}benzyloxy)ethoxy]ethyl Toluene-4-sulfonate (12): Compound

= 6 Hz, 1 H, CHT, 4-H], 7.01–7.07 (m, 12 H, phenyl), 7.06 [d,

11 (49.2 g, 79 mmol) in acetonitrile solution (300 mL) was added

J(H,H) = 9 Hz, 2 H, phenyl], 7.11 [d, J(H,H) = 9 Hz, 2 H, phenyl],

to 10 (6.00 g, 15.8 mmol) and NaOEt (1.53 g, 22.5 mmol) dissolved

7.27 [d, J(H,H) = 9 Hz, 2 H, phenyl] ppm. MS: [C₅₃H₅₄NO₄]⁺

in acetonitrile (100 mL). The reaction mixture was heated at reflux

calcd. 768.4047; found 768.4063 [M + H]⁺. C₅₃H₅₃NO₄(767.99):

for 4 h. After cooling and filtration, the solvent was removed under

calcd. C 82.89, H 6.96, N 1.82; found C 82.56, H 6.90, N 1.64.

reduced pressure. The remaining residue was purified by CC (cyclo-

1

9b: 585 mg (19%), m.p. 70–72 °C. ¹H NMR (300 MHz, [D₆]ace-

hexane/acetone, 8:1) yielding an oil (6.05 g, 76%). H NMR (300

tone, TMS): δ = 2.28 (s, 9 H, methyl), 2.67 [t J(H,H) = 5 Hz, 1 H, MHz, [D₆]acetone, TMS): δ = 2.17 (s, 6 H, methyl), 2.42 (s, 3 H,

CHT, 1-H], 2.84 (s, 2 H, NH₂), 3.69 (s, 4 H, oxyethylene), 3.78– methyl), 3.54 (m, 2 H, oxyethylene), 3.59 (m, 2 H, oxyethylene),

3.85 (m, 4 H, oxyethylene), 4.11 [t, J(H,H) = 5 Hz, 2 H, oxyethy-

lene], 4.16 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 5.43 (m, 1 H, CHT,

7-H), 5.23 (m, 1 H, CHT, 2-H), 6.28 (m, 1 H, CHT, 6-H), 6.34 [d,

3.66 (m, 4 H, oxyethylene), 3.69 (m, 2 H, oxyethylene), 3.82 [t,

J(H,H) = 5 Hz, 2 H, oxyethylene], 3.96 [t, J(H,H) = 5 Hz, 2 H,

oxyethylene], 4.16 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 4.49 (s, 2

J(H,H) = 9 Hz, 1 H, CHT, 3-H], 6.70 [d, J(H,H) = 9 Hz, 2 H, H, benzyl), 4.55 (s, 2 H, benzyl), 6.86 (s, 2 H, phenyl), 7.15–7.35

phenyl], 6.83 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.97 [d, J(H,H) = 8

Hz, 2 H, phenyl], 7.02–7.06 (m, 12 H, phenyl), 7.04 (CHT, 5-H),

7.07 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.10 [d, J(H,H) = 8 Hz, 2

H, phenyl], 7.46 [d, J(H,H) = 9 Hz, 2 H, phenyl] ppm. MS:

[C₅₃H₅₄NO₄]⁺calcd. 768.4047; found 768.4044 [M + H]⁺.

C₅₃H₅₃NO₄(767.99): calcd. C 82.89, H 6.96, N 1.82; found C

82.52, H 7.10, N 1.80.

(m, 15 H, phenyl), 7.30 (s, 2 H, phenyl), 7.32 (s, 3 H, phenyl), 7.44

[d, J(H,H) = 8 Hz, 2 H, phenyl], 7.80 [d, J(H,H) = 8 Hz, 2 H,

phenyl] ppm. C₅₀H₅₄SO₈(815.02): calcd. C 73.68, H 6.68, S 3.93;

found C 73.57, H 6.52, S 3.84.

4-{2-[2-(4-{2-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]ethoxy-

methyl}benzyloxy)ethoxy]ethoxy}but-2-yn-1-ol (13): 1,4-Butyndiol

(1.90 g, 22.1 mmol) and NaOEt (0.30 g, 4.42 mmol) were dissolved

4-{4-[4-(2-{2-[2-(4-Tris(p-tolylmethyl)phenoxy)ethoxy]- in DMSO (30 mL), and then slightly concentrated under vacuum

ethoxy}ethoxy)phenyl]cyclohepta-1,3,6-trienyl}phenylamine (9c):

Compound 9b (0.22 g, 0.286 mmol) in toluene (30 mL) was heated

at reflux for 30 h. After removal of the solvent, the residue was

purified by CC (toluene/ethyl acetate, 12:1), and a greenish-yellow

(15 mbar, 50 °C). Compound 12 (3.00 g, 3.68 mmol) in DMSO (20

mL) was added, and the solution was warmed to 90 °C. The solvent

was removed under reduced pressure, and the remaining residue

was distributed between water (200 mL) and dichloromethane (200

mL). The aqueous layer was extracted with dichloromethane

(3×100 mL). The combined organic phases were dried (Na₂SO₄)

and evaporated, yielding a crude oil that was purified by CC (cyclo-

hexane/acetone, 4:1) to give 13 (1.75 g, 65%). ¹H NMR (300 MHz,

[D₆]acetone, TMS): δ = 2.17 (s, 6 H, methyl), 3.58–3.67 (m, 10 H,

1

solid (0.165 g, 75%) resulted, m.p. 77–78 °C. H NMR (300 MHz,

[D₆]acetone, TMS): δ = 2.27 (s, 9 H, methyl). 2.77 [d, J(H,H) = 8

Hz, 2 H, CHT, 5-H], 3.67 (s, 4 H, oxyethylene), 3.78–3.84 (m, 4 H,

oxyethylene), 4.09 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 4.14 [t,

J(H,H) = 5 Hz, 2 H, oxyethylene], 5.53–5.62 (m, 1 H, CHT, 6-H),

6.38 [d, J(H,H) = 9 Hz, 1 H, CHT, 7-H], 6.51 [d, J(H,H) = 6 Hz, oxyethylene), 3.69–3.74 (m, 2 H, oxyethylene), 3.77–3.81 (m, 2 H,

1 H, CHT, 3-H], 6.70 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.82 [d,

J(H,H) = 9 Hz, 2 H, phenyl], 6.92 [d, J(H,H) = 9 Hz, 2 H, phenyl],

oxyethylene), 3.93–3.98 (m, 2 H, oxyethylene), 4.18 [t, J(H,H) = 2

Hz, 2 H, propargyl], 4.19- 4.23 (m, 2 H, propargyl), 4.52 (s, 2 H,

6.95 [d, J(H,H) = 6 Hz, 1 H, CHT, 2-H], 7.00–7.10 (m, 14 H, benzyl), 4.55 (s, 2 H, benzyl), 6.86 (s, 2 H, phenyl), 7.16–7.31 (m,

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A Photoswitchable Rotaxane with an Unfolded Molecular Thread

FULL PAPER

15 H, phenyl), 7.33 (s, 4 H, phenyl) ppm. C₄₇H₅₂O₇(728.37): calcd.

C 77.44, H 7.19; found C 77.06, H 7.38.

gyloxy), 3.92 (m, 2 H, propargyloxy), 4.00 (m, 2 H, oxyethylene),

4.00–4.03 (m, 6 H, oxyethylene), 4.04 (m, 2 H, 1-H), 4.23 [t, J(H,H)

= 5 Hz, 2 H, 6-H], 5.67 (m, 8 H, 1), 6.76 (br. d, 2 H, phenyl), 6.79

[d, J(H,H) = 9 Hz, 2 H, phenyl, A], 6.87 (s, 2 H, phenyl), 7.01–

7.10 (m, 14 H, phenyl), 7.16–7.27 (m, 17 H, phenyl), 7.81 (s, 8 H,

1), 7.82 (m, 2 H, phenyl, B), 7.84 [d, J(H,H) = 9 Hz, 2 H, phenyl,

A], 7.92 [d, J(H,H) = 7 Hz, 8 H, 1], 8.39 (m, 1 H, Tr, 6-H), 8.54

(m, 1 H, Tr, 5-H), 8.67 [d, J(H,H) = 12 Hz, 1 H, Tr, 3-H], 8.69 [d,

J(H,H) = 12 Hz, 1 H, Tr, 7-H], 8.78 [d, J(H,H) = 12 Hz, 1 H, Tr

2-H], 8.87 [d, J(H,H) = 7 Hz, 8 H, 1] ppm. ¹³C NMR (100 MHz,

CD₃CN, TMS): 164.5, 163.5, 162.0, 157.6 (phenyl), 154.2 (phenyl),

153.9, 149.0, 148.5, 148.0 (phenyl), 147.3, 146.7, 146.1, 145.5 (1),

145.4 (C–R1), 145.3, 143.5, 138.0 (1), 136.3 (phenyl), 133.5 (phenyl,

B), 132.7 (phenyl), 132.7, 132.2 (phenyl), 132.2, 131.6 (1), 131.6

(phenyl), 131.5 (phenyl, A), 131.4 (phenyl), 130.6 (phenyl), 129.1

(phenyl), 128.5 (Tr, 5-C), 127.9 (1), 127.7 (phenyl, C), 127.5, 126.8

(phenyl), 117.0 (phenyl, B), 115.1 (phenyl, A), 114.2 (phenyl), 83.0,

80.0, 72.5 (17-C, 18-C), 72.4 (benzyl), 71.4, 71.3, 71.3, 71.2, 71.1,

71.0, 71.0, 70.2, 70.0, 69.0, 68.2 (oxyethylene), 65.5 (1), 65.3 (tet-

raphenylmethyl), 64.1 (tetraphenylmethyl), 58.6 (8-C), 33.1 (7-C),

20.8 (methyl), 16.9 (methyl) ppm. C₁₃₆H₁₃₄F₃₀N₅O₁₀P₅(2723.47):

calcd. C 59.98, H 4.96, N 2.57; found C 60.38, H 5.41, N 2.48. UV/

Vis (MeCN): λ_max(ε) = 258 (63900), 400 (9400), 533.5 nm (34500).

2-{2-[2-(4-{2-[2-(4-Bromobut-2-ynyloxy)ethoxy]ethoxy-

methyl}benzyloxy)ethoxy]ethoxy}-1,3-dimethyl-5-tritylbenzol (14):

Compound 13 (0.40 g, 0.549 mmol) and 2,6-di-tert-butyl-4-methyl-

pyridine (0.10 g, 1.37 mmol) were dissolved in dry dichloromethane

(50 mL). The solution was cooled to –30 °C. PBr₃(0.30 g, 1.11

mmol) and 2,6-di-tert-butyl-4-methylpyridine (0.20 g, 2.74 mmol)

in dichloromethane (10 mL) were added. The solution was kept at

–30 °C for 1 h, followed by addition of DMF (2 mL). After warm-

ing to room temperature and stirring for 2 h, water (200 mL) was

added. The organic layer was separated, and the solvent was re-

moved. The crude product was purified by CC (cyclohexane/ace-

1

tone, 6:1) to give an oil (0.242 g, 56%). H NMR (300 MHz, [D₆]-

acetone, TMS): δ = 2.17 (s, 6 H, methyl), 3.61 (s, 8 H, oxyethylene),

3.62–3.67 (m, 2 H, oxyethylene), 3.69–3.73 (m, 2 H, oxyethylene),

3.76–3.81 (m, 2 H, oxyethylene), 3.93–3.98 (m, 2 H, oxyethylene),

4.15 (m, 2 H, propargyl), 4.22–4.25 (m, 2 H, propargyl), 4.52 (s, 2

H, benzyl), 4.55 (s, 2 H, benzyl), 6.86 (s, 2 H, phenyl), 7.15–7.30

(m, 15 H, phenyl), 7.33 (s, 4 H, phenyl) ppm. C₄₇H₅₁BrO₆(791.81):

calcd. C 71.29, H 6.49, Br 10.09; found C 70.78, H 6.35, Br 10.22.

Rotaxane 2

Compounds 9c (0.19 g, 0.247 mmol), 1 (0.27 g, 0.247 mmol) and

2,6-di-tert-butyl-4-methylpyridine (0.06 g, 0.297 mmol) were dis-

solved in DMF (1.9 mL). After 45 min, 14 (0.196 g, 0.247 mmol)

was added. The solution was stirred at room temperature for 2 d.

Dichloromethane (8 mL) was added in order to precipitate 1. Cy-

clohexane (50 mL) was added to the red filtrate. The filtrate was

concentrated under reduced pressure at 30 °C. The resulting pre-

cipitate was purified by CC (methanol/nitromethane/2 m aqueous

NH₄Cl, 4:4:1). The violet fraction was concentrated and the rotax-

ane precipitated. The precipitate was dissolved in a mixture of ace-

tone (20 mL) and water (100 mL). NH₄PF₆(0.50 g) was added in

order to precipitate 2. The precipitate was washed with water and

Rotaxane 22

3-[4-(2-{2-[2-(4-[Tris(p-tolyl)methyl]phenoxy)ethoxy]ethoxy)phenyl]-

propane-1-ol (17): Compounds 3 (3.40 g, 5.11 mmol), 16 (0.94 g,

6.18 mmol) and NaOEt (0.42 g, 6.17 mmol) were dissolved in ace-

tonitrile (150 mL). The solution was heated to reflux for 6 h, fil-

tered, and evaporated to give the crude product that was purified

by CC (cyclohexane/acetone, 4:1) to yield a colourless oil (3.20 g,

1

97%). H NMR (300 MHz, [D₆]acetone, TMS): δ = 1.76 (m, 2 H,

propane), 2.28 (s, 9 H, methyl), 2.60 [t, J(H,H) = 7 Hz, 2 H, ben-

zyl], 2.87 (br. s, 1 H, OH), 3.54 (m, 2 H, oxypropyl), 3.67 (s, 4 H,

oxyethylene), 3.79 (m, 2 H, oxyethylene), 3.81 (m, 2 H, oxyethy-

lene), 4.07 (m, 2 H, oxyethylene), 4.09 (m, 2 H, oxyethylene), 6.82

[d, J(H,H) = 9 Hz, 2 H, phenyl], 6.83 [d, J(H,H) = 9 Hz, 2 H,

phenyl],7.09 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.07 [d, J(H,H) = 9

Hz, 2 H, phenyl], 7.06 (s, 12 H, phenyl) ppm. MS (ESI): m/z =

667.5 [M + Na⁺]⁺calcd. 667.83. C₄₃H₄₈O₅(667.83): calcd. C 80.09,

H 7.50; found C 80.10, H 7.56.

1

dried, affording pure 2 (0.243 g, 38%), m.p. 150–157 °C. H NMR

(300 MHz, [D₆]acetone, TMS): δ = 2.12 (s, 6 H, methyl), 2.28 (s, 9

H, methyl), 2.76 [d, J(H,H) = 8 Hz, 1 H, CHT, 7-H], 3.69 (s, 4 H,

3-H, 4-H), 3.73–4.17 (m, 32 H, oxyethylene), 4.41 (br. s, 2 H,

phenyl, C), 4.45 (br. s, 2 H, phenyl, C), 5.16 (br. s, 1 H, NH), 5.61

(m, 1 H, CHT, 6-H), 6.02–6.10 (m, 8 H, cyclophane 1), 6.27 [d,

J(H,H) = 9 Hz, 1 H, CHT, 5-H], 6.44 (br. s, 2 H, phenyl, A), 6.47

[d, J(H,H) = 7 Hz, 1 H, CHT, 2-H], 6.85 (1 H, CHT, 3-H), 6.85

[d, J(H,H) = 9 Hz, 2 H, phenyl], 6.85 (s, 2 H, phenyl), 7.02–7.09

(m, 16 H, phenyl, A), 7.14–7.30 (m, 15 H, phenyl), 7.43 [d, J(H,H)

= 9 Hz, 2 H, phenyl, B], 8.12 (s, 8 H, 1), 8.32 [d, J(H,H) = 6 Hz,

8 H, 1], 9.39 [d, J(H,H) = 6 Hz, 8 H, 1] ppm. C₁₃₆H₁₃₅N₅O₁₀P₄F₂₄

(2579.51): calcd. C 63.33, H 5.28, N 2.72; found C 62.74, H 5,23,

N 2.64. UV/Vis: λ_max(ε) = 254 (59300), 352 (25900), 555 nm (380).

1-Bromo-3-[4-(2-[2-(2-[4-tris(p-tolyl)methyl]phenoxy)ethoxy]-

ethoxy)phenyl]propane (18): Compound 17 (1.10 g, 1.71 mmol) and

2,6-di-tert-butyl-4-methylpyridine (0.41 g, 2.00 mmol) dissolved in

dichloromethane (30 mL) were cooled to –30 °C. PBr₃(0.90 g, 3.3

mmol) in dichloromethane (10 mL) was added. After stirring for

2 h at –30 °C, DMF (2 mL) was added. The solution was kept at

room temperature for 18 h. After that period the solution was

poured into ice-water (100 mL). The organic phase was separated,

washed with water, and dried (Na₂SO₄). The solvent was removed,

and the residue was purified by CC (cyclohexane/acetone, 10:1),

affording a colourless oil (0.71 g, 59%). ¹H NMR (300 MHz, [D₆]-

acetone, TMS): δ = 2.10 (m, 2 H, propane), 2.29 (s, 9 H,

methyl),2.69 [t, J(H,H) = 8 Hz, 2 H, benzyl], 3.44 (m, 2 H, oxypro-

pyl), 3.67 (s, 4 H, oxyethylene), 3.80 (m, 2 H, oxyethylene), 3.81

(m, 2 H, oxyethylene), 4.08 (m, 2 H, oxyethylene), 4.10 (m, 2 H,

oxyethylene), 6.83 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.86 [d, J(H,H)

= 9 Hz, 2 H, phenyl], 7.06 (s, 12 H, phenyl), 7.07 [d, J(H,H) = 9 Hz,

2 H, phenyl], 7.12 [d, J(H,H) = 9 Hz, 2 H, H-19] ppm. C₄₃H₄₇BrO₄

(723.73): calcd. C 72.97, H 6.69, Br 11.29; found C 72.81, H 6.90,

Br 11.50.

Rotaxane 15

Rotaxane 2 (0.100 g, 0.039 mmol) dissolved in 0.1 m Et₄NPF₆/

MeCN solution (50 mL) was oxidized by a controlled potential

electrolysis (E_A= 0.9–1.3 V [SCE], HEKA PG285) at a Pt-electrode

in the anode region of an H cell until a charge output of 0.078 F

had been consumed. After evaporating the solvent and washing

with water, the remaining solid was purified by column chromatog-

raphy (silica gel, acetonitrile (400 mL), ethyl acetate (200 mL), cy-

clohexane (100 mL) containing ammonium hexafluorophosphate

(7 g)). The violet fraction was evaporated and the remaining solid

was washed with water yielding 6 (0.10 g, 70%) as a violet solid,

m.p. 152–161 °C. ¹H NMR (400 MHz, CD₃CN, TMS): δ = 2.08 (s,

6 H, methyl), 2.26 (s, 9 H, methyl), 3.61 (s, 2 H, benzyl, C), 3.66

(benzyl, C), 3.65–3.93 (m, 20 H, oxyethylene), 3.91 (m, 2 H, propar-

2-{2-[2-(2-{3-[4-(2-{2-[2-(4-tris(p-tolyl)phenoxy)ethoxy]-

ethoxy}ethoxy)phenyl]propoxy}ethoxy)ethoxy]ethoxy}ethyl Toluene-

4-sulfonate (19)

Eur. J. Org. Chem. 2006, 378–398

www.eurjoc.org

393

S. Schmidt-Schäffer, L. Grubert, U. W. Grummt, K. Buck, W. Abraham

FULL PAPER

a: A solution of tetraethylene glycol (1.94 g, 10.0 mmol) and Na-

phenyl], 6.84 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.06 (s, 12 H,

OEt (0.38 g, 5.58 mmol) in DMSO (8 mL) was stirred for 15 min phenyl), 7.07 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.10 [d, J(H,H) = 9

at 70 °C. Compound 37 (0.50 g, 0.71 mmol) was added, and the

solution was stirred at 95 °C for 5 h. The solution was concentrated

to 10 mL under reduced pressure, and the remaining mixture was

distributed between dichloromethane (250 mL) and water (200 mL)

containing NaCl (2 m). The aqueous phase was washed with dichlo-

romethane (3×200 mL).The collected organic phases were dried

and concentrated. The remaining residue was purified by CC (cy-

clohexane/acetone, 3:1) to give 2-{2-[2-(2-{3-[4-(2-{2-[2-(4-tris(p-

tolyl)methylphenoxy)ethoxy]ethoxy}ethoxy)phenyl]-

propoxy}ethoxy)ethoxy]ethoxy}ethanol as a colourless oil (0.31 g,

Hz, 2 H, phenyl] ppm. MS (ESI): m/z = 911.6 [M + Na]⁺, calcd.

C₅₅H₆₈NaO₁₀, 912.11. C₅₅H₆₈O₁₀(889.15): calcd. C 74.30, H 7.71;

found C 73.77, H 7.72.

1-Bromo-4-(2-{2-[2-(2-{3-[4-(2-{2-[2-(4-tris(p-tolyl)methylphenoxy)-

ethoxy]ethoxy}phenyl]propoxy}ethoxy)ethoxy]ethoxy}ethoxy)but-2-

yne (21): Compound 20 (0.68 g, 0.77 mmol) dissolved in dry dichlo-

romethane (30 mL) was cooled to –18 °C. PBr₃(2.0 g, 7.40 mmol)

and 2,6-di-tert-butyl-4-methylpyridine (0.16 g, 0.78 mmol) dis-

solved in dichloromethane (10 mL) were added. The reaction mix-

ture was kept at –30 °C for 30 min, then DMF (2 mL) was added.

The mixture was stirred at room temperature for 3 h, and water

(200 mL) was added. The organic phase was separated, dried, and

evaporated to give the crude product that was purified by CC (cy-

clohexane/acetone (6:1) to yield an oil (0.52 g, 71%). ¹H NMR (300

MHz, [D₆]acetone, TMS): δ = 1.79 (m, 2 H, propyl), 2.23 (s, 9 H,

methyl), 2.60 [t, J(H,H) = 8 Hz, 2 H, benzyl], 3.41 (m, 2 H, pro-

poxy), 3.52 (m, 2 H, oxyethylene), 3.58–3.60 (m, 14 H, oxyethy-

lene), 3.67 (s, 4 H, oxyethylene), 3.79 (m, 2 H, oxyethylene), 3.81

(m, 2 H, oxyethylene), 4.08 (m, 2 H, oxyethylene), 4.10 (m, 2 H,

oxyethylene), 4.16 (s, 2 H, bromomethyl), 4.23 (s, 2 H, oxyethylene),

6.83 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.84 [d, J(H,H) = 9 Hz, 2

H, phenyl], 7.06 (s, 12 H, phenyl), 7.07 [d, J(H,H) = 9 Hz, 2 H,

phenyl], 7.10 [d, J(H,H) = 9 Hz, 2 H, phenyl] ppm. MS (ESI):

m/z = 975.3845 [M + Na⁺]⁺; calcd. C₅₅H₆₇BrNaO₉, 975.3846.

1

53%). H NMR (300 MHz, [D₆]acetone, TMS): δ = 1.79 (m, 2 H,

propyl), 2.29 (s, 9 H, methyl), 2.60 [t, J(H,H) = 8 Hz, 2 H, benzyl],

2.83 (t, 1 H, OH), 3.41 (m, 2 H, propoxy), 3.51–3.52 (m, 4 H,

oxyethylene), 3.58–3.60 (m, 12 H, oxyethylene), 3.67 (s, 4 H, oxye-

thylene), 3.79 (m, 2 H, oxyethylene), 3.81 (m, 2 H, oxyethylene),

4.08 (m, 2 H, oxyethylene), 4.10 (m, 2 H, oxyethylene), 6.83 [d,

J(H,H) = 9 Hz, 2 H, phenyl], 6.84 [d, J(H,H) = 9 Hz, 2 H, phenyl],

7.06 (s, 12 H, phenyl), 7.07 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.10

[d, J(H,H) = 9 Hz, 2 H, phenyl] ppm. MS (ESI): m/z = 843.6 [M

+ Na⁺]⁺, calcd. 844.04. C₅₁H₆₄O₉(821.05): calcd. C 74.61, H 7.86;

found C 74.84, H 7.88.

b: NaOH (in powder form, 1.50 g, 3.75 mmol) was added to the

alcohol described above (1.39 g, 1.71 mmol) and p-toluenesulfonyl

chloride (1.90 g, 9.97 mmol) dissolved in dichloromethane (30 mL).

After stirring for 1 h at room temperature, the solution was heated

to reflux for 1 h. The solution was poured into ice-water (100 mL)

and extracted with dichloromethane (3 × 50 mL). The organic

phases were evaporated and the remaining residue was purified by

CC (cyclohexane/acetone, 5:1) affording 19 as an oil (1.37 g, 82%).

¹H NMR (300 MHz, [D₆]acetone, TMS): δ = 1.79 (m, 2 H, propyl),

2.29 (s, 9 H, methyl), 2.45 (s, 3 H, methyl), 2.60 [t, J(H,H) = 8 Hz,

2 H, benzyl], 3.40 (m, 2 H, propoxy), 3.51 (m, 6 H, oxyethylene),

3.56–3.57 (m, 6 H, oxyethylene), 3.65 (m, 2 H, oxyethylene), 3.67

(s, 4 H, oxyethylene), 3.79 (m, 2 H, oxyethylene), 3.81 (m, 2 H,

oxyethylene), 4.10 (m, 2 H, oxyethylene), 4.08 (m, 2 H), 4.15 (m, 2

H, oxyethylene), 6.83 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.84 [d,

J(H,H) = 9 Hz, 2 H, phenyl], 7.06 (s, 12 H, phenyl), 7.07 [d, J(H,H)

= 9 Hz, 2 H, phenyl], 7.10 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.47

[d, J(H,H) = 8 Hz, 2 H, phenyl], 7.81 [d, J(H,H) = 8 Hz, 2 H,

phenyl] ppm. MS (ESI): m/z = 997.6 [M + Na⁺]⁺, calcd.

C₅₈H₇₀NaO₁₁S 998.22. C₅₈H₇₀SO₁₁(975.23): calcd. C 71.43, H

7.24, S 3.29; found C 71.17, H 7.35, S 3.07.

Compound 21 (0.16 g, 0.163 mmol) in DMF solution (0.3 mL) was

added to the green solution of 9c (0.76 g, 0.10 mmol), 1 (0.12 g,

0.110 mmol) and 2,6-di-tert-butyl-4-methylpyridine (0.050 g, 0.24

mmol)) in DMF (1.5 mL). The reaction mixture was kept at 0 °C

for 14 d, followed by addition of dichloromethane (10 mL). Precipi-

tated 1 was filtered from the solution and the filtrate was poured

into MTBE (100 mL). The oily precipitate was separated and puri-

fied by CC (methanol/2 m/NH₄Cl(aq)/nitromethane (4:1:4). The

green fraction was evaporated and the rotaxane was dissolved in

water and a small amount of acetone. The rotaxane was then pre-

cipitated by addition of several equivalents of NH₄PF₆(aq). The

resulting green solid was washed with water several times and dried

(0.072 g, 27%), m.p. 133–140 °C. ¹H NMR (300 MHz, [D₆]acetone,

TMS): δ = 1.69 (m, 2 H, 18-H), 2.23 [t, J(H,H) = 8 Hz, 2 H, 19-

H], 2.27 (s, 18 H, methyl), 2.76 [d, 7 Hz, 2 H, CHT, 7-H], 3.41–

3.89 (m, 36 H, oxyethylene), 3.93 (s, 2 H, 7-H), 4.00–4.15 (m, 6 H,

oxyethylene), 4.26 (s, 2 H, 8-H), 5.63–5.78 (m, 12 H, 1, CHT, 1-H,

2-H, phenyl, C), 6.16 [d, J(H,H) = 6 Hz, 1 H, CHT, 4-H], 6.19 (br.

s, 2 H, phenyl, A), 6.31 [d, J(H,H) = 9 Hz, 2 H, phenyl, B], 6.34

[d, J(H,H) = 6 Hz, 1 H, CHT, 5-H], 6.64 [d, J = 9 Hz, 2 H], 6.70

[d, J(H,H) = 9 Hz, 2 H], 6.75 [d, J(H,H) = 9 Hz, 2 H], 7.01 [d,

J(H,H) = 9 Hz, 2 H, phenyl, B], 7.02–7.07 (m, 28 H, phenyl), 7.79–

7.82 (m, 8 H, 1), 7.86 (s, 8 H, 1), 8.85–8.89 (m, 8 H, 1) ppm.

MS: m/z = 1224.5315, 768.0323; calcd. C₁₄₄H₁₅₁N₅O₁₃P₂F₁₂(M –

2PF₆^–)²⁺, 1224.5313, C₁₄₄H₁₅₁N₅O₁₃PF₆(M – 3PF₆)^3–768.0328.

C₁₄₄H₁₅₁N₅O₁₃P₄F₂₄(2739.72): calcd. C 63.13, H 5.56, N 2.56;

found C 63.00, H 5.98, N 2.49.

4-(2-{2-[2-(2-{3-[4-(2-{2-[2-(4-Tris(p-tolyl)methylphenoxy)-

ethoxy]ethoxy}phenyl]propoxy}ethoxy)ethoxy]ethoxy}ethoxy)but-2-

yne-1-ol (20): NaOEt (0.11 g, 1.54 mmol) and but-2-yne-1,4-diol

(3.0 g, 35 mmol) in DMSO (20 mL) were heated to 70 °C for 1 h.

Compound 19 (1.05 g, 1.03 mmol) dissolved in DMSO (10 mL)

was added, and the mixture was heated to 90 °C for 1.5 h. The

solvent was removed at 95 °C (15 mbar). The residue was distrib-

uted between water (200 mL) and dichloromethane (200 mL), the

aqueous phase was washed with dichloromethane (3 ×100 mL),

and the combined organic phases were dried (Na₂SO₄). After re-

moval of the solvent, the residue was purified by CC (cyclohexane/

acetone, 4:1; 3:1; 2:1) to yield an oil (0.89 g, 93%). H NMR (300 m Et₄NPF₆MeCN solution (50 mL), was oxidized by a controlled

Rotaxane 23: Rotaxane 22 (0.063 g, 0.022 mmol), dissolved in 0.1

1

MHz, [D₆]acetone, TMS): δ = 1.79 (m, 2 H, propyl), 2.28 (s, 9 H,

methyl), 2.60 [t, J(H,H) = 8 Hz, 2 H, benzyl], 2.86 (br. s., 1 H,

OH), 3.41 (m, 2 H, propoxy), 3.52 (m, 2 H, oxyethylene), 3.58–3.59

(m, 14 H, oxyethylene), 3.67 (s, 4 H, oxyethylene), 3.79 (m, 2 H,

oxyethylene), 3.81 (m, 2 H, oxyethylene), 4.08 (m, 2 H, oxyethy-

lene), 4.10 (m, 2 H, oxyethylene), 4.17 (s, 2 H, OCH₂-but-2-yne),

potential electrolysis (E_A= 1.3 V [SCE], HEKA PG285) at a Pt-

electrode in the anode region of an H cell until a charge output of

4420 mC had been consumed. After evaporating the solution and

washing with water, the remaining solid was purified by column

chromatography [silica gel, acetonitrile (400 mL), ethyl acetate

(200 mL), cyclohexane (100 mL) containing ammonium hexafluo-

4.20 (s, 2 H, OCH₂-but-2-yne), 6.83 [d, J(H,H) = 9 Hz, 2 H, rophosphate (7 g)]. Rotaxane 23 (0.042 g, 67%) was obtained as a

394

www.eurjoc.org

Eur. J. Org. Chem. 2006, 378–398

A Photoswitchable Rotaxane with an Unfolded Molecular Thread

FULL PAPER

violet solid, m.p. 124–134 °C. ¹H NMR (400 MHz, CD₃CN, TMS):

δ = 1.54 (m, 2 H, 18-H), 1.82 (t, J(H,H) = 8 Hz, 2 H, 19-H), 2.26

(s, 9 H, methyl), 2.28 (s, 9 H, methyl), 3.30 (m, 2 H, oxyethylene),

3.99–4.04 (m, 4 H, oxyethylene), 4.12 (m, 2 H, 8-H), 4.21 (m, 2 H,

oxyethylene), 4.32 (br. d, 2 H, phenyl, C), 4.16 (m, 2 H, oxyethy-

lene), 4.22 [d, J(H,H) = 8 Hz, 2 H, phenyl, C], 5.58–5.72 (m, 8 H,

1), 6.27 [d, J(H,H) = 9 Hz, 2 H, phenyl, B], 6.67–6.77 (m, 4 H,

phenyl), 6.90 [d, J(H,H) = 9 Hz, 2 H, phenyl, A], 7.04 (s, 2 H,

phenyl), 7.13–7.33 (m, 30 H, phenyl), 7.53 [d, J(H,H) = 9 Hz, 2 H,

phenyl, B], 7.78 [d, J(H,H) = 9 Hz, 2 H, phenyl, A], 6.97 [d, J(H,H)

= 9 Hz, 2 H, phenyl, B], 7.01–7.09, (m, 30 H, phenyl), 7.77–7.82

(m, 16 H, 1), 7.89 [d, J(H,H) = 9 Hz, 2 H, Phenyl, A], 8.37 (m, 1

H, Tr, 6-H), 8.50 [d, J(H,H) = 10 Hz, 1 H, Tr, 5-H], 8.64 [d, J(H,H)

= 12 Hz, 1 H, Tr, 3-H], 8.72 [d, J(H,H) = 11 Hz, 1 H, Tr 7-H],

8.80 (m, 1 H, Tr, 2-H), 8.83 [d, J(H,H) = 6 Hz, 8 H, 1] ppm.

d: 2-(2-{2-[2-(3-{4-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]-

phenyl}propoxy)ethoxy]ethoxy}ethoxy)ethyl Toluene-4-sulfonate

(27)

a: Tetraethylene glycol (5 g, 26 mmol) and NaOEt (0.60 g, 8,82

mmol) dissolved in DMSO (70 mL) were heated to 70 °C for 15

min. Compound 26 (1.65 g, 7.7 mmol) in DMSO (15 mL) was

added. The mixture was heated to 90 °C for 90 min. The solvent

was removed under reduced pressure, and the residue was distrib-

uted between dichloromethane (250 mL) and an aqueous NaCl

solution (2 m, 200 mL). The organic layer was dried and concen-

trated. The residue was purified by CC (cyclohexane/acetone, 3:1)

affording 2-(2-{2-[2-(3-{4-[2-(2.6-Dimethyl-4-tritylphenoxy)ethoxy]

phenyl}propoxy)ethoxy]ethoxy}ethoxy)ethanol (1.33 g, 68%) as an

oil. ¹H NMR (300 MHz, [D₆]acetone, TMS): δ = 1.81 (m, 2 H,

methylene), 2.20 (s, 6 H, methyl), 2.62 [t, J(H,H) = 8 Hz, 2 H,

benzyl], 2.84 (br. s., 1H, OH), 3.39 (m, 2 H, oxymethylene), 3.43

(m, 2 H, hydroxymethylene), 3.52 (m, 2 H, oxyethylene), 3.58–3.59

(m, 5 H, oxyethylene), 4.17 (m, 2 H, oxyethylene), 4.30 (m, 2 H,

oxyethylene), 6.88 (s, 2 H, phenyl), 6.90 [d, J(H,H) = 9 Hz, 2 H,

phenyl], 7.15 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.17–7.32 (m, 15 H,

phenyl) ppm. C₄₆H₅₄O₇(718.92): calcd. C 76.85, H 7.57; found C

76.69, H 7.69.

1-[2-(4-{3-[2-(2-{2[2-(4-Bromobut-2-ynyloxy)ethoxy]ethoxy}ethoxy)-

ethoxy]propyl}phenoxy)ethoxy]-2,6-dimethyl-4-tritylbenzene (29)

a: 2-(2,6-Dimethyl-4-tritylphenoxy)ethyl Toluene-4-sulfonate (24):

Compound 10 (10 g, 27.4 mmol) and ethylene glycol bis(tosyl-

ate)^[19](38 g, 102 mmol), dissolved in acetonitrile (300 mL) were

treated with NaOEt (2.42 g, 35.6 mmol). The mixture was heated

to reflux for 16 h. After cooling, the solution was concentrated. The

precipitate was filtered, and the excess \tosylate was precipitated by

adding diethyl ether and hexane. The filtrate was concentrated and

the remaining residue was purified by CC (cyclohexane/acetone,

10:1). A white solid resulted by slow evaporation of the hexane/

diethyl ether solution, 13.3 g (86%), m.p. 133 °C. ¹H NMR (300

MHz, CDCl₃, TMS): δ = 2.09 (s, 6 H, methyl), 2.44 (s, 3 H, methyl),

3.98 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 4.33 [t, J(H,H) = 5 Hz,

2 H, oxyethylene], 6.79 (s, 2 H, phenyl), 7.14–7.25 (m, 15 H,

phenyl), 7.34 [d, J(H,H) = 8 Hz, 2 H, phenyl], 7.83 [d, J(H,H) = 8

Hz, 2 H, phenyl] ppm. C₃₆H₃₄SO₄(562.73): calcd. C 76.84, H 6.09,

S 5.70; found C 76.59, H 6.18, S 5.69.

b: 2-(2-{2-[2-(3-{4-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]-

phenyl}propoxy)ethoxy]ethoxy}ethoxy)ethanol (1.10 g, 1.53 mmol)

and tosyl chloride (1.50 g, 7.87 mmol) dissolved in dichlorometh-

ane (30 mL) were treated with NaOH (1.50 g, 37.5 mmol). The

solution was kept at room temperature for 1 h, then heated to re-

flux for 30 min. The resulting solution was distributed between ice-

water (100 mL) and dichloromethane (50 mL). The aqueous solu-

tion was extracted several times with dichloromethane. The com-

bined organic layers were dried, and the solvents were evaporated.

The remaining oil was purified by CC (cyclohexane/acetone, 5:1)

1

to yield 27 (1.27 g, 95%) as an oil. H NMR (300 MHz, [D₆]ace-

tone, TMS): δ = 1.80 (m, 2 H, methylene), 2.20 (s, 6 H, methyl),

2.45 (s, 3 H, methyl), 2.62 [t, J(H,H) = 8 Hz, 2 H, benzyl], 3.42

(m, 2 H, oxymethylene), 3.52 (m, 6 H, oxyethylene), 3.57 (m, 6 H,

oxyethylene), 3.65 (m, 2 H, oxyethylene), 4.15 (m, 2 H, oxyethy-

lene), 4.17 (m, 2 H, oxyethylene), 4.30 (m, 2 H, oxyethylene), 6.88

(s, 2 H, phenyl), 6.90 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.14 [d,

J(H,H) = 9 Hz, 2 H, phenyl], 7.17–7.31 (m, 15 H, phenyl) ppm.

C₅₃H₆₀SO₉(873.10): calcd. C 72.91, H 6.93, S 3.67; found C 72.28,

H 6.82, S 3.46.

b: 3-{4-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]phenyl}propan-1-ol

(25): Compounds 24 (2.5 g, 4.44 mmol), 16 (0.68 g, 4.44 mmol) and

NaOEt (0.36 g, 5.33 mmol) in acetonitrile were heated to reflux for

6 h. The solution was filtered and evaporated, and the residue was

purified by CC (cyclohexane/acetone, 4:1), affording 25 as viscous

oil (2.4 g, 99%). ¹H NMR (300 MHz, [D₆]acetone, TMS): δ = 1.78

(m, 2 H, methylene), 2.19 (s, 6 H, methyl), 2.63 [t, J(H,H) = 8 Hz,

2 H, benzyl], 2.84 (br. s, 1 H, OH), 3.54 (m, 2 H, oxymethylene),

4.16 (m, 2 H, oxyethylene), 4.29 (m, 2 H, oxyethylene), 6.88 (s, 2

H, phenyl), 6.89 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.14 [d, J(H,H)

= 9 Hz, 2 H, phenyl], 7.16–7.30 (m, 15 H, phenyl) ppm. C₃₈H₃₈O₃

(542.71): calcd. C 84.10, H 7.06; found C 84.29, H 7.35.

e: 4-[2-(2-{2-[2-(3-{4-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]-

phenyl}propoxy)ethoxy]ethoxy)ethoxy)ethoxy]but-2-yn-1-ol (28):

But-2-yne-1,4-diol (3 g, 35 mmol) and NaOEt (0.28 g, 2.1 mmol)

were dissolved in DMSO (100 mL).The solution was concentrated

to 2/3 of the volume under reduced pressure at 90 °C. Compound

27 (1.00 g, 1.15 mmol) in DMSO (20 mL) was added, and the solu-

tion was concentrated at 90 °C and 45 mbar for 45 min. Most of

the solvent was removed at 95 °C and 15 mbar. The remaining resi-

due was distributed between dichloromethane (200 mL) and water

(200 mL). The aqueous solution was extracted with dichlorometh-

ane (3 ×150 mL). The combined organic phases were dried and

concentrated. The remaining oil was purified several times by CC

c: 2-{2-[4-(3-Bromopropyl)phenoxy]ethoxy}-1,3-dimethyl-5-trityl-

benzene (26): Compound 25 (2.07 g, 3.81 mmol) and 2,6-di-tert-

butyl-4-methylpyridine (0.45 g, 2.2 mmol) were dissolved in dichlo-

romethane (30 mL) and cooled to –30 °C. PBr₃(2.70 g, 10 mmol)

was added, and the solution was kept at –30 °C for 2 h. After that

period, DMF (2 mL) was added and the solution was stirred at

room temperature for 18 h. The solution was poured into ice water

(100 mL). The organic layer was dried (Na₂SO₄) and the solvents

were evaporated. The residue was purified by CC (cyclohexane/

(cyclohexane/acetone, 4:1, 3:1, 2:1) affording colourless oil (0.86 g,

1

acetone, 10:1) affording a white solid (2.06 g, 87%), m.p. 139 °C. 96%). H NMR (300 MHz, [D₆]acetone, TMS): δ = 1.81 (m, 2 H,

¹H NMR (300 MHz, [D₆]acetone, TMS): δ = 2.12 (m, 2 H, methyl-

ene), 2.20 (s, 6 H, methyl), 2.71 [t, J(H,H) = 8 Hz, 2 H, benzyl],

3.43 (m, 2 H, hydroxymethyl), 4.16 (m, 2 H, oxyethylene), 4.29 (m,

2 H, oxyethylene), 6.86 (s, 2 H, phenyl), 6.90 [d, J(H,H) = 9 Hz, 2

H, phenyl], 7.14 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.16–7.30 (m, 15

H, phenyl) ppm. C₃₈H₃₇BrO₂(605.61): calcd. C 75.37, H 6.16, Br

13.19; found C 75.32, H 6.43, Br 13.48.

methylene), 2.20 (s, 6 H, methyl), 2.63 [t, J(H,H) = 8 Hz, 2 H,

benzyl], 3.43 (m, 2 H, oxymethylene), 3.53 (m, 2 H, oxyethylene),

3.56 (m, 2 H, oxyethylene), 3.58–3.60 (m, 12 H: oxyethylene), 4.17

(m, 4 H, oxyethylene), 4.18 (s, 2 H, oxyethylene), 4.30 (m, 2 H,

oxyethylene), 6.88 (s, 2 H, phenyl), 6.90 [d, J(H,H) = 9 Hz, 2 H,

phenyl], 7.14 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.17–7.32 (m, 15 H,

phenyl) ppm. MS (ESI): m/z = 809.4 [M + Na]⁺.

Eur. J. Org. Chem. 2006, 378–398

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395

S. Schmidt-Schäffer, L. Grubert, U. W. Grummt, K. Buck, W. Abraham

1-[2-(4-{3-[2-(2-{2[2-(4-Bromo-but-2-ynyloxy)ethoxy]ethoxy}- mmol) dissolved in dichloromethane (50 mL) was treated with trityl

FULL PAPER

ethoxy)ethoxy]propyl}phenoxy)ethoxy]-2,6-dimethyl-4-tritylbenzol

(29): Compound 28 (0.76 g, 0.97 mmol) and 2,6-di-tert-butyl-4-

methylpyridine (0.40 g, 1.95 mmol) were dissolved in dichlorometh-

ane (30 mL) and the solution was cooled to –18 °C. PBr₃(3.0 g, 270

mmol) and 2,6-di-tert-butyl-4-methylpyridine (0.20 g, 0.95 mmol)

dissolved in dry dichloromethane (10 mL) were added, and the

solution was kept at –30 °C for 15 min. After adding DMF (5 mL),

the solution was warmed to room temperature and stirred for 2 h.

Water (100 mL) was added to the reaction solution, the organic

phase was dried (Na₂SO₄), and the solvents evaporated. The re-

maining oil was purified by CC (cyclohexane/acetone, 6:1) afford-

perchlorate (2.44 g, 6.51 mmol). After stirring for 18 h, the red mix-

ture was filtered and. MTBE (400 mL) was added to the filtrate.

After 1 d the red oily precipitate was separated. The oil was washed

with MTBE and dried under vacuum affording 32 as a yellow foam

(2.64 g, 88%), m.p. 78–86 °C. ¹H NMR (300 MHz, CDCl₃): δ =

2.15 (s, 6 H, methyl), 3.78 (s, 4 H, oxyethylene), 3.82 [t, J(H,H) =

5 Hz, 2 H, oxyethylene], 3.91 [t, J(H,H) = 5 Hz, 2 H, oxyethylene],

3.95 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 4.21 [t, J(H,H) = 5 Hz,

2 H, oxyethylene], 6.80 (s, 2 H, phenyl), 7.06 [d, J(H,H) = 9 Hz, 2

H, phenyl], 7.12–7.25 (m, 15 H, phenyl), 7.89 [d, J(H,H) = 9 Hz,

2 H, phenyl], 8.71 (m, 2 H, tropylium), 8.81–8.91 (m, 2 H, tropyl-

ium), 9.11 [d, J(H,H) = 11 Hz, 2 H, tropylium] ppm. C₄₆H₄₅ClO₈

1

ing colourless oil (0.71 g, 86%). H NMR (300 MHz, [D₆]acetone,

TMS): δ = 1.81 (m, 2 H, methylene), 2.19 (s, 6 H, methyl), 2.62 [t, (761.30): calcd. C 72.57, H 5.96; found C 72.36, H 6.04.

J(H,H) = 8 Hz, 2 H, benzyl], 3.42 (m, 2 H, oxymethylene), 3.52

i: 4-{3-[4-(2-{2-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]ethoxy}-

ethoxy)phenyl]cyclohepta-2,4,6-trienyl}phenylamine (33a) and 4-{4-

[4-(2-{2-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]ethoxy}ethoxy)-

phenyl]cyclohepta-2,4,6-trienyl}phenylamine (33b): Aniline (3.47 g,

37.3 mmol) in acetonitrile (10 mL) was added to 32 (2.46 g, 3.23

mmol) dissolved in acetonitrile (10 mL). After 30 min, the solution

was evaporated under vacuum. The crude product was purified by

(m, 2 H, oxyethylene), 3.58–3.59 (m, 14 H, oxyethylene), 4.13 (m,

2 H, bromomethyl), 4.15 (m, 2 H, oxyethylene), 4.22 (s, 2 H, oxye-

thylene), 4.28 (m, 2 H, oxyethylene), 6.88 (s, 2 H, phenyl), 6.89 [d,

J(H,H) = 9 Hz, 2 H, phenyl], 7.13 [d, J(H,H) = 9 Hz, 2 H, phenyl],

7.16–7.29 (m, 15 H, phenyl) ppm. C₅₀H₅₇BrO₇(849.88): calcd. C

70.66, H 6.76, Br 9.40; found C 70.93, H 6.79, Br 9.72.

f: 2-{2-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]ethoxy}ethyl Tolu-

ene-4-sulfonate (30): NaOEt (0.80 g, 11.8 mmol) was added to trie-

thylene glycol bis(tosylate) 4 (30.0 g, 65.4 mmol) and 10 (3.00 g,

8.21 mmol) dissolved in acetonitrile (200 mL). The solution was

refluxed for 16 h. After cooling and filtration, the solvent was re-

moved under reduced pressure. The crude product was dissolved in

acetone, and excess 4 was precipitated by adding diethyl ether. The

filtrate was evaporated, and the remaining mixture was purified by

CC (cyclohexane/acetone, 10:1). Compound 30 (4.40 g, 82%) was

obtained as colourless oil. Slow evaporation of diethyl ether from

a solution of 30 in hexane/diethyl ether afforded white crystals, m.p.

CC (cyclohexane/acetone, 4:1). A second CC (toluene/ethyl acetate)

afforded 33a (0.47 g, 19%) and 33b (0.65 g, 27%). 33a: m.p. 79–

1

83 °C. H NMR (300 MHz, [D₆]acetone, TMS): δ = 2.16 (s, 6 H,

methyl), 2.65 [t, J(H,H) = 6 Hz, 1 H, CHT, 1-H], 3.69 (s, 4 H,

oxyethylene), 3.77 (m, 2 H, oxyethylene), 3.82 (m, 2 H, oxyethy-

lene), 3.94 (m, 2 H, oxyethylene), 4.13 (m, 2 H, oxyethylene), 5.37

(m, 1 H, CHT, 7-H), 5.38 [d, J(H,H) = 6 Hz, 1 H, CHT, 2-H], 6.29

(m, 1 H, CHT, 6-H), 6.72 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.85 (s,

2 H, phenyl), 6.85 (m, 1 H, CHT, 5-H), 6.90 [d, J(H,H) = 9 Hz, 2

H, phenyl], 6.94 [d, J(H,H) = 6 Hz, 1 H, CHT, 4-H], 7.10–7.27 (m,

15 H, phenyl), 7.29 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.37 [d, J(H,H)

= 9 Hz, 2 H, phenyl] ppm. MS: m/z = 754.3894 [M + H]⁺,

[C₅₂H₅₂NO₄]⁺, calcd. 754.3896. C₅₂H₅₁NO₄(753.97): calcd. C

82.84, H 6.82, N 1.86; found C 82.49, H 6.86, N 1.86.

1

75 °C. H NMR (300 MHz, [D₆]acetone, TMS): δ = 2.15 (s, 9 H,

methyl), 2.41 (s, 3 H, tosyl), 3.61 (m, 2 H, oxyethylene), 3.66 (m, 2

H, oxyethylene), 3.70 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 3.77 [t,

J(H,H) = 5 Hz, 2 H, oxyethylene], 3.92 [t, J(H,H) = 5 Hz, 2 H,

oxyethylene], 4.16 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 6.81 (s, 2

H, phenyl), 7.13–7.27 (m, 15 H, phenyl), 7.30 [d, J(H,H) = 8 Hz,

2 H, phenyl], 7.79 [d, J(H,H) = 8 Hz, 2 H, phenyl] ppm. C₄₀H₄₂SO₆

(650.82): calcd. (%): C 73.82, H 6.50, S 4.93; found C 73.87, H

6.73, S 5.00.

1

33b: M.p. 70–73 °C, H NMR (300 MHz, [D₆]acetone, TMS): δ =

2.17 (s, 6 H, methyl), 2.67 [t, J(H,H) = 6 Hz, 1 H, CHT, 1-H], 2.84

(s, 2 H, NH₂), 3.70 (s, 4 H, oxyethylene), 3.79 [t, J(H,H) = 5 Hz,

2 H, oxyethylene], 3.85 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 3.96

[t, J(H,H) = 5 Hz, 2 H, oxyethylene], 4.17 [t, J(H,H) = 5 Hz, 2 H,

oxyethylene], 5.44 (m, 1 H, CHT, 7-H), 5.53 (m, 1 H, CHT, 2-H),

g: 7-[4-(2-{2-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]- 6.29 (m, 1 H, CHT, 6-H), 6.34 [d, J(H,H) = 9 Hz, 1 H, CHT, 3-

ethoxy}ethoxy)phenyl]cyclohepta-1,3,5-triene (31): 7-(4-Hy-

droxyphenyl)-1,3,5-cycloheptatriene^[2](6), (1.40 g, 7.60 mmol), 30

(3.35 g, 5.15 mmol), and NaOEt (0.77 g, 11.00 mmol) were dis-

solved in acetonitrile (200 mL), and the solution was stirred at

room temperature for 15 min. The solution was heated to reflux

for 5 h. After cooling, the solution was filtered and the solvents

were evaporated. Purification of the crude product by CC (cyclo-

H], 6.70 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.86 [d, J(H,H) = 9 Hz,

2 H, phenyl], 6.97 [d, J(H,H) = 8 Hz, 2 H, phenyl], 7.05 [d, J(H,H)

= 6 Hz, 1 H, CHT, 5-H], 7.11 [d, J(H,H) = 9 Hz, 2 H, phenyl],

7.16–7.30 (m, 15 H, phenyl), 7.46 [d, J(H,H) = 9 Hz, 2 H, phenyl]

ppm. MS: m/z = 754.3896 [M + H]⁺, [C₅₂H₅₂NO₄]⁺, calcd.

754.3896. C₅₃H₅₃NO₄(754.27): calcd. C 82.84, H 6.82, N 1.86;

found C 82.85, H 6.81, N 1.86.

1

hexane/acetone, 6:1) afforded 31 (4.20 g, 94%) as an oil. H NMR

j: 4-{4-[4-(2-{2-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]ethoxy}-

ethoxy)phenyl]cyclohepta-1,3,6-trienyl}phenylamine (33c): Com-

pound 33b (0.24 g, 0.312 mmol) in toluene (20 mL) was heated to

reflux for 30 h. After the solvents were evaporated, the residue was

purified by CC (toluene/ethyl acetate, 12:1), and a greenish-yellow

(300 MHz, CDCl₃, TMS): δ = 2.17 (s, 9 H, methyl), 2.65 [t, J(H,H)

= 6 Hz, 2 H, CHT, 7-H], 3.77 (s, 4 H, oxyethylene), 3.82 [t, J(H,H)

= 5 Hz, 4 H, oxyethylene], 3.88 [t, J(H,H) = 5 Hz, 2 H, oxyethy-

lene], 3.96 [t, J(H,H) = 5 Hz, 2 H, oxyethylene], 4.14 [t, J(H,H) =

5 Hz, 2 H, oxyethylene], 5.38 (m, 2 H, CHT, 1-H, 6-H), 6.22 (m, 2

H, CHT, 2-H, 5-H), 6.73 [t, J(H,H) = 3 Hz, 2 H, CHT, 3-H, 4-H],

6.80 (s, 2 H, phenyl), 6.91 [d, J(H,H) = 9 Hz, 2 H, phenyl], 7.25

[d, J(H,H) = 9 Hz, 2 H, phenyl], 7.13–7.30 (m, 15 H, phenyl) ppm.

MS: m/z = 685.3287 [M + Na], [C₄₆H₄₆Na O₄]⁺, calcd. 685.3294.

C₄₆H₄₆O₄(662.84): calcd. C 83.35, H 7.00; found C 83.45, H 7.25.

1

solid (0.165 g, 70%) resulted, m.p. 69–71 °C. H NMR (300 MHz,

[D₆]acetone, TMS): δ = 2.17 (s, 6 H, methyl). 2.84 [d, J(H,H) = 6

Hz, 2 H, CHT, 5-H], 3.70 (s, 4 H, oxyethylene), 3.79 (m, 2 H,

oxyethylene), 3.84 (m, 2 H, oxyethylene), 3.95 (m, 2 H, oxyethy-

lene), 4.16 (m, 2 H, oxyethylene), 5.60 (m, 1 H, CHT, 6-H), 6.39

[d, J(H,H) = 9 Hz, 1 H, CHT, 7-H], 6.51 [d, J(H,H) = 7 Hz, 1 H,

CHT, 3-H], 6.70 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.86 (s, 2 H,

h: [4-(2-{2-[2-(2,6-Dimethyl-4-tritylphenoxy)ethoxy]ethoxy}ethoxy)-

phenyl]tropylium Perchlorate (32): Compound 31 (2.70 g, 4.07 phenyl), 6.93 [d, J(H,H) = 9 Hz, 2 H, phenyl], 6.98 [d, J(H,H) = 7

396 Eur. J. Org. Chem. 2006, 378–398

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A Photoswitchable Rotaxane with an Unfolded Molecular Thread

FULL PAPER

Hz, 1 H, CHT, 2-H], 7.17–7.30 (m, 17 H, phenyl), 7.50 [d, J(H,H)

H, methyl), 2.58 (m, 2 H, 19-H), 2.76 (dd, 2 H, CHT, 7-H), 3.40

= 9 Hz, 2 H, phenyl] ppm. MS: m/z = 776.3700 [M + Na]⁺, (m, 2 H, 17-H), 3.5 (m, 26 H, 1-H–5-H, 9-H–16-H), 4.0 (br. s, 2

[C₅₂H₅₁NNaO₄]⁺calcd., 776.3716. C₅₂H₅₁NO₄(753.97): calcd. C

82.84, H 6.82, N 1.86; found C 82.52, H 6.97, N 1.80.

H, 7-H), 4.2–4.3 (m, 8 H, 6-H, 8-H, 20-H, 21-H), 5.59 (m, 1 H,

CHT, 6-H), 6.40 [d, J(H,H) = 8 Hz, 1 H, CHT, 5-H], 6.51 [d,

J(H,H) = 6 Hz, 1 H, CHT, 2-H], 6.70 [d, J(H,H) = 9 Hz, 2 H,

phenyl, A], 6.9 (m, 6 H, phenyl, phenyl, B, phenyl,C), 7.0 [d,

J(H,H) = 6 Hz, 1 H, CHT, 3-H], 7.13 [d, J(H,H) = 9 Hz, 2 H,

phenyl, C], 7.3 (m, 17 H, phenyl, phenyl, C), 7.35 [d, J(H,H) = 9

Hz, 2 H, phenyl, A], 7.50 [d, J(H,H) = 9 Hz, 2 H, phenyl, B] ppm.

The NMR resonances were used to determine the CIS values of

the protons of 37.

Rotaxane 34: Compound 29 (0.230 g, 0.271 mmol) dissolved in

DMF (0.3 mL) was added to a solution of 33c (0.180 g, 0.239

mmol), 1 (0.342 g, 0.311 mmol) and 2,6-di-tert-butyl-4-methylpyri-

dine (0.100 g, 0.488 mmol) in DMF (2.8 mL). The reaction mixture

was stirred at 0 °C for 14 d, then dichloromethane (10 mL) was

added to the solution. Precipitated 1 was filtered off. The filtrate

was poured into cyclohexane (40 mL), and. the oily precipitate was

separated. Evaporation of the filtrate, and purification by CC (cy-

clohexane/acetone, 6:1), afforded the molecular thread 35 (0.07 g,

18%), m.p. 63–65 °C. ¹H NMR (300 MHz, CD₃CN, TMS): δ =

1.79 (m, 2 H, 18-H), 2.16 (s, 6 H, methyl), 2.18 (s, 6 H, methyl),

2.58 [t, J(H,H) = 8 Hz, 2 H, 19-H], 2.74 [d, J(H,H) = 7 Hz, 2 H,

CHT, 7-H], 3.40 [t, J(H,H) = 6 Hz, 2 H, 17-H], 3.52 (m, 2 H, 16-

H), 3.55–3.58 (m, 14 H, 9-H–15-H), 3.69 (s, 4 H, 3-H, 4-H), 3.78

(m, 2 H, 2-H), 3.83 (m, 2 H, 5-H), 3.93 (m, 2 H, 1-H), 4.01 (m, 2

H, 7-H), 4.13 (s, 2 H, 8-H), 4.14 (m, 2 H, 16-H), 4.15 (m, 2 H, 21-

H), 4.26 (m, 2 H, 20-H), 5.59 (m, 1 H, CHT, 6-H), 6.40 (m, 1 H,

CHT, 5-H), 6.51 [d, J(H,H) = 6 Hz, 1 H, CHT, 2-H], 6.75 [d,

J(H,H) = 9 Hz, 2 H, phenyl, A], 6.86 (s, 2 H, phenyl), 6.88 [d,

J(H,H) = 8Hz, 2 H, phenyl, C], 6.89 (s, 2 H, phenyl), 6.91 (br. s, 2

H, phenyl, B), 6.99 [d, J(H,H) = 6 Hz, 1 H, CHT, 3-H], 7.13 [d,

J(H,H) = 8 Hz, 2 H, phenyl, C], 7.15–7.30 (m, 30 H, phenyl), 7.35

[d, J(H,H) = 9 Hz, 2 H, phenyl, A], 7.48 [d, J(H,H) = 9 Hz, 2 H,

phenyl, B] ppm. MS: m/z = 1544.7764 [M + Na⁺]⁺,1522.7813 [M

+ H⁺]⁺; calcd. C₁₀₂H₁₀₇NNaO₁₁1544.7736, C₁₀₂H₁₀₈NO₁₁

1522.7917.

The precipitate, insoluble in MTBE, was treated with the solvent

mixture [acetonitrile (400 mL)/ethyl acetate (200 mL)/cyclohexane

(100 mL) containing NH₄PF₆(7 g)] that was used for the purifica-

tion of 37 by CC. The excess of 1 (insoluble in this solvent mixture)

was filtered (0.36 g) and the filtrate was used for CC. The evapora-

tion of the green fraction afforded a green solid (0.190 g, 21%),

which was washed with water and dried, m.p. 136–142 °C. ¹H

NMR (400 MHz, CD₃CN, TMS): δ = 1.7 (m, 8 H, adamantane),

1.7 (m, 2 H, 18-H), 1.9 (m, 7 H, adamantane), 2.09 (s, 6 H, methyl),

2.52 [t, J(H,H) = 8 Hz, 2 H, 18-H], 2.80 [d, J(H,H) = 7 Hz, 2 H,

CHT, 7-H], 3.4 (m, 8 H, oxyethylene), 3.4–3.6 (m, 6 H, oxyethy-

lene), 3.6 (m, 8 H, oxyethylene), 3.8 (m, 2 H, 5-H), 3.92 (br. s, 2

H, 7-H), 4.1 (m, 4 H, 5-H, oxyethylene), 4.1 (m, 4 H, 6-H, 21-H),

4.2 (m, 2 H, 20-H), 4.3 (br. d, 2 H, phenyl, A), 4.34 (s, 2 H, 8-H),

4.75 [d, J(H,H) = 9 Hz, 2 H, phenyl, A], 5.18 [d, J(H,H) = 10 Hz,

1 H, CHT, 5-H], 5.66 [d, J(H,H) = 7 Hz, 1 H, CHT, 3-H], 5.7 (1

H, CHT, 6-H), 5.8 (m, 9 H, 1, benzyl), 6.34 [d, J(H,H) = 7 Hz, 1

H, CHT, 2-H], 6.41 [br. d, J(H,H) = 8 Hz, 2 H, phenyl, B], 6.70

[br. d, J(H,H) = 8 Hz, 2 H, phenyl, C], 6.92 (s, 2 H, phenyl), 6.97

[br. d, J(H,H) = 8 Hz, 2 H, phenyl, C], 7.10 [br. d, J(H,H) = 8 Hz,

2 H, phenyl, B], 7.2–7.3 (m, 15 H, phenyl), 7.78 [d, J(H,H) = 7 Hz,

8 H, 1], 7.9 (m, 8 H, 1), 8.90 [d, J(H,H) = 7 Hz, 8 H, 1] ppm. UV/

Vis (MeCN): λ (ε) = 260 (43150), 360,5 (16930), 554 nm (764).

The oily precipitate, insoluble in hexane, was purified by CC (meth-

anol/nitromethane/water (4:4:1) containing NH₄Cl (2 m). The green

fraction was concentrated under reduced pressure, and the resulting

oil was dissolved in water/acetone. Rotaxane 34 was precipitated

by addition of excess saturated aqueous NH₄PF₆. The green solid

was filtered, washed with water, and dried under reduced pressure

(0.175 g, 28%), m.p. 135–143 °C. ¹H NMR (400 MHz, [D₆]acetone,

TMS): δ = 1.7 (m, 2 H, 18-H), 2.18 (s, 6 H, methyl), 2.22 (s, 6 H,

methyl), 2.6 [t, J(H,H) = 8Hz, 2 H, 19-H], 2.84 [d, J(H,H) = 7 Hz,

2 H, CHT, 7-H], 3.40–3.66 (m, 16 H, 10-H–17-H), 3.73 (m, 2 H,

6-H), 3.79–3.95 (m, 8 H, 2-H–5-H), 3.98 (s, 2 H, 7-H), 3.99 (m, 2

H, 1-H), 4.08 (m, 2 H, 6-H), 4.17 (m, 2 H, 20-H), 4.26 (m, 2 H,

21-H), 4.39 (s, 2 H, 8-H), 5.03 [d, J(H,H) = 8 Hz, 2 H, phenyl, A],

5.23 [d, J(H,H) = 8 Hz, 2 H, phenyl, A], 5.63 [d, J(H,H) = 9 Hz,

1 H, CHT, 5-H], 5.82 (m, 1 H, CHT, 6-H), 6.21–6.07 (m, 11 H, 1,

benzyl), 6.40 [d, J(H,H) = 7 Hz, 1 H, CHT, 3-H], 6.67 (br. d, 2 H,

phenyl, C), 6.87 (s, 2 H, phenyl), 6.90 (s, 2 H, phenyl), 6.90–6.92

(m, 4 H, phenyl, B; C), 7.16–7.34 (m, 30 H, phenyl), 8.19 (s, 8 H,

1), 8.30 [d, J(H,H) = 7 Hz, 2 H, 1], 9.45 [d, J(H,H) = 7 Hz, 8 H,

1] ppm.

C

₁₂₂H₁₃₁F₂₄N₅O₁₂P₄(2439.23): calcd. C 60.07, H 5.41, N 2.67;

found C 59.82, H 5.67, N 2.80.

Rotaxane 39: Rotaxane 34 (0.135 g, 0.052 mmol) dissolved in 0.1

m Et₄NPF₆MeCN solution (50 mL) was oxidized by a controlled

potential electrolysis (E_A= 0.9–1.2 V [SCE], HEKA PG285) at a

Pt-electrode in the anode region of an H cell until a charge output

of 9920 mC had been consumed. After evaporating and washing

with water, the remaining solid was purified by column chromatog-

raphy [silica gel, acetonitrile (400 mL), ethyl acetate (200 mL), cy-

clohexane (100 mL) containing ammonium hexafluorophosphate

(7 g)]. Rotaxane 39 (0.10 g, 70%) was obtained as a violet solid,

m.p. 160–167 °C. ¹H NMR (400 MHz, CD₃CN, 343 K, TMS): δ =

1.41 (m, 2 H, 18-H), 1.92 (m, 2 H, 19-H), 2.12 (s, 6 H, methyl),

2.38 (s, 6 H, methyl), 3.44–3.59 (m, 12 H, oxyethylene), 3.63–3.70

(m, 4 H, oxyethylene), 3.71 (s, 4 H, oxyethylene), 3.78 (m, 2 H,

oxyethylene), 3.83 (m, 2 H, oxyethylene), 3.92 (m, 2 H, oxyethy-

lene), 4.04 (m, 2 H, oxyethylene), 4.09 (s, 2 H, 7-H), 4.14 (s, 2 H,

8-H), 4.16 (m, 2 H, oxyethylene), 4.22 [d, J(H,H) = 8Hz, 2 H,

phenyl, C], 4.86 [d, J(H,H) = 8 Hz, 2 H, phenyl, C], 5.77 (s, 8 H,

1), 6.58 (br. d, 2 H, phenyl, B), 6.71 [d, J(H,H) = 9 Hz, 2 H, phenyl,

A], 6.85 (s, 2 H, phenyl), 7.04 (s, 2 H, phenyl), 7.13–7.33 (m, 30 H,

phenyl), 7.53 [d, J(H,H) = 9 Hz, 2 H, phenyl, B], 7.78 [d, J(H,H)

= 9 Hz, 2 H, phenyl, A], 7.85 (s, 8 H, 1), 7.92 [d, J(H,H) = 7 Hz,

8 H, 1], 8.43 (m, 1 H, Tr, 6-H), 8.46 (m, 1 H, Tr, 7-H), 8.60 [d,

J(H,H) = 12 Hz, 1 H, Tr, 2-H], 8.70 [d, J(H,H) = 12 Hz, 1 H, Tr,

5-H], 8.80 [d, J(H,H) = 12 Hz, 1 H, Tr 3-H], 8.93 [d, J(H,H) = 7

Hz, 8 H, 1] ppm.

Rotaxane 37: 2-[2-(2-{4-[4-(4-Aminophenyl)cyclohepta-1,3,5-tri-

enyl]phenoxy}ethoxy)ethoxy]ethyl adamantane-1-carboxylate^[5]

(36) (0.215 g, 0.377 mmol), 1 (0.621 g, 0.566 mmol) and 2,6-di-tert-

butyl-4-methylpyridine (0.077 g, 0.377 mmol) in DMF solution

(0.6 mL) were stirred for 30 min at room temperature. Compound

29 (0.320 g, 0.377 mmol) in DMF (0.6 mL) was added, and the

solution was stirred for 20 min at room temperature, then the reac-

tion mixture was kept at 0 °C for 16 d. The green solution was

evaporated, and the remaining residue was treated with MTBE

(50 mL). From the solution the molecular thread 38 was isolated

as an oily solid (0.110 g, 22 %). ¹H NMR (300 MHz, CD₃CN, Rotaxane 40: Rotaxane 37 (0.09 g) was oxidized as in the procedure

TMS): δ = 1.7 (m, 7 H, adamantane), 1.8 (m, 2 H, 18-H), 2.2 (s, 6 used for the synthesis of 39, providing a violet solid (0.05 g, 42%),

Eur. J. Org. Chem. 2006, 378–398

www.eurjoc.org

397

S. Schmidt-Schäffer, L. Grubert, U. W. Grummt, K. Buck, W. Abraham

FULL PAPER

1

m.p. 138–41 °C. H NMR (400 MHz, CD₃CN, TMS): δ = 1.4 (m,

rotaxane 34, UV/Vis spectra of rotaxanes 37, 40 and 43, UV spectra

monitored after irradiation of the molecular thread 44.

2 H, 18-H), 1.7 (m, 9 H, adamantane), 1.8 (m, 7 H, adamantane,

19-H), 2.4 (s, 6 H, methyl), 3.4–3.7 (m, 28 H, oxyethylene, phenyl,

C), 3.9 (m, 2 H, 5-H), 4.1 (m, 10 H, 6-H, 7,8-H, 20,21-H), 4.5 (br.

d, 2 H, phenyl, C), 5.75 (m, 8 H, 1), 6.58 (br. d, 2 H, phenyl, B),

6.76 [d, J(H,H) = 9 Hz, 2 H, phenyl, A], 6.9 (br., 2 H, phenyl, B),

7.1 (s, 2 H, phenyl), 7.2–7.3 (m, 15 H, phenyl), 7.7–7.9 (m, 20 H,

1, phenyl, A, B), 8.45 (m, 1 H, Tr, 6-H), 8.54 (m, 1 H, Tr, 7-H),

8.67 [d, J(H,H) = 12 Hz, 1 H, Tr, 2-H], 8.73 [d, J(H,H) = 12 Hz,

1 H, Tr, 5-H], 8.77 [d, J(H,H) = 12 Hz, 1 H, Tr, 3-H], 8.93 (m, 8

H, 1) ppm. UV/Vis (MeCN): λ (ε) = 262 (55200), 401.5 (9700), 552

nm (33500). C₁₂₂H₁₃₀F₃₀N₅O₁₂P₅(2581.79): calcd. C 56.72, H 5.07,

N 2.71; found C 56.92, H 4.77, N 2.90. MS (ESI): m/z = 1145.5956

([C₁₂₂H₁₃₀F₁₂N₅O₁₂P₃]²⁺) calcd. 1145.9321 (M – 2PF₆)²⁺, 715.6386

Acknowledgments

Financial support by the Deutsche Forschungsgemeinschaft

(DFG) is gratefully acknowledged.

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([C₁₂₂H₁₃₀F₁₂N₅O₁₂P₂]³⁺) calcd. 715.6333 (M – 3PF₆)³⁺

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Molecular Thread 41: Compound 38 (0.045 g) was oxidized as in

the procedure used for the synthesis of compound 39, providing a

violet solid (0.05 g, 42 %), m.p. 62–65 °C. ¹H NMR (400 MHz,

CD₃CN, TMS): 1.7 (m, 7 H, adamantane), 1.76 (m, 2 H, 18-H),

1.8 (m, 8-H, adamantane), 2.12 (s, 6 H, methyl), 2.54 [t, J(H,H) =

8 Hz, 2 H, 19-H], 3.38 [t, J(H,H) = 7 Hz, 2 H, 17-H], 3.5 (m, 14

H, oxyethylene), 3.6 (m, 8 H, oxyethylene), 3.8 (m, 2 H, 5-H), 4.0

(m, 2 H, 21-H), 4.1 (m, 6 H, 6-H, 7-H, 8-H), 4.2 (m, 4 H, 20-H,

oxyethylene), 6.21 (br. t, 1 H, NH), 6.81 [d, J(H,H) = 9 Hz, 2 H,

phenyl, C], 6.9 (m, 4 H, phenyl, phenyl, A), 7.08 [d, J(H,H) = 9

Hz, 2 H, phenyl, C], 7.13–7.17 (m, 17 H, phenyl, phenyl B), 7.80

[d, J(H,H) = 9 Hz, 2 H, phenyl, B], 7.88 [d, J(H,H) = 7 Hz, 2 H,

phenyl, A], 8.3 (m, 1 H, Tr, 6-H), 8.45 [dd, 1 H, Tr, 7-H], 8.60 dd,

1 H, Tr, 2-H), 8.65 (dd, 1 H, Tr, 5-H), 8.76 (dd, 1 H, Tr, 3-H) ppm.

UV/Vis (MeCN): λ (ε) = 273 (16830), 398 (7270), 555 nm (22930).

C₈₆H₉₈F₆NO₁₂P (1482.66): calcd. C 69.67, H 6.66, N 0.94; found

C 69.92, H 5.73, N 0.90. MS (ESI): m/z = 1336.7088 ([C₈₆H₉₈-

NO₁₂]⁺) calcd. 1336.7089 (M – PF₆)⁺.

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Methoxy-Substituted Rotaxanes 42 and 43: The isomeric mixture of

methoxy derivatives 42 and 43 were obtained by addition of meth-

anol (0.1 mL) to a solution of 39 or 40 (0.02 g) in MeCN (2 mL)

containing NaHCO₃(0.02 g). After stirring for 4 h, the violet color

disappeared. After filtration, the solvent was removed under re-

duced pressure. In order to record the NMR spectra, the solid was

dissolved with CD₃CN (0.6 mL). The spectra (¹H NMR (see Sup-

porting Information), H–H-COSY and ROESY) show the presence

of the main isomer 42a or 43a.

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43a: C₁₂₃H₁₃₃F₂₄N₅O₁₃P₄(2467.8467). MS (ESI): m/z = 1088.9586

([C₁₂₃H₁₃₃F₁₂N₅O₁₃P₂]²⁺) (M – 2PF₆)⁺, calcd. 1088.9592; 677.6508

([C₁₂₃H₁₃₃F₆N₅O₁₃P]³⁺) (M – 3PF₆)⁺, calcd. 677.6514. UV/Vis

(MeCN): λ (ε) = 265 (57130), 365 nm (sh) (15680).

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to a solution of compound 41 (0.03 g) in MeCN (2 mL) containing

NaHCO₃(0.02 g). The suspension was stirred until the violet color

disappeared. In order to record the NMR spectra, the solution was

filtered, evaporated, and the residue was dissolved in CD₃CN

(0.2 mL) and CD₃OH (0.4 mL).

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Supporting Information: (see footnote on the first page of this arti-

cle): NMR spectra of rotaxanes 22 and 42, 2D-NMR spectra of

Received: June 10, 2005

Published Online: October 25, 2005

398

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Article Doi

A photoswitchable rotaxane with an unfolded molecular thread

DOI: 10.1002/ejoc.200500421

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Article abstract of DOI:10.1002/ejoc.200500421

Full text of DOI:10.1002/ejoc.200500421

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