Synthesis of fullerene-stoppered rotaxanes bearing ferrocene groups on the macrocycle

Article abstract of DOI:10.1002/ejoc.200901309

The synthesis, characterisation and behaviour of a series of rotaxanes containing a fulleropyrrolidine stopper and two ferrocene moieties on the macrocycle is reported. Remarkably, the presence of large and bulky ferrocene groups does not interfere either in the synthesis or in the translocation of the macrocycle induced by π-π interactions between the macrocycle and the fullerene. The synthetic routes developed can also be applied to the preparation of rotaxane scaffolds that can be complexed to [Ru(CO)TPP] by axial coordination. Overall, the synthetic routes presented herein provide an efficient way to prepare a variety of rotaxanes and molecular shuttles with potential applications in different fields.

Full text of DOI:10.1002/ejoc.200901309

FULL PAPER
DOI: 10.1002/ejoc.200901309
Synthesis of Fullerene-Stoppered Rotaxanes Bearing Ferrocene Groups on the
Macrocycle
Aurelio Mateo-Alonso*[a,b] and Maurizio Prato*[c]
Dedicated to Professor Saverio Florio on the occasion of his 70th birthday
Keywords: Rotaxanes / Fullerenes / Porphyrinoids / Ferrocene / Molecular shuttles / Supramolecular chemistry
The synthesis, characterisation and behaviour of a series of
rotaxanes containing a fulleropyrrolidine stopper and two
ferrocene moieties on the macrocycle is reported. Remark-
ably, the presence of large and bulky ferrocene groups does
not interfere either in the synthesis or in the translocation
of the macrocycle induced by π–π interactions between the
macrocycle and the fullerene. The synthetic routes devel-
oped can also be applied to the preparation of rotaxane scaf-
folds that can be complexed to [Ru(CO)TPP] by axial coordi-
nation. Overall, the synthetic routes presented herein pro-
vide an efficient way to prepare a variety of rotaxanes and
molecular shuttles with potential applications in different
fields.
through charge-transfer reactions that increase the second
hyperpolarisability by the efficient delocalisation of
charge.[9] The preparation and study of a vast series of C60-
based dyes with different donor–acceptor spatial arrange-
ments have illustrated the dependency between molecular
architecture and ET and NLO properties.
Introduction
Fullerenes and especially C60 derivatives are valuable
building blocks for the preparation of materials with poten-
tial applications in different technological fields such as
photovoltaics, non-linear optics, optoelectronics and medic-
inal chemistry.[1–4] The properties of C60 derive mostly from
the three-dimensional extended π system that makes C60 an
excellent electron-acceptor[5] with very low reorganisation
energy[6] and thus a valuable component for the construc-
tion of molecular photovoltaic materials.[7] When C60 is
coupled with electron-donors of different nature,[1,3,4] elec-
tron-transfer (ET) reactions can take place upon photoex-
citation to give long-lived radical pairs, mimicking the key
process at photosynthetic reaction centres. Also, C60 deriva-
tives are known to exhibit a sizeable non-linear optical
(NLO) response[8,9] as a result of their ability to delocalise
charge extensively.[6] For this reason C60 derivatives have
been widely studied with the aim of incorporating their
properties into photonic devices such as optical switches,
optical limiters and deflectors.[10] It has been demonstrated
that the third-order NLO response of C60 can be enhanced
Fullerene-based donor–acceptor systems have been in-
troduced into mechanically interlocked architectures[11,12]
as they allow an intimate spatial and electronic coupling
through a non-covalent (mechanical) bond,[13–16] which at
the same time permits the study of the effect of particular
donor–acceptor geometries. In these supramolecular sys-
tems a fullerene electron-acceptor supported in one submo-
lecular fragment is coupled with an electron-donor sup-
ported in the second component (porphyrin,[17–23] phthalo-
cyanine,[24,25] ferrocene,[26–28] extended tetrathiafulvalene[29]
and aromatic amines[30]). Upon photoexcitation, long-lived
radical pairs have been observed. Among such mechanically
interlocked architectures, rotaxanes present the same struc-
ture as that of an abacus: a macrocycle locked onto a mo-
lecular thread by two bulky stoppers. Because both compo-
nents are mechanically bonded, the macrocycle can be sub-
jected to several types of submolecular motion such as
“shuttling” (translation of the macrocycle along the
thread), “pirouetting” (rotation of the macrocycle about a
fixed axis) and “rocking” (changes in the orientation of the
[a] Freiburg Institute for Advanced Studies (FRIAS), School of
Soft Matter Research, Albert-Ludwigs-Universität Freiburg
Albertstrasse 19, 79104 Freiburg, Germany
E-mail: amateo@frias.uni-freiburg.de
[b] Institut für Organische Chemie und Biochemie, Albert-Lud- macrocycle’s plane).
wigs-Universität Freiburg
In recent years we have become interested in the proper-
Albertstrasse 21, 79104 Freiburg, Germany
[c] Dipartimento di Scienze Farmaceutiche, Università degli Studi
di Trieste,
ties of rotaxanes equipped with fullerene stoppers and fer-
rocene electron-donors. In a series of articles we have shown
that fullerenes are not simply electro- and/or photoactive
stoppers,[31–33] but, more importantly, that they can be used
Piazzale Europa 1, 34127 Trieste, Italy
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200901309.
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Fullerene-Stoppered Rotaxanes Bearing Ferrocene Groups
to induce a large-amplitude translational motion[34–37] be- isophthaloyl chloride was then treated with an excess of
tween two distinct positions of the thread (stations). In such tBuOK to yield the tert-butyl isophthalate 2 in 57% yield
bistable rotaxanes (molecular shuttles), two well-defined after extraction without the need of column chromatog-
and distant co-conformations can be achieved electrochemi- raphy. Then 2 was esterified with ferrocenecarboxylic acid,
cally or by a solvent change.[34–37] Because such a submolec- which had been activated in situ by using EDC and DMAP,
ular rearrangement also implies a change of geometry of to give 3. Again the purification of 3 was easily achieved by
the two components (thread and macrocycle) of the rotax- simple extraction to give very high yields (93%). The acid
ane, it seemed reasonable that by inserting an electron-do- groups were deprotected quantitatively under acidic condi-
nor onto the macrocycle and displacing it along the thread tions to give acid 4, which was subsequently transformed
with respect to the fullerene electron-acceptor, it should be into 5-ferroceneacetoxyisophthaloyl chloride (5) in very
possible to modulate both the ET and the NLO response. high yield (94%) in the presence of oxalyl chloride and
In a preliminary account[35] we demonstrated that ET can DMF. Acyl chloride 5 was used immediately to prepare the
be tuned by placing the macrocycle equipped with two fer- rotaxane (see below).
rocene electron-donors at different positions along a thread
equipped with a fullerene stopper. We later also demon-
strated that the switchable behaviour of such systems can
also be used to modulate the NLO response of the fullerene
stopper.[37] Taking advantage of our knowledge of the syn-
thesis of rotaxanes equipped with donor–acceptor moieties,
we also reported a rotaxane scaffold used to organise three
photo/electroactive units along a supramolecular redox gra-
dient and we observed a two-electron-transfer cascade after
photoexcitation.[38] Herein, we report in detail the design,
synthesis and characterisation of such fullerene-stoppered
rotaxanes bearing ferrocene electron-donors on the macro-
cycle.
Results and Discussion
Scheme 1. Synthesis of the macrocycle precursor with a ferrocene
moiety.
Synthesis of Rotaxane Dyads
Our main purpose was to synthesise fullerene-stoppered
The precursors of the macrocycle being available, we pro-
rotaxanes bearing electron-donors on the macrocycle in or- ceeded to synthesise different molecular threads bearing the
der to study ET between the two interlocked components fullerene moiety. An advantage of C60 is its large size, which
and any other properties that might arise from electron makes it an excellent electroactive stopper. The ring-closure
transfer such as NLO properties. Leigh-type rotaxanes[39] of the benzylic amide macrocycle is assisted by a 1,4-di-
are particularly attractive for this purpose because they are amide template previously introduced between the stoppers,
not built from chromophores or redox groups and are thus which directs the five-component clipping reaction by hy-
the perfect scaffolds for studying the interactions between drogen-bond recognition.[39] A clear advantage of Leigh et
different photo- and electroactive components.
al.’s protocol is that a variety of 1,4-diamide templates can
We began our research with the preparation of macro- be used to clip the macrocycle; these templates display dif-
cycle precursors that would allow us to introduce electron- ferent affinities for the macrocycle (fumaramide ϾϾ suc-
donors onto the macrocycle. Leigh’s protocol relies on the cinamide Ͼ glycylglycine).[41,42]
addition under high-dilution conditions of isophthaloyl
To understand whether we could synthetically prepare
chloride and p-xylylenediamine to clip the macrocycle rotaxanes bearing large substituents on the macrocycle we
around the thread. Hence, we decided to use an isophthalic tested the rotaxane-forming reaction with thread 6[32]
acid derivative with a hydroxy group at the 5-position to (Scheme 2). The synthesis of thread 6 relies on the 1,3-
maintain the symmetry of the macrocycle and avoid the for- dipolar cycloaddition of azomethine ylides to C60.[43] An
mation of different regioisomers. Typically, the conditions advantage of this method is that the resulting fulleropyrrol-
require at least 9 equiv. of each of the macrocycle precur- idines present a higher stability in comparison with other
sors. Therefore we had to rely on a stable electron-donor fullerene adducts, which allows the detailed study of their
that can be easily processed. Ferrocenecarboxylic acid is electrochemical properties. We used fumaramide templates
commercially available, reasonably cheap for working on a as they are known to give the highest yields in rotaxane-
multigram scale and is red, which facilitates purification. forming reactions.[42] The excellent arrangement and rigid-
The route begins with the conversion of 5-hydroxyiso- ity of the hydrogen-bond recognition sites endow the fuma-
phthalic acid (1) into 5-hydroxyisophthaloyl chloride by ramide groups with a strong affinity for the macrocycle. The
heating at reflux in SOCl2 under argon without the need of lack of solubility of the combination of C60 and fumar-
protecting the hydroxy group (Scheme 1).[40] The resulting amide in the solvents necessary for the rotaxane-forming
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Scheme 2. Synthesis of the C60-stoppered rotaxane 7 with two ferrocene moieties on the macrocycle.
reactions was overcome by the introduction of a solubilising cycle relative to the protons of thread 6, which confirms
lateral chain in the cycloaddition step.[32] Then freshly pre- that the macrocycle is positioned over the fumaramide tem-
pared 5 and p-xylylenediamine (10 equiv. each) were added plate. Even though the solubility was enhanced by the pres-
to 6 under high-dilution conditions in the presence of NEt3 ence of the two ferrocene groups, we could not obtain a 13
C
to give a mixture of the desired rotaxane 7 and unreacted NMR spectrum with a sufficiently good signal/noise ratio
thread 6 (Scheme 2). Rotaxane 7 was separated from thread to analyse. The [M + H]+ ion of 7 was detected by MALDI-
6 by column chromatography and purified by reprecipi- TOF MS and the formation of the fulleropyrrolidine
tation. The yields were low (12%) in comparison with an monoadduct was confirmed by UV/Vis spectroscopy.
analogous rotaxane prepared without ferrocene substitu-
ents (25%)[32] because of the difficult chromatographic sep-
aration due to the close proximity of the thread and the
Synthesis of Bistable Rotaxane Dyads
rotaxane during elution.
1
The H NMR spectrum of 7 shows typical features of a
After the successful formation of 7, we decided to test
whether the large ferrocene substituent of 5 would also un-
fumaramide rotaxane[42] (Figure 1a and b): the protons B
(the assignments correspond to those shown in Scheme 2)
dergo the rotaxane-forming reaction when using templates
in 7 is shielded by the benzylic amide rings of the macro-
with a lower affinity for the macrocycle than fumaramide.
Dipeptidic templates possess a moderate affinity for the
macrocycle because the hydrogen-bonding sites are not ri-
gid and intramolecular hydrogen bonds can form. An ad-
vantage of using weaker templates is that they allow the
decomplexation of the macrocycle under certain conditions
and thus the templates can be used to prepare bistable rot-
axanes or molecular shuttles.[44] We have reported a series
of molecular shuttles[34,36,45] in which the shuttling is in-
duced by π–π interactions between the fullerene and the
macrocycle in the presence of dipeptidic and succinamide
templates. For this reason, we decided to test the rotaxane-
forming reaction with a weak template and, more import-
antly, to assess whether shuttling, which is effected by π–π
interactions between the fullerene stopper and the macro-
cycle, can take place if the macrocycle bears large and bulky
ferrocene groups. We chose to carry out the rotaxane-form-
ing reaction with thread 8,[36] which is comprised of a fuller-
opyrrolidine stopper, a triethylene glycol spacer, a dipeptide
and a diphenyl stopper. After the addition of 5-ferrocene-
acetoxyisophthaloyl chloride (5) and p-xylylenediamine to
thread 8 under high-dilution conditions followed by chro-
matographic purification, we obtained the desired rotaxane
9 in 22% yield (Scheme 3).
Figure 1. 1H NMR (400 MHz) spectra of a) thread 6 in CDCl3 and
b) rotaxane 7 in CDCl3. The assignments correspond to the letter-
ing shown in Scheme 2.
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Fullerene-Stoppered Rotaxanes Bearing Ferrocene Groups
Scheme 3. Synthesis and behaviour of the molecular shuttle 9.
1
The H NMR spectrum of rotaxane 9 (Figure 2b) con- because of the high solubility of rotaxane 9. The [M +
firmed its structure, showing typical features of dipeptide H]+ ion of 9 was detected by MALDI-TOF MS and signals
rotaxanes.[36,39] In addition, a 13C NMR spectrum with a corresponding to a fulleropyrrolidine monoadduct were ob-
suitable signal/noise ratio was recorded for the first time served by UV/Vis spectroscopy. The solvent-dependency of
1
Figure 2. H NMR (400 MHz) spectra of a) thread 8 in CDCl3, b) rotaxane 9 in CDCl3, c) thread 8 in [D6]DMSO and d) rotaxane 9 in
[D6]DMSO. The peaks highlighted with stars correspond to residual solvent peaks. The assignments correspond to the lettering shown
in Scheme 3.
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A. Mateo-Alonso, M. Prato
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the structure of 9 was investigated by NMR spectroscopy: to thread 12 followed by chromatography to separate unre-
rotaxane 9 was found to exist in different co-conformations acted thread 12 yielded rotaxane 13 in 17% yield. Surpris-
in different solvents (see Figure 2). In relatively non-polar ingly, rotaxane 13 eluted before thread 12 in the chromato-
1
solvents (i.e., CDCl3), protons G, C and D (Figure 2, a and graphic conditions used. The H NMR spectrum of rotax-
b) are shielded in rotaxane 9 in comparison with those of ane 13 shows typical features of dipeptidic rotaxanes (Fig-
thread 8, which confirms that the macrocycle is located pri- ure 3, b); protons D, I and L (the assignments correspond
marily over the peptidic residue (co-conformer 9A). In to the lettering shown in Scheme 4) are shielded by the ben-
highly polar solvents (i.e., [D7]DMF and [D6]DMSO), the zylic amide rings of the macrocycle by 0.9, 0.5 and 1.2 ppm
hydrogen bonds are weakened, thereby promoting the for- when compared with those of thread 12, which confirms
mation of π-stacking interactions between the macrocycle that the macrocycle is positioned over the dipeptide tem-
and the fullerene.[34–36] Therefore the macrocycle shuttles to plate.[36,39] Once again we recorded a 13C NMR spectrum
the opposite end of the thread, preferentially adopting the of rotaxane 13 suitable for analysis due to its high solubility.
stacked co-conformation 9B, which is reflected by the Additional confirmation of the structure came from the de-
shielding of protons E, L and F (Figure 2, c and d). Re- tection of the [M + Na]+ ion by MALDI-TOF MS and
markably, the presence of bulky ferroceneacetoxy groups on from signals corresponding to fulleropyrrolidine monoad-
rotaxane 9 has no effect on the shuttling efficiency of the ducts observed by UV/Vis spectroscopy.
macrocycle, which behaves exactly as an analogous rotax-
ane with no ferrocene on the macrocycle.[36]
Supramolecular Triads
Electron transfer is not limited to donor–acceptor cou-
ples (dyad). An elegant strategy in the development of arti-
ficial reaction centres involves the coupling of C60 to several
electron donors, typically, tetraphenylporphyrin (TPP),
metalloporphyrin (MTPP) and/or ferrocene (Fc), carefully
arranged.[46–48] A key factor is the organisation of the elec-
tron-donating/accepting units following an electrochemical
gradient, which promotes a unidirectional charge-transfer
cascade. Two consecutive charge-transfer reactions have
previously been observed between Fc–TPP–C60 triads
linked covalently and organised in that specific order.[47]
Motivated by these results, we chose to insert supramolec-
ularly an additional electron mediator into our rotaxane dy-
ads to investigate whether the electrochemical gradient ap-
proach could also be applied to supramolecular systems.
Taking into account the redox states of C60 and ferrocene
units, their spatial arrangement and the behaviour of coval-
ent Fc–TPP–C60 triads,[47] it was necessary to insert a TPP
between the macrocycle with the ferrocene moieties and the
C60 stopper. An advantage of MTPP is that it combines
the electronic properties of TPP with the ability to form
complexes typical of organometallic compounds. For in-
stance, C60-pyridine ligands form 1:1 complexes with
MTPP by axial coordination, giving supramolecular dy-
ads.[49–52] The 1,3-dipolar cycloaddition of azomethine
ylides[43] provides a straightforward way to functionalise
C60 with a triethylene glycol linker with a terminal-pro-
tected amine and a pyridine ligand (10).[53] Building block
10 has the groups necessary for assembling the triad: the
pyridyl ligand and a terminal amine. The long and flexible
triethylene glycol spacer was chosen to reduce the steric hin-
drance that might affect the bulky macrocycle function-
alised with two ferrocene groups. Deprotection of the amine
in 10 followed by the introduction of the template by
Figure 3. 1H NMR (400 MHz) spectra of a) thread 12, b) rotaxane
13 and c) triad 14 in CDCl3. The assignments correspond to the
lettering shown in Scheme 4.
An MTPP can be complexed to rotaxane 13 by axial co-
amidation using 11[44] gave thread 12. Addition of 5-ferro- ordination through the pending pyridyl group in non-coor-
ceneacetoxyisophthaloyl chloride (5) and p-xylylenediamine dinating solvents. In our study we used ruthenium tetra-
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Fullerene-Stoppered Rotaxanes Bearing Ferrocene Groups
Scheme 4. Synthesis of supramolecular triad 14.
phenylporphyrin [Ru(CO)TPP] as the Ru–N σ-coordination be complexed to [Ru(CO)TPP] by axial coordination. Over-
bond is reinforced by π-back-bonding to give robust supra- all, the synthetic routes presented herein provide an efficient
molecular dyads.[51] The addition of 1 equiv. of [Ru(CO)- way to prepare a variety of rotaxanes and molecular shut-
TPP] to a solution of the rotaxane 13 in CDCl3 or CD2Cl2 tles with potential applications in different fields.
resulted in the shielding of protons A, B, G, P and Q by
7.1, 2.2, 1.2, 1.1 and 0.8 ppm, respectively, which evidences
the formation of triad 14 (Figure 3). This shielding is con-
Experimental Section
sistent with previous observations[49–52] and is an effect of
General: NMR spectra were recorded with a Varian Gemini-200
(200 MHz) or JEOL (400 MHz) spectrometer at room temperature.
Chemical shifts are reported in ppm and referenced to residual sol-
vent peaks. The NMR assignments of rotaxanes 7, 9 and 13 corre-
the anisotropy of the porphyrin macrocycle over the pro-
tons A, B, G, P and Q that is a consequence of their prox-
imity to the flat porphyrin surface by coordination.
spond to the lettering shown in Schemes 2, 3 and 4, respectively.
Infrared spectra were recorded with a Jasco FTIR-200 spectrome-
ter. Mass Spectroscopy: MALDI-TOF experiments were recorded
at the Université Louis Pasteur. UV/Vis/NIR spectra were recorded
with a Varian 5000 UV/Vis/NIR spectrometer. Commercial com-
Conclusions
We have reported the synthesis, characterisation and be-
haviour of a series of rotaxanes containing a fulleropyrrol-
idine stopper and two ferrocene moieties on the macrocycle.
The rotaxanes were synthesised by using a modification of
Leigh’s protocol for the preparation of benzylic amide rot-
axanes based on the introduction of a ferroceneacetoxy
group on the isophthalic precursor of the benzylic amide
macrocycle. Taking into account the large amounts of
pounds were used as received. EDC: N-(3-dimethylaminopropyl)-
NЈ-ethylcarbodiimide hydrochloride; HOBt: 1-hydroxybenzotri-
azole hydrate; DMAP: 4-(dimethylamino)pyridine; DCM: dichlo-
romethane. Acid chloride 5 was freshly prepared before the rotax-
ane synthesis.
tert-Butyl 5-Hydroxyisophthalate (2): SOCl2 (5 mL) was added to a
solution of 5-hydroxyisophthalic acid (3 g, 16.47 mmol) in THF
macrocycle precursors required for this procedure, we have (anhydrous, 40 mL) and heated at reflux under argon for 3 h. The
solvent was removed under vacuum and the residue was dissolved
in THF (anhydrous, 50 mL), which was added dropwise to a solu-
tion of tBuOK (9.25 g, 65.89 mmol) in THF (anhydrous, 50 mL)
under argon (CAUTION: exothermic reaction). The remaining
solution was stirred overnight. Then water (250 mL) was added in
small portions to quench the excess tBuOK (CAUTION: exother-
mic reaction). The solution was then extracted with AcOEt. The
organic phase was washed with aqueous HCl (3.5%, 2ϫ), aqueous
NaHCO3 (50% water-diluted saturated solution, 2ϫ) and brine
(1ϫ). The organic phase was dried with MgSO4 and the solvent
developed a multigram-scale route for the preparation of 5-
ferroceneacetoxyisophthaloyl chloride that can be applied
to the insertion of other functional groups. The use of 5-
ferroceneacetoxyisophthaloyl chloride is compatible with
strong (fumaramide) and weak (dipeptidic) templates. Re-
markably, the presence of large and bulky ferrocene groups
does not interfere in either the synthesis or the translocation
of the macrocycle induced by π–π interactions between the
macrocycle and the fullerene. The routes developed can also
be applied to the preparation of rotaxane scaffolds that can was evaporated to give the title compound (2.757 g, 57%); m.p.
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123–125 °C. H NMR (CDCl3): δ = 8.13 (t, J = 1.4 Hz, 1 H, Ar),
1
1733.7, 1623.3, 1522.6, 1452.1, 1424.2, 1322.0, 1264.1, 1123.3,
7.77 (d, J = 1.4 Hz, 2 H, Ar), 7.08 (br. s, 1 H, OH), 1.59 (s, 18 H, 1091.0, 1021.6, 819.1, 756.9, 700.0 cm–1. UV/Vis (THF): λmax
=
tBu) ppm. 13C NMR (CDCl3): δ = 165.25, 159.21, 133.25, 122.44,
120.44, 82.00, 28.15 ppm. MS (ES): calcd. for C16H22O5 [M]+
294.3; found 294.9.
255, 317, 431, 704 nm.
Rotaxane 9: A solution of p-xylylenediamine (251 mg, 1.842 mmol)
in chloroform (anhydrous, stabilised with amylenes, 40 mL) con-
taining NEt3 (0.27 mL, 3.684 mmol) and a separate solution of 5
(761 mg, 1.842 mmol) in chloroform (anhydrous, stabilised with
amylenes, 40 mL) were added simultaneously over 4 h to a stirred
solution of thread 8 (169 mg, 0.147 mmol) in CHCl3 (anhydrous,
stabilised with amylenes, 25 mL) under argon. After the addition,
the reaction mixture was stirred for an additional 90 min at room
temperature. The solution was filtered through Celite and concen-
trated to dryness. Rotaxane 9 (70 mg, 22%) was separated from
the unreacted thread 6 by chromatography (CHCl3/MeOH, 99:1)
followed by reprecipitation (DCM/petroleum ether, ϫ3). 1H NMR
(CHCl3): δ = 8.37 (s, 2 H, a), 8.07 (s, 4 H, b), 7.48–7.46 (m, 4 H,
c), 7.40–7.10 (m, 10 H, A), 6.98 (s, 8 H, d), 6.67–6.59 (m, 1 H, B),
5.77–5.71 (m, 1 H, C), 5.01–4.98 (m, 4 H, e), 4.67–4.58 (m, 4 H,
g), 4.56–4.53 (m, 4 H, f), 4.53 (s, 1 H, D), 4.44 (s, 4 H, E), 4.36 (s,
10 H, i), 4.31–4.23 (m, 4 H, g), 3.98–3.93 (m, 2 H, F), 3.83–3.80
(m, 2 H, I), 3.74–3.68 (m, 2 H, I), 3.53–3.48 (m, 2 H, J), 3.38–3.19
(m, 4 H, L + K), 2.75–2.71 (m, 2 H, G) ppm. 13C NMR (CHCl3):
δ = 170.32, 168.98, 165.39, 145.77, 151.75, 147.19, 146.13, 145.95,
145.51, 145.27, 145.18, 144.42, 142.98, 142.53, 142.04, 141.95,
141.76, 140.01, 136.41, 137.32, 136.03, 135.71, 129.01, 126.87,
128.40, 127.86, 125.20, 121.06, 72.27, 70.74, 70.12, 69.30, 68.71,
68.24, 58.33, 54.09, 44.06 ppm. MS (ES): calcd. for
tert-Butyl 5-Ferroceneacetoxyisophthalate (3): EDC (1.360 g,
6.88 mmol) was added in small portions to a solution of compound
2 (2.026 g, 6.88 mmol), ferroceneacetic acid (1.583 g, 6.88 mmol)
and DMAP (0.840 g, 6.88 mmol) in DCM (160 mL). The solution
was stirred at room temperature for 24 h. Then the solution was
taken up in AcOEt and washed with aqueous HCl (3.5%, 2ϫ),
aqueous NaHCO3 (50% water-diluted saturated solution, 2ϫ) and
brine (1ϫ). The organic phase was dried with MgSO4 and the
solvent was evaporated to give the title compound (3.256 g, 93%);
1
m.p. 142–144 °C. H NMR (CDCl3): δ = 8.47 (t, J = 1.5 Hz, 1 H,
Ar), 7.92 (d, J = 1.5 Hz, 2 H, Ar), 4.95 (t, J = 1.8 Hz, 2 H, Fc),
4.52 (t, J = 1.8 Hz, 2 H, Fc), 4.32 (s, 5 H, Fc), 1.60 (s, 18 H,
tBu) ppm. 13C NMR (CDCl3): δ = 164.09, 150.65, 133.53, 127.52,
126.66, 81.92, 72.16, 70.65, 70.01, 28.13 ppm. MS (ES): calcd. for
C27H30FeNaO6 [M + Na]+ 529.1; found 529.0.
5-Ferroceneacetoxyisophthalic Acid (4): Trifluoroacetic acid
(25 mL) was added to a solution of 3 (4.210 g, mmol) in DCM
(200 mL). The resulting solution was stirred at room temperature
for 24 h. Evaporation of the solvent under vacuum gave the title
compound in a quantitative yield; m.p. 210 °C (decomposition). 1H
NMR (CD3OD): δ = 8.56 (t, J = 1.5 Hz, Ar), 8.01 (d, J = 1.5 Hz,
2 H, Ar), 5.00 (br. t, 2 H, Fc), 4.63 (br. t, 2 H, Fc), 4.36 (s, 5 H,
Fc) ppm. 13C NMR (CD3O3): δ = 177.85, 167.76, 152.35, 133.97,
128.86, 128.09, 73.65, 71.78, 71.17 ppm. MS (ES): calcd. for
C19H14FeNaO6 [M + Na]+ 417.0; found 417.1.
C
138H76Fe2N7O12 [M + H]+ 2135.4; found 2135.3. IR: ν = 2930.3,
˜
2854.1, 1728.9, 1644.0, 1603.5, 1581.3, 1513.8, 1462.7, 1376.9,
1264.1, 1123.3, 1089.6, 1021.1, 893.8, 821.5, 741.5, 704.8 cm–1. UV/
Vis (THF): λmax = 256, 303, 325, 431, 705 nm.
Thread 12: Compound 10[53] (1.36 g, 1.25 mmol) was stirred in a
mixture of trifluoroacetic acid (20 mL) and DCM (20 mL) for 22 h.
The solvent was evaporated under vacuum. EDC (0.272 g,
1.37 mmol), 11[44] (0.336 g, 1.25 mmol) and HOBt (0.185 g,
1.370 mol) were added to a solution of the residue in chloroform
(anhydrous, stabilised with amylenes, 50 mL) under argon. The
solution was stirred at room temp. for 10 min. Then NEt3 (3 mL)
was added and the solution was stirred under argon for 18 h. The
solvent was evaporated and the residue was subjected to
chromatography (CHCl3/MeOH, 99:1) to obtain the title com-
5-Ferroceneacetoxyisophthaloyl Chloride (5): Oxalyl chloride (5 mL)
was slowly added to a dispersion of 4 (500 mg, mmol) in hexane
(50 mL) in the presence of DMF (0.1 mL). The dispersion was
stirred overnight under argon and turned into a red solution. The
solution was filtered through cotton and the solvent was evapo-
rated under vacuum to yield the title compound (500 mg, 94%),
1
which was used immediately after preparation. H NMR (CDCl3):
δ = 8.74 (t, J = 1.6 Hz, 1 H, Ar), 8.23 (d, J = 1.6 Hz, 2 H, Ar),
4.98 (t, J = 1.7 Hz, 2 H, Fc), 4.57 (t, J = 1.7 Hz, 2 H, Fc), 4.33 (s,
5 H, Fc) ppm.
1
pound (146 mg, 10%). H NMR (CHCl3): δ = 8.67 (br. s, 2 H, A),
Rotaxane 7: A solution of p-xylylenediamine (176 mg, 1.290 mmol)
in chloroform (anhydrous, stabilised with amylenes, 40 mL) and a
separate solution of 5 (556 mg, 1.290 mmol) in chloroform (anhy-
drous, stabilised with amylenes, 40 mL) were added simultaneously
over 4 h to a stirred solution of thread 6[32] (176 mg, 0.145 mmol)
in CHCl3 (anhydrous, stabilised with amylenes, 70 mL) containing
NEt3 (0.4 mL, 2.573 mmol) under argon. After the addition, the
reaction mixture was stirred overnight at room temperature. The
solution was filtered through Celite and concentrated to dryness.
Rotaxane 7 (37 mg, 12%) was separated from the unreacted thread
6 by chromatography (DCM/CHCl3, 1:2) followed by reprecipi-
tation (CHCl3/diethyl ether, ϫ3). 1H NMR (CDCl3): δ = 8.30 (s, 2
H, a), 7.96 (s, 4 H, b), 7.74 (br. s, 2 H, c), 7.70 (br. s, 2 H, c), 7.31–
7.16 (m, 12 H, A + C + D), 6.97 (s, 8 H, d), 5.77 (d, J = 15 Hz, 1
H, B), 5.67 (d, J = 15 Hz, 1 H, B), 5.00 (t, J = 2 Hz, 8 H, e), 4.87
(d, J = 10 Hz, 1 H, E), 4.53 (t, J = 2 Hz, 8 H, f), 4.45 (br. s, 8 H,
g), 4.34 (s, 10 H, i), 4.25–4.19 (m, 3 H, F + G + E), 3.90–3.59 (m,
5 H, I + J + K), 3.26–3.14 (m, 1 H, L), 2.57–2.49 (m, 1 H, M),
2.39–2.27 (m, 1 H, N), 1.90–1.78 (m, 2 H, O), 1.48–1.36 (m, 2 H,
P), 1.35–1.11 (m, 10 H, alkyl), 0.82 (t, J = 7 Hz, 3 H, CH3) ppm.
7.77 (br. s, 2 H, B), 7.36–7.22 (m, 10 H, C), 6.57 (t, J = 5 Hz, 1 H,
D), 6.54 (t, J = 5 Hz, 1 H, D), 5.19 (d, J = 10 Hz, 1 H, F), 5.17 (s,
1 H, G), 4.96 (s, 1 H, I), 4.30 (d, 1 H, J = 10 Hz, J), 4.05–3.95 (m,
2 H, K), 3.93 (d, J = 5 Hz, 2 H, L), 3.74–3.68 (m, 4 H, M), 3.57
(t, J = 5 Hz, 2 H, N), 3.34 (c, J = 5 Hz, 2 H, O), 3.38–3.32 (m, 1
H, P), 2.93–2.87 (m, 1 H, Q) ppm. 13C NMR (CHCl3): δ = 172.26,
168.38, 155.73, 153.54, 152.28, 151.90, 147.24, 147.21, 146.20,
146.11, 146.08, 146.06, 146.01, 145.87, 145.85, 154.51, 145.43,
145.40, 145.36, 145.27, 145.21, 145.17, 145.11, 145.09, 145.60,
144.42, 144.31, 144.21, 143.07, 142.93, 142.62, 142.52, 142.50,
142.46, 142.09, 142.06, 142.05, 142.00, 141.97, 141.91, 141.84,
141.72, 141.66, 141.59, 141.46, 140.15, 140.12, 139.84, 139.41,
138.96, 136.95, 136.19, 135.97, 135.42, 128.75, 128.72, 128.66,
128.45, 127.28, 127.15, 81.00, 74.42, 70.48, 70.40, 70.14, 69.63,
69.18, 67.59, 58.71, 52.18, 43.37, 39.33 ppm. MS (ES): calcd. for
C89H34N4O4 [M]+ 1222.2; found 1222.2. IR (NaCl): ν = 3302.5,
˜
3057.6, 2920.7, 1653.7, 1597.7, 1540.8, 1492.6, 1450.21, 1415.5,
1354.7, 1263.1, 1177.3, 1119.5, 1031.73, 828.3, 734.7, 700.0 cm–1.
UV/Vis (DCM): λmax = 256, 309, 325, 430, 703 nm.
MS (MALDI-TOF): calcd. for C146H93Fe2N7O10 [M + H]+ Rotaxane 13:
2217.03; found 2217.2. IR (NaCl): ν = 3275.0, 2921.6, 2851.7, 1.499 mmol) in chloroform (anhydrous, stabilised with amylenes,
A
solution of p-xylylenediamine (204 mg,
˜
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Eur. J. Org. Chem. 2010, 1324–1332

Fullerene-Stoppered Rotaxanes Bearing Ferrocene Groups
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40 mL) containing NEt3 (0.217 mL, 3.000 mmol) and a separate
solution of 5 (646 mg, 1.499 mmol) in chloroform (anhydrous, sta-
bilised with amylenes, 40 mL) were added simultaneously over 4 h
to a stirred solution of thread 12 (146 mg, 0.119 mmol) in CHCl3
(anhydrous, stabilised with amylenes, 20 mL) under argon. After
the addition, the reaction mixture was stirred for an additional
60 min at room temperature. The solution was filtered through Ce-
lite and concentrated to dryness. Rotaxane 13 (45 mg, 17%) was
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35, 1135.
ϫ3). H NMR (CHCl3): δ = 8.63 (br. s, 2 H, A), 8.33 (s, 2 H, a),
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8.05 (s, 4 H, b), 7.95 (br. s, 2 H, B), 7.60–7.50 (m, 4 H, c), 7.38–
7.19 (m, 11 H, C + E), 6.95 (s, 8 H, d), 5.71 (br. s, 1 H, D), 5.26
(s, 1 H, G), 5.09 (d, J = 10 Hz, 1 H, F), 4.99 (t, J = 2 Hz, 4 H, e)
4.56–4.53 (m, 4 H, f), 4.55 (t, J = 2 Hz, 4 H, g), 4.48 (s, 1 H, I),
4.35 (s, 10 H, i), 4.32–4.22 (m, 5 H, f + J), 3.95–3.83 (m, 2 H, K),
3.70–3.62 (m, 4 H, M), 3.48 (t, J = 5 Hz, 3 H, N), 3.27–3.15 (m, 3
H, O + P), 2.90–2.80 (m, 1 H, Q), 2.73–2.69 (m, 2 H, L) ppm. 13C
NMR (CHCl3): δ = 172.41, 170.31, 169.06, 165.46, 155.44, 153.19,
151.81, 151.64, 151.27, 147.24, 147.19, 146.17, 146.11, 146.05,
146.01, 145.86, 145.80, 145.51, 145.43, 145.38, 145.29, 145.26,
145.18, 145.06, 144.56, 144.30, 144.15, 143.03, 142.92, 142.63,
142.52, 142.51, 142.42, 142.04, 141.97, 141.93, 141.88, 141.79,
141.62, 141.57, 141.54, 141.47, 140.11, 139.88, 139.32, 138.37,
137.16, 137.04, 136.08, 136.01, 135.65, 135.36, 129.02, 126.91,
128.82, 128.37, 127.82, 125.09, 121.22, 121.20, 80.30, 75.27, 72.28,
70.72, 70.51, 69.27, 69.10, 58.27, 52.15, 44.05, 42.30, 40.01 ppm.
MS (MALDI-TOF): calcd. for C144H82Fe2N3NaO12 [M + Na]+
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˜
2915.8, 2849.3, 1730.8, 1654.6, 1530.2, 1453.1, 1264.1, 1123.3,
1092.5, 1025.0, 930.49, 907.3, 822.5, 729.0, 695.2 cm–1. UV/Vis
(THF): λmax = 255, 310, 322, 431, 702 nm.
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Supporting Information (see also the footnote on the first page of
this article): NMR spectra of 2–5, 7, 9 and 12–14.
Acknowledgments
This work was carried out with partial support of the University of
Trieste, the Consorzio Interuniversitario Nazionale per la Scienza e
la Tecnologia dei Materiali, the Ministero dell’Instruzione dell’Uni-
versità e della Ricerca (PRIN 2006 project 200634372, and Firb
project RBNE033KMA), the European Union (EU) (Networks
“WONDERFULL” and “EMMMA”) and the Freiburg Institute
for Avanced Studies (Junior Fellowship).
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Received: November 16, 2009
Published Online: January 19, 2010
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Eur. J. Org. Chem. 2010, 1324–1332