Supramolecular pseudo-rotaxane type complexes from π-extended TTF dimer crown ether and C60

Article abstract of DOI:10.1016/j.tet.2005.07.122

A new cyclophane-type crown ether endowed with two exTTF units forms supramolecular ensembles with different dibenzylammonium salts with a binding constant of K_a～50 M^-1 determined by ¹H NMR and fluorescence experiments. Cy

Full text of DOI:10.1016/j.tet.2005.07.122

Tetrahedron 62 (2006) 1998–2002
Supramolecular pseudo-rotaxane type complexes from
p-extended TTF dimer crown ether and C60
a
Marta C. Dıaz, Beatriz M. Illescas, Nazario Martın, J. Fraser Stoddart, M. Angeles Canales,
a
a,
b
c
*
´
´
Jesus Jimenez-Barbero, Ginka Sarova and Dirk M. Guldi
c
d
d
´
´
a
´
´
´
Departamento de Quımica Organica, Facultad de Quımica, Universidad Complutense, E-28040 Madrid, Spain
bDepartment of Chemistry and Biochemistry, University of California at Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095, USA
c
´
Centro de Investigaciones Biologicas (CSIC), E-28040 Madrid, Spain
¨
Institute for Physical and Theoretical Chemistry, Universitat Erlangen, 91058 Erlangen, Germany
d
Received 22 June 2005; revised 10 July 2005; accepted 12 July 2005
Available online 18 November 2005
Abstract—A new cyclophane-type crown ether endowed with two exTTF units forms supramolecular ensembles with different
dibenzylammonium salts with a binding constant of Kaw50 MK1 determined by 1H NMR and fluorescence experiments. Cyclic voltammetry
studies show the existence of electronic interaction between the exTTF units due to the flexible nature of the crown ether chains.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
and cage molecules has recently been reviewed.8 The
incorporation of TTF into cyclophane hosts is expected to
amplify the host–guest interaction with a complementary
electroactive guest. Such interactions might electro-
chemically be signaled. Interestingly, some cyclophanes
containing two TTF units (i.e., 39 and 4,10 Chart 1) show the
presence of intramolecular interactions between the two
TTF units, either in their neutral (4) or in their
monooxidized form (3).
The well-known p-electron donor features of tetrathiaful-
valenes (TTFs) led to myriad applications.1 Initially,
incentives for their preparation involved the development
of novel molecular materials. In this context, the discovery
of, for example, the first TTF complex with metallic charge-
transfer properties (CT),2 tiggered implementation of TTF
in several areas of modern research. During recent years,
the utility of TTF (1) as a versatile building block in
macrocyclic and supramolecular chemistry3 has shown that
TTF is far more than a simple component for molecular
conductors.4–7
Unlike TTF, p-extended TTF 2 (Chart 1), in which the two
dithiole moieties are attached to a central benzene ring of an
anthracene linker, undergoes a single two-electron oxi-
dation to yield the corresponding dication. Strong steric
repulsions, due to the peri hydrogen atoms of the adjacent
benzene rings, enforce a ‘saddle-type’ conformation in the
neutral molecule. Dramatic structural changes accompany
the oxidation process.11
TTF is a non-aromatic 14p-electron molecule, which is
reversibly oxidized to the cation radical and dication in an
accessible potential window. Substitutions or chemical
modification of the TTF framework emerged as powerful
means to fine-tune these properties. Such characteristics
render TTF an interesting building block for molecular and
supramolecular assemblies,3,6 including macrocycles,
cyclophanes, cage molecules, catenanes, rotaxanes, dendri-
mers, polymers, etc.
Integrating exTTF into macrocyclic and supramolecular
systems has yet to be explored. To the best of our
knowledge, a limited number of cyclophane type derivatives
have been reported.12 To this end, compound 5 is the only
known exTTF based cyclophane derivative, in which,
however, no intramolecular interactions between the two
exTTF were observed.
One of the most interesting aspects of TTF chemistry,
namely, that of CT interactions in TTF-based cyclophanes
Implementation of C60 as a 3-dimensional electron acceptor
holds great promise on account of its small reorganization
energy in electron transfer reactions and has exerted
Keywords: Crown ether; Tetrathiafulvalene; Supramolecular complexes.
*
Corresponding author. Tel.: C34 91 3944227; fax: C34 91 3944103;
e-mail: nazmar@quim.ucm.es
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.07.122

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M. C. Dıaz et al. / Tetrahedron 62 (2006) 1998–2002
1999
S
S
S
S
S
S
S
S
S
S
S
S
S
S
TsO
O
OH
3
O
O
3
OR
OH
S
S
S
S
S
S
S
S
7
i
RO
O
O
HO
S
S
S
S
3
S
S
1
8: R = H
9: R = Ts
6
ii
3
2
MeS
S
O
O
O
O
O
O
O
S
S
MeS
S
O
S
S
S
S
S
S
S
S
S
S
iii
O
O
S
S
S
S
S
O
O
O
S
S
O
S
SMe
O
O
O
O
O
O
O
O
MeS
S
O
S
S
SMe
O
MeS
S
10
O
S
S
O
O
Scheme 1. (i) K2CO3/MeCN, D, 2 days; (ii) TsCl, DMAP, Et3N/CH2Cl2;
(iii) Cs2CO3, Bu4NI, CsOTs/DMF, 120 8C, 3 days.
S
S
S
O
O
4
S
SMe
O
SMe
different conformations of the TTF moieties. The signals of
the aromatic protons are observed as two doublets with a
coupling constant of JZ8.5 Hz [dw7.50 (2H) and dw7.43
(2H)], two doublets with a small JZ2.1 Hz [dw7.21 (2H)
and dw7.03 (2H)], and a multiplet at dw6.7 (4H), thus
appearing as two sets of signals. In the same way, the dithiol
ring protons are observed as two different multiplets at
dw6.52 and 6.48 integrating for 4 protons each. Finally, the
methylene protons of the polyether chains appear as
multiplets at d values between 4.1 and 3.7.
5
Chart 1.
noteworthy impact on the improvement of light-induced
charge-separation. The integration of C60 and TTF or exTTF
into photosynthetic model system is a particularly promis-
ing approach.13,14 In particular, photoexcitation of these
C60–TTF and C60–exTTF systems generates highly ener-
getic and long-lived charge separated states. Recently, we
reported the first example of a supramolecular C60–TTF
ensemble, in which the donor and acceptor units were
brought together through a complementary guanidinium–
carboxylate ion pair.15
We tested the cyclic exTTF (10) to form supramolecular
complexes with secondary amines (Scheme 2) that are
endowed with two different acceptors (i.e., a nitro group or a
fullerene cage). These salts (11 and 12) were prepared by
following previously reported procedures.17 First evidence
for complexation was obtained when comparing the 1H
NMR spectra of the free species with the spectrum of a
mixture of 10 and the corresponding salt.
In this work, we wish to report on the synthesis of the first
exTTF based crown ether derivative containing two exTTF
moieties. The supramolecular interactions between this
macrocyclic exTTF derivative and a functionalized C60
bearing a secondary ammonium salt has been tested by a
variety of techniques.
O
O
NO2
O
OEt
N
H2
N
H2
2. Results and discussion
-
PF
-
6
PF
6
11
12
The synthesis of the macrocyclic bis-p-extended TTF is
summarized in Scheme 1. In particular, dihydroxy exTTF
derivative 6 was prepared in a multistep synthetic procedure
that was previously reported by our group.13f Next,
alkylation of diol 6 with tetraethylenglycol monotosylate
(7) under basic conditions yielded the exTTF derivative 8,
which was then tosylated with tosyl chloride. The
cyclization takes place by a nucleophylic substitution
between diol 6 and the ditosylated derivative 9. The cyclic
derivative 10 is obtained in 30% yield as a yellow solid. On
the other hand, the employ of the corresponding dibromide
compound—instead of ditosylate 9—led to lower yields
(18%). The reaction is performed at low solute concen-
trations in the presence of cesium carbonate16 to favor the
cyclization over oligomerization processes.
10
10
CDCl3/CD3CN (1/1)
CDCl3/CD3CN (1/1)
O
O
O
O
O
O
O
O
O
O
S
S
S
S
S
S
S
S
NH2
NH2
S
S
S
S
S
S
S
S
O
O
O
O
O
O
O
O
O
O
-
-
PF6
PF6
O
NO2
[10·11]
O
O
OEt
[10·12]
Macrocycle 10 was characterized by FTIR, MS, 1H and 13
NMR. The 1H NMR spectrum indicates the presence of two
C
Scheme 2.

´
M. C. Dıaz et al. / Tetrahedron 62 (2006) 1998–2002
2000
We have determined the association constant (Ka) for
complexing benzyl-p-nitrobenzylammonium hexafluoro-
phosphate 11 with crown ether derivative 10. The Ka
value—50 MK1—was deduced from the complexation-
induced changes in the chemical shifts of the aromatic
10
9
8
7
6
1
5
protons of the exTTF cycle in H NMR binding tritations
(500 MHz, CDCl3/CD3CN 1:1, 298 K).18
4
3
2
The formation of complexes [10$11] and [10$12] was also
evidenced by electrospray mass spectrometry, where we
have observed the presence of the peaks corresponding to
the 1:1 complexes after loss of the counteranion (i.e., 1383
for [10$11] and 2200 for [10$12]).
1
0
-1
-2
-3
The redox potentials of compounds 10 and 12 were
determined by cyclic voltammetry (CV) measurements,
carried out in a dichloromethane/acetonitrile solvent
mixture at room temperature using glassy carbon (GC) as
working electrode, standard Ag/AgCl as reference electrode
and with tetrabutylammonium perchlorate (0.1 M) as
supporting electrolyte. The data are gathered in Table 1,
together with those measured for exTTF 2 under the same
experimental conditions.
-0.4
-0.2
0.0
0.2
0.4
E (V)
Figure 1. DPV and cyclic voltammogram of 10 in CH3CN/CH2Cl2 1:1 (Ag/
AgCl vs Pt) at 100 mV sK1
.
probably due to an irreversible proccess taking place after
the one-electron reduction. The intensity of the cathodic
peak of the third reduction wave clearly indicates that other
irreversible process accompanies the three-electron
reduction of the C60 moiety.20
Table 1
1,ox
pa
2,ox
pa
ox,a
pc
1,red
pc
2,red
pc
3,red
pc
4,red
E
pc
Compound
E
E
E
E
E
E
In complementary work the fullerene/macrocycle com-
plexation was tested in fluorescence experiments. The basis
for this approach are electron donor–acceptor interactions
between C60 and exTTF that effect the singlet excited state
deactivation of the photoexcited fullerene. In particular, the
fullerene (i.e., 2.95!10K6 M) fluorescence—photoexcited
at 330 nm—was followed in titration experiments, where
2
10
12
0.12
0.01 0.07
0.01
K0.03
K0.75 K1.13 K1.63 K2.01
In MeCN–CH2Cl2 (1/1), Ag/AgCl versus Pt, scan rate 100 mV sK1
a Reduction process from the dication to the neutral molecule.
.
variable concentrations of the macrocycle (i.e., 3.08!10K6
–
Unlike the parent TTF, exTTFs exhibit only one, two-
electron, quasireversible oxidation wave to form the
dication, which has been confirmed by Coulombimetric
analysis.19 The coalescence of the two one-electron
processes into one two-electron process reveals that the
presence of the quinonoid structure between the two 1,3-
dithiole rings leads to unstable, highly distorted, non-planar
radical cations.11 For compound 10—with two exTTF
units—two closely-spaced oxidation peaks are observed in
the cyclic voltammogram (Fig. 1). These are attributed to
consecutive oxidations of the first and second exTTF
moieties, respectively (i.e., D0–D0/D2C–D0/D2C–D2C).
Weak electronic interactions are thought to be responsible
for the difference in oxidation potentials between the first
and the second exTTF. Consequently, the oxidation of the
first moiety shifts the oxidation potential of the second unit
to slightly more positive potentials (Table 1). This
interaction is made possible by the flexibility of the
polyether chains, in contrast with the rigidity of the spacer
in 5 (Chart 1), which prevents electronic interaction
between the exTTF moieties.
3.39!10K5 M) were added. An illustration is given in
Figure 2, which documents that the fullerene fluorescence
decreases in intensity gradually as the macrocycle was
added.
In each measurement, the fluorescence was corrected by a
background spectrum that was recorded using matching
macrocycle concentrations. Then the non-linear quenching
of the fullerene fluorescence was used to quantify the
fullerene/macrocycle association constant through the
following relationship:
30000
20000
10000
0
For 12, four reduction waves were observed, which
correspond to the first four reduction steps of the fullerene
moiety. As expected, these reduction values are cathodically
shifted in comparison with parent C60, as a consequence of
the saturation of a double bond of the C60 core, which raises
the LUMO energy. As previously reported for this
compound,17 the first reduction wave shows a shoulder
650
700
750
800
850
Wavelength/nm
Figure 2. Room temperature fluorescence spectra of fullerene (2.95!
10K6 M) in ortho-dichlorobenzene upon adding variable concentrations of
macrocycle (3.08!10K6–3.39!10K5 M); 330 nm excitation wavelength.

´
M. C. Dıaz et al. / Tetrahedron 62 (2006) 1998–2002
2001
ꢀ
ꢁ
extracted with CH2Cl2 (2!25 mL). The combined organic
layers were evaporated in vacuo and the oily residue was
taken up in CH2Cl2 (50 mL). This solution was carefully
washed with a mixture of satd aq NaCl and 10% NaOH aq
solution (3:1, 3!50 mL). Drying (MgSO4) and evaporation
under reduced pressure followed by column chromato-
graphy (SiO2, CH2Cl2) afforded 8 as a yellow solid. Yield:
58%; mp: 251–253 8C (dec); 1H NMR (CDCl3, 400 MHz) d
7.57 (d, 2H, J1Z8.5 Hz), 7.22 (d, 2H, J2Z2.5 Hz), 6.83 (dd,
2H, J1Z8.5 Hz, J2Z2.5 Hz), 6.28 (s, 4H), 4.20 (t, 4H,
JZ4.5 Hz), 3.76 (t, 4H, JZ4,5 Hz), 3.76–3.59 (m, 24H),
2.60 (s, 2H); 13C NMR (100 MHz, CDCl3) d 156.7, 137.0,
134.1, 129.1, 128.6, 126.1, 121.8, 117.2, 112.1, 111.0, 72.5,
IN ÿ I0
2c0
IF Z I0 C
2
3
5
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ꢂ
ꢃ
!
Cc0 CcMC
K
Cc0 CcMC 2 ÿ 4c0cMC
1
1
4
KS
KS
Data, as, for example, taken at the 698 nm fluorescence
maximum (Fig. 3), were used to determined a Ks value of
55G5 MK1, which is in excellent agreement with the data
based on NMR experiments.
2,00E-03
70.8, 70.6, 70.5, 70.3, 69.7, 67.6, 61.7; FTIR (KBr) n (cmK1
)
3420, 2957, 2938, 2874, 1657, 1597, 1524, 1499, 1456, 1425,
1371, 1309, 1298, 1255, 1158, 1107, 1066, 1021, 950;MS(EI)
m/z 888 (MC).
1,00E-03
4.1.2. 2,6-Bis[2-[2-[2-(2-hydroxyethoxy)ethoxy]ethoxy]-
ethoxy]-9,10-bis-1,3-dithiol-2-ylidene-9,10-dihydro-
anthracene ditosylate (9). A solution of 8 (0.4 mmol) was
cooled to 0 8C and a catalytic amount of DMAP, TsCl
(1 mmol) and Et3N (2 mmol) were added, keeping the
mixture with vigorous stirring. The reaction was allowed to
warm to room temperature and let stand overnight. Cool
water (100 mL) was added and the mixture was extracted
with CH2Cl2 (3!50 mL). The combined organic layers
were dried (MgSO4) and evaporated to dryness, yielding a
residue, which was purified by column chromatography
(SiO2:CH2Cl2). Yield: 84%; mp: 265–267 8C (dec); 1H
NMR (400 MHz, CDCl3) d 7.77 (d, 4H, JZ8.2 Hz), 7.55 (d,
2H, J1Z8.5 Hz), 7.20 (d, 2H, J2Z2.3 Hz), 7.30 (d, 4H,
JZ8.2 Hz), 6.81 (dd, 2H, J1Z8.5 Hz, J2Z2.3 Hz), 6.26 (s,
4H), 4.18 (t, 4H, JZ4.9 Hz), 4.13 (t, 4H, JZ4.7 Hz), 3.86
(t, 4H, JZ4.9 Hz), 3.71–3.55 (m, 20H), 2.40 (s, 6H); 13C
NMR (100 MHz, CDCl3) d 158.0, 143.1, 133.2, 131.4,
130.5, 127.5, 126.5, 124.6, 124.1, 113.1, 111.5, 70.7, 70.6,
69.3, 68.7, 21.6; FTIR (KBr) n (cmK1) 2924, 2851, 1603,
1561, 1542, 1471, 1424, 1370, 1180, 1111, 821, 736, 700;
MS (EI) m/z 1073 (MC).
0,00E+00
0,000E+00 1,000E-05 2,000E-05 3,000E-05
[MC]
Figure 3. (IFKIo)/(INKIo) versus macrocycle concentration relationship
based on the fluorescence spectrum shown in Figure 2.
3. Conclusions
In summary, we have carried out the synthesis of the first
cyclophane-type crown ether (10) containing two exTTF
units. The flexible oligoether chains connecting the exTTF
moieties are responsible for the observed electronic
communication existing between them by cyclic voltam-
metry experiments.
Complexation of crown ether 10 with dibenzylammonium
salts bearing electron accepting groups such as p-nitro-
benzene (11) or [60]fullerene21 (12) afforded new supra-
molecular ensembles [10$11] and [11$12]. The binding
1
constants for complex [10$11] determined by H NMR (in
4.1.3. Compound 10. To a suspension of Cs2CO3
(3.3 mmol) in anhydrous DMF (4 mL) under argon, a
solution of diol 6 (0.33 mmol) in DMF (5 mL) was added,
and the mixture was heated to 60 8C. After 30 min, CsOTs
(0.66 mmol) and Bu4NI (0.03 mmol) were added. A
solution of the ditosylate derivative 9 (0.33 mmol) in
anhydrous DMF (5 mL) was slowly added over a period
of 2 h and, after addition, temperature was raised to 120 8C.
The mixture was kept with stirring and under reflux for
3 days and then was allowed to cool to room temperature.
The solution was filtered off and the residue washed with
DMF (30 mL). The solvent was removed in vacuo and the
residue was taken up in a mixture of toluene (20 mL) and
water (10 mL). After separation, the organic phase was
dried (CaCl2) and concentrated under reduced pressure,
yielding a residue, which was purified by column
chromatography (SiO2, CH2Cl2). The macrocyclic com-
pound 10 was obtained as a yellow solid. Yield: 30%; mp:
CDCl3/CD3CN) and fluorescence (in o-DCB) experiments
showed values of Kaw50 MK1. These findings reveal that
these new supramolecular structures are appealing systems
for further photoinduced electron transfer studies. Work is
in progress to synthesize other different sized macrocycles
in order to increase the binding constants of related systems,
thus mimicking the natural photosynthetic process.
4. Experimental
4.1. General
4.1.1. 2,6-Bis[2-[2-[2-(2-hydroxyethoxy)ethoxy]ethoxy]-
ethoxy]-9,10-bis-1,3-dithiol-2-ylidene-9,10-dihydro-
anthracene (8). To a degassed solution of the monotosylate
7 (1.3 mmol), K2CO3 (2.62 mmol) and a catalytic amount of
LiBr in MeCN anhydrous (10 mL), the dihydroxy derivative
6 (0.73 mmol) was added under argon. The mixture was
heated to reflux for 24 h and then filtered off. The residue
was taken up in H2O (10 mL), and the resulting solution was
1
273–275 8C (dec); H NMR (500 MHz, DMSO-d6) d 7.50
(d, 2H, JZ8.5 Hz), 7.43 (d, 2H, JZ8.5 Hz), 7.21 (d, 2H,
JZ2.1 Hz), 7.03 (d, 2H, JZ2.1 Hz), 6.77–6.70 (m, 4H),
6.52 (m, 4H), 6.48 (m, 4H), 4.14–4.05 (m, 8H), 3.86–3.81

´
M. C. Dıaz et al. / Tetrahedron 62 (2006) 1998–2002
2002
(m, 8H), 3.65 (m, 16H); 13C NMR (125 MHz, DMSO-d6) d
158.0, 133.5, 132.9, 126.8, 126.5, 124.5, 124.0, 113.0,
111.5, 70.3, 69.1, 67.7; FTIR (KBr) n (cmK1) 2925, 2852,
2718, 1601, 1562, 1543, 1508, 1471, 1424, 1226, 1111, 822,
737, 700; MS (EI) m/z 1140 (MC).
´ ´
Gonzalez, S.; Martın, N.; Guldi, D. M. J. Org. Chem. 2003, 68,
´ ´
779–791. (g) Gonzalez, S.; Martın, N.; Swartz, A.; Guldi, D. M.
´
´
Org. Lett. 2003, 5, 557. (h) Sanchez, L.; Perez, I.; Martın, N.;
´
´
Guldi, D. M. Chem. Eur. J. 2003, 9, 2457. (i) Sanchez, L.; Sierra,
´
M.; Martın, N.; Guldi, D. M.; Wienk, M. W.; Janssen, R. A. J.
Org. Lett. 2005, 7, 1691. (j) Guidi, D. M.; Giacalone, F.; de la
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Torre, G.; Segura, J. L.; Martın, N. Chem. Eur. J. 2005, 11, 1267.
´
(k) Giacalone, F., Segura, J. L., Martın, N., Ramey, J., Guidi,
D. M. Chem. Eur. J. 2005, 11, 4819.
Acknowledgements
Support of this work by MCYT of Spain (BQU-2002-
00855) is gratefully acknowledged. M.C. D. is indebted to
CAM for financial support (GR/MAT/0633/2004). This
work was carried out with partial support from the EU (RTN
networks “WONDERFULL” and “CASSIUSCLAYS”),
SFB 583, FCI and the Office of Basic Energy Sciences of
the US Department of Energy.
14. (a) Liddell, P. A.; Kodis, G.; de la Garza, L.; Bahr, J. L.;
Moore, A. L.; Moore, T. A.; Gust, D. Helv. Chim. Acta 2001,
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References and notes
´
´
17. Diederich, F.; Echegoyen, L.; Gomez-Lopez, M.; Kessinger, R.;
Stoddart, J. F. J. Chem. Soc., Perkin Trans. 2 1999, 1577.
18. To perform the 1H NMR binding studies, the concentration of
10 was kept constant (1 mM) and increasing amounts of 11
were added (from 0.3 to 30 mM). The chemical shifts of the
aromatic protons of 10 were observed. The complexation-
induced variation of the chemical shift (Dd) was plotted
against the concentration of 11. The Ka value was obtained by
a nonlinear regression analysis curve-fitting using SigmaPlot
v8.0.
1. TTF Chemistry: Fundamentals and Applications of Tetra-
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7. Segura, J. L.; Martın, N. Angew. Chem., Int. Ed. 2001, 40,
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Knight, B.; Martın, N.; Ohno, T.; Ortı, E.; Rovira, C.; Veciana,
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