Copper-complexed pirouetting [2]pseudorotaxanes with sulfur-containing end-groups attached to the thread: Synthesis, electrochemical studies, and deposition on gold electrodes

Article abstract of DOI:10.1071/CH09334

Two copper [2]pseudorotaxanes incorporating a macrocycle with two chelating sites (2,9-diphenyl-1,10-phenanthroline and 2,2′,6′,2″- terpyridine) and a thread based on crescent-shaped 2,2′-bipyridine derivatives have been synthesized and characterized. One

Full text of DOI:10.1071/CH09334

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2009, 62, 1231–1237
Copper-Complexed Pirouetting [2]pseudorotaxanes with
Sulfur-Containing End-Groups Attached to the Thread:
Synthesis, Electrochemical Studies, and Deposition
on Gold Electrodes
Jean-Paul Collin,A Pierre Mobian,A Jean-Pierre Sauvage,A,C Angélique Sour,A
Yi-Ming Yan,B and Itamar WillnerB
ALaboratoire de Chimie Ogano-Minérale, LC3 UMR 7177 du CNRS, Université de Strasbourg,
Institut de Chimie, 4 rue Blaise Pascal, 67070 Strasbourg Cedex, France.
BInstitute of Chemistry, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel.
CCorresponding author. Email: sauvage@chimie.u-strasbg.fr
Two copper [2]pseudorotaxanes incorporating a macrocycle with two chelating sites (2,9-diphenyl-1,10-phenanthroline
and 2,2ꢀ,6ꢀ,2ꢀꢀ-terpyridine) and a thread based on crescent-shaped 2,2ꢀ-bipyridine derivatives have been synthesized and
characterized. One of the threads was a hindering 2,2ꢀ-bipyridine functionalized by two thioctic-ended arms. The second
thread was an 8,8ꢀ-diphenyl-3,3ꢀ-biisoquinoline functionalized by two thioether-ended arms. The electrochemical studies
of the two copper [2]pseudorotaxanes, both in solution and anchored on a gold surface, showed only fast-moving systems
in solution. The reasons of the inertness of the deposited complexes on gold electrode have been explored.
Manuscript received: 15 June 2009.
Manuscript accepted: 11 August 2009.
Introduction
Molecular machines are particularly promising in relation to
future applications in various fields such as information stor-
age and processing, nano-scale electro- or photo-chemically
driven mechanical devices and imaging. This is illustrated by
recent spectacular results.[1–12] Catenanes and rotaxanes[13–19]
constitute an important family of such systems. The Strasbourg
team has been particularly interested in transition metal com-
plexed interlocking compounds.[20–33] When used in solution,
such dynamic systems could be important to catalyze given
chemical reactions or to facilitate various chemical processes
related to conformational changes. However, most of the devices
which could derive from these species are related to information
storage, nanometric mechanical tools or imaging, which implies
that the compounds are used in condensed phase (components of
liquid crystals or crystalline networks, vesicles and micelles, or
surface grafted species). Several examples of surface-deposited
catenanes and rotaxanes have been reported.[34–41] More impor-
tant in the context of molecular machines, a few recent examples
showed that machine-like species could be grafted on a given
surface and still retain their ability to undergo large amplitude
motions.[42–47]
ꢀ Cu(I)
ꢀ Cu(II)
Oxidation
Reduction
Fig. 1. Pirouetting principle of a [2]rotaxane on a surface. The U- and
W-shaped symbol represent bi- and tridentate chelates respectively.
which consist of rings incorporating a dpp fragment (dpp: 2,9-
diphenyl-1,10-phenanthroline), aterpychelate(terpy:2,2ꢀ,6ꢀ,2ꢀꢀ-
terpyridine) and a sterically undemanding axis threaded through
the ring. The most efficient systems in terms of fast movements
contain either a bipy (bipy: 2,2ꢀ-bipyridine) or a dpbiiq (dpbiiq:
8,8ꢀ-diphenyl-3,3ꢀ-biisoquinoline) unit in the thread.[31,52,53]
Results and Discussion
The pirouetting principle of a [2]rotaxane grafted on a surface
is represented in Fig. 1.
Sincethethreadedcomponentsshouldpreferablybecrescent-
shaped in order to facilitate a two-point attachment on the
surface, the 2,2ꢀ-bipy derivative substituted at the 5,5ꢀ positions
was excluded because of its linear geometry. The two selected
chelates are thus a functionalized bipy bearing two aromatic
groups at the 6 and 6ꢀ positions (dpbipy: 6,6ꢀ-diphenyl-2,2ꢀ-
bipyridine) and a dpbiiq fragment. The ring is the classical
two-chelate ring used by us for building several pirouetting
rotaxanes and catenanes.[24,31,52]
Transition metal-based systems have been shown to move
only very slowly or even not to undergo motions at all once
attached onto an electrode surface.[48–51] This disappointing
observation has prompted us to modify some of the species pre-
pared in our group whose motions are particularly fast in solution
and to attach them onto a gold electrode, with the hope that elec-
trochemically driven motions would be observed. The fastest-
moving systems in solution are ‘pirouetting’ [2]rotaxanes,
© CSIRO 2009
10.1071/CH09334
0004-9425/09/101231

RESEARCH FRONT
1232
J.-P. Collin et al.
1 R ꢀ H
(a)
(b)
N
N
S
2 R ꢀ CH2CH2OH
3 R ꢀ CH2CH2O
S S
RO
Br
OR
O
4
5
1
6
4
7
5 R ꢀ H
6 R ꢀ
a
N
N
(c)
b
S
RO
OR
Fig. 2. Reagents and conditions for the synthesis of the threads. (a) 2-(2-bromoethoxy)tetrahydro-2H-pyran,
Cs2CO3, DMF, 60◦C, 84%; (b) thioctic acid, DCC, DMAP, DMF, 53%; (c) 1-bromo-6-(hexylthio)hexane, Cs2CO3,
DMF, 45◦C, 55%.
4ꢄ
PFꢂ6
3ꢄ
5ꢄ
PFꢂ6
3
3ꢃ
6ꢃ
4
4ꢃ
N
N
N
N
N
N
N
N
N
6
O
O
O
O
O
a
N
N
N
N
d
b
Cuꢁ
Cuꢁ
c
N
N
N
N
N
N
O
O
3
8
O
O
7
4
5
6
O
O
O
O
S
S
S
S
84ꢁ
94ꢁ
7
S
S
Fig. 3. Macrocycle 7 and [2]pseudorotaxanes 8+4 and 94+.
Synthesis and Characterization of the Compounds
with the sulfur-containing arms 4 (obtained by reaction of 1,6-
dibromohexane with thiohexane[55]) in the presence of Cs2CO3
in DMF at 45◦C afforded thread 6 in 55% yield.
The preparation of the end-functionalized bidentate chelates 3
and 6 is illustrated in Fig. 2. Thread 3 was prepared in two
steps starting from 6,6ꢀ-di-p-hydroxyphenyl-2,2ꢀ-bipyridine (1),
which was synthesized according to the literature procedure.[54]
Reaction of 1 with protected 2-bromoethanol in the presence of
Cs2CO3 in N,N-dimethylformamide (DMF) at 60◦C, followed
by removal of the protecting groups with a catalytic amount of
HCl in ethanol afforded diol 2 (84% yield). An esterification
reaction performed with thioctic acid in the presence of N,Nꢀ-
dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine
(DMAP) in DMF at room temperature gave the desired thread
3 in 53% yield. Thread 6 was synthesized from 8,8ꢀ-di-
p-hydroxyphenyl-3,3ꢀ-biisoquinoline (5), whose synthesis has
already been described in the literature.[31] Treatment of 5
The gathering and threading steps leading to the [2]pseudo-
rotaxanes 8+4 and 9+4 have been performed in a classical manner
(Fig. 3).[20] Reaction of the macrocycle 7 with a stoichio-
metric amount of [Cu(CH3CN)]PF6 in CH3CN/CH2Cl2 and,
subsequently, the thread (3 and 6) at room temperature led
quantitatively to the deep red [2]pseudorotaxanes (8+4 and 94+,
respectively) as their PF−6 salt.
1H NMR and electronspray mass spectrometry (ES-MS)
spectra are in full accordance with the expected structures.+Fig. 4
1
presents the H NMR spectra of compounds 6, 7, and 94 and
illustrates the chemical shift changes characteristic of the copper
complexation. In particular, protons 1 and 4 of thread 6 undergo

RESEARCH FRONT
Synthesis, Electrochemical Studies, and Deposition on Gold Electrodes
1233
1582.67
CHCI3
(a)
1
a
b
7
5
6
4
500
2500 m/z
6,6ꢃ
3,3ꢃ
5,6
c
6
a
b
(b)
d
7
4
4,7
3ꢄ,5ꢄ
3,8
1
5
4,4ꢃ
4ꢄ
5,6
(c)
c
d
4,7
3,8
6,6ꢃ
3,3ꢃ 3ꢄ,5ꢄ
4ꢄ
4,4ꢃ
9.2
8.8
8.4
8.0
7.6
7.2
6.8
6.4
6.0
Fig. 4. 1H NMR spectra (300 MHz, aromatic part) of (a) thread 6 (in CDCl3), (b) [2]pseudorotaxane 9+4 (in CD2Cl2), and (c) macrocycle
7 (in CDCl3). Inset: ES-MS of 9+4 .
a strong upfield shift. The a, b, c, and d protons on the phenyl
rings of both constituents of the pseudorotaxane 9+4 also present
ꢂeꢂ
an upfield shift, which is more pronounced for macrocycle 7.
The green Cu(ii)-[2]pseudorotaxane 825+ has been obtained in a
similar manner from thread 3, macrocycle 7 and Cu(BF4)2 salt.
High resolution ES-MS spectra shows an intense peak observed
at m/z 1544.44 (calculated for [M]+ 1544.45).
Oxidation wave observed
CuI
CuII
around ꢁ0.6 V
Fast or slow
pirouetting
Fast
pirouetting
Electrochemical Studies
As previously demonstrated with related systems,[24,31,56] cyclic
voltammetry is very well adapted to study systems display-
ing coupled electron transfer and chemical reactions. A square
scheme as shown on Fig. 5 has been evidenced in the case of cop-
per complex rotaxanes and catenanes.[24,31,56] It is based on the
markedly different stereoelectronic requirements of copper(i)
and copper(ii) complexes. This characteristic will provide the
driving force of the chemical pirouetting reactions. Whereas a
coordination number of 4 implicates a stable monovalent cation,
copper(ii) requires a coordination number of 5 or 6. Thus, by
switching alternatively between copper(i) and copper(ii), the
whole molecule, by a pirouetting motion, will change its geo-
metry to afford a coordination favourable to the corresponding
oxidation state.
ꢁeꢂ
Reduction wave observed
CuI
CuII
around ꢂ0.2 V
Fig. 5. Pirouetting principle of the copper complexed [2]pseudorotaxanes
8+4 and 9+4 .
of −0.5V, no current is observed since 8+4 and 94+ are elec-
trochemically inactive below the oxidation potential at which
Cu(i) starts to be oxidized. On increasing the potential towards
anodic values, oxidation peaks around 0.6V are observed, as
expected for the oxidation process of copper(i) to copper(ii).
After the peak potential, Cu(ii) is obtained and the current inten-
sity decreases. By investigating the scan potential in the reverse
direction, starting from 1.1V towards the cathodic region, it is
expected that the Cu(ii) species can be reduced to Cu(i). If the
Cu(ii) complex is still four-coordinate, the return wave should be
The two complexes 84+ and 9+4 have been studied both in
solution and anchored on gold electrode surfaces. The cyclic
voltammograms of 84+ and 94+ in CH2Cl2/CH3CN mixture (9:1)
recorded at a scan rate of 200 mV s−1 are given in Fig. 6. By
starting the cyclic voltammograms (CV) at a potential value

RESEARCH FRONT
1234
J.-P. Collin et al.
(a)
6.0
4.0
ia [A]
e
d
c
8.40E–06
Slow pirouetting
2.40E–06
b
a
E [V] versus SCE
2.0
ꢂ0.5 ꢂ0.3 ꢂ0.1
0.1
0.3
0.5
0.7
0.9
1.1
3.60E–06
0.0
ia [A]
(b)
5.30E–06
OsIII/II
Fast pirouetting
1.30E–06
ꢂ2.0
ꢂ0.1
0.1
0.3
0.5
0.7
0.9
1.1
E [V] versus SCE
E [V] versus SCE
0.7 0.9 1.1
ꢂ0.5 ꢂ0.3 ꢂ0.1
0.1
0.3
0.5
Fig. 7. Cyclic voltammograms response of a gold bead electrode
(CH2Cl2/CH3CN (9:1) with 0.1 M Bu4NPF6) after dipping (30 min) in a
solution of 8+4 (10−3 M). The scan rates are a: 100, b: 200, c: 400, d: 600,
e: 800 mV s−1 respectively.
ꢂ2.70E–06
Fig. 6. Cyclic voltammograms of complexes 8+4 (a) and 94+ (b) recorded
on a Pt working electrode in CH2Cl2/CH3CN (1:9) with 0.1 M Bu4NPF6
at 200 mV s−1. The redox couple OsIII/II corresponds to the complex
Os(tterpy)2(PF6)2 (tterpy = 4ꢀ-p-tolyl-2,2ꢀ,6ꢀ,2ꢀ-terpyridine) used as internal
reference (E OsIII/II = 0.9V versus SCE in this electrolyte).
One part of the redox signal can be assigned to the species in
solution and the other part to a species confined at the surface of
the platinum electrode. This hypothesis is corroborated by CV
experiments with a carefully rinsed platinum electrode soaked
in pure electrolyte, which still displays the characteristic redox
observed, corresponding to a reversible redox process. By con-
trast, if the pirouetting motion is faster than the potential sweep
rate, the return wave corresponding to the reduction of the four-
coordinate Cu(ii) complex is not observed anymore. Instead, it is
replaced by another wave corresponding to the reduction of the
rearranged complex at a much lower potential (around −0.2V).
Complexes 8+4 and 9+4 showed a noticeable difference of elec-
trochemical behaviour especially at potential scan rate higher
than 200 mV s−1 (Fig. 6). Complex 8+4 shows an oxidation peak
at 0.72V as expected for oxidation processes and corresponds
couple 824+/+
.
Thesurfaceattachmentofcomplex 8+4 isalsoreadilyobtained
by dipping a gold bead electrode into a CH2Cl2 solution of 84+
for a period of a few minutes to hours. The electrode is then
rinsed carefully with CH2Cl2.The CV voltammograms obtained
with this electrode in a pure electrolyte at various scan rates are
represented on Fig. 7. For the 824+/+ redox couple, the inten-
sity of the anodic peak current increases linearly with the sweep
rate as expected for a surface-anchored redox species. However,
the various conditions (scan rates, potential ranges, continuous
polarization before scanning) used with this type of electrode
do not permit to observe any new redox wave and therefore any
molecular rearrangement inside the adsorbed copper rotaxane
species. This behaviour can be related to the structure of the
adsorbed layer. A high compactness can slow down or freeze all
large molecular motions. This should be especially true in an
amorphous and thick layer of copper pseudorotaxane. In fact,
it seems to be the case because an approximate calculation by
integration of current-voltage curves corresponds to four layers
deposited on the gold electrode surface. We tried to circumvent
this feature by adsorbing compound 9+4 in which the thioether
functions should lead to the deposition of a monolayer. Further-
more, the presence of a biisoquinoline ligand in the thread is
expected to allow fast rearrangement in solution.
Fig. 8 shows the characteristic CV curves, recorded at various
potential sweep rates, after deposition of 9+4 on a gold elec-
trode. In the phosphate buffer solution (pH 7.4) a reversible
electron transfer at 0.15V versus saturated calomel reference
electrode (SCE) can be assigned to the redox couple 924+/+. As
displayed on the inset of Fig. 8, the linear correlation between
the anodic potential peak and the scan rate demonstrates the
grafting of 9+4 on the gold surface. Unfortunately, as already
observed in the case of 84+ no other redox couples can be
to the formation of the four-coordinate Cu(ii) complex 842+
.
This redox couple obtained at 200 mV s−1 is probably due both
to 8+4 in solution and of the same species already fixed on
the platinum surface (vide infra). We essentially observe the
reduction of complex 824+ to 84+. Complex 9+4 also shows an
oxidation peak (at 0.50V), but the corresponding return wave
is only weakly detected signifying that the pirouetting motion
is faster than the potential sweep rate. Instead, a peak located
at −0.26V (corresponding to the reduction of the rearranged
5-coordinate complex 925+) is observed. At slow potential sweep
rate (50 mV s−1), the pirouetting motion is faster than the
potential sweep rate for both complexes, and the reduction of
the rearranged complexes 825+ or 952+ at negative potential is
observed (not shown).
As expected, the rate of the pirouetting motion for the ster-
ically hindered 8+4 is nearly 10 times slower than for its less
encumbered parent 9+4 as shown by CV experiments at vari-
ous scan rates. However, the electrochemical behaviour of 84+
seems also to indicate a slower motion than an analogous copper
complex rotaxane based on a 6,6ꢀ-dianisyl-2,2ꢀ-bipyridine.[31]
This latter copper rotaxane[31] and 8+4 differ in particular by the
nature of the end-groups attached to the threads. The thioctic
end-groups are known to have a very strong affinity for gold
surfaces, but they are also able to bind to platinum surfaces.[57]

RESEARCH FRONT
Synthesis, Electrochemical Studies, and Deposition on Gold Electrodes
1235
0.2
0.1
Ipa [µA]
40–63 µm). Nuclear Magnetic Resonance (NMR) spectra were
acquired on Bruker AVANCE 300 spectrometer. The 13C NMR
spectra were proton-decoupled. The spectra were referenced
to residual proton-solvent signals (1H: CD2Cl2 at 5.32 ppm,
CDCl3 at 7.25 ppm, d6-DMSO at 2.54 ppm; 13C: CD2Cl2 at
54.0 ppm, CDCl3 at 77.23 ppm). Mass spectra were obtained
by using a Bruker MicroTOF spectrometer (ES-MS). Matrix-
assisted laser desorpton–ionization analyses were performed
on an Autoflex II TOF/TOF Bruker Daltronics spectrometer.
Electrochemical measurements were performed with a three-
electrode system consisting of platinum working electrode, a
platinum wire counter electrode, and a silver wire as a pseudo-
reference electrode. All measurements were carried out at room
temperature under argon, in degassed spectroscopic grade sol-
vents, using 0.1 M n-Bu4NBF4 solutions in CH2Cl2/CH3CN
(1:9) as supporting electrolyte. A platinum disk electrode (2 mm
diameter) was used for CV experiments of the [2]rotaxanes
in solution. The gold bead working electrodes were made by
annealing the tip of a gold wire (99.999%, 0.5 mm diameter)
in a gas oxygen flame. After being cooled, the gold bead+was
immersed in a 10−3 mol L−1 solution of the [2]rotaxanes 84 or
825+ in CH2Cl2/CH3CN for times varying from 10 min to 18 h.
The electrode was then washed with pure CH2Cl2. An EG&G
PrincetonApplied Research model 273A potentiostat connected
to a computer was used. For compound 9+4 , the experimental
conditions were as follows: the Au/9+4 modified electrode was
prepared by assembling the clean Au-electrode (0.5 mm dia-
meter Au wire, geometrical area ∼0.29 cm2) in the solutions
of 9+4 (1.6 mg in 200 µL of DMF) for 24 h. Then, the modified
electrode was cleaned by washing with ethanol three times. A
conventional three-electrode cell, consisting of the modified Au
working electrode, a glassy carbon auxiliary electrode isolated
by a glass frit, and a SCE connected to the working volume
with a Luggin capillary, were used for the electrochemical mea-
surements. The pH 7.4 phosphate buffer (0.1 M) solution was
used as the electrolyte. All potentials are reported with respect
to the SCE. Argon bubbling was used to remove oxygen from
the solutions in the electrochemical cell. Cyclic voltammetry
was performed using anAutolab electrochemical analyzer (ECO
Chemie, Netherlands).
v [mV sꢂ1
]
1.0
0.5
0
50
100 150 200
0.0
ꢂ0.5
ꢂ1.0
ꢂ0.1
0.0
0.1
0.2
0.3
0.4
E [V] versus SCE
Fig. 8. Cyclic voltammograms (CV) of the gold-deposited 9+4 electrode
in the pH 7.4 phosphate buffer solution (0.1 M) at different scan rate: 10, 20,
50, 100, 200 mV s−1 (from inside to outside). Inset: the linear relationship
between the anodic peak current (Ipa) and the scan rate [mV s−1] recorded
from the CV of gold-deposited 9+4 electrode.
detected at negative potential. It seems that in the conditions used
in this type of experiments no rearrangement, implying large
amplitude motions, can be possible inside the layer of deposited
copper[2]pseudorotaxanes.
In conclusion, although several examples of surface-confined
molecular systems have been shown by other research groups
to behave as molecular machines, because they could be set
in motion by electrochemical signals, the copper-based cate-
nanes and rotaxanes elaborated and investigated in our team do
not seem to undergo large amplitude molecular motions once
attached onto an electrode surface. In contrast, these catenanes
and rotaxanes, as well as the two new rotaxanes presented in this
study can easily be set in motion in solution by using redox sig-
nals. Once again, we could confirm that steric hindrance plays
a determining role and that, in order for the systems to undergo
fast movements, the central copper atom has to be as accessi-
ble as possible so as to facilitate ligand substitution reactions.
As far as the surface-confined species are concerned, the steric
shielding ensured by the gold surface itself and by the deposited
layer is likely to have a similar detrimental effect on the rate of
the hypothetical rearrangement reactions as bulky substituents
around the copper atom for solution species. In the future, it
will be important to graft the compounds on the electrode sur-
face while making sure that the central metal can still be easily
accessed by potential ligands, thus facilitating ring motions.
Starting Materials
All chemicals were of the best commercially available grade
and used without further purification (except when mentioned).
Compounds 1,[54] 4,[55] 5,[31] and 7[24] were prepared according
to the literature procedures.
Compound 2
6,6ꢀ-Diphenol-2,2ꢀ-bipyridine 1 (150 mg, 0.44 mmol) was dis-
solved in degassed DMF (20 mL), Cs2CO3 (500 mg, 2.6 mmol)
was added and the resulting mixture was stirred at 60◦C
for 30 min. 2-(2-Bromoethoxy)tetrahydro-2H-pyran (500 mg,
2.4 mmol) was then added and the reaction was stirred overnight.
After evaporation of the solvent, the crude product was dissolved
in dichloromethane and the organic phase was washed with
water, dried over Na2SO4, filtered, and evaporated. The crude
material was then washed with pentane, and then dissolved in
ethanol (30 mL).This solution was heated under reflux overnight
in presence of a catalytic amount of HCl (3 drops).After cooling,
the solvent was removed under reduced pressure to afford a yel-
low solid, which was then taken with a mixture of EtOH/CH2Cl2
(1:10) and washed with aqueous NaHCO3 (10%, 10 mL) and
Experimental
General Methods
Dry solvents were distilled from suitable drying agents (CH3CN
from CaH2, CH2Cl2 from P2O5). TLC was carried out using
pre-coated polymeric sheets of silica gel (Macheray-Nagel,
POLYGRAM, SIL G/UV254). Preparative column chromato-
graphy was carried out using silica gel (Merck Kieselgel, silica
gel 60, 0.063–0.200 µm). Flash column chromatography was
carried out using silica gel (Merck Geduran, silica gel 60,

RESEARCH FRONT
1236
J.-P. Collin et al.
water. It was then concentrated under vacuum leading to the
precipitation of 2 which was filtered off (159 mg, 84%) Found:
C 68.88, H 5.49, N 6.00; C26H24N2O4·H2O requires C 69.94, H
5.87, N 6.27%. 1H NMR (300 MHz, d6-DMSO) δ 8.46 (2H, d,
J 7.0), 8.21 (4H, d, J 8.8), 8.01 (4H, m), 7.09 (4H, d, J 8.8), 4.92
(2H, m), 4.08 (4H, t, J 4.8). 13C NMR (75 MHz, d6-DMSO) δ
160.2, 155.6, 155.4, 155.1, 138.7, 137.6, 131.3, 128.4, 120.0,
115.1, 70.1, 60.0.
t, J 4.6), 6.70–3.50 (8H, m), 3.3–3.0 (8H, m), 2.40–2.20 (8H,
m), 1.87 (2H, m), 1.70–1.40 (20H, m). m/z (HR-MS) calc. for
C87H83N7O8CuS4 [M]+ 1544.45; found 1544.43.
Compound 825+
To a degassed solution of ligand 3 (11.9 mg, 0.014 mmol)
and macrocycle 7 (10 mg, 0.014 mmol) in a mixture of
dichloromethane and acetonitrile was added a stoichiometric
quantity of Cu(BF4)2. Upon addition of the copper salt, a green
colour appeared progressively.The resulting solution was stirred
overnight at room temperature and concentrated under vacuum
to afford 25 mg (95% yield) of a green solid. m/z (ES) calc. for
C87H83N7O8CuS4 [M]+ 1544.45; found 1544.44.
Compound 3
To a suspension of compound 2 (100 mg, 0.23 mmol) in dry
and degassed DMF (20 mL) was added thioctic acid (272 mg,
1.32 mmol).After 30 min of stirring, DMAP (32 mg, 0.26 mmol)
and DCC (364 mg, 3.1 mmol) were added. The mixture was
stirred for 24 h at room temperature and the solution became
limpid. DMF was removed under vacuum, and the crude mix-
ture was taken with dichloromethane (10 mL). The organic layer
was washed with water and dried over Na2SO4. The crude prod-
uct was purified over silica gel chromatography (CH2Cl2/MeOH
4%) affording 3 as a white solid in 53% yield (100 mg) Found:
C 58.76, H 5.92, N 3.12; C42H48N2O4·2H2O requires C 59.97,
H 6.23, N 3.33%. 1H NMR (300 MHz, CDCl3) δ 8.54 (2H, dd, J
0.8, 7.8), 8.12 (4H, d, J 11.7), 7.88 (2H, t, J 7.8), 7.72 (2H, d, J
7.8), 7.05 (2H, d, J 11.7), 4.48 (4H, t, J 4.3), 3.53 (2H, m), 3.11
(4H, m), 2.44–2.37 (6H, m), 1.70 (2H, m), 1.65–1.46 (16H, m).
13C NMR (75 MHz, d6-DMSO) δ 173.2, 159.5, 155.7, 155.7,
137.5, 132.3, 128.1, 119.4, 118.7, 114.6, 66.1, 62.5, 56.4, 54.1,
40.2, 38.5, 34.5, 33.9, 28.6, 24.6.
Compound 9+4
A degassed solution of macrocycle 7 (20 mg, 0.0295 mmol) in
CH2Cl2 was added to a degassed solution of Cu(CH3CN)4·PF6
(11 mg, 0.0295 mmol) in CH3CN. The mixture was stirred at
room temperature for 15 min. A degassed solution of compound
6 (24.8 mg, 0.0295 mmol) in CH2Cl2 was added. The resulting
deep red solution was stirred at room temperature for 4 h, and
the solvents are evaporated to dryness, giving 51 mg of a red
powder in a quantitative yield. 1H NMR (300 MHz, CD2Cl2) δ
8.88 (2H, d, J 8.0), 8.67 (2H, br. s), 8.61 (2H, s), 8.57 (2H, d, J
8.4), 8.49 (2H, d, J 7.9), 8.35 (2H, s), 8.09 (1H, t, J 7.9), 8.05
(2H, s), 8.00 (2H, d, J 8.4), 7.76 (4H, m), 7.59 (2H, dd, J 7.9,
1.9), 7.53–7.47 (6H, m), 7.10 (4H, d, J 8.6), 6.81 (4H, d, J 8.8),
6.12 (4H, d, J 8.8), 3.90 (4H, t, J 6.4), 3.34 (4H, t, J 6.2), 2.89
(4H, m), 2.49 (8H, m), 2.04 (4H, m), 1.72 (4H, m), 1.58–1.28
(28H, m), 0.88 (6H, m). m/z (ES) calc. for C99H103N7O4S2Cu+
[M]+ 1580.68; found 1580.67.
Compound 6
To a solution of compound 5 (120 mg, 0.272 mmol) in dry DMF
(20 mL) was added Cs2CO3 (266 mg, 0.816 mmol) under argon.
The resulting suspension was stirred at 50◦C for 1 h. A solu-
tion of 1-bromo-6-(hexylthio)hexane 4 (230 mg, 0.816 mol) in
CH2Cl2 (4 mL) was added and the mixture allowed to stir at
45◦C for 24 h. The solvents were then removed and the crude
compound was redissolved in CH2Cl2 (30 mL) and washed with
water (50 mL). The aqueous phase was further washed with in
CH2Cl2 (3 × 20 mL). The combined organic phases were dried
with Na2SO4, filtered and evaporated to dryness. The crude
product was subjected to a silica gel chromatography using
CH2Cl2/MeOH (0 to 4%) as the eluent to afford compound 6
(126 mg) in 55% yield.
Acknowledgement
We thank the CNRS and the EC STREP FET-open MOLDYNLOGIC for
financial support.
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