Synthesis of a Copper [3]Rotaxane Able To Function as an Electrochemically Driven Oscillatory Machine in Solution, and To Form SAMs on a Metal Surface

Article abstract of DOI:10.1021/ic0347034

Two new copper [3]rotaxanes have been synthesized. The axes are identical for both compounds and incorporate two bidentate chelates joined together by a disulfide bridge. The rings contain either the single phen (phen = 1,10-phenanthroline) chelate or two different chelates (phen and terpy; terpy = 2,2′,6′,2″-terpyridine, a tridentate chelate). The key intermediates for both synthetic routes are semi-rotaxanes obtained in high yields using the three-dimensional effect of copper(I). In the case where the wheels are heterobischelating macrocycles, large molecular motions, namely rotation or oscillation of the wheels around the axle, have been induced electrochemically. Anchoring of these two copper [3]rotaxanes on a gold electrode was carried out by standard procedures. Cleavage of the disulfide bridge and formation of monolayers of rotaxanes were evidenced by cyclic voltammetry. The adsorbed rotaxanes can be viewed as copper [2]rotaxanes for which the gold electrode surface acts as a stopper linked to one end of their axes.

Full text of DOI:10.1021/ic0347034

Inorg. Chem. 2003, 42, 6780−6792
Synthesis of a Copper [3]Rotaxane Able To Function as an
Electrochemically Driven Oscillatory Machine in Solution, and To Form
SAMs on a Metal Surface
Noe´mie Weber, Christine Hamann, Jean-Marc Kern,* and Jean-Pierre Sauvage*
Laboratoire de Chimie Organo-Mine´rale, UMR 7513 du CNRS, UniVersite´ Louis Pasteur,
Faculte´ de Chimie, 4, rue Blaise Pascal, 67070 Strasbourg Cedex, France
Received June 20, 2003
Two new copper [3]rotaxanes have been synthesized. The axes are identical for both compounds and incorporate
two bidentate chelates joined together by a disulfide bridge. The rings contain either the single phen (phen )
1,10-phenanthroline) chelate or two different chelates (phen and terpy; terpy ) 2,2′,6′,2′′-terpyridine, a tridentate
chelate). The key intermediates for both synthetic routes are semi-rotaxanes obtained in high yields using the
three-dimensional effect of copper(I). In the case where the wheels are heterobischelating macrocycles, large
molecular motions, namely rotation or oscillation of the wheels around the axle, have been induced electrochemically.
Anchoring of these two copper [3]rotaxanes on a gold electrode was carried out by standard procedures. Cleavage
of the disulfide bridge and formation of monolayers of rotaxanes were evidenced by cyclic voltammetry. The adsorbed
rotaxanes can be viewed as copper [2]rotaxanes for which the gold electrode surface acts as a stopper linked to
one end of their axes.
Introduction
be shifted from a given position to another one, thus closing
or opening the switch. Other spectacular examples can be
found in refs 1-3, including non-catenane nor rotaxane-type
organic compounds whose behavior is reminiscent of rotary
motors.3 These primitive rotary motors can be set in motion
either using a photonic signal5 or a chemical stimulus.6
The special feature of assemblies containing interlocked
(catenanes) or threaded (rotaxanes) rings originates from the
topological properties of their components: The mechanical
links between the elements prevents their dissociation. As a
consequence, they can undergo large amplitude but nonde-
structive motions in a precisely controlled fashion, and they
are ideal candidates for use as molecular machines.7,8 In this
field of artificial molecular machines, our group has devoted
special attention to copper-complexed catenanes and rotax-
anes. Intramolecular motions of a given component of these
assemblies could be triggered by varying the redox state of
The field of molecular machines and motors has experi-
enced a spectacular development in the course of the past
decade.1-3 Particularly significant are the results recently
published by Stoddart, Heath, and their co-workers on
molecule-based switches.4 These devices incorporate mono-
layers of rotaxanes or catenanes for which the ring(s) can
* To whom correspondence should be addressed. E-mail: sauvage@
chimie.u-strasbg.fr.
(1) Special issue: Acc. Chem. Res. 2001, 34 (6).
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Switches; Feringa, B. L., Ed.; Wiley-VCH: Weinheim, 2001.
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1994, 369, 133-137. (b) Zelikovich, L.; Libman, J.; Shanzer, A.
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M. J.; Reid, R. J. Macromolecules 1999, 32, 5982-5984 (g) Armarolli,
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J. Am. Chem. Soc. 1999, 121, 4397-4408.
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Mattersteig, G.; Wong, E. W.; Luo, Y.; Berverly, K.; Sampaio, J.;
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6780 Inorganic Chemistry, Vol. 42, No. 21, 2003
10.1021/ic0347034 CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/18/2003

Copper [3]Rotaxane Functioning as a Machine
Scheme 1. Schematic Representation of a SAM of Rotaxanes by Adsorption of a [3]Rotaxane on a Gold Surfacea
a In the immobilized rotaxanes, one of the end of the axis is connected to gold atoms, which acts as a blocking group, preventing dethreading of the
wheel. The second blocking group (grey circle) is a purely organic bulky moiety.
the metal. Indeed, the stereoelectronic requirements of this
metal depend strongly on its oxidation state: Cu(I) is
normally low-coordinate whereas Cu(II) is better stabilized
by penta- or hexacoordination. By reducing or oxidizing the
copper center from a situation corresponding to a stable
complex, the system is set out of equilibrium. The relaxation
process of the compound implies a significant amplitude
motion which will bring the system back to its new
equilibrium position. Gliding motion of one ring around
another in the case of catenanes9 and translation10 or
oscillation11 of a ring around a molecular thread have been
studied. The assembling of switchable systems into two- or
three-dimensional arrays should represent noticeable progress
in the field of information storage or processing at the
molecular level. Various approaches are possible. The use
of switchable ionic catenanes enabled the formation of
Langmuir films at an air-water interface.12 Using a different
technique, the threading or dethreading of pseudorotaxanes
trapped in a rigid matrix or tethered onto a silica film could
be performed.13 One promising method for confining an
active species onto a gold surface is by the formation of a
Au-S bond,14 following the strategy used successfully by
several groups to make functional SAMs (self-assembled
monolayers).15 More recently, we focused our attention on
monolayers of multicomponent systems organized on a metal
surface. Efficient adsorption of pseudo [2]rotaxanes and [2]-
catenanes was observed.16 Through adsorption onto a gold
electrode, immobilized catenanes are formed in which the
gold atoms of the surface are an integral fragment of one of
the rings of the catenane.
We would now like to report our efforts to make two-
dimensional arrays of multicomponent molecular systems,
consisting of rotaxane-like architectures anchored to a gold
surface. The wheel of these rotaxanes is either a mono-
chelating or a heterobischelating macrocycle. The axis is a
coordinating molecular thread, bearing an ancillary bulky
group at one end. The other end is anchored to a gold surface
which plays simultaneously the role of a stopper for the
rotaxane and of an input-output device between the surface-
confined machine and the external source of stimuli.
These monolayers of immobilized copper [2]rotaxanes
were obtained by adsorption of copper [3]rotaxanes (Scheme
1). The synthesis of two different copper [3]rotaxanes will
be described as well as the “machine” behavior in solution
of one of these architectures, and the first evidence of the
formation of SAMs of rotaxanes onto a gold surface.
Results and Discussion
Design and Synthesis. Obviously, the shortest way to keep
rotaxanes on a surface would be to adsorb a pseudo-rotaxane
assembly in which the axis is linked at one end to a
voluminous and chemically inert group and the other end to
a thiol functionality. However, due to the pronounced
reducing character of this function, the Cu center must be
kept reduced (i.e., Cu(I)) until the thiolate is immobilized
on the Au surface. Indeed, the corresponding copper(II)
rotaxanes are strong oxidants and are not compatible with
the presence of thiol functionalities.17 In addition, ligand
exchange processes around the metal can occur in the course
of the adsorption process of such pseudo-rotaxanes. To
overcome these difficulties, the synthesis of two different
[3]rotaxanes was undertaken. The schematic and the molec-
ular representations of these assemblies appear in Scheme 2
and in Figure 1, respectively.
(9) Livoreil, A.; Dietrich-Buchecker, C.; Sauvage, J.-P. J. Am. Chem. Soc.
1994, 116, 9399-9400.
(10) Collin, J.-P.; Gavin˜a, P.; Sauvage, J.-P. New J. Chem. 1997, 21, 525-
528.
(11) Raehm, L.; Kern, J.-M.; Sauvage, J.-P. Chem. Eur. J. 1999, 5, 3310-
3317.
(12) Asakawa, M.; Higuchi, M.; Mattersteig, G.; Nakamura, T.; Pease, A.
R.; Raymo, F. M.; Shimizu, T.; Stoddart, J. F. AdV. Mater. 2000, 12,
1099-1102.
(13) Chia, S.; Cao, J. Stoddart, J. F.; Zink, J. I. Angew. Chem. 2001, 112,
2513-2517; Angew. Chem., Int. Ed. 2001, 40, 2447-2451.
(14) (a) Lu, T.; Zhang, L.; Gokel, G. W.; Kaifer, A. E. J. Am. Chem. Soc.
1993, 115, 2542-2543. (b) Rojas, M. T.; Kaifer, A. E. J. Am. Chem.
Soc. 1995, 117, 5883-5884.
The axes are identical for both rotaxanes and are composed
each of two identical coordinating subunits connected to one
another through a disulfide bridge. The coordinating cores
are 1,10-phenanthroline moieties in which the R-positions
of the nitrogen atoms are substituted with phenyl groups.
Indeed, it was shown that low oxidation states of dpp-based
complexes are strongly stabilized.17,18 This is particularly true
(15) Ulman, A. Chem. ReV. 1996, 96, 1533-1554 and references therein.
(16) (a) Kern, J.-M.; Raehm, L.; Sauvage, J.-P. C. R. Acad. Sci., Ser. IIc:
Chim. 1999, 41-47. (b) Raehm, L.; Hamann, C.; Kern, J.-M.; Sauvage,
J.-P. Org. Lett. 2000, 14, 1991-1994. (c) Raehm, L.; Kern, J.-M.;
Sauvage, J.-P.; Hamann, C.; Palacin, S.; Bourgoin, J.-P. Chem. Eur.
J. 2002, 8, 2153-2162.
(17) The redox potential of CuII/I bis(2,9-diaryl)1,10-phenanthrolines is
located around 0.6 V vs SCE: (a) Federlin, P.; Kern, J.-M.; Rastegar,
A.; Dietrich-Buchecker, C.; Marnot, P. A.; Sauvage, J.-P. New J. Chem.
1990, 14, 9-12. (b) Balzani, V. In Electron Transfer in Chemistry;
Balzani, V., Ed.; Wiley-VCH: Weinheim, 2001; Vol 3, p 582-650.
Inorganic Chemistry, Vol. 42, No. 21, 2003 6781

Weber et al.
Scheme 2. Schematic Representation of Copper [3]Rotaxanes A and
one. The two units are joined through two C3 chains which
are linked to the 5,5′′-positions of the terpyridine on one
side and to the oxygen atoms of the 2,9-bis(4-oxyphenyl)-
1,10-phenanthroline on the other side. In both [3]rotaxanes,
the axle and the wheels are connected together through the
coordinated copper ions. More precisely, in [3]rotaxane A
(Scheme 2), the metal centers, whatever their oxidation state,
are tetracoordinated, the thread and the wheels providing each
a bidentate site to each metal. The situation is different for
[3]rotaxane B (Scheme 2): the wheels provide a bidentate
or a terdentate site each, and consequently, the coordination
number N of the metal centers is either 4 or 5. Cu(I) is most
of the time low-coordinate (N e 4) whereas Cu(II) is
preferably square planar or higher coordinate (N ) 5 or 6).
Scheme 2 represents rotaxane B in these two different
situations: B5 corresponds to the situation in which the two
metal centers (Cu(II)) are pentacoordinated, and B4 corre-
sponds to the situation in which the metals (Cu(I)) are
tetracoordinated. Thus, varying the oxidation state of the
metal can lead to a large rearrangement of the surrounding
ligands. By using this phenomenon, the gliding of a ring
within another one in the case of catenanes, the translation
of a ring along a molecular thread or the oscillation of a
ring around a thread in the case of rotaxanes, could be
triggered and monitored.9-11 Presently, we would like to
describe the synthesis, the electrochemical behavior of these
[3]rotaxanes in solution, and the first results on our attempts
to prepare rotaxane-like monolayers at a gold surface.
The main sequences leading to the two copper [3]rotaxanes
described here are represented in Scheme 3. A molecular
thread was prepared at first (Scheme 3a) which consists of
a dpp-type ligand connected to a bulky ancillary group at
one extremity and to a stable thiol precursor functionality at
the other one. During the second step (Scheme 3b,c), two
different semi-rotaxanes are formed by threading this seg-
ment through either a mono- or a bischelating macrocycle.
Ba
a The axes of A and B are identical. They incorporate two bidentate
ligands, each. In A, the wheels are monochelating macrocycles, each. In
B, the wheels of the rotaxane incorporate a bidentate and a terdentate site,
each. Consequently, the metal centers can be either tetracoordinated,
situation B4, or pentacoordinated, situation B5. The black circle represents
Cu(I), and the white circle represents Cu(II).
for copper complexes. A hexamethylene chain joins together
the coordinating 2,9-bis(p-phenoxy)-1,10-phenanthroline moi-
eties and the disulfide bridge. The two end groups of the
thread, that is, the stoppers of the [3]rotaxanes, are tetraaryl-
methane derivatives. In order to increase the size of the
stoppers and to lower solubility problems, lipophilic groups
(tert-butyl fragments) were introduced on the para positions
of three of the aryl groups. The stoppers and the coordinating
sites are linked through bis-ethoxy-ether spacers. Two
monochelating or two bisheterochelating macrocycles form
the wheels of [3]rotaxanes A and B (Scheme 2), respectively.
The monochelating ring (Figure 1) contains one coordinating
site, a dpp (dpp ) 2,9-diphenyl-1,10-phenanthroline), whose
end positions are connected through a pentaethyleneglycol
chain. The bis-heterochelating ring (Figure 1) contains two
different coordinating sites: a terpyridine moiety and a dpp
a
Scheme 3. Principle of the Synthesis of Rotaxanes A (Cu2122+) and B (Cu2152+
)
a Steps of the syntheses are the following: (a) formation of a monostoppered axis, bearing a precursor of a thiol functionality at one end, (b) threading
of the axis through the wheel, hydrolysis of the thioacetate, and oxidative dimerization [this strategy was used to synthesize A (Cu2122+)], or (c) hydrolysis
of the thioacetate group occurred, threading of the resulting axis through the wheel (i) followed by oxidative dimerization (ii). This strategy was used to
synthesize B4 (Cu2152+). The black circle represents Cu(I); the large gray circle represents the blocking group linked to the end of the axis.
6782 Inorganic Chemistry, Vol. 42, No. 21, 2003

Copper [3]Rotaxane Functioning as a Machine
Figure 1. Representation of the copper-complexed [3]rotaxanes Cu2122+ and Cu2152+, and of their precursors. 13 is the precursor of the axis of both
rotaxanes. Macrocycles 11 and 14 are the wheels of rotaxanes Cu2122+ and Cu2152+, respectively. Ring 11 includes a dpp unit as coordinating site. Ring 14
includes both a bidentate (dpp) and a tridentate (terpy) coordinating site.
Inorganic Chemistry, Vol. 42, No. 21, 2003 6783

Weber et al.
Figure 2. Synthetic route leading from 1,10-phenanthroline to the molecular thread 10. (a) Disymmetrization of the phenanthroline by substituting positions
2 and 9 with two different protected functionalities. (b) Desilylation of the phenoxy functionality and subsequent grafting of the bulky tetraaryl methane
derivative. (c) Introduction of a thiol precursor at the end position of the thread.
These threading operations were done before (Scheme 3b)
or after (Scheme 3c) hydrolysis of the thiol precursor. Finally,
clipping of each semi-rotaxane with itself by using a mild
oxidative reagent led to the two expected [3]rotaxanes.19
Their molecular representation, as well as that of the various
synthetic intermediates, is given in Figure 1. The synthetic
route leading to the functionalized monostoppered segment
is described in Figure 2.
Heterobifunctionalization of 1,10-phenanthroline (Scheme
3a and Figure 2a) was made in two steps: the controlled
addition of the lithio-derivative of silylated p-bromophenol
1 on 1,10-phenanthroline led, after hydrolysis and oxidation
of the adduct, to the monosubstituted phenanthroline 2.
Addition in a similar manner of the lithio derivative of 3 on
2 led to the 2,9-diaryl-phenanthroline 4 in which the two
para positions of the phenyl groups bear two different,
protected, functionalities. The overall yield, based on 1,10-
phenanthroline, is 74%. By desilylating 4 and reacting the
resulting phenol 5 with the stopper 6, one could obtain the
monostoppered thread 7 in an overall yield of 77%, based
on 4 (Figure 2b). Figure 2c represents the three-step sequence
which leads from 7 to compound 10, in which the air stable
SCOCH3 functionality is linked to the coordinating moiety
via a hexamethylene spacer. This was done by hydrolysis
of the tetrahydropyranyl ether 7, esterification of the resulting
alcohol 8 into 9, which was subsequently transformed into
10 by treatment with potassium thioacetate. At this stage,
the routes leading to the two [3]rotaxanes became different
(Scheme 3 and Figure 3). Semi-rotaxane Cu(10.11)+ was
prepared in the following manner (11 is a 30-membered
monochelating macrocycle, represented Figure 1): Cu(CH3-
CN)4BF4 was added to a solution of 11 in CH2Cl2/CH3CN.
The resulting orange solution was then treated with 10 to
give a dark-red solution of hemi-rotaxane Cu(10.11)+. The
almost quantitative yield of this threading reaction originates
from the exceptional stability of Cu(I)-bis(dpp)-derivative
complexes.20 Semi-rotaxane Cu(10.11)+ was refluxed in air
with a catalytic amount of HBF4. Copper(I) [3]rotaxane
Cu212(BF4)2 was isolated in 50% yield after purification by
1
chromatography. H NMR spectra of Cu2(12)2+ and semi-
rotaxane Cu(10.11)+ are quite similar, with a noticeable
exception for the signals H6′ in R position of the sulfur
atoms, for which a shielding of ∆δ ) 0.13 ppm is observed
when going from the H6′ protons in Cu(10.11)+ to the
corresponding protons in Cu2122+. Entwining of the dpp
moieties around the metal center was clearly observed by
(18) Dietrich-Buchecker, C.; Kern, J.-M.; Sauvage, J.-P. J. Am. Chem. Soc.
1989, 111, 7791-7800.
(19) An analogous molecular riVeting reaction was described recently by
Bush and al.: Kolchinski, A. G.; Alcock, N. W.; Roesner, R. A.; Bush,
D. H. Chem. Commun. 1998, 1437-1438.
(20) Arnaud-Neu, F.; Marques, E.; Schwing-Weill, M.-J.; Dietrich-
Buchecker, C. O.; Sauvage, J.-P.; Weiss, J. New J. Chem. 1988, 12,
15-20.
6784 Inorganic Chemistry, Vol. 42, No. 21, 2003

Copper [3]Rotaxane Functioning as a Machine
Figure 3. Representation of the threading and riveting reactions which are the key steps of the synthesis of [3]rotaxanes Cu2122+ and Cu2152+. Cu2122+
:
ring 11 is threaded on the linear fragment 10 before the hydrolysis of the thioacetate functionality and riveting of the resulting semi-rotaxane Cu(10.11)+.
Cu2152+: The hydrolysis of the linear fragment 10 is performed before its threading through ring 14. Riveting of the resulting semi-rotaxane Cu(13.14)+ is
done by stirring a dichloromethane solution of Cu(13.14)+ in air. The black circle represents Cu(I).
1H NMR. The meta protons Hm, Hm′, and Hm′′ (Figure 1)
of the three nonequivalent phenoxy moieties in Cu2122+
resonate at a significantly higher field than the corresponding
protons in the free macrocycle 11 and in 7 (Figure 4). For
instance, a shielding of ∆δ ) 0.11 ppm is observed from
the meta protons Hm” of the free ring 11 to the corresponding
protons in Cu122+. In the thread 10, the external (Hm′) and
internal (Hm) meta protons are nonequivalent. A similar shift,
∆δ ) 1.04 ppm, is observed for these protons after threading
of 10 through macrocycle 11, i.e., when going from 10 to
Cu(10.11)+ and to Cu2122+. The ratio of the relative
intensities of the signals corresponding to the meta protons
of the linear fragment, i.e., Hm and Hm′, to the meta protons
Hm′′ of the macrocycle is in accordance with the expected
value.
- 11 - Cu - 2BF4)+, 1684.0 (M - 2BF4)2+/2, 629.3 (11 +
Cu)+. Noteworthy are the peaks at m/z ) 2738.5 and 2172.2
corresponding to the loss of one and of both threaded
macrocycles 11, respectively.
The route leading to [3]rotaxane Cu2152+ is slightly
different from that leading to Cu2122+. Threading of the
heterobischelating macrocycle 14 onto 10 occurred as
efficiently as for macrocycle 11, but hydrolysis of the
resulting semi-rotaxane Cu(10.14)+ is accompanied by the
dethreading of the ring. To overcome this difficulty, the free
compound 10 was hydrolyzed in a strictly oxygen free
atmosphere. The resulting thiol-functionalized linear fragment
13 was not further stored but was immediately threaded
through macrocycle 14, following the same procedure as
described. The resulting semi-rotaxane Cu(13.14)+, in solu-
tion in CH3CN/CH2Cl2, was stirred for 2 h in air. Treatment
of the crude reaction product allowed us to isolate pure
copper [3]rotaxane Cu215(BF4)2 in 52% yield. 1H NMR and
FAB-MS spectroscopy confirmed the structure of Cu2122+-
-
(BF4 )2. Intense peaks (Figure 5) are observed at m/z )
3455.9 (M - BF4)+, 3369.2 (M - 2BF4 + 1e)+, 2738.5 (M
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Weber et al.
similar behavior (Figure 6a represents the anodic scan of
the CV, and Figure 2a in Supporting Information is the
complete CV): the two metal centers are tetracoordinated,
and their redox potential is localized at 0.62 V versus SCE
(∆Ep ) 80 mV). The ratio of the intensities of the anodic
and cathodic peaks is close to 1 and shows that no
transformation or reorganization of the coordination sphere
of the tetracoordinate Cu(II) centers occurs in the time scale
of the measurements (potential sweep rate: 100 mV s-1)
despite the presence of the terpy moiety in the wheels of
the rotaxane. But by changing drastically the time scale of
the experiment, substitution of the dpp sites of the wheels
by the terpy-sites in the copper(II) [3]rotaxane occurred. This
was performed by doing an exhaustive anodic oxidation of
Cu2152+ in CH2Cl2/CH3CN at a platinum electrode polarized
at 0.8 V versus SCE. The red color of the copper(I) rotaxane
disappeared, and the solution became green. The cyclic
voltammetry behavior of the resulting Cu(II) rotaxane
Cu2154+ is totally different from that of Cu2122+. The
potential sweep for the measurement was started at +0.9 V,
a potential at which no electron transfer should occur,
regardless of the nature of the surrounding of the Cu(II)
center (penta- or tetracoordination). An irreversible peak is
observed at -0.1 V and is assigned to the reduction of the
pentacoordinated complex (Figure 6b represents the cathodic
scan of the CV, and Figure 2b in Supporting Information is
the complete CV). The irreversibility of this peak means that
the pentacoordinated Cu(I) species formed in the diffusion
layer, when sweeping cathodically the electrode potential,
is transformed very rapidly into a new species, electrochemi-
cally silent in this cathodic potential range. Moreover, the
appearance of an anodic peak at 0.64 V suggests that the
transient species formed by reduction of Cu2154+ has
undergone a complete reorganization which leads to a
tetracoordinated copper(I) rotaxane.
Figure 4. Upfield shifts of the protons ortho and meta of the different
dpp units in [3]rotaxane Cu2122+ : representation of the 1HNM spectra of
thread 10 (spectrum a), macrocycle 11 (spectrum b), and copper-complexed
[3]rotaxane Cu2122+. Peaks labeled o, m and o′, m′ refer to ortho and meta
protons of, respectively, the internal and external phenyl groups of the thread
(labeling of the protons appears in Figures 1-3). Peaks labeled o′′ and m′′
refer respectively to ortho and meta protons of the ring. The nonequivalence
of protons m, m′, and m′′ as well as that of protons o, o′, and o′′ appears
distinctly on spectrum c.
This cyclic voltammetric experiment done after exhaustive
anodic oxidation of Cu2152+ shows that in the time scale of
the electrolysis (around 15 min) the rotation of the two
wheels around the axle is complete. These motions allow
the relaxation of the electrogenerated Cu(II)-complexed [3]-
rotaxane, by leading from a situation in which Cu(II) is only
tetracoordinated to a more stable situation in which each
Cu(II) is coordinated to five nitrogen atoms. Conversely, the
irreversibility (at 100 mV s-1) of the reduction peak of
Cu2154+, where the two metal centers are pentacoordinated,
shows that here again, although very rapidly, the system
relaxes by a new rotation of the rings to offer a tetracoor-
dination to the Cu(II) centers. Moreover, by changing the
time scale of the CV experiments, i.e. by increasing the
potential sweep rate, the system becomes progressively
reversible, as expected for the case where an electron transfer
is followed by an irreversible chemical reaction. This was
confirmed by the data analysis of the I/E (current/potential)
responses, following the method described by Nicholson and
Shain,21 and already used for the determination of the
spinning motion of a ring around an axle in a [2]rotaxane.
FAB-MS spectra are analogous to those of Cu2122+ and in
full accordance with the expected structure of Cu2152+.
Moreover, 1H NMR spectroscopy shows clearly that the dpp
moieties of the rings 14 are entwined around the metal
centers. As macrocycle 14 allows the metal to be either tetra-
or pentacoordinate, this observation underlines the preference
of CuI for tetracoordination.
Electrochemical Behavior of the Copper-Complexed [3]-
Rotaxanes Cu2122+ and Cu2152+. Observation of the
Spinning of the Wheels around the Axle in [3]Rotaxane
Cu2152+. The thermodynamics of Cu(dpp-based)2 and
Cu(dpp-terpy-based) complexes is well-known.17 The CuII/I
redox potential is relatively high for the former (0.6-0.7 V
vs SCE), that is, for tetracoordinated copper, and markedly
more cathodic for the second family of complexes (0 to -0.5
V vs SCE), that is, for pentacoordinated copper. The behavior
of Cu2122+ is characteristic of assemblies incorporating
Cu(dpp)2 moieties: in CH2Cl2/CH3CN, a reversible signal is
observed at 0.68 V versus SCE, and no electronic coupling
between the two redox centers can be detected (Figure 1 in
Supporting Information). [3]Rotaxane Cu2152+ displays a
(21) Nicholson, R. S.; Shain, I. Anal. Chem. 1964, 36, 706-723.
6786 Inorganic Chemistry, Vol. 42, No. 21, 2003

Copper [3]Rotaxane Functioning as a Machine
Figure 5. FAB-MS spectrum of [3]rotaxane Cu2122+. The stepwise fragmentation and subsequently loss of the two wheels is obvious and characterized
by the peaks ([M - 11 - Cu - 2BF4]+, m/z ) 2738.5) and ([M - 2(11) - Cu - 2BF4]+, m/z ) 2172.2). Fragmentation of the axis leads to [11 + Cu]+,
(m/z ) 629.3).
going from the [2]rotaxane11 to the [3]rotaxane, Cu2152+.
Indeed, a half-life time value of 0.056 s was determined for
the pentacoordinated copper(I) in the [2]rotaxane,11 the
corresponding values for the [3]rotaxane (Cu2152+)5 being
0.7 s (4 and 5 refer to the coordination number of the metal).
The spinning rate around tetracoordinated Cu(II) in (Cu2154+)4
has the same order of magnitude as that observed for the
[2]rotaxane,11 i.e., a half-life time t1/2 of minutes. Unfortu-
nately, due to adsorption of the substrate on the working
electrode, a more accurate value for t1/2 of (Cu2154+)4 could
Figure 6. Voltammetry curves recorded using a Pt working electrode at
a 100 mV s-1 potential sweep rate (CH3CN/CH2Cl2 (4:1), Bu4NBF4 0.1
not be obtained.
mol L-1). A Hg/HgSO4 electrode was used as reference electrode. (a) Cu-
(I)-complexed [3]rotaxane Cu2152+. Anodic potential sweep. The metal
Monolayers of Rotaxanes. Deposition onto a Gold
Surface. In the preliminary attempts described here to
prepare surface confined rotaxanes, Cu2122+ and Cu2152+
were deposited onto gold surfaces, and the adsorption
processes were followed by cyclic voltammetry. Gold bead
electrodes were dipped over 2 and 5 h into dichloromethane
solutions of Cu2122+ and Cu2152+, respectively. After the
adsorption time, the gold beads were thoroughly rinsed with
dichloromethane, dipped into dichloromethane containing
only Bu4NBF4 as supporting electrolyte, and used as working
electrodes. Figure 7 depicts the characteristic curves, recorded
at different potential sweep rates, after dipping gold bead
electrodes in solutions of Cu2122+ (Figure 7a) and Cu2152+
(Figure 7b). The presence of a reversible electron transfer
in each case is obvious, and the half-wave potential values
(E1/2 ) 0.56 V for Cu2122+, E1/2 ) 0.58 V for Cu2152+) attest
to the presence on the working electrodes of the Cu-bisdiaryl
phenanthroline moieties in each case. The ∆Ep values (∆Ep
is the difference in potential between the oxidation and
centers are tetracoordinated. (b) Cu(II)-complexed [3]rotaxane Cu2154+
.
Cathodic potential sweep. Cu2152+ was obtained by anodic oxidation of
Cu2152+. The voltammogramm was recorded immediately after the
electrolysis. The cathodic peak at -0.41 V corresponds to the reduction of
the pentacoordinated metal centers.
An average value of 1.0 ( 0.3 s-1 was found for the spinning
rate constant k. Thus, in the experimental conditions, i.e.,
acetonitrile/dichloromethane (4/1), Bu4NBF4 10-1 mol L-1,
the half-life time of the bis-pentacoordinated bis-CuI [3]-
rotaxane is 700 ( 200 ms. The overall process is represented
in Figure 6. In the system described in this work, the
reorganization rates of the ligand set around the metal centers
remain high by comparison with those observed in a
catenane9 or in a rotaxane where the axle is a hetero-
bischelating molecular thread and the wheel a monochelating
macrocycle.10 Nevertheless, comparison with the structurally
analogous copper complexed [2]rotaxane synthesized and
studied in previous work11 shows that the spinning rates
around pentacoordinated Cu(I) significantly decrease when
Inorganic Chemistry, Vol. 42, No. 21, 2003 6787

Weber et al.
and
Cu2152+ + Au f 2(Cu17+)4(ads)
The molecular-machine-like behavior of [3]rotaxane Cu2152+
was discussed in the previous section. The fast gliding of
the rings around pentacoordinated CuI and the significantly
slower motion around tetracoordinated CuII were demon-
strated. The CV curves represented in Figure 7b show that,
when going from the rotaxane in solution to the surface
confined species, the oxidation process, i.e, (Cu17+)4(ads)
f (Cu172+)4(ads), remains reversible. Any modification of
the cathodic branch of the CV curve was observed even when
the electrode potential was polarized at a positive value (0.8
V) for a certain period of time, and no well-defined reduction
peak localized around -0.1 V appeared. This seems to
indicate that, as for the molecular [3]rotaxane in solution,
the spinning of the wheel around CuII is too slow to be
detected on the time scale of the CV measurement. Con-
versely, adsorption onto gold of (Cu215)4+ whose metal
5
centers are pentacoordinated (vide supra) led only to unstable
adsorbates, whose responses to electrochemical inputs are
not reproducible. It is noteworthy that the same difficulty
was encountered in previous works in efforts to anchor CuII
catenanes on gold. Work is in progress to understand this
phenomenon and to overcome these difficulties.
Conclusion
The synthesis of two copper [3]rotaxanes is described. In
each case, the axle of the assembly includes two 2,9-diaryl-
1,10-phenanthroline sites connected together by a disulfide
bridge. The wheels of these rotaxanes are either two identical
monochelating macrocycles or two identical heterobischelat-
ing macrocycles. The synthetic routes are very similar. The
two key steps are the formation of a semi-rotaxane, based
on the template effect of CuI, followed by its oxidative
coupling. A molecular machine behavior was observed in
solution for the [3]rotaxane in which the wheels incorporate
a terdentate site as well as a bidentate one. By varying the
redox state of the coordinated metal centers, reversible
spinning of the rings around the axis could be observed,
although the spin rates around CuI and CuII are markedly
different. Adsorption experiments demonstrated the possibil-
ity of preparing layers of electroactive rotaxanes onto a gold
surface. The metal electrode acts simultaneously as a stopper
and as an input-output gate for the redox processes.
Combined STM-electrochemical studies are in progress in
order to trigger and subsequently to visualize rotation of the
ring around the axis in surface confined molecular machines.
Figure 7. Cyclic voltammetry responses of a gold bead electrode (CH2-
Cl2, 10-1 mol L-1 Bu4NBF4) after being dipped in CH2Cl2 solutions (10-3
mol L-1) of rotaxanes Cu2122+ (a) and Cu2152+ (b) and rinsed. Potential
sweep rates: (1) 50 mV s-1, (2) 100 mV s-1, (3) 200 mV s-1, (4) 200 mV
s-1, and (5) 400 mV s-1. Increasing of the oxidation current peak with the
potential sweep rate is represented in the two inserts in parts a and b.
reduction peaks) are less than 60 mV for each adsorbed
species (20 mV for Cu2122+ and 30 mV for Cu2152+ at 100
mV s-1 in each case). The intensity of the anodic and
cathodic peaks increases linearly with the potential sweep
rate, for both adsorbed species as represented in the inserts
of Figure 7. All these observations are in accordance with
the presence of immobilized electroactive species at the gold
surface.
The adsorbed layers resist several redox scans (after 60
scans, a decrease of only 20% of the electroactivity of
adsorbed Cu2152+ observed, for example). This stability is
consistent with an Au-S bond formation along with the
adsorption process. The disulfide bridges in Cu2122+ and in
Cu2152+ are likely to be cleaved14b,15 leading to two Au-S
bonds in each case. Consequently, one can assume that the
copper [3]rotaxanes Cu2122+ and Cu2152+ are converted,
respectively, to copper [2]rotaxanes Cu16+(ads) and
(Cu17+)4(ads), one stopper remaining a tetraaryl moiety, and
the gold atoms of the adsorbate’s host forming the second
stopper (Scheme 1 and Figure 8):
Experimental Section
General Methods. Oxygen- or water-sensitive reactions were
conducted under a positive pressure of argon in oven-dried
glassware, using Schlenk techniques. Column chromatography was
carried out on silica gel 60 (E. Merck, 70-230 mesh) or on
aluminum oxide 90 standardized (E. Merck). 1H NMR spectra were
obtained on either a Brucker WP 200 SY (200 MHz) or an AM
Cu2122+ + Au f 2Cu16+(ads)
6788 Inorganic Chemistry, Vol. 42, No. 21, 2003

Copper [3]Rotaxane Functioning as a Machine
Figure 8. Schematic representation of the adsorption process leading from the true copper-complexed [3]rotaxanes Cu2122+ (a) and Cu2152+ (b) in solution
to the surface confined [2]rotaxanes Cu16+(ads) and Cu17+4(ads), respectively. The gold atoms of the host metal act as a stopper for the immobilized
copper-complexed [2]rotaxanes.
Inorganic Chemistry, Vol. 42, No. 21, 2003 6789

Weber et al.
3
400 (400 MHz) spectrometer. NMR chemical shifts δ are expressed
in ppm relative to internal solvent peaks. Labels of the protons of
semi-rotaxane Cu(10.11)+ and Cu(13.14)+, of [3]rotaxanes Cu2122+
and Cu2152+, and of their precursors are provided in Figures 1-3.
Fast atom bombardment mass spectrometry (FAB MS) data were
recorded in the positive ion mode with a xenon primary atom beam
in conjunction with a 3-nitrobenzyl alcohol matrix and a ZAB-HF
mass spectrometer. A VG BIOQ triple quadrupole spectrometer
was used for the electrospray mass spectrometry measurements (ES-
MS) also in the positive ion mode. Electrochemical experiments
were carried out using a EGG Princeton 273 A model potentiostat
equipped with an X-Y recorder (Research Electrochemistry Soft-
ware). All experiments were run at room temperature. A standard
three-electrode cell was used. For the measurements performed on
the rotaxanes in solution, the potentials were determined either with
a mercury sulfate reference electrode or with a Ag wire pseudo-
reference electrode and referenced to SCE using ferrocene as
internal reference. For the measurements performed on the gold
adsorbates, the potentials are only referenced to the Ag wire
pseudoreference electrode. Tetrabutylammonium tetrafluoroborate
(0.1 mol L-1) in an acetonitrile/dichloromethane 4/1 mixture was
used as supporting electrolyte. A platinum disk electrode (2 mm
diameter) was used for CV experiments of the [3]rotaxanes in
solution. The gold bead working electrodes were made by annealing
the tip of a gold wire (99.9985%, 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 [3]rotaxanes Cu2122+ or Cu2152+
in CH2Cl2 for times varying from 10 min to 18 h. The electrode
was then washed with pure CH2Cl2. A platinum wire (0.6 mm
diameter, 52 cm long) was used as working electrode for electrolysis
at controlled potential.
2H: Hm), 1.4-1.2 (m, 3H: Hc), 1.16 (d, J ) 6.4 Hz, 18H: Hd).
MS (FAB-MS): found m/z ) 429.2 [M + H]+, calcd 429.65.
Compound 3. 1-(6-Bromohexyl)-2-(2-tetrahydro-2H-pyranyl)
ether (1.64 g, 9.5 mmol) and p-bromophenol (2.47 g, 9.3 mmol)
were dissolved in DMF (100 mL) under argon. Potassium carbonate
(6.57 g, 47.5 mmol) was added, and the solution was heated at 60
°C for 18 h. DMF was then removed, and the residue was taken
up into H2O/CH2Cl2. Extraction with CH2Cl2 and drying over Na2-
SO4 left, after the solvent was removed, a crude which was purified
by chromatography (SiO2, eluent: CH2Cl2) to afford 3 (881 mg,
1
2.47 mmol) in 26% yield. NMR H (CDCl3, 200 MHz): 7.31 (d,
3J ) 8.9 Hz, 2H: Hm), 6.62 (d, 3J ) 8.9 Hz, 2H: Ho), 4.53 (m, 3J
) 2.9 Hz, 1H: HR), 3.87 (t, J ) 6.4 Hz, 2H: H1), 3.67 (t, J )
6.2 Hz, 2H: H6), 3.60 (m, 2H: Hꢀ), 2.06-1.21 (m, 14H:
3
3
H
2,3,4,5,δ,â,ø).
Difunctionalized Phenanthroline 4. Compound 3 (2.14 g, 6.01
mmol) in degassed anhydrous THF (80 mL) was cooled at -60
°C under argon. tBuLi (1.7 mol L-1 in pentane, 7.5 mL, 12.0 mmol)
was added dropwise to this solution. The solution, initially colorless,
turned yellow. After the reaction mixture had been stirred for 3 h
at -60 °C, the temperature was allowed to rise to room temperature
for few minutes and brought down to -5 °C. This solution was
then added to a degassed solution of 2 (1.7 g, 3.97 mmol) in
anhydrous THF (80 mL), at room temperature. After stirring 15 h,
the red solution was hydrolyzed with 1.5 mL of water and then
turned orange. The reaction mixture was concentrated and extracted
3 times with CH2Cl2. The combined organic layers were rearoma-
tized with MnO2 under strong magnetic stirring, dried over MgSO4,
and filtered off on a sintered glass. The crude material was purified
by column chromatography (SiO2, CH2Cl2/0.1% MeOH) to give a
brown oil in 86% yield (2.4 g, 3.41 mmol). NMR 1H (CDCl3, 200
MHz): 8.40 (m, 4H: Ho,o′), 8.26 (d, 3J ) 8.3 Hz, 2H: H4,7), 8.08
(d, 3J ) 8.3 Hz, 2H: H3,8), 7.74 (s, 2H: H5,6), 7.10 (m, 4H: Hm,m′),
Synthesis. Common reagents and materials were purchased from
commercial sources. The following materials were prepared ac-
cording to literature procedures: 1,22 6,23 11,24 14,25 Cu(CH3-
CN)4BF4.18
3
4.60 (m, 1H: HR), 4.09 (t, J ) 6.4 Hz, 2H: H1′), 3.95-3.38 (m,
3
4H: H6′,ꢀ), 1.92-1.20 (m, 17H: H2′,3′,4′,5′,â,ø,δ,c), 1.15 (d, J ) 6.4
Hz 18H: Hd). MS (FAB-MS): found m/z ) 705.4 [M]+, calcd
705.03.
Monofunctionalized Phenanthroline 2. Compound 1 (5.49 g,
16.7 mmol) was dissolved in degassed anhydrous THF (200 mL)
and cooled at -60 °C under argon. tBuLi (1.7 mol L-1 in pentane,
19.7 mL, 33.4 mmol) was added dropwise to this solution. The
temperature should not get over -55 °C. The solution, initially
colorless, turned yellow. After the reaction mixture has been stirred
for 1 h at -60 °C, the temperature was allowed to rise to room
temperature for a few minutes and brought down to 7 °C. This
solution was then added to a degassed suspension of 1,10-
phenanthroline (2.02 g, 11.2 mmol) in anhydrous THF (200 mL)
kept between 5 and 7 °C. After stirring 4 h at 7 °C, the red solution
was brought down to 0 °C and hydrolyzed with 1 mL of water.
The reaction mixture was concentrated and extracted 3 times with
CH2Cl2. The combined organic layers were thereafter rearomatized
with MnO2 under strong magnetic stirring, dried over MgSO4, and
filtered off on a sintered glass. The filtrate was evaporated to
dryness. The crude product was purified by column chromatography
(SiO2, CH2Cl2) to give a brown oil in 86% yield (4.14 g, 9.6 mmol).
NMR 1H (CDCl3, 200 MHz): 9.25 (dd, 3J ) 4.4 Hz, 4J ) 1.7 Hz,
Compound 5. nBu4NF‚3H2O (0,37 g, 1.17 mmol) in 20 mL THF
was added to a solution of 4 (0.676 g, 0.96 mmol) in THF (80
mL). The solution turned to orange and was stirred for 1.5 h. The
THF was removed and the residue taken up into CH2Cl2. The
organic layer was thoroughly washed with a buffer solution (pH
7), and then with pure water. After drying over Na2SO4 and
removing of the solvent, an orange powder was recovered whose
purity was good enough (>95% by NMR) to be used without
1
3
purification. NMR H (CDCl3, 200 MHz): 8.37 (d, J ) 8.8 Hz,
3
2H: Ho), 8.25 (m, 4H: H4,7,o′), 8.03 (d, J ) 8.8 Hz, 2H: H3),
7.73 (s, 2H, H5,6), 7.07 (d, 3J ) 8.8 Hz, 2H: Hm), 7.96 (d, 3J ) 8.6
3
Hz, 2H: Hm′), 4.62 (m, 1H: HR), 4.05 (t, J ) 6.4 Hz, 2H: H1′),
3.95-3.38 (m, 4H: H6′,ꢀ), 1.86-1.42 (m, 14H: H2′,3′,4′,5′,â,ø,δ). MS
(FAB-MS): found m/z ) 549.2 [M + H]+, calcd 549.69.
Monostoppered Thread 7. A mixture of 6 (1.93 g, 2.59 mmol)
and 5 (1.23 g, 2.25 mmol) in 250 mL of degassed DMF was
introduced under argon to a 1 L round-bottom flask containing Cs2-
CO3 (3.9 g, 1.19 mmol) in suspension in 180 mL of degassed DMF.
The vessel was heated at 60 °C for 18 h. The solvent was removed
and the residue taken up into CH2Cl2/H2O. The organic layers were
combined and dried over Na2SO4, and after the solvent was
removed, the resulting brown solid was chromatographed (SiO2,
eluent CH2Cl2/1% MeOH) to give pure 7 in 82% yield. NMR H
(CDCl3, 200 MHz): 8.36 (m, 4H: Ho,o′), 8.30 (m, 2H: H4,7), 8.10
(m, 2H: H3,8), 7.78 (s, 2H: H5,6), 7.29-7.09 (m, 18H: Hm,m′,a,b,d),
6.81 (d, J ) 9.1 Hz, 2H: Hc), 4.56 (m, 1H: HR′), 4.27 (m, 2H:
3
1H: H9), 8.29-8.23 (m, 4H: Ho,4,7), 8.06 (d, J ) 8.6 Hz, 1H:
H3), 7.81 (d, 3J ) 8.6 Hz, 1H: H5), 7.75 (d, 3J ) 8.6 Hz, 1H: H6),
7.64 (dd, 3J ) 8.1 Hz, 3J ) 4.4 Hz, 1H: H8), 7.05 (d, 3J ) 8.6 Hz,
(22) Liptak, V. P.; Wulff, W. D. Tetrahedron 2000, 56, 10229-10248.
(23) Gibson, H. W.; Lee, S.-H.; Engen, P. T.; Lecavalier, P.; Sze, J.; Shen,
Y. X.; Bheda, M. J. Org. Chem. 1993, 58, 3748-3756.
(24) Dietrich-Buchecker, C.; Sauvage, J.-P. Tetrahedron 1990, 46, 503-
512.
(25) Livoreil, A.; Sauvage, J.-P.; Armaroli, N.; Balzani, V.; Flamigni, L.;
Venturi, B. J. Am. Chem. Soc. 1997, 119, 12114-12124.
1
3
6790 Inorganic Chemistry, Vol. 42, No. 21, 2003

Copper [3]Rotaxane Functioning as a Machine
H1′), 4.18-3.33 (m, 12H:
2′,3′,4′,5′,â′,ø′,δ′), 1.26 (s, 27H, -CH3). MS (FAB-MS): found m/z
) 1123.6 [M]+, calcd 1123.6.
H
6′,ꢀ′,R,â,ø,δ), 1.80-1.50 (m, 14H:
3J ) 8.3 Hz, 2H: H3′′), 7.47 (d, 3J ) 8.7 Hz, 2H: Ho), 7.43 (d, 3J
3
H
) 8.7 Hz, 2H: Ho′), 7.29-7.09 (m, 18H: Ho′′,a,d,b), 6.82 (d, J )
8.8 Hz, 2H: Hc), 6.05 (m, 4H: Hm,m′), 5.96 (d, 4H, Hm′′, 3J ) 8.6
Hz), 4.15 (m, 2H: Hδ), 3.91-3.45 (m, 28H: Hγ,R′,â,â′,R,γ′,δ′,1′,ꢀ′), 2.87
Alcohol 8. Compound 7 (2.06 g, 1.83 mmol) was dissolved in
CHCl3 (20 mL) in a 100 mL round-bottom flask equipped with a
condenser. EtOH (40 mL) was added, and the solution was heated
at 80 °C. Concentrated HCl (1 drop) was then added, and the
mixture was refluxed for 3 h. The solvents were removed in a
vacuum, and the residue was taken up into H2O/CH2Cl2. The
organic layer was washed with an aqueous saturated solution of
K2CO3 and then with pure H2O. Drying over Na2SO4 left, after the
solvent was removed, a white powder whose purity was good
enough (>95% by NMR) to be used without purification. NMR
1H (CDCl3, 200 MHz): 8.38 (m, 4H: Ho,o′), 8.27 (m, 2H: H4,7),
3
(t, J ) 7.3 Hz, 2H: H6′), 2.29 (s, 3H: -CH3 (thioester)), 1.51-
0.80 (m, 8H: H2′,3′,4′,5′), 1.26 (s, 27H: -CH3). MS (FAB-MS):
found m/z ) 1726.6 [Cu(10.11)]+, calcd 1725.70; 1159.4 [Cu(10)]+,
calcd 1761.06; 629.1 [Cu(11)]+, calcd 628.18.
Copper(I) Double Rotaxane Cu212(BF4)2. To a solution of Cu-
(10.11)BF4 (27 mg, 0.015 mmol) in THF (10 mL) was added 15
mL of MeOH and a few grids of DMAP. HBF4 (34%, 1 drop) was
then added, and the mixture was heated to 60 °C for 5 days. The
solvent was removed and the residue taken up into CH2Cl2/H2O.
The organic layers were combined and dried over Na2SO4, and after
the solvent was removed, the resulting dark red crude material was
chromatographed (Al2O3, eluent CH2Cl2/MeOH 2%) to give
Cu212(BF4)2 in 53% yield.
8.08 (m, 2H:
H
H3,8), 7.75 (s, 2H: H5,6); 7.26-7.07 (m, 18H:
m,m′,a,b,d), 6.79 (d, 3J ) 8.8 Hz 2H: Hc), 4.25 (m, 2H: H1′), 3.61-
3.15 (m, 10H: H6′,R,â,ø,δ), 1.84-1.50 (m, 8H: H2′,3′,4′,5′), 1.27 (s,
27H: -CH3). MS (FAB-MS): found m/z ) 1039.5 [M]+, calcd
1039.4.
1
3
NMR H (CD2Cl2, 200 MHz): 8.61 (d, J ) 8.6 Hz, 4H: H4),
3
3
8.60 (d, J ) 8.6 Hz, 4H: H7), 8.44 (d, J ) 8.3 Hz, 4H: H4′′),
8.22 (s, 4H: H5,6), 8.00 (s, 4H: H5′′), 7.86 (m, 4H: H3,8), 7.81 (d,
Mesylate 9. Compound 8 (1.24 g, 1.195 mmol) and triethylamine
(1.99 mL, 14.3 mmol) were dissolved in dry CH2Cl2 (35 mL) under
argon. The mixture was then cooled to -5 °C. Mesyl chloride (0.55
mL, 7.17 mmol) in CH2Cl2 (20 mL) was added over 30 min, and
the reaction mixture was then stirred for 5 h at -5 °C and 14 h at
room temperature. The solution was extracted with H2O/CH2Cl2
and dried over Na2SO4. The solvents were removed, and the brown
crude product was chromatographed (SiO2, eluent: CH2Cl2/0.2%
3
3
3J ) 8.3 Hz 4H: H3′′), 7.49 (d, J ) 8.3 Hz, 4H: Ho), 7.44 (d, J
3
) 8.5 Hz 4H: Ho′), 7.27-7.07 (m, 36H: Ho′′,a,d,b), 6.83 (d, J )
3
8.5 Hz, 4H: Hc), 6.06 (m, 8H: Hm,m′), 5.97 (d, J ) 8.6 Hz, 8H:
Hm′′), 4.18 (m, 4H: Hδ), 3.90-3.42 (m, 56H: Hγ,R′,â,â′,R,γ′,δ′,1′,ꢀ′),
2.74 (t, 3J ) 7.2 Hz, 4H: H6′), 1.60-0.83 (m, 16H: H2′,3′,4′,5′), 1.25
(s, 54H: -CH3). MS (FAB-MS): found m/z ) 3455.9 ([M - BF4]+,
calcd. 3456.0); m/z ) 1684.0 ([M - 2BF4]2+, calcd. 1684.4).
Thiol 13. Compound 10 (117.3 mg, 0.11 mmol) was dissolved
in THF (15 mL) in a 50 mL round-bottom flask. Methanol (15
mL) and HCl 37% (3 mL) were added, and the mixture was stirred
under argon at 60 °C for 6 days. The reaction was monitored by
1H NMR. The mixture was brought to room temperature, and 20
mL of a buffer solution at pH 7 was then added. The solvents were
removed, and the residue was taken up in CH2Cl2/H2O. Extraction
with CH2Cl2 and drying over Na2SO4 left, after the solvent was
removed, a yellow solid whose purity was >95% (by NMR) and
which was immediately used to do the threading step (see following
1
MeOH) to afford 9 (1.23 g, 1.10 mmol) in 92% yield. NMR H
(CDCl3, 200 MHz): 8.32 (m, 4H: Ho,o′), 8.21 (m, 2H: H4,7), 8.03
(m, 2H: H3,8), 7.69 (s, 2H: H5,6), 7.20-7.01 (m, 18H: Hm,m′,a,b,d),
3
6.72 (d, J ) 8.8 Hz, 2H: Hc), 4.18-3.81 (m, 12H: H1′,6′,R,â,ø,δ),
2.89 (s, 3H, -mesyl), 2.00-1.50 (m, 8H: H2′,3′,4′,5′), 1.32 (s, 27H:
-CH3). MS (FAB-MS): found m/z ) 1117.5 [M]+, calcd
1117.51.
Thioacetate 10. A solution containing a mixture of 9 (0.189 g,
0.169 mmol) and potassium thioacetate (25.5 mg, 0.223 mmol)
dissolved in DMF (60 mL) was heated to 60 °C for 15 h. The DMF
was removed and the residue taken up into CH2Cl2/H2O. The
organic layers were combined and dried over Na2SO4, and after
the solvent was removed, the resulting brown solid was chromato-
graphed (SiO2, eluent CH2Cl2/0.2% MeOH) to give pure 10 in 80%
yield. NMR 1H (CDCl3, 200 MHz): 8.41 (m, 4H: Ho,o′), 8.29 (m,
2H: H4,7),8.10 (m, 2H: H3,8), 7.78 (s, 2H: H5,6), 7.27-7.08 (m,
1
paragraph). NMR H (CD2Cl2, 300 MHz): 8.41 (m, 4H: Ho,o′),
8.30 (m, 2H: H4,7), 8.10 (m, 2H: H3,8), 7.79 (s, 2H: H5,6), 7.28-
3
7.14 (m, 18H: Hm,m′,a,b,d), 6.81 (d, J ) 8.8 Hz, 2H: Hc), 4.26 (t,
3J ) 4.7 Hz, 2H: Hδ), 4.17-4.07 (m, 4H: Hâ,γ), 3.98-3.91 (m,
3
4H: HR,1′), 2.55 (q, J ) 7.6 Hz, 2H: H6′), 1.86 (m, 2H: H5′),
1.72-1.50 (m, 6H: H2′,3′,4′), 1.42 (t, 3J ) 7.8 Hz, 1H: -SH), 1.30
(s, 27H: -CH3).
3
18H: Hm,m′,a,b,d), 6.81 (d, J ) 8.8 Hz, 2H: Hc), 4.30-3.90 (m,
10H: H1′,R,â,ø,δ), 2.89 (t, 3J ) 7.1 Hz, 2H: H6′), 2.30 (s, 3H, -CH3
(thioester)), 2.00-1.50 (m, 8H: H2′,3′,4′,5′), 1.29 (s, 27H: -CH3).
MS (FAB-MS): found m/z ) 1097.5 [M]+, calcd 1097.52.
Semi-Rotaxane Cu(10.11)BF4. By the cannula transfer tech-
nique, 23.9 mg (0.075 mmol) of Cu(CH3CN)4BF4 in degassed
acetonitrile (8 mL) was added under argon and at room temperature
to a stirred degassed solution of 11 (33.7 mg, 0.059 mmol) in CH2-
Cl2 (10 mL). A deep orange coloration appeared instantly. After
15 min at room temperature, a solution of 10 (64.7 mg, 0.058 mmol)
in CH2Cl2 (15 mL) was added to the solution which immediately
turned dark red. After the solution was stirred for 2 h under argon
at room temperature, the solvents were removed under high vacuum.
A dark red powder of crude Cu(10.11)BF4 was obtained quasi-
quantitatively (NMR control) (106 mg, 0.058 mmol). Due to its
instability on alumina and on silica gel, Cu(10.11)BF4 was not
further purified and was submitted to the next step without delay.
Threaded Copper(I) Complex. Cu(13.14)BF4. By the cannula
transfer technique, 25.3 mg (0.008 mmol) of Cu(CH3CN)4BF4 in
degassed acetonitrile (8 mL) was added under argon and at room
temperature to a stirred degassed solution of 14 (49.5 mg, 0.008
mmol) in CH2Cl2 (10 mL). A deep orange coloration appeared
instantly. After 15 min at room temperature, a solution of 13 (77
mg, 0.008 mmol) in CH2Cl2 (15 mL) was added to the solution
which immediately turned dark red. After the solution was stirred
for 2 h under argon at room temperature, the solvents were removed
under high vacuum. A dark red powder of crude Cu(13.14)PF6 was
obtained quantitatively (the purity was controlled by 1H NMR) and
immediately submitted to the next reaction (see the following
text).
Copper(I) Double Rotaxane. Cu215(PF6)2. A solution of
Cu(13.14)BF4 (140 mg, 0.007 mmol) in CH2Cl2 (10 mL) was stirred
in air for 2 h. After removing the solvent and exchanging the
counterions BF4- by PF6-, the resulting dark red solid was purified
by several flash column chromatographies (Al2O3 ; eluent CH2-
Cl2/MeOH 0-2%) to give a dark red powder (68 mg, 50%). NMR
1
3
NMR H (CD2Cl2, 200 MHz): 8.61 (d, J ) 7.8 Hz, 2H: H4),
3
3
8.59 (d, J ) 7.8 Hz, 2H: H7), 8.42 (d, J ) 8.3 Hz, 2H: H4′′),
8.21 (s, 2H: H5,6), 7.98 (s, 2H: H5′′), 7.99 (m, 2H: H3,8), 7.97 (d,
Inorganic Chemistry, Vol. 42, No. 21, 2003 6791

Weber et al.
3
1H (CD2Cl2, 400 MHz): 8.75 (d, J ) 8.4 Hz, 4H: Ht3), 8.63 (d,
Acknowledgment. We are grateful to the French Ministry
of Education for a fellowship to C.H. and the CNRS and
the European Community for financial support.
3J ) 1.8 Hz, 4H: Ht6), 8.43-8.38 (m, 12H: H4′′,4,7,t3′), 8.05 (t, J
3
) 7.6 Hz, 2H: Ht4′), 7.94 (s, 4H: H5′′), 7.78 (d, 3J ) 8.3 Hz, 4H:
3
H3′′), 7.72-7.63 (m, 12H: Ht4,3,8,5,6), 7.33 (d, J ) 8.7 Hz, 8H:
Ho′′), 7.30-7.12 (m, 36H: Ho′,o,a,b,d), 6.83 (d, J ) 8.8 Hz, 4H:
Hc), 6.03-5.95 (m, 16H: Hm′,m,m′′), 4.16 (m, 4H: Hδ), 3.88 (m,
4H: Hγ), 3.77 (m, 4H: Hâ), 3.70 (m, 4H: HR), 3.53 (t, J ) 6.7
Hz, 4H, H1′), 3.21 (t, J ) 6.8 Hz, 8H: Hγ′), 2.91 (m, 8H: HR′),
2.75 (t, J ) 7.2 Hz, 4H: H6′), 2.11 (m, 8H: Hâ′), 1.75 (m, 4H:
H5′), 1.62 (m, 4H: H2′), 1.55-1.30 (m, 8H: H4′,3′), 1.27 (s, 54H:
-CH3). MS (FAB-MS): found m/z ) 3738.1 ([M - PF6]+, calcd
3736.7), m/z ) 1795.5 ([M - 2PF6]2+, calcd 1795.8).
3
Supporting Information Available: Cyclic voltammogram of
copper-complexed [3]rotaxane Cu2122+ in solution (Figure S1),
2+
3
cyclic voltammogram of copper(I)-complexed [3]rotaxane Cu215
3
(Figure S2a), and the cyclic voltammogram of copper(II)-complexed
[3]rotaxane Cu2154+ obtained by anodic oxidation of Cu2152+
(Figure S2b). This material is available free of charge via the
Internet at http://pubs.acs.org.
3
IC0347034
6792 Inorganic Chemistry, Vol. 42, No. 21, 2003