Diels-alder active-template synthesis of rotaxanes and metal-ion-switchable molecular shuttles

Article abstract of DOI:10.1021/ja101029u

A synthesis of [2]rotaxanes in which Zn(II) or Cu(II) Lewis acids catalyze a Diels-Alder cycloaddition to form the axle while simultaneously acting as the template for the assembly of the interlocked molecules is described. Coordination of the Lewis acid to a multidentate endotopic 2,6- di(methyleneoxymethyl)pyridyl- or bipyridine-containing macrocycle orients a chelated dienophile through the macrocycle cavity. Lewis acid activation of the double bond causes it to react with an incoming stoppered diene, affording the [2]rotaxane in up to 91% yield. Unusually for an active-template synthesis, the metal binding site lives on in these rotaxanes. This was exploited in the synthesis of a molecular shuttle containing two different ligating sites in which the position of the macrocycle could be switched by complexation with metal ions [Zn(II) and Pd(II)] with different preferred coordination geometries.

Full text of DOI:10.1021/ja101029u

Published on Web 03/24/2010
Diels-Alder Active-Template Synthesis of Rotaxanes and
Metal-Ion-Switchable Molecular Shuttles
James D. Crowley,† Kevin D. Ha¨nni,† David A. Leigh,*,† and
Alexandra M. Z. Slawin‡
School of Chemistry, UniVersity of Edinburgh, The King’s Buildings, West Mains Road,
Edinburgh EH9 3JJ, United Kingdom, and School of Chemistry, UniVersity of St. Andrews,
Purdie Building, St. Andrews, Fife KY16 9ST, United Kingdom
Received February 4, 2010; E-mail: David.Leigh@ed.ac.uk
Abstract: A synthesis of [2]rotaxanes in which Zn(II) or Cu(II) Lewis acids catalyze a Diels-Alder
cycloaddition to form the axle while simultaneously acting as the template for the assembly of the interlocked
molecules is described. Coordination of the Lewis acid to a multidentate endotopic 2,6-di(methyleneoxy-
methyl)pyridyl- or bipyridine-containing macrocycle orients a chelated dienophile through the macrocycle
cavity. Lewis acid activation of the double bond causes it to react with an incoming “stoppered” diene,
affording the [2]rotaxane in up to 91% yield. Unusually for an active-template synthesis, the metal binding
site “lives on” in these rotaxanes. This was exploited in the synthesis of a molecular shuttle containing two
different ligating sites in which the position of the macrocycle could be switched by complexation with
metal ions [Zn(II) and Pd(II)] with different preferred coordination geometries.
Introduction
the copper(I)-catalyzed terminal alkyne-azide cycloaddition (the
CuAAC “click” reaction),3 palladium-3d,4 and copper-catalyzed5
Active-template synthesis is a strategy for the construction
of mechanically interlocked structures in which the metal ion
acts as both a template for entwining or threading the compo-
nents and a catalyst for capturing the interlocked final product
by covalent bond formation.1,2 In doing so, the metal often
changes the strength of coordination and preferred geometry
of its ligands several times during the reaction. Despite this
complexity of mechanism, several different metal-catalyzed
reactions have already proven suitable for the active-metal-
template synthesis of both rotaxanes and catenanes, including
alkyne homocouplings and heterocouplings, and palladium-
catalyzed oxidative Heck couplings6 and Michael additions.7
However, unlike traditional “passive” metal-template methods,
permanent recognition motifs are not intrinsically required on
each of the components to be interlocked in active-template
syntheses (i.e., the assembly can be traceless). This means that
one of the most widely exploited features of rotaxane template
assembly8sthat the intercomponent recognition motif “lives on”
in the rotaxane, providing a preferred binding site for the ring
on the thread that can be exploited in “molecular shuttles”sis
not automatically present using active-template syntheses.
† University of Edinburgh.
‡ University of St Andrews.
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1995, 95, 2725–2828. (b) Ja¨ger, R.; Vo¨gtle, F. Angew. Chem., Int.
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Knots: A Journey Through the World of Molecular Topology; Sauvage,
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Berna´, J.; Crowley, J. D.; Goldup, S. M.; Ha¨nni, K. D.; Leigh, D. A.;
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9
10.1021/ja101029u  2010 American Chemical Society
J. AM. CHEM. SOC. 2010, 132, 5309–5314 5309

A R T I C L E S
Crowley et al.
Here we report on the active-template synthesis of rotaxanes
utilizing the Lewis acid-catalyzed9 Diels-Alder10 cycloaddition.
The reaction proceeds in the presence of either Zn(II) or Cu(II)
salts with weakly coordinating triflate anions, generating [2]ro-
taxanes in up to 91% yield. The active-template reaction
“selects” 2-substituted cyclopentadienes over 1-substituted cy-
clopentadienes, generating one rotaxane isomer with 90-99%
selectivity as opposed to the four isomers produced for the
noninterlocked thread. Unusually for an active-template reaction,
the template site is fully incorporated into the interlocked
product, meaning that metal-chelated molecular shuttles can
readily be prepared. This is exemplified through the synthesis
of a molecule shuttle in which the position of the macrocycle
can be switched by varying the coordination requirements of
the metal ion present [trigonal-bipyramidal Zn(II) or square-
planar Pd(II)].
Design of a Lewis Acid-Catalyzed Diels-Alder Active-Template
Reaction. A wide range of Lewis acids, most often transition-
metal salts, have been shown to efficiently catalyze Diels-Alder
cycloadditions.9 R,ꢀ-Unsaturated 2-acyl-oxazolidinones, imi-
dazolidones, and pyrazolidinones11 are particularly effective
substrates and provide a well-defined chelation geometry around
the metal center as the Lewis acid-activated double bond reacts
with the diene. Inspired by some literature systems,12 we
postulated that coordination of some simple Lewis acid metal
salts with a tridentate macrocycle should lead to a metal-ligand
geometry with two replaceable ligands protruding through
opposite faces of the macrocycle. An acryloyl imidazolidone
unit (“stoppered” at one end) that is chelated to the metal center
would generate a threaded complex in which the activated
double bond is exposed to an incoming diene. If the diene were
also stoppered at one end, Lewis acid-catalyzed cycloaddition
through the cavity would lead to a [2]rotaxane.
Figure 1. X-ray crystal structures of Lewis acid-macrocycle complexes:
(a) [1aZn]Cl2 (the two Zn(II) environments, trigonal bipyramidal and
tetrahedral, should be noted); (b) [1bZn]Cl2; (c) [1cZn]Cl2; (d) [1aCu]Cl2.
coordinated Lewis acids were potentially suitable for rotaxane
formation, even though the exchangeable ligands were not
always directed through the cavity in the solid state. Rotaxane
formation from dieneophile 2, diene 3, and complexes of
macrocycle 1a with various Lewis acids was investigated
(Scheme 1 and Table 1). A complex between macrocycle 1a
(1 equiv) and the Lewis acid (1 equiv) in CH2Cl2 was formed
in situ. Addition of acryloyl imidazolidone 2 (1 equiv) at
room temperature and diene 3 (1 equiv) at -78 °C was
following by stirring at -78 °C for 20 h and at room
temperature for a further 4 h. Initial experiments with ZnCl2
were unsuccessful (Table 1, entry 1), possibly because the
two chloride ligands may have been too strongly coordinated
to the metal. However, we were delighted to find that
switching to Zn(OTf)2 afforded [2]rotaxane 4a in 8% yield
(Table 1, entry 2). Changing the Lewis acid from zinc triflate
to copper triflate increased the yield of [2]rotaxane to 47%
(Table 1, entry 3). Increasing the amounts of 2 and 3 and
extending the reaction time (48 h at -78 °C followed by
48 h at room temperature) improved the yield of 4a to 42%
with Zn(OTf)2 and 83% with Cu(OTf)2 (Table 1, entries 4
and 5).
The proposed mechanism for rotaxane formation is shown
in Scheme 1. Replacement of the two labile ligands by the
oxygen atoms of the acryloyl imidazolidone unit affords the
threaded complex II, in which the activated double bond must
react with the “stoppered” cyclopentadiene 3 on the macro-
cycle face opposite the dieneophile stopper group. Demeta-
lation with ammonia [for Cu(II)] or Na4EDTA [for Zn(II)]
generates the metal-free rotaxane 4a. Using the same reaction
conditions as in Table 1, entry 5 but with only 30 mol %
Results and Discussion
Various pyridine-based ligands, such as pyridine-2,6-
bis(oxazoline) (pybox),13 bipyridyl,14 and bisoxazolines
(box),13,15 have been shown to efficiency catalyze Lewis acid-
promoted cycloaddition reactions. A series of X-ray crystal
structures of multidentate pyridine- and bipyridine macro-
cycles (1a, 1b, 1c) complexed to ZnCl2 or CuCl2 (Figure 1)
were obtained, and they confirmed that the geometries of the
(9) (a) Yates, P.; Eaton, P. J. Am. Chem. Soc. 1960, 82, 4436–4437. (b)
Santelli, M.; Pons, J.-M. Lewis Acids and SelectiVity in Organic
Synthesis; CRC Press: Boca Raton, FL, 1995; Chapter 6, pp 267-
283. (c) Fringuelli, F.; Piermatti, O.; Pizzo, F.; Vaccaro, L. Eur. J.
Org. Chem. 2001, 439–455. (d) Kanemasa, S.; Oderaotoshi, Y.;
Sakagushi, S.; Yamamoto, H.; Tanaka, J.; Wada, E.; Curran, D. P.
J. Am. Chem. Soc. 1998, 120, 3074–3088. (e) Ishihara, K.; Fushimi,
M.; Akakura, M. Acc. Chem. Res. 2007, 40, 1049–1055.
(10) Diels, O.; Alder, K. Liebigs Ann. Chem. 1928, 460, 98–122.
(11) Sibi, M. P.; Stanley, L. M.; Nie, X.; Venkatraman, L.; Liu, M.;
Jasperse, C. P. J. Am. Chem. Soc. 2007, 129, 395–405.
(12) (a) Seitz, M.; Stempfhuber, S.; Zabel, M.; Schu¨tz, M.; Reiser, O.
Angew. Chem., Int. Ed. 2005, 44, 242–245. (b) Lai, W.; Berry, S. M.;
Bebout, D. C. Inorg. Chem. 2006, 45, 571–581. (c) Chen, P.-K.; Che,
Y.-X.; Li, Y.-M.; Zheng, J.-M. J. Solid State Chem. 2006, 2656–2662.
(13) (a) Sibi, M. P.; Ma, Z.; Itoh, K.; Prabagaran, N.; Jasperse, C. P. Org.
Lett. 2005, 7, 2349–2352. (b) Evans, D. A.; Fandrick, K. R.; Song,
H.-J.; Scheidt, K. A.; Xu, R. J. Am. Chem. Soc. 2007, 129, 10029–
10041.
(14) Muraki, T.; Fujita, K.; Kujime, M. J. Org. Chem. 2007, 72, 7863–7870.
(15) (a) Crosignani, S.; Desimoni, G.; Faita, G.; Filippone, S.; Mortoni,
A.; Righetti, P. P.; Zema, M. Tetrahedron Lett. 1999, 40, 7007–7010.
(b) Sibi, M. P.; Chen, J. J. Am. Chem. Soc. 2001, 123, 9472–9473.
(c) Sibi, M. P.; Itoh, K.; Jasperse, C. P. J. Am. Chem. Soc. 2004, 126,
5366–5367.
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Active-Template Diels-Alder Rotaxanes
A R T I C L E S
Scheme 1. Diels-Alder Active-Metal-Template Synthesis of
[2]Rotaxane 4a from Macrocycle 1a, Dienophile 2, and Diene 3a
Figure 2. Influence of the macrocyclic ligand on the Diels-Alder active-
metal-template rotaxane formation reaction analogous to that shown in
Scheme 1 with reagents and conditions as for Table 1, entry 5. The ratio of
the 1,4- and 1,3-isomers of each rotaxane is shown in parentheses after the
rotaxane yield.
1
by H NMR spectroscopy. The energy barrier for the [1,5]-
sigmatropic shift of monosubstitued cyclopentadienes, such as
the one that converts 1-methyl-1,3-cyclopentadiene into 2-meth-
yl-1,3-cyclopentadiene,16 is only ∼28 kcal mol-1, so the two
isomers of 3 interchange many times during the reaction period
at the temperatures used for the active-template reaction.
Interestingly, when subjected to the active-template reaction
conditions, only the 2-substituted isomer of 3 was found to react
with the activated double bond protruding through the cavity
of the macrocycle, since no rotaxane with a 1,2- or 1,5-
substitution pattern for the thread was detected in the product
mixture. Furthermore, 90% of the endo adduct [2]rotaxane
formed was the 1,4-isomer 4a, with the other 10% being the
1,3-isomer 4a′(1,3) (the assignments of the isomers were
determined by ROESY experiments; see the Supporting Infor-
mation). In contrast, all four isomers of the noninterlocked thread
[5(1,4), 5′(1,3), 6(1,2), and 6′(1,5)] were formed when the
thread-forming Diels-Alder reaction was carried out with a
nonmacrocyclic ligand for the Lewis acid (Scheme 1). Thus,
the active-template reaction selects heavily for the 2-substituted
cyclopentadiene reactant and the 1,4-cycloaddition rotaxane
product.
To explore the influence of the nature of the macrocyclic
ligand on the active-metal-template cycloaddition reaction
shown in Scheme 1, we substituted 1a with the four different
macrocycles 1b-e (Figure 2). Reaction of bipyridyl macro-
cycle 1b under these conditions generated the corresponding
[2]rotaxane 4b in 91% yield in a (1,4)/(1,3) ratio of >99:1.
Substitution of the benzylic ether oxygen atoms of 1a with
the strongly coordinating sulfur atoms in 1c, which would
reduce the Lewis acidity of the metal center, or the
noncoordinating methylene groups in 1d completely inhibited
rotaxane formation. Use of 1e without the pyridine nitrogen
atom also switched off rotaxane formation. It appears that at
least one strongly coordinating pyridine group is necessary
a For reaction conditions and reagent stoichiometries, see Table 1.
Table 1. Effect of Reactant Stoichiometry and Experimental
Conditions on the Diels-Alder Active-Template Synthesis of
Rotaxane 4aa
entry
Lewis acid
equiv of 2
equiv of 3
t (h)
yield of 4a (%)d
1b
2b
3b
4c
5c
ZnCl2
1
1
1
1.2
1.2
1
1
1
2
2
24
24
24
96
96
0
8
47
42
83
Zn(OTf)2
Cu(OTf)2
Zn(OTf)2
Cu(OTf)2
a Reactions were carried out using anhydrous CH2Cl2 and 9 mM 1a
under a nitrogen atmosphere (see the Experimental Section). b Reaction
conducted at -78 °C for 20 h followed by RT for 4 h. c Reaction
conducted at -78 °C for 48 h followed by RT for 48 h. d Calculated
with respect to 1a.
copper triflate reduced the yield of [2]rotaxane 4a to 37%,
suggesting that the rotaxane sequesters the metal ion,
preventing turnover of the active template to any significant
extent during the reaction.
Diene Isomer Selection during the Active-Template
Reaction. The cyclopentadiene derivative 3 used to form the
thread exists as an ∼55:45 mixture of the 1- and 2-substituted
isomers (3′ and 3, respectively) at 298 and 258 K, as determined
(16) Wang, Q.; Zhang, Y.; Rogers, W. J.; Mannan, M. S. J. Hazard. Mater.
2009, 165, 141–147.
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A R T I C L E S
Crowley et al.
Figure 3. 1H NMR spectra (400 MHz, CDCl3, 328 K) of (a) macrocycle 1a, (b) [2]rotaxane 4a:4a′ (9:1), and (c) noninterlocked threads 5 and 6 (61:39).
The assignments of 1a, 4a, 5, and 6 correspond to the lettering shown in Scheme 1. In (b), the resonances of minor rotaxane isomer 4a′ are not assigned to
specific protons. In (c), the resonances of the noninterlocked thread are, for the most part, not assigned to specific isomers.
to bind the Lewis acid within the macrocyclic cavity and
that the additional weakly ligating donor atoms are needed
to hold the chelated alkene in the orientation necessary for
the active-template cycloaddition.
typical of interlocked architectures in which the aromatic rings
of one component are positioned face-on to another component,
occurred for all of the aliphatic nonstopper resonances of the
axle (Hf-h, Hq-s, Hi, and Hj), indicating that the macrocycle
1H NMR Spectroscopy of [2]Rotaxane 4a:4a′. The 1H NMR
spectrum of [2]rotaxane 4a (and the minor isomer 4a′) in CDCl3
at 328 K shows an upfield shift of several signals with respect
to the noninterlocked components (Figure 3). The shielding,
Scheme 3. Determination of the Macrocycle Position by the Metal
Coordination Geometry in Molecular Shuttle 8a:8a′a
Scheme 2. Assembly of Molecular Shuttle 8a:8a′ from the
Diels-Alder Active-Metal-Template Reaction of Macrocycle 1a,
Dienophile 7, and Diene 3a
a (a) Macrocycle position upon coordination to Zn(II): [8a:
8a′Zn2]L2(OTf)4. (b) Metal-free rotaxane 8a:8a′. (c) Macrocycle position
upon coordination to Pd(II): [8a:8a′Pd]Cl2.
a Reagents and conditions: 1a (1 equiv), Cu(OTf)2 (1 equiv), 7 (1.2
equiv), 3 (2 equiv), CH2Cl2, -78 °C for 48 h followed by RT for 48 h.
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5312 J. AM. CHEM. SOC. VOL. 132, NO. 14, 2010

Active-Template Diels-Alder Rotaxanes
A R T I C L E S
Figure 4. 1H NMR spectra (400 MHz, 298 K, 9:1 CD2Cl2/CD3CN) of (a) threads 9 and 10 (68:32), (b) [2]rotaxane 8a:8a′ (95:5), (c) [2]rotaxane-Zn(II)
complex [8aZn2]L2(OTf)4, and (d) [2]rotaxane-Pd(II) complex [8aPd]Cl2. The assignments correspond to the lettering shown in Scheme 3.
spends more time over the less hindered parts of the thread in
the metal-free rotaxane, avoiding the bulky norbornene unit.
Coordination Control of the Macrocycle Position in a
Two-Station Molecular Shuttle. Unusually for an active-template
reaction, the metal binding site in the rotaxane-forming
Diels-Alder cycloaddition remains essentially unchanged in the
rotaxane product. To demonstrate the utility of this feature in
more complex rotaxanes, molecular shuttle 8a:8a′ was prepared
from pyridine-containing dienophile building block 7 and diene
3 (Scheme 2). The yield of [2]rotaxane 8a:8a′ (42%) was
remarkably good and a high (1,4)/(1,3) ratio (95:5) was
maintained despite the presence of the pyridine unit in building
block 7, which can compete with the macrocycle for complex-
ation with the Lewis acid, offering the building blocks an
unhindered site for the Lewis acid-catalyzed reaction to form
the thread. The pyridine unit and the R-carbonyl imidazolidone
functionalities that persist in [2]rotaxane 8a:8a′ could be used
as binding sites with different preferred coordination geometries
to control the position of the metal-coordinated macrocycle on
the thread (Scheme 3).
Zn(II) ion (structure [8a:8a′Zn2]L2(OTf)4 in Scheme 3a). Demeta-
lation (Na4EDTA, RT, 1 h) of the zinc complex liberated the metal-
free rotaxane 8a:8a′.
Addition of PdCl2 to 8a:8a′ results in formation of a different
rotaxane complex, [8a:8a′Pd]Cl2 (Scheme 3c). However, in the
1H NMR spectrum of [8a:8a′Pd]Cl2 (Figure 4d), it is the protons
adjacent to the thread pyridine unit (Hj and Hn) that are shielded
by the macrocycle aromatic rings (consistent with the chemical
shifts of a previously reported17 palladium-complexed rotaxane),
while signals of the R-carbonyl imidazolidone moiety appear at
chemical shifts similar to those of the noninterlocked thread (Figure
4b). Demetalation of [8a:8a′Pd]Cl2 with KCN (MeOH/CH2Cl2 1:1,
RT, 1 h) again afforded metal-free [2]rotaxane 8a:8a′.
Conclusions
The Diels-Alder cycloaddition is one of the most celebrated
and best-known transformations in organic synthesis. Its use to
form rotaxanes in high yields (up to 91%) through an active-
template reaction is yet another indication of its tremendous
versatility.18 The Diels-Alder reaction is unusual among active-
template reactions in that it produces rotaxanes in which the
metal binding sites on both the macrocycle and the thread persist
in the rotaxane. This can be exploited to construct molecular
shuttles in which the position of the macrocycle can be
controlled by the coordination requirements of metal ions
coordinated to the rotaxane. Such metal-ion-switchable systems
have historically required lengthy syntheses (10-20 steps),19
so the active-template Diels-Alder reaction should provide a
valuable addition to methods for the assembly of interlocked
molecular-level architectures.
As with the simpler rotaxane 4a:4a′, the room-temperature 1H
NMR spectrum of 8a:8a′ (400 MHz, 298 K, 9:1 CD2Cl2/CD3CN)
shows an upfield shift of the aliphatic and pyridine signals with
respect to those of the noninterlocked thread, particularly Hf-h
,
Hꢀ-δ, and Hk-m (Figure 4a,b), indicating that the macrocycle moves
freely but spends most of its time over the less-hindered parts of
the thread. Upon the addition of 1 equiv of Zn(OTf)2 to the NMR
1
tube containing 8a:8a′, the H NMR spectrum became complex,
suggesting that multiple coordinated species were present and
probably in exchange. However, saturating all of the rotaxane
binding sites by adding an additional 4 equiv of Zn(OTf)2 (5 equiv
total) led to a greatly simplified spectrum (Figure 4c). This spectrum
shows significant upfield shifts of the R-carbonyl imidazolidone
moiety (HR, HV, Hu, and Hz) and downfield shifts of the pyridine
station (Hj-n) with respect to the metal-free rotaxane (Figure 4b),
indicating that the macrocycle is held over the R-carbonyl imida-
zolidone unit as part of a trigonal-bipyrimidal-coordinated Zn(II)
complex while the thread pyridine group is coordinated to a second
(17) Crowley, J. D.; Leigh, D. A.; Lusby, P. J.; McBurney, R. T.; Perret-
Aebi, L.-E.; Petzold, C.; Slawin, A. M. Z.; Symes, M. D. J. Am. Chem.
Soc. 2007, 129, 15085–15090.
(18) For the use of the Diels-Alder reaction to bring about a (reversible)
change of position of the macrocycle in a molecular shuttle, see: Leigh,
D. A.; Pe´rez, E. M. Chem. Commun. 2004, 2262–2263.
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A R T I C L E S
Crowley et al.
Experimental Section
temperature for 30 min. A solution of acryloyl imidazolidone
stopper 2 (1.2 equiv, 0.017 mmol) in dry CH2Cl2 (0.5 mL) was
added, and the mixture was stirred for a further 30 min. The mixture
was cooled to -78 °C and stirred for 5 minutes, after which a
solution of diene 3 (2 equiv, 0.028 mmol) in dry CH2Cl2 (0.5 mL)
was added. The reaction mixture was stirred at -78 °C for 2 days
and then allowed to stir at room temperature for a further two days.
The reaction was quenched with ammonia (35% in water), and the
aqueous layer was extracted twice with CH2Cl2. The organic layers
were combined, washed three times with brine, dried (Na2SO4),
filtered, and concentrated under reduced pressure. Purification by
column chromatography (5:45:55 MeCN/hexane/CH2Cl2) provided
the [2]rotaxane as a colorless film (4a, 83%; 4b, 91%; 8a, 42%).
Full details of the experimental procedures and compound char-
acterizations are given in the Supporting Information.
General Experimental Procedure for Diels-Alder Active
Template Rotaxane Synthesis. A dry Schlenk tube was charged
with Zn(II) or Cu(II) triflate (1.0 equiv, 0.014 mmol) and macro-
cycle (1.0 equiv, 0.014 mmol) under a nitrogen atmosphere. Dry
CH2Cl2 (0.5 mL) was added, and the mixture was stirred at room
(19) For macrocycle translocation in metal-coordinated rotaxanes, see: (a)
Gavin˜a, P.; Sauvage, J.-P. Tetrahedron Lett. 1997, 38, 3521–3524. (b)
Armaroli, N.; Balzani, V.; Collin, J.-P.; Gavin˜a, P.; Sauvage, J.-P.;
Ventura, B. J. Am. Chem. Soc. 1999, 121, 4397–4408. (c) Durola, F.;
Sauvage, J.-P. Angew. Chem., Int. Ed. 2007, 46, 3537–3540. (d)
Periyasamy, G.; Collin, J.-P.; Sauvage, J.-P.; Levine, R. D.; Remacle, F.
Chem.sEur. J. 2009, 15, 1310–1313. (e) Durola, F.; Lux, J.; Sauvage,
J.-P. Chem.sEur. J. 2009, 15, 4124–4134. For macrocycle translocation
in metal-coordinated catenanes, see: (f) Livoreil, A.; Dietrich-Buchecker,
C. O.; Sauvage, J.-P. J. Am. Chem. Soc. 1994, 116, 9399–9400. (g)
Ca´rdenas, D. J.; Livoreil, A.; Sauvage, J.-P. J. Am. Chem. Soc. 1996,
118, 11980–11981. (h) Livoreil, A.; Sauvage, J.-P.; Armaroli, N.;
Balzani, V.; Flamigni, L.; Ventura, B. J. Am. Chem. Soc. 1997, 119,
12114–12124. For macrocycle rotation in metal-coordinated rotaxanes,
see: (i) Raehm, L.; Kern, J.-M.; Sauvage, J.-P. Chem.sEur. J. 1999, 5,
3310–3317. (j) Weber, N.; Hamann, C.; Kern, J.-M.; Sauvage, J.-P.
Inorg. Chem. 2003, 42, 6780–6792. (k) Poleschak, I.; Kern, J.-M.;
Sauvage, J.-P. Chem. Commun. 2004, 474–476. (l) Le´tinois-Halbes,
U.; Hanss, D.; Beierle, J. M.; Collin, J.-P.; Sauvage, J.-P. Org. Lett.
2005, 7, 5753–5756. For contraction/stretching in a rotaxane dimer
through Cu(I)-Zn(II) exchange, see: (m) Jime´nez, M. C.; Dietrich-
Buchecker, C.; Sauvage, J.-P. Angew. Chem., Int. Ed. 2000, 39, 3284–
3287. (n) Jime´nez-Molero, M. C.; Dietrich-Buchecker, C.; Sauvage,
J.-P. Chem.sEur. J. 2002, 8, 1456–1466. For a recent review of
transition-metal-complexed molecular machines, see: (o) Collin, J.-
P.; Sauvage, J.-P. L’Actualite´ Chim. 2009, 327-328, 114–119.
Acknowledgment. This work was supported by the Ramsay
Memorial Fellowships Trust and the EPSRC. D.A.L. is an EPSRC
Senior Research Fellow and holds a Royal Society-Wolfson
Research Merit Award. J.D.C. is a British Centenary Ramsay
Fellow. We thank the EPSRC National Mass Spectroscopy Service
Centre (Swansea, U.K.) for accurate mass data.
Supporting Information Available: Experimental procedures
and spectral data for all compounds and details of the X-ray
analyses of [1aZn]Cl2, [1bZn]Cl2, [1cZn]Cl2, and [1aCu]Cl2,
including CIF files. This material is available free of charge
via the Internet at http://pubs.acs.org.
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