Rotaxanes incorporating two different coordinating units in their thread: Synthesis and electrochemically and photochemically induced molecular motions

Article abstract of DOI:10.1021/ja984051w

Three different multicomponent molecular systems have been synthesized by means of the three-dimensional template effect of copper(I). These systems incorporate both a coordinating ring (2,9-diphenyl-1,10-phenanthroline-containing 30-membered ring) and a molecular string which consists of two different coordination sites (2,9-disubstituted-1,10-phenanthroline and 5,5″-disubstituted-2,2′:6′,2″-terpyridine unit). Each end of the string could be functionnalyzed by a small group or by a bulky stopper (tris(p-tert-butylphenyl)-(4-hydroxyphenyl)methane), leading to an unstoppered compound, to a semi-rotaxane, or to a real rotaxane. As in the case of a disymmetrical copper [2]-catenane, large reversible molecular motions have been induced both electrochemically and photochemically. The driving force of the rearrangement processes is the high stability of two markedly different coordination environments for the copper(I) and copper(II) ions. In the copper(I) state, two phenanthroline units (one of the ring, one of the string) interact with the metal ion in a tetrahedral geometry (Cu^I₍₄₎), whereas in the copper(II) state, one phenanthroline belonging to the ring and the terpyridine of the string afford a five-coordinate geometry (Cu^II₍₅₎). The rates of the molecular motion processes (from Cu^II₍₄₎ to Cu^II₍₅₎ and from Cu^I₍₅₎) to Cu^I₍₄₎) are respectively faster and slower (minutes time scale) as compared to those for the catenane species. This result could be interpreted on the basis of structural differences between the rotaxane and catenane systems.

Full text of DOI:10.1021/ja984051w

J. Am. Chem. Soc. 1999, 121, 4397-4408
4397
Rotaxanes Incorporating Two Different Coordinating Units in Their
Thread: Synthesis and Electrochemically and Photochemically
Induced Molecular Motions
Nicola Armaroli,*,‡ Vincenzo Balzani,*,§ Jean-Paul Collin,† Pablo Gavin˜a,†,
Jean-Pierre Sauvage,*,† and Barbara Ventura§
Contribution from the Laboratoire de Chimie Organo-Mine´rale, UMR du CNRS no. 7513, 4, rue Blaise
Pascal, Faculte´ de Chimie, UniVersite´ Louis Pasteur, 67070 Strasbourg Cedex, France, Istituto di
Fotochimica e Radiazioni d’Alta Energia del CNR, Via Gobetti 101, 40129 Bologna, Italy, and
Dipartimento di Chimica “G. Ciamician”, UniVersita` di Bologna, Via Selmi 2, 40126 Bologna, Italy
ReceiVed NoVember 23, 1998
Abstract: Three different multicomponent molecular systems have been synthesized by means of the three-
dimensional template effect of copper(I). These systems incorporate both a coordinating ring (2,9-diphenyl-
1,10-phenanthroline-containing 30-membered ring) and a molecular string which consists of two different
coordination sites (2,9-disubstituted-1,10-phenanthroline and 5,5′′-disubstituted-2,2′:6′,2′′-terpyridine unit). Each
end of the string could be functionnalyzed by a small group or by a bulky stopper (tris(p-tert-butylphenyl)-
(4-hydroxyphenyl)methane), leading to an unstoppered compound, to a semi-rotaxane, or to a real rotaxane.
As in the case of a disymmetrical copper [2]-catenane, large reversible molecular motions have been induced
both electrochemically and photochemically. The driving force of the rearrangement processes is the high
stability of two markedly different coordination environments for the copper(I) and copper(II) ions. In the
copper(I) state, two phenanthroline units (one of the ring, one of the string) interact with the metal ion in a
tetrahedral geometry (CuI(4)), whereas in the copper(II) state, one phenanthroline belonging to the ring and the
terpyridine of the string afford a five-coordinate geometry (CuII(5)). The rates of the molecular motion processes
(from CuII to CuII and from CuI(5) to CuI(4)) are respectively faster and slower (minutes time scale) as
(4)
(5)
compared to those for the catenane species. This result could be interpreted on the basis of structural differences
between the rotaxane and catenane systems.
Introduction
rotary motors have been identified and investigated.4 The most
spectacular example is that of ATPase, whose rotation motion
was postulated long ago5 but which could be directly observed
only recently.6 ATPase consists of a “stator”, with six proteins
(R3â3) assembled to form an orange-like unit, a seventh, rodlike,
protein (γ) being threaded in the hollow part of the R3â3 unit
to form the “rotor”. The γ subunit rotates inside the R3â3
assembly with concomitant hydrolysis of ATP or during ATP
synthesis when a pH gradient is present.
Threaded or interlocking rings are ideally suited to the
construction of fully artificial molecular motors.7 If a ring is
threaded onto a rod, it can either rotate around the axle or
undergo a translation movement. Similarly, in catenanes (i.e.,
interlocking ring multicomponent systems), a ring can glide at
will and spin within another ring. Several examples of such
compounds have been elaborated and studied in recent years,
using threaded and interlocked molecules based on either
In biology, many “molecular motors” or “machines” play an
essential role. These systems are multicomponent assemblies
undergoing large-amplitude geometrical changes or leading to
the locomotion of one of the components, under the action of
either an external stimulus (pH change, redox process, light
pulse, etc.) or a chemical gradient. Many examples are known
of proteins which undergo important shape modifications
(folding-defolding) after a signal has been sent to the protein.1
Real molecular motors consist of several units, among which
some parts will be considered as motionless and some others
will move continuously while a “fuel” is “burned”, which
translates, in biological systems, as: ATP is hydrolyzed. Linear
motors such as myosin2 (from skeletal muscle) or kinesin3 (from
brain) have been known for many years, and knowledge about
them has made considerable progress recently. By contrast, few
* Authors to whom correspondence should be addressed.
† Universite´ Louis Pasteur.
(2) Finer, J. T.; Simmons, R. M.; Spudlich, J. A. Nature 1994, 368, 113-
119. Whittaker M.; Wilson-Kubalek, E. M.; Milligan, R. A.; Sweeney, H.
L. Nature 1995, 378, 748-751
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Nature 1996, 380, 555-559. Meyho¨fer, E.; Howard, J. Proc. Natl. Acad.
Sci. U.S.A. 1995, 92, 574-578.
‡ Istituto di Fotochimica e Radiazioni d'Alta Energia del CNR.
§ Universita` di Bologna.
Present address: Departament de Quimica Orga`nica, Universitat de
Vale`ncia, Facultat de Farma`cia, Av. Vicent Andre´s Estelle´s s/n, 16100
Burjassot (Vale`ncia), Spain.
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10.1021/ja984051w CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/24/1999

4398 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Armaroli et al.
acceptor-donor and hydrogen-bonded complexes8 or transition
metal complexes.9 In the purely organic systems, interesting
processes have been evidenced, such as dethreading of an acyclic
component from a ring under the action of light10 or translation
of a ring between two distinct positions of a thread, induced by
a redox signal.11
The present system deals with copper complexes of rotaxane-
related compounds, i.e., a ring threaded on a molecular string,
both constitutive units being assembled via coordination to the
same metal center. Preliminary reports on the synthesis12 or the
electrochemical behavior13 of the compounds have been pub-
lished recently.
Results and Discussion
General Principle and Design of the Molecules. Coordina-
tion compounds are particularly attractive as components of
molecular machines whose motions are driven by an electro-
chemical signal. Since the stereoelectronic requirements of a
metal center can be strongly modified by changing its oxidation
state, redox-active transition metal complexes are expected to
undergo electrochemically induced rearrangement of the metal
coordination sphere. This is particularly true for copper com-
plexes: Cu(I) is usually low-coordinate (coordination number
CN e 4), whereas Cu(II) is preferably square planar or higher
coordinate (CN ) 5 or 6). In the molecular machines previously
made and investigated in our group, the same general principle
is utilized: 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 large-amplitude motion which will bring the system
to its new equilibrium position. In previous work on catenanes,
we studied the gliding motion of a ring within the other by
setting in motion either one cycle or both rings.9,14 In the
rotaxanes decribed in the present paper, a ring is translated along
a rodlike component on which it is threaded (Chart 1).
Figure 1. Square scheme in the threaded compounds 18+, 19+, or
24+. The subscripts 4 and 5 indicate the copper coordination number
in each complex. The stable CuI(4) complex is oxidized to an
intermediate tetrahedral divalent species, CuII(4), which undergoes a
rearrangement to afford the stable CuII complex. Upon reduction, a
(5)
CuI(5) species is formed as a transient, which finally reorganizes to
regenerate the starting complex. The black circle represents Cu(I), and
the white circle represents Cu(II).
fragment, the string being threaded through the ring via
coordination of both components to the same metal center. The
system can be switched from four-coordinate (low oxidation
state) to five-coordinate (high oxidation state) and vice versa
by oxidizing or reducing the transition metal, as represented in
Figure 1.
Synthesis of the Threaded Compounds. The target copper-
(I) rotaxane and its nonstoppered or partially stoppered ana-
logues are shown in Chart 2.
Chart 2
Chart 1
The ring incorporates a bidentate chelate, and the string
contains both a bidentate coordinating unit and a terdentate
(8) Ashton, P. R.; Ballardini, R.; Balzani, V.; Boyd, S. E.; Credi, A.;
Gandolfi, M. T.; Gomez-Lopez, M.; Iqbal, S.; Philp, D.; Preece, J. A.; Prodi,
L.; Ricketts, H.; Stoddart, J. F.; Tolley, M. S.; Venturi, M.; White, A. J. P.;
Williams, D. J. Chem. Eur. J. 1997, 3, 152. Philp, D.; Stoddart, J.-F. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1154-1196. Ashton, P. R.; Ballardini, R.;
Balzani, V.; Credi, A.; Gandolfi, M. T.; Menzer, S.; Pe´rez-Garcia, L.; Prodi,
L.; Stoddart, J. F.; Venturi, M.; White, A. J. P.; Williams, D. J. J. Am.
Chem. Soc. 1995, 117, 11171-11197. Credi, A.; Balzani, V.; Longford, S.
J.; Stoddart, J. F. J. Am. Chem. Soc. 1997, 119, 2679-2681.
(9) Livoreil, A.; Dietrich-Buchecker, C. O.; Sauvage, J.-P. J. Am. Chem.
Soc. 1994, 116, 9399-9400. Baumann, F.; Livoreil, A.; Kaim, W.; Sauvage,
J.-P. Chem. Commun. 1997, 35-36. Livoreil, A.; Sauvage, J.-P.; Armaroli,
N.; Balzani, V.; Flamigni, L.; Ventura, B. J. Am. Chem. Soc. 1997, 119,
12114-12124.
(10) Ballardini, R.; Balzani, V.; Gandolfi, M. T.; Prodi, L.; Venturi, M.;
Philp, D.; Ricketts, H. G.; Stoddart, J. F. Angew. Chem., Int. Ed. Engl.
1993, 32, 1301-1303.
(11) Bissell, R. A., Co´rdova, E.; Kaifer, A. E.; Stoddart J. F. Nature
1994, 369, 133.
(12) Gavin˜a, P.; Sauvage, J.-P. Tetrahedron Lett. 1997, 38, 3521-3524.
(13) Collin, J.-P.; Gavin˜a, P.; Sauvage, J.-P. J. Chem. Soc., Chem.
Commun. 1996, 2005-2006. Collin, J.-P.; Gavin˜a, P.; Sauvage, J.-P. New
J. Chem. 1997, 21, 525-528.
(14) Ca´rdenas, D. J.; Livoreil, A.; Sauvage, J.-P. J. Am. Chem. Soc. 1996,
118, 11980-11981.
The tetraarylmethane derivative used as stopper group was
selected because of its size (no possible threading through the
30-membered ring used as cyclic component) and for its relative
ease of access. The synthetic strategy is based on a transition

Rotaxanes with Two Different Coordinating Units
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4399
The 30-membered macrocycle 1718 was chosen as the
coordinating ring. The reaction between 17 and Cu(MeCN)4BF4
in CH2Cl2-MeCN under Ar at room temperature led to an
orange solution of Cu(17)(MeCN)2+, which was reacted with a
CH2Cl2 solution of 14 to give the desired pseudorotaxane 18+
in 75% yield after column chromatography as a brown-red solid.
The reaction proceeded regioselectively on the phenanthroline
ligand of the string, as was unambiguously shown by 1H NMR
1
and UV-vis spectroscopies. The H NMR spectrum of 18+
shows the typical upfield shifts of the aromatic protons of the
phenoxy moeities due to the ring current effect of the 1,10-
phenanthroline nuclei, consistent with two phenanthroline units
intertwined around a copper(I) center19 (5.95 and 5.88 ppm for
the Hm and Hm′ and 7.31 and 7.14 for Ho and Ho′). The
absorption at 442 nm in the visible spectrum is typical of these
bis(phen) complexes.19 FAB-MS confirmed the structure, show-
ing an intense peak at m/z 1216.4 corresponding to the loss of
the counterion. The main peak, at m/z 650.2, corresponds to
the loss of the counterion and the macrocycle.
Semi-Rotaxane 19+ and Rotaxane 24+. The main drawback
of compound 18+ is clearly related to the possibility of
undergoing a dethreading process, in either the monovalent or
the divalent state, leading to chemical irreversibility of the redox-
induced motions. An obvious improvement is to covalently
attach one or two stoppers at the ends of the thread to afford a
semi-rotaxane or a rotaxane, respectively. The chosen blocking
group was tris(p-tert-butylphenyl)(4-hydroxyphenyl)methane
since it is large enough to prevent dethreading of the string from
macrocycle 17, as was suggested by a CPK molecular model.
Figure 2. Construction principle: the bidentate chelate (phen,
represented by an inverted U) and the terdentate unit (terpy, represented
by a stylized M) have been incorporated in an acyclic ligand already
bearing a bulky stopper at one end. The ring contains a phen nucleus.
(i) In the threading step, copper(I) (represented by a black circle) forces
the string to pass through the ring. Since copper(I) has a strong tendency
to be four-coordinate, the threading reaction will selectively lead to
the precursor represented. (ii) The blocking reaction will be done by
attaching a voluminous group at the second end of the coordinating
string.
metal-directed process which has been used in our group
extensively to make various catenanes and rotaxanes, as depicted
in Figure 2. The starting compounds and the intermediate
molecules are represented in Figure 3.
Our first approach toward threaded linear systems displaying
electrochemically induced molecular motions involved the
synthesis of the most simple system: pseudorotaxane 18+,
whose ring incorporates a 2,9-diphenyl-1,10-phenanthroline
moiety and whose open-chain molecular string contains two
different coordination sites: a 2,9-disubstituted 1,10-phenan-
throline (phen) bidentate chelate and a terdentate ligand,
2,2′,6′,2′′-terpyridine (terpy), covalently linked by a four-carbon
aliphatic chain. Copper(I) was used as a gathering and tem-
plating metal center, forcing the string to thread through the
coordinating ring while generating a bis-chelate complex
between the metal ion and the two phen moieties.
The starting 5,5′′-dimethyl-2,2′:6′,2′′-terpyridine 1 was pre-
pared from 2-acetyl-5-picoline by Jameson’s method15 or,
alternatively, from 2-bromo-5-picoline and 2,6-dibromopyridine
following the Stille cross-coupling reaction.16 1 was deproto-
nated with LDA in THF, giving a deep purple compound which
was reacted with 1 equiv of THP-protected bromoethanol (THP
) tetrahydropyran-2-yl) to afford the monosubstituted derivative
2 in 44% yield. Hydrolysis of the acetal with a catalytic amount
of concentrated HCl in refluxing EtOH led to an 85% yield of
free alcohol 3, which was converted first to the mesylate 4 in
95% yield by reaction with mesyl chloride (MsCl) and NEt3 in
CH2Cl2 and then to the bromo derivative 5 (97%) by reaction
with anhydrous LiBr in refluxing acetone. Separately, the
bidentate coordinating unit 2-methyl-9-(p-anisyl)-1,10-phenan-
throline 13 was prepared from 1,10-phenanthroline as previously
reported.17 Deprotonation of 13 with LDA in THF, followed
by reaction with 5 at room temperature, afforded the target
bifunctional ligand 14 in 56% yield after workup and column
chromatography, as a yellow solid.
As in the case of pseudorotaxane 18+, a key step is the metal-
directed threading process (i) of Figure 2, in which copper(I)
forces the string to pass through the ring due to the strong
tendency of this metal ion to form pseudotetrahedral bis-chelate
complexes with two phen.
(a) Synthesis of the Ligands. The organic compounds used
as precursors as well as the bifunctional molecular string are
represented in Figure 3. 5,5′′-Dimethyl-2,2′:6′,2′′-terpyridine 1
was deprotonated with LDA in THF and then reacted with 2
equiv of THP-protected bromoethanol to afford 6 in 45% yield.
An excess of base or alkylating agent, or prolonged reaction
times, did not improve this yield. Deprotection with a catalytic
amount of concentrated HCl in refluxing EtOH led to the
corresponding diol 7 in high yield (white solid, 96%), which
was transformed into the dimesylate 8 in 90% yield by reaction
with MsCl and NEt3 in CH2Cl2 at -2 °C. On the other hand,
the phenolic blocking group 9 was prepared in three steps, from
4-bromo-tert-butylbenzene, methyl 4-tert-butylbenzoate, and
phenol as reported in the literature.20 Reaction of dimesylate 8
with 9 (1 equiv) in DMF at 75 °C in the presence of K2CO3
gave a mixture of mesylate 11 (46%), dialkylated product in
which the two mesylates had been replaced by two blocking
groups, and starting materials. During alumina column chro-
matography separation of this mixture, 11 was partially hydro-
lyzed to the corresponding alcohol 10. Nevertheless, the latter
could be easily converted again in mesylate 11 in almost
quantitative yield by reaction with MsCl in the usual conditions
(NEt3, CH2Cl2, -2 °C). 11 was transformed into the more
reactive bromo derivative 12 by reaction with anhydrous LiBr
(18) Dietrich-Buchecker, C. O.; Sauvage, J.-P. Tetrahedron 1990, 46,
503-512.
(15) Jameson, D. L.; Guise, L. E. Tetrahedron Lett. 1991, 32, 1999-
2002.
(16) Ca´rdenas, D. J.; Sauvage, J.-P. Synlett 1996, 916-918.
(17) Dietrich-Buchecker, C. O.; Nierengarten, J.-F.; Sauvage, J.-P.;
Armaroli, N.; Balzani, V.; De Cola, L. J. Am. Chem. Soc. 1993, 115, 11237-
11244.
(19) Dietrich-Buchecker, C. O.; Sauvage, J.-P.; Kern, J.-M. J. Am. Chem.
Soc. 1989, 111, 7791-7800. Ca´rdenas, D. J.; Gavina, P.; Sauvage, J.-P. J.
Am. Chem. Soc. 1997, 119, 2656-2664.
(20) Gibson, H. W.; Lee, S.-H.; Engen, P. T.; Lecavalier, P.; Sze, J.;
Shen, Y. X.; Bheda, M. J. Org. Chem. 1993, 58, 3748-.

4400 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Armaroli et al.
Figure 3. Intermediate compounds and demetalated rotaxane 25 synthesized.
in refluxing acetone. Finally, deprotonation of the phenanthro-
line-containing building block 13 with LDA in THF led to a
deep red compound, which was further reacted with 12 in THF
at room temperature to afford the desired string 15 (yellow solid,
61% isolated yield), incorporating a phen and a terpy unit and
a stopper at one end.
(b) Synthesis of a Cu(I) Complex Semi-Rotaxane and
Rotaxane. The coordinating macrocycle 17 was reacted with
Cu(MeCN)4PF6 in CH2Cl2-MeCN under Ar at room temper-
ature to give an orange solution of complex Cu(17)(MeCN)2PF6.
Subsequent addition of a CH2Cl2 solution of string 15 led to
semi-rotaxane 19‚PF6 in almost quantitative yield, which was
isolated as a red-brown solid. Again, as expected, the reaction
proceeded regioselectively on the phen unit of the string, and
no competition of the terpy ligand versus phen for Cu(I) was
observed. This behavior was already observed in previous
catenanes and related threaded systems9,19 containing similar
coordinating units.
For the preparation of the fully blocked rotaxane 24+, ligand
15 was first demethylated by reaction with EtSNa in dry DMF
at 110 °C to give the corresponding phenol 16 in 80% yield, as
a yellow solid. 16 was then threaded into ring 17 by coordination
to Cu(I) in the same way as for 19+. The threaded four-
coordinate copper(I) complex 20+ was thus obtained in nearly
quantitative yield as a brown-red solid. Separately, to effect the
blocking reaction, we had first to convert 9 into an appropiate
alkylating agent, able to react rapidly with the phenolic threaded
system 20+. Thus, 9 was allowed to react with THP-protected
bromoethanol and K2CO3 in DMF, followed by deprotection
with HCl to give alcohol 21 in 56% yield. This alcohol was

Rotaxanes with Two Different Coordinating Units
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4401
transformed into mesylate 22 (MsCl, NEt3, CH2Cl2; 97%), which
was further reacted with LiBr in refluxing acetone to obtain
the corresponding bromo derivative 23 in nearly quantitative
yield. Finally, the reaction of 20+, 23, and Cs2CO3 in DMF
under Ar at 55 °C, followed by counterion exchange (KPF6,
H2O, MeCN), led to rotaxane 24‚PF6 in 40% yield.
Both threaded structures, 19+ and 24+, were unambiguously
1
characterized by FAB-MS and H NMR and UV-vis spec-
troscopies. The 1H NMR spectra of both systems are very
similar. They both show the usual upfield shifts of the aromatic
protons of the phenoxy moieties attached to the phenanthrolines,
indicating the intertwined structures of the two phen around a
copper(I). For instance, in rotaxane 24+, the meta H signals
appear at δ 5.97 (4Hm′) and 5.92 (2Hm), and the ortho H signals
appear at δ 7.33 (4Ho′) and 7.11 (2Ho). Another interesting
feature is that the protons of the phenanthroline central ring of
the string (H5,6) appear as two doublets with different chemical
shifts (8.29 and 8.05 ppm), as shown by 1H COSY experiments,
while in string 15 both protons appear as one singlet (7.70 ppm,
2H). This different chemical environment of both protons in
the threaded Cu(I) complexes could be due to some shift of the
phen unit of the ring toward the phenoxy moeity attached to
the phenantroline of the string to favor a better π-stacking. The
protons of the first pyridine ring of the terpy moiety (H3t, H4t,
and H6t) closest to the phen also experience an upfield shift
with respect to the free string, indicating that they could also
be affected by the ring current of the phen nucleus of the ring.
The UV-vis spectra of 19+ and 24+ show an absorption at
442 nm (ꢀ ) 3100 and 2700 M-1 cm-1, respectively) charac-
+
teristic of the Cu(phen)2 species. FAB-MS confirmed the
threaded structures. For semi-rotaxane 19+, intense peaks are
observed corresponding to the loss of the counterion (m/z
1747.8) and the loss of the counterion and the ring (m/z 1180.5).
Similar features are observed for rotaxane 24+. It is interesting
to remark that no peaks are observed in the region lying between
the peak corresponding to the loss of the counterion (m/z 2265.2)
and the peak corresponding to the fragmentation and subsequent
loss of the macrocycle from the thread (m/z 1698.0).
Figure 4. (a) Cyclic voltammogram of 24+. (b) Same after electrolysis
during 1 h at +1.0 V; (c and d) Evolution of 242+ solution with time:
after 2 h (c) and after 4 h (d). (e) Cyclic voltammogram immediately
after electrolysis of 242+ solution at -0.3 V. Conditions: MeCN (0.1
M, n-Bu4NBF4), Pt electrode, ν ) 100 mV s-1, 25 °C.
for H6t and H18t, 8.48-8.45 for H3t and H15t, and 7.61-7.57
for H4t and H16t).
Demetalated Rotaxane 25. As has been previously reported,
Cu(I) complex rotaxanes can be easily demetalated by reaction
with cyanide in mild conditions, leading to rotaxanes with free
coordination sites.21 Thus, the reaction between 24+ and KCN
in a mixture of CH2Cl2-MeCN-H2O at room temperature
followed by column chromatography yielded the free rotaxane
25 as a white solid in 84% yield. The rotaxane structure was
immediately confirmed by FAB-MS. As in the case of the Cu-
(I) complex rotaxane 24+, no peaks are observed between the
molecular ion (m/z 2202.1) and the peak corresponding to the
fragmentation and loss of the ring (m/z 1635.9). This is a very
characteristic feature of interlocked and threaded systems. In
the 1H NMR spectrum, we can observe a downfield shift of the
aromatic protons of the phenoxy moieties attached to the
phenanthrolines, indicating that the intertwined structure of the
two phen around a copper(I) has disappeared. Thus, the meta
protons appear at δ 6.90 (4Hm’) and 7.17 (2Hm) and the ortho
at 8.31 and 8.29 ppm. These values are very close to the
chemical shifts of the ring and the free string (ca. 8.40 ppm for
H-ortho and 7.15 ppm for H-meta). Besides, the previously
mentioned protons of the phenanthroline central ring of the string
(H5,6) appear now as a singlet, and the protons of the first
pyridine ring of the terpy (H4t, H6t, and H3t) are again downfield
shifted to values close to those of the free string (δ 8.50-8.48
Electrochemically Driven Motion. From the previously
determined electrochemical behavior of the catenane-type
complexes,9 and assuming some analogous values for the redox
couples CuII(4)/CuI(4) and CuII(5)/CuI(5), we expect the same type
of electron-transfer-induced reaction.22
In the three rotaxanes 18+, 19+, and 24+, a square scheme,
as depicted Figure 1, takes place. The electrochemical and
chemical reactions are analyzed by cyclic voltammetry (CV)
and controlled potential electrolysis experiments. From the CV
measurements at differents scan rate (from 0.005 to 2 V s-1
)
both on the copper(I) and on the copper(II) species, it could be
inferred that the chemical steps (motions of the ring from the
phenanthroline to the terpyridine and vice versa) are slow on
the time scale of the experiments. As the two redox couples
involved in these systems are separated by 0.7 V, the concentra-
tions of the species in each environment (tetr-a or pentacoor-
dination) are directly deduced from the peak intensities of the
redox signals. In Figure 4 are displayed some voltammograms
(curves a-e) obtained on different oxidation states of the
rotaxane 24+ and at different times.
Curve a diplays the voltammogram of a red solution of 24+
in degassed acetonitrile. A reversible redox wave at 0.68 V (vs
SCE) attests to the tetrahedral environment around the copper-
(I) atom.9,14 During the potential scan, for rates between 0.005
and 2 V s-1, no redox signal corresponding to the pentacoor-
(21) Dietrich-Buchecker, C. O.; Sauvage, J.-P. Chem. ReV. 1987, 87,
795-810. Chambron, J.-C.; Heitz, V.; Sauvage, J.-P. J. Am. Chem. Soc.
1993, 115, 12378-12384.
(22) Evans, D. H. Chem. ReV. 1990, 90, 739-751.

4402 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Armaroli et al.
dination could be observed. This fact evidences the high kinetic
stability of the four-coordinate copper(II) rotaxane generated
at the electrode. At this stage, a controlled potential electrolysis
(applied potential ) +1.0 V) was performed until one Faraday
was exchanged per mole of complex. During the electrolysis,
the red color of the solution turned light green. Immediately
after the coulometry, the voltammogram on the copper(II)
species (curve b) showed the same redox couple at +0.68 V
and an additional small reversible couple at -0.03 V. These
signals are characteristic of the CuII(4)/CuI(4) and CuII(5)/CuI(5)
couples, respectively.9,14 After several hours at room tempera-
ture, without any visible color change, the progressive disap-
pearance of the redox couple at +0.68 V ( four-coordinate state)
and the concomitant growth of the couple at -0.03 V ( five-
coordinate state) attest to the coordination change around the
copper (II) ion (curves c and d). The analysis of the concentra-
tion of the two different copper(II) species with time leads to a
first-order rate constant of 1.5 × 10-4 s-1 for the chemical
reaction CuII(4), giving CuII(5). According to the invariant shape
of the signals with the scan rate of the copper(II) solution, it
can be inferred that the rate constant for the reaction CuI(5) to
CuI(4) is smaller than 10-2 s-1. A second electrolysis at -0.3 V
restores the initial red solution. The voltammogram (curve e)
performed immediately after the reductive electrolysis displays
the redox couple of 24+ and is invariant with time. As all the
CuI(5) species formed electrochemically are quantitavely trans-
formed into CuI(4) species during the electrolysis, we can give
a lower limit of 10-4 s-1 for the rate constante of the chemical
reaction. The residual signal at -0.03 V simply reflects an
incomplete electrolysis.
Figure 5. Absorption and (inset) uncorrected emission spectra in
acetonitrile solution at 298 K of 24+ (full line) and of the analogous,
previously studied copper(I) [2]-catenate catd (dashed line, see Chart
3 and ref 9). The stronger absorption of the rotaxane in the UV spectral
region is due to the presence of the aromatic-type stoppers.
Table 1. Spectroscopic and Kinetic Parameters of the Rotaxane
24+ and the Analogous Catenate catd (see ref 9)a
24+
catd
439
λ
max(abs), nmb
ꢀmax (MLCT), M-1 cm-1
max(em), nmc
439
3000
785
34
2300
735
60
λ
τ, ns
τ, nsd
64
115
kq, M-1 cm-1 e
kconv CuII(4)/CuII(5), s-1 f
kconv CuI(5)/CuI(4), s-1 g
1.6 × 109
4.1 × 108
2.8 × 10-5
1
1.5 × 10-4
10-4 e k e 10-2
The behavior of the systems constituted by the unstoppered
compound 18+, or the semirotaxane 19+,13 is related to that of
the fully blocked rotaxane 24+, i.e., the same redox couple can
be observed. Some variations of peak intensities with the scan
rate also indicate an acceleration of the chemical processes as
compared to that of 24+. However, additional signals corre-
a 298K, CH3CN solution, unless otherwise noted. b Absorption
maximun in the visible spectra region. c From emission maximun
corrected for the photomultiplier response. d CH2Cl2 solution. e Bimo-
lecular quenching constant obtained from Stern-Volmer plots, by using
f
p-NO2C6H4CH2Br as quencher; for more details, see text. Rate constant
for the conversion from the tetra- to pentacoordination of Cu(II), upon
electrolysis of a solution of CuI(4) g Rate constant for the conversion
.
sponding to the species CuI(MeCN)4 (E1/2 ) +1.02 V) and
+
from the penta- to tetracoordination of Cu(I), upon electrolysis of a
CuII ( six-coordinate state, E1/2 ) -0.41 V)14 reveal that the
solution of CuII
.
(5)
(6)
dethreading process becomes significant and occurs primarily
with the copper(II) species. The six-coordinate complex evi-
denced by CV originates from the dethreading and coordination
of the two linear fragments (14 or 15) via their terpy units to a
copper center.
nm and τ ) 34 ns in aerated acetonitrile solution at 298 K (inset
of Figure 5 and Table 1).
The spectroscopic properties and excited-state properties of
24+ are similar, but not identical, to those of the analogous
[2]-catenate, catd (Table 1 and Chart 3).9
Of these three systems, 24+ is the most promising compound
in relation with electrochemically induced molecular motions,
due to the perfect chemical reversibility of the processes.
Interestingly, the rates of the movements in rotaxane 24+ are
very different from those measured for a related catenane.14 The
conversion CuII to CuII is faster in 24+ than that in the
The most remarkable difference is the shorter excited-state
lifetime, which suggests that, in the rotaxane, the metal ion is
(23) (a) McMillin, D. R.; McNett, K. M. Chem. ReV. 1998, 98, 1201-
1219. (b) Egglestone, M. K.; McMillin, D. R.; Koenig, K. S.; Pallenberg,
A. J. Inorg. Chem. 1997, 36, 172-176. (c) Everly, R. M.; McMillin, D. R.
J. Phys. Chem. 1991, 95, 9071-9075. (d) Gushurst, A. K. I.; McMillin, D.
R.; Dietrich-Buchecker, C. O.; Sauvage, J.-P. Inorg. Chem. 1989, 28, 4070-
4072. (e) Kirchhoff, J. R.; Gamache, R. E., Jr.; Blaskie, M. W.; Del Paggio,
A. A.; Lengel, R. K.; McMillin, D. R. Inorg. Chem. 1983, 22, 2380-2384.
(24) (a) Kern, J.-M.; Sauvage, J.-P.; Weidmann, J.-L.; Armaroli, N.;
Flamigni, L.; Ceroni, P.; Balzani, V. Inorg. Chem. 1997, 36, 5329-5338.
(b) Dietrich-Buchecker, C. O.; Sauvage, J.-P.; Armaroli, N.; Ceroni, P.;
Balzani, V. Angew. Chem., Int. Ed. Engl. 1996, 35, 1119-1121. (c)
Armaroli, N.; Rodgers, M. A. J.; Ceroni, P.; Balzani, V.; Dietrich-Buchecker,
C. O.; Kern, J.-M.; Bailal, Sauvage, J.-P. Chem. Phys. Lett. 1995, 241,
555-558. (d) Armaroli, N.; Balzani, V.; Barigelletti, F.; De Cola, L.;
Flamigni, L.; Sauvage J.-P.; Hemmert, C. J. Am. Chem. Soc. 1994, 116,
5211-5217. (e) Dietrich-Buchecker, C. O.; Nierengarten, J.-F.; Sauvage,
J.-P.; Armaroli, N.; Balzani, V.; De Cola, L. J. Am. Chem. Soc. 1993, 115,
11237-11244. (f) Armaroli, N.; De Cola, L.; Balzani, V.; Sauvage, J.-P.;
Dietrich-Buchecker, C. O.; Kern, J.-M.; Bailal, A. J. Chem. Soc., Dalton
Trans. 1993, 3241-3247.
(4)
(5)
interlocking ring system previously described. This difference
could reflect a greater ability of CuII in 24+ to interact with
(4)
solvent molecules or anions, the copper(II) center being perhaps
loosely bound to a fifth ligand which would thus stabilize
intermediate states on the way to CuII
.
(5)
Photochemically Driven Motion. It is well known that Cu-
(I) complexes of polypyridine ligands absorb light throughout
the UV-vis spectral region, display luminescence from the
lowest triplet MLCT excited state, have a reasonably long
lifetime, and can play the role of electron-transfer reductant.23-25
This is also the case for the Cu(I)-based chromophoric unit of
rotaxane 24+. It shows (i) UV absorption bands due to ππ*
ligand-centered (LC) transitions, (ii) metal-to-ligand charge-
transfer (MLCT) bands in the 400-700-nm spectral region
(Figure 5), and (iii) a MLCT emission band with λmax ) 785
(25) Ruthkoski, M.; Castellano, F. N.; Meyer, G. J. Inorg. Chem. 1996,
35, 6406-6412.

Rotaxanes with Two Different Coordinating Units
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4403
Chart 3
Figure 6. Principle of the photochemically and chemically triggerred
rearrangement of the rotaxane 24+.
stantially met by p-NO2C6H4CH2Br (p-nitrobenzylbromide),29,30
which was successfully used to cause photooxidation of the
analogous catenane.9 A Stern-Volmer analysis31 of the quench-
ing of the luminescence of *24+ by p-NO2C6H4CH2Br showed
that the rate constant of the quenching process (eq 3) is 1.6 ×
109 M-1 s-1 in acetonitrile solution at 298 K, i.e., much larger
than that found in the case of the catenane species9 (Table 1).
This compensates for the shorter excited-state lifetime of the
rotaxane and allows its photooxidation to occur in a relatively
short time when a sufficiently high concentration of p-NO2C6H4-
CH2Br is present in the solution. The principle of the photo-
chemically triggered rearrangement of the rotaxane 24+ is given
Figure 6.
Photochemical experiments were performed by irradiating
with 464-nm light acetonitrile solutions containing 1.0 × 10-4
M 24+ and 1.8 × 10-2 M p-NO2C6H4CH2Br. Under these
conditions, all the exciting light is absorbed by the Cu(I)
catenate. Light irradiation was found to cause spectral changes
indicating the disappearance of the Cu(I) species within 20 min,
but no isosbestic point was present, contrary to what was found
for the analogous catenate.9 At the end of the photoreaction,
the irradiated solution was kept in the dark at 298 K; meanwhile,
the occurrence of a very slow reaction was evidenced by
spectrophotometric measurements. The final spectrum (after 24
h) was reminiscent of, but clearly different from, that found
upon photochemical oxidation of the analogous catenate and,
more generally, that exhibited by the [Cu(phen)2]2+-type chro-
mophoric units.23,24,32 At this stage, addition of an excess of
ascorbic acid (dissolved in MeOH) caused a gradual, slow
increase of the absorption spectrum in the 400-600-nm region,
but only about 70% of the initial 24+ species was recovered
when no further spectral changes were observed (after about 4
h). These results indicate that, under the experimental conditions
used, a substantial part of the Cu ions lose pyridine-type
coordination. The reason for such a behavior was not im-
mediately clear since the electrochemically driven oxidation-
reduction cycle is fully reversible. From the experimental
viewpoint, the only difference was that the electrochemical
processes were carried out in the presence of tetrabutylammo-
nium tetrafluoroborate (TBA(BF4)) as supporting electrolyte,
less protected toward interaction with solvent molecules;26,27
this is probably due to the lower number of phenyl substituents
on the phenanthroline units of the rotaxane, with respect to the
catenate.9 Despite the shorter excited-state lifetime, we thought
that it should be possible to cause the first step of the overall
swinging process indicated in Figure 1, namely the conversion
of 24+ into *24+, by light irradiation in the presence of a suitable
electron acceptor (A), as described by eqs 1-5:
24+ + hν f *24+
*24+ f 24+ + heat or hν′
*24+ + A f 242+ + A•-
242+ + A•- f 24+ + A
A•- f products
(1)
(2)
(3)
(4)
(5)
The occurrence of the excited-state electron-transfer process
(eq 3) competes with nonradiative deactivation and luminescence
(eq 2), which is therefore a useful handle to evaluate whether
reaction 3 takes place. A necessary condition for the occurrence
of reaction 3 is, of course, that it takes place with negative free
energy change. The reduction potential of the 242+/*24+ couple
can be evaluated from the reduction potential of the 242+/24+
couple (+0.68 V in acetonitrile)13 and the energy of the *24+
excited state (about 1.58 eV, as estimated from the onset of the
maximum of corrected emission band in the same solvent) by
the following equation:28
E°(242+/*24+) ∼ E°(242+/24+) - êo-o ) -0.90 V (6)
where êo-o is the energy of the *24+ excited state as determined
from the spectroscopic energy. This shows that even a mild
oxidant should be capable of oxidizing the photoexcited *24+
rotaxane (eq 3). As already pointed out, however,9 the choice
of the oxidant is not a trivial matter because other important
requirements have to be satisfied: (i) the oxidant should not
compete for light absorption, (ii) the reaction between *24+ and
the oxidant (eq 3) should be fast enough to compete with the
intrinsic excited-state decay (eq 2), and (iii) after reduction, the
oxidant should undergo a very fast, irreversible decomposition
reaction (eq 5) in order to prevent the occurrence of the back-
electron-transfer reaction (eq 4). Such requirements are sub-
(29) In acetonitrile solution, p-NO2C6H4CH2Br shows a band with λmax
) 273 nm which does not interfere in the visible light absorption of CuIN4.
On reduction of p-NO2C6H4CH2Br, a benzylic radical is formed which
undergoes a fast dimerization reaction. In the presence of dioxygen, the
benzylic radical gives rise to a series of reactions which end with formation
of benzaldehyde.30
(30) Kern, J.-M.; Sauvage, J.-P. J. Chem. Soc., Chem. Commun. 1987,
546-548.
(31) (a) Stern, O.; Volmer, M. Z. Phys. 1919, 20, 183. (b) Gilbert, A.;
Baggott, J. Essentials of Molecular Photochemistry; Blackwell Scientific
Publications: Oxford, U.K., 1991.
(26) (a) Everly, R. M.; McMillin, D. R. Photochem. Photobiol. 1989,
50, 711-. (b) Kirchhoff, J. R.; McMillin, D. R.; Robinson, W. R.; Powell,
D. R.; McKenzie, A. T.; Chen, S. Inorg. Chem. 1985, 24, 3928-3933.
(27) Miller, M. T.; Gantzel, P. K.; Karpishin, T. B. Inorg. Chem. 1998,
37, 2285-2290.
(28) Balzani, V.; Bolletta, F.; Gandolfi, M. T.; Maestri, M. Top. Curr.
Chem. 1978, 75, 1-64.
(32) (a) Phifer, C. C.; McMillin, D. R. Inorg. Chem. 1986, 25, 1329-
1333. (b) Karlsson, K.; Moucheron, C.; Kirsch-De Mesmaeker, A. New J.
Chem 1994, 18, 721-729.

4404 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Armaroli et al.
Figure 7. Spectral changes caused by photoirradiation of an acetonitrile
solution containing 1.0 × 10-4 M 24+, 1.8 × 10-2 M p-NO2C6H4CH2-
Br, and 1.0 × 10-1 M TBA(BF4). The isosbestic point is at 626 nm.
(i) Initial spectrum; (f) final spectrum obtained after 20 min of
irradiation.
Figure 8. Absorption spectra of an acetonitrile solution of 24+
containing 1.0 × 10-1 M TBA(BF4): (a) before light irradiation; (b)
at the end of the photoreaction (about 20 min irradiation) with
p-NO2C6H4CH2Br; (c) after subsequent 26 h in the dark; (d) 8 h after
subsequent addition of an excess of ascorbic acid.
whereas such a salt was not present under the photochemical
conditions. We have previously found that, in the analogous
catenate system,9 the rate of the structural rearrangement
processes is strongly affected by the nature of the solvent and
the presence of salts, presumably because the change in the
coordination number of the metal requires solvent/anion as-
sistance. Such assistance is likely to be more important in the
rotaxane than in the catenate because, in the former, the gliding
motions imply a shift of the copper ion along the thread with a
complete lack of a chelating unit. Therefore, we thought that
the different behavior found for the photoinduced compared to
the electrochemically induced process in the rotaxane could be
due to the absence and, respectively, presence of TBA(BF4).
To check this hypothesis, we carried out a new series of
photochemical experiments in the presence of 0.1 M TBA(BF4).
Under these conditions, light excitation was found to cause the
spectral changes shown in Figure 7, which clearly indicate the
photoinduced process has to be attributed to a competition
between back electron transfer (reaction 4) and the irreversible
decomposition of the primary reduced product of p-NO2C6H4-
CH2Br (reaction 5).
Conclusion
The motion of the ring and of the metal ion from the bidentate
to the tridentate site on the string can be carried out electro-
chemically or by an oxidative photochemical process and can
be fully reversed upon chemical reduction. A comparison with
the analogous catenate catd9 shows that, for 24+, (i) the excited-
state lifetime is shorter, (ii) the rate constant for the excited-
state quenching reaction by p-NO2C6H4CH2Br is higher, and
(iii) the thermal CuII(4)/CuII conversion is less clean in the
(5)
absence of TBA(BF4). These results show that the metal ion is
less protected from interaction with external species in the
rotaxane than in the catenate, as expected from structural
considerations. This is also in agreement with the faster and,
respectively, slower rate constant observed for the CuII(4)-to-
disappearance of 24+ and the concomitant formation of 242+
-
(CuII(4)) as the only reaction product. At the end of the
photoreaction, the irradiated solution was kept in the dark at
298 K. Spectrophotometric measurements showed that a slow
reaction was occurring, causing a general decrease in absor-
bance, particularly in the 600-800-nm region (Figure 8), as
expected for the transformation of 242+(CuII(4)) into the more
stable 242+(CuII(5)) species (Figure 6). After about 26 h, no
further spectral change was observed. At this stage, the spectrum
of the solution was that shown by curve c in Figure 8, which is
that of the stable CuII(5) species. To close the cycle (Figure 6),
an excess of ascorbic acid was added to the solution. A gradual,
complete reappearance of the spectrum of 24+(CuI(4)) was
observed, as happens when oxidation and successive reduction
are carried out electrochemically. After about 8 h, the spectrum
was practically coincident with the initial spectrum (Figure 8),
showing that the cyclic process (Figure 6) is fully reversible,
even when oxidation is photoinduced and reduction is chemi-
cally induced.33
CuII and the CuI(5)-to-CuI(4) conversions in the rotaxane
(5)
compared to the catenane species.
Experimental Section
Materials and General Procedures. The following chemicals were
prepared according to literature procedures: 5,5′′-dimethyl-2,2′:6′,2′′-
terpyridine (1),9 2-methyl-9-(p-anisyl)-1,10-phenanthroline (13),17 Cu-
(MeCN)4BF4,18 Cu(MeCN)4PF6,34 and tris(p-tert-butylphenyl)(4-hy-
droxyphenyl)methane (9).20 All other chemicals were of the best
commercially available grade and were used without further purification.
Dry solvents were distilled from suitable desiccants (DMF from CaH2
under reduced pressure, CH2Cl2 from P2O5 or CaH2, THF from Na
and benzophenone). Thin-layer chromatography (TLC) was carried out
on aluminum sheets coated with silica gel 60 F254 (Merck 5554) or on
plastic sheets precoated with aluminum oxide N/UV254 (Macherey Nagel
802021). After elution, the plates were either examined under a UV
lamp or exposed to I2. Column chromatography was performed with
silica gel 60 (Merck 9385, 230-400 mesh) or aluminum oxide 90
(neutral, act. II-III, Merck 1097). 1H NMR spectra were recorded on
either Bruker WP 200SY (200 MHz) or WP 400SY (400 MHz)
spectrometers (using the deuterated solvent as the lock and residual
solvent as the internal reference). Fast atom bombardment mass spectra
(FAB-MS) were recorded in the positive ion mode with either a krypton
primary atom beam in conjunction with a 3-nitrobenzyl alcohol matrix
and a Kratos MS80RF mass spectrometer coupled to a DS90 system,
The overall quantum yield of the photoreaction was about
3%. Since, under the experimental conditions used, the fraction
of *24+ excited states reacting with the quencher is ∼50%, the
fraction of quenching events that give rise to a permanent
formation of 242+ is ∼6%. Since p-NO2C6H4CH2Br cannot
quench *24+ by energy transfer, the low efficiency of the
(33) Since 242+ is not photosensitive and does not exhibit any long-
lived excited state, the reduction step cannot be induced by light; see ref 9.
(34) Kubas, G. J.; Monzik, B.; Crumbliss, A. Inorg. Synth. 1990, 28,
68-70.

Rotaxanes with Two Different Coordinating Units
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4405
or a xenon primary atom beam with the same matrix and a ZAB-HF
mass spectrometer. Melting points were mesured with a Bu¨chi SMP20
apparatus and are uncorrected. Electrochemical measurements were
performed with a three-electrode system consisting of a platinum
working electrode, a platinum wire counter electrode, and a standard
reference calomel electrode (SCE), versus which all potentials are
reported. All measurements were carried out under Ar, in degassed
spectroscopic grade solvents, using 0.1 M n-Bu4NBF4 solutions as
supporting electrolyte. An EG&G Princeton Applied Research model
273A potentiostat connected to a computer was used (software from
Program Research Electrochemistry Software), as well as a Bruker
E130M potentiostat, connected to a printing table.
All the spectroscopic and photochemical investigations were carried
out in 1-cm-path length cuvettes using acetonitrile as solvent (Carlo
Erba for spectroscopy). The absorption spectra were recorded with a
Perkin-Elmer Lambda-5 spectrophotometer. Emission spectra were
obtained with a Spex Fluorolog II spectrofluorometer (continuous Xe
lamp, Osram XBOW/1), equipped with a Hamamatsu R-928 photo-
multiplier tube. For the photochemical experiments, the concentration
of 24+ (as PF6- salt) was 1.0 × 10-4 M, and that of p-NO2C6H4CH2Br
was 1.8 × 10-2 M. The solutions, continuously stirred, were irradiated
with the spectrofluorometer lamp (see above) at 464 nm (1681B
minimate Spex monochromator) using slits of 2.5 mm (9.4 nm).The
quantum yield of the photoreaction was calculated by measuring the
intensity of the light source with the “microversion” of the ferric oxalate
actinometer.35 An IBH single-photon-counting equipment N2 lamp (λexc
) 337 nm) was used to obtain the excited-state lifetimes.
120.5 (2 CH), 61.5 (CH2), 33.8 (CH2), 29.1 (CH2), 18.4 (CH3); EI-MS
m/z (relative intensity) 305 (100, M+), 287 (18), 286 (38), 275 (35),
274 (45), 260 (65), 143 (20). Anal. Calcd for C19H19N3O: C, 74.73;
H, 6.27; N, 13.76. Found: C, 74.63; H, 6.19; N, 13.61.
5-(3-Methanosulfonyl-1-propyl)-5′′-methyl-2,2′:6′,2"-terpyri-
dine (4). A solution of 3 (3.38 g, 11.1 mmol) and freshly distilled NEt3
(9.3 mL, 66.6 mmol) in anhydrous CH2Cl2 (300 mL) was cooled to
-3 °C. Mesyl chloride (3.5 mL, 44.4 mmol) in anhydrous CH2Cl2 (85
mL) was added dropwise (-5 °C < T < -2 °C), and the resulting
mixture was stirred under Ar at -3 °C for 4 h. The reaction mixture
was washed with cold H2O and dried over Na2SO4. The organic phase
was filtered and concentrated to furnish a white solid, which was
purified through a short alumina column (CH2Cl2) to give 4 as a white
powder (4.05 g, 95%): mp 92-94 °C; 1H NMR (200 MHz, CDCl3) δ
) 8.58-8.48 (m, 4H), 8.40 (d, J ) 7.8 Hz, 2H), 7.93 (t, J ) 7.8 Hz,
1H), 7.72-7.64 (m, 2H), 4.29 (t, J ) 6.2 Hz, 2H), 3.03 (s, 3H), 2.86
(t, J ) 7.6 Hz, 2H), 2.42 (s, 3H), 2.22-2.08 (m, 2H); 13C{1H} NMR
(50 MHz, CDCl3, DEPT) δ ) 155.4 (C), 155.2 (C), 154.7 (C), 153.7
(C), 149.5 (CH), 149.2 (CH), 137.9 (CH), 137.6 (CH), 137.0 (CH),
135.9 (C), 133.6 (C), 121.1 (CH), 120.8 (CH), 120.7 (CH), 120.6 (CH),
68.7 (CH2), 37.5 (CH3), 30.5 (CH2), 28.7 (CH2), 18.5 (CH3); EI-MS
m/z (relative intensity) 383 (45, M+), 287 (49), 286 (52), 274 (100),
260 (38).
5-(3-Bromo-1-propyl)-5′′-methyl-2,2′:6′2′′-terpyridine (5). A mix-
ture of 4 (0.45 g, 1.17 mmol) and anhydrous LiBr (0.51 g, 5.9 mmol)
in acetone (30 mL) was refluxed under Ar for 1 h. After evaporation
of the solvent, the crude mixture was dissolved in CH2Cl2, washed
with H2O, and dried over Na2SO4. Solvent was evaporated to yield a
white solid (0.416 g, 97%), which was used in the next step without
further purification: 1H NMR (200 MHz, CDCl3) δ ) 8.57-8.48 (m,
4H), 8.39 (d, J ) 7.6 Hz, 2H), 7.93 (t, J ) 7.8 Hz, 1H), 7.73-7.64
(m, 2H), 3.44 (t, J ) 6.4 Hz, 2H), 2.89 (t, J ) 7.4 Hz, 2H), 2.42 (s,
3H), 2.30-2.16 (m, 2H).
Ligand 14. A titrated commercial solution of LDA in THF (ca. 1.3
M, 1.05 mL, 1.35 mmol) was added dropwise to a stirred solution of
2-methyl-9-(p-anisyl)-1,10-phenanthroline 13 (0.40 g, 1.33 mmol) in
anhydrous THF (20 mL) at -78 °C. The resulting deep red solution
was stirred under Ar for 2 h at -78 °C and then for 1 h from -78 to
10 °C. After the solution was cooled back to -78 °C, a degassed
solution of 5 (0.41 g, 1.11 mmol) in anhydrous THF (20 mL) was
added dropwise. The reaction mixture was left in an ice bath and
allowed to reach room temperature with stirring overnight. The resulting
blue solution was hydrolyzed at 0 °C with 10 mL of H2O. THF was
evaporated and the residue extracted with CH2Cl2. The combined
organic layers were washed with water, dried over Na2SO4, and filtered.
Solvent was evaporated to give an orange oil which was purified by
column chromatography on alumina (hexane-CH2Cl2) to yield 14
(0.364 g, 56%), as a yellow solid: 1H NMR (400 MHz, CDCl3) δ )
8.57 (d, J ) 2 Hz, 1H), 8.52 (d, J ) 2 Hz, 1H), 8.50 (d, J ) 8.0 Hz,
1H), 8.48 (d, J ) 8.0 Hz, 1H), 8.39-8.35 (m, 4H), 8.24 (d, J ) 8.5
Hz, 1H), 8.14 (d, J ) 8.2 Hz, 1H), 8.05 (d, J ) 8.5 Hz, 1H), 7.91 (t,
J ) 7.8 Hz, 1H), 7.75-7.70 (m, 3H), 7.64 (dd, J ) 8.0 and 2 Hz, 1H),
7.50 (d, J ) 8.2 Hz, 1H), 7.07 (d, J ) 8.8 Hz, 2H), 3.87 (s, 3H), 3.28
(t, J ) 7.8 Hz, 2H), 2.85 (t, J ) 7.6 Hz, 2H), 2.41 (s, 3H), 2.10 (qt, J
) 7.8 Hz, 2H), 1.92 (qt, J ) 7.6 Hz, 2H); FAB-MS m/z (relative
intensity) 588.2 (100, MH+), 313.1 (10, M - C18H16N3), 300.1 (16, M
- C19H17N3), 287.1 (15, C19H17N3), 274.1 (12, C18H16N3).
Pseudorotaxane 18‚BF4. A solution of Cu(MeCN)4BF4 (0.065 g,
0.207 mmol) in degassed MeCN (35 mL) was transferred by means of
a double-ended needle to a degassed solution of macrocycle 17 (0.122
g, 0.216 mmol) in CH2Cl2 (35 mL) under Ar. The mixture turned orange
instantaneously. After the mixture was stirred at room temperature for
20 min, a degassed solution of 14 (0.127 g, 0.216 mmol) in CH2Cl2
(35 mL) under Ar was added via a double-ended needle, resulting in
the immediate formation of a dark red solution. The reaction mixture
was stirred overnight under Ar at room temperature. After evaporation
of the solvents, the residue was chromatographed on an alumina column
(CH2Cl2-0.5% MeOH), yielding 18‚BF4 (0.212 g, 75%) as a brown-
red solid: 1H NMR (200 MHz, CD2Cl2) δ ) 8.67 (d, J ) 8.3 Hz, 1H),
8.55-7.65 (m, 19H), 7.57 (d, J ) 8.3 Hz, 1H), 7.31 (d, J ) 8.6 Hz,
4H), 7.14 (d, J ) 8.7 Hz, 2H), 5.95 (d, J ) 8.6 Hz, 4H), 5.88 (d, J )
5′′-Methyl-5-{3-[(tetrahydro-2H-pyran-2-yl)oxy]-1-propyl}-2,2′:
6′2′′-terpyridine (2). A titrated commercial solution of LDA in THF
(ca. 1.5 M, 20.2 mL, 30.3 mmol) was slowly added dropwise to a
solution of 5,5′′-dimethyl-2,2′:6′,2′′-terpyridine 1 (7.15 g, 27.4 mmol)
in anhydrous THF (275 mL) at -78 °C. The resulting deep purple
solution was stirred under Ar for 2 h at -78 °C and then for 0.5 h at
0 °C. After the solution was cooled back to -78 °C, a degassed solution
of 2-(2-bromoethoxy)tetrahydro-2H-pyran (5.72 g, 27.4 g mmol) in
anhydrous THF (270 mL) at 0 °C was added by means of a double-
ended needle. The resulting mixture was left at 0 °C and allowed to
reach room temperature with stirring for 16 h. Then it was cooled back
to 0 °C, and 100 mL of H2O was slowly added. THF was evaporated,
and the residue was taken in CH2Cl2, washed with water, dried over
MgSO4, and filtered. Solvent was evaporated, and the residue was
subjected to column chromatography on alumina (hexanes-Et2O),
1
yielding 2 (4.66 g, 44%) as a white solid: mp 67-69 °C; H NMR
(200 MHz, CDCl3) δ ) 8.55-8.49 (m, 4H), 8.39 (d, J ) 7.8 Hz, 2H),
7.93 (t, J ) 7.9 Hz, 1H), 7.72-7.64 (m, 2H), 4.60 (t, J ) 3.0 Hz, 1H),
3.95-3.77 (m, 2H), 3.58-3.39 (m, 2H), 2.82 (t, J ) 7.3 Hz, 2H), 2.42
(s, 3H), 1.99 (qt, J ) 7.4 Hz, 2H), 1.91-1.50 (m, 6H); 13C{1H} NMR
(50 MHz, CDCl3, DEPT) δ ) 155.5 (2C), 154.3 (C), 153.9 (C), 149.6
(CH), 149.4 (CH), 137.8 (CH), 137.5 (C), 137.4 (CH), 136.8 (CH),
133.4 (C), 120.9 (CH), 120.7 (CH), 120.4 (2CH), 99.1 (CH), 66.5 (CH2),
62.5 (CH2), 31.1 (CH2), 30.8 (CH2), 29.6 (CH2), 25.5 (CH2), 19.8 (CH2),
18.4 (CH3); EI-MS m/z (relative intensity) 389 (10, M+), 360 (11),
334 (8), 287 (69), 274 (73), 261 (100).
5-(3-Hydroxy-1-propyl)-5′′-methyl-2,2′:6′,2′′-terpyridine (3). A
solution of 2 (5.11 g, 13.1 mmol) in EtOH (300 mL) was heated to
reflux. Concentrated HCl (0.5 mL) was added, and the mixture was
refluxed for 3 h. The solution was allowed to cool to room temperature
and then neutralized with concentrated NaOH (ca. 30%). EtOH was
evaporated, and the residue was taken in CH2Cl2 and washed with brine.
The organic phase was dried over Na2SO4 and filtered. Evaporation of
the solvent led to a yellow solid (3.78 g) which was purified by column
chromatography on alumina (CH2Cl2 containing 0-1% MeOH) to give
pure alcohol 3 (3.40 g, 85%) as a white powder: mp 111-112 °C; 1H
NMR (200 MHz, CDCl3) δ ) 8.53-8.47 (m, 4H), 8.37 (d, J ) 7.8
Hz, 2H), 7.92 (t, J ) 7.8 Hz, 1H), 7.70-7.62 (m, 2H), 3.70 (t, J ) 6.3
Hz, 2H), 2.79 (t, J ) 7.7 Hz, 2H), 2.40 (s, 3H), 2.10 (br s, 1H), 1.99-
1.85 (m, 2H); 13C{1H} NMR (50 MHz, CDCl3, DEPT δ ) 155.4 (C),
155.3 (C), 154.2 (C), 153.7 (C), 149.5 (CH), 149.2 (CH), 137.8 (CH),
137.6 (C), 137.5 (CH), 136.9 (CH), 133.5 (C), 121.0 (CH), 120.9 (CH),
(35) Fisher, E. EPA Newsl. 1983, July, 33-34.

4406 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Armaroli et al.
8.7 Hz, 2H), 3.80 (s, 4H), 3.70-3.38 (m, 16H), 3.46 (s, 3H), 2.50 (t,
J ) 7.8 Hz, 2H), 2.43 (s, 3H), 2.29 (t, J ) 7.8 Hz, 2H), 1.55-1.45 (m,
2H), 1.30-1.20 (m, 2H); UV-vis (MeCN) λmax ) 442 nm (ꢀ 3100);
FAB-MS m/z (relative intensity) 1216.4 (39, [M - BF4]+; calcd 1216.4),
650.2 (100, [M - 17 - BF4]+; calcd 650.2), 629.1 (28, [M - 14 -
BF4]+; calcd 629.2), 588.2 (12, 14H+; calcd 588.3), 567.2 (17, 17H+;
calcd 567.2).
was obtained, which was subjected to column chromatography on
alumina (CH2Cl2 containing 0-1% MeOH) to afford a mixture of
alcohol 10 and mesylate 11 in 46% yield. A second fast alumina column
(CH2Cl2-0.5%) yielded pure alcohol 10 (0.374 g, 32%) and pure
mesylate 11 (0.166 g, 13%), both as white solids. 10: 1H NMR (200
MHz, CDCl3) δ ) 8.56-8.51 (m, 4H), 8.40 (d, J ) 7.8 Hz, 2H), 7.93
(t, J ) 7.8 Hz, 1H), 7.74-7.66 (m, 2H), 7.24 (d, J ) 8.8 Hz, 6H),
7.09 (d, J ) 8.8 Hz, 8H), 6.78 (d, J ) 8.9 Hz, 2H), 3.99 (t, J ) 6.0
Hz, 2H), 3.74 (t, J ) 6.3 Hz, 2H), 2.95-2.77 (m, 4H), 2.20-2.11 (m,
2H), 2.03-1.89 (m, 2H), 1.60 (br s, 1H), 1.30 (s, 27H); FAB-MS m/z
(relative intensity) 836.3 (100, MH+), 702.2 (9, [M - (t-BuC6H4)]+),
411.1 (24, [(t-BuC6H4)3C]+). 11: 1H NMR (200 MHz, CDCl3) δ )
8.58-8.51 (m, 4H), 8.41 (d, J ) 8.1 Hz, 2H), 7.94 (t, J ) 7.8 Hz,
1H), 7.74-7.67 (m, 2H), 7.24 (d, J ) 8.9 Hz, 6H), 7.09 (d, J ) 8.9
Hz, 8H), 6.78 (d, J ) 8.9 Hz, 2H), 4.29 (t, J ) 6.2 Hz, 2H), 3.99 (t,
J ) 6.0 Hz, 2H), 3.03 (s, 3H), 2.95-2.82 (m, 4H), 2.22-2.08 (m,
4H), 1.30 (s, 27H); FAB-MS m/z (relative intensity) 914.5 (100, MH+),
780.4 (14, [M - (t-BuC6H4)]+), 411.3 (53, [(t-BuC6H4)3C]+).
(b) Via Alcohol 10. Mesyl chloride (0.31 mL, 4.0 mmol) in
anhydrous CH2Cl2 (10 mL) was added dropwise over a stirred solution
of 10 (0.84 g, 1.0 mmol) and freshly distilled NEt3 (0.84 mL, 6.0 mmol)
in anhydrous CH2Cl2 (30 mL) at -3 °C, and the mixture was stirred at
-2 °C for 4 h. The reaction mixture was washed with cold H2O, dried
over Na2SO4, and filtered. Removal of the solvent led to a white solid
(0.91 g, 100%). TLC (alumina; CH2Cl2-1% MeOH) showed one spot,
and the product was used in the next step without further purification.
Bromo Derivative 12. A mixture of crude mesylate 11 (0.91 g)
and anhydrous LiBr (0.434 g, 5.0 mmol) in acetone (30 mL) was
refluxed under Ar for 2 h. Solvent was evaporated, and the residue
was taken in CH2Cl2, washed with cold H2O, dried over Na2SO4, and
filtered. Solvent was removed, and the crude was filtered through a
short alumina column (CH2Cl2) to yield pure 12 as a white solid (0.72
g, 80% yield from alcohol 10): 1H NMR (200 MHz, CDCl3) δ ) 8.57-
8.51 (m, 4H), 8.40 (d, J ) 7.8 Hz, 2H), 7.94 (t, J ) 7.8 Hz, 1H),
7.74-7.67 (m, 2H), 7.24 (d, J ) 8.9 Hz, 6H), 7.09 (d, J ) 8.9 Hz,
8H), 6.78 (d, J ) 8.9 Hz, 2H), 3.99 (t, J ) 6.0 Hz, 2H), 3.44 (t, J )
6.4 Hz, 2H), 2.95-2.85 (m, 4H), 2.30-2.10 (m, 4H), 1.30 (s, 27H);
FAB-MS m/z (relative intensity) 900.5 (100, MH+), 818.5 (13, [M -
Br]+), 766.4 (11, [M - (t-BuC6H4)]+), 411.3 (47, [(t-BuC6H4)3C]+).
Ligand 15. A titrated commercial solution of LDA in THF (ca. 1.5
M, 0.72 mL, 1.08 mmol) was slowly added dropwise to a degassed
solution of 2-methyl-9-(p-anisyl)-1,10-phenanthroline 13 (0.31 g, 1.03
mmol) in anhydrous THF (20 mL) at -78 °C. The resulting deep purple
solution was stirred under Ar at -78 °C for 2 h and then for 1 h from
-78 to 0 °C. The mixture was cooled again to -78 °C, and a degassed
solution of 12 (0.78 g, 0.86 mmol) in anhydrous THF (25 mL) was
added dropwise. The resulting deep purple mixture was left at 0 °C
and slowly allowed to reach room temperature during 16 h. The reaction
mixture was then hydrolyzed at 0 °C with H2O (20 mL). THF was
removed, and the residue was taken in CH2Cl2, washed with H2O, dried
over Na2SO4, and filtered. Solvent was evaporated, and the residue
was subjected to column chromatography on alumina (hexane-CH2-
Cl2) to yield 15 as a yellow solid (0.587 g, 61%): 1H NMR (200 MHz,
CDCl3) δ ) 8.57-8.48 (m, 4H), 8.40-8.34 (m, 4H), 8.26 (d, J ) 8.5
Hz, 1H), 8.15 (d, J ) 8.2 Hz, 1H), 8.06 (d, J ) 8.5 Hz, 1H), 7.92 (t,
J ) 7.9 Hz, 1H), 7.74-7.67 (m, 4H), 7.51 (d, J ) 8.2 Hz, 1H), 7.24
(d, J ) 8.7 Hz, 6H), 7.11-7.05 (m, 10H), 6.78 (d, J ) 8.9 Hz, 2H),
3.99 (t, J ) 6.0 Hz, 2H), 3.88 (s, 3H), 3.29 (t, J ) 7.6 Hz, 2H), 2.95-
2.81 (m, 4H), 2.21-2.07 (m, 4H), 2.00-1.88 (m, 2H), 1.30 (s, 27H);
FAB-MS m/z (relative intensity) 1118.6 (100, MH+; calcd 1118.6),
818.5 (13, [M - C20H15N2O]+), 411.3 (71, [(t-BuC6H4)3C]+), 300.1
(83, [C20H16N2O]+).
5,5′′-Bis{3-[(tetrahydro-2H-pyran-2-yl)oxy]-1-propyl}-2,2′:6′,2′′-
terpyridine (6). A titrated commercial solution of LDA in THF (ca.
1.5 M, 5.6 mL, 8.4 mmol) was slowly added dropwise over a solution
of 5,5′′-dimethyl-2,2′:6′,2′′-terpyridine 1 (1.0 g, 3.83 mmol) in anhy-
drous THF (40 mL) at -78 °C. The resulting purple solution was stirred
under Ar for 2 h at -78 °C and for 0.5 h at 0 °C. Then it was cooled
again to -78 °C, and a degassed solution of THP-protected bromoet-
hanol (1.76 g, 8.42 mmol) in anhydrous THF (40 mL) at 0 °C was
added under Ar by means of a double-ended needle. The resulting
mixture was left at 0 °C and allowed to reach room temperature with
stirring for 16 h. The blue solution thus obtained was hydrolyzed at 0
°C with 30 mL of H2O. THF was evaporated and the residue extracted
with CH2Cl2, dried over Na2SO4, and filtered. Evaporation of the solvent
led to an orange solid which was subjected to column chromatography
on alumina (ether-hexane) to afford 6 (0.89 g, 45%) as a white solid:
mp 71-73 °C; 1H NMR (200 MHz, CDCl3) δ ) 8.55 (br s, 2H), 8.53
(d, J ) 7.8 Hz, 2H), 8.39 (d, J ) 7.8 Hz, 2H), 7.93 (t, J ) 7.8 Hz,
1H), 7.69 (dd, J ) 7.8 and 2.3 Hz, 2H), 4.60 (t, J ) 3.5 Hz, 2H),
3.93-3.77 (m, 4H), 3.56-3.39 (m, 4H), 2.81 (t, J ) 7.2 Hz, 4H), 1.99
(qt, J ) 7.2 Hz, 4H), 1.92-1.50 (m, 12H); 13C NMR (50.3 MHz,
CDCl3, DEPT) δ ) 155.5 (C), 154.3 (C), 149.4 (CH), 137.8 (CH),
137.5 (C), 136.8 (CH), 120.9 (CH), 120.5 (CH), 99.1 (CH), 66.5 (CH2),
62.5 (CH2), 31.1 (CH2), 30.8 (CH2), 29.6 (CH2), 25.5 (CH2), 19.8 (CH2).
5,5′′-Bis(3-hydroxy-1-propyl)-2,2′:6′,2′′-terpyridine (7). Concen-
trated HCl (0.3 mL) was added to a refluxing solution of 6 (1.89 g,
3.65 mmol) in EtOH (100 mL). The mixture was refluxed for 3 h and
then allowed to reach room temperature with stirring overnight. After
neutralization with concentrated NaOH, EtOH was removed and the
residue taken in CH2Cl2 and washed with brine. Solvent was partially
evaporated, resulting in the precipitation of a white solid, which was
separated by filtration (0.98 g). The filtered organic phases were
gathered. Solvent was evaporated and the residue purified by column
chromatography (alumina, CH2Cl2-2% MeOH) to give other 0.25 g
of white solid (overall yield of 7, 96%). A small amount was
recrystallized from CH2Cl2, affording white needles of 7: mp 131-
1
132 °C; H NMR (200 MHz, CDCl3) δ ) 8.56 (br s, 2H), 8.53 (d, J
) 7.8 Hz, 2H), 8.39 (d, J ) 7.8 Hz, 2H), 7.94 (t, J ) 7.8 Hz, 1H),
7.70 (dd, J ) 7.8 and 2.3 Hz, 2H), 3.73 (q, J ≈ 5.9 Hz, 4H), 2.81 (t,
J ) 7.7 Hz, 4H), 2.02-1.88 (m, 4H), 1.40 (t, J ) 5.1 Hz, 2H); 13C
NMR (50.3 MHz, CDCl3) δ ) 155.4 (C), 154.4 (C), 149.3 (CH), 137.9
(CH), 137.5 (C), 136.8 (CH), 120.9 (CH), 120.6 (CH), 61.9 (CH2),
33.9 (CH2), 29.1 (CH2). Anal. calcd for C21H23N3O2: C, 72.18; H, 6.63;
N, 12.03. Found: C, 72.22; H, 6.69; N, 11.88.
5,5′′-Bis(3-methanosulfonyl-1-propyl)-2,2′:6′,2′′-terpyridine (8).
Mesyl chloride (0.93 mL, 12 mmol) in anhydrous CH2Cl2 (20 mL)
was slowly added dropwise over a stirred solution of diol 7 (0.524 g,
1.50 mmol) and freshly distilled NEt3 (2.51 mL, 18 mmol) in anhydrous
CH2Cl2 (40 mL) at -3 °C. The resulting mixture was stirred under Ar
at -2 °C for 4 h. The reaction mixture was then washed with cold
H2O, dried over Na2SO4, and filtered. Removal of the solvent led to a
yellow solid, which was filtered through a short alumina column (CH2-
Cl2) to give a white solid (0.68 g, 90%): 1H NMR (200 MHz, CDCl3)
δ ) 8.58-8.54 (m, 4H), 8.41 (d, J ) 7.8 Hz, 2H), 7.95 (t, J ) 7.8 Hz,
1H) 7.71 (dd, J ) 7.8 and 2.2 Hz, 2H), 4.30 (t, J ) 6.2 Hz, 4H), 3.04
(s, 6H), 2.87 (t, J ) 7.5 Hz, 4H), 2.21-2.11 (m, 4H); 13C NMR (50.3
MHz, CDCl3, DEPT) δ ) 155.3 (C), 154.8 (C), 149.3 (CH), 137.9
(CH), 136.9 (CH), 135.9 (C), 121.1 (CH), 120.7 (CH), 68.7 (CH2),
37.5 (CH3), 30.5 (CH2), 28.8 (CH2).
Ligand 16. A solution of 15 (0.28 g, 0.25 mmol) in dry DMF (13
mL) was added to EtSNa (0.105 g, 1.25 mmol), and the mixture was
stirred at 110 °C under a slow flow of Ar for 16 h. The solution was
allowed to reach 60 °C, and 15 mL of H2O was added. The mixture
was stirred at 60 °C for 20 min, poured into H2O (30 mL), and extracted
with CH2Cl2. The organic phase was separated, and the aqueous phase
was treated with solid NH4Cl and extracted again with more CH2Cl2.
The combined organic layers were washed with buffered aqueous
solution (pH ) 7) and then with water, dried over Na2SO4, and filtered.
Mesylate 11. (a) Directly from 8 and 9. A mixture of dimesylate
8 (0.71 g, 1.40 mmol), tris(p-tert-butylphenyl)(4-hydroxyphenyl)-
methane 9 (0.71 g, 1.40 mmol), and K2CO3 (0.29 g, 2.1 mmol) in DMF
(150 mL) was stirred at 75 °C under Ar for 18 h. Solvent was
evaporated and the crude treated with CH2Cl2, washed with H2O, dried
over Na2SO4, and filtered. After removal of the solvent, a yellow solid

Rotaxanes with Two Different Coordinating Units
J. Am. Chem. Soc., Vol. 121, No. 18, 1999 4407
Evaporation of the solvent led to a brown solid, which was purified by
column chromatography on alumina (CH2Cl2-2% MeOH) to yield a
yellow solid (0.222 g, 80%): 1H NMR (200 MHz, CDCl3) δ ) 8.55
(d, J ≈ 2 Hz, 1H), 8.51 (d, J ≈ 2 Hz, 1H), 8.44 (d, J ) 8.1 Hz, 1H),
8.43 (d, J ) 8.1 Hz, 1H), 8.36-8.31 (m, 2H), 8.18-8.13 (m, 2H),
8.05 (d, J ) 8.7 Hz, 2H), 7.93-7.84 (m, 2H), 7.69 (s, 2H), 7.69-7.62
(m, 2H), 7.50 (d, J ) 8.2 Hz, 1H), 7.23 (d, J ) 8.6 Hz, 6H), 7.11-
7.05 (m, 8H), 6.92 (d, J ) 8.7 Hz, 2H), 6.77 (d, J ) 8.9 Hz, 2H), 3.97
(t, J ) 6.0 Hz, 2H), 3.27 (t, J ) 7.4 Hz, 2H), 2.91-2.74 (m, 4H),
2.21-1.85 (m, 6H), 1.30 (s, 27H); FAB-MS m/z (relative intensity)
1104.8 (52, MH+; calcd 1104.6), 818.6 (7, [M - C19H13N2O]+), 411.4
(48, [(t-BuC6H4)3C]+), 286.2 (100, C19H14N2O+).
Semirotaxane 19‚PF6. A solution of Cu(MeCN)4PF6 (19.6 mg, 0.053
mmol) in degassed MeCN (9 mL) was transferred via a cannula to a
stirred solution of 17 (28.3 mg, 0.050 mmol) in CH2Cl2 (9 mL), all
under an atmosphere of Ar. The resulting orange solution was stirred
at room temperature for 30 min. Then it was added via a cannula to a
degassed solution of 15 (56 mg, 0.050 mmol) in CH2Cl2 (20 mL), and
the resulting brown red solution was stirred under Ar at room
temperature for 16 h. Solvent was evaporated and the residue filtered
through a short alumina column (CH2Cl2-0.5% MeOH) to give 19‚
PF6 as a brown-red solid (76 mg, 80%): 1H NMR (400 MHz, CD2-
Cl2) δ ) 8.68 (d, J ) 8.3 Hz, 1H), 8.57 (br s, 1H), 8.49-8.45 (m,
4H), 8.40 (d, J ) 7.5 Hz, 1H), 8.29 (d, J ) 8.8 Hz, 1H), 8.24 (d, J )
7.8 Hz, 1H), 8.23 (d, J ) 7.8 Hz, 1H), 8.10 (br s, 1H), 8.06 (d, J ) 8.8
Hz, 1H), 8.00 (s, 2H), 7.92 (d, J ) 8.3 Hz, 2H), 7.89 (t, J ) 7.8 Hz,
1H), 7.76-7.73 (m, 2H), 7.58 (d, J ) 8.3 Hz, 1H), 7.33 (d, J ) 8.7
Hz, 4H), 7.29-7.14 (m, 17H), 6.81 (d, J ) 9.0 Hz, 2H), 5.97 (d, J )
8.7 Hz, 4H), 5.90 (d, J ) 8.6 Hz, 2H), 4.02 (t, J ) 6.2 Hz, 2H), 3.81
(s, 4H), 3.70-3.66 (m, 4H), 3.57-3.52 (m, 8H), 3.46 (s, 3H), 3.46-
3.43 (m, 4H), 2.93-2.89 (m, 2H), 2.53-2.49 (m, 2H), 2.28 (t, J ) 7.2
Hz, 2H), 2.19-2.12 (m, 2H), 1.56-1.50 (m, 2H), 1.30 (s, 27H), 1.32-
1.26 (m, 2H); UV-vis (MeCN) λmax ) 442 nm (ꢀ ) 3100); FAB-MS
m/z (relative intensity) 1747.8 (21, [M - PF6]+; calcd 1747.8), 1180.5
(90, [M - 17 - PF6]+), 629.2 (80, [Cu(17)]+), 411.3 (100, [(t-
BuC6H4)3C]+).
Threaded Precursor 20+. A solution of Cu(MeCN)4PF6 (37.3 mg,
0.100 mmol) in degassed MeCN (10 mL) was transferred via a cannula
to a stirred solution of macrocycle 17 (56.7 mg, 0.100 mmol) in CH2-
Cl2 (10 mL) under Ar, and the resulting orange solution was stirred at
room temperature for 20 min. Then, a degassed solution of 16 (110
mg, 0.100 mmol) in CH2Cl2 (20 mL) was transferred via a cannula,
resulting in the immediate formation of a brown-red solution, which
was stirred under Ar at room temperature for 14 h. Solvent was
evaporated to give a brown-red solid (188 mg, 100%), which was pure
enough to be used in the following step without further purification:
1H NMR (200 MHz, CD2Cl2) δ ) 8.67 (d, J ) 8.3 Hz, 1H), 8.56 (br
s, 1H), 8.51-8.37 (m, 5H), 8.30-8.20 (m, 3H), 8.11 (br s, 1H), 8.06-
7.70 (m, 8H), 7.57 (d, J ) 8.3 Hz, 1H), 7.33-7.14 (m, 19H), 7.04 (d,
J ) 8.6 Hz, 2H), 6.80 (d, J ) 9.0 Hz, 2H), 5.94 (d, J ) 8.6 Hz, 4H),
5.86 (d, J ) 8.6 Hz, 2H), 4.01 (t, J ≈ 6 Hz, 2H), 3.80 (br s, 4H),
3.70-3.65 (m, 4H), 3.58-3.51 (m, 8H), 3.46-3.41 (m, 4H), 2.94-
2.86 (m, 2H), 2.54-2.42 (m, 2H), 2.32-2.24 (m, 2H), 2.18-2.10 (m,
2H), 1.60-1.50 (m, 2H), 1.30 (s, 27H), 1.34-1.24 (m, 2H).
2H), 2.00 (t, J ) 6.2 Hz, 1H), 1.30 (s, 27H); FAB-MS m/z (relative
intensity) 548.1 (33, M+; calcd 548.4), 415.1 (100, [M - (t-BuC6H4)]+),
411.3 (74, [(t-BuC6H4)3C]+).
2-Methanosulfonylethyl p-[Tris(p-tert-butylphenyl)methyl]phenyl
Ether (22). Mesyl chloride (0.06 mL, 0.77 mmol) in anhydrous CH2-
Cl2 (2.5 mL) was slowly added dropwise over a stirred solution of 21
(0.105 g, 0.19 mmol) and freshly distilled NEt3 (0.10 mL, 0.73 mmol)
in anhydrous CH2Cl2 (6 mL) at -3 °C. The mixture was stirred under
Ar at -2 °C for 3.5 h. The solution was then washed with cold water,
dried over Na2SO4, and filtered. Solvent was evaporated, and the
resulting crude was filtered through a short alumina column (CH2Cl2
as eluent), to afford 22 as a white solid (0.116 g, 97%): 1H NMR (200
MHz, CDCl3) δ ) 7.24 (d, J ) 8.7 Hz, 6H), 7.12 (d, J ) 9.0 Hz, 2H),
7.07 (d, J ) 8.7 Hz, 6H), 6.77 (d, J ) 9.0 Hz, 2H), 4.59-4.54 (m,
2H), 4.25-4.20 (m, 2H), 3.09 (s, 3H), 1.30 (s, 27H); FAB-MS m/z
(relative intensity) 626.5 (20, M+; calcd 626.3), 493.4 (100, [M - (t-
BuC6H4)]+), 411.5 (67, [(t-BuC6H4)3C]+).
2-Bromoethyl p-[Tris(p-tert-butylphenyl)methyl]phenyl Ether
(23). A mixture of 22 (0.116 g, 0.185 mmol) and anhydrous LiBr (0.079
g, 0.91 mmol) in acetone (6 mL) was refluxed under Ar for 2 h. Solvent
was evaporated, and the residue was taken in CH2Cl2, washed with
water, and dried over Na2SO4. After filtration and evaporation of the
solvent, a white-yellow solid was obtained (0.112 g, 100%). TLC
(alumina; CH2Cl2) showed only one pot, and the product was used in
the following step without further purification: 1H NMR (200 MHz,
CDCl3) δ ) 7.24 (d, J ) 8.7 Hz, 6H), 7.10 (d, J ) 8.9 Hz, 2H), 7.07
(d, J ) 8.7 Hz, 6H), 6.78 (d, J ) 8.9 Hz, 2H), 4.27 (t, J ) 6.3 Hz,
2H), 3.63 (t, J ) 6.3 Hz, 2H), 1.30 (s, 27H).
Rotaxane 24+. Cs2CO3 (65 mg, 0.20 mmol) in degassed DMF (10
mL) was transferred via a cannula, during a 1-h period, to an argon-
flushed solution of crude threaded complex 20+ (188 mg), bromoalkyl
derivative 23 (73 mg, 0.120 mmol), and ascorbic acid (4.4 mg, 0.025
mmol) in DMF (20 mL) at 45 °C. Once the addition was finished, the
mixture was stirred under Ar at 55 °C for 18 h and then at 65 °C for
6 h more. DMF was evaporated and the resulting crude taken in CH2-
Cl2 and washed with H2O. The organic solution was vigorously stirred
with excess of a KPF6-saturated aqueous solution at room temperature
for 4 h and then washed again with H2O. After evaporation of the
solvent and two successive column chromatographies on alumina (CH2-
Cl2 containing 0-0.2% MeOH), rotaxane 24‚PF6 was obtained as a
brown-red solid (88 mg, 40%): 1H NMR (400 MHz, CD2Cl2) δ )
8.70 (d, J ) 8.3 Hz, 1H), 8.56 (br s, 1H), 8.48-8.46 (m, 2H), 8.41-
8.36 (m, 3H), 8.29 (d, J ) 8.9 Hz, 1H), 8.24 (br d, J ≈ 7.8 Hz, 2H),
8.12 (br s, 1H), 8.05 (d, J ) 8.9 Hz, 1H), 7.89-7.85 (m, 5H), 7.76-
7.71 (m, 2H), 7.59 (d, J ) 8.3 Hz, 1H), 7.33 (d, J ) 8.7 Hz, 4H),
7.32-7.15 (m, 29H), 7.11 (d, J ) 8.6 Hz, 2H), 6.92 (d, J ) 9.0 Hz,
2H), 6.79 (d, J ) 9.0 Hz, 2H), 5.97 (d, J ) 8.7 Hz, 4H), 5.92 (d, J )
8.6 Hz, 2H), 4.26-4.24 (m, 2H), 4.00 (t, J ) 6.0 Hz, 2H), 3.89-3.87
(m, 2H), 3.80 (br s, 4H), 3.70-3.67 (m, 4H), 3.58-3.54 (m, 8H), 3.46-
3.43 (m, 4H), 2.91-2.87 (m, 2H), 2.53-2.49 (m, 2H), 2.33-2.29 (m,
2H), 2.18-2.12 (m, 2H), 1.60-1.54 (m, 2H), 1.30 (s, 27H), 1.29 (s,
27H), 1.34-1.26 (m, 2H); UV-vis (MeCN) λmax ) 442 nm (ꢀ ) 2700);
FAB-MS m/z 2265.2 ([M - PF6]+; calcd 2265.1), 1698.0 ([M - 17 -
PF6]+), 629.2 ([Cu(17)]+).
2-Hydroxyethyl p-[Tris(p-tert-butylphenyl)methyl]phenyl Ether
(21). A mixture of phenol 9 (0.51 g, 1.0 mmol), THP-protected
bromoethanol (0.23 g, 1.1 mmol), and K2CO3 (0.17 g, 1.2 mmol) in
DMF (40 mL) was stirred under Ar at 65 °C for 18 h. DMF was
evaporated and the residue taken in CH2Cl2, washed with brine, dried
over Na2SO4, and filtered. Evaporation of the solvent followed by
column chromatography on silica gel (hexanes-ether) led to the
corresponding THP-protected alcohol as a white solid (0.46 g). This
solid was refluxed in EtOH, in the presence of a catalytic amount of
concentrated HCl, for 16 h. The mixture was neutralized with some
drops of concentrated NaOH. Solvent was rotary evaporated, and the
residue was dissolved in CH2Cl2, washed with brine, dried over Na2-
SO4, and filtered. After evaporation of the solvent and column
chromatography on silica gel (hexanes-ether), alcohol 21 was obtained
as a white solid (0.31 g, 56%): 1H NMR (200 MHz, CDCl3) δ ) 7.24
(d, J ) 8.8 Hz, 6H), 7.10 (d, J ) 9.0 Hz, 2H), 7.08 (d, J ) 8.8 Hz,
6H), 6.79 (d, J ) 9.0 Hz, 2H), 4.09-4.05 (m, 2H), 3.98-3.91 (m,
Demetalated Rotaxane 25. A solution of KCN (0.117 g, 1.80 mmol)
in H2O (2 mL) was added to a stirred brown-red solution of rotaxane
24+ (82 mg, 0.034 mmol) in CH2Cl2-MeCN (2:3, 10 mL). The
resulting mixture was vigorously stirred at room temperature for 1 h
(the red color characteristic of the Cu(I) complex disappeared in about
5-10 min). Solvent was evaporated, and the residue was taken in CH2-
Cl2, washed with H2O, and dried over Na2SO4. After filtration and
evaporation of the solvent, there was obtained a white-yellow solid
(0.075 g), which was purified by column chromatography on alumina
(CH2Cl2 containing 0-0.5% MeOH) to afford a white solid (63 mg,
84%): 1H NMR (400 MHz, CD2Cl2) δ ) 8.50-8.45 (m, 4H), 8.37-
8.28 (m, 8H), 8.20 (d, J ) 8.4 Hz, 2H), 8.18 (d, J ) 8.6 Hz, 1H), 8.14
(d, J ) 8.2 Hz, 1H), 8.00 (d, J ) 8.6 Hz, 1H), 7.96 (d, J ) 8.4 Hz,
2H), 7.87 (t, J ) 7.9 Hz, 1H), 7.72 (s, 2H), 7.71 (s, 2H), 7.60 (dd, J
) 7.9 and 2.3 Hz, 1H), 7.58 (dd, J ) 7.9 and 2.3 Hz, 1H), 7.49 (d, J
) 8.2 Hz, 1H), 7.25-7.06 (m, 30H), 6.92-6.86 (m, 8H), 4.44-4.42
(m, 2H), 4.36-4.34 (m, 2H), 4.02-3.95 (m, 6H), 3.62-3.46 (m, 16H),

4408 J. Am. Chem. Soc., Vol. 121, No. 18, 1999
Armaroli et al.
3.19 (t, J ) 7.7 Hz, 2H), 2.81 (t, J ) 7.7 Hz, 2H), 2.73 (t, J ) 7.6 Hz,
2H), 2.14-2.06 (m, 2H), 2.03-1.95 (m, 2H), 1.84-1.77 (m, 2H), 1.29
(s, 27H), 1.27 (s, 27H); FAB-MS m/z (relative intensity) 220.1 (75,
[MH2]+, calcd 2202), 1635.9 (80, [MH2 - 17]+, calcd 1635), 567.3
(100, [17H]+, calcd 567).
Mareriali Innovativi), MURST (Progetto Dispositivi Supramole-
clari), and EC HCM network ERB CHR XCT 940492 “Transi-
tion Metals in Supramolecular catalysis”. We thank M. Ming-
hetti for technical assistance. P.G. thanks the Ministerio de
Educacion y Ciencia (Spain) for postdoctoral fellowship sup-
port.
Acknowledgment. This research was supported by the
CNRS (France), Italian CNR, University of Bologna (Progetto
JA984051W