Electrochemically and photochemically driven ring motions in a disymmetrical copper [2]-catenate

Article abstract of DOI:10.1021/ja9720826

By applying the three-dimensional template effect of copper(I), previously used for making various interlocking ring systems, a new disymmetrical [2]-catenate has been made which consists of two different interlocking rings. One ring contains a 2,9-diphenyl-1,10-phenanthroline (dpp) unit whereas the other cycle incorporates both a dpp motif and a 2,2',6',2''-terpyridine (terpy) fragment, the coordination site of these two chelates pointing toward the inside of the ring. Depending on the oxidation state of the central metal (Cu(I) or Cu(II)), and thus on its preferred coordination number, two distinct situations have been observed. With monovalent copper, the two dpp units interact with the metal and the terpy fragment remains free, at the outside of the molecule. By contrast, when the catenate is complexed to divalent copper, the terpy motif is bonded to the metal and it is now a dpp ligand which lies at the periphery of the complex. This dual coordination mode leads to dramatically different molecular shapes and properties for both forms. The molecular motion which interconverts the four- and the five-coordinate complexes can be triggered chemically, electrochemically, or photochemically by changing the oxidation state of the copper center (II/I). The process has been studied by electrochemistry and by UV-vis spectroscopy. Interestingly, once the stable 4-coordinate copper(I) complex has been oxidized to a thermodynamically unstable pseudo-tetrahedral copper-(II) species, the rate of the gliding motion of the rings which will afford the stable 5-coordinate species (copper(II) coordinated to dpp and terpy) can be controlled at will. Under certain experimental conditions, the changeover process is extremely slow (weeks), and the 4-coordinate complex is more or less frozen. By contrast, addition of a coordinating counterion to the medium (Cl^-) enormously speeds up the rearrangement and leads to the thermodynamically stable 5-coordinate complex within minutes.

Full text of DOI:10.1021/ja9720826

12114
J. Am. Chem. Soc. 1997, 119, 12114-12124
Electrochemically and Photochemically Driven Ring Motions in
a Disymmetrical Copper [2]-Catenate
Aude Livoreil,† Jean-Pierre Sauvage,*,† Nicola Armaroli,‡,§ Vincenzo Balzani,*,‡
Lucia Flamigni,§ and Barbara Ventura‡
Contribution from the Laboratoire de Chimie Organo-Mine´rale, URA 422 du CNRS, Institut Le
Bel, UniVersite´ Louis Pasteur, 4 rue Blaise Pascal, 67070 Strasbourg, France, Dipartimento di
Chimica “G. Ciamician”, UniVersita` di Bologna, Via Selmi 2, 40126 Bologna, Italy, and
Istituto FRAE/CNR, Via Gobetti 101, 40129 Bologna, Italy
ReceiVed June 23, 1997X
Abstract: By applying the three-dimensional template effect of copper(I), previously used for making various
interlocking ring systems, a new disymmetrical [2]-catenate has been made which consists of two different interlocking
rings. One ring contains a 2,9-diphenyl-1,10-phenanthroline (dpp) unit whereas the other cycle incorporates both a
dpp motif and a 2,2′,6′,2′′-terpyridine (terpy) fragment, the coordination site of these two chelates pointing toward
the inside of the ring. Depending on the oxidation state of the central metal (Cu(I) or Cu(II)), and thus on its
preferred coordination number, two distinct situations have been observed. With monovalent copper, the two dpp
units interact with the metal and the terpy fragment remains free, at the outside of the molecule. By contrast, when
the catenate is complexed to divalent copper, the terpy motif is bonded to the metal and it is now a dpp ligand which
lies at the periphery of the complex. This dual coordination mode leads to dramatically different molecular shapes
and properties for both forms. The molecular motion which interconverts the four- and the five-coordinate complexes
can be triggered chemically, electrochemically, or photochemically by changing the oxidation state of the copper
center (II/I). The process has been studied by electrochemistry and by UV-vis spectroscopy. Interestingly, once the
stable 4-coordinate copper(I) complex has been oxidized to a thermodynamically unstable pseudo-tetrahedral copper-
(II) species, the rate of the gliding motion of the rings which will afford the stable 5-coordinate species (copper(II)
coordinated to dpp and terpy) can be controlled at will. Under certain experimental conditions, the changeover
process is extremely slow (weeks), and the 4-coordinate complex is more or less frozen. By contrast, addition of a
coordinating counterion to the medium (Cl-) enormously speeds up the rearrangement and leads to the
thermodynamically stable 5-coordinate complex within minutes.
Introduction
of research, in which catenanes and other related systems
containing rings threaded by stringlike molecules (rotaxanes and
pseudo-rotaxanes) are particularly promising, is that of the so
called “molecular machines”5 or molecular assemblies whose
shape, physical, chemical, and dynamic properties can be
controlled by using an external signal. The general idea of
inducing a profound molecular rearrangement by reducing or
The fascination exerted by catenanes stems mainly from their
unusual topological properties (nonplanar molecular graph),1 but
it also originates from the potential novel properties displayed
by molecular systems containing virtually nonconstrained
constitutive elements, such as interlocking rings able to glide
freely within one another. Although catenanes have been known
for several decades,2 their chemical and physical characteristics
have been little studied, mostly due to the difficulty of
synthesizing them at a really preparative scale. In spite of this
limitation, dynamic studies using NMR relaxation time mea-
surements have been carried out on simple systems, showing
fast intramolecular molecular motions.3
Clearly, little constrain between interlocking rings of sufficient
size can in principle be extended to polymers. It is thus expected
that macromolecular systems incorporating interlocking ring
units will lead to interesting systems related to the high mobility
and flexibility of their polymer backbone.4 Another new area
(3) Fritz, H.; Hug, P.; Sauter, H.; Logemann, E. J. Mag. Reson. 1976,
21, 373-375. Kintzinger, J. P.; Bourgeois, H.; Edel, A.; Graff, R.;
Chambron, J. C.; Dietrich-Buchecker, C. O.; Sauvage, J. P. Computational
Approaches in Supramolecular Chemistry; Wipff, G., Ed.; Kluwer Academic
Publishers: Boston, 1994; pp 391-398. Anelli, P. L.; Ashton, P. R.;
Ballardini, R.; Balzani, V.; Delgado, M.; Gandolfi, M. T.; Goodnow, T.
T.; Kaifer, A. E.; Philp, D.; Pietraszkiewicz, M.; Prodi, L.; Reddington, M.
V.; Slawin A. M. Z.; Spencer, N.; Stoddart J. F.; Vicent, C.; Williams D.
J. J. Am. Chem. Soc. 1992, 114, 193-218.
(4) Weidmann, J. L.; Kern, J. M.; Sauvage, J. P.; Geerts, Y.; Muscat,
D.; Mu¨llen, K. Chem. Commun. 1996, 1243-1244.
(5) 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. Ashton, P. R.; Ballardini, R.; Balzani, V.; Boyd, S.
E.; Credi, A.; Gandolfi, M. T.; Go`mez-Lo`pez, M.; Iqbal, S.; Philp, D.;
Preece, J. A.; Prodi, L.; Ricketts, H. G.; Stoddart, J. F.; Tolley, M. S.;
Venturi, M.; White, A. J. P.; Williams, D. J. Chem. Eur.J. 1997, 3, 152-
170. Ballardini, R.; Balzani, V.; Credi, A.; Gandolfi, M. T.; Langford, S.
J.; Menzer, S.; Prodi, L.; Stoddart, J. F.; Venturi, M.; Williams, D. J. Angew.
Chem., Int. Ed. Engl. 1996, 35, 978-981. Bissel, R. A.; Co`rdova, E.; Kaifer,
A. E.; Stoddart, J. F. Nature 1994, 369, 133-137. Ashton, P. R.; Ballardini,
R.; Balzani, V.; Credi, A.; Gandolfi, M. T.; Menzer, S.; Pe´rez-Garc`ıa, 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. For a
photoswitchable catenane, see: Bauer, M.; Mu¨ller, W. M.; Mu¨ller, U.;
Rissanen, K.; Vo¨gtle, F. Liebigs Ann. 1995, 649-656. Vo¨gtle, F.; Mu¨ller,
W. M.; Mu¨ller, U.; Bauer, M.; Rissanen, K. Angew. Chem., Int. Ed. Engl.
1993, 32, 1295-1297.
† Universite´ Louis Pasteur.
‡ Universita` di Bologna.
§ Istituto FRAE/CNR.
X Abstract published in AdVance ACS Abstracts, November 15, 1997.
(1) For a representative collection of papers, see New. J. Chem. special
issue, 1993, vol 17, 10-11. Frisch, H. L.; Wasserman, E. J. Am. Chem.
Soc. 1961, 83, 3789. Amabilino, D. B.; Stoddart, J. F. Chem. ReV. 1995,
95, 2725-2828. Sauvage, J. P.; Hosseini, M. W., Eds.; Templating, Self-
Assembly, and Self-Organization. ComprehensiVe Chemistry, Pergamon:
New York, 1996, Vol. 9. Walba, D. M. Tetrahedron 1985, 41, 3161-3212.
(2) Wasserman, E. J. Am. Chem. Soc. 1960, 82, 4433. Schill, G.
Catenanes, Rotaxanes and Knots; Academic Press: New-York, London,
1971.
S0002-7863(97)02082-9 CCC: $14.00 © 1997 American Chemical Society

Ring Motions in a Disymmetrical Copper [2]-Catenate
J. Am. Chem. Soc., Vol. 119, No. 50, 1997 12115
oxidizing a constitutive element of a chemical system is certainly
of great interest in itself, but it is also related to biological
systems. Many proteins undergo dramatic conformational
changes in relation with their biological action although electron-
transfer proteins undergo very limited changes. Recent work
has stressed the importance of redox processes in folding-
unfolding reactions of redox proteins incorporating heme groups
and acting as electron-transfer agents (cytochrome).6 Among
synthetic systems, a non-catenane example mimics the action
of a brake by using the coordination properties of a fragment
of the compound to slow down a rotation process about a C-C
bond.7 A two-coordination site ligand has also been used to
demonstrate that hopping of a metal center (Fe(II) or Fe(III))
between two remote positions in the compound can be induced
by simply oxidizing or reducing the metal.8
Other elegant examples based on catenanes, rotaxanes, and
rotaxane-like systems exhibiting donor-acceptor interactions
have recently been described.5 They make use of chemical,
electrochemical, or photochemical properties to induce confor-
mational changes. Recently, a transition metal-bonded [2]-ca-
tenane has been described, which undergoes a complete
changeover process (gliding of one ring within the other) under
the action of an electrochemical signal.9 We would now like
to report the synthesis of the compound, its electrochemically
and photochemically driven motions, as well as the effect of
various experimental factors, such as nature of the solvent or
coordinating ability of the counterions used, on the rate of the
molecular rearrangement.
Figure 1. The linkage isomerisms subsequent to modification of the
metal center oxidation state. The white and black circles stand,
respectively, for Cu(I) and Cu(II), whereas the chelates (bi- or terdentate
coordinating fragments) incorporated in the rings are drawn with bold
broken lines. Once the Cu(I) complex gathering two bidentate chelates
is oxidized, the resulting Cu(II) complex undergoes a changeover
process leading to the catenate second coordination mode, based on
complexation of a bidentate and a terdentate ligand. Reversibly,
reduction of this complex regenerates the original coordination mode,
through a similar gliding motion of the rings.
This square scheme reminds of the one obtained by Sano
and Taube for ruthenium complexes showing linkage isomerism
with sulfoxide ligands.11 Thanks to their very different phys-
icochemical properties, e.g. redox potentials, those complexes
show cyclic voltammograms characteristic of a molecular hys-
teresis phenomenon. Other transition metal complexes have also
been shown to undergo rearrangement following reduction or
oxidation of the metal center.12 Similarly, our compound is an
example of hysteresis at the molecular level, but as we will see
later, the isomerism kinetics are even slower in our case. This
hysteresis property could be of great interest in the field of
information storage.
Results and Discussion
Design and Synthesis of the Catenane. Thanks to the
topological link1 existing between its two constitutive rings, a
[2]-catenane can adopt several geometries, defined by the
respective positions of both rings, while keeping its global
topology unchanged. This makes it a potential multistable
molecule, the interconversion from one stable state to the next
one consisting of the gliding motion of one ring into the other.
As illustrated by previous work in our group,10 a catenane can
also sometimes act as a ligand and form stable complexes with
several transition metal atoms such as copper, cobalt, zinc...
We thus synthesized a copper catenate,9 i.e. a copper complex
whose organic backbone is a [2]-catenane, able to adjust its
coordination geometry to the oxidation state of the metal by
changing the respective position of its rings. This catenane
offers two different coordination sites to the metal, each one
stabilizing a different oxidation state: a tetrahedral site consist-
ing of two bidentate chelates favors Cu(I), whereas a 5-coor-
dinating atom site, consisting of bidentate and terdentate chelates
stabilizes Cu(II). Consequently, oxidation or reduction of both
stable states generates a “metastable” compound, which rear-
ranges through a gliding motion of one ring into the other,
leading to the complex which best fits the new coordination
geometry of the metal center. These linkage isomerisms are
illustrated in Figure 1.
Our disymmetrical catenane consists of two different rings
(Figure 2): one includes the classical bidentate chelate, 2,9-
diphenyl-1,10-phenanthroline (dpp) and a polyethyleneglycol
fragment, the other comprises a dpp moiety and a terdentate
ligand, 2,2′:6′,2′′-terpyridine (terpy), both units being linked by
three methylene groups. Both macrocycles have a 33 atom-
long inner rim in order to minimize steric hindrance toward
rotation of one ring through the other. In order to distinguish
the different coordination modes, we introduce a notation
indicating the oxidation state of the metal and the number of
nitrogen atoms surrounding it in each case: the tetrahedral
complex is noted Cu(I/II)N4 and the 5-coordinate one Cu(I/II)N5.
The catenate is obtained as a Cu(I) pseudo-tetrahedral complex
(CuIN4) using a two-step procedure, as shown in Figure 2.
A threaded precursor is synthesized by complexation of a
Cu(I) cation by an acyclic dpp unit and a macrocycle consisting
of a second dpp motif. The sequential addition of the metal
cation to a solution of the macrocycle, followed by addition of
the open ligand, prevents formation of a mixture of complexes,
and allows quantitative obtention of the precursor. The reaction
of this complex with the missing fragment in high dilution
conditions leads to the desired catenate. The copper cation is
used as a template, its tetrahedral coordination geometry
inducing the threading and the subsequent interlocking of the
two rings.
(6) Bixler, J.; Bakker, G.; McLendon, G. J. Am. Chem. Soc. 1992, 114,
6938-6939. Pascher, T.; Chesick, J. P.; Winkler, J. R.; Gray, H. Science
1996, 271, 1558-1560.
(7) Kelly, T. R.; Bowyer, M. C.; Bhaskar, K. V.; Bebbington, D.; Garcia,
A.; Lang, F.; Kim, M. H.; Jette, M. P. J. Am. Chem. Soc. 1994, 116, 3657-
3658
(11) Tomita, A.; Sano, M. Inorg. Chem. 1994, 33, 5825-5830 and
references cited therein: Sano, M.; Taube, H. J. Am. Chem. Soc. 1991,
113, 2327-2328..
(12) Geiger, W. E.; Salzer, A.; Edwin, J.; Von Philipsborn, W.; Piantini,
U.; Rheingold, A. L. J. Am. Chem. Soc. 1990, 112, 7113-7121. Katz, N.
E.; Fagalde, F. Inorg. Chem. 1993, 32, 5391-5393. Joulie´, L. F.; Schatz,
E.; Ward, M. D., Weber, F.; Yellowlees, L. J. J. Chem. Soc., Dalton Trans.
1994, 799-804. Bond, A. M.; Hambley, T. W.; Mann, D. R., Snow, M. R.
Inorg. Chem. 1987, 26, 2257-2265.
(8) Zelikovich, L.; Libman, J.; Shanzer, A. Nature 1995, 374, 790-
792.
(9) Livoreil, A.; Dietrich-Buchecker, C. O.; Sauvage, J. P. J. Am. Chem.
Soc. 1994, 116, 9399-9400.
(10) Dietrich-Buchecker, C.; Sauvage, J. P. Tetrahedron 1990, 46, 2,
503-512. Dietrich-Buchecker, C.; Kintzinger, J. P.; Sauvage, J. P.
Tetrahedron Lett. 1983, 24, 5095-5098. Dietrich-Buchecker, C.; Sauvage,
J. P.; Kern, J. M. J. Am. Chem. Soc. 1989, 111, 7791-7800.

12116 J. Am. Chem. Soc., Vol. 119, No. 50, 1997
LiVoreil et al.
Figure 2. The synthesic strategy and the target molecule: the template effect of Cu(I) induces threading of the acyclic chelate through the macrocyclic
ligand, resulting in the formation of a tetrahedral precursor complex; reaction of this complex with the complementary fragment gives the catenate.
In our case, this molecule is comprised of two different chelates: a bidentate 2,9-diphenyl-1,10-phenanthroline (two units) and a terdentate 2,2′:
6′:2′′-terpyridine.
moiety, was prepared from 7 and the hexaethyleneglycol diiodo
derivative (yield 60%). Since our target-catenate is disym-
metrical, two different precursors are possible, according to the
two-step synthesis described above (vide supra). Both pos-
sibilities are illustrated in Figure 4.
The threaded precursor 10+ can be prepared from the
macrocycle 8 and the acyclic ligand 7 and then reacted with
the terpy-containing fragment 6. The precursor 12+ can also
be constructed with the macrocycle 9 and the acyclic ligand 7,
thus reacted afterwards with the hexaethyleneglycol diiodo
derivative. In both cases, the formation of the precursor is
quantitative thanks to the sequential addition of reactants and
1
is confirmed by H-NMR spectroscopy. Due to the presence
of the second chelate (terpy) in the macrocycle 9, a mixture of
two copper precursors could have been formed: one consisting
of the desired tetrahedral Cu(dpp)2+ complex, the other contain-
ing the 4-coordinate Cu(dpp)(η2-terpy)+. Neither TLC experi-
ments, nor NMR spectrocopy indicated formation of the latter,
+
leading to the conclusion that the complex Cu(dpp)2 is
thermodynamically more stable. This conclusion is supported
by literature,18 mentioning the better π-accepting properties of
a phenanthroline as compared to a bipyridine unit, as well as
the strong stabilizing effect of substituents on R positions for
Cu(I) complexes. From this point of view, the dpp unit, with
its two phenyl groups, is better suited than the terpy unit, one
pyridine playing the role of the R-substituent but the other ortho
position to a nitrogen atom being unsubstituted. This remark
will be of some importance in the following electrochemical
experiments (vide infra). In both cases, the target compound
11‚PF6 is obtained with 8-10% yield, via simultaneous addition
of reactants in a hot Cs2CO3/DMF suspension, and subsequent
ion exchange and chromatographies on silica gel columns. It is
characterized by NMR spectroscopy and elemental analysis, and
the characteristic fragmentation pattern was obtained by mass-
spectrometry asserting its topology.19 By action of KCN on
the catenate 11+, the free ligand 13 is obtained and character-
ized10 (Figure 5). Its topology is also confirmed by mass
spectrometry. Reaction of 13 with a copper(II) salt (Cu(BF4)2)
leads to the most stable coordination geometry, i.e. CuIIN5,
where the metal is complexed by one dpp unit and the terpy
nucleus. The composition of the complex is confirmed by mass
spectrometry and elemental analysis, its physicochemical prop-
erties supporting the 5-coordination hypothesis (vide infra).
Figure 3. Intermediate key-compounds synthesized.
The synthesis of the different moieties relies on already
described methodologies, especially the synthesis of 2,9-bis(p-
hydroxyphenyl)-1,10-phenanthroline10 (7) (Figure 3).
5,5′′-Dimethyl-2,2′:6′,2′′-terpyridine (2) was prepared from
2-acetyl-5-methylpyridine, first converted to 1, according to the
method used by Jameson and al.13 2 was transformed into the
organolithium derivative by action of LDA14 at low temperature
and added to a solution of protected bromoethanol, tetrahydro-
pyranyl-2-bromoethyl ether,15 giving 3. 4 was obtained by
deprotection of both alcohol functions in slightly acidic media15
and converted into 5 by reaction with mesylate chloride in CH2-
Cl2.16 6 was finally obtained from 5 and anhydrous LiBr in
acetone.17 6 and 7 were reacted in DMF (60 °C under argon)
in presence of Cs2CO3, in high dilution conditions, leading to
the macrocycle 9 with 58% yield. Using similar conditions,
the macrocycle 8, containing only one dpp unit and no terpy
(13) Guise, L.; Jameson, D. L. Tetrahedron Lett. 1991, 32, 1999-2002.
(14) Crane, J.; Sauvage, J. P. New. J. Chem. 1992, 16, 649-650.
Chambron, J. C.; Sauvage, J. P. Tetrahedron 1987, 43, no. 5, 895-904.
(15) Wa¨lchi, P. C.; Engster, R. HelV. Chim. Acta 1978, 61, 885-898.
(16) Martin, A. E.; Bulkowski, J. E. J. Org. Chem. 1982, 47, 415-418.
(17) Nierengarten, J. F.; Dietrich-Buchecker, C. O.; Sauvage, J. P. J.
Am. Chem. Soc. 1994, 116, 375-376.
(18) James, B. R.; Williams, R. J. P. J. Chem. Soc. 1961, 2007-2019.
(19) Vetter, W.; Logemann, E.; Schill, G. Org. Mass. Spectrom. 1977,
12, 351; Dietrich-Buchecker, C. O.; Sauvage, J. P. Chem. ReV. 1987, 87,
795.

Ring Motions in a Disymmetrical Copper [2]-Catenate
J. Am. Chem. Soc., Vol. 119, No. 50, 1997 12117
Figure 4. The two strategies based on a two-step approach: two threaded precursor (10+ and 12+) are possible, depending on which macrocycle
is used (8 and 9, respectively). Reaction of each precursor with the complementary fragment affords the target disymmetrical catenate 11+. In both
cases a 10% yield was obtained.
Figure 5. Decomplexation of the copper(I) catenate by reaction with KCN gives the free ligand 13. Remetalation leads to the thermodynamically
stable 5-coordinate Cu(II) catenate.
In the square scheme describing the behavior of our catenate
(Figure 1), two specific complexes can be directly obtained via
synthesis and thus be fully characterized: CuIN4 and CuIIN5.
CuIN4 corresponds to the coordination of both dpp units around
the cation, a complex already present in other catenates
synthesized previously in our group.10 Analysis of the data
compounds, whose structures have already been established. Its
redox potential is -0.07V vs SCE in acetonitrile, indicating a
good stabilization of the copper(II) state. UV-visible absorption
spectroscopy reveals a band centered at 636 nm (ꢀ 125) in
acetonitrile, corresponding to a d-d transition, resulting in a pale
olive-green solution. This value can be compared with the one
obtained for the 5-coordinated complex CuII(terpy)(bipy)-
(ClO4)2: 640 nm (ꢀ 120),21 as well as for the same complex
present in a copper(II) helicate recently synthesized.22 In
collaboration with Kaim and Baumann, EPR spectroscopy
measurements on the catenate23 were recently performed, which
showed an anisotropic signal characteristic of an axial symmetry
coordination around Cu(II) (g| ) 2.233; g ) 2.045; A| ) 16.6
mT in acetonitrile at 110 K). We compared these data with
those measured for a 5-coordinate complex [Cu(η3-L)(η2-L)]-
1
given by H-NMR spectroscopy, electrochemistry, and UV-
visible absorption spectroscopy provides the characteristics of
the pseudo-tetrahedral CuI(dpp)2 complex: (1) the signals of
the phenyl protons in position 2,9 are shifted to high field
because of the phenanthroline ring current;20 (2) the redox
potential of the CuI/IIN4 couple in acetonitrile is +0.63V vs SCE,
indicating a strong stabilization of the low oxidation state;10
(3) a MLCT absorption band is observed at 437 nm (ꢀ 2500) in
acetonitrile, resulting in a red-brown solution. This confirms
the entwined arrangement of both dpp units around Cu(I).
The geometry of the copper(II) catenate obtained via decom-
plexation and remetalation has been confirmed by comparison
of its physical and chemical properties with those of the literature
(21) Harris, C. M.; Lockyer, T. N. Aust. J. Chem. 1970, 23, 673-682.
Arena, G.; Bonomo, R. P.; Musumeci, S.; Purello, R.; Rizzarelli, E.;
Sammartano, S. J. Chem. Soc., Dalton Trans. 1983, 1279-1283.
(22) Hasenknopf, B.; Lehn, J.-M.; Baum, G.; Fenske, D. Proc. Natl. Acad.
Sci. U.S.A. 1996, 93, 1397-1400.
(23) Baumann, F.; Livoreil, A.; Kaim; W.; Sauvage, J. P. J. Chem. Soc.,
Chem. Commun. 1996, 35-36.
(20) Dietrich-Buchecker, C. O.; Marnot, P. A.; Sauvage, J. P.; Kintzinger,
J. P.; Maltese, P. NouV. J. Chim. 1984, 8, 573-582.

12118 J. Am. Chem. Soc., Vol. 119, No. 50, 1997
LiVoreil et al.
Figure 6. The molecular square scheme illustrating the response of the catenate to an electrochemical signal: oxidation or reduction generates a
metastable complex which rearranges to adopt the coordination mode best fitting the new oxidation state of the metal center. The white and black
circles stand, respectively, for Cu(I) and Cu(II). Each complex is distinguished through its number of coordinated nitrogen atoms (CuNx, x ) 4 or
5).
(ClO4)2, containing the potential terdentate 2,6-bis(benzimidazol-
2′-yl)pyridine ligand L and showing square-pyramidal config-
uration at the metal ion (g| ) 2.23, g ) 2.03; A| ) 16.7 mT).24
The similarity of all these data tends to confirm the 5-coordina-
tion of the metal cation in our catenate through entwining of
one dpp and the terpy, as summarized in the notation CuIIN5. It
also seems reasonable to suggest a square-pyramidal configu-
ration of the metal.
The Copper Catenate in Motion. The scheme we used to
describe the concept of the catenate motions (Figure 1) can now
be transcripted in terms of molecules, as illustrated in Figure
6.
can be explained in terms of a stronger ligand field around the
cation because of an increased coordination number, as well as
a modification of the coordination geometry (from pseudo-
tetrahedral to square-pyramidal).
We thus conclude that after oxidation of CuIN4, the catenate
underwent a linkage isomerization through a gliding motion of
one ring in the other, transforming the metastable complex
CuIIN4 into the more favorable one CuIIN5. Addition of
hydrazine monohydrate or ascorbic acid triggers the reverse
process: the solution turns red-brown and shows an absorption
identical to that of the CuIN4 starting complex. It is reasonable
to suggest that this form consists of both dpp units entwined
around the metal cation, since this complex appeared as the
most thermodynamically stable on synthesis of the precursor
12+ (vide supra). This hypothesis was also confirmed by the
following electrochemical experiments.
Electrochemically-Driven Motion. An acetonitrile electro-
lyte solution of the copper(I) catenate (CuIN4), was oxidized
on a platinum electrode (0.1 M TBABF4, applied potential )
+0.8V vs SCE, 1.5 h). The red solution progressively turns
deep green. A cyclic voltammogram of the solution shows a
reversible signal at 200 mV/s, centered at +0.63V vs SCE, i.e.
corresponding to the couple CuII/IN4. A series of linear-sweep
voltammetries were then carried out, indicating a decrease of the
signal at +0.63 V with time, while a new signal at -0.07 V
appeared (Figure 8). After several hours, the signal of the new
species has gained the original intensity of the tetrahedral species
CuIIN4, the signal of the latter having almost disappeared. The
color of the solution is then olive green.
As discussed in the previous section, we could isolate and
characterize the two most stable states CuIN4 and CuIIN5. In
addition, there are two states, corresponding to a nonappropriate
coordination of the metal center: CuIIN4 and CuIN5. Our aim
was to generate in situ a metastable state by oxidation or
reduction, and at monitoring its linkage isomerism toward the
stable complex best fitting the new oxidation state of the metal.
Each time, we compare the properties of the new species with
those of the two characterized stable complexes CuIN4 and
CuIIN5. We first monitored this process via UV-visible absorp-
tion spectroscopy. A solution of CuIN4 in acetonitrile, showing
an intense red-brown color, is oxidized by addition of Br2 in
solution in acetonitrile or NOBF4 as a solid (Figure 7). The
solution turns deep green (pine-tree green), the spectrum
indicating a d-d absorption band at 670 nm (ꢀ 800). The
spectrum is superimposable with those of catenates or complexes
2+
containing the same Cu(dpp)2 unit.10
The intensity of this absorption band decreases with time,
accompanied by a 30 nm hypsochromic shift, resulting in a
change of the solution color from pine-tree to pale olive green
(Figure 8). After several hours, the absorption band is centered
at 640 nm (ꢀ 125). This spectrum is completely superimposable
with the one obtained for the copper(II) catenate CuIIN5, under
the same conditions of concentration and solvent. This shift
The potential -0.07V is identical to the one measured for
the copper(II) metalated catenane, i.e. CuIIN5. Inversely, a
reductive electrolysis of the solution (-0.4 V, 1.5 h) regenerates
the original red color, as well as a unique signal at +0.63 V.
No signal corresponding to free copper in solution is observed,
nor has the intensity of the signal decreased. An electrospray
mass spectrometry experiment carried out on a sample of this
solution reveals no traces of free ligand. This indicates that
we have monitored electrochemically the oxidation of the
complex CuIN4 and its subsequent linkage isomerism leading
(24) Sanni, S. B.; Behm, H. J.; Beurskens, P. T.; Van Albada, G. A.;
Reedjik, J.; Lenstra, A. T. H.; Addison, A. W.; Palaniandavar, M. J. Chem.
Soc., Dalton Trans. 1988, 1429-1435.

Ring Motions in a Disymmetrical Copper [2]-Catenate
J. Am. Chem. Soc., Vol. 119, No. 50, 1997 12119
Figure 7. (a) Visible absorption spectra of a 0.35 × 10-4 M solution of the tetrahedral Cu(I) complex CuIN4 (λmax ) 437 nm, MLCT d f π*
transition) and of its oxidized form CuIIN4 (λmax ) 670 nm, d-d transition) in acetonitrile (oxidant: solid NOBF4) and (b) visible absorption spectroscopy
monitoring of the Cu(II) changeover process: (1) freshly oxidized solution of CuIN4 , (2) after 11h, (3) after 24h, (4) after 34h, (5) after 70 h, the
process is almost completed, CuIIN5 is the major species; (acetonitrile solution, 10-3 M, room temperature, oxidant Br2 in acetonitrile).
Figure 9. Cyclic voltammograms of a CuN52+ solution illustrating the
different rate constants of the two changeover processes: (a) scanning
from 1 V to -0.5 V first, (b) scanning from -0.5 V to 1 V first. (CH3-
Figure 8. Electrochemical monitoring of the Cu(II) changeover
process: after oxidative electrolysis of an acetonitrile solution of CuIN4
(10-3 M), linear-sweep voltammetry is carried out. The upper curve is
obtained immediately after electrolysis and corresponds predominently
to the 4-coordinate species. After 20 h, the bottom voltammogram is
obtained and shows almost exclusively the response of the 5-coordinate
complex. Redox Potentials (E1/2): CuII/IN4 + 0.63V; CuII/IN5 - 0.07
V; (0.1 M nBu4NBF4, BF4, Pt electrode, SCE, 5 mV/s, 1 V to -0.5
V).
CN, 0.1 M nBu4NBF4, BF4, Pt electrode SCE, 200 mV/s).
coordination geometry around the Cu(II) cation, in agreement
with the conversion of the pseudo-tetrahedral configuration in
CuIIN4 into the square-pyramidal configuration assumed in
CuIIN5.
As indicated by the above-mentioned experiments, the two
changeover processes, CuIIN4 to CuIIN5 and CuIN5 to CuIN4,
do not proceed at the same speed. The first one is a slow
evolution allowing to characterization of the metastable complex
CuIIN4, whereas the second one was too fast to allow isolation
of the complex CuIN5. This discrepancy clearly appears in the
cyclic voltammograms of a solution of the 5-coordinate complex
CuIIN5 (Figure 9).
to the complex CuIIN5. Inversely, the reduction of this complex
has triggered the reformation of the complex CuIN4, by an
opposite gliding motion of the ring.
A similar experiment was conducted in collaboration with
Kaim and Baumann:23 after electrochemical oxidation of an
acetonitrile electrolyte solution of the complex CuIN4, the
changeover process was monitored by EPR spectroscopy. The
evolution of the spectra with time indicated a relaxation of the
Cyclic voltammetry is carried out between +1.0 V and -0.5
V vs SCE, on platinum, using an acetonitrile electrolyte solution
(0.1 M nBu4NBF4, 200 mV/s). Starting at +1 V (voltammo-

12120 J. Am. Chem. Soc., Vol. 119, No. 50, 1997
LiVoreil et al.
gram a), the first wave represents the reduction of CuIIN5 into
CuIN5 at -0.07 V. On the reverse sweep, the corresponding
oxidation wave has a much smaller intensity, whereas a second
oxidation wave has appeared at +0.63 V, the characteristic
potential of the redox couple CuII/IN4. This indicates that as
soon as it was reduced at the electrode, a certain amount of the
5-coordinate complex CuIN5 rearranged rapidly into the 4-co-
ordinate form CuIN4. When the scan direction is reversed
(voltammogram b), i.e. starting at -0.5 V, the first wave at
-0.07 V represents the oxidation of the electrode-generated
5-coordinate complex CuIN5, where as the second wave at +0.63
V corresponds to the oxidation of the complex CuIN4. The
second wave is much higher than the first one, indicating a rapid
changeover from CuIN5 to CuIN4. By contrast, the signal of
the 4-coordinate complex is almost symmetrical, indicating that
the metastable species CuIIN4 evolves slowly. The height of
the reduction wave at -0.07 V (CuIIN5 to CuIN5) comes from
a diffusion phenomenon since we are in a CuIIN5 solution. An
approximate value of the rate constant of the changeover process
from CuIN5 to CuIN4 can be obtained using the method
described by Nicholson and Shain.25 By measuring the relative
intensity of oxidation and reduction waves of the CuII/IN5 couple
as a function of scan-rate, we obtained a value of 1 s-1 for the
changeover rate. This value is very small as compared to usual
substitution rate constants observed for copper(I) complexes.26
A topological effect is supposedly responsible for this com-
paratively slow process, similar to what had been observed in
the study of formation kinetics of copper(I) catenate.27 None-
theless, one can also reasonably assume that this rate is sensitive
toward the coordinative properties of the solvent and the
presence of any coordinating species in the medium. Indeed
such an influence has been observed and studied in detail in
the case of substitution of biquinoline by dimethylphenanthroline
on copper(I),28 indicating a strong accelerating effect of aceto-
nitrile as well as iodide ions. A more accurate study of the
kinetics of the Cu(I) changeover process in our catenate is
conducted at the moment.
isomerism process is slower, but the addition of chloride ions
(as a solution of nBu4NCl in CH2Cl2) increases the changeover
rate in a drastic manner: the total reaction time required for
complete transformation of CuIIN4 diminishes from hours to 2
min. We suspect that formation of a Cu-Cl bond weakens the
other Cu-N bonds in CuIIN4 (similar to a ligand-assisted
removal32 ) and thus enables the faster substitution of the dpp
unit by the terpy unit. In addition, in the course of the
changeover process, removal of a dpp unit from the copper(II)
coordination sphere has to proceed before any interaction
between the metal center and the entering terpy ligand is
possible. This implies that the copper(II) atom be “half-naked”
at some stage. If Cl- is present in the medium, it could interact
with the metal in this coordinatively unsaturated complex, in a
transitory fashion, and thus lower the activation barrier of the
rearrangement by stabilizing intermediate states.
The same rearrangement experiments performed in a Cu(II)-
or Cu(I)-containing medium indicates no influence of free
copper on the changeover rate constant. This supports the
hypothesis of an intramolecular process. As a conclusion,
concerning the kinetic aspects of the present system, the strong
dependence of the isomerism rate constants on the experimental
conditions can be considered as a “solvent and ion tuning”
opportunity. One can then determine the response of the
catenate to the signal, by including deliberately “accelerating”
or “decelerating” agents in the medium, such as chloride ions
or water, respectively.
Photochemically-Driven Motion. It is well known that in
Cu(I) complexes of polypyridine ligands the lowest triplet
MLCT excited state is luminescent, has a reasonably long
lifetime, and can play the role of electron-transfer reagent.33-35
CuIN4 shows a MLCT emission band (Figure 12, inset) with
λmax ) 750 nm and τ ) 60 ns in aerated acetonitrile solution at
298 K (730 nm and 115 ns in aerated CH2Cl2). Therefore, it
should be possible to cause the first step of the overall swinging
process indicated in Figure 6, namely the conversion of CuIN4
into CuIIN4, by photoexcitation (eq 1) followed by an excited
state oxidation process in the encounter with a suitable oxidant
(eq 3):
As for the Cu(II) changeover process, leading to CuIIN5 from
CuIIN4, the spectroscopic monitoring experiments carried out
in various conditions indicate a drastic influence on the kinetics
of the solvent, the traces of water, and the presence of chloride
ions. In each case, an electrolyte solution of the complex CuIN4
is chemically oxidized, and the intensity of the absorption band
characteristic of the complex CuIIN4 (670 nm) is monitored as
a function of time. The presence of water strongly slows down
the linkage isomerism process, supporting the hypothesis of
formation of a 5-coordinate complex including a water molecule,
CuIN4 + hν f *CuIN4
*CuIN4 f CuIN4 + heat or hν′
*CuIN4 + Ox f CuIIN4 + Red
(1)
(2)
(3)
CuIIN4 + Red f CuIN4 + Ox
Red f products
(4)
(5)
CuIIN4OH2. This has been already observed29,30 for the related
+2
complex Cu(dmp)2+2 and suspected for the complex Cu(dap)2
,
where dmp is 2,9-dimethyl-1,10-phenanthroline and dap is 2,9-
diphenyl-1,10-phenanthroline. As compared to the metastable
form CuIIN4, this 5-coordinate complex is kinetically stabilized.
By constrast, in the presence of chloride ions, the changeover
process is strongly accelerated.
The occurrence of the excited state electron transfer process
(eq 3) competes with the luminescence (eq 2) which is therefore
a useful tool to evaluate whether reaction 3 takes place.
The reduction potential of the CuIIN4/*CuIN4 couple can be
evaluated from the reduction potential of the CuIIN4/CuIN4
The formation of the CuII-Cl bond is mentioned in the
literature,31 its strength depending on the polarity of the solvent.
In dichloromethane, which is less polar than acetonitrile, the
(25) Nicholson, R. S.; Shain, I. Anal. Chem. 1964, 36, 4, 706-723.
(26) Inorg. Chem. 1975, 14, 1716-1717.
(27) Albrecht-Gary, A. M.; Dietrich-Buchecker, C. O.; Saad, Z.; Sauvage,
J. P. J. Am. Chem. Soc. 1988, 110, 1467-1472.
(31) McConnell, H. M.; Weaver, H. E. J. Chem. Phys. 1956, 25, 307-
311. Khan, M. A.; Schwing-Weill, M. J. Inorg. Chem. 1976, 15, 2202-
2205. Hall, J. R.; Marchant, N. K., Plowman, R. A. Aust.J. Chem. 1962,
15, 480-485. Kru¨ger, H. J. Chem. Ber. 1995, 128, 531-539.
(32) R. G. Wilkins, Kinetics and Mechanism of Reactions of Transition
Metal Complexes; VCH: New York, 1991; p 214.
(28) Frei, U. M.; Geier, G. Inorg. Chem. 1992, 31, 3132-3137.
(29) Hall, J. R.; Marchant, N. K.; Plowman, R. A. Aust. J. Chem. 1963,
16, 34-41. Sundararajan, S.; Wehry, E. L. J. Phys. Chem. 1972, 76, 1528-
1536. Al-Shatti, N.; Lappin, A. G.; Sykes, A. G. Inorg. Chem. 1981, 20,
1466-1469.
(30) Geoffroy, M.; Wermeille, M; Dietrich-Buchecker, C. O.; Sauvage,
J. P.; Bernardinelli, G. Inorg. Chim. Acta 1990, 167, 157-164.
(33) Gushurst, A. K. I.; McMillin, D. R.; Dietrich-Buchecker, C. O.;
Sauvage, J.-P. Inorg. Chem. 1989, 28, 4070-4072. Everly, R. M.; McMillin,
D. R. J. Phys. Chem. 1991, 95, 9071-9075, and references therein. 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. Armaroli,
N.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L.; Sauvage, J.-P.;
Hemmert, C. J. Am. Chem. Soc. 1994, 116, 5211-5217.

Ring Motions in a Disymmetrical Copper [2]-Catenate
J. Am. Chem. Soc., Vol. 119, No. 50, 1997 12121
couple (+0.63 V vs SCE, in acetonitrile) and the energy of the
*CuIN4 excited state (about 1.65 eV, as estimated from the
maximum of the emission band in the same solvent) by the
following equation:36
E°(CuIIN4/*CuIN4) ≈ E°(CuIIN4/CuIN4) - E′ ) -1.02 V
(7)
where E′ is the one-electron potential corresponding to the
spectroscopic energy of *CuIN4 excited state. This shows that
even a mild oxidant should be sufficient to oxidize the
photoexcited *CuIN4 catenate (eq 3). Nevertheless, the choice
of the oxidant is not a trivial matter because other important
requirements have to be satisfied: (i) the oxidant should not
compete with CuIN4 for light absorption, (ii) the reaction
between *CuIN4 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). In
the case of Ru(II) polypyridine compounds, photooxidation is
usually performed by using Co(III) amine complexes.37 We
have tried to use [Co(NH3)6]3+ and [Co(NH3)5(NO2)]2+, but we
have found that, because of the short excited state lifetime and
the slow rate of the bimolecular process (eq 3), the concentra-
tions of the Co(III) complexes should have been so high as to
prevent light absorption by the CuIN4 catenate. Therefore we
have decided to use p-nitrobenzylbromide, p-NO2C6H4CH2Br,
which satisfies requirements i and iii,38 and had previously been
used to quench the excited state of other Cu(I) complexes.39
By a Stern-Volmer analysis40 (Figure 10), we have found that
the rate constant of the quenching process (eq 3) was 4.1 ×
108 M-1 s-1 in acetonitrile solution. Since the lifetime of *CuIN4
in air-equilibrated acetonitrile at 25 °C is 60 ns, we have there-
fore estimated that a sufficiently large fraction of the *CuIN4
excited states can react with the quencher even using reasonably
low concentrations (10-1-10-2 M) of p-NO2C6H4CH2Br.
The photochemical experiments were performed by exciting
with 464 nm light acetonitrile solutions containing 1.0 × 10-4
M CuIN4 and 5.0 × 10-2 M p-NO2C6H4CH2Br. Under these
conditions, all the exciting light is absorbed by the Cu(I)
catenate. Light excitation was found to cause the spectral
changes shown in Figure 11. Such spectral changes clearly
indicate the disappearance of CuIN4 and the concomitant
formation of CuIIN4 as the only reaction product. The overall
quantum yield of the photoreaction was about 3%. Since the
Figure 10. Stern-Volmer plot for the quenching of the CuIN4
luminescence by p-NO2C6H4CH2Br in acetonitrile solution at 298 K.
The inset shows the uncorrected luminescence spectrum of CuIN4 in
acetonitrile solution at 298 K.
Figure 11. Spectral changes caused by photoexcitation of an aceto-
nitrile solution containing 1.0 × 10-4 M CuIN4 and 5.0 × 10-2
M
p-NO2C6H4CH2Br. The isosbestic point is at 625 nm. (i) The initial
spectrum; (f) the final spectrum obtained after 20 min of irradiation.
fraction of *CuIN4 excited states reacting with the quencher is
55%, the fraction of quenching events that give rise to a
permanent formation of CuIIN4 is ≈ 5%. Since p-NO2C6H4-
CH2Br cannot quench *CuIN4 by energy transfer, the low
efficiency of the photoinduced process has to be attributed to a
competition between reactions 4 and 5. Under the experimental
conditions used, practically complete transformation of CuIN4
into CuIIN4 was achieved in about 20 min. The results obtained
also showed that CuIIN4 is not photosensitive.
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 absorbance, particularly in the 600-800 nm region,
as expected for the transformation of CuIIN4 into the more stable
CuIIN5 species (Figure 6). After about 48 h, no further spectral
change was observed. At this stage, the spectrum of the solution
(curve c in Figure 12) was that of the stable CuIIN5 species. In
order to complete the cycle (Figure 6), we added to the solution
an excess of ascorbic acid (dissolved in MeOH). We observed
a gradual reappearance of the spectrum of CuIN4. After about
30 min, the spectrum was practically coincident with the initial
spectrum (Figure 12), showing that the cyclic process (Figure
6) was completed.
(34) Kirchoff, 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.
Blaskie, M. W.; McMillin, D. R. Inorg.Chem. 1980, 19, 3519-3522.
(35) Dietrich-Buchecker, C. O.; Marnot, P. A.; Sauvage, J. P.; Kirchhoff,
J. R.; McMillin, D. R. J. Chem. Soc. Chem. Commun. 1983, 513-515.
Gushurst, A. K. I.; McMillin, D. R.; Dietrich-Buchecker, C.; Sauvage, J.
P. Inorg.Chem. 1989, 28, 4070-4072. Dietrich-Buchecker, C. O.; Marnot,
P. A.; Sauvage, J. P. Tetrahedron Lett. 1982, 23, 5291-5294. Edel, A.;
Marnot, P. A.; Sauvage, J. P. NouV. J. Chim. 1984, 8, 495-498.
(36) Balzani, V.; Bolletta, F.; Gandolfi, M. T.; Maestri, M. Top. Curr.
Chem. 1978, 75, 1-64.
(37) See e. g. Sandrini, D.; Gandolfi, M. T.; Maestri, M.; Bolletta, F.;
Balzani, V.; Inorg.Chem. 1984, 23, 3017-3023. Zahir, K.; Boettcher, W.;
Haim, A. Inorg. Chem. 1985, 24, 1966-1968.
(38) In acetonitrile solution, p-NO2C6H4CH2Br shows a band with λmax
) 273 nm which does not interfere in the visible light absorption by 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 p-nitrobenzaldeyde.39
(39) Kern, J.-M.; Sauvage, J.-P. J. Chem. Soc., Chem. Commun. 1987,
546-548.
(40) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.;
Von Zelewsky, A. Coord. Chem. ReV. 1988, 84, 85-277.
One can wonder whether, besides the oxidation step, the
reduction step can also be induced by light. We believe that

12122 J. Am. Chem. Soc., Vol. 119, No. 50, 1997
LiVoreil et al.
After elution, the plates were either scrutinized under a UV lamp or
exposed to I2, or, for terpyridine derivatives, put in a solution of (NH4)2-
FeII(SO4)2,6H2O in MeOH/H2O 50:50. Column chromatography was
carried out on silica gel 60 (Merck 9385, 230-400 mesh) and neutral
alumina 90 (Merck 1076, 0.060-0.200mm). UV-visible spectra were
recorded on a Kontron Instruments UVIKON 860 spectrophotometer.
Fast atom bombardment mass spectrometry (FABMS), was 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, or a xenon primary atom
beam with the same matrix and a ZAB-HF mass spectrometer.
Electrospray mass spectrometry was recorded in the positive ion mode
by dissolving the compound or complex in MeCN or CH2Cl2 at a
concentration of 50 pmol mL-1, and injecting the solution into a VG
BioQ triple quadrupole spectrometer (VG BioTech Ltd., Altrincham,
UK), with a mass-to-charge (m/z) range of 4000, using a cone voltage
(Vc) of 40 V, with a source temperature of approximately 30 °C. The
1H NMR spectra were recorded on either Bruker AC 300 (300 MHz),
WP200 SY (200 MHz) or WP400SY (400 MHz) spectrometers (using
the deuterated solvent as the lock and residual solvent as the internal
reference).
Electrochemistry. Electrochemical experiments were performed
with a three-electrode system consisting of a platinum working
electrode, a platinum-wire counter-electrode, and a standard reference
calomel electrode, versus which all potentials are reported. All
measurements were carried out under argon, in degassed spectroscopic
grade solvents, using 0.1 M nBu4NBF4 solutions as electrolytes. A
potentiostat EG&G Princeton Applied Research Model 273A connected
to a computer was used (software: Programme Research Electrochem-
istry Software), as well as a potentiostat Bruker E130M, connected to
a printing table.
Photochemistry. All the photochemical experiments were per-
formed in acetonitrile (Carlo Erba for spectroscopy). The concentation
of CuIN4 (as PF6- salt) was 1.0 × 10-4 M and that of p-NO2C6H4CH2-
Br was 5.0 × 10-2 M. The solutions, continuously stirred, were
irradiated with a 150 W xenon lamp (Osram XBOW/1) at 464 nm using
a slit of 2.5 mm (9.4 nm). The absorption spectra were recorded with
a Perkin-Elmer l5 spectrophotometer, using 1 cm path length cuvettes.
The quantum yield of the photoreaction was calculated by measuring
the intensity of the light source with the “micro-version” of the ferric
oxalate actinometer.44 Emission spectra were recorded with a Spex
Fluorolog II spectrofluorimeter equipped with a Hamamatsu R-928
phototube. The spectra were corrected for the instrumental response.
An IBH single photon counting equipment N2 lamp, λexc ) 337 nm)
was used to obtain the excited state lifetime.
â-(Dimethylamino)vinyl 2-(5-Methyl)pyridyl Ketone 1. A mixture
of 2-acetyl-5-methylpyridine (10 g, 0.074 mol) and N,N-dimethylfor-
mamide dimethylacetal (DMFDMA) (12 mL; 0.089 mol) in anhydrous
toluene (40 mL) was refluxed for 7 h under argon. Two fractions of
DMFDMA (5 mL, 2 mL) were added after 2.5 h and 6 h heating,
respectively, the methanol produced being continuously distilled from
the mixture. Evaporation of solvent followed by addition of hexane
triggered precipitation of a brown powder (11.4 g, 0.06 mol, 81% yield).
Analytical sample was recrystallized from CH2Cl2/hexane. 1H NMR
(200 MHz, CDCl3): 8.04 (d, 1H, J ) 8 Hz); 7.59 (d, 1H, J ) 0.6 Hz);
8.44 (q, 1H, J ) 1.3 Hz); 7.89 (d, 1H, J ) 12.7 Hz); 6.42 (d, 1H, J )
12.7 Hz); 2.38 (s, 3H); 2.99 (s, 3H); 3.16 (s, 3H). Anal. Calcd for
C11H14N2O: C, 69.45, H, 7.42, N, 14.72. Found: C, 69.44, H, 7.44,
N, 14.68.
Figure 12. Absorption spectra of CuIN4 in acetonitrile solution: (a)
before light excitation; (b) at the end of the photoreaction with
p-NO2C6H4CH2Br (20 min irradiation); (c) after subsequent 24 h in
the dark; (d) 30 min after subsequent addition of an excess of ascorbic
acid.
this cannot be the case for the following reasons. CuIIN5 is not
photosensitive and does not exhibit any luminescence. This is
an expected result since in Cu(II) complexes (d9 electronic
configuration) the lowest excited state is a low energy, distorted
ligand-field level which undergoes very fast radiationless decay
to the ground state.41 Therefore it is not possible to involve
CuIIN5 in a bimolecular reaction where an excited state of the
complex should play the role of electron donor. On the other
hand, even a photochemical reaction based on the addition of an
electron donor photosensitizer seems impracticable not only for
the extreme complexity of the system (at this stage, the solution
would also contain a large amount of unreacted p-NO2C6H4-
CH2Br), but also because of the quenching by energy transfer
of the photosensitizer by CuIIN5.
Conclusion. The three-dimensional matrix effect of the
copper(I) cation has allowed the synthesis of a new copper
[2]-catenate. Thanks to its topology and to the different
composition of its constitutive macrocycles, this catenate is able
to adopt two geometries, each stabilizing preferentially a
different oxidation state of the metal center. The changeover
process from one geometry to the other can be triggered by
chemical, electrochemical, and photochemical stimuli. Its cyclic
functioning is reversible, reproducible and easily followed
through color changes. The speed of the response (changeover)
is controlled at will by the experimental conditions, allowing a
great variability of rates.
Experimental Section
Materials and General Procedures. The following chemicals were
obtained commercially and were used without further purification: Cs2-
CO3 (Aldrich), KCN (Jannsen), KPF6 (Jannsen), N,N-dimethylforma-
mide dimethylacetal (DMFDMA), tBuOK, LDA, MesCl, LiBr. nBu4-
NBF4 was recrystallized twice in a mixture of methanol and water and
dried under vacuum at 60 °C overnight. The following materials were
prepared according to literature procedures: Cu(MeCN)4PF6,42 2,9-bis-
(p-hydroxyphenyl)-1,10-phenanthroline,10 2-acetyl-5-methyl-pyridine,43
tetrahydropyranyl-2-bromoethanol.15 Dry solvents were distilled from
suitable desiccants (Et2O and THF from Na, MeCN and CH2Cl2 from
P2O5) according to literature methods. Thin-layer chromatography
(TLC) was performed on aluminum sheets coated with silica gel 60
5,5′′-Dimethylterpyridine 2. A THF solution (25 mL) of 2-acetyl-
5-methylpyridine (0.8 g, 6 mmol) and tBuOK in THF (12 mL, 12 mmol)
was stirred under argon at room temperature for 2 h. Then 1 (1 g, 6
mmol) was added as a solid. During 20 h stirring, the pink solution
progressively turned bright red. Addition of NH4OAc (4.6 g, 0.06 mol)
followed by 15 mL acetic acid caused the solution to turn light brown.
THF was distilled off over 3 h, acetic acid was evaporated under
vacuum, and the resulting black oil was treated with 40 mL of H2O.
This solution was neutralized with aqueous Na2CO3 solution (end-point
indicated by pH-paper) and extracted three times with CH2Cl2. The
combined organic layers were dried over MgSO4, filtered, and
F254 (Merck 5554), or coated with neutral alumina 60 F254 (Merck 5550).
(41) Jørgensen, C. K. AdV. Chem. Phys. 1963, 5, 33-146.
(42) Kubas, G. J.; Monzyk, B.; Crumbliss, A. L. Inorg. Synth. 1990, 28,
68-70.
(43) Parks, J. E.; Wagner, B. E.; Holm, R. H. J. Organometal. Chem.
1973, 56, 53-66.
(44) Fischer, E. EPA Newsl. July 1984, 33-34.

Ring Motions in a Disymmetrical Copper [2]-Catenate
J. Am. Chem. Soc., Vol. 119, No. 50, 1997 12123
concentrated to a black solid. This solid was dissolved in toluene (40
mL), filtered on paper, and separated on alumina (eluent hexane/ether),
to give terpyridine (0.721 g, 2.8 mmol, 45% yield). Analytical sample
was recrystallized from ethanol. 1H NMR (200 MHz, CDCl3): 2.42
(s, 6H); 8.40 (d, 2H, J ) 8.5 Hz); 7.67 (d, 2H); 8.53 (s, 2H); 8.51 (d,
2H, J ) 8.08 Hz); 7.93 (t, 1H). Anal. Calcd for C17H15N3: C, 78.13,
H, 5.79, N, 16.08. Found: C, 78.20, H, 5.79, N, 16.18.
grade at 60 °C. After the 13 h-long addition, the reaction mixture was
heated and stirred for another 16 h, its orange color progressively
intensifying. The solvent was evaporated under high vacuum and the
crude product was partitioned between CH2Cl2 and H2O. The organic
phases were gathered, dried over MgSO4, filtered, and concentrated to
leave a brown glassy solid. It was purified by column chromatography
over alumina (eluent CH2Cl2/hexane) to give a white powder (300 mg,
0.44 mmol; 57% yield). 1H NMR (200 MHz, CD2Cl2): 8.72 (d, 2H,
J ) 8 Hz); 8.60 (d, 2H, J ) 2 Hz); 8.39 (d, 2H, J ) 8 Hz); 8.29 (d,
2H, J ) 8 Hz); 8.27 (d, 4H, J ) 8 Hz); 8.06 (d, 2H); 7.94 (t, 1H, J )
8 Hz); 7.86 (dd, 2H); 7.77 (s, 2H); 7.03 (d, 4H); 4.04 (t, 4H, J ) 6
Hz); 3.01 (complex peak, 4H); 2.25 (complex peak, 4H). Anal. Calcd
for C45H35N5O2 (sample recrystallized from benzene): C, 79.74, H,
5.20. Found C, 79.86, H, 5.43. FABMS 678 [MH]+.
5,5"-Bis(γ-(tetrahydropyranyl)propyl)terpyridine 3. Lithium di-
isopropylamid (LDA) (1.8 mL, titrated commercial solution 1.41 M)
was added dropwise to a suspension of 2 (0.3 g, 1.15 mmol) in
anhydrous THF (20 mL) at -81 °C. After 2 h stirring at -80 °C the
violet solution was allowed to reach 0°C and then cooled back to -78
°C. A separate solution of protected bromoethanol (tetrahydropyranyl-
2-bromoethanol, 0.621 g, 2.99 mmol) in 10 mL anhydrous THF was
refrigerated to 0 °C. By the double-ended needle transfer technique
the organolithium solution was added to the alcohol solution. Within
20 h stirring the intense blue-green mixture was allowed to slowly warm
up to room temperature and was hydrolyzed with 10 mL water. After
evaporation of solvent and extraction with CH2Cl2, the organic phases
were gathered, dried over MgSO4, filtered, and concentrated to an
orange oil. It was separated by column chromatography on alumina
(eluent ether/hexane 40/60), giving a white powder (317 mg, 0.63 mmol,
55% yield). 1H NMR (200 MHz, CD2Cl2): 8.52 (d, 2H, J ) 7.8 Hz);
8.54 (s, 2H); 8.38 (d, 2H, J ) 7.8 Hz); 7.92 (t, 1H, J ) 7.8 Hz); 7.68
(dd, 2H, J ) 2.4 Hz), 4.59 (t, 2H, J ) 2.98 Hz); 3.84 (complex, 4H);
3.47 (complex, 4H); 2.80 (t, 4H, J ) 6.1 Hz); 1.98 (q, 4H, J ) 6.1
Hz); global peak between 1.3 and 1.7 ppm.
5,5′′-Bis(γ-hydroxypropyl)terpyridine 4. The previously obtained
3 was diluted in ethanol (30 mL and a few drops of chloroform) and
heated to reflux. On addition of a drop of concd HCl(aq) the solution
turned pale yellow. The reaction was followed by thin layer chroma-
tography. After 3 h refluxing, the ethanol was evaporated and the
resulting solid was partitioned between CH2Cl2 and H2O. The organic
phase was dried over MgSO4, filtered, and concentrated to give a white
powder (0.633 g), which was purified by column chromatography on
alumina (eluent CH2Cl2/MeOH). The pure diol 4 (293 mg, 0.84 mmol)
was isolated in 81% yield. 1H NMR (200 MHz, CDCl3): 8.53 (d, 2H,
J ) 8 Hz); 8.56 (s, 2H); 8.39 (d, 2H, J ) 7.8 Hz); 7.94 (t, 1H, J ) 8
Hz); 7.70 (dd, 2H, J ) 2.2 Hz), 3.73 (t, 4H, J ) 6.3 Hz); 2.81 (t, 4H,
J ) 7.3 Hz); 1.95 (tt, 4H, J ) 7.3 Hz and 6.3 Hz).
5,5′′-Bis(γ-mesylpropyl)terpyridine 5. A suspension of 4 (193 mg,
0.55 mmol) in anhydrous CH2Cl2 (35 mL) and freshly distilled NEt3
(0.88 mL, 6.3 mmol) was cooled down to -5 °C. Mesyl chloride (0.22
mL, 2.86 mmol) in anhydrous CH2Cl2 (5 mL) was added dropwise
(-5 < t < -2 °C) to the suspension, which turned progressively clear
yellow. According to thin layer chromatography, end-point was reached
within 2 h stirring below 0 °C. The reaction mixture was washed with
water, the organic phase was dried over MgSO4, filtered, and
concentrated to a beige powder. It was purified by column chroma-
tography on alumina (eluent CH2Cl2/hexane and then pure CH2Cl2),
giving an amorphous white powder (198 mg, 0.39 mmol, 71% yield).
1H NMR (200 MHz, CD2Cl2): 8.55 (d, 2H, J ) 8 Hz); 8.56 (d, 2H, J
) 2 Hz); 8.41 (d, 2H, J ) 7.8 Hz); 7.95 (t, 1H, J ) 8 Hz); 7.71 (dd,
2H, J ) 2 Hz and 7.8 Hz), 4.26 (t, 4H, J ) 6 Hz); 3.04 (s, 6H); 2.86
(t, 4H, J ) 7.2 Hz); 2.14 (complex, 4H, J ) 7.2 Hz and 6 Hz).
5,5′′-Bis(γ-bromopropyl)terpyridine 6. A mixture of 5 (402 mg,
0.8 mmol) and anhydrous LiBr (0.7 g, 8 mmol) in analytical grade
acetone (25 mL) was heated at reflux for 1 h under argon. After
evaporation of solvent, the crude mixture was partitioned between CH2-
Cl2 and H2O. The organic phases were gathered, dried over MgSO4,
filtered, and concentrated to give a yellowish glassy solid (0.369 g).
1H-NMR spectrum indicated at least a 90% proportion was the desired
product (95% yield). The solid was utilized in following steps without
further purification, owing to its poor stability. 1H NMR (200 MHz,
CD2Cl2): 8.67 (d, 2H, J ) 8 Hz); 8.67 (s, 2H); 8.57 (d, 2H, J ) 7.8
Hz); 8.01 (t, 1H, J ) 8 Hz); 7.90 (dd, 2H, J ) 2.2 Hz); 3.44 (t, 4H, J
) 6.3 Hz); 2.94 (t, 4H, J ) 7.3 Hz); 2.25 (tt, 4H, J ) 7.3 Hz and 6.3
Hz).
Macrocycle 8. A solution of 7 (970 mg, 2.6 mmol) and 1,12-
diiodohexaethyleneglycol (1.440 g, 2.8 mmol) in analytical grade DMF
(180 mL) was added dropwise to a stirred suspension of Cs2CO3 (2.72
g, 8.4 mmol) in analytical grade DMF (360 mL) at 60 °C. Another
0.1 equiv of diiodohexaethyleneglycol was added after 24 h, and the
solution was stirred under argon for 48 h, successively showing an
orange then yellow color. After evaporation of solvent under high
vacuum, the residual solid was partitioned between CH2Cl2 and H2O,
and the organic phases were gathered, dried over MgSO4, filtered, and
concentrated to an orange oil (2.9 g). A column chromatography over
silica gel (eluent CH2Cl2/MeOH, 98/2) yielded a yellow glassy product
(978 mg, 1.6 mmol, 61% yield). 1H NMR (200 MHz, CDCl3): 8.46
(d, 4H, J ) 6 Hz); 8.26 (d, 2H, J ) 8 Hz); 8.07 (d, 2H); 7.75 (s, 2H);
7.17 (d, 4H, J ) 6 Hz); 4.31 (t, 4H, J ) 5 Hz); 3.90 (t, 4H, J ) 5 Hz);
3.90 (complex signal, 16H).
-
Precatenate 10+‚PF6
synthesis of 12‚PF6.
.
The method is exactly the one used for
-
Precatenate 12+‚PF6
. Using the double-ended needle transfer
technique, a degassed solution of Cu(CH3CN)4PF6 (182 mg, 0,49 mmol)
in analytical grade acetonitrile (15 mL) was added under argon to a
degassed solution of macrocycle 9 (300 mg, 0.44 mmol) in analytical
grade CH2Cl2 (25 mL). A red-brown color formed immediately. After
stirring for 30 min, a solution of 7 (171 mg, 0.44 mmol) in analytical
grade DMF (25 mL) was similarly added under argon without any
further color change. After 2 h stirring at room temperature, the solvent
mixture was evaporated under high vacuum, giving an intensely red-
colored powder (0.56 g, 0.44 mmol). NMR analysis showed almost
quantitative formation of the precursor. 1H NMR (200 and 400 MHz,
COSY, DMSO-d6): 8.72 (d, 2H, J ) 8 Hz); 8.64 (d, 2H); 8.53 (d, 2H,
J ) 8 Hz); 8.42 (d, 2H, J ) 7.72 Hz); 8.34 (d, 2H, J ) 8.38 Hz); 8.13
(s, 2H); 7.75 (s, 2H); 8.05 (t, 1H, J ) 8 Hz); 7.80 (d, 2H, J ) 8.4 Hz);
7.70 (d, 2H, J ) 8.4 Hz); 7.68 (dd, 2H, J ) 8 Hz and 2 Hz); 7.38 (d,
4H, J ) 8.8 Hz); 7.23 (d, 4H, J ) 8.8 Hz); 5.98 (d, 8H, J ) 7.8 Hz);
3.23 (t, 4H, J ) 6.9 Hz); 2.93 (4H, complex peak); 2.12 (4H, complex
peak).
Catenate 11+‚PF6-. A degassed solution of precatenate 12+ (0.55
g, 0.44 mmol) and diiodohexaethyleneglycol (0.260 g, 0.52 mmol) in
analytical grade DMF (90 mL) was slowly added under argon to a
suspension of Cs2CO3 (0.55 g, 1.4 mmol) in analytical grade DMF (80
mL) at 60 °C. After the 10 h-long addition, the stirred solution was
maintained at 60 °C for another 48 h, after which it was filtrated on
paper and concentrated under high vacuum. The residual cherry-red
solid was partitioned between CH2Cl2 and H2O, the organic phases were
gathered and dried over MgSO4. After filtration, a saturated aqueous
solution of KPF6 was then added, and the mixture was allowed to stand
for 5 h at room temperature with good stirring. The brownish organic
phase was separated, washed with water, and dried over MgSO4. The
filtered solution was concentrated under high vacuum leaving a red-
brown powder (0.579 g). By successive column chromatographies over
silica gel and alumina (eluent CH2Cl2/hexane and CH2Cl2/MeOH), an
intense red powder was obtained (80 mg, 0.05 mmol; 10% yield) and
recrystallized from a mixture of CH2Cl2 and C6H6. 1H NMR (200 and
400 MHz, COSY, CD2Cl2): 8.72 (d, 2H, J ) 8 Hz); 8.64 (d, 2H);
8.53 (d, 2H, J ) 8 Hz); 8.42 (d, 2H, J ) 7.72 Hz); 8.34 (d, 2H, J )
8.38 Hz); 8.13 (s, 2H); 8.05 (t, 1H, J ) 8 Hz); 7.80 (d, 2H, J ) 8.4
Hz); 7.75 (s, 1H); 7.70 (d, 2H, J ) 8.36 Hz); 7.68 (dd, 2H, J ) 8 Hz
and 2 Hz); 7.38 (d, 4H, J ) 8.8 Hz); 7.23 (d, 4H, J ) 8.8 Hz); 5.98
(d, 8H, J ) 7.8 Hz); 3.74 (t, 4H); complex peak 3.68 (20H); 3.23 (t,
Macrocycle 9. A degassed solution of 7 (2,9-bis(p-hydroxyphenyl)-
1,10-phenanthroline, 0.292 g, 0.8 mmol) and 6 (0.369 g, 0.78 mmol)
in analytical grade DMF (80 mL) was added dropwise to a stirred
suspension of Cs2CO3 (0.82 g, 2.51 mmol) in 150 mL of DMF analytical

12124 J. Am. Chem. Soc., Vol. 119, No. 50, 1997
LiVoreil et al.
4H, J ) 6.9 Hz); 2.93 (4H, complex peak); 2.12 (4H, complex peak).
Anal. Calcd for C81H73N7O9CuPF6, (sample recrystallized from
benzene): C, 64.98, H, 4.91, N, 6.17. Found: C, 64.99, H, 5.22, N,
6.22. FABMS: 1350 [M - PF6]+.
Copper(II) Catenate 102+‚2BF4-. A solution of 13 (30 mg, 2.3 ×
10-5 mol) in 20 mL of CH2Cl2 was added to a solution of Cu-
(BF4)2.xH2O (8 mg, 2.3 × 10-5 mol) in 5 mL of acetonitrile. The
resulting pale olive-green solution was left overnight with stirring at
room temperature. After evaporation of solvent, the solid was
partitioned between CH2Cl2 and H2O; the organic phase was washed
with water, dried over MgSO4, filtered, and concentrated to leave a
bright pale green powder (29 mg, 85% yield), recrystallized from a
mixture of acetone and diisopropyl ether. ESMS in CH2Cl2: 675.9
[M]2+. Anal. Calcd for C81H73N7O9Cu(BF4)2: C, 63.77, H, 4.82, N,
6.43. Found: C, 63.56, H, 4.87, N, 6.49.
Catenand 13. The copper catenate 11 (112 mg, 0.07 mmol) was
dissolved in acetonitrile (30 mL), and an aqueous KCN solution (100
mg in 2 mL) was added, triggering spontaneous precipitation of a white
powder, which was dissolved on adding CH2Cl2 (3 mL). The resulting
beige solution was left overnight with stirring at room temperature.
After evaporation of solvent, the solid was partitioned between CH2-
Cl2 and H2O; the organic phase was washed with water, dried over
MgSO4, filtered, and concentrated to leave a yellowish glassy product
(100 mg). 1H NMR (200 and 400 MHz, NOESY, CD2Cl2): 8.87 (d,
2H, J ) 8 Hz); 8.62 (d, 2H); 8.45 (d, 4H, J ) 8.8 Hz); 8.45 (d, 2H, J
) 8 Hz); 8.30 (d, 4H, J ) 8.8 Hz); 8.27 (d, 4H, J ) 7.7 Hz); 8.06 (d,
4H, J ) 8.4 Hz); 7.97 (t, 1H, J ) 8 Hz); 7.75 (s, 4H); 7.76 (dd, 2H, J
) 8 Hz and 2 Hz); 7.05 (d, 4H, J ) 7.8 Hz); 6.09 (d, 4H, J ) 7.8 Hz);
3.92 (t, 4H); 3.92 (t, 4H, J ) 6.9 Hz); 3.64 (t, 4H); 3.49 (16H, complex
signal); 2.91 (4H, complex signal); 2.16 (4H, complex signal).
FABMS: 1288 [MH]+.
Acknowledgment. We would like to thank the CNRS for
its financial support and the Re´gion Alsace for a fellowship to
A.L. We are also grateful to the European Communities for
their support and to Dr. C. O. Dietrich-Buchecker for fruitful
discussions. This work was supported by the University of
Bologna (Funds for special research projects), CNR (Progetto
Strategico Tecnologie Chimiche Innovative), and NATO (CRG
951279).
JA9720826