Ion-triggered multistate molecular switching device based on regioselective coordination-controlled ion binding

Article abstract of DOI:10.1002/chem.200500625

Molecular devices capable of accessing different controlled conformational states, while optically signaling the occupied state, are attractive tools for nanotechnology since they relate to both areas of molecular mechanical devices and logic gates. We report here a simple molecular system that allows access to four distinct conformational and optical states. It is based on the regioselective complexation of metal ions to a heterocyclic ligand triad, which is dictated by the accessible coordination geometry and electrostatic properties of two distinct binding subunits. Thus, local conformational switching is brought about by tetrahedral coordination (of Cu^I) or octahedral coordination (of M²⁺ ions) to bidentate and tridentate binding subunits, respectively. The shape modifications undergone represent an ion-controlled nanomechanical device. They give controlled access to four different states that display different physico-chemical (e.g. optical) properties and provide a basis for logic gate operations.

Full text of DOI:10.1002/chem.200500625

DOI: 10.1002/chem.200500625
Ion-Triggered Multistate Molecular Switching Device Based on
Regioselective Coordination-Controlled Ion Binding
Anne Petitjean,[a] Nathalie Kyritsakas,[b] and Jean-Marie Lehn*[a]
Abstract: Molecular devices capable of
accessing different controlled confor-
mational states, while optically signal-
ing the occupied state, are attractive
tools for nanotechnology since they
relate to both areas of molecular me-
chanical devices and logic gates. We
report here a simple molecular system
that allows access to four distinct con-
formational and optical states. It is
based on the regioselective complexa-
tion of metal ions to a heterocyclic
ligand triad, which is dictated by the
accessible coordination geometry and
electrostatic properties of two distinct
binding subunits. Thus, local conforma-
tional switching is brought about by
tetrahedral coordination (of CuI)or oc-
tahedral coordination (of M2+ ions)to
bidentate and tridentate binding sub-
units, respectively. The shape modifica-
tions undergone represent an ion-con-
trolled nanomechanical device. They
give controlled access to four different
states that display different physico-
chemical (e.g. optical)properties and
provide a basis for logic gate opera-
tions.
Keywords: conformational change ·
coordination modes
·
dynamic
device · molecular switches · supra-
molecular chemistry
Introduction
states beyond two (0,1), which would lead to a higher densi-
ty of information storage and hence assist both miniaturiza-
tion and multiplexing. Among the potential modes of
switching, photo- and electro-induced processes have re-
ceived much attention.[5,6] Multistate switching may be diffi-
cult to implement in these systems as it requires performing
the selective photo/electro-excitation of more than two
units, and therefore designing multiple modules that have
no excitation overlap (wavelength or potential). In this
regard, switching through chemical triggers is more versatile.
Although pH switching suffers from the same limitations as
photo- and electro-induced switching (excitation of all sites
of pKa values higher than the imposed pH), this is not the
case for ion-controlled switching. Indeed, the electronic in-
formation stored in organic ligands combined with the in-
trinsic properties of metal ions offers a wide range of affini-
ties, providing a convenient handle on the selectivity, and,
hence, on the complexity. As photo- and electro-induced
switches are controlled by the intensity (power)and the ex-
citation value (wavelength and voltage respectively)of the
input stimulus, similarly ionic switches are operated on the
basis of the concentration and the nature of the ions. Fur-
thermore, the affinity of the ion may be modulated by addi-
tional factors such as oxidation state, hardness/softness of
the binding site,[7] intrinsic coordination geometry preferen-
ces of the ion,[8] as well as accessible geometries of the con-
sidered ligand. Hence, each ion itself displays a range of ex-
Molecular devices capable of dynamic interconversion be-
tween different states are basic building blocks for nano-
technology. In particular, molecular switches[1] based on op-
tical read-out (e.g., transmittance, luminescence)provide
nanoscale signaling and information processing devices,
while conformational switches open doors to the elaboration
of nanoscale machines. In all cases, a simple, compact, and
tractable molecule is desired, which integrates complex and
addressable functions. On the other hand, systems accessing
different states also play an important role in various biolog-
ical processes, as illustrated by the molecular mechanism of
vision.[2]
The design of molecular and supramolecular devices,[3,1a]
allows in particular the elaboration of molecular logic
gates[4] for nanotechnology. Much promise is to be found in
the high complexity generated by increasing the number of
[a] Dr. A. Petitjean, Prof. J.-M. Lehn
ISIS, UniversitØ Louis Pasteur
CNRS UMR 7006, BP 70028, 67083 Strasbourg (France)
Fax : (+33)390-245-140
E-mail: lehn@isis.u-strasbg.fr
[b] N. Kyritsakas
Institut de Cristallochimie, Institut le Bel
UniversitØ Louis Pasteur
4 rue Blaise Pascal, 67000 Strasbourg (France)
6818
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FULL PAPER
citation values, which adds further dimensions to the input
modulation. As such, ionic switches offer a rare richness in
accessible functional features.
We report here a molecular device that allows access to
four distinct conformational and optical states. It is based on
the regioselective coordination of two different metal ions
to the heterocyclic triad LH, which is dictated by their selec-
tive binding to two suitably designed ligand subunits. Ion
binding is accompanied by regioselective conformational
modifications and by optical changes.
We have based our design on the control potential offered
by the preference of metal ions for a given coordination ge-
ometry. Ligand LH (Scheme 1)was designed so as to offer a
bidentate 2-pyridyl-4-pyrimidine (py–pym)motif as a privi-
leged binding site with ions of tetrahedral coordination ge-
ometry, and a planar (O,N,N)tridentate unit including a 8-
hydroxyquinoline group (quinOH–pym), aimed at accommo-
dating preferentially metal ions of octahedral coordination
geometry. The latter was preferred over a terpyridine type
subunit since it provides further tunability by means of its
acido-basic activity. These bidentate and tridentate sites
share a bridging pyrimidine unit expected to participate in
both ion binding events. It was therefore anticipated that
the bidentate binding site could be regioselectively switched
by an ion such as copper(i), well-known to form tetracoordi-
nate complexes with polypyridyl ligands (see below), where-
as the terdentate subunit would preferentially bind a cation
such as zinc(ii)(Scheme 2). This binding selectivity may also
be associated with soft/soft (py–pym site, CuI), hard/hard
(quinOH–pym, ZnII)correspondence.
We have recently implemented in our group ligands con-
taining two metal cation binding subunits based on terpyri-
dine and bipyridine–pyrimidine groups, as ion-triggered
nanomechanical switching devices[9,10] involving interconver-
sion between two forms, of U and W shapes, of the ligand
molecule. The present results incorporate regioselective con-
trol of ion binding and significantly extend the earlier work.
The corresponding events are schematically represented
in Scheme 2. Furthermore, the overall process results in the
regioselective self-assembly of a tetranuclear heterometallic-
[2”2] grid architecture.[11]
Results and Discussion
Ligand LH: Ligand synthesis: A 2-substituted pyrimidine
was chosen as the bridging unit in ligand LH, as the alkyl-
phenyl substituent conveniently increases the solubility in
organic solvents while also providing structural information
(1H NMR spectroscopy). To this end, 2-(4-n-butylphenyl)-
4,6-dichloropyrimidine (1)[12] was successively coupled to a
pyridinyl stannane and a quinolinyl stannane under Stille
coupling conditions. 2-Tri-n-butylstannyl-6-methylpyridine[13]
was quantitatively obtained from 2-bromo-6-methylpyri-
dine[14] by nBuLi lithiation and reaction with tri-n-butyltin
chloride followed by distillation. It was then coupled stoi-
chiometrically with 1 to give 2
in moderate yields (Scheme 1).
The quinoline fragment was
prepared by oxidation of com-
mercially available 8-hydroxy-
quinoline to the N-oxide deriv-
ative, rearrangement to the
2-oxo-1,2-dihydroquinolin-8-yl
acetate 3 and bromination to
the 2-bromo-quinolin-8-yl ace-
tate 4. The latter reaction pro-
ceeded in low yields due to si-
multaneous hydrolysis of the
acetate. After stannylation of
4, a Stille coupling was per-
formed with the monochloro-
pyrimidine 2 to yield the ace-
tate-protected ligand 5. Hy-
drolysis of the acetate pro-
ceeded smoothly in pyridine to
yield the dissymmetric switch
LH in sufficient amounts.
Ligand conformation: The
1H NMR spectrum of ligand
LH is characteristic of this
type of U-shape molecule.[9]
The preferred transoid confor-
mation of 2,2’-bipyridine type
Scheme 1. Synthetic route to the heteroditopic ligand LH and proton numbering.
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J.-M. Lehn et al.
proton NMR spectrum of the
ligand
undergoes
marked
changes in the course of the ti-
tration (Figure 1). Whereas the
chemical shifts of the hydroxy-
quinoline protons remain con-
stant (Dd=Æ0.05 ppm), the
signals of the protons 1, 3py,
4py, and 5py undergo signifi-
cant shifts (Dd=À0.2, +0.2,
and +0.2 ppm, respectively).
The 2-pyrimidine aryl substitu-
ent protons (Ha and Hb)pro-
vide
a sensitive probe for
cation binding. Indeed, upon
titration their signals are
strongly
shielded
(d=
À0.5 ppm), in accordance with
the previously described U to
W switching of the py–pym–py
triad (validated by NOE analy-
sis). Compared to the anthryl-
and acridyl-substituted confor-
mational switches reported
previously,[9] the present ligand
bears just a methyl group in
position 6 of the pyridine unit,
introduced to limit the suscept-
ibility of CuI to oxidation. The
lack of substantial steric hin-
drance in this position allows
the stable 2:1, ligand–CuI com-
plex to form.
Scheme 2. Top: Schematic representation of the four-state structural switching of ligand LH operated by regio-
selective metal ion complexation; the bidentate and tridentate binding subunits in the ligand are represented
by two and three segments respectively; squares and hexagons represent metal ions of tetrahedral and octahe-
dral coordination geometry, respectively. Bottom: Structural representation of the ligand switching operated
by regioselective, coordination algorithm-controlled binding of CuI and ZnII cations.
diads[15] forces protons 1 and 3py (Scheme 1)to face the
lone pair of the vicinal nitrogen atom, resulting in a strong
downfield shift. Typically protons 1 and 3py give NMR sig-
nals at d=9.2 and 8.5 ppm, respectively, as illustrated by the
[9]
pyridine–pyrimidine–pyridine (py–pym–py)triad module.
The same deshielding effect holds for the quinolyl proton
H3. The correlation between these high chemical shifts and
the transoid conformation is confirmed by X-ray crystallog-
raphy of similar compounds.[9,16] In the present case, the
chemical shifts of protons 1, 3py, and 3 are indeed in agree-
ment with an all transoid conformation for the 8-hydroxy-
quinoline–pyrimidine–pyridine (quinOH–pym–py)triad in so-
lution.
Regioselective switching performed by a metal ion of tetra-
hedral coordination : U-shaped py–pym–py triads having
two identical bidentate binding sites have been reported
previously to switch from a U to a W shape by a double
conformational change upon the binding of two tetrahedral-
[9]
ly coordinated copper(i)ions.
Similarly, progressive addi-
tion of copper(i)triflate to a solution of quin OH–pym–py in
CDCl3/CD3CN induces a single conformational change that
affects only the pym–py subunit of ligand LH, to give an S-
shaped form, as illustrated in Scheme 2 and Figure 1. The
Figure 1. Aromatic region of the 200 MHz 1H NMR spectrum of ligand
I
LH (3.9 mm, 1:1 CDCl3/CD3CN)upon titration by a solution of Cu
-
(CH3CN)4BF4 (8 mm, same mixture of solvents). Proton numbering is
given in Scheme 1.
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Ion-Triggered Multistate Molecular Switches
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*
The free ligand and the complex are in fast exchange on
the NMR time scale, and analysis of the variation in chemi-
cal shifts upon copper titration[17a] (up to 1 equiv)is in
agreement with the formation of the bis-bidentate species
[CuI(LH)2] with a binding constant of intermediate strength:
log b [CuI(LH)2]=7.6Æ0.6 in 1:1 CDCl3/CD3CN. This value
is higher than for the 1:1 complex between 6,6’-dimethyl-
2,2’-bipyridine and CuI in pure acetonitrile (log b=6.1Æ
0.1).[17b] The corresponding bis-bidentate 2:1 complex is
about five orders of magnitude stronger (log b=11.6Æ
0.05)[17c] and presents a tetrahedral coordination geometry.[18]
As the 2:1 complex is much more stable than the 1:1 species,
only the former is detected in the range of CuI concentra-
tions used here. The dimerization also correlates with the
large NMR shielding shifts experienced by the protons on
the pym substituents (Ha, Hb, and Ha)and takes place by
formation of a tetrahedral CuI coordination site.[18] Electro-
spray mass spectrometry measurements show the coexis-
tence of both [CuLH]+ and [Cu(LH)2]+ complexes in the
gas phase. The lower binding constant compared to the
parent [CuI(2,2’-bipyridine)2] complex may result from a
combination of the less basic N coordination site of the pyri-
midine group in the pym–py diad compared to a pyridine N
site, and the steric constraints due to the aryl substituent on
the pym unit. In the ligands of the previously reported
switching devices,[9] the anthryl and acridinyl pyridyl sub-
stituents and the phenyl pyrimidyl substituent prohibit the
formation of the 2:1 complex, resulting in a weak coordina-
tion of CuI in a 1:1 stoichiometry (log b=2.93Æ0.07). Inde-
pendent of the exact stoichiometry of the complex, the
1H NMR titration spectra shown in Figure 1 clearly testify
that the present dissymmetric ligand LH is regioselectively
switched to the cisoid form on the pym–py side by a tetrahe-
drally coordinating “soft” cation such as CuI, as anticipated
from previous work.[9]
Up to 0.5 equivalents of Zn2+, a new complex is formed,
characterized by a lower chemical shift of H1 (dH1
=
8.30 ppm), consistent with switching to a cisoid confor-
mation. 1H NMR ROESY experiments show that pro-
tons H1 and H3 are indeed close to each other, whereas
no correlation was observed between H1 and H3py,
which confirms the regioselective conformational change
on the quinO–pym terdentate binding site. The strong
shielding of protons Ha and Hb, as in the titration with
CuI, suggests the formation of a dimeric complex, in
agreement with the FAB mass spectrum where the 2:1
complex is exclusively identified. X-ray crystallography
confirms the assignment of this first species as the neu-
tral ZnL2 complex, in which the quinO–pym subunit of
the two ligands is regioselectively switched (Figure 2). In
Figure 2. Solid-state molecular structure of the dimeric ZnL2 complex
(hydrogen atoms and solvent molecules are omitted for clarity).
Regioselective switching performed by a metal ion of octa-
hedral coordination: In contrast to the pym–py coordination
subunit already used previously,[9] the quinOH–pym motif is a
novel triad for switchable devices. In addition to the advant-
age of being tridentate and, hence, a strong binder, the pres-
ence of a hydroxy group provides an anchoring site for oxo-
philic and “hard” cations. Furthermore, its ionizable hydroxy
group provides pH tunability of this binding site (see below).
To enhance the differentiation of the two pym–py and
quinOH–pym coordination modules, the introduction of a di-
valent cation was coupled to ionization of the hydroxy site
to quinO–pym by addition of one equivalent of Me4NOH to
generate the phenoxide ligand LÀ.
the solid state, the zinc cation is strongly bound by the
À
À
hydroxyquinoline anion (Zn O1 2.078, Zn O2 2.066,
À
À
Zn N1 2.032, Zn N2 2.036 Š). The interactions between
the zinc cation and the pyrimidine nitrogen atoms N11
and N22 are much weaker with larger interatomic dis-
À
À
tances (Zn N11 2.51 and Zn N22 2.55 Š), as anticipated
in view of the lower basicity of these sites. This weaker
interaction allows additional stabilization elements to be
expressed, such as a weak hydrogen bond between the
pyrimidine nitrogen sites and the vicinal aryl proton
À
(Ha N12 2.63 Š)and p-stacking interactions between
the quinoline and the alkylaryl moieties (plane-to-plane
distance: 3.4 Š).
Conformational change induced by ZnII ions: Zinc(ii)is an
appropriate cation for coordination to the quinO–pym subu-
nit: being oxophilic, it should help targeting the oxygen-con-
taining binding site while keeping a reasonable affinity for
nitrogen-containing ligands. Addition of zinc(ii)triflate to a
Increasing the amount of Zn2+ above 0.5 equivalents re-
sults in the formation of a second complex, in slow ex-
change with ZnL2, in which the chemical shift of H1 is
still lower (dH1 =7.97 ppm; spectrum not shown). The ex-
istence of a cross-peak between H1 and H3py (as well as
one for H1 and H3)suggests that this new complex also
involves the pym–py binding subunit. ES mass spectrom-
*
solution of LÀ shows two regimes with increasing [Zn]2+
:
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J.-M. Lehn et al.
etry confirms the formation of multinuclear complexes
of the free ionized ligand LÀ (d=9.25 ppm)and that of the
dimeric ZnL2 complex (d=8.30 ppm)is in agreement with a
regioselective switch. One notes also that the pyridyl chemi-
cal shifts of the pym–py module (3py, 4py, and 5py), slightly
affected by the dimerization to ZnL2, are restored to their
initial in LÀ values. ROESY experiments confirm the regio-
selective conformational change of the quinO–pym binding
subunit, showing cross-peaks between H1 and H3, consistent
with a cisoid conformation of the quinO–pym unit, but not
between H1 and H3py. In addition, the conserved transoid
conformation of the py–pym fragment is confirmed by a
weak correlation between the pyridyl H3py and the aryl Ha
protons. The incorporation of the DMHP ligand into the
complex is supported by NOE cross-peaks between the
methyl groups of the DMHP moiety and the pyrimidine H1
proton on one hand, and the aryl Ha protons on the other;
both interactions can be accounted for if the DMHP ligand
is free to rock across the LÀ ligand (see model in Figure 3).
2+
of the type Zn3L3 and Zn2L3+. The involvement of the
pym–py binding site as a stoichiometric amount of Zn2+
is reached is not surprising, as the latter is a better
ligand than the solvent molecules (CD3CN or CD3OD).
To perform a regioselective switch of the quinO–pym with
a 1/1 stoichiometric amount of Zn2+, a capping ligand may
be introduced prior to titration. 2,6-Bis(N,N-dimethylhydra-
zonomethyl)pyridine (DMHP, Figure 3) was chosen as an
Conformational change induced by PbII ions: Lead(ii)ions
were also considered as potential triggers for the regioselec-
tive switching of the terdentate binding site. With an ionic
radius about 1.5 times that of zinc(ii), lead(ii)is a “softer”
cation. Still, it binds to the quinO–pym unit of LÀ as indicat-
1
ed by the H NMR data (not shown). In addition to the un-
changed chemical shifts of the pyridyl protons, the absence
of cross-peaks between H1 and H3py, complemented by the
proximity of Ha and H3py, support a transoid conformation
of the pym–py module. On the other hand, the quinO–pym
unit adopts a cisoid conformation, as shown by the NOE
cross-peak between H1 and H3. The examination of the ali-
phatic region of the spectrum suggests the interaction of two
ligands within the same complex, but not in a 2:1 ligand-to-
metal ratio, as it takes one equivalent to reach a well de-
fined spectrum, and the NOE cross-peaks between the first
aliphatic protons (Ha)and the H6 quinoline protons (see
Figure 3. Aromatic region of the 200 MHz 1H NMR spectrum of the 1:1
mixture of ligand LÀ and DMHP (3.5 mm in 1:1 CDCl3/CD3OD)upon ti-
tration by a solution of ZnII(TfO)2 (8.9 mm, same mixture of solvents).
Proton numbering is detailed in Scheme 1. A model of the final complex
is represented on the bottom right (the alkyl substituent is omitted).
Figure 4)cannot be explained by a ZnL -type complex. The
2
occurrence of dimerization was confirmed by a single-crystal
X-ray diffraction study of the complex, which showed the
formation of a dimeric species indeed incorporating two li-
gands and two lead ions bridged through the oxide groups
(Figure 4). The solid-state structure clearly displays the
binding of the quinO–pym unit with a strong contribution
additional terdentate ligand, analogous to terpyridine but
1
yielding fewer NMR signals. The H NMR spectra for the ti-
tration of a mixture of LÀ and DMHP by Zn2+ are shown in
Figure 3. Up to 0.5 equivalents, LÀ forms the same neutral
quinoline-bound complex ZnL2 as in the absence of DMHP.
The DMHP signals are not affected by the initial introduc-
tion of zinc(ii)ions, although the pyridine and hydrazone
binding sites themselves are expected to be strong enough
to override the weak pyrimidine nitrogen atom, showing the
importance of electrostatic interactions -OÀ,Zn2+ in this
system. Above 0.5 equivalents, DMHP is involved in a slow
exchange with a new compound; the chemical shift of its
proton signal in position 4 of the pyridine group increases
(as expected for a coordinated pyridine)and the protons
3pyD and 1D (Figure 3)are shielded, as anticipated for a
change from a transoid to a cisoid conformation. As for the
ligand, the intermediate chemical shift for H1 between that
À
À
from the quinoline heterocycle (Pb1 O1 2.275 Š, Pb1 N1
2.496 Š), and a weak contribution of the pyrimidine-nitro-
À
gen atom (Pb1 N11 2.780 Š). The two lead ions are unsym-
À
metrically bound to the two bridging oxide sites (Pb1 O2
2.554 Š)and two counteranions provide additional unsym-
À
À
metrical axial bridges (Pb1 O3 2.455, Pb2 O4 2.722 Š).
Overall, the lead cations adopt a distorted octahedral coor-
dination mode with two ligands LÀ essentially in the same
plane and triflate anions as axial ligands. This situation con-
fers an interesting long-range organization to the crystal,
consisting of intertwined tubular ionic channels in which the
cationic dimers are relayed by triflate anions, which them-
selves form hydrogen bonds to the H4py protons of periph-
eral channels. Overall, the stacked organic ligands define a
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Ion-Triggered Multistate Molecular Switches
FULL PAPER
plex whose spectrum resembles
that of ZnL2 (dH1 =8.41 ppm).
ES-MS is consistent with the
dimeric nature of this complex,
+
LaL2 being the only observed
species. ROESY NMR experi-
ments confirm the conforma-
tional change of the quinO–
pym unit exclusively, as H1 is
in close contact with H3 but
not with H3py. Addition of
one equivalent of TFA to the
complex protonates the ligand
and releases the lanthanum
cation, as evidenced by the re-
stored chemical shifts of ligand
LH (Figure 5). The protona-
tion/deprotonation cycle can
be consistently performed sev-
eral times, as illustrated in
Figure 5.
Figure 4. Solid-state molecular structure of the dimeric Pb2L2(TfOÀ)2 complex; left: dimer alone (the black
arrows represent NOEs observed in solution); right: side (top) and top (bottom) views of the ion-containing
channels formed in the crystal (hydrogen atoms, solvent molecules and noncoordinative counteranions are
omitted for clarity). Different levels of gray are used for the different layers of ligands. Pb2+ and coordinated
triflate ions are represented as CPK models.
four-fold symmetric intertwined
channel
right).
system
(Figure 4,
The 1H NMR and crystallo-
graphic studies therefore con-
firm the regioselective switch-
ing process from the transoid to
the cisoid form performed by
divalent metal cations on the
quinO–pym subunit of ligand
LÀ.
pH modulation of the binding
properties of the terdentate
quinOH–pym subunit: An acido-
basic switch for trivalent lantha-
nide cations: In the case of zinc,
ionization of ligand LH was
necessary to obtain well-de-
fined complexes, suggesting
that this borderline ion has suf-
ficient affinity for nitrogen sites
to bind to both quinO–pym and
py–pym modules in the neutral
3+
Figure 5. Aromatic region of the 200 MHz 1H NMR spectrum of LH (LÀ)in the presence of La
CDCl3/CD3OD), and reversible pH modulation of its binding affinity.
(4 mm, 1:1
state. It was therefore interesting to investigate cations that
would not bind the ligand in its neutral state, and become
good substrates upon basification, to perform pH-induced
conformational switching. Harder labile cations were there-
fore required, in particular trivalent lanthanide ions such as
lanthanum(iii), which offered the possibility to conveniently
Dual regioselective switching and ion-selective self-assembly
of [2”2] heterometallic grid complexes: The free ligand, the
copper(i)py–pym-bound complex, and the zinc( ii)quin
–
O
pym chelate provide three different ligand conformational
states. Since copper(i)and zinc( ii)can be incorporated inde-
pendently, we studied the access to a fourth state in which
both binding modules would be in a cisoid complexed form.
The proton NMR spectral changes occurring on addition of
copper(i)to the [Zn II(LÀ)(DMHP)]+ complex are displayed
in Figure 6, and show the formation of a new species in slow
exchange with the starting complex. This observation com-
1
monitor the conformational change by H NMR spectrosco-
py. As illustrated in Figure 5, addition of Ln3+ to LH does
not yield any significant change in the chemical shifts of the
ligand. Addition of one equivalent of tetramethylammonium
hydroxide to the solution cleanly gives rise to a single com-
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J.-M. Lehn et al.
of CuII, the color of the 4 L,2CuI,2CuII solution (see below)
and the mass spectrometry studies suggest the formation of
the analogous [(CuII)2(CuI)2(LÀ)4]2+ complex. The observa-
tion that a single cation in two different interconvertible oxi-
dation states may be used to operate the conformational
switch suggests exciting extensions towards electro-control-
led ionic conformational switches.
These processes amount to the regioselective self-assem-
bly of a heterometallic tetranuclear [2”2] grid-type architec-
ture, directed by the reading out of the ion-binding informa-
tion of ligand LÀ by tetrahedral and octahedral coordination
algorithms.[20] They represent the programmed introduction
in a single operation of different ions (ion selectivity)at pre-
cisely defined locations (toposelectivity)in a polymetallic
supramolecular architecture, an ultimate goal of self-organi-
zation of metallosupramolecular architectures.
Figure 6. 200 MHz 1H NMR spectra for the titration of [ZnII(LÀ)
Multistate ionic switching devices as the basis for complex
logic gates: Four different states can be accessed by the
present system depending on the species in presence, each
of them being characterized by different electronic absorp-
tion features. LH and its ionized form having their highest
absorption peak at 326 nm are colorless. Addition of Cu+ to
LH introduces an absorption band in the visible region
(391 nm)responsible for the pale orange color of the com-
plex. A red color, greatly enhanced in basic media, is acti-
vated by complexation of either Cu2+, Zn2+, Pb2+, or La3+
(broad band centered around 480 nm). Finally, the combina-
tion of both monovalent and multivalent ions provides a
fourth state absorbing at the highest wavelength (broad
band centered around 555 nm)and is responsible for a deep
purple color (Figure 8).
Marked interest has been shown recently in the design of
molecular and supramolecular devices presenting logic gate
features.[4,21] The processes undergone by the present system
may also be analyzed along such lines. Indeed, modulation
of the number of the input triggers generating the four opti-
cal output values gives access to a complex set of logic
states, as detailed in Table 1, Table 2, and Table 3.
+
(DMHP)]+ by CuI(CH3CN)4 in 2:1:1 CDCl3/CD3CN/CD3OD (aromatic
region).
bined with the deep violet color and the very shielded signal
for Ha and Hb protons suggests a more complex architec-
ture than the anticipated [ZnIICuI(L)(DMHP)]2+ complex.
ES-MS analysis of the titration end-point reveals that the
DMHP ligand is expelled from the complex and picks up
Cu+ and Zn2+ ions ([CuI(DMHP)2]+ and [ZnII(DMHP)2]2+
detected), whereas four L-type ligands assemble with two
copper(i)ions and two zinc( ii)ions giving ES-MS signals for
the
complexes:
[(ZnII)2(CuI)2(LÀ)2(LH)2]4+
;
[(ZnII)2-
(CuI)2(LÀ)2(LH)2]4+, TfOÀ, and [(ZnII)2(CuI)2(LÀ)4]2+. A
species with identical NMR signature is indeed obtained on
directly mixing LÀ with CuI and ZnII in a 4:2:2 ratio. It was
1
characterized by H NMR spectroscopy and by X-ray crys-
tallography (Figure 7), confirming the formation of a [2”2]
grid-like structure, with combined conformational change of
both coordination modules.[11,19]
Interestingly, CuII may be used instead of ZnII. Although
1H NMR spectroscopy could not serve to monitor the con-
formational change because of the paramagnetic properties
LH operates as an AND logic gate by activating the ab-
sorption around 480 nm when both HOÀ and multivalent
cations (Zn2+, Pb2+, Cu2+, or La3+)are present (Table 1.)
Either of the above-mentioned multivalent ions can be used,
therefore combining the AND function with an OR opera-
tion. The latter tolerates any multiply charged species since
it is based on the charge-controlled binding of the metal ion,
to the ionized phenoxo site. Therefore all divalent (Cu2+
Pb2+, Zn2+)and trivalent (La 3+)cations are possible opera-
,
tors. The binding is nevertheless conditioned by the ioniza-
tion of the phenoxide function responsible for the appropri-
ate hardness of the ligand, imposing an AND function
(Table 1).
In the case of the triply charged La3+ cation, there is no
interaction at all with neutral LH and deprotonation is nec-
essary for binding and any detectable coloring to occur. This
translates into a proton-induced INHIBIT operation at
480 nm, as expressed in Table 2.
Figure 7. Two views of the solid state molecular structure of complex
[Zn2Cu2L4]2+ (TfOÀ)2 (hydrogen atoms, solvent molecules and counter-
anions are omitted for clarity; the front ligand is represented in light gray
for clarity); see also reference [10].
6824
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Chem. Eur. J. 2005, 11, 6818 – 6828

Ion-Triggered Multistate Molecular Switches
FULL PAPER
pale yellow complexes absorb
in distinct visible regions
(390 nm and 480 nm)and act
as individual distinct outputs.
On the other hand, the purple
species is characterized by
broad bands covering all four
wavelengths significantly, and,
hence, activating several out-
puts simultaneously.
Conclusion
As demonstrated above, mole-
cule LH is able to access four
conformational states depend-
ing on its interaction with dif-
ferent ions such as CuI, ZnII,
LnIII, and H+/HOÀ. The ca-
pacity to specifically address
particular sites (e.g., H+/HOÀ
affect the hydroxy group, CuI
and ZnII target the py–pym
and quinO–pym modules re-
spectively)and the possibility
to activate all stimuli simulta-
neously are highly valuable
Figure 8. The system LH/metal ion/HOÀ as a iono-mechanical double switching device operated by several dif-
ferent inputs and generating four different outputs.
Table 1. Mn+ AND HOÀ logic gate (Mn+: Zn2+, Cu2+, Pb2+, La3+).
Table 3. Multiple input/multiple output logic gate (Mn+ are multivalent
ions such as Cu2+, Pb2+, Zn2+, and La3+). The state of the switch relates
to the anti (OFF)and syn (ON)conformations of the py–pym and
quinO–pym components, where syn is the form induced by cation binding.
Input 1
Mn+
Input 2
HOÀ
Output 3
480 nm
0
0
0
1
1
0
1
1
0
1
0
0
0
0
1
Input
Switch component state
Outputs
lmax [nm]
2
3 and 4
py–pym quinO–pym
1
2
3
4
Cu+
Mn+ and HOÀ
326 390 480 555
0
1
0
1
0
0
1
1
OFF
ON
OFF
ON
OFF
OFF
ON
1
1
1
1
0
1
0
1
0
0
1
1
0
0
0
1
ON
Table 2. INHIBIT logic gate
Input 1
La3+
Input 2
HOÀ
Input 3
H+
Output 3
480 nm
assets of ionically operated processes compared to the pho-
tonic and electronic modes. Furthermore, the ability of cati-
ons to modulate the electronic properties of their ligand
(not to mention the intrinsic electronic richness of d transi-
tion metal cations)confers an additional interest to ionic
switches. In the present case, the four different conforma-
tional states are associated with four distinct optical states,
namely the colorless LH and LÀ ligands (lmax =326 nm), the
0
1
0
0
1
1
0
1
0
0
1
0
1
0
1
1
0
0
0
1
0
1
1
1
0
0
0
0
1
0
0
0
py–pym switched light orange [Cu(LH)2] complex (lmax
=
In addition to integrating several operation modes de-
pending on the read output (and therefore on different
input triggers), the present unit LH operates via two switch-
ing components based on conformational changes, thus ena-
bling the activation of several output values simultaneously
or independently (Table 3). On the one hand, the red and
390 nm), the quinO–pym bound bright red [Zn(L)2],
[Zn(LÀ)(DMHP)]+, and [Ln(LÀ)2]+ complexes (lmax
=
480 nm), and the doubly switched deep purple [(ZnII)2-
(CuI)2(LÀ)4]2+ grid (lmax =555 nm). This system thus repre-
sents an opto-ionic molecular switching device[3,22] involving
multiple chemical/ionic inputs and multiple optical outputs,
Chem. Eur. J. 2005, 11, 6818 – 6828
ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6825

J.-M. Lehn et al.
2-Tri-n-butylstannyl-6-methylpyridine:[13] n-Butyllithium (17 mL; 1.6m in
hexane (27 mmol, 1.15 equiv)) was added dropwise to 2-bromo-6-methyl-
pyridine[14] (4.00 g, 23.3 mmol)solubilized in dry THF (30 mL)and
cooled down to À788C under argon. After the mixture had been stirred
for 1 h at À788C, tri-n-butyltin chloride (8.0 mL, 29 mmol, 1.3 equiv)was
added dropwise to the red solution. The orange solution was then stirred
overnight. After evaporation of the solvent, the residue was taken up in
diethyl ether (50 mL)and water (20 mL.) The organic layer was further
washed with brine (15 mL)and the combined aqueous layers extracted
with diethyl ether (2”15 mL). The combined organic layers were dried
(Na2SO4), filtered, and concentrated in vacuo. Distillation of the crude
product (115–1208C at 0.1 mmHg)afforded the desired stannane (8.8 g;
99% yield). 1H NMR (CDCl3): d=7.36 (t, 3J=7.3 Hz, 1H), 7.17 (d, 3J=
8 Hz, 1H), 6.95 (dd, 3J=7.7 Hz, 4J=0.9 Hz, 1H), 2.54 (s, 3H), 0.8–
1.7 ppm (m, 16H).
and effecting the generation and conversion of chemicals
signals, features of much interest for the development of
semiochemistry.[3] The combined controlled mechanical mo-
tions, the selective optical read-out and the addressing of
several distinct states demonstrate the potential of reversi-
ble, ionically operated, multistate molecular switching devi-
ces in accessing nanoscale entities presenting functional fea-
tures of interest for the design and operation of molecular
computational and signaling processes of increased complex-
ity.
2-(4-n-Butylphenyl)-4-chloro-6-(6-methylpyridin-2-yl)-pyrimidine (2): 2-
Tri-n-butylstannyl-6-methylpyridine (4.05 g, 10.6 mmol), 2-(4-n-butyl-
phenyl)-4,6-dichloropyrimidine[12] (3.06 g, 10.9 mmol, 1.05 equiv), and di-
Experimental Section
1H and 13C NMR spectra were recorded on a Bruker AC 200 (200 MHz
and 50 MHz respectively)at 25 8C. 1H NMR titrations were conducted on
a Bruker AC 200 spectrometer at 258C. CDCl3 was freshly neutralized
by passing through dried basic alumina prior to each experiment; all
NMR solvents were degassed by bubbling argon prior to titration. For
1H NMR titrations, determined volumes of a solution of the titrant (tri-
flate or tetrafluoroborate salt solution)of known concentration (typically
10–25 mm)in a solvent or mixture of solvents were added to a solution of
the receptor (typically 2–5 mm)in the same mixture of solvent, and the
chemical shift of all protons monitored. Mass spectrometry was per-
formed in the Laboratoire de SpectromØtrie de masse Bio-organique
(Strasbourg)and elemental analyses at the elemental analysis service of
Louis Pasteur University (Strasbourg). UV/Vis spectra were recorded on
a Shimadzu HYPER UV using 110-QS Hellma Cuve quartz (10 mm and
0.1 mm)and degassed solvents. As in the case of the NMR measure-
ments, CHCl3 was neutralized by passing through dried basic alumina
prior to preparing the stock solutions. All reagents were used as received.
Dry solvents (dichloromethane, toluene, THF)were distilled over drying
agents (calcium hydride, Na, Na/benzophenone, respectively)under
argon. DMHP was obtained by condensation of dimethylhydrazine with
commercially available 2,6-pyridinedicarboxaldehyde (Aldrich).[23] Crys-
tal data were collected at 173 K on a Nonius KappaCCD diffractometer,
and structures were solved by Nathalie Kyristakas at the Service
Commun de Cristallographie (Louis Pasteur University, Strasbourg)
using (Bruker)SAINT and SHELXTL 97 software.
chlorobistriphenylphosphinepalladium(ii)(155 mg,
2.2”10
À4 mol,
0.02 equiv)were mixed in degassed DMF under argon and heated at
808C for 36 h. After removal of the solvent, the solid residue was dis-
solved in diethyl ether (70 mL)and washed with an aqueous solution of
potassium fluoride (9 g in 90 mL). The aqueous layer was extracted with
diethyl ether (30 mL)and dried (Na 2SO4), filtered, and concentrated.
After purification by column chromatography (flash, SiO2, hexane/
CH2Cl2 50:5 to 50:10), a shiny white solid was obtained (1.84 g, 51%).
1H NMR (CDCl3) : d=8.4–8.5 (m, 3H), 8.29 (s, 1H), 7.78 (t, 3J=7.7 Hz,
3
1H), 7.2–7.4 (m, 3H), 2.70 (t, J=7.4 Hz), 2.66 (s, 3H, CH3), 1,66 (quint.,
3J=7.8 Hz), 1.39 (sext., 3J=7.8 Hz, 2H), 0.95 ppm (t, 3J=7.4 Hz, 3H);
13C NMR (CDCl3): d=165.1, 164.8, 162.6, 158.5, 152.7, 146.7, 137.2,
134.0, 128.7, 128.6, 125.4; 119.3, 115.0, 35.7, 33.4, 24.6, 22.4, 14.0 ppm: Rf
(SiO2, hexane/CH2Cl2 5:1)=0.28; m.p. 898C. EI: 337.3 ([M]À); elemental
analysis calcd (%)for C 20H20N3Cl·0.15CH2Cl2: C 70.89, H 5.95, N 12.35,
Cl 10.45; found: C 70.88, H 5.99, N 12.61.
8-Hydroxyquinoline-N-oxide:[24] Hydrogen peroxide (8 mL, 30–35% in
water)was added dropwise to a solution of commercially available 8-hy-
droxyquinoline (3.00 g, 20.7 mmol)in acetic acid (35 mL); the solution
was then refluxed for 40 min. After solvent removal, the oily residue was
taken up in dichloromethane (50 mL)and washed with a dilute aqueous
solution of hydrogen carbonate (pH 6–7). The aqueous layer was extract-
ed with dichloromethane (3”30 mL)and the combined organic layers
were dried (Na2SO4), filtered, and concentrated in vacuo before column
chromatography (SiO2, CH2Cl2/acetone 2.0:0.2 to 2.0:0.4)to afford a
yellow solid (3.85 g; 58%). 1H NMR (CDCl3): d=8.23 (d, 3J=6.0 Hz,
1H), 7.78 (d, 3J=8.4 Hz, 1H), 7.49 (t, 3J=8.0 Hz, 1H), 7.15–7.25 (m,
Crystallographic data: Single crystals of the complex ZnL2
([2C58H50N8O2Zn]·3CH3OH)were grown by slow diffusion of diethyl
ether into a mM solution (mixture of CDCl3 and CD3OD). Crystals were
placed in oil and a single dark red crystal of dimensions 0.10”0.10”
0.08 mm mounted on a glass fiber and placed in a low-temperature N2
3
4
2H), 7.06 ppm (dd, J=7.9 Hz, J=0.9 Hz, 1H).
¯
stream. The cell was triclinic; space group P1. Cell dimensions: a=
2-Oxo-1,2-dihydroquinolin-8-yl acetate (3):[25] A suspension of 8-hydroxy-
quinoline-N-oxide (2.00 g, 12.4 mmol)in acetic anhydride (12 mL)was
heated to 1008C for 7.5 h under an atmosphere of dinitrogen. The beige
solid was poured into water (50 mL), cooled in an ice bath, and neutral-
ized with a concentrated aqueous ammonia solution. The solid was fil-
tered, washed with water, and dried in vacuo, to afford a beige solid
(2.32 g; 92%). 1H NMR (CDCl3): d=10.8 (br s, 1H), 7.77 (d, 3J=9.6 Hz,
1H), 7.43 (dd, 3J=7.7 Hz, 4J=1.3 Hz, 1H), 7.36 (dd, 3J=8.0 Hz, 4J=
1.3 Hz, 1H), 7.19 (t, 3J=7.9 Hz, 1H), 6.66 (d, 3J=9.5 Hz, 1H), 2.53 ppm
(s, 3H).
2-Bromo-quinolin-8-yl acetate (4):[26] 2-Oxo-1,2-dihydroquinolin-8-yl ace-
tate (3; 300 mg, 1.47 mmol)and phosphoryltribromide (1.18 g, 4.1 mmol,
2.8 equiv)were refluxed in chloroform (1 mL; dried onto alumina)for
2 h under argon. At room temperature, the brown suspension was poured
into ice, filtered, and washed with chloroform (30 mL). The organic layer
was isolated and washed with brine (10 mL), dried (Na2SO4), filtered,
and concentrated in vacuo. The brown oil was taken up in chloroform,
treated with charcoal, and filtered through celite. The white crystals that
appeared upon addition of a mixture of hexane and ethyl acetate (~1:1)
were filtered to afford the expected bromide (137 mg, 35%). 1H NMR
(CDCl3): d=8.00 (d, 3J=8.6 Hz, 1H), 7.70 (dd, 3J=8.0 Hz, 4J=1.5 Hz,
11.5751, b=15.7037, c=15.7449 Š, a=g=67.3848, b=77.2128, g=
70.9648, V=2482.3, and Z=1 (FW=2009.06 and 1=1.34 gcmÀ1À3) . A
total of 14458 reflections were collected (2.58ꢀqꢀ30.068), of which
10530 were unique, having I>3s(I); 648 parameters. Final R factors
were R1 =0.049 (based on observed data)and wR2 =0.342 (based on all
À3
data), GOF=1.457, maximal residual electron density is 0.880 eŠ
.
Single crystals of the complex Pb2L2 ([C29H25N4OPb]·F3CSO3)spontane-
ously formed from a 2 mm solution of the complex in 1:1 CDCl3/CD3CN.
Crystals were placed in oil and a single yellow prism of dimensions 0.16”
0.14”0.12 mm mounted on a glass fiber and placed in a low-temperature
N2 stream. The cell was tetragonal; space group of I41/a. Cell dimen-
sions: a=b=29.9186, c=13.0566 Š, V=11687.3 and Z=16 (FW=801.81
and 1=1.82 gcmÀ3). A total of 8888 reflections were collected (2.58ꢀqꢀ
30.068), of which 5396 were unique, having I>3s(I); 356 parameters.
Final R factors were R1 =0.048 (based on observed data)and wR2 =0.078
(based on all data), GOF=1.433, maximal residual electron density is
À3
0.924 eŠ
.
CCDC-271555 (Pb2L2)and CCDC-271556 (ZnL )contain the supplemen-
2
tary crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
6826
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ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 6818 – 6828

Ion-Triggered Multistate Molecular Switches
FULL PAPER
1H), 7.56 (t, 3J=8.0 Hz, 1H), 7.54 (d, 3J=8.3 Hz, 1H), 7.46 (dd, 3J=
7.5 Hz, J=1.5 Hz, 1H), 2.50 ppm (s, 3H).
Stoddart, Angew. Chem. 2000, 112, 3484–4530; Angew. Chem. Int.
Ed. 2000, 39, 3348–3391; c)J. F. Stoddart, Acc. Chem. Res. 2001, 34,
409–522.
4
2-[2-(4-n-Butylphenyl)-6-(6-methylpyridin-2-yl)-pyrimidin-4-yl-quinolin-
8-yl acetate (5): 2-Bromoquinolin-8-yl acetate (4; 306 mg, 1.15 mmol)
was refluxed with 1,1,1,2,2,2-hexamethyldistannane (0.46 g, 1.4 mmol,
1.3 equiv)and tetrakistriphenylphosphinepalladium(0)(75 mg, 6.5”
10À4 mol, 0.05 equiv)in distilled toluene (23 mL)under argon for 1.5 h.
After removal of the solvent, the mixture was solubilized in fresh toluene
(15 mL), and 2-(4-n-butylphenyl)-4-chloro-6-(6-methylpyridin-2-yl)pyri-
midine (2; 423 mg, 1.26 mmol, 1.09 equiv)was added, together with tetra-
kistriphenylphosphinepalladium(0)(78 mg, 6.7”10 À4 mol, 0.06 equiv).
The solution was refluxed under argon for 17.5 h, after which the solvent
was evaporated under vacuum. The residue was solubilized in chloroform
(45 mL)and washed successively with water (15 mL)and brine (15 mL).
The aqueous layer was extracted with chloroform (3”10 mL), and the
combined organic layers were dried (Na2SO4), filtered, and concentrated
in vacuo. A shiny white product (372 mg; 66%)was obtained after
column chromatography (SiO2, CH2Cl2/hexane 2.0:0.5)and recrystalliza-
tion (CH2Cl2/EtOH). 1H NMR (CDCl3): d=9.53 (s, 1H), 8.91 (d, 3J=
8.5 Hz, 1H), 8.66 (d, 3J=8.2 Hz, 2H), 8.57 (d, 3J=7.9 Hz, 1H), 8.39 (d,
3J=8.8 Hz, 1H), 7.80 (t, 3J=7.6 Hz, 1H), 7.81 (dd, 3J=8.1 Hz, 4J=
1.7 Hz, 1H), 7.60 (t, 3J=7.8 Hz, 1H), 7.51 (dd, 3J=7.5 Hz, 4J=1.7 Hz,
1H), 7.38 (d, J=8.2 Hz, 2H), 7.29 (d, J=7.6 Hz, 1H), 2.81 (s, 3H), 2.74
(t, 3J=7.8 Hz, 2H), 2.68 (s, 3H), 1.70 (quint., 3J=7.8 Hz, 2H), 1.44
(sext., 3J=7.5 Hz, 2H), 0.97 ppm (t, 3J=7.2 Hz, 3H); 13C NMR (CDCl3):
d=170.0, 164.2, 163.5, 158.1, 154.3, 154.0, 148.4, 145.8, 140.5, 137.0, 137.0,
135.5, 130.2, 128.6, 128.4, 127.1, 125.5, 124.8, 121.4, 119.5, 118.8, 111.5,
35.6, 33.5, 24.5, 22.4, 21.1, 14.0 ppm; Rf (SiO2, CH2Cl2)=0.31; m.p.
2098C; FAB+: m/z: 489.2 ([MH]+), 446.2 ([MÀAcH]+); elemental anal-
ysis calcd (%)for C 31H28N4O2·0.08CH2Cl2: C 75.36, H 5.73, N 11.32, O
6.46; found: C 75.38, H 5.55, N 11.40.
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2-[2-(4-n-Butylphenyl)-6-(6-methylpyridin-2-yl)-pyrimidin-4-yl-quinolin-
8-ol (LH):[27] A solution of 20% aqueous KOH (0.5 mL)was added to
5
(51 mg, 1.04 mmol)suspended in a mixture of pyridine (2 mL)and water
(0.5 mL). The red solution was refluxed for 1 h and stirred at room tem-
perature for another 10 h. After addition of CH2Cl2 (4 mL)and water
(1 mL), the mixture was neutralized with dilute HCl and extracted with
CH2Cl2 (2”4mL). The combined organic layers were dried (Na2SO4), fil-
tered, and concentrated in vacuo. After column chromatography (SiO2,
CH2Cl2 then CH2Cl2/EtOAc 2.0:0.3)and recrystallization from CH 2Cl2/
hexane, the desired alcohol (35 mg)was isolated in 76% yield. 1H NMR
(CDCl3): d=9.32 (s, 1H), 8.84 (d, 3J=8.5 Hz, 1H), 8.63 (d, 3J=8.2 Hz,
2H), 8.53 (d, 3J=7.9 Hz, 1H), 8.46 (br s), 8.34 (d, 3J=8.5 Hz, 1H), 7.79
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[17] a)The variation of the chemical shifts of the proton signals was ana-
lyzed using the Chem. Equili. Software (version 6.1, 1998, V. P. Solo-
v’ev, Moscow University); b) Binding constants based on UV/Vis ti-
trations performed by Dr. Annie Marquis (private communication)
and fitted with LETAGROP, consistent with the association con-
stants reported for L=5,5’-dimethyl-2,2’-bipyridine (KCuL =6.0Æ0.3,
see: F. Arnaud-Neu, M. Sanchez, M.-J. Schwing-Weil, Nouv. J.
Chim. 1986, 10, 165–167.
3
3
3
(t, J=7.8 Hz, 1H), 7.52 (t, J=7.8 Hz, 1H), 7.40 (dd, J=7 Hz, 1H), 7.37
(d, 3J=8.2 Hz, 2H), 7.29 (d, 3J=8 Hz, 1H), 2.73 (s, 3H), 2.73 (t, 3J=
7.8 Hz, 2H), 1.70 (quint., 3J=7.8 Hz, 2H), 1.39 (sext., 3J=7.5 Hz, 2H),
0.98 ppm (t, 3J=7.2 Hz, 3H); 13C NMR (CDCl3): d=164.5, 164.3, 158.5,
154.1, 152.8, 152.7, 146.0, 137.9, 137.2, 137.1, 135.4, 129.3, 128.8, 128.7,
128.4, 125.0, 120.0, 119.1, 117.9, 111.3, 110.4, 35.7, 33.6, 24.7, 22.4,
14.0 ppm; Rf (SiO2, CH2Cl2/EtOAc 2.0:0.3)=0.25; m.p. 1658C; EI: m/z:
446.3 ([M]À); elemental analysis calcd (%) for C 31H28N4O2·0.08CH2Cl2: C
77.04, H 5.82, N 12.47, O 3.53; found: C 77.00, H 5.61, N 12.42.
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A.P. acknowledges the support of the French Minist›re de l’Éducation et
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Received: June 2, 2005
Published online: August 17, 2005
6828
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ꢀ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2005, 11, 6818 – 6828