A dicopper(I) trefoil knot with m-phenylene bridges between the ligand subunits: Synthesis, resolution, and absolute configuration

Article abstract of DOI:10.1002/(SICI)1521-3765(19990503)5:5<1432::AID-CHEM1432>3.0.CO;2-C

A molecular trefoil knot, constructed around two copper(I) centres used as a template, has been synthesized in 29% yield (cyclization step) by the use of 1,3-phenylene spacers between the 1,10-phenanthroline subunits; the double stranded helical precursor

Full text of DOI:10.1002/(SICI)1521-3765(19990503)5:5<1432::AID-CHEM1432>3.0.CO;2-C

FULL PAPER
A Dicopper(i) Trefoil Knot with m-Phenylene Bridges between the Ligand
Subunits: Synthesis, Resolution, and Absolute Configuration
[
a]
[a]
[a]
Christiane Dietrich-Buchecker, Gw e na eÈ l Rapenne, Jean-Pierre Sauvage,*
[b]
[b]
Andr e De Cian, and Jean Fischer
Abstract: A molecular trefoil knot, con-
structed around two copper(i) centres
used as a template, has been synthesized
in 29% yield (cyclization step) by the
use of 1,3-phenylene spacers between
the 1,10-phenanthroline subunits; the
double stranded helical precursor com-
plex is formed quantitatively. This latest
improvement allowed us to prepare this
topologically chiral molecule on a large
scale and hence to undertake the reso-
lution of its enantiomers. The resolution
technique is based on crystallization of
diastereomers with an enantiomerically
pure chiral counterion, (S)-(‡)-1,1'-bi-
meric excess (ee > 98%). The optical
purity was determined by H NMR and
1
circular dichroism (CD) spectroscopy.
The absolute configuration was estab-
lished on the basis of an X-ray diffrac-
tion study, the dextrorotatory knot cor-
responding to the left-handed knot.
Demetallation with excess KCN yielded
the free ligand, which could subsequent-
ly be remetallated with silver(i) or cop-
per(i). The chiroptical properties of each
species are reported.
naphtyl-2,2'-diyl
phosphate
[(‡)-
�
BNP ]. After anion exchange, several
tens of milligrams of each enantiomer
were isolated, with an excellent enantio-
Keywords: chiral resolution ´ cop-
per ´ molecular topology ´ template
synthesis ´ trefoil knot
Introduction
Euclidian or chemical chirality is the property of rigid
molecular objects not to be superimposable to any conforma-
tions of their mirror image. This type of chirality is associated
with the rigidity of the molecule and with chemically allowed
[
1±4]
conformational changes.
The topological properties of a
chemical object represent an upper level of description,
[
5±7]
leading to the notion of topological chirality.
In this
manner, contrary to Euclidian enantiomers, two topological
enantiomers can not be interconverted by a continuous
deformation in a three-dimensional space without breaking
a bond. Therefore topological chirality does not imply any
[
8, 9]
rigidity of the architecture.
Molecular knots are fascinating
objects, not only for their beauty, but also for their chirality.
Knots are topologically novel systems par excellence, with the
simplest of them, that is, the classical trefoil knot, being the
archetype of a topologically chiral object (Figure 1).[
Figure 1. The two topologically equivalent representations of both enan-
tiomers of a trefoil knot.
10±12]
According to Frisch and Wassermanꢀs definition,[7] structures
a and b are topological enantiomers.
[
a] Prof. J.-P. Sauvage, Dr. C. Dietrich-Buchecker, Dr. G. Rapenne
Laboratoire de Chimie Organo-Min e rale, UMR 7513 CNRS
Universit e Louis Pasteur, Institut Le Bel
The molecular graph of a topologically chiral molecule is
necessarily nonplanar. Made of a single knotted closed ring, a
knot can not be represented in a two-dimensional (2D) space
without a minimum number of crossing points, three in the
case of a trefoil knot. In Figure 2 some of the most well-known
prime knots are represented. However, if some knots are
chiral, it is noteworthy that others are not, for instance the
4, rue Blaise Pascal, F-67070 Strasbourg (France)
Fax: (‡33)388-607312
E-mail: sauvage@chimie.u-strasbg.fr
[
b] Dr. A. De Cian, Prof. J. Fischer
Laboratoire de Cristallographie et de Chimie Structurale
UMR 7513 CNRS, Universit e Louis Pasteur, Institut Le Bel
4, rue Blaise Pascal, F-67070 Strasbourg (France)
knot 4 represented in Figure 2.
1
1
432
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Chem. Eur. J. 1999, 5, No. 5

1
432±1439
the modest yield was due to the simultaneous formation of a
face-to-face complex (major species), in equilibrium with the
double helix.[ A 1,3-phenylene spacer, already used with
success by others in the construction of helical complexes,[
appeared very appealing to bridge the two phenanthroline
fragments in the precursor ligand.
19]
20±22]
Synthesis of a bisphenanthroline with a 1,3-phenylene bridge:
Bisphenanthroline 1 was obtained after reaction at room
temperature of 2-(p-anisyl)-1,10-phenanthroline[ with half
Figure 2. The first eight prime knots.
23]
an equivalent of 1,3-dilithiobenzene formed by interconver-
In 1989, the first trefoil knot was prepared at the molecular
[24]
sion of 1,3-dibromobenzene with tert-butyllithium.
After
level.[
13, 14]
More recently, two different syntheses have been
hydrolysis of the reaction mixture at 08C, followed by
rearomatization with excess manganese dioxide, chromatog-
raphy on alumina afforded pure 1 in a 66% yield. The
methylic ethers were deprotected in refluxing pyridinium
developed. The first one, introduced by Seeman and co-
[
15]
workers, utilizes synthetic single-stranded DNA fragments
that are combined and knotted using enzymes. The second
[
16]
one, developped by Stoddart et al.,
is based on the p-
[25]
chloride, according to a method described by Curphey et al.
donor± p-acceptor gathering effect between aromatic nuclei.
We present here the improvements in our strategy, thanks to
the optimization of structural parameters, which allowed its
Despite the hard reaction conditions, diphenol 2 was obtained
in a 94% yield after neutralization with 0.1m NaOH and
drying under vacuum in the presence of phosphorus pent-
oxide.
[
17]
preparation on a gram scale
resolution.
and led us to attempt its
[
18]
Preparation of a copper(i) double helix with a labile anion: To
introduce the chiral auxiliary necessary in the resolution step,
�
�
a labile anion, unlike the classical BF4 or PF6 which can not
easily be exchanged, is required. Therefore, we performed the
metallation of 1 with a copper salt bearing a labile, non-
coordinating counterion. Triflate, which is known for these
properties,[ seemed particularly well-suited. Copper(i) tri-
flate can be easily generated in situ by reaction of copper(ii)
triflate in the presence of a reducing agent. Copper(ii) triflate
was prepared following Jenkinsꢀ method,[ by addition of
triflic acid onto a solution of copper(ii) carbonate in acetoni-
trile. After recrystallization, this salt was obtained in 85%
yield.
Results and discussion
Synthesis of a racemic trefoil knot: Our strategy for making
knots takes advantage of the three-dimensional template
effect of transition metals that are able to gather and interlace
coordinating molecular strings prior to the ultimate cycliza-
tion step. The precursor of a molecular trefoil knot, as shown
in Figure 1, is a dinuclear double helix. In the first synthesis,
26]
27]
Abstract in French: Un núud de tr›fle molØculaire prØparØ
gr aà ce à lꢀeffet de matrice tridimensionnel induit par deux ions
cuivre(i) a ØtØ obtenu avec un rendement de 29% (Øtape de
cyclisation). Ce progr›s a ØtØ possible par lꢀutilisation du pont
One equivalent of copper(ii) triflate was then added at
room temperature to the bischelating diphenolic strand 2 in
the presence of a reductant (ascorbic acid or hydrazine). Mass
spectroscopy confirmed that the dark-red complex, obtained
quantitatively, contained two copper ions and two ligands, and
1
,3-phØnyl›ne entre les fragments 1,10-phØnanthroline, le
prØcurseur en double hØlice se formant alors de mani›re
quantitative. Cette amØlioration synthØtique a rendu possible la
prØparation de cette molØcule topologiquement chirale a
lꢀØchelle du gramme et ainsi à envisager son dØdoublement.
La mØthode de dØdoublement que nous avons utilisØe est
fondØe sur la cristallisation de diastØrØom›res, ceux-ci Øtant
1
H NMR showed that the molecule had a high degree of
symmetry. The four phenanthrolines, the four anisyls and the
two 1,3-phenylene bridges are magnetically equivalent; this is
a characteristic feature of a double helix that possesses three
[
2, 3, 13]
C symmetry axes.
2
1
In addition, this H NMR spectrum shows striking differ-
ences compared with that of the free ligand. Protons H are
significantly shielded (from 8.45 to 7.10 ppm), as well as Hm
from 6.93 to 5.75 ppm) and especially H (from 8.63 to 6.57).
formØs par lꢀutilisation dꢀun anion optiquement pur, (S)-(‡)-
�
1
,1'-binaphtyl-2,2'-diyl phosphate ((‡)-BNP ). Apr›s Øchange
o
de celui-ci par un anion optiquement inactif, il a ØtØ possible
dꢀobtenir plusieurs dizaines de milligrammes de chaque
(
3
All these protons are located in the shielding cones of the
phenanthroline fragments of the double helix. A crystallo-
graphic study finally confirmed the double-helical struc-
ture.[
A double helix is a classically (but not topologically) chiral
object. The coordination of the first copper(i) ion determines
the rotation direction of the helix and therefore its stereo-
chemistry. It can either turn right (P double helix) or left (M
double helix). This chirality, purely of Euclidian nature, is
responsible for the topological chirality of the copper(i) knot.
Ønantiom›re, ceci avec un excellent exc›s ØnantiomØrique
1
(ee > 98%). La puretØ optique a ØtØ dØterminØe par RMN- H
et par dichroïsme circulaire. La configuration absolue a
Øgalement ØtØ dØterminØe sur la base dꢀune Øtude par diffraction
des rayons X, le núud dextrogyre correspondant au núud
gauche. La dØmØtallation avec un exc›s de KCN nous permet
dꢀobtenir le ligand libre qui a ØtØ remØtallØ avec de lꢀargent(i) ou
du cuivre(i). Les propriØtØs optiques de chaques esp›ces sont
rapportØes.
17]
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J.-P. Sauvage et al.
FULL PAPER
Preparation of a copper(i) knot: The crystallographic study of
the double helix also showed that, owing to an important
twisting, the terminal phenolic functionalities are well-ori-
ented to favour the double cyclization leading to the knot. The
intermolecular reactions leading to oligomers are disfavoured
by the use of pseudo-high-dilution reaction conditions: a
suspension of cesium carbonate is progressively added to a
DMF solution containing in a 1:1 ratio the diiodo derivative of
[
28]
hexaethyleneglycol and the double helix (initial concen-
�
1
tration of ꢀ5 mmolL ). The reactive species (phenolate) is
therefore generated in very low concentration, which favours
intramolecular reactions and prevents the copper(i) complex
from being in a strongly basic medium, in which it is unstable.
After a reaction time of forty hours and performance of
chromatography twice in succession over silica, the triflate of
the copper(i) knot was isolated in a 29% yield; this is very
satisfying given that the cyclization involves the connection of
eight reaction centres.
1
2‡
�
The H NMR spectrum of 4 ´ 2TfO is very similar to that
of the double helix, except the appearance of a broad
multiplet (between 4.20 and 3.20 ppm) corresponding to the
signals expected for the 48 protons of the two hexaethylene-
glycol chains. The mass spectrum shows a large molecular ion
‡
peak at the expected value (m/z ˆ 2003.0 [M � TfO] ).
However, the knotted structure could only be strictly
evidenced by a 2D ROESY NMR experiment, which showed
interfragment NOE interactions between protons 5 and 6 of
the phenanthroline subunits (Figure 3) and the central pro-
tons of the polyoxyethylenic chains. Moreover, a crystallo-
graphic study confirmed the knotted structure of this complex
Figure 3. Synthetic strategy and chemical structure of the organic pre-
cursors and of the knots.
of both diastereomers (e.g., their solubility), making their
resolution possible by selective crystallization. The principle
of the resolution process is represented in Figure 4.
(
vide infra).
The racemic mixture of the knot was converted into
diastereomers by means of a liquid ± liquid extraction; this
takes advantage of the solubility of sodium triflate in water
compared with the insolubility of binaphthylphosphate salts.
Sodium binaphthylphosphate and the copper(i) knot triflate
were dissolved in dichloromethane. Sodium triflate was
progressively extracted by a water flow running through the
medium. The anion exchange was monitored by TLC (SiO2;
eluent: CH Cl /10% MeOH), the counterion having a strong
Resolution: The resolution step of a chiral molecule is
sometimes difficult but always crucial.
[
29, 30]
Topologically
[
31]
chiral [2]-catenanes have been described, but their reso-
lution could only be carried out at the analytical level.[ The
strategy used here to prepare knots implies that the target
molecules be obtained as cationic dicopper(i) complexes.
Therefore we considered the possibility of interconverting
both enantiomers into a pair of
32]
2
2
diastereomeric salts by combin-
ing them with an optically ac-
tive anion. Binaphthyl phos-
�
[33]
phate (BNP )
drew our at-
tention because its chirality
arises from the binaphthyl core,
which is twisted. This helical
structure is reminiscent of that
of the copper(i) double helix,
precursor of the knot. Besides,
both compounds are aromatic
and therefore, we could expect
some potentially helpful stack-
[
34]
ing interactions.
These structural similarities
should enable strong interac-
tions between the two moieties,
possibly leading to a marked
differentiation of the properties
2‡
Figure 4. Principle of the resolution of the dicopper(i) molecular trefoil knot 4 . The chiral auxiliary used is (S)-
(‡)-1,1'-binaphthyl-2,2'-diyl phosphate (BNP ).
�
1
434
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Chem. Eur. J. 1999, 5, No. 5

Trefoil Knots
1432±1439
Table 1. 1H NMR (400 MHz) chemical shifts of a selection of aromatic
influence on the polarity of the complex (the difference in Rf
is 0.2). After 48 hours at room temperature, the exchange was
complete.
2
‡
�
2‡
protons for the two diastereomers (� )-4 ´ 2(‡)-BNP and (‡)-4 ´ 2(‡)-
�
BNP .
The 1H NMR spectrum of the diastereomeric mixture
appeared to be very striking. Each signal was split into two,
which clearly indicated a strong difference in association
between the chiral auxiliary and each enantiomer of the knot.
This difference was large enough to confer the two diaster-
eomers different solubilities. Indeed we could crystallize (‡)-
Ha
H7
Hc
Ho
Hb
H3
Hm
2
‡
�
�
(� )-4 ´ 2(‡)-BNP
9.697 8.394 7.181 7.037 6.951 6.482 5.665
9.680 8.367 7.133 7.023 6.916 6.468 5.665
2
‡
(
‡)-4 ´ 2(‡)-BNP
Dd [ppm]
0.017 0.027 0.048 0.014 0.035 0.014
0
�
BNP anions. Differences appear large for the protons on the
2
‡
�
[18]
4
´ 2(‡)-BNP in a mixture of nitromethane and benzene,
m-phenylene spacer (Dd ˆ 0.035 and 0.048 for H and H ,
b
c
whereas the levorotatory knot remained in the mother liquor.
respectively) but weak for the peripheral ones (Dd ˆ 0.014
2‡
�
Typically, 100 mg of (Æ)-4 ´ 2(‡)-BNP were dissolved in
and 0.000 for H and H , respectively). These observed
o
m
5
mL of nitromethane and this solution was placed in a
chemical shifts arise most probably from a preferential
crystallization tube. Benzene (nonsolvent) was carefully
added on top, thereby provoking, by slow diffusion into the
nitromethane solution, the crystallization of dark-red needles.
After filtration of these needles, the mother liquor was
evaporated to dryness. By measuring the rotatory power of
�
interaction of the (‡)-BNP anion with the central core of
the double helix.
Optical properties: The molar rotation of each diastereomer
has been measured in dichloromethane. The experimental
values are not exactly opposite due to the contribution of the
1
both samples and by recording their H NMR spectra, we
could determine that the mother liquor contained 33.5 mg of
2
‡
�
�
optically pure (� )-4 ´ 2(‡)-BNP (diastereomeric excess
(‡)-BNP anion (see Experimental Section for more details).
�
>
98%) and that the 66.3 mg of crystals contained 70% of
In order to isolate the pure enantiomers, (‡)BNP was
2‡
�
�
(
‡)-4 ´ 2(‡)-BNP , that is, a 40% diastereomeric excess
more details are given in the Experimental Section).
A second crystallization by diffusion of benzene vapours in
exchanged for PF6 by addition of a large excess of potassium
(
hexafluorophosphate. Now, the molar rotations obtained for
each enantiomer are perfectly equal and opposit in sign. The
circular dichroism (CD) spectra of each enantiomer are
presented in Figure 6; they are mirror images over the whole
region of the spectrum. In the visible, De reaches an extremum
a nitromethane solution of these crystals yielded 44.1 mg of
2
‡
optically pure dextrorotatory diastereomer (‡)-4 ´ 2(‡)-
�
BNP .
1
� 1
� 1
The H NMR spectra (selection of the most interesting
(‡ or� 20.7 mol Lcm ) that corresponds to the absorption
maximum of the metal-to-ligand charge-transfer (MLCT)
transition at 510 nm.
aromatic signals) of each isolated diastereomer and of their
initial mixture are shown in Figure 5. Chemical shifts of the
most representative protons are given in Table 1.
The difference in chemical shift from one diastereomer to
the other may give some indication as to the location of the
Figure 6. Circular dichroism spectra of both enantiomers of the dicopper(i)
2
‡
�
2‡
�
trefoil knot (� )-4 ´ 2PF
6
(dotted line) and (‡)-4 ´ 2PF
6
(plain line) in
CH Cl ; these are perfect mirror images.
2
2
To finally accede to metal-free, purely topologically chiral
molecules, both enantiomers were demetallated separately by
refluxing them in acetonitrile in the presence of an excess of
potassium cyanide leading to the free knots (‡)-5 and (� )-5.
Both were pale-yellow glassy compounds and their molar
rotation was determined. A value of ‡ or � 20000 was found,
which is high and comparable with those reported for some
helicenes.[
35±37]
As expected, owing to the very different
hypothetical electronic spectra of both species, this value
strongly contrasts with the very low theoretical value calcu-
lated by Frisch and Wasserman for a knot made of 66 CH2
Figure 5. 1H NMR at 400 MHz in CD
Cl (aromatic region, selected
2 2
2‡
�
peaks) of a) the racemate, b) diastereomer (‡)-4 ´ 2(‡)-BNP and
c) diastereomer (� )-4 ´ 2(‡)-BNP�.
2‡
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1435

J.-P. Sauvage et al.
FULL PAPER
units.[38] The high rotatory power found in our case is probably
related to the large dissymmetry in the organic skeleton of
2
‡
�
knots (‡)- or (� )-4 ´ 2PF6 (flexible polyoxyethylenic frag-
ments alternating with rigid aromatic subunits).
Moreover, the chromophore also contributes greatly. From
[
30]
Drudeꢀs equation: a ˆ K/(l � l ), in which a is the rotatory
o
power measured at wavelength l, l the wavelength of the
o
closest absorption maximum and K a constant characteristic
of a molecule, one can see that the closer the wavelength used
for the measurment of a is to an absorption maximum, the
higher the rotatory power. In our case, l corresponds to the D
ray of sodium (589 nm), so it is much closer to the absorption
maximum of the n ± p* transition of the phenanthroline
groups (l ꢀ 310 nm) than to that of the s ± s* transition of the
o
methylenic groups (l < 200 nm) considered by Frisch and
o
Wasserman. Therefore a smaller rotatory power is expected in
the (CH2)66 case.
Remetallation of the free knotted ligand could be achieved
2‡
�
either with copper(i) or with silver(i). The 4 ´ 2PF6 complex
regenerated with copper(i) displayed, as expected, an identical
2
‡
�
rotatory power compared with that of the original 4 ´ 2PF ,
6
whereas a really different optical rotatory power is found for
the knot 62 ´ 2BF4 remetallated with silver(i) (see Exper-
imental Section for more details). This is in agreement with
the Drude equation,[ since the silver(i) knot does not absorb
in the visible region. Their CD spectra are also strongly
‡
�
30]
different from those observed for the copper(i) complexes
�
(
Figure 7). The BF4 counterion being optically inactive, they
are perfect mirror images over the entire domain. De reaches
�
1
� 1
an extremum, ‡ or � 750 mol Lcm , which corresponds to a
p ± p* transition at 336 nm.
Figure 8. Crystal structure of the dextrorotatory dicopper(i) trefoil knot
2
‡
�
(
‡)-4 ´ 2PF
6
. ORTEP representation showing the numbering scheme
adopted for copper and nitrogen atoms (for the sake of clarity, please note
the numbering of the nitrogen atoms is different from the original one
reported to Cambridge Crystallographic Data Centre). The solvent
6
molecules, PF anions and hydrogen atoms have been omitted and the
nitrogen atoms are shown in black.
passing through the central oxygens of the two polyoxy-
ethylene chains. Selected bond distances and angles are given
in Table 2.
The tight molecular structure of 42 is characterized by a
‡
very short Cu�Cu distance (4.76 Š), whereas the coordination
Figure 7. Circular dichroism spectra of both enantiomers of the disilver(i)
2
‡
�
2‡
�
trefoil knot (� )-6 ´ 2BF
CH Cl
4
(dotted line) and (‡)-6 ´ 2BF
4
(plain line) in
Table 2. Bond distances and angles of the two pseudo-tetrahedral copper
2
2
.
2
‡
�
centers in the complex (‡)-4 ´ 2PF
Cu1 environment
6
.
Cu2 environment
Radiocrystallographic study and absolute configuration:
Crystals suitable for X-ray analysis were obtained by dis-
solution of 60 mg of the dextrorotatory dicopper(i) knot (‡)-
Bond distances [Š]
Cu1�N1
2.057
2.066
2.057
2.066
Cu2�N3
2.067
2.063
2.067
2.064
Cu1�N2
Cu2�N4
2‡
�
�
�
4
´ 2PF6 in 2-nitropropane and liquid diffusion of benzene.
Cu1 N5
Cu2 N7
Cu1�N6
Cu2�N8
The absolute configuration of the dextrorotatory resolved
knot has been determined. The X-ray crystallographically
determined molecular structure is presented Figure 8.[
The molecule has effective D2 symmetry, with three
mutually perpendicular pseudo-twofold axes, one joining the
two copper cations, one passing through the middle of the two
bridges, and the third one being perpendicular to the others,
Angles [8]
N1-Cu1-N2
N1-Cu1-N5
N1-Cu1-N6
N2-Cu1-N5
N2-Cu1-N6
N5-Cu1-N6
82.14
138.05
112.14
112.14
141.16
82.14
N3-Cu2-N4
N3-Cu2-N7
N3-Cu2-N8
N4-Cu2-N7
N4-Cu2-N8
N7-Cu2-N8
80.94
140.16
113.14
113.14
139.86
80.94
39]
1
436
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Chem. Eur. J. 1999, 5, No. 5

Trefoil Knots
1432±1439
polyhedra around each metal appear as strongly distorded
tetrahedra, the two centers having very similar coordination
angles as shown in Table 2. The chelate bite of the phenan-
throline ligand imposes two N-Cu-N angle values of 80 to 828,
but the other N-Cu-N angles vary from 112 to 1418. Each
copper atom is bound to two phenanthrolines through four
nitrogen atoms. The Cu�N distances range from 2.05 to
reference. Potentiostat EG&G Princeton Applied Research model 273A.
(
nBu)
Preparation of bisphenanthroline 1: A solution of tert-butyllithium (12 mL,
6 mmol, 1.34m) was added dropwise and under argon to a degassed
solution of m-dibromobenzene (0.94 g, 4 mmol) in freshly distilled THF
50 mL) maintained at � 788C. The reaction mixture was stirred at � 788C
4 6
NPF 0.1m was used as support electrolyte.
1
(
for 1 hour; the temperature was then brought up to ‡108C and
immediately back down to � 788C for an additionnal hour. It was then
added through a cannula to a suspension of 2-(p-anisyl)-1,10-phenanthro-
line (2.3 g, 8 mmol) in anhydrous THF (150 mL). The purple solution thus
obtained was stirred for 50 hours under argon and at room temperature and
then hydrolyzed at 08C by adding water (150 mL). A red solid started to
precipitate. The THF was evaporated and the reaction mixture was taken
2.07 Š; they are close to the values found in other copper(i)
[
14, 17, 40]
complexes of related ligands.
Finally, it was possible to determine the absolute config-
2
‡
�
uration of (‡)-4 ´ 2PF . It was found that the crystals of the
6
up in CH
layer was extracted with CH
layers were rearomatized by treatment with MnO
MgSO and filtered and the filtrate was evaporated to dryness. Chroma-
tography on alumina (eluent: CHCl
2
Cl
2
/H
2
O (1:1). The organic layer was decanted and the aqueous
Cl
(3 Â 200 mL). The combined organic
(20 g, excess), dried over
dextrorotatory knot correspond to the L knot, that is, the
enantiomer containing a double helix of absolute configura-
tion M.
2
2
2
4
3
/0 ± 10% MeOH) afforded 1 in a 66%
‡
yield (1.69 g, 2.9 mmol) as a colourless solid. M.p. 2448C; MS (FAB ): m/z:
‡
2‡
6
47.2 ([M‡H] , calcd 647.2; 100%), 324.1 ([M‡2H] , calcd 324.1; 33%);
Conclusion
1
3
3
4
H NMR ([D
6
]DMSO, 200 MHz): d ˆ 9.93 (t, J ˆ 1.5 Hz, 1H; H
a
), 8.71 (d,
), 8.63 (d,
3
4
J ˆ 8.5 Hz, 2H; H
4
), 8.67 (dd, J ˆ 7.7 Hz, J ˆ 1.5 Hz, 1H; H
b
3
3
Selective crystallization allowed us to resolve a dicopper(i)
trefoil knot. To our knowledge, it is the first preparative
resolution of topological enantiomers. The absolute config-
uration has been determined by X-ray crystallography.
Topologically chiral molecules are those whose enantiomers
can not be interconverted by continuous deformation, there-
fore racemization is excluded as long as no bond in their
organic backbone is broken. The combination of this latter
topological property with the high thermodynamic stability of
copper(i) 2,9-diphenylphenanthroline complexes provides us
with potential reagents and catalysts for various enantiose-
lective processes.
J ˆ 8.5 Hz, 2H; H
3
), 8.54 (d, J ˆ 8.5 Hz, 2H; H
7
), 8.44 (d, J ˆ 8.8 Hz, 4H;
3
3
H
H
o
), 8.28 (d, J ˆ 8.5 Hz, 2H; H
8
), 8.05 (s, 4H; H5-6), 7.90 (t, J ˆ 7.7 Hz, 1H;
c
30 4 2
), 3.90 (s, 6H; OMe); C44H N O (646.74): calcd C 81.71, H 4.68, N 8.66;
found C 81.49, H 4.86, N 8.54.
Preparation of diphenol 2: Hydrochloric acid (17.6 mL, 12m) was added to
analytical grade pyridine (16 mL) under rapid mechanical stirring. The
flask was equipped for distillation and water was distilled from the mixture
until its internal temperature rose to 2108C. Once the anhydrous
pyridinium chloride solution had been cooled down to 1508C, 1 (1.14 g,
1.8 mmol) was added at once as a solid and under an argon flush. The
mixture was then refluxed (2108C) under argon for 3 hours. After
hydrolysis by hot water (60 mL), filtration onto filter paper gave 1.8 g of
a yellow solid. This solid was suspended in MeOH/H O (3:1, 140 mL) and
2
neutralized with a 0.1m NaOH solution. The resulting orange suspension
was filtered off and dried for 36 hours under high vacuum in the presence of
P
2
O
5
to yield 1.10 g of pure 2 (1.7mmol, 94% yield) as an orange solid.
1
3
H NMR ([D
2
6
]DMSO, 200 MHz): d ˆ 9.77 (s, 1H; H
a
), 8.76 (d, J ˆ 7.9 Hz,
3
3
H; H
b
), 8.71 (d, J ˆ 8.5 Hz, 2H; H
4
), 8.63 (d, J ˆ 8.5 Hz, 2H; H
3
), 8.53 (d,
Experimental Section
3
3
3
J ˆ 8.5 Hz, 2H; H
7
), 8.45 (d, J ˆ 8.5 Hz, 4H; H
o
), 8.31 (d, J ˆ 8.5 Hz, 2H;
3
3
H
H
8
), 8.03 (s, 4H; H5-6), 7.95 (t, J ˆ 7.9 Hz, 1H; H
c
), 6.93 (d, J ˆ 8.5 Hz, 4H;
General procedures: The following chemicals were obtained commercially
m
26 4 2
); C42H N O (618.69): calcd C 81.54, H 4.24, N 9.06; found C 81.05, H
and were used without further purification: Cs
Janssen), KPF (Janssen). Some materials were prepared according to
literature procedures: 2-(p-anisyl)-1,10-phenanthroline,
2 3
CO (Aldrich), KCN
‡
‡
4
6
.71, N 8.74; m.p. 2528C (decomp); MS (FAB ): m/z: 619.1 ([M‡H] , calcd
(
6
2
‡
19.2; 100%), 310 ([M‡2H] , calcd 310.1; 6%)
[23]
copper(ii) tri-
(S)-(‡)-1,1'-binaphthyl-2,2'-phos-
.[41] Dry solvents were obtained by
O and THF from Na/benzophe-
2 5
O , pyridine from potassium hydroxide). The other
‡
�
[
27]
[28]
Preparation of the dicopper(i) double helix 32 ´ 2TfO : A degassed
solution of copper(ii) triflate (621 mg, 1.72 mmol) in acetonitrile (20 mL)
was added under argon to a suspension of 2 (900 mg, 1.45 mmol) and
ascorbic acid (302 mg, 1.72 mmol) in DMF (100 mL) at room temperature.
The resulting dark-red mixture was stirred for one hour under argon. The
solvent was evaporated and the residue washed with water and dried under
flate,
hexaethyleneglycol diiodide,
phoric acid,[
distillation over suitable dessicants (Et
none, CH Cl from P
33]
4 6
and Cu(MeCN) PF
2
2
2
anhydrous solvents were of commercial analytical grade: acetonitrile,
dimethylformamide, methanol, absolute ethanol, toluene, nitromethane.
Thin-layer chromatography (TLC) was performed on aluminium sheets
coated with silica gel 60 F254 (Merck 5554), or coated with neutral alumina
vacuum. Pure 3 was obtained in a quantitative yield (1.22 g, 0.72 mmol) as a
1
dark-red solid. H NMR ([D
6
]DMSO, 200 MHz): d ˆ 9.55 (brs, 2H; H
a
),
3
3
3
8
8
7
.60 (d, J ˆ 8.5 Hz, 4H; H
7
), 8.04 (AB, J ˆ 8.9 Hz, 8H; H5-6), 7.93 (d, J ˆ
6
0 F254 (Merck 5550). After elution, the plates were either scrutinized
under a UV lamp or exposed to I . Column chromatography was carried
out on silica gel 60 (Merck 9385, 230 ± 400 mesh) or neutral alumina 90
Merck 1076, 0.060 ± 0.200 mm). UV/Vis spectra were recorded on a
3
3
.4 Hz, 4H; H
4
), 7.82 (d, J ˆ 8.5 Hz, 4H; H
8
), 7.16 (t, J ˆ 8.9 Hz, 2H; H
c
),
2
.10 (d, 3J ˆ 8.7 Hz, 8H; H
), 7.04 (d, 3J ˆ 8.9 Hz, 4H; H
), 6.57 (d, 3J ˆ
o
b
3
8
.4 Hz, 4H; H
3
), 5.75 (d, J ˆ 8.7 Hz, 8H; H
m
); m.p. 2388C (decomp); cyclic
(
II
I
o
3‡
voltammetry (CV): two reversible distinct waves for Cu �Cu with E (3
/
Kontron Instruments UVIKON 860 spectrophotometer. Fast atom bom-
bardment mass spectrometry (FABMS), were recorded in the positive-ion
mode with either a krypton primary-atom beam in conjunction with a
2
‡
4‡ 3‡
‡
3
1
1
) and (3 /3 ) ˆ ‡0.69 and ‡0.91 V vs. SCE in MeCN; MS (ES ): m/z
‡ 2‡
566.7 ([M � TfO] , calcd 1567.3; 12%), 709.2 ([M � 2TfO] , calcd 709.2;
00%); UV/Vis(CH Cl
): lmax (e) ˆ 233 (128700), 252 (118800), 326
3-nitrobenzyl alcohol matrix and a Kratos MS80RF mass spectrometer
2
2
(
76300), 427 (sh, 3900), 518 nm (3300).
coupled to a DS90 system, or a xenon primary-atom beam with the same
matrix and a ZAB-HF mass spectrometer. Electrospray mass spectrometry
Preparation of the dicopper(i) double helix 32 ´ 2BF
‡
�
or 3 ´ 2PF
2‡
�
6
: A
4
�
�
(
ES-MS) were recorded in the positive-ion mode with VG-BIOQ triple
degassed solution of copper(i)tetrakisacetonitrile BF
4
or PF
6
salt in
1
quadripole. The H NMR spectra were recorded on either Bruker
WP200SY (200 MHz) or AM400 (400 MHz) spectrometers. The melting
points were measured on a Bioblock IA 8103 apparatus or on a Büchi SMP-
acetonitrile (20 mL) was added under argon to a suspension of one
equivalent of 2 in DMF (100 mL) at room temperature. The resulting dark-
red mixture was stirred for one hour under argon. The solvent was
evaporated and the residue was washed with water and dried under
vacuum. Pure 3 was obtained in a quantitative yield as a dark-red solid. The
20 apparatus and are not corrected. Circular dichroism (CD) measure-
ments were performed in CH Cl with a Jobin Yvon CD6 spectropho-
2
2
1
tometer. Cyclic voltammetry (CV) was realized with a Pt working
electrode, a Pt control electrode and a saturated calomel electrode as
H NMR and UV/Vis spectra are analogous to the spectra obtained with
the triflate salt.
Chem. Eur. J. 1999, 5, No. 5
ꢁ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
0947-6539/99/0505-1437 $ 17.50+.50/0
1437

J.-P. Sauvage et al.
FULL PAPER
Preparation of the dicopper(i) knot 42‡ ´ 2TfO : Small fractions of a
�
3
J ˆ 8.4 Hz, 4H; H
), 7.9 ± 8.0 (m, 20H; H4-5-6-BNP), 7.2 ± 7.8 (m, 20H; H8-BNP),
7
3
), 7.04 (d, 3J ˆ 8.6 Hz, 8H; H
), 6.95 (dd, 3J ˆ
suspension of Cs CO in DMF (932 mg overall, 2.86 mmol) were added
through cannula to a solution of 3 ´ 2TfO (1.18 g, 0.70 mmol) and
hexaethyleneglycol diiodide (790 mg, 1.57 mmol) in DMF (300 mL) at
2
3
7.18 (t, J ˆ 7.8 Hz, 2H; H
c
o
2
‡
�
7.8 Hz, 4J ˆ 1.2 Hz, 4H; H
), 6.48 (d, 3J ˆ 8.4 Hz, 4H; H
), 5.67 (d, 3J ˆ
b
3
8.6 Hz, 8H; H
m
2
), 4.20 ± 3.20 (m, 48H; CH ).
6
08C under argon. The colour of the mixture progressively changed from
yellow to dark red. The reaction was followed by TLC on silica plates
eluent: CH Cl /MeOH 90:10) and showed the disappearance of the chain,
which was compensated for by a further addition of this reactant (466 mg,
.93 mmol) during the reaction. The reaction mixture was stirred at 608C
under argon for a further 24 hours. The DMF was then evaporated under
high vacuum (508C) and the dark-red residue dissolved in CH Cl /H
1:1). The organic layer was decanted, insoluble oligomers were eliminated
and the aqueous layer was extracted three times with CH Cl . The organic
layers were combined and the solvent was evaporated. The residue was
treated by a copper(ii) triflate solution (8 g, excess) in CH CN (300 mL) at
2‡
�
� 6
(
(
(
‡)-4 ´ 2(‡)-BNP : [M]
D
ˆ ‡73000 (c ˆ 4.57  10
2 2
in CH Cl ); CD
CH
2
Cl
2
): lmax (De) ˆ 265 (� 203), 299 (� 179), 333 (‡586), 508 nm
(
2
2
1
), 8.37 (d, 3J ˆ
‡20.7); H NMR (CD
2 2 a
Cl , 200 MHz): 9.68 (brs, 2H; H
8
.4 Hz, 4H; H
7
), 7.9 ± 8.0 (m, 20H; H4-5-6-BNP), 7.2 ± 7.8 (m, 20H; H8-BNP), 7.13
0
3
3
3
(
t, J ˆ 7.8 Hz, 2H; H
c
), 7.02 (d, J ˆ 8.6 Hz, 8H; H
o
), 6.92 (dd, J ˆ 7.8 Hz,
4
3
3
J ˆ 1.2 Hz, 4H; H
b
), 6.47 (d, J ˆ 8.4 Hz, 4H; H
3
), 5.67 (d, J ˆ 8.6 Hz, 8H;
2
2
2
O
H
), 4.20 ± 3.20 (m, 48H; CH
Preparation of the enantiomers (� )-4 ´ 2PF
aqueous solution of KPF
2
).
m
(
2
‡
�
2‡
�
6
6
and (‡)-4 ´ 2PF
: An
2
2
6
(100 mL, 0.5m) was added, through a cannula, to
2
‡
�
2‡
�
a
3
solution of (� )-4 ´ 2(‡)-BNP or (‡)-4 ´ 2(‡)-BNP (100 mg,
3
9 mmol) in dichloromethane (100 mL). After 2 hours of vigourous stirring
room temperature and was stirred for 24 hours. This was done in order to
have TfO as the only counter-anion (the reaction mixture also contains I
and CO
dissolved in CH
organic phase was dried over MgSO
evaporated to dryness and crude 4 ´ 2TfO was chromatographed on
silica (eluent: CH
�
�
at room temperature, the organic phase was decanted, washed three times
with water and dried over MgSO . After filtration, the filtrate was
evaporated to dryness and the crude mixture chromatographed (Al
2
�
anions). After evaporation of the solvent, the residue was
4
3
2
O
were
3
;
2 2
Cl and washed 3 times with water. After decantation, the
2
‡
�
2‡
�
eluent: CH
2
Cl
2
/0 ± 6% MeOH). (� )-4 ´ 2PF
6
or (‡)-4 ´ 2PF
6
4
and filtered. The filtrate was
1
2
‡
�
isolated in a quantitative yield (84 mg, 39 mmol). Their H NMR spectra,
showing the absence of the BNP ion, were similar to that of the copper(i)
complex of the knot with the triflate anion.
�
2
‡
�
2
Cl
2
/0 ± 12%MeOH) to yield 431 mg of pure 4 ´ 2TfO
1
(
0.20 mmol, 29% yield) as a dark-red solid. H NMR (CD
2
Cl
2
, 200 MHz):
3
3
2‡
�
� 6
d ˆ 9.72 (brs, 2H; H
a
), 8.42 (d, J ˆ 8.4 Hz, 4H; H
7
), 7.98 (AB, J ˆ 8.8 Hz,
(� )-4 ´ 2PF6 : [M] ˆ � 70000 (c ˆ 5.07  10 in CH Cl ); CD (CH Cl ):
D
2
2
2
2
3
3
8
H; H5-6), 7.96 (d, J ˆ 8.4 Hz, 4H; H
4
), 7.66 (d, J ˆ 8.4 Hz, 4H; H
8
), 7.23 (t,
l
(De) ˆ 245 (‡155), 267 (‡306), 302 (‡179), 335 (� 640), 507 nm
max
3
3
3
4
J ˆ 7.8 Hz, 2H; H
c
), 7.07 (d, J ˆ 8.6 Hz, 8H; H
o
), 6.98 (dd, J ˆ 7.8 Hz, J ˆ
(� 20.7)
3
3
1
.2 Hz, 4H; H
b
), 6.56 (d, J ˆ 8.4 Hz, 4H; H
3
), 5.70 (d, J ˆ 8.6 Hz, 8H; H
m
),
2‡
�
� 6
(
l
‡)-4 ´ 2PF
6
: [M]
D
ˆ ‡69000 (c ˆ 4.72  10 in CH
2 2 2 2
Cl ) CD (CH Cl ):
4
.20 ± 3.20 (m, 48H; CH
2
). The latter assignment was confirmed by 2D
max (De) ˆ 244 (� 154), 266 (� 306), 302 (� 180), 336 (‡640), 508 nm
‡
NMR spectroscopy (ROESY). M.p. >2808C; MS (FAB ): m/z: 2003.0
(
‡20.8).
‡
� ‡
(
1
[M � TfO] , calcd 2003.5; 14%), 1853.9 ([M � 2TfO‡e ] , calcd 1854.6;
� 2‡
Demetallation: (� )-5 and (‡)-5: Potassium cyanide (0.5 g, large excess)
3%), 927.2 ([M � 2TfO ] , calcd 927.3; 13%); UV/Vis (CH
2 2
Cl ): lmax
2
‡
�
2‡
�
6
(
(
e) ˆ 237 (118100), 253 (115000), 324 (69200), 425 (sh, 3700), 520 nm
was added to a solution of (� )-4 ´ 2PF
6
or (‡)-4 ´ 2PF
(50 mg,
2960); C110 (2155.22): calcd C 61.30, H 4.49, N 5.20; found
H96Cu
2
F
6
N
8
O
20
S
2
20 mmol) in refluxing wet acetonitrile (100 mL). The mixture was stirred at
808C for 4 hours, during which time the characteristic dark-red colour of
the copper(i) complex progressively disappeared. The solvent was evapo-
rated and the residue was dissolved in dichloromethane. The crude mixture
C 61.08, H 4.37, N 5.07. The same procedure can be applied to obtain the
dicopper(i) trefoil knot with BF
corresponding double-helix. For the complex with the BF
�
�
4
or PF
6
counter-anion starting with the
�
4
anion, the cyclic
voltammogram was measured (CV) showing two reversible distinct waves
4
was washed three times with ammonia (0.1m), dried over MgSO and
II
I
o
3‡ 2‡
4‡ 3‡
filtered off to give (� )-5 or (‡)-5 as pale-yellow solids in quantitative yield
for Cu �Cu with E (3 /3 ) and (3 /3 ) ˆ ‡0.68 and ‡0.92 V vs. SCE,
respectively, in MeCN.
(37 mg, 20 mmol).
�
6
(
� )-5: [M]
D
ˆ � 19000 (c ˆ 4.27  10 in CH
2 2
Cl )
Preparation of the diastereomers of the knot: An aqueous solution of
NaOH (3.3 mL, 0.33 mmol, 0.1m) was added to a suspension of binaph-
�
6
(‡)-5: [M] ˆ ‡20000 (c ˆ 4.88  10 in CH Cl )
D
2
2
thylphosphoric acid (115 mg, 0.33 mmol) in CH
3
CN (50 mL). The solvent
1
3
4
H NMR (CD
2
Cl
2
, 200 MHz): d ˆ 8.80 (dd, J ˆ 7.7 Hz, J ˆ 1.4 Hz, 4H;
2
‡
was evaporated and the residue dissolved in CH
2
Cl
2
(150 mL). (Æ)-4
´
3
3
H
4
b
), 8.72 (brs, 2H; H
a
), 8.37 (d, J ˆ 8.4 Hz, 4H; H
3
), 8.28 (d, J ˆ 8.4 Hz,
�
2
TfO (320 mg, 0.15 mmol) was then added; it immediately dissolved in
3
3
H; H
4
), 8.13 (d, J ˆ 8.7 Hz, 8H; H
o
), 8.09 (d, J ˆ 8.3 Hz, 4H; H
7
), 7.90 (d,
the mixture. Liquid ± liquid extraction was performed at room temperature
3
3
3
J ˆ 8.3 Hz, 4H; H
8
), 7.68 (t, J ˆ 7.7 Hz, 2H; H
c
), 7.55 (AB, J ˆ 8.8 Hz, 8H;
�
�
over 24 hours in order to replace TfO by binaphtylphosphate (BNP ). The
ion exchange was followed by TLC on alumina plates (eluent: CH Cl /5%
MeOH). The organic layer was then decanted and dried over MgSO . After
3
H
5-6), 6.98 (d, J ˆ 8.7 Hz, 8H; H
m
), 4.30 ± 3.60 (m, 48H; CH
2
).
2
2
2
‡
�
2‡
�
Remetallation with silver(i): (‡)-6 ´ 2BF
4
and (� )-6 ´ 2BF
4
: A solution
4
2‡
�
of AgBF4 (45 mg, 10 equiv) in MeOH (5 mL) was added, through a
filtration, the solvent was evaporated to give (Æ)-4 ´ 2(‡)-BNP as a red
1
cannula, to a solution of (� )-5 or (‡)-5 (37 mg, 20 mmol) in CH Cl
solid (380 mg, 0.15 mmol, quantitative yield). H NMR showed that each
2
2
I
(30 mL). The mixture was stirred at room temperature for 12 hours. The
solvent was evaporated and the residue dissolved in dichloromethane. The
signal of the Cu knot was split into two, which confirmed the presence of
two diastereomers and showed the presence of the BNP anion.
�
4
crude mixture was washed three times with water, dried over MgSO ,
2
‡
�
2‡
�
Resolution of (� )-4 ´ 2(‡)-BNP and (‡)-4 ´ 2(‡)-BNP : A saturated
solution of the diastereomers (510 mg, 0.2 mmol) in a 1:1 mixture of
dichloromethane and benzene was placed in a crystallization tube (internal
diameter 1 cm, length 20 cm). Some benzene was then added precautiously,
so that the surface of the red solution of knot was not damaged. After two
weeks diffusion, the needles obtained were filtered off and the mother
filtered and chromatographed (Al
(
2
O
3
, CH
2
Cl
2
/0 ± 2% MeOH) to give
2‡
�
2‡
�
� )-6 ´ 2BF
4
or (‡)-6 ´ 2BF
4
as colourless solids in a 95% yield.
2
‡
�
� 6
(
l
� )-6 ´ 2BF
4
: [M]
D
ˆ � 33000 (c ˆ 5.17  10 in CH
2 2 2 2
Cl ); CD (CH Cl ):
2
‡
max (De) ˆ 240 (� 194), 262 (‡359), 304 (‡180), 336 nm (� 760); (‡)-6
´
�
� 6
2
BF
4
: [M]
D
ˆ ‡34000 (c ˆ 5.34 10 in CH
2 2 2 2
Cl ); CD (CH Cl ): lmax (De):
1
240 (‡189), 263 (� 349), 304 (� 176), 335 nm (‡742); UV/Vis (CH
2
Cl
Cl
7
), 8.13 (d,
2
):
liquor was evaporated. From their H NMR spectra and their rotatory
1
l
max (e): 241 (110600), 269 (79600), 311 nm (65400); H NMR (CD
2
2
,
powers, it was established that the crystals (207 mg) were diastereomeri-
cally pure and that the mother liquor (303 mg) had been strongly enriched
into the other diastereomer (68%.diastereomeric excess). This sample was
crystallized a second time, with the use of a crystallization tube of 0.7 cm
internal diameter and of 20 cm length. After diffusion of benzene, the
needles obtained were filtered off and the mother liquor was evaporated.
2
00 MHz): d ˆ 9.88 (brs, 2H; H
a
), 8.47 (d, 3J ˆ 8.4 Hz, 4H; H
3
3
3
J ˆ 8.8 Hz, 4H; H
4
), 7.95 (AB, J ˆ 9.0 Hz, 8H; H5-6), 7.74 (d, J ˆ 8.4 Hz,
3
3
4
H; H
8
), 7.37 (t, J ˆ 7.9 Hz, 2H; H
c
), 7.07 (d, J ˆ 8.6 Hz, 8H; H
o
), 7.10 (d,
3
3
3
J ˆ 7.9 Hz, 4H; H
b
), 6.53 (d, J ˆ 8.8 Hz, 4H; H
3
), 5.85 (d, J ˆ 8.6 Hz, 8H;
m 2
H ), 4.20 ± 3.20 (m, 48H; CH ).
1
From their H NMR spectra and their rotatory powers, it was established
X-ray crystal structure analysis: Crystallographic data (excluding structure
factors) for the structures reported in this paper have been deposited with
the Cambridge Crystallographic Data Centre as supplementary publication
no. CCDC-105608. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax:
(‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
that the mother liquor (57 mg) was diastereomerically pure and that the
crystals (246 mg) were not (60% diastereomeric excess).
2
‡
�
� 6
(
(
(
� )-4 ´ 2(‡)-BNP : [M]
D
ˆ � 66000 (c ˆ 5.25  10
2 2
in CH Cl ); CD
CH
2
Cl
2
): lmax (De) ˆ 264 (‡337), 298 (‡176), 333 (� 631), 510 nm
1
� 21.3); H NMR (CD
2
Cl
2
, 200 MHz): d ˆ 9.70 (brs, 2H; H
a
), 8.39 (d,
1
438
ꢁ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
0947-6539/99/0505-1438 $ 17.50+.50/0
Chem. Eur. J. 1999, 5, No. 5

Trefoil Knots
1432±1439
[
[
[
[
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1
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96
8
14
2
6
6
6
192 ± 194; Angew. Chem. Int. Ed. 1989, 28, 189 ± 192.
rhombic, space group P2 2 2, a ˆ 29.098 (1), b ˆ 14.6590 (5), c ˆ
3
� 3
1
1
14] C. O. Dietrich-Buchecker, J. Guilhem, C. Pascard, J. P. Sauvage,
11.7333 (5) Š, Vˆ 5004.8 (6) Š , Z ˆ 2,
1
ˆ 1.48 gcm
,
calcd
�
1
Angew. Chem. 1990, 102, 1202 ± 1204; Angew. Chem. Int. Ed. 1990, 29,
m(MoKa) ˆ 0.546 mm . Data were collected on a Nonius Kappa
1154 ± 1156.
CCD diffractometer with Mo graphite monochromated radiation
Ka
[
15] N. C. Seeman, Acc. Chem. Res. 1997, 30, 357 ± 363.
(l ˆ 0.71073 Š) at 173 K. A dark-red crystal of dimensions 0.23 Â
3
[
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Chem. Soc. Chem. Commun. 1994, 2231 ± 2232.
0.20 Â 0.15 mm was used and a total of 31697 data were collected,
1.58 < q < 26.388. 3299 reflections having I > 3s(I) were used for
structure determination and refinement. The structure was solved
using direct methods and refined against jF j . Hydrogen atoms were
introduced as fixed contributors. No absorption corrections were
applied. For all computations the Nonius OpenMoleN package[ was
used. The absolute structure was determined by refining Flackꢀs x
parameter: x ˆ � 0.02(3). Final results : R(F) ˆ 0.073, Rw(F) ˆ 0.086,
[
[
[
[
[
[
[
18] G. Rapenne, C. O. Dietrich-Buchecker, J. P. Sauvage, J. Am. Chem.
42]
Soc. 1996, 118 , 10932 ± 10933.
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�
3
20] D. J. Williams, H. M. Colquhoun, C. A. OꢀMahoney, J. Chem. Soc.
Chem. Commun. 1994, 1643 ± 1644.
GOF ˆ 1.656, maximum residual electronic density ˆ 0.61 eŠ
.
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Structure Analysis, Nonius, Delft (The Netherlands), 1990
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oli, V. Balzani, L. De Cola, J. Am. Chem. Soc. 1993, 115, 11237 ±
11244.
Received: October 28, 1998 [F1418]
Chem. Eur. J. 1999, 5, No. 5
ꢁ WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999
0947-6539/99/0505-1439 $ 17.50+.50/0
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