Diastereoisomerically pure fulleropyrrolidines as chiral platforms for the design of optically active liquid crystals

Article abstract of DOI:10.1021/ja910128e

Incorporation of [60]fullerene (C₆₀) within self-organizing systems is conceptually challenging but allows us to obtain materials which combine the characteristics (anisotropy, organization) of condensed mesophases with the properties of C

Full text of DOI:10.1021/ja910128e

Published on Web 02/17/2010
Diastereoisomerically Pure Fulleropyrrolidines as Chiral
Platforms for the Design of Optically Active Liquid Crystals
Ste´phane Campidelli,†,⊥ Philippe Bourgun,† Boris Guintchin,† Julien Furrer,‡
Helen Stoeckli-Evans,§ Isabel M. Saez,| John W. Goodby,*,| and Robert Deschenaux*,†
Institut de Chimie, UniVersite´ de Neuchaˆtel, AVenue de BelleVaux 51, Case Postale 158,
2009 Neuchaˆtel, Switzerland, SerVice Analytique Facultaire, Institut de Chimie, UniVersite´ de
Neuchaˆtel, AVenue de BelleVaux 51, 2009 Neuchaˆtel, Switzerland, Institut de Physique,
UniVersite´ de Neuchaˆtel, Rue Emile-Argand 11, 2009 Neuchaˆtel, Switzerland, and Department of
Chemistry, The UniVersity of York, Heslington, York YO10 5DD, U.K.
Received December 2, 2009; E-mail: jwg500@york.ac.uk; robert.deschenaux@unine.ch
Abstract: Incorporation of [60]fullerene (C60) within self-organizing systems is conceptually challenging
but allows us to obtain materials which combine the characteristics (anisotropy, organization) of condensed
mesophases with the properties of C60 (photo- and electrochemical activity). Here, we report on the synthesis,
characterization, and liquid-crystalline properties of four optically active fullerodendrimers, which are chiral
at the point of conjunction between the fullerene scaffold and the mesogenic moieties. Thus, the novelty
of this study is to take advantage of the asymmetric carbon atom created during the 1,3-dipolar cycloaddi-
tion reaction on C60 in order to induce mesoscopic chirality in the materials. Four diastereoisomeric
fulleropyrrolidines ((R,S)-1, (R,R)-1, (S,R)-1, and (S,S)-1) were synthesized and associated with a second-
generation nematic (N) dendron to give fullerodendrimers ((R,S)-2, (R,R)-2, (S,R)-2, and (S,S)-2) which
display chiral nematic (N*) phases. The absolute configurations of the stereogenic centers were determined
by X-ray crystallography, 1D and 2D NMR experiments, and circular dichroism (CD) spectroscopy. The
liquid-crystalline properties of the fullerodendrimers were studied by polarized optical microscopy (POM)
and differential scanning calorimetry (DSC). The fulleropyrrolidine derivatives 2 exhibit supramolecular
helicoidal organizations with a right-handed helix for the (R,S)-2 and (R,R)-2 diastereoisomers and a left-
handed helix for the (S,R)-2 and (S,S)-2 diastereoisomers. This result suggests that the self-organization
of such supermolecular materials can be controlled at the molecular level by the introduction of only one
chiral center.
Introduction
in such mesophases opens opportunities for the design of liquid
crystals displaying novel electro- and photoactive properties
within a designed/desirable chiral supramolecular environment.
With the successful development of the nanotechnologies via
a bottom-up approach, the design of self-organizing nanostruc-
tures obtained by the organization of multifunctional molecular
units has attracted much attention in the scientific community.1,2
In this context, liquid crystals are important systems, as their
self-organization can be controlled in order to generate complex
supramolecular architectures, the properties of which can be
tuned by structural engineering at the molecular level.3 Chiral
nematic (N*) and chiral smectic C (SmC*) phases and their
attendant physical properties such as thermochromism, ferro-
electricity, and pyroelectricity have found numerous practical
applications in, for example, displays, light modulators, and
thermal imaging devices. The presence of [60]fullerene (C60)
The functionalization of C60 with mesomorphic malonates
(via the Bingel reaction4) or with mesomorphic aldehydes
(via the 1,3-dipolar cycloaddition reaction5,6) has led to
liquid-crystalline methanofullerenes or fulleropyrrolidines,
respectively, which display smectic,7-9 columnar,10-12 ne-
(4) Bingel, C. Chem. Ber. 1993, 126, 1957.
(5) Confalone, P. N.; Huie, E. M. J. Org. Chem. 1983, 48, 2994.
(6) (a) Prato, M.; Maggini, M. Acc. Chem. Res. 1998, 31, 519. (b)
Tagmatarchis, N.; Prato, M. Synlett 2003, 6, 768.
(7) (a) Dardel, B.; Guillon, D.; Heinrich, B.; Deschenaux, R. J. Mater.
Chem. 2001, 11, 2814. (b) Campidelli, S.; Va´zquez, E.; Milic, D.;
Prato, M.; Barbera´, J.; Guldi, D. M.; Marcaccio, M.; Paolucci, D.;
Paolucci, F.; Deschenaux, R. J. Mater. Chem. 2004, 14, 1266. (c)
Allard, E.; Oswald, F.; Donnio, B.; Guillon, D.; Delgado, J. L.; Langa,
F.; Deschenaux, R. Org. Lett. 2005, 7, 383. (d) Campidelli, S.; Lenoble,
J.; Barbera´, J.; Paolucci, F.; Marcaccio, M.; Paolucci, D.; Deschenaux,
R. Macromolecules 2005, 38, 7915. (e) Campidelli, S.; Pe´rez, L.;
Rodr´ıgez-Lo´pez, J.; Barbera´, J.; Langa, F.; Deschenaux, R. Tetrahe-
dron 2006, 62, 2115.
† Institut de Chimie, Universite´ de Neuchaˆtel.
‡ Service Analytique Facultaire, Universite´ de Neuchaˆtel.
§ Institut de Physique, Universite´ de Neuchaˆtel.
| University of York.
⊥ Current address: CEA, IRAMIS, Laboratoire d’Electronique Mole´cu-
laire, 91191 Gif sur Yvette, France.
(1) Huck, W. T. S. Nanoscale Assembly; Springer: New York, 2005.
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9
3574 J. AM. CHEM. SOC. 2010, 132, 3574–3581
10.1021/ja910128e  2010 American Chemical Society

Diastereoisomerically Pure Fulleropyrrolidines
A R T I C L E S
Scheme 1a
a Legend: (a) Et3N, THF, 0 °C and then room temperature, overnight, 65% for (R)-3, 63% for (S)-3; (b) C60, formaldehyde, toluene, reflux, 20 h, 26% for
(R,S)-1, 15% for (R,R)-1, 25% for (S,R)-1, 22% for (S,S)-1.
matic,7a,13 and chiral nematic14 phases. Our concept, the use
of dendrimers and dendrons7,11 (prepared by convergent
syntheses15) as mesomorphic promoters to functionalize C60,
is a successful approach because the nature and size of the
dendrons can be modified to tailor the liquid-crystalline proper-
ties of the fullerene derivatives. It is worth noting that
theoretical16 and experimental studies7,11 are in good agreement
to explain the supramolecular organizations of fullerene-based
molecular units within lamellar or columnar phases. The design
of the above-mentioned chiral fullerodendrimers (N* phase)
requires the synthesis of optically active dendrons, the purifica-
tion of which can be demanding. Therefore, only second-
generation dendrons could be prepared in reasonable yields and
quantities.17
During the formation of fulleropyrrolidines by 1,3-dipolar
cycloaddition, a stereogenic center in the pyrrolidine ring is
generated when functionalized aldehydes (RCHO with R * H)
and amino acids are used.6 For example, Prato et al. applied
this reaction to the preparation of chiral fulleroprolines,18 the
absolute configurations of which were determined on the basis
of experimental and calculated circular dichroism (CD) spectra.
Other examples of chiral fulleropyrrolidines obtained by dias-
tereo- and enantioselective syntheses have been reported.19
The aforementioned liquid-crystalline fulleropyrrolidines were
obtained as racemic mixtures, since the reactions were carried
out under standard conditions6 without chiral reagents. We
postulated that if optically active fulleropyrrolidines could be
prepared, they would represent an interesting chiral platform
for the design of optically active liquid crystals derived from
nonchiral mesomorphic promoters. In this case, the fullero-
pyrrolidine and dendritic addend would play complementary
roles: i.e., the dendron would generate mesophases (e.g., N,
SmC) and the fulleropyrrolidine would make the mesophases
chiral (i.e., N f N*, SmC f SmC*).
We describe herein the synthesis and liquid-crystalline and
optical properties of four diastereoisomeric fullerodendrimers.
A second-generation dendron which carries laterally branched
mesogens was selected in order to observe the N* phase for
the chiral fullerodendrimers. The stereochemistry for one
diastereoisomer was determined by means of X-ray diffraction.
From this result, the absolute configuration of the chiral centers
of all of the diastereoisomers was established.
Results and Discussion
Design. This study is based on the association of diastereo-
merically pure fulleropyrrolidines ((R,S)-1, (R,R)-1, (S,R)-1 and
(S,S)-1) (Scheme 1), used as sources of chirality, with a second-
generation dendron (9) (Scheme 2) which carries laterally
branched mesogens. Thus, nematic behavior was expected from
this dendritic system. Therefore, the optically active fullero-
dendrimers (Scheme 3) were expected to display the chiral
nematic, N*, phase.
Synthesis. The four diastereoisomeric fulleropyrrolidines
(R,S)-1, (R,R)-1, (S,R)-1, and (S,S)-1 were synthesized by the
addition of the tert-butyl ester protected amino acid (R)-3 or
(S)-3 with formaldehyde to C60 under standard 1,3-dipolar
addition conditions6 (Scheme 1). Compounds (R)-3 and (S)-3
were prepared by reacting commercially available (R)-(+)- or
(S)-(-)-R-methylbenzylamine with tert-butyl bromoacetate. The
mixtures of diastereoisomers, (R,S)-1/(R,R)-1 and (S,R)-1/(S,S)-
1, were separated by column chromatography. In their respective
syntheses, the (R,S)-1 and (S,R)-1 compounds eluted first. For
(10) Bushby, R. J.; Hamley, I. W.; Liu, Q.; Lozman, O. R.; Lydon, J. E.
J. Mater. Chem. 2005, 15, 4429.
(11) (a) Lenoble, J.; Maringa, N.; Campidelli, S.; Donnio, B.; Guillon, D.;
Deschenaux, R. Org. Lett. 2006, 8, 1851. (b) Lenoble, J.; Campidelli,
S.; Maringa, N.; Donnio, B.; Guillon, D.; Yevlampieva, N.; Des-
chenaux, R. J. Am. Chem. Soc. 2007, 129, 9941.
(12) De la Escosura, A.; Mart´ınez-D´ıaz, M. V.; Barbera´, J.; Torres, T. J.
Org. Chem. 2008, 73, 1475.
(13) (a) Tirelli, N.; Cardullo, F.; Habicher, T.; Suter, U. W.; Diederich, F.
J. Chem. Soc., Perkin Trans. 2 2000, 193. (b) Mamlouk, H.; Heinrich,
B.; Bourgogne, C.; Donnio, B.; Guillon, D.; Felder-Flesch, D. J. Mater.
Chem. 2007, 17, 2199.
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A R T I C L E S
Campidelli et al.
Scheme 2a
a Legend: (a) N,N′-dicyclohexylcarbodiimide (DCC), 4-(dimethylamino)pyridinium toluene-p-sulfonate (DPTS), 4-pyrrolidinopyridine (4-ppy), CH2Cl2,
0 °C and then room temperature, 20 h, 97%; (b) Zn(BF4)2, THF/H2O, 50 °C, 72 h, 88%; (c) 5, DCC, DPTS, 4-ppy, CH2Cl2, 0 °C and then room temperature,
24 h, 82%; (d) Zn(BF4)2, THF/H2O, 60 °C, 24 h, 85%.
the determination of the absolute configuration of the newly
formed stereogenic centers (in the pyrrolidine ring), see below.
Finally, the synthesis of diastereoisomeric fullerodendrimers
is described in Scheme 3. Deprotection of the tert-butyl ester
function of (R,S)-1, (R,R)-1, (S,R)-1, and (S,S)-1 with trifluo-
racetic acid led to the corresponding carboxylic acid derivatives,
which were condensed with the phenol-based dendron 9 in the
presence of DCC and DPTS to give (R,S)-2, (R,R)-2, (S,R)-2,
and (S,S)-2.
The synthesis of the second-generation dendron is shown
in Scheme 2. Esterification of 4 (see Scheme S1 in the
Supporting Information for the synthesis) with O-protected
5-hydroxyisophthalic acid 520 in the presence of N,N′-
dicyclohexylcarbodiimide (DCC), 4-(dimethylamino)pyri-
dinium toluene-p-sulfonate (DPTS), and 4-pyrrolidinopyridine
(4-ppy) gave the first-generation dendron 6, which was
deprotected with Zn(BF4)2 to give 7. Esterification of 5 with
7 led to the second-generation dendron 8, the deprotection
of which with Zn(BF4)2 gave the phenol derivative 9.
The structures and purities of the new compounds were
1
confirmed by H NMR spectroscopy and elemental analysis.
The fullerene derivatives were also characterized by UV-vis
and CD spectral analyses. The UV-vis spectra are in agreement
with the fulleropyrrolidine structure6 (illustrative examples are
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Diastereoisomerically Pure Fulleropyrrolidines
A R T I C L E S
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J. AM. CHEM. SOC. VOL. 132, NO. 10, 2010 3577

A R T I C L E S
Campidelli et al.
Figure 1. View of the molecular structure of the compound (R,S)-1 with
thermal ellipsoids drawn at the 50% probability level (the solvent molecule
of toluene has been omitted for clarity).
shown in Figure S1 in the Supporting Information). Size
exclusion chromatography (SEC) confirmed that monodisperse
macromolecules were obtained (Table S1, Supporting Informa-
tion).
Structure Determination. The slow diffusion of benzonitrile
in a toluene solution containing the compound that eluted first
on chromatography for the synthesis of (R,S)-1/(R,R)-1, i.e. from
(R)-(+)-R-methylbenzylamine, gave dark red rodlike crystals
which were analyzed by X-ray diffraction (Figure 1). The
(R,S)-1 derivative crystallized in the chiral orthorhombic space
group P212121 as a toluene solvate (see the Supporting Informa-
tion).
Chiroptical Properties. The CD spectra of (R,S)-1, (R,R)-1,
(R,S)-2, and (R,R)-2 are shown in Figure 2 (for (S,R)-1, (S,S)-
1, (S,R)-2, and (S,S)-2, see Figure S2 in the Supporting
Information). They all display a strong Cotton effect at 430 nm,
in agreement with the UV-vis spectra.18,21 Prato et al.
demonstrated that it is possible to correlate the sign of this CD
peak with the absolute configuration of the asymmetric carbon
atom of the pyrrolidine ring: i.e., a negative Cotton effect at
430 nm corresponds to the S configuration, whereas a positive
Cotton effect corresponds to the R configuration.18 This behavior
was confirmed with (R,S)-1, for which the absolute configuration
of the asymmetric carbon atom was determined by X-ray
diffraction (see above). Indeed, on the basis of studies by Prato’s
group,18 this compound should display a negative Cotton effect
at 430 nm, which is actually the case. From the results obtained
for (R,S)-1, the stereochemistry of the other diastereoisomers
can be unambiguously established.
Figure 2. CD spectra of (top) (R,R)-1 (dotted line) and (R,S)-1 (solid line)
and of (bottom) (R,R)-2 (dotted line) and (R,S)-2 (solid line) in CH2Cl2.
asymmetric center on the pyrrolidine resonates as a singlet at δ
5.62 and 4.87 ppm for (S,R)-1 and (S,S)-1, respectively. As
expected, similar results were obtained for the other two
diastereoisomers. The correct attribution of the diastereotopic
protons H2 and H2′ was achieved using 1D ROESY experiments
and on the basis of the structure obtained for (R,S)-1 (Figure
1). Interestingly, the change of the configuration of the asym-
metric carbon of the pyrrolidine ring from R to S has significant
and specific effects on the 1H chemical shifts, but only marginal
effects on the 13C chemical shifts. Not surprisingly, the
configuration of this carbon has nearly no effect on the aromatic
protons but induces a slight upfield shift (∼0.1-0.3 ppm) for
H2, H2′, and H3 (Figure 3). The effect on the H1 proton is more
subtle to understand, as it resonates at 5.62 ppm for (S,R)-1,
while it is downfield by 0.8 ppm in the case of (S,S)-1. To
explain this difference, 1D ROESY experiments with selective
excitation of the H1 resonance were performed. For (S,S)-1, an
intense ROE enhancement between H1 and Hortho and a weak
ROE enhancement between H1 and Hmeta is observed, while for
the (S,R)-1 isomer only a weak ROE enhancement between H1
and Hortho is observed (Figure 4). This result indicates the spatial
proximity between H1 and the aromatic ring in (S,S)-1: it can
be deduced from the simultaneous observation of ROE enhance-
ments between H1 and Hortho and between H1 and Hmeta that H1
lies in the shielding zone of the aromatic ring. This explains
why H1 in (S,S)-1 is downfield by 0.8 ppm relative to H1 in
(S,R)-1.
NMR Spectroscopy. The full and unequivocal attribution of
all 1H and 13C resonances of the four diastereoisomers 1
dissolved in CDCl3 was performed using standard 1D and 2D
NMR experiments. The diastereoisomeric signatures can be
1
easily confirmed. Indeed, comparison of the H NMR spectra
of (S,S)-1 (part A of Figure 3) and (S,R)-1 (part B of Figure 3)
shows different chemical shifts for the protons of the pyrrolidine
ring. The doublets (one for each H of the CH2 group of the
pyrrolidine) resonate at δ 5.10 and 4.39 ppm for (S,R)-1 and at
δ 5.33 and 4.72 ppm for (S,S)-1. The proton H1 of the
(14) (a) Campidelli, S.; Eng, C.; Saez, I. M.; Goodby, J. W.; Deschenaux,
R. Chem. Commun. 2003, 1520. (b) Campidelli, S.; Brandmu¨ller, T.;
Hirsch, A.; Saez, I. M.; Goodby, J. W.; Deschenaux, R. Chem.
Commun. 2006, 4282.
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Diastereoisomerically Pure Fulleropyrrolidines
A R T I C L E S
Figure 3. Expansions of the 1H NMR spectra of (S,S)-1 (A) and (S,R)-1 (B) showing the protons of the pyrrolidine ring and the attribution. The molecular
structures of the respective compounds are shown next to the spectra.
1
Figure 4. 1H NMR spectra of (S,R)-1 (C) and (S,S)-1 (D) and the corresponding 1D H selective ROESY spectra of (S,R)-1 (A) and (S,S)-1 (B) after H-1
was selectively excited. The protons H-1 are phased negatively such as ROE enhancements show positive signals.
Liquid-Crystalline Properties. The mesomorphic and thermal
Table 1. Phase-Transition Temperaturesa and Enthalpy Changes
properties of the liquid-crystalline materials were investigated
by polarized optical microscopy (POM) and differential scanning
calorimetry (DSC). The phase-transition temperatures and
enthalpy changes are reported in Table 1. The nonchiral
intermediates 4 and 6-9 exhibit the N phase, which was
identified by POM from the formation of schlieren and
homeotropic textures. The phenol derivatives give higher
clearing points than the corresponding O-protected precursors
(compare 6 with 7 and 8 with 9). This behavior is, most likely,
due to stronger intermolecular interactions because of the HO
groups that induce hydrogen bonding. Due to the limited thermal
stability of the phenol derivatives, their transition temperatures
are only indicative. As for the optically active fullerodendrimers
(R,S)-2, (R,R)-2, (S,R)-2, and (S,S)-2, they all display the N*
phase. The clearing points of the fullerodendrimers are lower
than those of the phenol precursors. This result is an indication
that C60 destabilizes the mesophases, possibly as a consequence
of its large molecular volume (about 700 Å3).
of the Mesogenic Unit, Dendrons, and Fullerodendrimers
compd
Tg (°C)
transition
temp (°C)
∆H (kJ mol-1
)
4
6
7
8
1
12
32
47
51
69
68
71
74
N f I
N f I
N f I
N f I
N f I
N* f I
N* f I
N* f I
N* f I
166
116b
185
135
164
109
108
106
106
0.76
0.84
1.84
2.16
2.21
0.94
0.86
0.23
0.36
9
(R,S)-2
(R,R)-2
(S,R)-2
(S,S)-2
a Definitions: Tg, glass transition temperature; N, nematic phase; N*,
chiral nematic phase; I ) isotropic liquid. Temperatures are given as the
onset of the peaks obtained during the second heating run; the Tg values
were determined during the first cooling run. b Determined as the
maximum of the peak obtained during the second heating run.
The samples were studied by POM on the pristine solids, on
untreated glass slides, and between a coverslip and slide, heating
9
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A R T I C L E S
Campidelli et al.
Figure 5. Grandjean-plane texture displayed by (R,S)-2 (left) and pseudofocal conic texture displayed by (R,R)-2 (right).
to the isotropic point and cooled at 0.2 °C min-1 to 108 °C, to
give a grainy, birefringent orange-colored melt without specific
characteristic textures or defects. However, upon annealing at
this temperature, most of the areas of the preparation evolved
to display the Grandjean plane texture with characteristic oily
streak defects, which allows for the unequivocal assignment of
the mesophase as chiral nematic (Figure 5). In some areas of
the preparations, the planar anchoring of the Grandjean texture
gradually became populated by the fingerprint defects arising
from homeotropic boundary conditions, which corresponds to
the helical pitch. However, it is interesting to note the contrast
in behavior between the four isomers: for example, (R,S)-2 and
(S,R)-2 develop characteristic natural textures on cooling from
the isotropic liquid with more ease than (R,R)-2 and (S,S)-2,
which required longer periods of annealing and/or alignment
layers to develop.
Figure 6. Fingerprint texture displayed by (R,S)-2 at room temperature.
The cholesteric pitch was determined from the fingerprint
texture (Figure 6), since the distance between adjacent,
equidistant dark (or bright) lines corresponds to half of the
pitch length.22 The F values (Table 2) indicate that these
materials have relatively long pitches (3-4 µm). The absolute
values are comparable with the results obtained for other low
Table 2. Structural Characterization of the N* Phase Displayed by
the Chiral Fullerodendrimers
pitch F (µm) at 25 °C
handedness of the cholesteric helix
(R,S)-2
(R,R)-2
(S,R)-2
(S,S)-2
2.8 ( 0.02
3.0 ( 0.1
4.0 ( 0.2
4.1 ( 0.1
right
right
left
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left
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Furthermore, we observe that the configuration of the
phenylamine carbon [PhCH(CH3)] seems to dominate the chiral
response in the mesophase; the isomers with an R configuration
at the phenylamine carbon produce a right-handed helix, whereas
the S configuration at the phenylamine carbon induces a left-
handed helix. However, these studies do not allow us to
distinguish at the present what is the contribution of the chiral
carbon at the pyrrolidine ring to the mesophase chirality.
Interestingly, the observation of the N* phase for (R,S)-2, (R,R)-
2, (S,R)-2, and (S,S)-2 is proof that the liquid-crystalline properties
of those compounds arise from the combination of the structural
characteristics of both molecular building blocks, i.e., the chiral
C60 unit and the nematogenic dendron, thus allowing for the first
time in this class of materials to establish the correlation between
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425.
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3580 J. AM. CHEM. SOC. VOL. 132, NO. 10, 2010

Diastereoisomerically Pure Fulleropyrrolidines
A R T I C L E S
molecular and mesophase chirality. Chiral fullerenes can therefore
be used as platforms for the design of optically active liquid crystals
that display chiral mesophases.
(i.e., the fulleropyrrolidine and the dendron) plays complemen-
tary roles to generate the desired mesophase in the final
materials. Interestingly, other chiral mesophases may be ob-
tained, such as the chiral smectic C (SmC*) phase, by selecting
an appropriate dendron. Our study represents a new and general
approach for the design of liquid-crystalline fullerenes, for which
the chiroptical and liquid-crystalline properties can be tailored
at the molecular level.
Conclusions
The synthesis of liquid-crystalline, diastereoisomerically pure
fullerodendrimers was successfully achieved. Four diastereoi-
somerically pure fulleropyrrolidines ((R,S)-1, (R,R)-1, (S,R)-1,
and (S,S)-1) were connected to a second-generation dendron
which displays the nematic (N) phase. The resulting fullero-
dendrimers ((R,S)-2, (R,R)-2, (S,R)-2, and (S,S)-2) exhibit the
chiral nematic (N*) phase. The formation and nature of the latter
mesophase arise from the combination of the chirality of the
fulleropyrrolidine units with the nematogenic behavior of the
dendritic liquid-crystalline promoter. Therefore, each subunit
Acknowledgment. R.D. thanks the Swiss National Science
Foundation (Grant No. 200020-119648) for financial support. We
also acknowledge support from the European Science Foundation
(ESF) under the EUROCORES SONS II - LCNANOP project.
Supporting Information Available: Text, figures, and tables
giving techniques, experimental details, and analytical data of
the new compounds and a CIF file giving crystallographic data
for compound (R,S)-1. This material is available free of charge
via the Internet at http://pubs.acs.org.
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