Influencing the Self-Sorting Behavior of [2.2]Paracyclophane-Based Ligands by Introducing Isostructural Binding Motifs

Article abstract of DOI:10.1002/chem.201905070

Two isostructural ligands with either nitrile (L^nit) or isonitrile (L^iso) moieties directly connected to a [2.2]paracyclophane backbone with pseudo-meta substitution pattern have been synthesized. The ligand itself (L^nit) or its precursors (L^iso) were resolved by HPLC on a chiral stationary phase and the absolute configuration of the isolated enantiomers was assigned by XRD analysis and/or by comparison of quantum-chemical simulated and experimental electronic circular dichroism (ECD) spectra. Surprisingly, the resulting metallosupramolecular aggregates formed in solution upon coordination of [(dppp)Pd(OTf)₂] differ in their composition: whereas L^nit forms dinuclear complexes, L^iso exclusively forms trinuclear ones. Furthermore, they also differ in their chiral self-sorting behavior as (rac)-L^iso undergoes exclusive social self-sorting leading to a heterochiral assembly, whereas (rac)-L^iso shows a twofold preference for the formation of homochiral complexes in a narcissistic self-sorting manner as proven by ESI mass spectrometry and NMR spectroscopy. Interestingly, upon crystallization, these discrete aggregates undergo structural transformation to coordination polymers, as evidenced by single-crystal X-ray diffraction.

Full text of DOI:10.1002/chem.201905070

A Journal of
Accepted Article
Title: Influencing the self-sorting behavior of [2.2]paracyclophane
based ligands by introducing isostructural binding motifs
Authors: Lucia Volbach, Niklas Struch, Fabian Bohle, Filip Topic,
Gregor Schnakenburg, Andreas Schneider, Kari Rissanen,
Stefan Grimme, and Arne Lützen
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To be cited as: Chem. Eur. J. 10.1002/chem.201905070
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Influencing the self-sorting behavior of [2.2]paracyclophane
based ligands by introducing isostructural binding motifs
L. Volbach,[a] N. Struch,[a]# F. Bohle,[b] F. Topić,[c]‡ G. Schnakenburg,[d] A. Schneider,[a] K. Rissanen,[c] S.
Grimme,[b] and A. Lützen*[a]
the heterochiral social[8,9] and the homochiral narcissistic self-
sortingl[10,11] have been reported in metallosupramolecular
chemistry. These studies revealed that there are several
possibilities to affect and fine-tune the self-sorting behavior, e.g.
by varying the overall size, the opening angle and the steric bulk
of bridging rigid V-shaped ligands.
Based on structural findings in those studies, we wanted to
introduce yet another variable concerning only the metal binding
unit, to get further insight into these processes and factors that
might rule their outcome. Herein, we report on the comparison of
two different coordination motifs with regard to self-sorting by
introducing two ligands with equal size, shape and coordination
angles. The ligands are designed to form supramolecular
architectures in solution and solid state upon coordination to cis-
protected palladium(II)-ions,[12] giving rise to [(dppp)nMnLn]
complexes which have been proven as a simple yet successful
platform for investigating changes in the self-sorting behavior.
Abstract: Two isostructural ligands with either nitrile (Lnit) or
isonitrile (Liso) moieties directly connected to a [2.2]paracyclophane
backbone with pseudo-meta substitution pattern have been
synthesized. The ligand itself (Lnit) or its precursors (Liso) were
resolved via HPLC on a chiral stationary phase and the absolute
configuration of the isolated enantiomers was assigned by XRD
analysis and/or by comparison of quantum-chemical simulated and
experimental
ECD-spectra.
Surprisingly,
the
resulting
metallosupramolecular aggregates formed in solution upon
coordination of [(dppp)Pd(OTf)2] differ in their composition: whereas
Lnit forms dinuclear complexes Liso exclusively forms trinuclear ones.
Furthermore, they also differ in their chiral self-sorting behavior as
(rac)-Liso undergoes exclusive social self-sorting leading to
a
heterochiral assembly whereas (rac)-Liso shows a twofold preference
for the formation of homochiral complexes in a narcissistic self-
sorting manner as proven by ESI mass spectrometry and NMR
spectroscopy. Interestingly, upon crystallization these discrete
aggregates undergo structural transformation to coordination
polymers as evidenced by single-crystal X-ray diffraction.
Results and Discussion
The design is based on an analogy to a meta-substituted
benzene core furnished with the commonly used 4-pyridyl
moiety. In literature there are several examples for directly
bound and elongated ligands with e.g. ethynyl-spacers
coordinating to palladium(II).[13] In order to study chiral self-
sorting behavior we decided to use a pseudo-meta substituted
[2.2]paracyclophane backbone as a chiral substitute for the
central meta-functionalized benzene ring which also arranges its
functional groups at an angle of about 120° designed to
construct discrete coordination architectures. Additionally, this
scaffold comes with some adaptability due to a possible twist of
approx. 12° between the aromatic decks.[14] Since we wanted to
study two different ligands with essentially equal size and shape,
we decided to use nitrile and isonitrile groups (bond length of the
CN bond in nitriles 1.5 Å and in isonitriles 1.7 Å, respectively),[15]
which are formally isoelectronic to carbon monoxide and have
been employed previously to construct metallosupramolecular
architectures.[9f,16] It is worth mentioning, though, that multitopic
oligoisonitrile ligands have – to the best of our knowledge – not
been used for the self-assembly of discrete cyclic or cage-like
metallosupramolecular aggregates so far. Both nitriles and
isonitriles represent very slim metal-binding motifs. However,
they differ in the relative strength of the metal-ligand interaction
as the isonitriles bind – similarly to pyridines – much stronger to
metal ions like palladium(II) ions than the corresponding
nitriles.[17]
Introduction
Mastering the self-sorting behavior in multicomponent mixtures
is of utmost importance to cope with the immense structural
complexity that such systems offer.[1] Geometrical (self-)
complementarity concerning shape and size but also chirality
have been used to achieve self-sorting either in a narcissistic[2]
(also known as self-recognition[3]) or social[4] (also called self-
discrimination[5]) manner. Among the features mentioned above,
high-fidelity self-sorting is most challenging with enantiomers
which are usually highly similar competitors due to their equal
size and shape and the chirality as the only difference. Although
successful chiral self-sorting is well established in the solid state
due to strong interactions and cooperative binding mechanisms
found in crystalline matter,[6] self-sorting of racemic mixtures in
solution is still a true challenge.[7] Nevertheless, both scenarios,
[a]
Dr. L. Volbach, Dr. N. Struch, A. Schneider, Prof. Dr. A. Lützen
Kekulé-Institute of Organic Chemistry and Biochemistry
University of Bonn
Gerhard-Domagk Straße 1, D-53121 Bonn, Germany
E-mail: arne.luetzen@uni-bonn.de
M.Sc. F. Bohle, Prof. Dr. S. Grimme
Mulliken Center for Theoretical Chemistry
University of Bonn
Beringstraße 4, D-53115 Bonn, Germany
Dr. F. Topić, Prof. Dr. K. Rissanen
Department of Chemistry
For our purpose, we synthesized two ligands with either two
nitrile or isonitrile moieties attached directly to the
[b]
[c]
[d]
[2.2]paracyclophane backbone in
a
pseudo-meta-4,15-
substitution pattern. This orientates the functional groups at an
angle of about 120° and positions the binding sites spatially
close to the planar chiral center, a design intended to give rise to
discrete coordination architectures and enable the study of the
influence of binding strength on self-sorting.
University of Jyväskylä
P. O. Box 35, FIN-40014 Jyväskylä, Finland
Dr. G. Schnakenburg
Institute of Inorganic Chemistry
University of Bonn
Gerhard-Domagk Straße 1, D-53121 Bonn, Germany
Supporting information for this article is given via a link at the end of
the document.
1
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10.1002/chem.201905070
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single crystal X-ray diffraction and subsequent analysis of the
Bijvoet differences using Bayesian statistics (vide infra).[22] Both
techniques proved that the (Rp)-enantiomer was the first to elute
(see SI).
New ligand Liso was obtained in a two-step synthesis with
excellent yields using the previously reported pseudo-meta-4,15-
diamino[2.2]paracyclophane[20] 4 as the starting material. First,
the 4,15-diformamido[2.2]paracyclophane 5 was obtained by
dissolving the starting material in an excess of formic acid and
sonicating the solution in an ultrasonic bath for 6 h. After
purification by filtration through a short silica column and
treatment with POCl3 in a 1:1 mixture of THF and triethylamine,
ligand Liso was obtained in 73% yield. Fortunately, pseudo-meta-
Scheme 1. pseudo-meta functionalized [2.2]paracyclophane ligands Lnit and
Liso
.
Synthesis
The synthesis of the two different ligands Lnit and Liso (Scheme
1) started with the commercially available unsubstituted
[2.2]paracyclophane 1 which can be easily functionalized via the
bromination method developed by Hopf et al. to yield 4,15-
dibromo[2.2]-paracyclophane 2 and its achiral regioisomer 4,16-
dibromo-[2.2]paracyclophane which could be separated by
recrystallization.[18]
4,15-diamino[2.2]paracyclophane
4
is
available
in
enantiomerically pure form, because all attempts to resolve
ligand Liso directly via HPLC using chiral columns in a sufficient
manner with regard to enantiomeric purity failed. Nevertheless,
the absolute configuration of the resolved enantiomers could be
confirmed by single crystal X-ray diffraction and subsequent
analysis of the Bijvoet differences using Bayesian statistics (vide
infra and SI).[22]
In this way, we had access to both ligands in racemic and
optically pure form which allowed us to compare their self-
sorting behavior in the self-assembly of metallosupramolecular
complexes upon coordination to cis-protected palladium(II) ions
in solution and solid state.
The synthesis of the racemic ligand Lnit was already reported by
Cram et al. in 1975[19] but it has neither been chirally resolved
nor used for metal complexation studies so far.
Coordination Studies – solution and
gas-phase studies
The metallosupramolecular aggregates were formed upon
mixing stoichiometric amounts of ligand (each either in racemic
or enantiomerically pure form) with [(dppp)Pd(OTf2)][23] in
different solvents and characterized by NMR techniques and,
where possible, by ESI-MS measurements.
Scheme 2. Synthesis of ligands Lnit and Liso
.
Figure 1. 1H-NMR (499 MHz in CD3NO2 at 298 K) of a) [(dppp)Pd(OTf)2], b) a
1:1 mixture of [(dppp)Pd(OTf)2] and (Sp)-Lnit, and c) ligand Lnit
.
We obtained the ligand Lnit by an alternative route achieving
higher yields. Namely, we performed the already reported
bromine-lithium exchange in THF at −78°C first by using t-BuLi
and quenched the dilithiated species with iodine to access the
diiodinated [2.2]paracyclophane 3 in 80% yield.[20] Next, we
synthesized Lnit by palladium-catalyzed cyanation reaction
providing the desired product in 85% yield.
Since we needed both the racemic and the enantiomerically
pure compounds for our studies, we next resolved ligand Lnit by
HPLC on a Chiralpak IB stationary phase both on the analytical
and semi-preparative scale (see SI). The absolute configuration
could be elucidated by comparison of experimentally recorded
CD spectra of the resolved material with theoretically simulated
ones obtained from sTD-DFT-calculations[21]. This assignment
was corroborated by determination of the Flack parameter via
Coordination of ligand Lnit can be observed in e.g. nitromethane.
The 1H-NMR spectra of the complex formed from
enantiomerically pure ligand Lnit shows only one set of sharp,
significantly shifted signals, indicating a successful formation of
a single discrete homochiral metallosupramolecular aggregate of
D2-symmetry (Figure 1).
Further proof of the exclusive formation of only one aggregate
was obtained by 1H-DOSY experiments (Figure 2): all signals
belong to a single species with a diffusion coefficient D = 4.42 ×
10−6 cm2 s−1, which translates to a hydrodynamic diameter d =
16.0 Å, according to the Stokes-Einstein equation. This is
considerably larger than the ligand Lnit alone but matches very
2
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well the calculated value[24] of the hydrodynamic diameter of a
dinuclear rhomb (about 16 Å, see Figure 4a).
metallosupramolecular aggregates. However, the 31P signals
differ in such a way that the signal observed for the heterochiral
complex is shifted even further to high field compared to that of
its homochiral stereoisomer.
Figure 2. 1H-DOSY NMR Spectra (499 MHz in CD3NO2 at 293 K) of the
aggregate obtained from a 1:1 mixture of [(dppp)Pd(OTf)2] and (Sp)-Lnit
.
Unfortunately, despite our best efforts, we have not been able to
obtain any mass spectra of this kind of complexes formed from
bis(nitrile) ligands, presumably due to the weak binding between
the palladium atoms and the nitrogen donors.
Nevertheless, we went on to analyze the behavior of the racemic
ligand (rac)-Lnit by recording a similar set of NMR experiments.
Comparing them with the spectra of the free ligand and the
homochiral complex formed from the optically pure ligand
revealed that a single metallosupramolecular complex is formed
which is different from the homochiral dinuclear complex as
indicated by significant shifts (Figure 3).
Figure 4. PBEh-3c/DCOSMO-RS(NO2CH3) optimized structures of the
cationic units of dinuclear metallosupramolecular rhombs: a) homochiral
[(dppp)2Pd2{(Rp)-Lnit}2](OTf)4 and b) heterochiral [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-
Lnit}](OTf)4 (hydrogen atoms are omitted, color scheme: carbon
– grey,
nitrogen – blue, phosphorous – orange, palladium – petrol, see SI for further
details).
This difference is not a result of an anion template effect as the
signals of the triflate anions in the 19F-NMR spectra were found
at the same shift for both dinuclear aggregates [(dppp)2Pd2{(Sp)-
Lnit}2](OTf)4 and [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}](OTf)4, while
being clearly different from that of the starting material
[(dppp)Pd(OTf)2] (see SI).
To complete these studies it is important to mention that
essentially the same behavior was observed when chlorinated
solvents like dichloromethane were used but acetonitrile and
acetone both proved to be too competitive as they (expectedly)
prohibited the complexation (see SI).[25]
Having established the highly diastereoselective self-sorting
during the self-assembly of ligand Lnit upon coordination to
[(dppp)Pd(OTf)2], we turned our attention to ligand Liso. Like Lnit,
enantiomerically pure Liso also gives rise to
a
single
metallosupramolecular species upon coordination to the cis-
protected Pd(II) complex fragment. Surprisingly, however,
analysis of the DOSY spectra clearly indicate that the aggregate
formed from enantiomerically pure Liso has a diameter of
d = 22.6 Å, thus being considerably larger than the dinuclear
homochiral complex obtained via self-assembly of optically pure
Lnit and [(dppp)Pd(OTf)2] (see SI).
Figure 3. 1H-NMR (499 MHz in CD3NO2 at 298 K) of a) 1:1 mixture of
[(dppp)Pd(OTf)2] and (Sp)-Lnit, b) a 1:1 mixture of [(dppp)Pd(OTf)2] and (rac)-
Lnit, and c) ligand Lnit
.
Fortunately, complexes of palladium(II) ions and isonitrile
ligands are more stable than their nitrile analogues,[17] and
hence, can be studied by ESI-MS (Figure 5). These studies
confirm the formation of trinuclear complexes with
enantiomerically pure and racemic Liso, as indicated by signals
As the 1H-DOSY experiment (see SI) again indicated the
formation of a dinuclear assembly, we conclude that the self-
assembly process involving (rac)-Lnit is still highly
diastereoselective but results in the exclusive formation of the
heterochiral C2v-symmetric complex (Figure 4b).
at
m/z
=
1463.2
which
can
be
assigned
to
{[(dppp)3Pd3(Liso)3](OTf)4}2+, or the signals at m/z = 811.2 and
925.1 which can both be assigned to superimposed signals
arising from triply charged ions {[(dppp)3Pd3(Liso)3](Cl)3}3+ and
{[(dppp)3Pd3(Liso)3](OTf)3}3+ and their singly charged fragments
{[(dppp)Pd(Liso)](X)}+ (X = Cl or OTf), respectively.[26]
This interpretation in favor of a diastereoselective self-sorting in
a
self-discriminating manner was further corroborated by
comparison of 31P-NMR spectra which show a single signal in
each case (see SI). Compared to [(dppp)Pd(OTf)2], the signals
of both the homochiral [(dppp)2Pd2{(Sp)-Lnit}2](OTf)4 and the
heterochiral [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}](OTf)4 are high-field
shifted indicating the selective formation of the desired dinuclear
3
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Figure 5. Positive ESI-MS spectrum of the 1:1 mixture of [(dppp)Pd(OTf)2] and
(rac)-Liso showing signals of trinuclear 3:3 aggregates and their fragments.
The inset shows the comparison of the experimentally determined isotope
pattern of the {[(dppp)3Pd3(Liso)3](OTf)4}2+ ion and the calculated one.
Figure7. Superimposed 1H-2D-DOSY NMR spectra (499 MHz in CD3NO2 at
298 K) of [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}](OTf)4 obtained upon mixing of
[(dppp)Pd(OTf)2] and (rac)-Lnit (black) and the mixture of [(dppp)2Pd2{(Sp)-
Liso}2{(Rp)-Liso}](OTf)6 and the [(dppp)2Pd2{(Sp)-Liso}3](OTf)6 and their
enantiomers, respectively, obtained upon mixing of [(dppp)Pd(OTf)2] and (rac)-
Liso (red).
Hence, we can conclude that the enantiomerically pure ligand
Liso successfully forms
a
discrete homochiral trinuclear
metallosupramolecular aggregate of D3-symmetry upon
coordination to [(dppp)Pd(OTf)2].
Next, we turned our attention to (rac)-Liso. Since ESI-MS already
revealed the formation of trinuclear complexes, NMR
spectroscopic experiments were performed to study its chiral
self-sorting behavior. Interestingly, the 1H-NMR spectrum of a
1:1 mixture of [(dppp)Pd(OTf)2] and (rac)-Liso in nitromethane-d3
looks rather complicated (Figure 6).
Figure 6. 1H-NMR (499 MHz in CD3NO2 at 293 K) of a) [(dppp)3Pd3{(Sp)-
Liso}3]OTf6, b) the complexes formed from a 1:1 mixture of [(dppp)Pd(OTf)2]
and (rac)-Liso, and c) ligand (rac)-Liso
.
2D-correlated spectra confirmed the formation of two different
1
species and H-DOSY experiments nicely show that these are
both of very similar size giving rise to a diffusion coefficient D =
3.20 × 10−6 cm2 s−1. This value is again considerably smaller
than that observed for the dinuclear complexes formed from
ligand Lnit (Figure 7) but nicely matches that of the homochiral
Figure 8. PBEh-3c/DCOSMO-RS(NO2CH3) optimized structures of the
cationic units of trinuclear metallosupramolecular triangles: a) the homochiral
[(dppp)3Pd3{(Rp)-Liso}3](OTf)6 and b) heterochiral [(dppp)3Pd3{(Rp)-Liso}2{(Sp)-
Liso}](OTf)6 (hydrogen atoms are omitted, color scheme: carbon – grey,
nitrogen – blue, phosphorous – orange, palladium – petrol, see SI for further
details).
trinuclear complex obtained from enantiomerically pure Liso
.
Therefore, we can assign the two species formed as the
homochiral trinuclear complex [(dppp)3Pd3{(Sp)-Liso}3](OTf)6 and
its enantiomer and the heterochiral complex [(dppp)3Pd3{(Sp)-
Liso}2{(Rp)-Liso}](OTf)6 and its enantiomer, respectively (Figure 8).
This is also in agreement with the analysis of the 31P NMR
spectra (see SI). Whereas the homochiral complex
4
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[(dppp)3Pd3{(Sp)-Liso}3](OTf)6 only gives rise to a single signal
that is significantly shifted compared to the signal observed for
[(dppp)Pd(OTf)2], the mixture of the racemic homochiral and
heterochiral trinuclear complexes gave rise to four signals that
are again shifted compared to that of [(dppp)Pd(OTf)2].
assembly of Liso is much less symmetric than its homochiral
diastereomer, and hence, might be less favoured. However, this
is only an empirical explanation based on our experience with
similar complexes, and hence, should be regarded with great
care.
Like in the case of Lnit, we did not observe any anion template
effect during the self-assembly of Liso as we observed only
single signals in each of the recorded 19F NMR spectra which
were considerably shifted compared to that of [(dppp)Pd(OTf)2]
(see SI).
Nevertheless, we performed quantum chemical calculations to
get further hints on the reasons for the striking differences of the
self-assembly behavior of our two ligands with regard to
complex composition because this is the only way to compare
the experimentally observed dinuclear palladium(II) complex of
Lnit with the corresponding hypothetical trinuclear one, and the
experimentally observed trinuclear complex of Liso with the
hypothetical dinuclear one, respectively.
1
Integration of the signals in the H NMR spectra revealed that
the homochiral and heterochiral aggregates do not just form
statistically in a 1:3 homo- to heterochiral ratio but rather in a 1
to 1.5 homo- to heterochiral ratio in an equilibrated solution (see
SI). This translates to a twofold amplified formation of the
homochiral assemblies in a narcissistic self-sorting manner.[27]
Thus, the bis(isonitrile) ligand Liso does not only show a different
behavior regarding the composition of the metallosupra-
molecular aggregate formed upon self-assembly with
[(dppp)Pd(OTf)2], but it also shows a contrary self-sorting
behavior compared to its almost isostructural bis(nitrile)
analogue Lnit (although the self-sorting with Liso is by far not as
perfect as with Lnit). This feature is truly remarkable having in
mind the close structural similarity of the two ligands. Obviously,
though, these two ligands differ in their dipole moments and their
binding strength towards palladium, as isonitrile ligands
generally coordinate to the metal center much more strongly
than nitrile ligands due to their better σ-donation and superior π-
backbonding ability.[16d,17,28] Consequently, the (M-)N-C-C and
(M-)C-N-C bond angles in nitrile and isonitrile complexes,
respectively, can differ as the nitriles tend to be linear whereas
considerable bending of isonitrile groups has been reported.[17]
This is also reflected by the results quantum chemical
calculations which were performed on acetonitrile and
isocycanomethane, respectively, in order to estimate the
energetic differences of the bending between the two groups
(Figure 9).
Table 1: Association free energies (∆Ga ) of di- and tri-nuclear Lnit
and Liso complexes (All energies and free energies in kcal·mol−1)
∆E
(PBE0/d
ef2-
∆GRRHO
(GFN2-
∆δGsolv
(COSMO-
RS
∆Edisp
(D4)
complex
∆Ga
xTB/ GBSA
QZVP)
(CH3CN))(a) (NO2CH3))
[(dppp)2Pd2
−8.2
102.7
−41.4
44.4
−37.5
−64.8
−35.5
−62.6
56.8
89.7
60.0
93.9
−66.0
−230.3
−70.5
−54.9
−102.7
−87.4
{(Rp)-Lnit}2]4+
[(dppp)3Pd3
{(Rp)-Lnit}3]6+
[(dppp)2Pd2
{(Rp)-Liso}2]4+
[(dppp)3Pd3
−237.6
−161.9
{(Rp)-Liso}3]6+
(a) Acetonitrile was used as solvent, since nitromethane is not
parametrized for the implicit solvation model GBSA and the dielectric
constant of acetonitrile is very close to that of nitromethane.
Table 2: Free energies of di- and tri-nuclear Lnit and Liso complexes
(All energies and free energies in kcal·mol−1)
∆∆G(b)
∆Ga
(GFN2-xTB/
GBSA
∆Ga PBE0-
D4/def2-QZVP
/COSMO-
∆∆G(b)
system
(2·M3L3
-
3·M2L2)
(2·M3L3
-3·M2L2)
a,c)
a)
(CH3CN))(
RS(NO2CH3))(
[(dppp)2Pd2
−99.8
−162.9
−149.3
−245.3
−54.9
{(Rp)-Lnit}2]4+
−26.3
−42.8
−40.9
−61.7
[(dppp)3Pd3
−102.7
−87.4
{(Rp)-Lnit}3]6+
[(dppp)2Pd2
{(Rp)-Liso}2]4+
[(dppp)3Pd3
−161.9
{(Rp)-Liso}3]6+
Figure 9. Acetonitrile [N-C-C] and isocyanomethane [C-N-C] bending angle
and energy correlation plots obtained when employing different quantum
chemical approaches..
(a) ∆Ga association free energies of the complexes. (b) ∆∆G free
energy for the reaction 3·M2L2 → 2·M3L3. (c) Acetonitrile was used
as solvent, since nitromethane is not parametrized for the implicit
solvation model GBSA and the dielectric constant of acetonitrile is
very close to the one of nitromethane.
This might explain the differences in the self-assembly behavior
with regard to the different composition although this needs to
be verified with other ligand scaffolds of similar rigidity in the
future.
A reason for the different self-sorting behavior might be that the
heterochiral 2:2 assembly obtained from Lnit is very symmetric
which might favour its formation. However, the heterochiral 3:3
Thermodynamic data of the tri- and di-nuclear complexes are
given in Table 2. The semiempirical quantum mechanical GFN2-
xTB[34] and high level PBE0-D4/QZ results show the trinuclear
complexes of both binding motifs to be thermodynamically more
stable than the dinuclear ones. Considering the efficiency of the
GFN2-xTB method compared to the DFT calculations (speed-up
of about a factor of 1000 of more), the observed differences in
5
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the computed free energies are acceptable and we can
recommend this method in general for screening purposes in
similar systems, given also that the computed structures are
fairly reliable. However, the consistently computed higher
stability of trinuclear complexes of Lnit compared to the dinuclear
ones is in stark contrast to the experimental findings. Although
the influence of explicit single solvent molecules at the palladium
centers was explored in the computations and did not change
the initial findings (see SI), explicit single molecule solvation and
implicit solvation models are still inadequate to describe the full
effect of solvation on the metallosupramolecular aggregates.
Obviously, one would have to take into account a whole
ensemble of solvent molecules and study its interaction with the
dinuclear and trinuclear complexes in order to get the same
trend as observed experimentally. Currently, however, this is
clearly beyond the boundaries of this theoretical approach.
Nevertheless, it is important to note that the trinuclear complex
of the isonitrile ligand Liso is not only strongly preferred
compared to its potential trinuclear analogue of the nitrile ligand
Lnit but it is also much more stabilized compared to the
corresponding dinuclear complex as reflected by an energy
difference that the solvent effects should not be able to
compensate for.
Coordination Studies – solid state studies
We were also able to obtain some single crystals of our ligands
(see SI) and some of their complexes suitable for X-ray analysis.
Enantiomerically pure Lnit crystallizes in the orthorhombic space
group P212121 upon evaporation of its dichloromethane solution.
The absolute configuration assigned by the comparison of
experimental and quantum chemically simulated ECD spectra
could be confirmed by the analysis of the Flack parameter and
the Bijvoet differences using Bayesian statistics derived from the
single crystal XRD analysis of Lnit and its coordination
complexes. A torsion angle of 119.81° between the two binding
units was measured. Enantiomerically pure Liso crystallizes in
the same orthorhombic space group P212121 upon evaporation
of solvent from a solution in dichloromethane. As Liso was
prepared from enantiomerically pure building blocks 4 its
stereochemistry was already known,[20] but the XRD analysis of
its single crystals as well as of its coordination complex further
confirmed the stereochemical assignment. As anticipated, a
dihedral angle of 117.94° between the coordinating isonitrile
groups and the centers of the phenyl rings in the
paracyclophane backbone was found (vide supra). Hence, the
difference in torsion angle between the two ligands amounts to
1.87°.
Figure 10. Top: capped sticks representation showing the helical homochiral
coordination polymer [(dppp)Pd{(Rp)-Lnit}]n(OTf)2n (view along the
a axis,
anions and solvent molecules are omitted for clarity, color scheme: grey –
carbon, blue – nitrogen, petrol – palladium, orange – phosphorous, white –
hydrogen). Bottom: space-filling representation of the coordination polymer
[(dppp)Pd{(Rp)-Lnit}]n(OTf)2n showing the parallel packing of the individual
polymer strands (hydrogen atoms, solvent molecules and counterions are
omitted for clarity).
Each metal center is coordinated to one dppp and two ligands
Lnit, forming a helical coordination polymer. Pd(dppp) moieties
form the outer edges while the paracyclophane ligands form the
inner core of the coordination polymer (Figure 10). The
polymeric helical strands, generated from the asymmetric unit by
a twofold screw axis, are parallel to the crystallographic axis a.
The triflate anions are placed in pockets formed by the organic
ligands above and below the coordination plane of the palladium
in apical positions (see SI). The complete helices are arranged
in a parallel and slightly tilted brick-like packing scheme.
Diffusion of cyclohexane into a solution of [(dppp)2Pd2{(Rp)-
Lnit}2](OTf)4 in dichloromethane and subsequent slow
evaporation of the solvent afforded single crystals suitable for
XRD analysis. Surprisingly, however, addition of the non-polar
solvent and concentration of the solution caused a massive
structural rearrangement resulting in a homochiral coordination
polymer [(dppp)Pd{(Rp)-L1}]n(OTf)2n crystallizing in the
A structural rearrangement also occurred when cyclopentane
was diffused into a solution of heterochiral [(dppp)2Pd2{(Sp)-
Lnit}{(Rp)-Lnit}](OTf)4 in dichloromethane and the solvents were
allowed to slowly evaporate. Here, however, we observed the
formation
of
a
heterochiral
coordination
polymer
orthorhombic
space
group
P212121.
The
observed
[(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}]n(OTf)4n crystallizing in the
orthorhombic space group Fdd2. The asymmetric unit contains
one ligand Lnit, a dppp-protected palladium ion and two
disordered triflate anions. Each metal center is coordinated with
one ligand of each enantiomer forming a nested-V-like structure
(Figure 11). The triflate anions are located between two dppp
ligands, again positioned above and below the coordination
plane of the palladium centers in apical positions (see SI). The
individual polymer strands are stacked in an interlocked fashion,
following the [101] and [101,¯] directions in the crystal.
polymerization of discrete complexes is most probably due to
concentration effects during the crystal growth.[35] Coordination
polymers with nitrile ligands are known in literature, but usually
contain
silver(I)-centers.[36]
The
asymmetric
unit
of
[(dppp)Pd{(Rp)-Lnit}]n(OTf)2n contains one ligand Lnit, a dppp-
protected palladium ion, two triflate anions and a disordered
dichloromethane molecule.
6
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10.1002/chem.201905070
Chemistry - A European Journal
FULL PAPER
concerning the orientation of the nitrile and isonitrile groups
(deviation of 1.87°), size and chirality. The only significant
difference between the two constitutional isomers is in the bond
strength towards the metal ion as isonitrile ligands generally
coordinate much more strongly than their nitrile analogues due
to better σ-donation and the superior π-backbonding ability.
We studied the self-assembly and self-sorting by means of NMR
spectroscopy, mass spectrometry and single crystal X-ray
diffraction studies. The aggregates of both ligands are formed
selectively with regard to their composition, yielding dinuclear
rhombs in case of ligand Lnit and trinuclear triangles in case of
ligand Liso
. Interestingly, this difference also leads to a
divergence in terms of their chiral self-sorting behavior. Ligand
(rac)-Lnit exclusively forms achiral heterochiral dinuclear rhombs
[(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}](OTf)4 in
a diastereoselective
manner resulting from social self-sorting in non-competitive
solvents like nitromethane, dichloromethane or chloroform. In
contrast to this, ligand (rac)-Liso rather shows
a twofold
preference for narcissistic self-sorting to yield a 1:1.5 mixture of
racemic homo- and heterochiral trinuclear complexes. This
might be due to the difference between (M-)N-C-C and (M-)C-N-
C bond angles in nitrile and isonitrile complexes, respectively,
being linear in case of nitriles with significant deviation from
linearity in case of the isonitrile groups. Obviously, it is a
combination of relative binding strength between the ligands and
the metal ions and the interaction with solvent molecules that is
responsible for this behavior. Unfortunately, however, simulating
this by state-of-the-art quantum chemical calculations is
currently not possible. Thus, future studies with other ligands of
similar rigidity are needed to establish whether this is general
trend.
Single crystal X-ray diffraction revealed that, upon crystallization,
the discrete homo- and heterochiral aggregates rearrange to
form coordination polymers.
These studies show that the self-sorting behaviour is obviously
not only dependent on rigid scaffolds with steric crowding or
certain bend angles of V-shaped ligands but even more on an
interplay of other important factors, e.g. the binding strength and
mode towards the coordinated metal centers and the resulting
structural changes in the metal binding motif.
Figure 11. Top: capped sticks representation of the crystal structure of the
heterochiral polymer [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}]n(OTf)4n showing the zig-
zag-structure (view along the [011] direction, anions and solvent molecules are
omitted for clarity, color scheme: grey – carbon, blue – nitrogen, petrol –
palladium, orange – phosphorous, white – hydrogen); bottom: Bottom: space-
filling representation of the coordination polymer [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-
Lnit}]n(OTf)4n showing the interlocked packing pattern of the individual polymer
chains (hydrogen atoms, solvent molecules and counterions are omitted for
clarity).
Diffusion of benzene into
a solution of [(dppp)3Pd3{(Sp)-
Liso}3](OTf)6 in acetonitrile and slow evaporation of the solvent
also resulted in the formation of a homochiral coordination
polymer [(dppp)Pd{(Sp)-Liso}]n(OTf)2n that turned out to be nearly
isostructural to the corresponding homochiral [(dppp)Pd{(Rp)-
Lnit}]n(OTf)2n coordination polymer. The most significant
difference is that solvate acetonitrile, instead of dichloromethane,
is packed aligned along [100] with head-to-tail configuration
between two parallel polymer chains (see SI).
Experimental Section
General: All solvents were distilled, dried and stored according
to literature procedures. Air- and moisture-sensitive reactions
were performed under argon using Schlenk techniques and
oven-dried glassware. Thin layer chromatography was
performed on aluminum TLC (silica 60F254 from Merck) and
detected with UV light (λ = 254 nm and 366 nm). Products were
purified by column chromatography on silica gel 60 (70-230
mesh) from Merck. NMR-spectra were recorded at 298 K with
Despite of our best efforts we did not succeed in obtaining
crystals suitable for single crystal XRD from solutions of the
mixture of the four stereoisomers of the trinuclear complex
formed from (rac)-Liso
.
Bruker Avance 400 or 500 spectrometer. H and 13C chemical
1
While the formation of helical polymeric structures from discrete
cyclic structures as observed in case of [(dppp)Pd{(Sp)-
Liso}]n(OTf)2n and [(dppp)Pd{(Rp)-Lnit}]n(OTf)2n is in accordance
with earlier observations[10d,f,-k,11b,c,9,16f] and other self-assembled
polymers,[37] the formation of bowl-shaped, concave yet
polymeric structures as observed in [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-
Lnit}]n(OTf)4n is more scarce, both on the level of discrete
supramolecular structures as well as on the level of self-
assembled polymers.
shifts are reported on δ scale (ppm) relative to residual solvent
signals (1H) or the solvent signal (13C) as internal standard. 31P
and 19F chemical shifts are reported on the δ scale (ppm)
relative to the chemical shifts of external standard (D3PO4 and
TFA-d) measured simultaneously in a sample tube with an inset
1
for the standard. All H and 13C signals were assigned on the
1
basis of H, 13C, HMQC and HMBC experiments. Mass spectra
were recorded with a microOTOF-Q instrument from Bruker and
a MAT 90 from Thermo Finnigan. Elemental analyses were
performed with a Heraeus Vario EL analyzer. However, CHN
analyses could only be conducted with fluorine-free compounds.
Conclusions
(rac)-4,15-diiodo[2.2]paracyclophane,[20]
(rac)-4,15-diamino-
[2.2]paracyclophane and the enantiomerically pure diamines[20]
and [(dppp)Pd(OTf)2][23] were prepared according to literature
procedures. Numbering schemes for all compounds are included
in the SI.
We have synthesized two ligands Lnit and Liso with nitrile and
isonitrile metal-binding motifs, respectively, in racemic and
enantiomerically pure form and investigated their coordination
behavior
towards
cis-protected
palladium
complex
[(dppp)Pd(OTf)2]. Both ligands are almost isostructural
7
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10.1002/chem.201905070
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FULL PAPER
Synthesis of (rac)-, (Sp)-, (Rp)-4,15-dicyano[2.2]paracyclo-
phane (Lnit):
(C-1, C-2), 30.4 (C-9, C-10). MS (EI) m/z (intesity %) = 258.2
(10) [M]+·, 129.1 (10) [M-C9H7N]+, 101.2 (20) [M-C2H4]+. High
resolution MS(EI): m/z = 257.1076 (calcd. for [C18H14N2 − H]+:
257.1079). C18H14N2 · 1/6 dichloromethane (258.32 g/mol): calcd.
C 80.08.18, H 5.30, N 10.28; found C 80.05, H 5.62, N 9.87.
Specific optical roation: (+)-(Sp)-L2: [훼]2퐷0 = +284.1° mL dm−1 g−1
(c = 2.37 g/L, CHCl3), (−)-(Rp)-L2: −287.4° mL dm−1 g−1 (c =
2.42 g/L, CHCl3).
(rac)- or (Sp)- or (Rp)-4,15-Diiodo[2.2]paracyclophane (200 mg,
0.43 mmol), zinc cyanide (408 mg, 3.48 mmol) and Pd(PPh3)4
(50 mg, 0.04 mmol) was dissolved in 3 mL of dry DMF and
heated for 48 h at 100°C. After cooling to room temperature,
dichloromethane (10 mL) and aqueous saturated EDTA-solution
(5 mL) were added. The phases were separated and the
aqueous layer was extracted with dichloromethane (3 x 20 mL).
The combined organic layers were dried with MgSO4, and the
solvent was removed under reduced pressure. The crude
product was purified by column chromatography on silica gel
[eluent: cyclohexane/ethyl acetate (3:1)] to give the product (Rf =
0.5) as an off-white crystalline powder in 85% yield (94 mg). The
analytical data are in accordance with the published ones.[75]
Specific optical roation: (−)-(Rp)-L1: [훼]2퐷0 = −286.2° mL dm−1 g−1
(c = 4.23 g/L, THF), (+)-(Sp)-L1: [훼]2퐷0 = +290.6° mL dm−1 g−1 (c
= 4.25 g/L, THF).
Synthesis
of
[(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}](OTf)4,
[(dppp)2Pd2{(Rp)-Lnit}2](OTf)4
and
[(dppp)2Pd2{(Sp)-
Lnit}2](OTf)4:
(rac)-, (Sp)-, or (Rp)-L1 (5 mg, 19.4 μmol) was dissolved in
0.4 mL CD3NO2. To this, a solution of [(dppp)Pd(OTf)2] (15.8 mg,
19.4 μmol) in 0.4 mL CD3NO2 was added. The solution turned
pale yellow indicating the formation of the complex. The solution
was characterized by NMR spectroscopy.
Analytical data of [(dppp)2Pd2{(Rp)-Lnit}2]OTf4 and its enantiomer
obtained from optically pure ligands (Rp)-Lnit and (Sp)-Lnit,
respectively: 1H-NMR (499 MHz, CD3NO2, 298 K): δ = 7.89-7.79
(m, 16 H, Hdppp(phenyl)), 7.71-7.64 (m, 8 H, Hdppp(phenyl)), 7.61-7.54
(m, 16 H, Hdppp(phenyl)), 6.85-6.78 (m, 8 H, H-8, H-13, H-5, H-16,
H-7, H-12), 3.28-3.06 (m, 16 H, H-1, H-2, H-9, H-10), 2.97-2.89
(m, 8 H, PCH2CH2CH2P), 2.53-2.37 (m, 4 H, PCH2CH2CH2P).
DOSY: D = 5.42 × 10−6 cm2 s−1. 31P-NMR (202 MHz, CD3NO2,
298 K): δ = 17.18 (s). 19F-NMR (470 MHz, CD3NO2, 298 K): δ =
−79.26 (s).
Synthesis of (rac)-, (Sp)-, (Rp)-4,15-diformamido[2.2]para-
cyclophane (5):
(rac)- or (Sp)- or (Rp)-4,15-Diamino[2.2]paracyclophane (34 mg,
0.14 mmol) was dissolved in 2 mL of formic acid. The solution
was sonicated for 6 h. After the reaction was completed, the
solution was neutralized with 6 M aqueous NaOH, diluted with
10 mL water and extracted with ethyl acetate (3 x 30 mL). The
combined organic layers were dried with MgSO4, and the solvent
was removed under reduced pressure. The crude product was
purified by column chromatography on silica gel [eluent: ethyl
acetate] to give the product (Rf = 0.8) as a light brown powder in
99% yield (41 mg). 1H-NMR (500 MHz, DMSO-d6, 363 K >
Analytical data for [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}](OTf)4 obtained
1
from (rac)-Lnit: H-NMR (499 MHz, CD3NO2, 298 K): δ = 7.86-
coalescence temperature): δ = 9.24 (br s, 2 H, H-19), 8.33 (br s,
7.78 (m, 16 H, Hdppp(phenyl)), 7.70-7.64 (m, 8 H, Hdppp(phenyl)), 7.60-
7.54 (m, 16 H, Hdppp(phenyl)), 6.84-6.75 (m, 8 H, H-8, H-13, H-5, H-
16, H-7, H-12), 3.25-3.04 (m, 16 H, H-1, H-2, H-9, H-10), 2.96-
3
2 H, NH-17), 6.90 (br s, 2 H, H-8, H-13), 6.72 (d, 2 H, J7,8
=
3J12,13 = 7.6 Hz, H-7, H-12), 6.33 (br s, 2 H, H-5, H-16), 3.31-3.20
(m, 2 H, H-1, H-2), 2.98-2.87 (m, 4 H, H-9, H-10), 2.81-2.71 (m,
2 H, H-1, H-2). 13C-NMR (75 MHz, DMSO-d6, 298 K): δ = 163.9
(C-18t), 159.0 (C-18m), 158.9 (C-18c), 140.7 (C-4, C-15), 140.6
(C-4, C-15), 139.9 (C-4, C-15), 139.8 (C-4, C-15), 137.1 (C-6, C-
11), 137.1 (C-6, C-11), 137.0 (C-6, C-11), 137.0 (C-6, C-11),
130.9 (C-8, C13), 130.8 (C-8, C13), 130.5 (C-8, C13), 130.1 (C-
8, C13), 129.9 (C-3, C-14), 129.8 (C-3, C-14), 129.7 (C-3, C-14),
129.6 (C-3, C-14), 128.7 (C-7, C-12), 128.4 (C-7, C-12), 128.0
(C-7, C-12), 127.8 (C-7, C-12), 125.6 (C-5, C-16), 125.6(C-5, C-
16), 122.8(C-5, C-16), 122.8(C-5, C-16), 34.2 (C-9, C-10), 34.1
(C-9, C-10), 34.0 (C-9, C-10), 30.7 (C-1, C-2), 30.5 (C-1, C-2),
30.3 (C-1, C-2), 30.2 (C-1, C-2), 30.1 (C-1, C-2). MS (EI) m/z
(intensity %) = 294.1 (95) [M]+., 266,1 (25) [M-CO]+, 147.1 (70)
[M-C9H9NO]+, 132.1 (5) [M-C10H12NO]+, 119.1 (100) [M-
C10H9NO2]+, 104.1 (35) [M-C11H12NO2]+. High resolution MS (EI):
m/z = 294.1368 (calcd. for [C18H18N2O2]+. 294.1368).
2.89 (m,
8
H, PCH2CH2CH2P), 2.52-2.36 (m,
4
H,
PCH2CH2CH2P). DOSY: D = 5.26 × 10−6 cm2 s−1. 31P-NMR
(202 MHz, CD3NO2, 298 K): δ = 17.80 (s). 19F-NMR (470 MHz,
CD3NO2, 298 K): δ = −79.24 (s).
Synthesis
of
[(dppp)2Pd2{(Sp)-Liso}2{(Rp)-Liso}](OTf)4/
[(dppp)2Pd2{(Rp)-Liso}2{(Sp)-Liso}](OTf)4,
[(dppp)3Pd3{(Sp)-
Liso}3](OTf)6, and [(dppp)3Pd3{(Rp)-Liso}3](OTf)6:
(rac)-, (Sp)-, or (Rp)-Liso (5 mg, 19.4 μmol) was dissolved in
0.4 mL CD3NO2. To this, a solution of [(dppp)Pd(OTf)2] (15.8 mg,
19.4 μmol) in 0.4 mL CD3NO2 was added. The solution turned
pale yellow indicating the formation of the complex. The solution
was characterized by NMR spectroscopy and ESI-MS.
Analytical data for [(dppp)3Pd3{(Rp)-Liso}3](OTf)6 and its
enantiomer obtained from (Rp)-Liso and (Rp)-Liso, respectively:
1H-NMR (499 MHz, CD3NO2, 298 K): δ = 7.88-7.79 (m, 12 H,
Synthesis of (rac)-, (Sp)-, (Rp)-4,15-diisocyano[2.2]paracyclo-
phane (Liso):
Hdppp(phenyl)), 7.79-7.66 (m, 18 H, Hdppp(phenyl)), 7.66-7.54 (m, 18 H,
3
Hdppp(phenyl)), 7.54-7.44 (m, 12 H, Hdppp(phenyl)), 6.60 (d, 6 H, J8,7
=
(rac)- or (Sp)- or (Rp)-5 (70 mg, 0.24 mmol) was suspended in an
equal mixture of THF and triethylamine (8 mL). Addition of
0.5 mL (5.52 mmol, 23 equiv.) POCl3 turned the suspension in a
reddish solution which was stirred for 13 h and quenched with
aqueous saturated NaCl (3 mL) and 2 M NaOH (10 mL) under
cooling. The aqueous phase was extracted with ethyl acetate (3
x 20 mL). The combined organic layers were dried with MgSO4,
and the solvent was removed under reduced pressure. The
crude product was purified by column chromatography on silica
gel [eluent: cyclohexane/ethyl acetate (5:1)] to give the product
(Rf = 0.5) as a light yellow crystalline solid in 73% yield (45 mg).
1H-NMR (400 MHz, CDCl3, 298 K): δ = 7.17 (d, 2 H, 3J8,7 = 3J13,12
3J13,12 = 8.6 Hz, H-8, H-13), 6.45 (d, 6H, J7,8 = J12,13 = 8.6 Hz,
4J7,5 = 4J12,16 = 1.8 Hz, H-7, H-12), 5.80 (d, 6 H, 4J5,7 = 4J16,12 = 1.8
Hz, H-5, H-16), 3.30-3.21 (m, 6 H, H-1, H-2, H-9, H-10), 3.09-
2.88 (m, 30 H, H-1, H-2, H-9, H-10, PCH2CH2CH2P), 2.58-2.40
(m, 6 H, PCH2CH2CH2P). DOSY: D = 3.12 × 10-6 cm2 s−1. 31P-
NMR (202 MHz, CD3NO2, 298 K): δ = 1.91 (s). 19F-NMR
(470 MHz, CD3NO2, 298 K): δ = −79.06 (s). MS-ESI (positive,
8 eV) m/z = 555.0 [Pd(dppp)Cl]+, 667.0 [Pd(dppp)(OTf)]+, 683.1
3
3
[Pd2(dppp)2Cl2]+,
811.2
[Pd(dppp)Cl]+,
926.1
[Pd3(dppp)3(Liso)3(OTf)3]3+ and [Pd(dppp)(Liso)(OTf)]+, 1463.7
[Pd3(dppp)3(Liso)3(OTf)3]2+.
Analytical data for the mixture of complexes obtained from (rac)-
= 8.0 Hz, H-8, H-13), 6.61 (dd, 2 H, 3J7,8 = 3J12,13 = 8.0 Hz, 4J7,5
=
Liso 1H-NMR (499 MHz, CD3NO2, 298 K, ratio homochiral :
:
4
4
3J12,16 = 1.9 Hz, H-7, H-12), 6.41 (d, 2 H, J5,7 = J16,12 = 1.9 Hz,
H-5, H-16), 3.49-3.38 (m, 2 H, H-9, H-10), 3.19-2.97 (m, 6 H, H-
9, H-10, H-1, H-2). 13C-NMR (101 MHz, CDCl3, 298 K): δ =
166.1 (C-17), 141.4 (C-3, C-14), 136.7 (C-6, C-11), 133.1 (C-7,
C-12), 131.7 (C-5, C-16), 130.2 (C-8, C-13), 128.8 (C-17), 34.5
heterochiral 1:1.5): δ = 8.03-7.26 (m, Hdppp(phenyl) (homo- and
3
heterochiral)), 6.96 (d, 2 H, J8,7
=
3J13,12 = 8.1 Hz, H-8/H-13
(heterochiral)), 6.74 (dd, 2 H, 3J7,8 = 3J12,13 = 8.1 Hz, 4J7,5 = 3J12,16
= 1.7 Hz, H-7/H-12 (heterochiral)), 6.60 (d, 2 H, J8,7 = J13,12
3
3
=
8
This article is protected by copyright. All rights reserved.

10.1002/chem.201905070
Chemistry - A European Journal
FULL PAPER
8.1 Hz, H-8/H-13(homochiral)), 6.48-6.42 (m, H-7/H-12
were performed using the TURBOMOLE 7.2.1 program package.
The resolution-of-identity (RI) approximation for the Coulomb
integrals[47] was generally applied using the matching default
auxiliary basis sets.[48] The integration of the exchange-
correlation contribution was evaluated on the numerical
quadrature grids m4 for PBEh-3c and PBE0. The default
convergence criteria for single-point energies were 10−7 Eh. For
the conductor-like screening model for real solvents (COSMO-
RS) free energy, two single-point calculations with BP86/TZ (one
in gas-phase and one in an ideal conductor) have to be
performed. The output of these calculations is then processed
by the COSMOtherm program.[49]
(homochiral), H-7’/H-12’ (heterochiral), H-8’/H-13’ (heterochiral)),
3
6.37 (d, 2 H, J8,7
=
3J13,12 = 8.1 Hz, H-8”/H-13” (heterochiral),
6.31 (d, 2 H, 4J5,7 = 4J16,12 = 1.8 Hz, H-5/H-16 (heterochiral)), 6.26
3
3
4
3
(dd, 2 H, J7,8 = J12,13 = 8.1 Hz, J7,5 = J12,16 = 1.7 Hz, H-7”/H-
12”(heterochiral)), 5.93 (d, 2 H, 4J5,7 = 4J16,12 = 1.8 Hz, H-5’/H-16’
4
(heterochiral)), 5.80 (d, 2 H, J5,7
(homochiral)), 5.61 (d, 2 H, J5,7
=
4J16,12 = 1.8 Hz, H-5/H-16
=
4J16,12 = 1.8 Hz, H-5”/H-16”
4
(heterochiral)), 3.32-3.29 (m, Hethylbridges, PCH2CH2CH2P (homo-
and heterochiral)), 2.60-2.39 (m, PCH2CH2CH2P (homo- and
heterochiral)). DOSY: D = 3.20 × 10-6 cm2 s−1. 31P-NMR
(202 MHz, CD3NO2, 298 K, ratio homochiral : heterochiral 1:1.5):
δ = 2.12 (s (heterochiral)), 1.95 (d, 2JP,P = 18.1 Hz (heterochiral)),
1.94 (s (homochiral)), 1.69 (d, 2JP,P = 18.1 Hz (heterochiral)). 19F-
NMR (470 MHz, CD3NO2, 298 K): δ = −79.03 (s). MS-ESI
Crystallographic details:
Data for (Sp)-Lnit, (Sp)-Liso and [(dppp)Pd{(Rp)-Lnit}]n(OTf)2n were
collected on a Bruker D8 Venture diffractometer, equipped with
a low temperature device (Cryostream 800er series, Oxford
Cryosystems, Oxford) using mirror-monochromated CuKα
radiation (λ = 1.54184 Å) of MoKα radiation (λ = 0.71073 Å).
Intensities were measured by fine-slicing φ- and ω-scans and
corrected for background, polarization and Lorentz effects.
Semi-empirical absorption corrections were applied for all data
sets following Blessing’s method.[50] The structures were solved
by intrinsic phasing methods[51] and refined anisotropically by the
(positive, 8 eV) m/z
=
555.0 [Pd(dppp)Cl]+, 667.0
[Pd(dppp)(OTf)]+, 683.1 [Pd2(dppp)2Cl2]+, 811.2 [Pd(dppp)Cl]+,
926.1 [Pd3(dppp)3(Liso)3(OTf)3]3+ and [Pd(dppp)(Liso)(OTf)]+,
1463.7 [Pd3(dppp)3(Liso)3(OTf)3]2+.
Computational details
All spectra calculations were performed for the Rp-enantiomer.
Two approaches were pursued for the calculation of the UV-Vis
and ECD spectra of L1. First, a single structure of L1 was
prepared and optimized using the composite method PBEh-3c
and the implicit solvation model COSMO(ε=36.6). On the
least-squares
procedure
implemented
in
the
ShelX
programsystem.[52] The hydrogen atoms were included
isotropically using the riding model on the bound carbon atoms.
optimized
geometry
a
sTD-CAM-B3LYP/def2-TZVP[38]
calculation including proceeding ground state calculation was
performed using sTD-DFT[21] as implemented in ORCA 4.0.1.[39]
The length form of the electric dipole transition moment is
employed for the absorption spectra whereas the velocity form is
used for the ECD spectra, which is guaranteeing gauge origin
independence. The computed spectra (UV-Vis and ECD) are
Data
[(dppp)Pd{(Sp)-Liso}]n(OTf)2n were collected on an Agilent
SuperNova Dual diffractometer, equipped with low
temperature device (Cryostream 700, Oxford Cryosystems,
Oxford) using mirror-monochromated CuKα radiation (λ
1.54184 Å). CrysAlisPro[51] software was used for data collection
for
[(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}]n(OTf)4n
and
a
=
redshifted by 0.2 eV to roughly match the experimental spectrum. and reduction as well as applying numerical absorption
In the second approach, conformational flexibility is considered
for the spectrum by generating snapshots from a GFN1-
xTB/GBSA(acetonitrile)[40] molecular dynamics simulation (at
298 K , using Hmass = 4 amu, timestep(dt/fs) = 1.0, mdtime =
1000 ps, and using the SHAKE algorithm). From the molecular
dynamic simulation the equilibration phase was removed and
200 equidistant snapshots were obtained. On these, sTD-BH-
LYP/def2-SVP/COSMO(ε=36.6)[41] calculations were performed
using the Turbomole 7.0.2 program package[42] and the sTDA
standalone program.[43] The computed spectra (UV-Vis and
ECD) are red-shifted by 0.4 eV to roughly match the
experimental spectrum. Free energies as discussed in the main
text were calculated using the following protocol: all geometries
were prepared manually and pre-optimized with the
correction based on gaussian integration. The structure was
solved by a dual-space algorithm using SHELXT-2014/5[52] and
refined by full-matrix least squares on F2 using SHELXL-
2017/1[53] within Olex2[54] and WinGX[55] environments. All non-
hydrogen atoms were refined anisotropically. All carbon-bound
hydrogen atoms were calculated to their optimal positions and
treated as riding on the parent atoms using isotropic
displacement parameters 1.2 (or 1.5 in case of methyl groups)
times larger than the respective parent atoms. Appropriate
geometry restraints were applied to the anions, making the 1,2-
and 1,3-distances equal. Rigid bond restraints were applied to
the atomic displacement parameters of the anions and solvents.
Triflate anions in [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}]n(OTf)4n were
found to exhibit both substitutional and positional disorder, and
were modelled accordingly, with their relative occupancies freely
refined and the similarity restraints applied to their atomic
displacement parameters.
semiempirical
quantum
chemical
method
GFN2-
xTB/GBSA(CH3CN)[34]
.
The geometries were subsequently
optimized with the composite method PBEh-3c[33] and the
implicit solvation model DCOSMO-RS(NO2CH3) using the
Turbomole program package. On the optimized geometries free
energies are calculated using a multilevel approach[44]. High
level single-point energies were calculated with the hybrid
density functional PBE0[29] in a large def2-QZVP[30] basis set.
The (long-range) London dispersion not accounted for by the
density functional was computed with the DFT-D4[31] method at
default settings. Solvation contributions to free energy were
calculated with COSMO-RS[32]. This term includes the volume
work RTln(Videal) to go from an ideal gas at 1 bar to 1 mol/L.
Thermostatistical contributions to free energy were calculated
using GFN2-xTB/ GBSA(CH3CN) and the slightly modified
RRHO-scheme (interpolation between the rigid-rotor- to the
harmonic-oscillator is applied at low-lying frequencies, see
Ref[44]). The total free energies are then calculated as the sum of
Crystallographic data and refinement parameters are shown in
Table 3.
CCDC-1824416 and CCDC-1824417 contain the supplementary
data
for
[(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}]n(OTf)4n
and
[(dppp)Pd{(Sp)-Liso}]n(OTf)2n. CCDC-1955599-1955601 contain
the supplementary data for (Sp)-Lnit, (Sp)-Liso and
[(dppp)Pd{(Rp)-Lnit}]n(OTf)2n. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/structures.
the
single-point
energy,
dispersion
contribution,
thermostatistical- and solvation contribution. The B3LYP/QZ-
SMD[45] single-point calculations were performed with the ORCA
4.1.0 with convergence criteria for single point energies: 1.0·10−6
Eh. All DFT (except for the B3LYP[46] single-point) calculations
9
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10.1002/chem.201905070
Chemistry - A European Journal
FULL PAPER
Table 3: Crystallographic data for (Sp)-Lnit, (Sp)-Liso, [(dppp)Pd{(Rp)-Lnit}]n(OTf)2n, [(dppp)2Pd2{(Sp)-Lnit}{(Rp)-Lnit}]n(OTf)4n and [(dppp)Pd{(Sp)-
Liso}]n(OTf)2n
Compound
(Sp)-Lnit
(Rp)-Liso
[(dppp)2Pd2
{(Sp)-Lnit}
{(Rp)-Lnit}]n(OTf)4n
1824416
[C45H40N2P2Pd]2+
2(CF3SO3)−
1075.27
123.0(1)
Cu-Kα
1.54184
orthorhombic
Fdd2
51.7823(8)
23.0531(3)
15.9229(3)
90
[(dppp)Pd
[(dppp)Pd
{(Rp)-Lnit}]n(OTf)2n
{(Sp)-Liso}]n(OTf)2n
CCDC Number
Empirical formula
1955599
C18H14N2
1955600
C18H14N2
1955601
1824417
[C48H42Cl2F6N2O6P2 [C45H40N2P2Pd]2+
PdS2]
1160.19
100
2(CF3SO3)− C2H3N
1116.32
123.0(1)
Cu-Kα
1.54184
orthorhombic
P212121
11.0937(2)
16.2458(3)
26.8214(6)
90
M [g mol−1]
T [K]
Radiation type
λ [Å]
Crystal system
Space group
Unit cell parameters
258.31
100
Cu-Kα
1.54178
orthorhombic
P212121
258.31
100
Cu-Kα
1.54178
orthorhombic
P212121
7.3476(4)
12.5435(8)
14.3903(9)
90
Mo-Kα
0.71073
orthorhombic
P212121
10.9490(14)
16.206(2)
27.128(3)
90
a [Å] 7.3642(5)
b [Å] 12.3891(10)
c [Å] 14.3728(11)
α [°] 90
β [°] 90
γ [°] 90
1311.31(17)
4
90
90
90
90
90
90
90
90
Vunit cell [Å3]
Z
1326.28(14)
4
1.294
multi-scan
0.595
19007.8(5)
16
1.503
gaussian
5.258
4813.6(10)
4
1.601
multi-scan
0.725
4833.91(17)
4
1.534
gaussian
5.186
ρcalcd [gcm−3]
Absorption correction
Absorption coefficient
µ [mm−1]
1.308
multi-scan
0.602
Min. and max. transmission
F(000)
0.3762, 0.7535
544.0
0.4073, 0.7536
544.0
0.469, 0.738
8736.0
0.5689, 0.7459
2352.0
0.605, 0.846
2272.0
Crystal color
clear colorless
0.30×0.16×0.05
9.424 to 135.482
16145 [0.0542]
2377
99.9
2377/181/0
1.069
R1 = 0.0372
wR2 = 0.0929
R1 = 0.0378
wR2 = 0.0936
0.23/−0.29
clear colorless
0.11×0.07×0.05
9.352 to 134.958
3883 [0.0235]
2109
95.6
2109/182/0
1.077
R1 = 0.0325
wR2 = 0.0811
R1 = 0.0345
wR2 = 0.0824
0.15/−0.19
pale yellow
0.258×0.103×0.069 0.21×0.06×0.05
6.828 to 149.028
73632 [0.0386]
9333
100.0
9592/741/955
1.048
R1 = 0.0368
wR2 = 0.0960
R1 = 0.0387
wR2 = 0.1002
1.085/−0.583
clear colorless
pale yellow
0.153×0.115×0.034
8.550 to 148.196
15248 [0.0401]
7804
99.2
9334/624/214
1.065
R1 = 0.0538
wR2 = 0.1358
R1 = 0.0678
wR2 = 0.1459
1.843/−0.671
Crystal size [mm3]
2θ range for data coll. [°]
Reflections collected [R(int)]
Reflections [I>2σ(I)]
Data completeness [%]
Data/parameters/restraints
Goodness-of-fit on F2
Final R indices [I>2σ(I)]
4.49 to 55.998
92605 [0.1572]
11632
99.9
11632/632/0
1.026
R1 = 0.0534
wR2 = 0.0995
R1 = 0.1208
wR2 = 0.1214
1.56/−1.57
Final R indices [all data]
Largest diff. peak/hole
[e Å−3]
Flack parameter x
P2(true) value
Torsion angles binding units [°] 119.81
0.3(2)
0.990
0.1(7)
1.000
117.94
−0.016(4)
0.004(14)
1.000
−132.66
−0.036(7)
−129.92
125.57
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Acknowledgements
Financial support from DFG (SFB 813 – Chemistry at Spin
Centers) and the Academy of Finland (K.R.: project no’s.
263256, 292746 and 265328) is gratefully acknowledged. N.S.
thanks Evonik Foundation for a doctoral scholarship and the
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Keywords: supramolecular chemistry • self-assembly • nitrile
ligands • isonitrile ligands • self-sorting
#
current address: Arlanxeo Netherlands B.V., Urmonderbaan 24, 6167
RD Geleen, The Netherlands
‡
current address: McGill University, Department of Chemistry, 801
Sherbrooke St. West, Montreal, Qc H3A 0B8, Canada
10
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Chemistry - A European Journal
FULL PAPER
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Entry for the Table of Contents
Layout 1:
FULL PAPER
Two isostructural ligands with either
L. Volbach, N. Struch, F. Bohle, F. Topić,
G. Schnakenburg, A. Schneider, K.
Rissanen, S. Grimme, A. Lützen*
nitrile (Lnit) or isonitrile (Liso) moieties
attached to
a [2.2]paracyclophane
backbone have been synthesized.
Surprisingly, the resulting discrete
Page No. – Page No.
metallosupramolecular
aggregates
Influencing the self-sorting behavior
of [2.2]paracyclophane based ligands
by introducing isostructural binding
motifs
formed in solution upon coordination
of [(dppp)Pd(OTf)2] differ in their
composition and in their chiral self-
sorting behavior. Upon crystallization
these discrete aggregates undergo
structural
transformation
to
coordination polymers.
13
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