A Rotaxane-like Cage-in-Ring Structural Motif for a Metallosupramolecular Pd6L12 Aggregate

Article abstract of DOI:10.1002/anie.201806814

A BODIPY-based bis(3-pyridyl) ligand undergoes self-assembly upon coordination to tetravalent palladium(II) cations to form a Pd₆L₁₂ metallosupramolecular assembly with an unprecedented structural motif that resembles a rotaxane-like cage-in-ring arrangement. In this assembly the ligand adopts two different conformations—a C-shaped one to form a Pd₂L₄ cage which is located in the center of a Pd₄L₈ ring consisting of ligands in a W-shaped conformation. This assembly is not mechanically interlocked in the sense of catenation but it is stabilized only by attractive π-stacking between the peripheral BODIPY chromophores and the ligands’ skeleton as well as attractive van der Waals interactions between the long alkoxy chains. As a result, the co-arrangement of the two components leads to a very efficient space filling. The overall structure can be described as a rotaxane-like assembly with a metallosupramolecular cage forming the axle in a metallosupramolecular ring. This unique structural motif could be characterized via ESI mass spectrometry, NMR spectroscopy, and X-ray crystallography.

Full text of DOI:10.1002/anie.201806814

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Accepted Article
Title: A New Rotaxane-like Cage-in-Ring Structural Motif for a
Metallosupramolecular Pd6L12 Aggregate
Authors: Matthias Käseborn, Julian J. Holstein, Guido H. Clever, and
Arne Lützen
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201806814
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10.1002/anie.201806814
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A New Rotaxane-like Cage-in-Ring Structural Motif for a
Metallosupramolecular Pd6L12 Aggregate
Matthias Käseborn,[a] Julian J. Holstein,[b] Guido H. Clever,[b]* Arne Lützen[a]*
Dedicated to Prof. Karl Heinz Dötz on the occasion of his 75th birthday
Abstract: A BODIPY-based bis(3-pyridyl) ligand undergoes self-assembly
upon coordination to tetravalent palladium(II) cations to form a Pd6L12
metallosupramolecular assembly with an unprecedented structural motif
that resembles a rotaxane-like cage-in-ring arrangement. In this assembly
the ligand adopts two different conformations – a C-shaped one to form a
Pd2L4 cage which is located in the center of a Pd4L8 ring consisting of
ligands in a W-shaped conformation. This assembly is not mechanically
interlocked in the sense of a catenation but it is stabilized only by attractive
π-stacking between the peripheral BODIPY chromophores and the ligands’
skeleton as well as attractive van-der-Waals interactions between the long
alkoxy chains. As a result, the co-arrangement of both components leads to
a very efficient filling of space. The overall structure can be described as a
chiral rotaxane-like assembly with a metallosupramolecular cage forming
the axle in a metallosupramolecular ring. This unique structural motif
could be characterized via ESI mass spectrometry, NMR spectroscopy, and
X-ray crystallography.
diaza-s-indacene (BODIPY) based bis(3-pyridyl) ligand L carrying an
additional peripheral alkoxy group that was supposed to form a Pd2L4
aggregates with an assumed Pd-Pd distance of ca. 2.3 nm. Ligand L
was synthesized via Sonogashira cross-coupling (Scheme 1) from
terminal alkyne 1 and diiodinated BODIPY 2 which could be prepared
in four and three steps, respectively (see SI).
Coordination-driven self-assembly has developed into one of the most
powerful strategies to gain access to nanoscopic objects with
interesting material properties.[1] One of the best studied and most
reliable approaches in this respect is the use of tetravalent PdII and PtII
ions and bridging divalent ligand motifs to access three dimensional
MnL2n aggregates.[2] Usually, the outcome of such self-assembly
processes can be predicted in terms of composition, shape, and size in a
rather reliable manner by assuming that the smallest aggregate should
result that obeys the maximum site occupancy rule and does not
experience too much steric stress. In this way, the assembly of
astonishing metallosupramolecular architectures ranging from cage-
Scheme 1. Synthesis of BODIPY-ligand L and L’.
[4]
like M2L4 complexes[2d,3] all the way up to giant M24L48 or even
M30L60 metallosupramolecular spheres[5] has been reported.
When we then mixed two equivalents of ligand L with one equivalent
of [Pd(CH3CN)4](BF4)2 in [D3]-acetonitrile/[D2]-dichloromethane and
heated this solution for four hours we were surprised to receive an ESI
Banana-shaped bridging ligands carrying 3-pyridyl coordination
groups usually self-assemble into PdII2L4 cages upon treatment with
PdII ions and these cages have found wide applications in, e.g., host-
guest chemistry, sensors or drug delivery.[2d,3,6] Recently, there have
also been a few reports where chromophores were integrated into
palladium organic assemblies in an unique spatial orientation which
gives rise to some exciting optical properties.[7] In order to make a first
contribution to this field we designed a 4,4-difluoro-4-bora-3a,4a-
mass spectrum that showed the exclusive formation of
a
[Pd6L12](BF4)12 rather than the expected [Pd2L4](BF4)4 aggregate as
indicated by a complete series of four- to twelve-fold positively
charged ions with a weight of more than 12 kDa (see SI).[8,9]
In fact, hexanuclear assemblies of tetravalent palladium(II) ions are
still rare, and there are only three different types of published structures
for such aggregates (Figure 1): The first one is a cube-shaped
aggregate in which V-shaped ligands bridge the metal ions that are
located on the faces of the cube (Figure 1a).[10] This kind of assembly
has only been observed with ligands containing 4-pyridyl or 1-
imidazolyl groups as metal binding motifs but not with 3-pyridyl
groups. A similar and topologically equivalent arrangement has been
reported for rod-like ligands with 3-pyridyl groups but they form
assemblies with an octahedral arrangement of the metal ions where the
M. Käseborn, Prof. Dr. A. Lützen
Rheinische Friedrich Wilhelms-Universität Bonn
Kekulé-Institut für Organische Chemie und Biochemie
Gerhard-Domagk-Straße 1, 53121 Bonn (Germany)
E-mail: arne.luetzen@uni-bonn.de
Dr. J. J. Holstein, Prof. Dr. G. H. Clever
Technische Universität Dortmund
ligands are located on the edges of the octahedron (Figure 1b).[11]
A
Fakultät für Chemie und Chemische Biologie
Otto-Hahn-Straße 6, 44227 Dortmund (Germany)
E-Mail: guido.clever@tu-dortmund.de
further possibility is a crown-like arrangement with neighboring metals
bridged by two ligands, each, and such a metallamacrocycle has
recently been reported (Figure 1c).[12] Banana-shaped ligands, however,
are also well known for forming mechanically interlocked structures
where two M2L4 cages are catenated with each other.[13] Such structures
Supporting information for this article is given via a link at the end of the
document.
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are usually a result of anion template effects where anions are
encapsulated within the interpenetrated cages. Similarly, Pd6L6Br6
triple-catenated structures have also been reported recently.[14]
Accordingly, one could also assume catenation of three Pd2L4 cages
which can appear in two different ways – either with an interlocking of
all three rings into each other (Figure 1d) or the two outer cages being
interlocked only with the central cage but not with each other (Figure
1e). The latter two structural motifs, however, have not been reported
so far.
Hence, we performed additional 19F NMR experiments to elucidate
whether some of the tetrafluoroborate anions experience any special
effects associated with encapsulation of single anions in the voids of
cages as it is usually the case in the catenated structures. Interestingly,
we observed only
a single signal at –150.9 ppm for the
tetrafluoroborate indicative for non-coordinated tetrafluoroborate, and
hence, no encapsulation of the counterion into the assembly.
Unexpectedly, however, the signals of the BODIPY fluorine nuclei
were split into three sets (see SI). Therefore, we also excluded the two
catenated structures which meant that our assembly should have a
completely different structure.
Figure 1. Schematic illustration of different Pd L12 aggregates. a) nanocage I: Pd(II)
6
ions on the faces of a cube bridged by V- or banana-shaped ligands, b) nanocage II:
Pd(II) ions at the vertices of an octahedron bridged by rod-like ligands, c) crown-like
metallamacrocycle, d) and e) isomeric {Pd
2
L
4
}3 triple catenanes.
The structural motifs shown above differ considerably concerning their
symmetry, and hence, NMR spectroscopy is a versatile tool to obtain
further information about the aggregate. Again we obtained quite
1
unexpected results. The H NMR spectra show a rather complex yet
still well defined set of signals that contains many more signals as the
ligand itself (Figure 2, SI). 2D H,1H COSY, 2D H,13C HMQC and
HMBC, 2D 1H,1H NOESY and 2D 1H DOSY NMR experiments
confirmed that all these signals belong to a single species more likely
than to a mixture of assemblies. Hence, we can conclude that our
aggregate neither has the cube-like, nor the octahedral, nor the crown-
like metallamacrocyclic structure as those should all give rise to rather
simple spectra that contain the same number of signals as that of the
free ligand itself due to their high symmetry.
1
1
Figure 2. 1H NMR spectra (700.1 MHz at 298 K) of a) the complex resulting from a
2:1 mixture of L and [Pd(CH
3
CN)
4
](BF
4
)2
in [D
3
]-acetonitrile / [D ]-dichloromethane
2
(5:1) and b) pure ligand L in [D
2
]-dichloromethane.
The fact that we observe a splitting of the pyridine signals into three
sets of exactly the same intensity and some of the signals of the
BODIPY protons experience a huge upfield shift and splitting would,
in principle, be in accordance with the catenated triple cages. However,
we were still reluctant to assign this structural motif to our aggregate
because of the results of the DOSY NMR experiments. These indicate
that the size of our aggregate should be larger (hydrodynamic radius
calculated according to the Stokes-Einstein equation of 2.2 nm, see SI)
than expected for the condensed catenated triple cage depicted in
Figure 1d) (estimated value for the hydrodynamic radius from a
molecular model 1.8-1.9 nm, see SI) but smaller than assumed for the
more extended catenated triple cage shown in Figure 1e) (expected
value by molecular modelling of approx. 2.6-2.7 nm, see SI). However,
one has to take into account that determining experimental values
calculated on the basis of DOSY experiments is always difficult for
non-spherically-shaped aggregates especially when they contain
flexible alkyl chains in the periphery and come as ions loosely
interacting with their counterions. Furthermore, one has to consider
that the experiments were performed in a mixed solvent whose
viscosity can only be estimated.
Fortunately, we were able to grow single crystals of our Pd6L12
aggregate by slow diffusion of benzene into the NMR solution, but
diffusing benzene into a solution of the complex in DMF yielded
higher quality crystals. Due to very weak scattering power of both
solvates, synchrotron radiation of DESY beamline P11[15] was
employed to achieve a resolution of 1.4 Å, which was just sufficient to
solve both structures with direct methods using SHELXT.[16] In both
cases our [Pd6(L)12] complex assembles in the same unprecedented
structural motif as exemplarily shown in Figure 3 for the DMF/benzene
solvate: it consists of two parts - a “common” Pd2L4 cage in the center
of the structure which is embedded in a crown-like metallamacrocyclic
Pd4L8 complex, and hence, is best described as a metallosupra-
molecular {[Pd2L4]@[Pd4L8]} aggregate. The asymmetric unit of
̅
triclinic space group P1 contains half of the aggregate. In the other
̅
case the asymmetric unit of triclinic space group P1 contains two half
aggregates, which are independent of each other. Due to minor
twinning, diffraction data is of lower quality and we therefore only
discuss the DMF/benzene solvate here. Pd-Pd distances are 23.6 Å in
the [Pd2L4] cage, 27.9 and 28.0 Å for neighboring Pd ions in the
[Pd4L8] ring and 39.5 Å for the diagonal Pd-Pd distance of the [Pd4L8]
ring. In order to form these two components ligand L has to adopt two
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Figure 3. Structure of the {[Pd
2
L
4
]@[Pd
4
L
8
]}(BF
4
)12 aggregate as determined by X-ray diffraction analysis (counterions, solvent molecules, and hydrogen atoms are omitted and
alkoxy chains have been truncated to methoxy groups for clarity): a) and b) structure of the cationic {[Pd
2
L
4
]@[Pd
4
L
8
]} unit in two different orientations; the inner [Pd
2
L4] cage is
highlighted in a transparent space filling model in red, color code: C grey (red in [Pd
cage-in-ring structural motif.
2
L
4
]), N blue, O red, B light-blue, Pd orange). c) schematic representation of the rotaxane-like
different conformations – a phenomenon that has rarely been observed
in self-assembled structures so far.[11a,17] In the cage-like Pd2L4 part the
ligand adopts a C-shaped conformation where its BODIPY moieties
are oriented in exohedral positions pointing towards the surrounding
Pd4L8 ring whereas the long alkoxy chains are pointing inwards filling
the cage’s void. The macrocylic Pd4L8 part resembles the shape of a
attractive forces, often requires several hours or even days of heating to
finally give rise to the thermodynamic most stable aggregate;[10a,19] the
complex structure here, however, turned out to be formed already after
five to ten minutes at room temperature (see SI). Mass spectrometric
studies of cooled solutions further support this as we could only detect
signals of ions corresponding to [Pd2L4] and {[Pd2L4]@[Pd4L8]}
four-pointed star in which the ligand
L
adopts
a
W-shaped
aggregates or fragments thereof but none corresponding to a
conformation. Thus, the BODIPY groups are now in endohedral
positions whereas the alkoxy chains are located in exohedral positions.
This makes the two parts perfectly complementary to form the
observed interpenetrated rotaxane-like structure: The Pd4L8 part offers
four clefts in which the exohedral BODIPY chromophores of the Pd2L4
can nicely intercalate to undergo attractive -stacking with mean
distances between the BODIPYs and the ligands’ skeletons of 3.5-4.0
Å. On the other hand the ligand skeleton of the Pd2L4 cage also offers
attractive π-stacking sites to interact with the endohedral oriented
BODIPY groups of the Pd4L8 ring. Overall this gives rise to a unique
chiral rotaxane-like structural arrangement in which the extended π-
conjugated parts of the ligand are mechanically interpenetrated without
being catenated.[18]
This fits perfectly to all of our mass spectrometric and NMR
spectroscopic observations and explains the initially unexpected
splitting of the signals arising from the pyridine and BODIPY protons
due to their fixation in distinct different spatial environments. In fact,
NMR experiments showed that the complexation of the
{[Pd2L4]@[Pd4L8]} aggregate happened extremely fast, indicating a
huge additional driving force due to these interactions besides the
formation of metal-ligand interaction. Even when the self-assembly of
comparable complicated structures, relying only on such weak
tetranuclear [Pd4L8] aggregate shortly after mixing the components.
This indicates that the [Pd2L4] cage might act as a template for the
formation of this unique hexanuclear aggregate (see SI).
Interestingly, the absorption behavior of the ligand’s chromophores
seems not to be affected much by the formation of the aggregate.
However, the emission behavior is affected by the presence of the
palladium ions that largely quench the luminescence, but not
completely (see SI).[20]
In summary, we prepared a bis(3-pyridyl) ligand L furnished with
a long alkoxy chain and a BODIPY moiety. Upon treatment with
tetravalent palladium(II) ions in
a mixture of acetonitrile and
dichloromethane or DMF and benzene this ligand self-assembles in a
chiral hexanuclear metallosupramolecular aggregate whose
unprecedented structural motif is best be described as a rotaxane-like
cage-in-ring {[Pd2L4]@[Pd4L8]}(BF4)12 aggregate. Within this structure
the ligand adopts two different conformations in the two
metallosupramolecular units – a C-shaped one in the [Pd2L4] complex
and a W-shaped one in the [Pd4L8] complex, respectively. Obviously,
the overall structure is a result of the perfect geometrical and
interactional complementarity of the cage-like [Pd2L4] and the
macrocyclic [Pd4L8] entities. Literally, this can be compared to the
self-assembly of a key which then templates the self-assembly of its
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aggregates seems to grow when we diluted the pure DMF solution with
dichloromethane to perform ESI MS experiments: here, we also found
aggregates of the dinuclear cage with an additional ligand and then also the
own lock in a very efficient manner – and all of this from only two
individual molecular building blocks. Future studies will evaluate if
this cage-in-ring structure is a more general motif that might be applied
to the assembly of supramolecular architectures with different alkoxy
or related groups and/or other chromophores and may be even two
different ones to investigate chromophore-chromophore interactions in
such a confined geometric arrangement.
Pd
6
L12 assembly. This agrees well with the fact that we were also able to
crystallize the Pd
6
L12 assembly form a mixture of DMF and benzene.
[10]
[11]
a) K. Suzuki, M. Tominaga, M. Kawano, M. Fujita, Chem. Commun. 2009,
1638–1640. b) C. Gütz, R. Hovorka, C. Klein, Q.-Q. Jiang, C. Bannwarth, M.
Engeser, C. Schmuck, W. Assenmacher, W. Mader, F. Topić, K. Rissanen, S.
Grimme, A. Lützen, Angew. Chem. 2014, 126, 1719–1724; Angew. Chem.
Int. Ed. 2014, 53, 1693–1698. c) B. Roy, R. Saha, A. K. Ghosh, Y. Patil, P. S.
Mukherjee, Inorg. Chem. 2017, 56, 3579–3588. d) M. Han, R. Michel, G. H.
Clever, Chem. Eur. J. 2014, 20, 10640–10644.
a) M. D. Wise, J. J. Holstein, P. Pattison, C. Besnard, E. Solari, R. Scopelliti,
G. Bricogne, K. Severin, Chem. Sci. 2015, 6, 1004–1010. b) P. Howlader, S.
Mukherjee, R. Saha, P. S. Mukherjee, Dalton Trans. 2015, 44, 20493–20501.
T. Zhang, L.-P. Zhou, X.-Q. Guo, L.-X. Cai, Q.-F. Sun, Nat. Commun. 2017,
8, 15898.
a) M. Frank, M. D. Johnstone, G. H. Clever, Chem. Eur. J. 2016, 22, 14104–
14125. b) G. H. Clever, P. Punt, Acc. Chem. Res. 2017, 50, 2233–2243.
R. Zhu, J. Lübben, B. Dittrich, G. H. Clever, Angew. Chem. 2015, 127, 2838–
2842; Angew. Chem. Int. Ed. 2015, 54, 2796–2800.
A. Burkhardt, T. Pakendorf, B. Reime, J. Meyer, P. Fischer, N. Stübe, S.
Panneerselvam, O. Lorbeer, K. Stachnik, M. Warmer, P. Rödig, D. Göries
and A. Meents, Eur. Phys. J. Plus, 2016, 131, 56.
Acknowledgements
[12]
[13]
[14]
[15]
We thank Laura Schneider, Robin Rudolf and Karin Peters-
Pflaumbaum for help with ESI-MS measurements.
This work has been supported by the Deutsche
Forschungsgemeinschaft (GC489/2-2).
Diffraction data was collected at PETRA III at DESY, a member of the
Helmholtz Association (HGF). The authors thank Dr. Anja Burkhardt
for assistance in using synchrotron beamline P11 (I-20160736).[15]
[16]
[17]
G. M. Sheldrick, Acta Cryst. A, 2015, 71, 3–8.
C. Klein, C. Gütz, M. Bogner, F. Topić, K. Rissanen, A. Lützen, Angew.
Chem. 2014, 126, 3814–3817; Angew. Chem. Int. Ed. 2014, 53, 3739–3742.
[18]
The alkoxy chain proved to be important to obtain the Pd L12 complex as we
6
have also tested a ligand lacking this group which does not form this type of
hexanuclear aggregate but rather a mixture of aggregates containing dinuclear
species as the main components (see SI).
a) M. Yoneya, T. Yamaguchi, S. Sato, M. Fujita, J. Am. Chem. Soc. 2012,
134, 14401–14407. b) M. Yoneya, S. Tsuzuki, T. Yamaguchi, S. Sato, M.
Fujita, ACS Nano 2014, 8, 1290–1296.
Keywords: self-assembly • BODIPY • palladium complexes •
metallosupramolecular chemistry • π-π-interaction
[19]
[20]
[1]
Some recent reviews: a) c) Y. Inokuma, M. Kawano, M. Fujita, Nat. Chem.
2011, 3, 349–358. b) R. Chakrabarty, P. S. Mukherjee, P. J. Stang, Chem.
Rev. 2011, 111, 6810–6918. c) R. S. Forgan, J.-P. Sauvage, J. F. Stoddart,
Chem. Rev. 2011, 111, 5434–5464. d) H. Amouri, C. Desmarets, J. Moussa,
Chem. Rev. 2012, 112, 2015–2041. e) N. J. Young, B. P. Hay, Chem.
Commun. 2013, 49, 1354–1379. f) T. K. Ronson, S. Zarra, S. P. Black, J. R.
Nitschke, Chem. Commun. 2013, 49, 2476–2490. g) T. R. Cook, Y.-R.
Zheng, P. J. Stang, Chem. Rev. 2013, 113, 734–777. h) M. D. Ward, P. R.
Raithby, Chem. Soc. Rev. 2013, 42, 1619–1636. i) M. M. J. Smulders, I. A.
Riddell, C. Browne, J. R. Nitschke, Chem. Soc. Rev. 2013, 42, 1728–1754. j)
J. G. Hardy, Chem. Soc. Rev. 2013, 42, 7881–7899. k) S. Mukherjee, P. S.
Mukherjee, Chem. Commun. 2014, 50, 2239–2248. l) C. J. Brown, F. D.
Toste, R, G. Bergmann, K. N. Raymond, Chem. Rev. 2015, 115, 3012–3035.
m) T. R. Cook, P. J. Stang, Chem. Rev. 2015, 115, 7001–7045. n) L. Chen, Q.
Chen, M. Wu, F. Jiang, M. Hong, Acc. Chem. Res. 2015, 48, 201–210. o) S.
Zarra, D. M. Wood, D. A. Roberts, J. R. Nitschke, Chem. Soc. Rev. 2015, 44,
419–432. p) S. H. A. M. Leenders, R. Gramaga-Doria, B. de Bruin, J. N. H.
Reek, Chem. Soc. Rev. 2015, 44, 433–448. q) L.-J. Chen, H.-B. Yang, M.
Shinoya, Chem. Soc. Rev. 2017, 46, 2555–2576.
Please note, that these experiments also revealed that the aggregate is only
stable at concentrations > 4 × 10–8 mol L–1 because we observed recovery of
the BODIPY’s fluorescence at lower concentration as
a result of the
decomposition of the assembly.
[2]
a) M. Fujita, K. Ogura, Bull. Chem. Soc. Jpn. 1996, 69, 1471–1482. b) N. B.
Debata, D. Tripathy, D. K. Chand, Coord. Chem. Rev. 2012, 256, 1831–1945.
c) K. Harris, D. Fujita, M. Fujita, Chem. Commun. 2013, 49, 6703–6712. d)
d) M. Han, D. M. Engelhard, G. H. Clever, Chem Soc Rev 2014, 43, 1848–
1860.
[3]
[4]
A. Schmidt, A. Casini, F. E. Kühn, Coord. Chem. Rev. 2014, 275, 19–36.
a) Q. F. Sun, J. Iwasa, D. Ogawa, Y. Ishido, S. Sato, T. Ozeki, S. Sakamoto,
K. Yamaguchi, M. Fujita, Science 2010, 328, 1144–1147. b) J. Bunzen, J.
Iwasa, P. Bonakdarzadeh, E. Numata, K. Rissanen, S. Sato, M. Fujita,
Angew. Chem. 2012, 124, 3215–3217; Angew. Chem. Int. Ed. 2012, 51,
3161–3163.
[5]
a) D. Fujita, Y. Ueda, S. Sato, N. Mizuno, T. Kumasaka, M. Fujita, Nature
2016, 540, 563–566. b) D. Fujita, Y. Ueda, S. Sato, H. Yokoyama, N.
Mizuno. T. Kumasaka, M. Fujita, Chem. 2016, 1, 91–101.
[6]
[7]
D. Preston, K. F. White, J. E. M. Lewis, R. A. S. Vasdev, B. F. Abrahams, J.
D. Crowley, Chem. Eur. J. 2017, 23, 10559–10567.
a) F. Würthner, A. Sautter, Org. Biomol. Chem. 2003, 1, 240–243. b) V.
Blanco, M. D. García, C. Peinador, J. M. Quintela, Chem. Sci. 2011, 2, 2407–
2416. c) M. Han, R. Michel, B. He, Y.-S. Chen, D. Stalke, M. John, G. H.
Clever, Angew. Chem. 2013, 125, 1358–1362; Angew. Chem. Int. Ed. 2013,
52, 1319–1323. d) X. Yan, T. R. Cook, P. Wang, F. Huang, P. J. Stang, Nat.
Chem. 2015, 7, 342–348. e) F. Kaiser, A. Schmidt, W. Heydenreuter, P. J.
Altmann, A. Casini, S. A. Sieber, F. E. Kühn, Eur. J. Inorg. Chem. 2016,
5189–5196. f) M. L. Saha, X. Yan, P. J. Stang, Acc. Chem. Res. 2016, 49,
2527–2539. g) G. Gupta, A. Das, K. C. Park, A. Tron, H. Kim, J. Mun, N.
Mandal, K.-W. Chi, C. Y. Lee, Inorg. Chem. 2017, 56, 4615–4621.
Please note that we chose low-boiling solvents to facilitate the ESI MS
studies. However, the ligand is not soluble in pure acetonitrile but in
dichloromethane and the palladium salt is not in pure dichloromethane but in
acetonitrile. Hence, dissolving the individual components in good solvents
and then mixing them proved to be successful.
[8]
[9]
Interestingly, we observed the formation of dinuclear cage [Pd
2
L
4
](BF
4
) in
4
pure DMF as proven by NMR experiments (symmetry of the 1H NMR
spectrum and DOSY) and mass spectrometry (see SI). However, the affinity
of the dinuclear cage to the ligand and the tendency to form the hexanuclear
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10.1002/anie.201806814
Angewandte Chemie International Edition
COMMUNICATION
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Metallosupramolecular
Chemistry
A BODIPY-based bis(3-pyridyl) ligand
Matthias Käseborn, Julian J. Holstein,
Guido H. Clever,* Arne Lützen*
__________ Page – Page
undergoes
coordination to tetravalent palladium(II)
cations to form Pd6L12
self-assembly
upon
a
metallosupramolecular assembly with
an unprecedented structural motif that
resembles a rotaxane-like cage-in-ring
arrangement. This assembly is not
mechanically interlocked in the sense of
a catenation but it is stabilized only by
attractive non-covalent interactions.
A New Rotaxane-like Cage-in-Ring
Structural Motif for a
Metallosupramolecular Pd6L12
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