Molecular self-assembly of arene-Ru based interlocked catenane metalla-cages

Article abstract of DOI:10.1039/c4cc01991a

Two interlocked trigonal prismatic metalla-cages are formed quantitatively through the self-assembly of π-electron rich arene-Ru acceptors with a new tridentate donor. Interestingly, non-π-electron rich arene-Ru acceptors furnish simple trigonal prisms when they are combined with a tridentate donor. the Partner Organisations 2014.

Full text of DOI:10.1039/c4cc01991a

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Molecular self-assembly of arene-Ru based
interlocked catenane metalla-cages†
Cite this: Chem. Commun., 2014,
50, 7542
Anurag Mishra,‡a Abhishek Dubey,‡a Jin Wook Min,a Hyunuk Kim,b Peter J. Stang*c
and Ki-Whan Chi*a
Received 17th March 2014,
Accepted 22nd May 2014
DOI: 10.1039/c4cc01991a
www.rsc.org/chemcomm
Two interlocked trigonal prismatic metalla-cages are formed quantita-
In 1999, Fujita and co-workers reported the spontaneous
tively through the self-assembly of p-electron rich arene-Ru acceptors self-assembly of ten components into two interlocked, three-
with a new tridentate donor. Interestingly, non-p-electron rich stranded discrete coordination cages.8a Formation of the inter-
arene-Ru acceptors furnish simple trigonal prisms when they are locked cages involved a reversible, metal-mediated process.
combined with a tridentate donor.
A decade later, Hardie and co-workers described cobalt and zinc-
based systems with similar topologies.9 Fukuda and co-workers
Over the past two decades, the use of coordination-driven self- reported an interlocked arrangement of two four-stranded palladium
assembly in the design and synthesis of supramolecular coordina- coordination cages.10 Beer and colleagues prepared an interlocked
tion complexes has emerged as a powerful methodology to access system in which the crossing cycles consisted of covalent entities.11
a wide library of metallacycles and cages under relatively benign This assembly was templated by sulfate ions, which remained bound
conditions with high efficiencies. The strategy of directional within the dimer after synthesis. The prevalent molecular phenomena
bonding, in which the edges, faces, and/or vertices of a target behind these exemplary interlocked structures are metal–ligand
polygon or polyhedron are encoded into molecular precursors that coordination and H-bonding interactions.12 Among these, there are
are then combined in appropriate stoichiometries, has defined few examples which invoke the importance of p–p interactions
routes towards a suite of 2D and 3D supramolecules1 ranging from between subunits.13 Mukherjee and co-workers reported a series of
small molecular boxes2 to nanometer-sized Archimedean solids.3 triply interlocked Pd12 coordination prisms, but they got converted
These supramolecular assemblies can be employed in molecular into non-interlocked Pd6 prisms, through p–p stacking interaction,
recognition and catalysis4 and have been shown to act as templates upon addition of an aromatic guest.14 Recently, we reported a self-
for the synthesis of core–shell nanoparticles.5 The inherent cyclic assembled arene-Ru metalla-rectangle which encapsulated a second,
nature of edge-directed self-assembly, in which metallacycles and identical rectangle, likely due to p–p interactions (Fig. 1a).15 The non-
cages possess internal cavities, naturally introduces routes towards catenane interlocked, macromolecule-in-a-macromolecule motif was
catenane and rotaxane structures wherein discrete architectures formed by multiple close p–p interactions between the tetracene-
can be fused or linked, motivating interest in using such containing arene-Ru acceptors and the four p-electron-rich
supramolecular constructs as molecular machines.6 Whereas donors, as evidenced by single crystal X-ray diffraction. Herein,
2D metallacycles have seen impressive use in the formation of we report the preparation of arene-Ru trigonal prisms that form
catenane and rotaxane species,7 few examples of catenated
coordination cages are known.8
a Department of Chemistry, University of Ulsan, Ulsan 680-749, Republic of Korea.
E-mail: kwchi@mail.ulsan.ac.kr
b Energy Materials and Convergence Research Department, Korea Institute of Energy
Research, Daejeon 305-343, Republic of Korea
c Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
E-mail: Stang@chem.utah.edu
† Electronic supplementary information (ESI) available: Text and figures showing
detailed experimental, spectroscopic and crystallographic studies. CCDC 991298.
Fig. 1 Schematic representation of (a) non-catenane (D2A3)2 interlocked
(b) catenane {D2A3}2 interlocked structures by arene-Ru acceptors and
N-donor ligands.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4cc01991a
‡ These authors contributed equally to this work.
7542 | Chem. Commun., 2014, 50, 7542--7544
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either discrete D2A3 cages or interlocked {D2A3}2 dimers by
significant p–p interactions depending on the specific molecular
clip used during self-assembly.
The formation of both singular and dimeric prisms follows a
similar 2 : 3 acceptor-to-donor stoichiometry in which 1,3,5-
tris(3-(pyridin-4-yl)-1H-pyrazol-1-yl)benzene (D1) is combined
with one of four molecular clips [( p-cymene)RuCl (OO-OO)
RuCl( p-cymene)] (A1,OO-OO = 5,8-dioxydo-1,4-naphtho-quinonato
(donq); A2, OO-OO = 5,11-dioxydo-6,12-tetracenquinonato (dotq);
A3, OO-OO = 2,20-[bisbenzo-dimidazole]-1,10-diide (bbid); A4,
Fig. 2 Theoretical (top) and experimental (bottom) ESI-MS results for
OO-OO = 4-carboxylato-2,6-dioxo-2,6-dihydro-1H-1,3,5-triazin- interlocked cages 1 (left) and 2 (right).
3-ide, (cddt)). When A1 and A2 are used, interlocked cages, as shown
in Scheme 1, are obtained and may represent a new paradigm for the
formation of interlocked supramolecular species which form with p–p 3 days resulted in no noticeable difference in the spectra (Fig. S4 and
interactions as the impetus. Conversely, A3 and A4 ultimately furnish S5, ESI†). In contrast, reaction mixtures forming 3 resulted in simple
simple D2A3 trigonal prisms when combined with D1.
proton spectra that supported the formation of a symmetric, discrete
Ligand D1 was synthesized in 50% yield by an Ullmann-type prism. Notable upfield shifts are observed for the resonances corres-
coupling with 1,3,5-tribromobenzene and 3-(4-pyridyl) pyrazole in ponding to protons on D1, suggesting that ring current shielding
the presence of the CuI catalyst (ESI†). The dinuclear arene offsets any loss of electron density associated with coordination and
ruthenium complexes [Ru2-(arene)2(OO-OO)Cl2] (A1–A4) react in induction (Fig. S6, ESI†).16 Although the aromatic proton signals were
nitromethane–methanol (1 : 1) at room temperature in the presence broadened and shifted upfield in the spectrum of 4 (Fig. S7, ESI†), the
of silver triflate as a halide scavenger with ligand D1 in a 2 : 3 ratio relatively simple spectrum is evidence for the formation of discrete
to give the trigonal prism cations 1–4 (1 = D1 and A1; 2 = D1 and A2; prisms. Further proof for the structural assignments of 1–4 was
3 = D1 and A3; 4 = D1 and A4) stabilized as triflate salts.
obtained using electrospray ionization mass spectrometry (ESI-MS).
The first indication of the interlocked nature of 1 and 2 was The ESI-MS spectrum of interlocked metalla-cage 1 exhibited one
1
found in the H NMR spectra of their reaction mixtures. When charge state at m/z = 1793.87, corresponding to [M-4OTf ]4+. For
assemblies were carried out in CD3NO2–CD3OD (1 : 1), the reaction interlocked metalla-cage 2, charge states at m/z 1944.64 were assigned
mixtures could be directly subjected to 1H NMR analysis, exhibiting to [M-4OTf ]4+ (Fig. 2). These charge states and isotopic spacings are
complex spectra after 24 h of stirring at room temperature.
unique to the {D2A3}2 dimeric structure. While discrete D2A3 prisms
The spectral complexity was initially interpreted as resulting would potentially show peaks at the same m/z values for the even
from incomplete assembly, giving rise to a number of unique charge states, the isotopic spacing would be different. Similarly, three
proton environments; however, elongating the reaction time to charge states were observed for 3 at m/z = 1190.32 [M-3OTf ]3+, 855.18
[M-4OTf ]4+, and 654.67 [M-5OTf ]5+, and for cage 4 at m/z = 1113.18
[M-3OTf ]3+, 797.89 [M-4OTf ]4+, and 608.04 [M-5OTf ]5+ (Fig. S8 and S9,
ESI†). These peaks were also isotopically resolved and in good
agreement with the calculated theoretical distributions for single
1
D2A3 structures. The H NMR spectra coupled with the HR-ESI-MS
data demonstrate that the {D2A3}2 dimeric structure is present in the
solution phase in the case of 1 and 2.
The interlocked nature of 2 was unambiguously determined by
single-crystal X-ray analysis using synchrotron radiation (Fig. 3).
The X-ray crystal structure of 2 revealed that each Ru center of A2 is
coordinated by one pyridine unit of D1 ligands to form the edge of
the cage. Thus, three A2 acceptors hold two D1 donors in a cofacial
arrangement to form each individual D2A3 cage (Fig. 3a).
The twisting of one arm of each D1 ligand renders each
individual cage of 2 into distorted trigonal prisms (Fig. S10, ESI†).
These distorted trigonal prisms are linked together, with the trigonal
face of one prism occupying the internal cavity of its counterpart.
The prisms are staggered with respect to one another to accommo-
date the molecular clip edges (Fig. 3c). A noteworthy feature of the
structure is the close contact between the D1 ligands in each cage,
supporting the presence of intermolecular p–p interactions with a
distance of approximately 3.4 Å (Fig. 3b). The tetracene bridging
ligands of the cages are bent outward with a distance of 8.40 Å
between the intramolecular moieties. While the tetracene frame
Scheme 1 Synthesis of a discrete D2A3 and {D2A3}2 dimeric supramole-
cules 1–4.
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These interlocked prisms are complemented by two examples
of simple, discrete prisms formed using the same donor with
alternative metal acceptors. As these cages lack the extensive
intra-molecular p–p stacking, no fused structures are observed.
Future work will explore the inclusion of particular guest
species such as any fluorescent molecules, enabling us to study
confinement effects in these systems.
This work was supported by the Basic Science Research
program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Science, ICT and Future Planning
(NRF-2013R1A1A2006859). Priority Research Centers program
(2009-0093818) through the NRF is also financially appreciated.
X-ray diffraction experiments using synchrotron radiation were
performed at the Pohang Accelerator Laboratory in Korea.
Notes and references
Fig. 3 X-ray crystal structure of 2: (a) a discrete cage (interlocked partner
omitted for clarity); (b) a space-filling model. (c) The complete, interlocked
cage. Hydrogen atoms, counter ions, and solvents of crystallization are
omitted for clarity.
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In conclusion, we have demonstrated for the first time two
interlocked metalla-cages, 1 and 2, which are formed quantitatively
through the self-assembly of p-electron rich arene-Ru acceptors
A1 and A2 with a tridentate1,3,5-tris(3-(pyridin-4-yl)-1H-pyrazol-1-
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7544 | Chem. Commun., 2014, 50, 7542--7544
This journal is ©The Royal Society of Chemistry 2014