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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Metallonanobelt: A Kinetically Stable Shape-Persistent Molecular Belt Prepared by Reversible Self-Assembly Processes Yoko Sakata,*,†,‡ Ryoichi Yamamoto,† Daiki Saito,† Yuko Tamura,† Keisuke Maruyama,† Tomoki Ogoshi,†,‡ and Shigehisa Akine*,†,‡ †
Graduate School of Natural Science and Technology and ‡WPI Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan
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ABSTRACT: A triptycene-based shape-persistent belt-shaped macrocycle, metallonanobelt, was synthesized by the selfassembly of 2,3,6,7-tetraaminotriptycene L and square planar Pd2+. The pentamer was selectively formed by the complexation of L with Pd2+ in the presence of the pillar[6]arene derivative P6 having triethylene glycol pendant as a template, whereas a mixture of a trimer, tetramer, and pentamer was obtained in the absence of the template. The pentamer was successfully isolated based on the solubility difference between the metallonanobelt and the template. It was also revealed that the isolated pentamer was remarkably stable in solutions such as acetonitrile or methanol thanks to the relatively inert planar chelate metal complex, [Pd(o-phenylenediamine)2] unit. Thus, we can handle the metallonanobelt almost as a static organic nanobelt that is synthesized covalently.
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INTRODUCTION Macrocyclic compounds having aromatic rings1 have been recognized as important materials because they have an intrinsic cavity for guest recognition. In particular, macrocyclic molecules having a cylindrical shape based on the aromatic walls have attracted much interest as carbon nanotube segments, which could show unique structural and electronic features.2 Most of the cylindrical aromatic molecules, such as pillararenes and cycloparaphenylenes, contain C−C single bonds that could allow flipping of the aromatic walls, whereas there are also shape-persistent belt-shaped macrocyclic compounds, that is, nanobelts, which have no rotatable single bonds.3,4 In these structures, all the panels such as benzene rings are doubly connected to each other, so that ring flipping cannot take place.3a,e,f They are quite attractive because of the well-defined rigid cavity for selective and entropically favored molecular recognition, but there are only a limited number of such shape-persistent molecules. One of the efficient synthetic strategies for such cylindrical belt-shaped molecules is to connect rigid bent aromatic compounds in a cyclic fashion. Triptycene analogues would be a suitable building block for nanobelt structures because they have a highly rigid bicyclo[2.2.2]octatriene structure with well-defined aromatic walls. There are some reports about the synthesis of iptycene-based belt-shaped compounds and related structures,5 but rigid nanobelt structures with a low conformational flexibility3d are generally difficult to be synthesized. This is because there are multiple macro© XXXX American Chemical Society
cyclization pathways available, alongside oligomerization pathways, which compete with a desired single macrocyclization pathway to produce the product and, given the reactions are irreversible, this leads to low yields of the desired product. In this context, metal-assisted self-assembly would be advantageous because this method could give the most thermodynamically stable cyclic structure in only one step and in high yields thanks to the reversible feature of the metal coordination bonds.6 Even if an equilibrium mixture of macrocyclic complexes with different sizes is initially formed, a single macrocycle would be enriched in the presence of the appropriate template.7 Therefore, we expected that nanobelt structures can be efficiently obtained by the complexation of triptycene derivatives with metal ions. However, most of the self-assembled metallomacrocycles reported previously have potentially rotatable M−L bonds based on the monodentate coordination structures (Scheme 1a). To obtain shapepersistent belt-shaped metallomacrocycles, the triptycene derivatives should be connected with nonrotatable planar units via multiple coordination bonds. Therefore, we chose the planar chelate-type complex, [Pd(o-phenylenediamine)2],8,9 as a connecting motif for the macrocyclization pathway. Its square planar metal units would also constitute the well-defined cylindrical wall of the nanobelt structure because they have no Received: October 3, 2018
A
DOI: 10.1021/acs.inorgchem.8b02804 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry Scheme 1. (a) Self-Assembly Based on Monodentate Coordination; the Resultant Metallomacrocycle Has Many Rotatable Panels; (b) Self-Assembly Based on Chelate Coordination; the Resultant Metallomacrocycle Has a Shape-Persistent Metallonanobelt with No Rotatable Panels; and (c) Formation of Shape-Persistent Metallonanobelt by the Self-Assembly of Rigid Bent Ligand L with Pd2+
Scheme 2. Schematic Illustration of Template-Directed Selective Formation of Metallonanobelt
rotatable M−L bonds (Scheme 1b). Here, we report a new belt-shaped structure, that is, the metallonanobelt, which can be obtained by the self-assembly of a rigid bent ligand, 2,3,6,7tetraaminotriptycene (L),10 and square planar Pd2+ (Scheme 1c). Although a mixture of a trimer, tetramer, and pentamer was obtained without using a template, the self-assembly in the presence of the pillar[6]arene derivative P6 as a template selectively gave the pentamer (Scheme 2), which is sufficiently stable to be isolated like an organic nanobelt after the removal of P6, thanks to the inertness of the chelate complex motif, [Pd(o-phenylenediamine)2].
containing [Pd3L3]6+, [Pd4L4]8+, and [Pd5L5]10+. As we expected, the tetramer [Pd4L4]8+ has a belt-shaped macrocyclic structure having four Pd2+ ions with a square planar geometry (Figures 3a, S1, and Table S1). The tetramer molecule has a crystallographically imposed center of symmetry. The tetramer has a rectangular shape with different Pd−Pd distances (Pd1− Pd1*, 14.552 Å; Pd2−Pd2*, 15.458 Å), which is slightly distorted from the ideal D4v symmetrical structure in solution as confirmed by the 1H NMR spectrum (Figure 3b). From the viewpoint of the geometric features of the subunits, the formation of the tetramer seemed to be unfavorable. Thus, we quantified the distortion of each subunit in terms of the dihedral angles α and β, which are defined by the neighboring benzene rings in the triptycene and [Pd(o-phenylenediamine)2] substructures, respectively (Figure 3c). The dihedral angles α of 117.07° and 111.51° for the triptycene units only slightly deviated from the ideal angle of 120°, whereas the angles β of 19.79° and 28.76° for the planar [Pd(ophenylenediamine)2] units were much more deviated from the ideal angle of 0°. Consequently, the geometrical distortion of the tetramer is mainly explained by the bending of the [Pd(o-phenylenediamine)2] units rather than the deformation of the triptycene units. Macrocyclization with Template. Although we obtained the metallonanobelts as a mixture of [Pd3L3]6+, [Pd4L4]8+, and [Pd5L5]10+, we could selectively obtain one of them if we use a suitable template. We initially expected that pillar[5]arene derivatives would act as a good template for the pentamer [Pd5L5]10+ because they have a pentagonal column structure
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RESULTS AND DISCUSSION Macrocyclization without Template. To obtain the metallonanobelt, we investigated the 1:1 complexation of L with [Pd(CH3CN)4](OTf)211 in acetonitrile at room temperature (Scheme 2a). We initially expected that the reaction would give a cyclic hexamer that has the least geometric strain. The electrospray ionization time-of-flight (ESI-TOF) mass spectrum of the mixture after 3 days, however, showed peaks assignable to the [Pd3L3]6+, [Pd4L4]8+, and [Pd5L5]10+ species (Figures 1a and S2). This result suggested the formation of the metallonanobelts as a mixture of the cyclic trimer, tetramer, and pentamer. The proton nuclear magnetic resonance (1H NMR) spectrum of the mixture in CD3CN showed three sets of signals (Figure 2b), and the major set can be assigned to the tetramer. On the basis of the 1H NMR integral ratios for Ha signals, we estimated that 62% of L was converted to the tetramer. Notably, the metallonanobelt was formed only in acetonitrile, whereas no cyclic oligomer was formed in other polar solvents, such as CD3SOCD3 and CD3OD. Crystal Structure of Tetranuclear Metallonanobelt [Pd4L4](OTf)8. Single crystals of [Pd4L4](OTf)812 suitable for X-ray crystallography were obtained from a reaction mixture B
DOI: 10.1021/acs.inorgchem.8b02804 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
Figure 3. X-ray crystal structure of [Pd4L4](OTf)8. (a) Space-filling representation and (b) thermal ellipsoid plot at the 30% probability level. The solvent molecules and triflate anions are omitted. (c) Definition of the dihedral angles, α and β.
was heated at 50 °C for 20 h. The 1H NMR spectrum of the mixture showed broad signals (Figure S6), which were different from any of the nontemplated products (Figure 2b). The ESI-TOF mass spectrum of the mixture showed a series of peaks assignable to the tetramer and the pentamer, which were mostly observed as adduct peaks with one P5 molecule, [Pd4L4·P5 − nH + mTfO](8−n−m)+ and [Pd5L5·P5 − nH + mTfO](10−n−m)+ (Figures 1b and S3). The template P5 efficiently suppressed the formation of the trimer based on the fact that no peak for the trimer was detected in the mass spectrum. However, P5 was not a very good template for the exclusive formation of one of the cyclic oligomers because it interacted with both the tetramer and the pentamer. In contrast, a larger template P6 having a pillar[6]arene scaffold13b significantly affected the product ratio (Scheme 2c). The P6-encapsulated pentamer, [Pd5L5·P6]10+, was quantitatively formed when a 1:1 mixture of L and Pd2+ was heated at 50 °C for 20 h in CD3CN in the presence of 2 equiv (per macrocycle) of P6. The 1H NMR spectrum of the mixture showed only one set of signals indicative of the exclusive formation of a single macrocyclic complex (Figure 2c). The ESI-TOF mass spectrum showed a series of peaks for the pentamer as P6 adducts, [Pd5L5·P6 − nH + mTfO](10−n−m)+, whereas no peaks assignable to the tetramer or the trimer were detected (Figures 1c and S4). Shneebeli et al. reported that both the shape-fit and π−π interaction play an important role for the recognition of P5 by iptycene-based molecular strips without having metal complex moieties.14 In contrast, in the present system, the shapemismatched hexagonal molecule P6 acted as a good template for the pentagonal macrocycle. To investigate the key factor of the template effects, we compared the cavity sizes of the metallonanobelts and the outer diameters of the pillar[n]arenes by a molecular modeling study. The tetramer and pentamer have a cavity that can accommodate a cylinder with diameters of 11.5 and 15.4 Å, respectively (Figure 4). Therefore, they have to deform their structures to efficiently interact with the pillar[5]arene derivatives (13.6 Å outer diameter). This is why P5 did not lead to the exclusive formation of one of them. On the other hand, the pillar[6]arene derivatives (15.3 Å outer diameter) seem to fit nicely into the cavity of the pentamer without a large deformation, which well explains the exclusive formation of the pentamer [Pd5L5]10+.
Figure 1. ESI-TOF mass spectra of (a) metallonanobelt mixture obtained in the absence of a template, (b) mixture obtained in the presence of P5, (c) mixture obtained in the presence of P6, (d) mixture obtained in the presence of P6′, and (e) isolated pentamer [Pd5L5](OTf)10.
Figure 2. 1H NMR spectra (400 MHz, CD3CN, [L] = 4 mM) of (a) L, (b) metallonanobelt mixture obtained in the absence of a template, (c) mixture obtained in the presence of P6, and (d) isolated pentamer [Pd5L5](OTf)10. See Scheme 2 for signal assignments.
that could nicely fit into the pentagonal cavity of [Pd5L5]10+. The electron-rich dialkoxybenzene units of the pillar[5]arene derivatives would interact with the electron-deficient [Pd(ophenylenediamine)2] units of the metallonanobelt via electrostatic and charge-transfer interactions. Thus, we first attempted to selectively obtain the pentamer by using a pillar[5]arene derivative with triethylene glycol (TEO) pendants (P5)13a as the template (Scheme 2b). A mixture of L, Pd2+, and P5 (1:1:0.4 molar ratio) in CD3CN C
DOI: 10.1021/acs.inorgchem.8b02804 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
Figure 6. Schematic illustration of template-directed selective formation of the pentamer with P6.
Figure 4. Comparison of the structures of pillar[n]arenes and metallonanobelts. The structures of pillar[n]arenes were obtained from crystal structures (ethyl groups are omitted for clarity).15 The structures of metallonanobelts were obtained from MM calculation/ UFF.
Isolation of Pentanuclear Metallonanobelt [Pd5L5](OTf)10. Importantly, the pentamer, [Pd5L5](OTf)10, can be isolated as a stable compound (Scheme 1b,c), which does not easily revert to the equilibrated mixture. The template P6 was successfully removed according to the solubility difference in chloroform between the ionic complex, [Pd5L5](OTf)10, and nonionic P6. The 1H NMR signals of the isolated [Pd5L5](OTf)10 well correspond to one of the three sets of signals for the mixture of [Pd3L3]6+, [Pd4L4]8+, and [Pd5L5]10+, and we clearly observed the peaks for both the outer and the inner NH2 protons with geminal coupling (J = 12.4 Hz) (Figure 2d). The complete removal of the template was also confirmed by ESI-TOF mass spectrometry (Figures 1e and S5). The isolated pentamer metallonanobelt [Pd5L5](OTf)10 showed an excellent stability in CD3CN, as expected from the chelate coordination structures; 74% of the pentamer still remained as the major species after heating at 30 °C for 6 days (Figure 7a). It took about 1 month to reach equilibrium,
Interestingly, no template effect was observed when P6′ having shorter pendant groups13c was used. The 1H NMR spectrum of a 1:1 mixture of L and Pd2+ in the presence of P6′ showed signals of the trimer, tetramer, and pentamer without any chemical shift changes, just as observed in the absence of P6′ (Figure S7). The ESI-TOF mass spectrum also confirmed that these oligomers have a negligible interaction with P6′ (Figure 1d). Obviously, the pendant groups of P6, rather than the cyclic array of the aromatic rings, contributed to the host− guest binding with the metallonanobelt scaffold. The hydrogen bonding between the TEO and [Pd(o-phenylenediamine)2] units probably accounts for the host−guest interactions because the template effect of P6 became negligible in the CD3SOCD3/CD3CN solution (Figure S8). This was also supported by the titration study using a mononuclear model compound (Figures 5 and S9−S12), which showed that the
Figure 5. Chemical structures of a mononuclear model compound [PdL2′](OTf)216 and 1,4-disubstituted benzene derivatives17 having different pendant groups (M1, M2, and M3) used in this study.
longer pendant group more strongly interacted with the [Pd(ophenylenediamine)2]2+ unit (Table 1). These results indicated that both the TEO chains and pillar[6]arene scaffold in P6 are essential for the selective formation of the pentamer because they work as anchoring units and size-exclusion unit, respectively (Figure 6).
Figure 7. Time course analysis of 1H NMR spectra (400 MHz) of the isolated pentamer metallonanobelt [Pd5L5](OTf)10 after heating at 30 °C (a) in CD3CN and (b) in CD3OD.
producing again a mixture containing [Pd3L3]6+, [Pd4L4]8+, and [Pd5L5]10+. It should be noted that this equilibration was completely suppressed in CD3OD. Even after heating at 30 °C for 1 month, no spectral change was observed (Figure 7b). Usually, the formation of self-assembled macrocycles requires reversible formation/cleavage processes of the metal−ligand coordination bond that could give the most thermodynamically stable structure. Therefore, if several metallomacrocyclic species are formed as an equilibrium mixture, it is generally difficult to isolate one of them because such attempts lead to the re-formation of the equilibrium
Table 1. Association Constantsa for the Complexation between the Model Compound [PdL′2](OTf)2 and 1,4Disubstituted Benzene Derivatives (M1, M2, and M3) 1,4-disubstituted benzene derivatives association constants (M−1)
M1 15 ± 2
M2 ∼3
M3 n.d.b
a
Determined by 1H NMR spectroscopy in CD3CN. bNot determined due to the weak interaction. D
DOI: 10.1021/acs.inorgchem.8b02804 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
of the panels and gives a well-defined rigid cavity. As this selfassembly approach quite efficiently gave the metallonanobelt, this method has an advantage over the synthesis of an organic nanobelt structure, which often leads to the target macrocycles in low yield. The isolated pentamer metallonanobelt can be treated almost as a static organic nanobelt that is synthesized covalently, although it was obtained by the self-assembly process resulting from dynamic equilibration. To our knowledge, this is the first nanobelt structure obtained by metalassisted self-assembly. We believe that this new type of shapepersistent belt-shaped metal complex would be applicable to the selective encapsulation/separation of target molecules by external stimuli such as redox reactions of the metal complex moieties or utilized as a building block for the rigid tubular structures.
mixture (Scheme 1a). In the present system, however, we can handle this pentamer metallonanobelt almost as a static organic nanobelt that is synthesized covalently. This high stability can be explained by the “inertness” of the chelate complex motif, [Pd(o-phenylenediamine)2] (Scheme 1b,c), which allows almost no ligand exchange for days.6b,c Guest Recognition of Pentanuclear Metallonanobelt [Pd5L5](OTf)10. We also investigated whether there is a relationship between the template effect and the binding affinity. The 1H NMR titration studies indicated that addition of 1 equiv of P6 completely converted (>90%) the pentamer into the host−guest complex, whereas almost no interaction was observed with P6′ having shorter pendant groups (Figures 8 and S13−S16). The pentamer also strongly interacted with
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EXPERIMENTAL SECTION
Materials and Methods. Reagents and solvents were purchased from commercial sources and used without further purification. 2,3,6,7-Tetraaminotriptycene,10 P5,13a P6,13b and P6′13c were prepared according to the procedure previously reported. 1H NMR spectra were recorded on JEOL JNM-ECS 400 (400 MHz). Chemical shifts were referenced with respect to tetramethylsilane (0 ppm) as an internal standard or solvent residual peak (1.94 ppm for CD3CN). ESI-TOF mass spectra were recorded on Bruker Daltonics micrOTOF II. X-ray Crystallography. The crystal of [Pd4L4](OTf)8 suitable for the single crystal X-ray crystallographic analysis was obtained by slow diffusion of diethyl ether into a chloroform/methanol solution of a mixture of trimer, tetramer, and pentamer of metallonanobelts. The intensity data were collected on a Bruker D8 VENTURE diffractometer (Cu Kα radiation, λ = 1.54178 Å). The data were corrected for Lorentz and polarization factors and for absorption by semiempirical methods based on symmetry-equivalent and repeated reflections. The structure was solved by direct methods (SHELXS-97) and refined by full-matrix least-squares on F2 using SHELXL-2014/ 7.18 All of the nonhydrogen atoms were anisotropically refined, whereas all hydrogen atoms were placed geometrically and refined using a riding model with Uiso constrained to be 1.2 times (for CH, NH) or 1.5 times (for CH3 and OH) Ueq of the carrier atom. All the triflate anions and methanol molecules were restrained to have similar geometries using DFIX and FLAT restraints. The anisotropic displacement parameters of the atoms in triflate, methanol, and diethyl ether molecules were restrained using ISOR and DELU restraints. The hydrogen atoms in some water molecules are not included. The crystallographic data for [Pd4L4](OTf)8 have been deposited with the Cambridge Crystallographic Data Centre under reference number CCDC 1833673. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK). The crystal data are summarized in Table S1. Synthesis of [Pd5L5](OTf)10. A solution of 2,3,6,7-tetraaminotriptycene L (30.4 mg, 96.7 μmol) in acetonitrile (12.1 mL) was mixed with a solution of [Pd(CH3CN)4](OTf)211 (55.0 mg, 96.8 μmol) in acetonitrile (2.4 mL) and a solution of P6 (96.6 mg, 38.9 μmol) in acetonitrile (2.4 mL). The resulting solution was heated at 50 °C for 20 h. After the solution was concentrated to dryness, the residue was dissolved in chloroform/methanol (1:1) (2 mL), and hexane/chloroform (1:1) was added. The precipitates were collected by filtration to give [Pd5L5](OTf)10 (63.1 mg, 14.5 μmol, 75%) as a pale brown powder. 1H NMR (400 MHz, CD3CN): δ 7.47−7.45 (m, 10H), 7.34 (s, 20H), 7.09−7.07 (m, 10H), 6.05 (d, J = 12.4 Hz, 20H), 5.76 (d, J = 12.4 Hz, 20H), 5.69 (s, 10H). ESI-MS m/z 1049.0 [Pd5L5 + 7OTf]3+. Anal. Calcd for C110H90F30N20O30Pd5S10·3CHCl3· 3C6H14·8H2O: C, 36.13; H, 3.49; N, 6.43. Found: C, 36.15; H, 3.45; N, 6.48.
Figure 8. 1H NMR spectra (400 MHz, CD3CN, [[Pd5L5](OTf)10] = 0.5 mM) of (a) pentamer metallonanobelt [Pd5L5](OTf)10 and (b− d) pentamer metallonanobelt [Pd5L5](OTf)10 after addition of 1 equiv of (b) P6′, (c) P6, and (d) P5. See Scheme 2 for signal assignments.
P5 having TEO chains. These results again support the importance of the interaction between the TEO chains of the template and the [Pd(o-phenylenediamine)2] units for the formation of the host−guest complex. The complexation/ decomplexation process for P6 was slow on the NMR timescale, whereas that for P5 was faster, implying that P6 more strongly interacted with the pentamer metallonanobelt. Indeed, when a 1:1 mixture of P6 and P5 was added to the pentamer, P6 was exclusively bound to the pentamer metallonanobelt (Figure S17). Even when a 10-fold excess amount of P5 was present, the formation of P6 complex was still favored (P6 complex/P5 complex = 68:32 ratio). On the basis of this competitive experiment, the P6/P5 selectivity coefficient was evaluated to be about 20. This indicated that the size-fit principle is also an important factor for the stronger binding toward the metallonanobelt (Figures 4 and S18).
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CONCLUSIONS In conclusion, a belt-shaped macrocycle, that is, a metallonanobelt, was efficiently obtained by the complexation of a triptycene-based rigid bent ligand L with a square planar Pd2+. The triptycene subunits, which are doubly connected by the chelate metal complex units [Pd(o-phenylenediamine)2], constitute the belt-shaped structure that allows no ring flipping E
DOI: 10.1021/acs.inorgchem.8b02804 Inorg. Chem. XXXX, XXX, XXX−XXX
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recognition, and molecular switching functions. Chem. Soc. Rev. 2015, 44, 532−546. (j) Tanaka, T.; Osuka, A. Chemistry of meso-ArylSubstituted Expanded Porphyrins: Aromaticity and Molecular Twist. Chem. Rev. 2017, 117, 2584−2640. (k) Ogoshi, T.; Yamagishi, T.-a.; Nakamoto, Y. Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry. Chem. Rev. 2016, 116, 7937−8002. (l) Murray, J.; Kim, K.; Ogoshi, T.; Yao, W.; Gibb, B. C. The aqueous supramolecular chemistry of cucurbit[n]urils, pillar[n]arenes and deep-cavity cavitands. Chem. Soc. Rev. 2017, 46, 2479− 2496. (m) Kawase, T.; Darabi, H. R.; Oda, M. Cyclic [6]- and [8]Paraphenylacetylenes. Angew. Chem., Int. Ed. Engl. 1996, 35, 2664−2666. (n) Gale, P. A.; Sessler, J. L.; Král, V.; Lynch, V. Calix[4]pyrroles: Old Yet New Anion-Binding Agents. J. Am. Chem. Soc. 1996, 118, 5140−5141. (o) Hoffmann, M.; Wilson, C. J.; Odell, B.; Anderson, H. L. Template-Directed Synthesis of a π-Conjugated Porphyrin Nanoring. Angew. Chem., Int. Ed. 2007, 46, 3122−3125. (p) O’Sullivan, M. C.; Sprafke, J. K.; Kondratuk, D. V.; Rinfray, C.; Claridge, T. D. W.; Saywell, A.; Blunt, M. O.; O’Shea, J. N.; Beton, P. H.; Malfois, M.; Anderson, H. L. Vernier templating and synthesis of a 12-porphyrin nano-ring. Nature 2011, 469, 72−75. (q) Jiang, H.-W.; Tanaka, T.; Mori, H.; Park, K. H.; Kim, D.; Osuka, A. Cyclic 2,12Porphyrinylene Nanorings as a Porphyrin Analogue of Cycloparaphenylenes. J. Am. Chem. Soc. 2015, 137, 2219−2222. (2) (a) Omachi, H.; Segawa, Y.; Itami, K. Synthesis of Cycloparaphenylenes and Related Carbon Nanorings: A Step toward the Controlled Synthesis of Carbon Nanotubes. Acc. Chem. Res. 2012, 45, 1378−1389. (b) Yamago, S.; Kayahara, E.; Iwamoto, T. Organoplatinum-Mediated Synthesis of Cyclic π-Conjugated Molecules: Towards a New Era of Three-Dimensional Aromatic Compounds. Chem. Rec. 2014, 14, 84−100. (c) Golder, M. R.; Jasti, R. Syntheses of the Smallest Carbon Nanohoops and the Emergence of Unique Physical Phenomena. Acc. Chem. Res. 2015, 48, 557−566. (d) Darzi, E. R.; Jasti, R. The dynamic, size-dependent properties of [5]− [12]cycloparaphenylenes. Chem. Soc. Rev. 2015, 44, 6401−6410. (e) Segawa, Y.; Yagi, A.; Matsui, K.; Itami, K. Design and Synthesis of Carbon Nanotube Segments. Angew. Chem., Int. Ed. 2016, 55, 5136− 5158. (f) Hitosugi, S.; Yamasaki, T.; Isobe, H. Bottom-up Synthesis and Thread-in-Bead Structures of Finite (n,0)-Zigzag Single-Wall Carbon Nanotubes. J. Am. Chem. Soc. 2012, 134, 12442−12445. (3) (a) Kohnke, F. H.; Slawin, A. M. Z.; Stoddart, J. F.; Williams, D. J. Molecular Belts and Collars in the Making: A Hexaepoxyoctacosahydro[12]cyclacene Derivative. Angew. Chem., Int. Ed. Engl. 1987, 26, 892−894. (b) Mathias, J. P.; Stoddart, J. F. Constructing a Molecular LEGO Set. Chem. Soc. Rev. 1992, 21, 215− 225. (c) Cory, R. M.; McPhail, C. L.; Dikmans, A. J.; Vittal, J. J. Macrocyclic Cyclophane Belts via Double Diels-Aider Cycloadditions: Macroannulation of Bisdienes by Bisdienophiles. Synthesis of a Key Precursor to an [8]Cyclacene. Tetrahedron Lett. 1996, 37, 1983− 1986. (d) Lou, K.; Prior, A. M.; Wiredu, B.; Desper, J.; Hua, D. H. Synthesis of Cyclododeciptycene Quinones. J. Am. Chem. Soc. 2010, 132, 17635−17641. (e) Povie, G.; Segawa, Y.; Nishihara, T.; Miyauchi, Y.; Itami, K. Synthesis of a carbon nanobelt. Science 2017, 356, 172−175. (f) Eisenberg, D.; Shenhar, R.; Rabinovitz, M. Synthetic approaches to aromatic belts: building up strain in macrocyclic polyarenes. Chem. Soc. Rev. 2010, 39, 2879−2890. (4) (a) Freeman, W. A.; Mock, W. L.; Shih, N. Y. Cucurbituril. J. Am. Chem. Soc. 1981, 103, 7367−7368. (b) Kim, J.; Jung, I.-S.; Kim, S.-Y.; Lee, E.; Kang, J.-K.; Sakamoto, S.; Yamaguchi, K.; Kim, K. New Cucurbituril Homologues: Syntheses, Isolation, Characterization, and X-ray Crystal Structures of Cucurbit[n]uril (n = 5, 7, and 8). J. Am. Chem. Soc. 2000, 122, 540−541. (c) Lagona, J.; Mukhopadhyay, P.; Chakrabarti, S.; Isaacs, L. The Cucurbit[n]uril Family. Angew. Chem., Int. Ed. 2005, 44, 4844−4870. (5) (a) Swager, T. M. Iptycenes in the Design of High Performance Polymers. Acc. Chem. Res. 2008, 41, 1181−1189. (b) Chong, J. H.; MacLachlan, M. J. Iptycenes in supramolecular and materials chemistry. Chem. Soc. Rev. 2009, 38, 3301−3315. (c) Chen, C.-F. Novel triptycene-derived hosts: synthesis and their applications in supramolecular chemistry. Chem. Commun. 2011, 47, 1674−1688.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b02804. Crystallographic data for [Pd4L4](OTf)8; ESI-TOF mass spectra of a mixture after the complexation in the absence/presence of the template; ESI-TOF mass spectrum of the isolated pentamer [Pd5L5](OTf)10; 1H NMR spectra of a mixture after the complexation in the presence of P5 or P6′; 1H NMR spectra of a mixture after the complexation in the presence of P6 in CD3SOCD3/CD3CN; 1H NMR titration study of the model compound [PdL′2](OTf)2 and the pentamer [Pd5L5](OTf)10; Geometrically optimized structures of the host-guest complexes (PDF) Accession Codes
CCDC 1833673 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
[email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected] (Y.S.). *E-mail:
[email protected] (S.A.). ORCID
Yoko Sakata: 0000-0002-6988-1171 Tomoki Ogoshi: 0000-0002-4464-0347 Shigehisa Akine: 0000-0003-0447-5057 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by JSPS KAKENHI grant numbers JP17K14459, JP18H04511 (Soft Crystals), and JP16H06510 (Coordination Asymmetry), Yazaki Memorial Foundation for Science and Technology, Inoue Science Research Award, Tokuyama Science Foundation, World Premier International Research Center Initiative (WPI), MEXT, Japan, and Kanazawa University CHOZEN Project.
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REFERENCES
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