Self-complementary

Three [3]catenanes with cavities large enough to accommodate aromatic guests have been designed and synthesized (yields = 5-20 %) by means of kinetically controlled self-assembly processes. The X-ray structural analysis of one of three [3]catenanes confirmed the presence of a rectangular cavity (dimensions = 7 x 11 A) lined by pi-electron-rich recognition sites and hydrogen-bond acceptor groups. In spite of their apparently ideal recognition features, none of these [3]catenanes bind guests incorporating a pi-electron-deficient bipyridinium unit. However, the template-directed syntheses of the [3]catenanes also produce, in yields of 2-23%, [2]catenanes incorporating a 1,5-dioxynaphtho[38]crown-10 interlocked with a bipyridinium-based tetracationic cyclophane. The X-ray structural analyses of two of these [2]catenanes revealed that a combination of [pi...pi] and [C-H...pi] interactions is responsible for the formation of supramolecular homodimers in the solid state. 1H NMR spectroscopic investigations of the four [2]catenanes demonstrated that supramolecular homodimers are also formed (Ka= 17-31M(-1), T= 185 K) in (CD3)2CO solutions. Dynamic 1H NMR spectroscopy revealed that the 1,5-dioxynaphtho[38]crown-10 and tetracationic cyclophane components in the four [2]catenanes and in the three [3]catenanes circumrotate (deltaGc(not equal to) = 9-14 kcal mol(-1)) through each other's cavity in (CD3)2CO. Similarly, the 1,5-dioxynaphthalene and the bipyridinium ring systems rotate (deltaGc(not equal to) =10-14 kcal mol(-1)) about their [O...O] and [N...N] axes, respectively, in solution.     

Photoinduced electron transfer between the interlocked components of porphyrin catenanes: effect of the presence of nonequivalent reduction sites on the charge recombination rate

[2]Catenanes made up of several polyether-strapped porphyrin macrocycles interlinked with the cyclic electron acceptor cyclobis(paraquat-p-phenylene) were spectroscopically, photophysically, and electrochemically characterized. The catenanes exhibit very rich redox behavior due to the presence of several different and interacting electro-active subunits. The redox patterns represent useful "fingerprints" that provide detailed information on the electronic interactions and the chemical environments that the electroactive subunits experience in the supramolecular arrays. A photoinduced electron transfer from the porphyrin excited state (charge separation CS) occurs with tau=20 ps in the catenanes with a larger strap and faster than 20 ps (instrumental resolution) in the catenanes with a shorter strap. The resulting charge-separated state recombines to the ground state (charge recombination CR) with lifetimes similar in all cases, 41+/-4 ps. Comparison of the electron transfer rates CS and CR in the host-guest complexes of the same porphyrins with the noncyclic electron acceptor paraquat, indicate slower reactions in the [2]catenanes. This behavior is assigned to the different separation between reacting partners determined by the type of bond (weak interaction or mechanical) and to a two-step consecutive electron transfer to different sites of the macrocyclic electron acceptor in the catenanes which retards charge recombination.     

Palladium(II)-directed self-assembly of dynamic donor-acceptor [2]catenanes

Highly efficient syntheses of donor-acceptor [2]catenanes were developed using a combination of templation and reversible metal-ligand coordination. The desired [2]catenanes were obtained within minutes through a five-component assembly, involving a donor-containing crown ether, an acceptor-containing ligand, two Pd(II) metal centers, and a dipyridyl ligand. The [2]catenane formation was characterized by 1H NMR and UV-vis spectroscopies and cold-spray ionization mass spectrometry. In particular, great translational selectivity was observed when a crown ether with two different donor units was employed.     

Oligothiophene catenanes and knots: a theoretical study

Oligothiophene [2]catenanes and knots containing up to 28 thiophene units have been studied at the BHandHLYP/3-21G level of theory. Small knots (less than 22 thiophene units) and [2]catenanes (less than 18 thiophene units) are strained molecules. Larger knots and [2]catenanes are almost strain-free. [2]Catenanes and knots having less than 18 and 24 units, respectively, show transversal electronic coupling destroying one-dimensionality of molecules reflecting in smaller band gaps compared to larger knots and catenanes. Ionization potentials of knots and catenanes are always higher compared to that of lineal oligomers due to less effective conjugation. Polaron formation in catenanes is delocalized only over one ring, leaving another intact. In the case of a knot containing 22 thiophene units, estimated polaron delocalization is 8 to 9 repeating units.     

Templated synthesis of desymmetrized [2]catenanes with excellent translational selectivity

Desymmetrized [2]catenanes were synthesized and shown to exhibit excellent translational selectivity. The templated synthesis takes effect from the formation of pseudorotaxanes between pi-rich crown ethers and a pi-deficient pyromellitic (PmI) unit, followed by macrocyclization around the crown ethers with the creation of a bipyridinium (BPy) unit. The crown ethers preferably encircle the BPy unit in the resulting [2]catenanes in both solution and the solid state, as indicated by various spectroscopic analyses.     

Switchable Reconfiguration of an Interlocked DNA Olympiadane Nanostructure

Interlocked DNA rings (catenanes) are interesting reconfigurable nanostructures. The synthesis of catenanes with more than two rings is, however, hampered, owing to low yields of these systems. We report a new method for the synthesis of catenanes with a controlled number of rings in satisfactory yields. Our approach is exemplified by the synthesis of a five‐ring DNA catenane that exists in four different configurations. By the use of nucleic acids as “fuels” and “antifuels”, the cyclic reconfiguration of the system across four states is demonstrated. One of the states, olympiadane, corresponds to the symbol of the Olympic Games. The five‐ring catenane was implemented as a mechanical scaffold for the reconfiguration of Au NPs. The advantages of DNA catenanes over supramolecular catenanes include the possibility of generating highly populated defined states and the feasibility of tethering nanoobjects to the catenanes, which act as a mechanical scaffold to reconfigure the nanoobjects.     

Organometallic Borromean Rings and [2]Catenanes Featuring Di-NHC Ligands

We report herein a series of organometallic Borromean rings (BRs) and [2]catenanes prepared from benzobiscarbene ligands. The reaction of dinickel complexes of the benzobiscarbenes 1 a – 1 c with a thiazolothiazole bridged bipyridyl ligand L² led by self-assembly to a series of organometallic BRs. Solvophobic effects played a crucial role in the formation and stability of the interlocked species. The stability of BRs is related to the N-alkyl substituents at the precursors 1 a – 1 c , where longer alkyl substitutes improve stability and inter-ring interactions. Solvophobic effects are also important for the stability of [2]catenanes prepared from 1 a – 1 c and a flexible bipyridyl ligand L³ . In solution, an equilibrium between the [2]catenanes and their macrocyclic building blocks was observed. High proportions of [2]catenanes were obtained in concentrated solutions or polar solvents. The proportion of [2]catenanes in solution could be further enhanced by lengthening of the N-alkyl substitutes.     

Highly Selective Synthesis of Iridium(III) Metalla[2]catenanes through Component Pre‐Orientation by π⋅⋅⋅π Stacking

A series of molecular metalla[2]catenanes featuring Cp*Ir vertices have been prepared by the template‐free, coordination‐driven self‐assembly of dinuclear iridium acceptors and 1,5‐bis[2‐(4‐pyridyl)ethynyl]anthracene donors. The metalla[2]catenanes were formed by using a strategically selected linker type that is capable of participating in sandwich‐type π–π stacking interactions. In the solid state, the [2]catenanes adopt two different configurations depending on the halogen atoms at the dinuclear metal complex bridge. Altering the solvent or the concentration, as well as the addition of guest molecules, enabled controlled transformations between metalla[2]catenanes and tetranuclear metallarectangles.     

Dynamic combinatorial donor-acceptor catenanes in water: access to unconventional and unexpected structures

We describe here the assembly of new types of donor-acceptor [2]catenanes from dynamic combinatorial libraries (DCL) in water. These new catenanes contain both the donor and acceptor components in at least one of the interlocked rings, thereby possessing unusual and unexpected DAAD or DADD stacking sequences of the π units in their structures. The efficiency of the catenane assembly process can be enhanced by manipulating the DCL equilibrium in a variety of ways: adding a guest, changing the building block stoichiometries, or increasing the library concentration or the ionic strength of the solvent. The formation of catenanes and their constitutions are found to be dependent on subtle differences in the geometry, dimension, and flexibility of the donor building blocks.     

Dynamic chirality: keen selection in the face of stereochemical diversity in mechanically bonded compounds

The template-directed syntheses, employing bisparaphenylene-[34]crown-10 (BPP34C10), 1,5-dinaphthoparaphenylene-[36]crown-10 (1/5NPPP36C10), and 1,5-dinaphtho-[38]crown-10 (1/5DNP38C10) as templates, of three [2]catenanes, whereby one of the two bipyridinium units in cyclobis(paraquat-p-phenylene) is replaced by a bipicolinium unit, are described. The crude reaction mixtures comprising the [2]catenanes all contain slightly more of the homologous [3]catenanes, wherein a "dimeric" octacationic cyclophane has the crown ether macrocycles encircling the alternating bipyridinium units with the bipicolinium units completely unfettered. X-ray crystallography, performed on all three [2]catenanes and two of the three [3]catenanes reveals co-conformational and stereochemical preferences that are stark and pronounced. Both the [3]catenanes crystallize as mixtures of diastereoisomers on account of the axial chirality associated with the picolinium units in the solid state. Dynamic (1)H NMR spectroscopy is employed to probe in solution the relative energy barriers for rotations by the phenylene and pyridinium rings in the tetracationic cyclophane component of the [2]catenanes. Where there are co-conformational changes that are stereochemically "allowed", crown ether circumrotation and rocking processes are also investigated for the relative rates of their occurrence. The outcome is one whereby the three [2]catenanes containing BPP34C10, 1/5NPPP36C10, and 1/5DNP38C10 exist as one major enantiomeric pair of diastereoisomers amongst two, four, and eight diastereoisomeric pairs of enantiomers, respectively. The diastereoisomerism is a consequence of the presence of axial chirality together with helical and/or planar chirality in the same interlocked molecule. These [2]catenanes constitute a rich reserve of new stereochemical types that might be tapped for their switching and mechanical properties.     

New hybrid [2]catenanes based on a 4,4'-bipyridinium ligand

The self-assembly-mediated synthesis of metallomacrocycles 4a and 4b from (en)M(NO3)2 (M = Pd, Pt) and bipyridinium ligand 3 is described. The reaction is templated by disodium p-phenyldiacetic dicarboxylate, which is inserted into the macrocyclic cavity. Similarly, the self-assembly process between ligand 3, (en)M(NO3)2 (M = Pd, Pt), and the macrocyclic polyether 6 resulted in the formation of hybrid catenanes 7a and 7b. In the [2]catenanes, the circumrotation of the macrocyclic polyether through the cavity of the metallocycle is slow on the 1H NMR time scale.     

Nondegenerate pi-donor/pi-acceptor [2]catenanes containing proton-ionizable 1H-1,2,4-triazole subunits: synthesis and spontaneous resolution

Chirality can hold the key to inducing directionality of motion in components of molecular devices. With this idea in mind, we describe here 1) the template-directed synthesis of two [2]catenanes wherein cyclobis(paraquat-p-phenylene) is interlocked with polyether macrocycles containing, in addition to one 3,5-bis(oxymethylene)-1H-1,2,4-triazole unit, either one 1,4-dioxybenzene or one 1,5-dioxynaphthalene ring system. We also report 2) the full characterization of both [2]catenanes by fast atom bombardment mass spectrometry (FABMS), X-ray crystallography, and dynamic (1)H NMR spectroscopy. We reveal 3) the fact that the [2]catenanes not only exist, both in the solution-state and in the solid-state, as strictly one of the two possible translational isomers, but that they also exhibit spontaneous resolution on crystallization leading to formation of homochiral crystals, as indicated by X-ray crystallography and circular dichroism (CD) experiments. Finally, we comment 4) on the chances of switching these catenanes chemically.     

Symbiotic Control in Mechanical Bond Formation

Since the advent of mechanically interlocked molecules (MIMs), many approaches to templating their formation using various different noncovalent bonding interactions have been introduced and explored. In particular, employing radical‐pairing interactions between BIPY^.+ units, the radical cationic state of 4,4′‐bipyridinium (BIPY²⁺) units, in syntheses is not only a convenient but also an attractive source of templation because of the unique properties residing in the resulting catenanes and rotaxanes. Herein, we report a copper‐mediated procedure that enables the generation, in the MIM‐precursors, of BIPY^.+ radical cations, while the metal itself, which is oxidized to Cu^I, catalyzes the azide–alkyne cycloaddition reactions that result in the efficient syntheses of two catenanes and one rotaxane, assisted by radical‐pairing interactions between the BIPY^.+ radical cations. This procedure not only provides a fillip for making and investigating the properties of Coulombically challenged catenanes and rotaxanes, but it also opens up the possibility of synthesizing artificial molecular machines which operate away from equilibrium.     

Exploring the formation pathways of donor-acceptor catenanes in aqueous dynamic combinatorial libraries

The discovery through dynamic combinatorial chemistry (DCC) of a new generation of donor-acceptor [2]catenanes highlights the power of DCC to access unprecedented structures. While conventional thinking has limited the scope of donor-acceptor catenanes to strictly alternating stacks of donor (D) and acceptor (A) aromatic units, DCC is demonstrated in this paper to give access to unusual DAAD, DADD, and ADAA stacks. Each of these catenanes has specific structural requirements, allowing control of their formation. On the basis of these results, and on the observation that the catenanes represent kinetic bottlenecks in the reaction pathway, we propose a mechanism that explains and predicts the structures formed. Furthermore, the spontaneous assembly of catenanes in aqueous dynamic systems gives a fundamental insight into the role played by hydrophobic effect and donor-acceptor interactions when building such complex architectures.     

Facile access to monodisperse ultralarge rings

A facile access to monodisperse ultralarge rings counting 126, 174, and 294 ring atoms is described. It follows a reaction sequence that is well suited for the preparation of [2]catenanes but altered just in the sequence of the two steps cyclization and carbonate formation. The carbonate acts as a covalent template that is easily formed and later cleaved. The obtained monocyclic products are constitutional isomers of the catenanes.     

Spectroscopic and Electrochemical Properties of Catenanes Containing the 2,7-Diazapyrenium Unit

Abstract

The spectroscopic and electrochemical properties of two cyclophanes containing one and, respectively, two 2,7-diazapyrenium electron-acceptor units, and of their [2]catenanes with macrocycles containing two dioxybenzene or dioxynaphthalene electrondonor units have been investigated. The absorption spectra of the catenanes show weak and broad bands in the visible region, assigned to charge-transfer (CT) interactions. The very strong and structured fluorescence (298 K) and the structured fluorescence and phosphorescence (77 K) of the diazapyrenium unit are maintained in the two cyclophanes, but they are no longer present in the [2]catenanes, presumably because of a quenching process caused by the lower energy CT excited states. Each diazapyrenium unit undergoes two distinct reduction processes - only the first one of which is fully reversible - that are hardly affected at all when the diazapyrenium units are incorporated in a cyclophane. In the [2]catenanes, the CT interaction displaces the reduction processes of the diazapyrenium units toward more negative potentials. The results obtained for the diazapyrenium and previously investigated 4,4′-bipyridinium salts, selected cyclophane derivatives, and some [2]catenanes obtained by interlocking the cyclophanes with macrocycles containing two dioxyaromatic electron-donor units are compared and discussed.     

One-Step Synthesis of Cyclophanes as Crystalline Sponge and Their [2]Catenanes through SNAr Reactions

This work reports that cyclophanes and their [2]catenanes were synthesized by the S_NAr reactions of disubstituted adamantanes bearing halophenol units and 3,6-dichlorotetrazine in moderate yields. In the crystalline state, the cyclophanes had hexagonal structures with a cavity. The [2]catenanes were composed of two macrocycles that were singly interlocked and orthogonally arranged, indicating the construction from eight component molecules through eight C−O bonds in a one-step reaction in up to 33 % yield. The cyclophanes were assembled to afford a supramolecular organic framework in the solid state, which exhibited permanent intrinsic porosity and adsorption of leaf alcohol or aldehyde in a single-crystal to single-crystal fashion. The molecular structures of the liquid guests were determined by single-crystal X-ray analysis. The formation of catenanes and the use of cyclophane-based porous crystals in the crystalline sponge method may be largely ascribed to the solvophobic effects and the van der Waals interactions that originate in the aliphatic and bulky nature of the adamantane units.     

Rational Design and Integrative Assembly of Heteromeric Metalla[2]Catenanes Featuring Cp*Ir/Rh Fragments

We report a design strategy for integrative assembly of heteromeric [2]catenanes. The design focuses on the shape and functional group match of two different metalla-rectangles. A series of dipyridyl ligands with different lengths, widths and functional groups were designed and used for assembly experiments. Six heteromeric [2]catenanes were obtained both by direct mixture of two pre-assembled metalla-rectangles and one-pot three-component self-assembly. Multiple analytic methods were employed to characterize the catenanes, including single crystal X-ray diffraction analysis, NMR spectroscopy, mass spectroscopy and elemental analysis.     

Backbone‐Directed Self‐Assembly of Interlocked Molecular Cyclic Metalla[3]Catenanes

The efficient backbone‐directed self‐assembly of cyclic metalla[3]catenanes by the combination of tetrachloroperylenediimide (TCPDI)‐based dinuclear rhodium(III) clips and 4,4′‐diazopyridine or 4,4′‐dipyridylethylene ligands is realized in a single‐step strategy. The topology and coordination geometry of the cyclic metalla[3]catenanes are characterized by NMR spectroscopy, ESI‐TOF‐MS spectrometry, UV/Vis‐NIR spectroscopy, and X‐ray diffraction studies. The most remarkable feature of the formed cyclic metalla[3]catenane is that it contains π‐aggregates (ca. 2.6 nm) incorporating six TCPDIs. Further studies revealed that cyclic metalla[3]catenanes can be converted reversibly to their corresponding sodium adducts and precursor building blocks, respectively. This strategy opens the possibility of generating unique supramolecular structures from discrete functional π‐aggregates with precise arrangements.     

Effect of metallosupramolecular polymer concentration on the synthesis of poly[n]catenanes

Poly[n]catenanes are a class of polymers that are composed entirely of interlocked rings. One synthetic route to these polymers involves the formation of a metallosupramolecular polymer (MSP) that consists of alternating units of macrocyclic and linear thread components. Ring closure of the thread components has been shown to yield a mixture of cyclic, linear, and branched poly[n]catenanes. Reported herein are investigations into this synthetic methodology, with a focus on a more detailed understanding of the crude product distribution and how the concentration of the MSP during the ring closing reaction impacts the resulting poly[n]catenanes. In addition to a better understanding of the molecular products obtained in these reactions, the results show that the concentration of the reaction can be used to tune the size and type of poly[n]catenanes accessed. At low concentrations the interlocked product distribution is limited to primarily oligomeric and small cyclic catenanes . However, the same reaction at increased concentration can yield branched poly[n]catenanes with an ca. 21 kg mol⁻¹, with evidence of structures containing as many as 640 interlocked rings (1000 kg mol⁻¹).

Concentration of the metallosupramolecular polymer precursors have a significant effect on the architecture and size of the resulting poly[n]catenanes formed via a ring closing metathesis step.