Construction of Pseudorotaxanes and Rotaxanes Based on Cucurbit[n]uril

¹H-NMR spectroscopic analysis indicates that cucurbit[7]uril can form a stable inclusion complex with 1,6-hexanediamine, while cucurbit[5]uril cannot form pseudorotaxane with 1,6-hexanediamine under our experimental conditions. This was confirmed by the crystal structure of the complex. The cavity of cucurbit[8]uril seems to be large for binding 1,6-hexanediamine efficiently. And a simple, mild, high-yield (>80%) method has been described for the synthesis of rotaxanes through the self-assembly of pseudorotaxanes of cucurbit[n]uril (n=6, 7)/1, 6-hexanediamine and sodium tetraphenylborate. The obtained rotaxanes are held intact solely by noncovalent interactions, and are characterized by elemental analysis, ¹H-NMR, ESI-MS and MALDI-TOF MS.     

Unravelling the Roles of Solvophobic Effects and π⋅⋅⋅π Stacking Interactions in the Formation of [2]Catenanes Featuring Di-(N-Heterocyclic Carbene) Building Blocks

A series of [2]catenanes has been prepared from di-NHC building blocks by utilizing solvophobic effects and/or π⋅⋅⋅π stacking interactions. The dinickel naphthobiscarbene complex syn-[ 1 ] and the kinked biphenyl-bridged bipyridyl ligand L² yield the [2]catenane [ 2-IL ](OTf)₄ by self-assembly. Solvophobic effects are pivotal for the formation of the interlocked species. Substitution of the biphenyl-linker in L² for a pyromellitic diimide group gave ligand L³ , which yielded in combination with syn-[ 1 ] the [2]catenane [ 3-IL ](OTf)₄. This assembly exhibits enhanced stability in diluted solution, aided by additional π⋅⋅⋅π stacking interactions. The π⋅⋅⋅π stacking was augmented by the introduction of a pyrene bridge between two NHC donors in ligand L⁴ . Di-NHC precursor H₂- L⁴ (PF₆)₂ reacts with Ag₂O to give the [Ag₂ L⁴ ₂]₂ [2]catenane [ 4-IL ](PF₆)₄, which shows strong π⋅⋅⋅π stacking interactions between the pyrene groups. This assembly was readily converted into the [Au₂ L⁴ ₂]₂ gold species [ 5-IL ](PF₆)₄, which exhibits exceptional stability based on the strong π⋅⋅⋅π stacking interactions and the enhanced stability of the Au-C_NHC bonds.     

Chloride‐Anion‐Templated Synthesis of a Strapped‐Porphyrin‐Containing Catenane Host System

The synthesis, structure and anion‐recognition properties of a new strapped‐porphyrin‐containing [2]catenane anion host system are described. The assembly of the catenane is directed by discrete chloride anion templation acting in synergy with secondary aromatic donor–acceptor and coordinative pyridine–zinc interactions. The [2]catenane incorporates a three‐dimensional, hydrogen‐bond‐donating anion‐binding pocket; solid‐state structural analysis of the catenane?chloride complex reveals that the chloride anion is encapsulated within the catenane’s interlocked binding cavity through six convergent CH????Cl and NH???Cl hydrogen‐bonding interactions and solution‐phase ¹H NMR titration experiments demonstrate that this complementary hydrogen‐bonding arrangement facilitates the selective recognition of chloride over larger halide anions in DMSO solution.     

Formation of Self‐Templated 2,6‐Bis(1,2,3‐triazol‐4‐yl)pyridine [2]Catenanes by Triazolyl Hydrogen Bonding: Selective Anion Hosts for Phosphate

We report the remarkable ability of 2,6‐bis(1,2,3‐triazol‐4‐yl)pyridine ( btp ) compounds 2 with appended olefin amide arms to self‐template the formation of interlocked [2]catenane structures 3 in up to 50 % yield when subjected to olefin ring‐closing metathesis in CH₂Cl₂. X‐ray diffraction crystallography enabled the structural characterization of both the [2]catenane 3 a and the non‐interlocked macrocycle 4 a . These [2]catenanes showed selective triazolyl hydrogen‐bonding interactions with the tetrahedral phosphate anion when screened against a range of ions; 3 a , b are the first examples of selective [2]catenane hosts for phosphate.     

Ultramacrocyclization in water via external templation

Condensing a dihydrazide and each of a series of cationic bisaldehyde compounds bearing polymethylene chains in weakly acidic water produces either a macrocycle in a [1 + 1] manner or its dimer namely a [2]catenane, or their mixture. The product distribution is determined by the length of the bisaldehydes. Addition of cucurbit[8]uril (CB[8]) drives the catenane/macrocycle equilibria to the side of macrocycles, by forming ring-in-ring complexes with the latter. When the polymethylene unit of the bisaldehyde is replaced with a more rigid p-xylene linker, its self-assembly with the dihydrazide leads to quantitative formation of a [2]catenane. Upon addition of CB[8], the [2]catenane is transformed into an ultra-large macrocycle condensed in a [2 + 2] manner, which is encircled by two CB[8] rings. The framework of this macrocycle contains one hundred and two atoms, whose synthesis would be a formidable task without the external template CB[8]. Removal of CB[8] with a competitive guest leads to recovery of the [2]catenane.

Condensing a bisaldehyde and a bisacylhydrazide in water in the presence of cucurbit[8]uril, produced an ultra-large ring whose framework contains more than one hundred atoms.     

[n]Cycloparaphenylene-Pillar[5]arene Bismacrocycles: Their Circularly Polarized Luminescence and Multiple Guest Recognition Properties

Both pillar[n]arenes (P[n]As) and [n]cycloparaphenylenes ([n]CPPs) play an important role in supramolecular chemistry. Herein, we report the precise synthesis of two multifunctional bismacrocycles [n]CPP-P[5]A by integrating P[5]A into the [n]CPP backbone. The photoluminescence quantum yield (Φ_F) of the bismacrocycles was found to show a dramatic increase relative to the corresponding [n]CPPs. The chiral enantiomers (pR)/(pS)-[8]CPP-P[5]A were successfully isolated by chiral HPLC, and showed promising properties of circularly polarized luminescence (g_lum≈0.02). In addition, [n]CPP-P[5]A bismacrocycles are capable of binding pyridinium salts and fullerene derivatives with high affinity and specificity within the two distinct cavities. Transient absorption studies showed that photo-induced electron transfer occurs in [10]CPP-P[5]A⊃C₆₀ complex. Our results suggest that [n]CPP-P[5]A are potentially useful in CPL-active materials, multiple guest recognition and supramolecular polymer preparation.     

A double ring-closing olefin metathesis approach to [3]catenanes

A [3]catenane with peripheral olefinic macrocycles was conveniently synthesized via a double ring-closing olefin metathesis. Highlights of this work include the synthesis of a 65-membered macrocycle featuring two phenanthroline ligands, a Cu(I)-templated synthesis of a [3]pseudorotaxane, and the key double ring-closing olefin metathesis to afford the desired [3]catenane in 71% yield.     

Isolated supramolecular [Ru(bpy)3]-viologen-[Ru(bpy)3] complexes with trapped CB[7,8] and photoinduced electron-transfer study in nonaqueous solution

The synthesis of two supramolecular diruthenium complexes, 1 ?CB[7] and 1 ?CB[8] (CB[n]=cucurbit[n]uril), which contain the respective host CB[7] and CB[8], were synthesized and isolated. In the case of host CB[8], the desired supramolecular complex was obtained by utilizing dihydroxynapthalene as a template during the synthesis. The ¹H NMR spectra, electrochemistry, and photochemistry of these supramolecular complexes were performed in nonaqueous solution. The results show that both CB[7,8] hosts mainly bind to the linker part in solution in acetonitrile. This binding also lowers the oxidation potential of the ruthenium metal center and hinders the quenching effect by the viologen moiety. It has also been shown that external methylviologen can be included into 1 ?CB[8]. Analysis with NMR spectroscopy, electrochemistry, and photochemistry clearly shows a viologen radical dimer formation between the bound viologen and free methylviologen, thereby showing that the unique abilities of the CB[8] host can be utilized even in nonaqueous solution.     

n-Butane,iso-Butane and 1-Butene Adsorption on Imidazolium-Based Ionic Liquids Studied with Molecular Beam Techniques

The interaction of molecules, especially hydrocarbons, at the gas/ionic liquid (IL) surface plays a crucial role in supported IL catalysis. The dynamics of this process is investigated by measuring the trapping probabilities of n-butane, iso-butane and 1-butene on a set of frozen 1-alkyl-3-methylimidazolium-based ILs [C_nC₁Im]X, where n=4, 8 and X⁻=Cl⁻, Br⁻, [PF₆]⁻ and [Tf₂N]⁻. The decrease of the initial trapping probability with increasing surface temperature is used to determine the desorption energy of the hydrocarbons at the IL surfaces. It increases with increasing alkyl chain length n and decreasing anion size for the ILs studied. We attribute these effects to different degrees of alkyl chain surface enrichment, while interactions between the adsorbate and the anion do not play a significant role. The adsorption energy also depends on the adsorbing molecule: It decreases in the order n-butane>1-butene>iso-butane, which can be explained by different dispersion interactions.     

六～八元瓜环与三种N-苄基取代笼状客体的相互作用

合成了3种具有对不同瓜环选择性各异的双探针N-苄基取代笼状客体, 它们分别是N-苄基六次甲基四胺盐酸盐(1), N-苄基喹啉环啶盐酸盐(2), N-苄基-1,4-二氮杂双环[2.2.1]辛烷盐酸盐(3), 利用¹H NMR和MS等方法对这些客体进行了表征. ¹H NMR显示, 六元瓜环仅对这些客体的苄基探针部分具有选择性作用, 形成作用比为1∶1的不对称包结配合物; 七元瓜环对客体1和3的苄基探针部分具有选择性作用, 形成作用比为1∶1的不对称包结配合物, 而对客体2的笼状奎宁环啶基部分具有选择性作用, 也形成作用比为1∶1的包结配合物; 八元瓜环也仅对这些客体的苄基探针部分具有选择性作用, 形成作用比为1∶2的对称包结配合物.     

The topological and chemical implications of introducing oriented rings to [3]catenanes

We report the synthesis of three donor–acceptor azido-functionalised catenanes, wherein the asymmetric positioning of the azide group on one or two of the ring components renders its resident macrocycle constitutionally asymmetric, and so it acts as an oriented ring. As a consequence, the analyses of (i) a monoazido[2]catenane, (ii) a monoazido[3]catenane and (iii) a bisazido[3]catenane, which exists as a mixture of two conditional topological isomers, are significantly complicated. Accordingly, characterisation of the catenanes, which was achieved by a combination of dynamic ¹H NMR spectroscopy, mass spectrometry and single crystal X-ray diffraction, is an arduous task. We expect that the difficulties in analysing these mechanically interlocked molecules will be encountered more frequently as chemists prepare entities with increasingly complex topologies.     

Catenanes: Fifty Years of Molecular Links

Half a century after Schill and Lüttringhaus carried out the first directed synthesis of a [2]catenane, a plethora of strategies now exist for the construction of molecular Hopf links (singly interlocked rings), the simplest type of catenane. The precision and effectiveness with which suitable templates and/or noncovalent interactions can arrange building blocks has also enabled the synthesis of intricate and often beautiful higher order interlocked systems, including Solomon links, Borromean rings, and a Star of David catenane. This Review outlines the diverse strategies that exist for synthesizing catenanes in the 21st century and examines their emerging applications and the challenges that still exist for the synthesis of more complex topologies.     

Dynamic [2]catenanes based on a hydrogen bonding-mediated bis-zinc porphyrin foldamer tweezer: a case study

This paper describes the self-assembly of a new class of three-component dynamic [2]catenanes, which are driven or stabilized by intramolecular hydrogen bonding, coordination, and electrostatic interaction. One of the component molecules 2, consisting of an aromatic oligoamide spacer and two peripheral zinc porphyrin units, was designed to adopt a folded preorganized conformation, which is stabilized by consecutive intramolecular three-centered hydrogen bonds. Component molecule 3 is a linear secondary ammonium bearing two peripheral pyridine units, which was designed to form a 1:1 complex with 24-crown-8 (5). The 1H NMR and UV-vis experiments in CDCl3-CD3CN (4:1 v/v) revealed that, due to the preorganized U-shaped feature, 2 could efficiently bind 3 through the cooperative zinc-pyridine coordination to generate highly stable 1:1 complex 2.3. Adding 5 to the 1:1 solution of 2 and 3 led to the formation of dynamic three-component [2]catenane 2.3.5 as a result of the threading of 3 through 5. 1H NMR studies indicated that in the 1:1:1 solution (3 mM) [2]catenane 2.3.5 was generated in 55% yield at 25 degrees C. The yield was increased with the reduction of the temperature and [2]catenane could be produced quantitatively in a 1:1:2 solution ([2]=3 mM) at -13 degrees C. Replacing 3 with 1,2-bis(4,4'-bipyridinium)ethane (4) in the three-component solution could also give rise to similar dynamic [2]catenane 2.4.5 albeit in slightly lower yield.     

A mass spectrometry study of alkanes in air plasma at atmospheric pressure

The positive APCI-mass spectra in air of linear (n-pentane, n-hexane, n-heptane, n-octane), branched [2,4-dimethylpentane, 2,2-dimethylpentane and 2,2,4-trimethylpentane (i-octane)], and cyclic (cyclohexane) alkanes were analyzed at different mixing ratios and temperatures. The effect of air humidity was also investigated. Complex ion chemistry is observed as a result of the interplay of several different reagent ions, including atmospheric ions O₂^+•, NO⁺, H₃O⁺, and their hydrates, but also alkyl fragment ions derived from the alkanes. Some of these reactions are known from previous selected ion/molecule reaction studies; others are so far unreported. The major ion formed from most alkanes (M) is the species [M − H]⁺, which is accompanied by M^+• only in the case of n-octane. Ionic fragments of C _n H_2n ^+1/+ composition are also observed, particularly with branched alkanes: the relative abundance of such fragments with respect to that of [M − H]⁺ decreases with increasing concentration of M, thus suggesting that they react with M via hydride abstraction. The branched C₇ and C₈ alkanes react with NO⁺ to form a C₄H₁₀NO⁺ ion product, which upon collisional activation dissociates via HNO elimination. The structure of t-Bu⁺(HNO) is proposed for such species, which is reasonably formed from the original NO⁺(M) ion/molecule complex via hydride transfer and olefin elimination. Finally, linear alkanes C₅–C₈ give a product ion corresponding to C₄H₇⁺(M), which we suggest is attributed to addition of [M − H]⁺ to C₄H₈ olefin formed in the charge-transfer-induced fragmentation of M. The results are relevant to applications of nonthermal plasma processes in the fields of air depuration and combustion enhancement.     

Irreversible but noncovalent Ru(II)-pyridine bond: its use for the formation of [2]-catenanes

The reaction between ligand 1, which consists of two terminal pyridines attached to a central 1,10-phenanthroline (phen), and the complex Ru(phen)2(CH3CN)2(PF6)2 has been studied. A new ruthenium containing metallamacrocycle has been obtained and fully characterized. Despite the relatively poor yield for the cyclization process involving the ruthenium center (20%), this strategy led to the synthesis of two different kinds of [2]-catenane. The first example reported in this article is a bimetallic Cu(I)/Ru(II) catenane 5(3+) consisting of a purely organic ring interlocked with the ruthenium(II)-incorporating metallacycle. Complex 5(3+) was selectively demetalated at the Cu(I) center to lead to the free Ru(II)-containing catenane. A trimetallic Ru(II)/Cu(I)/Ru(II) catenane 8(5+) was also synthesized showing that this approach is reliable and promising for the elaboration of photoactive multicomponent systems.     

三个异质同晶喹啉-8-氧醚乙酸配位聚合物的合成、结构及磁性质

本文通过溶剂热反应合成了3个异质同晶的配位聚合物[Ni(8-qoac)Cl]n(1,8-Hqoac=喹啉-8-氧醚乙酸),[Fe(8-qoac)Cl]n(2)和[Mn(8-qoac)Cl]n(3)。单晶结构分析表明,这些配合物结晶在Pbca空间群中,其中八面体配位的金属离子首先被2个氯离子桥连形成1个双核结构,双核单元再通过4个反-反配位模式的羧酸根与4个相邻的双核单元连接,形成1个以双核为节点的(4,4)网二维层状结构。磁学表征发现化合物1表现出类自旋倾斜的磁行为,而2和3只表现出简单的反铁磁行为,表明了金属离子的各向异性等特点对磁学行为会产生重要的影响。     

Overcoming Statistical Complexity: Selective Coordination of Three Different Metal Ions to a Ligand with Three Different Coordination Sites

In general, it is difficult to selectively introduce different metal ions at specific positions of a cluster‐like structure. This is mainly due to statistical problems as well as the reversibility of the formation of coordination bonds. To overcome this statistical problem, we used a carefully designed ligand, H₆L, which can accommodate three different kinds of metal ions in three types of coordination sites. The complex [LNiZn₂La]³⁺, which contains three different metals, was quantitatively obtained by a stepwise procedure, but different products were obtained when the metal ions were added in a different order. However, equilibration studies indicated that this complex was almost solely formed among 54 (=3×3×₃H₂) possible products upon heating; the formation efficiency (ca. 100 %) was significantly higher than the statistical probability (2.47 %). Such carefully designed ligands should be useful for the synthesis multimetallic systems, which are of interest because of the interplay between the different metals.     

Ruthenium(II) Complexes with Three Different Diimine Ligands

The synthesis of tri-heteroleptic complex of Ru(II) with diimine ligands is describe. Ten compounds [Ru(R₂bpy) (biq) (L)][PF₆]₂ (R = H, CH₃); L = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy), 2,2′-bipyrimidine (bpm), 2,2′-biisoquinoline (biiq), 1,10-phenanthroline (phen), dipyrido[3,2-c:2′,3′-e]pyridazine (taphen), 2,2′-biquinoline (biq), 6,7-dihydrodipyrido[2,3-b:3,2-j][1,10]-phenanthroline (dinapy), 2-(2[pyridyl)quinoline (pq), 1-(2-pyrimidyl)pyrazole] (pzpm), 2,2′-biimidazole (H₂biim) are characterized by elemental analysis, electronic and ¹H-NMR spectroscopy. The relative photosustitution rates of biq in MeCN are given at three temperatures.     

Noncovalent Modification of Cycloparaphenylene by Catenane Formation Using an Active Metal Template Strategy**

The active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes, allowing the synthesis of a variety of MIMs, including π-conjugated and multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule characterized by its cyclic π-conjugated structure and unique properties. Therefore, diverse modifications of CPPs are necessary for its wide application. However, most CPP modifications require early stage functionalization and the direct modification of CPPs is very limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2′-bipyridine macrocycle as a new CPP analogue that contains a reliable synthetic scaffold enabling diverse and concise post-modification. Following the AMT strategy, the [9]CPP-bipyridine catenane was successfully synthesized through Ni-mediated aryl-aryl coupling. Catalytic C−H borylation/cross-coupling and metal complexation of the bipyridine macrocycle moiety, an effective post-functionalization method, were also demonstrated with the [9]CPP-bipyridine catenane. Single-crystal X-ray structural analysis revealed that the [9]CPP-bipyridine catenane forms a tridentated complex with an Ag ion inside the CPP ring. This interaction significantly enhances the phosphorescence lifetime through improved intermolecular interactions.     

Combination of nitroxide‐mediated polymerization and SET‐LRP for the synthesis of high molar mass branched and star‐branched poly(n‐butyl acrylate) characterized by size exclusion chromatography and rheology

Branched and star‐branched polymers were successfully synthesized by the combination of two successive controlled radical polymerization methods. A series of linear and star poly(n‐butyl acrylate)‐co‐poly(2‐(2‐bromoisobutyryloxy) ethyl acrylate) statistical copolymers, P(nBA‐co‐BIEA)_x, were first synthesized by nitroxide‐mediated polymerization (NMP at T > 100 °C). The subsequent polymerization of n‐butyl acrylate by single electron transfer‐living radical polymerization (SET‐LRP at T = 25 °C), initiated from the brominated sites of the P(nBA‐co‐BIEA)_x copolymer, produced branched or star‐branched poly(n‐butyl acrylate) (PnBA). Both types of polymerizations (NMP and SET‐LRP) exhibited features of a controlled polymerization with linear evolutions of logarithmic conversion versus time and number‐average molar masses versus conversion for final M_n superior to 80,000 g mol^?1. The branched and star‐branched architectures with high molar mass and low number of branches were fully characterized by size exclusion chromatography. The Mark–Houwink Sakurada relationship and the analysis of the contraction factor (g′ = ([η]_branched/[η]_linear)_M) confirmed the elaboration of complex PnBA. The zero‐shear viscosities of the linear, star‐shaped, branched, and star‐branched polymers were compared. The modeling of the rheological properties confirmed the synthesis of the branched architectures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012