A Multifunctional,Charge-Neutral,Chiral Octahedral M12L12 Cage

A chiral, octahedral M₁₂L₁₂ cage, which is charge neutral and contains an internal void of about 2000 ų, is reported. The cage was synthesised as an enantiopure complex by virtue of amino-acid-based dicarboxylate ligands, which assemble around copper paddlewheels at the vertices of the octahedron. The cage persists in solution with retention of the fluorescence properties of the parent acid. The solid-state structure contains large pores both within and between the cages, and displays permanent porosity for the sorption of gases with retention of crystallinity. Initial tests show some enantioselectivity of the cage towards guests in solution.     

Post-Synthesis Conversion of an Unstable Imine Cage to a Stable Cage with Amide Moieties Towards Selective Receptor for Fluoride

Synthesis of robust covalent macrocycles/cages via multiple amide-bond forming reaction is highly challenging and generally it needs multistep reactions. One-pot reaction of appropriate di-/tri-acyl chloride with a diamine generally results polymers or oligomers instead of discrete architectures. To overcome this limitation, a strategy is reported here using dynamic imine chemistry for facile construction of imine-based macrocycle and cage upon treatment of a diamine with di- and tri-aldehydes respectively, followed by post-synthesis one-step conversion of imine bonds to amides to form the desired robust macrocycle and cage containing multiple amide bonds. While the macrocycle was found to form aggregates in DMSO, the cage was intact without any aggregation. Six amide groups in the confined pocket of the cage made it an ideal receptor for selective binding of fluoride with very high selectivity (∼3 10³ fold) over chloride, and it was silent towards other halides, phosphate, and other oxyanions.     

基于六苯基苯骨架四苯基乙烯衍生物的合成及聚集诱导发光性质研究

设计合成了三个基于六苯基苯骨架结构的四苯基乙烯衍生物HPB-nTPE (n=2, 4, 6), 它们的分解温度均在440 ℃以上, 具有很好的热稳定性. 研究了化合物的均相溶液、聚集体以及固体粉末的光物理性质. 该类化合物具有典型的聚集诱导发光性质, 在均相溶液中几乎不发光, 而形成聚集体后发出明亮的蓝绿色荧光, 荧光量子产率分别为0.37, 0.36和0.37, 与均相溶液中相比增强了400多倍. HPB-nTPE固态呈无定形结构, 荧光量子产率分别为0.39, 0.36和0.36, 约为固态四苯基乙烯的1.8倍. HPB-nTPE的聚集态和固态的高发光量子产率来自两方面的贡献, 一是凝聚态抑制了四苯基乙烯基团中苯环的自由旋转引起的激发态非辐射跃迁, 另一方面是星形刚性六苯基苯骨架进一步抑制了凝聚态分子内和分子间四苯基乙烯基团π-π堆积引起的激发态非辐射跃迁过程, 从而提高了四苯基乙烯基团的辐射跃迁效率. 本研究对高效有机光功能材料的发展有重要意义.     

Size-Selective Hydroformylation by a Rhodium Catalyst Confined in a Supramolecular Cage

Size-selective hydroformylation of terminal alkenes was attained upon embedding a rhodium bisphosphine complex in a supramolecular metal–organic cage that was formed by subcomponent self-assembly. The catalyst was bound in the cage by a ligand-template approach, in which pyridyl–zinc(II) porphyrin interactions led to high association constants (>10⁵ m ⁻¹) for the binding of the ligands and the corresponding rhodium complex. DFT calculations confirm that the second coordination sphere forces the encapsulated active species to adopt the ee coordination geometry (i.e., both phosphine ligands in equatorial positions), in line with in situ high-pressure IR studies of the host–guest complex. The window aperture of the cage decreases slightly upon binding the catalyst. As a result, the diffusion of larger substrates into the cage is slower compared to that of smaller substrates. Consequently, the encapsulated rhodium catalyst displays substrate selectivity, converting smaller substrates faster to the corresponding aldehydes. This selectivity bears a resemblance to an effect observed in nature, where enzymes are able to discriminate between substrates based on shape and size by embedding the active site deep inside the hydrophobic pocket of a bulky protein structure.     

Interpenetrated Cage Structures

This Review covers design strategies, synthetic challenges, host–guest chemistry, and functional properties of interlocked supramolecular cages. Some dynamic covalent organic structures are discussed, as are selected examples of interpenetration in metal–organic frameworks, but the main focus is on discrete coordination architectures, that is, metal‐mediated dimers. Factors leading to interpenetration, such as geometry, flexibility and chemical makeup of the ligands, coordination environment, solvent effects, and selection of suitable counter anions and guest molecules, are discussed. In particular, banana‐shaped bis‐pyridyl ligands together with square‐planar metal cations have proven to be suitable building blocks for the construction of interpenetrated double‐cages obeying the formula [M₄L₈]. The peculiar topology of these double‐cages results in a linear arrangement of three mechanically coupled pockets. This allows for the implementation of interesting guest encapsulation effects such as allosteric binding and template‐controlled selectivity. In stimuli‐responsive systems, anionic triggers can toggle the binding of neutral guests or even induce complete structural conversions. The increasing structural and functional complexity in this class of self‐assembled hosts promises the construction of intelligent receptors, novel catalytic systems, and functional materials.     

新型四苯乙烯衍生物的设计合成及其在羧酸酯酶活性分析中的应用

设计合成了一个含有p-乙酰氧基苄基单元的四苯乙烯吡啶盐衍生物,利用羧酸酯酶选择性地切除乙酰基以及所致的连锁反应将其从水溶性吡啶盐结构转为中性吡啶结构,使其聚集,实现荧光“点亮”,从而发展了新型的羧酸酯酶活性分析和抑制剂筛选的荧光探针.     

Component Selection in the Self‐Assembly of Palladium(II) Nanocages and Cage‐to‐Cage Transformations

Dynamic supramolecular systems involving a tetratopic palladium(II) acceptor and three different pyridine‐ and imidazole‐based donors have been used for self‐selection by a synergistic effect of morphological information and coordination ability of ligands through specific coordination interactions. Three different cages were first synthesized by two‐component self‐assembly of individual donor and acceptor. When all four components were allowed to interact in a reaction mixture, only one out of three cages was isolated. The preferential binding affinity towards a particular partner was also established by transforming a non‐preferred cage into a preferred cage by interaction with the appropriate ligand. Computational studies further supported the fact that coordination interaction of imidazole moiety to Pd^II is enthalpically more preferred compared to pyridine, which drives the selection process. Analysis of crystal packing of both complexes indicated the presence of strong hydrogen bonds between nitrate and water molecules and also H‐bonded 3D networks of water. Both complexes exhibit promising proton conductivity (10^?5 to ca. 10^?3 S cm^?1) at ambient temperature under a relative humidity of circa 98 % with low activation energy.     

Reversible Guest Uptake/Release by Redox‐Controlled Assembly/Disassembly of a Coordination Cage

Controlling the guest expulsion process from a receptor is of critical importance in various fields. Several coordination cages have been recently designed for this purpose, based on various types of stimuli to induce the guest release. Herein, we report the first example of a redox‐triggered process from a coordination cage. The latter integrates a cavity, the panels of which are based on the extended tetrathiafulvalene unit (exTTF). The unique combination of electronic and conformational features of this framework (i.e. high π‐donating properties and drastic conformational changes upon oxidation) allows the reversible disassembly/reassembly of the redox‐active cavity upon chemical oxidation/reduction, respectively. This cage is able to bind the three‐dimensional B₁₂F₁₂^2? anion in a 1:2 host/guest stoichiometry. The reversible redox‐triggered disassembly of the cage could also be demonstrated in the case of the host–guest complex, offering a new option for guest‐delivering control.     

A Self‐Sorting Scheme Based on Tetra‐Urea Calix[4]arenes

Size and shape do matter : When dimerized in nonpolar solvents, an equimolar mixture of eleven tetra‐urea calix[4]arenes with different wide‐rim substituents self‐sorts into only six out of 35 different homo‐ and heterodimers (see picture). Since the calixarene scaffold and the four urea units are the same in all cases, the self‐sorting process is driven only by the cooperative action of steric requirements and stoichiometry.

     

Engineering Porous Organic Cage Crystals with Increased Acid Gas Resistance

Both known and new CC3‐based porous organic cages are prepared and exposed to acidic SO₂ in vapor and liquid conditions. Distinct differences in the stability of the CC3 cages exist depending on the chirality of the diamine linkers used. The acid catalyzed CC3 degradation mechanism is probed via in situ IR and a degradation pathway is proposed and supported with computational results. CC3 crystals synthesized with racemic mixtures of diaminocyclohexane exhibited enhanced stability compared to CC3‐R and CC3‐S. Confocal fluorescent microscope images reveal that the stability difference in CC3 species originates from an abundance of mesoporous grain boundaries in CC3‐R and CC3‐S, allowing facile access of aqueous SO₂ throughout the crystal, promoting decomposition. These grain boundaries are absent from CC3 crystals made with racemic linkers.     

A family of calix[4]arene-supported [Mn(III)2Mn(II)2] clusters

In the cone conformation calix[4]arenes possess lower-rim polyphenolic pockets that are ideal for the complexation of various transition-metal centres. Reaction of these molecules with manganese salts in the presence of an appropriate base (and in some cases co-ligand) results in the formation of a family of calixarene-supported [Mn(III)(2)Mn(II)(2)] clusters that behave as single-molecule magnets (SMMs). Variation in the alkyl groups present at the upper-rim of the cone allows for the expression of a degree of control over the self-assembly of these SMM building blocks, whilst retaining the general magnetic properties. The presence of various different ligands around the periphery of the magnetic core has some effect over the extended self-assembly of these SMMs.     

Multicomponent Supramolecular Systems: Self‐Organization in Coordination‐Driven Self‐Assembly

The self‐organization of multicomponent supramolecular systems involving a variety of two‐dimensional (2 D) polygons and three‐dimensional (3 D) cages is presented. Nine self‐organizing systems, SS₁ – SS₉ , have been studied. Each involves the simultaneous mixing of organoplatinum acceptors and pyridyl donors of varying geometry and their selective self‐assembly into three to four specific 2 D (rectangular, triangular, and rhomboid) and/or 3 D (triangular prism and distorted and nondistorted trigonal bipyramidal) supramolecules. The formation of these discrete structures is characterized using NMR spectroscopy and electrospray ionization mass spectrometry (ESI‐MS). In all cases, the self‐organization process is directed by: 1) the geometric information encoded within the molecular subunits and 2) a thermodynamically driven dynamic self‐correction process. The result is the selective self‐assembly of multiple discrete products from a randomly formed complex. The influence of key experimental variables ‐ temperature and solvent ‐ on the self‐correction process and the fidelity of the resulting self‐organization systems is also described.     

Design and Assembly of a Chiral Metallosalen‐Based Octahedral Coordination Cage for Supramolecular Asymmetric Catalysis

Supramolecular containers featuring both high catalytic activity and high enantioselectivity represent a design challenge of practical importance. Herein, it is demonstrated that a chiral octahedral coordination cage can be constructed by using twelve enantiopure Mn(salen)‐derived dicarboxylic acids as linear linkers and six Zn₄‐p‐tert‐butylsulfonylcalix[4]arene clusters as tetravalent four‐connected vertices. The porous cage features a large hydrophobic cavity (≈3944 ų) decorated with catalytically active metallosalen species and is shown to be an efficient and recyclable asymmetric catalyst for the oxidative kinetic resolution of racemic secondary alcohols and the epoxidation of olefins with up to >99 % enantiomeric excess. The cage architecture not only prevents intermolecular deactivation and stabilizes the Mn(salen) catalysts but also encapsulates substrates and concentrates reactants in the cavity, resulting in enhanced reactivity and enantioselectivity relative to the free metallosalen catalyst.     

Stimuli-Responsive Self-Sorting Hybrid Hydrogen-Bonded/Metal-Coordinated Cage

The self-assembly of a unique molecular container is reported: a hybrid hydrogen-bonded/metal-coordinated cage where both hydrogen-bonding and metal-coordination form the crucial part of the topology. The hybrid cage was prepared combining hydrogen-bonded rosette motif and palladium(II)/platinum(II) coordination to a pyridine ligand. It was also shown that the hybrid cage could be prepared by integrative self-sorting from simple components. For the first time the genuine dual character of the hybrid cage was manifested as both self-assembling parts responded selectively to different stimuli (such as phosphine and cyanurate), which resulted in the disassembly of the cage.     

Trackable Supramolecular Fusion: Cage to Cage Transformation of Tetraphenylethylene‐Based Metalloassemblies

Herein, the trackable supramolecular transformation of a two‐component molecular cage to a three‐component cage through supramolecular fusion with another two‐component molecular square is described. The use of tetraphenylethene (TPE), a chromophore with aggregation‐induced emission (AIE) character, as a component for the molecular cages enables facile fluorescence monitoring of the transformation process: while both cages exhibit fluorescence emission via the restriction of intramolecular motion of the TPE motif, the interactions between TPE and 4,4′‐bipyridine introduced in the supramolecular fusion process result in partial fluorescence quenching and shifts in the emission maximum. This study provides a simple and efficient approach towards complex supramolecular cages with emergent functions and demonstrates that AIE features could provide unique opportunities for the characterization of complex, dynamic supramolecular transformation processes.