Chiral Metallacycles as Catalysts for Asymmetric Conjugate Addition of Styrylboronic Acids to α,β-Enones

BINOL-Based Chiral Macrocycles and Cages

Chirality, a fundamental principle in chemistry, biology, and medicine, is prevalent in nature and in organisms. Chiral molecules, such as DNA, RNA, and proteins, are crucial in biomolecular synthesis, as well as in the development of functional materials. Among these, 1,1'-binaphthyl-2,2'-diol (BINOL) stands out for its stable chiral configuration, versatile functionality, and commercial availability. BINOL is widely employed in asymmetric catalysis and chiral materials. This review mainly focuses on recent research over the past five years concerning the use of BINOL derivatives for constructing chiral macrocycles and cages. Their contributions to chiral luminescence, enantiomeric separation, transmembrane transport, and asymmetric catalysis were examined.

Biomimetic Chiral Nanomaterials with Selective Catalysis Activity

Chiral nanomaterials with unique chiral configurations and biocompatible ligands have been booming over the past decade for their interesting chiroptical effect, unique catalytical activity, and related bioapplications. The catalytic activity and selectivity of chiral nanomaterials have emerged as important topics, that can be potentially controlled and optimized by the rational biochemical design of nanomaterials. In this review, chiral nanomaterials synthesis, composition, and catalytic performances of different biohybrid chiral nanomaterials are discussed. The construction of chiral nanomaterials with multiscale chiral geometries along with the underlying principles for enhancing chiroptical responses are highlighted. Various biochemical approaches to regulate the selectivity and catalytic activity of chiral nanomaterials for biocatalysis are also summarized. Furthermore, attention is paid to specific chiral ligands, materials compositions, structure characteristics, and so on for introducing selective catalytic activities of representative chiral nanomaterials, with emphasis on substrates including small molecules, biological macromolecule, and in-site catalysis in living systems. Promising progress has also been emphasized in chiral nanomaterials featuring structural versatility and improved chiral responses that gave rise to unprecedented chances to utilize light for biocatalytic applications. In summary, the challenges, future trends, and prospects associated with chiral nanomaterials for catalysis are comprehensively proposed.

Uncovering tetrazoles as building blocks for constructing discrete and polymeric assemblies

Metal-organic self-assembly with flexible moieties is a budding field of research due to the possibility of the formation of unique architectures. Tetrazole, characterised by four nitrogen atoms in a five-member ring, exhibits immense potential as a component. Tetrazole offers four coordination sites for binding to the metal centre with nine distinct binding modes, leading to various assemblies. This review highlights different polymeric and discrete tetrazole-based assemblies and their functions. The meticulous manipulation of stoichiometry, ligands, and metal ions required for constructing discrete assemblies has also been discussed. The different applications of these architectures in separation, catalysis and detection have also been accentuated. The latter section of the review consolidates tetrazole-based cage composites, highlighting their applications in cell imaging and photocatalytic applications.

Highly robust supramolecular polymer networks crosslinked by a tiny amount of metallacycles

Supramolecular polymeric materials have exhibited attractive features such as self-healing, reversibility, and stimuli-responsiveness. However, on account of the weak bonding nature of most noncovalent interactions, it remains a great challenge to construct supramolecular polymeric materials with high robustness. Moreover, high usage of supramolecular units is usually necessary to promote the formation of robust supramolecular polymeric materials, which restrains their applications. Herein, we describe the construction of highly robust supramolecular polymer networks by using only a tiny amount of metallacycles as the supramolecular crosslinkers. A norbornene ring-opening metathesis copolymer with a 120° dipyridine ligand is prepared and self-assembled with a 60° or 120° Pt(II) acceptor to fabricate the metallacycle-crosslinked polymer networks. With only 0.28 mol% or less pendant dipyridine units to form the metallacycle crosslinkers, the mechanical properties of the polymers are significantly enhanced. The tensile strengths, Young's moduli, and toughness of the reinforced polymers reach up to more than 20 MPa, 600 MPa, and 150 MJ/m3, respectively. Controllable destruction and reconstruction of the metallacycle-crosslinked polymer networks are further demonstrated by the sequential addition of tetrabutylammonium bromide and silver triflate, indicative of good stimuli-responsiveness of the networks. These remarkable performances are attributed to the thermodynamically stable, but dynamic metallacycle-based supramolecular coordination complexes that offer strong linkages with good adaptive characteristics.

Cavity-Shape-Dependent Divergent Chemical Reaction inside Aqueous Pd6L4 Cages

Chemical reactions inside the confined pockets of enzyme-mimicking hosts, such as cages and macrocycles, have been an emerging field of interest over the past decade. Although many such reactions are known, the use of such cages toward the divergent synthesis of nonisomeric products has not been well explored. Divergent synthesis is a technique of forming two or more distinct products from the same reagents by changing the catalyst or reaction conditions. Changing the shape of the cage can also change the nature and magnitude of the host-guest interactions. Thus, is it possible for such changes to cause differences in the reaction pathways leading to formation of nonisomeric products? Herein, we report a divergent chemical transformation of anthrone [anthracen-9(10H)-one] inside different water-soluble M6L4 cages. When anthrone was encapsulated inside a newly synthesized M6L4 octahedral cage 1, it dimerized to form dianthrone [9,9'-bianthracen-10,10'(9H,9'H)-dione]. In contrast, when the same chemical reaction was performed inside a M6L4 double-square shaped cage 2, it was oxidized to form anthraquinone [anthracene-9,10-dione]. Similar results were obtained with a different set of isomeric aqueous Pd6 cages 3a (octahedral cage) and 3b (double-square cage), indicating the dependence of the shape of cavity on the divergent synthesis. The present report demonstrates a unique example of different outcomes/results of a reaction depending on the shape of the molecular container, which was driven by the host-guest interactions and the preorganization of the substrates.

Chiral SPINOL-Based Pt(II) Metallacycles For Immunogenic Cell Death

The incorporation of chirality endows Pt(II)-based metal-organic complexes (MOCs) with unique potentials in several fields such as nonlinear optics and chiral catalysis. However, the exploration of chiral Pt(II) metallacycles in biological responses remains underdeveloped. Herein, we designed and synthesized two chiral Pt(II) metallacycles 1 and 2 via the coordination-driven self-assembly of chiral 1,1'-spirobiindane-7,7'-diol (SPINOL)-derived ligands and cis-Pt(PEt3)2(OTf)2 (90°Pt). Their structures were well characterized by 1H NMR, 31P{1H} NMR, ESI-TOF-MS, and X-ray crystallography, and their photophysical properties were investigated by UV-vis absorption, fluorescence, and circular dichroism (CD) spectroscopies. Then, the antitumor activity of the two chiral metallacycles in vitro was further tested. Complexes 1 and 2 exhibited strong cytotoxicity, especially toward the A549 cells. The destruction of the mitochondrial function, the inhibition of the glutathione (GSH)/glutathione disulfide (GSSG) level, and the inactivation of superoxide dismutase (SOD) induced by complexes 1 and 2 led to the massive accumulation of reactive oxygen species (ROS). The overloaded ROS then triggered apoptotic cell death, and the release of damage-associated molecular patterns (DAMPs) further induced immunogenic cell death (ICD). To the best of our knowledge, this is the first example of Pt(II)-based metallacycles that can induce immunogenic cell death, providing a new strategy for the future design and construction of immune-modulating platinum agents in cancer therapy.

Homochiral Metallacycle Used as a Stationary Phase for Capillary Gas Chromatographic Separation of Chiral and Achiral Compounds

Metallacycles are a novel class of supramolecular materials with circular structures, internal cavities, and abundant host-guest chemical properties that have exhibited good application prospects in many fields. However, to the best of our knowledge, no research on the use of metallacycles as stationary phases for gas chromatographic (GC) separations has been published yet. In this work, we report for the first time the use of a homochiral metallacycle, [ZnCl2L]2, as a stationary phase for GC separations. [ZnCl2L]2 was synthesized by reaction of (S)-(1-isonicotinoylpyrrolidin-2-yl)methyl-isonicotinate (L) with ZnCl2 via coordination-driven self-assembly. The [ZnCl2L]2-coated column displayed an excellent separation performance not only of organic isomers but also of racemic compounds. Sixteen racemates (including alcohols, esters, amino acid derivatives, ethers, organic acids, and epoxides) and 21 isomeric compounds (including positional, structural, and cis/trans-isomers) were well separated on the [ZnCl2L]2-coated column. Impressively, some racemates were resolved with high resolution values (Rs), including 1,2-butanediol diacetate (Rs = 25.86), ethyl 3-hydroxybutyrate (Rs = 20.97), 1,3-butanediol diacetate (Rs = 18.09), and threonine derivative (Rs = 18.61). Compared with the commercial β-DEX 120 column for separation of the tested racemates, the [ZnCl2L]2-coated column exhibited good enantioseparation complementarity, enabling separation of some racemates that could not be separated, or were not well resolved, by the β-DEX 120 column. In addition, many organic mixtures, such as n-alkanes, alkylbenzenes, n-alcohols, and a Grob test mixture, were also well separated on the [ZnCl2L]2-coated column. The column also has good reproducibility and thermal stability on separation. This work not only reveals the great potential of metallacycles for GC separations but also opens up a new application of metallacycles in separation science.

Phenylthiol-BODIPY-based supramolecular metallacycles for synergistic tumor chemo-photodynamic therapy

The development of more effective tumor therapy remains challenging and has received widespread attention. In the past decade, there has been growing interest in synergistic tumor therapy based on supramolecular coordination complexes. Herein, we describe two triangular metallacycles (1 and 2) constructed by the formation of pyridyl boron dipyrromethene (BODIPY)-platinum coordination. Metallacycle 2 had considerable tumor penetration, as evidenced by the phenylthiol-BODIPY ligand imparting red fluorescent emission at ∼660 nm, enabling bioimaging, and transport visualization within the tumor. Based on the therapeutic efficacy of the platinum(II) acceptor and high singlet oxygen (¹O₂) generation ability of BODIPY, 2 was successfully incorporated into nanoparticles and applied in chemo-photodynamic tumor therapy against malignant human glioma U87 cells, showing excellent synergistic therapeutic efficacy. A half-maximal inhibitory concentration of 0.35 μM was measured for 2 against U87 cancer cells in vitro. In vivo experiments indicated that 2 displayed precise tumor targeting ability and good biocompatibility, along with strong antitumor effects. This work provides a promising approach for treating solid tumors by synergistic chemo-photodynamic therapy of supramolecular coordination complexes.

Chiral self-sorting and guest recognition of porous aromatic cages

The synthesis of ultra-stable chiral porous organic cages (POCs) and their controllable chiral self-sorting at the molecular and supramolecular level remains challening. Herein, we report the design and synthesis of a serial of axially chiral porous aromatic cages (PAC 1-S and 1-R) with high chemical stability. The theoretical and experimental studies on the chiral self-sorting reveal that the exclusive self-recognition on cage formation is an enthalpy-driven process while the chiral narcissistic and self-sorting on supramolecular assembly of racemic cages can be precisely regulated by π–π and C–H…π interactions from different solvents. Regarding the chemical stability, the crystallinity of PAC 1 is maintained in aqueous solvents, such as boiling water, high-concentrated acid and alkali; mixtures of solvents, such as 1 M H₂SO₄/MeOH/H₂O solution, are also tolerated. Investigations on the chiral sensing performance show that PAC 1 enables enantioselective recognition of axially chiral biaryl molecules.

The synthesis of stable chiral porous organic cages and the study of their chiral self-sorting properties is challenging. Here, the authors report axially chiral porous aromatic cages with high stability and solvent-controlled chiral self-sorting.

Enantioselective Conjugate Addition of Boronic Acids to α,β-Unsaturated 2-Acyl Imidazoles Catalyzed by Chiral Diols

Herein, we report the enantioselective conjugate addition of organic boronic acids to α,β-unsaturated 2-acyl imidazoles using (R)-3,3'-I₂-BINOL as the catalyst. The catalytic system shows high efficiency and tolerance to alkenylboronic acids and heteroarylboronic acids. The corresponding Michael addition products were obtained in moderate to excellent yields and with moderate to excellent enantioselectivities (up to 97% ee). A gram-scale reaction was also conducted, and the desired product was obtained in high yield with no erosion in enantioselectivity. Finally, the synthetic utility of the methodology was demonstrated by transforming the 2-acyl imidazole moiety to the corresponding aldehyde, carboxylic acid, ester, and amide derivatives.

A Near-Infrared BODIPY-Based Rhomboidal Metallacycle for Imaging-Guided Photothermal Therapy

Although boron dipyrromethene (BODIPY)-based metallacycles are expected to be promising candidates for imaging probes and therapeutic agents, their biomedical applications are restricted by their short absorption/emission wavelengths. In this work, we report a rhombic metallacycle M with broad absorption in the near-infrared (NIR) range and emissions at wavelengths >800 nm, which exhibits an efficient photothermal conversion capacity. Metallacycle M was encapsulated via Pluronic F127 to fit the biotic environment, resulting in the generation of F127/M nanoparticles (NPs) with high hydrophilicity and biocompatibility. In vitro studies demonstrated that the F127/M NPs underwent efficient cellular uptake and exhibited satisfactory photothermal therapeutic activity. Furthermore, in vivo experiments revealed that tumor growth was effectively inhibited, and the degree of undesirable biological damage was minimal in treatment with F127/M NPs and laser irradiation. Finally, the F127/M NPs could be visualized through NIR fluorescence imaging in living mice, thereby allowing their distribution to be monitored in order to enhance treatment accuracy during photothermal therapy. We envision that such BODIPY-based metallacycles will provide emerging opportunities for the development of novel therapeutic agents for biomedical applications.

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

Supramolecular catalysis is reviewed with an eye on heteroleptic aggregates/complexation. Since most of the current metallosupramolecular catalytic systems are homoleptic in nature, the idea of breaking/reducing symmetry has ignited a vivid search for heteroleptic aggregates that are made up by different components. Their higher degree of functional diversity and structural heterogeneity allows, as demonstrated by Nature by the multicomponent ATP synthase motor, a more detailed and refined configuration of purposeful machinery. Furthermore, (metallo)supramolecular catalysis is shown to extend beyond the single "supramolecular unit" and to reach far into the field and concepts of systems chemistry and information science.

Directionally aligned crown ethers as superactive organocatalysts for transition metal ion-free arylation of unactivated arenes

When one-dimensionally aligned to the same side, multiple non-covalently associated crown ether groups could act as a whole to yield a higher catalytic activity than an individual poorly active crown ether group, delivering the lowest catalyst loading of 1 - 2 mol% among all hitherto known organocatalysts for catalyzing direct arylation of unactivated arenes with haloarenes.

An electrically conductive metallocycle: densely packed molecular hexagons with π-stacked radicals

Electrical conduction among metallocycles has been unexplored because of the difficulty in creating electronic transport pathways. In this work, we present an electrocrystallization strategy for synthesizing an intrinsically electron-conductive metallocycle, [Ni6(NDI-Hpz)6(dma)12(NO3)6]·5DMA·nH2O (PMC-hexagon) (NDI-Hpz = N,N'-di(1H-pyrazol-4-yl)-1,4,5,8-naphthalenetetracarboxdiimide). The hexagonal metallocycle units are assembled into a densely packed ABCABC… sequence (like the fcc geometry) to construct one-dimensional (1D) helical π-stacked columns and 1D pore channels, which were maintained under the liberation of H2O molecules. The NDI cores were partially reduced to form radicals as charge carriers, resulting in a room-temperature conductivity of (1.2-2.1) × 10-4 S cm-1 (pressed pellet), which is superior to that of most NDI-based conductors including metal-organic frameworks and organic crystals. These findings open up the use of metallocycles as building blocks for fabricating conductive porous molecular materials.

Molecular Cavity for Catalysis and Formation of Metal Nanoparticles for Use in Catalysis

The employment of weak intermolecular interactions in supramolecular chemistry offers an alternative approach to project artificial chemical environments like the active sites of enzymes. Discrete molecular architectures with defined shapes and geometries have become a revolutionary field of research in recent years because of their intrinsic porosity and ease of synthesis using dynamic non-covalent/covalent interactions. Several porous molecular cages have been constructed from simple building blocks by self-assembly, which undergoes many self-correction processes to form the final architecture. These supramolecular systems have been developed to demonstrate numerous applications, such as guest stabilization, drug delivery, catalysis, smart materials, and many other related fields. In this respect, catalysis in confined nanospaces using such supramolecular cages has seen significant growth over the years. These porous discrete cages contain suitable apertures for easy intake of substrates and smooth release of products to exhibit exceptional catalytic efficacy. This review highlights recent advancements in catalytic activity influenced by the nanocavities of hydrogen-bonded cages, metal-ligand coordination cages, and dynamic or reversible covalently bonded organic cages in different solvent media. Synthetic strategies for these three types of supramolecular systems are discussed briefly and follow similar and simplistic approaches manifested by simple starting materials and benign conditions. These examples demonstrate the progress of various functionalized molecular cages for specific chemical transformations in aqueous and nonaqueous media. Finally, we discuss the enduring challenges related to porous cage compounds that need to be overcome for further developments in this field of work.

Chiral proline-substituted porous organic cages in asymmetric organocatalysis

The efficient preparation of chiral porous organic cages (POCs) with specific functions is challenging, and their application in asymmetric catalysis has not previously been explored. In this work, we have achieved the construction of chiral POCs based on a supramolecular tetraformyl-resorcin[4]arene scaffold with different chiral proline-modified diamine ligands and utilizing dynamic imine chemistry. The incorporation of V-shaped or linear chiral diamines affords the [4 + 8] square prism and [6 + 12] octahedral POCs respectively. The appended chiral proline moieties in such POCs make them highly active supramolecular nanoreactors for asymmetric aldol reactions, delivering up to 92% ee. The spatial distribution of chiral catalytic sites in these two types of POCs greatly affects their catalytic activities and enantioselectivities. This work not only lays a foundation for the asymmetric catalytic application of chiral POCs, but also contributes to our understanding of the catalytic function of biomimetic supramolecular systems.

Two calix[4]resorcinarene-based chiral POCs with different self-assembly forms were constructed. The difference in the spatial distribution of chiral organocatalytic sites leads to the two chiral POCs exhibiting distinct stereoselectivities.

BODIPY based Metal-Organic Macrocycles and Frameworks: Recent Therapeutic Developments

Boron dipyrromethene, commonly known as BODIPY, based metal-organic macrocycles (MOCs) and metal-organic frameworks (MOFs) represent an interesting part of materials due to their versatile tunability of structure and functionality as well as significant physicochemical properties, thus broadening their applications in various scientific domains, especially in biomedical sciences. With increasing concern over the efficacy of cancer drugs versus quality of patient's life dilemma, scientists have been trying to fabricate novel comprehensive therapeutic strategies along with the discovery of novel safer drugs where research with BODIPY metal complexes has shown vital advancements. In this review, we have exclusively examined the articles involving studies related to light harvesting and photophysical properties of BODIPY based MOCs and MOFs, synthesized through self-assembly process, with a special focus on biomolecular interaction and its importance in anti-cancer drug research. In the end, we also emphasized the possible practical challenges involved during the synthetic process, based on our experience on dealing with BODIPY molecules and steps to overcome them along with their future potentials. This review will significantly help our fellow research groups, especially the budding researchers, to quickly and comprehensively get the near to wholesome picture of BODIPY based MOCs and MOFs and their present status in anti-cancer drug discovery.

Chiral dihydroxytetraphenylene-catalyzed enantioselective conjugate addition of boronic acids to β-enaminones

An efficient (S)-2,15-Cl2-DHTP-catalyzed enantioselective conjugate addition of organic boronic acids to β-enaminones has been developed.

Enantioselective assembly and recognition of heterochiral porous organic cages deduced from binary chiral components

Chiral recognition and discrimination is not only of significance in biological processes but also a powerful method to fabricate functional supramolecular materials. Herein, a pair of heterochiral porous organic cages (HPOC-1), out of four possible enantiomeric products, with mirror stereoisomeric crystal structures were cleanly prepared by condensation occurring in the exclusive combination of cyclohexanediamine and binaphthol-based tetraaldehyde enantiomers. Nuclear magnetic resonance and luminescence spectroscopy have been employed to monitor the assembly process of HPOC-1, revealing the clean formation of heterochiral organic cages due to the enantioselective recognition of (S,S)-binaphthol towards (R,R)-cyclohexanediamine derivatives and vice versa. Interestingly, HPOC-1 exhibits circularly polarized luminescence and enantioselective recognition of chiral substrates according to the circular dichroism spectral change. Theoretical simulations have been carried out, rationalizing both the enantioselective assembly and recognition of HPOC-1.

Heterochiral organic cages based on enantioselective self-assembly of binary chiral components have been prepared, exhibiting circularly polarized luminescence property and enantioselective recognition ability towards chiral substrates according to the circular dichroism spectral change.

Phosphorus guiding palladium: [4+4] metallomacrocyclic PdII complex and self-assembly of heterometallic PdII/ZnII grid-type complex

The reaction of heteroditopic ligand 1 featuring a hard pyridine-hydrazone-pyrimidine (N,N,N) site and a softer pyrimidine-hydrazone-phosphane (N,N,P) pocket with [Pd(CH3CN4)](OTf)2 in different metal-to-ligand ratios (M:L) gave the homobimetallic PdII complex...

Crown Ether-Derived Chiral BINOL: Enantioselective Michael Addition of Alkenyl Boronic Acids to α,β-Unsaturated Ketones

A new class of aza-crown ether-derived chiral BINOL catalysts were designed, synthesized, and applied in the asymmetric Michael addition of alkenylboronic acids to α,β-unsaturated ketones. It was found that introducing aza-crown ethers to the BINOL catalyst could achieve apparently higher enantioselectivity than a similar BINOL catalyst without aza-crown ethers did, although the host-guest complexation of alkali ions by the aza-crown ethers could not further improve the catalysis effectiveness. Under mediation of the aza-crown ether-derived chiral BINOL and in the presence of a magnesium salt, an array of chiral γ,δ-unsaturated ketones were furnished in good enantioselectivities (81-95% ees).

Organocatalyzed Enantioselective Conjugate Addition of Boronic Acids to β,γ-Unsaturated α-Ketoesters

We report herein the (R)-3,3'-Br₂-BINOL-catalyzed enantioselective conjugate addition of organic boronic acids to β,γ-unsaturated α-ketoesters to generate the corresponding Michael addition products in moderate to high yields and with moderate to excellent enantioselectivities (up to 99% ee). This catalytic system features characteristics of mild reaction conditions, high efficiency, and tolerance to alkenylboronic acids and heteroarylboronic acids.

Adsorptive separation of cyclohexanol and cyclohexanone by nonporous adaptive crystals of RhombicArene

As feedstock chemicals with similar boiling points, cyclohexanol (CHOL) and cyclohexanone (CHON) are often obtained as mixtures during production processes. Separation of mixed CHOL and CHON is important but energy-consuming by distillation. Here we report the development of a new macrocycle RhombicArene, which forms a host-guest complex with CHON through C-H⋯π interactions and hydrogen bonds. The nonporous adaptive crystals of RhombicArene exhibit excellent capability for rapid (30 minutes), exclusive (>99.9%), and recyclable vapor adsorption of CHON in the presence of CHOL under mild and user-friendly conditions.

Molecular Approach to Alkali-Metal Encapsulation by a Prussian Blue Analogue FeII/CoIII Cube in Aqueous Solution: A Kineticomechanistic Exchange Study

The preparation of a series of alkali-metal inclusion complexes of the molecular cube [{Co^III(Me₃-tacn)}₄{Fe^II(CN)₆}₄]^4- (Me₃-tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), a mixed-valent Prussian Blue analogue bearing bridging cyanido ligands, has been achieved by following a redox-triggered self-assembly process. The molecular cubes are extremely robust and soluble in aqueous media ranging from 5 M [H⁺] to 2 M [OH^-]. All the complexes have been characterized by the standard mass spectometry, UV-vis, inductively coupled plasma, multinuclear NMR spectroscopy, and electrochemistry. Furthermore, X-ray diffraction analysis of the sodium and lithium salts has also been achieved, and the inclusion of moieties of the form {M-OH₂}⁺ (M = Li, Na) is confirmed. These inclusion complexes in aqueous solution are rather inert to cation exchange and are characterized by a significant decrease in acidity of the confined water molecule due to hydrogen bonding inside the cubic cage. Exchange of the encapsulated cationic {M-OH₂}⁺ or M⁺ units by other alkali metals has also been studied from a kineticomechanistic perspective at different concentrations, temperatures, ionic strengths, and pressures. In all cases, the thermal and pressure activation parameters obtained agree with a process that is dominated by differences in hydration of the cations entering and exiting the cage, although the size of the portal enabling the exchange also plays a determinant role, thus not allowing the large Cs⁺ cation to enter. All the exchange substitutions studied follow a thermodynamic sequence that relates with the size and polarizing capability of the different alkali cations; even so, the process can be reversed, allowing the entry of {Li-OH₂}⁺ units upon adsorption of the cube on an anion exchange resin and subsequent washing with a Li⁺ solution.

Constructing a triangular metallacycle with salen-Al and its application to a catalytic cyanosilylation reaction

A triangular metallosalen-based metallacycle was constructed in quantitative yield by the self-assembly of a 180° bis(pyridyl)salen-Al complex and a 60° diplatinum(II) acceptor in a 1 : 1 stoichiometric ratio. This metallacycle was then successfully used to cyanosilylate a wide range of benzaldehydes with trimethylsilyl cyanide.

Photooxidase Mimicking with Adaptive Coordination Molecular Capsules

One important feature of enzyme catalysis is the induced-fit conformational change after binding substrates. Herein, we report a biomimetic water-soluble molecular capsule featuring adaptive structural change toward substrate binding, which offers an ideal platform for efficient photocatalysis. The molecular capsule was coordination-assembled from three anthracene-bridged bis-TPT [TPT = 2,4,6-tris(4-pyridyl)-1,3,5-triazine] ligands and six (bpy)Pd(NO3)2 (bpy = 2,2'-bipyridine). Once substrates bind to its hydrophobic cavity, this capsule would undergo quantitative capsule-to-bowl transformation. Visible-light absorption brought about by both the anthracene units and the charge-transfer absorption on the late-formed quintuple π-π stacked host-guest complex efficiently facilitates aerobic photooxidation for the sulfide guests by visible-light irradiation under mild conditions. Desired turnover numbers and product selectivity (sulfoxide over sulfone) have been achieved by the transformable nature of the catalyst and the hydrophilicity of the sulfoxide product. Such a photocatalytic process enabled by an adaptive coordination capsule and substrates as the allosteric effector paves the way for constructing artificial systems to mimic enzyme catalysis.

Size- and Shape-Selective Catalysis with a Functionalized Self-Assembled Cage Host

A self-assembled Fe₄L₆ cage with internally oriented carboxylic acid functions was shown to catalyze a variety of dissociative nucleophilic substitution reactions that proceed via oxocarbenium ion or carbocation intermediates. The catalytic behavior of the cage was compared to that of other small acid catalysts, which illustrated large differences in reactivity of the cage-catalyzed reactions, dependent on the structure of the substrate. For example, only a 5% cage confers a 1000-fold rate acceleration of the thioetherification of vinyldiphenylmethanol when compared to the rate with free carboxylic acid surrogates but only a 52-fold acceleration in the formation of small thioacetals. Multiple factors control the variable reactivity in the host, including substrate inhibition, binding affinity, and accessibility of reactive groups once bound. Simple effective concentration increases or the overall charge of the cage does not explain the variations in reactivity shown by highly similar reactants in the host: small differences in structure can have large effects on reactivity. Reaction of large spherical guests is highly dependent on substitution, whereas flat guests are almost unaffected by size and shape differences. The cage is a promiscuous catalyst but has strong selectivity for particular substrate shapes, reminiscent of enzymatic activity.

Self-assembly of chiral BINOL cages via imine condensation

Condensation of an (S)- or (R)-BINOL-derived dialdehyde and tris(2-aminoethyl)amine produced chiral [2+3] imine cages, which were further reduced to furnish more stable chiral amine cages and applied in the enantioselective recognition of (1R,2R)- and (1S,2S)-1,2-diaminocyclohexane.

Anthracene-induced formation of highly twisted metallacycle and its crystal structure and tunable assembly behaviors

Polycyclic aromatic hydrocarbons (PAHs) continue to attract increasing interest with respect to their applications as luminescent materials. The ordered structure of the metal-organic complex facilitates the selective integration of PAHs that can be tuned to function cooperatively. Here, a unique highly twisted anthracene-based organoplatinum metallacycle was prepared via coordination-driven self-assembly. Single-crystal X-ray diffraction analysis revealed that the metallacycle was twisted through the cooperation of strong π···π stacking interactions and steric hindrance between two anthracene-based ligands. Notably, the intramolecular twist and aggregation behavior introduced restrictions to the conformational change of anthracenes, which resulted in increased emission intensity of the metallacycle in solution. The emission behaviors and suprastructures based on the highly twisted metallacycle can be modulated by the introduction of different solvents. This study demonstrates that this metallacycle with highly twisted structure is a promising candidate for sensing and bioimaging applications.

Self-Assembled Platinum Supramolecular Metallacycles Based on a Novel TADF Photosensitizer for Efficient Cancer Photochemotherapy

Recently, supramolecular coordination complexes (SCCs) based on photosensitizers as bridging ligands have attracted great attention in cancer therapy owing to their synergistic effect between photodynamic therapy (PDT) and chemotherapy. Herein, a highly emissive supramolecular platinum triangle BTZPy-Pt based on a novel type of photosensitizer BTZPy with thermally activated delayed fluorescence (TADF) was fabricated. The BTZPy and BTZPy-Pt exhibited strong luminescence emission in the visible range with high quantum yields (quantum yields (QYs) for BTZPy and BTZPy-Pt were about 78 and 62% in ethanol solutions, respectively). Additionally, BTZPy had been proved to be an excellent photosensitizer with superior ¹O₂ generation capability (the ¹O₂ generation quantum yield reached up to ca. 95%) for PDT. By the combination of the excellent phototoxicity of BTZPy and the antitumor activity of the Pt center, the platinum triangle BTZPy-Pt demonstrated a highly efficient anticancer performance toward HeLa cells (IC₅₀: 0.5 μg mL^-1). This study not only provides a blueprint to fabricate new types of photosensitizers but also paves a way to design novel SCCs for efficient PDT.

Efficient one-pot synthesis of [3]catenanes based on Pt(ii) metallacycles with a flexible building block

Three [3]catenanes were fabricated in high efficiency through the self-assembly of a 90° platinum(ii) receptor, a flexible bis(4,4′-bipyridinium) donor and a crown ether (DB24C8 or DB30C10).

Asymmetric double-conjugate addition of alkenylboronic acids to dienones catalyzed by chiral diols

An efficient asymmetric double-conjugate addition of organic boronic acids to dienones catalyzed by chiral 3,3′-disubstituted-BINOLs or hydroxytetraphenylenes has been developed.

Truncated Face-Rotating Polyhedra Constructed from Pentagonal Pentaphenylpyrrole through Graph Theory

Discovering novel families of molecular polyhedra through graph theory has attracted increasing interest. Nevertheless, the design principles of molecular polyhedra based on graph theory remain elusive, especially for those containing five-node units. Herein, we construct a series of chiral truncated face-rotating polyhedra (T-FRP) from pentagonal pentaphenylpyrrole (PPP) derivatives and chiral diamines. Graph theory is used to elucidate the geometry of these novel T-FRP, which represent a new family of molecular polyhedra. The phenyl flipping of PPP faces in these T-FRP is significantly restricted, thus making T-FRP chiral and strongly emissive in solution. In addition, T-FRP also generate circularly polarized luminescence. This study provides new insights into the rational design of novel molecular polyhedra through graph theory.

Oxidation triggers guest dissociation during reorganization of an FeII 4L6 twisted parallelogram

A three-dimensional FeII 4L6 parallelogram was prepared from ferrocene-containing ditopic ligands. The steric preference of the bulky ferrocene cores towards meridional vertex coordination brought about this new structure type, in which the ferrocene units adopt three distinct conformations. The structure possesses two distinct, bowl-like cavities that host anionic guests. Oxidation of the ferrocene FeII to ferrocenium FeIII causes rotation of the ferrocene hinges, converting the structure to an FeII 1L1 + species with release of anionic guests, even though the average charge per iron increases in a way that would ordinarily increase guest binding strength. The degrees of freedom exhibited by these new structures - derived from the different configurations of the three ligands surrounding a meridional FeII center and the rotation of ferrocene cores - thus underpin their ability to reconfigure and eject guests upon oxidation.