Shape-Persistent Arylene Ethynylene Organic Hosts for Fullerenes

Highly Rigid, Yet Conformationally Adaptable, Bisporphyrin sp2-Cage Receptors Afford Outstanding Binding Affinities, Chelate Cooperativities, and Substrate Selectivities

If we aim to develop efficient synthetic models of protein receptors and enzymes, we must understand the relationships of intra- and intermolecular interactions between hosts and guests and how they mutually influence their conformational energy landscape so as to adapt to each other to maximize binding energies and enhance substrate selectivities. Here, we introduce a novel design of cofacial (ZnII)bisporphyrin cages based on dynamic imine bonding, which is synthetically simple, but at the same time highly robust and versatile, affording receptors composed of only sp2-hybridized C and N atoms. The high structural rigidity of these cages renders them ideal hosts for ditopic molecules that can fit into the cavity and bind to both metal centers, leading to association constants as high as 109 M-1 in chloroform. These strong binding affinities are a consequence of the remarkable chelate cooperativities attained, with effective molarity (EM) values reaching record values over 103 M. However, we discovered that the cages can still adapt their structure to a more compact version, able to host slightly smaller guests. Such a conformational transition has an energy cost, which can be very different depending on the direction of the imine linkages in the cage skeleton and which results in EM values 2-3 orders of magnitude lower. This interplay between cooperativity and conformational adaptability leads to strong and unusual selectivities. Not only these metalloporphyrin receptors can choose to bind preferably to a particular guest, as a function of its size, but also the guest can select which host to bind, as a function now of the host's conformational rigidity. Such highly cooperative and selective associations are lost, however, in related flexible receptors where the imine bonds are reduced.

Columnar Organization of Nonalternant Fluorinated Dehydrobenzannulenes

Two new partially fluorinated dehydrobenzannulenes have been prepared by inter- and intramolecular oxidative homocoupling of diyne precursors. These systems contain fluorinated and nonfluorinated arene rings in a desymmetrized non-alternant arrangement. Both macrocycles are roughly planar and organize into extended columns in the solid state. The assembly of these columns is mediated by the combination of dispersion interactions, slipped [π⋅⋅⋅π] stacking interactions of the perfluorinated rings with each other, and their association with the nonfluorinated rings in the molecules of the neighboring macrocycles. These results suggest that partial fluorination of dehydrobenzannulenes can serve as a versatile motif for their assembly into columnar superstructures.

A π-extended molecular belt with selective binding capability for fullerene C70

A molecular belt incorporating naphthalene moieties, featuring an ellipsoidal cavity, was precisely engineered through bottom-up synthesis. Its pre-arranged geometry exhibits excellent complementarity to fullerene C70, resulting in remarkable selective binding ability (K = 1.3 × 106 M-1) for C70 compared to C60 (K = 176 M-1), forming a 1 : 1 complex. This superiority was unequivocally demonstrated by the single crystal structure of the complex, which revealed outstanding concave-convex shape complementarity between the two components. This highlights the potential application of molecular belts in the purification and separation of fullerenes.

Adsorptive Separation of Methylfuran and Dimethylfuran by a Robust Porous Organic Cage

As vital raw materials in the chemical industry, 2-methylfuran (MeF) and 2,5-dimethylfuran (DMeF) are commonly produced as mixtures. The selective separation of MeF and DMeF is crucial yet challenging, with significant industrial and economic implications. This study presents an energy-efficient separation technique using a robust calix[4]resorcinarene-based supramolecular porous organic cage (POC), CPOC-301, to effectively capture DMeF from an equimolar MeF/DMeF mixture within 2 h, yielding 95.3% purity. The exceptional separation efficiency stems from the superior structural stability of CPOC-301, maintaining its initial porous crystalline structure during separation. Calculations show that CPOC-301 forms more C-H···π hydrogen bonds with DMeF versus MeF, accounting for its DMeF selectivity. CPOC-301 can be easily regenerated via heat under a vacuum and reused for over five adsorption-desorption cycles without significant performance loss. This work introduces an approach to separate similar organic molecules effectively using POC materials.

Endohedral Hydrogen Bonding Templates the Formation of a Highly Strained Covalent Organic Cage Compound*

A highly strained covalent organic cage compound was synthesized from hexahydroxy tribenzotriquinacene (TBTQ) and a meta-terphenyl-based diboronic acid with an additional benzoic acid substituent in 2'-position. Usually, a 120° bite angle in the unsubstituted ditopic linker favors the formation of a [4+6] cage assembly. Here, the introduction of the benzoic acid group is shown to lead to a perfectly preorganized circular hydrogen-bonding array in the cavity of a trigonal-bipyramidal [2+3] cage, which energetically overcompensates the additional strain energy caused by the larger mismatch in bite angles for the smaller assembly. The strained cage compound was analyzed by mass spectrometry and 1 H, 13 C and DOSY NMR spectroscopy. DFT calculations revealed the energetic contribution of the hydrogen-bonding template to the cage stability. Furthermore, molecular dynamics simulations on early intermediates indicate an additional kinetic effect, as hydrogen bonding also preorganizes and rigidifies small oligomers to facilitate the exclusive formation of smaller and more strained macrocycles and cages.

A covalent organic cage compound acting as a supramolecular shadow mask for the regioselective functionalization of C60

A trigonal-bipyramidal covalent organic cage compound serves as an efficient host to form stable 1 : 1-complexes with C₆₀ and C₇₀. Fullerene encapsulation has been comprehensively studied by NMR and UV/Vis spectroscopy, mass spectrometry as well as single-crystal X-ray diffraction. Exohedral functionalization of encapsulated C₆₀via threefold Prato reaction revealed high selectivity for the symmetry-matched all-trans-3 addition pattern.

The taming of the Prato reaction: a covalent organic cage compound serves as a supramolecular template for the regioselective functionalization of C₆₀.

Selective guest recognition by a metallo-organic phthalocyanine-based host

In this manuscript, we have studied the selectivity in the complexation of fullerene species by a Fe[Formula: see text]Pc[Formula: see text] metallo-organic helicate (1) assembled using a bidentate phthalocyanine (Pc) as ligand. The large aromatic internal surface of this helicate shows a strong selectivity towards the encapsulation of C[Formula: see text] from a mixture of C[Formula: see text] and C[Formula: see text]. On the other hand, a bisimidazole-containing naphthalenediimide was used to perform guest exchange experiments over [fullerene [Formula: see text] 1] complexes, taking advantage of the strong coordination bond of the imidazole ring to the Zn centers in the Pc cavity.

Preferential Recognition and Extraction to Pentoses over Hexoses by a D6h-Symmetrical Ethynylphenol Macrocycle with Six Inner Phenolic Hydroxy Groups

A macrocycle consisting of six ethynylphenol units was developed as a host architecture for saccharides. The rigid framework of the macrocycle suppressed the intramolecular hydrogen-bonding between adjacent phenolic hydroxy groups and recognized saccharides by intermolecular hydrogen-bonding within the hole. The well-defined hydrogen-bonding sites enabled the size-selective guest recognition and showed preference to pentoses over hexoses.

Chiral hydrogen-bonded supramolecular capsules: synthesis, characterization and complexation of C70

Hydrogen-bonded nanocapsules were generated by multi-component self-assembly of phosphoric acids and amidines and could be used as hosts for C₇₀.

Product Distribution from Precursor Bite Angle Variation in Multitopic Alkyne Metathesis: Evidence for a Putative Kinetic Bottleneck

In the dynamic synthesis of covalent organic frameworks and molecular cages, the typical synthetic approach involves heuristic methods of discovery. While this approach has yielded many remarkable products, the ability to predict the structural outcome of subjecting a multitopic precursor to dynamic covalent chemistry (DCC) remains a challenge in the field. The synthesis of covalent organic cages is a prime example of this phenomenon, where precursors designed with the intention of affording a specific product may deviate dramatically when the DCC synthesis is attempted. As such, rational design principles are needed to accelerate discovery in cage synthesis using DCC. Herein, we test the hypothesis that precursor bite angle contributes significantly to the energy landscape and product distribution in multitopic alkyne metathesis (AM). By subjecting a series of precursors with varying bite angles to AM, we experimentally demonstrate that the product distribution, and convergence toward product formation, is strongly dependent on this geometric attribute. Surprisingly, we discovered that precursors with the ideal bite angle (60°) do not afford the most efficient pathway to the product. The systematic study reported here illustrates how seemingly minor adjustments in precursor geometry greatly affect the outcome of DCC systems. This research illustrates the importance of fine-tuning precursor geometric parameters in order to successfully realize desirable targets.

Cage-templated synthesis of highly stable palladium nanoparticles and their catalytic activities in Suzuki-Miyaura coupling

We report the controlled synthesis of small palladium nanoparticles (PdNPs) with narrow particle size distribution (1.8 ± 0.2 nm) using an organic molecular cage as a template. The well-defined cage structure and thioether anchoring groups inside the cavity are critical for the formation of narrowly distributed PdNPs, offering a confined organic molecular environment and guiding PdNP nucleation and growth. The resulting encapsulated PdNPs are resistant to agglomeration and stable in solution exposed to air at room temperature. When provided with a protective cage shell with minimum surface coverage, such PdNPs are capable of catalyzing organic reactions, showing high catalytic activity in Suzuki-Miyaura coupling reactions.

Synthesis, solvent-dependent emission and two-photon absorption of a triangular –[D–π–A]3– macrocycle

A large π–conjugated macrocycle featuring a –[D–π–A]₃– backbone is synthesized, exhibiting strongly solvent-dependent fluorescence and evident two-photon absorption ability.

Synthesis of Cyclic Porphyrin Trimers through Alkyne Metathesis Cyclooligomerization and Their Host-Guest Binding Study

Cyclic porphyrin trimers were synthesized through one-step cyclooligomerization via alkyne metathesis from diyne monomers. These macrocycles show interesting host-guest binding interactions with fullerenes, selectively binding C70 (6 × 10(3) M(-1)) over C60 and C84 (no binding observed). The fullerene-encapsulated host-guest complex can undergo guest or host exchange in the presence of another guest (2,4,6-tri(4-pyridyl)-1,3,5-triazine) or host (cage COP5) molecule with higher binding affinity.

Dynamic covalent synthesis of aryleneethynylene cages through alkyne metathesis: dimer, tetramer, or interlocked complex?

A modular dynamic covalent approach towards rigid aryleneethynylene covalent organic polyhedrons (COPs) and the mechanistic features were explored.

A dynamic covalent approach towards rigid aryleneethynylene covalent organic polyhedrons (COPs) was explored. Our study on the relationship of the COP structures and the geometry of their building blocks reveals that the topology of aryleneethynylene COPs strongly depends on the size of the building blocks. A tetramer (D_2h symmetric), dimer, or interlocked complex can be formed from monomers with the same face-to-edge angle but in different sizes. As alkyne metathesis is a self-exchange reaction and non-directional, the cyclooligomerization of multi-alkyne monomers involves both intramolecular cyclization and intermolecular metathesis reaction, resulting in complicated thermodynamic process disturbed by kinetic competition. Although a tetrahedron-shaped tetramer (T_d symmetric) has comparable thermodynamic stability to a D_2h symmetric tetramer, its formation is kinetically disfavored and was not observed experimentally. Aryleneethynylene COPs consist of purely unsaturated carbon backbones and exhibit large internal cavities, which would have interesting applications in host–guest chemistry and development of porous materials.