A Water-Stable Boronate Ester Cage

The reversible condensation of catechols and boronic acids to boronate esters is a paradigm reaction in dynamic covalent chemistry. However, facile backward hydrolysis is detrimental for stability and has so far prevented applications for boronate-based materials. Here, we introduce cubic boronate ester cages 6 derived from hexahydroxy tribenzotriquinacenes and phenylene diboronic acids with ortho-t-butyl substituents. Due to steric shielding, dynamic exchange at the Lewis acidic boron sites is feasible only under acid or base catalysis but fully prevented at neutral conditions. For the first time, boronate ester cages 6 tolerate substantial amounts of water or alcohols both in solution and solid state. The unprecedented applicability of these materials under ambient and aqueous conditions is showcased by efficient encapsulation and on-demand release of β-carotene dyes and heterogeneous water oxidation catalysis after the encapsulation of ruthenium catalysts.

Recent Expedition in Pd- and Rh-Catalyzed C(Ar) -B Bond Formations and Their Applications in Modern Organic Syntheses

Transition metal-catalyzed borylation has emerged as a powerful and versatile strategy for synthesizing organoboron compounds. These compounds have found widespread applications in various aspects, including organic synthesis, materials science, and medicinal chemistry. This review provides a concise summary of the recent advances in palladium- and rhodium-catalyzed borylation from 2013 to 2023. The review covers the representative examples of catalysts, substrates scope and reaction conditions, with particular emphasis on the development of catalyst systems, such as phosphine ligands, NHC-carbene, and more. The diverse array of borylative products obtained for further applications in Suzuki-Miyaura coupling, and other transformations, are also discussed. Future directions in this rapidly evolving field, with the goal of designing more efficient, selective borylation methodologies are highlighted, too.

Synthesis and Properties of Rubicene-Based Aromatic π-Conjugated Compounds as Five-Membered Ring Embedded Planar Nanographenes

Polycyclic aromatic hydrocarbons consisting of two or three rubicene substructures were designed as π-conjugated compounds embedding five-membered rings. The target compounds with t-butyl groups were synthesized by the Scholl reaction of precursors consisting of 9,10-diphenylanthracene units, even though a partially precyclized precursor was required for the synthesis of the trimer. These compounds were isolated as stable and dark blue solids. Single-crystal X-ray analysis and DFT calculations revealed the planar aromatic framework of these compounds. In the electronic spectra, the absorption and emission bands were considerably red-shifted compared with those of the reference rubicene compound. In particular, the emission band of the trimer extended to the near-IR region while retaining the emissive property. The narrowed HOMO-LUMO gap with the extension of the π-conjugation was confirmed by cyclic voltammetry and DFT calculations.

Synthesis of Non-centrosymmetric Dipolar 4,4'-Bipyridines: Potential Molecular Tectons for Programmed Assembly of Supramolecular Systems

In this report, we describe a modular synthesis approach towards a new series of non-centrosymmetric, dipolar 4,4'-bipyridines bearing 2,6- and 3,5-functionalized pyridyl moieties at the peripheries. Central to our strategy is the selective substitution on only one pyridyl motif that could contain electron-donating (-CH₃ ) or electron-withdrawing (-F, -Cl, -CF₃ ) groups which causes electronic/steric effects on one nitrogen atom in 4,4'-bipyridines. This synthetic protocol was further applied to prepare azo-functionalized (-N=N-) asymmetric bipyridines and non-centrosymmetric 4,4'-bipyridine N-oxide scaffolds, which overcome the synthetic hurdles oxidizing 4,4'-bipyridines to N-monoxides selectively at only one pyridine. Compared to the conventional symmetrical bipyridines, the dipolar non-centrosymmetric molecular tectons pave the way for the realization of non-centrosymmetric supramolecular assemblies because of the difference in the binding energy of the pyridyl nitrogen atoms.

Bis-isonicotinoyl linkers containing polyaromatic scaffolds: synthesis, structure and spectroscopic properties

In this study, a new series of extended linkers containing different polyaromatic chromophores (biphenyl, naphthalene, anthracene, fluorene, 9,9-dimethylfluorene and fluorenone) functionalized with isonicotinoyl moieties have been synthesized by Pd-catalyzed cross-coupling reactions involving isonicotinamide and the appropriate aromatic dibromide. The optimized protocol led to the isolation of the target molecules in good yield and with high purity. These were characterized by ¹H NMR, FTIR, MS, and elemental analysis and their solid state structures were solved by single-crystal X-ray diffraction analysis. Electronic absorption and emission spectra were collected both in solution (DMF) and in the solid state. TDDFT calculations were carried out to investigate the effect of the isonicotinoyl moieties on the spectral features of the central chromophores. Although in solution only the linker containing a fluorenone scaffold shows a weak fluorescence, all the isolated linkers turned out to be fluorescent in the solid state, thus paving the way for their use for the fabrication of fluorescent MOFs.

Isoreticular Crystallization of Highly Porous Cubic Covalent Organic Cage Compounds*

Modular frameworks featuring well-defined pore structures in microscale domains establish tailor-made porous materials. For open molecular solids however, maintaining long-range order after desolvation is inherently challenging, since packing is usually governed by only a few supramolecular interactions. Here we report on two series of nanocubes obtained by co-condensation of two different hexahydroxy tribenzotriquinacenes (TBTQs) and benzene-1,4-diboronic acids (BDBAs) with varying linear alkyl chains in 2,5-position. n-Butyl groups at the apical position of the TBTQ vertices yielded soluble model compounds, which were analyzed by mass spectrometry and NMR spectroscopy. In contrast, methyl-substituted cages spontaneously crystallized as isostructural and highly porous solids with BET surface areas and pore volumes of up to 3426 m2  g-1 and 1.84 cm3  g-1 . Single crystal X-ray diffraction and sorption measurements revealed an intricate cubic arrangement of alternating micro- and mesopores in the range of 0.97-2.2 nm that are fine-tuned by the alkyl substituents at the BDBA linker.

Halogen-bonded one-dimensional chains of functionalized ditopic bipyridines co-crystallized with mono-, di-, and triiodofluorobenzenes

A series of halogen-bonded (XB) 1D and zigzag supramolecular architectures involving a sterically hindered class of homologous para-xylenes bearing bipyridyl moieties at peripheries co-crystallized with mono-, di-, and triiodofluorobenzenes as XB donors are prepared.

Polymerization in MOF-Confined Nanospaces: Tailored Architectures, Functions, and Applications

This feature article describes recent trends and advances in structuring network polymers using a coordination-driven metal-organic framework (MOF)-based template approach to demonstrate the concept of crystal-controlled polymerization in confined nanospaces, forming tailored architectures ranging from simple linear one-dimensional macromolecules to tunable three-dimensional cross-linked network polymers and interwoven molecular architectures. MOF-templated network polymers combine the characteristics and advantages of crystalline MOFs (high porosity, structural regularity, and designability) with the intrinsic behaviors of soft polymers (flexibility, processability, stability, or biocompatibility) with widespread application possibilities and tunable properties. The article ends with a summary of the remaining challenges to be addressed, and future research opportunities in this field are discussed.

Advanced Photoresponsive Materials Using the Metal-Organic Framework Approach

When fabricating macroscopic devices exploiting the properties of organic chromophores, the corresponding molecules need to be condensed into a solid material. Since optical absorption properties are often strongly affected by interchromophore interactions, solids with a well-defined structure carry substantial advantages over amorphous materials. Here, the metal-organic framework (MOF)-based approach is presented. By appropriate functionalization, most organic chromophores can be converted to function as linkers, which can coordinate to metal or metal-oxo centers so as to yield stable, crystalline frameworks. Photoexcitations in such chromophore-based MOFs are surveyed, with a special emphasis on light-switchable MOFs from photochromic molecules. The conventional powder form of MOFs obtained using solvothermal approaches carries certain disadvantages for optical applications, such as limited efficiency resulting from absorption and light scattering caused by the (micrometer-sized) powder particles. How these problems can be avoided by using MOF thin films is demonstrated.