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1. Crystalline Porous Frameworks via Hierarchical Dynamic Covalent Assembly

   https://doi.org/10.1021/acs.accounts.5c00393  

   Ge, Yanqing; Huang, Shaofeng; Yuan, Zhehao; Zhang, Wei (August 2025, Accounts of Chemical Research)

   Crystalline porous frameworks, such as covalent organic frameworks (COFs), metal–organic frameworks (MOFs), and hydrogen-bonded organic frameworks (HOFs), have demonstrated exceptional potential in diverse applications, including gas adsorption/separation, catalysis, sensing, electronic devices, etc. However, the building blocks for constructing ordered frameworks are typically limited to multisubstituted aromatic small molecules, and uncontrolled interpenetration has remained a long-standing challenge in the field. Shape-persistent macrocycles and molecular cages have garnered significant attention in supramolecular chemistry and materials science due to their unique structures and novel properties. Using such preporous shape-persistent 2D macrocycles or 3D cages as building blocks to construct extended networks is particularly appealing. This macrocycle-to-framework/cage-to-framework hierarchical assembly approach not only mitigates the issue of interpenetration but also enables the integration of diverse properties in an emergent fashion. Since our demonstration of the first organic cage framework (OCF) in 2011 and the first macrocycle-based ionic COFs (ICOFs) in 2015, substantial advancements have been made over the past decade. In this Account, we will summarize our contributions to the development of crystalline porous frameworks, consisting of shape-persistent macrocycles and molecular cages as preporous building blocks, via hierarchical dynamic covalent assembly. We will begin by reviewing representative design strategies and the synthesis of shape-persistent macrocycles and molecular cages from small molecule-based primary building blocks, emphasizing the critical role of dynamic covalent chemistry (DCvC). Next, we will discuss the further assembly of preporous macrocycle/cage-based secondary building blocks into extended frameworks, followed by an overview of their properties and applications. Finally, we will highlight the current challenges and future directions for this hierarchical assembly approach in the synthesis of crystalline porous frameworks. This Account offers valuable insights into the design and synthesis of functional porous frameworks, contributing to the advancement of this important field. 

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2. Formation of nanostructured silicas through the fluoride catalysed self-polymerization of Q-type functional silica cages

   https://doi.org/10.1039/d2cc02672d  

   Hu, Nai-hsuan; Sims, Cory B.; Schrand, Tyler V.; Haver, Kathryn M.; Armenta, Herenia Espitia; Furgal, Joseph C. (August 2022, Chemical Communications)

   Octa(dimethylsiloxy)silica cages (Q8M8H) undergo rapid self-polymerization in the presence of a fluoride catalyst to form complex 3D porous structural network materials with specific surface areas up to 650 m2g−1. This establishes a new method to form bio-derived high inorganic content soft silicas with potential applications in filtration, carbon capture, catalysis, or hydrogen source. 

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3. Porous Salts as Platforms for Heterogeneous Catalysis

   https://doi.org/10.1002/smll.202207507  

   Korman, Kyle J.; Dworzak, Michael R.; Yap, Glenn P. A.; Bloch, Eric D. (April 2023, Small)

   Abstract The preparation of a new class of reactive porous solids, prepared via straightforward salt metathesis reactions, is described here. Reaction of the dimethylammonium salt of a magnesium‐based porous coordination cage with the chloride salt of [Cr^IICl(Me₄cyclam)]⁺affords a porous solid with concomitant removal of dimethylammonium chloride. The salt consists of the ions combined in the expected ratio based on their charge as confirmed by UV–vis and X‐ray photoelectron spectroscopies, ion chromatography (IC), and inductively coupled plasma mass spectrometry (ICP‐MS). The porous salt boasts a Brunauer‐Emmett‐Teller (BET) surface area of 213 m² g⁻¹. Single crystal X‐ray diffraction reveals the chromium(II) cations in the structure reside in the interstitial space between porous cages. Importantly, the chromium(II) centers, previously shown to react with O₂to afford reactive chromium(III)‐superoxide adducts, are still accessible in the solid state as confirmed by UV–vis spectroscopy. The site‐isolated reactive centers have competence toward hydrogen atom abstraction chemistry and display significantly increased stability and reactivity as compared to dissolved ions. 

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4. Tuning Material Properties of Porous Organic Cage CC3 with Postsynthetic Dynamic Covalent Chemistry

   https://doi.org/10.1002/ejoc.202101507  

   Rivera, Matthew_P; Liu, Ming; He, Donglin; Lively, Ryan_P (January 2022, European Journal of Organic Chemistry)

   Abstract Porous organic cages (POCs) represent a new class of microporous materials with an impressive breadth of potential applications. One of their many advantages is the degree of tunability of cage properties, similar to that seen in more established microporous materials like metal‐organic frameworks. In this work, a prototypical POC, CC3, is used to explore the potential to tune cage properties via post‐synthetic dynamic covalent chemistry. Ethylenediamine, the linker used in another POC, CC1, was partially substituted into the CC3 cage structure to varying degrees based on the starting relative molar ratios. The resulting products were investigated for the relative distribution of the two linkers, crystallinity, and surface area. It was found that even when small amounts of other compatible diamine linkers are introduced, they substitute into the existing cages, although some structural products are apparently favored over others within the reactant ratios investigated. 

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5. Efficient multigram procedure for the synthesis of large hydrazone-linked molecular cages

   https://doi.org/10.1039/D3QO00480E  

   Vestrheim, Olav; Schenkelberg, Mica E.; Dai, Qingsheng; Schneebeli, Severin T. (June 2023, Organic Chemistry Frontiers)

   Covalently linked molecular cages can provide significant advantages (including, but not limited to enhanced thermal and chemical stability) over metal-linked coordination cages. Yet, while large coordination cages can now be created routinely, it is still challenging to create chemically robust, covalently linked molecular cages with large internal cavities. This fundamental challenge has made it difficult, for example, to introduce endohedral functional groups into covalent cages to enhance their practical utility (e.g., for selective guest recognition or catalysis), since the cavities would have simply been filled up with such endohedral functional groups in most cases. Here we now report the synthesis of some of the largest known covalently linked molecular tetrahedra. Our new covalent cages all contain 12 peripheral functional groups, which keep them soluble. They are formed from a common vertex, which aligns the hydrazide functions required for the hydrazone linkages with atropisomerism. While we previously reported this vertex as a building block for the smallest member of our hydrazone-linked tetrahedra, our original synthesis was not feasible to be carried out on the larger scales required to successfully access the larger tetrahedra. To overcome this synthetic challenge, we now present an improved synthesis of our vertex, which only requires a single chromatographic step (compared to 3 chromatographic purification steps, which were needed for the initial synthesis). Our new synthetic route enabled us to create a whole family of molecular cages with increasing size (all linked with hydrolytically stable hydrazone bonds), with our largest covalent cage featuring p-quarterphenyl linkers and the ability to encapsulate a hypothetical sphere of approximately 3 nm in diameter. These results now open up the possibility to introduce functional groups required for selective recognition and catalysis into chemically robust covalent cages (without blocking the cavities of the covalent cages). 

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