A tetrahedral molecular cage with a responsive vertex

Spontaneous and Selective Macrocyclization in Nitroaldol Reaction Systems

Through a dynamic polymerization and self-sorting process, a range of lowellane macrocycles have been efficiently generated in nitroaldol systems composed of aromatic dialdehydes and aliphatic or aromatic dinitroalkanes. All identified macrocycles show a composition of two repeating units, resulting in tetra-β-nitroalcohols of different structures. The effects of the building block structure on the macrocyclization process have been demonstrated, and the influence from the solvent has been explored. In general, the formation of the lowellanes was amplified in response to phase-change effects, although solution-phase structures were, in some cases, favored.

Post‐Synthetic Modification of a Porous Hydrocarbon Cage to Give a Discrete Co 24 Organometallic Complex**

A new alkyne‐based hydrocarbon cage was synthesized in high overall yield using alkyne‐alkyne coupling in the cage forming step. The cage is porous and displays a moderately high BET surface area (546 m² g⁻¹). The cage loses crystallinity on activation and thus is porous in its amorphous form, while very similar cages have been either non‐porous, or retained crystallinity on activation. Reaction of the cage with Co₂(CO)₈ results in exhaustive metalation of its 12 alkyne groups to give the Co₂₄(CO)₇₂ adduct of the cage in good yield.

Purely Covalent Molecular Cages and Containers for Guest Encapsulation

Cage compounds offer unique binding pockets similar to enzyme-binding sites, which can be customized in terms of size, shape, and functional groups to point toward the cavity and many other parameters. Different synthetic strategies have been developed to create a toolkit of methods that allow preparing tailor-made organic cages for a number of distinct applications, such as gas separation, molecular recognition, molecular encapsulation, hosts for catalysis, etc. These examples show the versatility and high selectivity that can be achieved using cages, which is impossible by employing other molecular systems. This review explores the progress made in the field of fully organic molecular cages and containers by focusing on the properties of the cavity and their application to encapsulate guests.

Tandem Imine Formation and Alkyne Metathesis Enabled by Catalyst Choice

Three-rung molecular ladder 8 was prepared in one pot via tandem imine condensation and alkyne metathesis. Catalyst VI is demonstrated to successfully engender the metathesis of imine-bearing substrate 7, while catalyst III does not. The susceptibility of catalyst VI to deactivation by hydrolysis and ligand exchange is demonstrated. Assembly and disassembly of ladder 8 in one pot were demonstrated in the presence and absence of a Lewis acid catalyst.

By-design molecular architectures via alkyne metathesis

Shape-persistent purely organic molecular architectures have attracted tremendous research interest in the past few decades. Dynamic Covalent Chemistry (DCvC), which deals with reversible covalent bond formation reactions, has emerged as an efficient synthetic approach for constructing these well-defined molecular architectures. Among various dynamic linkages, the formation of ethynylene linkages through dynamic alkyne metathesis is of particular interest due to their high chemical stability, linearity, and rigidity. In this review, we focus on the synthetic strategies of discrete molecular architectures (e.g., macrocycles, molecular cages) containing ethynylene linkages using alkyne metathesis as the key step, and their applications. We will introduce the history and challenges in the synthesis of those architectures via alkyne metathesis, the development of alkyne metathesis catalysts, the reported novel macrocycle structures, molecular cage structures, and their applications. In the end, we offer an outlook of this field and remaining challenges.

The recent synthesis of novel shape-persistent 2D and 3D molecular architectures via alkyne metathesis is reviewed and the critical role of catalysts is also highlighted.

Highly active alkyne metathesis catalysts operating under open air condition

Alkyne metathesis represents a rapidly emerging synthetic method that has shown great potential in small molecule and polymer synthesis. However, its practical use has been impeded by the limited availability of user-friendly catalysts and their generally high moisture/air sensitivity. Herein, we report an alkyne metathesis catalyst system that can operate under open-air conditions with a broad substrate scope and excellent yields. These catalysts are composed of simple multidentate tris(2-hydroxyphenyl)methane ligands, which can be easily prepared in multi-gram scale. The catalyst substituted with electron withdrawing cyano groups exhibits the highest activity at room temperature with excellent functional group tolerance (-OH, -CHO, -NO₂, pyridyl). More importantly, the catalyst provides excellent yields (typically >90%) in open air, comparable to those operating under argon. When dispersed in paraffin wax, the active catalyst can be stored on a benchtop under ambient conditions without any decrease in activity for one day (retain 88% after 3 days). This work opens many possibilities for developing highly active user-friendly alkyne metathesis catalysts that can function in open air.

Alkyne metathesis catalysts usually suffer from high moisture/air sensitivity, which limit their wide applicability. Here, the authors report efficient alkyne metathesis catalysts that can operate under open-air conditions with a broad functional group tolerance.

Truxene-based covalent organic polyhedrons constructed through alkyne metathesis

Dynamic alkyne metathesis has successfully been employed toward the synthesis of a truxene-based shape-persistent covalent organic polyhedron (COP) with high binding affinity for fullerenes.

Enzymatic Noncovalent Synthesis

Enzymatic reactions and noncovalent (i.e., supramolecular) interactions are two fundamental nongenetic attributes of life. Enzymatic noncovalent synthesis (ENS) refers to a process where enzymatic reactions control intermolecular noncovalent interactions for spatial organization of higher-order molecular assemblies that exhibit emergent properties and functions. Like enzymatic covalent synthesis (ECS), in which an enzyme catalyzes the formation of covalent bonds to generate individual molecules, ENS is a unifying theme for understanding the functions, morphologies, and locations of molecular ensembles in cellular environments. This review intends to provide a summary of the works of ENS within the past decade and emphasize ENS for functions. After comparing ECS and ENS, we describe a few representative examples where nature uses ENS, as a rule of life, to create the ensembles of biomacromolecules for emergent properties/functions in a myriad of cellular processes. Then, we focus on ENS of man-made (synthetic) molecules in cell-free conditions, classified by the types of enzymes. After that, we introduce the exploration of ENS of man-made molecules in the context of cells by discussing intercellular, peri/intracellular, and subcellular ENS for cell morphogenesis, molecular imaging, cancer therapy, and other applications. Finally, we provide a perspective on the promises of ENS for developing molecular assemblies/processes for functions. This review aims to be an updated introduction for researchers who are interested in exploring noncovalent synthesis for developing molecular science and technologies to address societal needs.

Singlet oxygen stimulus for switchable functional organic cages

Molecular cages 1a and 2a incorporating a 9,10-diphenylanthracene (DPA) chromophore were synthesized through a templated ring-closure metathesis approach that allows variation in cavity size through the introduction of up to three different pillars. Reversible Diels–Alder reaction between the DPA moiety and photogenerated singlet oxygen smoothly converted 1a and 2a to the corresponding endoperoxide cages 1b and 2b, which are converted back to 1a and 2a upon heating. Endoperoxide formation constitutes a reversible covalent signal that combines structural changes in the interior of the cage with introduction of two additional coordination sites. This results in a large modulation of the binding ability of the receptors attributed to a change in the location of the preferred binding site owing to the added coordination by the endoperoxide oxygen lone pairs. Cages 1a and 2a form complexes with sodium and cesium whose association constants are modified by 4–20 fold for Na⁺ and 200–450 fold for Cs⁺ upon conversion to 1b and 2b. DFT calculations show that in the anthracene form, cages 1a and 2a can bind 2 metal cations in their periphery so that each cation is coordinated by 4 oxygens and one amine nitrogen, whereas the endoperoxide cages 1b and 2b bind cations centrally in a geometry that favors coordination to the endoperoxide oxygens.

Allosteric switchable organic cages allow variability in cation recognition.