Dynamic Interconversion between Boroxine Cages Based on Pyridine Ligation

Abstract

Dynamic interconversion between large covalent organic cages was achieved simply by heating or acid/base treatment. A mixture of the boroxine cages 12-mer and 15-mer was cleanly converted into a pyridine adduct of the 9-mer boroxine cage upon treatment with pyridine, and the geometry of N-coordinated boron atoms changed from trigonal to tetrahedral. The reverse reaction was achieved by heating or acid treatment. In this process, the larger boroxine cages 12-mer and 15-mer were found to be entropically favored owing to the release of free pyridine molecules from 9-mer⋅6 Py.

Development of a Strong, Recyclable Poly(dimethylsiloxane) Elastomer with Autonomic Self‐Healing Capabilities and Fluorescence Response Properties at Room Temperature

“…This phenomenon provides a mechanism for self-healing, so all self-healing materials based on the boroxine/boronic acid equilibrium require a special trigger condition, such as heating or wetting. [55][56][57][58] Herein, we report a novel molecular design strategy wherein multiple crosslinking networks promote the formation of poly(dimethylsiloxane)-based functional materials with excellent mechanical performance and self-healing capabilities by a straightforward preparation approach. Boroxines, which have high bond dissociation energies, are incorporated at pendant sites to enhance molecular mobility while forming a primary network.…”

Metal and Organic Templates Together Control the Size of Covalent Macrocycles and Cages

“…Where bonds are not formed reversibly, the formation of off-pathway kinetic products can limit the yield of a desired species, rendering product isolation challenging. Higher yields and cleaner products may be obtained through the use of templates 8 and reversibly formed linkages 9 such as imines, 10 boronic esters, 11 and alkenes 12 or alkynes 13 (with appropriate catalysts). The use of such dynamic covalent bonds leads to the formation of thermodynamic products, but such products may show limited stability due to cleavage of the dynamic bonds, such as hydrolysis of imines.…”

Constructing new metal–organic frameworks with complicated ligands from “One-Pot” in situ reactions

“…In these two reversible reactions, on the subtle synergetic effect of acid modulators and water molecules from the aggregation of ligand precursors, namely the covalent bond formation, good crystallization has been achieved in the final MOFs. In the case of BUT-108, the boroxine-based ligand L8 3– can hardly remain intact upon heating or exposure to moisture as a pre-synthesized ligand because it is vulnerable to hydrolysis,21 hindering its direct usage in MOF assembly. For L9 2– , although the condensation between two precursors is possible, the “one-pot” strategy can effectively facilitate the MOF synthesis and reduce the preparation time.…”