Synthesis of Covalent Boroxine Frameworks by Polycondensation of Tetrahydroxydiboron

Abstract

We have demonstrated synthesis of boroxine networks by condensation of tetrahydroxydiboron. The network material was obtained in quantitative yield by microwave-assisted heating of N,N-dimethylacetamide. The material had a crystalline structure and good stability. In addition, the material could be easily decomposed to the monomer by water addition.Various frameworks have recently attracted much attention because of their potential applications. 1 Metalorganic frameworks are a class of compounds consisting of metal ions coordinated to pillar organic ligands to form zero-to three-dimensional structures. 2 The combination of metals and ligands can be arranged to produce frameworks with different porosity, functionality, and shape. 2 Frameworks based on intermolecular interactions are also interesting and useful materials. 3 Porous molecular crystals have attracted much attention, including hydrogen-bonded organic frameworks, 3a supramolecular organic frameworks, 3b and porous organic salts. 3c Covalent organic frameworks (COFs) have also been widely studied as two-or three-dimensional materials, in which the building blocks are linked by strong covalent bonds. 4 Facile synthesis by polycondensation allows relatively easy access to the frameworks. Boron condensation of phenylenediboronic acid is the most popular route to synthesize COFs. 5 In this case, three boronic acid groups converge to form a planar six-membered boroxine ring through elimination of water.Not only can various arylboronic acids be used for COF synthesis, but the porosity and function can be controlled by their organic structure. However, there have been no reports of condensation of tetrahydroxydiboron, which could possibly give covalently bonded frameworks based on two elements (B and O). For synthesis of frameworks that do not contain organic structures, using tetrahydroxydiboron as a

The Structure of Boron Monoxide

“…Given that it can be used to synthesize diboron tetrachloride, it is known that the B–B bonds are preserved in BO. , The only new concrete information we have gained since the 1960s has been the observation of a 25 ppm 11 B nuclear magnetic resonance (NMR) signal, which agrees with a boron center possessing one bond to boron and two to oxygen, but this only manages to disprove the β-InS structure that has 4-coordinate boron centers. Perhaps due to the similar chemistry found when condensing organic boronic acids, such as in the synthesis of covalent organic frameworks (COFs), the current consensus on the structure of boron monoxide is that it likely forms boroxine subunits and leads to a planar structure analogous to that of COF-1. , …”

“…Perhaps due to the similar chemistry found when condensing organic boronic acids, such as in the synthesis of covalent organic frameworks (COFs), 24 the current consensus on the structure of boron monoxide is that it likely forms boroxine subunits and leads to a planar structure analogous to that of COF-1. 25,26 The models depicted in Figure 1 differ significantly in their local structure, which should enable them to be differentiated spectroscopically. For instance, one of the models initially proposed in 1955 1 features a rotation around the B−B bond axis that leads to a loss of planarity in the B 2 O 4 subunits while the cage structures also feature non-planar B 2 O 4 moieties, albeit this time due to a puckering.…”