Oligoboroxine-based architectures

Abstract

Boroxines are well-known six-membered ring compounds and their fundamental properties such as aromaticity, Lewis acidity, photophysical property, interactions with anions, thermal stability, and reactivity have been investigated. Since the 2000s, boroxine formation has been paid much attention as a reversible covalent bond formation. Boronic acids (RB–(OH)2) reversibly trimerize to afford the tripodal structure of boroxines. The equilibrium between boronic acids and boroxines can be controlled simply by the addition or removal of water. The addition of N-donor Lewis bases also promotes the reversible formation of boroxine⋅N-donor Lewis base adducts. To date, by using this unique reversible trimerization, various self-assembled boroxine-based covalent architectures and polymeric materials have been reported. Boroxine-based architectures are categorized into three types as follows. (a) Tripodal structures by monoboroxine formation, (b) network structures by polyboroxine formation including covalent organic frameworks (= COFs) and dynamic polymer materials, and (c) discrete structures by oligoboroxine formation. Compared to mono or polyboroxine-based architectures (a) or (b), oligoboroxine-based discrete architectures (c) containing a precise number of boroxines are an emerging research subject and have the potential to create a novel type of discrete covalent architectures. Thus, in this review, we summarize recent progress including our works in this field.