INVESTIGATION OF OLIGO(BENZOXAZABOROLE)S DERIVED FROM ALKYLLINKED BIS(AMINOPHENOL)S

Boronate ester-based materials have gained significant research interest and utility because of their ability to be formed through dynamic covalent bonds (DCBs). This reversible nature has been shown to organize molecular building blocks into the most thermodynamically stable structures such as linear polymers, nanotubes, macrocycles, and covalent organic frameworks (COFs). Previously, we reported the synthesis of simple boronate ester derivatives, benzoxazaboroles, using 2-(alkylamino)phenols and diboronic acids. However, the synthesis of benzoxazaboroles derived from bis(aminophenol)s is less explored. There is a possibility to yield macrocycles along with the linear polymers due to the ditopic functionality of the starting materials and an equilibrium between ring and chain structures may exist. In this research, we have synthesized investigated oligo(benzoxazaborole)s derived from alkyl-linked bis(aminophenol)s by both experimental and computational methods. Characterization of these materials was carried out using 1H NMR, 13C NMR, IR spectroscopy techniques. 1H NMR results indicate that the polymers exhibit dynamic covalent nature under mild conditions. Furthermore, IR spectroscopic analysis reveals that the degree of polymerization is quite high for the polymers due to the absence of signals related to the starting materials. The thermodynamic calculations predicted that the formation of benzoxazaboroles depends on the difference in the connectivity of the benzoxazaborole rings within the structure. Additionally, those calculations predicted that the linear benzoxazaboroles are more favorable than the ring structures. However, the energy difference is less than 53 kJ/mol.