Trimethylboroxine-free Mechanochemical Formation of Porous COF-1 from a Preconditioned Boronic-acid Precursor
Boris Irie-Bi *
Central Laboratory, University of Man, Man, Côte d’Ivoire and Laboratoire de Réactivité et Chimie des Solides (LRCS), Université de Picardie Jules Verne, Amiens, France.
Junior N’goyé Kanga
Central Laboratory, University of Man, Man, Côte d’Ivoire.
Souleymane Tuo
Central Laboratory, University of Man, Man, Côte d’Ivoire.
*Author to whom correspondence should be addressed.
Abstract
Boroxine-linked covalent organic frameworks are difficult to form mechanochemically because dehydrative condensation generates water that can hydrolyse newly formed B₃O₃ linkages. This study examines whether deliberate preconditioning of 1,4-benzenediboronic acid (BDBA) can enable trimethylboroxine-free formation of porous COF-1. BDBA was sequentially vacuum-dried, manually ground, continuously sonicated in anhydrous 1,4-dioxane, isolated, thermally dried, and then subjected to liquid-assisted planetary ball milling with a 1:1 1,4-dioxane/mesitylene mixture. The preconditioned precursor showed changes in the O–H envelope and low-frequency boron–oxygen region relative to pristine BDBA; these changes were interpreted qualitatively because pristine BDBA also contains spectral structure near ~704 cm⁻¹. Milling at 1100 rpm for 40 min with 70 µL of liquid produced a material with FTIR, PXRD, ¹³C CP/MAS NMR, and ¹¹B MAS NMR signatures consistent with COF-1. A matched direct-milling control prepared from pristine BDBA remained spectroscopically less converted after identical work-up, indicating that precursor history affects the extent of conversion under the conditions examined. Nitrogen adsorption at 77 K gave an apparent BET surface area of 711 m² g⁻¹. Across four mechanochemical runs, the isolated product mass recovery was 60.0 ± 0.7%. These findings establish a trimethylboroxine-free route to porous COF-1 under the investigated conditions while supporting further quantitative investigation of precursor-conditioning effects.
Keywords: COF-1, boroxine, mechanochemistry, trimethylboroxine-free synthesis, precursor conditioning, sonication, liquid-assisted grinding, covalent organic framework