Study On The Synthesis Of NO π-Conjugated Fluoroboron (Ⅲ) Complexes And Its Structural Functionalization

BF₃·OEt₂ is a compound through donor-acceptor bonding of BF3 and Et2 O, it is commonly used in various organic synthesis procedure because of its less causticity, convenient operation and simple workup after reaction. In general, BF₃·OEt₂ acts as a Lewis acid to achieve numerous reactions, including cyclization, alkylation, rearrangement, etc., through ligand exchange with electron-rich species. In the presence of water, it serves as a Br?nsted acid and mediates a variety of reactions, for instance, Friedel-Crafts alkylations, nucleophilic substitutions and reductions of alcohols where transition metal were indispensable before. At the same time, BF₃·OEt₂ can affords fluoro-boron souce to coordinate with organic π-electron donors for synthesizing π-conjugated organic fluoroboron（Ⅲ） compounds with excellent optical properties, which can be widely used in photoelectricity field, such as molecular probes, liquid-crystal display, organic light-emitting diodes（OLEDs）, organic photovoltaic devices and bioimaging.Synthesis of NO π-conjugated fluoroboron（Ⅲ） compounds through difluoroboronation of BF₃·OEt₂ with o-hydroxyaryl N-H ketimines has been developed herein. First, we investigated the influence of water toward the reaction and screened the reaction conditions including additive, solvent, the loading of BF₃·OEt₂, reaction time and temperature to establish the optimal reaction conditions by employing 4-bromo-2-（1-iminoethyl）phenol as standard substrate. Based on the optimized conditions, we investigated the substrate scope of o-hydroxyaryl N-H ketimines and constructed structurally diverse products. At last, the structural diversity of the desired NO π-conjugated fluoroboron（Ⅲ） compounds were further enriched through Suzuki coupling reaction of iodide-substituent with different organic boronic acids.During the investigation of the effect of water toward the reaction, we find that trace water in the reaction system can exchange ligand with Et2 O to prepare stronger Br?nsted acid BF3·H2O, which is key to improve the reaction. Whereas, excessive water is disadvantage to this transformation and enhancement of acidity promotes the decomposition of ketimines. Subsequently, we adjusted the best loading of water and optimized the reaction conditions, so that varieties of ketimines could go through this reaction smoothly to achieve corresponding fluoroboron（Ⅲ） species.Our synthesis of NO π-conjugated fluoroboron（Ⅲ） compounds has advantages of mild conditions, simple operation, low-cost and good tolerance of substrate scope to some extent, and can be widely used in the synthesis of its derivatives. In addition, these fluoroboron（Ⅲ） compounds reported are likely to be a new category of luminescent materials.