1,1-Difluoro-1,3,5,2-triazaborinines containing benzo-fused imidazo-, oxazolo-, and thiazolo-pyrimido as a new luminescent framework

Abstract

In this paper, we present for the first time an efficient method for synthesizing three novel tetra–coordinated BF₂ complexes, specifically 6,6-difluoro-2,4-dimethyl-6H-5λ⁴,6λ⁴-benzo [4,5]imidazo(oxazolo/thiazolo)[3,2-c]pyrimido [2,1-f][1,3,5,2]triazaborinines (4a–c). These compounds were synthesized via the reaction of selected N-(4,6-dimethylpyrimidin-2-yl)-benzo[d]imidazo(oxazolo/thiazolo)-2-amines (3a–c) with BF₃·OEt₂, employing Et₃N as a base. Optimized yields ranging from 64 to 69 % were achieved when the reactions were conducted in anhydrous CHCl₃ at room temperature for 24 h. The structural elucidation of BF₂ complexes 4a-c was performed through multinuclear NMR, FTIR, SC-XRD, and HRMS techniques. These compounds demonstrated thermal stability up to 150 °C as evidenced by thermogravimetric analysis. The spectroscopic properties (in both solution and solid states) and the electrochemical properties of the synthesized derivatives were thoroughly investigated using UV–Vis spectroscopy, steady-state, time-resolved fluorescence emission, TD-DFT calculations, and redox potential measurements. The results of this study highlighted a dependence of the compounds’ properties on the heteroatom (NH, O, or S) present within the heterocyclic skeleton.