Backbone Boron-Functionalized Imidazoles/Imidazolium Salts: Synthesis, Structure, Metalation Studies, and Fluoride Sensing Properties

Abstract

Incorporation of a Lewis acidic BMes₂ (Mes = mesityl) moiety at the backbone of the imidazole ring was achieved by metal–halogen exchange procedure. Among them, two isomeric boron-phosphine functionalized imidazoles (3 and 6), monoboron-functionalized imidazoles (4 and 5), and its corresponding imidazolium salts were synthesized and thoroughly characterized. The solid-state structure of 3 reveals a dimeric B–N adduct that possesses six-membered [C–B–N]₂ ring, and 5 crystallizes as tetrameric B–N adduct that forms an interesting 16-membered macrocycle, whereas 4 and 6 were obtained as monomeric BMes₂-substituted imidazoles. 6 behaves as a P^N-type ligand upon the coordination with CuI to afford luminescent L₂Cu₄I₄-type metal complexes (10 and 11) whose photophysical properties were also studied. The presence (in 10) and the absence (in 11) of BMes₂ made a remarkable impact on fluorescence emission causing shift from the green (10) to orange (11) region. The fluoride sensing properties of BMes₂-containing imidazoles (4 to 9) were studied using UV–vis and fluorescence spectroscopy.