Nitro-Substituted Stilbeneboronate Pinacol Esters and Their Fluoro-Adducts. Fluoride Ion Induced Polarity Enhancement of Arylboronate Esters

Abstract

A series of stilbeneboronate pinacol cyclic esters, containing none to three nitro groups, have been synthesized by various olefination reactions and characterized by X-ray single-crystal structure analysis. A stilbeneboronate ester bearing electron-acceptor groups experiences transition to a push-pull pi-electron system upon complexation with one fluoride ion at the boron atom. The UV-vis absorption maxima of the presented nitro-substituted stilbeneboronate esters are red-shifted upon addition of fluoride ions, indicating this binding event. The enhancement of the polarity of the investigated compounds and the changes in the electronic system were investigated by UV-vis absorption spectroscopy and solvatochromism. Additionally, studies were performed by natural bond orbital (NBO) analysis and RI-CC2 calculations of the vertical excitation energies. The synergism of fluoride ion complexation and solvation upon the UV-vis band shift is interpreted in terms of linear solvation energy relationships (LSERs) using the Kamlet-Taft solvent parameter set. It is found that the UV-vis absorption of the fluoro-boronates is strongly dependent on the solvents hydrogen-bond donating ability.

The transition metal catalyzed hydroboration of enamines

“…A resonance at 173 ppm in the 13 C NMR spectra and a strong band at 1671 cm À1 in the FT-IR indicate that the carbonyl functionality is still present. A peak at 32 ppm in the 11 B NMR spectrum indicates that the boron atom exists in a three coordinate environment in solution [57]. The linear hydroboration product was confirmed by a single crystal X-ray diffraction study, Fig.…”

Turn-on colorimetric sensing of fluoride ions by a cationic triarylborane bearing benzothiazolium

“…Huang et al reported that the charge on the boron atom in 2-(4-dimesitylborylphenyl)quinoline compound is significantly increased after fluoride binding and thereby the red-shifted CT transition from fluoroborate moiety to quinoline can be induced [76]. A similar red-shift in the absorption spectra after fluoride binding has also been observed in the arylboronic acid or arylboronate ester compounds [50,77]. The electronwithdrawing boronic acid or ester groups were changed into electron-donating groups upon fluoride binding, giving rise to the red-shifted ICT transition.…”

Covalent Interactions in Chemosensor Design

“…Among all the covalent functional group interactions, boronic acid stands out as the most commonly used in chemosensor construction because of its strong interactions with diols [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], aminoalcohols [20][21][22], α-amino acids [23], α-hydroxyl acids [24][25][26][27], alcohols [15,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44], as well as cyanide [45,46] and fluoride [47][48][49]…”

“…Small-molecule boronolectins (SBLs) have also shown tremendous potential in carbohydrate biomarker recognition and targeting [5,58]. Several recent reviews and research papers comprehensively summarize the use of boronic acids in sensor designs for carbohydrates [9,[14][15][16]66], fluoride [47][48][49][50][51], and cyanides [45,46], and have in-depth discussions of factors [15,19,67] that should be considered in designing such sensors. In addition, there have also been quite a few reviews [8,15,66] and research papers [54,[68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85] on boronic acids that change their fluorescent properties upon binding to a nucleophilic analyte or pH changes.…”

“…The resulting complex 47(48)/49 can switch on luminescence (λ max = 616 nm). The self-assembly ternary complex 47(48)/49 can thus be considered as a potential luminescent sensor, since the ligand (49) can be replaced by other suitable coordinating ligands such as anions. On the basis of this "displacement assay," various anions (∼1 mM) were added to a solution of the ternary complex at pH 7.4.…”