Nitro-substituted stilbeneboronate pinacol esters and their fluoro-adducts. Fluoride ion induced polarity enhancement of arylboronate esters.
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.
Oehlke
Alexander
A
Department of Polymer Chemistry, Institute of Chemistry, Chemnitz University of Technology, Strasse der Nationen 62, 09111 Chemnitz, Germany.
Auer
Alexander A
AA
Jahre
Ina
I
Walfort
Bernhard
B
Rüffer
Tobias
T
Zoufalá
Petra
P
Lang
Heinrich
H
Spange
Stefan
S