Highly electron-deficient and air-stable conjugated thienylboranes

Introduced herein is a series of conjugated thienylboranes, which are inert to air and moisture, and even resist acids and strong bases. X-ray analyses reveal a coplanar arrangement of the thiophene rings, an arrangement which facilitates p-π conjugation through the boron atoms despite the presence of highly bulky 2,4,6-tri-tert-butylphenyl (Mes*) or 2,4,6- tris(trifluoromethyl)phenyl (^FMes) groups. Short B⋯F contacts, which lead to a pseudotrigonal bipyramidal geometry in the ^FMes species, have been further studied by DFT and AIM analysis. In contrast to the Mes* groups, the highly electron-withdrawing ^FMes groups do not diminish the Lewis acidity of boron toward F^- anions. These compounds can be lithiated or iodinated under electrophilic conditions without decomposition, thus offering a promising route to larger conjugated structures with electron-acceptor character.