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- 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 ((F)Mes) groups. Short BF contacts, which lead to a pseudotrigonal bipyramidal geometry in the (F)Mes species, have been further studied by DFT and AIM analysis. In contrast to the Mes* groups, the highly electron-withdrawing (F)Mes 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.