Crystal Structure of Boryllithium with Two THF Molecules and DFT Analysis of Its Property as a Boryl Anion

The second crystal structure of boryllithium 2 with two coordinating THF solvent molecules was obtained. The 11B NMR chemical shift of a THF solution, made by dissolving single crystals of 2·(THF)2 in THF-d8, significantly and reversibly changed depending on temperature (from 20 to −100 °C). The calculated 11B chemical shift by GIAO method was close to two experimental values. The character of the sp2 lone pair on the boron center in opt-2·(THF)2 was shown to be similar to those in the calculated free phenyl anion and boryl anion. AIM analyses for opt-2·(THF)2 suggested that the B–Li bond of boryllithium is polarized, similar to the C–Li bond of alkyllithium.