Borylene - boron bearing a negative charge

Although boron sits just left to carbon on the periodic table, this atom does not share its neighbor's versatility in reactivity. Due to its empty p orbital, which is in contrast to the partially filled p orbital in carbon, boron containing compounds almost behave as Lewis acids and are ready to accept electrons from others during the reaction. In one approach, anionic organoboron alkali metal salts were reported as possible reactive intermediates in some reactions, but none could be isolated or conclusively characterized. Based on the theoretical prediction by Schleyer and coworkers, Segawa and coworkers utilized a boron-bromide precursor to synthesize the first stable diamino-substituted boryllithium. To date, boryllithium has already shown a broad spectrum of utilizations and can be viewed as an ion pair between lithium and a five-membered ring containing negative-charge boron (borylene). In this context, we summarize our previous investigations regarding the thermodynamic and kinetic stabilities and Lewis basicities of borylenes. By the hybrid DFT functional, MPW1K, we studied a series of borylenes and found that nitrogen can act as a good π donor to stabilize a borylene and the not-yet synthesized six-membered analogue is more stable than the known five-membered borylene. Moreover, like the isoelectronic counterparts, N-heterocyclic carbenes, borylenes can act as Lewis bases to complex with BH3 and reduce the bond dissociation energy of the B-H bond in BH3. The Lewis acid-base pair then can donate hydrogen atoms during a radical reaction.