Unlocking the Ambiphilicity of the Boryl Anion: Synthesis and Reactivity of an Anionic Diazoborane.

Reported boryl anions (R2B-) often exhibit n-p conjugation between the boron atom and adjacent heteroatoms, with their nucleophilicity being the primary focus. In this work, we present evidence that aryl-substituted boryl anions (Ar2B-) can exhibit ambiphilicity. Specifically, the diazoborane anion [K(2.2.2-cryptand)]+Dmp(Mes)BN2- (3, Dmp = 2,6-dimesitylphenyl, Mes = 2,4,6-trimethylphenyl) has been synthesized via diazo transfer using Carpino's hydrazine as a reagent. Compound 3 exhibits a strong tendency to release dinitrogen, acting as a free boryl anion Dmp(Mes)B- source. Ligand exchange reactions with carbon monoxide and 2,6-xylyl isocyanide highlight the metallomimetic (ambiphilic) behavior of 3. The ambiphilic nature of 3 further enables its reaction with nitrous oxide to yield an oxoborane anion (R2BO-). Compound 3 also reacts with carbon dioxide to form the cycloaddition product R2B(N2CO2)- (7). Additionally, the boryl-N2 anion undergoes N2 release upon heating with LiCl or irradiation, yielding different bond activation products. The underlying mechanisms of these reactions were investigated through in-depth DFT analysis.