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.