Interrogating Redox and Lewis Base Activations of Aminoboranes

Since their discovery, aminoboranes (R2N–BR2) have been applied as chemical hydrogen storage devices, asymmetric catalysts, semiconductors, and amination reagents. Recently, chemists have extended their application to reagents for difunctionalization reactions, wherein the N–B bond is cleaved and the amine and boronic ester fragments are distributed across an organic molecule. Generally, harsh conditions or loss of the borane fragment as waste is required to enable reactivity of the enthalpically stable partial sp2-hybridized N–B bond. In contrast, we sought to show that mild avenues also exist to disrupt the dative N–B π-bond. Herein, we survey the coordinative capabilities of neutral Lewis bases to (amino)pinacolboranes and whether the partial sp2-hybridized N-B bond can be oxidized electro- or photochemically in analogous fashion to C=C bonds. The results of these studies are strongly in the affirmative and should guide the thought processes of organic chemists when designing new reactions using aminoboranes.