Crystalline Diboryldiazomethane: Synthesis and Reactivities

Diboryldiazomethanes, featuring dual boryl substitution that can simultaneously stabilize and diversify the diazo carbon center, represent an appealing yet largely inaccessible class of diazo compounds. Here, a preorganized B₂N₂C scaffold is converted into a diboryldiazomethane via N₂O-mediated diazo transfer. Reactivity studies with Lewis acids reveal two distinct binding sites within the diazo unit, enabling selective engagement of the terminal nitrogen versus the carbon center. In contrast, methoxide triggers addition across a B-C bond with opening of the five-membered ring to furnish a monoboryl diazo derivative. All new species were fully characterized by multinuclear NMR spectroscopy and single-crystal X-ray diffraction (SC-XRD). These findings establish a stable entry to diboryldiazo chemistry and define a tunable reactivity model for main-group-controlled diazo platforms.