Uncatalyzed Hydrogenation of First-Row Main Group Multiple Bonds

Room temperature hydrogenation of an SIDep‐stabilized diboryne (SIDep=1,3‐bis(diethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene) and a cAAC‐supported diboracumulene (cAAC=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐ylidene) provided the first selective route to the corresponding 1,2‐dihydrodiborenes. DFT calculations showed an overall exothermic (ΔG=19.4 kcal mol−1) two‐step asynchronous H2 addition mechanism proceeding via a bridging hydride. No catalyst needed: Two new carbene‐stabilized 1,2‐dihydrodiborenes have been synthesized by the direct and selective monohydrogenation of boron–boron multiple bonds under mild conditions. Theoretical calculations show a two‐step asynchronous H2 addition mechanism proceeding via a bridging hydride.