Reactivity Enhancement of a Zerovalent Diboron Compound by Desymmetrization.

The desymmetrization of the cyclic (alkyl)(amino)carbene-supported diboracumulene B(cAAC) (cAAC = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) by monoadduct formation with IMe (1,3-dimethylimidazol-2-ylidene) yields the zerovalent sp-sp diboron compound B(cAAC)(IMe), which provides a versatile platform for the synthesis of novel symmetrical and unsymmetrical zerovalent sp-sp diboron compounds by adduct formation with IMe and CO, respectively. Furthermore, B(cAAC)(IMe) displays enhanced reactivity compared to its symmetrical precursor, undergoing spontaneous intramolecular C-H activation and facile twofold hydrogenation, the latter resulting in B-B bond cleavage and the formation of the mixed-base parent borylene (cAAC)(IMe)BH.