Reactivity Enhancement of a Zerovalent Diboron Compound by Desymmetrization

The desymmetrization of the cyclic (alkyl)­(amino)­carbene-supported diboracumulene B2(cAACMe)2 (cAACMe = 1-(2,6-diisopropylphenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene) by monoadduct formation with IMeMe (1,3-dimethylimidazol-2-ylidene) yields the zerovalent sp–sp2 diboron compound B2(cAACMe)2(IMeMe), which provides a versatile platform for the synthesis of novel symmetrical and unsymmetrical zerovalent sp2–sp2 diboron compounds by adduct formation with IMeMe and CO, respectively. Furthermore, B2(cAACMe)2(IMeMe) 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 (cAACMe)­(IMeMe)­BH.