Direct access to a cAAC-supported dihydrodiborene and its dianion

The two-fold reduction of (cAAC)BHX2 (cAAC = 1-(2,6-diisopropyl-phenyl)-3,3,5,5-tetramethylpyrrolidin-2-ylidene; X = Cl, Br) provides a facile, high-yielding route to the dihydrodiborene (cAAC)(2)B2H2. The (chloro)hydroboryl anion reduction intermediate was successfully isolated using a crown ether. Overreduction of the diborene to its dianion [(cAAC)(2)B2H2](2-) causes a decrease in the B-B bond order whereas the B-C bond orders increase.