Facile Access to Alkylideneborane and Diborabutadiene N-Heterocyclic Carbene Complexes.

A facile route to synthesis of B═C double-bonded systems has been developed. Specifically, both dibromofluorenylborane (FluH-BBr2) and a 1,1-dibromo-2,2-difluorenyldiborane/dimethyl sulfide adduct [(FluH)2B-BBr2(SMe2)] could be smoothly dehydrobrominated and subsequently coordinated by N-heterocyclic carbenes (NHCs) with formation of the respective alkylideneborane 1 and diborabutadiene 3. The electronic structures of 1 and 3 are interrogated and compared with those of base-free counterparts through density functional theory calculations.