Stabilization of the Elusive 9‐Carbene‐9‐Borafluorene Monoanion

<p dir="ltr">Abstract Two‐electron reduction of carbene‐supported 9‐bromo‐9‐borafluorenes with excess KC 8 , Na, or Li‐naphthalenide affords six N‐heterocyclic carbene (NHC)‐ or cyclic(alkyl)(amino) carbene (CAAC)‐stabilized borafluorene anions ( 3 – 8 )‐the first isolated and structurally authenticated examples of the elusive 9‐carbene‐9‐borafluorene monoanion. </p><p dir="ltr">The electronic structure, bonding, and aromaticity of the boracyclic anions were comprehensively investigated via computational studies. Compounds 5 and 8 react with metal halides via salt elimination to give new B‐E (E=Au, Se, Ge)‐containing materials ( 9 – 12 ). Upon reaction with diketones, the carbene ligand cleanly dissociates from 5 or 8 to yield new B‐O containing spirocycles ( 13 – 14 ) that cannot be easily obtained using “normal” valent borafluorene compounds. </p><p dir="ltr">Collectively, these results support the notion that carbene‐stabilized monoanionic borafluorenes may serve as a new platform for the one‐step construction of higher‐value boracyclic materials.</p>