Stabilization of the Elusive 9‐Carbene‐9‐Borafluorene Monoanion
Kelsie E. Wentz, Andrew Molino, Sarah L. Weisflog, Aishvaryadeep Kaur, Diane A. Dickie, David J. Wilson, Robert J. Gilliard
Abstract
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. 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. 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.