Synthesis and Ring Strain of a Benzoborirene-N-Heterocyclic Carbene Adduct

Abstract

The reduction of an N-heterocyclic carbene (1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene, IiPr ${}_{\mathrm{Me}{}_2}$ ) adduct of dichloro(ortho-bromophenyl)borane by tert-butyl lithium at low temperature yields the IiPr ${}_{\mathrm{Me}{}_2}$ adduct A of parent benzoborirene, a highly strained boron-containing bicyclic compound. A is unstable at room temperature and dimerizes at low temperature to the bis-IiPr ${}_{\mathrm{Me}{}_2}$ adduct of 9,10-dihydro-9,10-diboraanthracene, characterized by single-crystal X-ray crystallography.

Keywords: boron; fused ring systems; heterocycles; strained molecules; ylides.