Borata‐Alkene Species as Nucleophilic Reservoir
Ricardo J. Maza, Jorge J. Carbó, Elena Fernández
Abstract
Abstract α‐Monoboryl anions show remarkable stability due to the valence deficiency of the adjacent three‐coordinate boron center and can be expressed as its resonance form, the borata‐alkene systems [R 2 B=CH 2 ] − . The diversity of synthetic approaches as well as the properties of the C=B bond are disclosed in this review, dealing with both electronic and structural properties of the boryl moieties involved. Full characterization in solid state by X‐ray diffraction demonstrated the short distances between B and C, as a consequence of the boron ylide character in the boron‐stabilized carbanions. This review includes a collection of C−B length distances as well as 11 B NMR data that can be useful for diagnostic evidence of the partial boron‐carbon double‐bond character. Natural bond orbital (NBO) analysis on DFT computed structures also supports and justifies the borata‐alkene character. The reactivity of the C=B bond acting as nucleophilic synthon is unveiled through extensive electrophilic trapping examples. The homologation protocols with diborylmethane, via single carbon chain extension, involves a facile introduction of the C( sp 3 )−B bonds, which can be subsequently transformed into functionalized target products, containing C−O, C−N or C−C bonds. magnified image