Umpolung of an Aliphatic Ketone to a Magnesium Ketone-1,2-diide Complex with Vicinal Dianionic Charge

The new β-diketimine ^iPrDip nacnacH, HC(iPrCNDip)₂ H, Dip=2,6-iPr₂ -C₆ H₃ , was converted to the magnesium(I) complex [{(^iPrDip nacnac)Mg}₂ ] and reaction with 2-adamantanone (OAd) afforded the ketone-1,2-diide complex [{(^iPrDip nacnac)Mg}₂ (μ-OAd)]. The complex contains the first stable dianion of an aliphatic ketone with an electropositive metal and shows an OAd^2- unit with long C-O bond and pyramidal carbon centre. DFT studies reveal an anionic charge on both neighbouring C and O atoms. Reductions of aliphatic ketones with magnesium(I) complexes show that these likely proceed via highly reactive dianions and afforded a 1 : 1 mixture of an alkoxide and an enolate when an enolisable ketone was used, and rapid CH activations reactions, e.g., of stabilising ligand moieties, when non-enolisable ketones were employed.