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

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The new β‐diketimine i PrDip nacnacH, HC( i PrCNDip) 2 H, Dip=2,6‐ i Pr 2 ‐C 6 H 3 , was converted to the magnesium(I) complex [{( i PrDip nacnac)Mg} 2 ] and reaction with 2‐adamantanone (OAd) afforded the ketone‐1,2‐diide complex [{( i PrDip 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.