We report the first example of a structurally characterized oxyallyl −CH 2 C(O)CH 2 − group, trapped as a bridging ligand that spans two nickel centers. The ligand results from the double metalation of acetone on a nickel− NHC platform. A competing reaction leads to a single metalation of acetone. R ecent research from our group has targeted the chemistry of nickel complexes bearing NHC ligands. 1 We recently reported that nickel−NHC complexes are able to activate one of the C−H bonds of a labile acetonitrile ligand in the presence of a strong base. The reaction results in the formal loss of a hydrogen atom from the ligand, which does a sharp flip to give a neutral cyanomethyl−nickel complex (Scheme 1). 2 Here, we describe the synthesis of the dinickel complex [{Cp-(Mes 2 NHC)Ni} 2 {μ-CH 2 C(O)CH 2 }], in which an oxyallyl group is trapped as a bridging ligand spanning the two metal centers. The complex results from the deprotonation of two C−H bonds from the two different methyl groups of an acetone molecule on a nickel−NHC platform. While trimethylenemethane has been trapped as a ligand in many stable organometallic complexes, 3 the isoelectronic oxyallyl group has never been isolated free or even structurally characterized as a ligand. 4 Treatment of [Ni(Mes 2 NHC)ClCp] with AgBF 4 in acetone affords the red cationic η 1 -acetone complex [Ni(Mes 2 NHC)-{(O)C(CH 3) 2 }Cp] + BF 4