Metal(II) complexes of the carbonylnitronate ligands O2NCHC(O)R− (R = Ph, OMe or OEt) and X-ray structure of (DMANH)[Ni(O2NCHC(O)Ph)3] (DMAN = 1,8-bis(dimethylamino)naphthalene)

New coordination compounds involving carbonylnitronate ligands O2NCHC(O)R− (R=Ph, OMe or OEt) are prepared by a synthetic procedure based on the reaction of a nickel(II) or palladium(II) salt with benzoylnitromethane or alkyl nitroacetate in the presence of a deprotonating agent. The use of the proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) in tetrahydrofuran affords, in high yields, the anionic complexes (DMANH)[Ni(O2NCHC(O)R)3] as brilliant green solids. The benzoylnitronate complex (R=Ph) crystallises in a monoclinic unit cell [space group P21/n, a=13.061(2), b=16.415(2), c=17.827(2)Å, β=102.7(2)°], which contains four octahedral anionic nickel complexes each close to a big DMANH+ cation. One nitronate ligand is easily replaced by two molecules of ethanol to give the neutral complexes [Ni(O2NCHC(O)R)2(EtOH)2]. The nickel is O,O′-coordinated to the ligand through one carbonyl and one nitro oxygen atom. A different coordination mode, in which only the nitro group is bonded to the metal, is, however, observed in the palladium complexes [PdCl(O2NCHC(O)R)]2 (R=OMe, OEt).