N,O versus O,O coordination in beta-imino diketonato complexes: Role of the metal center and of the imino substituent

beta-Imino carbonyl enolato metal(II) complexes of general formula [M((RCO)(R'CO)CC(R '') NH)(2)] (M = Mn, Fe, Co, Ni, Cu, Zn, Pd, R = R' = Me, R '' = CCl(3); M = Cu, Pd, R = R' = Me, R '' = PhCO; R = Me, R' = Ph, R '' = PhCO; R = R' = Ph, R '' = PhCO) are easily synthesized by the reaction of metal(II) acetates with the proper beta-enaminodiones in 1/2 molar ratio in ethanol at room temperature. In all the cases the trifunctional NOO beta-imino carbonyl enolate ligand acts as bidentate to give ML(2) complexes, whose structure depends on the metal center and on the nature of the substituent R '' at the imino carbon. With R '' = CCl(3) an O,O coordination is observed for all the metal centers but one, in fact palladium(II) exhibits an N,O coordination through the imino nitrogen and one keto oxygen. By contrast with R '' = PhCO the ligand is always coordinated through the imino nitrogen and one keto oxygen atom.