Palladium(II)/β-diketonate complexes containing the enolates of N-acetyl-3-acyltetramic acids: Crystal structure of the Lewis base adduct, [Pd(py)4](abta)2

Progressive displacement of acac from [Pd(acac)2] occurs on reaction with different tetramic acids (HL=Hata, Habta) to give [Pd(acac)(η2-L)] and [Pd(η2-L)2] but, when HL=Haceta, only [Pd(acac)(η2-L)] is formed, even when the ratio of Pd–HL is 1:4; reaction of all these tetramic acids with an aqueous solution of K2[PdCl4] gives [Pd(η2-L)2]. In solution, NMR studies in non polar solvents show that there is only one isomer of [Pd(acac)(η2-L)] whereas there are usually two isomers of [Pd(η2-L)2] which are probably due to the presence of cis- and trans-isomers of the complex as a result of both the enolate ligands adopting a O,O′-mode of coordination via the functionalities associated with C4 and the acyl group at C3 in the pyrrolidine ring. In pyridine solution, [Pd(η2-abta)2] forms a Lewis base adduct, [Pd(py)4](abta)2, which has been characterised by X-ray analysis and shown to contain a square-planar Pd(py)4-group with trans-, monodentate, weakly bonded abta groups.