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)(eta(2)-L)] and [Pd(eta(2)-L)(2)] but, when HL = Haceta, only [Pd(acac)(eta(2)-L)] is formed, even when the ratio of Pd-HL is 1:4; reaction of all these tetramic acids with an aqueous solution of K-2[PdCl4] gives [Pd(eta(2)-L)(2)]. In solution, NMR studies in non polar solvents show that there is only one isomer of [Pd(acac)(eta(2)-L)] whereas there are usually two isomers of [Pd(eta(2)-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 0,O'-mode of coordination via the functionalities associated with C-4 and the acyl group at C-3 in the pyrrolidine ring. In pyridine solution, [pd(eta(2)-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. (C) 2003 Elsevier B.V. All rights reserved.