Reactions of planar pentadentate ligands with palladium and platinum chlorides. Crystal structures of cis-dichlorobis(N′-isopropylidenebenzohydrazide)platinum(II) and the cyclopalladated dianion of N′,N‴-(pyridine-2,6-diyldiethylidyne)bis(benzohydrazide)

Abstract

The products from the reactions of the planar pentadentate ligand N′,N‴-(pyridine-2,6-diyldiethylidyne)bis(benzohydrazide) L¹, with PdCl₄^2– and PtCl₂ have been investigated. In both cases extensive changes in the ligand L¹ occur so that square-planar complexes can be formed. With PdCl₄^2–, two cyclopalladation reactions take place involving the insertion of the Pd atom into a C–H and an N–H bond. The presence of an anionic nitrogen in a cyclopalladation product is unusual. The reaction of PtCl₂ in acetone with L¹ led to the displacement of the 2,6-diacetylpyridine group by acetone with the formation of the new ligand N′-isopropylidenebenzohydrazide, L², in the complex cis-[PtCl₂(L²)₂]. Surprisingly, an analysis of the Pt–Cl and Pt–N distances in 23 cis- and 18 trans-[PtCl₂L₂](L = nitrogen donor ligand) complexes revealed no significant differences in the dimensions of the two geometries. The average Pt–Cl distances were 2.293(15)Å in the cis and 2.293(9)Å in the trans isomers.