Fast reactions at planar four-co-ordinate complexes. Part 4. The reaction of chelate dichloropalladium(II) complexes with some bidentate ligands

Abstract

The reaction between the square-planar complexes [Pd(L–L)Cl₂][L–L = 1,2-bis(diphenylphosphino) ethane, o-phenylenebis (dimethylarsine), ethylenediamine, 1,10-phenanthroline, 2,2′-bipyridine, or 1,2-bis(phenylthio)ethane] and ethylenediamine proceeds in two consecutive stages yielding [Pd(en)₂]Cl₂ as a final product. The intermediate species is [Pd(L–L)(en)]Cl₂ or [Pd(en)Cl₂] when L–L is 1,2-bis(phenylthio)ethane. The rate of replacement of the first chloride co-ordinated to palladium(II) in the substrates [Pd(L–L)Cl₂] at 25 °C in dimethylformamide is strongly dependent on the nature of the ligand L–L, covering four orders of magnitude. The reaction between the substrates [M(bipy)Cl₂](M = Pd or Pt, bipy = 2,2′-bipyridine) and the bidentate nucleophiles ethylenediamine and dithio-oxamide proceeds according to an analoguous two-stage reaction scheme when M is palladium; in the platinum derivatives, however, the chelate bipyridine is inert towards substitution. In the solvent dimethylformamide the entering group ethylenediamine behaves as a very effective nucleophile.