Contrasting arsine and phosphine coordination behaviour: heteroleptic palladium(II) complexes with triphenylarsine and a crown thioether

Abstract

The synthesis, spectroscopic data and crystal structures of two new mononuclear Pd(II) heteroleptic complexes with the crown trithioether 1,4,7-trithiacyclononane (9S3) and the arsine ligand, triphenylarsine (AsPh₃) are presented. Reaction between [Pd(9S3)Cl₂] and AsPh₃ (1:2 stoichiometry) in nitromethane followed by metathesis to the hexafluorophosphate salt results in the formation of two different palladium(II) complexes, the expected bis arsine complex [Pd(9S3)(AsPh₃)₂](PF₆)₂ as well as, surprisingly, the intermediate mono arsine-chloro complex [Pd(9S3)(AsPh₃)(Cl)](PF₆). Both complexes exhibit the anticipated structure consisting of a cis square planar array of two sulfur atoms from the 9S3 and either two As donors (bis AsPh₃ complex) or one As and one Cl donor (mono AsPh₃ complex). The third 9S3 sulfur atom exhibits a long distance interaction with the palladium forming an elongated square pyramidal geometry with a coordination environment around the Pd best described as [S₂As₂ + S₁] or [S₂AsCl + S₁]. Structural, spectroscopic, and reactivity differences are observed between the arsine and related phosphine complexes due to the poorer donor qualities of AsPh₃.