Metal complexes of sulphur ligands. Part IV. Reaction of bis(dialkylphosphinodithioato)-platinum(II) and -palladium(II) with ligands containing Group VB atoms

Abstract

Reaction of the complexes [Pt(S₂PR₂)₂](R = Me or Et) with tertiary phosphines gives four co-ordinate complexes [Pt(S₂PR₂)₂PR₃′] and [Pt(S₂PR₂)(PR₃′)₂]S₂PR₂. Variable-temperature ¹H n.m.r. studies of the neutral complexes indicate rapid unidentate–bidentate exchange at ambient temperatures and a full line-shape analysis of this process for complexes of general type [Pt(S–S)₂ER₃′][(S–S)^–=^–S₂CNEt₂. ^–S₂P(OEt)₂, or ^–S₂PMea₂; E = P or As] suggests a concerted mechanism in which both bond-breaking and bond-making steps are important. For the complex [Pd(S₂PMe₂)₂], the ionic complexes are too unstable to be isolated in pure form because of facile rearrangement to the neutral complexes. However, addition of either NaBPh₄ or NaPF₆ to solutions containing the ionic species provides a general method of synthesising the complexes [M(S₂PR₂)(PR₃′)₂]X (M = Pt or Pd; R = Me or Ph; X = BPh₄^– or PF₆^–). For M = Pt and X = BPh₄, these complexes readily react with Ph₄AsY (Y = Cl, Br, or I) giving Ph₄AsBPh₄, and [Pt(S₂PMe₂)(PR₃′)₂]Y. However, for the complexes [Pd(S₂PR₂)(PPh₃)₂]BPh₄(R = Me or Ph) dissolution in CH₂Y₂–EtOH,CHY₃–EtOH (Y = Cl or Br), or in acetone containing added halide ion produces rapid rearrangement to give [Pd(S₂PR₂)Y(PPh₃)]. This rearrangement does not occur for X = PF₆^– and a tentative mechanism involving a labile π- or σ-bonded phenyl group is suggested. Finally, an empirical i.r. method for distinguishing unidentate, bidentate, and ionic modes of co-ordination of the dimethylphosphinodithioato-group to platinum and palladium is briefly discussed.