Evidence for asymmetrical cleavage of halide-bridged platinum(II) complexes by nucleophiles

Abstract

The addition of PMe₂Ph to [Pt₂Cl₄(PMe₂Ph)₂] at low temperatures produces the ions [PtCl(PMe₂Ph)₃]⁺ and [PtCl₃(PMe₂Ph)]^– as major products, as well as some of the expected [PtCl₂(PMe₂Ph)₂]. It is argued that the ionic species result from two molecules of the attacking nucleophile adding to a single platinum atom of the dimer, instead of the more common symmetrical attack. Less ionic product is produced from the addition of PBu₃ to [Pt₂Cl₄(PMe₂Ph)₂] and PMe₂Ph to [Pt₂Cl₄(PBu₃)₂], and none at all was detected from the addition of PBu₃ to [Pt₂Cl₄(PBu₃)₂], so the nature of the phosphine involved has a profound effect on the course of the reactions. The ionic materials are able to undergo rapid phosphine exchange even at –60 °C if excess ligand (PR₃ or Cl^–) is present. These exchange reactions can complicate the range of products observed unless precautions are taken to prevent local accumulations of the phosphine in the course of mixing the reactants.