Reactivity of the P–N bond in the halide salts of bis[bis(diphenylphosphino)methylamine]platinum(II)

Abstract

Conductivity measurements and ³¹P-{¹H} NMR spectroscopy suggested that the chloride and iodide salts of bis[bis(diphenylphosphino)methylamine]platinum(II)[Pt(dppma)₂]²⁺1 exist in solution equilibrium with the five-co-ordinate complexes [Pt(dppma)₂X]⁺(X = Cl or I). The magnitude of the interaction of the iodide ion with 1 is greater than that of the chloride ion. The extent of formation of the halide-associated species is dependent upon the nature of the solvent. Association equilibrium constants K_assoc= 0.0718 and 0.315 mol dm^–3 respectively were calculated for the chloride and iodide salts of 1 in MeNO₂. Addition of trace quantities of water to solutions of the chloride or iodide salts of 1 effected cleavage of both P–N bonds of one of its dppma ligands giving [Pt(dppma){(Ph₂PO)₂H}]⁺2. The structure of the cation was investigated crystallographically as a mixture of the iodide and tetrafluoroborate salts of the form I_0.21[BF₄]_0.79. The analogous reaction of the chloride salt of 1 with MeOH produces cleavage of only one P–N bond to give [Pt(dppma)(Ph₂POMe)(Ph₂PNHMe)]²⁺3 as the chloride salt. Phosphorus–nitrogen bond solvolysis of both ligands of 1 occurs to give the complex trans-[Pt(Ph₂POMe)₂(CN)₂]4 upon addition of 2 equivalents of sodium cyanide to methanolic solvent mixtures of [Pt(dppma)₂]X₂(X = BF₄, Cl or I). The product was characterised crystallographically. Possible mechanisms of formation of these complexes are discussed.