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

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 Kassoc= 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 I0.21[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.