The water-solubilisation of the metalloligand [Pt2(μ2-S)2(PPh3)4] using 1,3,5-triaza-7-phospha-adamantane (PTA)

Abstract

The synthesis of the platinum(II) μ2-sulfide complex [Pt2(μ2-S)2(PTA)4] (PTA = phosphatriazaadamantane), as a water-soluble analogue of the well-known triphenylphosphine complex [Pt2(μ2-S)2(PPh3)4], has been explored through a range of synthetic routes. A direct synthesis, from cis-[PtCl2(PTA)2] and Na2S·9H2O in benzene was found to be the most effective, while attempted ligand substitution of the PPh3 ligands of [Pt2(μ2-S)2(PPh3)4] with PTA resulted in rearrangement of the {Pt2S2} core, and formation of a series of PTA-substituted trinuclear species of the general composition [Pt3(μ3-S)2(PPh3)x(PTA)6-x]2+. The fully-substituted complex [Pt3(μ3-S)2(PTA)6]2+ was also obtained when cis-[PtCl2(PTA)2] was reacted with a sulfide ion-exchange resin. Reaction of [PtCl2(cod)] (cod = 1,5-cyclooctadiene) with Na2S·9H2O in benzene gave a red solid identified as crude [Pt2(μ2-S)2(cod)2]. Reaction of this labile {Pt2S2} precursor with PTA resulted in the formation of [Pt2(μ2-S)2(PTA)4] along with PTA -oxide and -sulfide. ESI mass spectrometry was widely employed as a convenient tool for exploring this chemistry, in conjunction with 31P{1H} NMR spectroscopy. These PTA-Pt-sulfide species, especially those containing {Pt2S2} cores, have a tendency to decompose in solution. Additional confirmation of the formation of [Pt2(μ2-S)2(PTA)4] was provided by its reaction with [Rh2(μ2-Cl)2(cod)2], resulting in the formation of the adduct [Pt2(μ3-S)2(PTA)4Rh(cod)]+, identified using ESI MS.