Moderating the nucleophilicity of the sulfide ligands in the dinuclear {Pt2S2} metalloligand system using triphenylarsine

Reaction of cis-[PtCl2(AsPh3)2] with excess sodium sulfide in benzene gave the triphenylarsine analogue of the well-known metalloligand [Pt2(μ-S)2(PPh3)4] as an orange solid.The compound was characterised by detailed mass spectrometry studies, and by conversion to various alkylated and metallated derivatives.The sulfide ligands in [Pt2(μ-S)2(AsPh3)4] are less basic than the triphenylphosphine analogue, and the complex gives a relatively weak [M+H]+ ion in the positive-ion electrospray (ESI) mass spectrum, compared with the phosphine analogue.Methylation of an equimolar mixture of [Pt2(μ-S)2(PPh3)4] and [Pt2(μ-S)2(AsPh3)4] with MeI gave the species [Pt2(μ-S)(μ-SMe)(AsPh3)4]+ and [Pt2(μ-SMe)2(PPh3)3I]+, indicating a reduced tendency for the sulfide of [Pt2(μ-S)(μ-SMe)(AsPh3)4]+ to undergo alkylation.The lability of the arsine ligands is confirmed by the reaction of an equimolar mixture of [Pt2(μ-S)2(PPh3)4] and [Pt2(μ-S)2(AsPh3)4] with n-butyl chloride, giving [Pt2(μ-S)(μ-SBu)(EPh3)4]+ (E = P, As), which with Me2SO4 gave a mixture of [Pt2(μ-SMe)(μ-SBu)(PPh3)4]2+ and [Pt2(μ-SMe)(μ-SBu)(AsPh3)3Cl]+.Reactivity towards 1,2-dichloroethane follows a similar pattern.The formation and ESI MS detection of mixed phosphine–arsine {Pt2S2} species of the type[Pt2(μ-S)2(AsPh3)n(PPh3)4−n] is also discussed. Coordination chemistry of [Pt2(μ-S)2(AsPh3)4] towards a range of metal-chloride substrates, forming sulfide-bridged trinuclear aggregates, has also been probed using ESI MS, and found to be similar to the phosphine analogue. The X-ray crystal structure of [Pt2(μ-S)2(AsPh3)4Pt(cod)](PF6)2 (cod = 1,5-cyclo-octadiene) has been determined for comparison with the (previously reported) triphenylphosphine analogue. ESI MS is a powerful tool in exploring the chemistry of this system; in some cases the derivatising agent p-bromobenzyl bromide is used to convert sparingly soluble and/or poorly ionising {Pt2S2} species into soluble, charged derivatives for MS analysis.

Graphical abstractThe complex [Pt2(μ-S)2(AsPh3)4], which is the triphenylarsine analogue of the extensively studied metalloligand [Pt2(μ-S)2(PPh3)4], has been synthesised and its chemistry studied, primarily using the technique of electrospray ionisation mass spectrometry.The results point towards a complex that contains somewhat less basic and nucleophilic sulfide centres, that together with the presence of labile arsine ligands modifies the chemistry of this complex towards alkylating agents.Figure optionsDownload full-size imageDownload as PowerPoint slide