Further studies on the chemistry of molybdenyl adducts of [Pt₂(μ-S)₂(PPh₃)₄]: Hydrolysis, condensation and ligand exchange processes

Abstract

Reaction of [Pt₂(μ-S)₂(PPh₃)₄] with [MoO₂(acac)₂] in methanol gives the known five-coordinate Mo(VI) adduct [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ isolated as its PF₆⁻, BPh₄⁻ and [Mo₈O₂₆]₄⁻ salts; the latter was structurally characterised, the polymolybdate anion being the uncommon γ form. Hydrolysis of [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ in wet dichloromethane initially produces [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OH)]⁺ and subsequently the bright yellow oxo-bridged dimolybdenum species [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺, structurally characterised as its tetraphenylborate salt, and found to contain two five-coordinate molybdenum centres. [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺ can be prepared directly from [Pt₂(μ-S)₂(PPh₃)₄] and [MoO₂(acac)₂] in wet MeCN. Slow reconversion to [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ occurs when [{Pt₂(μ-S)₂(PPh₃)₄MoO₂}₂O]₂⁺ is dissolved in methanol. [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OMe)]⁺ undergoes alkoxide exchange in dichloromethane-alcohol solutions to give [Pt₂(μ-S)₂(PPh₃)₄MoO₂(OR)]⁺ species (R = e.g. n-octyl). These reactions are easily monitored using electrospray ionisation mass spectrometry.