Reactions of elemental sulfur with tetrakis(triphenylphosphine)platinum(0). Formation of a complex containing very nucleophilic bridging sulfido ligands

Abstract

The reactions of Pt(PPh₃)₄ with elemental sulfur in ratios S/Pt = 3, 4, 5, and 6 give a mixture of compounds identified as [PtS(PPh₃)₂]₂ and PtS₄(PPh₃)₂; PtS₂(PPh₃)₂ is not detected. The dimeric complex also forms on reaction of PtS₄(PPh₃)₂ with 3 mol of Pt(C₂H₄)(PPh₃)₂. It is alkylated at one bridging sulfido ligand by CH₂Cl₂ and CHCl₃ to give cations [Pt₂(μ-S)-(μ-SR)(PPh₃)₄]⁺, R = CH₂Cl and CHCl₂, respectively, which are characterized as their hexafluorophosphate salts. The cations give extreme AA′BB′X ³¹Pmr spectra since their cis-phosphorus atoms (A,B) have very similar chemical shifts but different coupling constants to ¹⁹⁵Pt(X); spectral features are broadened by thiolate inversion processes. Reactions of bridging sulfido ligands with other electrophiles are discussed.