Stable mixed-valence diphenylphosphanido bridged platinum(ii)–platinum(iv) complexes

Abstract

The reaction between [NⁿBu₄][(C₆F₅)₂Pt^II(μ-PPh₂)₂Pt^IV(C^N)(I)₂] (C^N = κ²-N,C-benzoquinolinate, 1) and (i) bidentate S^S, N^S and O^O anionic ligands or (ii) monodentate S- N- or O-based anionic ligands was studied in order to investigate the factors that may guarantee the stability of Pt(II),Pt(IV) mixed-valence dinuclear phosphanido complexes. While reactions of 1 with S^S or N^S ligands afforded stable Pt(II),Pt(IV) species of general formula [(C₆F₅)₂Pt^II(μ-PPh₂)₂Pt^IV(C^N)(L^S)]^x− [(L^S)^(x−1) = 2-mercaptopyrimidinate (pymS⁻), 2-mercaptopyridinate (pyS⁻), dimethyldithiocarbamate (Me₂NCS₂⁻), ethyl xanthogenate (EtOCS₂⁻) and 1,2-benzenedithiolate (PhS₂²⁻)], the reaction of 1 with the O^O ligand sodium acetylacetonate gave several products, and no pure Pt(II),Pt(IV) complex could be isolated. The reaction of monodentate ligands such as PhS⁻, OH⁻ or N₃⁻ with 1 led to a stable Pt(II),Pt(IV) complex only in the case of N₃⁻. The reaction with OH⁻ afforded the Pt(II),Pt(II) complex [(C₆F₅)₂Pt^II(μ-PPh₂)(κ²-O,P-μ-O–PPh₂)Pt^II(C^N)]⁻ (8) deriving from reductive coupling of a diphenylphosphanide and an O-donor ligand coordinated to the Pt(IV) centre, while the reaction with PhS⁻ produced the unstable Pt(II),Pt(IV) complex [NⁿBu₄][(C₆F₅)₂Pt^II(μ-PPh₂)₂Pt^IV(C^N)(PhS)₂] (11) that evolved in solution to the Pt(II),Pt(II) species [NⁿBu₄][(C₆F₅)₂Pt^II(μ-PPh₂)₂Pt^II(C^N)] (9) by elimination of diphenyldisulfide. Thus, the stability of mixed valence Pt(II),Pt(IV) phosphanide complexes is affected by several concurrent factors, including the chelating effect of the ligands and the type of ligating atoms.