Dinuclear palladium(ii) compounds with bridging cyclometalated phosphines. Synthesis, crystal structure and electrochemical study

Abstract

The structural characterization of bis-cyclometalated palladium(II) compounds of formula Pd₂[(µ-(C₆X₄)PPh₂]₂(µ-O₂CR)₂ [X = H, R = CH₃ (3), CF₃ (4), C(CH₃)₃ (5) and C₆F₅ (6); X = F, R = CH₃ (7) and CF₃(8)], has confirmed its paddle wheel structure with two palladium atoms bridged by two acetates and two metalated phosphines in a head-to-tail arrangement. The Pd⋯Pd distances are in the range 2.6779(16)–2.7229(8) Å. Under cyclic voltammetric conditions, compounds 3–6, in CH₂Cl₂ solution, were found to undergo a reversible oxidation peak in the range of potential values 0.84–1.25 V. A second partially-reversible oxidation is observed at more positive potentials (1.37–1.55 V). For compounds 3–5 in the presence of chlorides, the first oxidation becomes a two-electron process presumably leading to a neutral [Pd(III)–Pd(III)] species with a metal–metal bond.