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

The structural characterization of bis-cyclometalated palladium(II) compounds of formula Pd2(micro-(C6X4)PPh2]2(micro-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) A. 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.