Cyclopalladated complexes containing 2-C6R4PPh2 ligands (R = H, F): one-electron electrochemical reduction leading to metal-carbon sigma-bond cleavage via palladium(I)

Three new ortho-metallated palladium complexes, [Pd(O,O′-hfacac)(κ2-2-C6F4PPh2)] (11), [Pd2(O,O′-hfacac)2(μ-2-C6F4PPh2)2] (12) and [Pd(O,O′-hfacac)(κC-2-C6F4PPh2)(PPh3)] (13) (hfacac = hexafluoroacetylacetonate), have been prepared and fully characterised. The electrochemical reductions of complexes 11–13, together with those of other cyclopalladated complexes containing 2-C6R4PPh2 ligands (R = H, F) were studied by cyclic, rotating disk and microelectrode voltammetry. Evidence for the one-electron reduction of [PdI(κ2-2-C6F4PPh2)(PPh2Fc)] (6) was obtained from coulometric analysis, although the product is unstable and undergoes further chemical processes. Preparative electro-reduction of [Pd2(μ-Br)2(κ2-2-C6F4PPh2)2] (7) in CH2Cl2 causes reductive cleavage of its Pd–C σ-bonds and formation of the complex [PdBr2{PPh2(2-C6F4H)}2] (14); possible mechanisms are discussed.