Cyclopalladated complexes containing 2-C 6 R 4 PPh 2 ligands (R = H, F): one-electron electrochemical reduction leading to metal–carbon σ-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 = hexafluoroace-tylacetonate), have been prepared and fully characterised. The electrochemical reductions of complexes 11–13, together with those of other cyclopalladated complexes containing 2C6R4PPh2 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.

Synthesis, X-ray structure and electrochemical characterization of palladium(II) bearing ferrocenyldiphenylphosphine complexes

Four new complexes, [PdX(κ2-2-C6R4PPh2)(PPh2Fc)] [X = Br, R = H (1), R = F (2); X = I, R = H (3), R = F (4)], containing ferrocenyldiphenylphosphine (PPh2Fc) have been prepared and fully characterised. The X-ray structures of complexes trans-1, cis-2 and cis-4, and that of a decomposition product of 4, [Pd(κ2-2-C6F4PPh2)(μ-I)(μ-2-C6F4PPh2)PdI(PPh2Fc)] (5), have been determined. These complexes show a distorted square planar geometry about the metal atom, the bite angles of the chelate ligands being about 69°, as expected. The cis/trans ratio of 1–4 in solution is strongly dependent on solvent. The new complexes and the uncoordinated PPh2Fc ligand were electrochemically characterised by cyclic and rotating disk voltammetry, UV-visible spectroelectrochemistry, and bulk electrolysis in dichloromethane and acetonitrile. In both cases, oxidation occurs at both the ferrocene and phosphine centres, but the complexes oxidise at more positive potentials than uncoordinated PPh2Fc; subsequently, the metal–phosphorus bond is cleaved, leading to free PPh2Fc+, which undergoes further chemical and electrochemical reactions.

Novel dithiolene complexes incorporating conjugated electroactive ligands

A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38–99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (−0.12 to −0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 × 10⁻⁶ to 7 × 10⁻⁸ S cm⁻¹.