Cyclopalladated complexes containing 2-C6R4PPh2 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)(κ(2)-2-C6F4PPh2)] (), [Pd2(O,O'-hfacac)2(µ-2-C6F4PPh2)2] () and [Pd(O,O'-hfacac)(κC-2-C6F4PPh2)(PPh3)] () (hfacac = hexafluoroacetylacetonate), have been prepared and fully characterised. The electrochemical reductions of complexes , 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(κ(2)-2-C6F4PPh2)(PPh2Fc)] () was obtained from coulometric analysis, although the product is unstable and undergoes further chemical processes. Preparative electro-reduction of [Pd2(µ-Br)2(κ(2)-2-C6F4PPh2)2] () in CH2Cl2 causes reductive cleavage of its Pd-C σ-bonds and formation of the complex [PdBr2{PPh2(2-C6F4H)}2] (); possible mechanisms are discussed.

Synthesis, X-ray structure and electrochemical oxidation of palladium(II) complexes of ferrocenyldiphenylphosphine.

Four new complexes, [PdX(κ(2)-2-C(6)R(4)PPh(2))(PPh(2)Fc)] [X = Br, R = H (1), R = F (2); X = I, R = H (3), R = F (4)], containing ferrocenyldiphenylphosphine (PPh(2)Fc) 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(κ(2)-2-C(6)F(4)PPh(2))(µ-I)(µ-2-C(6)F(4)PPh(2))PdI(PPh(2)Fc)] (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 PPh(2)Fc 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 PPh(2)Fc; subsequently, the metal-phosphorus bond is cleaved, leading to free PPh(2)Fc(+), which undergoes further chemical and electrochemical reactions.

Gold nanoparticle formation during bromoaurate reduction by amino acids.

The synthesis and characterization of water-soluble dispersions of gold nanoparticles by the reduction of a potassium tetrabromoaurate precursor solution using the amino acids L-tyrosine, glycyl-L-tyrosine, and L-arginine using alkaline synthesis conditions are reported. The particle sizes determined by small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM) measurements are found to be inversely proportional to the rate of particle formation, which was determined by time-resolved UV-visible spectrophotometry measurements, and vary very slowly at intermediate gold concentrations and rapidly at the extremes. Dispersions produced with a mixture of the two amino acids glycyl-L-tyrosine and L-tyrosine showed particle sizes and particle size distributions which were directly proportional to the ratio of the two L-amino acids, thus offering the possibility for control over the properties of the gold nanoparticle dispersions.