Abstract

The reaction of ppa^X {(4-X-phenyl)-pyridin-2-ylmethylene-amine; X = H, Me, Et, OMe, F, Cl, Br, and I} with [Ni(β-diketonate) <inf>2</inf>(H<inf>2</inf>O)<inf>2</inf>] {β-diketonate = 1,3-diphenylpropanedionate (dbm), 2,2,6,6-tetramethyl-3,5-heptadionate (tmhd), or hexafluoroacetylacetonate (hfac)} yields a series of nickel complexes. X-ray crystallography reveals octahedral coordinated nickel centres with a cis arrangement of the -diketonate ligands. The β-diketonate ligands adopt 'planar' or 'bent' coordination modes, whereas the aryl ring of the ppa ^X ligand is twisted with respect to the pyridylimine unit. The electrochemical behaviour of the complexes reveals quasi-reversible or irreversible one-electron oxidation to Ni(iii) in the case of the [Ni(tmhd) <inf>2</inf>(ppa^X)] and [Ni(dbm)<inf>2</inf>(ppa^X)] complexes, respectively. The peak potential for oxidation is dependent on the type of β-diketonate ligand but essentially independent of the substituent, X, on the ppa^X ligand. The [Ni(β-diketonate) <inf>2</inf>(ppa^X)] complexes (X = F, Cl, Br, and I) also undergo ligand based reduction. © 2010 CSIRO.