The synthesis and characterisation of phenolate complexes of Cu(II) and Ni(II) that are capable of supporting a phenoxyl radical ligand

New Cu-II and Ni-II complexes of potentially tridentate N2O Schiff base ligands 1 and 2 have been synthesised and characterised. [Cu(2)(OH2)](+) possesses a square planar geometry in the solid state whereas [Ni(1)(2)] possesses a distorted octahedral geometry in which the amine donors of 1 coordinate weakly to the Ni-II centre. EPR spectroscopy demonstrates that the N2O2 coordination sphere of [Cu(2)(OH2)](+) is retained in CH2Cl2 solution. [Cu(2)(OH2)](+) exhibits a reversible one electron oxidation at E-1/2=0.54V versus [Fc](+)/[Fc], the product of which has been characterised by UV-Vis absorption and EPR spectroscopies. The spectroscopic signature of the oxidised product is consistent with the formation of a stable phenoxyl radical ligand bound to a Cull centre. [Ni(1)2] possesses a reversible metal-based oxidation process at E-1/2 = 0.03 V versus [Fc](+)/[Fc] and a further oxidation, attributed to the generation of a phenoxyl radical centre at E-p(a) = 0.44 V versus [Fc](+)/[Fc]. UV-Vis absorption and EPR spectroscopic studies indicate that the lower potential process is a formal Ni-III/II couple. In contrast, the pro-ligands 1H and 2H exhibit chemically irreversible oxidation processes at E-p(a) = 0.42 and 0.40 V versus Fc(+)/Fc, respectively, and do not support the formation of stable phenoxyl radical species. (c) 2006 Elsevier B.V. All rights reserved.