Phenolate and phenoxyl radical complexes of Co(II) and Co(III)

The new phenol-imidazole pro-ligands (LH)-L-R react with Co(BF4)(2).6H(2)O in the presence of Et3N to form the corresponding [CoII(L-R)(2)] compound (R = Ph (1), PhOMe (2), or Bz (3)). Also, (LH)-L-Bz, reacts with Co(II) in the presence of Et3N and H2O2 to form [Co-III(L-Bz)(3)] (4). The structures of 1.2.5MeCN, 2.2DMF, 3.4MeOH, and 4.4DMF have been determined by X-ray crystallography. 1, 2, and 3 each involve Co(II) bound to two N,O-bidentate ligands with a distorted tetrahedral coordination sphere; 4 involves Co(III) bound to three N,O-bidentate ligands in a mer-N3O3 distorted octahedral geometry. [Co-II(L-R)(2)] (R = Ph or PhOMe) undergo two, one-electron, oxidations. The products of the first oxidation, [1](+) and [2](+), have been synthesised by the chemical oxidation of 1 and 2, respectively; these cations, formulated as [Co-II(L-R(.))(L-R)(2)](+), comprise one phenoxyl radical and one phenolate ligand bound to Co(II) and are the first phenoxyl radical ligand complexes of tetra-coordinated Co(II). 4 undergoes two, one-electron, ligand-based oxidations, the first of which produces [4](+), [Co-III(L-Bz(.))(L-Bz)(2)](+). Unlike [1](+) and [2](+), product of the one-electron oxidation of [Co-II(L-Bz)(2)], [3](+), is unstable and decomposes to produce [4](+). These studies have demonstrated that the chemical properties of [M-II(L-R(.))(L-R)(2)](+) (M = Co, Cu, Zn) are highly dependent on the nature of both the ligand and the metal centre.