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

The new phenol-imidazole pro-ligands ^RLH react with Co(BF ₄)₂·6H₂O in the presence of Et ₃N to form the corresponding [Co^II(^RL) ₂] compound (R = Ph (1), PhOMe (2), or Bz (3)). Also, ^BzLH, reacts with Co(II) in the presence of Et₃N and H₂O₂ to form [Co^III(^BzL) ₃] (4). The structures of l·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(^RL)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(^RL)(^RL)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(^BzL)(^BzL)₂]+. Unlike [l]⁺and [2]⁺, product of the one-electron oxidation of [Co^II(^BzL)₂], [3]⁺, is unstable and decomposes to produce [4]⁺. These studies have demonstrated that the chemical properties of [M^II(^RL)(^RL) ₂]⁺ (M = Co, Cu, Zn) are highly dependent on the nature of both the ligand and the metal centre.