SCHEDULED MAINTENANCE
Phenolate and phenoxyl radical complexes of Co(ii) and Co(iii)†
Abstract
The new phenol–imidazole pro-ligands RLH react with Co(BF4)2·6H2O in the presence of Et3N to form the corresponding [CoII(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 [CoIII(BzL)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. [CoII(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 [CoII(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]+, [CoIII(BzL˙)(BzL)2]+. Unlike [1]+ and [2]+, product of the one-electron oxidation of [CoII(BzL)2], [3]+, is unstable and decomposes to produce [4]+. These studies have demonstrated that the chemical properties of [MII(RL˙)(RL)2]+ (M = Co, Cu, Zn) are highly dependent on the nature of both the ligand and the metal centre.
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