The first example of a centro-symmetrical bis(imido)-bridged dinuclear cobalt(iii) complex: synthesis via oxidative dehydrogenation and phenoxazinone synthase activity

Abstract

A bis(imido)-bridged dinuclear cobalt(III) complex, [Co₂(amp)₂(μ-imp)₂Cl₂]Cl₂·2H₂O (1) [amp = 2-aminomethylpyridine; imp = 2-iminomethylpyridine anion], was synthesized by the reaction of cobalt(II) chloride with 2-aminomethylpyridine in the presence of alkaline hydrogen peroxide at room temperature. X-ray crystallography reveals that both the metal centres in the molecule are related to each other through an inversion centre, and the geometry of each of the Co^III ions is a distorted octahedral structure having a CoN₅Cl coordination environment. The most important feature of the structure is the modification of half of the coordinated amines by the oxidative dehydrogenation process which involves double bridging in the complex cation. To the best of our knowledge, this is the first example of a bis(imido)-bridged dinuclear cobalt(III) complex derived from metal-assisted oxidative dehydrogenation of the coordinated primary amine ligand. Complex 1 was found to be an excellent functional model for the phenoxazinone synthase, catalyzing the oxidative coupling of 2-aminophenol to the corresponding 2-aminophenoxazinone chromophore in dioxygen saturated methanol. The detailed kinetic investigations reveal that the phenoxazinone chromophore is produced via a potential complex–substrate intermediate.