Light-induced O2-dependent aliphatic carbon-carbon (C-C) bond cleavage in bipyridine-ligated Co(ii) chlorodiketonate complexes

Mononuclear bipyridine (bpy)-ligated Co(ii) chlorodiketonate complexes [(bpy)(2)Co(R-PhC(O)C(Cl)C(O)R-Ph)]ClO4 (R = -H (8), -CH3 (9), and -OCH3 (10)), were prepared, characterized and investigated for O-2-dependent aliphatic C-C bond cleavage reactivity. Complexes 8-10 have a distorted psuedo-octahedral geometry. H-1 NMR spectra of 8-10 in CD3CN show signals for the coordinated diketonate moiety, and signals suggesting ligand exchange reactivity leading to the formation of a small amount of [(bpy)(3)Co](ClO4)(2) (11) in solution. While 8-10 are air stable at room temperature, illumination at 350 nm results in oxidative cleavage reactivity within the diketonate moiety leading to the formation of 1,3-diphenylpropanetrione, benzoic acid, benzoic anhydride, and benzil. Illumination of 8 under O-18(2) results in a high level of O-18 incorporation (> 80%) in the benzoate anion. The product mixture, high level of O-18 incorporation, and additional mechanistic studies suggest a reaction sequence wherein light-induced reactivity leads to the formation of a triketone intermediate that undergoes either oxidative C-C bond cleavage or benzoyl migration promoted by a bipyridine-ligated Co(ii) or Co(iii) fragment.

Automated summary

Mononuclear bipyridine (bpy)-ligated Co(ii) chlorodiketonate complexes were synthesized and studied for O-2-dependent aliphatic C-C bond cleavage reactivity. The study found that illumination resulted in oxidative cleavage of the diketonate moiety, leading to the formation of several products.