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)2Co(R–PhC(O)C(Cl)C(O)R–Ph)]ClO4 (R = –H (8), –CH3 (9), and –OCH3 (10)), were prepared, characterized and investigated for O2-dependent aliphatic C–C bond cleavage reactivity. Complexes 8–10 have a distorted psuedo-octahedral geometry. 1H 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)3Co](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 18O2 results in a high level of 18O incorporation (>80%) in the benzoate anion. The product mixture, high level of 18O 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.