Oxygenation and Oxidative Coupling Processes of Alkyl Ligands of m-Dialkylcobalt(III) Complexes with Dioxygen Catalyzed by Coenzyme Analogues in the Presence of Perchloric Acid

Oxygenation of the benzyl ligand of cis-[(PhCH₂)₂Co(bpy)₂]⁺ (bpy = 2,2′-bipyridine) occurs efficiently in the presence of a catalytic amount of a coenzyme analogue, riboflavin, riboflavin-2′,3′,4′,S′-tetraacetate, lumazine, or aminopterin, in acetonitrile containing perchloric acid at 298 K to produce benzyl hydroperoxide, which decomposes to yield benzaldehyde as the final oxygenated product. In the case of ds-[R₂Co(bpy)₂]⁺ (R = Et, Me), however, no oxygenation of the ligands proceeds under the same conditions; instead, oxidative coupling of the alkyl ligands of m-[R₂Co(bpy)₂]⁺ takes place in the coenzyme-catalyzed oxidation by dioxygen to yield ethane and butane, respectively, when dioxygen is reduced to hydrogen peroxide. The origin of such a difference in the oxygenation and oxidative coupling pathways depending on the alkyl ligands is discussed based on the comparison of the products and kinetics with those of the one-electron oxidation of ds-[R₂Co(bpy)₂]⁺ by various oxidants in the absence and presence of dioxygen in acetonitrile at 298 K.