Aerobic Oxidation Catalysis by a Molecular Barium Vanadium Oxide

Aerobic catalytic oxidations are promising routes to replace environmentally harmful oxidants with O₂ in organic syntheses. Here, we report a molecular barium vanadium oxide, [Ba₄ (dmso)₁₄ V₁₄ O₃₈ (NO₃ )] (={Ba₄ V₁₄ }) as viable homogeneous catalyst for a series of oxidation reactions in N,N-dimethyl formamide solution under oxygen (8 bar). Starting from the model compound 9,10-dihydroanthracene, we report initial dehydrogenation/ aromatization leading to anthracene formation; this intermediate is subsequently oxidized by stepwise oxygen transfer, first giving the mono-oxygenated anthrone and then the di-oxygenated target product, anthraquinone. Comparative reaction analyses using the Neumann catalyst [PV₂ Mo₁₀ O₄₀ ]^5- as reference show that oxygen diffusion into the reaction mixture is the rate-limiting step, resulting in accumulation of the reduced catalyst species. This allows us to propose improved reactor designs to overcome this fundamental challenge for aerobic oxidation catalysis.