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.