Alcohol Oxidations Using Reduced Polyoxovanadates

A full account of our recently communicated room temperature alcohol oxidation using reduced polyoxovanadates (r-POVs) is presented. Extensive optimizations revealed optimal conditions employing 0.02 equiv. of r-POV catalyst Cs₅(V₁₄As₈O₄₂Cl), 5 equiv. tert-butyl hydrogen peroxide (^tBuOOH) as the terminal co-oxidant, in an acetone solvent for the quantitative oxidation of aryl-substituted secondary alcohols to their ketone products. The substrate scope tolerates most aryl substituted secondary alcohols in good to quantitative yields while alkyl secondary and primary activated alcohols were sluggish in comparison under similar conditions. Catalyst recyclability was successful on a 1.0 mmol scale of starting alcohol 1-phenylethanol. The oxidation was also successfully promoted by the V^IV/V^V mixed valent polyoxovanadate (POV) Cs₁₁Na₃Cl₅(V₁₅O₃₆Cl). Finally, a third POV, Cs_2.64(V₅O₉)(AsO₄)₂, was investigated for catalytic activity using our established reaction protocol, but proved ineffective as compared to the other two r-POV catalysts. This study expands the field of POM-mediated alcohol oxidations to include underexplored r-POV catalysts. While our catalysts do not supplant the best catalysts known for the transformation, their study may inform the development of other novel oxidative transformations mediated by r-POVs.