Heterogeneous Fe-N-C Cocatalyst for Hydroquinone Oxidation Enables Aerobic Oxidation of Primary Alcohols to Aldehydes

Benzoquinone (BQ) is commonly used as a cocatalyst in multi-component catalyst systems for aerobic oxidation of organic molecules. Such methods often proceed by a redox cascade in which a secondary catalyst supports aerobic oxidation of hydroquinone (HQ) to BQ. The present study shows that a commercially available non-precious metal heterogeneous catalyst, PAJ-Fe-N-C, is much more efficient than established homogeneous catalysts for aerobic oxidation of HQ to BQ, and this improved reactivity is crucial to support aerobic oxidation of primary alcohols to aldehydes with the homogeneous iridium catalyst, [Ir(trop₂DAD]OTf (trop₂DAD=N,N-bis(5-H-dibenzo[a,d]cycloheptene-5-yl)-1,4-diazabuta-1,3-diene). The combination of this heterogeneous/homogeneous catalyst system operates with Ir catalyst loadings as low as 0.05 mol % and turnover frequencies ≥350 h^-1.