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A series of Fe mixed picolinate and quinaldinate complexes that catalyze the H2O2 oxidation of alcohols are presented. The Fe catalysts are generated in situ by simple mixing of iron acetate with 6‐methylpicolinic acid (6‐MepicH) and 4‐chloropicolinic acid (4‐ClpicH); they showed high catalytic activity for H2O2 oxidation of 1‐phenylethanol to acetophenone. Fe complexes generated in situ as precatalysts were successfully isolated and structurally characterized. Based on the single‐crystal X‐ray analysis and electrochemical measurements of the Fe complexes, the lability of picolinate and/or quinaldinate ligand and the redox potential of FeIII were found to be important factors for the catalytic reaction.

Selective oxidation of α,β-unsaturated aldehydes to α,β-unsaturated carboxylic acids was performed using O 2 as the oxidant in the presence of a simple iron catalyst. The addition of an alkali metal carboxylate as a cocatalyst enhanced the selectivity for the desired product. Redox tuning of the iron catalyst via association with the alkali metal led to a controlled radical generation during the catalytic O 2 oxidation.Molecular oxygen (O 2 ) is a readily available, inexpensive oxidant and is regarded as a promising natural resource for oxygen-containing chemical products.1,2 Conventional chemical processes including oxidations often use stoichiometric amounts of hazardous oxidants, leading to the formation of equimolar amounts of a by-product as waste. Although oxidation by O 2 would proceed with 100% atom efficiency under ideal conditions and thus generate no waste, such dioxygenase-type reactions have been reported less frequently than monooxygenaseand oxidase-type oxidation reactions, in which only one O atom of O 2 incorporates into substrate and O 2 is consumed by reoxidation of catalyst, respectively.3 In particular, the synthesis of value-added chemical products should be replaced by dioxygenase-type reactions to reduce waste generated during multistep reactions.α,β-Unsaturated carboxylic acids are among the most valuable intermediates and precursors for chemical production and pharmaceuticals. 4 Although the oxidation of aliphatic aldehyde into carboxylic acids proceeds by O 2 even without a catalyst, 5,6 several methods have been developed for the preparation of α,β-unsaturated carboxylic acids from their aldehyde derivatives, requiring severe and complex reaction conditions.7 Recently, N-heterocyclic carbene (NHC)-catalyzed O 2 oxidation reactions of α,β-unsaturated aldehyde were developed by several groups, yet more than equimolar amounts of base were essential for good reaction yields.8 From the standpoint of green-sustainable chemistry, catalytic oxidation using O 2 without large amounts of base is promising even if an organocatalyst could be employed.9 Nobile et al. reported a Fe catalyst bearing 2-(acetoacetoxy)ethyl methacrylate ligandcatalyzed O 2 oxidation of trans-2-hexenal; however, substrates were limited and a halogenated solvent was required.10 Mukaiyama et al. proposed the effectiveness of β-diketonate ligand to activate metal-catalyzed oxidation.11 More useful methods and systems to activate a base-metal complex must be developed to realize practical O 2 oxidation for the production of valuable fine chemicals.It is widely accepted that non-redox metal ions have considerable effect on the redox state of redox-active metal, promoting electron-transfer reactions 12 as well as catalytic reactions. 13 An appropriate combination of redox-active and non-redox-active base metals might act as simpler catalysts exhibiting enhanced activity in oxidation reactions. Herein, we report the preparation of α,β-unsaturated carboxylic acids from α,β-unsaturated aldehydes using a combination of O 2 and a...