Tuning Selectivity in Iron-Catalyzed Alcohol Oxidation: Reaction Media-Induced Chemodivergent Aldehyde and Acid Selectivity.

Selective catalytic transformations play a crucial role in organic synthesis, with chemodivergent synthesis holding particular significance. Key reactions in this context involve the selective oxidations of alcohols, leading to either the formation of corresponding carbonyls or complete oxidation to carboxylic acids. The use of base metal iron in catalysis is noteworthy due to its abundance, cost-effectiveness, nontoxicity, and sustainability. As a result, research on iron-catalyzed alcohol oxidation holds considerable importance. A tridentate NNN ligand was employed to yield an air-stable iron complex (1), proving to be an efficient catalyst for the selective oxidation of primary alcohols to aldehydes using TBHP as the oxidant without the addition of any solvent. The same iron complex demonstrated high efficiency in the selective oxidation of primary alcohols to carboxylic acids in a deep eutectic solvent (DES). Notably, the DES environment allowed achieving ppm-level catalyst loading (TON: 100,000 and TOF: 100,000 h-1). This is an excellent example of reaction media-induced chemodivergent oxidation of primary alcohols to aldehydes and carboxylic acids. A wide range of activated and unactivated primary alcohols was oxidized to the corresponding aldehydes and carboxylic acids selectively. Control experiments suggest a plausible homogeneous catalytic reaction pathway involving a radical mechanism.