Cobalt-Catalyzed Hydrosilylative Deoxygenation of Carboxylic Acids and Esters

Abstract Selective hydrodeoxygenation of benzylic acids and esters to methyl-substituted aromatics enables direct synthesis of fine chemicals, pharmaceuticals, and renewable hydrocarbons. Traditional methods rely on stoichiometric hydrides, multistep sequences, or harsh conditions with poor selectivity. Herein, we report a mild, additive-free protocol employing Co2(CO)8 as a cheap, earth-abundant, and commercially available precatalyst. Under optimized conditions (1 mol % Co2(CO)8, THF, 120 °C), aryl and benzylic esters are efficiently converted to the corresponding alkanes within 12 h, while carboxylic acids undergo exhaustive reduction within 24 h. This protocol overcomes key limitations of earlier Co-, Ni-, Ti-, and B-based systems, which were often restricted to esters or required external additives and bases. Notably, the use of Co2(CO)8 eliminates the need for ligand synthesis and catalyst preactivation. The method tolerates amino, hydroxy, halo, nitro, polyaromatic, heterocyclic, and benzylic substituents and demonstrates clear chemoselectivity for esters over acids and carbonyls over esters. Mechanistic investigations suggest a homogeneous radical pathway initiated by Co2(CO)8 homolysis to Co(CO)4 radicals, followed by oxidative addition of the Si–H bond to Co-hydride and Co-silyl intermediates and sequential hydrosilylation-deoxygenation cycles. Overall, this practical and scalable cobalt carbonyl catalyst enables efficient conversion of oxygenated feedstocks into energy-dense hydrocarbons using an inexpensive, shelf-stable catalyst.