Tuning selectivity in Ru-MACHO-catalyzed ethanol upgrading

Ethanol upgrading into ethyl acetate and higher alcohols represents a sustainable route for producing value-added chemicals and biofuels from biomass-derived feedstocks. Ethyl acetate is formed via acceptorless dehydrogenative coupling of ethanol, generating hydrogen as a valuable co-product, while Guerbet-type reactions yield longer-chain alcohols such as 1-butanol. Ruthenium pincer complexes, particularly Ru-MACHO systems, efficiently catalyze both pathways under mild conditions. In this work, a series of aryl- and alkyl-substituted Ru-MACHO catalysts were synthesized and evaluated, revealing a strong dependence of catalytic performance on phosphine substituent identity. Aryl-substituted catalysts favor ethyl acetate formation, with tolyl derivatives showing enhanced activity compared to phenyl analogues. In contrast, bulky alkyl substituents, such as adamantyl groups, promote selective formation of 1-butanol. Ongoing mechanistic studies combining experimental and computational approaches provide insights into how ligand structure governs selectivity, offering a basis for rational catalyst design.