Theoretical Insight into Cp*Ir-Catalyzed Upgrading of Ethanol to n-Butanol: The Crucial Role of Cs2CO3

The ethanol-to- n -butanol upgrading process catalyzed by a Cp*Ir complex ( 1-Ir ) and mild base Cs 2 CO 3 was investigated using density functional theory calculations. Initially, Cs 2 CO 3 and 1-Ir form an active species 2 with an exothermicity of 12.9 kcal/mol. Ethanol dehydrogenation then occurs through the cooperation of the Ir center and Cs 2 CO 3 to produce an Ir–H complex 3 with the release of acetaldehyde and CsHCO 3 . Cs 2 CO 3 catalyzes the aldol condensation of acetaldehyde to produce a C 4 intermediate crotonaldehyde. Subsequently, the successive hydride and proton migrations occur from 3 and ethanol to crotonaldehyde, respectively, to produce butanal. The proton migration step is the rate-determining step (Δ G ‡ /Δ G = 29.1/–12.1 kcal/mol). Finally, n -butanol is produced via transfer hydrogenation of butanal with ethanol catalyzed by Cs 2 CO 3 . High selectivity for n -butanol is due to preferential hydrogenation of crotonaldehyde over its further condensation into C 6 species. Cs 2 CO 3 plays a critical role in promoting ethanol dehydrogenation, aldol condensation, and butanal hydrogenation. In contrast, Na 2 CO 3 significantly reduces reaction efficiency mainly due to its weaker basicity in the aldol condensation of acetaldehyde. These findings provide insights into the ethanol-to- n -butanol conversion and offer a foundation for developing milder bases for the reaction.