Mechanistic insights into CO2-driven hydration of propargylic alcohols catalyzed by oxometallate ionic liquids

Abstract

Oxometallate-based ionic liquids, exemplified by tetrabutylammonium molybdate, have recently emerged as efficient and recyclable catalysts for CO₂-assisted hydration of propargylic alcohols under mild conditions. In this work, density functional theory (DFT) is employed to provide an in-depth mechanistic investigation of the catalytic role of oxomolybdate-based ionic liquids in the formation of α-hydroxy ketones. The catalytic transformation proceeds through two interconnected cycles involving seven elementary steps, in which bifunctional activation by MoO₄²⁻–CO₂ adducts integrates CO₂ capture and activation with substrate transformation. Hydrolysis of the cyclic carbonate intermediate is identified as the overall rate-determining step, with a computed free energy barrier of 28.7 kcal mol⁻¹. A comparative analysis using the oxochromate analogue reveals comparable overall barriers but distinct rate-limiting steps, highlighting the influence of the metal center on individual reaction energetics. Electron Localization Function (ELF) and Non-Covalent Interaction (NCI) analyses elucidate the electronic reorganization and intermolecular interactions governing these differences. These insights establish a theoretical framework for the rational design of advanced oxometallate catalysts for efficient CO₂ utilization.