The rhodium riddle: computational insights into competitive β-hydride vs. β-fluoride elimination†

Abstract

Metal-catalyzed β-eliminations are elementary reaction mechanisms commonly leveraged in organometallic processes, including the renowned Mizoroki–Heck reaction. Although β-hydride elimination has traditionally been the focus of study, β-heteroatom elimination, in particular β-fluoride elimination, has seen a significant rise in contemporary organic methodologies. Intriguingly, rhodium(i) and palladium(ii), which are isoelectronic, display opposite chemoselectivity for β-hydride vs. β-fluoride elimination. We investigated the origin of preferential β-fluoride over β-hydride elimination under rhodium(i) catalysis using density functional theory (DFT) calculations. Our modelling indicates that the kinetic preference is to undergo β-hydride elimination, but the observed chemoselectivity arises due to the reversible nature of the reaction. Additional modelling reveals that a Curtin–Hammett scenario enabled by reversibility of β-hydride elimination under the employed reaction conditions accounts for the enantioselectivity observed experimentally.