A Phosphite-Pyridine/Iridium Complex Library as Highly Selective Catalysts for the Hydrogenation of Minimally Functionalized Olefins

Abstract

A modular library of readily available phosphite-pyridine ligands has been successfully applied for the first time in the iridium-catalyzed asymmetric hydrogenation of a broad range of minimally functionalized olefins. The modular ligand design has been shown to be crucial in finding highly selective catalytic systems for each substrate. Excellent enantioselectivities (ees up to 99%) have therefore been obtained in a wide range of E- and Z-trisubstituted alkenes, including more demanding triaryl-substituted olefins and dihydronaphthalenes. This good performance extends to the very challenging class of terminal disubstituted olefins, and to olefins containing neighbouring polar groups (ees up to 99%). Both enantiomers of the reduction product can be obtained in excellent enantioselectivities by simply changing the configuration of the carbon next to the phosphite moiety. The hydrogenations were also performed using propylene carbonate as solvent, which allowed the iridium catalyst to be reused and maintained the excellent enantioselectivities.