Iridium-Catalyzed Asymmetric Hydrogenation of Fluorinated Olefins Using N,P-Ligands: A Struggle with Hydrogenolysis and Selectivity

摘要

The enantioselective hydrogenation of olefins is one of the most powerful and studied transformations in asymmetric catalysis. The reaction is typically accomplished using complexes of chiral P,P-or N,P-chelating ligands with metals like ruthenium and rhodium. In the past decade, iridium complexes have proven to be efficient catalysts for the enantioselective hydrogenation of olefins. The iridium catalyst developed by Crabtree in 1977 was modified by Pfaltz in 1998 to give an iridium-phosphanodihydrooxazole (PHOX) catalyst that could hydrogenate tri- and tetrasubstituted olefins with enantiomeric excesses (ee's) up to 98%. Since then, several other stereoselective iridium-based N,P-ligand catalysts have been reported for the hydrogenation of a limited range of substrates.