Chromium-catalyzed stereodivergent E- and Z-selective alkyne hydrogenation controlled by cyclic (alkyl)(amino)carbene ligands

Abstract

AbstractThe hydrogenation of alkynes allows the synthesis of olefins, which are important feedstock for the materials, pharmaceutical, and petrochemical industry. Thus, methods that enable this transformation via low-cost metal catalysis are desirable. However, achieving stereochemical control in this reaction is a long-standing challenge. Here, we report on the chromium-catalyzedE- andZ-selective olefin synthesis via hydrogenation of alkynes, controlled by two carbene ligands. A cyclic (alkyl)(amino)carbene ligand that contains a phosphino anchor enables the hydrogenation of alkynes in atrans-addition manner, selectively formingE-olefins. With an imino anchor-incorporated carbene ligand, the stereoselectivity can be switched, giving mainlyZ-isomers. This ligand-enabled geometrical stereoinversion strategy by one metal catalysis overrides common methods in control of theE- andZ-selectivity with two different metal catalysis, allowing for highly efficient and on-demand access to bothE- andZ-olefins in a stereo-complementary fashion. Mechanistic studies indicate that the different steric effect between these two carbene ligands may mainly dominate the selective formingE- orZ-olefins in control of the stereochemistry.