Nickel-Catalyzed Asymmetric Hydrogenation of α-Substituted Vinylphosphonates and Diarylvinylphosphine Oxides

Chiral α-substituted ethylphosphonate and ethylphosphine oxide compounds are widely used in drugs, pesticides, and ligands. However, their catalytic asymmetric synthesis is still rare. Of the only asymmetric hydrogenation methods available at present, all cases use rare metal catalysts. Herein, we report an efficient earth-abundant transition-metal nickel catalyzed asymmetric hydrogenation affording the corresponding chiral ethylphosphine products with up to 99 % yield, 96 % ee (enantiomeric excess) (99 % ee, after recrystallization) and 1000 S/C (substrate/catalyst); this is also the first study on the asymmetric hydrogenation of terminal olefins using a nickel catalyst under a hydrogen atmosphere. The catalytic mechanism was investigated via deuterium-labelling experiments and calculations which indicate that the two added hydrogen atoms of the products come from hydrogen gas. Additionally, it is believed that the reaction involves a Ni^II rather than Ni⁰ cyclic process based on the weak attractive interactions between the Ni catalyst and terminal olefin substrate.

Cobalt-Catalyzed Asymmetric Hydrogenation of C=N Bonds Enabled by Assisted Coordination and Nonbonding Interactions

An efficient cobalt-catalyzed asymmetric hydrogenation of C=N bonds has been realized. Chiral hydrazines were obtained in high yields and with excellent enantioselectivities (95-98 % ee). The hydrogenation went smoothly at up to 2000 substrate/catalyst and on a gram scale. The success of this reaction relies on the presence of an NHBz group in the substrates, with the reactivity and enantioselectivity improved by an assisted coordination to the cobalt atom and a nonbonding interaction with the ligand. Furthermore, this reaction has practical applications for the synthesis of several useful chiral nitrogen-containing compounds.