Co-Catalyzed Asymmetric Hydrogenation. The Same Enantioselection Pattern for Different Mechanisms

Area of Science:

• Organometallic chemistry
• Asymmetric catalysis
• Computational chemistry

Background:

• The Co-(R,R)-QuinoxP* complex catalyzes asymmetric hydrogenation of enyne 1.
• Understanding the reaction mechanism is crucial for controlling enantioselectivity.

Purpose of the Study:

• To elucidate the mechanism of the catalyzed asymmetric hydrogenation of enyne 1.
• To investigate potential Co(I)-Co(III) and Co(0)-Co(II) catalytic cycles.
• To determine how the catalytic pathway influences enantioselection.

Main Methods:

• Density Functional Theory (DFT) calculations were employed.
• Computation of plausible catalytic pathways, including Co(I)-Co(III) and Co(0)-Co(II) cycles.
• Analysis of transition state stabilities and interactions.

Main Results:

• Two distinct chemical mechanisms were identified that both accurately reproduced the experimentally observed perfect stereoselection.
• The sense of enantioselection was consistent across both proposed mechanisms.
• Weak dispersive interactions between the catalyst and substrate were found to control the relative stabilities of transition states.

Conclusions:

• The study reveals that multiple catalytic pathways can lead to the same high level of enantioselectivity.
• The findings highlight the critical role of subtle catalyst-substrate interactions in stereochemical control.
• This work provides valuable insights into the mechanistic underpinnings of asymmetric hydrogenation reactions.