Knölker Iron Catalysts for Hydrogenation Revisited: A Nonspectator Solvent and Fine-Tuning

The reductive amination
process under hydrogen at high pressure
catalyzed by iron complexes is of great synthetic interest. In this
work, we report density functional theory (DFT) studies on the reductive
amination catalyzed by a Knölker-type iron complex. Different
modifications of the catalyst are explored to improve the efficiency
and guide experiments toward milder conditions. DFT calculations in
conjunction with analysis of the chemical structure in terms of geometry,
fragment partial charges, effective oxidation states (EOS), and aromaticity
allows us to conclude that the presence of electron-withdrawing substituents
on the cyclopentadienone ring induces a decrease of the activation
barriers of most relevant steps, leading to a more efficient catalysis.
The present work is a clear example that predictive catalysis can
have a fundamental role in sustainable catalytic transformations.