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

Abstract

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 Knolker-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.

Enhancement of Knölker Iron Catalysts for Imine Hydrogenation by Predictive Catalysis: From Calculations to Selective Experiments

“…Actually, the most demanding step corresponds especially to two steps. The first belongs to the preactivation, I → II (19.6 kcal/mol), and the second belongs to the catalytic pathway, III → IV (16.6 kcal/mol), which increases 2.0 kcal/mol with respect to the past study, since intermediate III was further stabilized by 2.0 kcal/mol.…”

Photoredox catalysis leading to triazolo-quinoxalinones at room temperature: selectivity of the rate determining step

“…3ic and 3id, the energy barriers decreased to 13.5 and 12.5 kcal mol −1 , respectively. In addition, on a simple exercise of predictive chemistry, [64][65][66][67] carboxylic acid and tert-butyl ester derivatives were studied, showing barriers of 13.2 and 14.6 kcal mol −1 , respectively, and thus showing a clear trend in which the bulkier the alkyl group, the higher the activation energy. Anyway, still insufficient for the latter compound to be not active like 3af, and compared to all the systems in Table 1.…”

A unified approach to the synthesis of amines through a highly selective and broadly applicable imine reduction using modified Pd-nanoparticles

“…We direct the reader to selected examples using Ir, [20][21][22] , Ni 23 , Co 24 , Fe 25 and Ru 26,27 . A recent patent landscape analysis by Glorius and Lecker and co-workers suggests that there remains significant interest in the development of new hydrogenation catalysts, including Pd.…”