Using computational methods to explore improvements to Knölker's iron catalyst

Abstract

Knölker's iron catalyst is characterized by low toxicity and relatively low price in comparison with precious metal catalysts. Density functional theory was used to explore improvements to this catalyst. It was found that electron-withdrawing substituents on the CpOH ring are favorable for improving the efficiency of iron catalysts. Increasing the acidity of CpOH is also an available means of improving the catalytic efficiency. However, replacing the hydroxyl of CpOH with the amino group is not a valid choice for improvement. In contrast, substituting phosphine ligands for carbonyls is the most effective method for improving the catalytic activity of the iron catalyst. But the PR₃ ligand must have electron-donating groups and its steric effect should be controlled in a suitable range. Replacing carbonyl groups by PH₃ and PPhH₂ ligands can effectually improve the catalytic activity for hydrogenation of ketones.