Catalitzadors Knölker de ferro per hidrogenació

Abstract

In this work, computational studies using Density Functional Theory (DFT) were carried out for the reaction of reduction of aldehydes with amines, catalyzed by an iron complex, that will be Knölker-type, since for his special characteristics has a place donor of protons in both the ligand and the own metallic center, as a hydride. This type of reaction is an important challenge for the chemical catalysis, since, although it use a catalyst, aggressive conditions are necessary and do not give easily. Thus, the main goal of this study is to improve the catalyst and, favouring both the reaction conditions and the velocity of this type of reactions. For this aim, the phenyl groups of the cyclopentadienone ring that forms part of the iron complex will be substituted by other groups with different electron-donating or electron-withdrawing character. For this, we will use the substituents H, CH3, CF3, NO2, OCH3, N(CH3)2, OH, N(Ph)2, and NH2. From here, we will do the computational calculations using DFT that allow to obtain information on energies, structures and atomic and molecular properties. Then, we can observe the energetic barriers in each step of the catalytic process for each substituent chosen in the study. Moreover, from these calculations, the steric and electronic effects will be also studied, by the Mayer Bond Orders (MBO) to determine the strength of bonds and the Nuclear Independent Chemical Shift (NICS) to evaluate the aromaticity on the cyclopentadienone ring of the iron complex. Unexpectedly, the results show that the energy barriers suffered relatively small changes for the different substituents, except for the CF3 case, which presents better results regarding the activation of the catalyst. Even though, with this substituent the reaction will not be faster since the rate determining step (rds) of the catalytic cycle imposes a high energetic cost. From the MBO results, the strength of the bond behaves as expected. Finally, the NICS(1)out allow us to explain, relatively, why the energy barrier of the rds are higher on the systems modified with electron-withdrawing groups. However, the small differences are only slightly significant