A Theoretical Study On Asymmetric Ketone Hydrogenation And Alcohol Dehydrogenation Catalyzed By Transition Metal Ruthenium

A theoretical study was made on asymmetric hydrogenation of ketone and alcohol dehydrogenation catalyzed by transition metal ruthenium in this paper. The contents including two aspects, one is asymmetric ketone hydrogenation catalyzed by Ru(diphosphine)(diamine) complexes, and the other is hydrogen production from Methanol (MeOH) dehydrogenation with ruthenium pincer complexes.1. Asymmetric hydrogenation of ketone catalyzed by Ru(diphosphine)(diamine) complexes.A quantitative structure-selectivity relationship (QSSR) model was established to study the relevance of the structure of 25 Ru(diphosphine)(diamine) catalysts to their enantioselectivities in this paper. The correlation coefficients of the models were obtained, that the q2 and r2 for the training set were 0.798 and 0.996, respectively. The r2 for the test set was 0.974. A judgment was made about the reliability and predictability for this model from the relevant parameters. The information given by contour maps of steric and electrostatic fields mainly focused on diamine ligands. New catalysts were designed by modification from the original catalyst on the basis of the information. A DFT study was made on the newly designed catalysts which improve the enantiomeric excess in order to understand them better. The analysis from the energy and frontier molecular orbitals indicated that the results of DFT and 3D-QSSR were consistent, that the enantioselectivity and activity of newly designed catalyst were improved.2. Hydrogen production from dehydrogenation of methanol with ruthenium pincer complexes.Hydrogen production from the dehydrogenation of MeOH catalyzed by ruthenium pincer complexes was studied with DFT method. Three reaction cycles of methanol, formaldehyde (HCHO) and formate (HCOOH) were studied respectively. Every cycle includes two process, dehydrogenation and hydrogen release. The dehydrogenation of HCHO is the easiest, followed by MeOH, and HCOOH is the slowest in the whole process. The participation of hydroxide in MeOH dehydrogenation produced the gem-diolate not the HCHO. This is the reason that the HCHO was not detected in the experiment. The quick dehydrogenation of HCHO explains why there is dioxide (CO2) in the initial phase. The methanol-assisted hydrogen release is easier than the direct hydrogen release step. The dehydrogenation of MeOH and HCHO was in accordance with the outer-sphere mechanism, while HCOOH dehydrogenation followed by both the out-sphere and inner-sphere mechanisms. The relationship between the outer-sphere and inner-sphere mechanism was transformational and competitive with each other. The bicarbonate (HCO3-) was produced by CO2 combined with OH-, which is the main way to decrease PH values in the experimenat and the driving force of the whole reaction. As a whole, the rate-determining steps are CO2 release and the methanol-assisted H2 release. According to the preceding research results, DFT analysis of modification on ligands and substituents concentrated on CO2 and H2 release steps. The results shown that, the barrier of CO2 release step decreased while H2 release step increased with the modification of ligands or substituents.