Abstract
Asymmetric hydrogenation in solution catalyzed by chiral catalysts is a powerful tool to obtain chiral secondary alcohols. It is possible to reach conversions and enantiomeric excesses close to 99%, but that frequently requires the use of non-optimal amounts of catalysts or long reaction times. That is in part caused by the lack of kinetic information needed for the design of large-scale reactors, including few reported details about catalyst deactivation. In this work, we present a kinetic model for the asymmetric hydrogenation in solution of acetophenone, a prochiral substrate, catalyzed by different bisphosphine-diamine Ru complexes. The experimental data was fitted with a first order model that includes first order deactivation of the catalyst and the presence of residual activity. The fit of the experimental data is very good, and an analysis of the kinetic and deactivation parameters gives further insight into the role of each ligand present in the Ru catalysts. This is the first report of a kinetic analysis of homogenous complexes’ catalysis including an analysis of their deactivation.
Highlights
Asymmetric hydrogenation of prochiral ketones is important to obtain chiral secondary alcohols [1], which are intermediates in the production of pharmaceuticals, agrochemicals and perfumes [2]
Besides the use of novel complexes as catalysts, this is the first report of the modeling modeling of deactivation for asymmetric hydrogenation catalyzed by Ru complexes in solution
The diamine ligand had a major influence on the conversion reached, while the bisphosphine ligand affected the ee values
Summary
Asymmetric hydrogenation of prochiral ketones is important to obtain chiral secondary alcohols [1], which are intermediates in the production of pharmaceuticals, agrochemicals and perfumes [2]. In the hydrogenation of the carbonyl group it is customary to use a homogeneous chiral catalyst to facilitate the reaction and to avoid the formation of undesired enantiomers [3] In this area, Noyori and his group [4] have developed a series of chiral Ru complexes used as catalysts that have an excellent performance during the asymmetric hydrogenation of several prochiral substrates. Abdur-Rashid et al [8]etconducted several experiments with thewith same reaction and observed observed in of thethe activity of the a bisphosphine/diamine‐Ru complex. They a decay in thedecay activity catalyst, alsocatalyst, a bisphosphine/diamine-Ru complex.
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