Correlation between Chiral Modifier Adsorption and Enantioselectivity in Hydrogenation Catalysis
Yufei Ni1, Alexander D Gordon1, Florisa Tanicala1
1Department of Chemistry and UCR Center for Catalysis, University of California, Riverside, CA, 92521, USA.
Abstract:
Infrared absorption spectroscopy performed in situ at the solid-liquid interface revealed that the adsorption on platinum supported catalysts of 1-(1-naphthyl)-ethylamine, which is used as a chiral modifier in hydrogenation catalysis, occurs through the amine group, not the aromatic ring as is widely believed. Comparisons were performed against a set of related modifier compounds with targeted substitutions to help identify the key moiety involved in the adsorption. It was determined that neither naphthalene-based modifiers without amine groups nor those with tertiary amine moieties are capable of adsorbing on the metal surface to any significant extent. A direct correlation was also found between the ability of the amines to adsorb on the platinum surface and their performance as chiral modifiers that impart enantioselectivity to the hydrogenation of α-keto esters such as ethyl pyruvate.
Related Concept Videos
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
02:13Reduction of Alkenes: Catalytic Hydrogenation
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
02:36Regioselectivity and Stereochemistry of Hydroboration
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
02:05Prochirality