Enantioselective heterogeneous catalysis I. A working model for the catalyst:modifier:substrate interactions in chiral pyruvate hydrogenations

New data on enantiomeric excess versus conversion during enantioselective hydrogenation of activated ketones on a platinum catalyst

“…It was established at an early stage of research that the efficiency of chiral hydrogenation is significantly affected not only by the experimental parameters, which play a decisive role, but also by the methods of execution [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. In general, four different methods and their variants [1,2] have been adopted for performing liquid-phase chiral hydrogenation:…”

Heterogeneous Enantioselective Hydrogenation over Cinchona Alkaloid Modified Platinum: Mechanistic Insights into a Complex Reaction

“…One enantioface of the reactant is shielded by the modifier in closed conformation. 50 The right panel shows the model proposed by Augustine and co-workers 51 and refined by Vayner and co-workers: 52 A zwitterionic adduct is formed by nucleophilic addition (arrow). This adduct is reduced with inversion on the Pt surface.…”

“…13 Another model implying nucleophilic catalysis involving the nitrogen of the chiral modifier and the ketone carbonyl has been proposed by Augustine and coworkers. 51 This nucleophilic addition scenario was recently studied by Vayner et al using a variety of computational techniques. 52 They proposed that the key interaction between cinchonidine and pyruvate is a strong covalent bond joining the amine of cinchonidine to the pyruvate ketone carbonyl group (arrow in Figure 7).…”

Going Beyond the Physical: Instilling Chirality onto the Electronic Structure of a Metal

“…Current models for the mechanism are based on solely geometric arguments, [16][17][18] in which the adsorbed chiral modifier interacts with the achiral reactants to control the stereochemistry of the surface transition state and, consequently, of the reaction products. The models can explain some but not all of the features of enantioselective reactions, and in particular they cannot predict in a meaningful way the effect of structural variations of the modifier on enantioselectivity.…”