Platinum nanoparticles supported on mesocellular silica foams as highly efficient catalysts for enantioselective hydrogenation

Enhancing Effect of Residual Capping Agents in Heterogeneous Enantioselective Hydrogenation of α-keto Esters over Polymer-Capped Pt/Al2O3

“…Additionally, the influence of H 2 pressure on the catalytic performance of the Pt catalysts with residual capping agents was investigated because CD-modified Pt catalysts, in general, exhibit enhanced enantioselectivity at high H 2 pressures. ,, The TOFs and ee’s of the CD-modified Pt catalysts in the enantioselective hydrogenation of α-keto esters at 0.1 and 5.0 MPa H 2 pressure are compared in Table . Similar to the reference catalyst, IMP-Pt/Al 2 O 3 , both PVP- and PVA-Pt/Al 2 O 3 catalysts showed improved activity and enantioselectivity.…”

“…All catalysts were pretreated in a flow of 5% H 2 /Ar at 673 K for 90 min. The reaction was conducted with a Pt catalyst (80 mg), a chiral modifier (6 mg), and the substrate (0.1 mL) in acetic acid (10 mL) at 298 K. Details of the procedures have been given in previous works. , The compositions of the reactant and chiral products in the solvent were analyzed by a gas chromatograph (YL6500) equipped with a Chirasil-Dex CB column (CP7502, Agilent). Turnover frequencies (TOFs) [h –1 ] were measured based on the number of surface Pt atoms determined by CO chemisorption for IMP-Pt/Al 2 O 3 and based on the number of surface Pt atoms predicted by the theoretical Pt NP model with average particle size of 3 nm for PVP- and PVA-Pt/Al 2 O 3 . − The enantiomeric excess (ee) of the chiral products was calculated as follows: ee [%] = |[ R ] – [ S ]|/([ R ] + [ S ]) × 100, where [ R ] and [ S ] are the concentrations of ( R )- and ( S )-product, respectively.…”

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

“…The more promising and more studied second group of chiral modifiers is based on cinchona alkaloids, which were originally added to platinum catalysts to enantioselectively hydrogenate α-ketoesters. The reaction was originally reported in the late ’70s by Orito and coworkers, , and has been studied extensively ever since. ,,− Excellent enantioselectivities have been reported with particular α-ketoesters such as ethyl pyruvate, − but the scope of this reaction, as in the case of the tartaric acid-modified nickel catalysts, is limited. There is a little more flexibility in this case, though, as examples have been identified for the promotion of hydrogenations with related reactants such as ketones, ,− other carbonyl-containing organic molecules, , and even reactants with CC double bonds, as well as for related reactions such as asymmetric C–C bond couplings .…”

One‐pot reduction‐hydrophobization of heterogenized platinum with 1,1,3,3‐tetramethyldisiloxane

“…[ 8 ] It has also been found that hydrophobic supports are more efficient for the deposition of hydrosilylation catalysts and others. [ 5 ] In general, hydrophilic‐supported catalysts, such as alumina [ 9 ] or silica, [ 10 ] lead to water exposure by capillary condensation, which prevents the diffusion of reactants to the active sites, and thus cause the inhibition of reaction or generation of side products. As a result of developments in chemistry, especially in the areas related to health, safety, and environment, the requirement for hydrophobic‐supported catalysts has emerged and several hydrophobic materials have been studied as catalytic supports.…”