Adsorption and Reactivity of Chiral Modifiers in Heterogeneous Catalysis: 1-(1-Naphthyl)ethylamine on Pt Surfaces

The adsorption from solution onto a Pt surface of 1-(1-naphthyl)ethylamine (1-NEA), a chiral modifier used to introduce enantioselectivity in catalytic hydrogenation reactions, as well as its subsequent chemical reactivity, was characterized by a combination of kinetic catalytic measurements, surface-science experiments, and quantum mechanics calculations. By using both H-1 NMR and gas chromatography/mass spectrometry detection, it was determined that 1-NEA can undergo H-D exchange with D-2 in solution when promoted by supported heterogeneous Pt catalysts. In situ infrared absorption spectroscopy studies at the solid-liquid interface afforded the detection of vibrational features indicative of the formation of N-D bonds, and quantum mechanics calculations helped with the peak assignment and provided evidence supporting an H-D exchange mechanism involving the formation of an intermediate-adsorbed protonated 1-NEA species. The reaction proved to be general, as it was observed with r- and s-1-NEA, r- and s-2-NEA, and cinchonine, and on Pt/SiO2 and Pt/Al2O3 catalysts. NEA adsorption and protonation through the amine N atom explain a number of reported but previously not fully understood observations and provide a way to envision the mechanism by which the NEA molecule bestows enantioselectivity to Pt hydrogenation catalysts.

Automated summary

The adsorption and chemical reactivity of 1-(1-naphthyl)ethylamine (1-NEA) on a Pt surface were studied using catalytic measurements, surface-science experiments, and quantum mechanics calculations. It was found that 1-NEA can undergo H-D exchange with D-2 in solution when promoted by Pt catalysts. This study provides insights into the mechanism by which 1-NEA imparts enantioselectivity to Pt hydrogenation catalysts.