| Abstract
| - O-Phenylcinchonidine (PhOCD) is known to efficiently induce inversion of enantioselectivitywith respect to cinchonidine (CD) in the enantioselective hydrogenation of various activated ketones onPt/Al2O3. To understand the origin of the switch of enantioselective properties of the catalyst, the adsorptionof PhOCD has been studied by in situ ATR-IR spectroscopy, in the presence of organic solvent and dissolvedhydrogen, i.e., under conditions used for catalytic hydrogenation. The adsorption structures and energiesof the anchoring group of CD and PhOCD were calculated on a Pt 38 cluster, using relativistically correcteddensity functional theory (DFT). Both approaches indicate that both modifiers are adsorbed via the quinolinering and that the spatial arrangement of the quinuclidine skeleton is critical for the chiral recognition. Newmolecular level information on the conformation of CD relative to PhOCD adsorbed on a surface is extractedfrom the ATR spectra and supported by DFT calculations. The result is a clearer picture of the role playedby the phenyl group in defining the chiral space created by the modifiers on Pt. Moreover, when CD wasadded to a pre-equilibrated adsorbed layer of PhOCD, a chiral adsorbed layer was formed with CD as thedominant modifier, indicating that CD adsorbs more strongly than PhOCD. Conversely, when PhOCD wasadded to preadsorbed CD, no significant substitution occurred. The process leading to nonlinear effects inheterogeneous asymmetric catalysis has been characterized by in situ spectroscopy, and new insight intoa heterogeneous catalytic R−S switch system is provided.
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