Ab initio study of solvent effects on reactant–modifier complexes in enantioselective hydrogenation

In order to investigate enantiodifferentiation mechanism on a molecular level one-to-one complexes between protonated cinchonidine and methyl pyruvate, ketopantolactone as well as 1-phenylpropane-1,2-dione with and without an acetic acid molecule were investigated computationally with ab initio quantum chemical method at the Hartree–Fock level using 6-31G* basis set. The stabilities of the diastereomeric complexes and the electronic structure of the reactants were examined in order to correlate molecular level properties and enantioselectivity with the solvent effect (acetic acid versus toluene). A correlation between the keto carbonyl orbital energies and the complex stability was found. However, the enantiodiscrimination could not solely be explained in these terms. Acetic acid was found to have a large influence on the keto carbonyl orbital energies.