A new rigid cinchona modified (α-IQ) platinum catalyst for the enantioselective hydrogenation of activated ketones: Data to the origin of enantioselection

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Abstract

The enantioselective hydrogenations of ethyl pyruvate (EP), methyl benzoylformate (MBF), ketopantolactone (KPL) and pyruvaldehyde dimethylacetal (PADA) were studied on Pt-alumina catalyst modified by a new modifier namely α-isoquinine (α-IQ) with rigid conformation and for comparison by quinine (Q) in toluene and in acetic acid. The effects of modifier concentration, mixtures of modifiers, hydrogenation of α-IQ and theoretical calculations were examined on the interpretation of features of reactions. Using the Engelhard 4759 catalyst under mild experimental conditions (room temperature, 1 bar hydrogen pressure) the ees were lower in the case of α-IQ than for Q. The inversion of enantioselectivity observed in the case of the previously studied β-isocinchonine (β-ICN) containing C8(R) and C9(S) atoms in toluene as solvent failed to occur in the presence of α-IQ containing C8(S) and C9(R) atoms. Indirect experimental evidence for structure of adsorbed chiral modifier was supported by studies on hydrogenation and relative adsorption strength of α-IQ as well as by theoretical calculations. The significant enantioselectivity changes along the series of otherwise structurally related modifiers (Q, α-IQ and β-ICN) were compared with the ab initio computed geometrical features. The results revealed that besides the effects disclosed up to now in the literature, the orientational angle of the N-lone pair in the quinuclidine moiety relative to the quinoline also influences the structure and the adsorption mode of the intermediate responsible for the enantioselection.

Original languageEnglish
Pages (from-to)265-274
Number of pages10
JournalJournal of Molecular Catalysis A: Chemical
Volume272
Issue number1-2
DOIs
Publication statusPublished - júl. 2 2007

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology
  • Physical and Theoretical Chemistry

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