Inversion of enantioselectivity in the hydrogenation of ketopantolactone on a Pt-β-ICN chiral catalyst

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Abstract

The enantioselective hydrogenation of ketopantolactone (KPL) both in AcOH and in toluene was studied on a Pt-alumina catalyst modified by α-isocinchonine (α-ICN) and β-isocinchonine (β-ICN). The effects of the modifier concentration, temperature, solvents, and mixtures of modifiers on the reaction rate and enantioselectivity were examined under mild experimental conditions (253-298 K, 1 bar H2 pressure, 0.001-0.1 mM/L modifier concentration). Formation of excess (S)-PL was observed in the presence of α-ICN in both solvents (eemax, 37%). In the enantioselective hydrogenation of KPL over a Pt-alumina-β-ICN chiral catalyst, the major enantiomer was (R)-PL (eemax, 60%) in toluene, whereas in AcOH, (S)-PL (ee, 5%) was formed. The (R) configuration was opposite to what was expected from the absolute configuration of the cinchonine backbone; namely, inversion of enantioselectivity occurred. The conformational rigidity of both chiral modifier and reactant provides new insight into the possible structure of intermediate complexes in the enantioselective hydrogenation of activated ketones. The proposed structure of the intermediate responsible for the inversion of enantioselectivity is an adsorbed 1:1 β-ICN-KPL surface complex [C1 pro(R) and C2 pro(R)] in which the β-ICN acts as a nucleophile and binds KPL.

Original languageEnglish
Pages (from-to)74-82
Number of pages9
JournalJournal of Catalysis
Volume239
Issue number1
DOIs
Publication statusPublished - Apr 1 2006

Fingerprint

Enantioselectivity
Hydrogenation
hydrogenation
inversions
catalysts
Catalysts
Toluene
toluene
Aluminum Oxide
Alumina
aluminum oxides
Nucleophiles
Enantiomers
nucleophiles
enantiomers
configurations
Ketones
rigidity
ketones
Rigidity

Keywords

  • α- and β-isocinchonine
  • Chiral hydrogenation
  • Conformation
  • Intermediate
  • Inversion of enantioselectivity
  • Ketopantolactone
  • Pt-alumina
  • Sense of enantioselection

ASJC Scopus subject areas

  • Catalysis
  • Process Chemistry and Technology

Cite this

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title = "Inversion of enantioselectivity in the hydrogenation of ketopantolactone on a Pt-β-ICN chiral catalyst",
abstract = "The enantioselective hydrogenation of ketopantolactone (KPL) both in AcOH and in toluene was studied on a Pt-alumina catalyst modified by α-isocinchonine (α-ICN) and β-isocinchonine (β-ICN). The effects of the modifier concentration, temperature, solvents, and mixtures of modifiers on the reaction rate and enantioselectivity were examined under mild experimental conditions (253-298 K, 1 bar H2 pressure, 0.001-0.1 mM/L modifier concentration). Formation of excess (S)-PL was observed in the presence of α-ICN in both solvents (eemax, 37{\%}). In the enantioselective hydrogenation of KPL over a Pt-alumina-β-ICN chiral catalyst, the major enantiomer was (R)-PL (eemax, 60{\%}) in toluene, whereas in AcOH, (S)-PL (ee, 5{\%}) was formed. The (R) configuration was opposite to what was expected from the absolute configuration of the cinchonine backbone; namely, inversion of enantioselectivity occurred. The conformational rigidity of both chiral modifier and reactant provides new insight into the possible structure of intermediate complexes in the enantioselective hydrogenation of activated ketones. The proposed structure of the intermediate responsible for the inversion of enantioselectivity is an adsorbed 1:1 β-ICN-KPL surface complex [C1 pro(R) and C2 pro(R)] in which the β-ICN acts as a nucleophile and binds KPL.",
keywords = "α- and β-isocinchonine, Chiral hydrogenation, Conformation, Intermediate, Inversion of enantioselectivity, Ketopantolactone, Pt-alumina, Sense of enantioselection",
author = "M. Bart{\'o}k and K. Bal{\'a}zsik and I. Bucsi and G. Sz{\"o}llősi",
year = "2006",
month = "4",
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TY - JOUR

T1 - Inversion of enantioselectivity in the hydrogenation of ketopantolactone on a Pt-β-ICN chiral catalyst

AU - Bartók, M.

AU - Balázsik, K.

AU - Bucsi, I.

AU - Szöllősi, G.

PY - 2006/4/1

Y1 - 2006/4/1

N2 - The enantioselective hydrogenation of ketopantolactone (KPL) both in AcOH and in toluene was studied on a Pt-alumina catalyst modified by α-isocinchonine (α-ICN) and β-isocinchonine (β-ICN). The effects of the modifier concentration, temperature, solvents, and mixtures of modifiers on the reaction rate and enantioselectivity were examined under mild experimental conditions (253-298 K, 1 bar H2 pressure, 0.001-0.1 mM/L modifier concentration). Formation of excess (S)-PL was observed in the presence of α-ICN in both solvents (eemax, 37%). In the enantioselective hydrogenation of KPL over a Pt-alumina-β-ICN chiral catalyst, the major enantiomer was (R)-PL (eemax, 60%) in toluene, whereas in AcOH, (S)-PL (ee, 5%) was formed. The (R) configuration was opposite to what was expected from the absolute configuration of the cinchonine backbone; namely, inversion of enantioselectivity occurred. The conformational rigidity of both chiral modifier and reactant provides new insight into the possible structure of intermediate complexes in the enantioselective hydrogenation of activated ketones. The proposed structure of the intermediate responsible for the inversion of enantioselectivity is an adsorbed 1:1 β-ICN-KPL surface complex [C1 pro(R) and C2 pro(R)] in which the β-ICN acts as a nucleophile and binds KPL.

AB - The enantioselective hydrogenation of ketopantolactone (KPL) both in AcOH and in toluene was studied on a Pt-alumina catalyst modified by α-isocinchonine (α-ICN) and β-isocinchonine (β-ICN). The effects of the modifier concentration, temperature, solvents, and mixtures of modifiers on the reaction rate and enantioselectivity were examined under mild experimental conditions (253-298 K, 1 bar H2 pressure, 0.001-0.1 mM/L modifier concentration). Formation of excess (S)-PL was observed in the presence of α-ICN in both solvents (eemax, 37%). In the enantioselective hydrogenation of KPL over a Pt-alumina-β-ICN chiral catalyst, the major enantiomer was (R)-PL (eemax, 60%) in toluene, whereas in AcOH, (S)-PL (ee, 5%) was formed. The (R) configuration was opposite to what was expected from the absolute configuration of the cinchonine backbone; namely, inversion of enantioselectivity occurred. The conformational rigidity of both chiral modifier and reactant provides new insight into the possible structure of intermediate complexes in the enantioselective hydrogenation of activated ketones. The proposed structure of the intermediate responsible for the inversion of enantioselectivity is an adsorbed 1:1 β-ICN-KPL surface complex [C1 pro(R) and C2 pro(R)] in which the β-ICN acts as a nucleophile and binds KPL.

KW - α- and β-isocinchonine

KW - Chiral hydrogenation

KW - Conformation

KW - Intermediate

KW - Inversion of enantioselectivity

KW - Ketopantolactone

KW - Pt-alumina

KW - Sense of enantioselection

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U2 - 10.1016/j.jcat.2006.01.016

DO - 10.1016/j.jcat.2006.01.016

M3 - Article

VL - 239

SP - 74

EP - 82

JO - Journal of Catalysis

JF - Journal of Catalysis

SN - 0021-9517

IS - 1

ER -