Enantioselective cyclopropanation reaction catalyzed by optically active cobalt(II) complexes and the catalyst design based on theoretical analysis

Taketo Ikeno, Mitsuo Sato, Izumi Iwakura, Ai Kokura, Takushi Nagata, Tohru Yamada

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Highly enantioselective cyclopropanation of styrene derivatives and diazoacetates was effectively catalyzed by ketoiminatocobalt(II) complexes. Addition of a catalytic amount of n-methylimidazole significantly accelerated the reaction and enhanced the enantioselectivity due to its coordination to the center cobalt atom of the complex as an axial ligand. Analysis of the transition states by the PM 3(tm) method indicated that the olefin approached parallel to the cobalt-carbene bond with bisecting an O-Co-O angle. The reaction pathway of the cyclopropanation was analyzed by the density functional method to reveal that the axial donor ligand produced two prominent effects. One is that the activation energy for the formation of the cobalt carbene complex was reduced and that the activation energy for the cyclopropanation step was increased. The other is that the distance of the carbene carbon above the ligand plane was shortened during the cyclopropanation step. It was revealed that the carbene-carbon bond of the ketoiminatocobalt-carbene complexes is characterized as an extraordinary single bond based on the theoretical and FT-IR analysis. The key reactive intermediate of borohydride reduction catalyzed by Schiff base-cobalt complexes is proposed to be the dichloromethyl-cobalt hydride with a sodium cation, based on experimental and theoretical studies. It was revealed that chloroform is not the solvent but the reactant that activates the cobalt catalyst. It was found that a catalytic amount of chloroform effectively activated the present catalytic system to convert various ketones into the corresponding reduced product with a high ee in the THF solvent. Furthermore, the theoretical simulation of various axial groups in cobalt complex catalysts predicted that the cobalt-carbene complexes could be employed as efficient catalysts. The newly designed complexes generated from cobalt complex and methyl diazoacetate made it possible to catalyze the enantioselective borohydride reduction in a halogen-free solvent.

Original languageEnglish
Pages (from-to)110-123
Number of pages14
JournalYuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry
Volume66
Issue number2
Publication statusPublished - 2008 Feb

Fingerprint

Cobalt
Catalysts
Borohydrides
Chloroform
Ligands
Carbon
Activation energy
Halogens
Styrene
Schiff Bases
Enantioselectivity
Alkenes
Ketones
Hydrides
carbene
Cations
Sodium
Derivatives
Atoms

Keywords

  • Carbene complex
  • Chloroform
  • DFT analysis
  • Enantioselective cyclopropanation
  • Optically active cobalt complex catalyst

ASJC Scopus subject areas

  • Organic Chemistry

Cite this

Enantioselective cyclopropanation reaction catalyzed by optically active cobalt(II) complexes and the catalyst design based on theoretical analysis. / Ikeno, Taketo; Sato, Mitsuo; Iwakura, Izumi; Kokura, Ai; Nagata, Takushi; Yamada, Tohru.

In: Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry, Vol. 66, No. 2, 02.2008, p. 110-123.

Research output: Contribution to journalArticle

@article{bab030690aff49baa0e11fa3a91f47ab,
title = "Enantioselective cyclopropanation reaction catalyzed by optically active cobalt(II) complexes and the catalyst design based on theoretical analysis",
abstract = "Highly enantioselective cyclopropanation of styrene derivatives and diazoacetates was effectively catalyzed by ketoiminatocobalt(II) complexes. Addition of a catalytic amount of n-methylimidazole significantly accelerated the reaction and enhanced the enantioselectivity due to its coordination to the center cobalt atom of the complex as an axial ligand. Analysis of the transition states by the PM 3(tm) method indicated that the olefin approached parallel to the cobalt-carbene bond with bisecting an O-Co-O angle. The reaction pathway of the cyclopropanation was analyzed by the density functional method to reveal that the axial donor ligand produced two prominent effects. One is that the activation energy for the formation of the cobalt carbene complex was reduced and that the activation energy for the cyclopropanation step was increased. The other is that the distance of the carbene carbon above the ligand plane was shortened during the cyclopropanation step. It was revealed that the carbene-carbon bond of the ketoiminatocobalt-carbene complexes is characterized as an extraordinary single bond based on the theoretical and FT-IR analysis. The key reactive intermediate of borohydride reduction catalyzed by Schiff base-cobalt complexes is proposed to be the dichloromethyl-cobalt hydride with a sodium cation, based on experimental and theoretical studies. It was revealed that chloroform is not the solvent but the reactant that activates the cobalt catalyst. It was found that a catalytic amount of chloroform effectively activated the present catalytic system to convert various ketones into the corresponding reduced product with a high ee in the THF solvent. Furthermore, the theoretical simulation of various axial groups in cobalt complex catalysts predicted that the cobalt-carbene complexes could be employed as efficient catalysts. The newly designed complexes generated from cobalt complex and methyl diazoacetate made it possible to catalyze the enantioselective borohydride reduction in a halogen-free solvent.",
keywords = "Carbene complex, Chloroform, DFT analysis, Enantioselective cyclopropanation, Optically active cobalt complex catalyst",
author = "Taketo Ikeno and Mitsuo Sato and Izumi Iwakura and Ai Kokura and Takushi Nagata and Tohru Yamada",
year = "2008",
month = "2",
language = "English",
volume = "66",
pages = "110--123",
journal = "Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry",
issn = "0037-9980",
publisher = "Society of Synthetic Organic Chemistry",
number = "2",

}

TY - JOUR

T1 - Enantioselective cyclopropanation reaction catalyzed by optically active cobalt(II) complexes and the catalyst design based on theoretical analysis

AU - Ikeno, Taketo

AU - Sato, Mitsuo

AU - Iwakura, Izumi

AU - Kokura, Ai

AU - Nagata, Takushi

AU - Yamada, Tohru

PY - 2008/2

Y1 - 2008/2

N2 - Highly enantioselective cyclopropanation of styrene derivatives and diazoacetates was effectively catalyzed by ketoiminatocobalt(II) complexes. Addition of a catalytic amount of n-methylimidazole significantly accelerated the reaction and enhanced the enantioselectivity due to its coordination to the center cobalt atom of the complex as an axial ligand. Analysis of the transition states by the PM 3(tm) method indicated that the olefin approached parallel to the cobalt-carbene bond with bisecting an O-Co-O angle. The reaction pathway of the cyclopropanation was analyzed by the density functional method to reveal that the axial donor ligand produced two prominent effects. One is that the activation energy for the formation of the cobalt carbene complex was reduced and that the activation energy for the cyclopropanation step was increased. The other is that the distance of the carbene carbon above the ligand plane was shortened during the cyclopropanation step. It was revealed that the carbene-carbon bond of the ketoiminatocobalt-carbene complexes is characterized as an extraordinary single bond based on the theoretical and FT-IR analysis. The key reactive intermediate of borohydride reduction catalyzed by Schiff base-cobalt complexes is proposed to be the dichloromethyl-cobalt hydride with a sodium cation, based on experimental and theoretical studies. It was revealed that chloroform is not the solvent but the reactant that activates the cobalt catalyst. It was found that a catalytic amount of chloroform effectively activated the present catalytic system to convert various ketones into the corresponding reduced product with a high ee in the THF solvent. Furthermore, the theoretical simulation of various axial groups in cobalt complex catalysts predicted that the cobalt-carbene complexes could be employed as efficient catalysts. The newly designed complexes generated from cobalt complex and methyl diazoacetate made it possible to catalyze the enantioselective borohydride reduction in a halogen-free solvent.

AB - Highly enantioselective cyclopropanation of styrene derivatives and diazoacetates was effectively catalyzed by ketoiminatocobalt(II) complexes. Addition of a catalytic amount of n-methylimidazole significantly accelerated the reaction and enhanced the enantioselectivity due to its coordination to the center cobalt atom of the complex as an axial ligand. Analysis of the transition states by the PM 3(tm) method indicated that the olefin approached parallel to the cobalt-carbene bond with bisecting an O-Co-O angle. The reaction pathway of the cyclopropanation was analyzed by the density functional method to reveal that the axial donor ligand produced two prominent effects. One is that the activation energy for the formation of the cobalt carbene complex was reduced and that the activation energy for the cyclopropanation step was increased. The other is that the distance of the carbene carbon above the ligand plane was shortened during the cyclopropanation step. It was revealed that the carbene-carbon bond of the ketoiminatocobalt-carbene complexes is characterized as an extraordinary single bond based on the theoretical and FT-IR analysis. The key reactive intermediate of borohydride reduction catalyzed by Schiff base-cobalt complexes is proposed to be the dichloromethyl-cobalt hydride with a sodium cation, based on experimental and theoretical studies. It was revealed that chloroform is not the solvent but the reactant that activates the cobalt catalyst. It was found that a catalytic amount of chloroform effectively activated the present catalytic system to convert various ketones into the corresponding reduced product with a high ee in the THF solvent. Furthermore, the theoretical simulation of various axial groups in cobalt complex catalysts predicted that the cobalt-carbene complexes could be employed as efficient catalysts. The newly designed complexes generated from cobalt complex and methyl diazoacetate made it possible to catalyze the enantioselective borohydride reduction in a halogen-free solvent.

KW - Carbene complex

KW - Chloroform

KW - DFT analysis

KW - Enantioselective cyclopropanation

KW - Optically active cobalt complex catalyst

UR - http://www.scopus.com/inward/record.url?scp=42649096371&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=42649096371&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:42649096371

VL - 66

SP - 110

EP - 123

JO - Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry

JF - Yuki Gosei Kagaku Kyokaishi/Journal of Synthetic Organic Chemistry

SN - 0037-9980

IS - 2

ER -