Homochiral and heterochiral dimers of the methylzinc alkoxide formed from dimethylzinc and enantiomeric 3-exo-(dimethylamino)isoborneol - Origin of the distinct differences in solution-phase behavior and crystal structures

M. Kitamura, M. Yamakawa, H. Oka, Seiji Suga, R. Noyori

Research output: Contribution to journalArticle

Abstract

Dimethylzinc reacts with (2S)or (2 R)-3-exo-(dimethylamino)isoborneol [(2S)- or (2R)-DAIB] to eliminate methane and produce a tricoordinate methylzinc aminoalkoxide, which forms a dimeric structure. The homochiral dimerization of the enantiomeric compound leads to the chiral, (S,S) or (R.R) dinuclear Zn complex, while the heterochiral interaction forms the meso (S,R) dinuclear compound. In both solution anti crystalline state, the heterochiral dimer is more stable than the homochiral dimer. This stability difference in solution is the origin of the chirality amplification observed in the amino alcohol promoted asymmetric addition of dimethylzinc to benxaldehyde. In toluene, the homochiral dimer dissociates more readily into the monomer than the heterochiral isomer and also undergoes dissociation of the N Zn dative bond making the two N-methyl groups equivalent. The differences in solution behavior between the diastereomers can be understood by comparing their crystal structures. X-ray analysis indicates that the labile Zn O and Zn N bonds in the (S,S) dimer are longer than those in the (S,R) isomer. Skeletal congestion caused by the polycyclic framework is the prime factor determining the properties of the dinuclear Zn complexes, with both steric and electronic factors governing their geometries. The distances between the C-2 proton and N-CH3 of the other DAIBmoiety in the homochiral dimer are close to the sum of the van der Waals radii. A significant nuclear Overhauser effect is seen between these protons in the homochiral dimer. The tetrahedral Zn atoms in the dinuclear complexes are linked covalently to the methyl group, to two oxygen atoms through covalent/electrostatic hybrid bonds, and to the dimethylamino group through electrostatic interaction. The repulsive interaction of the 1,3-syn-oriented Zn CH3 bonds significantly contributes to the lower stability of the homochiral dimeric complex. The N Zn interaction in the homochiral dimer is labile, owing to the increase in the electrostatic interaction between the Zn atom and the neighboring oxygen atoms. This view is supported by the ab initio molecular orbital calculations of the model systems.

Original languageEnglish
Pages (from-to)1173-1181
Number of pages9
JournalAngewandte Chemie - International Edition
Volume35
Issue number17
Publication statusPublished - 1996
Externally publishedYes

Fingerprint

Phase behavior
Dimers
Crystal structure
Atoms
Coulomb interactions
Isomers
Protons
Amino alcohols
Oxygen
Amino Alcohols
Lead compounds
Orbital calculations
Dimerization
Chirality
Methane
X ray analysis
Toluene
Molecular orbitals
isoborneol
dimethylzinc

Keywords

  • ab initio calculations
  • asymmetric alkylations
  • catalysis
  • structure elucidation
  • zinc complexes

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

@article{febb9141d0974a3fb35de5caa52afdbf,
title = "Homochiral and heterochiral dimers of the methylzinc alkoxide formed from dimethylzinc and enantiomeric 3-exo-(dimethylamino)isoborneol - Origin of the distinct differences in solution-phase behavior and crystal structures",
abstract = "Dimethylzinc reacts with (2S)or (2 R)-3-exo-(dimethylamino)isoborneol [(2S)- or (2R)-DAIB] to eliminate methane and produce a tricoordinate methylzinc aminoalkoxide, which forms a dimeric structure. The homochiral dimerization of the enantiomeric compound leads to the chiral, (S,S) or (R.R) dinuclear Zn complex, while the heterochiral interaction forms the meso (S,R) dinuclear compound. In both solution anti crystalline state, the heterochiral dimer is more stable than the homochiral dimer. This stability difference in solution is the origin of the chirality amplification observed in the amino alcohol promoted asymmetric addition of dimethylzinc to benxaldehyde. In toluene, the homochiral dimer dissociates more readily into the monomer than the heterochiral isomer and also undergoes dissociation of the N Zn dative bond making the two N-methyl groups equivalent. The differences in solution behavior between the diastereomers can be understood by comparing their crystal structures. X-ray analysis indicates that the labile Zn O and Zn N bonds in the (S,S) dimer are longer than those in the (S,R) isomer. Skeletal congestion caused by the polycyclic framework is the prime factor determining the properties of the dinuclear Zn complexes, with both steric and electronic factors governing their geometries. The distances between the C-2 proton and N-CH3 of the other DAIBmoiety in the homochiral dimer are close to the sum of the van der Waals radii. A significant nuclear Overhauser effect is seen between these protons in the homochiral dimer. The tetrahedral Zn atoms in the dinuclear complexes are linked covalently to the methyl group, to two oxygen atoms through covalent/electrostatic hybrid bonds, and to the dimethylamino group through electrostatic interaction. The repulsive interaction of the 1,3-syn-oriented Zn CH3 bonds significantly contributes to the lower stability of the homochiral dimeric complex. The N Zn interaction in the homochiral dimer is labile, owing to the increase in the electrostatic interaction between the Zn atom and the neighboring oxygen atoms. This view is supported by the ab initio molecular orbital calculations of the model systems.",
keywords = "ab initio calculations, asymmetric alkylations, catalysis, structure elucidation, zinc complexes",
author = "M. Kitamura and M. Yamakawa and H. Oka and Seiji Suga and R. Noyori",
year = "1996",
language = "English",
volume = "35",
pages = "1173--1181",
journal = "Angewandte Chemie - International Edition",
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TY - JOUR

T1 - Homochiral and heterochiral dimers of the methylzinc alkoxide formed from dimethylzinc and enantiomeric 3-exo-(dimethylamino)isoborneol - Origin of the distinct differences in solution-phase behavior and crystal structures

AU - Kitamura, M.

AU - Yamakawa, M.

AU - Oka, H.

AU - Suga, Seiji

AU - Noyori, R.

PY - 1996

Y1 - 1996

N2 - Dimethylzinc reacts with (2S)or (2 R)-3-exo-(dimethylamino)isoborneol [(2S)- or (2R)-DAIB] to eliminate methane and produce a tricoordinate methylzinc aminoalkoxide, which forms a dimeric structure. The homochiral dimerization of the enantiomeric compound leads to the chiral, (S,S) or (R.R) dinuclear Zn complex, while the heterochiral interaction forms the meso (S,R) dinuclear compound. In both solution anti crystalline state, the heterochiral dimer is more stable than the homochiral dimer. This stability difference in solution is the origin of the chirality amplification observed in the amino alcohol promoted asymmetric addition of dimethylzinc to benxaldehyde. In toluene, the homochiral dimer dissociates more readily into the monomer than the heterochiral isomer and also undergoes dissociation of the N Zn dative bond making the two N-methyl groups equivalent. The differences in solution behavior between the diastereomers can be understood by comparing their crystal structures. X-ray analysis indicates that the labile Zn O and Zn N bonds in the (S,S) dimer are longer than those in the (S,R) isomer. Skeletal congestion caused by the polycyclic framework is the prime factor determining the properties of the dinuclear Zn complexes, with both steric and electronic factors governing their geometries. The distances between the C-2 proton and N-CH3 of the other DAIBmoiety in the homochiral dimer are close to the sum of the van der Waals radii. A significant nuclear Overhauser effect is seen between these protons in the homochiral dimer. The tetrahedral Zn atoms in the dinuclear complexes are linked covalently to the methyl group, to two oxygen atoms through covalent/electrostatic hybrid bonds, and to the dimethylamino group through electrostatic interaction. The repulsive interaction of the 1,3-syn-oriented Zn CH3 bonds significantly contributes to the lower stability of the homochiral dimeric complex. The N Zn interaction in the homochiral dimer is labile, owing to the increase in the electrostatic interaction between the Zn atom and the neighboring oxygen atoms. This view is supported by the ab initio molecular orbital calculations of the model systems.

AB - Dimethylzinc reacts with (2S)or (2 R)-3-exo-(dimethylamino)isoborneol [(2S)- or (2R)-DAIB] to eliminate methane and produce a tricoordinate methylzinc aminoalkoxide, which forms a dimeric structure. The homochiral dimerization of the enantiomeric compound leads to the chiral, (S,S) or (R.R) dinuclear Zn complex, while the heterochiral interaction forms the meso (S,R) dinuclear compound. In both solution anti crystalline state, the heterochiral dimer is more stable than the homochiral dimer. This stability difference in solution is the origin of the chirality amplification observed in the amino alcohol promoted asymmetric addition of dimethylzinc to benxaldehyde. In toluene, the homochiral dimer dissociates more readily into the monomer than the heterochiral isomer and also undergoes dissociation of the N Zn dative bond making the two N-methyl groups equivalent. The differences in solution behavior between the diastereomers can be understood by comparing their crystal structures. X-ray analysis indicates that the labile Zn O and Zn N bonds in the (S,S) dimer are longer than those in the (S,R) isomer. Skeletal congestion caused by the polycyclic framework is the prime factor determining the properties of the dinuclear Zn complexes, with both steric and electronic factors governing their geometries. The distances between the C-2 proton and N-CH3 of the other DAIBmoiety in the homochiral dimer are close to the sum of the van der Waals radii. A significant nuclear Overhauser effect is seen between these protons in the homochiral dimer. The tetrahedral Zn atoms in the dinuclear complexes are linked covalently to the methyl group, to two oxygen atoms through covalent/electrostatic hybrid bonds, and to the dimethylamino group through electrostatic interaction. The repulsive interaction of the 1,3-syn-oriented Zn CH3 bonds significantly contributes to the lower stability of the homochiral dimeric complex. The N Zn interaction in the homochiral dimer is labile, owing to the increase in the electrostatic interaction between the Zn atom and the neighboring oxygen atoms. This view is supported by the ab initio molecular orbital calculations of the model systems.

KW - ab initio calculations

KW - asymmetric alkylations

KW - catalysis

KW - structure elucidation

KW - zinc complexes

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EP - 1181

JO - Angewandte Chemie - International Edition

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SN - 1433-7851

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