Ring-expanding olefin metathesis

A route to highly active unsymmetrical macrocyclic oligomeric co-salen catalysts for the hydrolytic kinetic resolution of epoxides

Xiaolai Zheng, Christopher W. Jones, Marcus Weck

Research output: Contribution to journalArticle

Abstract

In the presence of the third generation Grubbs catalyst, the ring-expanding olefin metathesis of a monocyclooct-4-en-1-yl functionalized salen ligand and the corresponding Co(II)(salen) complex at low monomer concentrations results in the exclusive formation of macrocyclic oligomeric structures with the salen moieties being attached in an unsymmetrical, flexible, pendent manner. The TOF-MALDI mass spectrometry reveals that the resulting macrocyclic oligomers consist predominantly of dimeric to tetrameric species, with detectable traces of higher homologues up to a decamer. Upon activation under aerobic and acidic conditions, these Co(salen) macrocycles exhibit extremely high reactivities and selectivities in the hydrolytic kinetic resolution (HKR) of a variety of racemic terminal epoxides under neat conditions with very low catalyst loadings. The excellent catalytic properties can be explained in terms of the new catalyst's appealing structural features, namely, the flexible oligomer backbone, the unsymmetrical pendent immobilization motif of the catalytic sites, and the high local concentration of Co(salen) species resulting from the macrocyclic framework. This ring-expanding olefin metathesis is suggested to be a simple way to prepare tethered metal complexes that are endowed with key features - (i) a high local concentration of metal complexes and (ii) a flexible, single point of attachment to the support - that facilitate rapid and efficient catalysis when a bimetallic transition state is required.

Original languageEnglish (US)
Pages (from-to)1105-1112
Number of pages8
JournalJournal of the American Chemical Society
Volume129
Issue number5
DOIs
StatePublished - Feb 7 2007

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Epoxy Compounds
Alkenes
Olefins
Metal complexes
Oligomers
Catalysts
Kinetics
Coordination Complexes
Catalyst supports
Catalysis
Mass spectrometry
Monomers
Chemical activation
Ligands
Matrix-Assisted Laser Desorption-Ionization Mass Spectrometry
Immobilization
Mass Spectrometry
Catalytic Domain
disalicylaldehyde ethylenediamine

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

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title = "Ring-expanding olefin metathesis: A route to highly active unsymmetrical macrocyclic oligomeric co-salen catalysts for the hydrolytic kinetic resolution of epoxides",
abstract = "In the presence of the third generation Grubbs catalyst, the ring-expanding olefin metathesis of a monocyclooct-4-en-1-yl functionalized salen ligand and the corresponding Co(II)(salen) complex at low monomer concentrations results in the exclusive formation of macrocyclic oligomeric structures with the salen moieties being attached in an unsymmetrical, flexible, pendent manner. The TOF-MALDI mass spectrometry reveals that the resulting macrocyclic oligomers consist predominantly of dimeric to tetrameric species, with detectable traces of higher homologues up to a decamer. Upon activation under aerobic and acidic conditions, these Co(salen) macrocycles exhibit extremely high reactivities and selectivities in the hydrolytic kinetic resolution (HKR) of a variety of racemic terminal epoxides under neat conditions with very low catalyst loadings. The excellent catalytic properties can be explained in terms of the new catalyst's appealing structural features, namely, the flexible oligomer backbone, the unsymmetrical pendent immobilization motif of the catalytic sites, and the high local concentration of Co(salen) species resulting from the macrocyclic framework. This ring-expanding olefin metathesis is suggested to be a simple way to prepare tethered metal complexes that are endowed with key features - (i) a high local concentration of metal complexes and (ii) a flexible, single point of attachment to the support - that facilitate rapid and efficient catalysis when a bimetallic transition state is required.",
author = "Xiaolai Zheng and Jones, {Christopher W.} and Marcus Weck",
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