Kinetic and spectroscopic studies on α- and β-cyclodextrin rotaxanes with (μ-N,N′-bis(4-pyridinylmethylene)-α,ω- alkanediimine)bis[pentacyanoferrate(II)] threads

Victor X. Jin, Donal H. Macartney, Erwin Buncel

Research output: Contribution to journalArticlepeer-review

5 Scopus citations

Abstract

[2]Pseudorotaxanes have been prepared by threading N,N′-bis(4- pyridinylmethylene)-1,2-ethanediimine (L2), -1,4-butanediimine (L4), and -1,6-hexanediimine (L6) ligands through α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD), and have subsequently been converted to the corresponding [2]rotaxane species by coordinating bulky [Fe(CN) 5]3- end groups. The stability constants for the [2]pseudorotaxanes were determined by 1H NMR chemical shift titrations and increase with the polymethylene chain length n. The rate constants for both the formation of the [Fe(CN)5(Ln)]3- complexes from the [Fe(CN)5OH2]3- ion and Ln, and the rate constants for the dissociation of Ln from the metal complexes, exhibit significant diminutions in the presence of α- and β-CD, owing to inclusions of the free and coordinated ligands, respectively. The lability of the iron(II)-pyridine bonds also permits the spontaneous self-assembly of the [2]rotaxane upon the addition of cyclodextrin to the iron dimer complexes. The mechanism for this process involves the rate-determining dissociation of a [Fe(CN)5]3- unit from [(NC)5Fe(Ln)Fe(CN) 5]6-, followed by CD inclusion of the Ln ligand to form a semirotaxane, and subsequent recomplexation by the [Fe(CN)5OH 2]3- ion.

Original languageEnglish (US)
Pages (from-to)195-201
Number of pages7
JournalCanadian Journal of Chemistry
Volume83
Issue number3
DOIs
StatePublished - Mar 1 2005
Externally publishedYes

Keywords

  • Cyclodextrins
  • Kinetics
  • Ligand substitution
  • Pentacyanoferrate(II)
  • Rotaxanes

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Organic Chemistry

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