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 language | English (US) |
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Pages (from-to) | 195-201 |
Number of pages | 7 |
Journal | Canadian Journal of Chemistry |
Volume | 83 |
Issue number | 3 |
DOIs | |
State | Published - Mar 1 2005 |
Externally published | Yes |
Keywords
- Cyclodextrins
- Kinetics
- Ligand substitution
- Pentacyanoferrate(II)
- Rotaxanes
ASJC Scopus subject areas
- Catalysis
- Chemistry(all)
- Organic Chemistry