Graftable chiral ligands for surface organometallic materials: Calixarenes bearing asymmetric centers directly attached to the lower rim

Andrew Solovyov, Justin M Notestein, Kathleen A. Durkin, Alexander Katz

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

A family of chiral lower-rim substituted calixarene ligands 1-14 is synthesized and characterized as prospective ligands for synthesis of asymmetric active sites for heterogeneous catalysis and adsorption using a surface organometallic approach. The ligands possess asymmetric centers directly attached to lower-rim oxygens; the asymmetric centers are tailored with sterically bulky naphthyl and electron withdrawing CF3 substituents. 1H and 13C NMR spectroscopies demonstrate that mono- and 1,3-di-alkylated calixarenes synthesized using this procedure adopt the cone-shaped conformation, which is stabilized by multiple hydrogen bonds at the lower rim. Smaller pendant groups and polar solvents increase the dialkylation/monoalkylation ratio. The reaction proceeds with full inversion of configuration as established via single crystal X-ray diffraction of an N-Cbz-protected aminocyclopentoxy-modified calixarene. The calixarenes synthesized by this approach are characterized using circular dichroism (CD) spectroscopy and ab initio modeling, which is used to identify the minimal molecular fragment responsible for the observed lowest energy Cotton effect in the CD spectrum. Factors that influence the intramolecular induction of asymmetry throughout the calixarene scaffold are investigated by systematically varying substituent steric bulk, connectivity of the asymmetric center to the calixarene core, and the extent of hydrogen bonding at the calixarene lower rim. The asymmetry of the calixarene core is quantified using 1H NMR spectroscopic shifts of aromatic meta and methylene bridge hydrogens and supported using ab initio calculations. The results demonstrate that calixarene core asymmetry is most strongly induced for rigid calixarene cores-an attribute that is expected to be preserved upon metal complexation and anchoring of these prospective ligands.

Original languageEnglish
Pages (from-to)1314-1325
Number of pages12
JournalNew Journal of Chemistry
Volume32
Issue number8
DOIs
Publication statusPublished - 2008

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Bearings (structural)
Calixarenes
Organometallics
Ligands
Hydrogen bonds
Circular dichroism spectroscopy
Dichroism
Complexation
Scaffolds
Catalysis
Nuclear magnetic resonance spectroscopy
Cotton
Conformations
Cones
Nuclear magnetic resonance
Single crystals
Adsorption
X ray diffraction
Hydrogen
Oxygen

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

Graftable chiral ligands for surface organometallic materials : Calixarenes bearing asymmetric centers directly attached to the lower rim. / Solovyov, Andrew; Notestein, Justin M; Durkin, Kathleen A.; Katz, Alexander.

In: New Journal of Chemistry, Vol. 32, No. 8, 2008, p. 1314-1325.

Research output: Contribution to journalArticle

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